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EFSA Journal 2012;10(5):2676

Suggested citation: EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP); ScientificOpinion on the safety and efficacy of L-carnitine and L-carnitine L-tartrate as feed additives for all animal species based on adossier submitted by Lonza Benelux BV. EFSA Journal 2012;10(5):2676. [23 pp.] doi:10.2903/j.efsa.2012.2676. Availableonline: www.efsa.europa.eu/efsajournal

European Food Safety Authority, 2012

SCIENTIFIC OPINION

Scientific Opinion on the safety and efficacy of L-carnitine and L-carnitine

L-tartrate as feed additives for all animal species based on a dossier

submitted by Lonza Benelux BV1

EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP)2,3

European Food Safety Authority (EFSA), Parma, Italy

ABSTRACT

L-Carnitine has a key role in the metabolism of fatty acids as a substrate for the reversible acetylation ofcoenzyme A and as a carrier for the transport of long-chain fatty acids from cytosol across the innermitochondrial membrane. L-Carnitine and L-carnitine L-tartrate administered via feed or water for drinking are

considered safe for the target species. The additives appear to have a wide margin of safety (> 10) at the levels

typically used in feed (1050 mg/kg feed). Very little information is available on the toxicology of L-carnitine.

Nevertheless, based on residue data obtained from multi-fold doses of the typical use levels, the FEEDAP Panel

concluded that typical supplementation of feed with L-carnitine or L-carnitine L-tartrate would not substantiallyincrease human exposure to carnitine from food of animal origin. Therefore, the FEEDAP Panel considers that

the use of L-carnitine and L-carnitine L-tartrate as additives in animal nutrition is safe for the consumer. L-

Carnitine and L-carnitine L-tartrate are not irritant to skin and eyes nor are they skin sensitisers. L-Carnitine and

L-carnitine L-tartrate showed limited dust formation. As inhalation toxicity studies were not available, adverse

effects in the respiratory tract cannot be fully excluded. The use of L-carnitine and L-carnitine L-tartrate in

animal nutrition is not expected to pose a risk to the environment. L-Carnitine and L-carnitine L-tartrate are

regarded as an effective source of L-carnitine in all animal species.

European Food Safety Authority, 2012

KEY WORDS

Nutritional additive, vitamins and provitamins, L-carnitine, L-carnitine L-tartrate, safety

1 On request from the European Commission, Question No EFSA-Q-2011-00251, adopted on 24 April 2012.2 Panel members: Gabriele Aquilina, Georges Bories, Andrew Chesson, Pier Sandro Cocconcelli, Joop de Knecht, Nol

Albert Dierick, Mikolaj Antoni Gralak, Jrgen Gropp, Ingrid Halle, Christer Hogstrand, Reinhard Kroker, Lubomir Leng,

Secundino Lpez Puente, AnneKatrine Lundebye Haldorsen, Alberto Mantovani, Giovanna Martelli, Mikls Mzes,

Derek Renshaw, Maria Saarela, Kristen Sejrsen and Johannes Westendorf. Correspondence: [email protected] Acknowledgement: The Panel wishes to thank the members of the Working Group on Watersoluble Vitamins, including

Annette Schuhmacher, for the preparatory work on this scientific opinion.

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L-Carnitine and L-carnitine L-tartrate for all animal species

EFSA Journal 2012;10(5):2676 2

SUMMARY

Following a request from the European Commission, the Panel on Additives and Products orSubstances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety andefficacy of L-carnitine and L-carnitine L-tartrate as additives to feed and water for drinking for allanimal species.

L-Carnitine has a key role in the metabolism of fatty acids as a substrate for the reversibleacetylation of coenzyme A and as a carrier for the transport of long-chain fatty acids from cytosolacross the inner mitochondrial membrane. Adult animals can synthesise carnitine from its precursorlysine; however, endogenous synthesis might be insufficient in juvenile animals. Nutritionalrequirement data for the different animal species and categories have not been established.

Oral administration routes of L-carnitine and L-carnitine L-tartrate via feed or water for drinking areconsidered bioequivalent.

L-Carnitine and L-carnitine L-tartrate are safe for the target species. The additives appear to have awide margin of safety (> 10) compared at the levels typically used in feed (1050 mg L-carnitine/kg

feed).

Very little information is available on the toxicology of L-carnitine. Nevertheless, based on residuedata obtained from multi-fold doses of the typical use levels, the FEEDAP Panel concluded that

typical supplementation of feed with L-carnitine or L-carnitine L-tartrate would not substantiallyincrease human exposure to carnitine from food of animal origin. As the absorption rate declines withincreasing L-carnitine intake, the endogenous carnitine pool may not significantly increase. Therefore,

the FEEDAP Panel considers that the use of L-carnitine and L-carnitine L-tartrate as additives inanimal nutrition is safe for the consumer.

L-Carnitine and L-carnitine L-tartrate are not irritant to skin and eyes nor are they skin sensitisers. L-Carnitine and L-carnitine L-tartrate showed limited dust formation. As inhalation toxicity studies werenot available, adverse effects in the respiratory tract cannot be fully excluded.

Carnitine is a naturally occurring substance, present in all animals and bacteria and, to a lesser extent,in some plants. The use of L-carnitine and L-carnitine L-tartrate in animal nutrition is not expected to

pose a risk to the environment.

L-Carnitine and L-carnitine L-tartrate are regarded as effective sources of L-carnitine in all animalspecies.

The FEEDAP Panel recommends the use of the specifications for L-carnitine according to PhEur (MG1339) considering purity, substance-related impurities and other impurities (sulphated ash and heavymetals).

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TABLE OF CONTENTS

Abstract .................................................................................................................................................... 1Summary .................................................................................................................................................. 2

Table of contents ...................................................................................................................................... 3

Background .............................................................................................................................................. 4

Terms of reference.................................................................................................................................... 4Assessment ............................................................................................................................................... 61. Introduction ..................................................................................................................................... 62. Characterisation ............................................................................................................................... 6

2.1. L-Carnitine ................................................................................................................................... 6

2.2. L-Carnitine L-tartrate ................................................................................................................... 72.3. Manufacturing process ................................................................................................................ 8

2.3.1. L-Carnitine .......................................................................................................................... 8

2.3.2. L-Carnitine L-tartrate .......................................................................................................... 82.4. Stability and homogeneity ........................................................................................................... 8

2.4.1. L-Carnitine .......................................................................................................................... 8

2.4.2.

L-Carnitine L-tartrate .......................................................................................................... 92.4.3. Homogeneity ...................................................................................................................... 9

2.5. Physico-chemical incompatibilities in feed ................................................................................. 92.6. Conditions of use ......................................................................................................................... 9

2.7. Evaluation of the analytical methods by the European Union Reference Laboratory (EURL). 103. Safety ............................................................................................................................................. 10

3.1. Safety for the target species ....................................................................................................... 103.1.1. Conclusions on the safety for target species ..................................................................... 10

3.2. Safety for the consumer ............................................................................................................. 10

3.2.1. Absorption, distribution, metabolism, residues and excretion .......................................... 103.2.2. Toxicological studies ........................................................................................................ 11

3.2.3. Assessment of consumer safety ........................................................................................ 11

3.2.4.

Conclusions on the safety for the consumer ..................................................................... 11

3.3. Safety for the user ...................................................................................................................... 12

3.3.1. Effects on the respiratory system ...................................................................................... 123.3.2. Effects on the eyes and skin ............................................................................................. 12

3.3.3. Conclusions on the safety for the user .............................................................................. 133.4. Safety for the environment ........................................................................................................ 13

4. Efficacy .......................................................................................................................................... 13

5. Post-market monitoring ................................................................................................................. 13Conclusions and recommendations ........................................................................................................ 14

Documentation provided to EFSA ......................................................................................................... 14

References .............................................................................................................................................. 14Appendices ............................................................................................................................................. 19Appendix A ............................................................................................................................................ 19

Appendix B ............................................................................................................................................ 21

References .............................................................................................................................................. 22

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BACKGROUND

Regulation (EC) No 1831/20034 establishes the rules governing the Community authorisation of

additives for use in animal nutrition. In particular, Article 4(1) of that Regulation lays down that anyperson seeking authorisation for a feed additive or for a new use of a feed additive shall submit anapplication in accordance with Article 7; in addition Article 10(2) of that Regulation also specifies that

for existing products within the meaning of Article 10(1), an application shall be submitted inaccordance with Article 7, at the latest one year before the expiry date of the authorisation givenpursuant to Directive 70/524/EEC for additives with a limited authorisation period, and within amaximum of seven years after the entry into force of this Regulation for additives authorised withouttime limit or pursuant to Directive 82/471/EEC.

The European Commission received a request from the company Lonza Benelux BV5 for (i)

authorisation of a new use (i.e. use in water for drinking), and (ii) re-evaluation of authorisation of theproduct carnitine in the form of L-carnitine and L-carnitine L-tartrate, when used as a feed additive forall animal species (category: nutritional additive; functional group: vitamins, provitamins andchemically well-defined substances having similar effect) under the conditions mentioned in Table 1.

According to Article 7(1) of Regulation (EC) No 1831/2003, the Commission forwarded theapplication to the European Food Safety Authority (EFSA) as an application under Article 4(1)

(authorisation of a feed additive or new use of a feed additive) and under Article 10(2) (re-evaluationof an authorised feed additive). EFSA received directly from the applicant the technical dossier insupport of this application.

6 According to Article 8 of that Regulation, EFSA, after verifying the

particulars and documents submitted by the applicant, shall undertake an assessment in order todetermine whether the feed additive complies with the conditions laid down in Article 5. The

particulars and documents in support of the application were considered valid by EFSA as of 20 April2011.7

Carnitine in the form of L-carnitine and L-carnitine L-tartrate has been authorised without time limitunder Council Directive 70/524/EEC

8for its use for all animal species as a nutritional additive.

The Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food(AFC) expressed an opinion related to L-carnitineL-tartrate for use in foods for particular nutritionalpurposes (EFSA, 2003). The Panel on Dietetic Products, Nutrition and Allergies (NDA) issued anopinion on substantiation of several health claims pursuant to Article 13(1) of Regulation (EC) No1924/2006 (EFSA, 2011).

TERMS OF REFERENCE

According to Article 8 of Regulation (EC) No 1831/2003, EFSA shall determine whether the feedadditive complies with the conditions laid down in Article 5. EFSA shall deliver an opinion on thesafety for the target animals, consumer, user and the environment and the efficacy of carnitine in the

form of L-carnitine and L-carnitine L-tartrate, when used under the conditions described in Table 1.

4 Regulation (EC) 1831/2003 of the European Parliament and of the Council of 22 September 2003 on additives for use in

animal nutrition. OJ L 268, 18.10.2003, p. 29.5 Lonza Benelux BV, Aluminiumstraat 1, 4800 AL Breda, NL.6 EFSA Dossier reference: FAD20100144.7 A new mandate was received in EFSA in March 2011.8 Commission list of the authorised additives in feedingstuffs published in application of Article 9t (b) of Council Directive

70/524/EEC concerning additives in feedingstuffs (2004/C 50/01). OJ C 50, 25.2.2004, p. 1.

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Table 1: Description and conditions of use of the additive as proposed by the applicant

AdditiveL-Carnitine

L-Carnitine L-tartrate

Registration number/EC No/No(if appropriate)

-

Category of additive 3. Nutritional additives

Functional group(s) of additiveA. Vitamins, pro-vitamins and chemically well defined

substances having a similar effect.

Description

Composition, descriptionChemical

formula

Purity criteria

(if appropriate)

Method of analysis

(if appropriate)

L-Carnitine C7H15NO3 min. 97.0 %Titration with

hydrochloric acid

L-Carnitine L-tartrate C18H36N2O12 min. 97.0 %Backtitration withhydrochloric acid

and sodium

hydroxide

Trade name (if appropriate) Not appropriate

Name of the holder of authorisation

(if appropriate)Not appropriate

Conditions of use

Species or category

of animal

Maximum

Age

Minimum contentMaximum

content Withdrawal

period(if appropriate)

mg kg-1

of complete feedingstuffs,supplementary feed (based on end feed)

and in water*

All animal species

and categories- - - -

Other provisions and additional requirements for the labelling

Specific conditions or restrictions for use (if

appropriate)Not applicable

Specific conditions or restrictions forhandling (if appropriate)

Please refer to MSDS

Post market monitoring

(if appropriate)Not applicable

Specific conditions for use in

complementary feedingstuffs or water(if appropriate)

Not applicable

Maximum Residue Limit (MRL) (if appropriate)

Marker residueSpecies or category of

animal

Target tissue(s)

or food products

Maximum

content in tissues- - - -

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EFSA Journal 2012;10(5):2676 6

ASSESSMENT

This opinion is based in part on data provided by a single company involved in the production ofcarnitine in the form of L-carnitine and L-carnitine L-tartrate. It should be recognised that these data

from a single applicant cover only a fraction of existing additives containing L-carnitine and L-

carnitine L-tartrate. The composition of the additives is not the subject of the application. The Panelhas sought to use the data provided, together with data from other sources, to deliver an opinion.

1. Introduction

L-Carnitine(-hydroxy--trimethyl aminobutyric acid), has a key role in the metabolism of fatty acids(energy) as a substrate for the reversible acetylation of coenzyme A and as a carrier for the transportof long-chain fatty acids from cytosol across the inner mitochondrial membrane. It is thereforeimportant for the energy metabolism of the animal. L-Carnitine is a dispensable compound as adultanimals can synthesize carnitine from its precursor lysine; however, endogenous synthesis might beinsufficient in juvenile animals (for details see Annex B).

Carnitine in the form of L-carnitine and L-carnitine L-tartrate is included in the European UnionRegister of Feed Additives pursuant to Regulation (EC) No 1831/2003. It is authorised without a timelimit in application of Article 9t (b) of Council Directive 70/524/EEC9 concerning additives infeedingstuffs (2004/C 50/01) for its use in all animal species as a nutritional additive.

The applicant has asked for a re-evaluation of the use of L-carnitine and L-carnitine L-tartrate asadditives to feed and for a new use in water for drinking. The substances are intended as nutritionaladditives under the functional group vitamins, pro-vitamins and chemically well-defined substanceshaving similar effects, for all animal species and categories.

L-Carnitine, L-carnitine hydrochloride and L-carnitine L-tartrate are authorised for addition for specificnutritional purposes in foods for particular nutritional uses (Regulation (EC) No 953/2009),

10 to

processed cereal-based foods and baby foods for infants and young children (Directive 2006/125/EC,Annex IV)

11and to infant formulae and follow-on formulae when reconstituted as instructed by the

manufacturer (Directive 2006/141/EC, Annex III).12Carnitine is also listed as a pharmacologicallyactive substance in veterinary medicinal products (Commission Regulation (EC) No 37/2010),

13and it

is not subject to maximum residue limits when used in food-producing animals.

Levocarnitine is described in the European Pharmacopeia (PhEur) in Monograph (MG) 1339.

2. Characterisation

2.1. L-Carnitine

L-Carnitine (IUPAC name: (3R)-3-hydroxy-4-(trimethylazaniumyl) butanoate; synonym: -hydroxy--

trimethyl aminobutyric acid) is identified by the CAS (Chemical Abstracts Service) number 541-15-1and the EINECS (European Inventory of Existing Chemical Substances) number 208-768-0. Thestructural formula of L-carnitine is shown in Figure 1.

9 Commission list of the authorised additives in feedingstuffs published in application of Article 9t (b) of Council Directive70/524/EEC concerning additives in feedingstuffs (2004/C 50/01). OJ C 50, 25.2.2004, p. 1.

10Commission Regulation (EC) 953/2009 of 13 October 2009 on substances that may added for specific nutritional purposes

in foods for particular nutritional uses. OJ L 269, 14.10.2009, p. 9.11Commission Directive 2006/125/EC of 5 December 2006 on processed cerealbased foods and babyfoods for infants and

young children. OJ L 339 6.12.2006, p. 16.12Commission Directive 2006/141/EC of 22 December 2006 on infant formulae and follow-on formulae and amending

Directive 1999/21/EC. OJ L 401 30.12.2006, p. 1.13 Commission Regulation (EU) 37/2010 of 22 December 2009 on pharmacologically active substances and their

classification regarding maximum residue limits in foodstuffs of animal origin. OJ L 15, 20.1.2010, p. 1.

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Figure 1: Structural formula of L-carnitine.

The molecular formula of L-carnitine is C7H15NO3and its molecular weight is 161.20. It has a meltingpoint of 180197 C, shows a bulk density of approximately 0.64 g/cm

3and is readily soluble in water

(12.7 g/mL at 2025 C according to different sources), soluble in ethanol and methanol and slightlysoluble in acetone.

L-Carnitine is a white to beige odourless hygroscopic powder. The analysis of five batches of theproduct showed an average content of 100.1 0.3 % L-carnitine and 0.3 0.2 % water,14which meetsthe minimum specifications of PhEur MG 1339 (98 % L-carnitine in the anhydrous substance). Themain impurity, 4-hydroxycrotonic acid, was below 0.01 % (0.0010.009 %). The amount ofsubstance-related impurities (impurities AD, according to PhEur) was below 0.05 % and complieswith the thresholds of PhEur, as demonstrated by the analysis of five batches

15. Data for residual

solvents indicated that VICH (International Cooperation on Harmonisation of Technical Requirementsfor Registration of Veterinary Medicinal Products) thresholds for class 2 and 3 are not exceeded.

Production batches are routinely screened for chemical and microbial contamination and impurities.From that routine survey the following values were reported as typical: mercury < 0.1 mg/kg,cadmium < 0.25 mg/kg, lead < 1.5 mg/kg, arsenic < 0.04 mg/kg, total aerobic microorganisms < 50colony-forming units (CFUs)/g.

Six batches of L-carnitine were analysed for particle size distribution determined by laser diffraction.The particle size distribution varied considerably from batch to batch: the fraction of particles below50 m was in the range 10.949.7 % (v/v). The additive (three batches) showed a low dustingpotential of 0.060.25 g/m3in the StauberHeubach test.16

2.2. L-Carnitine L-tartrate

L-Carnitine L-tartrate [IUPAC name 1-propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, (R)-,salt with (R-(R*,R*)-2,3-dihydroxybutanedioic acid (2:1); synonyms: -hydroxy--trimethylaminobutyrate, L-tartrate, L-carnitine L-tartrate (2:1)] is identified by CAS number 36687-82-8. The

structural formula of L-carnitine L-tartrate is shown in Figure 2.

Figure 2: Structural formula of L-carnitine L-tartrate.

The molecular formula of L-carnitine L-tartrate is C18H36N2O12and its molecular weight is 472.49. Ithas melting point of approximately 170 C (with decomposition), shows a bulk density ofapproximately 0.70 g/cm

3and is highly soluble in water (> 1 g/mL at 20 C).

14Technical dossier/Section II.15Technical dossier/Supplementary information February 2012.16Technical dossier/Section II and supplementary information October 2011/Annexes 2.33 and 2.34 and supplementary

information February 2012/Annexes 2.45 and 2.48.

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L-Carnitine L-tartrate is a crystalline white powder. The additive contains by specification at least97.0 % L-carnitine L-tartrate, which corresponds to at least 67 % L-carnitine and less than 0.5 % water.Analysis of five batches of the product showed an average content of L-carnitine, L-tartaric acid andwater of 68.5 0.7 %, 31.5 0.2 % and 0.2 0.1 %, respectively.17 The main impurity, 4-

hydroxycrotonic acid, was below 0.02 % (< 0.010.02 %) and total related impurities were below

0.05 % (determined by HPLC). Data for residual solvents indicated that VICH thresholds for class 2and 3 are not exceeded.

Production batches are routinely screened for chemical and microbial contamination and impurities.The following values were reported as typical: mercury < 0.005 mg/kg, cadmium < 0.02 mg/kg, lead

< 0.03 mg/kg, arsenic < 0.04 mg/kg, total aerobic microorganisms < 50 CFUs/g.

Three batches of L-carnitine L-tartrate were analysed for particle size distribution determined by laserdiffraction. The fraction of particles below 50 m was in the range 2.83.4 % (v/v). The substanceshowed a dusting potential of 0.19 g/m

3.18

2.3. Manufacturing process

2.3.1. L-Carnitine

L-Carnitine is produced by a two-step chemical synthesis process. In the first step, a solution of ethyl4-chloroacetoacetate in ethanol is hydrogenated using a chiral catalyst. In the second step, ethyl (R)-4-chloro-3-hydroxybutyrate is aminated with trimethylamine and hydrolysed with aqueous sodiumhydroxide, giving L-carnitine. The obtained aqueous L-carnitine solution is electrodialysed and re-crystallised in an organic solvent and then dried. The applicant provided a flow chart of the syntheticprocess.

A formulated product containing about 50 % L-carnitine is produced by the addition of a binder with ahigh water absorption capacity such as a silicon source.

2.3.2.

L-Carnitine L-tartrate

L-Tartaric acid in an organic solvent is added to an aqueous solution of L-carnitine. The solution iscooled and centrifuged. The resultant L-carnitine L-tartrate crystals are then dried.

2.4. Stability and homogeneity

2.4.1. L-Carnitine

2.4.1.1. Shelf life

L-Carnitine(one batch, stored in double polyethylene bags) was demonstrated to have a shelf life of 36months at 25 C. Shelf life under accelerated conditions at 40 C was shown for one batch of the

product to be six months. The shelf life of a formulated product containing 50 % L-carnitine (onebatch, stored in polyethylene bags at 25 C) did not differ from that of the active substance.

19

2.4.1.2. Stability of the additive when added to premixtures, feed and water for drinking

Three batches of a vitaminmineral premixture for piglets containing also choline chloride20

supplemented with 8 000 mg L-carnitine per kilogram (from an additive containing 50 % L-carnitine)

17Technical dossier/Section II and Supplementary information October 2011.18Technical dossier/Section II and Supplementary information October 2011/Annexes 2.35 and 2.36.19Technical dossier/Section II.20Technical dossier/Section II/Annexes 2.10 and 2.12.

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showed no reduction in the L-carnitine content when kept in polyethylene bags at 25 C for up to sixmonths.

21

Stability of L-carnitine was also investigated in mash and pelleted feed for piglets (three batches each)when added at 50 mg L-carnitine per kilogram complete feed. Feed processing did not affect the

concentration of L-carnitine in feed. After storage for three months at 25 C no reduction in the contentof L-carnitine was observed.22

No reduction in the concentration of L-carnitine (three batches) was seen in water for drinking when

added at 1 g/L and stored for 24 hours at 25 C.23

2.4.2. L-Carnitine L-tartrate

2.4.2.1. Shelf life

L-Carnitine L-tartrate (three batches stored in glass vials) was demonstrated to have a shelf life of 48months at 25 2 C.

24

2.4.2.2.

Stability of the additive when added to premixtures, feed and drinking water

The applicant provided no information on the stability of L-carnitine L-tartrate in premixtures andcomplete feed, but stated that the stability of L-carnitine L-tartrate is similar to that of L-carnitine. The

FEEDAP Panel is therefore not in the position to draw conclusions on the stability of the additive L-carnitine L-tartrate in premixtures and complete feed. However, even when hydrolysis occurs the L-

carnitine component is likely to be stable.

No reduction in the concentration of L-carnitine (intended value 1 g/L) was seen in water for drinking

when L-carnitine Ltartratee (three batches) was added at 1.4 g/L and stored for 24 hours at 25 C.25

2.4.3. Homogeneity

The capacity for homogeneous distribution was examined in feed for L-carnitine (intendedconcentration 50 mg/kg) and in a premixture and in feed for L-carnitine L-tartrate (intendedconcentration 5 000 and 60 mg L-carnitine/kg, respectively) by analysis in triplicate of five sampleseach. The coefficient of variation was 5.1 %, 3.4 % and 7.0 %, respectively.26

L-Carnitine and L-carnitine L-tartrate are highly soluble in water. Therefore, homogeneity in water fordrinking need not be demonstrated.

2.5. Physico-chemical incompatibilities in feed

No physico-chemical incompatibilities or interactions have been reported between L-carnitine/L-carnitine L-tartrate and feed materials, carriers, other approved additives or medicinal products when

added to premixtures and feed. No such incompatibilities or interactions were expected.

2.6. Conditions of use

L-carnitine and L-carnitine L-tartrate are intended for use via feed (premixtures, complete orcomplementary feed) and water for drinking in all animal species and categories without a maximumcontent or withdrawal period.

21Technical dossier/Section II/Annex 2.9.22Technical dossier/Section II/Annex 2.13.23Technical dossier/Section II/Annex 2.14 and supplementary information October 2011.24Technical dossier/Section II.25Technical dossier/Section II/Supplementary information October 2011/Annex 2.38.26Technical dossier/Section II/Annex 2.15 and supplementary information October 2011/Annexes 3.39 and 2.40.

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Two additives containing L-carnitine are mentioned in the dossier, one containing at least 97 % L-carnitine and intended for use in milk replacers, wet feed formulation and water for drinking andanother containing about 50 % L-carnitine intended for supplementation of other solid feed.

2.7. Evaluation of the analytical methods by the European Union Reference Laboratory

(EURL)EFSA has verified the EURL report as it relates to the methods used for the control of L-carnitine andL-carnitine L-tartrate in animal feed. The executive summary of the EURL report can be found inAppendix A.

3. Safety

According to Regulation (EC) No 429/2008, tolerance, metabolism and residue, and toxicological(concerning consumer safety) studies are not required for vitamins, pro-vitamins and chemicallydefined substances having similar effects which are already authorised as feed additives underDirective 70/524/EEC and whichdo not have the potential to accumulate, which FEEDAP considers isthe case for L-carnitine.

3.1. Safety for the target species

L-Carnitine is well tolerated by humans and all animal species, possibly because of its decreasingbioavailability with increasing dietary L-carnitine concentrations. In humans the bioavailability of L-carnitine declines to about 16 % and 5 % after oral administration of a single dose of 2 or 6 g L-carnitine (Harper et al., 1988).

In studies with Japanese quail (Coturnix coturnix subsp. japonica), a dietary concentration of8 000 mg L-carnitine/kg did not cause any adverse effect; also the addition of 8 000 mg D-carnitine/kg,which competitively inhibits the carrier-mediated transport and synthesis of L-carnitine, did not affectthe zootechnical parameters of the quail (Kliemant, 2000). In horses no adverse effects could beobserved when 5, 10 or 20 g of L-carnitine was administered via gavage every three days, or 12 g

daily via the feed; the increase from 5 to 20 g L-carnitine/day increased free and total carnitine in theplasma by only 25 % and 33 %, respectively (Schnitger, 2003). Doses of 1060 g per horse (as two orthree doses per day) were without adverse effects in thoroughbred horses (Foster et al., 1988; Harris etal., 1995). Studies with growing pigs and early weaned piglets suggest that dietary concentrations ofabout 5006 000 mg L-carnitine/kg are well tolerated (Newton and Haydon, 1988, 1989; Owen et al.,

1994, 1996, 2001a; Ghler, 2002; Heo et al., 2000).

3.1.1. Conclusions on the safety for target species

Based on the literature it can be concluded that L-carnitine and L-carnitine L-tartrate are safe for thetarget species. The additives appear to have a wide margin of safety (> 10) at the levels typically usedin feed (between 10 and 50 mg L-carnitine/kg feed).

3.2. Safety for the consumer

3.2.1. Absorption, distribution, metabolism, residues and excretion

After ingestion L-carnitine is absorbed in the small intestine via a sodium-dependent transport system(low carnitine concentration) or at pharmacological doses of carnitine via passive diffusion as freecarnitine and short-chain carnitine esters (Shaw et al., 1983; Gudjonsson et al., 1985; Hamilton et al.,

1986; Li et al., 1990; Marciani et al., 1991). The bioavailability of dietary L-carnitine is about 5487 % in humans and dependent on the dietary L-carnitine content (Rebouche and Chenard, 1991;Rebouche, 2004). The major portion of all carnitine in the body is found in the skeletal muscle (see,for example, Mitchell 1978). Studies with labelled L-carnitine suggest that carnitine is usually largely

not metabolised (e.g. Lindstedt and Lindstedt, 1961; Yue and Fritz, 1962; Brooks and MacIntosh,1975; Bremer, 1983); however, carnitine might be converted, for example to -methyl choline, duringstress and disease or depending on the dietary or physiological conditions (Mehlman et al., 1969;

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Mitchell, 1978). Carnitine is excreted mainly via the kidney with a highly efficient tubularreabsorption of about 9099 % at normal dietary intakes and normal plasma and tissue concentrations(Harper et al., 1988; Rebouche 2004); only 2 % of the ingested L-carnitine is voided in the faeces(Carroll et al., 1981).

In studies with Japanese quail fed a wheat/soybean-based diet without or with an addition of 2 000 mgL-carnitine per kilogram feed for 28 days, the total carnitine concentration (free carnitine, short-chainacyl-carnitine and long-chain acyl-carnitine) could be increased (P< 0.05) from 56 to 110 mg/kgskeletal muscle (M. pectoralis), from 52 to 110 mg/kg cardiac muscle and from 83 to 200 mg/kg liver(all values are fresh matter; Jger, 2000), i.e. the L-carnitine concentration had at least doubled in each

of the tissues as a result of dietary carnitine supplementation. Comparable results were obtained in anexperiment with early weaned piglets fed 0 or 632 mg L-carnitine/kg feed (wheat/soybean meal). After4956 days of feeding, the carnitine concentration significantly increased from 273 to 463 mg/kgskeletal muscle, from 100 to 169 mg/kg cardiac muscle, from 56 to 99 mg/kg kidney and from 35 to62 mg/kg liver of the control and carnitine-supplemented group, respectively (all values as freshmatter; Ghler, 2002).

3.2.2.

Toxicological studiesThe available toxicity data on L-carnitine L-tartrate have been assessed by the Panel on FoodAdditives, Flavourings, Processing Aids and Materials in Contact with Food (EFSA, 2003). A dose of3 g L-carnitine L-tartrate given daily to volunteers for threeweeks was tolerated.

An acute oral gavage toxicity test with L-carnitine L-tartrate in rats showed no effects at a dose of5000 mg/kg body weight.

A gene mutation test was performed with L-carnitine L-tartrate in SalmonellaTyphimurium strains TA1535, TA 1537, TA 1538, TA 98 and TA 100. It was tested at concentrations of 1.6, 8, 40, 200, 1 000and 5000 g per plate, without and with metabolic activation using rat liver S9 mix. There were two

independent experiments. There was no evidence of gene mutation (EFSA, 2003).

3.2.3. Assessment of consumer safety

No acceptable daily intake or tolerable upper intake level has been established for L-carnitine or L-carnitine L-tartrate.

L-Carnitineis present in the human diet in a variety of food sources. The richest sources of dietary L-carnitine (proximate L-carnitine content in brackets) are animal products, such as mutton (210 mg/kg),beef (60 mg/kg), pork (27 mg/kg) and fish (35 mg/kg). Lower levels of L-carnitine are found in dairy

products (2 mg/l cows milk), whereas most fruits and vegetables (05 mg/kg) contain minimalamounts of L-carnitine (for details see Mitchell, 1978; Rebouche 1984; Gtz, 1989; Demarquoy et al.,2004; Knttel-Gustavsen and Harmeyer, 2007).

Human dietary L-carnitine intake ranges from < 0.2 to about 2.4 mg/kg body weight per day(Rebouche, 2004).

3.2.4. Conclusions on the safety for the consumer

Based on residue data described under section 3.2.1, the FEEDAP Panel concluded that supplementingfeed with L-carnitine or L-carnitine L-tartrate at practical use levels between 10 and 50 mg L-

carnitine/kg feed would not substantially increase human exposure to carnitine from food of animalorigin. As the absorption rate declines with increasing L-carnitine intake, the endogenous carnitinepool may not significantly increase. Therefore, the FEEDAP Panel considers the use of L-carnitine andL-carnitine L-tartrate as additives in animal nutrition to be safe for consumers.

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3.3. Safety for the user

3.3.1. Effects on the respiratory system

L-Carnitine showed between 10 % and 49 % of particles (v/v) with a diameter < 50 m; thecorresponding figure for L-carnitine L-tartrate was 3 %. However, the dusting potential for both

additives was low (0.25 g/m3). In the absence of data on the inhalation toxicity of L-carnitine and L-carnitine L-tartrate, inhalation of dust is considered to be potentially hazardous.

3.3.2. Effects on the eyes and skin

3.3.2.1. L-Carnitine

In a skin irritation study [OECD (Organization for Economic Cooperation and Development)

guideline 404) the back skin of three New Zealand White rabbits was exposed to 0.5 g L-carnitine for4 hours.

27As slight erythema was observed at 1 hour but disappeared within two days, L-carnitine is

regarded as non-irritant to skin (Regulation (EC) No 1272/2008).28

For an acute eye irritation/corrosion study (OECD guideline 405) 0.1 mL of L-carnitine (67 mg) wasinstilled into one of the eyes of three New Zealand White rabbits.29Moderate conjunctival irritation

(redness, chemosis and discharge) and minimal to moderate conjunctival irritation was observed intwo treated eyes, in one case at 24 hours and in the other case at 48 hours. The results suggest that L-carnitine can be regarded as non-irritant to eyes (Regulation (EC) No 1272/2008).

In a Buehler test for skin sensitisation (OECD guideline 406) 20 albino guinea pigs were treated with75 % L-carnitine (w/w) in distilled water during the induction period, and 50 % and 75 % L-carnitine

(w/w) in distilled water during the challenge phase; 10 guinea pigs served as control group.30

No skinreaction was observed after topical challenge. The results indicate that L-carnitine is not a skin

sensitiser.

3.3.2.2.

L-Carnitine L-tartrateIn a dermal toxicity study (OECD guideline 402) L-carnitine L-tartrate was administered by a singledermal application (2000 mg/kg body weight) to five rats of each sex for 24 hours.31No abnormalitieswere observed at macroscopic post-mortem examination (day 15). The dermal LD50 value of L-carnitine L-tartrate was > 2 000 mg/kg.

In an acute skin irritation/corrosion study (OECD guideline 404) the skin of three New Zealand Whiterabbits was exposed to 0.5 g L-carnitine L-tartrate for four hours.

32At 1, 24, 48 and 72 hours after

removal no signs of either irritation or corrosion were observed. The results therefore indicate that L-carnitine L-tartrate is non-irritant.

For an acute eye irritation study (OECD guideline 405) 0.1 mL of L-carnitine L-tartrate (92 mg) wasinstilled into one eye of each of three New Zealand White rabbits.33Instillation resulted in irritation ofthe conjunctivae (redness, chemosis and discharge), which had cleared within 72 hours in two rabbits

and within 7 days in one rabbit. It was concluded that L-carnitine L-tartrate is non-irritant to eyes.

27Technical dossier/Section III/Reference 3.18.28Regulation (EC) 1272/2008 of 16 December 2008 on classification, labelling and packaging of substances and mixtures,

amending and repealing Directive 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJ C 353,

31.12.2008, p. 1.29Technical dossier/Section III/Reference 3.19.30Technical dossier/Section III/Reference 3.20.31Technical dossier/Section III/Reference 3.21.32Technical dossier/Section III/Reference 3.22.33Technical dossier/Section III/Reference 3.23.

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A local lymph node assay (OECD guideline 429) was performed to study the skin sensitisationpotential of L-carnitine L-tartrate.

34 Three groups of five female CBA strain mice each were treated

with 10 %, 25 % or 50 % L-carnitine L-tartrate, by open application on the ears. The results suggestedthat L-carnitine L-tartrate is not a skin sensitiser.

3.3.3.

Conclusions on the safety for the userL-Carnitine and L-carnitine L-tartrate are not irritating to skin and eyes and are not skin sensitisers. L-Carnitine and L-carnitine L-tartrate in the formulations described show limited dust formation. As noinformation is available on inhalation toxicity, adverse effects on the respiratory tract cannot be fullyexcluded.

3.4. Safety for the environment

Carnitine is a naturally occurring substance, present in all animals and bacteria and, to a lesser extent,in some plants. Its use in animal nutrition is not expected to substantially increase the concentration inthe environment. Therefore, any risk to the environment resulting from the use of carnitine in animalnutrition is not foreseen.

4. Efficacy

According to Regulation (EC) No 429/2008, efficacy studies are not required for vitamins, pro-vitamins and chemically well-defined substances having similar effects whichare already authorisedas feed additives.

Requirement/allowance data that could be used to derive feed supplementation levels are notestablished (McDowell, 2002; AWT, 2002). L-Carnitine and L-carnitine L-tartrate are regarded aseffective sources of L-carnitine in all animal species.

Intensive research has been done on the action of L-carnitine in the fatty acid and energy metabolismof humans and animals; a number of studies also deal with the effect of additional dietary L-carnitine

on endogenous carnitine concentrations and fat and energy utilisation, as well as on the performanceof various livestock animals (e.g. Newton and Haydon, 1986; Gnther, 1989; Musser et al., 1999a,b;Owen et al., 2001a,b; Rincker et al., 2003; Ramanau et al., 2004, 2005; Birkenfeld et al., 2006; Fischeret al., 2009) and pets and racing animals (e.g. Dubelaar et al., 1991a,b; Gevaert et al., 1991; Borghijsand DeWilde, 1992; Pelletier, 1992; Falaschini and Trombetta, 1993), as well as different fish species(Santulli and DAmelio, 1986; Santulli et al., 1988, 1990; Torrelle et al., 1991; Burtle, 1993; Ji et al.,1996). However, the carnitine doses stated to be effective for improving the performance varied notonly among the species investigated but also for one species between the research groups. Moreover,the occurrence of a carnitine effect is often inconsistent, possibly depending on the experimental diets,particularly the presence of the precursors, age and growth rate of the animal and the generalexperimental conditions (e.g. Burtle, 1990; Litz, 1993; Schuhmacher et al., 1993; Schuhmacher and

Gropp, 1998; Ghler, 2002). In studies with piglets and freshly hatched quail L-carnitine appeared toimprove weight gain and feed efficiency only if the metabolic precursors lysine or methionine were

deficient in the diets (Schuhmacher et al., 1993). However, it seems very unlikely that an amino acid-sparing effect on a molar basis was responsible for these findings.

5. Post-market monitoring

The FEEDAP Panel considers that there is no need for a specific post-market monitoring plan, otherthan the requirements established in the Feed Hygiene Regulation

35and good manufacturing practice.

34Technical dossier/Section III/Reference 3.24.35Regulation (EC) No 183/2005 of the European Parliament and of the Council of 12 January 2005 laying down

requirements for feed hygiene. OJ L 35, 8.2.2005, p. 1.

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CONCLUSIONS AND RECOMMENDATIONS

CONCLUSIONS

Oral administration routes of L-carnitine and L-carnitine L-tartrate via feed or water for drinking are

considered bioequivalent.

L-Carnitine and L-carnitine L-tartrate are safe for the target species. The additives appear to have a

wide margin of safety (> 10) at the levels typically used in feed (1050 mg L-carnitine/kg feed).

Very little information is available on the toxicology of L-carnitine. Nevertheless, based on residuedata obtained from multi-fold doses of the levels typically use, the FEEDAP Panel concluded that

typical supplementation of feed with L-carnitine or L-carnitine L-tartrate would not substantiallyincrease human exposure to carnitine from food of animal origin. As the absorption rate declines with

increasing L-carnitine intake, the endogenous carnitine pool may not significantly increase. Therefore,the FEEDAP Panel considers the use of L-carnitine and L-carnitine L-tartrate as additives in animalnutrition to be safe for the consumer.

L-Carnitine and L-carnitine L-tartrate are not irritant to skin and eyes, nor are they skin sensitisers. L-Carnitine and L-carnitine L-tartrate show limited dust formation. As inhalation toxicity studies are not

available, adverse effects in the respiratory tract cannot be fully excluded.

The use of L-carnitine and L-carnitine L-tartrate in animal nutrition is not expected to pose a risk to theenvironment.

L-Carnitine and L-carnitine L-tartrate are regarded as effective sources of L-carnitine in all animalspecies. Nutritional requirement data for the different animal species and categories have not been

established.

RECOMMENDATIONS

The FEEDAP Panel proposes to use the specifications for L-carnitine according to PhEur (MG 1339)considering purity, substance-related impurities and other impurities (sulphated ash and heavy metals).

DOCUMENTATION PROVIDED TOEFSA

1. L-Carnitine and L-carnitine L-tartrate as a feed additive for all animal species. October 2010.Submitted by Lonza Benelux BV.

2. L-Carnitine and L-carnitine L-tartrate as a feed additive for all animal species. Supplementaryinformation. October 2011. Submitted by Lonza Benelux BV.

3. L-Carnitine and L-carnitine L-tartrate as a feed additive for all animal species. Supplementary

information. February 2012. Submitted by Lonza Benelux BV.

4. Evaluation report of the European Union Reference Laboratory for Feed Additives on themethods(s) of analysis for L-carnitine and L-carnitine L-tartrate.

5. Comments from Member States received through the ScienceNet.

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APPENDICES

APPENDIXA

Executive Summary of the Evaluation Report of the European Union Reference Laboratory for

Feed Additives on the Method(s) of Analysis for L-Carnitine and L-Carnitine L-Tartrate36

In the current application authorisation is sought under article 4(1) and 10(2) for L-Carnitine1,2

andL-

Carnitine L-Tartrate (LCLT)2 under the category/functional group 3(a) "nutritional

additives"/"vitamins, pro-vitamins and chemically well defined substances having similar effect",according to the classification system of Annex I of Regulation (EC) No 1831/2003. Authorisation issought for the use of the two feed additivesfor all animal species and categories. According to theApplicants,L-CarnitineandLCLThave a minimum purity of 97 %. Both feed additivesare intended

to be used in premixturesor added directly into the feedingstuffsand water. None of the Applicantsproposed any minimum or maximum concentration of L-Carnitineor LCLTinfeedingstuffsor water,

as set in the previous regulations.

For the determination ofL-Carnitinein thefeed additive,Applicant

1

submitted the US Pharmacopoeiamethod. The EURL identified instead the European Pharmacopoeia method. Even though no

performance characteristics are provided, the EURL recommends for official control the EuropeanPharmacopoeia method (Ph. Eur. 6th Edition, monographs 1339), for the identification and

quantification ofL-Carnitinein thefeed additive.

For the determination of L-Carnitineinpremixtures,feedingstuffsand waterApplicant1submitted an

enzymatic method, specific for the L-Carnitineisomer. This single-laboratory validated method was

further verified by a second independent laboratory. The relative precisions (i.e. relative standarddeviations of repeatability(RSDr) and relative standard deviations of intermediate precision(RSDip)

ranging from 4.5 to 5.1 % were recalculated by the EURL using the experimental data provided by theApplicant1. Furthermore, the Applicant1reported a recovery rate (RRec) ranging from 94 to 102 % and

a limit of detection (LOD) of 15 mg L-Carnitine /kg feedingstuffs, which is well below the usualconcentrations of L-Carnitine in feedingstuffs or water.The experiments were carried out at 5 g L-Carnitine/kgpremixturesand 100-165 mgL-Carnitine/kgfeedingstuffsor water.

For the determination of L-Carnitine in premixtures, Applicant2 proposed an ion chromatography

method with electrical conductivity detection (IC-ECD), which does not distinguish between two

enantiomers L- andD-Carnitine. This single-laboratory validated method was further verified by asecond independent laboratory. The relative precisions ranging from 4.2 to 4.6 % were recalculated bythe EURL using the experimental data provided by the Applicant

2. Applicant

2reported RRecranging

from 92 to 100 %. The experiments were carried out at 8-10 gL-Carnitine/kgpremixtures.

For the determination of L-Carnitine in feedingstuffs, Applicant2 proposed a Reversed-Phase High

Performance Liquid Chromatography method using a fluorimetric detector (RP-HPLC), which doesnot distinguish between two enantiomersL- andD-Carnitine. The relative precisions ranging from 6.9to 12.4 % and LOD of 6.3 mg L-Carnitine/kgfeedingstuffswere recalculated by the EURL using theexperimental data provided by the Applicant

2. Applicant

2reported RRecranging from 88 to 115 %. The

experiments were carried out at 40-60 mgL-Carnitine/kgfeedingstuffs.

For the determination ofL-Carnitinein water, Applicant2proposed a potentiometric titration. RSDrof

0.1 % was reported by Applicant2.

Based on the above considerations and the performance characteristics presented, the EURLrecommends for official control the following single-laboratory validated and further verified methods

36The full report is available on the EURL website.http://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdf

aFAD-2010-0225; bFAD-2010-0144.
http://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdfhttp://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdfhttp://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdfhttp://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdfhttp://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdfhttp://irmm.jrc.ec.europa.eu/SiteCollectionDocuments/FinRep-2010-0144+0225.pdf

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EFSA Journal 2012;10(5):2676 20

based on the spectrophotometric method after enzymatic reaction with carnitine-acetyl-transferaseenzymatic reaction for the determination ofL-Carnitineinpremixtures,feedingstuffs and water,together with

ion chromatography method with electrical conductivity detection (IC-ECD) for the

determination ofL-Carnitineinpremixtures;Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) using a fluorimetricdetector for the determination ofL-Carnitineinfeedingstuffs;

potentiometric titration with hydrochloric acid for the determination of L-Carnitine in thewater.

For the determination of L-Carnitine L-Tartrate (LCLT) in the feed additive, Applicant2submitted a

potentiometric back-titration. The method was single-laboratory validated and further verified. RSDrranging from 0.72 to 1.19 % and RSDipof 1.19 were recalculated by the EURL using the experimental

data provided by the Applicant2. RRecranging from 99.8 to 101 % were reported by the Applicant

2.

Based on the performance characteristics presented, the EURL recommends for official control thesingle-laboratory validated and further verified potentiometric back-titration method to determine L-Carnitine L-Tartrate (LCLT)in thefeed additive.

L-Carnitine is released from the LCLTsalt during sample treatment. Therefore, the EURL considers

that all the analytical methods recommended for the determination of L-Carnitine in the matricesinvestigated are suitable for official control to determine LCLT (expressed as L-Carnitine) inpremixtures,feedingstuffsand water.

Further testing or validation of the methods to be performed through the consortium of NationalReference Laboratories as specified by Article 10 (Commission Regulation (EC) No 378/2005) is not

considered necessary.

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EFSA Journal 2012;10(5):2676 21

APPENDIXB

L-Carnitineits physiological role, endogenous synthesis and metabolism

L-Carnitine, a quaternary amine, has a key role in the metabolism of fatty acids (energy) as asubstrate for the reversible acetylation of coenzyme A (Friedmann and Fraenkel, 1955) and as acarrier for the transport of long-chain fatty acids from cytosol across the inner mitochondrialmembrane (Fritz and Marquis, 1965). Furthermore, it is suggested that L-carnitine improves theoxygen supply and utilisation of the skeletal and heart muscle (Liedtke et al., 1982; Shug, 1987;Pierpont, 1992; Broderick et al., 1995; Neu, 1995). Accordingly, carnitine might also be important inthe case of muscle exercise, particularly under anaerobic conditions (Cerretelli and Marconi, 1988).

L-Carnitine is synthesised endogenously in five enzyme-catalysed steps from its precursor lysine,which provides the carbon backbone, and with methionine as methyl group donor (e.g. Bremer, 1961,1962; Wolf and Berger, 1961; Tanphaichitr et al., 1973; Cox and Hoppel, 1973a,b, 1974; Horne andBroquist, 1973). The principles of the synthesis and metabolism of L-carnitine are given in Figure B1.

Figure B1: L-Carnitine synthesis and schematic metabolism and function of carnitine

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EFSA Journal 2012;10(5):2676 22

In juvenile organisms this synthesis is probably insufficient to meet endogenous carnitinerequirements, possibly due to the low activity of -butyrobetaine-hydroxylase (Rebouche and Engel,1980; Hahn, 1981) that occurs mainly in the liver and catalyses the last step of carnitine formation.The activity of the enzyme starts to increase about 48 days after birth, and the highest concentrations

are reached in adults (Hahn, 1981). Based on these observations carnitine is sometimes considered to

be conditionally essential. Dietary supplementation with L-carnitine is therefore expected to improveintermediary fatty acid and energy utilisation and therefore weight gain and feed efficiency in younganimals, particularly when diets marginally deficient in lysine and/or methionine are fed. However, upuntil now it has not been possible to define the requirement forL-carnitine.

After ingestion L-carnitine is absorbed in the small intestine via a sodium-dependent transport system(low carnitine concentration) or at pharmacological doses of carnitine via passive diffusion as freecarnitine and short-chain carnitine esters (Shaw et al., 1983; Gudjonsson et al., 1985; Hamilton et al.,1986; Li et al., 1990; Marciani et al., 1993). The bioavailability of dietary L-carnitine is about 5487 % in humans and is dependent on the dietary L-carnitine content (Rebouche and Chenard, 1991;Rebouche, 2004). The major portion of all carnitine in the body is found in the skeletal muscle (see,for example, Mitchell, 1978). Studies with labelled L-carnitine suggest that carnitine is usually largely

not metabolised (e.g. Lindstedt and Lindstedt, 1961; Yue and Fritz, 1962; Brooks and MacIntosh,1975; Bremer, 1983); however, carnitine might be converted, for example to -methyl choline, duringstress and disease or depending on the dietary or physiological conditions (Mehlman et al., 1969;Mitchell, 1978). Carnitine is excreted mainly via the kidney with a highly efficient tubularreabsorption of about 9099 % at normal dietary intakes and normal plasma and tissue concentrations(Harper et al., 1988; Rebouche, 2004); only 2 % of the ingested L-carnitine is voided in the faeces(Carroll et al., 1981).

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