Beneficial effects of certain phosphodiesterase inhibitors ... · Mostafa El Sayed El Sayed, Nehad Eid, Ahmed Seif El Din Kamel * Pharmacology & Toxicology Department, Faculty of

Bulletin of Faculty of Pharmacy, Cairo University (2014) 52, 179–189

HO ST E D BYCairo University

Bulletin of Faculty of Pharmacy, Cairo University

www.elsevier.com/locate/bfopcuwww.sciencedirect.com

ORIGINAL ARTICLE

Beneficial effects of certain phosphodiesterase

inhibitors on diabetes mellitus in rats

* Corresponding author. Mobile: +20 1222326524.

E-mail addresses: [email protected] (M.E.S. El

Sayed), [email protected] (N. Eid), Ahmed.seifeldin@

pharma.cu.edu.eg (A.S. El Din Kamel).

Peer review under responsibility of Faculty of Pharmacy, Cairo

University.

http://dx.doi.org/10.1016/j.bfopcu.2014.06.0011110-0931 ª 2014 Production and hosting by Elsevier B.V. on behalf of Faculty of Pharmacy, Cairo University.Open access under CC BY-NC-ND license.

Mostafa El Sayed El Sayed, Nehad Eid, Ahmed Seif El Din Kamel *

Pharmacology & Toxicology Department, Faculty of Pharmacy, Cairo University, Cairo, EgyptFaculty of Pharmacy, Kasr El Aini Street, Cairo 11562, Egypt

Received 18 March 2014; accepted 12 June 2014Available online 20 August 2014

KEYWORDS

Diabetes;

Streptozotocin;

Vinpocetine;

Sildenafil;

Insulin;

C-peptide

Abstract The present study is conducted to investigate the possible antidiabetic effect of certain

phosphodiesterase inhibitors. Diabetes mellitus was induced in 18 h-fasted male wistar albino rats

by intraperitoneal injection of streptozotocin (STZ) in a single dose (50 mg/kg). Gliclazide (Glcl) as

a reference standard in a dose of 10 mg/kg, sildenafil (Sild) in 3 doses (5, 10, 20 mg/kg) as PDE5

inhibitor and vinpocetine (Vinp) in 3 doses (10, 20, 40 mg/kg) as PDE1 inhibitor were injected intra-

peritoneal daily for 2 weeks. Their effects were assessed at different time intervals namely; 2 h after

first dose, 1 week and 2 weeks after drug administration. In the present study, STZ significantly ele-

vated serum blood glucose (SBG) level, lowered serum insulin, C-peptide levels and decreased liver

glycogen content (LGC). Glcl significantly elevated serum insulin and C-peptide levels accompanied

by reduction in serum glucose level and raised LGC. Vinp and Sild elevated serum insulin, C-pep-

tide levels, LGC and decreased SBG level. The antidiabetic effect of Glcl was significantly higher

than that of Vinp or Sild. It could be concluded that Vinp possibly produced its insulin stimulatory

action via inhibition of PDE1 while Sild stimulated insulin secretion through inhibition of PDE5.

The increase in serum C-peptide indicated that Vinp and Sild stimulated synthesis of insulin in

the b-cells and Vinp is more potent than Sild in this respect due to the difference in their mechanism

of action.ª 2014 Production and hosting by Elsevier B.V. on behalf of Faculty of Pharmacy, Cairo University.Open access under CC BY-NC-ND license.

1. Introduction

Diabetes mellitus (DM) is a metabolic disorder with chronic

hyperglycemia resulting from defects in insulin secretion, insu-lin action or both.1 Diabetes mellitus is classified into 4 subtypesnamely; type 1 diabetes mellitus (T1DM), type 2 diabetes melli-

tus (T2DM), gestational diabetes mellitus (GDM) and otherspecific types.2The pathophysiology of T2DM is primarilydue to insulin impairment accompanied by beta-cell failureresulting from prolonged and increased secretory demand.3

http://crossmark.crossref.org/dialog/?doi=10.1016/j.bfopcu.2014.06.001&domain=pdf

mailto:[email protected]

mailto:[email protected]

mailto:Ahmed.seifeldin@ pharma.cu.edu.eg

mailto:Ahmed.seifeldin@ pharma.cu.edu.eg

http://dx.doi.org/10.1016/j.bfopcu.2014.06.001

http://www.sciencedirect.com/science/journal/11100931

http://dx.doi.org/10.1016/j.bfopcu.2014.06.001

http://creativecommons.org/licenses/by-nc-nd/4.0/

http://creativecommons.org/licenses/by-nc-nd/4.0/

Table 1 Effect of Glcl, Sild and Vinp individually on SBG level of STZ-induced diabetic rats after 2 h of drug administration.

Drugs and doses Parameters

Serum glucose level

Absolute value €X± S.E. (mg %) % of diabetic control

Normal control (citrate buffer) 100.5 ± 4.552 23.67

Diabetic control (streptozotocin 50 mg/kg, I.P.) 424.5* ± 26.13 100

Gliclazide (10 mg/kg, I.P.) 64.86a ± 5.383 15.28

Sildenafil (5 mg/kg, I.P.) 384.7b ± 33.79 90.62

Sildenafil (10 mg/kg, I.P.) 354.5ab ± 25.13 83.51


Vinpocetine (10 mg/kg, I.P.) 373.4b ± 12.24 87.96

Vinpocetine (20 mg/kg, I.P.) 111.4ac ± 9.065 26.24

Vinpocetine (40 mg/kg, I.P.) 118.3ac ± 8.731 27.86

The number of animals in each group ranges between 6 and 8.

Data are expressed as mean ± S.E.

Statistical analysis was carried out by one way ANOVA followed by Post-test Newman–Keuls multiple comparison test.* Significantly different from normal control at P < 0.05.a Significantly different from diabetic control at P< 0.05.b Significantly different from gliclazide at P < 0.05.c Significantly different from sildenafil (20 mg/kg) at P < 0.05.

Table 2 Effect of Glcl, Sild and Vinp individually on SBG level of STZ-induced diabetic rats after 1 week of daily drug

administration.


Serum glucose level

Absolute value €X± S.E. (mg %) % of diabetic control



Gliclazide (10 mg/kg, I.P.) 142.9a ± 10.09 31.25

Sildenafil (5 mg/kg, I.P.) 442.8b ± 26.34 96.85


Sildenafil (20 mg/kg, I.P.) 141.3a ± 9.525 30.90

Vinpocetine (10 mg/kg, I.P.) 166.5a ± 8.371 36.41




Data were expressed as mean ± S.E.

Statistical analysis was carried out by one way ANOVA followed by Post-test Newman–Keuls multiple comparison test.* Significantly different from normal control at P < 0.05.a Significantly different from diabetic control at P< 0.05.b Significantly different from gliclazide at P < 0.05.

180 M.E.S. El Sayed et al.

The complications of diabetes include cardiovascular dis-ease, peripheral vascular disease, and cerebrovascular disease.4

Moreover, there is a relation between diabetes and growing

different types of cancer.5 The commonly used classes for man-agement of diabetes have adverse effects such as increased riskof hypoglycemia, gastrointestinal problems, heart failure6 andvomiting leading to their incompliance.7

Consequently, it deemed of importance to seek for antidia-betic drugs with more efficacy and less side effects.

Vinpocetine (Vinp) is a classic PDE1 inhibitor which ele-

vates intracellular levels of cGMP and cAMP.8 Vinp blocksvoltage dependent Ca2+/Na+ channel.9,10 Vinp is a cerebralvasodilator commonly used in ischemic stroke.11 While

sildenafil (Sild) is a selective PDE5 inhibitor which elevates

intracellular level of cGMP, commonly used in erectiledysfunction.12 Vinp and Sild show antioxidant activity13–15

which are expected to have potential effects on carbohydrate

metabolism.The aim of the present study is to investigate the beneficial

effects of PDEIs on DM.

2. Materials and methods

2.1. Animals

Adult male wistar albino rats weighing 200–250 g were used.They were obtained from animal house of Faculty of

Table 3 Effect of Glcl, Sild and Vinp individually on SBG level of STZ-induced diabetic rats after 2 weeks of daily drug

administration.


Serum glucose level

Absolute value €X ± S.E. (mg %) % of diabetic control


Diabetic control (streptozotocin 50 mg/kg, I.P.) 469.3*± 46.00 100

Gliclazide (10 mg/kg, I.P.) 72.29 a ± 5.415 15.40

Sildenafil (5 mg/kg, I.P.) 99.56 a ± 3.241 21.21



Vinpocetine (10 mg/kg, I.P.) 136.4 a ± 14.59 29.06



The number of animals in each group ranges between 6and 8.


Statistical analysis was carried out by one way ANOVA followed by Post-test Newman–Keuls multiple comparison test.* Significantly different from normal control at P < 0.05.a Significantly different from diabetic control at P < 0.05.

Beneficial effects of phosphodiesterase inhibitors on diabetes mellitus in rats 181

Pharmacy of Cairo University, Cairo, Egypt. The animals werekept in plastic cages and allowed to accommodate for one

week before being subjected to experimentation. They werefed purina-chew, water was allowed ad libitum. The studywas conducted in accordance with ethical procedures and pol-

icies approved by the ethics committee of Faculty of Phar-macy, Cairo University.

2.2. Drugs and chemicals

Glcl powder was supplied as a gift from Memphis Pharmaceu-tical and Chemical Industries, Egypt. Vinp and Sild powderswere supplied as a gift from Global Napi pharmaceuticals,

Egypt. STZ was purchased from Sigma–Aldrich, USA. Glu-cose kit was purchased from Vitro Scient, Egypt. Rat insulinELISA Kit was purchased from ALPCO, USA while Rat C-

peptide ELISA kit was purchased from Wako chemicals,USA. Glycogen standard powder was obtained from MerckDarmstadt, Germany. Any other analytical chemicals are of

equal quality or A.R. quality.

2.3. Induction of diabetes mellitus

Diabetes mellitus was induced by STZ in a single dose of50 mg/kg, I.P. in rats fasted for 18 h.16 STZ was freshly pre-pared in 0.01 m citrate buffer at pH 4.5.17 In the first day ofinjection of STZ, 5% oral glucose had been given to the rats

to overcome STZ-induced hypoglycemia.18 On the third dayof STZ injection, the diabetic rats with blood glucose morethan 150 mg/dl were elected.

2.4. Preparation of samples

Blood samples were collected from all groups at 2 h after first

dose, 1 week, and 2 weeks of daily drug administration. Bloodsamples were withdrawn from the retro-orbital sinus of ani-mals fasted for 12 h. Blood samples were centrifuged for

15 min at 6000 rpm to separate serum to investigate SBG level,serum C-peptide & serum insulin level. After 2 weeks, the ani-

mals were sacrificed by cervical dislocation and the liver wasrapidly isolated for determination of LGC.

2.5. Experimental design

Rats were randomly divided into 9 groups: group 1 receivedcitrate buffer used as normal control, group 2 received STZ

(50 mg/kg, I.P.) used as diabetic control, group 3 received Glcl(10 mg/kg, I.P.) used as reference standard, groups 4, 5, 6received Sild in doses 5, 10, 20 mg/kg, I.P. respectively, andgroups 7, 8, 9 received Vinp in doses 10, 20, 40 mg/kg, I.P.

respectively.

2.6. Determination of biochemical parameters

SBG level was determined according to enzymatic methoddescribed by Tinder.19 High amount of sodium fluoride wasadded to the serum before determination of serum glucose

level for extensive inhibition of glycolysis.20 Serum insulinand C-peptide levels were measured by enzyme-linked immu-nosorbent assay (ELISA) which is based on the sandwich prin-

ciple using kits (ALPCO, USA) and (Wako chemicals, USA),respectively. LGC was determined according to the methoddescribed by Kemp and Adrienne.21

2.7. Statistical analysis

Data were expressed as mean ± standard error (S.E.). Statisti-cal analysis was carried out by one way analysis of variance

(ANOVA) followed by Post-test Newman–Keuls multiplecomparison test for comparisons of means of different groupsusing the Graph Pad Prism 5 Program. For all statistical tests,

the level of significance was at P < 0.05. Graphical representa-tions were designed by the Graph Pad Prism 5 program Tables1–10.

Table 4 Effect of Glcl, Sild and Vinp individually on serum insulin level of STZ-induced diabetic rats after 2 h of drug administration.


Serum insulin level

Absolute value €X± S.E. (lIU/mL) % of diabetic control

Normal control (citrate buffer) 9.550 ± 0.27 764

Diabetic control (streptozotocin 50 mg/kg, I.P.) 1.250 * ± 0.08 100

Gliclazide (10 mg/kg, I.P.) 52.67 *a ± 2.30 4205

Sildenafil (5 mg/kg, I.P.) 10.30ab ± 0.34 824

Sildenafil (10 mg/kg, I.P.) 12.02 ab ± 0.36 961.6

Sildenafil (20 mg/kg, I.P.) 17.60 *ab ± 0.58 1408

Vinpocetine (10 mg/kg, I.P.) 20.94 *abc ± 0.37 1675.2

Vinpocetine (20 mg/kg, I.P.) 26.48*abc ± 0.88 2118.4





Table 5 Effect of Glcl, Sild and Vinp individually on serum insulin level of STZ-induced diabetic rats after 1 week of daily drug

administration.


Serum insulin level

Absolute value €X± S.E. (lIU/mL) % of diabetic control



Gliclazide (10 mg/kg, I.P.) 22.67 *a ± 0.632 1225.4

Sildenafil (5 mg/kg, I.P.) 3.77*ab ± 0.161 203.78


Sildenafil (20 mg/kg, I.P.) 7.40*ab ± 0.258 400

Vinpocetine (10 mg/kg, I.P.) 9.550 abc ± 0.197 516.2


Vinpocetine (40 mg/kg, I.P.) 13.58 *abc ± 0.197 734





3. Results

3.1. Effect of Glcl, Sild or Vinp on SBG level of STZ-induced

diabetic rats after 2 h of first dose, 1 week and 2 weeks of dailydrug administration

STZ significantly raised SBG level 4 times that of the normalcontrol. Glcl (10 mg/kg), significantly decreased SBG level to15.28%, 31.25%, 15.40% of diabetic control after 2 h, 1 week,

two weeks of daily drug administration respectively. Sild(10 mg/kg) significantly lowered SBG level to 83.51%,83.11%, 19.79% of diabetic control after 2 h, 1 week, 2 weeks

of daily drug administration respectively. While, a higher dose(20 mg/kg) significantly lowered SBG level to 76.49%, 30.90%,

23.67% of diabetic control after 2 h, 1 week, 2 weeks of dailydrug administration respectively. The lowest dose of sildenafil(5 mg/kg) significantly reduced SBG level to 21.21% of dia-

betic control on the second week of daily drug administration.Vinp (20 mg/kg) significantly lowered SBG level to

26.24%, 32.1%, 28.43% after 2 h, 1 week, 2 weeks of daily

drug administration respectively. However, the highest dose(40 mg/kg) significantly reduced SBG level to 27.86%,30.18%, 23.82% after 2 h, 1 week, 2 weeks of daily drugadministration respectively. The lowest dose of Vinp

(10 mg/kg) significantly decreased SBG level on the first

Table 6 Effect of Glcl, Sild and Vinp individually on serum insulin level of STZ-induced diabetic rats after two weeks of daily drug

administration.


Serum insulin level

Absolute value €X ± S.E. (lIU/mL) % of diabetic control



Gliclazide (10 mg/kg, I.P.) 35.61*a ± 1.50 1810.4




Vinpocetine (10 mg/kg, I.P.) 12.95*ab ± 0.11 658.36





Statistical analysis was carried out by one way ANOVA followed by Post-test Newman–Keuls multiple comparison test.* Significantly different from normal control at P < 0.05.a Significantly different from diabetic control at P < 0.05.b Significantly different from gliclazide at P < 0.05.c Significantly different from sildenafil (20 mg/kg) at P< 0.05.

Table 7 Effect of Glcl, Sild and Vinp individually on serum C-peptide level of STZ-induced diabetic rats after two hours of drug

administration.


Serum C-peptide level

Absolute value €X± S.E. (ng/ml) % of diabetic control



Gliclazide (10 mg/kg, I.P.) 13.47 *a ± 0.192 3169



Sildenafil (20 mg/kg, I.P.) 3.267 *ab ± 0.128 768.7








and second week to 36.41%, and 29.06% of diabetic control

respectively (Fig. 1).

3.2. Effect of Glcl, Sild or Vinp on serum insulin level ofSTZ-induced diabetic rats after 2 h of first dose, one weekand two weeks of daily drug administration

STZ significantly reduced serum insulin level to nearly 10% ofthe normal control value. Glcl (10 mg/kg) significantly raised

serum insulin level to 4205%, 1225.4%, 1810.4% of diabeticcontrol after 2 h, 1 week, 2 weeks of daily drug administrationrespectively. The lowest dose of Sild (5 mk/kg) significantly

increased serum insulin level to 824%, 203.78%, 383.73% of

diabetic control after 2 h, 1 week, 2 weeks of daily drug admin-

istration respectively. However, Sild (10 mg/kg) significantlyelevated serum insulin level to 961.6%, 228.1%, 468.73% ofdiabetic control after 2 h, 1 week, 2 weeks of daily drug admin-

istration respectively however a dose of 20 mg/kg significantlyraised serum insulin level to 1408%, 400%, 573.46% of dia-betic control after 2 h, 1 week, 2 weeks of daily drug adminis-tration respectively.

The lowest dose of Vinp (10 mg/kg) increased serum insulinlevel to 1675.2%, 516.2%, 658.36% after 2 h, 1 week, 2 weeksof daily drug administration respectively. While, a dose of

(20 mg/kg) raised serum insulin level to 2118.4%, 616.75%,781.4% after 2 h, 1 week, 2 weeks of daily drug administration

Table 8 Effect of Glcl, Sild and Vinp individually on serum C-peptide level of STZ-induced diabetic rats after one week of daily drug

administration.



Absolute value €X± S.E. (ng/ml) % of diabetic control



Gliclazide (10 mg/kg, I.P.) 4.685*a ± 0.209 1186


Sildenafil (10 mg/kg, I.P.) 0.956*ab ± 0.074 242


Vinpocetine (10 mg/kg, I.P.) 1.935abc ± 0.052 490






Table 9 Effect of Glcl, Sild and Vinp individually on serum C-peptide level of STZ-induced diabetic rats after two weeks of daily drug

administration.



Absolute value €X± S.E. (ng/ml) % of Diabetic control


Diabetic control (streptozotocin 50 mg/kg, I.P.) *0.6433 ± 0.053 100

Gliclazide (10 mg/kg, I.P.) *a9.278 ± 0.549 1442

Sildenafil (5 mg/kg, I.P.) *ab2.467 ± 0.124 383.67



Vinpocetine (10 mg/kg, I.P.) *abc4.402 ± 0.106 684.28

Vinpocetine (20 mg/kg, I.P.) *abc5.093 ± 0.126 792

Vinpocetine (40 mg/kg, I.P.) *abc6.452 ± 0.182 1003.42





respectively. The highest dose of Vinp (40 mg/kg) elevated

serum insulin level to 3038.4%, 734%, 979.66% after 2 h,1 week, 2 weeks of daily drug administration respectively(Fig. 2).

3.3. Effect of Glcl, Sild or Vinp on serum C-peptide level

of STZ-induced diabetic rats after 2 h of first dose, 1 weekand 2 weeks of daily drug administration

STZ significantly reduced serum insulin level to 25% of thenormal control value. Glcl (10 mg/kg) significantly elevatedserum C-peptide level to 3169%, 1186%, 1442% of diabetic

control after 2 h, 1 week, 2 weeks of daily drug administration

respectively. Sild (5 mg/kg) raised serum C-peptide level to412.9%, 195.7%, 383.6% of diabetic control after 2 h, 1 week,2 weeks of daily drug administration respectively. Sild (10 mg/

kg) elevated serum C-peptide level to 513.6%, 242%, 477.1%of diabetic control after 2 h, 1 week, 2 weeks of daily drugadministration respectively. A higher dose of Sild (20 mg/kg)increased serum C-peptide level to 768.7%, 367.7%, 586.6%

of diabetic control after 2 h, 1 week, 2 weeks of daily drugadministration respectively.

Vinp (10 mg/kg) significantly increased serum C-peptide

level to 933.6, 490, 684.3% of diabetic control after 2 h,

Table 10 Effect of Glcl, Sild and Vinp individually on wet LGC of STZ-induced diabetic rats after 2 weeks of daily drug

administration.


Liver glycogen content

Absolute value €X± S.E. (mg/g wet liver) % of diabetic control


Diabetic control (streptozotocin 50 mg/kg, I.P.) * 13.28 ± 1.795 100

Gliclazide (10 mg/kg, I.P.) *a 88.32 ± 10.95 665.06

Sildenafil (5 mg/kg, I.P.) *ab 53.02 ± 3.899 399.24

Sildenafil (10 mg/kg, I.P.) *ab 57.36 ± 3.735 431.92

Sildenafil (20 mg/kg, I.P.) *a 66.12 ± 7.188 497.89

Vinpocetine (10 mg/kg, I.P.) *ac 72.51 ± 4.448 546

Vinpocetine (20 mg/kg, I.P.) *ac 65.18 ± 9.063 490.81

Vinpocetine (40 mg/kg, I.P.) *abc 40.59 ± 2.336 305.64




Figure 1 Effect of Glcl, Sild and Vinp individually on SBG level

of STZ-induced diabetic rats after 2 h of drug administration. The

number of animals in each group ranges between 6 and 8. Data

were expressed as mean ± S.E. Statistical analysis was carried out

by one way ANOVA followed by Post-test Newman–Keuls

multiple comparison test. *Significantly different from normal

control at P < 0.05. aSignificantly different from diabetic control

at P < 0.05. bSignificantly different from gliclazide at P < 0.05.cSignificantly different from sildenafil (20 mg/kg) at P < 0.05.


of STZ-induced diabetic rats after 1 week of daily drug adminis-

tration. The number of animals in each group ranges between 6

and 8. Data were expressed as mean ± S.E. Statistical analysis

was carried out by one way ANOVA followed by Post-test

Newman–Keuls multiple comparison test. *Significantly different

from normal control at P < 0.05. aSignificantly different from

diabetic control at P < 0.05. bSignificantly different from glicla-

zide at P < 0.05. cSignificantly different from sildenafil (20 mg/kg)

at P < 0.05.


1 week, 2 weeks of daily drug administration respectively.Moderate dose of Vinp (20 mg/kg) significantly elevated serumC-peptide level to 1197.6, 593.6, 792% of diabetic control after

2 h, 1 week, 2 weeks of daily drug administration respectively.The highest dose of Vinp (40 mg/kg) significantly raised serumC-peptide level to 2021.6%, 753.1%, 1003.4% of diabetic con-

trol after 2 h, 1 week, 2 weeks of daily drug administrationrespectively (Fig. 3).

3.4. Effect of Glcl, Sild or Vinp on LGC of STZ-induced diabeticrats after 2 weeks of daily drug administration

STZ significantly lowered liver glycogen content to 10% of thenormal control value. Glcl (10 mg/kg) significantly raised LGC

to 665% of diabetic control. As well as, Sild (5, 10, 20 mg/kg)


of STZ-induced diabetic rats after 2 weeks of daily drug admin-

istration. The number of animals in each group ranges between 6

and 8. Data were expressed as mean ± S.E. Statistical analysis

was carried out by one way ANOVA followed by Post-test

Newman–Keuls multiple comparison test. *Significantly different

from normal control at P < 0.05. aSignificantly different from

diabetic control at P < 0.05. bSignificantly different from glicla-

zide at P< 0.05. cSignificantly different from sildenafil (20 mg/kg)

at P < 0.05.

Figure 4 Effect of Glcl, Sild and Vinp individually on serum

insulin level of STZ-induced diabetic rats after two hours of drug

administration. The number of animals in each group ranges

between 6 and 8. Data were expressed as mean ± S.E. Statistical

analysis was carried out by one way ANOVA followed by Post-

test Newman–Keuls multiple comparison test. *Significantly

different from normal control at P < 0.05. aSignificantly different

from diabetic control at P < 0.05. bSignificantly different from

gliclazide at P < 0.05. cSignificantly different from sildenafil

(20 mg/kg) at P < 0.0.5.


insulin level of STZ-induced diabetic rats after one week of daily

drug administration. The number of animals in each group ranges







(20 mg/kg) at P < 0.05.


significantly elevated liver glycogen content to 399.24%,431.9%, 497.9% of diabetic control respectively in a dosedependant manner. On the other hand, Vinp (10, 20, 40 mg/

kg) significantly raised liver glycogen content to 546%,490.8%, 305.6% of diabetic control respectively (Fig. 4).

4. Discussion

Diabetes mellitus is a chronic disease and affects many patientsworldwide. Complications of diabetes comprise hyperlipopro-

teinemia, myocardial disease, diabetic foot and kidney disease.It is of importance to screen substances with the hope of beingeffective in diabetes mellitus with more efficacy and safety.

Vinp is an alkaloid derivative of vincamine22 which inhibitsselectively PDE123 and is characterized by having antioxidantactivity.24 Sild is a selective inhibitor of PDE5 and is also char-acterized by antioxidant activity25 (Figs. 5–10).

To investigate the antidiabetic effects of Vinp and Sild,blood glucose level is determined in the current study. Thelevel of blood glucose is correlated primarily to insulin level

and hepatic glucose metabolizing enzymes. So serum bloodglucose, serum insulin, serum C-peptide levels and liver glyco-gen are determined for 2 weeks.

Results of the present study revealed that Sild (10, 20 mg/kg) significantly lowered SBG level starting from 2 h afterthe first dose and continued its hypoglycemic effect up to

2 weeks of daily drug administration. These data are in accor-dance with previous results of Abdollahi, who demonstratedthat Sild lowers blood glucose concentration at higher doses.26

On the other hand, Milani found that Sild (1 mg/kg) did

not lower hyperglycemia in male wistar albino rats startingfrom the first day and continued up to 15 days.27 The differ-ence in the results could be due to the difference in doses.

The mechanism of hypoglycemia induced by Sild could beproduced via increased insulin secretion parallel to its hypogly-cemic effect. Sild (5, 10, and 20 mg/kg) significantly increased

the synthesis of insulin as evidenced by the increase in serum


insulin level of STZ-induced diabetic rats after two weeks of daily








(20 mg/kg) at P < 0.05.

Figure 7 Effect of Glcl, Sild and Vinp individually on serum C-

peptide level of STZ-induced diabetic rats after 2 h of drug








(20 mg/kg) at P < 0.05.


peptide level of STZ-induced diabetic rats after 1 week of daily








(20 mg/kg) at P < 0.05.


peptide level of STZ-induced diabetic rats after 2 weeks of daily








(20 mg/kg) at P < 0.05.


Figure 10 Effect of Glcl, Sild and Vinp individually on wet LGC

of STZ-induced diabetic rats after two weeks of daily drug








(20 mg/kg) at P < 0.05.


C-peptide level. Moreover, the hypoglycemic effect of Sild isrelated to increase in LGC where SBG is converted to hepatic

glycogen. Effects of Sild on LGC were in agreement with thosereported by Abdollahi who found that Sild administrationmarkedly reduces liver glycogenolysis.26

Vinp (10, 20, and 40 mg/kg) significantly increased seruminsulin level starting from 2 h after the first dose and continuedits insulinotropic action up to two weeks of daily drugadministration.

These results are in agreement with the data published byHan, who demonstrated that 8-methoxymethyl-isobutylmeth-ylxanthine (8MM-IBMX) a selective PDE1 inhibitor signifi-

cantly increased glucose-induced insulin secretion frompancreatic islets.28 Also, Heimann et al., proved the presenceof PDE1 in human and rat pancreatic islets and their inhibi-

tion potentiates glucose-stimulated insulin secretion.29

On the other hand, our data are not in agreement with theresults obtained by Shafiee-Nick who found that zaprinast(PDE1/PDE5 inhibitor) did not modify glucose-induced insu-

lin release from pancreatic islets.30 The discrepancy in theresults may be due to the potent inhibition of zaprinast toPDE5 compared with PDE1 as rationalized by Ahmad et al.31

Therefore, the hypoglycemic action of Vinp could be attrib-uted to the increase in serum insulin level and the increase inserum C-peptide level. Vinp increases the synthesis of insulin

as reported by the increase in serum C-peptide level. The hypo-glycemic effect of Vinp could be produced via the increase inLGC where serum glucose is converted to liver glycogen.

Regarding the effect of Vinp on LGC, limited data areavailable in the literature. However, Vinp showed antioxidantactivity against oxidative stress induced in hepaticischemia–reperfusion (IR) injury.15

In the present study, Glcl significantly lowered SBG levelstarting from 2 h after the first dose and continued the

hypoglycemic action up to two weeks of daily drug administra-tion. These data are in accordance with Hong et al.32

The hypoglycemic action of Glcl could be due to insulino-

tropic effect of Glcl accompanied by parallel increase in C-pep-tide level. These findings were supported by Juhl et al.33

LGC was significantly improved after 2 weeks of daily

administration of Glcl in diabetic rats which demonstrate theextrapancreatic action of Glcl. These data are in consistencewith those recorded by Sivakumar.34

5. Conclusion

The study established the possible anti-diabetic effect of Vinp

and Sild which is accomplished through pancreatic and extra-pancreatic actions. The study confirmed the hypothesis that,cGMP and cAMP may have a role in the augmentation of

insulin secretion.35,36

6. Conflict of interest

None declared.

References

1. Diagnosis and classification of diabetes mellitus. Diabetes Care

2014;37(Suppl. 1):S81–90.

2. Mayfield J. Diagnosis and classification of diabetes mellitus: new

criteria. Am Fam Physician 1998;58:1355–70.

3. Kahn SE. The relative contributions of insulin resistance and beta-

cell dysfunction to the pathophysiology of Type 2 diabetes.

Diabetologia 2003;46:3–19.

4. Keen H, Clark C, Laakso M. Reducing the burden of diabetes:

managing cardiovascular disease. Diabetes Metab Res Rev

1999;15:186–96.

5. Garg SK, Maurer H, Reed K, Selagamsetty R. Diabetes and

cancer: two diseases with obesity as a common risk factor.

Diabetes Obes Metab 2013.

6. Bennett WL, Wilson LM, Bolen S, Maruthur N, Singh S,

Chatterjee R, Marinopoulos SS, Puhan MA, Ranasinghe P,

Nicholson WK, Block L, Odelola O, Dalal DS, Ogbeche GE,

Chandrasekhar A, Hutfless S, Bass EB and Segal JB, Oral diabetes

medications for adults with type 2 diabetes: an update, Comparative

effectiveness reviews, No. 27; 2011.

7. McIntosh B, Cameron C, Singh SR, Yu C, Dolovich L, Houlden

R. Choice of therapy in patients with type 2 diabetes inadequately

controlled with metformin and a sulphonylurea: a systematic

review and mixed-treatment comparison meta-analysis. Open Med

2012;6:e62–74.

8. Medina AE. Vinpocetine as a potent antiinflammatory agent. Proc

Natl Acad Sci USA 2010;107:9921–2.

9. Molnar P, Erdo SL. Vinpocetine is as potent as phenytoin to block

voltage-gated Na+ channels in rat cortical neurons. Eur J

Pharmacol 1995;273:303–6.

10. Sitges M, Guarneros A, Nekrassov V. Effects of carbamazepine,

phenytoin, valproic acid, oxcarbazepine, lamotrigine, topiramate

and vinpocetine on the presynaptic Ca2+ channel-mediated release

of 3Hglutamate: comparison with the Na+ channel-mediated

release. Neuropharmacology 2007;53:854–62.

11. Miskolczi P, Vereczkey L, Szalay L, Gondocs CS. Pharmacoki-

netics of vinpocetine and apovincaminic acid in patients with

impaired renal function. Eur J Drug Metab Pharmacokinet

1984;9:169–75.

12. Cheitlin MD, Hutter Jr AM, Brindis RG, Ganz P, Kaul S, Russell

Jr RO, et al. ACC/AHA expert consensus document. Use of

http://refhub.elsevier.com/S1110-0931(14)00033-7/h0005




































sildenafil (Viagra) in patients with cardiovascular disease. Amer-

ican College of Cardiology/American Heart Association. J Am

Coll Cardiol 1999;33:273–82.

13. Ozgur BC, Telli O, Yuceturk CN, Sarici H, Ozer E, Surer H, et al.

The effect of sildenafil and udenafil to the testicular damage

following ischemia/reperfusion injury in rats. J Urol 2014.

14. Zaitone SA, Abo-Elmatty DM, Elshazly SM. Piracetam and

vinpocetine ameliorate rotenone-induced Parkinsonism in rats.

Indian J Pharmacol 2012;44:774–9.

15. Zaki HF, Abdelsalam RM. Vinpocetine protects liver against

ischemia-reperfusion injury. Can J Physiol Pharmacol

2013;91:1064–70.

16. Hounsom L, Horrobin DF, Tritschler H, Corder R, Tomlinson

DR. A lipoic acid-gamma linolenic acid conjugate is effective

against multiple indices of experimental diabetic neuropathy.

Diabetologia 1998;41:839–43.

17. Becker DJ, Reul B, Ozcelikay AT, Buchet JP, Henquin JC,

Brichard SM. Oral selenate improves glucose homeostasis and

partly reverses abnormal expression of liver glycolytic and

gluconeogenic enzymes in diabetic rats. Diabetologia 1996;39:3–11.

18. Hajduch E, Darakhshan F, Hundal HS. Fructose uptake in rat

adipocytes: GLUT5 expression and the effects of streptozotocin-

induced diabetes. Diabetologia 1998;41:821–8.

19. Trinder P. Ann Clin Biochem 1969;6, p. 14–14.

20. Waring WS, Evans LE, Kirkpatrick CT. Glycolysis inhibitors

negatively bias blood glucose measurements: potential impact on

the reported prevalence of diabetes mellitus. J Clin Pathol

2007;60:820–3.

21. Kemp A, van Heijningen AJ. A colorimetric micro-method for the

determination of glycogen in tissues. Biochem J 1954;56:646–8.

22. Vinpocetine. Monograph, . Altern Med Rev 2002;7:240–3.

23. Ortiz-Capisano MC, Liao TD, Ortiz PA, Beierwaltes WH.

Calcium-dependent phosphodiesterase 1C inhibits renin release

from isolated juxtaglomerular cells. Am J Physiol Regul Integr

Comp Physiol 2009;297:R1469–76.

24. Pereira C, Agostinho P, Moreira PI, Duarte AI, Santos MS,

Oliveira CR. Neuroprotection strategies: effect of vinpocetine

in vitro oxidative stress models. Acta Med Port 2003;16:401–6.

25. Bivalacqua TJ, Musicki B, Hsu LL, Berkowitz DE, Champion

AL, Burnett AL. Sildenafil citrate-restored eNOS and PDE5

regulation in sickle cell mouse penis prevents priapism via control

of oxidative/nitrosative stress. PLoS One 2013;8:e68028.

26. Hoseini S, Esmaily H, Mohammadirad A, Abdollahi M. Effects of

sildenafil a phosphodiesterase 5 inhibitor on rat liver cell key

enzymes of gluconeogenesis and glycogenolysis. Int J Pharm

2006;2(3):280–5.

27. Milani E, Nikfar S, Khorasani R, Zamani MJ, Abdollahi M.

Reduction of diabetes-induced oxidative stress by phosphodies-

terase inhibitors in rats. Comp Biochem Physiol C Toxicol

Pharmacol 2005;140:251–5.

28. Han P, Werber J, SuranaM, Fleischer N, Michaeli T. The calcium/

calmodulin-dependent phosphodiesterase PDE1C down-regulates

glucose-induced insulin secretion. J Biol Chem 1999;274:22337–44.

29. Heimann E, Jones HA, Resjo S, Manganiello VC, Stenson L,

Degerman E. Expression and regulation of cyclic nucleotide

phosphodiesterases in human and rat pancreatic islets. PLoS One

2010;5:e14191.

30. Shafiee-Nick R, Pyne NJ, Furman BL. Effects of type-selective

phosphodiesterase inhibitors on glucose-induced insulin secretion

and islet phosphodiesterase activity. Br J Pharmacol

1995;115:1486–92.

31. Ahmad M, Abdel-Wahab YH, Tate R, Flatt PR, Pyne NJ,

Furman BL. Effect of type-selective inhibitors on cyclic nucleotide

phosphodiesterase activity and insulin secretion in the clonal

insulin secreting cell line BRIN-BD11. Br J Pharmacol

2000;129:1228–34.

32. Hong Z, Ping BU, Yan-hong X, Juan L, Min-xiang L, Zhao-hui

L, Er-yuan L. Effect of repaglinide and gliclazide on glycaemic

control, early-phase insulin secretion and lipid profiles in newly

diagnosed type 2 diabetics. Chin Med J 2011;124(2):172–6.

33. Juhl CB, Porksen N, Pincus SM, Hansen AP, Veldhuis JD,

Schmitz O. Acute and short-term administration of a sulfonylurea

(gliclazide) increases pulsatile insulin secretion in type 2 diabetes.

Diabetes 2001;50:1778–84.

34. Sivakumar S, Subramanian SP. D-pinitol attenuates the impaired

activities of hepatic key enzymes in carbohydrate metabolism of

streptozotocin-induced diabetic rats. Gen Physiol Biophys

2009;28:233–41.

35. Ishikawa T, Kaneko Y, Sugino F, Nakayama K. Two distinct

effects of cGMP on cytosolic Ca2+ concentration of rat pancreatic

beta-cells. J Pharmacol Sci 2003;91:41–6.

36. Smukler SR, Tang L, Wheeler MB, Salapatek AM. Exogenous

nitric oxide and endogenous glucose-stimulated beta-cell nitric

oxide augment insulin release. Diabetes 2002;51:3450–60.






















































































Documents

Beneficial effects of certain phosphodiesterase inhibitors ... · Mostafa El Sayed El Sayed, Nehad Eid, Ahmed Seif El Din Kamel * Pharmacology & Toxicology Department, Faculty of