British Journal ofIndustnial Medicine 1993;50:1104-11 10

Serum laminin, hydrocarbon exposure, andglomerular damage

P Hotz, N Thielemans, A Bernard, F Gutzwiller, R Lauwerys

AbstractIt has been postulated that occupational expo-sure to hydrocarbons may damage the kidneyand lead to glomerulonephritis and chronicrenal failure. As laminin is a ubiquitous base-ment membrane component that seems toplay a central part in the structure and func-tion of basement membranes and as thenormal renal filtration process is highlydependent on an intact glomerular basementmembrane, the serum laminiin concentrationwas examined in a population of workersexposed to hydrocarbons. The hydrocarbonexposure was assessed by exposure surrogates(exposure duration and exposure score). Aninteraction between occupational exposure tohydrocarbons and hypertension increased thelaminin concentration whereas the lamininconcentration decreased in workers exposedfor a long time probably because of a selectioneffect. In a subgroup of printers exposed totoluene whose hippuric acid excretion hadbeen recorded for several years this interac-tion was confirmed when the hippuric acidexcretion was substituted for the other expo-sure indices. In the exposed group, the age-related decline in creatinine clearance wasaccelerated. These results seem to confirmthat occupational exposure to hydrocarbons isa non-specific factor that may promote adeterioration ofrenal function.

(British 3rournal ofIndustrial Medicine 1993;50:1104-1 1 10)

Institut fUr Sozial- und Praventivmedizin,Sumatrastrasse 30, CH-8006 Zurich, SwitzerlandP Hotz, F GutzwillerUnite de toxicologie industrielle et de medecinedu travail. Clos Chapelleraux-Champs 30, B-1200Bruxelles, BelgiqueN Thielemans, A Bernard, R Lauwerys

Laminin is a ubiquitous component of basementmembranes that seems to play an importantstructural and functional part within basementmembranes. Indeed, this glycoprotein possessesbinding domains for heparan sulphate proteoglycanand nidogen and cell binding properties involved inthe anchorage of epithelial and endothelial cells tothe glomerular basement membrane. Polyanioniccharges of heparan sulphate proteoglycan are prob-ably implicated in the ionic control of filtrationthrough the glomerular basement membrane andnidogen mediates the binding of laminin to colla-gen IV, another major component of basementmembranes.' As the normal renal filtration processis highly dependent on an intact glomerular base-ment membrane it is not surprising that the serumlaminin concentration may increase2 and that anti-laminin antibodies may appear in patients diag-nosed with renal disease.3

As organic solvents are suspected of playing apart in chronic nephropathies, Viau et alP searchedfor antilaminin antibodies in refinery workersexposed to hydrocarbons and found a slightlyincreased prevalence of high titres in exposed work-ers. Furthermore, Mutti et aP have recentlydescribed an increased serum laminin concentra-tion in workers exposed to perchloroethylene. Inboth studies however, workers diagnosed with arenal or systemic disease were excluded. Thismight cause a selection bias as the workers with ahistory of kidney disease might constitute the groupmost at risk. Indeed, if renal disease is worsened byoccupational exposure to hydrocarbon, the renaldisease will progress more rapidly and it will bediscovered earlier. Therefore, these workers will beexcluded although hydrocarbons may have played apart in the progression of their renal disease. As aselection process of this kind is thought to be anexplanation for the paradoxical association betweenalbuminuria and ethnicity found in the crosssectional study of Gerber et al,6 the possibility thatstudies including only healthy workers have under-estimated the real risk of hydrocarbon nephrotoxic-ity in occupationally exposed workers cannot beexcluded.

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Serum laminin, hydrocarbon exposure, and glomerular damage

The purpose of this study was to measure theserum laminin concentration in a population ofworkers exposed to hydrocarbons, including sub-jects diagnosed with previous or present renal dis-ease or hypertension or both. The hypothesis wasthat a disturbance in the glomerular basementmembrane is induced by the interaction betweenhypertension and occupational exposure to hydro-carbons and, therefore, that serum laminin concen-tration would increase especially in the exposed andhypertensive workers. This hypothesis is based onthe results of a previous study with other markers ofrenal damage.78 We also attempted to confirm theseresults with a biological indicator of exposure ratherthan indirect exposure indices such as exposureduration and exposure score. Therefore, a group oftoluene exposed printers whose hippuric acid excre-tion was known was examined. Finally, the relationsbetween serum laminin or heparan sulphate proteo-glycan (assessed as total urinary glycosaminoglycanexcretion) and other markers of glomerular damagewere examined.

Subjects and methodsThe study population involved adult male workerswho were either invited to a general health exami-nation in the frame of studies assessing occupa-tional risks or had to undergo a periodic orpreplacement medical examination. To avoid arecall bias, patients referred to us because of apossible occupational disease were excluded.A detailed description of the selection rationale,

of the products used (mainly toluene alone or incombination), of the characteristics of the sub-groups, and of the study protocol has beenreported elsewhere.79 Six subgroups were identi-fied-namely, floor layers (heavy hydrocarbonexposure; n = 106), printers (moderate exposure; n= 25), roadmen (slight exposure; n = 40), controls(no exposure at all, n = 48), formerly exposedworkers (former exposure only; n = 35), "false"controls (present exposure not suggested by thepresent job title; n = 10). Fifteen (5-4%) workersdid not participate (10 refusals, five because oforganisational problems). There was not enoughserum for laminin analysis in 20 cases and fiveworkers had no satisfactory urine collection (proto-col not observed, too little urine).A hydrocarbon exposure is defined as an expo-

sure resulting from any of 27 occupations listed ina standardised questionnaire. The exposure indica-tors are the same as in our previous work.78 Briefly,lifetime exposure duration (LED, years) and life-time exposure score (LES; arbitrary units, years xintensity factor) were assessed on the basis of theoccupational history. Three exposure duration sub-groups were used (ED1, no hydrocarbon exposureat all: ED2, between 0.01 and 9-9 years, ED3;

> 10 years). Work related hydrocarbon inducedsymptoms (feeling drunk, having a non-specificgastric disturbance, dizziness, nausea, alcoholintolerance, or drowsiness) occurring during thefour to eight weeks before the clinical examinationwere considered as a crude index of recent exces-sive exposure to hydrocarbons. A symptom wasdefined as work related if there was a clear workrelated pattern and when this relation was consid-ered as probable. Doubtful or possible relationswere therefore classified as non-work related.Workers complaining of at least one such workrelated symptom were compared with workerswithout any such symptom. Workers complainingof symptoms of this kind that could not be consid-ered as work related constituted a third subgroup.

In the printer group, the exposure could also beestimated on the basis of hippuric acid (HA)concentrations in urine. As the individual HA con-centration had generally been measured every threemonths since 1978, individual yearly means of HAexcretion could be calculated. Their sum for eachworker gives the individual cumulative HA excre-tion. Details about these surveys and the analyticalmethods can be found elsewhere.'0 The examinedprinters represent the whole present workforce of aprinting house where lead was never used.

Exposure to lead, mercury, or cadmium waslooked for with a check list. If possible, an intensityscore was also assessed blindly by an industrialhygienist.7

Serum laminin (U/ml) was assayed by measuringits pepsin resistant fragment (laminin P1;Behringwerke, Marburg, Germany). Creatinine inblood and urine was assayed by the Jaffe method(Boehringer Diagnostica, Mannheim, Germany)and the endogeneous creatinine clearance wasmeasured over some hours (ml/min/1 73 M2;median sampling time 187 minutes). Albuminexcretion rate (U-alb; pg/min) was assayed byradioimmunoassay (Pharmacia, Uppsala, Sweden).The fractional albumin clearance was calculatedas (urinary albumin/serum albumin) x (plasmacreatinine/urinary creatinine). N-acetyl- fl-D-glucosaminidase activity (NAG; mU/mmol creati-nine), glycosaminoglycan concentration (GAG),erythrocyte counts (number/ml), retinol bindingprotein (RBP; ug/mmol creatinine), serum /l-2-microglobulin (S-,B2MG; mg/l), serum albumin(gil), and protein:creatinine ratio in the first andsecond morning urine (PCR-Ul and PCR-U2)were assessed as described previously.78 A PCR-U1>108 or a PCR-U2 > 127 indicate abnormalproteinuria. The GAG excretion was expressed as aconcentration (mg/l) standardised for a diuresis of1 ml/min.8

Several confounders were considered becauseserum laminum may be affected by liver dis-

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eases,'2 13 scleroderma,'4 cancer,'5 diabetes,'6 andperhaps age or glomerular filtration rate.2 All work-ers who had a clinical history with past or presentdisease capable of affecting the kidney (systemicdiseases such as hypertension or diabetes included)or the urinary tract, or who had regularly takendrugs for at least one month before the clinicalexamination constituted the "renal" disease group.Regular drug consumption was taken into consid-eration because it can affect sensitive markers ofrenal disease. Most workers in this group (52;44-1%) were hypertensive (systolic blood pressure>,160 or diastolic pressure > 95 mm Hg). Therewere too few workers with renal parenchymal dis-ease to constitute a more specific group.As Gosling and Beevers'7 showed that U-alb can

already increase above blood pressure values > 140or >. 90 mm Hg, we also defined subgroupsaccording to these cut off values. A "higher" bloodpressure (HBP) was then defined as any value) 140 or > 90 mmHg, a "lower" blood pressure(LBP) as values <140 and <90 mm Hg. Meanblood pressure is the sum of diastolic blood pres-sure and one third of the difference betweensystolic and diastolic blood pressure.The digestive disease group included all workers

with a clinical history of digestive, biliary, pancrea-tic, or hepatic disease, or regular drug consumptionas defined earlier. The liver disease group includedonly workers with a history of hepatic disease. Mostpatients (11; 58%) had a clinical history ofhepatitis. Further confounding factors were creati-nine clearance, age, alcohol consumption (indrinks/day'8), and exposure to heavy metals. Noworker suffered from scleroderma or primarybiliary cirrhosis.

Logistic regression analysis, variance analyses,and multiple regression (backward method) wereused to compare groups or to study a variable.'920If necessary, non-parametric tests or logarithmictransformations were used. For exposure score orexposure duration a normalisation or a betterresidual distribution could only be achieved bytaking the square root.

ResultsAge, body weight, body height, smoking (pack-years), LED, LES, S-02MG, S-creatinine, creati-nine clearance, PCR-U2, U-alb, GAG, and theprevalences of workers with symptoms of excessiveexposure, daily alcohol consumption, liver or"renal" disease, and hypertension were comparedbetween the group with missing values for one ormore of the most important biological measures(serum laminin, U-alb, GAG) and the group with-out missing values. Most missing values (n = 20;80%) was due to a missing serum laminin determi-nation (too little serum). These comparisons did

not show any trend with respect to exposure, renalfunction, or possible confounders that could havebiased the results. Medians (lOth-90th percentiles)were 37 years (21-57) for age, 8-9 years (0-30 2)for LED, 11-5 arbitrary units (0-42 8) for LES,1 87 U/ml (1-51-2-37) for S-lam, 1 70 mg/l(1-30-2-10) for S-/J2MG, 91 0,umol/l (79-0-103-0)for serum creatinine, 110-4 ml/min/1-73 m2(78-3-137-4) for creatinine clearance; 103-3(77-8-171-1) for PCR-U2; 5-08 ,ug/min(2 40-20 28) for U-alb, and 45-6 (34 5-62-5) forGAG (concentration standardised for a diuresis of1 ml/min), in the group without missing values.

Concentrations of serum laminin correlate withage (r = 0-17, p < 0-001) and systolic and diastolicblood pressure (r > 0 14, p < 0 005). Correlationswith serum creatinine, S-fl2MG, or creatinineclearance were at best of borderline significance(p > 0 07). The serum laminin concentrationswere not raised in the digestive disease group(p = 0 29) and did not show any pattern related tosmoking (p = 0 22) or alcohol consumption(p = 0-32), which was less than about 40 gethanol/day in 240 (90 9%) workers. A slight butnot significant trend towards higher values wasfound in the liver disease group (p = 0 39) whereasthe increase was clear in the "renal" disease group(p = 0 01) and still more in the hypertensive groupor the group with higher blood pressure (p <0 0001) although there were few patients withsevere hypertension (90th percentile: 158 and 98mm Hg, highest values 200/100 and 180/120 forsystolic and diastolic blood pressure respectively).Belonging to the liver or "renal" disease group andblood pressure, age, and creatinine clearance weretherefore considered as possible determinants infurther analyses.

In a first step, the influence of LED or LES, andblood pressure or "renal" disease on serum lamininconcentration was examined before taking possibleconfounders into account. Table 1 shows that theblood pressure increased serum laminin concentra-tion more in the exposed than in the non-exposedworkers. The same trend was found in the workergroup with long duration of exposure ( > 10 years).Table 1 is designed to allow a direct comparisonwith our previous results and shows that serumlaminin behaved similarly to U-alb or NAG.7 Theother possible combinations (LES quartiles withthe factor "renal" disease, or ED1-3 with LBP orHBP groups) showed a similar trend (details notgiven). In the multiple regression analysis the inter-action term between mean blood pressure andexposure index (LED or LES) was always statisti-cally significant and furthermore, the coefficientsremained fairly stable after the introduction of theconfounders (table 2). As discussed later, the nega-tive regression coefficient is probably due to a

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Serum laminin, hydrocarbon exposure, and glomerular damage

Table 1 Occupational hydrocarbon exposure, hypertension, and serum laminin concentration

Laminin concentration Laminin concentration

No of 90th No 90thworkers Median percentile p Value of workers Median percentile P Value

LBPgroup No "renal" diseaseESQ1 50 1-87 2-47 EDI 27 1-89 2-83ESQ2 48 1-79 2-08 ED2 57 1-79 2-05ESQ3 40 1-81 2-26 ED3 46 1-85 2-30ESQ4 40 1-81 2-37HBPgroup With "renal" diseaseESQI 10 1-96 2-34 0-54 EDI 8 2-18 - 0-22ESQ2 15 2-13 2-47 0-006 ED2 27 1-78 2-33 0 33ESQ3 13 2-04 2-72 0 003 ED3 70 1-95 2-40 0-07ESQ4 24 1 99 2-56 0-007

See methods section for definitions of LBP, HBP, "renal" disease group, and ED1-3; ESQ1-4 = exposure score quartiles (from 1 =lowest to 4 = highest); p by Mann-Whitney U test for the difference between LBP and HBP workers in each ESQ or between"renal" disease groups in each ED category.

selection effect. Concentrations of serum lamininwere not raised in the workers complaining ofsymptoms of excessive recent exposure. The samecalculations were done with the present job as an

index of present exposure but some subgroupswere too small to allow a meaningful statisticalanalysis.We also assessed the two basal membrane

components, serum laminin and GAG, as possiblepredictors of glomerular damage. The markers ofglomerular damage used were total proteinuria,erythrocyturia, and U-alb. Neither serum lamininnor GAG were clearly associated with PCR valuesand neither was a significant predictor of abnormalproteinuria (PCR-U1 > 108 or PCR-U2 > 127).GAG but not serum laminin was weakly associatedwith an increased erythrocyturia ( > 600 erythro-cytes/ml) (p = 0-05). In the multiple regressionanalysis with GAG excretion and serum lamininconcentration, GAG excretion, but not serumlaminin concentration, correlated with U-alb(determination coefficient 0-13). After consideringRBP concentration (as an indicator of proximaltubule dysfunction) and NAG activity (as an

indicator of tubular damage), the determinationcoefficient increased (0 22). This effect was inde-

pendent of blood pressure, which still increased thedetermination coefficient (0 27) without removingthe three other variables. In particular, GAGremained a good predictor of albuminuria (partialregression coefficient: 0 009, p < 0 0001) whereasthe serum laminin effect was non-significant in allregressions. The same results were obtained withthe fractional albumin clearance, which is thoughtto be a more reliable indicator of the properties ofthe glomerular filter than the albumin excretionrate.

It could be argued that the interaction betweenblood pressure and exposure for serum lamininconcentration is questionable because the exposureindicators are based on the occupational historyonly. Therefore, the regression analyses were doneagain after substitution of cumulative HA excretionin the LED or the LES. Simultaneously, the expo-

sure effect on the variables (U-alb, NAG, and to alesser extent PCR or erythrocyturia) that provedinteresting in our previous work7 were re-examinedwith this exposure index. Only the printers(n = 25) and the controls (n = 48) were includedin these analyses. Care was taken to exclude sixprinters who had had an important solvent expo-sure other than that due to work in the plant where

Table 2 Serum laminin

Other independent variablesExposure index MBP Age Interaction "Renal" disease Adjusted r'

LED -0-22 R 0 001 0 11 R(n = 240) (0 0001) (0-01) (0 0001) 0 09LES -0-18 R 0-001 0-09 R(n = 240) (0 0003) (0 005) (0-0004) 0 09cumulative HA -0 75 R R 0-37 R(n = 62) (0-03) (0-03) 0-06

Dependent variable = serum laminin. Each multiple regression analysis considers another exposure indicator but the same other inde-pendent variables. The values indicated are partial regression coefficients (B) and levels of significance (in parentheses); R = removedfrom the backward regression analysis (non-significant); r' = adjusted determination coefficient; MBP = mean blood pressure.Interaction = interaction between MBP and LED, LES, or cumulative HA, respectively; for renal disease; 1 = no, 2 = yes.

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Table 3 Multiple regression analysis with albumin excretion rate as dependent variable

Set of independent variables

SerumGAG laminin Cumulative RBPexcretion concentration HA MBP Interaction Renal disease concentration r2

121 R NC NC NC NC NC 0.10(0 008)NC NC -4-23 R 2-11 R NC 0 07

(0-01) (0-01)1-21 R -3 75 R 1-88 R NC 0-17(0 008) (0 03) (0 03)1-20 R -3 73 R 1-87 R R 0-16(0 009) (0 03) (0 03)

Each equation was run with a different set of independent variables; the partial regression coefficient (B) and the level of significance (inparentheses) are indicated; NC = none considered in this run; R = removed from the backward regression analysis (non-significant);MBP = mean blood pressure; r2 = adjusted coefficient of detennination; n = 66 (after exclusion of 6 workers; see text).

the biological monitoring was done. The inter-action between blood pressure and exposureincreased significantly the albumin excretion rate(table 3), the fractional albumin clearance (partialregression coefficient of the interaction: 2 18,p = 0-01), the serum laminin (table 2), and theNAG activity (partial regression coefficient: 1-27,p = 0 003). This interaction effect was also associ-ated with an abnormal PCR-U1 and PCR-U2 (r =0-25 and 0-20, p = 0-01 and 0-03 respectively;logistic regression analysis). Only the erythrocyturiawas not dependent on this interaction.

As the decline in creatinine clearance is agerelated, the interaction age-cumulative HA excre-tion was used to examine the interaction effect onthis variable. Again the interaction was significant(partial regression coefficient = - 0-60, p = 0-01).The results were similar if S-J2MG was usedinstead of creatinine clearance.

This interaction effect cannot be easily explainedby confounders as the known confounders wereconsidered in all equations and as the inclusion ofthe six excluded printers (see earlier) did notchange the results. Moreover, these results cannotbe explained by a high correlation between LED orLES and cumulative HA excretion because thiscorrelation is weak (r = 0-16, p = 0 25). As in themultiple regression analysis with age, body massindex, regular drug taking, cumulative HA excre-tion, and the factor "renal" disease, only age andbody mass index were associated with mean bloodpressure, an association between mean blood pres-sure and cumulative HA excretion cannot beviewed as a confounder. Finally, as heavy metalexposure was more frequent in the control groupthan in the printers' group (50 0% v 8-1%) itcannot be made responsible for the effects found.

It should be emphasised that the printers' expo-sure to toulene was never very high between 1978and 1987. The median of the individual meanyearly HA excretions for this 10 year period ranged

from a maximum of 1-5 in 1984 to a minimum of0 5 mmol HA/mmol creatinine in 1987. The yearlymedian excretion diminished (range of medians:1 1-1 5 between 1978 and 1984, 0-5-1-0 between1985 and 1987). The highest individual yearlymean was 3-3 mmol HA/mmol creatinine and wasregistered in 1984 (present biological exposurelimit: 1-58 mmol HA mmol/creatinine). Themedian cumulative HA excretion was 10-1 mmolHA/mmol creatinine (range: 0-3-15-3). Enoughworkers remained in the plant between 1978 and1987 to allow comparison of their yearly HA excre-tion with the yearly HA excretion of those who leftthe printing house. A cross sectional comparison ofthe yearly HA excretion of the two groups did notshow differences between them for any year (0- 14< p < 0 99) if the comparison was made year byyear. An analysis of the cumulative HA excretionover the whole employment time, however, showedthat the printers' group was not homogeneous.There was an obvious trend towards a lower expo-sure intensity in the workers who remained in theplant for a long time (p = 0 0002).

DiscussionThe most interesting result from this study was thefinding of an interaction between hypertension andcumulated HA excretion in a population of printersexposed to toluene whose urinary HA excretionwas regularly monitored. This interaction was sig-nificantly associated with an abnormal proteinuria,an increased serum laminin concentration, albuminexcretion rate, and NAG activity. It cannot beexplained by the confounders studied. Further-more, exposure to hydrocarbons seemed toaccelerate the age dependent decline in creatinineclearance. These results agree well with the conclu-sions drawn for several markers of kidney damagein a hydrocarbon exposed population in whichanamnestic exposure indices (LED, LES) wereused instead of biological monitoring.78

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Serum laminin, hydrocarbon exposure, and glomerular damage

The second interesting result was the relationbetween U-alb and the two markers of glomerularbasal membrane disturbances, serum laminin con-centration and GAG excretion. Although bothserum laminin concentration and GAG excretionare thought to increase in glomerular damage221GAG, but not serum laminin seems to be a predic-tor of U-alb, probably because its negative chargesrepel the albumin molecule and limit its filtration.22The hydrocarbon metabolites and hypertensioncould induce a metabolic disturbance at the level ofglomerular basal membranes causing a loss ofpolyanionic charges and an increased escape ofalbumin. One possible explanation of these rela-tions might be that hypertensive workers producemore nephrotoxic metabolites in the form ofthioethers than normotensive workers. Thishypothesis is based, however, only on animalexperiments23 24 and has to be verified in humans.The third interesting point is the influence of

hydrocarbon exposure and hypertension on theserum laminin concentration. In this regard, theserum laminin concentration showed the same

pattern as that already described for several othermarkers of glomerular and tubular damage withLED and LES.78 The lack of effect of alcohol andhepatitis is not surprising because the studypopulation included few heavy drinkers andbecause most of the hepatitis cases were probablyof type A. In the same study population, alcoholconsumption increased GGT and ALT activities(p < 0*0001 and p = 0 09 respectively, details notshown) so that the lack of effect of alcohol con-

sumption on serum laminin concentration cannotbe explained by inaccurate answers to the questionabout alcohol consumption. With respect to theexposure indices the negative partial regressioncoefficient may be explained by a selection effectdue to the cross sectional study design. Hyper-tensive workers have a higher risk of cardiovascularcomplications and, therefore, are more likely toleave the plant because of disease. Furthermore, as

shown by the relation between cumulative HAexcretion and exposure duration in the printergroup, it seems that the most heavily exposedworkers, who should have the greatest risk ofkidney damage, tended to leave the plant earlier.Selection because of disease and because of heavyexposure should therefore cause the progressiveformation of a subgroup of normotensive andhealthy workers with a fairly long exposure dura-tion but a rather low exposure intensity.Consequently, as both the cumulative indices andthe number of years during which the selectioneffect works increase with time, the partialregression coefficient becomes negative after takinginto account the interaction between hypertensionand exposure.

The fact that the lack of homogeneity of thestudy population is not apparent at first sight is notsurprising if the limitations of these exposureindices in the frame of a cross sectional design areconsidered. The LED only takes the exposureduration into account and neglects the individualdifferences of the exposure intensity. The LES andthe cumulative HA excretion consider both expo-sure duration and intensity but are unable to dis-tinguish between some years of heavy exposure andmany years of low exposure. Only the examinationof the exposure of all workers having ever beinghired during a period- of several years can disclosethese exposure differences. We are aware that thelack of medical data does prevent us from provingthis explanation but it should be borne in mindthat the results of the different kidney fuictiontests are consistent7 8 11 and that all importantknown confounders have been considered for eachtest without changing the results. Moreover, theseopposite processes might also partly explain thefact that cross sectional studies about the nephro-toxicity of organic solvents have often producedconflicting results.

It could be argued that the study results rely onsensitive biochemical markers that are not relevantfor prevention. This objection does not apply,however, to abnormal proteinuria or to increasedalbuminuria. Indeed, both are associated with theprogression of renal disease and an increasedprevalence of cardiovascular disease.25-28 Further-more, occupational exposure to hydrocarbons isalso associated with glomerulonephritis andchronic renal failure.2930 Owing to the occupa-tional, medical, social, and financial consequencesof chronic renal disease the practical importance ofgood control of occupational hydrocarbonexposure is obvious.

We thank Mr P Wuthrich, Mr R Schutz, and theSwiss National Accident Insurance Fund for theirgenerous financial grant and their administrativesupport, Mrs M Berode, C Berthod, J Pilliod, andMr F Rey for the analytical work, Mr P May andM A Boillat for their help in searching the records,and Mrs C Scheibling for typing the manuscript.

Requests for reprints to: Dr P Hotz, Institut furSozial- und Praventivmedizin; Sumatrastrasse 30;CH-8006 Zurich; Switzerland.

I Timpl R. Structure and biological activity of basementmembrane proteins. EurJ7 Biochem 1989;180:487-502.

2 Horikoshi S, Koide H. Serum laminin P1 fragment concentra-tion in renal diseases. Clin Chim Acta 1991;196:185-92.

3 Shinkai Y, Karai M, Osawa G, Sato M, Koshikawa S.Antimouse laminin antibodies in IgA nephropathy andvarious glomerular diseases. Nephron 1990;56:285-96.

4 Viau C, Bernard A, Lauwerys R, Buchet, JP, Quaeghebeur L,Cornu ME, et al. A cross-sectional survey of kidney function

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in refinery employees. Am Ind Med 1987;1 1:177-87.5 Mutti A, Alinovi R, Bergamaschi E, Biagini C, Cavazzini S,

Franchini I. et al. Nephropathies and exposure to per-chloroethylene in dry-cleaners. Lancet 1992;340:189-93.

6 Gerber LM, Shmukler C, Alderman MH. Differences in uri-nary albumin excretion rate between normotensive andhypertensive, white and nonwhite subjects. Arch Intern Med1992;152:373-7.

7 Hotz P, Pilliod J, Bernard A, Berode M, Rey P. Mazzocato C,et al. Hydrocarbon exposure, hypertension and kidney func-tion tests. Int Arch Occup Environ Health 1990;62:501-8.

8 Hotz P, Pilliod J, Berode M, Rey F, Boillat MA.Glycosaminoglycans, albuminuria and hydrocarbon expo-sure. Nephron 1991;58:184-91.

9 Hotz P, Tschopp A, S6derstr6m D, Holtz J, Boillat MA.Gutzwiller F. Smell or taste disturbances, neurologicalsymptoms, and hydrocarbon exposure. Int Arch OccupEnviron Health 1992;63:525-30.

10 Droz PO, Berode M, Boillat MA, Lob M. Biological monitor-ing and health surveillance of rotogravure printing workersexposed to toluene. In: Ho MH. Dillon HK, eds. Biologicalmonitoring of exposure to chemicals. Organic compounds. NewYork: John Wiley 1987:111-31.

11 Hotz P, Pilliod J, Bernard A, Rey F, Boillat MA. Erythrocytesglomerulaires, albuminurie, glycosaminoglycanes et exposi-tion aux hydrocarbures. Schweiz Med Wochenschr1990;120:999-1004.

12 van Zanten RAA, van Leeuwen RE, Wilson JHP. Serum pro-collagen III N-terminal peptide and laminin P1 fragmentconcentrations in alcoholic liver disease and primary biliarycirrhosis. Clin Chim Acta 1988;177:141-6.

13 Annoni G, Colombo M, Cantaluppi MC, Khlat B,Lampertico P, Rojkind M. Serum type III procollagen pep-tide and laminin (Lam-PI) detect alcoholic hepatitis inchronic alcohol abusers. Hepatology 1989;9:693-7.

14 Herrmann K, Schulze E, Heckmann M, Schubert I, MeurerM, Ziegler V, et al. Type m collagen aminopropeptide andlaminin PI levels in serum of patients with silicosis-associ-ated and idiopathic systemic scleroderma. Br J Dermatol1990;123: 1-7.

15 Felden F, Renkes P, Fremont S, Chambre JF, ChampigneulleB, Gaucher P, et al. Serum laminin P1 in metastatic coloncarcinoma. Clin Chem 1991;37:1795-6.

16 Hogemann B, Voss B. Altenwerth FJ, Schneider M,Rauterberg J, Gerlach U. Concentrations of 7S collagen andlaminin P1 in sera of patients with diabetes mellitus. KlinWochenschr 1986:64:382-5.

17 Gosling P, Beevers DG. Urinary albumin excretion and blood

pressure in the general population. Clin Sci 1989;76:39-42.18 Rollason JG, Pincherle G, Robinson D. Serum gamma glu-

tamyl transpeptidase in relation to alcohol consumption.Clin Chim Acta 1972;39:75-80.

19 SUGI SAS User's Group International. SUGI supplementallibrary user's guide. 5th ed. Cary, NC: SAS Institute Inc.1986:1-662.

20 SPSS'X. SPSS-XTM user's Guide. 3rd ed. Chicago: SPSSInc. 1988:1-1072.

21 Baggio B, Gambaro G, Briani C. Favaro S, Borsatti A.Urinary excretion of glycosaminoglycans and brush borderand lysosomal enzymes as markers of glomerular and tubu-lar involvement in kidney diseases. Contrib Nephrol1984;42: 107-10.

22 Reddi AS, Ramamurthi R, Miller M, Dhuper S, Lasker N.Enalapril improves albuminuria by preventing glomerularloss of heparan sulfate in diabetic rats. Biochem Med MetabBiol 1991;45:119-31.

23 Decarie S, Chakrabarti S. Metabolism and hepatorenal toxic-ity due to repeated exposure to styrene in spontaneouslyhypertensive rats (SHR). J Toxicol Environ Health 1989;27:455-65.

24 Craan AG, Malick MA. Structure-nephrotoxicity relationshipsof glutathione pathway intermediates derived from organicsolvents. Toxicology 1989;56:47-61.

25 Yudkin JS, Forrest RD, Jackson CA. Microalbuminuria aspredictor of vascular disease in non-diabetic subjects. Lancet1988;ii:530-3.

26 Ravid M, Savin H, Lang R, Jutrin I, Shoshana L, Lishner M.Proteinuria, renal impairment, metabolic control, and bloodpressure in type 2 diabetes mellitus. A 14-year follow-upreport on 195 patients. Arch Intern Med 1992;152:1225-9.

27 Messent JWC, Elliott TG, Hill RD, Jarrett RJ, Keen H,Viberti GC. Prognostic significance of microalbuminuria ininsulin-dependent diabetes mellitus: a twenty-three year fol-low-up study. Kidney Int 1992;41:836-9.

28 Kannel WB, Stampfer MJ, Casteili WP, Verter J. The prog-nostic significance of proteinuria: The Framingham study.Am Heart_t 1984;108:1347-52.

29 Bell GM, Gordon ACH, Lee P, Doig A, MacDonald MK,Thomson D, et al. Proliferative glomerulonephritis andexposure to organic solvents. Nephron 1985;40:161-5.

30 Steenland NK, Thun MJ, Fergusson CW, Port FK.Occupational and other exposures associated with maleend-stage renal disease: A case/control study. Am J PublicHealth 1990;80: 153-9.

Accepted 8 February 1993

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