Occupational and Environmental Medicine 1996;53:21 1-215

SHORT REPORT

Glutathione transferase activity and formation ofmacromolecular adducts in two cases of acutemethyl bromide poisoning

Robert Gamier, Marie-Odile Rambourg-Schepens, Andreas Muller, Ernst Hallier

Centre Andi-poisons,CliniqueToxicologique etInstitutInteruniversitaire deMedecine du Travail,Hopital FernandWidal, 200 rue duFaubourg Saint-Denis,75010 Paris, FranceR GamierCentre Anti-poisons,Hopital MaisonBlanche, 51092 Reimscedex, FranceM-O Rambourg-SchepensInstitut furArbeitsphysiologie ander UniversitaitDortmund,Ardeystrasse 67D-44139 Dortmund,GermanyE HallierA MullerCorrespondence to:Dr R Gamier, CentreAnti-poisons, CliniqueToxicologique et InstitutInteruniversitaire deMedecine du Travail,H6pital Fernand Widal,200 rue du FaubourgSaint-Denis, 75010 Paris,France.

Accepted 6 October 1995

AbstractObjectives-To determine the activity ofglutathione transferase and to measurethe S-methylcysteine adducts in bloodproteins, after acute inhalational expo-sure to methyl bromide. To examine theinfluence of the polymorphism of glu-tathione-S-transferase 0 (GSTT1) on theneurotoxicity ofmethyl bromide.Methods-Two workers acutely exposedto methyl bromide with inadequate respi-ratory protective devices were poisoned.Seven weeks after the accident, bloodsamples were drawn from both patients,for measurement of glutathione trans-ferase activity in erythrocytes (conjugatorstatus-that is, GSTT1 phenotype) andmeasurement of binding products ofmethyl bromide with blood proteins.Conjugator status was determined by astandard procedure. The binding productofmethyl bromide, S-methylcysteine, wasmeasured in globin and albumin.Results-Duration and intensity of expo-sure were identical for both patients asthey worked together with the same pro-tective devices and with similar physicaleffort. However, one patient had verysevere poisoning, whereas the other onlydeveloped mild neurotoxic symptoms.The first patient was a "conjugator" withnormal glutathione transferase activity,whereas this activity was undetectable inthe erythrocytes of the second patient,who consequently had higher concentra-tions of S-methylcysteine adduct in albu-min (149 v 91 nmollg protein) and inglobin (77 v 30 nmollg protein).Conclusions-Methyl bromide is geno-toxic and neurotoxic. Its genotoxicityseems to be the consequence of the alky-lating activity of the parent compound,and conjugation to glutathione has a pro-tective effect. The data presented heresuggest a different mechanism for methylbromide neurotoxicity which could berelated to the transformation of methyl-glutathione into toxic metabolites such asmethanethiol and formaldehyde. If suchmetabolites are the ultimate toxic species,N-acetylcysteine treatment could have atoxifying rather than a detoxifying effect.

(Occup Environ Med 1996;53:21 1-215)

Keywords: methyl bromide; poisoning; glutathionetransferase

Methyl bromide has been used since the endof the 18th century. Up until the late 1950s, itwas mainly used as a fire extinguisher.Nowadays, it is primarily a fumigant for thecontrol of nematodes, fungi, and weeds ingreenhouses, as well as for the eradication ofinsects and rodents in mills, warehouses, grainelevators, ships, and freight cars.'

Methyl bromide is a colourless gas; it is alsoodourless at concentrations up to several timesthe French maximum allowable concentrationof 20 mg/mi. Therefore high exposure mayoccur unknowingly and several hundreds ofcases of severe poisoning in humans have beenreported.2

Short exposures to high concentrations mayresult in gastrointestinal, neurological, andrespiratory symptoms. Early manifestations ofmethyl bromide poisoning include headache,nausea, vomiting, and dizziness; they may bepreceded by a symptom-free interval of upto two hours.3 Progression of neurologicalsymptoms to coma, myoclonus, generalisedseizures, and distal axonopathy may follow. Insuch severe cases, lung damage is generallyfound: the most frequently reported lesion ispulmonary oedema.2 At this acute stage,hepatic or renal impairment may also benoted, but is usually mild.2 Status epilepticus(or status myoclonicus) is associated with ahigh mortality.4 In non-fatal cases, recovery isslow and neurological or psychiatric sequelaeare frequent.2

Danse et all reported that methyl bromidewas carcinogenic in Wistar rats, which devel-oped squamous cell papillomas and carcino-mas of the forestomach after oral doses. Otherauthors, however, showed regression of theforestomach lesions after discontinuation of

6exposure. A chronic inhalation study, alsocarried out in rats, did not show any carcino-genic activity of methyl bromide.7 Methyl bro-mide is a methylating agent which readilyreacts with macromolecules. It was mutagenicin various procaryote and cellular systems' andinduced sister chromatid exchanges in humanperipheral lymphocyte cultures.8

There are no reliable indicators of exposureto methyl bromide: methyl bromide is rapidlyundetectable in human tissues, due to its shorthalf life,39 concentrations of blood bromide

211

on January 21, 2020 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.3.211 on 1 March 1996. D

ownloaded from

Gamier, Rambourg-Schepens, Muller, Hallier

and S-methylcysteine adduct are dependenton the metabolism of methyl bromide, whichdisplays genetic polymorphism.'0

Conjugation with glutathione to S-methyl-glutathione is the first step of the major meta-bolic pathway for all methyl halides in variousrodent species." '1 Conjugation of methyl bro-mide with glutathione is both non-enzymaticand catalysed by glutathione transferase inhuman erythrocytes. 14 This enzyme activityshows polymorphism.'0 Three quarters of thewestern European population are able to enzy-matically conjugate methyl bromide with glu-tathione; the remaining quarter lacks thisspecific enzyme activity."' It was shown thatmethyl bromide induced sister chromatidexchanges in vitro in the lymphocytes of non-conjugators, whereas such an effect was notfound in the lymphocytes of conjugators.'5This indicates that the genotoxicity of methylbromide is probably the consequence of themethylating activity of the parent compoundand that conjugation to glutathione has a pro-tective effect.To date, the mechanism of methyl bromide

neurotoxicity has not been elucidated. How-ever, it is generally postulated that neurotoxiceffects also result from direct alkylation ofmacromolecules; conjugation to glutathione isconsequently thought to have a protectiveeffect and giving N-acetylcysteine is recom-mended by some authors to prevent the acutesystemic effects of methyl bromide.'6 Wereport an accident involving two workers, inwhom the clinical and laboratory features donot support these propositions.

Patients and methodsThe first patient was admitted to the intensivecare unit of the Reims Poison Centre aboutfour hours after the end of exposure. The sec-ond patient was referred to the OccupationalHealth and Clinical Toxicology Departmentof Fernand-Widal Hospital, four days after theaccident.The circumstances of the accident were

obtained through interviews with the secondpoisoned worker.

Both patients had repeated clinical exami-nations by internists and neurologists. Furtherinvestigations included: routine haematology,biochemical tests, standard urinalysis, chestradiography, electrocardiography, electroen-cephalography, neuropsychological tests,brainstem auditory, visual, and somatosensoryevoked potentials, computed tomography andmagnetic resonance imaging of the brain, elec-troneuromyography, and measurement ofserum bromide concentrations.

Blood samples were drawn from bothpatients seven weeks after the accident formeasurement of glutathione transferase activ-ity in erythrocytes (conjugator status) andmeasurement of binding products of methylbromide with blood proteins. Conjugator sta-tus was ascertained by the standard procedurefor methyl bromide, according to Hallier etal.'5 The binding product of methyl bromide,S-methylcysteine, was measured in globin and

albumin according to the method of Mulleret al.'7

ResultsCIRCUMSTANCES OF THE ACCIDENTThe accident occurred in a nine floor mill. Onday 1, the two workers sealed all openingsexcept one door at the bottom of the building;they placed methyl bromide cylinders on eachfloor; then both of them, wearing canister res-pirators, opened the cylinders; they startedfrom the upper floors and immediately wentout of the building at the end of the operationwhich lasted less than 10 minutes, and thensealed the escape door.They returned on day 2, about 24 hours

after the beginning of fumigation. Protectiveclothing consisted of overalls, PVC gloves,working shoes and masks; as they thought therecommended airway protection was unneces-sarily uncomfortable, they only wore facemasks with disposable filters instead of theautonomous breathing apparatus which theyshould have used. At first, they removed sealsand opened doors and windows on the groundfloor. One of them then went up to the ninthfloor and the other went to the eighth wherethey performed the same operation. They metat the seventh floor and then worked together,opening all windows on each floor, while goingdownstairs. The total operation lasted about45 minutes. A sample of the atmosphere in thebuilding had been taken at the very beginningof the ventilation procedure: the methyl bro-mide concentration was measured to be17 000 mg/m3.

PATIENTSOn their return to the ground floor both work-ers noted a chloroform like odour throughtheir mask and experienced a slight burningsensation in the throat which prompted themto leave the building, remove their protectingdevices and clothes, and take a shower. A fewminutes after the end of exposure, both workersexperienced nausea, vomiting, headache, anddizziness. Two hours later, one of them(patient 1) had severe myoclonic seizures.Both patients were soon admitted to the nearestrural hospital. Patient 1 received thiopentaland flunitrazepam, and was intubated andmechanically ventilated. Both patients werethen transferred to the intensive care unit ofthe Reims poison centre.

Case 1Patient 1 was a previously healthy 43 year oldman. On admission, he showed generalisedseizures, cardiogenic shock, bilateral pul-monary oedema, profuse diarrhoea, and acuteanuric renal failure. As well as standard sup-portive measures, treatment with intravenousN-acetylcysteine was started five hours afterthe end of exposure: the initial dose of 140mg/kg was followed by 5 g doses every fourhours until the fifth day. Diarrhoea resolvedspontaneously within 24 hours. Pulmonaryoedema was rapidly controlled by permanent

212

on January 21, 2020 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.3.211 on 1 March 1996. D

ownloaded from

Glutathione transferase activity andformation of macromolecular adducts in two cases of acute methyl bromide poisoning

positive pressure ventilation. The haemody-namic disturbances required high doses of cat-echolamines for five days. Because of theunstable haemodynamic condition, continu-ous haemofiltration was initially performed for13 days, then haemodialysis was performeddaily for another 21 days; renal function nolonger required dialysis thereafter. Measure-ments of plasma bromide concentrations wereperformed on admission and on the next day.The initial bromide concentration was 156mg/l (normal range: 3-5-5 5 mg/i) andreturned to normal values on the second day,after 12 hours of haemofiltration. Surprisingly,liver function tests remained normal through-out the acute phase of poisoning. Necroticlesions of the skin appeared on the distalextremities of the fingers and toes in the firstseven days after admission; moist dressingsallowed complete healing within two weeks.The tonic clonic generalised convulsions wereonly partially controlled by repeated intra-venous doses of clonazepam and thiopental; afew days after admission, they turned into gen-eralised myoclonic jerks which required curari-sation with pancuronium until the 21st day.Suppression of myoclonic activity was thenachieved by long term treatment with carba-mazepine and clonazepam. Mechanical venti-lation was stopped on the 22nd day, but owingto absent gag reflex, the patient was finallyextubated only on the 33rd day. He was dis-charged from the intensive care unit to a phys-ical rehabilitation centre on the 52nd day. Hestill had ataxia and debilitating action/inten-tion myoclonus, bilateral cortical deafness,and mental deterioration. One year later, hissituation is unchanged and he is confined to awheelchair.

Case 2On admission, the second worker (patient 2)had only mild symptoms (nausea, headache,dizziness, epigastric pain) which persisted fortwo days. He did not develop seizures ormyoclonus. The serum bromide concentrationmeasured on the second day was 46-6 mg/l.No further investigations were performed dur-ing the first three days and this patient wasfinally referred to the Department of Occu-pational Health and Clinical Toxicology ofFernand-Widal hospital, four days after theaccident. The medical history of this 39 yearold man was unremarkable. He was not takingany medication. He was a non-smoker anddrank less than 40 g of alcohol daily. Fourdays after the accident, he complained ofheadache, insomnia, weakness, and memorydifficulties. Physical examination was unre-markable except for a bilaterally diminishedankle jerk reflex. Routine laboratory testsincluding blood cell count, serum biochem-istry (glucose, urea nitrogen, creatinine,sodium, potassium, chloride, bicarbonate,serum aspartate aminotransferase, and serumalanine aminotransferase, yrglutamyltranspep-tidase, and alkaline phosphatase), urinary glu-cose and urinary protein, chest x ray, and anelectrocardiogram showed no abnormalities.

Conjugator status and S-methylcysteine adducts inalbumin and globin from blood samples of the two patients

S-methylcysteine adducts(nmollg protein)

Patient Conjugator status Albumin Globin

1 Conjugator 91 302 Non-conjugator 149 77

Serum bromide concentration was below thelimit of detection. Neuropsychological testswere performed and showed impaired perfor-mance on memory tasks, especially thoseexploring immediate and verbal memory.Manual dexterity and reaction time were alsoimpaired. Electroencephalography was nor-mal. Interpeak latency I-V of brainstem audi-tory evoked potentials was bilaterallyincreased. Somatosensory and visual evokedpotentials were normal. Electroneuro-myography confirmed the mild distal motorneuropathy. On follow up, progressive recov-ery was reported by the patient and confirmedby tests: the distal motor neuropathy disap-peared within six months, latencies of brain-stem auditory evoked potentials returned tonormal within 12 months. Neuropsychologicaltests also progressively improved: one yearafter the accident, they only showed a milddefect of verbal memory.

DETERMINATION OF CONJUGATOR STATUSMeasurement of binding products of methylbromide with blood proteinsThe table shows the results of these investiga-tions. The first patient was a conjugator, andthe second was a non-conjugator. S-Methylcysteine adducts were high in bothalbumin and globin and were higher in thesecond patient who was a non-conjugator.

DiscussionConjugation with glutathione is the first stepin the main metabolic pathway of mono-halomethanes.'4 1819 Methylglutathione is thentransformed into S-methylcysteine by trans-peptidases. Further metabolism producesmethanethiol through methylthioacetic acid.Oxidation of methanethiol generates formal-dehyde and hydrogen sulphide which may befurther oxidised into formate and sulphaterespectively."I

Whether methyl bromide toxicity is due todirect alkylation of cellular components (pri-marily glutathione, then macromolecules) bythe parent compound, or can be attributed totoxic metabolites such as methanethiol andformaldehyde has been extensively disputedfor the past 10 years. Exposure to methyl bro-mide has induced glutathione depletion in var-ious systems." 20-22 However, the significanceof this finding is unclear, as shown by the con-flicting results of experimental studies. On theone hand, glutathione depletion was found toincrease methyl bromide toxicity in rats 21 andpretreatment of mice, rats, or rabbits withglutathione, cysteine, N-acetylcysteine, ormethionine had a protective effect,2324 on the

213

on January 21, 2020 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.3.211 on 1 March 1996. D

ownloaded from

Gamier, Rambourg-Schepens, Muller, Hallier

other hand, glutathione depletion before expo-sure inhibited toxicity of another mono-halomethane, methyl chloride, in mice.25These conflicting results may be explained bysignificant differences between species in themetabolism of monohalomethanes; such dif-ferences have been shown to exist-for exam-ple, glutathione transferase activity variesconsiderably from one species to another.'8Methodological bias may be another explana-tion for these discrepancies: the doses andconditions of exposure varied considerably inthe published studies.Some clarification of the mechanism of

methyl bromide toxicity was gained recently,when Hallier et al'5 showed that in vitro conju-gation with glutathione protected humanlymphocytes from the induction of sister chro-matid exchanges caused by this halomethane.This indicates that the genotoxic effects areprobably due to the parent compound.The data presented here suggest a different

mechanism for methyl bromide neurotoxicity.Indeed, these two workers experienced thesame exposure to the fumigant for an identicalduration and intensity, as they workedtogether and used the same protective devices.As they produced very similar physical efforts,it is highly probable that they absorbedamounts of methyl bromide which were notsignificantly different. However, one of them(patient 1) had very severe poisoning, whereasthe other (patient 2) developed only mildlyneurotoxic symptoms.

Glutathione transferase activity was mea-sured in erythrocytes of both patients. Thefirst patient was a conjugator: he possessedthis specific enzyme activity, which was lack-ing in the erythrocytes of the second patient (aso called non-conjugator). The glutathionetransferase responsible for the metabolism ofmethyl bromide belongs to class 0. It has beencharacterised by Schr6der et al.'0 The poly-morphism of glutathione transferase activity isnot restricted to erythrocytes. It was recentlyshown that it is genetically determined.26Conjugators are either homozygous or het-erozygous bearers of the gene, whereas non-conjugators have a homozygous null genotype.There is a wide variation in the prevalence ofthe null genotype in different ethnic groups: Ina recent study, 20-4% of whites, 218% ofAfrican-Americans, 64-6% of Chinese, 60-2%of Koreans, and 9-7% of Mexican-Americanslacked this gene.27

In non-conjugators, formation of S-methyl-glutathione is always very low, as it is limitedto the non-enzymatic reaction of methyl bro-mide with glutathione. This implies that, forthe same exposure, non-conjugators receive ahigher internal dose of the parent compound.Methyl bromide is a highly reactive moleculewhich can methylate cellular components.Non-conjugators are therefore expected tohave a higher level of alkylated proteins.Indeed, we found more S-methylcysteineadducts in globin and serum albumin of thesecond patient who was a non-conjugator. Itshould be emphasised that the concentrationsof adduct measured in both patients were veryhigh, as blood samples were drawn seven

weeks after exposure (table). The half lives ofalbumin and globin adducts are seven to 10days and about two months, respectively. Thenormal concentrations of S-methylcysteineadduct for people not exposed to methyl bro-mide are about 15 nmol/g (range: 13 to 18) inboth albumin and globin (14-8 (1-9) in albu-min and 14-5 (2 5) in globin).'6 In field stud-ies, soil fumigators had 26-6 (11-8) nmol/g ofS-methylcysteine adducts in globin and 38-1(31 4) nmol/g in albumin. Some people per-forming specific tasks with a high risk of expo-sure to methyl bromide had higherconcentrations: up to 65 nmol/g in globin and140 nmol/g in albumin. The concentrations ofadduct were higher for space fumigators thanfor soil fumigators: 32'9 (14-6) nmol/g in glo-bin and 74'3 (38'7) nmol/g in albumin. Allthese values were obtained from workerswhose blood was analysed immediately afterexposure to methyl bromide. 17 28

After exposure of whole blood to methylbromide in vitro, non-conjugators have higherconcentrations of S-methylcysteine adduct inproteins and also more sister chromatidexchanges in lymphocytes than conjugators.'5Patient 2, who was a non-conjugator, hadhigher concentrations of adduct but fewerneurotoxic effects than patient 1. This sug-gests that methylation of cellular componentsis not the mechanism of methyl bromide neu-rotoxicity and provides support for thehypothesis that the neurotoxic effects ofmonohalomethanes are related to their conju-gation with glutathione, S-methylglutathione,or some of its subsequent metabolites beingresponsible for the symptoms found afteracute exposure. Previous studies have sug-gested that methanethiol and formaldehydemay be the ultimate toxic metabolites."' 25 Thetoxic effects of methanethiol are probably dueto its rapid transformation into formaldehydeand hydrogen sulphide.29 30 Formaldehyde is ahighly reactive compound. Hydrogen sulphideis a strong inhibitor of cytochrome oxidase.3'

If the initial conjugation of methyl bromidewith glutathione has a toxifying rather than adetoxifying effect, treatment with N-acetylcys-teine, which has been proposed by someauthors,'6 should be questioned. N-Acetylcysteine is a precursor of glutathione.Indeed, if metabolites of S-methylglutathioneare the ultimate toxic species, to give N-acetyl-cysteine could have both a toxifying and adetoxifying effect: it would increase the pro-duction of methanethiol and formaldehydebut would also accelerate neutralisation offormaldehyde,'2 which is one of the two proba-ble ultimate toxic metabolites. Consequently,to give glutathione precursors could eitherincrease or decrease methyl bromide neuro-toxicity depending upon the conditions ofexposure and the therapeutic protocol. Patient1, who was a conjugator, received N-acetylcys-teine, but this treatment did not have anyobvious protective effect. From a practicalpoint of view, the consequences of N-acetyl-cysteine being given to cases with methyl bro-mide poisoning should certainly be furtherinvestigated before it can be recommended asspecific treatment.

214

on January 21, 2020 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.3.211 on 1 March 1996. D

ownloaded from

Glutathione transferase activity andformation ofmacromolecular adducts in two cases of acute methyl bromide poisoning

1 International Agency for Research on Cancer IARC.Monographs on the evaluation of the carcinogenic risk ofchemicals to humans. Vol 41-Some halogenated hydrocar-bons and pesticide exposures. Lyon: 1986:187-212.

2 Alexeef BV, Kilgore WW. Methyl bromide. Residue Reviews1983;88:101-53.

3 Hustinx WNM, Van de Laar RTH, Van Huffelen AC,Verwey JC, Meulenbelt J, Savelkoul TJF. Systemiceffects of inhalational methyl bromide poisoning: a studyof nine cases occupationally exposed due to inadvertentspread during fumigation. BrJIndMed 1993;50:155-9.

4 Mellerio F, Levy-Alcover MA. Myoclonies d'origine tox-ique. Revue d'Electroenciphalographie et de NeurophysiologieCliniquel982;12:210-8.

5 Danse LHJC, Van Velsen FL, Van der Heijden CA.Methyl bromide: carcinogenic effects in the ratfore-stomach. Toxicol Appl Pharmacol 1984;72:262-71.

6 Boorman GA, Hong HL, Jameson CW, Yoshitomi K,Maronpot RR. Regression of methyl bromide-inducedforestomach lesions in the rat. Toxicol Appl Pharmacol1986;86: 131-9.

7 Reuzel PGJ, Dreef-Van der Meulen HC, Hollanders VMH,Kuper CF, Feron VJ, Van der Heijden CA. Chronicinhalation toxicity and carcinogenicity study of methylbromide in Wistar rats. Fd Chem Toxicol 1991;29:31-9.

8 Tucker JD, Xu J, Stewart J, Baciu PC, Ong T. Detection ofsister chromatid exchanges induced by volatile genotoxi-cants. Teratogenesis Carcinog Mutagen 1986;6: 15-21.

9 IPCS. Environmental health criteria 166. Methyl bromide.Geneva: World Health Organization, 1995.

10 Schroder KR, Hallier E, Peter H, Bolt HM. Dissociation ofa new glutathione S-transferase activity in human ery-throcytes. Biochem Pharmacol 1992;43: 1671-4.

11 Kornbrust KS, Bus JS. The role of glutathione and cyto-chrome P-450 in the metabolism of methyl chloride.ToxicolAppl Pharmacol 1983;67:246-56.

12 Barnsley EA, Young L. Biochemical studies of toxic agents:the metabolism of iodomethane. Biochem J 1965;95:77-81.

13 Johnson MK. Studies on glutathione S-alkyltransferase inthe rat. BiochemJ_ 1966;98:44-56.

14 Hallier E, Deutschmann S, Reichel C, Bolt HM, Peter H. Acomparative investigation of the metabolism of methylbromide and methyl iodide in human erythrocytes. IntArch Occup Environ Health 1990;62:221-5.

15 Hallier E, Langhof T, Dannapel D, Leutbecher M,Schroder K, Goergens HW, et al. Polymorphism of glu-tathione conjugation of methyl bromide, ethylene oxideand dichloromethane in human blood: influence on theinduction of sister chromatid exchanges (SCE) in lym-phocytes. Arch Toxicol 1993;67:173-8.

16 Zwaveling JH, de Kort WLAH, Meulenbelt J, Hezemans-Boer M, Van Vloten WA, Sangster B. Exposure of theskin to methyl bromide: a study of six cases occupationallyexposed to high concentrations during fumigation. HumToxicol 1987;6:491-5.

17 MUller AMF, Hallier E, Westphal G, Schroder KR, BoltHM. Determination of methylated globin and albuminfor biomonitoring of exposure to methylating agentsusing HPLC with precolumn fluorescent derivatization.Fresenius JAnal Chem 1994;350:712-5.

18 Peter H, Deutschmann S, Reichel C, Hallier E.Metabolism of methyl chloride by human erythrocytes.Arch Toxicol 1989;63:351-5.

19 Bonnefoi MS, Davenport CJ, Morgan KT. Metabolismand toxicity of methyl iodide in primary dissociatedneural cell cultures. Neurotoxicology 1991;12:33-46.

20 Alexeef GV, Kilgore WW, Munoz P, Watt D. Determina-tion of acute toxic effects in mice following exposure tomethyl bromide. Jf Toxicol Environ Health 1985;15:109-23.

21 Thomas DA, Lacy SA, Morgan KT. Studies on the mecha-nisms of methyl bromide-induced olfactory toxicity.Toxicologist 1989;9:37.

22 Davenport CJ, Ali SF, Miller FJ, Lipe GW, Morgan KT,Bonnefoi MS. Effect of methyl bromide on regional brainglutathione, glutathione-S-transferases, monoamines,and amino acids in F 344 rats. Toxicol Appl Pharmacol1992;112: 120-7.

23 Mizynkova IG, Bakhishev GN. Specific treatment of acutepoisoning with methyl bromide. Vrach Delo 1971;7:128-31.

24 Hashimoto Y, Nagao N, Ishizu S. The effect of GSH as anantidote for MeBr poisoning in mice. Ludwigshafen:Medichem, 1986:494-7.

25 Chellman GJ, White RD, Norton RM, Bus JS. Inhibitionof the acute toxicity of methyl chloride in male B6C3F1mice by glutathione depletion. Toxicol Appl Pharmacol1986;86:93-104.

26 Pemble S, Schroder KR, Spencer SR, Meyer DJ, Hallier E,Bolt HM, et al. Human glutathione S-transferase theta(GST-l): cDNA cloning and the characterization of agenetic polymorphism. Biochem J 1994;300:271-6.

27 Nelson HH, Wiencke JK, Christiani DC, Cheng TJ, Zheng-Fa Z, Schwartz BS, et al. Ethnic differences in the preva-lence of the homozygous deleted genotype of glutathioneS-transferase theta. Carcinogenesis 1995;16: 1243-5.

28 Goergens HW, Hallier E, Muller A, Bolt HM.Macromolecular adducts in the use of methyl bromide asfumigant. Toxicol Lett 1994;72:199-203.

29 Blom HJ, Tangerman A. Methanethiol metabolism inwhole blood. J Lab Clin Med 1988;111:606-10.

30 Waller RL. Methanethiol inhibition of mitochondrial respi-ration. Toxicol Appl Pharmacol 1977;42:111-7.

31 Nicholls P. The effect of sulphide on cytochrome a,, isos-teric and allosteric shifts of the reduced alpha peak.Biochim BiophysActa 1975;396:24-35.

32 Casanova M, d'Heck AH. Further studies of the metabolicincorporation and covalent binding of inhaled (3H) and(14C) formaldehyde in Fischer 344 rats: effects of glu-tathione depletion. Toxicol Appl Pharmacol 1987;89:105-21.

215

on January 21, 2020 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.3.211 on 1 March 1996. D

ownloaded from