Document aDBN4jORv18ZNb1Y9Z0qLVjg9

mdon. ,: `lief h p e c - wer recent (Respirable shown that sidered for the recent re regarded :ht be coness controliovascular later areas, Val.Ann. occup. Hyg. 19, pp. 293-299. Pergarnon Press 1976. Printed in Great Bntain PLAINTIFF'S EXHIBIT HYDROCARBON NEUROPATHY R. A. SCALA Exxon Corporation, Medical Department, Linden, New Jersey, U.S.A. Abstract-Peripheral polyneuropathy has been described in individuals exposed to certain hydrocarbon solvents including hexane, petroleum benzine and mixtures containing both hexane and toluene. The disease involves motor and sensory changes with a symmetrical and `stocking-glove'distribution. Studies in animals have reproduced this effect with both hydrocarbons and methyl n-butyl ketone. A possible common metabolite such as 2,5-hexanedione has been postulated as a potential neurotoxic agent. This review includes comments on chemicallyinduced peripheral neuropathies, clinical reports of hydrocarbon neuropathy from hexane and solvent blends, experimental studies in animals, collateral studies on oxygenated solvents and metabolites and comments on possible mechanisms. HYDROCARBON neuropathy is a clinical entity of relatively recent description. Praditionally, the biological activity of aliphatic hydrocarbon molecules is believed to be related largely to the number of molecules present rather than to the type of molecule. In addition, aliphatic hydrocarbons were considered relatively inert in biochemical systems. Against this background the recent reports of metabolism of the simple linear alkanes by liver microsomal enzyme systems were unexpected. A prevalent theory regarding chemically-induced peripheral neuropathies is that the effect occurs in the cell body of the neuron, following which the metabolic machinery of the cell slows down and axonal nutrition is impaired. The distal portions of the longest axons become poorly nourished and degenerate. If the disease continues, the nerve fibres deteriorate steadily backwards towards the cells of origin. This gives rise to the descriptive term, `dying back` neuropathies. The ends of the longest nerves (sciatic) are involved first and frequently the disease has a symmetrical decrease in both sensation and movement, first in the feet, then in the hands-`a stocking-glove' distribution. If the disease process is arrested early, then complete recovery may be experienced. If not, there may be a permanent deficit with the sensory loss greater than the motor loss. The neurophysiological and anatomical signs of this peripheral neuropathy are noted below in connection with the case reports and the animal studies. These effects are illustrated in Fig. 1. CASE REPORTS The earliest hydrocarbon solvent neuropathies were associated with exposure to `n-hexane'. These arose in Japan in 1964 with five cases of polyneuropathy in printing plants. Subsequently, 93 cases of polyneuropathy were reported among sandal workers in a cottage industry setting in Japan. A complete report of this in English was published by YAMAMUR(1A969). The first report in the United States was by HERSKOWITZ e? al. (1971) and involved three adults in a New York City furniture finishing operation. The level of exposure of the workers to hexane in these operations was estimated 293 r r294 R.A.SCALA 0'5 0 .* : a LATE I. -a. REGENERATION FIG. 1. The sequence of events in axonal neuropathies (from SCHAUMBURG, 1973). to range from 500 to about 2500 ppm of hexane in Japan, and 650 to 1300 ppm in the United States. The Japanese occupational exposure limit for hexane at that time was 100 ppm; in the U.S. it was 500 ppm. The clinical features in the Japanese and U.S. cases are almost classic in their appearance. In Japan, the chief manifestation was a sensorimotor disorder of the extremities with both symmetrical and 'stocking-glove' distribution. The initial symptoms were predominantly sensory with the motor signs and symptoms arising later. The reports read like a catalogue of nervous system disturbances and included numbness, paraesthesias, tenderness, muscle weakness, fatigability, blurred vision, sensation of coldness in the limbs, headache, lassitude, constriction of the visual field, muscle atrophy, hypo- or hyperactive reflexes and frank pain. The degree of neurological disorder was dependent upon the hygienic conditions in the workplace including work hours, work load, and the vapour concentration. Of particular interest in the Japanese series was the notation that certain patients showed a continuous increase in the severity of symptoms, even after they were isolated and treatment had been instituted. In some cases the disease reached its maximum intensity within 1 to 4 months and then gradually subsided. No fatalities have been reported in any of the cases. There were no signs or symptoms of central nervous system lesions and no constant, significant laboratory findings. Biopsy of peripheral nerve showed destruction of myelin sheath with relatively well-preserved axon; some muscle atrophy was also noted. Associated with this was a reduction in nerve and muscle conduction velocities. The changes in muscle were typical of those seen with denervation of the muscle. The three cases in the United States clinically resembled the Japanese reports. While frank demyelinization and axonal degeneration were not reported, there were signs of histological abnormalities in the muscle and nerve biopsy sections. The reports suggest that hexane neuropathy is pathologically indistinguishable from that associated with triorthocresyl phosphate and acrylamide. On the ex2 central but de of othc HERSK done i to be 1 bons. using Th associ descri petrol with of PO comp the n respo carbc F musc (1974 gluesniffi ness fibre: was kn0v the g the a pn disti tion: clair invo patt Hov was fror glue Go. hex be I exP snif the N pm in the time was c in their ler of the tial symp sing later. ed numbm, sensaiual field, of neurovorkplace rl patients were isoits maxiities have 11 nervous ieripheral ed axon; nerve and seen with ' : 2 reports. here were ons. The icrom that '' . ,...-- Hydrocarbon neuropathy 295 One of the complicating features of these reports is a lack of certainty regarding the exact material to which the workers were exposed and the precise workroom concentrations. YAMAMUR(A1969) described the solvent as n-hexane with some toluene but defines the hexane as 'commercially available n-hexane containing a small amount of other compounds such as methyl pentane, and methyl cyclopentane'. The report of HERSKOWITetZal. (1971) describes the material only as 'n-hexane' ;however, analyses done at our request on a sample from the plant where the cases occurred revealed it to be 68 % acetone, 17% n-hexane, and the remainder isomeric C6 and C, hydrocar- bons. Limited evidence exists for the production of peripheral neuropathy in animals using reagent grade n-hexane (SPENCER and SCHAUMBURG, 1975). The hydrocarbon solvent neuropathies reported more recently have tended to be associated with materials other than n-hexane. A report by TAKEUCHI et af. (1975) described gait disturbances in four labourers who cleaned brocade sashes with petroleum benzine. This solvent was described as a mixture of C, to C9 paraffins with some cycloparaffins and aromatic hydrocarbons including benzene. The signs of polyneuropathy were similar to those reported for commercial n-hexane. The complexity of the petroleum benzine leaves unanswered the question of whether it is the n-hexane which is the causative agent; whether some other trace material was responsible; or whether the neurotoxic potential is shared by most or all hydrocarbons within that boiling range. Finally, attention may be given to the reports of peripheral polyneuropathy and muscular atrophy associated with glue-sniffing. SUZUKI et af. (1974), SHIRABE et af. (1974) and GOTOet al. (1974), have all reported peripheral polyneuropathy following glue-sniffing. SUZUKI described one case in a worker with a prolonged history of sniffing at least one tube of glue per day. The worker showed profound muscle weakness and loss of motor function. Muscle biopsy revealed degeneration of the muscle fibres and rare instances of myelin sheath swelling in the nerves. The glue solvent was described as 13% ethyl acetate, 34% toluene, and 53% n-hexane plus one unknown compound thought to be a hexane isomer. These investigators believed that the glue-sniffers were affected with a somewhat different form of the neuropathy than the workers with occupational exposure to n-hexane. Typical glue-sniffing cases have a predominance of motor disturbances with muscle atrophy and little, if any, sensory disturbance. SUZUKeIt al. suggest that the presence of toluene in these glue formulations may inhibit n-hexane metabolism and perhaps modify the clinical picture. They claim that toluene itself is rarely responsible for polyneuropathy. SHIRABE'S report involves two painters with 2.5 to 3 yr experience of sniffing glue. Their polyneuropathy was primarily motor in nature and the glue solvent was largely toluene initially. However, in the period immediately prior to the onset of the illness, the solvent system was 45 % n-hexane and 55 % toluene. GOTO'Sreport of four cases of polyneuropathy from glue-sniffing also revealed motor-predominant mixed type polyneuropathy. The glue solvents were largely n-hexane and toluene in approximately equal amounts. GOTOet ai. discern a clinical difference between the glue-sniffing cases and the nhexane polyneuropathy from occupational exposure. They claim the difference may be due to the presence of toluene in the glue or in the mode of exposure. Hexaneexposed workers had relatively longer inhalations at lower concentrations and the gluesniffers had relatively shorter periods of inhalation with much higher concentrations of the hydrocarbons. Reviewing the literature, GOTOet af. noted that chronic toluene 296 R. A. SCALA intoxication may cause peripheral nerve damage. This is in contrast with the opinion of Suzuki. It should be remembered, however, that in aU these cases, the relative motor versus sensory damage is a matter of judgment of the investigator making the observations., In France, eight cases of polyneuritis were reported among footwear craftsmen in the Bordeaux region shortly after introduction of a new glue formulation and in a belt factory in the Paris region (AUDRAN and CAMGNEAU1X97, 5). The clinical aspects of these cases closely resembled those observed in Japan and America, particularly with respect to the progessive and gradual onset, the association of sensory and motor disorders, the relationship of the intensity of the effect to the magnitude of exposure, and the slow and possibly incomplete recuperation after cessation of exposure. The work situations were also comparable in that there was a high density of workers, the ventilation was insufficient or nonexistent particularly during the winter period, the drying of the glued pieces was done in the work area and the glue was stored in that same area. The Paris region workers were exposed at hydrocarbon levels suspected to be of the order of 600-700 ppm. The French investigators paid more attention to the composition of the solvents, noting that hydrocarbons are rarely used alone in the glues associated with the clinical cases. The commonest cosolvents were ethyl acetate, methyl ethyl ketone, cyclohexane, and acetone. Even where described as n-hexane, other linear and alicyclic hydrocarbons were also present. They noted that technical grade hexane rarely contained more than 50% n-hexane. ANIMAL STUDIES Limited work has appeared in the published literature on animal studies assessing the peripheral neuropathy associated with hydrocarbon exposures. KURITA(1967) exposed Wistar rats for 143 days to 850 ppm `n-hexane'. The daily exposure duration was not reported and the number of animals was limited. Microscopic examination of peripheral nerve revealed degeneration of myelin and axon cylinders in the sciatic nerve but no attack on myoneural junction nerve sheets. The animals also showed a decrease in spontaneous movement. TRUHAUT et al. (1973) conducted studies on `technical grade hexane' and `technical grade' heptane. The former contained 45.8% n-hexane with the remainder C6 and C7aliphatics and alicyclics including 1.2% benzene. The technical grade heptane was 52.4 % normal heptane with the remainder C, and C8linear and alicyclic hydrocarbons as well as 0.1 % benzene and 2.8 % toluene. Wistar rats were exposed 5 h per day, 5 days per week to 2000 f200 ppm hexane or 1500& 150 ppm heptane for 1-6 months. In the hexane study, decreased conduction velocity, increased refractory time and decreased excitability of sciatic nerve were found. The study raises some questions regarding the actual composition and concentration of the material in the exposure chamber and the stability of that concentration. However, the changes reported in the experimental animals do confirm those in the industrial cases cited previously. In summary, these case reports and animal experiments indicate that exposure to 500-2000 ppm of `hexane' for 4-$ months can result in histological and physiological nerve changes. These, in turn, may progress to a clinical manifestation of peripheral neuropathy. A similar effect was reported in animals using heptane and a 5-6 month exposure at 2000 ppm. Th vent I! settinl worke and neuro MNB prodl repor 8 hp( these of 20 differ alone with neurc periF ing prov and dises n-he: are 2 are : met2 Othc whe lishc for weri new and bea POS hYd enz hex f the opinion the relative making the xaftsmen in on and in a iical aspects particularly y and motor of exposure, posure. The of workers, nter period, 'as stored in 1 levels susmore attenrarely used dvents were re described They noted ies assessing `RITA (1967) ire duration Zxamination n the sciatic $0showed a td `technical tder C, and ieptane was rdrocarbons I per day, 5 1-6 months. `y time and le questions he exposure reported in revious1y . exposure to ,hysiological if peripheral 15-6 month I Hydrocarbon neuropathy RELATED ANIMAL WORK The peripheral polyneuropathy associated with exposures to the oxygenated solvent methyl n-butyl ketone is well known. The effect has been seen in occupational settings as well as in animal studies. An early report of ALLEN et al. (1975) noted that workers exposed to high but undocumented levels of methyl ethyl ketone (MEK) and methyl n-butyl ketone (MNBK) in the ratio of 9: 1 developed peripheral polyneuropathy. The experimental animal studies of MCDONOUG(H1974) confirmed that MNBK at exposure levels of 1300 ppm, 6 h per day, 5 days per week, for 4 months produced nerve changes in rats similar to those reported in man. Subsequently it was reported by DUCKETTet al. (1974) that there were histological effects in rats exposed 8 h per day, 5 days per week for 6 weeks to 200 ppm MNBK. In a related experiment these workers also produced comparable neuropathy following exposure to a mixture of 2000 ppm MEK and 200 ppm MNBK. The report was brief and did not indicate differenceswhich may or may not have existed between the experiments using MNBK alone and those using MNBK and MEK. Much other work has been carried out with these oxygenated materials but an important point in examining hydrocarbon neuropathy is that a metabolite of MNBK, 2,5hexanedione, was capable of producing peripheral polyneuropathy in rats when administered subcutaneously or in the drinking water for a prolonged period. This work by RALEIGH et al. (1975) leads to the provocative suggestion that n-hexane and MNBK may have a common metabolite and that this may bear some relationship to the development of the neurological disease. DIVINCENZOand colleagues (1976) have demonstrated the metabolism of n-hexane to 2,5-hexanedione and 5-hydro-2-hexanone. The metabolites of MNBK are 2,5-hexanedione, 5-hydroxy-2-hexanone, and 2-hexanol. Clearly, a host of studies are suggested by these findings, including the treatment of animals with the various metabolites and a determination of whether or not the neuropathy can be produced. Other studies include inhibition of the production of one or more metabolites to see whether or not the unaltered parent compounds may also be active. In work just published, SPENCER and SCHAUMBURG (in press) fed rats a solution of various metabolites for periods of up to 3 months and found that 2,5-hexanedione and 2,5-hexanediol were neurotoxic and 2,4-hexanedione, 2,3-hexanedione and 1,6-hexanediol were nonneurotoxic. As noted previously, 2,5-hexanedione is a metabolite of both n-hexane and MNBK. No data are available on 5-hydroxy-2-hexanone or 2-hexanol. This work has suggested the possibility of a critical spacing between the oxygenbearing carbons in order to produce the neurotoxicity (Table 1). In examining this possibility closer, it is likely that the ( 0 - 1) carbon is the site of the oxidation or hydroxylation reaction. KRAMER et ai. (1974) have shown that liver microsomal enzymes can carry out this oxidation reaction with hexane or heptane. In fact, nhexane was as effective as phenobarbital in inducing this process. Kramer's work, TABLE 1. METABOLITES OF METHYL-+BUTYL KmONE Active Inactive Unknown 2,SHexanedione 2,5-Hexanediol 2,CHexanedione 2,3-Hexanedione 1,dHexanediol 5-OH-hexanone-2 2-Hexanoi L) I i i i i I ? I i i t 298 R. A. SCALA however, does not support the finding of DIVINCENZ(O1976) in that Kramer h a demonstrated oxidation at the C1, C2and C3 positions. FROMMER et al. (1972) using n-heptane have shown it at the C1, Cz, C, or C, position. Both Kramer and Frommer noted that the oxidation by liver microsomal enzymes occurred predominantly at the (o- 1) position. In short, the metabolism of n-hexane and MNBK to the corres. ponding 2-, or 2,5 oxidative products may be important in the formation of neurotoxic molecular species. This also suggests that the basic mechanism of interference with neuronal metabolism may occur not through the intervention of nonspecific hydrocarbon or oxygenated molecules but perhaps by mediation of a specific oxygenated metabolite. From personal conversations with various investigators in this field, we believe that work along these lines is being actively pursued. SUMMARY Hydrocarbon solvents of undefined quality have been shown to be associated with the production of peripheral polyneuropathy in Japan, America and France. n-Hexane has been a common component and a modifying effect from toluene has been proposed. The effect is characterized by degeneration of peripheral nerves as indicated by axonal swelling and myelin degeneration. Histological signs seem to appear early with clinical signs following up to 6 months after the onset of exposure. The occupational circumstances have pointed to excessive solvent vapour levels in the workplace. Confirmatory studies in animals have been conducted and based on collateral work with a ketone which also causes peripheral polyneuropathy, the suggestion is made that there is an oxygenated (2- or 2,5-) intermediate which is the active neurotoxic entity. Critical elements in production of the toxic intermediate may be the microsomal monooxygenase system. The possibility of a structurally nonspecific causation of the neuropathies from hydrocarbons is also accepted. Acknowledgements-In the preparation of this review, the contributions of Drs Peter Spencer and Herbert Schaumburg and my associate, Dr Gerard Egan, are gratefully acknowledged. REFERENCES ALLENN,., MENDELJL.,P., BILLMAIEDR.,J., FomAIm, R. E. and O'NEtLL, JR. (1975) Archs Neurol., Chicago 32,208-218. AUDRANR, . and CAVIGNEAUAX.,(1g75) Cah. Notes docum. Inst. nata Secur. Prkv. Accid. Travail 78, 65-69. DIVJNCENZOG,. D., KAPLAN, C. J. and DEDINASJ., (1976) Toxicol. appl. Pharmacol. 36, 511-522. DUCKEITS,., WILLIAMS, N. and FRANCIS, S. (1974) New Engl. J. Med. 290, 1264. FROMMERu.., ULLRIcH, v., STAUDINGER, H. and ORRENIUSS., (1972) Biochim. Biophys. Acta 280, 487494. GOTOI,., MATSLJMURMA., INOUEN, .. MURAIY, ., SHIDAK, ., SANTAT, . and KUROIWA, Y. (1974) J. Neurol. Neurosurg. Psychiat. 37, 848-853. HERSKOWZA, ., ISHI,N. and SCHAUMBURHG.,(1971) New Engl. J. Med. 285,8245. KRAMERA, ., STAUDINGERH,. and ULLRICVH.,(1974) Chem.-Biol. Interucf. 8, 11-18. KURITAH, . (1967) Jap. J. id.Hlth 9,672-677. MCDONOUGHJ., R. (1974) Archs emir. Hlrh 29, 120. RALEIGH,R. L., SPENCER, P. and SCHAUMBURG,H. H. (1975) Archs enuir. HIrh 30,317-318. SCHAUMBURHG. ,H. (1973) Med. Times, N . Y . 101,171-176. SHIRABET,. T., TERAU, A. and ARAKI,S. (1974) J. Neurol. Sci. 21, 101-113. SPENCER, P. and SCHAUMBURG,H. H. (1975) Neurosci. Abstr. 1, 703. SPENCER, P. and SCHAUMBURG,H. H. (in press) J. Neuropath. exp. Neurol. SUZUKI, T., SH med. 33, 11 TAKEUCHYI., , TRUHAIJTR, ., Arch. Mal. YAMAMURYA, I. LAVERY: I mention of the to comment oi Dr SCALA: Nc animals. The L habituation dt animal toxicit) imer h a 72) using Fronuner nantly at le corres. :urotoxic la1 meta1 or oxy:tabolite. .ieve that issociated ii France. luene has nerves as j seem to exposure. . levels in based on I, the sugich is the ermediate ructurally ted. Spencer and ~ c hNs eurol., 1. Travail 78, 6, 511-522. 's. Acta 280, 'A, Y . (1974) -318. Hydrocarbon neuropathy 299 SUZUKIT,., SHIMBOS.,, NISHITANHI,., OGA, T., IMAMURAT,. and IKEDA,M. (1974) Inf. Arch. Arbeifsmed. 33, 115-123. TAKEUCHYI,., MABUCHCI,. and TAKAGI, S. (1975) I n f . Arch. Arbeitsmed. 34, 185-197. TRUHAUTR, ., LAGETP, ., RAT, G., PHU-LICH, N., DUTERTRE-CATELHL. aAn,d HUYEN, V-N. (1973) Arch. Mal. Drof. MPd. trav. 34, 417426. Y A ~ A M U RY.A',(1969) Fdia psychiat. neurol. jap. 23, 45-57. DISCUSSION I. LAVERY: I am rather surprised that in your report on hydrocarbon neuropathy you made no mention of the effects of petrol vapour, of which there has been rather a long history. Would YOU like to comment on what is known? Dr SCALA: No mention was made of petrol vapour as there are no relevant published studies using animals. The data on humans show evidence of central nervous system depression and a form of habituation described as gasoline sniffing. The American Petroleum Institute is sponsoring some animal toxicity studies on gasoline in which nervous system effects will be studied. -- I