- Email: [email protected]
LENS OPACITIES INDUCED IN RAT LENSES BY METHYL ISOCYANATE
762
phases, reaction between MIC and water (or methylamine) produced a solid product which was identified by its infra-red spectrum as N,N’-dimethyl urea (DMU). The infra-red spectrum was compared with that of an authentic sample. It is therefore necessary to consider the possible toxicological effect of DMU in the sequelae of the Bhopal disaster. The very limited data on DMU do not indicate severe acute toxicity, but very little is known of its long-term effects or of its interaction with the toxicity of MIC or methylamine. The structural analogue, N-methyl formamide, is teratogenic3and cytotoxic.44 MIC, methylamine, and DMU may react with each other and with human tissue yielding polymers and oligomers from selfaddition reactions, carbamates, urethanes, amides (including
vapour
phosphoramides), and ureas. Inside the body, these produces could react with proteins (including lens proteins), phospholipids (in cell membranes), and other endogenous compounds. The reaction with body proteins is thought to lie behind the powerful hypersensitivity reaction induced by the volatile di-isocyanates used in the manufacture of polyurethane plastics. These immunological effects have yet to be demonstrated with mono-isocyanates such as MIC. Further chemical and toxicological investigations of these possibilities are in progress, the results of which should enrich the interpretation of symptom complexes recorded in the epidemiological field inquiry. In addition, it is feasible that these studies will provide insights into the longer term health risks of the exposed
Two control lenses (left) and contralateral lenses incubated in Fig501-mmol/l MIC (right) for iSh 37’C. at
Lenses from
53-day-old rats were incubated as Lenses photographed in modified MEM medium at
described 18’5°C.
previously.5
community. Department of Occupational Health, London School of Hygiene and Tropical Medicine, London WC1E 7HT
N. ANDERSSON
Professorial Unit, Moorfields Eye Hospital, London EC1
M. KERR MUIR
London School of Hygiene and Tropical Medicine
A. C. R. C.
Department Ophthalmology, Gandhi Medical College, Bhopal, Madhya Pradesh, India
P. C. MITTAL
Chattisgarh Eye Hospital, Fafadih, Raipur, Madhya Pradesh
V. MEHRA
Department of Occupational Health,
G. SALMON
J. WELLS B. BROWN
J. PURNELL Fig 2-Same lenses as in fig 1
1 Andersson N, Kerr Muir M, Mehra V. Bhopal eye Lancet 1984; ii: 1481. 2. Minassian DC, Mehra V, Jones BR. Dehydrational crises from severe diarrhoea or heat stroke and risk of cataract. Lancet 1984; i: 751-53. 3 Tuchmann-Duplessis H. Malformacion congenital des mammiferes. Paris: Masson,
1971. 4
Whitby H, Gescher A, Levy L. An investigation of the mechanism of hepatotoxicity of the anti-tumour agent N-methyl formamide in mice. Biochem Pharmacol 1984; 33: 295-302
LENS OPACITIES INDUCED IN RAT LENSES BY
METHYL ISOCYANATE
SIR,-During the disaster in the Indian city of Bhopal last December 45 tonnes of toxic methyl isocyanate (MIC) escaped, killing more than 2500 people and leaving 90 000 requiring medical treatment. MIC is toxic by both inhalation and by absorption I through the skin but little is known of its long-term toxicity, although the ocular damage is being investigated.2 Sodium isocyanate causes cataract and peripheral neuropathy3 and potassium isocyanate reacts with lens proteins in vitro,4causing modification of the protein surfaces and opacification.5 We report here that MIC causes a similar lens opacification and suggest that cataracts may be a long-term risk for those exposed in Bhopal. Young rat lenses incubatedin 50 mmol/1 MIC acquired nuclear or perinuclear opacities (fig 1) reminiscent of the phase-separation opacities produced by cooling young lenses or by potassium cyanate.5 Phase-separation opacification is reversible, and warming the lenses to 24- 5°C led to clarification (fig 2). The lenses were taken through the warming and cooling cycle three times and opacification and clarification occurred at the same temperature every time. MIC raised the phase-separation temperature from 16-7±1-4°C for controls (n=9) to 22-0±0-9°C (n= 12) for MIC-
at
in the same positions but photographed
24.5OC.
has been found in exposed lenses. A similar rise in temperature i galactose cataract6 and X-ray cataract. In our experiments the change in phase-separation temperature was presumably due to an alteration of surface charge pattern and thus of protein-protein and protein-water interactions5 which control the short-range order of the lens proteins, which is essential for transparency.8 Chemical modification of protein has been implicated in cataracts deriving from a wide variety of causes including diabetes, galactosaemia, renal failure, diarrhoea, cyanate, ethanol, naphthalene, and steroids, and the effects can be additive,9 so that in Bhopal exposure to MIC could add to the high risk of cataract already present in that area.lo Nuffield
Laboratory of Ophthalmology, University of Oxford, Oxford OX2 6AW
HARDING KENNETH C. RIXON
JOHN J.
1. Editorial Calamity at Bhopal. Lancet 1984, ii: 1378-79 2. Andersson N, Kerr Muir M, Mehra V Bhopal eye. Lancet 1984; ii 1481. 3 Nicholson DH, Harkness DR, Benson WE, Peterson CM. Cyanate-induced cataracts in patients with sickle-cell hemoglobinopathies. Arch Ophthalmol 1976, 94: 927-30 4 Beswick HT, Harding JJ Conformational changes induced in bovine lens &agr;-crystallin by carbamylation: Relevance to cataract Biochem J 1984; 223: 221-27. 5. Crompton M, Rixon KC, Harding JJ. Aspirin prevents carbamylation of soluble lens proteins and prevents cyanate-induced phase separation opacities in vitro, a possible mechanism by which aspirin could prevent cataract Exp Eye Res (in press) 6. Ishimoto C, Goalwin PW, Sun S-T, et al. Cytoplasmic phase separation in formation of galactosaemic cataract in lenses of young rats Proc Natl Acad Sci (USA) 1979; 76: 4414-16. 7 Clark JI, Giblin FJ, Reddy VN, Benedek GB. Phase separation in X-irradiated lenses of rabbit. Invest Ophthalmol 1982; 22: 186-90 8. Delaye M, Tardieu A. Short-range order of crystallin proteins accounts for eye lens transparency Nature 1983, 302: 415-17 9. Harding JJ. Crabbe MJC The lens Development, proteins, metabolism and cataract In: Davson H, ed. The eye, 3rd ed Vol Ib. London Academic Press, 1984 207-492. 10. Minassian DC, Mehra V, Jones BR Dehydrational crises from severe diarrhoea or heatstroke and risk of cataract Lancet 1984, i 751-53
phases, reaction between MIC and water (or methylamine) produced a solid product which was identified by its infra-red spectrum as N,N’-dimethyl urea (DMU). The infra-red spectrum was compared with that of an authentic sample. It is therefore necessary to consider the possible toxicological effect of DMU in the sequelae of the Bhopal disaster. The very limited data on DMU do not indicate severe acute toxicity, but very little is known of its long-term effects or of its interaction with the toxicity of MIC or methylamine. The structural analogue, N-methyl formamide, is teratogenic3and cytotoxic.44 MIC, methylamine, and DMU may react with each other and with human tissue yielding polymers and oligomers from selfaddition reactions, carbamates, urethanes, amides (including
vapour
phosphoramides), and ureas. Inside the body, these produces could react with proteins (including lens proteins), phospholipids (in cell membranes), and other endogenous compounds. The reaction with body proteins is thought to lie behind the powerful hypersensitivity reaction induced by the volatile di-isocyanates used in the manufacture of polyurethane plastics. These immunological effects have yet to be demonstrated with mono-isocyanates such as MIC. Further chemical and toxicological investigations of these possibilities are in progress, the results of which should enrich the interpretation of symptom complexes recorded in the epidemiological field inquiry. In addition, it is feasible that these studies will provide insights into the longer term health risks of the exposed
Two control lenses (left) and contralateral lenses incubated in Fig501-mmol/l MIC (right) for iSh 37’C. at
Lenses from
53-day-old rats were incubated as Lenses photographed in modified MEM medium at
described 18’5°C.
previously.5
community. Department of Occupational Health, London School of Hygiene and Tropical Medicine, London WC1E 7HT
N. ANDERSSON
Professorial Unit, Moorfields Eye Hospital, London EC1
M. KERR MUIR
London School of Hygiene and Tropical Medicine
A. C. R. C.
Department Ophthalmology, Gandhi Medical College, Bhopal, Madhya Pradesh, India
P. C. MITTAL
Chattisgarh Eye Hospital, Fafadih, Raipur, Madhya Pradesh
V. MEHRA
Department of Occupational Health,
G. SALMON
J. WELLS B. BROWN
J. PURNELL Fig 2-Same lenses as in fig 1
1 Andersson N, Kerr Muir M, Mehra V. Bhopal eye Lancet 1984; ii: 1481. 2. Minassian DC, Mehra V, Jones BR. Dehydrational crises from severe diarrhoea or heat stroke and risk of cataract. Lancet 1984; i: 751-53. 3 Tuchmann-Duplessis H. Malformacion congenital des mammiferes. Paris: Masson,
1971. 4
Whitby H, Gescher A, Levy L. An investigation of the mechanism of hepatotoxicity of the anti-tumour agent N-methyl formamide in mice. Biochem Pharmacol 1984; 33: 295-302
LENS OPACITIES INDUCED IN RAT LENSES BY
METHYL ISOCYANATE
SIR,-During the disaster in the Indian city of Bhopal last December 45 tonnes of toxic methyl isocyanate (MIC) escaped, killing more than 2500 people and leaving 90 000 requiring medical treatment. MIC is toxic by both inhalation and by absorption I through the skin but little is known of its long-term toxicity, although the ocular damage is being investigated.2 Sodium isocyanate causes cataract and peripheral neuropathy3 and potassium isocyanate reacts with lens proteins in vitro,4causing modification of the protein surfaces and opacification.5 We report here that MIC causes a similar lens opacification and suggest that cataracts may be a long-term risk for those exposed in Bhopal. Young rat lenses incubatedin 50 mmol/1 MIC acquired nuclear or perinuclear opacities (fig 1) reminiscent of the phase-separation opacities produced by cooling young lenses or by potassium cyanate.5 Phase-separation opacification is reversible, and warming the lenses to 24- 5°C led to clarification (fig 2). The lenses were taken through the warming and cooling cycle three times and opacification and clarification occurred at the same temperature every time. MIC raised the phase-separation temperature from 16-7±1-4°C for controls (n=9) to 22-0±0-9°C (n= 12) for MIC-
at
in the same positions but photographed
24.5OC.
has been found in exposed lenses. A similar rise in temperature i galactose cataract6 and X-ray cataract. In our experiments the change in phase-separation temperature was presumably due to an alteration of surface charge pattern and thus of protein-protein and protein-water interactions5 which control the short-range order of the lens proteins, which is essential for transparency.8 Chemical modification of protein has been implicated in cataracts deriving from a wide variety of causes including diabetes, galactosaemia, renal failure, diarrhoea, cyanate, ethanol, naphthalene, and steroids, and the effects can be additive,9 so that in Bhopal exposure to MIC could add to the high risk of cataract already present in that area.lo Nuffield
Laboratory of Ophthalmology, University of Oxford, Oxford OX2 6AW
HARDING KENNETH C. RIXON
JOHN J.
1. Editorial Calamity at Bhopal. Lancet 1984, ii: 1378-79 2. Andersson N, Kerr Muir M, Mehra V Bhopal eye. Lancet 1984; ii 1481. 3 Nicholson DH, Harkness DR, Benson WE, Peterson CM. Cyanate-induced cataracts in patients with sickle-cell hemoglobinopathies. Arch Ophthalmol 1976, 94: 927-30 4 Beswick HT, Harding JJ Conformational changes induced in bovine lens &agr;-crystallin by carbamylation: Relevance to cataract Biochem J 1984; 223: 221-27. 5. Crompton M, Rixon KC, Harding JJ. Aspirin prevents carbamylation of soluble lens proteins and prevents cyanate-induced phase separation opacities in vitro, a possible mechanism by which aspirin could prevent cataract Exp Eye Res (in press) 6. Ishimoto C, Goalwin PW, Sun S-T, et al. Cytoplasmic phase separation in formation of galactosaemic cataract in lenses of young rats Proc Natl Acad Sci (USA) 1979; 76: 4414-16. 7 Clark JI, Giblin FJ, Reddy VN, Benedek GB. Phase separation in X-irradiated lenses of rabbit. Invest Ophthalmol 1982; 22: 186-90 8. Delaye M, Tardieu A. Short-range order of crystallin proteins accounts for eye lens transparency Nature 1983, 302: 415-17 9. Harding JJ. Crabbe MJC The lens Development, proteins, metabolism and cataract In: Davson H, ed. The eye, 3rd ed Vol Ib. London Academic Press, 1984 207-492. 10. Minassian DC, Mehra V, Jones BR Dehydrational crises from severe diarrhoea or heatstroke and risk of cataract Lancet 1984, i 751-53