Ultrastructural changes in the respiratory tract of rats following methyl isocyanate inhalation

Bhopal Gas Tragedy: review of clinical and experimental findings after 25 years

The Bhopal gas tragedy is undoubtedly one of the worst industrial disasters in the history of mankind resulting in mortality of 2500-6000 and debilitating over 200 000 people. Inhabitants in the township were exposed to different degrees and there are more than 500 000 registered victims that survived the tragedy. Clinical studies have shown chronic illnesses such as pulmonary fibrosis, bronchial asthma, chronic obstructive pulmonary disease (COPD), emphysema, recurrent chest infections, keratopathy and corneal opacities in exposed cohorts. Survivors continue to experience higher incidence of reported health problems including febrile illnesses, respiratory, neurologic, psychiatric and ophthalmic symptoms. In-utero exposure to methyl isocyanate in the first trimester of pregnancy caused a persistent immune system hyper-responsiveness, which was in an evident way genetically linked with the organic exposure. Recent experimental studies have provided mechanistic understanding of methyl isocyanate exposure at a molecular level. Immunotoxic implications, toxico-genomic effect, inflammatory response, elicitation of mitochondrial oxidative stress, chromosomal and microsatellite instability have been studied comprehensively in cultured mammalian cells. Besides providing a framework for understanding potential mechanisms of toxicity of a host of other exposures, these studies may also uncover unique abnormalities thereby stimulating efforts to design newer and effective diagnostic and therapeutic strategies. The authors recommend long-term monitoring of the affected area and use of appropriate methods of investigation that include well-designed cohort studies, case-control studies for rare condition, characterization of personal exposure and accident analysis to determine the possible elements of the gas cloud.

Airway epithelial damage induced by sulfur mustard in guinea pigs, effects of glucocorticoids

Sulfur mustard (SM) represents a potential chemical warfare agent. In order to characterize SM-induced airway epithelial damage, we studied the effects of an intratracheal injection of 0.3 mg/kg of SM in guinea pigs, 5 h, 24 h, 14 days and 35 days after exposure. During the acute period, lesions prevailed in tracheal epithelium exhibiting intra-epithelial blisters, inflammatory cell infiltration and columnar cell shedding with exposure of basal cells. Fourteen days after intoxication, tracheal epithelium appeared disorganized and showed a significant decrease in height and cell density. Tracheal epithelium recovery was still not complete even 35 days after SM-intoxication. At day 14, in SM-intoxicated guinea pigs treated with betamethasone from day 7 to day 14, epithelium height, cell density and cell proliferation (evaluated by immunohistochemistry) were significantly increased compared to untreated guinea pigs. In conclusion, the lesions observed in SM-intoxicated guinea pigs seem to be in accordance with clinical human observations and are relevant to the study of airway epithelial damage induced by SM. This animal model could be used to illustrate tracheal epithelium regeneration mainly derived from basal cells and to show glucocorticoid effects on airway epithelial recovery after chemical aggression.

Comparative toxicity of methyl isocyanate and its hydrolytic derivatives in rats. I. Pulmonary histopathology in the acute phase

The present study describes the acute histopathological changes induced by methyl isocyanate (MIC) in the lungs of rats at 24 h after a single exposure to varied concentrations/doses of MIC by inhalation and subcutaneous (s.c.) routes and also delineates the effects due to the hydrolytic derivatives of MIC, viz., methylamine (MA) and N,N'-dimethyl urea (DMU). MIC, either inhaled or administered s.c., resulted in a wide range and extent of histopathological changes in the lungs, proportional to the exposure concentration/dose. The salient, effects of inhaled MIC are acute necrotizing bronchitis of the entire respiratory tract accompanied by varying degrees of confluent congestion, hyperemia and interstitial and intra-alveolar edema, while MIC administered s.c. led to prominent vascular endothelial damage, congestion and severe interstitial pneumonitis with apparently normal bronchial epithelium; and intra-alveolar edema only with the high dose. The only noteworthy lesion produced by MA and DMU (to some extent) was interstitial pneumonitis, suggesting their possible involvement in the subsequent inflammatory response of MIC. Except, for the endothelial changes, the overall spectrum of the histopathological lesions is quite comparable to those observed in the lungs of Bhopal victims during the acute phase.

Comparative toxicity of methyl isocyanate and its hydrolytic derivatives in rats. II. Pulmonary histopathology in the subacute and chronic phases

This paper describes the long-term (subacute and chronic) histopathological effects in the lungs of rats subjected to a single exposure to methyl isocyanate (MIC) by both the inhalation and subcutaneous (s.c.) routes as well as the role of methylamine (MA) and N,N'-dimethyl-urea (DMU), the hydrolytic derivatives of MIC in eliciting the observed changes. At the subacute phase, the intraalveolar and interstitial edema were prominent only in the inhalation group as against the more pronounced inflammatory response in the s.c. route. With the progress of time the evolution of lesions appeared to be similar, culminating in the development of significant interstitial pneumonitis and fibrosis. MA, one of the hydrolytic derivatives of MIC, also caused interstitial pneumonitis progressing to fibrosis, albeit to a lesser extent than MIC, indicating its contribution to the long-term pulmonary damage. The diffuse interstitial pulmonary fibrosis observed at 10 weeks after a single exposure to MIC by either route is of greater significance in the context of the occurrence of pulmonary fibrosis in the late autopsies of Bhopal gas victims and also clinical sequelae in some of the survivors.

Modulation of biochemical and cytological profile of bronchoalveolar lavage constituents in rats following split-dose multiple inhalation exposure to methyl isocyanate

1. Studies were carried out to explore the acute pulmonary effects of equal, split-dose, multiple inhalation exposures of rats to methyl isocyanate (MIC), (0.32 mg l-1, 8 min x 10 exposures) as reflected by alterations in bronchoalveolar lavage fluid (BALF) constituents and to evaluate recovery, if any, following survival in a MIC-free environment, 10 d after the last MIC exposure. 2. In the BALF of MIC-exposed rats, there was an increase in the total number of cells and the number of cells showing enhanced dye uptake and reduction of nitroblue tetrazolium chloride. The cell-free BALF showed increases in total protein, sialic acids and lactic acid contents and lactate dehydrogenase activity. 3. In rats exposed to MIC and sacrificed 10 d after survival in a MIC-free environment, there was a reduction in the cellular and biochemical constituents of BALF. The phagocytic potential of macrophages was, however, also decreased under this regime.

Inhalation toxicity of methyl isocyanate: biochemical and cytological profile of bronchoalveolar lavage fluid in rats

Acute pulmonary injury in rats following a single inhalation exposure to methyl isocyanate (3.2 mg l-1) was reflected by alterations in the biochemical and cytological constituents of bronchoalveolar lavage fluid (BALF) over a period of 30 days. Total protein, sialic acid and lactic acid contents of BALF were increased followed by a gradual decline to normalcy between day 3 and day 30 post-exposure. The activity of lactic dehydrogenase also increased progressively with time. The cellularity of BALF was increased significantly and primarily comprised of polymorphonuclear neutrophils at 8 days. The adherence of macrophages was unchanged but their viability was lowered at 30 days post-exposure. The results indicate the significance of bronchoalveolar lavage analysis in monitoring pulmonary toxicity by methyl isocyanate, which is characterized by the hypoxic condition and reduced cellular defence. Some toxic manifestations are potentially reversible with time after cessation of exposure.

Long term pulmonary impairment following a single exposure to methyl isocyanate

Groups of guinea pigs were exposed for 3 hr to 6, 13, 19, 27, or 37 ppm of methyl isocyanate (MIC). Pulmonary performance was evaluated immediately postexposure and for a period of 1 year in the animals surviving 19 or 37 ppm of MIC. At 6 and 13 ppm deterioration of pulmonary performance was observed but complete recovery occurred within a few weeks. In those animals surviving 19 or 37 ppm some recovery occurred but a long lasting impairment of pulmonary performance was observed. One year after a single exposure to MIC these animals presented a condition best described as chronic obstructive lung disease. Using flow-volume measurements during air breathing and during CO2 challenge, animals surviving at 19 or 37 ppm presented typical abnormalities associated with airflow limitation along the conducting airways. One year after exposure lung hyperinflation was also present. At this time the poor ventilatory response to CO2 was due to mechanical limitation of lung expansion during inspiration and airflow limitation during expiration. The findings were similar to humans with severe obstructive lung disease. Microscopic examination substantiated the flow-volume measurements in that the main bronchi, small bronchi, and bronchioles were found to have an increase in dense fibrous tissue, while the alveolar level was characterized by destruction of alveolar walls and an increase in septal thickness. Thus a single exposure to MIC, if the concentration is high enough, is sufficient to induce permanent pulmonary toxicity.

A study on the B cell activity in protein deficient rats exposed to methyl isocyanate vapour

The effect of MIC on the humoral immunity of the malnourished (protein deficient) subjects has been investigated. A single exposure of MIC (1.60 mg/l) on protein deficient rats showed no significant change in the body weight and mortality rate compared with the normal but the serum protein levels were found significantly low (P less than 0.01) in the protein deficient diet fed control (PDC) ones. Both PDC and protein deficient MIC exposed (PDMIC) rat showed diminished B-cell proliferation with the optimal dose of LPS, compared to the NDC and normal diet fed MIC exposed (NDMIC) group. Furthermore significant suppression (P less than 0.01) in the B-cell activation by LPS was observed in the PDMIC compared to PDC. The total IgM level in PDMIC was 43% less while 26% higher in NDMIC compared to NDC. The total IgG level in PDMIC and NDMIC was higher (20%) compared to NDC, while 25% less in PDC. The antigen specific B-cell immunity was affected in PDMIC, PDC and NDMIC. As the terminal differentiation process of B-cells were found equally affected in both PDC and NDMIC, it appears that MIC has no synergistic effect on the humoral immunity of the protein malnourished host.