Kewal K. Maudar

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.

Isocyanates induces DNA damage, apoptosis, oxidative stress, and inflammation in cultured human lymphocytes

Isocyanates, a group of low molecular weight aromatic and aliphatic compounds containing the isocyanate group (−NCO), are important raw materials with diverse industrial applications; however, pathophysiological implications resulting from occupational and accidental exposures of these compounds are hitherto unknown. Although preliminary evidence available in the literature suggests that isocyanates and their derivatives may have deleterious health effects including immunotoxicity, but molecular mechanisms underlying such an effect have never been addressed. The present study was carried out to assess the immunotoxic response of methyl isocyanate (MIC) on cultured human lymphocytes isolated from healthy human volunteers. Studies were conducted to evaluate both dose‐dependent and time‐course response (n = 3), using N‐succinimidyl N‐methylcarbamate, a surrogate chemical substitute to MIC. Evaluation of DNA damage by ataxia telangiectasia mutated (ATM) and γ H2AX protein phosphorylation states; measure of apoptotic index through annexin‐V/PI assay, apoptotic DNA ladder assay, and mitochondrial depolarization; induction of oxidative stress by CM‐H2DCFDA and formation of 8‐hydroxy‐2′ deoxy guanosine; levels of antioxidant defense system enzyme glutathione reductase; and multiplex cytometric bead array analysis to quantify the secreted levels of inflammatory cytokines, interleukin‐8, interleukin‐1β, interleukin‐6, interleukin‐10, tumor necrosis factor, and interleukin‐12p70 parameters were carried out. The results of the study showed a dose‐ and time‐dependent response, providing evidence to hitherto unknown molecular mechanisms of immunotoxic consequences of isocyanate exposure at a genomic level. We anticipate these data along with other studies reported in the literature would help to design better approaches in risk assessment of occupational and accidental exposure to isocyanates.

Regulation of isocyanate-induced apoptosis, oxidative stress, and inflammation in cultured human neutrophils: isocyanate-induced neutrophils apoptosis.

Implications of environmental toxins on the regulation of neutrophil function are being significantly appraised. Such effects can be varied and markedly different depending on the type and extent of chemical exposure, which results in direct damage to the immune system. Isocyanates with functional group (–NCO), are considered as highly reactive molecules with diverse industrial applications. However, patho-physiological implications resulting from their occupational and accidental exposures have not been well delineated. The present study was carried out to assess the immunotoxic response of isocyanates and their mode of action at a molecular level on cultured human neutrophils isolated from healthy human volunteers. Studies were conducted to evaluate both dose- and time-dependent (n = 3) response using N-succinimidyl N-methylcarbamate, a chemical entity that mimics the effects of methyl isocyanate in vitro. Measure of apoptosis through annexin-V-FITC/PI assay, active caspase-3, apoptotic DNA ladder assay and mitochondrial depolarization; induction of oxidative stress by CM-H2DCFDA and formation of 8′-hydroxy-2′-deoxyguanosine; and levels of antioxidant defense system enzyme glutathione reductase, multiplex cytometric bead array analysis to quantify the secreted cytokine levels (interleukin-8, interleukin-1β, interleukin-6, interleukin-10, interferon-γ, tumor necrosis factor, and interleukin-12p70) parameters were evaluated. Our results demonstrate that isocyanates induce neutrophil apoptosis via activation of mitochondrial-mediated pathway along with reactive oxygen species production; depletion in antioxidant defense states; and elevated pro-inflammatory cytokine response.

Mitochondrial oxidative stress elicits chromosomal instability after exposure to isocyanates in human kidney epithelial cells

The role of oxidative stress is often attributed in environmental renal diseases. Isocyanates, a ubiquitous chemical group with diverse industrial applications, are known to undergo bio-transformation reactions upon accidental and occupational exposure. This study delineates the role of isocyanate-mediated mitochondrial oxidative stress in eliciting chromosomal instability in cultured human kidney epithelial cells. Cells treated with 0.005 µM concentration of methyl isocyanate displayed morphological transformation and stress-induced senescence. Along the time course, an increase in DCF fluorescence indicative of oxidative stress, depletion of superoxide dismutase (SOD) and glutathione reductase (GR) and consistent accumulation of 8-oxo-dG were noticed. Thus, endogenous oxidative stress resulted in aberrant expression of p53, p21, cyclin E and CDK2 proteins, suggestive of deregulated cell cycle, chromosomal aberrations, centromeric amplification, aneuploidy and genomic instability.

In utero exposure to methyl isocyanate in the Bhopal gas disaster: evidence of persisting hyperactivation of immune system two decades later

The methyl isocyanate (MIC) gas leak from the Union Carbide Plant at Bhopal, India, in 1984 represents the worst chemical disaster in modern industrial history. The leak resulted in release of 30–40 tons of MIC spreading over approximately 30 square miles. The estimated mortality of this accident is believed to have been between 2500 and 6000 people, with up to 200 000 injured.1 Given the nature and intensity of the accident, many facets of the event have been studied through at least 24 cohort studies among survivors but exposure to MIC and its possible immunological implications never received much attention. Two early studies conducted on exposed adult victims by Deo et al 2 and Saxena et al 3 reported significant delay of the cell cycle and a decreased response to mitogen-activated stimulation of proliferative lymphocytes studied. The study was approved by the institutional review board of Bhopal Memorial …

Induction of genomic instability in cultured human colon epithelial cells following exposure to isocyanates

The toxic response of cultured human colon epithelial‐FHC cells to methyl isocyanate was investigated with regard to genomic instability. Qualitative and quantitative assessments of the extent of phosphorylation of DNA damage signaling factors such as ATM, γH2AX and p53, was increased in treated cells compared to controls. At the same time, many treated cells were arrested at the G2/M phase of the cell cycle, and had an elevated apoptotic index and increased inflammatory cytokine levels. Cytogenetic analyses revealed varied chromosomal anomalies, with abnormal expression of pericentrin protein. Analysis through ISSR PCR demonstrated increased microsatellite instability. The results imply that isocyanates can cause genomic instability in colonocytes.

Analysis of cellular response to isocyanate using N-succinimidyl N-methylcarbamate exposure in cultured mammalian cells

Isocyanates (RNCO), one of the highly reactive industrial intermediates, possess the capability to modulate the bio‐molecules by forming toxic metabolites and adducts which may cause adverse health effects. Some of their toxic degradations have previously been unknown and overlooked; of which, molecular repercussions underlying their genetic hazards upon occupational/accidental exposures still remain as an intricate issue and are hitherto unknown. To assess the genotoxic potential of methyl isocyanate in cultured mammalian cells after in vitro exposure, we performed a study in three different normal cell lines MM55.K (mouse kidney epithelial), B/CMBA.Ov (mouse ovarian epithelial), and NIH/3T3 (primary mouse embryonic fibroblast). Cellular DNA damage response was studied for qualitative phosphorylation states of ATM, γH2AX proteins and quantitative state of p53 phosphorylation; DNA cell cycle analysis and measure of cellular apoptotic index before and after treatment were also investigated. Our results demonstrate that methyl isocyanate by negatively regulating the DNA damage response pathway, might promote cell cycle arrest, and apoptosis in cultured mammalian cells suggestive of causing genetic alterations. We anticipate that these data along with other studies reported in the literature would help to design better approaches in risk assessment of occupational and accidental exposure to isocyanates. We also predict that increasing knowledge on DNA damage‐triggered signaling leading to cell death could provide new strategies for investigating the effects of DNA repair disorders and decreased repair capacity on the toxicity and carcinogenic properties of environmental toxins. Environ. Mol. Mutagen., 2009.

Circulating Biomarkers and their Possible Role in Pathogenesis of Chronic Hepatitis B and C Viral Infections

The present study evaluated the plausible role of circulating biomarkers in immune pathogenesis of chronic hepatitis considered a priority in clinical hepatology. Total viral load of chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) patients was quantified and correlation studies were performed with circulating levels of Th1/Th2 cytokines; C reactive protein and circulating nucleosomes; glutathione reductase (GR) and superoxide dismutase. To our knowledge, the study is first among its kind that validates strong positive correlation of viral load with IL-4, IL-6, GR in HBV and IL-6, IL-10, GR in HCV infections. Although, multi-centric studies including large cohorts are required for translating our findings to clinical practice, however, role of these biomarkers with potential diagnostic or prognostic significance might be helpful in clinical assessment of high-risk individuals, thereby, designing interventional strategies, towards development of personalized medicare. The results of our study also offer valuable insights of immune signaling mediators engaged in development of hepatocellular carcinoma.

Cell cycle deregulation by methyl isocyanate: Implications in liver carcinogenesis

Liver is often exposed to plethora of chemical toxins. Owing to its profound physiological role and central function in metabolism and homeostasis, pertinent succession of cell cycle in liver epithelial cells is of prime importance to maintain cellular proliferation. Although recent evidence has displayed a strong association between exposures to methyl isocyanate (MIC), one of the most toxic isocyanates, and neoplastic transformation, molecular characterization of the longitudinal effects of MIC on cell cycle regulation has never been performed. Here, we sequentially delineated the status of different proteins arbitrating the deregulation of cell cycle in liver epithelial cells treated with MIC. Our data reaffirms the oncogenic capability of MIC with elevated DNA damage response proteins pATM and γ‐H2AX, deregulation of DNA damage check point genes CHK1 and CHK2, altered expression of p53 and p21 proteins involved in cell cycle arrest with perturbation in GADD‐45 expression in the treated cells. Further, alterations in cyclin A, cyclin E, CDK2 levels along with overexpression of mitotic spindle checkpoints proteins Aurora A/B, centrosomal pericentrin protein, chromosomal aberrations, and loss of Pot1a was observed. Thus, MIC impacts key proteins involved in cell cycle regulation to trigger genomic instability as a possible mechanism of developmental basis of liver carcinogenesis.

Peri‐operative outcomes for pancreatoduodenectomy in India: a multi‐centric study

BACKGROUND There have been an increasing number of reports world-wide relating improved outcomes after pancreatic resections to high volumes thereby supporting the idea of centralization of pancreatic resectional surgery. To date there has been no collective attempt from India at addressing this issue. This cohort study analysed peri-operative outcomes after pancreatoduodenectomy (PD) at seven major Indian centres. MATERIALS AND METHODS Between January 2005 and December 2007, retrospective data on PDs, including intra-operative and post-operative factors, were obtained from seven major centres for pancreatic surgery in India. RESULTS Between January 2005 and December 2007, a total of 718 PDs were performed in India at the seven centres. The median number of PDs performed per year was 34 (range 9-54). The median number of PDs per surgeon per year was 16 (range 7-38). Ninety-four per cent of surgeries were performed for suspected malignancy in the pancreatic head and periampullary region. The median mortality rate per centre was four (range 2-5%). Wound infections were the commonest complication with a median incidence per centre of 18% (range 9.3-32.2%), and the median post-operative duration of hospital stay was 16 days (range 4-100 days). CONCLUSIONS This is the first multi-centric report of peri-operative outcomes of PD from India. The results from these specialist centers are very acceptable, and appear to support the thrust towards centralization.