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 gamma 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-1beta, 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.

In vitro and in vivo evaluation of the anticarcinogenic and cancer chemopreventive potential of a flavonoid-rich fraction from a traditional Indian herb Selaginella bryopteris

Prevention of cancer through nutritional intervention has gained significant recognition in recent years. Evidence revealed from mechanistic investigations coupled with molecular epidemiology show an inverse association of dietary flavonoids intake with cancer risk. The chemopreventive and anticarcinogenic potential of Selaginella bryopteris, a traditional Indian herb referred to as 'Sanjeevani' in the Ayurvedic system of medicine, was examined in the present study. Comprehensive in vitro and in vivo studies were conducted on the flavonoid-rich benzene fraction of the aqueous extract that demonstrated a significant cytoprotective activity. Biomarkers of chemoprevention such as proliferative index and status of cell-cycle regulatory proteins, antioxidant property, anti-inflammatory effect, reversal of stress-induced senescence and genoprotective effect were investigated in human and murine cell cultures. Chemopreventive potential was assessed in benzopyrene-induced lung carcinogenesis and 7,12-dimethyl benz(a)anthracene-mediated skin papillomagenesis test models. Inhibition of DNA fragmentation, unperturbed cell-cycle regulation, maintenance of intracellular antioxidant defence, anti-inflammatory activity, prevention of stress-induced senescence and genoprotective effects against methyl isocyanate carcinogenicity was observed. Medium-term anticarcinogenicity and two-stage skin papillomagenesis tests strongly substantiated our in vitro observations. Results from the present study provide evidence of anticarcinogenic and chemopreventive activities of S. bryopteris hitherto unreported and reaffirm the nutritional significance of flavonoids in cancer prevention.

Mitochondrial oxidative stress-induced epigenetic modifications in pancreatic epithelial cells

Emerging studies have linked prooxidative carbamate compound exposures with various human pathologies including pancreatic cancer. In these studies, our aim was to examine mitochondrial oxidative stress-mediated aberrant chromatin responses in human pancreatic ductal epithelial cells. Posttranslational histone modifications, promoter DNA methylation, and micro-RNA (miRNA) expression patterns were evaluated following induction of mitochondrial oxidative stress by N-succinimidyl N-methylcarbamate exposure. In treated cells, perturbation in mitochondrial machinery led to hypermethylation of p16 and smad4 gene promoters and downregulation of respective gene products. Posttranslational histone modifications that include hypoacetylation of acetylated histone (AcH) 3 and AcH4, hypermethylation of monomethylated histone 3 at lysine 9 and trimethylated histone 4 at lysine 20 ubiquitinated histone (uH) 2A/uH2B, and increased phosphorylation of H2AX and H3 were observed in the treated cells. Altered expression of miRNAs denoted possible location of corresponding genes at oxidatively damaged fragile sites. Collectively, our results provide a direct role of mitochondrial oxidative stress-mediated epigenetic imbalance to perturbed genomic integrity in oxygen radical-induced pancreatic injury. Further, identification and characterization of molecular switches that affect these epigenomic signatures and targets thereof will be imperative to understand the complex role of redox-regulatory network in pancreatic milieu.

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-H(2)DCFDA 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-1beta, interleukin-6, interleukin-10, interferon-gamma, 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.

Inflammatory response to isocyanates and onset of genomic instability in cultured human lung fibroblasts

Lungs comprise the primary organ exposed to environmental toxic chemicals, resulting in diverse respiratory ailments and other disorders, including carcinogenesis. Carcinogenesis is a multi-stage phenomenon, which involves a series of genetic alterations that begin with genomic instability provoked by certain factors such as inflammation and DNA damage and end with the development of cancer. Isocyanates such as methyl isocyanate are the chief metabolic intermediates in many industrial settings with diverse applications; exposure to them can lead to severe hypersensitive, mutagenic and genotoxic alterations. We examined the molecular mechanisms underlying isocyanate-mediated inflammatory responses and their probable role in the onset of genomic instability in cultured IMR-90 human lung fibroblasts. The isocyanates induced inflammation, resulting in extensive DNA damage, evidenced by increases in ATM, ATR, gammaH2AX, and p53 expression levels. The apoptotic index also increased. Chromosomal anomalies in treated cells included over-expression of centrosome protein and variable amplification of inter-simple sequence repeats, further demonstrating isocyanate-induced genomic instability. This information could be useful in the design of new approaches for risk assessment of potential industrial disasters.

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, gammaH2AX 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.

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, gammaH2AX 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.

Correlation of aberrant expression of p53, Rad50, and cyclin-E proteins with microsatellite instability in gallbladder adenocarcinomas

Gallbladder carcinoma is an uncommon, but highly malignant tumor, with poor prognostic, and diagnostic manifestations in early stages. The Indian Council of Medical Research reported increased incidence of gallbladder carcinoma in the surviving population of the Bhopal gas tragedy that involved exposure of more than 500,000 people to methyl isocyanate gas. The severity of exposure, and increased multi-systemic morbidity in the survivors stimulated us to examine the molecular changes leading to gallbladder carcinoma. Surgically resected samples (N = 40) of gallbladder carcinoma were studied for the p53, Rad50, and cyclin-E expression by immunohistofluorescence bioimaging. Among the 40 samples, 23, 11, and 10 showed p53, Rad50, and cyclin-E expression, respectively, in moderately differentiated adenocarcinomas, demonstrating the prevalence and invasiveness of this disease in the methyl isocyanate-exposed population (P = 0.0009). Nevertheless, co-expression of Rad50, and cyclin-E with p53 was absent in adenomas with dysplasia, demonstrating their independent roles. We conclude that there was altered expression of p53, Rad50, and cyclin-E in the malignant transformation of gallbladder carcinoma in this methyl isocyanate gas-exposed cohort. Hence, these proteins may be useful as markers to identify premalignant lesions that are likely to progress into malignant adenocarcinoma.

Molecular detection of Mycobacterium tuberculosis in formalin-fixed, paraffin-embedded tissues and biopsies of gastrointestinal specimens using real-time polymerase chain reaction system

BACKGROUND/AIMS

We aimed to perform the molecular detection of Mycobacterium tuberculosis in formalin-fixed, paraffin-embedded tissues and biopsies of gastrointestinal specimens using real-time polymerase chain reaction system.

METHODS

The study included three groups: (A) control (n=24), with no previous signs of M. tuberculosis complex (MTBC), (B) patients (n=28) with known TB origin and (C) patients (n=50) with clinical and histopathological signs of TB but who were culture- and acid-fast bacilli (AFB)-negative. The samples were obtained from the Medical and Surgical Gastroenterology Departments of Bhopal Memorial Hospital and Research Centre. We extracted DNA using DNeasy Blood & Tissue kit (QIAGEN, Germany) and performed realtime assay using Roche LightCycler 2.0 with fluorescence resonance energy transfer (FRET) hybridization probes obtained from Roche Molecular Diagnostics (USA) for the specific amplification of the 159 bp region of the mycobacterium genome.

RESULTS

All the samples (n=24) of Group A were found to be negative, while in Group B, 27 out of the 28 cases studied were found to be positive by LightCycler real-time polymerase chain reaction (LC PCR). In Group C, 18 out of the 50 cases studied were found to be positive, showing a positivity of 36%. The overall positive and negative predictive values of the test for clinical TB (Group C) were 100% and 96.9%, respectively.

CONCLUSIONS

Results of our investigation demonstrated that the real-time detection technology using FRET probes has much higher sensitivity for the detection of MTBC DNA in tissue biopsy samples and formalin-fixed paraffin-embedded surgically resected tissues of the gastrointestinal tract.

Prevalence of hepatitis C virus genotypes and impact of T helper cytokines in achieving sustained virological response during combination therapy: a study from Central India

Characterisation of host immune response to hepatitis C virus (HCV) genotypes may have an important prognostic and therapeutic implication. Genotype-3 was more prevalent in the examined cohort and demonstrated a significantly higher response to combination therapy than genotype-1. Sustained virological response (SVR) was 94.74% in genotype-3 and 45.45% in genotype-1. The patients who achieved SVR reported higher levels of circulating T helper 1 cytokines in comparison to subjects with no SVR in both the studied groups. Besides providing local prevalence, our study might also assist in understanding the host immune mechanisms involved to achieve SVR during combination therapy in chronic HCV patients.

Diagnosis of gastrointestinal tuberculosis: Using cytomorphological, microbiological, immunological and molecular techniques - A study from Central India

The present study included three groups: (A) age and gender matched control (n=24) with no previous signs of M. tuberculosis complex (MTBC) infection, (B) patients (n=28) diagnosed with gastro-intestinal TB (GITB), (C) patients (n=50) with clinical and histo-pathological signs of GITB, but were culture and AFB negative. Real time assay performed using fluorescence resonance energy transfer hybridization probes showed a positivity index of 36 % in group C, i.e. 18 were found reactive from the total 50 cases studied. In addition, immune characterization of these 18 cases showed depleted CD(4) (+) count and increased levels of IFN-γ and TNF-α cytokines. No positive case was found in group A, while in group B, out of total 28 cases studied 27 were found positive. A combinatorial diagnostic approach for rapid detection and characterization of GITB might provide specific therapeutic strategies for prevention and treatment of the infection in future.

Molecular bio-dosimetry for carcinogenic risk assessment in survivors of Bhopal gas tragedy

December 2014 marked the 30th year anniversary of Bhopal gas tragedy. This sudden and accidental leakage of deadly poisonous methyl isocyanate (MIC) gas instigated research efforts to understand the nature, severity of health damage and sufferings of 570 000 ailing survivors of this tragedy. In a decade-long period, our systematic laboratory investigations coupled with long-term molecular surveillance studies have comprehensively demonstrated that the risk of developing an environmental associated aberrant disease phenotype, including cancer, involves complex interplay of genomic and epigenetic reprogramming. These findings poised us to translate this knowledge into an investigative framework of "molecular biodosimetry" in a strictly selected cohort of MIC exposed individuals. A pragmatic cancer risk-assessment strategy pursued in concert with a large-scale epidemiological study might unfold molecular underpinnings of host-susceptibility and exposureresponse relationship. The challenges are enormous, but we postulate that the study will be necessary to establish a direct initiation-promotion paradigm of environmental carcinogenesis. Given that mitochondrial retrograde signaling-induced epigenetic reprogramming is apparently linked to neoplasticity, a cutting-edge tailored approach by an expert pool of biomedical researchers will be fundamental to drive these strategies from planning to execution. Validating the epigenomic signatures will hopefully result in the development of biomarkers to better protect human lives in an overburdened ecosystem, such as India, which is continuously challenged to meet population demands. Besides, delineating the mechanistic links between MIC exposure and cancer morbidity, our investigative strategy might help to formulate suitable regulatory policies and measures to reduce the overall burden of occupational and environmental carcinogenesis.

Prenatal exposure to environmental pro-oxidants induces mitochondria-mediated epigenetic changes: a cross-sectional pilot study

Mitochondria play a central role in maintaining cellular and metabolic homeostasis during vital development cycles of foetal growth. Optimal mitochondrial functions are important not only to sustain adequate energy production but also for regulated epigenetic programming. However, these organelles are subtle targets of environmental exposures, and any perturbance in the defined mitochondrial machinery during the developmental stage can lead to the re-programming of the foetal epigenetic landscape. As these modifications can be transferred to subsequent generations, we herein performed a cross-sectional study to have an in-depth understanding of this intricate phenomenon. The study was conducted with two arms: whereas the first group consisted of in utero pro-oxidant exposed individuals and the second group included controls. Our results showed higher levels of oxidative mtDNA damage and associated integrated stress response among the exposed individuals. These disturbances were found to be closely related to the observed discrepancies in mitochondrial biogenesis. The exposed group showed mtDNA hypermethylation and changes in allied mitochondrial functioning. Altered expression of mitomiRs and their respective target genes in the exposed group indicated the possibilities of a disturbed mitochondrial-nuclear cross talk. This was further confirmed by the modified activity of the mitochondrial stress regulators and pro-inflammatory mediators among the exposed group. Importantly, the disturbed DNMT functioning, hypermethylation of nuclear DNA, and higher degree of post-translational histone modifications established the existence of aberrant epigenetic modifications in the exposed individuals. Overall, our results demonstrate the first molecular insights of in utero pro-oxidant exposure associated changes in the mitochondrial-epigenetic axis. Although, our study might not cement an exposure-response relationship for any particular environmental pro-oxidant, but suffice to establish a dogma of mito-epigenetic reprogramming at intrauterine milieu with chronic illness, a hitherto unreported interaction.

A pragmatic & translational approach of human biomonitoring to methyl isocyanate exposure in Bhopal

Human biomonitoring has evolved beyond margins to ascertain exposure-response relationship in environmental associated human diseases. As occupational ailments continue to dominate global concerns, biomonitoring strategies have evolved better in terms of evaluating health risks associated with systemic uptake from chronic (long-term) environment exposures. Even though contributions of acute toxic exposures (short-term) towards initiation of disease processes have been gradually recognized, a comprehensive approach delineating mechanistic insights of such an implication remains elusive. Molecular biomonitoring in a strictly selected defined surviving cohort of the infamous Bhopal gas tragedy "as a model", could provide an unparallel opportunity to discern the long standing implications of acute exposures. Besides comprehending clinical significance of isocyanate toxicity, the results might provide a framework for understanding the molecular repercussions pertaining to a host of other such acute environmental exposures. The investigative strategy might also be helpful in identification of biomarkers with potential for translational research.