Oxidative and histopathological alterations after sub-acute exposure of diisopropyl phosphorofluoridate in mice: Beneficial effect of N­acetylcysteine.

AIMS: Protective efficacy of N­acetylcysteine (NAC) was assessed against sub-acute diisopropyl phosphorofluoridate (DFP) poisoning in mice. MAIN METHODS: Mice were allocated into nine groups of six each: vehicle control; DFP (0.125 LD50 ≈ 0.483 mg/kg bwt, s.c.); DFP + Atropine (ATR, 10 mg/kg bwt, i.p., 0 min); DFP + Pralidoxime (2-PAM, 30 mg/kg bwt, i.m., 0 min); DFP + NAC (150 mg/kg bwt, i.p., -60 min); DFP + ATR + NAC; DFP + 2-PAM + NAC; DFP + ATR + 2-PAM; and DFP + ATR + 2-PAM + NAC. Animals received various treatments for 21 d daily. Plasma butyrylcholinesterase (BChE) was measured after 7, 14 and 21 d of exposure. Brain acetylcholinesterase (AChE) and reduced glutathione (GSH), malondialdehyde (MDA), glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), and superoxide dismutase (SOD) were measured (brain, liver and kidney) after 21 d of exposure. Histopathology, immunohistochemistry, and Western blot for inducible nitric oxide synthase (iNOS) and c-fos were also performed. KEY FINDINGS: DFP significantly reduced BChE and AChE levels. Diminished GSH, CAT, SOD (brain and liver), GPx, GR, and elevated MDA (Brain) levels were also observed. DFP caused notable histopathology (brain, liver and kidney) and over expression of iNOS, and c-fos proteins (brain). NAC enhanced the protective efficacy of ATR and 2-PAM in most parameters, without any appreciable protection in iNOS and c-fos expression. SIGNIFICANCE: NAC as an adjunct with ATR and 2-PAM, exhibited marked beneficial effects against sub-acute DFP poisoning, indicating its possible implications in the management of OP poisoning.

Oxidative damage mediated iNOS and UCP-2 upregulation in rat brain after sub-acute cyanide exposure: dose and time-dependent effects.

Cyanide-induced chemical hypoxia is responsible for pronounced oxidative damage in the central nervous system. The disruption of mitochondrial oxidative metabolism has been associated with upregulation of uncoupling proteins (UCPs). The present study addresses the dose- and time-dependent effect of sub-acute cyanide exposure on various non-enzymatic and enzymatic oxidative stress markers and their correlation with inducible-nitric oxide synthase (iNOS) and uncoupling protein-2 (UCP-2) expression. Animals received (oral) triple distilled water (vehicle control), 0.25 LD50 potassium cyanide (KCN) or 0.50 LD50 KCN daily for 21 d. Animals were sacrificed on 7, 14 and 21 d post-exposure to measure serum cyanide and nitrite, and brain malondialdehyde (MDA), reduced glutathione (GSH), glutathione disulfide (GSSG), cytochrome c oxidase (CCO), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CA) levels, together with iNOS and UCP-2 expression, and DNA damage. The study revealed that a dose- and time-dependent increase in cyanide concentration was accompanied by corresponding CCO inhibition and elevated MDA levels. Decrease in GSH levels was not followed by reciprocal change in GSSG levels. Diminution of SOD, GPx, GR and CA activity was congruent with elevated nitrite levels and upregulation of iNOS and UCP-2 expression, without any DNA damage. It was concluded that long-term cyanide exposure caused oxidative stress, accompanied by upregulation of iNOS. The upregulation of UCP-2 further sensitized the cells to cyanide and accentuated the oxidative stress, which was independent of DNA damage.

Protective efficacy of various carbonyl compounds and their metabolites, and nutrients against acute toxicity of some cyanogens in rats: biochemical and physiological studies.

Cyanogens are widely used in industries and their toxicity is mainly due to cyanogenesis. The antidotes for cyanide are usually instituted for the management of cyanogen poisoning. The present study reports the protective efficacy of 14 carbonyl compounds and their metabolites, and nutrients (1.0 g/kg; oral; +5 min) against acute oral toxicity of acetonitrile (ATCN), acrylonitrile (ACN), malononitrile (MCN), propionitrile (PCN), sodium nitroprusside (SNP), succinonitrile (SCN), and potassium ferricyanide (PFCN) in rats. Maximum protection index was observed for alpha-ketoglutarate (A-KG) against MCN and PCN (5.60), followed by dihydroxyacetone (DHA) against MCN (2.79). Further, MCN (0.75 LD50) caused significant increase in cyanide concentration in brain, liver and kidney and inhibition of cytochrome c oxidase activity in brain and liver, which favorably responded to A-KG and DHA treatment. Up-regulation of inducible nitric oxide synthase by MCN, PCN and SNP, and uncoupling protein by PCN and SNP observed in the brain was abolished by A-KG administration. However, no DNA damage was detected in the brain. MCN and SNP significantly decreased the mean arterial pressure, heart rate, respiratory rate and neuromuscular transmission, which were resolved by A-KG. The study suggests a beneficial effect of A-KG in the treatment of acute cyanogen poisoning.

Time- and temperature-dependent changes in cytochrome c oxidase activity and cyanide concentration in excised mice organs and mice cadavers.

Postmortem stability of cyanide biomarkers is often disputed. We assessed the time and temperature-dependent changes in cytochrome c oxidase (CCO) activity and cyanide concentration in various organs of mice succumbing to cyanide. Immediately after death, excised mice organs and mice cadavers were stored at room temperature (35°C ± 5°C) or in frozen storage (-20°C ± 2°C). At various times after death, CCO activity and cyanide concentrations were measured in excised mice organs or organs removed from mice cadavers. The study revealed that (i) measuring both the biomarkers in mice cadavers was more reliable compared to excised mice organs, (ii) measuring temporal CCO activity and cyanide concentration in vital organs from mice cadavers (room temperature) was reliable up to 24 h, and (iii) CCO activity in the brain and lungs and cyanide concentration in organs from mice cadavers (frozen) were measurable beyond 21 days. This study will be helpful in postmortem determination of cyanide poisoning.

Acute toxicity of some synthetic cyanogens in rats: time-dependent cyanide generation and cytochrome oxidase inhibition in soft tissues after sub-lethal oral intoxication.

Cyanogens include complex nitrile-containing compounds that can generate free cyanide of toxicological significance. Acute toxicity, time-dependent cyanide generation and cytochrome oxidase (CYTOX) inhibition in soft tissues, and urinary thiocyanate levels were measured after acute cyanogen intoxication in rats. Order of cyanogens in terms of LD50 was: malononitrile (MCN)>propionitrile (PCN)≈sodium nitroprusside (SNP)>acrylonitrile (ACN)>succinonitrile (SCN)>acetonitrile (ATCN) for oral, and SNP>MCN>ACN>PCN>SCN>ATCN for intraperitoneal and subcutaneous routes. MCN was most toxic by oral (LD50=66.4 mg/kg) and SNP by intraperitoneal (LD50=16.7 mg/kg) and subcutaneous (LD50=11.9 mg/kg) routes. Minimum survival time (25 min) was recorded after 4.0 LD50 ATCN. Order of cyanogens (0.75 LD50; oral) on the basis of maximum blood cyanide and time of peak cyanide generation were: ATCN>SNP>SCN>PCN>MCN>ACN, and MCN (30 min)