Effects of repeated in vivo inhalant nitrite exposure on gene expression in mouse liver and lungs

Prognostic value of alcohol consumption and some other dietary habits for survival in a cohort of Chinese men with lung cancer

Background

Alcohol consumption and some other dietary habits are thought to be associated with lung cancer incidence. However, the effects of these habits on lung cancer prognosis have been studied rarely. The purpose of this study was to address these gaps in knowledge.

Methods

We studied a cohort of 1052 Chinese men in Hong Kong who were diagnosed with primary lung cancer. Cox proportional hazards models were used to determine the prognostic values of consumption of alcohol, fresh fruits or vegetables, meat, and fried or preserved food.

Results

Compared with never drinkers, men who drank alcohol 1–3 days per week had a more favorable lung cancer prognosis (hazard ratio [HR]: 0.82, 95% confidence interval [CI] 0.68–0.97); however, this survival advantage was not significant in men who drank alcohol more frequently (HR: 0.91, 95% CI 0.73–1.14). Compared with men who consumed preserved or fried food only occasionally, men who consumed these foods frequently had a higher risk of lung cancer mortality (HR: 1.20, 95% CI 1.00–1.42).

Conclusions

Occasional consumption of alcohol was a favorable survival factor for Chinese men with lung cancer. However, this survival benefit did not exist for frequent drinkers of alcohol. Chinese men with lung cancer who were frequent consumers of fried or preserved food had a worse prognosis than those who consumed these foods only occasionally.

Nitric oxide-deficiency regulates hepatic heme oxygenase-1

Nitric oxide plays a crucial role in the maintenance of liver function and integrity. During stress, the inducible heme oxygenase-1 protein and its reaction products, including carbon monoxide, also exert potent hepatoprotective effects. We investigated a potential relationship between endogenous nitric oxide synthesis and the hepatic regulation of heme oxygenase-1. Inhibition of nitric oxide synthesis in vivo by injection of l-NAME led to a dose-dependent induction of heme oxygenase-1 mRNA, protein and activity in the rat liver, whereas did not affect the expression of other heat shock proteins. The effect of l-NAME was demonstrated by hemodynamic changes within the liver circulation as measured by ultrasonic flow probes. Inhibition of nitric oxide synthase led to a decline in hepatic arterial and portal venous blood flow, and subsequently caused liver cell damage. In contrast, the combined administration of l-NAME and the nitric oxide-independent intestinal vasodilator dihydralazine completely restored portal venous flow, abolished the liver cell damage, and prevented the upregulation of heme oxygenase-1, despite inhibition of nitric oxide production. In conclusion, nitric oxide deficiency upregulates hepatic heme oxygenase-1, which is reversible by maintaining hepatic blood flow. This interdependence has important implications for the development of therapeutic strategies aimed at modulating the activity of these hepatoprotective mediator systems.

Inactivation of hepatic enzymes by inhalant nitrite--in vivo and in vitro studies

We examined the effects of acute isobutyl nitrite (ISBN) exposure on the activity of several hepatic enzymes. Two strains of adult male mice (Balb/c and C57BL/6) were exposed to 900 ppm ISBN or ambient air for 45 minutes. The enzyme activity of hepatic cytochrome P450 (CYP)-mediated deethylation, glutathione S-transferase (GST), and carboxylesterase (CBE) was monitored through the substrates 3-cyano-7-ethoxycoumarin (CEC), 1-chloro-2,4-dinitrobenzene, and p-nitrophenyl acetate, respectively. Acute ISBN exposure led to a significant reduction in hepatic CYP-mediated CEC deethylation, GST, and CBE activity in Balb/c mice (of 81.5%, 74.7%, and 25.2%, respectively, vs control mice, each at P < .05) when livers were harvested immediately after inhalant exposure. The corresponding decreases in C57BL/6 mice were smaller (with reductions of 21.8%, 18.8%, and 13.3%, respectively, each at P < .05). This enzyme activity, tested in C57BL/6 mice only, returned to control values after a 24-hour period of nonexposure. Follow-up mechanistic investigations using rat liver GST indicated that ISBN-mediated enzyme inactivation was not caused by its metabolites: inorganic nitrite ion (NO2-) or nitric oxide. This inactivation could be prevented, but not reversed, by added glutathione, suggesting irreversible protein oxidation. Using different NO donors as comparative agents, we found that GST inactivation by ISBN was not associated with protein S-nitrosylation or disulfide formation, but with tyrosine nitration. Inhalant nitrite exposure, therefore, led to a significant reduction in hepatic enzyme activity in mice, possibly through tyrosine nitration of hepatic proteins. This effect raises the possibility of drug-drug metabolic interactions from inhalant nitrite abuse. However, determining the applicability of these findings to humans will require further study.