No abstract

Research on the free radical gas, nitric oxide (NO), during the past twenty years is one of the most rapid growing areas in biology. NO seems to play a part in almost every organ and tissue. However, there is considerable controversy and confusion in understanding its role. The liver is one organ that is clearly influenced by NO. Acute versus chronic exposure to NO has been associated with distinct patterns of liver disease. In this paper we review and discuss the involvement of NO in various liver diseases collated from observations by various researchers. Overall, the important factors in determining the beneficial versus harmful effects of NO are the amount, duration, and site of NO production. A low dose of NO serves to maximize blood perfusion, prevent platelet aggregation and thrombosis, and neutralize toxic oxygen radicals in the liver during acute sepsis and reperfusion events. NO also demonstrates antimicrobial and antiapoptosis properties during acute hepatitis infection and other inflammatory processes. However, in the setting of chronic liver inflammation, when a large sustained amount of NO is present, NO might become genotoxic and lead to the development of liver cancer. Additionally, during prolonged ischemia, high levels of NO may have cytotoxic effects leading to severe liver injury. In view of the various possible roles that NO plays, the pharmacologic modulation of NO synthesis is promising in the future treatment of liver diseases, especially with the emergence of selective NO synthase inhibitors and cell-specific NO donors.

The haem oxygenase (HO)/carbon monoxide (CO) system has been implicated as a modulator of hepatobiliary function. This study investigated HO expression in the process of cirrhosis development, as well as its relationship to nitric oxide synthase (NOS). Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). HO mRNA expression was evaluated by competitive RT-PCR, while protein expression was determined by immunoblotting and immunohistochemistry. In liver tissue where cirrhosis had fully developed, the expression levels of HO-1 were greatly enhanced at both mRNA and protein level compared with sham livers. Immunohistochemistry showed that HO-1 was induced in hepatocytes and enhanced in some of the Kupffer-like cells in BDL livers. In contrast, there was no difference between the sham and the BDL livers for the expression levels of HO-2. Interestingly, administration of the NOS inhibitor aminoguanidine (AG) or N(G)-nitro-L-arginine methyl ester inhibited HO-1 expression. To study further the role of HO-1 in the development of liver cirrhosis, hepatocytes were isolated from the rats at different time points after BDL operation. HO-1 was expressed in hepatocytes at high levels during the early onset of cirrhosis but dropped slightly at a later stage of cirrhosis. Zinc protoporphyrin IX (ZnPP), an HO inhibitor, blocked HO-1 expression in hepatocytes from BDL cirrhotic rats, but enhanced the activity of inducible NOS (iNOS) in BDL hepatocytes. In conclusion, HO-1 was induced in the hepatocytes of rats undergoing cirrhosis, suggesting that HO-1 plays a role in the development of liver cirrhosis. Induction of HO-1 may be mediated partially by iNOS. However, once it is induced, HO-1 may be important in modulating iNOS activity, thus playing a protective role in liver cirrhosis.

The differences of NOS expression might be due to their differing roles in maintaining liver homeostasis and/or involvement in the pathology of cirrhosis. Sheer stress within the hypertensive liver may induce increased expression of eNOS. In turn, caveolin-1 is also increased. Whether this serves as a defense mechanism against further cirrhosis or is a consequence of cirrhosis, is yet unknown. The elevated expression of HO-1 and HO-2 suggest that CO may compensate in its role as a vasodilator albeit weakly. It is possible that CO and NO have parallel or coordinated functions within the liver and may work antagonistically in the pathophysiology of portal hypertension.

Hepatic iNOS can be induced in the early stage, which increases with time as cirrhosis develops. Its enzymatic activity is significantly correlated with protein expression and histological alterations of the liver, but not with systemic NO levels, nor with absolute values of liver function markers.

Chronic administration of AG could reduce systemic NO levels as well as suppress iNOS expression and activity in aorta of BDL rats. It also improved liver function, possibly because of its ability to increase hepatic NOS activity, and to correct the systemic hemodynamic disorders by decreasing vascular NO production.

Background/Aims: The prevalence of lifestyle-related chronic diseases is increasing and gene-diet interaction studies are limited among the Malaysian population. This study was conducted to evaluate the association and interaction effects of vascular endothelial growth factor receptor-2(VEGFR2) gene polymorphisms and dietary patterns on anthropometric and biochemical risk factors of chronic diseases in 179 Chinese Malaysian adults. Methods: Genotyping of rs1870377 and rs2071559 was performed by real-time PCR using TaqMan probes. Dietary patterns were constructed from the food frequency questionnaire using factor analysis. Anthropometric measurements: body mass index (BMI), systolic and diastolic blood pressure and biomarkers: blood glucose, glycated hemoglobin A1c (HbA1c) and lipids were obtained. Results: Two dietary patterns: ‘Balanced diet’ and ‘Meat, rice and noodles diet’ (MRND) were extracted. MRND was associated with higher BMI, blood pressure, blood glucose and lipids, while T alleles in both rs1870377 and rs2071559 were associated with higher blood lipids (p < 0.05). The interaction of MRND and rs1870377 had a borderline effect on blood HbA1c after adjusting for confounders (p = 0.057). Conclusions: A dietary pattern of MRND and VEGFR2 gene polymorphisms were both associated with increased health risks of lifestyle-related chronic diseases particularly blood glucose and lipid levels in Chinese Malaysian adults.

Genotype distribution and association of these polymorphisms with overweight/obesity vary between ethnic groups and genders. Nevertheless, the LEP G-2548A risk allele may be associated with overweight/obese Indian male adolescents in Malaysia.