In population studies of individuals given the antihypertensive drug debrisoquine, two distinct phenotypes have been described: extensive metabolizers excrete 10-200 times more of the urinary metabolite 4-hydroxydebrisoquine than poor metabolizers. In family studies the poor-metabolizer phenotype behaves as an autosomal recessive trait with an incidence between 5% and 10% in the white population of Europe and North America, and extends to the deficient metabolism of more than 20 commonly prescribed drugs. Clinical studies have shown that such individuals are at high risk for the development of adverse side effects from these and probably many other drugs. Here we show that poor metabolizers have negligible amounts of the cytochrome P450 enzyme P450db1. We have cloned the human P450db1 complementary DNA and expressed it in mammalian cell culture. Furthermore, by directly cloning and sequencing cDNAs from several poor-metabolizer livers, we have identified three variant messenger RNAs that are products of mutant genes producing incorrectly spliced db1 pre-mRNA, providing a molecular explanation for one of man's most commonly defective genes (frequency of mutant alleles 35-43%).

Increased oxidative/nitrosative stress is a major contributing factor to alcohol-mediated mitochondrial dysfunction. However, which mitochondrial proteins are oxidatively modified under alcohol-induced oxidative/nitrosative stress is poorly understood. The aim of this study was to systematically investigate oxidized and/or S-nitrosylated mitochondrial proteins and to use a biotin-N-maleimide probe to evaluate their inactivation in alcoholic fatty livers of rats. Binge or chronic alcohol exposure significantly elevated nitric oxide, inducible nitric oxide synthase, and ethanol-inducible CYP2E1. The biotin-N-maleimide-labeled oxidized and/or S-nitrosylated mitochondrial proteins from pair-fed controls or alcohol-fed rat livers were subsequently purified with streptavidin-agarose. The overall patterns of oxidized and/or S-nitrosylated proteins resolved by 2-dimensional polyacrylamide gel electrophoresis were very similar in the chronic and binge alcohol treatment groups. Seventy-nine proteins that displayed differential spot intensities from those of control rats were identified by mass spectrometry. These include mitochondrial aldehyde dehydrogenase 2 (ALDH2), ATP synthase, acyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase, and many proteins involved in chaperone activity, mitochondrial electron transfer, and ion transport. The activity of 3-ketoacyl-CoA thiolase involved in mitochondrial ␤-oxidation of fatty acids was significantly inhibited in alcohol-exposed rat livers, consistent with hepatic fat accumulation, as determined by biochemical and histological analyses. Measurement of activity and immunoblot results showed that ALDH2 and ATP synthase were also inhibited through oxidative modification of their cysteine or tyrosine residues in alcoholic fatty livers of rats. In conclusion, our results help to explain the underlying mechanism for mitochondrial dysfunction and increased susceptibility to alcohol-mediated liver damage. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

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Mice deficient small heterodimer partner (SHP) are protected from diet induced hepatic steatosis due to increased fatty acid oxidation and decreased lipogenesis. The decreased lipogenesis appears to be a direct consequence of very low expression of peroxisome proliferator activated receptor gamma 2 (PPARγ2), a potent lipogenic transcription factor, in the SHP−/− liver. The current study focuses on the identification of a SHP dependent regulatory cascade that controls PPARγ2 gene expression, thereby regulating hepatic fat accumulation. Illumina BeadChip array and real-time polymerase chain reaction were used to identify genes responsible for the linkage between SHP and PPARγ2 using hepatic RNAs isolated from SHP−/− and SHP-overexpressing mice. The initial efforts identify that hairy and enhancer of split 6 (Hes6), a novel transcriptional repressor, is an important mediator of the regulation of PPARγ2 transcription by SHP. The Hes6 promoter is specifically activated by the retinoic acid receptor (RAR) in response to its natural agonist ligand all-trans retinoic acid (atRA), and is repressed by SHP. Hes6 subsequently represses hepatocyte nuclear factor 4 alpha (HNF4α) activated-PPARγ2 gene expression via direct inhibition of the HNF4α transcriptional activity. Furthermore, we provide evidences that atRA treatment or adenovirus-mediated RARα overexpression significantly reduced hepatic fat accumulation in obese mouse models as observed in earlier studies and the beneficial effect is achieved via the proposed transcriptional cascade. Conclusions Our study describes a novel transcriptional regulatory cascade controlling hepatic lipid metabolism that identifies retinoic acid signaling as a new therapeutic approach to non-alcoholic fatty liver diseases.