Harry V. Gelboin

Bio: Harry V. Gelboin is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Cytochrome & Microsome. The author has an hindex of 45, co-authored 97 publications receiving 8860 citations. Previous affiliations of Harry V. Gelboin include Government of the United States of America.

Characterization of the common genetic defect in humans deficient in debrisoquine metabolism.

Abstract: 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%).

Hydroxylation of warfarin by human cDNA-expressed cytochrome P-450: a role for P-4502C9 in the etiology of (S)-warfarin-drug interactions.

Abstract: Previous kinetic studies have identified a high-affinity (S)-warfarin 7-hydroxylase present in human liver microsomes which appears to be responsible for the termination of warfarin's biological activity. Inhibition of the formation of (S)-7-hydroxywarfarin, the inactive, major metabolite of racemic warfarin in humans, is known to be the cause of several of the drug interactions experienced clinically upon coadministration of warfarin with other therapeutic agents. In order to identify the specific form(s) of human liver cytochrome P-450 involved in this particular toxicity, we have determined the metabolic profiles of 11 human cytochrome P-450 forms expressed in HepG2 cells toward both (R)- and (S)-warfarin. Of the 11 forms examined only 2C9 displayed the regioselectivity and stereoselectivity appropriate for the high-affinity human liver microsomal (S)-7-hydroxylase. We further compared Michaelis-Menten and sulfaphenazole inhibition constants for (S)-warfarin 7-hydroxylation catalyzed by cDNA-expressed 2C9 and by human liver microsomes. Similar kinetic constants were obtained for each enzyme source. It is concluded that 2C9 is likely to be a principal form of human liver P-450 which modulates the in vivo anticoagulant activity of the drug. It is further concluded that those drug interactions with warfarin that arise as a result of decreased clearance of the biologically more potent S-enantiomer may have as their common basis the inhibition of P-450 2C9.

Pharmacogenomics: Translating Functional Genomics into Rational Therapeutics

Abstract: Genetic polymorphisms in drug-metabolizing enzymes, transporters, receptors, and other drug targets have been linked to interindividual differences in the efficacy and toxicity of many medications. Pharmacogenomic studies are rapidly elucidating the inherited nature of these differences in drug disposition and effects, thereby enhancing drug discovery and providing a stronger scientific basis for optimizing drug therapy on the basis of each patient's genetic constitution.

Sequence diversity in CYP3A promoters and characterization of the genetic basis of polymorphic CYP3A5 expression.

Abstract: Variation in the CYP3A enzymes, which act in drug metabolism, influences circulating steroid levels and responses to half of all oxidatively metabolized drugs. CYP3A activity is the sum activity of the family of CYP3A genes, including CYP3A5, which is polymorphically expressed at high levels in a minority of Americans of European descent and Europeans (hereafter collectively referred to as 'Caucasians'). Only people with at least one CYP3A5*1 allele express large amounts of CYP3A5. Our findings show that single-nucleotide polymorphisms (SNPs) in CYP3A5*3 and CYP3A5*6 that cause alternative splicing and protein truncation result in the absence of CYP3A5 from tissues of some people. CYP3A5 was more frequently expressed in livers of African Americans (60%) than in those of Caucasians (33%). Because CYP3A5 represents at least 50% of the total hepatic CYP3A content in people polymorphically expressing CYP3A5, CYP3A5 may be the most important genetic contributor to interindividual and interracial differences in CYP3A-dependent drug clearance and in responses to many medicines.

Tobacco Smoke Carcinogens and Lung Cancer

Abstract: The complexity of tobacco smoke leads to some confusion about the mechanisms by which it causes lung cancer. Among the multiple components of tobacco smoke, 20 carcinogens convincingly cause lung tumors in laboratory animals or humans and are, therefore, likely to be involved in lung cancer induction. Of these, polycyclic aromatic hydrocarbons and the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone are likely to play major roles. This review focuses on carcinogens in tobacco smoke as a means of simplifying and clarifying the relevant information that provides a mechanistic framework linking nicotine addiction with lung cancer through exposure to such compounds. Included is a discussion of the mechanisms by which tobacco smoke carcinogens interact with DNA and cause genetic changes--mechanisms that are reasonably well understood--and the less well defined relationship between exposure to specific tobacco smoke carcinogens and mutations in oncogenes and tumor suppressor genes. Molecular epidemiologic studies of gene-carcinogen interactions and lung cancer--an approach that has not yet reached its full potential--are also discussed, as are inhalation studies of tobacco smoke in laboratory animals and the potential role of free radicals and oxidative damage in tobacco-associated carcinogenesis. By focusing in this review on several important carcinogens in tobacco smoke, the complexities in understanding tobacco-induced cancer can be reduced, and new approaches for lung cancer prevention can be envisioned.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders.

Abstract: Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.