Jacqueline A. Sinclair, Ph.D.
Active Emeritus Associate Professor of Biochemistry
Active Emeritus Associate Professor of Pharmacology & Toxicology
Pharmacology & Toxicology
New York University School of Medicine, PHD 1977New York University School of Medicine, MS 1975U. Kentucky, BS 1970
Pharmacology and Toxicology Graduate Program
Office: VA Hospital
Asst. Phone: 802-295-9363
Mechanisms by which: 1) consumption of alcoholic beverages increases liver damage from acetaminophen and 2) arsenic decreases cytochromes P450 in the liver.
Dr. Sinclair received her B.S. in 1970 from the University of Kentucky her M.S. in 1975 and her Ph.D. in 1977 from New York University Medical School. After post-doctoral work in England and Switzerland she joined the staff of the Veterans Administration Hospital in White River Junction, Vermont.
The cytochromes P450 (CYP) comprise a superfamily of hemoproteins that catalyze the oxidation of many endogenous and exogenous lipophilic chemicals. Although the chemical modifications by cytochrome P450-mediated reactions usually facilitate excretion, with certain chemicals, such as acetaminophen, the oxidized product is more toxic than the parent compound. In humans, chronic consumption of alcoholic beverages is associated with increases in drug metabolism and acetaminophen-mediated hepatotoxicity. We have found that ethanol, the major alcohol in alcoholic beverages, induces CYP3A in cultured human and rat hepatocytes and intact rats. In humans, CYP3A is currently considered responsible for the metabolism of the majority of drugs metabolized by P450. In addition, CYP3A converts acetaminophen to a hepatotoxic metabolite. Until our findings, CYP2E was considered the only form of cytochrome P450 responsible in alcohol consumption for the increased risk of acetaminophen hepatotoxicity. In rats, we have found that treatment with a specific inhibitor of CYP3A, triacetyloleandomycin, protects the animals from alcohol-mediated increases in acetaminophen hepatotoxicity, inidcating a major role of CYP3A. Our findings have major clinical implications since several drugs induce CYP3A in humans, and may increase the risk of developing liver damage from acetaminophen. We are investigating whether increases in CYP3A are themselves sufficient to increase acetaminophen hepatotoxicity.
Although ethanol constitutes the major alcohol in alcoholic beverages, higher chain alcohols are also present, with the amount depending on the type of beverage. Most experimental work on the effects of alcoholic beverages on drug metabolism and acetaminophen hepatoxicity has focused on ethanol and has ignored the potential contribution of the higher chain alcohols. Isopentanol constitutes up to 90% of the higher chain alcohol content of alcoholic beverages. We have found that combined treatment with ethanol and isopentanol, results in dramatic increases in acetaminophen hepatotoxicity.
Arsenic is a worldwide contaminant implicated in numerous pathological conditions in humans, including cancer and several forms of liver disease such as hepatocellular carcinoma, fibrosis and cirrhosis, and biliary occlusion. One of the contributing factors to these disorders may be the alteration of cytochrome P450 (CYP) levels by arsenic. CYPs are involved in the oxidative metabolism and elimination of numerous toxic chemicals. Heavy metals such as As induce heme oxygenase, the rate-limiting enzyme in the degradation of heme, and decrease levels of cytochrome P450. Previous studies have not distinguished the roles of heme oxygenase versus metal-induced oxidative damage in the breakdown of heme and cytochrome P450. In primary cultures of hepatocytes, we have found that arsenite-mediated decreases in at least 3 forms of CYPs, CYP3A23, CYP2B1/2 and CYP1A1/2, are not due to decreased availability of heme. The nuclear receptors PXR and RXRalpha are involved in expression of several CYPs from the 3A family. Arsenite decreases induction of CYP3A23 in rat hepatocytes by 2 mechanisms: decreased transcription and decreased association of CYP3A23 mRNA with polysomes. In human hepatocytes, arsenite decreases transcription of CYP3A4 through a mechanism that involves decreased nuclear levels of RXRalpha, but no decrease in its heterodimer partner PXR. In both hepatocyte systems, these effects occurr at concentrations of arsenite that do not decrease protein synthesis or cause oxidative damage. We are currently investigating the mechanisms by which arsenite decreases RXRalpha and whether arsenite affects expression of other genes regulated by RXRalpha. Since CYP3A4 is responsible for the metabolism of at least 50% of currently used drugs, exposure to arsenite can have a major impact on metabolism on these drugs.
Merit Review A006 (Sinclair, J) 4/01/01-3/31/05
Department of Veterans Affairs
Alcohol and acetaminophen hepatotoxicity: relation to alcoholic liver disease
The overall goal of this grant is to characterize the mechanism by which consumption of alcoholic beverages increases the risk of acetaminophen hepatotoxicity and the relationship to alcoholic liver disease.
RO1 AA12898-01A2 (Sinclair, J) 7/01/2002-6/30/2007
Alcohol and Acetaminophen Hepatotoxicity
The overall goal of this grant is to characterize the mechanism by which consumption of alcoholic beverages increases the risk of acetaminophen hepatotoxicity.
RO1-ES 10426-01 (Sinclair, J) 4/01/02-3/31/06
Effect of arsenic on cytochromes P450
The overall purpose of this proposal is to determine the mechanism by which arsenic decreases several forms of CYPs in cultured rat and human hepatocytes.
RO1-ES 06263-08 (Sinclair, P.) 7/1/99-6/30/03
Mechanism of porphyria caused by TCDD.
The overall goals of this research are to characterize the mechanism of development of hepatic uroporhyria caused by polyhalogenated aromatic hydrocarbons and to deterrmine the relationship to the human disease of uroporhyria, Porphyria Cutanea Tarda.
VA Merit Review(Sinclair, P) 10/01/02-9/30/07
Mechanism of Uroporphyria Accumulation by Ethanol
The long-term goal of this grant is to delineate the mechanism by which alcoholic beverages, the major risk factor in human uroporhyria, Porphyria Cutanea Tarda, precipitate uroporhyria, including a role in iron accumulation.
Wolf KK, Wood SG, Hunt JA, Walton-Strong BW, Yasuda K, Lan L, Duan SX, Hao Q, Wrighton SA, Jeffery EH, Evans RM, Szakacs JG, von Moltke LL, Greenblatt DJ, Court MH, Scheutz EG, Sinclair PR, Sinclair JF. Role of the nuclear receptor PXR in acetaminophen hepatotoxicity. Drug Metab Dispos. 2005 Sep 1; [Epub ahead of print] (view details on MedLine)
Noreault TL, Jacobs JM, Nichols RC, Trask HW, Wrighton SA, Sinclair PR, Sinclair JF. Mechanism of arsenite-mediated decreases in CYP3A23 in rat hepatocytes. Biochem Biophys Res Commun. 2005 Aug 12;333(4):1211-7. (view details on MedLine)
Noreault TL, Kostrubsky VE, Wood SG, Nichols RC, Strom SC, Trask HW, Wrighton SA, Evans RM, Jacobs JM, Sinclair PR, Sinclair JF. Arsenite decreases CYP3A4 and RXRalpha in primary human hepatocytes. Drug Metab Dispos. 2005 Jul;33(7):993-1003. Epub 2005 Apr 15. (view details on MedLine)
Noreault TL, Jacobs JM, Nichols RC, Trask HW, Wrighton SA, Sinclair PR, Evans RM, Sinclair JF. Arsenite decreases CYP3A23 induction in cultured rat hepatocytes by transcriptional and translational mechanisms. Toxicol Appl Pharmacol. 2005 Dec 1;209(2):174-82. (view details on MedLine)