Alcoholic liver disease: a matter of hormones?

Abstract

Women are more likely than men to develop alcoholic liver disease. Although this has been known for a long time, the mechanisms underlying this gender difference are only now being elucidated [1Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar, 2Thurman R.G. Mechanisms of hepatic toxicity II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin.Am J Physiol. 1998; 275: G605-G611PubMed Google Scholar]. The past decade has seen major advances in our understanding of the increased susceptibility of women to develop alcoholic liver disease. First, the group of C.S. Lieber in New York demonstrated a gastric first-pass metabolism of orally ingested ethanol, which was shown to be less in women than in men [1Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar, 3Frezza M. di Padova C. Pozzato G. Terpin M. Baraona E. Lieber C.S. High blood alcohol levels in women. The role of decreased gastric alcohol dehydrogenase activity and first-pass metabolism.N Engl J Med. 1990; 322: 95-99Crossref PubMed Scopus (1045) Google Scholar]. The lower effectiveness in women is due to a lower alcohol dehydrogenase (ADH) activity in the gastric mucosa [[3]Frezza M. di Padova C. Pozzato G. Terpin M. Baraona E. Lieber C.S. High blood alcohol levels in women. The role of decreased gastric alcohol dehydrogenase activity and first-pass metabolism.N Engl J Med. 1990; 322: 95-99Crossref PubMed Scopus (1045) Google Scholar]. Therefore, consumption of the same amount of ethanol results in higher blood ethanol levels in women than in men. The gastric mucosa contains several ADH isozymes, one of which is the type IV or σ-ADH (ADH7) which is not present in the liver and has a high capacity for ethanol metabolism [[1]Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar]. Since estrogens increase the expression of ADH isozymes [4Harada S. Tachiyashiki K. Imaizumi K. Effect of sex hormones on rat liver cytosolic alcohol dehydrogenase activity.J Nutr Sci Vitaminol. 1998; 44: 625-639Crossref PubMed Scopus (23) Google Scholar, 5Qulali M. Crabb D.W. Estradiol regulates class I alcohol dehydrogenase gene expression in renal medulla of male rats by a posttranscriptional mechanism.Arch Biochem Biophys. 1992; 297: 277-284Crossref PubMed Scopus (19) Google Scholar, 6Teschke R. Wannagat F.J. Lowendorf F. Strohmeyer G. Hepatic alcohol metabolizing enzymes after prolonged administration of sex hormones and alcohol in female rats.Biochem Pharmacol. 1986; 35: 521-527Crossref PubMed Scopus (26) Google Scholar], the reason for the lower gastric σ-ADH activity in females remains to be elucidated.Another major advance in the understanding of the gender differences in susceptibility to ethanol-induced liver injury was contributed by the group of R.G. Thurman [2Thurman R.G. Mechanisms of hepatic toxicity II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin.Am J Physiol. 1998; 275: G605-G611PubMed Google Scholar, 7Iimuro Y. Frankenberg M.V. Arteel G.E. Bradford B.U. Wall C.A. Thurman R.G. Female rats exhibit greater susceptibility to early alcohol-induced liver injury than males.Am J Physiol. 1997; 272: G1186-G1194PubMed Google Scholar, 8Ikejima K. Enomoto N. Iimuro Y. Ikejima A. Fang D. Xu J. et al.Estrogen increases sensitivity of hepatic Kupffer cells to endotoxin.Am J Physiol. 1998; 274: G669-G676PubMed Google Scholar, 9Kono H. Wheeler M.D. Rusyn I. Lin M. Seabra V. Rivera C.A. et al.Gender differences in early alcoho-induced liver injury: role of CD14, NF-κB and TNF-α.Am J Physiol. 2000; 278: G652-G661Google Scholar, 10Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar]. They demonstrated that estrogens contribute importantly to ethanol-induced liver injury. Administration of ethanol to female rats resulted in more hepatic steatosis, inflammation and necrosis compared to male rats, despite equal ethanol intake, metabolism and excretion [[7]Iimuro Y. Frankenberg M.V. Arteel G.E. Bradford B.U. Wall C.A. Thurman R.G. Female rats exhibit greater susceptibility to early alcohol-induced liver injury than males.Am J Physiol. 1997; 272: G1186-G1194PubMed Google Scholar]. Plasma endotoxin levels were also significantly higher in female rats than in male rats [[7]Iimuro Y. Frankenberg M.V. Arteel G.E. Bradford B.U. Wall C.A. Thurman R.G. Female rats exhibit greater susceptibility to early alcohol-induced liver injury than males.Am J Physiol. 1997; 272: G1186-G1194PubMed Google Scholar]. In another study they demonstrated that treatment of female rats with estrogens increased the sensitivity to endotoxin: estrogen pre-treatment significantly increased mortality after a sublethal dose of endotoxin [[8]Ikejima K. Enomoto N. Iimuro Y. Ikejima A. Fang D. Xu J. et al.Estrogen increases sensitivity of hepatic Kupffer cells to endotoxin.Am J Physiol. 1998; 274: G669-G676PubMed Google Scholar]. The increased sensitivity to endotoxin of estrogen-treated rats is explained by increased expression of the endotoxin receptor CD14 and the pro-inflammatory cytokine TNF-α in Kupffer cells [[8]Ikejima K. Enomoto N. Iimuro Y. Ikejima A. Fang D. Xu J. et al.Estrogen increases sensitivity of hepatic Kupffer cells to endotoxin.Am J Physiol. 1998; 274: G669-G676PubMed Google Scholar]. The sensitizing effect of estrogen was prevented by prior elimination of the Kupffer cell population [[8]Ikejima K. Enomoto N. Iimuro Y. Ikejima A. Fang D. Xu J. et al.Estrogen increases sensitivity of hepatic Kupffer cells to endotoxin.Am J Physiol. 1998; 274: G669-G676PubMed Google Scholar]. Likewise, ethanol ingestion resulted in a stronger activation of the inflammation-associated transcription factor NF-κB and a higher expression of CD14 and TNF-α in livers of female rats compared to male rats [[9]Kono H. Wheeler M.D. Rusyn I. Lin M. Seabra V. Rivera C.A. et al.Gender differences in early alcoho-induced liver injury: role of CD14, NF-κB and TNF-α.Am J Physiol. 2000; 278: G652-G661Google Scholar]. Lowering estrogen levels, by subjecting female rats to ovariectomy, resulted in a significant reduction of ethanol-induced liver injury including steatosis and inflammation [[10]Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar]. In addition, hepatic CD14 expression as well as plasma endotoxin levels were reduced [[10]Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar]. Taken together, these results indicate that females are more susceptible to ethanol-induced liver damage because: (1) gastric ADH-dependent ethanol metabolism is lower, resulting in higher blood ethanol levels; (2) plasma endotoxin levels are higher after ethanol ingestion; (3) the inflammatory response in the liver is more severe due to an estrogen-dependent sensitization to endotoxin.In this issue of the Journal of Hepatology, Järveläinen et al. [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar] further contribute to our understanding of the role of estrogens in the higher susceptibility of females to ethanol-induced liver injury. Using female rats they confirmed previous results that ethanol induced hepatic steatosis, inflammation and necrosis as well as increased expression of CD14 and TNF-α in Kupffer cells [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. Moreover, they demonstrate that the estrogen antagonist toremifene reduced ethanol induced hepatic inflammation and necrosis. Unexpectedly, toremifene failed to reduce hepatic steatosis and had no effect on the ethanol-induced hepatic expression of CD14 and TNF-α mRNA [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. Toremifene suppressed the ethanol-induced increase in the activity of the ethanol-metabolizing enzyme CYP2E1 and it counteracted the ethanol-induced reduction in selenium-dependent glutathione-peroxidase activity, an important anti-oxidant enzyme [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. The findings of Järveläinen et al. differ from previous findings in that the estrogen antagonist toremifene failed to reduce the expression of ethanol-induced inflammation-related genes like CD14 and TNF-α [10Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar, 11Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. The reason for this discrepancy remains to be elucidated but could be related to specific differences between anti-estrogens (toremifene) [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar] and ovariectomy [[10]Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar]. Methodological differences should not be overlooked: Järveläinen et al. used oral ingestion of ethanol avoiding cyclical changes in blood ethanol levels observed during intragastric ethanol administration [[10]Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar] and their study lasted for 6 weeks versus 4 weeks in Thurman's studies. However, the overall message is the same: estrogens aggravate the inflammatory response to ethanol.An important aspect of the study by Järveläinen et al. is that estrogens regulate enzymes involved in ethanol metabolism and in the generation and protection against oxidative stress. As mentioned earlier, estrogens increase the expression of the major ethanol metabolizing enzyme ADH [4Harada S. Tachiyashiki K. Imaizumi K. Effect of sex hormones on rat liver cytosolic alcohol dehydrogenase activity.J Nutr Sci Vitaminol. 1998; 44: 625-639Crossref PubMed Scopus (23) Google Scholar, 5Qulali M. Crabb D.W. Estradiol regulates class I alcohol dehydrogenase gene expression in renal medulla of male rats by a posttranscriptional mechanism.Arch Biochem Biophys. 1992; 297: 277-284Crossref PubMed Scopus (19) Google Scholar, 6Teschke R. Wannagat F.J. Lowendorf F. Strohmeyer G. Hepatic alcohol metabolizing enzymes after prolonged administration of sex hormones and alcohol in female rats.Biochem Pharmacol. 1986; 35: 521-527Crossref PubMed Scopus (26) Google Scholar]. Järveläinen et al. report that anti-estrogens reduce the ethanol-induced expression of the ethanol metabolizing enzyme CYP2E1. These results would suggest a more rapid metabolism of ethanol in females than in males and would implicate higher levels of the toxic metabolite acetaldehyde generated by ADH and CYP2E1. This prediction awaits experimental confirmation. Acetaldehyde is a very toxic and reactive compound, e.g. it promotes hepatic fibrogenesis [[12]Moshage H. Casini A. Lieber C.S. Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes.Hepatology. 1990; 12: 511-518Crossref PubMed Scopus (213) Google Scholar] and it reacts with proteins resulting in the formation of neo-antigens and the induction of an inappropriate immune response to these neo-antigens [13Hoerner M. Behrens U.J. Worner T.M. Blacksberg I. Braly L.F. Schaffner F. Lieber C.S. The role of alcoholism and liver disease in the appearance of serum antibodies against acetaldehyde adducts.Hepatology. 1988; 8: 569-574Crossref PubMed Scopus (84) Google Scholar, 14Li C-J. Nanji A.A. Siakotos A.N. Lin R.C. Acetaldehyde-modified and 4-hydroxynonenal-modified proteins in the livers of rats with alcoholic liver disease.Hepatology. 1997; 26: 650-657Crossref PubMed Scopus (73) Google Scholar].Another important consequence of the differences in regulation of CYP2E1 between females and males relates to the formation of reactive oxygen species by this enzyme. Part of ethanol-induced liver injury is the result of increased exposure to reactive oxygen species [1Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar, 2Thurman R.G. Mechanisms of hepatic toxicity II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin.Am J Physiol. 1998; 275: G605-G611PubMed Google Scholar, 15Meagher E.A. Barry O.P. Burke A. Lucey M.R. Lawson J.A. Rokach J. FitzGerald J. Alcohol-induced generation of lipid peroxidation products in humans.J Clin Invest. 1999; 104: 805-813Crossref PubMed Scopus (225) Google Scholar, 16Kurose I. Higuchi H. Kato S. Miura S. Ishii H. Ethanol-induced oxidative stress in the liver.Alcohol Clin Exp Res. 1996; 20: 77A-85ACrossref PubMed Scopus (91) Google Scholar, 17Takeyama Y. Kamimura S. Kuroiwa A. Sohda T. Irie M. Shijo H. Okumura M. Role of Kupffer cell-derived reactive oxygen species in alcoholic liver disease in rats in vivo.Alcohol Clin Exp Res. 1996; 20: 335A-339ACrossref PubMed Google Scholar]. The ethanol-inducible enzyme CYP2E1 is an important source of these reactive oxygen species [[18]Dai Y. Rashba-Step J. Cedarbaum A.I. Stable expression of human cytochrome P4502E1 in HepG2 cells: characterization of catalytic activity and production of reactive oxygen intermediates.Biochemistry. 1993; 32: 6928-6937Crossref PubMed Scopus (230) Google Scholar]. Indeed, inhibition of CYP2E1 activity significantly reduces ethanol-induced liver injury [19Gouillon Z. Lucas D. Li J. Hagbjork A.L. French B.A. Fu P. et al.Inhibition of ethanol-induced liver disease in the intragastric feeding rat model by chlormethiazole.Proc Soc Exp Biol Med. 2000; 224: 302-308Crossref PubMed Google Scholar, 20Fang C. Lindros K.O. Badger T.M. Ronis M.J.J. Ingelman-Sundberg M. Zonated expression of cytokines in rat liver: effect of chronic ethanol and the cytochrome P450 2E1 inhibitor, chlormethiazole.Hepatology. 1998; 27: 1304-1310Crossref PubMed Scopus (77) Google Scholar, 21Gebhardt A.C. Lucas D. Menez J.F. Seitz H.K. Chlormethiazole inhibition of cytochrome P450 2E1 as assessed by chlorzoxazone hydroxylation in humans.Hepatology. 1997; 26: 957-961Crossref PubMed Scopus (81) Google Scholar]. Thurman's group reported that ethanol-induced generation of reactive oxygen species is larger in female rats than in male rats [[22]Thurman R.G. Bradford B.U. Iimuro Y. Knecht K.T. Arteel G.E. Yin M. et al.The role of gut-derived bacterial toxins and free radicals in alcohol-induced liver injury.J Gastroenterol Hepatol. 1998; 13: S39-S50PubMed Google Scholar]. However, they also reported that alcoholic liver injury and generation of reactive oxygen species were similar in CYP2E1 knockout mice and normal mice [[23]Kono H. Bradford H.U. Yin M. Sulik K.K. Koop D.R. Peters J.M. et al.CYP2E1 is not involved in early alcohol-induced liver injury.Am J Physiol. 1999; 277: G1259-G1267PubMed Google Scholar]. These findings argue against an important role of CYP2E1 in the pathogenesis of alcoholic liver injury, although it is possible that a compensatory increase in the expression of other ethanol-metabolizing P-450 isozymes occurs in CYP2E1 knockout mice [[23]Kono H. Bradford H.U. Yin M. Sulik K.K. Koop D.R. Peters J.M. et al.CYP2E1 is not involved in early alcohol-induced liver injury.Am J Physiol. 1999; 277: G1259-G1267PubMed Google Scholar]. Based on Järveläinen's study, the effect of blocking estrogen action on the generation of reactive oxygen species is twofold: (1) attenuation of the ethanol-induced rise in CYP2E1 activity, resulting in reduced generation of reactive oxygen species and (2) partial prevention of the reduction in the activity of the anti-oxidant enzyme glutathione-peroxidase, thus preserving the protection against reactive oxygen species. Together, these effects counteract the pro-inflammatory and damaging effects of reactive oxygen species. Unfortunately, Järveläinen et al. did not measure the generation of reactive oxygen species in their study [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar].Important questions remain. It needs to be established whether the concepts based on studies with experimental animals are valid in humans. This will be a challenging task since there is a large interindividual variation in the expression and regulation of genes involved in inflammation, ethanol metabolism and detoxification of reactive oxygen species due to polymorphisms. Furthermore, many parameters, including the amount and duration of ethanol intake, age, diet and body mass index, have to be taken into account. In addition, analysis of gene expression in human liver tissue is technically challenging. Human in vitro preparations, e.g. human liver cells or human liver slices, preserving the interaction between hepatocytes and Kupffer cells, could also be used to study gender differences in the response to ethanol [24Moshage H. Yap S.H. Primary cultures of human hepatocytes: a unique system for studies in toxicology, virology, parasitology and liver pathophysiology in man.J Hepatol. 1992; 15: 404-413Abstract Full Text PDF PubMed Scopus (25) Google Scholar, 25Lerche-Langrand C. Toutain H.J. Precision-cut liver slices: characteristics and use for in vitro pharmaco-toxicology.Toxicology. 2000; 153: 221-253Crossref PubMed Scopus (168) Google Scholar]. Another important area of investigation is the elucidation of the mechanism by which estrogens modulate the response to ethanol. For example, the genes involved in inflammation, ethanol metabolism and generation and detoxification of reactive oxygen species should be analyzed for the presence of estrogen responsive elements in their promoters. Since the transcription factor NF-κB plays a central role in inflammation, the interaction between estrogens, ethanol and NF-κB also needs to be investigated. The literature is controversial here and opposing mechanisms could be at work: on the one hand, ethanol directly inhibits cytokine-induced activation of NF-κB and NF-κB-regulated genes [26Greenberg S.S. Ouyang J. Zhao X. Xie J. Wang J-F. Giles T.D. Interaction of ethanol with inducible nitric oxide synthase mRNA and protein: direct effects on autocoids and endotoxin in vivo.J Pharmacol Exp Ther. 1997; 282: 1044-1054PubMed Google Scholar, 27Kimura H. Miura S. Higuchi H. Kurose I. Tsuzuki Y. Shigematsu T. et al.Effect of chronic ethanol feeding on nitric oxide synthesis by rat Kupffer cells.Alcohol Clin Exp Res. 1996; 20: 69A-72ACrossref PubMed Scopus (18) Google Scholar, 28Zhang Y. Crichton R.R. Boelaert J.R. Jorens P.G. Herman A.G. Ward R.J. et al.Decreased release of nitric oxide (NO) by alveolar macrophages after in vivo loading of rats with either iron or ethanol.Biochem Pharmacol. 1998; 55: 21-25Crossref PubMed Scopus (39) Google Scholar, 29Diehl A.M. Effect of ethanol on tumor necrosis factor signaling during liver regeneration.Clin Biochem. 1999; 32: 571-578Crossref PubMed Scopus (34) Google Scholar, 30Zeldin G. Yang S.Q. Yin M. Lin H.Z. Rai R. Diehl A.M. Alcohol and cytokine-inducible transcription factors.Alcohol Clin Exp Res. 1996; 20: 1639-1645Crossref PubMed Scopus (55) Google Scholar]. On the other hand, ethanol ingestion causes increased plasma endotoxin levels, resulting in inflammation, NF-κB activation and production of cytokines [7Iimuro Y. Frankenberg M.V. Arteel G.E. Bradford B.U. Wall C.A. Thurman R.G. Female rats exhibit greater susceptibility to early alcohol-induced liver injury than males.Am J Physiol. 1997; 272: G1186-G1194PubMed Google Scholar, 9Kono H. Wheeler M.D. Rusyn I. Lin M. Seabra V. Rivera C.A. et al.Gender differences in early alcoho-induced liver injury: role of CD14, NF-κB and TNF-α.Am J Physiol. 2000; 278: G652-G661Google Scholar, 10Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar, 31Nanji A.A. Jokelainen K. Rahemtulla A. Miao L. Fogt F. Matsumoto H. et al.Activation of nuclear factor kappa B and cytokine imbalance in experimental alcoholic liver disease in the rat.Hepatology. 1999; 30: 934-943Crossref PubMed Scopus (197) Google Scholar]. Apparently, the latter mechanism dominates in animal models of ethanol administration. Likewise, estrogens have been reported to decrease the activation of NF-κB and the expression of NF-κB-regulated genes, e.g. iNOS [32Hsu S.M. Chen Y.C. Jiang M.C. 17beta-estradiol inhibits tumor necrosis factor-alpha-induced nuclear factor-kappa B activation by increasing NF-kappa B p105 level in MCF-7 breast cancer cells.Biochem Biophys Res Commun. 2000; 279: 47-52Crossref PubMed Scopus (50) Google Scholar, 33Cuzzocrea S. Santafati S. Sautebin L. Mazzon E. Calabro G. Serraino I. et al.17beta-estradiol antiinflammatory activity in carrageenan-induced pleurisy.Endocrinology. 2000; 141: 1455-1463Crossref PubMed Scopus (66) Google Scholar, 34Hayashi T. Yamada K. Esaki T. Muto E. Chaudhuri G. Iguchi A. Physiological concentrations of 17beta-estradiol inhibit the synthesis of nitric oxide synthase in macrophages via a receptor-mediated system.J Cardiovasc Pharmacol. 1998; 31: 292-298Crossref PubMed Scopus (79) Google Scholar, 35Vegeto E. Bonincontro C. Pollio G. Sala A. Viappiani S. Nardi F. et al.Estrogen prevents the lipopolysaccharide-induced inflammatory response in microglia.J Neurosci. 2001; 21: 1809-1818PubMed Google Scholar], yet estrogens aggravate the ethanol-induced hepatic inflammation [9Kono H. Wheeler M.D. Rusyn I. Lin M. Seabra V. Rivera C.A. et al.Gender differences in early alcoho-induced liver injury: role of CD14, NF-κB and TNF-α.Am J Physiol. 2000; 278: G652-G661Google Scholar, 10Yin M. Ikejima K. Wheeler M.D. Bradford B.U. Seabra V. Forman D.T. Sato N. Thurman R.G. Estrogen is involved in early alcohol-induced liver injury in a rat enteral feeding model.Hepatology. 2000; 31: 117-123Crossref PubMed Scopus (88) Google Scholar]. As suggested by Thurman's group [[9]Kono H. Wheeler M.D. Rusyn I. Lin M. Seabra V. Rivera C.A. et al.Gender differences in early alcoho-induced liver injury: role of CD14, NF-κB and TNF-α.Am J Physiol. 2000; 278: G652-G661Google Scholar], other effects of estrogens, e.g. on gut permeability and/or gut flora, resulting in increased translocation of endotoxin from the gut or a stimulatory effect of estrogens on Kupffer cell CD14 expression, could be involved as well. Together, these observations illustrate the need to resolve the complex interplay between estrogens, ethanol and NF-κB-controlled signal transduction pathways.Finally, can we interfere with the action of estrogens or CYP2E1 to prevent or treat ethanol-induced liver injury. The results from the current study using an estrogen antagonist as well as previous studies demonstrating a beneficial effect of CYP2E1 inhibition in experimental alcoholic liver injury, suggest we can [11Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar, 19Gouillon Z. Lucas D. Li J. Hagbjork A.L. French B.A. Fu P. et al.Inhibition of ethanol-induced liver disease in the intragastric feeding rat model by chlormethiazole.Proc Soc Exp Biol Med. 2000; 224: 302-308Crossref PubMed Google Scholar, 20Fang C. Lindros K.O. Badger T.M. Ronis M.J.J. Ingelman-Sundberg M. Zonated expression of cytokines in rat liver: effect of chronic ethanol and the cytochrome P450 2E1 inhibitor, chlormethiazole.Hepatology. 1998; 27: 1304-1310Crossref PubMed Scopus (77) Google Scholar, 21Gebhardt A.C. Lucas D. Menez J.F. Seitz H.K. Chlormethiazole inhibition of cytochrome P450 2E1 as assessed by chlorzoxazone hydroxylation in humans.Hepatology. 1997; 26: 957-961Crossref PubMed Scopus (81) Google Scholar]. Can we also use these interventions to treat non-alcoholic steatohepatitis (NASH)? This is a more controversial issue. There appears to be a clear connection between estrogen and development of steatosis and in Järveläinen's study, the anti-estrogen toremifene decreased the mild fatty infiltration seen in control rat livers [[11]Järveläinen H.A. Lukkari T.A. Heinaro S. Sippel H. Lindros K.O. The antiestrogen toremifene protects against alcoholic liver injury in female rats.J Hepatol. 2001; 35: 46-52Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar]. However, in humans, the long-term use of anti-estrogens, in particular tamoxifen, has been associated with hepatic steatosis [36Hamada N. Ogawa Y. Saibara T. Murata Y. Kariya S. Nishioka A. et al.Toremifene-induced fatty liver and NASH in breast cancer patients with breast-conservation treatment.Int J Oncol. 2000; 17: 1119-1123PubMed Google Scholar, 37Murata Y. Ogawa Y. Saibara T. Nishioka A. Fujiwara Y. Fukumoto M. et al.Unrecognized hepatic steatosis and non-alcoholic steatohepatitis in adjuvant tamoxifen for breast cancer patients.Oncol Rep. 2000; 7: 1299-1304PubMed Google Scholar]. Therefore, inhibition of CYP2E1 or other members of the P-450 family such as CYP4A could be more promising for the treatment of NASH, as recently reported by Leclercq et al. [[38]Leclerq I.A. Farrell G.C. Field J. Bell D.R. Gonzalez F.J. Robertson G.R. CYP2E1 and CYP4A as microsomal catalysts of lipid peroxides in murine nonalcoholic steatohepatitis.J Clin Invest. 2000; 105: 1067-1075Crossref PubMed Scopus (660) Google Scholar].Studies like the one by Järveläinen et al. contribute importantly to our understanding of the gender difference in susceptibility to alcohol-induced liver injury. They provide novel insights and inspire future research.Note Added in proof:Very recently, results of the group of Thurman suggested that reactive oxygen species derived from NADPH oxidase in Kupfler cells contribute to ethanol-induced liver injury (Kono H et al., Am J Physiol 2001;280:G1005–G1012 and Kono H et al., J Clin Invest 2000;106:867–872). Women are more likely than men to develop alcoholic liver disease. Although this has been known for a long time, the mechanisms underlying this gender difference are only now being elucidated [1Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar, 2Thurman R.G. Mechanisms of hepatic toxicity II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin.Am J Physiol. 1998; 275: G605-G611PubMed Google Scholar]. The past decade has seen major advances in our understanding of the increased susceptibility of women to develop alcoholic liver disease. First, the group of C.S. Lieber in New York demonstrated a gastric first-pass metabolism of orally ingested ethanol, which was shown to be less in women than in men [1Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2: 673-702Abstract Full Text Full Text PDF Google Scholar, 3Frezza M. di Padova C. Pozzato G. Terpin M. Baraona E. Lieber C.S. High blood alcohol levels in women. The role of decreased gastric alcohol dehydrogenase activity and first-pass metabolism.N Engl J Med. 1990; 322: 95-99Crossref PubMed Scopus (1045) Google Scholar]. The lower effectiveness in women is due to a lower alcohol dehydrogenase (ADH) activity in the gastric mucosa [[3]Frezza M. di Padova C. Pozzato G. Terpin M. Baraona E. Lieber C.S. High blood alcohol levels in women. The role of decreased gastric alcohol dehydrogenase activity and first-pass metabolism.N Engl J Med. 1990; 322: 95-99Crossref PubMed Scopus (1045) Google Scholar]. Therefore, consumption of the same amount of ethanol results in higher blood ethanol levels in women than in men. The gastric mucosa contains several ADH isozymes, one of which is the type IV or σ-ADH (ADH7) which is not present in the liver and has a high capacity for ethanol metabolism [[1]Lieber C.S. Metabolism of alcohol.Clin Liver Dis. 1998; 2