Alcoholic Liver Disease in Rats Fed Ethanol as Part of Oral or Intragastric Low-Carbohydrate Liquid Diets

The intragastric administration of ethanol as part of a lowcarbohydrate diet results in alcohol hepatotoxicity. We aimed to investigate whether comparable liver injury can be achieved by oral diet intake. Male Sprague-Dawley rats were fed ethanol as part of low-carbohydrate diets for 36–42 days either intragastrically or orally. Liver pathology, blood ethanol concentration, serum alanine amino transferase (ALT), endotoxin level, hepatic CYP2E1 induction, and cytokine profiles were assessed. Both oral and intragastric low-carbohydrate ethanol diets resulted in marked steatosis with additional inflammation and necrosis accompanied by significantly increased serum ALT, high levels of CYP2E1 expression, and production of auto-antibodies against malondialdehyde and hydroxyethyl free radical protein adducts. However, cytokine profiles differed substantially between the groups, with significantly lower mRNA expression of the anti-inflammatory cytokine interleukin 4 observed in rats fed low-carbohydrate diets orally. Inflammation and necrosis were significantly greater in rats receiving low-carbohydrate alcohol diets intragastrically than orally. This was associated with a significant increase in liver tumor necrosis factor α and interleukin 1β gene expression in the intragastric model. Thus, oral low-carbohydrate diets produce more ethanol-induced liver pathology than oral high-carbohydrate diets, but hepatotoxicity is more severe when a low-carbohydrate diet plus ethanol is infused intragastrically and is accompanied by significant increases in levels of proinflammatory cytokines.

Effect of chronic ethanol consumption on the expression of complement components and acute-phase proteins in liver

The complement system can provoke but also participate in the repair of liver injury. Here we investigated by microarray analysis the effect of chronic ethanol consumption on hepatic mRNA expression of complement components and acute-phase proteins in complement C3-deficient (C3(-/-)) and wild-type (C3(+/+)) mice. Up-regulation by ethanol of factor B, C1qA-chain and clusterin but down-regulation of factor H, Masp-2, factor D and the terminal components C6, C8alpha and C9 was seen in both strains. Ethanol up-regulated C2 and down-regulated C4bp only in C3(+/+) mice, while in C3(-/-) mice up-regulation of C1qB-chain and vitronectin was observed. The expression of factor B, C6, C1qB and factor I was lower but that of factor D higher in C3(-/-) than in C3(+/+) mice. Ethanol induced mRNA synthesis of many acute-phase proteins including SPARC and lipocalin-2, but reduced the expression of SAP. The induction of early classical and alternative pathway components and suppression of terminal pathway components and soluble regulators may thus contribute to alcohol-induced liver injury. Lipocalin-2 and SPARC emerge as new candidate markers for early detection of liver damage.

Hepatic gene expression and lipid parameters in complement C3(-/-) mice that do not develop ethanol-induced steatosis

BACKGROUND/AIMS

Fatty infiltration initiates alcohol-induced liver changes and complement component C3 affects lipid metabolism. We recently observed that ethanol-induced steatosis seen in normal (C3(+/+)) mice was absent in livers of C3-deficient (C3(-/-)) mice. To understand the underlying molecular mechanisms we analyzed lipid parameters and liver gene expression profiles in these mice.

METHODS

A Western-type high-fat diet with ethanol or carbohydrates (control) was fed for 6 weeks to C3(+/+) and C3(-/-) mice. Serum and liver lipid parameters were analyzed and liver mRNA expression patterns studied by micro-array analysis and RT-PCR.

RESULTS

In both genotypes ethanol markedly reduced serum cholesterol, apolipoprotein A-I, phospholipid transfer protein activity and hepatic mRNA levels of fatty acid-binding proteins and fatty acid beta-oxidation enzymes. In contrast, exclusively in C3(-/-) mice, ethanol treatment increased serum and liver adiponectin levels but down-regulated transcripts of lipogenic enzymes, adiponectin receptor 2 and adipose differentiation-related protein and up-regulated phospholipase D1.

CONCLUSIONS

We propose that these ethanol-induced alterations observed exclusively in C3(-/-) mice contribute to protection against fatty infiltration and subsequent inflammatory processes in the liver of these mice. The results suggest important cross-talk between complement factor C3 and lipid regulators in ethanol-induced steatosis.

Chronic effects of celecoxib, a cyclooxygenase-2 inhibitor, cause enhanced alcohol-induced liver steatosis in rats

BACKGROUND

The pathogenetic role of prostaglandins in steatosis, the first stage of alcoholic liver injury, is not well understood, especially that involving the inflammatory reactions controlled by prostaglandins and pro-inflammatory cytokines in the liver. We, therefore, studied the chronic effects of the COX-2 inhibitor, celecoxib, given to ethanol-treated rats.

METHODS

Rats were fed ethanol and a low dose of celecoxib (approximately 20 mg/kg daily) in a high-fat/low-carbohydrate liquid diet for six weeks.

RESULTS

Ethanol treatment caused liver steatosis, moderate cellular infiltration and enhanced levels of plasma alanine transaminase (ALT) and tumour necrosis factor-alpha (TNF-alpha). Co-administration of celecoxib further increased the steatosis, relative liver weights and increased plasma ALT and TNF-alpha levels above those in ethanol-treated rats. Also, celecoxib counteracted the ethanol-induced increase in hepatic prostaglandin E(2) receptor EP4 mRNA expression. In contrast, celecoxib alone increased plasma ALT and TNF-alpha levels.

CONCLUSIONS

These results suggest that prolonged low-dose celecoxib treatment with ethanol enhances alcohol-induced steatosis and liver inflammatory reactions above that from ethanol or celecoxib alone. It is suggested that reduction in PGE(2) by treatment with celecoxib removes the endogenous protective effect of this prostaglandin.

Complement C3 contributes to ethanol-induced liver steatosis in mice

BACKGROUND

It is becoming increasingly clear that liver steatosis, a typical early consequence of alcohol exposure, sensitizes the liver to more severe inflammatory and fibrotic changes. On the other hand, activation of the key complement component C3, a central player in causing inflammation and tissue damage, is also known to be involved in the regulation of lipid metabolism. This prompted us to study the development of alcoholic liver steatosis in mice lacking C3 (C3-/-).

RESULTS

Both C3-/- and normal C3+/+ mice were fed a steatosis-promoting high-fat diet with or without ethanol for 6 weeks. The diet without ethanol caused moderate liver steatosis in C3-/- but not in C3+/+ mice. As expected, ethanol-containing diet caused marked macrovesicular steatosis and increased the liver triglyceride content in C3+/+ mice. In contrast, ethanol diet tended to reduce steatosis and had no further effect on liver triglycerides in C3-/- mice. Furthermore, while in normal mice ethanol significantly increased the liver/body weight ratio, liver malondialdehyde level and serum alanine aminotransferase (ALT) activity, these effects were absent or small in C3-/- mice. A separate experiment with mice on chow diet confirmed the aberrant steatotic effect of ethanol in C3-/-mice: 4 hours after acute dosing of ethanol the liver triglyceride level had increased by 138% in C3+/+ mice (P<0.001), but only by 64% in C3-/- mice (n.s.).

CONCLUSION

In C3-/- mice alcohol-induced liver steatosis is absent or strongly reduced after chronic or acute alcohol exposure. This suggests that the complement system and its component C3 contribute to the development of alcohol-induced fatty liver and its consequences.

Chronic systemic endotoxin exposure: an animal model in experimental hepatic encephalopathy

Plasma levels of gut-derived endotoxins (lipopolysaccharides, LPS) are often elevated in cirrhotics and are thought to contribute to hepatic encephalopathy. Circulating LPS activates macrophages to produce tumor necrosis factor alpha (TNF-alpha) and other potentially cytotoxic proinflammatory mediators. A pathogenic role for endotoxins is supported by studies showing that treatment with Lacto-bacillusor antibiotics, both of which reduce LPS-producing intestinal Gram-negative bacteria, alleviates experimental liver damage. To mimic the "leaky gut" syndrome with endotoxin translocation into the circulation in cirrhotics, a new animal model was developed. Rats were chronically exposed to ethanol and for the four last weeks also infused with endotoxin into the jugular vein from subcutaneously implanted osmotic minipumps. Animals receiving endotoxin had elevated hepatic expression of both pro- and anti-inflammatory cytokines, but compared to ethanol treatment alone hepatic steatosis and inflammatory changes were only marginally increased. This demonstrates marked endotoxin tolerance, probably as a consequence of a counteracting anti-inflammatory cytokine response. The role of gut-derived endotoxin in hepatic encephalopathy has recently received considerable attention. To further delineate the role and actions of endotoxin and its extrahepatic effects, studies applying both acute challenge and chronic infusion seem warranted. The chronic endotoxin model, mimicking the "leaky gut," may best be combined with more robust ways to impair liver function, such as carbon tetrachloride treatment, bile duct ligation, or galactosamine administration.

Protective function of complement against alcohol-induced rat liver damage

The complement system can promote tissue damage or play a homeostatic role in the clearance and disposal of damaged tissue. We assessed the role of the terminal complement pathway in alcohol-induced liver damage in complement C6 (C6-/-) genetically deficient rats. C6-/- and corresponding C6+/+ rats were continuously exposed to ethanol by feeding ethanol-supplemented liquid diet for six weeks. Liver samples were analyzed for histopathology and complement component deposition by immunofluorescence microscopy. Prostaglandin E receptors and cytokine mRNA levels were analyzed by RT-PCR and plasma cytokines by ELISA. Deposition of complement components C1, C3, C8 and C9 was observed in C6+/+ rats, but not in C6-/- animals. The histopathological changes, the liver weight increase and the elevation of the plasma pro-/anti-inflammatory TNF-alpha/IL-10 ratio were, on the other hand, more marked in C6-/- rats. Furthermore, ethanol enhanced the hepatic mRNA expression of the prostaglandin E receptors EP2R and EP4R exclusively in the C6-/- rats. Our results indicate that a deficient terminal complement pathway predisposes to tissue injury and promotes a pro-inflammatory cytokine response. This suggests that an intact complement system has a protective function in the development of alcoholic liver damage.

Oral chronic ethanol administration to rodents by agar gel diet

BACKGROUND

Chronic ethanol administration to rodents requires specially designed equipment and is labor intensive. Here we report a new procedure.

METHOD

A commercial liquid diet preparation was made into a gel by addition of 0.5% agar. The gel, containing 5.3% ethanol, was offered in Falcon tubes equipped with a feeding opening.

RESULTS

The gel consumption by C57/Bl mice resulted in high blood ethanol levels (average 43 mM). After 6 weeks, marked liver steatosis and significantly increased serum alanine aminotransferase levels had developed.

CONCLUSIONS

Administration of ethanol in a nutritionally adequate gel provides a simple method for studies on chronic ethanol effects in rodents.

Lack of sexual dimorphism in alcohol-induced liver damage (ALD) in rats treated chronically with ethanol-containing low carbohydrate diets: The role of ethanol metabolism and endotoxin

Evidence has been presented suggesting that females are significantly more susceptible to alcohol-induced liver damage (ALD) than males. In the current study, we examined sexual dimorphism in hepatic pathology, metabolism and cytokine profiles using two different rat models of ALD. Male and female Sprague-Dawley or Wistar rats were fed ethanol-containing low-carbohydrate liquid diets using oral or intragastric methods for 42 or 60 days. In both models, ethanol treatment produced similar significant liver hyperplasia accompanied by increases in plasma ALT, steatosis, inflammation and necrosis (p < 0.05). Greater pathology scores were observed in the intragastrically infused rats. Males did not differ significantly from females in serum ALT values or pathology despite greater elevations in TNFalpha and IL-1beta mRNAs in ethanol-treated female rat livers (p < 0.05). Furthermore, there was no sexual dimorphism in blood ethanol concentrations or CYP2E1-induction even though sexually dimorphic alterations in other hepatic cytochrome P450 enzymes were observed. These data do not support previous observations that female rats have a greater susceptibility to ethanol-induced hepatotoxicity than males.

Acute but not chronic ethanol exposure impairs retinol oxidation in the small and large intestine of the rat

BACKGROUND AND AIM

Ethanol has been shown to inhibit retinol oxidation at the level of alcohol dehydrogenase in liver and colon but not previously in the small intestine. In the present study we investigated how chronic alcohol feeding and acute ethanol exposure affects retinol dehydrogenase activity in the colon and small intestine of the rat.

METHODS

Rats were fed ethanol in a liquid diet for six weeks. Control rats received a similar diet but with ethanol isocalorically replaced by carbohydrates. Retinol dehydrogenase was analyzed from cell cytosol samples from the small and the large intestine with respect to maximum activity (V(max)), Michaelis-Menten constant (K(m)), and inhibition by ethanol (2-43 mM) in vitro.

RESULTS

Both the V(max) and the catalytic efficiency (V(max)/K(m)) were found to be significantly higher in the colon than in the small intestine (2.9-3.6 and 54-70 times higher, respectively). While chronic alcohol feeding did not affect these parameters, acute ethanol exposure reduced V(max) and V(max)/K(m) dose-dependently (p < 0.001) in both intestinal segments.

CONCLUSION

The present data demonstrate that ethanol markedly inhibits in vitro cytosolic retinol oxidation in the small intestinal mucosa, which is considerably lower than that found in the colon. Considering the vital importance of retinol on intestinal integrity, our finding suggests that this might contribute to the ethanol-induced increase in intestinal permeability.

Hepatic expression of multiple acute phase proteins and down-regulation of nuclear receptors after acute endotoxin exposure

Acute systemic lipopolysaccharide (endotoxin, LPS) exposure, which can lead to septic shock, enhances the hepatic expression of inflammatory and acute-phase proteins (APPs). To better understand how LPS aggravates damage, changes in hepatic gene expression after a single LPS dose was screened by using microarrays for 1176 rat genes. We detected more than 20 new potential LPS-induced APPs. Following acute LPS challenge, significant up-regulation of the steady-state mRNA levels of several important early transcription factors, such as c-jun and STAT3, and cytokine-associated genes, was observed. In contrast, RT-PCR analysis revealed marked down-regulation of the nuclear receptors RXRalpha, PXR, FXR, LXR, PPARalpha and CAR. Also genes encoding lipolytic, antioxidant as well as drug- and alcohol-metabolizing enzymes were down-regulated. These data suggest that acute LPS treatment induces important early transcription factors and co-ordinately down-regulates nuclear receptors, and that this results in altered expression of a large number of downstream genes.

Phagocytosis and LPS-stimulated production of cytokines and prostaglandin E2 is different in Kupffer cells isolated from the periportal or perivenous liver region

BACKGROUND

Kupffer cells can release pro-inflammatory mediators and contribute to damage, which often appears in a zonated fashion.

METHODS

To assess position-associated functional differences, functions of intact Kupffer cells isolated from either the periportal or perivenous acinar region of rat liver were compared.

RESULTS

Kupffer cells from the periportal region phagocytosed 2-3 times more FITC-labelled zymosan particles than corresponding perivenous cells, as determined by confocal microscopy and fluorescence assay. Periportal cells also produced more TNF-alpha and IL-1beta, but less NO and PGE2, compared to perivenous cells and the stimulation by addition of lipopolysaccharides (LPS) was moderate. In contrast, after overnight culture LPS dramatically increased TNF-alpha release and significantly more so in perivenous Kupffer cells (26-fold) than in periportal cells (11-fold).

CONCLUSION

Our study suggests that periportal Kupffer cells are responsible for a major part of phagocytosis by the liver. The stronger LPS response of recovered perivenous Kupffer cells suggests a dominant role of these cells in pro-inflammatory events that ultimately may contribute to development of damage in this region.

Alcohol affects the skeletal muscle proteins, titin and nebulin in male and female rats

Alcoholic myopathy is characterized by decreased protein synthesis and contents resulting in atrophy of muscle fibers. We investigated the effect of alcohol on the cytoskeletal muscle proteins, nebulin and titin. Because women are more susceptible than men to the toxic effects of alcohol, male and female rats were included. Four groups were investigated: alcoholic males, pair-fed males, alcoholic females, pair-fed females. Alcohol consumption per unit body weight was 12.9 g/kg.d, with no difference between males and females. After 10 wk, male and female rats fed alcohol had lower gastrocnemius and plantaris protein and RNA contents (P < 0.001), with no effect on soleus, indicating myopathy of type II fibers. The gastrocnemius was fractionated to measure myofibrillary protein contents. Low percentage SDS-gel electrophoresis was performed to determine myosin heavy chain (MHC), nebulin and titin contents. Alcohol reduced gastrocnemius myofibrillary protein and MHC contents, and the plantaris RNA/protein ratio (P < 0.01). The titin/MHC and nebulin/MHC ratios were unaffected, suggesting a concomitant reduction in titin and nebulin. The decreases in titin and nebulin contents may affect muscle function. An interaction between gender and alcohol was noted for the plantaris RNA/protein ratio (P < 0.025), suggesting a reduced capacity for muscle protein synthesis in females.

Activation of complement components and reduced regulator expression in alcohol-induced liver injury in the rat

The purpose of this study was to evaluate the possible contribution of complement-mediated inflammation to the development of alcoholic liver disease. Male Wistar rats were fed ethanol by liquid diet in a model that results in continuous ethanol intoxication and induces early signs of alcoholic liver injury. After a six-week study period liver samples were analyzed for the deposition of complement components (C1, C3, and C8) and expression of cell membrane-bound regulators (Crry and CD59). Activation of the homologous complement system in vitro was tested by treating frozen liver sections with normal rat serum (NRS). Immunohistochemical analysis showed deposits of C8 in the liver sections of ethanol-treated rats. When frozen liver sections from these rats were treated with NRS, periportal deposition of both C3 and C8, but only slight C1 deposition, was observed. Immunohistochemical and Western blot analysis both revealed a reduced expression of the complement regulators Crry and CD59. These results suggest an induction of complement-activating capacity in the liver after chronic ethanol treatment. Lack of C1 deposition in the lesions suggests that complement activation occurs primarily via the alternative pathway. The reduced expression of the critical complement regulatory proteins Crry and CD59 may sensitize the liver to complement-mediated damage.

Acinar distribution of rat liver arylamine N-acetyltransferase: effect of chronic ethanol and endotoxin exposure

The expression of most drug-metabolising enzymes is highest in the perivenous region of the liver, where drug-induced damage is commonly initiated. Arylamine N-acetyltransferase plays an important role in activation or detoxification of many drugs, carcinogens, pesticides and other xenobiotics, but its acinar distribution is unknown. In this study we have analysed the activity of N-acetyltransferase in cell lysates obtained from the periportal or perivenous region by digitonin treatment during in situ liver perfusion. Livers from control animals were compared with rats chronically exposed either to ethanol by liquid diet or to lipopolysaccharide (endotoxin) by intravenous administration. The activity of N-acetyltransferase in the perivenous region was slightly (+ 20%) higher than in the periportal region. Although chronic ethanol exposure did not change total activity, the acinar distribution was reversed to a higher activity in the periportal region. In contrast, chronic endotoxin significantly increased N-acetyltransferase activity, but did not affect the acinar distribution. This increase was counteracted by simultaneous ethanol treatment. N-Acetyltransferase activity in perivenous lysates was significantly reduced after the co-administration of ethanol and endotoxin compared to that after endotoxin alone. Thus, the perivenous zonation of liver N-acetyltransferase is moderate compared to other transferases or P450 isozymes, and the cellular capacity for N-acetylation in the perivenous region, where xenobiotic activation to reactive intermediates dominates, may be insufficient.

Models of alcoholic liver disease in rodents: a critical evaluation

This article represents the proceedings of a workshop at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were J. Christian Bode and Hiroshi Fukui. The presentations were (1) Essentials and the course of the pathological spectrum of alcoholic liver disease in humans, by P. de la M. Hall; (2) Lieber-DeCarli liquid diet for alcohol-induced liver injury in rats, by C. S. Lieber and L. M. DeCarli; (3) Tsukamoto-French model of alcoholic liver injury, by S. W. French; (4) Animal models to study endotoxin-ethanol interactions, by K. O. Lindros and H. Järveläinen; and (5) Jejunoileal bypass operation in rats-A model for alcohol-induced liver injury? by Christiane Bode, Alexandr Parlesak, and J. Christian Bode.

The antiestrogen toremifene protects against alcoholic liver injury in female rats

BACKGROUND/AIMS

Females are generally considered to be more susceptible to alcohol-induced liver injury than males. To elucidate whether gonadal hormones are involved, female rats were chronically treated with ethanol and with an antiestrogen.

METHODS

Ethanol was administered in a low-carbohydrate liquid diet. Estrogen action was blocked by daily intubation of toremifene, a non-hepatotoxic second generation estrogen receptor antagonist.

RESULTS

The female rats consuming intoxicating amounts of ethanol diet for 6 weeks developed massive microvesicular/macrovesicular steatosis, frequent inflammatory foci and spotty necrosis. Serum alanine aminotransferase increased 7-fold. Toremifene treatment did not affect steatosis, but significantly reduced inflammation and necrosis. Ethanol increased the expression of CD14 and tumor necrosis factor- (TNF) alpha mRNA and also the production of TNF-alpha by isolated Kupffer cells, but toremifene had no significant counteracting effect. However, toremifene significantly alleviated both ethanol induction of the pro-oxidant enzyme CYP2E1 and ethanol reduction of the oxidant-protective enzyme Se-glutathione peroxidase.

CONCLUSIONS

The partial protection by toremifene against ethanol-induced liver lesions suggests a pathogenic contribution of estrogens, possibly associated with an oxygen radical mediated mechanism.

Promoter polymorphism of the CD14 endotoxin receptor gene as a risk factor for alcoholic liver disease

Twin concordance studies indicate that genetic factors influence the individual susceptibility for alcoholic liver disease (ALD). Both clinical and experimental data suggest that Kupffer cell activation by gut-derived endotoxins and other bacterial products is an important pathogenic factor. Activated Kupffer cells release proinflammatory cytokines, a process that is regulated by the CD14 endotoxin receptor (CD14). Recently, a C-->T (-159) polymorphism in the promoter region of the CD14 gene was detected and found to confer increased CD14 expression. In the present study, the association of CD14 promoter polymorphism with different forms of ALD was examined in 3 separate autopsy series. Among 442 men with valid alcohol-consumption data, 381 men had been moderate or heavy alcohol consumers. The allele frequency of the CD14 promoter genotype, determined by a modified cycle minisequencing technique, was 0.34 (CC), 0.51 (CT), and 0.16 (TT). The T allele was found to be associated with advanced ALD, i.e., with alcoholic hepatitis (odds ratio [OR]: 2.48; P = .018), and especially with cirrhosis (OR: 3.45; P = .004), but not with fatty liver, periportal fibrosis, or bridging fibrosis. The overall age-adjusted risk for cirrhosis was 3.08 (P = .01) for the carriers of the CT genotype, and 4.17 (P = .005) for the homozygous TT genotype. These results suggest that in the relatively isolated Finnish population, the T allele confers increased risk of alcoholic liver damage. In particular, TT homozygotes are at a high risk to develop cirrhosis.

Models of alcoholic liver disease in rodents: a critical evaluation

This article represents the proceedings of a workshop at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were J. Christian Bode and Hiroshi Fukui. The presentations were (1) Essentials and the course of the pathological spectrum of alcoholic liver disease in humans, by P. de la M. Hall; (2) Lieber-DeCarli liquid diet for alcohol-induced liver injury in rats, by C. S. Lieber and L. M. DeCarli; (3) Tsukamoto-French model of alcoholic liver injury, by S. W. French; (4) Animal models to study endotoxin-ethanol interactions, by K. O. Lindros and H. Järveläinen; and (5) Jejunoileal bypass operation in rats-A model for alcohol-induced liver injury? by Christiane Bode, Alexandr Parlesak, and J. Christian Bode.

Sex difference in alcohol-related organ injury

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Nobuhiro Sato and Kai O. Lindros. The presentations were (1) Sex differences in ethanol pharmacokinetics, by E. Baraona; (2) Estrogen regulates the sensitivity to endotoxin in hepatic Kupffer cells, by K. Ikejima; (3) Sex difference in alcohol-related organ injury, by E. Mezey; (4) Aggravated ethanol-induced liver injury in female rats: Protection by the antiestrogen toremifene, by Harri A. Järveläinen; and (5) Alcohol metabolism in Asian subjects: Sex differences and flushing response, by V. A. Ramchandani.

Triiodothyronine downregulates the periportal expression of alpha class glutathione S-transferase in rat liver

Most drug-metabolizing phase I and phase II enzymes, including the glutathione S-transferases (GST), exhibit a zonated expression in the liver, with lower expression in the upstream, periportal region. To elucidate the involvement of pituitary-dependent hormones in this zonation, the effect of hypophysectomy and 3,3',5-triiodo-L-thyronine (T3) on the distribution of GST was studied in rats. Hypophysectomy increased total GST activity both in the periportal and perivenous liver region. Subsequent T3 treatment counteracted this effect in the perivenous zone. However, analysis for either mu class M1/M2-specific (1,2-dichloro-4-nitrobenzene) or alpha class A1/A2-specific (7-chloro-4-nitrobenzo-2-oxa-1,3-diazole) GST activity revealed that T3 treatment did not significantly affect the perivenous activity of these GST classes. In contrast, T3 was found to significantly counteract the increase of alpha class GST activity caused by hypophysectomy in the periportal zone. To establish whether this effect was T3-specific, hepatocytes were isolated from either the periportal and perivenous zone by digitonin/collagenase perfusion and cultured either as pyruvate-supplemented monolayer or as co-culture with rat liver epithelial cells. Only in the latter it was found that T3 suppressed the A1/A2-specific GST activity and alpha class proteins predominantly in periportal cells. The data demonstrate that T3 is an important factor responsible for the low expression of alpha GST in the periportal region. T3 may be involved in the periportal downregulation of other phase I and II enzymes as well.

Effect of long-term ethanol exposure on the acinar distribution of hepatic glutathione S-transferase

The ability of ethanol to affect the regional distribution of individual glutathione S-transferase (GST) isoenzymes in rat liver was investigated by analyzing the expression levels in cell lysates obtained from the periportal or perivenous liver region after in situ digitonin perfusion. In control rats, a significant perivenous dominance of GST proteins and activities measured by the substrates 1-chloro-2,4-dinitrobenzene (broad spectrum), 1, 2-dichloro-4-nitrobenzene (M1/M2-specific), and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (A1/A2-specific) was found. In pair-fed rats exposed to ethanol (36% of total calories) for 2 weeks, all GST activities measured were significantly increased in both acinar zones. However, the relative increase was greater in the perivenous region. The induction of the A1/A2-specific activity was the most pronounced. HPLC analysis revealed for both regions that this increase was largely confined to the A2 subunit, with only minor effects observed on the A1 subunit. At the mRNA level, the constitutive perivenous dominance of both GST A1 and GST A2 expression became more pronounced after ethanol administration. The results demonstrate that long-term ethanol exposure induces individual GST isoenzymes differently and might have a profound effect on xenobiotic-induced regional liver damage.

Effect of ethanol on the expression of hepatic glutathione S-transferase: an in vivo/in vitro study

Ethanol, a human toxicant and a solvent in pharmacological research, is known to interfere with biotransformation of xenobiotics. We compared the in vivo and in vitro long-term effects of ethanol exposure on the expression of glutathione S-transferases (GST, EC 2. 5.1.18) in rat liver. Long-term in vivo ethanol treatment to achieve blood ethanol levels ranging between 10-50 mM was by liquid diet feeding. For in vitro experiments, rat hepatocytes co-cultured with rat liver epithelial cells were exposed to 17 and 68 mM ethanol for up to 10 days. Two weeks of liquid diet ethanol treatment increased total GST activity. Both Mu and Alpha classes and in particular the A1 and A2 subunits and the amount of their corresponding mRNAs were increased. Total GST activity was also increased in co-cultures after exposure to 68 mM ethanol for 10 days. However, the Mu class subunits M1 and M2 and the corresponding mRNAs were increased, rather than the Alpha class subunits. Thus, long-term exposure to ethanol induces hepatic GST both in vivo and in vitro, but different isoenzymes are affected. Consequently, extrapolation of in vitro data on GST expression and regulation to the in vivo situation must be judicious. During xenobiotic metabolism in cell culture, a shift in relative expression and induction of different GST forms may occur, resulting in either an under- or overestimation of effects.

Kupffer cell inactivation alleviates ethanol-induced steatosis and CYP2E1 induction but not inflammatory responses in rat liver

BACKGROUND/AIMS

Gadolinium chloride inactivates Kupffer cells and alleviates alcohol-induced liver lesions. We investigated the mechanism of gadolinium chloride protection after oral ethanol feeding.

METHODS

Rats were maintained ethanol-intoxicated for 6 weeks by feeding ethanol in a low-carbohydrate/high-fat liquid diet. Macrophages were inactivated by intravenous administrations of gadolinium chloride. At termination, liver samples and cell lysates obtained from the periportal and perivenous region were analyzed for histopathology, mRNA expression of endotoxin-associated parameters and cytokines and for enzymes involved in oxidative stress.

RESULTS

Ethanol treatment alone caused marked microvesicular/macrovacuolar steatosis and focal inflammation. Gadolinium significantly alleviated pathology, by reducing steatosis but not inflammation. Gadolinium treatment eliminated ED2 immunopositive Kupffer cells, which were larger and more frequent periportally. Ethanol significantly increased the mRNA expression of the endotoxin (LPS) receptor CD14 and the LPS binding protein LBP, but not that of the pro-inflammatory cytokines TNF-alpha and IL-1beta. The mRNA of CD14 was found to be expressed preferentially in the perivenous region, but gadolinium treatment had no significant effect on the expression or the distribution. However, gadolinium significantly moderated the ethanol induction of CYP2E1 and this effect correlated to the degree of steatosis. Ethanol increased glutathione transferase and reduced glutathione peroxidase activity, but these changes persisted after gadolinium treatment.

CONCLUSIONS

Our results suggest that gadolinium chloride reduces symptoms of ALD mainly by counteracting steatosis, and that CD14-positive Kupffer cell populations are not involved in gadolinium protection. The strong correlation between pathology and CYP2E1 induction might suggest a steatopathogenic role for this enzyme.

Growth hormone-regulated periportal expression of CYP2C7 in rat liver

Most drug- and steroid-metabolizing cytochrome P450 (CYP) enzymes are expressed in the mammalian liver in a characteristic zonated pattern, with high expression in the downstream perivenous (centrilobular) region. Here, we report that CYP2C7, a member of the rat CYP2 family, is expressed preferentially in the opposite, periportal region. CYP2C7 mRNA, as detected by reverse transcription-polymerase chain reaction, was detected almost exclusively in cell lysates obtained from the periportal region, indicating a very steep acinar gradient. The amount of immunoreactive CYP2C7 protein in periportal cell lysates was also higher than in samples from the perivenous region. This gradient was reversed by hypophysectomy, which markedly and selectively reduced the periportal CYP2C7 protein content. Subsequent growth hormone infusion by osmotic minipumps restored the zonation by selectively increasing the amount of periportal CYP2C7 protein. Although hypophysectomy suppressed CYP2C7 mRNA and growth hormone counteracted it, regulation at this level did not appear to occur in a zone-specific fashion. This indicates that growth hormone-mediated zonal regulation of CYP2C7 protein has additional translational or posttranslational components. Ethanol treatment, which has been shown to affect growth hormone levels, significantly induced CYP2C7 mRNA, but not zone specifically. Our results demonstrate that growth hormone up-regulates the CYP2C7 gene by enhancing the expression of the protein specifically in the periportal liver region. Growth hormone may up-regulate other periportally expressed liver genes in a similar fashion.

Dose-dependent localization of TCDD in isolated centrilobular and periportal hepatocytes

Dose-response relationships for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suggest a differential sensitivity of liver cell types to the induction of cytochrome P450 gene expression, and that the induction of hepatic protein CYP1A2 causes sequestration of TCDD. In addition, immunolocalization of hepatic CYP1A1/1B1/1A2 proteins is not uniform after exposure to TCDD. The mechanism for the regio-specific induction of hepatic P450s by TCDD is unknown, but may involve the differential distribution of participants in the AhR-mediated pathway and/or regional P450 isozymes, as well as, non-uniform distribution/sequestration of TCDD. Therefore, this study examined the effects of TCDD in unfractionated, centrilobular and periportal hepatocytes isolated from female Sprague-Dawley rats acutely exposed (3 days) to a single oral dose of 0.01-10.0 microg [3H]TCDD/kg. A dose-dependent increase in concentration of TCDD was accompanied by a dose-dependent increase in CYP1A1, CYP1A2, and CYP1B1 mRNA expression and associated enzymes in all liver-cell populations. Centrilobular hepatocytes showed a 2.7- to 4.5-fold higher concentration of TCDD as compared to the periportal hepatocytes at doses up to 0.3 microg TCDD/kg. Centrilobular hepatocytes also exhibited an elevated MROD activity as compared to the periportal hepatocytes at doses up to 0.3 microg TCDD/kg. Furthermore, centrilobular hepatocytes showed an elevated concentration of induced CYP1A2 and CYP1B1 mRNA as compared to periportal hepatocytes within the 0.01- and 0.3-microg TCDD/kg-treatment groups. This is the first study to demonstrate that a dose-dependent difference in distribution of TCDD exists between centrilobular and periportal cells that might be related to regional differences in P450 induction.

Acetaldehyde prevents nuclear factor-kappa B activation and hepatic inflammation in ethanol-fed rats

Acetaldehyde has been proposed as one of the mediators of liver injury in alcoholic liver disease. We investigated whether increased acetaldehyde levels affected the development of alcoholic liver injury. Male Wistar rats were fed a liquid diet containing fish oil and ethanol by intragastric infusion. Sustained elevations of acetaldehyde were achieved by daily treatment with two inhibitors of aldehyde dehydrogenase (ALDH): disulfiram and benzcoprine. Pathologic changes, plasma and liver acetaldehyde, nuclear factor-kappa B (NF-kappaB) and I kappa B alpha (I kappaB alpha) protein, tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase 2 (COX-2) mRNA were evaluated. Treatment with the ALDH inhibitors led to increased acetaldehyde in liver and plasma but prevented necrosis and inflammation. Steatosis was not affected. Both inhibitors decreased activation of NF-kappaB and down-regulated TNF-alpha and COX-2 expression. Decreased activation of NF-kappaB was accompanied by I kappaB alpha preservation. Acetaldehyde probably inhibits NF-kappaB activation through I kappaB alpha preservation. Down-regulation of TNF-alpha and COX-2 occur secondary to inhibition of NF-kappaB and account for the absence of necrosis and inflammation in the ALDH inhibitor-treated groups.

Short-term ethanol exposure increases the expression of Kupffer cell CD14 receptor and lipopolysaccharide binding protein in rat liver

Gut-derived endotoxins (lipopolysaccharide, LPS) complexed to LPS-binding protein (LBP) activate liver Kupffer cells via their CD14 receptor. Pro-inflammatory cytokines are released and this is postulated to promote liver injury. We previously demonstrated enhanced expression of CD14 endotoxin receptor after 2 weeks of alcohol administration. A similar result, based on 6 weeks of ethanol treatment, was recently reported and suggested to correlate with alcohol-induced liver injury. To establish whether this occurs prior to or after the initiation of damage, we investigated the temporal effect of continuous ethanol exposure on the expression of CD14 and the associated LBP. In addition, we studied the effect of treatment with gadolinium chloride (GdCl3) that inactivates Kupffer cells and alleviates alcohol-induced liver damage. The amount of CD14 and LBP mRNA, as determined by reverse transcriptase-polymerase chain reaction (RT-PCR), was unchanged 4-8 h after intragastric ethanol administration. However, after 24-48 h of repeated ethanol administration, CD14 and LBP mRNA both increased significantly and reached a level similar to that observed after 6 weeks of ethanol exposure by liquid diet. Immunostaining experiments with ED2 antibody demonstrated that GdCl3 efficiently inactivated Kupffer cells. However, there was no concomitant reduction in the expression of CD14 mRNA, suggesting that compensatory infiltration by ED2-negative, but CD14-positive, macrophages had occurred. Our results demonstrate that soon after the initiation of ethanol exposure, i.e. within 24-48 h, the hepatic expression of both the CD14 receptor and LBP is increased. This suggests that these increases could contribute to the initiation of alcoholic damage rather than being a consequence of the injury.

Effect of chronic coadministration of endotoxin and ethanol on rat liver pathology and proinflammatory and anti-inflammatory cytokines

To better understand how gut-derived endotoxins influence alcohol-induced liver injury and the expression of inflammatory cytokines a new animal model was developed. After 2 weeks on a modified ethanol-containing liquid diet, some rats also were infused with endotoxin via osmotic minipumps for 4 additional weeks. Ethanol diet alone increased plasma endotoxin threefold to 9.3 pg/mL. Endotoxin infusion increased the levels to 388 and 513 pg/mL in controls and ethanol-fed animals, respectively. Panlobular macrovesicular and microvesicular steatosis and inflammatory foci were observed in livers from both ethanol- and ethanol-endotoxin-treated animals, but there was no significant potentiation by endotoxin. Only minor changes, mainly polymorphonuclear infiltration, were seen in animals treated with endotoxin alone although the messenger RNA (mRNA) expression of both proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta) and anti-inflammatory cytokines IL-4 and IL-10 were markedly increased, as shown by competitive polymerase chain reaction (PCR) analysis using cyclophilin as standard. The effect of endotoxin infusion on cytokine mRNA expression in ethanol-fed animals was not significantly different. Expression of transforming growth factor beta1 (TGF-beta1) mRNA was increased twofold by ethanol, eightfold by endotoxin, but only threefold by ethanol-endotoxin treatment. The mRNA expression of lipopolysaccharide binding protein (LBP) and CD14 endotoxin receptor was not significantly increased by chronic endotoxin treatment, contrasting with the marked elevation observed after acute endotoxin challenge. These results suggest that the tolerance observed despite sustained hepatic expression of proinflammatory cytokines is counteracted by the anti-inflammatory cytokines and by down-regulation of CD14 and LBP. Furthermore, a similar adaptation may occur in alcoholics with continuous endotoxemia.

No significant expression of CYP2E1 in rat liver stellate cells

The putative role of the ethanol-inducible cytochrome P450(CYP)2E1 in stimulating collagen synthesis by rat liver stellate cells was studied. Analysis of carefully isolated stellate cells revealed that their content of immunoreactive CYP2E1 protein and of CYP2E1 mRNA, as determined by reverse transcription, polymerase chain reaction (RT-PCR), was very low, i.e. only 0-4% of that in hepatocytes. We conclude that it is improbable that such low expression of CYP2E1 in stellate cells would have functional importance.

Induction of UDP-glycosyltransferase family 1 genes in rat liver: different patterns of mRNA expression with two inducers, 3-methylcholanthrene and beta-naphthoflavone

Uridine diphosphate (UDP)-glucuronosyltransferases (UGTs), presently called UDP-glycosyltransferases, catalyse the detoxification of many toxic and carcinogenic compounds. Glucuronidation is also a major metabolic pathway for numerous drugs. The UGT1A6 gene (formerly known as UGT1*06 and UGT1A1) has been suggested to belong to the aryl hydrocarbon (Ah) gene battery, which consists of several genes encoding for drug-metabolising enzymes regulated by dioxin and other ligands of the Ah receptor. In this study, we analysed the localisation of UGT1A6 expression in rat liver by in situ hybridisation to mRNA. Two different RNA probes were used, one which was specific to UGT1A6 and the other against the C terminal sequence shared by all UGT1 genes. In this study, no UGT1A6 mRNA was detected in the control animals. However, other gene(s) of the UGT1 family were expressed in the perivenous region surrounding the central veins as detected by hybridisation with the probe against the common region of the UGT1 genes. Treatment with the lower dose (5 mg/kg) of 3-methylcholanthrene (3MC) induced expression of UGT1A6 perivenously. Treatment with the higher dose (25 mg/kg) of 3-Methylcholanthrene resulted in a more panacinar expression pattern. In contrast to the perivenous induction observed with 3-methylcholanthrene, treatment with 15 mg/kg of beta-naphthoflavone (BNF) resulted in strong induction in the periportal region. The results reveal an inducer-specific pattern of UGT1A6 expression similar to that demonstrated earlier for other Ah battery genes, namely CYP1A1, CYP1A2, GSTYalpha and ALDH3. The finding further supports the notion that common factors regulate the regional hepatic expression of Ah battery genes.

High blood endotoxin does not affect ethanol elimination in rats

Gut-derived endotoxins have been proposed as mediators of the enhancement of ethanol elimination after chronic alcohol administration. We investigated whether chronically elevated blood-endotoxin levels affect the rate of ethanol elimination in a study where endotoxin was administered chronically from an osmotic minipump to rats fed ethanol in a liquid diet. As expected, an acute dose of ethanol (1.2 g/kg body wt, i.p.) was eliminated significantly faster (329+/-11 mg/kg/h) by chronically ethanol-fed animals than by pair-fed controls (285+/-9 mg/kg/h). However, although endotoxin administration significantly elevated blood-endotoxin levels, the rate of ethanol elimination in endotoxin-treated groups was almost identical when compared either to controls (289 vs 285) or to ethanol-fed rats (328 vs 329). We conclude that chronic endotoxin exposure at levels that only resulted in mild hepatic changes, had no effect on the rate of ethanol elimination and that it is unlikely that endotoxins are involved in the induction of the ethanol elimination rate following chronic alcohol administration.

A new oral low-carbohydrate alcohol liquid diet producing liver lesions: a preliminary account

Male Wistar rats were administered a modified, but nutritionally adequate, ethanol liquid diet with a low content of carbohydrate (5.5% of energy). The high daily intake of ethanol (mean 12.9 g/kg body wt) resulted in consistently sustained elevation of diurnal blood ethanol levels (mean 40.3 +/- 14.9mmol/l, corresponding to 180mg/dl). Marked micro- and macrovesicular panlobular steatosis, occasional inflammatory foci and a threefold elevation of serum alanine aminotransferase activity developed in 6 weeks. In livers from rats on regular 11% carbohydrate diet, lesions beyond periportally located steatosis were rare. These observations suggest that oral administration of a low-carbohydrate liquid ethanol diet may provide an affordable alternative to the technically demanding intragastric feeding model for experimental studies of alcoholic liver disease.

Zonated expression of cytokines in rat liver: effect of chronic ethanol and the cytochrome P450 2E1 inhibitor, chlormethiazole

The release of proinflammatory cytokines by endotoxins and during oxidative stress is considered to be an early key step in the pathogenesis of alcoholic liver disease (ALD). Ethanol-inducible cytochrome P450 2E1 (CYP2E1) has potentially pro-oxidative and toxicological properties, and its expression is restricted to the perivenous region of liver. We investigated zonal differences of cytokine expression in rat liver and how these are affected by alcohol exposure and by chlormethiazole (CMZ), a transcriptional and posttranslational inhibitor of hepatic CYP2E1. Periportal and perivenous cell lysates were obtained by the digitonin pulse technique from livers of rats treated with ethanol and CMZ for 38 days. Cytokine expression on the mRNA and protein levels was quantified using competitive polymerase chain reaction (PCR) and Western blot, respectively. Chronic ethanol treatment significantly increased the expression of CYP2E1, microsomal p-nitrophenol hydroxylase activity (indicative for CYP2E1 enzyme activity), and the expression of transforming growth factor beta1 (TGF-beta1), tumor necrosis factor alpha (TNF-alpha), and interleukin (IL)-1beta (1.4- to 4.6-fold). In contrast, ethanol caused a decrease in IL-4 expression and had no influence on IL-6 expression. CMZ treatment caused a reduction in hepatic CYP2E1 expression and in the ethanol-induced cytokine expression by 40% to 60%. Expression of IL-6, IL-2, and IL-4 mRNA occurred preferentially in the periportal region, whereas ethanol caused a pronounced increase in the perivenous expression of TGF-beta1, which was inhibited by CMZ as monitored both on the mRNA and protein levels. These results show the zonated expression of several cytokines and the counteraction of CMZ on all effects of ethanol on cytokine expression. The data further strengthen a link between increased CYP2E1 expression and enhanced cytokine expression as important events in the development of ALD.

Aryl hydrocarbon receptor-associated genes in rat liver: regional coinduction of aldehyde dehydrogenase 3 and glutathione transferase Ya

The tumor-associated aldehyde dehydrogenase 3 (ALDH3) and the glutathione transferase (GST)Ya form are coded by members of the Ah (aryl hydrocarbon) battery group of genes activated in the liver by polycyclic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The physiological role of the Ah receptor (AHR), its gene-activating mechanism and its endogenous ligands are still poorly clarified. We had previously observed that 3-methylcholanthrene (3MC) and beta-naphthoflavone (betaNF) induced the AHR-associated CYP1A1/1A2 pair in different liver regions, an effect not explained by the acinar distribution of the AHR protein. Here, we investigated AHR-associated regional induction by comparing the expression patterns of ALDH3 and GSTYa. Analysis of samples from periportal and perivenous cell lysates from 3MC-treated animals revealed that ALDH3 mRNA, protein and benzaldehyde-NADP associated activity were all confined to the perivenous region. In contrast, such regio-specific induction was not seen after beta-NF induction. Immunohistochemically, a peculiar mono- or oligocellular induction pattern of ALDH3 was seen, consistently surrounding terminal hepatic veins after 3MC but mainly in the midzonal region after betaNF. A ligand-specific difference in regional induction of GSTYa1 mRNA was also observed: The constitutive perivenous dominance was preserved after 3MC while induction by betaNF was mainly periportal. A 3MC-betaNF difference was also seen by immunohistochemistry and at the GSTYa protein level, in contrast to that of the AHR-unassociated GSTYb protein. However, experiments with hepatocytes isolated from the periportal or perivenous region to replicate these inducer-specific induction responses in vitro were unsuccessful. These data demonstrate that the different acinar induction patterns by 3MC and betaNF previously observed for CYP1A1 and CYP1A2 are seen also for two other Ah battery genes, GSTYa1 and ALDH3, but in a modified, gene-specific form. We hypothesize that unknown protein(s) operating in vivo and modifying the Ah-mediated response at the common XRE element located upstream of these genes is affected zonespecifically by 3MC and betaNF.

Alcohol-induced expression of the CD14 endotoxin receptor protein in rat Kupffer cells

Gut-derived endotoxins (lipopolysaccharide, LPS) are believed to contribute to alcohol-induced liver disease (ALD) by stimulating Kupffer cells, the resident liver macrophages, to release proinflammatory cytokines. This activation is largely mediated by CD14, a high-affinity membrane-anchored receptor for LPS. We observed, by chemiluminescence-enhanced detection, an increase in immunoreactive CD14 protein in Kupffer cells isolated from rats treated with ethanol for 2 weeks. Immunocytofluorescence experiments confirmed that this increase was confined to the membranes of Kupffer cells from the alcohol-treated rats. The increase was regulated pretranslationally: a 3-fold elevation (p < 0.01) in the hepatic level of CD14 mRNA was observed. The marked increase in CD14 expression suggests a new mechanism by which alcohol increases the LPS-mediated cytokine signaling by the liver macrophages, thus promoting the interaction between alcohol and endotoxins in the development of liver damage.

The stimulation of the mitochondrial permeability transition by dihydrolipoate and alpha-lipoate

The effect of alpha-lipoate and dihydrolipoate on the mitochondrial permeability transition was investigated. Both substances promoted the permeability transition in isolated rat liver mitochondria and in permeabilized hepatocytes, dihydrolipoate most potently in spite of it being a dithiol. The stimulation was prevented by Cyclosporin A or hydroxybutyltoluene but not by ascorbate. It is suggested that the greater potency of dihydrolipoate could be due to formation of a radical.

Zonation of hepatic cytochrome P-450 expression and regulation

The CYP genes encode enzymes of the cytochrome P-450 superfamily. Cytochrome P-450 (CYP) enzymes are expressed mainly in the liver and are active in mono-oxygenation and hydroxylation of various xenobiotics, including drugs and alcohols, as well as that of endogenous compounds such as steroids, bile acids, prostaglandins, leukotrienes and biogenic amines. In the liver the CYP enzymes are constitutively expressed and commonly also induced by chemicals in a characteristic zonated pattern with high expression prevailing in the downstream perivenous region. In the present review we summarize recent studies, mainly based on rat liver, on the factors regulating this position-dependent expression and induction. Pituitary-dependent signals mediated by growth hormone and thyroid hormone seem to selectively down-regulate the upstream periportal expression of certain CYP forms. It is at present unknown to what extent other hormones that also affect total hepatic CYP activities, i.e. insulin, glucagon, glucocorticoids and gonadal hormones, act zone-specifically. The expression and induction of CYP enzymes in the perivenous region probably have important toxicological implications, since many CYP-activated chemicals cause cell injury primarily in this region of the liver.

Zonal distribution of transcripts of four hepatic transcription factors in the mature rat liver

Within the liver acinus the majority of genes are expressed in an ascending or descending gradient from the portal to the central vein. The regulatory factors involved in this spatial pattern of gene expression are still poorly understood. Many liver genes are regulated by liver-enriched transcription factors. Here we report on mRNA distribution of four transcription factors in cell lysates obtained from either the periportal or the perivenous region after zone-specific digitonin infusion and by in-situ hybridization. Northern blot analysis revealed that there were slightly more transcripts of C/EBP, HNF1 beta (n.s.) and HNF4 (p < 0.05), but fewer of HNF3 gamma (n.s.), in perivenous than in periportal lysates. A somewhat stronger staining in the perivenous region of HNF4 was also seen by in-situ hybridization. The moderate acinar zonation of the mRNAs of these transcription factors suggests that at best they could modulate but not govern the zonated expression of liver genes in the mature liver.

Zonation of cytochrome P450 expression, drug metabolism and toxicity in liver

1. In this brief review, current concepts on the zonated expression of liver genes involved in phase I and phase II drug metabolism will be presented. 2. It is now clear that the P450 isoforms involved in drug activation and steroid metabolism exhibit a particularly prominent zonation, with high expression and preferential induction in hepatocytes of the perivenous region. 3. In comparison, among the phase II enzymes, the perivenous dominance of glutathione transferases and UDP-glucuronyltransferases is less prominent, and glutathione peroxidase displays an opposite, periportally dominated pattern. 4. The factors regulating the zonated expression of these and other liver genes are poorly known. We have observed that pituitary-dependent hormones, particularly growth hormone, extinguish the periportal (upstream) expression of several CYP forms (CYP2B1/2 and CYP3A1/2). However, the zonation of other CYP forms (CYP2A, CYP2E1, CYP 2C11 and CYP 2C12) is less affected, suggesting that hormonal factors are important, but that the zonation of each P450 form is orchestrated by a different set of factors. 5. Because many hepatotoxins cause zone-specific damage, further unravelling the factors governing zonal expression of phase I and phase II enzymes will be necessary to clarify how drug-specific patterns of liver damage arise.

Selective centrilobular expression of the aryl hydrocarbon receptor in rat liver

The aryl hydrocarbon receptor (AHR) is a transcriptional activator of genes encoding a group of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1), glutathione S-transferase, tumor-associated aldehyde dehydrogenase and quinone reductase. Both the constitutive and inducible expression of these genes in the liver is zonated, i.e., dominant in hepatocytes of the centrilobular region, a poorly understood position-dependent phenomenon. By comparing cell lysates obtained from opposite acinar regions we observed that immunoreactive AHR protein was almost exclusively confined to centrilobular cells. The AHR mRNA, as analyzed from cell lysates by reverse transcriptase polymerase chain reaction, exhibited a similar, although somewhat less pronounced zonation. By contrast, only slight zonation of the AHR nuclear translocator mRNA was observed. Treatment of rats with omeprazole, an atypical nonligand activator of the AHR, caused a zone-specific induction of CYP1A1 in the centrilobular region similar to that seen after pretreatment with the AHR ligand 3-methylcholanthrene. Our results suggest that the zone-restricted expression of AHR protein will allow the constitutive and inducible expression of AHR-regulated genes in the centrilobular region, but will limit their expression in the periportal region.

Distribution of glutathione S-transferase isoforms in rat liver after induction by beta-naphthoflavone or 3-methylcholanthrene

Regional differences in vulnerability to xenobiotic liver damage may relate to the distribution of the detoxication capacity of the glutathione S-transferases (GST). HPLC analysis of cell lysates obtained by digitonin infusion from either the periportal or the perivenous region revealed that the content of all the GST subunits investigated (1, 2, 3, 4 and 8) was higher in the perivenous region. The strongest perivenous dominance was observed for subunit 1 (Ya) and the alpha class appeared to be more zonated that the mu class. A similar perivenous dominance was observed by analysis of GST activity with either 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloronitrobenzene (DCNB) or trans-4-phenyl-3-buten-2-one (PBO) as substrate. In contrast, with cumene hydroperoxide (CuOOH) or tert-butyl hydroperoxide (tBOOH) as substrate a reciprocal twofold periportal dominance was observed. Induction by pretreatment with beta-naphthoflavone reduced or abolished the perivenous dominance of the alpha-subunits 1, 2 and 8. In contrast, after pretreatment with 3-methylcholanthrene, only the acinar gradient of subunits 2 (Yc) was abolished, while the strong perivenous gradient subunit 1 (Ya) was maintained and that of subunit 8 (Yk) increased. CDNB based assays demonstrated that beta-naphtoflavone treatment reduced (from 2.1 to 1.4) while 3-methyl cholanthrene enhanced (to 2.6) the perivenous/periportal GST activity ratio. Assays based on CuOOH or tBOOH indicated that neither the Se-dependent nor the Se-independent glutathione peroxidase activity nor its acinar distribution was affected by the inducers. These results demonstrated that although the expression of all investigated members of the alpha and mu classes is higher in the perivenous region, there are marked isozyme differences, the acinar gradient being particularly prominent for subunit 1 (Ya). The distinct difference in the acinar induction pattern of GST Ya between beta-naphthoflavone and 3-methylcholanthrene resembles that reported for cytochrome P450 (CYP1A1 and CYP1A2), also members of the aryl hydrocarbon (Ah) receptor genes, suggesting common regionally acting regulatory elements in the expression of these genes in the liver.

Zonation of cytochrome P450 enzyme expression in rat liver. Isozyme-specific regulation by pituitary dependent hormones

The effect of hypophysectomy and subsequent infusion of growth hormone (GH) or injections of triiodothyronine (T3) on the acinar expression pattern of four homonally regulated P450 isozymes was studied to elucidate the involvement of pituitary dependent hormones in regulating the characteristic centrilobular expression pattern of most members of the cytochrome P450 (CYP) gene family in rat liver. Hypophysectomy was previously observed to allow high expression of CYP2B1/2 and 3A1/2 in the normally silent periportal region. In the present study, it had much less effect on the zonation of the ethanol-inducible P450 2E1 form: only a moderate shift of 2E1 staining towards the periportal region was observed by immunohistochemistry. Subsequent injections with T3 moderately decreased CYP2E1 expression in the periportal region and no significant countereffect of GH was discerned. T3 treatment, previously observed to block only the periportal expression of CYP3A1/2, counteracted the increased CYP2B1/2 expression caused by hypophysectomy equally in the periportal and perivenous region. This was true both at the protein and mRNA level, as analysed from cell lysates obtained by in situ perfusion of livers by zone-restricted digitonin treatment. Thus, although hypophysectomy and subsequent GH and T3 treatment affect the total expression of CYP2B1/2, 2E1, and 3A1/2 similarly, the zonal effects were isozyme-specific. In contrast, the perivenous zonation normally seen for the dioxin-inducible P450 1A2 form was steepened rather than diminished by hypophysectomy, both in male and female rats. Administration of GH by the female-type continuous infusion had no effect in male rats, but partially counteracted the effect of hypophysectomy in females, suggesting an involvement of GH. In contrast to other CYP genes investigated, the female-characteristic expression of CYP2C12 was found to be completely non-zonated. Hypophysectomy and continuous GH administration dramatically affected the amount of mRNA of both P450 2C12 and the male-specific 2C11 form, but analysis of periportal and perivenous cell lysates indicated that these effects were not zone-specific. The distribution of the GH receptor was investigated to explain the zonal effects of GH. Immunohistochemically, a moderate perivenous dominance was observed, whereas the mRNA abundance of both GH receptor and GH binding protein was slightly higher in the periportal region. Thus, zonal regulation by GH does not appear to result from a GH receptor zonation; rather, a sinusoidal GH gradient may be involved. These data, combined with our previous results, indicate that pituitary-dependent hormones regulate the zone-specific expression of some P450 forms strongly (i.e. 2B1/2 and 3A1/2), and other forms are moderately regulated (i.e. 1A2 and 2E1), or are affected across the whole acinus (i.e. 2C11, 2C12).

Distribution of catalase in rat brain: aminergic neurons as possible targets for ethanol effects

Ethanol is metabolized at a slow but measurable rate in rodent brain. Recent studies indicate that this process is mediated mainly by catalase. The spatial distribution of this enzyme in different brain structures is poorly known. To explore possible local imbalances between the production and elimination of ethanol-derived acetaldehyde, we investigated the regional and cellular distribution of catalase, histo- and immunohistochemically, using serial cryostat sections from male Wistar rats. Compared to the strong peroxisomal staining seen in liver, brain catalase staining was weak and was not immunologically detected with an anti-sheep bovine catalase antibody. Activity was observed only in microperoxisomes, mainly in perikaryons of aminergic neurons, in the known groups of adrenergic, nonadrenergic and serotonergic neurons of the brain stem. Little peroxisomal staining was seen in other types of brain structures. This result contrasted to that of aldehyde dehydrogenase, which we previously observed to be widely distributed in brain structures, but with low activity in perikaryons of aminergic (especially catecholaminergic) neurons, as compared to cholinergic neurons. Our data indicate that catalase-mediated oxidation of ethanol to acetaldehyde takes place mainly in aminergic neurons, which seem to have a limited capacity for the subsequent removal via aldehyde dehydrogenase. This suggests that locally produced acetaldehyde could mediate CNS effects of ethanol in these structures.