Hepatitis A: old and new.

The hepatitis A virus (HAV), a picornavirus, is a common cause of hepatitis worldwide. Spread of infection is generally person to person or by oral intake after fecal contamination of skin or mucous membranes; less commonly, there is fecal contamination of food or water. Hepatitis A is endemic in developing countries, and most residents are exposed in childhood. In contrast, the adult population in developed countries demonstrates falling rates of exposure with improvements in hygiene and sanitation. The export of food that cannot be sterilized, from countries of high endemicity to areas with low rates of infection, is a potentially important source of infection. After ingestion and uptake from the gastrointestinal tract, the virus replicates in the liver and is excreted into the bile. Cellular immune responses to the virus lead to destruction of infected hepatocytes with consequent development of symptoms and signs of disease. Humoral immune responses are the basis for diagnostic serologic assays. Acute HAV infection is clinically indistinguishable from other causes of acute viral hepatitis. In young children the disease is often asymptomatic, whereas in older children and adults there may be a range of clinical manifestations from mild, anicteric infection to fulminant hepatic failure. Clinical variants include prolonged, relapsing, and cholestatic forms. Management of the acute illness is supportive, and complete recovery without sequelae is the usual outcome. Research efforts during World War II led to the development of passive immunoprophylaxis. Pooled immune serum globulin is efficacious in the prevention and attenuation of disease in exposed individuals. More recently, active immunoprophylaxis by vaccination has been accomplished. Future eradication of this disease can now be contemplated.

Multiple mechanisms, independent of sterol regulatory element binding proteins, regulate low density lipoprotein gene transcription.

Transcription of the LDL receptor gene is markedly enhanced in the Jurkat T cell line by stimulation with the combination of the phorbol ester phorbol 12-myristate 13-acetate (PMA) and the protein synthesis inhibitor cycloheximide (CHX). The DNA sequences necessary for this response were identified by analysis of Jurkat T cells permanently transfected with reporter gene expression vectors containing fragments of the LDL receptor promoter extending from 68 bp to 1472 bp 5' of the major transcription start site. The magnitude of the response of this array of promoter fragments to stimulation with PMA and CHX was similar to that previously observed with a approximately 6.5 kb promoter fragment. However, the various promoter fragments differed with regard to the role of the sterol regulatory element-1 (SRE-1) sequence. Thus, whereas a 142 bp promoter mediated transcription stimulated by PMA and CHX independently of SRE-1, a shorter 115 bp promoter was absolutely dependent on SRE-1. Furthermore, internal deletion of promoter sequences from -142 bp to -113 bp from longer promoter constructs in which the SRE-1 was mutated prevented the induction of transcription by PMA and CHX. Electrophoretic mobility shift assays (EMSAs) demonstrated sequence-specific, stimulus-independent binding by Jurkat nuclear proteins to the novel response element mapped between -142 and -115. Even though the minimal 115 bp or 68 bp promoter fragment required an intact SRE-1 to respond to PMA and CHX, transcriptional induction persisted when nuclear levels of sterol regulatory element binding proteins (SREBPs) were made undetectable by culture in suppressive sterols. Taken together, these data indicate that non-sterol stimuli such as the combination of PMA and CHX induce LDL receptor gene transcription through at least two distinct promoter elements, neither of which requires the presence of SREBPs. However, the element proximal to the transcription start site is dependent on the SRE-1.

Sterol-independent, sterol response element-dependent, regulation of low density lipoprotein receptor gene expression.

Stimulation with phorbol 12-myristate 13-acetate (PMA) and the calcium ionophore ionomycin increased native low density lipoprotein (LDL) receptor gene expression in the human leukemic T cell line Jurkat when cells were cultured in the absence of sterols and also increased nuclear accumulation of sterol regulatory element binding protein (SREBP)-1. PMA and ionomycin likewise increased LDL receptor mRNA levels when cells were cultured in the presence of suppressive concentrations of sterols, when neither SREBP-1 nor SREBP-2 was detectable in the nucleus. These findings indicated that mitogen-induced up-regulation of the LDL receptor gene could be independent of sterol-regulated transcription factors. The involvement of sterol regulatory element (SRE)-1 was analyzed by transfection of LDL receptor promoter constructs. Promoter fragments of either the 5' 1472 or 142 base pairs induced reporter gene expression after mitogenic stimulation when cells were cultured in the absence or presence of sterols. Mutation of the SRE-1 sequence in either construct abolished sterol-mediated regulation of transcription. However, mutation of the SRE-1 sequence in the 1472 base pair promoter fragment did not alter mitogenic induction of transcription, whereas mutation of SRE-1 in the 142 base pair promoter fragment completely prevented up-regulation of transcription. Taken together, these results demonstrate that the LDL receptor promoter contains at least one 5' SRE-independent as well as an SRE-dependent response element. Furthermore, the data suggest that the SRE-dependent response may not involve the action of either SREBP-1 or -2. Thus, mitogen-induced transcription of the LDL receptor promoter is regulated by diverse sterol-independent mechanisms.

Overexpression of cholesterol 7alpha-hydroxylase (CYP7A) in mice lacking the low density lipoprotein (LDL) receptor gene. LDL transport and plasma LDL concentrations are reduced.

This study was undertaken to determine the effect of transient overexpression of hepatic cholesterol 7alpha-hydroxylase on low density lipoprotein (LDL) cholesterol transport in mice lacking LDL receptors (LDL receptor-/-). Primary overexpression of hepatic 7alpha-hydroxylase in LDL receptor-/- mice was accompanied by a dose-dependent decrease in the rate of LDL cholesterol appearance in plasma (whole body LDL cholesterol transport) and a corresponding reduction in circulating LDL cholesterol levels. The increase in hepatic 7alpha-hydroxylase activity necessary to achieve a 50% reduction in plasma LDL cholesterol concentrations was approximately 10-fold. In comparison, cholestyramine increased hepatic 7alpha-hydroxylase activity approximately 3-fold and reduced plasma LDL cholesterol concentrations by 17%. This study demonstrates that augmentation of hepatic 7alpha-hydroxylase expression is an effective strategy for lowering plasma LDL concentrations even in animals with a genetic absence of LDL receptors.

Wilson's disease. Update of a systemic disorder with protean manifestations.

In Wilson's disease, a genetic defect in a copper transporter causes defective incorporation of copper into apo-ceruloplasmin and the failure to excrete copper into bile. Copper accumulated in hepatocytes generates damage via reactive oxygen species. Release of copper from necrotic hepatocytes leads to damage of other tissues, including the brain, urinary tract, red blood cells, heart, endocrine glands, skin, pancreas, bones, and joints. Treatment is designed to chelate the excess copper for urinary excretion, prevent copper absorption, and render tissue copper nontoxic. Liver transplantation, with replacement of the defective hepatic gene, may be necessary in some cases.

Regulation of proliferation and Ras localization in transformed cells by products of mevalonate metabolism.

Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl (HMG) CoA reductase, and 6-fluoromevalonate (Fmev), an inhibitor of diphosphomevalonate decarboxylase, blocked the synthesis of downstream mevalonate products, including prenyl-derived lipids, and prevented membrane localization of Ras in the myeloid cell line U-937. In contrast to lovastatin, which induced cytosol localization of Ras in U-937 cells, Fmev failed to increase cytosolic Ras and also completely prevented the proliferation of U-937 cells. Growth of U-937 cells was restored by the addition of lovastatin to Fmev-blocked cells. These results implied that a product of mevalonate metabolism proximal to isopentenyl diphosphate was responsible for the suppression of proliferation. To delineate the action of this endogenous inhibitor of cell proliferation and determine the relationship between its impact on Ras localization and cell proliferation, the effect of Fmev on a variety of leukemia- and lymphoma-derived cells was examined. Whereas Fmev blocked the growth of these cell lines, there were more than 50-fold differences in the concentrations required to inhibit the growth of individual cell lines by 90%. Regardless of its effect on cell proliferation, the biochemical effect of Fmev was similar. Thus, Fmev uniformly prevented the conversion of radiolabeled mevalonate to isopentenyl diphosphate and other downstream products, including synthesis of sterol and nonsterol lipids and prenylation of proteins. A correlation was noted between higher intrinsic rates of mevalonate synthesis by a cell and susceptibility to inhibition by Fmev. Thus, sensitivity of a cell line to inhibition by Fmev was associated with markedly increased rates of HMG CoA reductase activity that were further increased by incubation with Fmev. Whereas Fmev depleted cellular levels of the prenylated protein Ras in the sensitive cell line U-937, there was no depletion of cellular Ras levels in the resistant cell line EL-4, but rather, there was a shift of Ras from membrane to cytosol, as expected for inhibition of prenylation. These results suggest that leukemic cells with increased HMG CoA reductase activity produce increased levels of an endogenous mevalonate-derived inhibitor that leads to Ras depletion and suppression of cell growth. As a result, inhibition of the growth of these transformed cells might be specifically accomplished by Fmev.

Acute sporadic non-A, non-B, non-C, non-D, non-D, non-E hepatitis.

Patients presenting with clinical and laboratory features consistent with a diagnosis of acute non-A, non-B hepatitis were evaluated for evidence of hepatitis C or hepatitis E infection and for evidence of severe or prolonged disease. Antibody to hepatitis C virus (anti-HCV) was detected in 75 of 108 (69%) patients, antibody to hepatitis E virus (anti-HEV) in three patients (3%), and neither antibody in 31 (29%) patients. One patient had both anti-HCV and anti-HEV. HCV RNA was not detected in sera from any of 20 patients with seronegative (non-ABCDE) hepatitis, but in all 10 patients with anti-HCV who were tested by polymerase chain reaction (PCR). Compared with patients with acute hepatitis C, those with non-ABCDE hepatitis had a lower incidence of parenteral risk factors (6% vs. 70%; P < .001), higher peak serum bilirubin levels (45% vs. 5% with peak levels > 15 mg/dL; P < .001), more prolonged jaundice (25% vs. 0% with peak bilirubin >5 weeks after onset; P < .01), more severe prothrombin time abnormalities (26% vs. 0% with >3 second prolongation; P < .001), more severe hypoalbuminemia (39% vs. 9% with albumin <3 g/dL; P < .01), and more frequent major clinical complications (13% vs. 0% with encephalopathy; P < .01; 10% vs. 0% with death or transplant; P = .024). Patients with acute non-ABCDE hepatitis were less likely to develop chronic hepatitis than those with acute hepatitis C (23% vs. 68%; P < .05). Thus, patients with acute non-ABCDE hepatitis are epidemiologically distinct from those with acute hepatitis C and have a significantly more severe acute illness.

Feedback regulation of hepatic 7alpha-hydroxylase expression by bile salts in the hamster.

Hepatic 7alpha-hydroxylase activity appears to be regulated at the transcriptional level by the quantity of bile salts fluxing through the enterohepatic circulation. Whether bile salts directly suppress 7alpha-hydroxylase expression at the level of the hepatocyte or do so indirectly by promoting the release or absorption of an intestinal factor has not been resolved. We have investigated the ability of primary bile salts to suppress hepatic 7alpha-hydroxylase expression in bile-diverted hamsters. Biliary diversion was accompanied by derepression of both hepatic 7alpha-hydroxylase activity (4-5-fold) and bile salt secretion (approximately 3-fold). Derepression of hepatic 7alpha-hydroxylase expression could be prevented by several interventions that increase the availability of bile salts within the hepatocyte including 1) overexpression of an exogenous 7alpha-hydroxylase gene by adenovirus-mediated gene transfer, 2) obstruction of the common bile duct, and 3) intravenous infusions of taurocholate. In contrast, none of these interventions prevented derepression of hepatic cholesterol synthesis or significantly down-regulated hepatic low density lipoprotein receptor expression over the relatively short time course (24 h) of these studies. Together, these data indicate that primary bile salts contribute to the regulation of bile salt synthesis through feedback repression of 7alpha-hydroxylase expression at the level of the hepatocyte.

Steroid therapy of chronic hepatitis: characteristics associated with response in anti-hepatitis C virus-positive and -negative patients.

OBJECTIVES: The goals of this study were to examine responses to corticosteroid-containing therapy in non-B chronic hepatitis patients with different anti-hepatitis C virus (HCV), autoantibody, and biochemical test results and to determine what factors correlate with response. METHODS: Patients with a prior or current history of steroid therapy for putative autoimmune or chronic non-A, non-B hepatitis were assessed. Responses during the first 6 months of therapy were categorized as "complete" (normal aminotransferases for > or = 1 month), "partial" ( > 50% reduction), or "no response." RESULTS: Sufficient data available to permit evaluation in 32 patients. Complete responses were noted in 17, partial responses in 12, and no response in three subjects. By multivariate analysis, only absence of anti-HCV and presence of cirrhosis were independent predictors of response. Nonresponders were found to have lower scores in a proposed autoimmune hepatitis scoring system, but scores of complete and partial responders were not significantly different. Despite a lower likelihood of a complete response, 80% (12/15) of patients with multiantigen positive anti-HCV tests had either partial or complete initial responses to corticosteroid-containing therapy, and, in nine patients, aminotransferases fell to < 2 times the upper limit of normal. All 15 anti-HCV-negative patients, but only three of 15 anti-HCV-positive patients, entered complete responses that were sustained (aminotransferases < twofold abnormal) on regimens containing < 20 mg/day or prednisolone or prednisone. CONCLUSIONS: Although anti-HCV-positive patients frequently exhibit partial initial responses to immunosuppressive therapy, the absence of specific anti-HCV antibodies was better as a predictor of completeness of response than assessment of autoantibodies or degree of biochemical abnormalities.

Skin irritation testing in man for hazard assessment--evaluation of four patch systems.

1. The limitations of the Draize rabbit skin irritation test for hazard evaluation for man are widely documented. Nevertheless it remains the prescribed method for determining acute skin irritations hazard. 2. While the use of human testing for risk assessment of irritants is well established, the use of predictive testing in man for hazard identification has not been explored widely, and this is the object of the research programme. 3. The experiment described in this report evaluates the sensitivity of four patch testing systems (Finn chamber, Hill Top patch, Van der Bend chamber, and Webril patch) using a total of six irritant substances. 4. Following preliminary range-finding experiments, test materials were applied to the upper outer arm for up to 4 h. Assessments were performed immediately after patch removal and at 1, 24, 48, and 72 h. 5. Webril and Hill Top patches generated the greatest levels of response, although responses with Finn and Van der Bend were observed. Hill Top patches are recommended for future development work. 6. The use of very small preliminary panels to predict the effects in larger panels using different volunteers was only of limited value as each volunteer was found to have different irritant thresholds.

Wilson's disease: a new gene and an animal model for an old disease.

Wilson's disease is an autosomal recessive, inherited disorder of copper metabolism. In normal individuals, copper homeostasis is controlled by the balance between intestinal absorption of dietary copper and hepatic excretion of excess copper in bile. In Wilson's disease, hepatic copper is neither excreted in bile nor incorporated into ceruloplasmin and copper accumulates to toxic levels. The Wilson's disease gene (WND) encodes a putative copper-transporting protein that is expressed almost exclusively in the liver. The predicted structure of the protein product is that of a P-type ATPase with striking homology to bacterial copper transporters and the gene product of another inherited disorder of copper metabolism, Menkes' disease. A rat model of Wilson's disease has recently been identified. The Long-Evans Cinnamon (LEC) rat manifests elevated hepatic copper, defective incorporation of copper into ceruloplasmin, and reduced biliary excretion of copper. The rat homologue of the WND is abnormal in LEC rats. Clinical manifestations of Wilson's disease arise directly from copper-induced damage to hepatocytes (hepatic presentation) or indirectly after the release of copper from the liver with subsequent damage to the brain (neuropsychiatric presentation) and other organs. Genetic heterogeneity (different mutations in a single gene) may account for some of the variability in Wilsonian presentations. The diagnosis of Wilson's disease depends on the demonstration of disordered copper metabolism, manifested as elevated urinary and hepatic copper and low ceruloplasmin levels. However, none of the abnormal findings in Wilson's disease is pathognomonic. Genetic diagnosis, in the absence of family studies, is likely to be difficult since many different mutations result in the disease. Management of Wilson's disease involves decreasing excess levels of copper accumulated in the liver, brain, and other organs. Copper chelation therapy, to increase urinary excretion of copper, is the mainstay of treatment. In addition, oral zinc therapy may be useful at decreasing absorption of dietary copper and rendering tissue copper nontoxic, by increasing the formation of complexes with copper-binding proteins. Liver transplantation can be necessary for individuals with acute hepatic failure or complications of cirrhosis. Gene therapy may evolve in the future; however, medical management is effective in most patients.

Adenovirus-mediated transfer of a gene encoding cholesterol 7 alpha-hydroxylase into hamsters increases hepatic enzyme activity and reduces plasma total and low density lipoprotein cholesterol.

Clinical interventions that accelerate conversion of cholesterol to bile acids reduce circulating low density lipoprotein (LDL) cholesterol concentrations. The initial and rate-limiting step in the bile acid biosynthetic pathway is catalyzed by hepatic cholesterol 7 alpha-hydroxylase. To examine the effects of transient primary overexpression of this enzyme on sterol metabolism and lipoprotein transport, we constructed a recombinant adenovirus in which a cDNA encoding rat 7 alpha-hydroxylase is expressed from the human cytomegalovirus immediate-early promoter (AdCMV7 alpha). Syrian hamsters administered AdCMV7 alpha intravenously accumulated transgene-specific mRNA in the liver and demonstrated a dose-dependent increase in hepatic microsomal 7 alpha-hydroxylase activity. The increased conversion of cholesterol to bile acids resulted in a compensatory increase in hepatic cholesterol synthesis. In addition, overexpression of 7 alpha-hydroxylase reduced the rate of LDL cholesterol entry into the plasma space and, in animals maintained on a Western-type diet, restored hepatic LDL receptor expression. As a consequence, plasma LDL concentrations fell by approximately 60% in animals maintained on control diet and by approximately 75% in animals consuming a Western-type diet. Plasma high density lipoprotein cholesterol levels were reduced to a lesser degree. These results demonstrate that transient upregulation of bile acid synthesis by direct transfer of a 7 alpha-hydroxylase gene favorably alters circulating lipoprotein profiles and suggest one potential molecular target for genetic strategies aimed at reducing cardiovascular risk.

Regulatory effects of n-3 polyunsaturated fatty acids on hepatic LDL uptake in the hamster and rat.

These studies were undertaken to investigate the mechanisms involved in the regulation of hepatic low density lipoprotein (LDL) transport by n-3 fatty acids in the hamster and rat. Animals were fed n-3 or n-6 fatty acids with a cholesterol-free, very-low-fat semisynthetic diet, or with a diet enriched with cholesterol and saturated fat. Although the enrichment of liver lipids with dietary n-3 fatty acids was similar in hamsters and rats, the effect of n-3 fatty acids on hepatic LDL transport differed in the two species. In the hamster, n-3 fatty acids had no effect on hepatic receptor-dependent LDL uptake in animals fed a cholesterol-free, very-low-fat diet and suppressed receptor-dependent transport in animals fed a diet enriched with cholesterol and saturated triglyceride. In hamsters fed n-3 fatty acids, changes in receptor-dependent LDL transport were accompanied by parallel changes in LDL receptor mRNA, indicating regulation of the receptor at the pretranslational level. In the rat, on the other hand, dietary n-3 fatty acids enhanced hepatic receptor-dependent LDL uptake by nearly twofold regardless of the background diet; however, hepatic LDL receptor protein and mRNA were unchanged. Dietary n-3 fatty acids did not enhance hepatic chylomicron remnant clearance in the rat. These studies confirm marked species differences in response to n-3 fatty acids and suggest that n-3 fatty acids accelerate hepatic receptor-dependent LDL transport in the rat by altering the distribution or recycling of LDL receptors or via effects on a different receptor pathway.

Suppression of the proliferation of Ras-transformed cells by fluoromevalonate, an inhibitor of mevalonate metabolism.

Mevalonate is the precursor of a number of different products potentially required for the growth of cells, including the prenylated oncoprotein Ras. To determine whether inhibition of mevalonate metabolism would selectively block proliferation of Ras-transformed cells, 6-fluoromevalonate (Fmev), an inhibitor of diphosphomevalonate decarboxylase, was used to block the synthesis of prenyl-derived lipids and prenylated proteins in interleukin-3 (IL-3)-dependent FDC-P1 cells (control FDC-P1 cells) and FDC-P1 cells transformed with oncogenic Ras (RasDC cells) that proliferated in the absence of IL-3. Fmev completely inhibited synthesis of prenyl-derived lipids and prenylated proteins and blocked proliferation of FDC-P1 and RasDC cells. Restoration of the proliferation of Fmev-blocked FDC-P1 cells required both an exogenous source of cholesterol and prevention of the accumulation of mevalonate and the mevalonate phosphates with lovastatin. In contrast, ongoing IL-3-independent proliferation of Fmev-blocked RasDC cells was not completely restored by providing exogenous cholesterol and preventing the accumulation of inhibitory mevalonate product(s). However, these cells proliferated when cultures were supplemented with IL-3 together with exogenous cholesterol and lovastatin, implying that Fmev had prevented Ras-dependent, IL-3-independent growth. Fmev markedly diminished total cellular Ras in RasDC cells. In contrast, lovastatin depleted membrane-associated Ras and increased cytosolic Ras but did not diminish total cellular Ras. These data indicate that Fmev depletes total cellular Ras and specifically inhibits the autonomous growth of Ras-transformed cells.

Regulation of hepatic 7 alpha-hydroxylase expression and response to dietary cholesterol in the rat and hamster.

Although dietary cholesterol raises plasma total and low density lipoprotein (LDL) cholesterol concentrations, the response to a given intake of cholesterol varies enormously among different species and even among individuals of the same species. The mechanisms responsible for differing sensitivity to dietary cholesterol were examined by comparing the rat, which is able to adapt to large fluctuations in sterol intake or loss with little change in plasma LDL levels, with the hamster, where changes in sterol balance strongly influence plasma LDL concentrations. When fed the same cholesterol-free diet, hepatic 7 alpha-hydroxylase activity was 16-fold higher in the rat than in the hamster. As a consequence, rates of hepatic cholesterol synthesis were 20-fold higher in the rat than in the hamster. In both species, hepatic cholesterol synthesis was suppressed > 90% in response to increasing loads of dietary cholesterol. However, the quantitative importance of this adaptive mechanism was much greater in the rat since the absolute reduction in hepatic cholesterol synthesis in the rat (2,110 nmol/h/g) was much larger than in the hamster (103 nmol/h/g). In the rat, the high basal level of 7 alpha-hydroxylase expression was further induced by substrate (cholesterol) allowing these animals to convert excess dietary cholesterol to bile acids efficiently. In contrast, the low basal level of enzyme expression in the hamster was not induced by dietary cholesterol. Thus, the low basal rates of bile acid and cholesterol synthesis coupled with a lack of 7 alpha-hydroxylase induction by cholesterol render the hamster much more sensitive than the rat to the cholesterolemic effects of dietary cholesterol.

Non-sterol regulation of low density lipoprotein receptor gene expression in T cells.

Non-sterol regulation of low density lipoprotein (LDL) receptor gene expression was examined in a mitogen-responsive human T cell line. Stimulation of the leukemic T cell line Jurkat with the phorbol ester phorbol 12-myristate 13-acetate (PMA) and the calcium ionophore ionomycin rapidly and transiently increased LDL receptor mRNA levels. Inhibition of protein synthesis with cycloheximide (CHX) or puromycin resulted in superinduction of LDL receptor mRNA levels by mitogenic stimulation. The increase in LDL receptor mRNA levels resulted from increased gene transcription rather than stabilization of mRNA half-life. Thus, similar results were obtained when reporter gene expression was assessed in Jurkat cells transfected with LDL receptor promoter constructs and mRNA half-life was not significantly altered by the stimuli. Neither mitogenic induction nor superinduction of LDL receptor mRNA levels in Jurkat cells was prevented by sterol downregulation of LDL receptor gene expression. The protein synthesis inhibitors CHX and anisomycin, but not puromycin, also directly stimulated LDL receptor mRNA levels, suggesting that these compounds could provide a signal required for LDL receptor gene transcription. Taken together, these data indicate that various non-sterol stimuli, including activation of protein kinase C, increases in intracellular calcium, inhibition of protein synthesis, and signals generated by the protein synthesis inhibitors CHX and anisomycin, induce LDL receptor gene expression. Thus, transcription of the LDL receptor gene is not only regulated by ambient sterols but also by a variety of influences that govern the various primary response or immediate early genes. These stimuli may play an important role in normal regulation of LDL receptor gene expression.

Hepatitis C: progress and problems.

The hepatitis C virus (HCV), a single-stranded RNA virus, is the major cause of posttransfusion hepatitis. HCV isolates differ in nucleotide and amino acid sequences. Nucleotide changes are concentrated in hypervariable regions and may be related to immune selection. In most immunocompetent persons, HCV infection is diagnosed serologically, using antigens from conserved regions. Amplification of RNA may be necessary to detect infection in immunosuppressed patients. Transmission by known parenteral routes is frequent; other means of spread are less common and may represent inapparent, percutaneous dissemination. Infection can lead to classical acute hepatitis, but most infected persons have no history of acute disease. Once infected, most individuals apparently remain carriers of the virus, with varying degrees of hepatocyte damage and fibrosis ensuing. Chronic hepatitis may lead to cirrhosis and hepatocellular carcinoma. However, disease progression varies widely, from less than 2 years to cirrhosis in some patients to more than 30 years with only chronic hepatitis in others. Determinants important in deciding outcome are unknown. Alpha interferon, which results in sustained remission in selected patients, is the only available therapy. Long-term benefits from such therapy have not been demonstrated. Prevention of HCV infection by vaccination is likely to be challenging if ongoing viral mutation results in escape from neutralization and clearance.

Regulation of hepatic 7 alpha-hydroxylase expression by dietary psyllium in the hamster.

Soluble fiber consistently lowers plasma total and low density lipoprotein (LDL)-cholesterol concentrations in humans and various animal models including the hamster; however, the mechanism of this effect remains incompletely defined. We performed studies to determine the activity of dietary psyllium on hepatic 7 alpha-hydroxylase, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and LDL receptor expression in the hamster. In animals fed a cholesterol-free semisynthetic diet containing 7.5% cellulose (avicel) as a fiber source, substitution of psyllium for avicel increased hepatic 7 alpha-hydroxylase activity and mRNA levels by 3-4-fold. Comparable effects on 7 alpha-hydroxylase expression were observed with 1% cholestyramine. Psyllium also increased hepatic 7 alpha-hydroxylase activity and mRNA in animals fed a diet enriched with cholesterol and triglyceride. Activation of 7 alpha-hydroxylase was associated with an increase in hepatic cholesterol synthesis that was apparently not fully compensatory since the cholesterol content of the liver declined. Although dietary psyllium did not increase hepatic LDL receptor expression in animals fed the cholesterol-free, very-low-fat diet, it did increase (or at least restore) receptor expression that had been downregulated by dietary cholesterol and triglyceride. Thus, 7.5% dietary psyllium produced effects on hepatic 7 alpha-hydroxylase and LDL metabolism that were similar to those of 1% cholestyramine. Induction of hepatic 7 alpha-hydroxylase activity by dietary psyllium may account, in large part, for the hypocholesterolemic effect of this soluble fiber.

Dietary fatty acids regulate hepatic low density lipoprotein (LDL) transport by altering LDL receptor protein and mRNA levels.

The concentration of LDL in plasma is strongly influenced by the amount and the type of lipid in the diet. Recent studies in the hamster have shown that dietary fatty acids differentially affect circulating LDL levels primarily by altering receptor-dependent LDL uptake in the liver. To investigate the mechanistic basis of this effect, rates of receptor-dependent LDL transport in the liver were correlated with LDL receptor protein and mRNA levels in hamsters fed safflower oil or coconut oil and varying amounts of cholesterol. Hepatic LDL receptor activity was significantly lower in animals fed coconut oil than in animals fed safflower oil at all levels of cholesterol intake (26, 53, and 61% lower at cholesterol intakes of 0, 0.06, and 0.12%, respectively). These fatty acid-induced changes in hepatic LDL receptor activity were accompanied by parallel changes in hepatic LDL receptor protein and mRNA levels, suggesting that dietary fatty acids regulate the LDL receptor pathway largely at the mRNA level.