Epidemiology, clinical course and treatment of chronic viral hepatitis

Chronic hepatitis may take the form of a hepatitis B infection, a delta virus infection, or a non-A, non-B hepatitis including hepatitis C. All the viruses involved are transmitted predominantly by parenteral or sexual routes. New insights into the structure of the hepatitis B virus (HBV) and the immune response mechanisms of the organism permit a clear definition of the replicative state of the virus, and allow predictions to be made about the outcome of the disease. Development of cirrhosis and hepatocellular carcinoma are the major complications associated with impaired life expectancy. Recently, the hepatitis C virus (HCV) was identified as the agent responsible for most cases of chronic non-A, non-B hepatitis. The development of an assay for the detection of HCV-antibodies facilitated the diagnosis of this type of hepatitis. Moreover, the use of screening tests for hepatitis B and hepatitis C in blood donors will decrease the risk of acquiring hepatitis via contaminated blood products. Treatment of chronic hepatitis B and C with alpha-interferon has shown promising results. However, the dosage schedule, the period of treatment, and the selection of patients needs to be evaluated in further studies.

Iron uptake by human upper small intestine microvillous membrane vesicles. Indication for a facilitated transport mechanism mediated by a membrane iron-binding protein

To investigate the hypothesis that iron absorption in man involves a carrier-mediated cellular uptake mechanism, influx velocity (Vo) of 59Fe3+ by isolated human microvillous membrane (MVM) vesicles of the upper small intestine was examined. Vo revealed saturation kinetics (Km = 315 nM; Vmax = 361 pmol Fe3+ x min-1 x mg protein-1) was temperature dependent and inhibited by pronase pretreatment of MVM. In the presence of an inwardly directed Na(+)-gradient a typical overshoot phenomenon with maximal uptake at 30-40 s was observed. The suggestion of an active, carrier-mediated uptake mechanism for iron was pursued by isolation of a 160-kD iron-binding protein from solubilized human MVM proteins. This glycoprotein was assembled as a trimer composed of 54-kD monomers. A monospecific antibody against the 54-kD subunit inhibited vesicular influx of Fe3+ into MVM by greater than 50%. Immunofluorescence and immunoblot analysis confirmed the localization of the protein in brush border plasma membranes. It was detectable in human intestinal mucosa and liver, but not in esophagus. These data indicate that the translocation of Fe3+ across human MVM represents a facilitated transport mechanism which is, at least in part, mediated by a membrane iron-binding protein.

The membrane fatty acid-binding protein is not identical to mitochondrial glutamic oxaloacetic transaminase (mGOT)

For evaluation whether the membrane fatty acid-binding protein is related to mGOT, studies on the structure and function of both purified proteins were performed. Physicochemical characterization revealed that both proteins are different: the membrane fatty acid-binding protein has a molecular weight of 40 kD and a pI of 8.5-9.0, whereas rat mGOT has a molecular weight of 44 kD and a pI of 9.5-10.0. According to this distinct differences, they migrated separately on 2-dimensional electrophoresis. Furthermore, monospecific antibodies against the membrane fatty acid binding protein did not react with rat mGOT. In co-chromatography studies only the membrane fatty acid-binding protein showed affinity for long chain fatty acids, but not mGOT. Moreover, membrane binding studies were performed with the monospecific antibody to the membrane fatty acid binding protein. The inhibitory effect of this antibody on plasma membrane binding of oleate was reversed after preabsorption of the antibody with the membrane fatty acid binding protein, but was not affected after preabsorption with mGOT. These results indicate that the membrane fatty acid binding protein and mGOT are structurally and functionally not related. The data also support the significance of this membrane protein in the plasma membrane binding process of long chain fatty acids.

Uptake of palmitic acid by rabbit alveolar type II cells

Alveolar type II cells require a source of palmitic acid for synthesis of dipalmitoyl phosphatidylcholine (DPPC), a major constituent of pulmonary surfactant. Previous studies indicated that maximal rates of DPPC synthesis are achieved only if exogenous palmitate is available to the type II cell. Little is known of the mechanisms by which fatty acids enter type II cells. To determine if uptake is mediated by a membrane carrier system, as described in other cell types, we examined the kinetics of palmitate uptake. Using freshly isolated rabbit type II cells, we demonstrated that radiolabeled palmitate uptake was maximal and linear for 45 s; after 1 min the apparent rate of uptake declined. The initial uptake phase was taken as a measure of cellular fatty acid influx because intracellular radiolabeled palmitate remained 80% nonesterified at this time but was 55% esterified by 2 min. Cellular influx of palmitate showed saturation kinetics with increasing concentration of nonalbumin bound palmitate. Michaelis constant was 52.6 nM, and maximum velocity was 152 pmol.10(6) cells-1.min-1. The hypothesis that saturable cellular influx of palmitate is likely linked to the previously identified membrane fatty acid binding protein (MFABP) was supported by Western-blot analysis of rat lung tissue with an antibody to MFABP that demonstrated the presence of this carrier protein in lung tissue. These data suggest that palmitate uptake by type II cells is saturable and may be mediated by a membrane-associated carrier as described in other cell types.

Cellular uptake of conjugated bilirubin and sulfobromophthalein (BSP) by the human hepatoma cell line Hep G2 is mediated by a membrane BSP/bilirubin binding protein

Cellular influx kinetics of 4-50 microM bilirubin diglucuronide and sulfobromophthalein (BSP) by the human hepatoma cell line Hep G2 was examined at 37 degrees C. In confluent monolayer cultures, cellular influx of increasing concentrations of conjugated bilirubin and BSP revealed similar saturation kinetics with Km values of 9.9 and 12.1 microM, and Vmax values of 0.512 and 0.473 nmol.mg cell protein-1.min-1, respectively. Uptake of [3H]bilirubin diglucuronide was competitively inhibited by unlabeled BSP, and was temperature dependent with maximal cellular influx rates at 37 degrees C. When the confluent monolayer cultures were pretreated with a monospecific antibody to the rat liver BSP/bilirubin binding membrane protein, initial uptake rates of conjugated and unconjugated bilirubin as well as of BSP were significantly inhibited, whereas uptake of oleate was not affected. Furthermore, immunoblot analysis of the homogenate of Hep G2 cells with the same antibody revealed predominant reactivity with a 55 kDa protein. These data suggest that cellular uptake of bilirubin and related cholephilic organic anions by the human hepatoma cell line Hep G2 is mediated by a specific 55 kDa membrane BSP/bilirubin binding protein.

Intestinal absorption of unconjugated dihydroxy bile acids: non-mediation by the carrier system involved in long chain fatty acid absorption

Experiments were performed using isolated mucosal cells from the rat jejunum or using the perfused jejunum in the anesthetized rat to test whether lipophilic unconjugated dihydroxy bile acids are absorbed from the proximal small intestine via the same carrier mechanism involved in the uptake of long chain fatty acids. With isolated jejunal mucosal cells, the cellular uptake rate of deoxycholic acid or chenodeoxycholic acid increased linearly with time, showed no evidence of saturation, and was not decreased by the presence of a monospecific antibody to the membrane fatty acid binding protein. In contrast, oleate uptake was saturable, was inhibited by the same antibody, but was not affected by the presence of chenodeoxycholic acid or deoxycholic acid. Bile acid uptake by isolated enterocytes occurred at one-eighth the rate of fatty acid uptake if expressed in relation to total solute concentration; if expressed in relation to monomeric concentration, initial bile acid uptake was four orders of magnitude slower than fatty acid uptake. In the isolated perfused jejunal segment, chenodeoxycholic acid and deoxycholic acid uptake was not influenced by the presence of the antibody to membrane fatty acid binding protein, whereas absorption of oleate was inhibited by more than 70%. These experiments indicate that absorption of unconjugated lipophilic dihydroxy bile acids in the rodent jejunum does not involve the carrier mediated uptake mechanism involved in the absorption of long chain fatty acids--the mechanism is likely to be passive nonionic diffusion.

Cellular influx of sulfobromophthalein by the biliary epithelium carcinoma cell line Sk-Cha-1 reveals kinetic criteria of a carrier-mediated uptake mechanism

Cellular uptake of the cholephilic organic anion sulphobromophthalein (BSP) by the human biliary epithelium carcinoma cell line Sk-Cha-1 was examined at 37 degrees C. In confluent monolayer cultures the cellular influx rate of increasing concentrations of [35S]BSP followed saturation kinetics with a Km value of 18 microM and a Vmax value of 243 pmol.min-1.mg protein-1. Uptake of [35S]BSP was competitively inhibited by the presence of bilirubin diglucuronide, but not by taurocholate or cholate. Furthermore, uptake was temperature dependent with maximal cellular influx rates at 37 degrees C.

Mechanism of hepatic fatty acid uptake

In recent years a new concept of the mechanism of hepatic fatty acid uptake has been described. It was shown that this major class of energy yielding substrates enters hepatocytes by a carrier-mediated uptake system. After the dissociation of the fatty acid-albumin complex at the sinusoidal liver cell plasma membrane, fatty acid binds with high affinity to a specific, newly identified, 40 kDa membrane fatty acid binding protein (MFABP). This protein functions as transmembrane transporter for long chain fatty acids. Hepatocellular uptake of fatty acids was shown to be sodium-dependent and electrogenic, compatible with a Na+-fatty acid cotransport system.

Fatty acid uptake by human hepatoma cell lines represents a carrier-mediated uptake process

Cellular influx kinetics of a representative long chain fatty acid, [3H]oleate, were examined in monolayer cultures of three different human hepatoma cell lines (Hep G2; PLC/PRF 5; Mz-Hep-1). The cultures were incubated with 173 microM [3H]oleate in the presence of various concentrations of albumin which served to modulate the unbound oleate concentration in the medium. For all [3H]oleate-albumin complexes incubated, it was shown that cellular uptake of [3H]oleate over the initial 30 s incubation period was maximal, linear and independent of intracellular fatty acid metabolism, representing cellular influx. With increasing unbound oleate concentrations in the medium cellular influx by all three cell lines revealed similar saturation kinetics with Km values of 112.6 +/- 14.5 nM and Vmax values of 7.19 +/- 0.32 nmol.min-1 per mg cell protein. When these hepatoma cell lines were pretreated with the IgG fraction of a monospecific antibody to the rat liver membrane fatty acid binding protein (MFABP), initial uptake of [3H]oleate was selectively inhibited compared to controls pretreated with the IgG fraction of the preimmune serum. Furthermore, immunoblot analysis with the monospecific antibody to the rat MFABP revealed reactivity with a single 40 kDa protein in the homogenates of all three cell lines. These data suggest that uptake of fatty acids by human hepatoma cells may be mediated by a specific membrane fatty acid binding protein.

[Epidemiology and clinical aspects of chronic hepatitis B and non-A, non-B virus infections]

Hepatitis B and Non-A-non-B infections often become chronic and proceed to cirrhosis associated with a shortened life expectancy. Both infections are transmitted by parenteral or sexual routes. New insights in the structure of the hepatitis B virus (HBV) as well as in the immune response mechanism of the organism permit by serological testing a clear definition of the replicative state of the virus. Together with the parameters of inflammation (e.g. transaminases, liver histology) it is possible to determine the activity of the hepatitis. The most effective treatment of chronic HBV-infection today is the therapy with alpha- or beta-interferon. The aim of this treatment is the inhibition of HBV replication and accellerated elimination of the virus, indicated by seroconversion of HBEAg to anti-HBEAg. The most significant advance in the knowledge of percutaneous Non-A-non-B hepatitis is the identification of the responsible virus and the development of a diagnostic test for its serological detection. Since this type of hepatitis becomes chronic in 50-60% of the cases, therapy is urgently required. Clinical studies showed that also for Non-A-non-B virus infection alpha-interferon is most effective. Currently the optimal dosage, duration and point in time for interferon treatment is being evaluated.

Transmembrane transport of fatty acids in the heart

Although fatty acid uptake by the myocardium is rapid and efficient, the mechanism of their transmembrane transport has been unclear. Fatty acids are presented to the plasma membrane of cardiomyocytes as albumin complexes within the plasma. Since albumin is not taken up by the cells, it was postulated that specific high affinity binding sites at the sarcolemma may mediate the dissociation of fatty acids from the albumin molecules, before they are transported into the cells. In studies with a representative long-chain fatty acid, oleate, it was in fact shown that fatty acids bind with high affinity to isolated plasma membranes of rat heart myocytes revealing a KD of 42 nM. Moreover, a specific membrane fatty acid-binding protein (MFABP) was isolated from these membranes. It had a molecular weight of 40 kD, an isoelectric point of 9.0, and lacked carbohydrate or lipid components. Binding to a specific membrane protein might represent the first step of a carrier mediated uptake process. Therefore, the uptake kinetics of oleate by isolated rat heart myocytes was determined under conditions where only cellular influx and not metabolism occurred. Uptake revealed saturation kinetics and was temperature dependent which were considered as specific criteria for a facilitated transport mechanism. For evaluation whether uptake is mediated by MFABP, the effect of a monospecific antibody to this protein on cellular influx of oleate was examined. Inhibition of uptake of fatty acids but not of glucose by the antibody to MFABP indicated the physiologic significance of this protein as transmembrane carrier in the cellular uptake process of fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of fatty acids by jejunal mucosal cells is mediated by a fatty acid binding membrane protein

The previous identification of a membrane fatty acid binding protein (MFABP) in brush border plasma membranes of the jejunum suggested that mucosal cell uptake of fatty acids might represent a carrier-mediated transport system. For evaluation of this hypothesis cellular influx kinetics (V0) of [3H]-oleate were examined in isolated rat jejunal mucosal cells. With increasing unbound oleate concentration in the medium V0 was saturable (Km = 93 nM; Vmax = 2.1 nmol X min-1 per 10(6) cells) and temperature dependent with an optimum at 37 degrees C. Pretreatment of the cells with a monospecific antibody to MFABP significantly inhibited V0 of oleate, other long-chain fatty acids, and D-monopalmitin, but not of L-alanine. Moreover, in the in vivo system of isolated perfused jejunal segments the physiologic significance of MFABP in the directed overall intestinal absorption process of fatty acids was documented. In the presence of the anti-MFABP oleate absorption was markedly reduced, whereas uptake of L-alanine remained unaltered. By antibody inhibition studies it was suggested that this membrane carrier also reveals transport competence for various other long-chain fatty acids, D-monopalmitin, L-lysophosphatidylcholine, and cholesterol. These data support the hypothesis that absorption of fatty acids is mediated by a fatty acid binding membrane protein.

Regional myocardial free fatty acid extraction in normal and ischemic myocardium

The rate constant for free fatty acid influx (k1) was studied in normal and ischemic myocardium. In 15 normal subjects and 30 patients with coronary artery disease, 201Tl and 15-(p-123I-iodophenyl)-pentadecanoic acid (IPPA) were administered during exercise under fasting conditions and at rest. In 10 patients, the study was repeated after percutaneous transluminal coronary angioplasty; in three patients, the study was repeated after infarction. The initial accumulation of IPPA, related to that of 201Tl (both background and crossover corrected), was used for determinations of the regional rate constant of IPPA influx into myocardial tissue (k1*). In normal subjects, no significant differences in k1* between major myocardial segments were found; the average value of k1* was 0.57 +/- 0.13/min (mean +/- SD) at rest and 0.42 +/- 0.06/min at exercise (average workload, 123 +/- 47 W). With increasing free fatty acid plasma concentration and perfusion, free fatty acid influx increased in a saturable fashion. The Michaelis-Menten constant (KM*) and the maximal velocity (Vmax*) for IPPA influx into myocardial tissue were estimated to be 470 nmol/g and 430 nmol/g.min, respectively. In ischemic areas, k1* was reduced to 57 +/- 18% of k1* value in nonaffected segments. The areas were larger than those showing reduced 201Tl uptake. Preinfarction and postinfarction studies showed that the size of 201Tl defects in postinfarction images corresponded with the size of the area with reduced k1* observed in preinfarction scintigrams. Revascularization led to an increase of 201Tl uptake and to normalization of k1*.

What's new in the hepatocellular uptake mechanism of bilirubin and fatty acids?

Although hepatocellular uptake of bilirubin and fatty acids represents a major function of the liver, little was known about the molecular mechanism of their translocation across the plasma membrane. This review provides evidence that these classes of albumin-bound organic anions enter hepatocytes via specific membrane associated carrier systems. After dissociation of the albumin-ligand complexes at the cell surface, bilirubin and related cholephilic organic anions bind to a 55 kDa membrane glycoprotein, while fatty acids bind to a 40 kDa membrane protein. Both proteins function as carrier of their respective ligand across the plasma membrane. Although the driving forces for the influx of bilirubin are still unknown, it could be demonstrated that the translocation of fatty acids across the plasma membrane is driven by an active, potential-sensitive, sodium-dependent transport system.

[Orthotopic liver transplantation in Wilson's disease and acute liver failure]

Liver histology demonstrated progressive cirrhosis in a 19-year-old girl with a subacute form of Wilson's disease. Despite D-penicillamine administration her liver functions rapidly deteriorated further. Orthotopic liver transplantation was performed. Postoperatively there were two mild rejection episodes, an organic psychiatric syndrome and generalized tremor. Copper metabolism and clinical symptoms became normal postoperatively. Five months after the transplantation she was in a good general condition, able to continue her education.

Survival and causes of death in hemochromatosis. Observations in 163 patients

Survival and causes of death were analyzed among 163 patients with hemochromatosis diagnosed between 1959 and 1983. Mean followup was 10.5 +/- 5.6 years (+/- SD). Cumulative survival was 76% at 10 years and 49% at 20 years. Life expectancy was reduced in patients who presented with cirrhosis or diabetes compared to patients who presented without these complications at the time of diagnosis. Patients who could be depleted of iron during the first 18 months of venesection therapy had a markedly better prognosis compared to those patients who could not be depleted during this time period, probably due to greater amounts of excessive iron. Prognosis was not influenced by sex. Patients without cirrhosis or diabetes had a life expectancy that was virtually identical to that of an age-matched normal population. Analysis of the causes of death in 53 patients showed that liver cancer (n = 16) was 219 times more frequent, cardiomyopathy (n = 3) was 306 times more frequent, liver cirrhosis (n = 10) was 13 times more frequent, and diabetes mellitus (n = 3) was seven times more frequent compared to death rates expected for an age-matched normal population. The risk of death from other causes, including extrahepatic cancer (n = 7), did not differ from rates expected. Thus, patients with hemochromatosis diagnosed in a precirrhotic stage and treated by venesection have a normal life expectancy. Cirrhotic patients had a shortened life expectancy and a high risk of death from liver cancer even when complete iron depletion has been achieved.

Abnormalities in estrogen, androgen, and insulin metabolism in idiopathic hemochromatosis

Of 44 male patients with idiopathic hemochromatosis who were diagnosed at an early stage without morphological or biochemical evidence of liver disease, 25% suffered from impotence and 34% manifested glucose intolerance. Impotence was correlated with a 50% reduction in plasma testosterone, resulting from a 63% decrease in testosterone production. Testicular atrophy was caused by insufficient secretion of gonadotropins due to the selective accumulation of iron in gonadotropic cells of the pituitary gland. However, peripheral sexual hormone metabolism, in particular the conversion of androgens to estrogens, remained unaltered. It was therefore possible to employ substitution therapy successfully with testosterone in these men, and hyperestrogenism was not observed as a side effect. The pathogenetic factors in the development of diabetes mellitus in patients with idiopathic hemochromatosis include impaired insulin secretion caused by the selective deposition of iron in B-cells of the pancreas and insulin resistance due to iron accumulation in the liver. In particular, the insulin resistance is markedly improved after depletion of body iron stores by phlebotomy treatment, resulting in lower insulin requirements in patients with insulin-dependent diabetes as well as improvement of carbohydrate metabolisms in about half of the patients with non-insulin-dependent diabetes. We have concluded that hypogonadism and carbohydrate intolerance are caused by the specific distribution pattern of excess iron in the organism, accompanied by functional impairment of affected parenchymal cells.