Taurocholate transport by liver plasma membrane vesicles is not altered in cirrhotic rats

Study of the eye and lacrimal glands in experimental iron overload in rats in vivo

A variety of syndromes leading to hemosiderosis in men cause ocular lesions. The purpose of the present study was to determine the distribution of iron and of transferrin in the eyes and lacrimal glands of rats in experimental hemosiderosis, so as to achieve a better understanding of the formation of the ocular lesions observed in patients with advanced hemosiderosis. In order to achieve hemosiderosis the rats were fed 3% (w/w) carbonyl iron or received i.p. or i.v. polymaltose iron. Hemosiderin deposits were detected in macrophages lying in the interlobular connective tissue of lacrimal glands, in the interstitial connective tissue of the choroid, in the ciliary body, in the iris and extracellularly in the sclera in all animals that received iron i.v. Also, scanty hemosiderin laden macrophages were found to a lesser degree in interstitial connective tissue of the choroid and in the interlobular connective tissue of lacrimal glands in animals that received iron i.p. No iron deposits were detected in the eye and lacrimal glands of control rats and in rats that were on an iron enriched diet. No transferrin was detected in the eye and in the lacrimal glands, neither in the control rats nor in the rats that received iron. Experimental iron overload leads to increased iron deposition in tissues of the eye and lacrimal glands, whereas no transferrin could be detected in the aforementioned organs.

Characterization of a sodium-dependent transport system for butyrobetaine into rat liver plasma membrane vesicles

Butyrobetaine transport into the liver was studied using isolated rat hepatocyte plasma membrane vesicles. In the presence of a sodium chloride gradient, an overshoot could be observed, indicating active sodium-dependent transport. A similar overshoot was recorded in the presence of lithium, but not of potassium, cesium, or choline chloride. Investigation of several sodium salts revealed that an overshoot could only be observed in the presence of chloride, but not of nitrate, thiocyanate, sulfate, or gluconate. An osmolarity plot in the presence of sodium chloride revealed a slope different from zero and a positive intercept, indicating active transport and nonspecific binding, respectively. In agreement with the osmolarity plot, the kinetic characterization of butyrobetaine transport revealed a binding and a saturable component. The saturable component could be described by Michaelis-Menten kinetics, with a Km of 4.88 +/- 0.70 mmol/L and a Vmax of 4.16 +/- 0.73 picomoles per milligram of protein per second. Butyrobetaine transport could be inhibited significantly (30%) by 250 micromol/L propionylcarnitine, but not by D- or L-carnitine, other acylcarnitines (acetylcarnitine, isovalerylcarnitine, palmitoylcarnitine), trimethyllysine, or quinine. Butyrobetaine transport activity was also expressed in Xenopus laevis oocytes by injecting mRNA isolated from rat liver or kidney. After 5 days of cultivation, the endogenous butyrobetaine transport activity was increased by 82% in oocytes injected with liver mRNA and by 99% in oocytes injected with kidney mRNA. The studies show that butyrobetaine is transported actively across the basolateral plasma membrane of hepatocytes and that this transport is driven by sodium and chloride gradients. This transport is quite specific for butyrobetaine and is not rate-limiting for carnitine biosynthesis.

Cellular expression and regulation of iron transport and storage proteins in genetic haemochromatosis

Genetic haemochromatosis is a common iron overload disorder of unknown aetiology. To characterize the defect of iron metabolism responsible for this disease, this study localized and semi-quantified the mRNA and protein expression of transferrin, transferrin receptor and ferritin in the liver and duodenum of patients with genetic haemochromatosis. Biopsies were obtained from iron-loaded non-cirrhotic patients with genetic haemochromatotic and control patients with normal iron stores. Additional duodenal biopsies were obtained from patients with iron deficiency. Immunohistochemical and in situ hybridization analysis for transferrin, transferrin receptor and ferritin was performed. Hepatic transferrin, transferrin receptor and ferritin protein expression was localized predominantly to hepatocytes and was increased in patients with genetic haemochromatosis when compared with normal controls. Interestingly, hepatic ferritin mRNA expression was not increased in these same patients. In the genetic haemochromatotic duodenum, ferritin mRNA and protein was localized mainly to crypt and villus epithelial cells and the level of expression was decreased compared with normal controls, but similar to iron deficiency. Duodenal transferrin receptor mRNA and protein levels colocalized to epithelial cells of the crypt and villus were similar to normal controls. Early in the course of genetic haemochromatosis and before the onset of hepatic fibrosis, transferrin receptor-mediated iron uptake by hepatocytes contributes to hepatic iron overload. Increased hepatic ferritin expression suggests this is the major iron storage protein. While persisting duodenal transferrin receptor expression may be a normal response to increased body iron stores in patients with genetic haemochromatosis, decreased duodenal ferritin levels suggest that duodenal mucosa is regulated as if the patient were iron deficient.

Toxicity of bile acids on the electron transport chain of isolated rat liver mitochondria

The toxicity of hydrophilic (cholate) and lipophilic (deoxycholate, chenodeoxycholate, and lithocholate) bile acids on the function of the electron transport chain was investigated in intact and disrupted rat liver mitochondria. In intact mitochondria, lipophilic bile acids used at a concentration of 100 mumol/L (0.1 mumol/mg protein) inhibited state 3 and state 3u (dinitrophenol-uncoupled) oxidation rates for L-glutamate, succinate, duroquinol or ascorbate/N,N,N',N'-tetramethyl-p-phenylenediamine as substrates. In contrast, state 4 oxidation rates and ADP/oxygen ratios were not significantly affected. At a bile acid concentration of 10 mumol/L (0.01 mumol/mg protein), the state 3 oxidation rate for L-glutamate was decreased in the presence of deoxycholate, chenodeoxycholate or lithocholate, whereas only lithocholate inhibited state 3 oxidation for succinate or duroquinol. In broken mitochondria, inhibition of oxidative metabolism was found for NADH or duroquinol as substrate in the presence of 100 mumol/L lithocholate (0.2 mumol/mg protein) and for duroquinol in the presence of 100 mumol/L chenodeoxycholate. Direct assessment of the activities of the enzyme complexes of the electron transport chain revealed decreased activities of complex I and complex III in the presence of 100 mumol/L deoxycholate or chenodeoxycholate or 10 mumol/L lithocholate. Inhibition of complex IV required higher bile acid concentrations (300 mumol/L for chenodeoxycholate or 30 mumol/L for lithocholate), and complex II was not affected. Both chenodeoxycholate and lithocholate were incorporated into mitochondrial membranes. The phospholipid content of mitochondrial membranes decreased in incubations containing 100 mumol/L (0.1 mumol/mg protein) chenodeoxycholate but was not affected in the presence of 100 mumol/L lithocholate.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversibility of secondary biliary fibrosis by biliodigestive anastomosis in the rat

Biliary cirrhosis with portal hypertension and hepatocellular failure is a well-known complication of extrahepatic obstruction. It is unclear to what extent these changes are reversible by biliodigestive anastomosis. Therefore a rat model of relief of biliary obstruction was developed by performing Roux-en-Y choledochojejunostomy in rats after bile duct obstruction. Patency of the biliodigestive anastomosis was documented by biliary scintigraphy. Microsomal function was assessed in vivo by the aminopyrine breath test and portal hypertension by spleen pulp pressure. Microsomal function was markedly impaired in obstructed animals but recovered after biliodigestive anastomosis. Microsomal cytochrome P450 content paralleled these changes. Similarly, portal hypertension was reversed after successful relief of obstruction. Stereologic analysis showed that biliodigestive anastomosis partially reversed bile ductular proliferation and fibrosis. Studying the time course of recovery showed that restoration of microsomal function was achieved after 2 weeks whereas recovery from portal hypertension required 4 weeks of biliary drainage. Recovery of microsomal function was paralleled by normalization of microsomal lipid composition while resolution of portal hypertension occurred parallel to resolution of the histologic abnormalities.

Reduced activity of the electron transport chain in liver mitochondria isolated from rats with secondary biliary cirrhosis

Mitochondrial metabolism was studied in liver mitochondria isolated from rats with secondary biliary cirrhosis induced by bile duct ligation for 5 wk. State 3 oxidation rates were decreased in mitochondrial preparations from bile duct-ligated rats as compared with sham-operated control rats by 63% and 42% using beta-hydroxybutyrate and succinate as substrates, respectively. In contrast, when the substrate was ascorbate/N,N,N',N'-tetramethyl-p-phenylenediamine state 3 oxidation rates were not affected by bile duct ligation. Oxidation rates after uncoupling with dinitrophenol were decreased for both beta-hydroxybutyrate and succinate as substrates in mitochondria from bile duct-ligated rats. The phosphate potential was reduced in mitochondria from bile duct-ligated rats (12.5 +/- 0.5 vs. 13.6 +/- 0.2 kcal in control and bile duct-ligated rats, respectively; p less than 0.05). The inner mitochondrial membrane of liver mitochondria from rats with secondary biliary cirrhosis contained three times more cholesterol as compared with control rats, whereas the phospholipid composition was essentially unchanged. Mitochondrial protein content expressed per liver (calculated on the basis of activities of mitochondrial enzymes determined in liver homogenate and in isolated mitochondria) was increased by 50% in bile duct-ligated rats as compared with control rats. In conclusion, the function of the electron transport chain in liver mitochondria isolated from rats with secondary biliary cirrhosis is impaired. This decrease could be related to altered lipid composition of the inner mitochondrial membrane.