Gm Liver Research Articles

Bilirubin mono- and diglucuronide formation by human liver in vitro: assay by high-pressure liquid chromatography.

Bilirubin diglucuronide, the major pigment in human bile is formed in two steps. Bilirubin is converted to bilirubin monoglucuronide by transfer of the glucuronosyl moiety of uridine diphosphoglucuronic acid catalyzed by the microsomal enzyme, uridine diphosphoglucuronate glucuraonosyl transferase (UDP glucuronyl transferase, EC 2.4.1.17). Bilirubin monoglucuaronide is converted to bilirubin diglucuronide in vitro by two enzymatic mechanisms: (a) UDP glucuronyl transferase-mediated transfer of a second mole of glucuronic acid form UDP-glucuronic acid to bilirubin monoglucuronide; (b) dismutation of 2 moles of bilirubin monoglucuronide to 1 mole of bilirubin diglucuronide and 1 mole of unconjugated bilirubin, catalyzed by bilirubin monoglucuronide dismutase (bilirubin glucuronoside glucuronosyl transferase EC 2.4.1.95). Assay methods for the three enzymatic mechanisms in human liver homogenate by high-pressure liquid chromatography analysis of underivatized bilirubin tetrapyrroles have been developed. UDP glucuronyl transferase was activated in five human liver homogenates with digitonin, Triton X-100, or UDP-N-acetylglucosamine. Greatest activation was observed with Triton X-100. The pH optimum for conversion of bilirubin to bilirubin monoglucuronide was 7.4, and UDP glucuronyl transferase activity was 625 +/- 51 nmoles per 20 min per gm liver. At high initial bilirubin concentrations (342 microM), the product of UDP glucuronyl transferase assay with bilirubin as substrate was predominantly bilirubin monoglucuronide. At lower initial bilirubin concentrations (6.5 to 34 microM), up to 15% bilirubin diglucuronide was formed. Glucuronyl transferase-mediated UDP glucuronic acid-dependent conversion of bilirubin monoglucuronide to diglucuronide was assayed using UDP-14-C-glucuronic acid. The pH optimum was 7.4, and the rate was 21 +/- 7 nmoles per gm liver per 20 min. The rate of bilirubin diglucuronide formation by enzymatic dismutation of bilirubin monoglucuronide was 470 +/- 112 nmoles per gm liver per min. The pH optimum was 6.6. The products of enzymatic dismutation were of the IX alpha configuration.

Transport of heme by hemopexin to the liver: Evidence for receptor-mediated uptake

We used carefully defined heme-hemopexin complexes to investigate the role of hemopexin in the catabolism of heme in vivo. Uptake of rabbit [ 59Fe]heme-[ 125I]hemopexin by rat liver was rapid. The liver-associated 125I reached a maximum 5 minutes after injection, nearly 7-fold higher than apo-hemopexin, whereas liver-associated 59Fe increased with time. This together with an inverse relationship of [ 125I]hemopexin in the liver and serum during the course of heme transport suggests that hemopexin was released from the liver back to the circulation. Saturation of uptake with heme-hemopexin, reaching about 170 pmol [ 125I]hemopexin (gm liver) −1 5 minutes after injection of 11 nmol, indicates a receptor-mediated process. We conclude that hemopexin delivers heme to the liver via interaction with a finite number of receptors and returns to the circulation.

IgM levels, specific IgM antibodies and liver involvement in cytomegalovirus infection. Report of 17 patients.

AbstractIgM cytomegalovirus (CMV) antibody titres, immunoglobulin levels and liver function were determined in sera of 17 adults with a virologically and/or serologically proven CMV infection. There seems to be a fairly good correlation between IgM levels and presence of IgM CMV-antibodies in acute stage disease. IgM levels were found to be elevated in 10 out of 13 patients with IgM CMV-antibodies, and normal in the remaining 3 patients with and in all of 4 patients without IgM CMV-antibodies. Specific IgM antibodies could persist for months after the infection while IgM levels declined to the normal range in about 6 weeks. IgM antibodies may well be correlated with liver function disturbance, as liver function was found abnormal in 13 patients, 12 of whom had specific IgM antibodies and 10 elevated IgM levels.

The hypolipidemic effect of SU-13,437 in rats with natural endogenous hypertriglyceridemia.

AbstractThe oral administration of 25 mg 2‐methyl‐2‐[p‐(1,2,3,4‐tetrahydro‐1‐naphthyl)‐phenoxy] propionic acid (SU‐13,437) per kilogram body weight per day in two‐month‐old female rats with naturally occurring hypertriglyceridemia resulted in a 31% decrease (P<0.01) in the serum triglyceride concentration after 14 days of treatment, compared with littermate controls receiving diluent (Polyethylene glycol‐300) only. Phospholipid, cholesterol, free fatty acid, glucose, red blood cell and white blood cell concentrations were similar in the blood of treated and control animals after 14 days of treatment. Liver total and relative weight was increased as a result of SU‐13,437 treatment (P<0.01). The liver total lipid concentration per 10 gm liver decreased (P<0.05) due to a decrease in triglyceride (P<0.01), cholesterol (P<0.01), and free fatty acid (P<0.05) concentration following treatment. The relative liver glycogen concentration was elevated in treated rats at 7 (P<0.01) and 14 (P<0.05) days of treatment.

Stabilization of coenzyme binding by conjugated steroids and carboxylic acids

Estradiol disulfate and diethylstilbestrol disulfate, which interfere with the binding of pyridoxal phosphate to kynurenine apotransaminase and protect the apoenzyme from proteolytic inactivation, retarded the dissociation of pyridoxal phosphate from the holo transaminase in freshly homogenized rat kidney. At higher concentrations, dehydroepiandrosterone sulfate and several carboxylic acids also stabilized pyridoxal phosphate binding. Similar stabilization was observed with partially purified serine transhydroxymethylase of rabbit liver and with the tyrosine-α-ketoglutarate transaminase of freshly homogenized rat liver. Tyrosine transaminase activity in fresh liver homogenates (1 gm liver per 12 mls of water) lost 50% of its activity during incubation for 1 hr at 37°. This activity could not be restored by adding pyridoxal phosphate although the loss could be largely prevented by the presence of 10 −5 M PLP and by 10 −3 M α-ketoglutarate. Benzoate, p-aminobenzoate, α-naphtoate, salicylate, and diethylstilbestrol disulfate, all of which were shown previously to induce hepatic tyrosine transaminase in vivo , retarded the inactivation. Hydrocortisone or diethylstilbestrol disulfate injections also resulted in decreased rates of inactivation in liver homogenates prepared 3 hours after injection as compared with those prepared immediately after injection.