Search PubMed⌕ Search

Biomedical subjects

M L Hu

Publications and source records attributed to M L Hu.

45 records · Page 3Linked to original sources
PubMed1988

Interactions of gold with cytosolic selenium-containing proteins in rat kidney and liver.

Rats injected with aurothioglucose (ATG) for 5 days were subsequently injected with [75Se]selenious acid and killed after 3 days. Kidney and liver cytosols were chromatographed on Sephadex G-150. 75Se in kidney was associated with high molecular weight (HMW), 85,000 Mr, 26,000 Mr, and 10,000 Mr proteins and with a nonprotein fraction. The elution profile of liver cytosol was similar to that of kidney, but without a 26,000 Mr protein. ATG injection increased the association of 75Se with all fractions of kidney cytosol except the 85,000 Mr fractions, which contained Se-glutathione peroxidase (SeGSHPx) activity; 75Se in liver was increased only in HMW fractions. Unfractionated kidney cytosolic SeGSHPx activity was decreased 14% by ATG injection, but liver enzyme activity was not changed. However, Sephadex G-150 chromatography showed that total and specific activities, respectively, were decreased 28 and 23% in kidney and 25 and 16% in liver. Au coeluted with HMW and 10,000 Mr 73Se-containing kidney proteins; the latter contained 50% of the Au eluted from the column. DEAE Sephacel chromatography of the 10,000 Mr kidney protein showed that both Au and 75Se were tightly associated with metallothionein-like proteins. This study demonstrates the interaction of Au with rat liver and kidney 75Se-containing proteins.

Animals↗
PubMed1988

Aurothioglucose effect on sulfhydryls and glutathione-metabolizing enzymes: in vivo inhibition of selenium-dependent glutathione peroxidase.

Fisher 344 rats injected with a total of 20.8 +/- 1.5 mg of gold (Au) as aurothioglucose over an 8-wk period were used to study the effect of long-term Au treatment on selenium-dependent glutathione peroxidase (SeGSHPx), other enzymes related to GSH metabolism, GSH, nonprotein sulfhydryls, and total sulfhydryls (SH) in various tissues. The indirect coupled assay for SeGSHPx revealed decreased activity in platelets of Au-treated rats but not in other tissues. Inhibition of SeGSHPx by Au is reversible upon dilution. A direct assay of GSH consumption by concentrated tissue cytosols that was developed to minimize enzyme dilution provided evidence of in vivo inhibition of SeGSHPx in kidney and liver from Au-injected rats. Kidneys of these rats had decreased (P less than 0.05) activities of GSSG reductase (36%), gamma-glutamylcysteine synthetase (19%), and gamma-glutamyl transpeptidase (26%), and increased (P less than 0.05) activities of glucose 6-phosphate dehydrogenase (90%) and GSH S-transferase (130%). The reactivity of fresh plasma SH groups with 5,5'-dithiobis-(2-nitrobenzoic acid) increased as a function of injection time. Enhanced SH reactivity suggests that Au may react with protein GSH-disulfides to release GSH. New findings were (i) decreased platelet SeGSHPx and kidney GSSG reductase in aurothioglucose-injected rats, (ii) direct in vivo inhibition of kidney and liver SeGSHPx in aurothioglucose-injected rats, and (iii) no significant correlation between the activity of GSH-metabolizing enzymes and levels of tissue GSH.

Animals↗
PubMed1987

Effect of aurothioglucose on glutathione and glutathione-metabolizing and related enzymes in rat liver and kidney.

The antirheumatic drug aurothioglucose is an inhibitor of the selenoenzyme GSH peroxidase. During chrysotherapy, the decreased levels of erythrocyte GSH and serum sulfhydryls of rheumatoid arthritis patients are normalized concomitant with clinical efficacy. This investigation examined the in vivo and in vitro effect of gold(I) as aurothioglucose on enzymes related to the GSH redox cycle or metabolism. The enzymes measured were GSH peroxidase, GSSG reductase, gamma-glutamyl transpeptidase, gamma-glutamylcysteine synthetase, GSH S-transferase, GSH thiotransferase, glucose-6-phosphate dehydrogenase, superoxide dismutase and catalase. Rats were injected with 30 mumol aurothioglucose/kg body wt. daily for 7 days by intramuscular injection. GSH levels in aurothioglucose-treated rats were 68% higher in erythrocytes (P less than 0.005) and 45% higher in kidney (P less than 0.001) than in control rats. Treatment with aurothioglucose did not elevate plasma or liver GSH. The enzyme activities that were changed by aurothioglucose treatment were GSH peroxidase in kidney (41% decreased, P = 0.005) and liver (13% decreased, P less than 0.05), gamma-glutamyl transpeptidase in kidney (15% decreased, P less than 0.05), and catalase in kidney (58% decreased, P less than 0.001). Kidney glucose-6-phosphate dehydrogenase activity was increased 50% (P less than 0.005) and GSH S-transferase was increased 72% (P less than 0.001). In vitro the only liver enzymes inhibited more than 50% by concentrations of less than 50 microM aurothioglucose were GSH peroxidase (50% inhibited by 25 microM aurothioglucose) and GSH thiotransferase (50% inhibited by 5 microM aurothioglucose). Studies of in vitro enzyme inhibition by aurothioglucose could not be used to predict decreased enzyme activities in vivo. Although decreased activities of two major enzymes that utilize GSH, GSH peroxidase and gamma-glutamyl transpeptidase, coincided with elevated GSH in kidneys of aurothioglucose-treated rats, a direct cause and effect relationship remains speculative.

Animals↗
PubMed1987

Selenium as a sulfhydryl redox catalyst and survey of potential selenium-dependent enzymes.

The ability of selenium (Se) to act as a redox catalyst is an important factor in understanding the biological function of selenoproteins in addition to that of GSH peroxidase. Selenocystine at micromolar levels exhibited pseudothiotransferase activity by enhancing the reduction of 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) by thiols. In contrast, selenite inhibited the reduction of DTNB by thiols. Selenite was more catalytic than selenocystine in the reduction of cytochrome c by GSH, whereas GSH peroxidase was a weak catalyst. Tissues from Se-deficient and Se-supplemented rats were assayed for activities of GSH-thiotransferase, NADPH cytochrome c reductase, formaldehyde dehydrogenase, and a hypothesized GSH cytochrome c reductase. GSH-thiotransferase activity was significantly increased in the liver of Se-deficient rats. No appreciable activity of this enzyme was found in the kidney of rats from either dietary group. No enzymatic activity for cytochrome c reduction by GSH was detected in cytosols, mitochondria, or microsomes from liver and kidney of Se-deficient or Se-supplemented rats. Formaldehyde dehydrogenase was significantly higher in liver cytosols from Se-supplemented rats than from Se-deficient rats. The higher activity was not attributed to Se-containing proteins, but to an unknown small molecular-weight factor. This study did not support the hypothesis that physiological levels of Se may be involved in sulfhydryl-disulfide exchange reactions in vivo, or that selenium may enhance cytochrome c reduction by GSH in vivo.

Animals↗
PubMed1985

Dietary selenium and aniline-induced methemoglobinemia in rats.

Depletion of selenium from rats for 8 weeks decreased blood glutathione peroxidase activity to 5.7% of that in selenium-supplemented (0.5 ppm selenium as Na2SeO3) rats. Aniline (60 mg/kg, i.p.) resulted in no significant difference in methemoglobin and blood reduced glutathione (GSH) levels between Se-deficient and Se-supplemented rats. A lowered aniline dose (36 mg/kg, i.p.) also resulted in no difference in methemoglobin levels. The selenium-deficient rat was able to reduce methemoglobin induced by aniline as efficiently as the selenium-sufficient rat.

Aniline Compounds↗
PubMed1984

Hematologic data of selenium-deficient and selenium-supplemented rats.

Effect of dietary selenium as sodium selenite on in vivo hematological parameters of Sprague-Dawley rats was examined over a 7-month period. Dietary selenium did not alter total hemoglobin, hematocrits, erythrocyte counts, or the osmotic fragility pattern of rat blood. Selenium-excessive (1.0 ppm) rats showed slightly lower but not significantly lower methemoglobin levels than selenium-adequate (0.1 ppm) or selenium-deficient rats. Platelet counts tended to be higher in selenium-excessive rats and lower in selenium-deficient rats than in selenium-adequate rats, but the differences were not statistically significant. No clear trends were observed regarding the effect of dietary selenium on total leukocyte and differential leukocyte counts. After 7 months of dietary treatment blood glutathione peroxidase activity in selenium-deficient rats and in selenium-excessive rats was 16.8% and 142.2% of the activity in selenium-adequate rats. The results indicate that long-term selenium deficiency in rats produces no abnormal hematological parameters or any compensated hemolytic anemia in vivo.

Animals↗
PubMed1983

In vitro hemolysis of rat erythrocytes by selenium compounds.

Rat erythrocytes were incubated in vitro with various selenium compounds at 37 degrees. Hemolysis occurred with some selenium compounds but not with corresponding sulfur analogues. Selenite induced more rapid loss of intracellular glutathione (GSH) than did selenocystine but was less hemolytic. Cystine caused neither loss of intracellular GSH nor hemolysis. Addition of GSH to the incubation medium enhanced hemolysis by selenite and selenium dioxide but inhibited hemolysis by selenocystine. Inclusion of glucose in the incubation medium also inhibited selenocystine-induced lysis of erythrocytes from both selenium-supplemented rats and selenium-deficient rats. The results suggest a relationship between the oxidation of intracellular GSH and the hemolysis by selenocystine, selenite and selenium dioxide.

Animals↗
PubMedDate not supplied

Reaction of cyclohexylamine with hypochlorite and enhancement of oxidation of plasma sulfhydryl groups by hypochlorite in vitro.

In this study we investigated the reaction of cyclamate and its major metabolite, cyclohexylamine (CyhNH2), with NaOCl. NaOCl at 100 microM was allowed to react with various concentrations of cyclamate and CyhNH2, and the reactivity was compared with those of reduced glutathione (GSH) and ascorbic acid. The results showed that CyhNH2 was less reactive with NaOCl than GSH but was slightly more reactive than ascorbic acid at concentrations below 50 microM. CyhNH2 at 75 and 100 microM did not further decrease NaOCl. Cyclamate was much less reactive than CyhNH2, with only 43% loss in NaOCl at 100 microM cyclamate. When human blood plasma was incubated with 0.75 microM NaOCl, inclusion of CyhNH2 enhanced oxidation of sulfhydryl groups in a concentration-dependent manner, with complete oxidation of SH groups at 7.5 mM CyhNH2. Cyclamate had no effect. This enhancement by CyhNH2 suggests the formation of reactive products from the reaction of CyhNH2 with NaOCl. Absorption spectra demonstrated that reaction of CyhNH2 with NaOCl at pH 7.4 produced N-monochloramine, as evidenced by the appearance of a new peak at 245 nm and by the disappearance of the 292-nm peak of NaOCl. Cyclamate, which contains a sulfamic acid instead of a primary amine, also reacted with NaOCl at pH 7.4, but the reaction was much less pronounced and the product was probably not monochloramine since the peak was at 270 nm rather than at 245 nm. Because cyclamate is an important sweetener in many countries for people with diabetes mellitus, the possibility exists that CyhNH2 may enhance oxidation of important proteins by HOCl/OCl-.

Ascorbic Acid↗