Effect of ethanol and high-fat feeding on hepatic gamma-glutamylcysteine synthetase subunit expression in the rat

Glutathione (GSH) is important in antioxidant defense. A major determinant of the rate of GSH synthesis is the activity of the rate-limiting enzyme, gamma-glutamylcysteine synthetase (GCS). A heavy (HS) and light subunit (LS) make up GCS; oxidative stress regulates both transcriptionally. Cis-acting elements important for the oxidative stress-induced transcriptional up-regulation of both subunits are antioxidant response element (ARE) and activator protein-1 (AP-1). Nuclear factor-kappaB (NF-kappaB) may also regulate the heavy subunit. Chronic ethanol ingestion causes oxidative stress, increases AP-1 expression, and depletes hepatic GSH. Data conflict regarding GSH synthesis and are lacking regarding GCS subunit gene expression. We examined the effect of chronic ethanol ingestion on ARE, AP-1, and NF-kappaB activity and GCS subunit expression. Male Wistar rats were fed an ethanol and high-fat (28.7% cal) diet intragastrically for 9 weeks. Liver GSH level fell by 40%, although GCS activity doubled. GCS-HS mRNA level doubled, whereas GCS-LS mRNA level remained unchanged. Electrophoretic mobility shift assay (EMSA) showed that binding to ARE, AP-1, and NF-kappaB probes all increased. In conclusion, chronic ethanol ingestion increased GCS-HS expression and GCS activity by activating cis-acting elements important for transcriptional up-regulation of GCS-HS. GCS-LS mRNA level remained unchanged despite activation of ARE and AP-1, suggesting that negative transcriptional factors may be involved or the mRNA may be unstable. Despite induction in GCS activity, GSH level fell because of alterations in the other factors important in determining the steady-state GSH level.

Oncospheres of Taenia solium and T. saginata asiatica develop into metacestodes in normal and immunosuppressed mice

Normal and immunosuppressed mice were infected with oncospheres of Taenia saginata asiatica and T. solium. Although normal ICR mice were not susceptible to these two parasites, cysticerci were recovered from the immunosuppressed ones following venous injection. For T. s. asiatica, immunosuppressed ICR mice had an infection rate of 12.5% and six cysticerci of this parasite were recovered from three males. After injection of T. solium oncospheres, a high infection rate of 57% was obtained and 23 cysticerci were collected from 13 male immunosuppressed ICR mice. The immunosuppressed C57 mice had the highest infection rate (100%) and cysticercus recovery rate (2.4%) for T. solium. The infection rate and cysticercus recovery rate in six normal C57 mice were 40% and 3% respectively. The immunosuppressed ICR, Balb/c and C3H mice were also susceptible to T. s. asiatica.

Differential effect of thioacetamide on hepatic methionine adenosyltransferase expression in the rat

Liver-specific and non-liver-specific methionine adenosyltransferase (MAT) are products of two genes, MAT1A and MAT2A, respectively, that catalyze the formation of S-adenosylmethionine (SAM), the principal methyl donor. Mature liver expresses mainly MAT1A. We showed a switch from MAT1A to MAT2A gene expression in human liver cancer cells that may offer a growth advantage. To gain a better understanding of the chronology and significance of the change in MAT expression, we examined changes in hepatic MAT expression after acute treatment of rats with a hepatocarcinogen, thioacetamide (TAA). TAA treatment for 3 weeks did not change the MAT1A mRNA level but reduced the liver-specific MAT protein level to below 30% of control. TAA also acutely reduced the activity of liver-specific MAT when added to normal liver homogenates. In contrast, both the mRNA and protein levels of non-liver-specific MAT were induced. Because liver-specific MAT exhibits a much higher Km for methionine (mmol/L) than non-liver-specific MAT ( approximately 10 micromol/L), MAT activity was decreased at 5 mmol/L but increased at 20 micromol/L methionine concentration. The SAM level, SAM-to-S-adenosylhomocysteine (SAH) ratio, and DNA methylation all fell during treatment. In summary, TAA treatment induced differential changes in hepatic MAT expression. The reduction in liver-specific MAT protein level represents a novel mechanism of inactivation of liver-specific MAT. This along with induction in MAT2A contributed to a fall in the SAM-to-SAH ratio. The resulting DNA hypomethylation may be important in the process of hepatocarcinogenesis.

Regulation of hepatic glutathione synthesis

Glutathione (GSH) is one of the most important intracellular peptides, playing a multifunctional role ranging from antioxidant defense to modulation of immune function. GSH is synthesized by all mammalian cells, and the synthesis of GSH is a tightly regulated process. Two of the major determinants of GSH synthesis are the availability of cysteine, the sulfur amino acid precursor, and the activity of the rate-limiting enzyme, gamma-glutamylcysteine synthetase (GCS). In the liver, the major factors that determine the availability of cysteine are the activities of the membrane transport processes of the three sulfur amino acids--cysteine, cystine (under certain oxidative stress conditions) and methionine--and the conversion of methionine to cysteine through the trans-sulfuration pathway. Since the molecular cloning of GCS, there has been an explosion of knowledge regarding how this enzyme is regulated. Both transcriptional and posttranscriptional regulation play important roles in modulating the activity of this critical cellular enzyme.

Cloning and functional characterization of the 5'-flanking region of human methionine adenosyltransferase 2A gene

Methionine adenosyltransferase (MAT) is a critical cellular enzyme which catalyzes the formation of S-adenosylmethionine, the principal methyl donor. In mammals, two different genes, MAT1A and MAT2A, encode for liver-specific and non-liver-specific MAT, respectively. We have cloned and characterized a 1.4-kb 5'-flanking region of the human MAT2A (GenBank Accession No. AF039088). Two major transcriptional start sites were identified by primer extension and S1 nuclease protection analysis; one was within 10 nucleotides downstream and the other was located at 158 nucleotides upstream from the consensus TATA box, respectively. The promoter is highly GC rich (75%) in the first 300 base pairs and contains several Sp-1 binding sites, a C/EBP, a HSF2, a STATx, a c-Myb, several v-Myb, and numerous GATA consensus binding sites. The human MAT2A promoter was able to efficiently drive luciferase expression in both Jurkat and 293 cells, but sequential deletion analysis of the promoter revealed that different regions of the promoter are important for cell-specific MAT2A expression.

Porcine spleen deoxyribonuclease II. Covalent structure, cDNA sequence, molecular cloning, and gene expression

Porcine spleen DNase II, a lysosomal acid hydrolase, is a noncovalently linked alpha.beta heterodimer (Liao, T.-H. (1985) J. Biol. Chem. 260, 10708-10713). The alpha subunit, after disulfide cleavage, yields two chains, alpha1 and alpha2. The complete amino acid sequences of the alpha1, beta, and alpha2 chains were elucidated by protein sequencing, and the pairings of one interchain disulfide between alpha1 and alpha2 and of three intrachain disulfides in alpha2 were assigned. Six carbohydrate attachment sites, two in beta and four in alpha2, were detected by sugar analyses. The cDNA of DNase II was amplified using primers synthesized on the basis of the amino acid sequences determined. The amplified fragments shown to be a cDNA sequence of 1,292 bases. This cDNA sequence has an open reading frame encoding a 364-amino acid polypeptide containing a putative transmembrane peptide at the NH2-end, two small connecting peptides in the middle, and a peptide at the COOH terminus. These are evidently removed to form mature DNase II. Thus, all three chains in the sequence alpha1, beta, and alpha2 are coded by the same cDNA. When Chinese hamster ovary cells were transfected with a cloned plasmid with an inserted cDNA fragment encoding the entire reading frame, the expressed protein was released into the growth medium as an active form of DNase II.

Changes in methionine adenosyltransferase during liver regeneration in the rat

Liver-specific and non-liver-specific methionine adenosyltransferase (MAT) are products of two genes (MAT1A and MAT2A, respectively) that catalyze the formation of S-adenosylmethionine (SAM), the principal methyl donor. We previously showed that MAT2A expression was associated with more rapid cell growth. Here we examined changes in hepatic MAT gene expression and related consequences after two-thirds partial hepatectomy (PH) in rats. The mRNA levels of both MAT forms increased from 3 to 6 h, but the MAT1A level then fell below baseline from 12 to 24 h, whereas the MAT2A level remained elevated up to 4 days after PH. The increase in the MAT2A mRNA level was due to increased gene transcription and mRNA stabilization. The change in the MAT1A mRNA level was posttranscriptional and did not require de novo protein synthesis. Changes in MAT activity were consistent with an increased amount of MAT isozymes. SAM levels, the ratio of SAM to S-adenosylhomocysteine (SAH), and DNA methylation fell from 6 to 24 h, whereas SAH levels increased slightly at 12 and 24 h after PH. Both increased SAM utilization and MAT2A gene expression likely contributed to the fall in SAM.

Differential expression of methionine adenosyltransferase genes influences the rate of growth of human hepatocellular carcinoma cells

Methionine adenosyltransferase (MAT) catalyzes the formation of S-adenosylmethionine (SAM), the principal methyl donor, and is essential to normal cell function. The two forms of MAT, liver specific and non-liver specific, are products of two genes, MAT1A and MAT2A, respectively. We have reported a switch from MAT1A to MAT2A gene expression in human liver cancer cells. In the current work, we examined whether the type of MAT expressed by the cell influences cell growth. HuH-7 cells were stably transfected with MAT1A and were subsequently treated with antisense oligonucleotides directed against MAT2A. MAT2A antisense treatment reduced the amount of MAT2A mRNA by 99% but had no effect on MAT1A mRNA. Cell growth and DNA synthesis rates were reduced by approximately 20-25% after transfection with MAT1A and by an additional 30-40% after MAT2A antisense treatment. SAM level and SAM:S-adenosylhomocysteine (SAH) ratio increased by 50-75% after MAT1A transfection and by an additional 60-80% after MAT2A antisense treatment. DNA methylation changed in parallel to changes in SAM level and SAM:SAH ratio. Supplementing untransfected HuH-7 cells with SAM in the culture medium increased SAM level, SAM:SAH ratio, and DNA methylation and decreased cell growth and DNA synthesis. In conclusion, cell growth is influenced by the type of MAT expressed. The mechanism likely involves changes in SAM:SAH ratio and DNA methylation.

The Rana catesbeiana rcr gene encoding a cytotoxic ribonuclease. Tissue distribution, cloning, purification, cytotoxicity, and active residues for RNase activity

Rana catesbeiana ribonuclease (RC-RNase) is a pyrimidine-guanine sequence-specific ribonuclease found in R. catesbeiana (bullfrog) oocytes. It possesses both ribonuclease activity and cytotoxicity against tumor cells. We report here for the first time the cloning of RC-RNase cDNA from liver rather than from oocytes where RC-RNase is stored. An internal fragment of cDNA was obtained by reverse transcription-PCR using deduced oligonucleotides as primers. Full-length cDNA was obtained by 5'- and 3'-RACE technique. The cDNA clone, named rcr gene, contained a 5'-untranslated region, a putative signal peptide (22 amino acids), a mature protein (111 amino acids), a 3'-untranslated region, and a polyadenylation site. The cDNA which encoded the mature protein was fused upstream with a modified pelB signal peptide DNA and inserted into pET11d for expression in Escherichia coli strain BL21(DE3). The secretory RC-RNase in the culture medium was enzymatically active and was purified to homogeneity. The recombinant RC-RNase had the same amino acid sequence, specific activity, substrate specificity, antigenicity, and cytotoxicity as that of native RC-RNase from frog oocytes. Amino acid residues His-10, Lys-35, and His-103 are involved in RC-RNase catalytic activity. Ribonucleolytic activity was involved in and may be essential for RC-RNase cytotoxicity. DNA sequence analysis showed that RC-RNase had approximately 45% identity to that of RNase superfamily genes. This indicates that RC-RNase is a distinct ribonuclease gene in the RNase superfamily.

Cloning, sequencing and expression of a cDNA encoding bovine pancreatic deoxyribonuclease I in Escherichia coli: purification and characterization of the recombinant enzyme

The bovine pancreatic (bp-) DNase I gene has been cloned from bp-cDNA and expressed in E. coli. A polynucleotide sequence of 1295 base pairs was deduced from clones of the cDNA. The sequence showed an open reading frame which can be translated as a 282-amino acid polypeptide, including a hydrophobic signal peptide and the polypeptide of bp-DNase I. An expression plasmid was constructed by inserting into the vector pET-15b, a cDNA fragment coding for bp-DNase I ligated with a hexanucleotide coding for Met-Ala at the 5'-end. The plasmid was transformed into E. coli strain DH5alpha and the active recombinant bovine (rb-) DNase I was produced after induction of protein synthesis. From the induced culture medium, rb-DNase I was purified by chromatography on a Mono Q column. The purified rb-DNase I showed a molecular mass of 29 kDa and had the same specific activity as bp-DNase I. The NH2-terminus of rb-DNase I was Ala, not Met, and at position 19, corresponding to the carbohydrate attachment site of bp-DNase I, Asn was not glycosylated.

Changes in glutathione homeostasis during liver regeneration in the rat

We have shown previously that plating primary cultures of rat hepatocytes under low density, which stimulates hepatocytes to shift from the G0 to the G1 phase of the cell cycle, resulted in increased levels of glutathione (GSH) and cysteine, and increased activity of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis (Lu et al., Am. J. Physiol. 1992;263:C1181-C1189). In the current work we examined changes in GSH homeostasis after two-thirds partial hepatectomy (PH). Male Sprague-Dawley rats underwent two-thirds PH or sham operation. GSH, oxidized glutathione (GSSG), cysteine, GSH efflux, DNA synthesis, changes in GCS subunit messenger RNA (mRNA), and protein levels were measured 12 and 24 hours after PH. Both liver GSH and cysteine levels were doubled at 12 hours and remained elevated at 24 hours after PH. GSSG levels also increased, but the ratio of GSH to GSSG levels remained unchanged. The increase in GSH and cysteine levels preceded the increase in DNA synthesis. Sinusoidal GSH efflux was unchanged after two-thirds PH, but biliary GSH efflux decreased. However, total GSH efflux was minimally altered after two-thirds PH. The increase in GSH can be largely accounted for by the increase in both cysteine availability and the activity of GCS. The steady-state mRNA and protein levels of the GCS heavy subunit were increased at 12 hours after PH. The mRNA level of the GCS light subunit was unchanged. In summary, early in the course of liver regeneration the steady-state hepatic GSH levels double because of an increase in the biosynthesis of GSH.

Molecular cloning of a defective hepatitis C virus genome from the ascitic fluid of a patient with hepatocellular carcinoma

A defective hepatitis C virus (HCV) genome in the ascitic fluid of a patient with hepatocellular carcinoma was cloned and sequenced up to the 3' poly(U) stretch. When compared with the published Taiwanese HCV sequence, this defective genome contained deletions of single nucleotides at eight sites, double nucleotides at two sites, triple nucleotides at four sites, quadruple nucleotides at one site and replacement of a short stretch of sequence at one site. For comparison, the corresponding regions containing these mutations were also cloned from a serum sample from this patient. Except for deletions of two triple nucleotides in the hypervariable region, the reading frames of all serum-derived clones were intact. The defective HCV genome encoded a truncated core protein with 90 amino acid residues (the last 20 amino acid residues came from a different reading frame), whereas the serum-derived genome encoded a full-length core protein. When expressed in Huh-7 cells, these two proteins were localized to the nucleus and cytoplasm, respectively. Using specific primer-sets, ascites- and serum-derived genomes were each detected alone in ascitic fluid and serum samples, respectively, whereas both sequences were present in ascitic mononuclear cells. The defective sequence thus constituted the major virus population in the ascitic fluid whereas a putative helper genome coexisted with it inside the ascitic mononuclear cells. This sequence is possibly a defective and interfering genome.

Fish oil lowers plasma lipid concentrations and increases the susceptibility of low density lipoprotein to oxidative modification in healthy men

This study was designed to investigate the effects of fish oil on plasma lipid and lipoprotein concentrations and on the susceptibility of low density lipoprotein (LDL) to oxidation in normolipidemic young men. Two groups of eight men were assigned to a low cholesterol (50 mg/4187 kJ) or a high cholesterol (250 mg/4187 kJ) diet. Both groups consumed n-6 polyunsaturated fatty acid (PUFA)-rich soybean oil diets for 3 weeks, followed by n-3 PUFA-rich fish oil diets for 3 weeks. The fish oil diet significantly reduced the plasma concentrations of total cholesterol, total triglyceride, very low density lipoprotein (VLDL)-cholesterol, and VLDL-triglyceride (p < 0.05) compared with the soybean oil diet, irrespective of dietary cholesterol content. The fish oil diet increased incorporation of eicosapentachoic acid into LDL particles, shortened the lag time for conjugated diene formation in LDLs, and increased the production of thiobarbituric acid-reactive substances after exposure of LDL to 10 mumol/L Cu2+. Gel chromatographic analysis indicated that LDL particles obtained at the end of the fish oil diet were smaller than those obtained after the soybean oil diet. There was no significant difference between the low and high cholesterol groups in the parameters mentioned above during the 6-week treatment period. Our results suggest that fish oil lowers plasma lipid levels significantly but results in a form of LDL that is more susceptible to oxidation in vitro.

Differential regulation of gamma-glutamylcysteine synthetase heavy and light subunit gene expression

gamma-Glutamylcysteine synthetase (GCS) is the rate-limiting enzyme in the biosynthesis of glutathione and is composed of a heavy and a light subunit. Although the heavy subunit is enzymically active alone, the light subunit plays an important regulatory role by making the holoenzyme function more efficiently. In the current study we examined whether conditions which are known to influence gene expression of the heavy subunit also influence that of the light subunit, and the mechanisms involved. Treatment of cultured rat hepatocytes with hormones such as insulin and hydrocortisone, or plating hepatocytes under low cell density increased the steady-state mRNA level of the heavy subunit only. Treatment with diethyl maleate (DEM), buthionine sulphoximine (BSO) and t-butylhydroquinone (TBH) increased the steady state mRNA level and gene transcription rates of both subunits. These treatments share in common their ability to induce oxidative stress and activate nuclear factor kappa B (NF-kappa B). Treatment with protease inhibitors 7-amino-1-chloro-3-tosylamido-2-heptanone (TLCK) or L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK) had no influence on the basal NF-kappa B and GCS subunit mRNA levels, but blocked the activation of NF-kappa B by DEM, BSO and TBH, and the increase in GCS heavy subunit mRNA level by BSO and TBH. On the other hand, the DEM-, BSO- and TBH-induced increase in GCS light-subunit mRNA level was unaffected by TLCK and TPCK. Thus only the heavy subunit is hormonally regulated and growth sensitive, whereas both subunits are regulated by oxidative stress. Signalling through NF-kappa B is involved only in the oxidative-stress-mediated changes in the heavy subunit gene expression.

Progressive defect in biliary GSH secretion in streptozotocin-induced diabetic rats

This study examined the effect of streptozotocin-induced diabetes on biliary reduced glutathione (GSH) efflux. Biliary GSH efflux was measured before and after acivicin, an irreversible inhibitor of gamma-glutamyl transpeptidase (GGT). One week after streptozotocin treatment, liver GGT activity doubled in diabetic rats but was inhibited by approximately 90% after acivicin to levels comparable to controls. Despite maximal GGT inhibition, biliary GSH efflux in untreated diabetic rats decreased progressively to approximately 10% of control levels by week 4 and was partially restored by insulin. The mechanism for the decrease in biliary GSH efflux was not increased paracellular permeability. GSH transport kinetics, ATP-stimulated taurocholate, and oxidized glutathione (GSSG) transport in canalicular liver plasma membrane prepared from diabetic and control rats were similar. Inhibition of protein kinase C (PKC) with high-dose H-7 increased biliary GSH efflux in diabetic animals to near control basal levels. In conclusion, streptozotocin-induced diabetic rats exhibit a progressive impairment in biliary GSH transport. One of the responsible mechanisms is heightened PKC tone in diabetic animals.

Regulation of gamma-glutamylcysteine synthetase by protein phosphorylation

We previously reported that the activity of gamma-glutamylcysteine synthetase (GCS; EC 6.3.2.2), the rate-limiting enzyme in GSH synthesis, can be acutely inhibited approximately 20-40% by agonists of various signal transduction pathways in rat hepatocytes [Lu, Kuhlenkamp, Garcia-Ruiz and Kaplowitz (1991) J. Clin. Invest. 88, 260-269]. We have now examined the possibility that GCS is phosphorylated directly by activation of protein kinase A (PKA), protein kinase C (PKC) and Ca2+/calmodulin-dependent kinase II (CMK). Phosphorylation of GCS was studied using both purified rat kidney GCS and cultured rat hepatocytes by immunoprecipitating the reaction product with specific rabbit anti-(rat GCS heavy subunit) (anti-GCS-HS) antibodies. All three kinases, PKA, PKC and CMK, phosphorylated rat kidney GCS-HS in a Mg(2+)-concentration-dependent manner, with the highest degree of phosphorylation occurring at 20 mM Mg2+. The maximum incorporation of phosphate in mol/mol of GCS was 1.17 for PKA, 0.70 for PKC and 0.62 for CMK. The degree of phosphorylation was correlated with the degree of loss of GCS activity, and no additional inhibition occurred when GCS was phosphorylated by all three kinases, suggesting that the kinases phosphorylated the same site(s). Phosphoamino analysis showed that all three kinases phosphorylated serine and threonine residues. Two-dimensional phosphopeptide mapping demonstrated that all three kinases phosphorylated the same five peptides, both PKA and PKC phosphorylated two other peptides, and only PKA phosphorylated one additional peptide. Phosphorylation of GCS decreased its Vmax for cysteine and glutamate without changing its K(m). Finally, treatment of cultured rat hepatocytes with dibutyryl cAMP and phenylephrine significantly increased the phosphorylation of GCS, suggesting a potentially important physiological role. In summary, we have demonstrated that GCS is phosphorylated and suggest that phosphorylation/dephosphorylation may regulate GCS activity.

Changes in S-adenosylmethionine synthetase in human liver cancer: molecular characterization and significance

S-adenosylmethionine synthetase (SAMS) catalyzes the formation of S-adenosylmethionine (SAM) and is essential to normal cell function. There are two forms of SAMS, liver-specific and nonliver-specific (often referred to as "kidney"), which are products of two different genes. SAMS isoenzymes differ greatly in kinetic parameters and sensitivity to inhibition by methionine analogs. The current work studied changes in SAMS and their significance in liver cancer. Northern blot analysis showed that while normal liver expresses only liver-specific SAMS, both HepG2 and HuH-7 cells express only nonliver-specific SAMS. Absence of liver-specific SAMS messenger RNA (mRNA) was not because of gene deletion or rearrangement but complete lack of gene transcription. Reverse-transcription polymerase chain reaction (RT-PCR) with liver- and kidney-specific SAMS primers showed that liver-specific SAMS mRNA was absent with only kidney SAMS mRNA present in HepG2, HuH-7, Hep3B, and HuH-1 cells, and four consecutive hepatocellular carcinoma (HCC) specimens. Normal liver tissues from the same patients express both forms of SAMS mRNA. As a result of the change in SAMS expression, SAMS activity was higher in HepG2 and HuH-7 cells at physiologically relevant methionine concentrations but lower at high (mmol/L) methionine concentrations than rat hepatocytes. Treatment with ethionine and seleno-D,L-ethionine, two inhibitors known to have I50 values 50 to 60 times lower against SAMS purified from Novikoff hepatoma cells as compared with SAMS purified from normal rat liver, resulted in increased cell lysis in HepG2 and HuH-7 cells but not cultured rat hepatocytes. These agents did not affect cellular adenosine triphosphate (ATP) levels but inhibited SAMS activity in HepG2 and HuH-7 cells when added to their protein extracts. In summary, expression of SAMS is altered in human liver cancer. This occurrence may provide a potentially exploitable target for cancer chemotherapy.

A high cholesterol, (n-3) polyunsaturated fatty acid diet induces hypercholesterolemia more than a high cholesterol (n-6) polyunsaturated fatty acid diet in hamsters

This study was designed to study the effects of (n-3) polyunsaturated fatty acids (PUFA) on plasma and liver lipids, particularly lipoprotein cholesterol concentrations, in hamsters. Diets rich in (n-3) PUFA (21 g/100 g fatty acid) or (n-6) PUFA (37.4 g/ 100 g fatty acid) with or without 5 g/kg cholesterol (C) supplements were given for 4 wk to male hamsters weighing 70-90 g. The VLDL- and (IDL + LDL)-cholesterol concentrations were 114 and 128% higher in hamsters fed the (n-3) PUFA + C diet than in those fed the (n-6) PUFA + C diet. However, these differences were not observed when cholesterol was not supplemented. Hamsters fed the (n-3) PUFA diet had significantly lower plasma and hepatic triglyceride concentrations than those fed the (n-6) PUFA diet. Concentrations were comparable in hamsters fed (n-6) PUFA + C and (n-3) PUFA + C. Hepatic cholesteryl esters were significantly lower, while hepatic microsomal acyl-CoA:cholesterol acyltransferase activity and VLDL cholesteryl esters were significantly higher in hamsters fed the (n-3) PUFA + C diet than in those fed the (n-6) PUFA + C diet. Our results demonstrate that elevation of VLDL- and (IDL + LDL)-cholesterol in hamsters by (n-3) PUFA, compared with (n-6) PUFA, is dependent on dietary cholesterol supplementation and may be due to decreased catabolism of these lipoproteins.

Alterations in glutathione homeostasis in mutant Eisai hyperbilirubinemic rats

Eisai hyperbilirubinemic rats (EHBR) are mutant Sprague-Dawley rats that exhibit impaired biliary organic anion and reduced glutathione (GSH) secretion. In addition, liver GSH levels are twice that of age-matched controls. The mechanisms for the defect in biliary GSH secretion and the increase in cell GSH are not fully understood. We previously showed that canalicular membrane-enriched vesicles isolated from EHBR livers exhibited normal GSH transport. In the present study, we examined the steady-state rat canalicular reduced glutathione transporter (RcGshT) messenger RNA (mRNA) and protein levels, as well as the mechanisms for the increase in cell GSH. Both Northern and Western blot analyses of EHBR livers showed nearly identical RcGshT mRNA and polypeptide levels, respectively, as compared with controls. Treatment with phenobarbital, which increased steady-state RcGshT mRNA by five- to sixfold, RcGshT polypeptide, and biliary GSH secretion by onefold in controls, had a smaller effect on steady-state RcGshT-mRNA level in EHBR (by 1.5-fold) and did not increase RcGshT polypeptide or biliary GSH secretion. In examining possible mechanisms for increased liver GSH, both cysteine level and gamma-glutamylcysteine synthetase (GCS) activity were significantly higher than controls, while the activity of GSH synthetase was unchanged. Northern and Western blot analyses also showed increased steady-state GCS heavy subunit (GCS-HS) mRNA and polypeptide levels, respectively. In addition to liver, GSH levels in kidney, duodenal, jejunal, and ileal mucosa of EHBR were 200% to 300% of age-matched control rats. GCS activity was also increased in kidney cytosol of EHBR. Thus, the defect in biliary GSH secretion in EHBR most likely is either at the posttranslational level of RcGshT or in the inhibition exerted by retained endogenous organic anions. In addition, there is a widespread up-regulation of GSH synthesis capacity in the tissues of EHBR.

Role of two recently cloned rat liver GSH transporters in the ubiquitous transport of GSH in mammalian cells

Recently our laboratory has cloned both the rat canalicular and sinusoidal GSH transporters (RcGshT and RsGshT, respectively; Yi, J., S. Lu, J. Fernandez-Checa, and N. Kaplowitz. 1994. J. Clin. Invest. 93:1841-1845; and 1995. Proc. Natl. Acad. Sci. USA. 92:1495-1499). The current work characterized GSH transport and the expression of these two GSH transporters in various mammalian cell lines. The average cell GSH levels (nmol/10(6) cells) were 25, 22, 32, 13, and 13 in HepG2, HeLa, CaCo-2, MDCK, and Cos-1 cells, respectively. GSH efflux was temperature dependent and averaged 0.018, 0.018, 0.012, 0.007, and 0.019 nmol/10(6) cells/min from HepG2, HeLa, CaCo-2, MDCK, and Cos-1 cells, respectively. Dithiothreitol (DTT), which stimulates rat sinusoidal GSH efflux, stimulated GSH efflux only in HepG2 and HeLa cells which was partially reversed by subsequent cystine treatment. GSH uptake (1 mM plus 35S-GSH) was temperature dependent, linear up to 45 min, and Na+-independent with average rates of 1.12, 0.91, 0.45, and 0.45 nmol/10(6) cells/30 min for HepG2, HeLa, CaCo-2, MDCK, and Cos-1 cells, respectively. BSP-GSH (2mM), which cis-inhibits sinusoidal GSH uptake in rat liver and HepG2 cells, inhibited GSH uptake only in HeLa cells. mRNA and polypeptide of RcGshT are expressed in all cells whereas those of RsGshT are expressed only in HepG2 and HeLa cells. In conclusion, bidirectional GSH transport, mediated by the "canalicular" GSH transporter, is ubiquitous in mammalian cells. Sinusoidal GSH transporter expression is more restricted, being present in HepG2 and HeLa cells. DTT and BSP-GSH affect GSH transport only in cells expressing the sinusoidal transporter confirming their selective action on this transporter.

Lipoprotein responses to fish, coconut and soybean oil diets with and without cholesterol in the Syrian hamster

Thirty-six young male Syrian hamsters were fed with test diets containing coconut oil, soybean oil or fish oil with and without 0.5% cholesterol for 6 weeks. Without dietary cholesterol supplementation, animals on the fish oil diet had significantly lower plasma total triglyceride (TG) and total cholesterol than those on the coconut oil or soybean oil diet. The decrease of TG was seen mainly in the very low density lipoprotein (VLDL) fraction. The degree of decrease in cholesterol was similar in all of the lipoprotein fractions. With 0.5% dietary cholesterol supplementation, there was no significant difference in plasma TG level among the three dietary groups. However, the fish oil group had significantly higher plasma cholesterol than the coconut oil and soybean oil groups. The increase of cholesterol was mainly in the VLDL and low density lipoprotein (LDL) fractions. In contrast to the plasma cholesterol level, the hepatic cholesteryl ester content was significantly lower in the cholesterol-supplemented fish oil group than in the coconut oil and soybean oil counterparts. The cholesterol-supplemented fish oil group showed higher liver microsomal acyl-coenzyme A:cholesterol acyltransferase activity than the other two groups, while there was no significant difference in the excretion of fecal neutral and acidic sterols among the three dietary groups.

[Disseminated Strongyloides stercoralis infection mimicking pneumonia]

Strongyloides stercoralis is an intestinal nematode. In an immunocompetent host, Strongyloides infections usually produce only mild gastrointestinal symptoms. However, in an immunocompromised host, widespread dissemination of larvae to the extra-intestinal organs may occur. If unrecognized, the mortality rate is high. Here we report a case of disseminated strongyloidiasis in a chronic obstructive pulmonary disease (COPD) subject whose chest radiograph demonstrated multiple pneumonic patches and interstitial infiltrates. Strongyloides larvae were found in stool, sputum, and urine, and embryonated eggs were also found in sputum. The patient was treated successfully with mebendazole and alben albendazole. In conclusion, although high mortality rate is noted in disseminated strongyloidiasis, it is still a curable disease when early diagnosis and treatment could be made.

Effects of 3-morpholinosydnonimine-N-ethylcarbamide on hypoxia-induced mechanical and electric responses of isolated pig coronary artery

AIM

To study effects of 3-morpholinosydnonimine-N -ethylcarbamide (SIN-1) on hypoxia-induced mechanical and electric activities of the isolated pig coronary artery.

METHODS

Mechanical tension and membrane potential were measured simultaneously.

RESULTS

Hypoxia initially caused a transient vascular smooth muscle cell membrane hyperpolarization followed by a membrane depolarization in isolated pig coronary artery. Subsequent addition of SIN-1 100 mumol . L-1 or verapamil (Ver) 10 mumol . L-1 led to membrane repolarization and relaxation of the vascular smooth muscle. Nitro-L-arginine (NLA) 0.2 mmol . L-1 and KCI 40 mmol . L-1 also induced membrane depolarization and vasoconstriction, which were similarly suppressed by SIN-1 or Ver.

CONCLUSION

Hypoxic contractile response in isolated pig coronary artery is mediated by an increased Ca2+ influx via suppression of nitric oxide release.

Bidirectional glutathione transport by cultured human retinal pigment epithelial cells

PURPOSE

To characterize glutathione (GSH) transport by cultured human retinal pigment epithelial (HRPE) cells.

METHODS

Cultured HRPE cells were pretreated with acivicin for GSH efflux and with buthionine sulfoximine for GSH uptake to prevent the breakdown and resynthesis of GSH. Efflux was measured by the linear rate of accumulation of GSH in the supernatant; uptake was measured using [35S] GSH plus varying concentrations of GSH. Molecular forms were verified by high-performance liquid chromatography. HRPE cell mRNA was probed for the presence of the two recently cloned rat sinusoidal and canalicular GSH transporters, (RsGshT and RcGshT), by Northern blot analysis.

RESULTS

Glutathione efflux was temperature dependent (undetectable at 4 degrees C), and its averaged 23 +/- 3.3 pmol/10(6) cells/minute or 10% of the total GSH effluxed per hour (total cell GSH = 13.6 +/- 1.5 nmol/10(6) cells). Efflux was not influenced by dithiothreitol or sulfobromophthalein-reduced GSH adduct, agents known to affect liver sinusoidal GSH transport. Glutathione uptake was linear up to 45 minutes and was temperature dependent. The difference between 37 degrees C and 4 degrees C uptake values represented true uptake. Glutathione uptake (2 microCi/ml + 1 mM mass) was Na independent and was inhibited significantly by phenol-3,6-dibromphthalein disulfonate. The kinetics of GSH uptake was assessed by measuring uptake with 35S-GSH and 0.05 to 40 mM extracellular GSH for 30 minutes. Uptake was saturable with Vmax = 18.7 +/- 1.7 nmol/10(6) cells/30 minutes, Km = 12.1 +/- 1.9 mM, n (binding site) = 1. On Northern blot analysis, HRPE cells express mRNA for RcGshT but not for RsGshT.

CONCLUSIONS

The similarities in functional characteristics of GSH transport and the presence of RcGshT-like mRNA suggest GSH transport in HRPE cells is mediated by a RcGshT homolog. Although the transporter can operate bidirectionally, it is expected to be a net efflux pump under normal physiologic conditions because the intracellular GSH concentration is much higher.

Hormonal and cell density regulation of hepatic gamma-glutamylcysteine synthetase gene expression

We previously reported that the activity of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis, is under both hormonal and cell density regulation in cultured rat hepatocytes. Specifically, the addition of insulin or hydrocortisone to culture media or the lowering of the initial plating cell density increased cell GSH by increasing the activity of GCS. In the present study, we examined the molecular mechanism of these effects. To determine whether the increase in GCS activity is associated with an increase in GCS heavy subunit (GCS-HS) mRNA expression, the steady state mRNA levels of GCS-HS were examined with the use of Northern blots. After 24-hr treatment of high density (0.6 x 10(5) cells/cm2) cultured rat hepatocytes with insulin (1 micrograms/ml) or hydrocortisone (50 nM), the steady state GCS-HS mRNA level increased by approximately 1-2 fold. When the plating density was decreased to 0.1 x 10(5) cells/cm2, the steady state GCS-HS mRNA level also increased by 1-2 fold 24 hr later. An increase in the steady state GCS-HS mRNA level was found within 4 hr of either hormonal treatment or cell density manipulation. The increase in steady state GCS-HS mRNA level resulted from increased gene transcription, as the transcriptional rates of GCS-HS after hormonal or cell density manipulation were increased by 2-3-fold, whereas the rates of GCS-HS mRNA degradation remained unchanged. Western blotting confirmed the increase in GCS-HS protein level after hormone treatment or lowering of plating cell density. When examined in vivo, the steady state GCS-HS mRNA level decreased by 50% in a rat in which diabetes had been induced with streptozotocin for 1 week; this was prevented with insulin replacement. In summary, GCS-HS gene expression is under both hormonal and cell density regulation.

Inhibition of reduced glutathione synthesis by cyanobacterial alkaloid cylindrospermopsin in cultured rat hepatocytes

Cylindrospermopsin (CY) is a naturally occurring alkaloid produced by the cyanobacterium Cylindrospermopsis raciborskii, which has been linked to an outbreak of hepatoenteritis in humans. We previously showed that CY is cytotoxic to primary cultures of rat hepatocytes and that CY lowers cell reduced glutathione (GSH) at nontoxic doses. Lower cell GSH also potentiates CY-induced cytotoxicity (Runnegar et al., Biochem Biophys Res Commun 201: 235-241, 1994). Our current work examined the mechanism of the fall in cell GSH induced by CY. We excluded several possible explanations for the loss in GSH, namely increased formation of oxidized glutathione (GSSG), increased GSH efflux, hidden forms of GSH, decreased GSH precursor availability, or decreased cellular ATP level. To address whether the fall in GSH was due to decreased GSH synthesis or increased GSH consumption, we examined the rate of fall in total GSH after 5 mM buthionine sulfoximine (BSO, an irreversible inhibitor of GSH synthesis) treatment. The rates of fall in total GSH (nmol/10(6) cells/hr) were 8.2 +/- 2.5, 6.0 +/- 1.7 and 5.9 +/- 1.3 for control, 2.5 microM and 5 microM CY-pretreated cells, respectively. This suggests that the fall in GSH induced by CY was due to the inhibition of GSH synthesis rather than increased consumption, because in the latter case the rate of fall in GSH would have been accelerated by CY pretreatment. Furthermore, excess GSH precursor (20 mM N-acetylcysteine), which supported GSH synthesis in control cells, did not prevent the fall in GSH or toxicity induced by CY. Treatment of cells with the cytochrome P450 inhibitor alpha-naphthoflavone protected partially from CY-mediated toxicity and from the fall in cell GSH. Thus, it is likely that cytochrome P450 is involved in the metabolism of CY, and the metabolite(s) that is generated may be more toxic and/or potent in inhibiting GSH synthesis. Inhibition of GSH synthesis is most likely an important factor in the cytotoxicity of CY.

Specificity and directionality of thiol effects on sinusoidal glutathione transport in rat liver

In rats the sinusoidal glutathione (GSH) carrier transports GSH bidirectionally, and its activity is influenced by the thiol-disulfide status; the Vmax of sinusoidal GSH efflux was increased by dithiothreitol (DTT) and decreased by cystine. In the present work we examined the specificity and directionality of the thiol effect. Using in situ perfused livers, we found that 1 mM DTT and other dithiols, including 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol, stimulated sinusoidal GSH efflux by 200-500% but dihydrothioctic acid, which is negatively charged, had no effect. Uncharged or positively charged monothiols (2 mM), such as dimercaprol, monothioglycerol, 2-mercaptoethanol, 3-mercapto-2-butanol, 1-mercapto-2-propanol, and cysteamine, also exerted a stimulatory effect on sinusoidal GSH efflux. In contrast, monothiols containing a negatively charged substituent, such as penicillamine, captopril, N-acetylcysteine, mercaptopropionylglycine, mercaptoethanesulfonic acid, mercaptoacetic acid, and mercaptopropionic acid, had no effect. The thiol moiety was essential for activity, inasmuch as ethanol, propanol, propanediol, and glycerol had no effect on sinusoidal GSH efflux. The effect of DTT or cystine pretreatment (2 mM or 0.5 mM, respectively, for 30 min) on GSH uptake was then examined using cultured rat hepatocytes. The linear rate of [35S]GSH uptake and the concentration dependence were measured after cells were pretreated with acivicin (0.5 mM, for 15 min) and buthionine sulfoximine (10 mM, 15 min), to prevent breakdown and resynthesis of GSH from precursors, respectively. Uptake buffer also contained 20 mM alpha-(methylamino)isobutyric acid and 20 mM threonine (inhibitors of amino acid transport systems A and ASC, respectively), to prevent uptake of cysteine. Pretreatment with DTT decreased the Vmax of GSH uptake by approximately 50% (control Vmax value, 24 nmol/10(6) cells/30 min), whereas the Km remained unaffected (approximately 8 mM). Cystine pretreatment had no influence on GSH uptake but inhibited efflux. In conclusion, the presence of at least one thiol group and the absence of negative charge are required to stimulate sinusoidal GSH efflux. The direction of GSH transport is modulated by the thiol-disulfide status, so that thiol reduction changes the GSH transporter from a bidirectional GSH transporter into a preferentially unidirectional (outward) transporter by inhibiting uptake while stimulating efflux and thiol oxidation favors inward transport by inhibiting only efflux.

The role of glutathione in the toxicity of a novel cyanobacterial alkaloid cylindrospermopsin in cultured rat hepatocytes

Cylindrospermopsin (CY) is a newly isolated alkaloid produced by the cyanobacterium Cylindrospermopsis raciborskii, which has been linked to an outbreak of hepatoenteritis in man. The current work examined the suitability of primary cultures of rat hepatocytes as an in vitro model for studying the cytotoxicity of CY. We found that CY (3.3-5.0 microM) caused significant cell death (40-67% of cells by LDH release) in cultured hepatocytes after 18 hr incubation. While investigating possible mechanisms for CY toxicity, we found that lower, nontoxic doses of CY (1.6-2.5 microM) decreased cell glutathione (GSH) to about 50% of control. For toxic doses (5 microM), the loss of GSH preceded the onset of toxicity by six hr. Lowering cell GSH predisposed cells to CY toxicity. In conclusion, cultured hepatocytes are a suitable model for studies of CY cytotoxicity and GSH is involved in the detoxification of CY.

Comparison of sulfur amino acid utilization for GSH synthesis between HepG2 cells and cultured rat hepatocytes

HepG2 cells are widely used as a model of human hepatocytes for studies of drug metabolism and toxicity. However, GSH metabolism in HepG2 cells is poorly characterized. This report describes the utilization of sulfur amino acids for GSH synthesis in HepG2 cells. In contrast to primary cultures of rat hepatocytes, which rely mostly on methionine for GSH synthesis, HepG2 cells use cystine. Their inability to utilize methionine for GSH synthesis was not due to lack of methionine uptake or low cellular ATP levels, but rather to the lack of S-adenosyl-methionine synthetase activity. When HepG2 cells were cultured overnight in medium containing cystine as the only sulfur amino acid, addition of glutamate or acivicin had minimal to no effect on cell GSH; however, addition of threonine significantly depleted cell GSH. When cystine (0.18 mM) uptake was measured, glutamate (2.5 mM), which inhibited cystine uptake in cultured rat hepatocytes, had a minimal effect in HepG2 cells. Instead, threonine (20 mM) strongly inhibited the apparent uptake of cystine by HepG2 cells. Strong inhibition by threonine of apparent cystine uptake was actually due to inhibition of cysteine uptake, which resulted from GSH-cystine mixed disulfide exchange. Radio-HPLC confirmed this. After incubating cells with [35S]cystine (0.18 mM) for 10 min, the total counts inside the cell matched the counts in the uptake medium in the form of GSH-cysteine mixed disulfide. Finally, HepG2 cells took up cysteine by both Na(+)-dependent and -independent mechanisms. The former exhibited high affinity and low capacity, whereas the latter exhibited the opposite. At a physiologic concentration of cysteine (10 microM), 68% of cysteine uptake occurred via the Na(+)-dependent system and 32% via system L1.

Identification of the 5' regulatory elements of avian lipoprotein lipase gene: synergistic effect of multiple factors

The organization of cis-acting regulatory elements of the chicken lipoprotein lipase gene was investigated in 5.4 kb of 5' flanking sequences. Various lengths of 5' flanking sequence were linked to the bacterial chloramphenicol acyltransferase (CAT) gene and transfected into primary cultures of chicken adipocytes by DEAE-dextran transfection method. Negative elements are present between -1947 and -139 of the 5' flanking sequence. Removal of these sequences revealed the presence of positive elements located within 138 bp upstream of the major transcription start site. Sequence analysis showed that the region from the major transcription start site to -138 contains an inverted GC box (ACCACGCCCC), a CCAAT element and two direct repeats of the octamer motif, ATTTGCAT. DNase I footprinting assays using a probe extending from -175 to +191, identified three sites protected by nuclear factors. Site I (-126 to -123), a C-rich sequence, GCCC, was identified only on the coding strand. Site II covered the sequence from -95 to -68 and includes the GC box. Site III, from -53 to -26, contained two octamer repeats. Site I is the 5' portion of a 10 bp sequence (CCCTCCCCCC; -126/-116) which is perfectly conserved in the avian and the human promoter. Single or multiple copies of a 37 bp DNA fragment (-138/-102) containing the 10 bp conserved sequence were cloned into LPLCAT-51, upstream or downstream of the major transcription start site and in both orientations; transfection and CAT activity assays with these constructs indicate that the -138/-102 fragment has an enhancer like activity. Additional 5' and internal deletions of LPLCAT-138 suggest that the factors binding to the C-rich element, the GC box and the two octamer repeats have a synergistic effect on promoter activity.

Bidirectional membrane transport of intact glutathione in Hep G2 cells

Rat hepatocytes exhibit bidirectional carrier-mediated transport of reduced glutathione (GSH) across the plasma membrane. Transport of GSH has not been well characterized in human-derived cells. We examined Hep G2 cells as a possible human liver model for GSH homeostasis. Hep G2 cell GSH averaged 25.9 +/- 1.4 nmol/10(6) cells. When Hep G2 cells were incubated in buffer, no GSH appeared in the medium over 2 h. However, after pretreatment with acivicin to inhibit gamma-glutamyl transpeptidase activity, GSH efflux was unmasked and measured 30 +/- 4 pmol x 10(6) cells-1 x min-1, which is comparable to rat hepatocytes. GSH efflux was inhibited by sulfobromophthalein GSH adduct (BSP-GSH) and cystathionine, agents that inhibit sinusoidal efflux in the rat, and was stimulated by adenosine 3',5'-cyclic monophosphate-dependent agents. GSH uptake was measured after cells were pretreated with acivicin and buthionine sulfoximine to prevent breakdown of GSH and resynthesis of GSH from precursors, respectively. In the presence of 4 microCi/ml of [35S]GSH and 10 mM unlabeled GSH, GSH uptake was linear up to 45 min and did not require Na+ or Cl-. GSH uptake exhibited saturability with a maximal velocity of 4.15 +/- 0.23 nmol.mg-1 x 30 min-1, a Michaelis constant of 2.36 +/- 0.26 mM, and two interactive transport sites. BSP-GSH cis-inhibited GSH uptake in a dose-dependent manner with an inhibitory constant of 0.46 +/- 0.05 mM. Inhibition by BSP-GSH (1 mM) of GSH uptake was through a single inhibitor site and was overcome at > 10 mM GSH, which is consistent with competitive inhibition. Similar to the rat, 10 mM extracellular GSH trans-stimulated GSH efflux. These findings may be important in gaining better insights into GSH homeostasis in human liver cells.

Thiol-disulfide effects on hepatic glutathione transport. Studies in cultured rat hepatocytes and perfused livers

In cultured rat hepatocytes, cystine led to an inhibition of GSH efflux by lowering the Vmax by approximately 35% without affecting the Km. The cystine-mediated inhibition of GSH efflux was rapid in onset (< 1 h), with near maximum effect at 0.1 mM. Inhibition was still observed when cystine uptake was prevented. Cystine and sulfobromophthalein-GSH, a selective inhibitor of sinusoidal transport of GSH, did not exhibit additive inhibitory effects on GSH efflux. Depletion of ATP or membrane depolarization after cystine treatment were excluded as potential mechanisms. DTT not only reversed the cystine-mediated inhibition of GSH efflux, it stimulated GSH efflux up to 400-500%. The DTT effect was immediate in onset, reaching maximum after 30 min, and was partially reversed by cystine, suggesting that the two share a common site(s) of action. DTT treatment did not alter cellular ATP levels or change the membrane potential. In cultured hepatocytes, DTT treatment increased the Vmax of GSH efflux by approximately 500% without affecting the Km. Inhibition of microtubular function and vesicular acidification did not affect basal or DTT stimulated efflux. Both cystine and DTT effects on sinusoidal GSH efflux were confirmed in perfused livers. In summary, the capacity of the sinusoidal GSH transporter is markedly influenced by thiol-disulfide status.

Restoration of gap-junctional intercellular communication in a communication-deficient rat liver cell mutant by transfection with connexin 43 cDNA

To study the biochemical basis of gap-junctional intercellular communication (GJIC) and its role in tumorigenesis, a mammalian cell expression vector carrying both a rat connexin 43 (Cx43) cDNA and an amplifiable dihydrofolate reductase (DHFR) gene was transfected into the GJIC-deficient rat liver mutant cell line aB1. Two stable transfectants were selected for further amplification of the transfected Cx43 gene by increasing stepwise the concentration of methotrexate (MTX) in the culture medium. The results indicate that GJIC was restored in these two Cx43 cDNA transfectants after they became highly resistant to MTX but not in the control-vector transfectants, in which the DHFR gene was similarly amplified. The amount of Cx43 DNA revealed by Southern blot analysis and the expression of Cx43 gene revealed by northern and western blot analyses were concomitantly increased in the Cx43 cDNA transfectants resistant to high concentrations of MTX. Western blot analysis, using an antipeptide antibody that specifically recognizes Cx43 protein, further revealed that an approximately 46-kDa phosphorylated Cx43 protein that was prominent in the parental GJIC-competent cells was absent in the aB1 cells. This Cx43 protein, however, reappeared in the two Cx43 cDNA transfectants after amplification. After treatment of the membrane proteins with alkaline phosphatase in vitro, the approximately 46- and 44-kDa proteins disappeared, whereas the approximately 42-kDa proteins remained with increasing intensity, indicating that the higher molecular-weight proteins were the phosphorylated Cx43. These results indicate that a defect in posttranslational phosphorylation of Cx43 protein associated with low expression of the Cx43 gene might be responsible for the GJIC deficiency in aB1 cells and that increased expression of Cx43 by gene amplification might restore this phosphorylated Cx43 protein and so reestablish GJIC.

Loss of suppression of GSH synthesis at low cell density in primary cultures of rat hepatocytes

Primary cultures of adult rat hepatocytes shift into the growth phase when plated at low density (LD). We used this model to examine changes in glutathione (GSH) metabolism, since cells undergoing active growth may be more susceptible to environmental toxins. When primary cultures of adult rat hepatocytes were plated on collagen or Matrigel-precoated dishes, cell number and GSH varied inversely. This density effect on cell GSH occurred as early as 2 h after plating, when the media contained 1 mM methionine, but was delayed until 20 h if the media contained only 0.5 mM cystine. The density effect on GSH synthesis occurred in the absence of serum, hormones, changes in cell volume, GSH efflux, ATP levels, and uptake of methionine or cystine and was blocked by cycloheximide or actinomycin D. When methionine was available, the cellular cysteine level was 65% higher at LD than at high density (HD). gamma-Glutamylcysteine synthetase (GCS) activity was 64% higher at LD than at HD. GSH synthetase activity was unaffected by density. Both the increase in cellular cysteine levels and GCS activity were blocked by cycloheximide and actinomycin D. When cells were cocultured using cluster plates and Transwell inserts for 4 h, cell GSH of HD cells was unaffected by the density of cocultured cells; however, LD cells exhibited significantly lower GSH and GCS activity when cocultured with HD cells than when cocultured with LD cells. Cysteine levels were elevated in the LD cells regardless of the density of cocultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin and glucocorticoid dependence of hepatic gamma-glutamylcysteine synthetase and glutathione synthesis in the rat. Studies in cultured hepatocytes and in vivo

We reported that glucagon and phenylephrine decrease hepatocyte GSH by inhibiting gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis (Lu, S.C., J. Kuhlenkamp, C. Garcia-Ruiz, and N. Kaplowitz. 1991. J. Clin. Invest. 88:260-269). In contrast, we have found that insulin (In, 1 microgram/ml) and hydrocortisone (HC, 50 nM) increased GSH of cultured hepatocytes up to 50-70% (earliest significant change at 6 h) with either methionine or cystine alone as the sole sulfur amino acid in the medium. The effect of In occurred independent of glucose concentration in the medium. Changes in steady-state cellular cysteine levels, cell volume, GSH efflux, or expression of gamma-glutamyl transpeptidase were excluded as possible mechanisms. Both hormones are known to induce cystine/glutamate transport, but this was excluded as the predominant mechanism since the induction in cystine uptake required a lag period of greater than 6 h, and the increase in cell GSH still occurred when cystine uptake was blocked. Assay of GSH synthesis in extracts of detergent-treated cells revealed that In and HC increased the activity of GCS by 45-65% (earliest significant change at 4 h) but not GSH synthetase. In and HC treatment increased the Vmax of GCS by 31-43% with no change in Km. Both the hormone-mediated increase in cell GSH and GCS activity were blocked with either cycloheximide or actinomycin D. Finally, when studied in vivo, streptozotocin-treated diabetic and adrenalectomized rats exhibited lower hepatic GSH levels and GCS activities than respective controls. Both of these abnormalities were prevented with hormone replacement. Thus, both in vitro and in vivo, In and glucocorticoids are required for normal expression of GCS.

The structure and complete nucleotide sequence of the avian lipoprotein lipase gene

The entire gene for chicken lipoprotein lipase (LPL) has been isolated and characterized by primer extension and sequence analysis. The gene is 17 kilobase pairs long and comprises 10 exons and 9 introns. As determined by primer extension analysis the start sites of transcription map 176, 204 and 218 nucleotides upstream of the initiator methionine codon. The 1947 base pairs of 5' flanking sequence contains several putative regulatory elements including two adjacent Oct I binding elements, four glucocorticoid regulatory elements and a sequence very homologous to the previously described fat specific element at--1402 nt. The first intron is very large (6433 bp) and contains four consensus SpI binding-site sequences. Five polyadenylation signals are found in the 3' untranslated region, the last three of which give predicted mRNA species identical in size to those determined by Northern blot. The 5' flanking sequences of the LPL, pancreatic lipase and hepatic lipase genes do not show homology, however. This may account for the homologous amino acid sequences but dissimilar gene expression of these enzymes.

Hormone-mediated down-regulation of hepatic glutathione synthesis in the rat

Our present work characterized the role of hormone-mediated signal transduction pathways in regulating hepatic reduced glutathione (GSH) synthesis. Cholera toxin, dibutyryl cAMP (DBcAMP), and glucagon inhibited GSH synthesis in cultured hepatocytes by 25-43%. Cellular cAMP levels exhibited a lower threshold for stimulation of the GSH efflux than inhibition of its synthesis. The effect of DBcAMP was independent of the type of sulfur amino acid precursor and cellular ATP levels and unassociated with increased GSH mixed disulfide formation or altered GSH/oxidized glutathione ratio. In liver cytosols, addition of DBcAMP and cAMP-dependent protein kinase (A-kinase) inhibited GSH synthesis from substrates (cysteine, ATP, glutamate, and glycine) by approximately 20% which was prevented by the A-kinase inhibitor. However, if only substrates of the second step in GSH synthesis were used (gamma-glutamylcysteine, glycine, and ATP), DBcAMP and A-kinase exerted no inhibitory effect. Phenylephrine, vasopressin, and phorbol ester also inhibited GSH synthesis in cultured cells by approximately 20%, and depleted cell GSH independent of the type of sulfur amino acid precursor. Cellular cysteine level was unchanged despite the significant fall in GSH after glucagon or phenylephrine treatment. Pretreatment with either staurosporine, C-kinase inhibitor, or calmidazolium, a calmodulin inhibitor, partially prevented but, together, completely prevented the inhibitory effect of phenylephrine. The same combination had no effect on the inhibitory effect of glucagon. The effects of hormones were confirmed in both the intact perfused liver and after in vivo administration. Thus, two classes of hormones acting through distinct signal transduction pathways may down-regulate hepatic GSH synthesis by phosphorylation of gamma-glutamylcysteine synthetase.

Hormonal regulation of glutathione efflux

The efflux of GSH has been shown previously to be a saturable process in both isolated rat hepatocytes and perfused liver, suggesting a carrier-mediated transport mechanism. The possibility in hormonal regulation of this process has been raised by recent reports. Our present work examined the role of hormones known to affect intracellular signal transduction mechanisms on GSH efflux in cultured rat hepatocytes and perfused rat livers. We found that cAMP-dependent factors, such as cholera toxin (CT), dibutyryl cAMP, forskolin, and glucagon all stimulated GSH efflux in cultured rat hepatocytes. The efflux kinetics were compared in cultured cells incubated with or without CT; the stimulation of GSH efflux was related to a near doubling of the Vmax while exhibiting no significant alteration of the Km. The increase in intracellular cAMP level associated with the threshold for this stimulatory effect was 25% above control. The stimulatory effect of CT could not be blocked by cyclohexamide pretreatment or reversed by colchicine treatment. The stimulatory effect of glucagon was abolished in the presence of ouabain but not in the presence of barium. On the other hand, hormones which act through Ca2+ and protein kinase C, such as phenylephrine and vasopressin, had no effect on GSH efflux in the cultured cells. In the perfused liver model, glucagon (10 nM) and dibutyryl cAMP (8 microM) stimulated sinusoidal GSH efflux to 130 and 144% of control values, respectively, and increased bile flow while not affecting biliary GSH efflux. Finally, the physiological significance of glucagon-mediated stimulation of sinusoidal GSH efflux was assessed by both plasma GSH and glucose levels in response to in vivo glucagon infusion. The threshold dose of glucagon for significant increase in plasma GSH (5.21 pmol/min) was lower than for glucose (15.61 pmol/min). At the highest glucagon infusion rate (261 pmol/min), plasma GSH level doubled while glucose level increased 80%. In conclusion, increased cAMP stimulates GSH efflux in cultured rat hepatocytes and perfused livers. The stimulatory effect of cAMP is exerted at the sinusoidal pole and appears to be mediated by hyperpolarization of hepatocytes by stimulation of Na(+)-K(+)-ATPase. In vivo studies confirmed the importance of cAMP-mediated stimulation of sinusoidal GSH efflux as it resulted in significant elevation of the plasma GSH level.

Frontiers of gallstone therapy. How far have we come with nonsurgical methods?

In the next few years, much will be learned about nonsurgical treatment of gallstones, and the role of each method will be more clearly defined. At present, each used alone has limitations (table 1). Oral chemolysis can be used for any number of gallstones, but only about 20% of patients are candidates for this method. Complete dissolution of stones can take months to years. Direct-contact dissolution therapy is rapidly effective, is inexpensive, and can be used for any size and number of gallstones. However, it is invasive, and only about 20% of patients are suitable candidates. Extracorporeal shock wave lithotripsy is noninvasive and avoids the complications and long recovery period of surgery. Up to three stones can be treated, but patients with certain medical conditions are excluded. About 20% to 30% of patients can undergo this treatment. None of these nonsurgical treatments prevents recurrence. Shock wave lithotripsy and dissolution with methyl tert-butyl ether are still in the experimental stage, so results of further study--particularly of combinations of the methods--are eagerly awaited by persons who have had symptomatic gallstones.

[A study on the histologic basis of human bile duct peristalsis]

In 62 human cadavers, full length specimen of bile duct including right hepatic intersegmental duct (from fetus, infants, children and adult up to 74 yrs of age) was examined with light and electron microscopy. 1 for longitudinal maximum section, 61 for cross serial section of each of 6 selected tissue blocks stained with HE for general survey, Mallory, Van-Gieson stain and PAP anti-desmin for smooth muscle, Weigert stain for elastic fiber. No muscle bundles were found in the bile-duct. Some cases have scattered smooth muscle cells in the fibrous duct wall, with the frequency in pancreatic portion as 54/62, supraduodenal portion 33/62, common hepatic 15/62, right hepatic 2/61, and intrahepatic o/62, but never in full layers, circular or longitudinal, nor right joint of cell membrane existed. Total area of muscle cells measured in slide is less than 8% that of the fibrous wall. No myofibroblast was found. It is concluded that, there is no characteristic histologic structure of contractile potential and wave transmission. There is no other contractile element in intrahepatic duct capable of initiating propulsive movement. The so-called bile duct movement is most likely passive and should not be interpreted as peristalsis.

Role of glutathione status in protection against ethanol-induced gastric lesions

The role of glutathione status in gastric mucosal cytoprotection has been a subject of controversy. Cysteamine, an exogenous sulfhydryl agent and diethyl maleate (DEM), an endogenous glutathione (GSH) depletor both appear to protect rats from ethanol-induced gastric lesions. In this study, we used various agents to alter gastric mucosal GSH levels and assessed the effects on susceptibility to ethanol injury. We found that DEM and buthionine sulfoximine both depleted gastric GSH but only DEM protected against ethanol-induced gastric lesions. L-Oxothiazolidine-4-carboxylate (OXT) and N-acetyl-L-cysteine (NAC) both potentiated ethanol-induced gastric lesions even though only NAC significantly raised the GSH level. The depletion of GSH by DEM was reversed by supplying cysteine in the form of OXT or NAC so that the net result was a GSH level close to normal control. The potentiation of ethanol injury by NAC and OXT was still apparent. These experiments show no relation between gastric GSH levels and susceptibility to ethanol injury.

Parasitological studies at a new breeding area of Oncomelania hupensis chiui in Taipei county, Taiwan

Oncomelania hupensis chiui was found at the Jui-Ping area, Linkow District, Taipei County, Taiwan, which is located on the north coast of the island approximately 10 km of the mouth of the Tamasui River. The habitat of the snails at this area is similar to the type locality at Alilao, on the slope of the hills along of coast. The snails from this new breeding area, are similar to the Alilao snails, and are highly susceptible to the infection with geographic strains of Schistosoma japonicum including the Changhua, Ilan, Japanese, Philippine and Chinese strains. Examinations of 7,758 snails and intradermal tests on 736 inhabitants along with stool examinations of 622 people indicated that there was no evidence of the presence of Schistosoma japonicum at this area. Results obtained from stool examination demonstrated high prevalence of hookworm infection (53.4%) and relatively low infection rates of Asearis lumbricoides (37.0%) and Trichuris trichiura (14.1%). The protozoan infections were low in general. A single Scotch-tape technique for Enterobius vermicularis among 499 school children yielded a 55.7% infection rate.

Culture and morphological observations on Trypanosoma melphagium

The cultural characteristics of Trypanosoma melophagium of sheep were studied. Aspects investigated were size of the inoculum and population growth in Modified Monophasic Medium for Trypanosomes (MMMT), population growth in Medium 199 with 10% inactivated calf serum containing 5, 10, and 15% hemolyzed defibrinated rabbit blood (199-CS-5, 199--CS-10, 199-CS-15) at 27 degrees C, effects on population growth of temperature and hydrogen ion concentration in MMMT, and morphology and morphometrics of the developmental stages found under different experimental conditions. The best growth occurred in medium MMMT at 30 degrees, C, pH 7.25. Temperature seemed to be a critical factor for differentiation of epimastigotes to trypomastigotes. Statistically significant differences were found between the trypomastigotes in MMMT and 199--cs-5 at 37 degrees C on day 4 of incubation for the following measurements: PK (distance from posterior end to kinetoplast), KN (from kinetoplast to middle of nucleus), PN (from posterior end to middle of nucleus), and nuclear and kinetoplastic indices. The trypomastigotes formed in both media were much smaller in size than the blood forms reported by Hoare (1972).