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Biomedical subjects

A Yasutake

Publications and source records attributed to A Yasutake.

At least 37 records · Page 2Linked to original sources
PubMed1996

Influence of dietary protein levels on the acute toxicity of methylmercury in mice.

The influence of dietary protein levels on the acute toxicity of methylmercury (MeHg) was investigated using C57BL/6N male mice fed either a 24.8% protein diet (normal protein diet, NPD) or a 7.5% protein diet (low protein diet, LPD). When MeHg was administered to each group of mice, all mice died at a medium or high dose (80 or 120 mumol/kg, respectively) within 16 or 7 days, respectively, but not at a low dose (40 mumol/kg) in both dietary groups. Although no difference was observed in the survival rate at a medium dose, NPD-fed mice died earlier despite lower brain Hg than LPD-fed mice at a high dose. Accordingly, death, in our observations, could not be due to neural damage by MeHg. When a high dose of MeHg was administered to mice, plasma aspartate aminotransferase and alanine aminotransferase activities increased in NPD-fed mice but not in LPD-fed mice in spite of similar hepatic Hg levels. Therefore, the higher susceptibility of the liver could be reason for the shorter survival period in NPD-fed mice. Since plasma creatinine increased within 24 h after MeHg administration at a medium or high dose, renal dysfunction could be a major factor in death. The present results suggest that susceptibility to acute MeHg toxicity was higher in NPD-fed mice than in LPD-fed mice, possibly due to the difference in hepatic susceptibility.

Alanine Transaminase↗
PubMed1996

Methylmercury transport across the placenta via neutral amino acid carrier.

Methylmercury (MeHg) penetrates the placental barrier to affect developing fetuses in the uterus. However, the mechanism of placental MeHg transport is not well defined. To clarify the MeHg transport system that functions in the placenta, pregnant rats were intravenously administered MeHg on day 18 of gestation. The fetal blood was collected from the umbilical cord at 30 and 60 min after the administration, and its mercury concentration was measured. MeHg was found to be rapidly transported to the fetal blood in a time- and dose-dependent manner, and predominantly distributed in the blood cells there. MeHg transport was effectively suppressed by the co-injection of neutral amino acids, i.e., L-methionine and L-phenylalanine, suggesting that MeHg is actively transported as its cysteine conjugate via the neutral amino acid carrier system. The suppression by methionine was not so marked as by phenylalanine. Since methionine administration caused a rapid increase of the cysteine, which functioned as a predominant carrier in MeHg transport, in the maternal plasma, newly synthesized cysteine seemed to accelerate the mercury uptake. Accordingly, the acceleration by the extra cysteine would compensate partly the competitive effect of methionine as a neutral amino acid.

Amino Acid Transport Systems↗
PubMed1994

Influence of dietary levels of protein and sulfur amino acids on the fate of methylmercury in mice.

We previously reported that the fate of methylmercury (MeHg) in mice was affected by dietary protein levels. To study the mechanism of this alteration, we investigated the effect of sulfur amino acid supplement for a lowered protein diet on the fate of MeHg. C57BL/6N male mice were fed on a 24.8% protein diet (normal protein diet, NPD), a 7.5% protein diet (low protein diet, LPD), or LPD supplemented by methionine and cystine so as maintain the normal levels (amino acid supplemented diet, ASD) for 5 days. NPD-fed mice were used as controls. The mice were orally administered MeHg chloride (20 mumol/kg), and were examined after 24 h distribution and excretion of Hg. The Hg level in brain increased with LPD feeding and was further enhanced by ASD feeding. The hepatic Hg level increased only with ASD feeding. Although Hg levels in kidney, blood and plasma did not change with LPD feeding, these decreased with ASD feeding. The urinary Hg level that decreased with LPD feeding was recovered and exceeded by far the control levels with ASD feeding. When mice were intravenously injected with MeHg-bovine serum albumin, the Hg uptake rate in the brain increased in LPD-fed mice and was further enhanced in ASD-fed mice. The brain uptake of intravenously injected L-[14C]phenylalanine was also accelerated with LPD or ASD feeding, which indicated that LPD or ASD feeding increased activity of neutral amino acid transport in the brain. This would cause increased Hg uptake in the brain, since MeHg reaches the brain through this transport system. Hg ratio in plasma low molecular weight fraction increased in ASD-fed mice, but not in LPD-fed mice. This might contribute to the further enhanced Hg uptake in the brain with ASD feeding. Analysis of thiol compounds in plasma and urine revealed increased levels with ASD feeding. The present results suggest that insufficiency of sulfur amino acids in LPD is one reason for the alteration in the fate of MeHg induced by LPD feeding. It is also suggested that the change in neutral amino acid transport caused by LPD feeding is involved in the alteration in the fate of MeHg.

Animals↗
PubMed1994

Mechanism of methylmercury efflux from cultured astrocytes.

To study the mechanism of methylmercury (MeHg) efflux from the central nervous system cells, cultured astroglia obtained from neonatal rats were incubated with 10 microM MeHg-cysteine (CySH) for 30 min. After being washed four times, cells were incubated in Hg-free medium, and the release of MeHg from the cells was monitored. The amount of MeHg released in the medium approached a plateau level (ca. 31% of the loaded amount) at 4 hr. Treatment of the cells with a CySH precursor, 2-oxothiazolidine-4-carboxylic acid (OTC), resulted in a significant increase of cellular levels of CySH and glutathione (GSH). OTC also increased 1.5-fold the MeHg efflux from the loaded cells. Another GSH enhancer, GSH isopropyl ester, also stimulated MeHg export from the cells. Ion-exchange column chromatography using DEAE-Sephadex revealed that the MeHg metabolite thus released was exclusively MeHg-GSH conjugate, both with and without OTC. Since the MeHg efflux was suppressed significantly by the presence of probenecid, the efflux occurred via the probenecid-sensitive organic acid transport system. Even though the cellular GSH levels were depleted drastically by treatment with L-buthionine-(S,R)-sulfoximine (BSO), a considerable level (90% of the control) of Hg efflux was detected. Since neither GSH- nor CySH-MeHg was detected in the culture medium of the BSO-treated cells, GSH depletion may trigger some other secretion system(s) in the cells. These results suggest that conjugation with GSH is the major pathway for MeHg efflux in rat astroglia, and that elevation in the cellular GSH level would possibly be a logical therapy for MeHg poisoning, promoting the accelerated elimination of MeHg from the critical tissues.

Animals↗
PubMed1994

Acute effects of methylmercury on hepatic and renal glutathione metabolisms in mice.

Because of its high affinity to the sulfhydryl group, the in vivo fate of methylmercury (MeHg) is closely related to the glutathione (GSH) metabolism. Here, to examine the possible effects of MeHg on the GSH metabolism, C57BL female mice were challenged by this heavy metal at a marginal dose level to induce slight renal dysfunction. Liver and blood GSH levels decreased by 16% and 20%, respectively, 24 h after MeHg (160 mumol/kg) administration, whereas kidney and plasma levels drastically increased. The GSH half-lives obtained using L-buthionine-(S,R)-sulfoximine were shortened by 17% in the liver, but lengthened by 28% in the kidney. The accelerated secretion of GSH from the liver and/or blood cells might have caused increased plasma levels of the tripeptide, which in turn could increase the supply of the constituent amino acids for GSH synthesis to the kidney. Furthermore, renal gamma-glutamylcysteine synthetase activity, a rate-determining enzyme in GSH biosynthesis, was found to be enhanced in the MeHg-treated group. The marked increase in the renal GSH levels induced by MeHg could be due to the increased synthesis and the decreased efflux of the tripeptide in this tissue. The MeHg-induced alterations of GSH metabolism described here might reflect one of the defense mechanisms of bioorganisms against the challenge by MeHg.

Animals↗
PubMed1993

Further study of effects of chelating agents on excretion of inorganic mercury in rats.

The effects of three chelating agents, N-benzyl-D-glucamine dithiocarbamate (BGD), 2,3-dimercaptopropanol (BAL) and D-penicillamine (D-PEN), on the excretion of mercury in rats exposed to mercuric chloride (HgCl2), the chemical forms of mercury compounds excreted in the bile and urine and the intestinal reabsorption of mercury compounds in the bile were studied. Rats were injected intraperitoneally with 203HgCl2 (300 micrograms Hg and 74 kBq of 203Hg/kg) and 24 h later, they were injected intraperitoneally with a chelating agent (a quarter of an LD50). The injection of the chelating agents significantly enhanced the biliary and urinary excretions of mercury. The enhancing effect of BGD on the excretions of mercury was almost the same as that of BAL and much larger than that of D-PEN. The major chemical form of mercury in the bile and urine of rats injected with BGD after HgCl2 treatment was Hg-BGD compounds. The chemical form of mercury in the bile and urine of rats injected with BAL after HgCl2 treatment was mainly Hg-GSH compound. The mercury after HgCl2 and D-PEN treatment was excreted mainly via the urine in the form of Hg-D-PEN compound. The intestinal reabsorption of mercury from the bile of rats injected with BGD or D-PEN was only 0.18% or 0.38% of the dose, respectively. The intestinal reabsorption of mercury from the bile of rats injected with BAL was 27.38% of the dose. It was suggested that the Hg-GSH compound excreted in the bile after HgCl2 and BAL treatment is partly degraded to Hg-cysteine (Cys) by the intestinal membranous enzymes and that the ligand of Hg-Cys is replaced by BAL in the bile, resulting in the effective reabsorption of Hg-BAL compound from the intestine.

Animals↗
PubMed1992

Influence of dietary protein levels on the fate of methylmercury and glutathione metabolism in mice.

We investigated the influence of dietary protein levels on the fate of methylmercury (MeHg), the tissue glutathione (GSH) levels and the efflux rates of GSH in C57BL/6N male mice. One group of mice was fed a 7.5% protein diet (low protein diet, LPD) and the other was fed a 24.8% protein diet (normal protein diet, NPD). The cumulative amount of Hg in urine in LPD-fed mice was approximately 3.7-times lower than in NPD group during the 7 days after oral administration of MeHg (20 mumol/kg), although the fecal Hg levels were identical in the two groups. Hg concentration in kidney, liver and blood decreased time-dependently for 7 days after the administration in both groups of mice, whereas the brain levels continued to increase during this period. Tissue Hg levels in the LPD group were significantly higher than in the NPD group except for the liver. Although the hepatic GSH level in LPD-fed mice was significantly lower than in NPD-fed mice, the levels in the kidney, brain, blood and plasma were not different between the two groups. The efflux rate (mumol/g body weight per day) of hepatic GSH in LPD-fed mice was significantly lower than in the NPD group, whereas the efflux rates of renal GSH were identical in both groups. When MeHg (20 mumol/kg)-pretreated mice were injected with acivicin, a specific inhibitor of gamma-glutamyltranspeptidase, the urinary Hg levels increased by 60- and 36-fold in groups fed LPD and NPD, respectively. As a result, the difference in urinary Hg levels between the two groups disappeared with acivicin treatment. This result indicated that LPD feeding might decrease urinary Hg excretion by increasing the retention of MeHg metabolite(s) in renal cells. Thus, our present study suggested that the dietary protein status, which could modulate the metabolism of thiol compounds, played an important role in determining the fate of MeHg.

Animals↗
PubMed1990

Interaction of methylmercury compounds with albumin.

The nature of interaction between bovine serum albumin (BSA) and methylmercurial compounds has been investigated by ultrafiltration analysis. Four types of BSA samples, mercaptalbumin, its mixed disulfides with glutathione (GSH) and L-cysteine (CySH), and S-carbamidomethylated derivative, were used for binding assays with methylmercury (MM) chloride (MMC) and three kinds of MM mercaptides of low molecular weight thiols, GSH (GS-MM), CySH (CyS-MM) and cysteinylglycine (CG-MM). Among various ligands tested, MMC showed the highest affinity for all BSA species, and the BSA-bound fraction of the ligand did not change with ligand/protein ratio. MMC strongly and stoichiometrically bound to mercaptalbumin even at a molar ratio of 1:1. In contrast, the albumin bound fractions of three other MM ligands increased with concomitant decrease in ligand/protein ratio and with time except for the alkylated albumin, the highest binding being shown by mercaptalbumin. Binding of S-2-nitrophenyl-glutathione, a GSH analog with a hydrophobic S-substituent, to albumin species occurred similarly to that of GS-MM. However, GSH and oxidized glutathione (GSSG) interacted differently with albumin; mercaptalbumin showed the lowest affinity for GSH, and GSSG scarcely interacted with all BSA species. These results suggest that the sulfhydryl group at Cys-34 is not the only site of BSA that interacts with MM compounds and that albumin interacts preferentially with the hydrophobic domains of a mercurial ligand rather than its hydrophilic peptide moiety.

Animals↗
PubMed1990

Sex difference in acute renal dysfunction induced by methylmercury in mice.

To investigate the sex-related difference of susceptibility of renal function to methylmercury (MeHg) toxicity, various doses of MeHg chloride (MMC, 20-200 mumol/kg) were orally administered to C57BL/6N mice of both sexes. On days 1, 3, 5, and 7 after MMC administration, the extent of damage to renal function and the renal Hg levels were examined. After dosing, female mice survived much longer than males. With the increase in the dose level to 200 mumol/kg, the changes of the renal Hg levels 24 h after administration showed biphasic features with a plateau of around 85 micrograms/g. The renal Hg in male mice increased more rapidly to the plateau than in females. The doses by which the renal Hg level reached the plateau were 80 and 120 mumol/kg for males and females, respectively. The time-dependent decrease of the renal Hg became much slower with dose levels exceeding 80 and 160 mumol/kg for males and females, respectively. Inhibition of phenolsulfonphthalein excretion and increase of plasma creatinine after the MMC administration were more marked in males than in females. Inorganic Hg levels in the kidney of MeHg-intoxicated mice were much lower than that of HgCl2-intoxicated mice, indicating that the involvement of inorganic Hg, a product of biotransformation of MeHg, in the renal failure caused by MMC treatment would be negligible. Although pathological changes in the renal proximal tubules of HgCl2-intoxicated mice were marked, those of the MeHg-intoxicated group were slight.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Mechanism of urinary excretion of methylmercury in mice.

To elucidate the mechanisms by which methyl-mercury (MeHg) is eliminated from organisms, male C57BL/6N mice were orally administered with MeHg chloride (5 mg/kg) and the chemical forms of its metabolites in plasma, urine and kidney were determined by column chromatographic analysis. Orally administered MeHg rapidly entered the circulation, accumulated in the kidney and other tissues, and was slowly excreted in the urine. Ultrafiltration and gel filtration analysis revealed that most of plasma MeHg was accounted for by its albumin conjugate. Cell fractionation analysis revealed that about 80% of renal MeHg was recovered from the 15,000 g supernatant fraction of the kidney homogenate. If the kidney was homogenized in the presence of serine-borate complex, a potent inhibitor of gamma-glutamyltranspeptidase (gamma-GTP), about 50% of the MeHg in the supernatant fraction was recovered as its glutathione S-conjugate while the rest was bound to cytosolic protein(s). The major part of urinary MeHg was accounted for by its cysteine conjugate. However, urinary excretion of its glutathione conjugate increased significantly if animals were pretreated with acivicin, an affinity labeling reagent for gamma-GTP. These and other results suggested that MeHg bound to albumin accumulated in the kidney predominantly via some non-filtrating peritubular mechanism, and localized in renal cytosolic compartment as its glutathione- and protein-bound forms. The glutathione S-conjugate of MeHg in the tubule cells might be transferred to the lumenal space, hydrolyzed to the cysteine S-conjugate, and then excreted in urine. These sequential events might constitute an important eliminatory pathway for a hazardous mercurial metabolite in mice.

Animals↗
PubMed1988

Sex and strain differences of susceptibility to methylmercury toxicity in mice.

Excretion and organ distribution of mercury and susceptibility to methylmercury (MeHg) toxicity were compared between strains and sexes after successive oral administration of MeHg chloride (5 mg/kg per day) using BALB/cA (C) and C57BL/6N (B6) mice. Every mouse died several days after initiation of toxic symptoms, and significant strain and sex differences were found with regard to length of survival. C mice of both sexes died earlier than B6 mice. B6 males survived much longer (greater than 6 weeks) than B6 females (3 weeks), whereas C males died earlier than C females. B6 male mice showed remarkably higher urinary Hg excretion and lower Hg levels in the brain, liver, kidney and blood than the other 3 groups. With daily MeHg administration, the Hg levels in all tissues except the kidney showed linear increase until the manifestation of toxic symptoms. Mercury accumulation in the kidney, the tissue with the greatest uptake of Hg in the mice examined herein, was biphasic: accumulation was rapid for 7-10 days after which the rate of increase was greatly reduced until death. It is suggested that conditions resulting in saturation of the rate of kidney Hg uptake might cause inhibition of urinary Hg excretion via some disturbance of renal function. Subsequently, Hg accumulation would be accelerated in various tissues, including the brain, leading to manifestation of toxic symptoms.

Animals↗
PubMed1988

Mercury accumulation in lens following single administration of methylmercury.

Mercury levels in the lens, aqueous humor, blood and plasma after a single administration of methylmercuric chloride (MMC, 10 mg/kg or 20 mg/kg) were studied in Wistar rats. The animals were sacrificed on the 1st, 3rd, 7th, 14th, 21st and 180th days following administration. Mercury levels in each tissue after MMC 20 mg/kg treatment were higher than after 10 mg/kg treatment. Mercury levels in the blood, plasma and aqueous humor on the 1st day following administration were significantly high. On the other hand, the highest mercury level in the lens was shown on the 7th day after administration. Total concentration of the lens mercury on the 180th day was almost equal to that on the 21st day. These results suggested active accumulation of mercury takes place in the lens and that retention is at a high concentration for over half a year even after only a single administration.

Animals↗
PubMed1987

Anti-chymotrypsin and anti-elastase activities of a synthetic bicyclic fragment containing a chymotrypsin-reactive site of soybean Bowman-Birk inhibitor.

A bicyclic hexadecapeptide, which corresponds to the sequence 36-51 and contains the chymotrypsin-reactive Leu-43-Ser-44 bond of soybean Bowman-Birk inhibitor, has been synthesized. This peptide consists of two loops formed by disulfide bridges between Cys-36 and Cys-51 and between Cys-41 and Cys-49. The bicyclic peptide showed a strong anti-chymotryptic activity with a Ki of 7.1.10(-7) M. Comparison of inhibitory activity and digestive stability against chymotrypsin with other hexadecapeptides having the same sequence but lacking one or both disulfide bridges suggested that the compact bicyclic structure increases the activity and protects the Leu-Ser bond from chymotryptic digestion. Interestingly, the bicyclic peptide was found to inhibit porcine pancreatic elastase with a Ki of 4.3.10(-5) M, indicating the broad specificity of this ring system.

Amino Acid Sequence↗
PubMed1987

Effect of sex hormones on the fate of methylmercury and on glutathione metabolism in mice.

To investigate the mechanisms for the sex-related difference in the in vivo fate of methylmercury (MeHg), the effects of hormonal manipulation on the distribution and urinary excretion of the mercurial moiety (Hg) of injected MeHg and on hepato-renal metabolism of glutathione were studied in C57BL/6N mice. Twenty-four hours after oral administration of MeHg, urinary Hg levels were significantly higher in males than in females. Tissue Hg levels of males were higher in the kidney, but lower in the brain, liver and plasma than those of females. The fate of injected MeHg in castrated males was similar to that in normal females except for its brain levels. This feminization of the mercurial behavior in the castrated males was restored by treating with testosterone propionate (TP). When control mice were treated with TP, urinary excretion of Hg increased in both sexes, whereas renal Hg level increased only in females. Administration of estradiol benzoate (EB) to males decreased the renal accumulation and urinary excretion of Hg, whereas its hepatic levels increased. However, no significant change in the fate of MeHg was found in females pretreated with EB. Castration of females slightly decreased the urinary excretion of Hg. Thus, tissue distribution and urinary excretion of the administered MeHg seem to be subject to sex hormone control. Since MeHg has a high affinity for GSH, effects of hormonal manipulation on the metabolism of hepato-renal glutathione were also investigated. A significant sex-related difference in glutathione levels was found in plasma but not in the kidney, liver and erythrocytes. The half-lives of glutathione in the liver and kidney were significantly shorter in males than in females as determined by treatment with buthionine sulfoximine, a specific inhibitor of GSH synthesis. This difference was also modulated by the hormonal treatment. Since half-lives of GSH in the liver and kidney predominantly reflect the rate of its efflux from these tissues, the results suggest that GSH metabolism and/or secretory transport may be regulated by sex hormones. These and other observations suggest that the fate of MeHg may be modulated by way of regulating the inter-organ metabolism and transport of glutathione and its derivatives.

Animals↗