Seminal plasma biochemistry. I. Preliminary report: a possible mechanism for the liquefaction of human seminal plasma and its relationship to spermatozoal motility.
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Based on indirect evidence it has been suggested that the liquefaction of human seminal plasma involves fibrinolytic and proteolytic enzymes and that the coagulum is formed by proteins. In this preliminary investigation evidence is presented for the involvement of seminal plasma sialyltransferase in liquefaction which suggests that the coagulum may be composed of glycoproteins. It is proposed that the glycoproteins form a polymer by the chelation of divalent metal ions via the carboxylic acid moieties of the sialic acid groups of the glycoproteins. The glycoprotein polymer may then be dismantled by the reduction of the meal ions by the oxidation of L-ascorbic acid, possibly allowing enzymes to complete the liquefaction process. A total of 100 semen samples from 30 male subjects whose semen profiles were considered "normal" by an independent assessor, were examined for the following: (i) liquefaction time of the seminal plasma; (ii) seminal plasma sialyltransferase activity; (iii) spermatozoal motility, defined as directional or nondirectional; (iv) spermatozoal count, and (v) seminal plasma content of free L-ascorbic acid, dehydroascorbic acid and glutathione. Linear regression analysis showed a significant correlation between sialyltransferase activity and the liquefaction time for seminal plasma. Similarly, multilinear regression analysis of the data showed that as the seminal plasma levels of L-ascorbic acid, total dehydroascorbic acid and glutathione increase, there is a decrease in spermatozoal motility and a decrease in the liquefaction time of the seminal plasma. The possible metabolic relationship of seminal plasma L-ascorbic acid and glutathione is discussed and a metabolic pathway is suggested.Keywords:
Dehydroascorbic acid
Sialyltransferase
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Abstract. Effects of deficiency in ascorbic acid on in vivo production of corticosterone and testosterone were examined using a mutant strain of rats unable to synthesize ascorbic acid. The adrenal weight of scorbutic rats was larger, and corticosterone levels in plasma and adrenal tissues were higher than those of ascorbic acid-supplied (ascorbutic) rats. Acute and chronic stimulation with ACTH increased corticosterone levels in both ascorbutic and scorbutic rats. In contrast, weights of seminal vesicles and ventral prostates in unstimulated scorbutic rats were smaller, and testosterone levels in plasma and testicular tissues were lower than those in ascorbutic rats. Acute stimulation with hCG increased testosterone levels only slightly in plasma and not in testicular tissues of scorbutic rats, when testosterone levels in ascorbutic rats reached a maximum. Chronic stimulation with hCG increased testosterone levels remarkably in both ascorbutic and scorbutic rats. These findings seem to indicate that ascorbic acid is not essential for the synthesis of steroid hormones. The scurvy seems to increase plasma ACTH levels secondary to the stress, resulting in the stimulation of the adrenals. In contrast, a prolonged deficiency in ascorbic acid appears to decrease plasma gonadotropin levels, and may reduce the sensitivity of testes to gonadotropins.
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Dehydroascorbic acid
Cytochalasin B
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Liver is the site of ascorbic acid synthesis in most mammals. As human liver cannot synthesize ascorbate de novo, it may differ from liver of other species in the capacity or mechanism for ascorbate recycling from its oxidized forms. Therefore, we compared the ability of cultured liver-derived cells from humans (HepG2 cells) and rats (H4IIE cells) to take up and reduce dehydroascorbic acid (DHA) to ascorbate. Neither cell type contained appreciable amounts of ascorbate in culture, but both rapidly took up and reduced DHA to ascorbate. Intracellular ascorbate accumulated to concentrations of 10-20 mM following loading with DHA. The capacity of HepG2 cells to take up and reduce DHA to ascorbate was more than twice that of H4IIE cells. In both cell types, DHA reduction lowered glutathione (GSH) concentrations and was inhibited by prior depletion of GSH with diethyl maleate, buthionine sulfoximine, and phenylarsine oxide. NADPH-dependent DHA reduction due to thioredoxin reductase occurred in overnight-dialyzed extracts of both cell types. These results show that cells derived from rat liver synthesize little ascorbate in culture, that cultured human-derived liver cells have a greater capacity for DHA reduction than do rat-derived liver cells, but that both cell types rely largely on GSH- or NADPH-dependent mechanisms for ascorbate recycling from DHA.
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The present study was undertaken to assess effect of reduced glutathione (GSH) on sperm motility, viability, total sperm abnormality, acrosomal and plasma membrane integrity, super oxide dismutase(SOD)and catalase, cholesterol efflux and malonaldehyde (MDA) production. Ejaculates (50) were collected twice a week from 8 mithun bulls and semen was split into 4 equal aliquots, diluted with the TEYC extender. Group 1: semen without additives (control), group 2 to group 4:semen was diluted with 5 mM, 10 mM and 15 mM of reduced glutathione (GSH), respectively. Inclusion of GSH into diluent resulted in significant decrease in percentages of dead spermatozoa, abnormal spermatozoa and acrosomal integrity at different hours of storage periods as compared with control group. Additionally, GSH at 5 and 15 mM were inferior to GSH 10 mM treatments as regards to these characteristics and GSH at 10 mM has significant improvement in quality of mithun semen in in- vitro stored for up to 30 h. It was concluded that the possible protective effects of GSH on sperm parameters are, it enhanced the function of antioxidant enzymes, prevented efflux of cholesterol from cell membrane, and reduced malonaldehyde(MDA) production during preservation.
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Human myeloid leukemia cells (HL-60) transport only the oxidized form of vitamin C (dehydroascorbic acid) and accumulate the vitamin in the reduced form, ascorbic acid. We performed a detailed study of the role of glutathione in the intracellular trapping/accumulation of ascorbic acid in HL-60 cells. Uptake studies using HL-60 cells depleted of glutathione by treatment with L-buthionine-(S,R) sulfoximine and diethyl maleate, revealed no changes in the cells' ability to transport dehydroascorbic acid and accumulate ascorbic acid. Similar transport and accumulation rates were obtained using HL-60 cells containing intracellular glutathione concentrations from 6 mM to 1 μM. HL-60 cells, containing as little as 5 μM glutathione, were able to accumulate up to 150 mM ascorbic acid intracellularly when incubated with dehydroascorbic acid. Glutathione was capable of reducing dehydroascorbic acid by a direct chemical reaction, but only when present in a greater than 10-fold stoichiometric excess over dehydroascorbic acid. The accumulation of ascorbic acid by HL-60 cells was strongly temperature-dependent and was very inefficient at 16°C. On the other hand, the direct chemical reduction of dehydroascorbic acid by excess glutathione proceeded efficiently at temperatures of 16°C. Our data indicate that glutathione-dependent reductases in HL-60 cells are not responsible for the ability of these cells to accumulate millimolar concentrations of ascorbic acid. These findings indicate that alternative enzymatic mechanisms are involved in the cellular reduction of dehydroascorbic acid. Human myeloid leukemia cells (HL-60) transport only the oxidized form of vitamin C (dehydroascorbic acid) and accumulate the vitamin in the reduced form, ascorbic acid. We performed a detailed study of the role of glutathione in the intracellular trapping/accumulation of ascorbic acid in HL-60 cells. Uptake studies using HL-60 cells depleted of glutathione by treatment with L-buthionine-(S,R) sulfoximine and diethyl maleate, revealed no changes in the cells' ability to transport dehydroascorbic acid and accumulate ascorbic acid. Similar transport and accumulation rates were obtained using HL-60 cells containing intracellular glutathione concentrations from 6 mM to 1 μM. HL-60 cells, containing as little as 5 μM glutathione, were able to accumulate up to 150 mM ascorbic acid intracellularly when incubated with dehydroascorbic acid. Glutathione was capable of reducing dehydroascorbic acid by a direct chemical reaction, but only when present in a greater than 10-fold stoichiometric excess over dehydroascorbic acid. The accumulation of ascorbic acid by HL-60 cells was strongly temperature-dependent and was very inefficient at 16°C. On the other hand, the direct chemical reduction of dehydroascorbic acid by excess glutathione proceeded efficiently at temperatures of 16°C. Our data indicate that glutathione-dependent reductases in HL-60 cells are not responsible for the ability of these cells to accumulate millimolar concentrations of ascorbic acid. These findings indicate that alternative enzymatic mechanisms are involved in the cellular reduction of dehydroascorbic acid.
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Chronic administration of triiodothyronine (T3) in high daily doses (40, 25 μg; 3–36 days) to male and female rats induced hyperactivity of the adrenal cortex, as indicated by marked increases in corticoid concentrations of plasma and adrenal and by hypertrophy of the gland. An inverse relationship was found between ascorbic acid and corticosterone concentration in adrenals of severely hyperthyroid animals. Adrenal ascorbic acid concentration was consistently reduced (14–24%) with higher doses of T3, while corticosterone levels in gland and plasma increased 2- to 4-fold and 40–80%, respectively. Ascorbic acid content of enlarged adrenals in the male increased significantly, however. It is concluded that in the hyperthyroid animal increased adrenocortical secretion occurs which can be maintained for at least several weeks. Cortical hormone elaboration by the adrenal in experimental hyperthyroidism bears no quantitative relationship to its ascorbic acid content. (Endocrinology74: 509, 1964)
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Glutathione reductase
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Ascorbic acid (vitamin C) and the tripeptide thiol, glutathione gamma-glutamyl cysteinyl glycine (glutathione) are the major low molecular weight soluble antioxidants in plant cells. The pathway of glutathione biosynthesis is similar in animals and plants while that of ascorbate biosynthesis differs considerably between the two kingdoms. The potential for obtaining substantial constitutive changes in the tissue contents of these antioxidants by manipulation of the biosynthetic enzymes has been demonstrated. Moreover, the concentrations of ascorbate and glutathione are greatly modified in response to a variety of environmental triggers, particularly those that cause increased oxidative stress. It is essential that the signals and associated signal transduction pathways that trigger enhanced antioxidant accumulation are elucidated as these offer an important alternative means of achieving greater nutritional value in edible plant organs.
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