Salvage of pyrimidine nucleosides by Trichomonas vaginalis

Trichomonas vaginalis is incapable of de novo pyrimidine biosynthesis because it cannot incorporate bicarbonate, aspartate or orotate into its pyrimidine nucleotides or nucleic acids. The organism can salvage exogenous cytidine greater than uridine greater than uracil and thymidine, and incorporate them into the nucleotide pool. A portion of cytidine is converted to CMP, CDP and CTP by cytidine phosphotransferase and nucleotide kinases. Some cytidine and most of uracil are, however, converted first to uridine by cytidine deaminase and uridine phosphorylase respectively; uridine is then incorporated into UMP, UDP and UTP by uridine phosphotransferase and nucleotide kinases. The two phosphotransferases, found mainly in the non-sedimentable fraction of T. vaginalis, provide the main avenue of pyrimidine salvage. No significant levels of pyrimidine phosphoribosyl transferase or nucleoside kinases can be detected in the extract. T. vaginalis has no appreciable dihydrofolate reductase or thymidylate synthetase; it grows normally in millimolar concentrations of methotrexate, pyrimethamine, or trimethoprim, and cannot incorporate labels from exogenous uracil or uridine into DNA. It has an enzyme thymidine phosphotransferase in the sedimentable fraction which converts thymidine to TMP. Thymidine salvage in T. vaginalis is thus totally isolated from the rest of the pyrimidine salvage.     

The possible role of TNF-α and IL-2 in inducing tumor-associated metabolic alterations

This study was conducted to investigate the role of tumor necrosis factor- (TNF-) and interleukin-2 (IL-2) in inducing cancer cachexia, and the results were compared with those obtained from our previous study on Fisher 344 rats with methylcholanthrene-induced sarcoma. Three groups of male Fisher 344 rats received one of the following regimens: 4×10⁴ IU of human recombinant TNF- per rat per day subcutaneously (sc) for 5 consecutive days (n=5), 3.5×10⁵ U human recombinant IL-2 per rat per day sc for 14 consecutive days (n=5), or normal saline (n=5). The activities of both phosphoenolpyruvate carboxykinase (PEPCK) and malic enzyme (ME) were increased slightly in the IL-2 group. Furthermore, LPL activity was significantly increased in the adipose tissue of the TNF group and in the cardiac muscle of the IL-2 group, but not in that of the TNF group. These results show that there is a significant difference between the metabolic alterations seen in the tumor-bearing state and those induced by either TNF- or IL-2 alone. Thus, it is unlikely that IL-2 or TNF- is the sole mediator of cancer cachexia in this tumor and rat model.     

Phosphoenolpyruvate in rat pancreatic islets: A possible intracellular trigger of insulin release?

Summary The content of phosphoenolpyruvate (PEP) has been measured in isolated rat islets of Langerhans incubated in vitro. Islet PEP was higher in islets incubated with 16.7 mmol/l glucose than in islets incubated with zero or 2.8 mmol/l glucose. Islet PEP content was also increased in islets incubated with 5 mmol/l D-glyceraldehyde. Mannoheptulose abolished the glucose-induced rise in PEP content but not that elicited by D-glyceraldehyde. These results are consistent with a role for PEP as an intracellular mediator of glucose- and glyceraldehyde-induced insulin release. The kinetics of pyruvate kinase in extracts of rat islets were studied. The maximal extractable activity was considerably higher than known rates of glycolytic flux. The Km values were found to be 0.16 mmol/l for PEP and 0.5 mmol/l for ADP. The control of islet PEP content and the possible role of PEP in insulin release are discussed.     

The phenotype of a flavin-containing monooyxgenase knockout mouse implicates the drug-metabolizing enzyme FMO1 as a novel regulator of energy balance

Flavin-containing monooxygenases (FMOs) of mammals are thought to be involved exclusively in the metabolism of foreign chemicals. Here, we report the unexpected finding that mice lacking Fmos 1, 2 and 4 exhibit a lean phenotype and, despite similar food intake, weigh less and store less triglyceride in white adipose tissue (WAT) than wild-type mice. This is a consequence of enhanced whole-body energy expenditure, due mostly to increased resting energy expenditure (REE). This is fuelled, in part, by increased fatty acid β-oxidation in skeletal muscle, which would contribute to depletion of lipid stores in WAT. The enhanced energy expenditure is attributed, in part, to an increased capacity for exercise. There is no evidence that the enhanced REE is due to increased adaptive thermogenesis; instead, our results are consistent with the operation in WAT of a futile energy cycle. In contrast to FMO2 and FMO4, FMO1 is highly expressed in metabolic tissues, including liver, kidney, WAT and BAT. This and other evidence implicates FMO1 as underlying the phenotype. The identification of a novel, previously unsuspected, role for FMO1 as a regulator of energy homeostasis establishes, for the first time, a role for a mammalian FMO in endogenous metabolism. Thus, FMO1 can no longer be considered to function exclusively as a xenobiotic-metabolizing enzyme. Consequently, chronic administration of drugs that are substrates for FMO1 would be expected to affect energy homeostasis, via competition for endogenous substrates, and, thus, have important implications for the general health of patients and their response to drug therapy.     

p38丝裂原活化蛋白激酶在能量代谢控制和心血管疾病中的作用

p38是丝裂原活化蛋白激酶家族中的成员之一,大量研究显示p38在能量代谢中具有广泛的作用.p38参与脂肪组织、骨骼肌、胰岛细胞和肝脏等组织、器官的能量代谢,这些组织、器官都是控制能量代谢的主要组织与器官.在白色脂肪组织,p38对脂肪细胞分化和葡萄糖摄取的重要作用是一致公认的,尽管p38对脂肪细胞葡萄糖摄取究竟是促进还是抑制至今尚未定论;在棕色脂肪组织,p38对解偶联蛋白-1基因转录起促进作用.在骨骼肌,虽然p38对葡萄糖摄取的作用仍有争议,但p38对骨骼肌细胞分化和骨骼肌线粒体生成的重要作用是非常肯定的.在胰岛细胞,p38似乎与细胞凋亡有关;p38还可能控制胰岛素原基因转录,但对胰岛素分泌无明显作用.在肝脏,p38在肝脏的糖、脂代谢中起核心作用,一方面,p38通过抑制肝脏糖原合成,增加肝脏糖异生,使血糖升高;另一方面,p38通过抑制肝脏脂肪合成、促进脂肪酸在肝脏的氧化代谢,从而抑制脂肪在肝脏的贮存;另外,p38还通过调节低密度脂蛋白受体基因表达和胆汁代谢对胆固醇代谢起关键作用.p38不仅参与心肌细胞的各种生理、病理过程;也通过影响单核-巨噬细胞、血管内皮细胞和血管平滑肌细胞参与动脉粥样硬化斑块的形成.     

结核杆菌磷酸烯醇型丙酮酸羧基酶诱导小鼠细胞和体液免疫应答

目的检测结核杆菌磷酸烯醇型丙酮酸羧激酶(phosphoenolpyruvate carboxykinase,PEPCK)对BALB/c小鼠的免疫保护作用。方法选清洁级BALB/c小鼠60只,随机分为两组,实验组和对照组。实验组每只小鼠用表达的PEPCK融合蛋白10μg加弗氏不完全佐剂进行腹腔免疫注射,对照组小鼠仅用弗氏不完全佐剂注射。每隔2w免疫1次,共免疫3次。末次免疫2w后,分别取小鼠脾脏、血清,流式细胞仪检测CD4+和CD8+T细胞,MTT法检测淋巴细胞对刺激的应答水平,ELISA检测血清各种细胞因子及抗PEPCK抗体。结果实验组小鼠的脾脏明显大于对照组小鼠的脾脏,且粘连严重,CD4+T细胞增殖明显(73.5±3.69),CD4+/CD8+比值显著升高(5.1±0.98)(P<0.01);且淋巴细胞的应答能力明显强于对照组小鼠;实验组小鼠血清中IFN-γ、IL-12和TNF-α明显高于对照组,血清抗体滴度随免疫次数逐步增高。结论结核杆菌PEPCK能够有效的刺激机体产生细胞免疫反应和体液免疫反应,尤以细胞免疫反应为主,是很好的抗结核候选疫苗分子之一。     

Dietary intervention with vitamin D,calcium, and whey protein reduced fat mass and increased lean mass in rats

The aim of the current study was to determine the effects and the mechanisms of inclusion of dietary whey protein, high calcium, and high vitamin D intake with either a high-sucrose or high-fat base diets on body composition of rodents. Male Wistar rats were assigned to either no whey protein, suboptimal calcium (0.25%), and vitamin D (400 IU/kg) diet (LD), or a diet containing whey protein, high calcium (1.5%), and vitamin D (10 000 IU/kg) diet (HD), and either high-fat (40% of energy) or high-sucrose (60%) base diets for 13 weeks. Liver tissue homogenates were used to determine [¹⁴C]glucose and [¹⁴C]palmitate oxidation. mRNA expression of enzymes related to energy metabolism in liver, adipose, and muscle, as well as regulators of muscle mass and insulin receptor was assessed. The results demonstrated that there was reduced accumulation of body fat mass (P = .01) and greater lean mass (P = .03) for the HD- compared to LD-fed group regardless of the background diet. There were no consistent differences between the LD and HD groups across background diets in substrate oxidation and mRNA expression for enzymes measured that regulate energy metabolism, myostatin, or muscle vascular endothelial growth factor. However, there was an increase in insulin receptor mRNA expression in muscle in the HD compared to the LD groups. In conclusion, elevated whey protein, calcium, and vitamin D intake resulted in reduced accumulation of body fat mass and increased lean mass, with a commensurate increase in insulin receptor expression, regardless of the level of calories from fat or sucrose.     

The anti-diabetic effects of ethanol extract from two variants of Artemisia princeps Pampanini in C57BL/KsJ-db/db mice.

The anti-diabetic effects of two variants of Artemisia princeps Pampanini, sajabalssuk (SB) and sajuarissuk (SS), were investigated in type 2 diabetic animal using their ethanol extracts. Male C57BL/KsJ-db/db (db/db) mice were divided into control, SB ethanol extract (SBE), SS ethanol extract (SSE), or rosiglitazone (RG) groups and their age-matched littermates (db/+) were used. Supplementation of the SBE (0.171 g/100g diet), SSE (0.154 g/100g diet), and RG (0.005 g/100g diet) improved glucose and insulin tolerance and significantly lowered blood glycosylated hemoglobin levels, as compared to the control group. Plasma insulin, C-peptide and glucagon levels in db/db mice were higher in the db/+ mice, however these values were significantly lowered by SBE, SSE or RG-supplement. Hepatic GK activity was significantly lower in the db/db mice than in the db/+ mice, while hepatic G6Pase activity was vice versa. Supplementation of SBE, SSE and RG reversed these hepatic glucose-regulating enzyme activities. In addition, SBE and SSE markedly increased the hepatic glycogen content and muscle ratio as compared to the control group, but they did not alter the food intake, body weight and plasma leptin level. The RG group, however, showed a significant increase in the food intake, body weight and plasma leptin. These results suggest that SBE and SSE exert an anti-diabetic effect in type 2 diabetic mice.