Exogenous Supply (exogenous + supply)

Distribution by Scientific Domains

Selected Abstracts

Fructose-mediated non-enzymatic glycation: sweet coupling or bad modification

Casper G. Schalkwijk
Abstract The Maillard reaction is a process in which reducing sugars react spontaneously with amino groups in proteins to advanced glycation endproducts (AGEs). Although an elevated level of glucose had been thought to play a primary role in the Maillard reaction, on a molecular basis, glucose is among the least reactive sugars within biological systems. The formation of AGEs is now also known to result from the action of various metabolites other than glucose, which are primarily located intracellularly and participate in the non-enzymatic glycation reaction at a much faster rate, such as fructose, trioses and dicarbonyl compounds. In this review, we considered the glycation reaction with particular attention to the potential role of fructose and fructose metabolites. The two sources for fructose are an exogenous supply from the diet and the endogenous formation from glucose through the aldose reductase pathway. Despite its ,eightfold higher reactivity, the contribution of extracellular glycation by fructose is considerably less than that by glucose, because of the low plasma concentration of fructose (5 mmol/L glucose vs 35 µmol/L fructose). Intracellularly, fructose is elevated in a number of tissues of diabetic patients in which the polyol pathway is active. In the cells of these tissues, the concentrations of fructose and glucose are of the same magnitude. Although direct evidence is not yet available, it is likely that the high reactivity of fructose and its metabolites may substantially contribute to the formation of intracellular AGEs and may contribute to alterations of cellular proteins, dysfunction of cells and, subsequently, to vascular complications. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Reactive oxygen species in rats with chronic post-ischemia pain

Background: An emerging theme in the study of the pathophysiology of persistent pain is the role of reactive oxygen species (ROS). In the present study, we examined the hypothesis that the exogenous supply of antioxidant drugs during peri-reperfusion would attenuate pain induced by ischemia/reperfusion (IR) injury. We investigated the analgesic effects of three antioxidants administered during peri-reperfusion using an animal model of complex regional pain syndrome-type I consisting of chronic post-ischemia pain (CPIP) of the hind paw. Methods: Application of a tight-fitting tourniquet for a period of 3 h produced CPIP in male Sprague,Dawley rats. Low-dose allopurinol (4 mg/kg), high-dose allopurinol (40 mg/kg), superoxide dismutase (SOD, 4000 U/kg), N -nitro- l -arginine methyl ester (l -NAME, 10 mg/kg), or SOD (4000 U/kg)+l -NAME (10 mg/kg) was administered intraperitoneally just after tourniquet application and at 1 and 2 days after reperfusion for 3 days. The effects of antioxidants in rats were investigated using mechanical and cold stimuli. Each group consisted of seven rats. Results: Allopurinol caused significant alleviation in mechanical and cold allodynia for a period of 4 weeks in rats with CPIP. Both SOD and l -NAME, which were used to investigate the roles of superoxide (O2 ,,) and nitric oxide (NO) in pain, also attenuated neuropathic-like pain symptoms in rats for 4 weeks. Conclusions: Our findings suggest that O2 ,, and NO mediate IR injury-induced chronic pain, and that ROS scavengers administered during the peri-reperfusion period have long-term analgesic effects. [source]

Effects of glucose on formation of cytotoxic end-products and proteolytic activity of Prevotella intermedia, Prevotella nigrescens and Porphyromonas gingivalis

Kaoru Saito
Black-pigmented bacteria which produce cytotoxic metabolic end-products and cell membrane-associated proteases have been reported to play an important role in the pathogenesis of periodontal diseases. These bacterial virulence factors can be modified by the environmental conditions including nutrients supplied variously into the oral cavity. Although glucose is one of the most essential nutrients for oral bacteria, the exogenous supply of glucose may be discontinuous and the glucose concentration in a periodontal pocket may be influenced by the depth of the periodontal pocket. Therefore, effects of glucose as an environmental factor on the virulence factors of Prevotella intermedia, Prevotella nigrescens and Porphyromonas gingivalis were studied. When grown in the presence of glucose, both P. intermedia and P. nigrescens markedly decreased the production of cytotoxic end-products including succinate, isobutyrate, isovalerate and ammonia, although their growth was increased. Furthermore, the proteolytic activities such as immunoglobulin-, albumin- and casein-degrading activities of these bacteria were decreased in the presence of glucose. On the other hand, no effect of glucose on the metabolic activity of P. gingivalis was observed. These results suggest that pathogenicity of P. intermedia and P. nigrescens may be decreased by the presence of glucose. [source]

A wheat embryo cell-free protein synthesis system not requiring an exogenous supply of GTP

Hirohisa Koga
Abstract Most in vitro protein synthesis systems require a supply of GTP for the formation of translation initiation complexes, with two GTP molecules per amino acid needed as an energy source for a peptide elongation reaction. In order to optimize protein synthesis reactions in a continuous-flow wheat embryo cell-free system, we have examined the influence of adding GTP and found that the system does not require any supply of GTP. We report here the preparation of a wheat embryo extract from which endogenous GTP was removed by gel filtration, and the influence of adding GTP to the system on protein synthesis reactions. Using Green Fluorescent Protein (GFP) as a reporter, higher levels of production were observed at lower concentrations of GTP, with the optimal level of production obtained with no supply of GTP. A HPLC-based analysis of the extract and the translation mixture containing only ATP as an energy source revealed that GTP was not detectable in the extract, however, 35 ,M of GTP was found in the translation mixture. This result suggests that GTP could be generated from other compounds, such as GDP and GMP, using ATP. A similar experiment with a C-terminally truncated form of human protein tyrosine phosphatase 1B (hPTP1B1-320) gave almost the same result. The wheat embryo cell-free translation system worked most efficiently without exogenous GTP, producing 3.5 mg/mL of translation mixture over a 48-h period at 26°C. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]