Glycation and glycoxidation studies in vitro on isolated human vitreous collagen.

BACKGROUND: Structural and functional impairment in vitreous collagen plays an important role in the pathogenesis of diabetic retinopathy. Collagen being a long-lived protein is prone to both glycation and glycoxidation, resulting in accumulation of advanced glycation end products (AGE). The objective of our study was to explore the extent of glycation by glucose, and iron- and copper-mediated glycoxidation of human vitreous collagen, and also to study the beneficial effects of lysine, inositol and aminoguanidine as antiglycating and anti-cross linking agents. MATERIAL/METHODS: Vitreous from human donor eyeballs was pooled and collagen was extracted using 0.9 M NaCl. Collagen was estimated by measuring the hydroxyproline content. The extracted collagen was used for glycation and glycoxidation studies. Glycation studies were conducted using U14C glucose, along with anti-glycating agents, such as lysine and aminoguanidine. Metal-mediated glycoxidation studies were done by measuring collagen content in cyanogen bromide insoluble fraction, in the presence and absence of an anti-cross linking agent, inositol. RESULTS: Human vitreous collagen extractable with 0.9 M NaCl was glycated by glucose at 5 and 10 mM concentrations under physiological conditions of temperature and pH. An anti-glycating effect was exhibited by lysine, inositol and aminoguanidine, of which lysine was the best (76% antiglycating activity) followed by inositol. Inositol was also found to be useful in inhibiting glycoxidation. CONCLUSIONS: Vitreous collagen undergoes glycation, as well as iron- and copper-mediated glycoxidation, leading to possible structural and functional impairment. Glycation and glycoxidation are inhibited, significantly by lysine and inositol respectively.

Presence of a 88 kDa Eales protein in uveitis, tuberculosis, leprosy and rheumatoid arthritis.

BACKGROUND: Eales disease (ED) is an idiopathic retinal vasculitis affecting young adult males. We have earlier reported the identification, purification and partial characterization of a novel 88 kDa protein found in the serum of patients with ED. The aim of the present study was to look for the 88 kDa protein in serum samples obtained from cases of retinal vasculitis mimicking ED and in other systemic inflammatory diseases. MATERIAL/METHODS: Serum samples from healthy volunteers and from patients with ED, uveitis, parsplanitis ocular sarcoidosis, toxoplasmosis, leprosy, diabetic retinopathy, viral hepatitis, and rheumatoid arthritis were analyzed for the presence of the 88 kDa protein by polyacralymide gel electrophoresis (PAGE). The immunological identity of the 88 kDa protein found in ED and in other diseases was investigated by Western blot. Immunohistochemistry was performed on epiretinal membranes (ERM) obtained from ED patients to localize the 88 kDa protein. RESULTS: 88 kDa protein were detected in serum samples obtained from patients with posterior uveitis, tuberculosis, leprosy and rheumatoid arthritis. The 88 kDa protein found in serum from patients with ED is immunologically identical to that found in other systemic inflammatory conditions. 88 kDa protein was localized in inflammatory cells and in nonvascular endothelium in ERMs obtained from patients with ED. CONCLUSIONS: We have identified a novel acute phase reactant, which is elaborated in ocular and systemic inflammatory conditions other than Eales disease. Further work is necessary to decipher the precise role of the 88 kDa protein in the pathophysiology of these inflammatory diseases.

Effect of oral supplementation of free amino acids in type 2 diabetic patients-- a pilot clinical trial.

BACKGROUND: Oral amino acid intake reduces plasma glucose in Streptozotocin-induced diabetic rats. This study examined the effect of oral amino acid supplementation in patients with type 2 diabetes mellitus (DM). MATERIAL/METHODS: A double blind pilot clinical trial was conducted for a period of 2 months on 77 subjects with type 2 DM. Subjects of both sexes, ages 30-60, were included in the trial. All were receiving oral antidiabetic tablets. They were divided into groups on the basis of oral supplementation: (A) lysine, (B) essential amino acids, (C) amino acids and vitamins (fat and water-soluble), and (D) calcium phosphate (control). The subjects were periodically examined for fasting and post-prandial plasma glucose, fasting and post-prandial immunoreactive insulin, plasma amino acids, glycosylated haemoglobin (HbA1c), proteins and albumin in serum, urea and creatinine in plasma and sugar, and proteins and ketones in urine. RESULTS: The results revealed a significant decrease in PP plasma glucose (P<0.05) in group B when compared to groups C and D after 45 days. Plasma Arginine was increased in group C from 3.84 to 9.24 mg/dl. There were no statistically significant changes seen in other parameters between groups and visits. CONCLUSIONS: Oral supplementation with amino acids for patients with type 2 DM appears to decrease PP plasma glucose without any change in plasma insulin levels, perhaps due to improved insulin sensitivity. However, the long term effects of amino acids need further study.