José D. Méndez

Trends in advanced glycation end products research in diabetes mellitus and its complications

Advanced glycation end-products (AGEs) are heterogeneous groups of compounds that result from the non-enzymatic reaction of reducing sugars with free amino groups of biological molecules such as proteins, lipids, and nucleic acids. A large number of studies have been focused on AGEs metabolism, analysis, treatments, and their implications in the pathogenesis of diseases, especially in diabetes mellitus. Here, we review recent advances in the understanding of pathological complications caused by the production of AGEs. We provide an overview of the most important issues published within this area in last years; we also present the number of scientific papers related to AGEs available since 1950 until 2008 in the most important fields including metabolism, physiology, and pharmacology, thus as analytical methods for AGE detection and quantification and studies carried out in human body fluids. Data were collected from ovidSP.

Inhibition of Platelet Aggregation by Putrescine, Spermidine, and Spermine in Hypercholesterolemic Rabbits

BACKGROUND Hypercholesterolemia causes alterations in platelet function. Platelet hyperaggregation is considered a predisposing factor for atherosclerosis. In this paper, the antiaggregating effect of the polyamines putrescine, spermidine, and spermine was studied on platelets of normal and hypercholesterolemic rabbits. METHODS New Zealand rabbits were fed with a cholesterol-enriched diet for 10 weeks. Lipids and glucose were determined in serum. The assays of platelet aggregation were carried out using platelet-rich plasma (PRP) obtained from both control and cholesterol-fed rabbits. We used 2.5 micromol /mL ADP and 2 microg/mL collagen as inductors of platelet aggregation. In addition, arginase activity and L-arginine content were determined in PRP. RESULTS Serum total cholesterol and LDL-cholesterol concentrations were increased from 26.3 +/- 8.1 to 1,485.0 +/- 26.8 mg/dL and from 15.9 +/- 5.9 to 1,383.8 +/- 58.9 mg/dL, respectively, whereas triglyceride concentration increased from 88.3 +/- 35.6 to 411.0 +/- 154.5 mg/dL upon cholesterol feeding. Seventy-five percent of platelet aggregation inhibition was observed with 10 microM of polyamines in PRP of normal rabbits. Spermine inhibited platelet aggregation by 54% in PRP of hypercholesterolemic rabbits when ADP was used as agonist. The order of polyamine action was spermine > spermidine > putrescine. In addition, we found that platelet arginase activity and L-arginine content were unaltered upon hypercholesterolemia. CONCLUSIONS These results show that the polyamines putrescine, spermidine, and spermine have antagonist action in platelet aggregation and suggest a key role of polyamines in platelet aggregation under normal and hypercholesterolemic conditions.

Prevention by l-arginine and polyamines of delayed development and embryotoxicity caused by chemically-induced diabetes in rats

Diabetes mellitus induction with alloxan at a dose of 110 mg/kg i.p. in rats on Day 4 of pregnancy causes delayed development and resorptions as signs of embryotoxicity. In the present study, the administration of human NPH insulin at doses of 1 to 5 U/d to rats or 1.0 mL of 10 mM L-arginine for 8 d, starting the day following diabetes induction, prevented embryotoxicity and delayed development. Similar results were obtained when the polyamines putrescine, spermidine, or spermine were administered at doses of 1.0 mL of a 10 microM solution to each rat daily. However, even though L-arginine and polyamines prevented adverse effects of severe diabetes on the conceptus, and caused normalization of glucose, beta-hydroxybutyrate levels remained elevated. These results support the hypothesis that the mechanisms of normal and altered development could be mediated by the action of polyamines.

Effect of l-arginine on arginase activity in male accessory sex glands of alloxan-treated rats

Arginase activity has been identified in the prostate, and may be important in the synthesis of polyamines in accessory sex glands in the male. Polyamines in turn may mediate the action of androgens. Diabetic patients have disordered androgen synthesis. The purpose of this work was to evaluate the effect of L-arginine on arginase activity in accessory sex glands of male rats under normal and diabetic conditions (alloxan 120 mg/kg, i.p.). Normal and diabetic male rats were untreated or were treated with insulin or L-arginine for 96 h, and sacrificed. Arginase activity was measured in serum and in accessory sex glands. Arginase activity in accessory glands did not change significantly with induction of diabetes. Arginase activity was increased in diabetic insulin-treated rats, but there was no arginase response to L-arginine administration in diabetic animals. These findings stand in contrast to beneficial effects of L-arginine previously observed when this amino acid was administered for a long time (at least 10 days). We suspect that altered arginase activity in accessory sex glands may play a role in the reproductive dysfunction caused by diabetes, inasmuch as arginase activity can be increased in experimentally diabetic rats by the administration of insulin.

Increased uptake of oxidized LDL by macrophages from type 2 diabetics is inhibited by polyamines

The aim of this study was to evaluate the effect of polyamines putrescine, spermidine and spermine on human LDL oxidation and to assess the ability of macrophages derived from type 2 diabetic patients to uptake oxLDL. Polyamine effect was compared with α-tocopherol. Four healthy subjects and eight type 2 diabetic patients were included in this study. To characterize type 2 diabetic patients and non-diabetic subjects, laboratory test were carried out. Glucose, glycated haemoglobin (HbA1C), triglycerides, low (LDL) and high density lipoproteins (HDL) and serum lipid peroxidation were measured in blood. The study was performed in three stages. For each stage, ten experimental conditions comparing the effect of polyamines with α-tocopherol (10μM solutions) on LDL oxidation and the uptake of oxLDL by macrophages were analyzed. MDA concentration was found to be significantly higher in type 2 diabetic patients compared to healthy subjects (5.6±0.58 vs. 2.66±0.31μM MDA, respectively, (P<0.05)). Percent of macrophages containing oxLDL was determined by means of red oil staining. The uptake of oxLDL by macrophages derived from diabetic patients was clear. The uptake of oxLDL was inhibited when the oxidation was prevented by polyamines or α-tocopherol. Spermine showed high antioxidant capacity (96.67±1.53% vs. 25.67±2.30%) compared to α-tocopherol (96.67±1.53% vs. 47.00±7.20%) at the concentration tested. In conclusion, polyamines especially spermine, has a potent antioxidant effect compared to α-tocopherol on human LDL oxidation, followed by spermidine and putrescine. The results have clinical relevance in the diabetic complications and add knowledge on the role of polyamines as natural antioxidants. This research is not a clinical evaluation rather a functional analysis utilizing clinical samples.