Although resveratrol has widely been studied for its potential health benefits, little is known about its metabolic effects in humans. Our aims were to determine whether the polyphenol resveratrol improves insulin sensitivity in type 2 diabetic patients and to gain some insight into the mechanism of its action. After an initial general examination (including blood chemistry), nineteen patients enrolled in the 4-weeklong double-blind study were randomly assigned into two groups: a resveratrol group receiving oral 2 £ 5 mg resveratrol and a control group receiving placebo. Before and after the second and fourth weeks of the trial, insulin resistance/sensitivity, creatinine-normalised ortho-tyrosine level in urine samples (as a measure of oxidative stress), incretin levels and phosphorylated protein kinase B (pAkt):protein kinase B (Akt) ratio in platelets were assessed and statistically analysed. After the fourth week, resveratrol significantly decreased insulin resistance (homeostasis model of assessment for insulin resistance) and urinary ortho-tyrosine excretion, while it increased the pAkt:Akt ratio in platelets. On the other hand, it had no effect on parameters that relate to b-cell function (i.e. homeostasis model of assessment of b-cell function). The present study shows for the first time that resveratrol improves insulin sensitivity in humans, which might be due to a resveratrol-induced decrease in oxidative stress that leads to a more efficient insulin signalling via the Akt pathway.Key words: Resveratrol: Type 2 diabetes: Insulin sensitivity: Oxidative stress: Akt Despite the rather high average daily fat intake in France, compared with other European countries, epidemiological surveys document a relatively low rate of cardiovascular mortality. This phenomenon, which is often called the French paradox, is thought to be explained by a fairly high red wine consumption by the French (1,2) . Red wine is known to be rich in various polyphenolic compounds that might have a variety of health benefits. Among these polyphenols, the stilbene derivative resveratrol seems to be the most vigorously studied, which is probably due to the fact that it apparently affects a wide array of physiological and biochemical processes as shown in animal and cell culture studies (3) . On the other hand, human studies with conclusive results on resveratrol are regrettably lacking.Resveratrol is considered to have beneficial effects on the cardiovascular system, as it has been found to improve vasodilatation (4) , ischaemic preconditioning (5,6) , both of which seem to be the result of the activation of the endothelial NO synthase enzyme (7) , and to inhibit both platelet aggregation (3) and vascular smooth muscle cell proliferation (8) . In addition, resveratrol has also been demonstrated to show anti-inflammatory (9) and anti-tumour activities (3) , and it might even have considerable anti-ageing properties as it provokes changes in cell signalling that mimics those found upon energy restriction (3) .Oxidative stress, whi...

We purposed to determine the impact of erythropoietin on altering glucose metabolism in the settings of in vitro and in vivo experiments. The acute effect of erythropoietin on lowering blood glucose levels was studied in animal experiments. In [³H]-deoxy-D-glucose isotope studies we measured glucose uptake with insulin and erythropoietin using 3T3-L1 cells cultured under normal or high glucose conditions. Altered activation of Akt and ERK pathways was evaluated in immunoblot analyses. Immunocytochemistry was conducted to determine the glucose transporter 4 translocation to the plasma membrane. Addition of erythropoietin significantly lowered blood glucose levels in vivo in rats. The glucose uptake was markedly increased by erythropoietin treatment (at concentrations 0.15, 0.3, and 0.625 ng/ml) in adipocytes grown in high glucose medium (p<0.05), but it remained unaltered in cells under normal glucose conditions. Significant increase of phosphorylation of ERK and Akt was detected due to erythropoietin (p<0.05). Co-administration of erythropoietin and insulin resulted in higher phosphorylation of Akt and [³H]-deoxy-D-glucose uptake in adipocytes than insulin treatment alone. We found that erythropoietin induced the trafficking of glucose transporter 4 to the plasma membrane. Our data showed that erythropoietin significantly decreased blood glucose levels both in vivo and in vitro, in part, by increasing glucose uptake via the activation of Akt pathway. Preliminary data revealed that adipocytes most likely exhibit a specific receptor for erythropoietin.

We conclude that the G900C polymorphism associates with the level of HbA (1c) and the onset of the disease, but not with either of the diabetic microvascular complications.

Background/Aims: Erythropoietin-resistance is an unsolved concern in the treatment of renal anaemia. We aimed to investigate the possible role of ortho- and meta-tyrosine - the hydroxyl free radical products of L-phenylalanine - in the development of erythropoietin-resistance. Methods: TF-1 erythroblast cell line was used. Cell concentration was determined on day 1; 2 and 3 by two independent observers simultaneously in Bürker cell counting chambers. Protein concentration was determined with colorimetric method. Para-, ortho- and meta-tyrosine levels were measured using reverse phase-HPLC with fluorescence detection. Using Western blot method activating phosphorylation of STAT5 and ERK1/2 were investigated. Results: We found a time- and concentration-dependent decrease of erythropoietin-induced proliferative activity in case of ortho- and meta-tyrosine treated TF-1 erythroblasts, compared to the para-tyrosine cultured cells. Decreased erythropoietin-response could be regained with a competitive dose of para-tyrosine. Proteins of erythroblasts treated by ortho- or meta-tyrosine had lower para-tyrosine and higher ortho- or meta-tyrosine content. Activating phosphorylation of ERK and STAT5 due to erythropoietin was practically prevented by ortho- or meta-tyrosine treatment. Conclusion: According to this study elevated ortho- and meta-tyrosine content of erythroblasts may lead to the dysfunction of intracellular signaling, resulting in erythropoietin-hyporesponsiveness.

Oxidative stress processes play a major role in the development of the complications associated with diabetes and other diseases via non-enzymatic glycation, the hexosamine pathway, the polyol pathway and diacylglycerol-protein kinase C. Oxidative stress may lead to the production of hydroxyl free radicals, which can attack macromolecules, such as lipids, nucleic acids or amino acids. Phenylalanine (Phe) can be enzymatically converted to the physiological para-tyrosine (p-Tyr); however, a hydroxyl free radical attack on Phe may yield meta- and ortho-tyrosine (m- and o-Tyr, respectively) in addition to p-Tyr. Hence, m- and o-Tyr may be regarded as markers of hydroxyl free radical-induced damage. Their accumulation has been described; e.g., this accumulation has been found in the urine of patients with diabetes mellitus (DM) and/or chronic kidney disease, in cataract lenses, in vessel walls, in irradiated food and in amniotic fluid, and it may serve as an indicator of oxidative stress. The use of resveratrol to treat patients with type 2 DM led to a decrease in the urinary excretion of o-Tyr and concomitantly led to an improvement in insulin signaling and insulin sensitivity. Literature data also suggest that m- and o-Tyr may interfere with intracellular signaling. Our group has shown that erythropoietin (EPO) has insulin-like metabolic effects on fat cells in addition to its ability to promote the proliferation of erythroid precursor cells. We have shown that the supplementation of cell culture medium with m- and o-Tyr inhibits erythroblast cell proliferation, which could be ameliorated by p-Tyr. Additionally, in vivo, the o-Tyr/p-Tyr ratio is higher in patients with renal replacement therapy and a greater need for EPO. However, the o-Tyr/p-Tyr ratio was an independent determinant of EPO-resistance indices in our human study. The o-Tyr content of blood vessel walls inversely correlates with insulin- and acetylcholine-induced vasodilation, which could be further impaired by artificial oxidative stress and improved by the use of antioxidants. In rats that receive o-Tyr supplements, decreased vasorelaxation is detected in response to insulin. Additionally, o-Tyr supplementation led to the incorporation of the unnatural amino acid into cellular proteins and caused a decrease in the insulin-induced phosphorylation of endothelial nitric oxide synthase. Our data suggest that m- and o-Tyr may not only be markers of oxidative stress; instead, they may also be incorporated into cellular proteins, leading to resistance to insulin, EPO and acetylcholine.