Fructose-induced peroxynitrite production is mediated by methylglyoxal in vascular smooth muscle cells

Plasma 15-F2t isoprostane concentrations are increased during acute fructose loading in type 2 diabetes

OBJECTIVE

Fructose consumption is increasing worldwide and is likely to play a role in metabolic disorders. Dietary fructose is often recommended for diabetic patients, as this form of carbohydrate leads to a lower postprandial rise in plasma glucose and insulin. However, fructose contributes to the generation of free radicals. The aim of this work was to investigate the acute effects of a fructose load in patients with type 2 diabetes mellitus (T2DM), compared with healthy controls, on several metabolic oxidative biomarkers, particularly plasma 15-F2t isoprostanes (15-F2t isoPs).

RESEARCH DESIGN AND METHODS

Six T2DM patients and six healthy subjects were recruited. All patients underwent a single fructose tolerance test (75 g of anhydrous fructose). Plasma 15-F2t isoPs concentrations, plasma total antioxidant capacity (TAS) and thiobarbituric acid reactive substances (TBARS) were measured at baseline, and at 60, 120, 180 and 240 min after fructose absorption.

RESULTS

Baseline plasma 15-F2t isoPs concentrations were significantly increased in T2DM patients compared with controls (310+/-47 versus 237+/-20 pg/mL, respectively; P<0.01) and rose significantly (P<0.01) to 414+/-45 pg/mL in diabetic patients. No change in TAS or TBARS was observed in either group.

CONCLUSION

Plasma 15-F2t isoPs are increased during acute fructose loading in T2DM. Knowing the potentially deleterious effect of plasma 15-F2t isoPs-in particular, vascular lesions-and in light of our results, it is necessary to reconsider fructose consumption in T2DM patients, as we can now show, for the first time, a possible association between acute fructose loading and deleterious effects in such patients.

Proinflammatory and proapoptotic effects of methylglyoxal on neutrophils from patients with type 2 diabetes mellitus

OBJECTIVE

To determine the effect of methylglyoxal (MG) on cytokine production by, and apoptosis of, neutrophils from type 2 diabetes mellitus (T2DM) patients.

DESIGN AND METHODS

The levels of plasma MG, cytokines released by isolated neutrophils and the apoptotic status of neutrophils were determined.

RESULTS

The higher level of plasma MG in T2DM patients was correlated positively with glycated hemoglobin levels, fasting plasma glucose levels and urine albumin/creatinine ratios. The basal levels of cytokines released from neutrophils were markedly higher in patients. MG treatment of the neutrophils isolated from diabetic patients either did not alter, or decreased, the production of cytokines. In contrast, MG induced the release of cytokines from neutrophils of non-diabetics. Moreover, the neutrophils from T2DM patients showed a greater proclivity for apoptosis, which was further increased by in vitro MG treatment.

CONCLUSION

MG stimulated neutrophils to release more cytokines, which might play a role in the development of infection in T2DM.

Accumulation of endogenous methylglyoxal impaired insulin signaling in adipose tissue of fructose-fed rats

Increased accumulation of methylglyoxal (MG) has been linked to different insulin resistance states including diabetes and hypertension. In this study, the effects of MG on insulin signaling pathway were investigated. Following 9 weeks of fructose treatment, an insulin resistance state was developed in Sprague-Dawley (SD) rats, demonstrated as increased triglyceride and insulin levels, high blood pressure, and decreased insulin-stimulated glucose uptake by adipose tissue. More importantly, we observed a close correlation between the development of insulin resistance and elevated MG level in serum and adipose tissue. Both insulin resistance state and the elevated MG level were reversed by the MG scavenger, N-acetyl cysteine (NAC). When 3T3-L1 adipocytes were treated directly with MG, the impaired insulin signaling was also observed, indicated by decreased insulin-induced insulin-receptor substrate-1 (IRS-1) tyrosine phosphorylation and the decreased kinase activity of phosphatidylinositol (PI) 3-kinase (PI3K). The ability of NAC to block MG-impairment of PI3K activity and IRS-1 phosphorylation further confirmed the role of MG in the development of insulin resistance. In conclusion, the increase in endogenous MG accumulation impairs insulin-signaling pathway and decreases insulin-stimulated glucose uptake in adipose tissue, which may contribute to the development of insulin resistance.

Methylglyoxal, oxidative stress, and hypertension

Pathogenic mechanisms for essential hypertension are unclear despite striking efforts from numerous research teams over several decades. Increased production of reactive oxygen species (ROS) has been associated with the development of hypertension and the role of ROS in hypertension has been well documented in recent years. In this context, it is important to better understand pathways and triggering factors for increased ROS production in hypertension. This review draws a causative linkage between elevated methylglyoxal level, methylglyoxal-induced production of ROS, and advanced glycation end products in the development of hypertension. It is proposed that elevated methylglyoxal level and resulting protein glycation and ROS production may be the upstream links in the chain reaction leading to the development of hypertension.