Peter G. Scheffer

Effects of sex steroids on components of the insulin resistance syndrome in transsexual subjects

objective Sex differences are found in most components of the insulin resistance syndrome and the associated cardiovascular risk profile. These differences are attributed to sex‐specific sex steroid profiles, but the effects of sex steroids on the individual components of the insulin resistance syndrome remain incompletely understood.

Dietary nitrate attenuates oxidative stress, prevents cardiac and renal injuries, and reduces blood pressure in salt-induced hypertension

AIMS Reduced bioavailability of endogenous nitric oxide (NO) is a central pathophysiological event in hypertension and other cardiovascular diseases. Recently, it was demonstrated that inorganic nitrate from dietary sources is converted in vivo to form nitrite, NO, and other bioactive nitrogen oxides. We tested the hypothesis that dietary inorganic nitrate supplementation may have therapeutic effects in a model of renal and cardiovascular disease. METHODS AND RESULTS Sprague-Dawley rats subjected to unilateral nephrectomy and chronic high-salt diet from 3 weeks of age developed hypertension, cardiac hypertrophy and fibrosis, proteinuria, and histological as well as biochemical signs of renal damage and oxidative stress. Simultaneous nitrate treatment (0.1 or 1 mmol nitrate kg⁻¹ day⁻¹), with the lower dose resembling the nitrate content of a diet rich in vegetables, attenuated hypertension dose-dependently with no signs of tolerance. Nitrate treatment almost completely prevented proteinuria and histological signs of renal injury, and the cardiac hypertrophy and fibrosis were attenuated. Mechanistically, dietary nitrate restored the tissue levels of bioactive nitrogen oxides and reduced the levels of oxidative stress markers in plasma (malondialdehyde) and urine (Class VI F2-isoprostanes and 8-hydroxy-2-deoxyguanosine). In addition, the increased circulating and urinary levels of dimethylarginines (ADMA and SDMA) in the hypertensive rats were normalized by nitrate supplementation. CONCLUSION Dietary inorganic nitrate is strongly protective in this model of renal and cardiovascular disease. Future studies will reveal if nitrate contributes to the well-known cardioprotective effects of a diet rich in vegetables.

Myeloperoxidase: a useful biomarker for cardiovascular disease risk stratification?

BACKGROUND Inflammation and oxidative stress are associated with atherosclerosis. Myeloperoxidase (MPO) is linked to both inflammation and oxidative stress by its location in leukocytes and its role in catalyzing the formation of oxidizing agents. Recent evidence suggests that MPO activity precipitates atherogenesis. Measurement of MPO in plasma may therefore contribute to cardiovascular disease (CVD) risk stratification. CONTENT Cross-sectional studies, case-control studies, and prospective-cohort studies investigating the relation between MPO and CVD have been evaluated. Differences in study populations, sample materials, sample handling, and assays were ascertained. Potential causal mechanisms linking MPO to accelerated atherosclerosis are discussed here. A majority of studies indicate that measurement of MPO in plasma was associated with improved CVD risk stratification above and beyond risk stratification results obtained with markers used in routine clinical practice. However, comparison of these epidemiological studies with regard to MPO and outcome is hampered because the reported MPO concentration depends on the assay method, sampling material, and preanalytical and analytical procedures. The link between MPO and CVD can, at least partly, be explained by MPO-dependent oxidation of LDL and HDL, subsequently leading to cholesterol accumulation in the arterial wall. Furthermore, MPO may reduce the bioavailability of nitric oxide, resulting in endothelial dysfunction. Finally, MPO destabilizes atherosclerotic plaques. SUMMARY Increasing evidence suggests that MPO is causally linked to atherosclerosis and its measurement may improve CVD risk estimation. Before MPO can be used in routine clinical practice, however, standardization of sampling and laboratory procedures is needed.

Overexpression of Glyoxalase-I Reduces Hyperglycemia-induced Levels of Advanced Glycation End Products and Oxidative Stress in Diabetic Rats

The reactive advanced glycation end product (AGE) precursor methylglyoxal (MGO) and MGO-derived AGEs are associated with diabetic vascular complications and also with an increase in oxidative stress. Glyoxalase-I (GLO-I) transgenic rats were used to explore whether overexpression of this MGO detoxifying enzyme reduces levels of AGEs and oxidative stress in a rat model of diabetes. Rats were made diabetic with streptozotocin, and after 12 weeks, plasma and multiple tissues were isolated for analysis of AGEs, carbonyl stress, and oxidative stress. GLO-I activity was significantly elevated in multiple tissues of all transgenic rats compared with wild-type (WT) littermates. Streptozotocin treatment resulted in a 5-fold increase in blood glucose concentrations irrespective of GLO-I overexpression. Levels of MGO, glyoxal, 3-deoxyglucosone, AGEs, and oxidative stress markers nitrotyrosine, malondialdehyde, and F2-isoprostane were elevated in the diabetic WT rats. In diabetic GLO-I rats, glyoxal and MGO composite scores were significantly decreased by 81%, and plasma AGEs and oxidative stress markers scores were significantly decreased by ∼50%. Hyperglycemia induced a decrease in protein levels of the mitochondrial oxidative phosphorylation complex in the gastrocnemius muscle, which was accompanied by an increase in the lipid peroxidation product 4-hydroxy-2-nonenal, and this was counteracted by GLO-I overexpression. This study shows for the first time in an in vivo model of diabetes that GLO-I overexpression reduces hyperglycemia-induced levels of carbonyl stress, AGEs, and oxidative stress. The reduction of oxidative stress by GLO-I overexpression directly demonstrates the link between glycation and oxidative stress.

Two consecutive high‐fat meals affect endothelial‐dependent vasodilation, oxidative stress and cellular microparticles in healthy men

Summary.  Background: A large body of evidence has accumulated indicating a relation between postprandial hyperglycemia and hypertriglyceridemia, and the risk of cardiovascular disease. Objective: We studied possible mechanisms underlying the postprandial proatherogenic state by exposing healthy males to two consecutive high‐fat mixed meals. Patients/methods: Seventeen healthy males [age 25.4 ± 3 years, body mass index 23.6 ± 2 kg m−2] were studied during two randomized visits. During the meal visit, subjects consumed standardized meals (50 g of fat, 55 g of carbohydrates and 30 g of proteins) as breakfast and 4 h later as lunch. During the control visit, subjects remained fasted. Prior to each blood collection (before and every 2 h after the first meal), flow‐mediated dilation (FMD) of the brachial artery was measured. Results: Although within the normal range, postprandial plasma glucose and triacylglycerol concentrations increased significantly, especially after the second meal, as compared with baseline (4.8 ± 0.3 to 5.4 ± 0.4, 0.8 ± 0.2 to 1.7 ± 0.7 mmol L−1, respectively; both P < 0.05) and the fasting visit. After the second meal, FMD was significantly impaired (6.9% vs. 3.7%, P < 0.05) whereas oxidized low‐density lipoprotein (oxLDL)/LDL cholesterol ratio and malondialdehyde concentrations were markedly elevated (both P < 0.01). Finally, an increase in total microparticle (MP) numbers was observed during the meal visit (P < 0.05). Conclusions: In healthy males, after two consecutive fat‐rich meals, mild elevations in plasma glucose and triacylglycerol were paralleled by impaired FMD, increased markers of oxidative stress and circulating MPs, in particular, after the second meal. These findings may have consequences for subjects with postprandial dysmetabolism, including those with Type 2 diabetes.

Liver alanine aminotransferase, insulin resistance and endothelial dysfunction in normotriglyceridaemic subjects with type 2 diabetes mellitus.

Background  Plasma levels of liver transaminases, including alanine aminotransferase (ALT), are elevated in most cases of nonalcoholic fatty liver disease (NAFLD). Elevated ALT levels are associated with insulin resistance, and subjects with NAFLD have features of the metabolic syndrome that confer high‐risk cardiovascular disease. Alanine aminotransferase predicts the development of type 2 diabetes (DM2) in subjects with the metabolic syndrome. However, the role of elevated ALT levels in subjects with overt DM2 has yet not been explored.

Associations of LDL size with in vitro oxidizability and plasma levels of in vivo oxidized LDL in Type 2 diabetic patients

Aims Oxidative modification of low‐density lipoprotein (LDL) is believed to be a key step in the genesis of atherosclerotic lesions. The presence of small, dense LDL is associated with accelerated atherosclerosis and is common in diabetic patients. The aim of this study was to investigate the relationship of in vitro LDL oxidizability and circulating in vivo oxidized LDL with LDL particle size in Type 2 diabetic patients and healthy control subjects.

Metabolic Efficacy of Preprandial Administration of Lys(B28), Pro(B29) Human Insulin Analog in IDDM Patients: A comparison with human regular insulin during a three-meal test period

OBJECTIVE The objective of this study was to compare the efficacy of the rapid-acting Lys(B28), Pro(B29) human insulin analog, insulin lispro, with currently available short-acting human insulin in a multiple injection therapy (MIT) regimen with respect to blood glucose and plasma insulin profiles and to serum metabolites (lactate, free fatty acids, glycerol, and β-hydroxybutyrate) in 12 well-controlled type 1 diabetic subjects (8 male, HbA1c 6.8 ± 0.9% [mean ± SD]). RESEARCH DESIGN AND METHODS After a run-in period of 4 weeks, patients were treated with either lispro at mealtime or human insulin 30 min before the meal for two periods of 4 weeks in a randomized open-label crossover study. Intermediate-acting insulin (NPH insulin) was given at bedtime. At the end of both study periods, metabolic profiles were assessed from 10:00 P.M. to 7:00 P.M. the next day. RESUlTS During the treatment periods, glycemic control was stable during lispro but improved during human insulin (ΔHbA1c lispro 0.1 ± 0.48, NS; human insulin −0.41 ± 0.34%, P < 0.05). Glucose excursions, as measured by the incremental AUC, during the day and for the 2-h postprandial periods, were lower, although not significantly, for lispro. Insulin profiles demonstrated a faster rise after administration of lispro as compared with human insulin, peaking at 61 ± 11.9 and 111 ± 48.1 min (P < 0.01). Glycerol levels showed a slight increase before lunch and dinner, suggestive of enhanced lipolytic activity and compatible with the lower insulin levels. CONCLUSIONS Lispro insulin applied in an MIT regimen creates more physiologic insulin profiles and tends to lower the glycemic excursions during the day compared with short-acting insulin. The analog can be applied safely in an MIT regimen, with mealtime intervals up to 5 h.

Cysteamine restores glutathione redox status in cultured cystinotic proximal tubular epithelial cells

Recent evidence implies that impaired metabolism of glutathione has a role in the pathogenesis of nephropathic cystinosis. This recessive inherited disorder is characterized by lysosomal cystine accumulation and results in renal Fanconi syndrome progressing to end stage renal disease in the majority of patients. The most common treatment involves intracellular cystine depletion by cysteamine, delaying the development of end stage renal disease by a yet elusive mechanism. However, cystine depletion does not arrest the disease nor cures Fanconi syndrome in patients, indicating involvement of other yet unknown pathologic pathways. Using a newly developed proximal tubular epithelial cell model from cystinotic patients, we investigate the effect of cystine accumulation and cysteamine on both glutathione and ATP metabolism. In addition to the expected increase in cystine and defective sodium-dependent phosphate reabsorption, we observed less negative glutathione redox status and decreased intracellular ATP levels. No differences between control and cystinosis cell lines were observed with respect to protein turnover, albumin uptake, cytosolic and mitochondrial ATP production, total glutathione levels, protein oxidation and lipid peroxidation. Cysteamine treatment increased total glutathione in both control and cystinotic cells and normalized cystine levels and glutathione redox status in cystinotic cells. However, cysteamine did not improve decreased sodium-dependent phosphate uptake. Our data implicate that cysteamine increases total glutathione and restores glutathione redox status in cystinosis, which is a positive side-effect of this agent next to cystine depletion. This beneficial effect points to a potential role of cysteamine as anti-oxidant for other renal disorders associated with enhanced oxidative stress.

Circulating oxidized LDL: determinants and association with brachial flow-mediated dilation

Circulating oxidized LDL (oxLDL) levels are strongly correlated to LDL-cholesterol (LDL-c) and apolipoprotein-B100 (apoB100), making it difficult to disentangle their independent contributions to cardiovascular risk. We explored the determinants of oxLDL and the relation between oxLDL and flow-mediated dilation (FMD) of the brachial artery to investigate whether the oxLDL/LDL-c and oxLDL/apoB100 ratios are more informative than the separate variables. FMD of the brachial artery and plasma concentrations of oxLDL, LDL-cholesterol, and apoB100 were measured in 624 men and women (age range 50 to 87 years), participating in a population-based cohort study. OxLDL was strongly correlated with apoB100 (r = 0.82, P < 0.001) and LDL-c (r = 0.67, P < 0.001). Other major independent determinants of oxLDL were sex, HDL-cholesterol, and LDL particle size. LDL-c and apoB100 concentrations were not significantly associated with FMD. After adjustment for age, sex, glucose tolerance status, and Framingham risk score, the oxLDL/apoB100 ratio was negatively related to FMD (P = 0.017). This association was weaker for the oxLDL/ LDL-c ratio (P = 0.062) and absent for oxLDL level (P = 0.27). In contrast to oxLDL, the oxLDL/apoB100 ratio, and to a lesser extent the oxLDL/LDL-c ratio, are related to a functional measure of atherosclerosis. Therefore correction of oxLDL for LDL particle number may improve the clinical usefulness of oxLDL measurement.