Endothelial function in the post-prandial state

Circulating antioxidant defences are decreased in healthy people after a high-fat meal

The aim of this study was to examine the responses of uric acid, antioxidant defences and pro-oxidant variables after a high-fat meal. Twenty-five healthy persons without criteria for the metabolic syndrome, underwent a high-fat meal with Supracal®(60 g fat). Measurements were made at baseline and 3 h after the meal of TAG, uric acid, HDL-cholesterol, total proteins and oxidative stress. Following the high-fat meal, we detected a significant increase in pro-oxidative variables and a decrease in antioxidative variables. The uric acid concentrations were significantly lower after the high-fat meal and the reduction correlated significantly with the oxidative stress variables. The inverse relation between reduced uric acid and increased carbonylated proteins remained in multiple regression analysis. We conclude that uric acid is a powerful antioxidant and its reduction following a high-fat meal may be related with its acute antioxidative action.

Postprandial oxidative stress is exacerbated in cigarette smokers

Both cigarette smoking and high fat meals induce oxidative stress, which is associated with the pathogenesis of numerous diseases. We compared blood antioxidant status, oxidative stress biomarkers and TAG in twenty smokers and twenty non-smokers, matched for age and physical activity, in response to a high fat test meal standardized to body mass. Blood samples were collected before feeding (resting and fasted) and at 1, 2, 4 and 6 h post feeding and analysed for antioxidant capacity (trolox equivalent antioxidant capacity; TEAC), xanthine oxidase activity (XO), hydrogen peroxide (H2O2), malondialdehyde (MDA) and TAG. Smoking status (P < 0.001) and time (P < or = 0.01) effects were noted for all variables, with smokers demonstrating higher values compared with non-smokers for all variables except for TEAC, for which values were lower for smokers. XO, H2O2, MDA and TAG increased following feeding with a peak response at the 4 h post feeding time point, with the opposite response occurring for TEAC. Although no interaction effects were noted (P>0.05), contrasts revealed greater values in smokers compared with non-smokers for XO, H2O2, MDA and TAG, and lower values for TEAC at times from 1-6 h post feeding (P < or = 0.05). Our findings indicate that young cigarette smokers experience an exaggerated oxidative stress response to feeding, as well as hypertriacylglycerolaemia, as compared with non-smokers. These data provide insight into another possible mechanism associating cigarette smoking with ill health and disease.

Fatty acid composition of nuts--implications for cardiovascular health

It is well established that, due to their high content of saturated fatty acids (SFA), the intake of meat and meat products is strongly associated with elevated blood cholesterol concentrations and an increased risk of hypertension, diabetes and cardiovascular diseases. Conversely, the intake of foods rich in unsaturated fatty acids, such as those contained in most vegetable fats and oils and oily fish, is associated with improved lipid profiles, a lower potency of intermediate biomarkers of atherosclerosis and lesser incidence of cardiovascular diseases. There are persuasive evidences that dietary substitution of monounsaturated fatty acids (MUFA) or n-6 polyunsaturated fatty acids (PUFA) for SFA lowers blood cholesterol and may have beneficial effects on inflammation, thrombosis, and vascular reactivity. MUFA may have an advantage over PUFA because enrichment of lipoprotein lipids with MUFA increases their resistance to oxidation. Marine n-3 PUFA have a number of anti-atherosclerotic effects, including anti-arrhythmic properties and, at relatively high doses, reduce serum triglycerides. These effects appear to be shared in part by vegetable n-3 PUFA. Nuts are natural foods rich in unsaturated fatty acids; most nuts contain substantial amounts of MUFA, while walnuts are especially rich in both n-6 and n-3 PUFA. Healthy fats in nuts contribute to the beneficial effects of frequent nut intake observed in epidemiological studies (prevention of coronary heart disease, diabetes, and sudden death) and in short-term feeding trials (cholesterol lowering, LDL resistance to oxidation, and improved endothelial function).

Beneficial metabolic effects of nateglinide versus acarbose in patients with newly-diagnosed type 2 diabetes

AIM

To investigate the acute and chronic effects of nateglinide versus acarbose on plasma asymmetric dimethylarginine (ADMA) levels and lipid profiles in patients with newly-diagnosed type 2 diabetes.

METHODS

A crossover trial of nateglinide and acarbose was conducted on 16 drug-naïve patients with newly-diagnosed type 2 diabetes during a total period of 9 weeks. Plasma glucose, serum insulin, free fatty acids (FFA), lipids and lipoproteins, and plasma ADMA were measured.

RESULTS

The efficiencies of a single dose of nateglinide (120 mg) and acarbose (50 mg) for lowering postprandial hyperglycemia were similar. Compared to acarbose, nateglinide significantly increased postprandial insulin release after a standard meal test in patients with type 2 diabetes. Nateglinide acutely decreased postprandial 120 min FFA concentrations and 240 min ADMA levels more significantly than acarbose. The fasting high-density lipoprotein cholesterol level increased and the low-density lipoprotein cholesterol level decreased significantly, but the fasting levels of triglycerides, total cholesterol, and ADMA were unchanged after 4 weeks of treatment with nateglinide. Acarbose did not affect fasting lipid profiles or the ADMA levels after 4 weeks of treatment.

CONCLUSION

These results suggest that the reduction of postprandial FFA and ADMA concentrations induced by nateglinide may be associated with the partial restoration of early-phase insulin secretion and may impart a cardiovascular advantage in comparison with acarbose.

Acute Effects of High-Fat Meals Enriched With Walnuts or Olive Oil on Postprandial Endothelial Function

OBJECTIVES

We sought to investigate whether the addition of walnuts or olive oil to a fatty meal have differential effects on postprandial vasoactivity, lipoproteins, markers of oxidation and endothelial activation, and plasma asymmetric dimethylarginine (ADMA).

BACKGROUND

Compared with a Mediterranean diet, a walnut diet has been shown to improve endothelial function in hypercholesterolemic patients. We hypothesized that walnuts would reverse postprandial endothelial dysfunction associated with consumption of a fatty meal.

METHODS

We randomized in a crossover design 12 healthy subjects and 12 patients with hypercholesterolemia to 2 high-fat meal sequences to which 25 g olive oil or 40 g walnuts had been added. Both test meals contained 80 g fat and 35% saturated fatty acids, and consumption of each meal was separated by 1 week. Venipunctures and ultrasound measurements of brachial artery endothelial function were performed after fasting and 4 h after test meals.

RESULTS

In both study groups, flow-mediated dilation (FMD) was worse after the olive oil meal than after the walnut meal (p = 0.006, time-period interaction). Fasting, but not postprandial, triglyceride concentrations correlated inversely with FMD (r = -0.324; p = 0.024). Flow-independent dilation and plasma ADMA concentrations were unchanged, and the concentration of oxidized low-density lipoproteins decreased (p = 0.051) after either meal. The plasma concentrations of soluble inflammatory cytokines and adhesion molecules decreased (p < 0.01) independently of meal type, except for E-selectin, which decreased more (p = 0.033) after the walnut meal.

CONCLUSIONS

Adding walnuts to a high-fat meal acutely improves FMD independently of changes in oxidation, inflammation, or ADMA. Both walnuts and olive oil preserve the protective phenotype of endothelial cells.

Treatment of fibrate-induced rhabdomyolysis with plasma exchange in ESRD

Hypertriglyceridemia is a common metabolic disorder in patients with chronic renal failure. Fibrate derivatives are often used for lipid lowering in this population with adjusted dosage. However, fibrate-related adverse reaction still occasionally occurs. The authors report a case of end-stage renal disease in a patient who underwent hemodialysis regularly, taking a reduced dosage of bezafibrate (200 mg/d) for refractory hypertriglyceridemia. She did not take any statins, cyclosporine, monoamine oxidase inhibitors, or warfarin concurrently. Rhabdomyolysis was complicated along with an increased serum bezafibrate level. Plasma exchange was performed, which dramatically decreased the level of bezafibrate, and rhabdomyolysis resolved rapidly thereafter. A lower dose of bezafibrate, 200 mg every third day, was prescribed with cautious monitoring of symptoms and laboratory parameters, and better triglyceride control was achieved uneventfully. This is the first report using plasma exchange to remove excessive bezafibrate, a highly protein-bound molecule that is unlikely to be cleared by hemodialysis in an end-stage renal disease patient with serious adverse reaction caused by accumulation of bezafibrate. In contrast to a traditional wait-and-see strategy, plasma exchange seems to be a safe and effective treatment in addition to supportive care for rhabdomyolysis in such clinical scenarios.

Oxidation of ascorbic acid in stored orange juice is associated with reduced plasma vitamin C concentrations and elevated lipid peroxides

Ascorbic acid oxidizes in refrigerated orange juice, but the physiological relevance of this deterioration is unknown. We compared changes in plasma vitamin C and total lipid peroxides (thiobarbituric acid-reactive substances, TBARS) in the 2-hour period following consumption of commercial orange juices on day 1 vs day 8 of storage (4 degrees C). The ascorbic acid content decreased significantly after storage in juice reconstituted from frozen concentrate (117+/-8 vs 89+/-8 mg/8 fl oz, P =.001), but did not change in chilled juice (69+/-5 vs 64+/-12 mg/8 fl oz.). The mean incremental TBARS value was less on day 1 vs day 8 for juice from frozen concentrate (-0.46+/-0.72 and 0.70+/-0.53, P =.046), but did not differ for chilled juice (0.00+/-0.49 and 0.54+/-0.89). The incremental values for plasma TBARS and vitamin C in the 2-hour postprandial period were inversely related (r=-0.48, P =.017). These data indicate that the loss of ascorbic acid in refrigerated juice may impact postprandial oxidative stress.

Apple procyanidins decrease cholesterol esterification and lipoprotein secretion in Caco-2/TC7 enterocytes

Decrease of plasma lipid levels by polyphenols was linked to impairment of hepatic lipoprotein secretion. However, the intestine is the first epithelium that faces dietary compounds, and it contributes to lipid homeostasis by secreting triglyceride-rich lipoproteins during the postprandial state. The purpose of this study was to examine the effect of apple and wine polyphenol extracts on lipoprotein synthesis and secretion in human Caco-2/TC7 enterocytes apically supplied with complex lipid micelles. Our results clearly demonstrate that apple, but not wine, polyphenol extract dose-dependently decreases the esterification of cholesterol and the enterocyte secretion of lipoproteins. Apple polyphenols decrease apolipoprotein B (apoB) secretion by inhibiting apoB synthesis without increasing the degradation of the newly synthesized protein. Under our conditions, cholesterol uptake, apoB mRNA, and microsomal triglyceride protein activity were not modified by apple polyphenols. The main monomers present in our mixture did not interfere with the intestinal lipid metabolism. By contrast, apple procyanidins reproduced the inhibition of both cholesteryl ester synthesis and lipoprotein secretion. Overall, our results are compatible with a mechanism of action of polyphenols resulting in impaired lipid availability that could induce the inhibition of intestinal lipoprotein secretion and contribute to the hypolipidemic effect of these compounds in vivo.

A novel pathway to the manifestations of metabolic syndrome

Pathways leading from obesity to the manifestations of metabolic syndrome involve a number of metabolic risk factors, as well as adipokines, mediators of inflammatory response, thrombogenic and thrombolytic parameters, and vascular endothelial reactivity. Increased adipose tissue mass contributes to augmented secretion of proinflammatory adipokines, particularly tumor necrosis factor-alpha (TNF alpha), along with diminished secretion of the "protective" adiponectin. In our view, TNF alpha and adiponectin are antagonistic in stimulating nuclear transcription factor-kappa B (NF-kappa B) activation. Through this activation, TNF alpha induces oxidative stress, which exacerbates pathological processes leading to oxidized low-density lipoprotein and dyslipidemia, glucose intolerance, insulin resistance, hypertension, endothelial dysfunction, and atherogenesis. NF-kappa B activation further stimulates the formation of additional inflammatory cytokines, along with adhesion molecules which promote endothelial dysfunction. Elevated free fatty acid, glucose, and insulin levels enhance this NF-kappa B activation and further downstream modulate specific clinical manifestations of metabolic syndrome.

A single dose of nateglinide improves post-challenge glucose metabolism and endothelial dysfunction in Type 2 diabetic patients

AIMS

This randomized crossover placebo-controlled study aimed to assess the efficacy of nateglinide, a phenylalanine-derived insulin secretagogue, on forearm endothelial function in diabetic subjects before and after an oral glucose load.

METHODS

Forearm blood flow (FBF) was measured using strain-gauge plethysmography during reactive hyperaemia before and after an oral glucose load (75 g) with a prior use of placebo or nateglinide (90 mg) in 15 diet-treated Type 2 diabetic patients or age-matched controls with normal glucose tolerance.

RESULTS

The peak FBF response and total reactive hyperaemic flow (flow debt repayment: FDR), indices of resistance artery endothelial function, were decreased after an oral glucose load in diabetic patients, but unchanged in controls. Nateglinide administered to diabetic patients accelerated insulin secretion and reduced post-challenge plasma glucose, and also abolished the post-challenge impairment of endothelial function. The peak FBF and FDR were well correlated with 120-min glucose levels and 30-min insulinogenic index.

CONCLUSIONS

A single challenge of glucose was shown to impair endothelial function in diabetic patients, and the post-challenge endothelial dysfunction was improved by a prior use of nateglinide. Long-term effects of nateglinide on endothelial function in Type 2 diabetic patients need to be clarified in future studies.

Effects of short-term detraining on postprandial metabolism, endothelial function, and inflammation in endurance-trained men: dissociation between changes in triglyceride metabolism and endothelial function. j.gill@bio.gla.ac.uk

Endurance-trained athletes experience a low level of postprandial lipaemia, but this rapidly increases with detraining. We sought to determine whether detraining-induced changes to postprandial metabolism influenced endothelial function and inflammation. Eight endurance-trained men each undertook two oral fat tolerance tests [blood taken fasted and for 6 h following a high-fat test meal (80 g fat, 80 g carbohydrate)]: one during a period of their normal training (trained) and one after 1 wk of no exercise (detrained). Endothelial function in the cutaneous microcirculation was assessed using laser Doppler imaging with iontophoresis in the fasted state and 4 h postprandially during each test. Fasting plasma triglyceride (TG) concentrations increased by 35% with detraining (P = 0.002), as did postprandial plasma (by 53%, P = 0.002), chylomicron (by 68%, P = 0.02) and very low-density lipoprotein (by 51%, P = 0.005) TG concentrations. Endothelial function decreased postprandially in both the trained (by 17%, P = 0.03) and detrained (by 22%, P = 0.03) conditions but did not differ significantly between the trained and detrained conditions in either the fasted or the postprandial states. These results suggest that, although fat ingestion induces endothelial dysfunction, interventions that alter postprandial TG metabolism will not necessarily concomitantly influence endothelial function.