Role of vascular oxidative stress in obesity and metabolic syndrome

Mitochondrial hormesis and diabetic complications

The concept that excess superoxide production from mitochondria is the driving, initial cellular response underlying diabetes complications has been held for the past decade. However, results of antioxidant-based trials have been largely negative. In the present review, the data supporting mitochondrial superoxide as a driving force for diabetic kidney, nerve, heart, and retinal complications are reexamined, and a new concept for diabetes complications--mitochondrial hormesis--is presented. In this view, production of mitochondrial superoxide can be an indicator of healthy mitochondria and physiologic oxidative phosphorylation. Recent data suggest that in response to excess glucose exposure or nutrient stress, there is a reduction of mitochondrial superoxide, oxidative phosphorylation, and mitochondrial ATP generation in several target tissues of diabetes complications. Persistent reduction of mitochondrial oxidative phosphorylation complex activity is associated with the release of oxidants from nonmitochondrial sources and release of proinflammatory and profibrotic cytokines, and a manifestation of organ dysfunction. Restoration of mitochondrial function and superoxide production via activation of AMPK has now been associated with improvement in markers of renal, cardiovascular, and neuronal dysfunction with diabetes. With this Perspective, approaches that stimulate AMPK and PGC1α via exercise, caloric restriction, and medications result in stimulation of mitochondrial oxidative phosphorylation activity, restore physiologic mitochondrial superoxide production, and promote organ healing.

Nitric oxide and mitochondria in metabolic syndrome

Metabolic syndrome (MS) is a cluster of metabolic disorders that collectively increase the risk of cardiovascular disease. Nitric oxide (NO) plays a crucial role in the pathogeneses of MS components and is involved in different mitochondrial signaling pathways that control respiration and apoptosis. The present review summarizes the recent information regarding the interrelations of mitochondria and NO in MS. Changes in the activities of different NO synthase isoforms lead to the formation of metabolic disorders and therefore are highlighted here. Reduced endothelial NOS activity and NO bioavailability, as the main factors underlying the endothelial dysfunction that occurs in MS, are discussed in this review in relation to mitochondrial dysfunction. We also focus on potential therapeutic strategies involving NO signaling pathways that can be used to treat patients with metabolic disorders associated with mitochondrial dysfunction. The article may help researchers develop new approaches for the diagnosis, prevention and treatment of MS.

Cross-sectional and longitudinal associations between serum bilirubin and dyslipidemia in a health screening population

OBJECTIVE

To investigate cross-sectional and longitudinal associations between serum total bilirubin (TB) and dyslipidemia.

METHODS

Odds ratios (ORs) of prevalent dyslipidemia for TB were calculated in 2113 men and 1265 women. Correlation coefficients between baseline TB as well as the change in TB over 5 years and baseline log triglycerides, baseline HDL cholesterol and the changes in log triglycerides and HDL cholesterol over 5 years were calculated. Hazard ratios (HRs) of incident hypertriglyceridemia and hypo-HDL cholesterolemia for TB over 5 years were calculated in 1324 men and 915 women and 1583 men and 884 women, respectively.

RESULTS

The ORs of prevalent hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.83 (p < 0.001) in men and 0.71 (p = 0.074) in women and 0.64 (p < 0.001) in men and 0.78 (p = 0.089) in women, respectively adjusted for age, smoking, and other confounders. The baseline TB was significantly correlated with baseline log triglycerides and HDL cholesterol both in men and women while the change in TB was significantly correlated with the changes in log triglycerides and HDL cholesterol in men and the change in HDL cholesterol in women. The HRs of incident hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.99 (p = 0.848) in men and 0.74 (p = 0.033) in women and 1.08 (p = 0.345) in men and 0.85 (p = 0.220) in women, respectively adjusted for age, smoking, and other confounders.

CONCLUSION

Baseline TB was significantly associated with both prevalent hypertriglyceridemia and hypo-HDL cholesterolemia in men and with incident hypertriglyceridemia in women.

A blueberry-enriched diet improves renal function and reduces oxidative stress in metabolic syndrome animals: potential mechanism of TLR4-MAPK signaling pathway

Background

Metabolic syndrome (MetS) is characterized by a cluster of health factors that indicate a higher risk for cardio-renal diseases. Recent evidence indicates that antioxidants from berries are alternative to attenuate oxidative stress and inflammation. We tested the hypothesis that inflammation-induced renal damage is triggered by the activation of TLR4, and subsequent modulation of redox-sensitive molecules and mitogen-activated protein kinase (MAPK) pathway.

Methods

Five-week old lean and obese Zucker rats (LZR and OZR) were fed a blueberry-enriched diet or an isocaloric control diet for 15 weeks. A glucose tolerance test and acute renal clearance experiments were performed. Gene and protein expression levels for TLR4, cytokines and phosphorylation of ERK and p38MAPK were measured. Kidney redox status and urinary albumin levels were quantified. Renal pathology was evaluated histologically.

Results

Control OZR exhibited lower glucose tolerance; exacerbated renal function parameters; increased oxidative stress. Gene and protein expression levels of TLR4 were higher and this was accompanied by increased renal pathology with extensive albuminuria and deterioration in antioxidant levels in OZR. In addition, OZR had increased phosphorylation of ERK and p38MAPK. Blueberry-fed OZR exhibited significant improvements in all these parameters compared to OZR.

Conclusion

TLR4-MAPK signaling pathway is a key to the renal structural injury and dysfunction in MetS and blueberry (BB) protect against this damage by inhibiting TLR4.

Significance

This is the first study to put forth a potential mechanism of TLR4-induced kidney damage in a model of MetS and to elucidate a downstream mechanism by which blueberry exert their reno-protective effects.

Oxidatively modified forms of albumin in patients with risk factors of metabolic syndrome

BACKGROUND

Metabolic syndrome (MetS) is a complex metabolic disease connected especially with lipid and carbohydrate disturbances. It is postulated that oxidative stress (OS) is linked to metabolic syndrome, constituting a novel component of its pathogenesis.

AIM

We aimed to examine the plasma level of oxidatively modified proteins--advanced oxidation protein products (AOPP) and ischemia modified albumin (IMA)--as well as thiol (SH) groups and evaluate their connection with metabolic agents in relation to MetS prevalence.

SUBJECTS AND METHODS

The levels of AOPP, IMA and SH groups were measured spectrophotometrically in 106 patients with MetS risk factors and in 32 control subjects.

RESULTS

The levels of examined parameters differed significantly between patients with MetS risk factors and the control group. AOPP significantly correlated with glucose (r = 0.30, p = 0.008), HDL-Ch (r = -0.34, p = 0.005), TG (r = 0.48, p < 0.001) and fibrinogen (r = 0.37, p < 0.001). The levels of AOPP and IMA increased progressively with the number of MetS risk factors, being the most significant for AOPP. The highest values of AOPP were associated with the presence of at least three risk factors. Only AOPP were an independent determinant for MetS occurrence in the studied population (OR = 2.72, p = 0.04). Mutual dependence between metabolic, oxidative stress and inflammatory parameters was revealed.

CONCLUSIONS

Oxidative modifications of proteins are increased in MetS and accumulation of MetS risk factors enhances manifestation of OS. AOPP is the most appropriate parameter for determination of OS, with potential diagnostic value in MetS patients.

Netrin-1 abrogates ischemia/reperfusion-induced cardiac mitochondrial dysfunction via nitric oxide-dependent attenuation of NOX4 activation and recoupling of NOS

Despite an established role of mitochondrial dysfunction in cardiac ischemia/reperfusion (I/R) injury, the upstream activators have remained incompletely defined. We have recently identified an innovative role of exogenously applied netrin-1 in cardioprotection, which is mediated by increased nitric oxide (NO) bioavailability. Here, we tested the hypothesis that this "pharmacological" treatment of netrin-1 preserves mitochondrial function via novel mechanisms that are NO dependent. Freshly isolated C57BL6 mouse hearts were perfused using a Langendorff system, and subjected to a 20min global ischemia/60min reperfusion, in the presence or absence of netrin-1. I/R induced marked increases in infarct size, total superoxide and hydrogen peroxide production, activity and protein abundance of NADPH oxidase (NOX) isoform 4 (NOX4), as well as impaired mitochondrial integrity and function, all of which were attenuated by netrin-1. This protective effect of netrin-1 is attributed to cGMP, a downstream effector of NO. The protein levels of NOX1 and NOX2 were however unaffected, and infarct size from NOX1 and NOX2 knockouts was not different from wild type animals. Scavenging of NO with PTIO reversed inhibitory effects of netrin-1 on NOX4, while NO donor attenuated NOX4 protein abundance. In vivo NOX4 RNAi, or sepiapterin perfusion, resulted in recoupling of NOS, decreased infarct size, and blockade of dysfunctional mitochondrial swelling and mitochondrial superoxide production. These data demonstrate that netrin-1 induces cardioprotection through inhibition of NOX4 activity, which leads to recoupling of NOS, augmented NO bioavailability, reduction in oxidative stress, and ultimately preservation of mitochondrial function. The NO-dependent NOX4 inhibition connects with our previously established pathway of DCC/ERK1/2/eNOS/NO/DCC feed-forward mechanism, to maintain NOS in the coupling state to attenuate oxidative stress to preserve mitochondrial function. These findings may promote development of novel therapeutics for cardiac I/R injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

Obesity and the cardiovascular health effects of fine particulate air pollution

OBJECTIVE

This review examines evidence related to the potential impact of obesity on the cardiovascular health effects of fine particulate air pollution (PM₂.₅).

METHODS

A PubMed search was conducted in December, 2013 and studies were included if they examined the relationship between PM₂.₅ and cardiovascular health as well as effect modification by obesity.

RESULTS

One hundred twenty-one citations were reviewed; three large prospective cohort studies and 14 panel studies with short-term follow-up met the above criteria. All three cohort studies reported stronger associations between PM₂.₅ and cardiovascular mortality among obese subjects and one reported a significant trend of increased risk with increased body mass index. Similarly, 11 of 14 panel studies reported stronger associations between PM₂.₅ and acute changes in physiological measures of cardiovascular health among obese subjects including outcomes such as blood pressure and arrhythmia. Although interactions were not always statistically significant, the consistent pattern of stronger associations among obese subjects suggests that obesity may modify the impact of PM2.5 on cardiovascular health.

CONCLUSIONS

Epidemiological evidence suggests that obesity may increase susceptibility to the cardiovascular health effects of PM₂.₅. This an important area of research as the public health impacts of air pollution could increase with increasing prevalence of obesity.