MITOCHONDRIA-TARGETED ANTIOXIDANT AMELIORATES DIET-INDUCED DIABETES AND DIASTOLIC DYSFUNCTION

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.

Quercetin Prevents Diastolic Dysfunction Induced by a High-Cholesterol Diet: Role of Oxidative Stress and Bioenergetics in Hyperglycemic Rats

Alterations in cardiac energy metabolism play a key role in the pathogenesis of diabetic cardiomyopathy. Hypercholesterolemia associated with bioenergetic impairment and oxidative stress has not been well characterized in the cardiac function under glycemic control deficiency conditions. This work aimed to determine the cardioprotective effects of quercetin (QUE) against the damage induced by a high-cholesterol (HC) diet in hyperglycemic rats, addressing intracellular antioxidant mechanisms and bioenergetics. Quercetin reduced HC-induced alterations in the lipid profile and glycemia in rats. In addition, QUE attenuated cardiac diastolic dysfunction (increased E:A ratio), prevented cardiac cholesterol accumulation, and reduced the increase in HC-induced myocyte density. Moreover, QUE reduced HC-induced oxidative stress by preventing the decrease in GSH/GSSG ratio, Nrf2 nuclear translocation, HO-1 expression, and antioxidant enzymatic activity. Quercetin also counteracted HC-induced bioenergetic impairment, preventing a reduction in ATP levels and alterations in PGC-1α, UCP2, and PPARγ expression. In conclusion, the mechanisms that support the cardioprotective effect of QUE in rats with HC might be mediated by the upregulation of antioxidant mechanisms and improved bioenergetics on the heart. Targeting bioenergetics with QUE can be used as a pharmacological approach to modulate structural and functional changes of the heart under hypercholesterolemic and hyperglycemic conditions.

Troxerutin attenuates diet-induced oxidative stress, impairment of mitochondrial biogenesis and respiratory chain complexes in mice heart

Mitochondrial abnormality is thought to play a key role in cardiac disease originating from the metabolic syndrome (MS). We evaluated the effect of troxerutin (TX), a semi-synthetic derivative of the natural bioflavanoid rutin, on the respiratory chain complex activity, oxidative stress, mitochondrial biogenesis and dynamics in heart of high fat, high fructose diet (HFFD) -induced mouse model of MS. Adult male Mus musculus mice of body weight 25-30 g were fed either control diet or HFFD for 60 days. Mice from each dietary regimen were divided into two groups on the 16th day and were treated or untreated with TX (150 mg/kg body weight [bw], per oral) for the next 45 days. At the end of experimental period, respiratory chain complex activity, uncoupling proteins (UCP)-2 and -3, mtDNA content, mitochondrial biogenesis and dynamics, oxidative stress markers and reactive oxygen species (ROS) generation were analyzed. Reduced mtDNA abundance with alterations in the expression of genes related to mitochondrial biogenesis and fission and fusion processes were observed in HFFD-fed mice. Disorganized and smaller mitochondria, reduction in complexes I, III and IV activities (by about 55%) and protein levels of UCP-2 (52%) and UCP-3 (46%) were noted in these mice. TX administration suppressed oxidative stress, improved the oxidative capacity and biogenesis and restored fission/fusion imbalance in the cardiac mitochondria of HFFD-fed mice. TX protects the myocardium by modulating the putative molecules of mitochondrial biogenesis and dynamics and by its anti-oxidant function in a mouse model of MS.

Diastolic dysfunction in spontaneous type 2 diabetes rhesus monkeys: a study using echocardiography and magnetic resonance imaging

BACKGROUND

Diastolic heart failure is a common and deadly complication of diabetes mellitus, with the development of diabetic cardiomyopathy as one of the key determinants of the disease's complex pathology. The cause of the association is unknown and has no approved therapy strategies as of yet. However significant advances in this area may come from studies on suitable animal models.

METHODS

A total of 25 male rhesus monkeys (12-16 years, 9-13 kg) were enrolled. Fifteen of them were diagnosed as spontaneous type 2 diabetes mellitus (T2DM, FPG ≥ 104 mg/dl, HbA1c: 4.7-5.5 %, diabetes duration: 1-4 years). The other 10 monkeys were non-diabetic (ND, FPG < 90 mg/dl). Echocardiography and cardiac magnetic resonance were used for evaluating the cardiac structure and function. One T2DM monkey with impaired diastolic function and another ND monkey were both sacrificed to gain the necessary pathology and protein expression studies displayed here.

RESULTS

Six out of 15 T2DM rhesus monkeys were diagnosed with diastolic dysfunction (DD) by echocardiography. Additionally, no abnormalities were found in the group which we determined as the ND monkeys. The six DD monkeys all showed low e' velocity and decreased e'/a' ratio, among which three of them showing decreased E/A ratio and the other 3 having elevated E/A ratio, this appears to be similar to the impaired relaxation pattern and pseudonormal pattern found in human patients respectively. The EF and FS of monkeys with pseudonormal pattern decreased significantly compared with ND subjects. A CMR study showed that LVID at end systole of 5 DD monkeys is significantly longer than that of 3 ND monkeys. Of great interest, myocardium lesions and mitochondria impairments and increased expression of AGEs and caspase-3 were found in a sacrificed DD subject.

CONCLUSION

The changes in the imaging and physiological markers of spontaneous T2DM rhesus monkeys are similar to those key markers found in human type 2 diabetes and diastolic dysfunction. This monkey model could help the medical community and us to understand the pathology of this debilitating disease and serve as a beginning to explore important measures to prevent and treat diabetic cardiomyopathy.

Diastolic dysfunction

Despite the growing number of patients affected, the understanding of diastolic dysfunction and heart failure with preserved ejection fraction (HFpEF) is still poor. Clinical trials, largely based on successful treatments for systolic heart failure, have been disappointing, suggesting that HFpEF has a different pathology to that of systolic dysfunction. In this review, general concepts, epidemiology, diagnosis, and treatment of diastolic dysfunction are summarized, with an emphasis on new experiments suggesting that oxidative stress plays a crucial role in the pathogenesis of at least some forms of the disease. This observation has lead to potential new diagnostics and therapeutics for diastolic dysfunction and heart failure caused by diastolic dysfunction.