Activation of PPARγ by pioglitazone does not attenuate left ventricular hypertrophy following aortic banding in rats

Protective effects of tannic acid on pressure overload-induced cardiac hypertrophy and underlying mechanisms in rats

Objectives

The aim of this study was to examine the cardioprotective effects and latent mechanism of tannic acid (TA) on cardiac hypertrophy.

Methods

Abdominal aortic banding (AAB) was used to induce pressure overload-induced cardiac hypertrophy in male Wistar rats, sham-operated rats served as controls. AAB rats were treated with TA (20 and 40 mg/kg) or captoril.

Key findings

Abdominal aortic banding rats that received TA showed ameliorated pathological changes in cardiac morphology and coefficients, decreased cardiac hypertrophy and apoptosis, a reduction in over expressions of angiotensin type 1 receptor (AT1R), angiotensin type 2 receptor (AT2R), phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and transforming growth factor-β (TGF-β) mRNA, and modified expression of matrix metal proteinase-9 (MMP-9) mRNA in AAB rat hearts. Furthermore, TA treatment contributed to a decrease in malondialdehyde (MDA) and endothelin-1 (ET-1) activities and content, while it caused an increase in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), nitric oxide (NO) and endothelial NO synthase (e-NOS). Furthermore, TA downregulated expression of tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), bax, caspase-3 and upregulated expression of bcl-2.

Conclusions

Tannic acid displayed obvious suppression of AAB-induced cardiac hypertrophy in rats. The cardioprotective effects of TA may be attributed to multitargeted inhibition of oxidative stress, inflammation, fibrosis and apoptosis in addition to an increase in NO levels, decrease in ET-1 levels, and downregulation of angiotensin receptors and the phosphorylation of ERK1/2.

Pioglitazone increases PGC1-α signaling within chronically ischemic myocardium

The peroxisome proliferator-activated receptor (PPAR)-γ drug pioglitazone (PIO) has been shown to protect tissue against oxidant stress. In a swine model of chronic myocardial ischemia, we tested whether PIO increases PGC1-α signaling and the expression of mitochondrial antioxidant peptides. Eighteen pigs underwent a thoracotomy with placement of a fixed constrictor around the LAD artery. At 8 weeks, diet was supplemented with either PIO (3 mg/kg) or placebo for 4 weeks. Regional myocardial function and blood flow were determined at the time of the terminal study. PGC1-α expression was quantified from nuclear membranes by gels and respiration, oxidant stress markers and proteomics by iTRAQ were determined from isolated mitochondria. In the chronically ischemic LAD region, wall thickening from the PIO and control groups was 42 ± 6 and 45 ± 5 %, respectively (NS) with no intergroup differences in basal blood flow (0.72 ± 0.04 versus 0.74 ± 0.04 ml/min g, respectively; NS). In the PIO group, the expression of nuclear bound PGC1-α was higher (11.3 ± 2.6 versus 4.4 ± 1.4 AU; P < 0.05) and the content of mitochondrial antioxidant peptides including superoxide dismutase 2, aldose reductase, glutathione S-transferase and thioredoxin reductase were greater than controls. Although isolated mitochondria from the PIO group showed lower state 3 respiration (102 ± 13 versus 161 ± 22 nmol/min mg; P < 0.05), no differences in oxidant stress were noted by protein carbonyl (1.7 ± 0.7 versus 1.1 ± 0.1 nmol/mg). Chronic pioglitazone does not reduce regional myocardial blood flow or function in a swine model of chronic myocardial ischemia, but may have an important role in increasing expression of antioxidant proteins through PGC1-α signaling.

Variable effects of anti-diabetic drugs in animal models of myocardial ischemia and remodeling: a translational perspective for the cardiologist

Diabetes and heart failure are very prevalent, and affect each other's incidence and severity. Novel therapies to reduce post-myocardial infarction (MI) remodeling that progresses into heart failure are urgently needed, especially in diabetic patients. Clinical studies have suggested that some oral anti-diabetic agents like metformin exert cardiovascular protective effects in heart failure patients with diabetes, whereas other agents may be deleterious. In the current review, we provide an overview of the cardio-specific effects of oral anti-diabetic drugs in animal models of acute MI, post-MI remodeling, and heart failure. Metformin has consistently been shown to ameliorate cardiac remodeling after ischemia/reperfusion (I/R) injury, as well as in several models of heart failure. Sulfonylurea derivatives are controversial with respect to their direct effects on the cardiovascular system. Thiazolidinediones protect against myocardial I/R injury, but their effects on post-MI remodeling are less clear and clinical studies raised concerns about their cardiovascular safety. Glucagon-like peptide-1 analogs have potential beneficial effects on the cardiovascular system that require further confirmation, whereas the results with dipeptidyl peptidase-4 inhibitors are equivocal. Current clinical guidelines, in the absence of prospective clinical trials that evaluated if certain oral anti-diabetic agents are superior over others, only provide generic recommendations, and do not take into account interesting experimental and mechanistic data. The available experimental evidence indicates that some anti-diabetic agents should be preferred over others if cardioprotective effects are warranted. These experimental clues need to be confirmed by clinical trials.

Chronic Akt blockade aggravates pathological hypertrophy and inhibits physiological hypertrophy

The attenuation of adverse myocardial remodeling and pathological left ventricular (LV) hypertrophy is one of the hallmarks for improving the prognosis after myocardial infarction (MI). The protein kinase Akt plays a central role in regulating cardiac hypertrophy, but the in vivo effects of chronic pharmacological inhibition of Akt are unknown. We investigated the effect of chronic Akt blockade with deguelin on the development of pathological [MI and aortic banding (AB)] and physiological (controlled treadmill running) hypertrophy. Primary cardiomyocyte cultures were incubated with 10 μmol deguelin for 48 h, and Wistar rats were treated orally with deguelin (4.0 mg·kg(-1)·day(-1)) for 4 wk starting 1 day after the induction of MI or AB. Exercise-trained animals received deguelin for 4 wk during the training period. In vitro, we observed reduced phosphorylation of Akt and glycogen synthase kinase (GSK)-3β after an incubation with deguelin, whereas MAPK signaling was not significantly affected. In vivo, treatment with deguelin led to attenuated phosphorylation of Akt and GSK-3β 4 wk after MI. These animals showed significantly increased heart weights and impaired LV function with increased end-diastolic diameters (12.0 ± 0.3 vs. 11.1 ± 0.3 mm, P < 0.05), end-diastolic volumes (439 ± 8 vs. 388 ± 18 μl, P < 0.05), and cardiomyocyte sizes (+20%, P < 0.05) compared with MI animals receiving vehicle treatment. Furthermore, activation of Ca(2+)/calmodulin-dependent kinase II in deguelin-treated MI animals was increased compared with the vehicle-treated group. Four wk after AB, we observed an augmentation of pathological hypertrophy in the deguelin-treated group with a significant increase in heart weights and cardiomyocyte sizes (>20%, P < 0.05). In contrast, the development of physiological hypertrophy was inhibited by deguelin treatment in exercise-trained animals. In conclusion, chronic Akt blockade with deguelin aggravates adverse myocardial remodeling and antagonizes physiological hypertrophy.