The Protective Effect of 11-Keto-β-Boswellic Acid against Diabetic Cardiomyopathy in Rats Entails Activation of AMPK

Abstract

This study examined the protective effect of 11-keto-β-boswellic acid (AKBA) against streptozotocin (STZ)-induced diabetic cardiomyopathy (DC) in rats and examined the possible mechanisms of action. Male rats were divided into 5 groups (n = 8/each): (1) control, AKBA (10 mg/kg, orally), STZ (65 mg/kg, i.p.), STZ + AKBA (10 mg/kg, orally), and STZ + AKBA + compound C (CC/an AMPK inhibitor, 0.2 mg/kg, i.p.). AKBA improved the structure and the systolic and diastolic functions of the left ventricles (LVs) of STZ rats. It also attenuated the increase in plasma glucose, plasma insulin, and serum and hepatic levels of triglycerides (TGs), cholesterol (CHOL), and free fatty acids (FFAs) in these diabetic rats. AKBA stimulated the ventricular activities of phosphofructokinase (PFK), pyruvate dehydrogenase (PDH), and acetyl CoA carboxylase (ACC); increased levels of malonyl CoA; and reduced levels of carnitine palmitoyltransferase I (CPT1), indicating improvement in glucose and FA oxidation. It also reduced levels of malondialdehyde (MDA); increased mitochondria efficiency and ATP production; stimulated mRNA, total, and nuclear levels of Nrf2; increased levels of glutathione (GSH), heme oxygenase (HO-1), superoxide dismutase (SOD), and catalase (CAT); but reduced the expression and nuclear translocation of NF-κB and levels of tumor-necrosis factor-α (TNF-α) and interleukin-6 (IL-6). These effects were concomitant with increased activities of AMPK in the LVs of the control and STZ-diabetic rats. Treatment with CC abolished all these protective effects of AKBA. In conclusion, AKBA protects against DC in rats, mainly by activating the AMPK-dependent control of insulin release, cardiac metabolism, and antioxidant and anti-inflammatory effects.

Keywords: 11-keto-β-boswellic acid; AMPK; Nrf2; diabetic cardiomyopathy; oxidative stress; streptozotocin.

Figure 1

The experimental design used in the study.

Figure 2

Activities of AMPKα (A), total levels of ATP (B), and the maximum reduction of Vmax as a marker of mitochondrial membrane potential (mtPTP) opening (C) in the left ventricles (LVs) of all rat groups. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC—compound C (a selective AMPK inhibitor).

Figure 3

Activities of phosphofructokinase (A), pyruvate dehydrogenase (PDH) (B), levels of malonyl CoA (C), activities of acetyl CoA carboxylase (D), and levels of carnitine palmitoyltransferase I (CPT1) (E) in the left ventricles (LVs) of all groups of rats. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC–compound C (a selective AMaPK inhibitor).

Figure 4

Morphological images of the left ventricles of all rat groups. (A,B) were taken from control and AKBA-treated rats and showed normal cardiomyocyte structure having normal striation (long arrow) and oval nuclei (short arrow). (C,D) were taken form STZ-diabetic LV and showed loss of muscle tissue (short arrow) with increased vacuolization (long arrow). Many nuclei were shrunk, abnormally round, and necrotic. (E) was taken from STZ + AKB-treated rats and showed almost normal morphology with normal cardiomyocytes and nuclei. (F) was taken from the LV of STZ + AKAB + CC-treated animals and showed similar loss of cardiomyocytes (arrow), increased vacuolization of the cardiomyocytes, and abnormally shrunk and round necrotic cells.

Figure 5

Total, nuclear, and mRNA levels of Nrf2 (A–C), and levels of heme oxygenase-1 (HO-1) (D) in the left ventricles (LVs) of all rat groups. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC–compound C (selective AMPK inhibitor).

Figure 6

Total levels of malondialdehyde (MDA) (A), glutathione (GSH) (B), superoxide dismutase (SOD) (C), and glutathione peroxidase (GPx) (D) in the left ventricles (LVs) of all rat groups. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC–compound C (a selective AMPK inhibitor).

Figure 7

Total levels of interleukin-6 (IL-6) (A) and tumor necrosis factor-α (TNF-α) (B), as well as total, nuclear, and mRNA levels of NF-κB p65 (C–E) in the left ventricles (LVs) of all rat groups. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC–compound C (a selective AMPK inhibitor).

Figure 8

Cytoplasmic levels of caspase-3 (A), Bax (B), Bcl2 (C), and cytochrome-c (D) in the left ventricles (LVs) of all rat groups. Data were analyzed with one-way ANOVA followed by Tukey’s test. Values are presented as mean ± SD (n = 8/group). Data were considered significantly different at p < 0.5. a: significantly different as compared to control rats; b: significantly different as compared to AKBA-treated rats; c: significantly different as compared to STZ-diabetic rats; d: significantly different as compared to STZ + AKBA-treated rats. CC–compound C (a selective AMPK inhibitor).