Metformin attenuates ventricular hypertrophy by activating the AMP-activated protein kinase-endothelial nitric oxide synthase pathway in rats.

1. Metformin is an activator of AMP-activated protein kinase (AMPK). Recent studies suggest that pharmacological activation of AMPK inhibits cardiac hypertrophy. In the present study, we examined whether long-term treatment with metformin could attenuate ventricular hypertrophy in a rat model. The potential involvement of nitric oxide (NO) in the effects of metformin was also investigated. 2. Ventricular hypertrophy was established in rats by transaortic constriction (TAC). Starting 1 week after the TAC procedure, rats were treated with metformin (300 mg/kg per day, p.o.), N(G)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg per day, p.o.) or both for 8 weeks prior to the assessment of haemodynamic function and cardiac hypertrophy. 3. Cultured cardiomyocytes were used to examine the effects of metformin on the AMPK-endothelial NO synthase (eNOS) pathway. Cells were exposed to angiotensin (Ang) II (10⁻6 mol/L) for 24 h under serum-free conditions in the presence or absence of metformin (10⁻³ mol/L), compound C (10⁻6 mol/L), L-NAME (10⁻6 mol/L) or their combination. The rate of incorporation of [³H]-leucine was determined, western blotting analyses of AMPK-eNOS, neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) were undertaken and the concentration of NO in culture media was determined. 4. Transaortic constriction resulted in significant haemodynamic dysfunction and ventricular hypertrophy. Myocardial fibrosis was also evident. Treatment with metformin improved haemodynamic function and significantly attenuated ventricular hypertrophy. Most of the effects of metformin were abolished by concomitant L-NAME treatment. L-NAME on its own had no effect on haemodynamic function and ventricular hypertrophy in TAC rats. 5. In cardiomyocytes, metformin inhibited AngII-induced protein synthesis, an effect that was suppressed by the AMPK inhibitor compound C or the eNOS inhibitor L-NAME. The improvement in cardiac structure and function following metformin treatment was associated with enhanced phosphorylation of AMPK and eNOS and increased NO production. 6. The findings of the present study indicate that long-term treatment with metformin could attenuate ventricular hypertrophy induced by pressure overload via activation of AMPK and a downstream signalling pathway involving eNOS-NO.

[Relationship between the polymorphism of the variable number of tandem repeats region 3' of the apolipoprotein B gene and serum lipid levels in the Guangxi Heiyi Zhuang populations].

OBJECTIVE: To study the relationship between the polymorphism of the variable number of tandem repeats region 3' of the apolipoprotein B gene (3'APOB-VNTR) and serum lipid levels in the Guangxi Heiyi Zhuang population. METHODS: A total of 548 people of Heiyi Zhuang nationatity were surveyed by a cluster sampling. Epidemiological data were collected and serum lipid and apolipoprotein levels were measured. The genotypes and alleles of the 3' APOB-VNTR were determined by polymerase chain reaction combined with gel electrophoresis, and then analyzed by direct sequencing in the most common alleles. The results were compared with those in 496 people of Han nationality also live in that district. RESULTS: There were 19 alleles of the 3'APOB-VNTR in both ethnic groups. They were hypervariable elements (HVEs) 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62 and 64, but HVEs 56 and 58 in Heiyi Zhuang nationality and HVEs 48 and 62 in Han nationality were not be detected. The most common allele is HVE32 in Heiyi and Zhuang nationality (25.9%), and HVE34 in Han nationality (27.2%). The frequencies of HVEs 26, 30, 46, heterozygote, and short alleles (< 38 repeats, S) were higher in Heiyi Zhuang nationality than in Han nationality, whereas the frequencies of HVEs 34, 38, 40, homozygote, and long alleles (>or= 38 repeats, L) were lower in Heiyi Zhuang nationality than in Han nationality. The levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and apolipoprotein (apo) B in Heiyi Zhuang nationality were higher in VNTR-LS (carrier of one long and one short alleles) than in VNTR-LL genotypes (the individual carrying two long alleles) genotypes. The levels of TC, triglycerides, HDL-C and apo B in Heiyi Zhuang nationality were also higher in homozygotes than in heterozygotes. There were no significant differences in the detected lipid parameters between the VNTR-SS (carrier of two short alleles) and VNTR-LS or VNTR-LL genotypes in both ethnic groups. CONCLUSION: The 3'APOB-VNTR polymorphism is found to be significant difference between Heiyi Zhuang nationality and Han populations, and is associated with the serum lipid levels in Heiyi Zhuang nalionality but not in Han nationality.

[Effects of AMPK on the transcriptional activity of FOXO1 and ubiquitin ligase MuRF1 expression in rat cardiomyocytes].

OBJECTIVE: To investigate the effects of AICAR on the activity of transcription factor FOXO1 and expression of ubiquitin ligase MuRF1 in rat cardiomyocytes, and explore the possible role of AMP-activated protein kinase (AMPK) in proteolysis pathways. METHODS: In vitro cultured neonatal rat cardiac myocytes were treated with AICAR, and Western blotting was used to detect the phosphorylation of FOXO1 and expression of MuRF1 in the cells. RESULTS: AICAR activated AMPK in rat cardiac myocytes. Activated AMPK significantly inhibited the phosphorylation of FOXO1 and increased MuRF1 protein expression. CONCLUSION: AMPK may regulate proteolysis by activating FOXO1 transcription factor and up-regulating MuRF1 expression.