Metformin Prevents Low-dose Isoproterenol-induced Cardiac Dilatation and Systolic Dysfunction in Male Sprague Dawley Rats.

ABSTRACT: Myocardial metabolic abnormalities are well-recognized alterations in chronic heart failure, effects that may contribute to progressive cardiac dysfunction. However, whether metabolic alterations in-part mediate their deleterious effects by modifying the chronic impact of excess low-dose sympathetic stimulation on cardiac chamber dilatation is uncertain. We therefore aimed to determine the effect of metformin administration on cardiac function and mitochondrial architectural changes in a rat model of chronic sympathetic-induced left ventricular (LV) remodeling and systolic dysfunction [daily subcutaneous isoproterenol (ISO) injection at a low dose of 0.02 mg/kg for 7 months]. Echocardiography was used to assess in vivo LV dimensions and function, and mitochondrial and myofibril arrangement was assessed using transmission electron microscopy. Seven months of low-dose ISO administration increased LV diastolic diameter (in mm) [control (CONT): 7.29 ± 0.19 vs. ISO: 8.76 ± 0.21; P = 0.001], an effect that was attenuated by metformin (ISO + MET: 7.63 ± 0.29 vs. ISO: P = 0.001) administration. Similarly, ISO increased LV end-systolic diameter (CONT: 4.43 ± 0.16 vs. ISO: 5.49 ± 0.16: P < 0.0001), an effect prevented by metformin (ISO + MET: 4.04 ± 0.25 vs. ISO: P < 0.0001). Moreover, chronic ISO administration reduced LV endocardial fractional shortening (P = 0.0001), midwall fractional shortening (P = 0.0001), and ejection fraction (P = 0.0001), effects similarly prevented by metformin administration. Furthermore, changes in mitochondrial arrangement and relative mitochondrial area (CONT: 37.7 ± 2.2 vs. ISO: 28.1 ± 2.9; P = 0.05) were produced by ISO administration, effects prevented by metformin. In conclusion, metformin offers cardiac protection against chronic sympathetic-induced LV dilatation and systolic dysfunction. These data support a role for myocardial metabolic changes in mediating LV dilatation and LV dysfunction produced by chronic neurohumoral activation in cardiac disease.

Dietary-induced obesity hastens the progression from concentric cardiac hypertrophy to pump dysfunction in spontaneously hypertensive rats.

We explored whether dietary-induced obesity hastens the transition from concentric left ventricular (LV) hypertrophy to pump dysfunction in spontaneously hypertensive rats (SHRs) and the mechanisms thereof. After feeding rats a diet for 4 to 5 months, obesity was induced in SHRs and Wistar-Kyoto (WKY) control rats. Obesity was not associated with abnormal blood glucose control (glycosylated hemoglobin) or with increases in systolic blood pressure. However, in SHRs, but not in WKY rats, obesity was associated with a reduced LV chamber systolic function, as determined by echocardiography, and in isolated perfused heart studies. A marked increase in LV end diastolic diameter and a right shift in the LV diastolic pressure-volume relation were noted in obese SHRs but not in obese WKY rats. Moreover, LV intrinsic myocardial systolic function, as determined from the slope of the linearized LV systolic stress-strain relationship (LV myocardial end systolic elastance), was markedly reduced in obese as compared with lean SHRs, whereas LV myocardial end systolic elastance was maintained in obese WKY rats. Obesity increased LV weight, cardiomyocyte width, cardiomyocyte apoptosis (TUNEL), the activity of myocardial matrix metalloproteinases (zymography), and serum leptin concentrations in SHRs but not in WKY rats. In conclusion, SHRs are susceptible to the adverse effects of dietary-induced obesity on the heart, an effect that hastens the progression from concentric LV hypertrophy to pump dysfunction independent of blood pressure changes or alterations in glycosylated hemoglobin. This effect may be mediated through a proclivity of SHRs to developing both obesity-induced effects on cardiomyocyte apoptosis and activation of myocardial collagenases through leptin resistance and obesity-induced hypertrophy.

The relationship between blood pressure and left ventricular mass index depends on an excess adiposity.

AIM: To determine whether blood pressure (BP)-LVM relationships depend in-part on the influence of an excess adiposity and whether this translates into a greater effect of hypertension on LVM in obese as compared with lean people. METHODS: In 399 randomly recruited participants from a general population with a high prevalence of excess adiposity ( approximately 68%), we assessed whether the relationships between conventional blood pressure (BP) and LVM indexed for height (LVMI) (determined from echocardiography) are influenced by adiposity. We confirmed these outcomes using 24-h ambulatory measurements in 297 participants; and carotid-femoral pulse wave velocity (PWV) (applanation tonometry) in 328 participants and from plasma leptin concentrations, we assessed whether leptin could mediate this effect. RESULTS: After adjustments for appropriate confounders, including the individual terms for adiposity and BP, interactions between adiposity indices (either waist circumference or the mean of subscapular and triceps skin-fold thickness) and either conventional systolic BP (SBP), 24-h SBP, PWV, conventional pulse pressure (PP), or 24-h PP were independently associated with LVMI (P < 0.001 for interactions). The adiposity index-haemodynamic interaction translated into a steeper slope of the BP-LVMI and PWV-LVMI relations in obese as compared with lean participants. Every one SD increase in conventional SBP ( approximately 22 mmHg) was associated with a 1.61 g/m increase in LVMI in participants with a normal waist circumference, in comparison to a 5.24 g/m increase in LVMI in those with an increased waist circumference (P < 0.0001). Furthermore, the adiposity index-haemodynamic interaction resulted in an increased LVMI in never-treated hypertensives with central obesity (LVMI, normotensives = 45.6 g/m, hypertensives = 51.0 g/m, P < 0.02), but not in participants with a normal waist circumference (LVMI, normotensives = 43.4 g/m, hypertensives = 45.0 g/m). Significant plasma leptin concentration-haemodynamic interactions were also associated with LVMI independent of confounders and adiposity indices, an effect that translated into a steeper slope of the haemodynamic factor-LVMI relations in participants with a plasma leptin concentration above as compared with those below the median for the group. CONCLUSION: Adiposity-induced increases in LVM reflect an enhanced effect of BP on LV growth, an effect that may be mediated by leptin. This translates into an impact of never-treated hypertension on LVMI in centrally obese, but not in lean people in groups of African descent in South Africa.

Gender-specific brachial artery blood pressure-independent relationship between pulse wave velocity and left ventricular mass index in a group of African ancestry.

AIM: As it is uncertain whether arterial stiffness is related to left ventricular mass and left ventricle mean wall thickness independent of blood pressure measured at the brachial artery, we aimed to ascertain this effect in never-treated participants with a high prevalence of risk factors for large artery dysfunction. METHODS: The conventional and ambulatory blood pressure-independent relations between indices of large artery function and either left ventricular mass or mean wall thickness were determined in 309 never-treated randomly recruited South Africans of African ancestry with prevalent risk factors for large artery changes [24% were hypertensive, 63% were overweight/obese, and 17% had diabetes mellitus or abnormal blood glucose control (glycosylated hemoglobin A1c > 6.1%)]. Large artery function was assessed from applanation tonometry performed at the carotid, radial and femoral arteries and central augmentation index and aortic pulse wave velocity (carotid femoral pulse wave velocity) derived from these measures. Left ventricular mass indexed for height (left ventricular mass index) and mean wall thickness were determined using echocardiography. RESULTS: Pulse wave velocity was associated with left ventricular mass index (r = 0.67, P < 0.0001) and mean wall thickness (r = 0.61, P < 0.0001) in women, but not in men (r = 0.04-0.08) (P < 0.0001 for the interaction between pulse wave velocity and gender). On multivariate analysis with appropriate adjustments including either conventional systolic blood pressure, pulse pressure or mean arterial pressure, pulse wave velocity was independently associated with left ventricular mass index (partial r = 0.25, P < 0.005 after adjustments for systolic blood pressure) and with mean wall thickness (partial r = 0.17, P < 0.05 after adjustments for systolic blood pressure) in women, but not in men. With the inclusion of 24-h ambulatory rather than conventional systolic blood pressure, pulse pressure or mean arterial pressure in the regression equation, pulse wave velocity was similarly independently associated with left ventricular mass index (partial r = 0.39, P < 0.001 after adjustments for 24-h systolic blood pressure) and mean wall thickness (partial r = 0.33, P < 0.003 after adjustments for 24-h systolic blood pressure) in women, but not in men. Central augmentation index was not independently associated with left ventricular mass index or mean wall thickness. In women, the contribution of pulse wave velocity to left ventricular mass index or mean wall thickness independent of systolic blood pressure (standardized beta-coefficient for left ventricular mass index=0.37 +/- 0.13, P < 0.005) was equivalent to the contribution of systolic blood pressure (standardized beta-coefficient for left ventricular mass index = 0.38 +/- 0.13, P < 0.005). Moreover, after adjusting for clinic or ambulatory systolic blood pressure and other confounders, in women every one standard deviation increase in pulse wave velocity (2.1 m/s) translated into a 4.3 or 6.2 g/m increase in left ventricular mass index, respectively. CONCLUSION: Arterial stiffness is associated with left ventricular mass index and left ventricle wall thickness independent of conventional or ambulatory blood pressure and additional confounders in a never-treated population sample of women, but not men, of African ancestry with prevalent risk factors for large artery dysfunction.

The association of waist circumference with ambulatory blood pressure is independent of alternative adiposity indices.

AIM: The relationship between waist circumference (WC) and conventional blood pressure (BP) is independent of other clinical indices of adiposity. As ambulatory BP may offer more prognostic information than conventional BP, we aimed to identify whether indices of central adiposity are associated with ambulatory BP independent of other indices of adiposity. METHODS: The relationship between indices of adiposity [WC, waist-to-hip ratio, body mass index (BMI) or skin-fold thickness] and ambulatory or conventional BP was determined in 300 randomly selected individuals of African descent living in an urban developing community in South Africa. Relationships were determined with multiple indices of adiposity in the same regression model and after adjusting for age, gender, alcohol and tobacco intake, the presence or absence of diabetes mellitus or inappropriate blood glucose control [haemoglobin A1c (HbA1c)], antihypertensive therapy and menopausal status. RESULTS: Sixty-five per cent of participants were overweight or obese. With respect to the relationships between indices of adiposity, BMI and WC showed the strongest correlation (r=0.84, P<0.0001). After including all indices of adiposity and confounders in the model, WC was the only clinical index of adiposity which independently predicted 24-h (partial r=0.15, P<0.005) and conventional (partial r=0.14, P<0.005) systolic BP and 24-h (partial r=0.13, P<0.02) and conventional (partial r=0.40, P<0.0001) diastolic BP. After adjusting for other adiposity indices and confounders, every 1 SD (15 cm) increase in WC resulted in a 4.04 mmHg increase in 24-h systolic BP and a 4.33 mmHg increase in 24-h diastolic BP. Similar results were obtained in the subgroup of 237 participants not receiving antihypertensive therapy. CONCLUSION: WC is the only clinical index of adiposity that is associated with 24-h and conventional BP independent of other adiposity indices in a community with a high prevalence of obesity.

Upstream stimulatory factor 1 transactivates the human gene promoter of the cardiac isoform of acetyl-CoA carboxylase.

E-box cis-elements act as binding sites for upstream stimulatory factors (USFs), putative glucose-responsive transcriptional modulators. Since four E-boxes were identified on the human ACCbeta promoter, we hypothesized that USF1 induces ACCbeta expression in a glucose-dependent manner. Here, murine cardiac ACCbeta expression was significantly increased in response to high carbohydrate re-feeding after fasting. However, transfection studies showed no difference in ACCbeta promoter activity in neonatal cardiomyocytes and CV-1 fibroblasts after low (5.5mM) and high (25 mM) glucose exposure. USF1 overexpression significantly increased ACCbeta promoter activity in both cell lines under low glucose conditions. With high glucose exposure, USF1 further induced ACCbeta promoter activity only in CV-1 fibroblasts. USF1-induced ACCbeta promoter responsiveness was markedly attenuated when co-transfecting cardiomyocytes with a -93/+65 or -38/+65 promoter deletion construct (lacking E-boxes 1-3). Thus, USF1 transactivates the human ACCbeta promoter in the heart, likely through an E-box cis-element located close to the transcription start site.

H-89, a non-specific inhibitor of protein kinase A, promotes post-ischemic cardiac contractile recovery and reduces infarct size.

Myocardial ischemia is associated with increased production of cyclic adenosine monophosphate (cAMP), with potentially deleterious effects. We hypothesized that the ischemia-induced activation of cAMP-dependent protein kinase A (PKA), could beneficially be inhibited by a PKA-inhibitor N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide (H-89). H-89 when given to isolated perfused rat hearts before 30 minutes of global ischemia-reperfusion improved postischemic function and decreased infarct size. In another series, H-89 administered prior to preconditioning by 10 minutes of transient global ischemia decreased PKA activity (measured at the end of the preconditioning protocol) and augmented postischemic mechanical recovery. H-89 given for 5 minutes before the 10 minutes of transient ischemia further decreased infarct size from 13.4 +/- 1.0% (preconditioning alone) to 7.0 +/- 0.93 (P < 0.01). In a third series, forskolin (0.3 muM, 5 minutes, 10 minutes washout prior to ischemia) increased PKA activity and reduced infarct size. Prior H-89 decreased PKA activity after 5 minutes of forskolin and further reduced infarct size versus forskolin alone. In conclusion, three procedures increased postischemic recovery and reduced infarct size: H-89; preconditioning by transient ischemia; or forskolin as a preconditioning-mimetic. PKA-inhibition by H-89 further decreased infarct size beyond preconditioning or forskolin. Despite the reservation that H-89 could be non-selective in its actions, we propose H-89 as a candidate cardioprotective agent.