Danelle Badenhorst

Cross-linking influences the impact of quantitative changes in myocardial collagen on cardiac stiffness and remodelling in hypertension in rats

OBJECTIVE To assess whether the variable impact of quantitative changes in myocardial collagen on left ventricular (LV) diastolic myocardial stiffness (myocardial k) and remodelling (increased volume intercept of diastolic pressure-volume relations) in LV hypertrophy (LVH) is associated with alterations in myocardial collagen cross-linking. METHODS We evaluated myocardial collagen content (hydroxyproline concentrations [HPRO]) and the degree of myocardial collagen cross-linking (solubility to cyanogen bromide digestion) in 14-15- and 21-22-month-old spontaneously hypertensive rats (SHRs), and in aortic-banded rats with pressure overload hypertrophy (POH). RESULTS In rats with POH and in SHRs irrespective of age, increases in myocardial [HPRO] were noted. However, hypertensive rats differed in the material and geometric properties of the myocardium, and in qualitative aspects of fibrosis. In 14-15-month-old SHRs myocardial k (determined from diastolic stress-strain relations) and insoluble (cross-linked) [HPRO] were increased, but no LV remodelling or increases in myocardial soluble (non-cross-linked) [HPRO] were noted. In rats with POH, LV remodelling and increases in soluble myocardial [HPRO] occurred, but no increase in k or insoluble myocardial [HPRO] were observed. In 21-22-month-old SHRs, increases in k, soluble and insoluble myocardial [HPRO], as well as LV remodelling occurred. CONCLUSIONS Collagen cross-linking may determine the diverse relation that exists between increases in myocardial collagen concentrations and either myocardial stiffness or chamber remodelling in hypertension. These findings support the notion that fibrosis contributes to myocardial stiffness as well as LV dilatation in LVH, albeit an effect that is modulated by collagen quality.

Effects of pentoxifylline on cytokine profiles and left ventricular performance in patients with decompensated congestive heart failure secondary to idiopathic dilated cardiomyopathy.

Patients with severe heart failure have plasma cytokine concentrations that are more than twofold greater than those in patients with moderate heart failure. Although pentoxifylline, an immunomodulatory agent that inhibits tumour necrosis factor-alpha (TNF-alpha) production, improves pump function in mild-to-moderate heart failure, its effects on advanced heart failure have not been determined. In a prospective, randomized, double-blind, placebo-controlled study we compared the effects of 1-month therapy with pentoxifylline (400 mg 3 times daily) (n = 9) and placebo (n = 9) on left ventricular systolic function and dimensions as well as on plasma TNF-alpha (picograms per milliliter), interleukin-10 (IL-10), and the apoptosis-signaling receptor Fas/Apo-1 in patients with idiopathic dilated cardiomyopathy and advanced heart failure. All patients had New York Heart Association functional class IV heart failure, required intravenous inotropic agents for >72 hours at the beginning of the study, and received diuretics, digoxin, and an angiotensin-converting enzyme inhibitor for the duration of the study. Marked increases in TNF-alpha and Fas/Apo-1 concentrations were noted in the 18 patients compared with patients with functional class II to III heart failure and controls (p <0.001). Baseline characteristics were the same between the pentoxifylline and placebo groups. Pentoxifylline administration resulted in reduced TNF-alpha and Fas/Apo-1 concentrations, and an increase in ejection fraction at 1 month (p <0.05 compared with baseline and with placebo), effects that were not observed in the placebo-treated group. These data suggest that pentoxifylline may be a useful adjunct to conventional therapy in patients with severe heart failure.

β-Adrenergic Activation Initiates Chamber Dilatation in Concentric Hypertrophy

Abstract—It is uncertain whether chronic &bgr;-adrenoreceptor (&bgr;-AR)–activation in hypertension could initiate the progression from compensated left ventricular (LV) hypertrophy to pump dysfunction. It is also uncertain if this effect is through adverse LV remodeling (chamber dilatation with wall thinning and pump dysfunction) or intrinsic myocardial contractile dysfunction. We evaluated the effect of 5 months of isoprenaline (0.02 mg · kg−1 · d−1) on hemodynamics, LV wall thickness, cavity size, and interstitial characteristics in spontaneously hypertensive rats (SHR) with compensated LV hypertrophy. In the absence of myocyte necrosis, changes in volume preload, pressure afterload, and heart rate or decreases in baseline systolic myocardial elastance (load independent measure of intrinsic myocardial contractility), ISO produced a right shift in LV diastolic pressure–volume (P-V) relations (chamber dilatation), a decrease in LV wall thickness despite a further increase in LV weight in SHR, LV pump dysfunction (right shift in LV systolic P-V relations), and deleterious interstitial remodeling (increments in total and noncrosslinked myocardial collagen concentrations). The isoprenaline-induced LV geometric, chamber performance, and interstitial changes were similar to alterations noted during decompensation in older SHR. In summary, in the absence of tissue necrosis and baseline intrinsic myocardial contractile dysfunction, chronic &bgr;-AR activation induces interstitial and chamber remodeling and, hence, pump dysfunction. These data suggest that chronic sympathetic activation initiates the progression from compensated concentric LV hypertrophy in hypertension to cardiac dysfunction primarily through deleterious cardiac remodeling rather than intrinsic myocardial contractile dysfunction.

T594M variant of the epithelial sodium channel β-subunit gene and hypertension in individuals of African ancestry in South Africa

BACKGROUND The T594M variant of the beta-subunit of the sodium epithelial channel (ENaC) gene may contribute to hypertension in individuals of African origin. METHODS A case-control study was performed to assess the role of the ENaC gene variant as an independent risk factor for hypertension in subjects of African ancestry. The effects of the ENaC gene variant on ambulatory blood pressure (BP) in hypertensive individuals and on office BP in hypertensive individuals and control subjects were also assessed. A total of 519 hypertensive patients with 24-h ambulatory BP (ABP) values determined while off medication, and 514 normotensive South African individuals of African ancestry were genotyped for the T594M polymorphism of the ENaC gene. RESULTS A total of 22 (4.2%) hypertensive participants compared with 23 (4.5%) normotensive participants possessed the T594M variant (odds ratio = 1.06, confidence interval = 0.58 to 1.92, not significant). A similar genotype frequency distribution was noted in subjects representing the two predominant chiefdoms (Nguni and Sotho) in both case and control groups. No differences in frequency distribution of the T594M variant were noted with respect to either body mass index or gender. There were no differences in clinic or ambulatory mean, day, or night BP between hypertensive patients with or without the variant. Similarly, no differences were noted in clinic BP between control subjects with or without the variant. Other phenotypic parameters (including age and hypertension duration and severity) were also similar among hypertensive patients with or without the variant. CONCLUSION These results do not support an important role for the T594M variant of the ENaC gene contributing to either the development or severity of hypertension in subjects of African ancestry.

Functional variants of the angiotensinogen gene determine antihypertensive responses to angiotensin-converting enzyme inhibitors in subjects of African origin.

Objective To determine whether the response to angiotensin-converting enzyme inhibitor (ACEI) monotherapy in subjects of African origin is determined by genetic variants within the angiotensinogen (AGT) gene. Methods A total of 194 hypertensive patients of African ancestry were recruited from district clinics in Johannesburg, South Africa. Eighty patients received open-label ACEI (enalapril or lisinopril) monotherapy, and 114 open-label calcium antagonist (nifedipine) as a drug class comparator. Twenty-four hour ambulatory blood pressure (ABP) monitoring was performed at baseline (off medication) and after 2 months of therapy. DNA was analysed for functional variants (−217G→A and −20A→C) of the AGT gene. The impact of genotype on ABP responses to ACEI monotherapy or calcium antagonists; and on plasma aldosterone and renin levels after ACEI monotherapy was assessed. Results Adjusting for baseline ABP and type of ACEI in the ACEI-treated group, the −217G→A variant predicted ABP responses to ACEI (n = 77; P < 0.01), but not to nifedipine (n = 108). ACEI in patients with the AA genotype of the −217G→A variant failed to elicit an antihypertensive response [change in ABP, mmHg: systolic blood pressure (SBP) +0.84 ± 2.89, P = 0.78; diastolic blood pressure (DBP) −0.47 ± 1.74, P = 0.79]. In contrast, those patients with at least one copy of the −217G allele developed a 7.23 ± 1.55 and 5.38 ± 1.12 mmHg decrease (P < 0.0001) in SBP and DBP, respectively, after ACEI administration. Similarly, the −20A→C variant predicted ABP responses to ACEI monotherapy (P < 0.01) but not to nifedipine. Moreover, patients who were AA genotype for both variants failed to develop an antihypertensive response to ACEI (change in ABP, mmHg: SBP +1.06 ± 3.05, P = 0.73; DBP −0.39 ± 1.83, P = 0.83); whereas patients with at least one copy of both the −217G and the −20C allele developed substantial decreases in ABP (change in ABP, mmHg: SBP −14.08 ± 3.72, P < 0.0001; DBP −9.62 ± 2.74, P < 0.0001). Patients with at least one copy of the −217G allele demonstrated a significant reduction in the aldosterone-to-renin ratio (−0.098 ± 0.035, P < 0.01), whereas in those patients who were −217AA genotype the ratio was unchanged (−0.03 ± 0.16, P = 0.85). Conclusion Functional variants of the AGT gene contribute to the variability of antihypertensive responses to ACEI monotherapy in individuals of African ancestry, with genotype determining whether or not responses occur.

Impact of Aldosterone Receptor Blockade on the Deleterious Cardiac Effects of Adrenergic Activation in Hypertensive Rats

Although in hypertension β-adrenoreceptor activation promotes the transition from cardiac hypertrophy to pump dysfunction, the use of β-blockers is controversial. As adrenergic activation may mediate adverse effects on the heart through the renin-angiotensin-aldosterone system, we evaluated the effects of the aldosterone receptor blocker, spironolactone (SPIRO), on isoproterenol (ISO)-induced changes in left ventricular cavity size and pump function and the determinants thereof in spontaneously hypertensive rats (SHR). ISO administered for 4.5 months resulted in increases in left ventricular dimensions and a decrease in pump function in SHR but not in normotensive rats, changes that, without affecting blood pressure, were abolished by SPIRO. In SHR, 4-5 days of ISO increased myocardial matrix metalloproteinase-2 activity, which was associated with matrix metalloproteinase-2 but not tissue inhibitor of MMP expression; persisted at 4.5 months; and was prevented by SPIRO. Moreover, after 4.5 months, ISO increased non-cross-linked myocardial collagen concentrations in SHR, which was abolished by SPIRO. Although after 4.5 months, ISO was not associated with increased cardiomyocyte apoptosis, an early (4-5 days) ISO-induced apoptotic effect was noted, which was prevented by SPIRO. Hence, aldosterone receptor blockade may be sufficient to prevent those adverse effects of β-adrenoreceptor activation responsible for the transition from concentric cardiac hypertrophy to pump dysfunction in hypertension.

The relationship between the nitric oxide synthase gene and the risk of hypertension defi ned according to ambulatory blood pressures

Although nitric oxide (NO) plays an important role in blood pressure (BP) control, whether variation of genes involved in regulating the synthesis of NO infl uences BP is uncertain. As the heritability of BP is stronger for ambulatory than it is for conventional BP, we assessed the independent association of the well described functional exon 7 Glu298Asp variant of the eNOS gene with the presence of hypertension in 511 randomly selected normotensive control participants and 503 hypertensives with a diagnosis of hypertension confi rmed with 24-hour ambulatory BP profiles whilst off therapy. We also assessed the relationship between eNOS genotype and 24 hour ambulatory BP. Comparisons of genotype and allele frequencies indicated a lack of association of the exon 7 Glu298Asp gene variant with hypertension (Odds ratio of genotype predicting the presence of hypertension=0.97, confidence interval=0.70-1.30, p=0.92). However, patients with the Glu/Glu genotype of the Glu298Asp variant (n=424) had increased 24-hour systolic and diastolic blood pressures (152±1/97±1 mm Hg) in comparison to patients heterozygous for the Glu298Asp variant or homozygous for the 298Asp allele (n=79) (145±1/94±1 mm Hg, p‹0.005 for systolic BP and p‹0.001 for diastolic BP after multiple adjustments including age, gender, body mass index and the presence of diabetes mellitus). Differences in systolic and diastolic BP between genotype groups were noted during the day as well as at night. The association of eNOS genotype with ambulatory BP translated into an increased risk of more severe grades of hypertension in patients with the Glu/Glu genotype (grade II and III vs. grade I, Odds ratio=2.20, confidence interval=1.34-3.59, p‹0.0002). In conclusion, a functional gene variant (Glu298Asp) at the eNOS locus contributes ~1.4-2.5% to the variation in ambulatory blood pressure within hypertensives, but is not associated with the presence of hypertension in patients in whom the diagnosis has been confirmed by 24-hour ambulatory BP values. The relationship between eNOS genotype and 24-hour ambulatory BP and the severity of hypertension warrants further study.