Control of left ventricular mass by moxonidine involves reduced DNA synthesis and enhanced DNA fragmentation

Abstract

Background and purpose: Left ventricular hypertrophy (LVH) is a maladaptive process associated with increased cardiovascular risk. Regression of LVH is associated with reduced complications of hypertension. Moxonidine is an antihypertensive imidazoline compound that reduces blood pressure primarily by central inhibition of sympathetic outflow and by direct actions on the heart to release atrial natriuretic peptide, a vasodilator and an antihypertrophic cardiac hormone. This study investigated the effect of moxonidine on LVH and the mechanisms involved in this effect.

Experimental approach: Spontaneously hypertensive rats were treated with several doses of moxonidine (s.c.) over 4 weeks. Blood pressure and heart rate were continuously monitored by telemetry. Body weight and water and food intake were measured weekly. Measurements also included left ventricular mass, DNA content, synthesis, fragmentation, and apoptotic/anti-apoptotic pathway proteins.

Key results: The decrease in mean arterial pressure stabilized at approximately -10 mm Hg after 1 week of treatment and thereafter. Compared to vehicle-treated rats (100%), left ventricular mass was dose- and time-dependently reduced by treatment. This reduction remained significantly lower after normalizing to body weight. Moxonidine reduced left ventricular DNA content and inhibited DNA synthesis. DNA fragmentation transiently, but significantly increased at 1 week of moxonidine treatment and was paralleled by elevated active caspase-3 protein. The highest dose significantly decreased the apoptotic protein Bax and all doses stimulated anti-apoptotic Bcl-2 after 4 weeks of treatment.

Conclusions and implications: These studies implicate the modulation of cardiac DNA dynamics in the control of left ventricular mass by moxonidine in a rat model of hypertension.

Figure 1

The effect of 4 weeks treatment with various concentrations of moxonidine on body weight. ^*P<0.001 vs basal; ^**P<0.01 vs corresponding vehicle-treated groups; n=8–23 rats per group.

Figure 2

The effect of 1-, 2- and 4-week treatment with various concentrations of moxonidine on (a) left ventricular mass and (b) left ventricular DNA content, presented as percentage of corresponding vehicle-treated rats (100%). (c) Correlation between percentage decrease in left ventricular mass vs percentage decrease in DNA content in 4-week moxonidine-treated spontaneously hypertensive rat (SHR). ^*P<0.01 vs corresponding vehicle-treated groups. n=6–8 rats per group.

Figure 3

The effect of 1-, 2- and 4-week treatment with various concentrations of moxonidine on left ventricular ³H-thymidine incorporation, presented as percentage of corresponding vehicle-treated rats (100%). ^*P<0.04; ^**P<0.01 vs corresponding vehicle-treated groups; n=3–5 rats per group.

Figure 4

The effect of 1-, 2- and 4-week treatment with various concentrations of moxonidine on left ventricular DNA fragmentation. (a) DNA laddering, n=3–7 rats per group. (b) Cell death detection by ELISA, n=3–6 rats per group. ^*P<0.01; ^#P<0.05 vs corresponding vehicle-treated groups. ^$P<0.05 vs corresponding 100 μg kg⁻¹ h⁻¹ moxonidine-treated group. Data are presented as percentage of vehicle-treated control (100%).

Figure 5

Representative western blot analysis of the effect of 1-, 2- and 4-week treatment with moxonidine on left ventricular Bax and Bcl-2 proteins. Column graph represents Bax/Bcl-2 ratio. ^*P<0.01 vs corresponding vehicle-treated spontaneously hypertensive rat (SHR); n=5–7 rats per group.

Figure 6

Western blot analysis of the effect of 1-, 2- and 4-week treatment with moxonidine on left ventricular pro- and cleaved caspase-3 protein expression. Column graph represents cleaved to pro-caspase-3 ratio. ^*P<0.05; ^**P<0.01 vs vehicle-treated spontaneously hypertensive rat (SHR). n=6–9 rats per group.