Renal protective effects of efonidipine in partially nephrectomized spontaneously hypertensive rats

Renal microcirculation and calcium channel subtypes

It has recently been reported that voltage-dependent Ca channel subtypes, e.g., L-, T-, N-, and P/Q-type, are expressed in renal arterioles and renal tubules, and the inhibition of these channels exerts various effects on renal microcirculation. For example, selective blockade of L-type Ca channels with nifedipine preferentially dilates the afferent arteriole and potentially induces glomerular hypertension. On the other hand, recently developed Ca channel blockers (CCBs) such as mibefradil and efonidipine block both T-type and L-type Ca channels and consequently dilate both afferent and efferent arterioles, leading to lowering of intraglomerular pressure. Interestingly, aldosterone has recently been recognized as a factor exacerbating renal diseases, and its secretion from adrenal gland is mediated by T-type Ca channels. Furthermore, T-type CCBs were shown to ameliorate renal dysfunction by suppressing inflammatory processes and renin secretion. On the basis of histological evaluations, N-type Ca channels are present in peripheral nerve terminals innervating both afferent and efferent arterioles. Further, it was suggested that N-type CCBs such as cilnidipine suppress renal arteriolar constriction induced by enhanced sympathetic nerve activity, thereby lowering intraglomerular pressure. Taken together, various Ca channel subtypes are present in the kidney and blockade of selective channels with distinct CCBs exerts diverse effects on renal microcirculation. Inhibition of T-type and N-type Ca channels with CCBs is anticipated to exert pleiotropic effects that would retard the progression of chronic kidney disease through modulation of renal hemodynamic and non-hemodynamic processes.

T-type Ca channel blockade as a determinant of kidney protection

Voltage-dependent Ca channels are classified into several subtypes based on the isoform of their α1 subunits. Traditional Ca channels blockers (CCBs), including nifedipine and amlodipine, act predominantly on L-type Ca channels, whereas novel CCBs such as efonidipine, benidipine and azelnidipine inhibit both L-type and T-type Ca channels. Furthermore, cilnidipine blocks L-type and N-type Ca channels. These CCBs exert divergent actions on renal microvessels. L-type CCBs preferentially dilate afferent arterioles, whereas both L-/T-type and L-/N-type CCBs potently dilate afferent and efferent arterioles. The distinct actions of CCBs on the renal microcirculation are reflected by changes in glomerular capillary pressure and subsequent renal injury: L-type CCBs favor an increase in glomerular capillary pressure, whereas L-/T-type and L-/N-type CCBs alleviate glomerular hypertension. The renal protective action of L-/T-type CCBs is also mediated by non-hemodynamic mechanisms, i.e., inhibition of the inflammatory process and inhibition of Rho kinase and aldosterone secretion. Finally, a growing body of evidence indicates that T-type CCBs offer more beneficial action on proteinuria and renal survival rate than L-type CCBs in patients with chronic kidney disease (CKD). Similarly, in CKD patients treated with renin-angiotensin blockers, add-on therapy with N-type CCBs is more potent in reducing proteinuria than that with L-type CCBs, although no difference is found in the subgroup with diabetic nephropathy. Thus, the strategy for hypertension treatment with CCBs has entered a new era: treatment selection depends not only on blood pressure control but also on the subtypes of CCBs.

Impact of renal function on cardiovascular events in elderly hypertensive patients treated with efonidipine

This study evaluated the impact of renal function on cardiovascular outcomes in elderly hypertensive patients enrolled in the Japanese Trial to Assess Optimal Systolic Blood Pressure in Elderly Hypertensive patients. The patients were randomly assigned to either a strict-treatment group (target systolic blood pressure (BP) <140 mm Hg, n=2212) or a mild-treatment group (target systolic BP, 140 to <160 mm Hg, n=2206), each with efonidipine (a T/L-type Ca channel blocker)-based regimens. Cardiovascular events (stroke, cardiovascular disease and renal disease) were evaluated during the 2-year follow-up period following the prospective randomized open-blinded end-point method. Estimated glomerular filtration rate (eGFR) was elevated throughout the trial period in both the strict-treatment (59.4-62 ml min⁻¹ per 1.73 m²) and the mild-treatment group (58.8-61.4 ml min⁻¹ per 1.73 m²). This tendency was also observed in diabetic patients and patients aged ≥75 years, with baseline eGFR<60 ml min⁻¹ per 1.73 m². Baseline eGFR (<60 vs. ≥60 ml min⁻¹ per 1.73 m²) had no definite relationship with the incidence of cardiovascular events, nor did the level of BP control. Proteinuria at the time of entry into the study, however, was significantly correlated with cardiovascular event rates (7.1%), an association that was more apparent in patients with eGFR<60 ml min⁻¹ per 1.73 m² (8.2%). Furthermore, the event rate was more elevated in patients with greater declines in eGFR and was amplified when the baseline eGFR was <60 ml min⁻¹ per 1.73 m². In conclusion, the rates of decline of renal function and proteinuria constitute critical risk factors for cardiovascular events in elderly hypertensive patients, trends that are enhanced when baseline eGFR is diminished. Furthermore, the fact that efonidipine-based regimens ameliorate renal function in elderly hypertensive patients with chronic kidney disease may offer novel information on the mechanisms of cardiovascular protection.

Combination therapy with irbesartan and efonidipine for attenuation of proteinuria in Dahl salt-sensitive rats

Angiotensin receptor blockers (ARBs) or T- and L-type calcium channel blockers (CCBs) are useful for glomerular protection; however, the protective effects of combination therapy remain unclear. In this study, Dahl salt-sensitive rats were fed a high-salt diet and were treated daily with placebo, irbesartan (60 mg kg(-1)), efonidipine (30 mg kg(-1)), irbesartan (60 mg kg(-1))+efonidipine (30 mg kg(-1)), amlodipine (3 mg kg(-1)), or irbesartan (60 mg kg(-1))+amlodipine (3 mg kg(-1)) for 4 weeks. Significant reductions in systolic blood pressure were seen in the irbesartan-, efonidipine- and amlodipine-treated groups compared with the placebo-treated group; a further significant reduction was seen in the irbesartan+efonidipine-treated group compared with the irbesartan-treated group. Compared with the placebo-treated group, proteinuria was significantly lower in the irbesartan- and efonidipine-treated groups, but not in the amlodipine-treated group. Furthermore, a significant attenuation of proteinuria in the irbesartan+efonidipine-treated group compared with the irbesartan-treated group was observed; this effect was not observed in the irbesartan+amlodipine-treated group. The glomerulosclerosis index was significantly attenuated by all active treatments except amlodipine. The glomerulosclerosis index in the irbesartan+efonidipine-treated group, but not in the irbesartan+amlodipine-treated group, was significantly lower than that in the irbesartan-treated group. Significant attenuations of gene expressions of p22(phox), transforming growth factor-beta, monocyte chemoattractant protein-1 and collegen I were observed in the irbesartan- and efonidipine-treated groups, but not in the amlodipine-treated group. Values for these parameters were reduced to control levels in the irbesartan+efonidipine-treated group. Combination therapy with ARB and T- and L-type CCB might produce a powerful renal protective effect.

Development of newer calcium channel antagonists: therapeutic potential of efonidipine in preventing electrical remodelling during atrial fibrillation

Calcium channel antagonists are most frequently prescribed for the treatment of hypertension and the majority specifically inhibit the L-type Ca2+ channel. In order to prevent reflex sympathetic over activity caused by L-type calcium channel antagonists (calcium channel blockers [CCBs]), increasing attention has focused on the blockade of the T-type Ca2+ channel. The T-type Ca2+ channel is found in the kidney and can also appear in the ventricle of the heart when in failure. Therefore, the T-type Ca2+ channel is a possible new target for the treatment of nephropathy and heart failure. In clinical trials, the efficacy and safety of T-type CCBs in hypertension and chronic renal disease have been reported. It is well known that the T-type Ca2+ channel is present in the adult atrium and plays a role in the cardiac pacemaker, but recent experimental studies suggest that this current also promotes electrical remodelling of the atrium. Using efonidipine, a dual L- and T-type CCB, it has been demonstrated that atrial electrical remodelling can be diminished in dogs. Furthermore, the T-type Ca2+ channel has recently been found in the pulmonary veins, contributing to the pulmonary vein pacemaker activity and triggered activity. A variety of drugs having T-type CCB effects have been shown to be effective in the management of atrial fibrillation, suggesting that this channel may be a novel therapeutic target.

T-type calcium channel blockade as a therapeutic strategy against renal injury in rats with subtotal nephrectomy

T-type calcium channel blockers have been previously shown to protect glomeruli from hypertension by regulating renal arteriolar tone. To examine whether blockade of these channels has a role in protection against tubulointerstitial damage, we used a stereo-selective T-type calcium channel blocker R(-)-efonidipine and studied its effect on the progression of this type of renal injury in spontaneously hypertensive rats that had undergone subtotal nephrectomy. Treatment with racemic efonidipine for 7 weeks significantly reduced systolic blood pressure and proteinuria. The R(-)-enantiomer, however, had no effect on blood pressure but significantly reduced proteinuria compared to vehicle-treated rats. Both agents blunted the increase in tubulointerstitial fibrosis, renal expression of alpha-smooth muscle actin and vimentin along with transforming growth factor-beta (TGF-beta)-induced renal Rho-kinase activity seen in the control group. Subtotal nephrectomy enhanced renal T-type calcium channel alpha1G subunit expression mimicked in angiotensin II-stimulated mesangial cells or TGF-beta-stimulated proximal tubular cells. Our study shows that T-type calcium channel blockade has renal protective actions that depend not only on hemodynamic effects but also pertain to Rho-kinase activity, tubulointerstitial fibrosis, and epithelial-mesenchymal transitions.

New Generation Calcium Channel Blockers in Hypertensive Treatment

During a couple of decades, a number of antihypertensive drugs have been developed, and the choice of hypertension treatment has been expanded. Among antihypertensive drugs, calcium channel blockers, which inhibit L-type voltage-gated calcium channels, are potent vasodilators, and have been used as a first- or second-line drug. Dihydropyridine-class calcium channel blockers are categorized into three generations according to the length of activity, and long-acting calcium channel blockers cause less activation of sympathetic nervous system, and are reported to offer beneficial action compared with short-action agents. Furthermore, novel types of calcium channel blockers have been developed that possess the blocking action on other calcium channel subtypes (T- and N-type), and exert agent-specific action apart from their class effects, such as the effects on heart rate and renin/aldosterone release. These additional benefits conferred by T/N-type calcium channel blockade are anticipated to provide organ protective actions in the treatment of hypertension, in addition to the blood pressure-lowering effect of L-type calcium channel blockade. In conclusion, novel calcium channel blockers with sustained activity and T/N-type calcium channel blocking action could provide more beneficial effects than classical blockers, and may expand the clinical utility of these agents.

Pathophysiological significance of T-type Ca2+ channels: role of T-type Ca2+ channels in renal microcirculation

Since conventional Ca(2+) antagonists, with predominant blockade of L-type voltage-dependent Ca(2+) channels, elicit preferential dilation of afferent arterioles, they might ostensibly aggravate glomerular hypertension. Recently, novel Ca(2+) antagonists, with inhibitory action on L-/T-type Ca(2+) channels, have been reported to dilate both afferent and efferent arterioles. The present review attempted to characterize the renal action of these Ca(2+) antagonists and evaluated the consequences following the treatment with these agents. In contrast to conventional Ca(2+) antagonists (e.g., nifedipine), novel antagonists (e.g., benidipine, efonidipine) potently dilated afferent and efferent arterioles; their action on efferent arterioles appeared to be mediated by the T-type Ca(2+) channel blockade, probably through the inhibition of the intracellular Ca(2+) release. The comparison of the anti-proteinuric action in subtotally nephrectomized rats showed that efonidipine exerted more prominent action than nifedipine. Furthermore, Ca(2+) antagonists with T-type Ca(2+) inhibitory action inhibited renin/aldosterone release and proinflammatory process. Finally, patients with chronic renal disease given a 48-week efonidipine treatment showed reduced proteinuria, and this effect was seen even when mean arterial blood pressure failed to become less than 100 mmHg. Collectively, T-type Ca(2+) channel blockade provides beneficial action in renal injury. Various mechanisms serve to protect against renal injury, including systemic/glomerular hemodynamic action and non-hemodynamic mechanisms.

Effects of efonidipine hydrochloride on renal arteriolar diameters in spontaneously hypertensive rats

Efonidipine, a calcium antagonist, has been reported to dilate not only afferent but also efferent arterioles, thereby reducing glomerular hydrostatic pressure. We investigated the effect of chronic treatment with efonidipine or lisinopril on the afferent and efferent arteriolar diameters by the vascular cast technique. Four-week-old spontaneously hypertensive rats (SHR) were divided into three groups: untreated, efonidipine (25 mg/kg/day)-treated, and lisinopril (3 mg/kg/day)-treated. At 22 weeks of age, the renal vasculatures were fixed at the maximally dilated condition. The morphometrical measurements showed that the treatments with efonidipine and lisinopril caused structural alteration of the vasculature, resulting in significantly greater efferent arteriolar diameters than in untreated SHR. In addition, lisinopril-treated rats had wider afferent lumina. The renoprotective effect of efonidipine and lisinopril might be partly due to the structurally larger efferent arteriolar lumen.

Efonidipine hydrochloride: a dual blocker of L- and T-type ca(2+) channels

T-type Ca(2+) channels have properties different from those of the L-type and are involved in cardiac pacemaking and regulation of blood flow, but not in myocardial contraction. Efonidipine is an antihypertensive and antianginal drug with dihydropyridine structure that was recently found to block both L- and T-type Ca(2+) channels. In isolated myocardial and vascular preparations, efonidipine has potent negative chronotropic and vasodilator effects but only a weak negative inotropic effect. In experimental animals and patients, reduction of blood pressure by the drug was accompanied by no or minimum reflex tachycardia leading to improvement of myocardial oxygen balance and maintenance of cardiac output. Efonidipine increased glomerular filtration rate without increasing intraglomerular pressure. By relaxing both the afferent and efferent arterioles, efonidipine markedly reduced proteinuria. Thus, efonidipine, an L- and T-type dual Ca(2+) channel blocker, appears to have an ideal profile as an antihypertensive and antianginal drug with organ-protective effects in the heart and kidney.

Comparison of L-type and mixed L- and T-type calcium channel blockers on kidney injury caused by deoxycorticosterone-salt hypertension in rats

The efficiency of calcium channel blockers (CCBs) in the treatment of chronic renal disease (CRD) is controversial. In this study, we investigated whether combined T- and L-type CCBs, using mibefradil (30 mg/kg/d), provided superior protection versus traditional L-type voltage-gated CCBs, using amlodipine (10 mg/kg/d), in the deoxycorticosterone acetate (DOCA)-salt model of high glomerular blood pressure (P(GC)) and rapidly developing kidney damage. After 4 to 5 weeks of DOCA-salt, amlodipine did not reduce proteinuria (protein, 341 +/- 90 versus 482 +/- 54 mg/24 h; P = not significant) or degree of glomerular damage (20% +/- 4% versus 28% +/- 6% damaged glomeruli; P = not significant) compared with untreated rats. Conversely, mibefradil reduced proteinuria and glomerular damage versus untreated DOCA-salt rats (protein, 244 +/- 75 mg/24 h; P < 0.02; damaged glomeruli, 11% +/- 3%; P < 0.05). Both CCBs had similar antihypertensive actions, returning blood pressure to the untreated sham value. Of note, P(GC) also was reduced by a similar extent (and to the sham value) with both mibefradil (58 +/- 2 mm Hg; P < 0.001) and amlodipine (61 +/- 2 mm Hg; P < 0.005) versus untreated DOCA-salt rats (70 +/- 1 mm Hg). This study shows that combined T- and L-type CCBs provide superior protection against CRD in the DOCA-salt model compared with L-type CCBs alone. However, this protection was not hemodynamic because similar systemic and glomerular antihypertensive responses occurred with both mibefradil and amlodipine. Although mibefradil was withdrawn from the market because of adverse drug interactions not associated with CCBs, other mixed channel blockers may provide an alternative or adjunctive therapy to angiotensin-converting enzyme inhibition in CRD.

Divergent renal vasodilator action of L- and T-type calcium antagonists in vivo

OBJECTIVE

To assess the in-vivo action on the renal microvasculature of the calcium antagonists nifedipine (L-type blocker), efonidipine (L/T-type blocker), and mibefradil (predominant T-type blocker).

DESIGN

An intravital needle-type charge-coupled device (CCD) camera videomicroscope was introduced to visualize the renal microcirculation directly in vivo.

METHODS

In anesthetized mongrel dogs, nifedipine (0.01-1 mg/kg per min), efonidipine (0.033-0.33 mg/kg per min), or mibefradil (0.01-1 mg/kg per min) was infused intravenously after the insertion of a CCD probe into the kidney. Renal microvascular responses to calcium antagonists were directly evaluated, with concomitant observation of renal clearance.

RESULTS

Each calcium antagonist caused modest vasodepressor action without affecting heart rate. Nifedipine (1 mg/kg per min, n = 9) increased renal plasma flow (RPF) (14 +/- 4%, P < 0.05) and glomerular filtration rate (GFR) (19 +/- 5%, P < 0.05), and tended to increase the filtration fraction (5 +/- 2% increment, P = 0.07). Efonidipine (0.33 mg/kg per min, n = 9), however, had no effect on filtration fraction, with 14 +/- 6% increments in RPF (P < 0.05) and 14 +/- 7% increments in GFR (P = 0.08). Rather, mibefradil (1 mg/kg per min, n = 9) elicited 6 +/- 2% decreases in filtration fraction (P < 0.05), with slight increments in RPF (6 +/- 3%) and no changes in GFR. In direct in-vivo microvasculature observations, nifedipine caused predominant (22 +/- 2%) dilatation of afferent arterioles (from 15.5 +/- 0.4 to 18.9 +/- 0.4 microm, n = 5), compared with that of efferent arterioles (10 +/- 2%; from 11.0 +/- 0.4 to 12.1 +/- 0.3 microm). In contrast, efonidipine caused a similar magnitude of vasodilatation (16 +/- 4%) compared with 18 +/- 2%; n = 6), and mibefradil caused greater dilatation of efferent arterioles (20 +/- 4%, n = 7) than that of afferent arterioles (13 +/- 4%).

CONCLUSIONS

There exists marked heterogeneity in action of nifedipine, efonidipine and mibefradil on the renal microvascular in canine kidneys in vivo. Furthermore, our current observations suggest an important contribution of T-type calcium channel activity to efferent arteriolar tone in vivo.

Distinct action of aranidipine and its active metabolite on renal arterioles, with special reference to renal protection

Aranidipine, a newly developed calcium antagonist, possesses unique pharmacologic characteristics in that its metabolite (M-1) still has antihypertensive action. We examined the effects of both agents on renal microcirculation using the isolated perfused hydronephrotic rat kidney. During norepinephrine-induced constriction, the addition of aranidipine dilated both afferent and efferent arterioles in a dose-dependent manner; at 10(-6) M, 83 +/- 6% and 90 +/- 6% reversal, respectively. In contrast, its active metabolite exerted dilator action predominantly on the afferent arteriole (79 +/- 4% vs. 44 +/- 17% at 10(-6) M for afferent and efferent arterioles, respectively). We further examined the long-term (8 weeks) effect of these agents on the development of renal injury in salt-loaded subtotally nephrectomized spontaneously hypertensive rats. Both aranidipine and M-1 reduced blood pressure by a similar magnitude. The decreases in proteinuria were observed in the aranidipine-treated group at weeks 6, 8, and 10, whereas in the M-1 group, significant reduction was attained only at week 6. Histopathologic examination revealed that both treatments improved glomerular and arteriolar sclerosis. Glomerular sclerosis, however, was less pronounced in the aranidipine-treated group than in the M-1 group. In conclusion, aranidipine has dilator action on both arterioles, whereas M-1 caused predominant dilation of afferent arterioles. Such metabolic changes may constitute a determinant of efferent arteriolar action of the calcium antagonist.

Antihypertensive therapy and progression of chronic renal disease

This paper reviews findings on the relationship between blood pressure control and the progression of renal disease. Experimental studies demonstrate a correlation between systemic blood pressure and histologic glomerular injury and the delay in progression of renal disease with antihypertensive therapy, particularly with angiotensin-converting enzyme inhibitors. Recent clinical findings are reviewed, including epidemiologic data linking hypertension to subsequent renal disease, and clinical studies showing a beneficial effect on progression of renal disease with lower than usual blood pressure targets.

Renal afferent and efferent arteriolar dilation by nilvadipine: studies in the isolated perfused hydronephrotic kidney

Although calcium antagonists are believed to exert preferential vasodilator action on the renal preglomerular afferent arteriole, we recently demonstrated that efonidipine, a novel calcium antagonist, vasodilates both afferent and efferent arterioles. Nilvadipine also is reported to increase renal blood flow and reduce filtration fraction, suggesting indirectly afferent and efferent arteriolar vasodilation. No direct investigation, however, has been conducted examining the renal microvascular action of nilvadipine. We therefore characterized the renal microvascular reactivity to nilvadipine, by using the isolated perfused rat hydronephrotic kidney. The administration of angiotensin II (0.3 nM) caused marked vasoconstriction of afferent (from 13.5 +/- 0.6 to 9.2 +/- 0.6 microm, p < 0.01, n = 6) and efferent arterioles (from 11.5 +/- 1.0 to 7.4 +/- 0.7 microm, p < 0.01; n = 5). The subsequent addition of nilvadipine (10 nM, 100 nM, and 1 microM) caused 37 +/- 5%, 91 +/- 4%, and 95 +/- 8% reversal of afferent arteriolar constriction, respectively. Similarly, efferent arterioles manifested 59 +/- 12% reversal by 1 microM nilvadipine. Thus unlike nifedipine, which we previously reported to cause modest efferent arteriolar dilation (21 +/- 1% reversal at 1 microM), nilvadipine possesses the greater ability to dilate efferent arterioles (p < 0.01 vs. nifedipine), although both antagonists cause similar magnitudes of afferent arteriolar vasodilation. Variable effects on the efferent arteriole suggest the heterogeneity in the calcium antagonist with regard to the renal microvascular action of this agent.