OPC-13340, a new dihydropyridine calcium channel blocker attenuates rapid vascular smooth muscle cell growth in spontaneously hypertensive rats

The Effects of Calcium Channel Blockers are not Related to their Chemical Structure in the Collar Model of the Rabbit

Placing a silicone collar around the rabbit carotid artery induces intimal thickening, an early stage in atherosclerosis and restenosis. We investigated whether treatment with oral pranidipine, a new potent, long-lasting dihydropyridine calcium channel blocker (CCB), inhibited collar-induced intimal thickening in addition to the changes in vascular reactivity usually observed in this model. Pranidipine treatment did not inhibit collar-induced intimal thickening. Placing the collar around the carotid artery resulted in the characteristic changes in vascular reactivity, such as increased sensitivity to 5-hydroxytryptamine. Treatment with Nω-nitro-l-arginine (100 μM) and pranidipine, however, did not affect collar-induced changes in vascular reactivity. From results of this and previous studies, we conclude that pranidipine does not prevent collar-induced intimal thickening or collar-induced changes in vascular reactivity. Not all CCBs prevent collar-induced intimal thickening, suggesting that the effects of these agents are not related to their chemical structure and/or their calcium channel-blocking actions.

AQP4 knockout impairs proliferation, migration and neuronal differentiation of adult neural stem cells

Aquaporin-4 (AQP4), a key molecule for maintaining water and ion homeostasis in the central nervous system, is expressed in adult neural stem cells (ANSCs) as well as astrocytes. However, little is known about the functions of AQP4 in the ANSCs in vitro. Here we show that AQP4 knockout inhibits the proliferation, survival, migration and neuronal differentiation of ANSCs derived from the subventricular zone of adult mice. Flow cytometric cell cycle analysis revealed that AQP4 knockout increased the basal apoptosis and induced a G2-M arrest in ANSCs. Using Fluo-3 Ca2+ imaging, we show that AQP4 knockout alters the spontaneous Ca2+ oscillations by frequency enhancement and amplitude suppression, and suppresses KCl-induced Ca2+ influx. AQP4 knockout downregulated the expression of connexin43 and the L-type voltage-gated Ca2+ channel CaV1.2 subtype in ANSCs. Together, these findings suggest that AQP4 plays a crucial role in regulating the proliferation, migration and differentiation of ANSCs, and this function of AQP4 is probably mediated by its action on intracellular Ca2+ dynamics.

Long-acting calcium channel antagonist pranidipine prevents ventricular remodeling after myocardial infarction in rats

The purpose of this study was to examine the effects of the long-acting calcium channel antagonist pranidipine on ventricular remodeling, systolic and diastolic cardiac function, circulating humoral factors, and cardiac mRNA expression in myocardial infarcted rats. Myocardial infarction (MI) was produced by ligation of the coronary artery in Wistar rats. Three mg/kg per day of pranidipine was randomly administered to the infarcted rats. Hemodynamic measurements, Doppler echocardiographic examinations, analyses of the plasma levels of humoral factors, and myocardial mRNA expression were performed at 4 weeks after myocardial infarction. Left ventricular end-diastolic pressure (LVEDP) and central venous pressure (CVP) increased to 24.2 +/- 1.2mmHg and 5.4 +/- 0.6 mmHg. Pranidipine reduced LVEDP and CVP to 13.6 +/- 1.4mmHg (P < 0.01) and 2.5 +/- 0.4mmHg (P < 0.01). The weight of the left and right ventricles in MI was significantly higher than in the sham-operated rats (sham, 2.02 +/- 0.04 and 0.47 +/- 0.02g/kg; MI, 2.18 +/- 0.05 and 0.79 +/- 0.04g/ kg; P < 0.01). Left ventricular end-diastolic dimension (LVDd) in MI increased to 10.3 +/- 0.3mm (P < 0.01) (sham, 6.4 +/- 0.3mm). Pranidipine prevented an increase in the weight of the left and right ventricles (2.02 +/- 0.04 and 0.6 +/- 0.03g/kg, P < 0.01) and LVDd (7.9 +/-0.2mm, P < 0.01 to MI). Plasma renin activity (PRA), and plasma epinephrine, norepinephrine, and dopamine concentrations in MI were higher than those of the sham-operated rats. Pranidipine decreased the PRA and plasma cathecolamine levels of the myocardial infarcted rats to the level of the sham-operated rats. Moreover, the rats in MI showed systolic dysfunction, shown by decreased fractional shortening (sham, 31 +/- 2% vs MI, 15 +/- 1%; P < 0.01) and diastolic dysfunction shown by the E-wave deceleration rate (sham, 12.8 +/- 1.1 m/s2; MI, 32.6 +/- 2.1 m/s2; P < 0.01). Pranidipine significantly prevented systolic and diastolic dysfunction. The increases in beta-myosin heavy chain (MHC), alpha-skeletal actin, and atrial natriuretic polypeptide mRNAs in the noninfarcted left ventricle and right ventricle at 4 weeks after the myocardial infarction were significantly suppressed by the treatment with pranidipine. On the other hand, depressed alpha-MHC was restored to normal levels by pranidipine in both regions. In conclusion, pranidipine prevents the left ventricular remodeling process accompanied by systolic and diastolic dysfunction, and inhibits abnormal cardiac gene expression after myocardial infarction.

Mibefradil-induced inhibition of proliferation of human peripheral blood mononuclear cells

To evaluate the role of intracellular calcium and particularly Ca2+-uptake in the initiation of lymphocyte mitogenesis, the effect of mibefradil, which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels, on the proliferation of human peripheral blood mononuclear cells (PBMCs) is compared with the effect of nifedipine, which blocks only the L-type calcium channel. The rate of [3H]thymidine incorporation into control and concanavalin A-stimulated PBMCs in the presence or absence of the calcium channel blockers mibefradil or nifedipine (1, 10, or 50 microM), and of the intracellular calcium antagonist 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB-8; 1, 10, 25, or 50 microM) was assayed in the cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures also was determined in mibefradil- or nifedipine-treated control or stimulated cells. Restoration of the proliferative response in mibefradil- or nifedipine-treated cells was investigated by addition of exogenous interleukin-2. Interleukin-2-receptor expression in the cells was monitored by using anti-activated T-cell antigen (Tac) antibody, and the interleukin-2 production in the cell supernatants of the cultures was determined by an enzyme-amplified sensitive immunoassay. Mibefradil and nifedipine concentration-dependently reduced the cell number and the [3H]thymidine incorporation or the de novo DNA synthesis in control and concanavalin A-stimulated human PBMCs. Mibefradil exhibited a more pronounced inhibition of the proliferation of human PBMCs than did nifedipine. The inhibitory effect of mibefradil or nifedipine on DNA synthesis was dependent on the timing of treatment with the drugs. The inhibitory effect of mibefradil or nifedipine on the lymphoproliferative response was nearly abolished if the drugs were added 20 h after cell stimulation. A markedly reduced inhibitory effect was found when mibefradil or nifedipine was added 1-7 h after cell stimulation. However, regardless of time of addition, TMB-8 caused a persistent inhibition of the proliferation of human PBMCs. The inhibitory effect of mibefradil or nifedipine on the proliferation of human PBMCs is nearly abolished by addition of the calcium channel activator Bay K 8644. The proliferative response of mibefradil- or nifedipine-treated cells is restored by addition of exogenous interleukin-2. The normal expression of interleukin-2 receptors was preserved, whereas the interleukin-2 production was blocked in the presence of mibefradil or nifedipine. Our data show that mibefradil has a more pronounced inhibitory effect on the proliferation of human PBMCs than nifedipine and that this inhibitory effect on DNA synthesis is dependent on the timing of treatment with both drugs.

Amlodipine inhibition of serum-, thrombin-, or fibroblast growth factor-induced vascular smooth-muscle cell proliferation

Atherosclerosis, like several other vascular diseases, exhibits structural and functional abnormalities resulting partially from an exaggerated proliferation of vascular smooth-muscle cells (VSMCs). Ca2+ channel blockers, such as amlodipine, have been suggested to retard or even prevent the progression of atherosclerosis. To determine the mechanisms involved in these effects, we investigated the influence of amlodipine on VSMC proliferation by using rat aortic VSMCs in culture. Amlodipine (0.1-10 microM) inhibited serum-, basic fibroblast growth factor (bFGF)-, and thrombin-induced VSMC proliferation and DNA synthesis in a concentration-dependent manner, as demonstrated by cell count and bromodeoxyuridine (BrdU)-incorporation measurements, respectively. Delayed addition of amlodipine after VSMC stimulation showed that the drug exerted its effect early in G1 phase of the cell cycle. This observation was confirmed by the finding that amlodipine did not influence DNA synthesis in VSMCs arrested to the G1/S boundary by hydroxyurea treatment. Consistent with its effects on VSMC growth/proliferation, amlodipine also decreased c-myc, c-fos, and c-jun protooncogene expression induced by serum, thrombin, or bFGF within 1 h after cell activation, as assessed by semiquantitative reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis. The calcium channel agonist Bay K 8644, which counteracted the inhibition by nifedipine of bFGF-, thrombin- or serum-induced DNA synthesis, was ineffective to antagonize the inhibitory effect of amlodipine. The aforementioned effects of amlodipine were of similar amplitude, irrespective of the growth-enhancing agent used. This strongly indicates that amlodipine acts downstream of receptor activation to exert its antiproliferative action, probably early in the G1 phase of the cell cycle. Moreover, the lack of antagonistic effect between amlodipine and Bay K 8644 suggests that, in addition to its L-type Ca2+ channel inhibitory effect, amlodipine inhibits other intracellular signaling pathways. Such an interference of amlodipine with mitogenic signaling pathways might contribute to confer a blood vessel-protecting potential on amlodipine.

Pharmacologic treatment of atherosclerosis: beyond lipid-lowering therapy

Increased proliferation of intimal smooth muscle cells (SMCs), resulting in myointimal hyperplasia and luminal narrowing, is a characteristic of the early phase of atherogenesis. Since agents that reduce this process could potentially be considered as alternatives to lipid-lowering therapy in the prevention/treatment of atherosclerosis, it is of interest to elucidate the mechanisms involved in myointimal proliferation. This review focuses on the main mechanisms that control vascular SMC reactivity/proliferation with particular reference to spontaneously hypertensive rat-derived arterial cells, which exhibit exaggerated growth and hyperresponsiveness to stimuli compared with cells from normotensive Wistar-Kyoto rats. In view of the fact that overall cell reactivity is under the control of free Ca2+ ions, the beneficial effects of calcium antagonists on the prevention/treatment of atherosclerosis are discussed. In particular, the mechanisms whereby amlodipine--a vascular selective inhibitor of inward Ca2+ current carried by the L-type Ca2+ channels--can affect cell growth and exhibit antiatherogenic properties are reviewed.

Amlodipine and vascular hypertrophy

In both atherosclerosis and arterial hypertension, structural and functional abnormalities result in vascular hypertrophy that is associated with an increased ratio of vascular media thickness to lumen diameter and hyperreactivity of vascular smooth muscle cells (VSMCs), resulting in uncontrolled cell migration and growth in vivo. In culture, VSMCs isolated from the spontaneously hypertensive rat (SHR) also display exaggerated growth and/or proliferation compared to VSMCs isolated from normotensive control Wistar Kyoto (WKY) rats. In vitro studies of cultured VSMCs can therefore be used as a model to investigate the mechanisms whereby a drug such as amlodipine can exert its antihypertensive and antiatherogenic effects. The present in vitro investigations examine the mechanisms whereby amlodipine reduces VSMC growth/proliferation promoted by basic fibroblast growth factor (bFGF), a peptide growth factor likely to participate in the vascular smooth muscle hypertrophy of the SHR. VSMCs from SHR and/or WKY rat aortae were isolated, passaged, and cultured. The influence of amlodipine on VSMC growth/proliferation was studied by measuring DNA synthesis and cell number under experimental conditions, which allowed us to determine the cell cycle phase in which amlodipine exerts its effects. Amlodipine was found to inhibit growth and bFGF-induced DNA synthesis in a concentration-dependent manner. Delayed addition of amlodipine showed that the drug exerts its effect early in the G1 phase, a result that was confirmed by the finding that amlodipine could not inhibit bFGF-induced DNA synthesis in VSMCs arrested at the G1/S boundary. In comparative experiments, the inhibitory effect of amlodipine on both cell growth and DNA synthesis was found to be of similar magnitude in SHR- and WKY-derived VSMCs. It is therefore likely that by modulating cell growth/proliferation induced by bFGF, amlodipine may reduce the vascular hypertrophy of the SHR. Since amlodipine also has been found to inhibit VSMC migration, one may reasonably envisage that these characteristics are important components of the antiatherogenic properties of the drug.

Decreased L-arginine-nitric oxide pathway in cultured myoblasts from spontaneously hypertensive versus normotensive Wistar-Kyoto rats

The hypertrophy of the arterial media exhibited by spontaneously hypertensive rats is related to the hyperproliferation of their smooth muscle cells in culture. Using two methods to assay nitric oxide synthase activity, we showed that this abnormal proliferation results from a decreased activity of the inducible NOS II and less modulation of this enzymatic activity by these cells compared to control Wistar Kyoto cells.

Mechanism of action of the inhibitory effect of nifedipine on the growth of cultured aortic cells from spontaneously hypertensive and normotensive rats

1. To gain insight into the parameters which control vascular structure, we investigated the mechanisms whereby nifedipine, and other dihydropyridines, inhibit the growth of cultured fibroblasts isolated from the adventitia of the aorta of spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. 2. The effects of nifedipine on cell proliferation and on serum-induced DNA synthesis were determined by measuring the cell number and the incorporation of [3H]-thymidine, respectively. The mechanism of action of nifedipine was studied by adding the drug either to randomly growing cells or to quiescent, G0/G1 arrested and synchronized cells. The effects of varying the duration of drug treatment were also examined. 3. In randomly growing cultures nifedipine, like other dihydropyridines concentration-dependently inhibited cell proliferation; the rank order of effect (measured at a concentration of 10 microM) was nifedipine > nisoldipine > nitrendipine approximately nimodipine. 4. In G0/G1 arrested cell cultures, nifedipine concentration-dependently inhibited serum-induced [3H]-thymidine incorporation. In this respect it had similar effects in cell cultures from WKY and SHR. In both SHR and WKY cultures, nifedipine delayed the transition from G0/G1 to S phase, and inhibited serum-induced DNA synthesis possibly by acting on the early G1 phase. 5. In cell cultures from both SHR and WKY, serum-induced DNA synthesis was similarly (approximately 40%) inhibited after a 1 day treatment with 10 microM nifedipine. In contrast, after 5 days treatment with the drug, the inhibition of DNA synthesis was approximately 65% and approximately 10% in SHR and WKY cultures, respectively. The inhibitory effects of nifedipine against proliferation of fibroblasts were 25% and 60%, respectively,after 1 and 5 days of treatment, and were similar in cells derived from SHR and WKY. This indicates that 5 days treatment with nifedipine inhibited the proliferation of SHR and WKY fibro blasts by acting mostly on the early G1 phase and the M phase, respectively.6. Irrespective of the duration of treatment (1 or 5 days) with 10 microM nifedipine, the inhibition of DNA synthesis could be abolished and partially reduced by Bay K 8644 (1 microM) in WKY and SHR fibroblasts,respectively. In cell cultures from both SHR and WKY the inhibitory effects of a short term and of along term treatment with nifedipine against cell proliferation were reduced and unaffected, respectively by Bay K 8644.7. These results indicate that nifedipine inhibited cell proliferation and serum-induced DNA synthesis by altering the cell cycle through different mechanisms in SHR and WKY fibroblasts. They also suggest the existence in aortic fibroblasts of interactions between calcium channel blockers of the dihydropyridine series and the mitogenic signalling pathways of growth factors contained in serum.

New synthetic ligands for L-type voltage-gated calcium channels

The pharmacology of the L-type Ca2+ channel has been the subject of considerable basic and clinical investigation over the past two decades primarily because of the clinical activities of nifedipine, verapamil and diltiazem. However, it is quite clear that this Ca2+ channel is, in common with other pharmacologic receptors, a multiple drug receptor. There are probably as many as six or more discrete drug binding sites associated with this Ca2+ channel. Continued investigation of these sites may yield both new therapeutic agents, structural clues to ligands active at other classes of Ca2+ channel and structures active at other classes of ion channel.

Autogenous vein grafts in hypertensive (SHRSR) rats have increased smooth muscle cell hyperplasia in the graft neo-intima, compared with grafts in normotensive rats

This study examined the effects of raised intralumenal blood pressure on smooth muscle cell hyperplasia in the neo-intimal layer of experimental vein-to-artery grafts in rats. Autogenous vein grafts 1 mm in diameter and 4 mm long were inserted microsurgically into the left common iliac arteries of 24 genetically hypertensive (SHRSR) rats. At 2, 4, 6, 12, and 26 weeks after insertion, the grafts and contralateral unoperated iliac arteries were perfused at constant pressure and removed for histological and morphometric analyses. Neo-intimal thicknesses of the grafts and the intima-plus-media thicknesses of the contralateral arteries in the same rats were measured and compared statistically. From previous studies it is clear than in normotensive rats the neo-intima stabilises once it reaches the equivalent thickness of the contralateral arterial intima-plus-media, about 4 weeks after graft insertion. In the SHRSR rats the graft neo-intima developed at a similar rate (over the first 4 weeks) to that seen in previous studies in normotensive rats, but the development continued to occur over a longer period (6 weeks); therefore the neo-intima became significantly thicker. The graft neo-intima in SHRSR rats also became much thicker than the functionally equivalent intima-plus-media of the contralateral unoperated iliac arteries in the same rats. It was hypothesised that higher intralumenal blood pressure to SHRSR rats stimulates neo-intimal hyperplasia, resulting in the development of a thicker graft neo-intima, compared with that in normotensive rats.