Calcium channel blockers, apoptosis and cancer: is there a biologic relationship?

Metabolic syndrome and cancer risk

OBJECTIVE

The purpose of this population-based study is to explore for the first time the link between metabolic syndrome and cancer risk using information from the health information system of the Cancer Registry.

METHODS

Referring to all pharmaceutical prescriptions between 1 January 1999 and 31 December 2005, coded with the Anatomical Therapeutic Chemical classification, all subjects aged 40 and over resident in Milan, which were simultaneously prescribed with antihypertensive, hypolypemic and hypoglycaemic drugs, were considered affected by metabolic syndrome. New cancer cases among cohort subjects were identified trough the local Cancer Registry and standardised incidence ratios (and corresponding 95% exact confidence intervals) were computed.

RESULTS

Overall 16,677 subjects were identified corresponding to 45,828 person-years; among them 823 incidents cancers occurred. Significantly increased risks for pancreatic cancer in males--SIR 178 (114-266)--and colorectal cancer in females--SIR 133 (101-170)--were observed. Non-significantly increased risks were also observed in women for liver, gallbladder and biliary tract, breast and endometrial cancers.

CONCLUSIONS

Our study suggests that the risk for several cancers increases in subjects affected by metabolic syndrome. The pharmacological control of the syndrome seems to be inadequate for reducing cancer risk, even though both a high competitive mortality effect and short duration of follow up have to be considered.

Dihydropyridine calcium channel antagonists in the management of hypertension

Dihydropyridine calcium channel antagonists have been maligned in recent years because of concerns regarding their cardiovascular and overall safety profile. Specifically, it was widely publicised in the mid-1990s that these agents might increase the risk of myocardial infarction, gastrointestinal bleeding and cancer. Data linking these agents with increased cardiovascular risk were based on nonrandomised studies and implicated short-acting, immediate-release agents. These results were inappropriately extrapolated to longer-acting compounds, extended-release products, and to the non-dihydropyridine class. Fortunately, recent studies have vindicated the class from safety allegations. These studies are reviewed herein. Compared with both diuretics and contemporary agents, amlodipine decreases cardiovascular events to a similar or greater extent without evidence for increased coronary heart disease, gastrointestinal bleeding or cancer. Despite these data, initial concerns have had lasting repercussions, as the use of dihydropyridine calcium channel antagonists appears to lag behind what emerging data would support. Dihydropyridine calcium channel antagonists have several noteworthy attributes that merit consideration in the management of hypertension. The blood pressure response to this class of drugs is less contingent on patient factors such as age and race compared with other antihypertensive agents (e.g. ACE inhibitors). Dihydropyridine calcium channel antagonists may exert effects that protect against stroke that are independent of their blood pressure-lowering mechanism. Unlike diuretics and beta-adrenoceptor anatagonists (beta-blockers), dihydropyridine calcium channel antagonists are lipid neutral and do not disturb glucose homeostasis. Dihydropyridine calcium channel antagonists demonstrate a highly desirable profile when administered as part of combination therapy. Combinations of dihydropyridine calcium channel antagonists and ACE inhibitors or angiotensin receptor antagonists display additive efficacy and an enviable adverse-effect profile. Collectively, the cardiovascular benefit, metabolic neutrality and homogeneous blood pressure response illuminated in recent studies, and reviewed here, represent a reaffirmation of the benefit of long-acting dihydropyridine calcium channel antagonists and should serve to help reinforce the critical importance of these agents in the therapeutic armamentarium against cardiovascular disease.

Protective effects of a calcium channel blocker on apoptosis in thymus of neonatal STZ-diabetic rats

Streptozotocin (STZ) is known to induce insulin-dependent diabetes in experimental animals. In STZ-induced diabetes, atrophy of the thymus is caused by elevated intracellular calcium levels leading to apoptosis. Hyperglycemia is known to result in a decrease in numbers of T cells in the thymus and circulation. Intracellular calcium levels increase in diabetic animals after induction by STZ. Hyperglycemia inhibits Ca2+-ATPase and increases intracellular calcium levels. We have investigated apoptosis in thymus tissue of neonatal STZ (n-STZ)-diabetic rats and the effects of isradipine as a calcium channel blocker (CCB) on apoptosis. Five groups of newborn Wistar rats were used. On the second day after birth, 100 mg/kg STZ was given i.p. to the first two groups. The first group was n-STZ diabetic. To the second group, starting from the 12th week, 5 mg/kg/day isradipine (i.p) was given for 6 weeks. To the third group, the same dose of isradipine was given on the second day, followed by STZ treatment. The fourth group was non-diabetic and treated with 5 mg/kg/day isradipine for six weeks. The fifth group consisted of non-diabetic rats. To the sixth group, dexamethasone (5 mg/kg i.p.) was given to adult rats. For detection of apoptotic cells in paraffin-embedded thymus sections, the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) assay was used. The DNA ladder method was performed for analysis of DNA fragmentation. In the isradipine-treated non-diabetic group, typical apoptotic banding patterns were found, whereas thick bands between 123 and 246 bp length were found in the n-STZ- and n-STZ+isradipine-treated groups. More apoptotic cells were observed in the thymus of isradipine-treated, n-STZ-treated and n-STZ+isradipine-treated groups when compared with the non-diabetic control and isradipine+n-STZ-treated groups. In conclusion, we observed that long-term STZ diabetes results in apoptosis in the thymus. We also found that isradipine administered before STZ has protective effects against apoptosis, whereas isradipine alone induces apoptosis.

The role of existing and newer calcium channel blockers in the treatment of hypertension

Calcium channel blockers (CCBs), which include both dihydropyridines such as nifedipine and amlodipine and non-dihydropyridines (verapamil and diltiazem), are among the most widely prescribed agents for the management of essential hypertension. Several large outcome risk trials and comprehensive meta-analyses have found that CCBs reduce the cardiovascular morbidity and mortality associated with uncontrolled hypertension, including stroke. CCBs, however, appear less effective than angiotensin-converting enzyme inhibitors and diuretics for preventing heart failure and myocardial infarction. CCBs are among the agents listed as potential first-line therapy, either alone or in combination with other agents in hypertension management guidelines. Furthermore, CCBs are suitable for add-on therapy in combination with diuretics, angiotensin-converting enzyme inhibitors, and angiotensin-II receptor blockers. CCBs may be partially suitable for patients with comorbid Raynaud's syndrome, isolated systolic hypertension (dihydropyridine), or angina pectoris (non-dihydropyridine). The newer inherently long-acting dihydropyridine agents (e.g., lacidipine, lercanidipine), which are not currently available in the United States, appear to have comparable efficacy to older agents of the dihydropyridine class but may have an improved tolerability profile, especially with regard to peripheral edema.

Inverse association between prostate cancer and the use of calcium channel blockers

Calcium channel blockers block calcium signal-mediated apoptosis. It is hypothesized that the use of these drugs may be associated with the development of cancer. This study investigated the association between daily use of calcium channel blockers and prostate cancer in a community-based cohort of men who participated in a longitudinal study of lower urinary tract symptoms. Study subjects were men ages 40 to 79 years by January 1, 1990, and were randomly selected from Olmsted County in Minnesota. At baseline, participants underwent an interview to determine all medications taken on a daily basis, including calcium channel blockers and to elicit a family history of prostate cancer. During follow-up, all men with a histological diagnosis of prostate cancer were identified through patient self-report and by a review of the complete medical record. Over 12,668 person years of follow-up, 15 (6.8%) of 220 calcium channel blocker users and 120 (10.5%) of 1142 nonusers developed prostate cancer (P = 0.09; odds ratio, 0.62; 95% confidence interval, 0.36-1.10). With adjustment for age and family history of prostate cancer, the risk (odds ratio, 95% confidence interval) of prostate cancer was 0.55 (0.31-0.97) in calcium channel blocker users compared with nonusers. In analyses stratified by family history of prostate cancer, the risk of prostate cancer was 0.45 (0.23-0.88) in men without a family history and 2.64 (0.82-8.47) in men with a family history of prostate cancer (P = 0.006). These findings suggest an association between prostate cancer and daily use of calcium channel blockers that varies by family history of prostate cancer.

Neuropeptides bombesin and calcitonin inhibit apoptosis-related elemental changes in prostate carcinoma cell lines

BACKGROUND

Etoposide-induced apoptosis in prostate carcinoma cells is associated with changes in the elemental content of the cells. The authors previously reported that calcitonin and bombesin inhibited etoposide-induced apoptosis in these cells. In the current study, the authors investigated whether these neuropeptides block the etoposide-induced changes in elemental content.

METHODS

Cells from the PC-3 and Du 145 prostate carcinoma cell lines were grown either on solid substrates or on thin plastic films on titanium electron microscopy grids, and they were exposed to etoposide for 48 hours in the absence or presence of calcitonin and bombesin. After the exposure, the cells were frozen and freeze dried, and their elemental content was analyzed by energy-dispersive X-ray microanalysis in both in the scanning electron microscope and the scanning transmission electron microscope.

RESULTS

Etoposide treatment consistently induced an increase in the cellular Na concentration and a decrease in the cellular K concentration, resulting in a marked increase of the Na/K ratio and also an increase in the phosphorus:sulphur (P/S) ratio. Both bombesin and calcitonin inhibited the etoposide-induced changes in the cellular Na/K ratio, and calcitonin, but not bombesin, inhibited the changes in the P/S ratio. No significant elemental changes were found with bombesin or calcitonin alone.

CONCLUSIONS

The neuropeptides bombesin and calcitonin, which inhibited etoposide-induced apoptosis, also inhibited the etoposide-induced elemental changes in prostate carcinoma cells. This important fact strengthens the link between apoptosis and changes in the intracellular elemental content. This correlation provides an objective basis for the study of neuropeptide target points and may be helpful for alternative therapeutic protocols using neuropeptide inhibitors in the treatment of patients with advanced prostatic carcinoma.

NPC-14686, a novel anti-inflammatory agent, increased intracellular Ca(2+) concentrations in MDCK renal tubular cells

The effect of NPC-14686 (Fmoc-L-homophenylalanine), a novel anti-inflammatory agent on intracellular free Ca(2+) concentrations ([Ca(2+)](i)) in Madin Darby canine kidney (MDCK) renal tubular cells, was investigated, using fura-2 as a Ca(2+) dye. At concentrations between 10 and 200 microM NPC-14686 increased [Ca(2+)](i) concentration dependently. The [Ca(2+)](i) signal comprised an initial rise and a sustained phase. Ca(2+) removal inhibited the Ca(2+) signals by 90%. In Ca(2+)-free medium, pretreatment with 100 microM NPC-14686 nearly abolished the [Ca(2+)](i) increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) and abolished the [Ca(2+)](i) increase induced by 2 microM carbonylcyanide m-chlorophenylhydrazone (CCCP) (a mitochondrial uncoupler). NPC-14686 (100 microM) induced a slight [Ca(2+)](i) increase after pretreatment with 2 microM CCCP and 1 microM thapsigargin. Addition of 3 mM Ca(2+) elicited a [Ca(2+)](i) increase in cells pretreated with 100 microM NPC-14686 in Ca(2+)-free medium. Inhibition of inositol-1,4,5-trisphosphate (IP(3)) production by suppressing phospholipase C with 2 microM U73122 did not alter NPC-14686-induced Ca(2+) release. Trypan blue exclusion revealed that incubation with 10 or 200 microM NPC-14686 for 1-30 min decreased cell viability by 10-20% concentration dependently. Collectively, the results demonstrate that, in MDCK tubular cells, NPC-14686 induced Ca(2+) release followed by Ca(2+) entry, with the latter playing a major role. NPC-14686 appears to release intracellular Ca(2+) in an IP(3)-uncoupled manner. NPC-14686 may be of mild cytotoxicity.

Current status of safety and efficacy of calcium channel blockers in cardiovascular diseases: a critical analysis based on 100 studies

Recently, serious concerns have been expressed about the long-term safety of the calcium channel blockers (CCBs) as a group. Safety and efficacy are, however, ultimately linked to each other; therefore both must be evaluated especially in the therapy of angina and hypertension, the main clinical indications for CCBs. The structural, functional, and pharmacokinetic heterogeneity of CCBs means that the efficacy and dangers of one subclass, such as the short-acting dihydropyridines (DHPs), in one situation, such as unstable angina, do not necessarily apply in other clinical situations. One hundred studies are reviewed according to their methods of data collection: case series, case control, cohort, randomized controlled trials (RCTs), and meta-analyses. Large, well-designed RCTs and the meta-analyses based on these trials remain the gold standard. Observational studies, though potentially less reliable sources of information because of selection bias, may nevertheless produce hypotheses that must then be tested in RCTs. Regarding safety, both observational studies and RCTs suggest that adverse effects of CCBs may be linked to short-acting agents, specifically short-acting nifedipine. Two good studies favor the safety of verapamil, even in short-acting form. Incomplete but increasing overall evidence favors the safety of longer-acting DHPs. Heart failure remains a class contraindication to the use of all CCBs, with some exceptions. Regarding efficacy, there are positive results of RCTs with CCBs in 2 specific clinical situations, namely, verapamil in postinfarct protection in the absence of pre-existing heart failure, and 2 outcome studies on hypertension with longer acting DHPs. These results cannot automatically be applied to other clinical situations and to other CCBs. For example, there is no evidence for the safety or efficacy of DHPs used without beta blockers in postinfarct patients. In diabetic hypertensives, 2 relatively large RCTs show that the blood pressure can be reduced by DHP-based therapy in diabetics, with a reduction in hard end points. To achieve current blood pressure goals, combination therapy is almost always necessary, and in diabetics there is strong evidence that 1 essential component should be an angiotensin converting enzyme inhibitor. The future aim with CCBs must be to obtain a large database gathered from RCTs, which will give the same certainty about efficacy and safety that already holds for use of the diuretics in hypertension, beta-blockers in postmyocardial infarction patients, and the angiotensin converting enzyme inhibitors in heart failure.