Suppression by pravastatin, an inhibitor of p21ras isoprenylation, of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

In-vitro anticancer activity of Rauvolfia tetraphylla extract on mcf-7 breast cancer cell lines

The medicinal herb Rauwolfia tetraphylla is utilized by South Indian tribes to treat various medical ailments, although its cytotoxicity action has not been studied. As a result, the emphasis of the current investigation is on the anticancer activity of Rauvolfia tetraphylla extracts on MCF-7 breast cancer cell lines, as well as their effects on the levels of gene expression for BCl2 and TGF. The study found that the anticancer activity of R. tetraphylla extract demonstrated significant cytotoxic activity against MCF-7 breast cancer cell lines. Because of this, its anticancer effect may be caused by apoptosis, which is caused by DNA breaking and is helped by active phytochemicals like alkaloids, phenols, and flavonoids in the extracts. It also promotes apoptosis by altering Bcl-2 and TGF expression levels. The present study suggests using R. tetraphylla extract as an anticancer agent in traditional medicine.

Antitumor Effects and Mechanisms of Metabolic Syndrome Medications on Hepatocellular Carcinoma

Liver cancer has a high incidence and mortality rate worldwide, with hepatocellular carcinoma (HCC) being the most common histological type. With the decrease in the number of newly infected patients and the spread of antiviral therapy, hepatitis virus-negative chronic liver diseases including steatohepatitis are increasingly accounting for a large proportion of HCC, and an important clinical characteristic is the high prevalence of metabolic syndrome including hypertension, type 2 diabetes (T2D), dyslipidemia, and obesity. Since patients with steatohepatitis are less likely to undergo surveillance for early detection of HCC, they may be diagnosed at an advanced stage and have worse prognosis. Therefore, treatment strategies for patients with HCC caused by steatohepatitis, especially in advanced stages, become increasingly important. Further, hypertension, T2D, and dyslipidemia may occur as side effects during systemic treatment, and there will be increasing opportunities to prescribe metabolic syndrome medications, not only for originally comorbid diseases, but also for adverse events during HCC treatment. Interestingly, epidemiological studies have shown that patients taking some metabolic syndrome medications are less likely to develop various types of cancers, including HCC. Basic studies have also shown that these drugs have direct antitumor effects on HCC. In particular, angiotensin II receptor blockers (a drug group for treating hypertension), biguanides (a drug group for treating T2D), and statins (a drug group for treating dyslipidemia) have shown to elucidate antitumor effects against HCC. In this review, we focus on the antitumor effects of metabolic syndrome medications on HCC and their mechanisms based on recent literature. New therapeutic agents are also increasingly being reported. Analysis of the antitumor effects of metabolic syndrome medications on HCC and their mechanisms will be doubly beneficial for HCC patients with metabolic syndrome, and the use of these medications may be a potential strategy against HCC.

Hepatocellular Carcinoma and Statins

HMG-CoA reductase inhibitors (known as statins) are commonly prescribed worldwide for the management of coronary heart disease and the underlying dyslipidemia. This class of drugs has been shown to infer a significant decrease in the risk of cardiovascular morbidity and mortality. Only recently though have the beneficial effects of statins in other diseases such as non-alcoholic steatohepatitis been highlighted. Importantly, also, multiple studies have revealed that statin use was associated with lower cancer-associated mortality across multiple types of cancers. This work aims to review those studies with a particular focus on liver cancer. We also provide a review of the proposed mechanisms of action describing how statins can induce chemo-preventive and antitumor effects.

Statin Use Decreases the Incidence of Hepatocellular Carcinoma: An Updated Meta-Analysis

Statins can decrease hepatocellular carcinoma (HCC) occurrence, but the magnitude and the predictors of these effects remain unclear. This meta-analysis provides a pooled estimate of the impact of statin use on HCC occurrence. Pooled effects were calculated using a random-effects model by means of the DerSimonian and Laird test. Primary endpoint was the time-dependent correlation between statin use and HCC incidence expressed as hazard ratio (HR), both crude and adjusted. The crude and adjusted odds ratios (OR) for HCC occurrence between statin users and non-users were analyzed. Twenty-five studies with 1,925,964 patients were included. Crude OR for HCC incidence was 0.59 (95% CI: 0.47-0.74), confirmed in adjusted analysis (OR: 0.74, 95% CI: 0.70-0.78). Adjusted HR was 0.73 (95% CI: 0.69-0.76). This effect was more pronounced in HBV patients (HR: 0.46, 95% CI: 0.36-0.60) and with a cumulative daily dose beyond 365 (HR: 0.27, 95% CI: 0.11-0.67). Lipophilic statins were associated with reduced HCC incidence (HR: 0.49, 95% CI: 0.39-0.62). Atorvastatin determined the greater magnitude of effect (HR: 0.43, 95% CI: 0.28-0.65). This meta-analysis demonstrates the beneficial chemopreventive effect of statins against HCC occurrence. This effect is dose-dependent and more pronounced with lipophilic statins.

Combination Therapy of Metformin and Statin May Decrease Hepatocellular Carcinoma Among Diabetic Patients in Asia

Previous studies have shown that metformin or statins may decrease hepatocellular carcinoma (HCC) in diabetic patients. Accordingly, this article evaluates whether combination therapy may further reduce HCC. Newly diagnosed type 2 diabetes mellitus (DM) patients, excluding those with history of malignancy prior to the date of DM diagnosis, were recruited to a DM cohort. DM patients developed HCC as the cancer cohort and the date for HCC diagnosis as index date. Non-cancer cohort was frequency matched with 4:1 according to age, sex, DM-year, and index date as case group from DM cohort. Patients who were treated with statins showed a 63% decreased risk of HCC (odds ratio [OR] = 0.37; 95% confidence interval [CI] = 0.27-0.49). Patients who consumed simvastatin, atorvastatin, or rosuvastatin significantly decreased risk for HCC (OR = 0.32, 0.31, and 0.22; 95% CI = 0.18-0.58, 0.19-0.52, and 0.08-0.61, respectively). Metformin combinations with simvastatin, atorvastatin, or rosuvastatin may decrease HCC (OR = 0.30, 0.30, and 0.24; 95% CI = 0.15-0.59, 0.16-0.54, and 0.08-0.70, respectively). The comorbidities for HCC were decreased by consuming simvastatin and atorvastatin (OR = 0.31 and 0.29; 95% CI = 0.14-0.67 and 0.15-0.57, respectively). Only combination therapy of metformin and simvastatin may significantly decreased HCC comorbidities (OR = 0.26; 95% CI = 0.11-0.60) in our study. In Asia, not all metformin combinations with statins may reduce the incidence of HCC and not all of this kind of combination therapy may decrease the HCC comorbidities.

Combination of Pitavastatin and melatonin shows partial antineoplastic effects in a rat breast carcinoma model

Our previous results indicated significant tumor-suppressive effects of different statins in rat mammary carcinogenesis. The purpose of this experiment was to examine the chemopreventive effects of Pitavastatin alone and in combination with the pineal hormone melatonin in the model of N-methyl-N-nitrosourea-induced mammary carcinogenesis in female Sprague-Dawley rats. Pitavastatin was administered dietary (10mg/kg) and melatonin in an aqueous solution (20μg/ml). Chemoprevention began 7 days prior to carcinogen administration and subsequently continued for 15 weeks until autopsy. At autopsy, mammary tumors were removed and prepared for histopathological and immunohistochemical analysis. Compared to controls, Pitavastatin alone reduced average tumor volume by 58% and lengthened latency by 8 days; on the other hand, the drug increased tumor frequency by 23%. Combined administration of Pitavastatin with melatonin decreased tumor frequency by 23%, tumor volume by 44% and lengthened tumor latency by 5.5 days compared to control animals. The analysis of carcinoma cells showed significant increase in caspase-3 expression in both treated groups and a tendency of increased caspase-7 expression after Pitavastatin treatment alone. Significant expression decrease of Ki67 was found in carcinoma cells from both treated groups. Compared to control carcinoma cells, Pitavastatin alone increased VEGF expression by 41%, however melatonin totally reversed its undesirable effect. Pitavastatin combined with melatonin significantly increased femur compact bone thickness in animals. Pitavastatin alone decreased plasma triglycerides and total cholesterol levels, however it significantly increased levels of glucose. In summary, our results show a partial antineoplastic effect of Pitavastatin combined with melatonin in the rat mammary gland carcinoma model.

Melatonin potentiates the anti-tumour effect of pravastatin in rat mammary gland carcinoma model

Previous studies in the field of cancer research have suggested a possible role for statins in the reduction of risk in certain malignancies. The purpose of these studies was to examine the chemopreventive effects of pravastatin alone and in combination with pineal hormone melatonin in the N-methyl-N-nitrosourea-induced mammary carcinogenesis model. Pravastatin was given orally (1 00 mg/kg) and melatonin was added to the water (20 μg/ml). Chemoprevention began seven days prior to carcinogen administration and subsequently continued for 15 weeks until autopsy. At autopsy, mammary tumours were removed and prepared for histopathological and immunohistochemical analysis. Parameters of experimental carcinogenesis, mechanism of action (biomarkers of apoptosis, angiogenesis and proliferation) and side effects after long-term treatment in animals were assessed. Pravastatin alone suppressed tumour frequency by 20.5% and average tumour volume by 15% compared with controls. Combined administration of the drugs decreased tumour frequency by 69% and lengthened tumour latency by nine days compared with control animals. The ration between high and low grade carcinomas was apparently reduced in both treated groups. The analysis of carcinoma cells showed significant expression increase in caspase-3 and caspase-7 after pravastatin treatment; however, combined treatment even more pronounced increase in the expression of both caspases. Regarding VEGFR-2 expression, a small effect in carcinomas of both treated groups was found. In plasma metabolism evaluation, pravastatin alone significantly decreased levels of glucose and triacylglycerols. Our results suggest a mild anti-neoplastic effect of pravastatin in this rat mammary gland carcinoma model. Statins co-administered with other suitable drug (e.g. melatonin) should be further evaluated for tumour-preventive properties.

Statins in oncological research: from experimental studies to clinical practice

Statins, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors are commonly used drugs in the treatment of dyslipidemias, primarily raised cholesterol. Recently, many epidemiological and preclinical studies pointed to anti-tumor properties of statins, including anti-proliferative activities, apoptosis, decreased angiogenesis and metastasis. These processes play an important role in carcinogenesis and, therefore, the role of statins in cancer disease is being seriously discussed among oncologists. Anti-neoplastic properties of statins combined with an acceptable toxicity profile in the majority of individuals support their further development as anti-tumor drugs. The mechanism of action, current preclinical studies and clinical efficacy of statins are reviewed in this paper. Moreover, promising results have been reported regarding the statins' efficacy in some cancer types, especially in esophageal and colorectal cancers, and hepatocellular carcinoma. Statins' hepatotoxicity has traditionally represented an obstacle to the prescription of this class of drugs and this issue is also discussed in this review.

Combination of 13-Cis retinoic acid and lovastatin: marked antitumor potential in vivo in a pheochromocytoma allograft model in female athymic nude mice

Currently, there are no reliably effective therapeutic options for metastatic pheochromocytoma (PCC) and paraganglioma. Moreover, there are no therapies that may prevent the onset or progression of tumors in patients with succinate dehydrogenase type B mutations, which are associated with very aggressive tumors. Therefore, we tested the approved and well-tolerated drugs lovastatin and 13-cis-retinoic acid (13cRA) in vitro in an aggressive PCC mouse cell line, mouse tumor tissue-derived (MTT) cells, and in vivo in a PCC allograft nude mouse model, in therapeutically relevant doses. Treatment was started 24 hours before sc tumor cell injection and continued for 30 more days. Tumor sizes were measured from outside by caliper and sizes of viable tumor mass by bioluminescence imaging. Lovastatin showed antiproliferative effects in vitro and led to significantly smaller tumor sizes in vivo compared with vehicle treatment. 13cRA promoted tumor cell growth in vitro and led to significantly larger viable tumor mass and significantly faster increase of viable tumor mass in vivo over time compared with vehicle, lovastatin, and combination treatment. However, when combined with lovastatin, 13cRA enhanced the antiproliferative effect of lovastatin in vivo. The combination-treated mice showed slowest tumor growth of all groups with significantly slower tumor growth compared with the vehicle-treated mice and significantly smaller tumor sizes. Moreover, the combination-treated group displayed the smallest size of viable tumor mass and the slowest increase in viable tumor mass over time of all groups, with a significant difference compared with the vehicle- and 13cRA-treated group. The combination-treated tumors showed highest extent of necrosis, lowest median microvessel density and highest expression of α-smooth muscle actin. The combination of high microvessel density and low α-smooth muscle actin is a predictor of poor prognosis in other tumor entities. Therefore, this drug combination may be a well-tolerated novel therapeutic or preventive option for malignant PCC.

Statins are associated with a reduced risk of hepatocellular cancer: a systematic review and meta-analysis

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality worldwide. Several studies have shown that statins could have chemopreventive effects on HCC. We performed a systematic review and meta-analysis of studies that evaluated the effects of statins on the risk of HCC.

METHODS

We conducted a systematic search of MEDLINE, Embase, and Web of Science through May 2012 and manually reviewed the literature. Studies were included if they evaluated and clearly defined exposure to statins, reported the incidence of HCC, and reported relative risks or odds ratios (ORs) or provided data for their estimation. Ten studies reporting 4298 cases of HCC in 1,459,417 patients were analyzed. Summary OR estimates with 95% confidence intervals (CIs) were calculated using the random effects model. Statistical heterogeneity was assessed with the Cochran's Q statistic and I(2) statistic.

RESULTS

Statin users were less likely to develop HCC than statin nonusers (adjusted OR, 0.63; 95% CI, 0.52-0.76), although the results were heterogeneous (P = .01, I(2) = 59%). This heterogeneity could be accounted for by study location (Asian population [n = 4]: adjusted OR, 0.52; 95% CI, 0.42-0.64; Western population [n = 6]: adjusted OR, 0.67; 95% CI, 0.53-0.85) and design (observational studies [n = 7]: adjusted OR, 0.60; 95% CI, 0.49-0.73; clinical trials [n = 3]: adjusted OR, 0.95; 95% CI, 0.62-1.45).

CONCLUSIONS

Based on meta-analysis, statin use is associated with a reduced risk of HCC, most strongly in Asian but also in Western populations. Randomized clinical trials in populations at high risk for HCC (especially in Asian populations with hepatitis B) are warranted.

Pravastatin inhibits cell proliferation and increased MAT1A expression in hepatocarcinoma cells and in vivo models

BACKGROUND

Statins may have therapeutic effects on hepatocarcinoma (HCC). This type of disorder is the most common malignant primary tumour in the liver. Our objective was to determine whether pravastatin had a therapeutic effect in vitro and in vivo models.

METHOD

We design in vitro and in vivo model. In vitro we used PLC and determine cell proliferation. In vivo, we used and animal model to determined, PCNA and MAT1A expression and transaminases levels.

RESULTS

We found that pravastatin decreases cell proliferation in vitro (cell proliferation in pravastatin group was 82%, in sorafenib group 51% and in combined group 40%) and in vivo (in pravastatin group 80%, in sorafenib group 76.4% and in combined group 72.72%). The MAT1A levels, was significantly higher in Pravastatin group (D 62%, P 94%, S 71%, P + S 91%). The transaminases levels, decreased significantly in Pravastatin group (GOT and GPT levels D 619.5 U/L; 271 U/L) (P 117.5 U/L; 43.5 U/L) (S 147 U/L; 59 U/L) (P + S 142 U/L; 59 U/L).

CONCLUSION

The combination of pravastatin + sorafenib were more effective than Sorafenib alone.

Pharmacological actions of statins: a critical appraisal in the management of cancer

Statins, among the most commonly prescribed drugs worldwide, are cholesterol-lowering agents used to manage and prevent cardiovascular and coronary heart diseases. Recently, a multifaceted action in different physiological and pathological conditions has been also proposed for statins, beyond anti-inflammation and neuroprotection. Statins have been shown to act through cholesterol-dependent and -independent mechanisms and are able to affect several tissue functions and modulate specific signal transduction pathways that could account for statin pleiotropic effects. Typically, statins are prescribed in middle-aged or elderly patients in a therapeutic regimen covering a long life span during which metabolic processes, aging, and concomitant novel diseases, including cancer, could occur. In this context, safety, toxicity, interaction with other drugs, and the state of health have to be taken into account in subjects treated with statins. Some evidence has shown a dichotomous effect of statins with either cancer-inhibiting or -promoting effects. To date, clinical trials failed to demonstrate a reduced cancer occurrence in statin users and no sufficient data are available to define the long-term effects of statin use over a period of 10 years. Moreover, results from clinical trials performed to evaluate the therapeutic efficacy of statins in cancer did not suggest statin use as chemotherapeutic or adjuvant agents. Here, we reviewed the pharmacology of the statins, providing a comprehensive update of the current knowledge of their effects on tissues, biological processes, and pathological conditions, and we dissected the disappointing evidence on the possible future use of statin-based drugs in cancer therapy.

Rho GTPases in hepatocellular carcinoma

Rho GTPases are major regulators of signal transduction pathways and play key roles in processes including actin dynamics, cell cycle progression, cell survival and gene expression, whose deregulation may lead to tumorigenesis. A growing number of in vitro and in vivo studies using tumor-derived cell lines, primary tumors and animal cancer models strongly suggest that altered Rho GTPase signaling plays an important role in the initiation as well as in the progression of hepatocellular carcinoma (HCC), one of the deadliest human cancers in the world. These alterations can occur at the level of the GTPases themselves or of one of their regulators or effectors. The participation into the tumorigenic process can occur either through the over-expression of one of these components which presents an oncogenic activity as illustrated with RhoA and C or through the attenuation of the expression of a component presenting tumor suppressor activity as for Cdc42 or the RhoGAP, DLC-1. Consequently, these observations reflect the heterogeneity and the complexity of liver carcinogenesis. Recently, pharmacological approaches targeting Rho GTPase signaling have been used in HCC-derived models with relative success but remain to be validated in more physiologically relevant systems. Therefore, therapeutic approaches targeting Rho GTPase signaling may provide a novel alternative for anti-HCC therapy.

Pravastatin reduces lung metastasis of rat hepatocellular carcinoma via a coordinated decrease of MMP expression and activity

BACKGROUND/AIMS

Statins have beneficial effects in early pre-clinical models of hepatocellular carcinoma (HCC). Our aim was to test the efficacy of pravastatin on the progression of established HCC in rat, and to study its mechanisms.

METHODS

HCC was induced with diethylnitrosamine and N-nitrosomorpholine. After 14 weeks, all rats developed HCC and then received pravastatin or its solvent for 10 weeks (10 rats/group).

RESULTS

Liver tumor mass was lower in pravastatin group (PG) than control group (CG), as estimated from the number of liver tumors (p<0.004) and the liver weight/body weight ratio (p<0.04). Every CG rat surviving at 24 weeks (4/4) had lung metastasis, against only 5/8 in PG. Moreover, the percentage of lung surface occupied by metastasis was 10-fold smaller in PG than CG (p<0.016). Pravastatin decreased liver matrix metalloproteinase (MMP)-9 activity and mostly suppressed MMP-2 activation (p<0.004), likely because it decreased expression of MMP-14 and tissue inhibitor of matrix metalloproteinases-2 (p<0.01), required for MMP-2 activation.

CONCLUSIONS

Pravastatin reduces progression and limits metastatic diffusion of established HCC. This could be linked to the decreased MMP activity. These results, obtained in a very aggressive HCC model, further suggest the potential benefit of statins in human HCC.

The role of statins in cancer therapy

Administration of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, to ambulatory patients is associated with a lower incidence of long-term adverse cardiovascular events, including death, myocardial infarction, stroke, atrial fibrillation, and renal dysfunction. However, increasing clinical evidence suggests that statins, independent of their effects on serum cholesterol levels, may also play a potential role in the prevention and treatment of cancer. Specifically, statins have been shown to exert several beneficial antineoplastic properties, including decreased tumor growth, angiogenesis, and metastasis. The feasibility and efficacy of statins for the prevention and treatment of cancer is reviewed.

Inhibiting Ras signaling in the therapy of breast cancer

Ras is a small guanosine triphosphate-binding protein that plays an important role in signal transduction pathways that influence cellular proliferation, apoptosis, cytoskeletal organization, and other important biological processes. Prenylation of Ras proteins by the enzyme farnesyltransferase renders the protein hydrophobic, causing localization to the inner surface of the cell membrane, where it exerts its biological effects. Ras mutations that result in constitutive activation of the Ras pathway are common in certain human cancers, and transfection of cell lines with mutant Ras renders them tumorigenic. Farnesyltransferase inhibitors (FTIs) were initially developed to inhibit growth of cancers harboring Ras mutations, but preclinical data suggests that they also have antiproliferative effects in cell lines with wild-type Ras. Preclinical data suggest that FTIs have antiproliferative and antitumor effects in breast cancer cell lines, but the precise target(s) remain to be defined. One phase II trial has demonstrated that one orally administered FTI has significant antitumor activity in metastatic breast cancer. In addition, preclinical evidence suggests that FTIs may augment the activity of cytotoxic agents and hormonal therapy. Clinical trials are currently underway evaluating whether these agents have a useful role in the management of advanced breast cancer.

Inhibition by d-limonene of experimental hepatocarcinogenesis in Sprague-Dawley rats does not involve p21(ras) plasma membrane association

The effects of d-limonene on hepatocarcinogenesis induced by N-nitrosomorpholine (NNM) and on membrane-associated p21(ras) and labeling and apoptotic indices of the liver were investigated in male Sprague-Dawley rats. Rats were given drinking water containing NNM for 8 weeks, and from the beginning of experimental week 9, they received chow pellets containing 1% or 2% limonene. The preneoplastic and neoplastic liver lesions (cellular alteration foci, neoplastic nodules and hepatocellular carcinomas), and hepatic foci staining positive for glutathione-S-transferase, placental type (GST-P) were examined microscopically and histochemically. At week 16, quantitative histologic analysis showed that oral administration of 1% or 2% limonene resulted in significant reductions in the number and mean area of GST-P-positive hepatic foci and the number of cellular alteration foci, neoplastic nodules and hepatocellular carcinomas. Limonene, at both doses, also caused significant decreases in the labeling indices and significant increases in the apoptotic indices of cellular alteration foci, neoplastic nodules, hepatocellular carcinomas and adjacent liver. However, limonene, at both doses, had no significant influence on the production of membrane-associated p21(ras) in the visible liver white nodules. These findings indicate that limonene inhibits hepatocarcinogenesis and suggest that this effect may be clearly related to its effect in inhibiting cell proliferation and in enhancing apoptosis, but not through ras oncoprotein plasma membrane association.

ras p21 Isoprenylation inhibition induces flat colon tumors in Wistar rats

PURPOSE

The effect of pravastatin, an inhibitor of ras p21 isoprenylation, on the gross type of colon tumors induced by azoxymethane was investigated in Wistar rats.

METHODS

Rats received ten weekly subcutaneous injections of 7.4 mg/kg body weight of azoxymethane and intraperitoneal injections of 10 or 20 mg/kg body weight of pravastatin every other day until the end of the experiment at Week 45.

RESULTS

Administration of pravastatin at both dosages had no significant effect on the incidence of colon tumors but significantly increased the incidence of rats with adenomas only. In contrast to the elevated adenomas in control rats, flat adenomas were significantly more prevalent in rats given pravastatin. Pravastatin at both doses significantly decreased the labeling index, but not the apoptotic index, of elevated adenomas, whereas it significantly decreased the labeling index but increased the apoptotic index of flat adenomas. Administration of pravastatin at both dosages also significantly decreased the amounts of membrane-associated ras p21 in colon tumors.

CONCLUSIONS

These findings suggest that the ras oncogene may be closely related to the development of adenocarcinomas from adenomas and the development of elevated or polypoid tumors of the colon.

Low-density lipoprotein-independent effects of statins

Statins have pleiotropic properties that complement their cholesterol-lowering effects. These properties may partly account for their established benefit in the prevention of coronary artery disease beyond the reduction of LDL-cholesterol levels. The most widely recognized properties are reviewed here. They include: (i) nitric oxide-mediated improvement of endothelial dysfunction and upregulation of endothelin-1 expression; (ii) antioxidant effects; (iii) anti-inflammatory properties; (iv) inhibition of cell proliferation with anticarcinogenic actions in animals; (v) stabilization of atherosclerotic plaques; (vi) anticoagulant effects; and (vii) inhibition of graft rejection after heart and kidney transplantation. As advances are made in our knowledge, new properties are steadily being uncovered. Pleiotropic effects are currently being given consideration when instituting combination therapy for patients at high cardiovascular risk. Some pleiotropic effects are negative, and may account for occasional untoward drug interactions. For many of these new properties, the clinical relevance has not been established. The challenge for the future will be to design and carry out appropriate clinical trials to establish their relative importance in the prevention of coronary artery disease.

Inhibition by D-limonene of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effect of prolonged oral administration of D-limonene on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the labeling and apoptotic indices of gastric cancers were investigated in Wistar rats. After 25 weeks of the carcinogen treatment, rats were given chow pellets containing 1% or 2% limonene. In week 52, long-term oral administration of 2%, but not 1%, limonene significantly decreased the incidence of gastric cancers. Limonene also significantly decreased the labeling index and significantly increased the apoptotic index of gastric cancers. No K-ras mutations were detected in gastric cancers induced by MNNG in either group. These findings indicate that limonene inhibits the development of gastric cancers through increased apoptosis and decreased DNA synthesis of gastric cancers, but not through ras oncoprotein plasma membrane association.