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Abstracts

Life Extension Magazine November 2010
Abstracts

Metformin

Long-term metformin use is associated with decreased risk of breast cancer.

OBJECTIVE: To evaluate whether use of oral hypoglycemic agents is associated with an altered breast cancer risk in women. RESEARCH DESIGN AND METHODS: Using the U.K.-based General Practice Research Database, we conducted a nested case-control analysis among 22,621 female users of oral antidiabetes drugs with type 2 diabetes. We evaluated whether they had an altered risk of breast cancer in relation to use of various types of oral hypoglycemic agents. Case and control patients with a recorded diagnosis of type 2 diabetes were matched on age, calendar time, and general practice, and the multivariate conditional logistic regression analyses were further adjusted for use of oral antidiabetes drugs, insulin, estrogens, smoking BMI, diabetes duration, and HbA1c (A1C). RESULTS: We identified 305 case patients with a recorded incident diagnosis of breast cancer. The mean +/- SD age was 67.5 +/- 10.5 years at the time of the cancer diagnosis. Long-term use of >or=40 prescriptions (>5 years) of metformin, based on 17 exposed case patients and 120 exposed control patients, was associated with an adjusted odds ratio of 0.44 (95% CI 0.24-0.82) for developing breast cancer compared with no use of metformin. Neither short-term metformin use nor use of sulfonylureas or other antidiabetes drugs was associated with a materially altered risk for breast cancer. CONCLUSIONS: A decreased risk of breast cancer was observed in female patients with type 2 diabetes using metformin on a long-term basis.

Diabetes Care. 2010 Jun;33(6):1304-8

Metformin attenuates the stimulatory effect of a high-energy diet on in vivo LLC1 carcinoma growth.

We investigated the effects of metformin on the growth of lewis lung LLC1 carcinoma in C57BL/6J mice provided with either a control diet or a high-energy diet, previously reported to lead to weight gain and systemic insulin resistance with hyperinsulinemia. Forty-eight male mice were randomized into four groups: control diet, control diet+metformin, high-energy diet, or high-energy diet+metformin. Following 8 weeks on the experimental diets, selected groups received metformin in their drinking water. Three weeks following the start of metformin treatment, mice were injected with 0.5x10(6) LLC1 cells and tumor growth was measured for 17 days. By day 17, tumors of mice on the high-energy diet were nearly twice the volume of those of mice on the control diet. This effect of diet on tumor growth was significantly attenuated by metformin, but metformin had no effect on tumor growth of the mice on the control diet. Metformin attenuated the increased insulin receptor activation associated with the high-energy diet and also led to increased phosphorylation of AMP kinase, two actions that would be expected to decrease neoplastic proliferation. These experimental results are consistent with prior hypothesis-generating epidemiological studies that suggest that metformin may reduce cancer risk and improve cancer prognosis. Finally, these results contribute to the rationale for evaluation of the anti-neoplastic activity of metformin in hyperinsulinemic cancer patients.

Endocr Relat Cancer. 2008 Sep;15(3):833-9

Metformin: new understandings, new uses.

Metformin, a biguanide, has been available in the US for the treatment of type 2 diabetes mellitus for nearly 8 years. Over this period of time, it has become the most widely prescribed antihyperglycaemic agent. Its mechanism of action involves the suppression of endogenous glucose production, primarily by the liver. Whether the drug actually has an insulin sensitising effect in peripheral tissues, such as muscle and fat, remains somewhat controversial. Nonetheless, because insulin levels decline with metformin use, it has been termed an ‘insulin sensitiser’. Metformin has also been shown to have several beneficial effects on cardiovascular risk factors and it is the only oral antihyperglycaemic agent thus far associated with decreased macrovascular outcomes in patients with diabetes. Cardiovascular disease, impaired glucose tolerance and the polycystic ovary syndrome are now recognised as complications of the insulin resistance syndrome, and there is growing interest in the management of this extraordinarily common metabolic disorder. While diet and exercise remain the cornerstone of therapy for insulin resistance, pharmacological intervention is becoming an increasingly viable option. We review the role of metformin in the treatment of patients with type 2 diabetes and describe the additional benefits it provides over and above its effect on glucose levels alone. We also discuss its potential role for a variety of insulin resistant and prediabetic states, including impaired glucose tolerance, obesity, polycystic ovary syndrome and the metabolic abnormalities associated with HIV disease.

Drugs. 2003;63(18):1879-94

Decreased mortality associated with the use of metformin compared with sulfonylurea monotherapy in type 2 diabetes.

OBJECTIVE: The aim of this study was to examine the relationship between use of metformin and sulfonylurea and mortality in new users of these agents. RESEARCH DESIGN AND METHODS: Saskatchewan Health databases were used to examine population-based mortality rates for new users of oral antidiabetic agents. Individuals with prescriptions for sulfonylurea or metformin in 1991-1996 and no use in the year prior were identified as new users. Prescription records were prospectively followed for 1-9 years; subjects with any insulin use were excluded. Causes of death were identified based on ICD-9 codes in an electronic vital statistics database. Multivariate logistic regression and survival analyses were used to assess the differences in mortality between drug cohorts, after adjusting for potential confounding variables.RESULTS: The total study sample comprised 12,272 new users of oral antidiabetic agents; the average length of follow-up was 5.1 (SD 2.2) years. In subjects with at least 1 year of drug exposure and no insulin use, mortality rates were 750/3,033 (24.7%) for those receiving sulfonylurea monotherapy, 159/1,150 (13.8%) for those receiving metformin monotherapy, and 635/4,683 (13.6%) for those receiving combination therapy over an average 5.1 (SD 2.2) years of follow-up. The adjusted odds ratio (OR) for all-cause mortality for metformin monotherapy was 0.60 (95% CI 0.49-0.74) compared with sulfonylurea monotherapy. Sulfonylurea plus metformin combination therapy was also associated with reduced all-cause mortality (OR 0.66, 95% CI 0.58-0.75). Reduced cardiovascular-related mortality rates were also observed in metformin users compared with sulfonylurea monotherapy users. CONCLUSIONS: Metformin therapy, alone or in combination with sulfonylurea, was associated with reduced all-cause and cardiovascular mortality compared with sulfonylurea monotherapy among new users of these agents.

Diabetes Care. 2002 Dec;25(12):2244-8

Metformin inhibits aromatase expression in human breast adipose stromal cells via stimulation of AMP-activated protein kinase.

AMP-activated protein kinase (AMPK) is recognized as a master regulator of energy homeostasis. In concert with the AMPK-kinase LKB1, it has been shown to provide a molecular link between obesity and postmenopausal breast cancer via its actions to inhibit aromatase expression, hence estrogen production, within the breast. The anti-diabetic drug metformin is known to increase the activity of AMPK and was therefore hypothesized to inhibit aromatase expression in primary human breast adipose stromal cells. Results demonstrate that metformin significantly decreases the forskolin/phorbol ester (FSK/PMA)-induced expression of aromatase at concentrations of 10 and 50 muM. Consistent with the hypothesized actions of metformin to increase AMPK activity, treatment with 50 muM metformin results in a significant increase in phosphorylation of AMPK at Thr172. Interestingly, metformin also causes a significant increase in LKB1 protein expression and promoter activity, thereby providing for the first time an additional mechanism by which metformin activates AMPK. Furthermore, metformin inhibits the nuclear translocation of CRTC2, a CREB-coactivator known to increase aromatase expression which is also a direct downstream target of AMPK. Overall, these results suggest that metformin would reduce the local production of estrogens within the breast thereby providing a new key therapeutic tool that could be used in the neoadjuvant and adjuvant settings and conceivably also as a preventative measure in obese women.

Breast Cancer Res Treat. 2010 Sep;123(2):591-6

Is it the time for metformin to take place in adjuvant treatment of Her-2 positive breast cancer? Teaching new tricks to old dogs.

Breast cancer is the most common malignancy diagnosed among women. According to the new molecular subclassification, basal like and Her-2 positive breast cancers have the worst outcome and these are the ones in which chemotherapy is a must as a part of adjuvant treatment. New treatment options that could be used as an adjuvant maintenance treatment are still being investigated. Insulin hormone is one of the reasons of breast cancer recurrence and death in breast cancer survivors. Targeting insulin as a therapeutic modality in breast cancer could be an option in the adjuvant treatment of breast cancer. It seems that insulin may signal to activate a cascade of proliferative and anti-apoptotic events in the cancer cell. Metformin, an oral anti-diabetic known for 50 years, may also have direct effects on cancer cells. Metformin causes Her-2 suppression via the inhibition of mTOR in breast cancer cells. Thus, we believe that the time has arrived both to target insulin reduction and to alter Her-2 oncogene based molecular pathogenetic steps in breast cancer by using metformin as an adjuvant therapy in breast cancer patients.

Med Hypotheses. 2009 Oct;73(4):606-7

Metformin and cancer: Doses, mechanisms and the dandelion and hormetic phenomena.

In the early 1970s, Professor Vladimir Dilman originally developed the idea that antidiabetic biguanides may be promising as geroprotectors and anticancer drugs (“metabolic rehabilitation”). In the early 2000s, Anisimov’s experiments revealed that chronic treatment of female transgenic HER2-/neu mice with metformin significantly reduced the incidence and size of mammary adenocarcinomas and increased the mean latency of the tumors. Epidemiological studies have confirmed that metformin, but not other anti-diabetic drugs, significantly reduces cancer incidence and improves cancer patients’ survival in type 2 diabetics. At present, pioneer work by Dilman & Anisimov at the Petrov Institute of Oncology (St. Petersburg, Russia) is rapidly evolving due to ever-growing preclinical studies using human tumor-derived cultured cancer cells and animal models. We herein critically review how the antidiabetic drug metformin is getting reset to metabolically fight cancer. Our current perception is that metformin may constitute a novel “hybrid anti-cancer pill” physically combining both the long-lasting effects of antibodies-by persistently lowering levels of blood insulin and glucose-and the immediate potency of a cancer cell-targeting molecular agent-by suppressing the pivotal AMPK/mTOR/S6K1 axis and several protein kinases at once, including tyrosine kinase receptors such as HER1 and HER2-. In this scenario, we discuss the relevance of metformin doses in pre-clinical models regarding metformin’s mechanisms of action in clinical settings. We examine recent landmark studies demonstrating metformin’s ability to specifically target the cancer-initiating stem cells from which tumor cells develop, thereby preventing cancer relapse when used in combination with cytotoxic chemotherapy (dandelion hypothesis). We present the notion that, by acting as an efficient caloric restriction mimetic, metformin enhanced intrinsic capacity of mitotically competent cells to self-maintenance and repair (hormesis) might trigger counterintuitive detrimental effects. Ongoing chemopreventive, neoadjuvant and adjuvant trials should definitely establish whether metformin’s ability to kill the “dandelion root” beneath the “cancer soil” likely exceeds metformin-related dangers of hormesis.

Cell Cycle. 2010 Mar 21;9(6)

Improved clinical outcomes associated with metformin in patients with diabetes and heart failure.

OBJECTIVE: Metformin is considered contraindicated in patients with heart failure because of concerns over lactic acidosis, despite increasing evidence of potential benefit. The aim of this study was to evaluate the association between metformin and clinical outcomes in patients with heart failure and type 2 diabetes. RESEARCH DESIGN AND METHODS: Using the Saskatchewan Health databases, 12,272 new users of oral antidiabetic agents were identified between the years 1991 and 1996. Subjects with incident heart failure (n = 1,833) were identified through administrative records based on ICD-9 code 428 and grouped according to antidiabetic therapy: metformin monotherapy (n = 208), sulfonylurea monotherapy (n = 773), or combination therapy (n = 852). Multivariate Cox proportional hazards models were used to assess differences in all-cause mortality, all-cause hospitalization, and the combination (i.e., all-cause hospitalization or mortality). RESULTS: Average age of subjects was 72 years, 57% were male, and average follow-up was 2.5 +/- 2.0 (SD) years. Compared with sulfonylurea therapy, fewer deaths occurred in subjects receiving metformin: 404 (52%) for sulfonylurea monotherapy versus 69 (33%) for metformin monotherapy (hazard ratio [HR] 0.70 [95% CI 0.54-0.91]) and 263 (31%) for combination therapy (0.61 [0.52-0.72]). A reduction in deaths or hospitalizations was also observed: 658 (85%) for sulfonylurea monotherapy versus 160 (77%) for metformin monotherapy (0.83 [0.70-0.99]) and 681 (80%) for combination therapy (0.86 [0.77-0.96]). There was no difference in time to first hospitalization between study groups. CONCLUSIONS: Metformin, alone or in combination, in subjects with heart failure and type 2 diabetes was associated with lower morbidity and mortality compared with sulfonylurea monotherapy.

Diabetes Care. 2005 Oct;28(10):2345-51

Metformin attenuates ovarian cancer cell growth in an AMP- kinase dispensable manner.

ABSTRACT Metformin, the most widely used drug for type 2 diabetes activates AMP-activated protein kinase (AMPK), which regulates cellular energy metabolism. Here, we report that ovarian cell lines VOSE, A2780, CP70, C200, OV202, OVCAR3, SKOV3ip, PE01 and PE04 predominantly express -alpha1, -beta1, -gamma1 and -gamma2 isoforms of AMPK subunits. Our studies show that metformin treatment (1) significantly inhibited proliferation of diverse chemo-responsive and -resistant ovarian cancer cell lines (A2780, CP70, C200, OV202, OVCAR3, SKVO3ip, PE01 and PE04), (2) caused cell cycle arrest accompanied by decreased cyclin D1 and increased p21 protein expression, (3) activated AMPK in various ovarian cancer cell lines as evident from increased phosphorylation of AMPKalpha and its downstream substrate; ACC (Acetyl Co-carboxylase) and enhanced beta- oxidation of fatty acid, (4) attenuated mTOR-S6RP phosphorylation, inhibited protein translational and lipid biosynthetic pathways, thus implicating metformin as a growth inhibitor of ovarian cancer cells. We also show that metformin mediated effect on AMPK is dependent on LKB1(Liver kinase B1) as it failed to activate AMPK-ACC pathway and cell cycle arrest in LKB1 null mouse embryo fibroblasts (mefs). This observation was further supported by using siRNA approach to downregulate LKB1 in ovarian cancer cells. In contrast, metformin inhibited cell proliferation in both wild type and AMPKalpha1/2 null mefs as well as in AMPK silenced ovarian cancer cells. Collectively, these results provide evidence on the role of metformin as an anti-proliferative therapeutic that can act through both AMPK dependent as well as independent pathways.

J Cell Mol Med. 2009 Oct 29

New users of metformin are at low risk of incident cancer: a cohort study among people with type 2 diabetes.

OBJECTIVE: The antidiabetic properties of metformin are mediated through its ability to activate the AMP-activated protein kinase (AMPK). Activation of AMPK can suppress tumor formation and inhibit cell growth in addition to lowering blood glucose levels. We tested the hypothesis that metformin reduces the risk of cancer in people with type 2 diabetes. RESEARCH DESIGN AND METHODS: In an observational cohort study using record-linkage databases and based in Tayside, Scotland, U.K., we identified people with type 2 diabetes who were new users of metformin in 1994-2003. We also identified a set of diabetic comparators, individually matched to the metformin users by year of diabetes diagnosis, who had never used metformin. In a survival analysis we calculated hazard ratios for diagnosis of cancer, adjusted for baseline characteristics of the two groups using Cox regression. RESULTS: Cancer was diagnosed among 7.3% of 4,085 metformin users compared with 11.6% of 4,085 comparators, with median times to cancer of 3.5 and 2.6 years, respectively (P < 0.001). The unadjusted hazard ratio (95% CI) for cancer was 0.46 (0.40-0.53). After adjusting for sex, age, BMI, A1C, deprivation, smoking, and other drug use, there was still a significantly reduced risk of cancer associated with metformin: 0.63 (0.53-0.75). CONCLUSIONS: These results suggest that metformin use may be associated with a reduced risk of cancer. A randomized trial is needed to assess whether metformin is protective in a population at high risk for cancer.

Diabetes Care. 2009 Sep;32(9):1620-5

Metformin, independent of AMPK, inhibits mTORC1 in a rag GTPase-dependent manner.

Dysfunctional mTORC1 signaling is associated with a number of human pathologies owing to its central role in controlling cell growth, proliferation, and metabolism.

Regulation of mTORC1 is achieved by the integration of multiple inputs, including those of mitogens, nutrients, and energy. It is thought that agents that increase the cellular AMP/ATP ratio, such as the antidiabetic biguanides metformin and phenformin, inhibit mTORC1 through AMPK activation of TSC1/2-dependent or -independent mechanisms. Unexpectedly, we found that biguanides inhibit mTORC1 signaling, not only in the absence of TSC1/2 but also in the absence of AMPK. Consistent with these observations, in two distinct preclinical models of cancer and diabetes, metformin acts to suppress mTORC1 signaling in an AMPK-independent manner. We found that the ability of biguanides to inhibit mTORC1 activation and signaling is, instead, dependent on the Rag GTPases.

Cell Metab. 2010 May 5;11(5):390-401

Metformin Suppresses Colorectal Aberrant Crypt Foci in a Short-term Clinical Trial.

The biguanide metformin is widely used for treating diabetes mellitus. We previously showed the chemopreventive effect of metformin in two rodent models of colorectal carcinogenesis. However, besides epidemiologic studies, little is known about the effects of metformin on human colorectal carcinogenesis. The objective of this pilot study was to evaluate the chemopreventive effect of metformin on rectal aberrant crypt foci (ACF), which are an endoscopic surrogate marker of colorectal cancer. We prospectively randomized 26 nondiabetic patients with ACF to treatment with metformin (250 mg/d, n = 12) or no treatment (control, n = 14); 23 patients were evaluable for end point analyses (9 metformin and 14 control); the two groups were similar in ACF number and other baseline clinical characteristics. Magnifying colonoscopy determined the number of rectal ACF in each patient at baseline and after 1 month in a blinded fashion (as were all laboratory end point analyses). We also examined proliferative activity in colonic epithelium (via proliferating cell nuclear antigen labeling index) and apoptotic activity (via terminal deoxynucleotidyl transferase dUTP nick-end labeling). At 1 month, the metformin group had a significant decrease in the mean number of ACF per patient (8.78 +/- 6.45 before treatment versus 5.11 +/- 4.99 at 1 month, P = 0.007), whereas the mean ACF number did not change significantly in the control group (7.23 +/- 6.65 versus 7.56 +/- 6.75, P = 0.609). The proliferating cell nuclear antigen index was significantly decreased and the apoptotic cell index remained unaltered in normal rectal epithelium in metformin patients. This first reported trial of metformin for inhibiting colorectal carcinogenesis in humans provides preliminary evidence that metformin suppresses colonic epithelial proliferation and rectal ACF formation in humans, suggesting its promise for the chemoprevention of colorectal cancer.

Cancer Prev Res (Phila Pa). 2010 Sep;3(9):1077-83

Metformin prevents tobacco carcinogen-induced lung tumorigenesis.

Activation of the mammalian target of rapamycin (mTOR) pathway is an important and early event in tobacco carcinogen-induced lung tumorigenesis, and therapies that target mTOR could be effective in the prevention or treatment of lung cancer. The biguanide metformin, which is widely prescribed for the treatment of type II diabetes, might be a good candidate for lung cancer chemoprevention because it activates AMP-activated protein kinase (AMPK), which can inhibit the mTOR pathway. To test this, A/J mice were treated with oral metformin after exposure to the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Metformin reduced lung tumor burden by up to 53% at steady-state plasma concentrations that are achievable in humans. mTOR was inhibited in lung tumors but only modestly. To test whether intraperitoneal administration of metformin might improve mTOR inhibition, we injected mice and assessed biomarkers in liver and lung tissues. Plasma levels of metformin were significantly higher after injection than oral administration. In liver tissue, metformin activated AMPK and inhibited mTOR. In lung tissue, metformin did not activate AMPK but inhibited phosphorylation of insulin-like growth factor-I receptor/insulin receptor (IGF-1R/IR), Akt, extracellular signal-regulated kinase (ERK), and mTOR. This suggested that metformin indirectly inhibited mTOR in lung tissue by decreasing activation of insulin-like growth factor-I receptor/insulin receptor and Akt upstream of mTOR. Based on these data, we repeated the NNK-induced lung tumorigenesis study using intraperitoneal administration of metformin. Metformin decreased tumor burden by 72%, which correlated with decreased cellular proliferation and marked inhibition of mTOR in tumors. These studies show that metformin prevents tobacco carcinogen-induced lung tumorigenesis and support clinical testing of metformin as a chemopreventive agent.

Cancer Prev Res (Phila Pa). 2010 Sep;3(9):1066-76

Metformin extended release treatment of adolescent obesity: a 48-week randomized, double-blind, placebo-controlled trial with 48-week follow-up.

BACKGROUND: Metformin has been proffered as a therapy for adolescent obesity, although long-term controlled studies have not been reported. OBJECTIVE: To test the hypothesis that 48 weeks of daily metformin hydrochloride extended release (XR) therapy will reduce body mass index (BMI) in obese adolescents, as compared with placebo. DESIGN: Multicenter, randomized, double-blind, placebo-controlled clinical trial. SETTING: The 6 centers of the Glaser Pediatric Research Network from October 2003 to August 2007. PARTICIPANTS: Obese (BMI > or = 95th percentile) adolescents (aged 13-18 years) were randomly assigned to the intervention (n = 39) or placebo groups. Intervention Following a 1-month run-in period, subjects following a lifestyle intervention program were randomized 1:1 to 48 weeks’ treatment with metformin hydrochloride XR, 2,000 mg once daily, or an identical placebo. Subjects were monitored for an additional 48 weeks. Main Outcome Measure Change in BMI, adjusted for site, sex, race, ethnicity, and age and metformin vs placebo. RESULTS: After 48 weeks, mean (SE) adjusted BMI increased 0.2 (0.5) in the placebo group and decreased 0.9 (0.5) in the metformin XR group (P = .03). This difference persisted for 12 to 24 weeks after cessation of treatment. No significant effects of metformin on body composition, abdominal fat, or insulin indices were observed. CONCLUSION: Metformin XR caused a small but statistically significant decrease in BMI when added to a lifestyle intervention program.

Arch Pediatr Adolesc Med. 2010 Feb;164(2):116-23

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