Diabetes, cancer, and metformin: connections of metabolism and cell proliferation.
ABSTRACT Diabetes is associated with an increased risk of developing and dying from cancer. This increased risk may be due to hyperglycemia, hyperinsulinemia, and insulin resistance or other factors. Metformin has recently gained much attention as it appears to reduce cancer incidence and improve prognosis of patients with diabetes. In vitro data and animal studies support these findings from human epidemiological studies. Metformin has multiple potential mechanisms by which it inhibits cancer development and growth. For example, metaformin inhibits hepatic gluconeogenesis, thus decreasing circulating glucose levels, and it increases insulin sensitivity, thus reducing circulating insulin levels. Intracellularly, metformin activates AMPK, which decreases protein synthesis and cell proliferation. Metaformin also reduces aromatase activity in the stromal cells of the mammary gland. Finally, metformin may diminish the recurrence and aggressiveness of tumors by reducing the stem cell population and inhibiting epithelial to mesenchymal transition. Here, we discuss the metabolic abnormalities that occur in tumor development and some of the mechanisms through which metformin may alter these pathways and reduce tumor growth.
SourceAvailable from: Alice Ceacareanu
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ABSTRACT: Hyperglycemia has been associated with poor outcomes of patients with various diseases. There were several studies published to assess the association between hyperglycemia and prognosis of patients with brain tumors, but no consistent conclusion was available. We therefore performed a meta-analysis of available studies to evaluate the prognostic role of hyperglycemia in brain tumors. Several common databases were searched for eligible studies on the association between hyperglycemia and survival of patients with brain tumors. Two investigators used a set of predefined inclusion criteria to assess eligible studies independently. The pooled hazard ratios (HRs) with 95 % confidence intervals (95 % CIs) were used to assess the prognostic role of hyperglycemia. Finally, seven studies with a total of 2168 patients with brain tumors were included into the meta-analysis. Meta-analysis of total seven studies showed that hyperglycemia was significantly associated with shorter overall survival of brain tumors (HR = 2.04, 95 % CI 1.51-2.76, P < 0.001). Meta-analysis of studies focusing on hyperglycemia showed that hyperglycemia was still significantly associated with shorter overall survival of brain tumors (HR = 1.82, 95 % CI 1.29-2.59, P = 0.001). Meta-analysis of three studies on diabetes showed that diabetes was significantly associated with shorter overall survival of brain tumors (HR = 2.09, 95 % CI 1.22-3.57, P = 0.007). Meta-regression analysis showed that there was no obvious difference in the roles of between hyperglycemia caused by glucocorticoids and hyperglycemia from diabetes (P = 0.25). Thus, hyperglycemia has an obvious prognostic significance in patients with brain tumors, and hyperglycemia is significantly associated with shorter overall survival of brain tumors.Molecular Neurobiology 02/2015; DOI:10.1007/s12035-015-9115-4 · 5.29 Impact Factor
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ABSTRACT: Epidemiologic studies have shown that diabetics receiving the biguanide metformin, as compared with sulfonylureas or insulin, have a lower incidence of breast cancer. Metformin increases levels of activated AMPK (AMP-activated protein kinase) and decreases circulating IGF-1; encouraging its potential use in both cancer prevention and therapeutic settings. In anticipation of clinical trials in nondiabetic women, the efficacy of metformin in nondiabetic rat and mouse mammary cancer models was evaluated. Metformin was administered by gavage or in the diet, at a human equivalent dose, in standard mammary cancer models: (i) methylnitrosourea (MNU)-induced estrogen receptor-positive (ER(+)) mammary cancers in rats, and (ii) MMTV-Neu/p53KO ER(-) (estrogen receptor-negative) mammary cancers in mice. In the MNU rat model, metformin dosing (150 or 50 mg/kg BW/d, by gavage) was ineffective in decreasing mammary cancer multiplicity, latency, or weight. Pharmacokinetic studies of metformin (150 mg/kg BW/d, by gavage) yielded plasma levels (Cmax and AUC) higher than humans taking 1.5 g/d. In rats bearing small palpable mammary cancers, short-term metformin (150 mg/kg BW/d) treatment increased levels of phospho-AMPK and phospho-p53 (Ser20), but failed to reduce Ki67 labeling or expression of proliferation-related genes. In the mouse model, dietary metformin (1,500 mg/kg diet) did not alter final cancer incidence, multiplicity, or weight. Metformin did not prevent mammary carcinogenesis in two mammary cancer models, raising questions about metformin efficacy in breast cancer in nondiabetic populations. Cancer Prev Res; 1-9. ©2014 AACR. ©2014 American Association for Cancer Research.