Protective effect of metformin in CD1 mice placed on a high carbohydrate-high fat diet

Developmental metformin exposure does not rescue physiological impairments derived from early exposure to altered maternal metabolic state in offspring mice

OBJECTIVE

The incidence of gestational diabetes mellitus (GDM) and metabolic disorders during pregnancy are increasing globally. This has resulted in increased use of therapeutic interventions such as metformin to aid in glycemic control during pregnancy. Even though metformin can cross the placental barrier, its impact on offspring brain development remains poorly understood. As metformin promotes AMPK signaling, which plays a key role in axonal growth during development, we hypothesized that it may have an impact on hypothalamic signaling and the formation of neuronal projections in the hypothalamus, the key regulator of energy homeostasis. We further hypothesized that this is dependent on the metabolic and nutritional status of the mother at the time of metformin intervention. Using mouse models of maternal overnutrition, we aimed to assess the effects of metformin exposure on offspring physiology and hypothalamic neuronal circuits during key periods of development.

METHODS

Female C57BL/6N mice received either a control diet or a high-fat diet (HFD) during pregnancy and lactation periods. A subset of dams was fed a HFD exclusively during the lactation. Anti-diabetic treatments were given during the first postnatal weeks. Body weights of male and female offspring were monitored daily until weaning. Circulating metabolic factors and molecular changes in the hypothalamus were assessed at postnatal day 16 using ELISA and Western Blot, respectively. Hypothalamic innervation was assessed by immunostaining at postnatal days 16 and 21.

RESULTS

We identified alterations in weight gain and circulating hormones in male and female offspring induced by anti-diabetic treatment during the early postnatal period, which were critically dependent on the maternal metabolic state. Furthermore, hypothalamic agouti-related peptide (AgRP) and proopiomelanocortin (POMC) neuronal innervation outcomes in response to anti-diabetic treatment were also modulated by maternal metabolic state. We also identified sex-specific changes in hypothalamic AMPK signaling in response to metformin exposure.

CONCLUSION

We demonstrate a unique interaction between anti-diabetic treatment and maternal metabolic state, resulting in sex-specific effects on offspring brain development and physiological outcomes. Overall, based on our findings, no positive effect of metformin intervention was observed in the offspring, despite ameliorating effects on maternal metabolic outcomes. In fact, the metabolic state of the mother drives the most dramatic differences in offspring physiology and metformin had no rescuing effect. Our results therefore highlight the need for a deeper understanding of how maternal metabolic state (excessive weight gain versus stable weight during GDM treatment) affects the developing offspring. Further, these results emphasize that the interventions to treat alterations in maternal metabolism during pregnancy need to be reassessed from the perspective of the offspring physiology.

Systematic review of antitumour efficacy and mechanism of metformin activity in prostate cancer models

Metformin, the first line pharmacotherapy for type 2 diabetes has demonstrated favourable effects in prostate cancer (PCa) across a range of studies evaluating PCa patient outcomes amongst metformin users. However, a lack of rigorously conducted prospective studies has stalled clinical use in this setting. Despite multiple studies evaluating the mechanisms underpinning antitumour effects of metformin in PCa, to date, no reviews have compared these findings. This systematic review and meta-analysis consolidates the mechanisms accounting for the antitumour effect of metformin in PCa and evaluates the antitumour efficacy of metformin in preclinical PCa studies. Data were obtained through Medline and EMBASE, extracted by two independent assessors. Risk of bias was assessed using the TOXR tool. Meta-analysis compared in vivo reductions of PCa tumour volume with metformin. In total, 447 articles were identified with 80 duplicates, and 261 articles excluded based on eligibility criteria. The remaining 106 articles were assessed and 71 excluded, with 35 articles included for systematic review, and eight included for meta-analysis. The mechanisms of action of metformin regarding tumour growth, viability, migration, invasion, cell metabolism, and activation of signalling cascades are individually discussed. The mechanisms by which metformin inhibits PCa cell growth are multimodal. Metformin regulates expression of multiple proteins/genes to inhibit cellular proliferation, cell cycle progression, and cellular invasion and migration. Published in vivo studies also conclusively demonstrate that metformin inhibits PCa growth. This highlights the potential of metformin to be repurposed as an anticancer agent, warranting further investigation of metformin in the setting of PCa.

Inhibition of Heme Export and/or Heme Synthesis Potentiates Metformin Anti-Proliferative Effect on Cancer Cell Lines

Simple Summary

Tumor initiation and progression are sustained by the ability of the cancer cell to reshape its metabolism in a way that favors cell proliferation and survival. Recently, it was shown that heme metabolism contributes to metabolic adaptation of tumor cell and that interfering with heme homeostasis reduces tumor cell growth. Here, we show that the alteration of heme metabolism, either by RNA-interference or pharmacological approaches, increases the sensitivity of tumor cell lines to the antitumor agent metformin. These findings strengthen the concept of targeting heme metabolism to counteract tumor progression.

Abstract

Cancer is one of the leading causes of mortality worldwide. Beyond standard therapeutic options, whose effectiveness is often reduced by drug resistance, repurposing of the antidiabetic drug metformin appears promising. Heme metabolism plays a pivotal role in the control of metabolic adaptations that sustain cancer cell proliferation. Recently, we demonstrated the existence of a functional axis between the heme synthetic enzyme ALAS1 and the heme exporter FLVCR1a exploited by cancer cells to down-modulate oxidative metabolism. In colorectal cancer cell lines, the inhibition of heme synthesis-export system was associated with reduced proliferation and survival. Here, we aim to assess whether the inhibition of the heme synthesis-export system affects the sensitivity of colorectal cancer cells to metformin. Our data demonstrate that the inhibition of this system, either by blocking heme efflux with a FLVCR1a specific shRNA or by inhibiting heme synthesis with 5-aminolevulinic acid, improves metformin anti-proliferative effect on colorectal cancer cell lines. In addition, we demonstrated that the same effect can be obtained in other kinds of cancer cell lines. Our study provides an in vitro proof of concept of the possibility to target heme metabolism in association with metformin to counteract cancer cell growth.

In Utero Exposure to Metformin Reduces the Fertility of Male Offspring in Adulthood

Metformin is a drug used for the treatment of type 2 diabetes and disorders associated with insulin resistance. Metformin is also used in the treatment of pregnancy disorders such as gestational diabetes. However, the consequences of foetal exposure to metformin on the fertility of exposed offspring remain poorly documented. In this study, we investigated the effect of in utero metformin exposure on the fertility of female and male offspring. We observed that metformin is detectable in the blood of the mother and in amniotic fluid and blood of the umbilical cord. Metformin was not measurable in any tissues of the embryo, including the gonads. The effect of metformin exposure on offspring was sex specific. The adult females that had been exposed to metformin in utero presented no clear reduction in fertility. However, the adult males that had been exposed to metformin during foetal life exhibited a 30% reduction in litter size compared with controls. The lower fertility was not due to a change in sperm production or the motility of sperm. Rather, the phenotype was due to lower sperm head quality - significantly increased spermatozoa head abnormality with greater DNA damage - and hypermethylation of the genomic DNA in the spermatozoa associated with lower expression of the ten-eleven translocation methylcytosine dioxygenase 1 (TET1) protein. In conclusion, while foetal metformin exposure did not dramatically alter gonad development, these results suggest that metabolic modification by metformin during the foetal period could change the expression of epigenetic regulators such as Tet1 and perturb the genomic DNA in germ cells, changes that might contribute to a reduced fertility.

Drug-Drug Interaction between Metformin and Sorafenib Alters Antitumor Effect in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and is one of the leading causes of cancer-related deaths worldwide. The multitarget inhibitor sorafenib is a first-line treatment of patients with advanced unresectable HCC. Recent clinical studies have evidenced that patients treated with sorafenib together with the antidiabetic drug metformin have a survival disadvantage compared with patients receiving sorafenib only. Here, we examined whether a clinically relevant dose of metformin (50 mg/kg per day) could influence the antitumoral effects of sorafenib (15 mg/kg per day) in a subcutaneous xenograft model of human HCC growth using two different sequences of administration, i.e., concomitant versus sequential dosing regimens. We observed that the administration of metformin 6 hours prior to sorafenib was significantly less effective in inhibiting tumor growth (15.4% tumor growth inhibition) than concomitant administration of the two drugs (59.5% tumor growth inhibition). In vitro experiments confirmed that pretreatment of different human HCC cell lines with metformin reduced the effects of sorafenib on cell viability, proliferation, and signaling. Transcriptomic analysis confirmed significant differences between xenografted tumors obtained under the concomitant and the sequential dosing regimens. Taken together, these observations call into question the benefit of parallel use of metformin and sorafenib in patients with advanced HCC and diabetes, as the interaction between the two drugs could ultimately compromise patient survival. SIGNIFICANCE STATEMENT: When drugs are administered sequentially, metformin alters the antitumor effect of sorafenib, the reference treatment for advanced hepatocellular carcinoma, in a preclinical murine xenograft model of liver cancer progression as well as in hepatic cancer cell lines. Defective activation of the AMP-activated protein kinase pathway as well as major transcriptomic changes are associated with the loss of the antitumor effect. These results echo recent clinical work reporting a poorer prognosis for patients with liver cancer who were cotreated with metformin and sorafenib.

Doxycycline in Extremely Low Dose Improves Glycemic Control and Islet Morphology in Mice Fed a High-Fat Diet

PURPOSE

Chronic low-grade inflammation is detected in obese and diabetic individuals. Tetracyclines, used as antibiotics for years, have been demonstrated to have diverse non-bactericidal effects, including anti-tumor and anti-inflammatory activities. This study aimed to investigate whether doxycycline at sub-antimicrobial concentrations could improve glycemic control in mice fed a high-fat diet, through its anti-inflammatory activities.

METHODS

C57BL/6J mice were fed with a high-fat diet to induce diabetic and obese conditions. Three sub-antimicrobial dosages of doxycycline (200, 20, and 2 μg/mL) were added to drinking water for 23 weeks during the housing phase.

RESULTS

Doxycycline at 200 μg/mL tended to increase body weight, islet mass, and the percentage of large islets (diameter >350 μm). At 20 μg/mL, doxycycline significantly improved glucose tolerance and decreased fasting blood glucose. At 2 μg/mL, doxycycline increased the percentage of small islets (diameter <80 μm). Serum C-reactive protein and lipopolysaccharide levels significantly decreased while the beta-cell ratio increased in all doxycycline-administered mice.

CONCLUSION

Our results suggest that doxycycline, even at an extremely low dose, could improve glycemic control and islet morphology via its anti-inflammatory activities.

Resveratrol and Metformin Recover Prefrontal Cortex AMPK Activation in Diet-Induced Obese Mice but Reduce BDNF and Synaptophysin Protein Content

BACKGROUND

Obesity, insulin resistance, and type 2 diabetes are established risk factors for the development of Alzheimer's disease (AD). Given this connection, two drugs, metformin (MET) and resveratrol (RESV), are considered for the clearance of amyloid-β peptides through AMPK-mediated activation of autophagy. However, overactivation of AMPK observed in late-stage AD brains and relationships between AMPK and neurogenesis (through mTORC1 inhibition), questions treatment with these drugs.

OBJECTIVE

To examine if MET and/or RESV supplementation activates brain AMPK, regulates markers of autophagy, and affects markers of neuronal health/neurogenesis.

METHODS

8-week-old male C57BL/6J mice were fed a low (N = 12; 10% kcal fat; LFD) or high fat diet (N = 40; 60% kcal fat; HFD) for 9 weeks to induce insulin resistance and obesity. HFD mice were then treated with/without MET (250 mg/kg/day), RESV (100 mg/kg/day), or COMBO (MET: 250 mg/kg/day, RESV: 100 mg/kg/day) for 5 weeks. Hippocampus and prefrontal cortex were extracted for western blotting analysis.

RESULTS

Cortex AMPK (T172) and raptor (S792, the regulatory subunit of mTORC1) phosphorylation were upregulated following RESV, COMBO treatments. mTOR (S2448) and ULK1 (S555) activation was seen following MET, COMBO and RESV, COMBO treatments, respectively, in the cortex and hippocampus. p62 content was decreased following RESV, COMBO, with LC3 content being increased following RESV treatment in the cortex. Brain derived neurotropic factor (BDNF) was significantly decreased following RESV, COMBO, and synaptophysin following all treatment in the cortex.

CONCLUSION

These results demonstrate that while treatments upregulated markers of autophagy in the prefrontal cortex, reductions in neuronal health markers question the efficacy of AMPK as a therapy for AD.

The impact of antidiabetic treatment on human hypothalamic infundibular neurons and microglia

Animal studies indicate that hypothalamic dysfunction plays a major role in type 2 diabetes mellitus (T2DM) development, and that insulin resistance and inflammation are important mechanisms involved in this disorder. However, it remains unclear how T2DM and antidiabetic treatments affect the human hypothalamus. Here, we characterized the proopiomelanocortin (POMC) immunoreactive (-ir) neurons, the neuropeptide-Y-ir (NPY-ir) neurons, the ionized calcium-binding adapter molecule 1-ir (iba1-ir) microglia, and the transmembrane protein 119-ir (TMEM119-ir) microglia in the infundibular nucleus (IFN) of human postmortem hypothalamus of 32 T2DM subjects with different antidiabetic treatments and 17 matched nondiabetic control subjects. Compared with matched control subjects, T2DM subjects showed a decrease in the number of POMC-ir neurons, but no changes in NPY-ir neurons or microglia. Interestingly, T2DM subjects treated with the antidiabetic drug metformin had fewer NPY-ir neurons and microglia than T2DM subjects not treated with metformin. We found that the number of microglia correlated with the number of NPY-ir neurons, but only in T2DM subjects. These results indicate that different changes in POMC and NPY neurons and microglial cells in the IFN accompany T2DM. In addition, T2DM treatment modality is associated with highly selective changes in hypothalamic neurons and microglial cells.

Determination of metformin bio-distribution by LC-MS/MS in mice treated with a clinically relevant paradigm

Metformin, an anti-diabetes drug, has been recently emerging as a potential “anti-aging” intervention based on its reported beneficial actions against aging in preclinical studies. Nonetheless, very few metformin studies using mice have determined metformin concentrations and many effects of metformin have been observed in preclinical studies using doses/concentrations that were not relevant to therapeutic levels in human. We developed a liquid chromatography-tandem mass spectrometry protocol for metformin measurement in plasma, liver, brain, kidney, and muscle of mice. Young adult male and female C57BL/6 mice were voluntarily treated with metformin of 4 mg/ml in drinking water which translated to the maximum dose of 2.5 g/day in humans. A clinically relevant steady-state plasma metformin concentrations were achieved at 7 and 30 days after treatment in male and female mice. Metformin concentrations were slightly higher in muscle than in plasma, while, ~3 and 6-fold higher in the liver and kidney than in plasma, respectively. Low metformin concentration was found in the brain at ~20% of the plasma level. Furthermore, gender difference in steady-state metformin bio-distribution was observed. Our study established steady-state metformin levels in plasma, liver, muscle, kidney, and brain of normoglycemic mice treated with a clinically relevant dose, providing insight into future metformin preclinical studies for potential clinical translation.

Diabetes-induced hypomagnesemia is not modulated by metformin treatment in mice

Approximately 30% of patients with type 2 diabetes mellitus (T2D) have hypomagnesemia (blood magnesium (Mg²⁺) concentration <0.7 mmol/L). In T2D patients, treatment with metformin is associated with reduced blood Mg²⁺ levels. To investigate how T2D and metformin affect Mg²⁺ homeostasis db/m and db/db mice were treated with metformin or placebo. Mice were housed in metabolic cages to measure food and water intake, and to collect urine and feces. Serum and urinary Mg²⁺ concentrations were determined and mRNA expression of magnesiotropic genes was determined in kidney and distal colon using RT-qPCR. Db/db mice had significantly lower serum Mg²⁺ levels than db/m mice. Mild hypermagnesuria was observed in the db/db mice at two weeks, but not at four weeks. Metformin-treatment had no effect on the serum Mg²⁺ concentration and on the urinary Mg²⁺ excretion. Both in kidney and distal colon of db/db mice, there was a compensatory upregulation in the mRNA expression of magnesiotropic genes, such as transient receptor potential melastatin 6 (Trpm6), whereas metformin treatment did not affect gene expression levels. In conclusion, we show that T2D causes hypomagnesemia and that metformin treatment has no effect on Mg²⁺ homeostasis in mice.

Metformin in Reproductive Biology

Initially produced in Europe in 1958, metformin is still one of the most widely prescribed drugs to treat type II diabetes and other comorbidities associated with insulin resistance. Metformin has been shown to improve fertility outcomes in females with insulin resistance associated with polycystic ovary syndrome (PCOS) and in obese males with reduced fertility. Metformin treatment reinstates menstrual cyclicity, decreases the incidence of cesareans, and limits the number of premature births. Notably, metformin reduces steroid levels in conditions associated with hyperandrogenism (e.g., PCOS and precocious puberty) in females and improves fertility of adult men with metabolic syndrome through increased testosterone production. While the therapeutical use of metformin is considered to be safe, in the last 10 years some epidemiological studies have described phenotypic differences after prenatal exposure to metformin. The goals of this review are to briefly summarize the current knowledge on metformin focusing on its effects on the female and male reproductive organs, safety concerns, including the potential for modulating fetal imprinting via epigenetics.

H19 lncRNA alters methylation and expression of Hnf4α in the liver of metformin-exposed fetuses

Metformin is the most widely used anti-diabetic medication worldwide. However, human and animal studies suggest that prenatal metformin exposure may increase the risk of metabolic disorders in adult offspring, yet the underpinning mechanism remains unclear. Here we report that metformin-exposed mouse fetuses exhibit elevated expression of the H19 long noncoding RNA, which induces hypomethylation and increased expression of hepatocyte nuclear factor 4α (HNF4α). As a transcription factor essential for morphological and functional differentiation of hepatocytes, HNF4α also has an indispensable role in the regulation of expression of gluconeogenic genes. Consistently, H19 overexpression in a human liver cell line leads to decreased methylation and increased expression of Hnf4α, with concomitant activation of the gluconeogenic program. Mechanistically, we show that the methylation change of Hnf4α is induced by H19-mediated regulation of S-adenosylhomocysteine hydrolase. We also provide evidence that altered H19 expression is a direct effect of metformin in the fetal liver. Our results suggest that metformin from the mother can directly act upon the fetal liver to modify Hnf4α expression, a key factor for both liver development and function, and that perturbation of this H19/Hnf4α-mediated pathway may contribute to the fetal origin of adult metabolic abnormalities.

Low dose doxycycline decreases systemic inflammation and improves glycemic control, lipid profiles, and islet morphology and function in db/db mice

The aim of this study was to determine whether low dose doxycycline as an anti-inflammatory agent could improve glucose metabolism in diabetic animals. Therefore, doxycycline was supplemented in drinking water to 6-week-old male db/db mice for 10 weeks. Doxycycline reduced perirenal/epididymal fat, Lee's index, and liver cholesterol. Blood HDL-cholesterol increased, but total cholesterol and aspartate transaminase decreased. Glucose and insulin tolerances were improved, accompanying with reduced fasting blood glucose, insulin, HOMA-IR and advanced glycation end products. Islet number, β-cell percentage and mass increased, while islet size decreased. Consistently, less apoptosis but more β-cell proliferation were found in islets of treated mice. Freshly isolated islets from treated mice showed higher insulin content and enhanced glucose stimulated insulin secretion (GSIS). In addition, purified islets of Balb/c mice showed increased GSIS after cultivation in vitro with doxycycline, but not with chloramphenicol and levofloxacin. Inflammation markers, including lipopolysaccharides (LPS) and C-reactive protein (CRP) in serum as well as CD68-positive cells in treated islets, decreased significantly. Finally, LPS stimulated the production of inflammatory factors but inhibited GSIS of MIN6 cells; however, the effects were completely reversed by doxycycline. The results support further study of possible long-term usage of sub-antimicrobial doxycycline in diabetic patients.

Antidiabetic Effect of Tibetan Medicine Tang-Kang-Fu-San on High-Fat Diet and Streptozotocin-Induced Type 2 Diabetic Rats

The aim of this study was to investigate the antidiabetic effects of a Tibetan medicine, Tang-Kang-Fu-San (TKFS), on experimental type 2 diabetes mellitus (T2DM) rats and to explore its underlying mechanisms. Firstly two major chemical compositions of TKFS, gallic acid and curcumin, were characterized by HPLC fingerprint analysis. Next T2DM in rats was induced by high-fat diet and a low-dose streptozotocin (STZ 35 mg/kg). Then oral gavage administration of three different doses of TKFS (0.3 g/kg, 0.6 g/kg, and 1.2 g/kg) was given to T2DM rats. Experimental results showed that TKFS dramatically reduced the levels of fasting blood glucose, fasting blood insulin, triglyceride, total cholesterol, LDL cholesterol, and HDL cholesterol, even though it did not alter the animal body weight. The downregulation of phosphorylation-AKT (p-AKT) and glucose transporter-4 (GLUT4) in skeletal muscle of T2DM rats was restored and abnormal pathological changes in pancreas tissues were also improved. Our work showed that TKFS could alleviate diabetic syndromes, maintain the glucose homeostasis, and protect against insulin resistance in T2DM rats, and the improvement of AKT phosphorylation and GLUT4 translocation in skeletal muscle would be one of its possible underlying mechanisms.

Increased efficacy of metformin corresponds to differential metabolic effects in the ovarian tumors from obese versus lean mice

Obesity is a significant risk factor for ovarian cancer (OC) and associated with worse outcomes for this disease. We assessed the anti-tumorigenic effects of metformin in human OC cell lines and a genetically engineered mouse model of high grade serous OC under obese and lean conditions. Metformin potently inhibited growth in a dose-dependent manner in all four human OC cell lines through AMPK/mTOR pathways. Treatment with metformin resulted in G1 arrest, induction of apoptosis, reduction of invasion and decreased hTERT expression. In the K18-gT₁₂₁^+/-; p53^fl/fl; Brca1^fl/fl (KpB) mouse model, metformin inhibited tumor growth in both lean and obese mice. However, in the obese mice, metformin decreased tumor growth by 60%, whereas tumor growth was only decreased by 32% in the lean mice (p=0.003) compared to vehicle-treated mice. The ovarian tumors from obese mice had evidence of impaired mitochondrial complex 2 function and energy supplied by omega fatty acid oxidation rather than glycolysis as compared to lean mice, as assessed by metabolomic profiling. The improved efficacy of metformin in obesity corresponded with inhibition of mitochondrial complex 1 and fatty acid oxidation, and stimulation of glycolysis in only the OCs of obese versus lean mice. In conclusion, metformin had anti-tumorigenic effects in OC cell lines and the KpB OC pre-clinical mouse model, with increased efficacy in obese versus lean mice. Detected metabolic changes may underlie why ovarian tumors in obese mice have heightened susceptibility to metformin.

Beneficial effects of combined resveratrol and metformin therapy in treating diet-induced insulin resistance

The polyphenol compound resveratrol (RSV) has attracted attention due to its reputed beneficial effects on insulin sensitivity. Our lab has previously identified protective effects of RSV against the development of type 2 diabetes in rats. These effects occurred in a manner similar to thiazolidinedione's (TZDs), a class of insulin sensitizing drugs. TZDs are commonly prescribed in combination with metformin (MET) and thus we sought to examine the combined effects of RSV and MET in treating insulin resistance. Male C57BL6 mice were fed a low‐ (LFD; 10% Kcal from fat) or high‐fat diet (HFD; 60% Kcal from fat) for 9 weeks to induce glucose and insulin intolerance. HFD mice were then assigned to control (HFD), MET (231.28 ± 12.24 mg/kg/day), RSV (93.68 ± 3.51 mg/kg/day), or combined (COM; MET 232.01 ± 17.12 mg/kg/day and RSV 92.77 ± 6.92 mg/kg/day) treatment groups. Changes in glucose and insulin tolerance and tissue‐specific insulin signaling were measured 4 weeks post‐treatment. RSV or MET alone did not have beneficial effects on glucose tolerance, although MET significantly improved insulin tolerance compared to HFD. Glucose and insulin tolerance were significantly improved in COM compared to HFD and this was mirrored by enhanced insulin‐stimulated AKT phosphorylation in triceps muscle and inguinal subcutaneous adipose tissue in COM compared to HFD mice. Improvements with COM treatment were not explained by differences in body weight, adiposity, or markers of adipose tissue inflammation. In summary, this study provides evidence of beneficial effects of combined RSV and MET therapy in treating impairments in glucose homeostasis.

Antidiabetic activity of the ethyl acetate fraction of Ficus lutea (Moraceae) leaf extract: comparison of an in vitro assay with an in vivo obese mouse model

Background

Ficus lutea crude acetone leaf extracts were previously shown to stimulate glucose uptake and insulin secretion of established cells and, inhibit α-amylase and α-glucosidase activities.

Methods

For this study, F. lutea acetone extracts were subjected to solvent-solvent fractionation to yield fractions with differing polarities (hexane, chloroform, dichloromethane, ethyl acetate, n-butanol and water) in an attempt to obtain a more potent fraction with in vitro and probably in vivo activity.

Results

Among these fractions, the ethyl acetate fraction had the highest total polyphenol content (100.5 ± 1.6 mg GAE/g dried extract) and α-glucosidase inhibitory activity (126.8 ± 30.6 μg/ml). It also stimulated the highest glucose uptake of C2C12 muscle cells and decreased extracellular glucose concentration of H-4-II-E liver cells with low cytotoxic activity. The ethyl acetate fraction (10.88 ± 0.55 μg/L at 250 μg/ml) enhanced insulin secretion in RIN-m5F pancreatic β-cells to the same degree as the positive control glibenclamide (11.09 ± 0.07 μg/L at 1μM). While fractionation increased α-glucosidase inhibition and glucose uptake of cells, in the ethyl acetate fraction, the α-amylase inhibition and insulin secretion decreased. The weight reducing and glucose control potential of the ethyl acetate fraction in an obese mouse model, important factors in the amelioration of type II diabetes was determined. The extract had no statistical significant weight reducing activity.

Conclusion

A major finding was the decrease in the area under the curve of the glucose concentration over time in animals that were treated with both a change in diet and with the plant extract. This is linked to increased glucose uptake within the cells, the most likely mechanism is either an increased insulin response or increased insulin secretion.

Metformin for cancer and aging prevention: is it a time to make the long story short?

During the last decade, the burst of interest is observed to antidiabetic biguanide metformin as candidate drug for cancer chemoprevention. The analysis of the available data have shown that the efficacy of cancer preventive effect of metformin (MF) and another biguanides, buformin (BF) and phenformin (PF), has been studied in relation to total tumor incidence and to 17 target organs, in 21 various strains of mice, 4 strains of rats and 1 strain of hamsters (inbred, outbred, transgenic, mutant), spontaneous (non- exposed to any carcinogenic agent) or induced by 16 chemical carcinogens of different classes (polycycIic aromatic hydrocarbons, nitroso compounds, estrogen, etc.), direct or indirect (need metabolic transformation into proximal carcinogen), by total body X-rays and γ- irradiation, viruses, genetic modifications or special high fat diet, using one stage and two-stage protocols of carcinogenesis, 5 routes of the administration of antidiabetic biguanides (oral gavage, intraperitoneal or subcutaneous injections, with drinking water or with diet) in a wide ranks of doses and treatment regimens. In the majority of cases (86%) the treatment with biguanides leads to inhibition of carcinogenesis. In 14% of the cases inhibitory effect of the drugs was not observed. Very important that there was no any case of stimulation of carcinogenesis by antidiabetic biguanides. It was conclude that there is sufficient experimental evidence of anti-carcinogenic effect of antidiabetic biguanides.

Cellular Stress, Excessive Apoptosis, and the Effect of Metformin in a Mouse Model of Type 2 Diabetic Embryopathy

Increasing prevalence of type 2 diabetes in women of childbearing age has led to a higher incidence of diabetes-associated birth defects. We established a model of type 2 diabetic embryopathy by feeding 4-week-old female mice a high-fat diet (HFD) (60% fat). After 15 weeks on HFD, the mice showed characteristics of type 2 diabetes mellitus (DM) and were mated with lean male mice. During pregnancy, control dams fed a normal diet (10% fat) were maintained on either normal diet or HFD, serving as a control group with elevated circulating free fatty acids. DM dams produced offspring at a rate of 11.3% for neural tube defect (NTD) formation, whereas no embryos in the control groups developed NTDs. Elevated markers of oxidative stress, endoplasmic reticulum stress, caspase activation, and neuroepithelial cell apoptosis (causal events in type 1 diabetic embryopathy) were observed in embryos of DM dams. DM dams treated with 200 mg/kg metformin in drinking water ameliorated fasting hyperglycemia, glucose intolerance, and insulin resistance with consequent reduction of cellular stress, apoptosis, and NTDs in their embryos. We conclude that cellular stress and apoptosis occur and that metformin effectively reduces type 2 diabetic embryopathy in a useful rodent model.

Leucine amplifies the effects of metformin on insulin sensitivity and glycemic control in diet-induced obese mice

BACKGROUND AND OBJECTIVE

The Sirt1/AMPK signaling pathway is a key sensor of energy status and regulates glucose and lipid metabolism. Leucine (Leu) activates Sirt1 by lowering its Km for NAD(+) and potentiates other sirtuin/AMPK-activators, resulting in improvement of insulin sensitivity. Since metformin (Met) converges on this pathway, we hypothesized that leucine would amplify its gluco-regulatory effects.

MATERIALS AND METHODS

The effects of Leu (24 g/kg diet)+Met (0.05-0.5 g/kg diet) combinations were compared to standard therapeutic Met (1.5 g/kg diet; ~300 mg/kg BW) on glycemic control in high fat diet induced insulin resistant mice for 6 weeks. The effects of Leu on Met stimulation of Sirt1 and AMPK activities were further evaluated in adipocytes.

RESULTS

Sub-therapeutic levels of Met combined with Leu resulted in increases in Sirt1 activity and in tissue P-AMPK/AMPK ratio and corresponding dose-responsive improvements in fasting and post-prandial glucose, in glucose response to an insulin tolerance test and in the area under the curve in glucose tolerance tests. Changes were evident within 7 days of treatment and sustained throughout the 6-week study duration. The Leu+Met (0.25 g/kg)-combinations produced a comparable effect to a standard therapeutic Met dose, while the Leu+Met (0.5 g/kg diet) resulted in greater improvements. Since resveratrol also synergizes with leucine to augment sirtuin signaling and insulin sensitivity, we tested the addition of resveratrol to Leu-Met and found no additional benefit.

CONCLUSION

These data demonstrate that adding Leu to Met enables a dose reduction of 66% with improved efficacy and of 83% with comparable efficacy to standard metformin in diet-induced obese mice, and addition of resveratrol does not provide further benefit.

Impacts of metformin and aspirin on life history features and longevity of crickets: trade-offs versus cost-free life extension?

We examined the impacts of aspirin and metformin on the life history of the cricket Acheta domesticus (growth rate, maturation time, mature body size, survivorship, and maximal longevity). Both drugs significantly increased survivorship and maximal life span. Maximal longevity was 136 days for controls, 188 days (138 % of controls) for metformin, and 194 days (143 % of controls) for aspirin. Metformin and aspirin in combination extended longevity to a lesser degree (163 days, 120 % of controls). Increases in general survivorship were even more pronounced, with low-dose aspirin yielding mean longevity 234 % of controls (i.e., health span). Metformin strongly reduced growth rates of both genders (<60 % of controls), whereas aspirin only slightly reduced the growth rate of females and slightly increased that of males. Both drugs delayed maturation age relative to controls, but metformin had a much greater impact (>140 % of controls) than aspirin (~118 % of controls). Crickets maturing on low aspirin showed no evidence of a trade-off between maturation mass and life extension. Remarkably, by 100 days of age, aspirin-treated females were significantly larger than controls (largely reflecting egg complement). Unlike the reigning dietary restriction paradigm, low aspirin conformed to a paradigm of "eat more, live longer." In contrast, metformin-treated females were only ~67 % of the mass of controls. Our results suggest that hormetic agents like metformin may derive significant trade-offs with life extension, whereas health and longevity benefits may be obtained with less cost by agents like aspirin that regulate geroprotective pathways.

Prenatal metformin exposure in a maternal high fat diet mouse model alters the transcriptome and modifies the metabolic responses of the offspring

AIMS

Despite the wide use of metformin in metabolically challenged pregnancies, the long-term effects on the metabolism of the offspring are not known. We studied the long-term effects of prenatal metformin exposure during metabolically challenged pregnancy in mice.

MATERIALS AND METHODS

Female mice were on a high fat diet (HFD) prior to and during the gestation. Metformin was administered during gestation from E0.5 to E17.5. Male and female offspring were weaned to a regular diet (RD) and subjected to HFD at adulthood (10-11 weeks). Body weight and several metabolic parameters (e.g. body composition and glucose tolerance) were measured during the study. Microarray and subsequent pathway analyses on the liver and subcutaneous adipose tissue of the male offspring were performed at postnatal day 4 in a separate experiment.

RESULTS

Prenatal metformin exposure changed the offspring's response to HFD. Metformin exposed offspring gained less body weight and adipose tissue during the HFD phase. Additionally, prenatal metformin exposure prevented HFD-induced impairment in glucose tolerance. Microarray and annotation analyses revealed metformin-induced changes in several metabolic pathways from which electron transport chain (ETC) was prominently affected both in the neonatal liver and adipose tissue.

CONCLUSION

This study shows the beneficial effects of prenatal metformin exposure on the offspring's glucose tolerance and fat mass accumulation during HFD. The transcriptome data obtained at neonatal age indicates major effects on the genes involved in mitochondrial ATP production and adipocyte differentiation suggesting the mechanistic routes to improved metabolic phenotype at adulthood.

Do metformin a real anticarcinogen? A critical reappraisal of experimental data

Evidence has emerged that antidiabetic biguanides [phenformin (PF), buformin (BF) and metformin (MF)] are promising candidates for prevention of cancer. It was shown that antidiabetic biguanides postpone spontaneous carcinogenesis as well as inhibit carcinogenesis induced by chemical, radiation and biological factors (virus, transgene, genetic modifications, special diet, etc.) in a number of organs and tissues in various strains of mice and rats. The present review focused on some details of experiments such as design of studies, dose and route of administration of biguanide, and age of animals at start of treatment etc. Conclusion may be done that there are rather sufficient evidence of cancer-preventive activity of antidiabetic biguanides in experimental animals.

Altered gene products involved in the malignant reprogramming of cancer stem/progenitor cells and multitargeted therapies

Recent studies in the field of cancer stem cells have revealed that the alterations in key gene products involved in the epithelial-mesenchymal transition (EMT) program, altered metabolic pathways such as enhanced glycolysis, lipogenesis and/or autophagy and treatment resistance may occur in cancer stem/progenitor cells and their progenies during cancer progression. Particularly, the sustained activation of diverse developmental cascades such as hedgehog, epidermal growth factor receptor (EGFR), Wnt/β-catenin, Notch, transforming growth factor-β (TGF-β)/TGF-βR receptors and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) can play critical functions for high self-renewal potential, survival, invasion and metastases of cancer stem/progenitor cells and their progenies. It has also been observed that cancer cells may be reprogrammed to re-express different pluripotency-associated stem cell-like markers such as Myc, Oct-3/4, Nanog and Sox-2 along the EMT process and under stressful and hypoxic conditions. Moreover, the enhanced expression and/or activities of some drug resistance-associated molecules such as Bcl-2, Akt/molecular target of rapamycin (mTOR), nuclear factor-kappaB (NF-κB), hypoxia-inducible factors (HIFs), macrophage inhibitory cytokine-1 (MIC-1) and ATP-binding cassette (ABC) multidrug transporters frequently occur in cancer cells during cancer progression and metastases. These molecular events may cooperate for the survival and acquisition of a more aggressive and migratory behavior by cancer stem/progenitor cells and their progenies during cancer transition to metastatic and recurrent disease states. Of therapeutic interest, these altered gene products may also be exploited as molecular biomarkers and therapeutic targets to develop novel multitargeted strategies for improving current cancer therapies and preventing disease relapse.

Metformin inhibits food intake and neuropeptide Y gene expression in the hypothalamus

Metformin may reduce food intake and body weight, but the anorexigenic effects of metformin are still poorly understood. In this study, Sprague-Dawley rats were administered a single intracere-broventricular dose of metformin and compound C, in a broader attempt to investigate the regula-tory effects of metformin on food intake and to explore the possible mechanism. Results showed that central administration of metformin significantly reduced food intake and body weight gain, par-ticularly after 4 hours. A reduction of neuropeptide Y expression and induction of AMP-activated protein kinase phosphorylation in the hypothalamus were also observed 4 hours after metformin administration, which could be reversed by compound C, a commonly-used antagonist of AMP-activated protein kinase. Furthermore, metformin also improved lipid metabolism by reducing plasma low-density lipoprotein. Our findings suggest that under normal physiological conditions, central regulation of appetite by metformin is related to a decrease in neuropeptide Y gene expres-sion, and that the activation of AMP-activated protein kinase may simply be a response to the anorexigenic effect of metformin.

The key role of growth hormone-insulin-IGF-1 signaling in aging and cancer

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors in aging. GH/Insulin/insulin-like growth factor-1 (IGF-1) signaling molecules that have been linked to longevity include daf-2 and InR and their homologues in mammals, and inactivation of the corresponding genes increases lifespan in nematodes, fruit flies and mice. The life-prolonging effects of caloric restriction are likely related to decreasing IGF-1 levels. Evidence has emerged that antidiabetic drugs are promising candidates for both lifespan extension and prevention of cancer. Thus, antidiabetic drugs postpone spontaneous carcinogenesis in mice and rats, as well as chemical and radiation carcinogenesis in mice, rats and hamsters. Furthermore, metformin seems to decrease the risk for cancer in diabetic patients.

Prenatal metformin exposure in mice programs the metabolic phenotype of the offspring during a high fat diet at adulthood

AIMS

The antidiabetic drug metformin is currently used prior and during pregnancy for polycystic ovary syndrome, as well as during gestational diabetes mellitus. We investigated the effects of prenatal metformin exposure on the metabolic phenotype of the offspring during adulthood in mice.

METHODS

Metformin (300 mg/kg) or vehicle was administered orally to dams on regular diet from the embryonic day E0.5 to E17.5. Gene expression profiles in liver and brain were analysed from 4-day old offspring by microarray. Body weight development and several metabolic parameters of offspring were monitored both during regular diet (RD-phase) and high fat diet (HFD-phase). At the end of the study, two doses of metformin or vehicle were given acutely to mice at the age of 20 weeks, and Insig-1 and GLUT4 mRNA expressions in liver and fat tissue were analysed using qRT-PCR.

RESULTS

Metformin exposed fetuses were lighter at E18.5. There was no effect of metformin on the maternal body weight development or food intake. Metformin exposed offspring gained more body weight and mesenteric fat during the HFD-phase. The male offspring also had impaired glucose tolerance and elevated fasting glucose during the HFD-phase. Moreover, the expression of GLUT4 mRNA was down-regulated in epididymal fat in male offspring prenatally exposed to metformin. Based on the microarray and subsequent qRT-PCR analyses, the expression of Insig-1 was changed in the liver of neonatal mice exposed to metformin prenatally. Furthermore, metformin up-regulated the expression of Insig-1 later in development. Gene set enrichment analysis based on preliminary microarray data identified several differentially enriched pathways both in control and metformin exposed mice.

CONCLUSIONS

The present study shows that prenatal metformin exposure causes long-term programming effects on the metabolic phenotype during high fat diet in mice. This should be taken into consideration when using metformin as a therapeutic agent during pregnancy.

Synergistic effects of metformin, resveratrol, and hydroxymethylbutyrate on insulin sensitivity

BACKGROUND

The purpose of this study was to determine whether a mixture of the polyphenol, resveratrol, and the leucine metabolite, hydroxymethylbutyrate (HMB), acts synergistically with low doses of metformin to impact insulin sensitivity and AMP-activated protein kinase-dependent outcomes in cell culture and in diabetic mice.

METHODS

C2C12 skeletal myotubes and 3T3-L1 adipocytes were treated with resveratrol 0.2 μM, HMB 5 μM, and metformin 0.1 mM alone or in combination. db/db mice were treated for 2 weeks with high (1.5 g/kg diet), low (0.75 g/kg diet), or very low (0.25 g/kg diet) doses of metformin alone or in combination with a diet containing resveratrol 12.5 mg and CaHMB 2 g/kg.

RESULTS

The combination of metformin-resveratrol-HMB significantly increased fat oxidation, AMP-activated protein kinase, and Sirt1 activity in muscle cells compared with metformin or resveratrol-HMB alone. A similar trend was found in 3T3L1 adipocytes. In mice, the two lower doses of metformin exerted no independent effect but, when combined with resveratrol-HMB, both low-dose and very low-dose metformin improved insulin sensitivity (HOMA(IR)), plasma insulin levels, and insulin tolerance test response to a level comparable with that found for high-dose metformin. In addition, the metformin-resveratrol-HMB combination decreased visceral fat and liver weight in mice.

CONCLUSION

Resveratrol-HMB combined with metformin may act synergistically on AMP-activated protein kinase-dependent pathways, leading to increased insulin sensitivity, which may reduce the therapeutic doses of metformin necessary in the treatment of diabetes.

Enhanced cytotoxic effect of low doses of metformin combined with ionizing radiation on hepatoma cells via ATP deprivation and inhibition of DNA repair

Metformin, one of the most widely used antidiabetic drugs, has recently been associated with potential antitumorigenic effects. In this study, we evaluated the possible cytotoxic impact of combined low doses of metformin and ionizing radiation (IR) on 2 human hepatoma cell lines. The cytotoxic effect of metformin combined with IR was subsequently determined by clonogenic survival and cell cycle assays, assessment of mitochondrial complex I and lactate dehydrogenase (LDH) activity, measurement of cellular adenosine triphosphate (ATP) levels, comet assay and analyses of the formation and disappearance of phosphorylated histone H2AX (γ-H2AX) protein. The combination of metformin and IR caused a much stronger cytotoxicity than the treatment with metformin or IR alone, leading to an ~80% decrease in cell viability and ~35% increase in the accumulation of cells in the G2/M phase of the cell cycle in the 2 hepatoma cell lines. In addition, a reduction in mitochondrial complex I activity (~70%) and a significant increase in LDH activity, as well as lactate production were observed in the cells exposed to metformin. Interestingly, a severe depletion in ATP, increased olive tail moment and the delayed disappearance of γ-H2AX expression were detected in the hepatoma cells treated by metformin plus IR. These findings show that the combination of a low concentration of metformin and IR results in the considerable enhancement of cytotoxic effects in human hepatoma cell lines, leading to decreased DNA repair by reducing ATP production. The data provided in this study may elucidate the remarkable efficiency of this combination treatment and suggest that metformin may be used as a potential adjunct to the radiotherapy of hepatocellular carcinoma.

Metformin enhances the antiproliferative and apoptotic effect of bicalutamide in prostate cancer

BACKGROUND

Prostate cancer incidence and mortality vary dramatically by geographical location. Both are higher in developed countries. Some attribute this to westernized lifestyles of high-energy diets and limited physical activity with consequent obesity. Obesity and obesity-related diseases like diabetes cause hyperinsulinaemia, which upregulates pro-survival cell signalling. Previous work revealed diet-induced hyperinsulinaemia enhances prostate cancer xenograft growth in vivo. Metformin, an antidiabetic medication, reduces hyperinsulinaemia and also exhibits antineoplastic properties. Herein, we assess the potential additive benefit of combining bicalutamide antiandrogen therapy with metformin, in vitro and in vivo.

METHODS

Using clonogenic assays, we assessed the effect of bicalutamide and/or metformin on clonogenicity in prostate cancer cell lines. Western blot and cell cycle analyses were used to elucidate mechanisms of interaction between the drugs in androgen receptor (AR)-positive (LNCaP) and AR-negative (PC3) cell lines. The combination treatment regimen was assessed in vivo using an LNCaP murine xenograft model.

RESULTS

Micromolar bicalutamide or millimolar metformin caused a significant dose-dependent reduction in clonogenicity (P<0.001). Combination treatment further significantly reduced clonogenicity (P<0.005) with greater effects in AR-positive cells. Western blot and cell cycle analyses suggested differing mechanisms of interaction in AR-positive and -negative cell lines. Following combination treatment, LNCaP cells exhibited an altered cell proliferation (decreased phospho mammalian target of rapamycin expression) and perturbed cell cycle kinetics (G1/S cell cycle arrest). PC3 cells showed evidence of enhanced apoptosis (increased Bcl-2-associated X protein and decreased total caspase 3 expression). Markedly diminished tumour growth occurred following combination treatment in vivo (P<0.001).

CONCLUSIONS

Combining bicalutamide and metformin significantly reduces prostate cancer cell growth further than either monotherapy. In AR-positive cells, this effect appeared to be mediated by reducing proliferation rates, whereas in AR-negative cells the combination treatment appeared to promote apoptosis. This combination drug regimen may improve prostate-cancer-specific survival by the direct antineoplastic properties outlined.

Metformin use is associated with better survival of diabetic patients with pancreatic cancer

PURPOSE

Accumulating evidence suggests that metformin has antitumor activity. The aim of this study was to determine whether metformin use has a survival benefit in patients with pancreatic cancer.

EXPERIMENTAL DESIGN

We conducted a retrospective study of patients with diabetes and pancreatic cancer treated at The University of Texas MD Anderson Cancer Center (Houston, TX). Information on diabetes history, including treatment modalities and clinical outcome of pancreatic cancer, was collected using personal interviews and medical record review. Survival analysis was carried out using a Kaplan-Meier plot, log-rank test, and Cox proportional hazards regression models.

RESULTS

Among the 302 patients identified, there were no significant differences in demographic or major clinical characteristics between the patients who had received metformin (n = 117) and those who had not (n = 185). The 2-year survival rate was 30.1% for the metformin group and 15.4% for the non-metformin group (P = 0.004; χ(2) test). The median overall survival time was 15.2 months for the metformin group, and 11.1 months for the non-metformin group (P = 0.004, log-rank test). Metformin users had a 32% lower risk of death; the HR (95% confidence interval) was 0.68 (0.52-0.89) in a univariate model (P = 0.004), 0.64 (0.48-0.86) after adjusting for other clinical predictors (P = 0.003), and 0.62 (0.44-0.87) after excluding insulin users (P = 0.006). Metformin use was significantly associated with longer survival in patients with nonmetastatic disease only.

CONCLUSIONS

Our finding that metformin use was associated with improved outcome of patients with diabetes and pancreatic cancer should be confirmed in independent studies. Future research should prospectively evaluate metformin as a supplemental therapy in this population.

Metformin as an antitumor agent in cancer prevention and treatment

Recent epidemiological investigations conducted in diabetic cohorts and cancer patients have found that metformin users have lower risks for cancer than those using insulin or insulin secretagogues. Studies conducted in various animal tumor models and cancer cell lines have demonstrated that metformin prevents tumor development or inhibits cell proliferation. In addition, a recent clinical trial has shown that short-term use of metformin reduces aberrant crypt foci (ACF) formation in non-diabetic patients with ACF. The antitumor activity of metformin may be mediated through its regulatory effect on hormonal, metabolic, and immune functions. Metformin achieves glycemic control by reducing hepatic glucose production and increasing the muscle intake of glucose, thus lowering levels of circulating glucose and, consequently, insulin. The major molecular targets of metformin are the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) signaling and mammalian target of rapamycin (mTOR) pathways, which are central in the regulation of cellular energy homeostasis and play a crucial role in the control of cell division and cell proliferation. Metformin has been shown to improve endothelial function, decrease inflammatory activity, and regulate immune function. Increasing experimental evidence provides a strong biological rationale for metformin as an antitumor and chemopreventive agent. Metformin is being tested as an adjuvant cancer therapy in clinical settings, and metformin is recommended for all cases of Type 2 diabetes without contraindications. As described in this review, the chemopreventive value of metformin is not restricted to diabetic or obese individuals.

Prenatal androgenization of female mice programs an increase in firing activity of gonadotropin-releasing hormone (GnRH) neurons that is reversed by metformin treatment in adulthood

Prenatal androgenization (PNA) of female mice with dihydrotestosterone programs reproductive dysfunction in adulthood, characterized by elevated luteinizing hormone levels, irregular estrous cycles, and central abnormalities. Here, we evaluated activity of GnRH neurons from PNA mice and the effects of in vivo treatment with metformin, an activator of AMP-activated protein kinase (AMPK) that is commonly used to treat the fertility disorder polycystic ovary syndrome. Estrous cycles were monitored in PNA and control mice before and after metformin administration. Before metformin, cycles were longer in PNA mice and percent time in estrus lower; metformin normalized cycles in PNA mice. Extracellular recordings were used to monitor GnRH neuron firing activity in brain slices from diestrous mice. Firing rate was higher and quiescence lower in GnRH neurons from PNA mice, demonstrating increased GnRH neuron activity. Metformin treatment of PNA mice restored firing activity and LH to control levels. To assess whether AMPK activation contributed to the metformin-induced reduction in GnRH neuron activity, the AMPK antagonist compound C was acutely applied to cells. Compound C stimulated cells from metformin-treated, but not untreated, mice, suggesting that AMPK was activated in GnRH neurons, or afferent neurons, in the former group. GnRH neurons from metformin-treated mice also showed a reduced inhibitory response to low glucose. These studies indicate that PNA causes enhanced firing activity of GnRH neurons and elevated LH that are reversible by metformin, raising the possibility that central AMPK activation by metformin may play a role in its restoration of reproductive cycles in polycystic ovary syndrome.