Metformin (Glucophage) inhibits tyrosine phosphatase activity to stimulate the insulin receptor tyrosine kinase

Modulation of Insulin Resistance by Silybum marianum Leaves, and its Synergistic Efficacy with Gymnema sylvestre, Momordica charantia, Trigonella-foenum graecum Against Protein Tyrosine Phosphatase 1B

Prolonged insulin resistance is considered one of the reasons for Type 2 Diabetes Mellitus. Upregulation of Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signalling, has been well studied as a key regulator in prognosis to insulin resistance. It has been widely studied as a desirable molecular therapeutic target. The study aimed to evaluate the efficacy of leaf extract of the medicinal plants Silybum marianum on the inhibition of PTP1B activity. It also explored the synergistic effect with extracts of Gymnema sylvestre (leaves), Momordica charantia (seeds), and Trigonella foenum graecum (seeds). The S. marianum leaves showed dose-dependent inhibition of PTP1B ranging from 9.48-47.95% (25-1000 μg mL-1). Assay with individual plant extracts showed comparatively lesser inhibition of PTP1B as compared to metformin as a control (38% inhibition). However, a synergistic effect showed nearly 45% PTP1B inhibition (higher than metformin) after the assay was done with selected four plant extracts in combination. The effect of leaf extracts of S. marianum was studied for glucose uptake efficiency in yeast cell lines which was found to be increased by 23% as compared to the control (without extract). Metformin improves glucose upake by yeast cells by ~15-31%. GC-MS analysis revealed 23 phytochemicals, some of which possessed anti-diabetic properties. A dose-dependent increase in antioxidant activity of S. marianum leaves extracts was observed (40-53%). The findings of the study highlighted the presence of various phytochemicals in leaves extracts that are effective against PTP1B inhibition and may help in reinvigorating drug development.

Impact of metformin on tyrosine kinase inhibitor response in chronic myeloid leukemia

Objective

Oral tyrosine kinase inhibitors (TKIs) are first line therapy for chronic myeloid leukemia (CML). A complete cytogenetic response (CCyR) correlates with increased overall survival, however only 66%–88% of patients achieve CCyR after one year of TKI treatment. Because TKI therapy alone cannot eliminate CML stem cells, strategies aimed at achieving faster and deeper responses are needed to improve long-term survival. Metformin is a widely prescribed glucose-lowering agent for patients with diabetes and in preclinical studies, has been shown to suppress cell viability, induce apoptosis, and downregulate the mTORC1 signaling pathway in imatinib resistant CML cell lines (K562R). This study aims to investigate the utility of metformin added to TKI therapy in patients with CML.

Data Sources

An observational study at an academic medical center (Salt Lake City, UT) was performed for adults with newly diagnosed, chronic-phase CML to evaluate attainment of CCyR from TKI therapy with or without concomitant metformin use. Descriptive analyses were used to describe baseline characteristics and attainment of response to TKI therapy.

Data Summary

Fifty-nine patients were evaluated. One hundred percent (5 of 5) in the metformin group and 73.6% (39 of 54) in the non-metformin group achieved CCyR. Approximately 20% of patients in both groups relapsed (defined by a loss of CCyR during study) after a median 34.5 months of follow-up.

Conclusions

Future research is warranted to validate these findings and determine the utility of metformin added to TKI therapy.

An update on mode of action of metformin in modulation of meta-inflammation and inflammaging

Type 2 diabetes mellitus (T2DM) is the most common chronic metabolic condition. Several genetic and environmental factors are involved in developing T2DM. Aging, inflammation, and obesity are the main contributors to the initiation of T2DM. They cause chronic sterile meta-inflammation and insulin resistance, thereby making a person more susceptible to developing T2DM. Metformin, a natural cationic biguanide, is widely used as the first-line treatment of T2DM. The exact action mechanism behind the glucose-lowering effect of metformin is not clear, but, presumably, metformin utilizes a broad spectrum of molecular mechanisms to control blood glucose including decreasing intestinal glucose absorption, inhibition of the hepatic gluconeogenesis, decreasing insulin resistance, etc. Recent studies have shown that metformin exerts its effects through the inhibition of mitochondrial respiratory chain complex 1 and the AMP-activated protein kinase (AMPK) activation, but it has been identified in the other studies that AMPK is not the sole hub in metformin mode of action or there are other unknown mechanisms which are involved and yet to be explored. Therefore, here, we discuss the updated findings of the mechanism of action of metformin that contributes to the meta-inflammation and inflammaging action. It is proposed that figuring out the precise mechanism of action of metformin could improve its application in the fields of obesity, inflammation, aging, and inflammaging.

Metformin Protects against Podocyte Injury in Diabetic Kidney Disease

Metformin is the most commonly prescribed drug for treating type 2 diabetes mellitus (T2D). Its mechanisms of action have been under extensive investigation, revealing that it has multiple cellular targets, either direct or indirect ones, via which it regulates numerous cellular pathways. Diabetic kidney disease (DKD), the serious complication of T2D, develops in up to 50% of the individuals with T2D. Various mechanisms contribute to the development of DKD, including hyperglycaemia, dyslipidemia, oxidative stress, chronic low-grade inflammation, altered autophagic activity and insulin resistance, among others. Metformin has been shown to affect these pathways, and thus, it could slow down or prevent the progression of DKD. Despite several animal studies demonstrating the renoprotective effects of metformin, there is no concrete evidence in clinical settings. This review summarizes the renoprotective effects of metformin in experimental settings. Special emphasis is on the effects of metformin on podocytes, the glomerular epithelial cells that are central in maintaining the glomerular ultrafiltration function.

The effect of metformin on esophageal cancer risk in patients with type 2 diabetes mellitus: a systematic review and meta‑analysis

OBJECTIVE

Recently, numerous studies have yielded inconsistent results regarding the effect of metformin on esophageal cancer risk in type 2 diabetes mellitus patients. The purpose of this study is to systematically assess this effect using meta-analysis.

METHODS

We searched clinical studies on metformin and esophageal cancer risk in PubMed, Embase, and the Cochrane Library. After literature screening, a series of meta-analyses were conducted using RevMan 5.3 software. The pooled hazard ratio (HR) and the corresponding 95% confidence interval (CI) were used as the effect size.

RESULTS

Five eligible studies (four cohort studies and one case-control study) were included for our meta-analysis using a random-effect model. The analysis showed that metformin could not reduce esophageal cancer risk in type 2 diabetes mellitus patients (HR 0.88, 95% CI 0.60-1.28, P > 0.05). Subgroup analyses by geographic location showed that metformin significantly reduced esophageal cancer risk in Asian patients with type 2 diabetes mellitus (HR 0.59, 95% CI 0.39-0.91, P = 0.02), without heterogeneity between studies (P = 0.80 and I² = 0%).

CONCLUSIONS

Overall, our systematic review and meta-analysis demonstrate that metformin does not reduce esophageal cancer risk in type 2 diabetes mellitus patients. However, a significant reduction in esophageal cancer risk in Asian populations remains to be clarified.

Therapeutic approach for metabolic disorders and infertility in women with PCOS

Polycystic ovary syndrome (PCOS) is a complex endocrine disorder affecting 5-10% of women of reproductive age. It generally shows with oligo/amenorrhea, anovulatory cycles, clinical o biochemical hirsutism, polycystic ovaries and, in a significant percentage of cases, insulin resistance. PCOS is defined as a multifactorial pathology, determined by the association of many factors: genetic, endocrine and environmental. The first and most effective treatment of PCOS is to change life-style and lose weight. The use of oral contraceptives has been shown effective in reducing acne and hirsutism and regulates the menstrual cycle. For women with severe hirsutism, the addition of antiandrogens to estrogen-progestin therapy has significantly improved the results. In cases of anovulatory infertility, the drug of first choice is clomiphene citrate, followed by low-dose gonadotropins. Recently, insulin-sensitizing drugs have been widely prescribed for PCOS patients. They are particularly effective in reducing insulin resistance and improving ovulatory performance. Besides insulin-sensitizing drugs, natural substances, such as inositol, seems to have good efficacy, similar to metformin with fewer side effects. New substances that could be used include statins and natural statins, such as monakolin, alone or combined with myo-inositol. These substances do not have side effects and greatly reduce the hyperandrogenic component in these patients.

A marriage of two "Methusalem" drugs for the treatment of psoriasis?: Arguments for a pilot trial with metformin as add-on for methotrexate

In this article we present arguments that the “antidiabetic” drug metformin could be useful as an add-on therapy to methotrexate for the treatment of psoriasis and, perhaps, for rheumatoid arthritis as well. Biochemical data suggest that both drugs may share a common cellular target, the AMP-activated protein kinase (AMPK). This enzyme is a master regulator of metabolism and controls a number of downstream targets, e.g., important for cellular growth or function in many tissues including T-lymphocytes. Clinical observations as well as experimental results argue for anti-inflammatory, antineoplastic and antiproliferative activities of metformin and a case-control study suggests that the drug reduces the risk for psoriasis.

Patients with psoriasis have higher risk of metabolic syndrome, type 2 diabetes and cardiovascular mortality. Metformin has proven efficacy in the treatment of prediabetes and leads to a pronounced and sustained weight loss in overweight individuals. We expect that addition of metformin to methotrexate can lead to positive effects with respect to the PASI score, reduction of the weekly methotrexate dose and of elevated cardiovascular risk factors in patients with metabolic syndrome and psoriasis. For reasons explained later we suggest that only male, overweight patients are to be included in a pilot trial. On the other side of the coin are concerns that the gastrointestinal side effects of metformin are intolerable for patients under low dose, intermittent methotrexate therapy. Metformin has another side effect, namely interference with vitamin B₁₂ and folate metabolism, leading to elevated homocysteine serum levels. As patients must receive folate supplementation and will be controlled with respect to their B₁₂ status increased hematological toxicity is unlikely to result.

Potential utility of sodium selenate as an adjunct to metformin in treating type II diabetes mellitus in rats: a perspective on protein tyrosine phosphatase

Metformin is widely regarded as the standard first-line antidiabetic agent, in terms of efficacy and safety profiles. However, in most patients with type II diabetes mellitus (T2DM), it was found that metformin alone is not enough to adequately control hyperglycemia. Thus, we designed this study with the aim to investigate the effect of sodium selenate, a protein tyrosine phosphatase (PTP) inhibitor, individually and as an adjunct to metformin, on a rat model that simulates the metabolic characteristics of human T2DM. T2DM model was achieved by feeding the rats with high-fat, high-fructose diet (HFFD) for 8 weeks followed by a low dose of streptozotocin (STZ) (35 mg/kg/day, i.p.). Changes in serum glucose, insulin, adiponectin, homeostasis model assessment of insulin resistance (HOMA-IR) index, and the lipid profile were assessed. In addition, the level of reduced glutathione (GSH) and the activity of PTP were determined in the liver. Results showed that the addition of sodium selenate to metformin was able to restore hepatic GSH back to normal levels. Also, this combination therapy corrected the altered serum total cholesterol (TC), triglycerides (TG), and adiponectin levels. In conclusion, additive therapeutic effect was recorded when sodium selenate was used as an adjunct to 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.

Defining the contribution of AMP-activated protein kinase (AMPK) and protein kinase C (PKC) in regulation of glucose uptake by metformin in skeletal muscle cells

The importance of AMP-activated protein kinase (AMPK) and protein kinase C (PKC) as effectors of metformin (Met) action on glucose uptake (GU) in skeletal muscle cells was investigated. GU in L6 myotubes was stimulated 2-fold following 16 h of Met treatment and acutely enhanced by insulin in an additive fashion. Insulin-stimulated GU was sensitive to PI3K inhibition, whereas that induced by Met was not. Met and its related biguanide, phenformin, stimulated AMPK activation/phosphorylation to a level comparable with that induced by the AMPK activator, 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (AICAR). However, the increase in GU elicited by AICAR was significantly lower than that induced by either biguanide. Expression of a constitutively active AMPK mimicked the effects of AICAR on GU, whereas a dominant interfering AMPK or shRNA silencing of AMPK prevented AICAR-stimulated GU and Met-induced AMPK signaling but only repressed biguanide-stimulated GU by ∼20%. Consistent with this, analysis of GU in muscle cells from α1(-/-)/α2(-/-) AMPK-deficient mice revealed a significant retention of Met-stimulated GU, being reduced by ∼35% compared with that of wild type cells. Atypical PKCs (aPKCs) have been implicated in Met-stimulated GU, and in line with this, Met and phenformin induced activation/phosphorylation of aPKC in L6 myotubes. However, although cellular depletion of aPKC (>90%) led to loss in biguanide-induced aPKC phosphorylation, it had no effect on Met-stimulated GU, whereas inhibitors targeting novel/conventional PKCs caused a significant reduction in biguanide-induced GU. Our findings indicate that although Met activates AMPK, a significant component of Met-stimulated GU in muscle cells is mediated via an AMPK-independent mechanism that involves novel/conventional PKCs.

Metformin induces differentiation in acute promyelocytic leukemia by activating the MEK/ERK signaling pathway

Recent studies have shown that metformin, a widely used antidiabetic agent, may reduce the risk of cancer development. In this study, we investigated the antitumoral effect of metformin on both acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL) cells. Metformin induced apoptosis with partial differentiation in an APL cell line, NB4, but only displayed a proapoptotic effect on several non-M3 AML cell lines. Further analysis revealed that a strong synergistic effect existed between metformin and all-trans retinoic acid (ATRA) during APL cell maturation and that metformin induced the hyperphosphorylation of extracellular signal-regulated kinase (ERK) in APL cells. U0126, a specific MEK/ERK activation inhibitor, abrogated metformin-induced differentiation. Finally, we found that metformin induced the degradation of the oncoproteins PML-RARα and c-Myc and activated caspase-3. In conclusion, these results suggest that metformin treatment may contribute to the enhancement of ATRA-induced differentiation in APL, which may deepen the understanding of APL maturation and thus provide insight for new therapy strategies.

Protein-tyrosine phosphatases are involved in interferon resistance associated with insulin resistance in HepG2 cells and obese mice

Insulin resistance is a risk factor for non-response to interferon/ribavirin therapy in patients with chronic hepatitis C. The aim of this study was to determine the role played by protein-tyrosine phosphatases (PTPs) in the absence of interferon-α (IFNα) response associated with insulin resistance. We induced insulin resistance by silencing IRS-2 or by treating HepG2 cells with tumor necrosis factor-α (TNFα) and analyzed insulin response by evaluating Akt phosphorylation and IFNα response by measuring Stat-1 tyrosine phosphorylation and 2',5'-oligoadenylate synthase and myxovirus resistance gene expression. The response to IFNα was also measured in insulin-resistant obese mice (high fat diet and ob/ob mice) untreated and treated with metformin. Silencing IRS-2 mRNA induces insulin resistance and inhibits IFNα response. Likewise, TNFα suppresses insulin and IFNα response. Treatment of cells with pervanadate and knocking down PTP-1B restores insulin and IFNα response. Both silencing IRS-2 and TNFα treatment increase PTP and PTP-1B activity. Metformin inhibits PTP and improves IFNα response in insulin-resistant cells. Insulin-resistant ob/ob mice have increased PTP-1B gene expression and activity in the liver and do not respond to IFNα administration. Treatment with metformin improves this response. In HepG2 cells, insulin resistance provokes IFNα resistance, which is associated with an increased PTP-1B activity in the liver. Inhibition of PTP-1B activity with pervanadate and metformin or knocking down PTP-1B reestablishes IFNα response. Likewise, metformin decreases PTP-1B activity and improves response to IFNα in insulin-resistant obese mice. The use of PTP-1B inhibitors may improve the response to IFNα/ribavirin therapy.

The effect of metformin on the efficacy of antiviral therapy in patients with genotype 1 chronic hepatitis C and insulin resistance

OBJECTIVES

Insulin resistance (IR) affects sustained virological response (SVR) in chronic hepatitis C (CHC). The aim of this study was to investigate the effect of adding metformin to peginterferon alfa-2a and ribavirin on the efficacy in patients with genotype 1 CHC and IR.

METHODS

Ninety-eight patients with genotype 1 CHC and IR were randomized into the treatment group (n=49) and the control group (n=49). Patients in the control group received peginterferon alfa-2a and ribavirin, and patients in the treatment group received metformin in addition to peginterferon alfa-2a and ribavirin. The rate of virological response, changes in the homeostasis model assessment of insulin resistance (HOMA-IR) index, and the incidence of side effects were compared between the two groups. Factors influencing the SVR were studied by multivariate analysis.

RESULTS

The SVR rate of the treatment group was significantly higher than that of the control group (59.2%, 29/49 vs. 38.8%, 19/49; Chi-square=4.083, p=0.043). The HOMA-IR index of patients in the treatment group was lower than that of patients in the control group at weeks 12, 24, and 48 of the treatment period, and at week 24 of follow-up (3.00±0.65 vs. 3.50±0.72, 1.90±0.45 vs. 2.90±0.64, 1.75±0.40 vs. 2.74±0.48, and 1.60±0.35 vs. 2.60±0.55, respectively; t=3.610, 8.947, 11.091, and 10.738, respectively; p<0.01). Diarrhea was more often seen in the treatment group (28.6%, 14/49 vs. 10.2%, 5/49; Chi-square=5.288, p=0.021). In the multivariate logistic regression analysis, the independent factors associated with SVR were treatment method (p=0.009) and HOMA-IR <2 at week 24 (p=0.011).

CONCLUSIONS

A combination of metformin, peginterferon alfa-2a, and ribavirin improved insulin sensitivity and increased the SVR rate of patients with hepatitis C genotype 1 and IR, with a good safety profile.

Paracrine and endocrine effects of adipose tissue on cancer development and progression

The past few years have provided substantial evidence for the vital role of the local tumor microenvironment for various aspects of tumor progression. With obesity and its pathophysiological sequelae still on the rise, the adipocyte is increasingly moving center stage in the context of tumor stroma-related studies. To date, we have limited insight into how the systemic metabolic changes associated with obesity and the concomitant modification of the paracrine and endocrine panel of stromal adipocyte-derived secretory products ("adipokines") influence the incidence and progression of obesity-related cancers. Here, we discuss the role of adipocyte dysfunction associated with obesity and its potential impact on cancer biology.

Metabolic Syndrome and Breast Cancer Risk: Is There a Role for Metformin?

Obesity is one of the most important known preventable causes of cancer, accounting for up to 20% of cancer deaths in women. Obese women have increased risk of dying from breast cancer as well as an increased risk of distant metastasis. Metabolic Syndrome (MetSyn) is a group of metabolic conditions that include 1) abdominal obesity, 2) atherogenic dyslipidemia, 3) elevated blood pressure, and 4) insulin resistance. MetSyn is known to promote the development of cardiovascular disease and diabetes and may be associated with increased breast cancer risk. Emerging evidence supports an association between mammary adipocytes and their secreted adipocytokines and breast cancer initiation and progression. Metformin (1,1-dimethylbiguanide hydrochloride) is a drug used to treat type 2 diabetes and MetSyn. We review the potential association between MetSyn in promoting breast cancer and emerging evidence for the use of metformin in cancer prevention.

Metformin for aging and cancer prevention

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors in aging. 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 life span in nematodes, fruit flies and mice. It is possible that the life-prolonging effect of caloric restriction is due to decreasing IGF-1 levels. Evidence has emerged that antidiabetic drugs are promising candidates for both life span 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 cancer risk in diabetic patients.

Treatment of insulin resistance with metformin in naïve genotype 1 chronic hepatitis C patients receiving peginterferon alfa-2a plus ribavirin

Insulin resistance affects sustained virological response (SVR) in chronic hepatitis C. To know whether adding metformin to standard antiviral treatment improves SVR, we conducted a prospective, multicentered, randomized, double-blinded, placebo-controlled trial in 19 Spanish hospitals, including 123 consecutive patients with genotype 1 chronic hepatitis C and insulin resistance. Patients were randomized to receive either metformin (arm A; n = 59) or placebo (arm B; n = 64) in addition to peginterferon alfa-2a (180 microg/week) and ribavirin (1000-1200 mg/day). The primary end point was SVR, and secondary endpoints were viral clearance at weeks 12, 24, and 48, and changes in the homeostasis model assessment (HOMA) index over the first 24 weeks. There were no differences between arms at baseline. In the intent-to-treat analysis, SVR was observed in 53% versus 42% in arm A and arm B, respectively (P = NS). In the subgroup analyses, SVR was higher in females (n = 54) receiving metformin: arm A, 58% (15/26) versus 29% (8/28) arm B (P = 0.03). In the per protocol analysis (PPA; n = 101), SVR was 67% in arm A and 49% in arm B (P = 0.06). Viral decline during the first 12 weeks was greater in females receiving metformin: -4.88 (1.18) versus -4.0 (1.44) (P = 0.021), whereas no differences were seen in males. The triple therapy was well tolerated, but diarrhea was more often seen in arm A (34% versus 11%; P < 0.05).

CONCLUSION

Adding metformin to peginterferon and ribavirin was safe and improved insulin sensitivity. Although the study failed to show a statistically significant difference between arms, it did show an improved SVR in females.

[Metformin effects upon blood pressure and glucose metabolism of monossodium glutamate induced-obese spontaneously hypertensive rats]

OBJECTIVES

To make available experimental model for the metabolic syndrome (MS) and verify effects of chronic oral treatment with metformin upon blood pressure (BP), body weight (BW), glucose metabolism, epididimal fat content (EF).

METHOD

Males SHR received monossodium glutamate (MSG, 2 mg/kg/day/sc) during first 11 days of life. Control animals received saline. After 12 weeks, animals were separated in two groups, treated either with metformin 500 mg/ kg/day or vehicle during 12 weeks. PA and BW were determined. At the end of the follow-up, animals underwent an oral glucose tolerance test (OGTT) and insulin sensitivity index was determined. Upon sacrifice EF was measured.

RESULTS

MSG worsened insulin resistance and induced visceral obesity in SHR, without change BP. Treatment with metformin improved glucose metabolism and reduces EF and BP.

CONCLUSIONS

These observations emphasize the role of hepatic insulin resistance on MS and point out for beneficial cardiovascular effects with improvement in the insulin sensitivity.

Metformin induces apoptosis of pancreatic cancer cells

AIM

To assess the role and mechanism of metformin in inducing apoptosis of pancreatic cancer cells.

METHODS

The human pancreatic cancer cell lines ASPC-1, BxPc-3, PANC-1 and SW1990 were exposed to metformin. The inhibition of cell proliferation and colony formation via apoptosis induction and S phase arrest in pancreatic cancer cell lines of metformin was tested.

RESULTS

In each pancreatic cancer cell line tested, metformin inhibited cell proliferation in a dose dependent manner in MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays). Flow cytometric analysis showed that metformin reduced the number of cells in G1 and increased the percentage of cells in S phase as well as the apoptotic fraction. Enzymelinked immunosorbent assay (ELISA) showed that metformin induced apoptosis in all pancreatic cancer cell lines. In Western blot studies, metformin induced poly-ADP-ribose polymerase (PARP) cleavage (an indicator of caspase activation) in all pancreatic cancer cell lines. The general caspase inhibitor (VAD-fmk) completely abolished metformin-induced PARP cleavage and apoptosis in ASPC-1 BxPc-3 and PANC-1, the caspase-8 specific inhibitor (IETD-fmk) and the caspase-9 specific inhibitor (LEHD-fmk) only partially abrogated metformin-induced apoptosis and PARP cleavage in BxPc-3 and PANC-1 cells. We also observed that metformin treatment dramatically reduced epidermal growth factor receptor (EGFR) and phosphorylated mitogen activated protein kinase (P-MAPK) in both a time- and dose-dependent manner in all cell lines tested.

CONCLUSION

Metformin significantly inhibits cell proliferation and apoptosis in all pancreatic cell lines. And the metformin-induced apoptosis is associated with PARP cleavage, activation of caspase-3, -8, and -9 in a time- and dose-dependent manner. Hence, both caspase-8 and -9-initiated apoptotic signaling pathways contribute to metformin-induced apoptosis in pancreatic cell lines.

Berberine potently inhibits protein tyrosine phosphatase 1B: Investigation by docking simulation and experimental validation

Berberine was investigated as an inhibitor of human protein tyrosine phosphatase 1B (h-PTP 1B) in an attempt to explain its anti-hyperglycemic activitiy. The investigation included simulated docking experiments to fit berberine within the binding pocket of h-PTP 1B. Berberine was found to readily fit within the binding pocket of h-PTP 1B in a low energy orientation characterized with optimal electrostatic attractive interactions bridging the isoquinolinium positively charged nitrogen atom of berberine and the negatively charged acidic residue of ASP 48 of h-PTP 1B. Experimentally, berberine was found to potently competitively inhibit recombinant h-PTP 1B in vitro (Ki value = 91.3 nM). Our findings strongly suggest that h-PTP 1B inhibition is at least one of the reasons for the reported anti-hyperglycemic activities of berberine.

Targeting AMPK: a new therapeutic opportunity in breast cancer

BACKGROUND

This paper reviews the mammalian Target Of Rapamycin (mTOR) pathway dysregulation in breast cancer, and the current evidence targeting this pathway directly or through activation of AMP-activated protein kinase (AMPK) as an additional therapeutic opportunity for intervention in breast cancer.

METHODS

Relevant articles were identified through computerised searches of Medline and Pubmed. Secondary articles were identified from the reference lists of key papers and by hand searching.

RESULTS AND CONCLUSION

The current consensus to target the AMPK/mTOR pathway in breast cancer is based on in vitro and epidemiological evidences. A low incidence of cancer in diabetic patients on metformin has been explained in vitro by the drug's anti-proliferative effect through activation of AMPK. There is a need to explore the anticancer effects of metformin and the potential to develop the therapeutic avenues offered by targeting the AMPK/mTOR pathway.

Anti-diabetic effects of compound K versus metformin versus compound K-metformin combination therapy in diabetic db/db mice

Compound K (CK) is a major intestinal metabolite of ginsenosides derived from ginseng radix. In our preliminary studies, CK has shown to exhibit anti-hyperglycemic effect through its insulin-secreting action, similar to that of insulin secretagogue sulfonylureas. Metformin, a biguanide, improves insulin resistance by reducing gluconeogenesis and enhancing peripheral glucose uptake, promoting reduction of the plasma glucose level. The aim of this study was to compare the anti-diabetic effects of CK and metformin due to differences in their mechanisms of action and also to investigate whether treatment of CK and metformin in combination show synergistic or additive effects compared to each drug alone. Seven week-old male db/db mice were treated for 8 weeks. CK was given at a dose of 10 mg/kg, metformin at 150 mg/kg and the same dosage of each drug was applied to CK plus metformin combination group. Significant improvements were observed in plasma glucose and insulin levels, homeostasis model assessment-insulin resistance (HOMA-IR) index and in hematoxylin and eosin-stained liver tissues in combination group. Although further studies to elucidate the benefits of co-administration of CK and metformin are needed, our findings may provide basis to the discovery of a new combination therapy on diabetes control in type 2 diabetics.

Metformin Is an AMP Kinase–Dependent Growth Inhibitor for Breast Cancer Cells

Recent population studies provide clues that the use of metformin may be associated with reduced incidence and improved prognosis of certain cancers. This drug is widely used in the treatment of type 2 diabetes, where it is often referred to as an "insulin sensitizer" because it not only lowers blood glucose but also reduces the hyperinsulinemia associated with insulin resistance. As insulin and insulin-like growth factors stimulate proliferation of many normal and transformed cell types, agents that facilitate signaling through these receptors would be expected to enhance proliferation. We show here that metformin acts as a growth inhibitor rather than an insulin sensitizer for epithelial cells. Breast cancer cells can be protected against metformin-induced growth inhibition by small interfering RNA against AMP kinase. This shows that AMP kinase pathway activation by metformin, recently shown to be necessary for metformin inhibition of gluconeogenesis in hepatocytes, is also involved in metformin-induced growth inhibition of epithelial cells. The growth inhibition was associated with decreased mammalian target of rapamycin and S6 kinase activation and a general decrease in mRNA translation. These results provide evidence for a mechanism that may contribute to the antineoplastic effects of metformin suggested by recent population studies and justify further work to explore potential roles for activators of AMP kinase in cancer prevention and treatment.

Global gene expression analysis in liver of obese diabetic db/db mice treated with metformin

AIMS/HYPOTHESIS

Metformin is widely used as a hypoglycaemic reagent for type 2 diabetes. While the reduction of hepatic gluconeogenesis is thought to be a key effect, the detailed molecular mechanism of action of metformin remains to be elucidated. To gain insight into this, we performed a global gene expression profiling study.

MATERIALS AND METHODS

We performed DNA microarray analysis to study global gene expression in the livers of obese diabetic db/db mice 2 h after a single administration of metformin (400 mg/kg).

RESULTS

This analysis identified 14 genes that showed at least a 1.5-fold difference in expression following metformin treatment, including a reduction of glucose-6-phosphatase gene expression. The mRNA levels of glucose-6-phosphatase showed one of the best correlations with blood glucose levels among 12,000 genes. Enzymatic activity of glucose-6-phosphatase was also reduced in metformin-treated liver. Moreover, intensive analysis of the expression profile revealed that metformin effected significant alterations in gene expression across at least ten metabolic pathways, including those involved in glycolysis-gluconeogenesis, fatty acid metabolism and amino acid metabolism.

CONCLUSIONS/INTERPRETATION

These results suggest that reduction of glucose-6-phosphatase activity, as well as suppression of mRNA expression levels of this gene, in liver is of prime importance for controlling blood glucose levels in vivo, at least at early time points after metformin treatment. Our results also suggest that metformin not only affects expression of specific genes, but also alters the expression level of multiple genes linked to the metabolic pathways involved in glucose and lipid metabolism in the liver.

Pharmacophoric features of biguanide derivatives: an electronic and structural analysis

The structure and electronic structure of drugs determine their mechanism of action. Correct structural representation of drugs helps in the proper identification of pharmacophoric features. Biguanide derivatives are a very important class of drugs, but their electronic structure was not clearly understood. Ab initio MO and density functional studies revealed the structure of the most stable tautomer of biguanide. (i) Electron delocalization, (ii) 1,3-H shift, (iii) 1,5-H shift, (iv) protonation, and (v) deprotonation processes, etc., have been investigated for biguanide. The molecular electrostatic potential (MESP) surfaces of neutral, protonated, and deprotonated biguanide have been shown to be similar in their most stable arrangements. The electrostatic potential of the complementary surface where these systems may bind also could be identified. Finally, the most stable structure of the important biguanide derivatives has been given after performing a conformational search.

Metformin alters insulin signaling and viability of human granulosa cells

OBJECTIVE

To study whether insulin signaling pathways in the ovary are altered by metformin.

DESIGN

In vitro human granulosa cell culture system.

SETTING

Academic research environment.

PATIENT(S)

Infertility patients undergoing oocyte retrieval for IVF/ICSI.

MAIN OUTCOME MEASURE(S)

Cell viability and phosphorylated protein kinase B (PKB/AKT) and p44/42 mitogen-activated protein kinase (MAPK) expression of human primary and HGL5 granulosa cells.

RESULT(S)

Basal cell viability of primary granulosa cells was significantly increased relative to control by metformin preincubation, without an additional stimulatory effect of insulin or IGF. Phosphorylated AKT expression in lysates of the human granulosa cell line HGL5 was significantly increased in contrast to decreased phosphorylated MAPK expression by metformin preincubation.

CONCLUSION(S)

Besides systemic effects, the ovulation inducing action of metformin may at least partially be due to direct effects on insulin signaling intermediates and follicular growth patterns in the ovary.

Metformin decreases intracellular production of reactive oxygen species in aortic endothelial cells

Beyond its antidiabetic activity justifying its use in the treatment of the type 2 diabetes, metformin (MET [dimethylguanidine, Glucophage]) has been shown to exhibit antioxidant properties in vitro, which could contribute to limit the deleterious vascular complications of diabetes. We investigated whether MET, at the pharmacological level of 10 -5 mol/L, was able to modulate intracellular production of reactive oxygen species (ROS) both in quiescent bovine aortic endothelial cells (BAECs) and in BAECs stimulated by a short incubation with high levels of glucose (30 mmol/L, 2 hours) or angiotensin II (10 -7 mol/L, 1 hour). Intracellular ROS production was measured by fluorescence of the DCF (2,7-dichlorodihydrofluorescein) probe. Our results showed that MET was able to reduce the intracellular production of ROS in both nonstimulated BAECs (-20%, P < .05) and BAEC stimulated by high levels of glucose or angiotensin II (-28% and -72%, respectively, P < .01). Experiments performed in the presence of the nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase inhibitor apocynin or the respiratory mitochondrial chain inhibitor rotenone indicated that MET exerted its effect partly through an inhibition of the formation of ROS produced mainly by NAD(P)H oxidase and also, to a lesser extent, by the respiratory mitochondrial chain.