Effect of plasma metformin concentrations on serum lipid levels in type II diabetic patients

Metformin alleviates sphingolipids dysregulation and improves obesity-related kidney disease in high-fat diet rats

Obesity-related kidney disease (ORKD) has recently become a global health issue. Metformin is widely used in patients with type 2 diabetes with concomitant obesity, but its effects on ORKD are insufficiently understood. Accumulation of lipid species including sphingolipids has been reported to disrupt glomerular functions and drive progression of chronic kidney disease. The present study aimed to test the hypothesis that metformin could exert beneficial effects on ORKD, which may be associated with changes in renal lipidomics. Male Sprague-Dawley rats were divided into normal chow diet (ND) group or high-fat diet (HFD)-fed group. After 8 weeks, HFD-fed group was subdivided into metformin treatment (HFD-Met) group and control (HFD-C) group for an additional 8 weeks. Sphingolipids and phospholipids in renal cortex were measured by targeted lipidomics. Compared with ND group, HFD-C group developed histopathological features of ORKD. Metformin alleviated dyslipidemia, renal dysfunction, proteinuria, glomerular hypertrophy, podocyte damage, and renal fibrosis in HFD-fed rats. Renal sphingolipid analysis showed elevations of total ceramide, sphingosine, glucosylceramide, and galactosylceramide levels in HFD-C versus ND group. Specific species, such as ceramide d18:1/22:0, glucosylceramide d18:1/20:0, and galactosylceramide d18:1/16:0, which were positively associated with oxidative stress and insulin resistance, were reduced in HFD-Met versus HFD-C group. Renal phospholipid analysis showed increased levels of total phosphatidylcholine and lysophosphatidylcholine (LPC) in HFD-C rats versus ND rats. The ratio of saturated and monounsaturated LPCs to polyunsaturated LPCs was significantly reduced in HFD-Met rats. These results suggest that metformin alleviates sphingolipids dysregulation and improves ORKD in HFD-fed rats. SIGNIFICANCE STATEMENT: To date, this is the first report to explore effects of metformin on renal lipidomics. These findings reveal specific changes of renal lipid species, which are crucial for deeper understanding the underlying mechanisms of obesity-related kidney disease and effects of metformin on it. The associated signature sphingolipids and phospholipids in the study may have significant implications for developing targeted therapeutic strategies for obesity-related kidney disease.

SPHK1 Is a Novel Target of Metformin in Ovarian Cancer

The role of phospholipid signaling in ovarian cancer is poorly understood. Sphingosine-1-phosphate (S1P) is a bioactive metabolite of sphingosine that has been associated with tumor progression through enhanced cell proliferation and motility. Similarly, sphingosine kinases (SPHK), which catalyze the formation of S1P and thus regulate the sphingolipid rheostat, have been reported to promote tumor growth in a variety of cancers. The findings reported here show that exogenous S1P or overexpression of SPHK1 increased proliferation, migration, invasion, and stem-like phenotypes in ovarian cancer cell lines. Likewise, overexpression of SPHK1 markedly enhanced tumor growth in a xenograft model of ovarian cancer, which was associated with elevation of key markers of proliferation and stemness. The diabetes drug, metformin, has been shown to have anticancer effects. Here, we found that ovarian cancer patients taking metformin had significantly reduced serum S1P levels, a finding that was recapitulated when ovarian cancer cells were treated with metformin and analyzed by lipidomics. These findings suggested that in cancer the sphingolipid rheostat may be a novel metabolic target of metformin. In support of this, metformin blocked hypoxia-induced SPHK1, which was associated with inhibited nuclear translocation and transcriptional activity of hypoxia-inducible factors (HIF1α and HIF2α). Further, ovarian cancer cells with high SPHK1 were found to be highly sensitive to the cytotoxic effects of metformin, whereas ovarian cancer cells with low SPHK1 were resistant. Together, the findings reported here show that hypoxia-induced SPHK1 expression and downstream S1P signaling promote ovarian cancer progression and that tumors with high expression of SPHK1 or S1P levels might have increased sensitivity to the cytotoxic effects of metformin. IMPLICATIONS: Metformin targets sphingolipid metabolism through inhibiting SPHK1, thereby impeding ovarian cancer cell migration, proliferation, and self-renewal.

Stimulating effect of palmitate and insulin on cell migration and proliferation in PNT1A and PC3 prostate cells: Counteracting role of metformin

BACKGROUND

A potential association between obesity and prostate cancer has been proposed. Metformin, an antidiabetes drug, has antiproliferative effects being proposed for cancer treatment. However, under intense proliferative stimulation conditions such as those found in obesity, its efficacy is still uncertain. Thus, we analyzed the effects of saturated fatty acid and/or insulin under high concentrations, with or without metformin, on the proliferation and migration of prostate cells.

METHODS

Human prostate epithelial cell lines non-tumor (PNT1A) and tumor (PC3) were treated with control media (DMEM, C), palmitate (100 µM, HF), and/or insulin (50 µU, HI) with or without metformin (100 µM) for 24 or 48 h.

RESULTS

Both PNT1A and PC3 cells had greater proliferation when treated with HF, while HI treatment stimulated only PNT1A. Metformin inhibited cell proliferation caused by HF in both cell lines, but it did not block the proliferative action of HI in PNT1A cells. PNT1A increased cell migration after all treatments, while only HF influenced PC3; metformin inhibited the migration stimulated by all obese microenvironments. Both HF and HI treatments in PNT1A and HF treatment in PC3 augmented vimentin expression, resulting in a higher epithelial-mesenchymal transition (which, in turn, could influence cell migration). Metformin inhibited vimentin expression in both normal and tumor cells. Although HF treatment had increased AMPK activation, it also increased the levels of activated ERK1/2, which could be responsible for high cell proliferation in both cell lines. In contrast, HI decreased AMPK activation in both cell lines, whereas it increased ERK1/2 levels in PNT1A and decreased them in PC3 (reflecting greater cell proliferation only in non-tumor cells). Metformin maintained high activation of AMPK and decreased ERK1/2 levels after HF in both cell lines and only after HI in PNT1A, which was able to decrease the cell proliferation triggered by these treatments.

CONCLUSIONS

Higher concentrations of palmitate on PC3 cells and palmitate and insulin on PNT1A cells stimulate cellular activities that could favor cancer progression. Metformin inhibited most of these stimuli, showing the efficacy of this drug for cancer adjuvant therapy in obese patients (a group at increased risk for the development of prostrate cancer).

Maternal and neonatal circulating markers of metabolic and cardiovascular risk in the metformin in gestational diabetes (MiG) trial: responses to maternal metformin versus insulin treatment

OBJECTIVE

This study was designed to compare glucose, lipids, and C-reactive protein (CRP) in women with gestational diabetes mellitus treated with metformin or insulin and in cord plasma of their offspring and to examine how these markers relate to infant size at birth.

RESEARCH DESIGN AND METHODS

Women with gestational diabetes mellitus were randomly assigned to metformin or insulin in the Metformin in Gestational Diabetes trial. Fasting maternal plasma glucose, lipids, and CRP were measured at randomization, 36 weeks' gestation, and 6-8 weeks postpartum as well as in cord plasma. Women with available cord blood samples (metformin n = 236, insulin n = 242) were included.

RESULTS

Maternal plasma triglycerides increased more from randomization to 36 weeks' gestation in women treated with metformin (21.93%) versus insulin (9.69%, P < 0.001). Maternal and cord plasma lipids, CRP, and neonatal anthropometry did not differ between treatments. In logistic regression analyses adjusted for confounders, the strongest associations with birth weight >90th centile were maternal triglycerides and measures of glucose control at 36 weeks.

CONCLUSIONS

There were few differences in circulating maternal and neonatal markers of metabolic status and no differences in measures of anthropometry between the offspring of women treated with metformin and the offspring of women treated with insulin. There may be subtle effects of metformin on maternal lipid function, but the findings suggest that treating gestational diabetes mellitus with metformin does not adversely affect lipids or CRP in cord plasma or neonatal anthropometric measures.

Metformin reduces the stimulatory effect of obesity on in vivo Walker-256 tumor development and increases the area of tumor necrosis

AIMS

The objective of this study was to analyze the influence of obesity and insulin resistance on tumor development and, in turn, the effect of insulin sensitizing agents.

MAIN METHODS

Male offspring of Wistar rats received monosodium glutamate (400mg/kg) (obese) or saline (control) from the second to sixth day after birth. Sixteen-week-old control and obese rats received 5×10(5) Walker-256 tumor cells, subcutaneously injected into the right flank. Some of the obese and control rats received concomitant treatment with metformin (300mg/kg) by gavage. At the 18th week, obesity was characterized. The percentage of rats that developed tumors, the tumor relative weight and the percentage of cachexia incidence were analyzed. The tumor tissue was evaluated histologically by means of hematoxylin and eosin staining.

KEY FINDINGS

Metformin did not correct the insulin resistance in obese rats. The tumor development was significantly higher in the obese group, whereas metformin treatment reduced it. After pathological analysis, we observed that the tumor tissues were similar in all groups except for adipocytes, which were found in greater quantity in the obese and metformin-treated obese groups. The area of tumor necrosis was higher in the group treated with metformin when compared with the untreated one.

SIGNIFICANCE

Metformin reduced Walker-256 tumor development but not cachexia in obese rats. The reduction occurred independently of the correction of insulin resistance. Metformin increased the area of necrosis in tumor tissues, which may have contributed to the reduced tumor development.

Assessment of efficacy and tolerability of once-daily extended release metformin in patients with type 2 diabetes mellitus

AIMS

To determine prospectively the efficacy, tolerability and patient satisfaction of an extended release formulation of metformin (metformin XR) in hospital based outpatients with type 2 diabetes mellitus currently treated with standard metformin.

METHODS

Patients on immediate release standard metformin either alone or combined with other oral agents were switched to extended release metformin XR 500 mg tablets and titrated to a maximum dose of 2000 mg/day Measurements to include glucose and lipid control, blood pressure, body weight, waist circumference, C-reactive protein, adverse events and patient satisfaction were recorded at baseline, three and six months.

RESULTS

Complete data were obtained for 35 of the 61 patients enrolled to the study. At three and six months no changes were reported for any of the cardiovascular risk factors except for lipids where there was a modest rise in plasma triglycerides. These effects were achieved with a reduced dose of metformin XR compared to pre-study dosing with standard metformin (1500 mg +/- 402 vs 1861 +/- 711 p = 0.004). A total of 77% of patients were free of gastrointestinal side effects and 83% of patients stated a preference for metformin XR at the end of the study. Ghost tablets were reported in the faeces by the majority of the patients (54.1%).

CONCLUSIONS

Patients switched to extended release metformin XR derived the same clinical and metabolic benefits as for standard metformin but with reduced dosage, fewer gastrointestinal side effects and a greater sense of well being and satisfaction on medication.

Metformina e AMPK: um antigo fármaco e uma nova enzima no contexto da síndrome metabólica

A metformina é uma das drogas antidiabéticas orais mais prescritas mundialmente, entretanto seu mecanismo de ação permanece desconhecido. Os estudos do Diabetes Prevention Program Research Group demonstraram que tanto a administração de metformina como a mudança no estilo de vida (dieta e exercício físico) podem reduzir a incidência de diabetes melito tipo 2 (DM2). Uma possível conexão bioquímica entre essas duas terapias pode ser a proteína quinase ativada por AMP (AMPK). Essa enzima foi inicialmente descrita como um sensor energético celular, sendo ativada pelo exercício físico. Por outro lado, várias evidências experimentais indicam que a AMPK seja um alvo importante da ação da metformina. Este artigo discute as várias formas da regulação da AMPK, sugerindo um possível mecanismo para sua ativação pela metformina que envolve a formação de espécies reativas de nitrogênio. A ativação da AMPK determina ampla variedade de efeitos fisiológicos, incluindo o aumento da captação de glicose pelos músculos esqueléticos e aumento do catabolismo de lipídios, podendo ser interessante não apenas na prevenção e tratamento do DM2, mas também no contexto da síndrome metabólica. A descoberta da ativação da AMPK pela metformina faz dessa enzima importante alvo farmacológico.

Metformin revisited: re-evaluation of its properties and role in the pharmacopoeia of modern antidiabetic agents

BACKGROUND

The usefulness of metformin as an oral antidiabetic agent is widely accepted. However, several other classes of oral antidiabetic agents have been recently introduced, raising the need to evaluate the role of metformin as initial therapy and in combination with these newer drugs for treatment of type 2 diabetes mellitus (DM).

METHODS

Synthesis of information was preceded by a comprehensive review of the English language literature using Medline. We also reviewed bibliographies of relevant articles. The studies most pertinent to the mechanism of action, efficacy, toxicity and administration of metformin were selected for citation in this review.

RESULTS

Metformin acts by increasing tissue sensitivity to insulin, principally in the liver. Beneficial properties of metformin include weight reduction, favourable effects on the lipid profile and the fibrinolytic pathway, and improvement of ovarian function in some insulin-resistant women. It does not cause hyperinsulinaemia or hypoglycaemia. Metformin is effective as monotherapy and, in combination with both insulin secretagogues and thiazolidinediones (TZDs), may obviate the need for insulin treatment. Several fixed-dose combination pills containing metformin and other agents are available. A protocol for the initiation of therapy with contemporary oral agents for type 2 DM is presented, with emphasis on the continuing central role of metformin.

CONCLUSIONS

Metformin remains a safe and effective agent for the therapy of patients with type 2 DM. It is useful as monotherapy or in combination regimens with the newer insulin secretagogues, TZDs or insulin. It is still in most circumstances the agent of choice for initial therapy of the typical obese patient with type 2 DM and mild to moderate hyperglycaemia.

Clinical pharmacokinetics of metformin

The biguanide metformin (dimethylbiguanide) is an oral antihyperglycaemic agent widely used in the management of non-insulin-dependent diabetes mellitus (NIDDM). Considerable renewal of interest in this drug has been observed in recent years. Metformin can be determined in biological fluids by various methods, mainly using high performance liquid chromatography, which allows pharmacokinetic studies in healthy volunteers and diabetic patients. Metformin disposition is apparently unaffected by the presence of diabetes and only slightly affected by the use of different oral formulations. Metformin has an absolute oral bioavailability of 40 to 60%, and gastrointestinal absorption is apparently complete within 6 hours of ingestion. An inverse relationship was observed between the dose ingested and the relative absorption with therapeutic doses ranging from 0.5 to 1.5 g, suggesting the involvement of an active, saturable absorption process. Metformin is rapidly distributed following absorption and does not bind to plasma proteins. No metabolites or conjugates of metformin have been identified. The absence of liver metabolism clearly differentiates the pharmacokinetics of metformin from that of other biguanides, such as phenformin. Metformin undergoes renal excretion and has a mean plasma elimination half-life after oral administration of between 4.0 and 8.7 hours. This elimination is prolonged in patients with renal impairment and correlates with creatinine clearance. There are only scarce data on the relationship between plasma metformin concentrations and metabolic effects. Therapeutic levels may be 0.5 to 1.0 mg/L in the fasting state and 1 to 2 mg/L after a meal, but monitoring has little clinical value except when lactic acidosis is suspected or present. Indeed, when lactic acidosis occurs in metformin-treated patients, early determination of the metformin plasma concentration appears to be the best criterion for assessing the involvement of the drug in this acute condition. After confirmation of the diagnosis, treatment should rapidly involve forced diuresis or haemodialysis, both of which favour rapid elimination of the drug. Although serious, lactic acidosis due to metformin is rare and may be minimised by strict adherence to prescribing guidelines and contraindications, particularly the presence of renal failure. Finally, only very few drug interactions have been described with metformin in healthy volunteers. Plasma levels may be reduced by guar gum and alpha-glucosidase inhibitors and increased by cimetidine, but no data are yet available in the diabetic population.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.