Folate administration reduces circulating homocysteine levels in NIDDM patients on long-term metformin treatment

Folic acid supplementation on inflammation and homocysteine in type 2 diabetes mellitus: systematic review and meta-analysis of randomized controlled trials

BACKGROUND

The beneficial effects of folate have been observed under different conditions, but the available evidence on inflammation and reduction of cardiovascular disease (CVD) in type 2 diabetes mellitus (T2DM) is limited. The study aimed to explore the effects of folate on inflammation and homocysteine amongst individuals with T2DM.

METHODS

PubMed, Scopus, and Cochrane Library were used to search for evidence. A random-effect model meta-analysis through Review Manager (version 5.4) and metaHun was performed. Results were reported as standardized mean differences (SMD) and 95% confidence intervals graphically using forest and funnel plots.

RESULTS

Data from 9 trials with 426 patients living with T2DM were analyzed. Folic acid supplementation significantly revealed a large effect size on homocysteine levels compared to placebo, SMD = -1.53, 95%CI (-2.14,-0.93), p < 0.05. Additionally, we observed a medium marginal effect size on C-reactive protein (SMD = -0.68, 95%CI (-1.34, -0.01), p = 0.05). However, no significant effect on tumor necrosis factor-α (SMD = -0.86, 95%CI (-2.65, 0.93), p = 0.34), and interleukin-6 (SMD = -0.04, 95%CI (-1.08, 1.01), p = 0.95) was observed.

CONCLUSION

Evidence analyzed in this study suggests that folic acid supplementation in T2DM reduces homocysteine and may mitigate CVDs. However, its effect on inflammation is inconclusive.

One-Carbon Metabolism Nutrients, Genetic Variation, and Diabetes Mellitus

Diabetes mellitus (DM) affects about 9.3% of the population globally. Hyperhomocysteinemia (HHcy) has been implicated in the pathogenesis of DM, owing to its promotion of oxidative stress, β-cell dysfunction, and insulin resistance. HHcy can result from low status of one-carbon metabolism (OCM) nutrients (e.g., folate, choline, betaine, vitamin B6, B12), which work together to degrade homocysteine by methylation. The etiology of HHcy may also involve genetic variation encoding key enzymes in OCM. This review aimed to provide an overview of the existing literature assessing the link between OCM nutrients status, related genetic factors, and incident DM. We also discussed possible mechanisms underlying the role of OCM in DM development and provided recommendations for future research and practice. Even though the available evidence remains inconsistent, some studies support the potential beneficial effects of intakes or blood levels of OCM nutrients on DM development. Moreover, certain variants in OCM-related genes may influence metabolic handling of methyl-donors and presumably incidental DM. Future studies are warranted to establish the causal inference between OCM and DM and examine the interaction of OCM nutrients and genetic factors with DM development, which will inform the personalized recommendations for OCM nutrients intakes on DM prevention.

The efficacy of vitamin B12 supplementation for treating vitamin B12 deficiency and peripheral neuropathy in metformin-treated type 2 diabetes mellitus patients: A systematic review

BACKGROUND AND AIMS

Metformin-treated type 2 diabetes mellitus (T2DM) patients are at higher risk of vitamin B₁₂ deficiency and more severe neuropathy symptoms. There is still no guideline suggesting vitamin B₁₂ supplementation for this population. This study aimed to analyze the efficacy of vitamin B₁₂ supplementation in this population.

METHOD

Studies reporting the efficacy of vitamin B₁₂ supplementation in metformin-treated T2DM patients were systematically searched in PubMed, Cochrane, EBSCOHost, and Scopus following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Additional relevant studies were searched manually through citations. Study quality and risk of bias were assessed using suitable tools.

RESULTS

Seven clinical trials with a total of 506 participants were included. Using the Cochrane's Risk of Bias 2 tools for clinical trials, 4 studies were assessed to have high risk of bias and 3 studies had low risk of bias. There were 5 studies that measured changes in serum vitamin B₁₂ level, all of which reported a statistically significant increase after supplementation. Significant reductions in homocysteine after supplementation were found in 2 studies. Its effect on neuropathy symptoms was still unclear, with 2 studies reporting a significant improvement and 1 study reporting no significant effect.

CONCLUSIONS

The results of this systematic review support the implementation of vitamin B₁₂ supplementation for metformin-treated T2DM to prevent or treat vitamin B₁₂ deficiency and neuropathy. More high-quality clinical studies are required to generate quantitative analysis and to encourage supplementation in available guidelines.

Folic Acid Supplementation Improves Glycemic Control for Diabetes Prevention and Management: A Systematic Review and Dose-Response Meta-Analysis of Randomized Controlled Trials

Background: There is a growing interest in the considerable benefits of dietary supplementations, such as folic acid, on the glycemic profile. We aimed to investigate the effects of folic acid supplementation on glycemic control markers in adults. Methods: Randomized controlled trials examining the effects of folic acid supplementation on glycemic control markers published up to March 2021 were detected by searching online databases, including Scopus, PubMed, Embase, and ISI web of science, using a combination of related keywords. Mean change and standard deviation (SD) of the outcome measures were used to estimate the mean difference between the intervention and control groups at follow-up. Meta-regression and non-linear dose-response analysis were conducted to evaluate the association between pooled effect size and folic acid dosage (mg/day) and duration of the intervention (week). From 1814 detected studies, twenty-four studies reported fasting blood glucose (FBG), fasting insulin, hemoglobin A1C (HbA1C), and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) as an outcome measure. Results: Results revealed significant reductions in FBG (weighted mean difference (WMD): −2.17 mg/dL, 95% CI: −3.69, −0.65, p = 0.005), fasting insulin (WMD: −1.63 pmol/L, 95% CI: −2.53, −0.73, p < 0.001), and HOMA-IR (WMD: −0.40, 95% CI: −0.70, −0.09, p = 0.011) following folic acid supplementation. No significant effect was detected for HbA1C (WMD: −0.27%, 95% CI: −0.73, 0.18, p = 0.246). The dose-response analysis showed that folic acid supplementation significantly changed HOMA-IR (r = −1.30, p-nonlinearity = 0.045) in non-linear fashion. However, meta-regression analysis did not indicate a linear relationship between dose, duration, and absolute changes in FBG, HOMA-IR, and fasting insulin concentrations. Conclusions: Folic acid supplementation significantly reduces some markers of glycemic control in adults. These reductions were small, which may limit clinical applications for adults with type II diabetes. Further research is necessary to confirm our findings.

Beneficial effects of folic acid supplementation on lipid markers in adults: A GRADE-assessed systematic review and dose-response meta-analysis of data from 21,787 participants in 34 randomized controlled trials

Folic acid supplementation has received considerable attention in the literature, yet there is a large discrepancy in its effects on lipid markers in adults. Therefore, this systematic review and meta-analysis of 38 randomized controlled trials (RCTs) evaluated the effects of folic acid supplementation on triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol concentrations in a cohort of 21,787 participants. A systematic search current as of March 2021 was performed in PubMed/Medline, Scopus, Web of Science, and Embase using relevant keywords to identify eligible studies. A fix or random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence intervals (CIs). Thirty-four RCTs were included in this meta-analysis. The pooled analysis revealed that serum TG (WMD: -9.78 mg/dL; 95% CI: -15.5 to -4.00; p = 0.001, I²=0.0%, p = 0.965) and TC (WMD: -3.96 mg/dL; 95% CI: -6.71 to -1.21; p = 0.005, I²=46.9%, p = 0.001) concentrations were significantly reduced following folic acid supplementation compared to placebo. However, folic acid supplementation did not affect serum concentrations of LDL (WMD: -0.97 mg/dL; 95% CI: -6.82 to 4.89; p = 0.746, I²=60.6%, p < 0.001) or HDL cholesterol (WMD: 0.44 mg/dL; 95% CI: -0.53 to 1.41; p = 0.378, I²= 0.0%, p = 0.831). A significant dose-response relationship was observed between the dose of folic acid supplementation and serum concentrations of HDL cholesterols (r = 2.22, p = 0.047). Folic acid supplementation reduced serum concentrations of TG and TC without affecting LDL or HDL cholesterols. Future large RCTs on various populations are needed to show further beneficial effects of folic acid supplementation on lipid profile.

Metformin and Micronutrient Status in Type 2 Diabetes: Does Polypharmacy Involving Acid-Suppressing Medications Affect Vitamin B12 Levels?

Metformin is the first-choice drug in uncomplicated type 2 diabetes (T2DM) and is effective in improving glycaemic control. It is the most widely prescribed oral antidiabetic medicine and has a good safety profile. However, there is an abundance of evidence that metformin use is associated with decreased Vitamin B12 status, though the clinical implications of this in terms of increased risk of diabetic peripheral neuropathy are debated. There is growing evidence that other B vitamins, vitamin D and magnesium may also be impacted by metformin use in addition to alterations to the composition of the microbiome, depending on the dose and duration of therapy. Patients using metformin for prolonged periods may, therefore, need initial screening with intermittent follow-up, particularly since vitamin B₁₂ deficiency has similar symptoms to diabetic neuropathy which itself affects 40-50% of patients with T2DM at some stage. Among patients with T2DM, 40% are reported to experience symptomatic gastroesophageal reflux disease (GORD), of whom 70% use oral antidiabetic medications. The most common medications used to treat GORD are proton pump inhibitors (PPIs) and antagonists of histamine selective H₂ receptors (H₂RAs), both of which independently affect vitamin B₁₂ and magnesium status. Research indicates that co-prescribing metformin with either PPIs or H₂RAs can have further deleterious effects on vitamin B₁₂ status. Vitamin B12 deficiency related to metformin and polypharmacy is likely to contribute to the symptoms of diabetic neuropathy which may frequently be under-recognised. This review explores current knowledge surrounding these issues and suggests treatment strategies such as supplementation.

Effect of folate supplementation on insulin sensitivity and type 2 diabetes: a meta-analysis of randomized controlled trials

Background

Various mechanisms link higher total homocysteine to higher insulin resistance (IR) and risk of type 2 diabetes (T2D). Folate supplementation is recognized as a way to lower homocysteine. However, randomized controlled trials (RCTs) show inconsistent results on IR and T2D outcomes.

Objective

The aim of this study was to examine the effect of folate supplementation on IR and T2D outcomes.

Design

We conducted a systematic literature search in PubMed, Web of Science, and EMBASE and prior systematic reviews and meta-analyses and identified 29 RCTs (22,250 participants) that assessed the effect of placebo-controlled folate supplementation alone or in combination with other B vitamins on fasting glucose, insulin, homeostasis model assessment for insulin resistance (HOMA-IR), glycated hemoglobin (HbA1c), or risk of T2D. The meta-analysis was conducted using both random- and fixed-effects models to calculate weighted mean differences (WMDs) or risk ratios with 95% CIs. Subgroup analyses were conducted based on intervention type (folate alone or in combination with other B vitamins), as well as analysis based on population characteristics, duration, dose, and change in homocysteine.

Results

When compared with placebo, folate supplementation lowered fasting insulin (WMD: -13.47 pmol/L; 95% CI: -21.41, -5.53 pmol/L; P < 0.001) and HOMA-IR (WMD: -0.57 units; 95% CI: -0.76, -0.37 units; P < 0.0001), but no overall effects were observed for fasting glucose or HbA1c. Heterogeneity was low in all meta-analyses, and subgroup analysis showed no signs of effect modification except for change in homocysteine, with the most pronounced effects in trials with a change of >2.5 µmol/L. Changes in homocysteine after folate supplementation correlated with changes in fasting glucose (β = 0.07; 95% CI: 0.01, 0.14; P = 0.025) and HbA1c (β = 0.46; 95% CI: 0.06, 0.85; P = 0.02). Only 2 studies examined folate supplementation on risk of T2D, and they found no change in RR (pooled RR: 0.91; 95% CI: 0.80, 1.04; P = 0.16).

Conclusion

Folate supplementation might be beneficial for glucose homeostasis and lowering IR, but at present there are insufficient data to conclusively determine the effect on development of T2D. This trial was registered on the Prospero database as CRD42016048254.

A Structural Basis for Biguanide Activity

Metformin is the most commonly prescribed treatment for type II diabetes and related disorders; however, molecular insights into its mode(s) of action have been limited by an absence of structural data. Structural considerations along with a growing body of literature demonstrating its effects on one-carbon metabolism suggest the possibility of folate mimicry and anti-folate activity. Motivated by the growing recognition that anti-diabetic biguanides may act directly upon the gut microbiome, we have determined structures of the complexes formed between the anti-diabetic biguanides (phenformin, buformin, and metformin) and Escherichia coli dihydrofolate reductase (ecDHFR) based on nuclear magnetic resonance, crystallographic, and molecular modeling studies. Interligand Overhauser effects indicate that metformin can form ternary complexes with p-aminobenzoyl-l-glutamate (pABG) as well as other ligands that occupy the region of the folate-binding site that interacts with pABG; however, DHFR inhibition is not cooperative. The biguanides competitively inhibit the activity of ecDHFR, with the phenformin inhibition constant being 100-fold lower than that of metformin. This inhibition may be significant at concentrations present in the gut of treated individuals, and inhibition of DHFR in intestinal mucosal cells may also occur if accumulation levels are sufficient. Perturbation of folate homeostasis can alter the pyridine nucleotide redox ratios that are important regulators of cellular metabolism.

Study of Vitamin B12 deficiency and peripheral neuropathy in metformin-treated early Type 2 diabetes mellitus

BACKGROUND

Long-term therapy with metformin was shown to decrease the Vitamin B₁₂ level and manifested as peripheral neuropathy.

AIM

The aim of this study is to define the prevalence of Vitamin B₁₂ deficiency in early Type 2 diabetic patients (duration ≤5 years or drug treatment ≤3 years) and the relationship among metformin exposure and levels of cobalamin (Cbl), folic acid, and homocysteine (Hcy) with severity of peripheral neuropathy.

METHODOLOGY

This is a cross-sectional study involving randomly selected ninety patients (male 56, female 34) between age groups of 35 and 70 years, comparing those who had received >6 months of metformin (Group A) (n = 35) with those without metformin (Group B) (n = 35) and patients taking metformin with other oral hypoglycemic agent (Group C) (n = 20). Comparisons were made clinically, biochemically (serum Cbl, fasting Hcy, and folic acid), and with electrophysiological measures (nerve conduction studies of all four limbs). Comorbidities contributing to neuropathy were excluded from the study.

RESULTS

Group A patients (54.28%) were prone to develop peripheral neuropathy comparing Group B (28.57%) and Group C (35%). There was significantly low plasma level of Cbl in Group A (mean 306.314 pg/ml) than in Group B (mean 627.543 pg/ml) and Group C (mean 419.920 pg/ml). There was insignificant low-level plasma folic acid in Group A (16.47 ng/ml) than in Group B (16.81 ng/ml) and Group C (22.50 ng/ml). There was significantly high level of Hcy in Group A (mean 17.35 µmol/L) and Group C (mean 16.99 µmol/L) than in Group B (mean 13.22 µmol/L). Metformin users even for 2 years showed evidence of neuropathy on nerve conduction velocity though their body mass index and postprandial blood sugar were maintained. There was significant difference in between groups regarding plasma Cbl, folic acid, and Hcy level as significance level <0.05 in all three groups (F [2, 87] = 28.1, P = 0.000), (F [2, 87] = 7.43, P = 0.001), (F [2, 87] = 9.76, P = 0.000). Post hoc study shows significant (P < 0.05) lowering of Cbl and Hcy level in Group A (mean = 306.314, standard deviation [SD] = 176.7) than in Group C (mean = 419.92, SD = 208.23) and Group B (mean = 627.543, SD = 168.33).

DISCUSSION

Even short-term treatment with metformin causes a decrease in serum Cbl folic acid and increase in Hcy, which leads to peripheral neuropathy in Type 2 diabetes patients. A multicenter study with heterogeneous population would have increased the power of the study. We suggest prophylactic Vitamin B₁₂ and folic acid supplementation or periodical assay in metformin user.

Vitamin B12 status of patients treated with metformin: a cross-sectional cohort study

Aim

To assess the vitamin B12 status of patients with type 2diabetes who had been receiving metformin treatment for at least one year.

Methods

Patients with type 2 diabetes attending a diabetes clinic were included in a cross-sectional cohort study. Patients exposed to metformin for more than one year (n=53) were compared with a non-exposed control group (n=31). Serum cobalamin and other variables reflecting vitamin B12 status were measured.

Results

Patients on metformin had lower cobalamin (289±137 vs. 395±162 pmol/L; p<0.01) and holotranscobalamin (76±49 vs. 97±41 pmol/L; p<0.05), and higher HCy (11.3+3.3 vs. 10.3±2.3 µmol/L; p<0.05); these changes were correlated. Eight metformin patients, but no controls, had holotranscobalamin below the normal range (p<0.05). Methylmalonic acid and folate were similar in both groups.

Conclusion Patients exposed to long-term metformin therapy had 26.7% lower cobalamin, 21.6% lower holotranscobalamin and 9.7% higher HCy serum concentrations than control subjects. Such changes indicate a potential risk for development of vitamin B12 deficiency. Our results highlight the necessity of checking B12 status during metformin therapy.

Diabetic neuropathy is not associated with homocysteine, folate, vitamin B12 levels, and MTHFR C677T mutation in type 2 diabetic outpatients taking metformin

BACKGROUND

Hyperhomocysteinemia and vitamin B12 deficiency may be involved in the development of diabetic peripheral neuropathy (DPN). Metformin therapy may reduce vitamin B12 plasma levels, thus contributing to DPN.

AIM AND METHODS

The purposes of this cross-sectional study were to assess (1) the potential associations of DPN with serum levels of homocysteine (tHcy), B-vitamins, and/or the common methylenetetrahydrofolate reductase (MTHFR) C677T mutation; (2) the influence of chronic treatment with metformin on tHcy and B-vitamins concentrations and, finally, (3) to evaluate whether, by this influence, metformin is a risk factor for DPN in a group of type 2 diabetic outpatients.

RESULTS

Our data showed that fasting tHcy, folate, and vitamin B12 levels and the MTHFR C677T genotype distribution were comparable between subjects with (n = 79, 30 %) and without DPN (n = 184, 70 %). Metformin-treated subjects (n = 124, 47 %) showed significantly lower levels of vitamin B12 (P < 0.001), but the prevalence of DPN was not different when compared to those not treated with this drug (33 vs. 27 %, P = NS). At univariate regression analysis, DPN was associated with age, duration of diabetes, HbA1c, creatinine levels, and the presence of coronary heart disease (CHD), and negatively with HDL-C concentrations (P < 0.05 all), but at multivariate regression analysis, high creatinine levels (P = 0.06), low HDL-C levels (P = 0.013), and a higher prevalence of CHD (P = 0.001) were the only variables independently associated with DPN in this population.

CONCLUSIONS

In conclusion, in these type 2 diabetic outpatients circulating levels of tHcy, folate, and the MTHFR C677T mutation are not associated with DPN, which was predicted by creatinine levels, CHD, and dyslipidemia. Metformin therapy is associated with a mild vitamin B12 level reduction, but not with DPN.

Metformin and cancer: Between the bioenergetic disturbances and the antifolate activity

For decades, metformin has been the first-line drug for the treatment of type II diabetes mellitus, and it thus is the most widely prescribed antihyperglycemic drug. Retrospective studies associate the use of metformin with a reduction in cancer incidence and cancer-related death. However, despite extensive research about the molecular effects of metformin in cancer cells, its mode of action remains controversial. In this review, we summarize the current molecular evidence in an effort to elucidate metformin's mode of action against cancer cells. Some authors describe that metformin acts directly on mitochondria, inhibiting complex I and restricting the cell's ability to cope with energetic stress. Furthermore, as the drug interrupts the tricarboxylic acid cycle, metformin-induced alteration of mitochondrial function leads to a compensatory increase in lactate and glycolytic ATP. It has also been reported that cell cycle arrest, autophagy, apoptosis and cell death induction is mediated by the activation of AMPK and Redd1 proteins, thus inhibiting the mTOR pathway. Additionally, unbiased metabolomics studies have provided strong evidence to support that metformin alters the methionine and folate cycles, with a concomitant decrease in nucleotide synthesis. Indeed, purines such as thymidine or hypoxanthine restore the proliferation of tumor cells treated with metformin in vitro. Consequently, some authors prefer to refer to metformin as an "antimetabolite drug" rather than a "mitochondrial toxin". Finally, we also review the current controversy concerning the relationship between the experimental conditions of in vitro-reported effects and the plasma concentrations achieved by chronic treatment with metformin.

Folate status in type 2 diabetic patients with and without retinopathy

Background

Folate deficiency is associated with cardiovascular disease, megaloblastic anemia, and with hyperhomocysteinemia. This study has been undertaken to investigate the role of folate status during the progression of the diabetic retinopathy.

Methods

We measured the plasma levels of homocysteine, folic acid, and red cell folate in 70 diabetic type 2 patients with nonproliferative diabetic retinopathy (NPDR), 65 with proliferative diabetic retinopathy (PDR), 96 without diabetic retinopathy, and 80 healthy subjects used as a control group.

Results

We found higher plasma levels of homocysteine in the NPDR group compared to the control group (P<0.001) and in the PDR group compared to control group (P<0.001) and NPDR group (P<0.01). The severity of diabetic retinopathy was associated with lower folic acid and red cell folate levels, and a significant difference was observed between PDR and NPDR groups (P<0.05).

Conclusion

The folate status could play a role in the development and progression of diabetic retinopathy.

Type 2 diabetes and cardiovascular disease: Have all risk factors the same strength?

Diabetes mellitus is a chronic condition that occurs when the body cannot produce enough or effectively use of insulin. Compared with individuals without diabetes, patients with type 2 diabetes mellitus have a considerably higher risk of cardiovascular morbidity and mortality, and are disproportionately affected by cardiovascular disease. Most of this excess risk is it associated with an augmented prevalence of well-known risk factors such as hypertension, dyslipidaemia and obesity in these patients. However the improved cardiovascular disease in type 2 diabetes mellitus patients can not be attributed solely to the higher prevalence of traditional risk factors. Therefore other non-traditional risk factors may be important in people with type 2 diabetes mellitus. Cardiovascular disease is increased in type 2 diabetes mellitus subjects due to a complex combination of various traditional and non-traditional risk factors that have an important role to play in the beginning and the evolution of atherosclerosis over its long natural history from endothelial function to clinical events. Many of these risk factors could be common history for both diabetes mellitus and cardiovascular disease, reinforcing the postulate that both disorders come independently from “common soil”. The objective of this review is to highlight the weight of traditional and non-traditional risk factors for cardiovascular disease in the setting of type 2 diabetes mellitus and discuss their position in the pathogenesis of the excess cardiovascular disease mortality and morbidity 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.

Vitamin B12 and homocysteine status during pregnancy in the metformin in gestational diabetes trial: responses to maternal metformin compared with insulin treatment

AIM

The aim of the study is to compare the effects of metformin and insulin treatment for gestational diabetes mellitus (GDM) on vitamin B12 and homocysteine (Hcy) status.

METHODS

Women with GDM, who met criteria for insulin treatment, were randomly assigned to metformin (n = 89) or insulin (n = 91) in the Adelaide cohort of the metformin in gestational diabetes (MiG) trial. Fasting serum total vitamin B12 (TB12), holotranscobalamin (HoloTC), a marker of functional B12 status and plasma Hcy concentrations were measured at 20-34 weeks (at randomization) and 36 weeks gestation, then at 6-8 weeks postpartum.

RESULTS

Circulating TB12, HoloTC and Hcy were similar in both treatment groups at each time point. Women who were taking dietary folate supplements at randomization had higher serum TB12 and HoloTC at randomization than those not taking folate. Overall, serum TB12 fell more between randomization and 36 weeks gestation in the metformin group than in the insulin group (metformin: -19.7 ± 4.7 pmol/l, insulin: -6.4 ± 3.6 pmol/l, p = 0.004). The decrease in serum TB12 during treatment was greater with increasing treatment duration in metformin-treated (p < 0.001), but not in insulin-treated women.

CONCLUSIONS

Total, but not bioavailable, vitamin B12 stores were depleted during pregnancy to a greater extent in metformin-treated than in insulin-treated women with GDM, but neither analyte differed between groups at any stage. This adds further evidence supporting metformin as a safe alternative treatment to insulin in GDM. Further investigation is needed to evaluate whether women treated with metformin for longer periods in pregnancy require additional B12 or other supplementation.

Metabolomic fingerprint reveals that metformin impairs one-carbon metabolism in a manner similar to the antifolate class of chemotherapy drugs

Metabolomic fingerprint of breast cancer cells treated with the antidiabetic drug metformin revealed a significant accumulation of 5-formimino-tetrahydrofolate, one of the tetrahydrofolate forms carrying activated one-carbon units that are essential for the de novo synthesis of purines and pyrimidines. De novo synthesis of glutathione, a folate-dependent pathway interconnected with one-carbon metabolism was concomitantly depleted in response to metformin. End-product reversal studies demonstrated that thymidine alone leads to a significant but incomplete protection from metformin's cytostatic effects. The addition of the substrate hypoxanthine for the purine salvage pathway produces major rightward shifts in metformin's growth inhibition curves. Metformin treatment failed to activate the DNA repair protein ATM kinase and the metabolic tumor suppressor AMPK when thymidine and hypoxanthine were present in the extracellular milieu. Our current findings suggest for the first time that metformin can function as an antifolate chemotherapeutic agent that induces the ATM/AMPK tumor suppressor axis secondarily following the alteration of the carbon flow through the folate-related one-carbon metabolic pathways.

Inflammatory-metabolic parameters in obese and nonobese normoandrogenemic polycystic ovary syndrome during metformin and oral contraceptive treatment

Our aim was to evaluate the optimal treatment strategy addressing cardiovascular risk in obese and nonobese patients with polycystic ovary syndrome (PCOS). We planned a prospectıve randomized clinical study. Normoandrogenemic and oligoamenorrheic women with PCOS and impaired glucose tolerance (n = 96) were enrolled in the study. Six months of treatment with metformin HCL or oral contraceptive pills (OCPs) were given to the patients. Group 1 were obese and receiving metformin. Group 2 were obese and receiving OCPs. Group 3 were nonobese and receiving metformin, and Group 4 were nonobese receiving OCPs. ADMA, homocysteine, high sensitive C-reactive protein (hs-CRP) and homeostasis model assessment estimate of insulin resistance (HOMA-IR) were investigated. ADMA, homocysteine, hs-CRP and HOMA-IR were similar in obese and nonobese groups before the treatment. After 6 months of treatment, a significant decrease was observed in ADMA, homocysteine and HOMA-IR levels in Groups 1 and 3. An increase in ADMA and hs-CRP levels was observed in Groups 2 and 4. In this study, metformin treatment leads to improvement in hormonal and metabolic parameters and decreases ADMA and homocysteine levels possibly independent of BMI. However, the use of oral contraceptives in obese and nonobese patients with PCOS with impaired glucose tolerance increases ADMA and hs-CRP levels and creates an increase in the metabolic risk.

Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus

BACKGROUND

Metformin is an oral anti-hyperglycemic agent that has been shown to reduce total mortality compared to other anti-hyperglycemic agents, in the treatment of type 2 diabetes mellitus. Metformin, however, is thought to increase the risk of lactic acidosis, and has been considered to be contraindicated in many chronic hypoxemic conditions that may be associated with lactic acidosis, such as cardiovascular, renal, hepatic and pulmonary disease, and advancing age.

OBJECTIVES

To assess the incidence of fatal and nonfatal lactic acidosis, and to evaluate blood lactate levels, for those on metformin treatment compared to placebo or non-metformin therapies.

SEARCH STRATEGY

A comprehensive search was performed of electronic databases to identify studies of metformin treatment. The search was augmented by scanning references of identified articles, and by contacting principal investigators.

SELECTION CRITERIA

Prospective trials and observational cohort studies in patients with type 2 diabetes of least one month duration were included if they evaluated metformin, alone or in combination with other treatments, compared to placebo or any other glucose-lowering therapy.

DATA COLLECTION AND ANALYSIS

The incidence of fatal and nonfatal lactic acidosis was recorded as cases per patient-years, for metformin treatment and for non-metformin treatments. The upper limit for the true incidence of cases was calculated using Poisson statistics. In a second analysis lactate levels were measured as a net change from baseline or as mean treatment values (basal and stimulated by food or exercise) for treatment and comparison groups. The pooled results were recorded as a weighted mean difference (WMD) in mmol/L, using the fixed-effect model for continuous data.

MAIN RESULTS

Pooled data from 347 comparative trials and cohort studies revealed no cases of fatal or nonfatal lactic acidosis in 70,490 patient-years of metformin use or in 55,451 patients-years in the non-metformin group. Using Poisson statistics the upper limit for the true incidence of lactic acidosis per 100,000 patient-years was 4.3 cases in the metformin group and 5.4 cases in the non-metformin group. There was no difference in lactate levels, either as mean treatment levels or as a net change from baseline, for metformin compared to non-metformin therapies.

AUTHORS' CONCLUSIONS

There is no evidence from prospective comparative trials or from observational cohort studies that metformin is associated with an increased risk of lactic acidosis, or with increased levels of lactate, compared to other anti-hyperglycemic treatments.

Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus

BACKGROUND

Metformin is an oral anti-hyperglycemic agent that has been shown to reduce total mortality compared to other anti-hyperglycemic agents, in the treatment of type 2 diabetes mellitus. Metformin, however, is thought to increase the risk of lactic acidosis, and has been considered to be contraindicated in many chronic hypoxemic conditions that may be associated with lactic acidosis, such as cardiovascular, renal, hepatic and pulmonary disease, and advancing age.

OBJECTIVES

To assess the incidence of fatal and nonfatal lactic acidosis, and to evaluate blood lactate levels, for those on metformin treatment compared to placebo or non-metformin therapies.

SEARCH STRATEGY

A comprehensive search was performed of electronic databases to identify studies of metformin treatment. The search was augmented by scanning references of identified articles, and by contacting principal investigators.

SELECTION CRITERIA

Prospective trials and observational cohort studies in patients with type 2 diabetes of least one month duration were included if they evaluated metformin, alone or in combination with other treatments, compared to placebo or any other glucose-lowering therapy.

DATA COLLECTION AND ANALYSIS

The incidence of fatal and nonfatal lactic acidosis was recorded as cases per patient-years, for metformin treatment and for non-metformin treatments. The upper limit for the true incidence of cases was calculated using Poisson statistics. In a second analysis lactate levels were measured as a net change from baseline or as mean treatment values (basal and stimulated by food or exercise) for treatment and comparison groups. The pooled results were recorded as a weighted mean difference (WMD) in mmol/L, using the fixed-effect model for continuous data.

MAIN RESULTS

Pooled data from 347 comparative trials and cohort studies revealed no cases of fatal or nonfatal lactic acidosis in 70,490 patient-years of metformin use or in 55,451 patients-years in the non-metformin group. Using Poisson statistics the upper limit for the true incidence of lactic acidosis per 100,000 patient-years was 4.3 cases in the metformin group and 5.4 cases in the non-metformin group. There was no difference in lactate levels, either as mean treatment levels or as a net change from baseline, for metformin compared to non-metformin therapies.

AUTHORS' CONCLUSIONS

There is no evidence from prospective comparative trials or from observational cohort studies that metformin is associated with an increased risk of lactic acidosis, or with increased levels of lactate, compared to other anti-hyperglycemic treatments.

Metformin and polycystic ovary syndrome

PURPOSE OF REVIEW

The aim of this article is to describe the role of insulin resistance in the etiology of polycystic ovary syndrome and to review the results of treatment with the insulin sensitizing drug metformin.

RECENT FINDINGS

Polycystic ovary syndrome is a heterogeneous combination of clinical, hormonal, and reproductive abnormalities associated with insulin resistance and increased cardiovascular risk factors. Reduction of hyperinsulinism and improvement of insulin sensitivity with metformin has been reported to ameliorate these abnormalities in many, but not all studies, with few adverse effects.

SUMMARY

Metformin may be the drug of first choice for most, if not all women with polycystic ovarian syndrome, either alone or in combination with other treatments. Further investigation is necessary to determine the optimal dose and duration of treatment necessary to maximize response.

Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus

BACKGROUND

Metformin is an oral anti-hyperglycemic agent used in the treatment of type 2 diabetes mellitus. The results of the UK Prospective Diabetes Study indicate that metformin treatment is associated with a reduction in total mortality compared to other anti-hyperglycemic treatments. Metformin, however, is thought to increase the risk of lactic acidosis, and is considered to be contraindicated in many chronic hypoxemic conditions that may be associated with lactic acidosis, such as cardiovascular, renal, hepatic and pulmonary disease, and advancing age.

OBJECTIVES

To assess the incidence of fatal and nonfatal lactic acidosis with metformin use compared to placebo and other glucose-lowering treatments in patients with type 2 diabetes mellitus. A secondary objective was to evaluate the blood lactate levels for those on metformin treatment compared to placebo or non-metformin therapies.

SEARCH STRATEGY

A search was performed of The Cochrane Library (up to 8/2005), MEDLINE (up to 8/2005), EMBASE (up to 11/2000), OLD MEDLINE, and REACTIONS (up to 8/2005), in order to identify all studies of metformin treatment from 1966 to August 2005. The Cumulated Index Medicus was used to search relevant articles from 1959 to 1965. The search was augmented by scanning references of identified articles, and by contacting principal investigators. Date of latest search: August 2005.

SELECTION CRITERIA

Prospective trials in patients with type 2 diabetes that lasted longer than one month were included if they evaluated metformin, alone or in combination with other treatments, compared to placebo or any other glucose-lowering therapy. Observational cohort studies of metformin treatment lasting greater than one month were also included.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials to be included, assessed study quality and extracted data. The incidence of fatal and nonfatal lactic acidosis was recorded as cases per patient-years, for metformin treatment and for placebo or other treatments. The upper limit for the true incidence of cases in the metformin and non-metformin groups were calculated using Poisson statistics. In a second analysis lactate levels were measured as a net change from baseline or as mean treatment values (basal and stimulated by food or exercise) for treatment and comparison groups. The pooled results were recorded as a weighted mean difference (WMD) in mmol/L, using the fixed effect model for continuous data.

MAIN RESULTS

Pooled data from 206 comparative trials and cohort studies revealed no cases of fatal or nonfatal lactic acidosis in 47,846 patient-years of metformin use or in 38,221 patients-years in the non-metformin group. Using Poisson statistics with 95% confidence intervals the upper limit for the true incidence of metformin-associated lactic acidosis was 6.3 cases per 100,000 patient-years, and the upper limit for the true incidence of lactic acidosis in the non-metformin group was 7.8 cases per 100,000 patient-years. There was no difference in lactate levels, either as mean treatment levels or as a net change from baseline, for metformin compared to placebo or other non-biguanide therapies. The mean lactate levels were slightly lower for metformin treatment compared to phenformin (WMD -0.75 mmol/L, 95% CI -0.86 to -0.15).

AUTHORS' CONCLUSIONS

There is no evidence from prospective comparative trials or from observational cohort studies that metformin is associated with an increased risk of lactic acidosis, or with increased levels of lactate, compared to other anti-hyperglycemic treatments if prescribed under the study conditions.

Insulin-sensitizing antihyperglycemic drugs and mortality after acute myocardial infarction: insights from the National Heart Care Project

OBJECTIVE

Thiazolidinediones (TZDs) and metformin are insulin-sensitizing antihyperglycemic agents with reported benefits on atherosclerosis. Despite extensive use in patients with diabetes and cardiovascular disease, there is a paucity of outcomes data with metformin and none yet with TZDs. We sought to determine the impact of these insulin sensitizers on outcomes in diabetic patients after hospitalization with acute myocardial infarction (AMI).

RESEARCH DESIGN AND METHODS

We conducted a retrospective cohort study of 24,953 Medicare beneficiaries with diabetes discharged after hospitalization with AMI between April 1998 and March 1999 or July 2000 and June 2001. The independent association between discharge prescription for metformin, TZD, or both agents and outcomes at 1 year was assessed in multivariable Cox proportional hazards models, adjusting for patient, physician, and hospital variables. The primary outcome was time to death within 1 year of discharge; secondary outcomes were time to first rehospitalization within 1 year of discharge for AMI, heart failure, and all causes.

RESULTS

There were 8,872 patients discharged on an antihyperglycemic agent, of which 819 were prescribed a TZD, 1,273 metformin, and 139 both drugs. After multivariable analysis, compared with patients prescribed an antihyperglycemic regimen that included no insulin sensitizer, mortality rates were not significantly different in patients treated with either metformin (hazard ratio [HR] 0.92 [95% CI 0.81-1.06]) or a TZD (0.92 [0.80-1.05]) but were lower in those prescribed both drugs (0.52 [0.34-0.82]). The results were similar among patients with heart failure. The prescription of a TZD was associated with a borderline higher risk of all-cause readmission (1.09[1.00-1.20]), predominately due to a higher risk for heart failure readmission (1.17 [1.05-1.30]).

CONCLUSIONS

Individually, prescription of insulin-sensitizing drugs is not associated with a significantly different risk of death in older diabetic patients within 1 year following AMI compared with other antihyperglycemic agents. Combined, however, metformin and TZDs may exert benefit. TZD prescription is associated with a higher risk of readmission for heart failure after myocardial infarction.

Administration of B-group vitamins reduces circulating homocysteine in polycystic ovarian syndrome patients treated with metformin: a randomized trial

BACKGROUND

The aim of the current study was to assess the effects of B-group vitamins and folic acid administration on serum levels of homocysteine (Hcy) in patients with polycystic ovarian syndrome (PCOS) on short-term metformin treatment.

METHODS

Patients were randomly assigned to one of three treatment groups. Group 1 patients (n = 20) received metformin (850 mg twice daily); group 2 patients (n = 20) received metformin (850 mg twice daily) and B-group vitamins (vitamin B1, 250 mg; vitamin B6, 250 mg; vitamin B12, 1000 microg twice daily); and group 3 patients (n = 20) received metformin (850 mg twice daily) and folic acid (174 microg twice daily). In all groups, lipid profiles and plasma total Hcy, vitamin B12, folic acid and glucose levels were recorded at baseline and at 3 months.

RESULTS

A 26.5% increase in Hcy levels was seen after 12 weeks of metformin therapy, while 21.17 and 8.33% decreases in Hcy levels were detected when B-group vitamins or folic acid plus metformin were given respectively. There were no statistically significant differences recorded in insulin sensitivity using homeostasis model assessment in the three groups.

CONCLUSION

These findings suggest that B-group vitamins and folic acid administration counteract the Hcy-increasing effect seen with metformin therapy.

Correlates of total homocysteine plasma concentration in type 2 diabetes

BACKGROUND

Although well-defined in the general population, correlates of total homocysteine (tHcy) plasma concentration have not been sufficiently evaluated in diabetes. We investigated factors potentially associated with tHcy concentration in a cohort of type 2 diabetic subjects.

MATERIALS AND METHODS

The common methylene tetrahydrofolate reductase (MTHFR) C677T polymorphism, fasting tHcy, vitamin B12 and folate plasma levels were assessed in 312 diabetic subjects, whose clinical, metabolic and lifestyle information was also available.

RESULTS

The MTHFR genotype distribution was comparable to the Hardy-Weinberg equilibrium, with an overall TT homozygous frequency of 22%. Fasting tHcy concentration was significantly higher in men than in women (P < 0.001). Multivariate-adjusted tHcy concentration was significantly different across the quartiles of age (P < 0.001), folate (P = 0.01), vitamin B12 (P = 0.03), creatinine concentrations (P = 0.001) and smoking (P = 0.02). Overall, significant trends were noted for creatinine clearance (P for trend = 0.02) and systolic blood pressure (BP) (unadjusted P for trend = 0.01), whereas no differences were noted according to BMI, diastolic BP, presence of hypertension, and diabetes-related variables, such as diabetes duration, fasting glucose and glycated haemoglobin concentrations, current treatment and diabetes long-term complications. Total homocysteine levels significantly correlated with age, systolic BP, vitamin B12, creatinine and creatinine clearance, but only age, creatinine, folate and vitamin B12 levels were independently associated with tHcy concentration in stepwise regression analysis.

CONCLUSIONS

Age, creatinine, folate, vitamin B12, and to a minor extent, sex, smoking, TT genotype and systolic BP were significantly associated with Hcy plasma concentration in type 2 diabetes, whereas no significant associations were noted with diabetes-related variables.

The Role of Antioxidant Micronutrients in the Prevention of Diabetic Complications

Diabetes mellitus is associated with an increased production of reactive oxygen species and a reduction in antioxidant defenses. This leads to oxidative stress, which is partly responsible for diabetic complications. Tight glycemic control is the most effective way of preventing or decreasing these complications. Nevertheless, antioxidant micronutrients can be proposed as adjunctive therapy in patients with diabetes. Indeed, some minerals and vitamins are able to indirectly participate in the reduction of oxidative stress in diabetic patients by improving glycemic control and/or are able to exert antioxidant activity. This article reviews the use of minerals (vanadium, chromium, magnesium, zinc, selenium, copper) and vitamins or cofactors (tocopherol [vitamin E], ascorbic acid [vitamin C], ubidecarenone [ubiquinone; coenzyme Q], nicotinamide, riboflavin, thioctic acid [lipoic acid], flavonoids) in diabetes, with a particular focus on the prevention of diabetic complications. Results show that dietary supplementation with micronutrients may be a complement to classical therapies for preventing and treating diabetic complications. Supplementation is expected to be more effective when a deficiency in these micronutrients exists. Nevertheless, many clinical studies have reported beneficial effects in individuals without deficiencies, although several of these studies were short term and had small sample sizes. However, a randomized, double-blind, placebo-controlled, multicenter trial showed that thioctic acid at an oral dosage of 800 mg/day for 4 months significantly improved cardiac autonomic neuropathy in type 2 diabetic patients. Above all, individuals with diabetes should be educated about the importance of consuming adequate amounts of vitamins and minerals from natural food sources, within the constraints of recommended sugar and carbohydrate intake.

Effects of short-term treatment with metformin on serum concentrations of homocysteine, folate and vitamin B12 in type 2 diabetes mellitus: a randomized, placebo-controlled trial

OBJECTIVE

Metformin is a key treatment option in type 2 diabetes. However, metformin may decrease vitamin B12 levels and increase levels of homocysteine, a cardiovascular risk factor. We investigated whether 16 weeks of treatment with metformin affects serum concentrations of homocysteine, folate and vitamin B12 in subjects with type 2 diabetes treated with insulin.

DESIGN

Placebo-controlled, randomized trial.

MEASUREMENTS

at baseline and 16 weeks later.

SETTING

This trial was conducted in the outpatient clinics of three general hospitals in The Netherlands.

SUBJECTS

A total of 745 patients with type 2 diabetes, treated with insulin and not known with a contraindication for the use of metformin, were approached; 390 gave informed consent and entered the study. Thirty-seven subjects dropped out (12 placebo and 25 metformin users).

INTERVENTION

Addition of metformin or placebo to insulin therapy. PRIMARY OUTCOME PARAMETERS: Serum homocysteine, folate, vitamin B12, indices of glycaemic control and body weight.

RESULTS

Amongst those who completed 16 weeks of treatment, metformin use, as compared with placebo, was associated with an increase in homocysteine of 4% (0.2 to 8; P=0.039) and with decreases in folate [-7% (-1.4 to -13); P=0.024] and vitamin B12 [-14% (-4.2 to -24); P<0.0001]. In addition, the increase in homocysteine could be explained by the decreases in folate and vitamin B12.

CONCLUSION

In patients with type 2 diabetes, 16 weeks of treatment with metformin reduces levels of folate and vitamin B12, which results in a modest increase in homocysteine. The clinical significance of these findings remains to be investigated.

Comparison between repaglinide and glimepiride in patients with type 2 diabetes mellitus: a one-year, randomized, double-blind assessment of metabolic parameters and cardiovascular risk factors

BACKGROUND

Repaglinide and glimepiride are relatively new oral hypoglycemic agents. Few data are available concerning their effects on metabolic parameters other than measures of glycemic control.

OBJECTIVES

In addition to assessing the effects of repaglinide and glimepiride on glycemic control in patients with type 2 diabetes mellitus, this study also examined the effects of these agents on 3 metabolic parameters known to be cardiovascular risk factors--lipoprotein(a) (Lp[a]), plasminogen activator inhibitor-1 (PAI-1), and homocysteine (Hcy).

METHODS

This randomized, placebo-controlled, double-blind trial was conducted at a single center in Italy. Eligible patients were nonsmokers; had no hypertension or coronary heart disease; were taking no hypolipidemic drugs, diuretics, beta-blockers, or thyroxin; and had normal renal function. After an initial 4-week placebo washout period, patients were randomized to receive repaglinide 1 mg/d or glimepiride 1 mg/d. The dose of study drug was optimized over an 8-week titration period, which was followed by a 12-month treatment period. Measures of glycemic control (glycated hemoglobin [HbA1c], fasting plasma glucose [FPG], postprandial plasma glucose [PPG], fasting plasma insulin [FPI], postprandial plasma insulin [PPI]) and the other metabolic parameters of interest were assessed after 6 and 12 months of treatment.

RESULTS

One hundred twenty-four patients (63 women, 61 men) completed the study, 62 in each treatment group. There were no significant differences in demographic characteristics between groups. After 6 and 12 months of treatment, FPG levels and HbA1c values were significantly reduced from baseline in both groups (6 months, P < 0.05; 12 months, P < 0.01). After 6 months, PPG levels were significantly decreased only in the repaglinide group (P < 0.05 vs baseline); at 12 months, however, PPG levels were significantly reduced from baseline in both groups (P < 0.01 repaglinide, P < 0.05 glimepiride). No significant changes from baseline in FPI or PPI levels were seen in either group at 6 months, although FPI levels were significantly increased in the repaglinide group at 12 months (P < 0.05). Repaglinide significantly lowered levels of Lp(a), PAI-1, and Hcy after 12 months (all, P < 0.05 vs baseline). Glimepiride significantly lowered levels of Lp(a) and Hcy after 6 months (both, P < 0.05 vs baseline) and levels of Lp(a) (P < 0.01 vs baseline), Hcy (P < 0.01 vs baseline), and PAI-1 (P < 0.05 vs baseline) after 12 months.

CONCLUSIONS

Repaglinide and glimepiride improved glycemic control and reduced levels of other metabolic parameters of interest in this population of patients with type 2 diabetes. It is possible that the reductions in Lp(a), PAI-1, and Hcy were the result of improved glucose metabolism; however, the possibility that repaglinide and glimepiride may have a direct effect on these parameters should not be excluded.

Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus

BACKGROUND

Metformin is an oral anti-hyperglycemic agent used in the treatment of type 2 diabetes mellitus. The results of the UK Prospective Diabetes Study indicate that metformin treatment is associated with a reduction in total mortality compared to other anti-hyperglycemic treatments. Metformin, however, is thought to increase the risk of lactic acidosis, and is considered to be contraindicated in many chronic hypoxemic conditions that may be associated with lactic acidosis, such as cardiovascular, renal, hepatic and pulmonary disease, and advancing age.

OBJECTIVES

To assess the incidence of fatal and nonfatal lactic acidosis with metformin use compared to placebo and other glucose-lowering treatments in patients with type 2 diabetes mellitus. A secondary objective was to evaluate the blood lactate levels for those on metformin treatment compared to placebo or non-metformin therapies.

SEARCH STRATEGY

A search was performed of the Cochrane Controlled Trials Register and the Database of Abstracts of Reviews of Effectiveness (up to 4/2000), Medline (up to 11/2000), Embase (up to 11/2000), Oldmedline, and Reactions (up to 5/2000), in order to identify all studies of metformin treatment from 1966 to November 2000. The Cumulated Index Medicus was used to search relevant articles from 1959 to 1965. The search was augmented by scanning references of identified articles, and by contacting principal investigators. Date of latest search: November 2000.

SELECTION CRITERIA

Prospective trials in patients with type 2 diabetes that lasted longer than one month were included if they evaluated metformin, alone or in combination with other treatments, compared to placebo or any other glucose-lowering therapy. Observational cohort studies of metformin treatment lasting greater than one month were also included.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials to be included, assessed study quality and extracted data. The incidence of fatal and nonfatal lactic acidosis was recorded as cases per patient-years, for metformin treatment and for placebo or other treatments. The upper limit for the true incidence of cases in the metformin and non-metformin groups were calculated using Poisson statistics. In a second analysis lactate levels were measured as a net change from baseline or as mean treatment values (basal and stimulated by food or exercise) for treatment and comparison groups. The pooled results were recorded as a weighted mean difference (WMD) in mmol/L, using the fixed effects model for continuous data.

MAIN RESULTS

Pooled data from 176 comparative trials and cohort studies revealed no cases of fatal or nonfatal lactic acidosis in 35,619 patient-years of metformin use or in 30,002 patients-years in the non-metformin group. Using Poisson statistics with 95% confidence intervals the upper limit for the true incidence of metformin-associated lactic acidosis was 8.4 cases per 100,000 patient-years, and the upper limit for the true incidence of lactic acidosis in the non-metformin group was 9 cases per 100,000 patient-years. There was no difference in lactate levels, either as mean treatment levels or as a net change from baseline, for metformin compared to placebo or other non-biguanide therapies. The mean lactate levels were slightly lower for metformin treatment compared to phenformin (WMD -0.75 mmol/L, 95% CI -0.86 to -0.15).

REVIEWER'S CONCLUSIONS

There is no evidence from prospective comparative trials or from observational cohort studies that metformin is associated with an increased risk of lactic acidosis, or with increased levels of lactate, compared to other anti-hyperglycemic treatments if prescribed under the study conditions, taking into account contra-indications.

Combination of insulin and metformin in the treatment of type 2 diabetes

OBJECTIVE

To investigate the metabolic effects of metformin, as compared with placebo, in type 2 diabetic patients intensively treated with insulin.

RESEARCH DESIGN AND METHODS

Metformin improves glycemic control in poorly controlled type 2 diabetic patients. Its effect in type 2 diabetic patients who are intensively treated with insulin has not been studied. A total of 390 patients whose type 2 diabetes was controlled with insulin therapy completed a randomized controlled double-blind trial with a planned interim analysis after 16 weeks of treatment. The subjects were selected from three outpatient clinics in regional hospitals and were randomly assigned to either the placebo or metformin group, in addition to insulin therapy. Intensive glucose monitoring with immediate insulin adjustments according to strict guidelines was conducted. Indexes of glycemic control, insulin requirements, body weight, blood pressure, plasma lipids, hypoglycemic events, and other adverse events were measured.

RESULTS

Of the 390 subjects, 37 dropped out (12 in the placebo and 25 in the metformin group). Of those who completed 16 weeks of treatment, metformin use, as compared with placebo, was associated with improved glycemic control (mean daily glucose at 16 weeks 7.8 vs. 8.8 mmol/l, P = 0.006; mean GHb 6.9 vs. 7.6%, P < 0.0001); reduced insulin requirements (63.8 vs. 71.3 IU, P < 0.0001); reduced weight gain (-0.4 vs. +1.2 kg, P < 0.01); and decreased plasma LDL cholesterol (-0.21 vs. -0.02 mmol/l, P < 0.01). Risk of hypoglycemia was similar in both groups. CONCLUSIONS-In type 2 diabetic patients who are intensively treated with insulin, the combination of insulin and metformin results in superior glycemic control compared with insulin therapy alone, while insulin requirements and weight gain are less.

Circadian rhythm of serum total homocysteine in men

Serum homocysteine levels were examined in a 24-hour study of 7 healthy and 5 diabetic men, revealing a statistically significant circadian rhythm (p = 0.030), normal concentrations of 11.83 +/- 1.2 vs 12.99 +/- 1.2 micromol/L, with peak values occurring during the evening (10:37 P.M.) and lowest levels occurring during the morning. These findings imply that increased atherosclerotic risk in insulin-resistant diabetics during morning hours does not appear to be explained by differences in homocysteine levels in the normal population.

[Lowering high levels of fasting total homocysteine with folic acid and vitamins B in patients with venous thromboembolism: relationship between response and the C677T methylenetetrahydrofolate reductase (MTHRF) genotype]

BACKGROUND

High levels of plasma total homocysteine (tHcy) are involved in arterial or venous occlusive diseases. It essentially depends on the nutritional status of folic acid (FA) and vitamins B12 or B6, but also on the methylenetetrahydrofolate reductase (MTHFR) enzymatic activity. We aim to evaluate the response of the hyperhomocysteinemia (HHcy) to a standard schedule of vitamin supplementation, according with the MTHFR genotype.

PATIENTS AND METHODS

227 patients, diagnosed with venous thromboembolism (VTE) were analysed for tHcy (in fasting conditions), and for the MTHFR-C677T gene polymorphism. When the tHcy exceeded the cut-off point (men = 16, women = 15 mumol/l), the patients were supplemented with a dose equivalent to 1 mg FA, 0.2 mg B12 and 100 mg of B6, daily by 6 weeks. Afterwards they were reanalysed and the reduction was stratified by MTHFR genotype, looking for any difference in the response.

RESULTS

The mean fasting tHcy was 12.3 mumol/l (SD = 8). The 51 hyperhomocysteinemic patients (22%) were older (65.1 y) than the normal ones (55.0 y) (p = 0.0001). The treatment was carried out properly in 46 patients (90%). The pre-treatment mean Hcy was 23.2 (SD = 10.5) mumol/l, and it was reduced to 13.0 (SD = 5.9) (p = 0.0001) (mean reduction = 42.1%). By genotype, the C/C reduced from 21.0 to 13.2 mumol/l (37%) (n = 18), the C/T from 25.0 to 12.6 mumol/l (46%) (n = 24), and the abnormal homozygotes T/T from 22.7 to 14.5 mumol/l (39%) (n = 4), although no statistical significant differences were found. In 80% of cases (37/46), tHcy values normalised. A negative correlation (r = -0.471) (p = 0.005) was observed between age and response.

CONCLUSIONS

The FA/B6/B12 based therapy reduces in a simple, quick and effective way (> 40% in 6 weeks) the pathologic tHcy levels on a VTE population and this is not influenced by the MTHFR genotype. As HHcy seems related with recurrences of venous thrombosis, we could speculate if it would be useful to analyse routinely the tHcy, attempting reduction in selected cases.