Effects of metformin or rosiglitazone on serum concentrations of homocysteine, folate, and vitamin B12 in patients with type 2 diabetes mellitus

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.

Biomarkers in Diabetic Retinopathy

There is a global diabetes epidemic correlating with an increase in obesity. This coincidence may lead to a rise in the prevalence of type 2 diabetes. There is also an as yet unexplained increase in the incidence of type 1 diabetes, which is not related to adiposity. Whilst improved diabetes care has substantially improved diabetes outcomes, the disease remains a common cause of working age adult-onset blindness. Diabetic retinopathy is the most frequently occurring complication of diabetes; it is greatly feared by many diabetes patients. There are multiple risk factors and markers for the onset and progression of diabetic retinopathy, yet residual risk remains. Screening for diabetic retinopathy is recommended to facilitate early detection and treatment. Common biomarkers of diabetic retinopathy and its risk in clinical practice today relate to the visualization of the retinal vasculature and measures of glycemia, lipids, blood pressure, body weight, smoking, and pregnancy status. Greater knowledge of novel biomarkers and mediators of diabetic retinopathy, such as those related to inflammation and angiogenesis, has contributed to the development of additional therapeutics, in particular for late-stage retinopathy, including intra-ocular corticosteroids and intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') agents. Unfortunately, in spite of a range of treatments (including laser photocoagulation, intraocular steroids, and anti-VEGF agents, and more recently oral fenofibrate, a PPAR-alpha agonist lipid-lowering drug), many patients with diabetic retinopathy do not respond well to current therapeutics. Therefore, more effective treatments for diabetic retinopathy are necessary. New analytical techniques, in particular those related to molecular markers, are accelerating progress in diabetic retinopathy research. Given the increasing incidence and prevalence of diabetes, and the limited capacity of healthcare systems to screen and treat diabetic retinopathy, there is need to reliably identify and triage people with diabetes. Biomarkers may facilitate a better understanding of diabetic retinopathy, and contribute to the development of novel treatments and new clinical strategies to prevent vision loss in people with diabetes. This article reviews key aspects related to biomarker research, and focuses on some specific biomarkers relevant to diabetic retinopathy.

Associations between medication use and homocysteine levels in an older population, and potential mediation by vitamin B12 and folate: data from the B-PROOF Study

BACKGROUND

Elevated homocysteine levels are a risk indicator for cardiovascular disease, fractures and cognitive decline. Previous studies indicated associations between homocysteine levels and medication use, including antihypertensive, lipid-lowering and antidiabetic medication. However, results were often contradictory and inconclusive. Our objective was to study the associations established previously in more detail by sub-classifying medication groups, and investigate the potential mediating role of vitamin B12 and folate status.

MATERIALS AND METHODS

Baseline data from the B-PROOF (B-vitamins for the PRevention Of Osteoporotic Fractures) study were used. We included 2,912 participants aged ≥65 years, with homocysteine levels of 12-50 μmol/L and creatinine levels ≤150 μmol/L, for whom self-reported medication data were available. We used multivariable linear regression models and analysis of covariance to assess the association between medication use and plasma homocysteine levels, and the potential mediation by serum vitamin B12 and folate.

RESULTS

The mean age was 74 years (standard deviation, 6.5), 50 % were women, and median homocysteine levels were 14 µmol/L [interquartile range, 13-17 µmol/L]. Higher mean homocysteine levels were observed in users vs. non-users for diuretics (15.2 vs. 14.9, p = 0.043), high-ceiling sulphonamide diuretics (16.0 vs. 14.9, p < 0.001), medication acting via the renin-angiotensin system (15.2 vs. 14.9, p = 0.029) and metformin (15.6 vs. 15.1, p = 0.006). Non-selective β-blocker use was associated with lower mean homocysteine levels (14.4 vs. 15.0, p = 0.019). Only this association was mediated by an underlying association with vitamin B12 and folate levels.

CONCLUSION

The associations between homocysteine levels and medication use appear to be fairly modest. Our results suggest that medication use is unlikely to contribute to clinically relevant changes in plasma homocysteine levels.

The role of metformin on vitamin B12 deficiency: a meta-analysis review

Metformin is the only biguanide oral hypoglycemic drug, that is used to treat patients with type-2 diabetes mellitus. There are some reports of metformin being associated with decreased serum levels of vitamin B12 (VB12). The objective of this study is to systematically analyze the impact of metformin on the frequency of VB12 deficiency and serum levels of VB12. A search of various databases provided 18 retrospective cohort studies and 11 randomized controlled trials. Pooled estimates of odds ratio with 95% confidence interval using random effect model were conducted. Studies were examined for heterogeneity, publication bias and sensitivity analysis. Separate analysis of randomized control trials (RCTs) including both low-risk and high-risk bias was also conducted. 29 studies were selected with a total of 8,089 patients. 19 studies were rated intermediate or high quality. Primary outcome suggested increased incidence of VB12 deficiency in metformin group (OR = 2.45, 95% CI 1.74-3.44, P < 0.0001.) Heterogeneity was relatively high (I(2) = 53%), with minor publication bias. Secondary outcome suggested lower serum VB12 concentrations in metformin group (Mean difference = -65.8, 95% CI -78.1 to -53.6 pmol/L, P < 0.00001) with high heterogeneity (I(2) = 98%,) and low publication bias. RCTs analysis of low-and high-risk group revealed similar trends. We conclude that metformin treatment is significantly associated with an increase in incidence of VB12 deficiency and reduced serum VB12 levels.

Higher prevalence of metformin-induced vitamin B12 deficiency in sulfonylurea combination compared with insulin combination in patients with type 2 diabetes: a cross-sectional study

Long-term and high-dose treatment with metformin is known to be associated with vitamin B₁₂ deficiency in patients with type 2 diabetes. We investigated whether the prevalence of B₁₂ deficiency was different in patients treated with different combination of hypoglycemic agents with metformin during the same time period. A total of 394 patients with type 2 diabetes treated with metformin and sulfonylurea (S+M group, n = 299) or metformin and insulin (I+M group, n = 95) were consecutively recruited. The vitamin B₁₂ and folate levels were quantified using the chemiluminescent enzyme immunoassay. Vitamin B₁₂ deficiency was defined as vitamin B₁₂≤300 pg/mL without folate deficiency (folate>4 ng/mL). The mean age of and duration of diabetes in the subjects were 59.4±10.5 years and 12.2±6.7 years, respectively. The mean vitamin B₁₂ level of the total population was 638.0±279.6 pg/mL. The mean serum B₁₂ levels were significantly lower in the S+M group compared with the I+M group (600.0±266.5 vs. 757.7±287.6 pg/mL, P<0.001). The prevalence of vitamin B₁₂ deficiency in the metformin-treated patients was significantly higher in the S+M group compared with the I+M group (17.4% vs. 4.2%, P = 0.001). After adjustment for various factors, such as age, sex, diabetic duration, duration or daily dose of metformin, diabetic complications, and presence of anemia, sulfonylurea use was a significant independent risk factor for B₁₂ deficiency (OR = 4.74, 95% CI 1.41–15.99, P = 0.012). In conclusion, our study demonstrated that patients with type 2 diabetes who were treated with metformin combined with sulfonylurea require clinical attention for vitamin B₁₂ deficiency and regular monitoring of their vitamin B₁₂ levels.

Vitamin B12 deficiency is associated with adverse lipid profile in Europeans and Indians with type 2 diabetes

Background

Metformin, a standard therapy in type 2 diabetes, reduces vitamin B12 levels. Studies linking low vitamin B12 levels and cardiovascular disease are equivocal and suggest improving B12 levels may help in primary prevention. The role of vitamin B12 deficiency on cardiovascular risk factors, especially in type 2 diabetes has not been explored. The aim of this study is to investigate whether vitamin B12 deficiency in type 2 diabetes patients is associated with cardiovascular risk factors in two different ethnic groups in UK and India.

Methods

Type 2 diabetes patients from two secondary care diabetic centres (Europeans - UK and Indians - India) were studied. Serum vitamin B12, folate and biochemical parameters were measured.

Results

The prevalence rates of vitamin B12 deficiency (<191 ng/L) were 27% and 12% in Europeans and Indians, respectively and higher in metformin treated type 2 diabetes patients. In linear regression analysis, after adjusting for all likely confounding factors, vitamin B12 independently associated with triglycerides in both the populations and cholesterol/HDL ratio in Indians. Logistic regression showed type 2 diabetes patients with vitamin B12 deficiency were at significantly higher odds of having coexisting coronary artery disease (CAD) in Europeans with similar but non-significant trend in Indians, after adjusting for all likely confounding factors.

Conclusions

The prevalence of vitamin B12 deficiency is common in type 2 diabetes patients and is associated with adverse lipid parameters. Type 2 diabetes management guidelines should include the recommendation for regular testing for B12 levels, especially for those on metformin.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-014-0129-4) contains supplementary material, which is available to authorized users.

Effect of Diabetes Mellitus and Its Control on Myocardial Contractile Function in Rats

AIM: This work was done to study the effect of both types of diabetes mellitus (DM) on myocardial contractility in rats. Also, we investigated the role of treatment of DM with insulin and rosiglitazone (used as treatment for type 1 and type 2 DM respectively) in improvement of myocardial dysfunction in diabetic rats.METHODS: The study included 50 male Wistar albino rats, divided into 5 groups: control (group I), streptozotocin induced type 1 DM (group II), fructose induced type 2 DM (group III), insulin treated type 1 diabetic rats (group IV) and rosiglitazone treated type 2 diabetic rats (group V). At the end of the study, retro-orbital blood samples were withdrawn and blood glucose, plasma triglyceride (TG), total cholesterol (TC) and thyroid hormones levels were measured. Rats were then anesthetized and their hearts were excised and connected to Langendorff apparatus to perform mechanical cardiac performance tests including heart rate (HR), left ventricular developed pressure (LVDP) and maximum rate of pressure rise (+dp/dt).RESULTS: Data of the study showed that relative to control group, there was significant increase in blood glucose, plasma TG and TC levels while, thyroid hormones and myocardial performance parameters showed significant decrease in both type 1 and type 2 diabetic rats. Treatment of type 1 diabetic rats with insulin and type 2 with rosiglitazone resulted in significant decrease in blood glucose, plasma TG and TC levels associated with significant improvement in thyroid hormones and myocardial performance parameters. The results also showed that insulin treatment of type 1 was more effective in ameliorating all parameters than treatment of type 2 by rosiglitazone.CONCLUSION: We concluded that the induction of both types of diabetes resulted in decreased myocardial performance parameters. The  treatment of type 1 and type 2 diabetes by insulin and oral rosiglitazone respectively improved to a great extent the altered metabolism and  mechanical myocardial parameters, with more improving effect of  insulin in type 1 than rosiglitazone in type 2 DM.

Microbiota and diabetes: an evolving relationship

The gut microbiota affects numerous biological functions throughout the body and its characterisation has become a major research area in biomedicine. Recent studies have suggested that gut bacteria play a fundamental role in diseases such as obesity, diabetes and cardiovascular disease. Data are accumulating in animal models and humans suggesting that obesity and type 2 diabetes (T2D) are associated with a profound dysbiosis. First human metagenome-wide association studies demonstrated highly significant correlations of specific intestinal bacteria, certain bacterial genes and respective metabolic pathways with T2D. Importantly, especially butyrate-producing bacteria such as Roseburia intestinalis and Faecalibacterium prausnitzii concentrations were lower in T2D subjects. This supports the increasing evidence, that butyrate and other short-chain fatty acids are able to exert profound immunometabolic effects. Endotoxaemia, most likely gut-derived has also been observed in patients with metabolic syndrome and T2D and might play a key role in metabolic inflammation. A further hint towards an association between microbiota and T2D has been derived from studies in pregnancy showing that major gut microbial shifts occurring during pregnancy affect host metabolism. Interestingly, certain antidiabetic drugs such as metformin also interfere with the intestinal microbiota. Specific members of the microbiota such as Akkermansia muciniphila might be decreased in diabetes and when administered to murines exerted antidiabetic effects. Therefore, as a 'gut signature' becomes more evident in T2D, a better understanding of the role of the microbiota in diabetes might provide new aspects regarding its pathophysiological relevance and pave the way for new therapeutic principles.

Metformin and phenformin deplete tricarboxylic acid cycle and glycolytic intermediates during cell transformation and NTPs in cancer stem cells

Metformin, a first-line diabetes drug linked to cancer prevention in retrospective clinical analyses, inhibits cellular transformation and selectively kills breast cancer stem cells (CSCs). Although a few metabolic effects of metformin and the related biguanide phenformin have been investigated in established cancer cell lines, the global metabolic impact of biguanides during the process of neoplastic transformation and in CSCs is unknown. Here, we use LC/MS/MS metabolomics (>200 metabolites) to assess metabolic changes induced by metformin and phenformin in an Src-inducible model of cellular transformation and in mammosphere-derived breast CSCs. Although phenformin is the more potent biguanide in both systems, the metabolic profiles of these drugs are remarkably similar, although not identical. During the process of cellular transformation, biguanide treatment prevents the boost in glycolytic intermediates at a specific stage of the pathway and coordinately decreases tricarboxylic acid (TCA) cycle intermediates. In contrast, in breast CSCs, biguanides have a modest effect on glycolytic and TCA cycle intermediates, but they strongly deplete nucleotide triphosphates and may impede nucleotide synthesis. These metabolic profiles are consistent with the idea that biguanides inhibit mitochondrial complex 1, but they indicate that their metabolic effects differ depending on the stage of cellular transformation.

Vitamin B12 status in metformin treated patients: systematic review

OBJECTIVE

Randomized controlled trials and observational studies have yielded inconsistent results on the effects of metformin on vitamin B12 reduction. We therefore performed a systematic review to analyze the effects of metformin on vitamin B12 concentration.

METHODS

PubMed, Medline, Embase, and the Cochrane central registry of controlled trials were searched to identify randomized controlled trials and observational studies exploring the association between metformin and vitamin B12 concentration in patients with type 2 diabetes mellitus or polycystic ovary syndrome. The main outcome measure was changes in serum vitamin B12 concentration after 6-208 weeks of treatment with metformin, as compared with placebo or other anti-hyperglycemic therapy.

RESULTS

Six randomized controlled trials met the inclusion criteria. Serum vitamin B12 concentrations were significantly lower in patients treated with metformin than in those who received placebo or rosiglitazone (mean difference [MD], -53.93 pmol/L; 95% confidence interval [CI], -81.44 to -26.42 pmol/L, P = 0.0001). Subgroup analysis identified four trials in which patients received a lower dose of metformin (<2000 mg/d) and two in which they received a higher dose (≥2000 mg/d), with MDs in vitamin B12 concentration after metformin treatment of -37.99 pmol/L (95% CI, -57.44 to -18.54 pmol/L, P = 0.0001) and -78.62 pmol/L (95% CI, -106.37 to -50.86 pmol/L, P<0.00001), respectively.

CONCLUSIONS

The reduction of vitamin B12 may be induced by metformin in a dose dependent manner.

Neuroenhancement with vitamin B12-underestimated neurological significance

Vitamin B12 is a cofactor of methionine synthase in the synthesis of methionine, the precursor of the universal methyl donor S-Adenosylmethionine (SAMe), which is involved in different epigenomic regulatory mechanisms and especially in brain development. A Vitamin B12 deficiency expresses itself by a wide variety of neurological manifestations such as paraesthesias, skin numbness, coordination disorders and reduced nerve conduction velocity. In elderly people, a latent Vitamin B12 deficiency can be associated with a progressive brain atrophy. Moderately elevated concentrations of homocysteine (>10 µmol/L) have been associated with an increased risk of dementia, notably Alzheimer's disease, in many cross-sectional and prospective studies. Raised plasma concentrations of homocysteine is also associated with both regional and whole brain atrophy, not only in Alzheimer's disease but also in healthy elderly people. Clinician awareness should be raised to accurately diagnose and treat early Vitamin B12 deficiency to prevent irreversible structural brain damage.

Higher homocysteine and lower betaine increase the risk of microangiopathy in patients with diabetes mellitus carrying the GG genotype of PEMT G774C

BACKGROUND

Diabetes represents one of the greatest medical and socioeconomic threats worldwide. The pathogenesis involved is complicated. The effect of methyl donors and genetic polymorphisms in metabolic enzymes on the risk of microangiopathy in patients with diabetes is not well understood. This study investigates the association of homocysteine, choline and betaine levels and phosphatidylethanolamine N-methyltransferase (PEMT) G774C (rs12325817) genotypes with the risk of diabetes and its related microangiopathic complications.

METHODS

Between January 2009 and June 2010, 184 diabetic patients and 188 non-diabetic control subjects were enrolled in the hospital-based case-control study. Serum concentrations of betaine and choline were determined by high-performance liquid chromatography (HPLC)-mass spectrometry. Serum concentrations of homocysteine were assayed using HPLC. PEMT gene mutations were detected by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

After adjustment for potential confounders, serum total homocysteine had a significant dose-dependent positive association, and serum choline had an inverse association with the risks of diabetes and its microangiopathic complications (both p < 0.001). Although serum betaine was not associated with the risk of diabetes, it had a significant inverse association with diabetic microangiopathy. Compared with GG genotype, the CC genotype of PEMT G774C was associated with a decreased risk of diabetes (OR 0.559, 95% CI 0.338, 0.926) and its microangiopathy (OR 0.452, 95% CI 0.218, 0.937).

CONCLUSION

The GG genotype of the PEMT G774C polymorphism, higher levels of serum homocysteine and lower levels of serum betaine are associated with an increased risk of microangiopathy in patients with diabetes.

Worms need microbes too: microbiota, health and aging in Caenorhabditis elegans

Many animal species live in close association with commensal and symbiotic microbes (microbiota). Recent studies have revealed that the status of gastrointestinal tract microbiota can influence nutrition-related syndromes such as obesity and type-2 diabetes, and perhaps aging. These morbidities have a profound impact in terms of individual suffering, and are an increasing economic burden to modern societies. Several theories have been proposed for the influence of microbiota on host metabolism, but these largely remain to be proven. In this article we discuss how microbiota may be manipulated (via pharmacology, diet, or gene manipulation) in order to alter metabolism, immunity, health and aging in the host. The nematode Caenorhabditis elegans in combination with one microbial species is an excellent, defined model system to investigate the mechanisms of host–microbiota interactions, particularly given the combined power of worm and microbial genetics. We also discuss the multifaceted nature of the worm–microbe relationship, which likely encompasses predation, commensalism, pathogenicity and necromeny.

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.

Effects of rosiglitazone on serum paraoxonase activity and metabolic parameters in patients with type 2 diabetes mellitus

Human serum paraoxonase contributes to the anti-atherogenic effect of high-density lipoprotein cholesterol (HDL-C) and has been shown to protect both low-density lipoprotein cholesterol (LDL-C) and HDL-C against lipid peroxidation. We investigated the effects of rosiglitazone on paraoxonase activity and metabolic parameters in patients with type 2 diabetes mellitus [50 patients (30 males, 20 females); mean±SD age: 58.7±9.2 years, body mass index: 28.2±4.1'kg/m²], in whom glucose control could not be achieved despite treatment with metformin, sulphonylurea, and/or insulin. The patients were given 4'mg/day rosiglitazone for 3 months in addition to their usual treatment. Serum paraoxonase activity, malondialdehyde, homocysteine, and lipid profile were measured at the time of initiation and at the end of therapy with rosiglitazone. After rosiglitazone therapy, serum levels of HDL-C, apolipoprotein A-1, and paraoxonase activity increased significantly (P<0.05) and malondialdehyde, homocysteine, lipoprotein(a), and glucose levels decreased significantly (P<0.05), but no significant changes in levels of total cholesterol and apolipoprotein B were observed. Triglyceride levels also increased significantly (P<0.05). Rosiglitazone treatment led to an improvement in glycemic control and to an increase in paraoxonase activity and HDL-C levels. Although rosiglitazone showed favorable effects on oxidant/antioxidant balance and lipid profile, further studies are needed to determine the effect of rosiglitazone on cardiovascular risk factors and cardiovascular morbidity and mortality.

Adverse effect of metformin therapy on serum vitamin B12 and folate: short-term treatment causes disadvantages?

Diabetes is a global public health challenge that imposes heavy burdens on communities and individuals. Metformin, the first-line medication for diabetes, has the superiority of reducing risk of macrovascular diseases, all-cause mortality and even possibly cancers. Recent observational studies, however, have demonstrated that long-term metformin therapy increases the probability of vitamin B12 and folate deficiency, and might contribute to the progression of diabetic peripheral neuropathy. Despite metformin is widely used and extensively studied, randomized controlled trials performed to explore the effects of metformin on vitamin B12 and folate are limited. Besides, whether short-term treatment causes vitamin deficiency is a pending issue. We postulate that even a few-month treatment with metformin results in the decrease of vitamin B12 and folate. However, supplementation of vitamin B12 rather than the combination of vitamin B12 and folate might be profitable based on the mechanism of metformin on vitamins in patients with type 2 diabetes. This viewpoint differs from those of majority that a combined supplementation of vitamin B12 and folate is inclined to be advised.

Metformin retards aging in C. elegans by altering microbial folate and methionine metabolism

The biguanide drug metformin is widely prescribed to treat type 2 diabetes and metabolic syndrome, but its mode of action remains uncertain. Metformin also increases lifespan in Caenorhabditis elegans cocultured with Escherichia coli. This bacterium exerts complex nutritional and pathogenic effects on its nematode predator/host that impact health and aging. We report that metformin increases lifespan by altering microbial folate and methionine metabolism. Alterations in metformin-induced longevity by mutation of worm methionine synthase (metr-1) and S-adenosylmethionine synthase (sams-1) imply metformin-induced methionine restriction in the host, consistent with action of this drug as a dietary restriction mimetic. Metformin increases or decreases worm lifespan, depending on E. coli strain metformin sensitivity and glucose concentration. In mammals, the intestinal microbiome influences host metabolism, including development of metabolic disease. Thus, metformin-induced alteration of microbial metabolism could contribute to therapeutic efficacy—and also to its side effects, which include folate deficiency and gastrointestinal upset.

PaperClip

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.

Cardiovascular Risk in Women With PCOS

Polycystic ovary syndrome (PCOS), or Stein-Leventhal syndrome, is a common endocrine disorder defined by two of the three following features: i) oligoovulation or anovulation, ii) clinical and/or biochemical signs of hyperandrogenism, or iii) polycystic ovaries, once the related endocrinological and gynaecological disorders have been excluded. PCOS does not exclusively involve the reproductive apparatus , it has a complex number of systemic relevancy symptoms. It leads to Metabolic Syndrome, with severe consequences on the cardiovascular apparatus. Many clinical studies have underlined the connection between PCOS and the cardiovascular risk profile of such female patients, due to a lipid/glucose altered metabolism, hypertension, systemic inflammatory condition (assessable by markers such as VES, TNF-alfa, citokines and C-reactive protein (hsPCR) levels), and vascular injuries. Considering the early onset of the disease, PCOS could be considered as a real cardiovascular risk factor which affects the quality of life seriously. The current review aimed to point out the main connections between PCOS and cardiovascular risk factors according to the latest findings coming from literature data analysis, and try to depict the great influences that such a common disease can have on the patients' health integrity.

Vitamin B(12) in type 2 diabetic patients treated with metformin

OBJECTIVE

To test vitamin B12 plasma levels in type 2 diabetic patients treated with metformin in our area.

METHODS

A cross-sectional, observational study of consecutive type 2 diabetic patients on drug treatment attending an internal medicine outpatient clinic.

RESULTS

One hundred and nine patients (81 treated with metformin) were enrolled into the study. Mean time on metformin treatment was 43.5 months and mean drug dose was 1,779 mg/day. Patients treated with metformin had significantly lower vitamin B(12) plasma levels (393.5 vs. 509 pg/mL, P = .0008). Seven (8.6%) of 81 patients treated with metformin and none of the 28 patients not treated with the drug had vitamin B(12) plasma levels lower than 197 pg/mL. No correlation was found between vitamin B12 plasma levles and metformin treatment time or dosage.

CONCLUSIONS

In type 2 diabetic patients, treatment with metformin is associated to lower vitamin B12 plasma levels. Vitamin B12 deficiency associated with metformin is relatively common in our area.

Recommendations for diagnosis and management of metformin-induced vitamin B12 (Cbl) deficiency

Metformin treatment is a known pharmacological cause of vitamin B12 (Cbl) deficiency with controversial responsible mechanisms. A possible diagnosis of this deficiency is based mainly on the combination of patient's medical history (usually long-term metformin use), clinical examination (possible neuropsychiatric symptoms and signs), laboratory studies which confirm a Cbl deficiency (haematological abnormalities, low serum Cbl levels, elevated serum total homocysteine and methylmalonic acid levels), and exclusion other causes of Cbl deficiency (as pernicious anaemia, food-cobalamin malabsorption syndrome, other drugs, etc.). In our review, recommendations for diagnosis and management of metformin-induced Cbl deficiency (MICD) in diabetic patients based on medical bibliography are presented and discussed.

An observational study of the effect of metformin on B12 status and peripheral neuropathy

Aims

Metformin is associated with lowering of vitamin B12 levels. We hypothesise that holotranscobalamin (holoTC) and methylmalonic acid (MMA) are more sensitive indicators of B12 deficiency in patients receiving metformin therapy, and that these correlate with declining peripheral neurological function.

Methods

Patients with type 2 diabetes were recruited and divided into those receiving metformin for greater than 6 months and a non-metformin group. Baseline characteristics were measured in both groups including vitamin B12, holoTC and MMA concentrations. Neurological function was assessed using neurothesiometry, monofilament, Neuropathy Total Symptom Score-6 questionnaire and the Self-administered Leeds Assessment of Neuropathic Symptoms and Signs questionnaire.

Results

In total, 202 patients were recruited: 152 in the metformin group and 50 in the non-metformin group. Vitamin B12 levels were lower in the metformin group (219.1±105.4 ng/L, 281.4±95.1 ng/L, p<0.001). HoloTC was significantly lower in the metformin group (54.8±30.5 pmol/L, 70.1±26.0 pmol/L, p=0.002). No significant difference in serum MMA was observed between the two groups (0.40±0.26 μmol/L, 0.35±0.22, p=0.23). No significant difference in neurological function was observed between the groups.

Conclusion

Although metformin therapy is associated with lower vitamin B12 status there does not appear to be any significant effect on peripheral neuropathy in those receiving metformin. We do not recommend changing current practice to routinely monitor or replace patients receiving metformin with vitamin B12 unless clinically indicated.

Homocysteine metabolism in polycystic ovary syndrome

Homocysteine, a sulfur-containing amino acid formed during the metabolism of methionine, exert cytotoxic effects on vascular endothelium. Molecular mechanisms of homocysteine-induced cellular dysfunction include increased inflammatory cytokine expression, altered nitric oxide bioavailability, induction of oxidative stress, activation of apoptosis and defective methylation. Hyperhomocysteinemia is associated with an increased risk of atherosclerotic and thromboembolic disorders, as well as hyperinsulinemia and may partially account for increased risk of cardiovascular disease associated with insulin resistance. Women with PCOS are more likely to develop components of the metabolic syndrome such as disturbances of carbohydrate metabolism, obesity, hypertension and dyslipidemia, which in turn are risk factors for cardiovascular disease. A number of studies confirmed the presence of increased serum homocysteine concentration in PCOS patients and the possible determinants of this observation are still debated. PCOS treatment options can influence homocysteine levels.

Association of biochemical B₁₂ deficiency with metformin therapy and vitamin B₁₂ supplements: the National Health and Nutrition Examination Survey, 1999-2006

OBJECTIVE

To describe the prevalence of biochemical B(12) deficiency in adults with type 2 diabetes taking metformin compared with those not taking metformin and those without diabetes, and explore whether this relationship is modified by vitamin B(12) supplements.

RESEARCH DESIGN AND METHODS

Analysis of data on U.S. adults ≥50 years of age with (n = 1,621) or without type 2 diabetes (n = 6,867) from the National Health and Nutrition Examination Survey (NHANES), 1999-2006. Type 2 diabetes was defined as clinical diagnosis after age 30 without initiation of insulin therapy within 1 year. Those with diabetes were classified according to their current metformin use. Biochemical B(12) deficiency was defined as serum B(12) concentrations ≤148 pmol/L and borderline deficiency was defined as >148 to ≤221 pmol/L.

RESULTS

Biochemical B(12) deficiency was present in 5.8% of those with diabetes using metformin compared with 2.4% of those not using metformin (P = 0.0026) and 3.3% of those without diabetes (P = 0.0002). Among those with diabetes, metformin use was associated with biochemical B(12) deficiency (adjusted odds ratio 2.92; 95% CI 1.26-6.78). Consumption of any supplement containing B(12) was not associated with a reduction in the prevalence of biochemical B(12) deficiency among those with diabetes, whereas consumption of any supplement containing B(12) was associated with a two-thirds reduction among those without diabetes.

CONCLUSIONS

Metformin therapy is associated with a higher prevalence of biochemical B(12) deficiency. The amount of B(12) recommended by the Institute of Medicine (IOM) (2.4 μg/day) and the amount available in general multivitamins (6 μg) may not be enough to correct this deficiency among those with diabetes.

Metabolic correction in the management of diabetic peripheral neuropathy: improving clinical results beyond symptom control

Current Clinical Management Guidelines of Diabetic Peripheral Neuropathy (DPN) are based on adequate glucose control and symptomatic pain relief. However, meticulous glycemic control could delay the onset or slow the progression of diabetic neuropathy in patients with DM type 2, but it does not completely prevent the progression of the disease. Complications of DPN as it continues its natural course, produce increasing pain and discomfort, loss of sensation, ulcers, infections, amputations and even death. In addition to the increased suffering, disability and loss of productivity, there is a very significant economic impact related to the treatment of DPN and its complications. In USA alone, it has been estimated that there are more than 5,000,000 patients suffering from DPN and the total annual cost of treating the disease and its complications is over $10,000 million dollars. In order to be able to reduce complications of DPN, it is crucial to improve or correct the metabolic conditions that lead to the pathology present in this condition. Pathophysiologic mechanisms implicated in diabetic neuropathy include: increased polyol pathway with accumulation of sorbitol and reduced Na+/K+-ATPase activity, microvascular damage and hypoxia due to nitric oxide deficit and increased oxygen free radical activity. Moreover, there is a decrease in glutathione and increase in homocysteine. Clinical trials in the last two decades have demonstrated that the use of specific nutrients can correct some of these metabolic derangements, improving symptom control and providing further benefits such as improved sensorium, blood flow and nerve regeneration. We will discuss the evidence on lipoic acid, acetyl-L-carnitine, benfotiamine and the combination of active B vitamins L-methylfolate, methylcobalamin and piridoxal-6-phosphate. In addition, we discuss the role of metformin, an important drug in the management of diabetes, and the presence of specific polymorphic genes, in the risk of developing DPN and how metabolic correction can reduce these risks.

Recent diabetes issues affecting the primary care clinician

Diabetes accounts for millions of office visits each year to primary care offices in the United States. Successful care of the patient with type 2 diabetes requires not only focus on glucose management but also on comorbidities such as hypertension, dyslipidemia and obesity which are closely linked to microvascular and macrovascular complications. Primary care clinicians must stay abreast of frequently published diabetes literature and new treatments to care for these increasingly complex patients. Metformin and its effect on B12 absorption continues to be an issue encountered by clinicians in daily clinical practice. There has also been recent discussion regarding the increased risk of diabetes with statins; data to date on this issue have been conflicting. Rosiglitazone continues to face public scrutiny and there are now Food and Drug Administration regulations regarding its increased risk of cardiovascular disease. Liraglutide and saxagliptin represent new treatment options for type 2 diabetes, increasing the available options for treating this complex disease. A review of the primary literature involving these topics is provided.

Effect of folic acid supplementation on biochemical indices in overweight and obese men with type 2 diabetes

AIMS

This study performed to determine the effects of folate supplementation on indices of glycemic control, insulin resistance and lipid profile in overweight and obese men with type 2 diabetes under metformin (at least 1500 mg daily) treatment.

METHODS

The study was a double-blind randomized controlled clinical trial. Forty-eight overweight and obese men (aged 58.2±8.9 years; BMI=28.6±2.9 kg/m(2)) with type 2 diabetes participated in the study. Patients were divided randomly into two groups of folic acid (5 mg/d) and placebo. All patients received the tablets for eight weeks.

RESULTS

Supplementation with folic acid led to 8% decrease in HbA1C (p=0.048), 7.5% in fasting blood glucose (p=0.051), 16.2% in serum insulin (p=0.021), 20.5% in insulin resistance (p=0.041) and 21.2% in plasma homocysteine (p=0.000). A significant increase in serum folate and B12 levels (19% and 17.3%, p=0.000, respectively) were observed in the folic acid group, whereas no significant changes occurred in the placebo group. Also, in the folic acid and placebo groups, there were no significant changes in body weight.

CONCLUSIONS

Folic acid supplementation lowered plasma level of homocysteine, improved glycemic control and insulin resistance in patients with type 2 diabetes.

Thyroidal effect of metformin treatment in patients with polycystic ovary syndrome

OBJECTIVE

Metformin is widely used for the treatment of type 2 diabetes. Growing evidence supports the beneficial effects of metformin also in patients with polycystic ovary syndrome (PCOS). It was recently reported that metformin has a TSH-lowering effect in hypothyroid patients with diabetes being treated with metformin.

DESIGN

Aim of this study was to evaluate the effect of metformin treatment on the thyroid hormone profile in patients with PCOS.

PATIENTS AND MEASUREMENTS

Thirty-three patients with PCOS were specifically selected for being either treated with levothyroxine for a previous diagnosis of hypothyroidism (n = 7), untreated subclinically hypothyroid (n = 2) or euthyroid without levothyroxine treatment (n = 24) before the starting of metformin. The serum levels of TSH and FT(4) were measured before and after a 4-month period of metformin therapy.

RESULTS

Thyroid function parameters did not change after starting metformin therapy in euthyroid patients with PCOS. In the 9 hypothyroid patients with PCOS, the basal median serum levels of TSH (3·2 mIU/l, range = 0·4-7·1 mIU/l) significantly (P < 0·05) decreased after a 4-month course of metformin treatment (1·7 mIU/l, range = 0·5-5·2 mIU/l). No significant change in the serum levels of FT4 was observed in these patients. The TSH-lowering effect of metformin was not related to the administered dose of the drug, which was similar in euthyroid as compared with hypothyroid patients with PCOS (1406 ± 589 vs 1322 ± 402 mg/day, respectively; NS).

CONCLUSIONS

These results indicate that metformin treatment has a TSH-lowering effect in hypothyroid patients with PCOS, both treated with l-thyroxine and untreated.

Homocysteine and Hypertension in Diabetes: Does PPARgamma Have a Regulatory Role?

Dysfunction of macro- and microvessels is a major cause of morbidity and mortality in patients with cardio-renovascular diseases such as atherosclerosis, hypertension, and diabetes. Renal failure and impairment of renal function due to vasoconstriction of the glomerular arteriole in diabetic nephropathy leads to renal volume retention and increase in plasma homocysteine level. Homocysteine, which is a nonprotein amino acid, at elevated levels is an independent cardio-renovascular risk factor. Homocysteine induces oxidative injury of vascular endothelial cells, involved in matrix remodeling through modulation of the matrix metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) axis, and increased formation and accumulation of extracellular matrix protein, such as collagen. In heart this leads to increased endothelial-myocyte uncoupling resulting in diastolic dysfunction and hypertension. In the kidney, increased matrix accumulation in the glomerulus causes glomerulosclerosis resulting in hypofiltration, increased renal volume retention, and hypertension. PPARγ agonist reduces tissue homocysteine levels and is reported to ameliorate homocysteine-induced deleterious vascular effects in diabetes. This review, in light of current information, focuses on the beneficial effects of PPARγ agonist in homocysteine-associated hypertension and vascular remodeling in diabetes.

Effect of lipopenic and hypotensive treatment on homocysteine levels in type 2 diabetics

AIM

Evaluate the effect of lipopenic and hypotensive treatment on homocysteine levels.

METHODS

We recruited 145 type 2 diabetics and 130 control subjects. Thirty-seven diabetics had no complications, 54 had microvascular complications and 54 had macrovascular complications. We determined the parameters homocysteine of lipid, vitamin B12, triglycerides, and folates for all subjects. Associated treatments used one or more of the following drugs, statin, fibrate, angiotensin-converting enzyme inhibitor and beta-blockers.

RESULTS

Hyperhomocysteinemia was present in 35.6% of patients. Diabetics had elevated serum levels of triglycerides (P < 0.001), homocysteine (P < 0.01), folates (P < 0.01) and vitamin B12 (P < 0.001). A strong association was found between type 2 diabetes and hyperhomocysteinemia (P < 0.001). Diabetics with associated treatment had elevated homocysteine, vitamin B12 and folate levels when compared to diabetes-free controls. For diabetics with macrovascular complications, we found significant differences in homocysteine (P = 0.010) and folate (P = 0.014) between those taking associated drugs and those who did not. For diabetics with microvascular complications, a significant difference was found in folate only (P = 0.012).

CONCLUSION

Drugs used for hypertension and hyperlipidemia may have an effect on homocysteine levels, for this reason the interaction between drug action and homocysteine levels should be taken into consideration.

Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial

OBJECTIVES

To study the effects of metformin on the incidence of vitamin B-12 deficiency (<150 pmol/l), low concentrations of vitamin B-12 (150-220 pmol/l), and folate and homocysteine concentrations in patients with type 2 diabetes receiving treatment with insulin.

DESIGN

Multicentre randomised placebo controlled trial.

SETTING

Outpatient clinics of three non-academic hospitals in the Netherlands.

PARTICIPANTS

390 patients with type 2 diabetes receiving treatment with insulin.

INTERVENTION

850 mg metformin or placebo three times a day for 4.3 years.

MAIN OUTCOME MEASURES

Percentage change in vitamin B-12, folate, and homocysteine concentrations from baseline at 4, 17, 30, 43, and 52 months.

RESULTS

Compared with placebo, metformin treatment was associated with a mean decrease in vitamin B-12 concentration of -19% (95% confidence interval -24% to -14%; P<0.001) and in folate concentration of -5% (95% CI -10% to -0.4%; P=0.033), and an increase in homocysteine concentration of 5% (95% CI -1% to 11%; P=0.091). After adjustment for body mass index and smoking, no significant effect of metformin on folate concentrations was found. The absolute risk of vitamin B-12 deficiency (<150 pmol/l) at study end was 7.2 percentage points higher in the metformin group than in the placebo group (95% CI 2.3 to 12.1; P=0.004), with a number needed to harm of 13.8 per 4.3 years (95% CI 43.5 to 8.3). The absolute risk of low vitamin B-12 concentration (150-220 pmol/l) at study end was 11.2 percentage points higher in the metformin group (95% CI 4.6 to 17.9; P=0.001), with a number needed to harm of 8.9 per 4.3 years (95% CI 21.7 to 5.6). Patients with vitamin B-12 deficiency at study end had a mean homocysteine level of 23.7 micromol/l (95% CI 18.8 to 30.0 micromol/l), compared with a mean homocysteine level of 18.1 micromol/l (95% CI 16.7 to 19.6 micromol/l; P=0.003) for patients with a low vitamin B-12 concentration and 14.9 micromol/l (95% CI 14.3 to 15.5 micromol/l; P<0.001 compared with vitamin B-12 deficiency; P=0.005 compared with low vitamin B-12) for patients with a normal vitamin B-12 concentration (>220 pmol/l).

CONCLUSIONS

Long term treatment with metformin increases the risk of vitamin B-12 deficiency, which results in raised homocysteine concentrations. Vitamin B-12 deficiency is preventable; therefore, our findings suggest that regular measurement of vitamin B-12 concentrations during long term metformin treatment should be strongly considered. Trial registration Clinicaltrials.gov NCT00375388.

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.

Effects of metformin with or without supplementation with folate on homocysteine levels and vascular endothelium of women with polycystic ovary syndrome

OBJECTIVE

To evaluate whether the administration of metformin exerts any effects on serum homocysteine (Hcy) levels in patients with polycystic ovary syndrome (PCOS) and whether supplementation with folate enhances the positive effects of metformin on the structure and function of the vascular endothelium.

RESEARCH DESIGN AND METHODS

A total of 50 patients affected by PCOS, without additional metabolic or cardiovascular diseases, were enrolled in a prospective nonrandomized placebo-controlled double-blind clinical study. They were grouped into two treatment arms that were matched for age and BMI. Patients were treated with a 6-month course of metformin (1,700 mg daily) plus folic acid (400 microg daily; experimental group, n = 25) or placebo (control group, n = 25). Complete hormonal and metabolic patterns, serum Hcy, folate, vitamin B12, endothelin-1 levels, brachial artery diameter at the baseline (BAD-B) and after reactive hyperemia (BAD-RH), flow-mediated dilation, and intima-media thickness in both common carotid arteries were evaluated.

RESULTS

After treatment, a significant increase in serum Hcy levels was observed in the control group compared with the baseline values and the experimental group. A beneficial effect was observed in the concentrations of BAD-B, BAD-RH, flow-mediated dilation, intima-media thickness, and serum endothelin-1 in both groups. However, the results were improved more significantly in the experimental group than in the control subjects.

CONCLUSIONS

Metformin exerts a slight but significant deleterious effect on serum Hcy levels in patients with PCOS, and supplementation with folate is useful to increase the beneficial effect of metformin on the vascular endothelium.

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.

Protection from olanzapine-induced metabolic toxicity in mice by acetaminophen and tetrahydroindenoindole

OBJECTIVE

In mice and in humans, treatment with the second-generation antipsychotic drug olanzapine (OLZ) produces excessive weight gain, adiposity and secondary metabolic complications, including loss of glucose and insulin homeostasis. In mice consuming a high-fat (HF) diet, a similar phenotype develops, which is inhibited by the analgesic acetaminophen (APAP) and by the antioxidant tetrahydroindenoindole (THII). Therefore, we examined the ability of APAP and THII to prevent metabolic changes in mice receiving OLZ.

DESIGN AND MEASUREMENT

C57BL/6J mice received either a normal diet or a HF diet, and were administered daily dosages of OLZ (3 mg kg(-1) body weight), alone or with APAP (30 mg kg(-1) body weight) or THII (4.5 mg kg(-1) body weight), for 10 weeks. Parameters of body composition and metabolism, including glucose and insulin homeostasis and oxidative stress, were examined.

RESULTS

OLZ treatment doubled the HF diet-induced increases in body weight and percent body fat. These increases were partially prevented by both APAP and THII, although food consumption was constant in all groups. The THII protection was associated with an increase in whole body and mitochondrial respiration. OLZ also exacerbated, and both APAP and THII prevented, HF diet-induced loss of glucose tolerance and insulin resistance. As increased body fat promotes insulin resistance by a pathway involving oxidative stress, we evaluated production of reactive oxygen and lipid peroxidation in white adipose tissue (WAT). HF diet caused an increase in lipid peroxidation, NADPH-dependent O(2) uptake and H(2)O(2) production, which were further exacerbated by OLZ. APAP, THII and the NADPH oxidase inhibitor, diphenyleneiodonium chloride, each abolished oxidative stress in WAT.

CONCLUSIONS

We conclude that both APAP and THII intervene in the development of obesity and metabolic complications associated with OLZ treatment.

Comorbidities and microvascular complications of type 2 diabetes in children and adolescents

The comorbidities of type 2 diabetes in children and adolescents are mainly related to coexistent insulin resistance and compounded by poverty. The prevalence of dyslipidemia, fatty liver, and hypertension may not be higher than the rates in obese children and adolescents, but the stakes are higher in children with diabetes because the diabetes confers a higher cardiovascular risk. This risk is exaggerated further in children with poor hygiene, smoking, and primary renal disease. Sexuality, contraception, preconception counseling, and psychiatric conditions require unique considerations in youth with type 2 diabetes.

Relationship between two sequence variations in the gene for peroxisome proliferator-activated receptor-gamma and plasma homocysteine concentration. Health in men study

The concentration of circulating homocysteine has been associated with a variety of diseases, including myocardial infarction, stroke, venous thrombosis and cognitive decline. Genetic variation has been demonstrated to play an important role in determining plasma homocysteine, however, the genes involved are incompletely understood. Ligation of the transcription factor peroxisome proliferator-activated gamma (PPARG) has been demonstrated to lower plasma homocysteine. We examined the association of two sequence variations in PPARG with plasma concentrations of homocysteine in a population-based study of 3,875 elderly men. PPARG c.34G > C and PPARG c.1347C > T sequence variations were determined by real-time quantitative PCR and related to logarithm transformed homocysteine concentrations using linear regression, adjusting for the co-variants age, renal function, smoking, coronary heart disease, waist to hip ratio, diabetes, hypertension and MTHFR g.677C > T sequence variation. Median plasma homocysteine concentration was 10% higher in men who were homozygous for the rare allelic variation in PPARG c.34G > C and PPARG c.1347C > T by comparison to those who had wild type sequence variation. PPARG c.1347C > T (beta = 0.038, P = 0.01 recessive model; beta = 0.036, P = 0.02 dominant model) sequence variation was positively associated with homocysteine concentration after adjusting for co-variants. The two PPARG sequence variations were in linkage disequilibrium and the common haplotype was associated with lower plasma homocysteine (P = 0.005). Our findings demonstrate a new genotypic association with plasma homocysteine. Replication will be required in other cohorts.

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.