Impact of insulin resistance and nephropathy on homocysteine in type 2 diabetes

The association of homocysteine level with the risk of diabetic nephropathy and diabetic retinopathy in NHANES

AIMS

To examine the association of homocysteine (Hcy) with diabetic nephropathy (DN) and diabetic retinopathy (DR) in a representative United States population.

METHODS

This was a cross-sectional study using data from participants in the National Health and Nutrition Examination Survey 2005-2006. Metrics including Hcy level, urinary albumin to creatinine ratio, estimated glomerular filtration rate, and retinopathy grading were collected. Multiple logistic regression models were employed to assess the association of Hcy with DN and DR.

RESULTS

630 participants were included in this study. The Hcy level was significantly higher in those with DN and DR than those without DN and DR. Hcy was associated with an increased risk of DN (OR = 1.31, 95% CI 1.18-1.46; P < 0.001). In the fully adjusted model of DN (model II), compared to participants in quartiles 1 of Hcy, the adjusted ORs for participants in quartiles 2-4 were 1.49 (95% CI 0.52-4.26; P = 0.426), 3.81 (95% CI 1.35-10.73; P = 0.015), and 14.08 (95% CI 3.84-51.66; P = 0.001), respectively. Hcy was also associated with an increased risk of DR (OR = 2.260, 95% CI 1.212-4.216; P = 0.014), but this association was non-significant in the fully adjusted model of DR (model II).

CONCLUSIONS

In diabetic patients, Hcy was associated with increased risk of DN in a non-linear manner. In addition, Hcy was associated with the risk of DR, but the association was attenuated after adjusting for confounders. In the future, Hcy can potentially be used as an early screening indicator for diabetic microvascular complications.

Homocysteine and diabetes: Role in macrovascular and microvascular complications

Diabetes mellitus (DM) can lead to the development of macro- and microvascular complications. Homocysteine (Hcy) may play a role in the development of cardiovascular (CV) diseases (CVDs). The role of Hcy in the development of the vascular complications associated with DM is not clearly defined. Despite a strong initial assumption regarding the importance of Hcy in DM and its complications, over time "enthusiasm has waned" because several studies showed unconvincing and occasionally contradictory results. A universal conclusion is not easy to draw given the diversity of studies (e.g. number of patients, design, folic acid and vitamin B status, ethnic differences, genetic background). For some complications, most results encourages further investigation. Impaired renal function is a major independent determinant of high total Hcy (tHcy) levels. However, the role of hyperhomocysteinaemia (HHcy) in the development of diabetic kidney disease (DKD) has yet to be determined. Hcy-lowering therapies can significantly decrease Hcy levels but their effects on CVD risk reduction are conflicting. Further studies are needed to determine the influence of Hcy-lowering therapy on CVD risk reduction, especially in patients with DM.

Homocysteine and Asymmetrical Dimethylarginine in Diabetic Rats Treated with Docosahexaenoic Acid-Loaded Zinc Oxide Nanoparticles

Hyperglycemia, the hallmark of diabetes mellitus, is considered one of the endothelial dysfunction risk factors, the main reason of vascular complication. In this study, we aimed to evaluate homocysteine (Hcy) and asymmetrical dimethylarginine (ADMA) levels in diabetic rats and the possibility to attenuate the elevation of these two parameters by supplementation of docosahexaenoic acid (DHA) alone or loaded zinc oxide nanoparticles (ZnONPs) to improve endothelial dysfunction in streptozotocin (STZ)-induced diabetic rats. Forty male albino rats weighing 180-200 g were classified as control, diabetic, diabetic treated with DHA, and diabetic treated with DHA-loaded zinc oxide nanoparticles (DHA/ZnONPs) groups. Fasting blood glucose, insulin, ADMA, Hcy, and nitric oxide (NO) were estimated. Fatty acids (linoleic acid (LA), arachidonic acid (AA), DHA, α-linolenic acid (ALA), and oleic acid (OA)) were also evaluated by reversed phase HPLC using a UV detector. The results showed that fasting blood sugar, insulin resistance, LA, AA, OA, ADMA, and Hcy increased significantly in diabetic rats compared with control while fasting insulin, DHA, ALA, and NO decreased significantly in diabetic rats. In both treated groups, fasting blood sugar, insulin resistance, LA, AA, OA, ADMA, and Hcy significantly decreased as compared with the diabetic group while fasting insulin, DHA, ALA, and NO were significantly increased. In conclusion, DHA and DHA/ZnONP supplementation protect against diabetic complications and improve endothelial dysfunction as well as hyperhomocysteinemia in diabetes. DHA/ZnONP-treated group appeared more efficient than DHA alone.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Effects of myo-inositol, gymnemic acid, and L-methylfolate in polycystic ovary syndrome patients

Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine and metabolic disorder, characterized by chronic anovulation/oligomenorrhea, hyperandrogenism, and insulin-resistance. Moreover, some studies propose a possible association between insulin resistance and hyperhomocysteinemia, which is a significant long-term risk for factor for atherogenesis and chronic vascular damage, especially in situations where insulin levels are increased. Insulin-sensitizing agents are used in the treatment of PCOS: in fact, inositols were shown to have insulin-mimetic properties. Synergic action to myo-inositol is that of gymnemic acids that have antidiabetic, anti-sweetener, and anti-inflammatory activities. Gymnemic acid formulations have also been found useful against obesity due to their ability to delay the glucose absorption in the blood. L-methyl-folate increases peripheral sensitivity to insulin, maintaining folatemia stable, and thus restoring normal homocysteine levels. Unlike folic acid, L-methyl folate has a higher bioavailability, no drug/food interferences, high absorption, and it is stable to UV-A exposure. The aim of our study is to compare the clinical, endocrine, and metabolic parameters in 100 PCOS women treated with myo-inositol, gymnemic acid, and l-methylfolate (Group A) or myo inositol and folic acid only (Group B), continuously for 6 months. From a clinical point of view, it was noticed a more significant improvement of the menstrual cycle regularity and a more significant reduction of BMI in Group A. Moreover, a more significant decrease of total testosterone and increase of SHBG serum levels were noticed in Group A. The metabolic assessment found a more significant decrease of total cholesterol and homocysteine levels; OGTT glycemia and insulinemia values were significantly more improved after treatment with myo-inositol + gymnemic acid. In conclusion, we can state that a good option for the treatment of PCOS is the combined administration of myo-inositol + gymnemic acid + l-methyl-folate, especially for overweight/obese patients with marked insulin resistance and with associated hyperhomocysteinemia.

Inverse association between plasma homocysteine concentrations and type 2 diabetes mellitus among a middle-aged and elderly Chinese population

BACKGROUND AND AIMS

Plasma homocysteine concentrations have been reported to be associated with type 2 diabetes mellitus (T2DM) with controversial findings. The aim of the present study was to investigate the association between plasma homocysteine concentrations and T2DM.

METHODS AND RESULTS

A cross-sectional study including 19,085 eligible participants derived from the Dongfeng-Tongji cohort was conducted. Plasma homocysteine concentrations were measured by Abbott Architect i2000 Automatic analyzer and T2DM was defined according to American Diabetes Association criteria. Logistic regression model was used to explore the association between plasma homocysteine concentrations and T2DM. The prevalence of T2DM was 19.0% in the whole population (mean age 62.9 years), 21.8% in males, and 17.1% in females. In the multivariable logistic regression analyses, compared with those in the lowest quintile, the OR (95% CI) of T2DM was 1.05 (0.92-1.21), 0.99 (0.86-1.14), 0.90 (0.78-1.05), and 0.77 (0.66-0.90) for quintile 2 to quintile 5 of homocysteine concentrations after adjustment for potential confounders (P for trend < 0.0001). Homocysteine concentrations were associated with decreased T2DM prevalence risk (OR = 0.88 per SD increase of homocysteine concentration; 95% CI: 0.84-0.93). A significant interaction between homocysteine concentrations and drinking status on T2DM prevalence risk was observed (P for interaction = 0.03). The inverse association of plasma homocysteine concentrations with T2DM prevalence risk was observed in non-drinkers but not in current drinkers.

CONCLUSION

Plasma homocysteine concentrations were inversely correlated with T2DM among a middle-aged and elderly Chinese population.

Association between insulin resistance and total plasma homocysteine levels in type 2 diabetes mellitus patients in south west Nigeria

AIM

To determine the levels of serum homocysteine and its association with insulin resistance among T2DM patients at Obafemi Awolowo University Teaching Hospital, Ile Ife Nigeria.

METHODS

It was a cross sectional study. It involved consecutive recruitment of 100 T2DM subjects with 100 age and sex matched controls. The fasting plasma glucose, serum creatinine, fasting lipid profile, glycosylated haemoglobin levels, fasting serum insulin and plasma homocysteine concentration were done. Insulin resistance was also determined. SPSS version 17.0 was used for data analysis.

RESULTS

The mean age of subjects was not significantly different from controls. (58.9±8.3 vs. 59.0±8.3years, p=0.926 respectively). Mean Homocysteine level (tHcy) was significantly higher among T2DM subjects compared to controls (27.4±12.1 and 8.3±3.2μmol/L respectively, p=0.0001). Hyperhomocystinaemia was commoner among diabetic subjects compared with controls (81% vs. 5%, p<0.0001). T2DM with hyperhomocystinaemia were more likely to have poorer glucose control profile using glycated haemoglobin (7.4±1.9 vs 6.4±1.4%, p=0.04) and fasting blood glucose 8.6±2.2 vs 7.5±2.4mmol/L p=0.047 and insulin resistance (4.4±4.3 vs. 2.0±0.6, p=0.02) compared with T2DM with normohomocystenaemia. There were significant associations between hyperhomocystinaemic T2DM patients and IR, HbA1c, TC, TG and LDL cholesterol.

CONCLUSION

The study showed higher homocysteine levels in T2DM than controls. Homocysteine level is worsened by increasing insulin resistance, dyslipidaemia and poor glucose control. Homocysteine level is a potential cardiovascular risk marker in type 2 diabetic mellitus subjects.

Plasma homocysteine levels are associated with macular thickness in type 2 diabetes without diabetic macular edema

PURPOSE

To explore the relationships between macular thickness and the plasma concentrations of homocysteine, vitamin B12, folate, and other known risk factors for patients with diabetes without diabetic macular edema (DME).

METHODS

Fasting venous blood samples were collected from 252 subjects (126 relatively healthy subjects with type 2 diabetes without diabetic macular edema and 126 age- and gender-matched controls). Measurement of macular thickness and volume was performed for those subjects using SD-OCT. The plasma concentrations of homocysteine, vitamin B12, folate, and other known risk factors were analyzed in all the patients and controls using multiple linear regression models.

RESULTS

An increase in the serum levels of homocysteine was present within patients with type 2 diabetes compared to healthy individuals. The mean total plasma homocysteine levels were associated with a greater central subfield macular thickness (CSMT), average macular thickness (AMT), and average macular volume (AMV) in patients with type 2 diabetes without DME, after adjusting for age, sex, duration of diabetes, and HbA1c. Each 1 mmol/L increase in tHcy level was associated with a 6.57 µm greater CSMT (95% confidence interval [CI] 1.78, 11.36), a 4.51 µm greater AMT (95% CI 1.05, 7.98), and a 4.72 mm³ greater AMV (95% CI 1.23, 8.21).

CONCLUSIONS

Higher homocysteine levels were associated with an increased CSMT, AMT, and AMV in diabetic patients without DME. This link may indicate that patients with type 2 diabetes with increased levels of plasma tHcy are more prone to develop a clinical manifestation of DME.

Type II diabetes mellitus and hyperhomocysteinemia: a complex interaction

BACKGROUND

Elevated homocysteine (Hc) levels have a well-established and clear causal relationship to epithelial damage leading to coronary artery disease. Furthermore, it is strongly associated with other metabolic syndrome variables, such as hypertension, which is correlated with type II diabetes mellitus (T2DM). Studies on T2DM in relation to Hc levels have shown both positive and negative associations. The aim of the present study is to examine the relationship between Hc levels and risk of T2DM in the Lebanese population.

METHODS

We sought to identify whether Hc associates positively or negatively with diabetes in a case-control study, where 2755 subjects enrolled from patients who had been catheterized for coronary artery diagnosis and treatment. We further sought to identify whether the gene variant MTHFR 667C>T is associated with T2DM, and how Hc and MTHFR 667C>T also impact other correlates of T2DM, including the widely used diuretics in this study population.

RESULTS

We found that Hc levels were significantly reduced among subjects with diabetes compared to those without diabetes when adjusted for all potential confounders (OR 0.640; 95% CI [0.44-0.92]; p = 0.0200). The associations between Hc levels and other variates contradicted the result: hypertension associates positively with high Hc levels, and with T2DM. The MTHFR 667C>T only associated significantly with high Hc levels.

CONCLUSION

These results suggest population-specific variations among a range of mechanisms that modulate the association of Hc and T2DM, providing a probe for future studies.

Hyperhomocysteinemic Diabetic Cardiomyopathy: Oxidative Stress, Remodeling, and Endothelial-Myocyte Uncoupling

Accumulation of oxidized-matrix (fibrosis) between the endothelium (the endothelial cells embedded among the myocytes) and cardiomyocytes is a hallmark of diabetes mellitus and causes diastolic impairment. In diabetes mellitus, elevated levels of homocysteine activate matrix metalloproteinase and disconnect the endothelium from myocytes. Extracellular matrix functionally links the endothelium to the cardiomyocyte and is important for their synchronization. However, in diabetes mellitus, a disconnection is caused by activated metalloproteinase, with subsequent accumulation of oxidized matrix between the endothelium and myocyte. This contributes to endothelial-myocyte uncoupling and leads to impaired diastolic relaxation of the heart in diabetes mellitus. Elevated levels of homocysteine in diabetes are attributed to impaired homocysteine metabolism by glucose and insulin and decreased renal clearance. Homocysteine induces oxidative stress and is inversely related to the expression of peroxisome proliferators activated receptor (PPAR). Several lines of evidence suggest that ablation of the matrix metalloproteinase (MMP-9) gene ameliorates the endothelial-myocyte uncoupling in diabetes mellitus. Homocysteine competes for, and decreases the PPARγ activity. In diabetes mellitus, endothelial-myocyte uncoupling is associated with matrix metalloproteinase activation and decreased PPARγ activity. The purpose of this review is to discuss the role of endothelial-myocyte uncoupling in diabetes mellitus and increased levels of homocysteine, causing activation of latent metalloproteinases, decreased levels of thioredoxin and peroxiredoxin, and cardiac tissue inhibitor of metalloproteinase (CIMP) in response to antagonizing PPARγ.

Relationship between High Serum Cystatin C Levels and the Risk of Gestational Diabetes Mellitus

Aims

Serum cystatin C (CysC) has recently been shown to be associated with the incidence of type 2 diabetes mellitus (T2DM) and progression to the pre-diabetic state. The aim of this study was to explore the relationship between serum CysC and the risk of gestational diabetes mellitus (GDM) in Chinese pregnant women.

Methods

This cross-sectional study consisted of 400 pregnant women including111 with GDM and 289 with normal glucose tolerance at 24–28 weeks of gestation. The subjects were further divided into four groups according to the CysC quartiles, and their clinical characteristics were compared. The serum CysC concentration was measured using immunoturbidimetry and the degree of insulin resistance was assessed by the homeostasis model assessment of insulin resistance (HOMA-IR).

Results

Serum CysC levels were significantly higher in pregnant women with GDM than in the healthy pregnant women[1.0(0.8–1.8) vs 0.7(0.6–1.0), P<0.01). The Spearman’s correlation analysis showed that serum CysC was positively associated with HOMA-IR(r = 0.118, P<0.05) and the occurrence of GDM(r = 0.348, P<0.01). The pregnant women were divided into quartiles according to their serum CysC concentrations. Compared to the first quartile, pregnant women in Q2 (OR, 2.441; P = 0.025), Q3 (OR, 3.383; P = 0.001) and Q4 (OR, 5.516; P<0.001) had higher risk of GDM after adjusted for age, BMI, HbA1c and HOMA-IR. Further, with a rise in the serum CysC, there was an increasing trend in the HOMA-IR levels (P<0.05). A binary logistic regression analysis after adjusting for other confounding variables revealed a significant and independent association between serum CysC and GDM [OR = 14.269; 95% confidence interval, 4.977–40.908, P<0.01].The receiver operating characteristic curve analysis revealed that the optimal cutoff point for serum CysC to indicate GDM was 0.95mg/L.

Conclusions

Serum CysC is significantly and independently associated with insulin resistance and GDM. It may be a helpful biomarker to identify the risk of GDM in Chinese pregnant women.

Folic Acid and Vitamins D and B12 Correlate With Homocysteine in Chinese Patients With Type-2 Diabetes Mellitus, Hypertension, or Cardiovascular Disease

Elevated serum homocysteine has been shown to be a risk factor for hypertension, cardiovascular disease (CVD), and type-2 diabetes mellitus (T2DM).We characterized the relationships between the serum levels of homocysteine, folic acid, and vitamins D2, D3, and B12 in patients with T2DM, CVD, and hypertension in Shanghai, China. The levels of these serum biochemical markers were determined for 9311 Chinese patients (mean age: 79.50 ± 13.26 years) with T2DM (N = 839), hypertension (N = 490), or CVD (N = 7925). The demographic and serum biochemical data were compared using an analysis of variance. We performed stratified analyses using Pearson linear regression to investigate correlations between the different variables in the T2DM, CVD, and hypertension groups and in patients aged < 50, 50 to 64, 65 to 80, and ≥80 years. A subgroup analysis was also performed to identify correlations between the serum biochemical markers. Stratified chi-squared analyses were performed based on the levels of folic acid and total vitamin D.In all 3 patient groups, elevated levels of vitamin D2 and homocysteine were observed, whereas the levels of folic acid and vitamins D3 and B12 were lower than the reference range for each serum marker (P < 0.05 for all). The linear regression and stratified analyses showed that the highest levels of folic acid and vitamins D2 and D3 correlated with the lowest level of homocysteine in T2DM, CVD, and hypertension patients (P < 0.05 for all), whereas the highest level of vitamin B12 correlated with a lowest level of homocysteine in CVD patients only (P < 0.05).Our results indicate that the contributions of both vitamin D2 and vitamin D3 should be considered in investigations of the effects of vitamin D supplements in T2DM, CVD, and hypertension patients. Our findings warrant future studies of the benefits of vitamin D and folic acid supplements for reducing the risk of T2DM, CVD, and hypertension in elderly Chinese people, as well as the benefits of vitamin B12 supplements for reducing the risk of CVD alone.

Hyperhomocysteinemia and hyperglycemia induce and potentiate endothelial dysfunction via μ-calpain activation

Plasma homocysteine (Hcy) levels are positively correlated with cardiovascular mortality in diabetes. However, the joint effect of hyperhomocysteinemia (HHcy) and hyperglycemia (HG) on endothelial dysfunction (ED) and the underlying mechanisms have not been studied. Mild (22 µmol/L) and moderate (88 µmol/L) HHcy were induced in cystathionine β-synthase wild-type (Cbs(+/+)) and heterozygous-deficient (Cbs(-/+)) mice by a high-methionine (HM) diet. HG was induced by consecutive injection of streptozotocin. We found that HG worsened HHcy and elevated Hcy levels to 53 and 173 µmol/L in Cbs(+/+) and Cbs(-/+) mice fed an HM diet, respectively. Both mild and moderate HHcy aggravated HG-impaired endothelium-dependent vascular relaxation to acetylcholine, which was completely abolished by endothelial nitric oxide synthase (eNOS) inhibitor N(G)-nitro-L-arginine methyl ester. HHcy potentiated HG-induced calpain activation in aortic endothelial cells isolated from Cbs mice. Calpain inhibitors rescued HHcy- and HHcy/HG-induced ED in vivo and ex vivo. Moderate HHcy- and HG-induced μ-calpain activation was potentiated by a combination of HHcy and HG in the mouse aorta. μ-Calpain small interfering RNA (μ-calpsiRNA) prevented HHcy/HG-induced ED in the mouse aorta and calpain activation in human aortic endothelial cells (HAECs) treated with DL-Hcy (500 µmol/L) and d-glucose (25 mmol) for 48 h. In addition, HHcy accelerated HG-induced superoxide production as determined by dihydroethidium and 3-nitrotyrosin staining and urinary 8-isoprostane/creatinine assay. Antioxidants rescued HHcy/HG-induced ED in mouse aortas and calpain activation in cultured HAECs. Finally, HHcy potentiated HG-suppressed nitric oxide production and eNOS activity in HAECs, which were prevented by calpain inhibitors or μ-calpsiRNA. HHcy aggravated HG-increased phosphorylation of eNOS at threonine 497/495 (eNOS-pThr497/495) in the mouse aorta and HAECs. HHcy/HG-induced eNOS-pThr497/495 was reversed by µ-calpsiRNA and adenoviral transduced dominant negative protein kinase C (PKC)β2 in HAECs. HHcy and HG induced ED, which was potentiated by the combination of HHcy and HG via μ-calpain/PKCβ2 activation-induced eNOS-pThr497/495 and eNOS inactivation.

Relationship of MTHFR gene 677C → T polymorphism, homocysteine, and estimated glomerular filtration rate levels with the risk of new-onset diabetes

East Asian patients with diabetes have a higher risk for renal complications and strokes than Europeans. We aimed to evaluate the effect of methylenetetrahydrofolate reductase (MTHFR) gene 677 C → T polymorphism, which was associated with a higher stroke risk and was common in the Chinese population, as well as homocysteine and estimated glomerular filtration rate (eGFR) levels on the risk of new-onset diabetes (NOD). A total of 2422 subjects without diabetes were followed-up for 7 years. NOD was defined as fasting plasma glucose ≥ 7.0 mmol/L or self-reported physician diagnosis of diabetes. Compared with subjects with MTHFR 677 CC genotype, those with TT genotype had a higher risk of NOD in females (odds ratio 2.78, 95% confidence interval 1.39-5.56) but not in males (0.80, 0.40-1.61, P for interaction = 0.008). Furthermore, MTHFR 677 C → T polymorphism was more strongly associated with the risk of NOD among females with higher body mass index (BMI, ≥ 23 vs <23 kg/m(2), P for interaction = 0.009) or lower high-density lipoprotein-cholesterol (HDL-C, <1.3 vs ≥ 1.3 mmol/L, P for interaction = 0.015) levels. Hyperhomocysteinemia (≥ 16 vs <10 μmol/L) was not significantly associated with NOD in males (0.88, 0.42-1.85) or females (1.52, 0.65-3.57). However, mildly decreased eGFR (<90 vs 90-120 mL/min/1.73 m(2)) was associated with NOD mainly in males (1.96, 1.01-3.78; females, 0.74, 0.32-1.72, P for interaction = 0.134). Females with MTHFR 677 TT genotype had a significantly higher risk of NOD, particularly those with higher BMI or low HDL-C levels. The higher risk of NOD associated with mildly decreased eGFR also warrants more investigation. Our results provide insights into the ethnic differences of diabetic complications between East Asian patients and Europeans.

Associations of common variants in methionine metabolism pathway genes with plasma homocysteine and the risk of type 2 diabetes in Han Chinese

BACKGROUND/AIMS

An association of genetic variants of homocysteine (Hcy) metabolic genes with type 2 diabetes mellitus (T2DM) has been reported. The objective of the present study was to investigate the relationship between the genetic variants in Hcy metabolism-related genes and plasma Hcy levels and T2DM susceptibility in Han Chinese.

METHODS

A total of 774 patients with T2DM and 500 healthy individuals were recruited. Single-nucleotide polymorphism was determined by standard methods.

RESULTS

The Hcy-increasing allele score was positively associated with plasma Hcy levels in both T2DM patients and healthy subjects (r = 0.171 and 0.247, respectively). Subjects with the genotype CC of MTHFR (rs1801131) had a significantly higher likelihood of T2DM compared with subjects with the AA or AA+AC genotypes (OR = 1.93 for CC vs. AA, p = 0.041; OR = 3.13 for CC vs. AA+AC, p = 0.017, respectively). Subjects with the genotype AA of the MTHFD variant (rs2236225) had a significantly lower likelihood of T2DM compared with subjects with the GG or GG+GA genotypes (OR = 0.36 for AA vs. GG, p = 0.027; OR = 0.36 for AA vs. GG+GA, p = 0.017, respectively). In addition, the genotype CT+TT of the PEMT (rs4646356) variants displayed a significant association with an increased risk of T2DM (OR = 1.52 for CT+TT vs. CC, p = 0.042).

CONCLUSIONS

MTHFR rs1801131 C allele and PEMT rs4646356 T allele were associated with a high risk of T2DM in these Han Chinese.

Erythrocyte glutathione transferase activity: a possible early biomarker for blood toxicity in uremic diabetic patients

Erythrocyte glutathione transferase (e-GST) displays increased activity in patients with renal damage and positive correlation with homocysteine (Hcy) in patients under maintenance hemodialysis. Here, we determined e-GST, Hcy, and erythrocyte catalase (e-CAT) in 328 patients affected by type 2 diabetes mellitus (T2DM), 61 diabetic non-nephropathic patients and 267 affected by diabetes and by chronic kidney disease (CKD) under conservative therapy subdivided into four stages according to K-DOQI lines. e-GST activity was significantly higher in all T2DM patients compared to the control group (7.90 ± 0.26 vs. 5.6 ± 0.4 U/g(Hb)), and we observed an enhanced activity in all subgroups of CKD diabetic patients. No significant correlation or increase has been found for e-CAT in all patients tested. Mean Hcy in diabetic patients is higher than that in healthy subjects (33.42 ± 1.23 vs. 13.6 ± 0.8 μM), and Hcy increases in relation to the CKD stage. As expected, a significant correlation was found between e-GST and Hcy levels. These findings suggest that e-GST hyperactivity is not caused directly by diabetes but by its consequent renal damage. e-GST, as well as Hcy, may represent an early biomarker of renal failure.

Association between homocysteine status and the risk of nephropathy in type 2 diabetes mellitus

BACKGROUND

It is well documented that hyperhomocysteinemia induces renal injury. However, the association between homocysteine level and type 2 diabetic nephropathy (T2DN) remains elusive.

METHODS

We evaluated the alteration of plasma level of homocysteine in T2DN patients with macroalbuminuria or microalbuminuria compared with type 2 diabetes mellitus (T2DM) controls without albuminuria by performing a meta-analysis. We searched the PubMed, Embase and Cochrane databases from January 1990 to October 2013 to identify studies that met predefined criteria.

RESULTS

Seven studies were included in this investigation. T2DN patients with macroalbuminuria demonstrated a significantly higher level of plasma homocysteine than T2DM without albuminuria (4 studies, random effects SMD: 1.66, 95% CI: 0.46 to 2.87, P=0.007) and T2DN with microalbuminuria (3 studies, random effects SMD: 0.99, 95% CI: 0.62 to 1.36, P<0.001). T2DN patients with microalbuminuria demonstrated significantly higher level of plasma homocysteine than T2DM without albuminuria (6 studies, random effects SMD: 1.29, 95%. CI: 0.59 to 2, P<0.001). Exclusion of any single study had little impact on the pooled SMDs. No evidence of publication bias was observed.

CONCLUSIONS

Our findings indicate that the status of plasma homocysteine is associated with both the risk and severity of nephropathy in T2DM. Frequent monitoring and early intervention should be recommended.

Association of homocysteine with type 2 diabetes: a meta-analysis implementing Mendelian randomization approach

BACKGROUND

We tested the hypothesis that elevated homocysteine (Hcy) level is causally associated with increased risk of type 2 diabetes mellitus (T2DM).

RESULTS

The meta-analysis and Mendelian randomization analysis were performed among 4011 cases and 4303 controls. The absolute pooled mean Hcy concentration in subjects with MTHFR 677TT was 5.55 μmol/L (95% CI, 1.33 to 9.77) greater than that in subjects with MTHFR 677CC in T2DM. Overall, the T allele of the MTHFR 677 C > T conferred a greater risk for T2DM [Random effect (RE) OR = 1.31(1.17-1.64), I² = 41.0%, p = 0.055]. The random effect (RE) pooled OR associated with T2DM for MTHFR 677TT relative to the 677CC was [RE OR = 1.38(1.18-1.62)]. The fixed-effect pooled OR of the association for the MTHFR 677 TT vs CT was 1.29 (95% CI, 1.09-1.51). MTHFR 677 TT showed a significantly higher risk for T2DM compared with MTHFR 677 CC + CT [Fixed effect (FE) OR = 1.32(1.14-1.54), I² = 0.0%, p = 0.686]. The absolute pooled mean Hcy concentration in individuals with T2DM was 0.94 μmol/L (95% CI, 0.40-1.48) greater than that in control subjects. The estimated causal OR associated with T2DM was 1.29 for 5 μmol/L increment in Hcy.

CONCLUSIONS

Our findings provided strong evidence on the causal association of Hcy level with the development of T2DM.

Preoperative oral rehydration therapy with 2.5 % carbohydrate beverage alleviates insulin action in volunteers

Preoperative carbohydrate loading enhances insulin action by approximately 50 %. In some Japanese hospitals, preoperative oral rehydration therapy is performed for preventing dehydration during surgery. We hypothesized that preoperative oral rehydration therapy with a 2.5 % carbohydrate beverage that is widely used in Japan can enhance insulin action. Therefore, we investigated the effect of this 2.5 % carbohydrate beverage on insulin action in volunteers. Six healthy volunteers participated in this crossover randomized study. The participants were segregated into 2 groups: an oral rehydration therapy with 2.5 % carbohydrate beverage group (group A) and a control group (group B). Subjects in group B were allowed to drink only water from 9 pm the day before the test; conversely, group A fasted from 9 pm onward and drank 500 ml of the beverage containing 2.5 % carbohydrate (OS-1; Otsuka Pharmaceutical Factory, Tokushima, Japan) between 9 and 12 pm and again at 6.30 am. At 8.30 am, a hyperinsulinemic normoglycemic clamp was initiated using an artificial pancreas STG-22 (Nikkiso, Tokyo, Japan). Insulin action was evaluated in both groups using the glucose infusion rate. Blood glucose levels at the initiation of the clamp procedure were similar. However, the glucose infusion rate for group A was significantly higher than that of group B (8.6 ± 1.5 vs. 6.8 ± 2.0 mg/kg/min, p = 0.009). In conclusion, the hyperinsulinemic normoglycemic clamp using an artificial pancreas showed that the administration of a 2.5 % carbohydrate oral rehydration solution for preoperative oral rehydration therapy improves insulin action in volunteers.

Undercarboxylated osteocalcin does not correlate with insulin resistance as assessed by euglycemic hyperinsulinemic clamp technique in patients with type 2 diabetes mellitus

BACKGROUND

Recent in vitro and in vivo studies have suggested a critical role of osteocalcin (OC), especially the undercarboxylated form (ucOC), in insulin secretion and insulin sensitivity. The objective of this study was to investigate the association between serum ucOC levels and insulin resistance in humans with type 2 diabetes mellitus.

FINDINGS

We measured serum ucOC levels in 129 patients with type 2 diabetes. Insulin resistance was assessed using the euglycemic hyperinsulinemic clamp technique. The insulin resistance indices used were the M value, which is the total body glucose disposal rate, and the M/I value, which is the M value adjusted for the steady state plasma insulin level. ucOC levels were not correlated with the M value (ρ = -0.013, p = 0.886) or the M/I value (ρ = 0.001, p = 0.995).

CONCLUSIONS

We found no association between ucOC levels and insulin resistance in patients with type 2 diabetes mellitus.

Vegetarianism, vitamin B12 status, and insulin resistance in a group of predominantly overweight/obese South Asian women

OBJECTIVES

Asian Indians are an at-risk group for vitamin B12 deficiency (because of vegetarianism) and insulin resistance (IR). Vegetarianism and consequent vitamin B12 deficiency may be associated with IR. This study aimed to describe the vitamin B12 status of predominantly overweight/obese women of South Asian origin living in Auckland and to correlate serum vitamin B12 and vegetarian status with IR as part of the larger Surya Study looking at health and lifestyle in this population.

METHODS

This was a cross-sectional study of 135 women at least 20 y of age who were not taking vitamin B supplements or medications that could affect vitamin B12 concentrations (serum vitamin B12 < 800 pmol/L). Data collection included serum vitamin B12, serum folate, measurements of IR (HOMA2-IR), and anthropometry. Vegetarian status was established for 124 subjects (90 non-vegetarians, 34 vegetarians).

RESULTS

Mean serum vitamin B12 was 227 pmol/L (95% confidence interval 210-245), serum folate was 19.1 nmol/L (18.0-20.2), and HOMA2-IR was 1.24 (1.13-1.36). Non-vegetarians had higher serum vitamin B12 levels (257 pmol/L, 235-281) than vegetarians (181 pmol/L, 159-207), P < 0.001. Vitamin B12 deficiency (<150 pmol/L) in vegetarians was 24% versus 9% in non-vegetarians. Non-vegetarians had increased body mass index (25.9 kg/m², 25.0-26.9, versus 23.9 kg/m², 22.6-25.3), waist circumference (81 ± 10.1 versus 75.8 ± 9.88 cm), and HOMA2-IR levels (1.30, 1.17-1.46, versus 1.00, 0.83-1.22). No correlation was found between serum vitamin B12 and HOMA2-IR. A significant positive correlation between non-vegetarian status and IR disappeared after controlling for body mass index.

CONCLUSIONS

This study population has a low serum vitamin B12 status, especially if vegetarian. The high rates of observed obesity may have overshadowed any other contributing factor to IR.

Inhibition of hepatic glycogen synthesis by hyperhomocysteinemia mediated by TRB3

Recently, epidemiological and experimental studies have linked hyperhomocysteinemia (HHcy) to insulin resistance. However, whether HHcy impairs glucose homeostasis by affecting glycogenesis in the liver is not clear. In the present study, we investigated the effect of HHcy on hepatic glycogen synthesis. Hyperhomocysteinemia was induced in mice by drinking water containing two percent methionine. Mice with HHcy showed an increase in the phosphorylation of glycogen synthase and a significant decrease in hepatic glycogen content and the rate of glycogen synthesis. The expression of TRB3 (tribbles-related protein 3) was up-regulated in the liver of mice with HHcy, concomitantly with the dephosphorylation of glycogen synthase kinase-3β and Akt. The knockdown of TRB3 by short hairpin RNA suppressed the dephosphorylation of these two kinases. Homocysteine induced an increase in the levels of hepatic cAMP and cAMP response element-binding protein phosphorylation, which in turn up-regulated the expression of peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α and TRB3. The inhibition of PPAR-α by its inhibitor, MK886, or knockdown of PPAR-α by small interfering RNA significantly inhibited the expression of TRB3 induced by homocysteine. The current study demonstrates that HHcy impairs hepatic glycogen synthesis by inducing the expression of TRB3. These results provide a novel explanation for the development and progression of insulin resistance in HHcy.

Homocysteine levels are associated with hippocampus volume in type 2 diabetic patients

BACKGROUND

Elevated total plasma homocysteine (tHcy) levels are associated with cognitive dysfunction, in which changes in the hippocampus plausibly play a pivotal role. We tested the hypothesis that elevated tHcy levels are correlated with hippocampus volume and insulin resistance in nondementia patients with type 2 diabetes.

MATERIALS AND METHODS

The study included 43 nondementia patients with type 2 diabetes, who were divided into two groups: a high tHcy group (age: 65 ± 8 years, mean ± standard deviation, n = 16) and a normal tHcy group (64 ± 9 years, n = 27). Hippocampus volume was quantified with a computer-assisted analysis using a magnetic resonance imaging (MRI) voxel-based specific regional analysis system developed for the study of Alzheimer's disease (VSRAD), which yields a Z-score as the end point for the assessment of hippocampal volume. Results  The Z-score was higher in the high tHcy group compared to the normal tHcy group (P < 0·0001). The fasting plasma glucose (P < 0·01) and insulin (P < 0·0001) concentrations and the homoeostasis model assessment (HOMA) index (P < 0·0001) were higher in the high tHcy group than in the normal tHcy group. Multiple regression analysis showed that the main factors that influenced tHcy levels may be the Z-score and the HOMA index.

CONCLUSIONS

Our results indicate that the elevated levels of tHcy in Japanese nondementia patients with type 2 diabetes are characterised by hippocampal atrophy and insulin resistance and that the Z-score and HOMA index may be the primary factors that influence tHcy levels.

The genetics of vascular complications in diabetes mellitus

Prospective identification of which individuals with diabetes mellitus (DM) are at greatest risk for developing cardiovascular disease (CVD) complications would have considerable public health importance by allowing the allocation of limited resources to be focused on those individuals who would most benefit from aggressive intervention. Over the past 20 years genetic disease association studies have demonstrated that polymorphisms at specific genetic loci may identify those individuals at greatest risk for developing CVD in the setting of DM. This article reviews the evidence accumulated to date on four polymorphic loci with the aim of explaining how these polymorphisms modify the risk for CVD in DM by modifying the functional activity of a specific gene. Use of the knowledge of these genetic differences among individuals in targeting drug therapy (pharmacogenomics) is also discussed.

Acute hyperhomocysteinaemia blunts endothelial dependent and endothelial independent vasodilatation in diabetic patients

The aim of this study was to investigate the effects of acute, methionine-induced hyperhomocysteinaemia on endothelial function of skin microcirculation in diabetic compared with non-diabetic persons. Endothelial- and non-endothelial-dependent vasodilatation of the skin microcirculation were evaluated in 20 persons with type 2 diabetes (59.95+/-2.36 years old) and 24 age- and gender-matched controls using laser Doppler flowmetry, during fasting and four hours after 0.1 g/kg methionine-induced acute hyperhomocysteinaemia. Methionine loading caused a comparable increase of homocysteine in the two groups. Four hours after induction of acute hyperhomocysteinaemia, endothelial-dependent vasodilatation (acetylcholine effect) was lower in the diabetic patients compared with the controls ([mean+/-SEM] 8.09+/-1.18-fold increase in diabetic patients vs. 11.11+/-1.33-fold increase in controls, p=0.027). The same was observed for the endothelial-independent vasodilatation (sodium-nitroprusside effect, 7.55+/-0.80-fold increase in the diabetic patients vs. 12.19+/-1.26-fold increase in controls, p=0.008). Acute hyperhomocysteinaemia causes a decreased response of both endothelial-dependent and endothelial-independent vasodilatation of the skin microcirculation in diabetic compared with non-diabetic persons. These alterations might contribute to the vascular complications of hyperhomocysteinaemia in diabetes, and especially the microvascular ones.

Serum N-terminal-pro-brain natriuretic peptide (NT-pro-BNP) and homocysteine levels in type 2 diabetic patients with asymptomatic left ventricular diastolic dysfunction

AIMS

: The aim of this study was to determine serum NT-proBNP and plasma Hcy levels and to explore the relationship between serum NT-proBNP and plasma Hcy levels in type 2 diabetic patients with and without asymptomatic LVDD.

METHODS

: NT-proBNP and Hcy levels were measured 31 patients with type 2 diabetes mellitus. According to echocardiographic data, diabetic patients were divided into two groups: normal LV function or LV diastolic dysfunction.

RESULTS

: Serum NT-proBNP levels in diabetic patients with LVDD were significantly higher than in diabetic patients with normal LV function and controls. The area under the receiver-operating characteristic (ROC) curve for NT-proBNP to separate normal vs. diastolic dysfunction was 0.96 in type 2 diabetic patients. Plasma Hcy levels were significantly higher in both diabetic groups than in controls. Positive correlation was noted between NT-proBNP and Hcy levels in diabetic patients with LVDD (r=0.881, p=0.0001).

CONCLUSIONS

: The correlation between elevated NT-proBNP and Hcy levels in diabetic patients with LVDD suggest an association between homocysteinemia and increased NT-proBNP secretion. Our data indicate that NT-proBNP may be a simple screening tool to select diabetic patients with LVDD requiring further examination with echocardiography.

Hyperhomocysteinemia stimulates hepatic glucose output and PEPCK expression

Homocysteine is an intermediate in the sulfur amino acid metabolism. Recent studies suggested that there might be links between hyperhomocysteinemia and insulin resistance. In the present study, we investigated the effect of homocysteine on glucose metabolism. We demonstrated that the levels of insulin were significantly higher in mice with hyperhomocysteinemia than those in the normal mice after administration of glucose. The effect of insulin on glucose output was significantly blocked in the homocysteine-treated hepatocytes. In addition, the expression of phosphoenolpyruvate carboxykinase (PEPCK) gene was elevated in the liver of mice with hyperhomocysteinemia and primary mouse hepatocytes treated with homocysteine. The action of homocysteine was suppressed by H89, a protein kinase A (PKA) inhibitor. Thus, hyperhomocysteinemia may be considered as a risk factor that contributes to the development of insulin resistance with respect to elevated glucose output and upregulation of PEPCK, probably via the PKA pathway. Our study provides a novel mechanistic explanation for the development of insulin resistance in hyperhomocysteinemia.

Genetic and environmental influences on total plasma homocysteine and coronary artery disease (CAD) risk among South Indians

BACKGROUND

Hyperhomocysteinemia, a documented risk factor for CAD is highly prevalent in Indians. The rationale behind the current study is to explore the genetic and environmental causes for such high prevalence as there are limited studies in this context.

METHODS

A total of 108 CAD cases and 108 controls were analyzed for tHcy and 4 folate pathway genetic polymorphisms [methylene tetrahydrofolate reductase (MTHFR) C677T, 5-methyltetrahydrofolate homocysteine methyl transferase (MTR) A2756G, methionine synthase reductase (MTRR) A66G and glutamate carboxypeptidase II (GCPII) C1561T] using reverse phase HPLC and PCR-RFLP methods respectively.

RESULTS

MTHFR 677T, MTRR 66A, GCPII 1561T, male gender, alcohol intake, smoking, diabetes, creatinine and hypertension were found to influence tHcy. After controlling for confounding factors, Hyperhomocysteinemia and two of its genetic determinants i.e. MTHFR C677T [OR: 1.96, 95% CI: 1.06-3.61] and GCP II C1561T [OR: 2.09, 95% CI: 1.09-3.97] were found to be associated with risk for CAD. Significant epistatic interactions were observed between MTHFR 677T/MTR 2756G and GCP II 1561T/MTRR 66G. Alcohol intake in subjects with MTR 2756G allele was found to inflate the risk for CAD [OR: 4.15, 95% CI: 1.35-12.69].

CONCLUSION

Hyperhomocysteinemia, C677T MTHFR and C1561T GCPII are risk factors for CAD. Potential gene--gene and gene--environment interactions indicate the need for multi-variate analyses for risk prediction.

Menopause modulates homocysteine levels in diabetic and non-diabetic women

High total homocysteine (tHcy) plasma levels may contribute to the increased cardiovascular risk of Type 2 diabetic women. However, to date, data on factors modulating tHcy concentration in this population are scarce. Fasting tHcy, vitamin B12, folate plasma levels, and the methylene tetrahydrofolate reductase (MTHFR) C677T genotype as well as clinical, biochemical, and lifestyle variables were compared in 91 Type 2 diabetic and 91 matched non-diabetic women (40 pre- and 51 post-menopausal, in each group). Fasting tHcy concentration did not differ between diabetic and control women, even after multivariable adjustment. In both groups, tHcy levels increased after menopause, but the differences were weakened after multivariable adjustment. The MTHFR genotype distribution was in accordance with the Hardy-Weinberg equilibrium, with a similar TT frequency in diabetic (22.2 %) and control women (19.8%). Overall, tHcy plasma concentration was higher in TT homozygous compared to other genotypes. We found a menopause-genotype interaction on tHcy levels (p=0.068 for menopause*genotype interaction); overall, the increase of tHcy concentration in TT subjects was limited to pre-menopause (p<0.0001; adjusted p=0.024), and this was confirmed after considering diabetic and control women separately (p=0.001 and p=0.01, respectively). At multivariate analysis, menopause was an independent correlate of tHcy concentration, together with creatinine, folate and MTHFR genotype. Our data show that menopause has a strong influence on tHcy concentration even in Type 2 diabetic women and demonstrate, for the first time, that it may modulate the association between tHcy and the common MTHFR polymorphism both in diabetic and non-diabetic women.

Homocysteine upregulates resistin production from adipocytes in vivo and in vitro

OBJECTIVE

Homocysteine (Hcy) is epidemiologically related to insulin resistance, which has been speculated to be a low-grade systemic inflammatory condition. Resistin acts as a critical mediator of insulin resistance associated with inflammatory conditions. We aimed to determine whether Hcy can induce insulin resistance by directly regulating the expression and secretion of resistin from adipose tissue.

RESEARCH DESIGN AND METHODS

The effect of Hcy on the expression and secretion of resistin and insulin resistance was investigated using primary rat adipocytes and mice with hyperhomocysteinemia (HHcy).

RESULTS

Hcy impaired glucose transport and, particularly, the insulin signaling pathway as shown by decreased insulin-stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate (IRS)-1, increased serine phosphorylation of IRS-1, and inhibited Akt phosphorylation both in vitro and in vivo, and these impairments were accompanied by an increase in resistin expression. Compared with normal mice, HHcy mice with a clinically relevant level of plasma Hcy (19 micromol/l) showed significantly increased resistin production from adipose tissue (33.38 +/- 3.08 vs. 19.27 +/- 1.71 ng/ml, P < 0.01). Hcy (300-1000 micromol/l) also increased mRNA expression of resistin in primary rat adipocytes in a time- and concentration-dependent manner, with maximal induction at 24 h of approximately fourfold with 1,000 micromol/l. In addition, Hcy-induced resistin expression attenuated by treatment with reactive oxygen species (ROS) scavengers, protein kinase C (PKC), and nuclear factor (NF)-kappaB inhibitors implies a role in the process for ROS, PKC, and NF-kappaB.

CONCLUSIONS

HHcy may promote insulin resistance through the induction of resistin expression and secretion from adipocytes via the activation of the ROS-PKC-NF-kappaB pathway.

Factors associated with serum total homocysteine level in type 2 diabetes

OBJECTIVES

The aim of this study was to investigate the determinants of serum total homocysteine level (tHcy) in patients with type 2 diabetes mellitus (DM) according to sex.

METHODS

A total of 1,276 Japanese, diabetics (n = 280) with a control group of non-diabetics (n = 996), were enrolled into the study from 2003 to 2005. This cross-sectional study was conducted for all the subjects, using personal data regarding clinical characteristics and lifestyle. Multiple regression analysis was performed to analyze the association of tHcy with selected factors.

RESULTS

In diabetic subjects, estimated glomerular filtration rate (eGFR) and serum creatinine levels (Cre), even those within the normal range, were strongly associated with tHcy after adjustment in both sexes; the standardized partial regression coefficient of eGFR for tHcy was -0.251, (p = 0.001) in diabetic men and -0.523, (p < 0.001) in diabetic women. Furthermore, the eGFR of the diabetics, except patients with nephropathy, also had significant association with tHcy in both sexes. Fasting plasma glucose levels and serum triglyceride levels were strongly associated with tHcy in diabetic men only. HbA1c was also associated with tHcy in diabetic men only, though not as significantly. Age and presence of hypertension were significantly associated with tHcy in women.

CONCLUSIONS

This study suggests that there are some differences in the factors associated with tHcy between diabetics and non-diabetics, and between the sexes. There is, therefore, circumstantial evidence that elevated tHcy should be evaluated clinically. Because tHcy was strongly associated with eGFR and Cre, even within the normal ranges, tHcy may have important implications regarding the microangiopathy of the kidney and atherosclerosis.

Circulating homocysteine levels in patients with type 2 diabetes mellitus

BACKGROUND AND AIM

Previous studies have shown conflicting results regarding circulating homocysteine levels in patients with type 2 diabetes.

METHODS AND RESULTS

This observational study included 2121 patients with angiographically proven coronary artery disease (507 patients with type 2 diabetes and 1614 patients without diabetes). Circulating homocysteine levels, methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism, renal function, presence of coronary artery disease (CAD) diagnosed by coronary angiography, and circulating folate and vitamin B12 status were assessed. Plasma homocysteine levels [median (25th; 75th percentile)] were significantly higher in patients with diabetes than in those without [12.4 micromol/L (9.9 micromol/L; 15.9 micromol/L) versus 11.7 micromol/L (9.6 micromol/L; 14.5 micromol/L), P=0.011]. Diabetes affected homocysteine levels only in patients with a glomerular filtration rate <90 mL/min [13.0 micromol/L (10.5 micromol/L; 16.7 micromol/L) in patients with diabetes versus 12.2 micromol/L (10.1 micromol/L; 15.2 micromol/L) in patients without diabetes, P=0.006] but not in those with a glomerular filtration rate > or = 90 mL/min [10.1 micromol/L (8.1 micromol/L; 12.4 micromol/L) versus 10.2 micromol/L (8.8 micromol/L; 12.3 micromol/L), P=0.267]. Multivariable analysis did not show an independent association between diabetes and homocysteine level (P=0.342).

CONCLUSION

Circulating homocysteine levels are increased in patients with type 2 diabetes compared with non-diabetic patients due to a more diabetes-associated adverse risk profile rather than to diabetes itself.

Correlations between homocysteine levels and atherosclerosis in Japanese type 2 diabetic patients

Elevated total plasma homocysteine (tHcy) level and aortic stiffness are associated with high mortality in type 2 diabetic patients. We tested the hypothesis that tHcy correlates with aortic stiffness and insulin resistance in type 2 diabetic patients. The study consisted of 40 Japanese patients with type 2 diabetes mellitus and high tHcy levels (mean age +/- SD, 57 +/- 7 years) and a control group of 45 age-matched patients with normal tHcy levels (mean age +/- SD, 57 +/- 6 years). Brachial-ankle pulse wave velocity (BaPWV) was measured by an automatic oscillometric method. Brachial-ankle pulse wave velocity was used as an index of atherosclerosis. Body mass index values (P < .05), waist circumferences (P < .05), and the waist-to-hip ratios (P < .05) were larger in the high-tHcy group than in the normal-tHcy group. The BaPWV was higher in the high-tHcy group than in the normal-tHcy group (P < .0001). Fasting plasma glucose (P < .005) and insulin concentrations (P < .0001), and the homeostasis model assessment (HOMA) index (P < .0001) were higher in the high-tHcy group than in the normal-tHcy group. Multiple regression analysis showed that tHcy levels were independently predicted by BaPWV and the HOMA index. In conclusion, our results indicate that the elevated level of tHcy in Japanese patients with type 2 diabetes mellitus is characterized by increased aortic stiffness and insulin resistance, and that the BaPWV and the HOMA index are independent predictors of tHcy.

Hyperhomocysteinemia is associated with visceral adiposity in Japanese patients with type 2 diabetes mellitus

This study aims to investigate the relationship between the circulating level of homocysteine and body adiposity in Japanese patients with type 2 diabetes mellitus. We measured the body mass index (BMI), waist and hip circumferences, visceral and subcutaneous adiposities, visceral/subcutaneous (V/S) adiposity ratio, and insulin resistance as assessed by the Homeostasis Model Assessment (HOMA) index in patients with hyperhomocysteinemia. The study group consisted of 17 Japanese patients with type 2 diabetes and hyperhomocysteinemia (age: 62+/-10 years, mean+/-S.D.), and the control group consisted of 24 age-matched type 2 diabetes patients with normohomocysteinemia (60+/-11 years). The visceral adiposity, HOMA index, and V/S ratio were significantly higher in the hyperhomocysteinemia group than in the normohomocysteinemia group (P<0.05). In contrast, the BMI, hip circumference, and subcutaneous adiposity were similar between the two groups (P>0.1). Furthermore, multiple regression analysis showed that hyperhomocysteinemia was closely related to insulin resistance and visceral adiposity. Our results indicate that the presence of hyperhomocysteinemia in our population of Japanese patients with type 2 diabetes-associated insulin resistance was associated with increased visceral but not subcutaneous adiposity.

Cardiac synchronous and dys-synchronous remodeling in diabetes mellitus

Glucose-mediated impairment of homocysteine (Hcy) metabolism and decrease in renal clearance contribute to hyperhomocysteinemia (HHcy) in diabetes. The Hcy induces oxidative stress, inversely relates to the expression of peroxisome proliferators activated receptor (PPAR), and contributes to diabetic complications. Extracellular matrix (ECM) functionally links the endothelium to the myocyte and is important for cardiac synchronization. However, in diabetes and hyperhomocysteinemia, a "disconnection" is caused by activated matrix metalloproteinase with subsequent accumulation of oxidized matrix (fibrosis) between the endothelium and myocyte (E-M). This contributes to "endothelial-myocyte uncoupling," attenuation of cardiac synchrony, leading to diastolic heart failure (DHF), and cardiac dys-synchronizatrion. The decreased levels of thioredoxin and peroxiredoxin and cardiac tissue inhibitor of metalloproteinase are in response to antagonizing PPARgamma.

Hyperhomocysteinemia induces insulin resistance in male Sprague-Dawley rats

Association between elevated plasma homocysteine levels and insulin resistance has been reported, however, whether hyperhomocysteinemia induces insulin resistance or it is actually hyperinsulinemia that causes elevated plasma homocysteine levels, the direction of causality in this association is not still clear. In this study, we examined the hypothesis that hyperhomocysteinemia may cause hyperinsulinemia leading to insulin resistance in rats. Plasma glucose, insulin and total homocysteine concentrations were determined in two groups of male Sprague-Dawley rats, a test group that administered with homocysteine and a control group with no homocysteine in daily drinking water before and after 50 days. Oral glucose tolerance tests were also performed in control and test groups before and after 50 days. Mean fasting plasma insulin level was significantly higher (42.5+/-20.4 mU/L versus 23.2+/-5.9 mU/L, p=0.01), whereas mean glucose: insulin ratio was significantly lower in test rats than in control rats (0.12+/-0.07 versus 0.17+/-0.05, p=0.04) after 50 days. In addition, mean homeostasis assessment insulin resistance index was significantly higher in test rats than in control rats (7.5+/-3.5 versus 4.0+/-1.6, p=0.02) after 50 days. The mean plasma glucose level was not significantly different (4.1+/-1.1 mmol/L versus 3.9+/-0.8 mmol/L, p=0.57) between controls and test rats, however, the results from oral glucose tolerance tests showed the development of insulin resistance in test rats after 50 days administration of homocysteine. Results from this in vivo study suggest that homocysteine can cause insulin resistance and this relationship may need to be considered when evaluating the role of plasma homocysteine as a risk factor in patients with obesity and type II diabetes.

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

OBJECTIVES

Metformin is widely used in patients with type 2 diabetes but may decrease vitamin B(12) levels and increase levels of homocysteine (Hcy), a cardiovascular risk factor. Rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, may reduce markers of inflammation. We investigated whether 6 weeks' treatment with metformin or rosiglitazone affects serum concentrations of Hcy, folate, or vitamin B(12) in subjects with newly diagnosed type 2 diabetes compared with controls.

METHODS

We examined 165 patients with type 2 diabetes. Fasting blood samples, a physical examination, and a complete medical history were performed at the beginning and at the end of the treatment. All blood samples were obtained after a 12-h fast.

RESULTS

After treatment, metformin use was associated with an increase in levels of Hcy by 2.36 micromol/l and decreases in folate and vitamin B(12) concentrations by -1.04 ng/ml and -20.17 pg/ml. During rosiglitazone treatment, Hcy levels decreased by -0.92 micromol/l; folate and vitamin B(12) levels remained unchanged. Metformin and rosiglitazone significantly decreased levels of triglyceride (TG), low-density lipoprotein (LDL), total cholesterol (total-C), HbA1c, insulin, and homeostasis model assessment (HOMA). Metformin also significantly decreased body weight. In controls, there was no change in Hcy, folic acid, vitamin B(12), TG, LDL, total-C, HbA1c, insulin, or HOMA levels. Homocysteine change did not correlate with insulin, folate, or vitamin B(12) changes in the metformin and rosiglitazone groups.

CONCLUSIONS

In patients with type 2 diabetes, metformin reduces levels of folate and vitamin B(12) and increases Hcy. Conversely, rosiglitazone decreases Hcy levels in this time period. The clinical significance of these findings remains to be investigated.

Nontraditional atherosclerotic risk factors and extent of coronary atherosclerosis in patients with combined impaired fasting glucose and impaired glucose tolerance

Partially inconsistent data exist on mutual relations between nontraditional atherosclerotic risk factors, including the magnitude of insulin resistance (IR), as well as on their relevance for atherogenesis in the metabolic syndrome. Subjects exhibiting combined impaired fasting glucose and impaired glucose tolerance (IFG/IGT) are exposed to an exceptionally high risk for atherogenesis and development of type 2 diabetes mellitus. Because of islet Beta-cell dysfunction, the usefulness of commonly used indices of IR is limited in IFG/IGT. Our aim was to assess the relationship between extent of angiographic coronary artery disease (CAD) and nontraditional atherosclerotic risk factors (including IR by a clamp-based golden standard method) in IFG/IGT. Fifty-three subjects (32 men, 21 women; mean age, 55 +/- 11 years) with stable angina, preserved left ventricular systolic function, and IFG/IGT were divided into 3 groups: group A (no coronary stenoses >50%, n = 22), group B (1-vessel CAD, n = 15), and group C (2/3-vessel CAD, n = 16). Insulin sensitivity was quantified by a hyperinsulinemic euglycemic clamp technique and expressed as M. M value, plasma homocysteine (Hcy) level, and asymmetric dimethyl-L-arginine (ADMA)/L-arginine ratio were independent determinants of CAD extent as shown by forward stepwise discriminant function analysis. Compared with group A (M = 32.7 +/- 9.3 micromol/kg fat-free mass [FFM] per minute; Hcy, 8.1 +/- 1.4 micromol/L), lower M and higher Hcy levels were found in group B (M = 16.9 +/- 8.2 micromol/kg FFM per minute, P < .001; Hcy, 11.2 +/- 2.9 micromol/L, P = .003) and C (M = 16.4 +/- 7.8 micromol/kg FFM per minute, P < .001; Hcy, 12.8 +/- 3.9 micromol/L, P < .001). The ADMA/L-arginine ratio was increased in group C (0.0078 +/- 0.0011) compared with group A (0.0063 +/- 0.0013, P = .03) and B (0.0058 +/- 0.0012, P = .01). Multivariate correlates (P < .05) of plasma Hcy concentrations were M (beta = -.34 +/- .12, P = .008), creatinine clearance (beta = -.23 +/- .10, P = .03) and fasting insulin (beta = .25 +/- .12, P = .04). This indicates an additive contribution of IR, plasma Hcy, and elevated ADMA/L-arginine ratio to the extent of angiographic CAD in combined IFG/IGT.

Adiponectin and mortality in patients undergoing coronary angiography

CONTEXT

The adipokine adiponectin has been suggested to protect against coronary artery disease (CAD). However, studies addressing the association between adiponectin and mortality are sparse.

OBJECTIVE

The objective of the study was to elucidate the relationship between adiponectin and mortality.

DESIGN, SETTING, AND PARTICIPANTS

Adiponectin was determined in 2473 persons with and 673 persons without angiographic CAD. During a mean follow-up period of 5.45 yr, 427 persons with CAD and 55 persons without CAD died.

MAIN OUTCOME MEASURE

Hazard ratios for mortality according to adiponectin levels were measured.

RESULTS

Adiponectin was positively related to female gender, age, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, homocysteine, and N-terminal pro-B-type natriuretic peptide. It was inversely related to glomerular filtration rate, body mass index, and triglycerides and was low in diabetes mellitus and CAD. An increase of 1 sd in adiponectin was associated with unadjusted and fully adjusted hazard ratios for death from any cause of 1.31 [95% confidence interval (CI) 1.20-1.42] and 1.22 (95% CI 1.12-1.34), and for death from cardiovascular causes of 1.32 (95% CI 1.19-1.45) and 1.23 (95% CI 1.11-1.37), respectively. In angiographic CAD, stable CAD, and unstable CAD, the predictive value of adiponectin was similar to that in the entire cohort, but it did not attain statistical significance in persons without angiographic CAD. Adiponectin was also positively related to the risk of death from noncardiovascular causes.

CONCLUSIONS

Despite the common view about adiponectin as a protective molecule in cardiovascular disease, high adiponectin independently predicts all-cause, cardiovascular, and noncardiovascular mortality in individuals with CAD.

High glucose and homocysteine synergistically affect the metalloproteinases-tissue inhibitors of metalloproteinases pattern, but not TGFB expression, in human fibroblasts

AIMS/HYPOTHESIS

Atherosclerosis is particularly aggressive in patients with diabetes. Hyperhomocysteinaemia causes oxidative stress and cytokine secretion: its atherogenic effect is mediated by an enhanced inflammatory response. Matrix metalloproteinases (MMPs) regulate extracellular matrix degradation and remodelling, and contribute to the vulnerability of the atherosclerotic lesion. Fibroblasts contribute to collagen biosynthesis and participate in plaque remodelling via expression and release of MMP2 and MMP9. To explore the role of hyperhomocysteinaemia in cellular pathways involved in plaque growth and stability in diabetic patients, we studied the effect of hyperhomocysteinaemia in human fibroblasts grown in the presence of normal or high glucose concentrations.

MATERIALS AND METHODS

In fibroblasts of five normal subjects, grown at 5.5 or 22 mmol/l glucose and treated with homocysteine, we determined: (1) MMP2, MMP9 and tissue inhibitor of metalloproteinases (TIMP)-1 (an MMP inhibitor) production by western blot analysis; (2) their activity by zymography; (3) TGFB1 expression by real-time PCR; and (4) TGFB, fibronectin and IL6 release by ELISA.

RESULTS

Hyperhomocysteinaemia increased the production and enzymatic activity of MMP2 and MMP9, the effect being more pronounced in high glucose. Conversely, TIMP1 production was reduced by hyperhomocysteinaemia in both conditions, especially in high glucose. Hyperhomocysteinaemia also stimulated IL6 release, at least in part through nuclear factor-kappaB activation. TGFB1 expression was not affected by hyperhomocysteinaemia either in normal or in high glucose.

CONCLUSIONS/INTERPRETATION

Homocysteine upregulates the MMP-TIMP pathway and IL6 release, the effect being stronger in the presence of high glucose. These actions of homocysteine may contribute to the increased atherogenesis observed in diabetic patients with poor metabolic control.

Homocysteine levels are associated with the results of 123I-metaiodobenzylguanidine myocardial scintigraphy in type 2 diabetic patients

PURPOSE

Elevated total plasma homocysteine (tHcy) levels and cardiovascular autonomic dysfunction are associated with a high mortality in type 2 diabetic patients. We tested the hypothesis that hyperhomocysteinemia is associated with insulin resistance and cardiovascular autonomic dysfunction in type 2 diabetic patients not receiving insulin treatment.

METHODS

The study group consisted of 17 type 2 diabetic patients with high tHcy levels (>15 mmol/l, age 58+/-5 years, high tHcy group). The control group consisted of 23 age-matched type 2 diabetic patients with normal tHcy levels (<or=15 mmol/l, age 58+/-9 years, normal tHcy group). Cardiovascular autonomic function was assessed by baroreflex sensitivity, heart rate variability, plasma norepinephrine concentrations, and cardiac (123)I-metaiodobenzylguanidine (MIBG) scintigraphy.

RESULTS

Early and delayed (123)I-MIBG myocardial uptake values were lower (p<0.005 and p<0.01, respectively) and the percent washout rate of (123)I-MIBG was higher (p<0.001) in the high tHcy group than in the normal tHcy group. The fasting plasma insulin concentrations (p<0.0001) and the homeostasis model assessment (HOMA) index values (p<0.0001) were higher in the high tHcy group than in the normal tHcy group. Multiple regression analysis revealed that the level of tHcy was independently predicted by the HOMA index values and the myocardial uptake of (123)I-MIBG at the delayed phase.

CONCLUSION

Our results demonstrate that high levels of tHcy are associated with depressed cardiovascular autonomic function and insulin resistance in patients with type 2 diabetes mellitus.