Low total plasma homocysteine concentrations in patients with type 1 diabetes

Review: Homocysteine, endothelial dysfunction and oxidative stress in type 1 diabetes mellitus

Type 1 diabetes is associated with an increased risk of cardiovascular disease, which cannot be fully explained by traditional risk factors. Elevated plasma homocysteine is an independent risk factor for macrovascular disease in the general population. This review examines the evidence for hyperhomocysteinaemia in patients with type 1 diabetes and describes the mechanisms that may lead to increased macrovascular susceptibility.

While reports of plasma homocysteine levels in type 1 diabetes are inconsistent, increased plasma homocysteine levels have been found in subgroups of patients with microalbuminuria, nephropathy and macrovascular disease. Although a direct causal relationship between plasma homocysteine and atherosclerosis remains to be proven, potential mechanisms of vascular damage by homocysteine include endothelial dysfunction linked to increased oxidative stress. This could contribute to the association between hyperhomocysteinaemia and macrovascular disease in type 1 diabetes.

Folic acid, vitamin B12, and homocysteine levels during fasting and after methionine load in patients with Type 1 diabetes mellitus

AIMS

To assess plasma concentrations of folic acid, vitamin B12, and total plasma homocysteine (tHCY) during fasting and after methionine load in young patients with Type 1 diabetes mellitus (T1DM).

METHODS

We enrolled 41 young patients with T1DM without any sign of microvascular complications and 123 healthy controls in a 1:3 case-control study. Fasting and post-methionine load (PML) tHCY, folic acid, and vitamin B12 levels were measured in both groups. Data regarding chronological age, metabolic control (assessed by mean values of glycated hemoglobin in the last 12 months) and disease duration were also recorded.

RESULTS

Fasting and PML tHCY levels were significantly lower in patients than in controls: 7.3+/-2.7 micromol/l vs 8.3+/-2.5 micromol/l (p=0.01), and 16.7+/-5.8 micromol/l vs 17.3+/-4.3 micromol/l (p=0.01), respectively. No correlation was found between fasting and PML tHCY levels and chronological age, disease duration, metabolic control, and insulin requirement. Patients had significantly higher vitamin B12 levels compared to controls: 767+/-318 pg/ml vs 628+/-236 pg/ml (p=0.003), while folic acid turned out to be lower in patients than in controls: 5.3+/-1.9 nmol/l vs 7.5+/-2.6 nmol/l (p<0.0001).

CONCLUSIONS

Adolescents and young adults with T1DM without microvascular complications showed lower tHCY both during fasting and after methionine load. Lower folate concentrations in these patients might benefit from food fortification.

Elevated plasma adiponectin and decreased plasma homocysteine and asymmetric dimethylarginine in children with type 1 diabetes

OBJECTIVE

Type 1 diabetes has a bad prognosis concerning the pathogenesis of cardiovascular diseases (CVD). The purpose of this study was to evaluate different possible new risk indices for CVD in children with type 1 diabetes.

MATERIAL AND METHODS

The present study included 30 children with diabetes (mean HbA1C 9.8%), aged between 4.7 and 18.6 years and with no clinical evidence of vascular complications, and 30 healthy subjects matched by sex, age and body mass index. Blood pressure was measured and blood samples were obtained for lipid profile, creatinine, glucose, high sensitive C-reactive protein (hsCRP), intercellular adhesion molecule-1 (ICAM-1), asymmetric dimethylarginine (ADMA), adiponectin and homocysteine.

RESULTS

Children with diabetes had significantly higher blood pressure, plasma hsCRP, ICAM-1, adiponectin levels and lower homocysteine, ADMA concentrations than their control subjects. In multivariate regression analysis, the best predictors for systolic blood pressure were diabetes group, plasma homocysteine concentration and BMI (Adj R(2) = 0.38, p<0.0001), and for diastolic blood pressure diabetes group and triglycerides level (Adj R(2) = 0.27, p<0.0001).

CONCLUSIONS

Children with diabetes, in view of their higher future risk of CVD, are characterized by a higher concentration of protective adiponectin and paradoxically lower blood concentrations of some other possible risk markers of atherosclerosis, i.e. ADMA and homocysteine compared to healthy children.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Plasma total homocysteine levels in children with type 1 diabetes: relationship with vitamin status, methylene tetrahydrofolate reductase genotype, disease parameters and coronary risk factors

The objectives of this study were: to determine plasma total homocysteine tHcy levels and the prevalence of hyperhomocysteinemia in children with type 1 diabetes, to determine correlates of plasma tHcy levels with nutritional factor such as serum folic acid and vitamin B12 levels, genetic factors as methylenetetrahydrofolate reductase MTHFR gene polymorphism (C677T and A1298C), to attempt to identify possible dependencies between tHcy and the degree of metabolic control, the duration of the disease and presence of complications, and also to determine the relationship between other coronary risk factors. Plasma tHcy levels and other related parameters performed in 32 children with type 1 diabetes and 23 age-sex matched healthy children. Median tHcy level was higher in the patient group (11.38, 3.28 to 66.01 micromol/l) than the control group (8.78, 1.06 to 13.66 mol/l) (p < 0.05). A 28.1 per cent (n = 9) of the diabetic patients had hyperhomocysteinemia, four case with mild and five case with moderate. Plasma tHcy levels were positively correlated with disease duration and C-reactive protein CRP levels and negatively correlated with disease onset age. The hyperhomocysteinemic group had higher CRP levels, longer disease duration and early onset of disease than non-hyperhomocysteinemic group (p < 0.05 in both), respectively. The hyperhomocysteinemic group had significantly higher CRP, total cholesterol, triglyceride, apolipoprotein B, systolic blood pressure, blood urea nitrogen and creatinine levels and lower folate, apolipoprotein A1 levels and glomerular filtration rate values than the control group. Plasma tHcy levels were higher in diabetic children with poor metabolic control. Because of hyperhomocysteinemia is common in diabetic children and plasma tHcy levels correlated with early onset of the disease and disease duration, we recommend the usage of plasma tHcy levels as a risk indicator parameter with other coronary risk factor for detecting and preventing cardiovascular disease in diabetic children.

Are plasma total homocysteine and other amino acids associated with glucose intolerance in uncomplicated pregnancies and preeclampsia?

OBJECTIVE

To evaluate the possible association between plasma total homocysteine or other amino acid concentrations and gestational diabetes or glucose intolerance (GI), in normotensive and preeclamptic pregnant women.

STUDY DESIGN

Prospective study including 243 pregnant women without previous risk factors. O'Sullivan test (plus oral glucose tolerance test when necessary) was performed, and homocysteine, B vitamins and plasma amino acids (AA) were measured at 24-25 weeks. Homocysteine and other amino acids were also measured in the third trimester.

RESULTS

Significant differences were observed in the incidence of preeclampsia in relation to abnormal glucose tolerance (P < 0.012). In normotensive patients, the glucose intolerance group showed significantly lower tHcy (P = 0.021) and increased plasma alanine concentrations in comparison with controls (P = 0.046), although no correlation was observed between both amino acid concentrations.

CONCLUSIONS

(a) A higher incidence of preeclampsia was observed in abnormal glucose tolerance patients, (b) total homocysteine and alanine were the only individual amino acids whose plasma concentrations varied according to the glucose tolerance classes, and (c) an association between hyperhomocysteinemia and glucose intolerance in our preeclamptic patients could not be demonstrated.

Fasting homocysteine levels in adults with type 1 diabetes and retinopathy

BACKGROUND AND METHODS

Whether hyperhomocysteinemia is associated with diabetic retinopathy is still being debated. We measured homocysteine and thrombomodulin, a marker of endothelial cell damage, in patients with type 1 diabetes mellitus and retinopathy (n=25) and in a well-matched group of diabetic patients without retinopathy (n=23). All patients had normal serum creatinine and no macroalbuminuria.

RESULTS

Fasting homocysteine levels were higher in the group with retinopathy than in the group without retinopathy (8.75+/-1.9 vs. 7.69+/-1.6 micromol/l, P<0.05). Microalbuminuria was more prevalent in the group with diabetic retinopathy and it correlated with homocysteine levels in this group (p<0.05). Microalbuminuria was the most powerful independent determinant of homocysteine levels in multiple regression analysis in the group with retinopathy (p<0.01). Thrombomodulin levels were not different in the two groups (36.6+/-9.7 vs. 34.9+/-11.1, p>0.1) and there was no correlation between homocysteine and thrombomodulin levels in either group.

CONCLUSIONS

The slight rise in homocysteine levels in patients with diabetic retinopathy was possibly caused by the early nephropathy as indicted by microalbuminuria. This small rise in homocysteine levels was not associated with endothelial dysfunction, as measured by serum thrombomodulin levels.

Homocysteine and methylmalonic acid in diagnosis and risk assessment from infancy to adolescence

The concentration of total homocysteine (tHcy) in serum and plasma is elevated in both folate and cobalamin deficiencies, whereas methylmalonic acid (MMA) in serum, plasma, or urine is a specific marker of cobalamin function. The combined measurement of both metabolites is useful for the diagnosis and follow-up of these deficiency states. In addition, tHcy is elevated under various pathologic states (eg, renal failure), and hyperhomocysteinemia is associated with an increased risk of cardiovascular disease, cognitive dysfunction, and adverse pregnancy outcomes. The diagnostic utility of tHcy and MMA concentrations as markers of folate and cobalamin deficiencies in healthy and diseased children has been documented. This article briefly summarizes the biochemical background of tHcy and MMA and the associations of tHcy and MMA with various disease states and focuses on novel data obtained in infants, children, and adolescents, with emphasis on cobalamin status in infants. The utility of tHcy and MMA as indicators of cobalamin and folate deficiencies in adults can be extended to infants and older children. Furthermore, as in adults, tHcy is related to unhealthy lifestyle factors and is a risk factor for vascular disease. High MMA concentrations in newborns, occasionally denoted as benign methylmalonic aciduria, may reflect impaired cobalamin function.

Hyperhomocysteinemia and B-Vitamin Deficiencies in Infants and Children

Measurement of total homocysteine (tHcy) in healthy and diseased children has documented the utility of this marker in pediatric research and diagnostics. This article focuses on novel data obtained in infants, children and adolescents, with emphasis on cobalamin status in infants. In children, determinants of plasma tHcy are similar to those established in adults, and include age, gender, nutrition, B-vitamin status, and some drugs interfering with B-vitamin function. In infants (age < 1 year), tHcy is moderately elevated and related to serum cobalamin, whereas in older children and throughout childhood, plasma tHcy is low (about 60% of adult levels), and folate status becomes a strong tHcy determinant. As in adults, hyperhomocysteinemia in childhood is a risk factor for stroke, and folate-responsive hyperhomocysteinemia has been detected in children with renal failure. tHcy seems to be a sensitive indicator of folate deficiency in children on a poor diet, in HIV-infected children, and in children treated with anti-folate drugs. In children at increased risk of cobalamin deficiency, which includes children born to vegetarian mothers or children in developing countries on a poor diet, tHcy and methylmalonic acid are responsive indicators of a deficiency state. In newborns and infants born to mothers with an adequate nutrition, there are consistent observations of low cobalamin, elevated tHcy and methylmalonic acid, and reduction of both metabolites by cobalamin supplementation. These data have raised the question whether cobalamin deficiency may be widespread and undetected in babies born to non-vegetarian women on a Westernized diet.