Homocysteine levels during fasting and after methionine loading in adolescents with diabetic retinopathy and nephropathy

Folic acid effect on homocysteine, sortilin levels and glycemic control in type 2 diabetes mellitus patients

Aim

The present study aimed to determine the folic acid supplement (FAS) effects on serum homocysteine and sortilin levels, glycemic indices, and lipid profile in type II diabetic patients.

Method

A double-blind randomized controlled clinical trial have been performed on 100 patients with T2DM randomly divided into two groups that received either placebo or folic acid 5 mg/d for 12 weeks.

Results

FAS caused a significant decrease in homocysteine and sortilin serum levels (28.2% and 33.7%, P < 0.0001, respectively). After 3 months of intervention, 8.7% decrease in fasting blood glucose (P = 0.0005), 8.2% in HbA1c (P = 0.0002), 13.7% in serum insulin (P < 0.0001) and 21.7% in insulin resistance (P < 0.0001) were found in the folic acid group, however no significant difference was observed in the placebo group. Serum hs-CRP level showed significant positive associations with sortilin (r = 0.237, P = 0.018), homocysteine (r = 0.308, P = 0.002) and fasting blood glucose (r = 0.342, P = 0.000). There were no significant changes in lipid profile in both groups after 12 weeks.

Conclusion

FAS might be beneficial for reducing homocysteine and sortilin levels, enhancing glycemic control, and improved insulin resistance in patients with T2DM.

Protecting the aging eye with hydrogen sulfide

Research demonstrates that senescence is associated with tissue and organ dysfunction, and the eye is no exception. Sequelae arising from aging have been well defined as distinct clinical entities and vision impairment has significant psychosocial consequences. Retina and adjacent tissues like retinal pigmented epithelium and choroid are the key structures that are required for visual perception. Any structural and functional changes in retinal layers and blood retinal barrier could lead to age-related macular degeneration, diabetic retinopathy, and glaucoma. Further, there are significant oxygen gradients in the eye that can lead to excessive reactive oxygen species, resulting in endoplasmic reticulum and mitochondrial stress response. These radicals are source of functional and morphological impairment in retinal pigmented epithelium and retinal ganglion cells. Therefore, ocular diseases could be summarized as disturbance in the redox homeostasis. Hyperhomocysteinemia is a risk factor and causes vascular occlusive disease of the retina. Interestingly, hydrogen sulfide (H2S) has been proven to be an effective antioxidant agent, and it can help treat diseases by alleviating stress and inflammation. Concurrent glutamate excitotoxicity, endoplasmic reticulum stress, and microglia activation are also linked to stress; thus, H2S may offer additional interventional strategy. A refined understanding of the aging eye along with H2S biology and pharmacology may help guide newer therapies for the eye.

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.

Relationship between homocysteine level and diabetic retinopathy: a systematic review and meta-analysis

Background

The relationship between homocysteine (Hcy) and diabetic retinopathy (DR) remains unclear to date. Therefore, a systematic review and meta-analysis was performed on the relationship between Hcy level and DR.

Methods

Studies were identified by searching PubMed, Embase, and Web of Science databases until 5 May, 2014.

Results

A total of 31 studies involving 6,394 participants were included in the meta-analysis. After pooling the data from each included study, the blood Hcy concentration in the DR group was observed to be higher than that in the control group [WMD = 2.55; 95% confidence interval (CI), 1.70–3.40], and diabetes mellitus (DM) patients with hyperhomocysteinemia were at a risk for DR [odds ratio (OR) = 1.93; 95% CI, 1.46–2.53]. Considering the different DM types, hyperhomocysteinemia in T1DM (OR = 1.83, 95% CI, 1.28–2.62) was associated with DR rather than in T2DM (OR = 1.59, 95% CI, 0.72–3.51). Considerable statistical heterogeneity in the overall summary estimates was partly explained by the geographical differences.

Conclusions

Results from this current meta-analysis indicate that hyperhomocysteinemia is a risk factor for DR, especially proliferative DR. Differences between geographical regions were observed in the relationship between hyperhomocysteinemia with T1DM risk. Given the heterogeneous results, the relationship between high Hcy and DR needs further investigation.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_167

Novel risk factors in long-term hypertension incidence in type 1 diabetes mellitus

BACKGROUND

Data from longitudinal studies suggest that biomarkers of inflammation and endothelial dysfunction are associated with development of hypertension. None of these studies have examined the association of these markers with hypertension risk in persons with diabetes. We examined the associations of inflammatory and endothelial dysfunction markers with long-term hypertension incidence in persons with type 1 diabetes mellitus.

METHODS

The 15-year cumulative incidence of hypertension was measured in Wisconsin Epidemiologic Study of Diabetic Retinopathy participants (n = 795). Hypertension was defined as a systolic blood pressure > or =140 mm Hg and/or a diastolic blood pressure > or =90 mm Hg and/or history of current antihypertensive treatment. We measured serum high-sensitivity C-reactive protein, interleukin-6, tumor necrosis factor-alpha, soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1, and serum total homocysteine as "novel" markers of hypertension development. The relation of risk factors to hypertension incidence was determined using a proportional hazards approach with discrete linear logistic regression modeling.

RESULTS

After controlling for age, gender, diabetes duration, body mass index, glycosylated hemoglobin, baseline systolic and diastolic blood pressure, proteinuria, and chronic kidney disease status, sVCAM-1 was significantly related to higher odds of developing incident hypertension (odds ratio per log sVCAM-1 1.95, 95% CI 1.01-3.74). None of the other markers of inflammation and endothelial dysfunction were related to incident hypertension in the cohort.

CONCLUSIONS

Our data showed that sVCAM-1 as a marker of endothelial dysfunction was the strongest predictor of hypertension risk in individuals with type 1 diabetes. This association was independent of the presence of diabetic nephropathy.

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.

The relation of markers of inflammation and endothelial dysfunction to the prevalence and progression of diabetic retinopathy: Wisconsin epidemiologic study of diabetic retinopathy

OBJECTIVE

To determine the relation of glycemia, blood pressure, and serum total cholesterol level as systemic markers of inflammation and endothelial dysfunction to the prevalence and incidence of diabetic retinal outcomes in persons with long-duration type 1 diabetes mellitus.

METHODS

Longitudinal population-based study of persons with type 1 diabetes mellitus who received care for their diabetes in south central Wisconsin from July 1, 1979, to June 30, 1980. Data for this investigation were obtained from the 1990-1992 through the 2005-2007 follow-up examinations. Main outcome measures included the severity of diabetic retinopathy (DR) and macular edema (ME).

RESULTS

In the 1990-1992 prevalence data, soluble vascular cell adhesion molecule, tumor necrosis factor, and homocysteine levels were associated with increased odds of more severe DR (odds ratios [highest vs lowest quartile], 3.95 [95% confidence interval, 1.66-9.39], 5.46 [2.38-12.52], and 7.46 [2.91-19.16], respectively) in those with kidney disease while controlling for relevant confounders. Similar odds were found for proliferative DR. Only total homocysteine level was associated with increased odds of ME (3.80 [95% confidence interval, 1.91-7.54]), irrespective of kidney disease. None of the markers were associated with incidence of proliferative DR, ME, or progression of DR 15 years later.

CONCLUSIONS

A limited number of markers are associated with increased odds of prevalent retinal outcomes in persons with type 1 diabetes mellitus and kidney disease. Only homocysteine level is associated with ME in those with and without kidney disease. In the absence of kidney disease, the markers do not add to the more conventional descriptors and predictors of DR in persons with type 1 diabetes mellitus. This may reflect the close association of DR and kidney disease in diabetic persons.

Inflammatory, hemostatic, and other novel biomarkers for diabetic retinopathy: the multi-ethnic study of atherosclerosis

OBJECTIVE

There are conflicting data regarding relationships of systemic biomarkers of inflammation, hemostasis, and homocysteine with diabetic retinopathy. We examined these relationships in the Multi-Ethnic Study of Atherosclerosis.

RESEARCH DESIGN AND METHODS

A total of 921 participants with diabetes were included. Diabetic retinopathy was graded from retinal photographs. We defined two outcomes: any diabetic retinopathy and vision-threatening diabetic retinopathy (severe nonproliferative diabetic retinopathy or worse). Systemic markers analyzed were C-reactive protein, homocysteine, fibrinogen, plasmin-alpha(2)-antiplasmin complex (PAP), interleukin-6, d-dimer, factor VIII, serum creatinine, and urinary albumin-to-creatinine (UAC) ratio.

RESULTS

Prevalence of diabetic retinopathy was 33.2% and vision-threatening diabetic retinopathy 7.1%. After adjusting for established risk factors (diabetes duration, A1C, systolic blood pressure, waist-to-hip ratio, and use of diabetes medications), fibrinogen (odds ratio 1.14 [95% CI 1.01-1.32], P = 0.05) and PAP (1.25 [1.05-1.50], P = 0.01) were associated with any diabetic retinopathy, while PAP (1.54 [1.13-2.11], P = 0.007) and homocysteine (1.57 [1.16-2.11], P = 0.003) were associated with vision-threatening diabetic retinopathy. Only PAP remained significant after additional adjustment for serum creatinine and UAC ratio. Area under receiver-operator characteristic curve (AUROC) for diabetic retinopathy was constructed for established and novel risk factors. Established risk factors accounted for a 39.2% increase of the AUROC, whereas novel markers (fibrinogen, PAP, homocysteine, serum creatinine, and UAC ratio) only accounted for an additional 2.2%.

CONCLUSIONS

There were few associations of novel markers of inflammation, hemostasis, and homocysteine with diabetic retinopathy after controlling for established risk factors. These data suggest that there is limited clinical use of these biomarkers for prediction of diabetic retinopathy.

[Total homocysteine levels in children with diabetes type 1. Conditional factors]

OBJECTIVES

To measure the plasma levels of total homocysteine (tHcy) in children with type I diabetes mellitus and their relationship with the control of the disease.

MATERIAL AND METHODS

We studied a total of 46 patients with ages between 4 and 19 years. The analyzed variables were: sex, age, puberty stage by Tanner, BMI, years of evolution of the illness, self-monitoring, associated diseases, tHcy, folic acid, vitamin B12, glycosylated haemoglobin (HbA1c), lipid profile and renal function.

RESULTS

The mean tHcy was of 5.48 +/- 1,64 microm/l, similar to that in our control population. There was a positive correlation with tHcy when analyzing the puberty stage by the Tanner scale. The years of evolution of diabetes varied between 0.4 and 15, with a mean of 5.77 +/- 3.69, with no correlation with tHcy. The glycosylated haemoglobin mean was 7.35 %, with no correlation with tHcy. The levels of folic acid and vitamin B12 were similar to the control population. The lipid profile of our patients was normal, with no association with tHcy levels. There was no correlation between GFR and tHcy.

CONCLUSIONS

A clinically correct control of children with diabetes mellitus type 1, appears to ensure a normal total homocysteinemia, with no significant differences with the healthy individuals of the same age and social environment.

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.

Homocysteine and diabetic retinopathy

OBJECTIVE

Homocysteine is an emerging risk factor for cardiovascular and nondiabetic ocular vaso-occlusive diseases. However, studies of the relationship between homocysteine and diabetic retinopathy have reported inconsistent results. The purpose of this study was to evaluate the relationship between plasma total homocysteine concentration and diabetic retinopathy.

RESEARCH DESIGN AND METHODS

We assessed the homocysteine-retinopathy relationship in 168 men and women with type 2 diabetes in a community-based, cross-sectional study. We photodocumented diabetic retinopathy status and measured plasma total homocysteine concentration using a commercial fluorescence polarization immunoassay enzymatic kit. Data for selected clinical/demographic variables and established risk factors for diabetic retinopathy were obtained from fasting blood samples and an interviewer-assisted lifestyle questionnaire.

RESULTS

A higher mean plasma total homocysteine concentration was observed in diabetic individuals with retinopathy than in those without retinopathy (11.5 mumol/l [95% CI 10.4-12.5] vs. 9.6 mumol/l [9.1-10.2], P = 0.001). Furthermore, the relationship between homocysteine and diabetic retinopathy was not explained by renal dysfunction and was independent of the other major risk factors for diabetic retinopathy (duration of diabetes, A1C, and systolic blood pressure) and determinants of higher homocysteine concentrations (age, sex, and red cell folate) (odds ratio 1.20 [95% CI 1.023-1.41], P = 0.024).

CONCLUSIONS

Plasma total homocysteine concentration may be a useful biomarker and/or a novel risk factor for increased risk of diabetic retinopathy in people with type 2 diabetes.

Plasma homocysteine, oxidative stress and endothelial function in patients with Type 1 diabetes mellitus and microalbuminuria

AIMS

The purpose of this study was to examine the associations between endothelial function, plasma homocysteine and oxidative stress in patients with Type 1 diabetes mellitus (DM) and microalbuminuria compared with DM patients with normoalbuminuria and non-diabetic control subjects. We wished to test the hypothesis that increased cardiovascular risk in patients with Type 1 diabetes and microalbuminuria may be in part as a result of hyperhomocysteinaemia-mediated oxidative stress leading to impaired endothelial function.

METHODS

We measured forearm blood flow, total plasma homocysteine, total antioxidant status (TAOS) and whole blood glutathione in 31 DM patients, 16 with microalbuminuria and 15 with normoalbuminuria, and 15 non-diabetic control subjects.

RESULTS

Plasma homocysteine levels were significantly higher in the microalbuminuric diabetic patients compared with the normoalbuminuric patients and the control subjects. TAOS was significantly lower in the micoalbuminuric and normoalbuminuric diabetic patients compared with the control subjects, although TAOS levels were similar in both groups of diabetic patients. There was no difference in forearm blood flow between the groups and no association between measured endothelial function and antioxidant defence/oxidative stress and homocysteine in each group. There was no association between plasma total homocysteine and TAOS or whole blood glutathione within the groups.

CONCLUSIONS

We have found mild hyperhomocysteinaemia in microalbuminuric DM patients compared with normoalbuminuric DM patients and non-diabetic subjects and some evidence for reduced antioxidant defence in DM patients. These findings add to our understanding of the increased risk of vascular disease in patients with Type 1 diabetes.

Arterial wall thickening and stiffening in children and adolescents with type 1 diabetes

OBJECTIVE

We evaluated structural and functional characteristics of the common carotid artery (CCA), a marker of early carotid atherosclerosis, and investigated their relation to metabolic and anthropometric parameters in children and adolescents with type 1 diabetes.

MATERIALS AND METHODS

Non-invasive ultrasonographic measurements were made in 45 type 1 diabetic patients and 33 controls. Age, sex, and body mass index were matched between patients and controls. We investigated intima-media thickness (IMT), compliance, distensibility, diastolic wall stress (DWS) and incremental elastic modulus (IEM) of the CCA. Metabolic and anthropometric parameters such as serum lipids, plasma glycated haemoglobin, body mass index, waist-hip ratio and blood pressure were assessed.

RESULTS

The diabetic patients had significantly higher CCA-IMT than the controls (0.48+/-0.06mm versus 0.33+/-0.07mm; p<0.001). The diabetic children had significantly higher values than the controls for DWS (1.18+/-0.29mmHgx10(2) versus 0.81+/-0.25mmHgx10(2); p<0.001) and for IEM (1.26+/-0.57mmHgx10(3) versus 0.77+/-0.28mmHgx10(3); p<0.001). The difference was not significant between patients and controls for arterial compliance and for distensibility (p>0.05). In a multivariate regression model for all subjects, diabetic state was the best predictor of IMT (p<0.001), DWS (p<0.001) and IEM (p=0.001).

CONCLUSION

Our results suggested that children and adolescent patients with type 1 diabetes are associated with early impairment of CCA structure and function and that diabetic state may be the main risk factor for CCA wall stiffening and thickening, which are of considerable concern as possible early events in the genesis of atheroma.

Homocysteine and vascular disease in diabetes: a double hit?

Cardiovascular disease is a major problem in diabetes, and risk factors presumably unrelated to diabetes, such as hyperhomocysteinaemia, may be related to the development of cardiovascular complications in diabetic individuals. Plasma homocysteine levels are usually normal in diabetes, although both lower and higher levels have been reported. Homocysteine levels in diabetes are modulated by hyperfiltration and renal dysfunction, as well as low folate status. Insulin resistance does not appear to be a major determinant of plasma homocysteine level. Hyperhomocysteinaemia has been associated with microalbuminuria and retinopathy in type 1 and type 2 diabetes. In patients with type 2 diabetes, plasma homocysteine concentration is a significant predictor of cardiovascular events and death. This relation seems to be stronger in subjects with diabetes than without. The underlying pathophysiological mechanism of this increased vascular risk remains unexplained, but may be related to worsening of endothelial dysfunction and/or structural vessel properties induced by oxidative stress. Because homocysteine and diabetes have apparent synergistic detrimental vascular effects, patients with diabetes are candidates for screening and treatment with folic acid until the results of ongoing clinical trials are available.

Plasma homocysteine levels in noninsulin-dependent diabetes mellitus with retinopathy and neovascular glaucoma

AIM

This study was designed to evaluate plasma homocysteine levels in noninsulin-dependent diabetes mellitus patients (NIDDM) with preproliferative retinopathy and neovascular glaucoma. The experimental goal was to determine the relationship between plasma homocysteine content and the development of microvascular lesions.

METHODS

Plasma homocysteine levels were assessed in three experimental groups consisting of healthy controls (n = 30), NIDDM patients with preproliferative retinopathy (n = 20) and NIDDM patients with neovascular glaucoma (n = 20). Homocysteine levels were determined via a fluorescence polarization immunoassay method by an Abbot IMX instrument.

RESULTS

Plasma homocysteine levels in NIDDM patients with preproliferative retinopathy and neovascular glaucoma (n = 40) were found to be significantly higher than those of controls (n = 30) (p < 0.01). When statistical analysis was performed separately among the three experimental groups, no significant difference in plasma homocysteine levels were found in patients with preproliferative retinopathy compared to controls. However, homocysteine levels in patients with neovascular glaucoma were found to be significantly higher than the control group (p < 0.001). No significant difference in plasma homocysteine levels could be detected between patients with preproliferative retinopathy and neovascular glaucoma.

CONCLUSIONS

Hyperhomocysteinemia is a risk factor for the development of microvascular lesions in patients with NIDDM but cannot be used as a marker to assess the progression of lesions observed in neovascular glaucoma.

Hyper-homocysteinemia is Not a Main Feature of Juvenile Uncomplicated Type 1 Diabetes

Total plasma homocysteine (tHcy) was measured by high pressure liquid chromatography (HPLC) method in 28 patients (12 females and 16 males) at the onset of type 1 diabetes mellitus (T1DM), 4 females during diabetes ketoacidosis (DKA) and 154 (68 females and 86 males) during follow-up. Serum folate, pyridoxal 5' phosphate (PLP) and Vitamin B12 (Vit B12) were also measured. Plasma tHcy levels were not found significantly different in T1DM patients known to have diabetes (males 9.2 +/- 7.7 and females 7.0 +/- 2.8 micromol/l) and in those who were newly diagnosed (males 9.7 +/- 4.8 and females 7.16 +/- 2.8 micromol/l) than in healthy controls (males 8.7 +/- 3.5 and females 7.8 +/- 2.55 micromol/l). Only a significant difference for sex was observed in known diabetes (p = 0.0281). Serum folate, PLP and Vit B12 were normal (12.6 +/- 3.6 ng/ml, 20.11 +/- 0.8 ng/ml and 416.7 +/- 41.9 pg/ml) in all T1DM patients. Age significantly correlated with plasma tHcy. Only in 4 patients, studied during DKA, plasma tHcy was significantly lower (2.76 +/- 1.33 micromol/l, p < 0.001) than the healthy controls.

Limited effectiveness of betaine therapy for cystathionine beta synthase deficiency

BACKGROUND

Orally administered betaine (Bet) is regarded as an effective and safe therapy for homocystin-uria. However, even when patients' serum Bet concentrations are increased by supplementation, serum homocysteine (Hcy) concentrations are often not lowered to the normal range. The present study tested the hypothesis that with relatively high serum methionine (Met), serum Hcy does not adequately decrease, even when serum Bet concentrations are potentially therapeutic.

METHODS

The present study examines the relationship between these amino acids by high-performance liquid chromatography (HPLC) in a total of 63 samples obtained over 2 years from two patients with cystathionine beta synthase (CBS) deficiency.

RESULTS

When serum Met was less than 80 micro mol/L (1.2 mg/dL), the treatment reduced serum Hcy to within the normal range. When serum Met exceeded 80 micro mol/L, serum Hcy showed only a limited decrease, despite sufficient doses of Bet (serum concentration, over 250 micro mol/L). The findings of the present study suggest that it is necessary to follow a low methionine diet that keeps serum Met within the normal range when treating patients with homocystinuria due to CBS deficiency when Bet is administered. Homocystinuria is a rare congenital metabolic disease and the data presented in the present paper, although it relates to only two patients, is worth reporting.

Variability of post-methionine load plasma homocysteine assays

BACKGROUND

Numerous variations of the methionine load test are frequently used as dynamic function tests to assess homocysteine metabolism. Lack of standardization impedes inter-laboratory comparisons. Criteria based on biological variation are suggested to standardize the methionine load test.

METHODS

Weekly methionine load tests (n=5) with blood sampling at 0, 4, 6 and 8 h were performed on 15 young men. For both basal and post-methionine load homocysteine measurements, total variance (sigma(S)(2)), within-subject variance (sigma(I)(2)), between-subject variance (sigma(G)(2)) and analytical variance (sigma(A)(2)) were calculated from an appropriate analysis of variance (ANOVA).

RESULTS

Plasma homocysteine concentrations measured 6 h after methionine loading had analytical, within-subject and between-subject coefficients of variation of 5.2%, 17.5% and 9.7%, respectively. Measurements at 4 h had a higher within-subject coefficient of variation. Adjustment of post-methionine load homocysteine concentrations for basal levels resulted in considerable increases of all the measures of variation.

CONCLUSIONS

Adjustment of post-methionine load plasma homocysteine concentrations for basal levels does not improve the interpretation of changes in serial results due to the higher analytical and biological variance of adjusted concentrations. It is suggested that the methionine load test is standardized to a single, unadjusted homocysteine measurement at 6 h.

Apoptotic cell death in the mouse retinal ganglion cell layer is induced in vivo by the excitatory amino acid homocysteine

Homocysteine, an excitatory amino acid and a homolog of cysteine, induces neuronal cell death in brain via stimulation of N-methyl-D-aspartate (NMDA) receptors. It also selectively activates NMDA receptors of retinal ganglion cells, but it is not known if high levels of homocysteine are toxic to these cells. The purpose of this study was to determine whether increased levels of homocysteine caused death of neurons in the ganglion cell layer; if so whether this death occurred via an apoptotic mechanism and to determine the consequences of simultaneous elevation of homocysteine and glutamate, a known retinal excitotoxin, on the viability of neurons of the ganglion cell layer. C57BL/6 mice were injected intravitreally with either homocysteine or glutamate/homocysteine combined (final concentrations: 25, 75, and 200 microM); injection of glutamate (25 and 200 microM) served as a positive control. Eyes were harvested and cryosections prepared 5-6 days post-injection. Systematic morphometric analysis of retinas of mice injected with homocysteine indicated that the total number of cells in the ganglion cell layer decreased by about 23% following exposure to 200 microM homocysteine. To determine whether the neurons of the ganglion cell layer were dying by apoptosis, the TUNEL method was used and was confirmed by immunohistochemical studies of caspase-3, known to be expressed at high levels during retinal ganglion cell apoptosis. Microscopic analysis revealed significantly more TUNEL-positive cells in the ganglion cell layer in homocysteine-injected eyes than in contralateral PBS-injected eyes. Retinas injected with 75 and 200 microM homocysteine displayed significantly more TUNEL-positive neurons in the ganglion cell layer (2 and 2.9, respectively) than PBS-injected retinas (0.25). In eyes injected simultaneously with homocysteine/glutamate, the number of apoptotic cells in the ganglion cell layer almost doubled that for homocysteine or glutamate injections alone. Immunohistochemical analysis of activated caspase-3 revealed numerous positively labelled neurons in the ganglion cell layer in homocysteine and homocysteine/glutamate-injected eyes, but not in PBS-injected eyes. Quantification of this data revealed a significantly greater number of caspase-3-positive neurons in the ganglion cell layer of retinas injected with 75 and 200 microM homocysteine (2.9 and 4.4, respectively) than for PBS-injected retinas (0.5). This confirms that death of neurons in the ganglion cell layer is occurring by apoptosis. The present study provides the first evidence that homocysteine is toxic to neurons of the ganglion cell layer. In addition, it provides evidence that these retinal neurons are dying by apoptosis and it demonstrates for the first time that excitotoxic damage to neurons of the ganglion cell layer is potentiated by simultaneous elevation of homocysteine and glutamate. These findings are relevant to retinal ganglion cell death characteristic of diabetic retinopathy, which is thought to be mediated by overstimulation of the NMDA receptor.