Hyperhomocysteinemia leads to exacerbation of ischemic brain damage: Role of GluN2A NMDA receptors.

Hyperhomocysteinemia has been implicated in several neurodegenerative disorders including ischemic stroke. However, the pathological consequences of ischemic insult in individuals predisposed to hyperhomocysteinemia and the associated etiology are unknown. In this study, we evaluated the outcome of transient ischemic stroke in a rodent model of hyperhomocysteinemia, developed by subcutaneous implantation of osmotic pumps containing L-homocysteine into male Wistar rats. Our findings show a 42.3% mortality rate in hyperhomocysteinemic rats as compared to 7.7% in control rats. Magnetic resonance imaging of the brain in the surviving rats shows that mild hyperhomocysteinemia leads to exacerbation of ischemic injury within 24 h, which remains elevated over time. Behavioral studies further demonstrate significant deficit in sensorimotor functions in hyperhomocysteinemic rats compared to control rats. Using pharmacological inhibitors targeting the NMDAR subtypes, the study further demonstrates that inhibition of GluN2A-containing NMDARs significantly reduces ischemic brain damage in hyperhomocysteinemic rats but not in control rats, indicating that hyperhomocysteinemia-mediated exacerbation of ischemic brain injury involves GluN2A-NMDAR signaling. Complementary studies in GluN2A-knockout mice show that in the absence of GluN2A-NMDARs, hyperhomocysteinemia-associated exacerbation of ischemic brain injury is blocked, confirming that GluN2A-NMDAR activation is a critical determinant of the severity of ischemic damage under hyperhomocysteinemic conditions. Furthermore, at the molecular level we observe GluN2A-NMDAR dependent sustained increase in ERK MAPK phosphorylation under hyperhomocysteinemic condition that has been shown to be involved in homocysteine-induced neurotoxicity. Taken together, the findings show that hyperhomocysteinemia triggers a unique signaling pathway that in conjunction with ischemia-induced pathways enhance the pathology of stroke under hyperhomocysteinemic conditions.

Effect of Methionine Diet on Metabolic and Histopathological Changes of Rat Hippocampus.

Hyperhomocysteinemia (hHcy) is regarded as an independent and strong risk factor for cerebrovascular diseases, stroke, and dementias. The hippocampus has a crucial role in spatial navigation and memory processes and is being constantly studied for neurodegenerative disorders. We used a moderate methionine (Met) diet at a dose of 2 g/kg of animal weight/day in duration of four weeks to induce mild hHcy in adult male Wistar rats. A novel approach has been used to explore the hippocampal metabolic changes using proton magnetic resonance spectroscopy (1H MRS), involving a 7T MR scanner in combination with histochemical and immunofluorescence analysis. We found alterations in the metabolic profile, as well as remarkable histo-morphological changes such as an increase of hippocampal volume, alterations in number and morphology of astrocytes, neurons, and their processes in the selective vulnerable brain area of animals treated with a Met-enriched diet. Results of both methodologies suggest that the mild hHcy induced by Met-enriched diet alters volume, histo-morphological pattern, and metabolic profile of hippocampal brain area, which might eventually endorse the neurodegenerative processes.

Association between hyperhomocysteinemia and stroke with atherosclerosis and small artery occlusion depends on homocysteine metabolism-related vitamin levels in Chinese patients with normal renal function.

This study was conducted to investigate the role of different homocysteine metabolism-related vitamin (HMRV) levels in the correlation between hyperhomocysteinemia (HHCY) and ischemic stroke (IS) subtypes. Three hundred and forty-eight IS patients manifesting different vascular subtypes were subclassified on the basis of HMRV deficiencies. Correlation between HHCY and IS subtypes was investigated in all the subgroups. In this study, HHCY was significantly correlated with the IS subtypes in large artery atherosclerosis (OR 1.126, 95%CI: 1.051 ~ 1.206, P = 0.001) and small artery occlusion (OR 1.105, 95%CI: 1.023 ~ 1.193, P = 0.012). Subgroup analysis revealed a correlation between HHCY and IS subgroup (OR 1.201, 1.178, 95%CI: 1.081 ~ 1.334, 1.058 ~ 1.313, P = 0.001, P = 0.003, respectively) in HMRV deficiency, but not significantly with the IS subgroup in normal HMRV levels. Serum vitamin B12 concentrations are inversely correlated with both IS subtypes in HMRV deficiency subgroups (OR 0.992, 0.995, 95%CI: 0.987 ~ 0.996, 0.991 ~ 0.999, P < 0.001, P = 0.007, respectively), which may contribute to HHCY incidence in these populations. The correlation between HHCY and IS subtypes is affected by HMRV levels in this case-control study. Our findings are helpful to understand the inconsistency in prior homocysteine studies. Serum vitamin B12 levels may play a critical role in HHCY incidence in this Chinese population.Cerebrovascular disease has emerged as the leading cause of disability and mortality in both urban and rural areas of China (Neurology branch of Chinese Medical Association 2015). Ischemic stroke (IS) constitutes 60% to 80% of all cerebrovascular disease (Neurology branch of Chinese Medical Association 2014). Among a variety of risk factors, hyperhomocysteinemia (HHCY) has been closely correlated with IS due to intracranial small-vessel disease and extracranial large-artery disease (Selhub et al. 1995; Eikelboom et al. 2000; Alvarez et al. 2012; Jeon et al. 2014). However, the failure to lower homocysteine (HCY) via homocysteine metabolism-related vitamin (HMRV, including folic acid and vitamin B12 but not vitamin B6 in this study) supplementation to reduce stroke morbidity questions the role of HCY as a risk factor for stroke (Lonn et al. 2006; Hankey et al. 2010). Theoretically, HMRV supplementation merely lowers the incidence of stroke induced by HHCY resulting from HMRV deficiency, whereas HHCY-induced stroke concomitant with normal HMRV levels may be refractory to treatment. The correlation between HCY varying with HMRV levels and IS subtypes is still unclear. In this study, we investigated the impact of variation in HMRV levels on the correlation between HHCY and IS subtypes in 348 acute IS patients with large and small vessel diseases. We sought to determine the factors underlying the conflicting results associated with lowering HCY by HMRV supplementation to reduce stroke incidence.

Association of Hyperhomocysteinemia with Stroke Recurrence after Initial Stroke.

BACKGROUND AND PURPOSE: Homocysteine (Hcy) is closely associated with stroke. Despite the fact that Hcy has consistently been shown to predict development of recurrent stroke, prior studies on the association of Hcy and stroke subtypes have been inconclusive. METHODS: Data from the Ege Stroke Registry were examined and 5-year follow-up data were analyzed. Multivariate survival analyses were undertaken using Cox proportional hazards models to determine the prognostic value of Hcy in different ischemic stroke subtypes. RESULTS: Of the 9522 patients with stroke, 307 (27%) with hyperhomocysteinemia (hHcy) had recurrent stroke. Univariate Cox regression model showed that hHcy group was associated with recurrent stroke (crude hazard ratio [HR] 1.16; 95% CI 1.02-1.30). But there was no such association in multivariate regression models (adjusted HR 1.11; 95% CI .97-1.26). hHcy was not associated with any ischemic stroke subtypes at 5 years. Univariate Cox regression model showed that hHcy group was associated with overall cardiovascular events (crude HR 1.44; 95% CI 1.32-1.57). However, this association no longer existed in multivariate regression models (adjusted HR 1.01; 95% CI .93-1.12). Higher plasma Hcy group was significantly associated with higher mortality compared with normal plasma Hcy group (OR 1.83; 95% CI .45-2.32). CONCLUSIONS: Our results showed that elevated Hcy is not associated independently with stroke recurrence and overall cardiovascular events in patients with ischemic stroke. There was no association between the hHcy and stroke recurrence in the stroke subtypes within 5 years.

Hyperhomocysteinemia associates with small vessel disease more closely than large vessel disease.

BACKGROUND: Hyperhomocysteinemia was believed to be an independent risk factor for stroke and associate with small vessel disease (SVD) related stroke and large vessel disease (LVD) related stroke differently. However it's still unclear which type of stroke associated with homocysteine (HCY) more strongly because the conclusions of previous studies were contradictory. In this study we focused on the subclinical angiopathies of stroke, i.e., SVD and LVD instead of stroke subtypes and sought to compare the associations between HCY level and different angiopathies. METHODS: 324 non-stroke patients were enrolled. Sex, age, HCY level and other vascular risk factors were collected. MRI and angiographies were used to determine the type of angiopathies and their severity, i.e., the scores of leukoaraiosis (LA), plaques and numbers of silent brain infarctions (SBI). LVD was defined as the presence of atherosclerotic plaques of cerebral arteries. SVD was defined as the presence of either LA or SBI. 230 patients were deemed to have LVD; 180 patients were deemed to have SVD. Spearman's correlation test and logistic regression were used to analyze the association between HCY level and different angiopathies. RESULTS: The correlation between HCY level and scores of plaques was weaker than that of the scores of LA and numbers of SBI. Hyperhomocysteinemia was an independent risk factor for SVD (OR = 1.315, P <0.001), whereas the association between HCY level and LVD was not that significant (OR = 1.058, P = 0.075). CONCLUSION: HCY level associated with SVD more strongly than LVD.

[Metabolic status and bone mineral density in patients with pseudarthrosis of long bones in hyperhomocysteinemia].

In article described research of the metabolic status and bone mineral density in 153 patients with with pseudarthrosis of long bones, in individuals with consolidated fractures and healthy people. The violations of reparative osteogenesis at hyperhomocysteinemia are accompanied by disturbances of the functional state of bone tissue, inhibition of biosynthetic and increased destruction processes, reduced bone mineral density in the formation of osteopenia and osteoporosis. The degree and direction of change of bone depends on the type of violation of reparative osteogenesis.

Functional consequences of the collagen/elastin switch in vascular remodeling in hyperhomocysteinemic wild-type, eNOS-/-, and iNOS-/- mice.

A decrease in vascular elasticity and an increase in pulse wave velocity in hyperhomocysteinemic (HHcy) cystathionine-beta-synthase heterozygote knockout (CBS(-/+)) mice has been observed. Nitric oxide (NO) is a potential regulator of matrix metalloproteinase (MMP) activity in MMP-NO-tissue inhibitor of metalloproteinase (TIMP) inhibitory tertiary complex. However, the contribution of the nitric oxide synthase (NOS) isoforms eNOS and iNOS in the activation of latent MMP is unclear. We hypothesize that the differential production of NO contributes to oxidative stress and increased oxidative/nitrative activation of MMP, resulting in vascular remodeling in response to HHcy. The overall goal is to elucidate the contribution of the NOS isoforms, endothelial and inducible, in the collagen/elastin switch. Experiments were performed on six groups of animals [wild-type (WT), eNOS(-/-), and iNOS(-/-) with and without homocysteine (Hcy) treatment (0.67 g/l) for 8-12 wk]. In vivo echograph was performed to assess aortic timed flow velocity for indirect compliance measurement. Histological determination of collagen and elastin with trichrome and van Gieson stains, respectively, was performed. In situ measurement of superoxide generation using dihydroethidium was used. Differential expression of eNOS, iNOS, nitrotyrosine, MMP-2 and -9, and elastin were measured by quantitative PCR and Western blot analyses. The 2% gelatin zymography was used to assess MMP activity. The increase in O(2)(-) and robust activity of MMP-9 in eNOS(-/-), WT+Hcy, and eNOS(-/-)+Hcy was accompanied by the gross disorganization and thickening of the ECM along with extensive collagen deposition and elastin degradation (collagen/elastin switch) resulting in a decrease in aortic timed flow velocity. Results show that an increase in iNOS activity is a key contributor to HHcy-mediated collagen/elastin switch and resulting decline in aortic compliance.

Asymptomatic Mongolian middle-aged women with high homocysteine blood level and atherosclerotic disease.

Growing numbers of studies have shown that hyperhomocysteinemia is an independent, modifiable risk factor for cardiovascular diseases. Hyperhomocysteinemia has been found to be negatively associated with the vitamin B group, especially folate and cobalamin. Because of the relative scarcity of fruits and vegetables in Mongolian foods, and the high cardiovascular diseases rate in Mongolia, we examined homocysteine level and its relation with atherosclerotic change in middle-aged Mongolian women. This cross-sectional study included 79 female asymptomatic residents of Ulaanbaatar, Mongolia. Besides analysis of homocysteine and chemistry tests, participants were interviewed and underwent physical and Doppler ultrasound examination of extracranial vessels. The mean homocysteine level was 9.87 +/- 3.6 micromol/l, and the 2.5th and 97.5th percentiles were 2.2 micromol/l and 19.9 micromol/l. Participants with abnormal Doppler ultrasound finding had significantly higher homocysteine levels (12.8 +/- 4.5 micromol/l vs 8.7 +/- 2.3 micomol/l, P < 0.001) and homocysteine was significantly associated with having atherosclerotic change (odds ratio 2.2, 95% confidence interval = 1.42-3.49, P < 0.001) after adjustment for age, low-density lipoprotein, diastolic blood pressure, and body mass index. Hyperhomocysteinemia was found to be significantly associated with atherosclerotic change in female Mongolian adults. Further studies are necessary to determine factors associated with homocysteine elevation among the Mongolian population.

Subclinical atherosclerosis is weakly associated with lower cognitive function in healthy hyperhomocysteinemic adults without clinical cardiovascular disease.

OBJECTIVE: Atherosclerosis is the most common pathologic process underlying cardiovascular disease (CVD). It is not well known whether subclinical atherosclerosis is an independent risk factor for lower cognitive function among individuals without clinically evident CVD. METHODS: We examined cross-sectional associations between subclinical atherosclerosis and cognitive function in a community-based sample of otherwise healthy adults with plasma homocysteine >or=8.5 micromol/L enrolled in the BVAIT study (n = 504, mean age 61 years). Carotid artery intima-media thickness (CIMT), coronary artery calcium (CAC) and abdominal aortic calcium (AAC) were used to measure subclinical atherosclerosis. Cognitive function was assessed with a battery of neuropsychological tests. A principal components analysis was used to extract five uncorrelated cognitive factors from scores on individual tests, and a measure of global cognition was derived. Multivariable linear regression was used to examine the association between subclinical atherosclerosis and cognitive function, adjusting for other correlates of cognition. RESULTS: Increasing thickness of CIMT was associated with significantly lower scores on the verbal learning factor (beta = -0.07 per 0.1 mm increase CIMT [SE(beta) = 0.03], p = 0.01). CAC and AAC were not individually associated with any of the cognitive factors. CONCLUSIONS: This study provides evidence that increasing CIMT is weakly associated with lower verbal learning abilities but not global cognition in a population of otherwise healthy middle-to-older aged adults with elevated plasma homocysteine levels but without clinically evident CVD. The association between CIMT and poor verbal learning may pertain particularly to men.

Hyperhomocysteinemia as a Risk Factor for Intracranial Aneurysms: A Case-Control Study.

OBJECTIVE: Homocysteine, an amino acid derived from methionine metabolism, has gained great importance as an important risk factor for cardiovascular diseases as the result of its thrombogenic properties and endothelial injury association. However, its role in the etiology and screening of intracranial aneurysms (IAs) has not been well studied. We aimed to test the hypothesis of a positive association between hyperhomocysteinemia (HHcy) and IAs. METHODS: A case-control study was performed at a vascular neurosurgery unit in Brazil between 2016 and 2017. In total, 180 patients were included: 142 patients with previous IAs (case group) and 38 patients with a previous diagnosis of arteriovenous malformation and no aneurysms on imaging evaluation (control group). HHcy was defined as homocysteine levels greater than 15 µmol/L. Multivariate models were designed to adjust for potential confounders: age, sex, hypertension, dyslipidemia, and smoker status. RESULTS: The case group was older (56.3 ± 12.6 years vs. 40.9 ± 14.0 years, P < 0.001) and had a greater prevalence of women (76.1% vs. 55.3%, P = 0.012), as well as hypertension (45.1% vs. 2.6%, P < 0.001), dyslipidemia (60.6% vs. 10.5%, P = 0.001), and smokers (41.5% vs. 0.0%, P < 0.001). Median homocysteine in the cases was similar to the controls (10.5 µmol/L [8.3-14.0] vs. 10.7 µmol/L [8.2-13.3], respectively, P = 0.450). There was a trend toward greater HHcy prevalence in the case group (20.4% vs. 7.9%, P = 0.073). HHcy was associated with greater age, male sex, hypertension, and smoking status. After multivariate adjustment, HHcy had no association with IAs (odds ratio 1.34, 95% confidence interval 0.30-5.97, P = 0.703). CONCLUSIONS: No association was found between HHcy and IAs.

Correlation of hippocampal atrophy with hyperhomocysteinemia in hemodialysis patients: An exploratory pilot study.

BACKGROUND: Cognitive impairment is one of the important critical issues in hemodialysis (HD) patients. However, the associating factors of brain atrophy in HD patients have not been fully elucidated. PURPOSE AND METHODS: Brain magnetic resonance imaging (MRI) was performed in 34 of total 72 HD outpatients in our dialysis center. These MRI images were analyzed by an application software; Voxel-based Specific Regional Analysis System for Alzheimer's Disease (VSRAD). VSRAD quantitatively calculates the extent of brain atrophy (percent of volume reduction) comparing with a MRI imaging database of 80 age-matched healthy controls. The extent of both hippocampal and whole-brain atrophy was evaluated with possible contributing factors. RESULTS: In all patients, the mean extent of hippocampal atrophy was 27.3%, and the mean extent of whole-brain atrophy was 11.2%. The extent of hippocampal atrophy was significantly correlated with low body mass index (BMI), total serum homocysteine (tHcy) levels, and brachial-ankle pulse wave velocity (baPWV). The extent of whole-brain atrophy showed significant correlations with age, hypoalbuminemia, and baPWV. Based on the multiple regression analysis, tHcy was an independent determinant of hippocampal atrophy (ß = 0.460, R2 = 0.189, P<0.01); while age was an independent determinant of whole-brain atrophy (ß = 0.594, R2 = 0.333, P<0.01). CONCLUSIONS: In this exploratory pilot study, hippocampal atrophy was significantly correlated with hyperhomocysteinemia in HD patients.

Mild hyperhomocysteinaemia is associated with increased aortic stiffness in general population.

Total homocysteine (tHcy) level was identified as a strong and independent predictor of cardiovascular events. We investigated the association between tHcy and mechanical properties of large arteries in a random, general population-based sample of 251 subjects (mean age 48 years). Large artery properties, such as aortic and peripheral (lower-limb) pulse wave velocity (PWV), and augmentation index of radial artery were measured using semi-automatic Sphygmocor device. Aortic PWV (APWV) positively correlated with tHcy (r = 0.28, P<0.0001), and a significant increasing trend of APWV was found by tHcy quartiles (P = 0.0003 by ANOVA). This association remained significant after adjustment for conventional cardiovascular risk factors (age, gender, smoking, overweight, hypertension, dyslipidaemia and impaired glucose metabolism) and for usual homocysteine confounders (folate, B12, renal function). Subjects with mild hyperhomocysteinaemia (i.e. with tHcy > or = 15 micromol/l) had 2.74 times higher risk of having their APWV over 8.42 m/s (i.e. in the top quartile). No such association was found either for PWV measured at lower extremity or for radial augmentation index. In conclusion, in our series of subjects from general population, we found a strong and independent relationship between homocysteine concentration and APWV, a parameter of stiffness of central arteries.

Increase of carotid artery stiffness and decrease of baroreflex sensitivity in exfoliation syndrome and glaucoma.

AIM: To investigate the distensibility of the common carotid artery (CCA), baroreflex sensitivity (BRS) and its relation to plasma homocysteine concentration in exfoliation syndrome or exfoliation glaucoma (XFS/XFG). METHODS: Homocysteine concentrations were measured in 30 XFS/XFG patients and 18 age matched controls. In 21 patients and 17 controls the end diastolic diameter of the CCA and pulsatile distension were measured and BRS was calculated. RESULTS: There was no significant difference between the groups in sex distribution, age, heart rate, blood pressure, systemic diseases, or medication. In XFS/XFG patients homocysteine concentration was significantly elevated (unpaired t test, p = 0.023), and CCA stiffness was higher (p<0.05), while strain, cross sectional compliance coefficient, distensibility, and BRS were significantly reduced compared to the controls (Mann-Whitney U test, p< or =0.013 for each parameter). In XFS/XFG patients a positive correlation was found between age and plasma homocysteine level (Pearson's correlation, r = 0.490, p = 0.007), and a negative correlation between age and BRS (Kendall's correlation r = -0.374, p = 0.021), as well as between homocysteine concentration and BRS (Kendall's correlation r = -0.377, p = 0.024). No correlation was seen between these variables in the control group. CONCLUSIONS: These results suggest a pathological large artery function as well as altered parasympathetic vascular control in XFS/XFG which increases with age and with higher homocysteine concentration.

CerefolinNAC Therapy of Hyperhomocysteinemia Delays Cortical and White Matter Atrophy in Alzheimer's Disease and Cerebrovascular Disease.

We examined whether using a medical food therapy for hyperhomocysteinemia (HHcy) in patients with Alzheimer's disease (AD) or cognitive impairment due to cerebrovascular disease (CVD) with Cerefolin®/CerefolinNAC® (CFLN: L-methylfolate, methylcobalamin, and N-acetyl-cysteine) slowed regional brain atrophy. Thirty HHcy patients with AD and related disorders (ADRD) received CFLN (HHcy+CFLN: duration [µ ±  σ] = 18.6±16.1 months); a sub-sample of this group did not receive CFLN for varying periods of time (HHcy+NoCFLN: duration [µ ±  σ] = 12.6±5.6 months). Thirty-seven NoHHcy patients with ADRD did not receive CFLN (NoHHcy+NoCFLN: duration [µ ±  σ] = 13.3±17.7 months). No participant took supplemental B vitamins. Regional brain volumes were measured at baseline and end of study, and covariate-adjusted rates of hippocampal, cortical, and forebrain parenchymal (includes white matter) atrophy were predicted. The HHcy+CFLN group's hippocampal and cortical atrophy adjusted rates were 4.25 and 11.2 times slower than those of the NoHHcy+NoCFLN group (p < 0.024). The HHcy+CFLN group's forebrain parenchyma atrophy rate was significantly slower only for CVD; the rate of slowing was proportional to the degree of homocysteine lowering (p < 0.0001). CFLN was associated with significantly slowed hippocampal and cortical atrophy rates in ADRD patients with HHcy, and forebrain parenchymal atrophy rates in CVD patients with HHcy. The present results should be further validated.

Cardiovascular disease among patients with type 2 diabetes: Role of Homocysteine as an inflammatory marker.

It is known that inflammation has a role in the pathogenesis of cardiovascular diseases; measurement of inflammatory markers improves the risk prediction of cardiovascular diseases. Hyperhomocysteinemia has been correlated with the occurrence of blood clots, heart attacks and strokes; though it is unclear whether hyperhomocysteinemia is an independent risk factor for these conditions. In the present study, we aimed to evaluate the role of homocysteine in type 2 diabetes patients with cardiovascular disease in a population of Madhya Pradesh India. Total 100 type 2 diabetes patients were included in the study, of these 50 had angiographically proven cardiovascular disease and 50 had no evidence of it. High sensitivity C-reactive protein, fibrinogen, and lipoprotein (a) were measured in serum. Homocysteine, blood glucose in plasma, erythrocyte sedimentation rate, glycated haemoglobin were measured in whole blood. A albumin excretion rate, creatinine clearance rate were measured in the urine sample for renal function. It was shown that, levels of homocysteine and other inflammatory markers were elevated significantly in the group II (n = 50). A correlation between hyperhomocysteinemia and inflammatory markers in patients with impaired renal function was observed. It was concluded that impairment of renal function is a key factor that affects homocysteine level.

Homocysteine impairs coronary microvascular dilator function in humans.

OBJECTIVES: We sought to use positron emission tomography (PET) to test the hypothesis that hyperhomocysteinemia adversely effects coronary microvascular dilator function. BACKGROUND: Hyperhomocysteinemia is associated with abnormal endothelium-dependent vasodilation in peripheral human arteries. However, its effect on the coronary circulation is not known. METHODS: Eighteen healthy humans, age 24 to 56 years, were enrolled in a double-blind, crossover trial. Basal and adenosine-stimulated myocardial blood flow (MBF) was determined by PET: after ingestion of placebo and after methionine-induced hyperhomocysteinemia. Further, brachial ultrasonography was used to assess flow-mediated vasodilation. Additionally, to assess the role of nitric oxide (NO) in adenosine-mediated vasodilation, the MBF response to adenosine was measured in the presence and absence of the NO synthase antagonist NG-monomethyl-l-arginine (l-NMMA) (0.3 mg/kg/min intravenously). RESULTS: Hyperhomocysteinemia resulted in a reduction in the MBF dose-response curve to adenosine (p < 0.05). This was most apparent with low dose adenosine, where MBF augmentation was significantly blunted during hyperhomocysteinemia (1.06 +/- 1.00 ml/min/g vs. 0.58 +/- 0.78 ml/min/g, placebo vs. methionine, p < 0.05). Similarly, flow-mediated brachial artery vasodilation was impaired during hyperhomocysteinemia (4.4 +/- 2.6% vs. 2.6 +/- 2.3%, placebo vs. methionine, p < 0.05). In a separate series of experiments, MBF during adenosine was reduced in the presence of l-NMMA (p < 0.05 analysis of variance). This was most apparent at the low dose of adenosine, where MBF response to adenosine was blunted in the presence of l-NMMA (2.08 +/- 1.34 ml/min/g vs. 1.48 +/- 1.32 ml/min/g, placebo vs. l-NMMA, p < 0.05). CONCLUSION: The data, therefore, support the hypothesis that acute hyperhomocysteinemia impairs microvascular dilation in the human coronary circulation as a result of reduced NO bioavailability.

Effect of acute hyperhomocysteinemia on coronary flow reserve in healthy adults.

BACKGROUND: B-mode ultrasound studies indicate that hyperhomocysteinemia is associated with preclinical structural and functional arterial abnormalities. This study was designed to evaluate the effect of elevated plasma homocysteine levels on coronary flow reserve (CFR). METHODS: A total of 20 healthy subjects aged 41 +/- 7 years were studied on 2 separate days, a week apart, before and after methionine load (100 mg/kg of body weight) or placebo in a double-blind crossover study. At each visit, homocysteine levels were measured by high performance liquid chromatography and CFR was determined by transthoracic Doppler echocardiography. RESULTS: After methionine load, plasma homocysteine increased from 10.7 +/- 2.8 mumol/L to 30.4 +/- 5.1 mumol/L ( P < .0001) and CFR decreased from 3.0 +/- 0.4 to 2.3 +/- 0.3 ( P < .001). CFR was inversely related to postload homocysteine levels ( r = -0.21, P = .02). After placebo, there was no change in CFR. CONCLUSION: In asymptomatic adults, acute hyperhomocysteinemia is associated with a significant reduction in CFR.

Effect of experimental hyperhomocysteinemia on cardiac structure and function in the rat.

Male Sprague-Dawley rats were subjected for 2 weeks to daily injections of homocysteine (Hcy), which increased plasma Hcy approximately 2-fold. Echocardiography indicated significant increases in left ventricular diastolic (13%) and systolic (31%) dimensions and decreases in posterior wall thickness (diastolic, -17%; systolic, -20%) in Hcy-treated animals. Slight changes were noted in the ejection fraction, systolic fractional shortening, and maximal aortic valvular blood flow velocity, but they were not statistically significant or were similar to those in vehicle controls. The results suggest that an initial effect of Hcy administration involves loss of myocardial structure without a direct influence on myocardial contractile function. Consistent with this conclusion, in vitro evaluation of the myocardial ring contractile response showed no significant difference in left ventricular maximal isometric force between the control (13.9 +/- 2.7 g/g tissue) and Hcy-injected (11.0 +/- 2.8 g/g tissue) animals.