Homocysteine inhibits inactivation of factor Va by activated protein C

Homozygous MTHFR C677T carriers develop idiopathic portal vein thrombosis 20 years earlier than wild type

The aim of this study was to evaluate the impact of methylene tetrahydrofolate reductase (MTHFR) rs1801133 (C→T667 transition) on age at first idiopathic portal vein thrombosis (PVT) and to identify clinical and/or laboratory variables influencing age at first PVT, including plasma homocysteine and the prothrombin rs1799963 PT (G→A transition at position 20210) (PT) mutation. A retrospective cross-sectional cohort, including 15 MTHFR TT, 32 MTHFR TC and 22 MTHFR CC idiopathic PVT participants contributing demographics, age at PVT, plasma concentrations of homocysteine and of natural anticoagulants. MTHFR TT carriers presented with a lower age at PVT than heterozygous or wild-type genotypes (31 ± 8 vs. 48 ± 15 vs. 52 ± 13 years, P  = 0.001) and were more likely to have a plasma HC concentration above the cut-off (73.3 vs. 32 vs. 50%, P  = 0.04). MTHFR TT and protein C predicted age at PVT ( P  < 0.0001 and P  = 0.06); MTHFR TT predicted plasma homocysteine ( P  = 0.05). In the MTHFR TT group, plasma homocysteine inversely related to protein C ( P  = 0.03). Plasma homocysteine predicted the extent of PVT ( P  = 0.03). Compound MTHFR TT + PT GA did not lower age at first PVT compared to MTHFR TT alone (35 ± 9 vs. 30 ± 8 years). MTHFR TT is associated with a 20-year earlier PVT presentation than heterozygous and wild-type MTHFR genotypes. The inverse relation between plasma homocysteine and protein C contributes to the prematurity of PVT in the MTHFR TT group, whereas plasma homocysteine contributes to the extent of PVT. The recent exclusion of MTHFR genotyping from the thrombophilia screen needs revisiting in this setting.

Plasma thiol levels and methylenetetrahydrofolate reductase gene c.665C > T and c.1286A > C variants affect fibrin clot properties in Polish venous thromboembolic patients

BACKGROUND AND AIMS

Aminothiols, including cysteine (Cys) and glutathione (GSH) in relation to fibrin clot phenotype were not investigated in patients with venous thromboembolism (VTE) and 5,10-methylenetetrahydrofolate reductase (MTHFR) gene variants. We aimed to explore the associations between MTHFR variants and plasma oxidative stress indicators including aminothiols as well as fibrin clot properties with plasma oxidative status and fibrin clot properties in this group of patients.

METHODS

In 387 VTE patients the MTHFR c.665C > T and c.1286A > C variants were genotyped, together with chromatographic separation of plasma thiols. We also determined nitrotyrosine levels and fibrin clot properties, including clot permeability (Ks), lysis time (CLT), and fibrin fibers thickness.

RESULTS

There were 193 patients with MTHFR c.665C > T (49.9%) and 214 (55.3%) with c.1286A > C variants. Both allele carriers with total homocysteine (tHcy) levels >15 μM (n = 71, 18.3%), compared to patients with tHcy ≤15 μM had 11.5% and 12.5% higher Cys levels, 20.6% and 34.3% higher GSH levels as well as 28.1% and 57.4% increased nitrotyrosine levels, respectively (all P < 0.05). The MTHFR c.665C > T carriers with tHcy levels >15 μM compared to tHcy ≤15 μM had 39.4% reduced Ks and 9% reduced fibrin fibers thickness (both P < 0.05) with no differences in CLT. In the MTHFR c.1286A > C carriers with tHcy levels >15 μM, Ks was decreased by 44.5%, CLT prolonged by 46.1%, and fibrin fibers thickness was reduced by 14.5% compared to patients with tHcy ≤15 μM (all P < 0.05). Nitrotyrosine levels in MTHFR variants carriers correlated with Ks (r = -0.38, P < 0.05) and fibrin fibers diameter (r = -0.50, P < 0.05).

CONCLUSIONS

Our study indicates that patients with MTHFR variants and tHcy >15 μM are characterized by elevated Cys and nitrotyrosine levels associated with prothrombotic fibrin clot properties.

Does Risk of Hyperhomocysteinemia Depend on Thiol-Disulfide Exchange Reactions of Albumin and Homocysteine?

Significance: Increased plasma concentrations of total homocysteine (tHcy; mild-moderate hyperhomocysteinemia: 15-50 μM tHcy) are considered an independent risk factor for the onset/progression of various diseases, but it is not known about how the increase in tHcy causes pathological conditions. Recent Advances: Reduced homocysteine (HSH ∼1% of tHcy) is presumed to be toxic, unlike homocystine (∼9%) and mixed disulfide between homocysteine and albumin (HSS-ALB; homocysteine [Hcy]-albumin mixed disulfide, ∼90%). This and other notions make it difficult to explain the pathogenicity of Hcy because: (i) lowering tHcy does not improve pathological outcomes; (ii) damage due to HSH usually emerges at supraphysiological doses; and (iii) it is not known why tiny increments in plasma concentrations of HSH can be pathological. Critical Issues: Albumin may have a role in Hcy toxicity, because HSS-ALB could release toxic HSH via thiol-disulfide (SH/SS) exchange reactions in cells. Similarly, thiol-disulfide exchange processes of reduced albumin (albumin with free SH group of Cys34 [HS-ALB]) or N-homocysteinylated albumin are plausible alternatives for initiating Hcy pathological events. Adverse effects of albumin and other data reviewed here suggest the hypothesis of a role of albumin in Hcy toxicity. Future Directions: HSS-ALB might be involved in disruption of the antioxidant/oxidant balance in critical tissues (brain, liver, kidney). Since homocysteine-albumin mixed disulfide is a possible intermediate of thiol-disulfide exchange reactions, we suggest that homocysteinylated albumin could be a new pathological factor, and that studies on the redox role of albumin and mixed disulfide production via thiol-disulfide exchange reactions could offer new therapeutic insights for reducing Hcy toxicity.

Liver Cirrhosis Patients Homozygous for MTHFR C677T Develop Portal Vein Thrombosis 8 Years Earlier Than Wild Type

BACKGROUND AND AIM

Age at portal vein thrombosis (PVT) in liver cirrhosis (LC) carriers of the methylene tetrahydrofolate reductase (MTHFR) rs1801133 (C → T667 transition) polymorphism has never been addressed; we compared age at PVT in LC patients genotyped for the MTHFR and explored the interrelated clinical and laboratory factors predicting age at PVT.

APPROACH AND RESULTS

Retrospective cross-sectional cohort study. PVT participants: MTHFR CC n = 36, MTHFR CT n = 53, MTHFR TT n = 19; age, sex, age at PVT, Child-Pugh score, rs1799963 PT polymorphisms (G → A 20,210 transition), plasma HC and natural anticoagulants available for all participants. Age at PVT was lower in MTHFR TT than CT and CC (56 ± 13 vs. 57 ± 13 vs. 64 ± 9 years, p = 0.001); median (IQR) plasma HC was higher in MTHFR TT than in the other groups [(17 (9.4, 23.3) vs 13 (8,14.7) vs 11 (8.9, 12.7) μmol/l, p = 0.03)]. MTHFR TT, male gender and protein C predicted age at PVT (p = 0.02, p = 0.04 and p = 0.08); MTHFR TT and Child-Pugh score predicted plasma HC (p = 0.005 and p = 0.01) as well as low plasma protein C (p < 0.0001 and p = 0.0002). Plasma HC inversely related to protein C in the MTHFR TT group (p < 0.0001). Compound MTHFR TT with PT GA had lower age at PVT compared to MTHFR TT alone (49 ± 18 vs 58 ± 12 years).

CONCLUSIONS

MTHFR TT anticipates PVT associated with LC by an average of 8 years; MTHFR TT associates with severity of liver disease and to high plasma HC; the latter may contribute to the prematurity of PVT by interfering with the anticoagulant activity of protein C.

Assessing Factor V Antigen and Degradation Products in Burn and Trauma Patients

INTRODUCTION

Proposed mechanisms of acute traumatic coagulopathy (ATC) include decreased clotting potential due to factor consumption and proteolytic inactivation of factor V (FV) and activated factor V (FVa) by activated protein C (aPC). The role of FV/FVa depletion or inactivation in burn-induced coagulopathy is not well characterized. This study evaluates FV dynamics following burn and nonburn trauma.

METHODS

Burn and trauma patients were prospectively enrolled. Western blotting was performed on admission plasma to quantitate levels of FV antigen and to assess for aPC or other proteolytically derived FV/FVa degradation products. Statistical analysis was performed with Spearman's, Chi-square, Mann-Whitney U test, and logistic regression.

RESULTS

Burn (n = 60) and trauma (n = 136) cohorts showed similar degrees of FV consumption with median FV levels of 76% versus 73% (P = 0.65) of normal, respectively. Percent total body surface area (TBSA) was not correlated with FV, nor were significant differences in median FV levels observed between low and high TBSA groups. The injury severity score (ISS) in trauma patients was inversely correlated with FV (ρ = -0.26; P = 0.01) and ISS ≥ 25 was associated with a lower FV antigen level (64% versus. 93%; P = 0.009). The proportion of samples showing proteolysis-derived FV was greater in trauma than burn patients (42% versus. 16%; P = 0.0006).

CONCLUSIONS

Increasing traumatic injury severity is associated with decreased FV antigen levels, and a greater proportion of trauma patient samples exhibit proteolytically degraded FV fragments. These associations are not present in burns, suggesting that mechanisms underlying FV depletion in burn and nonburn trauma are not identical.

Pernicious anemia: Pathophysiology and diagnostic difficulties

Pernicious anemia (PA) is the most common cause of vitamin B12 (cobalamin) deficiency anemia in the world. It is an autoimmune disease, comprising of salient features of autoimmune chronic atrophic gastritis (CAG) and cobalamin deficiency (CD). Although the anemia was first described as pernicious, it may well be controlled with vitamin B12 replacement. The onset and progression of PA is often insidious. Alternatively, patients may have no anemic symptoms since they become acclimatized to the subtle nature of the disease. Oftentimes, there is a possibility that the underlying disease may be missed unless a full blood count (FBC) is investigated, leading to hindrance in the treatment journey. Diagnostic challenges remain tangible for many practicing clinicians, since there is lack of reliable cobalamin assays to diagnose CD as well as clinical mimics, which simulate many other hematological conditions, such as myelodysplastic syndrome, acute leukemia, sideroblastic anemias, bone marrow failure states, thrombotic microangiopathy, and thromboembolism. Moreover, prompt recognition of the symptoms of CD is also vital, because some neurologic sequalae may become irreversible despite replenishing cobalamin. Herein, we discuss a literature review on the pathophysiology, challenging clinical presentations and diagnostic difficulties of PA. Since the cobalamin replacement therapy for PA is straightforward, it will not be discussed in this review.

Homocysteine Serum Levels as Prognostic Marker of Hepatocellular Carcinoma with Portal Vein Thrombosis

BACKGROUND

Portal vein thrombosis (PVT) is a common complication of endstage hepatocellular carcinoma (HCC). The aim of our study was to evaluate the role of Homocysteine (Hcy) in HCC patient with PVT. Hcy is a sulphur amino-acid involved in two pathways, trans-sulphuration and remethylation, that involve vitamins B6, B12 and folates.

METHODS

We recruited 54 patients with HCC and PVT, 60 patients with HCC and without PVT and 60 control subjects. We measured serum levels of Hcy, folate, vitamins B6 and B12.

RESULTS

The comparison between HCC patients with PVT versus HCC without PVT was shown that mean values of Hcy were 6.4 nmol/L (p<0.0073) higher, LDL cholesterol were 4.8 mg/dl (p<0.0079) lower, vitamin B6 were 4.6 nmol/L(p=0.0544) lower, vitamins B 12 were 22.1 pg/ml (p=0.0001) lower.

CONCLUSION

High serum levels of Hcy are an established thrombotic risk factor in the general population. We found significantly higher levels of Hcy in HCC patients with PVT versus both HCC patients without PVT and controls.

Venous thromboembolism and hyperhomocysteinemia as first manifestation of pernicious anemia: a case series

BACKGROUND

Hyperhomocysteinemia has been suspected of favoring thrombosis. Several case-control studies and even a meta-analysis have confirmed a link between venous thrombosis and hyperhomocysteinemia. Homocysteine is due to genetic and acquired factors (poor diet in folate and vitamin B12, older age, renal impairment, thyroid diseases, and malignancies) induced by the intake and the concentrations of vitamin B9 or B12 in the majority of cases.

CASES PRESENTATION

We report the cases of four Moroccan patients who presented with acute vein thrombosis of different sites: a 34-year-old man, a 60-year-old man, a 58-year-old man, and a 47-year-old woman. All patients had a low level of cobalamin with marked hyperhomocysteinemia with normal serum and red cell folic acid. Venous thrombosis revealed pernicious anemia in all patients. Their low levels of cobalamin, atrophic gastritis, and positive results for gastric parietal cell antibodies confirmed the diagnosis of pernicious anemia. There was no evidence of immobilization, recent surgery, malignancy, antiphospholipid antibody, myeloproliferative disorder, or hormone replacement therapy. No deficiencies in protein C and protein S were detected; they had normal antithrombin III function and factor V Leiden; no prothrombin gene mutations were detected. Treatment included orally administered anticoagulation therapy and cobalamin supplementation. The outcome was favorable in all cases.

CONCLUSIONS

These reports demonstrate that pernicious anemia, on its own, can lead to hyperhomocysteinemia that is significant enough to lead to thrombosis. Understanding the molecular pathogenesis of the development of thrombosis in patients with hyperhomocysteinemia related to Biermer disease would help us to identify patients at risk and to treat them accordingly. The literature concerning the relationship between homocysteine and venous thrombosis is briefly reviewed.

Hyperhomocysteinemia exacerbates Alzheimer's disease pathology by way of the β-amyloid fibrinogen interaction

Essentials Evidence suggests a comorbidity between hyperhomocysteinemia (HHC) and Alzheimer's disease (AD). Homocysteine (HC) could affect the β-amyloid (Aβ)-fibrinogen interaction in AD pathology. AD patients with concomitant HHC have increased fibrin and Aβ deposits in their brains. HC contributes to AD pathology via the Aβ-fibrinogen interaction.

SUMMARY

Background Accumulating clinical evidence suggests that hyperhomocysteinemia (HHC) is correlated with Alzheimer's disease (AD) and vascular dementia. Objective This study was carried out to elucidate the specific role of elevated homocysteine (HC) levels in AD pathophysiology. Methods Immunohistochemistry was used to examine β-amyloid (Aβ) deposition along blood vessels, also known as cerebral amyloid angiopathy (CAA), fibrin(ogen) deposition, and their correlation to each other in the brains of AD patients with and without HHC. To study AD-HHC co-morbidity in detail, an AD mouse model was administered a high methionine diet for several months. Parenchymal Aβ plaques, CAA-positive vessels and fibrin deposits were then assessed by immunohistochemistry at different stages of AD progression. Memory deficits were evaluated with contextual fear conditioning and the Barnes maze. Additionally, the effect of HC and its metabolite, homocysteine thiolactone (HCTL), on the Aβ-fibrinogen interaction was analyzed by pull-down, ELISA and fibrin clot formation and fibrinolysis assays in vitro. Results We found increased fibrin(ogen) levels and Aβ deposits in the blood vessels and brain parenchyma of AD patients with HHC. We demonstrate that HC and HCTL enhance the interaction between fibrinogen and Aβ, promote the formation of tighter fibrin clots and delay clot fibrinolysis. Additionally, we show that diet-induced HHC in an AD mouse model leads to severe CAA and parenchymal Aβ deposition, as well as significant impairments in learning and memory. Conclusions These findings suggest that elevated levels of plasma HC/HCTL contribute to AD pathology via the Aβ-fibrin(ogen) interaction.

[Clinical manifestations of the onset and diagnostic problems in children with moyamoya disease]

Moyamoya disease in children is a rarely diagnosed entity. Frequent headache is the first symptom of the disease. Headache associated with moya-moya disease (HAMD) is a separated entity reported in the literature. Variants of onset, a spectrum of primary diagnoses and diagnosis verification rate of moyamoya disease in 7 children are presented. A clinical case of moya-moya disease in a 9-year boy, who was primarily diagnosed with migraine with aura, is reported. The results presented by the authors as well as literature data indicate the necessity of using magnetic-resonance angiography in children with headache attacks and focal neurologic symptoms to identify this progressive vascular pathology and timely recommend a surgical treatment.

Effect of resveratrol on hemostatic properties of human fibrinogen and plasma during model of hyperhomocysteinemia

Resveratrol (3,4', 5 - trihydroxystilben), a phenolic antioxidant synthesized in grapes and vegetables and presents in wine, has been supposed to be beneficial for the prevention of cardiovascular events. In this study the influence of resveratrol on the clot formation (using human plasma and purified fibrinogen) and the fibrin lysis during model of hyperhomocysteinemia was investigated. We induced this process using a reduced form of Hcys (at final dose of 0.1mM) and the most reactive form of Hcys - its cyclic thioester, homocysteine thiolactone (HTL, 0.5μM). The aim of our study in vitro was to investigate the modifications of human plasma total proteins after incubation with Hcys, HTL and resveratrol. We observed that HTL, like its precursor, Hcys stimulated polymerization of fibrinogen. Our present results also demonstrated that Hcys (0.1mM) and HLT at lower doses than Hcys (0.5μM) reduced the fibrin lysis in human plasma. Moreover, Hcys and HTL change the level of thiol and amino groups in plasma total proteins. Our results indicate that resveratrol reduced the toxicity action of Hcys and HTL on hemostatic properties of fibrinogen or plasma, suggesting its possible protector role in hyperhomocysteinemia - induced cardiovascular diseases.

Therapeutical approach to plasma homocysteine and cardiovascular risk reduction

Homocysteine is a sulfur-containing aminoacid produced during metabolism of methionine. Since 1969 the relationship between altered homocysteine metabolism and both coronary and peripheral atherotrombosis is known; in recent years experimental evidences have shown that elevated plasma levels of homocysteine are associated with an increased risk of atherosclerosis and cardiovascular ischemic events. Several mechanisms by which elevated homocysteine impairs vascular function have been proposed, including impairment of endothelial function, production of reactive oxygen species (ROS) and consequent oxidation of low-density lipids. Endothelial function is altered in subjects with hyperhomocysteinemia, and endothelial dysfunction is correlated with plasma levels of homocysteine. Folic acid and B vitamins, required for remethylation of homocysteine to methionine, are the most important dietary determinants of homocysteine and daily supplementation typically lowers plasma homocysteine levels; it is still unclear whether the decreased plasma levels of homocysteine through diet or drugs may be paralleled by a reduction in cardiovascular risk.

The elevated homocysteine stimulates changes of haemostatic function of plasma isolated from breast cancer patients

The aim of our study was to explain the effect of elevated homocysteine (measured by HPLC) on haemostatic activity of plasma from breast cancer patients (fibrin polymerization and lysis; the thrombin and prothrombin time), because homocysteine (Hcys) induces changes in haemostasis, as well blood clotting as fibrinolysis. Patients were hospitalized in Department of Oncological Surgery, Medical University of Lodz, Poland. All patients have not had preadjuvant therapy, and samples from patients were taken before surgery. We observed that changes of selected parameters of haemostatic properties of plasma, e.g., the prothrombin time and thrombin time were prolonged in plasma from invasive breast cancer when compared with the control group (healthy subjects) and patients with benign breast diseases. Our results showed also that the correlation between the increased amount of Hcys and changes of selected parameters of haemostasis in invasive breast cancer patients exists. Considering the data presented in this study, we suggest that the elevated Hcys in invasive breast cancer patients may induce the changes of haemostatic properties of plasma isolated from these patients.

Hyperhomocysteinemia in patients with pulmonary embolism

Investigation of hyperhomocysteinemia (HHcy) as an important risk factor for pulmonary thromboembolism (PTE), which represents a most dangerous consequence of a unique phenomenon of venous thromboembolism which still suffers from sometimes conflicting or inadequately clarified results. The role of homocysteine in the clinical manifestation of this life-threatening disease and its treatment (in which any further information may be decisive) requires detailed examination. The purpose of this study is to determine the differences in HHcy incidence and homocysteinemia levels between patients with PTE and healthy persons. The study enrolled 70 patients with PTE and 50 healthy persons. Homocysteine was measured using the HPLC method with fluorescent detection and HHcy was defined as homocysteinemia above 12 ?mol/L. Statistical analyses included chi-square and Mann Whitney U tests. The median homocysteinemia value was significantly higher (p=0.017) in the patients (12.10 ?mol/L) than in the controls (10.35 ?mol/L). The comparison of HHcy incidence between the patients (51.5%) and controls (30%) revealed a significant difference (p=0.021). In patients, homocysteinemia was significantly higher (p=0.002) in men (14.05?mol/L) than in women (10.01 ?mol/L). HHcy was present in 67.6% of men with PTE, which was significantly higher (p=0.006) than the incidence in women with PTE (33.3%). Healthy males had significantly higher (p=0.001) homocysteinemia (12.54 ?mol/L) than healthy females (9.4 ?mol/L). A significant difference (p=0.031) was observed between the incidences of HHcy in healthy males (44.0%) and healthy females (16.0%). We conclude that the incidence of hyperhomocysteinemia and homocysteinemia are significantly higher in all the patients compared with the healthy persons, as well as in both healthy males and males with PTE compared with healthy females and female patients. This indicates that HHcy findings in PE are likely to have a clinical importance.

Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism

BACKGROUND

Patent foramen ovale (PFO) is an independent risk factor for cerebral infarction. Since ~25% of the population have a PFO, the simple association of PFO with stroke is not enough to establish the diagnosis of paradoxical embolism. We evaluated possible clinical clues to the diagnosis of paradoxical embolism.

METHODS

Among patients with cryptogenic ischemic stroke (CS) who were investigated for a right-to-left shunt (RLS), we compared clinical, coagulation and biochemical parameters in patients with PFO versus without PFO.

RESULTS

Among 1689 new patients referred for TIA/non-disabling stroke between 2001 and 2007, 175 with cryptogenic stroke (CS) were investigated for RLS by transcranial Doppler (TCD) bubble studies; 89 (5.5%) with positive TCD had a PFO confirmed by TEE. In multivariate logistic regression, a history of DVT or pulmonary embolism (OR, 4.39; 95% CI, 1.23-15.69; p=0.023), prolonged travel (OR, 8.77; 95% CI, 1.775-43.3; p=0.008) , migraine (OR, 2.30: 95% CI, 1.07-4.92; p=0.031), a Valsalva maneuver preceding the onset of focal neurological symptoms (OR, 3.33; 95% CI, 1.15-9.64; p=0.026) and waking up with stroke/TIA (OR, 4.53, 95% CI, 1.26-16.2; p=0.018) were independently associated with PFO-associated cerebrovascular events. Patients with PFO had higher plasma total homocysteine levels than patients without PFO (8.9+/-3 versus 7.9+/-2.6 micromol/L respectively; p=0.021).

CONCLUSIONS

A history of DVT or pulmonary embolism, migraine, recent prolonged travel, sleep apnea, waking up with TIA or stroke or a Valsalva maneuver preceding the event are clinical clues to the diagnosis of paradoxical embolism among patients with CS.

Predicting protein homocysteinylation targets based on dihedral strain energy and pKa of cysteines

A multitude of complex diseases have been linked to elevated homocysteine levels; however, till date there is no plausible explanation for a single amino acid's involvement in so many diseases. Since homocysteine is a reactive thiol amino acid and the majority of plasma homocysteine is protein thiol bound, we hypothesized that homocysteine might bind to accessible cysteine residues in target proteins, thereby modulating its structure or function or both. The parameters that dictate homocysteine-protein interaction are not well understood, and the few known homocysteine binding proteins were identified by a candidate protein approach. In this study, we identified potential homocysteine interacting proteins based on cysteine content, solvent accessibility of cysteine residues, and dihedral strain energies and pKa of these cysteines. Pathway mapping of the cysteine-rich proteins revealed that proteins in the coagulation cascade, notch receptor-mediated signaling, LDL endocytosis, programmed cell death, and extracellular matrix proteins were significantly over-represented with cysteine-rich proteins, and we believe that homocysteine has a high probability to bind to proteins in these pathways. In fact, several clinical studies have implicated high homocysteine levels to be associated with diseases like thrombosis, neural tube defects, and so forth, which result from dysfunction of one or more of the proteins identified in our study. Further, we successfully validated our prediction parameters on the proteins that have already been experimentally shown to bind homocysteine, and our structural analysis argues a plausible explanation for these prior reported protein interactions with homocysteine that could not be previously explained.

Cysteinylation and homocysteinylation of plasma protein thiols during ageing of healthy human beings

The purpose of the present study was to determine the relative amount of S-thiolated proteins (i.e. S-homocysteinylated, S-cysteinylglycinylated, S-glutathionylated and S-cysteinylated proteins) to the total protein thiols (i.e. the sum of reduced protein sulphydryl groups (PSHs) and protein mixed disulphides with homocysteine [HcySH], cysteinylglycine, cysteine [CysSH] and glutathione) in the plasma of healthy individuals aged 20 to 93. After plasma separation, total protein thiols, S-thiolated proteins, as well as CysSH, cystine, HcySH and homocystine were measured by high-performance liquid chromatography (HPLC) with fluorescence determination of the thiol-monobromobimane conjugate. Determination of plasma levels of protein thiols was performed by spectrophotometry with 5,5′-dithiobis(2-nitrobenzoic acid) as a titrating agent. The present study demonstrates an age-dependent reduction in the amount of PSHs, and an age-dependent increase in cysteinylated and homocysteinylated plasma proteins in healthy human beings. This indicates that the efficiency of the reduced protein thiol pool as an antioxidant defence system decreases with age, possibly causing an increased risk of irreversible oxidation (i.e. further oxidation to sulphinic and sulphonic acids, which are usually not reducible by thiol reducing agents) of sulphydryl groups of plasma proteins. The drop in the plasma level of protein sulphydryl groups suggests depletion and/or impairment of the antioxidant capacity of plasma, likely related to an alteration of the delicate balance between the different redox forms of thiols.

Hyperhomocysteinemia in women with advanced breast cancer

Patients with malignancy have an increased risk of venous thromboembolic disease but the pathophysiology of this association has not been precisely defined. Hyperhomocysteinemia has become established as one of the commonest conditions associated with venous and arterial thrombosis. We examined the prevalence of hyperhomocysteinemia in women with early (group A, n = 31), metastatic breast cancer (group B, n = 41) and in a group of healthy females (group C, n = 29). Blood samples were collected at diagnosis or prior to treatment. We measured both total plasma homocysteine (tHcy) and red cell folate (RCF). The Mean (SD) tHcy were group A - 9.43 micromol/l (5.6), group B - 11.34 micromol/l (5.1) and group C - 7.9 micromol/l (1.5). A total of 39% of patients with metastatic and 22.6% with early breast cancer had tHcy concentrations above the upper limit of normal. Women with metastatic disease had significantly higher tHcy compared with controls (P < 0.01) but not when compared with women with early breast cancer. Also, no difference was observed when women with early disease were compared with controls. We found no correlation between age and tHcy. Lower RCF levels were identified in group B compared with group A, but this does not fully explain the increased tHcy levels seen within the same group. We conclude that hyperhomocysteinemia is common in women with advanced breast cancer. This observation could explain the high rate of venous thrombosis in women with metastatic breast malignancy.

Role of redox reactions in the vascular phenotype of hyperhomocysteinemic animals

Hyperhomocysteinemia is a risk factor for cardiovascular disease, stroke, and thrombosis. Several animal models of hyperhomocysteinemia have been developed by using both dietary and genetic approaches. These animal models have provided considerable insight into the mechanisms underlying the adverse vascular effects of hyperhomocysteinemia. Accumulating evidence suggests a significant role of altered cellular redox reactions in the vascular phenotype of hyperhomocysteinemia. Redox effects of hyperhomocysteinemia are particularly important in mediating the adverse effects of hyperhomocysteinemia on the endothelium, leading to loss of endothelium-derived nitric oxide and vasomotor dysfunction. Redox reactions also may be key factors in the development of vascular hypertrophy, thrombosis, and atherosclerosis in hyperhomocysteinemic animals. In this review, we summarize the metabolic relations between homocysteine and the cellular redox state, the vascular phenotypes that have been observed in hyperhomocysteinemic animals, the evidence for altered redox reactions in vascular tissue, and the specific redox reactions that may mediate the vascular effects of hyperhomocysteinemia.

Molecular targeting of proteins by L-homocysteine: mechanistic implications for vascular disease

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, complications of pregnancy, cognitive impairment, and osteoporosis. That elevated homocysteine leads to vascular dysfunction may be the linking factor between these apparently unrelated pathologies. Although a growing body of evidence suggests that homocysteine plays a causal role in atherogenesis, specific mechanisms to explain the underlying pathogenesis have remained elusive. This review focuses on chemistry unique to the homocysteine molecule to explain its inherent cytotoxicity. Thus, the high pKa of the sulfhydryl group (pKa, 10.0) of homocysteine underlies its ability to form stable disulfide bonds with protein cysteine residues, and in the process, alters or impairs the function of the protein. Studies in this laboratory have identified albumin, fibronectin, transthyretin, and metallothionein as targets for homocysteinylation. In the case of albumin, the mechanism of targeting has been elucidated. Homocysteinylation of the cysteine residues of fibronectin impairs its ability to bind to fibrin. Homocysteinylation of the cysteine residues of metallothionein disrupts zinc binding by the protein and abrogates inherent superoxide dismutase activity. Thus, S-homocysteinylation of protein cysteine residues may explain mechanistically the cytotoxicity of elevated L-homocysteine.

Hyperhomocysteinemia and thrombosis: an overview

CONTEXT

Homocysteine, a sulfur-containing amino acid, absent in natural diets, is a metabolic intermediary in transmethylation and transsulfuration reactions. Such reactions are essential to normal cellular growth, differentiation, and function. Excess homocysteine is associated with vascular disease and related disorders.

OBJECTIVE

To review homocysteine metabolism, the pathogenesis and classification of hyperhomocysteinemia, and the published literature investigating the association of homocysteine and methylenetetrahydrofolate reductase defects with arterial and venous thromboembolism and related disorders. The role of vitamin supplementation in patients with hyperhomocysteinemia is addressed.

DATA SOURCES

Published medical and scientific literature. Articles addressing the objectives were selected and reviewed. Pertinent studies and conclusions were summarized, grouped, and contrasted.

CONCLUSIONS

The association of hyperhomocysteinemia and arterial and venous thrombosis is controversial. Severe hyperhomocysteinemia is associated with atherosclerosis. The effect of mild hyperhomocysteinemia is less certain. Coinheritance of methylenetetrahydrofolate reductase defects and factor V Leiden is likely to increase the risk of venous thromboembolism. The association of methylenetetrahydrofolate reductase defects combined with no additional thrombophilic risk factors with venous thrombosis is less clear. High doses of folic acid to lower homocysteine levels might not be necessary.

Hyperhomocysteinemia and venous thrombosis

It has been recognized, since the first description of the disease, that arterial and venous thrombosis are common in patients with homocysteinuria. Interest in the condition increased with reports from a large number of mainly retrospective studies showing that mildly elevated homocysteine levels are also associated with venous thromboembolism (VTE), thrombotic stroke, and peripheral vascular disease. This association is less strong when populations are studied prospectively. Vitamin supplementation, primarily with folic acid, and to a lesser degree with pyridoxine and vitamin B(12), is effective in reducing elevated levels of plasma homocysteine. Surprisingly, however, recent prospective intervention studies showed that despite lowering of the homocysteine level with such treatment, there was no impact on the risk of recurrence of venous or arterial disease.

Long-chain n-3 fatty acid supplementation in men increases resistance to activated protein C

It has recently and controversially been demonstrated that fish oil supplementation may not be beneficial for everyone, but to date there have been no biological explanations. We suggest that resistance to the anticoagulant, activated protein C (APC), be considered as a potential mechanism, because it has been demonstrated that the type of fatty acids on phospholipids modulates function of the APC pathway. The APC ratio in plasma was decreased by 7% after fish oil supplementation in healthy men (P<.005; n=35). The decrease in APC ratio equates to an increase in APC resistance. Fish oil lowered the APC ratio by (1) increasing low-density lipoprotein (LDL) cholesterol (P<.01) and apolipoprotein B (P<.05) and (2) increasing platelet microparticles (P<.05). In vitro, purified LDL decreased the APC ratio and increased microparticle formation. These changes affecting the anticoagulant APC could contribute toward a prothrombotic state, potentially explaining the recent observation that fish oil supplementation may not always be of benefit. These findings will need to be repeated in different disease states.

Changes in haemostasis during normal pregnancy: does homocysteine play a role in maintaining homeostasis?

Homocysteine, derived from the demethylation of the ammo acid methionine, is either further catabolised by trans-sulfuration to cysteine or remethylated to methionine. Remethylation to methionine requires the cofactors, folate and vitamin B12. Folate is an effective homocysteine-lowering agent and, thus, homocysteine and folate status are inversely related. Hyperhomocysteinaemia is a strong independent risk factor for venous thromboembolism (VTE) and is associated with adverse pregnancy outcomes such as pre-eclampsia, placental abruption, early pregnancy loss and neural-tube defects. Pregnancy is a risk factor for VTE as a result of prothrombotic changes in levels of haemostatic factors. However, despite this hypercoagulable state, the incidence of pregnancy-associated VTE is relatively low. Hyperhomocysteinaemia is associated with abnormalities in markers of coagulation activation, and recent research suggests that folic acid supplementation, as well as lowering homocysteine, lowers markers of coagulation activation and increases levels of coagulation inhibitors. Tissue factor (TF) is the initiator of blood coagulationin vivo, and homocysteine induces TF expressionin vitro. During pregnancy, monocyte TF expression is lower than that in the non-pregnant state, and this lowering of TF may act to counterbalance increases in coagulation activation. Furthermore, despite a high folate requirement, several studies have reported that homocysteine is lower in normal pregnancy than in the non-pregnant state. Although the exact mechanism of homocysteine lowering during pregnancy is unclear, one possible outcome of lower homocysteine may be the protection of women from pregnancy complications and VTE, and thus lower homocysteine may contribute to maintaining homeostasis in haemostasis.

Mechanisms of homocysteine toxicity in humans

Homocysteine, a non-protein amino acid, is an important risk factor for ischemic heart disease and stroke in humans. This review provides an overview of homocysteine influence on endothelium function as well as on protein metabolism with a special respect to posttranslational modification of protein with homocysteine thiolactone. Homocysteine is a pro-thrombotic factor, vasodilation impairing agent, pro-inflammatory factor and endoplasmatic reticulum-stress inducer. Incorporation of Hcy into protein via disulfide or amide linkages (S-homocysteinylation or N-homocysteinylation) affects protein structure and function. Protein N-homocysteinylation causes cellular toxicity and elicits autoimmune response, which may contribute to atherogenesis.

Factors Affecting S-Homocysteinylation of LDL Apoprotein B

Background: Hyperhomocysteinemia is an important risk factor for vascular disease and atherosclerosis, but the mechanisms by which homocysteine exerts its deleterious effects are not known. Because oxidation and/or homocysteinylation may increase atherogenicity of LDL, we investigated S-homocysteinylation of LDL as a possible contributor to atherosclerosis pathogenesis.

Methods: We used capillary electrophoresis to measure LDL-bound thiols [homocysteine, cysteine (Cys), cysteinylglycine, glutathione, and glutamylcysteine] in 104 healthy study participants We also assessed total plasma thiol concentrations and lipid profiles.

Results: Our data suggest that apoprotein B (apoB)-cysteinylglycine (CysGly), apoB-Hcy, and apoB-Cys concentrations are markedly higher in men than in women. The percentage of CysGly and glutathione on apoB was higher than that of the same thiols in plasma, whereas the other thiols were markedly less prevalent in lipoprotein than in plasma. Pearson correlation showed that among all thiols, only total plasma Hcy is related to apoB-Hcy concentrations. Multiple correlation analysis confirmed that total Hcy was the most important determinant of apoB-Hcy. Age and LDL cholesterol also showed positive associations, but Cys and, mainly, CysGly were negatively associated with apoB-Hcy concentrations.

Conclusions: apoB-Hcy derivative formation is mainly dependent on total homocysteine concentration. Increased cholesterol concentrations are related to increased apoB-Hcy. CysGly seems to compete with Hcy for binding to LDL apoprotein, suggesting that CysGly may protect against atherosclerosis by decreasing the concentrations of Hcy transferred by LDL from plasma to endothelial and subendothelial spaces.

Venous thrombosis associated with pernicious anaemia. A report of two cases and review

Since homocystinuria, an inborn metabolism error is complicated by venous thrombosis in about half of the patients, hyperhomocysteinemia has been suspected of favouring thrombosis. Several case-control studies and even meta-analysis have confirmed a link between venous thrombosis and mild hyperhomocysteinemia. Nevertheless, the proper role of homocysteine remains debated. Hyperhomocysteinemia is induced by vitamin B9 or B12 deficiencies in a vast majority of cases. The authors report on two patients with venous thrombosis revealing pernicious anemia and review nine similar cases found in the world literature. The literature concerning the relationships between homocysteine and venous thrombosis is briefly reviewed.

Distribution of low-density lipoprotein-bound low-molecular-weight thiols: A new analytical approach

We have recently demonstrated that low-density lipoprotein (LDL) apoprotein is able to bind the most concentrated plasma thiols such as cysteine, cysteinylglycine, and homocysteine by disulfide linkage. However, the LIF CE assay employed to measure linked thiols was not sensitive enough to verify whether low concentrated plasma thiols as glutathione and glutamylcysteine are also linked to apoprotein. By modifying sample treatment and electrophoretic parameters we set up a new method with an LOQ of about 1.5 nmol/L, by which we demonstrate that LDL apoprotein binds all physiological plasma thiols. The increased sensitivity was obtained by drying released apoB thiols after reduction treatment, dissolving them directly in a low volume of derivatization buffer and decreasing the dilution factor of derivatized sample before CE injection. Moreover, by increasing the concentration of the electrolyte buffer, we improved the selectivity of peaks, in particular between glutathione (GSH) and the impurity peak derived from unreacted 5-iodoacetamidofluorescein, which in the previous electrophoretic conditions were overlapped. The method optimization, reached by searching the best combination between sample matrix and CE run buffer, is fully described. Given the potential pathologic significance of protein thiolation, the proposed method may be useful to understand the mechanisms and the balances that regulate the interaction between thiols and -SH free groups of proteins.

Homocysteine- and cysteine-mediated growth defect is not associated with induction of oxidative stress response genes in yeast

Intracellular thiols like cysteine, homocysteine and glutathione play a critical role in the regulation of important cellular processes. Alteration of intracellular thiol concentration results in many diseased states; for instance, elevated levels of homocysteine are considered to be an independent risk factor for cardiovascular disease. Yeast has proved to be an excellent model system for studying many human diseases since it carries homologues of nearly 40% of human disease genes and many fundamental pathways are highly conserved between the two organisms. In the present study, we demonstrate that cysteine and homocysteine, but not glutathione, inhibit yeast growth in a concentration-dependent manner. Using deletion strains (str2Delta and str4Delta) we show that cysteine and homocysteine independently inhibit yeast growth. Transcriptional profiling of yeast treated with cysteine and homocysteine revealed that genes coding for antioxidant enzymes like glutathione peroxidase, catalase and superoxide dismutase were down-regulated. Furthermore, transcriptional response to homocysteine did not show any similarity to the response to H2O2. We also failed to detect induction of reactive oxygen species in homocysteine- and cysteine-treated cells, using fluorogenic probes. These results indicate that homocysteine- and cysteine-induced growth defect is not due to the oxidative stress. However, we found an increase in the expression of KAR2 (karyogamy 2) gene, a well-known marker of ER (endoplasmic reticulum) stress and also observed HAC1 cleavage in homocysteine- and cysteinetreated cells, which indicates that homocysteine- and cysteine-mediated growth defect may probably be attributed to ER stress. Transcriptional profiling also revealed that genes involved in one-carbon metabolism, glycolysis and serine biosynthesis were up-regulated on exogenous addition of cysteine and homocysteine, suggesting that cells try to reduce the intracellular concentration of thiols by up-regulating the genes involved in their metabolism.

Plasma homocysteine affects fibrin clot permeability and resistance to lysis in human subjects

OBJECTIVE

Homocysteine (Hcy) is a risk factor for thrombosis. We investigated a hypothesis that the clot permeability and its resistance to fibrinolysis is associated with plasma total Hcy (tHcy) in human subjects.

METHODS AND RESULTS

We studied healthy men not taking any medication (n=76), male patients with advanced coronary artery disease (CAD) taking low-dose aspirin (n=33), men with diabetes mellitus diagnosed recently (median hemoglobin A(1c) 7.65%; n=16), and patients with isolated hypercholesterolemia (>7.0 mmol/L; n=15). We assessed clot permeability and turbidimetric lysis time as the determinants of fibrin clot structure. In a regression model, including age and fibrinogen, plasma tHcy was an independent predictor of clot permeation and fibrinolysis time in healthy subjects (R2=0.88, P<0.0001 and R2=0.54, P<0.0001, respectively). In CAD patients, tHcy and fibrinogen were stronger predictors of the permeation coefficient (R2=0.84; P<0.0001) than was fibrinogen alone (R2=0.66; P<0.0001), whereas tHcy was the only predictor of lysis time (R2=0.69; P<0.0001). Elevated tHcy levels observed after methionine load were not associated with any of the fibrin clot properties. In patients with diabetes or hypercholesterolemia, the influence of Hcy on permeation and, to a lesser extent, on the lysis time was obscured by dominant effects of glucose and cholesterol. In 20 asymptomatic men with hyperhomocysteinemia treated with folic acid, reduction in tHcy levels resulted in increased clot permeability (P=0.0002) and shorter lysis time (P<0.0001).

CONCLUSIONS

Our results indicate that plasma tHcy predicts clot permeation and susceptibility to fibrinolysis in healthy men and CAD patients. Our data are consistent with a mechanism of thrombosis in hyperhomocysteinemia, which involves modification of fibrinogen by Hcy-thiolactone.

Mining literature for a comprehensive pathway analysis: a case study for retrieval of homocysteine related genes for genetic and epigenetic studies

Homocysteine is an independent risk factor for cardiovascular diseases. It is also known to be associated with a variety of complex disorders. While there are a large number of independent studies implicating homocysteine in isolated pathways, the mechanism of homocysteine induced adverse effects are not clear. Homocysteine-induced modulation of gene expression through alteration of methylation status or by hitherto unknown mechanisms is predicted to lead to several pathological conditions either directly or indirectly. In the present manuscript, using literature mining approach, we have identified the genes that are modulated directly or indirectly by an elevated level of homocysteine. These genes were then placed in appropriate pathways in an attempt to understand the molecular basis of homocysteine induced complex disorders and to provide a resource for selection of genes for polymorphism screening and analysis of mutations as well as epigenetic modifications in relation to hyperhomocysteinemia. We have identified 135 genes in 1137 abstracts that either modulate the levels of homocysteine or are modulated by elevated levels of homocysteine. Mapping the genes to their respective pathways revealed that an elevated level of homocysteine leads to the atherosclerosis either by directly affecting lipid metabolism and transport or via oxidative stress and/or Endoplasmic Reticulum (ER) stress. Elevated levels of homocysteine also decreases the bioavailability of nitric oxide and modulates the levels of other metabolites including S-adenosyl methionine and S-adenosyl homocysteine which may result in cardiovascular or neurological disorders. The ER stress emerges as the common pathway that relates to apoptosis, atherosclerosis and neurological disorders and is modulated by levels of homocysteine. The comprehensive network collated has lead to the identification of genes that are modulated by homocysteine indicating that homocysteine exerts its effect not only through modulating the substrate levels for various catalytic processes but also through regulation of expression of genes involved in complex diseases.

Homocysteine transport by human aortic endothelial cells: identification and properties of import systems

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Transport of L-homocysteine into and out of the human vascular endothelium is poorly understood. We hypothesized that cultured human aortic endothelial cells (HAEC) would import L-homocysteine on one or more of the L-cysteine transport systems. Inhibitors of the transporters were used to characterize the uptake of [35S]L-homocysteine, [35S]L-homocystine, and [35S]L-cysteine. We found that L-homocysteine uptake is mediated by the sodium-dependent cysteine transport systems X(AG), ASC, and A, and the sodium-independent transport system L. Thus, HAEC utilize multiple cysteine transporters (X(AG) > or = L > ASC > A) to import L-homocysteine. Kinetic analysis supported the uptake results. Michaelis-Menten constants (Km) for the four systems yielded values of 19.0, 27.1, 112, and 1000 microM for systems L, X(AG), ASC, and A, respectively. The binding and uptake of [35S]L-homocystine, the disulfide homodimer of L-homocysteine, was mediated by systems X(AG), L, and ASC but not by system A. In contrast to [35S]L-homocysteine, system x(c) was active for [35S]L-homocystine uptake. A similar pattern was observed for [35S]L-cysteine. Thus, L-homocysteine and L-homocystine found in hyperhomocysteinemic subjects can gain entry into the vascular endothelium by way of multiple L-cysteine transporters.

Low levels of vitamin B12 and venous thromboembolic disease in elderly men

OBJECTIVES

Hyperhomocysteinaemia is a well-known risk factor for venous thromboembolic disease (VTD). However, it is not clear whether homocysteine (Hc) itself or a related metabolite or a cofactor is primarily responsible for VTD. We carried out a case-control study to investigate whether vitamin concentrations that are involved in the Hc metabolism are associated or not with an elevated risk of VTD.

DESIGN

Case-control study.

METHODS

We measured serum vitamin B12, folate, creatinine and albumin concentrations and plasma Hc concentrations in 101 consecutive patients with VTD, diagnosed by image tests and 101 control subjects, matched for age and sex.

RESULTS

Serum vitamin B12 concentrations were significantly lower in VTD patients than in the control subjects. There were no differences in plasma Hc or serum folate concentrations between the groups. Among the male subgroup aged more than 70 years, serum vitamin B12 concentrations were significantly lower (240.88 +/- 103.07 vs. 421.20 +/- 314.31 pmol L(-1); P = 0.03) and plasma Hc concentrations were significantly higher (13.1 +/- 4.18 vs. 10.56 +/- 3.06 micromol L(-1); P =0.04) in VTD patients than in the control group. On multivariate analysis, in patients aged more than 70 years, serum vitamin B12 concentrations were independently associated with VTD. Compared with the highest quartile of vitamin B12 (>512.6 pmol L(-1)) the odds ratio (OR) for VTD in the lowest quartile (<230.9 pmol L(-1)) was 3.8 (95% CI 1.44-10.18; P = 0.01). In the VTD group, lowest vitamin B12 concentrations (percentile 10 <152.8 pmol L(-1)) were associated with the factor V Leiden mutation (OR = 6.07, 95% CI 0.93-38.55; P = 0.04).

CONCLUSIONS

Measuring vitamin B12 concentrations in elderly males may help in identifying people at risk of venous thromboembolism in our population.

Mechanisms of homocysteine-induced atherothrombosis

Elevation of plasma homocysteine level is a risk factor for cardiovascular disease, stroke, and venous thromboembolism. It is still uncertain, however, whether hyperhomocysteinemia is a causative factor or a marker of vascular disease. The strongest evidence that homocysteine plays a causal role in atherothrombosis has been provided by studies using animal models. In the past decade, considerable progress in defining the vascular effects of hyperhomocysteinemia was achieved through the use of genetic and dietary approaches to induce hyperhomocysteinemia in experimental animals. A key vascular phenotype observed in hyperhomocysteinemic animals is endothelial dysfunction, manifested by decreased bioavailability of endothelium-derived nitric oxide. Impairment of endothelial function may be mediated by either accelerated oxidative inactivation of nitric oxide or inhibition of nitric oxide production caused by the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine. Hyperhomocysteinemia also increases susceptibility to arterial thrombosis and accelerates the development of atherosclerosis in susceptible models such as the apolipoprotein E-deficient mouse. Mechanisms of atherothrombosis may include homocysteine-induced thiolation or acylation of plasma or endothelial proteins and endoplasmic reticulum stress, which activates signal transduction pathways leading to inflammation and apoptosis.

Antiphospholipid antibodies and thrombosis: association with acquired activated protein C resistance in venous thrombosis and with hyperhomocysteinemia in arterial thrombosis

Although antiphospholipid antibodies (aPL) are associated with thrombosis, it is not known who with aPL is at higher risk for thrombosis. It was the aim of this cross-sectional study to investigate how thrombophilic factors contribute to venous or arterial thrombosis in aPL-positive individuals. In outpatient test centres at two tertiary care hospitals, two hundred and eight (208) persons requiring aPL testing were matched by age, gender and centre to 208 persons requiring a complete blood count. Persons were classified as aPL-positive (having anticardiolipin, lupus anticoagulant and/or anti-beta(2)-glycoprotein I antibodies) or aPL-negative. Several thrombophilic factors were studied using logistic regression modelling. Results showed that the aPL-positive group had three-fold more events (37%) than the aPL-negative group (12%). In unadjusted analyses, clinically important associations were observed between factor V Leiden and venous thrombosis, hyperhomocysteinemia and arterial thrombosis, and activated protein C resistance (APCR) and venous thrombosis (OR, 95% CI = 4.00, 1.35-11.91; 4.79, 2.03-11.33; and 2.03, 1.03-3.97, respectively). After adjusting for recruitment group, persons with both APCR and aPL had a three-fold greater risk (OR, 95% CI = 3.31, 1.30-8.41) for venous thrombosis than those with neither APCR nor aPL. Similarly, after adjusting for hypertension, family history of cardiovascular disease, gender and recruitment group, persons with both hyperhomocysteinemia and aPL had a five-fold increased risk (OR, 95% CI = 4.90, 1.37-17.37) for arterial thrombosis compared to those with neither risk factor. In conclusion, APCR phenotype and hyperhomocysteinemia are associated with a higher risk of venous and arterial thrombosis, respectively, in the presence of aPL.

Prevalence of hyperhomocysteinaemia, activated protein C resistance and prothrombin gene mutation in inflammatory bowel disease

BACKGROUND

Thromboembolic disease is a significant cause of morbidity and mortality in patients with inflammatory bowel disease (IBD). A hypercoagulable state exists in IBD that may involve many components of haemostasis and is closely linked to the disease pathogenesis. It has been proposed that microvascular thrombosis and infarction may trigger the underlying inflammatory process.

AIM

To determine the prevalence of prothrombotic factors including hyperhomocysteinaemia, activated protein C (APC) resistance and prothrombin gene mutations as well as vitamin levels in the local IBD population.

METHOD

A total of 68 patients (37 men and 31 women) attending the IBD clinic were enrolled into the study. Citrated and ethylenediamine tetraacetic acid blood samples were collected from all patients as well as from 30 controls. Homocysteine levels were measured using the IMX immunoassay. APC resistance was measured using an unmodified activated partial thromboplastin time-based clotting assay. Prothrombin mutations were determined using polymerase chain reaction with the HB-gene factor II detection system.

RESULTS

Mean homocysteine levels were significantly higher and APC resistance ratios significantly lower in IBD patients compared with controls. No significant difference was detected between patients with ulcerative colitis or Crohn's disease. There was no significant increase in the incidence of prothrombin mutation in IBD patients. IBD patients had lower vitamin B12 and higher serum folate levels than controls.

CONCLUSION

High homocysteine and high serum folate may be associated with low vitamin B12 levels in IBD patients. We did not find any association between a low APC ratio and the factor V Leiden mutation or high factor VIII levels. Both hyperhomocysteinaemia and a low APC ratio may contribute to an increased risk of thromboembolic disease in IBD patients.

In Vitro and in Vivo Interactions of Homocysteine with Human Plasma Transthyretin

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease and an emerging risk factor for cognitive dysfunction and Alzheimer's disease. Greater than 70% of the homocysteine in plasma is disulfide-bonded to protein cysteine residues. The identity and functional consequences of protein homocysteinylation are just now emerging. The amyloidogenic protein transthyretin (prealbumin), as we now report, undergoes homocysteinylation at its single cysteine residue (Cys10) both in vitro and in vivo. Thus, when human plasma or highly purified transthyretin was incubated with 35S-L-homocysteine followed by SDS-PAGE and PhosphorImaging, two bands corresponding to transthyretin dimer and tetramer were observed. Treatment of the labeled samples with beta-mercaptoethanol prior to SDS-PAGE removed the disulfide-bound homocysteine. Transthyretin-Cys10-S-S-homocysteine was then identified in vivo in plasma from normal donors, patients with end-stage renal disease, and homocystinurics by immunoprecipitation and high performance liquid chromatography/electrospray mass spectrometry. The ratios of transthyretin-Cys10-S-S-homocysteine and transthyretin-Cys10-S-S-sulfonate to that of unmodified transthyretin increased with increasing homocysteine plasma concentrations, whereas the ratio of transthyretin-Cys10-S-S-cysteine to that of unmodified transthyretin decreased. The hyperhomocysteinemic burden is thus reflected in the plasma levels of transthyretin-Cys10-S-S-homocysteine, which in turn may contribute to the pathological consequences of amyloid disease.

Hyperhomocysteinemia due to folate deficiency is thrombogenic in rats

Although hyperhomocysteinemia (HH) appears to be an independent risk factor for thrombosis, the pathophysiologic mechanisms seen in thrombus formation are largely unresolved. The aim of the present study was to investigate whether HH is accompanied by thrombogenic alterations as assessed by whole blood thromboelastographic profiles. Severe (111 micro mol/L) and intermediate (42 micro mol/L) HH were induced in two series of rats by feeding them a folate-depleted diet. Each group was compared with a separate control group. In rats suffering severe HH (n = 30), initiation of the coagulation was protracted, with a clotting time of 79.7 s (95% CI, 76.2-83.4) compared with 70.4 s (95% CI, 66.5-74.6) in controls (P = 0.001). The velocity of the propagation of coagulation was increased, reaching 0.119 mm/s (95% CI, 0.111-0.127) in HH rats compared with 0.104 mm/s (95% CI, 0.099-0.108) in controls (P < 0.001). The maximum clot firmness also was increased, i.e., 41.9 mm (95% CI, 40.5-43.4) in HH rats compared with 37.6 mm (95% CI, 36.5-38.7) in controls (P < 0.001). The resting thrombin-antithrombin complex concentration in plasma tended to be lower in HH rats [5.60 micro g/L (95% CI, 3.76-8.34) than in controls [8.56 micro g/L (95% CI, 6.44-11.37)] (P = 0.074). In the series of rats with intermediate HH (n = 16), the changes in the whole blood coagulation profile (WBCP) were similar to those in rats with severe HH although only the prolongation of the initiation phase was significant. In conclusion, our study revealed that the WBCP was influenced by high plasma homocysteine by 1) prolonging the initiation phase, 2) increasing the velocity of the coagulation propagation and 3) increasing the maximum clot firmness. These changes in WBCP may contribute to the increased risk of thrombosis in hyperhomocysteinemic individuals.