Over the last 30 years, a growing body of evidence has documented the role of hyperhomocysteinemia (HHcy) as an independent vascular risk factor. However, the mechanisms through which elevated circulating levels of homocysteine (Hcy) cause vascular injury and promote thrombosis remain elusive. Most findings have been achieved in in vitro studies employing exceedingly high concentrations of Hcy, whereas only a few studies have been carried out in vivo in humans. In homocystinuric patients, homozygotes for mutations of the gene coding for the cystathionine β-synthase enzyme, abnormalities of coagulation variables reflecting a hypercoagulable state, have been reported. In vitro studies provide a biochemical background for such a state. In homocystinuric patients, an in vivo platelet activation has also been reported. The latter abnormality is not corrected by the bolus infusion of concentrations of hirudin, which determines a long-lasting impairment of the conversion of fibrinogen to fibrin by thrombin; in contrast, it appears at least in part lowered by the administration of the antioxidant drug probucol. During the autooxidation of Hcy in plasma, reactive oxygen species are generated. The latter initiate lipid peroxidation in cell membranes (potentially responsible for endothelial dysfunction) and in circulating lipoproteins. Oxidized low-density lipoproteins (LDL) may trigger platelet activation as well as some of the hemostatic abnormalities reported in such patients. Thus the oxidative stress induced by Hcy may be a key process in the pathogenesis of thrombosis in HHcy. Accumulation of adenosylhomocysteine in cells (a consequence of high circulating levels of homocysteine) inhibits methyltransferase enzymes, in turn preventing repair of aged or damaged cells. This mechanism has been recently documented in patients with renal failure and HHcy and provides an additional direction to be followed to understand the tendency to thrombosis in moderate HHcy.

Summary. Background: Immune tolerance induction (ITI) is the only therapeutic approach that can eradicate factor VIII (FVIII) inhibitors in patients with hemophilia A. Predictors of ITI outcome are still debated, and the role of F8 gene mutations in this is not well established. Objectives: To investigate the relationship between F8 genotype and ITI outcome in patients with severe hemophilia A and high‐responding inhibitors. Patients and Methods:F8 mutations were identified in 86 patients recruited as part of the Italian ITI registry (the PROFIT study). ITI outcome was centrally reviewed according to the following definitions: success (undetectable inhibitor and normal FVIII pharmacokinetics), partial success (inhibitor titer < 5 BU mL⁻¹ and/or abnormal FVIII pharmacokinetics), and failure. Results:F8 mutations known to be associated with a high risk of inhibitor development (large deletions, inversions, nonsense mutations and splice site mutations) were found in 70 patients (81%); among these, the intron 22 inversion was present in 49 patients (57%). In 16 patients (19%) lower‐risk F8 defects (small insertions/deletions and missense mutations) were identified. The latter group of patients showed a significantly higher ITI success rate than those carrying high‐risk mutations [13/16 (81%) vs. 33/70 (47%); risk ratio 1.7, 95% confidence interval (CI) 1.1–2.1, P = 0.01]. On multivariate analysis, the mutation risk class remained a significant predictor of success [adjusted odds ratio (OR) 6.2, 95% CI 1.1–36.0, P = 0.04], as were inhibitor titer at ITI start (< 5 BU mL⁻¹, OR 11.8, 95% CI 3.5–40.2, P < 0.001), and peak titer during ITI (< 100 BU mL⁻¹, OR 11.4, 95% CI 3.2–40.8, P < 0.001). Conclusions: ITI success is influenced by F8 genotype. This knowledge should contribute to the stratification of prognosis, and to the clinical choices made for ITI in patients with high‐responding inhibitors.

Background — Severe hyperhomocysteinemia due to cystathionine β-synthase deficiency (CβSD) is associated with early atherothrombotic vascular disease. Homocysteine may exert its effects by promoting oxidative damage. In the present study, we investigated whether in vivo formation of 8-iso-prostaglandin (PG) F _2α , a platelet-active product of arachidonic acid peroxidation, is enhanced in CβSD and whether it correlates with in vivo platelet activation, as reflected by thromboxane (TX) metabolite excretion. Methods and Results — Urine and blood samples were obtained from patients with homozygous CβSD (n=13) and age-matched healthy subjects. Urinary 8-iso-PGF _2α excretion was significantly higher in CβSD patients than in control subjects (640±384 versus 213±43 pg/mg creatinine; P =0.0015) and correlated with plasma homocysteine (ρ=0.398, P =0.0076). Similarly, urinary 11-dehydro-TXB ₂ excretion was enhanced in CβSD (1166±415 versus 324±72 pg/mg creatinine; P =0.0015) and correlated with urinary 8-iso-PGF _2α (ρ=0.362, P =0.0153). Vitamin E supplementation (600 mg/d for 2 weeks) was associated with a statistically significant increase in its plasma levels (from 16.6±4.6 to 40.4±8.7 μmol/L, P =0.0002) and with reductions in 8-iso-PGF _2α (from 790±159 to 559±111 pg/mg creatinine, P =0.018) and 11-dehydro-TXB ₂ (from 1273±383 to 913±336 pg/mg creatinine, P =0.028). A statistically significant inverse correlation was found between urinary 8-iso-PGF _2α and plasma vitamin E levels (ρ=−0.745, P =0.0135). Conclusions — The results of the present study suggest that enhanced peroxidation of arachidonic acid to form bioactive F ₂ -isoprostanes may represent an important mechanism linking hyperhomocysteinemia and platelet activation in CβSD patients. Moreover, they provide a rationale for dose-finding studies of vitamin E supplementation in this setting.

Peer reviewed article authored by (Antonio Coppola, Mirko Di Capua, Matteo Nicola Dario, et al.). Read article or submit your manuscript for publishing.