Role for mitochondrial uncoupling protein-2 (UCP2) in hyperhomocysteinemia and venous thrombosis risk?

BACKGROUND: Hyperhomocysteinemia has been associated with an increased risk of venous thrombosis, which might be mediated through an oxidative stress dependent mechanism. The function of uncoupling protein-2 (UCP2) is still under debate, but it has been suggested to play a role in reduction of mitochondrial reactive oxygen species. In the present study, we investigated whether the 45 bp deletion/insertion (del/ ins) polymorphism in the UCP2 gene is associated with elevated homocysteine levels and whether it might be associated with an increased risk of recurrent venous thrombosis (RVT). METHODS: The 45 bp del/ins polymorphism in the UCP2 gene was genotyped by PCR analysis in 161 RVT cases and 386 controls of Caucasian origin in which fasting- and post-load homocysteine levels were previously determined. Statistical analysis was performed to assess whether the UCP2 45 bp del/ins polymorphism was associated with plasma total homocysteine levels and venous thrombosis risk. RESULTS: Post-load homocysteine levels were positively associated with UCP2 45 bp ins/ins genotype (P = 0.02). None of the UCP2 45 bp ins/del genotypes were associated with fasting plasma homocysteine levels. The frequency of the UCP2 45 bp ins/ins genotype was 12.4% in RVT cases compared to 8.3% in controls, which resulted in an odds ratio of 1.8 (95% CI 1.0-3.4). CONCLUSIONS: The results of our study show that the common 45 bp del/ins polymorphism in the UCP2 gene is associated with hyperhomocysteinemia, which might increase the risk of venous thrombosis. However, the mechanism is not fully understood and additional studies should be performed to confirm our findings.

Antibody-based assay for N-deacetylase activity of heparan sulfate/heparin N-deacetylase/N-sulfotransferase (NDST): novel characteristics of NDST-1 and -2.

A new assay was developed to measure the N-deacetylase activity of the glucosaminyl N-deacetylase/N-sulfotransferases (NDSTs), which are key enzymes in sulfation of heparan sulfate (HS)/heparin. The assay is based on the recognition of NDST-generated N-unsubstituted glucosamine units in Escherichia coli K5 capsular polysaccharide or in HSs by monoclonal antibody JM-403. Substrate specificity and potential product inhibition of the NDST isoforms 1 and 2 were analyzed by comparing lysates of human 293 kidney cells stably transfected with mouse NDST-1 or -2. We found HSs to be excellent substrates for both NDST enzymes. Both NDST-1 and -2 N-deacetylate heparan sulfate from human aorta ( approximately 0.6 sulfate groups/disaccharide) with comparable high efficiency, apparent Km values of 0.35 and 0.76 microM (calculation based on [HexA]) being lower (representing a higher affinity) than those for K5 polysaccharide (13.3 and 4.7 microM, respectively). Comparison of various HS preparations and the unsulfated K5 polysaccharide as substrates indicate that both NDST-1 and -2 can differentially N-sulfate polysaccharides already modified to some extent by various other enzymes involved in HS/heparin synthesis. Both enzymes were equally inhibited by N-sulfated sequences (>or=6 sugar residues) present in N-sulfated K5, N-deacetylated N-resulfated HS, and heparin. Our primary findings were confirmed in the conventional N-deacetylase assay measuring the release of 3H-acetate of radiolabeled K5 or HS as substrates. We furthermore showed that NDST N-deacetylase activity in crude cell/tissue lysates can be partially blocked by endogenous HS/heparin. We speculate that in HS biosynthesis, some NDST variants initiate HS modification/sulfation reactions, whereas other (or the same) NDST isoforms later on fill in or extend already modified HS sequences.