James G. Taylor

Comparison of the genomic structure and variation in the two human sodium-dependent vitamin C transporters, SLC23A1 and SLC23A2

Vitamin C (L-ascorbic acid) is an essential co-factor for eight mammalian enzymes and quenches reactive oxygen species. Sodium-dependent vitamin C transport is mediated by two transporters, SVCT 1 and SVCT 2, encoded by SLC23A1 and SLC23A2. We characterized the genomic structures of SLC23A1 and SLC23A2, determined the extent of genetic variation and linkage disequilibrium across each gene, analyzed nucleotide diversity to estimate the effect of selective pressure, and compared sequence variation across species. In SLC23A1, the majority of single nucleotide polymorphisms (SNPs) are population-specific in either African Americans or Caucasians, including three of four non-synonymous SNPs. In contrast, most SNPs in SLC23A2 are shared between African Americans and Caucasians, and there are no non-synonymous SNPs in SLC23A2. Our analysis, combined with previous in vitro and in vivo studies, suggests that non-synonymous variation appears to be tolerated in SLC23A1 but not SLC23A2, and that this may be a consequence of different selective pressures following past gene duplication of the sodium-dependent vitamin C transporters. Genetic association studies of these two genes will need to account for the differences in haplotype structure and the population-specific variants. Our data represent a fundamental step toward the application of genetics to refining nutrient recommendations, specifically for vitamin C, and may serve as a paradigm for other vitamins.

Pleiotropic effects of intravascular haemolysis on vascular homeostasis.

The breakdown of senescent or defective red blood cells releases red cell contents, especially haemoglobin, which scavenges nitric oxide (NO) and decomposes to haem and free iron. These are potent oxidants, all of which have promoted the evolution of inducible and vasculoprotective compensatory pathways to rapidly clear and detoxify haemoglobin, haem and iron. Chronic haemolytic red cell disorders as diverse as sickle cell disease, thalassaemia, unstable haemoglobinopathy, cytoskeletal defects and enzymopathies have been linked to a clinical constellation of pulmonary hypertension, priapism, leg ulceration and possibly cerebrovascular disease and thrombosis. Besides free haemoglobin, haemolysis has been associated with extracellular arginase that limits substrate availability to NO synthase, endogenous inhibitors of NO synthase activity, and inappropriate activation of haemostatic pathways. This article reviews the haemolytic disorders that have been reported to manifest vascular complications, and explores the speculative possibility that haemolysis mediates some of the vascular complications of inflammation and diabetes.

Severe Vaso-Occlusive Episodes Associated with Use of Systemic Corticosteroids in Patients with Sickle Cell Disease

Patients with sickle cell disease (SCD) are occasionally prescribed systemic corticosteroids to treat steroid-responsive conditions. Additionally, use of systemic corticosteroids for sickle cell pain episodes and acute chest syndrome is under investigation. We report 4 patients with SCD who developed severe vaso-occlusive events following the administration of systemic steroids. We also review similar cases from the literature and suggest measures for reducing the potential risk associated with use of systemic corticosteroids in this group of patients. We conclude that corticosteroids should be used with caution in patients with SCD.

Association between Chronic Disseminated Candidiasis in Adult Acute Leukemia and Common IL4 Promoter Haplotypes

Chronic disseminated candidiasis (CDC) is a form of Candida species infection observed primarily in patients with acute leukemia. To investigate possible genetic factors associated with CDC, we conducted a pilot study of 40 patients with both leukemia and CDC and 50 control patients with leukemia only. A common haplotype of the IL4 promoter (-1098T/-589C/-33C) was overrepresented in patients with CDC (P= .01; odds ratio [OR], 2.16), whereas another common haplotype (-1098T/-589T/-33T) appeared to be protective against CDC (P= .018; OR, 0.47). Genetic variants of IL4 could contribute to the development of CDC in patients with acute leukemia.

Lipid levels in sickle-cell disease associated with haemolytic severity, vascular dysfunction and pulmonary hypertension

Pulmonary hypertension (PH) in sickle cell disease (SCD) is an emerging and important clinical problem. In a single‐institution adult cohort of 365 patients, we investigated lipid and lipoprotein levels and their relationship to markers of intravascular haemolysis, vascular dysfunction and PH. In agreement with prior studies, we confirm significantly decreased plasma levels of total cholesterol, high‐density lipoprotein‐cholesterol (HDL‐C) and low‐density lipoprotein‐cholesterol (LDL‐C) in SCD versus ethnically‐matched healthy controls. Several cholesterol parameters correlated significantly with markers of anaemia, but not endothelial activation or PH. More importantly, serum triglyceride levels were significantly elevated in SCD compared to controls. Elevated triglyceride levels correlated significantly with markers of haemolysis (lactate dehydrogenase and arginase; both P < 0·0005), endothelial activation (soluble E‐selectin, P < 0·0001; soluble P‐selectin, P = 0·02; soluble vascular cell adhesion molecule‐1, P = 0·01), inflammation (leucocyte count, P = 0·0004; erythrocyte sedimentation rate, P = 0·02) and PH (amino‐terminal brain natriuretic peptide, P = 0·002; prevalence of elevated tricuspid regurgitant velocity (TRV), P < 0·001). In a multivariate analysis, triglyceride levels correlated independently with elevated TRV (P = 0·002). Finally, forearm blood flow studies in adult patients with SCD demonstrated a significant association between increased triglyceride/HDL‐C ratio and endothelial dysfunction (P < 0·05). These results characterize elevated plasma triglyceride levels as a potential risk factor for PH in SCD.

Common polymorphisms in critical genes of innate immunity do not contribute to the risk for chronic disseminated candidiasis in adult leukemia patients

Chronic disseminated candidiasis is a serious fungal infection in immunocompromised patients, particularly those undergoing therapy for acute leukemia. Coordination between innate and adaptive immune system is critical to resistance or susceptibility to Candida infection. In order to investigate possible genetic contribution to chronic disseminated candidiasis of key molecules in the innate immune pathway, we performed a case control study using the candidate gene approach. Forty subjects with chronic disseminated candidiasis and 50 controls without chronic disseminated candidiasis but an underlying diagnosis of leukemia were enrolled in the Helsinki University Central Hospital during the period 1980-1998. Candidate genes were selected for analysis based upon the following criteria: a common polymorphism (>5% frequency) and existence a priori of clinical and biological data suggesting a role for the variant in the pathogenesis of chronic disseminated candidiasis. Six genes were selected from critical microbicidal and innate immune pathways, including three low-affinity Fcgamma receptors (FCGR2A, FCGR3A and FCGR3B), chitotriosidase (CHIT1), p22-phox NADPH oxidase (CYBA), and mannose binding lectin (MBL2). There was no statistically significant association of susceptibility to chronic disseminated candidiasis with the polymorphisms in this study. Common variants in the six studied genes most likely do not contribute to the risk for chronic disseminated candidiasis in patients with acute leukemia.

Genomic and functional analysis of the sodium-dependent vitamin C transporter SLC23A1–SVCT1

Vitamin C, an essential co-factor for at least eight enzymatic reactions, might also be involved in development or treatment of cancer, cardiovascular diseases, diabetes, and stroke. Ascorbic acid, the reduced form of vitamin C is transported across epithelial barriers by the sodium dependent vitamin C transporters 1 (SVCT1). SVCT1 is encoded by SLC23A1 and mapped to 5q31.2 [1, 2]. Recently, the pattern of common genetic variants has been characterized for both ascorbic acid transporters, SLC23A1 and SLC23A2, which share common intron/exon borders, are 58% similar in sequence across the coding region, but differ greatly in size and linkage disequilibrium patterns [3]. Here we characterize the genetic variation in the less constrained SLC23A1 gene in more detail and test for functional consequences. SLC23A1 is expressed in tissues critical for absorption and reabsorption of vitamin C (kidney, intestinal, and hepatic tissues) [4]. Therefore functional consequences of variations in SVCT1 would impact on dietary requirements and recommendations.

Identification of novel microRNA signatures linked to acquired aplastic anemia

Emerging evidence indicates that microRNA control and modulate immunity. MicroRNA have not been investigated in acquired aplastic anemia, a T-cell-mediated immune disease. Analysis of 84 microRNA expression levels in CD4+ and CD8+ T cells of patients with aplastic anemia revealed concurrent down-regulation of miR-126-3p, miR-145-5p, miR-223-3p, and miR-199a-5p (>3-fold change, P<0.05) in both T-cell populations, which were unique in aplastic anemia compared to other hematologic disorders. MiR-126-3p and miR-223-3p were down-regulated in CD4+ T effector memory cells, and miR-126-3p, miR-145-5p, and miR-223-3p were down-regulated in CD8+ T effector memory and terminal effector cells. Successful immunosuppressive therapy was associated with restoration to normal expression levels of miR-126-3p, miR-145-5p, and miR-223-3p (>2-fold change, P<0.05). In CD4+ and CD8+ T cells in aplastic anemia patients, MYC and PIK3R2 were up-regulated and proved to be targets of miR-145-5p and miR-126-3p, respectively. MiR-126-3p and miR-145-5p knockdown promoted proliferation and increased interferon-γ and granzyme B production in both CD4+ and CD8+ T cells. Our work describes previously unknown regulatory roles of microRNA in T-cell activation in aplastic anemia, which may open a new perspective for development of effective therapy. Clinicaltrials.gov identifier: NCT 01623167

Toward quantitative genetic analysis of host and parasite traits in the manifestations of Plasmodium falciparum malaria

The complex human and parasite determinants that influence disease severity in Plasmodium falciparum malaria reflect thousands of years of selective pressure. Emerging genetic and genomic resources offer the prospect of unraveling interactions of these determinants.

Prostacyclin-analog therapy in sickle cell pulmonary hypertension.

Sickle cell disease (SCD) is associated with pulmonary hypertension (PH) which results in high morbidity and mortality. There are well-established therapies for pulmonary arterial hypertension (PAH), but few reports about their use in SCDPH. We report the clinical course of 11 SCDPH patients on maximal supportive therapy including other pulmonary vasodilators, who received compassionate therapy with prostacyclin-analogs at four PH treatment centers. Inclusion criteria for this retrospective study included PH diagnosis by standard right heart catheterization (RHC), and prostacyclin-analog therapy via any route of delivery for at least four weeks. Data were collected subject to availability in the medical record, including type of prostacyclin-analog therapy, maximal dose and duration, and follow-up data at least 100 days after initiating therapy. Statistical analyses were performed using GraphPad Prism version 5.0 (La Jolla, CA, USA), using paired t-test and