Hemostatic gene polymorphisms and the prevalence of thrombotic complications in polycythemia vera and essential thrombocythemia.

Patients with polycythemia vera and essential thrombocythemia are at risk for thrombotic and bleeding complications. Currently, no diagnostic test can predict thrombohemorrhagic complications. In a prospective study of 86 patients with polycythemia vera (43 patients) or essential thrombocythemia (43 patients), we examined the possible role of polymorphisms of platelet adhesion receptors [glycoprotein (GP) Ibalpha, GPIa, GPIIIa) and clotting factor II (prothrombin's G20210A mutation) and clotting factor V (Leiden mutation) in determining the risk of thrombotic or bleeding complications. Except for an association between vasomotor symptoms and prothrombin mutation (P < 0.001), no significant correlation between polymorphism of clotting factors and thrombohemorrhagic complications was identified. When the entire patient cohort was considered, the polymorphisms of platelet adhesion receptors were not associated with the risk for thrombotic or bleeding complications. However, among patients with polycythemia vera, the presence of the PlA2 allele of GPIIIa was associated with an increased risk of arterial thrombosis. In view of previous studies linking the presence of the PlA2 allele of GPIIIa to a higher risk for coronary artery thrombosis, our data have physiologic relevance. However, they need to be confirmed in a larger study.     

Efficacy of tramadol in treatment of chronic low back pain

OBJECTIVE: To evaluate the efficacy and safety of tramadol in the treatment of chronic low back pain. METHODS: A 3 phase trial: (1) a washout/screening phase; (2) a 3 week, open label, run-in phase; and (3) a 4 week, randomized, placebo controlled, double blind treatment phase. Three hundred eighty outpatients between 21 and 79 years with chronic low back pain with no or a distant history of back surgery enrolled in the open label phase and were treated with tramadol up to 400 mg/day. At the end of the open label phase, patients who tolerated tramadol and perceived benefit from it were randomized to continue treatment with tramadol or to convert to placebo in the double blind phase. Reasons for discontinuing from the open label phase included adverse events, 78 patients (20.5%); drug ineffective, 23 patients (6.1%); and other reasons, 25 patients (6.6%). Two hundred fifty-four patients entered the double blind phase, during which the daily dose was maintained within the range 200-400 mg tramadol or equivalent amount of placebo. The primary outcome measure in the double blind phase was the time to discontinuation due to inadequate pain relief. RESULTS: The distribution of time to therapeutic failure was significantly (p < or = 0.0001) different in the tramadol group compared to placebo. Kaplan-Meier estimate of the cumulative discontinuation rate due to therapeutic failure was 20.7% in the tramadol group and 51.3% in the placebo group. There were significantly lower (p < or = 0.0001) mean pain visual analog scores (10 cm scale) among tramadol patients (3.5 cm) compared to placebo patients (5.1 cm) at the final visit of the double blind phase. Tramadol patients scored significantly better on the McGill Pain Questionnaire (p = 0.0007) and the Roland Disability Questionnaire (p = 0.0001). Five of 127 tramadol treated patients and 6/127 placebo treated patients discontinued treatment during the double blind phase due to an adverse event. Commonly reported adverse events with tramadol included nausea, dizziness, somnolence, and headache. CONCLUSION: Among patients who tolerated it well, tramadol was effective for the treatment of chronic low back pain.     

Physiological Stress Elicits Impaired Left Ventricular Function in Preterm-Born Adults

Background

Experimental and clinical studies show that prematurity leads to altered left ventricular (LV) structure and function with preserved resting LV ejection fraction (EF). Large-scale epidemiological data now links prematurity to increased early heart failure risk.

First structure of full-length mammalian phenylalanine hydroxylase reveals the architecture of an autoinhibited tetramer

Improved understanding of the relationship among structure, dynamics, and function for the enzyme phenylalanine hydroxylase (PAH) can lead to needed new therapies for phenylketonuria, the most common inborn error of amino acid metabolism. PAH is a multidomain homo-multimeric protein whose conformation and multimerization properties respond to allosteric activation by the substrate phenylalanine (Phe); the allosteric regulation is necessary to maintain Phe below neurotoxic levels. A recently introduced model for allosteric regulation of PAH involves major domain motions and architecturally distinct PAH tetramers [Jaffe EK, Stith L, Lawrence SH, Andrake M, Dunbrack RL, Jr (2013) Arch Biochem Biophys 530(2):73–82]. Herein, we present, to our knowledge, the first X-ray crystal structure for a full-length mammalian (rat) PAH in an autoinhibited conformation. Chromatographic isolation of a monodisperse tetrameric PAH, in the absence of Phe, facilitated determination of the 2.9 Å crystal structure. The structure of full-length PAH supersedes a composite homology model that had been used extensively to rationalize phenylketonuria genotype–phenotype relationships. Small-angle X-ray scattering (SAXS) confirms that this tetramer, which dominates in the absence of Phe, is different from a Phe-stabilized allosterically activated PAH tetramer. The lack of structural detail for activated PAH remains a barrier to complete understanding of phenylketonuria genotype–phenotype relationships. Nevertheless, the use of SAXS and X-ray crystallography together to inspect PAH structure provides, to our knowledge, the first complete view of the enzyme in a tetrameric form that was not possible with prior partial crystal structures, and facilitates interpretation of a wealth of biochemical and structural data that was hitherto impossible to evaluate.Mammalian phenylalanine hydroxylase (PAH) (EC 1.14.16.1) is a multidomain homo-multimeric protein whose dysfunction causes the most common inborn error in amino acid metabolism, phenylketonuria (PKU), and milder forms of hyperphenylalaninemia (OMIM 261600) (1). PAH catalyzes the hydroxylation of phenylalanine (Phe) to tyrosine, using nonheme iron and the cosubstrates tetrahydrobiopterin and molecular oxygen (2, 3). A detailed kinetic mechanism has recently been derived from elegant single-turnover studies (4). PAH activity must be carefully regulated, because although Phe is an essential amino acid, high Phe levels are neurotoxic. Thus, Phe allosterically activates PAH by binding to a regulatory domain. Phosphorylation at Ser16 potentiates the effects of Phe, with phosphorylated PAH achieving full activation at lower Phe concentrations than the unphosphorylated protein (5, 6). Allosteric activation by Phe is accompanied by a major conformational change, as evidenced by changes in protein fluorescence and proteolytic susceptibility, and by stabilization of a tetrameric conformer (3).There are >500 disease-associated missense variants of human PAH; the amino acid substitutions are distributed throughout the 452-residue protein and among all its domains (Fig. 1A) (7–9). Of those disease-associated variants that have been studied in vitro (e.g., ref. 10), some confound the allosteric response, and some are interpreted as structurally unstable. We also suggest that the activities of some disease-associated variants may be dysregulated by an altered equilibrium among conformers having different intrinsic levels of activity, arguing by analogy to the enzyme porphobilinogen synthase (PBGS) and its porphyria-associated variants (11). Consistent with this notion, we have recently established that PAH can assemble into architecturally distinct tetrameric conformers (12), and propose that these conformers differ in activity due to differences in active-site access. This idea has important implications for drug discovery, as it implies that small molecules could potentially modulate the conformational equilibrium of PAH, as has already been demonstrated for PBGS (e.g., ref. 13). Deciphering the relationship among PAH structure, dynamics, and function is a necessary first step in testing this hypothesis.Open in a separate windowFig. 1.The structure of PAH. (A) The annotated domain structure of mammalian PAH. (B) The 2.9 Å PAH crystal structure in orthogonal views, colored as in part A, subunit A is shown in ribbons; subunit B is as a Cα trace; subunit C is in sticks; and subunit D is in transparent spheres. In cyan, the subunits are labeled near the catalytic domain (Top); in red, they are labeled near the regulatory domain (Bottom). The dotted black circle illustrates the autoregulatory domain partially occluding the enzyme active site (iron, in orange sphere). (C) Comparison of the subunit structures of full-length PAH and those of the composite homology model; the subunit overlay aligns residues 144–410. The four subunits of the full-length PAH structure (the diagonal pairs of subunits are illustrated using either black or white) are aligned with the two subunits of 2PAH (cyan) and the one subunit of 1PHZ (orange). The catalytic domain is in spheres, the regulatory domain is in ribbons, and the multimerization domain is as a Cα trace. The arrow denotes where the ACT domain and one helix of 2PAH conflict.Numerous crystal structures are known for one- and two-domain constructs of mammalian PAH (14).

Table S1.

Mammalian PAH structures available in the PDB (August 2015)

Mentoring in Clinical‐Translational Research: A Study of Participants in Master's Degree Programs

Research projects in translational science are increasingly complex and require interdisciplinary collaborations. In the context of training translational researchers, this suggests that multiple mentors may be needed in different content areas. This study explored mentoring structure as it relates to perceived mentoring effectiveness and other characteristics of master''s‐level trainees in clinical‐translational research training programs. A cross‐sectional online survey of recent graduates of clinical research master''s program was conducted. Of 73 surveys distributed, 56.2% (n = 41) complete responses were analyzed. Trainees were overwhelmingly positive about participation in their master''s programs and the impact it had on their professional development. Overall the majority (≥75%) of trainees perceived they had effective mentoring in terms of developing skills needed for conducting clinical‐translational research. Fewer trainees perceived effective mentoring in career development and work‐life balance. In all 15 areas of mentoring effectiveness assessed, higher rates of perceived mentor effectiveness was seen among trainees with ≥2 mentors compared to those with solo mentoring (SM). In addition, trainees with ≥2 mentors perceived having effective mentoring in more mentoring aspects (median: 14.0; IQR: 12.0–15.0) than trainees with SM (median: 10.5; IQR: 8.0–14.5). Results from this survey suggest having ≥2 mentors may be beneficial in fulfilling trainee expectations for mentoring in clinical‐translational training.