All platelets are not equal: COAT platelets

Collagen- and thrombin-activated (COAT) platelets were first described in 2000 and have attracted considerable interest, changing the interpretation of the way in which platelets contribute to thrombin generation and how their procoagulant activity is organized. Platelets activated by two agonists coming from glycoprotein VI or Fc gamma-receptor IIA agonists on the one hand and thrombin on the other produce a population of approximately 50% highly procoagulant active platelets. This subgroup is formed by tissue transglutaminase and factor XIIIa linking of serotonin to the procoagulant proteins from granules or plasma, and these serotonylated proteins bind to fibrinogen or thrombospondin on the platelet surface. Serotonylation in the platelet cytoplasm has recently been shown to be an important regulating mechanism governing the activation of small GTPases and their function in granule release. Recent studies with Tph-/- mice in which the peripheral serotonin, including that in platelets, is very strongly reduced, have shown a prolonged bleeding time, suggesting it has an important hemostatic role in the release of platelet von Willebrand factor. More knowledge about how COAT platelets are formed will be important for a better understanding of the physiology and pathology of hemostasis.

Variation in human platelet glycoprotein VI content modulates glycoprotein VI-specific prothrombinase activity

- Glycoprotein VI (GPVI) is a platelet-specific receptor for collagen that figures prominently in signal transduction. An addition to binding to type I and III collagens, GPVI is also bound specifically by collagen-related peptide and convulxin (CVX), a snake venom protein. We developed a quantitative assay of platelet GPVI in which biotin-conjugated CVX binds selectively to GPVI in separated total platelet proteins by a ligand blot procedure. Using this approach, we have documented a 5-fold range in platelet GPVI content among 23 normal healthy subjects. In addition, we have determined that CVX-induced or collagen-related peptide-induced prothrombinase activity is directly proportional to the platelet content of GPVI. A statistically significant correlation was observed at 2 CVX concentrations: 14.7 ng/mL (R(2)=0.854 and P<0.001, n=11) and 22 ng/mL (R(2)=0.776 and P<0.001, n=12). In previous studies, we established a similar range of expression of the integrin collagen receptor alpha(2)beta(1) on platelets of normal subjects. Among 15 donors, there is a direct correlation between platelet alpha(2)beta(1) density and GPVI content (R(2)=0.475 and P=0.004). In view of the well-documented association of GPVI with platelet procoagulant activity, this study suggests that the variation in GPVI content is a potential risk factor that may predispose individuals to hemorrhagic or thromboembolic disorders.

Discordant responses to potent antiretroviral treatment in previously naive HIV-1-infected adults initiating treatment in resource-constrained countries: the antiretroviral therapy in low-income countries (ART-LINC) collaboration

OBJECTIVES: To assess the frequency of and risk factors for discordant responses at 6 months on highly active antiretroviral therapy (HAART) in previously treatment-naive HIV patients from resource-limited countries. METHODS: The Antiretroviral Therapy in Low-Income Countries Collaboration is a network of clinics providing care and treatment to HIV-infected patients in Africa, Latin America, and Asia. Patients who initiated therapy between 1996 and 2004, were aged 16 years or older, and had a baseline CD4 cell count were included in this analysis. Responses were defined based on plasma viral load (PVL) and CD4 cell count at 6 months as complete virologic and immunologic (VR(+)IR(+)), virologic only (VR(+)IR(-)), immunologic only (VR(-)IR(+)), and nonresponse (VR(-)IR(-)). Multinomial logistic regression was used to assess the association between therapy responses and clinical and demographic variables. RESULTS: Of the 3111 patients eligible for analysis, 1914 had available information at 6 months of therapy: 1074 (56.1%) were VR(+)IR(+), 364 (19.0%) were VR(+)IR(-), 283 (14.8%) were (VR(-)IR(+)), and 193 (10.1%) were VR(-)IR(-). OF THE 3111 patients eligible for analysis, 1914 had available information at 6 months of therapy: 1074 (56.1%) were VRIR, 364 (19.0%) were VRIR, 283 (14.8%) were (VRIR), and 193 (10.1%) were VRIR. Compared with complete responders, virologic-only responders were older, had a higher baseline CD4 cell count, had a lower baseline PVL, and were more likely to have received a nonstandard HAART regimen; immunologic-only responders were younger, had a lower baseline CD4 cell count, had a higher baseline PVL, and were more likely to have received a protease inhibitor-based regimen. CONCLUSIONS: The frequency of and risk factors for discordant responses were comparable to those observed in developed countries. Longer follow-up is needed to assess the long-term impact of discordant responses on mortality in these resource-limited settings.

Synthesis of the bicyclo-[4.3.0]thymidyl nucleoside via Pd(II)-mediated ring expansion chemistry

A variety of modified nucleosides to improve antisense oligodeoxynucleotide properties such as target affinity, nuclease resistance, and pharmacokinetics were developed in the last two decades. In the context of conformational restriction we present here the synthesis of the [4.3.0]-bicyclo-DNA thymine monomer via Pd(II)-mediated ring expansion of an intermediate of the tricyclo-DNA synthesis.

Photochemically induced RNA and DNA abasic sites

Two phosphoramidite building blocks were synthesized that can easily be deprotected by UV light to reveal natural abasic sites in oligoribonucleotides as well as in oligodeoxyribonucleotides. Another building block which releases a 2 ′-O-methylated abasic site upon UV radiation is also described.

Meta-analysis: chondroitin for osteoarthritis of the knee or hip

BACKGROUND: Previous meta-analyses described moderate to large benefits of chondroitin in patients with osteoarthritis. However, recent large-scale trials did not find evidence of an effect. PURPOSE: To determine the effects of chondroitin on pain in patients with osteoarthritis. DATA SOURCES: The authors searched the Cochrane Central Register of Controlled Trials (1970 to 2006), MEDLINE (1966 to 2006), EMBASE (1980 to 2006), CINAHL (1970 to 2006), and conference proceedings; checked reference lists; and contacted authors. The last update of searches was performed on 30 November 2006. STUDY SELECTION: Studies were included if they were randomized or quasi-randomized, controlled trials that compared chondroitin with placebo or with no treatment in patients with osteoarthritis of the knee or hip. There were no language restrictions. DATA EXTRACTION: The authors extracted data in duplicate. Effect sizes were calculated from the differences in means of pain-related outcomes between treatment and control groups at the end of the trial, divided by the pooled SD. Trials were combined by using random-effects meta-analysis. DATA SYNTHESIS: 20 trials (3846 patients) contributed to the meta-analysis, which revealed a high degree of heterogeneity among the trials (I2 = 92%). Small trials, trials with unclear concealment of allocation, and trials that were not analyzed according to the intention-to-treat principle showed larger effects in favor of chondroitin than did the remaining trials. When the authors restricted the analysis to the 3 trials with large sample sizes and an intention-to-treat analysis, 40% of patients were included. This resulted in an effect size of -0.03 (95% CI, -0.13 to 0.07; I2 = 0%) and corresponded to a difference of 0.6 mm on a 10-cm visual analogue scale. A meta-analysis of 12 trials showed a pooled relative risk of 0.99 (CI, 0.76 to 1.31) for any adverse event. LIMITATIONS: For 9 trials, the authors had to use approximations to calculate effect sizes. Trial quality was generally low, heterogeneity among the trials made initial interpretation of results difficult, and exploring sources of heterogeneity in meta-regression and stratified analyses may be unreliable. CONCLUSIONS: Large-scale, methodologically sound trials indicate that the symptomatic benefit of chondroitin is minimal or nonexistent. Use of chondroitin in routine clinical practice should therefore be discouraged.

A novel secretin receptor splice variant potentially useful for early diagnosis of pancreatic carcinoma

BACKGROUND ; AIMS: Pancreatic and bile duct carcinomas represent highly aggressive malignancies that evolve from secretin receptor-rich ductular cells. With premessenger RNA splicing abnormalities common in cancer, we evaluated whether an abnormal secretin receptor spliceoform were present, characterized it, and developed a serum assay for it. METHODS: Cancer cell lines and healthy and neoplastic tissue were studied by nested reverse-transcription polymerase chain reaction and sequencing. A promising spliceoform was isolated and characterized, and monoclonal antibodies were raised to 2 distinct regions. A dual antibody enzyme-linked immunosorbent assay was developed and applied to blinded serum samples from 26 patients with pancreatic carcinoma, 10 patients with chronic pancreatitis, and 14 controls. RESULTS: Each of 9 pancreatic cancer specimens and no normal tissue expressed a secretin receptor variant with exons 3 and 4 deleted. This encoded a 111-residue peptide with its first 43 residues identical to wild-type receptor, but, subsequent to a shift in coding frame and early truncation, the next 68 residues were unique in the transcriptome/proteome. This nonfunctional soluble protein did not bind or signal in response to secretin and was secreted from transfected MiaPaCa-2 cells. Elevated serum levels of this variant were present in 69% of pancreatic cancer patients, 60% of chronic pancreatitis patients, and 1 of 14 controls. CONCLUSIONS: We identified a novel abnormal spliceoform of the secretin receptor in pancreatic and bile duct cancers and developed a dual antibody sandwich enzyme-linked immunosorbent assay to measure it in the circulation. Initial application of this assay in patients with pancreatic cancer and chronic pancreatitis was promising, but additional validation will be required to evaluate its clinical utility.