4-amino-5-hexynoic Acid-a potent inhibitor of tetrapyrrole biosynthesis in plants

4-Amino-5-hexynoic acid, a suicide inactivator of the mammalian pyridoxal phosphate-dependent 4-aminobutyric acid:2-oxoglutaric acid aminotransferase, inhibits phytochrome and chlorophyll synthesis in developing oat (Avena sativa L.), corn (Zea mays L.), pea (Pisum sativum L.), and cucumber (Cucumis sativus L.) seedlings. In Avena and Cucumis seedlings, respectively, inhibition of phytochrome and chlorophyll accumulation by 4-amino-5-hexynoic acid can be significantly reversed by application of 5-aminolevulinic acid. These results indicate that 4-amino-5-hexynoic acid inhibits the synthesis of 5-aminolevulinic acid in plants.     

Phytochrome A and Phytochrome B Have Overlapping but Distinct Functions in Arabidopsis Development

Plant responses to red and far-red light are mediated by a family of photoreceptors called phytochromes. In Arabidopsis thaliana, there are genes encoding at least five phytochromes, and it is of interest to learn if the different phytochromes have overlapping or distinct functions. To address this question for two of the phytochromes in Arabidopsis, we have compared light responses of the wild type with those of a phyA null mutant, a phyB null mutant, and a phyA phyB double mutant. We have found that both phyA and phyB mutants have a deficiency in germination, the phyA mutant in far-red light and the phyB mutant in the dark. Furthermore, the germination defect caused by the phyA mutation in far- red light could be suppressed by a phyB mutation, suggesting that phytochrome B (PHYB) can have an inhibitory as well as a stimulatory effect on germination. In red light, the phyA phyB double mutant, but neither single mutant, had poorly developed cotyledons, as well as reduced red-light induction of CAB gene expression and potentiation of chlorophyll induction. The phyA mutant was deficient in sensing a flowering response inductive photoperiod, suggesting that PHYA participates in sensing daylength. In contrast, the phyB mutant flowered earlier than the wild type (and the phyA mutant) under all photoperiods tested, but responded to an inductive photoperiod. Thus, PHYA and PHYB appear to have complementary functions in controlling germination, seedling development, and flowering. We discuss the implications of these results for possible mechanisms of PHYA and PHYB signal transduction.     

Dephosphorylation of photosystem II core proteins is light-regulated in vivo.

A number of photosystem II (PSII)-associated proteins, including D1, D2, CP43 and LHCII, are phosphorylated post-translationally by a membrane-bound, redox-regulated kinase activity. In vitro studies have demonstrated that these proteins can be dephosphorylated by membrane-bound phosphatase activity, reportedly insensitive to light or redox control. We demonstrate here that the PSII core proteins, D1, D2 and CP43, undergo light-stimulated, linear electron-transport-independent dephosphorylation in vivo. The in vivo dephosphorylation of D1 was characterized further and shown to depend upon light intensity, and to occur throughout the visible light spectrum with characteristics most consistent with light absorption by chlorophyll. PSII core protein dephosphorylation in vivo was stimulated by photosystem I (PSI)-specific far-red light, and inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, an inhibitor of plastoquinol oxidation by the cytochrome b6f complex. Based on these findings, we propose that PSI excitation is involved in regulating dephosphorylation of PSII core proteins in vivo.     

Investigating the combination of single-pass tangential flow filtration and anion exchange chromatography for intensified mAb polishing

There is growing interest within the biopharmaceutical industry to improve manufacturing efficiency through process intensification, with the goal of generating more product in less time with smaller equipment. In monoclonal antibody (mAb) purification, a unit operation that can benefit from intensification is anion exchange (AEX) polishing chromatography. Single-pass tangential flow filtration (SPTFF) technology offers an opportunity for process intensification by reducing intermediate pool volumes and increasing product concentration without recirculation. This study evaluated the performance of an AEX resin, both in terms of host cell protein (HCP) purification and viral clearance, following concentration of a mAb feed using SPTFF. Results show that preconcentration of AEX feed material improved isotherm conditions for HCP binding, resulting in a fourfold increase in resin mAb loading at the target HCP clearance level. Excellent clearance of minute virus of mouse and xenotropic murine virus was maintained at this higher load level. The increased mAb loading enabled by SPTFF preconcentration effectively reduced AEX column volume and buffer requirements, shrinking the overall size of the polishing step. In addition, the suitability of SPTFF for extended processing time operation was demonstrated, indicating that this approach can be implemented for continuous biomanufacturing. The combination of SPTFF concentration and AEX chromatography for an intensified mAb polishing step which improves both manufacturing flexibility and process productivity is supported.     

Temporal Trends in Treatment Outcomes for HIV-1 and HIV-2-Infected Adults Enrolled in C?te d'Ivoire's National Antiretroviral Therapy Program

Background

In Côte d''Ivoire during 2004–2007, numbers of ART enrollees increased from <5,000 to 36,943. Trends in nationally representative ART program outcomes have not yet been reported.

Methodology/Principal Findings

We conducted a retrospective chart review to assess trends in patient characteristics and attrition [death or loss to follow-up (LTFU)] over time, among a nationally representative sample of 3,682 adults (≥15 years) initiating ART during 2004–2007 at 34 health facilities. Among ART enrollees during 2004–2007, median age was 36, the proportion female was 67%, the proportion HIV-2-infected or dually HIV-1&2 reactive was 5%, and median baseline CD4⁺ T-cell (CD4) count was 135 cells/µL. Comparing cohorts initiating ART in 2004 with cohorts initiating ART in 2007, median baseline weight declined from 55 kg to 52 kg (p = 0.008) and the proportion weighing <45 kg increased from 17% to 22% (p = 0.014). During 2004–2007, pharmacy-based estimates of the percentage of new ART enrollees ≥95% adherent to ART declined from 74% to 60% (p = 0.026), and twelve-month retention declined from 86% to 69%, due to increases in 12-month mortality from 2%–4% and LTFU from 12%–28%. In univariate analysis, year of ART initiation was associated with increasing rates of both LTFU and mortality. Controlling for baseline CD4, weight, adherence, and other risk factors, year of ART initiation was still strongly associated with LTFU but not mortality. In multivariate analysis, weight <45 kg and adherence <95% remained strong predictors of LTFU and mortality.

Conclusions

During 2004–2007, increasing prevalence among ART enrollees of measured mortality risk factors, including weight <45 kg and ART adherence <95%, might explain increases in mortality over time. However, the association between later calendar year and increasing LTFU is not explained by risk factors evaluated in this analysis. Undocumented transfers, political instability, and patient dissatisfaction with crowded facilities might explain increasing LTFU.     

Outcomes of Nigeria's HIV/AIDS Treatment Program for Patients Initiated on Antiretroviral Treatment between 2004-2012

BackgroundThe Nigerian Antiretroviral therapy (ART) program started in 2004 and now ranks among the largest in Africa. However, nationally representative data on outcomes have not been reported.MethodsWe evaluated retrospective cohort data from a nationally representative sample of adults aged ≥15 years who initiated ART during 2004 to 2012. Data were abstracted from 3,496 patient records at 35 sites selected using probability-proportional-to-size (PPS) sampling. Analyses were weighted and controlled for the complex survey design. The main outcome measures were mortality, loss to follow-up (LTFU), and retention (the proportion alive and on ART). Potential predictors of attrition were assessed using competing risk regression models.ResultsAt ART initiation, 66.4 percent (%) were females, median age was 33 years, median weight 56 kg, median CD4 count 161 cells/mm³, and 47.1% had stage III/IV disease. The percentage of patients retained at 12, 24, 36 and 48 months was 81.2%, 74.4%, 67.2%, and 61.7%, respectively. Over 10,088 person-years of ART, mortality, LTFU, and overall attrition (mortality, LTFU, and treatment stop) rates were 1.1 (95% confidence interval (CI): 0.7–1.8), 12.3 (95%CI: 8.9–17.0), and 13.9 (95% CI: 10.4–18.5) per 100 person-years (py) respectively. Highest attrition rates of 55.4/100py were witnessed in the first 3 months on ART. Predictors of LTFU included: lower-than-secondary level education (reference: Tertiary), care in North-East and South-South regions (reference: North-Central), presence of moderate/severe anemia, symptomatic functional status, and baseline weight <45kg. Predictor of mortality was WHO stage higher than stage I. Male sex, severe anemia, and care in a small clinic were associated with both mortality and LTFU.ConclusionModerate/Advanced HIV disease was predictive of attrition; earlier ART initiation could improve program outcomes. Retention interventions targeting men and those with lower levels of education are needed. Further research to understand geographic and clinic size variations with outcome is warranted.     

Phytochrome chromophore biosynthesis. Treatment of tetrapyrrole-deficient Avena explants with natural and non-natural bilatrienes leads to formation of spectrally active holoproteins

Etiolated Avena seedlings grown in the presence of 4-amino-5-hexynoic acid, an inhibitor of 5-aminolevulinic acid synthesis in plants, contain less than 10% of the spectrally detectable levels of phytochrome found in untreated seedlings (Elich, T.D., and Lagarias, J.C. (1988) Plant Physiol. 88, 747-751). In this study, incubation of explants from such seedlings with [14C]biliverdin IX alpha led to rapid covalent incorporation of radiolabel into a single 124-kDa polypeptide in soluble protein extracts. Immunoprecipitation experiments confirmed that this protein was phytochrome. Parallel experiments were performed with four unlabeled linear tetrapyrroles, the naturally occurring biliverdin IX alpha isomer, two non-natural isomers, biliverdin XIII alpha and biliverdin III alpha, and phycocyanobilin-the cleaved prosthetic group of the light-harvesting antenna protein C-phycocyanin. In all cases, except for the III alpha isomer of biliverdin, a time-dependent recovery of photoreversible phytochrome was observed. The newly formed phytochrome obtained after incubation with biliverdin IX alpha exhibited spectral characteristics identical with those of the native protein. In contrast, the spectral properties of phytochromes formed during incubation with biliverdin XIII alpha and phycocyanobilin differed significantly from those of the native chromoprotein. These results indicate that biliverdin IX alpha is an intermediate in the biosynthesis of the phytochrome chromophore and that phytochromes with prosthetic groups derived from bilatrienes having non-natural D-ring substituents are photochromic.