73 research outputs found
Protection mechanisms in the resurrection plant Xerophyta viscosa: cloning, expression, characterisation and role of XvINO1, a gene coding for a myo-inositol 1-phosphate synthase
No full textInternational audienceWe have used reverse transcription-PCR coupled with 5′- and 3′-RACE to isolate a full length INO1 cDNA (1692 bp with an ORF of 1530) from the resurrection plant Xerophyta viscosa Baker. XvINO1 encodes 510 amino acids, with a predicted MW of 56.7kD and contains four sequence motifs that are highly conserved in plant myo-inositol-1-phosphate synthases (MIPS, EC5.5.1.4), the enzyme that catalyses the first step in the formation of myo-inositol (Ino). Northern and western analyses show that the transcript and protein are constitutively present in leaves but their expression increases, temporarily, in response to both accumulative salt stress (~300 mM NaCl) and desiccation (to 5% relative water content). Leaf Ino concentration increases 40-fold during the first 6 h of salt stress, and levels of this and other carbohydrates (galactinol, sucrose, raffinose, stachyose and hexoses) remain elevated relative to control leaves for the duration of salt stress treatment. The timing and pattern of accumulation of these carbohydrates differ under desiccation stress and we propose that they perform different functions in the respective stresses. These are elaborated in discussion of our data
Exploring the trends in prevalence of human immunodeficiency virus drug resistance in South Africa over the course of the HIV epidemic
No full textMagister Public Health - MPHBackground: Antiretroviral therapy (ART) was rolled out in South Africa in the public sector
in 2004 and the treatment coverage has increased over the years to 56% in 2016. The increased
treatment coverage has the potential to increase the level of HIV drug resistance. Drug
resistance presents a major challenge to the management of HIV infection through
antiretroviral therapy at the population level. The aim of this study was to determine the impact
of the public sector antiretroviral therapy rollout on the prevalence of HIV drug resistance in
South Africa and the factors associated with drug resistance.
Methodology: A cross-sectional analytical study was used to determine the prevalence of drug
resistance before and after ART rollout. The study population was HIV infected South Africans
(infected between 1996 and 2011) who were not on antiretroviral therapy. The study sample
was therapy naïve HIV infected South Africans who participated in published studies
conducted between 1996 and 2011. HIV DNA sequences and associated data (participants’
age, gender, geographic location and estimated year of HIV infection) were accessed through
the Los Alamos HIV Database. The database contains all HIV DNA sequences and associated
data from all published studies and the data was freely accessible. A descriptive analysis was
carried out on the data to determine characteristics of the study sample. Drug resistance
mutations were detected using Calibrated Population Resistance Program on the Stanford
University HIV Drug Resistance database. The output from the Calibrated Population
Resistance Program analysis were used to determine the prevalence of drug resistance
mutations.
Results: There were 1701 DNA sequences obtained from the Los Alamos HIV Database for
the three gene regions targeted by ART (reverse transcriptase, protease and integrase). Of these,
604 (35,5%) were for reverse transcriptase, 794 (46,7%) were for protease and 303 (17,8%)
were for integrase. There was overrepresentation of DNA sequences from female participants
(91%). There was no significant difference in the prevalence of drug resistance mutations
between 1996-2004 (before ART rollout) and 2005-2011 (after ART rollout) in all the drug
classes. There was also no association between drug resistance and age as well as gender.
Conclusion: The data from this study suggest that the public sector rollout of ART did not
result in an increase in the prevalence of drug resistance mutations in therapy naïve HIVinfected
South Africans. There is need for further studies, which have a wider coverage of the
South African population
Molecular characterization of XvlNO1, a myo-inositol 1-phosphate synthase gene from Xerophyta viscosa
No full textIncludes bibliographical references.Myo-inositol I-phosphate synthase (INO 1) catalyses the conversion of glucose-6-phosphate to myo-inositol I-phosphate, which is subsequently dephosphorylated to myo-inositol. Myo-inositol is a precursor for a number of important metabolites that include membrane components, storage molecules, phytohormones and a variety of osmoprotectants. Xerophyta viscosa Baker (Family Velloziaceae) is a monocotyledonous angiosperm which has the ability to resume full physiological function after desiccation. The full-length cDNA for INO1 from X viscosa was isolated using the RACE technique
Impact of Cytotoxic T Lymphocyte (CTL) escape mutations in acute/Early HIV-1 Subtype C Infection on Disease Progression
No full textIncludes abstract.
Includes bibliographical references (leaves 139-162).Most HIV vaccines currently in development aim to protect people from infection or disease by eliciting strong anti-HIV cytotoxic T lymphocyte (CTL) responses. Evolved evasion mutations that undermine host immune responses pose a major challenge to the development of such vaccines. Understanding the mechanisms that selectively favour the emergence of CTL evasion mutations in vivo and the impact of these mutations on both disease progression and long-term HIV evolution will not only contribute to our understanding of HIV pathogenesis, but will also inform vaccine design strategies. This study aimed at investigating CTL escape mutations in HIV-1 Gag and Nef, during the acute and early phases of infection and the impact of these mutations on subsequent disease progression in a cohort of recently HIV-1 subtype C infected females. Of 36 women recruited into the study within 12 weeks of infection (median 6 weeks) and followed for six months, 32 were infected with single viruses. Two participants were infected with epidemiologically unlinked viruses (dual infection), and in a further two individuals the viruses were highly divergent suggestive of dual infection and/or recombination. These individuals were excluded from further analysis as it was difficult to predict CTL escape due to high degrees of diversity between sequences. In the remaining 32 study participants, there was a high frequency of CTL escape with putative escape mutations identified in 21 of 32 individuals (66%). Twelve of these 21 (33%) harboured viruses which developed escape mutations in Gag, and 17 (53%) developed escape mutations in Nef. In the conserved structural protein, p24, potential reversion mutations were more frequent than potential escape mutations. During the first six months of infection whereas potential reversion mutations occurred at low entropy sites, potential escape mutations occurred
at high entropy sites. Although there was no detectable association between the timing of escape mutations and disease progression, there was an association between the degree of deviation of the p24 sequence from the subtype-C population consensus (a measure of escape mutation load) and CD4+ counts. Analysis of the earliest sampled viruses from HLA-B*57/B*5801 negative study participants for viral genetic markers associated with disease progression identified two iv polymorphisms, A146X (n = 9) and T242N (n =6), that were associated with improved viral control. The polymorphisms are well-known escape mutations in HLAB* 57/B*5801 restricted epitopes. This suggested transmission of these variants from individuals carrying these alleles. Further evidence that viruses carrying the T242N and/or A146X mutations had been previously passaged through B*57/B*5801 positive individuals came from the fact that the observed T242N mutations reverted to wild type during follow-up. There was no significant change in viral load and CD4+ counts upon reversion of the T242N mutations. In vitro replication assays using chimeric viruses containing gag sequences from one of participants showed that the virus harbouring the T242N mutation was fitter than that carrying the reversion mutation. These viruses harboured other T242N associated compensatory mutations suggesting that these compensatory mutations may themselves carry a fitness cost in the absence of the T242N mutation. This suggests that there possibly exist networks of B*57/B*5801 associated mutations and that reversion of some of these mutations in isolation does not necessarily restore viral fitness. Lastly, the kinetics of CTL escape in HLA-B*5801 positive participants (n = 6) and the impact of escape on disease progression was investigated. CTL escape within B *5801 positive individuals was found to predominantly occur within
the TW10 in Gag (n = 4) and KAF9 in Nef (n = 6) epitopes. The emergence of the T242N mutation in TW10 was always preceded by mutations elsewhere in the epitope and was associated with the occurrence of previously described compensatory mutation upstream of the epitope. The targeting of TW10 and the emergence of T242N escape mutations were associated with higher CD4+ counts at 12 months postinfection in the B*5801 positive individuals (p = 0.0231 and p = 0.0282, respectively). Independent of host HLA genotypes, the presence of the A146X and T242X mutations was associated with higher CD4+ counts (p = 0.0495). This study provides some useful insights into HIV-1 subtype C pathogenesis. The notion that CTL escape mutations do not invariably result in less fit viruses is evidenced by the observation that escape was not obviously associated with disease progression in this cohort, while escape mutations in the Gag p24 region within B*5801 positive individuals v in particular, was associated with improved viral control. There is therefore evidently a complex interaction between escape and compensatory mutations and further work is required to identify the impact of compensatory mutations on viral fitness. Overall, this study provides further evidence that vaccines need to elicit responses that specifically target the functionally constrained regions of the HIV proteome
Immune-mediated attenuation of HIV-1
No full text Immune escape mutations selected by human leukocyte antigen class I-restricted CD8+ cytotoxic T lymphocytes (CTLs) can result in biologically and clinically relevant costs to HIV-1 replicative fitness. This phenomenon may be exploited to design an HIV-1 vaccine capable of stimulating effective CTL responses against highly conserved, mutationally constrained viral regions, where immune escape could occur only at substantial functional costs. Such a vaccine might ‘channel’ HIV-1 evolution towards a less-fit state, thus lowering viral load set points, attenuating the infection course and potentially reducing the risk of transmission. A major barrier to this approach, however, is the accumulation of immune escape variants at the population level, possibly leading to the loss of immunogenic CTL epitopes and diminished vaccine-induced cellular immune responses as the epidemic progresses. Here, we review the evidence supporting CTL-driven replicative defects in HIV-1 and consider the implications of this work for CTL-based vaccines designed to attenuate the infection course. </jats:p
Inhibition of CYP2B6 by Medicinal Plant Extracts: Implication for Use of Efavirenz and Nevirapine-Based Highly Active Anti-Retroviral Therapy (HAART) in Resource-Limited Settings
No full textHighly active antiretroviral therapy (HAART) has greatly improved health parameters of HIV infected individuals. However, there are several challenges associated with the chronic nature of HAART administration. For populations in health transition, dual use of medicinal plant extracts and conventional medicine poses a significant challenge. There is need to evaluate interactions between commonly used medicinal plant extracts and antiretroviral drugs used against HIV/AIDS. Efavirenz (EFV) and nevirapine (NVP) are the major components of HAART both metabolized by CYP2B6, an enzyme that can potentially be inhibited or induced by compounds found in medicinal plant extracts. The purpose of this study was to evaluate the effects of extracts of selected commonly used medicinal plants on CYP2B6 enzyme activity. Recombinant human CYP2B6 was used to evaluate inhibition, allowing the assessment of herb-drug interactions (HDI) of medicinal plants Hyptis suaveolens, Myrothamnus flabellifolius, Launaea taraxacifolia, Boerhavia diffusa and Newbouldia laevis. The potential of these medicinal extracts to cause HDI was ranked accordingly for reversible inhibition and also classified as potential time-dependent inhibitor (TDI) candidates. The most potent inhibitor for CYP2B6 was Hyptis suaveolens extract (IC50 = 19.09 ± 1.16 µg/mL), followed by Myrothamnus flabellifolius extract (IC50 = 23.66 ± 4.86 µg/mL), Launaea taraxacifolia extract (IC50 = 33.87 ± 1.54 µg/mL), and Boerhavia diffusa extract (IC50 = 34.93 ± 1.06 µg/mL). Newbouldia laevis extract, however, exhibited weak inhibitory effects (IC50 = 100 ± 8.71 µg/mL) on CYP2B6. Launaea taraxacifolia exhibited a TDI (3.17) effect on CYP2B6 and showed a high concentration of known CYP450 inhibitory phenolic compounds, chlorogenic acid and caffeic acid. The implication for these observations is that drugs that are metabolized by CYP2B6 when co-administered with these herbal medicines and when adequate amounts of the extracts reach the liver, there is a high likelihood of standard doses affecting drug plasma concentrations which could lead to toxicity
Transmission of HIV-1 CTL escape variants provides HLA-mismatched recipients with a survival advantage
No full textAuthor Summary Following infection with HIV, it is well established that a person's genetic makeup is a major determinant of how quickly they will progress to AIDS. Particularly important is the class I Human leukocyte antigen (HLA) gene that is responsible for alerting the immune system to HIV's presence. One of the reasons our immune systems are unable to beat HIV is that the virus can mutate to forms that our HLA genes no longer recognise. However, some people have versions of the HLA gene (for example HLA-B*57 and HLA-B*5801) that are known to force HIV to tolerate mutations that damage its ability to reproduce. Slower HIV reproduction is thought to be one reason that HLA-B*57 and HLA-B*5801 positive people progress to AIDS more slowly than most other HIV infected persons. We report here on a study of HLA-B*57 and HLA-B*5801 negative women in which better control of disease tended to be associated with their being infected with viruses carrying mutations that have been previously shown to reduce replication. These mutations characterise viruses found infecting HLA-B*57 and HLA-B*5801 positive people. This indicates for the first time that HLA-B*57 or HLA-B*5801 negative people that are infected by such reproductively compromised viruses may also experience better survival prospects
Brief report: selection of HIV-1 variants with higher transmission potential by 1% tenofovir gel microbicide.
No full textCAPRISA, 2017.Abstract available in pdf
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