Department of Biochemistry and Microbiology
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Browsing Department of Biochemistry and Microbiology by Author "Bessong, Pascal O."
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Item Open Access Characterization of cholesterol 25-hydroxylase expression in human macrophages(2019-09-20) Magoro, Tshifhiwa; Bessong, Pascal O.; Hahn, Young Shin; Jennelle, LucasBackground Conversion of Cholesterol to 25-HydroxyCholesterol (25HC) by Cholesterol 25-hydroxylase (CH25H) has been shown to exert broad antiviral properties. Given its antiviral activities, CH25H is part of an increasingly appreciated connection between type I interferon (IFN-I) and lipid metabolism. Moreover, the details of this connection appear to differ in mouse and human cells. Nevertheless, the molecular basis for the induction of CH25H in humans is not known. Objective Elucidation of signaling and transcriptional events for induction of CH25H expression is critical to design therapeutic antiviral agents. Materials and methods: Wildtype THP-1 monocytic cell-line or THP-1 MyD88 Knockout cell-line were treated with PMA for 72 hours for differentiation into macrophages. Differentiated macrophages or Microglial cells were stimulated with either TLR-agonists, pro-inflammatory cytokine, or interferons, and CH25H mRNAs expression levels were measured by qPCR. Results In this study, we show that CH25H is induced by Zika virus infection or TLR stimulation. Interestingly, CH25H is induced by pro-inflammatory cytokines including 1L- 1, TNF-, and IL-6, and this induction depends on STAT-1 transcription factor. Additionally, we have observed that ATF3 weakly binds to the CH25H promoter, suggesting co-operation with STAT-1. However, ZIKV induced CH25H was independent of type I interferon. Conclusion This study has demonstrated for the first time that pro-inflammatory cytokines such as 1L-1, TNF-, and IL-6 induce CH25H expression. Moreover, this provides further understanding to the connection between innate immunity and sterol metabolism and encourages the exploration of cytokines in antiviral immunity.Item Open Access Detection and characterization of Human Herpes Virus -8 in an HIV-infected cohort in Cameroon(2017-05-18) Alayande, Doyinmola Paul; Bessong, Pascal O.; Mavhandu, Lufuno G.Background: Human Herpes Virus-8 (HHV-8) and Human Immunodeficiency Virus (HIV) are endemic in sub-Saharan Africa. However, the prevalence of HHV-8 in HIV-infected individuals in sub-Saharan Africa has not been fully described and characterized. Objectives: The objective of this study was to determine the seroprevalence and genetic subtypes of HHV-8 in an HIV-infected population in Cameroon. Methodology: KSHV/HHV-8 Enzyme-linked Immunosorbent Assay (ELISA) kit (Advanced Biotechnologies Inc., USA) was used to detect IgG antibodies in the plasma of 406 HIV-infected outpatients of the Mutengene Baptist Health Centre, Cameroon. To detect the viral presence, a 233 bp fragment of the ORF 26 gene of HHV-8 was targeted by polymerase chain reaction (PCR) in total DNA purified from patients’ whole blood. A 453 bp of the K1 gene was amplified by nested PCR, sequenced and phylogenetically analysed to infer subtypes. The online tool, Synonymous Non-synonymous Analysis Program (SNAP), was used to determine the rate of synonymous and nonsynonymous mutations in the K1 gene. The genetic variability among the derived K1 nucleotide sequences was determined by mean genetic distance analysis. Results: Of the 406 participants, an HHV-8 seroprevalence of 79.1% was obtained. There was a statistically significant association of seroprevalence with age (p= 0.00), CD4+ cell count (p= 0.02), marital status (p= 0.02) and ownership of a transistor radio set (p= 0.00). Seventy samples (23.3%) were successfully amplified for ORF 26 gene confirming the presence of replicating virus. K1 sequences were obtained for 14 of the 20 (70%) K1 amplified DNAs. The mean genetic diversity of K1 sequences ranges from 0.0%-22.3%. Phylogenetic analysis revealed two infecting viral subtypes in the study cohort: subtype A5 (57.1%), and subtype B (35.7%). Greater positive selection and genetic diversity were observed in A5 subtype compared to B subtype of K1. Interestingly, one sample (BM 547) clustered with an unclassifiable sequence from South Africa. Conclusions and recommendation: This study revealed the endemicity of HHV-8 infection in the studied population, with subtypes A5 and B as the most important epidemiological genetic variants. In addition, targeting the ORF 26 region by PCR could be an approach to detect replicating virus in individuals. Further studies should investigate the association between HHV-8 infection and KS development in the study area which is endemic for HIV. This study contributes data to the HIV/HHV-8 co-infection landscape in the study area and in Africa at large.Item Open Access Diversity in APOBEC3 and CCR5 host genes and HIV-1 in a South African population(2018-09-21) Matume, Nontokozo D.; Bessong, Pascal O.; Hammarskjold, Marie-Louise; Rekosh, DavidIntroduction Human Immunodeficiency Virus (HIV-1) continues to be a global public health concern, even though Antiretroviral drugs (ARV), especially Highly Active Antiretroviral Therapy (HAART) has significantly reduced morbidity and mortality due to AIDS globally in developed and developing countries. However, there is still a great need to explore every avenue for new therapeutic interventions due to the limitations and side effects of HAART. Potential major breakthroughs for future therapeutic development were the discoveries more than 10 years ago of the role of HIV-1 co-receptors and anti-viral activities of host restriction factors such as APOBEC3G protein, which is a member of the DNA cytosine deaminase family. Entry of HIV in to the host cell is through the attachment of the viral envelope glycoprotein to the CD4 receptor, and subsequent interaction, mainly with either CCR5 or CXCR4 co-receptors. Inhibitors, such as Maraviroc, which binds to CCR5 inhibiting entry of CCR5 utilizing viruses (R5 viruses), is currently reserved for salvage therapy in many countries including South Africa. In the course of HIV infection, CXCR4 utilizing viruses (X4 viruses) may emerge and outgrow R5 viruses, and potentially limit the effectiveness of Maraviroc. Several host cell APOBEC3 genes (A3D, A3F, A3G and A3H) have been shown to restrict HIV, and the HIV viral infectivity factor (Vif) protein serves to antagonize the action of APOBEC3 proteins, promoting viral replication. The CCR5 co-receptor and the HIV Env V3 loop have also been documented as playing roles in HIV-1 disease progression. The interplay between host and viral genes still needs widespread attention, given that disease outcomes of HIV depend on many factors, including host cell genetics. Since the discovery of these genes and their role in HIV replication, many studies have been conducted that show their association with viral polymorphism. The polymorphisms found in host cell genes can have significant effects on viral replication, transmission and fitness and can also contribute to the overall diversity in HIV-1 populations. It is hypothesized that there are significant polymorphisms in HIV-1 and cellular genes that may differ among different populations. Population-based studies have tried to establish a relationship between host factors such as APOBEC3 and CCR5 polymorphism and the rate of disease progression, but most studies have focused on Caucasian populations. In vi contrast, little information is available for the effects of variation in these genes in African populations such as South Africa, where the HIV epidemic has expanded at an alarming rate. Although several population studies have focused on African Americans, these do not give us a complete picture of the potential variation in Africans, though the studies can be a good guide on which to base additional studies. A more comprehensive analysis involving different African populations will likely provide a better understanding of the mechanisms underlying host-pathogen interactions, especially in view of the fact that African Americans are primarily infected with HIV subtype B, which is rarely seen in Africa. Methodology This study characterized the genetic variability of the APOBEC3 D, F, G and H genes as well as the HIV-1 vif, in an ethnically diverse HIV-1 infected South African cohort using Next Generation Sequencing (NGS). In addition, polymorphism in CCR5 was analyzed in conjunction with an analysis of the V3 loop sequences in HIV-1 from this cohort. Genomic DNA was extracted from peripheral blood mononuclear cells (PBMCs) of 192 HIV-1 infected drug-experienced individuals who presented for routine care at the HIV/AIDS Prevention Group Wellness Clinic (HAPG) in Bela-Bela, Donald Fraser Hope Clinic (DFHC) in Vhufhuli and in local clinics in the Vhembe district of Limpopo Province, South Africa. Next generation sequencing custom based (Tn5 tagmentation and amplicon based) protocols to prepare libraries for host and HIV-1 genes were developed and validated with commercially available library preparation kits. The Tn5 tagmentation methods were used for longer DNA fragments and the custom amplicon based methods were used mainly for the shorter DNA fragments. To determine the variability of the APOBEC3 and CCR5 host genes, gene-specific primers were designed to amplify complete 12.16 kb A3D, 13.31 kb A3F, 10.74 kb A3G, 6.8 kb A3H and 1.3 kb CCR5 genes targeting the regions containing the exons. Libraries for the resulting amplicons were prepared using Tn5 transposase tagmentation methods and sequenced on an NGS Illumina MiSeq platforms generating millions of reads with good read coverage for variant calling. Single nucleotide polymorphisms (SNPs) and indels were determined, verified in dbSNPs and compared to SNPs in other populations reported in the 1000 Genome Phase III and HapMap. A Chi-square goodness-of-fit was used to verify if whether observed genotype frequencies were in agreement with the Hardy-Weinberg Equilibrium. Haplotypes and Linkage disequilibrium were inferred to determine SNP association. vii The HIV-1 vif and env V3 loop genes were also sequenced to determine their degree of variability of these genes and to infer co-receptor usage in the South African population. Gene-specific primers were designed to amplify the 579 bp Vif region and 440 bp containing the 105 bp V3 loop. Sequencing libraries from the resulting amplicons were prepared using either the Tn5 transposase or custom-based library preparation methods and sequenced on either an Illumina MiSeq or a MiniSeq platform generating millions of reads with good read coverage for variant calling. Phylogenetic analysis was done to determine the relatedness of the sequences. Major and minor variants were determined for HIV-1 and env V3 loop quasispecies was analysed for co-receptor usage; in an effort to draw inferences for the subsequent utility of Maraviroc as salvage therapy in South Africa. Results and Discussion Next generation library preparation; Tn5 tagmentation based and custom amplicon based protocols to sequence host and HIV genes were successfully developed and used to sequence and characterize variability in host cell APOBEC3D, F, G H, CCR5 and the HIV-1 vif gene and the V3 loop region of the env gene. The HIV-1 env V3 loop sequences generated (and quasispecies analyzed) were used to infer co-receptor usage in treatment-experienced individuals; in an effort to draw inferences for the subsequent utility of Maraviroc as salvage therapy in South Africa. Quality V3 loop sequences were obtained from 72 patients, with 5 years (range: 0-16) median duration on treatment. Subtypes A1, B and C viruses were identified at frequencies of 4% (3/72), 4% (3/72) and 92% (66/72) respectively. Fifty four percent (39/72) of patients were predicted to exclusively harbor R5 viral quasispecies; and 21% (15/72) to exclusively harbor X4 viral quasispecies. Twenty five percent of patients (18/72) were predicted to harbor a dual/mixture of R5X4 quasispecies. Of these 18 patients, about 28% (5/18) were predicted to harbor the R5+X4, a mixture with a majority R5 and minority X4 viruses, while about 72% (13/18) were predicted to harbor the R5X4+ a mixture with a majority X4 and minority R5 viruses. The proportion of all patients who harboured X4 viruses either exclusively or dual/mixture was 46% (33/72). Thirty-five percent (23/66) of the patients who were of HIV-1 subtype C were predicted to harbor X4 viruses (χ2=3.58; p=0.058), and 57% of these (13/23) were predicted to harbor X4 viruses exclusively. CD4+ cell count less than 350 cell/μl was associated with the presence of X4 viruses (χ2=4.99; p=0.008). The effectiveness of Maraviroc as a component in salvage therapy may be compromised for a significant number of chronically infected patients harboring CXCR4 utilizing viii viruses in the study cohort. Although from the current study a subset of patients harboring CCR5 utilizing viruses may benefit from Maraviroc, characterizing and identifying if variation in CCR5 are located at Maraviroc binding sites was of importance to investigate. The following variants; P35P, S75S, Y89Y, A335V and Y339F and their varying frequencies were detected in the CCR5 gene. The A335V variant was detected at a higher frequency of 17.4% (29/167). The G265S variant is reported for the first time in this study at 0.6% (1/167) frequency. The SNPs detected were in strong LD (D’= 1, R2 = 0.0) with minor deviation from the Hardy-Weinberg Equilibrium. These variants were not located at the binding motif of Maraviroc. The variants A335V and Y339F were detected at a higher frequency in this study than previously reported in South Africa. Variability in APOBEC3 host cell genes was also characterized in our study cohort. The following APOBEC3 variants compared to the GRCh37 consensus sequence were detected: R97C, R248K and T316T in A3D; R48P, A78V, A108S, S118S, R143R, I87L, Q87L, V231I, E245E, S229S, Y307C and S327S in A3F; S60S, H186R, R256H, Q275E and G363R in A3G and N15Δ, G105R, K140E, K121D, E178D in A3H. Minor allele frequency variants (MAF<5%); L221L, T238I, C224Y and C320Y in A3D; I87L, P97L and S229S in A3F; R256H, A109A, F119F and L371L in A3G, which are frequent in the European population, were also detected. In addition, novel R6K, L221R and T238I variants in A3D and I117I in A3F were detected. Most of the SNPs were in strong LD with minor deviation from the Hardy-Weinberg Equilibrium. Four, six, four, and three haplotypes were identified for A3D, A3F, A3G, and A3H respectively. In general, polymorphism in A3D, 3F, 3G and 3H were higher in our South African cohort than previously reported among other African, European and Asian populations. The APOBEC3 antagonist HIV-1 vif gene was also sequenced to determine the level of diversity in a South African population and also correlated with APOBEC3 variation. Functional Vif without frameshift mutation was observed in all samples except in 4 samples. The functional domain and motifs, such as Zn binding motifs, proline-rich domain, human casein kinase, and the N and C-terminal CBF interaction site were highly conserved. APOBEC binding motifs and the nuclear localization signal were less conserved in the South African HIV-1 Vif. APOBEC3 H variation strongly correlates with Vif variation. All the Vif sequences were subtype C, except one sample, which was identified as an A1/C recombinant. The vif gene in a South African population was under purifying selection, with the dS= 0.2581 and dN= 0.0684 and the dN/dS value = 0.265. There is a high genetic diversity in the South African vif gene, which may ix influence the neutralization and restriction of APOBEC genes. Conclusions In conclusion, the protocols developed in this study can be applied to amplify and sequence any host and HIV-1 genes of interest allowing much deeper and more sensitive profiling of host gene and HIV-1 genetic diversity. Our findings show that a highly significant number of chronically HIV-1 subtype C infected patients in Maraviroc-free treatment harbor CXCR4 utilizing viruses. The data is useful in the consideration of whether to include entry antagonists such as Maraviroc in alternative forms of treatment for patients failing second line treatment regimen in the study setting. The determination of co-receptor usage prior to initiation of therapy consisting of Maraviroc is suggested. Variation in the CCR5 coding region were observed at higher frequencies compare to other studies conducted in South African populations at different locations. This data may suggest that different populations in South Africa have different SNP frequencies. All the polymorphisms identified in the study were not located at the Maraviroc binding motif, therefore the subset of patient infected by R5 viruses may benefit from this drug. We have shown that significant APOBEC3 variation exists among an ethnically diverse population of South Africa by providing extensive data for 4 different A3 genes that are known to restrict HIV infection, but have only been sparsely studied in African populations. This study provides a baseline for future studies that would functionally characterize SNPs identified in this population, in order to understand the role of novel and/or low frequency variants observed. Ex vivo and in vivo studies will increase our understanding of how these variants might have cumulatively impacted the epidemic in Northern South Africa. This study also shows that there is a high level of HIV-1 Vif diversity in the study area. This diversity may impact the expression and packaging of Vif proteins, and the infectivity of HIV. In addition, a significant correlation was observed between HIV-1 Vif variation and APOBEC3 H haplotypes.Item Open Access Further screening of Venda medicinal plants for activity against HIV type 1 reverse transcriptase and integrase(2006-03-15) Bessong, Pascal O.; Rojas, Luis B; Obi, Larry C.; Tshisikhawe, Peter M.; Igunbor, Eunice O.The use of medicinal plants for AIDS-related conditions is common in South Africa. In order to establish an antiviral rationale for the use of these plants we screened fractions of the methanol extracts of medicinal plants for activity against HIV-1 reverse transcriptase (RT) and integrase (IN). The n-butanol fraction obtained from the crude methanol extracts of the roots of Bridelia micrantha (Hochst) Baill. (Euphorbiaceae) was observed to be as the most active inhibiting the RNA-dependent-DNA polymerization (RDDP) activity of HIV-1 RT with an IC50 of 7.3 g/ml. However, it had no activity on the 3’-end processing activity of HIV integrase. Bioassay-guided fractionation of the n-butanol fraction yielded friedelin and -sistosterol, which did not inhibit the RDDP of RT or 3’-end processing functions of IN even at a concentration of 500 M. An uncharacterized fraction obtained in the bioassay-guided fractionating process inhibited the RDDP with an IC50 of 9.6 g/ml, but had no inhibition on IN. Phytochemical screening indicated the presence of flavonoids and tannins in the uncharacterized fraction.Item Open Access In-vitro bioactivity of fractions from a local medicinal plant on HIV-1 replication, and selected fungal and bacterial pathogens(2009-03) Mutshembele, Awelani Mirinda; Bessong, Pascal O.; Eloff, Jacobus N.; Obi, LarrySee the attached abstract below.Item Open Access Malaria infection and anaemia in HIV-infected children in Mutengene, South west Cameroon: a cross sectional study(BioMed Central, 2016) Bate, Ayukenchengamba; Kimbi, Helen K.; Lum, Emmaculate; Lehman, Leopold G.; Onyoh, Elias F.; Ndip, Lucy M.; Njabi, Conica M.; Tonga, Calvin; Wempnje, Godlove B.; Ndip, Roland N; Bessong, Pascal O.Background: Malaria is one of the leading causes of morbidity and mortality in children and HIV infection as well as other factors may worsen the situation. This study was aimed at determining the factors influencing malaria parasite prevalence and density as well as anaemia in HIV-infected children in Mutengene, Cameroon from November, 2012 to April, 2013. Methods: A semi-structured questionnaire was used to record information on socio-demographic factors and use of preventive measures by caregivers of HIV-infected children aged 1–15 years and of both sexes. Venous blood was collected; blood films were prepared and Giemsa-stained for parasite detection and speciation. Haemoglobin concentration was measured and the anaemic status determined. Data was analysed using Epi Info 7 software. Results: A total of 234 children were studied. The overall malaria parasite prevalence was 24.8 % (58) and was significantly higher (31.9 %, P = 0 .004) in females, those who did not implement any preventive measure at all (66.7 %, P = 0.03) and children who used antiretroviral therapy (ART) (28.6 %, P = 0.02) when compared with their respective counterparts. Geometric mean parasite density (GMPD) was significantly higher (3098.4, P = 0.02) in children who presented with fever, had CD4 T cells ≥500 cells/μL (491.3, P = 0.003) and those with moderate anaemia (1658.8, P = 0.03) than their respective counterparts. Although there was no significant difference, GMPD was however higher in males (549.0); those not on ART (635.0) and highest in children <5 years old (633.0) than their respective counterparts. The overall prevalence of anaemia was 49.6 % (116). The value was significantly highest (58.3 %, P = 0.01) in the 11–15 years age group; those with CD4 T cell level 200–499 (72.7 %, P = 0.001) and children with fever (85.7 %, P = 0.01). Conclusion: Implementation of proper and integrated malaria preventive measures as well as frequent monitoring of anaemia on prescription of ART could likely improve the health conditions of HIV-infected children thus avoiding malaria-related morbidity and mortality.Item Open Access Overexpression and structure-function characterization of HIV-1 Subtype C. reverse transcriptase and protease(2019-09-20) Tambani, Tshifhiwa; Bessong, Pascal O.; Shonhai, AddmoreHigh genetic diversity is a major contributory factor in the development of drug resistance, in addition to challenges in diagnosis and treatment monitoring in the therapeutics of human immunodeficiency virus (HIV) .Within the wide HIV-1 diversity, differences in mutational frequency, disease progression, drug response and transmission amongst HIV-1 subtypes have been shown. In spite HIV-1 subtype C (HIV-1C) being the most prevalent variant globally, none of the available drugs nor screening assays for inhibitory molecules have been developed targeting the genetics of this important subtype. This study therefore aimed to overexpress and biophysically characterize HIV-1C reverse transcriptase and protease to serve as reagents in the development of assays for routine screening of molecules inhibitory to HIV-1C. Heterologous expression of HIV-1C reverse transcriptase and protease isolates that are prevalent in South Africa was carried out in Escherichia coli (E. coli (BL21-DE3). The secondary and tertiary structures of the proteins were determined using, circular dichroism (CD) and fluorescence spectroscopy respectively. Thereafter, interaction studies to delineate interaction properties of natural products for possible inhibition of protease were conducted. Furthermore, in silico studies to determine binding interactions, further confirmed by in vitro binding assays of a pepsin inhibitor homolog (Bm-33) from Brugia malayi , against protease were also conducted. Expressed reverse transcriptase and protease from the globally prevalent HIV-1C were shown to be structurally and functionally intact for application in downstream HIV-1 inhibition assays. Interaction studies on the other hand revealed successful inhibition of the expressed HIV-1C PR with gallotanin. Furthermore, binding interactions of Bm-33 and HIV-1 PR revealed the first intermolecular interactions of the two molecules displaying possible inhibition of HIV-1 PRItem Open Access Recombination events and epitope prediction in HIV-1 strains from Southwest Cameroon(2017-08-18) Ogola, Bixa O.; Bessong, Pascal O.; Tebit, Denis M.See the attached abstract belowItem Open Access Studies on human immunodeficiency virus genetic drug resistance and subtype distribution in Northern South Africa(2014-01-10) Nwobegahay, Julius; Bessong, Pascal O.; Selabe, Gloria