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Applications of Recurrent Neural Networks in Modeling the COVID-19 Pandemic
(University of the Witwatersrand, Johannesburg, 2024-03) Hayashi, Kentaro; Mellado, Bruce
This study attempted to introduce moving averages and a feature selection method to the forecasting model, with the aim of improving the fluctuating values and unstable accuracy of the risk index developed by the University of Witwatersrand and iThemba LABS and used by the Gauteng Department of Health. It was confirmed that the introduction of moving averages improved the fluctuation of the values, with the seven-day moving average being the most effective. For feature selection, Correlation-based Feature Selection(CFS), the simplest of the filter methods with low computational complexity, was introduced as it is not possible to spend as much time as possible on daily operations due to providing information timely. The introduction of CFS was found to enable efficient feature selection.
Optimization of Prostate Plan in a Pelvic Prosthesis Phantom
(University of the Witwatersrand, Johannesburg, 2024-09) Dumela, Khombo Eunice; Oderinde, Oluwaseyi M.; Usman, IyaboT.
Background: An increasing number of elderly prostate cancer patients with high-density material hip prosthesis are referred for external beam Radiotherapy (EBRT). Radiation treatment of pelvis cancer patients with high-density hip prosthesis needs special attention because of the artifacts created in the computed tomography (CT) field of view and the radiotherapy dosimetry challenges. The accuracy of the treatment planning dose calculation algorithms determines the accuracy of the dose delivered to the patient during radiation therapy. However, the most available algorithms do not accurately model the absorption of high-density metals’ scattering properties and underestimate the resulting dose perturbations. Aim: This study aims to optimize the dose distribution of prostate 3D conformal treatment, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in an in-house metallic hip prosthesis phantom. Methods and materials: In this study, an ionization chamber and Gafchromic (EBT3) films were used to physically measure the prostate point dose in an in-house pelvic phantom. The pelvic phantom was irradiated on the Linac with four static fields, namely, (1) anterior field, (2) posterior field, (3) right lateral field passing through the bone of the normal hip and (4) left lateral passing through the hip prosthesis. IMRT and VMATs plans were also generated on the phantom. The phantom was also irradiated with IMRT and VMATs plan. The use of single arc versus two arcs with avoidance sector were also evaluated. The phantom consists of different materials; Nylon-12 (a solid water-equivalent material) to simulate the prostate with a central cavity to accommodate an ionization chamber and film, superflab gel bolus to simulate human soft tissue, dental wax to simulate human soft tissue, bone anatomy for the right hip and a titanium implant to replace the bony structure of the left hip. For the static fields, an in-house pelvic phantom was simulated using the EGSnrc Monte Carlo code, and 6 and 15 MV photon energies were employed as in an experimental setting. The prostate point doses computed by the Treatment Planning System (TPS), measured using ionisation chamber, and Gafchromic EBT3 film were compared with the prostate point doses simulated by Monte Carlo code. Results and discussion: The novel phantom was constructed using superflab gel bolus, Nylon-12, dental wax, pig bone insert and a titanium alloy hip replacement. The radiological equivalence of the superflab gel bolus and dental wax was determined employing linear attenuation coefficients and then compared to an RW3 Solid water phantom. EGSnrc Monte Carlo (MC) code was used in this study. Before using Monte Carlo codes, they need to be validated by comparing the Linear accelerator Monte Carlo simulated dose distribution with the experimental data measured in a Linear accelerator using water and ionization chamber for 6 MV and 15 MV photon beams of different field sizes. The EGSnrc dose distributions were compared with the experimental measurements using a gamma analysis, employing a 2 %/2 mm distance-to-agreement criterion. The EGSnrc Monte Carlo calculated dose distribution agreed well with experimental measurements within 2 %. The MC beam model was then used to compute the dose distribution in an in-house pelvic phantom. The comparison of the measurements between the TPS calculated prostate point dose and ionization chamber for the 6 MV and 15 MV photon beams was: anterior (gantry 0°) 1.8 % and -0.5 %; posterior (gantry 180°) 1.7 % and -0.2 %; left lateral (gantry 90°) 6.3% and 4.2 %; right lateral (gantry 270°) -2.2 % and -2.1 % respectively. Results obtained for Gafchromic EBT3 film measured doses were: anterior 2.3 % and 1.3 %; posterior -0.9 % and 0.2 %, left lateral 4.5 % and 3.5 %; right lateral -2.1 % and -2.5%, for the 6 MV and 15 MV photon beams, respectively. Consequently, results obtained for comparison of TPS, ion chamber and Film with MC simulated doses were: anterior 3.9 %, -2.1 and -1.6% %; posterior 1.8 %, -0.1% and -2.7 %; left lateral -0.2 %, 6.5 % and 4.7 %; right lateral 0.4 %, -2.6% and -2.5 %, for the 6 MV photon beam. And for 15 MV photon beam the results were: anterior 1.9 %, -3.8 and -0.6%; posterior 2.0 %, -2.3 % and -2.2 %; left lateral 0.5 %, 3.7 % and 2.9 %; right lateral 0.4 %, -2.4 % and -2.9 %. Monte Carlo simulations and film measurements have a statistically significant difference of p<0.001, with the film measurements having a higher value than MC simulations except on the left lateral field. Monte Carlo simulations and ionization chamber measurements also show a significant difference of p<0.001, with the ionization chamber having a higher value than the MC simulation, except for the left lateral field passing through the hip prosthesis. The comparison of the measurements between the TPS calculated prostate point dose with ionization chamber and Gafchromic EBT3 film for the 6 MV IMRT plan of the beam passing through the prosthesis was 2.2 % and 3.3%, respectively. While the IMRT plan with avoided beam was 1.9 % and 3.1% for ionization chamber and Gafchromic EBT3 film, respectively. The comparison of the measurements between the TPS calculated prostate point dose for the 6 MV VMAT plan without avoiding for the beam passing through the prosthesis was 1.1 % and 2.2 % for ionization chamber and Gafchromic EBT3 film, respectively. While for VMAT plan with avoided sector as 3.0 % and 4.0% for ionization chamber and Gafchromic EBT3 film, respectively. The test suggested a significant difference of p=0.0001 between the distribution of film measurements and TPS calculated dose. Meanwhile, for ionization chamber measurements and TPS calculated dose; the test indicated a significant difference between ion chamber measurements and TPS calculated dose with a significant level of less than 0.001. in addition, MC simulated dose and TPS calculated dose; the test shows a percentage difference of -0.2 % and 0.5 % for 6 MV and 15 MV photon beams in the lateral field that passes through the prosthesis. The test indicated the significant difference of p=0.001 which is slightly lower compared to the other comparisons. Conclusion: The dual dosimetric pelvic prosthesis phantom is easy to assembly and is more convenient for second dose check for patients with hip prostheses. Through the use of the pelvic phantom, it was possible to measure the prostate point dose using ionization chamber and films. The TPS overestimated the prostate point dose because the treatment planning algorithm could not accurately determine the CT number and the electron density of the prosthesis due to the limitation on the CT scanner. The maximum deviation calculated in this study for TPS, ionization chamber Gafchromic EBT3 films when compared to Monte Carlo simulated dose comes from the lateral fields passing through the prosthesis for both 6 MV and 15 MV photon beams.
Electrocatalytic detection of biomarkers of tuberculosis and cervical cancer
(University of the Witwatersrand, Johannesburg, 2024-07) Peteni, Siwaphiwe; Ozoemena, Kenneth Ikechukwu
The need for simpler, low cost and efficient diagnostic methods remains a matter of urgency. This has opened numerous streams of research. Electrochemistry is a simple, cost effective and efficient method that has been used for the detection of several diseases such as tuberculosis (TB) and human papilloma virus (HPV). TB has been ranked amongst the most problematic diseases in HIV/AIDS burdened communities, this alone calls for concern. Biomarkers of TB not only indicate mycobacterium infection but can also assist in the early detection of TB which is highly beneficial for the infected person and the health care system. HPV is the causative agent for cervical cancer. Cervical cancer is ranked as the fourth disease that causes mortality amongst women. With that in mind, HPV-16 L1 early detecting means possible early detection of cervical cancer. In this thesis, methyl nicotinate (MN), which is one of TB’s biomarkers was detected in phosphate buffer solution (PBS, pH 6.0) and commercial human serum using cobalt nanoparticles supported on carbon derived from trimesic acid (TMA) (abbreviated as Co-NPs@CTMA) and biphenyldicarboxylic acid (BPDC) abbreviated as Co-NPs@CBPDC) as electrocatalysts. These electrocatalysts were obtained using microwave-assisted metal-organic framework process with TMA and BPDC as ligands. XRD data showed that these electrocatalysts are cobalt nanoparticles with dominant {111} and {200} phase with traces of cobalt oxide (CoO). XPS and Raman data showed that Co-NPs@CBPDC is defect-rich compared to the Co-NPs@CTMA counterpart. BET showed that CoPs@CBPDC has higher surface area and pore size and volume than the Co-NPs@CTMA catalyst. Both electrocatalysts showed reversible cobalt nanoparticle oxidation and reduction reactions, in the absence and in the presence of the MN, thereby allowing for a facile indirect electrochemical detection of this biomarker. The calibration curves showed low limit of detection (LoD) of 0.47 and 0.147 µM for Co-NPs@CTMA and Co-NPs@CBPDC, respectively. The higher performance of the latter is attributed to its enhanced physico-chemical properties compared to the former. Next, HPV-16 L1, which is the conventional high-risk antigen that is present in cervical cancer, was detected using onion-like carbon (OLC) and polyacrylonitrile fibre integrated with OLC (OLC-PAN) as electrode platforms. Two electrode platforms were used; onion-like carbon (OLC) and its polyacrylonitrile (OLC-PAN) composites. Both platforms led to the detection in a wide linear concentration range (1.95 fg/ml to 50 µg/ml), excellent sensitivity (>5.2 µA/log([HPV-16 L1, fg/mL]) and ultra-low detection of ca. 1.0 and 1.4 fg/ml for OLC-PAN and OLC-based immunosensors, respectively. The high specificity of detection was proven by experimenting with an anti-Ovalbumin antibody (anti-Ova) and native Ovalbumin protein (Ova). An immobilized antigenic HPV-16-L1 peptide showed insignificant interaction with anti-OVA in contrast with the excellent interaction with anti-HPV-16 LI antibody. The immunosensors showed satisfactory stability of ~ 3 days of re-usability. The application of the immunosensor as a potential point-of-care diagnostic (PoC) device was investigated with the screen printed carbon electrode which showed the ability to detect ultra-low (~ 0.7 fg/ml) and high (~ 12 µg/ml) concentrations. This study opens the door of opportunity for further investigation with other electrode platforms and realization of PoC diagnostic devicesfor screening and testing of HPV biomarker for cervical cancer.
The effect of cholesterol depletion on TGF-ß-induced epithelial-mesenchymal transition in pancreatic cancer cells
(University of the Witwatersrand, Johannesburg, 2024-06) Breytenbach, Andrea; Kaur, Mandeep
Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic cancer that relies on the epithelial to mesenchymal transition (EMT) program for its spread. EMT is a cell plasticity program that involves the reorganization of cell structure as cells transition from an epithelial to a mesenchymal phenotype. The dysregulated cholesterol metabolism resulting from metabolic reprogramming in PDAC is thought to play a role in EMT by affecting EMT-related signalling pathways. However, no publication has yet investigated the impact of EMT on cholesterol content in PDAC. To shed light on these dynamics, EMT was induced in PANC-1 cells using TGF-β1, thereafter the effect of cholesterol-depleting agents (KS-01 and methyl-β-cyclodextrin) alone or in combination with chemotherapeutic agents (Gemcitabine (GEM) and 5-Fluorouracil (5-FU)) on cholesterol content, EMT state, drug resistance, and invasion were investigated. Our results showed that mesenchymal cells rely on reduced membrane cholesterol levels, synthesis, and uptake, while storing more cholesterol and promoting efflux. EMT also promoted drug resistance via upregulation of ABCB1 expression and reduced hENT1 expression. Targeting cholesterol using cyclodextrins promoted a cholesterol compensatory mechanism, leading to a hybrid EMT state, drug resistance, and metastatic potential. Treating mesenchymal PANC-1 cells with GEM or 5-FU monotherapies were seen to promote EMT-transcription factors, as well as promote cholesterol efflux, synthesis, and import, an unexpected result as these chemotherapeutic agents are not known to affect cholesterol. When GEM was combined with KS-01, drug resistance, invasion, EMT-transcription factors, vimentin, and E-cadherin was promoted indicating the promotion of a hybrid EMT state. Interestingly however, combining KS-01 with 5-FU resulted in an interplay that was seen to mitigate the EMT-promoting effects typically associated with cholesterol depletion alone. The exact mechanism linking the cholesterol compensatory mechanism to EMT remains complex and unknown. Based on work presented in this dissertation, it is proposed that targeting cellular cholesterol should be continued to be investigated, particularly in understanding the repercussions of the use of cholesterol depleting agents for the treatment of other disorders in patients with PDAC.
Modelling and analysis of COVID-19 outspread at micro-levels using spatial autocorrelation: Case of eThekwini
(University of the Witwatersrand, Johannesburg, 2024-09) Ngubane, Samukelisiwe; Chimhamhiwa, Dorman; Adam, Elhadi
The alarming effects of the COVID-19 pandemic on different socio-economic spheres have been felt across the globe. These destructive effects have prompted plenty of research to understand and control the coronavirus pandemic. Notably, one strategic method of mitigating the effects of the coronavirus epidemic has been the utilisation of spatial and geostatistical models to gain insights into the potential predictors of the prevalence of the coronavirus. Considering the above, it was the aim of this study to explore the use of advanced geospatial modelling and analysis techniques, including Moran’s I, spatial error models, spatial lag models, MGWR, and GWR for analysing and modelling the settlement level determining factors of COVID-19 incidence within the eThekwini Metro to inform effectual micro-level planning. Notably, the lack of micro-level modelling of COVID-19 prevalence predictors also motivated the undertaking of this study. To the above aim, the objectives of the research were to utilise spatial autocorrelation to map the granular level COVID-19 spatial distribution over the 3rd wave in the eThekwini Metro, compare the applicability of global and local models in analysing and modelling micro-level COVID-19 incidence, analyse the spatial dependence of the occurrence of COVID-19 on local level variables through Moran’s I and to spatially model the effects of significant local-level determinants on COVID-19. The incidence of COVID-19 cases for the 3rd wave, which was from the 2nd of May 2021 to the 11th of September 2021, was analysed and modelled. The Moran’s I result illustrated that COVID-19 incidence within the eThekwini settlement places had a positive spatial autocorrelation, with a Moran’s I value of 0.14 and a p-value of 0.00. Also, the MGWR model's local R2 value was greater (72.5%) as compared to the other models. Moreover, economic wellness score, the sum of TB cases and population density came out as the significant determining factors of settlement level incidence of COVID-19. This research report offers a great foundation for gaining insights into the applicability of advanced geospatial models in guiding targeted COVID-19 interventions at lower levels.
Investigating the DNA methylation status of the PXDN and PXDNL promoter regions in OSCC cell lines
(University of the Witwatersrand, Johannesburg, 2024-06) Sebastian, Mistral; Mavri-Damelin, Demetra
Background: Oesophageal squamous cell carcinoma (OSCC) is the most prevalent form of oesophageal cancer in South Africa. Aberrant DNA methylation is a well-established epigenetic mechanism involved in various cancers, including OSCC. This study focuses on the DNA methylation status of the peroxidasin (PXDN) and perodixasin like (PXDNL) promoter regions and the expression of PXDN and PXDNL in OSCC cell lines. PXDN consolidates the basement membrane through collagen IV unit oligomerization, influences epithelial-mesenchymal transition and correlates with poor prognosis in various cancers. PXDNL modulates the extracellular matrix (ECM) by antagonising PXDN. Since PXDNL shares domains with PXDN, that allow PXDN to interact with the ECM, it is speculated that PXDNL may possess other ECM modulation roles that require further elucidation. Dysregulated PXDNL expression also correlates with poor cancer prognosis. To date, within the context of South African derived OSCC cell lines, no studies pertaining to the DNA methylation status of the PXDN and PXDNL promoter regions and the expression of PXDN and PXDNL have been carried out. Aim: The aim of this project was to investigate the DNA methylation status of the PXDN and PXDNL promoter regions and observe PXDN and PXDNL expression in the SNO and WHCO5 OSCC cell lines. Methods: PXDN and PXDNL localisation was observed using immunofluorescence microscopy; expression of PXDN and PXDNL was quantified using western blotting and the DNA methylation status of the PXDN and PXDNL promoters was assessed using methylation specific PCR and bisulfite sequencing, respectively. Results: Immunofluorescence microscopy results indicated that both cell lines show varying degrees of PXDN and PXDNL expression. In addition, these results also showed that PXDN and PXDNL localise in the ECM. The western blotting results established that these cell lines express the canonical version of PXDN and possibly a PXDNL isoform (146kDa). Methylation specific PCR has shown that the promoter region of PXDN is differentially methylated across both cell lines. The sequencing results of the bisulfite converted PXDNL promoter region were unsuccessful. Hence, bisulfite sequencing requires further optimisation before the DNA methylation status of the PXDNL promoter region can be determined. Conclusion: This study is the first to show the novel finding that PXDN and PXDNL are expressed in South African derived OSCC cell lines. Within the context of OSCC, further investigation is warranted in order to elucidate the underlying mechanisms that these proteins play a role in. In addition, further study may determine whether a correlation exists between PXDN and PXDNL promoter methylation, protein expression as well as prognosis and whether these aspects should serve as novel markers for diagnosis and therapy. This may subsequently lead to increased OSCC patient survival rates by contributing to early diagnosis of OSCC and efficacious targeted therapeutic intervention.
Identifying Markers of Differentiation in Monocyte-Derived-Macrophages
(University of the Witwatersrand, Johannesburg, 2024-08) Gibson, Matthew Leo; Cronjé, Marianne; Gentle, Nikki
The importance of monocytes and monocyte-derived macrophages (MDMs) in both adaptive and innate immunity makes their study a topic of interest. Monocytes differentiate into macrophages through transcriptomic alterations, resulting in extensive changes in gene expression. Macrophage colony stimulating factor (M-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF) are the two primary cytokines that stimulate this differentiation, and are known to cause partial polarisation towards the M2 and M1 macrophage subtypes, respectively. However, the degree to which this polarisation takes place is not well-characterised. Therefore, this study aimed to use a computational approach to identify the differences and similarities in gene expression changes in macrophages induced with M-CSF and GM-CSF. RNA sequencing data for three human donors was obtained through EBI and used to quantify gene expression changes associated with M-CSF or GM-CSF treatment. Differential gene expression analysis was performed to identify the genes that were differentially expressed as a result of either treatment relative to the untreated monocytes. Over-representation analysis was used to determine the biological processes in which the differentially expressed genes (DEGs) were involved. Finally, transcription factors were identified within the lists of DEGs, as well as the genes encoding their known protein-protein interacting partners. Treatment with M-CSF and GM-CSF induced 4 072 and 4 399 DEGs, respectively, 2 734 of which were common. An examination of these DEGs revealed that the resultant macrophages lacked changes in expression of genes commonly associated with the M1 and M2 polarisation states. An investigation of the DEGs involved in myeloid cell differentiation and the regulation of inflammatory response revealed CCR2, IGF1 and INHBA to be inversely regulated by the two treatments. Furthermore, nine uniquely differentially expressed transcription factors involved in these biological processes were identified, each of which may be contributing to the lack of complete polarisation following differentiation. These results revealed that M-CSF and GM-CSF-induced macrophages, in the absence of activation, experience highly similar gene expression changes and lack changes in the expression of key polarisation marker genes.
Synthesis and characterization of onion-like carbons for adsorption of tartrazine dye in water
(University of the Witwatersrand, Johannesburg, 2024-08) Cwayi, Herbert Qaqambile; Maubane-Nkadimeng, Manoko S.; Coville, Neil J.; Maboya, Winny K.
Industrial effluent often can contain a significant amount of synthetic dyes. The discharge of wastewater containing dyes into water streams without proper treatment consequently enters the soil and disturbs the aquatic and terrestrial life. Several wastewater treatment technologies have been proposed that can efficiently reduce the amount of synthetic dyes from the environment, in particular azo dyes. Among all the existing technologies for wastewater treatment, physical adsorption is a popular technology because it is inexpensive, simple, and efficient. The aim of this study is to synthesize, modify, and characterize onion-like carbons (OLCs) derived from four different waste oils for the adsorption of tartrazine dye in water. The OLCs derived from different carbon precursors (waste household oil, restaurant waste oil, engine waste oil, and paraffin oil bath waste) were synthesized using a flame pyrolysis method. The synthesized materials were doped with nitrogen using a chemical vapor deposition technique using 10% ammonia gas as a source of nitrogen. The N-doped OLCs were attached with hydroxyl groups through oxidation reactions to improve their solubility and adsorption efficacy. According to the high-resolution transmission electron microscopy and scanning electron microscopy images, the OLCs from all four-carbon precursor were quasi-spherical, agglomerated, and presented a chain-like structures of multi-layers. The distance between the graphitic layers was found to be 0.32 nm. The average particle size of OLCs was calculated to be 40.2 ± 2.5 nm. Adsorption studies revealed that the initial dye concentration, contact time, and pH of the dye solutions influenced the adsorption capacity of the tetrazine. Nitrogen doping of OLCs increased its capacity to adsorb the tartrazine dye. The nitrogen doped OLCs from household waste oil (H-N-OLCs) and engine waste oil (E-N- OLCs) were used in equilibrium adsorption studies in this work. For a concentration of 20 mg/L of tartrazine dye, an adsorption capacity of 28.9 mg/g was achieved using the N- doped OLCs from household waste oil. The adsorption process follows the pseudo second- order kinetic model. The adsorption isotherm is best fitted to the Freundlich mathematical model. The results obtained show that, the source of oil did not have major effect on the physicochemical properties of OLCs and that incorporation of nitrogen onto carbon matrix enhanced the adsorption of the anionic tartrazine dye in aqueous solution.
Unveiling the biochemical pathway between Type 2 Diabetes Mellitus and early Alzheimer’s disease
(University of the Witwatersrand, Johannesburg, 2024-08) Tooray, Shweta; van der Merwe, Eloise
Research related to Alzheimer's Disease (AD) remains a focal point in neurodegeneration studies. This is due to the severity of AD and the clear necessity for non-palliative treatment approaches, as underscored by the high prevalence of the disease. The combined formation of extracellular senile plaques and neurofibrillary tangles (NFTs) plays a crucial role in the development of the cognitive and behavioural symptoms observed in individuals with AD. Despite extensive research efforts, discovering a definitive cure for the disease remains a challenge. Therefore, it is imperative to explore new perspectives and identify the upstream molecular mechanisms that contribute to the onset of the disease. Metabolic disorders are widely recognized as a significant risk factor for AD. Specifically, the metabolic syndrome, Type 2 Diabetes Mellitus (T2DM), is connected to neurodegeneration by promoting the accumulation of neurotoxins, inducing neuronal stress, affecting synaptic communication, and leading to brain atrophy. Individuals with T2DM have an increased risk of developing dementia, with hyperglycaemia exacerbating the impact of AD by causing mitochondrial dysfunction and oxidative stress through reactive oxygen species (ROS) formation, which are also present in AD. Additionally, patients with T2DM exhibit shorter telomeres linked to cell death, which is an associated risk factor for developing AD. These key pathways involved in connecting T2DM and AD were explored in the current study to enhance the understanding of the early events that precede AD. Glucose uptake was measured and observed to decrease over time as a potentially protective response of the cell. Subsequently, mitochondrial activity, assessed using the Alamar blue assay, was found to be heightened as an initial protective mechanism of Aβ42. This was later overwhelmed by the elevated ROS detected through a Total ROS assay kit, induced by the hyperglycaemic state of T2DM. In turn causing the amount of Aβ42 to become toxic and leading to a decline in mitochondrial DNA (mtDNA) over time as measured through qPCR. Additionally, the increases in ROS induced by hyperglycaemia resulted in oxidative damage to telomeres. Simultaneously, Aβ42 physically hinders telomere-telomerase binding, leading to reduced telomerase activity and consequently, shorter telomeres. Furthermore, this study reveals, for the first time, that the novel glucose-lowering drug (GLD) caused an increase in Aβ42 production in the T2DM cell model, whilst effectively decreasing ROS production over a 24-hour period compared to the untreated cell model. The rise in Aβ42 levels caused by GLD could potentially be working to prevent the increase in hyperglycaemia-induced ROS through its metal chelating antioxidant properties by scavenging ROS, in the presence of oxidative stress associated with T2DM. These findings are indicative of an appealing function of GLD by reducing ROS and thereby impeding the progression towards AD. Hence making GLD an attractive therapeutic option for the treatment and/or prevention of AD.
Comparison of different bioassay methods for the assessment of dose-response relationships of entomopathogens and toxins against Helicoverpa armigera (Hübner, 1809) (Lepidoptera: Noctuidae)
(University of the Witwatersrand, Johannesburg, 2024-11) Mogadingoane, Keitumetse Neo; Bouwer, Gustav
Bioassays are an important tool for developing bioinsecticides against agricultural pests. The aim of this study was to compare two bioassay methods – diet overlay and droplet feeding – to identify the most suitable method for assessing dose-response relationships of entomopathogens and toxins against second instar larvae of Helicoverpa armigera. The toxins used were purified Bacillus thuringiensis Cry1A.105 and Cry2Ab2.820 proteins, the spore-crystal complex (SCC) of B. thuringiensis subspecies kurstaki strain HD-73, and the entomopathogen Helicoverpa armigera nucleopolyhedrovirus (HearNPV). Based on the heterogeneity factor, coefficient of variance (CV) and relative precision, the diet overlay bioassay was determined to be the best fit for use with HD-73 SCC and HearNPV. Suitable bioassay methods could not be determined for the purified B. thuringiensis proteins due to a poor probit model fit and low precision of estimated LC50s and LD50s. Validation of CV and relative precision across bioassays will ensure the most suitable methods are used for sustainable integrated pest management.

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