Browsing by Author "Byamukama, Robert"

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    Antimycobacterial Activity of the Extract and Isolated Compounds From the Stem Bark of Zanthoxylum leprieurii Guill. and Perr.
    (SAGE Publications, 2021-08-24) Oloya, Benson; Namukobe, Jane; Heydenreich, Matthias; Ssengooba, Willy; Schmidt, Bernd; Byamukama, Robert
    Zanthoxylum leprieurii Guill. and Perr. (Rutaceae) stem bark is used locally in Uganda for treating tuberculosis (TB) and cough-related infections. Lupeol (1), sesamin (2), trans-fagaramide (3), arnottianamide (4), (S)-marmesinin (5), and hesperidin (6) were isolated from the chloroform/methanol (1:1) extract of Z. leprieurii stem bark. Their structures were elucidated using spectroscopic techniques and by comparison with literature data. Furthermore, the extract and isolated compounds were subjected to antimycobacterial activity. The extract exhibited moderate activity against the susceptible (H37Rv) TB strain, but weak activity against the multidrug resistant (MDR)-TB strain with minimum inhibitory concentrations (MICs) of 586.0 and 1172.0 μg/mL, respectively. Compound 3 (trans-fagaramide) showed significant antimycobacterial activity against the susceptible (H37Rv) TB strain (MIC 6 μg/mL), but moderate activity against the MDR-TB strain (MIC 12.2 μg/mL). Compounds 2, 5, 6, and 1 showed moderate activities against the susceptible (H37Rv) strain (MIC 12.2-98.0 μg/mL) and moderate to weak activities against theMDR-TB strain (MIC 24.4-195.0 μg/mL). This study reports for the first time the isolation of compounds 1 to 6 from the stem bark of Z leprieurii. trans-Fagaramide (3) may present a vital template in pursuit of novel and highly effective TB drugs.
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    Antimycobacterial activity, acute toxicity, and characterisation of compounds from selected medicinal plants used in the treatment of Tuberculosis in Uganda
    (Natural Product Research Network for East and Central Africa (NAPRECA), 2021-11-25) Oloya, Benson; Namukobe, Jane; Heydenreich, Matthias; Ssengooba, Willy; Afayoa, Mathias; Schmidt, Bernd; Byamukama, Robert
    Tuberculosis (TB) is one of the leading causes of death globally, and the rise in drug-resistant forms of TB has become a significant threat (WHO, 2020). Subsequently, it is crucial to explore new, effective and safe anti-TB agents. Several plant species are used in traditional medicine for the treatment of TB in Africa. In Uganda, Acacia hockii, Albizia coriaria, Combretum molle, Warburgia ugandensis, and Zanthoxylum leprieurii are among the plant species used locally to treat tuberculosis, and they could have antimycobacterial compounds that may justify their traditional use but without scientific validation of their bioactivity and toxicity (Anywar et al., 2020; Bunalema et al., 2014; Muthee et al., 2011; Tabuti et al., 2010). This study aimed to conduct antimycobacterial activity and acute toxicity of the selected plant species’ crude extracts and isolate compounds from the stem bark of Z. leprieurii. The aqueous and methanol/dichloromethane (DCM) (1:1) extracts of each of the selected plant species and the isolated compounds were tested for antimycobacterial activity using microplate alamar blue assay (Lawal et al., 2011). For acute toxicity, a single dose (2000 mg/kg) of the aqueous extracts was orally administered to each adult female Winstar albino rat and then observed for 14 days (Lipnick et al., 1995; OECD, 2008). At the end of the experiment, blood samples were collected for haematological and biochemical analyses, while tissue samples from vital organs were collected for histopathological analysis. Isolation and purification of the compounds from the Z. leprieurii stem bark extract were performed using repeated column chromatography. Structure elucidation of the compounds was carried out using spectroscopic methods and by comparison with literature data. Aqueous extracts showed moderate-weak activity against the susceptible (H37Rv) TB strain and weak activity against the multidrug-resistant (MDR) TB strain. Methanol/DCM extracts showed significant-moderate activity against the susceptible (H37Rv) TB strain and moderate-weak activity against the MDR TB strain. After the acute toxicity tests, one mortality and significant lesions in the examined organs following histopathological analyses were recorded from the A. coriaria treated group. Still, the LD50 of all the extracts was estimated to be above 2000 mg/kg. Lupeol, sesamin, trans-fagaramide, arnottianamide, (S)-marmesinin, and hesperidin were isolated from the chloroform/methanol (1:1) extract of Z. leprieurii stem bark, and trans-Fagaramide showed significant antimycobacterial activity against the susceptible (H37Rv) TB strain (Oloya et al., 2021). A. hockii methanol/DCM extract had significant antimycobacterial activity against the susceptible (H37Rv) TB strain, and the methanol/DCM extracts of all the other selected plants had good antimycobacterial activity. The selected plant extracts except A. coriaria exhibited low acute toxicity levels and could be safe for formulations into herbal products. trans-Fagaramide may present a vital template in pursuit of novel and highly effective TB drugs.
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    Phytochemical screening, antimycobacterial activity and acute toxicity of crude extracts of selected medicinal plant species used locally in the treatment of tuberculosis in Uganda
    (Springer Nature, 2022-02-17) Oloya, Benson; Namukobe, Jane; Ssengooba, Willy; Afayoa, Mathias; Byamukama, Robert
    Background Tuberculosis (TB) is one of the leading causes of death globally, and the rise in drug-resistant forms of TB has become a significant threat. Subsequently, it is crucial to explore new, effective and safe anti-TB agents. This study aimed at conducting phytochemical screening, antimycobacterial activity, and acute toxicity of the selected plant species’ crude extracts to assess their toxicological potentials and efficacies against TB. Methods The aqueous and methanol/dichloromethane (DCM) (1:1) extracts of each selected plant species were subjected to phytochemical screening and antimycobacterial activity using microplate alamar blue assay. For acute toxicity, a single dose (2000 mg/kg) of the aqueous extracts was orally administered to each animal following the Organization for Economic Cooperation and Development (OECD) guidelines No. 425 and then observed for 14 days. The animals were closely observed on the general behavior and clinical signs of toxicity, and body weights were recorded. After the termination of the experiment, hematological, biochemical, and histopathological analyses were performed. Results The extracts contained alkaloids, flavonoids, tannins, saponins, steroids, terpenoids, resins, cardiac glycosides, phenolic compounds, and coumarins. Aqueous extracts showed moderate to weak activity against the susceptible (H37Rv) M. tuberculosis strain and weak activity against the MDR-TB strain with Minimum Inhibitory Concentrations (MIC μg/mL) ranging from 293.0–2344.0 and 1172.0–4688.0, respectively. Methanol/DCM extracts showed significant to moderate activity against the susceptible TB strain and moderate to weak activity against the MDR-TB strain with MIC (μg/mL) ranging from 98.0–586.0 and 293.0–781.0, respectively. One mortality was recorded from the A. coriaria treated group following the acute toxicity tests, but the LD50 of all the extracts was estimated to be above 2000 mg/kg. Histopathological analyses did not show any significant lesions in the examined organs except those from the A. coriaria treated group. Conclusion Phytochemical screening of the extracts revealed the presence of alkaloids, tannins, saponins, flavonoids, steroids, terpenoids, resins, cardiac glycosides, phenolic compounds, and coumarins. All the methanol/DCM extracts of the plant species studied have promising antimycobacterial activity. The selected plant extracts studied exhibited low acute toxicity levels except for A. coriaria and could be safe for formulations into herbal products.
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    Two new compounds and the anti-mycobacterial activity of the constituents from Zanthoxylum leprieurii root bark
    (Elsevier Ltd., 2023-02-08) Oloya, Benson; Namukobe, Jane; Heydenreich, Matthias; Ssengooba, Willy; Martin, Johannes; M¨oller, Heiko Michael; Schmidt, Bernd; Byamukama, Robert
    The emergence of resistance to the existing TB drugs necessitated a search for new anti-mycobacterial compounds from Z. leprieurii root bark, which is used locally for the treatment of tuberculosis (TB) in Uganda. Two new compounds: (E)-N-isobutyl-3-(4-((3-methylbut-2-en-1-yl)oxy)phenyl)acrylamide (1) and 4-(5,5a,6,8,8a,9-hexahydrofuro[3′,4′:6,7]-naphtha[2,3-d][1,3]dioxol-5-yl)-2-methoxyphenol (2), were isolated from the dichloromethane (DCM) extract. In addition, sixteen known compounds were isolated from the DCM and methanol extracts, with two of them, N-isobutylcinnamamide (9) and (E)-3-(4-hydroxy-3-methoxyphenyl)-N-isobutylacrylamide (14), being reported from a natural source for the first time. The structures of the isolates were elucidated by a combination of spectroscopic techniques. The isolated compounds were subjected to anti-mycobacterial activity testing using the microplate Alamar blue assay (MABA). Five compounds, 10 (MIC, 0.98 μg/mL), 11 (MIC, 7.82 μg/mL), 12 (MIC, 1.95 μg/mL), 13 (MIC, 3.91 μg/mL), and 14 (MIC, 3.91 μg/mL) exhibited significant anti-mycobacterial activities against the susceptible (H37Rv) strain and could provide vital templates for developing new and highly effective TB drugs. Also, compounds 4 (MIC, 62.50 μg/mL), 7 (MIC, 62.50 μg/mL) and 16 (MIC, 62.50 μg/mL) exhibited moderate activity against H37Rv.