C.E.J. van Rensburg

Investigation of the Anti-HIV Properties of Oxihumate

A unique process has been developed to convert bituminous coal by controlled wet oxidation followed by base treatment to a water-soluble humate called oxihumate. Oxihumate inhibited HIV-1 infection of MT-2 cells with an IC50 of 12.5 µg/ml. Treatment of free and cell-attached HIV with oxihumate irreversibly reduced infectivity, while the susceptibility of target cells to the virus was not impaired by treatment prior to infection. The infectivity of the HIV particles was inhibited by interference with CD4 binding and the V3 loop-mediated step of virus entry. No viral resistance to oxihumate developed over a 12-week period in vitro. Oxihumate therefore holds promise for the treatment of HIV-infected patients.

Characterization of intracellular activity of antitubercular constituents from the roots of Euclea natalensis

Abstract Naphthoquinones and triterpenes isolated from the roots of Euclea natalensis. A.DC (Ebenaceae) were evaluated for their inhibitory activity against Mycobacterium tuberculosis.. Crude extract, diospyrin and 7-methyljuglone isolated from the plant, exhibited minimum inhibitory concentrations of 8.0, 8.0, and 0.5 µg ml−1, respectively, against M. tuberculosis. H37 Rv (ATCC 27294), a drug-sensitive strain. Minimum inhibitory concentrations (MICs) of 7- methyljuglone against a panel of clinical pan-sensitive and drug-resistant strains of M. tuberculosis. ranged from 0.32 to 1.25 µg/ml. The concentration of 7-methyljuglone that effected a 90% reduction of growth of M. tuberculosis. Erdman within J774.1 macrophages was 0.57 µg/ml. The superior intracellular and extracellular inhibition of M. tuberculosis. by 7-methyljuglone relative to that of the antituberculosis drugs streptomycin and ethambutol suggests that this compound be considered as a lead for further investigations.

Vitamin E protects mononuclear leucocyte DNA against damage mediated by phagocyte-derived oxidants

The protective effects of physiological concentrations (3-12.5 micrograms/ml) of vitamin E (VE, dl-alpha-tocopherol) on the formation of DNA single-strand breaks in mononuclear leukocytes (MNL) in close proximity to activated phagocytes have been investigated in vitro. Human neutrophils, activated by phorbol myristate acetate (PMA), induced DNA-strand breaks in neighbouring lymphocytes. Vitamin E caused dose-related protection of MNL DNA against phagocyte-mediated oxidative damage. This apparently novel protective activity of vitamin E is due primarily to the inhibitory effects of this agent on the generation of reactive oxidants by activated neutrophils and is apparently unrelated to the classical oxidant-scavenging properties of VE.

Antioxidant scavenging potential of South African export herbal teas

The flavonoid content as well as the superoxide anion and hydroxyl radical scavenging activities of water extracts of rooibos ( Aspalathus linearis (Burm. f.) R. Dahlgr.), honeybush ( Cyclopia intermedia E. Mey.) and roselle ( Hibiscus sabdariffa L.), three South African herbal teas which are commercial products exported world-wide, were investigated. The results indicated that the water extracts of rooibos exhibited the best scavenging activity for both the hydroxyl radical and superoxide anion followed by honeybush and then roselle. This seems to be due to the total flavonoid concentration, which was the highest in rooibos and lowest in roselle.

An in vitro Investigation of the Intraphagocytic Bioactivity of Difloxacin, Ciprofloxacin, Pefloxacin and Fleroxacin

In this study the intraphagocytic bioactivity of difloxacin, ciprofloxacin, pefloxacin and fleroxacin was investigated using human neutrophils and a combination of a radioassay, a colony-counting method and a fluorescence microassay which enables us to differentiate between intracellular bacteriostatic and bactericidal mechanisms. Staphylococcus aureus and Listeria monocytogenes were used as the test intraphagocytic microbial pathogens. It was found that difloxacin, ciprofloxacin and to a lesser extent pefloxacin and fleroxacin possess intracellular bacteriostatic activity for S. aureus and L. monocytogenes.

The anti-tumour properties and biodistribution (as determined by the radiolabeled equivalent) of Au-compounds intended as potential chemotherapeutics

The anti-tumour activity of the Au (I) phosphine complex [Au(dppe(2)]Cl was first discovered in the mid 1980s although promising results were obtained it did not pass clinical studies because of its toxicity to organs such as the liver and heart. The aim of this study was to determine whether the two novel gold compounds (MM5 and MM6), selected for this study, have higher selectivity for cancer cells with less toxicity towards normal cells than [Au(dppe)(2)]Cl, and also to determine whether they have improved bio distribution compared to [Au(dppe)(2)]Cl. The Au-compounds as potential chemotherapeutic drugs were evaluated by using radioactive tracers in the in vitro and in vivo studies. Results obtained from these experiments showed that the uptake of these experimental compounds was dependent on their octanol/water partition coefficient. However; the inhibition of cell growth did not correlate with the uptake of these compounds by the cells that were tested. In terms of the total uptake it was found that the compounds that were less lipophilic (MM5, MM6) were taken up less efficiently in cells than those that are more lipophilic. Therefore hydrophilic drugs are expected to have a limited biodistribution compared to lipophilic drugs. This might imply a more selective tumour uptake.

An in vitro investigation of the bioactivities of ciprofloxacin and the new fluoroquinolone agents clinafloxacin (CI-960) and PD 131628 against Mycobacterium tuberculosis in human macrophages.

In this study the intracellular bioactivity of ciprofloxacin and the new fluoroquinolone agents clinafloxacin (CI-960) and PD 131628 against Mycobacterium tuberculosis (H37Rv) was compared with rifampicin using human macrophages. Monocyte-derived macrophages were infected with M. tuberculosis in the presence of 10% autologous serum and treated with the antibiotics for 2 days, either immediately after infection or 3 days post-infection. The survival of the intracellular microorganisms was determined using the BACTEC tuberculosis system. Clinafloxacin, although not as active, compared favourably with rifampicin at concentrations ranging from 0.1 to 5 micrograms/ml in both systems, whereas PD 131628 performed reasonably well only when added directly after infection. However, ciprofloxacin was relatively unimpressive with intracellular bioactivity detected only with the highest concentration used (5 micrograms/ml). The ability of clinafloxacin, but not PD 131628, to inhibit mycobacteria after most of the organisms have escaped from the fused phagosomes emphasizes the importance of using a prolonged incubation time after infection when screening new antituberculosis drugs for intracellular bioactivity.

Effects of benoxaprofen on the binding to and inactivation of leucoattractants by human polymorphonuclear leucocytesin vitro

Benoxaprofen was previously found to inhibit the random and leucoattractant-induced migration of human polymorphonuclear leucocytesin vitro by a pro-oxidative mechanism [1]. In this study the effects of benoxaprofen on the binding to PMNL of the synthetic chemotactic tripeptide FMLP, on the oxidative inactivation of this leucoattractant by PMNL and on PMNL chemotaxis, chemokinesis and orientation in an FMLP gradient have been investigated. At concentrations of 10−5M (3 μg/ml) benoxaprofen inhibited PMNL random and leucoattractant-induced migration and increased PMNL membraneassociated oxidative metabolism and cellular auto-oxidation. These effects of benoxaprofen on PMNL migration and auto-oxidation were prevented by the anti-oxidant cysteine (10−3M). Benoxaprofen inhibited both FMLP-induced chemotaxis and chemokinesis but did not affect the binding of radiolabelled FMLP to PMNL or orientation of the cells in a positive gradient of the leucoattractant. Benoxaprofen at concentrations of 5×10−5M significantly increased the oxidative inactivation of FMLP by PMNL. Inhibition of PMNL migration by benoxaprofen is mediated by the two different pro-oxidative mechanisms, viz. a cell-directed auto-oxidative mechanism and potentiation of the oxidative inactivation of leucoattractants by PMNL.