Antimycobacterial, immunomodulatory and hepato-protective activities of quinones and organosulphur compounds

Abstract

Tuberculosis is one of the world’s deadliest diseases. It is caused by the bacterium Mycobacterium tuberculosis. Two groups of samples: Quinones and Garlic polysulfide mixtures were assessed for their antituberculosis activity. The microtitre alamar blue (MABA) and microtitre presto blue assays (MPBA), on Mycobacterium tuberculosis were conducted to determine the minimum inhibitory concentrations (MICs). Twenty quinones and six garlic oil polysulfide mixtures were tested for their in vitro antimycobacterial activity and cytotoxicity. The antimycobacterial activity was tested on the H37Rv Mycobacterium tuberculosis strain and the cytotoxicity was tested on primary peripheral blood mononuclear cells and secondary U937 human monocytes. Six quinone samples showed antimycobacterial activity with minimum inhibitory concentrations less than 3.125 μg/ml and one garlic sample had a minimum inhibitory concentration of 2.5 μg/ml. Samples KM 108-1 and IL 143 had selective indices above 8 and KM 140 had a selective index of 55. Twenty quinone samples and six garlic polysulfide mixtures were also evaluated for their immune stimulatory effects as well as their liver protective activity. The immune response was assessed by evaluating the Th1/Th2 cytokine production levels by the peripheral blood mononuclear cells on exposure with various concentrations of the samples. The induced toxicity on Liver cells (C3A - hepatocytes), by acetaminophen, were used to assess the hepatoprotective efficacy of the samples. Three quinone compounds showed immune stimulatory effects (KM94, KM108-1 and KM117), and five showed significant hepatoprotective effects of 60-100% (KM108, KM140, AqsNH4, CB5 and IL107) at ¼ Inhibitory Concentration of 50%. Garlic samples G5 and G6 showed slight immune stimulatory effects, while G6 was found to be the only sample to have hepatoprotective activity of 22%, probably due to the higher amount of diallyl tetrasulfide within the mixture. All the quinone samples were evaluated for their subversive substrate activities on three flavoprotein disulfide reductases: Glutathiol, Mycothiol and Thioredoxin reductase. Glutathiol reductase is the human analog while Mycothiol and Thioredoxin are bacterial analogs. Substrate binding affinity was determined and it was found that quinones act as substrates for all three enzymes with the highest affinity for Thioredoxin reductase. Samples; Aqs and KM80 had half the maximum velocity (Km-value) of lower than 30 μM. It can also be concluded that anthraquinones had a higher affinity to these disulfide enzymes as compared to naphthoquinones.