Antibacterial Activity of Defatted and Nondefatted Methanolic Extracts of Aframomum melegueta K. Schum. against Multidrug-Resistant Bacteria of Clinical Importance.

The antibacterial activity of the extracts of Aframomum melegueta including n-hexane extract (NHE), nondefatted methanol extract (NDME), and defatted methanol extract (DME) was investigated in this study. The NHE exhibited no antibacterial activity. The DME showed higher antibacterial activity than the NDME against the different isolates. At the highest concentration of 10 mg/mL in agar diffusion, NDME produced inhibition zones ranging from 11 to 29 mm against the microorganisms while DME produced inhibition zones ranging from 20 to 40 mm with the concentration of 10 mg/mL against the microorganisms. 0.1 mg/mL of the DME produced inhibition zones ranging between 12 and 14 mm in Aeromonas hydrophila ATCC 35654 and Pseudomonas aeruginosa ATCC 15442, respectively, while none of the isolates were inhibited by the NDME at a concentration of 1 mg/mL or less. In the agar dilution assay, the MICs of the NDME and DME ranged between 0.31 and 10 mg/mL, but more isolates were inhibited at 0.31 mg/mL of DME than those in NDME. In macrobroth assay, the MICs of the NDME ranged between 0.15 and 5.0 mg/mL and the MBCs ranged between 0.63 and 5.0 mg/mL, and the MICs of the DME ranged between 0.08 and 5.0 mg/mL and the MBCs were between 0.31 and 5.0 mg/mL. This study indicated that DME was more active with higher antibacterial activity than the NDME of this plant, and extracting the fatty portion of plant materials prior susceptibility testing would allow plant extracts to be more effective as well as justifying the use of Aframomum melegueta in traditional medicine for the treatment of bacterial infections.

Mechanism of the cytotoxicity of the diazoparaquinone antitumor antibiotic kinamycin F.

The bacterial metabolite kinamycin F, which is being investigated as a potent antitumor agent, contains an unusual and potentially reactive diazo group, a paraquinone, and a phenol functional group. Kinamycin F reacted with glutathione (GSH) in a complex series of reactions which suggested that kinamycin F may have its cytotoxicity modulated by GSH. Consistent with this idea, 2-oxo-4-thiazolidinecarboxylic acid treatment to increase cellular GSH levels and buthionine sulfoximine treatment to decrease GSH levels resulted in decreased and increased kinamycin F cytotoxicity, respectively, in K562 leukemia cells. Kinamycin F weakly bound to DNA and induced DNA damage in K562 cells that was independent of GSH levels. The GSH-promoted DNA nicking induced by kinamycin F in vitro was attenuated by deferoxamine, dimethyl sulfoxide, and catalase, which indicated that DNA damage initiated by this agent occurred in an iron-, hydrogen-peroxide-, and hydroxyl-radical-dependent manner. Electron paramagnetic resonance spectroscopy experiments showed that the GSH/kinamycin F system produced a semiquinone free radical and that the hydrogen peroxide/peroxidase/kinamycin F system generated a phenoxyl free radical. In conclusion, the results indicated that kinamycin F cytotoxicity may be due to reductive and/or peroxidative activation to produce DNA-and protein-damaging species.

In vitro pharmacological interaction of caffeine and first-line antibiotics is antagonistic against clinically important bacterial pathogens.

The in vitro antibacterial activity of pure caffeine powder and its interaction with first line antibiotic against bacterial isolates were investigated with the macrobroth dilution and the checkerboard assay methods. This study showed that caffeine and the antibiotics exhibited various degrees of antibacterial activities. While caffeine had MICs ranging between 67.19 and 268.75 µg/ml, chloramphenicol was characterized by MICs between 0.98 and 31.25 µg/ml, kanamycin - 15.63-62.5 µg/ml, nalidixic acid - 0.49-250 µg/ml, erythromycin - 0.49-62.5 µg/ml, tetracycline - 1.99-62.5 µg/ml and metronidazole - 15.63-31.25 µg/ml. Combining ½ MICs and MICs of caffeine with the antibiotics as well as direct combination of caffeine and the antibiotics resulted in significant reduction of antibiotics' effectiveness. The fractional inhibitory concentration index (FICI) for the combination of ½ MICs of caffeine with different antibiotics showed antagonistic interactions with the antibiotics except kanamycin which had additive and indifferent interactions with caffeine. The FICI of the MICs of caffeine combined with antibiotics showed a reduction in the number of antagonistic interactions as chloramphenicol, nalidixic acid and erythromycin showed some indifferent interactions while kanamycin was the only antibiotic that showed indifferent interaction against all the bacterial isolates. The direct combination of caffeine and the antibiotics resulted in significant antagonistic interactions higher than in the case when caffeine, at the ½ MICs and MICs, was combined with the antibiotics. Although caffeine demonstrated significant antibacterial activity against the selected bacterial isolates, its combination with the selected antibiotics resulted in significant antagonistic interactions. Caffeine should not be combined with antibiotics as this could result in serious therapeutic failure and, possibly, drug toxicity in vivo.

Kinamycins A and C, bacterial metabolites that contain an unusual diazo group, as potential new anticancer agents: antiproliferative and cell cycle effects.

The cell growth and cell cycle inhibitory properties of the bacterial metabolites kinamycin A and kinamycin C were investigated in an attempt to determine their mechanism of action and to develop these or their analogs as anticancer agents. Both kinamycin A and kinamycin C have a highly unusual and potentially reactive diazo group. Even with short incubations, both the kinamycins were shown to have very potent cell growth inhibitory effects on either Chinese hamster ovary or K562 cells. Kinamycin C induced a rapid apoptotic response in K562 cells. The cell cycle analysis results in synchronized Chinese hamster ovary cells treated with kinamycin A revealed that they only displayed a G1/S phase block upon entry to the second cycle. Both kinamycins inhibited the catalytic decatenation activity of DNA topoisomerase IIalpha, but neither kinamycin acted as a topoisomerase II poison. Their inhibition of catalytic activity was not correlated with cell growth inhibitory effects. Pretreatment of the kinamycins with dithiothreitol protected the topoisomerase IIalpha activity, which suggested that they may be targeting critical protein sulfhydryl groups, either through reaction with the quinone or with an activated electrophilic diazo group. Neither kinamycin A nor kinamycin C intercalated into DNA, nor were they able to cross-link DNA. Although the cellular target(s) of the kinamycins has yet to be identified, the cluster map analysis, and the cell cycle and proapoptotic effects suggest that kinamycin C has a target different than other established anticancer compounds.