Polymyxin E2 Sulfate

Combinations of polymyxins and phytochemicals were tested for antimicrobial activity against two gram-negative bacteria. Various degrees of potentiation were found against Pseudomonas aeruginosa and Escherichia coli with (E)-2-hexenal and indole. Three-compound combinations were found to further increase the activity of polymyxin B sulfate and colistin methanesulfonate against both bacteria. Combinations with colistin against P. aeruginosa resulted in the highest degree of potentiation, with a 512-fold increase in colistin antimicrobial activity. These results indicate the potential efficacy of phytochemical combinations with antibiotics to enhance total biological activity.

Interleukin-6 (IL-6) is a multifunctional cytokine that is elevated in vivo during acute infection, chronic inflammation, and some hematopoietic malignancies. To understand how IL-6 becomes elevated in vivo, it is important to identify factors that can stimulate its secretion from effector cells. We found that commercial preparations of bovine serum albumin (BSA) stimulated murine macrophages to secrete high levels of IL-6. In fact, BSA was at least as potent as bacterial lipopolysaccharide (LPS) in stimulating IL-6 production. Stimulation was clearly visible at concentrations as low as 20 micrograms/mL and reached saturation at 0.5 to 1 mg/mL albumin, at which concentration 1.1 x 10(6) oil-elicited macrophages produced 6,000 +/- 700 B9 units of IL-6 in an overnight incubation. Prostaglandin E2 production was induced by the same concentrations of BSA. Both resident and oil-elicited peritoneal cells were responsive to the albumin. The stimulatory activity did not derive from contamination of the protein with Escherichia coli LPS; when compared directly with LPS, the response to BSA was more rapid, had a higher amplitude, and was not inhibitable by polymyxin B. In addition, macrophages isolated from C3H/HeJ mice, which have an inherited defect in their ability to respond to LPS, secreted IL-6 in response to BSA but not to LPS. The stimulatory activity was stable to heat, mild acid, and reduction/alkylation and copurified with albumin on Cibachron Blue agarose (Sigma, St Louis, MO) and anti-albumin immunoaffinity chromatography. Comparison of different sources and preparations of albumin showed differences in the levels of IL-6-inducing activity; three different lots of commercial fatty acid-free BSA and one lot of polymer-enhanced BSA stimulated IL-6 secretion by more than 100-fold over basal levels whereas other preparations showed more limited activity. A sample of BSA that was active in vitro caused a marked elevation of IL-6 when injected into BALB/c mice, thus demonstrating inflammatory activity in vivo. When the albumin preparations were fractionated by ion exchange and gel filtration chromatography and then analyzed by sodium dodecyl sulfate-gel electrophoresis and Western blot immunoassay, it was found that the IL-6-inducing activity resided in high molecular weight polymers of albumin. The ability of albumin polymers to stimulate IL-6 production represents a novel mechanism for modulation of this cytokine.

The supernatant of Mycoplasma arginini-infected murine L5178Y T lymphoma cell cultures (SN-L51) synergizes with small concentrations of IFN-gamma to activate murine peritoneal, thioglycollate-elicited macrophages (M phi) to exhibit cytostatic activity against tumor cells. Treatment of M phi with IFN-gamma and SN-L51 sequentially, but not in the reverse order, activates M phi, which indicates that SN-L51 contains a M phi-triggering factor (MTF). MTF activity could be inhibited by small concentrations of prostaglandin E2, but not by polymyxin B. M phi activated by IFN-gamma plus MTF produce cytostatic effects on tumor cells through a nitric oxide-dependent pathway. MTF activity in SN-L51 is associated with infection of L5178Y cells by M. arginini. Mycoplasma-free L5178Y cells do not produce MTF activity, infection of these L5178Y cells with M. arginini generates the activity, and supernatants of pure M. arginini cultures contain MTF activity. MTF activity is thermostable and resistant to acid, dilute alkali, proteases, and nucleases. MTF was partially purified by ammonium sulfate precipitation, chromatography, electrophoresis, and electroelution. On 12.5% SDS-urea gels, MTF activity migrated with a molecular mass of 2.5 to 4 kDa. MTF activity and the silver staining of this band was resistant to proteinase K; however, Coomassie staining of this band was abolished by proteinase K. The combined data suggest that MTF is either a stable peptide or a peptide linked to lipid or carbohydrate.