Pimaricin

Pimaricin, Streptomyces chattanoogensis is an antifungal macrolide polyene that binds to cell membrane sterols. Macrolides belong to a group of antibiotics that bind to the 50S ribosomal subunit and inhibit protein synthesis. Investigations show that the

Safety and efficacy of intrastromal injection of 5% natamycin in experimental fusarium keratitis.[Pubmed:24919100]

J Ocul Pharmacol Ther. 2014 Sep;30(7):543-7.

PURPOSE: To compare the efficacy of combined intrastromal injection and topical natamycin 5% to standard topical therapy alone in an experimental rabbit model of Fusarium keratitis. METHODS: Fungal keratitis was induced in the right eyes of 12 New Zealand rabbits by stromal injection of Fusarium solani spore suspension into the cornea. Four days after inoculation, animals were randomly assigned to 2 different treatment groups (n=6 in each group). The study group received intrastromal injections of natamycin 5% on treatment day 1 and 4, combined with topical natamycin 5% eye drops given hourly between 8:00 and 20:00 for the first 2 days, followed by 4 times daily on days 3-11. The control group received only topical natamycin 5% at identical intervals. Eyes were examined clinically on days 1, 4, 7, and 11 for status of corneal healing, corneal vascularization, and hypopyon. Animals were sacrificed on day 11, and corneas were subjected to histopathological examination. RESULTS: Both groups showed significant improvement in terms of conjunctival hyperemia, size and density of corneal infiltrate, corneal edema, and total clinical score. In the study group, there was a significant improvement in the height of hypopyon in the anterior chamber, while there was also an increased amount of vascularization. CONCLUSIONS: This study showed that intrastromal injection of natamycin 5% combined with topical treatment has little beneficial effect over topical therapy in a Fusarium keratitis rabbit model. The addition of intrastromal injection should be reserved to the most severe or recalcitrant cases.

The negligible effects of the antifungal natamycin on cholesterol-dipalmitoyl phosphatidylcholine monolayers may explain its low oral and topical toxicity for mammals.[Pubmed:25048356]

Colloids Surf B Biointerfaces. 2014 Oct 1;122:202-208.

Natamycin is an effective, broad spectrum antifungal with no reported resistance, in contrast to most antimicrobials. It also exhibits reduced (oral and topical) toxicity to humans, which is probably associated with the lack of effects on mammalian cell membranes. In this paper we employ Langmuir monolayers to mimic a cell membrane, whose properties are interrogated with various techniques. We found that natamycin has negligible effects on Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC), but it strongly affects cholesterol monolayers. Natamycin causes the surface pressure isotherm of a cholesterol monolayer to expand even at high surface pressures since it penetrates into the hydrophobic chains. It also reduces the compressibility modulus, probably because natamycin disturbs the organization of the cholesterol molecules, as inferred with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In mixed cholesterol/DPPC monolayers, strong effects from natamycin were only observed when the cholesterol concentration was 50mol% or higher, well above its concentration in a mammalian cell membrane. For a sterol concentration that mimics a real cell membrane in mammals, i.e. with 25mol% of cholesterol, the effects were negligible, which may explain why natamycin has low toxicity when ingested and/or employed to treat superficial fungal infections.

Genome-wide analysis of the regulation of pimaricin production in Streptomyces natalensis by reactive oxygen species.[Pubmed:24413916]

Appl Microbiol Biotechnol. 2014 Mar;98(5):2231-41.

To investigate the molecular mechanisms that interplay between oxygen metabolism and secondary metabolism in Streptomyces natalensis, we compared the transcriptomes of the strains CAM.02 (DeltasodF), Pimaricin under-producer phenotype, and CAM.04 (DeltaahpCD), Pimaricin over-producer phenotype, with that of the wild type at late exponential and stationary growth phases. Microarray data interpretation was supported by characterization of the mutant strains regarding enzymatic activities, phosphate uptake, oxygen consumption and Pimaricin production.Both mutant strains presented a delay in the transcription activation of the PhoRP system and Pimaricin biosynthetic gene cluster that correlated with the delayed inorganic phosphate (Pi) depletion in the medium and late onset of Pimaricin production, respectively. The carbon flux of both mutants was also altered: a re-direction from glycolysis to the pentose phosphate pathway (PPP) in early exponential phase followed by a transcriptional activation of both pathways in subsequent growth phases was observed. Mutant behavior diverged at the respiratory chain/tricarboxylic acid cycle (TCA) and the branched chain amino acid (BCAA) metabolism. CAM.02 (DeltasodF) presented an impaired TCA cycle and an inhibition of the BCAA biosynthesis and degradation pathways. Conversely, CAM.04 (DeltaahpCD) presented a global activation of BCAA metabolism.The results highlight the cellular NADPH/NADH ratio and the availability of biosynthetic precursors via the BCAA metabolism as the main Pimaricin biosynthetic bottlenecks under oxidative stress conditions. Furthermore, new evidences are provided regarding a crosstalk between phosphate metabolism and oxidative stress in Streptomyces.