Assessment of free fatty acids and cholesteryl esters delivered in liposomes as novel class of antibiotic.

BACKGROUND: Healthcare associated infections (HAI) with multidrug-resistant (MDR) bacteria continue to be a global threat, highlighting an urgent need for novel antibiotics. In this study, we assessed the potential of free fatty acids and cholesteryl esters that form part of the innate host defense as novel antibacterial agents for use against MDR bacteria. METHODS: Liposomes of six different phospholipid mixtures were employed as carrier for six different fatty acids and four different cholesteryl esters. Using a modified MIC assay based on DNA quantification with the fluoroprobe Syto9, formulations were tested against Gram-positive and Gram-negative bacteria implicated in HAI. Formulations with MIC values in the low µg/mL range were further subjected to determination of minimal bactericidal activity, hemolysis assay with sheep erythrocytes, and cytotoxicity testing with the human liver cell line HepG2. The potential for synergistic activity with a standard antibiotic was also probed. RESULTS: Palmitic acid and stearic acid prepared in carrier 4 (PA4 and SA4, respectively) were identified as most active lipids (MIC against MDR Staphylococcus epidermidis was 0.5 and 0.25 µg/mL, respectively; MIC against vancomycin resistant Enterococcus faecalis (VRE) was 2 and 0.5 µg/mL, respectively). Cholesteryl linoleate formulated with carrier 3 (CL3) exhibited activity against the S. epidermidis strain (MIC 1 µg/mL) and a Pseudomonas aeruginosa strain (MIC 8 µg/mL) and lowered the vancomycin MIC for VRE from 32-64 µg/mL to as low as 4 µg/mL. At 90 µg/mL PA4, SA4, and CL3 effected less than 5 % hemolysis over 3 h and PA4 and CL3 did not exhibit significant cytotoxic activity against HepG2 cells when applied at 100 µg/mL over 48 h. CONCLUSIONS: Our results showed that selected fatty acids and cholesteryl esters packaged with phospholipids exhibit antibacterial activity against Gram-positive and Gram-negative bacteria and may augment the activity of antibiotics. Bactericidal activity could be unlinked from hemolytic and cytotoxic activity and the type of phospholipid carrier greatly influenced the activity. Thus, fatty acids and cholesteryl esters packaged in liposomes may have potential as novel lipophilic antimicrobial agents.

Assessment of epithelial innate antimicrobial factors in sinus tissue from patients with and without chronic rhinosinusitis.

BACKGROUND: Airway secretions contain endogenous antimicrobial factors (AMFs) that contribute to the innate host defense of the respiratory tract. Antibacterial peptides as well as host-derived lipids including cholesteryl esters have been detected in maxillary lavage fluid. Sterol O-acyltransferase 1 (SOAT1) is a key enzyme in cholesteryl ester production. The purpose of this study is to determine if such intrinsic microbicidal molecules are acutely expressed within sinus tissue and to compare levels of expression between patients with and without chronic rhinosinusitis (CRS). METHODS: Sinus tissue was obtained from subjects with (24) and without (9) a history of CRS. Six CRS patients had nasal polyposis (CRSwNP). Immunofluorescence staining for human neutrophil peptide (HNP) was done as a marker for inflammation. Real-time polymerase chain reaction (RT-PCR) following RNA extraction was used to quantify the expression of SOAT-1, the epithelial beta-defensins (HBD2 and HBD3), and the cathelicidin LL37 with ribosomal protein, large, P0 (RPLP0) as the housekeeping gene. RESULTS: Immunofluorescence showed significant increase in HNP staining in CRS patients without nasal polyposis (CRSsNP) vs non-CRS specimens (p = 0.010), in agreement with clinical inflammation status. SOAT1 messenger RNA (mRNA) expression was also upregulated in CRSsNP compared to non-CRS (p = 0.041) and CRSwNP (p = 0.005) patients, whereas increases for HBD2 and HBD3 were less prominent. LL37 was either absent or expressed at very low levels in all samples. CONCLUSION: Increased biosynthesis of SOAT1, a key enzyme for antimicrobial cholesteryl ester production, was observed in the sinus tissue of CRSsNP patients but not in CRSwNP patients. This further supports the novel concept of lipid-mediated innate mucosal defense and delineates CRS with and without nasal polyposis as distinct subtypes.