A FASII inhibitor prevents staphylococcal evasion of daptomycin by inhibiting phospholipid decoy production

Abstract

30Daptomycin is a treatment of last resort for serious infections caused by drug-resistant Gram-positive 31 pathogens such as methicillin-resistant Staphylococcus aureus. We have shown recently that S. aureus 32 can evade daptomycin by releasing phospholipid decoys that sequester and inactivate the antibiotic, 33 leading to treatment failure. Since phospholipid release occurs via an active process we hypothesised 34 that it could be inhibited, thereby increasing daptomycin efficacy. To identify opportunities for 35 therapeutic interventions that block phospholipid release, we first determined how the host 36 environment influenced the release of phospholipids and inactivation of daptomycin by S. aureus. The 37 addition of certain host-associated fatty acids to the growth medium enhanced phospholipid release. 38

Elucidating the Impact of Bacterial Lipases, Human Serum Albumin, and FASII Inhibition on the Utilization of Exogenous Fatty Acids byStaphylococcus aureus

“…We determined that in addition to serum lipoproteins, human serum albumin can serve as a source of eFAs for the bacteria, primarily supplying oleic and linoleic acid (Figure 4A). Although a previous report demonstrated that albumin could sequester exogenous oleic acid from S. aureus, preventing the inactivation of the antibiotic daptomycin, that study used fatty acid-free HSA at 10 mg/L (18). Furthermore, we observed that eFA utilization by S. aureus had an inverse relationship with albumin concentration, where lower HSA levels promoted FFA incorporation whereas higher levels reduced incorporation.…”

“…This data indicates S. aureus preferably continued to initiate new acyl chains, leading to intermediate accumulation, rather than completely favor FASII bypass with eFA; however, preferred pathways and adaptive mechanisms differ based on experimental conditions such as fatty acid sources or FASII inhibitor concentrations (9,10,55,63,65). AFN-1252 has demonstrated promising synergistic effects when combined with daptomycin by blocking decoy phospholipid release or bacterial growth (18,65). We speculate that the increased UFA ratio of S. aureus in the presence of AFN-1252 could also contribute to enhanced daptomycin activity, as daptomycin targets specific fluid areas of the membrane (15,25,66).…”

“…FFAs in the bloodstream are typically bound to human serum albumin (HSA), a carrier protein present at high concentrations (35-50 mg/mL) in human blood (44). Albumin concentrations vary throughout the body and sites of infection and decrease with increasing age, highlighting the importance of understanding the effect of HSA on the utilization of serum fatty acids in S. aureus (18,(44)(45)(46). Here, the WT and ΔfakA strains were grown in the presence and absence of fatty acid-containing and fatty acid-free HSA.…”

“…FASII modification and eFA utilization with AFN-1252 exposure. Therapeutic value of FASII inhibitors remains in debate, as S. aureus can bypass suppressed endogenous fatty acid synthesis by utilizing eFAs (9,11,18). Lipidomics of S. aureus grown with AFN-1252-only revealed a significant increase in the proportion of UFAs with abnormally long chains (C19:1) and phospholipids with various fatty acid combinations (C14:1, C16:1, C17:1, or C19:1), suggesting accumulation of the acyl-ACP intermediate at the inhibited FabI step (9,55,64).…”

“…In our recent study, lipidomics analysis of S. aureus grown in human serum showed that bacteria incorporate UFAs into the bacterial membrane lipids, and cholesteryl esters and triglycerides are the major donors of fatty acid substrates in serum (3). Human serum albumin, an abundant carrier protein in the bloodstream that binds to acidic and lipophilic compounds, has been shown to sequester FFAs to restrict their exploitation by the bacteria (17,18), but we hypothesize that it may also serve as a reservoir of fatty acids.…”