Biochemistry and Pharmacology - Research Publications
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ItemUntargeted metabolomics to evaluate polymyxin B toxicodynamics following direct intracerebroventricular administration into the rat brain(ELSEVIER, 2022)There is a dearth of studies focused on understanding pharmacokinetics, pharmacodynamics and toxicodynamics of polymyxins following direct administration to the central nervous system (CNS). In this study, for the first time, untargeted metabolomics were employed to ascertain the perturbations of brain metabolism in the rat cerebral cortex following direct brain injection of 0.75 mg/kg polymyxin B (1 and 4 h) through the right lateral ventricle. In the right cortex metabolome, ICV polymyxin B induced a greater perturbation at 1 h compared to negligible effect at 4 h. Pathway enrichment analysis showed that sphingolipid, arginine, and histidine metabolism, together with aminoacyl-tRNA biosynthesis were significantly affected in the right cortex metabolome. Furthermore, intracerebroventricular (ICV) polymyxin B dysregulated the two arms (CDP-choline and CDP-ethanolamine) of the Kennedy pathway that governs the de novo biosynthesis of neuronal phospholipids. Importantly, the key intermediates of metabolic pathways that maintain cellular redox balance (e.g., glutathione metabolism) and mitochondrial function (e.g., electron transport chain) were markedly depleted. The abundance of key metabolites (e.g., N-acetyl-l-glutamate) associated with diverse CNS disorders (e.g., neurodegenerative disease) were also significantly perturbed. The biological significance of these metabolic perturbations on the CNS includes impaired oxidant-antioxidant balance, impaired neuronal lipid homeostasis and mitochondrial dysfunction. Furthermore, ICV polymyxin B caused a significant alteration in the abundance of several metabolic biomarkers associated with cerebral ischemia, oxidative stress as well as certain neurological disorders. These findings may facilitate the development of new pharmacokinetic/pharmacodynamic strategies to attenuate polymyxins ICV related CNS toxicities and stimulate the discovery of safer next-generation polymyxin-like lipopeptide antibiotics.
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ItemInwardly rectifying potassium channels mediate polymyxin-induced nephrotoxicity(SPRINGER BASEL AG, 2022-06)Polymyxin antibiotics are often used as a last-line defense to treat life-threatening Gram-negative pathogens. However, polymyxin-induced kidney toxicity is a dose-limiting factor of paramount importance and can lead to suboptimal treatment. To elucidate the mechanism and develop effective strategies to overcome polymyxin toxicity, we employed a whole-genome CRISPR screen in human kidney tubular HK-2 cells and identified 86 significant genes that upon knock-out rescued polymyxin-induced toxicity. Specifically, we discovered that knockout of the inwardly rectifying potassium channels Kir4.2 and Kir5.1 (encoded by KCNJ15 and KCNJ16, respectively) rescued polymyxin-induced toxicity in HK-2 cells. Furthermore, we found that polymyxins induced cell depolarization via Kir4.2 and Kir5.1 and a significant cellular uptake of polymyxins was evident. All-atom molecular dynamics simulations revealed that polymyxin B1 spontaneously bound to Kir4.2, thereby increasing opening of the channel, resulting in a potassium influx, and changes of the membrane potential. Consistent with these findings, small molecule inhibitors (BaCl2 and VU0134992) of Kir potassium channels reduced polymyxin-induced toxicity in cell culture and mouse explant kidney tissue. Our findings provide critical mechanistic information that will help attenuate polymyxin-induced nephrotoxicity in patients and facilitate the design of novel, safer polymyxins.
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ItemNo Preview AvailableComparative metabolomics reveals key pathways associated with the synergistic activity of polymyxin B and rifampicin combination against multidrug-resistant Acinetobacter baumannii(PERGAMON-ELSEVIER SCIENCE LTD, 2021-02)Multidrug-resistant (MDR) Acinetobacter baumannii presents a critical challenge to human health worldwide and polymyxins are increasingly used as a last-line therapy. Due to the rapid emergence of resistance during polymyxin monotherapy, synergistic combinations (e.g. with rifampicin) are recommended to treat A. baumannii infections. However, most combination therapies are empirical, owing to a dearth of understanding on the mechanism of synergistic antibacterial killing. In the present study, we employed metabolomics to investigate the synergy mechanism of polymyxin B-rifampicin against A. baumannii AB5075, an MDR clinical isolate. The metabolomes of A. baumannii AB5075 were compared at 1 and 4 h following treatments with polymyxin B alone (0.75 mg/L, i.e. 3 × MIC), rifampicin alone (1 mg/L, i.e. 0.25 × MIC) and their combination. Polymyxin B monotherapy significantly perturbed glycerophospholipid and fatty acid metabolism at 1 h, reflecting its activity on bacterial outer membrane. Rifampicin monotherapy significantly perturbed glycerophospholipid, nucleotide and amino acid metabolism, which are related to the inhibition of RNA synthesis. The combination treatment significantly perturbed the metabolism of nucleotides, amino acids, fatty acids and glycerophospholipids at 1 and 4 h. Notably, the intermediate metabolite pools from pentose phosphate pathway were exclusively enhanced by the combination, while most metabolites from the nucleotide and amino acid biosynthesis pathways were significantly decreased. Overall, the synergistic activity of the combination was initially driven by polymyxin B which impacted pathways associated with outer membrane biogenesis; and subsequent effects were mainly attributed to rifampicin via the inhibition of RNA synthesis. This study is the first to reveal the synergistic killing mechanism of polymyxin-rifampicin combination against polymyxin-susceptible MDR A. baumannii at the network level. Our findings provide new mechanistic insights for optimizing this synergistic combination in patients.
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ItemA synthetic lipopeptide targeting top-priority multidrug-resistant Gram-negative pathogens(NATURE PORTFOLIO, 2022-03-25)The emergence of multidrug-resistant (MDR) Gram-negative pathogens is an urgent global medical challenge. The old polymyxin lipopeptide antibiotics (polymyxin B and colistin) are often the only therapeutic option due to resistance to all other classes of antibiotics and the lean antibiotic drug development pipeline. However, polymyxin B and colistin suffer from major issues in safety (dose-limiting nephrotoxicity, acute toxicity), pharmacokinetics (poor exposure in the lungs) and efficacy (negligible activity against pulmonary infections) that have severely limited their clinical utility. Here we employ chemical biology to systematically optimize multiple non-conserved positions in the polymyxin scaffold, and successfully disconnect the therapeutic efficacy from the toxicity to develop a new synthetic lipopeptide, structurally and pharmacologically distinct from polymyxin B and colistin. This resulted in the clinical candidate F365 (QPX9003) with superior safety and efficacy against lung infections caused by top-priority MDR pathogens Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae.