Polymyxin B Induces Apoptosis in Kidney Proximal Tubular Cells

Tetrahydrocurcumin Attenuates Polymyxin B Sulfate-Induced HK-2 Cells Apoptosis by Inhibiting Endoplasmic Reticulum Stress-Mediated PERK/eIF2α/ATF4/CHOP Signaling Pathway Axis

The clinical application of polymyxin B (PMB) is limited by its nephrotoxic effects, making the reduction of PMB-induced nephrotoxicity has become a pressing concern for clinicians. Tetrahydrocurcumin (THC), known for its beneficial characteristics in biological functions, presents an attractive option for intervention therapy to mitigate PMB-induced nephrotoxicity. However, the underlying mechanism of how THC mitigates PMB-induced nephrotoxicity is still poorly understood. Here, we first evaluated the potential of THC intervention therapy to mitigate PMB-induced nephrotoxicity in an in vitro model of PMB-induced cell injury. Moreover, we demonstrated that THC effectively protected HK-2 cells from PMB-induced apoptosis by using cell counting kit-8 and flow cytometry assay. THC could also suppress PMB-induced endoplasmic reticulum (ER) stress via PERK/eIF2α/ATF4/CHOP pathway. In addition, using PERK inhibitor GSK2606414 to inhibit ER stress also alleviated PMB-induced apoptosis. Taken together, these findings provide novel insights that THC possesses the ability to alleviate PMB-induced nephrotoxicity by inhibiting the ER stress-mediated PERK/eIF2α/ATF4/CHOP axis, which sheds light on the benefits of THC as an intervention strategy to reduce PMB-induced nephrotoxicity, thus providing a potential avenue for improved clinical outcomes in patients receiving PMB treatment.

Comparison of the Impact of VRP-034 and Polymyxin B upon Markers of Kidney Injury in Human Proximal Tubule Monolayers In Vitro

In this study, we assessed the impact of commercially available polymyxin B against VRP-034 (novel formulation of polymyxin B) using a validated in vitro human renal model, aProximateTM. Freshly isolated primary proximal tubule cells (PTCs) were cultured in Transwell plates and treated with various concentrations of the formulations for up to 48 h. The functional expression of megalin-cubilin receptors in PTC monolayers was validated using FITC-conjugated albumin uptake assays. Polymyxin B and VRP-034 were evaluated at six concentrations (0.3, 1, 3, 10, 30, and 60 µM), and nephrotoxicity was assessed through measurements of transepithelial electrical resistance (TEER), intracellular adenosine triphosphate (ATP) levels, lactate dehydrogenase (LDH) release, and novel injury biomarkers [kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and clusterin]. Additionally, histological analysis using annexin V apoptosis staining was performed. Our results indicated a significant decrease in TEER with polymyxin B at concentrations ≥10 μM compared to VRP-034. Toxic effects were observed from ATP and LDH release only at concentrations ≥30 μM for both formulations. Furthermore, injury biomarker release was higher with polymyxin B compared to VRP-034, particularly at concentrations ≥10 µM. Histologically, polymyxin B-treated PTCs showed increased apoptosis compared to VRP-034-treated cells. Overall, VRP-034 demonstrated improved tolerance in the aProximateTM model compared to polymyxin B, suggesting its potential as a safer alternative for renal protection.

Antimicrobial Peptides towards Clinical Application-A Long History to Be Concluded

Antimicrobial peptides (AMPs) are molecules with an amphipathic structure that enables them to interact with bacterial membranes. This interaction can lead to membrane crossing and disruption with pore formation, culminating in cell death. They are produced naturally in various organisms, including humans, animals, plants and microorganisms. In higher animals, they are part of the innate immune system, where they counteract infection by bacteria, fungi, viruses and parasites. AMPs can also be designed de novo by bioinformatic approaches or selected from combinatorial libraries, and then produced by chemical or recombinant procedures. Since their discovery, AMPs have aroused interest as potential antibiotics, although few have reached the market due to stability limits or toxicity. Here, we describe the development phase and a number of clinical trials of antimicrobial peptides. We also provide an update on AMPs in the pharmaceutical industry and an overall view of their therapeutic market. Modifications to peptide structures to improve stability in vivo and bioavailability are also described.

Dextrin conjugation to colistin inhibits its toxicity, cellular uptake and acute kidney injury in vivo

The acute kidney injury (AKI) and dose-limiting nephrotoxicity, which occurs in 20-60% of patients following systemic administration of colistin, represents a challenge in the effective treatment of multi-drug resistant Gram-negative infections. To reduce clinical toxicity of colistin and improve targeting to infected/inflamed tissues, we previously developed dextrin-colistin conjugates, whereby colistin is designed to be released by amylase-triggered degradation of dextrin in infected and inflamed tissues, after passive targeting by the enhanced permeability and retention effect. Whilst it was evident in vitro that polymer conjugation can reduce toxicity and prolong plasma half-life, without significant reduction in antimicrobial activity of colistin, it was unclear how dextrin conjugation would alter cellular uptake and localisation of colistin in renal tubular cells in vivo. We discovered that dextrin conjugation effectively reduced colistin's toxicity towards human kidney proximal tubular epithelial cells (HK-2) in vitro, which was mirrored by significantly less cellular uptake of Oregon Green (OG)-labelled dextrin-colistin conjugate, when compared to colistin. Using live-cell confocal imaging, we revealed localisation of both, free and dextrin-bound colistin in endolysosome compartments of HK-2 and NRK-52E cells. Using a murine AKI model, we demonstrated dextrin-colistin conjugation dramatically diminishes both proximal tubular injury and renal accumulation of colistin. These findings reveal new insight into the mechanism by which dextrin conjugation can overcome colistin's renal toxicity and show the potential of polymer conjugation to improve the side effect profile of nephrotoxic drugs.

Genetic predisposition and high exposure to colistin in the early treatment period as independent risk factors for colistin-induced nephrotoxicity

Colistin is known to cause nephrotoxicity due to its extensive reabsorption and accumulation in renal tubules. In vitro studies have identified the functional role of colistin transporters such as OCTN2, PEPT2, megalin, and P-glycoprotein. However, the role of these transporter gene variants in colistin-induced nephrotoxicity has not been studied. Utilizing targeted next-generation sequencing, we screened for genetic polymorphisms covering the colistin transporters (SLC15A1, SLC15A2, SLC22A5, LRP2, and ABCB1) in 42 critically ill patients who received colistimethate sodium. The genetic variants rs2257212 ((NM_021082.4):c.1048C>G) and rs13397109 ((NM_004525.3):C.7626C > T) were identified as being associated with an increased incidence of acute kidney injury (AKI) on Day 7. Colistin area under the curve (AUC) was predicted using a previously published pharmacokinetic model of colistin. Using logistic regression analysis, the predicted 24-h AUC of colistin was identified as an important contributor for increased odds of AKI on Day 7. Among 42 patients, 4 (9.5%) were identified as having high predisposition to colistin-induced AKI based on the presence of predisposing genetic variants. Determination of the presence of the abovementioned genetic variants and early therapeutic drug monitoring may reduce or prevent colistin-induced nephrotoxicity and facilitate dose optimization of colistimethate sodium.

Identification of prognostic biomarkers for antibiotic associated nephrotoxicity in cystic fibrosis

BACKGROUND

Our objective was to discover novel urinary biomarkers of antibiotic-associated nephrotoxicity using an ex-vivo human microphysiological system (MPS) and to translate these findings to a prospectively enrolled cystic fibrosis (CF) population receiving aminoglycosides and/or polymyxin E (colistin) for a pulmonary exacerbation.

METHODS

We populated the MPS with primary human kidney proximal tubule epithelial cells (PTECs) from three donors and modeled nephrotoxin injury through exposure to 50 µg/mL polymyxin E for 72 h. We analyzed gene transcriptional responses by RNAseq and tested MPS effluents. We translated candidate biomarkers to a CF cohort via analysis of urine collected prior to, during and two weeks after antibiotics and patients were followed for a median of 3 years after antibiotic use.

RESULTS

Polymyxin E treatment resulted in a statistically significant increase in the pro-apoptotic Fas gene relative to control in RNAseq of MPS: fold-change = 1.63, FDR q-value = 7.29 × 10-5. Effluent analysis demonstrated an acute rise of soluble Fas (sFas) concentrations that correlated with cellular injury. In 16 patients with CF, urinary sFas concentrations were significantly elevated during antibiotic treatment, regardless of development of AKI. Over a median of three years of follow up, we identified seven cases of incident chronic kidney disease (CKD). Urinary sFas concentrations during antibiotic treatment were significantly associated with subsequent development of incident CKD (unadjusted relative risk = 2.02 per doubling of urinary sFas, 95 % CI = 1.40, 2.90, p < 0.001).

CONCLUSIONS

Using an ex-vivo MPS, we identified a novel biomarker of proximal tubule epithelial cell injury, sFas, and translated these findings to a clinical cohort of patients with CF.

Zoledronic acid and ibandronate-induced nephrotoxicity in 2D and 3D proximal tubule cells derived from human and rat

Drug-induced proximal tubule (PT) injury remains a serious safety concern throughout drug development. Traditional in vitro 2-dimensional (2D) and preclinical in vivo models often fail to predict drug-related injuries presented in clinical trials. Various 3-dimensional (3D) microphysiological systems (MPSs) have been developed to mimic physiologically relevant properties, enabling them to be more predictive toward nephrotoxicity. To explore the capabilities of an MPS across species, we compared cytotoxicity in hRPTEC/TERT1s and rat primary proximal tubular epithelial cells (rPPTECs) following exposure to zoledronic acid and ibandronate (62.5-500 µM), and antibiotic polymyxin B (PMB) (50 and 250 µM, respectively). For comparison, we investigated cytotoxicity using 2D cultured hRPTEC/TERT1s and rPPTECs following exposure to the same drugs, including overlapping concentrations, as their 3D counterparts. Regardless of the in vitro model, bisphosphonate-exposed rPPTECs exhibited cytotoxicity quicker than hRPTEC/TERT1s. PMB was less sensitive toward nephrotoxicity in rPPTECs than hRPTEC/TERT1s, demonstrating differences in species sensitivity within both 3D and 2D models. Generally, 2D cultured cells experienced faster drug-induced cytotoxicity compared to the MPSs, suggesting that MPSs can be advantageous for longer-term drug-exposure studies, if warranted. Furthermore, ibandronate-exposed hRPTEC/TERT1s and rPPTECs produced higher levels of inflammatory and kidney injury biomarkers compared to zoledronic acid, indicating that ibandronate induces acute kidney injury, but also a potential protective response since ibandronate is less toxic than zoledronic acid. Our study suggests that the MPS model can be used for preclinical screening of compounds prior to animal studies and human clinical trials.

Ten-year Single Center Experience With Colistin Therapy in NICU

BACKGROUND

Colistin, a cationic polypeptide antibiotic of the polymyxin class has come back into use due to its potent antimicrobial activity against multidrug-resistant Gram-negative bacteria and the lack of new antibiotics. The purpose of this study was to assess the critically ill infants treated with colistin in our neonatal intensive care unit and to identify predisposing factors for the emergence of acute kidney injury (AKI) following colistin treatment.

METHODS

This was a retrospective case-control study that included infants with proven or suspected nosocomial infections in the neonatal intensive care unit of a University Hospital between January 2012 and March 2022. Over the same time period, the clinical and laboratory characteristics and outcomes of patients who received antibiotic combination with colistin were compared to patients who received antibiotic combination without colistin.

RESULTS

A total of 77 patients were in the colistin group (ColG) and 77 patients were in the control group. The demographic and clinical characteristics of the study groups were similar. In the ColG compared to the control group, hyponatremia, hypokalemia, hypophosphatemia, hypomagnesia and AKI were all more prevalent ( P < 0.05). The most important finding in our study was the higher incidence of AKI and mortality in ColG, as well as the increasing nephrotoxic effect of other medications when used in conjunction with colistin.

CONCLUSION

During colistin therapy, newborn infants must be closely monitored for AKI. Clinicians should be aware of an increased incidence of hyponatremia, hypokalemia, hypophosphatemia, hypomagnesia, AKI and its consequences in infants given colistin. As awareness increases, harmful effects will decrease.

Prostaglandin F2α analogue, bimatoprost ameliorates colistin-induced nephrotoxicity

Colistin (polymyxin E) is an antibiotic that is effective against multidrug-resistant gram-negative bacteria. However, the high incidence of nephrotoxicity caused by colistin limits its clinical use. To identify compounds that might ameliorate colistin-induced nephrotoxicity, we obtained 1707 compounds from the Korea Chemical Bank and used a high-content screening (HCS) imaging-based assay. In this way, we found that bimatoprost (one of prostaglandin F2α analogue) ameliorated colistin-induced nephrotoxicity. To further assess the effects of bimatoprost on colistin-induced nephrotoxicity, we used in vitro and in vivo models. In cultured human proximal tubular cells (HK-2), colistin induced dose-dependent cytotoxicity. The number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells, indicative of apoptosis, was higher in colistin-treated cells, but this effect of colistin was ameliorated by cotreatment with bimatoprost. The generation of reactive oxygen species, assessed using 2,7-dichlorodihydrofluorescein diacetate, was less marked in cells treated with both colistin and bimatoprost than in those treated with colistin alone. Female C57BL/6 mice (n = 10 per group) that were intraperitoneally injected with colistin (10 mg/kg/12 hr) for 14 days showed high blood urea nitrogen and serum creatinine concentrations that were reduced by the coadministration of bimatoprost (0.5 mg/kg/12 hr). In addition, kidney injury molecule-1 (KIM1) and Neutrophil gelatinase-associated lipocalin (NGAL) expression also reduced by bimatoprost administration. Further investigation in tubuloid and kidney organoids also showed that bimatoprost attenuated the nephrotoxicity by colistin, showing dose-dependent reducing effect of KIM1 expression. In this study, we have identified bimatoprost, prostaglandin F2α analogue as a drug that ameliorates colistin-induced nephrotoxicity.

Zileuton ameliorates aminoglycoside and polymyxin-associated acute kidney injury in an animal model

OBJECTIVES

Aminoglycosides and polymyxins are antibiotics with in vitro activity against MDR Gram-negative bacteria. However, their clinical use is hindered by dose-limiting nephrotoxicity. The objective of this project was to determine if zileuton can reduce nephrotoxicity associated with amikacin and polymyxin B in a rat model of acute kidney injury.

METHODS

Sprague Dawley rats (n = 10, both genders) were administered either amikacin (300 mg/kg) or polymyxin B (20 mg/kg) daily for 10 days. Zileuton (4 and 10 mg/kg) was delivered intraperitoneally 15 min before antibiotic administration. Blood samples were collected at baseline and daily to determine serum creatinine concentration. Nephrotoxicity was defined as a ≥2× elevation of baseline serum creatinine. Time-to-event analysis and log rank test were used to compare the onset of nephrotoxicity in different cohorts. Histopathological analysis was also conducted to characterize the extent of kidney injury.

RESULTS

Animals receiving amikacin or polymyxin B alone had nephrotoxicity rates of 90% and 100%, respectively. The overall rate was reduced to 30% in animals receiving adjuvant zileuton. The onset of nephrotoxicity associated with amikacin and polymyxin B was also significantly delayed by zileuton at 4 and 10 mg/kg, respectively. Histopathology confirmed reduced kidney injury in animals receiving amikacin concomitant with zileuton.

CONCLUSIONS

Our pilot data suggest that zileuton has the potential to attenuate nephrotoxicity associated with last-line antibiotics. This would allow these antibiotics to treat MDR Gram-negative bacterial infections optimally without dose-limiting constraints. Further studies are warranted to optimize drug delivery and dosing in humans.

Effects of melatonin against acute kidney injury: A systematic review and meta-analysis

INTRODUCTION

Melatonin is a hormone synthesized by the pineal gland, and has antioxidative effects in reducing acute kidney injury (AKI). In the past three years, an increasing number of studies have evaluated whether melatonin has a protective effect on AKI. The study systematically reviewed and assessed the efficacy and safety of melatonin in preventing AKI.

MATERIAL AND METHODS

A systematic literature search was conducted in the PubMed, Embase, and Web of Science databases on February 15, 2023. Eligible records were screened according to the inclusion and exclusion criteria. The odds ratio and Hedges' gwith the corresponding 95% confidence intervals were selected to evaluate the effects of melatonin on AKI. We pooled extracted data using a fixed- or random-effects model based on a heterogeneity test.

RESULTS

There were five studies (one cohort study and four randomized controlled trials) included in the meta-analysis. Although the glomerular filtration rate (GFR) may be significantly improved by melatonin, the incidence of AKI was not significantly decreased in the melatonin group compared with the control group in randomized controlled trials (RCTs).

CONCLUSIONS

In our study, the present results do not support a direct effect of melatonin use on the reduction of AKI. More well-designed clinical studies with larger sample size are required in the future.

Ferroptosis is involved in polymyxin B-induced acute kidney injury via activation of p53

Polymyxin B (PMB) is one of the most effective drugs for the treatment of multi-resistant and pan-resistant gram-negative infections. However, it can induce acute kidney injury (AKI), the mechanism of which has not yet been fully elucidated. In this study, RNA sequencing and in vitro and in vivo experiments demonstrated that PMB induced AKI by promoting ferroptosis. Moreover, the metallothionein-1 (MT-1) level was significantly increased in the AKI group and clinical cases revealed that iron and MT-1 levels in urine were significantly higher in patients with AKI than in those without AKI. To explore the mechanism of PMB induced ferroptosis, we silenced p53 in human kidney-2 (HK2) cells according to RNA sequencing, which showed that p53 was obviously enhanced in the PMB treated group. While PMB significantly enhanced Fe²⁺, lipid peroxidation, malondialdehyde (MDA), transferrin receptor protein 1 (TFR1), and arachidonate 12-lpoxygenase (ALOX12), decreased the survival rate, solute carrier family 7 member 11 (SLC7A11), glutathione peroxidase 4 (GPX4), and glutathione (GSH), downregulation of p53 reversed these effects, suggesting PMB induced ferroptosis by activating p53. Studies have shown p53 can promote ferroptosis by regulating the downstream factors SLC7A11 or TFR1. Further, we verified that silencing TFR1 expression as well as overexpression of SLC7A11 inhibited ferroptosis and significantly increased the survival rate of HK2 cells. Overall, PMB induces ferroptosis in renal tubular cells by activating p53 to reduce SLC7A11 expression and elevate TFR1, leading to AKI; MT-1 and iron levels in urine were significantly increased when PMB induced ferroptosis.

Targeted Desorption Electrospray Ionization Mass Spectrometry Imaging for Drug Distribution, Toxicity, and Tissue Classification Studies

With increased use of mass spectrometry imaging (MSI) in support of pharmaceutical research and development, there are opportunities to develop analytical pipelines that incorporate exploratory high-performance analysis with higher capacity and faster targeted MSI. Therefore, to enable faster MSI data acquisition we present analyte-targeted desorption electrospray ionization–mass spectrometry imaging (DESI-MSI) utilizing a triple-quadrupole (TQ) mass analyzer. The evaluated platform configuration provided superior sensitivity compared to a conventional time-of-flight (TOF) mass analyzer and thus holds the potential to generate data applicable to pharmaceutical research and development. The platform was successfully operated with sampling rates up to 10 scans/s, comparing positively to the 1 scan/s commonly used on comparable DESI-TOF setups. The higher scan rate enabled investigation of the desorption/ionization processes of endogenous lipid species such as phosphatidylcholines and a co-administered cassette of four orally dosed drugs—erlotininb, moxifloxacin, olanzapine, and terfenadine. This was used to enable understanding of the impact of the desorption/ionization processes in order to optimize the operational parameters, resulting in improved compound coverage for olanzapine and the main olanzapine metabolite, hydroxy-olanzapine, in brain tissue sections compared to DESI-TOF analysis or matrix-assisted laser desorption/ionization (MALDI) platforms. The approach allowed reducing the amount of recorded information, thus reducing the size of datasets from up to 150 GB per experiment down to several hundred MB. The improved performance was demonstrated in case studies investigating the suitability of this approach for mapping drug distribution, spatially resolved profiling of drug-induced nephrotoxicity, and molecular–histological tissue classification of ovarian tumors specimens.

Transcriptomic Responses to Polymyxin B and Analogues in Human Kidney Tubular Cells

Polymyxins are last-line antibiotics for the treatment of Gram-negative 'superbugs'. However, nephrotoxicity can occur in up to 60% of patients administered intravenous polymyxins. The mechanisms underpinning nephrotoxicity remain unclear. To understand polymyxin-induced nephrotoxicity, human renal proximal tubule cells were treated for 24 h with 0.1 mM polymyxin B or two new analogues, FADDI-251 or FADDI-287. Transcriptomic analysis was performed, and differentially expressed genes (DEGs) were identified using ANOVA (FDR < 0.2). Cell viability following treatment with polymyxin B, FADDI-251 or FADDI-287 was 66.0 ± 5.33%, 89.3 ± 3.96% and 90.4 ± 1.18%, respectively. Transcriptomics identified 430, 193 and 150 DEGs with polymyxin B, FADDI-251 and FADDI-287, respectively. Genes involved with metallothioneins and Toll-like receptor pathways were significantly perturbed by all polymyxins. Only polymyxin B induced perturbations in signal transduction, including FGFR2 and MAPK signaling. SIGNOR network analysis showed all treatments affected essential regulators in the immune system, autophagy, cell cycle, oxidative stress and apoptosis. All polymyxins caused significant perturbations of metal homeostasis and TLR signaling, while polymyxin B caused the most dramatic perturbations of the transcriptome. This study reveals the impact of polymyxin structure modifications on transcriptomic responses in human renal tubular cells and provides important information for designing safer new-generation polymyxins.

Synthesis and Evaluation of Polymyxins Bearing Reductively Labile Disulfide-Linked Lipids

Polymyxins are a class of lipopeptide anti-infective agents with potent and specific activity against Gram-negative bacteria. While toxicity concerns associated with polymyxin B and E (colistin) have historically limited their clinical application, today they are increasingly used as last-resort antibiotics given the rise of multidrug-resistant Gram-negative pathogens. The adverse side effects of polymyxins are well known, particularly as related to their nephrotoxicity. Here, we describe the synthesis and evaluation of a novel series of polymyxin analogues, aimed at reducing their nephrotoxic effects. Using a semisynthetic approach, we explored modifications of the exocyclic part of the polymyxin scaffold, namely, the terminal amino acid and lipophilic tail. By incorporating a reductively labile disulfide linkage in the lipid tail, we obtained novel polymyxins that exhibit potent antibacterial activity on par with polymyxin B but with reduced toxicity toward human renal proximal tubular epithelial cells.

Treatment of Acinetobacter baumannii severe infections

Acinetobacter baumannii is a Gram-negative, multidrug-resistant (MDR) pathogen that causes nosocomial infections, especially in intensive care units (ICUs) and immunocompromised patients. A. baumannii has developed a broad spectrum of antimicrobial resistance, associated with a higher mortality rate among infected patients compared with other non-baumannii species. In terms of clinical impact, resistant strains are associated with increases in both in-hospital length of stay and mortality. A. baumannii can cause a variety of infections, especially ventilator-associated pneumonia, bacteremia, and skin wound infections, among others. The most common risk factors for the acquisition of MDR A. baumannii are previous antibiotic use, mechanical ventilation, length of ICU and hospital stay, severity of illness, and use of medical devices. Current efforts are focused on addressing all the antimicrobial resistance mechanisms described in A. baumannii, with the objective of identifying the most promising therapeutic scheme.

Erythro-PmBs: A Selective Polymyxin B Delivery System Using Antibody-Conjugated Hybrid Erythrocyte Liposomes

As a result of the growing worldwide antibiotic resistance crisis, many currently existing antibiotics have become ineffective due to bacteria developing resistive mechanisms. There are a limited number of potent antibiotics that are successful at suppressing microbial growth, such as polymyxin B (PmB); however, these are often deemed as a last resort due to their toxicity. We present a novel PmB delivery system constructed by conjugating hybrid erythrocyte liposomes with antibacterial antibodies to combine a high loading efficiency with guided delivery. The retention of PmB is enhanced by incorporating negatively charged lipids into the red blood cells' cytoplasmic membrane (RBC_cm). Anti-Escherichia coli antibodies are attached to these hybrid erythrocyte liposomes by the inclusion of DSPE-PEG maleimide linkers. We show that these erythro-PmBs have a loading efficiency of ∼90% and are effective in delivering PmB to E. coli, with values for the minimum inhibitory concentration (MIC) being comparable to those of free PmB. The MIC values for Klebsiella aerogenes, however, significantly increased well beyond the resistant breakpoint, indicating that the inclusion of the anti-E. coli antibodies enables the erythro-PmBs to selectively deliver antibiotics to specific targets.

HSP70 and their co-chaperones in the human malaria parasite P. falciparum and their potential as drug targets

As part of their life-cycle, malaria parasites undergo rapid cell multiplication and division, with one parasite giving rise to over 20 new parasites within the course of 48 h. To support this, the parasite has an extremely high metabolic rate and level of protein biosynthesis. Underpinning these activities, the parasite encodes a number of chaperone/heat shock proteins, belonging to various families. Research over the past decade has revealed that these proteins are involved in a number of essential processes within the parasite, or within the infected host cell. Due to this, these proteins are now being viewed as potential targets for drug development, and we have begun to characterize their properties in more detail. In this article we summarize the current state of knowledge about one particular chaperone family, that of the HSP70, and highlight their importance, function, and potential co-chaperone interactions. This is then discussed with regard to the suitability of these proteins and interactions for drug development.

Does Monitoring Total and Free Polymyxin B1 Plasma Concentrations Predict Polymyxin B-Induced Nephrotoxicity? A Retrospective Study in Critically Ill Patients

INTRODUCTION

The correlation between total and free polymyxin B (PMB including PMB1 and PMB2) exposure in vivo and acute kidney injury (AKI) remains obscure. This study explores the relationships between plasma exposure of PMB1 and PMB2 and nephrotoxicity, and investigates the risk factors for PMB-induced acute kidney injury (AKI) in critically ill patients.

METHODS

Critically ill patients who used PMB and met the criteria were enrolled. The total plasma concentration and plasma binding of PMB1 and PMB2 were analysed by liquid chromatography-tandem mass spectrometry and equilibrium dialysis.

RESULTS

A total of 89 patients were finally included, and AKI developed in 28.1% of them. The peak concentration of PMB1 (C_max (B1)) (adjusted odds ratio (AOR) = 1.68, 95% CI 1.08-2.62, p = 0.023), baseline BUN level (AOR = 1.08, 95% CI 1.01-1.16, p = 0.039) and hypertension (AOR = 3.73, 95% CI 1.21-11.54, p = 0.022) were independent risk factors for PMB-induced AKI. The area under the ROC curve of the model was 0.799. When C_max (B1) was 5.23 μg/ml or more, the probability of AKI was higher than 50%. The ratio of PMB1/PMB2 decreased after PMB preparation entered into the body. The protein binding rate in critically ill patients indicated significant individual differences. Free C_max (B) and free C_max (B1) levels in the AKI group were significantly (p < 0.05) higher than those in the non-AKI group. Total and free concentrations of PMB in patients showed a positive correlation.

CONCLUSIONS

Both the ROC curve and logistic regression model showed that C_max (B1) was a good predictor for the probability of PMB-induced AKI. Early therapeutic drug monitoring (TDM) of PMB should be considered in critically ill patients. Compared with C_min (B), C_max (B) and C_max (B1) may be helpful for the early prediction of PMB-induced AKI in critically ill patients.

Efficacy of stem cell-based therapies for colistin-induced nephrotoxicity

The increase in infections with multidrug resistant bacteria has forced to return to the use of colistin, antibiotic with known nephrotoxicity. Mesenchymal stem cells (MSCs) are being extensively investigated for their potential in regenerative medicine. This study aimed to investigate the possible protective mechanisms of the MSCs against kidney injury induced by colistin. Forty adult female albino rats were randomly classified into 4 equal groups; the control group, the MSC-treated group (a single dose of 1 ×10⁶ /ml MSCs through the tail vein), the colistin-treated group (36 mg/kg/day colistin was given for 7 days), and the both colistin and MSC group (36 mg/kg/day colistin and 1 ×10⁶ /ml MSCs). Main outcome measures were histopathological alterations, kidney malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT) and immunohistological autophagy evaluation. MSC repressed the progression of colistin-induced kidney injury as evidenced by the improvement of histopathological alterations and the substantial increase MDA, and decrease SOD and CAT in serum levels. Moreover, MSC resulted in a profound reduction in oxidative stress as manifested by decreased MDA and increased SOD in serum. Notably, MSC suppressed colistin-induced autophagy; it reduced renal levels of Beclin-1, P62 and LC3A/B. Furthermore, MSC decreased renal levels of eNOS. Lastly, MSC efficiently decreased expression of the TUNEL positive cell number. MSC confers protection against colistin-induced kidney injury by alleviating oxidative stress, nitric oxide synthase besides modulating reducing autophagy and apoptosis.

Secondary Prophylaxis With Inhaled Colistin to Prevent Recurrence of Pseudomonas aeruginosa and Extended-spectrum β-lactamase-producing Enterobacterales Pneumonia in ICU After Lung Transplantation: A Before-and-after Retrospective Cohort Analysis

BACKGROUND

Early pneumonia is an independent risk factor for 1-y mortality after lung transplantation (LTx). Pseudomonas aeruginosa is the most common isolate in early pneumonia and is also associated with an increased risk of chronic lung allograft dysfunction. The aim of our study was to evaluate the efficacy of secondary prophylaxis with inhaled colistin (IC) in preventing the recurrence of P aeruginosa or extended-spectrum β-lactamase-producing Enterobacterales (ESBL-PE) pneumonia in the postoperative period in the intensive care unit after LTx.

METHODS

We conducted a before-and-after retrospective cohort study by including all patients who underwent LTx between January 2015 and December 2020 in our center. Secondary prophylaxis with IC was instituted in January 2018 (observation period from January 2015 to December 2017, intervention period from January 2018 to December 2020).

RESULTS

A total of 271 lung transplants were included (125 in the observation period and 146 in the intervention period). The patients were predominately male (64.2%) with a median age of 57 y and received double LTx (67.9%) for chronic obstructive pulmonary disease/emphysema (36.2%) or interstitial lung disease (48.3%). The proportion of patients who experienced at least 1 recurrence of P aeruginosa or ESBL-PE pneumonia was significantly lower in the intervention period than in the observation period (0.7% versus 7.2%, P = 0.007).

CONCLUSIONS

Our study suggests a potential benefit of secondary prophylaxis with IC to prevent the recurrence of P aeruginosa or ESBL-PE pneumonia in the intensive care unit after LTx.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

The polypeptide antibiotic polymyxin B acts as a pro-inflammatory irritant by preferentially targeting macrophages

Polymyxin B (PMB) is an essential antibiotic active against multidrug-resistant bacteria, such as multidrug-resistant Pseudomonas aeruginosa (MDRP). However, the clinical use of PMB is limited, because PMB causes serious side effects, such as nephrotoxicity and neurotoxicity, probably due to its cytotoxic activity. However, cytotoxic mechanisms of PMB are poorly understood. In this study, we found that macrophages are particularly sensitive to PMB, when compared with other types of cells, including fibroblasts and proximal tubule (PT) cells. Of note, PMB-induced necrosis of macrophages allowed passive release of high mobility group box 1 (HMGB1). Moreover, upon exposure of PMB to macrophages, the innate immune system mediated by the NLR family pyrin domain containing 3 (NLRP3) inflammasome that promotes the release of pro-inflammatory cytokines such as interleukin-1β (IL-1β) was stimulated. Interestingly, PMB-induced IL-1β release occurred in the absence of the pore-forming protein gasdermin D (GSDMD), which supports the idea that PMB causes plasma membrane rupture accompanying necrosis. Emerging evidence has suggested that both HMGB1 and IL-1β released from macrophages contribute to excessive inflammation that promote pathogenesis of various diseases, including nephrotoxicity and neurotoxicity. Therefore, these biochemical properties of PMB in macrophages may be associated with the induction of the adverse organ toxicity, which provides novel insights into the mechanisms of PMB-related side effects.

Use of in vitro metabolomics in NRK cells to help predicting nephrotoxicity and differentiating the MoA of nephrotoxicants

We describe a strategy using an in vitro metabolomics assay with tubular rat NRK-52E cells to investigate the Modes of Action (MoAs) of nephrotoxic compounds. Chemicals were selected according to their MoAs based on literature information: acetaminophen, 4-aminophenol and S-(trichlorovinyl-)L-cysteine (TCVC), (covalent protein binding); gentamycin, vancomycin, polymycin B and CdCl₂ (lysosomal overload) and tenofovir and cidofovir (mitochondrial DNA-interaction). After treatment and harvesting of the cells, intracellular endogenous metabolites were quantified relative to vehicle control. Metabolite patterns were evaluated in a purely data-driven pattern generation process excluding published information. This strategy confirmed the assignment of the chemicals to the respective MoA except for TCVC and CdCl₂. Finally, TCVC was defined as unidentified and CdCl₂ was reclassified to the MoA "covalent protein binding". Hierarchical cluster analysis of 58 distinct metabolites from the patterns enabled a clear visual separation of chemicals in each MoA. The assay reproducibility was very good and metabolic responses were consistent. These results support the use of metabolome analysis in NRK-52E cells as a suitable tool for understanding and investigating the MoA of nephrotoxicants. This assay could enable the early identification of nephrotoxic compounds and finally reduce animal testing.

Interactions of polymyxin B with lipopolysaccharide-containing membranes

Bacterial resistance to antibiotics constantly remodels the battlefront between infections and antibiotic therapy. Polymyxin B, a cationic peptide with an anti-Gram-negative spectrum of activity is re-entering use as a last resort measure and as an adjuvant. We use fluorescence dequenching to investigate the role of the rough chemotype bacterial lipopolysaccharide from E. coli BL21 as a molecular facilitator of membrane disruption by LPS. The minimal polymyxin B/lipid ratio required for leakage onset increased from 5.9 × 10⁻⁴ to 1.9 × 10⁻⁷ in the presence of rLPS. We confirm polymyxin B activity against E. coli BL21 by the agar diffusion method and determined a MIC of 291 μg ml⁻¹. Changes in lipid membrane stability and dynamics in response to polymyxin and the role of LPS are investigated by ³¹P NMR and high resolution ³¹P MAS NMR relaxation is used to monitor selective molecular interactions between polymyxin B and rLPS within bilayer lipid membranes. We observe a strong facilitating effect from rLPS on the membrane lytic properties of polymyxin B and a specific, pyrophosphate-mediated process of molecular recognition of LPS by polymyxin B.

Polymyxin B uses bacterial LPS as docking receptor to cross the outer membrane.

Polymyxin-Induced Metabolic Perturbations in Human Lung Epithelial Cells

Inhaled polymyxins are associated with toxicity in human lung epithelial cells that involves multiple apoptotic pathways. However, the mechanism of polymyxin-induced pulmonary toxicity remains unclear. This study aims to investigate polymyxin-induced metabolomic perturbations in human lung epithelial A549 cells. A549 cells were treated with 0.5 or 1.0 mM polymyxin B or colistin for 1, 4, and 24 h. Cellular metabolites were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and significantly perturbed metabolites (log₂ fold change [log₂FC] ≥ 1; false-discovery rate [FDR] ≤ 0.2) and key pathways were identified relative to untreated control samples. At 1 and 4 h, very few significant changes in metabolites were observed relative to the untreated control cells. At 24 h, taurine (log₂FC = -1.34 ± 0.64) and hypotaurine (log₂FC = -1.20 ± 0.27) were significantly decreased by 1.0 mM polymyxin B. The reduced form of glutathione (GSH) was significantly depleted by 1.0 mM polymyxin B at 24 h (log₂FC = -1.80 ± 0.42). Conversely, oxidized glutathione (GSSG) was significantly increased by 1.0 mM both polymyxin B (log₂FC = 1.38 ± 0.13 at 4 h and 2.09 ± 0.20 at 24 h) and colistin (log₂FC = 1.33 ± 0.24 at 24 h). l-Carnitine was significantly decreased by 1.0 mM of both polymyxins at 24 h, as were several key metabolites involved in biosynthesis and degradation of choline and ethanolamine (log₂FC ≤ -1); several phosphatidylserines were also increased (log₂FC ≥ 1). Polymyxins perturbed key metabolic pathways that maintain cellular redox balance, mitochondrial β-oxidation, and membrane lipid biogenesis. These mechanistic findings may assist in developing new pharmacokinetic/pharmacodynamic strategies to attenuate the pulmonary toxicities of inhaled polymyxins and in the discovery of new-generation polymyxins.

Nebulized Colistin in Ventilator-Associated Pneumonia and Tracheobronchitis: Historical Background, Pharmacokinetics and Perspectives

Clinical evidence suggests that nebulized colistimethate sodium (CMS) has benefits for treating lower respiratory tract infections caused by multidrug-resistant Gram-negative bacteria (GNB). Colistin is positively charged, while CMS is negatively charged, and both have a high molecular mass and are hydrophilic. These physico-chemical characteristics impair crossing of the alveolo-capillary membrane but enable the disruption of the bacterial wall of GNB and the aggregation of the circulating lipopolysaccharide. Intravenous CMS is rapidly cleared by glomerular filtration and tubular excretion, and 20-25% is spontaneously hydrolyzed to colistin. Urine colistin is substantially reabsorbed by tubular cells and eliminated by biliary excretion. Colistin is a concentration-dependent antibiotic with post-antibiotic and inoculum effects. As CMS conversion to colistin is slower than its renal clearance, intravenous administration can lead to low plasma and lung colistin concentrations that risk treatment failure. Following nebulization of high doses, colistin (200,000 international units/24h) lung tissue concentrations are > five times minimum inhibitory concentration (MIC) of GNB in regions with multiple foci of bronchopneumonia and in the range of MIC breakpoints in regions with confluent pneumonia. Future research should include: (1) experimental studies using lung microdialysis to assess the PK/PD in the interstitial fluid of the lung following nebulization of high doses of colistin; (2) superiority multicenter randomized controlled trials comparing nebulized and intravenous CMS in patients with pandrug-resistant GNB ventilator-associated pneumonia and ventilator-associated tracheobronchitis; (3) non-inferiority multicenter randomized controlled trials comparing nebulized CMS to intravenous new cephalosporines/ß-lactamase inhibitors in patients with extensive drug-resistant GNB ventilator-associated pneumonia and ventilator-associated tracheobronchitis.

Microfluidic assembly of pomegranate-like hierarchical microspheres for efflux regulation in oral drug delivery

Herein, a multi-functional nano-in-micro hierarchical microsphere system is demonstrated for controlling the intestinal efflux pumps that affect the oral bioavailability of many therapeutic drugs. The hierarchical particles were generated by a co-flow microfluidic device and consisted of porous silica nanoparticles packed in Eudragit® polymeric matrix. Meropenem (MER), a last-resort antibacterial drug, was loaded into porous silica (MCM-48) with a loading capacity of 34.3 wt%. In this unique materials combination, MCM-48 enables ultrahigh loading of a hydrophilic MER, while the Eudragit® polymers not only protect MER from gastric pH but also act as an antagonist for p-glycoprotein protein efflux pumps to reduce the efflux of MER back into the gastrointestinal lumen. We investigated the in-vitro temporal MER release and bidirectional (absorptive and secretory) drug permeation model across the Caco-2 monolayer. The bioavailability of MER was significantly improved by all of the prepared formulations (i.e. increased absorptive transport and reduced secretory transport). The Eudragit® RSPO formulated MER-MCM showed the best performance with an efflux ratio (i.e. secretory transport/absorptive transport) of 0.35, which is 7.4 folds less than pure MER (2.62). Lastly, the prepared formulations were able to retain the antibacterial activity of MER against Staphylococcus aureus and Pseudomonas aeruginosa. STATEMENT OF SIGNIFICANCE: Meropenem (MER) is a last resort antibiotic used for the treatment of drug-resistant and acute infections and only available as intravenous injectable dosage due to its poor chemical and thermal stability, and ultra-poor oral bioavailability because of the efflux action of P-glycoprotein (P-gp) pumps. Multifunctional colloidal micro/nanoparticles can help to solve these issues. Herein, we designed pomegranate-like hierarchical microspheres comprised of porous silica nanoparticles and enteric Eudragit® polymers (Eudragit®S100, Eudragit®RSPO, and Eudragit®RS100) using a co-flow microfluidic device. Our formulations allow for ultrahigh loading of hydrophilic MER, protects MER from gastric pH, and also block P-gp efflux pumps for enhanced MER permeation/retention with Eudragit®RSPO - showing 13.9-folds higher permeation and 7.4-folds reduction in efflux ratio in a bi-directional Caco-2 monolayer culture system.

Synchrotron-based X-ray fluorescence microscopy reveals accumulation of polymyxins in single human alveolar epithelial cells

Intravenous administration of the last-line polymyxins results in poor drug exposure in the lungs and potential nephrotoxicity; while inhalation therapy offers better pharmacokinetics/pharmacodynamics for pulmonary infections by delivering the antibiotic to the infection site directly. However, polymyxin inhalation therapy has not been optimized and adverse effects can occur. This study aimed to quantitatively determine the intracellular accumulation and distribution of polymyxins in single human alveolar epithelial A549 cells. Cells were treated with an iodine-labeled polymyxin probe FADDI-096 (5.0 and 10.0 μM) for 1, 4, and 24 h. Concentrations of FADDI-096 in single A549 cells were determined by synchrotron-based X-ray fluorescence microscopy. Concentration- and time-dependent accumulation of FADDI-096 within A549 cells was observed. The intracellular concentrations (mean ± SEM, n ≥ 189) of FADDI-096 were 1.58 ± 0.11, 2.25 ± 0.10, and 2.46 ± 0.07 mM following 1, 4 and 24 h of treatment at 10 μM, respectively. The corresponding intracellular concentrations following the treatment at 5 μM were 0.05 ± 0.01, 0.24 ± 0.04, and 0.25 ± 0.02 mM (n ≥ 189). FADDI-096 was mainly localized throughout the cytoplasm and nuclear region over 24 h. The intracellular zinc concentration increased in a concentration- and time-dependent manner. This is the first study to quantitatively map the accumulation of polymyxins in human alveolar epithelial cells and provides crucial insights for deciphering the mechanisms of their pulmonary toxicity. Importantly, our results may shed light on the optimization of inhaled polymyxins in patients and the development of new-generation safer polymyxins.

Rescuing the Last-Line Polymyxins: Achievements and Challenges

Antibiotic resistance is a major global health challenge and, worryingly, several key Gram negative pathogens can become resistant to most currently available antibiotics. Polymyxins have been revived as a last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacterales. Polymyxins were first discovered in the late 1940s but were abandoned soon after their approval in the late 1950s as a result of toxicities (e.g., nephrotoxicity) and the availability of "safer" antibiotics approved at that time. Therefore, knowledge on polymyxins had been scarce until recently, when enormous efforts have been made by several research teams around the world to elucidate the chemical, microbiological, pharmacokinetic/pharmacodynamic, and toxicological properties of polymyxins. One of the major achievements is the development of the first scientifically based dosage regimens for colistin that are crucial to ensure its safe and effective use in patients. Although the guideline has not been developed for polymyxin B, a large clinical trial is currently being conducted to optimize its clinical use. Importantly, several novel, safer polymyxin-like lipopeptides are developed to overcome the nephrotoxicity, poor efficacy against pulmonary infections, and narrow therapeutic windows of the currently used polymyxin B and colistin. This review discusses the latest achievements on polymyxins and highlights the major challenges ahead in optimizing their clinical use and discovering new-generation polymyxins. To save lives from the deadly infections caused by Gram negative "superbugs," every effort must be made to improve the clinical utility of the last-line polymyxins. SIGNIFICANCE STATEMENT: Antimicrobial resistance poses a significant threat to global health. The increasing prevalence of multidrug-resistant (MDR) bacterial infections has been highlighted by leading global health organizations and authorities. Polymyxins are a last-line defense against difficult-to-treat MDR Gram negative pathogens. Unfortunately, the pharmacological information on polymyxins was very limited until recently. This review provides a comprehensive overview on the major achievements and challenges in polymyxin pharmacology and clinical use and how the recent findings have been employed to improve clinical practice worldwide.

PLGA encapsulated γ-cyclodextrin-meropenem inclusion complex formulation for oral delivery

Meropenem (MER) is one of the last resort antibiotics used to treat resistant bacterial infections. However, the clinical effectiveness of MER is hindered due to chemical instability in aqueous solution and gastric pH, and short plasma half-life. Herein, a novel multi-material delivery system based on γ-cyclodextrin (γ-CD) and poly lactic-co-glycolic acid (PLGA) is demonstrated to overcome these challenges. MER showed a saturated solubility of 14 mg/100 mL in liquid CO₂ and later it was loaded into γ-CD to form the inclusion complex using the liquid CO₂ method. The γ-CD and MER inclusion complex (MER-γ-CD) was encapsulated into PLGA by the well-established double emulsion solvent evaporation method. The formation of the inclusion complex was confirmed using FTIR, XRD, DSC, SEM, and ¹H NMR and docking study. Further, MER-γ-CD loaded PLGA nanoparticles (MER-γ-CD NPs) were characterized by SEM, DLS, and FTIR. The drug loading and entrapment efficiency for MER-γ-CD were 21.9 and 92. 2% w/w, respectively. However, drug loading and entrapment efficiency of MER-γ-CD NPs was significantly lower at up to 3.6 and 42.1% w/w, respectively. In vitro release study showed that 23.6 and 27.4% of active (non-degraded drug) and total drug (both degraded and non-degraded drug) were released from MER-γ-CD NPs in 8 h, respectively. The apparent permeability coefficient (Papp) (A to B) for MER, MER-γ-CD, and MER-γ-CD NPs were 2.63 × 10^-6 cm/s, 2.81 × 10^-6 cm/s, and 2.92 × 10^-6 cm/s_, respectively. For secretory transport, the Papp (B to A) were 1.47 × 10^-6 cm/s, 1.53 × 10^-6 cm/s, and 1.58 × 10^-6 cm/s for MER, MER-γ-CD and MER-γ-CD NPs_, respectively. Finally, the MER-γ-CD inclusion complex and MER-γ-CD NPs retained MER's antibacterial activities against Staphylococcus aureus and Pseudomonas aeruginosa. Overall, this work demonstrates the significance of MER-γ-CD NPs to protect MER from gastric pH with controlled drug release, while retaining MER's antibacterial activity.

Polymyxin-induced nephrotoxicity and its predictors: a systematic review and meta-analysis of studies conducted using RIFLE criteria of acute kidney injury

Polymyxins are last-resort antibiotics re-emerged to treat infections caused by multidrug resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacterial infections. However, polymyxin-associated nephrotoxicity has become the main safety concern. Therefore, we conducted this systematic review and meta-analysis on polymyxin-induced nephrotoxicity and its predictors using studies conducted based on the validated RIFLE (Risk, Injury, Failure, Loss of Function and End-stage renal disease) criteria of acute kidney damage. Literature search was carried out through visiting legitimate databases and indexing services including PubMed, MEDLINE (Ovid®), EMBASE (Ovid®), and Scopus to retrieve relevant studies. Following screening and eligibility evaluation, relevant data were extracted from included studies and analyzed using STATA 15.0 and Rev-Man 5.3. Inverse variance method with random effects pooling model was used for the analysis of outcome measures at 95% confidence interval. Besides, meta-regression, meta-influence, and publication bias analyses were conducted. A total of 48 studies involving 6,199 adult patients aged ≥ 18 years were included for systematic review and meta-analysis. The pooled incidence of polymyxin-induced nephrotoxicity was found to be 45% (95% CI: 41- 49%; I² = 92.52%). Stratifying with RIFLE severity scales, pooled estimates of polymyxin-treated patients identified as 'risk', 'injury' and 'failure' were 17% (95% CI: 14-20%), 13% (95% CI: 11-15%), and 10% (95% CI: 9-11%), respectively. Besides, the pooled incidence of colistin-induced nephrotoxicity was about 48% (95% CI: 42-54%), whereas that of polymyxin B was 38% (95% CI: 32-44%). Likewise, colistin had 37% increased risk of developing nephrotoxicity compared to the polymyxin B treated cohorts (RR = 1.37, 95% CI: 1.13-1.67; I² = 57%). Older age (AOR = 1.03, 95% CI: 1.01-1.05), daily dose (AOR = 1.46, 95% CI: 1.09-1.96), underlying diabetes mellitus (AOR = 1.81, 95% CI: 1.25-2.63), and concomitant nephrotoxic drugs (AOR = 2.31, 95% CI: 1.79-3.00) were independent risk factors for polymyxin-induced nephrotoxicity. Patients with high serum albumin level were less likely (AOR = 0.69, 95% CI: 0.56-0.85] to experience nephrotoxicity compared to those with low albumin level. Despite the resurgence of these antibiotics for the chemotherapy of MDR/XDR-Gram-negative superbugs, the high incidence of nephrotoxicity has become a contemporary clinical concern. Being elderly, high daily dose, having underlying diseases such as diabetes, and use of concomitant nephrotoxic drugs were independent predictors of nephrotoxicity. Therefore, therapeutic drug monitoring should be done to these patients to outweigh the potential benefits of polymyxin therapy from its risk.

Effect of Common Medications on the Expression of SARS-CoV-2 Entry Receptors in Kidney Tissue

Besides the respiratory system, severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection was shown to affect other essential organs such as the kidneys. Early kidney involvement during the course of infection was associated with worse outcomes, which could be attributed to the direct SARS-CoV-2 infection of kidney cells. In this study, the effect of commonly used medications on the expression of SARS-CoV-2 receptor, angiotensin-converting enzyme (ACE)2, and TMPRSS2 protein in kidney tissues was evaluated. This was done by in silico analyses of publicly available transcriptomic databases of kidney tissues of rats treated with multiple doses of commonly used medications. Of 59 tested medications, 56% modified ACE2 expression, whereas 24% modified TMPRSS2 expression. ACE2 was increased with only a few of the tested medication groups, namely the renin-angiotensin inhibitors, such as enalapril, antibacterial agents, such as nitrofurantoin, and the proton pump inhibitor, omeprazole. The majority of the other medications decreased ACE2 expression to variable degrees with allopurinol and cisplatin causing the most noticeable downregulation. The expression level of TMPRSS2 was increased with a number of medications, such as diclofenac, furosemide, and dexamethasone, whereas other medications, such as allopurinol, suppressed the expression of this gene. The prolonged exposure to combinations of these medications could regulate the expression of ACE2 and TMPRSS2 in a way that may affect kidney susceptibility to SARS-CoV-2 infection. Data presented here suggest that we should be vigilant about the potential effects of commonly used medications on kidney tissue expression of ACE2 and TMPRSS2.

Polymyxin-Induced Cell Death of Human Macrophage-Like THP-1 and Neutrophil-Like HL-60 Cells Associated with the Activation of Apoptotic Pathways

Innate immunity is crucial for the host to defend against infections, and understanding the effect of polymyxins on innate immunity is important for optimizing their clinical use. In this study, we investigated the potential toxicity of polymyxins on human macrophage-like THP-1 and neutrophil-like HL-60 cells. Differentiated THP-1 human macrophages (THP-1-dMs) and HL-60 human neutrophils (HL-60-dNs) were employed. Flow cytometry was used to measure the concentration-dependent effects (100 to 2,500 μM for THP-1-dMs and 5 to 2,500 μM for HL-60-dNs) and time-dependent effects (1,000 μM for THP-1-dMs and 300 μM for HL-60-dNs) of polymyxin B over 24 h. Effects of polymyxin B on mitochondrial activity, activation of caspase-3, caspase-8, and caspase-9, and Fas ligand (FasL) expression in both cell lines were examined using fluorescence imaging, colorimetric, and fluorometric assays. In both cell lines, polymyxin B induced concentration- and time-dependent loss of viability at 24 h with 50% effective concentration (EC₅₀) values of 751.8 μM (95% confidence interval [CI], 692.1 to 816.6 μM; Hill slope, 3.09 to 5.64) for THP-1-dM cells and 175.4 μM (95% CI, 154.8 to 198.7 μM; Hill slope, 1.42 to 2.21) for HL-60-dN cells. A concentration-dependent loss of mitochondrial membrane potential and generation of mitochondrial superoxide was also observed. Polymyxin B-induced apoptosis was associated with concentration-dependent activation of all three tested caspases. The death receptor apoptotic pathway activation was demonstrated by a concentration-dependent increase of FasL expression. For the first time, our results reveal that polymyxin B induced concentration- and time-dependent cell death in human macrophage-like THP-1 and neutrophil-like HL-60 cells associated with mitochondrial and death receptor apoptotic pathways.

Structure-Interaction Relationship of Polymyxins with the Membrane of Human Kidney Proximal Tubular Cells

Multidrug-resistant Gram-negative bacteria are a serious global threat to human health. Polymyxins are increasingly used in patients as a last-line therapy to treat infections caused by these life-threatening 'superbugs'. Unfortunately, polymyxin-induced nephrotoxicity is the major dose-limiting factor and understanding its mechanism is crucial for the development of novel, safer polymyxins. Here, we undertook the first all-atom molecular dynamics simulations of the interaction between four naturally occurring polymyxins A1, B1, M1 and colistin A (representative structural variations of the polymyxin core structure) and the membrane of human kidney proximal tubular cells. All polymyxins inserted spontaneously into the hydrophobic region of the membrane where they were retained, although their insertion abilities varied. Polymyxin A1 completely penetrated into the hydrophobic region of the membrane with a unique folded conformation, whereas the other three polymyxins only inserted their fatty acyl tails into this region. Furthermore, local membrane defects and increased water penetration were induced by each polymyxin, which may represent the initial stage of cellular membrane damage. Finally, the structure-interaction relationship of polymyxins was investigated based on atomic interactions at the cell membrane level. The hydrophobicity at positions 6/7 and stereochemistry at position 3 regulated the interactions of polymyxins with the cell membrane. Collectively, our results provide new mechanistic insights into polymyxin-induced nephrotoxicity at the atomic level and will facilitate the development of new-generation polymyxins.

Polymyxin B prevents the development of adjuvant arthritis via modulation of TLR/Cox-2 signaling pathway

AIMS

Several microbial toll-like receptor (TLR) ligands, bacterial DNA and bacterial cell wall fragments have been identified in the synovium of rheumatoid arthritis (RA) patients, proving bacterial involvement in the pathogenesis of RA. The current study aimed to verify that low dose polymyxin B could prevent the development of chronic inflammatory arthritis.

METHODS

Twelve days post adjuvant injection, Sprague-Dawley rats were treated twice weekly with methotrexate (0.5 mg/kg) or daily with polymyxin B (1 mg/kg) or with combination of both for 1 or 2 weeks. Arthritis progression was assessed by hind paw swelling, serum levels of tumor growth factor-1β (TGF-1β), tumor necrosis factor-alpha (TNF-α), high sensitivity C-reactive protein (HS-CRP) and nuclear factor kappa B (NF-κB) were measured using ELISA. Cyclooxygenase-1 (Cox-1) and Cox-2 activities, as well as mRNA expression of TLR-2 and TLR-4 were determined. Histopathological examination of the ankle joint was performed as well as immunohistochemistry for anti-TLR-4. Histopathological assessment of toxic effects on the kidney was performed.

KEY FINDINGS

Adjuvant arthritis led to a significant swelling of the hind paw and alteration in all serum parameters, TLR-2 and TLR-4 expression, as well as Cox-2 activity. These alterations were associated with histopathological changes of the joints. Polymyxin B reduced significantly all biomarkers of inflammation, showing better effect of the combination in most of the studied parameters, with minimal signs of nephrotoxicity.

SIGNIFICANCE

In conclusion, results showed that polymyxin B possesses significant anti-arthritic activity which may be attributed to inhibition of the TLR-4, NF-κB and Cox-2 signaling pathway.

Epidemiology and Treatment of Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa Infections

In recent years, the worldwide spread of the so-called high-risk clones of multidrug-resistant or extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa has become a public health threat. This article reviews their mechanisms of resistance, epidemiology, and clinical impact and current and upcoming therapeutic options. In vitro and in vivo treatment studies and pharmacokinetic and pharmacodynamic (PK/PD) models are discussed. Polymyxins are reviewed as an important therapeutic option, outlining dosage, pharmacokinetics and pharmacodynamics, and their clinical efficacy against MDR/XDR P. aeruginosa infections. Their narrow therapeutic window and potential for combination therapy are also discussed. Other "old" antimicrobials, such as certain β-lactams, aminoglycosides, and fosfomycin, are reviewed here. New antipseudomonals, as well as those in the pipeline, are also reviewed. Ceftolozane-tazobactam has clinical activity against a significant percentage of MDR/XDR P. aeruginosa strains, and its microbiological and clinical data, as well as recommendations for improving its use against these bacteria, are described, as are those for ceftazidime-avibactam, which has better activity against MDR/XDR P. aeruginosa, especially strains with certain specific mechanisms of resistance. A section is devoted to reviewing upcoming active drugs such as imipenem-relebactam, cefepime-zidebactam, cefiderocol, and murepavadin. Finally, other therapeutic strategies, such as use of vaccines, antibodies, bacteriocins, anti-quorum sensing, and bacteriophages, are described as future options.

Pro-caspase-3 protects cells from polymyxin B-induced cytotoxicity by preventing ROS accumulation

Polymyxin B (PMB), a last-line antibiotic used against antibiotic-resistant superbugs, causes undesirable cytotoxic side effects. However, its mechanisms remain unknown. In this study, we unexpectedly found that caspase-3, a main executor of apoptosis, plays a protective role in PMB-induced cytotoxicity. Caspase-3 knockout (KO) cells exhibited higher susceptibility to PMB-induced cytotoxicity compared with wild-type (WT) cells, accompanied by increased levels of reactive oxygen species (ROS). Interestingly, co-treatment with the antioxidant N-acetylcysteine (NAC) rescued cell viability to a similar extent as WT cells. Furthermore, PMB failed to facilitate the processing of inactive caspase-3 (pro-caspase-3) into active forms, suggesting that pro-caspase-3 nonenzymatically suppresses PMB-driven ROS accumulation and its cytotoxicity. Thus, our findings that demonstrate the potential ability of PMB to stimulate ROS generation, but which is normally masked by pro-caspase-3-dependent mechanisms, may provide novel insights into the mechanisms of PMB-induced side effects.

Rat models of colistin nephrotoxicity: previous experimental researches and future perspectives

Colistin is an old antibiotic, which is abandoned decades ago because of high nephrotoxicity rates. However, it is reintroduced to clinical medicine due to lack of newly discovered antibiotics and is still widely used for the treatment of resistant gram-negative infections. Discovering mechanisms to reduce nephrotoxicity risk is of significant importance since exposed patients may have many other factors that alter kidney functions. Several agents were evaluated in animal models of colistin nephrotoxicity as a means to prevent kidney injury. Considerable heterogeneity exists in terms of reporting colistin dosing and experimental designs. This issue leads clinicians to face difficulties in designing studies and sometimes may lead to report dosing strategies inadequately. Here, we present a review according to animal models of colistin nephrotoxicity using data gathered from previous experiments to draw attention on possible complexities that researchers may encounter.

Polymyxin Acute Kidney Injury: Dosing and Other Strategies to Reduce Toxicity

Polymyxins are valuable antimicrobials for the management of multidrug-resistant Gram-negative bacteria; however, nephrotoxicity associated with these drugs is a very common side effect that occurs during treatment. This article briefly reviews nephrotoxic mechanisms and risk factors for polymyxin-associated acute kidney injury (AKI) and discusses dosing strategies that may mitigate kidney damage without compromising antimicrobial activity. Polymyxins have a very narrow therapeutic window and patients requiring treatment with these drugs are frequently severely ill and have multiple comorbidities, which increases the risk of AKI. Notably, there is a significant overlap between therapeutic and toxic plasma polymyxin concentrations that substantially complicates dose selection. Recent dosing protocols for both colistin and polymyxin B have been developed and may help fine tune dose adjustment of these antibiotics. Minimizing exposure to modifiable risk factors, such as other nephrotoxic agents, is strongly recommended. The dose should be carefully selected, particularly in high-risk patients. The administration of oxidative stress-reducing drugs is a promising strategy to ameliorate polymyxin-associated AKI, but still requires support from clinical studies.

Mechanisms of Polymyxin-Induced Nephrotoxicity

Polymyxin-induced nephrotoxicity is the major dose-limiting factor and can occur in up to 60% of patients after intravenous administration. This chapter reviews the latest literature on the mechanisms of polymyxin-induced nephrotoxicity and its amelioration. After filtration by glomeruli, polymyxins substantially accumulate in renal proximal tubules via receptor-mediated endocytosis mainly by megalin and PEPT2. It is believed that subsequently, a cascade of interconnected events occur, including the activation of death receptor and mitochondrial apoptotic pathways, mitochondrial damage, endoplasmic reticulum stress, oxidative stress and cell cycle arrest. The current literature shows that oxidative stress plays a key role in polymyxin-induced kidney damage. Use of antioxidants have a potential in the attenuation of polymyxin-induced nephrotoxicity, thereby widening the therapeutic window. Mechanistic findings on polymyxin-induced nephrotoxicity are critical for the optimization of their use in the clinic and the discovery of safer polymyxin-like antibiotics.

Human kidney on a chip assessment of polymyxin antibiotic nephrotoxicity

Drug-induced kidney injury, largely caused by proximal tubular intoxicants, limits development and clinical use of new and approved drugs. Assessing preclinical nephrotoxicity relies on animal models that are frequently insensitive; thus, potentially novel techniques - including human microphysiological systems, or "organs on chips" - are proposed to accelerate drug development and predict safety. Polymyxins are potent antibiotics against multidrug-resistant microorganisms; however, clinical use remains restricted because of high risk of nephrotoxicity and limited understanding of toxicological mechanisms. To mitigate risks, structural analogs of polymyxins (NAB739 and NAB741) are currently in clinical development. Using a microphysiological system to model human kidney proximal tubule, we exposed cells to polymyxin B (PMB) and observed significant increases of injury signals, including kidney injury molecule-1 KIM-1and a panel of injury-associated miRNAs (each P < 0.001). Surprisingly, transcriptional profiling identified cholesterol biosynthesis as the primary cellular pathway induced by PMB (P = 1.22 ×10-16), and effluent cholesterol concentrations were significantly increased after exposure (P < 0.01). Additionally, we observed no upregulation of the nuclear factor (erythroid derived-2)-like 2 pathway, despite this being a common pathway upregulated in response to proximal tubule toxicants. In contrast with PMB exposure, minimal changes in gene expression, injury biomarkers, and cholesterol concentrations were observed in response to NAB739 and NAB741. Our findings demonstrate the preclinical safety of NAB739 and NAB741 and reveal cholesterol biosynthesis as a potentially novel pathway for PMB-induced injury. To our knowledge, this is the first demonstration of a human-on-chip platform used for simultaneous safety testing of new chemical entities and defining unique toxicological pathway responses of an FDA-approved molecule.

Technology Transfer of the Microphysiological Systems: A Case Study of the Human Proximal Tubule Tissue Chip

The adoption of a new technology into basic research, and industrial and clinical settings requires rigorous testing to build confidence in the reproducibility, reliability, robustness, and relevance of these models. Tissue chips are promising new technology, they have the potential to serve as a valuable tool in biomedical research, as well as pharmaceutical development with regards to testing for efficacy and safety. The principal goals of this study were to validate a previously established proximal tubule tissue chip model in an independent laboratory and to extend its utility to testing of nephrotoxic compounds. Here, we evaluated critical endpoints from the tissue chip developer laboratory, focusing on biological relevance (long-term viability, baseline protein and gene expression, ammoniagenesis, and vitamin D metabolism), and toxicity biomarkers. Tissue chip experiments were conducted in parallel with traditional 2D culture conditions using two different renal proximal tubule epithelial cell sources. The results of these studies were then compared to the findings reported by the tissue chip developers. While the overall transferability of this advanced tissue chip platform was a success, the reproducibility with the original report was greatly dependent on the cell source. This study demonstrates critical importance of developing microphysiological platforms using renewable cell sources.

Cytochrome C suppresses renal accumulation and nephrotoxicity of polymyxin B

The receptor megalin plays an important role in the accumulation of polymyxin B (PMB) in renal cells in vitro. This study aimed to examine the effects of cytochrome c (cyto c), a typical megalin ligand, on renal accumulation and nephrotoxicity of PMB in vivo. Thirty Sprague-Dawley rats were randomly divided into the vehicle control group, PMB group, PMB + cyto c 50, 100, or 200 mg/kg group, respectively, and were treated with intravenous cyto c 30 min before the administration of PMB 4.0 mg/kg once a day for consecutive 5 days. On the 4th day after administration, 24 h urine was collected to determine N-acetyl-β-D-glucosaminidase excretion. Six hours after the last injection on the 5th day, kidneys were harvested to assay PMB concentration and observe pathological alterations, and blood samples were collected to assay serum creatinine (SCr), blood urea nitrogen (BUN), and blood β₂-microglobulin (β₂-MG) levels. Cyto c 50, 100, and 200 mg/kg decreased the accumulation of PMB in the kidney by 18.5%, 39.1% ( p < 0.01), and 36.8% ( p < 0.01), respectively, and reduced 24 h N-acetyl-β-D- glucosaminidase excretion by 22.5% ( p < 0.05), 40.4% ( p < 0.01), and 40.4% ( p < 0.01), respectively. Kidney pathological damage induced by PMB was markedly reduced by cyto c 100 mg/kg and 200 mg/kg. However, there were no significant differences in SCr, BUN, and blood β₂-MG levels among the groups. These results indicated that cyto c may inhibit the renal accumulation and nephrotoxicity of PMB in a rat model, further proving the role of megalin in the accumulation of PMB.