Oral Administration of a Nano-Enabled Anti-antibiotic Prevents Vancomycin Resistance in the GI Tract

Introduction: Vancomycin (VAN) is a key antibiotic in the treatment of serious, life-threatening infections caused by Gram-positive bacteria that are unresponsive to other antibiotics. In clinical treatments, this cationic glycopeptide antibiotic is typically administered intravenously (IV) to patients (Figure 1A) and is largely excreted in urine. However, biliary excretion of a small fraction (~ 5-10%) of the administered dose leads to VAN bioavailability in the gastrointestinal (GI) tract that may result in microbiome dysbiosis and select for VAN-resistant bacteria. VAN-resistant E. faecium (VREfm) may enter the bloodstream via moving across the intestinal lining and passing through the liver, which potentially causes infective endocarditis when contacting the heart. Besides, fecal contamination of environment may lead to the VREfm transmission to other patients via contaminating the medical equipment or communal surfaces in hospitals. We hypothesize that capturing off-target VAN in the GI tract prevents the evolution and transmission of VREs. Currently, VAN is only removed from the bloodstream by hemodialysis in critically ill septic patients, but not from the GI tract. Given that developing new antibiotics for VAN-resistant bacteria may be extremely expensive and time consuming, we aimed to break the connection between IV VAN administration and the emergence of antimicrobial resistance to protect VAN as a last-resort antibiotic. To this end, we developed a super-capacity anti-antibiotic compound to sequester off-target VAN from the GI tract via hybridizing highly functional cellulose nanoparticles, known as anionic hairy cellulose nanocrystals (AHCNC), and the FDA-approved resin cholestyramine (CHA).

Materials and

Methods: The AHCNC-CHA biomaterials were prepared by incubating CHA microparticles with varying concentrations of AHCNC dispersions for 24 h at ambient temperature. The AHCNC-CHA formulation was optimized to maximize the charge density. We elucidated the mechanism of AHCNC-CHA-mediated VAN removal and investigated the competitive adsorption of intestinal fluid components, such as bile acid (BA), maleic acid (MA), and lecithin (i.e., phosphatidylcholine, PC). Furthermore, AHCNC-CHA-mediated VAN removal was investigated via an antibacterial microdilution assay against VSEfm. Finally, we assessed the efficacy of orally administered AHCNC-CHA anti-antibiotics in alleviating the evolution and onward transmission of resistance in mice treated with systemic VAN.

Results, Conclusions, and Discussions: The orally administrable anti-VAN biomaterial, AHCNC-CHA anti-antibiotic, had a high content of negatively charged carboxylate groups (~ 3 mmol g-1). The VAN removal capacity of AHCNC-CHA was considerably high (~ 850 mg g-1) (Figure 1B). At initial VAN concentrations ranging from 1 to 8 mg mL-1, the R was ~ 95%. When the initial VAN concentration increased beyond 8 mg mL-1, R decreased as a result of VAN-induced AHCNC-CHA carboxylate group saturation (neutralization). At a dose of only 20 mg mL-1, it removed more than 95% of VAN (concentration = 1 mg mL-1). The results were also validated in the fasted state simulated intestinal fluid (FaSSIF) and fed state simulated intestinal fluid (FeSSIF), wherein R was ~ 95% at the initial VAN concentrations of < 2 mg mL-1 (Figure 1C). Although VAN removal is controlled by electrostatic interactions, as confirmed in vitro via varying pH and ionic strengths, AHCNC-CHA remained efficient in the complex GI environment as a result of high charge density and partial VAN-selectively of dicarboxylate groups. Additionally, the incubation of AHCNC-CHA anti-antibiotic with VAN resulted in no antibiotic activity against VSEfm (Figure 1D). Aligned with the in vitro findings, oral AHCNC-CHA treatment of subcutaneously VAN-injected mice effectively reduced the fecal shedding of VAN-resistant E. faecium by up to 63% and prevented VAN resistance (Figure 1E). We envision that this adjuvant therapy is translatable to humans to prevent the selection and spread of VAN-resistant pathogens, the main cause of nosocomial hospital-acquired infections in modern healthcare systems.

Acknowledgements (Optional):