Imaging the distribution of polymyxins in the kidney.
OBJECTIVE
Dose-limiting nephrotoxicity remains the Achilles' heel of polymyxin B and polymyxin E (also known as colistin), which are important last-line antibiotics used against infections caused by MDR Gram-negative 'superbugs'. An understanding of the mechanisms of nephrotoxicity, including renal tissue distribution, is crucial for the development of safer polymyxin lipopeptide antibiotics. This is the first study to visualize the kidney distribution of polymyxin B using a mouse nephrotoxicity model and in situ immunostaining of kidney sections.


METHODS
Polymyxin B nephrotoxicity in mice was induced over the course of 3 days (accumulated intravenous dose 175 mg/kg) and kidneys were harvested and frozen sectioned. The sections were fixed in cold acetone, dried and treated with 1% hydrogen peroxide. Endogenous mouse immunoglobulins were blocked and the tissue sections were treated with anti-polymyxin B mouse IgM antibody. The sections were incubated with a biotinylated anti-mouse secondary antibody conjugate followed by an Alexa Fluor 647-streptavidin conjugate. Polymyxin B distribution in the kidney sections was then visualized using a fluorescence scanning microscope. Kidney sections were also subjected to haematoxylin and eosin staining to assess pathological damage from the polymyxin-induced nephrotoxicity.


RESULTS
Immunostaining of kidney sections from a mouse with polymyxin B-induced nephrotoxicity revealed that polymyxin B distributed predominantly within the renal cortex. More specifically, polymyxin B accumulated within the proximal tubular cells.


CONCLUSIONS
The observed accumulation of polymyxin B within proximal tubular cells is consistent with the extensive renal reabsorption of polymyxins and the likely cause of the associated nephrotoxicity.
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Bo
B
Yun
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Mohammad A K
MA
Azad
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Jiping
J
Wang
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Roger L
RL
Nation
Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Philip E
PE
Thompson
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Kade D
KD
Roberts
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
Tony
T
Velkov
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia colistin.polymyxin@gmail.com.
Jian
J
Li
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects* / Q000032:analysis; D004195:Disease Models, Animal; D005260:Female; D007668:Kidney / Q000737:chemistry* / Q000187:drug effects* / Q000473:pathology; D051379:Mice; D008856:Microscopy, Fluorescence; D011113:Polymyxins / Q000008:administration & dosage / Q000009:adverse effects* / Q000032:analysis; D051437:Renal Insufficiency / Q000139:chemically induced* / Q000473:pathology
D000900:Anti-Bacterial Agents; D011113:Polymyxins
mice; nephrotoxicity; polymyxin B