Multiphoton imaging for assessing renal disposition in acute kidney injury

Estimation of renal function and drug renal disposition in acute kidney injury (AKI), is important for appropriate dosing of drugs and adjustment of therapeutic strategies, but is challenging due to fluctuations in kidney function. Multiphoton microscopy has been shown to be a useful tool in studying drug disposition in liver and can reflect dynamic changes of liver function. We extend this imaging technique to investigate glomerular filtration rate (GFR) and tubular transporter functional change in various animal models of AKI, which mimic a broad range of causes of AKI such as hypoxia (renal ischemia- reperfusion), therapeutic drugs (e.g. cisplatin), rhabdomyolysis (e.g. glycerol-induced) and sepsis (e.g. LPSinduced). The MPM images revealed acute injury of tubular cells as indicated by reduced autofluorescence and cellular vacuolation in AKI groups compared to control group. In control animal, systemically injected FITC-labelled inulin was rapidly cleared from glomerulus, while the clearance of FITC-inulin was significantly delayed in most of animals in AKI group, which may reflect the reduced GFR in AKI. Following intravenous injection, rhodamine 123, a fluorescent substrate of p-glycoprotein (one of tubular transporter), was excreted into urine in proximal tubule via p-glycoprotein; in response to AKI, rhodamine 123 was retained in tubular cells as revealed by slower decay of fluorescence intensity, indicating P-gp transporter dysfunction in AKI. Thus, real-time changes in GFR and transporter function can be imaged in rodent kidney with AKI using multiphoton excitation of exogenously injected fluorescent markers.