HFD-induced Alterations in Renal Tubular Oatp4c1-P-gp Transport Systems in Mice: Impact on Digoxin Renal Excretion and Gadolinium-Enhanced Radiological Manifestations.

Objective: The clearance of digoxin in obese patients with renal impairment is reduced, leading to elevated serum concentrations and increased risks of digoxin toxicity. However, the exact mechanism of such alterations in obese patients remains unclear. Previous studies have suggested that the organic anion transport-ing polypeptide 4c1 (Oatp4c1, Slco4c1) mediates the elimination of digoxin at the basal membrane of the proximal tubule (PT), indicating its potential role in the pharmacokinetic changes in obese patients. This study aims to investigate the effects of a high-fat diet on digoxin pharmacokinetics and transporter expression in mouse models and further analyze its significance by detecting the expression of transporters in human renal tissue samples.

Methods: First, a high-fat diet (HFD)-induced obese mouse model was established. Mice were intraperitoneally injected with digoxin, and 24-hour urine samples and blood samples at five time points were collected. Pharmacokinetic evaluation was performed using liquid chromatography-tandem mass spectrometry. Renal pathological changes and the expression of digoxin transporters (Oatp4c1 and P-glycoprotein (P-gp)) were assessed using histological staining, Western blots (WB), as well as quantitative polymerase chain reaction (qPCR). Human renal pathologic alterations and expression of transporter proteins showed consistency with the results of animal experiments. To explore the potential use of gadolinium-ethoxybenzyl-diethylenetri-amine-pentaacetic acid (Gd-EOB-DTPA) as a marker for Oatp4c1 function, drug interactions between digoxin and Gd-EOB-DTPA were assessed in mice.

Results: HFD-induced obese mice showed significant increases in body weight, blood glucose, and triglyceride, along with elevated blood concentration of digoxin, increased areas under the curve, reduced renal clearance rate (CLr), and prolonged half-life (t1/2). Histological staining revealed proximal tubular epithelial cell detachment and slight fibrosis in the kidney of the HFD group, with decreased expression of villin, the protein marker for PT. Immunofluorescent staining and Western blots for digoxin transporters showed a significant reduction of Oatp4c1 and P-gp proteins, suggesting that the renal elimination of digoxin was affected solely by the reduced level of Oatp4c1 and P-gp proteins. Co-administration of digoxin and Gd-EOB-DTPA resulted in a reduced clearance of Gd-EOB-DTPA, suggesting that both share the same transporter. The blood concentration of Gd-EOB-DTPA was higher (77.5%) in the HFD group. Renal magnetic resonance imaging (MRI) intensity was lower in the HFD group after Gd-EOB-DATP administration compared to the Chow group.

Conclusion: Obesity-induced kidney damage results in decreased Oatp4c1 and P-gp expression and function in PT, resulting in a reduction of digoxin renal clearance. The inhibition of Gd-EOB-DTPA clearance by digoxin co-administration and the increased Gd-EOB-DTPA blood concentration in the HFD group both sug-gest its potential use in characterizing the Oatp4c1 function in vivo.