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HEMODYNAMICS AND CARDIORENAL INTEGRATION

Influence of genetic knockout of Pept2 on the in vivo disposition of endogenous and exogenous carnosine in wild-type and Pept2 null mice

¹Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor; ²College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, Zhejiang, Peoples Republic of China; ³Departments of Neurosurgery and Physiology, Medical School, University of Michigan, Ann Arbor, Michigan

Submitted 3 September 2008 ; accepted in final form 12 February 2009

Carnosine (β-alanyl-L-histidine), an endogenous dipeptide substrate of the proton-coupled oligopeptide transporter PEPT2, plays an important role in many physiological processes. This study examined the effect of PEPT2 on the disposition of endogenous and exogenous carnosine in wild-type and Pept2 null mice. After exogenous dosing of [³H]carnosine (1 nmol/g iv bolus), a marked increase was observed in its systemic clearance in Pept2 null mice (0.50 vs. 0.29 ml/min), resulting in a decreased systemic exposure of dipeptide (area under the curve = 43.7 vs. 73.0 minxµM). Carnosine uptake was substantially reduced in the kidney of Pept2 null mice, and renal clearance increased 18-fold in this genotype (206 vs. 11.5 µl/min). Fractional reabsorption of carnosine in Pept2 null mice was only one-fifth that in wild-type animals (0.20 vs. 0.94). PEPT2 also had a substantial impact in brain where the cerebrospinal fluid (CSF)-to-plasma concentration ratio of carnosine was eightfold greater in Pept2 null mice (0.70 vs. 0.08). With respect to endogenous carnosine levels, significant reductions were observed in Pept2 null compared with wild-type mice for choroid plexus (0.026 vs. 0.20 mmol/kg), olfactory bulb (1.12 vs. 1.79 mmol/kg), and spleen (0.019 vs. 0.029 mmol/kg). In contrast, carnosine levels in the skeletal muscle of Pept2 null mice were significantly increased (1.70 vs. 1.14 mmol/kg), and no differences were observed between genotypes for endogenous carnosine levels in plasma and CSF. These results demonstrate that PEPT2 significantly modulates the disposition of exogenous carnosine. However, endogenous carnosine levels may be under homeostatic control to maintain systemic and central concentrations under physiological in vivo conditions.

kidney; proximal tubule; choroid plexus; transporter; dipeptide