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ABSORPTION, DISTRIBUTION, METABOLISM, AND EXCRETION

Novel Organic Cation Transporter 2-Mediated Carnitine Uptake in Placental Choriocarcinoma (BeWo) Cells

Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas

The placental transport of carnitine is significant because the fetus cannot supply itself with adequate amounts of this nutrient. Carnitine deficiencies in infants can lead to symptoms ranging from muscle weakness to sudden infant death. Objectives of this study include the characterization of novel organic cation transporter 2 (OCTN2) function in the BeWo cell line and the inhibition of placental carnitine uptake by amphetamine derivatives. BeWo cells were seeded in 12- or 24-well tissue culture plates and incubated at 37°C until monolayers were confluent. Uptake studies with radiolabeled L-carnitine and inhibitors in Hanks' balanced salt solution were carried out in the plates at 37°C for 30 min. Uptake of L-carnitine in BeWo cells was Na⁺-dependent and saturable (K_m = 9.8 ± 2.4 µM, V_max = 800 ± 70 pmol/mg of protein/30 min) with a nonsaturable constant of 2.8 ± 0.3 µl/mg of protein/30 min. Among the amphetamine analogs studied, IC₅₀ values ranged from 2.3 to 9.2 mM, and the inhibition of carnitine uptake was stronger for compounds having a methyl-substituted nitrogen atom. Lineweaver-Burk plots show that inhibition by tetraethylammonium and valproate was competitive; inhibition by ephedrine was not completely competitive. The observed kinetics, Western blot, and inhibition profiles indicate that high-affinity carnitine uptake in the BeWo cell line is mediated by OCTN2. Inhibition of carnitine transport by amphetamines potentially poses serious consequences for fetal development.

Address correspondence to: Dr. Kenneth L. Audus, School of Pharmacy, University of Kansas, 1251 Wescoe Hall Dr., Lawrence, KS 66045. E-mail: audus{at}ku.edu

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