Regulatory Role of Testosterone in Organic Cation Transport: in Vivo and in Vitro Studies

Abstract

Renal organic cation transporters (OCTs) play a significant role in the elimination of a wide variety of organic cations, including endogenous compounds (e.g., monoamine neurotransmitter 1) and creatinine 2) ), drugs (e.g., cimetidine 3) metformin, 4) pramipexol 5) and cisplatin 6) ) and xenobiotics (e.g., tetraethylammonium (TEA) and 1-methyl-4-phenylpyridinium (MPP ϩ ) 3) ). OCTs are expressed in the basolateral membrane of renal proximal tubular cells, where they mediate the initial step of renal secretion of organic cation compounds. [7][8][9] The OCTs mediate facilitated diffusion of organic cations driven by a transmembrane potential difference. Several members of the OCT family have been cloned and identified, including OCT1, OCT2 and OCT3. Expression studies have shown that OCT1 is expressed in liver, kidney and small intestine. [10][11][12][13] OCT2 is expressed mostly in the kidney and is considered to be the major transporter for organic cation transport.14-16) OCT3 is mainly expressed in placenta and ovary, but is also present at low levels in many tissues. 14,17) For net transepithelial organic cation transport, in addition to its uptake, extrusion at the apical membrane into tubular lumen is also important. Previously, several transporters including organic cation/carnitine transporter 1, 2 (OCTN1, OCTN2) and multidrug resistance protein 1 (MDR1) were thought to participate in the extrusion of organic cation at the apical side.18-20) Very recently, other luminal H ϩ /organic cation antiporters, human (h) multidrug and toxin extrusion (MATE)1, hMATE2, rat (r) MATE1 and mouse (m)MATE1 and mMATE2, have been also suggested to contribute to renal organic cation transport. [21][22][23] It appears that testosterone can affect plasma levels of organic cations by modulating the activity of renal OCT2. This notion is supported by the observation that OCT2 mRNA levels are higher in kidneys of male than that of female mice and rats.14,24,25) Furthermore, testosterone treatment increased rOCT2 mRNA expression and TEA accumulation in renal slices of both sexes.26) Additional studies indicated that testosterone enhanced expression of rOCT2, but not rOCT1 and rOCT3, via the androgen receptor-mediated transcriptional pathway. 27) Recently, Lickteig et al. 28) reported that mMATE1 mRNA is more highly expressed in the kidney of male than that of female mice. However, the regulatory role of testosterone in MATE1 has not been elucidated. Clearly, functional changes in OCT expression would affect the pharmacokinetics of endogenous OC as well as cationic drugs. However, little information is available regarding the physiological role of transporter regulation in the whole animal.To gain more insight into the role of testosterone in regulating renal OC transport, we first examined the effect of testosterone on organic cation transport mediated by OCTs in the whole animal. The mechanism of testosterone induced changes in OC secretion was then assessed in vitro using isolated mouse renal proximal tubule (mRPT). In additio...

Role of Estrogen in Renal Handling of Organic Cation, Tetraethylammonium: in Vivo and in Vitro Studies

“…22) In brief, after anesthesia and surgical procedures, mice were given a priming dose of 4 mCi of [ 14 C]-TEA at an infusion rate of 0.45 ml/h. Following an equilibration period of 60 min to allow plasma TEA to achieve a steady state, urine and blood samples were collected for 3 periods of 20 min each.…”

“…The kidneys were removed and dissected for renal proximal tubules as described previously. 22) All dissections were performed at 4°C. Dissected tubules are collapsed and thus are only capable of basolateral transport.…”

“…Uptake of 1 mM Quantitative Polymerase Chain Reaction (qPCR) Analysis The messenger RNA level analysis of various candidate transporters was performed as our previous study. 22) Briefly, total RNA was isolated from kidney cortex of mice from the 3 groups using TRIZOL reagent (Invitrogen Life Technologies, Carlsbad, CA, U.S.A.) and RNeasy kit (Qiagen, Valencia, CA, U.S.A.) according to the manufacturer's instruction. cDNA was synthesized using SuperScript III (Invitrogen Life Technologies, Carlsbad, CA, U.S.A.) and qPCR performed using SYBR Green real-time PCR assay kit (Applied Biosystems, Foster City, CA, U.S.A.).…”

“…21) Recently, we reported testosterone-stimulated transport of OC in male mice. 22) Estrogen administration produced a small decrease in OCT2 expression level and TEA uptake in male rat and MDCK cells. 20,23) In addition, estrogen reduced OC transport in opossum kidney cell culture via a reduction in OCT1 protein expression.…”

Endocrine and metabolic regulation of renal drug transporters

“…It has been suggested that elevated Oct2 levels enhance renal clearance of the nephrotoxicant cisplatin in male rodents (142). Gonadectomy of male rats and mice decreases Oct2 mRNA as well as renal clearance of the organic cation TEA (22,143). With testosterone treatment, renal Oct2 mRNA and protein expression and TEA uptake increase to control male levels while estrogen supplementation has no effect (22,143,144).…”