Involvement of the Pyrilamine Transporter, a Putative Organic Cation Transporter, in Blood-Brain Barrier Transport of Oxycodone

Abstract

ABSTRACT:The purpose of this study was to characterize blood-brain barrier (BBB) transport of oxycodone, a cationic opioid agonist, via the pyrilamine transporter, a putative organic cation transporter, using conditionally immortalized rat brain capillary endothelial cells (TR-BBB13). Oxycodone and [ 3 H]pyrilamine were both transported into TR-BBB13 cells in a temperature-and concentration-dependent manner with K m values of 89 and 28 M, respectively. The initial uptake of oxycodone was significantly enhanced by preloading with pyrilamine and vice versa. Furthermore, mutual uptake inhibition by oxycodone and pyrilamine suggests that a common mechanism is involved in their transport. Transport of both substrates was inhibited by type II cations (quinidine, verapamil, and amantadine), but not by classic organic cation transporter (OCT) substrates and/or inhibitors (tetraethylammonium, 1-methyl-4-phenylpyridinium, and corticosterone), substrates of OCTN1 (ergothioneine) and OCTN2 (L-carnitine), or organic anions. The transport was inhibited by metabolic inhibitors (rotenone and sodium azide) but was insensitive to extracellular sodium and membrane potential for both substrates. Furthermore, the transport of both substrates was increased at alkaline extracellular pH and decreased in the presence of a protonophore (carbonyl cyanide-ptrifluoromethoxyphenylhydrazone). Intracellular acidification induced with ammonium chloride enhanced the uptakes, suggesting that the transport is driven by an oppositely directed proton gradient. The brain uptake of oxycodone measured by in situ rat brain perfusion was increased in alkaline perfusate and was significantly inhibited by pyrilamine. These results suggest that blood-brain barrier transport of oxycodone is at least partly mediated by a common transporter with pyrilamine, and this transporter is an energy-dependent, proton-coupled antiporter.

Clonidine Transport at the Mouse Blood—Brain Barrier by a New H+ Antiporter that Interacts with Addictive Drugs

“…Moreover, morphine is poorly transported at the rodent's BBB, even after the P-gp efflux is inhibited (Cisternino et al, 2004;Oldendorf et al, 1972). These observations suggest that morphine is probably not an efficient substrate of this amines/H + antiporter, unlike oxycodone (Okura et al, 2008). Although little differences exist in the molecular structure between morphine, codeine, and heroin (diacetylmorphine), it was postulated that the great differences in the brain uptake of these cationic drugs are due to their passive permeability at the BBB (Oldendorf et al, 1972).…”

“…However, studies on the transport of secondary or tertiary amine drugs, such as methylenedioxymethamphetamine (MDMA, ecstasy), oxycodone, and clonidine, led to the discovery of an H + antiporter that is not inhibited by TEA. Its functional properties differ from those of any of the already identified organic cation transporters (Fischer et al, 2006;Okura et al, 2008;Kuwayama et al, 2008). However, as the molecular nature of the transporter involved has not been identified, it is commonly known as the 'tertiary or secondary amine/H + ' antiporter.…”

Functional expression of carnitine/organic cation transporter OCTN1 in mouse brain neurons: Possible involvement in neuronal differentiation

“…The expression level of OCTN1 was minimal in immortalized rat brain endothelial cells (Okura et al, 2008). In fact, the brain/plasma concentration ratio of [ 3 H]ERGO after intravenous administration was similar in wild-type and octn1 -/-mice , suggesting that OCTN1 may not be functionally expressed in the blood-brain barrier.…”

“…In the brain, OCTN1 is not functionally expressed in brain capillary endothelial cells (Okura et al, 2008) and is not expressed at the mRNA level in astrocytes (Inazu et al, 2006). Therefore, the distribution of ERGO to brain parenchyma (Fig.…”

“…OCTN1 is also expressed in the brain (Alnouti et al, 2006;Lamhonwah et al, 2008;Okura et al, 2008), although its function has not been clarified. The expression level of OCTN1 was minimal in immortalized rat brain endothelial cells (Okura et al, 2008).…”