Placental P-glycoprotein (P-gp) acts to protect the developing fetus from exogenous compounds. This protection declines with advancing gestation leaving the fetus and fetal brain vulnerable to these compounds and potential teratogens in maternal circulation. This vulnerability may be more pronounced in pregnancies complicated by infection, which is common during pregnancy. Pro-inflammatory cytokines (released during infection) have been shown to be potent inhibitors of P-gp, but nothing is known regarding their effects at the developing blood-brain barrier (BBB). We hypothesized that P-gp function and expression in endothelial cells of the developing BBB will be inhibited by pro-inflammatory cytokines. We have derived brain endothelial cell (BEC) cultures from various stages of development of the guinea pig: gestational day (GD) 50, 65 (term ∼68 days) and postnatal day (PND) 14. Once these cultures reached confluence, BECs were treated with various doses (100–104 pg/mL) of pro-inflammatory cytokines: interleukin-1β (IL-1β), interleukin-6 (IL-6) or tumor necrosis factor- α (TNF-α). P-gp function or abcb1 mRNA (encodes P-gp) expression was assessed following treatment. Incubation of GD50 BECs with IL-1β, IL-6 or TNF-α resulted in no change in P-gp function. GD65 BECs displayed a dose-dependent decrease in function with all cytokines tested; maximal effects at 42%, 65% and 34% with IL-1β, IL-6 and TNF-α treatment, respectively (P<0.01). Inhibition of P-gp function by IL-1β, IL-6 and TNF-α was even greater in PND14 BECs; maximal effects at 36% (P<0.01), 84% (P<0.05) and 55% (P<0.01), respectively. Cytokine-induced reductions in P-gp function were associated with decreased abcb1 mRNA expression. These data suggest that BBB P-gp function is increasingly responsive to the inhibitory effects of pro-inflammatory cytokines, with increasing developmental age. Thus, women who experience infection and take prescription medication during pregnancy may expose the developing fetal brain to greater amounts of exogenous compounds – many of which are considered potentially teratogenic.

Background and PurposeRetention of substances from systemic circulation in the brain and testes are limited due to high levels of P-glycoprotein (P-gp) in the luminal membranes of brain and testes capillary endothelial cells. From a clinical perspective, P-gp rapidly extrudes lipophilic therapeutic agents, which then fail to reach efficacious levels. Recent studies have demonstrated that acute administration of selective serotonin reuptake inhibitors (SSRI) can affect P-gp function, in vitro and in vivo. However, little is known concerning the time-course of these effects or the effects of different SSRI in vivo.Experimental ApproachThe P-gp substrate, tritiated digoxin ([3H] digoxin), was co-administered with fluoxetine or sertraline to determine if either compound increased drug accumulation within the brains and testes of mice due to inhibition of P-gp activity. We undertook parallel studies in endothelial cells derived from brain microvessels to determine the dose-response and time-course of effects.Key Results In vitro, sertraline resulted in rapid and potent inhibition of P-gp function in brain endothelial cells, as determined by cellular calcein accumulation. In vivo, a biphasic effect was demonstrated. Brain accumulation of [3H] digoxin was increased 5 minutes after treatment with sertraline, but by 60 minutes after sertraline treatment, brain accumulation of digoxin was reduced compared to control. By 240 minutes after sertraline treatment brain digoxin accumulation was elevated compared to control. A similar pattern of results was obtained in the testes. There was no significant effect of fluoxetine on P-gp function, in vitro or in vivo.Conclusions and ImplicationsAcute sertraline administration can modulate P-gp activity in the blood-brain barrier and blood-testes barrier. This clearly has implications for the ability of therapeutic agents that are P-gp substrates, to enter the brain when co-administered with SSRI.