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Despite effective systemic therapy, HIV-1 infection within the brain results in neuronal degradation and neurocognitive dysfunction. This neurocognitive dysfunction is worsened in the setting of opiate abuse. The central nervous system (CNS) is protected by the blood-brain barrier (BBB), a selective barrier regulating the passage of substances from peripheral circulation into the CNS. The BBB is composed of microvascular endothelial cells encased by basal lamina, pericytes, and perivascular astrocyte endfeet. Intracellular junctional complexes comprising of adherens and tight junctions are located between the endothelial cells and form tight barrier, preventing traffic of compounds between cells (paracellular flux). Clinical and in vitro data suggest that BBB integrity is compromised in HIV infection, which leads to a leaky barrier. Brain microvascular endothelial cells also express efflux transporters that are responsible for the extrusion of substances from the brain back into the blood. P-glycoprotein is a drug efflux transporter involved in the efflux of many antiretroviral drugs and overexpression of P-glycoprotein can limit therapeutic concentrations of substrate drugs within the brain. Additionally, P-glycoprotein expression and/or function may be altered in the setting of HIV infection and in the setting of drug abuse.
In order to study the impact of morphine, a commonly used opiate drug of abuse, on drug-efflux proteins at the BBB, we measured the effects of morphine and the HIV-1 protein Tat on P-glycoprotein expression and function. hCMEC/D3 cells, which are human derived brain microvascular endothelial cells, were pre-treated for 24 hours with Tat (100nM), morphine (500nM), or Tat (100nM) + morphine (500nM). P-glycoprotein function was evaluated by measuring intracellular accumulation of the prototypical P-glycoprotein substrate, rhodamine-123. Compared to control, statistically significant increases in cellular accumulation of rhodamine-123 were observed in both the morphine (mean±SEM; 118±6.5%, p<0.05) and Tat+morphine (118 ±13.1%, p<0.05) groups, suggesting decreased efflux activity of P-glycoprotein. Protein expression of P-glycoprotein was measured using western blot analysis. Significant decreases in P-glycoprotein expression was observed in all treatment groups as compared to control; Tat (63±4.2%, p< 0.05), morphine (64±13.5%, p<0.05) and Tat+morphine (69±15.6%, p<0.05). Understanding the factors that influence efflux transporter function and expression in the BBB are crucial in optimizing antiretroviral penetration into the brain, even in the setting of drug abuse.
Blood-Brain Barrier, HIV, substance abuse drugs, drug-efflux proteins, morphine, P-glycoprotien
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