Effect of chronic exposure to morphine on the rat blood–brain barrier: focus on the P‐glycoprotein

Abstract

Morphine is well tolerated but addictive, especially for heroin consumers, as heroin is rapidly metabolised to morphine in humans. The hypothesis that psychostimulant drugs, like morphine and/or its withdrawal may cause severe stress that could affect the properties of the blood-brain barrier (BBB) by modifying BBB constitutive markers has been poorly investigated. A recent study has shown that the integrity of the BBB of rats chronically given morphine is altered from 1 day after the last morphine dose, which would be related to the morphine-induced withdrawal syndrome (Sharma and Ali 2006) Abbreviations used: ABC, ATP-binding cassette; BBB, blood-brain barrier; BSA, bovine serum albumin; GFAP, glial fibrillary acidic protein; HIP, hippocampus; Mdr, multidrug resistance; Mrp, multidrug resistance-associated protein; NA, nucleus accumbens; PB, phosphate buffer; PBS, phosphate-buffered saline; P-gp, P-glycoprotein; qRT-PCR, quantitative RT-PCR; RT, room temperature; ZO, zonula occludens. AbstractMorphine may affect the properties of the blood-brain barrier (BBB) by modifying the expression of certain BBB markers. We have determined the effect of chronic morphine treatment on the expression and function of some BBB markers in the rat. The mRNAs of 19 selected genes encoding caveolins, endothelial transporters, receptors and tight junctions proteins in the total RNA of isolated cortex microvessels were assayed by quantitative RT-PCR (qRT-PCR). The expression of genes Mdr1a, Mrp1, Bcrp, Glut-1 and Occludin, was slightly increased, while that of Flk-1 was decreased in microvessels from morphine-treated rats. The expression of the Mrd1a and Mdr1b genes encoding the P-glycoprotein (P-gp) also increased in the whole hippocampus and cortex of morphinetreated rats. The Mdr1a gene induction (1.38-fold) observed by qRT-PCR was also confirmed using in situ hybridization technique (1.40-fold). Immunoblotting revealed an increase in P-gp expression in the hippocampus (1.8-fold) and cortex (1.36-fold) of morphine-treated rats, but no effect in isolated microvessels. In contrast, morphine treatment increased by 1.48-fold the expression of P-gp in a large vessel-enriched fraction. The integrity of the BBB, measured by in situ brain perfusion of [ 14 C]-sucrose, and the activity of P-gp at the BBB, measured with the P-gp substrate [ 3 H]-colchicine, were not modified by morphine. Immunohistofluorescence experiments revealed that P-gp expression is restricted to large vessels and microvessels in control rats and that morphine treatment did not induce the expression of P-gp in the brain parenchyma (astrocytes or neurons). Taken together, our results showed that chronic morphine treatment does not significantly alter BBB integrity or P-gp activity. The impact of morphine-mediated P-gp induction observed in large vessels remains to be determined in terms of brain disposition of drugs that are P-gp substrates.

Detection of doxorubicin hydrochloride accumulation in the rat brain after morphine treatment by mass spectrometry

“…In rats chronically treated with morphine, in situ perfusion of sucrose did not allow its penetration into the BBB [15].…”

“…Data on the effects of chronic exposure to morphine are conflicting [14,15]. In rats chronically treated with morphine, in situ perfusion of sucrose did not allow its penetration into the BBB [15].…”

Effect of Subchronic Intravenous Morphine Infusion and Naloxone-Precipitated Morphine Withdrawal on P-gp and Bcrp at the Rat Blood–Brain Barrier

“…11,23 The aim of this new work was to know whether morphine itself or its subsequent precipitated withdrawal syndrome was responsible for P-gp and Bcrp upregulation in the rat BBB.…”

Quantitative Membrane Protein Expression at the Blood–Brain Barrier of Adult and Younger Cynomolgus Monkeys

“…It was also reported that the relative mRNA expression of breast cancer resistance protein (BCRP/ABCG2) to MDR1/mdr1a/ABCB1 was higher in human brain microvessels than in rat brain microvessels. 6,7 However, mRNA expression levels do not necessarily correlate with protein expression levels. Indeed, it was reported that the protein expression of MDR1 and BCRP was downregulated by activation of estrogen receptor "-related pathways without any change of mRNA expression.…”