Lipopolysaccharide impairs blood-brain barrier P-glycoprotein function in mice through prostaglandin- and nitric oxide-independent pathways

Abstract

P-glycoprotein (P-gp) is a brain-to-blood efflux system that controls the ability of many drugs and endogenous substances to access the brain. In vitro work has shown that inflammatory states mediated through lipopolysaccharide (LPS) and tumor necrosis factor-alpha first impair and then stimulate P-gp activity. Here, we determined whether LPS can affect P-gp function in vivo. Mice treated with a single intraperitoneal injection of LPS (3 mg/kg) showed an inhibition of P-gp function. As assessed by brain perfusion, inhibition began 18 h after LPS administration and lasted until 36 h after administration. P-gp protein was increased by 44%, consistent with P-gp inhibition occurring through post-translational mechanisms. Unlike other effects of LPS on blood-brain barrier function, neither nitric oxide nor prostaglandin inhibition had an effect. We conclude that induction of proinflammatory states as exemplified by LPS treatment can inhibit P-gp function in vivo at the blood-brain barrier.

Fig. 1

LPS increases retention of H-Ver. a Preliminary time curve with single i.p. injection of LPS (3 mg/kg) and subsequent evaluation of H-Ver retention as assessed by brain perfusion. Only the 24 h showed an increased retention (*p<0.05), consistent with inhibition of P-gp. b C-Suc and uncorrected H-Ver values at various time points (a and b are the only experiments in which H-Ver was not corrected for C-Suc space). c Time curve showing single i.p. injection of LPS produces statistically significant (*p<0.05) inhibition of P-gp 18, 24, and 36 h after LPS injection. H-Ver uptake was studied by brain perfusion. d Inhibition of H-Ver efflux with cyclosporin. e Mice were treated with a single injection of LPS and at various times after given i.v. injections of H-Ver and C-Suc. Brain/serum ratios corrected for the C-Suc space showed increased uptake at 6, 8, and 24 h after LPS administration (*p<0.05; **p<0.01). f LPS (3 mg/kg) was injected i.p. at 0, 6, and 24 h and uptake of H-Ver studied by brain perfusion at 28 h. Mice treated with LPS retained more H-Ver (*p<0.05) demonstrating inhibition of P-gp.

Fig. 2

a Typical Western blots of P-gp and actin. b Quantitation of Western blotting of brain for P-gp protein. LPS treatment produced a significant increase in P-gp protein

Fig. 3

a Prostaglandin inhibition with indomethacin did not affect control or LPS-induced uptake of H-Ver. b Nitric oxide inhibition with l-NAME did not inhibit control or LPS-induced uptake of H-Ver. c Indomethacin and l-NAME blocked LPS-enhanced transport or insulin across the blood–brain barrier