Abstract
BackgroundDisruption of the blood-brain barrier (BBB) occurs in many diseases and is often mediated by inflammatory and neuroimmune mechanisms. Inflammation is well established as a cause of BBB disruption, but many mechanistic questions remain.MethodsWe used lipopolysaccharide (LPS) to induce inflammation and BBB disruption in mice. BBB disruption was measured using 14C-sucrose and radioactively labeled albumin. Brain cytokine responses were measured using multiplex technology and dependence on cyclooxygenase (COX) and oxidative stress determined by treatments with indomethacin and N-acetylcysteine. Astrocyte and microglia/macrophage responses were measured using brain immunohistochemistry. In vitro studies used Transwell cultures of primary brain endothelial cells co- or tri-cultured with astrocytes and pericytes to measure effects of LPS on transendothelial electrical resistance (TEER), cellular distribution of tight junction proteins, and permeability to 14C-sucrose and radioactive albumin.ResultsIn comparison to LPS-induced weight loss, the BBB was relatively resistant to LPS-induced disruption. Disruption occurred only with the highest dose of LPS and was most evident in the frontal cortex, thalamus, pons-medulla, and cerebellum with no disruption in the hypothalamus. The in vitro and in vivo patterns of LPS-induced disruption as measured with 14C-sucrose, radioactive albumin, and TEER suggested involvement of both paracellular and transcytotic pathways. Disruption as measured with albumin and 14C-sucrose, but not TEER, was blocked by indomethacin. N-acetylcysteine did not affect disruption. In vivo, the measures of neuroinflammation induced by LPS were mainly not reversed by indomethacin. In vitro, the effects on LPS and indomethacin were not altered when brain endothelial cells (BECs) were cultured with astrocytes or pericytes.ConclusionsThe BBB is relatively resistant to LPS-induced disruption with some brain regions more vulnerable than others. LPS-induced disruption appears is to be dependent on COX but not on oxidative stress. Based on in vivo and in vitro measures of neuroinflammation, it appears that astrocytes, microglia/macrophages, and pericytes play little role in the LPS-mediated disruption of the BBB.
Highlights
Disruption of the blood-brain barrier (BBB) occurs in many diseases and is often mediated by inflammatory and neuroimmune mechanisms
Soluble TREM2 ELISA To quantify the concentrations of soluble triggering receptor expressed on myeloid cells 2 (TREM2) extracellular domain in mouse EDTA-plasma samples, we adapted an anti-TREM2 ELISA system similar to that reported by Kleinberger et al [35,36,37]
The highest dose of LPS (3 mg/kg) administered to CD-1 mice produced a significant increase in BBB permeability as measured with 14C-sucrose (Fig. 1), whereas the lower two doses were without effect
Summary
Disruption of the blood-brain barrier (BBB) occurs in many diseases and is often mediated by inflammatory and neuroimmune mechanisms. Inflammation has long been known to disrupt the BBB. Eckman et al as early as 1958 and Allen a few years later showed that gram-negative endotoxin was associated with BBB disruption [3, 4]. Gram-negative endotoxin in its more purified form of lipopolysaccharide (LPS) is known to disrupt the BBB and alters many other aspects of BBB function, including adsorptive transcytosis, immune cell trafficking, and various transport functions [5,6,7,8,9]. A number of diseases that include multiple sclerosis, Alzheimer’s disease, diabetes mellitus, obesity, and stroke have been associated with both inflammation and BBB disruption [10,11,12,13,14]
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