Lipopolysaccharide-induced blood-brain barrier disruption: roles of cyclooxygenase, oxidative stress, neuroinflammation, and elements of the neurovascular unit

Background: Disruption 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. Methods: We 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. Results: In 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. Conclusions: The 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

Angiotensin II AT1 Receptor Blockade Ameliorates Brain Inflammation

Brain inflammation has a critical role in the pathophysiology of brain diseases of high prevalence and economic impact, such as major depression, schizophrenia, post-traumatic stress disorder, Parkinson's and Alzheimer's disease, and traumatic brain injury. Our results demonstrate that systemic administration of the centrally acting angiotensin II AT1 receptor blocker (ARB) candesartan to normotensive rats decreases the acute brain inflammatory response to administration of the bacterial endotoxin lipopolysaccharide (LPS), a model of brain inflammation. The broad anti-inflammatory effects of candesartan were seen across the entire inflammatory cascade, including decreased production and release to the circulation of centrally acting proinflammatory cytokines, repression of nuclear transcription factors activation in the brain, reduction of gene expression of brain proinflammatory cytokines, cytokine and prostanoid receptors, adhesion molecules, proinflammatory inducible enzymes, and reduced microglia activation. These effects are widespread, occurring not only in well-known brain target areas for circulating proinflammatory factors and LPS, that is, hypothalamic paraventricular nucleus and the subfornical organ, but also in the prefrontal cortex, hippocampus, and amygdala. Candesartan reduced the associated anorexic effects, and ameliorated associated body weight loss and anxiety. Direct anti-inflammatory effects of candesartan were also documented in cultured rat microglia, cerebellar granule cells, and cerebral microvascular endothelial cells. ARBs are widely used in the treatment of hypertension and stroke, and their anti-inflammatory effects contribute to reduce renal and cardiac failure. Our results indicate that these compounds may offer a novel and safe therapeutic approach for the treatment of brain disorders