Viability of microvascular endothelial cells to direct exposure of formalin, λ-carrageenan, and complete Freund's adjuvant

We investigated three inflammatory agents to establish if these substances elicit a direct effect on the functional and structural integrity of the blood-brain barrier. Cellular cytotoxicity and paracellular permeability were assessed in vitro using primary bovine brain microvascular endothelial cells exposed to formalin, λ-carrageenan, or complete Freund's adjuvant for 1, 3, or 72 h, respectively. Results showed that only the highest concentration (0.025%) of formalin produced a decrease in cell viability (∼34%) and a significant increase in cell permeability to [¹⁴C]sucrose at 120 min (∼137%). Brain perfusion using female Sprague-Dawley rats showed no difference in paracellular permeability to [¹⁴C]sucrose for any inflammatory agent. Western blot analyses were performed on isolated rat brain microvessels to assess the structural integrity of blood-brain barrier tight junctions. Results indicate that expression of zonula occludens-1, occludin, claudin-1, and actin remain unchanged following intravenous exposure to inflammatory agents. This study confirms that changes seen at the blood-brain barrier following a peripheral inflammation are due to physiological responses to the given inflammatory agent and not to any direct interaction between the inflammatory agent and the brain microvasculature.