Loss of shear stress induces leukocyte‐mediated cytokine release and blood–brain barrier failure in dynamic in vitro blood–brain barrier model

Abstract

Brain ischemia is associated with an acute release of pro-inflammatory cytokines, notably TNF-alpha and IL-6 and failure of the blood-brain barrier. Shear stress, hypoxia-hypoglycemia, and blood leukocytes play a significant role in blood-brain barrier failure during transient or permanent ischemia. However, these mechanisms have not been studied as independent variables for in vitro ischemia. The present study, using a dynamic in vitro blood-brain barrier model, showed that flow cessation/reperfusion under normoxia-normoglycemia or hypoxia-hypoglycemia without blood leukocytes in the luminal perfusate had a modest, transient effect on cytokine release and blood-brain barrier permeability. By contrast, exposure to normoxic-normoglycemic flow cessation/reperfusion with blood leukocytes in the luminal perfusate led to a significant increase in TNF-alpha and IL-6, accompanied by biphasic blood-brain barrier opening. Enhanced permeability was partially prevented with an anti-TNF-alpha antibody. In leukocyte-free cartridges, the same levels of IL-6 had no effect, while TNF-alpha caused a moderate increase in blood-brain barrier permeability, suggesting that blood leukocytes are the prerequisite for cytokine release and blood-brain barrier failure during reduction or cessation of flow. These cells induce release of TNF-alpha early after ischemia/reperfusion; TNF-alpha triggers release of IL-6, since blockade of TNF-alpha prevents IL-6 release, whereas blockade of IL-6 induces TNF-alpha release. Pre-treatment of blood leukocytes with the cyclooxygenase (COX) inhibitor, ibuprofen, inhibited cytokine release and completely preserved blood-brain barrier permeability during the reperfusion period. In conclusion, loss of flow (flow cessation/reperfusion) independent of hypoxia-hypoglycemia plays a significant role in blood-brain barrier failure by stimulating leukocyte-mediated inflammatory mechanisms.

Increased muscle sympathetic nerve activity predicts mortality in heart failure patients

“…The reduction in forearm blood flow may lead to activation of tissue pro-inflammatory agents [25], and cachexia [26], thereby worsening outcomes. The consequences of such changes are exercise intolerance, early fatigue, and progression in heart failure [27,28].…”

A novel in vitro ischemia/reperfusion injury model

“…Compelling body of evidence has indicated that ischemia/reperfusion injury is closely associated with inflammatory reactions in vascular endothelium. For example, Krizanac-Bengez et al (2006) showed that exposure of a dynamic in vitro blood-brain barrier (BBB) model to flow cessation/ reperfusion resulted in an acute release of proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and IL-6, and disruptions of BBB integrity. It was also found that myocardial ischemia/ reperfusion injury is related to an inflammatory response through attachment of polymorphonuclear leukocytes (PMNs) to the vascular endothelium with subsequent infiltration into the damaged myocardium (Hansen, 1995;Onai et al, 2003).…”

Immortalized Human Brain Endothelial Cells and Flow-Based Vascular Modeling: A Marriage of Convenience for Rational Neurovascular Studies

“…These data were confirmed by measurements of IL-1b, IL-6, and MMP-9 release in medium samples (Figure 10). Pretreatment with ibuprofen significantly reduced the release of proinflammatory cytokines IL-1b, IL-6, and of MMP-9, all of which have been shown to be involved in the regulation of BBB permeability (Krizanac-Bengez et al, 2006;Shigemori et al, 2006). It should be noted that HCMEC/D3 cells grown in the DIV-BBB system under flow in the absence of astrocytes are capable of mimicking the physiological behavior of the BBB in vivo in response to systemic inflammation.…”

“…In particular, the effect of loss of shear stress in presence of WBC under normoglycemic condition causes BBB failure by triggering proinflammatory events such as release of cytokines and MMPs and the activation of WBC (Gasche et al, 2006;Krizanac-Bengez et al, 2006;Latour et al, 2004). Figure 9A shows the baseline TEER values of the four separate control DIV-BBB modules established with the brain microvascular human cell line HCMEC/D3.…”