We examined the role of VAP-1 in the increased leukocyte adhesion seen in cerebral venules during the reperfusion period following transient forebrain ischemia (TFI). We used a model associated with a high level of post-ischemic leukocyte adhesion and infiltration — diabetic (6–8 wks post-streptozotocin) OVX females given 1 week of estrogen replacement therapy (ERT). The behavior of rhodamine 6G-labeled leukocytes in pial venules was monitored through a closed cranial window, using intravital microscopy and digital videometry. The rats were observed over 10 h reperfusion after 20 min TFI. We compared rats treated (at 0 h or 6 h reperfusion) with saline or the novel and selective VAP-1 blocker, LJP-1207 (30 mg/kg iv). Since results in the 2 control groups were indistinguishable, the data was pooled (n=6). In controls, increased neutrophil adherence was observed within 1 h of reperfusion onset. The intravascular accumulation of adherent leukocytes was seen to gradually rise up to the point where neutrophil infiltration commenced (at >6 h, in 83% of controls — fig. 1). Not counting extravasated cells, neutrophil adhesion reached ∼17% of the viewed venular area at 6–10 h (fig. 2). In the rats treated with LJP-1207 at the onset of reperfusion (0 h, n=5), limited neutrophil adhesion, and no infiltration, was observed over the entire 10 h period of post-ischemic observation (fig. 1), with the level of adhesion rising only to ∼5% of the venular area (fig. 2). In rats treated at 6 h reperfusion (n=4), the pattern of neutrophil adhesion was similar to that of the control group up to 6 h, but subsequent infiltration was much more limited vs controls (fig. 1), and the level of adhesion actually declined (from ∼14% to ∼9%) when going from 6–10 h reperfusion (fig. 2). These findings indicate that VAP-1, presumably on cerebral vascular endothelium, plays a major role in the process of leukocyte adhesion, as well as infiltration, in diabetic OVX females provided with chronic ERT.
