Concern about intracerebral hemorrhage (ICH) is the primary reason for withholding tPA therapy from patients with ischemic stroke. Early blood brain barrier (BBB) damage is the major risk factor for fatal post-thrombolysis ICH, but rapidly assessing BBB damage before tPA administration is highly challenging. We recently reported that ischemia induced rapid degradation of tight junction protein occludin in cerebromicrovessels. The present study investigates whether the cleaved occludin is released into the blood stream and how blood occludin levels correlate to the extent of BBB damage using a rat model of ischemic stroke. Cerebral ischemia induced a time-dependent increase of blood occludin with a sharp increase at 4.5-hour post-ischemia onset, which concurrently occurred with the loss of occludin from ischemic cerebral microvessels and a massive BBB leakage at 4.5-hour post-ischemia. Two major occludin fragments were identified in the blood during cerebral ischemia. Furthermore, blood occludin levels remained significantly higher than its basal level within the first 24 hours after ischemia onset. Our findings demonstrate that blood occludin levels correlate well with the extent of BBB damage and thus may serve as a clinically relevant biomarker for evaluating the risk of ICH before tPA administration.

Abuse of methamphetamine (METH) is a major and significant societal problem in the US, as a number of studies have suggested that METH is associated with increased cerebrovascular events, hemorrhage or vasospasm. Although cellular and molecular mechanisms involved in METH-induced toxicity are not completely understood, changes in brain O2 may play an important role and contribute to METH-induced neurotoxicity including dopaminergic receptor degradation. Given that O2 is the terminal electron acceptor for many enzymes that are important in brain function, the impact of METH on brain tissue pO2 in vivo remains largely uncharacterized. This study investigated striatal tissue pO2 changes in male C57BL/6 mice (16–20g) following METH administration using EPR oximetry, a highly sensitive modality to measure pO2 in vivo, in situ and in real time. We demonstrate that 20 min after a single injection of METH (8 mg/kg i.v.), the striatal pO2 was reduced to 81% of the pretreatment level and exposure to METH for 3 consecutive days further attenuated striatal pO2 to 64%. More importantly, pO2 did not recover fully to control levels even 24 hrs after administration of a single dose of METH. and continual exposure to METH exacerbates the condition. We also show a reduction in cerebral blood flow associated with a decreased brain pO2 indicating an ischemic condition. Our findings suggests that administration of METH can attenuate brain tissue pO2, which may lead to hypoxic insult, thus a risk factor for METH-induced brain injury and the development of stroke in young adults.

Background and Purpose: Fear of symptomatic intracerebral hemorrhage (ICH) has been the primary reason for withholding tPA thrombolysis from acute ischemic stroke patients. Early blood brain barrier (BBB) damage is appreciated to be closely associated with post-thrombolysis ICH, while it remains a technical challenge for rapid assessment of BBB damage before tPA administration. Our recent data showed that cerebral ischemia induced rapid degradation of tight junction protein occludin in ischemic cerebromicrovessels. This study further investigates whether the cleaved occludin is released into the blood stream and how blood occludin levels correlate to the extent of ischemic BBB damage. Methods: Male Sprague Dawley rats were subjected to 1.5, 3, 4.5, 12 and 24 hours of middle cerebral artery occlusion (MCAO), followed by 5-min reperfusion. Blood samples were taken before and after MCAO. Blood occludin was assessed by ELISA. BBB permeability was measured by Evans blue dye leakage. Occludin cleavage was identified on immunoblots. Results: MCAO induced Evans blue dye leakage and blood occludin increase in a duration-dependent manner. Blood occludin increase concurrently occurred with the loss of occludin from ischemic cerebral microvessels. Western blot analysis identified two cleaved occludin fragments (31- and 55- kDa) in the blood. Lastly, blood occludin levels remained significantly higher than its basal level within the first 24 hours after MCAO onset. Conclusions: Our results indicate that blood occludin levels correlate well with the extents of BBB damage and thus may serve as a potential biomarker for evaluating the risk of hemorrhagic transformation before tPA administration.