This study was conducted to test the hypothesis that dietary supplementation of arginine, the physiologic precursor of nitric oxide (NO), reduces fat mass in the Zucker diabetic fatty (ZDF) rat, a genetically obese animal model of type-II diabetes mellitus. Male ZDF rats, 9 wk old, were pair-fed Purina 5008 diet and received drinking water containing arginine-HCl (1.51%) or alanine (2.55%, isonitrogenous control) for 10 wk. Serum concentrations of arginine and NO(x) (oxidation products of NO) were 261 and 70% higher, respectively, in arginine-supplemented rats than in control rats. The body weights of arginine-treated rats were 6, 10, and 16% lower at wk 4, 7, and 10 after the treatment initiation, respectively, compared with control rats. Arginine supplementation reduced the weight of abdominal (retroperitoneal) and epididymal adipose tissues (45 and 25%, respectively) as well as serum concentrations of glucose (25%), triglycerides (23%), FFA (27%), homocysteine (26%), dimethylarginines (18-21%), and leptin (32%). The arginine treatment enhanced NO production (71-85%), lipolysis (22-24%), and the oxidation of glucose (34-36%) and octanoate (40-43%) in abdominal and epididymal adipose tissues. Results of the microarray analysis indicated that arginine supplementation increased adipose tissue expression of key genes responsible for fatty acid and glucose oxidation: NO synthase-1 (145%), heme oxygenase-3 (789%), AMP-activated protein kinase (123%), and peroxisome proliferator-activated receptor gamma coactivator-1alpha (500%). The induction of these genes was verified by real-time RT-PCR analysis. In sum, arginine treatment may provide a potentially novel and useful means to enhance NO synthesis and reduce fat mass in obese subjects with type-II diabetes mellitus.

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Tetrahydrobiopterin (BH4) is a member of the pterin family that has a core structure of pyrazino-2,3-d-pyrimidine rings. Because BH4 is an essential cofactor for the biosynthesis of nitric oxide (a major vasodilator), there is growing interest in BH4 biochemistry in endothelial cells (the cells that line blood vessels). BH4 is synthesized via de novo and salvage pathways from guanosine 5'-triphosphate (GTP) and 7,8-dihydrobiopterin, respectively, in animal cells. GTP cyclohydrolase-I (GTP-CH) is the first and rate-controlling enzyme in the de novo pathway. Available evidence shows that endothelial GTP-CH expression and BH4 synthesis are stimulated by a wide array of nutritional (phenylalanine and arginine), hormonal (insulin and estrogen), immunological (inflammatory cytokines including interleukin [IL]-1, interferon-gamma, and tumor necrosis factor-alpha), therapeutic (statins and cyclosporin A), and endothelium-derived (basic fibroblast growth factor and H2O2) factors. In contrast, glucocorticoids and anti-inflammatory cytokines (IL-4, IL-10, and transforming growth factor [TGF]-beta) inhibit endothelial BH4 synthesis. Because BH4 is oxidized to 7,8-dihydrobiopterin and 7,8-dihydropterin at physiological pH, endothelial BH4 homeostasis is regulated by both BH4 synthesis and its oxidation. Vitamin C, folate, and other antioxidants enhance endothelial BH4 bioavailability through chemical stabilization or scavenging of reactive oxygen species, thereby contributing to the maintenance of physiological homeostasis in the endothelium. New knowledge about the cellular and molecular mechanisms for the regulation of endothelial BH4 synthesis and bioavailability is beneficial for developing effective means to prevent and treat cardiovascular disorders, the leading cause of death in developed nations.

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Autophagy, an important intracellular degradation pathway, has been reported to clear impaired mitochondria and reduce mitochondria-mediated injury in ischemic disease. Our study and other recent investigations have shown that AKT-dependent autophagy contributes to the neuroprotection afforded by limb remote ischemic conditioning (RIC) in experimental stroke. However, how AKT triggers RIC-based autophagy and whether RIC-afforded autophagy is beneficial for mitochondrial function after cerebral ischemia remains unclear. The disruption of the Bcl-2/Beclin1 complex has been reported to trigger autophagy formation in the condition of Bcl-2 phosphorylation at Ser70. We investigated whether Bcl-2 phosphorylation triggers RIC-based autophagy and thereby confers RIC-induced neuroprotection against mitochondrial injury, using a transient cerebral ischemic rat model. We demonstrated that rats undergoing RIC treatment 30 min after the onset of ischemia (I-30) and at reperfusion (R-0) significantly upregulated Bcl-2 phosphorylation. Immunoprecipitation revealed that RIC increased dissociation of the Bcl-2/Beclin1 complex, leading to a higher level of autophagy than in ischemia/reperfusion rats. Furthermore, AKT activation was shown to play a critical role in regulating Bcl-2-mediated autophagy, as an AKT inhibitor (LY294002, AKTi) administered 30 min prior to ischemia significantly suppressed Bcl-2 phosphorylation and Bcl-2/Beclin1 complex dissociation, thereby reducing autophagy in RIC rats. Blocking Bcl-2 phosphorylation-dependent autophagy with AKTi suppressed RIC-afforded protection on mitochondrial potential and mitochondrial-dependent cell death effector pathway. These findings indicate that Bcl-2 phosphorylation and thereby Bcl-2/Beclin1 complex disruption play a crucial role in triggering autophagy and reducing mitochondrial damage in RIC rats after cerebral ischemia and require the involvement of the AKT activation.

Background and purpose Damage of the blood-brain barrier (BBB) increases the incidence of neurovascular complications, especially for cerebral hemorrhage after tPA therapy. Currently there is no effective method to evaluate the extent of BBB damage to guide tPA use. Herein, we investigated whether blood levels of tight junction proteins could serve as biomarker of BBB damages in acute ischemic stroke (AIS) in both rats and patients. We examined whether this biomarker could reflect the extent of BBB permeability during cerebral ischemia/reperfusion, and the effects of normobaric hyperoxia (NBO) on BBB damage. Methods Rats were exposed to NBO (100%O2) or normoxia (21%O2) during middle cerebral artery occlusion. BBB permeability was determined. Occludin and claudin-5 in blood and cerebromicrovessels were measured. AIS patients were assigned to oxygen therapy or room air for 4 hours, and blood occludin and claudin-5 were measured at different time points after stroke. Results Cerebral ischemia/reperfusion resulted in the degradation of occludin and claudin-5 in microvessels, leading to increased BBB permeability in rats. In blood samples, occludin increased with 4-h ischemia and remained elevated during reperfusion, correlating well with its loss from ischemic cerebral microvessels. NBO treatment both prevented occludin degradation in microvessels and reduced occludin levels in blood, leading to improved neurological functions in rats. In AIS patients receiving intravenous tPA thrombolysis, the blood occludin was already elevated when patients arrived at hospital (within 4.5 h since symptoms appeared) and remained at a high level for 72 hours. NBO significantly lowered the level of blood occludin and improved neurological functions in AIS patients. Conclusions Blood occludin may be a clinically viable biomarker for evaluating BBB damage during ischemia/reperfusion. NBO therapy has the potential to reduce blood occludin, protect BBB and improve outcome in AIS patients with intravenous tPA thrombolysis.

Background and purpose Prolonged ischemia causes blood-brain barrier (BBB) damage and increases the incidence of neurovasculature complications secondary to reperfusion. Therefore, targeting ischemic BBB damage pathogenesis is critical to reducing neurovasculature complications and expanding the therapeutic time window of tissue-type plasminogen activator (tPA) thrombolysis. This study investigates whether increasing cerebral tissue pO2 through normobaric hyperoxia (NBO) treatment will slow the progression of BBB damage and thus improve the outcome of delayed tPA treatment after cerebral ischemia. Methods Rats were exposed to NBO (100%O2) or normoxia (21%O2) during 3, 5, or 7-h middle cerebral artery occlusion. Fifteen min before reperfusion, tPA was continuously infused to rats over 30min. Neurological score, mortality rate, and BBB permeability were determined. MMP-9 was measured by gelatin zymography, and tight junction proteins (occludin and cluadin-5) by Western blot in the isolated cerebral microvessels. Results NBO slowed the progression of ischemic BBB damage pathogenesis, evidenced by reduced Evan’s blue leakage, smaller edema and hemorrhagic volume in NBO-treated rats. NBO treatment reduced MMP-9 induction and the loss of tight junction proteins in ischemic cerebral microvessels. NBO-afforded BBB protection was maintained during tPA reperfusion, resulting in improved neurological functions, significant reductions in brain edema, hemorrhagic volume and mortality rate, even when tPA was given after prolonged ischemia (7-h). Conclusions Early NBO treatment slows ischemic BBB damage pathogenesis and significantly improves the outcome of delayed tPA treatment, providing new evidence supporting NBO as an effective adjunctive therapy to extend the time window of tPA thrombolysis for ischemic stroke.

Background and Purpose Although intracellular zinc accumulation has been shown to contribute to neuronal death following cerebral ischemia, the mechanism by which zinc keeps on accumulating to cause severe brain damage remains unclear. Herein the dynamic cause-effect relationships between zinc accumulation and ROS production during cerebral ischemia/reperfusion are investigated. Methods Rats were treated with zinc chelator, ROS scavenger, mitochondria-targeted ROS inhibitor, or NADPH oxidase inhibitor during a 90-minute middle cerebral artery occlusion. Cytosolic labile zinc, ROS level, cerebral infarct volume, and neurological functions were assessed after ischemia/reperfusion. Results Zinc and ROS were colocalized in neurons, leading to neuronal apoptotic death. Chelating zinc reduced ROS production at 6 and 24h after reperfusion, whereas eliminating ROS reduced zinc accumulation only at 24h. Furthermore suppression of mitochondrial ROS production reduced the total ROS level and brain damage at 6h after reperfusion, but did not change zinc accumulation, indicating that ROS is produced mainly from mitochondria during early reperfusion and the initial zinc release is upstream of ROS generation following ischemia. Suppression of NADPH oxidase decreased ROS generation, zinc accumulation and brain damage only at 24h after reperfusion, indicating that the majority of ROS is produced by NADPH oxidase at later reperfusion time. Conclusions This study provides the direct evidence that there exists a positive feedback loop between zinc accumulation and NADPH oxidase-induced ROS production, which greatly amplifies the damaging effects of both. These findings reveal that different ROS-generating source contributes to ischemia-generated ROS at different time, underscoring the critical importance of spatial and temporal factors in the interaction between ROS and zinc accumulation, and the consequent brain injury, following cerebral ischemia/reperfusion.