We previously demonstrated that the high levels of oxidative stress in the brains of ten-week-old strokeprone hypertensive rats (SHRSP) were attributable to intrinsic, not extrinsic factors (Biol. Pharm. Bull., 33, 2010, Michihara et al.). The aim of the present study was to determine whether increases in the enzymes producing reactive oxygen species (ROS), reductions in the enzymes and proteins removing ROS, or increases in an enzyme and transporter removing antioxidants promoted oxidative stress in the SHRSP cerebrum. No significant decreases were observed in the mRNA levels of enzymes that remove ROS between SHRSP and normotensive Wistar Kyoto rats. The activity of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) and the protein and mRNA levels of NOX3, an enzyme that produces ROS, were significantly increased in the SHRSP cerebrum. These results suggested that the high expression levels of NOX3 increased oxidative stress in the SHRSP cerebrum.Key words oxidative stress; brain; oxidase; stroke; rat Reactive oxygen species (ROS), including superoxide, hydrogen peroxide, and the hydroxyl radical, are byproducts of oxygen metabolism in cells, and are produced in all oxygenutilizing organs. Oxidative stress is known to occur when an imbalance exists between the production and removal of ROS by the antioxidant system. 1) Oxidative stress has been implicated in the development of several diseases such as cancer, Alzheimer's disease, cardiovascular disease, hypertension, and stroke.2,3) The main cause of stroke is hypertension. An epidemiological study identified lower serum cholesterol levels as a cause of cerebral hemorrhage.4) On the other hand, ROS have been shown to play a role in the development of brain injury following cerebral hemorrhage, 5) and secondary brain injury after cerebral hemorrhage has also been associated with oxidative stress. 6) These findings suggest that not only hypertension and lower serum cholesterol levels, but also oxidative stress is responsible for the development of stroke.Oxidative stress is generally caused by an increase in the levels of enzymes producing ROS and free radicals, or a reduction in antioxidant levels or the enzymes that remove ROS and free radicals. Superoxide dismutase (SOD) catalyzes the conversion of superoxide to hydrogen peroxide (H 2 O 2 ), which is then reduced to H 2 O and O 2 by catalase (CAT), the glutathione system, comprising glutathione peroxidase (GPX) and glutathione reductase (GR), 7) or the thioredoxin system, which consists of thioredoxin (TXN), peroxiredoxin (PRX), and thioredoxin reductase (TXNR).8) A previous study reported that the main enzymes detoxifying H 2 O 2 were the glutathione system in the brain, the TXN system in mitochondria, and catalase in peroxisomes. 9) Uncoupling protein 2 (UCP2), which is a mitochondrial inner membrane carrier protein, acts as a negative regulator of ROS production. 10) Uric acid, which is a natural antioxidant, was previously reported to be effluxed by ATP-binding cassette subfamily G ...

A lower serum cholesterol level was recently shown to be one of the causes of stroke in an epidemiological study. Spontaneously hypertensive rats stroke-prone (SHRSP) have lower serum cholesterol levels than normotensive Wistar-Kyoto rats (WKY). To elucidate the mechanisms responsible for the lower serum cholesterol levels in SHRSP, we determined whether the amounts of cholesterol biosynthetic enzymes or the receptor and transporter involved in cholesterol uptake and efflux in the liver were altered in SHRSP. When the mRNA levels of seven cholesterol biosynthetic enzymes were measured using real-time polymerase chain reaction (PCR), farnesyl pyrophosphate synthase and squalene epoxidase (SQE) levels in the liver of SHRSP were significantly lower than those in WKY. SQE protein levels were significantly reduced in tissues other than the brain of SHRSP. No significant differences were observed in low-density lipoprotein (LDL) receptor (uptake of serum LDL-cholesterol) or ATP-binding cassette transporter A1 (efflux of cholesterol from the liver/formation of high-density lipoprotein (HDL)) protein levels in the liver and testis between SHRSP and WKY, whereas scavenger receptor class B type 1 (SRB1: uptake of serum HDL-cholesterol) protein levels were higher in the livers of SHRSP. These results indicated that the lower protein levels of SQE and higher protein levels of SRB1 in the liver were involved in the reduced serum cholesterol levels in SHRSP.Key words squalene epoxidase; scavenger receptor class B type 1; stroke; cholesterol; liver An epidemiological study identified lower serum cholesterol levels as one of the causes of cerebral hemorrhage because the risk of death from cerebral hemorrhage was found to be threefold higher in men with lower serum cholesterol levels than in those with higher cholesterol levels. 1,2)Cholesterol is a major constituent of cellular membranes; therefore, reductions in the cholesterol content in the cell have been shown to reduce the proliferation of cells, enhance cell membrane fluidity, and lead to fragile plasma membranes. 3-5)Therefore, lower serum cholesterol is regarded as an important cause of cerebral hemorrhage.Spontaneously hypertensive rats (stroke-prone) (SHRSP) are rats with severe hypertension and stroke.6,7) Serum cholesterol levels in these rats are lower than those in normotensive Wistar Kyoto rats (WKY).8) Shiota et al. reported that the pathogenesis of stroke in SHRSP was inhibited by the feeding of high fat and cholesterol diets. 9) These findings showed that reductions in the content of cholesterol in vascular endothelial cells (VECs) in the SHRSP brain due to lower serum cholesterol levels may lead to cerebral hemorrhage following a disruption in the blood-brain barrier (BBB). Disruptions in the BBB have previously been reported in the hypothalamus and hippocampus of SHRSP.10,11) Furthermore, damage to endothelial cells has been implicated in disruptions in the BBB. Therefore, lower serum cholesterol levels in SHRSP may play a role in the development of cerebral...