Effects of nicotine on blood flow and delayed neuronal death following intermittent transient ischemia in rat hippocampus

A cholinergic neural vasodilative response in the cerebral cortex and hippocampus, independent of metabolic vasodilation, was recently demonstrated by activating the nicotinic acetylcholine receptors (nAChRs) via activation of cholinergic neurons originating in the nucleus basalis of Meynert and septal complex in the basal forebrain and projecting to the cortex and hippocampus (see reviews by Sato A and Sato Y: Neurosci Res 14: 242--274, 1992; Sato A and Sato Y: Alzheimer Dis Assoc Disord 9: 28--38, 1995). In the present study, we aimed to examine whether an increase in regional blood flow in the hippocampus (Hpc-BF) following stimulation of the nAChRs by i.v. injection of nicotine could improve the delayed death of the hippocampal neurons following transient ischemia in rats. Hpc-BF was measured by using a laser Doppler flowmeter. During intermittent (every 2 min) transient occlusion for a total of 6 min of bilateral carotid arteries besides permanent ligation of bilateral vertebral arteries, Hpc-BF decreased to about 16% of the preocclusion level, and 5 or 7 d later, after the occlusion, delayed neuronal death occurred in approximately 70% of the CA1 hippocampal neurons. Hpc-BF was increased dose-dependently by injection of nicotine (30--100 microg/kg, i.v.), independent of mean arterial pressure. Nicotine (30--100 microg/kg) administered 5 min before occlusion slightly but significantly attenuated the occlusion-induced decrease in Hpc-BF. The delayed death of the CA1 hippocampal neurons occurring after transient occlusion was attenuated by pretreatment with nicotine (30--100 microg/kg) to approximately 50% of the total neurons. The results indicate that nAChR stimulation-induced increases in Hpc-BF can protect against ischemia-induced delayed death of hippocampal neurons.     

Mechanisms underlying the impaired regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in aged rat liver

As the main risk factor for cardiovascular disease, hypercholesterolemia is one of the most studied age-related metabolic alterations. In the liver, cholesterol homeostasis is strictly regulated through the modulation of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), the key enzyme of cholesterol biosynthesis. With ageing, hepatic HMG-CoA reductase becomes completely activated and cholesterol content increases in the blood. The research reported in this paper uses the regulatory enzymes of reductase (i.e., the AMP-dependent kinase (AMPK) and the protein phosphatase 2A (PP2A)), the HMG-CoA reductase thermodependent activity and the "in vitro" enzyme degradation to elucidate the role played by the HMG-CoA reductase regulation and its membrane interaction. Related experiments were performed on 3 and 24 months "ad libitum" (AL) fed rats and 24 months caloric-restricted rats. The results show no changes in the PP2A level and the activation state of AMP dependent kinase in aged "ad libitum" fed rats. By contrast, the activation state of the kinase is enhanced in the aged caloric-restricted animals. With respect to the adult, the thermodependent activity of reductase remains unchanged, while the degradation rate of the HMG-CoA reductase is slower and independent on proteasome. These findings support the hypothesis that a different arrangement of the HMG-CoA reductase membrane domain in aged rats is a cause of reductase deregulation.     

Hepatic effects in beagle dogs administered atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, for 2 years.

The chronic toxicity of atorvastatin (AT), an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, was evaluated in beagle dogs. Dogs were treated with 0, 10, 40, or 120 mg/kg of AT daily. Treatment lengths were 52 wk, 52 wk followed by 12 wk without drug, or 104 wk. Decreases in cholesterol levels were dose related and stable throughout the treatment period. Increases in alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase were transient and dose related in severity at > or = 40 mg/kg. Two dogs administered 120 mg/kg of AT daily were sacrificed moribund during the first 9 wk of treatment. Hepatic lesions were reversible with or without continued treatment and dose related in severity and distribution. Hepatic microgranulomas and hepatocellular degeneration were seen at the 120-mg/kg dose in dogs sacrificed before 53 wk. Before 53 wk, hepatocellular lipofuscin deposits were increased in dogs given > or = 40 mg/kg of AT daily but were similar to controls after 12 wk without drug and after 104 wk of continuous treatment. Bile stasis occurred in dogs given > or = 40 mg/kg of AT daily at all time points but was less severe after reversal and at week 104 compared with week 52.     

Co-existence of necrosis and apoptosis in rat hippocampus following transient forebrain ischemia

Morphological changes of CA1 and CA3 pyramidal neurons in rat hippocampus at different intervals following transient forebrain ischemia were examined to determine the nature of post-ischemic cell death in these regions. In the CA1 region, swelling of small dendrites occurred at approximately 24 h reperfusion. At approximately 48 h reperfusion, swelling was found in large dendrites of many CA1 neurons and the mitochondria and endoplasmic reticulum (ER) were dilated. A small portion of neurons showed chromatin aggregation and nuclear indentation without swelling signs. At approximately 60 h reperfusion, swelling of somata was evident in many neurons. Large dense chromatin clumps with round or ovoid contour were found in other neurons. At 72 and 96 h after ischemia, many large vacuoles and glias with active phagocytosis were observed. At 7 days after ischemia, the tissue was compact and many glias were found in the region. Most of the CA3 neurons had normal appearance after ischemia. A total of 5-10% CA3 neurons exhibited shrinking nuclei and chromatin aggregation at approximately 24 h reperfusion. The number of these neurons decreased overtime and disappeared at 72 h after ischemia. These results demonstrate the co-existence of necrosis and apoptosis in the CA1 region after transient forebrain ischemia. Most CA3 neurons remained intact after ischemia while a small portion of them showed apoptotic cell death.     

Sequence comparisons reveal two classes of 3-hydroxy-3-methylglutaryl coenzyme A reductase

Both in eukaryotes and in archaebacteria the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (E.C. 1.1. 1.34) is known to catalyze an early reaction unique to isoprenoid biosynthesis. In humans, the HMG-CoA reductase reaction is rate-limiting for the biosynthesis of cholesterol and therefore constitutes a prime target of drugs that reduce serum cholesterol levels. Recent advances in genome sequencing that permitted comparison of 50 HMG-CoA reductase sequences has revealed two previously unsuspected classes of this enzyme. Based on sequence and phylogenetic considerations, we propose the catalytic domain of the human enzyme and the enzyme from Pseudomonas mevalonii as the canonical sequences for Class I and Class II HMG-CoA reductases, respectively. These sequence comparisons have revealed, in addition, that certain true bacteria, including several human pathogens, probably synthesize isoprenoids by reactions analogous to those of eukaryotes and that there therefore exist two distinct pathways for isoprenoid biogenesis in true bacteria.     

Preventive effect of simvastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on coronary atherosclerosis in cholesterol-fed rabbits

A study was made on the effect of simvastatin (the generic name of MK-733), a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, on coronary atherosclerosis in cholesterol-fed rabbits with focus on the serum lipids and morphology. Twenty-seven Japanese white rabbits were divided according to dosage of simvastatin into four groups as follows, group P (placebo, 5 rabbits), group MK 1 (simvastatin 1mg/kg, 5 rabbits), group MK 3 (simvastatin 3mg/kg, 6 rabbits) and group MK 5 (simvastatin 5mg/kg, 5 rabbits). They were placed on a 0.5% cholesterol atherogenic diet for 16 weeks and measurements were made of the concentration of serum lipids weekly. After sacrifice, the degree of surface involvement (SI) of aorta stained with Sudan III and the degree of coronary stenosis (CS) of the left circumflex artery were measured using an image-processing system. Serum total cholesterol (TC) level and beta-lipoprotein level decreased dose-dependently in MK groups compared with group P. High density lipoprotein cholesterol level increased in groups MK 3 and MK 5 slightly. Triglyceride level decreased in groups MK 3 and MK 5. The progressions of SI and CS were suppressed in MK groups dose-dependently. Integrated TC, that is, sum of the serum TC values obtained at each week multiplied by 7 corresponded more closely to CS than SI. Intimal thickening constructed from large foam cells originated from macrophages and proliferating smooth muscle cells included lipid droplets in MK groups was almost similar in group P. But it was likely that lipid droplets in each smooth muscle cell in MK groups were less than in group P. In conclusion, the development of coronary atherosclerosis in cholesterol-fed rabbits was suppressed dose-dependently by simvastatin and it was suggested that this preventive effect was due to reducing the integrated TC and local action to vessel walls by simvastatin. (Fukuoka Acta Med.)     

Potential utility of statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in diabetic retinopathy

Diabetic retinopathy is a common and potentially devastating microvascular complication in diabetes and is a leading cause of acquired blindness among the people of occupational age. However, therapeutic options for the treatment of proliferative diabetic retinopathy, photocoagulation and vitrectomy, are limited by considerable side effects. Therefore, to develop novel therapeutic strategies that specifically target diabetic retinopathy is desired for patients with diabetes. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress. There is a growing body of evidence to show that AGEs-their receptor (RAGE) interactions are involved in the development and progression of diabetic retinopathy. Statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, have been recently shown to reduce the risk for cardiovascular events in diabetic patients with or without coronary artery disease. However, the efficacy of statin therapy for diabetic retinopathy is not fully investigated. We have recently found that protein prenylation is crucial for the AGE-RAGE signaling in microvascular endothelial cells. By blocking the protein prenylation, cerivastatin completely prevented the AGE-RAGE-elicited angiogenesis via suppression of vascular endothelial growth factor (VEGF). These observations let us to speculate that statins might be a promising remedy for treating patients with diabetic retinopathy by acting as a potential inhibitor of the AGE-RAGE signaling pathway in microvascular endothelial cells. In this paper, we would like to propose the possible ways of testing our hypotheses. (1) Does treatment with statins decrease the risk for the development and progression of diabetic retinopathy in patients with normocholesterolemia? (2) If the answer is yes, is this beneficial effect of statins superior to that of other cholesterol-lowering agents with equihypolipidemic properties? (3) Does statin treatment suppress retinal VEGF expression in diabetic patients? (4) Does treatment with pyridoxamine, a post-Amadori inhibitor of AGE formation, attenuate the beneficial effects of statins on diabetic retinopathy? These clinical studies could clarify whether the use of statins is of benefit in patients with AGE-RAGE-related disorders such as diabetic retinopathy, even in the absence of hypercholesterolemia.     

PBN fails to suppress in delayed neuronal death of hippocampal CA1 injury following transient forebrain ischemia in gerbils

Free radicals have been suggested to be involved in the genesis of ischemic brain damage, as shown by the protective effects of alpha-phenyl-N-tert-butyl nitrone (PBN), a spin trapping agent, in ischemic cerebral injury. However, the involvement of free radicals in transient ischemic-induced delayed neuronal death is not fully understood. To clarify this, in the present study, we evaluated the effect of PBN on delayed neuronal death and on the levels of free radicals in hippocampal CA1 region in the gerbil. The administration of PBN (10 mg/kg, i.v.) failed to show any preventive effect on the delayed neuronal death, examined by hematoxylin and eosin staining and the TUNEL method. Furthermore, we observed no free radical formation in delayed neuronal death, determined immunohistochemically using a specific 8-OHdG antibody, after transient ischemic insult. These results suggest that free radical formation may not contribute to the formation of delayed neuronal death.     

Expression and function of A1 adenosine receptors in the rat hippocampus following transient forebrain ischemia

We investigated how transient cerebral ischemia affects the gene expression, immunoreactive protein levels, and the function of the A1 subtype of adenosine receptor in the rat hippocampus at different times following reperfusion. A1 receptor mRNA levels were altered significantly in different hippocampal subfields as early as 6 h following insult. However, these changes in mRNA levels were not paralleled at the protein level, as western blotting with A1 receptor-specific antibodies revealed that hippocampal A1 adenosine receptor prevalence did not differ from sham control at either 6 or 24 h following insult. The lack of change in A1 receptor prevalence was consistent with functional examinations, as only marginal changes were observed in the ability of A1 receptors to attenuate excitatory post-synaptic potentials in the CA1 subfield at 24 h following reperfusion. These data illustrate that although the mRNA expression levels of the A1 adenosine receptor are altered by transient cerebral ischemia, the immunoreactive prevalence and function of this receptor are maintained in the post-ischemic hippocampus at times preceding the death of the vulnerable neurons.     

Relationship between neuronal vulnerability and potassium-chloride cotransporter 2 immunoreactivity in hippocampus following transient forebrain ischemia

Cation chloride cotransporters have been reported to be expressed in neurons in the hippocampus and to regulate intracellular Cl(-) concentration. The neuron-specific K-Cl cotransporter 2 (KCC2) is necessary for maintaining the low intracellular chloride concentration required for the hyperpolarizing actions of GABA. In this study we examined the vulnerability of KCC2-containing neurons as well as the changes in the pattern of KCC2 distribution in the rat hippocampus following 15 min ischemia induced by four-vessel occlusion. Immunostaining for the 72 kDa heat shock protein (HSP-72) was used to investigate the extent of damage in neuronal populations previously shown to be vulnerable to ischemia. At 6-24 h after ischemia, when the pyramidal cells in the CA1 (subfield of cornu Ammonis) region showed no morphological signs of damage, a small rise of KCC2 immunoreactivity was already observed. After 2 days, when the CA1 pyramidal cells started to degenerate, a progressive downregulation of the KCC2 protein was visible. Interestingly, in the same areas, the parvalbumin containing interneurons showed no signs of ischemic damage, and KCC2 immunoreactivity was retained on their membrane surface. In CA1 pyramidal cells, the reduction in KCC2 expression may lead to an elevation of intracellular Cl(-) concentration, which causes a shift in equilibrium potential toward more positive levels. Consequently, the reduction of the inhibitory action of GABA through downregulation of KCC2 function may be involved in the pathomechanisms of delayed neuronal death in the CA1 subfield.     

Role of tissue plasminogen activator/plasmin cascade in delayed neuronal death after transient forebrain ischemia

We studied the possible involvement of the tissue plasminogen activator (t-PA)/plasmin system on both delayed neuronal death in the hippocampus and the associated enhancement of locomotor activity in rats, after transient forebrain ischemia induced by a four-vessel occlusion (FVO). Seven days after FVO, locomotor activity was abnormally increased and, after 10 days, pyramidal cells were degraded in the CA1 region of the hippocampus. FVO increased the t-PA antigen level and its activity in the hippocampus, which peaked at 4 h. Both the enhanced locomotor activity and the degradation of pyramidal cells were significantly suppressed by intracerebroventricular injection of aprotinin, a plasmin inhibitor, at 4 h but not during FVO. These results suggest the importance of the t-PA/plasmin cascade during the early pathological stages of delayed neuronal death in the hippocampus following transient forebrain ischemia.     

Glial cell line-derived neurotrophic factor protects against delayed neuronal death after transient forebrain ischemia in rats

Glial cell line-derived neurotrophic factor, a member of the transforming growth factor-beta superfamily, is a potent neurotrophic factor, which has a variety of biological activities that affect several types of neurons in both the central and peripheral nervous systems. In this study, we examined the effects of glial cell line-derived neurotrophic factor on delayed neuronal death in the hippocampal CA1 region of rats after transient forebrain ischemia. In the control rats pretreated with the vehicle, transient forebrain ischemia-induced delayed neuronal death in the hippocampal CA1 region was observed seven days after reperfusion. Pretreatment with glial cell line-derived neurotrophic factor (1.0 microg), which was directly microinjected into the right hippocampal CA1 region, gave significant protection against the delayed hippocampal neuronal death. On the contralateral side of the hippocampus, which was not injected with glial cell line-derived neurotrophic factor, delayed neuronal death similar to that seen in vehicle-treated control animals was observed. Intracerebroventricular glial cell line-derived neurotrophic factor (2.5 microg) injection also protected against delayed neuronal death. In addition, pretreatment with glial cell line-derived neurotrophic factor gave significant protection against apoptotic cell death induced by brain ischemia in the hippocampal CA1 region, as determined by in situ staining for DNA fragmentation. These findings suggest that glial cell line-derived neurotrophic factor plays an important role in delayed neuronal death induced by brain ischemia.     

Activation of Src tyrosine kinase in microglia in the rat hippocampus following transient forebrain ischemia

To better understand the pathophysiological role of Src protein, a non-receptor protein tyrosine kinase of 60kDa, in the ischemic brain, we investigated the time course and regional distribution of active Src expression by using a specific antibody against Tyr416 phosphorylated Src (phospho-Src) in the rat hippocampus after transient forebrain ischemia. In the hippocampus of the control animals, active Src expression was too low to be detected by immunolabeling. Beginning 4h after reperfusion, active Src expression became evident and, after 1 day, had increased preferentially in the CA field of the hippocampus proper and the dentate gyrus. By day 3, active Src expression markedly increased in the pyramidal cell layer of CA1 and the dentate hilar region in temporal correlation with neuronal cell death occurring in these areas, where cells typical of phagocytic microglia showed phospho-Src immunoreactivity. Double-labeling experiments revealed that cells expressing active Src were microglia that stained for biotinylated lectin derived from Griffonia simplicifolia (GSI-B4). Active Src expression began to decline at day 7 and returned to the basal level by day 14 after reperfusion. These results demonstrate increased phosphorylation of Src in activated microglia of the post-ischemic hippocampus, indicating that Src signaling may be involved in the microglial reaction to an ischemic insult.     

Effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on ageing: Molecular mechanisms

Human ageing is determined by degenerative alterations and processes with different manifestations such as gradual organ dysfunction, tissue function loss, increased population of aged (senescent) cells, incapability of maintaining homeostasis and reduced repair capacity, which collectively lead to an increased risk of diseases and death. The inhibitors of HMG-CoA reductase (statins) are the most widely used lipid-lowering agents, which can reduce cardiovascular morbidity and mortality. Accumulating evidence has documented several pleiotropic effects of statins in addition to their lipid-lowering properties. Recently, several studies have highlighted that statins may have the potential to delay the ageing process and inhibit the onset of senescence. In this review, we focused on the anti-ageing mechanisms of statin drugs and their effects on cardiovascular and non-cardiovascular diseases.     

沙土鼠短暂性脑缺血后海马迟发性神经元死亡机理的研究

本实验通过结扎沙土鼠双侧颈总动脉20分钟后再灌流2天或7天造成海马迟发性神经元死亡(DND)模型,检测背侧海马Ca~(2 )及脂质过氧化物含量的变化,并用海马CA_1区神经元密度作为指标,观察尼莫地平及超氧化物歧化酶(SOD)对海马DND的影响。结果:再灌流2天后背侧海马组织Ca~(2 )及MDA含量增加;尼莫地平及SOD均可改善海马CA_1区DND,使海马CA_1区神经元密度增加。本实验提示:Ca~(2 )及氧自由基导致的脂质过氧化物在短暂性脑缺血后海马DND的发生中起重要作用,钙拮抗剂及自由基清除剂对海马DND有保护作用。     

Bicyclol attenuates oxidative stress and neuronal damage following transient forebrain ischemia in mouse cortex and hippocampus

To assess its potential neuroprotective effect against ischemia/reperfusion (IR) injury in mice, bicyclol was administered intragastrically once a day for 3 days. After 6 h of bicyclol pretreatment on the third day, forebrain ischemia was induced for 1 h by bilateral occlusion of the carotid arteries. After different times of reperfusion, the histopathological changes and the levels of mitochondria-generated reactive oxygen species (ROS), malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) in the cortex and hippocampus were measured. We found that extensive neuronal death occurred in the cortex and the CA1 area of the hippocampus at day 7 after IR and that bicyclol significantly attenuated IR-induced neuronal death in a dose-dependent manner. We also found that pretreatment with bicyclol dose dependently decreased the generation of ROS and the MDA content and reduced the compensatory increase in SOD activity in the cortex and hippocampus at 4 h of reperfusion. These results suggest that bicyclol protects the mouse brain against cerebral IR injury by attenuating oxidative stress and lipid peroxidation.     

Cigarette smoking decreases neurotrophin-3 expression in rat hippocampus after transient forebrain ischemia

Stroke is a common cause of death and severe disability among adults in developed countries. Cigarette smoking adversely affects human health in many ways and is considered to be a risk factor for a stroke. However, the mechanism that determines the relative importance of neurotrophins in this process remains unclear. To study the effect of chronic cigarette smoking on ischemic stroke, in situ hybridization and immunohistochemistry were employed to detect the mRNA and protein expression of neurotrophin-3 (NT-3), respectively, which is thought to play a critical role in protection against neuronal death in brain ischemia. Rats, with or without chronic cigarette smoking, were subjected to 20 min of transient forebrain ischemia. Distribution and quantification of mRNA and protein of NT-3 in the whole hippocampus and the cell death in the hippocampal CA1–CA3 regions were determined in these rats. Experimental results show that chronic cigarette smoking produces a significantly delay and persistent down-regulation of ischemia-induced NT-3 mRNA and protein changes at 6–24 h post-ischemia, and seemly increases neuron death 7 days after reperfusion. These experimental results indicate that by influencing NT-3 expression, directly or indirectly, chronic cigarette smoking has a potentially harmful effect when acute brain ischemia attacks.     

Progressive loss of messenger RNA and delayed neuronal death following transient cerebral ischemia in gerbils

We examined mRNA, cytoplasmic RNA and structural damage in the hippocampus of the gerbil brain after transient ischemia by in situ hybridization, Acridine orange histochemistry and immunohistochemistry. Progressive decline of mRNA became visible in the CA1 region after reperfusion for 3 h and loss of cytoplasmic RNA and emergence of structural damage in 3 days. Reduction of mRNA in the CA3-CA4 region was transient. The findings suggested positive correlation between progressive loss of mRNA and delayed neuronal death.