The beta2-adrenoceptor agonist clenbuterol modulates Bcl-2, Bcl-xl and Bax protein expression following transient forebrain ischemia

Developmental neurotoxicity resulting from pharmacotherapy of preterm labor, modeled in vitro: Terbutaline and dexamethasone, separately and together

Terbutaline and dexamethasone are used in the management of preterm labor, often for durations of treatment exceeding those recommended, and both have been implicated in increased risk of neurodevelopmental disorders. We used a variety of cell models to establish the critical stages at which neurodifferentiation is vulnerable to these agents and to determine whether combined exposures produce a worsened outcome. Terbutaline selectively promoted the initial emergence of glia from embryonic neural stem cells (NSCs). The target for terbutaline shifted with developmental stage: at later developmental stages modeled with C6 and PC12 cells, terbutaline had little effect on glial differentiation (C6 cells) but impaired the differentiation of neuronotypic PC12 cells into neurotransmitter phenotypes. In contrast to the specificity shown by terbutaline, dexamethasone affected both neuronal and glial differentiation at all stages, impairing the emergence of both cell types in NSCs but with a much greater impairment for glia. At later stages, dexamethasone promoted glial cell differentiation (C6 cells), while shifting neuronal cell differentiation so as to distort the balance of neurotransmitter phenotypes (PC12 cells). Finally, terbutaline and dexamethasone interacted synergistically at the level of late stage glial cell differentiation, with dexamethasone boosting the ability of terbutaline to enhance indices of glial cell growth and neurite formation while producing further decrements in glial cell numbers. Our results support the conclusion that terbutaline and dexamethasone are directly-acting neuroteratogens, and further indicate the potential for their combined use in preterm labor to worsen neurodevelopmental outcomes.

Protective effect of hydroxysafflor yellow A alone or in combination with acetylglutamine on cerebral ischemia reperfusion injury in rat: A PET study using 18F-fuorodeoxyglucose

Hydroxysafflor yellow A (HSYA) and acetylglutamine (NAG) are extensively applied in the treatment of brain injury. In this study, we investigated the neuroprotective effect and underlying mechanism of HSYA alone or together with NAG using a rat model of cerebral ischemia reperfusion injury. Male Sprague-Dawley (SD) rats (n = 5) were intraperitoneally injected with 5, 10, 20 mg/kg HSYA, 300 mg/kg NAG and 10 mg/kg HSYA+300 mg/kg NAG after the onset of reperfusion and once each day for the following 7 days. After assessing the neurological deficit and infarct volume, we used ¹⁸F-FDG-PET to evaluate the regional cerebral metabolic rate of glucose consumption, immunohistochemical analysis to detect the expression of GFAP, NGF, Bcl-2, Bax, caspase-3 and ICAM-1 in brain tissue at day 7 after cerebral I/R injury. Meanwhile, the mRNA levels of ICAM-1, IL-1ß, TNF-α and NF-κB were determined by qRT-PCR, the protein levels of Bcl-2, Bax and caspase-3 were detected by western blot. The results indicated that HSYA significantly up-regulated glucose metabolism, improved neurological function, decreased cerebral infarction volume. HSYA alone or together with NAG attenuated apoptosis and inflammation by up-regulating GFAP, NGF and Bcl-2 expression, suppressing the expression of Bax, caspase-3 and ICAM-1, IL-1ß, TNF-α and NF-κB. These finding suggested that HSYA exerted neuroprotection against cerebral I/R injury by modulating inflammation and apoptosis process, and HSYA in combination with NAG possessed a synergetic effect on protecting cerebral I/R brain injury.

Electroacupuncture alleviates cerebral ischemia and reperfusion injury via modulation of the ERK1/2 signaling pathway

Electroacupuncture (EA) has anti-oxidative and anti-inflammatory actions, but whether the neuroprotective effect of EA against cerebral ischemia-reperfusion (I/R) injury involves modulation of the extracellular regulated kinase 1/2 (ERK1/2) signaling pathway is unclear. Middle cerebral artery occlusion (MCAO) was performed in Sprague-Dawley rats for 2 hours followed by reperfusion for 24 hours. A 30-minute period of EA stimulation was applied to both Baihui (DU20) and Dazhui (DU14) acupoints in each rat (10 mm EA penetration depth, continuous wave with a frequency of 3 Hz, and a current intensity of 1-3 mA) when reperfusion was initiated. EA significantly reduced infarct volume, alleviated neuronal injury, and improved neurological function in rats with MCAO. Furthermore, high mRNA expression of Bax and low mRNA expression of Bcl-2 induced by MCAO was prevented by EA. EA substantially restored total glutathione reductase (GR), glutathione (GSH) and glutathione peroxidase (GSH-Px) levels. Additionally, Nrf2 and glutamylcysteine synthetase (GCS) expression levels were markedly increased by EA. Interestingly, the neuroprotective effects of EA were attenuated when ERK1/2 activity was blocked by PD98059 (a specific MEK inhibitor). Collectively, our findings indicate that activation of the ERK1/2 signaling pathway contributes to the neuroprotective effects of EA. Our study provides a better understanding of the regulatory mechanisms underlying the therapeutic effectiveness of EA.

Clenbuterol activates the central IL-1 system via the β2-adrenoceptor without provoking inflammatory response related behaviours in rats

The long-acting, highly lipophilic, β2-adrenoceptor agonist clenbuterol may represent a suitable therapeutic agent for the treatment of neuroinflammation as it drives an anti-inflammatory response within the CNS. However, clenbuterol is also known to increase the expression of IL-1β in the brain, a potent neuromodulator that plays a role in provoking sickness related symptoms including anxiety and depression-related behaviours. Here we demonstrate that, compared to the immunological stimulus lipopolysaccharide (LPS, 250μg/kg), clenbuterol (0.5mg/kg) selectively up-regulates expression of the central IL-1 system resulting in a mild stress-like response which is accompanied by a reduction in locomotor activity and food consumption in rats. We provide further evidence that clenbuterol-induced activation of the central IL-1 system occurs in a controlled and selective manner in tandem with its negative regulators IL-1ra and IL-1RII. Furthermore, we demonstrate that peripheral β2-adrenoceptors mediate the suppression of locomotor activity and food consumption induced by clenbuterol and that these effects are not linked to the central induction of IL-1β. Moreover, despite increasing central IL-1β expression, chronic administration of clenbuterol (0.03mg/kg; twice daily for 21days) fails to induce anxiety or depressive-like behaviour in rats in contrast to reports of the ability of exogenously administered IL-1 to induce these symptoms in rodents. Overall, our findings suggest that clenbuterol or other selective β2-adrenoceptor agonists could have the potential to combat neuroinflammatory or neurodegenerative disorders without inducing unwanted symptoms of depression and anxiety.

Effect of ukrain on ischemia/reperfusion-induced kidney injury in rats

BACKGROUND

The aim of this study was to investigate the potential protective effect of ukrain on an experimental kidney injury model induced by ischemia and reperfusion (IR) in rats.

MATERIAL AND METHODS

A total of 24 male Sprague-Dawley rats were equally and randomly separated into three groups as follows: group-1: controls (C; only laparotomy); group 2: renal ischemia-reperfusion (IR; occlusion of the renal artery for 30 min and 2 h of reperfusion); and group 3: ukrain treatment and IR applied group (U + IR; occlusion of the renal artery for 30 min and 2 h of reperfusion; ukrain was intraperitoneally administered 1 h before the IR process).

RESULTS

Serum total oxidant status (TOS) and total antioxidant status (TAS) levels were measured. The oxidative stress index was determined by calculating the TOS/TAS ratio. TAS serum levels significantly increased, and TOS serum levels also prominently decreased in U + IR group, when compared with the IR group (P < 0.001). Mean NGAL level was remarkably higher in IR group, when compared with the U + IR group (P < 0.001). Caspase-3 messenger RNA (mRNA) expression level increased in IR and decreased in U + IR group (P < 0.001). Bcl-xL serum and mRNA expression levels increased in the U + IR group (P < 0.001). In addition, serum iNOS and mRNA expression levels increased in IR group and decreased in U + IR group (P < 0.001).

CONCLUSIONS

Data established from the present study suggest that ukrain may exhibit protective effect against IR-induced kidney injury and that antioxidant activity primarily modulates this effect.

Electroacupuncture Attenuates Cerebral Ischemia and Reperfusion Injury in Middle Cerebral Artery Occlusion of Rat via Modulation of Apoptosis, Inflammation, Oxidative Stress, and Excitotoxicity

Electroacupuncture (EA) has several properties such as antioxidant, antiapoptosis, and anti-inflammatory properties. The current study was to investigate the effects of EA on the prevention and treatment of cerebral ischemia-reperfusion (I/R) injury and to elucidate possible molecular mechanisms. Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion for 24 h. EA stimulation was applied to both Baihui and Dazhui acupoints for 30 min in each rat per day for 5 successive days before MCAO (pretreatment) or when the reperfusion was initiated (treatment). Neurologic deficit scores, infarction volumes, brain water content, and neuronal apoptosis were evaluated. The expressions of related inflammatory cytokines, apoptotic molecules, antioxidant systems, and excitotoxic receptors in the brain were also investigated. Results showed that both EA pretreatment and treatment significantly reduced infarct volumes, decreased brain water content, and alleviated neuronal injury in MCAO rats. Notably, EA exerts neuroprotection against I/R injury through improving neurological function, attenuating the inflammation cytokines, upregulating antioxidant systems, and reducing the excitotoxicity. This study provides a better understanding of the molecular mechanism underlying the traditional use of EA.

Electroacupuncture at different frequencies (5Hz and 25Hz) ameliorates cerebral ischemia-reperfusion injury in rats: possible involvement of p38 MAPK-mediated anti-apoptotic signaling pathways

Background

This study aimed to determine the effects of electroacupuncture stimulation at the Baihui (GV20) and Fengfu (GV16) acupoints, at frequencies of 5Hz (EA-5Hz) and 25Hz (EA-25Hz), 7 days after cerebral ischemia-reperfusion (I/R) injury, and to evaluate the possible signaling mechanisms involved in mitogen-activated protein kinase (MAPK) pathways.

Methods

Rats were subjected to 30 min of middle cerebral artery occlusion (MCAo) followed by 7 days of reperfusion. EA-5Hz or EA-25Hz was applied immediately after MCAo and then once daily for 7 consecutive days.

Results

Results indicated that EA-5Hz and EA-25Hz both markedly attenuated cerebral infarction and neurological deficits. EA-5Hz and EA-25Hz both markedly downregulated cytosolic glial fibrillary acidic protein (GFAP), mitochondrial Bax, mitochondrial and cytosolic second mitochondrial-derived activator of caspase/direct inhibitor of apoptosis protein-binding protein with low isoelectric point (Smac/DIABLO), and cytosolic cleaved caspase-3 expression, and effectively restored cytosolic phospho-p38 MAPK (p-p38 MAPK), cytosolic cAMP response element-binding protein (CREB), mitochondrial Bcl-xL, and cytosolic X-linked inhibitor of apoptosis protein (XIAP) expression, in the ischemic cortical penumbra 7 days after reperfusion. Both EA-5Hz and EA-25Hz also significantly increased the ratios of mitochondrial Bcl-xL/Bax and Bcl-2/Bax, respectively.

Conclusions

Both EA-5Hz and EA-25Hz effectively downregulate reactive astrocytosis to provide neuroprotection against cerebral infarction, most likely by activating the p38 MAPK/CREB signaling pathway. The modulating effects of EA-5Hz and EA-25Hz on Bax-mediated apoptosis are possibly due to the activation of p38 MAPK/CREB/Bcl-xL and p38 MAPK/CREB/Bcl-2 signaling pathways, respectively, and eventually contribute to the prevention of Smac/DIABLO translocation and subsequent restoration of XIAP-mediated suppression of caspase-3 in the cortical periinfarct area 7 days after reperfusion.

Dose-effects of aorta-infused clenbuterol on spinal cord ischemia-reperfusion injury in rabbits

Background

The β₂ adrenergic receptor (β₂AR) plays an important role in ischemia-reperfusion (I/R) injury in various organs. Recently, a selective β₂AR agonist clenbuterol was suggested to protect against cerebral I/R injury. This study was designed to investigate changes of β₂ARs after spinal cord I/R injury and dose-effects of aorta-infused clenbuterol on spinal cord I/R injury in rabbits.

Methods

Spinal cord ischemia was induced in New Zealand white rabbits by infrarenal abdominal aortic occlusion with a balloon catheter for 30 minutes except the sham group. During occlusion, nothing (I/R group), normal saline (NS group) or clenbuterol at different doses of 0.005, 0.01, 0.05, 0.1, 0.5, or 1 mg/kg (C_0.005, C_0.01, C_0.05, C_0.1, C_0.5, and C₁ groups) was infused into the occluded aortic segments. The hemodynamic data, blood glucose and serum electrolytes were measured during experimental period. Neurological function was assessed according to the modified Tarlov scales until 48 hours after reperfusion. After that, the lumbar spinal cord was harvested for β₂AR immunohistochemistry and histopathologic evaluation in the anterior horns.

Results

The β₂AR expression in the anterior horns of the spinal cord was significantly higher in the I/R group than in the sham group. Tarlov scores and the number of viable α-motor neurons were higher in C_0.01-C_0.5 groups than in the NS group, C_0.005 and C₁ groups and were highest in the C_0.1 group. Hypotension and hyperglycemia were found in the C₁ group.

Conclusion

β₂ARs in the anterior horn were upregulated after spinal cord I/R injury. Aortic-infused clenbuterol (0.01–0.5 mg/kg) can attenuate spinal cord I/R injury dose-dependently during the ischemic period. The Optimal dosage was 0.1 mg/kg. Activation of β₂AR could be a new therapeutic strategy for the treatment of spinal cord I/R injury.

β2 adrenergic-mediated reduction of blood glutamate levels and improved neurological outcome after traumatic brain injury in rats

BACKGROUND

Isoflurane-anesthetized rats subjected to traumatic brain injury (TBI) show a transient reduction in blood L-glutamate levels. Having previously observed that isoproterenol produces a sustained decrease in blood glutamate levels in naive rats, we investigated the possible effects of nonselective and selective β1 and β2 adrenergic agonists and antagonists both on blood glutamate levels and on the neurological outcomes of rats subjected to TBI.

METHODS

Rats received either 10 mL/kg of isotonic saline 1 hour after TBI, 50 µg/kg of isoproterenol pretreatment 30 minutes before TBI, 10 mg/kg of propranolol pretreatment 60 minutes before TBI, 10 mg/kg of metoprolol pretreatment 60 minutes before TBI, or 10 mg/kg of butaxamine pretreatment 40 minutes before TBI and 10 minutes before pretreatment with 50 µg/kg isoproterenol or 10 mg/kg of propranolol 60 minutes after TBI. A neurological severity score (NSS) was measured at 1, 24, and 48 hours after TBI. Blood glutamate, blood glucose, mean arterial blood pressure, and heart rate were measured at the time of drug injection, at the time of TBI, 60 minutes after TBI, and 90 minutes after TBI.

RESULTS

Blood glutamate levels decreased spontaneously by 60 minutes after TBI in the control group (P<0.05), reverting to baseline levels by 90 minutes after TBI. A pretreatment with either 10 mg/kg of metoprolol 60 minutes before TBI or with 50 µg/kg of isoproterenol 30 minutes before TBI also reduced blood glutamate levels (P<0.05) both at 90 minutes after TBI and improved the NSS measured 24 and 48 hours after TBI in comparison with the control saline-treated group. However, a 10-mg/kg butoxamine pretreatment 40 minutes before TBI and 10 minutes before pretreatment with 50 µg/kg of isoproterenol or 10 mg/kg of propranolol 60 minutes before TBI neither affected blood glutamate levels across time after TBI nor caused any significant change in the NSS measured 24 and 48 hours after TBI in comparison with the control saline-treated group. A strong correlation (r(2)=0.73) was demonstrated between the percent decrease in blood glutamate levels at 90 minutes after TBI and the percent improvement of NSS measured 24 hours after TBI.

CONCLUSIONS

The results suggest that the transient blood glutamate reduction seen after TBI is the result of a stress response and of the activation of the sympathetic nervous system through the β2 adrenergic receptors, causing an increase of the brain-to-blood efflux of glutamate observed with excess brain glutamate levels after a brain insult. This strongly correlates with the neurological improvement observed 24 hours after TBI.

The effect of adrenergic β(2) receptor agonist on paraplegia following clamping of abdominal aorta

INTRODUCTION

Surgical repair of an aortic aneurysm might be complicated by spinal cord injury and paraplegia. Since β-adrenoreceptor agonists showed neuroprotective effects, the study was designed to investigate the effect of clenbuterol on post-aortic clamping paraplegia and to identify if there is hyperemia associated with paraplegia.

MATERIAL AND METHODS

Thirty rabbits were divided into two groups: 15 control and 15 experimental (given clenbuterol 9 mg in drinking water 24 h prior to surgery). All the animals were subjected to laparotomy whereas the abdominal aorta was identified. Using a vascular clamp, the abdominal aorta was clamped just distal to the renal arteries. Abdominal aortic blood flow was recorded with a transonic flow meter. The neurological assessment was made according to Tarlov's Neurological Scale upon recovering from anesthesia. Anal sphincter tonus and bladder sphincter function were also checked.

RESULTS

Four rabbits (2 control and 2 experimental) developed complete paraplegia within 30 min of cross-clamping of the aorta. Of the 13 controls, 77% developed paraplegia, and of the 13 experimental rabbits administered clenbuterol 24 h prior to surgery with 22 min of aortic cross-clamping, 38% developed paraplegia The rabbits which did not develop paraplegia had a minimal increase in aortic blood flow, whereas the rabbits which developed paraplegia had a significant increase in aortic blood flow measurements after aortic decamping.

CONCLUSIONS

Post-aortic clamping paraplegia is associated with hyperemia and clenbuterol has a significant neuroprotective effect, obviously by preventing an increase in aortic blood flow following unclamping.

Noradrenaline acting at central beta-adrenoceptors induces interleukin-10 and suppressor of cytokine signaling-3 expression in rat brain: implications for neurodegeneration

Evidence indicates that the monoamine neurotransmitter noradrenaline elicits anti-inflammatory actions in the central nervous system (CNS), and consequently may play a neuroprotective role where inflammatory events contribute to CNS pathology. Here we examined the ability of pharmacologically enhancing central noradrenergic tone to induce expression of anti-inflammatory cytokines in rat brain. Administration of the noradrenaline reuptake inhibitor reboxetine (15mg/kg; ip) combined with the alpha(2)-adrenoceptor antagonist idazoxan (1mg/kg; ip) induced interleukin-10 (IL-10) expression in rat cortex and hippocampus. In addition, these drug treatments induced IL-10 signaling as indicated by increased STAT3 phosphorylation and suppressor of cytokine signaling-3 (SOCS-3) mRNA expression. In contrast to the profound increase in IL-10 induced by the reboxetine/idazoxan combination, the other two broad spectrum anti-inflammatory cytokines IL-4 and TGF-beta were not induced by this treatment. The ability of combined treatment with reboxetine and idazoxan to induce IL-10 and SOCS3 expression was mediated by beta-adrenoceptor activation, as their induction was blocked by pre-treatment with the beta-adrenoceptor antagonist propranolol. Moreover, administration of the brain penetrant beta(2)-adrenoceptor agonist clenbuterol induced a time- and dose-dependent increase in central IL-10 and SOCS3 expression, and the ability of clenbuterol to induce IL-10 and SOCS-3 expression was blocked by the centrally acting beta-adrenoceptor antagonist, propranolol, and was mimicked by the highly selective beta(2)-adrenoceptor agonist formoterol. In all, these data indicate that increasing central noradrenergic tone induces IL-10 production and signaling in the CNS, which may protect against neurodegeneration.

Role of beta-adrenoceptor signaling in skeletal muscle: implications for muscle wasting and disease

The importance of beta-adrenergic signaling in the heart has been well documented, but it is only more recently that we have begun to understand the importance of this signaling pathway in skeletal muscle. There is considerable evidence regarding the stimulation of the beta-adrenergic system with beta-adrenoceptor agonists (beta-agonists). Although traditionally used for treating bronchospasm, it became apparent that some beta-agonists could increase skeletal muscle mass and decrease body fat. These so-called "repartitioning effects" proved desirable for the livestock industry trying to improve feed efficiency and meat quality. Studying beta-agonist effects on skeletal muscle has identified potential therapeutic applications for muscle wasting conditions such as sarcopenia, cancer cachexia, denervation, and neuromuscular diseases, aiming to attenuate (or potentially reverse) the muscle wasting and associated muscle weakness, and to enhance muscle growth and repair after injury. Some undesirable cardiovascular side effects of beta-agonists have so far limited their therapeutic potential. This review describes the physiological significance of beta-adrenergic signaling in skeletal muscle and examines the effects of beta-agonists on skeletal muscle structure and function. In addition, we examine the proposed beneficial effects of beta-agonist administration on skeletal muscle along with some of the less desirable cardiovascular effects. Understanding beta-adrenergic signaling in skeletal muscle is important for identifying new therapeutic targets and identifying novel approaches to attenuate the muscle wasting concomitant with many diseases.

Effect of beta2-adrenergic agonist clenbuterol on ischemia/reperfusion injury in isolated rat hearts and cardiomyocyte apoptosis induced by hydrogen peroxide

AIM

To observe the effect of beta2-adrenergic agonist clenbuterol on ischemia/reperfusion (I/R) injury in isolated rat hearts and hydrogen peroxide (H2O2)-induced cardiomyocyte apoptosis.

METHODS

Isolated rat hearts were subjected to 30 min global ischemia and 60 min reperfusion on a Langendorff apparatus. Cardiac function was evaluated by heart rate, left ventricular end-diastolic pressure (LVEDP), left ventricular systolic pressure, maximal rise rate of left ventricular pressure [+dp/dt(max)], and the coronary effluent (CF). Lactate dehydrogenase (LDH) in the coronary effluent, malondialdehyde (MDA), superoxide dismutase (SOD), and Ca2+-ATPase activity in the cardiac tissue were measured using commercial kits. The apoptotic cardiomyocyte was detected by terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) assay. Bax/Bcl-2 mRNA levels and the expression of caspase-3 were detected by RT-PCR and immunoblotting, respectively. Cultured newborn rat cardiomyocytes were preincubated with clenbuterol, and oxidative stress injury was induced by H2O2. Cell viability and cardiomyocyte apoptosis were evaluated by flow cytometry (FCM).

RESULTS

In the isolated rat hearts after I/R injury, clenbuterol significantly improved diastolic function (LVEDP and CF) and Ca2+-ATPase activity. Treatment with clenbuterol increased SOD activity and decreased the MDA level and LDH release compared with the I/R group (P<0.05). Moreover, clenbuterol decreased apoptosis, which was associated with a reduction in TUNEL-positive cells, Bax/Bcl-2 mRNA, and caspase-3 expression. In H2O2-induced cardiomyocyte injury, clenbuterol increased cell viability and attenuated cardiomyocyte apoptosis. Pretreatment with ICI118551 (selective beta2-adrenergic antagonist) decreased these effects compared with the clenbuterol-treated group (P<0.05).

CONCLUSION

Clenbuterol ameliorated ventricular diastolic function by enhancing Ca2+-ATPase activity and reduced oxidative stress and cardiac myocyte apoptosis in an experimental rat model of myocardium I/R. It decreased cardiomyocyte apoptosis induced by H2O2 in vitro. It plays a key role in the cardiac protection against myocardium I/R injury.

Zinc-dependent multi-conductance channel activity in mitochondria isolated from ischemic brain

Transient global ischemia is a neuronal insult that induces delayed cell death. A hallmark event in the early post-ischemic period is enhanced permeability of mitochondrial membranes. The precise mechanisms by which mitochondrial function is disrupted are, as yet, unclear. Here we show that global ischemia promotes alterations in mitochondrial membrane contact points, a rise in intramitochondrial Zn2+, and activation of large, multi-conductance channels in mitochondrial outer membranes by 1 h after insult. Mitochondrial channel activity was associated with enhanced protease activity and proteolytic cleavage of BCL-xL to generate its pro-death counterpart, deltaN-BCL-xL. The findings implicate deltaN-BCL-xL in large, multi-conductance channel activity. Consistent with this, large channel activity was mimicked by introduction of recombinant deltaN-BCL-xL to control mitochondria and blocked by introduction of a functional BCL-xL antibody to post-ischemic mitochondria via the patch pipette. Channel activity was also inhibited by nicotinamide adenine dinucleotide, indicative of a role for the voltage-dependent anion channel (VDAC) of the outer mitochondrial membrane. In vivo administration of the membrane-impermeant Zn2+ chelator CaEDTA before ischemia or in vitro application of the membrane-permeant Zn2+ chelator tetrakis-(2-pyridylmethyl) ethylenediamine attenuated channel activity, suggesting a requirement for Zn2+. These findings reveal a novel mechanism by which ischemic insults disrupt the functional integrity of the outer mitochondrial membrane and implicate deltaN-BCL-xL and VDAC in the large, Zn2+-dependent mitochondrial channels observed in post-ischemic hippocampal mitochondria.

Beta2-adrenoreceptor agonist-enhanced recovery of locomotor function after spinal cord injury is glutathione dependent

The beta2-adrenoreceptor agonist, clenbuterol, has been shown to spare spinal cord tissue and enhance locomotor recovery in an experimental model of spinal cord contusion injury. A likely mechanism of neurodegeneration following spinal cord injury involves generation of toxic levels of reactive oxygen species (ROS), e.g., O2-*, H2O2 and OH*, which overwhelm endogenous antioxidants. Agents, such as clenbuterol, that oppose neurodegeneration and improve recovery of locomotor function may possibly act by improving redox status. Consistent with reduced oxidative stress by beta2-agonist treatment following injury, prior blockade of synthesis of the antioxidant tripeptide, glutathione, with buthionine sulfoximine completely inhibited the ability of clenbuterol to enhance locomotor recovery and spare spinal cord tissue. Moreover, at 8 h postinjury, clenbuterol caused an increase in glutathione reductase activity, an indicator of cellular redox status, at the injury site that was also blocked by buthionine sulfoximine. Although clenbuterol improved locomotor recovery only when administered within a therapeutic window of several days postinjury, the accumulation of protein carbonyls in the spinal cord at 1 week postinjury, a consequence of ongoing ROS-mediated neurodegeneration, was also decreased by clenbuterol in a glutathione-dependent manner. Together, these results suggest that activation of beta2-adrenoreceptors during the acute phase of injury stimulates glutathione-dependent antioxidative processes, that lead to reduced oxidative damage and greater locomotor function as the injury evolves during the subacute and chronic phases.

[Beta 2-adrenoceptor function in the kidney]

The majority of beta(2)-adrenoceptor (beta(2)-AR) agonists is eliminated via the kidneys as an unchanged substance. It is likely that such agents will exert pharmacological effects during their passage through the nephron. However, these pharmacological effects have, to our knowledge, not been taken into consideration when using these compounds in clinical practice because the role of beta(2)-AR in the regulation of renal function remains unclear. Renal beta(2)-ARs are predominantly localized to the proximal tubular epithelia and the membranes of smooth muscle cells from renal arteries. From this morphologic evidence, it is proposed that beta(2)-AR activation may regulate glomerular function and thereby sodium and water balance in the nephron segments. Actually, beta(2)-AR agonists given acutely cause a marked decrease in glomerular filtration rate. On the other hand, beta(2)-AR agonists inhibit the renal production of inflammatory cytokines such as TNF-alpha. Furthermore, the administration of beta(2)-AR agonists is found to attenuate apoptosis associated with shigatoxin in the hemolytic uremic syndrome (HUS). Increased understanding of the pharmacological basis of beta(2)-AR function in the kidney provides important new information relevant to the clinical use of beta(2)-AR agonists in airway diseases and potential applications of these drugs in renal inflammation and injury associated with sepsis or HUS.

Dynamic changes of the anti- and pro-apoptotic proteins Bcl-w, Bcl-2, and Bax with Smac/Diablo mitochondrial release after photothrombotic ring stroke in rats

The anti-apoptotic proteins Bcl-w and Bcl-2 and the pro-apoptotic protein Bax may mediate cell death or survival via regulation of the mitochondria including second mitochondria-derived activator of caspase (Smac)/direct inhibitor of apoptosis protein (IAP)-binding protein with low pI (DIABLO) release. This study aimed to explore alterations in Bcl-w, Bcl-2, and Bax and the relationship between these proteins and Smac/DIABLO by means of in situ hybridization, immunohistochemical (IHC) staining, and Western blots after low- and high-intensity photothrombotic ring stroke. At 4 h after low-intensity irradiation, we found widespread bcl-w overexpression on both the mRNA and protein levels in the bilateral cortex except the ring lesion region and in subcortical regions. A prolonged elevation of Bcl-2 with relatively unchanged Bax in the mitochondrial fraction was demonstrated from 4 to 72 h. These upregulated anti-apoptotic proteins combined with little Smac/DIABLO release might be associated with increased cell survival and thereby remarkable morphological recovery after low-intensity irradiation. After high-intensity irradiation, we observed decreased bcl-w and bcl-2 mRNA with increased Bcl-2 protein in the cytosolic fraction, whereas the Bax protein remained in scattered ischaemic cells in the ring lesion and the region at risk that corresponded with release of Smac/DIABLO from mitochondria to the cytosol at 1-24 h. These changes might be related to the massive cell death observed after high-intensity irradiation. Taken together, the balance and the location of anti-apoptotic proteins vs. pro-apoptotic proteins could be associated with the translocation of Smac/DIABLO from the mitochondria to the cytosol and therefore closely related to cell death or survival after focal cerebral ischaemia.

Combination therapy in ischemic stroke: synergistic neuroprotective effects of memantine and clenbuterol

BACKGROUND AND PURPOSE

Although excitotoxic overactivation of glutamate receptors has been identified as a major mechanism of ischemic brain damage, glutamate receptor antagonists failed in stroke trials, in most cases because of limited therapeutic windows or severe adverse effects. Therefore, we chose memantine and clenbuterol, both approved safe and efficient in their respective therapeutical categories, and examined combinations of these neuroprotectants for possible therapeutic interactions in ischemic stroke.

METHODS

Combinations of the N-methyl-D-aspartate (NMDA) receptor antagonist memantine (20 mg/kg) with the beta2-adrenoceptor agonist clenbuterol (0.3 to 3 mg/kg) were tested in a mouse model of permanent focal cerebral ischemia. In addition, combinations of memantine (1 to 10 nmol/L) and clenbuterol (1 to 10 nmol/L) were examined in cultured hippocampal neurons exposed to glutamate (500 micromol/L) or staurosporine (200 nmol/L).

RESULTS

The infarct size was further reduced by combination therapy as compared with effects of the respective neuroprotectants alone. Of note, in combination with memantine, the therapeutic window of clenbuterol was significantly prolonged up to 2 hours after ischemia. Experiments in postnatal cultures of rat hippocampal neurons exposed to glutamate or staurosporine confirmed that neuroprotection by combinations of memantine and clenbuterol exceeded the effects of the individual compounds.

CONCLUSIONS

Combinations of memantine with clenbuterol extend the respective therapeutic window and provide synergistic cerebroprotective effects after stroke.

beta-Adrenergic receptor agonists increase apoptosis of adipose tissue in mice

beta-Adrenergic receptor (beta-AR) agonists increase muscle mass and decrease body fat in rodents and livestock. With oral administration, however, the effects of beta1-AR and beta2-AR can be different, depending on the species tested. We tested the effects of clenbuterol, a beta2-AR agonist, and ractopamine, a beta1/beta2-AR agonist, on growth, adiposity and adipose tissue apoptosis in male and female mice by feeding diets containing control, 200 ppm clenbuterol, or 200 or 800 ppm ractopamine. Food intake (FI) was measured daily; body weight (BW) and temperatures (BT) were measured on days 0, 3, 7, 10, 14, 17, and 20. On day 21 mice were sacrificed, body composition was determined using PIXImus densitometry, and muscle and adipose tissues were collected. There were no treatment effects on BT, FI, BW, feed efficiency or body composition. Retroperitoneal (Rp) and epididymal/parametrial (Epi/Par) fat pad masses were reduced in both 800 ppm ractopamine (40+/-3mg and 207+/-20mg, respectively) and clenbuterol (35+/-7 mg and 211+/-22 mg) treated mice compared to control (66+/-8 mg and 319+/-30 mg, P<0.05). Brown adipose tissue (BAT) mass was greater (P<0.05) in clenbuterol treated mice compared to other treatments. Adipose tissue apoptosis (% DNA fragmentation) was increased in Epi/Par fat pads in clenbuterol (5.2+/-1.1%) and 800 ppm ractopamine (4.1+/-0.8%) treated mice compared to control (1.7+/-0.4%, P<0.05). These findings show that WAT apoptosis can be induced by activation of beta-AR in mice, although the mechanism is unknown.

β2-Adrenergic receptor responsiveness of the calpain–calpastatin system and attenuation of neuronal death in rat hippocampus after transient global ischemia

In the CNS, where Ca(2+) overload has been established as a mechanism contributing to neuronal damage associated with excitotoxicity, stroke and ischemia, there is interest in understanding the role of calpain inhibition in rescuing neurons from death. In these settings, the activation of large stores of latent calpain may rapidly lead to the demise of the neuron within hours. The activity of calpain is strictly regulated by calcium concentrations and interactions with calpastatin (endogenous calpain inhibitor). The interaction between calpains and calpastatin is calcium dependent, and little is known about the regulation of the neuronal calpain-calpastatin system in vivo. It has been postulated that calpastatin can be modulated by nerve growth factors (NGFs). We have demonstrated in vitro as well as in vivo a neuroprotective effect of the beta(2)-adrenoceptor agonist clenbuterol (CLN) mediated through an increased NGF expression. In this study we attempt to find out whether CLN is capable (1) of modulating proteolysis regulated by the calpain-calpastatin system and (2) of attenuating DNA-fragmentation induced by cerebral ischemia. Rats received CLN daily for 1 week, were then subjected to ischemia and finally perfused at different times post-ischemia. The proteolytic activity of calpain was measured by the immunolocalisation of calpastatin and spectrin-breakdown products (SBP). The time course of apoptosis was assessed by terminal dUTP nick end-labeling (TUNEL)-staining. CLN reduced CA1-hippocampal cell damage by 23%, attenuated DNA-laddering and decreased proteolysis of spectrin by enhancing calpastatin activity. These results provide evidence that CLN is a potent neuroprotective substance, which through the enhancement of calpastatin synthesis attenuates the apoptotic machinery and modulates proteolysis.

Apoptosis in the adult striatum after transient forebrain ischemia and the effects of ischemic severity

The mechanisms of neuronal injury after cerebral ischemia have been under active investigation. The medium-size neurons in the dorsal striatum die within 24 h after transient cerebral ischemia. Using electron microscopy, the present study examined the nature of neuronal death in the striatum of adult rats following transient forebrain ischemia and tested the hypothesis that the ischemic severity might influence the nature of cell death. After severe ischemia (approximately 21 min ischemic depolarization), most neurons in the dorsal striatum died with swollen organelles and small irregular chromatin clumps resembling necrosis. The tissue damage in the dorsomedial striatum was less severe than that in the dorsolateral striatum and approximately 5% of the neurons in this region died with large chromatin clumps and relatively intact organelles resembling apoptosis. Some neurons displayed a mixture of necrotic- and apoptotic-like appearance. In contrast, the neurons with large somata only exhibited mild ultrastructural changes. After moderate ischemia (approximately 15 min ischemic depolarization), the tissue damage was less severe and the process of necrosis was temporally prolonged compared with that after severe ischemia. The apoptotic-like neuronal death was observed not only in the dorsomedial (approximately 6%) but also in the dorsolateral striatum (approximately 7%). The neurons in the striatum showed transient reversible changes after mild ischemia (approximately 10 min ischemic depolarization). The present study demonstrates that both apoptosis and necrosis occur in the adult striatum following transient forebrain ischemia and apoptosis occurs in the regions with less severe ischemia. These results suggest that ischemic severity might be one of the contributing factors to necrosis or apoptosis following transient global ischemia.

Beta2-adrenoceptor activation inhibits Shiga toxin2-induced apoptosis of renal tubular epithelial cells

Apoptosis is regulated by several pathways, such as caspases, mitogen activated protein kinase (MAPK) and cAMP/cAMP-dependent protein kinase A (PKA) cascade. This study investigated the effect of beta(2)-adrenoceptor activation on Shiga toxin (Stx)2-induced apoptosis in renal tubular cells and the contribution of these signalling pathways. Cultured human adenocarcinoma-derived tubular cells were exposed to Stx2 (64 pg/mL) for 2-24hr following the addition of the beta(2)-adrenoceptor agonist (terbutaline) to the incubation medium. Stx2-induced apoptosis and its amelioration by beta(2)-adrenoceptor activation was confirmed using DNA degradation assays and by flow cytometry for annexin V, mitochondrial membrane potential and caspase(-3 and -7) activity. Exposure of cells to Stx2 for 24hr increased the DNA fragmentation to 11.6+/-0.9%, compared to 3.3+/-0.2% in control cells (P<0.05) but was decreased to approximately 5-7% (P<0.05) in the presence of terbutaline. Furthermore, Stx2-stimulated apoptosis, detected by TUNEL, annexin V and mitochondrial potential, was inhibited by terbutaline (P<0.05) which was prevented by cAMP-PKA inhibitors and a beta(2)-adrenoceptor antagonist. However, inhibition of Stx2-mediated caspase activity by terbutaline was partially blocked by cAMP-PKA inhibitors. On the other hand, p38MAPK inhibition by terbutaline prevented Stx2-induced apoptosis and caspase activity through a cAMP-independent pathway via beta(2)-adrenoceptor. These data indicate that beta(2)-adrenoceptor activation can inhibit Stx2-induced apoptosis of the cells, which may be caused by a reduction in caspase activity through cAMP-PKA activation and the p38MAPK pathway.

Nerve growth factor survival signaling in cultured hippocampal neurons is mediated through TrkA and requires the common neurotrophin receptor P75

The role of the common neurotrophin receptor p75 (p75NTR) in neuronal survival and cell death remains controversial. On the one hand, p75NTR provides a positive modulatory influence on nerve growth factor (NGF) signaling through the high affinity neurotrophin receptor TrkA, and hence increases NGF survival signaling. However, p75NTR may also signal independently of TrkA, causing cell death or cell survival, depending on the cell type and stage of development. Here we demonstrate that TrkA is expressed in primary cultures of hippocampal neurons and is activated by NGF within 10 min of exposure. In primary hippocampal cultures neuroprotection by NGF against glutamate toxicity was mediated by NF-kappaB and accompanied by an increased expression of neuroprotective NF-kappaB target genes Bcl-2 and Bcl-xl. In mouse hippocampal cells lacking p75NTR (p75NTR-/-) activation of TrkA by NGF was not detectable. Moreover, neuroprotection by NGF against glutamate toxicity was abolished in p75NTR-/- neurons, and the expression of bcl-2 and bcl-xl was markedly reduced as compared to wildtype cells. NGF increased TrkA phosphorylation in hippocampal neurons and provided protection that required phosphoinositol-3-phosphate (PI3)-kinase activity and Akt phosphorylation, whereas the mitogen-activated protein kinases (MAPK), extracellular-regulated kinases (Erk) 1/2, were not involved. P75NTR signaling independent of TrkA, such as increased neutral sphingomyelinase (NSMase) activity causing enhanced levels of ceramide, were not detected after exposure of hippocampal neurons to NGF. Interestingly, inhibition of sphingosine-kinase blocked the neuroprotective effect of NGF, suggesting that sphingosine-1-phosphate was also involved in NGF-mediated survival in our cultured hippocampal neurons. Overall, our results indicate an essential role for p75NTR in supporting NGF-triggered TrkA signaling pathways mediating neuronal survival in hippocampal neurons.

Developmental toxicity of terbutaline: critical periods for sex-selective effects on macromolecules and DNA synthesis in rat brain, heart, and liver

beta-Adrenoceptors (betaARs) control cell replication/differentiation, and during development, signaling is not subject to desensitization. We examined the effects of terbutaline, a beta(2)AR agonist used as a tocolytic, on development in rat brain regions and peripheral tissues with high betaAR concentrations. Prenatal terbutaline (gestational days 17-20) decreased cell numbers (DNA content) in the fetal brain and liver. Early postnatal exposure (PN2-5) reduced DNA synthesis in early-developing brain regions of females, with sensitization of the effect upon repeated terbutaline administration; after multiple terbutaline injections, DNA content was reduced in male cerebellum. The cerebellum was targeted later (PN11-14), exhibiting decreased DNA synthesis in both sexes; in contrast, cardiac DNA synthesis decreased after one injection but increased after the fourth daily injection. Our results suggest that excessive betaAR stimulation by terbutaline alters cell development in brain regions and peripheral tissues, with the net effect depending on sex and the timing of exposure. These effects may contribute to neuropsychiatric, cognitive, cardiovascular, and metabolic abnormalities reported in the offspring of women treated with beta-agonist tocolytics.

Maternal behavior regulates long-term hippocampal expression of BAX and apoptosis in the offspring

Naturally occurring variations in maternal care influence hippocampal development in the rat. In the present study we found that variations in maternal licking/grooming (LG) during the first week of life are associated with altered hippocampal expression of BAX (group-1 tumor necrosis factor family mediated cell death effector) in 90-day-old male offspring. BAX-like immunoreactivity on western blots is significantly increased in the adult offspring of low-level LG mothers. There is no effect of maternal care on levels of either B-cell lymphoma-2 (BCL-2) (group-II mitochondria mediated cell death suppressor) or BAD (group-III endoplasmic reticulum mediated cell death effector). The most striking biochemical event in apoptosis is DNA fragmentation. Terminal deoxynucleotidyl transerferase (Tdt)-mediated dUTP-biotin nick-end labeling (TUNEL) and 4',6'-diamidino-2-phenylindole hydrochloride (DAPI) staining showed that the number of TUNEL-positive cells in both the dentate gyrus and CA1 region of the hippocampus is significantly increased in the adult offspring of low-level LG mothers. In conclusion, we propose that hippocampal neurons in the offspring of low-level LG mothers may be more vulnerable to loss through apoptosis.

Stimulation of beta-adrenoceptors activates astrocytes and provides neuroprotection

Our previous studies established that induction of growth factor synthesis and neuroprotection by the beta(2)-adrenoceptor agonist clenbuterol in vitro and in vivo was associated with the activation of astrocytes, the major source of trophic factors in the brain. In the present study, we further investigated the specificity of beta(2)-adrenoceptor-mediated effects on astrocyte activation and neuroprotection. In mixed hippocampal cultures neuroprotection against glutamate-induced cell death by clenbuterol (1 microM) was blocked by the beta(1/2)-adrenoceptor antagonist propranolol and the specific beta(2)-adrenoceptor antagonists 1-[2,3-(Dihydro-7-methyl-1H-inden-4-yl)-oxy]-3-[(1-methylethyl)-amino]-2-butanol (ICI 118,551, 10 microM) and butoxamine (10 microM), while the beta(1)-adrenoceptor-selective antagonist metoprolol (10 microM) showed no effect. The beta(2)-adrenoceptor agonists clenbuterol (1-100 microM) and salmeterol (0.01-1 microM) induced profound morphological changes of cultured astrocytes which transformed into activated astroglia with pronounced dendrite-like processes. This phenomenon was blocked by butoxamine (1 mM) and propranolol (10 microM), but not by metoprolol (10 microM). However, similar morphological changes in astrocytes were also observed after stimulation of beta(1)-adrenoceptors by dobutamine (1-10 microM) and norepinephrine (1-10 microM). This effect was blocked by propranolol (10 microM) and metoprolol (10 microM) but not by butoxamine (1 mM), suggesting that stimulation of either beta(1)- or beta(2)-adrenoceptors was sufficient to induce activation of astrocytes. In addition, beta(1)-adrenoceptor stimulation by dobutamine (1-10 microM) protected hippocampal neurons against glutamate toxicity. In a model of focal cerebral ischemia in mice the cerebroprotective effect of clenbuterol (0.3 mg/kg) was blocked by propranolol (5 mg/kg) and butoxamine (5 mg/kg). Interestingly, the infarct size was reduced after co-treatment with clenbuterol (0.3 mg/kg) and metoprolol (5 mg/kg) as compared to clenbuterol treatment (0.3 mg/kg) alone. In conclusion, activation of astrocytes and neuroprotection can be achieved by stimulation of either beta(1)- or beta(2)-adrenoceptors in vitro, whereas in vivo neuroprotection is preferentially mediated through beta(2)-adrenoceptors.

Beta(2)-adrenoceptor stimulation enhances latent transforming growth factor-beta-binding protein-1 and transforming growth factor-beta1 expression in rat hippocampus after transient forebrain ischemia

A protective capacity of transforming growth factor-beta1 (TGF-beta1) against various insults inducing neurone cell death in vitro and in vivo has been well established. We have recently shown the rapid up-regulation and persistent expression of TGF-beta1 in surviving CA1 pyramidal cells after cerebral ischemia suggesting an endogenous mechanism of neuroprotection by this multifunctional cytokine. In the present study, we demonstrated that intraperitoneal administration of clenbuterol, a lipophilic beta(2)-adrenoceptor agonist, caused an increase in TGF-beta1 expression in non-ischemic rats and further enhanced TGF-beta1 protein levels in rat CA1 pyramidal neurones after transient forebrain ischemia. In the hippocampus neuroprotection by clenbuterol (0.5 mg/kg) was accompanied by increased TGF-beta1 immunoreactivity as early as 3 h, and remained elevated up to 2 days after ischemia. The corresponding increased TGF-beta1 mRNA levels after ischemia were not further enhanced by clenbuterol, suggesting post-transcriptional regulation of TGF-beta1 protein after beta(2)-adrenoceptor stimulation. In saline-treated rats latent TGF-beta-binding protein-1 (LTBP-1) immunoreactivity was moderately elevated 3 and 6 h after ischemia, and returned to control levels after 1 day of reperfusion. In parallel with the up-regulation of TGF-beta1 immunoreactivity, LTBP-1 levels in the hippocampus were considerably increased by clenbuterol from 3 h to 2 days after ischemia. Our data demonstrate a concomitant increase in LTBP-1 and TGF-beta1 expression in the ischemic hippocampus after stimulation of beta(2)-adrenoceptors.

Iodoacetate protects hippocampal neurons against excitotoxic and oxidative injury: involvement of heat-shock proteins and Bcl-2

Mild metabolic stress may increase resistance of neurons in the brain to subsequent, more severe insults, as demonstrated by the ability of ischemic pre-conditioning and dietary restriction to protect neurons in experimental models of stroke- and age-related neurodegenerative disorders. In the present study we employed iodoacetic acid (IAA), an inhibitor of glyceraldehyde-3-phosphate dehydrogenase, to test the hypothesis that inhibition of glycolysis can protect neurons. Pre-treatment of cultured hippocampal neurons with IAA can protect them against cell death induced by glutamate, iron and trophic factor withdrawal. Surprisingly, protection occurred with concentrations of IAA (2-200 nM) much lower than those required to inhibit glycolysis. Pre-treatment with IAA results in suppression of oxyradical production and stabilization of mitochondrial function in neurons after exposure to oxidative insults. Levels of the stress heat-shock proteins HSP70 and HSP90, and of the anti-apoptotic protein Bcl-2, were increased in neurons exposed to IAA. Our data demonstrate that IAA can stimulate cytoprotective mechanisms within neurons, and suggest the possible use of IAA and related compounds in the prevention and/or treatment of neurodegenerative conditions.

Evidence for the involvement of Par-4 in ischemic neuron cell death

After a stroke many neurons in the ischemic brain tissue die by a process called apoptosis, a form of cell death that may be preventable. The specific molecular cascades that mediate ischemic neuronal death are not well understood. The authors recently identified prostate apoptosis response-4 (Par-4) as a protein that participates in the death of cultured hippocampal neurons induced by trophic factor withdrawal and exposure to glutamate. Here, the authors show that Par-4 levels increase in vulnerable populations of hippocampal and striatal neurons in rats after transient forebrain ischemia; Par-4 levels increased within 6 hours of reperfusion and remained elevated in neurons undergoing apoptosis 3 days later. After transient focal ischemia in mice, Par-4 levels were increased 6 to 12 hours after reperfusion in the infarcted cortex and the striatum, and activation of caspase-8 occurred with a similar time course. Par-4 immunoreactivity was localized predominantly in cortical neurons at the border of the infarct area. A Par-4 antisense oligonucleotide protected cultured hippocampal neurons against apoptosis induced by chemical hypoxia and significantly reduced focal ischemic damage in mice. The current data suggest that early up-regulation of Par-4 plays a pivotal role in ischemic neuronal death in animal models of stroke and cardiac arrest.

Tolerance-Inducing dose of 3-nitropropionic acid modulates bcl-2 and bax balance in the rat brain: a potential mechanism of chemical preconditioning

Many studies have reported ischemia protection using various preconditioning techniques, including single dose 3-nitropropionic acid (3-NPA), a mitochondrial toxin. However, the cellular signal transduction cascades resulting in ischemic tolerance and the mechanisms involved in neuronal survival in the tolerant state still remain unclear. The current study investigated the mRNA and protein expression of the antiapoptotic bcl-2 and the proapoptotic bax. two antagonistic members of the bcl-2 gene family, in response to a single dose of 3-NPA, to global cerebral ischemia-reperfusion. and to the combination of both 3-NPA-pretreatment and subsequent global cerebral ischemia-reperfusion. Brain homogenates of adult Wistar rats (n = 25) were analyzed for bcl-2 and bax mRNA expression using a new highly sensitive and quantitative polymerase chain reaction (PCR) technique that allows real-time fluorescence measurements of the PCR product (LightCycler; Roche Diagnostics, Mannheim, Germany). Animals for mRNA analysis received 3-NPA (20 mg/kg, intraperitoneal; "chemical preconditioning") or vehicle (normal saline), and were either observed for 24 plus 3 hours or were subjected to 15 minutes of global cerebral ischemia 24 hours after the pretreatment and observed for 3 hours of reperfusion. Immunohistochemistry was applied to serial brain sections of additional rats (n = 68) to determine amount and localization of the respective Bcl-2 and Bax protein expression in various brain areas. One set of animals was injected with 3-NPA and observed for 3, 12, 24, and 96 hours; a second set was exposed to 15 minutes global cerebral ischemia, 3, 12, and 24 hours reperfusion; and a third set was pretreated with 3-NPA or saline 24 hours before the ischemic brain insult and observed for 96 hours of reperfusion. The authors found single dose 3-NPA treatment to be associated with an elevated bcl-2:bax ratio (increased bcl-2 expression, decreased bax expression), both on the transcriptional (mRNA) and the translational (protein) level. The differential influence of 3-NPA was maintained during early recovery from global cerebral ischemia (3 hours), when 3-NPA pretreated animals showed higher bcl-2 and lower bax mRNA levels compared with rats with saline treatment. Respective changes in protein expression were localized predominately in neurons vulnerable to ischemic damage. Compared with baseline, Bcl-2 protein was significantly higher in surviving neurons at 96 hours after the insult, whereas Bax protein remained unchanged. However, at this late time of postischemic recovery (96 hours), the protein expression pattern of surviving neurons was not different between animals with and without 3-NPA pretreatment. To the authors' knowledge, the current study is the first report on the differential expression of pro- and antiapoptotic genes after a single, nonlethal dose of 3-NPA. The current results suggest alterations in the balance between pro- and antiapoptotic proteins as a potential explanation for the reported protection provided by chemical preconditioning using 3-NPA in rats.

Apoptosis after experimental stroke: fact or fashion?

This review examines the appearance of hallmarks of apoptosis following experimental stroke. The reviewed literature leaves no doubt that ischemic cell death in the brain is active, that is, requires energy; is gene directed, that is, requires new gene expression; and is capase-mediated, that is, uses apoptotic proteolytic machinery. However, sufficient differences to both classical necrosis and apoptosis exist which prevent easy mechanistic classification. It is concluded that ischemic cell death in the brain is neither necrosis nor apoptosis but is a chimera which appears on a continuum that has apoptosis and necrosis at the poles. The position on this continuum could be modulated by the intensity of the ischemic injury, the consequent availability of ATP and new protein synthesis, and both the age and context of the neuron in question. Thus the ischemic neuron may look necrotic but have actively died in an energy dependent manner with new gene expression and destruction via the apoptotic proteolytic machinery.

The expression of transforming growth factor-beta1 (TGF-beta1) in hippocampal neurons: a temporary upregulated protein level after transient forebrain ischemia in the rat

Exogenous TGF-beta1 has been shown to protect neurons from damage induced in vitro and in vivo. In this study we attempted to examine the expression of endogenous TGF-beta1 mRNA and protein in the hippocampus of non-ischemic and ischemic rats, and to localize TGF-beta1 protein and DNA fragmentation by double-staining. Transient ischemia was induced for 10 min in Wistar rats by clamping both common carotid arteries and lowering blood pressure to 40 mmHg. Bioactive TGF-beta1 was selectively determined in CA1 pyramidal neurons of non-ischemic rats. It was upregulated after 3 h and 6 h of reperfusion corresponding to the increase in TGF-beta1 mRNA level detected by RT-PCR. Lectin and GFAP staining showed no detectable activated microglial cells and astrocytes in the hippocampus 3 h and 6 h after ischemia. When neuronal damage proceeded through day 2 to day 4 after ischemia as demonstrated by TUNEL-staining, TGF-beta1 immunoreactivity (ir) disappeared in damaged neurons but persisted in viable neurons although TGF-beta1 mRNA levels continuously increased. Double-staining revealed that TUNEL-positive neurons did not express TGF-beta1, while TUNEL-negative neurons in the CA1 subfield exhibited a distinct TGF-beta1 ir. These data indicate that hippocampal CA1 neurons can express TGF-beta1 under physiological conditions and upregulate its expression during the first hours after ischemia, that is independent of the activation of glial cells. The endogenous TGF-beta1 expressed in neurons may play a role in the pathological process of DNA degradation and delayed neuronal death after transient forebrain ischemia.