Alzheimer's disease and post-operative cognitive dysfunction

Anesthesia and incident dementia: a population-based, nested, case-control study

OBJECTIVE

To test the hypothesis that exposure to procedures requiring general anesthesia during adulthood is not significantly associated with incident dementia using a retrospective, population-based, nested, case-control study design.

PARTICIPANTS AND METHODS

Using the Rochester Epidemiology Project and the Mayo Clinic Alzheimer's Disease Patient Registry, residents of Olmsted County, Minnesota, diagnosed as having dementia between January 1, 1985, and December 31, 1994, were identified. For each incident case, a sex- and age-matched control was randomly selected from the general pool of Olmsted County residents who were dementia free in the index year of dementia diagnosis. Medical records were reviewed to determine exposures to procedures requiring anesthesia after age 45 years and before the index year. Data were analyzed using logistic regression.

RESULTS

We analyzed 877 cases of dementia, each with a corresponding control. Of the dementia cases, 615 (70%) underwent 1681 procedures requiring general anesthesia; of the controls, 636 (73%) underwent 1638 procedures. When assessed as a dichotomous variable, anesthetic exposure was not significantly associated with dementia (odds ratio, 0.89; 95% CI, 0.73-1.10; P=.27). In addition, no significant association was found when exposure was quantified as number of procedures (odds ratios, 0.87, 0.86, and 1.0 for 1, 2-3, and ≥4 exposures, respectively, compared with none; P=.51).

CONCLUSION

This study found no significant association between exposure to procedures requiring general anesthesia after age 45 years and incident dementia.

Altered functional connectivity in an aged rat model of postoperative cognitive dysfunction: a study using resting-state functional MRI

Background

Postoperative cognitive impairment is a common complication after cardiac and major non-cardiac surgery in the elderly, but its causes and mechanisms remain unclear. The purpose of the current study was to use resting-state functional magnetic resonance imaging (fMRI) to explore changes in the functional connectivity, i.e. the synchronization of low frequency fluctuation (LFF), in an animal model of cognitive impairment in aged rats.

Methods

Aged (22 months) rats were anaesthetized with 40 µg/kg fentanyl and 500 µg/kg droperidol (intraperitoneal) for splenectomy. Cognitive function was assessed using Y maze prior to operation and on postoperative days 1, 3 and 9. To evaluate functional connectivity, resting-state fMRI data were acquired using a 3T MR imaging system with a 4 channel phase array rat head coil.

Results

Cognitive function was impaired at postoperative days 1 and 3 compared with preoperative. Significant synchronized LFF was detected bilaterally in the primary somatosensory cortex and hippocampus preoperatively. By contrast, no significant LFF synchronization was detected in the right primary somatosensory cortex and right hippocampus on postoperative days 1 and 3, although the pattern of functional connectivity had become almost normal by day 9.

Conclusion

Splenectomy performed under neuroleptic anaesthesia triggers a cognitive decline that is associated with altered spontaneous neuronal activity in the cortex and hippocampus.

Early postoperative cognitive dysfunction is associated with higher cortisol levels in aged patients following hip fracture surgery

This study aimed to evaluate the relationship between plasma cortisol levels and the occurrence of postoperative cognitive dysfunction (POCD) in aged patients following hip fracture surgery. A total of 175 patients, aged 65 years or older, who were scheduled for hip fracture surgery with spinal anesthesia were enrolled. Perioperative plasma levels of cortisol and neurocognitive tests were determined at 1 day preoperatively and 7 days postoperatively. Seventy-seven patients completed both blood sample collections and neurocognitive tests. POCD occurred in 29.9 % of patients at 7 days postoperatively. POCD patients presented significantly higher cortisol levels compared with non-POCD patients (P < 0.05). Furthermore, plasma cortisol levels were negatively correlated with mini-mental state examination (MMSE) scores at 7 days postoperatively (P < 0.0001). A specificity of 93 % and a sensitivity of 35 % were identified for the plasma cortisol measurement to discriminate POCD patients from non-POCD patients. The results suggest higher plasma cortisol levels are associated with POCD in aged patients following hip fracture surgery with spinal anesthesia.

Anesthesia and Alzheimer's disease: time to wake up!

It has long been observed that some patients suffer a significant cognitive impact following anesthesia and surgery. This should not be surprising when considering that not only is the target organ for general anesthetic agents the brain itself but also that the process of anesthesia is a form of deep, pharmacologically induced coma rather than “sleep.” The expectation that such a process should be fully reversible with transient neurophysiological effects contradicts our experience with repeated abuse of other central nervous system depressants such as glue, petrol, and alcohol. Of great concern is that, while approximately 10% of populations in developed countries undergo anesthesia and surgery of some form each year, the proportion of the elderly making up this group is much greater. In addition, it is the elderly who are potentially at a greater risk of cognitive impairment following such procedures because many have decreased cognitive reserve, either due to pre-existing mild cognitive impairment (MCI) or frank dementia, which may be diagnosed or unknown. The impact of anesthesia on these individuals is poorly understood, as are the implications of the emerging laboratory data that suggest an effect of anesthetic agents on the pathological processes of Alzheimer's Disease (AD) itself.

The role of the TLR4 signaling pathway in cognitive deficits following surgery in aged rats

Postoperative cognitive dysfunction (POCD), common in elderly patients, refers to a decline in cognitive function following surgery, which may persist or even evolve into Alzheimer's disease (AD). Despite great efforts, the mechanism of POCD remains unclear. In the present study, we tested the hypothesis that Toll-like receptor 4 (TLR4) on microglia contributes to POCD. Shortly after surgery, aged rats demonstrated significant deficits in memory and learning, accompanied by the activation of microglia, marked upregulation of TLR4 on microglia in the hippocampus, as well as an increased expression of two downstream factors [myeloid differentiation factor 88 (MyD88) and TIR-domain-containing adapter-inducing interferon-β (TRIF)] and pro-inflammatory cytokines [including tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β)]. With an increase in time following surgery, the expression of TLR4 and the aforementioned factors and pro-inflammatory cytokines gradually returned to normal, as did the cognitive function of the aged rats. In conclusion, our study suggests that the activation of TLR4 signaling on microglia may act as an underlying mechanism of POCD.

Isoflurane increases neuronal cell death vulnerability by downregulating miR-214

Since accumulating evidence suggests the application of anesthetics may increase the risk of Alzheimer’s disease (AD), we investigated the cytotoxicity of inhaled general anesthesia in neurons and its underlying mechanism. Using primary cultured rat hippocampal neurons as the study model, here we show that isoflurane increases vulnerability to intracellular or extracellular amyloid β with or without serum deprivation. This isoflurane-induced effect is mediated by the downregulation of miR-214 level that lead to an elevated expression of Bax, a prominent target for miR-214. We conclude that isoflurane increases cell death in the presence of amyloid β by increasing Bax level through downregulating miR-214. Our data provide a new insight for inhaled anesthetics toxicity and indicate a possible mechanistic link between anesthetic application and neurodegenration in AD.

The neuroinflammatory response of postoperative cognitive decline

BACKGROUND

Aseptic surgical trauma provokes a homeostatic neuroinflammatory response to promote healing and protect the organism from further injury. When this response is dysregulated, harmful consequences can follow, including postoperative cognitive decline.

SOURCES OF DATA

We performed a comprehensive search on PubMed related to postoperative cognitive dysfunction (POCD).

AREAS OF AGREEMENT

Although the precise pathogenic mechanisms for POCD remain unclear, certain risk factors are known.

AREAS OF CONTROVERSY

The mechanisms that lead to exaggerated and persistent neuroinflammation and the best way to counteract it are still unknown. AREAS FOR DEVELOPING RESEARCH: It is imperative that we identify the underlying processes that increase the risk of cognitive decline in elderly surgical patients. In this review we explore non-resolution of inflammation as an underlying cause of developing exaggerated and persistent POCD. If interventions can be developed to promote resolution of neuroinflammation, the patient's postoperative recovery will be enhanced and long-term consequences can be prevented.

Epigenetics as a new therapeutic target for postoperative cognitive dysfunction

Persistent memory and learning disabilities may occur postoperatively and may be related to neurodegenerative processes. Epigenetic dysregulation has been implicated to abnormal brain function and neurodegenerative diseases. Some risk factors contributing to postoperative cognitive disorder (POCD) have been identified, including exposure to general anesthesia, hypotension, hypoxia, psychoactive drugs, hippocampal inflammation induced by the surgical intervention, etc. The current evidence supports these risk factors might induce epigenetic dysfunction in the brain. It is possible that epigenetic regulation might be the common downstream pathway of these risk factors, since the chromatin remodeling is necessary for the memory-associated gene transcription and expression. Here, we present our hypothesis that the epigenetic dysregulation might be a critical mechanism underlying POCD. Our hypothesis may lead to a new therapeutic strategy of epigenetic intervention for POCD.

Surgery upregulates high mobility group box-1 and disrupts the blood-brain barrier causing cognitive dysfunction in aged rats

AIM

Postoperative cognitive dysfunction (POCD) is a growing and largely underestimated problem without defined etiology. Herein, we sought to determine the relationship between cognitive decline, blood-brain barrier (BBB) permeability, and inflammation, namely high mobility group box-1 (HMGB1), after surgery in aged rats.

METHODS

Aged rats were randomly assigned as surgery group (n = 45, splenectomy under general anesthesia), anesthesia (n = 45, 2% isoflurane for 2 h), and naïve control (n = 15). Markers of inflammation were measured in plasma and brain. Blood-brain barrier ultrastructure and permeability were measured by transmission electron microscope (TEM) and IgG immunohistochemistry. Cognitive function was assessed in a reversal learning version of the Morris water maze (MWM).

RESULTS

Surgical trauma under general anesthesia caused distinct changes in systemic and central proinflammatory cytokines. Levels of HMGB1 and the receptor for advanced glycation end products (RAGE) were significantly upregulated in the hippocampus of operated animals. Immunohistochemistry and TEM showed BBB disruption induced by surgery and anesthesia. These molecular changes were associated with cognitive impairment in latency with the MWM up to postoperative day 3.

CONCLUSIONS

HMGB1 and RAGE signaling appear pivotal mediators of surgery-induced cognitive decline and may contribute to the changes in BBB permeability after peripheral surgical trauma.

Gender-specific differences in the central nervous system's response to anesthesia

Males and females are physiologically distinct in their responses to various anesthetic agents. The brain and central nervous system (CNS), the main target of anesthesia, are sexually dimorphic from birth and continue to differentiate throughout life. Accordingly, gender has a substantial impact on the influence of various anesthetic agents in the brain and CNS. Given the vast differences in the male and female CNS, it is surprising to find that females are often excluded from basic and clinical research studies of anesthesia. In animal research, males are typically studied to avoid the complication of breeding, pregnancy, and hormonal changes in females. In clinical studies, females are also excluded for the variations that occur in the reproductive cycle. Being that approximately half of the surgical population is female, the exclusion of females in anesthesia-related research studies leaves a huge knowledge gap in the literature. In this review, we examine the reported sex-specific differences in the central nervous system's response to anesthesia. Furthermore, we suggest that anesthesia researchers perform experiments on both sexes to further evaluate such differences. We believe a key goal of research studying the interaction of the brain and anesthesia should include the search for knowledge of sex-specific mechanisms that will improve anesthetic care and management in both sexes.

MicroPET/CT Imaging of [18F]-FEPPA in the Nonhuman Primate: A Potential Biomarker of Pathogenic Processes Associated with Anesthetic-Induced Neurotoxicity

Background. The inhalation anesthetics nitrous oxide (N2O) and isoflurane (ISO) are used in surgical procedures for human infants. Injury to the central nervous system is often accompanied by localization of activated microglia or astrocytosis at the site of injury. The tracer that targets to the peripheral benzodiazepine receptor (PBR), [18F]N-2-(2-fluoroethoxy)benzyl)-N-(4-phenoxypyridin-3-yl)acetamide ([18F]-FEPPA), has been reported as a sensitive biomarker for the detection of neuronal damage/inflammation. Methods. On postnatal day (PND) 5 or 6 rhesus monkey neonates were exposed to a mixture of N2O/oxygen and ISO for 8 hours and control monkeys were exposed to room air. MicroPET/CT images with [18F]-FEPPA were obtained for each monkey 1 day, one week, three weeks, and 6 months after the anesthetic exposure. Results. The radiotracer quickly distributed into the brains of both treated and control monkeys on all scan days. One day after anesthetic exposure, the uptake of [18F]-FEPPA was significantly increased in the temporal lobe. One week after exposure, the uptake of [18F]-FEPPA in the frontal lobe of treated animals was significantly greater than that in controls. Conclusions. These findings suggest that microPET imaging is capable of dynamic detection of inhaled anesthetic-induced brain damage in different brain regions of the nonhuman primate.

Advanced pre-clinical research approaches and models to studying pediatric anesthetic neurotoxicity

Advances in pediatric and obstetric surgery have resulted in an increase in the duration and complexity of anesthetic procedures. A great deal of concern has recently arisen regarding the safety of anesthesia in infants and children. Because of obvious limitations, it is not possible to thoroughly explore the effects of anesthetic agents on neurons in vivo in human infants or children. However, the availability of some advanced pre-clinical research approaches and models, such as imaging technology both in vitro and in vivo, stem cells, and non-human primate experimental models, have provided potentially invaluable tools for examining the developmental effects of anesthetic agents. This review discusses the potential application of some sophisticated research approaches, e.g., calcium imaging, in stem cell-derived in vitro models, especially human embryonic neural stem cells, along with their capacity for proliferation and their potential for differentiation, to dissect relevant mechanisms underlying the etiology of the neurotoxicity associated with developmental exposures to anesthetic agents. Also, this review attempts to discuss several advantages for using the developing rhesus monkey model (in vivo), when combined with dynamic molecular imaging approaches, in addressing critical issues related to the topic of pediatric sedation/anesthesia. These include the relationships between anesthetic-induced neurotoxicity, dose response, time-course, and developmental stage at time of exposure (in vivo studies), serving to provide the most expeditious platform toward decreasing the uncertainty in extrapolating pre-clinical data to the human condition.

Hippocampal glutamate level and glutamate aspartate transporter (GLAST) are up-regulated in senior rat associated with isoflurane-induced spatial learning/memory impairment

Postoperative cognitive decline is a clinical concern especially for senior patients. It is generally recognized that glutamatergic system plays a crucial role in the physiopathologic process of neurocognitive deterioration. However, alterations of glutamatergic system in prolonged isoflurane-induced learning/memory decline are still unclear. This study investigates the question whether glutamate concentration and corresponding transporters or receptors display any alternations in aged rat suffering from isoflurane-induced learning/memory impairment. 111 male Sprague-Dawley rats (>18 months) were randomly divided into two main groups: hippocampal microdialysis group (n = 38) and western blotting group (n = 73). Each group was subdivided into three subgroups including (1) control subgroup (n = 6 and 10, receiving no behavioral trial, anesthesia or air exposure); (2) air-exposed subgroup (n = 7 and 15, receiving behavioral trial and air exposure but not anesthesia); (3) isoflurane anesthesia subgroup (n = 25 and 48, receiving both behavioral trial and anesthesia). The isoflurane-exposed rats were further divided into a learning/memory-impaired subgroup and a non-learning/memory-impaired subgroup according to their behavioral performance, which was measured using Morris water maze. Hippocampal glutamate concentrations in microdialysates were determined by high-performance liquid chromatography. Expression levels of GLAST, GLT-1, NMDAR1, NMDAR2A/B, AMPAR and tau in hippocampus were assessed via quantitative Western blotting. The incidences of learning/memory impairment of isoflurane-exposed rats in hippocampal microdialysis group and western blotting group were 12.0 (3/25) and 10.4 % (5/48) respectively. The intra-anesthesia hippocampal glutamate levels were significantly lower than those of non-anesthesized rats. The learning/memory-impaired rats showed a long-lasting increased glutamate level from 24 h after isoflurane exposure to the end of the study, but the other 22 isoflurane-exposed rats did not. The learning/memory-impaired subgroup displayed a significantly higher GLAST level than the other three subgroups (p = 0.026, 0.02 and 0.032 respectively). The expression levels of GLT-1, NMDAR1, NMDAR2A/B and AMPAR of every subgroup were comparable. We found a continuous raised hippocampal glutamate and an up-regulation of GLAST rather than GLT-1, NMDAR1, NMDAR2A/B, AMPAR or tau in hippocampus of aged rats associated with isoflurane-induced learning/memory impairment.

Postoperative cognitive dysfunction is correlated with urine formaldehyde in elderly noncardiac surgical patients

Post-operative cognitive dysfunction (POCD), especially in elderly patients, has been reported in many studies. Although increasing age, duration of anesthesia, postoperative infections, and respiratory complications were regarded as the risk factors for POCD, no extracerebral diagnostic biomarkers have been identified as indicators of POCD. Ninety-five patients, ages 65-80 years, scheduled for major orthopedic or abdominal surgery were enrolled. Twenty-two patients aged between 20 and 40 years undergoing the same procedures served as controls. Subjects received neuropsychological tests one-day prior and one week post procedure. To determine the presence of POCD, the criteria were used as described in most previous studies. Morning urine samples were obtained one day before surgery and on day 1, day 2 and day 7 post operatively. Urine formaldehyde was determined with high-performance liquid chromatography. The urine formaldehyde level of all patients with and without POCD increased on the first 2 days after surgery. But the formaldehyde concentration (on day 7) in patients with POCD was significantly higher than that in patients without POCD (p < 0.01). In the young control group, no patient was diagnosed with POCD. Although the changes in urine formaldehyde of young patients during perioperative period were similar to those in elderly patients without POCD, the formaldehyde concentrations measured at four time points were all significantly lower than those in elderly patients (p < 0.05). Levels of urine formaldehyde were elevated in the perioperative period, with the highest levels at day 7 in patients with POCD. This suggests that the increase on day 7 may provide a new physiologic marker along with neuropsychological assessments to assist in the diagnosis of POCD.

Effect of synthetic aβ peptide oligomers and fluorinated solvents on Kv1.3 channel properties and membrane conductance

The impact of synthetic amyloid β (1–42) (Aβ_1–42) oligomers on biophysical properties of voltage-gated potassium channels Kv 1.3 and lipid bilayer membranes (BLMs) was quantified for protocols using hexafluoroisopropanol (HFIP) or sodium hydroxide (NaOH) as solvents prior to initiating the oligomer formation. Regardless of the solvent used Aβ_1–42 samples contained oligomers that reacted with the conformation-specific antibodies A11 and OC and had similar size distributions as determined by dynamic light scattering. Patch-clamp recordings of the potassium currents showed that synthetic Aβ_1–42 oligomers accelerate the activation and inactivation kinetics of Kv 1.3 current with no significant effect on current amplitude. In contrast to oligomeric samples, freshly prepared, presumably monomeric, Aβ_1–42 solutions had no effect on Kv 1.3 channel properties. Aβ_1–42 oligomers had no effect on the steady-state current (at −80 mV) recorded from Kv 1.3-expressing cells but increased the conductance of artificial BLMs in a dose-dependent fashion. Formation of amyloid channels, however, was not observed due to conditions of the experiments. To exclude the effects of HFIP (used to dissolve lyophilized Aβ_1–42 peptide), and trifluoroacetic acid (TFA) (used during Aβ_1–42 synthesis), we determined concentrations of these fluorinated compounds in the stock Aβ_1–42 solutions by ¹⁹F NMR. After extensive evaporation, the concentration of HFIP in the 100× stock Aβ_1–42 solutions was ∼1.7 μM. The concentration of residual TFA in the 70× stock Aβ_1–42 solutions was ∼20 μM. Even at the stock concentrations neither HFIP nor TFA alone had any effect on potassium currents or BLMs. The Aβ_1–42 oligomers prepared with HFIP as solvent, however, were more potent in the electrophysiological tests, suggesting that fluorinated compounds, such as HFIP or structurally-related inhalational anesthetics, may affect Aβ_1–42 aggregation and potentially enhance ability of oligomers to modulate voltage-gated ion channels and biological membrane properties.

Isoflurane-induced spatial memory impairment by a mechanism independent of amyloid-beta levels and tau protein phosphorylation changes in aged rats

OBJECTIVES

The molecular mechanism of postoperative cognitive dysfunction is largely unknown. Isoflurane has been shown to promote Alzheimer's disease neuropathogenesis. We set out to determine whether the effect of isoflurane on spatial memory is associated with amyloid-beta (A-beta) levels and tau phosphorylation in aged rats.

METHODS

Eighteen-month-old male Sprague-Dawley rats were randomly assigned as anesthesia group (n = 31, received 1.4% isoflurane for 2 hours and had behavioral testing), training group (n = 20, received no anesthesia but had behavioral testing), and control group (n = 10, received no anesthesia and had no behavioral testing). Spatial memory was measured before and 2 days after the anesthesia by the Morris water maze. We divided the anesthesia group into an isoflurane-induced severe memory impairment group (SIG, n = 6) and a no severe memory impairment group (NSIG, n = 25), according to whether the escape latency was more than 1.96 stand deviation of that from the training group. Levels of A-beta and tau in the hippocampus were determined by enzyme-linked immunosorbent assay and quantitative western blot at the end of behavioral testing.

RESULTS

We found that isoflurane increased the escape latency in the SIG as compared to that in the training group and NSIG without affecting swimming speed. However, there were no differences in the levels of A-beta and tau among SIG, NSIG, training, and control groups.

CONCLUSIONS

Isoflurane may induce spatial memory impairment through non-A-beta or tau neuropathogenesis mechanisms in aged rats.

Rutin prevents cognitive impairments by ameliorating oxidative stress and neuroinflammation in rat model of sporadic dementia of Alzheimer type

The objective of the present study was to assess the neuroprotective role of rutin (vitamin P) and delineate the mechanism of action. Recent evidence indicates that rutin exhibits antioxidant potential and protects the brain against various oxidative stressors. More precisely, the aim of the present study was to examine the modulating impacts of rutin against cognitive deficits and oxidative damage in intracerebroventricular-streptozotocin (ICV-STZ)-infused rats. Rats were injected bilaterally with ICV-STZ (3 mg/kg), whereas sham rats received the same volume of vehicle. After 2 weeks of streptozotocin (STZ) infusion, rats were tested for cognitive performance using Morris water maze tasks and thereafter euthanized for further biochemical, histopathological, and immunohistochemical studies. Rutin pretreatment (25 mg/kg, orally, once daily for 3 weeks) significantly attenuated thiobarbituric acid reactive substances (TBARS), activity of poly ADP-ribosyl polymerase, and nitrite level and decreased level of reduced glutathione (GSH) and activities of its dependent enzymes (glutathione peroxidase [GPx] and glutathione reductase [GR]) and catalase in the hippocampus of ICV-STZ rats. ICV-STZ rats showed significant cognitive deficits, which was improved significantly by rutin supplementation. The results indicate that rutin attenuates STZ-induced inflammation by reducing the expression of cyclooxygenase-2 (COX-2), glial fibrillary acidic protein (GFAP), interleukin-8 (IL-8), inducible nitric oxide synthase (iNOS), nuclear factor-kB, and preventing the morphological changes in hippocampus. The study thereby suggests the effectiveness of rutin in preventing cognitive deficits and might be beneficial for the treatment of sporadic dementia of Alzheimer type (SDAT).

A potential role for zinc alterations in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), one of the major causes of disability and mortality in Western societies, is a progressive age-related neurodegenerative disorder. Increasing evidence suggests that the etiology of AD may involve disruptions of zinc (Zn) homeostasis. This review discusses current evidence supporting a potential role of Zn and zinc transporters (ZnTs) in processing of the amyloid beta protein precursor (APP) and amyloid beta (Aβ) peptide generation and aggregation.

2-Deoxy-D-glucose attenuates isoflurane-induced cytotoxicity in an in vitro cell culture model of H4 human neuroglioma cells

BACKGROUND

β-Amyloid protein (Aβ) accumulation and caspase activation have been shown to contribute to Alzheimer disease neuropathogenesis. Aβ is produced from amyloid precursor protein through proteolytic processing by aspartyl protease β-site amyloid precursor protein-cleaving enzyme (BACE). The inhaled anesthetic isoflurane has been shown to induce caspase activation and increase levels of BACE and Aβ. However, the underlying mechanisms and interventions of the isoflurane-induced neurotoxicity remain largely to be determined. The glucose analog 2-deoxy-d-glucose (2-DG) has neuroprotective effects. Therefore, we sought to determine whether 2-DG can reduce caspase-3 activation and the increase in the levels of BACE and reactive oxygen species (ROS) induced by isoflurane.

METHODS

H4 human neuroglioma cells were treated with saline or 2-DG (5 mM) for 1 hour followed by a control condition or 2% isoflurane for 6 hours. The levels of caspase-3 cleavage (activation), BACE, cytosolic calcium, and ROS were determined. Two-way analysis of variance was used to assess the interactions of 2-DG and isoflurane on caspase-3 activation, and levels of BACE and ROS.

RESULTS

In H4 human neuroglioma cells, 2-DG reduced the caspase-3 activation (477% vs 186%, F = 8.68; P = 0.019) and the increase in BACE levels (345% vs 123%, F = 42.24; P = 0.0002) induced by isoflurane. 2-DG decreased the levels of cytosolic calcium and ROS (100% vs 66%, F = 1.94; P = 0.014).

CONCLUSIONS

These results suggest that 2-DG may decrease oxidative stress and increase cytosolic calcium levels, thus attenuating isoflurane-induced neurotoxicity.

Chronic divalproex sodium use and brain atrophy in Alzheimer disease

OBJECTIVE

We evaluated the effect of the divalproex sodium formulation of valproic acid on brain volumes using MRI in people with mild to moderate Alzheimer disease (AD) and assessed for changes associated with behavioral and cognitive effects.

METHODS

Eighty-nine of 313 participants randomized to divalproex or placebo in a 24-month, parallel-group trial received MRI scans at baseline and 12 months. Interval MRI annual percent changes in whole brain, ventricular, and hippocampal volumes were the primary outcomes of interest. Change from baseline in clinical outcomes was assessed at 6-month intervals.

RESULTS

There were no baseline differences between active treatment and placebo groups in age, education, brain volumes, clinical rating scores, or APOE ε4 carrier status. The group treated with divalproex showed a greater rate of decline in left and right hippocampal and brain volumes (-10.9% and -12.4% vs -5.6% and -6.3%, and -3.5% vs -1.4%, respectively), and a greater rate of ventricular expansion (24.5% vs 9.9%) (p < 0.001). Mini-Mental State Examination scores showed a more rapid decline with divalproex through month 12 (placebo = -2.0 ± 4.3, divalproex = -3.9 ± 4.0) (p = 0.037), although there were no changes on other cognitive, behavioral, or functional ratings at 12 and 24 months.

CONCLUSIONS

Divalproex treatment was associated with accelerated brain volume loss over 1 year and perhaps with greater cognitive impairment. The long-term clinical effects of these changes are not known.

Perioperative cognitive decline in the aging population

Elderly patients who have an acute illness or who undergo surgery often experience cognitive decline. The pathophysiologic mechanisms that cause neurodegeneration resulting in cognitive decline, including protein deposition and neuroinflammation, also play a role in animal models of surgery-induced cognitive decline. With the aging of the population, surgical candidates of advanced age with underlying neurodegeneration are encountered more often, raising concerns that, in patients with this combination, cognitive function will precipitously decline postoperatively. This special article is based on a symposium that the University of California, San Francisco, convened to explore the contributions of surgery and anesthesia to the development of cognitive decline in the aged patient. A road map to further elucidate the mechanisms, diagnosis, risk factors, mitigation, and treatment of postoperative cognitive decline in the elderly is provided.

RNA interference-mediated silencing of BACE and APP attenuates the isoflurane-induced caspase activation

Background

β-Amyloid protein (Aβ) has been shown to potentiate the caspase-3 activation induced by the commonly used inhalation anesthetic isoflurane. However, it is unknown whether reduction in Aβ levels can attenuate the isoflurane-induced caspase-3 activation. We therefore set out to determine the effects of RNA interference-mediated silencing of amyloid precursor protein (APP) and β-site APP-cleaving enzyme (BACE) on the levels of Aβ and the isoflurane-induced caspase-3 activation.

Methods

H4 human neuroglioma cells stably transfected to express full-length human APP (H4-APP cells) were treated with small interference RNAs (siRNAs) targeted at silencing BACE and APP for 48 hours. The cells were then treated with 2% isoflurane for six hours. The levels of BACE, APP, and caspase-3 were determined using Western blot analysis. Sandwich Enzyme-linked immunosorbent assay (ELISA) was used to determine the extracellular Aβ levels in the conditioned cell culture media.

Results

Here we show for the first time that treatment with BACE and APP siRNAs can decrease levels of BACE, full-length APP, and APP c-terminal fragments. Moreover, the treatment attenuates the Aβ levels and the isoflurane-induced caspase-3 activation. These results further suggest a potential role of Aβ in the isoflurane-induced caspase-3 activation such that the reduction in Aβ levels attenuates the isoflurane-induced caspase-3 activation.

Conclusion

These findings will lead to more studies which aim at illustrating the underlying mechanism by which isoflurane and other anesthetics may affect Alzheimer's disease neuropathogenesis.

The potential dual effects of anesthetic isoflurane on hypoxia-induced caspase-3 activation and increases in β-site amyloid precursor protein-cleaving enzyme levels

BACKGROUND

β-Amyloid protein (Aβ) accumulation, caspase activation, apoptosis, and hypoxia-induced neurotoxicity have been suggested to be involved in Alzheimer disease neuropathogenesis. Aβ is produced from amyloid precursor protein through proteolytic processing by the aspartyl protease β-site amyloid precursor protein-cleaving enzyme (BACE) and γ-secretase. Inhaled anesthetics have long been considered to protect against neurotoxicity. However, recent studies have suggested that the inhaled anesthetic isoflurane may promote neurotoxicity by inducing caspase activation and apoptosis, and by increasing levels of BACE and Aβ. We therefore sought to determine whether isoflurane can induce concentration-dependent dual effects on hypoxia-induced caspase-3 activation and increases in BACE levels: protection versus promotion.

METHODS

H4 human neuroglioma cells were treated with hypoxia (3% O(2)) alone, different concentrations of isoflurane (0.5% and 2%), and the combination of hypoxia and 0.5% or 2% isoflurane. The levels of caspase-3 cleavage (activation), BACE, and Bcl-2 were determined by Western blot analysis.

RESULTS

We show for the first time that treatment with 0.5% isoflurane for 8 hours attenuated, whereas treatment with 2% isoflurane for 8 hours enhanced, hypoxia-induced caspase-3 activation and increases in BACE levels. The 2% isoflurane treatment also enhanced a hypoxia-induced decrease in Bcl-2 levels.

CONCLUSIONS

These results suggest a potential concept that isoflurane has dual effects (protection versus promotion) on hypoxia-induced toxicity, which may act through Bcl-2 family proteins. These findings could lead to more systematic studies to determine the potential dual effects of anesthetics on Alzheimer disease-associated neurotoxicity.

Alzheimer's disease and anesthesia

Cognitive disorders such as postoperative cognitive dysfunction, confusion, and delirium, are common following anesthesia in the elderly, with symptoms persisting for months or years in some patients. Alzheimer's disease (AD) patients appear to be particularly at risk of cognitive deterioration following anesthesia, and some studies suggest that exposure to anesthetics may increase the risk of AD. Here, we review the literature linking anesthesia to AD, with a focus on the biochemical consequences of anesthetic exposure on AD pathogenic pathways.

Carnosine protects against the neurotoxic effects of a serotonin-derived melanoid

Anesthesia-related postoperative cognitive dysfunction (POCD) leads to morbidity in the elderly. Lipid peroxidative byproducts (i.e. acrolein) accumulate in aging and may play a role. Sevoflurane, an inhaled anesthetic, sequesters acrolein and enhances the formation of a serotonin-derived melanoid (SDM). SDM may be a biologically relevant polymeric melanoid that we previously showed exhibits redox activity and disrupts lipid bilayers. In this study, we examined the toxicity of SDM in cell culture and looked at protection using L-carnosine. SDM's toxic effects were tested on neuronal-like SH-SY5Y cells, causing an exponential decrease in viability, while human dermal fibroblasts were completely resistant to the toxic effects. SDM brought about morphological changes to differentiated SH-SY5Y cells, particularly to neuronal processes. Co- but not pre-treatment with L-carnosine protected differentiated SH-SY5Y cells exposed to SDM. Our mechanism suggests focal sevoflurane-induced sequestration of age-related acrolein leading to SDM synthesis and neuronal impairment, which is prevented by L-carnosine.

Anesthetic sevoflurane causes neurotoxicity differently in neonatal naïve and Alzheimer disease transgenic mice

BACKGROUND

Recent studies have suggested that children undergoing surgery under anesthesia could be at an increased risk for the development of learning disabilities, but whether anesthetics contribute to this learning disability is unclear. Therefore, the authors set out to assess the effects of sevoflurane, the most commonly used inhalation anesthetic, on caspase activation, apoptosis, beta-amyloid protein levels, and neuroinflammation in the brain tissues of neonatal naïve and Alzheimer disease (AD) transgenic mice.

METHODS

Six-day-old naïve and AD transgenic (B6.Cg-Tg[amyloid precursor protein swe, PSEN1dE9]85Dbo/J) mice were treated with sevoflurane. The mice were killed at the end of the anesthesia, and the brain tissues were harvested and then subjected to Western blot, immunocytochemistry, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction.

RESULTS

Herein, the authors show for the first time that sevoflurane anesthesia induced caspase activation and apoptosis, altered amyloid precursor protein processing, and increased beta-amyloid protein levels in the brain tissues of neonatal mice. Furthermore, sevoflurane anesthesia led to a greater degree of neurotoxicity in the brain tissues of the AD transgenic mice when compared with naïve mice and increased tumor necrosis factor-alpha levels in the brain tissues of only the AD transgenic mice. Finally, inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenyl borate attenuated sevoflurane-induced caspase-3 activation and beta-amyloid protein accumulation in vivo.

CONCLUSION

These results suggest that sevoflurane may induce neurotoxicity in neonatal mice. AD transgenic mice could be more vulnerable to such neurotoxicity. These findings should promote more studies to determine the potential neurotoxicity of anesthesia in animals and humans, especially in children.

Isoflurane anesthesia elicits protein pattern changes in rat hippocampus

Postoperative cognitive dysfunction (POCD) is a known phenomenon occurring after anesthesia with volatile anesthetics (VA), such as isoflurane. Recent reports suggest that VA interact with neurodegenerative disease-associated proteins including compounds with pathogenic relevance in Alzheimer disease (AD) and induce processes that may be linked to AD neuropathology. Unfortunately, our present understanding of the exact anesthetics' molecular mechanisms of action, their side effects on the brain, and their catenation with AD pathology is still limited. The present study analyzes the differential proteome of the hippocampus immediately after and 3 days after a 3-hour 1 minimal alveolar concentration isoflurane anesthesia in rats. Differential 2-dimensional electrophoresis, mass spectrometry, and functional network mapping were used to identify and functionally classify 12 different hippocampal proteins, which were significantly regulated after isoflurane anesthesia (6 up-regulated, 11 down-regulated with P<0.01). Induction of differential expression ranged from 0.05 (25-fold down-regulation) to 4.4 (4.4-fold up-regulation). Ten proteins were regulated immediately after and 7 proteins 3 days after isoflurane exposure. The proteome displays isoflurane-responsive protein candidates, which have also been shown to play a role in AD. They were grouped according to their key biologic activities, which showed that isoflurane affects selected biologic processes including synaptic plasticity, stress response, detoxification, and cytoskeleton in early and late recovery phases after anesthesia. These processes are also affected in AD. Results are discussed in view of AD, the toxicity mechanisms of isoflurane as well as the implications for our present understanding and conduction of clinical anesthesia.

Alterations of zinc transporter proteins ZnT-1, ZnT-4 and ZnT-6 in preclinical Alzheimer's disease brain

Our previous studies demonstrate alterations of zinc (Zn) transporter proteins ZnT-1, ZnT-4 and ZnT-6 in vulnerable brain regions of subjects with mild cognitive impairment (MCI), and early and late stage Alzheimer's disease (AD), suggesting disruptions of Zn homeostasis may play a role in the pathogenesis of AD. A preclinical stage of AD (PCAD) has been described in which subjects show no overt clinical manifestations of AD, but demonstrate significant AD pathology at autopsy. To determine if alterations of ZnT proteins occur in PCAD, we measured ZnT-1, ZnT-4 and ZnT-6 in the hippocampus/parahippocampal gyrus (HPG) and cerebellum (CER) of seven PCAD subjects and seven age-matched normal control (NC) subjects using Western blot analysis and immunohistochemistry. Our results show a significant decrease (P < 0.05) of ZnT-1 in HPG of PCAD subjects, along with an increase of ZnT-4 in PCAD CER and ZnT-6 in PCAD HPG, but a significant decrease in PCAD CER compared to NC subjects. Confocal microscopy of representative sections of HPG shows altered ZnTs are associated with neurons immunopositive for MC-1, a monoclonal antibody that identifies neurons early in formation of neurofibrillary tangles. Overall, our results suggest that alterations in Zn transport proteins may contribute to the pathology observed in PCAD subjects before onset of clinical symptoms.

Perianesthesia care of the Alzheimer's patient

Surgery can be a confusing and traumatizing experience for the patient with Alzheimer's Disease (AD). The perianesthesia nurse can better care for the AD patient by acquiring knowledge of the symptoms and stages of the disease, communication skills specific to AD patients, and techniques useful in dealing with AD behaviors. An understanding of AD factors related to anesthesia administration, pain and pain management, as well as general post-operative care, is necessary to create a plan of care that focuses on the AD patient's unique needs. It is important that there be thorough communication along the continuum of care. The health care professional, using well-established nursing skills, paired with Alzheimer's Disease educational resources, can make the challenge of caring for the AD surgical patient less stressful and, hopefully, more satisfying for both the AD patient and the nurse.

Long-term cognitive decline in older subjects was not attributable to noncardiac surgery or major illness

BACKGROUND

Persistent postoperative cognitive decline is thought to be a public health problem, but its severity may have been overestimated because of limitations in statistical methodology. This study assessed whether long-term cognitive decline occurred after surgery or illness by using an innovative approach and including participants with early Alzheimer disease to overcome some limitations.

METHODS

In this retrospective cohort study, three groups were identified from participants tested annually at the Washington University Alzheimer's Disease Research Center in St. Louis, Missouri: those with noncardiac surgery, illness, or neither. This enabled long-term tracking of cognitive function before and after surgery and illness. The effect of surgery and illness on longitudinal cognitive course was analyzed using a general linear mixed effects model. For participants without initial dementia, time to dementia onset was analyzed using sequential Cox proportional hazards regression.

RESULTS

Of the 575 participants, 214 were nondemented and 361 had very mild or mild dementia at enrollment. Cognitive trajectories did not differ among the three groups (surgery, illness, control), although demented participants declined more markedly than nondemented participants. Of the initially nondemented participants, 23% progressed to a clinical dementia rating greater than zero, but this was not more common after surgery or illness.

CONCLUSIONS

The study did not detect long-term cognitive decline independently attributable to surgery or illness, nor were these events associated with accelerated progression to dementia. The decision to proceed with surgery in elderly people, including those with early Alzheimer disease, may be made without factoring in the specter of persistent cognitive deterioration.

Cognitive impairment in the Tg6590 transgenic rat model of Alzheimer's disease

Recently, interest in the rat as an animal model of Alzheimer's disease (AD) has been growing. We have previously described the Tg6590 transgenic rat line expressing the amyloid precursor protein containing the Swedish AD mutation (K670M/N671L) that shows early stages of Abeta deposition, predominantly in cerebrovascular blood vessels, after 15 months of age. Here we show that by the age of 9 months, that is long before the appearance of Abeta deposits, the Tg6590 rats exhibit deficits in the Morris water maze spatial navigation task and altered spontaneous behaviour in the open-field test. The levels of soluble Abeta were elevated both in the hippocampus and cortex of transgenic animals. Magnetic resonance imaging showed no major changes in the brains of transgenic animals, although they tended to have enlarged lateral ventricles when compared to control animals. The Tg6590 transgenic rat line should prove a suitable model of early AD for advanced studies including serial cerebrospinal fluid sampling, electrophysiology, neuroimaging or complex behavioural testing.

Anesthesia induces phosphorylation of tau

Abnormal hyperphosphorylation and aggregation of microtubule-associated protein tau play a crucial role in neurodegeneration of Alzheimer's disease (AD). Anesthesia has been associated with cognitive impairment and the risk for AD. Here we investigated the effects of anesthesia on site-specific tau phosphorylation and the possible mechanisms. We found that anesthesia for short periods (30 sec to 5 min) induced tau phosphorylation at Thr181, Ser199, Thr205, Thr212, Ser262, and Ser404 to small, but significant, extents, which appeared to result from anesthesia-induced activation of stress-activated protein kinases. Anesthesia for a longer time (1~h) induced much more dramatic phosphorylation of tau at the above sites, and the further phosphorylation may be associated with hypothermia induced by anesthesia. Anesthesia-induced tau phosphorylation appears to be specific because the increased phosphorylation was only seen at half of the tau phosphorylation sites studied and was not observed in global brain proteins. These studies clarified the dynamic changes of tau phosphorylation at various sites and, thus, served as a fundamental guide for future studies on tau phosphorylation by using brains of anesthetized experimental animals. Our findings also provide a possible mechanism by which anesthesia may cause postoperative cognitive impairment and increase the risk for AD.

Anesthesia, calcium homeostasis and Alzheimer's disease

While anesthetics are indispensable clinical tools generally safe and effective, in some situations there is grown concern about selective neurotoxicity of these agents; the clinical significance is unclear as of yet. The mechanisms for inhalational anesthetics mediated cell damage are still not clear, although a role for calcium dysregulation has been suggested. For example, the inhaled anesthetic isoflurane decreases endoplasmic reticulum (ER) calcium concentration and increases that in the cytosol and mitochondria. Inhibition of ER calcium release, via either IP(3) or ryanodine receptors, significantly inhibited isoflurane neurotoxicity. Neurons made vulnerable to calcium dysregulation by overexpression of mutated presenilin-1 (PS1) or huntingtin (Q-111) proteins showed enhanced apoptosis upon isoflurane exposure. Sevoflurane and desflurane were less potent than isoflurane in altering intracellular calcium, and produced less apoptosis. Short exposures to inhalational anesthetics may provide neuroprotection by preconditioning via a sublethal stress, while prolonged exposures to inhalational anesthetics may induce cell damage by apoptosis through direct cytotoxic effects.

Consensus statement: First International Workshop on Anesthetics and Alzheimer's disease

In order to review the current status of the potential relationship between anesthesia and Alzheimer's disease, a group of scientists recently met in Philadelphia for a full day of presentations and discussions. This special article represents a consensus view on the possible link between Alzheimer's disease and anesthesia and the steps required to test this more definitively.

Acceleration and persistence of neurofibrillary pathology in a mouse model of tauopathy following anesthesia

Alzheimer's disease and other tauopathies are characterized by the presence of intracellular neurofibrillary tangles composed of hyperphosphorylated, insoluble tau. General anesthesia has been shown to be associated with increased risk of Alzheimer's disease, and we have previously demonstrated that anesthesia induces hypothermia, which leads to overt tau hyperphosphorylation in the brain of mice regardless of the anesthetic used. To investigate whether anesthesia enhances the long-term risk of developing pathological forms of tau, we exposed a mouse model with tauopathy to anesthesia and monitored the outcome at two time points-during anesthesia, or 1 wk after exposure. We found that exposure to isoflurane at clinically relevant doses led to increased levels of phospho-tau, increased insoluble, aggregated forms of tau, and detachment of tau from microtubules. Furthermore, levels of phospho-tau distributed in the neuropil, as well as in cell bodies increased. Interestingly, the level of insoluble tau was increased 1 wk following anesthesia, suggesting that anesthesia precipitates changes in the brain that provoke the later development of tauopathy. Overall, our results suggest that anesthesia-induced hypothermia could lead to an acceleration of tau pathology in vivo that could have significant clinical implications for patients with early stage, or overt neurofibrillary tangle pathology.

Anesthesia-induced hyperphosphorylation detaches 3-repeat tau from microtubules without affecting their stability in vivo

In Alzheimer's disease, tau is hyperphosphorylated, which is thought to detach it from microtubules (MTs), induce MT destabilization, and promote aggregation. Using a previously described in vivo model, we investigated whether hyperphosphorylation impacts tau function in wild-type and transgenic mice. We found that after anesthesia-induced hypothermia, MT-free tau was hyperphosphorylated, which impaired its ability to bind MTs and promote MT assembly. MT-bound tau was more resistant to hyperphosphorylation compared with free tau and tau did not dissociate from MTs in wild-type mice. However, 3-repeat tau detached from MT in the transgenic mice. Surprisingly, dissociation of tau from MTs did not lead to overt depolymerization of tubulin, and there was no collapse, or disturbance of axonal MT networks. These results indicate that, in vivo, a subpopulation of tau bound to MTs does not easily dissociate under conditions that extensively phosphorylate tau. Tau remaining on the MTs under these conditions is sufficient to maintain MT network integrity.

General anesthetic-induced neurotoxicity: an emerging problem for the young and old?

PURPOSE OF REVIEW

A growing body of evidence from cells, rodents, and sub-human primates suggests that general anesthetics can be neurotoxic to the developing and senescent brain. We review this evidence and put the studies into perspective for the practicing clinician.

RECENT FINDINGS

Studies indicate that a variety of general anesthetics, which act primarily as gamma-amino-butyric acid receptor modulators and N-methyl-D-aspartic acid glutamate receptor antagonists, produce apoptotic neurodegeneration in the developing rodent and nonhuman primate brain. Vulnerability to this neurotoxicity is greatest during the period of synaptogenesis and presumably reflects disruption of the normal balance between excitation and inhibition during a critical period of brain development. Moreover, in the rodent, the neurodegeneration is associated with cognitive impairment into adulthood. Recent data also reveal that general anesthesia produces enduring cognitive impairment in aged but not young rodents and that halothane and isoflurane increase the generation and toxicity of amyloid beta, a protein strongly implicated in the pathogenesis of Alzheimer's disease. The meaning of these experimental results for human surgical patients is unclear, however, because human studies are lacking.

SUMMARY

General anesthetics produce neurotoxicity and enduring cognitive impairment in young and aged animals but it is premature to change clinical practice because the issue has not been adequately studied in humans.

Anesthesia leads to tau hyperphosphorylation through inhibition of phosphatase activity by hypothermia

Postoperative cognitive dysfunction, confusion, and delirium are common after general anesthesia in the elderly, with symptoms persisting for months or years in some patients. Even middle-aged patients are likely to have postoperative cognitive dysfunction for months after surgery, and Alzheimer's disease (AD) patients appear to be particularly at risk of deterioration after anesthesia. Several investigators have thus examined whether general anesthesia is associated with AD, with some studies suggesting that exposure to anesthetics may increase the risk of AD. However, little is known on the biochemical consequences of anesthesia on pathogenic pathways in vivo. Here, we investigated the effect of anesthesia on tau phosphorylation and amyloid precursor protein (APP) metabolism in mouse brain. We found that, regardless of the anesthetic used, anesthesia induced rapid and massive hyperphosphorylation of tau, rapid and prolonged hypothermia, inhibition of Ser/Thr PP2A (protein phosphatase 2A), but no changes in APP metabolism or Abeta (beta-amyloid peptide) accumulation. Reestablishing normothermia during anesthesia completely rescued tau phosphorylation to normal levels. Our results indicate that changes in tau phosphorylation were not a result of anesthesia per se, but a consequence of anesthesia-induced hypothermia, which led to inhibition of phosphatase activity and subsequent hyperphosphorylation of tau. These findings call for careful monitoring of core temperature during anesthesia in laboratory animals to avoid artifactual elevation of protein phosphorylation. Furthermore, a thorough examination of the effect of anesthesia-induced hypothermia on the risk and progression of AD is warranted.

Brain and behavior changes in 12-month-old Tg2576 and nontransgenic mice exposed to anesthetics

Inhaled anesthetics have been shown to increase the aggregation of amyloid beta in vitro through the stabilization of intermediate toxic oligomers, which are thought to contribute to neurocognitive dysfunction in Alzheimer's disease. Inhaled anesthetics may escalate cognitive dysfunction through enhancement of these intermediate oligomer concentrations. We intermittently exposed 12-month-old Tg2576 transgenic mice and nontransgenic littermates to isoflurane and halothane for 5 days. Cognitive function was measured before and after anesthetic exposures using the Morris Water Maze; amyloid beta plaque burden and caspase-3 mediated apoptosis were quantified by immunohistochemistry. At 12 months of age, anesthetic exposure did not further enhance cognitive decline in the transgenic mice. Immunohistochemistry, however, revealed that the halothane-exposed Tg2576 mice had more amyloidopathy than the isoflurane treated mice or the nonexposed transgenic mice. Isoflurane exposure impaired cognitive function in the nontransgenic mice, implying an alternative pathway for neurodegeneration. These findings indicate that inhaled anesthetics influence cognition and amyloidogenesis, but that the mechanistic relationship remains unclear.

The inhalation anesthetic isoflurane induces a vicious cycle of apoptosis and amyloid beta-protein accumulation

The anesthetic isoflurane has been reported to induce apoptosis and increase Abeta generation and aggregation. However, the molecular mechanism underlying these effects remains unknown. We therefore set out to assess whether the effects of isoflurane on apoptosis are linked to amyloid beta-protein (Abeta) generation and aggregation. For this purpose, we assessed the effects of isoflurane on beta-site amyloid beta precursor protein (APP)-cleaving enzyme (BACE) and gamma-secretase, the proteases responsible for Abeta generation. We also tested the effects of inhibitors of Abeta aggregation (iAbeta5, a beta-sheet breaker peptide; clioquinol, a copper-zinc chelator) on the ability of isoflurane to induce apoptosis. All of these studies were performed on naive human H4 neuroglioma cells as well as those overexpressing APP (H4-APP cells). Isoflurane increased the levels of BACE and gamma-secretase and secreted Abeta in the H4-APP cells. Isoflurane-induced Abeta generation could be blocked by the broad-based caspase inhibitor Z-VAD. The Abeta aggregation inhibitors, iAbeta5 and clioquinol, selectively attenuated caspase-3 activation induced by isoflurane. However, isoflurane was able to induce caspase-3 activation in the absence of any detectable alterations of Abeta generation in naive H4 cells. Finally, Abeta potentiated the isoflurane-induced caspase-3 activation in naive H4 cells. Collectively, these findings suggest that isoflurane can induce apoptosis, which, in turn, increases BACE and gamma-secretase levels and Abeta secretion. Isoflurane also promotes Abeta aggregation. Accumulation of aggregated Abeta in the media can then promote apoptosis. The result is a vicious cycle of isoflurane-induced apoptosis, Abeta generation and aggregation, and additional rounds of apoptosis, leading to cell death.