Anesthetic effects in Alzheimer transgenic mouse models.

Research has improved the diagnosis of Alzheimer's disease, and at earlier stages, but effective therapy continues to be elusive. Current effort is focused on delay. Environmental factors are thought to interact with genetics to modulate the progression of the disease, and one such environmental factor is exposure to general anesthetics. The possibility that some anesthetic effects have long-term consequences is of general interest and concern. The difficulty of studying a chronic, age-related disease in humans combined with the fact that anesthetics are rarely given without surgery, has led to a focus on animal models. Transgenic mouse models have been developed to mimic the hallmarks of Alzheimer's disease, including amyloid beta accumulation (plaque), neurofibrillary tangles, and cognitive dysfunction. While none of the models recapitulate the human disease with high fidelity, they allow a first look at anesthetic-Alzheimer interactions in a reasonable time frame. In studies found to date, none have concluded that anesthetics alone cause a significant change in cognitive decline, but rather an acceleration in Alzheimer neuropathology. Further studies are required to define the best anesthetic paradigm for our elderly population to mitigate changes in neuropathology and potentially cognition.

Modulation of murine Alzheimer pathogenesis and behavior by surgery.

OBJECTIVE: Previous research suggests that a link between anesthetic exposure and Alzheimer disease exists. Because anesthetics are rarely given alone, we ask whether addition of surgery further modulates Alzheimer disease. BACKGROUND: Cognitive dysfunction occurs after surgery in humans. Anesthesia alone produces cognitive decline in both older wild-type (WT) mice and rats, and the addition of surgery produces transient decline in young, adult WT mice. Because neuroinflammation has been implicated and occurs early in Alzheimer disease, we hypothesized that the neuroinflammatory stress associated with surgery would accelerate the progression of Alzheimer disease. METHODS: Cecal ligation and excision were performed on presymptomatic 5- to 11-month-old triple-transgenic Alzheimer disease (3×TgAD) and C57BL/6 WT mice under desflurane anesthesia. Surgery animals were compared with aged-matched 3×TgAD and WT mice exposed to air or desflurane alone. Cognitive function was assessed via Morris water maze at 2 and 13 weeks postoperatively. Amyloid and tau pathology and inflammation and synaptic markers were quantified with immunohistochemistry, Luminex assay, enzyme-linked immunosorbent assay, or Western blot assays. RESULTS: A significant cognitive impairment in 3×TgAD mice that underwent surgery compared with air or desflurane controls persisted to at least 14 weeks after surgery. Microglial activation, amyloidopathy, and tauopathy were enhanced by surgery as compared with desflurane alone. No differences between surgery, anesthetic, or air controls were detected in WT mice CONCLUSIONS: Surgery causes a durable increment in Alzheimer pathogenesis, primarily through a transient activation of neuroinflammation.

Neurodevelopmental consequences of sub-clinical carbon monoxide exposure in newborn mice.

Carbon monoxide (CO) exposure at high concentrations results in overt neurotoxicity. Exposure to low CO concentrations occurs commonly yet is usually sub-clinical. Infants are uniquely vulnerable to a variety of toxins, however, the effects of postnatal sub-clinical CO exposure on the developing brain are unknown. Apoptosis occurs normally within the brain during development and is critical for synaptogenesis. Here we demonstrate that brief, postnatal sub-clinical CO exposure inhibits developmental neuroapoptosis resulting in impaired learning, memory, and social behavior. Three hour exposure to 5 ppm or 100 ppm CO impaired cytochrome c release, caspase-3 activation, and apoptosis in neocortex and hippocampus of 10 day old CD-1 mice. CO increased NeuN protein, neuronal numbers, and resulted in megalencephaly. CO-exposed mice demonstrated impaired memory and learning and reduced socialization following exposure. Thus, CO-mediated inhibition of neuroapoptosis might represent an important etiology of acquired neurocognitive impairment and behavioral disorders in children.

Human Alzheimer and inflammation biomarkers after anesthesia and surgery.

BACKGROUND: The prevalence of postoperative cognitive disturbance, coupled with growing in vitro, cell, and animal evidence suggesting anesthetic effects on neurodegeneration, calls for additional study of the interaction between surgical care and Alzheimer neuropathology. The authors studied human cerebrospinal fluid (CSF) biomarkers during surgery. METHODS: Eleven patients undergoing idiopathic nasal CSF leak correction were admitted to this Institutional Review Board-approved study. Lumbar subarachnoid catheters were placed before the procedure. Anesthesia was total intravenous propofol or remifentanil or inhalational sevoflurane, depending on provider choice. CSF samples were taken after catheter placement (base), at procedure end (0 h), and then at 6, 24, and 48 h. CSF was analyzed using xMAP Luminex immunoassay (Luminex, Austin, TX). RESULTS: Of the 11 patients (age range, 53 ± 6 yr), 8 were women; 4 received intravenous anesthesia, 6 sevoflurane, and 1 mixed. Procedures lasted 6.4 ± 2 h. Mean CSF amyloid-ß(1-42) remained unchanged, but total-tau and phosphorylated-tau181P increased progressively until at least 48 h. Total-tau, phosphorylated-tau, or amyloid-ß(1-42) concentrations were not different between anesthetic groups. CSF interleukin-10, S100Beta, and tumor necrosis factor α were increased similarly in both anesthetic groups at 24 h, but interleukin-6 was increased more in the inhalational group. CONCLUSION: These data indicate a robust neuroinflammatory response, including not only the usual markers (interleukin-6, tumor necrosis factor α, interleukin-10), but also S100Beta and tau, markers of injury. The total-tau/amyloid-ß(1-42) ratio increased in a pattern consistent with Alzheimer disease, largely because of an increase in total-tau rather than a decline in amyloid-ß(1-42). The differences in CSF interleukin-6 concentrations suggest that anesthetic management may make a difference in neuroinflammatory response.

Anesthesia in presymptomatic Alzheimer's disease: a study using the triple-transgenic mouse model.

BACKGROUND: Experimental evidence suggests that anesthetics accelerate symptomatic neurodegenerative disorders such as Alzheimer's disease (AD). Because AD pathology precedes symptoms, we asked ourselves whether anesthetic exposure in the presymptomatic interval accelerated neuropathology and appearance of symptoms. METHODS: Triple-transgenic AD mice were exposed to general aesthetics, either halothane or isoflurane, at 2, 4, and 6 months of age, they then underwent water maze cognitive testing 2 months later, and subsequently their brains were analyzed using enzyme-linked immunosorbent assay, immunoblots, and immunohistochemistry for amyloid and tau pathology and biomarkers. RESULTS: Learning and memory improved after halothane exposure in the 2-month-old group relative to controls, but no changes were noted in the isoflurane group. When gender was examined in all age groups, females exposed to halothane performed better as compared with those exposed to isoflurane or controls. Therefore, improvement in the 2-month exposure group is most likely because of a gender effect. Level of phospho-tau in the hippocampus was significantly increased 2 months after anesthesia, especially in the 6-month exposure group, but changes in amyloid, caspase, microglia, or synaptophysin levels were not detected. CONCLUSIONS: These results indicate that exposure to two different inhalation-type anesthetics during the presymptomatic phase of AD does not accelerate cognitive decline, after 2 months, and may cause a stress response, marked by hippocampal phosphorylated tau, resulting in preconditioning against the ongoing neuropathology, primarily in female mice.

Anesthetic modulation of neuroinflammation in Alzheimer's disease.

PURPOSE OF REVIEW: To summarize key studies and recent thought on the role of neuroinflammation in chronic neurodegeneration, and whether it can be modulated by anesthesia and surgery. RECENT FINDINGS: A large and growing body of evidence shows that neuroinflammation participates in the development of neurodegeneration associated with Alzheimer's disease. Modulation may be possible early in the pathogenesis, and less so when cognitive symptoms appear. A dysfunctional hypoinflammatory response may permit accelerated damage due to other mechanisms in late disease. The peripheral inflammatory response elicited by surgery itself appears to provoke a muted neuroinflammatory response, which enhances ongoing neurodegeneration in some models. Anesthetics have both anti-inflammatory and proinflammatory effects depending on the drug and concentration, but in general, appear to play a small role in neuroinflammation. Human studies at the intersection of chronic neurodegeneration, neuroinflammation, and surgery/anesthesia are rare. SUMMARY: The perioperative period has the potential to modulate the progression of chronic neurodegenerative diseases. The growing number of elderly having surgery, combined with the expanding life expectancy, indicates the potential for this interaction to have considerable public health implications, and call for further research, especially in humans.