Person:

Zhang, Yiying

Background: The inhalation anesthetic isoflurane has been shown to open the mitochondrial permeability transition pore (mPTP) and induce caspase activation and apoptosis, which may lead to learning and memory impairment. Cyclosporine A, a blocker of mPTP opening might attenuate the isoflurane-induced mPTP opening, lessening its ripple effects. Magnesium and anesthetic propofol are also mPTP blockers. We therefore set out to determine whether propofol and magnesium can attenuate the isoflurane-induced caspase activation and mPTP opening. Methods: We investigated the effects of magnesium sulfate (Mg2+), propofol, and isoflurane on the opening of mPTP and caspase activation in H4 human neuroglioma cells stably transfected to express full-length human amyloid precursor protein (APP) (H4 APP cells) and in six day-old wild-type mice, employing Western blot analysis and flowcytometry. Results: Here we show that Mg2+ and propofol attenuated the isoflurane-induced caspase-3 activation in H4-APP cells and mouse brain tissue. Moreover, Mg2+ and propofol, the blockers of mPTP opening, mitigated the isoflurane-induced mPTP opening in the H4-APP cells. Conclusion: These data illustrate that Mg2+ and propofol may ameliorate the isoflurane-induced neurotoxicity by inhibiting its mitochondrial dysfunction. Pending further studies, these findings may suggest the use of Mg2+ and propofol in preventing and treating anesthesia neurotoxicity.

Anesthetic isoflurane has been shown to promote Alzheimer’s disease (AD) neuropathogenesis by inducing caspase activation and accumulation of β-amyloid (Aβ). Phosphorylation of tau protein is another important feature of AD neuropathogenesis. However, the effects of isoflurane on phosphorylated tau levels remain largely to be determined. We therefore set out to determine whether isoflurane can increase phosphorylated tau levels. 5 to 8 month-old wild-type and AD transgenic mice [B6.Cg-Tg (APPswe, PSEN1dE9)85Dbo/J] were treated with 1.4% isoflurane for two hours. The mice brain tissues were harvested at six, 12 and 24 hours after the anesthesia. For the in vitro studies, primary neurons from wild-type and the AD transgenic mice were exposed to 2% isoflurane for six hours, and were harvested at the end of anesthesia. The harvested brain tissues and neurons were subjected to Western blot analysis by which the levels of phosphorylated tau protein at Serine 262 (Tau-PS262) were determined. Here we show that the isoflurane anesthesia increased Tau-PS262 levels in brain tissues and primary neurons from the wild-type and AD transgenic mice. Moreover, the isoflurane anesthesia may induce a greater increase in Tau-PS262 levels in primary neurons and brain tissues from the AD transgenic mice. Finally, caspase activation inhibitor Z-VAD and Aβ generation inhibitor L-685,458 attenuated the isoflurane-induced increases in Tau-PS262 levels. In conclusion, clinically relevant isoflurane anesthesia increases phosphorylated tau levels, which may result from the isoflurane-induced caspase activation and Aβ generation. These findings will promote more studies to determine the effects of anesthetics on tau phosphorylation.

Objective: The neuropathogenesis of postoperative delirium remains unknown. Low cerebrospinal fluid (CSF) β-amyloid protein (Aβ) and high CSF Tau levels are associated with Alzheimer's disease. We, therefore, assessed whether lower preoperative CSF Aβ/Tau ratio was associated with higher incidence and greater severity of postoperative delirium. Methods: One hundred and fifty-three participants (71 ± 5 years, 53% men) who had total hip/knee replacement under spinal anesthesia were enrolled. CSF was obtained during initiation of spinal anesthesia. The incidence and severity of postoperative delirium were determined by Confusion Assessment Method (CAM) and Memorial Delirium Assessment Scale (MDAS) on postoperative day 1 and 2. Aβ40, Aβ42, and Tau levels in the CSF were measured by enzyme-linked immunosorbent assay. The relationships among these variables were determined, adjusting for age and gender. Results: Participants in the lowest quartile of preoperative CSF Aβ40/Tau and Aβ42/Tau ratio had higher incidence (32% vs. 17%, P = 0.0482) and greater symptom severity of postoperative delirium (Aβ40/Tau ratio: 4 vs. 3, P = 0.034; Aβ42/Tau ratio: 4 vs. 3, P = 0.062, the median of the highest MDAS score) as compared to the combination of the rest of the quartiles. The preoperative CSF Aβ40/Tau or Aβ42/Tau ratio was inversely associated with MDAS score (Aβ40/Tau ratio: −0.12 ± 0.05, P = 0.014, adj. −0.12 ± 0.05, P = 0.018; Aβ42/Tau ratio: −0.65 ± 0.26, P = 0.013, adj. −0.62 ± 0.27, P = 0.022). Interpretation Lower CSF Aβ/Tau ratio could be associated with postoperative delirium, pending confirmation of our preliminary results in further studies. These findings suggest potential roles of Aβ and/or Tau in postoperative delirium neuropathogenesis.

Postoperative delirium is associated with increased morbidity, mortality and cost. However, its neuropathogenesis remains largely unknown, partially owing to lack of animal model(s). We therefore set out to employ a battery of behavior tests, including natural and learned behavior, in mice to determine the effects of laparotomy under isoflurane anesthesia (Anesthesia/Surgery) on these behaviors. The mice were tested at 24 hours before and at 6, 9 and 24 hours after the Anesthesia/Surgery. Composite Z scores were calculated. Cyclosporine A, an inhibitor of mitochondria permeability transient pore, was used to determine potential mitochondria-associated mechanisms of these behavioral changes. Anesthesia/Surgery selectively impaired behaviors, including latency to eat food in buried food test, freezing time and time spent in the center in open field test, and entries and duration in the novel arm of Y maze test, with acute onset and various timecourse. The composite Z scores quantitatively demonstrated the Anesthesia/Surgery-induced behavior impairment in mice. Cyclosporine A selectively ameliorated the Anesthesia/Surgery-induced reduction in ATP levels, the increases in latency to eat food, and the decreases in entries in the novel arm. These findings suggest that we could use a battery of behavior tests to establish a mouse model to study postoperative delirium.

Post-operative cognitive dysfunction (POCD) is associated with increased cost of care, morbidity, and mortality. However, its pathogenesis remains largely to be determined. Specifically, it is unknown why elderly patients are more likely to develop POCD and whether POCD is dependent on general anesthesia. We therefore set out to investigate the effects of peripheral surgery on the cognition and Alzheimer-related neuropathology in mice with different ages. Abdominal surgery under local anesthesia was established in the mice. The surgery induced post-operative elevation in brain β-amyloid (Aβ) levels and cognitive impairment in the 18 month-old wild-type and 9 month-old Alzheimer's disease transgenic mice, but not the 9 month-old wild-type mice. The Aβ accumulation likely resulted from elevation of beta-site amyloid precursor protein cleaving enzyme and phosphorylated eukaryotic translation initiation factor 2α. γ-Secretase inhibitor compound E ameliorated the surgery-induced brain Aβ accumulation and cognitive impairment in the 18 month-old mice. These data suggested that the peripheral surgery was able to induce cognitive impairment independent of general anesthesia, and that the combination of peripheral surgery with aging- or Alzheimer gene mutation-associated Aβ accumulation was needed for the POCD to occur. These findings would likely promote more research to investigate the pathogenesis of POCD.

Commonly used anesthetic isoflurane has been reported to promote Alzheimer’s disease (AD) neuropathogenesis by inducing caspase-3 activation. However, the up-stream mechanisms of isoflurane’s effects remain largely to be determined. Specifically, there is a lack of a good model/system to elucidate the underlying mechanism of the isoflurane-induced caspase-3 activation. We therefore set out to assess and compare the effects of isoflurane on caspase-3 activation in neural progenitor cells (NPCs) and in primary neurons from wild-type (WT) and AD transgenic (Tg) mice. The NPCs and neurons were obtained, cultured and then treated with either 2% isoflurane or under control condition for 6 h. The NPCs or neurons were harvested at the end of the treatment and were subjected to Western blot analysis. Here we showed for the first time that the isoflurane treatment induced caspase-3 activation in neurons, but not in NPCs, from either WT or AD Tg mice. Consistently, the isoflurane treatment increased cytosol levels of cytochrome c, a potential up-stream mechanism of isoflurane-induced caspase-3 activation in the mice neurons, but not NPCs. Finally, the isoflurane treatment induced a greater casapse-3 activation in the neurons, but not the NPCs, from AD Tg mice as compared to the WT mice. These data demonstrated that investigation and comparison of isoflurane’s effects between mice NPCs and neurons would serve as a model/system to determine the underlying mechanism by which isoflurane induces caspase-3 activation. These findings would promote more research to investigate the effects of anesthetics on AD neuropathogenesis and the underlying mechanisms.

Post-operative cognitive dysfunction is associated with morbidity and mortality. However, its neuropathogenesis remains largely to be determined. Neuroinflammation and accumulation of β-amyloid (Aβ) have been reported to contribute to cognitive dysfunction in humans and cognitive impairment in animals. Our recent studies have established a pre-clinical model in mice, and have found that the peripheral surgical wounding without the influence of general anesthesia induces an age-dependent Aβ accumulation and cognitive impairment in mice. We therefore set out to assess the effects of peripheral surgical wounding, in the absence of general anesthesia, on neuroinflammation in mice with different ages. Abdominal surgery under local anesthesia was established in 9 and 18 month-old mice. The levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), Iba1 positive cells (the marker of microglia activation), CD33, and cognitive function in mice were determined. The peripheral surgical wounding increased the levels of TNF-α, IL-6, and Iba1 positive cells in the hippocampus of both 9 and 18 month-old mice, and age potentiated these effects. The peripheral surgical wounding increased the levels of CD33 in the hippocampus of 18, but not 9, month-old mice. Finally, anti-inflammatory drug ibuprofen ameliorated the peripheral surgical wounding-induced cognitive impairment in 18 month-old mice. These data suggested that the peripheral surgical wounding could induce an age-dependent neuroinflammation and elevation of CD33 levels in the hippocampus of mice, which could lead to cognitive impairment in aged mice. Pending further studies, anti-inflammatory therapies may reduce the risk of postoperative cognitive dysfunction in elderly patients.

The inhalation anesthetic isoflurane has been reported to induce caspase activation and apoptosis, which may lead to learning and memory impairment. However, the underlying mechanisms of these effects are largely unknown. Isoflurane has been shown to induce elevation of cytosol calcium levels, accumulation of reactive oxygen species (ROS), opening of the mitochondrial permeability transition pore, reduction in mitochondria membrane potential, and release of cytochrome c. The time course of these effects, however, remains to be determined. Therefore, we performed a pilot study to determine the effects of treatment with isoflurane for various times on ROS levels in HEK-293 cells. The cells were treated with 2% isoflurane plus 21% O2 and 5% CO2 for 15, 30, 60, or 90 min. We then used fluorescence imaging and microplate fluorometer to detect ROS levels. We show that 2% isoflurane for 60 or 90 min, but not 15 or 30 min, induced ROS accumulation in the cells. These data illustrated that isoflurane could cause time-dependent effects on ROS levels. These findings have established a system to further determine the time course effects of isoflurane on cellular and mitochondria function. Ultimately, the studies would elucidate, at least partially, the underlying mechanisms of isoflurane-induced cellular toxicity.

Alzheimer’s disease (AD) is the most common form of dementia. At the present time, however, AD still lacks effective treatments. Our recent studies showed that chronic treatment with anesthetic propofol attenuated brain caspase-3 activation and improved cognitive function in aged mice. Accumulation of β-amyloid protein (Aβ) is a major component of the neuropathogenesis of AD dementia and cognitive impairment. We therefore set out to determine the effects of chronic treatment with propofol on Aβ levels in brain tissues of aged mice. Propofol (50 mg/kg) was administrated to aged (18 month-old) wild-type mice once a week for 8 weeks. The brain tissues of mice were harvested one day after the final propofol treatment. The harvested brain tissues were then subjected to enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Here we report that the propofol treatment reduced Aβ (Aβ40 and Aβ42) levels in the brain tissues of the aged mice. Moreover, the propofol treatment decreased the levels of β-site amyloid precursor protein cleaving enzyme (the enzyme for Aβ generation), and increased the levels of neprilysin (the enzyme for Aβ degradation) in the brain tissues of the aged mice. These results suggested that the chronic treatment with propofol might reduce brain Aβ levels potentially via decreasing brain levels of β-site amyloid precursor protein cleaving enzyme, thus decreasing Aβ generation; and via increasing brain neprilysin levels, thus increasing Aβ degradation. These preliminary findings from our pilot studies have established a system and postulated a new hypothesis for future research.