Yun Yue

The Mitochondrial Pathway of Anesthetic Isoflurane-induced Apoptosis

The common inhalation anesthetic isoflurane has been shown to induce apoptosis, which then leads to accumulation of β-amyloid protein, the hallmark feature of Alzheimer disease neuropathogenesis. The underlying molecular mechanism of the isoflurane-induced apoptosis is largely unknown. We, therefore, set out to assess whether isoflurane can induce apoptosis by regulating Bcl-2 family proteins, enhancing reactive oxygen species (ROS) accumulation, and activating the mitochondrial pathway of apoptosis. We performed these studies in cultured cells, primary neurons, and mice. Here we show for the first time that treatment with 2% isoflurane for 6 h can increase pro-apoptotic factor Bax levels, decrease anti-apoptotic factor Bcl-2 levels, increase ROS accumulation, facilitate cytochrome c release from the mitochondria to the cytosol, induce activation of caspase-9 and caspase-3, and finally cause apoptosis as compared with the control condition. We have further found that isoflurane can increase the mRNA levels of Bax and reduce the mRNA levels of Bcl-2. The isoflurane-induced ROS accumulation can be attenuated by the intracellular calcium chelator BAPTA. Finally, the anesthetic desflurane does not induce activation of mitochondrial pathway of apoptosis. These results suggest that isoflurane may induce apoptosis through Bcl-2 family proteins- and ROS-associated mitochondrial pathway of apoptosis. These findings, which have identified at least partially the molecular mechanism by which isoflurane induces apoptosis, will promote more studies aimed at studying the potential neurotoxic effects of anesthetics.

The Inhalation Anesthetic Desflurane Induces Caspase Activation and Increases Amyloid β-Protein Levels under Hypoxic Conditions

Perioperative factors including hypoxia, hypocapnia, and certain anesthetics have been suggested to contribute to Alzheimer disease (AD) neuropathogenesis. Desflurane is one of the most commonly used inhalation anesthetics. However, the effects of desflurane on AD neuropathogenesis have not been previously determined. Here, we set out to assess the effects of desflurane and hypoxia on caspase activation, amyloid precursor protein (APP) processing, and amyloid β-protein (Aβ) generation in H4 human neuroglioma cells (H4 naïve cells) as well as those overexpressing APP (H4-APP cells). Neither 12% desflurane nor hypoxia (18% O2) alone affected caspase-3 activation, APP processing, and Aβ generation. However, treatment with a combination of 12% desflurane and hypoxia (18% O2) (desflurane/hypoxia) for 6 h induced caspase-3 activation, altered APP processing, and increased Aβ generation in H4-APP cells. Desflurane/hypoxia also increased levels of β-site APP-cleaving enzyme in H4-APP cells. In addition, desflurane/hypoxia-induced Aβ generation could be reduced by the broad caspase inhibitor benzyloxycarbonyl-VAD. Finally, the Aβ aggregation inhibitor clioquinol and γ-secretase inhibitor L-685,458 attenuated caspase-3 activation induced by desflurane/hypoxia. In summary, desflurane can induce Aβ production and caspase activation, but only in the presence of hypoxia. Pending in vivo confirmation, these data may have profound implications for anesthesia care in elderly patients, and especially those with AD.

The effects of isoflurane and desflurane on cognitive function in humans.

BACKGROUND: The etiology of postoperative cognitive decline (POCD) remains to be determined. Anesthetic isoflurane, but not desflurane, may induce neurotoxicity. However, the functional consequences of these effects have not been assessed. We therefore performed a pilot study to determine the effects of isoflurane and desflurane on cognitive function in humans. METHODS: The subjects included patients who had lower extremity or abdominal surgery under spinal anesthesia alone (S, n = 15), spinal plus desflurane anesthesia (SD, n = 15), or spinal plus isoflurane anesthesia (SI, n = 15) by randomization. Each of the subjects received cognitive tests immediately before and 1 week after anesthesia and surgery administered by an investigator who was blinded to the anesthesia regimen. POCD was defined using the scores from each of these tests. RESULTS: We studied 45 subjects, 24 males and 21 females. The mean age of the subjects was 69.0 ± 1.9 years. There was no significant difference in age and other characteristics among the treatment arms. The mean number of cognitive function declines in the S, SD, and SI groups was 1.13, 1.07, and 1.40, respectively. POCD incidence after SI (27%), but not SD (0%), anesthesia was higher than that after S (0%), P = 0.028 (3-way comparison). CONCLUSION: These findings from our pilot study suggest that isoflurane and desflurane may have different effects on postoperative cognitive function, and additional studies with a larger sample size and longer times of follow-up testing are needed.

The incidence of intra-operative awareness during general anesthesia in China: a multi-center observational study.

Background: The incidence of awareness in patients undergoing general anesthesia is 0.1–0.2% in Western countries. The medical literatures about awareness during general anesthesia are still rare in China, but some previous studies have reported a higher incidence (1.4–6%) of intra‐operative awareness. To find out the reason why the incidence reported in China is much higher than that in Western countries, we performed a prospective, multicenter, non‐randomized observational study to determine the true incidence of intra‐operative awareness in China.

Anesthetic propofol attenuates the isoflurane-induced caspase-3 activation and Aβ oligomerization.

Accumulation and deposition of β-amyloid protein (Aβ) are the hallmark features of Alzheimers disease. The inhalation anesthetic isoflurane has been shown to induce caspase activation and increase Aβ accumulation. In addition, recent studies suggest that isoflurane may directly promote the formation of cytotoxic soluble Aβ oligomers, which are thought to be the key pathological species in AD. In contrast, propofol, the most commonly used intravenous anesthetic, has been reported to have neuroprotective effects. We therefore set out to compare the effects of isoflurane and propofol alone and in combination on caspase-3 activation and Aβ oligomerization in vitro and in vivo. Naïve and stably-transfected H4 human neuroglioma cells that express human amyloid precursor protein, the precursor for Aβ; neonatal mice; and conditioned cell culture media containing secreted human Aβ40 or Aβ42 were treated with isoflurane and/or propofol. Here we show for the first time that propofol can attenuate isoflurane-induced caspase-3 activation in cultured cells and in the brain tissues of neonatal mice. Furthermore, propofol-mediated caspase inhibition occurred when there were elevated levels of Aβ. Finally, isoflurane alone induces Aβ42, but not Aβ40, oligomerization, and propofol can inhibit the isoflurane-mediated oligomerization of Aβ42. These data suggest that propofol may mitigate the caspase-3 activation by attenuating the isoflurane-induced Aβ42 oligomerization. Our findings provide novel insights into the possible mechanisms of isoflurane-induced neurotoxicity that may aid in the development of strategies to minimize potential adverse effects associated with the administration of anesthetics to patients.

Effects of anesthetic isoflurane and desflurane on human cerebrospinal fluid Aβ and τ level.

Background:Accumulation of &bgr;-amyloid protein (A&bgr;) and tau protein is the main feature of Alzheimer disease neuropathogenesis. Anesthetic isoflurane, but not desflurane, may increase A&bgr; levels in vitro and in animals. Therefore, we set out to determine the effects of isoflurane and desflurane on cerebrospinal fluid (CSF) levels of A&bgr; and tau in humans. Methods:The participants were assigned into spinal anesthesia (N = 35), spinal plus desflurane anesthesia (N = 33), or spinal plus isoflurane anesthesia (N = 38) group by randomization using computer-generated lists. Pre- and postoperative human CSF samples were obtained through an inserted spinal catheter. The levels of A&bgr; (A&bgr;40 and A&bgr;42) and total tau in the CSF were determined. Results:Here, we show that isoflurane, but not desflurane, was associated with an increase in human CSF A&bgr;40 levels (from 10.90 to 12.41 ng/ml) 24 h after the surgery under anesthesia compared to spinal anesthesia (from 11.59 to 11.08 ng/ml), P = 0.022. Desflurane, but not isoflurane, was associated with a decrease in A&bgr;42 levels 2 h after the surgery under anesthesia (from 0.39 to 0.35 ng/ml) compared to spinal anesthesia (from 0.43 to 0.44 ng/ml), P = 0.006. Isoflurane and desflurane did not significantly affect the tau levels in human CSF. Conclusions:These studies have established a system to study the effects of anesthetics on human biomarkers associated with Alzheimer disease and cognitive dysfunction. These findings have suggested that isoflurane and desflurane may have different effects on human CSF A&bgr; levels.

Regulation of AMPA receptors in spinal nociception

The functional properties of α-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) receptors in different brain regions, such as hippocampus and cerebellum, have been well studied in vitro and in vivo. The AMPA receptors present a unique characteristic in the mechanisms of subunit regulation during LTP (long-term potentiation) and LTD (long-term depression), which are involved in the trafficking, altered composition and phosphorylation of AMPA receptor subunits. Accumulated data have demonstrated that spinal AMPA receptors play a critical role in the mechanism of both acute and persistent pain. However, less is known about the biochemical regulation of AMPA receptor subunits in the spinal cord in response to painful stimuli. Recent studies have shown that some important regulatory processes, such as the trafficking of AMPA receptor subunit, subunit compositional changes, phosphorylation of AMPA receptor subunits, and their interaction with partner proteins may contribute to spinal nociceptive transmission. Of all these regulation processes, the phosphorylation of AMPA receptor subunits is the most important since it may trigger or affect other cellular processes. Therefore, these study results may suggest an effective strategy in developing novel analgesics targeting AMPA receptor subunit regulation that may be useful in treating persistent and chronic pain without unacceptable side effects in the clinics.

Sevoflurane inhibits neurogenesis and the Wnt-catenin signaling pathway in mouse neural progenitor cells.

Recent population studies suggest that children who receive anesthesia and surgery could be at an increased risk for developing learning disabilities. The underlying reason for this clinical observation is largely unknown. Whether undergoing anesthesia contributes to learning disability development, or if the need for anesthesia and surgery is a marker for other unidentified factors that contribute to the development of learning disabilities, remains to be determined. Neurogenesis, regulated by the Wnt-catenin signaling pathway, has been shown to be involved in learning and memory, and sevoflurane is the most commonly used inhalation anesthetic in children. We therefore set out to determine the effects of sevoflurane on neurogenesis and the Wnt-catenin signaling pathway in mouse neural progenitor cells (NPCs) using immunofluorescence and Western blot analysis. Here we show for the first time that 4.1%, but not 2.0%, sevoflurane reduced mouse NPC proliferation, increased Glycogen synthase kinase-3β(GSK-3β) levels, and decreased levels of β-Catenin in mouse NPCs. The GSK-3β inhibitor Lithium attenuated the sevoflurane-induced reduction in mouse NPC proliferation. The data suggest that sevoflurane may reduce neurogenesis through the Wnt-catenin signaling pathway. These findings would promote further studies to investigate the effects of anesthesia on neurogenesis and function of learning and memory, as well as the underlying mechanisms in vitro and in vivo. Ultimately these efforts would lead to safer anesthesia care and better postoperative outcomes in children.

Prognosis of Diabetic Patients Undergoing Coronary Artery Bypass Surgery Compared With Nondiabetics: A Systematic Review and Meta–analysis

OBJECTIVE The influence of diabetes mellitus (DM) on mortality and morbidity in patients undergoing coronary artery bypass graft (CABG) surgery has remained uncertain due to conflicting conclusions from clinical trials measuring the association between diabetes and perioperative risk. Therefore, a quantitative meta-analysis was undertaken to evaluate the available evidence from prospective and historic cohort clinical trials. The purpose of this study was to determine the significance and magnitude of impact of DM on mortality, morbidity and resource-related outcomes for patients undergoing CABG over the past few decades and in the contemporary setting. METHODS MEDILINE, EMBase, BIOSIS Preview, CBMDisc, CNKI and WanFang databases were searched, supplemented by hand search, without language limitations, for studies published from January 1981 to October 2008. Data extraction included study design, setting, inclusion/exclusion criteria, population characteristics, statistical method, length of follow-up and clinical outcomes. Eligible studies were assessed for quality. RESULTS Of the 132 identified studies, 24 cohort studies with a median follow-up of 4.3 years were selected for analysis. A total of 100,217 patients (28,168 with DM and 72,049 without DM), were included in the meta-analysis. The pooled RR (95% CI) for mortality of diabetic versus non-diabetic patients was significantly increased at 30 days (RR 1.64, 95% CI 1.39, 1.93), 1 year (RR 1.83, 95% CI 1.56, 2.15), 3 years (RR 1.81, 95% CI 1.58, 2.09), 5 years (RR 1.66, 95% CI 1.53, 1.79) and 10 years (RR 1.55, 95% CI 1.43, 1.68) after CABG. Significant differences were also found for DM versus non-DM patients post-CABG for perioperative cerebrovascular accidents (RR 1.52; 95% CI 1.31, 1.77), postoperative acute renal failure (RR 1.63; 95% CI 1.48, 1.79), sternal infection (RR; 1.70, 95% CI 1.41-2.04) and blood transfusion (RR 1.15; 95% CI 1.08, 1.21). No significant differences were found for postoperative atrial fibrillation (AF), postoperative myocardial infarction (MI) and re-exploration for bleeding. Insufficient and/or heterogeneous data did not allow for pooled analysis of ventilator time, ICU stay, angina recurrence, repeat revascularization, hospital stay and hospital costs. CONCLUSIONS Current evidence suggests that patients with DM who are undergoing CABG are at increased risk of mortality, stroke, renal failure, sternal infection and blood transfusion when compared to those without DM. This increased relative risk for perioperative mortality and complications has remained, despite evolving definitions of DM and practice patterns. Future randomized studies should focus on interventions targeted toward these complications to mitigate the risk for patients with DM.

The Potential Dual Effects of Anesthetic Isoflurane on Aβ-Induced Apoptosis

β-amyloid protein (Aβ)-induced neurotoxicity is the main component of Alzheimers disease (AD) neuropathogenesis. Inhalation anesthetics have long been considered to protect against neurotoxicity. However, recent research studies have suggested that the inhalation anesthetic isoflurane may promote neurotoxicity by inducing apoptosis and increasing Aβ levels. We therefore set out to determine whether isoflurane can induce dose- and time-dependent dual effects on Aβ-induced apoptosis: protection versus promotion. H4 human neuroglioma cells, primary neurons from naive mice, and naive mice were treated with Aβ and/or isoflurane, and levels of caspase-3 cleavage (activation), apoptosis, Bcl-2, Bax, and cytosolic calcium were determined. Here we show for the first time that the treatment with 2% isoflurane for six hours or 30 minutes potentiated, whereas the treatment with 0.5% isoflurane for six hours or 30 minutes attenuated, the Aβ-induced caspase-3 activation and apoptosis in vitro. Moreover, anesthesia with 1.4% isoflurane for two hours potentiated, whereas the anesthesia with 0.7% isoflurane for 30 minutes attenuated, the Aβ-induced caspase-3 activation in vivo. The high concentration isoflurane potentiated the Aβ-induced reduction in Bcl-2/Bax ratio and caused a robust elevation of cytosolic calcium levels. The low concentration isoflurane attenuated the Aβ-induced reduction in Bcl-2/Bax ratio and caused only a mild elevation of cytosolic calcium levels. These results suggest that isoflurane may have dual effects (protection or promotion) on Aβ-induced toxicity, which potentially act through the Bcl-2 family proteins and cytosolic calcium. These findings would lead to more systematic studies to determine the potential dual effects of anesthetics on AD-associated neurotoxicity.