Increasing evidence suggests that commonly used inhaled anesthetics, especially isoflurane, cause neuronal apoptosis in the developing brain, which is associated with memory loss and learning disabilities. The long term goal of this research is to understand the mechanisms of anesthesia-mediated neurotoxicity, with an expectation that this knowledge will eventually lead to more efficacious and safer use of inhaled anesthetics. The immediate goal of the study is to test our central hypothesis that inhaled anesthetics induce cell death by apoptosis in a dose- and time-dependent manner by causing excessive calcium release from the endoplasmic reticulum (ER) via over activation of a calcium channel (IP3 receptor) on the ER membrane. An additional goal of this project is to study and better understand the double features of isoflurane's neurotoxic and neuroprotective effects in both cell culture and animal models. We will test these hypotheses via the following specific aims: (1).
Aim 1 will test whether prolonged exposure of isoflurane induces apoptosis by causing excessive calcium release from the ER and depletion of ER calcium via over activation of IP3 receptor. We will examine whether these effects lead to neuronal death by apoptosis, especially in neurons with elevated IP3 receptor activity such as cells with Alzheimer's presenilin-1 mutation or Huntington's Q111 mutation. (2).
Aim 2 will test whether prolonged exposure of Isoflurane induces neuronal apoptosis, subsequent memory and learning disabilities in developing rat brains by over activation of IP3 receptors. We will also test whether these effects can be inhibited by the IP3 receptor antagonist xestospongin C. (3).
Aim 3 will examine whether a short exposure of isoflurane in cell culture and animal models provides neuroprotection by preconditioning neurons with a moderate calcium release from the ER via activation of IP3 receptors.
Aim 3 will further examine whether these induced endogenous neuroprotective mechanisms occur by over expression of some ER stress proteins (e.g. GRP78, HSP70) or changes of apoptotic regulatory proteins (e.g. Bcl-2/Bax). Our preliminary studies have suggested that sevoflurane and desflurane, at equipotent concentrations, have much less potency than isoflurane to cause apoptosis, as well as abnormal calcium release from the ER. We will further compare the neurotoxic effects of isoflurane, sevoflurane and desflurane in both cell culture and animal models.
Our preliminary studies suggest that commonly used inhaled anesthetics, especially isoflurane, induce apoptotic neuronal death by causing excessive calcium release from the endoplasmic reticulum via over activation of a calcium channel (IP3 receptor) on the ER membrane. We therefore intend to study the mechanisms through which inhaled anesthetics induce neuronal apoptosis via disruption of intracellular calcium homeostasis. Ultimately we hope to develop a strategy to prevent these harmful effects. This research will increase our understanding of general anesthesia-mediated neurotoxicity and make a safer use of inhaled anesthetics to surgical patients.
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