One of the common questions we get at the Lighthouse from Huntington's patients facing surgery or complex dental procedures is about anesthesia. Are some anesthesias contra-indicated for HD patients?
A new study using a striatal cell model of HD concludes that the anesthesia isoflurane (brand name Forane) is not appropriate for Huntington's patients since it induces apoptosis (cell death) in those neurons made vulnerable by the disease. Isoflurane is a general anesthesia which is inhaled, much like the older anesthesia ether.
Isoflurane induces cell apoptosis by an unknown mechanism. The authors hypothesized that isoflurane activates inositol 1,4,5-trisphosphate (IP3) receptors on the endoplasmic reticulum (ER) membrane, causing excessive calcium release, triggering apoptosis.
The authors determined isoflurane-induced cytotoxicity by measuring caspase-3 activity, lactate dehydrogenase release, MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) reduction, and imaging analysis of cell damage markers (annexin V and propidium iodide staining) in different cell types. The authors used the chicken B lymphocyte with a total knock-out of IP3 receptors, PC12 cells with elevated IP3 receptor activity (transfected with L286V presenilin 1), striatal cells with a knock-in of Q111 Huntingtin, and each cell line's corresponding wild-type controls. The authors also measured the isoflurane-evoked changes of calcium concentration in cytosol and/or mitochondria in these cells.
Isoflurane induced apoptosis concentration- and time-dependently, and sequentially elevated cytosolic and then mitochondrial calcium in the chicken B-lymphocyte wild-type but not the IP3 receptor total knock-out cells. Thapsigargin, a calcium adenosine triphosphatase inhibitor on ER membranes, induced apoptosis and elevations of calcium in cytosol and mitochondria in both chicken B-lymphocyte wild-type and IP3 receptor total knock-out cells. Isoflurane induced significantly more neurotoxicity and greater calcium release from the ER in L286V PC12 and Q111 Huntingtin striatal cells than in their corresponding wild-type controls, both of which were significantly inhibited by the IP3 receptor antagonist xestospongin C.
These findings suggest that isoflurane activates the ER membrane IP3 receptor, producing excessive calcium release and triggering apoptosis. Neurons with enhanced IP3 receptor activity, as in certain cases of familial Alzheimer or Huntington disease, may be especially vulnerable to isoflurane cytotoxicity.