Volatile Anesthetics and the Microtubule Cytoskeleton

For more than half a century, researchers have studied how volatile anesthetics affect ion channels and receptors. However, their precise molecular mechanisms remain unclear. Evidence suggests that volatile anesthetics may also target cytoplasmic proteins like tubulin, which forms microtubules, a critical part of the cytoskeleton that is essential for neuronal structure, intracellular transport, and receptor function. Experimental findings demonstrate volatile anesthetics at high concentrations can bind to tubulin and interfere with its polymerization into microtubules.¹ Additionally, microtubule destabilization and neuronal protein interference (for proteins such as tau) are linked to neurodegenerative diseases such as Alzheimer’s and Parkinson’s. To better understand how anesthesia causes these deleterious interactions, computational methods such as molecular dynamics and binding site prediction are being used to complement experimental approaches, which do not account for protein dynamics and neglect local protein atom rearrangement and the resulting change in binding site availability.

In a 2012 computational study, molecular dynamics simulations and homology modeling were used to generate minimized structures of human tubulin isotypes, including both the protein body and C-terminal tails. In parallel, microtubule polymerization assays with purified bovine brain tubulin were performed to test the effects of halothane (alone and with paclitaxel) on microtubule assembly.²

In this study, the researchers show how halothane, a volatile anesthetic, interacts with tubulin, the building block of microtubules. The researchers predicted multiple binding sites for halothane on both the tubulin body and the flexible C-terminal tails, with binding primarily driven by van der Waals forces from halothane’s chlorine and bromine atoms. Importantly, some predicted binding sites overlapped with known drug-binding regions for microtubule-modifying agents like colchicine and vinblastine, suggesting that halothane could interfere with microtubule-targeting drugs.

Functionally, these interactions point to a role of halothane in altering microtubule stability and dynamics,since binding at these critical regions may reduce tubulin’s ability to polymerize into microtubules. The authors note that halothane reduces colchicine binding to tubulin and may subtly disrupt microtubule assembly. These findings suggest that volatile anesthetics like halothane may contribute to side effects such as postoperative cognitive dysfunction by directly perturbing the microtubule cytoskeleton in neurons.²

A 2013 pre-clinical study exposed neonatal rats (n=37) to either sevoflurane, also a volatile anesthetic, or air and then subjected their hippocampi to histological, Western blot, and real-time polymerase chain reaction analyses. Rats exposed to 3% sevoflurane for 6 hours showed disrupted microtubule organization, with structures appearing disordered and nonparallel compared to the neat arrangement in their control counterparts. Sevoflurane exposure also increased tau mRNA levels at 1 and 7 days, although this effect stabilized and returned to “normal” levels by day 14.³

In addition, tau protein showed excessive phosphorylation at Ser396 and Ser404 after sevoflurane anesthesia, with elevations persisting for up to 14 days at Ser404. These changes in tau phosphorylation are closely tied to microtubule instability, as hyperphosphorylated tau detaches from microtubules, leading to cytoskeletal disarray. Overall, the findings suggest that sevoflurane disrupts microtubule structure by altering tau regulation, potentially contributing to anesthesia-related neurotoxicity in the developing brain.³ In support of these findings, a separate murine study found rats exposed to sevoflurane anesthesia (1 MAC) had significantly less tubulin protein, suggesting sevoflurane negatively affects the cytoskeleton by down-regulating tubulin and preventing its polymerization into microtubules.⁴

Taken together, these studies suggest that volatile anesthetics not only act on ion channels and receptors but also affect the neuronal cytoskeleton. By binding to tubulin and disrupting microtubule polymerization, halothane may alter neuronal stability and interfere with the function of other microtubule-targeting drugs. Similarly, sevoflurane has been shown to cause microtubule disarray and promote tau hyperphosphorylation, both of which compromise microtubule integrity. These mechanisms provide a plausible link between anesthetic exposure and postoperative cognitive dysfunction or neurotoxicity. Further research is needed to clarify the long-term neurological risks of volatile anesthetics and identify strategies that minimize their cytoskeletal effects.

References

1. Hinkley R.E., Samson F.E., Anesthetic-Induced Transformation of Axonal Microtubules. Journal of Cell Biology. 1972;53(1), 258-263. https://doi.org/10.1083/jcb.53.1.258
2. Travis, Marc St. George, Freedman H., et al. Computational Predictions of Volatile Anesthetic Interactions with the Microtubule Cytoskeleton: Implications for Side Effects of General Anesthesia. PLOS ONE. 2012;7(6) 37251-37251. https://doi.org/10.1371/journal.pone.0037251
3. Hu Z., Jin H., Xu L., Zhu Z., Jiang Y., Seal R., Effects of Sevoflurane on the Expression of Tau Protein mRNA and Ser396/404 Site in the Hippocampus of Developing Rat Brain. Pediatric Anesthesia. 2013;23(12):1138-1144. https://doi.org/10.1111/pan.12263
4. Armin Kalenka, Jochen Hinkelbein, Feldmann R.E., Wolfgang Kuschinsky, Waschke K.F., Maurer M.H., The Effects of Sevoflurane Anesthesia on Rat Brain Proteins: A Proteomic Time-Course Analysis. Anesthesia & Analgesia. 2007;104(5):1129-1135. https://doi.org/10.1213/01.ane.0000260799.37107.e6