Dietary caffeine synergizes adverse peripheral and central responses to anesthesia in malignant hyperthermia susceptible mice

Ryanodine receptor (RYR1) mutations confer stress-triggered malignant hyperthermia susceptibility (MHS). Dietary caffeine (CAF) is the most commonly consumed psychoactive compound by humans. CAF-triggered Ca²⁺ release and influences on skeletal muscle contractility are widely used as experimental tools to study RYR1 function/dysfunction. We hypothesize that dietary CAF achieving blood levels measured in human plasma exacerbates the penetrance of RYR1 MHS mutations triggered by gaseous anesthetic, affecting both central and peripheral adverse responses. Heterozygous R163C-RYR1 MHS mice (HET) are used to investigate the influences of dietary CAF on both peripheral and central responses before and after induction of halothane anesthesia (HAL). CAF+HAL are studied on RYR1 single channel currents and myotubes expressing HET to define molecular mechanisms of gene-by-environment synergism. HET mice have 2.4-fold lower baseline cortical EEG total power (EEGTP) compared to wildtype mice (WT) in the absence CAF. HET receiving dietary CAF (median plasma CAF 893 ng/ml) have an exaggerated EEGTP increase compared to WT, negating genotype differences without altering blood chemistry. HAL anesthesia produces shorter delays to isoelectric EEG_TP, ECG and respiratory arrest in the HET+CAF group, whereas these measures are unaffected in WT regardless of CAF. Dantrolene mitigated adverse responses in HET. Strong pharmacological synergism between CAF and HAL is demonstrated in myotubes prepared from adult HET and RYR1 channel recordings. Central and peripheral nervous systems mediate adverse responses to HAL in a HET model of MHS exposed to dietary CAF, a modifiable lifestyle factor that may mitigate risks of acute and chronic diseases associated to RYR1 mutations. SIGNIFICANCE STATEMENT: Dietary caffeine attaining a human relevant plasma dose synergizes adverse peripheral and central responses to anesthesia in malignant hyperthermia susceptible mice. Synergism of these drugs can be attributed to their actions at ryanodine receptors.

Keywords: Caffeine; Neuromuscular pharmacology; Ryanodine receptors.