Is lymphocyte adenosine a diagnostic marker of clinical malignant hyperthermia? A pilot study

Objective: Malignant hyperthermia is a pharmacogenetic disorder typically triggered by potent inhalation anesthetics and/or the depolarizing muscle relaxant succinylcholine in malignant hyperthermia-susceptible individuals. Since lymphocytes express the same Ca²⁺ channel mutation found in malignant hyperthermia-susceptible muscle, we investigated agonist-induced adenosine formation in lymphocytes as an index of sarcoplasmic reticulum Ca²⁺-release-induced adenosine 5′-triphosphate turnover as a potential minimally invasive functional malignant hyperthermia assay. Design: Application of lymphocytes for malignant hyperthermia diagnosis. Setting: Hospitals and university laboratory. Subjects: Malignant hyperthermia-susceptible patients (n = 13) and normal subjects (n = 11). Interventions: Adenosine formation due to malignant hyperthermia-triggering agent halothane or the ryanodine receptor Ca²⁺channels agonist 4-chloro-m-cresol was compared in blood lymphocytes from malignant hyperthermia-susceptible patients and normal subjects. Measurements and Main Results: Ca²⁺_i and adenosine were measured in fresh or immortalized blood lymphocytes incubated with 0-10 mM 4-chloro-m-cresol or 0-10.7 mM halothane. Ca²⁺_i levels were significantly higher in immortalized malignant hyperthermia-susceptible B cells treated with 0.75 mM 4-chloro-m-cresol relative to controls. Similarly, at 1 mM 4-chloro-m-cresol or 0.96 mM halothane, adenosine levels were significantly higher in malignant hyperthermia-susceptible lymphocytes or immortalized B cells relative to controls. Receiver-operating characteristic analyses showed areas under the 4-chloro-m-cresol receiver-operating characteristic curves near more than or equal to 0.96 (p ≈ 0.0001), suggesting that 4-chloro-m-cresol-induced adenosine could readily distinguish between malignant hyperthermia-susceptible and normal controls cells. Conclusions: Both 4-chloro-m-cresol and halothane caused adenosine accumulation in blood lymphocytes. Adenosine accumulation was markedly increased in malignant hyperthermia-susceptible lymphocytes compared with controls reflecting higher than normal adenosine 5′-triphosphate degradation in the malignant hyperthermia-susceptible cells. Although 4-chloro-m-cresol receiver-operating characteristic curves revealed that adenosine accumulation could readily distinguish between normal and malignant hyperthermia-susceptible lymphocytes, independent confirmation is required with a substantially larger number of enrolled subjects to correctly appreciate the clinical utility of the novel lymphocyte-adenosine protocol for malignant hyperthermia testing.