In vitro accumulation of technetium-99m-sestamibi in human parathyroid mitochondria

Background. Technetium-99m-sestamibi (sestamibi) is the imaging agent of choice for preoperative parathyroid localization. The subcellular localization of sestamibi uptake in enlarged parathyroid glands in patients with hyperparathyroidism has not been determined. This study investigated the mechanism of retention of sestamibi by human parathyroid tissue. Methods. Twenty-three freshly harvested and 15 cryopreserved parathyroid glands excised from patients with primary or secondary hyperparathyroidism were analyzed for subcellular localization of Tc-99m-sestamibi. Tissues were incubated with 100 μ Ci of sestamibi and isolated for mitochondria by differential centrifugation, and the integrity of subcellular fractions was quantified with the mitochondrial enzyme marker, succinate dehydrogenase. Results. Ninety-two percent of sestamibi activity was associated with mitochondria. Furthermore, after adding the mitochondrial uncoupler, carbonylcyanide m-chlorophenylhydrazone (CCCP), to fresh parathyroid tissues, 84.96% and 73.86% of sestamibi was released from the mitochondrial and tissue fragment components, respectively. In addition, sestamibi activity in the mitochondrial component of cryopreserved human parathyroid tissue decreased to the same amount as the CCCP-treated group. Conclusions. These data confirm that mitochondrial activity is the major component of sestamibi uptake by human parathyroid tissue in patients with hyperparathyroidism.