Introduction: 99mTc-d,I-hexamethylpropylene amine oxime (99m Tc-HMPAO) retention in brain is proportional to cerebral blood flow and related to both the local hemodynamic state and to the cellular content of reduced glutathione. Alterations of the regional distribution of 99mTc-HMPAO retention, with discrepant results, have been reported at functional brain imaging of unipolar depression. Since mitochondrial involvement has been reported in depressed patients, the aim of the study was to explore whether the 99mTc-HMPAO retention at single-photon emission computed tomography in depressed patients may relate to different levels of mitochondrial function.

Methods: All patients had audiological and muscular symptoms, somatic symptoms that are common in depression. Citrate synthase (CS) activity assessed in muscle mitochondria correlated strongly with the activities of three mitochondrial respiratory chain enzymes and was used as a marker of mitochondrial function. K-means clustering performed on CS grouped eight patients with low and 11 patients with normal CS. Voxel-based analysis was performed on the two groups by statistical parametric mapping.

Results: Voxel-based analysis showed significantly higher 99mTc-HMPAO retention in the patients with low CS compared with the patients with normal CS in the posterior and inferior frontal cortex, the superior and posterior temporal cortex, the somato-sensory cortex, and the associative parietal cortex.

Conclusion: Low muscle CS in depressed patients is related to higher regional 99mTc-HMPAO retention that may reflect cerebrovascular adaptation to impaired intracellular metabolism and/or intracellular enzymatic changes, as previously reported in mitochondrial disorder. Mitochondrial dysfunction in varying proportions of the subjects may explain some of the discrepant results for 99mTc-HMPAO retention in depression.

For decades following the 1906 identification of Alzheimer’s disease (AD), it was believed that the disorder was untreatable. Only in the late 1970s, with the introduction of the cholinergic hypothesis of the underlying mechanisms of AD, were treatment options considered possible. The first positive treatment study was conducted in 1985. In 1993, tacrine, a cholinesterase inhibitor, was approved for the treatment of AD; three similar drugs soon followed. Memantine, an NMDA receptor antagonist, was approved in 2003, representing a second therapeutic class for AD.

Cholinesterase inhibitors were the first therapeutic options successfully employed, and there is strong evidence these agents confer benefits. The addition of memantine to the standard course of therapy can be beneficial as well, particularly at the moderate stages of the disorder (Mini-Mental State Exam score of ≤14). For patients without cardiovascular disease, diabetes, or statin use, 1,000 IU vitamin E BID is a consideration to mitigate the effects of AD. However, there is presently concern over the risks involved in vitamin E therapy. Unfortunately, there are no established treatments for mild cognitive impairment (MCI). Vitamin E is ineffective in treating MCI, and cholinesterase inhibitors, while possibly risky, are only minimally effective. The need for effective treatment remains expansive. The benefits of the available agents are modest, and there are currently no treatments for individuals with memory impairment who do not yet meet the diagnostic criteria for AD.