The pleiotropic functionality of endogenous 3-iodothyronamine (T1AM) and synthetic thyronamine-like analogs: a powerful tool to target interlinked diseases such as obesity and neurodegeneration

Accumulating evidence has suggested the presence of a strong correlation between obesity and neurodegeneration. Neurodegenerative diseases (NDDs) are characterized by a progressive loss of memory and cognition, which ultimately can lead to death. This deterioration is mostly due to inflammation triggered by aberrant protein deposition, oxidative stress and modification in lipid pathways. Because of these multifactorial aspects, the design of multi-target directed ligand (MTDL) could represent a potential strategy for the treatment of NDDs. In this context, the polypharmacology described in good detail for naturally occurring 3-iodothyronamine (T1AM), and rapidly emerging also for thyronamine-like analogs SG-1 and SG-2, may provide a novel pleiotropic therapeutic approach for the treatment of NDDs. With the aim to provide a detailed characterization of the pharmacological profile of these new drug candidates, in the present work we evaluated their ability to promote lipolysis in HepG2 cells, as well as, to activate clearing pathways, such as autophagy (ATG) and ubiquitine proteasome (UP) in human glioblastoma cells (U87-MG). Methods: Cultured HepG2 cells were incubated for 24 h with 10 µM T1AM or SG-2 and Oil-red O staining was used to monitor intracellular lipid accumulation. Cell culture supernatants were also collected and analyzed for free glycerol release. In another set of experiments, cultured U87-MG cells were treated with 1 µM T1AM, SG-1, SG-2 or vehicle for 30 min, 4, 8 and 24 h and the induction of ATG was monitored morphologically by using transmission electron microscopy (TEM) and immunofluorescence (IF) microscopy. Ultrastructural morphometry, based on the stoichiometric binding of immunogold particles, allowed the quantitative evaluation of ATG and UP component (i.e. LC3 and P20S, respectively) within autophagosomes and autophagoproteasomes. RT-qPCR and Western blot assays were applied to detect the expression of ATG and UP indicators. Results: A significant decrease in lipid accumulation was observed in HepG2 cells treated with T1AM or SG-2, possibly due to increased lipolytic activity, further confirmed by accumulation of glycerol (an end product of triglyceride lipolysis) in the culture media. Treatment with T1AM, SG-1 or SG-2 induced autophagy in U87-MG cells, by promoting autophagosome formation and up-regulating LC3-II expression and p62 degradation. Notably, increased 20S proteasome recruitment to autophagosome was also observed, suggesting that these compounds might modulate both ATG and UP protein clearing pathways within the autophagoproteasomes. Conclusions: Our studies highlight the potential of T1AM and its synthetic analogs, SG-1 and SG-2, as novel drugs for the treatment of obesity and NDDs.