Growing evidence has indicated that iron deposition in the substantia nigra plays an important role in Parkinson’s disease (PD). However, the underlying mechanism is still elusive. Using primary dopaminergic neurons and SH-SY5Y cells cultured in vitro, we observed that iron loading increased α-synuclein and reactive oxygen species (ROS) levels in these cells but did not affect the intracellular α-synuclein mRNA levels. Furthermore, iron loading significantly downregulated Beclin-1 levels and decreased the ratio of microtubule-associated protein 1 light chain 3 isoforms (LC3 II/LC3 I). However, a significant change in the levels of autophagy-related gene 5 (Atg5) was not observed in either neurons or SH-SY5Y cells after iron treatment. After treatment with rapamycin, the iron loading-induced increase in the α-synuclein level was significantly reversed and ROS generation was alleviated in both cultured neurons and SH-SY5Y cells. These results indicate that the inhibition of autophagy is critical for the pathological alterations in α-synuclein induced by iron loading. Moreover, treatment with vitamin E did not affect the increase in the α-synuclein levels but significantly eliminated the iron-induced ROS production. Together, our study shows that autophagy dysfunction contributes to iron-induced α-synuclein pathology.

Reduction of glucose metabolism in brain is one of the main features of Alzheimer's disease. Thiamine (vitamin B1)-dependent processes are critical in glucose metabolism and have been found to be impaired in brains from patients with Alzheimer's disease. However, thiamine treatment exerts little beneficial effect in these patients. Here, we tested the effect of benfotiamine, a thiamine derivative with better bioavailability than thiamine, on cognitive impairment and pathology alterations in a mouse model of Alzheimer's disease, the amyloid precursor protein/presenilin-1 transgenic mouse. We show that after a chronic 8 week treatment, benfotiamine dose-dependently enhanced the spatial memory of amyloid precursor protein/presenilin-1 mice in the Morris water maze test. Furthermore, benfotiamine effectively reduced both amyloid plaque numbers and phosphorylated tau levels in cortical areas of the transgenic mice brains. Unexpectedly, these effects were not mimicked by another lipophilic thiamine derivative, fursultiamine, although both benfotiamine and fursultiamine were effective in increasing the levels of free thiamine in the brain. Most notably, benfotiamine, but not fursultiamine, significantly elevated the phosphorylation level of glycogen synthase kinase-3alpha and -3beta, and reduced their enzymatic activities in the amyloid precursor protein/presenilin-1 transgenic brain. Therefore, in the animal Alzheimer's disease model, benfotiamine appears to improve the cognitive function and reduce amyloid deposition via thiamine-independent mechanisms, which are likely to include the suppression of glycogen synthase kinase-3 activities. These results suggest that, unlike many other thiamine-related drugs, benfotiamine may be beneficial for clinical Alzheimer's disease treatment.

Non-alcoholic fatty liver disease (NAFLD) is characterized by steatosis associated with liver inflammation. As NAFLD progresses, triglycerides increase within hepatocytes, causing typical vacuoles that resemble adipocytes. However, whether these morphological changes in hepatocytes indicate potential functional changes is unclear. C57BL/6J mice were fed a high-fat diet (HFD) containing 42% fat. Markers for adipocytes in the liver were measured using real-time PCR, Western blot, and double immunofluorescent labeling. Cytokines in cell culture supernatants were quantified with ELISA. To determine the macrophage phenotype, hepatic classical M1 markers and alternative M2 markers were analyzed. After a 24-week feeding period, adipocyte markers aP2 and PPARγ increased at both the mRNA and protein level in the liver of HFD-fed mice. FITC-labeled aP2 and rhodamine-labeled albumin were both stained in the cytoplasm of steatotic hepatocytes as observed under confocal laser scanning microscopy. Cell membrane-bound E-cadherin and albumin expression were reduced in steatotic hepatocytes compared to controls. However, hepatic adiponectin and adiponectin receptor-2 expression decreased with upregulation of hepatic CD36, suggesting impaired adiponectin activity in livers of HFD-fed mice. Moreover, steatotic primary hepatocytes not only released pro-inflammatory cytokines such as TNFα, MCP-1, IL-6, and IL-18, but also could activate macrophages when co-cultured in vitro. In vivo, hepatic expression of M1 genes such as iNOS and TNFα was markedly increased in HFD-fed mice. In contrast, hepatic expression of M2 genes such as Arg1 and CD206 was significantly reduced. Specifically, the ratio of TNFα to CD206 in HFD-fed mice was notably upregulated. Overexpression of adipocyte-specific genes in hepatocytes and their secretory function and epithelial phenotype impairment in NAFLD cause functional changes in steatotic hepatocytes aside from morphological changes. This suggests that adipogenic changes in hepatocytes are involved in pathogenesis of NAFLD.