Epidemiological studies have linked herbicides and Parkinson's disease (PD), with the strongest associations resulting from long exposure durations. Paraquat (PQ), an herbicide, induces PD-like syndromes and has widely been accepted as a PD mimetic. Currently, there is still no cure to prevent the progression of PD, and the search for effective therapeutic ways is urgent. Recently, the impairing activity of sirtuins (SIRTs), such as SIRT1, may correlate with PD etiology. However, the nonspecificity of SIRT1 agonists has made the protective mechanisms against PD unclear and hampered the therapeutic application of SIRT1. Thus, this study investigated the protective mechanism and therapeutic potential of SRT1720, a more specific agonist for SIRT1 synthesized by Sirtris, in alleviating the toxicity of PQ-induced cellular and animal models of PD. Here we show that SRT1720 alleviates PQ-induced toxicity in cell and animal models. Genetic silencing and pharmacological inhibition of SIRT1 attenuated SRT1720's protection against PQ-induced toxicity. Moreover, SRT1720 not only attenuated PQ-induced increased oxidative stress and mitochondrial free radical formations but also decreased mitochondrial membrane potential. Furthermore, SRT1720 reversed PQ-induced decreased PGC-1α levels and mitochondrial biogenesis. Although PQ and SRT1720 elevated NRF2 and antioxidative enzyme levels, only PQ decreased antioxidative enzyme activity but not SRT1720. NRF2 and PGC-1α silencing attenuated SRT1720 protection against PQ-induced toxicity. SRT1720 targeted SIRT1 and activated downstream PGC-1α and NRF2 signalings to prevent PQ-induced toxicity involving oxidative stress and mitochondrial dysfunction. Thus, SRT1720 might have therapeutic potential in preventing PD.

It is well known that cytokinins are a class of phytohormones that promote cell division in plant roots and shoots. However, their targets, biological functions, and implications in mammalian systems have rarely been examined. In this study, we show that one cytokinin, zeatin riboside, can prevent pheochromocytoma (PC12) cells from serum deprivation-induced apoptosis by acting on the adenosine A_2A receptor (A_2A-R), which was blocked by an A_2A-R antagonist and a protein kinase A (PKA) inhibitor, demonstrating the functional ability of zeatin riboside by mediating through A_2A-R signaling event. Since the A_2A-R was implicated as a therapeutic target in treating Huntington’s disease (HD), a cellular model of HD was applied by transfecting mutant huntingtin in PC12 cells. By using filter retardation assay and confocal microscopy we found that zeatin riboside reversed mutant huntingtin (Htt)-induced protein aggregations and proteasome deactivation through A_2A-R signaling. PKA inhibitor blocked zeatin riboside-induced suppression of mutant Htt aggregations. In addition, PKA activated proteasome activity and reduced mutant Htt protein aggregations. However, a proteasome inhibitor blocked both zeatin riboside-and PKA activator-mediated suppression of mutant Htt aggregations, confirming mediation of the A_2A-R/PKA/proteasome pathway. Taken together, zeatin riboside might have therapeutic potential as a novel neuroprotectant and a lead for treating neurodegenerative disorders.

Huang Lian Jie Du Tang (HLJDT) is a traditional Chinese medical decoction for heat-fire clearing and detoxication. Theoretically, the cause of Parkinson's disease (PD) has been attributed to the dysregulations of internal wind, phlegm, fire, and stasis. Thus, HLJDT has been used to treat PD. However, the molecular mechanism is unknown. Besides, paraquat (PQ) as an herbicide has been known to impair midbrain dopaminergic neurons, resemblance to the pathology of PD. Thus, the molecular mechanism of HLJDT in treating PD and PQ-induced in vitro PD model was investigated in this study. Primarily, the dose-response of PQ (0.1∼1 mM)-induced neurotoxicity for 24 h was performed in the human neuroblastoma SH-SY5Y cells. The LD50 of PQ is around 0.3 mM and was applied throughout the following experiments. The neutral red assay was used to estimate cell viability. Co-transfection of the mitochondrial marker and proapoptotic factor genes were applied to measure the release of mitochondrial proapoptotic factors during PQ intoxication and HLJDT protection. The fluorescent dyes were used to detect mitochondrial membrane potential and free radical formation. Western blot and dot-blot analysis and immunocytochemistry were used to estimate the level of proteins related to apoptosis and mitophagy. PINK1 gene silencing was used to determine the significance of mitophagy during PQ intoxication. In this study, HLJDT attenuated PQ-induced apoptosis in SH-SY5Y cells. HLJDT reversed PQ-induced decreased mitochondrial membrane potential and suppressed PQ-induced increased cytosolic and mitochondrial free radical formations and mitochondrial proapoptotic factor releases. Furthermore, HLJDT mitigated PQ-induced increases in full-length PINK1, phosphorylations of Parkin and ubiquitin, mitochondrial translocation of phosphorylated Parkin, and mitophagy. PINK1 gene silencing attenuated PQ-induced neurotoxicity. Therefore, HLJDT attenuated PQ-induced cell death by regulating mitophagy.

Liu Jun Zi Tang (LJZT) has been used to treat functional dyspepsia and depression, suggesting its effects on gastrointestinal and neurological functions. LJZT is currently used as a complementary therapy to attenuate cisplatin-induced side effects, such as dyspepsia. However, its effect on chemotherapy-induced neuropathic pain or neurotoxicity has rarely been studied. Thus, we explored potential mechanisms underlying LJZT protection against cisplatin-induced neurotoxicity. We observed that LJZT attenuated cisplatin-induced thermal hyperalgesia in mice and apoptosis in human neuroblastoma SH-SY5Y cells. Furthermore, it also attenuated cisplatin-induced cytosolic and mitochondrial free radical formation, reversed the cisplatin-induced decrease in mitochondrial membrane potential, and increased the release of mitochondrial pro-apoptotic factors. LJZT not only activated the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) promoter region, but also attenuated the cisplatin-induced reduction of PGC-1α expression. Silencing of the PGC-1α gene counteracted the protection of LJZT. Taken together, LJZT mediated, through anti-oxidative effect and mitochondrial function regulation, to prevent cisplatin-induced neurotoxicity.