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1-O-Hexyl-2,3,5-trimethylhydroquinone (HTHQ) has previously been found to have effective anti-oxidant and anti-lipid-peroxidative activity. We aimed to elucidate whether HTHQ can prevent dopaminergic neuronal cell death by investigating the effect on l-DOPA-induced cytotoxicity in PC12 cells. HTHQ protected from both l-DOPA-induced cell death and superoxide dismutase activity reduction. When assessing the effect of HTHQ on oxidative stress-related signaling pathways, HTHQ inhibited l-DOPA-induced phosphorylation of sustained extracellular signal-regulated kinases (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK1/2). HTHQ also normalized l-DOPA-reduced Bcl-2-associated death protein (Bad) phosphorylation and Bcl-2-associated X protein (Bax) expression, promoting cell survival. Taken together, HTHQ exhibits protective effects against l-DOPA-induced cell death through modulation of the ERK1/2-p38MAPK-JNK1/2-Bad-Bax signaling pathway in PC12 cells. These results suggest that HTHQ may show ameliorative effects against oxidative stress-induced dopaminergic neuronal cell death, although further studies in animal models of Parkinson’s disease are required to confirm this.

The effects of anonaine, an aporphine isoquinoline alkaloid, on dopaminebiosynthesis and L-DOPA-induced cytotoxicity in PC12 cells were investigated. Anonaineat concentration ranges of 0.01-0.2 μM showed a significant inhibition of dopaminecontent at 24 h, with an IC50 value of 0.05 μM. Anonaine at 0.05 μM inhibited tyrosinehydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) activities to 38.4-40.2% and 78.4-90.2% of control levels at 12-24 h and 3-6 h, respectively. TH activity wasmore influenced than AADC activity. Anonaine also decreased intracellular cyclic AMPlevels, but not intracellular Ca2+ concentrations. In addition, anonaine (0.05 μM) reducedL-DOPA (50 μM and 100 μM)-induced increases in dopamine content at 24 h. However,anonaine (0.05 μM) did not enhance L-DOPA (50 μM and 100 μM)-induced cell death 476after 24 h. These results suggest that anonaine inhibits dopamine biosynthesis by mainlyreducing TH activity without aggravating L-DOPA-induced cytotoxicity in PC12 cells.

Abstract: The effects of sesamin on dopamine biosynthesis and l-DOPA-induced cytotoxicity in PC12 cells were investigated. Sesamin at concentration ranges of 20–75 μM exhibited a significant increase in intracellular dopamine levels at 24 h: 50 μM sesamin increased dopamine levels to 133% and tyrosine hydroxylase (TH) activity to 128.2% of control levels. Sesamin at 20–100 μM rapidly increased the intracellular levels of cyclic AMP (cAMP) to 158.3%–270.3% of control levels at 30 min. At 50 μM, sesamin combined with l-DOPA (50, 100 and 200 μM) further increased the intracellular dopamine levels for 24 h compared to l-DOPA alone. In the absence or presence of l-DOPA (100 and 200 μM), sesamin (50 μM) increased the phosphorylation of TH, cAMP-dependent protein kinase (PKA), and cAMP-response element-binding protein (CREB), as well as the mRNA levels of TH and CREB for 24 h, an effect which was reduced by l-DOPA (100 and 200 μM). In addition, 50 μM sesamin exhibited a protective effect against l-DOPA (100 and 200 μM)-induced cytotoxicity via the inhibition of reactive oxygen species (ROS) production and superoxide dismutase reduction, induction of extracellular signal-regulated kinase (ERK)1/2 and BadSer112 phosphorylation and Bcl-2 expression, and inhibition of cleaved-caspase-3 formation. These results suggested that sesamin enhanced dopamine biosynthesis and l-DOPA-induced increase in dopamine levels by inducing TH activity and TH gene expression, which was mediated by cAMP-PKA-CREB systems. Sesamin also protected against l-DOPA (100–200 μM)-induced cytotoxicity through the suppression of ROS activity via the modulation of ERK1/2, BadSer112, Bcl-2, and caspase-3 pathways in PC12 cells. Therefore, sesamin might serve as an adjuvant phytonutrient for neurodegenerative diseases. [Copyright &y& Elsevier]

The effects of catalponol (1) on dopamine biosynthesis and l-DOPA-induced cytotoxicity in PC12 cells were investigated. Catalponol at concentration ranges of 1-5 μM increased the intracellular levels of dopamine at 12-48 h. Catalponol at concentrations of up to 10 μM did not alter cell viability. Tyrosine hydroxylase (TH) activity was enhanced by 1 at 3 μM in a time-dependent manner, but aromatic l-amino acid decarboxylase activity was not. Catalponol also increased the intracellular levels of cyclic AMP and TH phosphorylation. In addition, catalponol at 3 μM associated with l-DOPA (20-50 μM) further enhanced the increases in dopamine levels induced by l-DOPA (50-100 μM) at 24 h. Catalponol at 2-5 μM inhibited l-DOPA (100-200 μM)-induced cytotoxicity at 48 h. These results suggest that 1 enhanced dopamine biosynthesis by inducing TH activity and protected against l-DOPA-induced cytotoxicity in PC12 cells, which was mediated by the increased levels of cyclic AMP. [ABSTRACT FROM AUTHOR]

The effects of asimilobine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis and l-DOPA-induced cytotoxicity in PC12 cells were investigated. Asimilobine at concentration ranges of 0.05-0.2 μM showed a significant inhibition of intracellular dopamine levels for 24 h in a concentration-dependent manner with an IC50 value of 0.13 μM. Asimilobine at 0.15 μM inhibited tyrosine hydroxylase (TH) and aromatic l-amino acid decarboxylase (AADC) activities at 24 h (73.2% inhibition of TH activity): the inhibition of TH activity was stronger and longer than that of AADC activity. Asimilobine also decreased TH mRNA levels and intracellular cyclic AMP levels, but not the basal Ca2 + concentrations. In addition, asimilobine at 0.05-5.0 μM, but not 10 μM, did not alter cell viability toward PC12 cells. A non-cytotoxic asimilobine (0.15 μM) associated with l-DOPA (20, 50, and 100 μM) for 24 h inhibited l-DOPA-induced increases in dopamine levels and enhanced l-DOPA-induced cell death when compared with l-DOPA alone. These results suggest that asimilobine inhibits dopamine biosynthesis by mainly reducing the TH activity and TH mRNA expression, and enhances l-DOPA-induced cytotoxicity in PC12 cells. [ABSTRACT FROM AUTHOR]

Abstract: The effects of catalpalactone on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells were investigated. Catalpalactone at 5–30μM decreased intracellular dopamine content with the IC50 value of 22.1μM. Catalpalactone at 5–20μM, but not 30μM, did not alter cell viability. Catalpalactone at 20μM inhibited tyrosine hydroxylase (TH) and aromatic-l-amino acid decarboxylase (AADC) activities. Catalpalactone also decreased cyclic AMP levels and inhibited TH phosphorylation. In addition, catalpalactone at 20μM reduced the increases in dopamine levels induced by L-DOPA (20–50μM). Catalpalactone (5–30μM) associated with L-DOPA (50–100μM) enhanced L-DOPA-induced cytotoxicity at 48h, which was prevented by N-acetyl-l-cysteine. These results suggest that catalpalactone inhibited dopamine biosynthesis by reducing TH and AADC activities and enhanced L-DOPA-induced cytotoxiciy in PC12 cells. [Copyright &y& Elsevier]

1- O -Hexyl-2,3,5-trimethylhydroquinone (HTHQ) has previously been found to have effective anti-oxidant and anti-lipid-peroxidative activity. We aimed to elucidate whether HTHQ can prevent dopaminergic neuronal cell death by investigating the effect on l-DOPA-induced cytotoxicity in PC12 cells. HTHQ protected from both l-DOPA-induced cell death and superoxide dismutase activity reduction. When assessing the effect of HTHQ on oxidative stress-related signaling pathways, HTHQ inhibited l-DOPA-induced phosphorylation of sustained extracellular signal-regulated kinases (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK1/2). HTHQ also normalized l-DOPA-reduced Bcl-2-associated death protein (Bad) phosphorylation and Bcl-2-associated X protein (Bax) expression, promoting cell survival. Taken together, HTHQ exhibits protective effects against l-DOPA-induced cell death through modulation of the ERK1/2-p38MAPK-JNK1/2-Bad-Bax signaling pathway in PC12 cells. These results suggest that HTHQ may show ameliorative effects against oxidative stress-induced dopaminergic neuronal cell death, although further studies in animal models of Parkinson's disease are required to confirm this.