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para-Phenylenediamine (p-PD) is a potential carcinogen, and widely used in marketed hair dye formulations. In the present study, the role of the protein tyrosine kinase (PTK)/Ras/Raf/c-Jun N-terminal kinase (JNK) and phosphoinositide 3-kinase (PI3k)/protein kinase B (Akt) pathways on the growth of NRK-52E cells was investigated. The results demonstrated that p-PD reduced cell viability in a dose-dependent manner. The cell death due to apoptosis was confirmed by cell cycle analysis and an Annexin-V-fluorescein isothiocyanate binding assay. Subsequent to staining with 2',7'-dichlorofluorescin diacetate, the treated cells demonstrated a significant increase in reactive oxygen species (ROS) generation compared with the controls. The effects of p-PD on the signalling pathways were analysed by western blotting. p-PD-treated cells exhibited an upregulated phospho-stress-activated protein kinase/JNK protein expression level and downregulated Ras and Raf protein expression levels; however, Akt, Bcl-2, Bcl-XL and Bad protein expression levels were not significantly altered compared with the control. In conclusion, p-PD induced apoptosis by a PTK/Ras/Raf/JNK-dependent pathway and was independent of the PI3K/Akt pathway in NRK-52E cells. [ABSTRACT FROM AUTHOR]

Neurodegenerative diseases remain a global issue which affects the ageing population. Efforts towards determining their aetiologies to understand their pathogenic mechanisms are underway in order to identify a pathway through which therapeutic measures can be applied. One such pathogenic mechanism, oxidative stress (OS), is widely considered to be involved in neurodegenerative disease. Antioxidants, most notably flavonoids, have promising potential for therapeutic use as shown in in vitro and in vivo studies. In view of the importance of flavonoids for combating OS, this study investigated the neuroprotective effects of orientin, which has been reported to be capable of crossing the blood‑brain barrier. The maximum non‑toxic dose (MNTD) of orientin against SH‑SY5Y neuroblastoma cells was determined using a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay. The effects of the MNTD and the half MNTD (½MNTD) of orientin on cell cycle progression and intracellular reactive oxygen species (ROS) levels, as well as the activity of caspases 3/7, 8 and 9 after exposure to 150 µM of hydrogen peroxide (H2O2) were also determined using flow cytometry, a 2',7'‑dichlorodihydrofluorescein‑diacetate (DCFH‑DA) assay and caspase assay kits, respectively. The results revealed that orientin at ≤20 µM was not cytotoxic to SH‑SY5Y cells. After treatment with orientin at the MNTD, the percentage of apoptotic cells was significantly reduced compared with that in cells treated with 150 µM H2O2 alone. The results also showed that, although orientin at the MNTD and ½MNTD did not reduce intracellular ROS levels, it significantly inhibited the activity of caspases 3/7. Caspase 9 was significantly inactivated with orientin at the MNTD. Findings from this study suggest that the neuroprotection conferred by orientin was the result of the intracellular mediation of caspase activity.