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Oral mucositis is a common adverse effect of chemotherapy that limits the required dose of chemotherapeutic agents. Numerous attempts to mitigate chemotherapy-induced oral mucositis have failed to identify an appropriate treatment. Recently, it has been indicated that rebamipide prevents chemoradiotherapy-induced oral mucositis in patients. However, the details of the underlying mechanism involved in the cytoprotective effect of rebamipide remain obscure. In the present study, we investigated the mechanism behind rebamipide cytoprotective effect in the oral mucosa using primary normal human oral keratinocytes (NHOK cells). We found that rebamipide prevented 5-fluorouracil (5-FU)-induced cell death in NHOK cells. In addition, rebamipide increased the levels of phosphorylated Akt and mTOR, enhanced the Bcl-2 and Bcl-xL expressions, and suppressed the expression of Bax and Bim. This is in contrast to 5-FU-induced suppression of Akt and mTOR activation, Bcl-2 and Bcl-xL expressions, and the enhanced expression of Bax and Bim. These findings suggest that rebamipide can potentially be used for the protection of oral mucosa from chemotherapy-induced mucositis. This is the first study that elucidates the specific molecular pathway for the cytoprotective effect of rebamipide., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

6-Mercaptopurine (6-MP), an analogue of hypoxanthine, is used in the therapy of acute lymphoblastic leukemia and causes fetal neurotoxicity. To clarify the mechanisms of 6-MP-induced fetal neurotoxicity leading to the cell cycle arrest and apoptosis of neural progenitor cells, pregnant rats were treated with 50 mg/kg 6-MP on embryonic day (E) 13, and the fetal telencephalons were examined at 12 to 72 h (h) after treatment. Flow-cytometric analysis confirmed an accumulation of cells at G2/M, S, and sub-G1 (apoptotic cells) phases from 24 to 72 h. The number of phosphorylated histone H3-positive cells (mitotic cells) decreased from 36 to 72 h, and the phosphorylated (active) form of p53 protein, which is a mediator of apoptosis and cell cycle arrest, increased from 24 to 48 h. An executor of p53-mediated cell cycle arrest, p21, showed intense overexpression at both the mRNA and protein levels from 24 to 72 h. Cdc25A protein, which is needed for the progression of S phase, decreased at 36 and 48 h. In addition, phosphorylated cdc2 protein, which is an inactive form of cdc2 necessary for G2/M progression, increased from 24 to 48 h. These results suggest that 6-MP induced G2/M arrest, delayed S-phase progression, and finally induced apoptosis of neural progenitor cells mediated by p53 in the fetal rat telencephalon.

Toluene can be considered an ototoxic chemical compound in the rat. Outer hair cells are particularly sensitive to this aromatic organic solvent or to one of its metabolites. The objective of the present study was to evaluate the possible role played by cysteine S-conjugates in the ototoxic process in Long-Evans rats. To this end, renal and hepatic metabolism of toluene was modified by treatment with acivicin, an inhibitor of gamma-glutamyl transferase (gamma-GT). First, the efficacy of the acivicin treatment was established from a dose-response investigation in which urinary gamma-GT was measured daily in rats exposed to 1750 ppm toluene, 6 h per day for five days. A twice weekly 5 mg/kg dose was reduced urinary gamma-GT by 70-78%. In a subacute experiment, rats were exposed to 1750 ppm toluene for four consecutive weeks, in which the efficacy of the acivicin treatment was monitored by quantifying the urinary end product of the conjugate pathway: benzyl mercapturic acid (BMA). A 38.5% decrease in BMA was measured at the end of the exposure period. Hearing impairment was evaluated using auditory (inferior colliculus) evoked potentials and completed with conventional histological approaches. The toluene-exposed and the acivicin-treated rats exposed to toluene both had a 7-dB permanent auditory threshold shift at 16-20 kHz. Hair cell loss was not dependent on acivicin treatment. Therefore, the partial inhibition of gamma-GT did not modify the toluene ototoxicity, suggesting that toluene-induced hearing loss is not strongly mediated by the production of cysteine S-conjugates. However, the data do not rule out the possibility that these metabolites may play a minor role.

Oxidative stress and apoptosis play pivotal roles in the pathogenesis of neurodegenerative diseases. We investigated the effects of vitamin E analogs on oxidative stress and apoptosis using primary neuronal cultures of rat striatum. A tocotrienol-rich fraction of edible oil derived from palm oil (Tocomin 50%), which contains alpha-tocopherol, and alpha-, gamma- and delta-tocotrienols, significantly inhibited hydrogen peroxide (H2O2)-induced neuronal death. Each of the tocotrienols, purified from Tocomin 50% by high-performance liquid chromatography, significantly attenuated H2O2-induced neurotoxicity, whereas alpha-tocopherol did not. alpha-, gamma- and delta-Tocotrienols also provided significant protection against the cytotoxicity of a superoxide donor, paraquat, and nitric oxide donors, S-nitrosocysteine and 3-morpholinosydnonimine. Moreover, tocotrienols blocked oxidative stress-mediated cell death with apoptotic DNA fragmentation caused by an inhibitor of glutathione synthesis, L-buthionine-[S,R]-sulfoximine. In addition, alpha-tocotrienol, but not gamma- or delta-tocotrienol, prevented oxidative stress-independent apoptotic cell death, DNA cleavage and nuclear morphological changes induced by a non-specific protein kinase inhibitor, staurosporine. These findings suggest that alpha-tocotrienol can exert anti-apoptotic neuroprotective action independently of its antioxidant property. Among the vitamin E analogs examined, alpha-tocotrienol exhibited the most potent neuroprotective actions in rat striatal cultures.