Rebamipide suppresses 5-fluorouracil-induced cell death via the activation of Akt/mTOR pathway and regulates the expression of Bcl-2 family proteins.

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.

Activation of NF-κB by the RANKL/RANK system up-regulates snail and twist expressions and induces epithelial-to-mesenchymal transition in mammary tumor cell lines.

BACKGROUND: Increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT), which occurs during cancer progression and metastasis. Recent studies have indicated the expression of receptor activator of nuclear factor-κB (RANK) in various solid tumors, including breast cancer. Although activation of the RANK ligand (RANKL)/RANK system promotes cell migration, metastasis, and anchorage-independent growth of tumor-initiating cells, it remains to be investigated if RANKL induces EMT in breast cancer cells. In this study, we investigated whether RANKL induces EMT in normal breast mammary epithelial cells and breast cancer cells, and the mechanism underlying such induction. METHODS: Expression levels of vimentin, N-cadherin, E-cadherin, Snail, Slug, and Twist were examined by real-time polymerase chain reaction. Cell migration and invasion were assessed using Boyden chamber and invasion assays, respectively. The effects of RANKL on signal transduction molecules were determined by western blot analyses. RESULTS: We found that stimulation by RANKL altered the cell morphology to the mesenchymal phenotype in normal breast epithelial and breast cancer cells. In addition, RANKL increased the expression levels of vimentin, N-cadherin, Snail, and Twist and decreased the expression of E-cadherin. We also found that RANKL activated nuclear factor-κB (NF-κB), but not extracellular signal-regulated kinase 1/2, Akt, mammalian target of rapamycin, c-Jun N-terminal kinase, and signal transducer and activator of transcription 3. Moreover, dimethyl fumarate, a NF-κB inhibitor, inhibited RANKL-induced EMT, cell migration, and invasion, and upregulated the expressions of Snail, Twist, vimentin, and N-cadherin. CONCLUSIONS: The results indicate that RANKL induces EMT by activating the NF-κB pathway and enhancing Snail and Twist expression. These findings suggest that the RANKL/RANK system promotes tumor cell migration, invasion, and metastasis via the induction of EMT.

Quercetin and NPPB-induced diminution of aldosterone action on Na+ absorption and ENaC expression in renal epithelium.

In renal epithelial A6 cells, aldosterone applied for 24 h increased the transepithelial Cl- secretion over 30-fold due to activation of the Na+/K+/2Cl- cotransporter and stimulated the transepithelial Na+ absorption, activity of epithelial Na+ channel (ENaC), and alpha-ENaC mRNA expression. The stimulatory action of aldosterone on the transepithelial Na+ absorption, ENaC activity, and alpha-ENaC mRNA expression was diminished by 24h-pretreatment with quercetin (an activator of Na+/K+/2Cl- cotransporter participating in Cl- entry into the cytosolic space) or 5-nitro 2-(3-phenylpropylamino)benzoate (NPPB) (a blocker of Cl- channel participating in Cl- release from the cytosolic space), while 24h-pretreatment with bumetanide (a blocker of Na+/K+/2Cl- cotransporter) enhanced the stimulatory action of aldosterone on transepithelial Na+ absorption. On the other hand, under the basal (aldosterone-unstimulated) condition, quercetin, NPPB or bumetanide had no effect on transepithelial Na+ absorption, activity of ENaC or alpha-ENaC mRNA expression. These observations suggest that although aldosterone shows overall its stimulatory action on ENaC (transepithelial Na+ transport), aldosterone has an inhibitory action on ENaC (transepithelial Na+ transport) via activation of the Na+/K+/2Cl- cotransporter, and that modification of activity of Cl- transporter/channel participating in the transepithelial Cl- secretion influences the aldosterone-stimulated ENaC (transepithelial Na+ transport).

Adoptive transfer of macrophages ameliorates renal fibrosis in mice.

We performed adoptive transfer of bone marrow-derived (BM) macrophages following pharmacological depletion of leukocytes in a mouse model of unilateral ureteral obstruction (UUO). Treatment with cyclophosphamide (CPM) caused marked decrease in the numbers of F4/80-positive interstitial macrophages as well as in peripheral blood leukocyte counts, and adoptive transfer of BM macrophages to CPM-treated mice resulted in significant increase in the numbers of interstitial macrophages both at day 5 and at day 14 after UUO. At day 5 after UUO, no significant change was observed in the degree of renal interstitial fibrosis either by treatment with CPM or with CPM+macrophage. However, at day 14 after UUO, treatment with CPM caused significant increase in the degree of interstitial fibrosis, and adoptive macrophage transfer to these mice attenuated this enhancement in renal fibrosis. Our result suggests the role of infiltrating macrophages on facilitating tissue repair at late stage of UUO.

Effect of hematopoietic cytokines on renal function in cisplatin-induced ARF in mice.

In this study, the effect of hematopoietic cytokines, i.e., granulocyte-colony stimulating factor (G-CSF), stem cell factor (SCF), and granulocyte-macrophage-colony stimulating factor (GM-CSF), on renal function was studied in cisplatin-induced acute renal failure in mice. Treatment with G-CSF significantly ameliorated both BUN and serum creatinine increase induced by cisplatin administration with concomitant alleviation in the degree of necrotic change, enhancement in DNA synthesis, and decrease in apoptosis of renal tubular cells. There was no significant change observed among these parameters following treatment with SCF or with GM-CSF. Serum hepatocyte growth factor level was significantly lower in mice treated with cisplatin and G-CSF compared with that in those treated with cisplatin only. In conclusion, G-CSF, but not SCF or GM-CSF, acts to accelerate regeneration and prevent apoptosis of renal tubular epithelial cells and leads to reduced renal injury in cisplatin-induced acute renal failure in mice.

Renal tubular regeneration by bone marrow-derived cells in a girl after bone marrow transplantation.

Recent studies have indicated that bone marrow cells can contribute to regeneration of the kidney in experimental models. However, renal regeneration by apparent bone marrow-derived cells has not been shown previously in humans. The authors here report on a 7-year-old girl who received whole bone marrow transplantation from a male donor, and the contribution of bone marrow cells to the regeneration after renal damage was shown by in situ hybridization for the Y chromosome on autopsy specimens of the kidney. This observation suggests the clinical potential of bone marrow cells as a therapeutic option for renal injury.