Evaluation of acute and subacute toxicity of sodium taurodeoxycholate in rats.

Taurodeoxycholate (TDCA) inhibits various inflammatory responses suggesting potential clinical application. However, the toxicity of TDCA has not been evaluated in detail in vivo. We investigated the acute toxicity and 4-week repeated-dose toxicity of TDCA following intravenous infusion under Good Laboratory Practice regulations. In the sighting study of acute toxicity, one of two rats (one male and one female) treated with 300 mg/kg TDCA died with hepatotoxicity, suggesting that the approximate 50% lethal dose of TDCA is 300 mg/kg. Edema and discoloration were observed at the injection sites of tails when rats were infused with 150 mg/kg or higher amount of TDCA once. In 4-week repeated-dose toxicity study, no treatment-related mortality or systemic changes in hematology and serum biochemistry, organ weights, gross pathology, or histopathology were observed. However, the tail injection site showed redness, discharge, hardening, and crust formation along with histopathological changes such as ulceration, edema, fibrosis, and thrombosis when rats were infused with 20 mg/kg TDCA. Taken together, TDCA induced no systemic toxicity or macroscopic lesions at the injection site at a dose of 10 mg/kg/day, which is 33 times higher than the median effective dose observed in a mouse sepsis model. These findings suggest that TDCA might have a favorable therapeutic index in clinical applications.

Nonclinical toxicology studies with sodium taurodeoxycholate: acute and subacute toxicity in dogs.

Sodium taurodeoxycholate (TDCA) has been investigated for various inflammatory disorders such as sepsis. We recently evaluated nonclinical safety profile of TDCA using rats infused intravenously. As a series of preclinical safety investigations, we further conducted toxicity studies with TDCA delivered to dogs via intravenous administration under Good Laboratory Practice regulation in this study. In dose range-finding study (dose escalation study), dogs given with TDCA at a dose of 150 mg/kg showed marked changes in clinical signs, hematology, and serum biochemistry. And biochemical markers of liver damage and local skin lesions were observed following intravenous infusion of 100 mg/kg TDCA, suggesting that 100 mg/kg was chosen as the highest dose of TDCA for 4-week repeated-dose toxicity study using dogs. Despite no treatment-related significant changes in body weight, food consumption, ophthalmoscopy, and urinalysis, skin lesions were observed at the injection site of animals administered with higher than 50 mg/kg of TDCA along with biochemical and histopathological changes associated with liver injury. However, most of off-target effects were found to be reversible since these were recovered after stopping TDCA infusion. These findings indicate that the no-observed-adverse-effect-level (NOAEL) for TDCA in dogs was considered to be 5 mg/kg/d. Taken together, our results provide important toxicological profiles regarding the safe dose of TDCA for drug development or clinical application.

Ganciclovir augments the lytic induction and apoptosis induced by chemotherapeutic agents in an Epstein-Barr virus-infected gastric carcinoma cell line.

Epstein-Barr virus is an oncogenic herpesvirus and has been associated with several human malignancies, including gastric cancer. In Epstein-Barr virus-associated gastric cancer, Epstein-Barr virus is found in virtually all tumor cells, but rarely in normal epithelial cells, thus implying that Epstein-Barr virus-targeting therapies are likely to be an effective treatment strategy. Using the SNU-719 gastric cancer cell line, which is naturally infected with Epstein-Barr virus, we found that the chemotherapeutic agents, such as 5-fluorouracil, cis-platinum and taxol, induced the expressions of BMRF1, BZLF1 and BRLF1 proteins that are usually found in the lytic form of the virus. This effect was found to require various signal transduction pathways involving phosphatidylinositol 3' kinase, mitogen-activated protein/extracellular signal-regulated kinase, protein kinase C delta and p38 mitogen-activated protein kinase. Moreover, the combination of ganciclovir with these agents increased the lytic transformation and induced apoptosis in Epstein-Barr virus-associated gastric carcinoma. We conclude that ganciclovir enhances the therapeutic efficacy of 5-fluorouracil, cis-platinum and taxol in Epstein-Barr virus-positive gastric cancer cells. It is hoped that this information will be found useful during the establishment of treatment strategies for Epstein-Barr virus-associated gastric cancer.

Aberrant methylation of the specific CpG island portion regulates cyclooxygenase-2 gene expression in human gastric carcinomas.

Although it has been well established that overexpression of cyclooxygenase-2 (Cox-2) favors tumorigenesis and metastasis, the molecular mechanism that regulates Cox-2 expression has not been well defined in gastric carcinoma. Aberrant methylation of the CpG island is known to be one of the powerful mechanisms for the suppression of gene expression, and usually, CpG islands are very rich in promoter region and exon-1 region. But, it is controversial whether Cox-2 gene expression is regulated by methylation of promoter region or exon-1 region. In this study, we examined whether the hyper-methylation mediated transcriptional silencing of Cox-2 also occurred in human gastric carcinoma tissues and which portion of CpG island methylation is important in Cox-2 gene expression. Genomic DNAs from human gastric carcinoma tissues were treated with three methylation-sensitive restriction enzymes and then Southern blot analysis was performed. Out of 30 primary gastric tumor samples, 26 cases (86.6%) showed overexpression of Cox-2. Four cases (13.3%) with relatively decreased Cox-2 gene expression were associated with the presence of aberrant methylation of Cox-2 CpG island. We also found that methylation of promoter region and not exon-1 region is related with the transcriptional silencing of Cox-2 in gastric carcinoma cancer by detailed methylation mapping using bisulfite sequencing analysis. Our results suggest that the DNA methylation-mediated transcriptional silencing of Cox-2 is a predominant mechanism for the down-regulation of Cox-2 expression in human gastric carcinoma. Furthermore, the results suggest that methylation of not exon-1 region but promoter region is important to regulation of Cox-2 gene expression.