Hematogenous apoptotic mechanism in salivary glands in chronic periodontitis.

OBJECTIVE: The aim of the study is to investigate the apoptotic mechanism in salivary glands in the rat experimental periodontitis model. DESIGN: A rat periodontitis model was prepared by using a ligature around the second upper molar. In the salivary (parotid and submandibular) glands and blood samples, putative apoptotic factors and pathway molecules were investigated in vivo and in vitro. RESULTS: Four weeks of ligation (chronic periodontitis) demonstrated significant apoptotic atrophy of the salivary gland, but one week of ligation (initial periodontitis) did not. In the blood plasma, tumor necrosis factor-α (TNF-α) was increased in the periodontitis model, but interleukin-1ß and -6 were not. TNF-α receptor type 1, which has an intracellular apoptotic pathway, was expressed in the salivary glands of rats. Western blot analysis of cultured rat primary salivary gland cells demonstrated that TNF-α induced cleavage of poly (ADP-ribose) polymerase (PARP) and caspase-3 in a dose-dependent manner, indicating apoptosis induction. Additionally, we found increment of circulating lymphocytes in the model. Expression of mRNA and immunoreactive cells for the B lymphocyte marker CD19 were increased in the salivary gland in the model. Western blotting showed that coculture with extracted B cells from the periodontitis model increased cleaved PARP in salivary gland cells. CONCLUSIONS: Chronic periodontitis status leads to an increase in circulating TNF-α and B lymphocyte infiltration, resulting in apoptotic atrophy of the salivary gland as a periodontitis-induced systemic response.

[Aging and immortalization of human cells].

In vitro models of malignant transformation of human cells may provide considerable insight into the mechanisms of multistep carcinogenesis. It is well established that normal human cells must be immortalized before they are malignantly transformed, but normal human cells are extremely refractory to immortalization, making malignant transformation very difficult. Thus immortalization is a rate-limiting step in the malignant transformation of human cells. In order to immortalize normal human cells with a chemical carcinogen, 4-nitroquinoline 1-oxide, or with 60Co gamma rays, the cells had to be repeatedly treated with these agents. This indicates that the immortalization process involves multiple mutational events and is itself a multi-step process. Then we found that there were mutations in p53 in all our immortalized cell lines. This encouraged us to attempt to immortalize human cells with the mutant p53. We introduced the mutant p53 (codon 273Arg-His) into normal human fibroblasts to learn whether the cells could be immortalized. The p53 extended the life-span of the cells but could not immortalize them. However, when we treated the p53-introduced cells with 4NQO, the cells were immortalized. The 4NQO treatment alone did not make the cells immortal. These results indicate that the p53 gene play a role in immortalization of human cells rather than in their malignant transformation.