High levels of endogenous nitric oxide produced after burn injury in rats arrest activated T lymphocytes in the first G1 phase of the cell cycle and then induce their apoptosis.

Major physical traumas provoke a systemic inflammatory response and immune dysfunction. In a model of thermal injury in rats, we previously showed that an overproduction of nitric oxide (NO) was responsible for the collapse of lymphoproliferative responses. In the present work, we performed a time-course analysis of cell proliferation and cell death parameters in order to establish the sequence of events triggered by the high NO output in Wistar/Han rat splenocytes activated with Con A, 10 days after burn injury. We demonstrate that activated T cells from burned rats never divided whereas normal T cells underwent four division cycles. However, T cells from both burned and normal rat entered the G1 phase as shown by increase of cell size, mitochondria hyperpolarization, and expression of cyclin D1. Burned rat T cells progressed to the late G1 phase as shown by expression of the nuclear Ki-67 antigen, but they never entered the S phase. They underwent apoptosis as shown by morphological parameters, disruption of transmembrane mitochondrial potential, and DNA fragmentation. Persistent accumulation of the p53 protein accompanied these phenomena. NO synthase inhibitors antagonize alterations of cell proliferation and cell death parameters in burned rat T cells and accelerated p53 turnover.

Nitric oxide inhibits spleen cell proliferative response after burn injury by inducing cytostasis, apoptosis, and necrosis of activated T lymphocytes: role of the guanylate cyclase.

We previously showed that an overproduction of nitric oxide (NO) by macrophages was responsible for the collapse of lymphoproliferative responses after burn injury in rats. First, we demonstrate here that 10 days post-burn, the inhibition of splenocyte response to concanavalin-A results from cytostatic, apoptotic, and necrotic effects of NO on activated T cells. This was evidenced by various criteria at the levels of DNA, mitochondria, and plasma membrane. Inhibition of NO synthase by S-methylisothiourea (10 microM) normalized all the parameters. Second, we show that two soluble guanylate cyclase (sGC) inhibitors, LY83583 and ODQ, restored the proliferative response in a concentration-dependent manner. LY83583 (0.5 microM) rescued T cells from apoptosis. Similar results were obtained with KT5823 (5 microM) a specific inhibitor of protein kinase G (PKG). In contrast, neither LY83583 nor KT5823 inhibited NO-induced necrosis. These results suggest that NO blocked T cells in the G1 phase and induced apoptosis through a sGC-PKG-dependent pathway and necrosis through an independent one.

Carbon ions-induced apoptosis in hematopoietic tumor cell lines.

BACKGROUND: The purpose of this study was to assess apoptosis in hematopoietic tumor cells irradiated with carbon ions, in order to define its contribution to the cytotoxicity of these high-LET radiations. MATERIALS AND METHODS: RDM4 (murine T lymphoma), MOLT-4, TK6 and WTK1 (human lymphoblastoid) cells were irradiated with 12C or 13C. Apoptosis was assessed by flow cytometry. Cell growth and activities of caspases were determined during the same periods. RESULTS: The ability of carbon ions to induce apoptosis markedly varied according to the cell line. MOLT-4 and TK6 cells underwent apoptosis at 1 Gy within 12 hours post-irradiation, whereas RDM4 and WTK1 showed little apoptosis under the same conditions. CONCLUSION: These results indicate that apoptosis contributes to the overall cytotoxicity of carbon ions towards hematopoietic tumor cells although other death mechanisms must also account for this cytotoxicity.