Pentoxifylline inhibits perforin-dependent natural cytotoxicity in vitro.

Pentoxifylline (PTX) is commonly used in peripheral blood vessel diseases, however it has also been found to decrease the level of proinflammatory cytokines such as IL-12, TNF-alpha and IFN-gamma. Moreover, some authors reported that PTX suppresses spontaneous cytotoxicity of peripheral blood mononuclear cells (PBMC) in vitro. It could influence the mechanism of killing target cells by PBMC. For this reason we evaluated the influence of PTX on spontaneous cytotoxicity of PBMC against K562 and CaSki cell lines. Subsequently, we compared this effect to that evoked by dexamethasone, one of the most effective anti-inflammatory drugs. Our study revealed that PTX inhibits natural cytotoxicity preferentially through inhibition of perforin-mediated cell membrane damage, without a statistically significant influence on apoptosis induction. Furthermore, pentoxifylline inhibits natural cytotoxicity as effectively as dexamethasone. However, the result of PTX inhibitory influence is observed much earlier than that of dexamethasone. Currently PTX is commonly used in diseases that occur more frequently in elderly patients. We suggest that PTX, inhibiting perforin-dependent PBMC cytotoxic activity, could weaken anti-cancer action of immune system thus accelerating the progress of neoplasm formation in these patients.

Clinical aspects of disrupted Hedgehog signaling (Review).

The Hedgehog (HH) signaling pathway is involved in patterning and development of a variety of organ systems, including the nervous system, the skeletal system, the craniofacial structures, and the gastrointestinal tract. Recent evidence also implicates this signaling pathway in the postembryonic regulation of stem-cell number in epithelia and blood. The family of HH proteins consists of at least three different members, i.e., sonic HH (SHH), Indian HH (IHH), and desert HH (DHH). SHH is the most broadly expressed member of this family and is probably responsible for the major effects of this signaling pathway. The HH signal is received and transduced via a specific receptor complex composed of patched (PTCH) and smoothened (SMOH) transmembrane proteins. Abnormalities in this signaling cascade have been found in various developmental pathologies and neoplasms such as basal cell carcinoma. The abnormalities are associated with congenital or sporadic genetic alteration affecting function of different components of the HH signaling pathway, including SHH, PTCH, SMOH and GLI proteins.

Influence of culture medium pH on cytotoxicity of CD95L in vitro.

CD95L belongs to the tumor necrosis factor-alpha (TNF-alpha) family, the members of which induce apoptosis by activation of their specific receptors. However, there are a few publications suggesting that two of these factors, TNF-alpha and TNF-beta, are able to reveal cytotoxic effect in pH-dependent manner. Therefore we investigated, whether CD95L may also reveal pH-dependent cytotoxicity. We analyzed influence of CD95L on U937 and K562 human cell lines at pH 5.1 and pH 7.4 using radioactive chromium release and tetrazolium salt (MTT) reduction assays. Expression of CD95 in both cell lines was estimated using RNase Protection Assay and FACS analysis. It has been found that short incubation of cells at pH 5.1 did not visibly affect their viability, as measured after 16 or 20 h. Incubation of U937 with CD95L at pH 7.4 resulted in a dose-dependent cell cytotoxicity. The effect was significantly augmented by incubation of cells with CD95L at pH 5.1. K562 cell line was resistant to CD95L at pH 7.4. This result correlated with the lack of CD95 expression in K562 cells. However, incubation at pH 5.1 resulted in a sensitization of K562 cells to CD95L. Our results suggest that CD95L, similarly to TNF-alpha, is able to reveal its cytotoxic activity in a receptor-independent manner and this activity strongly depends on pH of the environment.