2,4-Toluene diisocyanate suppressed the calcium signaling of ligand gated ion channel receptors

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Cytosolic Ca2+ shifts as early markers of cytotoxicity

The determination of the cytotoxic potential of new and so far unknown compounds as well as their metabolites is fundamental in risk assessment. A variety of strategic endpoints have been defined to describe toxin-cell interactions, leading to prediction of cell fate. They involve measurement of metabolic endpoints, bio-energetic parameters or morphological cell modifications. Here, we evaluated alterations of the free cytosolic Ca²⁺ homeostasis using the Fluo-4 dye and compared results with the metabolic cell viability assay Alamar Blue. We investigated a panel of toxins (As₂O₃, gossypol, H₂O₂, staurosporine, and titanium(IV)-salane complexes) in four different mammalian cell lines covering three different species (human, mouse, and African green monkey). All tested compounds induced an increase in free cytosolic Ca²⁺ within the first 5 s after toxin application. Cytosolic Ca²⁺ shifts occurred independently of the chemical structure in all tested cell systems and were persistent up to 3 h. The linear increase of free cytosolic Ca²⁺ within the first 5 s of drug treatment correlates with the EC₂₅ and EC₇₅ values obtained in Alamar Blue assays one day after toxin exposure. Moreover, a rise of cytosolic Ca²⁺ was detectable independent of induced cell death mode as assessed by caspase and poly(ADP-ribose) polymerase (PARP) activity in HeLa versus MCF-7 cells at very low concentrations. In conclusion, a cytotoxicity assay based on Ca²⁺ shifts has a low limit of detection (LOD), is less time consuming (at least 24 times faster) compared to the cell viability assay Alamar Blue and is suitable for high-troughput-screening (HTS).

Exocrine pancreatic carcinogenesis and autotaxin expression

Exocrine pancreatic cancer is an aggressive disease with an exceptionally high mortality rate. Genetic analysis suggests a causative role for environmental factors, but consistent epidemiological support is scarce and no biomarkers for monitoring the effects of chemical pancreatic carcinogens are available. With the objective to identify common traits for chemicals inducing pancreatic tumors we studied the National Toxicology Program (NTP) bioassay database. We found that male rats were affected more often than female rats and identified eight chemicals that induced exocrine pancreatic tumors in males only. For a hypothesis generating process we used a text mining tool to analyse published literature for suggested mode of actions (MOA). The resulting MOA analysis suggested inflammatory responses as common feature. In cell studies we found that all the chemicals increased protein levels of the inflammatory protein autotaxin (ATX) in Panc-1, MIA PaCa-2 or Capan-2 cells. Induction of MMP-9 and increased invasive migration were also frequent effects, consistent with ATX activation. Testosterone has previously been implicated in pancreatic carcinogenesis and we found that it increased ATX levels. Our data show that ATX is a target for chemicals inducing pancreatic tumors in rats. Several lines of evidence implicate ATX and its product lysophosphatidic acid in human pancreatic cancer. Mechanisms of action may include stimulated invasive growth and metastasis. ATX may interact with hormones or onco- or suppressor-genes often deregulated in exocrine pancreatic cancer. Our data suggest that ATX is a target for chemicals promoting pancreatic tumor development.

Toluene diisocyanate (TDI) induces calcium elevation and interleukine-4 (IL-4) release - early responses upon TDI stimulation

Occupational exposure to toluene diisocyanats (TDI) may cause asthma. In asthma patients, the allergic syndromes correlate cytokine production with the elevation in cytosolic calcium concentration [Ca(2+)](c) of lymphocytes in airway. We previously found TDI induces calcium signaling in neuronal cells. TDI mainly gets into human body via inhalation; therefore this study investigated the possibility of TDI inducing the changes in [Ca(2+)](c) in airway. We used human lung epithelial cell line H1355, human T-cell line Jurkat, and human neuroblastoma SH-SY5Y cells to present the kinds of cells existing in airway. The changes of [Ca(2+)](c) were measured by Fura-2 fluorescent dye. Results show that TDI induced an elevation in [Ca(2+)](c )in those cell lines and two primary isolated cells, bovine adrenal chromaffin cells and human white blood cells. Cytokine release and their gene expressions of Jurkat cells and human white blood cells were measured by ELISA and reverse transcription polymerase chain reaction. TDI acutely promoted the interleukine-4 (IL-4) release significantly in both Jurkat cells and human white blood cells. TDI-induced IL-4 release was suppressed in the presence of 1,2-bis- (O-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid (BAPTA), an intracellular Ca(2+) chelator, in Jurkat cells. In the hand of gene expression, TDI induced an increase in the mRNA level of TNF-alpha and IL-4 in Jurkat cells. We conclude that the release of IL-4 were coupled with the elevation in [Ca(2+)](c) induced by TDI. Further studies are required to clarify the roles of TDI-induced IL-4 secretion in acute inflammation.