Meso-2,3-dimercaptosuccinic acid induces calcium transients in cultured rhesus monkey kidney cells

Paradoxical effect of 2,3-dimercapto-1-propanesulfonic acid (DMPS) on enhancing antitumor activity of cisplatin in ascites sarcoma 180 cells

We investigated the enhancing effect of two metal-chelating compounds, 2,3-dimercapto-1-propanesulfonic acid (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA), on the antitumor activity of cisplatin (CDDP). In the in vivo experiments, DMPS showed a clear synergistic effect and significantly enhanced the antitumor activity of CDDP in terms of survival and life span in mice transplanted with ascites sarcoma 180 cells (S180 cells) at a dose of <100 micromol/kg, s.c., but not at a dose of >500 micromol/kg. On the other hand, DMSA did not enhance the antitumor activity of CDDP. DMPS (50 micromol/kg, s.c.) combined with CDDP also potently suppressed [(3)H]thymidine uptake in S180 cells implanted in mice, whereas DMSA did not. In the in vitro experiments, DMPS (10(-6) to 10(-5) M) produced a time- and dose-dependent decrease in intracellular Ca(2+) concentrations ([Ca(2+)](i)) in S180 cells and, in combination with CDDP, yielded a significant increase in intracellular platinum accumulation compared to that in cells treated with CDDP alone. These results indicate that DMPS used in combination with CDDP may be of considerable benefit in enhancing the cytotoxicity of CDDP in tumor cells, especially at a low dose. The results also suggest that the enhancing effect of DMPS is closely related to a decrease in [Ca(2+)](i) and that the suitable dose and adequate administrational time of DMPS are important for its effective action.

A conserved domain of the gp85/trans-sialidase family activates host cell extracellular signal-regulated kinase and facilitates Trypanosoma cruzi infection

Chagas' disease is a chronic, debilitating and incapacitating illness, caused by the protozoan parasite Trypanosoma cruzi when infective trypomastigotes invade host cells. Although the mechanism of trypomastigotes interaction with mammalian cells has been intensively studied, a final and integrated picture of the signal transduction mechanisms involved still remains to be elucidated. Our group has previously shown that the conserved FLY domain (VTVXNVFLYNR), present in all members of the gp85/trans-sialidase glycoprotein family coating the surface of trypomastigotes, binds to cytokeratin 18 (CK18) on the surface of LLC-MK(2) epithelial cells, and significantly increases parasite entry into mammalian cells. Now it is reported that FLY, present on the surface of trypomastigotes or on latex beads binds to CK18, promotes dephosphorylation and reorganization of CK18 and activation of the ERK1/2 signaling cascade culminating in an increase of approximately 9-fold in the number of parasites/cell. Inhibition of ERK1/2 phosphorylation completely blocks the adhesion of FLY to cells and blocks by 57% the host cell infection by T. cruzi. Taken together our results indicate that the conserved FLY domain is an important tool that trypomastigotes have evolved to specific exploit the host cell machinery and guarantee a successful infection.

Heparin and chondroitin sulfate inhibit adenine nucleotide hydrolysis in liver and kidney membrane enriched fractions

The inhibition of adenine nucleotide hydrolysis by heparin and chondroitin sulfate (sulfated polysaccharides) was studied in membrane preparations from liver and kidney of adult rats. Hydrolysis was measured by the activity of NTPDase and 5'-nucleotidase. The inhibition of NTPDase by heparin was observed at three different pH values (6.0, 8.0 and 10.0). In liver, the maximal inhibition observed for ATP and ADP hydrolysis was about 80% at pH 8.0 and 70% at pH 6.0 and 10.0. Similarly to the effect observed in liver, heparin caused inhibition of ATP and ADP hydrolysis that reached a maximum of 70% in kidney (pH 8.0). Na(+), K(+) and Rb(+) changed the inhibitory potency of heparin, suggesting that its effects may be related to charge interaction. In addition to heparin, chondroitin sulfate also caused a dose-dependent inhibition in liver and kidney membranes. The maximal inhibition observed for ATP and ADP hydrolysis was about 60 and 50%, respectively. In addition, the hepatic and renal activity of 5'-nucleotidase was inhibited by heparin and chondroitin sulfate, except for kidney membranes where chondroitin sulfate did not alter AMP hydrolysis. On this basis, the findings indicate that glycosaminoglycans have a potential role as inhibitors of adenine nucleotide hydrolysis on the surface of liver and kidney cell membranes in vitro.

Lead inhibits meso-2,3-dimercaptosuccinic acid induced calcium transients in cultured rhesus monkey kidney cells

Previously we have shown that meso-2,3-dimercaptosuccinic acid (DMSA, 15-500 microM) elicits concentration-dependent increases in intracellular calcium levels ([Ca2+]i) in untreated rhesus monkey kidney cells (LLC-MK2) (Pokorski et al., 1997, unpublished results). Little is known about the restorative effects of the chelating agent 2,3-dimercaptosuccinic acid on intracellular calcium homeostasis in the presence of lead. Lead interacts at numerous sites in Ca2+ homeostasis and may mimic Ca2+ to interfere with Ca2+-mediated intracellular signaling. To examine the effects of lead on [Ca2+]i and DMSA-induced calcium transients, LLC-MK2 were plated on 35 mm coverslip dishes (10(4) cells/dish) and pre-treated with non-cytotoxic concentrations of lead (0-100 microM) for 24 h. Cells were washed, loaded with the calcium-sensitive probe Fura-2/AM, rinsed again, and examined in loading buffer in the absence of any additional lead. Intracellular calcium was measured using a dual-wavelength calcium imaging system. Basal [Ca2+]i levels did not change between Pb-exposed (0-50 microM, 24 h) and non-lead exposed cells. In cells treated with > or = 10 microM lead for 24 h, the ability of DMSA to elicit a calcium response was blocked. These results provide evidence that pre-exposure to lead blocks the entry of extracellular calcium into LLC-MK2 cells when stimulated by specific calcium mobilizing agents.