Parameters for cellular viability and membrane function in chenopodium cells show a specific response of extracellular pH to heat shock with extreme Q10

The effect of brief heat shock on Chenopodium cells was investigated by measuring biochemical parameters for cellular vitality, membrane function and integrity: extracellular pH, release of osmotic compounds, phosphatase, protein and betalain, and cellular reduction of DCPIP and MTT. A threshold temperature was found at 45 degrees C, where release of osmotic compounds, protein and betalain, and reduction of DCPIP and MTT indicate loss of vitality. Extracellular pH and an alkaline phosphatase responded 10-20 degrees C below this threshold, suggesting that extracellular alkalinization, and probably the release of a phosphatase, are part of a specific cellular response to abiotic stress induced by heat shock. The extracellular proton concentration did not increase above 45 degrees C: this may indicate equilibration of gradients driving this process or an inactivation of cellular mechanisms responsible for extracellular alkalinization. The response of extracellular pH to heat shock in Chenopodium cell suspensions was fast, i.e., up to +1 pH in 5 min. Addition of the K+/H+ antiporter nigericin to Chenopodium cells caused an extracellular alkalinization similar to heat shock. The heat shock-induced extracellular alkalinization was characterized by Q10 values for distinct ranges of temperature (Q10 of 56 for 24-31 degrees C, 2.3 for 31-42 degrees C, and 1.0 for 42-50 degrees C). To the author's knowledge, the Q10 of 56 is the highest found up to now. These results suggest that extracellular protons are involved in temperature sensing and signalling in plant cells, probably via a channel-mediated pathway.     

Multidrug resistance associated protein 1 protects against bilirubin-induced cytotoxicity

We have shown that multidrug resistance associated protein 1 (MRP1) mediates ATP-dependent extrusion of bilirubin, possibly limiting its potentially toxic accumulation in cells. To determine directly if Mrp1 protects cells against unconjugated bilirubin (UCB) toxicity, mouse embryo fibroblasts (MEF) were isolated from Mrp1 knockout (-/-) mice and their wild type (WT) (+/+) littermates. Compared to WT cells, cultured MEF (-/-) cells exposed to 40-140 nM unbound [H3]-bilirubin accumulated twice as much [H3]-bilirubin (P<0.01). This was associated with greater, dose-related cytotoxicity, assessed by the methylthiazoletetrazolium test, lactate dehydrogenase release and cellular ATP content. The data confirm that Mrp1 limits intracellular accumulation of UCB and thus decreases its cytotoxicity.     

The selenium analog of the chemopreventive compound S,S′-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea is a remarkable inducer of apoptosis and inhibitor of cell growth in human non-small cell lung cancer

Lung cancer continues to be the leading cause of cancer deaths throughout the world and conventional therapy remains largely unsuccessful. Although, chemoprevention is a plausible alternative approach to curb the lung cancer epidemic, clinically there are no effective chemopreventive agents. Thus, development of novel compounds that can target cellular and molecular pathways involved in the multistep carcinogenesis process is urgently needed. Previous studies have suggested that substitution of sulfur by selenium in established cancer chemopreventive agents may result in more effective analogs. Thus in the present study we selected the chemopreventive agent S,S′-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea (PBIT), also known to inhibit inducible nitric oxide synthase (iNOS), synthesized its selenium analog (Se-PBIT) and compared both compounds in preclinical model systems using non-small cell lung cancer (NSCLC) cell lines (NCI-H460 and A549); NSCLC is the most common histologic type of all lung cancer cases. Se-PBIT was found to be superior to PBIT as an inducer of apoptosis and inhibitor of cell growth. Se-PBIT arrested cell cycles at G1 and G2-M stage in both A549 and H460 cell lines. Although both compounds are weakly but equally effective inhibitors of iNOS protein expression and activity, only Se-PBIT significantly enhanced the levels of p53, p38, p27 and p21 protein expression, reduced levels of phospholipase A2 (PLA2) but had no effect on cyclooxygenase-2 (COX-2) protein levels; such molecular targets are involved in cell growth inhibition, induction of apoptosis and cell cycle regulation. The results indicate that Se-PBIT altered molecular targets that are involved in the development of human lung cancer. Although, the mechanisms that can fully account for these effects remain to be determined, the results are encouraging to further evaluate the chemopreventive efficacy of Se-PBIT against the development of NSCLC in a well-defined animal model.     

The mitochondrial respiratory chain of Ustilago maydis

Ustilago maydis mitochondria contain the four classical components of the electron transport chain (complexes I, II, III, and IV), a glycerol phosphate dehydrogenase, and two alternative elements: an external rotenone-insensitive flavone-sensitive NADH dehydrogenase (NDH-2) and an alternative oxidase (AOX). The external NDH-2 contributes as much as complex I to the NADH-dependent respiratory activity, and is not modulated by Ca²⁺, a regulatory mechanism described for plant NDH-2, and presumed to be a unique characteristic of the external isozyme. The AOX accounts for the 20% residual respiratory activity after inhibition of complex IV by cyanide. This residual activity depends on growth conditions, since cells grown in the presence of cyanide or antimycin A increase its proportion to about 75% of the uninhibited rate. The effect of AMP, pyruvate and DTT on AOX was studied. The activity of AOX in U. maydis cells was sensitive to AMP but not to pyruvate, which agrees with the regulatory characteristics of a fungal AOX. Interestingly, the presence of DTT during cell permeabilisation protected the enzyme against inactivation.The pathways of quinone reduction and quinol oxidation lack an additive behavior. This is consistent with the competition of the respiratory components of each pathway for the quinol/quinone pool.     

Luteolin as a glycolysis inhibitor offers superior efficacy and lesser toxicity of doxorubicin in breast cancer cells

Luteolin (Lu) exhibits a wide spectrum of anti-tumor activities, the present study was to observe whether Lu can sensitize breast cancer cells to doxorubicin (Dox) and to explain the basis underlying this phenomenon. In vitro, Lu at dose less than 100 μM had only slight effect on cells growth and cytotoxicity of Dox in 4T1 and MCF-7 cells under normoxia, but it could reverse tumor resistance to Dox and promote death of tumor cells under hypoxia. In vivo, Lu alone had also no effect on tumor growth delay, however, it could offer superior efficacy and lesser toxicity of Dox in 4T1 and MCF-7 bearing mice. Further study showed that Lu was able to suppress glycolytic flux but did not affect glucose uptake, the P-glycoprotein, anti-oxidative enzymes under hypoxia in vitro, and had not also effect on the intratumor Dox level in vivo. In addition, the activity of SOD and CAT was increased in serum and was decreased in tumor by Lu in vivo. These results suggest that luteolin as a glycolytic inhibitor might be a new adjuvant agent for chemotherapy.