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    Antisense oligonucleotides and prevention of tumor growth: a different approach and proposal for a new method
    (Churchill Livingstone, 2005) Yildiz, D; Oztas, H; Ates, BH
    There have been several attempts to prevent tumor formation and growth. However, none of the developed methods gives a completely satisfying result for the treatment of tumor masses. The most often used therapies against tumor cells are radiotherapy and chemotherapy. However, utilization of these methods to treat cancer generally result in generation of undesired side effects. In recent years, the antisense oligonucleotide technology has been employed, with success to an extent, in prevention of tumor growth. However, this method has its limitations. One of the most important limitation is that all of the crucial genes that play certain roles and are specifically expressed in tumor cells have not yet been identified. Therefore, only a few numbers of genes that are shown to play a rote in tumor cells are targeted by the antisense oligonucleotide method. The aim of the present study is to propose a hypotheses and outline the involved procedure which could be used to generate oligonucleotides that are antisense to genes or mRNAs that display certain specific functions in tumor cells but are yet to be identified. The proposed hypotheses involves first, a careful isolation of differentially expressed mRNAs by using the tumor and the corresponding normal cells. These mRNAs should represent the genes that operate in tumor cells but not in the corresponding normal cells. Following the isolation of the differentially expressed mRNAs, they will be reverse transcribed and the desired amounts of cDNA copies will be obtained. The cDNA copies will then be used differentially as a source for oligonucleotides that are antisense to genes or mRNAs. To obtain the desired length oligonucleotides that will be used as antisense oligonucleotides the cDNA copies will be subjected to Maxam-Gilbert fragmentation and/or controlled enodonuclease digestion. These two mentioned procedures could be optimized and used together or separately to obtain the desired length oligonucleotides that will be used against tumor cells. (C) 2004 Elsevier Ltd. All rights reserved.
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    L-cysteine influx and efflux in human erythrocytes: the role of red blood cells in redox and metabolite homeostasis in the plasma
    (Pharmaceutical Soc Japan, 2006) Yildiz, D; Ates, BH; Uslu, C; Oztas, H
    The objective of this study was to investigate L-cysteine influx and efflux in human erythrocytes. L-cysteine is an amino acid required for glutathione synthesis in erythrocytes. In addition to being incorporated into glutathione, the soluble antioxidant L-cysteine plays a role in the maintenance of a proper intracellular or extracellular redox status. Recent investigations have pointed out that L-cysteine may contribute to redox homeostasis in the plasma and in the periplasm of some bacteria. Thus L-cysteine availability in the plasma may influence the oxidized/reduced state of several other metabolites normally found in the plasma. Our L-cysteine uptake studies demonstrated that erythrocytes can respond to an increase in the L-cysteine concentration in the extracellular media and influx L-cysteine in a concentration dependent-manner. The L-cysteine efflux is also time and concentration dependent. Erythrocytes pretreated with higher concentration of L-cysteine displayed higher efflux rates. Erythrocytes pretreated with L-cysteine 1 mM displayed efflux and increased the free-SH concentrations up to 0.184 +/- 0.010 mM in the incubation media in 1 hr. While this concentration reached 0.843 +/- 0.012 mM in 10 mM-L-cysteine pretreated erythrocytes. Our results also showed that the L-cysteine efflux is partly mediated by the Alanine-Serine-Cysteine (ASC) system. The presence of alanine or serine in the incubation media decreased the rate of efflux by about 16%. Our results also showed that the L-cysteine efflux process is not a simple diffusion but a carrier-mediated process. When compared with N-acetyl-L-cysteine (NAC), which is known to diffuse through the membranes, L-cysteine displayed a higher efflux rate under the same conditions. Pretreatment of erythrocytes with L-cysteine 4 mM increased the free-SH concentration to 0.48 +/- 0.005 mM whereas the same concentration of NAC brought the free-SH concentration to 0.36 +/- 0.01 mM in the incubation media. Our results suggest that erythrocytes may contribute to redox and metabolite homeostasis of the plasma.