Role of intracellular deoxynucleoside triphosphate levels in DNA repair in human lymphocytes

Improved high-performance liquid chromatographic analysis of intracellular deoxyribonucleoside triphosphate levels

The ability to measure intracellular deoxyribonucleoside triphosphate (dNTP) pool sizes is important for understanding the intracellular metabolism of DNA synthesis and repair. We have developed an improved method for measuring intracellular dNTP pool size by high-performance liquid chromatography (HPLC). Previous methods have enabled accurate measurement of dNTPs only in concentrations greater than approximately 10 pmol per 10(6) cells due to the inability to partially purify cell extracts, to the inability to apply extracts from extremely large numbers of cells, to the lack of efficient columns, to the presence of incompatible solvents, and to the inability to inject large volumes. We have modified a low-pressure strong anion-exchange column pre-step developed by others to concentrate and partially purify oxidized cell extracts while at the same time eluting them in a more compatible solvent for HPLC injection. The HPLC column is a YMC ODS-AQ column operating in a combined hydrophobic-interaction chromatography-reversed-phase chromatography mode. The injection and elution solvents are both phosphate-based. Using this method it is possible to measure intracellular dNTP levels well below 0.5 pmol per 10(6) cells or at the sensitivity of the DNA polymerase assay.

A simplified HPLC method for simultaneously quantifying ribonucleotides and deoxyribonucleotides in cell extracts or frozen tissues

Agents and conditions that induce alterations in deoxyribonucleotide pools can have important regulatory effects on the rate of DNA synthesis as well as cell cycle progression. A simplified procedure for the separation of both ribonucleoside triphosphates (NTP) and deoxyribonucleoside triphosphates (dNTP) is presented which utilizes reversed phase high-performance liquid chromatography coupled with diode array detection. The simultaneous resolution of NTP and dNTP peaks within the same cell extract effectively eliminates the need for post-extraction steps such as periodate oxidation and/or boronate affinity chromatography previously used to degrade or isolate co-eluting NTP from dNTP. The resolution of two nucleotides, dGTP and ADP, was found empirically to vary with the efficiency of the C18 column. High efficiency columns (> 90,000 plates/m) provided good separation; however, less efficient columns resulted in co-elution of dGTP and ADP. These co-eluting nucleotides can be accurately quantified, if necessary, using diode array technology and a mathematical expression which incorporates molar peak coefficients and peak areas obtained by monitoring at dual wave-lengths. Tissue samples or single cell suspensions were extracted with trichloroacetic acid and the neutralized extract was injected directly into the column without prior lyophilization. The per cent recovery of standards was > or = 99% and replicate extractions within or between samples were highly reproducible (SD < 5%). The single step method described minimizes potential losses associated with post-extraction manipulation and provides the capability to examine alterations in nucleotide precursor-product metabolism under various physiological and pharmacological conditions.