Assay of urinary 8-hydroxy-2'-deoxyguanosine by capillary electrophoresis with spectrophotometric detection using a high-sensitivity detection cell and solid-phase extraction

Approaching Sites of Action of Temozolomide for Pharmacological and Clinical Studies in Glioblastoma

Temozolomide (TMZ), together with bulk resection and focal radiotherapy, is currently a standard of care for glioblastoma. Absorption, distribution, metabolism, and excretion (ADME) parameters, together with the mode of action of TMZ, make its biochemical and biological action difficult to understand. Accurate understanding of the mode of action of TMZ and the monitoring of TMZ at its anatomical, cellular, and molecular sites of action (SOAs) would greatly benefit precision medicine and the development of novel therapeutic approaches in combination with TMZ. In the present perspective article, we summarize the known ADME parameters and modes of action of TMZ, and we review the possible methodological options to monitor TMZ at its SOAs. We focus our descriptions of methodologies on mass spectrometry-based approaches, and all related considerations are taken into account regarding the avoidance of artifacts in mass spectrometric analysis during sampling, sample preparation, and the evaluation of results. Finally, we provide an overview of potential applications for precision medicine and drug development.

Novel dual methylation of cytidines in the RNA of mammals

RNA modifications play critical roles in regulating a variety of physiological processes. Methylation is the most prevalent modification occurring in RNA. Three isomeric cytidine methylation modifications have been reported in RNA, including 3-methylcytidine (m³C), N4-methylcytidine (m⁴C), and 5-methylcytidine (m⁵C), in mammals. Aside from the single methylation on the nucleobase of cytidines, dual methylation modifications occurring in both the 2′ hydroxyl of ribose and the nucleobase of cytidines also have been reported, including N4,2′-O-dimethylcytidine (m⁴Cm) and 5,2′-O-dimethylcytidine (m⁵Cm). m⁴Cm has been found in the 16S rRNA of E. coli, while m⁵Cm has been found in the tRNA of terminal thermophilic archaea and mammals. However, unlike m⁴Cm and m⁵Cm, the presumed dual methylation of 3,2′-O-dimethylcytidine (m³Cm) has never been discovered in living organisms. Thus, the presence of m³Cm in RNA remains an open question. In the current study, we synthesized m³Cm and established a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method to determine the dimethylation of cytidines, m³Cm, m⁴Cm and m⁵Cm. Under optimized analytical conditions, m³Cm, m⁴Cm and m⁵Cm can be clearly distinguished. Using the method, we discovered the existence of m³Cm in the RNA of mammals. The identified m³Cm is a novel modification that hasn't been reported in the three-domain system, including archaea, bacteria, and eukaryotes. We confirmed that m³Cm mainly existed in the small RNA (<200 nt) of mammals. In addition, we identified, for the first time, the presence of m⁴Cm in the 18S rRNA of mammalian cells. The stable isotope tracing monitored by mass spectrometry demonstrated that S-adenosyl-l-methionine was a methyl donor for all three dimethylations of cytidines in RNA. The discovery of m³Cm broadens the diversity of RNA modifications in living organisms. In addition, the discovery of m³Cm and m⁴Cm in mammals opens new directions in understanding RNA modification-mediated RNA processing and gene expression regulation.

We synthesized 3,2′-O-dimethylcytidine (m³Cm) and determined the dimethylation of cytidines in mammals by mass spectrometry analysis. We discovered m³Cm in small RNA and N4,2′-O-dimethylcytidine (m⁴Cm) in 18S rRNA of mammals.

Simultaneous analysis of two urinary biomarkers of oxidative damage to DNA and RNA based on packed-fiber solid phase extraction coupled with high-performance liquid chromatography

The determination of the concentrations of urinary biomarkers of oxidative damage to DNA and RNA is difficult due to the low content of targets and the complex matrix of urine. A method using polystyrene/polypyrrole (PS/PPY) electronspun nanofibers as the adsorbent was introduced to the routine urinary treatment and determination of 8-OHdG and 8-oxoG for the first time. And 2-aminoethyl diphenylborate (DPBA) solution was creatively used in the loading and rinsing steps in order to promote the retention of the analytes as well as remove impurities. Under optimal conditions, 8-OHdG, 8-oxoG and IS were separated very well and exhibited a good linearity in the range of 0.5-50 ng mL^-1, with correlation coefficients of R² > 0.996. Limits of detection (LOD) were 0.058 ng mL^-1 and 0.093 ng mL^-1, and limits of quantification (LOQ) were 0.195 ng mL^-1 and 0.309 ng mL^-1, respectively. The recoveries were 88.8-104.9%. The proposed method was so simple and economical that it had the potential to be applied to batch quantitative analysis of 8-OHdG and 8-oxoG in urine. And it was successfully applied to real urine samples of cancer patients.

Association between Oxidative DNA Damage and Risk of Colorectal Cancer: Sensitive Determination of Urinary 8-Hydroxy-2'-deoxyguanosine by UPLC-MS/MS Analysis

Oxidative DNA damage plays crucial roles in the pathogenesis of numerous diseases including cancer. 8-hydroxy-2′-deoxyguanosine (8-OHdG) is the most representative product of oxidative modifications of DNA, and urinary 8-OHdG is potentially the best non-invasive biomarker of oxidative damage to DNA. Herein, we developed a sensitive, specific and accurate method for quantification of 8-OHdG in human urine. The urine samples were pretreated using off-line solid-phase extraction (SPE), followed by ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. By the use of acetic acid as an additive to the mobile phase, we improved the UPLC-MS/MS detection of 8-OHdG by 2.7−5.3 times. Using the developed strategy, we measured the contents of 8-OHdG in urine samples from 142 healthy volunteers and 84 patients with colorectal cancer (CRC). We observed increased levels of urinary 8-OHdG in patients with CRC and patients with tumor metastasis, compared to healthy controls and patients without tumor metastasis, respectively. Additionally, logistic regression analysis and receiver operator characteristic (ROC) curve analysis were performed. Our findings implicate that oxidative stress plays important roles in the development of CRC and the marked increase of urinary 8-OHdG may serve as a potential liquid biomarker for the risk estimation, early warning and detection of CRC.