Zhiyu Guo

Inhibition of nicotine-DNA adduct formation in mice by six dietary constituents

Nicotine [3-(1-methyl-2-pyrrolidinyl)-pyridine] is a major alkaloid in tobacco products and has proven to be a potential genotoxic compound. Many natural dietary products can suppress the DNA adduction, and hence act as inhibitors of cancer. In this study, we investigated the inhibitory effects of curcumin, garlic squeeze, grapeseed extract, tea polyphenols, vitamin C, and vitamin E on nicotine-DNA adduction in vivo using an ultrasensitive method of accelerator mass spectrometry (AMS). The results demonstrated that all the dietary constituents induced marked dose-dependent decrease in nicotine-DNA adducts as compared with the control. The reduction rate reached about 50% for all agents, except garlic squeeze (40%), even at its highest dose level. Amongst the six agents, grapeseed extract exhibited the strongest inhibition to the DNA adduct formation. Therefore, we may arrive at a point that these dietary constituents are beneficial to prevent the harmful adduct formation, and thus to block the potential carcinogenesis induced by nicotine.

Genotoxicity Study on Nicotine and Nicotine-Derived Nitrosamine by Accelerator Mass Spectrometry

We have studied DNA adduction with 14C-labe1ed nicotine and nicotine-derived nitrosamine, 4-(methylnitrosamino)- 1-(3-pyridyl)-1-butanone (NNK), by accelerator mass spectrometry (AMS) in mouse liver at doses equivalent to lowlevel exposure of humans. The dose ranges of nicotine and NNK administered were from 0.4μg to 4.Ox 10^2μg kg b.w.-1, and from 0.1 μg to 2.0x10^4 μg kg b.w.-1, respectively. In the exposure of mice to either nicotine or NNK, the number of DNA adducts increased linearly with increasing dose. The detection limit of DNA adducts was 1 adduct per 1011 nucleotide molecules. This limit is 1-4 orders of magnitude lower than that of other techniques used for quantification of DNA adducts. The results of our animal experiments enabled us to speculate that nicotine is a potential carcinogen. According to the procedure for 14C-labeled-NNK synthesis, we discuss the ultimate chemical speciation of NNK bound to DNA. From the animal tests we derived a directly perceivable relation between tobacco consumption and DNA adduction as the carcinogenic risk assessment.

The use of AMS radiocarbon dating for Xia–Shang–Zhou chronology

Abstract The possibility and problems of using radiocarbon dating to historical chronology are discussed. The current situation of ancient Chinese chronology and the project of Xia–Shang–Zhou chronology are introduced. A chronological study requires the AMS radiocarbon dating with high precision, high reliability and high efficiency. The Peking University AMS facility (PKUAMS) has been upgraded and a series of quality control steps were adopted. To reduce the error of calendar age, wiggle matching with serial samples should be used. Some preliminary results of Xia–Shang–Zhou chronology are presented.

STATUS OF THE TANDEM ACCELERATOR MASS-SPECTROMETRY FACILITY AT PEKING-UNIVERSITY

Abstract A description of the EN tandem accelerator mass spectrometry system at Peking University is given. Progress in the bench test of the ion source, the reassembly and commissioning of the EN tandem and the sample preparation facilities is presented. In addition to 14 C and 10 Be analysis, 26 Al and 36 Cl will also be studied.

Optimising tandem accelerator stripping efficiency by simulation of charge changing processes

Abstract The knowledge of charge changing processes which affect the quality of an ion beam is of great importance for the design of a beam transport system of maximum transmission through the accelerator. The stripping yield depends on the cross sections of charge exchange processes, the ion velocity, the stripper medium and the stripper thickness. We have determined the cross sections for electron loss and capture processes for C and Be in the range from 1 to 6 MeV. A simulation procedure was developed for the charge distribution of an ion beam in order to optimise the stripping yield and to estimate mass fractionation effects in these processes. From curves fitted to the experimental data, the stripping yield and beam losses due to charge exchange processes can be calculated for various tandem accelerators and stripper configurations as a function of terminal voltage and stripper medium and density. The model was tested with our new stripper.

Improvements of PKUAMS for precision 14C analysis of the project of Xia–Shang–Zhou Chronology

To meet the requirements of the Xia‐Shang‐Zhou Chronology project, an upgrade of the AMS facility at Peking University has been carried out, commencing in 1996, and a new sample preparation system with high eAciency and low memory has been set up in the Department of Archaeology. A NEC MC-SNICS ion source has been installed and the injection system has been reconstructed. Computer control of the beam line has been implemented using Group 3 ControlNet, and a new data acquisition system has been developed. The alignment and vacuum of the beam line have also been improved. The upgraded system was commissioned in 1998. Subsequent experience has led to eAcient procedures for beam tuning and 14 C/ 13 C measurement. A precision of 0.5% in the 14 C/ 13 C ratio has been achieved. Many samples have now been measured for the Xia‐Shang‐Zhou Chronology project. ” 2000 Elsevier Science B.V. All

AMS radiocarbon dating of cemetery of Jin Marquises in China

Abstract Bones are very important samples to determine the hosts of the cemetery of Jin Marquises which were excavated at Tianma-Qucun site in Shanxi Province in China. In order to obtain accurate AMS radiocarbon dates, bones were pretreated by two kinds of methods, the gelatin-extraction method and the amino-acid method. Charcoals collected from the same sites were also used. The measured dates agree with historical record.

Accelerator mass spectrometry at Peking University: experiments and progress

Abstract The Peking University accelerator mass spectrometer (PKUAMS) has been put into routine operation. 14C measurements of archaeological samples with fast cycling injection have shown good results. The new multi-target high-intensity sputtering ion source has been tested and 10Be measurements were carried out with a new detector in which both the stopping of the intense flux of 10B ions and the identification of 10Be ions are performed. 26A1 samples were also measured. While various applications show good prospects for PKUAMS, further upgrade is desirable.

Data analysis and calibration of radiocarbon dating results from the cemetery of the Marquises of Jin

The chronology study of the cemetery of Marquises of Jin is valuable to improving the chronological table of Marquis of Jin family. It is also helpful for improving the chronological table of the Zhou Dynasty. The samples were measured at Peking University (PKUAMS). We also made an interlaboratory check with Isotrace to ensure the accuracy. By careful analysis of archaeological information, we built different models and calibrated by OxCal. The calibration results, both sampling contexts and estimations, are in very good agreement with the historical record. Because the dates of some events correspond to the special part of the curve, the calibration gets very high precision. The calibration result of tomb M93 suggests that its host is Marquis Shangshu instead of Marquis Wen.

The CO2 preparation system for AMS dating at Peking University

Abstract CN analyzer was already applied in CO2 preparation system for AMS dating in the Research Lab for Archaeology & the History of Art in Oxford several years ago [1] . Now a line of combustion with an Elementar Vario EL CHNS elemental analyzer was built in the Dating Lab in the Department of Archaeology at Peking University. This system has many advantages, such as obtaining purer CO2, simultaneously measuring C, N, S etc. elements and C/N. A sample gases (i.e., CO2, CO etc.) recollection system was also built in this lab to recover the CO2 in case of the failure of graphitization.