Hysteresis response of daytime net ecosystem exchange during drought

Continuous measurements of net ecosystem CO<sub>2</sub> exchange (NEE) using the eddy-covariance method were made over an agricultural ecosystem in the southeastern US. During optimum environmental conditions, photosynthetically active radiation (PAR) was the primary driver controlling daytime NEE, accounting for as much as 67 to 89% of the variation in NEE. However, soil water content became the dominant factor limiting the NEE-PAR response during the peak growth stage. NEE was significantly depressed when high PAR values coincided with very low soil water content. The presence of a counter-clockwise hysteresis of daytime NEE with PAR was observed during periods of water stress. This is a result of the stomatal closure control of photosynthesis at high vapor pressure deficit and enhanced respiration at high temperature. This result is significant since this hysteresis effect limits the range of applicability of the Michaelis-Menten equation and other related expressions in the determination of daytime NEE as a function of PAR. The systematic presence of hysteresis in the response of NEE to PAR suggests that the gap-filling technique based on a non-linear regression approach should take into account the presence of water-limited field conditions. Including this step is therefore likely to improve current evaluation of ecosystem response to increased precipitation variability arising from climatic changes

Association of arterial stiffness with single nucleotide polymorphism rs1333049 and metabolic risk factors

The electronic version of this article is the complete one and can be found online at: http://www.cardiab.com/content/12/1/93. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.BACKGROUND: Increased arterial stiffness is a cardiovascular outcome of metabolic syndrome (MetS). The chromosome 9p21 locus has been identified as a major locus for risk of coronary artery disease (CAD). The single nucleotide polymorphism (SNP), rs1333049 on chromosome 9p21.3 has been strongly associated with CAD and myocardial infarction. Increased arterial stiffness could be the link between the 9p21 polymorphism and increased cardiovascular risk. Since the impact of a genetic polymorphism on arterial stiffness especially in Asian populations has not been well defined, we aimed to investigate the association of arterial stiffness with rs 1333049 variant on chromosome 9p21.3 in Thai subjects with and without MetS risk factors. METHODS: A total of 208 Thai subjects, aged 35-75 years, 135 with and 73 without MetS, according to IDF and NCEP-ATPIII criteria, were included in this study. Aortic-femoral pulse wave velocity (afPWV), brachial-ankle pulse wave velocity (baPWV) and aortic ankle pulse wave velocity (aaPWV) were measured and used as markers of arterial stiffness. The chromosome 9p21.3 locus, represented by the rs 1333049 variant and blood biochemistry were evaluated. RESULTS: Arterial stiffness was elevated in subjects with MetS when compared with nonMetS subjects. PWV, especially afPWV increased progressively with increasing number of MetS risk factors (r = 0.322, P <0.001). We also found that the frequency distribution of the rs1333049 genotypes is significantly associated with the afPWV (P <0.05). In multivariate analyses, there was an association between homozygous C allele and afPWV (Odds ratio (OR), 8.16; 95% confidence interval (CI), 1.91 to 34.90; P = 0.005), while the GC genotype was not related to afPWV (OR, 1.79; 95% CI, 0.84 to 3.77; P = 0.129) when compared with the GG genotype. CONCLUSIONS: Our findings demonstrate for the first time that arterial stiffness is associated with genetic polymorphism in 9p21 and metabolic risk factors in a Thai population

Group versus modified individual standard-setting on multiple-choice questions with the Angoff method for fourth-year medical students in the internal medicine clerkship

Vichai Senthong,1,* Jarin Chindaprasirt,1,* Kittisak Sawanyawisuth,1 Noppadol Aekphachaisawat,2 Suteeraporn Chaowattanapanit,1 Panita Limpawattana,1 Charoen Choonhakarn,1 Aumkhae Sookprasert1 1Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand; 2Central Library, Silpakorn University, Bangkok, Thailand *These authors contributed equally to this work Background: The Angoff method is one of the preferred methods for setting a passing level in an exam. Normally, group meetings are required, which may be a problem for busy medical educators. Here, we compared a modified Angoff individual method to the conventional group method. Methods: Six clinical instructors were divided into two groups matched by teaching experience: modified Angoff individual method (three persons) and conventional group method (three persons). The passing scores were set by using the Angoff theory. The groups set the scores individually and then met to determine the passing score. In the modified Angoff individual method, passing scores were judged by each instructor and the final passing score was adjusted by the concordance method and reliability index. Results: There were 94 fourth-year medical students who took the test. The mean (standard deviation) test score was 65.35 (8.38), with a median of 64 (range 46&ndash;82). The three individual instructors took 45, 60, and 60 minutes to finish the task, while the group spent 90 minutes in discussion. The final passing score in the modified Angoff individual method was 52.18 (56.75 minus 4.57) or 52 versus 51 from the standard group method. There was not much difference in numbers of failed students by either method (four versus three). Conclusion: The modified Angoff individual method may be a feasible way to set a standard passing score with less time consumed and more independent rather than group work by instructors. Keywords: Angoff, individual, passing score, standard-setting, multiple-choice questions, internal medicin

The nitrosated bile acid DNA lesion O6-carboxymethylguanine is a substrate for the human DNA repair protein O6-methylguanine-DNA methyltransferase

The consumption of red meat is a risk factor in human colorectal cancer (CRC). One hypothesis is that red meat facilitates the nitrosation of bile acid conjugates and amino acids, which rapidly convert to DNA-damaging carcinogens. Indeed, the toxic and mutagenic DNA adduct O(6)-carboxymethylguanine (O(6)-CMG) is frequently present in human DNA, increases in abundance in people with high levels of dietary red meat and may therefore be a causative factor in CRC. Previous reports suggested that O(6)-CMG is not a substrate for the human version of the DNA damage reversal protein O(6)-methylguanine-DNA methyltransferase (MGMT), which protects against the genotoxic effects of other O(6)-alkylguanine lesions by removing alkyl groups from the O(6)-position. We now show that synthetic oligodeoxyribonucleotides containing the known MGMT substrate O(6)-methylguanine (O(6)-MeG) or O(6)-CMG effectively inactivate MGMT in vitro (IC(50) 0.93 and 1.8 nM, respectively). Inactivation involves the removal of the O(6)-alkyl group and its transfer to the active-site cysteine residue of MGMT. O(6)-CMG is therefore an MGMT substrate, and hence MGMT is likely to be a protective factor in CRC under conditions where O(6)-CMG is a potential causative agent