Application of LASSO and its extended method in variable selection of regression analysis / 中华预防医学杂志

Multicollinearity is an important issue affecting the results of regression analysis. LASSO developed in recent years has great advantages in selecting explanatory variables, processing high-dimensional data, and solving multicollinearity problems. This method adds a penalty term to the model estimation, which can compress the regression coefficients of some unnecessary variables to zero and then remove them from the model to achieve the purpose of variable screening. This paper focuses on the LASSO method and compares it with optimal subsets, ridge regression, adaptive LASSO, and elastic net results. It is found that both LASSO and adaptive LASSO have good performance in solving independent variable multicollinearity problems and enhancing model interpretation and prediction accuracy.

[Sources, Distribution, and Fluxes of Major and Trace Elements in the Yangtze River].

Surface water samples were collected from 20 sampling sites in the main stream and its major tributaries of the Yangtze River from April to May 2017. The concentrations of dissolved trace and major elements were analyzed to determine the spatial variation, source identification, and riverine fluxes using various multivariate statistical techniques, including correlation analysis, principal component analysis (PCA), and cluster analysis (CA) with the goal of determining the influence of natural factors and human activities, including the operation of the Three Gorges Dam on the distribution and loading of major and trace elements in the Yangtze River water environment. Spatial distribution results showed that Cu, Zn, Pb, Cd, and As were the major elements affected by human activities in the Yangtze River, and their concentrations downstream were significantly higher than those in the middle and upper reaches (P<0.05). All elements had fairly high concentration values in both channels of the Yangtze River mainstream in Chongqing city and Hanjiang River in Wuhan city, which were mainly related to the enhanced human activities. However, the low concentrations of multi-elements in the reach of the Yangtze River in Yichang were largely caused by the retention effect of Three Gorges Project on element transport, which decreased the riverine loadings of multi-elements. Principal component analysis (PCA) indicated that Na, Mg, K, Ca, Fe, Mn, Co, Ni, Mo, Cr, and V were mainly associated with the weathering and erosion of various rocks and minerals in the river basin. And Cu, Zn, and Pb were mainly affected by enhanced human activities, such as industrial wastewater, metal smelting, and mineral mining, whereas Cd and As were mainly related to agricultural activities. The spatial distribution of trace and major elements showed that concentrations of some elements in the Yangtze River channels were enhanced by human activities. Generally, the heavy metal pollution in the Yangtze River Basin was lower than that in other rivers of the world. However, the annual fluxes of Cu, Zn, Pb, Cd, and As could have far-reaching ecological effects on the Yangtze River estuary and offshore ecological environment.

Glutathione homeostasis and Cd tolerance in the Arabidopsis sultr1;1-sultr1;2 double mutant with limiting sulfate supply.

KEY MESSAGE: Cadmium sensitivity in sultr1;1 - sultr1;2 double mutant with limiting sulfate supply is attributed to the decreased glutathione content that affected oxidative defense but not phytochelatins' synthesis. In plants, glutathione (GSH) homeostasis plays pivotal role in cadmium (Cd) detoxification. GSH is synthesized by sulfur (S) assimilation pathway. Many studies have tried to investigate the role of GSH homeostasis on Cd tolerance using mutants; however, most of them have focused on the last few steps of S assimilation. Until now, mutant evidence that explored the relationship between GSH homeostasis on Cd tolerance and S absorption is rare. To further reveal the role of GSH homeostasis on Cd stress, the wild-type and a sultr1;1-sultr1;2 double mutant which had a defect in two distinct high-affinity sulfate transporters were used in this study. Growth parameters, biochemical or zymological indexes and S assimilation-related genes' expression were compared between the mutant and wild-type Arabidopsis plants. It was found that the mutations of SULTR1;1 and SULTR1;2 did not affect Cd accumulation. Compared to the wild-type, the double mutant was more sensitive to Cd under limited sulfate supply and suffered from stronger oxidative damage. More importantly, under the same condition, lower capacity of S assimilation resulted in decreased GSH content in mutant. Faced to the limited GSH accumulation, mutant seedlings consumed a large majority of GSH in pool for the synthesis of phytochelatins rather than participating in the antioxidative defense. Therefore, homeostasis of GSH, imbalance between antioxidative defense and severe oxidative damage led to hypersensitivity of double mutant to Cd under limited sulfate supply.

[Study on fluorescence labeling and determination of polypeptide (PC2~PC6) by high performance liquid chromatography].

This study was based on the thiol groups (-SH) of PC2~PC6, which could be reacted with the Monobromobimane (mBBr), in order to get polypeptide derivatives with fluorescent signal. A new method was developed for measuring the Polypeptides by high performance liquid chromatography with fluorescence detector, then the chromatographic conditions of HPLC was optimized; meawhile the reaction proportion of PCs and mBBr was identified by Trap-MS. The results showed that, the reaction proportion of PCs and mBBr was 1:1, the polypeptide derivatives had good stability; the five compounds separation was better, and the peak time focused on the 16.6~22.0 min; the linear correlation coefficient of PC2, PC3, PC4, PC5 and PC6 was >0.9991, and the limits of quantification were 0.3, 0.05, 0.3, 0.5 and 0.8 mg · L(-1) respectively, the recovery rate was 83.0%-102.0%; the method was reproducible, RSD<2%, this method for measuring the peptide compounds was rapid and accurate.

[Determination and distribution patterns analysis of rare earth elements in sediments of Prydz Bay].

A sensitive quantificational method was developed for the analysis of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, etc. in sediments of Prydz Bay by inductively coupled plasma mass spectrometry, and then the REE distribution patterns were analyzed. The samples were digested by microwave using HNO3-H2O2-HF as oxidant. The results showed that the total contents of rare earth elements in eight sites ranged from 117.35 to 348.63 microg x g(-1) and the maximum value was 2.97 times of the minimum value. The REE distribution patterns of different sites in sediments were basically identical and there was an obvious fractionation between LREEs and HREEs. The linear correlation of the method was preferable (r=0.999 7 - 1.000 0). The RSDs (n=3) were no more than 5.0%, and the relative errors were no more than 10%. The detection limits of rare earth elements reached ng x L(-1) level except for Sc. This method was suitable for the analysis of REEs in sediments with the advantages of rapidness, simplicity, high precision and accuracy.

[Nonradioactive iodine-labeled antibodies-inductively coupled plasma mass spectrometry for immunoassay].

In the present study, the system of nonradioactive iodine-labeled-antibodies linking inductively coupled plasma mass spectrometry for immunoassay was reported. The goat-anti-Escherichia coli and goat anti rabbit were considered as simulant antigen and antibody respectively in order to establish a new method of immunoassay by inductively coupled plasma mass spectrometry which has the advantage of high sensitivity, low detection limit and preferable linearity range. During the experiment, the N-bromosuccinimide, a mild oxidant, was used to oxidize the non-radioactive iodine (127 I) that labeled the protein. The method of nonradioactive iodine labeled protein was established and the best labeling condition was explored. The compound of I was purified by Sephadex G50 column chromatography, then the stability and activity were examined. The results showed that the labeling program was simple, reaction time was within two minutes, the labeling yield achieved 63.12% and none of I shed from the compound after 96 hours. The simulant antigen and antibody reacted on polystyrene microtiter plate and the I was detected by ICP-MS, the detection limit of the method was 0.12 mg x L(-1), relative standard deviation (n = 9) was less than 3% and the linearly dependent coefficient was 0.998 7. This system can also be used in analysis of other protein, nucleic acid and so on.