Time-dependent response of A549 cells upon exposure to cadmium

Cadmium is considered one of the most harmful carcinogenic heavy metals in the human body. Although many scientists have performed research on cadmium toxicity mechanism, the toxicokinetic process of cadmium toxicity remains unclear. In the present study, the kinetic response of proteome in/and A549 cells to exposure of exogenous cadmium was profiled. A549 cells were treated with cadmium sulfate (CdSO₄ ) for different periods and expressions of proteins in cells were detected by two-dimensional gel electrophoresis. The kinetic expressions of proteins related to cadmium toxicity were further investigated by reverse transcription-polymerase chain reaction and western blotting. Intracellular cadmium accumulation and content fluctuation of several essential metals were observed after 0-24 hours of exposure by inductively coupled plasma mass spectrometry. Fifty-four protein spots showed significantly differential responses to CdSO₄ exposure at both 4.5 and 24 hours. From these proteins, four expression patterns were concluded. Their expressions always exhibited a maximum abundance ratio after CdSO₄ exposure for 24 hours. The expression of metallothionein-1 and ZIP-8, concentration of total protein, and contents of cadmium, zinc, copper, cobalt and manganese in cells also showed regular change. In synthesis, the replacement of the essential metals, the inhibition of the expression of metal storing protein and the activation of metal efflux system are involved in cadmium toxicity.

In Situ Atomic-Scale Study of Particle-Mediated Nucleation and Growth in Amorphous Bismuth to Nanocrystal Phase Transformation

Understanding classical and nonclassical mechanisms of crystal nucleation and growth at the atomic scale is of great interest to scientists in many disciplines. However, fulfilling direct atomic-scale observation still poses a significant challenge. Here, by taking a thin amorphous bismuth (Bi) metal nanosheet as a model system, direct atomic resolution of the crystal nucleation and growth initiated from an amorphous state of Bi metal under electron beam inside an aberration-corrected transmission electron microscope is provided. It is shown that the crystal nucleation and growth in the phase transformation of Bi metal from amorphous to crystalline structure takes place via the particle-mediated nonclassical mechanism instead of the classical atom-mediated mechanism. The dimension of the smaller particles in two contacted nanoparticles and their mutual orientation relationship are critical to governing several coalescence pathways: total rearrangement pathway, grain boundary migration-dominated pathway, and surface migration-dominated pathway. Sequential strain analyses imply that migration of the grain boundary is driven by the strain difference in two Bi nanocrystals and the coalescence of nanocrystals is a defect reduction process. The findings may provide useful information to clarify the nanocrystal growth mechanisms of other materials on the atomic scale.

Mechanisms of starch digestion by α-amylase-Structural basis for kinetic properties

Recent studies of the mechanisms determining the rate and extent of starch digestion by α-amylase are reviewed in the light of current widely-used classifications for (a) the proportions of rapidly-digestible (RDS), slowly-digestible (SDS), and resistant starch (RS) based on in vitro digestibility, and (b) the types of resistant starch (RS 1,2,3,4…) based on physical and/or chemical form. Based on methodological advances and new mechanistic insights, it is proposed that both classification systems should be modified. Kinetic analysis of digestion profiles provides a robust set of parameters that should replace the classification of starch as a combination of RDS, SDS, and RS from a single enzyme digestion experiment. This should involve determination of the minimum number of kinetic processes needed to describe the full digestion profile, together with the proportion of starch involved in each process, and the kinetic properties of each process. The current classification of resistant starch types as RS1,2,3,4 should be replaced by one which recognizes the essential kinetic nature of RS (enzyme digestion rate vs. small intestinal passage rate), and that there are two fundamental origins for resistance based on (i) rate-determining access/binding of enzyme to substrate and (ii) rate-determining conversion of substrate to product once bound.