Preference analysis on the online learning attributes among senior high school students during the COVID-19 pandemic: A conjoint analysis approach.

The COVID-19 pandemic has resulted in the shift from face-to-face to fully online learning. The purpose of this study was to evaluate the preference of senior high school students on online learning attributes during the COVID-19 pandemic by utilizing a conjoint analysis approach. Six attributes which consist of delivery type, assigned tasks, evaluation, virtual laboratory, interface layout, and delivery platform were simultaneously analyzed through orthogonal design. A total of 1189 senior high school students were collected via purposive sampling approach through the social media platform. The respondents voluntarily participated and answered 29 stimuli with 2 holdouts generated by using SPSS 25 utilizing a 7-point Likert scale. The results indicated that evaluation was found to be the most significant attribute and followed by virtual laboratory, delivery type, and delivery platform. Interestingly, multiple choice evaluation, not requiring virtual laboratories, mixed delivery type (synchronous with recorded lectures), and MS Teams as delivery platform were considered as the keys for the preference. This study is the first study that utilized a conjoint approach to analyze the senior high school students' preference on the online learning attributes during the COVID-19 pandemic. Finally, the conjoint approach can be applied and extended to evaluate the online learning attributes globally by utilizing the attributes and design created in this study.

VEGF 165 b, an antiangiogenic VEGF-A isoform, binds and inhibits bevacizumab treatment in experimental colorectal carcinoma: balance of pro- and antiangiogenic VEGF-A isoforms has implications for therapy.

Bevacizumab, an anti-vascular endothelial growth factor (VEGF-A) antibody, is used in metastatic colorectal carcinoma (CRC) treatment, but responses are unpredictable. Vascular endothelial growth factor is alternatively spliced to form proangiogenic VEGF(165) and antiangiogenic VEGF(165)b. Using isoform-specific enzyme-linked immunosorbent assay and quantitative polymerase chain reaction, we found that over 90% of the VEGF in normal colonic tissue was VEGF(xxx)b, but there was a variable upregulation of VEGF(xxx) and downregulation of VEGF(xxx)b in paired human CRC samples. Furthermore, cultured colonic adenoma cells expressed predominantly VEGF(xxx)b, whereas colonic carcinoma cells expressed predominantly VEGF(xxx). However, adenoma cells exposed to hypoxia switched their expression from predominantly VEGF(xxx)b to predominantly VEGF(xxx). VEGF(165)b overexpression in LS174t colon cancer cells inhibited colon carcinoma growth in mouse xenograft models. Western blotting and surface plasmon resonance showed that VEGF(165)b bound to bevacizumab with similar affinity as VEGF(165). However, although bevacizumab effectively inhibited the rapid growth of colon carcinomas expressing VEGF(165), it did not affect the slower growth of tumours from colonic carcinoma cells expressing VEGF(165)b. Both bevacizumab and anti-VEGF(165)b-specific antibodies were cytotoxic to colonic epithelial cells, but less so to colonic carcinoma cells. These results show that the balance of antiangiogenic to proangiogenic isoforms switches to a variable extent in CRC, regulates tumour growth rates and affects the sensitivity of tumours to bevacizumab by competitive binding. Together with the identification of an autocrine cytoprotective role for VEGF(165)b in colonic epithelial cells, these results indicate that bevacizumab treatment of human CRC may depend upon this balance of VEGF isoforms.

Pharmacokinetic study of 45Ca administered intravenously following intramuscular injection of vitamin D3 or 25-hydroxyvitamin D3 in early weaned lambs.

The objective of this study was to evaluate the pharmacokinetic parameters of 45Ca administered intravenously at a dose of 50 microCi in young lambs. The experiment was performed on 18 female lambs allocated to three treatments. Six animals received intravenous calcium only; six received intramuscularly vitamin D3 8 days prior to the administration of calcium; and six received intramuscularly 25-hydroxyvitamin D3 5 days prior to the administration of calcium. Blood samples were collected from 15 min up to 8 days after the administration of 45Ca. The different pharmacokinetic parameters (area under the curve, clearance, mean residence time and volume of distribution) were estimated using non-compartmental and compartmental approaches. Statistical analysis of the results showed no significant differences in the pharmacokinetic parameters of the three groups. It can be concluded that vitamin D does not modify either the elimination or the distribution of calcium in the lambs receiving adequate dietary vitamin D.

Control of lipid membrane stability by cholesterol content.

Cholesterol has a concentration-dependent effect on membrane organization. It is able to control the membrane permeability by inducing conformational ordering of the lipid chains. A systematic investigation of lipid bilayer permeability is described in the present work. It takes advantage of the transmembrane potential difference modulation induced in vesicles when an external electric field is applied. The magnitude of this modulation is under the control of the membrane electrical permeability. When brought to a critical value by the external field, the membrane potential difference induces a new membrane organization. The membrane is then permeable and prone to solubilized membrane protein back-insertion. This is obtained for an external field strength, which depends on membrane native permeability. This approach was used to study the cholesterol effect on phosphatidylcholine bilayers. Studies have been performed with lipids in gel and in fluid states. When cholesterol is present, it does not affect electropermeabilization and electroinsertion in lipids in the fluid state. When lipids are in the gel state, cholesterol has a dose-dependent effect. When present at 6% (mol/mol), cholesterol prevents electropermeabilization and electroinsertion. When cholesterol is present at more than 12%, electropermeabilization and electroinsertion are obtained under milder field conditions. This is tentatively explained by a cholesterol-induced alteration of the hydrophobic barrier of the bilayer core. Our results indicate that lipid membrane permeability is affected by the cholesterol content.

Tertiary structure-dependence of misfolding substitutions in loops of the maltose-binding protein.

We previously identified and characterized amino acid substitutions in a loop connecting helix I to strand B, the alphaI/betaB loop, of the N-domain that are critical for in vivo folding of the maltose-binding protein (MalE31). The tertiary context-dependence of this mutation in MalE folding was assessed by probing the tolerance of an equivalent alphabeta loop of the C-domain to the same amino acid substitutions (MalE219). Moving the loop mutation from the N- to the C-domain eliminated the in vivo misfolding step that led to the formation of inclusion bodies. In vitro, both loop variants exhibited an important decrease of stability, but their intrinsic tendency to aggregate was well correlated with their periplasmic fates in Escherichia coli. Furthermore, the noncoincidence of the unfolding and refolding transition curves and increase of light scattering during the refolding of MalE31 indicate that a competing off-pathway reaction could occurs on the folding pathway of this variant. These results strongly support the notion that the formation of super-secondary structures of the N-domain is a rate-limiting step in the folding pathway of MalE.

Electroinsertion of glycophorin A in interdigitation-fusion giant unilamellar lipid vesicles.

Previously we demonstrated that transmembrane back insertion of glycophorin A, a solubilizable intrinsic protein, can be obtained in dipalmitoylphosphatidylcholine multilamellar vesicles, MLVs, by electropulsation (Raffy, S., and Teissié, J. (1995) Eur. J. Biochem. 230, 722-732). Here we report that transmembrane back insertion of protein is obtained by electropulsion of unilamellar giant vesicles, termed interdigitation-fusion vesicles (IFVs), which are better membrane models than MLVs due to their unilamellarity. Electropulsation promotes a field-dependent local permeabilization of the lipid layer, as shown by the associated leakage of entrapped calcein. Glycophorin insertion is assayed by immunofluorescence. Electroinsertion is obtained by pulsing the vesicle/protein mixture. Glycophorin insertion is observed under more drastic electrical conditions than needed for permeabilization. Direct observation of glycophorin insertion in the vesicles under a microscope shows a localized process in agreement with the theoretical prediction. A quantitative evaluation of the immunofluorescence pattern shows that insertion was higher on one side of the vesicle than on the other. This suggests that an electrophoretic movement of the solubilized glycophorin could take place during electropulsation. Insertion of glycophorin, a prefolded intrinsic protein, is then obtained in the lipid bilayer brought transiently to the electropermeabilized state.

Surface charge control of electropermeabilization and glycophorin electroinsertion with 1,2-diacyl-sn-glycero-3-phosphocholine (lecithin) liposomes.

Back insertion of a solubilized membrane protein, glycophorin A, has been obtained in lipid multilamellar vesicles by applying calibrated electric field pulses on a lipid/protein mixture. Experimental evidence for insertion is given by means of immunofluorescence. Insertion was obtained only under field conditions that induced the leakage of a soluble hydrophilic molecule, calcein, which was trapped between the lipid layers. Studies were performed on mixed liposomes where charged species were present. The critical permeabilizing field is the same whatever the composition, but with overcritical fields the associated calcein transmembraneous flow is higher with positively charged lipids. Field conditions that where prone to trigger glycophorin insertion were similar to those that induced electropermeabilization. No electroinsertion has been obtained with stearylamine (SteNH2)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (Pam2GroPCho) liposomes under the same conditions. Calcein efflux as well as glycophorin insertion are controlled by the electric surface charge of the host liposome. These observations confirm our previous conclusions that spontaneous membrane protein insertion is obtained when the host membrane is brought to its electropermeabilized state, but show that a strong control due to the surface charges is nevertheless present.

Insertion of glycophorin A, a transmembraneous protein, in lipid bilayers can be mediated by electropermeabilization.

Transmembraneous back-insertion of a solubilized membrane protein, glycophorin A, has been obtained in 1,2 dipalmitoyl-sn-glycero-3-phosphocholine (Pam2GroPCho) cell-size-like liposomes by submitting the lipid/protein mixture to calibrated electric field pulses. Field conditions which are prone to trigger glycophorin insertion are similar to those which mediate lipid layer electropermeabilization. The efflux of calcein, trapped in the liposomes during their preparation, was observed only when field strength is higher than 1.3 kV/cm. Electroinsertion was detected only above the same critical field intensity. Calcein efflux as well as glycophorin insertion were increased by increasing field intensity, pulse duration and/or number of pulses. Experimental evidence of protein insertion was provided by physico-chemical as well as biochemical methods. Direct observation of the pulsed vesicles under the microscope revealed the insertion by means of immunofluorescence and fluorescence. Electroinsertion of fluorescent glycophorin A revealed that the inner bilayers were also labeled. The gel-to-liquid phase transition temperature of Pam2GroPCho decreased after insertion but its cooperativity was not affected. A narrow 31P-NMR peak was observed after electroinsertion showing that the polar headgroups of phospholipids had been altered. Analysis of trypsin-digested peptides revealed that the two trans-orientations of the protein across the external lipid layer were present after electroinsertion. Localized perturbation of the polar headgroup region of phospholipids, which supports the transient permeabilization of lipid layers, allows spontaneous transinsertion of glycophorin across the lipid bilayers.