[Research on early warning model of the hearing loss of workers exposed to noise]

Objective: To explore the change of hearing threshold of workers exposed to noise, establish an individual-based hearing loss early warning model, accurately and differentiated the health of workers exposed to noise. Methods: In September 2019, all physical examination data of 561 workers exposed to noise from an enterprise were collected since their employment. Three indicators of average hearing threshold of the better ear, namely, at high frequency, 4000 Hz and speech frequency, were constructed. The generalized estimating equation (GEE) was used to adjust gender and age and establish the warning model of each indicator. Finally, sensitive indicators and warning models were screened according to AUC and Yoden index. Results: Among the 561 workers exposed to noise, 26 (4.6%) workers had hearing loss. The sensitivity indicators were the average hearing threshold at speech frequency ≥20 dB, high frequency ≥30 dB and 4000 Hz ≥25 dB. The AUC of each index was 0.602, 0.794 and 0.804, and the Youden indexes were 0.204, 0.588 and 0.608, respectively. In GEE of hearing loss warning models, high-frequency hearing threshold ≥20 dB and 4000 Hz hearing threshold ≥25 dB were the optimal models, with AUC of 0.862. Conclusion: Combined with the changes of individual hearing threshold over the years, can accurately assess the risk of individual hearing loss of workers exposed to noise.

[Discussion on the application of ventilatory threshold in classification of physical workload in plateau]

Objective: To explore the application of the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2) in the classification of physical workload for plateau workers, to provide reference for formulating the classification in plateau. Methods: In August 2018, 88 male workers from substations at different altitudes (500 m, 2000 m, 3000 m and 4000 m) of a company were selected as study subjects by cluster sampling. They were divided into plain group and plateau groups.The intensities of workload were simulated by power bicycle, and physiologic parameters, including VO(2), heart rate (HR) and energy metabolic rate per body surface area (E/BSA) , were recorded in test system when reaching VT1, VT2 and peak oxygen uptake (VO(2)Peak) . The ratios of VT1, VT2 and VO(2)Peak to the quiet and work potential at different altitudes were compared. Results: In a quiet state, compared with the plain group, the HR and E/BSA of the workers in the 2000 m and 3000 m groups increased, and the differences were statistically significant (P<0.05) . At VT2, compared with the plain group, the HR of the workers in the 4000 m group decreased, the difference was statistically significant (P<0.05) . VO(2) and E/BSA of workers in each plateau group were lower than those in the plain group at VO(2)Peak, and the differences were statistically significant (P<0.05) . At VT2 and VO(2)Peak, the ratios of VO(2), HR, and E/BSA relative to the quiet state of the workers in each plateau group were lower than those of the plain group, and the differences were statistically significant (P<0.05) . In the quiet state and VT1, compared with the plain group, the remaining percentages of VO(2) and E/BSA of workers in each plateau group decreased, and the differences were statistically significant (P<0.05) . Taking VT1, VT2 and VO(2)Peak as cut-off points and VO(2), HR and E/BSA as indicators, the physical workload in plateau could be divided into four levels, namely medium, heavy, extremely heavy and extreme physical workload. Conclusion: It is practicable to use ventilatory threshold to classification of physical workload. VT1 and VT2 can be applied to the classification in plateau to supplement and optimize current national standard of physical workload.

Abrogation of DNA vector-based RNAi during apoptosis in mammalian cells due to caspase-mediated cleavage and inactivation of Dicer-1

RNA interference (RNAi) is used as a reverse-genetic tool to examine functions of a gene in different cellular processes including apoptosis. As key cellular proteins are inactivated during apoptosis, and as RNAi requires cooperation of many cellular proteins, we examined whether DNA vector-based RNAi would continue to function during apoptosis. The short hairpin RNA transcribed from the DNA vector is processed by Dicer-1 to form small interfering RNA that is incorporated in the RNA-induced silencing complex (RISC) to guide a sequence-specific silencing of the target mRNA. We report here that DNA vector-based RNAi of three different genes, namely poly(ADP-ribose) polymerase-1, p14(ARF) and lamin A/C are abrogated during apoptosis. The failure of DNA vector-based RNAi was not at the level of Ago-2 or RISC-mediated step of RNAi but due to catalytic inactivation of Dicer-1 on specific cleavage at the STTD(1476) and CGVD(1538) sites within its RNase IIIa domain. Using multiple approaches, caspase-3 was identified as the major caspase responsible for the cleavage and inactivation of Dicer-1. As Dicer-1 is also the common endonuclease required for formation of microRNA (miRNA) in mammalian cells, we observed decreased levels of mature forms of miR-16, miR-21 and let-7a. Our results suggest a role for apoptotic cleavage and inactivation of Dicer-1 in controlling apoptotic events through altered availability of miRNA.