COVID-19 is the current public health threat all over the world. Unfortunately, there is no specific prevention and treatment strategy for this disease. We aim to explore the potential role of angiotensin-converting enzyme 2 (ACE2) in this regard through this literature review. As a crucial enzyme of renin-angiotensin-aldosterone system (RAAS), ACE2 not only mediates the virus entry but also affects the pathophysiological process of virus-induced acute lung injury (ALI), as well as other organs’ damage. As interaction of COVID-19 virus spike and ACE2 is essential for virus infection, COVID-19-specific vaccine based on spike protein, small molecule compound interrupting their interaction, human monoclonal antibody based on receptor-binding domain, and recombinant human ACE2 protein (rhuACE2) have aroused the interests of researchers. Meanwhile, ACE2 could catalyze angiotensin II (Ang II) to form angiotensin 1-7 (Ang 1-7), thus alleviates the harmful effect of Ang II and amplifies the protection effect of Ang1-7. ACE inhibitor and angiotensin II receptor blocker (ARB) have been shown to increase the level of expression of ACE2 and could be potential strategies in protecting lungs, heart, and kidneys. ACE2 plays a very important role in the pathogenesis and pathophysiology of COVID-19 infection. Strategies targeting ACE2 and its ligand, COVID-19 virus spike protein, may provide novel method in the prevention and management of novel coronavirus pneumonia.

Objective— We aimed to assess whether exposure to higher levels of ambient air pollution impairs HDL (high-density lipoprotein) function and to elucidate the underlying biological mechanisms potentially involved. Approach and Results— In the Beijing AIRCHD study (Air Pollution and Cardiovascular Dysfunction in Healthy Adults), 73 healthy adults (23.3±5.4 years) were followed-up with 4 repeated study visits in 2014 to 2016. During each visit, ambient air pollution concentrations, HDL function metrics, and parameters of inflammation and oxidative stress were measured. Average daily concentrations of ambient particulate matter in diameter <2.5 μm were 62.9 µg/m 3 (8.1–331.0 µg/m 3 ). We observed significant decreases in HDL cholesterol efflux capacity of 2.3% (95% CI, −4.3 to −0.3) to 5.0% (95% CI, −7.6 to −2.4) associated with interquartile range increases in moving average concentrations of particulate matter in diameter <2.5 μm and traffic-related air pollutants (black carbon, nitrogen dioxide, and carbon monoxide) during the 1 to 7 days before each participant’s clinic visit. Higher ambient air pollutant levels were also associated with significant reductions in circulating HDL cholesterol and apoA-I (apolipoprotein A-I), as well as elevations in HDL oxidation index, oxidized LDL (low-density lipoprotein), malondialdehyde, and high-sensitivity C-reactive protein. Conclusions— Higher ambient air pollution concentrations were associated with impairments in HDL functionality, potentially because of systemic inflammation and oxidative stress. These novel findings further our understanding of the mechanisms whereby air pollutants promote cardiometabolic disorders.

The stability of single-sideband (SSB) modulator based recirculating frequency shifter (RFS) is analyzed theoretically. The optimum radio frequency (RF) drive peak-to-peak voltage used to drive the modulator is studied with considering the amplified spontaneous emission (ASE) noise of optical amplifier and crosstalk so as to obtain a maximum overall effective optical signal to noise ratio (OSNR) which is defined to quantify the quality of generated tones. Small desired tones number and lower RF peak-to-peak voltage can reduce the crosstalk effectively. While the trade-off should be considered since the larger desired tones number it is, the higher optimum drive voltage should be used when the SSB-based RFS reached the maximum OSNR. The theoretical results show that the optimum operation condition is helpful to improve the performance of RFS which can be a good application for the T-bit/s optical transmission in practice.