Angiotensin II-pretreated hucMSCs attenuate inflammation and reverse pulmonary fibrosis in SD rat lung (preprint)

Background: Pulmonary fibrosis (PF) is an irreversible disease with a poor prognosis and a serious impact on patients' health. PF is also associated with COVID-19, especially in immunocompromised people. Herein, efforts have been made to treat PF using pretreatment of human umbilical cord mesenchymal stem cells (hucMSCs) with angiotensin II (Ang II) as a novel therapeutic method. Methods: PF model of Sprague Dawley (SD) rats were established by tracheal injection of bleomycin (BLM) (5U/Kg). On day 15 after modeling, PBS, hucMSCs or hucMSCs-Ang II were injected into tail vein. On the 23rd day after modeling, samples were taken and corresponding indexes were tested.Results: Our results first showed that Ang II pretreatment induced more hucMSCs to reach the injured lung and alleviated pulmonary fibrosis. Transplantation of hucMSCs-Ang II reduced inflammatory infiltration, increased IL-10 expression and enhanced macrophage matrix-metallopeptidase-9 (MMP-9) expression for collagen degradation. Moreover, the Ang II-treated hucMSCs decreased hydroxyproline (HYP) and alpha-smooth muscle actin (α-SMA) expression in SD rats and promoted collagen and collagen fiber degradation.Conclusions: Ang II pretreatment enhanced the homing ability of hucMSCs, and hucMSCs-Ang II transplantation reversed PF by inhibiting inflammation and promoting collagen and collagen fiber degradation, promising its clinical application in the treatment of post-inflammatory PF caused by various disorders, including COVID-19 and related pneumonia. 

Face Masks Against COVID-19: An Evidence Review (preprint)

The science around the use of masks by the general public to impede COVID-19 transmission is advancing rapidly. Policymakers need guidance on how masks should be used by the general population to combat the COVID-19 pandemic. In this narrative review, we develop an analytical framework to examine mask usage, considering and synthesizing the relevant literature to inform multiple areas: population impact; transmission characteristics; source control; PPE; sociological considerations; and implementation considerations. A primary route of transmission of COVID-19 is via respiratory droplets, and is known to be transmissible from presymptomatic and asymptomatic individuals. Reducing disease spread requires two things: first, limit contacts of infected individuals via physical distancing and other measures, and second, reduce the transmission probability per contact. The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at reducing spread of the virus when compliance is high. The decreased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Given the current shortages of medical masks we recommend the adoption of public cloth mask wearing, as an effective form of source control, in conjunction with existing hygiene, distancing, and contact tracing strategies. Because many respiratory droplets become smaller due to evaporation, we recommend increasing focus on a previously overlooked aspect of mask usage: mask-wearing by infectious people ("source control") with benefits at the population-level, rather than mask-wearing by susceptible people, such as health-care workers, with focus on individual outcomes. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.

Calibrated Intervention and Containment of the COVID-19 Pandemic (preprint)

Within a short period of time, COVID-19 grew into a world-wide pandemic. Transmission by pre-symptomatic and asymptomatic viral carriers rendered intervention and containment of the disease extremely challenging. Based on reported infection case studies, we construct an epidemiological model that focuses on transmission around the symptom onset. The model is calibrated against incubation period and pairwise transmission statistics during the initial outbreaks of the pandemic outside Wuhan with minimal non-pharmaceutical interventions. Mathematical treatment of the model yields explicit expressions for the size of latent and pre-symptomatic subpopulations during the exponential growth phase, with the local epidemic growth rate as input. We then explore reduction of the basic reproduction number R_0 through specific disease control measures such as contact tracing, testing, social distancing, wearing masks and sheltering in place. When these measures are implemented in combination, their effects on R_0 multiply. We also compare our model behaviour to the first wave of the COVID-19 spreading in various affected regions and highlight generic and less generic features of the pandemic development.