Presentations of coronavirus disease 2019 (COVID-19) range from asymptomatic to severe pneumonia with respiratory failure that can lead to invasive mechanical ventilation and/or death.^1,2 In patients with COVID-19 and severe lung disease, hyperinflammation is frequently observed, with an increased plasma concentrations of various proinflammatory cytokines, including interleukin (IL)-6, and acute phase reactants.^3-5 This exaggerated inflammatory response caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents one of the most important negative prognostic factors in these patients.⁶

Background —Native and oxidized LDLs (n-LDL and ox-LDL) are involved in the atherogenic process and affect endothelium-dependent vascular tone through their interaction with nitric oxide (NO). Methods and Results —In this study we evaluated directly, by using a porphyrinic microsensor, the effect of increasing lipoprotein concentrations on endothelial NO and superoxide (O ₂ ⁻ ) production. We investigated where lipoproteins may affect the l -arginine–NO pathway by pretreating cells with l -arginine, l - N -arginine methyl ester (L-NAME), and superoxide dismutase. Bovine aortic endothelial cells were exposed for 1 hour to increasing concentrations of n-LDL (from 0 to 240 mg cholesterol/dL) and ox-LDL (from 0 to 140 mg cholesterol/dL). A stimulated (calcium ionophore) NO concentration decreased to 29% of the control at n-LDL concentration of 80 mg cholesterol/dL and to 15% of the control at 20 mg cholesterol/dL of ox-LDL. l -Arginine partially neutralized the inhibitory effect of n-LDL and ox-LDL on the NO generation. Superoxide dismutase pretreatment did not modify NO production, whereas L-NAME blunted NO generation at all LDL concentrations. O ₂ ⁻ production was increased at low n-LDL and very low ox-LDL concentrations; this was reversed by l -arginine. Conclusions —These findings confirm the inhibitory role of n-LDL and ox-LDL on NO generation and suggest that lipoproteins may induce a decreased uptake of l -arginine. The local depletion of the l -arginine substrate may derange the NO synthase, leading to overproduction of O ₂ ⁻ from oxygen, the other substrate of NO synthase.

This investigation aimed to compare the response of young and older adult men to bed rest (BR) and subsequent rehabilitation (R). Sixteen older (OM, age 55-65 yr) and seven young (YM, age 18–30 yr) men were exposed to a 14-day period of BR followed by 14 days of R. Quadriceps muscle volume (QVOL), force (QF), and explosive power (QP) of leg extensors; single-fiber isometric force (Fo); peak aerobic power (V̇o_2peak); gait stride length; and three metabolic parameters, Matsuda index of insulin sensitivity, postprandial lipid curve, and homocysteine plasma level, were measured before and after BR and after R. Following BR, QVOL was smaller in OM (−8.3%) than in YM (−5.7%, P = 0.031); QF (−13.2%, P = 0.001), QP (−12.3%, P = 0.001), and gait stride length (−9.9%, P = 0.002) were smaller only in OM. Fo was significantly smaller in both YM (−32.0%) and OM (−16.4%) without significant differences between groups. V̇o_2peak decreased more in OM (−15.3%) than in YM (−7.6%, P < 0.001). Instead, the Matsuda index fell to a greater extent in YM than in OM (−46.0% vs. −19.8%, respectively, P = 0.003), whereas increases in postprandial lipid curve (+47.2%, P = 0.013) and homocysteine concentration (+26.3%, P = 0.027) were observed only in YM. Importantly, after R, the recovery of several parameters, among them QVOL, QP, and V̇o_2peak, was not complete in OM, whereas Fo did not recover in either age group. The results show that the effect of inactivity on muscle mass and function is greater in OM, whereas metabolic alterations are greater in YM. Furthermore, these findings show that the recovery of preinactivity conditions is slower in OM.