Background Thromboembolic disease is a frequent cause of death during SARS CoV-2 infection. Lupus anticoagulant (LA) appears frequently during the acute phase of infection. It is not clear whether it is merely an epiphenomenon or whether it is related to the patients' outcome. Methods Prospective observational cohort of 211 patients (118 women, mean age 65 years, range: 18 to 99) hospitalized for COVID-19. All patients were tested for LA at admission and retested six months after discharge. Results The LA test was positive in 128 patients (60.7%). The survival probability at 31 days was clearly worse in the LA-positive group (60%) than in the LA-negative group (90%) ( P = 0.023). This notable difference in survival was confirmed by multivariate analysis (HR 3.9, 95% CI 1.04–14.5, P = 0.04). However, it was not explained by differences in thrombotic events (three in either group, P = 0.6). LA-positive patients had higher ferritin, CRP and IL-6 levels, and lower PAFI ratio and lymphocyte and platelet counts. Six months after discharge, LA was negative in the vast majority of positive cases (94%). Conclusion LA is an independent predictor of in-hospital mortality in COVID-19 patients. It is associated with inflammation and disease severity but not with thromboembolic events. This marker usually disappears at six months.

Cardiac glycosides are a group of compounds widely known for their action in cardiac tissue, some of which have been found to be endogenously produced (ECG). We have previously studied the effect of ouabain, an endogenous cardiac glycoside, on the physiology of epithelial cells, and we have shown that in concentrations in the nanomolar range, it affects key properties of epithelial cells, such as tight junction, apical basolateral polarization, gap junctional intercellular communication (GJIC), and adherent junctions. In this work, we study the influence of digoxin and marinobufagenin, two other endogenously expressed cardiac glycosides, on GJIC as well as the degree of transepithelial tightness due to tight junction integrity (TJ). We evaluated GJIC by dye transfer assays and tight junction integrity by transepithelial electrical resistance (TER) measurements, as well as immunohistochemistry and western blot assays of expression of claudins 2 and 4. We found that both digoxin and marinobufagenin improve GJIC and significantly enhance the tightness of the tight junctions, as evaluated from TER measurements. Immunofluorescence assays show that both compounds promote enhanced basolateral localization of claudin-4 but not claudin 2, while densitometric analysis of western blot assays indicate a significantly increased expression of claudin 4. These changes, induced by digoxin and marinobufagenin on GJIC and TER, were not observed on MDCK-R, a modified MDCK cell line that has a genetically induced insensitive α1 subunit, indicating that Na-K-ATPase acts as a receptor mediating the actions of both ECG. Plus, the fact that the effect of both cardiac glycosides was suppressed by incubation with PP2, an inhibitor of c-Src kinase, PD98059, an inhibitor of mitogen extracellular kinase-1 and Y-27632, a selective inhibitor of ROCK, and a Rho-associated protein kinase, indicate altogether that the signaling pathways involved include c-Src and ERK1/2, as well as Rho-ROCK. These results widen and strengthen our general hypothesis that a very important physiological role of ECG is the control of the epithelial phenotype and the regulation of cell-cell contacts.

Ouabain is a cardiac glycoside, initially isolated from plants, and currently thought to be a hormone since some mammals synthesize it endogenously. It has been shown that in epithelial cells, it induces changes in properties and components related to apical–basolateral polarity and cell–cell contacts. In this work, we used a whole-cell patch clamp to test whether ouabain affects the properties of the voltage-gated potassium currents (Ik) of epithelial cells (MDCK). We found that: (1) in cells arranged as mature monolayers, ouabain induced changes in the properties of Ik; (2) it also accelerated the recovery of Ik in cells previously trypsinized and re-seeded at confluence; (3) in cell–cell contact-lacking cells, ouabain did not produce a significant change; (4) Na+/K+ ATPase might be the receptor that mediates the effect of ouabain on Ik; (5) the ouabain-induced changes in Ik required the synthesis of new nucleotides and proteins, as well as Golgi processing and exocytosis, as evidenced by treatment with drugs inhibiting those processes; and (5) the signaling cascade included the participation of cSrC, PI3K, Erk1/2, NF-κB and β-catenin. These results reveal a new role for ouabain as a modulator of the expression of voltage-gated potassium channels, which require cells to be in contact with themselves.

Gap junctions are molecular structures that allow communication between neighboring cells. It has been shown that gap junctional intercellular communication (GJIC) is notoriously reduced in cancer cells compared to their normal counterparts. Ouabain, a plant derived substance, widely known for its therapeutic properties on the heart, has been shown to play a role in several types of cancer, although its mechanism of action is not yet fully understood. Since we have previously shown that ouabain enhances GJIC in epithelial cells (MDCK), here we probed whether ouabain affects GJIC in a variety of cancer cell lines, including cervico-uterine (CasKi, SiHa and Hela), breast (MDA-MB-321 and MCF7), lung (A549), colon (SW480) and pancreas (HPAF-II). For this purpose, we conducted dye transfer assays to measure and compare GJIC in monolayers of cells with and without treatment with ouabain (0.1, 1, 10, 50 and 500 nM). We found that ouabain induces a statistically significant enhancement of GJIC in all of these cancer cell lines, albeit with distinct sensitivity. Additionally, we show that synthesis of new nucleotides or protein subunits is not required, and that Csrc, ErK1/2 and ROCK-Rho mediate the signaling mechanisms. These results may contribute to explaining how ouabain influences cancer.