Elevated markers of gut leakage and inflammasome activation in COVID-19 patients with cardiac involvement.

BACKGROUND: A high proportion of COVID-19 patients have cardiac involvement, even those without known cardiac disease. Downregulation of angiotensin converting enzyme 2 (ACE2), a receptor for SARS-CoV-2 and the renin-angiotensin system, as well as inflammatory mechanisms have been suggested to play a role. ACE2 is abundant in the gut and associated with gut microbiota composition. We hypothesized that gut leakage of microbial products, and subsequent inflammasome activation could contribute to cardiac involvement in COVID-19 patients. METHODS: Plasma levels of a gut leakage marker (LPS-binding protein, LBP), a marker of enterocyte damage (intestinal fatty acid binding protein, IFABP), a gut homing marker (CCL25, ligand for chemokine receptor CCR9) and markers of inflammasome activation (IL-1ß, IL-18 and their regulatory proteins) were measured at three time points (day 1, 3-5 and 7-10) in 39 hospitalized COVID-19 patients and related to cardiac involvement. RESULTS: Compared to controls, COVID-19 patients had elevated plasma levels of LBP and CCL25 but not IFABP, suggesting impaired gut barrier function and accentuated gut homing of T cells without excessive enterocyte damage. Levels of LBP were twice as high at baseline in patients with elevated cardiac markers compared with those without and remained elevated during hospitalization. Also, markers of inflammasome activation were moderately elevated in patients with cardiac involvement. LBP was associated with higher NT-pro-BNP levels, whereas IL-18, IL-18BP and IL-1Ra were associated with higher troponin levels. CONCLUSION: Patients with cardiac involvement had elevated markers of gut leakage and inflammasome activation, suggestive of a potential gut-heart axis in COVID-19.

Rickettsia conorii is a potent complement activator in vivo and combined inhibition of complement and CD14 is required for attenuation of the cytokine response ex vivo.

Mediterranean spotted fever caused by Rickettsia conorii is a potentially lethal disease characterized by vascular inflammation affecting multiple organs. Studies of R. conorii so far have focused on activation of inflammatory cells and their release of inflammatory cytokines, but complement activation has not been investigated in R. conorii-infected patients. Here, we performed a comprehensive analysis of complement activation markers and the soluble cross-talking co-receptor CD14 (sCD14) in plasma from R. conorii-infected patients. The clinical data were supplemented with ex vivo experiments where the cytokine response was characterized in human whole blood stimulated with R. conorii. Complement activation markers at the level of C3 (C3bc, C3bBbP) and terminal pathway activation (sC5b-9), as well as sCD14, were markedly elevated (p <0.01 for all), and closely correlated (p <0.05 for all), in patients at admission compared with healthy matched controls. All tested markers were significantly reduced to baseline values at time of follow up. Rickettsia conorii incubated in human whole blood was shown to trigger complement activation accompanied by release of the inflammatory cytokines interleukin-1ß (IL-1ß), IL-6, IL-8 and tumour necrosis factor. Whereas inhibition of either C3 or CD14 had only a minor effect on released cytokines, combined inhibition of C3 and CD14 resulted in significant reduction, virtually to baseline levels, of the four cytokines (p <0.05 for all). Our data show that complement is markedly activated upon R. conorii infection and complement activation is, together with CD14, responsible for a major part of the cytokine response induced by R. conorii in human whole blood.

CXCL16 in HIV infection - a link between inflammation and viral replication.

BACKGROUND: While some chemokines are thought to be protective in HIV-infected individuals by their ability to block HIV entry into T cells and macrophages, chemokines could also have harmful effects in HIV infection through their ability to promote inflammation. Here, we examined the regulation and the effects of CXCL16, a newly discovered chemokine of the CXC family, in HIV-infected patients. MATERIALS AND METHODS: We examined serum levels of CXCL16 in clinically well-defined subgroups of HIV-infected individuals both before (n = 62) and during HAART (n = 40) as well as in age- and sex-matched healthy controls (n = 30). We also examined the effects of CXCL16 on inflammatory and anti-inflammatory cytokines and HIV replication in peripheral blood mononuclear cells (PBMC). RESULTS: Our main and novel findings were: (i) HIV-infected patients had significant raised CXCL16 levels according to disease severity and progression. (ii) During HAART, the immunological improvement was accompanied by a modest increase in CXCL16 level. (iii) While soluble CXCL16 promoted an anti-inflammatory response in PBMC from those on successful HAART, it induced an inflammatory response and enhanced HIV replication in PBMC from those with high viral load irrespectively of ongoing HAART. (iv) Recombinant HIV-tat protein significantly increased CXCL16 release in THP-1 macrophages. CONCLUSIONS: Our findings suggest a complex interaction between CXCL16 and HIV, promoting both inflammatory and anti-inflammatory effects as well as HIV replication, partly dependent on accompanying HIV replication.

Altered composition of HDL3 in FH subjects causing a HDL subfraction with less atheroprotective function.

BACKGROUND: Subjects with familial hypercholesterolemia (FH) are associated with increased risk of premature atherosclerosis and coronary artery disease (CAD). However, onset of clinically manifested CAD varies widely among subjects with heterozygous FH. The purpose of this study was to investigate whether FH subjects with an identical mutation in the low-density lipoprotein (LDL) receptor gene have a high-density lipoprotein (HDL)3 that is characterized by a less atheroprotective functions than that of healthy controls and within subgroups of FH. DESIGN: Twenty-two adults <75 years of age with FH and 17 healthy sex- and age-matched controls were included. HDL3 was isolated and the composition was characterized from each subject, and its ability to suppress tumor necrosis factor(TNF)-alpha stimulated expression of ICAM-1 on HUVEC was investigated. In addition, plasma level of soluble sICAM-1 and VCAM-1 was measured. RESULTS: Compared to controls, FH subjects had lower content of phospholipids in their HDL3 subfraction and a higher serum ICAM-1 level. No differences in sVCAM-1 were observed. HDL3 isolated from FH with body mass index(BMI)>25 and from FH subjects with premature CAD contained higher content of triglycerides compared to the HDL3 from FH subjects with BMI<25 and without CAD, respectively. Most important, when testing the function of HDL3 in the two FH subgroups characterized by elevated BMI and premature CAD, lower inhibition of ICAM-1 expression on HUVEC was observed. CONCLUSIONS: The altered composition of HDL3 from FH subjects with BMI>25 and FH subjects with premature CAD may be responsible for a HDL3 subfraction with less protective properties assessed as inhibition of ICAM-1 expression on HUVEC consequently leading to more proatherogenic endothelial surface.

Platelet shape change induced by the peptide YFLLRNP.

Platelet shape change represents an early response to activating agents. Whereas the PAR-1-activating peptide SFLLRN induces a total platelet activation, YFLLRNP brings the process only to the shape change step in a process independent of the cytosolic Ca2+ concentration. In this paper, the YFLLRNP-induced shape change has been observed in human citrated platelet-rich plasma (PRP). Scanning electron microscopy of platelets activated by 300 microM YFLLRNP showed platelets that had changed shape and extended long pseudopods. The protein content of the material sedimenting at 13,000 x g from 1% Triton X-100 extracts increased during the shape change, indicating a reorganization of the cytoskeleton. This was supported by electrophoresis. The GP IIb-IIIa complex was not activated, however, and the platelets that had undergone shape change did not support clot retraction. As no increase in binding of FITC-labeled annexin V (FITC-annexin V) was observed, the extensive shape change was not associated with a disturbance of the membrane phospholipid asymmetry. Platelet aggregation was never observed with 300 microM YFLLRNP, but could be seen at much higher concentrations, neither was secretion from dense granules observed at 300 microM as no extracellular ATP could be observed. These studies confirm and extend the concept of the Ca2+-independent shape change as a distinct and sharply delineated process that, in itself, may be of little pathophysiological importance if such "partly activated" platelets occur in the circulation.

Persistently elevated levels of von Willebrand factor antigen in HIV infection. Downregulation during highly active antiretroviral therapy.

Levels of circulating von Willebrand factor (vWf) antigen are thought to reflect endothelial involvement in various disorders. In the present study we found markedly elevated plasma levels of vWf in HIV-infected patients demonstrated on both cross-sectional and longitudinal testing. Notably, we found that a persistent rise in vWf antigen was associated with progression of HIV-related disease. This elevation of vWf antigen represented functionally normal vWf as evaluated by plasma FVIII, ristocetin cofactor assay and vWf multimer analyses. While HIV-infected patients showed enhanced platelet activation, platelets did not contribute substantially to the increased vWf levels. The high vWf levels were significantly correlated with high viral load, and during HAART, the pronounced decline in HIV RNA levels was accompanied by a corresponding decrease in vWf. The persistent elevation of functionally normal vWf during HIV infection, most probably reflecting a persistent endothelial cell activation, may have an important role in the pathogenesis of HIV infection.