Carboxiterminal pro-endothelin-1 as an endothelial cell biomarker in thrombotic thrombocytopenic purpura

Anti-Inflammatory Cytokine Profiles in Thrombotic Thrombocytopenic Purpura-Differences Compared to COVID-19

Thromboinflammation/immunothrombosis plays a role in several diseases including thrombotic thrombocytopenic purpura (TTP) and COVID-19. Unlike the extensive research that has been conducted on COVID-19 cytokine storms, the baseline and acute phase cytokine profiles of TTP are poorly characterized. Moreover, we compared the cytokine profiles of TTP and COVID-19 to identify the disease-specific/general characteristics of thromboinflammation/immunothrombosis. Plasma concentrations of 33 soluble mediators (SMs: cytokines, chemokines, soluble receptors, and growth factors) were measured by multiplex bead-based LEGENDplex™ immunoassay from 32 COVID-19 patients (32 non-vaccinated patients in three severity groups), 32 TTP patients (remission/acute phase pairs of 16 patients), and 15 control samples. Mainly, the levels of innate immunity-related SMs changed in both diseases. In TTP, ten SMs decreased in both remission and acute phases compared to the control, one decreased, and two increased only in the acute phase compared to remission, indicating mostly anti-inflammatory changes. In COVID-19, ten pro-inflammatory SMs increased, whereas one decreased with increasing severity compared to the control. In severe COVID-19, sixteen SMs exceeded acute TTP levels, with only one higher in TTP. PCA identified CXCL10, IL-1RA, and VEGF as the main discriminators among their cytokine profiles. The innate immune response is altered in both diseases. The cytokine profile of TTP suggests a distinct pathomechanism from COVID-19 and supports referring to TTP as thromboinflammatory rather than immunothrombotic, emphasizing thrombosis over inflammation as the driving force of the acute phase.

Is Endothelial Activation a Critical Event in Thrombotic Thrombocytopenic Purpura?

Thrombotic thrombocytopenic purpura (TTP) is a severe thrombotic microangiopathy. The current pathophysiologic paradigm suggests that the ADAMTS13 deficiency leads to Ultra Large-Von Willebrand Factor multimers accumulation with generation of disseminated microthrombi. Nevertheless, the role of endothelial cells in this pathology remains an issue. In this review, we discuss the various clinical, in vitro and in vivo experimental data that support the important role of the endothelium in this pathology, suggesting that ADAMTS13 deficiency may be a necessary but not sufficient condition to induce TTP. The "second hit" model suggests that in TTP, in addition to ADAMTS13 deficiency, endogenous or exogenous factors induce endothelial activation affecting mainly microvascular cells. This leads to Weibel-Palade bodies degranulation, resulting in UL-VWF accumulation in microcirculation. This endothelial activation seems to be worsened by various amplification loops, such as the complement system, nucleosomes and free heme.

Local renal complement activation mediates immune kidney injury by inducing endothelin-1 signalling and inflammation in trichloroethylene-sensitised mice

Trichloroethylene (TCE) is a widely used industrial solvent that causes trichloroethylene hypersensitivity syndrome (THS) with multi-system damage, including kidney injury. Clinical studies have shown that the complement system is important for TCE-induced kidney injury. Our previous study found excessive deposition of complement C3, mainly on the glomerulus, indicating that local renal complement is activated after TCE sensitisation. However, whether local renal complement activation mediates TCE-induced immune kidney injury and the underlying mechanisms remain unknown. Therefore, we established a TCE percutaneous sensitisation BALB/c mouse model to explore the mechanisms by pretreating with or without the complement activation antagonist, cathepsin L inhibitor (CatLi). As expected, more C3 and C3a were detected mainly on glomerulus of TCE positive sensitisation (TCE⁺) mice. Renal dysfunction and pathological damage were also clearly observed in TCE⁺ mice. Moreover, the mRNA and protein expression of ET-1 increased significantly with local renal complement activation after TCE sensitisation, leading to cytokines release and inflammation. In addition, activation of p38MAPK and NF-κBp65 pathways were detected in kidneys of TCE⁺ mice, and CatLi pretreatment decreased these changes through complement activation antagonisation. Our research uncovered a novel role of local renal complement activation during immune kidney injury after TCE sensitisation through induction of ET-1 signalling and inflammation.