Epidemiology, Outcomes, and Complement Gene Variants in Secondary Thrombotic Microangiopathies.

BACKGROUND: The identification of complement defects as major drivers of primary atypical hemolytic uremic syndrome (HUS) has transformed the landscape of thrombotic microangiopathies (TMAs), leading to the development of targeted therapies and better patient outcomes. By contrast, little is known about the presentation, genetics, and outcomes of TMA associated with specific diseases or conditions, also referred to as secondary TMA. METHODS: In this study, we assessed the relative incidence, clinical and genetic spectra, and long-term outcomes of secondary TMA versus other TMAs in consecutive patients hospitalized with a first episode of TMA from 2009 to 2019 at two European reference centers. RESULTS: During the study period, 336 patients were hospitalized with a first episode of TMA. Etiologies included atypical HUS in 49 patients (15%), thrombotic thrombocytopenic purpura (TTP) in 29 (9%), shigatoxin-associated HUS in 70 (21%), and secondary TMA in 188 (56%). The main causes of secondary TMA were hematopoietic stem-cell transplantation ( n =56, 30%), solid-organ transplantation ( n =44, 23%), and malignant hypertension ( n =25, 13%). Rare variants in complement genes were identified in 32 of 49 patients (65%) with atypical HUS and eight of 64 patients (13%) with secondary TMA; pathogenic or likely pathogenic variants were found in 24 of 49 (49%) and two of 64 (3%) of them, respectively ( P < 0.001). After a median follow-up of 1157 days, death or kidney failure occurred in 14 (29%), eight (28%), five (7%), and 121 (64%) patients with atypical HUS, TTP, shigatoxin-associated HUS, and secondary TMA, respectively. Unadjusted and adjusted Cox regressions showed that patients with secondary TMA had the highest risk of death or kidney failure (unadjusted hazard ratio [HR], 3.35; 95% confidence interval [CI], 1.85 to 6.07; P < 0.001; adjusted HR, 4.11; 95% CI, 2.00 to 8.46; P < 0.001; considering atypical HUS as reference). CONCLUSIONS: Secondary TMAs represent the main cause of TMA and are independently associated with a high risk of death and progression to kidney failure.

Serum uric acid, disease severity and outcomes in COVID-19.

BACKGROUND: The severity of coronavirus disease 2019 (COVID-19) is highly variable between individuals, ranging from asymptomatic infection to critical disease with acute respiratory distress syndrome requiring mechanical ventilation. Such variability stresses the need for novel biomarkers associated with disease outcome. As SARS-CoV-2 infection causes a kidney proximal tubule dysfunction with urinary loss of uric acid, we hypothesized that low serum levels of uric acid (hypouricemia) may be associated with severity and outcome of COVID-19. METHODS: In a retrospective study using two independent cohorts, we investigated and validated the prevalence, kinetics and clinical correlates of hypouricemia among patients hospitalized with COVID-19 to a large academic hospital in Brussels, Belgium. Survival analyses using Cox regression and a competing risk approach assessed the time to mechanical ventilation and/or death. Confocal microscopy assessed the expression of urate transporter URAT1 in kidney proximal tubule cells from patients who died from COVID-19. RESULTS: The discovery and validation cohorts included 192 and 325 patients hospitalized with COVID-19, respectively. Out of the 517 patients, 274 (53%) had severe and 92 (18%) critical COVID-19. In both cohorts, the prevalence of hypouricemia increased from 6% upon admission to 20% within the first days of hospitalization for COVID-19, contrasting with a very rare occurrence (< 1%) before hospitalization for COVID-19. During a median (interquartile range) follow-up of 148 days (50-168), 61 (12%) patients required mechanical ventilation and 93 (18%) died. In both cohorts considered separately and in pooled analyses, low serum levels of uric acid were strongly associated with disease severity (linear trend, P < 0.001) and with progression to death and respiratory failure requiring mechanical ventilation in Cox (adjusted hazard ratio 5.3, 95% confidence interval 3.6-7.8, P < 0.001) or competing risks (adjusted hazard ratio 20.8, 95% confidence interval 10.4-41.4, P < 0.001) models. At the structural level, kidneys from patients with COVID-19 showed a major reduction in urate transporter URAT1 expression in the brush border of proximal tubules. CONCLUSIONS: Among patients with COVID-19 requiring hospitalization, low serum levels of uric acid are common and associate with disease severity and with progression to respiratory failure requiring invasive mechanical ventilation.

Oxidative Stress-Induced Sirtuin1 Downregulation Correlates to HIF-1α, GLUT-1, and VEGF-A Upregulation in Th1 Autoimmune Hashimoto's Thyroiditis.

In Hashimoto's thyroiditis (HT), oxidative stress (OS) is driven by Th1 cytokines' response interfering with the normal function of thyrocytes. OS results from an imbalance between an excessive production of reactive oxygen species (ROS) and a lowering of antioxidant production. Moreover, OS has been shown to inhibit Sirtuin 1 (SIRT1), which is able to prevent hypoxia-inducible factor (HIF)-1α stabilization. The aims of this study were to determine the involvement of NADPH-oxidases (NOX), SIRT1, and HIF-1α in HT pathophysiology as well as the status of antioxidant proteins such as peroxiredoxin 1 (PRDX1), catalase, and superoxide dismutase 1 (SOD1). The protein expressions of NOX2, NOX4, antioxidant enzymes, SIRT1, and HIF-1α, as well as glucose transporter-1 (GLUT-1) and vascular endothelial growth factor A (VEGF-A), were analyzed by Western blot in primary cultures of human thyrocytes that were or were not incubated with Th1 cytokines. The same proteins were also analyzed by immunohistochemistry in thyroid samples from control and HT patients. In human thyrocytes incubated with Th1 cytokines, NOX4 expression was increased whereas antioxidants, such as PRDX1, catalase, and SOD1, were reduced. Th1 cytokines also induced a significant decrease of SIRT1 protein expression associated with an upregulation of HIF-1α, GLUT-1, and VEGF-A proteins. With the exception of PRDX1 and SOD1, similar results were obtained in HT thyroids. OS due to an increase of ROS produced by NOX4 and a loss of antioxidant defenses (PRDX1, catalase, SOD1) correlates to a reduction of SIRT1 and an upregulation of HIF 1α, GLUT-1, and VEGF-A. Our study placed SIRT1 as a key regulator of OS and we, therefore, believe it could be considered as a potential therapeutic target in HT.

Diagnostic and Risk Factors for Complement Defects in Hypertensive Emergency and Thrombotic Microangiopathy.

Hypertensive emergency can cause thrombotic microangiopathy (TMA) in the kidneys with high rates of end-stage renal disease (ESRD) and vice versa. The conundrum of hypertension as the cause of TMA or consequence of TMA on the background of defects in complement regulation remains difficult. Patients with hypertensive emergency and TMA on kidney biopsy were tested for ex vivo C5b9 formation on the endothelium and rare variants in complement genes to identify complement-mediated TMA. We identified factors associated with defects in complement regulation and poor renal outcomes. Massive ex vivo C5b9 formation was found on resting endothelial cells in 18 (69%) out of 26 cases at the presentation, including the 9 patients who carried at least one rare genetic variant. Thirteen (72%, N=18) and 3 (38%, N=8) patients with massive and normal ex vivo complement activation, respectively, progressed to ESRD (P=0.03). In contrast to BP control, inhibition of C5 activation prevented ESRD to occur in 5 (83%, N=6) patients with massive ex vivo complement activation. TMA-related graft failure occurred in 7 (47%, N=15) donor kidneys and was linked to genetic variants. The assessment of both ex vivo C5b9 formation and screening for rare variants in complement genes may categorize patients with hypertensive emergency and TMA into different groups with potential therapeutic and prognostic implications. We propose an algorithm to recognize patients at the highest risk for defects in complement regulation.

Regional citrate anticoagulation and influence of recirculation on ionized calcium levels in the circuit.

Regional citrate anticoagulation is now widely used during continuous renal replacement therapy (CRRT), and especially in patients at risk for hemorrhagic complications. A close monitoring is required to avoid citrate overload, leading to metabolic alkalosis or citrate intoxication causing metabolic acidosis. This case report describes a dysfunction of the regional citrate anticoagulation due to the development of a deep vein thrombosis close to the site of insertion of the venous CRRT catheter. The result was a local recirculation in the circuit with a local citrate overload (acidosis and non-measurable calcium). In the patient's blood samples, the [calciumtotal/Ca2+systemic] ratio remained normal as a proof of local citrate accumulation without systemic effects. Initially, CRRT remained effective, but due to the progressive decrease of serum creatinine and cystatin C clearance, the site of catheter insertion was changed.

Oxidative Stress and Upregulation of Antioxidant Proteins, Including Adiponectin, in Extraocular Muscular Cells, Orbital Adipocytes, and Thyrocytes in Graves' Disease Associated with Orbitopathy.

BACKGROUND: Graves' orbitopathy (GO) is the main extrathyroidal manifestation associated with Graves' disease (GD). It is characterized by reduced eye motility due to an increased volume of orbital fat and/or of extraocular muscles (EOMs) infiltrated by fibrosis and adipose tissue. The pathogenetic mechanisms leading to fibrosis and adipogenesis are mainly based on the interaction between orbital fibroblasts and immune cells (lymphocytes and mast cells) infiltrating the GO EOMs. METHODS: Analysis of the morphological status, oxidative stress (OS), and antioxidant defenses in the orbital muscular cells and adipocytes in GO patients compared with controls was conducted. RESULTS: Both cell types are affected by OS, as shown by the increased expression of 4-hydroxynonenal, which leads to apoptosis in muscular cells. However, the EOMs and the adipocytes possess antioxidant defenses (peroxiredoxin 5 and catalase) against the OS, which are also upregulated in thyrocytes in GD. The expression of adiponectin (ApN) and proliferator-activated receptor gamma (PPARγ) is also increased in GO muscular cells and adipocytes. OS and antioxidant proteins expression are correlated to the level of blood antithyrotropin receptor antibodies (TSHR-Ab). CONCLUSION: Even when TSHR-Ab level is normalized, OS and antioxidant protein expression is high in EOM muscular cells and adipocytes in GO compared with controls. This justifies a supplementation with antioxidants in active as well as chronic GO patients. Orbital muscular cells are also the sources of PPARγ and ApN, which have direct or indirect local protective effects against OS. Modulation of these proteins could be considered as a future therapeutic approach for GO.