Ali Mahdi

Aims: Inflammatory bowel diseases (IBD) have been associated with an increased long-term risk of arrhythmia. However, clinical outcomes following catheter ablation in patients with IBD are unknown. Methods and results: In this nationwide Swiss cohort study of adults undergoing catheter ablation for arrhythmia between 2012 and 2022, patients with IBD were propensity score–matched 1:10 to comparators without IBD. The primary endpoint was a composite of the first occurrence of any of the following events: reablation, cardioversion, or hospitalization for arrhythmia. Secondary endpoints were each individual component of the primary endpoint. An additional win ratio-based hierarchical analysis was performed. Hazard ratios (HRs) and incidence rates (IRs) were calculated using Cox proportional hazards modelling. A total of 251 patients with IBD and 2429 matched comparators were included in the study. After a median follow-up time of 2.6 years (IQR 0.8–5.6), the primary endpoint occurred in 81 (32.3%, IR: 100.8/1000 person-years) patients with IBD and in 640 (26.3%, IR: 73.3/1000 person-years) matched comparators, yielding an HR of 1.30 [95% confidence interval (CI) = 1.03–1.64]. Among the individual components of the primary endpoint, hospitalization for arrhythmia was more frequent in patients with IBD (HR 1.29, 95% CI = 1.02–1.64), while the remaining components did not differ between groups. In hierarchical win ratio analysis, patients with IBD had worse composite outcomes than matched comparators (win ratio 0.80, 95% CI = 0.65–0.99, P = 0.04). Conclusion: Patients with IBD undergoing catheter ablation exhibited 30% higher hazards of adverse arrhythmia-related outcomes.

Background: Arginase influences cardiac tolerance to ischemia–reperfusion by modulating nitric oxide (NO) signaling. In type 2 diabetes (T2D), elevated arginase activity may worsen ischemic injury through red blood cells (RBCs), but the specific roles of arginase isoforms are unclear. Methods: C57BL/6 and db/db mice were pretreated with ARG1 or ARG2 antisense oligonucleotides (ASO) for six weeks. Conditional ARG1 knockout (ARG1^fl/fl/Tie2Cre^tg/−) and wild-type littermates were also studied. Mice underwent coronary artery ligation and reperfusion in vivo for infarct size assessment. In ex vivo experiments, buffer-perfused hearts were subjected to global ischemia–reperfusion with or without RBCs to evaluate recovery of left ventricular developed pressure (LVDP). Results: ARG1 knockdown, but not ARG2, improved post-ischemic recovery of LVDP in isolated hearts. RBCs from ARG1 ASO-treated mice enhanced recovery in wild-type hearts, while ARG1 knockout reduced infarct size compared with controls. Cardioprotection was abolished by NO synthase inhibition. RBCs from male and female ARG1 knockout mice improved LVDP recovery compared with RBCs from wild-type mice. In T2D mice, impaired recovery was restored by ARG1 ASO or RBCs from ARG1 ASO-treated T2D mice. Conclusions: Arginase 1, but not arginase 2, limits cardiac tolerance to ischemia–reperfusion and contributes to increased vulnerability in T2D.

Red blood cells (RBCs) induce endothelial dysfunction in type 2 diabetes (T2D), but the mechanism by which RBCs communicate with the endothelium is unknown. This study tested the hypothesis that extracellular vesicles (EVs) secreted by RBCs act as mediators of endothelial dysfunction in T2D. Despite a lower production of EVs derived from RBCs of T2D patients (T2D RBC-EVs), their uptake by endothelial cells was greater than that of EVs derived from RBCs of healthy individuals (H RBC-EVs). T2D RBC-EVs impaired endothelium-dependent relaxation, and this effect was attenuated following inhibition of arginase in EVs. Inhibition of vascular arginase or oxidative stress also attenuated endothelial dysfunction induced by T2D RBC-EVs. Arginase-1 was detected in RBC-derived EVs, and arginase-1 and oxidative stress were increased in endothelial cells following coincubation with T2D RBC-EVs. T2D RBC-EVs also increased arginase-1 protein in endothelial cells following mRNA silencing and in the endothelium of aortas from endothelial cell arginase-1–knockout mice. It is concluded that T2D-RBCs induce endothelial dysfunction through increased uptake of EVs that transfer arginase-1 from RBCs to the endothelium to induce oxidative stress and endothelial dysfunction. These results shed important light on the mechanism underlying endothelial dysfunction mediated by RBCs in T2D.

The mechanisms underlying endothelial dysfunction in Type 1 and Type 2 diabetes (T1DM and T2DM) are unresolved. The red blood cells (RBCs) with increased arginase activity induce endothelial dysfunction in T2DM, but the implications of RBCs and the role of arginase inhibition in T1DM are unexplored. We aimed to investigate the differences in endothelial function in patients with T1DM and T2DM, with focus on RBCs and arginase. Thirteen patients with T1DM and twenty-six patients with T2DM, matched for HbA1c and sex were included. In vivo endothelium-dependent and -independent vasodilation (EDV and EIDV) were assessed by venous occlusion plethysmography before and after administration of an arginase inhibitor. RBCs were co-incubated with rat aortic segments for 18h followed by evaluation of endothelium-dependent (EDR) and -independent relaxation (EIDR) in isolated organ chambers. In vivo EDV, but not EIDV, was significantly impaired in patients with T2DM compared with patients with T1DM. Arginase inhibition resulted in improved EDV only in T2DM. RBCs from patients with T2DM induced impaired EDR but not EIDR in isolated aortic segments, whereas RBCs from patients with T1DM did not affect EDR nor EIDR. The present study demonstrates markedly impaired EDV in patients with T2DM in comparison with T1DM. In addition, it highlights the divergent roles of RBCs and arginase in mediating endothelial dysfunction in T1DM and T2DM. While endothelial dysfunction is mediated via RBCs and arginase in T2DM, these phenomena are not prominent in T1DM thereby indicating distinct differences in underlying mechanisms.

Background. Postacute sequelae of SARS-CoV-2 infection (PASC) are a novel clinical syndrome characterized in part by endothelial dysfunction. Enhanced external counterpulsation (EECP) produces pulsatile shear stress, which has been associated with improvements in systemic endothelial function. Objective. To explore the effects of EECP on symptom burden, physical capacity, mental health, and health-related quality of life (HRQoL) in patients with PASC-associated angina and microvascular dysfunction (MVD). Methods. An interventional pilot study was performed, including 10 patients (male=5, mean age 50.3years) recruited from a tertiary specialized PASC clinic. Patients with angina and MVD, defined as index of microcirculatory resistance (IMR) 25 and/or diagnosed through stress perfusion cardiac magnetic resonance imaging, were included. Patients underwent one modified EECP course (15 one-hour sessions over five weeks). Symptom burden, six-minute walk test, and validated generic self-reported instruments for measuring psychological distress and HRQoL were assessed before and one month after treatment. Results. At baseline, most commonly reported PASC symptoms were angina (100), fatigue (80), and dyspnea (80). Other symptoms included palpitations (50), concentration impairment (50), muscle pain (30), and brain fog (30). Mean IMR was 63.6. After EECP, 6MWD increased (mean 29.5m, median 21m) and angina and fatigue improved. Mean depression scores showed reduced symptoms (0.8). Mean HRQoL scores improved in seven out of eight subscales (+0.2 to 10.5). Conclusions. Patients with PASC-associated angina and evidence of MVD experienced subjective and objective benefits from EECP. The treatment was well-tolerated. These findings warrant controlled studies in a larger cohort.

Post-acute COVID-19 (PACS) are associated with cardiovascular dysfunction, especially postural orthostatic tachycardia syndrome (POTS). Patients with PACS, both in the absence or presence of POTS, exhibit a wide range of persisting symptoms long after the acute infection. Some of these symptoms may stem from alterations in cardiovascular homeostasis, but the exact mechanisms are poorly understood. The aim of this study was to provide a broad molecular characterization of patients with PACS with (PACS + POTS) and without (PACS-POTS) POTS compared to healthy subjects, including a broad proteomic characterization with a focus on plasma cardiometabolic proteins, quantification of cytokines/chemokines and determination of plasma sphingolipid levels. Twenty-one healthy subjects without a prior COVID-19 infection (mean age 43 years, 95% females), 20 non-hospitalized patients with PACS + POTS (mean age 39 years, 95% females) and 22 non-hospitalized patients with PACS-POTS (mean age 44 years, 100% females) were studied. PACS patients were non-hospitalized and recruited ≈18 months after the acute infection. Cardiometabolic proteomic analyses revealed a dysregulation of ≈200 out of 700 analyzed proteins in both PACS groups vs. healthy subjects with the majority (> 90%) being upregulated. There was a large overlap (> 90%) with no major differences between the PACS groups. Gene ontology enrichment analysis revealed alterations in hemostasis/coagulation, metabolism, immune responses, and angiogenesis in PACS vs. healthy controls. Furthermore, 11 out of 33 cytokines/chemokines were significantly upregulated both in PACS + POTS and PACS-POTS vs. healthy controls and none of the cytokines were downregulated. There were no differences in between the PACS groups in the cytokine levels. Lastly, 16 and 19 out of 88 sphingolipids were significantly dysregulated in PACS + POTS and PACS-POTS, respectively, compared to controls with no differences between the groups. Collectively, these observations suggest a clear and distinct dysregulation in the proteome, cytokines/chemokines, and sphingolipid levels in PACS patients compared to healthy subjects without any clear signature associated with POTS. This enhances our understanding and might pave the way for future experimental and clinical investigations to elucidate and/or target resolution of inflammation and micro-clots and restore the hemostasis and immunity in PACS.

Red blood cells (RBCs) mediate cardioprotection via nitric oxide–like bioactivity, but the signaling and the identity of any mediator released by the RBCs remains unknown. We investigated whether RBCs exposed to hypoxia release a cardioprotective mediator and explored the nature of this mediator. Perfusion of isolated hearts subjected to ischemia-reperfusion with extracellular supernatant from mouse RBCs exposed to hypoxia resulted in improved postischemic cardiac function and reduced infarct size. Hypoxia increased extracellular export of cyclic guanosine monophosphate (cGMP) from mouse RBCs, and exogenous cGMP mimicked the cardioprotection induced by the supernatant. The protection induced by hypoxic RBCs was dependent on RBC-soluble guanylate cyclase and cGMP transport and was sensitive to phosphodiesterase 5 and activated cardiomyocyte protein kinase G. Oral administration of nitrate to mice to increase nitric oxide bioactivity further enhanced the cardioprotective effect of hypoxic RBCs. In a placebo-controlled clinical trial, a clear cardioprotective, soluble guanylate cyclase–dependent effect was induced by RBCs collected from patients randomized to 5 weeks nitrate-rich diet. It is concluded that RBCs generate and export cGMP as a response to hypoxia, mediating cardioprotection via a paracrine effect. This effect can be further augmented by a simple dietary intervention, suggesting preventive and therapeutic opportunities in ischemic heart disease.