#2850 Elevation of serum indoxyl-sulfate in mice with normal kidney function triggers cardiac and vascular dysfunctions
Authors: Pommerolle Pierre , Caillard Pauline , Louvet Loic , Slama Michel , Maizel Julien , Boullier Agnès , Chatelain Denis , Spicher Pierre , Choukroun Gabriel , Kamel Said , Hénaut Lucie , Benis Youssef 
Published: May 2024

Abstract

Background and Aims
Acute kidney disease (AKD) is associated with a long-term risk of cardiovascular mortality and major cardiovascular events, particularly heart failure and acute myocardial infarction. To date, the underlying mechanisms responsible for this elevated cardiovascular risk remain poorly understood. Patients with AKD show increased circulating levels of indoxyl-sulfate (IS), a uremic toxin known to promote oxidative stress, inflammation and apoptosis in cultured vascular and cardiac cells. In this context, we hypothesized that IS elevation during AKD might promote acute myocardial and vascular lesions, which over time favour the onset of cardiovascular events. In a first attempt to test this hypothesis, we aimed to verify whether IS elevation in mice with normal renal function induces myocardial and vascular dysfunctions similar to that observed in AKD.

Method
Thirty female C57BL6J mice were divided into three groups: control (CT, n = 10), IS (n = 10) and AKD (n = 10). AKD was induced by 5/6 nephrectomy. Blank surgeries were performed in the CT and IS groups. IS was administered continuously for 15 days via drinking water (2.5 g/L) to reach, in IS mice, the IS serum concentrations found in AKD mice, as monitored by a validated high-performance liquid chromatography-tandem mass spectrometry method. Cardiac and vascular functions were assessed by echocardiography at baseline and at D15. Expression of markers of contractility (SERCA-2a for myocardium, αSMA for aorta), inflammation (TNF-α, IL-1β), and endothelial dysfunction (VCAM-1, ICAM-1, iNOS) were assessed by qRT-PCR and western blot. The presence of cardiac lesions was assessed histologically.

Results
Elevation of serum IS concentrations was similar in IS and AKD mice (serum IS: 10.7 ± 3.4 µg/mL in IS-group and 10.9 ± 5.8 µg/mL in AKD-group vs. 4.0 ± 2.1 µg/mL in CT-group (p &lt; 0.001 in CT vs IS and AKD group). Compared with CT mice, IS and AKD mice showed systolic and diastolic dysfunctions as evidenced by decreased ejection fraction (EF: 62.4% [58.0-72.3] in CT vs. 50.1% [45.0-57.0] in IS (p &lt; 0.05 vs CT) and 51.3% [45.6-57.1] in AKD (p &lt; 0.01 vs CT)), decreased fractional shortening (FS: 33.6% [30.1-40.4] in CT vs. 24.8% [21.9-29.7] in IS (p &lt; 0.05 vs CT) and 25.8% [22.4-29.6] in AKD (p &lt; 0.01 vs CT)) and increased isovolumic relaxation time (IVRT: 17.2 ± 1.6 ms in CT vs. 20.7 ± 1.3 ms in IS (p &lt; 0.001 vs CT) and 19.0 ± 1.7 ms in AKD (p &lt; 0.05 vs CT)), respectively. For all echocardiographic parameters assessed, there were no significant differences observed between IS and AKD mice. Myocardium from IS and AKD mice showed decreased expression of SERCA-2a and elevated expression of both IL-1β and TNF-α at the mRNA and protein levels compared to CT mice. Aortas from IS and AKD mice also showed decreased mRNA expression of α-SMA and increased mRNA expression of IL-1β, VCAM-1, and iNOS compared to aortas from CT mice. The mRNA and protein expression of these inflammatory and contractile markers were not statistically different in the hearts and aortas from IS compared to AKD mice. No signs of vascular dysfunction were observed in either of the groups on ultrasound.

Conclusion
Systemic exposure to IS in mice without renal failure leads to significant cardiac and vascular dysfunctions that were similar to those observed in mice with AKD. Additional studies are needed to confirm the causal role of IS in the cardiovascular impact of AKD, and to determine whether IS could represent a valuable prognostic tool and therapeutic target for preventing AKD-associated cardiovascular complications.