The Summarized Assessment of Endothelin A Receptor Expression in Renal Transplant Compartments Associated with Antibody-Mediated Rejection

The occurrence of anti-endothelin A receptor antibodies may be useful in diagnosis of transplant damage. We noticed that the presence of the endothelin A receptor (ETA receptor) in biopsy compartments is yet to be defined. We decided therefore to analysed the presence and relevance of the ETA receptor in biopsy to define the cause. Our study aims to evaluate the expression of ETA receptors in renal recipients after a biopsy due to the worsening of transplant function. Methods: The expression of ETA receptors was analyzed in renal transplant biopsies using the immunohistochemical method. The evaluation of ETA receptors was performed on paraffin sections. ETA receptor expression was analyzed in four compartments of renal transplant biopsies: glomeruli; vessels; tubular epithelium; and interstitium. The assessment was presented using a three-step scale (0: lack of expression; 1: mild to moderate immunoreactivity; 2: high expression). The results of each compartment from a single biopsy were summarized and assessed in the context of antibody-mediated rejection (AMR). Results: We analyzed 156 patients who had a renal allograft biopsy after renal transplantation. For each patient, we created a summarized ETA receptor expression score. The summarized ETA receptor expression score analysis showed statistically significant differences in patients with and without AMR. In addition, we noticed that patients with AMR had a significantly higher mean summarized expression of ETA receptor score of 3.28 ± 1.56 compared to patients who had a biopsy for other reasons with a mean summarized ETA receptor expression score of 1.47 ± 1.35 (p < 0.000001). ROC analysis of the ETA receptor expression score for detecting AMR status showed that the most appropriate cut-off for the test of the chosen binary classifier is between 2 and 3 of the summarized ETA receptor expression score. Conclusions: The expression of endothelin A receptors in renal transplant compartments may be associated with antibody-mediated rejection. The positive ETA receptor staining might be a vital feature in the diagnosis of damage in AMR. The summarized ETA receptor expression score seems to be an exciting diagnostic tool in transplant injury assessment.

Endothelin-1 Receptor A Blockade Attenuates Metabolic and Proinflammatory Profile in Mice Fed a High Fat Diet

Endothelin-1 (ET-1) is elevated in patients with obesity; however, its contribution to the pathophysiology related to obesity is not fully understood. Obesity is associated with dyslipidemia and insulin resistance, which may in part be mediated by inflammation and alterations to immune cell subsets within the adipose tissue. ET-1 promotes inflammation via the ET-1 type A (ETA) receptor, and blockade of ETA receptors improves dyslipidemia in patients with chronic kidney disease. We hypothesized that ET-1 causes dyslipidemia and inflammation within the adipose tissue of obese mice. To test this hypothesis, C57BL/6J mice were fed either normal diet (NMD) or high fat diet (HFD) for 8 weeks followed by 2 weeks of treatment with either vehicle or atrasentan (ETA receptor antagonist, 10mg/kg/day). HFD mice had significantly higher fat mass than NMD mice, with no significant effect of treatment with atrasentan. HFD mice had significantly higher circulating non-esterified free fatty acids, an effect that was ameliorated in mice treated with atrasentran (1.03±0.07 vs 0.58±0.02 mEq/L, p&lt;0.05). Atrasentan-treated mice had significantly attenuated increase in liver triglycerides compared to non-treated HFD mice (3.8±0.7 vs 7.5±1.3mg/dL respectively, p&lt;0.05). Mice treated with atrasentan had significantly improved glucose tolerance (10150±1031 vs 6563±975 AUC, p&lt;0.05) and insulin tolerance (-2796±386 vs -9825±319 AUC, p&lt;0.05) compared to non-treated insulin-resistant HFD mice. Plasma adiponectin, an insulin sensitizing adipokine that is inversely associated with adiposity and insulin resistance, was significantly increased in atrasentan-treated mice compared to non-treated HFD (4.8±0.1326 vs 6.5±0.3 µg/ml, p&lt;0.05), with no differences in plasma insulin levels. Gene expression analysis of visceral fat showed improved expression of genes negatively associated with insulin resistance that were downregulated in non-treated HFD mice vs. NMD (IRS-1, PPAR-gamma, GLUT4, and adiponectin). Flow cytometric analyses of visceral adipose tissue indicated that HFD mice had a significantly higher number of both CD4+ and CD8+ T cells compared to NMD mice, which was attenuated by treatment with atrasentan. Further, eosinophils, which are important in maintaining adipose tissue health and reducing inflammation, were significantly decreased in HFD mice compared to NMD. Atrasentan treatment abolished the decrease in eosinophils. Taken together, these data indicate that ETA receptor blockade improves peripheral glucose homeostasis, dyslipidemia, and liver triglyceride levels, and also attenuates the proinflammatory immune profile in visceral adipose tissue. These data suggest a potential use for ETA receptor blockers in the treatment of obesity-associated dyslipidemia and insulin resistance.

Endothelin A Receptors Expressed in Glomeruli of Renal Transplant Patients May Be Associated with Antibody-Mediated Rejection

Background: Non-human leukocyte antigen (HLA) anti-endothelin A receptor antibodies are presented as being potentially important, but the expression of the endothelin A receptor in glomeruli (ETA receptor (g+)) has not yet been described. We decided to evaluate the presence and relevance of the ETA receptor in for-cause renal transplant biopsies. The aim of our study was to evaluate the immunoreactivity of the ETA receptor and its significance in patients who underwent a renal transplant biopsy due to the deterioration of transplant function, with detailed characterization of staining in glomeruli. Methods: The immunohistochemical expression of ETA receptor (ETAR) was analyzed in renal transplant biopsies. Microscopic evaluation was performed on paraffin sections in glomeruli. The analysis was performed using a two-step scale (0: lack of ETAR expression; 1: the presence of ETAR expression—mild to moderate immunoreactivity). Results: We analyzed 149 patients who underwent renal allograft biopsy after renal transplantation. Positive staining of ETA receptors in glomeruli (ETA receptor (g+)) was noticed in 13/149 (8.7%) patients. Five of these 13 (38.5%) patients with ETA receptor (g+) developed antibody-mediated rejection (AMR), while 13 of the remaining 136 (9.5%) ETA receptor (g-) patients developed AMR (p = 0.0022). Graft loss was noticed in all but one ETA receptor (g+) patient with AMR (4/5; 80%), but only in 2/13 (15%) ETA receptor (g-) patients with AMR (p = 0.009) during the first year after biopsy. Conclusions: The expression of endothelin A receptors in glomeruli seems to be a potentially important feature in the diagnosis of damage during antibody-mediated rejection. It may help to identify patients at a higher risk of allograft rejection and injury.

ETA Receptor Blockade and Vascular Function in Patients with Sickle Cell Disease

Endothelin-1 (ET1) is a potent vasoconstrictor, mitogen, proinflammatory mediator, and a mediator of nociception, whose synthesis is increased by hypoxia, ischemia, shear stress, oxidative stress and reduced nitric oxide (NO) bioavailability, all of which are well documented mechanisms in the pathophysiology of sickle cell disease (SCD). We earlier reported on our studies on the role of ET-1 in SCD, and in transgenic mouse models showed that ETA receptor blockade with ambrisentan provides renal protection by preventing the development of glomerular hyperfiltration and proteinuria (Kasztan et al, 2017, Taylor et al, 2019, Kasztan and Pollock, 2019). ETA receptor blockade was also shown to decrease pulmonary inflammation in response to hypoxia/reoxygenation and LPS (Meiler et al.). Additionally, Lutz et al (2018) showed that pharmacologic inhibition or neuron specific knockdown of ETA receptor in primary sensory neurons of dorsal root ganglia in Berk mice alleviated basal and post-hypoxia evoked pain sensitivity. More recently (Kutlar et al, Blood 2019, 617,130036) we reported the preliminary results of a placebo controlled, double-blind phase I trial of ambrisentan in 26 subjects with SCD (SS and S-ß0 thalassemia) and microalbuminuria, and showed that the drug was well tolerated without any dose limiting toxicities and patients on ambrisentan had a reduction in microalbuminuria, especially in the subgroup who had been on concomitant ACEi/ARB therapy at a stable dose for at least six months (n=6, 286.1 mg/g Cr at baseline to 197.7 mg/g on day 85, p=0.06). FMD measurements showed increased arterial diameter, and improved microvascular function. We analyzed data collected on secondary end points during the phase I study, including Tricuspid regurgitant jet velocity (TRV), Transcranial Doppler (TCD) velocities in distal internal carotid (dICA) and middle cerebral (MCA) arteries, and eGFR (calculated with CKD-Epi formula). Fig. 1a shows eGFRs in ambrisentan and placebo groups; Fig. 1b and Fig. 1c show a breakdown of ambrisentan and placebo groups based on concomitant ACEi/ARB usage. There is a reduction in glomerular hyperfiltration in the ambrisentan group compared to placebo, more pronounced in the subgroup who have not been on ACEi/ARBs. Fig. 1d depicts the change in flow velocity in MCA (TAMMV, Time Averaged Mean Maximal Velocity, cm/sec) between the ambrisentan and placebo groups; similarly, Fig. 1e and 1f show the breakdown of baseline and Day 85 TAMMVs in MCA according to ACEi/ARB usage. A similar trend is also observed in dICA flow (fig. 1g-1i), and suggests a synergistic effect of ETA receptor blockade with ACEi/ARBs in preventing an increase in blood flow velocities. TRV was available on 7 subjects, 6 of which were in the ambrisentan group. Fig. 1j shows the change in TRV in the ambrisentan group, and again is suggestive of a synergistic effect of ambrisentan and ACEi/ARBs in decreasing TRV. These data are clearly very preliminary, and are obtained on a small number of subjects, and as such, do not warrant any conclusions and or speculations. Nevertheless, an interesting observation is the apparent interaction of ETA receptor blockade and ACEi/ARBs in altering vascular flow/function in SCD patients. Decrease in microalbuminuria has been reported with ACEi and ARBs in SCD (Yee et al, 2018), without any effect on GFR. A reduction in hyperfiltration would likely have a significant renoprotective effect, at an earlier stage in the development of sickle nephropathy. ETA receptor antagonists are approved for the treatment of pulmonary arterial hypertension; thus, a decrease in TRV would have a beneficial effect. Increase in blood flow velocity in major intracranial vessels is a well established risk factor for ischemic stroke in children with SCD; however, much less is known in adults. In summary, the effect of ETA receptor blockade with or without ACEi/ARB, may have a significant effect on vascular function/blood flow in different organ systems, and should be explored in a large, multi-center phase II trial, with and without concomitant and or serial ACEi/ARBs, for a longer period of time, with a dose escalation, to further clarify the pleiotropic effects on multiple aspects of SCD pathology. Figure 1 Disclosures Kutlar: NIH/NHLBI (SCDIC): Research Funding; Global Blood Therapeutics: Research Funding, Speakers Bureau; Micelle Biopharma: Consultancy; Novartis Pharmaceuticals: Consultancy, Research Funding; Novo Nordisk: Research Funding; Forma Therapeutics: Research Funding; REACH: Other: DSMB Member; NOHARM: Other: DSMB Member; Bluebird Bio: Other: DSMB Member.

Abstract P016: Sex Differential Effects Of Hyperoxia And Thioredoxin Reductase-1 Inhibition On The Kidney Endothelin-1 System

The vasoactive peptide endothelin-1 (ET-1) is critical in lung and kidney injury. Notably, renal damageand hyperoxia-induced lung disease are more prevalent in males than females. Aurothioglucose (ATG),an inhibitor of thioredoxin reductase-1, attenuates hyperoxia-induced lung injury in mice; however, theeffects of hyperoxia and/or ATG treatment on the kidney ET-1 system remain unknown. Wehypothesized that hyperoxia would activate the renal ET-1 system and that ATG treatment wouldattenuate this activation. Male and female adult C57Bl/6 mice received a single injection of saline orATG (25mg/Kg, i.p.) and were exposed to room air (RA) or >90% O2 for 72 hours. Kidney and spleen werecollected for assessment of the ET-1 system by RT-PCR and glomerular morphology and immune cellinfiltration were evaluated by histology and immunohistochemistry, respectively. In male mice,hyperoxia reduced the cortical expression of ET-1 (RA vs. hyperoxia: 1 ± 0.05 vs. 0.34 ± 0.04, p<0.05;n=3-4/group) and ameliorated the expression of ETA receptor. In RA males, treatment with ATGsignificantly halved the expression of ET-1 and ETB receptor (saline vs. ATG, ET-1: 1 ± 0.05 vs. 0.45 ± 0.07,p<0.05; n=3-4/group; ETB receptor: 1 ± 0.09 vs. 0.37 ± 0.10, p<0.05; n=3-4/group), but had no effect inhyperoxic males. Contrarily, hyperoxic females demonstrated a 3-fold upregulation of corticalETB receptor expression, which was significantly prevented by ATG (saline vs. ATG: 2.80 ± 0.37 vs. 0.95 ±0.27, p<0.05; n=3-4/group). ATG treatment in hyperoxic females also decreased the cortical expressionof ET-1 and ETA receptor. No changes in cortical inflammation or glomerular morphology were observed.Further preliminary results showed that hyperoxia led to a 4-fold increase in splenic ET-1 expression insaline-treated mice, and a 7-fold increase in mice treated with ATG. These results demonstrate sexdifferences in the effects of hyperoxia and ATG treatment in the renal ET-1 system and highlight ATG asa possible therapeutic target to attenuate hyperoxia-induced kidney damage. Funded by NIHK01HL145324 and UAB Diabetes Research Center Pilot Project grant to CDM.

Diabetes-related sex differences in the brain endothelin system following ischemia in vivo and in human brain endothelial cells in vitro

The endothelin (ET) system has been implicated to contribute to the pathophysiology of cognitive impairment and stroke in experimental diabetes. Our goals were to test the hypotheses that (1) circulating and (or) periinfarct ET-1 levels are elevated after stroke in both sexes and this increase is greater in diabetes, (2) ET receptors are differentially regulated in the diabetic brain, (3) brain microvascular endothelial cells (BMVEC) of female and male origin express the ETA receptor subtype, and (4) diabetes- and stroke-mimicking conditions increase ET-1 levels in BMVECs of both sexes. Control and diabetic rats were randomized to sham or stroke surgery. BMVECs of male (hBEC5i) and female (hCMEC/D3) origin, cultured under normal and diabetes-mimicking conditions, were exposed to normoxia or hypoxia. Circulating ET-1 levels were higher in diabetic animals and this was more pronounced in the male cohort. Stroke did not further increase plasma ET-1. Tissue ET-1 levels were increased after stroke only in males, whereas periinfarct ET-1 increased in both control and diabetic females. Male BMVECs secreted more ET-1 than female cells and hypoxia increased ET-1 levels in both cell types. There was sexually dimorphic regulation of ET receptors in both tissue and cell culture samples. There are sex differences in the stroke- and diabetes-mediated changes in the brain ET system at the endothelial and tissue levels.

SUN-592 Adipocyte Specific Endothelin a Receptor Knockout Increases Adiposity in Mice

Obesity is associated with increased levels of Endothelin-1 (ET-1). Blockade of ET-1 type A receptors (ETA) improves lipid profile in patients with chronic kidney disease; however the mechanism is unknown.[1] In adipocytes ETA activation increases lipolysis, a potential mechanism for elevated lipids in obese individuals.[2] Therefore, the goal of this study was to determine if adipocyte specific knockout (KO) of the ETA receptor in mice alters genes associated with lipid metabolism in adipose and improves plasma lipids. 24-week old adipocyte ETA knockout mice had significantly elevated body weight compared to floxed controls (32.6±1.0 vs. 29.5±0.7 g respectively). Echo MRI revealed that the increased body weight was due to greater adiposity (10.1±0.9 vs. 14.7±1.8 % body weight; floxed vs. KO), while no statistical difference was observed in lean weight (88.9±2.4 vs. 86.8±2.6 % body weight; floxed vs. KO). Surprisingly, there were no statistical differences in plasma total cholesterol or triglycerides. RNA sequencing indicated downregulation of 597 genes and upregulation of 444 genes in visceral adipose and downregulation of 368 and upregulation of 847 genes in subcutaneous adipose. KEGG pathway analysis revealed that most genes altered in visceral adipose were related to metabolic pathways. These data implicate a role for adipose tissue ETA receptors in regulating adiposity and promoting pathophysiology related to obesity. 1. Farrah, T.E., et al., Endothelin Receptor Antagonism Improves Lipid Profiles and Lowers PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) in Patients With Chronic Kidney Disease. Hypertension, 2019. 74(2): p. 323-330. 2. Eriksson, A.K., et al., Endothelin-1 stimulates human adipocyte lipolysis through the ET A receptor. Int J Obes (Lond), 2009. 33(1): p. 67-74.

The Class III PI3K/Beclin-1 Autophagic Pathway Participates in the mmLDL-Induced Upregulation of ETA Receptor in Mouse Mesenteric Arteries

Minimally modified low-density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. The current study explored the effect of mmLDL on the endothelin type A (ETA) receptor in mouse mesenteric arteries in vivo, as well as the role of autophagy in this process. mmLDL was injected via the caudal vein, and the Class III PI3K autophagic pathway inhibitor 3-methyladenine (3-MA) was injected intraperitoneally. The animals were divided into physiological saline (NS), mmLDL, and mmLDL + 3-MA groups. The dose-effect curve of endothelin-1- (ET-1-) induced mesenteric artery contraction was measured using myography, while ETA receptor mRNA expression was detected using real-time polymerase chain reactions, and the protein levels of the ETA receptor, class III PI3K, Beclin-1, LC3 II/I, p62, NF-κB, and p-NF-κB were observed using Western blot analysis. mmLDL significantly strengthened ET-1-induced contraction (the Emax value increased from 184.87 ± 7.46% in the NS group to 319.91 ± 20.31% in the mmLDL group (P<0.001), and the pEC50 value increased from 8.05 ± 0.05 to 9.11 ± 0.09 (P<0.01). In addition to upregulating the protein levels of Class III PI3K, Beclin-1, and LC3 II/I and downregulating that of p62, mmLDL significantly increased the mRNA expression and protein level of the ETA receptor and increased the protein level of p-NF-κB. However, these effects were significantly inhibited by 3-MA. mmLDL activates autophagy via the Class III PI3K/Beclin-1 pathway and upregulates the ETA receptor via the downstream NF-κB pathway. Understanding the effect of mmLDL on the ETA receptor and the underlying mechanisms may provide a new idea for the prevention and treatment of cardiovascular diseases.