Abstract P242: The Role Of Kappa Opioid Receptors In The Development Of Hypertension And Kidney Injury In Sprague-Dawley Rats

The extensive use of opioid-based pain management strongly correlates with poor cardiovascular and cardiorenal outcomes. Our recent studies suggest that treatment with kappa opioid receptor (KOR) agonist BRL 52537 leads to the progression of chronic kidney disease (CKD) and aggravation of salt-sensitive hypertension. We hypothesize that stimulation of KORs leads to blood pressure elevation, albuminuria, and kidney damage in healthy Sprague-Dawley (SD) rats. To characterize the effect of the KOR agonist BRL 52537 on the development of blood pressure and kidney function in vivo , SD rats were treated with a daily i.v. bolus infusion of BRL 52537 or a corresponding vehicle. To test the contribution of KOR stimulation on calcium homeostasis in podocytes, BRL 52537 was used on freshly isolated glomeruli from SD rats. Single-channel analysis was applied to assess the effect of KORs stimulation on TRPC6 channel activity in the human immortalized podocytes. Chronic treatment with BRL 52537 leads to increased mean arterial pressure (88±1 vs 101±4 mmHg, vehicle vs treated, p<0.05), podocyte basal calcium (90±12 vs 216±16 a.u., vehicle vs treated, p<0.05), and GFB impairment in SD rats which is reflected by a transient increase in albumin excretion (Alb/cre ratio 0.35±0.1 vs 0.72±0.2, vehicle vs treated, p<0.05). Cumulative probability distribution analysis of the glomerular injury score revealed a rightward shift toward a high glomerular injury score in the group treated with BRL 52537 (p<0.05). Angiotensin II level was higher in a BRL-treated group (156±17 vs 232±59 pmol, vehicle vs treated, p=0.065); however, it did not reach a statistical difference. Acute application of BRL 52537 resulted in sustained calcium response (0.23±0.01 a.u., Fluo4/FuraRed, maximum calcium response) in freshly isolated glomeruli from SD rats. Furthermore, patch-clamp experiments in human immortalized podocytes (cell-attached configuration) revealed that BRL 52537 activated TRPC6 channels. Taken together, these data support the hypothesis that administration of opioids in SD rats leads to activation of the KOR/TRPC6 pathway, which in turn led to glomerular filtration barrier impairment, increased glomerular damage, and blood pressure elevation.

Novel allosteric ligands of the angiotensin receptor AT1R as autoantibody blockers

While orthosteric ligands of the angiotensin II (AngII) type 1 receptor (AT1R) are available for clinical and research applications, allosteric ligands are not known for this important G protein-coupled receptor (GPCR). Allosteric ligands are useful tools to modulate receptor pharmacology and subtype selectivity. Here, we report AT1R allosteric ligands for a potential application to block autoimmune antibodies. The epitope of autoantibodies for AT1R is outside the orthosteric pocket in the extracellular loop 2. A molecular dynamics simulation study of AT1R structure reveals the presence of a druggable allosteric pocket encompassing the autoantibody epitope. Small molecule binders were then identified for this pocket using structure-based high-throughput virtual screening. The top 18 hits obtained inhibited the binding of antibody to AT1R and modulated agonist-induced calcium response of AT1R. Two compounds out of 18 studied in detail exerted a negative allosteric modulator effect on the functions of the natural agonist AngII. They blocked antibody-enhanced calcium response and reactive oxygen species production in vascular smooth muscle cells as well as AngII-induced constriction of blood vessels, demonstrating their efficacy in vivo. Our study thus demonstrates the feasibility of discovering inhibitors of the disease-causing autoantibodies for GPCRs. Specifically, for AT1R, we anticipate development of more potent allosteric drug candidates for intervention in autoimmune maladies such as preeclampsia, bilateral adrenal hyperplasia, and the rejection of organ transplants.

Epitope Binning of Novel Monoclonal Anti F1 and Anti LcrV Antibodies and Their Application in a Simple, Short, HTRF Test for Clinical Plague Detection

Mouse monoclonal antibodies were raised against plague disease biomarkers: the bacterial capsular protein fraction 1 (F1) and the low-calcium response—LcrV virulence factor (Vag). A novel tandem assay, employing BioLayer Interferometry (BLI), enabled the isolation of antibodies against four different epitopes on Vag. The tandem assay was carried out with hybridoma supernatants, circumventing the need for antibody purification. The BioLayer assay was further adopted for characterization of epitope-repetitive antigens, enabling the discovery of two unique epitopes on F1. The selected antibodies were purified and applied as “oligo-clonal” reagents for the immuno-detection of both biomarkers. The developed Homogenous Time Resolved Fluorescence (HTRF) tests were short (10 min) and simple (no washing steps), allowing for detection of 10 ng/mL F1 and 2.5 ng/mL Vag. The tests were successfully applied for detection of disease biomarkers produced by various Y. pestis strains during growth in blood culture vials.

The epoxyeicosatrienoic pathway is intact in endothelial and smooth muscle cells exposed to aldosterone excess

ObjectivesEndothelial dysfunction (ED) is considered to be a major driver of the increased incidence of cardiovascular disease in primary aldosteronism (PA). Whether the epoxyeicosatrienoic acid (EET) pathway, involving the release of beneficial endothelium-derived lipid mediators, contributes to ED in PA is unknown. Preclinical evidence suggests this pathway to be relevant in the pathogenesis in various models of experimental hypertension. In addition, an orally available soluble epoxide hydrolase inhibitor, which halts the breakdown of EETs, has already passed a phase 1 clinical trial.We, therefore, exposed primary human coronary artery endothelial cells to 1 nM aldosterone.MethodsWe used qPCR to investigate changes in the expression levels of essential genes for the synthesis and degradation of EETs as well as mass spectrometry to determine endothelial synthetic capacity to release EETs upon stimulation. We also assessed primary human coronary artery smooth muscle cells for expression of putative EET receptor ion channels or downstream mediators as well as for the calcium response to EETs using calcium imaging.ResultsNo major aldosterone-related expression changes were detected on the endothelial as well as the smooth muscle side. Stimulated release of endothelial EETs was unaffected. Likewise, the smooth muscle calcium response was unchanged after aldosterone excess.ConclusionsThe EET pathway is not negatively affected by increased aldosterone concentrations as seen in PA. Modulating the EET pathway with therapeutic intent in patients with PA might therefore be assessed in future preclinical and clinical trials to address ED.

Optimal pulse length of insonification for Piezo1 activation and intracellular calcium response

Ultrasound (US) neuromodulation, especially sonogenetics, has been demonstrated with potential applications in noninvasive and targeted treatment of various neurological disorders. Despite the growing interest, the mechanism for US neuromodulation remains elusive, and the optimal condition for eliciting a neural response with minimal adverse effect has not been identified. Here, we investigate the Piezo1 activation and intracellular calcium response elicited by acoustical streaming induced shear stress under various US exposure conditions. We find that Piezo1 activation and resultant intracellular calcium response depend critically on shear stress amplitude and pulse length of the stimulation. Under the same insonification acoustic energy, we further identify an optical pulse length that leads to maximum cell deformation, Piezo1 activation, and calcium response with minimal injury, confirmed by numerical modeling of Piezo1 channel gating dynamics. Our results provide insight into the mechanism of ultrasonic activation of Piezo1 and highlight the importance of optimizing US exposure conditions in sonogenetics applications.

Nitric oxide resets kisspeptin-excited GnRH neurons via PIP2 replenishment

Fertility relies upon pulsatile release of gonadotropin-releasing hormone (GnRH) that drives pulsatile luteinizing hormone secretion. Kisspeptin (KP) neurons in the arcuate nucleus are at the center of the GnRH pulse generation and the steroid feedback control of GnRH secretion. However, KP evokes a long-lasting response in GnRH neurons that is hard to reconcile with periodic GnRH activity required to drive GnRH pulses. Using calcium imaging, we show that 1) the tetrodotoxin-insensitive calcium response evoked by KP relies upon the ongoing activity of canonical transient receptor potential channels maintaining voltage-gated calcium channels in an activated state, 2) the duration of the calcium response is determined by the rate of resynthesis of phosphatidylinositol 4,5-bisphosphate (PIP2), and 3) nitric oxide terminates the calcium response by facilitating the resynthesis of PIP2via the canonical pathway guanylyl cyclase/3′,5′-cyclic guanosine monophosphate/protein kinase G. In addition, our data indicate that exposure to nitric oxide after KP facilitates the calcium response to a subsequent KP application. This effect was replicated using electrophysiology on GnRH neurons in acute brain slices. The interplay between KP and nitric oxide signaling provides a mechanism for modulation of the refractory period of GnRH neurons after KP exposure and places nitric oxide as an important component for tonic GnRH neuronal pulses.