Renal Sympathetic Nerves and Inflammation in Hypertension: Assessing Temporal Renal Inflammation Responses to Renal Denervation by Urinary Cytokine Excretion in the DOCA‐Salt Rat
Authors: Banek Christopher T. , Osborn John W. 
Published: June 2021

Preclinical and clinical studies demonstrate renal sympathetic denervation (RDN) may be an effective treatment for hypertension and end stage renal disease; however, the mechanisms of this effect remain unknown. We recently reported (RDN) mitigates hypertension in addition to the concomitant renal inflammation in the deoxycorticosterone acetate (DOCA)‐salt rat model. In this model, renal inflammation is hypothesized to drive the hypertension, but the timing and relationship to arterial pressure remain elusive. In this study, we aimed to elucidate the temporal renal inflammatory and arterial pressure response to DOCA‐salt through repeated‐measurement of urinary pro‐inflammatory cytokine excretion, and test the responsiveness to renal sympathetic denervation. We hypothesize that (a) RDN would mitigate renal and urinary cytokine content, and (b) a decrease urinary cytokine content due to RDN would precede changes in arterial pressure. To test this hypothesis, 12 uninephrectomized adult male Sprague Dawley rats (300–325 g) were implanted with radiotelemeters to measure 24‐hour mean arterial pressure (MAP) weekly, and received either surgical renal denervation (RDN; n=6) or sham procedure (Sham; n=6). One week following, both groups were administered DOCA (100 mg, s.c.) and 0.9% saline for 21 days. 6‐hour urine samples were collected weekly over ice using metabolic cage housing. At day 21, rats were anesthetized, and renal tissue was collected for cytokine and histological analysis. Pro‐inflammatory cytokines (IL‐1β, IL‐2, IL‐6, GRO/KC, MCP‐1) were measured by Luminex assay in both urine and renal tissue. Renal and urinary cytokine content were normalized to total protein and creatinine, respectively. Temporal response data analyzed by two‐way repeated measured ANOVA with Bonferroni post‐hoc test (α=0.05). All other data were analyzed by Student's t‐test. Data presented as mean±SEM. MAP response over 21‐day DOCA‐salt treatment was attenuated (*p<.05) by RDN vs. Sham, where MAP significantly diverged at Days 14–21 (see Data Table). Similarly, all measured pro‐inflammatory cytokines in renal parenchymal protein isolates were markedly reduced (*p<.05) in RDN vs. Sham ‐ a reduction of 42–70% of Sham values (see Data Table). Interestingly, urinary cytokine excretion on day 21 mirrored this effect, where each cytokine was lower (*p<.05) in RDN vs. Sham – similarly reduced by 44–84% Sham values (see Data Table). Of note, no difference was observed between RDN and Sham urinary cytokine content on Days 0–7, and only urinary IL‐1β and IL‐2 were reduced (*p<.05) at Day 14 (see Data Table). Histological analysis of renal injury and immune cell (macrophage, T‐cell) infiltration is currently underway to establish the end organ damage and immune cell specificity in the reported anti‐inflammatory effects of RDN. Taken together, these data support our first hypothesis of urinary cytokines reflect renal inflammatory cytokine content, and both are abated by RDN. However, our second hypothesis was not supported by the current data, as MAP was reduced in the RDN‐treated group prior to a significant reduction of most urinary cytokines. With these findings, we hypothesize that DOCA‐salt hypertension may precede the renal inflammation in this model. Further studies are necessary to elucidate the source of renal inflammation in this model, and its relationship to arterial pressure control.Support or Funding InformationThis project was supported in part by NIH HL116476 (JWO) and AHA 17POST33661003 (CTB).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.