Urolithin A, a Product of the Microbiome, Attenuates the Palmitate‐TLR4 Inflammatory Pathway in Renal Tubule Cells

Abstract

Obesity is a major risk factor for cardiovascular disease and chronic renal injury. Tubulointerstial inflammation may reflect increased exposure of saturated fatty acids (sFA) to the renal epithelium and activation of the toll‐like receptor 4 (TLR4). Obesity‐induced inflammation may also facilitate gut microbiome dysbiosis and potentially alter the processing of exogenous polyphenolic compounds to metabolites with enhanced protective effects. Indeed, Urolithin A, the primary product of the microbiome metabolism of ellagitanins, promotes gut barrier function and attenuates colonic inflammation. However, the role of Urolithin A to attenuate tubular injury and inflammation has not been assessed. We propose that Urolithin A has anti‐inflammatory actions in rat proximal tubule cells (PTCs) chronically exposed to the sFA palmitate.PTCs (NRK‐52e cells) were exposed to palmitate [200 μM] for a 24 hours in the presence or absence of Urolithin A [50 μM], the TLR4 inhibitor TAK242 [1 μM], the EGFR inhibitor AG1478 [1 μM] and cSRC kinase inhibitor Dasatinib [10 μM] as both EGFR and cSRC may be integral to TLR4 activation. Cytokine expression in the PTCs was quantified by separate ELISAs.Palmitate exposure stimulated the robust release of PAI‐1 6‐fold [4.3 ± 0.3 vs. 24.2 ± 0.4 ng/ml; P<0.001, n=3], CCL2 150‐fold [0.04 ± 0.01 vs. 6.2 ± 0.4 ng/ml; P<0.001, n=3] and CCL5 10‐fold [23.4 ± 0.1 vs. 255 ± 11 pg/ml; P<0.001, n=3]. The TLR4 inhibitor abolished the increase in CCL2 and CCL5, and markedly attenuated PAI‐1 release [70%, P<0.01]. The EGFR inhibitor partially inhibited all three cytokines [40–50%, P<0.01] while the cSRC inhibitor abolished PAI‐1 and partially inhibited CCL5, but failed to inhibit CCL2 release. Urolithin A essentially abolished the increase in PAI‐1 and CCL5, and markedly inhibited CCL2 release to palmitate [70%, P<0.01].We conclude that Urolithin A may be renoprotective in obesity‐induced injury by targeting activation of TLR4 within the renal epithelium to attenuate the cytokine release. Moreover, a deficit in the microbiome‐dependent generation of Urolithin A may potentially promote renal inflammation.Support or Funding InformationChronic Disease Research Fund, AHA Transformative Grant 18TPA34170522; NIH R01HL146818, the Farley Hudson Foundation, the Hypertension & Vascular Research Center