The ellagitannin metabolite urolithin C is a glucose‐dependent regulator of insulin secretion through activation of L‐type calcium channels

Abstract

Background and Purpose The pharmacology of polyphenol metabolites on beta‐cell function is largely undetermined. We sought to identify polyphenol metabolites that enhance the insulin‐secreting function of beta‐cells and to explore the underlying mechanisms. Experimental Approach INS‐1 beta‐cells and rat isolated islets of Langerhans or perfused pancreas preparations were used for insulin secretion experiments. Molecular modelling, intracellular Ca2+ monitoring, and whole‐cell patch‐clamp recordings were used for mechanistic studies. Key Results Among a set of polyphenol metabolites, we found that exposure of INS‐1 beta‐cells to urolithins A and C enhanced glucose‐stimulated insulin secretion. We further characterized the activity of urolithin C and its pharmacological mechanism. Urolithin C glucose‐dependently enhanced insulin secretion in isolated islets of Langerhans and perfused pancreas preparations. In the latter, enhancement was reversible when glucose was lowered from a stimulating to a non‐stimulating concentration. Molecular modelling suggested that urolithin C could dock into the Cav1.2 L‐type Ca2+ channel. Calcium monitoring indicated that urolithin C had no effect on basal intracellular Ca2+ but enhanced depolarization‐induced increase in intracellular Ca2+ in INS‐1 cells and dispersed cells isolated from islets. Electrophysiology studies indicated that urolithin C dose‐dependently enhanced the L‐type Ca2+ current for levels of depolarization above threshold and shifted its voltage‐dependent activation towards more negative potentials in INS‐1 cells. Conclusion and Implications Urolithin C is a glucose‐dependent activator of insulin secretion acting by facilitating L‐type Ca2+ channel opening and Ca2+ influx into pancreatic beta‐cells. Our work paves the way for the design of polyphenol metabolite‐inspired compounds aimed at ameliorating beta‐cell function.

Urolithin C increases glucose‐induced ERK activation which contributes to insulin secretion

“…INS-1 cells were incubated for 1 h with 20 µM or 100 µM urolithin C in the absence or presence of 10 µM U0126 under glucose stimulating condition (Figure 4). As previously shown [25], urolithin C enhanced glucosestimulated insulin secretion and its effect was higher when used at 100 µM with respect to 20 µM (Figure 4 and see also Figure 5). Blocking ERK1/2 activation with 10 µM U0126 reduced the capacity of glucose to stimulate insulin secretion and inhibited the stimulatory effect of urolithin C regardless of its concentration (Figure 4).…”

“…This is particularly well described for urolithin A whose administration or dietary supplementation at pharmacological active dose was shown for instance to ameliorate insulin sensitivity [39], to protect from colonic diseases [40] and to attenuate age-related decline in mice [41,42]. In contrast to urolithin A, the potential beneficial effects that could ensue from the use of urolithin C are only emerging [25,[43][44][45] and its pharmacological mechanism has been poorly defined. In this context, we recently reported that urolithin C is a glucose-dependent activator of insulin secretion by facilitating L-type Ca 2+ channels opening in b-cells [25].…”

“…Effect of urolithin C on ERK1/2 activation We examined whether urolithin C modulated ERK1/2 activation by assessing their phosphorylation levels. To this aim, we used INS-1 cells as a model system because we previously reported that urolithin C modulated insulin secretion in this cell line in a similar fashion to that in isolated rat pancreatic islets and isolated perfused pancreas [25]. First, INS-1 cells were incubated for 1 h under non-stimulating (1.4 mM glucose) or 8.3 mM glucose-stimulated conditions with or without 20 µM of urolithin C, and then, Western blot analyses were carried out to assess ERK1/2 phosphorylation.…”

“…We found that urolithin C enhanced ERK1/2 phosphorylation under both glucose concentrations ( Figure 1). Since we previously found that the effect of urolithin C on glucose-induced insulin secretion peaked at 100 µM [25], INS-1 cells were next incubated under 8.3 mM glucosestimulated condition with or without urolithin C (20 and 100 µM) and ERK1/2 phosphorylation levels were analysed. As shown in Figure 2, we observed that the phosphorylation levels of ERK1/2 were higher following exposure of INS-1 cells to 100 µM urolithin C compared to 20 µM which suggested a dose-dependent effect of the compound.…”

“…Besides polyphenols, we recently reported that a few of their metabolites also exert pharmacological action in pancreatic b-cells. In particular, urolithin C, a gut microbiota-derived ellagitannin metabolite, elicited glucosedependent activation of insulin secretion in different pancreatic models [25]. However, it is still unknown whether urolithin C regulates key intracellular signalling proteins and the functional consequence of such potential modulation in pancreatic b-cells.…”