β-hydroxybutyrate Alters Cell Composition and Gives Rise to Bihormonal Cells in Human Pancreatic Islets

Yun Suk Chae1, Ezra van der Wel1, Maaike de Vries1, Françoise Carlotti1, Marten Engelse1, Eelco de Koning1

1 Department of Internal Medicine, Leiden University Medical Center, Leiden, Netherlands

Yun Suk Chae: y.s.chae@lumc.nl

Background: Fasting triggers a metabolic switch from an anabolic to a catabolic state, resulting in increased lipolysis, and consequently ketogenesis. The most abundant type of ketone body produced through ketogenesis is β-hydroxybutyrate (βHB). βHB serves as an alternative fuel and a signaling molecule that alters gene expression and influences insulin and glucagon secretion. We hypothesized that βHB alters islet cell identity in human islets.

Methods: Isolated human islets were incubated with R-βHB or S-βHB, the non-metabolizable enantiomer, for 48 hours. Samples were taken for immunofluorescence staining, qPCR for ARX and PAX4 (transcription factors characteristic for β-cell and α-cell identity, respectively) and glucose stimulated insulin secretion.

Results: Immunofluorescence showed an increased α-to-β-cell ratio from 0.37±0.12 to 0.72±0.16 (p<0.0015), an increased proportion of C-peptide+/glucagon+ bihormonal cells from 3.0±1.7% to 4.7±2.3% (p<0.0117), and an increased proportion of NKX6.1+/glucagon+ cells from 5.0±1.1% to 9.4±3.3% (p<0.0338) (n=4-6). Control S-βHB did not result in alterations in islet cell composition. R-βHB treated islets showed an 1.85 fold upregulation of PAX4 and 1.7 fold upregulation of ARX (p<0.0071 and p<0.032; n =5). Furthermore, R-βHB resulted in a 46% reduction in insulin stimulation index (AUCinsulin 488±206 vs 263±83, p = 0.026; n=4). Staining for key components of ketone body metabolism revealed the presence of monocarboxylate transporter 1, relevant for ketone body transport into the cell in human islets.

Conclusion: The effects of β-hydroxybutyrate on reduction of insulin secretory capacity may not only be related to changes in β-cell function, but also to changes in islet cell identity. Thus, nutritional status may not only affect islet function but also islet cell composition.