Impact of novel amino acid substituted and acylated spexin analogues on pancreatic beta-cell function, appetite and glucose homeostasis

Objective: The neuropeptide spexin is recognised as a satiety-inducing hormone, but overall effects on metabolism are less characterised. Rapid enzymatic metabolism means elucidating biological effects of spexin is challenging, because the bioactive profile is short. Methods: Therefore, in the present study, an Asp¹ for Asn¹ substituted spexin analogue, D¹Spx, alongside two related fatty acid derivatised analogues, (γGlu-Pal)-D¹Spx and (K¹¹γGlu-Pal)-D¹Spx, were synthesised and effects on pancreatic beta-cell secretory function and health investigated together with impact on appetite and glucose homeostasis in mice. Results: Spexin immunoreactivity was initially confirmed in BRIN-BD11 beta-cells. Interestingly, like native spexin, D¹Spx was liable to plasma enzyme degradation, but the fatty acid derivatised molecules remained intact. None of the peptides augmented insulin secretion from BRIN-BD11 cells. Moreover, the spexin peptides inhibited alanine‐induced insulin secretion, with native spexin having no effect on intracellular calcium. However, all spexin peptides (10⁻⁸ and 10⁻⁶ M) promoted beta-cell proliferation, whilst native spexin and (γGlu-Pal)-D¹Spx protected against cytokine-induced beta-cell apoptosis. When administered intraperitoneally to mice, spexin peptides lacked effects on appetite regulation, even at elevated doses of 250 nmol/kg. Following conjoint injection with saline, none of the spexin peptides affected blood glucose levels barring a negligible increase by D¹Spx. When administered together with glucose, (γGlu-Pal)-D¹Spx slightly increased blood glucose at 30 min post-injection, but there was no overall difference between the spexin peptides when compared to glucose alone. Conclusions: Acylation creates stable spexin analogues with similar bioactivity as native spexin, including promotion of beta-cell proliferation and partial protection against apoptosis.