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.