The metabolic actions of neurotensin secreted from the gut

Mechanisms underlying probiotic effects on neurotransmission and stress resilience in fish via transcriptomic profiling

In recent years, studies have highlighted the significant impact of probiotic treatment on the central nervous system (brain) and stress regulation through the microbiota-gut-brain axis, yet there have been limited knowledge on this axis in fish. Therefore, this study aimed to enhance the current understanding of the mechanisms underlying probiotic effects on neurotransmission and stress alleviation in fish through transcriptomic profiling. In this study, olive flounders (Paralichthys olivaceus) were subjected to two trial setups: a 1-month lab-scale trial and a 6-month field-scale trial, with and without the probiotic strain Lactococcus lactis WFLU12. RNA-Seq analysis was performed using liver samples collected from fish at one-month post-feeding (mpf) in both trials. Additionally, fish growth was monitored monthly, and serological parameters were measured at one mpf in the field-scale experiment. The results of the lab-scale trial showed that probiotic administration significantly upregulated genes related to neurotransmission, such as htr3a, mao, ddc, ntsr1, and gfra2. These findings highlight the impact of probiotics on modulating neurotransmission via the microbiota-gut-brain axis. In the field-scale experiment, fish growth was significantly promoted and the sera levels of AST, LDH, and cortisol were significantly higher in the control group compared to the probiotics group. Furthermore, genes involved in stress responses (e.g. hsp70, hsp90B1, hspE1, prdx1, and gss) and transcriptional regulators (e.g. fos, dusp1, and dusp2) exhibited significant upregulation in the control group compared to the probiotics group, indicating that probiotic administration can alleviate stress levels in fish. Overall, this study provides valuable insights into the mechanisms underlying the beneficial effects of probiotics in fish, specifically regarding their impact on neurotransmission and stress alleviation.

Increased meal-induced neurotensin response predicts successful maintenance of weight loss - Data from a randomized controlled trial

BACKGROUND

The gut derived anorexigenic hormone neurotensin (NT) is upregulated after bariatric surgery which may contribute to the sustained weight loss. In contrast, diet-induced weight loss is most often followed by weight regain. We therefore investigated whether diet-induced weight loss impacts levels of circulating NT in mice and humans and whether NT levels predicts body weight change after weight loss in humans.

METHODS

In vivo mice study: Obese mice were fed ad-libitum or a restricted diet (40-60 % of average food intake) for 9 days to obtain similar weight loss as observed in the human study. At termination, intestinal segments, the hypothalamus and plasma were collected for histological, real time PCR, and radioimmunoassay (RIA) analysis.

CLINICAL TRIAL

Plasma samples from 42 participants with obesity, completing an 8-week low-calorie diet in a randomized controlled trial, were analyzed. Plasma NT was measured by RIA at fasting and during a meal test before and after diet-induced weight loss and after one year of intended weight maintenance.

RESULTS

In obese mice, food restriction-induced body weight loss of 14 % was associated with a 64 % reduction in fasting plasma NT (p < 0.0001). In the mouse duodenum (p = 0.07) and jejunum (p < 0.05), NT tissue concentration was decreased without tissue atrophy indicative of a physiological downregulation. In the mouse hypothalamus a downregulation of Pomc (p < 0.01) along with upregulation of Npy (p < 0.001) and Agrp (p < 0.0001) expression was found after restricted feeding in support of increased hunger after diet-induced weight loss. Therefore, we investigated the NT response in humans undergoing weight loss maintenance. In humans, similar to the mice, the low-calorie diet induced weight loss of 13 % body weight was associated with 40 % reduction in fasting plasma NT levels (p < 0.001). Meal-induced NT peak responses were greater in humans who lost additional weight during the 1 year maintenance phase compared to participants who regained weight (p < 0.05).

CONCLUSION

Diet-induced weight loss decreased fasting plasma NT levels in both humans and mice with obesity, and regulated hunger-associated hypothalamic gene expression in mice. Meal-induced NT responses were greater in humans who lost additional weight during the 1 year maintenance phase compared to participants who regained weight. This indicates that increased peak secretion of NT after weight loss may contribute to successful maintenance of weight loss.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02094183.

Comparison of independent and combined effects of the neurotensin receptor agonist, JMV-449, and incretin mimetics on pancreatic islet function, glucose homeostasis and appetite control

BACKGROUND

Neurotensin receptor activation augments the biosctivity of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). JMV-449, a C-terminal neurotensin-like fragment with a reduced peptide bond, represents a neurotensin receptor agonist.

METHODS

The present study assessed the actions of JMV-449 on pancreatic beta-cells alone, and in combination with GIP and GLP-1. Further studies examined the impact of JMV-449 and incretin mimetics on glucose homeostasis and appetite control in mice.

RESULTS

JMV-449 was resistant to plasma enzyme degradation and induced noticeable dose-dependent insulin-releasing actions in BRIN-BD11 beta-cells. In combination with either GIP or GLP-1, JMV-449 augmented (P < 0.05) the insulinotropic actions of both hormones, as well as enhancing (P < 0.001) insulin secretory activity of both incretin peptides. JMV-449 also increased beta-cell proliferation and induced significant benefits on beta-cell survival in response to cytokine-induced apoptosis. JMV-449 (25 nmol/kg) inhibited (P < 0.05-P < 0.001) food intake in overnight fasted lean mice, and enhanced (P < 0.01) the appetite supressing effects of an enzymatically stable GLP-1 mimetic. When injected co-jointly with glucose, JMV-449 evoked glucose lowering actions, but more interestingly significantly augmented (P < 0.05) the glucose lowering effects of established long-acting GIP and GLP-1 receptor mimetics. In terms of glucose-induced insulin secretion, only GIP receptor signalling was associated with increases in insulin concentrations, and this was not enhanced by JMV-449.

CONCLUSION

JMV-449 is a neurotensin receptor agonist that positively augments key aspects of the biological action profile of GIP and GLP-1.

GENERAL SIGNIFICANCE

These observations emphasise the, yet untapped, therapeutic potential of combined neurotensin and incretin receptor signalling for diabetes.