Secretin: Should we revisit its metabolic outcomes?

Expression of Secretin and its Receptor Along the Intestinal Tract in Type 2 Diabetes Patients and Healthy Controls

CONTEXT

The hormone secretin (SCT) is released from intestinal S cells and acts via the SCT receptor (SCTR). Circulating SCT levels increase after Roux-en-Y gastric bypass surgery and have been associated with massive weight loss and high remission rates of type 2 diabetes (T2D) linked to these operations. Exogenous SCT was recently shown to reduce ad libitum food intake in healthy volunteers.

OBJECTIVE

To understand SCT biology and its potential role in T2D pathophysiology, we examined the intestinal mucosal expression profile of SCT and SCTR and evaluated the density of S cells along the intestinal tract of individuals with T2D and healthy controls.

METHODS

Using immunohistochemistry and messenger RNA (mRNA) sequencing, we analyzed intestinal mucosa biopsies sampled along the small intestine at 30-cm intervals and from 7 well-defined anatomical sites along the large intestine (during 2 sessions of double-balloon enteroscopy) in 12 individuals with T2D and 12 healthy controls.

RESULTS

Both groups exhibited a progressive and similar decrease in SCT and SCTR mRNA expression and S-cell density along the small intestine, with reductions of 14, 100, and 50 times, respectively, in the ileum compared to the duodenum (used as reference). Negligible amounts of SCTR and SCT mRNA, as well as low S-cell density, were found in the large intestine. No significant differences were observed between the groups.

CONCLUSION

SCT and SCTR mRNA expression and S-cell density were abundant in the duodenum and decreased along the small intestine. Very low SCT and SCTR mRNA levels and S-cell numbers were observed in the large intestine, without aberrations in individuals with T2D compared to healthy controls.

Jejunal response to secretin is independent of the pancreatic response in secretin-enhanced magnetic resonance cholangiopancreatography

PURPOSE

To investigate whether jejunal secretions are independent of the pancreatic response to secretin in secretin-enhanced Magnetic Resonance Cholangiopancreatography (s-MRCP) examination of subjects with and without chronic pancreatitis (CP).

METHODS

Patients were identified through a search of s-MRCP examinations performed between 2014-2016 (n = 513) as well as the multidisciplinary pancreatitis clinic registry (n = 586). Fifty cases with CP (based on M-ANNHEIM criteria) and 50 matched controls were selected. Signal intensity changes after secretin administration (˜1-5 min' post-secretin response) in three locations were assessed: second portion of the duodenum (D2), third/fourth portions of the duodenum (D3-4), and the jejunum. The post-secretin response was compared between (cases vs. controls) and within the study groups.

RESULTS

There was a significantly lower 1-5 min' post-secretin response among CP patients in D2 (all p-values <0.01). However, no significant difference in 1-5 min' post-secretin response was detected in the jejunum. Minute-by-minute analysis of the post-secretin response showed a significant increase up to the 5th minute only in D2 of the control group. The post-secretin response in the jejunum was significant after 1 min but was similar among patients with CP and controls. CP was a significant determinant of post-secretin response in D2 but not in the jejunum.

CONCLUSIONS

Early post-secretin response at jejunum is independent of the pancreatic response that can be detected at D2, and should not be misinterpreted as a rapid pancreatic response. Therefore, pancreatic function on s-MRCP should be assessed by the presence of fluid in D2 and not jejunum.

Lipolytic actions of secretin in mouse adipocytes

Secretin (Sct), a classical gut hormone, is now known to play pleiotropic functions in the body including osmoregulation, digestion, and feeding control. As Sct has long been implicated to regulate metabolism, in this report, we have investigated a potential lipolytic action of Sct. In our preliminary studies, both Sct levels in circulation and Sct receptor (SctR) transcripts in adipose tissue were upregulated during fasting, suggesting a potential physiological relevance of Sct in regulating lipolysis. Using SctR knockout and Sct knockout mice as controls, we show that Sct is able to stimulate lipolysis in vitro in isolated adipocytes dose- and time-dependently, as well as acute lipolysis in vivo. H-89, a protein kinase A (PKA) inhibitor, was found to attenuate lipolytic effects of 1 μM Sct in vitro, while a significant increase in PKA activity upon Sct injection was observed in the adipose tissue in vivo. Sct was also found to stimulate phosphorylation at 660^ser of hormone sensitive lipase (HSL) and to bring about the translocation of HSL from cytosol to the lipid droplet. In summary, our data demonstrate for the first time the in vivo and in vitro lipolytic effects of Sct, and that this function is mediated by PKA and HSL.

Effect of secretin on preadipocyte, differentiating and mature adipocyte functions

OBJECTIVE

Several gastrointestinal peptides are now recognized to have target functions beyond the intestinal wall, including effects on adipocytes. Secretin (SEC), one of the first identified, has not been evaluated in this context.

METHODS

Using cultured 3T3-L1 preadipocytes, adipocytes and primary rat adipocytes we evaluated the effect of SEC on cell proliferation, mitochondrial activity, differentiation, triglyceride (TG) synthesis, lipolysis as well expression of the SEC receptor (SCTR) in rodent and human adipose tissues.

RESULTS

In preadipocytes, SEC significantly increased mitochondrial activity (115%; P<0.01), thymidine incorporation (149.7%; P<0.05) and C/EBPβ expression (123.4%; P<0.05). During standard differentiation, SCTR mRNA increased up to a maximum of ninefold (P<0.001). In human adipose tissue, SCTR correlated with body mass index and plasma insulin, and SCTR mRNA expression was also detected in rat adipose tissues. SEC supplementation during differentiation enhanced TG accumulation (+138%; P<0.01). In mature adipocytes, SEC increased fatty acid (FA) uptake (186%; P<0.01), adiponectin and monocyte chemotactic protein-1 secretion (+142% and +149%, respectively; P<0.05) and mRNA expression of PPARγ (+206%; P<0.01), FABP4 (+164%; P<0.001), DGAT-1 (+144%; P<0.01), adiponectin (+138%; P<0.001) and CD36 (+149%; P<0.05). In primary rat adipocytes, SEC also increased FA uptake (137%; P<0.05). Pretreatment with a SEC antagonist impaired SEC-induced FA uptake and cAMP accumulation. SEC treatment simultaneously stimulated lipolysis measured as glycerol release in 3T3-L1 adipocytes and rat adipose tissue.

CONCLUSION

The present results suggest that SEC is a potent modulator of adipocyte functions, demonstrating overall a role in enhanced substrate cycling.

Secretin-enhanced MRCP: review of technique and application with proposal for quantification of exocrine function

OBJECTIVE

The purpose of this article is to present a proposal for quantification of exocrine function using secretin-enhanced MRCP for the diagnosis of chronic pancreatitis. The article also reviews the technique and application of secretin-enhanced MRCP in evaluating various pancreatic abnormalities.

SUBJECTS AND METHODS

One hundred thirty-four consecutive patients with chronic abdominal pain undergoing secretin-enhanced MRCP for suspected chronic pancreatitis were included. Patients were divided into four clinical groups (normal, equivocal, early chronic pancreatitis, established pancreatitis) on the basis of clinical symptoms and additional investigations, including CT (n=98), endoscopic pancreatic function test (n=65), endoscopic ultrasound (n=84), and ERCP (n=36). The volume of secretion was obtained by drawing a region of interest around T2 bright fluid secreted on postsecretin HASTE images. The maximal rate of secretion in response to secretin was obtained by plotting change in signal intensity on sequential postsecretin images. The analysis of variance test was used to compare the clinical groups with the volume and rate of secretion.

RESULTS

Significant volume differences were found between the normal and established pancreatitis groups (p<0.0001) as well as the equivocal and established pancreatitis groups (p<0.0005). Marginally significant differences were found between the normal and early pancreatitis groups (p=0.0150) as well as early and established pancreatitis groups (p=0.0351). Differences in the maximal rate of secretion were not statistically significant.

CONCLUSION

Secretory volume measurement of secretin-enhanced MRCP data is a simple method that brings out significant differences between normal, early, and established pancreatitis patients.