Liraglutide alters DPP4 in the circumvallate papillae of type 2 diabetic rats

Glucagon-like peptide-1, a matter of taste?

Understanding of gustatory coding helps to predict, and perhaps even modulate the ingestive decision circuitry, especially when eating behaviour becomes dysfunctional. Preclinical research demonstrated that glucagon like peptide 1 (GLP-1) is locally synthesized in taste bud cells in the tongue and that GLP-1 receptor exists on the gustatory nerves in close proximity to GLP-1 containing taste bud cells. In humans, the tongue has not yet been addressed as clinically relevant target for GLP-1 based therapies. The primary aim of the current review was to elaborate on the role of GLP- 1 in mammalian gustatory system, in particular in the perception of sweet. Secondly, we aimed to explore what modulates gustatory coding and whether the GLP-1 based therapies might be involved in regulation of taste perception. We performed a series of PubMed, Medline and Embase databases systemic searches. The Population-Intervention-Comparison-Outcome (PICO) framework was used to identify interventional studies. Based on the available data, GLP-1 is specifically involved in the perception of sweet. Aging, diabetes and obesity are characterized by diminished taste and sweet perception. Calorie restriction and bariatric surgery are associated with a diminished appreciation of sweet food. GLP-1 receptor agonists (RAs) modulate food preference, yet its modulatory potential in gustatory coding is currently unknown. Future studies should explore whether GLP-1 RAs modulate taste perception to the extent that changes of food preference and consumption ensue.

Glucagon-Like Peptide 1 and Taste Perception: From Molecular Mechanisms to Potential Clinical Implications

Preclinical studies provided some important insights into the action of glucagon-like peptide 1 (GLP-1) in taste perception. This review examines the literature to uncover some molecular mechanisms and connections between GLP-1 and the gustatory coding. Local GLP-1 production in the taste bud cells, the expression of GLP-1 receptor on the adjacent nerves, a functional continuum in the perception of sweet chemicals from the gut to the tongue and an identification of GLP-1 induced signaling pathways in peripheral and central gustatory coding all strongly suggest that GLP-1 is involved in the taste perception, especially sweet. However, the impact of GLP-1 based therapies on gustatory coding in humans remains largely unaddressed. Based on the molecular background we encourage further exploration of the tongue as a new treatment target for GLP-1 receptor agonists in clinical studies. Given that pharmacological manipulation of gustatory coding may represent a new potential strategy against obesity and diabetes, the topic is of utmost clinical relevance.

Glucagon-like peptide-1, a matter of taste?

Understanding of gustatory coding helps to predict, and perhaps even modulate the ingestive decision circuitry, especially when eating behaviour becomes dysfunctional. Preclinical research demonstrated that glucagon like peptide 1 (GLP-1) is locally synthesized in taste bud cells in the tongue and that GLP-1 receptor exists on the gustatory nerves in close proximity to GLP-1 containing taste bud cells. In humans, the tongue has not yet been addressed as clinically relevant target for GLP-1 based therapies. The primary aim of the current review was to elaborate on the role of GLP- 1 in mammalian gustatory system, in particular in the perception of sweet. Secondly, we aimed to explore what modulates gustatory coding and whether the GLP-1 based therapies might be involved in regulation of taste perception. We performed a series of PubMed, Medline and Embase databases systemic searches. The Population-Intervention-Comparison-Outcome (PICO) framework was used to identify interventional studies. Based on the available data, GLP-1 is specifically involved in the perception of sweet. Aging, diabetes and obesity are characterized by diminished taste and sweet perception. Calorie restriction and bariatric surgery are associated with a diminished appreciation of sweet food. GLP-1 receptor agonists (RAs) modulate food preference, yet its modulatory potential in gustatory coding is currently unknown. Future studies should explore whether GLP-1 RAs modulate taste perception to the extent that changes of food preference and consumption ensue.

GLP 1 Regulated Intestinal Cell's Insulin Expression and Selfadaptation before the Onset of Type 2 Diabetes

Purpose: Basically insulin is known to be secreted by β cells of the pancreas. Recently, it has also been found to be produced and expressed by intestinal epithelial cells with the help of L cells secreting glucagon like peptide 1 (GLP 1). Here, we have studied the same intestinal insulin expression property in T2D rats.

Methods: Following 2 weeks of high fat diet (HFD) consumption, we have been given a single dose of streptozotocin (STZ) (35 mg/kg bw). Rats were then sacrificed after 1, 7 and 21 days. The GLP 1 analogue, liraglutide was also given to one group of diabetic rats, upto their respective durations. Intestinal cells apoptosis were checked by tunnel assay, Incretin hormones secretion and dipeptidyl peptidase 4 (DPP-IV) activity were analyzed through ELISA and immunohistochemistry was used to determine the insulin expression of intestine at different time interval during diabetes progression.

Results: As compared to 1 and 21 days, we have found minor cells apoptosis in 7 days group along with high level of GLP 1 in diabetic model. Further, these effects were enhanced by liraglutide. In response to these we have found, decreased insulin expression after 21 days and with no significant effect upto 7 days in diabetic control groups. In contrast to this, GLP-1 level and insulin expression enhances prominently after 7 days of liraglutide treatment.

Conclusion: These results explain the self-adapting approach of intestinal cells against diabetes onset and insulin expression enhancing property of liraglutide under stressful conditions. This study should be continued in future for the development of intestinal insulin producing drugs, to control diabetes under irreversible β cells damage.

Nonglycemic Effects of GLP-1 Agonists: From a Starling to Lizards to People

With the approval of exenatide in 2005, physicians had a new class of hypoglycemic agents available for the treatment of type 2 diabetes-the glucagon-like peptide-1 receptor agonists (or GLP-1 receptor agonists). As of this writing, there are seven drugs in this class available in the United States. In addition to demonstrating either cardiovascular risk neutrality or overt benefit, as now mandated by the United States Food and Drug Administration (FDA), many of these drugs have other, unexpected actions. It is our goal to outline these actions, some beneficial, some not. We have reviewed English-language articles in this area, not for an exhaustive study, but rather a broad search to define current understanding and perhaps generate further investigation.

Dysregulation of DPP4 Is Associated with the AMPK/JAK2/STAT3 Pathway in Adipocytes Under Insulin Resistance Status and Liraglutide Intervention

PURPOSE

Dipeptidyl peptidase 4 (DPP4) is one of the newly identified adipokines, which acts as paracrine in adipose tissue and as endocrine hormones in the liver, muscles and central nervous system. Expression of DPP4 was significantly upregulated in obese patients upon insulin resistance (IR) conditions, but the mechanism underlying the dysregulation of DPP4 remains unclear. This study aimed to investigate the DPP4 expression in adipose tissue and adipocytes under IR conditions or with liraglutide intervention, and explore the potential molecular mechanisms.

METHODS

Obesity-associated IR animal and cell models were, respectively, constructed by using high-fat diet and palmitic acid (PA) stimulation. Expression of DPP4 in adipose tissues and adipocytes was estimated by quantitative real-time RT-PCR and Western-blot. Effects of the AMPK/JAK2/STAT3 pathway on DPP4 were examined by regulating the activity of AMPK and the JAK2/STAT signaling. The therapeutic efficacy of liraglutide in the IR models was evaluated, and its regulatory effects on DPP4 expression and the underlying molecular mechanisms were explored.

RESULTS

The expression of DPP4 was markedly upregulated in both the animal and cell IR models. In the adipocyte, DPP4 expression was found to be suppressed by the activation of AMPK, and this inhibition effect was mediated by the JAK2/STAT3 signaling. Moreover, liraglutide could alleviate the obesity-induced IR, and led to the downregulation of DPP4 in IR animal and cell models. Liraglutide intervention resulted in the activation of AMPK and deactivation of the JAK2/STAT3 signaling in the adipocytes.

CONCLUSION

Taken together, the expression of DPP4 is upregulated in adipose tissues and adipocytes upon IR conditions, but is reduced after liraglutide intervention. The dysregulation of DPP4 in the adipocytes may be performed by the AMPK/JAK2/STAT3 pathway.