Combined treatment with dipeptidyl peptidase 4 (DPP4) inhibitor sitagliptin and elemental diets reduced indomethacin-induced intestinal injury in rats via the increase of mucosal glucagon-like peptide-2 concentration

Pylorus ligation-induced hyperacidity: synergistic prophylactic effects of linagliptin and L-arginine via up-regulation of EP4 receptor subtype and improvement of vascular endothelial damage

Gastric hyperacidity and ulceration are chronic diseases characterized by repeated healing followed by re-exacerbation. The study aims to protect against gastric hyperacidity without interfering with gastric acid secretion. Pylorus ligation-induced hyperacidity is commonly utilized in the induction of gastric ulcers.Forty-two rats were distributed into seven groups (n = 6). Group I comprised sham-operated group. Group II served as pylorus-ligation group. Groups III-VII were given oral Linagliptin (LN; 3 and 6 mg/kg), L-arginine (LA; 150 and 300 mg/kg) and their combination (LN 3 + LA 150 mg/kg), respectively for 7 days. On the 8th day, groups II-VII were subjected to pylorus-ligation.Treatment of pylorus-ligated rats with LN, LA and their combination improved the gastric hyperacidity as exhibited by a marked reduction in the gastric juice volume, total and free acidities and pepsin contents with a noticeable increase in pH. Pre-treatment with LN, LA and their combination showed a marked alleviation in the gastric inflammatory indicators evidenced by reduction in the gastric levels of MCP-1and Il-1β as well as elevation of eNOS levels versus the sham-operated group. A marked up-regulation in the gastric gene expression of PGE, EP4 and VEGF accompanied by an improvement of the histopathologic pictures/scores, and TNF-α and caspase-3 immuno-staining were also recorded.By estimating the combination-index, it can be concluded that combining LN with LA exhibited prophylactic synergistic effects in ameliorating pylorus ligated-induced hyperacidity, mainly via up-regulation of EP4 receptor and improvement of vascular endothelial damage through VEGF expression in gastric mucosa.

Metabolic profiling and biological activity of two Livistona species: L. chinensis and L. australis

Livistona is a genus of family Arecaceae and widely grown in tropical areas. The phytochemical analysis of the leaves and fruits of two Livistona species, L. chinensis and L. australis were carried out using UPLC/MS and determination of the total phenolic and total flavonoid contents, in addition to the isolation and identification of five phenolic compounds and one fatty acid from L. australis fruits. The total phenolic compounds varied from 19.72 to 78.87 mg GAE g^-1 dry plant, while the total flavonoid contents were in the range of 4.82-17.75 mg RE g^-1 dry plant. The UPLC/MS analysis of the two species led to the characterization of forty-four metabolites belonging mainly to the different classes of flavonoids and phenolic acids, while the compounds isolated from L. australis fruits were identified as gallic acid, vanillic acid, protocatechuic acid, hyperoside, quercetin 3-O-α-d-arabinopyranoside and dodecanoic acid. The in vitro biological evaluation of L. australis leaves and fruits were estimated as anticholinesterase, telomerase reverse transcriptase (TERT) potentiation and anti-diabetic through measuring the capacity of the extracts to inhibit dipeptidyl peptidase (DPP-IV). The results revealed that the leaves showed remarkable anticholinesterase and antidiabetic activity compared to fruits with IC₅₀ values of 65.55 ± 3.75 ng mL^-1 and 90.8 ± 4.48 ng mL^-1, respectively. In the TERT enzyme assay, the leaves extract triggered a 1.49-fold increase in telomerase activity. This work showed that the Livistona species are a good source for flavonoids and phenolics, which play an important role in anti-aging and the treatment of chronic diseases, such as diabetes and Alzheimer's.

Repurposing of existing antibiotics for the treatment of diabetes mellitus

Proline specific serine protease enzyme, dipeptidyl peptidase IV (DPP-4) has become a promising target for diabetes, as it stops glucagon-like peptide 1 (GLP-1) from becoming inactive, resulting in higher levels of active GLP-1. This lowers glucose levels by increasing insulin secretion and decreasing glucagon secretion. DPP-4 is also linked to a higher BMI and a 0.7 to 1% reduction in HbA1c. Currently available DPP-4 inhibitor drugs showed less promising anti-diabetic activity as this class associated with many side effects due to non-selectivity and therefore searching on more potent DPP-4 inhibitors are still ongoing. In our present study, we investigate the inhibition of DPP-4 through a series of antibiotic compounds which were previously reported to be used in diabetic foot infections and compared with existing DPP-4 inhibitors. To obtain this objective, three-dimensional crystal structure of DPP-4 was retrieved from the protein data bank (PDB id: 1 × 70). A systematic computational method combining molecular docking, MM-GBSA binding energy calculation, MD simulations, MM-PBSA binding free energy calculations and ADME were used to find best DPP-4 inhibitor. Molecular docking results revealed that clindamycin has a higher affinity towards the catalytic sides of DPP-4 and built solid hydrophobic and polar interactions with the amino acids involved in the binding region of DPP-4, such as S1 subsite, S2 subsite and S2 extensive subsite. MD simulations results showed clindamycin as potent virtual hit and suggested that it binds with DPP-4 in competitive manner, which virtually indicate that besides antibiotic activity clindamycin has anti-diabetic activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-021-00118-6.

The Role of Dipeptidyl Peptidase 4 as a Therapeutic Target and Serum Biomarker in Inflammatory Bowel Disease: A Systematic Review

BACKGROUND

The roles dipeptidyl peptidase 4 (DPP4), aminopeptidase N (APN), and their substrates in autoimmune diseases are being increasingly recognized. However, their significance in inflammatory bowel diseases (IBD) is not entirely understood. This systematic review aims to discuss the pathophysiological processes related to these ectopeptidases while comparing findings from preclinical and clinical settings.

METHODS

This review was conducted according to the PRISMA guidelines. We performed a literature search in PubMed, SCOPUS, and Web of Science to identify all reports from inception until February 2020. The search included validated animal models of intestinal inflammation and studies in IBD patients. Quality assessment was performed using SYRCLE's risk of bias tool and CASP qualitative and cohort checklists.

RESULTS

From the 45 included studies, 36 were performed in animal models and 12 in humans (3 reports included both). Overall, the methodological quality of preclinical studies was acceptable. In animal models, DPP4 and APN inhibition significantly improved intestinal inflammation.Glucagon-like peptide (GLP)-1 and GLP-2 analogs and GLP-2-relase-inducing drugs also showed significant benefits in recovery from inflammatory damage. A nonsignificant trend toward disease remission with the GLP-2 analog teduglutide was observed in the sole interventional human study. All human studies reported an inverse correlation between soluble DPP4/CD26 levels and disease severity, in accordance with the proposal of DPP4 as a biomarker for IBD.

CONCLUSIONS

The use of DPP4 inhibitors and analogs of its substrates has clear benefits in the treatment of experimentally induced intestinal inflammation. Further research is warranted to validate their potential diagnostic and therapeutic applications in IBD patients.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, in patients with short bowel syndrome and colon in continuity: an open-label pilot study

OBJECTIVE

Patients with short bowel syndrome (SBS) and colon in continuity have better adaptation potential compared with patients with jejunostomy. Adaptation may involve enhanced postprandial secretion of the enteroendocrine hormones glucagon-like peptide (GLP)-1 and GLP-2 which are normally degraded by dipeptidyl peptidase (DPP)-4. Nevertheless, some patients with SBS with colon in continuity suffer from high-volume faecal excretions and have been shown to benefit from treatment with GLP-2. Therefore, we aimed to evaluate efficacy of sitagliptin, a DPP-4 inhibitor, on reducing faecal excretions in this patient group.

DESIGN

In an open-label, case series, proof-of-concept pilot study, 100 mg oral sitagliptin was given two times per day for 8 weeks to patients with SBS with ≥50% colon in continuity with or without the need for parenteral support (PS). To assess intestinal function, metabolic balance studies were done at baseline and following 8 weeks of treatment.

RESULTS

Of the 10 patients planned for enrolment, 8 patients were included; 7 patients completed the study. Although postprandial endogenous GLP-2 concentrations increased by 49 hours×pmol/L (39, 105; p=0.018) (median (min, max)), sitagliptin did not significantly reduce median faecal wet weight (-174 g/day (-1510, 675; p=0.176)) or increase intestinal wet weight absorption. However, heterogeneity in the treatment effect was observed: intestinal wet weight absorption increased in all four patients with intestinal failure. One patient achieved a reduction in PS by 500 mL per administration day.

CONCLUSION

Following this negative, small pilot study, larger, placebo-controlled, studies are needed to establish the therapeutic potential of DPP-4 inhibition in patients with SBS.

Structure⁻Activity Relationship and Molecular Docking of Natural Product Library Reveal Chrysin as a Novel Dipeptidyl Peptidase-4 (DPP-4) Inhibitor: An Integrated In Silico and In Vitro Study

Numerous studies indicate that diets with a variety of fruits and vegetables decrease the incidence of severe diseases, like diabetes, obesity, and cancer. Diets contain a variety of bioactive compounds, and their features, like diverge scaffolds, and structural complexity make them the most successful source of potential leads or hits in the process of drug discovery and drug development. Recently, novel serine protease dipeptidyl peptidase-4 (DPP-4) inhibitors played a role in the management of diabetes, obesity, and cancer. This study describes the development of field template, field-based qualitative structure⁻activity relationship (SAR) model demonstrating DPP-4 inhibitors of natural origin, and the same model is used to screen virtually focused food database composed of polyphenols as potential DPP-4 inhibitors. Compounds’ similarity to field template, and novelty score “high and very high”, were used as primary criteria to identify novel DPP-4 inhibitors. Molecular docking simulations were performed on the resulting natural compounds using FlexX algorithm. Finally, one natural compound, chrysin, was chosen to be evaluated experimentally to demonstrate the applicability of constructed SAR model. This study provides the molecular insights necessary in the discovery of new leads as DPP-4 inhibitors, to improve the potency of existing DPP-4 natural inhibitors.

Dipeptidyl peptidase-4 inhibitors have adverse effects for the proliferation of human T cells

Dipeptidyl peptidase-4 (DPP-4) is a critical molecule for the metabolism of incretins. In addition, DPP-4 is known as CD26, the receptor of T cells, and plays important role in activation of T cells. Recently, DPP-4 inhibitors (DPP4i) are reported to have several immunologic effects beyond glycemic control. DPP4i seem to have anti-inflammatory effects in patients with type 2 diabetes. This might be direct effects on T cells. However, the close mechanism is not clear. To evaluate the possibility, we performed ex vivo assays by using primarily human CD4⁺ T cells (CD4) and CD8⁺ T cells (CD8). We purified primary naïve CD4 and CD8 from human peripheral blood. Then, we evaluated the effect of DPP4i on the proliferation of naïve T cells and the cytokine production in ex vivo experiments. The proliferation of CD4 and CD8 were suppressed by adding DPP4i in a dose dependent manner. However, DPP4i did not inhibit cytokine production from CD4. It was revealed by phospho-flow that the T cell receptor (TCR) signaling was attenuated in the presence of DPP4i. Taken together, DPP4i modulated TCR signaling, which contributed to attenuate the proliferation of CD4 and CD8. DPP4i have adverse effects for the proliferation of human T cells.

Effect of egualen sodium hydrate on small-intestinal mucosal damage induced by low-dose aspirin: a prospective randomized clinical trial

Low-dose aspirin, which is widely used to reduce the risk of cardio- and cerebrovascular thrombosis, often induces gastroenteropathy by increasing the permeability of the mucosa. However, therapeutic strategies for patients with low-dose aspirin-induced small intestinal injury have not been determined. We evaluated the preventative effect of egualen sodium hydrate, a gastro-protective agent that suppresses indomethacin-induced small-intestinal damage in rats, against small-intestinal mucosal damage induced by low-dose aspirin in healthy adult male volunteers. Participants were randomly allocated to receive aspirin 100 mg/kg daily (control group, n = 10) or aspirin 100 mg/kg plus egualen sodium 30 mg daily (egualen sodium group, n = 10). Small intestinal mucosal injury was evaluated by capsule endoscopy two weeks after initiation of drug administration. Fecal analyses (occult blood test, immunochemical test, transferrin measurement and calprotectin measurement) were carried out before and after treatment. Egualen sodium significantly suppressed the total number of small intestinal injuries detected by capsule endoscopy and the positive ratio for the fecal occult blood test. Daily use of 30 mg of egualen sodium showed a preventative effect on low-dose aspirin-induced small intestinal injury. Since acid suppression therapy was reported to exacerbate NSAIDs-induced enteropathy via dysbiosis, egualen sodium may be useful for patients treated with low-dose aspirin.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, suppresses CXCL5 and SDF-1 and does not accelerate intestinal neoplasia formation in ApcMin/+ mice fed a high-fat diet

The relationship between type 2 diabetes mellitus and intestinal neoplasia has been shown epidemiologically. A high-fat diet (HFD) is also known to promote insulin resistance, which is a risk factor for intestinal neoplasia. Dipeptidyl peptidase-4 (DPP-4) inhibitors are used in the clinic for the treatment of type 2 diabetes and also to prolong the effects of glucagon-like peptide-1 (GLP-1). However, since the intestinotrophic hormone GLP-2 and chemokines, such as CXCL5 and stromal cell-derived factor-1 (SDF-1), are also substrates of DPP-4, DPP-4 inhibitors may increase the risk of intestinal carcinogenesis. In this study, we evaluated the impact of a DPP-4 inhibitor on intestinal tumorigenesis in Apc^Min/+ mice fed a HFD. Six-week-old male Apc^Min/+ mice were randomized to either a normal diet (10 kcal% fat) group, a HFD (60 kcal% fat) group, or a HFD group treated with sitagliptin (STG). The mice were euthanized nine weeks after the start of treatment. Daily treatment with STG did not increase number of intestinal tumors in the HFD group; however, this increase was not statistically significant. The mucosal concentration of total GLP-2 was significantly increased in the HFD group. The chemokine protein array showed elevated plasma concentrations of CXCL5 and SDF-1 in the HFD group. The administration of STG significantly suppressed the levels of plasma CXCL5 and SDF-1 in mice fed a HFD. Since CXCL5 expression is increased in patients with type 2 diabetes, and GLP-2, CXCL5 and SDF-1 are associated with tumor progression, DPP-4 inhibition may have potential as an agent for decreasing the risk of cancer in obese or diabetic patients.

FFA3 Activation Stimulates Duodenal Bicarbonate Secretion and Prevents NSAID-Induced Enteropathy via the GLP-2 Pathway in Rats

BACKGROUND

Therapy with nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with enteropathy in humans and experimental animals, a cause of considerable morbidity. Unlike foregut NSAID-associated mucosal lesions, most treatments for this condition are of little efficacy. We propose that the endogenously released intestinotrophic hormone glucagon-like peptide-2 (GLP-2) prevents the development of NSAID-induced enteropathy. Since the short-chain fatty acid receptor FFA3 is expressed on enteroendocrine L cells and on enteric nerves in the gastrointestinal tract, we further hypothesized that activation of FFA3 on L cells protects the mucosa from injury via GLP-2 release with enhanced duodenal HCO₃^- secretion. We thus investigated the effects of synthetic selective FFA3 agonists with consequent GLP-2 release on NSAID-induced enteropathy.

METHODS

We measured duodenal HCO₃^- secretion in isoflurane-anesthetized rats in a duodenal loop perfused with the selective FFA3 agonists MQC or AR420626 (AR) while measuring released GLP-2 in the portal vein (PV). Intestinal injury was produced by indomethacin (IND, 10 mg/kg, sc) with or without MQC (1-10 mg/kg, ig) or AR (0.01-0.1 mg/kg, ig or ip) treatment.

RESULTS

Luminal perfusion with MQC or AR (0.1-10 µM) dose-dependently augmented duodenal HCO₃^- secretion accompanied by increased GLP-2 concentrations in the PV. The effect of FFA3 agonists was inhibited by co-perfusion of the selective FFA3 antagonist CF3-MQC (30 µM). AR-induced augmented HCO₃^- secretion was reduced by iv injection of the GLP-2 receptor antagonist GLP-2(3-33) (3 nmol/kg), or by pretreatment with the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR_inh-172 (1 mg/kg, ip). IND-induced small intestinal ulcers were dose-dependently inhibited by intragastric administration of MQC or AR. GLP-2(3-33) (1 mg/kg, ip) or CF3-MQC (1 mg/kg, ig) reversed AR-associated reduction in IND-induced enteropathy. In contrast, ip injection of AR had no effect on enteropathy.

CONCLUSION

These results suggest that luminal FFA3 activation enhances mucosal defenses and prevents NSAID-induced enteropathy via the GLP-2 pathway. The selective FFA3 agonist may be a potential therapeutic candidate for NSAID-induced enteropathy.

Gastrointestinal defense mechanisms

PURPOSE OF REVIEW

To summarize and illuminate the recent findings regarding gastroduodenal mucosal defense mechanisms and the specific biomolecules involved in regulating this process, such as glucagon-like peptides (GLPs).

RECENT FINDINGS

There has been a growing interest in luminal nutrient chemosensing and its physiological effects throughout the digestive system. From the ingestion of food in the oral cavity to the processing and absorption of nutrients in the intestines, nutrient chemosensing receptors signal the production and release of numerous bioactive peptides from enteroendocrine cells, such as the proglucagon-derived peptides. There has been a major emphasis on two proglucagon-derived peptides, namely GLP-1 and GLP-2, due to their apparent beneficial effect on gut structure, function, and on metabolic processes. As an incretin, GLP-1 not only enhances the effect and release of insulin on pancreatic βcells but also has been implicated in having trophic effects on the intestinal epithelium. In addition, GLP-2, the other major proglucagon-derived peptide, has potent intestinotrophic effects, such as increasing the rate of mucosal stem cell proliferation, mucosal blood flow, and fluid absorption, as well as augmenting the rate of duodenal bicarbonate secretion to improve gastric mucosal health and longevity.

SUMMARY

Understanding the mechanisms underlying nutrient chemosensing and how it relates to GLP release can further elucidate how the gut functions in response to cellular changes and disturbances. Furthermore, a more in-depth comprehension of GLP release and its tissue-specific effects will help improve the utility of GLP-1 and GLP-2 receptor agonists in clinical settings. This, in turn, should help patients suffering from intestinal failure, malabsorption, and mucosal injury.

Sitagliptin can inhibit the development of hepatic steatosis in high-fructose diet-fed ob/ob mice

The beneficial effect of dipeptidyl peptidase-4 inhibition on diet-induced extra-pancreatic effects, especially on liver tissue remains poorly understood. Thus, we made the experimental designs as follows; five-week-old male ob/ob mice, which develop type 2 diabetic mellitus and nonalcoholic fatty liver disease by taking a high-carbohydrate diet (HCD), were divided into a group in which a HCD was given for 8 weeks as control, and another in which a HCD added with 0.0018% sitagliptin was given for 8 weeks. Hepatic steatosis was seen in all mice, but the mean grade of steatosis in the sitagliptin-administrated mice was significantly decreased. The acetyl-CoA concentrations were lower in sitagliptin-administrated mice, although the differences were not significant. However, the malonyl-CoA concentrations were significantly lower in sitagliptin-administrated mice. The expression of acetyl-CoA carboxylase 1 was inhibited in sitagliptin-administrated mice, irrespective of expressions of carbohydrate responsive element-binding protein (ChREBP) or sterol regulatory element-binding protein (SREBP)-1c. In conclusion, sitagliptin may affect the development of nonalcoholic fatty liver disease by inhibiting the production of malonyl-CoA and thus synthesis of fatty acids in the liver.