Apelin's effects on young rat gastrointestinal tract maturation

Metabolic hormones in human breast milk are preserved by high hydrostatic pressure processing but reduced by Holder pasteurization

In human milk banks (HMBs), donor milk (DM) is commonly sterilized by Holder pasteurization (HoP). High hydrostatic pressure (HHP) processing is an innovative, alternative method for DM sterilization. We evaluated the impact of HHP processing on the concentration of seven metabolic milk hormones. Eight samples of raw DM were aliquoted. One aliquot was sterilized by HoP (62 °C for 30 min), and another was processed by HHP (350 MPa at 38 °C). Compared with raw DM, HoP milk displayed reduced concentrations of insulin, nesfatin-1, cortisol, leptin, apelin and GLP-1, though adiponectin levels were unchanged. HHP processing maintained the levels of insulin, nesfatin-1, cortisol and leptin at their initial levels in raw DM, reduced apelin and adiponectin levels, but increased GLP-1 level. Sterilization of DM by HHP thus preserves the main metabolic hormones in human milk, underlining the interest of this method for use in HMBs.

The role of adropin, HIF-1α and apelin biomarkers in the diagnosis of acute mesentaric ischemia

OBJECTIVE

The absence of a specific biomarker for acute mesenteric ischemia diagnosis results in a delay in diagnosis and treatment, as well as a high mortality rate. The current research examined whether the proteins adropin, HIF-1α, and apelin may be used to help in the early detection of acute mesenteric ischemia.

MATERIALS AND METHODS

A total of 20 patients with acute mesenteric ischemia, 20 patients with abdominal pain, and 20 healthy controls were included in the study. The levels of adropin, HIF-1, and apelin in the serum were determined using the ELISA method.

RESULTS

Adropin concentrations were significantly higher in the acute mesenteric ischemia group than in the abdominal pain and healthy control groups (p < 0.05). HIF-1α levels were considerably greater in patients with acute mesenteric ischemia compared to both the abdominal pain group and the healthy control group (p < 0.05). There was no difference in apelin levels between the acute mesenteric ischemia and abdominal pain groups (p > 0.05). HIF-1α was found to be moderate (AUC: 0.705) and adropin was found to be a weak biomarker (AUC: 0.692) in the ROC analysis for acute mesenteric ischemia.

CONCLUSION

In this study of 20 patients with acute mesenteric ischemia, we found adropin and HIF-1α levels to be increased compared to patients with abdominal pain who did not have acute mesenteric ischemia.

Molecular mechanism of apelin-13 regulation of colonic motility in rats

Apelin is a novel neuropeptide identified as the endogenous ligand for the apelin receptor. Apelin and its receptor are widely distributed in the gastrointestinal tract. Studies have reported that apelin-13 is involved in modulating gastrointestinal motility; however, the evidence is insufficient and the relevant mechanism is still not fully clear. Consequently, our study designed to explore the effect induced by exogenous apelin-13, to analyze the mechanism of action in isolated rat colons and colonic smooth muscle cells. The spontaneous contractions of colonic smooth muscle strips from rat were measured in an organ bath system. L-type calcium currents and large conductance Ca2+-activated K+ (BKCa) currents in rat colonic smooth muscle cells were investigated using the electrophysiological patch-clamp technique. Apelin-13 decreased the spontaneous contractile activity of colonic smooth muscle strips in a dose-dependent manner, and the inhibitory effect was not abolished by tetrodotoxin. The electrophysiological recordings revealed that apelin-13 reduced the crest currents of L-type calcium in a concentration-dependent manner in colonic smooth muscle cells at the test potential of 0 mV. Moreover, apelin-13 moved the current-voltage (I-V) curves of L-type calcium channels upward, but did not change their contour. Furthermore, the characteristics of L-type calcium channels with steady-state activation and steady-state inactivation were not significantly changed. Similarly, application of apelin-13 also significantly decreased BKCa currents in a concentration-dependent manner. In conclusion, apelin-13 inhibited the spontaneous contractile activity of isolated rat colons via the suppression of L-type calcium channels and BKCa channels in colonic smooth muscle cells.

Breast milk apelin level increases with maternal obesity and high-fat feeding during lactation

OBJECTIVE

Recent evidence indicates that levels of breast milk (BM) hormones such as leptin can fluctuate with maternal adiposity, suggesting that BM hormones may signal maternal metabolic and nutritional environments to offspring during postnatal development. The hormone apelin is highly abundant in BM but its regulation during lactation is completely unknown. Here, we evaluated whether maternal obesity and overnutrition impacted BM apelin and leptin levels in clinical cohorts and lactating rats.

METHODS

BM and plasma samples were collected from normal-weight and obese breastfeeding women, and from lactating rats fed a control or a high fat (HF) diet during lactation. Apelin and leptin levels were assayed by ELISA. Mammary gland (MG) apelin expression and its cellular localization in lactating rats was measured by quantitative RT-PCR and immunofluorescence, respectively.

RESULTS

BM apelin levels increased with maternal BMI, whereas plasma apelin levels decreased. BM apelin was also positively correlated with maternal insulin and C-peptide levels. In rats, maternal HF feeding exclusively during lactation was sufficient to increase BM apelin levels and decrease its plasma concentration without changing body weight. In contrast, BM leptin levels increased with maternal BMI in humans, but did not change with maternal HF feeding during lactation in rats. Apelin is highly expressed in the rat MG during lactation and was mainly localized to mammary myoepithelial cells. We found that MG apelin gene expression was up-regulated by maternal HF diet and positively correlated with BM apelin content and maternal insulinemia.

CONCLUSIONS

Our study indicates that BM apelin levels increase with long- and short-term overnutrition, possibly via maternal hyperinsulinemia and transcriptional upregulation of MG apelin expression in myoepithelial cells. Apelin regulates many physiological processes, including energy metabolism, digestive function, and development. Further studies are needed to unravel the consequences of such changes in offspring development.

Function and regulation of apelin/APJ system in digestive physiology and pathology

Apelin is an endogenous ligand of seven-transmembrane G-protein-coupled receptor APJ. Apelin and APJ are distributed in various tissues, including the heart, lung, liver, kidney, and gastrointestinal tract and even in tumor tissues. Studies show that apelin messenger RNA is widely expressed in gastrointestinal (GI) tissues, including stomach and small intestine, which is closely correlated with GI function. Thus, the apelin/APJ system may exert a broad range of activities in the digestive system. In this paper, we review the role of the apelin/APJ system in the digestive system in physiological conditions, such as gastric acid secretion, control of appetite and food intake, cell proliferation, cholecystokinin secretion and histamine release, gut-brain axis, GI motility, and others. In pathological conditions, the apelin/APJ system plays an important role in the healing process of stress gastric injury, the clinical features and prognosis of patients with gastric cancers, the reduction of inflammatory response to enteritis and pancreatitis, the mediation of liver fibrogenesis, the promotion of liver damage, the inhibition of liver regeneration, the contribution of splanchnic neovascularization in portal hypertension, the treatment of colon cancer, and GI oxidative damage. Overall, the apelin/APJ system plays diversified functions and regulatory roles in digestive physiology and pathology. Further exploration of the relationship between the apelin/APJ system and the digestive system will help to find new and effective drugs for treating and alleviating the pain of digestive diseases.

Review: Apelin in disease

Apelin, a regulatory peptide, is a ligand of the APJ receptor that belongs to the G protein-coupled receptor family. Apelin and APJ are widely distributed in the body and play potential physiological roles in the cytoprotection of many internal organs. This review article summarizes information about the roles of the apelin/APJ system in neurological, metabolic, hypertension, respiratory, gastrointestinal, hepatic, kidney and cancerous diseases. It is suggested that apelin positively affects the treatment of non-cancerous diseases and may be considered as a therapeutic drug in many illnesses. However, in cancers, apelin appears as a tumour growth stimulator, and its suggested role is as a marker in the diagnosis of tumour cancers in tissues. In summary, apelin has certain therapeutic abilities and can be useful in the treatment of, e.g., insulin resistance, hypertension, etc., but it also can sometimes serve as a negative factor.