Functional interaction between Ghrelin and GLP-1 regulates feeding through the vagal afferent system.

The gastrointestinal tract transmits feeding-regulatory signals to the brain via neuronal and hormonal pathways. Here we studied the interaction between the orexigenic gastric peptide, ghrelin, and the anorectic intestinal peptide, glucagon-like peptide 1 (GLP-1), in terms of feeding regulation via the vagal afferents. GLP-1 preadministration 30 min before ghrelin administration to rats and mice abolished ghrelin-induced food intake, while ghrelin preadministration abolished the anorectic effect of GLP-1. Ghrelin preadministration suppressed GLP-1-induced Fos expression in the nodose ganglia (NG). Electrophysiological assessment confirmed that the initially administered peptide abolished the vagal afferent electrical alteration induced by the subsequently administered peptide. Both the growth hormone secretagogue receptor (GHSR) and the GLP-1 receptor (GLP-1R) are co-localised in a major proportion of NG neurons that innervate the stomach. In these Ghsr+Glp1r+ neurons, ghrelin preadministration abolished the GLP-1-induced calcium response. Ghrelin generated a hyperpolarising current and GLP-1 generated a depolarising current in isolated NG neurons in a patch-clamp experiment. Ghrelin and GLP-1 potently influenced each other in terms of vagally mediated feeding regulation. This peptidergic interaction allows for fine control of the electrophysiological properties of NG neurons.

Concurrent Use of Teneligliptin and Canagliflozin Improves Glycemic Control with Beneficial Effects on Plasma Glucagon and Glucagon-Like Peptide-1: A Single-Arm Study.

INTRODUCTION: We investigated the mechanisms of the glucose-lowering effects of teneligliptin and canagliflozin, a sodium-glucose cotransporter-2 (SGLT2) inhibitor, by monitoring several gastrointestinal peptides using the most appropriate measuring methods during multiple meal tolerance tests (MTTs) and flash glucose monitoring. METHODS: Twelve Japanese patients with type 2 diabetes were enrolled in the 14-day study. Subjects were treated with teneligliptin 20 mg/day from day 4, followed by a combination tablet of teneligliptin 20 mg and canagliflozin 100 mg (T/C) per day from day 11. MTTs were conducted on days 3 (premedication; Pre), 10 (teneligliptin; T) and 13 (T/C) to evaluate plasma glucose, C-peptide, glucagon, active glucagon-like peptide-1 (GLP-1), active gastric inhibitory polypeptide (GIP), ghrelin and des-acyl ghrelin. RESULTS: Plasma glucose was significantly decreased with the progress of treatment intervention, and C-peptide was significantly decreased in T/C compared to the others. Plasma postprandial glucagon was increased for 90 min from fasting in Pre, but only for 30 min in T and T/C. Plasma postprandial active GLP-1 was significantly increased in T compared to Pre, and that of T/C was significantly higher than T. Plasma postprandial active GIP was increased in T and T/C compared to Pre. Plasma ghrelin and des-acyl ghrelin levels did not change during the treatment. CONCLUSION: Teneligliptin increased incretin hormones and suppressed postprandial glucagon secretion as expected. Concurrent use of canagliflozin and teneligliptin improved glycemic control without increasing postprandial glucagon secretion, and increased postprandial GLP-1 secretion and decreased the required amount of postprandial insulin secretion. The underlying mechanisms may involve canagliflozin's inhibitory activity against not only SGLT2 but also SGLT1. TRIAL REGISTRATION: UMIN identifier, UMIN000030043. FUNDING: Mitsubishi Tanabe Pharma Corporation and a Grant for Clinical Research from Miyazaki University Hospital.

Clinical application of ghrelin for diabetic peripheral neuropathy.

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, and its progression significantly worsens the patient's quality of life. Although several drugs are available for DPN, all of these provide only symptomatic relief. We investigated the therapeutic effects of ghrelin for DPN, based on its various physiological functions. Seven patients with type 2 diabetes with typical clinical signs and symptoms of DPN were hospitalized. Synthetic human ghrelin (1.0 µg/kg) was administered intravenously for 14 days. Motor nerve conduction velocity (MCV) of the posterior tibial nerve improved significantly after the treatment, compared to that at baseline (35.1 ± 1.8 to 38.6 ± 1.8 m/s, p < 0.0001), while the MCV in six untreated patients did not change throughout hospitalization. The subjective symptoms assessed based on the total symptom score also significantly improved (15.6 ± 3.1 to 11.1 ± 2.2, p = 0.047). Although sensory nerve conduction velocity (SCV) of the sural nerve could not be detected in three patients at baseline, it was detected in two of the three patients after 14 days of ghrelin administration. Overall, SCV did not change significantly. Plasma glucose, but not serum C peptide, levels during a liquid meal tolerance test significantly improved after treatment. These results suggest that ghrelin may be a novel therapeutic option for DPN; however, a double-blind, placebo-controlled trial is needed in the future.

Effects of Miglitol, Acarbose, and Sitagliptin on Plasma Insulin and Gut Peptides in Type 2 Diabetes Mellitus: A Crossover Study.

INTRODUCTION: Both dipeptidyl peptidase-4 inhibitors and α-glucosidase inhibitors (α-GI) have been reported to change the incretin and insulin secretion. To examine the effects of acarbose, miglitol, and sitagliptin on glucose metabolism and secretion of gut peptides, we conducted a crossover study in patients with type 2 diabetes mellitus (T2DM). METHODS: Eleven Japanese patients with T2DM underwent four meal tolerance tests with single administration of acarbose, miglitol, sitagliptin, or nothing. Fasting and postprandial plasma levels of glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), ghrelin, and des-acyl ghrelin were measured. RESULTS: Early-phase insulin secretion was reduced following acarbose and miglitol, and the areas under the curve (AUC) of insulin at 180 min following acarbose and miglitol were significantly lower than sitagliptin. AUC of plasma glucose at 180 min after acarbose, miglitol, and sitagliptin tended to be lower than in controls, and plasma glucose levels at 30-60 min following miglitol were significantly lower than in controls. Plasma glucagon, ghrelin, and des-acyl ghrelin levels did not differ among the four conditions. Postprandial plasma active GLP-1 levels and AUC of GLP-1 increased significantly in both the sitagliptin and miglitol groups compared to control. Postprandial plasma total GIP levels increased following sitagliptin but decreased after acarbose and miglitol. Changes in incretin levels tended to be greater with miglitol than acarbose. CONCLUSION: These results showed that sitagliptin and α-GIs, miglitol more so than acarbose, improved hyperglycemia in patients with T2DM after single administration, and had different effects on insulin and incretin secretion. TRIAL REGISTRATION: UMIN-CTR number, UMIN000009981.

Teneligliptin improves glycemic control with the reduction of postprandial insulin requirement in Japanese diabetic patients.

Teneligliptin is a novel peptidomimetic-chemotype prolylthiazolidine-based inhibitor of dipeptidyl peptidase-4 (DPP-4). The aim of this study was to evaluate the effects of teneligliptin on 24 h blood glucose control and gastrointestinal hormone responses to a meal tolerance test, and to investigate the glucose-lowering mechanisms of teneligliptin. Ten patients with type 2 diabetes mellitus (T2DM) were treated for 3 days with teneligliptin (20 mg/day). Postprandial profiles for glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1), active glucose-dependent insulinotropic polypeptide (GIP), ghrelin, des-acyl ghrelin, and 24 h glycemic fluctuations were measured via continuous glucose monitoring for 4 days. Once daily teneligliptin administration for 3 days significantly lowered postprandial and fasting glucose levels. Significant elevations of fasting and postprandial active GLP-1 and postprandial active GIP levels were observed. Teneligliptin lowered postprandial glucose elevations, 24 h mean blood glucose levels, standard deviation of 24 h glucose levels and mean amplitude of glycemic excursions (MAGE) without hypoglycemia. Serum insulin levels in the fasting state and 30 min after a meal were similar before and after teneligliptin treatment; however significant reductions at 60 to 180 min after treatment were observed. A significant elevation in early-phase insulin secretion estimated by insulinogenic and oral disposition indices, and a significant reduction in postprandial glucagon AUC were observed. Both plasma ghrelin and des-acyl ghrelin levels were unaltered following teneligliptin treatment. Teneligliptin improved 24 h blood glucose levels by increasing active incretin levels and early-phase insulin secretion, reducing the postprandial insulin requirement, and reducing glucagon secretion. Even short-term teneligliptin treatment may offer benefits for patients with T2DM.

Neuroendocrine regulatory peptide-1 and -2 (NERPs) inhibit the excitability of magnocellular neurosecretory cells in the hypothalamus.

Neuroendocrine regulatory peptide (NERP)-1 and NERP-2 (NERPs) are novel carboxy-terminally amidated peptides derived from the neurosecretory protein VGF. NERPs are colocalized with vasopressin in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus, and suppress vasopressin secretion evoked by intracerebroventricular administration of angiotensin II (AngII) and hypertonic saline or bath administration of AngII. Magnocellular neurosecretory cells (MCNs) of the hypothalamus release vasopressin and oxytocin from their dendrites and soma. The two cell types have common electrophysiological properties in response to glutamate and AngII. We investigated the mechanisms underlying the suppressive effects of NERPs on MCNs. Microdialysis of the PVN demonstrated that NERPs suppressed glutamate release induced by AngII. A whole-cell patch-clamp study of the SON showed that NERPs suppressed the potentiation of excitatory postsynaptic currents (EPSCs) evoked by AngII without affecting the amplitude, indicating that NERPs suppressed EPSCs by a presynaptic mechanism. The suppressive effect of NERP-2, but not NERP-1, was blunted in the presence of tetrodotoxin and bicuculline, a γ-aminobutyric acid (GABA) A receptor antagonist. These results indicate that NERP-1 suppresses presynaptic glutamatergic neurons connected to MNCs, whereas NERP-2 activates GABAergic interneurons, which suppress presynaptic glutamatergic neurons; thus, both peptides suppress vasopressin release. This study demonstrates that NERPs function as inhibitory modulators of vasopressin release.

Exploratory trial of intranasal administration of glucagon-like peptide-1 in Japanese patients with type 2 diabetes.

OBJECTIVE: This study aimed to assess the efficacy and safety of our newly developed nasal glucagon-like peptide-1 (GLP-1) compound and injector. RESEARCH DESIGN AND METHODS: Twenty-six patients with type 2 diabetes were enrolled in this double-blind placebo-controlled study. The nasal compound containing 1.2 mg of human GLP-1 (7-36) amide or placebo was administered immediately before every meal for 2 weeks. RESULTS: The plasma peak concentration of active GLP-1 was 47.2 pmol/L, and its Tmax was 8.1 min. The early phase of insulin and glucagon secretion were recovered and suppressed, respectively, in the GLP-1 group. Glycoalbumin levels became significantly lower and 1,5-anhydroglucitol levels significantly higher after GLP-1 administration. No marked adverse events were observed after using nasal GLP-1. CONCLUSIONS: The newly developed nasal GLP-1 compound may be a potential treatment for type 2 diabetes. The long-term application of the drug should be evaluated in future trials.

Ghrelin prevents the development of experimental diabetic neuropathy in rodents.

Ghrelin is an acylated peptide discovered in gastric extracts as an endogenous ligand for the growth hormone secretagogue (GHS) receptor. This peptide increases food intake and growth hormone secretion, suppresses inflammation and oxidative stress, and promotes cell survival and proliferation. Our study investigated the pharmacological effect of ghrelin in the prevention of polyneuropathy in streptozotocin-induced diabetes mellitus in C57BL/6N mice, GHS receptor-deficient mice, and growth hormone-deficient rats. Ghrelin or desacyl-ghrelin was administered daily for four weeks immediately after disease onset. The effects of ghrelin on food intake, body weight, blood glucose and plasma insulin levels, nerve conduction velocities, temperature sensation, and 8-isoprostaglandin F2α (8-iso-PGF2α) levels were examined. We found that ghrelin administration did not change food intake, body weight gain, blood glucose levels, or plasma insulin levels in C57BL/6N mice in comparison with mice treated with saline or desacyl-ghrelin administration. Ghrelin administration, but not desacyl-ghrelin, prevented motor and sensory polyneuropathy and reduced the plasma concentrations of 8-iso-PGF2α in C57BL/6N mice. Ghrelin also prevented the reduction in nerve conduction velocities in growth hormone-deficient rats, but not in GHS receptor-knockout mice. In conclusion, ghrelin administration in a rodent model of diabetes prevented polyneuropathy, and this effect was mediated through the GHS receptor and was independent of growth hormone. The protection against the development of experimental diabetic polyneuropathy by ghrelin could be key in preventing this otherwise intractable disorder.

A novel nonsense mutation in the DMP1 gene in a Japanese family with autosomal recessive hypophosphatemic rickets.

Autosomal recessive hypophosphatemic rickets (ARHR) is an extremely rare disorder of autosomal recessive inheritance, characterized by hypophosphatemia resulting from renal phosphate wasting. Dentin matrix protein 1 (DMP1), a noncollagenous extracellular protein, plays critical roles in bone mineralization and phosphate homeostasis. Recently, loss-of-function mutations in DMP1 gene have been identified as the molecular cause of ARHR. Here, we describe a Japanese family that includes two ARHR-affected siblings carrying a novel mutation of the DMP1 gene. The patients were a 53-year-old woman and a 50-year-old man with short stature and skeletal deformities who were the offspring of a first-cousin marriage. Biochemical examination revealed hypophosphatemia with renal phosphate excretion and low levels of 1,25(OH)(2)D. Serum calcium, parathyroid hormone, and urinary calcium excretion were within the normal range, leading to clinical diagnosis of ARHR. Sequence analysis of peripheral leukocytes from the patients revealed that they carried a novel homozygous nonsense mutation in the DMP1 gene (98G>A, W33X), which leads to a truncated DMP protein with no putative biological function. Unaffected family members were heterozygous for the mutation. This is the first report of a Japanese family with ARHR carrying a novel mutation of the DMP1 gene.

Myasthenia gravis complicated with primary aldosteronism and hypokalemic myopathy.

A 34-year-old Japanese man was admitted to an outside hospital with an elevated creatinine kinase level and suspected myositis. He was treated with high dose methylprednisolone, which caused severe aggravation of muscle weakness. He was transferred to our hospital at that time. On admission, chest computed tomography (CT) and the presence of anti-acetylcholine receptor antibodies supported a diagnosis of myasthenia gravis and thymoma. Laboratory findings showed hypokalemia, low plasma renin activity and high serum aldosterone. Further studies, including abdominal CT and adrenal venous sampling suggested primary aldosteronism. At first, thymectomy was performed, and one month later, he was treated with laparoscopic adrenalectomy. Immediately after this procedure, he suffered from myasthenic crisis, which was successfully managed with mechanical ventilation and steroid pulse therapy followed by oral prednisolone. This case presented a serious difficulty in differentiating from various myopathies and giving proper treatment because of a rare combination of independent diseases and their masquerading clinical features.