Discovery and SAR of a novel series of Natriuretic Peptide Receptor-A (NPR-A) agonists.

Novel thienopyrimidine compounds 2 and 3 were discovered from high-throughput screening as Natriuretic Peptide Receptor A (NPR-A) agonists. Scaffold hopping of a thienopyrimidine ring to a quinazoline ring, introduction of the basic functional group and optimization of the substituent on the 6-position of the benzene ring of quinazoline led to improved agonistic activity. We discovered compound 48, which showed potent agonistic activity for NPR-A with an EC50 value of 0.073µM, indicating 350-fold potency compared to the hit compound 3.

Discovery and dimeric approach of novel Natriuretic Peptide Receptor A (NPR-A) agonists.

Novel agonists of the Natriuretic Peptide Receptor A (NPR-A) were obtained through random screening and subsequent structural modification of triazine derivatives. The key structural feature to improve in vitro activity was the dimerization of triazine monomer derivatives. The non peptide derivative 7c and 13a showed highly potent NPR-A agonistic activity in vitro and diuretic activity in vivo. These results implied that non-peptidic small molecules open the possibility of new therapy for congestive heart failure.

Discovery and in vivo effects of novel human natriuretic peptide receptor A (NPR-A) agonists with improved activity for rat NPR-A.

Natriuretic peptide receptor A (NPR-A) agonists were evaluated in vivo by optimizing the structure of quinazoline derivatives to improve agonistic activity for rat NPR-A. A 1,4-Cis-aminocyclohexylurea moiety at 4-position and hydroxy group of d-alaninol at 2-position on the quinazoline ring were found to be important factors in improving rat NPR-A activity. We identified potent quinazoline and pyrido[2,3-d]pyrimidine derivatives against rat NPR-A, with double-digit nanomolar EC50 values. The in vivo results showed that compound 56b administered at 1.0 mg/kg/min significantly increased plasma cGMP concentration and urine volume in rats. We discovered novel potent NPR-A agonists that showed agonistic effects similar to those of atrial natriuretic peptide.

Involvement of guanylin and GC-C in rat mesenteric macrophages in resistance to a high-fat diet.

A high-fat diet (HFD) is a well-known contributing factor in the development of obesity. Most rats fed HFDs become obese. Those that avoid obesity when fed HFDs are considered diet resistant (DR). We performed a microarray screen to identify genes specific to the mesenteric fat of DR rats and revealed high expression of guanylin and guanylyl cyclase C (GC-C) in some subjects. Our histologic studies revealed that the cellular source of guanylin and GC-C is macrophages. Therefore, we developed double-transgenic (Tg) rats overexpressing guanylin and GC-C in macrophages and found that they were resistant to the effects of HFDs. In the mesenteric fat of HFD-fed Tg rats, Fas and perilipin mRNAs were downregulated, and those of genes involved in fatty acid oxidation were upregulated, compared with the levels in HFD-fed wild-type rats. In vitro studies demonstrated that lipid accumulation was markedly inhibited in adipocytes cocultured with macrophages expressing guanylin and GC-C and that this inhibition was reduced after treatment with guanylin- and GC-C-specific siRNAs. Our results suggest that the macrophagic guanylin-GC-C system contributes to the altered expression of genes involved in lipid metabolism, leading to resistance to obesity.

Possible involvement of melanocortin-4-receptor and AMP-activated protein kinase in the interaction of glucagon-like peptide-1 and leptin on feeding in rats.

Glucagon-like peptide-1 (GLP-1) and leptin are anorectic hormones produced in the small intestine and white adipose tissue, respectively. Investigating how these hormones act together as an integrated anorectic signal is important to elucidate a mechanism to maintain energy balance. In the present study, coadministration of subthreshold GLP-1 and leptin dramatically reduced feeding in rats. Although coadministration of GLP-1 with leptin did not enhance leptin signal transduction in the hypothalamus, it significantly decreased phosphorylation of AMP-activated protein kinase (AMPK). In addition, coadministration of GLP-1 with leptin significantly increased proopiomelanocortin (POMC) mRNA levels. Considering that α-melanocortin stimulating hormone (α-MSH) is derived from POMC and functions through the melanocortin-4-receptor (MC4-R) as a key molecule involved in feeding reduction, the interaction of GLP-1 and leptin on feeding reduction may be mediated through the α-MSH/MC4-R system. As expected, the interaction of GLP-1 and leptin was abolished by intracerebroventricular preadministration of the MC4-R antagonists agouti-related peptide and SHU9119. Taken together, GLP-1 and leptin cooperatively reduce feeding at least in part via inhibition of AMPK following binding of α-MSH to MC4-R.

[Epstein-Barr virus-associated subacute sensorimotor neuropathy with multiple cerebellar microbleeding: a case report].

We report the case of an 82-year-old male with subacute sensorimotor neuropathy associated with Epstein-Barr virus (EBV) infection, who presented with diplopia followed by gait disturbance due to limb weakness. Pathological findings of a biopsied cervical lymph node showed a high frequency of EBV-positive cells. EBV-DNA was detected in blood. A nerve conduction study suggested a mixture of axonal damage and demyelination. Brain MRI showed multiple microbleeds in cerebellar cortices, but cerebrospinal fluid EBV-PCR was negative, suggesting bleeding due to EBV-related vasculitis. Corticosteroid therapy improved the neurological symptoms and the patient was able to walk independently four months later. The main pathogenesis of the neuropathy in this case is likely to be a mixture of vasculitic neuropathy and immune-mediated demyelinating neuropathy, which are considered to be due to EBV reactivation.

The Japanese Society for Apheresis clinical practice guideline for therapeutic apheresis.

Most of the diseases for which apheresis therapy is indicated are intractable and rare, and each patient has a different background and treatment course prior to apheresis therapy initiation. Therefore, it is difficult to conduct large-scale randomized controlled trials to secure high-quality evidence. Under such circumstances, the American Society for Apheresis (ASFA) issued its guidelines in 2007, which were repeatedly revised until the latest edition in 2019. The ASFA guidelines are comprehensive. However, in the United States, a centrifugal separation method is mainly used for apheresis, whereas the mainstream procedure in Japan is the membrane separation method. The target diseases and their backgrounds are different from those in Japan. Due to these differences, the direct adoption of the ASFA guidelines in Japanese practice creates various problems. One of the features of apheresis in Japan is the development of treatment methods using hollow-fiber devices such as double filtration plasmapheresis (DFPP) and selective plasma exchange and adsorption-type devices such as polymyxin B-immobilized endotoxin adsorption columns. Specialists in emergency medicine, hematology, collagen diseases/rheumatology, respiratory medicine, cardiovascular medicine, gastroenterology, neurology, nephrology, and dermatology who are familiar with apheresis therapy gathered for this guideline, which covers 86 diseases. In addition, since apheresis therapy involves not only physicians but also clinical engineers, nurses, dieticians, and many other medical professionals, this guideline was prepared in the form of a worksheet so that it can be easily understood at the bedside. Moreover, to the clinical purposes, this guideline is designed to summarize apheresis therapy in Japan and to disseminate and further develop Japanese apheresis technology to the world. As diagnostic and therapeutic techniques are constantly advancing, the guidelines need to be revised every few years. In order to ensure the high quality of apheresis therapy in Japan, both the Japanese Society for Apheresis Registry and the guidelines will be inseparable.

Effect of atrial natriuretic peptide on left ventricular remodelling in patients with acute myocardial infarction.

Atrial natriuretic peptide (ANP) is a member of the natriuretic peptide family that exerts various biological effects via acting on the receptor-guanylyl cyclase system, increasing the content of intracellular cyclic guanosine monophosphate (cGMP). ANP was first identified as a diuretic/natriuretic and vasodilating hormone, but subsequent studies revealed that ANP has a very important function in the inhibition of the renin-angiotensin-aldosterone system (RAAS), endothelin synthesis, and sympathetic nerve activity. Evidence is also accumulating from recent work that ANP exerts its cardioprotective functions not only as a circulating hormone but also as a local autocrine and/or paracrine factor. ANP inhibits apoptosis and hypertrophy of cardiac myocytes, and inhibits proliferation and fibrosis of cardiac fibroblasts. Reperfusion of the ischaemic myocardium by percutaneous coronary intervention (PCI) reduces the infarct size and improves left ventricular (LV) function in patients with acute myocardial infarction (AMI). However, the benefits of PCI in AMI are limited by reperfusion injury. Animal studies have shown that ANP inhibits ischaemia/reperfusion injury, and reduces infarct size. We and others have recently shown that the intravenous administration of ANP inhibits RAAS, sympathetic nerve activity and reperfusion injury, prevents LV remodelling, and improves LV function in patients with AMI. ANP has a variety of cardioprotective effects and is considered to be a very promising adjunct drug for the reperfusion therapy in patients with AMI.

ASB20123: A novel C-type natriuretic peptide derivative for treatment of growth failure and dwarfism.

C-type natriuretic peptide (CNP) and its receptor natriuretic peptide receptor B (NPR-B) are physiological potent positive regulators of endochondral bone growth; therefore, the CNP/NPR-B signaling pathway is one of the most promising therapeutic targets for treating growth failure and dwarfism. In this article, we summarized the pharmacological properties of a novel CNP analog peptide ASB20123 as a therapeutic agent for short stature. ASB20123, one of the CNP/ghrelin chimeric peptides, is composed of CNP(1-22) and human ghrelin(12-28, E17D). Compared to CNP(1-22), ASB20123 showed similar agonist activity for NPR-B and improved biokinetics with a longer plasma half-life in rats. In addition, the distribution of ASB20123 to the cartilage was higher than that of CNP(1-22) after single subcutaneous (sc) injection to mice. These results suggested that the C-terminal part of ghrelin, which has clusters of basic amino acid residues and a BX7B motif, might contribute to the retention of ASB20123 in the extracellular matrix of the growth plate. Multiple sc doses of ASB20123 potently stimulated skeletal growth in rats in a dose-dependent manner, and sc infusion was more effective than bolus injection at the same dose. Our data indicated that high plasma levels of ASB20123 would not necessarily be required for bone growth acceleration. Thus, pharmaceutical formulation approaches for sustained-release dosage forms to allow chronic exposure to ASB20123 might be suitable to ensure drug effectiveness and safety.

Foramen magnum stenosis and midface hypoplasia in C-type natriuretic peptide-deficient rats and restoration by the administration of human C-type natriuretic peptide with 53 amino acids.

C-type natriuretic peptide (CNP)-knockout (KO) rats exhibit impaired skeletal growth, with long bones shorter than those in wild-type (WT) rats. This study compared craniofacial morphology in the CNP-KO rat with that in the Spontaneous Dwarf Rat (SDR), a growth hormone (GH)-deficient model. The effects of subcutaneous administration of human CNP with 53 amino acids (CNP-53) from 5 weeks of age for 4 weeks on craniofacial morphology in CNP-KO rats were also investigated. Skulls of CNP-KO rats at 9 weeks of age were longitudinally shorter and the foramen magnum was smaller than WT rats. There were no differences in foramen magnum stenosis and midface hypoplasia between CNP-KO rats at 9 and 33 weeks of age. These morphological features were the same as those observed in CNP-KO mice and activated fibroblast growth factor receptor 3 achondroplasia-phenotype mice. In contrast, SDR did not exhibit foramen magnum stenosis and midface hypoplasia, despite shorter stature than in control rats. After administration of exogenous CNP-53, the longitudinal skull length and foramen magnum size in CNP-KO rats were significantly greater, and full or partial rescue was confirmed. The synchondrosis at the cranial base in CNP-KO rats is closed at 9 weeks, but not at 4 weeks of age. In contrast, synchondrosis closure in CNP-KO rats treated with CNP-53 was incomplete at 9 weeks of age. Administration of exogenous CNP-53 accelerated craniofacial skeletogenesis, leading to improvement in craniofacial morphology. As these findings in CNP-KO rats are similar to those in patients with achondroplasia, treatment with CNP-53 or a CNP analog may be able to restore craniofacial morphology and foramen magnum size as well as short stature.

Safety assessment of a novel C-type natriuretic peptide derivative and the mechanism of bone- and cartilage-specific toxicity.

ASB20123, a C-type natriuretic peptide/ghrelin chimeric peptide, was designed as a novel peptide and demonstrated full agonistic activity for natriuretic-peptide receptor B and a significantly longer half-life in plasma compared with the native peptide. We researched the toxicological profile of ASB20123, the correlation between the morphological change of the epiphyseal plate and bone and cartilage toxicity, and biomarkers to detect the toxicity. ASB20123 was systemically administered to male and female rats at daily dose levels of 0.5, 1.5, and 5.0 mg/kg/day for 4 weeks. In this study, toxicity was observed as changes related to bone and cartilage tissues, and no other toxicological changes were observed in all animals. Next, ASB20123 was administered to 12-month-old rats with a little epiphyseal plate. The toxic changes related to bone and cartilage tissues were not observed in any animal with a closed epiphyseal plate, indicating that the toxic changes were triggered by the growth-accelerating effect on the bone and cartilage. Furthermore, we searched for the biomarker related to the bone and cartilage toxicity using rats treated with ASB20123 at doses of 0.005, 0.05, 0.5, and 5.0 mg/kg/day for 4 weeks. A close correlation between necrosis/fibrosis in the epiphysis and metaphysis and thickness of the epiphyseal plate in the femur was confirmed in this study. A decrease in the bone mineral density (BMD) of the femur also was associated with the appearance of bone toxicity. These results indicated that the toxicity of ASB20123 was limited to bone- and cartilage-specific changes, and these changes were triggered by an excessive growth accelerating effect. Furthermore, our data suggested that the thickness of the epiphyseal plate and BMD could be reliable biomarkers to predict bone toxicity.

Rats deficient C-type natriuretic peptide suffer from impaired skeletal growth without early death.

We have previously investigated the physiological role of C-type natriuretic peptide (CNP) on endochondral bone growth, mainly with mutant mouse models deficient in CNP, and reported that CNP is indispensable for physiological endochondral bone growth in mice. However, the survival rate of CNP knockout (KO) mice fell to as low as about 70% until 10 weeks after birth, and we could not sufficiently analyze the phenotype at the adult stage. Herein, we generated CNP KO rats by using zinc-finger nuclease-mediated genome editing technology. We established two lines of mutant rats completely deficient in CNP (CNP KO rats) that exhibited a phenotype identical to that observed in mice deficient in CNP, namely, a short stature with severely impaired endochondral bone growth. Histological analysis revealed that the width of the growth plate, especially that of the hypertrophic chondrocyte layer, was markedly lower and the proliferation of growth plate chondrocytes tended to be reduced in CNP KO rats. Notably, CNP KO rats did not have malocclusions and survived for over one year after birth. At 33 weeks of age, CNP KO rats persisted significantly shorter than wild-type rats, with closed growth plates of the femur in all samples, which were not observed in wild-type rats. Histologically, CNP deficiency affected only bones among all body tissues studied. Thus, CNP KO rats survive over one year, and exhibit a deficit in endochondral bone growth and growth retardation throughout life.

Exogenous C-type natriuretic peptide restores normal growth and prevents early growth plate closure in its deficient rats.

Signaling by C-type natriuretic peptide (CNP) and its receptor, natriuretic peptide receptor-B, is a pivotal stimulator of endochondral bone growth. We recently developed CNP knockout (KO) rats that exhibit impaired skeletal growth with early growth plate closure. In the current study, we further characterized the phenotype and growth plate morphology in CNP-KO rats, and the effects of exogenous CNP in rats. We used CNP-53, an endogenous form of CNP consisting of 53 amino acids, and administered it for four weeks by continuous subcutaneous infusion at 0.15 or 0.5 mg/kg/day to four-week old CNP-KO and littermate wild type (WT) rats. We demonstrated that CNP-KO rats were useful as a reproducible animal model for skeletal dysplasia, due to their impairment in endochondral bone growth. There was no significant difference in plasma bone-turnover markers between the CNP-KO and WT rats. At eight weeks of age, growth plate closure was observed in the distal end of the tibia and the calcaneus of CNP-KO rats. Continuous subcutaneous infusion of CNP-53 significantly, and in a dose-dependent manner, stimulated skeletal growth in CNP-KO and WT rats, with CNP-KO rats being more sensitive to the treatment. CNP-53 also normalized the length of long bones and the growth plate thickness, and prevented growth plate closure in the CNP-KO rats. Using organ culture experiment of fetal rat tibia, gene set enrichment analysis indicated that CNP might have a negative influence on mitogen activated protein kinase signaling cascades in chondrocyte. Our results indicated that CNP-KO rats might be a valuable animal model for investigating growth plate physiology and the mechanism of growth plate closure, and that CNP-53, or its analog, may have the potential to promote growth and to prevent early growth plate closure in the short stature.

Design and evaluation of novel natriuretic peptide derivatives with improved pharmacokinetic and pharmacodynamic properties.

C-type natriuretic peptide (CNP) and its receptor, natriuretic peptide receptor B (NPR-B), are potent positive regulators of endochondral bone growth, making the CNP pathway one of the most promising therapeutic targets for the treatment of growth failure. However, the administration of exogenous CNP is not fully effective, due to its rapid clearance in vivo. Modification of CNP to potentially druggable derivatives may result in increased resistance to proteolytic degradation, longer plasma half-life (T1/2), and better distribution to target tissues. In the present study, we designed and evaluated CNP/ghrelin chimeric peptides as novel CNP derivatives. We have previously reported that the ghrelin C-terminus increases peptide metabolic stability. Therefore, we combined the 17-membered, internal disulfide ring portion of CNP with the C-terminal portion of ghrelin. The resultant peptide displayed improved biokinetics compared to CNP, with increased metabolic stability and longer plasma T1/2. Repeated subcutaneous administration of the chimeric peptide to mice resulted in a significant acceleration in longitudinal growth, whereas CNP(1-22) did not. These results suggest that the ghrelin C-terminus improves the stability of CNP, and the chimeric peptide may be useful as a novel therapeutic agent for growth failure and short stature.

Hepatocyte Nuclear Factor-1ß Induces Redifferentiation of Dedifferentiated Tubular Epithelial Cells.

Tubular epithelial cells (TECs) can be dedifferentiated by repetitive insults, which activate scar-producing cells generated from interstitial cells such as fibroblasts, leading to the accumulation and deposition of extracellular matrix molecules. The dedifferentiated TECs play a crucial role in the development of renal fibrosis. Therefore, renal fibrosis may be attenuated if dedifferentiated TECs are converted back to their normal state (re-epithelialization). However, the mechanism underlying the re-epithelialization remains to be elucidated. In the present study, TGF-ß1, a profibrotic cytokine, induced dedifferentiation of cultured TECs, and the dedifferentiated TECs were re-epithelialized by the removal of TGF-ß1 stimulation. In the re-epithelialization process, transcription factor hepatocyte nuclear factor 1, beta (HNF-1ß) was identified as a candidate molecule involved in inducing re-epithelialization by means of DNA microarray and biological network analysis. In functional validation studies, the re-epithelialization by TGF-ß1 removal was abolished by HNF-1ß knockdown. Furthermore, the ectopic expression of HNF-1ß in the dedifferentiated TECs induced the re-epithelialization without the inhibition of TGF-ß/Smad signaling, even in the presence of TGF-ß1 stimulation. In mouse renal fibrosis model, unilateral ureteral obstruction model, HNF-1ß expression in the TECs of the kidney was suppressed with fibrosis progression. Furthermore, the HNF-1ß downregulated TECs resulted in dedifferentiation, which was characterized by expression of nestin. In conclusion, HNF-1ß suppression in TECs is a crucial event for the dedifferentiation of TECs, and the upregulation of HNF-1ß in TECs has a potential to restore the dedifferentiated TECs into their normal state, leading to the attenuation of renal fibrosis.

The role of the vagal nerve in peripheral PYY3-36-induced feeding reduction in rats.

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

Chronic exposure to cigarette smoke causes extrapulmonary abnormalities in rats.

Pathophysiological features of chronic obstructive pulmonary disease (COPD) include systemic abnormalities, such as weight loss and skeletal muscle wasting. Although cigarette smoke (CS) is a major risk factor in COPD, the systemic effects of CS exposure remain to be elucidated. In this study, rats were exposed to CS or smoke-free air for 12 weeks. CS-exposed rats developed emphysema and had significantly lower body weight and food intake than control rats. The plasma ghrelin levels significantly increased with an upregulation of gastric ghrelin mRNA expression induced by CS exposure. Further, we observed low plasma insulin-like growth factor-1 levels and high tumor necrosis factor-α levels. A significant reduction of skeletal muscle strength and an increase in the mRNA expression of catabolic factors was observed in CS-exposed rats. These results indicated that chronic CS exposure induced not only pulmonary emphysema but also systemic abnormalities related to muscle catabolism associated with inflammatory responses.

Ghrelin ameliorates catabolic conditions and respiratory dysfunction in a chronic obstructive pulmonary disease model of chronic cigarette smoke-exposed rats.

Cigarette smoking, which is a well-known major risk factor for chronic obstructive pulmonary disease (COPD), causes both pulmonary and extrapulmonary abnormalities. Ghrelin is a gastric peptide that regulates energy homeostasis. In the present study, we investigated the effects of ghrelin on the catabolic changes, respiratory function and emphysema in an animal model of COPD induced by chronic exposure to cigarette smoke. Rats were exposed to cigarette smoke, and they were administered human ghrelin (0.1 or 1 mg/kg, subcutaneous, twice daily) for 12 weeks. Compared with air-exposed rats, body weight gain, food intake, food efficiency, tidal volume, peak expiratory flow rate, and forced expiratory volume at 100 ms were significantly lower, while functional residual capacity, lung capacity, and neutrophils in bronchoalveolar lavage fluid were significantly higher in cigarette smoke-exposed rats. These indicated that the systemic abnormalities associated with COPD developed after the exposure to cigarette smoke. Ghrelin significantly and dose-dependently increased the body weight gain and food efficiency in cigarette smoke-exposed rats. In ghrelin-treated rats, skeletal muscle strength, which tended to be lowered by cigarette smoke exposure, was improved. Ghrelin ameliorated respiratory function and emphysema in a dose-dependent manner, but did not inhibit the increase in neutrophils in the bronchoalveolar lavage fluid. The respiratory functional parameters and lung capacity were significantly correlated with body weight gain. These results suggest that ghrelin inhibited the development of the catabolic changes, respiratory dysfunction, and emphysema that were induced by cigarette smoke exposure in rats, at least in part, through the amelioration of nutritional status.

Ghrelin improves body weight loss and skeletal muscle catabolism associated with angiotensin II-induced cachexia in mice.

Ghrelin is a gastric peptide that regulates energy homeostasis. Angiotensin II (Ang II) is known to induce body weight loss and skeletal muscle catabolism through the ubiquitin-proteasome pathway. In this study, we investigated the effects of ghrelin on body weight and muscle catabolism in mice treated with Ang II. The continuous subcutaneous administration of Ang II to mice for 6 days resulted in cardiac hypertrophy and significant decreases in body weight gain, food intake, food efficiency, lean mass, and fat mass. In the gastrocnemius muscles of Ang II-treated mice, the levels of insulin-like growth factor 1 (IGF-1) were decreased, and the levels of mRNA expression of catabolic factors were increased. Although the repeated subcutaneous injections of ghrelin (1.0mg/kg, twice daily for 5 days) did not affect cardiac hypertrophy, they resulted in significant body weight gains and improved food efficiencies and tended to increase both lean and fat mass in Ang II-treated mice. Ghrelin also ameliorated the decreased IGF-1 levels and the increased mRNA expression levels of catabolic factors in the skeletal muscle. IGF-1 mRNA levels in the skeletal muscle significantly decreased 24h after Ang II infusion, and this was reversed by two subcutaneous injections of ghrelin. In C2C12-derived myocytes, the dexamethasone-induced mRNA expression of atrogin-1 was decreased by IGF-1 but not by ghrelin. In conclusion, we demonstrated that ghrelin improved body weight loss and skeletal muscle catabolism in mice treated with Ang II, possibly through the early restoration of IGF-1 mRNA in the skeletal muscle and the amelioration of nutritional status.

A new strategy for metabolic stabilization of motilin using the C-terminal part of ghrelin.

Ghrelin consists of 28 amino acid residues with an octanoyl modification at the third serine residue. Recently we have found that the C-terminal part of ghrelin protects the ester bond of 3-octanoyled serine from plasma esterases and plays the essential role to prolong the plasma half-life and to show its biological activity in vivo. In the present study, we researched whether the C-terminal part of ghrelin has a potential to prolong the plasma half-life of motilin, by comparing the pharmacokinetics of various chimeric peptides of ghrelin and motilin. Motilin is another gastro-intestinal peptide hormone related with ghrelin structurally, binding to the same family of G protein-coupled receptors. Chimeric peptides were designed to be composed of motilin(1-12) fragment, the active core binding to the motilin receptor, GPR38, and C-terminal part of ghrelin. The modification of motilin(1-12) fragment by C-terminal part of ghrelin hardly influenced its agonist activity to GPR38 and almost all these chimeric peptides showed more than two times longer plasma half-lives than motilin in rats. From the relationship between structures of chimeric peptides and their corresponding plasma half-lives, the mid-region of ghrelin rich in basic amino acids ((15)RKESKK(20)) was considered to be the most important in prolonging the plasma half-life of motilin. The deletion of these fragments or replacement of 17th glutamic acid with a neutral amino acid resulted in short plasma half-lives. In conclusion, our data suggested that the C-terminal part of ghrelin has a potential to improve the biokinetics of motilin probably by a metabolic stabilizing effect.