Salusin-β as a powerful endogenous antidipsogenic neuropeptide

Relationship between salusin beta levels and the severity of acute pancreatitis in patients

BACKGROUND

This study aimed to evaluate the significance of serum salusin beta (SAL-β) levels in predicting the severity of acute pancreatitis (AP) in patients diagnosed with this condition and to assess its relationship with disease and prognosis.

METHODS

Sixty-four patients between 18 and 100 years of age diagnosed with AP, were included in the study. Patients were categorized into 3 groups based on the Revised Atlanta Classification: mild, moderate, and severe AP. Eighteen healthy adults were included as the control group. Sex, age, height, weight, presence of additional diseases, laboratory results, imaging findings, levels of white blood cells, neutrophil-lymphocyte ratio, mean platelet volume, amylase, lipase, sensitive C-reactive protein, sedimentation, and serum SAL-β were measured and recorded. SAL-β levels were reevaluated on the third day of hospitalization.

RESULTS

The average age of the patients included in the study was 62.66 ± 17.67. Gallstones were present in 64.1% of the patients. The difference in the SAL-β averages on the 1st and 3rd days was statistically significant (P < .05). On the first day, the SAL-β averages of those with severe Atlanta scores were higher than those with mild and moderate Atlanta severity. Similarly, on the third day, the SAL-β averages of those with severe Atlanta scores were higher than those with mild and moderate Atlanta severity. According to receiver operating characteristic analysis using the Youden index, the cutoff value for SAL-β for severe pancreatitis was 178.8 pg/mL on the 1st day and 207.5 pg/mL on the 3rd day.

CONCLUSION

SAL-β can be used to detect and monitor severe pancreatitis. Further extensive clinical studies with larger case series are needed.

The relationship of salusins with Parkinson's Disease, Alzheimer's Disease, and acute ischemic stroke: A preliminary study

Neuroinflammation, oxidative stress, and apoptosis play important roles in the pathophysiology of Alzheimer's Disease (AD), Parkinson's Disease (PD), and Acute Ischemic Stroke (AIS). Salusin-α and salusin-β peptides, which were shown to be present in many tissues, including the central nervous system, were also shown to be associated with apoptosis, inflammation, and oxidative stress. In the present study, the relationship between Salusin-α and salusin-β peptides and AD, PD, and AIS were investigated. A total of 179 people were included in the present study, including 46 AD, 44 PD, 42 AIS, and 47 controls. Plasma Salusin-α and salusin-β levels were measured with the ELISA Method. The plasma salusin-β levels of AD, PD, and AIS patients were lower than the control group at significant levels (p < 0.05). It was also found that there were correlations between salusin-α and salusin-β levels and age, triglyceride, LDL-c, total cholesterol, and hemoglobin levels. In this study, we found that salusin- β, an endogenous neuropeptide, was associated with AD, PD and AIS. The low level of salusin-β in these diseases in which neuronal damage occurs may be related to the neuroprotective properties of this endogenous peptide. Further studies are needed to fully understand the relationship between salusin-β and the pathophysiology of these diseases.

Serum salusin-α and -β levels in patients with parkinson's disease

BACKGROUND

The etiology of Parkinson's disease (PD) is not well known and there is increasing evidence that oxidative stress also plays an important role in its pathogenesis. Salusins alpha (salusin-α) and beta (salusin-β) affect the central nervous system, vasculature, and kidneys to increase the inflammatory response in endothelial cells, stimulate oxidative stress, and increase monocyte-endothelial adhesion. Neuroinflammation and oxidative stress play roles in the etiopathogenesis of PD.

PURPOSE

To investigate whether salusin-α and -β are related to PD and whether they are correlated with the development of atherosclerosis, body mass index, disease duration, and the Parkinson's Hoehn and Yahr stage.

RESULTS

The low-density lipoprotein cholesterol (LDL-C), total cholesterol, and salusin-β levels were significantly lower and age was significantly higher in Parkinson patients compared to healthy controls (ρ < 0.005). We found a negative linear correlation between salusin-β and the Hoehn and Yahr stage (ρ < 0.001, r = -0.515) in the patients.

CONCLUSIONS

There was a relationship between salusin-β and PD and a correlation between the salusin-β levels and Parkinson's stage. A possible underlying disease mechanism is an increase in oxidative stress and decrease in neuroprotective effects due to low salusin-β levels. Therefore, the effects of salusin-β in treating Parkinson disease should be evaluated. Further studies are needed to understand the effects of salusin-β treatment on preventing or slowing the course of PD.

Upregulated expression of a TOR2A gene product-salusin-β in the paraventricular nucleus enhances sympathetic activity and cardiac sympathetic afferent reflex in rats with chronic heart failure induced by coronary artery ligation

AIM

Enhanced cardiac sympathetic afferent reflex (CSAR) promotes sympathetic hyperactivation in chronic heart failure (CHF). Salusin-β is a torsin family 2 member A (TOR2A) gene product and a cardiovascular active peptide closely associated with cardiovascular diseases. We aimed to determine the roles of salusin-β in the paraventricular nucleus (PVN) in modulating enhanced CSAR and sympathetic hyperactivation in rats with CHF induced by coronary artery ligation and elucidate the underlying molecular mechanisms.

METHODS

CSAR was evaluated based on the responses of mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) to the epicardial administration of capsaicin in rats under anesthesia.

RESULTS

Salusin-β protein expression was upregulated in the PVN of the CHF compared with sham-operated rats. Salusin-β microinjection into the PVN dose-dependently increased MAP and RSNA and enhanced CSAR, while anti-salusin-β IgG exerted opposite effects. The effect of salusin-β was inhibited by reactive oxygen species (ROS) scavenger or NAD(P)H oxidase inhibitor but promoted by superoxide dismutase inhibitor. The effect of anti-salusin-β IgG was interdicted by nitric oxide (NO) synthase inhibitor. Furthermore, chronic salusin-β gene knockdown in PVN attenuated CSAR, reduced sympathetic output, improved myocardial remodeling and cardiac function, decreased NAD(P)H oxidase activity and ROS levels, and increased NO levels in the CHF rats.

CONCLUSION

Increased salusin-β activity in the PVN contributes to sympathetic hyperactivation and CSAR in CHF by inhibiting NO release and stimulating NAD(P)H oxidase-ROS production. Reducing endogenous central salusin-β expression might be a novel strategy for preventing and treating CHF in the future.

ANGT_HUMAN[448–462], an Anorexigenic Peptide Identified using Plasma Peptidomics

The discovery of bioactive peptides is an important research target that enables the elucidation of the pathophysiology of human diseases and provides seeds for drug discovery. Using a large number of native peptides previously identified using plasma peptidomics technology, we sequentially synthesized selected sequences and subjected them to functional screening using human cultured cells. A 15-amino-acid residue proangiotensinogen-derived peptide, designated ANGT_HUMAN[448–462], elicited cellular responses and bound to cultured human cells. Synthetic fluorescent-labeled and biotinylated ANGT_HUMAN[448–462] peptides were rendered to bind to cell- and tissue-derived proteins and peptide-cell protein complexes were retrieved and analyzed using liquid chromatography-tandem mass spectrometry, revealing the β-subunit of ATP synthase as its cell-surface binding protein. Because ATP synthase mediates the effects of anorexigenic peptides, the ability of ANGT_HUMAN[448–462] to modulate eating behavior in mice was investigated. Both intraperitoneal and intracerebroventricular injections of low doses of ANGT_HUMAN[448–462] suppressed spontaneous food and water intake throughout the dark phase of the diurnal cycle without affecting locomotor activity. Immunoreactive ANGT_HUMAN[448–462], distributed throughout human tissues and in human-derived cells, is mostly co-localized with angiotensin II and is occasionally present separately from angiotensin II. In this study, an anorexigenic peptide, ANGT_HUMAN[448–462], was identified by exploring cell surface target proteins of the human native peptides identified using plasma peptidomics.

Suprabasin-derived bioactive peptides identified by plasma peptidomics

Identification of low-abundance, low-molecular-weight native peptides using non-tryptic plasma has long remained an unmet challenge, leaving potential bioactive/biomarker peptides undiscovered. We have succeeded in efficiently removing high-abundance plasma proteins to enrich and comprehensively identify low-molecular-weight native peptides using mass spectrometry. Native peptide sequences were chemically synthesized and subsequent functional analyses resulted in the discovery of three novel bioactive polypeptides derived from an epidermal differentiation marker protein, suprabasin. SBSN_HUMAN[279-295] potently suppressed food/water intake and induced locomotor activity when injected intraperitoneally, while SBSN_HUMAN[225-237] and SBSN_HUMAN[243-259] stimulated the expression of proinflammatory cytokines via activation of NF-κB signaling in vascular cells. SBSN_HUMAN[225-237] and SBSN_HUMAN[279-295] immunoreactivities were present in almost all human organs analyzed, while immunoreactive SBSN_HUMAN[243-259] was abundant in the liver and pancreas. Human macrophages expressed the three suprabasin-derived peptides. This study illustrates a new approach for discovering unknown bioactive peptides in plasma via the generation of peptide libraries using a novel peptidomic strategy.

Identification of the salusin-β receptor using proteoliposomes embedded with endogenous membrane proteins

Although orphan G protein-coupled receptors (GPCRs) have been used as targets to discover unidentified natural ligands, increasing numbers of non-GPCRs have been found to mediate important biological functions. Bioinformatics of genome and cDNA resources predict putative bioactive peptides, demanding an alternative approach to efficiently unravel cell surface targets. In silico analysis of a full-length cDNA library previously allowed us to identify salusin-β, a parasympathomimetic/pro-atherosclerotic peptide with unique physicochemical properties. Here, we show that the β-chain of ATP synthase is a cell surface receptor for salusin-β by utilizing artificial liposomes embedded with endogenous membrane proteins directly transferred from animal tissues while retaining the ligand-binding capability. Conventional techniques using detergents identified a β-actin-profilin complex as membrane-associated salusin-β-binding proteins, but failed to identify the cell surface receptor. Since the α-chain of ATP synthase is a principal cell surface target for angiostatin, a potent endogenous angiogenesis inhibitor, we investigated whether salusin-β modulates angiogenesis. Salusin-β inhibited cell surface ATP synthase activity and prevented sarcoma cell-induced angiogenesis in an in vivo mouse air sac model. Therefore, salusin-β binds to membrane-bound ATP synthase and acts as an angiogenesis inhibitor. The current methodology allows the identification of novel cell surface targets, irrespective of the receptor structure.

Identification and quantification of plasma free salusin-β, an endogenous parasympathomimetic peptide

Salusin-β is an endogenous parasympathomimetic proatherosclerotic peptide. Salusin-β was initially predicted from bioinformatic analyses and later immunologically detected in human biofluids. However, elucidation of salusin-β bioactivity has faced enormous challenges because of its unique physicochemical characteristics that cause it to strongly adhere to laboratory apparatus materials. In the strictest sense, the discovery of bioactive peptides is not complete until their exact native sequences have been confirmed in the peripheral circulation. In this study, we determined the plasma molecular form and levels of free salusin-β to determine its pathophysiological significance. Ultra-high-yield enrichment and preseparation of non-tryptic human plasma was followed by LC-MS/MS, and full-length salusin-β and seven different endogenous fragment sequences were identified. We established a new ELISA that specifically detects plasma free salusin-β without cross-reacting with any of its identified endogenous fragments. Free salusin-β levels exhibited a profound early morning nadir and rapidly decreased in response to parasympathetic nervous augmentation. Our technical advance in plasma native peptide analysis successfully identified a hard-to-detect bioactive peptide, salusin-β, together with its formerly unrecognized fragments, and further suggests that conventional immunological measurements of target peptides may not be fully representative.

The cardiovascular functions of salusin-β mediated by muscarinic receptors, glutamate receptors or L-type calcium channels within the rostral ventrolateral medulla of rats

Salusin-α and salusin-β are newly identified bioactive peptides of 28 and 20 amino acids, respectively, that were initially predicted using in silico analyses and are widely distributed in the endocrine system, hematopoietic system, and central nervous system. The goal of our study was to investigate the cardiovascular effect of salusin-β microinjections into the rostral ventrolateral medulla (RVLM) in anesthetized rats and study their mechanism of action. Microinjection of the artificial cerebrospinal fluid (aCSF) into the RVLM did not affect the blood pressure (BP) or heart rate (HR) in anesthetized rats. Topical application of salusin-β into the RVLM produced a dose-dependently increase of BP in anesthetized rats. Microinjection of higher dose salusin-β produced significant tachycardia. Prior application of the L-NAME into the RVLM of rats did not alter the hypertension and tachycardia induced by intra-RVLM salusin-β. Notable, the cardiovascular functions elicited by intra-RVLM salusin-β were significantly decreased by pretreatment with Nic, KYN and atropine. In conclusion, the present study shows that the hypertension and tachycardia induced by intra-RVLM salusin-β might be partly mediated, at least in our opinion, by muscarinic receptors, glutamate receptors or L-type calcium channels.