Expression of prosalusin in human neuroblastoma cells

Salusins: advance in cardiovascular disease research

Salusins are discovered in 2003 and divided into salusin-α and salusin-β, which are bioactive peptides with hemodynamic and mitotic activity and mainly distributed in plasma, urine, endocrine glands and kidneys. A large number of studies have shown that salusins can regulate lipid metabolism, inflammatory response and vascular proliferation. Despite the profound and diverse physiological properties of salusins, the exact mechanism of their cardiovascular effects remains to be determined. The potential mechanisms of action of salusins in cardiovascular-related diseases such as atherosclerosis, hypertension, heart failure, myocardial infarction and myocarditis, and their use as biomarkers of cardiovascular disease are discussed. This review aims to provide a new strategy for the diagnosis and prevention of clinical cardiovascular diseases.

Serum salusin-α and salusin-β levels in patients with psoriatic arthritis

INTRODUCTION

Psoriatic arthritis (PsA) is a chronic inflammatory disease characterized by skin lesions and joint involvement. Salusin-α and salusin-β are two new bioactive molecules. It is reported that salusins may have role in regulation of the immune system and inflammation. The aim of our study was to evaluate the serum salusin-α and salusin-β levels in PsA patients and to establish the possible relationship with the disease features.

MATERIAL AND METHODS

Our study included 40 PsA patients who fulfilled the CASPAR criteria and 40 healthy volunteers. Demographic, clinical, laboratory and radiological data and disease activity indices (PASI, BASDAI, BASFI, HAQ) were recorded in all patients. The enzyme-linked immunosorbent assay (ELISA) method was used to measure serum salusin-α and salusin-β levels.

RESULTS

The demographic data were as follows: 13 patients (32.5%) were males and 27 (67.5%) were female, mean age was 48.5 years and mean disease duration was 2.4 years. Patients' history was taken and clinical assessment was performed; 20 (50%) patients had a family history, 18 (45%) patients were smoker, 19 (47.5%) patients had HLA-B27 positivity, 33 (82.5%) had sacroiliitis, 36 (90%) had enthesitis, 23 (57.5%) had distal interphalangeal (DIP) joint and nail involvement, 26 (65%) had wrist involvement, and 11 (27.5%) had ankle involvement. Laboratory data of the patients were recorded; 20 (50%) patients had elevated CRP level and 25 (62.5%) patients had an elevated ESR level. The study results showed that PsA patients had an elevated serum salusin-α level when compared with the control group (p = 0.004). The association between serum salusin-α level and ankle arthritis was found (p = 0.04). Serum levels of salusin-β were similar in PsA patients and controls both (p = 0.285).

CONCLUSIONS

We found elevated serum salusin-α in PsA patients while the serum salusin-β levels were normal. Salusin-α may have a possible role in disease pathogenesis and it may be use as a reliable biomarker in PsA patients. Multicenter prospective studies are needed in this regard.

A New Marker for Determining Cardiovascular Risk: Salusin Alpha

Background and objective Prevention of atherosclerotic cardiovascular diseases (ASCVD) is possible with early recognition of individuals at risk. Salusin alpha is an endogenous bioactive peptide with anti-atherogenic properties. We aimed to reveal the relationship between salusin alpha levels and cardiovascular (CV) risk using the Systematic COronary Risk Estimation 2 (SCORE2) and Pooled Cohort Equation (PCE) algorithms. Methods A total of 137 asymptomatic outpatients were included in the study. The participants were divided into four quartile groups according to the distribution of salusin alpha levels: Q1 (n = 34), Q2 (n = 35), Q3 (n = 34), and Q4 (n = 34). The relationships of salusin alpha with cardiovascular risk scores and groups were investigated. Results The means of SCORE2 and PCE risk scores (11.24 ± 1.24 and 13.30 ± 1.71, respectively; p < 0.001 for both), baseline scores in the presence of SCORE2 and PCE optimal risk factors (4.82 ± 0.71 (p = 0.034); 4.20 ± 0.77 (p = 0.010)), and means of Δ SCORE2 and Δ PCE risk score (6.41 ± 0.67 and 9.10 ± 1.10, respectively; p < 0.001 for both) were significantly higher in the Q1 group. The SCORE2 "very high" cardiovascular (CV) risk group was significantly represented in the Q1 group (n = 17 (50%)), while the "low-moderate" risk group was more heavily represented in the Q4 group (n = 15 (44.1%)) (p < 0.001). The PCE "high" CV risk group was significantly represented in the Q1 group (n = 9 (26.5%)), while the "low" risk group was more intensely represented in the Q4 group (n = 20 (58.8%)) (p < 0.001). Salusin alpha had a significantly negative moderate correlation with SCORE2 and PCE risk scores. As a result of receiver operating characteristic (ROC) analysis, it was found that salusin alpha had significant diagnostic power in the prediction of CV risk groups determined by SCORE2 and PCE risk scores. Salusin alpha was observed to be a risk-reducing factor in SCORE2 and PCE CV risk groups (odds ratio (OR) (95% confidence interval (CI)): 0.989 (0.982-0.997) (p = 0.002) and OR (95% CI): 0.988 (0.978-0.998) (p = 0.009) respectively). Conclusion Salusin alpha has a negative correlation with SCORE2 and PCE risk scores. It has significant diagnostic power in the prediction of CV risk groups and is an independent variable that has a risk-reducing effect in the distribution of risk groups.

Intracerebroventricular salusin-β infusion to rats increases hypothalamus-pituitary-testicular axis hormones

Salusin-β (Sal-β), which originates from preprosalusin, is a multifunctional hormone with a peptide structure. Sal-β exists in the hypothalamus and can stimulate the pituitary gland. The present study was conducted to determine the effects of Sal-β on hormones that play roles in the male reproductive system. Forty male Wistar Albino rats were used in the study. No infusions were performed on the control group, and infusions were applied to the infusion groups (artificial cerebrospinal fluid to the sham group, 2 and 20 nM Sal-β to the experimental group) through intracerebroventricular infusion for 7 days at 10 μl/hour rate. The animals were decapitated after 7 days of infusion; and the hypothalamus, testicles, and blood tissue samples were collected. The gonadotropin-releasing hormone (GnRH) mRNA levels were determined from the hypothalamus tissues by using the Real Time-PCR Method, and the serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone levels were determined using the ELISA method. Also, Hematoxylin-Eosin Staining Method was used for histopathological evaluations in the testicle tissues. As a result, Sal-β infusion increased GnRH mRNA levels in hypothalamus tissues (p < 0.05) besides, serum LH, FSH, and testosterone levels of the rats were higher at significant levels following Sal-β infusion compared to the control and sham group (p < 0.05). In the histological examination of the testicle tissues, Sal-β application was found to decrease the seminiferous tubule diameter and germinal epithelial thickness (p < 0.05). This evidence is the first, indicating that Sal-β, which is administered to male rats with central infusion, stimulates hypothalamus and pituitary tissues, and causes increased secretion of male reproductive hormones.

The role of serum salusin alpha and beta levels and atherosclerotic risk factors in idiopathic sudden hearing loss pathogenesis

PURPOSE

The aim of this study was to investigate the importance of atherosclerosis in the pathogenesis of sudden hearing loss by evaluating the newly discovered markers, serum salusin-α and salusin-β. We also aimed to evaluate atherosclerosis risk factors, such as lipid profile, smoking, body mass index, waist circumference and mean blood pressure of the patients.

METHODS

Fifty-two patients diagnosed with sudden hearing loss (study group) and fifty healthy people (control group) were included in the study. Detailed history was taken from the patients and risk factors for atherosclerosis, such as smoking, body mass index, waist circumference, lipid profile, mean blood pressure and serum salusin-α and salusin-β levels, were evaluated. The study group was divided into recovery group (subgroup I) and non-recovery group (subgroup II).

RESULTS

The salusin-β median value was found to be significantly higher in the study group compared to the control group (p < 0.05). The salusin-β median value was found to be significantly higher in subgroup 2 and was found to be a poor prognostic factor (p < 0.05).

CONCLUSION

From the results obtained in this study, it is thought that salusin-β peptide is increased in patients with sudden hearing loss and it can be evaluated as a poor prognostic factor.

Increased serum salusin-α by aerobic exercise training correlates with improvements in arterial stiffness in middle-aged and older adults

Aging causes arterial stiffening which can be mitigated by increased physical activity. Although low circulating levels of salusin-α are associated with cardiovascular disease, whether salusin-α decreases with aging and whether the reduced arterial stiffening occurring with exercise training is associated with increased serum salusin-α is unknown. Herein we assessed carotid-femoral pulse wave velocity (cfPWV), systolic (SBP) and diastolic (DBP) blood pressures in a cross-sectional study that compared young (20-39-year-old, n=45) versus middle-aged and older (40-80-year-old, n=60) subjects. We also performed an interventional study in which 36 young and 40 middle-aged and older subjects underwent eight weeks of aerobic exercise training. In the cross-sectional study, serum salusin-α levels were lesser in middle-aged and older subjects compared to young individuals and negatively correlated with age, SBP, DBP, or cfPWV. In the interventional study, exercise training increased serum salusin-α in middle-aged and older subjects. Notably, negative correlations were noted between the exercise training-induced changes in serum salusin-α and cfPWV, SBP and DBP. Results indicate that advanced age associates with low circulating salusin-α, the levels of which can be augmented by exercise training. Importantly, increased serum salusin-α with exercise correlates with improvements in arterial stiffness and a reduction in blood pressure.

Relationship of salusin-alpha and salusin-beta levels with atherosclerosis in patients undergoing haemodialysis

INTRODUCTION

In patients undergoing haemodialysis, cardiovascular mortality and morbidity, characterised by accelerated atherosclerosis and increased inflammation, are elevated. Salusins are newly defined molecules in the atherosclerotic processes, and while salusin-alpha (Sal-α) acts as an antiatherogenic factor, salusin-beta (Sal-β) has a proatherogenic role. Their roles are as yet undefined in patients undergoing haemodialysis.

METHODS

In this cross-sectional study, salusin levels, carotid intima-media thickness (CIMT) from the common carotid artery and pulse wave velocity (PWV) were measured for 180 patients undergoing haemodialysis and 90 healthy controls.

RESULTS

Mean Sal-α and Sal-β levels in patients undergoing haemodialysis (Sal-α: 726.4 ± 578.7 pg/mL; Sal-β: 1,080.4 ± 757.1 pg/mL) and healthy controls (Sal-α: 325.8 ± 303.7 pg/mL; Sal-β: 268.1 ± 409.0 pg/mL) were determined. Negative correlation was observed between Sal-α levels and CIMT (patients undergoing haemodialysis: r = -0.330, p < 0.0001; healthy controls: r = -0.223, p = 0.035) and PWV (patients undergoing haemodialysis: r = -0.210, p = 0.005; healthy controls: r = -0.378, p < 0.0001) in both groups. In patients undergoing haemodialysis, positive correlation was observed between Sal-β/Sal-α ratio and CIMT (r = 0.190, p = 0.012) and PWV (r = 0.155, p = 0.041). On subgroup analysis, Sal-α levels were found to be low in patients with diabetes mellitus.

CONCLUSION

Patients undergoing haemodialysis have higher Sal-β and Sal-α levels, and their higher Sal-β/Sal-α ratio, in comparison with healthy controls, might have cardiovascular risk implications.

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.

Salusins and adropin: New peptides potentially involved in lipid metabolism and atherosclerosis

Dyslipidemia is one of the most potent risk factors for the development of atherosclerosis. The high atherosclerotic risk in dyslipidemic patients is associated with endothelial dysfunction. During the last two decades, novel bioactive peptides have emerged as potential biomarkers of endothelial dysfunction and dyslipidemia-salusins and adropin. Salusin-alpha is likely to prevent atherosclerosis, while salusin-beta may act as a potential proatherogenic factor. Adropin was recently identified as important for energy homeostasis and lipid metabolism. Adropin is closely related to the inhibition of atherosclerosis by up-regulation of the endothelial nitric oxide synthase expression through the vascular endothelial growth factor receptor-2. These peptides represent a novel target to limit diseases characterized by endothelial dysfunction and may form the basis for the development of new therapeutic agents for treating metabolic disorders associated with atherosclerosis.

Blockade of Salusin-β in Hypothalamic Paraventricular Nucleus Attenuates Hypertension and Cardiac Hypertrophy in Salt-induced Hypertensive Rats

Salusin-β, a multifunctional bioactive peptide, is considered as a promising candidate biomarker for predicting cardiovascular diseases. This study was designed to determine whether inhibition of salusin-β in the hypothalamic paraventricular nucleus (PVN) delays the progression of hypertension and attenuates cardiac hypertrophy by restoring neurotransmitters and cytokines. Male Sprague Dawley rats were fed with a normal salt diet (NS, 0.3%) or a high salt diet (HS, 8%) for 8 weeks to induce hypertension. Then, these rats received bilateral PVN infusion of a specific salusin-β blocker, antisalusin-β IgG (SIgG), or control IgG (CIgG) for 2 weeks. HS rats exhibited higher mean arterial pressure and cardiac hypertrophy as indicated by increased whole heart weight/bodyweight ratio, whole heart weight/tibia length ratio, left ventricular weight/tibia length ratio, and messenger RNA levels of cardiac atrial natriuretic peptide (ANP), and β-myosin heavy chain. Compared with NS rats, HS rats had higher levels of glutamate, norepinephrine, tyrosine hydroxylase, proinflammatory cytokines, and lower levels of gamma-aminobutyric acid, interleukin 10, and the 67-kDa isoform of glutamate decarboxylase (GAD67) in the PVN, and higher plasma levels of proinflammatory cytokines. Chronic PVN infusion of SIgG attenuated all these changes in HS rats. Our findings suggest that HS rats have an imbalance between excitatory and inhibitory neurotransmitters, as well as an imbalance between proinflammatory and anti-inflammatory cytokines in the PVN; and chronic inhibition of salusin-β in the PVN restores neurotransmitters and cytokines in the PVN, thereby attenuating hypertensive responses and cardiac hypertrophy.

Is the serum level of salusin-β associated with hypertension and atherosclerosis in the pediatric population?

BACKGROUND

Salusins are recently identified endogenous bioactive peptides that have hypotensive and bradycardiac effects. Salusin-β is involved in the pathogenesis of human atherosclerosis.

METHODS

This was a prospective cohort study of a young patient population with hypertension (HTN). Based on ambulatory blood pressure monitoring (ABPM), the adolescents were categorized into two groups, namely, a hypertensive group consisting of patients with essential (primary) HTN (HTN group) and a group consisting of patients with white-coat HTN [reference (R) group]. Correlations between serum salusin-β level and clinical, laboratory and ambulatory blood pressure (BP) variables were assessed.

RESULTS

The median salusin-β concentration was significantly higher in patients with essential HTN than in those with white-coat HTN (R group). Salusin-β was positively correlated with the body mass index Z-score, systolic and diastolic blood pressure (BP) from three independent measurements, mean systolic BP during the daytime, triglyceride (TG) level, and atherogenic index (TG/high-density lipoprotein-cholesterol ratio).

CONCLUSIONS

The results of this preliminary study suggest that salusin-β may play an important role in the pathogenesis of HTN in a young population. Further research should focus on the role of salusin-β in the mechanism of essential HTN and the assessment of possible correlations between salusin-β and other well-known markers of atherosclerosis in both teenagers and adults. This research should serve as a base for future studies in this field.

Microinjection of salusin-beta into the nucleus tractus solitarii inhibits cardiovascular function by suppressing presympathetic neurons in rostral ventrolateral medulla in rats

Salusin-beta is newly identified bioactive peptide of 20 amino acids, which is widely distributed in hematopoietic system, endocrine system, and the central nervous system (CNS). Although salusin-beta extensively expressed in the CNS, the central cardiovascular functions of salusin-beta are unclear. Our main objective was to determine the cardiovascular effect of microinjection of salusin-beta into the nucleus tractus solitarii (NTS) in anesthetized rats. Bilateral or unilateral microinjection of salusin-beta (0.94-94 microg/rat) into the NTS dose-dependently decreased blood pressure and heart rate. Bilateral NTS microinjection of salusin-beta (9.4 microg/rat) did not alter baroreflex sensitivity. Prior application of the glutamate receptor antagonist kynurenic acid (0.19 microg/rat, n=9) into the NTS did not alter the salusin-beta (9.4 microg/rat) induced hypotension and bradycardia. However, pretreatment with the GABA receptor agonist muscimol (0.5 ng/rat) within the rostral ventrolateral medulla (RVLM) completely abolished the hypotension (-14+/-5 vs. -3+/-5 mm Hg, P<0.05) and bradycardia (-22+/-6 vs. -6+/-5 bpm, P<0.05) evoked by intra-NTS salusin-beta (9.4 microg/rat). In addition, we found that vagotomy didn't influence the actions of salusin-beta (9.4 microg/rat) in the NTS. In conclusion, our present study shows that microinjection of salusin-beta into the NTS significantly produces hypotension and bradycardia, presumably by suppressing the activities of presympathetic neurons in the RVLM.

Salusins: potential use as a biomarker for atherosclerotic cardiovascular diseases

Human salusin- α and salusin- β are related peptides produced from prosalusin. Bolus injection of salusin- β into rats induces more profound hypotension and bradycardia than salusin- α . Central administration of salusin- β increases blood pressure via release of norepinephrine and arginine-vasopressin. Circulating levels of salusin- α and salusin- β are lower in patients with essential hypertension. Salusin- β exerts more potent mitogenic effects on human vascular smooth muscle cells (VSMCs) and fibroblasts than salusin- α . Salusin- β accelerates inflammatory responses in human endothelial cells and monocyte-endothelial adhesion. Human macrophage foam cell formation is stimulated by salusin- β but suppressed by salusin- α . Chronic salusin- β infusion into apolipoprotein E-deficient mice enhances atherosclerotic lesions; salusin- α infusion reduces lesions. Salusin- β is expressed in proliferative neointimal lesions of porcine coronary arteries after stenting. Salusin- α and salusin- β immunoreactivity have been detected in human coronary atherosclerotic plaques, with dominance of salusin- β in macrophage foam cells, VSMCs, and fibroblasts. Circulating salusin- β levels increase and salusin- α levels decrease in patients with coronary artery disease. These findings suggest that salusin- β and salusin- α may contribute to proatherogenesis and antiatherogenesis, respectively. Increased salusin- β and/or decreased salusin- α levels in circulating blood and vascular tissue are closely linked with atherosclerosis. Salusin- α and salusin- β could be candidate biomarkers and therapeutic targets for atherosclerotic cardiovascular diseases.

Effects of Salusin-β on action potential and ionic currents in ventricular myocytes of rats

AIM

Salusin-β is a regulatory peptide that exerts negative inotropic effect on ventricular muscle, but its electrophysiological effects on ventricular myocytes are still unknown.

METHODS

Action potential and channel currents such as sodium current (I(N) (a) ), transient outward potassium current (I(to) ), steady-state potassium current (I(sus) ), sodium-calcium exchange current (I(N) (aCa) ) and inward rectifier potassium current (I(K) (1) ) were measured in ventricular myocytes isolated from 12 to 16 weeks rats by whole-cell voltage-clamp techniques.

RESULTS

Salusin-β dose-dependently shortened the duration of action potential in rat ventricular myocytes. Furthermore, salusin-β significantly inhibited I(N) (aCa) and increased I(to) , but did not affect I(N) (a) , I(sus) and I(K) (1) .

CONCLUSION

These results suggest that the effect of salusin-β on action potential may be partly attributed to a decrease in inward currents and an increase in outward currents.

Distinct systemic distribution of salusin-α and salusin-β in the rat

Salusin-α and salusin-β are multifunctional bioactive peptides that were initially predicted using in silico analyses. These peptides should be concomitantly biosynthesized from prosalusin in humans. However, little information is available yet on the biosynthesis and mode of presence of salusin-α and salusin-β in non-human species. In the present study, we examined whether salusin-α and salusin-β are conserved in the rat and whether salusin-α and salusin-β show distinct systemic distributions. Immunohistochemical analysis of rat tissues using a specific anti-rat salusin-α antibody detected immunoreactivity extensively in neuronal cells and fibers, and abundantly in the epithelial tissues throughout the organs. This distribution contrasts sharply with that of salusin-β, which is mainly localized to the neuroendocrine and hematopoietic systems. Western blot analysis of rat spleen extracts showed the presence of cleaved fragments corresponding to putative rat salusin-α. Reverse-phase and gel filtration high performance liquid chromatography analyses coupled with radioimmunoassay detection of rat urine extracts revealed a major immunoreactive component that co-eluted with synthetic putative rat salusin-β. These data support the processing of rat prosalusin into salusin-α and salusin-β despite absent dibasic amino acids between the two.

Inhibition of L-type calcium currents by salusin-beta in rat cardiac ventricular myocytes

Salusin-beta is a new regulatory peptide relevant to the cardiovascular system and exerts negative inotropic effect on ventricular muscle. The purpose of the present study was to determine whether salusin-beta can inhibit cardiac L-type calcium channel current (I(Ca,L)). Using whole-cell voltage-clamp techniques, I(Ca,L) was measured in ventricular myocytes isolated from 12 to 16 weeks rats. Salusin-beta dose-dependently and reversibly reduced the magnitude of I(Ca,L) in rat ventricular myocytes. Neither threshold potential nor the peak potential of current-voltage relationship was affected. Salusin-beta increased the rate of I(Ca,L) inactivation without altering its gating properties. These results suggest salusin-beta inhibited I(Ca,L) by increasing the rate of I(Ca,L) inactivation and the inhibition of L-type Ca(2+) channels induced by salusin-beta may contribute to its negative inotropic effect on ventricular muscle.

Serum levels and urinary excretion of salusin-alpha in renal insufficiency

Salusin-alpha was recently shown to exert anti-atherosclerotic effects and its potential role as a clinical marker for atherosclerosis has been proposed. We determined serum salusin-alpha concentrations in 99 patients across a diverse range of renal functions and urinary salusin-alpha excretions in 12 patients with non-dialyzed renal failure using a highly sensitive and specific radioimmunoassay. Serum salusin-alpha concentrations in patients with moderate to advanced renal insufficiency (eGFR < 30 ml/min/1.73 m(2)) were significantly lower than those with preserved renal function (eGFR > 60 ml/min/1.73 m(2)) (6.1 + or - 2.4 pmol/l vs. 11.8 + or - 1.1 pmol/l, p < 0.05). Since renal failure is frequently associated with atherosclerosis, we analyzed the relationship between serum salusin-alpha and eGFR after excluding patients with advanced atherosclerotic diseases. The serum salusin-alpha level was correlated with eGFR values (n = 94, p < 0.005). Patients with renal insufficiency showed reduced urinary salusin-alpha excretion, but the magnitude of the reduction was less than that for the decrease in serum salusin-alpha. Consequently, their salusin-alpha clearance often exceeded endogenous creatinine clearance levels. In conclusion, the decreased serum concentrations of salusin-alpha, an anti-atherosclerotic peptide, may be associated with impaired renal function, suggesting a potential role of decreased salusin-alpha in the acceleration of atherosclerosis in chronic kidney diseases. Urinary salusin-alpha may originate from the renal tubules, and may not necessarily represent the peptides filtered at the glomerulus.

Release of salusin-beta from human monocytes/macrophages

Salusin-alpha and salusin-beta are related bioactive peptides biosynthesized from the same precursor, prosalusin. Despite the potent hemodynamic and proatherosclerotic activities of salusin-beta, its exact distribution and biological functions remain largely undetermined because of technical difficulties associated with its unique physicochemical characteristics, such as marked adhesiveness to polypropylene and polystyrene. By circumventing these problems, we recently established a specific radioimmunoassay for detecting immunoreactive human salusin-beta. In the current study, we demonstrated the release of salusin-beta from the human monoblastic leukemia cell lines, THP-1 and U937. Dilution curves of extracted conditioned media from both cells were parallel with those of standard human salusin-beta by radioimmunoassay. Reverse-phase high performance liquid chromatography coupled with radioimmunoassay detection of the culture supernatants revealed a major immunoreactive component that co-eluted with authentic salusin-beta. Both cell lines secreted salusin-beta-like immunoreactivity (LI) into serum-free media as a function of time (1234.3 + or - 122.7 and 186.7 + or - 9.1 fmol/10(5) cells per 24h). When THP-1 and U937 cells differentiated into macrophages after incubation with 2-O-tetradecanoylphorbol-13-acetate (TPA), they secreted far greater amounts of salusin-beta-LI into the culture supernatant (3351.9 + or - 899.3 and 1545.8 + or - 183.3 fmol/10(5) cells per 24h). TPA treatment accelerated the processing of prosalusin into its cleaved fragments, suggesting that the increased secretion of salusin-beta-LI in THP-1-derived macrophages was caused by the enhanced intracellular processing of prosalusin. Stimulation with the inflammatory cytokines, tumor necrosis factor alpha (TNF-alpha) and lipopolysaccharide (LPS), resulted in increased secretion of salusin-beta without inducing expression of the gene for preprosalusin, suggesting that TNF-alpha and LPS stimulated the release of salusin-beta. These data demonstrate that salusin-beta, which induces macrophage foam cell formation, is secreted in its authentic form from human monocytes/macrophages.