The relationship among serum lipocalin 2, bone turnover markers, and bone mineral density in outpatient women

Interrelationships among metabolic syndrome, bone-derived cytokines, and the most common metabolic syndrome-related diseases negatively affecting bone quality

Metabolic syndrome (MetS), as a set of medical conditions including hyperglycemia, hypertension, abdominal obesity, and dyslipidemia, represents a highly prevalent disease cluster worldwide. The individual components of MetS together increase the risk of MetS-related disorders. Recent research has demonstrated that bone, as an endocrine organ, releases several systemic cytokines (osteokines), including fibroblast growth factor 23 (FGF23), lipocalin 2 (LCN2), and sclerostin (SCL). This review not only summarizes current knowledge about MetS, osteokines and the most common MetS-related diseases with a detrimental impact on bone quality (type 2 diabetes mellitus: T2DM; cardiovascular diseases: CVDs; osteoporosis: OP), but also provides new interpretations of the relationships between osteokines and individual components of MetS, as well as between osteokines and MetS-related diseases mentioned above. In this context, particular emphasis was given on available clinical studies. According to the latest knowledge, FGF23 may become a useful biomarker for obesity, T2DM, and CVDs, as FGF23 levels were increased in patients suffering from these diseases. LCN2 could serve as an indicator of obesity, dyslipidemia, T2DM, and CVDs. The levels of LCN2 positively correlated with obesity indicators, triglycerides, and negatively correlated with high-density lipoprotein (HDL) cholesterol. Furthermore, subjects with T2DM and CVDs had higher LCN2 levels. SCL may act as a potential biomarker predicting the incidence of MetS including all its components, T2DM, CVDs, and OP. Elevated SCL levels were noted in individuals with T2DM, CVDs and reduced in patients with OP. The aforementioned bone-derived cytokines have the potential to serve as promising predictors and prospective treatment targets for MetS and MetS-related diseases negatively affecting bone quality.

The role of adipokines in osteoporosis management: a mini review

The prevalence of osteoporosis has been on the rise globally. With ageing populations, research has sought therapeutic solutions in novel areas. One such area is that of the adipokines. Current literature points to an important role for these chemical mediators in relation to bone metabolism. Well-established adipokines have been broadly reported upon. These include adiponectin and leptin. However, other novel adipokines such as visfatin, nesfatin-1, meteorin-like protein (Metrnl), apelin and lipocalin-2 are starting to be addressed pre-clinically and clinically. Adipokines hold pro-inflammatory and anti-inflammatory properties that influence the pathophysiology of various bone diseases. Omentin-1 and vaspin, two novel adipokines, share cardioprotective effects and play essential roles in bone metabolism. Studies have reported bone-protective effects of omentin-1, whilst others report negative associations between omentin-1 and bone mineral density. Lipocalin-2 is linked to poor bone microarchitecture in mice and is even suggested to mediate osteoporosis development from prolonged disuse. Nesfatin-1, an anorexigenic adipokine, has been known to preserve bone density. Animal studies have demonstrated that nesfatin-1 treatment limits bone loss and increases bone strength, suggesting exogenous use as a potential treatment for osteopenic disorders. Pre-clinical studies have shown adipokine apelin to have a role in bone metabolism, mediated by the enhancement of osteoblast genesis and the inhibition of programmed cell death. Although many investigations have reported conflicting findings, sufficient literature supports the notion that adipokines have a significant influence on the metabolism of bone. This review aims at highlighting the role of novel adipokines in osteoporosis while also discussing their potential for treating osteoporosis.

Lipocalin-2 is associated with FGF23 in WNT1 and PLS3 osteoporosis

BACKGROUND

The pathogenic mechanisms of early-onset osteoporosis caused by WNT1 and PLS3 mutations are incompletely understood and diagnostic biomarkers of these disorders are limited. Recently, lipocalin-2 has been recognized as an osteokine involved in bone development and homeostasis. However, the role of lipocalin-2 in WNT1 and PLS3 osteoporosis is unknown.

OBJECTIVE

We aimed to investigate if plasma lipocalin-2 could be utilized as a biomarker for WNT1 and PLS3 osteoporosis and to evaluate the association between lipocalin-2 and other parameters of bone metabolism.

METHODS

We measured plasma lipocalin-2 in 17 WNT1 and 14 PLS3 mutation-positive patients and compared them to those of 34 mutation-negative (MN) healthy subjects. We investigated possible associations between lipocalin-2 and several bone biomarkers including collagen type I cross-linked C-telopeptide (CTX), alkaline phosphatase (ALP), type I procollagen intact N-terminal propeptide (PINP), intact and C-terminal fibroblast growth factor 23 (FGF23), dickkopf-1 (DKK1) and sclerostin as well as parameters of iron metabolism (iron, transferrin, transferrin saturation, soluble transferrin receptor and ferritin).

RESULTS

We found no differences in plasma lipocalin-2 levels in WNT1 or PLS3 patients compared with MN subjects. However, lipocalin-2 was associated with C-terminal FGF23 in WNT1 patients (r=0.62; p=0.008) and PLS3 patients (r=0.63, p=0.017), and with intact FGF23 in PLS3 patients (r=0.80; p<0.001). In addition, lipocalin-2 correlated with serum transferrin in WNT1 patients (r=0.72; p=0.001).

CONCLUSION

We conclude that plasma lipocalin-2 is not altered in WNT1 or PLS3 mutation-positive subjects but is associated with FGF23 in abnormal WNT1 or PLS3 signaling and with iron status in abnormal WNT1 signaling.

Association of plasma neutrophil gelatinase-associated lipocalin with parameters of CKD-MBD in maintenance hemodialysis patients

INTRODUCTION

Neutrophil gelatinase-associated lipocalin (NGAL) is not only a biomarker of kidney injury but also a bone-derived factor involved in metabolism. We aimed to explore relationships between plasma NGAL and chronic kidney disease-mineral bone disorder (CKD-MBD) parameters in maintenance hemodialysis (MHD) patients.

MATERIALS AND METHODS

First, a cross sectional observational study, including 105 MHD patients, was conducted to explore relationships between plasma NGAL levels and CKD-MBD parameters. Second, impact of parathyroidectomy and auto-transplantation (PTX + AT) on plasma NGAL was investigated in 12 MHD patients with severe secondary hyperparathyroidism (SHPT).

RESULTS

According to Spearman correlation analysis, plasma NGAL levels were positively correlated with female (r = 0.243, P = 0.012), vintage (r = 0.290, P = 0.003), Klotho (r = 0.234, P = 0.016), calcium(Ca) (r = 0.332, P = 0.001), alkaline phosphatase (ALP) (r = 0.401, P < 0.001) and intact parathyroid hormone (iPTH) (r = 0.256, P = 0.008); while inversely correlated with albumin(Alb) (r = - 0.201, P = 0.039). After adjusting for age, sex, vintage, Alb and all parameters of CKD-MBD(Ca, P, lg(ALP), lg(iPTH), Klotho and fibroblast growth factor 23(FGF23)), lg(NGAL) were positively correlated with Ca (r = 0.481, P < 0.001), P (r = 0.336, P = 0.037), lg(ALP) (r = 0.646, P < 0.001) in Partial correlation analysis; further multiple linear regression analysis showed same positive associations between lg(NGAL) and Ca (β = 0.330, P = 0.002), P (β = 0.218, P = 0.037), lg(ALP) (β = 0.671, P < 0.001). During the 4-7 days after PTX + AT, plasma NGAL decreased from 715.84 (578.73, 988.14) to 688.42 (660.00, 760.26) ng/mL (P = 0.071), Klotho increased from 496.45 (341.73, 848.30) to 1138.25 (593.87, 2009.27) pg/mL (P = 0.099).

CONCLUSION

Plasma NGAL levels were positively associated with ALP in MHD patients; and downtrends were shown after PTX + AT in patients with severe SHPT. These findings suggest that NGAL is a participant in CKD-MBD under MHD condition.

Lipocalin 2 serum levels correlate with age and bone turnover biomarkers in healthy subjects but not in postmenopausal osteoporotic women

Purpose

Lipocalin 2 (LCN2) is an adipokine involved in many physiological functions, including bone metabolism. We previously demonstrated its implication in mouse models of mechanical unloading-induced osteoporosis and in a cohort of bed rest volunteers. We therefore aimed at studying its involvement in postmenopausal osteoporosis.

Methods

We measured serum LCN2 and correlated its levels to Dickkopf WNT Signaling Pathway Inhibitor 1 (DKK1), Tartrate Resistant Acid Phosphatase 5B (TRAcP5B), sclerostin, urinary N-terminal telopeptide of type I collagen (NTX), serum C-terminal telopeptide of type I collagen (CTX), parathyroid hormone and vitamin K by ELISA performed in a cohort of younger (50–65 years) and older (66–90 years) osteoporotic women in comparison to healthy subjects. A cohort of male healthy and osteoarthritic patients was also included. Sobel mediation analysis was used to test indirect associations among age, LCN2 and DKK1 or NTX.

Results

LCN2 levels were unchanged in osteoporotic and in osteoarthritis patients when compared to healthy subjects and did not correlate with BMD. However, serum LCN2 correlated with age in healthy women (R = 0.44; P = 0.003) and men (R = 0.5; P = 0.001) and serum concentrations of DKK1 (R = 0.47; P = 0.003) and urinary NTX (R = 0.34; P = 0.04). Sobel mediation analysis showed that LCN2 mediates an indirect relationship between age and DKK1 (P = 0.02), but not with NTX, in healthy subjects.

Conclusions

Taken together, the results suggest a hitherto unknown association between LCN2, DKK1 and age in healthy individuals, but not in postmenopausal osteoporotic women.

Bone: Another potential target to treat, prevent and predict diabetes

Type 2 diabetes mellitus is now a worldwide health problem with increasing prevalence. Mounting efforts have been made to treat, prevent and predict this chronic disease. In recent years, increasing evidence from mice and clinical studies suggests that bone-derived molecules modulate glucose metabolism. This review aims to summarize our current understanding of the interplay between bone and glucose metabolism and to highlight potential new means of therapeutic intervention. The first molecule recognized as a link between bone and glucose metabolism is osteocalcin (OCN), which functions in its active form, that is, undercarboxylated OCN (ucOC). ucOC acts in promoting insulin expression and secretion, facilitating insulin sensitivity, and favouring glucose and fatty acid uptake and utilization. A second bone-derived molecule, lipocalin2, functions in suppressing appetite in mice through its action on the hypothalamus. Osteocytes, the most abundant cells in bone matrix, are suggested to act on the browning of white adipose tissue and energy expenditure through secretion of bone morphogenetic protein 7 and sclerostin. The involvement of bone resorption in glucose homeostasis has also been examined. However, there is evidence indicating the implication of the receptor activator of nuclear factor κ-B ligand, neuropeptide Y, and other known and unidentified bone-derived factors that function in glucose homeostasis. We summarize recent advances and the rationale for treating, preventing and predicting diabetes by skeleton intervention.