[Clinical study on growth impairment induced by oral glucocorticoids based on FGF23/Klotho homeostasis observations]. / 基于FGF23/Klothoç¨³æ€è§‚å¯Ÿå£æœç³–çš®è´¨æ¿€ç´ è‡´ç”Ÿé•¿éšœç¢çš„ä¸´åºŠç ”ç©¶.

OBJECTIVES: To observe the correlation between growth impairment induced by long-term oral glucocorticoids (GC) therapy and the ratio of FGF23/Klotho in children with primary nephrotic syndrome (PNS). METHODS: A prospective study was conducted on 56 children with GC-sensitive PNS who had discontinued GC therapy for more than 3 months and revisited the Department of Pediatrics of the First Affiliated Hospital of Henan University of Traditional Chinese Medicine between June 2022 and December 2022. After monitoring qualitative and quantitative urine protein levels upon admission, the children with proteinuria relapse were treated with GC (GC group; n=29), while those without relapse did not receive GC treatment (non-GC group; n=27). In addition, 29 healthy children aged 3 to prepuberty were selected as the control group. Height, bone age, growth rate, and the FGF23/Klotho ratio were compared among the groups. The correlations of the FGF23/Klotho ratio with height, bone age, and growth rate were analyzed. RESULTS: The FGF23/Klotho ratio in the GC group was significantly higher than that in the non-GC group after 1 month of GC therapy (P<0.05), and the height and bone age growth rates within 6 months were lower than those in the non-GC group (P<0.05). Correlation analysis showed significant negative correlations between the FGF23/Klotho ratio after 1 month of treatment and the growth rates of height and bone age within 6 months in children with PNS (r=-0.356 and -0.436, respectively; P<0.05). CONCLUSIONS: The disturbance in FGF23/Klotho homeostasis is one of the mechanisms underlying the growth impairment caused by long-term oral GC therapy.

Quercetin promotes cutaneous wound healing in mice through Wnt/ß-catenin signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Oxytropis falcata Bunge is a legume distributed in Northwest China, which is mainly used to treat knife wounds and inflammation. Quercetin is a bioactive flavonoid in O. falcata and becomes a promising healing compound for its angiogenic and anti-inflammatory activities. However, the healing mechanism of quercetin in cutaneous wound remains elusive. AIM OF THE STUDY: The purpose of this study was to evaluate the healing effect of quercetin on cutaneous wound models in vivo and in vitro, and to reveal the Wnt/ß-catenin pathway and Telomerase reverse transcriptase (TERT) involved mechanisms. MATERIALS AND METHODS: The effects of quercetin on the proliferation and migration of 4 kinds of skin cells were determined by CCK-8 and scratch assay. The wound-healing capacity of quercetin was evaluated in cutaneous wound model of C57BL/6 mice and the wound healing degree was observed by histological staining. The expressions of inflammatory factors, growth factors and the related proteins were detected via Western blot and RT-qPCR analyses. The molecular docking was adopted to evaluate the binding ability of quercetin and TERT. RESULTS: Quercetin could promote both proliferation and migration of fibroblasts, and enhance cutaneous wound healing capacity in mice. Compared to the control group, the wound healing rates in low (1.5 mg/mL), medium (3.0 mg/mL) and high dose (6.0 mg/mL) quercetin groups reached 94.67%, 97.31% and 98.42%, respectively. Moreover, the dermal structure in quercetin treated mice restored normal and the content of collagen fiber became abundant after administration. The levels of inflammatory factors, including tumor necrosis factor-α, interleukin-1ß and interleukin-6 were significantly reduced after quercetin administration. Among which, the level of IL-1ß in cutaneous wound was 0.007 times higher than that of the control group when treated with quercetin of high dose (6.0 mg/mL). The improved level of GSH in quercetin treated cutaneous wounds also indicated its higher antioxidant ability. In addition, dose-dependent positive associations were found in the expression levels of vascular endothelial growth factor, fibroblast growth factor and alpha smooth muscle actin in quercetin treated cutaneous wounds. The significantly upregulated protein levels of Wnt and ß-catenin further indicated the important role of quercetin in promoting wound healing in mice. According to molecular docking analysis, the formed hydrogen bonds between quercetin and Ala195, Gln308, Asn369 and Lys372 residues of TERT also indicated the indispensable role of TERT in improving wound healing capacity. CONCLUSION: Quercetin effectively promoted cutaneous wound healing by enhancing the proliferation and migration of fibroblasts, as well as inhibiting inflammation and increasing the expression of growth factors in mice via Wnt/ß-catenin signaling pathway and TERT. It provides a basis for a more thorough understanding of mechanism of action of O. falcata Bunge in the treatment of knife wounds and burns.

C-type natriuretic peptide stimulates osteoblastic proliferation and collagen-X expression but suppresses fibroblast growth factor-23 expression in vitro.

BACKGROUND: The effects of C-type natriuretic peptide (CNP) and fibroblast growth factor (FGF)-23 appear to oppose each other during the process of bone formation, whereas few studies exist on the interaction between CNP and FGF-23. The main objective of the present study is to probe whether CNP is directly responsible for the regulation of osteoblast or via antagonizing FGF-23. METHODS: Osteoblasts were cultured in the absence or presence of CNP (0, 10, and 100 pmol/L) for 24 h, 48 h and 72 h, respectively. RESULTS: The findings of the present study indicated that: (1) CNP significantly stimulated osteoblastic proliferation and collagen (Col)-X expression; (2) both osteoblastic (osteocalcin, procollagen type I carboxy-terminal propeptide, total alkaline phosphatase and bone-specific alkaline phosphatase) and osteolytic (tartrate-resistant acid phosphatase and cross-linked carboxyterminal telopeptide of type I collagen) bone turnover biomarkers were up-regulated by CNP in osteoblasts; (3) FGF-23 mRNA and protein were significantly down-regulated at 24 h by CNP in osteoblasts, but the expression of FGF receptor-1/Klotho had no significant change. CONCLUSIONS: CNP stimulates osteoblastic proliferation and Col-X expression via the down-regulation of FGF-23 possibly in vitro. However, the specific mechanisms of the interaction between CNP and FGF-23 in osteoblasts are still unclear according to our findings. A further study on osteoblasts cultured with CNP and FGF-23 inhibitor will be undertaken in our laboratory.

Effect of prolactin and estrogen on the serum level of 1,25-dihydroxy vitamin D and FGF23 in female rats.

INTRODUCTION: Estrogen and prolactin affect vitamin D metabolism. In conditions such as pregnancy and lactation, their interaction in regulating vitamin D metabolism and circulating FGF23 is not clearly defined. The aim of this study is to investigate this interaction in female rats. METHOD: This study was performed on 50 female adult rats, which were divided into five groups of Sham, ovariectomized rats (O), and three groups of ovariectomized rats were indicated with prolactin alone (OP), estradiol alone (OE), and a combination of estradiol and prolactin (OEP). Serum levels of 25(OH)D, 1,25(OH)2D3, FGF23, PTH, vitamin D-binding protein, calcium, and phosphorous were evaluated. RESULTS: Serum 1,25(OH)2D3 and PTH in OE were higher than the O group (P < 0.001 and P = 0.003, respectively). Serum FGF23 in the OE group was lower than the O group (P = 0.016). Serum 1,25(OH)2D3 increased in OP compared to the O group (P < 0.001) and OE group (P < 0.001). Serum FGF23 in OP was lower than the O group (P = 0.04). Furthermore, combining estradiol and prolactin showed no extra effect on increasing serum 1,25(OH)2D3. Serum 1,25(OH)2D3 was positively correlated with serum prolactin levels (r = 0.318, P = 0.017) in all five groups. CONCLUSION: It is suggested that estradiol could increase 1,25(OH)2D3 by elevating PTH and decreasing serum FGF23; however, prolactin was able to increase 1,25(OH)2D3 by lowering serum FGF23. Moreover, prolactin was shown to be more potent in augmenting serum 1,25(OH)2D3 than estrogen itself, which is important in maternal and fetal calcium supply during late pregnancy and lactation.

Neurofibromatosis type 1 associated with hypophosphatemic osteomalacia due to hypersecretion of fibroblast growth factor 23: a case report.

BACKGROUND: Neurofibromatosis type 1 is characterized by multiple café au lait spots and cutaneous and plexiform neurofibromas, and is one of the most common autosomal dominant hereditary disorders caused by mutations of the neurofibromatosis type 1 tumor suppressor gene. Osteomalacia in neurofibromatosis type 1 is very rare and is characterized by later onset in adulthood. In humans, fibroblast growth factor 23, which is a causative factor of tumor-induced osteomalacia, is not only a paracrine and autocrine factor, but is also a physiological regulator of phosphate balance in normal serum. CASE PRESENTATION: Our patient was a 65-year-old Japanese woman whose neurofibromas began to appear when she was in elementary school. At age 28, she was diagnosed as having neurofibromatosis type 1. A spinal compression fracture and multiple rib fractures were identified in 2012 and 2017, respectively. Her laboratory findings revealed hypophosphatemia due to renal phosphate wasting and a high serum level of fibroblast growth factor 23. Neurofibromas located on the surface of her right forearm and left upper arm, in which a slight abnormal accumulation of tracers was observed on 111indium-pentetreotide scintigraphy, were surgically removed, but there was no improvement in hypophosphatemia or serum fibroblast growth factor 23 after surgery. Therefore, we administered eldecalcitol, which also failed to produce improvement in abnormal data. Subsequent combination with dibasic calcium phosphate hydrate led to improvement in some of the abnormalities, including hypophosphatemia. Immunohistochemical staining using anti-human fibroblast growth factor 23 antibody revealed slightly positive results, however, only one out of three amplifications of the fibroblast growth factor 23 gene was observed by real-time polymerase chain reaction, and no clear fibroblast growth factor 23 gene expression in the resected neurofibromas could be confirmed. CONCLUSIONS: We here describe a first rare case of a 65-year-old woman with neurofibromatosis type 1 associated with hypophosphatemic osteomalacia in which a high serum fibroblast growth factor 23 level was confirmed.

Involvement of estrogen in phosphorus-induced nephrocalcinosis through fibroblast growth factor 23.

Excessive phosphorus intake adversely affects bone and mineral metabolism. Estrogen is one of the factors affecting fibroblast growth factor 23 (FGF23), a phosphorus-regulating hormone. However, the interaction between excess phosphorus and estrogen status has not been fully elucidated. This study investigated the involvement of estrogen in the effects of high phosphorus intake on bone metabolism and ectopic calcification in ovariectomized (OVX) rats. The interaction between high phosphorus diet and OVX was not observed in bone mineral density and aortic calcium. In contrast, high phosphorus intake markedly increased renal calcium concentration in sham rats, whereas the effect was attenuated in OVX rats, which was reversed by a selective estrogen-receptor modulator treatment. A strong positive correlation between renal calcium and serum FGF23 was observed. In addition, fibroblast growth factor receptor 1 (FGFR1: a predominant receptor of FGF23) inhibitor treatment partially decreased renal calcium concentrations in rats with high phosphorus intake. In conclusion, the effect of high phosphorus intake on bone metabolism and aortic calcification did not depend on the estrogen status; in contrast, high phosphorus intake synergistically induced nephrocalcinosis in the presence of estrogenic action on the bone. Furthermore, FGF23 was involved in the nephrocalcinosis induced by high phosphorus intake partially through FGFR1 signaling.

[Potential application of fibroblast growth factor 23-klotho axis in chronic kidney disease]. / Potentielle application de l'axe fibroblast growth factor 23-Klotho dans la maladie rénale chronique.

Membrane Alpha Klotho (α-klotho) is expressed in the kidney and functions as a co-receptor of FGF receptors (FGFRs) to activate specific fibroblast growth factor 23 (FGF23) signal pathway. FGF23 is produced in bones and participates in mineral homeostasis. The extracellular domain of transmembrane αklotho can be cleaved by proteases and released into the circulation as soluble α-klotho. Klotho deficiency is a pathogenic factor for chronic kidney disease progression and cardiovascular diseases. The FGF23 excess may also contribute to cardiovascular diseases where its pathogenic effect acts via the FGFR4 and independently of α-klotho. The decline in serum α-klotho followed by a rise in serum FGF23 at an early stage of chronic kidney disease can serve as a robust predictor for risk of cardiovascular diseases and mortality in both CKD patients and the general population. The first randomized trials suggest the possibility to reduce FGF23 excess in chronic kidney disease by controlling the phosphate serum using phosphate binders and reducing PTH levels with calcimimetic drug. New strategies emerge, including the administration of α-klotho recombinant and the use of epidrugs in order to correct the klotho deficiency. The FGR4 inhibitors are promising to limit the development of left ventricular hypertrophy linked to FGF23 excess. Finally, a better understanding of the molecular mechanisms of FGF23/α-klotho axis will allow us to find new strategic approaches and improve the CKD patient's management and their outcomes.

Theabrownin from Pu-erh tea attenuates hypercholesterolemia via modulation of gut microbiota and bile acid metabolism.

Pu-erh tea displays cholesterol-lowering properties, but the underlying mechanism has not been elucidated. Theabrownin is one of the most active and abundant pigments in Pu-erh tea. Here, we show that theabrownin alters the gut microbiota in mice and humans, predominantly suppressing microbes associated with bile-salt hydrolase (BSH) activity. Theabrownin increases the levels of ileal conjugated bile acids (BAs) which, in turn, inhibit the intestinal FXR-FGF15 signaling pathway, resulting in increased hepatic production and fecal excretion of BAs, reduced hepatic cholesterol, and decreased lipogenesis. The inhibition of intestinal FXR-FGF15 signaling is accompanied by increased gene expression of enzymes in the alternative BA synthetic pathway, production of hepatic chenodeoxycholic acid, activation of hepatic FXR, and hepatic lipolysis. Our results shed light into the mechanisms behind the cholesterol- and lipid-lowering effects of Pu-erh tea, and suggest that decreased intestinal BSH microbes and/or decreased FXR-FGF15 signaling may be potential anti-hypercholesterolemia and anti-hyperlipidemia therapies.

Short-Term Effects of Very-Low-Phosphate and Low-Phosphate Diets on Fibroblast Growth Factor 23 in Hemodialysis Patients: A Randomized Crossover Trial.

BACKGROUND AND OBJECTIVES: The short-term effects of low-phosphate diets on fibroblast growth factor 23 (FGF23) level and the optimal amount of dietary phosphate restriction in patients undergoing hemodialysis remain unknown. DESIGN SETTING, PARTICIPANTS, & MEASUREMENTS: This was a randomized, active-controlled trial with a crossover design that included 35 adults with ESKD undergoing thrice-weekly hemodialysis and with a serum phosphate level >5.5 mg/dl or between 3.5 and 5.5 mg/dl with regular phosphate binder use at a hemodialysis unit of tertiary teaching hospital in Taiwan. Subjects were randomized 1:1 to receive a very-low-phosphate diet, with a phosphate-to-protein ratio of 8 mg/g, or a low-phosphate diet, with a phosphate-to-protein ratio of 10 mg/g for 2 days, each with a 5-day washout during which subjects adhered to their usual diet. The primary outcome measure was mean difference in change-from-baseline intact FGF23 level between intervention groups. Secondary outcomes included difference in change-from-baseline serum phosphate, intact parathyroid hormone (PTH), and C-terminal FGF23 level between intervention groups. RESULTS: There was no significant difference in the mean change-from-baseline in intact FGF23 levels between the two study diets. The very-low-phosphate diet significantly lowered serum phosphate (mean difference, 0.6 mg/dl; 95% confidence interval [95% CI], 0.2 to 1.0; P=0.002). There were no significant differences in change-from-baseline intact PTH and C-terminal FGF23 levels between the two study diets. CONCLUSIONS: Over the 2-day period, the FGF23-lowering effect of the very-low-phosphate diet is similar to that of the low-phosphate diet. The very-low-phosphate diet has an additional phosphate-lowering effect compared with the low-phosphate diet.

Escalated Oxycodone Self-Administration Causes Differential Striatal mRNA Expression of FGFs and IEGs Following Abstinence-Associated Incubation of Oxycodone Craving.

Addiction to prescribed opioids including oxycodone has reached tragic levels. Herein, we investigated the relevance of fibroblast growth factors (FGFs) and immediate early genes (IEGs) to withdrawal-induced incubation of drug craving following escalated oxycodone self-administration (SA). Rats were trained to self-administer oxycodone for 4 weeks. Seeking tests were performed at various intervals during 1 month of drug withdrawal. Rats were euthanized 1 day after the last test and nucleus accumbens and dorsal striata were dissected for use in PCR analyses. Rats given long access (LgA, 9 h), but not short access (ShA, 3 h) to drug escalated their oxycodone intake and exhibited incubation of oxycodone seeking during withdrawal. These rats exhibited dose-dependent increases in fgf2 expression in the dorsal striatum. Fgfr2 expression was also significantly increased in the striatum in LgA, but not ShA groups. Similarly, striatal c-fos and junB mRNA levels showed greater increases in LgA rats. The observations that fgf mRNA levels were more altered in the dorsal striatum than in the NAc of LgA rats suggest that changes in striatal FGF expression may be more salient to incubation of oxycodone craving than alterations in the NAc. Targeting FGF signaling pathways might offer novel strategies against opioid addiction.

Effects of Nicotinamide and Lanthanum Carbonate on Serum Phosphate and Fibroblast Growth Factor-23 in CKD: The COMBINE Trial.

BACKGROUND: Higher serum phosphate and fibroblast growth factor-23 (FGF23) levels may be modifiable to prevent cardiovascular disease in CKD. Short-term studies have reported modest efficacy in phosphate and FGF23 reduction with intestinal phosphate binders in CKD. METHODS: To investigate effects of lanthanum carbonate (LC; a phosphate binder) and/or nicotinamide (NAM; an inhibitor of active intestinal phosphate transport) on serum phosphate and FGF23 in stage 3b/4 CKD, we conducted a randomized trial among individuals with eGFR 20-45 ml/min per 1.73 m2 to NAM (750 mg twice daily) plus LC (1000 mg thrice daily), NAM plus LC placebo, LC plus NAM placebo, or double placebo for 12 months. Dual primary end points were change from baseline in serum phosphate and intact FGF23 concentrations. RESULTS: Mean eGFR for the 205 participants was 32ml/min per 1.73 m2. At baseline, serum phosphate was 3.7 mg/dl and median FGF23 was 99 pg/ml (10th, 90th percentiles: 59, 205). Mean rates of change in phosphate increased slightly over 12 months in all groups and did not differ significantly across arms. Similarly, percent changes in FGF23 per 12 months increased for all arms except LC plus placebo, and did not differ significantly across arms. Gastrointestinal symptoms limited adherence. Adverse events rates were similar across arms. CONCLUSIONS: LC and/or NAM treatment did not significantly lower serum phosphate or FGF23 in stage 3b/4 CKD over 12 months. Although these agents appeared safe, intestinal symptoms limited adherence. Reducing phosphate and FGF23 in nondialysis CKD will require new approaches.

Clinical Pharmacokinetics and Pharmacodynamics of Nintedanib.

Nintedanib is an oral, small-molecule tyrosine kinase inhibitor approved for the treatment of idiopathic pulmonary fibrosis and patients with advanced non-small cell cancer of adenocarcinoma tumour histology. Nintedanib competitively binds to the kinase domains of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF). Studies in healthy volunteers and in patients with advanced cancer have shown that nintedanib has time-independent pharmacokinetic characteristics. Maximum plasma concentrations of nintedanib are reached approximately 2-4 h after oral administration and thereafter decline at least bi-exponentially. Over the investigated dose range of 50-450 mg once daily and 150-300 mg twice daily, nintedanib exposure increases are dose proportional. Nintedanib is metabolised via hydrolytic ester cleavage, resulting in the formation of the free acid moiety that is subsequently glucuronidated and excreted in the faeces. Less than 1% of drug-related radioactivity is eliminated in urine. The terminal elimination half-life of nintedanib is about 10-15 h. Accumulation after repeated twice-daily dosing is negligible. Sex and renal function have no influence on nintedanib pharmacokinetics, while effects of ethnicity, low body weight, older age and smoking are within the inter-patient variability range of nintedanib exposure and no dose adjustments are required. Administration of nintedanib in patients with moderate or severe hepatic impairment is not recommended, and patients with mild hepatic impairment should be monitored closely and the dose adjusted accordingly. Nintedanib has a low potential for drug-drug interactions, especially with drugs metabolised by cytochrome P450 enzymes. Concomitant treatment with potent inhibitors or inducers of the P-glycoprotein transporter can affect the pharmacokinetics of nintedanib. At an investigated dose of 200 mg twice daily, nintedanib does not have proarrhythmic potential.

Effects of vitamin D supplementation on FGF23: a randomized-controlled trial.

PURPOSE: Fibroblast growth factor-23 (FGF23) is critical for phosphate homeostasis. Considering the high prevalence of vitamin D deficiency and the association of FGF23 with adverse outcomes, we investigated effects of vitamin D3 supplementation on FGF23 concentrations. METHODS: This is a post-hoc analysis of the Styrian Vitamin D Hypertension trial, a single-center, double-blind, randomized, placebo-controlled trial, conducted from 2011 to 2014 at the Medical University of Graz, Austria. Two hundred subjects with 25(OH)D concentrations < 30 ng/mL and arterial hypertension were randomized to receive either 2800 IU of vitamin D3 daily or placebo over 8 weeks. Primary outcome was the between-group difference in FGF23 levels at study end while adjusting for baseline values. RESULTS: Overall, 181 participants (mean ± standard deviation age, 60.1 ± 11.3; 48% women) with available c-term FGF23 concentrations were considered for the present analysis. Mean treatment duration was 54 ± 10 days in the vitamin D3 group and 54 ± 9 days in the placebo group. At baseline, FGF23 was significantly correlated with serum phosphate (r = 0.135; p = 0.002). Vitamin D3 supplementation had no significant effect on FGF23 in the entire cohort (mean treatment effect 0.374 pmol/L; 95% confidence interval - 0.024 to 0.772 pmol/L; p = 0.065), but increased FGF23 concentrations in subgroups with baseline 25(OH)D concentrations below 20 ng/mL (n = 70; mean treatment effect 0.973 pmol/L; 95% confidence interval - 0.032 to 1.979 pmol/L; p = 0.019) and 16 ng/mL (n = 40; mean treatment effect 0.593 pmol/L; 95% confidence interval 0.076 to 1.109; p = 0.022). CONCLUSIONS: Vitamin D3 supplementation had no significant effect on FGF23 in the entire study cohort. We did, however, observe an increase of FGF23 concentrations in subgroups with low baseline 25(OH)D.

Effect of ferric citrate on serum phosphate and fibroblast growth factor 23 among patients with nondialysis-dependent chronic kidney disease: path analyses.

BACKGROUND: Among patients with nondialysis-dependent chronic kidney disease (NDD-CKD) and iron-deficiency anemia (IDA), ferric citrate increases hemoglobin and iron parameters and reduces serum phosphate and fibroblast growth factor 23 (FGF23), a key phosphate-regulating hormone. We conducted post hoc analyses of a phase 3 trial to explore associations between iron replacement, serum phosphate changes and FGF23 regulation. METHODS: We employed multivariable regression and longitudinal mixed-effects models to identify and confirm, respectively, whether baseline demographic and laboratory variables were associated with ferric citrate-induced changes in serum phosphate or FGF23 concentrations. We employed path analyses to determine whether changes in FGF23 concentrations were mediated via changes in serum phosphate and/or transferrin saturation (TSAT). RESULTS: We analyzed a total of 117 and 115 ferric citrate-treated and placebo-treated patients, respectively. At 16 weeks, ferric citrate significantly reduced serum phosphate versus placebo (P = 0.006) only among patients with elevated baseline serum phosphate (≥4.5 mg/dL) and did not reduce serum phosphate among patients with baseline serum phosphate within the population reference range. Ferric citrate reduced intact FGF23 and C-terminal FGF23 partially via changes in TSAT (for C-terminal FGF23) and serum phosphate (for intact FGF23) and partially via unknown/unmeasured mechanisms. CONCLUSIONS: Ferric citrate reduced serum FGF23 concentrations (partially via effects on serum phosphate and iron balance) and did not reduce serum phosphate among patients with baseline serum phosphate concentrations within the population reference range.

Identification of a crucial amino acid responsible for the loss of specifying FGFR1-KLB affinity of the iodinated FGF21.

Previous studies suggest that specific binding to the complex consisting of fibroblast growth factor receptor-1 (FGFR1) and the coreceptor beta-Klotho (KLB) is the premise for human FGF19 and FGF21 activating the downstream signaling cascades, and regulating the metabolic homeostasis. However, it was found that human FGF21 loses its ability to bind to FGFR1-KLB after iodination with Na125 I and chloramine T, whereas human FGF19 retained its affinity for FGFR1-KLB even after iodination. The molecular mechanisms underlying these differences remained elusive. In this study, we first demonstrated that an intramolecular disulfide bond was formed between cysteine-102 and cysteine-121 in FGF21, implying that the oxidation of the cysteine to cysteic acid, which may interfere with the active conformation of FGF21, did not occur during the iodination procedures, and thus ruled out the possibility of the two conserved cysteine residues mediating the loss of FGF21 binding affinity to FGFR1-KLB upon iodination. Site-directed mutagenesis and molecular modeling were further applied to determine the residue(s) responsible for the loss of FGFR1-KLB affinity. The results showed that mutation of a single tyrosine-207, but not the other five tyrosine residues in FGF21, to a phenylalanine retained the FGFR1-KLB affinity of FGF21 even after iodination, whereas replacing the corresponding phenylalanine residue with tyrosine in FGF19 did not alter its binding affinity to FGFR1-KLB, but decreased the receptor binding ability of the iodinated protein, suggesting that tyrosine-207 is the crucial amino acid responsible for the loss of specifying FGFR1-KLB affinity of the iodinated FGF21.

The suppressive effect of soluble Klotho on fibroblastic growth factor 23 synthesis in UMR-106 osteoblast-like cells.

Fibroblastic growth factor 23 (FGF23) is a hormone secreted primarily by bone. FGF23 is elevated in the serum of chronic kidney disease (CKD) patients, but the exact mechanism is not well known. Klotho is identified as an aging suppressor, which is mainly expressed in the kidney, and the level of soluble Klotho is negatively associated with FGF23 in CKD. The aim of this study was to investigate the effect and possible mechanism of Klotho on FGF23 synthesis in osteoblast-like UMR-106 cells. UMR-106 cells were divided into five groups: (i) control group; (ii) ß-glycerophosphate (ß-GP) group; (iii) ß-GP + Klotho group; (iv) ß-GP+ lithium chloride (LiCl, a Wnt/ß-catenin pathway agonist) group; and (v) ß-GP + Klotho + LiCl group. Subsequently, UMR-106 cells were cultured for 72 h, and the expression of FGF23, P-glycogen synthase kinase-3ß (P-GSK-3ß), and glycogen synthase kinase-3ß(GSK-3ß) were measured with Western blot analysis. The mRNA levels of FGF23 and the Wnt/ß-catenin pathway target gene c-myc were determined with RT-qPCR. The results showed that ß-GP induced increased expression of FGF23 mRNA and protein. Compared with the ß-GP group, expression of FGF23 mRNA and protein expression were downregulated in the ß-GP + Klotho group. In addition, ß-GP induced increased expression of P-GSK-3ß/GSK-3ß and c-myc, which were all downregulated in the ß-GP + Klotho group. Moreover, the expression of FGF23, P-GSK-3ß/GSK-3ß, and c-myc mRNA were upregulated when treated with LiCl. These results demonstrate that soluble Klotho suppresses FGF23 synthesis in osteoblast-like UMR-106 cells. The mechanism of this suppression may be partially through the inhibition of the Wnt/ß-catenin pathway.

Canagliflozin triggers the FGF23/1,25-dihydroxyvitamin D/PTH axis in healthy volunteers in a randomized crossover study.

BACKGROUND: Sodium glucose cotransporter-2 (SGLT2) inhibitors are the most recently approved class of drugs for type 2 diabetes and provide both glycemic efficacy and cardiovascular risk reduction. A number of safety issues have been identified, including treatment-emergent bone fractures. To understand the overall clinical profile, these safety issues must be balanced against an attractive efficacy profile. Our study was designed to investigate pathophysiological mechanisms mediating treatment-emergent adverse effects on bone health. METHODS: We conducted a single-blind randomized crossover study in hospitalized healthy adults (n = 25) receiving either canagliflozin (300 mg/d) or placebo for 5 days. The primary end-point was the drug-induced change in AUC for plasma intact fibroblast growth factor 23 (FGF23) immunoactivity between 24 and 72 hours. RESULTS: Canagliflozin administration increased placebo-subtracted mean levels of serum phosphorus (+16%), plasma FGF23 (+20%), and plasma parathyroid hormone (PTH) (+25%), while decreasing the level of 1,25-dihydroxyvitamin D (-10%). There was substantial interindividual variation in the magnitude of each of these pharmacodynamic responses. The increase in plasma FGF23 was correlated with the increase in serum phosphorus, and the decrease in plasma 1,25-dihydroxyvitamin D was correlated with the increase in plasma FGF23. CONCLUSIONS: Canagliflozin induced a prompt increase in serum phosphorus, which triggers downstream changes in FGF23, 1,25-dihydroxyvitamin D, and PTH, with potential to exert adverse effects on bone health. These pharmacodynamic data provide a foundation for future research to elucidate pathophysiological mechanisms of adverse effects on bone health, with the objective of devising therapeutic strategies to mitigate the drug-associated fracture risk. TRIAL REGISTRATION: ClinicalTrial.gov (NCT02404870). FUNDING: Supported by the Intramural Program of NIDDK.

FGF21 Is Associated with Metabolic Effects and Treatment Response in Depressed Bipolar II Disorder Patients Treated with Valproate.

Background: Patients with bipolar disorder are at high risk of metabolic disturbance after mood stabilizer treatment. However, the mediators linking the two conditions remain unknown. In this study, we investigated whether fibroblast growth factor-21 (FGF21) was associated with metabolic effects and treatment response in depressed bipolar disorder patients. Methods: We recruited 78 community-dwelling controls and 137 bipolar disorder patients; the latter were interviewed using the Chinese Version of the Modified Schedule of Affective Disorder and Schizophrenia-Life Time. Upon study entry, the bipolar disorder patients were all in a major depressive status, with 17-item Hamilton Depression Rating Scale (HDRS) scores >15. They received valproate (500-1000 mg daily) for 12 weeks, and fluoxetine 20 mg daily was permitted to treat depressive symptoms. Fasting plasma level of FGF21, lipid profiles, and body weight were collected at baseline and after 12 weeks of treatment. Results: At baseline, the demographic characteristics, FGF21 level, and metabolic indices did not differ significantly between the controls and bipolar disorder patients. After 12 weeks of treatment, the FGF21 level (167.7±122.0 to 207.1±162.3 pg/mL, P=.001), body weight and waist circumference had increased significantly (P<.001 and P=.028, respectively). Moreover, the change in FGF21 level was significantly correlated with the changes in HDRS score (r=0.393, P=.002), total cholesterol (r=-0.344, P=.008), and low-density lipoprotein (r=-0.347, P=.007). Conclusions: The central and peripheral mediating effects of FGF21 on bipolar disorder depression treatment might be opposite. High peripheral FGF21 levels might link regulation of metabolic effect and resistance to treatment in bipolar disorder.

Oral Versus Intravenous Iron Supplementation for the Treatment of Iron Deficiency Anemia in Patients on Maintenance Hemodialysis-Effect on Fibroblast Growth Factor-23 Metabolism.

OBJECTIVE: Iron administration affects serum levels of intact (I-) fibroblast growth factor-23 (FGF23) and its cleavage product C-terminal (C-) FGF23 in iron-deficient patients on maintenance hemodialysis (MHD). The objective of this study was to compare the effect of oral or intravenous iron administration on serum levels of I-FGF23 and C-FGF23 in iron-deficient patients on MHD. DESIGN AND METHODS: A prospective randomized study. SUBJECTS: Participants on MHD with severe iron deficiency (n = 61). INTERVENTION: Participants were randomized to receive oral iron (50 mg of sodium ferrous citrate daily; oral group, n = 29) or intravenous iron (40 mg of saccharated ferric oxide weekly; IV group, n = 32). MAIN OUTCOME MEASURE: Changes in I-FGF23 and C-FGF23 after 10 weeks of treatment. RESULTS: Iron supplementation significantly increased hemoglobin, mean corpuscular volume, ferritin, and transferrin saturation rate, and decreased erythropoiesis-stimulating agent dose and erythropoiesis-stimulating agent resistance index value. Serum phosphate, calcium, and intact parathyroid hormone levels did not change significantly during the study. I-FGF23 levels increased significantly in the IV group and did not change in the oral group, whereas C-FGF23 levels were significantly reduced in both groups. Serum interleukin-6 and tumor necrosis factor-α levels were increased in both groups. Multiple regression analysis indicated the relationship between iron or erythropoiesis and FGF23 metabolism. CONCLUSION: Iron administration to patients on MHD with severe iron deficiency decreased C-FGF23 levels, whereas intravenous iron increased I-FGF23 levels though oral iron did not. If the target of chronic kidney disease-mineral and bone disorder therapy is reducing I-FGF23 levels, we suggest the use of oral iron.

Parsing the Potential Neuroendocrine Actions of FGF21 in Primates.

Fibroblast growth factor (FGF) 21, a unique, largely liver-derived endocrine member of the FGF superfamily, is often thought of as a fasting factor owing to its induction in rodents during starvation. However, FGF21 is not increased by fasting for periods of <7 days in humans; instead, it rises sharply after acute alcohol and sugar intake and also after several days of overfeeding, suggesting another role in states of positive energy balance. Recent studies suggest that in the postingestive state, FGF21 may regulate energy intake and discourage consumption of alcohol and sugars, most likely through effector circuits in the central nervous system. FGF21 also increases fat oxidation in the liver, improves markers of insulin sensitivity, and stimulates adiponectin production. Thus, in primates, FGF21 may defend against hepatic nutrient overload by promoting adaptations that reduce ectopic lipid storage, including inhibiting sugar and alcohol appetite and promoting lipid sequestration in adipose tissue.