Elevated fibroblast growth factor 23 in women with malignant ovarian tumors

A Rare Association Between Osteomalacia, Phosphaturic Mesenchymal Tumor, and Ovarian Cancer: A Case Report and Literature Review

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia, bone mineralization disorders with increased risk of fragility fractures, muscle pain, and progressive weakness. TIO has been associated with increased production of the phosphaturic hormone Fibroblast Growth Factor 23 (FGF23) usually by mesenchymal tumors of soft tissue or bone (Phosphaturic Mesenchymal Tumors-PMTs). In rare cases TIO may be observed in association with other malignancies. We report the case of a 66-year-old woman with an occasional diagnosis of both a PMT and an ovarian cancer during the evaluation of TIO. We also systematically review the literature to discover possible correlations between osteomalacia, FGF23 production, and ovarian cancer. Four studies were eligible for the analysis. Two case reports described an association between TIO development and ovarian cancer, whereas the two case-control studies hypothesized a possible correlation between FGF/FGF receptor axis and cancer development. Although it does not provide conclusive evidence regarding the association between TIO and ovarian cancer, this case report highlights the possibility that in the diagnostic workup of suspected TIO, both FGF23-secreting tumors distinct from PMT and tumors unrelated to the clinical presentation of TIO could be identified. This information is important for guiding successful tumor staging and determining the necessity for surgical intervention and/or eventual adjuvant therapy.

FGF23 Expression Is a Promising Immunohistochemical Diagnostic Marker for Undifferentiated Pleomorphic Sarcoma of Bone (UPSb)

Background: Undifferentiated pleomorphic sarcoma of bone (UPSb) is a rare primary bone sarcoma that lacks a specific line of differentiation. Distinguishing between UPSb and other malignant bone sarcomas, including dedifferentiated chondrosarcoma and osteosarcoma, is challenging due to their overlapping features. We have previously identified that UPSb tumours have elevated mRNA levels of Fibroblast Growth Factor 23 (FGF23) transcripts compared to other sarcomas including osteosarcoma. In the present study, we evaluated the specificity and practicality of FGF23 immunoreactivity as a specific diagnostic tool to differentiate UPSb tumours from osteosarcomas and dedifferentiated chondrosarcomas. Methods: A total of 10 UPSb, 10 osteosarcoma, and 10 dedifferentiated chondrosarcoma cases (all high-grade), were retrieved and immunohistochemistry for FGF23 was performed. Results: FGF23 protein was expressed at high levels in 80-90% of undifferentiated pleomorphic sarcoma of the bone cases, whereas it was expressed at significantly lower levels in dedifferentiated chondrosarcoma and osteosarcoma cases. A semiquantitative analysis, considering the intensity of immunoreactivity, confirmed significantly elevated FGF23 expression levels in UPSb tissues compared to those observed in osteosarcoma and dedifferentiated chondrosarcoma tissues. Conclusions: The results we present here suggest that FGF23 immunohistochemistry may be a useful tool to aid in differentiating UPSb from morphologically similar malignant bone sarcomas, especially in situations where sampling is restricted and there is limited clinical information available.

Fibroblast Growth Factor 23 is a Potential Prognostic Biomarker in Uterine Sarcoma

BACKGROUND

Uterine sarcoma (US) is a highly malignant cancer with poor prognosis and high mortality in women. In this study, we evaluated the expression of human fibroblast growth factor 23 (FGF23) in different US subtypes and the relationship between survival and clinicopathological characteristics.

METHODS

We conducted a comparative analysis of FGF23 gene expression in different pathological types of US. Utilizing a cohort from The Cancer Genome Atlas of 57 patients, a 50-patient microarray dataset (GSE119043) from the Gene Expression Omnibus and a Suining cohort of 44 patients, we analyzed gene expression profiles and corresponding clinicopathological information. Immunohistochemistry was used to examine the expression level of FGF23 in four US subtypes. Survival analysis was used to assess the relationship between FGF23 expression and prognosis in US patients.

RESULTS

Compared with uterine normal smooth muscle and uterine leiomyoma, FGF23 expression was significantly upregulated in US and was differentially expressed in four US subtypes. Uterine carcinosarcoma exhibited the highest expression of FGF23 among the subtypes. Survival analysis revealed no correlation between FGF23 expression and either overall survival or progression-free survival in US (P > 0.05). Similar results were obtained from the validation cohorts. Univariate and multivariate analyses showed no significant correlation between FGF23 expression and the US prognosis. Tumor stage, CA125, and tumor recurrence were independent prognostic factors for survival of US patients.

CONCLUSION

FGF23 was highly expressed in US and was promising as a novel potential biomarker for the diagnosis and prognosis of US.

An artificial intelligence prediction model based on extracellular matrix proteins for the prognostic prediction and immunotherapeutic evaluation of ovarian serous adenocarcinoma

Background: Ovarian Serous Adenocarcinoma is a malignant tumor originating from epithelial cells and one of the most common causes of death from gynecological cancers. The objective of this study was to develop a prediction model based on extracellular matrix proteins, using artificial intelligence techniques. The model aimed to aid healthcare professionals to predict the overall survival of patients with ovarian cancer (OC) and determine the efficacy of immunotherapy. Methods: The Cancer Genome Atlas Ovarian Cancer (TCGA-OV) data collection was used as the study dataset, whereas the TCGA-Pancancer dataset was used for validation. The prognostic importance of 1068 known extracellular matrix proteins for OC were determined by the Random Forest algorithm and the Lasso algorithm establishing the ECM risk score. Based on the gene expression data, the differences in mRNA abundance, tumour mutation burden (TMB) and tumour microenvironment (TME) between the high- and low-risk groups were assessed. Results: Combining multiple artificial intelligence algorithms we were able to identify 15 key extracellular matrix genes, namely, AMBN, CXCL11, PI3, CSPG5, TGFBI, TLL1, HMCN2, ESM1, IL12A, MMP17, CLEC5A, FREM2, ANGPTL4, PRSS1, FGF23, and confirm the validity of this ECM risk score for overall survival prediction. Several other parameters were identified as independent prognostic factors for OC by multivariate COX analysis. The analysis showed that thyroglobulin (TG) targeted immunotherapy was more effective in the high ECM risk score group, while the low ECM risk score group was more sensitive to the RYR2 gene-related immunotherapy. Additionally, the patients with low ECM risk scores had higher immune checkpoint gene expression and immunophenoscore levels and responded better to immunotherapy. Conclusion: The ECM risk score is an accurate tool to assess the patient's sensitivity to immunotherapy and forecast OC prognosis.

Neo-vascularization-based therapeutic perspectives in advanced ovarian cancer

The process of angiogenesis is well described for its potential role in the development of normal ovaries, and physiological functions as well as in the initiation, progression, and metastasis of ovarian cancer (OC). In advanced stages of OC, cancer cells spread outside the ovary to the pelvic, abdomen, lung, or multiple secondary sites. This seriously limits the efficacy of therapeutic options contributing to fatal clinical outcomes. Notably, a variety of angiogenic effectors are produced by the tumor cells to initiate angiogenic processes leading to the development of new blood vessels, which provide essential resources for tumor survival, dissemination, and dormant micro-metastasis of tumor cells. Multiple proangiogenic effectors and their signaling axis have been discovered and functionally characterized for potential clinical utility in OC. In this review, we have provided the current updates on classical and emerging proangiogenic effectors, their signaling axis, and the immune microenvironment contributing to the pathogenesis of OC. Moreover, we have comprehensively reviewed and discussed the significance of the preclinical strategies, drug repurposing, and clinical trials targeting the angiogenic processes that hold promising perspectives for the better management of patients with OC.

The regulation of FGF23 under physiological and pathophysiological conditions

Fibroblast growth factor 23 (FGF23) is an important bone hormone that regulates phosphate homeostasis in the kidney along with active vitamin D (1,25(OH)₂D₃) and parathyroid hormone (PTH). Endocrine effects of FGF23 depend, at least in part, on αKlotho functioning as a co-receptor whereas further paracrine effects in other tissues are αKlotho-independent. Regulation of FGF23 production is complex under both, physiological and pathophysiological conditions. Physiological regulators of FGF23 include, but are not limited to, 1,25(OH)₂D₃, PTH, dietary phosphorus intake, and further intracellular and extracellular factors, kinases, cytokines, and hormones. Moreover, several acute and chronic diseases including chronic kidney disease (CKD) or further cardiovascular disorders are characterized by early rises in the plasma FGF23 level pointing to further mechanisms effective in the regulation of FGF23 under pathophysiological conditions. Therefore, FGF23 also serves as a prognostic marker in several diseases. Our review aims to comprehensively summarize the regulation of FGF23 in health and disease.

Role of Fibroblast Growth Factor 23 (FGF23) and αKlotho in Cancer

Together with fibroblast growth factors (FGFs) 19 and 21, FGF23 is an endocrine member of the family of FGFs. Mainly secreted by bone cells, FGF23 acts as a hormone on the kidney, stimulating phosphate excretion and suppressing formation of 1,25(OH)₂D₃, active vitamin D. These effects are dependent on transmembrane protein αKlotho, which enhances the binding affinity of FGF23 for FGF receptors (FGFR). Locally produced FGF23 in other tissues including liver or heart exerts further paracrine effects without involvement of αKlotho. Soluble Klotho (sKL) is an endocrine factor that is cleaved off of transmembrane Klotho or generated by alternative splicing and regulates membrane channels, transporters, and intracellular signaling including insulin growth factor 1 (IGF-1) and Wnt pathways, signaling cascades highly relevant for tumor progression. In mice, lack of FGF23 or αKlotho results in derangement of phosphate metabolism and a syndrome of rapid aging with abnormalities affecting most organs and a very short life span. Conversely, overexpression of anti-aging factor αKlotho results in a profound elongation of life span. Accumulating evidence suggests a major role of αKlotho as a tumor suppressor, at least in part by inhibiting IGF-1 and Wnt/β-catenin signaling. Hence, in many malignancies, higher αKlotho expression or activity is associated with a more favorable outcome. Moreover, also FGF23 and phosphate have been revealed to be factors relevant in cancer. FGF23 is particularly significant for those forms of cancer primarily affecting bone (e.g., multiple myeloma) or characterized by bone metastasis. This review summarizes the current knowledge of the significance of FGF23 and αKlotho for tumor cell signaling, biology, and clinically relevant parameters in different forms of cancer.

Exploring the prognostic significance of preoperative high normocalcemia in epithelial ovarian carcinoma

PURPOSE

We investigated the association between serum ionized calcium and prognosis of EOC and determined the optimal cutoff value of ionized calcium level to predict the prognosis of EOC.

METHODS

The medical records of patients who were newly diagnosed with EOC from 2001 to 2016 were retrieved. Preoperative ionized calcium test was performed within 2 weeks before surgery, and the cutoff of high normocalcemia was defined based on the receiver operating characteristic (ROC) curve for recurrence. Cox proportional hazards regression models were used to identify independent prognostic factors for progression-free survival (PFS).

RESULTS

From 2001 to 2016, 83 patients diagnosed with EOC were identified at a single institution. The optimal cutoff value was set to 4.7 mg/dL (high normocalcemia vs. control group) by plotting the ROC curve for recurrence. Stages III/IV were more frequent in high normocalcemia, with borderline significance (72.9% vs. 52.2%, p = 0.053). Recurrence (67.6% vs. 43.5%, p = 0.029) and death (46.0% vs. 15.2%, p < 0.01) were significantly more frequent in the high normocalcemia group. In multivariate analysis, high normocalcemia (HR 1.9, 95% CI 1.03-3.61, p = 0.04), age (HR 1.04, 95% CI 1.01-1.08, p = 0.02), stage (HR 3.67, 95% CI 1.13-11.92, p = 0.03), residual tumor > 1 cm (HR 3.79, 95% CI 1.61-8.95, p < 0.01), and lymph node metastasis (HR 2.46, 95% CI 1.27-4.78, p < 0.01) were independent risk factors for recurrence.

CONCLUSION

This study showed positive association between relatively high level of ionized calcium level and recurrence risk of EOC. High normocalcemia showed the potential as a biomarker for prognosis of EOC.

Cathepsin D in the Tumor Microenvironment of Breast and Ovarian Cancers

Cancer remains a major and leading health problem worldwide. Lack of early diagnosis, chemoresistance, and recurrence of cancer means vast research and development are required in this area. The complexity of the tumor microenvironment in the biological milieu poses greater challenges in having safer, selective, and targeted therapies. Existing strategies such as chemotherapy, radiotherapy, and antiangiogenic therapies moderately improve progression-free survival; however, they come with side effects that reduce quality of life. Thus, targeting potential candidates in the microenvironment, such as extracellular cathepsin D (CathD) which has been known to play major pro-tumorigenic roles in breast and ovarian cancers, could be a breakthrough in cancer treatment, specially using novel treatment modalities such as immunotherapy and nanotechnology-based therapy. This chapter discusses CathD as a pro-cancerous, more specifically a proangiogenic factor, that acts bi-functionally in the tumor microenvironment, and possible ways of targeting the protein therapeutically.

Nuclear action of FGF members in endocrine-related tissues and cancer: Interplay with steroid receptor pathways

Dysregulation of the fibroblast growth factors/fibroblast growth factor receptor (FGF/FGFR) pathway has been implicated in a wide range of human disorders and several members have been localized in the nuclear compartment. Hormone-activated steroid receptors or ligand independent activated receptors form nuclear complexes that activate gene transcription. This review aims to highlight the interplay between the steroid receptor and the FGF/FGFR pathways and focuses on the current knowledge on nuclear action of FGF members in endocrine-related tissues and cancer. The nuclear trafficking and targets of FGF/FGFR members and the available evidence on the interplay with steroid hormones and receptors is described. Finally, the data on aberrant FGF/FGFR signaling is summarized and the nuclear action of FGF members on endocrine resistant breast cancer is highlighted. Identifying the mechanisms underlying FGF-induced endocrine resistance will be important to understand how to efficiently target endocrine-related diseases and even enhance or restore endocrine sensitivity in hormone receptor positive tumors.

Advances in anti-angiogenic agents for ovarian cancer treatment: The role of trebananib (AMG 386)

Ovarian cancer is a multifaceted and genomically complex disease and has emerged as leading cause of death among gynecological malignancies. Gold-standard treatment consisted of cytoreductive surgery and paclitaxel-carboplatin chemotherapy. Recently, promising results of randomized trials have definitively confirmed the importance of angiogenesis in oncogenesis and ovarian cancer behavior, by showing a significant prolongation of progression-free survival with the addiction of an angiogenesis inhibitor to standard treatment in the first and second line setting. Research over the years has sequentially provided a rapidly broadening signaling landscape and many drugs targeting different signaling pathways of angiogenesis have been developed and investigated. Recently accumulating scientific evidence has started to shed light on the efficacy of AMG 386, a new peptibody reported to neutralize the interaction between angiopoietins (Ang1/2) and their Tie2 receptors, thus representing a promising alternative, both in terms of efficacy and toxicity profile and is considerably under investigation. The aim of this review is to summarize the recent researches and clinical progresses of AMG 386 as a novel target agent in ovarian cancer.

A novel chromogenic in situ hybridization assay for FGF23 mRNA in phosphaturic mesenchymal tumors

Phosphaturic mesenchymal tumors of the mixed connective tissue type (PMT) are very rare tumors of bone and soft tissues. Most patients with PMT have long-standing osteomalacia secondary to production of fibroblast growth factor 23 (FGF23), a hormone that inhibits phosphate reuptake within the renal proximal tubule. Previously, we have reported the detection of FGF23 mRNA in PMT by reverse transcription polymerase chain reaction (PCR); however, the low specificity and risk for nontumoral tissue contamination inherent in PCR-based methodology limit its clinical utility. We evaluated RNAscope as a semiquantitative method of in situ FGF23 mRNA detection in the diagnosis of PMT. Twenty-five PMTs (median 52 y, range 5 to 73 y) occurred in patients with tumor-induced osteomalacia (TIO), manifesting as masses (mean 3.9 cm, range 1.4 to 12 cm) in various bones and soft tissues. FGF23 mRNA was positive in 96% (22/23) informative cases of PMT: 16 cases scored 3+; 5 scored as 2+; 1 scored as 1+. Among these cases, FGF23 mRNA was detected in 3 malignant PMTs along with their metastases. Forty control cases included aneurysmal bone cyst (N=4), chondromyxoid fibroma (N=8), high-grade osteosarcomas (N=8), and (nonfamilial) tumoral calcinosis, as well as miscellaneous cartilage-forming tumors or osteoid-forming tumors and soft tissue tumors. All control cases were negative for FGF23 mRNA in the lesional cells. One aneurysmal bone cyst had rare FGF23 mRNA-expressing osteocytes clustered around remodeled bone. One ovarian serous carcinoma in a patient with disseminated disease, elevated serum FGF23, and TIO was negative for FGF23 mRNA in the neoplastic cells. We conclude that RNAscope is a highly sensitive and specific, semiquantitative in situ hybridization method of FGF23 mRNA detection applicable to formalin-fixed, paraffin-embedded tissues. Detection of FGF23 expression is a valuable diagnostic adjunct, especially in patients with occult TIO. Compared with reverse transcription PCR, this method preserves tissue morphology and reduces "false positives" related to detection of endogenous FGF23 mRNA expression by osteocytes.

Ovarian cancer-related hypophosphatemic osteomalacia--a case report

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused primarily by benign mesenchymal tumors. It has been associated with malignancies in rare cases. High serum levels of fibroblast growth factor (FGF) 23 reported in a group of patients with ovarian cancer had normal serum phosphate levels. There had been no ovarian cancer-related hypophosphatemic osteomalacia in a search of the literature.

OBJECTIVE

We investigated a 57-year-old woman with progressive low back pain.

DESIGN AND INTERVENTION

Clinical, biochemical, and radiological assessments were performed. The patient's serum phosphate and FGF23 levels were evaluated at baseline and after treatment for ovarian cancer.

RESULTS

The patient presented with progressive low back pain and weight loss during the previous 6 months. Imaging studies revealed low bone mineral density and multiple suspicious spinal metastatic lesions. Laboratory examination showed hypophosphatemia, hyperphosphaturia, normocalcemia, an elevated serum alkaline phosphatase level, and an elevated serum FGF23 level. Because TIO was suspected, a tumor survey was performed, and ovarian carcinoma with multiple metastasis was detected. After surgery and chemotherapy treatments for ovarian cancer, the serum phosphate and FGF23 levels returned to normal, and the low back pain improved.

CONCLUSIONS

To our knowledge, this is the first case of ovarian cancer-related hypophosphatemic osteomalacia reported in the literature. TIO should be considered in patients with ovarian cancer presenting with weakness, bone pain, and fractures. Investigation of TIO is appropriate when these patients present hypophosphatemia.

FGF23: mediator of poor prognosis in a sizeable subgroup of patients with castration-resistant prostate cancer presenting with severe hypophosphatemia?

Castration-resistant prostate cancer (CRPC) is an advanced and incurable stage of the second most frequently diagnosed malignancy in men globally. Current treatment options improve survival modestly but eventually fail due to intrinsic or acquired therapeutic resistance. A hypothesis is presented wherein circulating levels of fibroblast growth factor 23 (FGF23), an endocrine member of the fibroblast growth factor family with phosphaturic properties, are proposed as a prognostic and predictive marker to identify CRPC patients with poor prognosis that are amenable to FGF23 antibody therapy (FGF23i) or treatment with fibroblast growth factor receptor inhibitors (FGFRi). With respect to the latter, FGF23 may also serve as a pharmacodynamic marker enabling individualized FGFRi dosing. We recently discovered that the development of severe and sustained hypophosphatemia in CRPC patients undergoing zoledronic acid therapy for bone metastases was associated with markedly worse prognosis compared to patients without or with only mild and transient hypophosphatemia. Severe hypophosphatemia is a typical manifestation of tumor-induced hypophosphatemic osteomalacia (TIO), a paraneoplastic condition mediated by FGF23 overexpression in most instances. While the postulated tumor-promoting role of FGF23 in CRPC or other malignancies has not yet been studied, several lines of evidence suggest that FGF23 may mediate both severe hypophosphatemia (via its endocrine properties) and aggressive CRPC behavior (via autocrine and paracrine activities): (i) FGF23 and the necessary signalling machinery (i.e. members of the fibroblast growth factor receptor [FGFR] family and the essential co-receptor α-KLOTHO [KL]) are highly expressed in a sizeable subgroup of CRPC patients; (ii) FGF/FGFR signalling plays important roles in prostate cancer; (iii) FGF23 can induce its own expression via a positive autocrine feedback loop involving FGFR1; and (iv) this positive feedback loop may be triggered by bone-targeted therapies frequently used for the treatment of CRPC-associated bone metastases. While there is a lack of personalized treatment strategies in the management of CRPC to date, FGF23 targeted therapy has the potential to fill this unmet clinical need in the not-so-distant future. In fact, FGFRi are currently in advanced clinical testing for a number of malignancies such as kidney and lung cancer, but there is a lack of conclusive data on FGFRi therapy in patients selected for FGF/FGFR pathway activation.

Expression of fibroblast growth factor 23 by canine soft tissue sarcomas

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of humans. Some mesenchymal tumours (often resembling haemangiopericytomas) express molecules that normally regulate phosphorus metabolism; most frequently, fibroblast growth factor 23. Patients develop renal phosphate wasting and inappropriately low serum concentrations of 1, 25 (OH)2 vitamin D3 , leading to osteomalacia. Surgical removal of the tumour is curative. The authors examined expression of canine fibroblast growth factor 23 in 49 soft tissue sarcomas, and control tissues from normal adult dogs. RNA extracted from bone or formalin-fixed, paraffin-embedded tissues was analysed by end point and quantitative reverse transcriptase-polymerase chain reaction. Fibroblast growth factor 23 expression was detected in bone, lung, kidney, lymph node and thymus. Fifteen of 49 sarcomas (31%) expressed fibroblast growth factor 23, three of these had high relative expression and some features resembling phosphatonin-expressing mesenchymal tumours of humans. Further work is required to determine whether TIO may occur in dogs.

Angiogenesis-related pathways in the pathogenesis of ovarian cancer

Ovarian Cancer represents the most fatal type of gynecological malignancies. A number of processes are involved in the pathogenesis of ovarian cancer, especially within the tumor microenvironment. Angiogenesis represents a hallmark phenomenon in cancer, and it is responsible for tumor spread and metastasis in ovarian cancer, among other tumor types, as it leads to new blood vessel formation. In recent years angiogenesis has been given considerable attention in order to identify targets for developing effective anti-tumor therapies. Growth factors have been identified to play key roles in driving angiogenesis and, thus, the formation of new blood vessels that assist in "feeding" cancer. Such molecules include the vascular endothelial growth factor (VEGF), the platelet derived growth factor (PDGF), the fibroblast growth factor (FGF), and the angiopoietin/Tie2 receptor complex. These proteins are key players in complex molecular pathways within the tumor cell and they have been in the spotlight of the development of anti-angiogenic molecules that may act as stand-alone therapeutics, or in concert with standard treatment regimes such as chemotherapy. The pathways involved in angiogenesis and molecules that have been developed in order to combat angiogenesis are described in this paper.

Renal phosphate handling: Physiology

Phosphorus is a common anion. It plays an important role in energy generation. Renal phosphate handling is regulated by three organs parathyroid, kidney and bone through feedback loops. These counter regulatory loops also regulate intestinal absorption and thus maintain serum phosphorus concentration in physiologic range. The parathyroid hormone, vitamin D, Fibrogenic growth factor 23 (FGF23) and klotho coreceptor are the key regulators of phosphorus balance in body.

Update on fibroblast growth factor 23 in chronic kidney disease

Chronic kidney disease (CKD) is a public health epidemic that affects millions of people worldwide. Presence of CKD predisposes individuals to high risks of end-stage renal disease, cardiovascular disease and premature death. Disordered phosphate homeostasis with elevated circulating levels of fibroblast growth factor 23 (FGF23) is an early and pervasive complication of CKD. CKD is likely the most common cause of chronically elevated FGF23 levels, and the clinical condition in which levels are most markedly elevated. Although increases in FGF23 levels help maintain serum phosphate in the normal range in CKD, prospective studies in populations of pre-dialysis CKD, incident and prevalent end-stage renal disease, and kidney transplant recipients demonstrate that elevated FGF23 levels are independently associated with progression of CKD and development of cardiovascular events and mortality. It was originally thought that these observations were driven by elevated FGF23 acting as a highly sensitive biomarker of toxicity due to phosphate. However, FGF23 itself has now been shown to mediate “off-target,” direct, end-organ toxicity in the heart, which suggests that elevated FGF23 may be a novel mechanism of adverse outcomes in CKD. This report reviews recent advances in FGF23 biology relevant to CKD, the classical effects of FGF23 on mineral homeostasis, and the studies that established FGF23 excess as a biomarker and novel mechanism of cardiovascular disease. The report concludes with a critical review of the effects of different therapeutic strategies targeting FGF23 reduction and how these might be leveraged in a future randomized trial aimed at improving outcomes in CKD.

Plasma intact fibroblast growth factor 23 levels in women with bulimia nervosa: A cross-sectional pilot study

Fibroblast growth factor (FGF) 23, a circulating 26-kDa peptide produced by osteogenic cells, is a novel phosphaturic factor. In our previous study, binge-eating/purging type anorexia nervosa (AN-BP) patients had elevated plasma intact FGF23 (iFGF23) levels, while restricting type (AN-R) patients had plasma iFGF23 levels similar to healthy controls. Although bulimia nervosa (BN) patients as well as some patients with AN-BP regularly engage in binge eating, there have been no studies regarding plasma iFGF23 levels in BN patients. Therefore, this study was performed to determine plasma iFGF23 concentrations in BN patients and healthy controls. The study population consisted of 13 female BN patients and 11 healthy female controls. Blood samples were collected from all subjects after overnight fasting. Plasma iFGF23 was measured using an ELISA kit in a cross-sectional manner. The two-tailed Mann-Whitney U-test was used to assess differences between BN patients and healthy controls. In addition, BN patients were divided into two groups based on questionnaire-reported binge eating frequency immediately prior to participation in this study: high frequency of binge eating (once a week or more; HF group; n = 8) and low frequency of binge eating (less than once a week; LF group; n = 5). Two-tailed Mann-Whitney U-test with Bonferroni's correction was performed after the Kruskal-Wallis test to assess differences between HF group, LF group, and healthy controls. Median (quartiles) plasma iFGF23 levels were greater in BN patients (35.5 [14.8-65.0] pg/ml) than in controls (3.8 [not detected-5.3] pg/ml; p = 0.002). In addition, median (quartiles) plasma iFGF23 levels were greater in the HF group (62.3 [44.4-73.4] pg/ml) than in controls (p < 0.001) and in the LF group (12.9 [not detected-30.3] pg/ml; p = 0.011), while there were no differences between the LF group and controls (p = 0.441). This is the first study to show that BN patients have elevated plasma iFGF23 levels. Moreover, this study showed that BN patients with a high frequency of binge eating have elevated plasma iFGF23 levels, while iFGF23 levels are similar to healthy controls in those with a low frequency of binge eating. Plasma iFGF23 level may be a suitable indicator of binge eating in BN patients.

Circulating fibroblast growth factor-23 is associated with increased risk for metachronous colorectal adenoma

Background:

Fibroblast growth factor-23 (FGF-23) is a phosphaturic peptide and a key component of an endocrine feedback loop along with the hormonal vitamin D metabolite 1,25(OH)₂D. Vitamin D has been shown to be inversely related to colorectal neoplasia; therefore, we hypothesized that the effect of FGF-23 on vitamin D metabolite concentrations could have implications for the risk of colorectal neoplasia.

Materials and Methods:

The purpose of this study was to prospectively evaluate the association between circulating concentrations of FGF-23 and the risk of metachronous (recurrent) colorectal adenomas. FGF-23 levels were assessed in 100 male and female participants from the Ursodeoxycholic Acid Trial, 50 of whom had a metachronous colorectal adenoma and 50 who did not.

Results:

Compared to the lowest tertile of FGF-23, the adjusted odds ratios (95% CIs) for the second and third tertiles were 2.80 (0.94 to 8.31) and 3.41 (1.09 to 10.67), respectively (P-trend=.03). In a linear regression model, there was also a statistically significant inverse relationship between FGF-23 and 1,25(OH)₂D (β-coefficient=–1.2; P=.001). In contrast, no statistically significant trend was observed between FGF-23 and 25(OH)D concentrations (β-coefficient=0.55; P=.10).

Conclusions:

The current work presents novel preliminary evidence of a relationship between FGF-23 and the risk for colorectal neoplasia. FGF-23 activity may be mediated through biologic effects on individual serum and colonic 1,25(OH)₂D levels, or it may be independent from the vitamin D pathway. Further studies in larger populations are necessary for confirmation and expansion of these hypothesis-generating results.

Mechanisms of renal phosphate loss in liver resection-associated hypophosphatemia

OBJECTIVE

To determine precisely the role of parathyroid hormone (PTH) and of phosphatonins in the genesis of posthepatectomy hypophosphatemia.

BACKGROUND

Posthepatectomy hypophosphatemia has recently been related to increased renal fractional excretion of phosphate (FE P). To address the cause of hypophosphatemia, we measured serum concentrations of PTH, various phosphatonins, and the number of removed hepatic segment in patients with this disorder.

METHODS

Serum phosphate (PO4), ionized calcium (Ca++), HCO3-, pH and FE P, intact PTH (I-PTH), carboxyl-terminal fibroblast growth factor 23 (C-FGF-23) and intact fibroblast growth factor 23 (I-FGF-23), FGF-7, and secreted frizzled related-protein-4 (sFRP-4) were measured before and on postoperative (po) days 1, 2, 3, 5, and 7, in 18 patients undergoing liver resection. The number of removed hepatic segments was also assessed.

RESULTS

Serum PO4 concentrations decreased within 24 hours, were lowest (0.66 +/- 0.03 mmol/L; P < 0.001) at 48 hours, and returned to normal within 5 days of the procedure. FE P peaked at 25.07% +/- 2.26% on po day 1 (P < 0.05). Decreased ionized calcium concentrations (1.10 +/- 0.01 mmol/L; P < 0.01) were observed on po day 1 and were negatively correlated with increased I-PTH concentrations (8.8 +/- 0.9 pmol/L; P < 0.01; correlation: r = -0.062, P = 0.016). FE P was positively related to I-PTH levels on po day 1 (r = 0.52, P = 0.047) and negatively related to PO4 concentrations (r = -0.56, P = 0.024). Severe hypophosphatemia and increased urinary phosphate excretion persisted for 72 hours even when I-PTH concentrations had returned to normal. I-FGF-23 decreased to its nadir of 7.8 +/- 6.9 pg/mL (P < 0.001) on po day 3 and was correlated with PO4 levels on po days 0, 3, 5, and 7 (P < 0.001). C-FGF-23, FGF-7 and sFRP-4 levels could not be related to either PO4 concentrations or FE P.

CONCLUSION

Posthepatectomy hypophosphatemia is associated with increased FE P unrelated to I-FGF-23 or C-FGF-23, FGF-7, or sFRP-4. I-PTH contributes to excessive FE P partially on po day 1 but not thereafter. Other yet defined factors should explain post hepatectomy hypophosphatemia.

Plasma intact fibroblast growth factor 23 levels in women with anorexia nervosa

BACKGROUND

Fibroblast growth factor (FGF)23 is a novel phosphaturic factor associated with inorganic phosphate homeostasis. Previous human studies have shown that serum FGF23 levels increase in response to a high phosphate diet. For anorexia nervosa (AN) patients, inorganic phosphate homeostasis is important in the clinical course, such as in refeeding syndrome. The purpose of this study was to determine plasma levels of intact FGF23 (iFGF23) in restricting-type AN (AN-R) patients, binge-eating/purging-type AN (AN-BP) patients, and healthy controls.

METHODS

The subjects consisted of 6 female AN-R patients, 6 female AN-BP patients, and 11 healthy female controls; both inpatients and outpatients were included. Plasma iFGF23, 1,25-dihydroxyvitamin D (1,25-(OH)2D), and 25-hydroxyvitamin D (25-OHD) levels were measured. Data are presented as the median and the range. A two-tailed Mann-Whitney U-test with Bonferroni correction was used to assess differences among the three groups, and a value of p < 0.017 was considered statistically significant.

RESULTS

There were no differences between AN-R patients and controls in the iFGF23 and 1,25-(OH)2D levels. In AN-BP patients, the iFGF23 level (41.3 pg/ml; range, 6.1-155.5 pg/ml) was significantly higher than in controls (3.8 pg/ml; range, not detected-21.3 pg/ml; p = 0.001), and the 1,25-(OH)2D was significantly lower in AN-BP patients (7.0 pg/ml; range, 4.2-33.7 pg/ml) than in controls (39.7 pg/ml; range, 6.3-58.5 pg/ml; p = 0.015). No differences in plasma 25-OHD levels were observed among the groups.

CONCLUSION

This preliminary study is the first to show that plasma iFGF23 levels are increased in AN-BP patients, and that these elevated plasma FGF23 levels might be related to the decrease in plasma 1,25-(OH)2D levels.

Regulation of phosphate homeostasis by the phosphatonins and other novel mediators

A variety of factors regulate the efficiency of phosphate absorption in the intestine and phosphate reabsorption in kidney. Apart from the well-known regulators of phosphate homeostasis, namely parathyroid hormone (PTH) and the vitamin D-endocrine system, a number of peptides collectively known as the "phosphatonins" have been recently identified as a result of the study of various diseases associated with hypophosphatemia. These factors, fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein 4 (sFRP-4), fibroblast growth factor 7 (FGF-7) and matrix extracellular phosphoglycoprotein (MEPE), have been shown to play a role in the pathogenesis of various hypophosphatemic and hyperphosphatemic disorders, such as oncogenic osteomalacia, X-linked hypophosphatemic rickets, autosomal dominant hypophosphatemic rickets, autosomal recessive hypophosphatemia and tumoral calcinosis. Whether these factors are true hormones, in the sense that they are regulated by the intake of dietary phosphorus and the needs of the organism for higher or lower amounts of phosphorus, remains to be firmly established in humans. Additionally, new information demonstrates that the intestine "senses" luminal concentrations of phosphate and regulates the excretion of phosphate in the kidney by elaborating novel factors that alter renal phosphate reabsorption.

"Phosphatonins" and the regulation of phosphorus homeostasis

Phosphate ions are critical for normal bone mineralization, and phosphate plays a vital role in a number of other biological processes such as signal transduction, nucleotide metabolism, and enzyme regulation. The study of rare disorders associated with renal phosphate wasting has resulted in the discovery of a number of proteins [fibroblast growth factor 23 (FGF-23), secreted frizzled related protein 4 (sFRP-4), matrix extracellular phosphoglycoprotein, and FGF 7 (FGF-7)] that decrease renal sodium-dependent phosphate transport in vivo and in vitro. The "phosphatonins," FGF-23 and sFRP-4, also inhibit the synthesis of 1alpha,25-dihydroxyvitamin D, leading to decreased intestinal phosphate absorption and further reduction in phosphate retention by the organism. In this review, we discuss the biological properties of these proteins, alterations in their concentrations in various clinical disorders, and their possible physiological role.