The FGF-23/klotho axis and its relationship with phosphorus, calcium, vitamin D, PTH, aldosterone, severity of disease, and outcome in hospitalised foals

Endocrine fibroblast growth factors in domestic animals

Fibroblast growth factors (FGFs) are a group of structurally homologous yet functionally pleiotropic proteins. Canonical and intracellular FGFs have primarily autocrine or paracrine effects. However, the FGF19 subfamily, composed of FGF15/19, FGF21, and FGF23, act as endocrine hormones that regulate bile acid, metabolic, and phosphorus homeostasis, respectively. Current research in human and rodent models demonstrates the potential of these endocrine FGFs to target various diseases, including disorders of inherited hypophosphatemia, chronic liver disease, obesity, and insulin resistance. Many diseases targeted for therapeutic use in humans have pathophysiological overlaps in domestic animals. Despite the potential clinical and economic impact, little is known about endocrine FGFs and their signaling pathways in major domestic animal species compared with humans and laboratory animals. This review aims to describe the physiology of these endocrine FGFs, discuss their current therapeutic use, and summarize the contemporary literature regarding endocrine FGFs in domestic animals, focusing on potential future directions.

Extra-adrenal aldosterone: a mini review focusing on the physiology and pathophysiology of intrarenal aldosterone

PURPOSE

Accumulating evidence has demonstrated the existence of extra-adrenal aldosterone in various tissues, including the brain, heart, vascular, adipocyte, and kidney, mainly based on the detection of the CYP11B2 (aldosterone synthase, cytochrome P450, family 11, subfamily B, polypeptide 2) expression using semi-quantitative methods including reverse transcription-polymerase chain reaction and antibody-based western blotting, as well as local tissue aldosterone levels by antibody-based immunosorbent assays. This mini-review highlights the current evidence and challenges in extra-adrenal aldosterone, focusing on intrarenal aldosterone.

METHODS

A narrative review.

RESULTS

Locally synthesized aldosterone may play a vital role in various physio-pathological processes, especially cardiovascular events. The site of local aldosterone synthesis in the kidney may include the mesangial cells, podocytes, proximal tubules, and collecting ducts. The synthesis of renal aldosterone may be regulated by (pro)renin receptor/(pro)renin, angiotensin II/Angiotensin II type 1 receptor, wnt/β-catenin, cyclooxygenase-2/prostaglandin E2, and klotho. Enhanced renal aldosterone release promotes Na+ reabsorption and K+ excretion in the distal nephron and may contribute to the progress of diabetic nephropathy and salt-related hypertension.

CONCLUSIONS

Inhibition of intrarenal aldosterone signaling by aldosterone synthase inhibitors or mineralocorticoid receptor antagonists may be a hopeful pharmacological technique for the therapy of diabetic nephropathy and saltrelated hypertension. Yet, current reports are often conflicting or ambiguous, leading many to question whether extra-adrenal aldosterone exists, or whether it is of any physiological and pathophysiological significance.

Kalsiyum, D vitamini ve paratiroid hormon düzeylerinin kritik hastaların prognozuna etkisi

Amaç: Sepsisli hastalarda elektrolit ve hormonlardaki değişimi değerlendiren yeterli çalışma yoktur. Çalışmamızın amacı serum kalsiyum (Ca), magnezyum (Mg), fosfor (P), 25-hidroksivitamin D (25(OH)D) ve paratiroid hormon (PTH) düzeylerindeki değişimler ile sepsisli hastalarda mortalite arasındaki ilişkiyi değerlendirmektir. Gereç ve Yöntem: Çalışmamız Ekim 2017-Ocak 2019 tarihleri arasında yoğun bakım ünitesinde (YBÜ) yatan sepsisli hastalar üzerinde yapılmıştır. Kalsiyum, Mg, P, 25(OH)D ve PTH düzeyleri, demografik ve klinik özellikleri ile birlikte hayatta kalan ve ölen hastalar karşılaştırıldı. Bulgular: Çalışmaya toplam 225 hasta alındı. 225 hastanın 94'ü (%41,2) öldü ve 131'i (%58,8) taburcu edildi. Ölen hastalarda hayatta kalan hastalardan, PTH ve P seviyeleri anlamlı derecede daha yüksek, 25(OH)D, Ca ve Mg seviyeleri ise anlamlı derecede daha düşük bulundu. Sonuç: Sepsis sırasında hassas bir denge içinde olan Ca metabolizmasının hipokalsemi, hipomagnezemi, hiperfosfatemi, düşük 25(OH)D ve yüksek PTH yönünde değişmesi mortalite ile ilişkilendirildi.

The bone is the major source of high circulating intact fibroblast growth factor-23 in acute murine polymicrobial sepsis induced by cecum ligation puncture

Fibroblast growth factor-23 (FGF23), a bone-produced hormone, plays a critical role in mineral homeostasis. Human diseases associated with excessive intact circulating FGF23 (iFGF23) result in hypophosphatemia and low vitamin D hormone in patients with normal kidney function. In addition, there is accumulating evidence linking FGF23 with inflammation. Based on these studies and the frequent observation of hypophosphatemia among septic patients, we sought to elucidate further the relationship between FGF23 and mineral homeostasis in a clinically relevant murine polymicrobial sepsis model. Medium-severity sepsis was induced by cecum ligation puncture (CLP) in adult CD-1 mice of both sexes. Healthy CD-1 mice (without CLP) were used as controls. Forty-eight hours post-CLP, spontaneous urine was collected, and serum, organs and bones were sampled at necropsy. Serum iFGF23 increased ~20-fold in CLP compared to control mice. FGF23 protein concentration was increased in the bones, but not in spleen or liver of CLP mice. Despite the ~20-fold iFGF23 increase, we did not observe any significant changes in mineral homeostasis or parathyroid hormone levels in the blood of CLP animals. Urinary excretion of phosphate, calcium, and sodium remained unchanged in male CLP mice, whereas female CLP mice exhibited lower urinary calcium excretion, relative to healthy controls. In line with renal FGF23 resistance, expression of phosphate-, calcium- and sodium-transporting proteins did not show consistent changes in the kidneys of male and female CLP mice. Renal expression of the co-receptor αKlotho was downregulated in female, but not in male CLP mice. In conclusion, our data demonstrate that the dramatic, sex-independent rise in serum iFGF23 post-CLP was mainly caused by an upregulation of FGF23 secretion in the bone. Surprisingly, the upsurge in circulating iFGF23 did not alter humoral mineral homeostasis in the acutely septic mice. Hence, the biological function of elevated FGF23 in sepsis remains unclear and warrants further studies.

Bone biomarkers in koalas: validation of assays and preliminary analyses

Traumatic injury, including bone fracture, is, to date, one of the leading causes of koala mortality in the South East Queensland region of Australia. Further, the specialist diet of koalas, which is restricted to certain Eucalyptus spp., may impact their normal bone physiology. Considering the dramatic koala population decline and high incidence of trauma, a greater understanding of koala bone physiology may support conservation. We retrieved from GenBank the protein sequences of parathyroid hormone (PTH), osteocalcin (OCN), and tissue-nonspecific alkaline phosphatase (TNALP) in human, dog, cattle, horse, koala, and gray short-tailed opossum. After homology was determined, plasma samples from 13 koalas were analyzed with human PTH, OCN, and bone-specific ALP (BALP) assay kits. Although koala PTH exhibited relatively low sequence homology with placental mammals, high sequence homology between humans and koalas was observed for both OCN and TNALP, and successful cross-reactivity was achieved using human enzyme immunoassay kits for detection of OCN and BALP biomarkers in koala plasma. However, we identified no correlation between OCN and BALP concentrations of healthy and trauma-affected koalas (p = 0.66 and p = 0.79, respectively). Further analysis of OCN and BALP in healthy and diseased koalas will allow a better understanding of bone physiology in this unique marsupial.

Vitamin D Metabolism and Profiling in Veterinary Species

The demand for vitamin D analysis in veterinary species is increasing with the growing knowledge of the extra-skeletal role vitamin D plays in health and disease. The circulating 25-hydroxyvitamin-D (25(OH)D) metabolite is used to assess vitamin D status, and the benefits of analysing other metabolites in the complex vitamin D pathway are being discovered in humans. Profiling of the vitamin D pathway by liquid chromatography tandem mass spectrometry (LC-MS/MS) facilitates simultaneous analysis of multiple metabolites in a single sample and over wide dynamic ranges, and this method is now considered the gold-standard for quantifying vitamin D metabolites. However, very few studies report using LC-MS/MS for the analysis of vitamin D metabolites in veterinary species. Given the complexity of the vitamin D pathway and the similarities in the roles of vitamin D in health and disease between humans and companion animals, there is a clear need to establish a comprehensive, reliable method for veterinary analysis that is comparable to that used in human clinical practice. In this review, we highlight the differences in vitamin D metabolism between veterinary species and the benefits of measuring vitamin D metabolites beyond 25(OH)D. Finally, we discuss the analytical challenges in profiling vitamin D in veterinary species with a focus on LC-MS/MS methods.

Association of serum calcium and phosphorus with measures of left ventricular structure and function: The ARIC study

BACKGROUND AND AIMS

Elevated serum calcium and phosphorus have been associated with increased risk of cardiovascular disorders. We evaluated whether abnormal calcium and high serum phosphorus are associated cross-sectionally with echocardiographic measures of left ventricular (LV) structure and function, as doing so may provide insight into the etiology of cardiac disorders.

METHODS AND RESULTS

Included in the analysis were 5213 Atherosclerosis Risk in Communities Study (ARIC) participants who in 2011-2013 had echocardiography and serum calcium and phosphorus measurements. We evaluated the association of serum calcium (corrected for albumin) and phosphorus quintiles with measures of LV structure and function, after adjusting for other cardiovascular risk factors. Participants were on average 75.3 years old; 59.1% were female and 19.8% were African American. Mean (±SD) concentrations of calcium and phosphorus were 9.33 ± 0.38 and 3.46 ± 0.45 mg/dL, respectively. Higher calcium was associated with lower LV end-diastolic diameter (LVEDD) but greater prevalence of concentric remodeling (p-trend: 0.005 and 0.004 respectively). We observed association between high phosphorus and high septal E/e' (p-trend: 0.02). Likewise, higher serum phosphorus was associated with higher left atrial volume index (p-trend: 0.001) and LV hypertrophy prevalence (p-trend: 0.04).

CONCLUSIONS

In conclusion, higher calcium was associated with more concentric remodeling but lower LVEDD, suggesting complex associations between calcium and cardiac function. Serum phosphorus was related to worse indices of LV diastolic function and LV hypertrophy, but not to LV systolic function. However, the magnitudes of association were modest, so clinical implications of these findings may be limited.

Changes in saliva analytes in equine acute abdominal disease: a sialochemistry approach

BACKGROUND

The biochemical components of saliva can change in certain pathologies in horses, for example in acute abdominal disease. The aim of this study was (1) to evaluate if a panel of biochemical analytes usually used in serum can be measured in saliva of horses and (2) to study the possible changes of these biochemical analytes in saliva of horses affected by acute abdominal disease. A panel of 23 analytes was analytically validated in saliva of horses and possible changes in these analytes in a pilot study with six healthy horses and six horses with acute abdominal disease were evaluated. The analytes with significant changes were then evaluated in a larger population of 20 healthy and 37 diseased horses.

RESULTS

Seven analytes showed significant increases in the pilot study which were confirmed in the larger population. The analytes which showed significant changes, and their median fold increase and significance shown in the larger population were salivary γ-glutamyl transferase (gGT, 2.3 fold, P = 0.001), creatine kinase (CK, 6.2 fold, P < 0.001), urea (2.3 fold, P = 0.001), total bilirubin (2.6 fold, P < 0.001), total proteins (3.2 fold, P < 0.001), phosphorus (P, 4.5 fold, P < 0.001) and alpha-amylase (sAA, 8.5 fold, P < 0.001). Total proteins, P and sAA showed sensitivities higher than 70% at their optimal cut-off points and a specificity of 100% in differentiating between healthy horses and those with acute abdominal disease.

CONCLUSIONS

A panel of 23 biochemical analytes can be measured in saliva of horses, where gGT, CK, urea, total bilirubin, total protein, P and sAA levels are raised in horses with acute abdominal disease.

[Effect of Ronghuang Granule on serum FGF23, FGFRs and Klotho in non-dialysis patients with CKD-MBD and kidney deficiency and damp-heat syndrome]

OBJECTIVE

To observe the effect of Ronghuang granule on serum fibroblast growth factor 23 (FGF23), fibroblast growth factor receptor (FGFRs) and Klotho protein levels in non-dialysis patients with chronic kidney disease-mineral and bone disorder (CKD-MBD) and kidney deficiency and damp heat syndrome.

METHODS

Seventy non-dialysis CKD-MBD patients with kidney deficiency and dampness-heat syndrome were randomized into control group (n=35) and treatment group (n=35). All the patients were given routine treatment combined with traditional Chinese medicine retention enema, and the patients in the treatment group received additional Ronghuang granule treatment (3 times a day). After the 12-week treatments, the patients were examined for changes of TCM syndromes. Serum levels of Ca, P, parathyroid hormone (iPTH), FGF23, FGFRs and Klotho proteins were detected before and after treatment. These parameters were also examined in 20 healthy volunteers.

RESULTS

Sixty-five patients completed the study, including 33 in the control group and 32 in the treatment group. The patients in the treatment group showed significantly better treatment responses than those in the control group (P &lt; 0.05 or 0.01). At 4, 8, and 12 weeks of treatment, the patients in the treatment group had significantly lowered scores of TCM syndromes compared with the score before treatment (P &lt; 0.05 or 0.01), while in the control group, significant reduction of the scores occurred only at 12 weeks (P &lt; 0.05); at each of the time points, the treatment group had significantly greater reductions in the score than the control group (P &lt; 0.01). Significant improvements in serum Ca, P and iPTH levels were observed at 4, 8, and 12 weeks in the treatment group (P &lt; 0.05) but only at 12 weeks in the control group (P &lt; 0.05). The patients in the control and treatment groups all showed elevated serum levels of FGF23, FGFRs and Klotho protein compared with the normal subjects (P &lt; 0.01); FGF23, FGFRs and Klotho levels were significantly reduced in the treatment group (P &lt; 0.05) but remained unchanged in the control group (P&gt;0.05), showing significant differences between the two groups.

CONCLUSIONS

Ronghuang granule improves the clinical symptoms of non-dialysis CKD-MBD patients with kidney deficiency and dampness heat syndrome by reducing serum levels of FGF23, FGFRs and Klotho, improving calcium and phosphorus metabolism disorder, and inhibiting secondary hyperparathyroidism.