Mediation of the relationship between proteinuria and serum phosphate: Insight from the KNOW-CKD study

Phosphocalcic metabolism and its potential association with biomarkers of kidney disease in dogs with spontaneous hyperadrenocorticism

The pathogenesis of increased serum phosphate concentration and proteinuria in dogs with spontaneous hyperadrenocorticism (HAC) is unclear. A potential link between proteinuria and calcium/phosphate metabolism has never been studied in dogs with HAC. The aims of the study were: (1) To evaluate calcium/phosphate metabolism in dogs with spontaneous HAC and compare to healthy dogs as well as to dogs with non-HAC illness; (2) to look for associations between markers of calcium/phosphate metabolism and biomarkers of kidney disease in dogs with HAC. Fifty-four dogs were included in the study, classified as HAC (n=27), non-HAC disease (n=17), and healthy (n=10). Serum calcium, phosphate, 25(OH)Vitamin D, 1,25(OH)2Vitamin D, plasma intact parathyroid hormone concentration (iPTH), FGF23, and urinary fractional excretion of calcium and phosphate were evaluated in all dogs at diagnosis and compared between each group. The correlation between these variables and urine protein-to-creatinine ratio (UPC) and urinary N-acetylglucosaminidase-to-creatinine ratio (uNAG/C) was evaluated in the HAC group. Medians [range] of serum phosphate concentration, urinary fractional excretion of calcium (FE(Ca)), and iPTH were significantly higher in dogs with HAC than in dogs with non-HAC illness (P<0.01) and healthy dogs (P<0.01). Increased 1,25(OH)2Vitamin D/25(OH)Vitamin D was also observed (P<0.001). In HAC group, UPC was significantly negatively correlated with 25(OH)Vitamin D (r(s): -0.54; P<0.01). Urinary NAG/C was significantly positively correlated with serum phosphate (r(s): 0.46; P=0.019). Increased serum phosphate, urinary excretion of calcium, and hyperparathyroidism were observed in dogs with HAC. Vitamin D metabolism may be shifted towards increased 1-alpha hydroxylation.

Fibroblast growth factor 23 and kidney function in patients with type 1 diabetes

Diabetic kidney disease (DKD) is a key determinant of morbidity and mortality in patients with type 1 diabetes (T1D). Identifying factors associated with early glomerular filtration rate (GFR) decline in T1D is important in prevention or early intervention for DKD. This study investigated whether phosphate metabolism, including fibroblast growth factor 23 (FGF23) is associated with the kidney function of patients with T1D. We randomly recruited 118 patients with T1D with a normal or mildly impaired kidney function [chronic kidney disease (CKD) stages of G1/G2, A1/A2], and measured their serum FGF23 levels. Serum FGF23 was significantly negatively associated with the estimated GFR (eGFR) (r = -0.292, P = 0.0016), but not urinary albumin creatinine ratio (UACR), and positively associated with serum phosphate (Pi; r = 0.273, P = 0.0027). Serum FGF23 increased with decreasing eGFR quartiles (P for linear trend = 0.0371), while FGF23 was modestly higher in the higher quartiles of UACR (not statistically significant). The multiple linear regression analysis also showed a significant inverse association between FGF23 and eGFR (Model 1: β = -0.149, P = 0.0429; Model 2: β = -0.141, P = 0.0370). The association remained significant after adjustment for Pi. We identified that FGF23 was inversely associated with the eGFR in T1D patients with a normal or mildly impaired kidney function.

Renoprotection Induced by Aerobic Training Is Dependent on Nitric Oxide Bioavailability in Obese Zucker Rats

Aerobic training (AT) promotes several health benefits that may attenuate the progression of obesity associated diabetes. Since AT is an important nitric oxide (NO⁻) inducer mediating kidney-healthy phenotype, the present study is aimed at investigating the effects of AT on metabolic parameters, morphological, redox balance, inflammatory profile, and vasoactive peptides in the kidney of obese-diabetic Zucker rats receiving L-NAME (N(omega)-nitro-L-arginine methyl ester). Forty male Zucker rats (6 wk old) were assigned into four groups (n = 10, each): sedentary lean rats (CTL-Lean), sedentary obese rats (CTL-Obese), AT trained obese rats without blocking nitric oxide synthase (NOS) (Obese+AT), and obese-trained with NOS block (Obese+AT+L-NAME). AT groups ran 60 min in the maximal lactate steady state (MLSS), five days/wk/8 wk. Obese+AT rats improved glycemic homeostasis, SBP, aerobic capacity, renal mitochondria integrity, redox balance, inflammatory profile (e.g., TNF-α, CRP, IL-10, IL-4, and IL-17a), and molecules related to renal NO⁻ metabolism (klotho/FGF23 axis, vasoactive peptides, renal histology, and reduced proteinuria). However, none of these positive outcomes were observed in CTL-Obese and Obese+AT+L-NAME (p < 0.0001) groups. Although Obese+AT+L-NAME lowered BP (compared with CTL-Obese; p < 0.0001), renal damage was observed after AT intervention. Furthermore, AT training under conditions of low NO⁻ concentration increased signaling pathways associated with ACE-2/ANG1-7/MASr. We conclude that AT represents an important nonpharmacological intervention to improve kidney function in obese Zucker rats. However, these renal and metabolic benefits promoted by AT are dependent on NO⁻ bioavailability and its underlying regulatory mechanisms.

Accelerated Atherosclerosis in Systemic Lupus Erythematosus: Role of Fibroblast Growth Factor 23- Phosphate Axis

PURPOSE

Despite management advances, accelerated atherosclerotic cardiovascular disease (ACVD) remains a major cause of morbimortality in systemic lupus erythematosus (SLE) patients; that is not fully explained by traditional risk factors. Fibroblast growth factor-23 (FGF23) is a bone-derived phosphaturic hormone with multiple klotho-dependent and independent effects, including promotion of atherosclerosis and vascular calcification, particularly in the context of chronic kidney disease. Increased circulating FGF23 was reported in SLE patients, particularly with lupus nephritis (LN); but its atherogenic role in these disorders was not explored.

SUBJECTS AND METHODS

Three study groups of predominantly middle-aged females were categorized by the 2012 SLE International Collaborating Clinics (SLICC) criteria as SLE (without LN), LN, or controls matching for traditional CVD risk profile. Measures of SLE activity, damage, steroid therapy, and glomerular filtration rate were calculated. Fasting blood samples were checked for serum lipid profile, anti-DNA, urea, creatinine, uric acid, proteins, albumin, calcium, phosphorus, C3, C4, CRP, vitamin-D3, intact parathyroid hormone and FGF23 (iFGF23). By carotid ultrasonography, mean common carotid artery intima-media thickness (CC-IMT), plaque score (PS) and internal carotid resistive index (ICRI) were recorded.

RESULTS

CC-IMT, ICRI and serum iFGF23 differed along the study groups (LN>SLE>controls). In both SLE and LN patients, serum iFGF23 had a significant positive correlation with serum phosphorus, CC-IMT and PS. On multivariate analysis, the strongest predictor of increased CC-IMT was cumulative steroid dose in SLE and serum iFGF23 in LN patients. Most significant independent predictors of increased serum iFGF23 were hyperphosphatemia in SLE and proteinuria in LN patients.

CONCLUSION

FGF23-phosphate axis has a key role in accelerated ACVD in SLE patients. Serum phosphorus and iFGF23 should be included in ACVD risk profile assessment of these patients. Prospective studies shall define the role of dietary and/or pharmacologic control of hyperphosphatemia and proteinuria in reducing circulating iFGF23 and ACVD in them.

New Potential Biomarkers for Chronic Kidney Disease Management-A Review of the Literature

The prevalence of chronic kidney disease (CKD) is increasing worldwide, and the mortality rate continues to be unacceptably high. The biomarkers currently used in clinical practice are considered relevant when there is already significant renal impairment compromising the early use of potentially successful therapeutic interventions. More sensitive and specific biomarkers to detect CKD earlier on and improve patients' prognoses are an important unmet medical need. The aim of this review is to summarize the recent literature on new promising early CKD biomarkers of renal function, tubular lesions, endothelial dysfunction and inflammation, and on the auspicious findings from metabolomic studies in this field. Most of the studied biomarkers require further validation in large studies and in a broad range of populations in order to be implemented into routine CKD management. A panel of biomarkers, including earlier biomarkers of renal damage, seems to be a reasonable approach to be applied in clinical practice to allow earlier diagnosis and better disease characterization based on the underlying etiologic process.