Interorgan handling of fibroblast growth factor-23 in humans

Kidney function and the prognostic value of myocardial performance index

A decreased glomerular filtration rate (GFR) is a risk factor for cardiovascular disease even after adjustment for conventional risk factors. The myocardial performance index (MPI) is defined as (isovolumetric relaxation time (IVRT) + isovolumetric contraction time (IVCT))/ejection time (ET). It has been shown to be an independent predictor of cardiovascular events. We hypothesized the MPI could prove valuable for assessing cardiac risk in subjects of the general population with decreased estimated GFR (eGFR). MPI was measured in 1915 subjects from a large general population prospective cohort study using color tissue Doppler imaging (TDI) M-mode through the mitral valve. We compared the prognostic capabilities of the MPI between subjects with eGFR ≥ 75 mL/min/1.73 m² and subjects with eGFR < 75 mL/min/1.73 m² using multivariable adjusted Cox regression models. The composite endpoint was heart failure, myocardial infarction or cardiovascular death. Mean age was 58 years (SD 16.2), 58% were women, 42% had hypertension and 8.3% diabetes. During a median follow-up time of 12.4 years [IQR 10.6-12.7 years] 269 participants reached the combined endpoint. eGFR modified the prognostic capability of MPI (p-value for interaction < 0.001): After multivariable adjustment, MPI remained an independent predictor of the composite endpoint only in participants with eGFR < 75 mL/min/1.73 m²: HR 1.18 (95% CI 1.02-1.38), p = 0.03, vs. in subjects with eGFR ≥ 75 mL/min/1.73 m²: HR 1.14 (95% CI 0.94-1.39), p = 0.17. These results suggest the MPI could be particularly valuable for identifying elevated cardiac risk in individuals from the general population with decreased eGFR.

The Organ Handling of Soluble Klotho in Humans

BACKGROUND

Chronic kidney disease (CKD) reduces both Klotho expression and its shedding into circulation, an effect that accelerates progression and cardiovascular complications. However, the mechanisms that regulate Klotho release by the human kidney are still unknown.

METHODS

We measured plasma Klotho across the kidney, splanchnic organs and lung in 22 patients (71 ± 2 years, estimated glomerular filtration rate [eGFR] 60 ± 5.4 mL/min 1.73 m2) during elective diagnostic cardiac catheterizations.

RESULTS

Although the Klotho average renal vein concentrations were remarkably higher (by ∼9%) than arterial values, the kidney removed Klotho (or was at zero balance) in 7 subjects, indicating that the kidney contribution to systemic Klotho is not constant. Klotho fractional enrichment across the kidney was inversely related to plasma sodium (r = 0.43, p = 0.045) and acid uric acid levels (r = 0.38, p = 0.084) and directly, to renal oxygen extraction (r = 0.56, p = 0.006). In multivariate analysis, renal oxygen extraction was the only predictor of the enrichment of Klotho across the kidney, suggesting the dependence of renal Klotho release on tubular hypoxia or oxidative metabolism. Klotho balance was neutral across the lung. In patients with eGFR <60 mL/min, Klotho was also removed by splanchnic organs (single pass fractional extraction ∼11%).

CONCLUSIONS

The present study identifies kidney oxygen uptake as a predictor of Klotho release, and splanchnic organs as a site for Klotho removal. This study provides new understanding of kidney Klotho release and suggests that modulating kidney oxygen metabolism could increase Klotho delivery, as an option to slow disease progression and blunt organ damage.

The Biomarkers NT-proBNP and CA-125 are Elevated in Patients with Idiopathic Atrial Fibrillation

BACKGROUND

Blood biomarkers related to AF could be useful to detect silent AF and to develop stratified strategies for AF prevention. Previous studies identified markers that predict incident AF. However, it is difficult to differentiate whether biomarkers relate to underlying cardiovascular diseases, are generated by the atria in response to an AF episode, or both. We therefore measured a panel of blood biomarkers in patients without overt CVD with and without AF to investigate the association between biomarkers and atrial fibrillation (AF) in patients without overt cardiovascular disease (CVD).

METHODS

Blood samples - drawn remote from an AF episode - of 60 patients with AF but without overt forms of CVD (idiopathic AF; iAF) were compared to 120 matched patients with sinus rhythm only. A novel antibody-based method for quantification of blood biomarkers (OlinkProseek Multiplex Cardiovascular) was used to compare 92 biomarkers between the two groups.

RESULTS

N-terminal pro-B-type natriuretic peptide (NT-proBNP), Cathepsin L1, Endothelial cell-specific molecule 1, Cancer Antigen-125 (CA-125), Heat shock 27kDa protein, Galanin peptides, Proteinase-activated receptor 1, Stem cell factor, and CD40-ligand were all higher in iAF patients than in SR controls. Both NT-proBNP (OR1.55(1.07-2.25);p=0.022) and CA-125 (OR1.68(1.07-2.64);p=0.026) were independently associated with iAF.

CONCLUSIONS

This exploratory study, investigating over 90 cardiovascular blood biomarkers in patients without known CVD, identified one established biomarker for paroxysmal AF, NT-proBNP, and a novel marker, CA-125. CA-125 - previously unrelated to paroxysmal AF in an otherwise healthy population - may thus be a potential indicator of remote paroxysms of AF.

The interrelation between FGF23 and glucose metabolism in humans

AIMS

Different studies point to a link between glucose metabolism and Fibroblast Growth Factor 23 (FGF23), an osteocyte-derived phosphaturic hormone. We aimed to investigate in humans the effect of (I) a glucose load and (II) a hyperinsulinemic-euglycemic clamp on FGF23 concentrations and conversely (III) the effect of a diet-induced increase in FGF23 concentration on glucose and insulin concentrations.

METHODS

Plasma cFGF23 concentrations were measured during: I. an oral glucose tolerance test in eight adults with impaired glucose tolerance and vitamin D deficiency and II. a hyperinsulinemic-euglycemic clamp in nine healthy adults. III. Serum glucose and insulin concentrations were measured in nine healthy adults receiving a single-day phosphate-enriched or -restricted diet.

RESULTS

I. A glucose load decreased FGF23 and phosphate concentrations. II. The hyperinsulinemic-euglycemic clamp decreased phosphate concentrations, but did not affect FGF23 concentrations. III. Fasting insulin and glucose concentrations remained unchanged after a diet-induced increase in FGF23 concentration.

CONCLUSIONS

An oral glucose load in vitamin D deficient patients with impaired glucose metabolism decreased FGF23 concentrations, which cannot be attributed to changes in insulin concentration. Thus, bone may react rapidly after glucose loading by alternating FGF23 secretion. A diet-induced increase in FGF23 concentrations did not affect fasting glucose or insulin levels.