Urinary EGF Reflects Distal Tubular Mass and Is Associated with Hypertension, Serum Magnesium, and Kidney Outcomes

Abstract

Key Points:

1. Donor nephrectomy reduced urinary EGF (uEGF) by half and correlated with the reduction in kidney volume, suggesting that uEGF reflects tubular mass.

2. In the general population, lower uEGF/creatinine was associated with lower eGFR, lower serum magnesium, and higher BP.

3. Lower uEGF/creatinine, was associated with incident CKD, and this association was stronger in people without hypertension.

Background: EGF is expressed in the distal tubule and secreted in urine (urinary EGF [uEGF]) after cleavage of membrane-bound pro-EGF. Lower uEGF is associated with kidney disease progression. EGF also plays a role in the regulation of serum magnesium and BP, but whether uEGF is associated with these parameters is unknown. We hypothesized that uEGF is a distal tubule marker associated with serum magnesium, BP, and kidney outcomes.

Methods: We first used a cohort of kidney donors (N=20) and measured uEGF to analyze the association with tubular mass and pro-EGF in urinary extracellular vesicles as proxy for tubular expression. Next, we measured uEGF in a population-based cohort (N=2382) to investigate the associations with serum magnesium, hypertension, and kidney outcomes (incident eGFR <60 or <45 ml/min per 1.73 m², 40% loss of eGFR, or kidney failure).

Results: Kidney donation decreased eGFR from 86 to 54 ml/min per 1.73 m² (36% reduction; 95% confidence interval [CI], 31% to 42%), uEGF from 28 to 14 µg/24 hours (49% reduction; 95% CI, 42% to 55%), and pro-EGF by 29% (95% CI, 12% to 45%). The decrease in uEGF correlated with the decrease in kidney volume. In the population cohort, lower uEGF was significantly associated with hypertension and lower serum magnesium. The association between uEGF and serum magnesium was stronger in participants with lower eGFR, hypertension, and diuretic use. Lower uEGF at baseline was also associated with worse kidney outcomes, and this association was stronger for normotensive participants.

Conclusions: uEGF is a marker of distal tubular mass that is not only associated with kidney disease progression, but also with serum magnesium and BP. Future studies should address whether normotensive people with low uEGF excretion represent a group that may benefit from kidney-protective treatment.

Graphical abstract

Figure 1

Effects of donor nephrectomy on 24-hour uEGF excretion. (A) Three months after kidney donation eGFR decreased from 85.5 to 54.3 ml/min per 1.73 m² (−36%), while 24-hour uEGF excretion decreased from 28 to 14 µg/24 hours (−49%). (B) The change in 24-hour uEGF excretion correlated with the change in kidney volume. CI, confidence interval; uEGF, urinary EGF.

Figure 2

Effects of donor nephrectomy on pro-EGF expression. (A) Immunoblot of pro-EGF in uEVs. Each number represents an individual kidney donor. (B) Donor nephrectomy reduced pro-EGF protein abundance in uEVs by 29%. AU, arbitrary units; uEVs, urinary extracellular vesicles.

Figure 3

Determinants of uEGF excretion and the association with kidney function. (A) Effect plots from a multivariable model including all four possible determinants. (B) Associations between uEGF excretion (uEGF/creatinine), eGFR, and albuminuria. Microalbuminuria was defined as 3–30 mg/mmol and macroalbuminuria as >30 mg/mmol. Effect plots from a multivariable model adjusting for the determinants of uEGF excretion (age, sex, BMI, smoking status). BMI, body mass index.

Figure 4

Associations between uEGF excretion and kidney outcomes. Kaplan–Meier plots for tertiles of uEGF excretion (uEGF/creatinine) and four kidney outcomes. P values from log-rank test.

Figure 5

Subgroup analysis for the association between uEGF excretion and incident eGFR <60 ml/min per 1.73 m². Subgroup analysis from the fully corrected model (model 3). See also Supplemental Figures 4–7. The dashed vertical line depicts the HR of the whole cohort and the dotted line a HR of 1.0. CVD, cardiovascular disease; HR, hazard ratio.