Intrinsic carnosine metabolism in the human kidney - PubMed (original) (raw)

Intrinsic carnosine metabolism in the human kidney

Verena Peters et al. Amino Acids. 2015 Dec.

Abstract

Histidine-containing dipeptides like carnosine and anserine have protective functions in both health and disease. Animal studies suggest that carnosine can be metabolized within the kidney. The goal of this study was to obtain evidence of carnosine metabolism in the human kidney and to provide insight with regards to diabetic nephropathy. Expression, distribution, and localization of carnosinase-1 (CNDP1), carnosine synthase (CARNS), and taurine transporters (TauT) were measured in human kidneys. CNDP1 and CARNS activities were measured in vitro. CNDP1 and CARNS were located primarily in distal and proximal tubules, respectively. Specifically, CNDP1 levels were high in tubular cells and podocytes (20.3 ± 3.4 and 15 ± 3.2 ng/mg, respectively) and considerably lower in endothelial cells (0.5 ± 0.1 ng/mg). CNDP1 expression was correlated with the degradation of carnosine and anserine (r = 0.88 and 0.81, respectively). Anserine and carnosine were also detectable by HPLC in the renal cortex. Finally, TauT mRNA and protein were found in all renal epithelial cells. In diabetic patients, CNDP1 seemed to be reallocated to proximal tubules. We report compelling evidence that the kidney has an intrinsic capacity to metabolize carnosine. Both CNDP1 and CARNS are expressed in glomeruli and tubular cells. Carnosine-synthesizing and carnosine-hydrolyzing enzymes are localized in distinct compartments in the nephron and increased CNDP1 levels suggest a higher CNDP1 activity in diabetic kidneys.

Keywords: Anserine; Carnosinase (CNDP1); Carnosine; Diabetic nephropathy; Metabolism.

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Figures

Fig. 1

Fig. 1

a Immunohistochemistry showing the presence of CNDP1 in the glomeruli and distal tubules (arrows). b Immunohistochemistry showing CARNS expression in proximal tubules and glomeruli (arrows). The nuclei were counterstained with hematoxylin. c Immunofluorescence showing carnosinase (red) and carnosine synthase (green) in separate compartments in tubular cells. Immunohistochemistry showing CARNS expression in proximal tubules and glomeruli (arrows). d Immunofluorescence showing non-overlapping expression of CARNS (red) in the proximal tubules and Tamm-Horsfall protein (green) in the distal tubules. e Immunohistochemistry showing that the TauT is expressed in proximal tubules (red arrow) and distal tubules (black arrow) in human kidney samples. The highest proteins levels were present in the distal tubules. The nuclei were counterstained with hematoxylin

Fig. 2

Fig. 2

CDNP1 mRNA was amplified from human kidney samples (1.00 ± 1.12) (N = 8), human glomeruli (Glom) (0.802 ± 1.1) (N = 8), immortalized human podocytes (0.016 ± 0.0013) (N = 2), human endothelial cells (HUVEC) (0.001 ± 0.0013) (N = 5), and human proximal tubular epithelial cells (HK2 cells) (0.000185) (N = 1). All values were normalized to the mean value obtained from the human kidney samples. Note that the _y_-axis is plotted on a logarithmic scale, expressed as mean ± SD of relative units

Fig. 3

Fig. 3

CNDP1 activity (in nmol/mg/h) was measured as the rate of degradation of carnosine (black) and anserine (grey) in mouse podocytes (2.8 ± 1.7 and 2.9 ± 1.5 nmol/mg/h, respectively) and human proximal tubular epithelial cells (HK2 cells) (1.3 ± 0.4 and 0.05 ± 0.08 nmol/mg/h, respectively), expressed as mean ± SD

Fig. 4

Fig. 4

CARNS mRNA was amplified from human kidney samples (1.00 ± 0.63) (N = 8), glomeruli (Glom) (0.4136 ± 0.08) (N = 4), immortalized human podocytes (1.07 ± 0.15) (N = 2), human endothelial cells (HUVEC) (0.032 ± 0.02) (N = 5), and proximal tubular epithelial cells (HK2 cells) (0.035 ± 0.005) (N = 2). All values were normalized to the mean value obtained from the human kidney samples. Note that the _y_-axis is plotted on a logarithmic scale, expressed as mean ± SD of relative units

Fig. 5

Fig. 5

Relative CARNS mRNA level is plotted against the relative CNDP1 mRNA level measured in human kidney samples. Each data point represents a separate sample. The solid line is a linear fit of the data. r = 0.81 (N = 13)

Fig. 6

Fig. 6

Concentrations of anserine (4 ± 2.7) [95 % CI 2.3–6.4] and carnosine (1.8 ± 0.9) [95 % CI 1.1–2.8] in human kidney samples (N = 3) measured using HPLC, expressed as mean ± SD

Fig. 7

Fig. 7

CNDP1 in diabetic patient (N = 14) and control (N = 7). Immunohistochemistry and intensity score *(p = 0.029). It shows a reallocation of CNDP1 from distal to proximal tubules in diabetic patients with renal damage. a Healthy control (0.857 ± 0.8997), b diabetic nephropathy patients (1.171 ± 0.726), c negative control, d intensity staining difference; red arrow proximal tubules, black arrow distal tubules; expressed in mean ± SD

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