Caloric restriction reduces proteinuria in male rats with established nephropathy

Abstract

Reducing proteinuria is a crucial approach in preventing kidney function loss. Previous preclinical studies indicated that caloric restriction (CR) imposed at a young age protects against age-related proteinuria. However, these studies have not explored CR in established renal disease. Therefore, this study aimed to investigate the impact of CR on established proteinuria. Rats, aged 12 ± 2 weeks, were administered 2.1 mg/kg of Adriamycin. Six weeks after injection, protein excretion was measured, and a [¹³ N]ammonia positron emission tomography (PET) scan was conducted to assess kidney perfusion. After 7 weeks rats were divided into four groups: ad libitum (AL) and CR groups fed either a 12% or a 20% protein diet. All groups were treated for 12 weeks. Blood pressure was measured and a second PET scan was acquired at the end of the study. The animals subjected to CR exhibited a 20.3% decrease in protein excretion (p = 0.003) compared to those in the AL groups. Additionally, blood pressure in the CR group was 21.2% lower (p < 0.001) than in the AL groups. While kidney function declined over time in all groups, the 20% CR group demonstrated the smallest decline. Thus CR effectively reduces urinary protein excretion and lowers blood pressure in rats with established proteinuria.

Keywords: 13[N]ammonia PET; caloric restriction; protein excretion; proteinuria.

FIGURE 1

Weekly measurements of body weight in each group from the moment of the Adriamycin injection until the end of the study at week 19. ● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.

FIGURE 2

Biochemical measurements performed in 24‐h rat urine per time point per group, to assess kidney functionality. (a) Urinary protein excretion, (b) plasma creatinine (c) urine sodium excretion. ● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.

FIGURE 3

(a) Creatinine clearance at baseline and at the end of the study. Creatinine clearance is expressed as mL per minute per cm³ of kidney (obtained from the PET scans). Kidney perfusion in the cortex (b), medullary region (c) and total kidney (d) at baseline and at the end of the study. Perfusion is expressed as mL/min/cm³. ● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.

FIGURE 4

[¹³N]ammonia PET scans (expressed as standardized uptake value (SUV)) of rats with the kidneys in the field of view, made at the end of the study. (a) a rat from the LP‐AL group with a ROI drawn around the cortical and medullar region to determine kidney perfusion, (b) a rat from the LP‐CR group with a ROI drawn around the abdominal part of the aorta for an image‐derived input function and a ROI around both kidney to determine kidney volume, (c) a rat from the HP‐AL group with enlarged kidneys, (d) a rat from the HP‐CR group. (e) Total kidney volume per time point per group. (f) Total kidney volume corrected for body weight (cm³/g _{body weight}) per time point per group. (g) Urine production in mL/24 h. ● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.

FIGURE 5

(a) Mean arterial pressure (mmHg) per group at the end of the study. (b) Correlation between mean arterial pressure and proteinuria. ● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.

FIGURE 6

Representative renal sections with ED1 positive cells (brown spots) (a) LP‐AL, (b) LP‐CR, (c) HP‐AL, (d) HP‐CR. (e) Quantitative analysis of ED1 positive cells per glomerulus per group expressed as positive and strong positive pixels per glomerulus. (f) Correlation between ED1 positive cells and proteinuria.● LP‐AL, LP‐CR, ■ HP‐AL, HP‐CR. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.