CHRONIC SALT LOADING AND CARDIOVASCULAR-ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

Factors affecting the progression of renal dysfunction and the importance of salt restriction in patients with type 2 diabetic kidney disease

BACKGROUND

Type 2 diabetic kidney disease (DKD) is the most common cause of end-stage renal failure, and the prevention of its progression has been a topic of discussion.

METHODS

Sixty type 2 DKD patients were retrospectively evaluated for 1 year. Factors independently affecting the annual Ccr decline were examined by multivariable linear regression analysis. Patients were further divided into 2 groups based on their degree of renal function, and between-group differences at study initiation were evaluated.

RESULTS

Ccr values were 21.0 ± 11.8 mL/min/1.73 m(2) at study initiation, and 15.7 ± 10.9 mL/min/1.73 m(2) after 1 year of observation. The multivariable linear regression analysis indicated salt intake (standardized coefficient: -0.34, P = 0.010) and urinary protein excretion (standardized coefficient: -0.33, P = 0.011) to be factors independently affecting the annual Ccr decline. Although decliners (-9.8 ± 4.7 mL/min/1.73 m(2)/year) had a significantly higher salt intake than non-decliners (-1.1 ± 3.8 mL/min/1.73 m(2)/year) at study initiation, this difference disappeared at the end of the study as a result of intensive dietary education. In 21 decliners with an additional year of follow-up, the annual Ccr decline significantly improved from -10.1 ± 5.3 to -5.3 ± 7.4 mL/min/1.73 m(2)/year (P = 0.02).

CONCLUSION

Salt intake and urinary protein excretion were associated with annual Ccr decline in type 2 DKD patients. Furthermore, dietary education covering salt intake may have positively affected the change in Ccr.

Effect of treatment with losartan on salt sensitivity and SGLT2 expression in hypertensive diabetic rats

Sodium-glucose cotransporters (SGLTs) in the kidney, may be involved in hypertension, diabetes and salt sensitivity. We evaluate the effect of losartan on blood pressure (BP) and SGLT2 expression in diabetic rats with high or normal salt diet. Losartan prevented an increase in BP and SGLT2 expression in diabetic rats.

High salt loading alters the expression and localization of glial aquaporins in rat retina

In the neural retina, glial cells control the ionic concentrations in part by mediation of transmembrane water fluxes through aquaporin (AQP) water channels. The expression and immunolocalization of two water channels, AQP1 and AQP4, in the rat retina during experimental high salt loading were investigated in this study. Six-week-old Wistar rats were allowed free access to rat chow with 8% NaCl concentration. Of these rats, 6 were killed after 2, 6, 10 and 20 weeks. Twelve-week-old and 26-week-old Wistar rats with a normal diet (0.5% NaCl concentration) were used as controls. Retinal tissues were collected. Ultrathin sections stained with uranyl acetate and lead citrate were photographed using a transmission electron microscope (TEM). Retinal whole mounts and cryosections were immunostained with AQP1 and AQP4 antibodies to detect the immunolocalization changes by confocal microscopy. The AQP1 and AQP4 contents were evaluated by western blot analysis. In control tissues, no intracellular edema and mitochondria swelling were observed by TEM. The immunoreactive AQP4 was expressed by glial cells (Müller cells and astrocytes) predominantly in the inner retina, and AQP1 was expressed in the outer retina. In the retinas of high salt loading animals, obvious intracellular edema was observed by TEM in retinal ganglion cell (RGC) and mitochondria swelling was observed in glial cells. Strong expression of AQP1 was found in glial cells located in the innermost retinal layers, mainly in astrocytes. The superficial retinal vessels were surrounded by AQP4 in control retinas, but by both AQP4 and AQP1 in retina of high salt loading animals. A similar alteration in the localization of AQP1 has been described in the rat retina after transient ischemia and diabetes. Western blot results supported the conclusion that the AQP1 expression increased during high salt diet. Our findings indicate that high salt loading may induce neural retina edema, and that altered glial cell-mediated water transport via AQP channels in the retina may be one of the reasons for intracellular edema in the neural retina.