LAUSR

Chronic kidney disease (CKD) is connected with accumulation of uremic toxins that leads to dysfunction of many systems including skeletal system. Indoxyl sulfate (IS) is one of the most potent protein-bound uremic toxin. However, its impact on bone and mineral disorders remains unclear. Sirtuins (SIRT) are members of the class III type nicotinamide adenine dinucleotide-dependent histone deacetylases. Their roles are commonly linked to aging, metabolism, and antioxidant defense. However, SIRT1, SIRT3 and SIRT7 maintain also bone formation. In turn, reduction of SIRT2 has a protective role due to reduced activation of osteoclasts-mediated bone resorption. Thus, the aim of this work was to evaluate IS impact on bone metabolism and bone properties, and SIRT genes expression. Male Wistar rats weighting 180 – 210 g were divided into 2 groups: experimental receiving IS in the dose of 200 mg/kg of b.w. for four weeks (200IS), and control receiving pure water (CON). After four weeks the femurs and tibiae were collected, and geometrical parameters (CI – cortical index, CSA – cortical sectional area, CSMI – cross sectional moment of inertia, MRWT – mean relative wall thickness) were measured. The IS bone (cortical and trabecular), plasma and urine levels were determined by high-performance liquid chromatography (HPLC). The concentrations of Ca, Mg, Zn, Fe, Mn, and Cu in bone tissue were determined by the flame atomic absorption spectrometry. Bone turnover markers (alkaline phosphatase – ALP, and tartrate-resistant acid phosphatase - TRAP) were determined in homogenates from trabecular and cortical left femurs. The expression of ALP, TRAP, SIRT1, SIRT2, SIRT3 and SIRT7 gene was assessed by QRT-PCR in right femurs. Plasma, urine, cortical and trabecular bone IS concentrations were increased in 200IS compared to CON. Geometrical properties of femur (CI, CSA, CSMI and MRWT) were significantly reduced in 200IS. There were no differences in relative femur weight and length between studied groups. The activity of ALP and TRAP in bone tissue were significantly lower in 200IS compared to CON. In turn, the expression of TRAP gene was increased in 200IS. There were no difference in concentrations of Ca, Mg, Fe, Mn, and Cu in bone tissue. Only Zn concentration in cortical bone was reduced in 200IS. The expressions of SIRT3 and SIRT7 were decreased in 200IS, whereas SIRT2 was increased in 200IS. Chronic exposure to IS did not affect expression of SIRT1. Obtained results suggest that IS affects bone properties and bone metabolism, and has impact on expression of SIRT2, SIRT3, and SIRT7 genes. Our findings may help to better understand mechanisms leading to dysfunction of skeletal system during CKD. This work was supported by Polish National Science Centre (Grant No. 2017/27/N/NZ4/00033).