MO564CHRONIC EXPOSURE TO INDOXYL SULFATE CHANGES BONE PROPERTIES AND EXPRESSION OF SIRT2, SIRT3, AND SIRT7 GENES*

Background and Aims

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.

Method

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.

Results

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.

Conclusion

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).

P0690CORRELATIONS BETWEEN OPG/RANKL/RANK AXIS, VITAMIN D STATUS, PTH AND VASCULAR CALCIFICATION IN AN ADENINE-INDUCED MODEL OF CHRONIC KIDNEY DISEASE

Background and Aims

Chronic kidney disease (CKD) is a major public health problem worldwide and refers to a wide range of disorders in bone and mineral metabolism, abnormalities of biochemical parameters and pathological calcification of the blood vessels. Vascular calcification (VC) is a common complication in CKD patients, contributes to cardiovascular disease (CVD), and associates with increased mortality and morbidity. The precise mechanism of VC in CKD is not yet fully understood. Recently discovered molecules such as osteoprotegerin (OPG), its ligand receptor activator of nuclear factor NF-κB ligand (RANKL) and RANK are not only well-known to play a crucial role in bone homeostasis, but they has also been implicated in the process of development of vascular complications However the exact role of OPG/RANKL/RANK axis in the process of VC has not been yet fully assessed. Thus, the aim of this work is to evaluate the role of OPG/RANKL/RANK axis in the process of calcification in CKD.

Method

Seventy two male Wistar rats weighing 260-290 g (8-weeks old) were initially divided into 6 groups containing 12 animals in each group. Rats were divided into six groups: control rats (K4, K6, K8) and CKD rats (B4, B6, B8). Control group rats received standard diet, whereas CKD rats were fed a low adenine – diet containing 0.3 % adenine, 1.0 % Ca, 1.2 % Pi through 4 (K4, B4), 6 (K6, B6) and 8 (K8, B8) weeks. Subsequently, CKD and control rats were sacrificed at weeks 4 (n=24), 6 (n=24) and 8 (n=24). One day before being killed, the rats were placed in metabolic cages for 24-hour urine collection. Thereafter, the rats were anesthetized and samples of blood, as well as aortas were collected. Next, the OPG, RANKL, parathyroid hormone (PTH), 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxy vitamin D3 1,25(OH)2D3 concentrations were determined using appropriate ELISA kits. Then the sRANKL/OPG ratio was calculated. The OPG, RANK and RANKL gene expression was assessed using real-time PCR (RT-PCR). The VC was quantified by measurement of the arterial calcium (Ca) and phosphate (Pi) content using flame atomic absorption. Serum levels of urea nitrogen, creatinine, uric acid, Ca, Pi and urinary levels of creatinine, Ca and Pi were measured.

Results

There was a progressive increase in serum urea nitrogen, creatinine, uric acid and PTH of CKD rats in comparison to control values. We also observed significantly decreased levels of 25(OH)D, 1,25(OH)2D and serum Ca. Total Ca content in the aorta was significantly increased in CKD rats in comparison with control group, whereas total Pi content in the aorta was significantly increased only in B8 group in comparison to appropriate controls. There were no differences in serum OPG and sRANKL levels between CKD and control rats. In contrast, we observed decreased OPG, RANKL and RANK gene expression in a B4 group in comparison to appropriate controls, whereas in a B6 group we noticed increased OPG, RANKL and decreased RANK gene expression. B8 group revealed increased RANKL and RANK gene expression, but there were no differences in OPG gene expression between CKD rats and control group. Furthermore, we observed positive correlations between serum sRANKL and OPG and RANK gene expression. Ca and P content in the aorta inversely corelated with RANKL gene expression, whereas positively with OPG gene expression. Serum 25(OH)D concentrations correlated inversely with Ca in aorta. PTH was positively correlated with serum RANKL and OPG and gene expression these cytokines.

Conclusion

Our results suggest that OPG/RANK/RANKL axis may be involved in the process of vascular calcification in chronic kidney disease. However, its role and evaluation of precise mechanism in this field requires further evaluation.

The Mechanism of the Osteoprotective Action of a Polyphenol-Rich Aronia melanocarpa Extract during Chronic Exposure to Cadmium is Mediated by the Oxidative Defense System

Recently, we demonstrated in a rat model that consumption of a polyphenol-rich extract obtained from the berries of Aronia melanocarpa could protect from cadmium-induced disorders in bone turnover and changes in bone mineral status. The aim of this study was to investigate whether the osteoprotective effect of this extract is mediated by the oxidative defense system. Enzymatic and nonenzymatic antioxidants, total antioxidative and oxidative status, hydrogen peroxide, and markers of oxidative protein, lipid, and DNA damage were determined in bone tissue at the distal femoral epiphysis of female Wistar rats receiving 0.1 % aqueous A. melanocarpa extract (prepared from the lyophilized commercial extract containing 65.74 % of polyphenols) as the only drinking fluid and/or cadmium in the diet (1 and 5 mg/kg) for 3, 10, 17, and 24 months. The total oxidative and antioxidative status of the serum was also evaluated. The administration of A. melanocarpa extract provided significant protection from cadmium-induced oxidative stress in the bone and serum, and from lipid peroxidation and oxidative damage to the protein and DNA in the bone tissue. Numerous correlations were noted between indices of the oxidative/antioxidative bone status and markers of bone metabolism previously assayed in the animals receiving A. melanocarpa extract. The results allow the conclusion that the ability of A. melanocarpa extract to mediate the oxidative defense system and prevent oxidative modifications of protein, lipid, and DNA in the bone tissue plays an important role in its osteoprotective action under exposure to cadmium. The findings provide further evidence supporting our suggestion that chokeberry may be a promising natural agent for protection against the toxic action of cadmium in women chronically exposed to this metal.

Estimation of Polish cigarettes contamination with cadmium and lead, and exposure to these metals via smoking

To estimate exposure to cadmium (Cd) and lead (Pb) through cigarette smoking, the concentrations of both metals in the blood or/and urine of smokers (20 cigarettes or more per day for 10 years or longer) and their non-smoking counterparts inhabiting an environmentally unpolluted area (Bialystok, Poland) were evaluated, as well as Cd and Pb contents in the cigarette brands (produced in Poland) smoked by the participants, including intact cigarettes, pre-smoking (tobacco, paper and filter) and post-smoking (butt, ash and smoke) cigarette components. Blood and urinary Cd concentrations in the smokers have been already reported by us to be 2-4 times higher than in the non-smokers (Galazyn-Sidorczuk et al. Polish Journal of Environmental Studies, 13 (Suppl.1):91-95, 2004). All the other measurements are the subject of the present paper. Pb concentration in the blood of the cigarette smokers (52.12 +/- 15.51 microg l(-1)) was higher by 29% than in the non-smokers (40.42 +/- 11.19 microg l(-1)). The mean Cd and Pb contents in the cigarettes were 0.6801 +/- 0.1765 and 0.6853 +/- 0.0746 microg per cigarette, respectively. Under cigarette burning, performed using a machine for self-acting burning, on average 33% of Cd and 11% of Pb present in the whole cigarette was released into the smoke. For Cd, unlike Pb, there was a high positive correlation between the metal content in cigarettes and tobacco and its release into the smoke. Moreover, the subjects smoking cigarettes containing the highest Cd amount had higher blood Cd concentration than smokers of other cigarette brands. The results give clear evidence that in the case of inhabitants of areas unpolluted with Cd and Pb habitual cigarette smoking, due to tobacco contamination, creates a serious source of chronic exposure to these metals, especially to Cd.

The effect of zinc supply on cadmium-induced changes in the tibia of rats

It has been determined that zinc supplementation (240 microg Zn/ml) during (for 12 weeks) or after (for 2 weeks) cadmium exposure (50 microg Cd/ml for 12 weeks) can prevent the accumulation and toxic action of Cd in the tibia of rats. The exposure to Cd led to disturbances in bone metabolism reflected by changes in the chemical composition of bone and decreased bone mineral density (osteomalacian changes). The Zn supply in conditions of Cd intoxication completely prevented the Cd-induced increase in percentage of water content and decrease in tibia ash weight, ash weight/dry weight, non-org. comp./org. comp., Zn content and concentration. Moreover, Zn partly protected from the decrease in Ca concentration and content, percentage of non-organic components content, Ca/wet weight, Ca/ash weight and Ca/dry weight. Zn administered after Cd exposure partly, but not completely, protected from Cd-induced decrease in percentage of non-organic components content, Ca/wet weight as well as Ca content and concentration. This protective effect on bone was most evident when Zn was administered during Cd exposure. But Zn, independently of the manner of its administration, did not prevent Cd accumulation in the tibia. Our results suggest that Zn supply in conditions of simultaneous exposure can prevent Cd-induced bone loss to some extent, and used after Cd treatment can give therapeutic benefits.