BONE REGULATORY MECHANISMS DESTRUCTION IN EXPERIMENTAL CHRONIC KIDNEY DISEASE

The aim of our study was to investigate the role of intercellular mediators – interleukin-1 receptor antagonist (IL-1 RA), interleukin-17 (IL-17), receptor activator of nuclear factor kB ligand (RANKL) and osteoprotegerin in the mechanisms of metabolic regulation of renal and bone tissue on model of violations of bone remodeling in chronic kidney disease (CKD). It was found a significant increase in the content of cytokines IL-1 RA (4,207 ± 0,546 pg/ml), IL-17 (33,944 ± 0,938 pg/ ml), osteoprotegerin (28,338 ± 1,223 pg/ml) and RANKL (0,184 ± 0,018 pmol/l) in the serum of animals in violation of bone remodeling in CKD compared with the contents of the studied cytokines in animals in the control group (2,529 ± 0,132 pg/ml, 28,166 ± 0,526 pg/ml, 21,588 ± 0,763 pg/ml and 0,131 ± 0,006 pmol/l, respectively) (P<0.05). The obtained correlations reflect the relationship between regulation of bone remodeling and the development of inflammation in CKD. The imbalance between pro- and anti-inflammatory cytokine plays an important role both in the development of CKD and in processes of bone remodeling.

Native LDL-induced oxidative stress in human proximal tubular cells: multiple players involved

Dyslipidemia is a well-established condition proved to accelerate the progression of chronic kidney disease leading to tubulo-interstitial injury. However, the molecular aspects of the dyslipidemia-induced renal damage have not been fully clarified and in particular the role played by low-density lipoproteins (LDLs). This study aimed to examine the effects of native non-oxidized LDL on cellular oxidative metabolism in cultured human proximal tubular cells. By means of confocal microscopy imaging combined to respirometric and enzymatic assays it is shown that purified native LDL caused a marked increase of cellular reactive oxygen species (ROS) production, which was mediated by activation of NADPH oxidase(s) and by mitochondrial dysfunction by means of a ROS-induced ROS release mechanism. The LDL-dependent mitochondrial alterations comprised inhibition of the respiratory chain activity, enhanced ROS production, uncoupling of the oxidative phosphorylation efficiency, collapse of the mtΔΨ, increased Ca²⁺ uptake and loss of cytochrome c. All the above LDL-induced effects were completely abrogated by chelating extracellular Ca²⁺ as well as by inhibition of the Ca²⁺-activated cytoplas-mic phospholipase A2, NADPH oxidase and mitochondrial permeability transition. We propose a mechanicistic model whereby the LDL-induced intracellular redox unbalance is triggered by a Ca²⁺ inward flux-dependent commencement of cPLA2 followed by activation of a lipid- and ROS-based cross-talking signalling pathway. This involves first oxidants production via the plasmamembrane NADPH oxidase and then propagates downstream to mitochondria eliciting redox- and Ca²⁺-dependent dysfunctions leading to cell-harming conditions. These findings may help to clarify the mechanism of dyslipidemia-induced renal damage and suggest new potential targets for specific therapeutic strategies to prevent oxidative stress implicated in kidney diseases.