Calcitriol and calcimimetics are used to treat hyperparathyroidism secondary to chronic kidney disease (CKD). Calcitriol administration and the subsequent increase in serum calcium concentration ...decrease parathyroid hormone (PTH) levels, which should reduce bone remodeling. We have previously reported that, when maintaining a given concentration of PTH, the addition of calcimimetics is associated with an increased bone cell activity. Whether calcitriol administration affects bone cell activity while PTH is maintained constant should be evaluated in an animal model of renal osteodystrophy. The aim of the present study was to compare in CKD PTH‐clamped rats the bone effects of calcitriol and calcimimetic administration. The results show that the administration of calcitriol and calcimimetic at doses that induced a similar reduction in PTH secretion produced dissimilar effects on osteoblast activity in 5/6 nephrectomized (Nx) rats with secondary hyperparathyroidism and in Nx rats with clamped PTH. Remarkably, in both rat models, the administration of calcitriol decreased osteoblastic activity, whereas calcimimetic increased bone cell activity. In vitro, calcitriol supplementation inhibited nuclear translocation of β‐catenin and reduced proliferation, osteogenesis, and mineralization in mesenchymal stem cells differentiated into osteoblasts. In conclusion, besides the action of calcitriol and calcimimetics at parathyroid level, these treatments have specific effects on bone cells that are independent of the PTH level.
In vivo studies used 5/6 nephrectomy with parathyroidectomy and replacement of exogenous PTH to eliminate the osteogenic effect of PTH comparing the bone effects of calcitriol vs calcimimetic. The osteogenesis of mesenchymal stem cells in presence of calcitriol was also evaluated. Results show calcimimetic increases bone formation, while calcitriol reduces it. In vitro, calcitriol presence reduces mineralization and osteogenesis of stem cells into osteoblasts. In this experimental study and independently of PTH, we demonstrate that calcitriol administration reduces bone formation.
Some of the critical mechanisms that mediate chronic kidney disease (CKD) progression are associated with vascular calcifications, disbalance of mineral metabolism, increased oxidative and metabolic ...stress, inflammation, coagulation abnormalities, endothelial dysfunction, or accumulation of uremic toxins. Also, it is widely accepted that pathologies with a strong influence in CKD progression are diabetes, hypertension, and cardiovascular disease (CVD). A disbalance in magnesium (Mg) homeostasis, more specifically hypomagnesemia, is associated with the development and progression of the comorbidities mentioned above, and some mechanisms might explain why low serum Mg is associated with negative clinical outcomes such as major adverse cardiovascular and renal events. Furthermore, it is likely that hypomagnesemia causes the release of inflammatory cytokines and C-reactive protein and promotes insulin resistance. Animal models have shown that Mg supplementation reverses vascular calcifications; thus, clinicians have focused on the potential benefits that Mg supplementation may have in humans. Recent evidence suggests that Mg reduces coronary artery calcifications and facilitates peripheral vasodilation. Mg may reduce vascular calcification by direct inhibition of the Wnt/β-catenin signaling pathway. Furthermore, Mg deficiency worsens kidney injury induced by an increased tubular load of phosphate. One important consequence of excessive tubular load of phosphate is the reduction of renal tubule expression of α-Klotho in moderate CKD. Low Mg levels worsen the reduction of Klotho induced by the tubular load of phosphate. Evidence to support clinical translation is yet insufficient, and more clinical studies are required to claim enough evidence for decision-making in daily practice. Meanwhile, it seems reasonable to prevent and treat Mg deficiency. This review aims to summarize the current understanding of Mg homeostasis, the potential mechanisms that may mediate the effect of Mg deficiency on CKD progression, CVD, and mortality.
Anemia is a complication of chronic kidney disease (CKD). Phosphate and fibroblast growth factor-23 (FGF23) have a close relationship, as both are related to the pathogenesis of anemia. However, the ...possible interplay between them regarding their effect on anemia has not been evaluated. This was a cross-sectional study of 896 participants from the NEFRONA study (273 CKD3, 246 CKD4-5, 282 dialysis and 95 controls). The levels of 25(OH) and 1,25(OH)2 vitamin D, intact FGF23 (iFGF23) and soluble Klotho were measured, together with standard blood biochemistries. Anemia was defined as hemoglobin levels < 13 g/dL in men and <12 g/dL in women. Patients with anemia (407, 45.4%) were younger, mostly men and diabetic; were in advanced CKD stages; had lower calcium, 1,25(OH)2 vitamin D and albumin levels; and had higher ferritin, phosphate, intact PTH, and iFGF23. An inverse correlation was observed between hemoglobin and both iFGF23 and phosphate. The multivariate logistic regression analyses showed that the adjusted risk of anemia was independently associated with higher serum phosphate and LogiFGF23 levels (ORs (95% CIs) of 4.33 (2.11−8.90) and 8.75 (3.17−24.2), respectively (p < 0.001)). A significant interaction between phosphate and iFGF23 (OR of 0.66 (0.53−0.83), p < 0.001) showed that the rise in the adjusted predicted risk of anemia with the increase in iFGF23 was steeper when phosphate levels were low. Phosphate levels acted as modifiers of the effect of iFGF23 concentration on anemia. Thus, the effect of the increase in iFGF23 levels was stronger when phosphate levels were low.
Background: Increased FGF23 levels are an early pathological feature in chronic kidney disease (CKD), causing increased cardiovascular risk. The regulation of FGF23 expression is complex and not ...completely understood. Thus, Ca2+ has been shown to induce an increase in FGF23 expression, but whether that increase is mediated by simultaneous changes in parathyroid hormone (PTH) and/or vitamin D is not fully known. Methods: Osteoblast-like cells (OLCs) from vitamin D receptor (VDR)+/+ and VDR−/− mice were incubated with Ca2+ for 18 h. Experimental hypercalcemia was induced by calcium gluconate injection in thyro-parathyroidectomized (T-PTX) VDR +/+ and VDR−/− mice with constant PTH infusion. Results: Inorganic Ca2+ induced an increase in FGF23 gene and protein expression in osteoblast-like cells (OLCs), but the increase was blunted in cells lacking VDR. In T-PTX VDR +/+ and VDR−/− mice with constant PTH levels, hypercalcemia induced an increase in FGF23 levels, but to a lower extent in animals lacking VDR. Similar results were observed in FGF23 expression in bone. Renal and bone 1α-hydroxylase expression was also modulated. Conclusions: Our study demonstrates that Ca2+ can increase FGF23 levels independently of vitamin D and PTH, but part of the physiological increase in FGF23 induced by Ca2+ is mediated by vitamin D signaling.
Vitamin D (VD) deficiency has been associated with cancer and diabetes. Insulin signaling through the insulin receptor (IR) stimulates cellular responses by activating the PI3K/AKT pathway. PTEN is a ...tumor suppressor and a negative regulator of the pathway. Its absence enhances insulin signaling leading to hypoglycemia, a dangerous complication found after insulin overdose. We analyzed the effect of VD signaling in a model of overactivation of the IR. We generated inducible double KO (DKO) mice for the VD receptor (VDR) and PTEN. DKO mice showed severe hypoglycemia, lower total cholesterol and increased mortality. No macroscopic tumors were detected. Analysis of the glucose metabolism did not show clear differences that would explain the increased mortality. Glucose supplementation, either systemically or directly into the brain, did not enhance DKO survival. Lipidic liver metabolism was altered as there was a delay in the activation of genes related to β-oxidation and a decrease in lipogenesis in DKO mice. High-fat diet administration in DKO significantly improved its life span. Lack of vitamin D signaling increases mortality in a model of overactivation of the IR by impairing lipid metabolism. Clinically, these results reveal the importance of adequate Vitamin D levels in T1D patients.
Periodontitis is a complex pathology characterized by the loss of alveolar bone. The causes and the mechanisms that promote this bone resorption still remain unknown. The knowledge of the critical ...regulators involved in the alteration of alveolar bone homeostasis is of great importance for developing molecular therapies. Procaine is an anesthetic drug with demethylant properties, mainly used by dentists in oral surgeries. The inhibitor role of Wnt signaling of procaine was described in vitro in colon cancer cells.
In this work we evaluated the role of procaine (1 uM) in osteo/odontogenesis of rat bone marrow mesenchymal stem cells. Similarly, the mechanisms whereby procaine achieves these effects were also studied.
Procaine administration led to a drastic decrease of calcium content, alkaline phosphatase activity, alizarin red staining and an increase in the expression of Matrix Gla Protein. With respect to osteo/odontogenic markers, procaine decreased early and mature osteo/odontogenic markers. In parallel, procaine inhibited canonical Wnt/β-catenin pathway, observing a loss of nuclear β-catenin, a decrease in Lrp5 and Frizzled 3, a significant increase of sclerostin and Gsk3β and an increase of phosphorylated β-catenin. The combination of osteo/odontogenic stimuli and Lithium Chloride decreased mRNA expression of Gsk3β, recovered by Procaine. Furthermore it was proved that Procaine alone dose dependently increases the expression of Gsk3β and β-catenin phosphorylation. These effects of procaine were also observed on mature osteoblast. Interestingly, at this concentration of procaine no demethylant effects were observed.
Our results demonstrated that procaine administration drastically reduced the mineralization and osteo/odontogenesis of bone marrow mesenchymal stem cells inhibiting Wnt/β-catenin pathway through the increase of Gsk3β expression and β-catenin phosphorylation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Background and Aims
Chronic kidney disease (CKD) represents a significant public health burden worldwide, mainly driven by the increase of the incidence of associated risk factors like ...diabetes. Decreased renal Klotho expression is an early feature of CKD, driving an increase on circulating FGF23 and phosphate. These alterations in mineral metabolism have a direct negative impact on the progression of renal dysfunction and can cause bone alterations, vascular calcification and heart failure. In parallel, during the early stages of CKD, kidneys activate molecular mechanisms of hypertrophy in an attempt to counteract the loss of renal function. The PI3K/Akt/mTOR pathway, activated by growing factors like insulin-like growing factor-1 (IGF-1) participates in compensatory renal growth. The aim of the present study is to investigate the possible role of PI3K/Akt activation on renal Klotho levels during renal compensatory hypertrophy.
Method
We generated a mice model of kidney compensatory hypertrophy (UNX mice) in which kidney klotho levels and circulating mineral metabolism parameters were analyzed. Furthermore, some of the mice were treated with inhibitors of the PI3K/Akt/mTOR pathway. In vitro, proximal tubular epithelial human cells (PTEC) were stimulated with IGF-1 in order to activate the PI3K/Akt pathway, and the effects on Klotho expression were determined.
Results
UNX mice present with an activation of the PI3K/Akt/mTOR pathway in kidney, which correlates with the loss on renal Klotho expression. Moreover, UNX mice showed an increase on both, plasma phosphate and FGF23, and a decrease in the fractional excretion of phosphate (% FEPi). Renal function, estimated by BUN plasma levels, was unaltered. Pharmacological inhibition of the pathway restored Klotho and decreased FGF23 levels, normalizing renal phosphate excretion and blood levels. In vitro, IGF-1 stimulated PI3K/Akt activation in PTEC and induced a decline on Klotho expression, which was restored with PI3K/AKT inhibitors.
Conclusion
The overactivation of PI3K/Akt/mTOR pathway in renal hypertrophy modulates Klotho expression and has direct effects on FGF23 and phosphate. Our findings constitute an important breakthrough in the research of new therapeutic targets in order to maintain renal Klotho levels, and it may be useful in the treatment of kidney disease patients.
Abstract
Background and Aims
Obesity and hyperlipidemia are well established risks factors for kidney injury that can lead to chronic kidney disease (CKD). N-methyl-D-aspartate receptors (NMDARs) are ...expressed in the kidney and they are involved in the pathology of different renal diseases. The main objective of this study was to establish the role of the NMDAR in the lipotoxicity-induced kidney injury.
Method
In vivo, we used C57BL/6J mice fed a normal diet (ND) and high fat diet (HFD), as well as mice co-treated with HFD and NMDAR antagonists (HFD+memantine and HFD+MK-801). In vitro, we used renal proximal tubular epithelial cells (HK-2) treated with free fatty acids (FFAs) and a combination of FFAs and NMDAR antagonists. Lipid accumulation was analysed using Oil-Red staining. Expression of NMDAR1 and inflammation, fibrosis and oxidative stress markers were assessed by qPCR and western blot.
Results
After 10 weeks of diet, mice fed a HFD showed elevated levels of lipids in serum and kidney, compared with the ND. HFD induced an increase of expression of renal NMDAR mRNA and protein, as well as the expression of IL6, ICAM1, MCP1, TNFα and IL1β mRNA. Furthermore, HFD induced an increase of αSMA, vimentin, TGFβ1, fibronectin, OPN and NGAL levels in the kidney. Co-treatment with NMDAR antagonists significantly decreased levels of inflammatory markers, as well as the renal expression of αSMA, OPN and NGAL, but it did not have any effect on the hyperlipidemia induced by HFD. In vitro, treatment of HK-2 with different concentrations of FFAs induced accumulation of lipids in the cell, as well as the increase of the expression of NMDAR1 and markers of inflammation and oxidative stress. Co-treatment with NMDAR antagonists reversed changes induced by FFAs in HK-2 cells. The results were confirmed at the protein level.
Conclusion
Our results indicate that the NMDAR could be a new therapeutic target in the lipotoxicity-induced kidney injury.
Abstract Background and Aims The physiological function of sclerostin (SOST) remains unknown. It is known that SOST is produced in osteocytes and functions as an inhibitor of the Wnt/β-catenin ...pathway. Similarly, it is well-established that low levels of SOST lead to bone alterations affecting cortical bone, resulting in osteopetrosis and reduced calciuria. High levels of SOST are associated with osteoporosis. In this study, we aimed to investigate the impact of three elevated doses of SOST on cortical, trabecular, and subchondral bone, as well as its relationship with other parameters of mineral metabolism. Method Bone histomorphometry, mCT, immunohistochemistry, and analysis of mineral metabolism parameters revealed that high doses of SOST over a 14-day period led to a reduction in trabecular bone volume due to a significant increase in bone resorption through the direct activation of osteoclastogenesis. Results Bone resorption, as measured by TRAP activity, was higher in trabecular, cortical, and subchondral bone. Similarly, high doses of SOST increased the number of hypertrophic chondrocytes, consequently expanding the growth plate area. Cortically, positive TRAP staining was observed, suggesting osteocytic osteolysis and trabecularization of cortical bone. The increased bone resorption resulted in a substantial rise in urinary excretion of phosphorus and calcium, accompanied by elevated levels of FGF23 and a significant decrease in PTH. Conclusion The findings suggest that elevated levels of SOST promote bone resorption through the activation of osteoclasts and the generation of osteocytic osteolysis. The increase in calcium and phosphorus levels led to changes in mineral metabolism, indicating a close relationship between SOST and other mineral metabolism parameters.
PDF
