Non-Additive Effects of Combined NOX1/4 Inhibition and Calcimimetic Treatment on a Rat Model of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD)

Chronic kidney disease‐mineral and bone disorder (CKD‐MBD) increases cardiovascular calcification and skeletal fragility in part by increasing systemic oxidative stress and disrupting mineral homeostasis through secondary hyperparathyroidism. We hypothesized that treatments to reduce reactive oxygen species formation and reduce parathyroid hormone (PTH) levels would have additive beneficial effects to prevent cardiovascular calcification and deleterious bone architecture and mechanics before end‐stage kidney disease. To test this hypothesis, we treated a naturally progressive model of CKD‐MBD, the Cy/+ rat, beginning early in CKD with the NADPH oxidase (NOX1/4) inhibitor GKT‐137831 (GKT), the preclinical analogue of the calcimimetic etelcalcetide, KP‐2326 (KP), and their combination. The results demonstrated that CKD animals had elevated blood urea nitrogen, PTH, fibroblast growth factor 23 (FGF23), and phosphorus. Treatment with KP reduced PTH levels compared with CKD animals, whereas GKT treatment increased C‐terminal FGF23 levels without altering intact FGF23. GKT treatment alone reduced aortic calcification and NOX4 expression but did not alter the oxidative stress marker 8‐OHdG in the serum or aorta. KP treatment reduced aortic 8‐OHdG and inhibited the ability for GKT to reduce aortic calcification. Treatments did not alter heart calcification or left ventricular mass. In the skeleton, CKD animals had reduced trabecular bone volume fraction and trabecular number with increased trabecular spacing that were not improved with either treatment. The cortical bone was not altered by CKD or by treatments at this early stage of CKD. These results suggest that GKT reduces aortic calcification while KP reduces aortic oxidative stress and reduces PTH, but the combination was not additive

Adverse effects of autoclaved diets on the progression of chronic kidney disease (CKD) and CKD-Mineral Bone Disorder in rats

Background: Autoclaving rodent diets is common in laboratory animals, but autoclaving increases the formation of dietary advanced glycation end-products (AGE). We studied the effect of autoclaved (AC) diet alone or in combination with a diet high in bioavailable phosphorus on biochemistries of chronic kidney disease-mineral and bone disorder (CKD-MBD), intestinal gene expression, and oxidative stress. Methods: Male CKD rats (Cy/+) and normal littermates were fed 1 of 3 diets: AC 0.7% phosphorus grain-based diet for 28 weeks (AC); AC diet for 17 weeks followed by non-autoclaved (Non-AC) 0.7% phosphorus casein diet until 28 weeks (AC + Casein); or Non-AC diet for 16 weeks followed by a Non-AC purified diet until 30 weeks (Non-AC + Casein). Results: AC diets contained ~3× higher AGEs and levels varied depending on the location within the autoclave. Rats fed the AC and AC + Casein diets had higher total AGEs and oxidative stress, irrespective of kidney function. Kidney function was more severely compromised in CKD rats fed AC or AC + Casein compared to Non-AC + Casein. There was a disease-by-diet interaction for plasma phosphorus, parathyroid hormone, and c-terminal fibroblast growth factor-23, driven by high values in the CKD rats fed the AC + Casein diet. Compared to Non-AC + Casein, AC and AC + Casein-fed groups had increased expression of receptor of AGEs and intestinal NADPH oxidase dual oxidase-2, independent of kidney function. Conclusions: Autoclaving rodent diets impacts the progression of CKD and CKD-MBD, highlighting the critical importance of standardizing diets in experiments

Skeletal muscle metabolic responses to physical activity are muscle type specific in a rat model of chronic kidney disease

Chronic kidney disease (CKD) leads to musculoskeletal impairments that are impacted by muscle metabolism. We tested the hypothesis that 10-weeks of voluntary wheel running can improve skeletal muscle mitochondria activity and function in a rat model of CKD. Groups included (n = 12–14/group): (1) normal littermates (NL); (2) CKD, and; (3) CKD-10 weeks of voluntary wheel running (CKD-W). At 35-weeks old the following assays were performed in the soleus and extensor digitorum longus (EDL): targeted metabolomics, mitochondrial respiration, and protein expression. Amino acid-related compounds were reduced in CKD muscle and not restored by physical activity. Mitochondrial respiration in the CKD soleus was increased compared to NL, but not impacted by physical activity. The EDL respiration was not different between NL and CKD, but increased in CKD-wheel rats compared to CKD and NL groups. Our results demonstrate that the soleus may be more susceptible to CKD-induced changes of mitochondrial complex content and respiration, while in the EDL, these alterations were in response the physiological load induced by mild physical activity. Future studies should focus on therapies to improve mitochondrial function in both types of muscle to determine if such treatments can improve the ability to adapt to physical activity in CKD

miRNA is concentrated in MV compared to VSMC from CKD rats.

<p>Total RNA from VSMC or MV was isolated from CKD rats and quantification performed using Agilent 2100 Bioanalyzer total and Small RNA kit. The results demonstrated that the total RNA level (A) is greater but miRNA levels are lower in VSMC compared to MV (B). n = 3, Data were expressed as mean±SEM, *p<0.05, MV vs. VSMC.</p

RT-PCR validation of selected miRNAs n MV and VSMC.

<p>To validate the miRNA identified by the arrays that regulate multiple genes, we performed Real time PCR on VSMc and MV to determine the expression of miR-667, miR-702, miR-3562, mir-3568 and miR-3584 and normalized by U6. Each sample (n = 3 with MV and VSMC isolated from 3 CKD rats, same samples as arrays) was assayed in triplicate. The results demonstrated increased expression in MV compared to VSMC for each of these miRNAs, confirming the array results. Data were expressed as mean ± SEM. * p<0.05, MV vs. VSMC.</p

Network of up-regulated miRs and the targets (genes) controlled by them.

<p>Red/orange nodes represent miRNA, with number corresponding to the table; the larger the node the more genes targeted. The green/yellow nodes represent genes regulated by these miRNA and the black lines the connectivity between miRNa and target genese. The highest degree which was observed to be 381 targets in this network. Network is generated using Cytoscape.</p

Enrichment of biological functions in the gene set controlled by at least 3 miRs using ClueGo.

<p>Analyses of those genese controlled by at least three miRNA were performed to identify important pathways. The genes were categorized based on ClueGo, a plugin of the cytoscape and all the functions reported are at p-value < = 0.05. The size of the nodes represents the number of miRNAs that regulate the genes, and the connectivity of multiple miRNAs regulating multiple genes within a common pathway are shown by the black lines. Purine biosynthesis and cAMP regulation demonstrated the most miRNA regulation (purple nodes).</p

The fold change in expression of 33 miRs dysregulated in MV compared to VSMC from CKD rats.

<p>All the 33 miRs were filtered at p-value < = 0.001 and FDR = 5% and isolated from 3 different rats Blue color represents the up-regulated miRs whereas the orange color represents the down-regulated miRs.</p