Relationship between aortic mineral elements and osteodystrophy in mice with chronic kidney disease

Mouse Models of Mineral Bone Disorders Associated with Chronic Kidney Disease

Patients with chronic kidney disease (CKD) inevitably develop mineral and bone disorders (CKD–MBD), which negatively impact their survival and quality of life. For a better understanding of underlying pathophysiology and identification of novel therapeutic approaches, mouse models are essential. CKD can be induced by surgical reduction of a functional kidney mass, by nephrotoxic compounds and by genetic engineering specifically interfering with kidney development. These models develop a large range of bone diseases, recapitulating different types of human CKD–MBD and associated sequelae, including vascular calcifications. Bones are usually studied by quantitative histomorphometry, immunohistochemistry and micro-CT, but alternative strategies have emerged, such as longitudinal in vivo osteoblast activity quantification by tracer scintigraphy. The results gained from the CKD–MBD mouse models are consistent with clinical observations and have provided significant knowledge on specific pathomechanisms, bone properties and potential novel therapeutic strategies. This review discusses available mouse models to study bone disease in CKD.

Acute Tissue Mineral Deposition in Response to a Phosphate Pulse in Experimental CKD

Pathogenic accumulation of calcium (Ca) and phosphate (PO₄ ) in vasculature is a sentinel of advancing cardiovascular disease in chronic kidney disease (CKD). This study sought to characterize acute distribution patterns of radiolabeled ³³ PO₄ and ⁴⁵ Ca in cardiovascular tissues of rats with CKD (0.25% dietary adenine). The disposition of ³³ PO₄ and ⁴⁵ Ca was assessed in blood and 36 tissues after a 10-minute intravenous infusion of one of the following: (i) PO₄  pulse + tracer ³³ PO₄ ; (ii) PO₄  pulse + tracer ⁴⁵ Ca; or (iii) saline + tracer ⁴⁵ Ca in CKD and non-CKD animals. After the infusion, ³³ PO₄ in blood was elevated (2.3× at 10 minutes, 3.5× at 30 minutes, p < 0.05) in CKD compared with non-CKD. In contrast, there was no difference in clearance of ⁴⁵ Ca from the blood. Compared with controls, CKD rats had a markedly increased ³³ PO₄ incorporation in several tissues (skeletal muscle, 7.8×; heart, 5.5×), but accrual was most pronounced in the vasculature (24.8×). There was a significant, but smaller, increase in ⁴⁵ Ca accrual in the vasculature of CKD rats (1.25×), particularly in the calcified rat, in response to the acute phosphate load. Based on the pattern of tissue uptake of ³³ PO₄ and ⁴⁵ Ca, this study revealed that an increase in circulating PO₄ is an important stimulus for the accumulation of these minerals in vascular tissue in CKD. This response is further enhanced when vascular calcification is also present. The finding of enhanced vascular mineral deposition in response to an acute PO₄  pulse provides evidence of significant tissue-specific susceptibility to calcification. © 2018 American Society for Bone and Mineral Research.

The renal mitochondrial dysfunction in patients with vascular calcification is prevented by sodium thiosulfate

PURPOSE

Vascular calcification (VC) is an impact of calcium accumulation in end-stage renal diseases, normally initiated in the mitochondria. Sodium thiosulfate (STS) is effective in rescuing mitochondrial function in the neurovascular complications associated with VC, but has limitation in protecting the cardiac mitochondria. However, the STS efficacy in restoring the renal mitochondrial function has not been studied, which is the primary focus of this study.

METHODS

Wistar rats (n = 6/group) were administered 0.75 % adenine in the diet for 28 days to induce renal failure. STS (400 mg/kg) was given in two regimens STS_Pre (preventive: along with adenine for 28 days) and STS_Cur (curative: 29th to 49th day). Renal failure was assessed by plasma and urinary markers. The effectiveness of treatment was assessed from oxidative stress, DNA damage, mitochondrial physiology and enzymology in the renal tissue.

RESULTS

0.75 % adenine diet caused renal medullary swelling, tubular interstitial nephropathy and impaired renal function (creatinine, urea, uric acid and ALP), which were recovered after STS treatment. The renal failure was due to oxidative stress as measured by elevated malondialdehyde (29 %) and lowered reduced glutathione (27 %) levels. STS reduced the lipid peroxidation and significantly (p < 0.05) elevated the antioxidant enzymes. Further, it improved renal mitochondrial respiratory capacity by maintaining the hyperpolarized membrane potential and restored the complex enzyme activities. Absence of renal DNA fragmentation supports the above findings.

CONCLUSION

STS protects the kidney by preserving renal mitochondria, in experimental adenine-induced vascular calcified rats. The efficacy was prominent when given after induction, i.e., in STS_Cur group.

Magnesium and cardiovascular complications of chronic kidney disease

Cardiovascular complications are the leading cause of death in patients with chronic kidney disease (CKD). Abundant experimental evidence suggests a physiological role of magnesium in cardiovascular function, and clinical evidence suggests a role of the cation in cardiovascular disease in the general population. The role of magnesium in CKD-mineral and bone disorder, and in particular its impact on cardiovascular morbidity and mortality in patients with CKD, is however not well understood. Experimental studies have shown that magnesium inhibits vascular calcification, both by direct effects on the vessel wall and by indirect, systemic effects. Moreover, an increasing number of epidemiologic studies in patients with CKD have shown associations of serum magnesium levels with intermediate and hard outcomes, including vascular calcification, cardiovascular events and mortality. Intervention trials in these patients conducted to date have had small sample sizes and have been limited to the study of surrogate parameters, such as arterial stiffness, vascular calcification and atherosclerosis. Randomized controlled trials are clearly needed to determine the effects of magnesium supplementation on hard outcomes in patients with CKD.