The calcified vasculature in chronic kidney disease secretes factors that inhibit bone mineralization

Association between fibrinogen-to-albumin ratio and bone metabolism markers (β-CTX and P1NP) in Chinese individuals with osteoporotic fracture: a cross-sectional investigation

OBJECTIVE

Research on the link between inflammatory indicators and markers of bone metabolism is currently lacking, especially the interaction between Procollagen type 1 N-terminal propeptide (P1NP), the β-C-terminal telopeptide of type 1 collagen (β-CTX), and the fibrinogen-to-albumin ratio (FAR). This study intends to fill that knowledge gap by investigating the possible link between inflammatory indicators and bone metabolism.

METHODS

This observational study included 718 individuals diagnosed with osteoporotic fractures from Kunshan Hospital Affiliated to Jiangsu University between January 2017 and July 2022. After accounting for several confounders, the independent connection between FAR levels and β-CTX and P1NP was investigated via Generalized Estimating Equations (GEE). On top of that, we used a generalized additive model (GAM) to find any non-linear correlations, and a two-piecewise linear regression model to find the threshold effects in the smoothing curves that came out of it. To ensure the aforementioned result was stable, a subgroup analysis was carried out.

RESULTS

The results showed a positive linear correlation between FAR and β-CTX [β = 1.077, 95% confidence interval (CI): 0.24 to 1.92, P = 0.012]. The study's findings demonstrated that FAR and P1NP fit curves in an inverted U-shaped pattern, and an inflection point K = 0.0685 for FAR was detected. P1NP showed a positive correlation with FAR below the inflection point (β = 306.10, 95% CI: 47.37 to 564.83, P = 0.021), and a negative correlation with FAR beyond the inflection point (β = -117.57, 95% CI: -231.34 to -3.80, P = 0.043). The subgroup analysis revealed that women had a more significant association between FAR and β-CTX in women than in men.

CONCLUSIONS

The results provide useful insights into the potential association between FAR and markers of bone metabolism. The study may provide a novel clinical implication by introducing FAR as a potential reference indicator for assessing bone health, offering a cost-effective and conveniently obtainable biomarker to monitor inflammation to improve bone metabolism in the treatment of osteoporosis.

The Bone-Vascular Axis: A Key Player in Chronic Kidney Disease Associated Vascular Calcification

Background

The bone-vascular axis plays a key role in the pathogenesis of vascular calcification (VC) in patients with chronic kidney disease (CKD). Understanding and managing the role of the bone-vascular axis in CKD-mineral and bone disorder (CKD-MBD) is critical for preventing and treating associated complications, including osteoporosis, arterial calcification, and cardiovascular diseases. This study aimed to comprehensively summarize the role of bone metabolism markers in uremic VC.

Summary

The skeleton, as an endocrine organ, can regulate systemic metabolic processes by secreting various bioactive substances. These molecules can induce the transdifferentiation of vascular smooth muscle cells, promoting their transition to other functional states, thereby affecting vascular growth and remodeling.

Key Messages

The prevalence of VC in individuals with CKD is notably high. CKD-associated VC is characterized by the widespread accumulation of hydroxyapatite within the arterial media, which occurs as a result of the transformation of smooth muscle cells into osteoblastic smooth muscle cells under the influence of uremic toxins. Osteoblasts and osteoclasts in bone tissue secrete mineral metabolic proteins, which can influence neighboring cells, primarily vascular smooth muscle cells, through paracrine signaling. Both circulating and osteocytic sclerostin can exert a protective effect by inhibiting wingless/integrated (WNT)-induced calcification. The therapeutic goal for CKD-MBD is to reduce production of sclerostin by decreasing the osteogenic transdifferentiation of vascular smooth muscle cells. Calciprotein particles act as a physiological agent for delivering calcium-phosphate the bone and inducing fibroblast growth factor-23 expression in osteoblasts.

In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

The Bone-Vascular Axis in Chronic Kidney Disease: From Pathophysiology to Treatment

PURPOSE OF REVIEW

This review aims to describe the pathogenic factors involved in bone-vessel anomalies in CKD which are the object of numerous experimental and clinical research.

RECENT FINDINGS

Knowledge on the pathophysiological mechanisms involved in the regulation of vascular calcification and mineral-bone disorders is evolving. Specific bone turnover anomalies influence the vascular health while recent studies demonstrate that factors released by the calcified vessels also contribute to bone deterioration in CKD. Current therapies used to control mineral dysregulations will impact both the vessels and bone metabolism. Available anti-osteoporotic treatments used in non-CKD population may negatively or positively affect vascular health in the context of CKD. It is essential to study the bone effects of the new therapeutic options that are currently under investigation to reduce vascular calcification. Our paper highlights the complexity of the bone-vascular axis and discusses how current therapies may affect both organs in CKD.

Updates in the chronic kidney disease-mineral bone disorder show the role of osteocytic proteins, a potential mechanism of the bone-Vascular paradox, a therapeutic target, and a biomarker

The chronic kidney disease-mineral bone disorder (CKD-MBD) is a complex multi-component syndrome occurring during kidney disease and its progression. Here, we update progress in the components of the syndrome, and synthesize recent investigations, which suggest a potential mechanism of the bone-vascular paradox. The discovery that calcified arteries in chronic kidney disease inhibit bone remodeling lead to the identification of factors produced by the vasculature that inhibit the skeleton, thus providing a potential explanation for the bone-vascular paradox. Among the factors produced by calcifying arteries, sclerostin secretion is especially enlightening. Sclerostin is a potent inhibitor of bone remodeling and an osteocyte specific protein. Its production by the vasculature in chronic kidney disease identifies the key role of vascular cell osteoblastic/osteocytic transdifferentiation in vascular calcification and renal osteodystrophy. Subsequent studies showing that inhibition of sclerostin activity by a monoclonal antibody improved bone remodeling as expected, but stimulated vascular calcification, demonstrate that vascular sclerostin functions to brake the Wnt stimulation of the calcification milieu. Thus, the target of therapy in the chronic kidney disease-mineral bone disorder is not inhibition of sclerostin function, which would intensify vascular calcification. Rather, decreasing sclerostin production by decreasing the vascular osteoblastic/osteocytic transdifferentiation is the goal. This might decrease vascular calcification, decrease vascular stiffness, decrease cardiac hypertrophy, decrease sclerostin production, reduce serum sclerostin and improve skeletal remodeling. Thus, the therapeutic target of the chronic kidney disease-mineral bone disorder may be vascular osteoblastic transdifferentiation, and sclerostin levels may be a useful biomarker for the diagnosis of the chronic kidney disease-mineral bone disorder and the progress of its therapy.