Metabolic bone disorder is usually caused by abnormalities of minerals and hormones metabolism. Recently, it has been proved by several studies that the renin-angiotensin system (RAS) in local bone tissue is directly involved in bone metabolism. Activation of skeletal RAS plays an important role in bone metabolic disorders. Based on in vitro, in vivo, and clinical studies, this review explains the roles of RAS in bone metabolism and also covers the potential approaches and beneficial effects of RAS inhibition on bone health. Differential strategies for inhibiting RAS can be employed to maintain bone health, which are attributed primarily to the reduced level of angiotensin II (AngII) and suppressed stimulation of the AngII signaling pathway. The use of renin inhibitors, angiotensin-converting enzyme inhibitors, and AngII receptor blockers either individually or in combination with each other could have promising results in fighting bone metabolic disorders associated with other cardiovascular diseases as well as independent bone injuries.

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There are contradictory results about the effect of angiotensin-converting enzyme inhibitors (ACEIs) on bone. This study was performed to address the skeletal renin-angiotensin system (RAS) activity and the effects of the ACEI, captopril, on the bone of streptozotocin-induced type 1 diabetic mice. Histochemical assessment on bone paraffin sections was conducted by Safranin O staining and tartrate-resistant acid phosphatase staining. Micro-computed tomography was performed to analyze bone biological parameters. Gene and protein expression were determined by real-time polymerase chain reaction and immunoblotting, respectively. Type 1 diabetic mice displayed osteopenia phenotype and captopril treatment showed no osteoprotective effects in diabetic mice as shown by the reduction of bone mineral density, trabecular thickness and bone volume/total volume. The mRNA expression of ACE and renin receptor, and the protein expression of renin and angiotensin II were markedly up-regulated in the bone of vehicle-treated diabetic mice compared to those of non-diabetic mice, and these molecular changes of skeletal RAS components were effectively inhibited by treatment with captopril. However, treatment with captopril significantly elevated serum tartrate-resistant acid phosphatase 5b levels, reduced the ratio of osteoprotegerin/receptor activator of nuclear factor-κB ligand expression, increased carbonic anhydrase II mRNA expression and the number of matured osteoclasts and decreased transforming growth factor-β and osteocalcin mRNA expression in the tibia compared to those of diabetic mice. The present study demonstrated that the use of the ACEI, captopril, has no beneficial effect on the skeletal biological properties of diabetic mice. However, this could be attributed, at least partially, to its suppression of osteogenesis and stimulation of osteoclastogenesis, even though it could effectively inhibit high activity of local RAS in the bone of diabetic mice.

Together, it is concluded that the obstructive nephropathy has defective effects on bone, and the underlying mechanisms are the reduction of bone formation and the increase of bone resorption, which is mediated, at least partially through local angiotensin II signalling.

Objective: Emerging evidence suggests that C3aR (C3a anaphylatoxin receptor) signaling has protective roles in various inflammatory-related diseases. However, its role in atherosclerosis has been unknown. The purpose of the study was to investigate the possible protective role of C3aR in aortic atherosclerosis and explore molecular and cellular mechanisms involved in the protection. Approach and Results: C3ar −/− /Apoe −/− mice were generated by cross-breeding of atherosclerosis-prone Apoe −/− mice and C3ar −/− mice. C3ar −/− /Apoe −/− mice and Apoe −/− mice (as a control) underwent high-fat diet for 16 weeks were assessed for (1) atherosclerotic plaque burden, (2) aortic tissue inflammation, (3) recruitment of CD11b + leukocytes into atherosclerotic lesions, and (4) systemic inflammatory responses. Compared with Apoe −/− mice, C3ar −/− /Apoe −/− mice developed more severe atherosclerosis. In addition, C3ar −/− /Apoe −/− mice have increased local production of proinflammatory mediators (eg, CCL2 [chemokine (C-C motif) ligand 2], TNF [tumor necrosis factor]-α) and infiltration of monocyte/macrophage in aortic tissue, and their lesional macrophages displayed an M1-like phenotype. Local pathological changes were associated with enhanced systemic inflammatory responses (ie, elevated plasma levels of CCL2 and TNF-α, increased circulating inflammatory cells). In vitro analyses using peritoneal macrophages showed that C3a stimulation resulted in upregulation of M2-associated signaling and molecules, but suppression of M1-associated signaling and molecules, supporting the roles of C3a/C3aR axis in mediating anti-inflammatory response and promoting M2 macrophage polarization. Conclusions: Our findings demonstrate a protective role for C3aR in the development of atherosclerosis and suggest that C3aR confers the protection through C3a/C3aR axis–mediated negative regulation of proinflammatory responses and modulation of macrophage toward the anti-inflammatory phenotype.