Osteopontin Expression in Vascular Smooth Muscle Cells in Patients With End-Stage Renal Disease

Endothelial cells exposed to phosphate and indoxyl sulphate promote vascular calcification through interleukin-8 secretion

BACKGROUND

Vascular calcification (VC) is amplified during chronic kidney disease, partly due to uraemic toxins such as inorganic phosphate (Pi) and indoxyl sulphate (IS) that trigger osteogenic differentiation of vascular smooth muscle cells (VSMCs). These toxins also alter endothelial cell (EC) functions but whether this contributes to VC is unknown. Here, we hypothesized that ECs exposed to Pi and IS promote VSMC calcification.

METHODS

Human umbilical vein ECs were treated with Pi, IS or both, and then the conditioned media [endothelial cell conditioned medium (EC-CM)] was collected. Human aortic SMCs (HASMCs) were exposed to the same toxins, with or without EC-CM, and then calcification and osteogenic differentiation were evaluated. Procalcifying factors secreted from ECs in response to Pi and IS were screened. Rat aortic rings were isolated to assess Pi+IS-induced calcification at the tissue level.

RESULTS

Pi and Pi+IS induced HASMCs calcification, which was significantly exacerbated by EC-CM. Pi+IS induced the expression and secretion of interleukin-8 (IL-8) from ECs. While IL-8 treatment of HASMCs stimulated the Pi+IS-induced calcification in a concentration-dependent manner, IL-8 neutralizing antibody, IL-8 receptors antagonist or silencing IL-8 gene expression in ECs before collecting EC-CM significantly prevented the EC-CM procalcifying effect. IL-8 did not promote the Pi+IS-induced osteogenic differentiation of HASMCs but prevented the induction of osteopontin (OPN), a potent calcification inhibitor. In rat aortic rings, IS also promoted Pi-induced calcification and stimulated the expression of IL-8 homologues. Interestingly, in the Pi+IS condition, IL-8 receptor antagonist lifted the inhibition of OPN expression and partially prevented aortic calcification.

CONCLUSION

These results highlight a novel role of IL-8, whose contribution to VC in the uraemic state results at least from interaction between ECs and VSMCs.

Curative effect of sesame oil in a rat model of chronic kidney disease

AIM

Chronic kidney disease causes a progressive and irreversible loss of renal function. We investigated the curative effect of sesame oil, a natural, nutrient-rich, potent antioxidant, in a rat model of chronic kidney disease.

METHODS

Chronic kidney disease was induced by subcutaneously injecting uni-nephrectomized rats with deoxycorticosterone acetate (DOCA) and 1% NaCl [DOCA/salt] in drinking water. Four weeks later, the rats were gavaged with sesame oil (0.5 or 1 mL/kg per day) for 7 days. Renal injury, histopathological changes, hydroxyl radical, peroxynitrite, lipid peroxidation, Nrf2, osteopontin expression, and collagen were assessed 24 h after the last dose of sesame oil.

RESULTS

Blood urea nitrogen, creatinine, urine volume, and albuminuria were significantly higher in the DOCA/salt treated rats than in control rats. Sesame oil significantly decreased these four tested parameters in DOCA/salt treated rats. In addition, creatinine clearance rate and nuclear Nrf2 expression were significantly decreased in the DOCA/salt treated rats compared to control rats. Sesame oil significantly decreased hydroxyl radical, peroxynitrite level, lipid peroxidation, osteopontin, and renal collagen deposition, but increased creatinine clearance rate and nuclear Nrf2 expression in DOCA/salt treated rats.

CONCLUSION

We conclude that supplementation of sesame oil mitigates DOCA/salt induced chronic kidney disease in rats by activating Nrf2 and attenuating osteopontin expression and inhibiting renal fibrosis in rats.

Indoxyl sulphate induces oxidative stress and the expression of osteoblast-specific proteins in vascular smooth muscle cells

BACKGROUND

Previously, we demonstrated that indoxyl sulphate (IS), a uraemic toxin, induced aortic calcification in hypertensive rats. This study aimed to determine if IS induces the production of reactive oxygen species (ROS) and the expression of osteoblast-specific proteins in human aortic smooth muscle cells (HASMCs).

METHODS

In order to achieve these goals, HASMCs were incubated with IS. ROS were detected using probes with a fluorescence detector. The expression of alkaline phosphatase (ALP), osteopontin and organic anion transporters (OAT1, OAT3) was studied by western blotting. The expression of core binding factor 1 (Cbfa1), ALP, osteopontin and NADPH oxidases (Nox1, Nox2 and Nox4) was analysed by reverse transcription-polymerase chain reaction (RT-PCR). Knockdown of Nox4 was performed by RNA interference (RNAi).

RESULTS

IS induced ROS generation and the expression of Nox4, Cbfa1, ALP and osteopontin in HASMCs. A NADPH oxidase inhibitor and antioxidants inhibited IS-induced ROS production and mRNA expression of Cbfa1 and ALP. Knockdown of Nox4 using small interfering RNA (siRNA) inhibited IS-induced ROS production and mRNA expression of Cbfa1, ALP and osteopontin. OAT3 was expressed in HASMCs.

CONCLUSIONS

IS induces ROS generation by upregulating Nox4, and the expression of osteoblast-specific proteins such as Cbfa1, ALP and osteopontin in HASMCs.

Vascular calcification inhibitors in relation to cardiovascular disease with special emphasis on fetuin-A in chronic kidney disease

The mortality rate is extremely high in chronic kidney disease (CKD), primarily due to the high prevalence of cardiovascular disease (CVD) in this patient group. Apart from traditional Framingham risk factors, evidences suggest that nontraditional risk factors, such as inflammation, oxidative stress, endothelial dysfunction, and vascular calcification also contribute to this extremely high risk of CVD. Disturbance in the mineral metabolism, especially in the ions of Ca and PO4, are linked to enhanced calcification of blood vessels. Although the mechanism(s) of this enhanced calcification process are not fully understood, current knowledge suggests that a large number (and an imbalance between them) of circulating promoters and inhibitors of the calcification process, that is, fetuin-A (or alpha 2-Heremans-Schmid glycoprotein, AHSG), matrix-Gla protein (MGP), osteoprotegerin (OPG), osteopontin (OPN), bone morphogenetic proteins (BMPs), and inorganic pyrophosphate (PPi), are involved in the deterioration of vascular tissue. Thus, an imbalance in these factors may contribute to the high prevalence of vascular complications in CKD patients. Among these mediators, studies on fetuin-A deserve further attention as clinical studies consistently show that fetuin-A deficiency is associated with vascular calcification, all-cause and cardiovascular mortality in CKD patients. Both chronic inflammation and the uremic milieu per se may contribute to fetuin-A depletion, as well as specific mutations in the AHSG gene. Recent experimental and clinical studies also suggest an intriguing link between fetuin-A, insulin resistance, and the metabolic syndrome.