Background: Cardiovascular disease (CVD) is the major cause of morbidity and mortality in subjects with type 2 diabetes (T2D). The differentiation of monocytes towards the osteoblast-like phenotype of myeloid calcifying cells (MCCs) can contribute to CVD and vascular calcification in diabetes. No treatments have been proposed to target MCC. PPARgamma agonists improve CVD and inhibit both osteoblastogenesis and monocyte activation. Therefore, the activation of PPARgamma could be a candidate pathway to target MMCs in diabetes.
Aims: Evaluate the effects of the PPARgamma agonist pioglitazone on MCCs levels in subjects with T2D [Study A] and the effects of pioglitazone and metformin on the acquisition of an osteoblast-like phenotype of cultured human monocytes [Study B].
Methods: Study A will be an observational study. We will enroll patients initiating therapy with pioglitazone plus metformin [Arm A] and those initiating metformin alone [Arm B] for a total of 80 patients observed for 3 months. The primary efficacy endpoint will be the percentage of MCCs, evaluated by polychromatic flow cytometry and defined as CD45+CD14+OCN+ cells, on the total number of CD45+ cells. Moreover, in a in vitro study [Study B] we will evaluate the effects of pioglitazone on the differentiation of cultured human monocytes towards an osteoblast-like phenotype. THP-1 cells will be treated with oxidized LDL (OxLDL) ± pioglitazone or metformin at 24, 48 and 72 hours. Surface expression of osteocalcin will be evalueted by flow cytometry and expression of osteoblast-related genes by qRT-PCR.
Expected results: We hypothesize that pioglitazone can prevent the differentiation of monocytes towards an osteoblast-like phenotype and can reduce the levels of circulating MCCs. We expect to show that 3 months treatment with pioglitazone will significantly reduce the number of circulating MCCs in subjects with T2D and will inhibit, in vitro, the drift of human monocytes towards a procalfic phenotype.
We expect to show that 1 and 3 months treatment with pioglitazone will significantly reduce the number of circulating myeloid calcifying cells in subjects affected by T2D. To this aim we will study in vitro the expression of osteoblast related-genes and osteocalcin surface expression and production in human monocytes after treatment with OxLDL ± pioglitazone. Our previous data showed that OxLDL, a known activator of monocytes involved in the pathogenesis of atherosclerosis, induces the surface expression and production of osteocalcin in human monocytes. However, no investigations have been conducted yet to evaluate agents that can potentially inhibit the differentiation of monocytes towards an osteogenic phenotype.
Furthermore, as metformin has been shown to inhibit monocyte-to-macrophage differentiation through AMPK activation, we will also investigate in vitro the effects of metformin on the differentiation of monocytes towards the osteoblast-like phenotype.
This project will be the first evaluating pharmacological treatments to target MCCs, which have been identified as a new mechanism of cardiovascular injury, in diabetes. Finally, our expected results will generate new hypothesis about the molecular mechanisms causing the pro-calcific drift of monocytes by specifically evaluating the role of PPAR¿ and AMPK activators on the expression of osteoblast markers in cultured human monocytes.
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