Background and aims: Circulating monocytes expressing osteocalcin (CD14+/OCN+) may have a role in vascular calcification in type 2 diabetes (T2D). Considering the protective role of GLP-1 receptor agonists (RA) and pioglitazone on vascular complications of diabetes, we hypothesized that they could prevent monocytic differentiation towards a calcifying phenotype. We aimed to evaluate the acute effect of metformin, GLP1-RA and pioglitazone on the expression of osteocalcin on CD14+ monocytes. Methods: People with T2D on metformin monotherapy starting add-on therapy with a GLP-1 RA (Group A, n=6), or continuing with metformin alone (Group B, n=27) were enrolled. People with HbA1c >7.5%, aged >80 years or estimated glomerular filtration rate ≤30 ml/min/1.73m2 were excluded from the study. Peripheral blood mononuclear cells (PBMCs) were isolated at baseline and one week after enrollment, and levels of CD14+/OCN+ were measured by flow cytometry. Furthermore, an in vitro study was conducted to evaluate the surface expression of osteocalcin in THP-1 cells after 48 hours incubation with oxLDL, metformin or pioglitazone, alone or in combination. Results: Group A and group B were similar in terms of age (65 [62-71] years vs 64 [56-73] years, respectively, p=0.48) and BMI (28.4 [26.0-36.7] kg/m2 vs 28.6 [26.4-31.3] kg/m2, p=0.50), although people starting GLP1-RA showed slightly higher HbA1c values (6.9 [6.7-7.0]% vs 6.2 [6.0-6.5]%, p=0.0013). One week after enrolment, the relative reduction in CD14+/OCN+ circulating cells was significantly greater in group A compared to group B (-53.1[-79.3; -23.6]% vs -16.8[-49.0; -1.9]%, p=0.038). In vitro, oxLDL treatment increased osteocalcin expression (p<0.05), while pioglitazone significantly decreased osteocalcin expression both alone (p=0.03) and combined with oxLDL (p<0.001) (Fig.). In vitro, treatment with metformin did not impact on osteocalcin expression of THP-1 cells. Conclusion: Our data suggests that the expression of osteocalcin on human monocytes may be modulated by GLP1-RA and by pioglitazone, suggesting a novel mechanism of vascular protection for such compounds, which should be confirmed by enlarging the sample size of our observational study and by further mechanistic investigations.
Fig. Expression of OCN on THP-1 cells treated with medium alone, OxLDL or pioglitazone, alone or in combination. Values are percentage relative to THP-1 cells treated with medium alone.