Objectives Erythropoietin (EPO) have received considerable interest in immunity and inflammation. The increasing number of evidences have shown that inflammation is involved in the initial and development of atherogenesis. We hypothesised that EPO treatment may stabilise atherosclerotic plaques by inhibiting inflammatory cytokine secretion and matrix metalloproteinases (MMPs) expression and promote the proliferation of smooth muscle cells (SMC) in atherosclerotic lesions.

Methods We established a vulnerable carotid plaque model in apolipoprotein E- knockout mice (ApoE-/-) which were feed on high fat diet (HFD). Mice were divided into control, phosphate buffered saline (PBS) and EPO. EPO was injected in tail vein 1 week before HFD and 3 week after HFD twice a week. 8 week after HFD, the mice were sacrificed and drawn tissue after that. The levels of serum total cholesterol (TC) were detected in all mice at immediately, 8 weeks after HFD. The histopathological method was used to detect the parameters of plaque rupture. Immunohistochemical method was used to detect the quantity of macrophages and smooth muscle cells (SMC), the levels of protein expression of matrix metalloproteinase-9 (MMP-9), matrix etalloproteinase-2 (MMP-2), proinflammatory cytokines including transforming growth factor and interleukin-10 in carotid plaque of each group. The differences among the groups were analysed by statistical methods.

Results Lipid levels were significantly higher after 8 weeks of HFD in each experimental group, there was significant difference compared with Lipid level immediately after HFD, but cholesterol levels between groups on day 0, 8 week were no significant differences. At 8 week after HFD, Histopathological analysis showed that the plaque disruption rate was 49%, 49% and 25% in the control, PBS, and EPO group. EPO treatment resulted in a significant decrease in the relative contents of macrophages and lipids and a substantial increase in those of SMCs and collagen in the carotid plaque, leading to an almost 48.9% reduction of plaque vulnerability index. Furthermore, EPO treatment decreased the expression of proinflammatory cytokines, MMP-2 and MMP-9. Most of these therapeutic effects of EPO were found to be mediated by transforming growth factor and interleukin-10. Statistical analysis found that plaque stable index were significantly statistically different and significantly higher in EPO group than the other groups (P < 0.01).

Conclusions Adoptive transfer of EPO changed plaque composition to a stable plaque phenotype and lowered the incidence of plaque disruption in ApoE-/- mice. The major mechanisms involved reduced expression of inflammatory cytokines and MMP-2 and MMP-9, increased the contents of SMCs in the carotid plaque. EPO may provide a novel approach to the treatment of vulnerable plaques.