Angiogenin and osteopontin and coronary collateral circulation

We read the publication on “The association between serum angiogenin (AGN) and osteopontin (OPN) levels and coronary collateral circulation in patients with chronic total occlusion” with a great interest. Gürses et al. (1) concluded that “AGN and OPN are associated with better developed coronary collateral circulation and may have therapeutic implications for the promotion of coronary collateral development” and also noted that “the underlying mechanisms remain largely unknown”. We would like to share our ideas on this report. First, the results in this study inconsistent with those reported previously, which demonstrated that AGN level was associated with complications of acute coronary syndrome and AGN was not a marker for revascularization or collateral circulation formation (2). The adjustment for the background of the patients in both the groups might help increasing the clarity of the findings. Certainly, many possible background conditions might affect the result of AGN investigation. For example, the underlying genetic hemoglobin disorders might result in a high AGN level regardless of the occurrence of the acute coronary syndrome or collateral circulation formation (3). In addition, the use of an ACE inhibitor, which is a common drug in the patient with cardiovascular disease, can also affect the level of OPN (4). We agree with the conclusion by Gürses et al. (1) that there might be an unknown mechanism linking AGN or OPN and collateral circulation formation, but there is a possibility that there might be interference or background factors that can alter the AGN or OPN level.