Guanhua Chen,1,2,* Yuan Zhang,1,2,* Weimin Wang,2,3,* Yali Jing1,2,* 

1Department of Endocrinology, Endocrine and Metabolic Disease Medical Center, Nanjing Drum Tower Hospital Clinical College of Nanjing University of Chinese Medicine, Nanjing, People’s Republic of China; 2Branch of National Clinical Research Centre for Metabolic Diseases, Nanjing, People’s Republic of China; 3Department of Endocrinology, Endocrine and Metabolic Disease Medical Center, Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Yali Jing, Department of Endocrinology, Endocrine and Metabolic Disease Medical Center, Nanjing Drum Tower Hospital Clinical College of Nanjing University of Chinese Medicine, Nanjing, 210008, People’s Republic of China, Email jingyalidr@163.com

Background: Given the association between diabetic microvascular disease and bone metabolism, we aimed to investigate the correlation between the concentration of the serum bone turnover marker procollagen type I N-terminal propeptide (PINP) and diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM) in this study.
Methods: This was a cross-sectional study. T2DM patients aged ≥ 18 years were consecutively recruited from the inpatient population of the Department of Endocrinology at Nanjing Drum Tower Hospital, between January 2016 and January 2018, and participants were divided into DR and non-DR groups. We compared clinical and laboratory data of patients in the two groups. Logistic regression analysis was employed to investigate the overall risk of DR at the PINP quartiles. Receiver operating characteristic (ROC) curves were conducted to estimate the predictive power of PINP for DR.
Results: A total of 509 patients with T2DM were included in this study (390 males and 194 females), including 148 patients with DR. Age and diabetes duration were independent risk factors for DR, PINP was also an independent protective factor (all P < 0.05). According to the interquartile range of PINP, all participants were divided into four groups. After adjustment for confounders, patients in Q2, Q3 and Q4 all had a decreased risk of DR compared with Q1 group (OR 0.501, 95% CI 0.280~0.894; OR 0.289, 95% CI 0.157~0.533; OR 0.077, 95% CI 0.036~0.165) respectively. Meanwhile, the AUC of DR diagnosed by the combined diagnostic model of PINP with age and duration of diabetes was 0.8271 (95% CI: 0.7911– 0.863).
Conclusion: The PINP level is associated with diabetic retinopathy in patients with T2DM, and PINP was an independent protective factor for DR and may help to predict its progression.

Keywords: diabetic retinopathy, DR, type 2 diabetes mellitus, T2DM, type I N-terminal propeptide, PINP