Cystatin C: its correlation with some markers of immune system, inflammation, and its role in progression of diabetic retinopathy in type 2 diabetes

Aim: To study the correlations between Cystatin C (Cys-C) level and values of the markers of immune system and inflammation, and clinical manifestations of diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (DM). Material and Methods. 3 groups of patients with type 2 diabetes and different stages of diabetic retinopathy were formed (21 people in each). Group I – with nonproliferative diabetic retinopathy (NPDR), Group II – with pre-proliferative diabetic retinopathy (PPDR), Group III – with proliferative diabetic retinopathy (PDR). The comparison group included patients with type 2 diabetes without vascular complications. Clinical study included: visometry, tonometry, assessing critical flicker fusion frequency, biomicroscopy of the anterior segment of the eye, ophthalmoscopy, biomicroscopy and ultrasound of the retina, crystalline lens, vitreous body, photographic recording of the fundus, optical coherence tomography. The content of Cystatin C (Cys-C), soluble forms of molecules B7.2 (CD86), 4-1BB, CTLA-4, Tim-3, LAG-3, PD-1, PD-L1, Galectin-9, proteins sICAM-1, SAA, NGAL and enzymes (MPO, MMP-2, MMP-9) was examined in the blood serum with the use of multiplex analysis. Results. As DR progresses, the level of Cys-C increases and becomes higher than in individuals with diabetes: with NPDR higher by 94.1% (p < 0.001), with PPDR – higher by 293.6% (p < 0.001). In individuals with PDR, the concentration of Cys-C is maximum. With DR, the amount of PD-1, PD-1L, NGAL, ICAM-1, MMP-9, and MPO increases in the blood serum; as the severity of DR worsens, the levels of ICAM-1, MPO, and MMP-9 increase. Direct correlations were found between the Cys-C values, on the one hand, and the values of some studied indicators, on the other. Conclusions. In type 2 diabetes and DR, the amount of Cys-C in the blood serum increases relative to individuals with diabetes without microangiopathy; in groups with worsening severity of ophthalmopathy, an increase in Cys-C concentration was recorded with a statistically significant difference between the groups. In groups with DR, the level of ICAM-1, MMP-9, and MPO increases with increasing severity. Moderate direct correlations were found between the amount of Cys-C on the one hand and PD-1, PD-L1, as well as the noticeable ones with the values of ICAM-1, NGAL, MMP-9, MPO on the other. A direct noticeable correlation was revealed between the level of Cys-C and the values of the fundus scale.