1 Pomeranian J Life Sci 2021;67(2):1-5 doi: 10.21164/pomjlifesci.728 Can laser therapy modify the secretion of the tissue-type plasminogen activator and its inhibitor in an endothelial cell culture under hyperglycemia? Krzysztof Góralczyk 1, A , Justyna Szymańska 2, B , Zbigniew Ziętek 3, C  , Katarzyna Szot 1 , Jacek Fisz 2, D , Danuta Rość 1, E 1 Nicolaus Copernicus University in Toruń, Collegium Medicum in Bydgoszcz, Department of Pathophysiology, Curie-Skłodowskiej 9, 85-094 Bydgoszcz, Poland 2 Nicolaus Copernicus University in Toruń, Collegium Medicum in Bydgoszcz, Department of Physiotherapy, Techników 3, 85-801 Bydgoszcz, Poland 3 Pomeranian Medical University in Szczecin, Department of Normal and Clinical Anatomy, Powstańców Wlkp. 72, 70-111 Szczecin, Poland A ORCID: 0000-0002-0804-6412; B ORCID: 0000-0003-4091-3704; C ORCID: 0000-0003-4049-7851; D ORCID: 0000-0003-1128-5286; E ORCID: 0000-0002-2971-9882  zzietek@poczta.onet.pl ABSTRACT Introduction: The effect of low-level laser therapy on the secre- tion of tissue-type plasminogen activator (t-PA) and its inhibitor (PAI-1) in an endothelial cell (EC) culture under hyperglycemia is the subject of the presented work. Hyperglycemia associated with diabetes causes vascular EC dysfunction. Low-level laser therapy is a good method to sup- port the pharmacological treatment of diabetes complications. Materials and methods: We used lasers of 2 wavelengths: 635 nm and 830 nm with dose of 2 J/cm2. The experiment was per- formed in vitro in 4 groups of EC: 1 – no glucose in culture medium, no irradiation (control), 2 – glucose, no irradiation, 3 – glucose, laser 635 nm, 4 – glucose, laser 830 nm. After 2 irradiations, cells were counted and the t-PA and PAI-1 antigen (Ag) concentration in the supernatant was measured. Results: In group 2, we observed a statistically significant lower number of cells (p < 0.0001) and a higher concentration of t-PA:Ag and PAI-1:Ag (p < 0.05) compared to the control group. However, in groups 3 and 4, the number of cells increased and the concen- tration of t-PA:Ag and PAI-1:Ag decreased compared to group 2 and nearly reached the values in the control group. Conclusions: Hyperglycemia affects the fibrinolytic activity of ECs which is manifested by a significant increase in t-PA:Ag and PAI:Ag concentrations – recognized markers of endothelial dam- age. Irradiation of ECs by a low-power laser caused attenuation of the adverse effects of hyperglycemia. A tendency towards a decrease in t-PA:Ag and PAI-1:Ag concentration in the super- natant was observed with a significant increase in the number of cells to values close to control. Keywords: low-level laser therapy; endothelial cell culture; t-PA; PAI-1; hyperglycemia. INTRODUCTION A high glucose level in diabetes mellitus (DM) causes a dysfunc- tion in the vascular endothelium that lines the interior surface of blood vessels. The endothelium plays a key role in maintaining vascular homeostasis via the secretion of active agents involved in many biological processes such as hemostasis, angiogene- sis and inflammation [1]. Hyperglycemia induces changes such as an increase of plasminogen activator inhibitor-1 (PAI-1) and endothelin-1 or a decrease in nitric oxide (NO) in the fibrinolytic and vasoactive components. Nitric oxide, by dilating vessels and inhibiting thrombocyte adhesion, is an important factor pre- venting thrombosis [2, 3]. Under conditions of elevated glucose levels, the weakening of endothelial fibrinolytic activity is also associated with an impairment in the binding of tissue-type plasminogen activator (t-PA) with inactive proenzyme plasmi- nogen, which in turn leads to a decrease in plasmin generation – an active enzyme that is responsible for thrombus degrada- tion [4]. A balance in t-PA and its inhibitor PAI-1 is a requirement for the proper functioning of the hemostatic system. Impaired fibrinolysis under hyperglycemic conditions disturbs this state leading to pro-thrombotic complications [5]. Elevated levels of t-PA and PAI-1 were observed in diabetic patients with car- diovascular complications and in patients with ischemic heart disease [6, 7]. Plasminogen activator inhibitor-1 is an independ- ent risk factor for the development of diabetes in healthy peo- ple as elevated levels were observed in patients with DM and cardiovascular diseases [8]. High levels of t-PA and PAI-1 are considered a predictor of vascular complications [9, 10]. Many studies have shown that hyperglycemia reduces cell prolifera- tion and migration, increases apoptosis and also affects the rate of cell aging [11, 12, 13, 14] which interferes with the wound healing process. The treatment of diabetes and its vascular complications, such as leg ulcers, are still a huge challenge for modern medi- cine. A good method for supporting the pharmacological treat- ment of diabetes complications is low-level laser therapy (LLLT) which was developed in the 1960s. During irradiation, photons are absorbed in the mitochondria of the cells, allowing for an improvement in energy metabolism and stabilization of the cell membrane [15, 16]. Low-level laser therapy has a biostimu- lative effect without a temperature increase, is painless, non- invasive and has no side effects, brings pain relief and affects faster recovery [17].