EVect of panretinal photocoagulation on serum levels of laminin in patients with diabetes: a prospective study

Background/aim—Laminin, a major specific non-collagenous glycoprotein of basement membrane, has been proposed as an index of diabetic retinopathy and high serum concentrations have been reported in patients with proliferative diabetic retinopathy. On the other hand, panretinal photocoagulation (PRP) prevents the progression of severe diabetic retinopathy and reverses preretinal neovascularisation. The aim of the study was to investigate the eVect of PRP on serum levels of laminin in patients with diabetes. Methods—20 patients with diabetes undergoing PRP and 15 patients with mild or moderate non-proliferative diabetic retinopathy in whom a PRP was not performed were included in the study. Serum laminin-P1 (Lam-P1), the largest pepsin resistant fragment of laminin, was determined by radioimmunoassay in each patient before starting PRP and 3 months after it was accomplished. Similarly, a baseline and a 4 month sample were analysed in the non-photocoagulated controls. Results—Serum Lam-P1 concentrations obtained 3 months after PRP were significantly lower when compared with the initial values (1.62 (SD 0.36) U/ml v 1.91 (0.37) U/ml; p <0.001). A decrease of serum levels of Lam-P1 could be seen in all patients. By contrast, in those patients with mild or moderate non-proliferative diabetic retinopathy in whom a PRP was not performed, no significant changes were detected in serum Lam-P1 concentrations (1.72 (0.20) U/ml v 1.74 (0.17); p=0.250). Conclusion—PRP decreases serum Lam-P1 levels in patients with severe diabetic retinopathy. Thus, the studies addressed to evaluate the usefulness of Lam-P1 as a marker of diabetic retinopathy should consider previous PRP as an influencing factor. Finally, our results suggest that retinal source of Lam-P1 strongly contributes to serum Lam-P1 in patients with severe diabetic retinopathy. (Br J Ophthalmol 1999;83:1056–1059) Diabetic microangiopathy is associated with important disturbances in the metabolism of basement membranes. Because the serum levels of basement membrane (BM) constituents could reflect these metabolic changes, their usefulness as markers of diabetic microangiopathy has been extensively investigated. In this regard, serum levels of laminin, a major specific non-collagenous glycoprotein of BM, have been proposed as an index of diabetic microangiopathy, and high concentrations have been reported in patients with diabetes with proliferative diabetic retinopathy. 3 Notably, laminin contributes to the net increase in BMs that occurs during diabetic retinopathy (DR) and is one of the main constituents of the periodic acid SchiV positive material deposited in BMs of retinal vessels of patients with DR. Proliferative DR is characterised by the presence of complex mechanisms that favour degradation and synthesis of BM de novo. Proliferating endothelial cells digest BMs mainly proteolytically during the migratory phase of their growth and lay down new BM components as new vessels become established. 6 Retinal ischaemia has a crucial role as a trigger of these phenomena. 8 Panretinal photocoagulation (PRP) eliminates ischaemic areas and allows redistribution of blood flow to spared areas, thus improving the situation of retinal hypoxia and clinical studies have demonstrated the eYcacy of PRP in preventing the progression of severe DR and reverting to preretinal neovascularisation. Thus, it is tempting to speculate that PRP could decrease laminin serum concentrations in patients with diabetes with proliferative DR. However, PRP has not been previously considered as a variable that could influence serum laminin concentrations in patients with diabetic retinopathy (DR), and there are no studies focused on the eVect of PRP on serum levels of laminin. Furthermore, because of the isolated intervention of laser treatment on ocular vessels, the eVect of PRP on serum concentrations of laminin could provide a new insight into the contribution of the retinal source of laminin to its serum levels in patients with severe DR. On this basis, we have designed a prospective study to determine the eVect of PRP on serum laminin-P1 (the largest pepsin resistant fragment of laminin) levels in patients with severe DR. Patients and methods Twenty consecutive patients undergoing bilateral PRP because of severe DR (>51 according to the Wisconsin grading system) were included in the study. Fifteen patients with mild or moderate non-proliferative DR and comparable for variables shown in Table 1 Br J Ophthalmol 1999;83:1056–1059 1056 Diabetes Unit, Endocrinology Division, Hospital General Vall d’Hebron, Barcelona, Spain