The results of the current study showed that serum albumin concentration was the major systemic risk factor for the occurrence of TRD in the patients with PDR who underwent vitrectomy with non-silicone oil tamponade.
Albumin, which is the most abundant plasma protein in mammals, playing a decisive role in the maintenance of homeostasis and making a balance between intravascular hydrostatic and colloid osmotic pressure. Serum albumin also has binding substances, anti-inflammatory, antioxidant and other physiological functions. Studies have shown that a decrease in serum albumin concentration enhances vascular endothelial cell permeability possibly by decreasing plasma colloid osmotic pressure and inducing oxidative stress and endothelial inflammatory injury, leading to tissue edema[7, 8].
Increasing the permeability of albumin is a typical feature of diabetic microvasculature, and diabetic retinopathy is one of the diabetic microvascular complications. Some studies have demonstrated that hyperglycemia can increases albumin permeability through a-calpain-dependent mechanism.Coupled with the increase of endothelial cell permeability and the breakdown of the blood-retinal barrier lead to albumin and macromolecule exudation, which lead to vitreous cavity haze and intraretinal exudate formation[10, 11].On the one hand, cell damage or death can lead to exudative fluid accumulation in the subretinal space, which can lead to exudative retinal detachment.On the other hand, this exudate may be an excellent culture medium for proliferating cells, which can form preretinal membrane due to continuous exudation, and its contraction provided mechanical strength for TRD[10, 13] .
Retinal homeostasis disorder can activate Müller cells, lead to cell proliferation, cellular shape change, produce stress fibers, which provided traction for the process of tractive retinal detachment. In addition to Müller cells, astrocytes and microglia are also contribute to retinal fibrosis[13, 14].Hypoosmotic gradients across glial membranes are present in the neural tissues of the retina under conditions associated with ischemia hypoxia and some pathological processes (such as hypoalbuminemia). Under this hypotonic condition, serum albumin can cause the swelling of the glia cells.In order to prevent such osmotic swelling under pathological conditions, retinal glial cells induce the continuous release of purines (in particular, ATP and adenosine)by activating a glutamatergic purinergic receptor[8, 15].In addition, purinergic signals can stimulate the proliferation of retinal progenitor cells and Müller cells, leading to the formation of epiretinal membranes. Furthermore, the traction produced by membrane contraction can further induce Müller cells to release ATP, to aggravate the disease and eventually lead to TRD.
In addition to albumin, there were also differences between the TRD group and the control group in blood urea nitrogen, serum creatinine and PRP before operation. The association between PRP and TRD has been controversial. The PRP could inhibit the expression of some cytokines to reduce neovascularization and retinal vascular leakage[12, 16]. However, a sufficient amount of PRP during the operation would also destroy endothelial cells and aggravate the inflammatory response. Serum creatinine and blood urea nitrogen are markers of vascular pathology and inflammation. Previous studies proved that high blood urea nitrogen and high serum creatine could aggravate the progress of DR. Furthermore, studies have shown that blood glucose and glycated albumin may be associated with postoperative complications of PDR[19, 20]. The consistently elevated blood glucose in retina could destroy the integrity of retinal blood vessels and increase the vascular permeability through oxidative stress and the secretion of pro-inflammatory cytokines, which could lead to the formation of retinal neovascularization, continuous exudation, and epiretinal membranes[19, 20]. However, there was no significant difference in blood glucose and glycated albumin between the two groups in our study, which may be due to the fact that all patients received the same control criteria for preoperative blood glucose levels before the operation.