Profile of Lipid and Protein Autocoids in Diabetic Vitreous Correlates with the Progression of Diabetic Retinopathy

Abstract

Purpose: : The vitreous is a sink accumulating lipids and proteins with a paracrine function from the retina. This study was aimed at obtaining partial profile of these entities in the normal and diabetic vitreous (V) and exploring whether their presence correlates with retinal pathology.

Methods: : Central V samples were recovered during vitrectomy from individuals without retinal detachment (control), with retinal detachment but without an underlying diabetic retinopathy (NDR), with proliferative (PDR) and non-proliferative (NPDR) diabetic retinopathy. Lipid autocoid profiles were determined by mass spectrometry-based lipidomics using a triple quadruple linear ion trap LC/MS/MS system and multiple reaction monitoring of specific transition ions. Proteins were screened for 40+ angiogenic modulators and selected proteins were targeted for quantitative analysis (QA) using protein arrays.

Results: : Lipid autocoid profiles reveal the presence of arachidonic acid (AA)-derived 5-hydroxyeicosatetraenoic acid (HETE), 15-HETE and 19-HETE and the docosahexaenoic acid (DHA)-derived resolvin 4-HDHA in the diabetic but not the control samples. Only the levels of 5-HETE, a product of 5-lipoxygenase (LOX), was more than 2 times higher in NPDR as compared to PDR patients (109.66±17.49 vs. 46.13±9.92 pg/mg protein, p=0.005). Protein array analysis revealed marked differences in the distribution of numerous angiogenic modulators in the control vs the pathological samples with a pattern suggesting that retinal detachment contributes to many of these changes. QA reveals, however, marked differences in the concentration range of specific proteins in the different sets of samples.

Conclusions: : The diabetic vitreous contains elevated levels of many angiogenic proteins with some of these changes attributable to retinal detachment and other changes associated with diabetic progression. In contrast, the lipidomic changes appear to be diabetic-specific. Lipoxygenases are regulators of chronic inflammation and oxidative stress generation. A recent study showed that diabetes-induced retinopathy was significantly reduced in 5-LOX-deficient mice (Gubitosi-Klug et al, 2008). 5-HETE is the initial AA metabolite of the 5-LOX cascade; its increased levels may be an index of elevated inflammatory and oxidative processes, which underlie the pathogenesis of diabetic retinopathy.

Keywords: diabetic retinopathy • vitreous • eicosanoids