Neuroprotective and Blood-Retinal Barrier-Preserving Effects of Cannabidiol in Experimental Diabetes

Abstract

Diabetic retinopathy is characterized by blood-retinal barrier (BRB) breakdown and neurotoxicity. These pathologies have been associated with oxidative stress and proinflammatory cytokines, which may operate by activating their downstream target p38 MAP kinase. In the present study, the protective effects of a nonpsychotropic cannabinoid, cannabidiol (CBD), were examined in streptozotocin-induced diabetic rats after 1, 2, or 4 weeks. Retinal cell death was determined by terminal dUTP nick-end labeling assay; BRB function by quantifying extravasation of bovine serum albumin-fluorescein; and oxidative stress by assays for lipid peroxidation, dichlorofluorescein fluorescence, and tyrosine nitration. Experimental diabetes induced significant increases in oxidative stress, retinal neuronal cell death, and vascular permeability. These effects were associated with increased levels of tumor necrosis factor-␣, vascular endothelial growth factor, and intercellular adhesion molecule-1 and activation of p38 MAP kinase, as assessed by enzyme-linked immunosorbent assay, immunohistochemistry, and/or Western blot. CBD treatment significantly reduced oxidative stress; decreased the levels of tumor necrosis factor-␣, vascular endothelial growth factor, and intercellular adhesion molecule-1; and prevented retinal cell death and vascular hyperpermeability in the diabetic retina. Consistent with these effects, CBD treatment also significantly inhibited p38 MAP kinase in the diabetic retina. These results demonstrate that CBD treatment reduces neurotoxicity, inflammation, and BRB breakdown in diabetic animals through activities that may involve inhibition of p38 MAP kinase.

Vascular endothelial growth factor in eye disease

“…Research demonstrating increased levels of the peroxynitrite biomarker nitrotyrosine in retinas of diabetic patients and experimental animal models supports this concept and implies a role for peroxynitrite in the development of diabetic complications (Abu El-Asrar et al, 2004;Du et al, 2002;ElRemessy, 2003b;Kowluru and Odenbach, 2004;Obrosova et al, 2005). Studies in animal and tissue culture models have demonstrated that increased peroxynitrite formation is directly correlated with diabetes, high glucose-induced VEGF expression, and increased retinal vascular permeability (El-Remessy, 2003a;El-Remessy, 2003b;El-Remessy et al, 2006;El-Remessy et al, 2005). This cycle can be interrupted by treatments that reduce superoxide or peroxynitrite levels or inhibit NOS activity.…”

“…Moreover, exogenous peroxynitrite increases VEGF expression in cultured RECs (Platt et al, 2005). Increases in retinal nitrotyrosine levels and lipid peroxidation have been shown to correlate with VEGF overexpression and breakdown of the blood-retinal barrier, and treatments that reduce peroxynitrite formation have been shown to block the early signs of diabetic retinopathy (El-Remessy, 2003b;El-Remessy et al, 2006). Moreover, VEGF itself has been shown to promote the formation of superoxide anion and peroxynitrite in cultured endothelial cells (El-Remessy et al, 2007;Ushio-Fukai et al, 2002).…”

Diabetes-induced peroxynitrite impairs the balance of pro-nerve growth factor and nerve growth factor, and causes neurovascular injury

“…Blood-retinal barrier function Integrity of the BRB was measured as previously described by our group [3,12]. Plasma was assayed for fluoresciene concentration using a plate reader (excitation 370 nm, emission 460 nm) (BioTek).…”

“…These changes lead to accelerated cell death within the inner retinal and ganglion cells [1][2][3] and blood-retinal barrier (BRB) breakdown resulting in macular oedema and neovascularisation [4]. Clinically, the disease manifests as diabetic retinopathy and eventually leads to impaired vision.…”

“…The molecular link between two well-documented early hallmarks of diabetic retinopathy, i.e. accelerated neuronal death and vascular permeability, remains obscure [1][2][3][10][11][12][13]. While proinflammatory cytokines are known to activate Rho family kinases leading to actin cytoskeleton rearrangement and cell permeability in vasculature, Rho family members are also essential regulators of neuronal survival in the nervous system, as reviewed by Linseman and Loucks [14].…”