Netrin as a Novel Biomarker and Its Therapeutic Implications in Diabetes Mellitus and Diabetes-Associated Complications

Table 1

The expression of Netrin in retinopathy.

Model	Methods and interventions	Treatment outcomes	References
Streptozotocin-induced diabetic rats (Sprague-Dawley rats).	After diabetes has been induced, rats were randomly divided into group 1 (diabetic eyes without treatment), group 2 (diabetic eyes with PBS treatment), 3^rd group (diabetic eyes with Netrin-1 (5.0 μg/mL) received group), and 4^th group (diabetic eyes with Netrin-1 (5.0 μg/mL) administered group).	The Netrin-1-receiving group was found to suppress and reverse retinal neovascularization significantly at a concentration of 5 μg/mL compared to control and lowest concentration for the Netrin-1-administered group.	[43]
		While a 0.1 μg/mL Netrin-1 displayed a meaningful raise in the no. of new retinal blood vessels, after six weeks’ administration compared to diabetic controls
Patients who have diabetic retinopathy (DR)	A total of 18 diabetic patients were included, of which 10 of them were patients having DR and 8 patients were without DR.	The levels of Netrin-1 and VEGF in the vitreous of patients having DR were expressively higher than those in the controls.	[45]
Oxygen-induced retinopathy (OIR) mouse models	Vitreous liquid samples were collected from the eyes of both groups using the pars plana vitrectomy technique.	Netrin-1 was primarily expressed in GCL and INL of the mouse retina.
	Adequate blood samples were also collected.	Both Netrin-1 and VEGF were substantially upregulated in OIR mice.
Type 2 diabetes patients and streptozotocin- (STZ-) induced diabetes mouse model.	Diabetic patients with DME and control patients without DMF were enrolled +	A substantial elevation of vitreous truncated Netrin-1 by 8 folds in patients with DME	[42]
	Mice received either STZ or sodium citrate buffer as a control group.	A significant augmentation of retinal edema was detected in DMF patients compared to the control.
	After 8 weeks STZ administration, retinal vascular permeability rises by greater than two-fold as compared to the control group.	Truncated Netrin-1 expression was also significantly amplified in the STZ-treated mice.
		An elevation of collagenase matrix metalloprotease 9 (MMP-9) was noted to have the capability of cleaving Netrin-1 into the laminin (VI-V) fragment.
Animal model of oxygen-brought retinopathy (OIR) in C57BL/6J mice	Mice were placed in an oxygen chamber and exposed to less concentrated oxygen for 5 days and returned to room air to induce retinal neovascularization.	Asymmetrical neovascularization and fluorescein outflow were detected around the unperfused parts in the hypoxic cluster.	[46]
	Control mice were exposed only to room air for the same period of time.	The hypoxic cluster showed distended neovascular nuclei into the vitreous humor than the corresponding controls.
	Reverse transcriptase PCR and Western blot analyses were used to examine retinal Netrin-1 mRNA and protein expression.	Netrin-1 mRNA levels were substantially increased in mouse retina of the hypoxic group compared to control.
		Similarly, the extent of Netrin-1 protein in hypoxic than normoxic mice was highly expressed.
Animal model of oxygen-induced retinopathy (OIR) in C57BL/6J mice	Mice were exposed to oxygen (75 ± 2%) for 5 days and then returned to normal air to induce retinal neovascularization.	Excluding UNC5A, Netrin-1 receptor subtypes UNC5B, UNC5C, UNC5D, DCC, and neogenin altogether were expressively amplified in the retinas of OIR mice.	[47]
	Reverse transcriptase PCR and Western blot were used to assess the expression of Netrin-1 receptor subtypes in the mouse retinas.	OIR mice treated with recombinant UNC5B shRNA displayed an intense reduction in neovascular extension into the interior restrictive membrane.
Streptozotocin- (STZ-) induced diabetes rats (adult male Sprague-Dawley rats)	Rats were assigned randomly to a diabetic group (DM) and a control group (C), each group was containing of 10 rats.	Diabetic rats exhibited typical signs of diabetes.	[49]
	A single dose of STZ was administered to the diabetic group, and the control group received just a citrate buffer.	Cataract was detected in the DM group at 3 months after administration of STZ.
		Both Netrin-1 mRNA and protein expression were notably augmented in the retina of DM rats compared to the control group.

PBS: phosphate-buffered saline; DR: proliferative diabetic retinopathy; GCL: ganglion cell layer; INL: the inner nucleic layer; DME: diabetic macular edema; OIR: oxygen-induced retinopathy; STZ: streptozotocin; PCR: polymerase chain reaction; DCC: deleted colorectal cancer; VEGF: vascular endothelial growth factor.