Mobilisation of endothelial progenitor cells: one of the possible mechanisms involved in the chronic administration of melatonin preventing erectile dysfunction in diabetic rats

Abstract

Diabetes-induced oxidative stress plays a critical role in the mobilisation of endothelial progenitor cells (EPCs) from the bone marrow to the circulation. This study was designed to explore the effects of chronic melatonin administration on the promotion of the mobilisation of EPCs and on the preservation of erectile function in type I diabetic rats. Melatonin was administered to streptozotocin-induced type I diabetic rats. EPCs levels were determined using flow cytometry. Oxidative stress in the bone marrow was indicated by the levels of superoxide dismutase and malondialdehyde. Erectile function was evaluated by measuring the intracavernous pressure during an electrostimulation of the cavernous nerve. The density of the endothelium and the proportions of smooth muscle and collagen in the corpus cavernosum were determined by immunohistochemistry. The administration of melatonin increased the superoxide dismutase level and decreased the malondialdehyde level in the bone marrow. This effect was accompanied by an increased level of circulating EPCs in the diabetic rats. The intracavernous pressure to mean arterial pressure ratio of the rats in the treatment group was significantly greater, compared with diabetic control rats. The histological analysis demonstrated an increase in the endothelial density of the corpus cavernosum after the administration of melatonin. However, melatonin treatment did not change the proportions of smooth muscle and collagen in the corpus cavernosum of diabetic rats. Chronic administration of melatonin has a beneficial effect on preventing erectile dysfunction (ED) in type I diabetic rats. Promoting the mobilisation of EPCs is one of the possible mechanisms involved in the improvement of ED.

Figure 1

CD34⁺/KDR⁺ endothelial progenitor cells (EPCs) in circulation. The level of CD34⁺/KDR⁺ cells in peripheral blood was expressed as percentage of CD34⁺/KDR⁺ cells in mononuclear cells. *P<0.05 compared with the diabetic group. DM, diabetic group; Mt, melatonin treatment group; N, normal group.

Figure 2

Erectile function evaluation. (a–c) Representative images of intracavernous pressure (ICP) responding to stimulation of the cavernous nerve of each experimental group: (a) normal group; (b) diabetic group; (c) melatonin treatment group. Red bars represent 60-s electronic stimulation. (d) Results of erectile function expressed as the ratio between ICP and mean arterial pressure (MAP). *P<0.05 compared with the diabetic group. DM, diabetic group; Mt, melatonin treatment group, N, normal group.

Figure 3

Endothelium density in the corpuscavernosum. (a–c) Representative images of endothelium in the corpus cavernosum of each experimental group: (a) normal group; (b) diabetic group; (c) melatonin treatment group. Original magnification is ×100. Scare bar=200 µm. High magnifications of the boxed area in (a′–c′) further show the anti-von Willebrand factor (vWF) expression in corpus cavernosum. Original magnification is ×400. Scare bar=50 µm. (d–f) Representative images of endothelium in dorsal artery of each group: (d) normal group; (e) diabetic group; (f) melatonin treatment group. Original magnification is ×400. Scar bar=50 µm. (g) Results of the endothelium quantification expressed as the ratio of vWF-positive endothelium to in the corpus cavernosum. (h) Results of the endothelium quantification expressed as the ration of vWF-positive endothelium to the α-SMA-positive smooth muscle in dorsal artery. (i) The field in the boxed area was used for quantitative analysis. ^#P<0.05 compared with the diabetic group. α-SMA, α-smooth muscle actin.

Figure 4

Masson's trichrome staining. (a–c) Representative images of Masson's trichrome staining of each experimental group: (a) normal group; (b) diabetic group; (c) melatonin treatment group. Original magnification is ×100. Scar bar=200 µm. (d) Results expressed as the ratio between smooth muscle and collagen in corpus cavernosum. (e) The field in the boxed area was used for quantitative analysis. *P<0.05 compared with the diabetic group.