Background  5-aminolevulinic acid (5-ALA) is a naturally occurring amino acid found in plants and animals. Current studies have found that 5-ALA can enhance insulin sensitivity and improve glucose tolerance, but its role and mechanism in hyperglycemia-induced endothelial cell injury are still unclear.

Objective  This experiment investigates the role of 5-ALA in the oxidative injury of human umbilical vein endothelial cells (HUVECs) induced by persistent hyperglycemia.

Methods  The experiment was designed to include a negative control group, a persistent hyperglycemia group, and 1.0, 10.0, 50.0, 100.0, and 200.0 mmol·L^-1 5-ALA intervention groups. The treatment protocol was that the cells in the 5-ALA intervention groups were pretreated with 5-ALA for 24 h, and then glucose was added to the cell culture solution to a final concentration of 30 mmol·L^-1 for 48 h; the cells in the persistent hyperglycemia group were cultured in a medium with a glucose concentration of 30 mmol·L^-1 for 48 h; the cells in the negative control group were cultured in regular medium for 48h. After the treatment, the cell viability was detected by CCK-8, and the reactive oxygen species (ROS) level, the activities of intracellular antioxidant enzymestotal superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) content were detected with corresponding kits.

Results  Compared with the negative control group, the persistent hyperglycemia group showed decreased HUVECs viability (t=6.620, P < 0.01), increased ROS level (t=-10.671, P < 0.01), decreased activities of antioxidant enzymes T-SOD, CAT, and GSH-Px, and increased content of MDA (t=11.348, 14.302, 14.951, and -12.562, respectively, P < 0.01). After the designed 5-ALA intervention, compared with the persistent hyperglycemia group, the intervention groups showed increased HUVECs viability to varying degrees, of which the 50.0 mmol·L^-1 5-ALA intervention group was the most obvious (t=-5.032, P < 0.01); the intervention groups showed reduced ROS levels in HUVECs to different degrees, of which the 200 mmol·L^-1 5-ALA group had the sharpest reduction (t=11.232, P < 0.01). The 5-ALA intervention also increased the antioxidant enzyme activities and reduced the MDA content. For T-SOD, GSH-Px, and MDA, the effect in the 50.0 mmol·L^-1 5-ALA intervention was the best (t=-8.562, -14.273, and 12.526, respectively, P < 0.01); for CAT, the 100.0 mmol·L^-1 5-ALA intervention had the best effect (t=-21.467, P < 0.01).

Conclusion  Persistent hyperglycemia can increase the level of ROS in endothelial cells, reduce the activities of T-SOD, CAT and GSH-Px, and increase the content of MDA; 5-ALA can extenuate the oxidative injury induced by persistent hyperglycemia to a certain extent.