[Exploration about the protection mechanism of 5-hydroxy-1-methylhydantoin on paraquat poisoning model]

To investigate the effects of 5-hydroxy-1-methylhydantoin (HMH) on kidney injury induced by paraquat (PQ).

Fifteen SPF healthy Kunming mice were randomly divided into normal saline (NS) control group, PQ poisoning model group and HMH intervention group, with 5 mice in each group. PQ poisoning model was challenged by one-time gavage of 30 mg/kg PQ solution. The NS group received the same amount of NS by gavage. The HMH group was given 100 mg/kg of HMH immediately after the model was made and continued to be gavaged. Mice in each group were sacrificed 1 day after HMH gavage and heart blood and renal tissue were harvested for examination. The morphological changes of renal tissue were observed under light microscope by hematoxylin-eosin (HE) staining. The content of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) in renal tissue were detected according to the instructions of the kit. The expression of heme oxygenase-1 (HO-1) and interleukin-1β (IL-1β) in renal tissues were detected by Western Blot. The serum metabolites were detected by gas chromatography time-of-flight mass spectrometry (GC-TOF-MS), the overall distribution of each sample was observed by principal component analysis (PCA), the accuracy of the model was evaluated by multidimensional analysis orthogonal partial least squares-discriminant analysis (OPLS-DA), and the difference metabolites were screened by variable importance in the projection (VIP) value > 1.

Light microscopic observation showed that: glomerular structure in NS group was clear, there was no hyperemia and inflammatory cell infiltration in renal interstitium and blood vessels. In PQ group, some glomeruli atrophy and necrosis, capillary congestion in glomeruli, infiltration of inflammatory cells around glomeruli, swelling of renal tubular epithelial cells, slight stenosis of lumen, and occasional necrosis and exfoliation of epithelial cells occurred. The degree of kidney injury in HMH group was significantly less than that in PQ group. Compared with the NS group, the content of MDA in the PQ group was significantly increased (nmol/g: 6.70±0.84 vs. 2.70±0.43, P < 0.01) and the activity of SOD was significantly decreased (kU/L: 33.30±4.66 vs. 50.20±3.23, P < 0.05), the protein expression of HO-1 and IL-1β were significantly increased (HO-1/β-actin: 1.11±0.12 vs. 0.61±0.13, IL-1β/β-actin: 0.93±0.13 vs. 0.32±0.06, both P < 0.05). Compared with the PQ group, the content of MDA in the HMH group was significantly decreased (nmol/g: 5.10±0.93 vs. 6.70±0.84, P < 0.05) and the activity of SOD was significantly increased (kU/L: 61.00±9.02 vs. 33.30±4.66, P < 0.05), the protein expression of HO-1 was significantly decreased (HO-1/β-actin: 0.77±0.07 vs. 1.11±0.12, P < 0.05), however, there was no significant difference in the protein expression of IL-1β (IL-1β/β-actin: 0.87±0.13 vs. 0.93±0.13, P > 0.05). Metabolite detection results showed that: compared with NS group, the levels of creatinine, glycine, succinic acid, fumaric acid and citric acid were significantly increased in the PQ group (VIP value was 1.50, 1.58, 1.64, 1.74 and 1.95 respectively, all P < 0.05), while the levels of palmitic acid,α-tocopherol and 6-phosphogluconic acid were significantly decreased (VIP value was 1.10, 1.55 and 1.56 respectively, all P < 0.05). Compared with the PQ group, the levels of creatinine and citric acid were significantly decreased in the HMH group (VIP value was 1.50 and 1.86, both P < 0.05), while trans-4-hydroxy-proline, D-glyceric acid, 2, 6-fructose phosphate, 6-phosphate gluconic acid and aminomalonic acid were significantly increased (VIP value was 1.36, 1.55, 1.63, 1.68 and 1.76 respectively, all P < 0.05).

HMH protects kidney injury caused by PQ poisoning by correcting tricarboxylic acids cycle disturbance, lipid peroxidation and energy metabolism disturbance, and its mechanism is related to the regulation of HO-1 protein expression through Nrf2 pathway.