Plantaginis Semen ameliorates diabetic kidney disease via targeting the sphingosine kinase 1/sphingosine-1-phosphate pathway

Plantaginis Semen (PS) is widely utilized as a common herb in several Asian countries, particularly China, due to its diuretic, anti-hypertensive, anti-hyperlipidemic, and anti-hyperglycemic properties. Furthermore, it is acknowledged for its ability to mitigate renal complications associated with metabolic syndrome. Despite its extensive usage, there is limited systematic literature elucidating its therapeutic mechanisms, thus emphasizing the necessity for comprehensive investigations in this field. This study aims to comprehensively evaluate the therapeutical potential of PS in treating diabetic kidney disease (DKD) and to elucidate the underlying mechanisms through in vivo and in vitro models. The main composition of PS were characterized using the UPLC-QTOF-MS method. For the in vivo investigation, a mouse model mediated by streptozocin (STZ) associated with a high-fat diet (HFD) and unilateral renal excision was established. The mice were split into 6 groups (n = 8): control group(CON group), DKD group, low-dose of Plantago asiatica L. seed extract group (PASE-L group, 3g/kg/d), medium-dose of PASE group (PASE-M, 6g/kg/d), high-dose of PASE group (PASE-H, 9g/kg/d), and positive drug group (valsartan, VAS group, 12 mg/kg/d). After 8 weeks of treatment, the damage induced by DKD was evaluated by using relevant parameters of urine and blood. Furthermore, indicators of inflammation and factors associated with the SphK1-S1P signaling pathway were investigated. For the in vitro study, the cell line HBZY-1 was stimulated by high glucose (HG), they were then co-cultured with different concentrations of PASE, and the corresponding associated inflammatory and sphingosine kinase 1/sphingosine-1-phosphate (SphK1-S1P) factors were examined. A total of 59 major components in PS were identified, including flavonoids, iridoids, phenylethanol glycosides, guanidine derivatives, and fatty acids. In the mouse model, PS was found to significantly improve body weight, decrease fasting blood glucose (FBG) levels, increased glucose tolerance and insulin tolerance, improved kidney-related markers compared to the DKD group, pathological changes in the kidneys also improved dramatically. These effects showed a dose-dependent relationship, with higher PASE concentrations yielding significantly better outcomes than lower concentrations. However, the effects of the low PASE concentration were not evident for some indicators. In the cellular model, the high dose of PASE suppressed high glucose (HG) stimulated renal mesangial cell proliferation, suppressed inflammatory factors and NF-κB, and decreased the levels of fibrillin-1(FN-1) and collagen IV(ColIV). Our results indicate that PS exerts favorable therapeutic effects on DKD, with the possible mechanisms including the inhibition of inflammatory pathways, suppression of mRNA levels and protein expressions of SphK1 and S1P, consequently leading to reduced overexpression of FN-1 and ColIV, thereby warranting further exploration.