Diabetic kidney disease (DKD) is a complication of kidney triggered by diabetes, emerging as a microvascular complication under prolonged hyperglycemic conditions (Huang et al., 2019). In China, DKD prevalence among diabetic individuals ranges from 20% to 40%, resulting in a significant increase in morbidity, disability, and mortality rates associated with this condition. Consequently, DKD has been acknowledged as the principal cause of end-stage renal disease (ESRD) and chronic kidney diseases (Xie et al., 2013). Epidemiological statistical analysis has projected that the global population of DKD patients will exceed 100 million by 2030 (Zhang et al., 2015). Additionally, a current retrospective survey revealed that approximately one-third of diabetic inpatients in China have nephropathy (Dai et al., 2023).

The initial indication of diabetic nephropathy is characterized by an increase in renal volume. As the disease progresses, the following can be observed: hyperplasia of renal tethered cells, increase in the tethered matrix, the emergence of fibrinogen deposits, and in severe instances, typical glomerulosclerosis lesions may manifest (Sun and Xie, 2017). Glomerular mesangial cells (GMCs) are the primary functional units of glomeruli, playing vital roles in the functioning of the kidneys. Studies have indicated that the proliferation and hypertrophy of GMCs, coupled with their increased secretion of extracellular matrix (ECM), represent the primary pathological mechanisms driving glomerulosclerosis and fibrosis in DKD (Satirapoj, 2012; Jiang et al., 2011). The ECM components fibronectin-1 (FN-1) and collagen IV (ColIV) are recognized as pivotal constituents. (Apte et al., 2023; Batal et al., 2024). Transforming growth factor-β (TGF-β) is acknowledged as a pivotal component within the intricate cytokine network of DKD and serves as a crucial cytokine in the process of inducing renal collagen deposition (Wolf, 2002; Wolf et al., 2005). Nuclear factor-κB (NF-κB) is a regulator of gene expression involved in inflammation, cell differentiation, apoptosis, and tumorigenesis. It is predominantly distributed in glomerular, interstitial and cells of the tubular epithelium in the kidney (García-García et al., 2014) and is an important component of inflammatory response signaling (Viatour et al., 2005). Studies have confirmed that under the stimulation of hyperglycemia, various inflammatory cells locally appear in the kidney, releasing inflammatory factors, chemokines, adhesion factors, etc., leading to local proliferation and sclerotic pathological changes in the kidney, in which NF-κB has been shown to play a crucial position in multiple signaling pathways associated with these conditions (Snider et al., 2010; Kuhad and Choprak, 2009). The sphingosine kinase 1-1 sphingosine phosphate (Sphk1-S1P) pathway has been shown to promote renal fibrosis by participating in the proliferation of GMCs, excessive deposition of ECM, and local inflammatory responses of glomeruli under diabetic conditions (Xie et al., 2023). Additionally, it may also mediate the local inflammatory response of DKD kidneys through involvement in the NF-κB inflammatory system (Snider et al., 2010; Kuhad and Choprak, 2009).

Plantaginis semen (PS), derived from the seeds of Plantago asiatica L. or Plantago depressa Willd., has a documented history dating back to the ancient ‘Shennong Ben Cao Jing’. Renowned for their high quality as a Chinese herb, these seeds have therapeutic properties, including heat dissipation, diuretic effects, diarrhea alleviation, dampness mitigation, vision enhancement, and facilitation of phlegm expulsion. They are prescribed for various symptoms such as heat drenching, astringent pain, edema, distension, summer dampness, diarrhea, eye redness and swelling, phlegm-heat cough, and gout (Chinese Pharmacopoeia Commission, 2020). Modern pharmacological research has indicated that PS exhibits various beneficial effects, including diuretic, immunomodulatory, hepatoprotective, antioxidant, anti-inflammatory, antiviral, anti-aging, pro-defecation, anti-gout, and other properties (Zeng et al., 2015; Feng et al., 2012; Geng et al., 2009; Huang et al., 2009a, Huang et al., 2009b; Hu et al., 2013; Tang et al., 2007). Additionally, pharmacological investigations have highlighted the efficacy of PS in managing cardiovascular diseases including hyperlipidemia, hyperglycemia, and hypertension (Sun et al., 2019; Lan et al., 2021). The major constituents of PS include iridoids, phenylethanol glycosides, polysaccharides, flavonoids, alkaloids, and others. Iridoids are well-known for their anti-inflammatory, hepatoprotective, and choleretic effects, which help prevent metabolic dysfunction caused by conditions such as hypertension, diabetes, obesity, and more (Zhao et al., 2021; Liu et al., 2019; Hua et al., 2014). Phenylethanol glycosides exhibit a broad range of pharmacological efficacy, low toxicity, and excellent safety characteristics and have been described to be effective against metabolic diseases and their complications (Xue et al., 2018; Fu et al., 2008). Guanidine derivatives have been reported to relieve disorders in glucose metabolism in diabetic mice and alleviate renal injuries in DKD (Gomes et al., 2023; Liu, 2020). Flavonoids are bioactive compounds existing in herbs and have various properties, including antioxidant, anti-inflammatory, antibacterial, antifungal, and anti-tumor activities, which make them significant in both nutrition and pharmacology. Flavonoids have also been shown to have palliative effects on conditions such as diarrhea, mucositis, neuropathic pain, Parkinson's disease, alteration of the bacterial composition of the intestinal flora, reduction of pathogenic strains, promotion of the growth of beneficial strains, and alleviation of clinical symptoms related to cancer chemotherapy (Fernández et al., 2021; Açar et al., 2023; Park et al., 2020). Polysaccharides have been identified to possess anti-tumor, antidepressant, immune-enhancing, and anti-diarrheal activities (Peng et al., 2019; Ma et al., 2023). Moreover, constituents of PS, such as plantagoamidinic acid A, acteoside, and geniposidic acid, have been reported to effectively reduce hyperlipidemia and hyperglycemia (Wang et al., 2009). Investigations have proved the positive therapy effect of PS on kidney disease, including the reduction of blood uric acid levels, inhibition of uric acid transporter protein expression, and decrease in serum creatinine and overexpression of inflammatory factors (Cicero et al., 2021; Yang et al., 2021). Earlier studies conducted by our research have also highlighted the beneficial impact of PS on renal lesions in diabetes mellitus (Yang, 2016), although systematic studies exploring these effects and their underlying mechanisms remain limited.

Herein, we performed this investigation to identify the main chemical compounds of PS through UPLC-QTOF-MS. Furthermore, the research investigated the influence of PS on DKD using both the high glucose (HG) -induced renal mesangial cell model and the streptozocin (STZ) combined unilateral nephrectomy model paired with a high-fat diet (HFD) -induced DKD model. An initial exploration into the role of the SphK1-S1P pathway was also conducted, shedding light on the potential mechanisms involved in the therapeutic benefits of PS in DKD.