The essential role of prednisolone and the efficacy of immunosuppressive agents in the treatment of INS significantly suggest the involvement of the immune system in its pathogenesis. Both T cells and B cells have been implicated [15]. Noninvasive biomarkers to predict steroid responsiveness could enhance prognostic accuracy, preserve kidney function, and enable a more tailored approach to management. However, there are still unmet needs [4, 16].

Previous reports have discussed the role of LTs in the pathogenesis of NS [7, 14, 17, 18]. However, no prior research has compared urinary LTE4 levels in children with SSNS and SRNS. In the current study, urinary LTE4 levels were found to be significantly elevated in children diagnosed with NS prior to the initiation of steroid therapy, in comparison to healthy controls, which could suggest a potential role of leukotriene pathways in the early inflammatory processes associated with NS. However, the urinary LTE4/U cr ratio did not differ significantly between groups, and pairwise comparisons showed no significant differences among subgroups. The wide 95% confidence intervals of median differences suggest a substantial inter-individual variability, possibly reflecting limitations in sample size. Furthermore, urinary LTE4 levels demonstrated poor predictive performance based on ROC curve analysis, limiting their utility as a biomarker in this cohort.

Although our study focused on the initial steroid response assessed at 4 weeks, as defined by the KDIGO guidelines, we acknowledge that late steroid responders represent a clinically relevant subgroup. To address this, we retrospectively reviewed the full medical records of enrolled patients over the entire two-year study period. No cases of delayed response were identified among the initially steroid-resistant patients, supporting the validity of our classification.

A prior study reported comparable findings, focusing exclusively on patients with SSNS. The urinary LTE4 to U cr ratios were observed to be markedly elevated in the SSNS group compared to the control group. Additionally, children with SSNS exhibited significantly increased levels of urinary LTB4 and LTC4 relative to the controls. In that study, plasma LTE4 and LTB4 levels were found to be significantly higher than in the controls. Yet, a significant correlation was found between proteinuria and urinary LTC4, LTD4, LTB4, and plasma LTB4 in children with SSNS, suggesting a possible involvement of LTs in the development of proteinuria and edema [14].

Consistent results were reported in another study. Patients with active NS revealed gene expression of 5-LO and LTA4 hydrolase compared to controls, whereas there was no significant difference in the degree of expression between SSNS and SRNS. In the patient group, there was also a significant positive correlation between the degree of proteinuria and the expression of 5-LO [18].

Contrary to previous findings, a prior study found no significant difference in LTB4 biosynthesis in polymorphonuclear (PMN) leukocytes between SSNS patients before steroid therapy and a control group of patients with non-inflammatory disease. Also, no significant change was noted in PMN LTB4 biosynthesis in children with SSNS after steroid therapy. The authors concluded that the inhibition of LTB4 production was not involved in the mechanism underlying steroid action in SSNS [17].

While some previous studies have reported a positive correlation between proteinuria and leukotriene levels, we did not observe such a relationship in our cohort. This discrepancy may be due to differences in sample size, or underlying patient characteristics. Our findings suggest that urinary LTE4 levels may not directly reflect proteinuria severity in all clinical contexts and could be influenced by other immunologic factors.

Despite the novel insights provided by this preliminary study, several limitations should be acknowledged. This was a single-center study with small subgroups of patients, and subgroup analyses were not considered in the initial sample size calculation. This may have contributed to the non-significant differences between SSNS and SRNS. Additionally, plasma LTE4 levels were not measured, which could have provided complementary data on systemic leukotriene activity and strengthened the interpretation of urinary findings.

In conclusion, LTs could contribute to the pathogenesis of NS. However, urinary LTE4, when measured at the time of diagnosis and prior to the initiation of corticosteroid therapy, does not appear to serve as a reliable biomarker for predicting steroid sensitivity in children with NS. Future large-scale multicenter studies incorporating both plasma and urinary leukotriene profiles are needed to better define their role in NS pathogenesis and treatment responsiveness.