Supplementary Material for: Non-invasive serum LOX: a prognostic signature for fibrosis progression and renal survival in IgA nephropathy

Background: IgA nephropathy (IgAN), the most common primary glomerulonephritis, often presents with advanced renal failure and end-stage renal disease at diagnosis.Till now, there remains a lack of reliable biomarkers for effectively assessing the progression risk of IgAN. Here, we propose lysyl oxidase (LOX), a marker of collagen cross-linking, as a potential biomarker for assessing fibrosis in IgAN.
Method: After evaluating the fibrosis degree by -Masson staining-, measuring LOX levels in serum and kidney tissues, and collecting clinical information, we analyzed the association between LOX and renal fibrosis. Logistic regression analysis was employed to identify significant variables, which were incorporated into a nomogram and machine learning (ML) model.
Results: A total of 128 IgAN patients were enrolled in the study, of which 89 were included in the training cohort and 39 patients in the validation cohort. Serum LOX levels correlated with the area of renal fibrosis (r = 0.673, p <0.001). ROC analysis of LOX showed an AUC of 0.793 and 0.785 with optimal cut-off value of 297.59 pg/mL and 395.02 pg/mL for the prediction of mild and moderate to severe renal fibrosis, respectively. The diagnostic nomogram model for predicting renal function decline within three years incorporated traditional clinical determinants along with the Oxford MEST histological score (model 1), achieving an AUC of 0.740 (95% CI: 0.565-0.914, p < 0.05). In contrast, a model (model 2) that combined traditional clinical determinants with LOX instead of the Oxford MEST histological score demonstrated improved predictive performance, yielding an AUC of 0.806 (95% CI: 0.655-0.956, p < 0.01).
Conclusions: Serum LOX has the potential to predict renal fibrosis in IgAN. When combined with traditional clinical indicators, it may enhance the prediction of IgAN prognosis.

背景：IgA肾病（IgA nephropathy, IgAN）是最常见的原发性肾小球肾炎，确诊时常已进展至晚期肾衰竭及终末期肾病。迄今为止，仍缺乏可有效评估IgAN进展风险的可靠生物标志物。本研究提出，胶原交联标志物赖氨酰氧化酶（lysyl oxidase, LOX）可作为评估IgAN肾纤维化的潜在生物标志物。
方法：本研究通过Masson染色（Masson staining）评估肾纤维化程度，检测血清及肾组织中LOX水平，并收集临床资料，分析LOX与肾纤维化的关联。采用Logistic回归分析筛选显著变量，将其纳入列线图及机器学习（machine learning, ML）模型构建。
结果：本研究共纳入128例IgAN患者，其中89例纳入训练队列，39例纳入验证队列。血清LOX水平与肾纤维化面积呈显著正相关（r=0.673，P<0.001）。LOX的受试者工作特征曲线（Receiver Operating Characteristic curve, ROC）分析显示，其预测轻度肾纤维化的曲线下面积（Area Under Curve, AUC）为0.793，最佳截断值为297.59 pg/mL；预测中重度肾纤维化的AUC为0.785，最佳截断值为395.02 pg/mL。纳入传统临床指标及牛津MEST组织学评分（Oxford MEST histological score）的诊断列线图模型（模型1），可预测3年内肾功能下降，其AUC为0.740（95%CI：0.565~0.914，P<0.05）。相较之下，将牛津MEST组织学评分替换为LOX、联合传统临床指标构建的模型（模型2）预测性能更优，AUC达0.806（95%CI：0.655~0.956，P<0.01）。
结论：血清LOX有望预测IgAN患者的肾纤维化程度，与传统临床指标联合应用时，可进一步提升IgAN预后预测效能。