紅斑性狼瘡與非紅斑性狼瘡受試者尿中的嗜中性白血球明膠酶相關性脂質運載蛋白與腎臟發炎的相關性

Abstract

研究目的：狼瘡腎炎（lupus nephritis)至今仍是全身性紅斑性狼瘡 (systemic lupus erythematosus，SLE) 病患發生併發症與死亡的主因之一，早期診斷與迅速治療對於改善狼瘡腎炎病患長期腎臟存活非常重要。嗜中性白血球明膠酶相關性脂質運載蛋白（neutrophil gelatinase-associated lipocalin，NGAL）在多種急性腎臟損傷與慢性腎臟疾病被證實為一個新的生物標記。本研究假設24小時尿中NGAL的排出總量可作為狼瘡腎炎一個新的預測因子。 研究方法：我們共收錄37位SLE病人；19位其他自體免疫疾病的病人作為疾病對照組（disease control group，DC），包括6位修格蘭氏症（SjÖgren’s syndrome）、3位抗磷脂症候群（anti-phospholipid syndrome）、2位混合性結締組織疾病（mixed connective tissue disease）、2位血管炎（vasculitidies）、1位類風溼性關節炎與全身性硬化症重疊症（rheumatoid arthritis and systemic sclerosis overlap）、1位多發性肌炎（polymyositis）、1位成人史迪爾氏症（adult-onset Still’s disease）、1位膜性腎絲球炎（membranous glomerulonephritis）、1位天疱瘡（pemphigus）與1位急性蕁麻疹（acute urticaria）；以及12位健康自願者作為正常對照組（normal control group，NC）。SLE病人組與疾病對照組進一步被分為活動性腎炎組（active nephritis group）與無腎臟侵犯組（non-renal group），分別以SLE-nephritis、SLE-non-renal、DC-nephritis與DC-non-renal組來表示。目前有感染（尤其是泌尿道感染）與糖尿病者皆需排除。SLE病人的疾病活性採全身性紅斑性狼瘡疾病活性指標2000（Systemic Lupus Erythematosus Disease Activity Index-2000，SLEDAI-2K）來評估，而所有病人的腎臟疾病活性採相對應腎臟部份的SLEDAI來評估，統稱為腎臟疾病活性指標（renal Disease Activity Index，renal DAI）。我們以酵素連結免疫吸附法（enzyme-linked immunosorbent assay，ELISA）測量所有研究受試者24小時尿中NGAL與其他三種發炎性標記介白質-10（interleukin-10，IL-10)、變形生長因子-β1（transforming growth factor-β1，TGF-β1)及腫瘤壞死因子-α（tumor necrosis factor-α，TNF-α)的排出總量，並分析其與各臨床指標的相關性，尤其著重於疾病活性與腎臟侵犯的情形。 結果：在所有病人中，只有24小時尿中NGAL（而非其他三種所測量的尿中發炎性標記）的排出總量在活動性腎炎組較無腎臟侵犯組（p = 0.001）與正常對照組（p = 0.000）二組為高；更甚者SLE-nephritis組較DC-non-renal組有顯著性較高的尿中NGAL排出量（p = 0.000），且尿中NGAL的排出量在SLE-nephritis組也有較SLE-non-renal組為高的傾向（p = 0.055）。在所有病人中，尿中NGAL的排出量與腎臟DAI的分數（rs = 0.327，p = 0.022）、血清肌酸酐（rs = 0.398，p = 0.003）、血清白蛋白（rs = -0.400，p = 0.004）、24小時肌酸酐廓清率（rs = -0.420，p = 0.017）與24小時尿蛋白（rs = 0.477，p = 0.000）有顯著性的相關；但若研究族群限制為SLE病人，尿中NGAL的排出量則與SLEDAI的總分（rs = 0.055，p = 0.764）、腎臟以外SLEDAI的分數（rs = -0.234，p = 0.196）及腎臟DAI的分數（rs = 0.099，p = 0.578）沒有顯著性的相關。在多變項邏輯迴歸（logistic regression）的模式，將年齡與性別作控制，24小時尿中NGAL的排出總量被發現為所有病人活動性腎炎一個顯著性的預測因子（p = 0.017），勝算比（odds ratio，OR）為1.112，95%信賴區間（confidence interval，CI）為1.019-1.214。在所有病人中，24小時尿中NGAL的排出總量用接受者操作特徵（receiver operating characteristic，ROC）曲線分析來偵測病人是否有活動性腎炎，其ROC曲線下面積為0.793 （p = 0.001），95%信賴區間為0.660至0.926。 結論：在本研究中，有活動性腎炎的病人較無腎炎者有較高的24小時尿中NGAL排出總量，且與腎臟疾病活性及數種腎臟實驗室指標有很好的相關性，這顯示尿中的NGAL具有潛力可作為腎臟發炎新的生物標記。

Objective: Lupus nephritis remains a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Early diagnosis and prompt treatment are important to improve the long-term renal survival of lupus nephritis. Neutrophil gelatinase-associated lipocalin (NGAL) has been demonstrated as a novel biomarker in various acute kidney injuries and chronic kidney diseases. This study hypothesized that 24-hour urinary NGAL excretion can serve as a new predictor for lupus nephritis. Methods: We enrolled 37 SLE patients, 19 patients with other autoimmune diseases (including 6 SjÖgren’s syndrome, 3 anti-phospholipid syndrome, 2 mixed connective tissue disease, 2 vasculitidies, 1 rheumatoid arthritis and systemic sclerosis overlap, 1 polymyositis, 1 adult-onset Still’s disease, 1 membranous glomerulonephritis, 1 pemphigus and 1 acute urticaria) as the disease control group（DC）, and 12 health volunteers as the normal control group （NC）. The SLE and disease control groups were further subclassified as the active nephritis and non-renal groups, shown as the SLE-nephritis, SLE-non-renal, DC-nephritis and DC-non-renal groups, respectively. Subjects with current infection (especially urinary tract infection) and diabetes mellitus were excluded. Disease activity of SLE patients was assessed by the SLE Disease Activity Index-2000 (SLEDAI-2K). Renal disease activity of all patients was measured by the renal portion of SLEDAI, known as the renal Disease Activity Index (renal DAI). We measured 24-hour urinary excretion of NGAL and other three inflammatory markers, including interleukin-10 (IL-10), transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α) by enzyme-linked immunosorbent assay (ELISA) in all study subjects. We analyzed the relationship between 24-hour urinary excretion of inflammatory markers and clinical parameters, with focus on disease activity and kidney involvement. Results: In all patients, only 24-hour urinary NGAL excretion rather than those of other three measured urinary inflammatory markers was significantly higher in the active nephritis group than in the non-renal (p = 0.001) and normal control groups (p = 0.000). Furthermore, the SLE-nephritis group had significantly higher urinary NGAL excretion than the DC-non-renal group did (p = 0.000) and a tendency of higher urinary NGAL excretion than the SLE-non-renal group did (p = 0.055). In all patients, urinary NGAL excretion was significantly correlated with the renal DAI scores (rs = 0.327, p = 0.022), serum creatinine levels (rs = 0.398, p = 0.003), serum albumin levels (rs = -0.400, p = 0.004), 24-hour Ccr (rs = -0.420, p = 0.017) and 24-hour urine protein (rs = 0.477, p = 0.000). However, when the study population was confined to the SLE patients, urinary NGAL excretion did not correlate with the total SLEDAI scores (rs = 0.055, p = 0.764), extrarenal SLEDAI scores (rs = -0.234, p = 0.196) and renal DAI scores (rs = 0.099, p = 0.578). In a multivariate logistic regression model after adjusting for age and sex, 24-hour urinary NGAL excretion was found to be a significant predictor for active nephritis in all patients (p = 0.017) with an odds ratio (OR) of 1.112 (95% confidence interval (CI): 1.019-1.214). The area under the receiver operating characteristic (ROC) curve of 24-hour urinary NGAL excretion for active nephritis in all patients was 0.793 (p = 0.001), with a 95% CI of 0.660-0.926. Conclusion: In the present study, 24-hour urinary NGAL excretion was higher in patients with active nephritis than in those without nephritis, and was well correlated with renal disease activity and several renal laboratory parameters, which indicates the potential use of urinary NGAL as a novel biomarker for renal inflammation.