A high triglyceride to high-density lipoprotein cholesterol ratio is associated with poor renal outcome in IgA nephropathy patients

Wei Qin (  qinweihx@scu.edu.cn ) West China Hospital of Sichuan University Gaiqin Pei West China Hospital of Sichuan University Aiya Qin West China Hospital of Sichuan University Lingqiu Dong West China Hospital of Sichuan University Siqing Wang West China Hospital of Sichuan University Xiang Liu West China Hospital of Sichuan University Dandan Yang West China Hospital of Sichuan University Jiaxing Tan West China Hospital of Sichuan University Xiaoyuan Zhou West China Forth Hospital of Sichuan University Yi Tang West China Hospital of Sichuan University


Background
Immunoglobulin A (IgA) nephropathy (IgAN), characterized by diffusely deposited IgA in the kidneys, is the most prevalent primary glomerulonephritis and a leading cause of end-stage renal disease (ESRD), in which 20-40% of IgAN patients reach ESRD 10-20 years after the initial diagnosis [1]. Recognizing risk factors of ESRD would be bene cial for to slowing the progression of IgAN.
Abnormal lipoprotein metabolism, as indicated by a high level of triglycerides (TGs) or a low level of highdensity lipoprotein cholesterol (HDL-C), is common in chronic kidney disease (CKD) [2]. However, TG levels uctuate substantially based on feeding status, thus limiting its utility as a predictive biomarker [3]. The combination of TG and HDL-C, which is the TG/HDL-C ratio, could therefore overcome this problem and has been proposed as a more practical and easy-to-use atherogenic marker than the individual lipid measures alone [4]. Evidence has indicated that it is a good marker for cardiovascular disease (CVD) [4,5] and is correlated with the prevalence of CKD [6,7]. Moreover, it was used as a prognostic factor for different classes of diseases, including mortality in peritoneal dialysis [8], coronavirus disease 2019 [9], type 2 diabetes [10], and CKD [11]. However, there is still a lack of research on the relationship between the TG/HDL-C ratio and IgAN. Whether the TG/HDL-C ratio could be another predictor of IgAN progression remains unknown. To clarify these issues, we conducted this study.

Clinical Data
Patient information, including age, sex, clinical manifestations, laboratory indexes, renal pathology reports, and treatment strategies, was obtained from electronic medical records. Laboratory values included 24-h proteinuria (UPRO), hematuria level (URBC), hemoglobin (Hb), serum albumin (ALB), serum creatinine (Cr), estimated glomerular ltration rate (eGFR), uric acid (UA), triglycerides (TG), total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C). The TG/HDL-C ratio was obtained by dividing the serum triglyceride level by the plasma high-density lipoprotein cholesterol level. Hypertension was de ned as blood pressure > 140/90 mmHg or the use of antihypertensive agents [12]. eGFR was calculated using the CKD-EPI equation [13]. Anemia and hyperuricaemia was de ned as described previously [14]. Renal biopsy samples were evaluated by an experienced pathologist and a nephrologist according to the Oxford classi cation [15] Treatments All patients received optimal support treatment, including a full dose of angiotensin-converting-enzyme inhibitor (ACEI) or angiotensin receptor blockers (ARBs). Glucocorticoids and immunosuppressant therapy included cyclophosphamide (2 mg/kg daily for 3 months), mycophenolate mofetil (1-2 g daily for 6-8 months), tacrolimus (0.03-0.05 mg/kg daily for 6-8 months) or cyclosporin was used based on pathological classi cation and clinical severity according to the guidelines.

Outcome de nition
The renal outcome was progression to ESRD, de ned by commencement of renal replacement therapy or an eGFR < 15 mL/min/1.73 m 2 .

Statistical Analysis
Continuous variables are expressed as the means ± SDs or medians (interquartile ranges). Categorical variables were expressed as numbers and percentages (%). Student's t test or the Mann-Whitney U test was used for continuous variables, and the χ2 test was used for categorical variables. The optimal thresholds of the TG/HDL ratio were obtained according to the highest Youden's index using receiver operating curve (ROC) analyses. Kidney survival in each group was estimated by the Kaplan-Meier method. Univariate and multivariate Cox proportional hazard models were used to evaluate the in uence of clinical and pathological variables on renal outcomes. Three statistical models were used in analysis: model 1 (demographics + pathological features + TG/HDL-C), model 2 (demographics + clinical features + TG/HDL-C) and model 3 (demographics + clinical + pathological features + TG/HDL-C). All of these data were analysed by the software package SPSS 23.0 software package (SPSS, Chicago, IL, USA) and GraphPad Prism 8.0. Two-tailed P < 0.05 was considered statistically signi cant.

Demographic and Clinicopathological Characteristics
A total of 1149 biopsy-proven IgA nephropathy patients from West China Hospital of Sichuan University were nally enrolled in this retrospective study ( Figure 1). The demographic, clinical, and pathologic characteristics of the included patients are shown in Table 1. The median age of the patients was 33 (26-42) years, and 44.5% were men. The median follow-up period was 54.0 months, ranging from 35.6 to 73.2 months. ROC analysis revealed that the optimal cut-off TG/HDL-C ratio with which to predict the progression of ESRD in patients with IgAN was 1.495 (Supplementary Figure 1). Thus, according to their TG/HDL-C ratio at the time of renal biopsy, patients were divided into two groups: a high TG/HDL-C group (TG/HDL ≥ 1.495, N=383) and a low TG/HDL group (TG/HDL-C < 1.495, N=766). The median eGFR in the high TG/HDL-C and low TG/HDL-C groups was 99.9 and 81.3 mL/min/1.73 m 2 , respectively. Compared with the low TG/HDL-C group, patients in the high TG/HDL-C group had a higher incidence of anemia, hyperuricemia and hypertension (all P <0.001), a higher proportion of males (P <0.001), and worse renal function (P<0.001). Moreover, higher levels of TG (P<0.001), TC (P=0.003), UPRO (P<0.001), and Cr (P<0.001) and lower HDL-C (P<0.001) and URBC (P=0.009) levels were observed in the high TG/HDL-C group. Regarding pathological lesions, patients with a high TG/HDL-C always had mesangial hypercellularity (P=0.031), segmental glomerulosclerosis (P=0.028) and tubular atrophy/interstitial brosis (P<0.001). Correlation of the TG/HDL-C ratio with clinical parameters and pathological lesions The correlations between the TG/HDL-C levels and clinicopathological ndings are illustrated in Table 2 and Table 3. Our results showed that TG/HDL-C was signi cantly negatively correlated with the eGFR (r = -0.248, P < 0.001) but positively correlated with proteinuria (r = 0.229, P < 0.001) and serum uric (r =0.306, P< 0.001). Logistic regression analysis was conducted to analyse the relationship between TG/HDL and clinicopathologic features.

Renal Survival
During a median follow-up period of 54.0 (35.6-73.2) months, a total of 78 (6.8%) patients developed ESRD. Kaplan-Meier survival analysis and log-rank tests were used to determine the association of the TG/HDL-C ratio with patient survival. Our results demonstrate that TG/HDL-C ≥1.495 was signi cantly associated with ESRD ( Figure 2, P < 0.001). Subgroup analysis of mesangial hypercellularity and tubular atrophy/interstitial brosis, eGFR<60 mL/min/1.73 m 2 and proteinuria for ESRD by Kaplan-Meier analysis is shown in Figure 3. Our results indicated that a high TG/HDL-C ratio was a risk factor for ESRD in patients with IgAN, especially patients with eGFR<60 mL/min/1.73 m 2 (P = 0.028) (Figure 3. A), 24hour urine protein ≥1 g/day (P< 0.001) (Figure 3. B), or mesangial hypercellularity and tubular atrophy/interstitial brosis (Figure 3. C&D) in pathologic lesions.

Discussion
Dyslipidemia is common in China, with a prevalence of 41.9%, and is commonly characterized by the presence of high TG and low HDL-C in CKD [16]. Recently, the combination of TG and HDL-C, the TG/HDL-C ratio, has attracted increasing attention for its better predictive power for cardiovascular events and insulin resistance than the lonely combination [7,17]. Noticeably, several studies have shown a positively relationship between the TG/HDL-C ratio and renal function decline in CKD patients [6,7,16,18]. However, whether dyslipidemia has a role in IgAN progression remains unknown.
In this study, in a cohort of 1149 biopsy-proven IgAN patients, 78 (6.8%) patients developed ESRD. A higher TG/HDL-C ratio in patients with IgAN was associated with more severe clinical features and pathologic lesions. Our further analysis revealed a higher serum TG/HDL-C level was a risk factor for the progression to ESRD (HR 2.118, 95% CI 1.333-3.367, P = 0.002).
Previous studies have reported that the reduction in renal function in patients is related to high TG/HDL-C levels [11,16], but no study has focused on IgAN patients. To our knowledge, this is the rst study assessing the correlation between the TG/HDL-C ratio and ESRD in IgAN patients. Moreover, the TG/HDL-C ratio has a greater in uence in advanced IgAN patients (eGFR < 60 mL/min/1.73 m 2 ) or these with 24hour urine protein of ≥ 1 g/day in our study. This might be due to the slow progression of mild renal disease, especially within a limited follow-up period [14]. Additionally, we would like to stress that high TG/HDL-C patients tend to have hypertension and more severe renal pathologic lesions of segmental glomerulosclerosis and tubular atrophy/interstitial brosis. Considering that abnormalities in lipid parameter levels could accelerated atherosclerosis is plausible to believe that pathology of IgAN patients with a high TG/HDL-C level.
Abnormalities in lipid parameter levels could lead to impaired renal function and accelerated atherosclerosis [19]. TG usually increases in the early stages of CKD and is associated with delayed catabolism and decreased activity of hepatic TG lipase and peripheral lipoprotein lipase. However, based on feeding status, TG levels could uctuate substantially, thus limiting its utility as a predictive biomarker [3]. HDL-C, inversely associated with outcomes, decreases in patients with CKD [11]. The combination of these two markers could therefore overcome this problem and lead to a far more consistent, stable, fasting measurement of dyslipidaemia, which has indeed attracted much more attention in disease prognosis, including cardiovascular disease [4], diabetes [10], and peritoneal dialysis [8]. Here, the potential mechanisms by which the TG/HDL-C ratio serves as a prognostic biomarker in IgAN patients may be as follows. TG/HDL-C is a reliable indicator of insulin resistance, which induces oxidative stress. Oxidative stress impairs the activation of nuclear factor erythroid-2related factor-2, which protects against kidney tissue injury[16]. The ltered proteins, such as fatty acids, phospholipids, and cholesterol contained in the ltered proteins (albumin and lipoproteins), could include direct toxic effects of lipids on glomerular cells and promote matrix production [2,20]. Moreover, these materials act as damage-associated molecular patterns (DAMPs) and are recognized by Toll-like receptors (TLR2 and TLR4), which can activate in ammatory responses, causing tubulointerstitial brosis and injury in the reabsorption process [21,22]. Additionally, further tissue injury is contributed owing to impaired HDL-mediated reverse cholesterol transport by limiting the unloading of the excess cellular cholesterol and phospholipid burden [21]. Thus, in the future, recognizing the TG/HDL-C ratio as a potentially modi able risk factor for patients may allow the utilization of preventative strategies to optimize both treatment and survival outcomes.
Some limitations warrant consideration. First, this was a retrospective study based on a single-center database. Further multicenter validation in different ethnic populations was needed. Second, the mean follow-up time of 54 months was relatively short. In addition, no data are available on the relationship between the TG/HDL-C ratio and CVD mortality.

Conclusion
The TG/HDL-C ratio may serve as a potential prognostic biomarker in IgAN patients. More attention must be paid to patients with advanced IgAN who have a high TG/HDL-C ratio, eGFR < 60 mL/min/1.73 m 2 , and 24-hour urine protein of ≥ 1 g/day.

Declarations
Ethics approval and consent to participate The research was in compliance with the Declaration of Helsinki and was approved by the ethical committees of West China Hospital of Sichuan University (2019-33). Informed consent was obtained from each patient or their legal guardians prior to treatment.

Consent for publication
All participants signed the consent form and agreed to use data for publish.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.