Baseline characteristics
Among 10,999 study participants, 9221 (83.8%) were followed up during 2011–2016. Of these participants, 1058 patients were diagnosed with diabetes. We excluded 277 patients with one or more glycaemic measures missing at baseline. Additionally, the highest and lowest 0.5% for ANGPTL8 was trimmed, leaving 781 patients for analysis. After the propensity matching, we acquired 769 matched pairs of diabetic patients and control subjects (Figure S1). In diabetic patients, 60.6% (N=466) were newly diagnosed with diabetes, and 39.4% (N=303) had pre-existing diabetes (Table S1). Only 19.5% (N=150) of patients were treated with oral antidiabetic drugs (OADs) or insulin. In patients with medications, 86.6% patients were treated with OADs, 4.7% patients with insulin and 10.7% with a combination of OADs and insulin.
We found that serum ANGPTL8 levels were elevated in diabetic patients compared to control subjects (618.82 318.08 vs 581.20 299.54 pg/mL, p =0.03, Table S2). Furthermore, levels of HbA1c, FPG, 2h PG, fasting insulin, HOMA-IR, low density lipoprotein (LDL), TG, cholesterol, creatinine, and incident rates of hypertension and hyperlipidaemia in diabetic patients were higher than in the control subjects (all p <0.05, Table S2). During up to 5 years of follow-up, there were 19 participants (2.5%) who died and 44 (5.7%) incident cases for the secondary outcomes among 769 control subjects. The incidence of death (N =56, 7.3%) and the secondary outcomes (N =91, 11.8%) were increased in patients with diabetes (all p<0.05, Table S2).
Baseline characteristics of participants with and without diabetes according to quartiles of ANGPTL8 are presented in Table 1. Age, sex, aspartate aminotransferase (AST), creatinine, eGFR and smoking status changed with ANGPTL8 levels in both the diabetic patients and control subjects (all p values <0.05). In control subjects, ANGPTL8 levels were also associated with waist-hip ratio (WHR), systolic blood pressure (SBP), HbA1c and incidence of hypertension (all p values <0.05). ANGPTL8 levels were associated with BMI, smoking status and incidence of hyperlipidaemia in the diabetic patients (all p values <0.05).
Next, we studied correlations between ANGPTL8 levels and related variables in control subjects and diabetic patients using Pearson’s correlation analysis. After controlling for multiple variables, ANGPTL8 levels positively correlated with age (r =0.42), BMI (r =0.10), and creatinine (r =0.11) but inversely correlated with eGFR (r =-0.12) in the control subjects (all p values <0.05) (Table S3, model 3). Moreover, ANGPTL8 levels positively correlated with age (r =0.18), duration of diabetes (r =0.08), 2 h PG (r =0.08), alanine transaminase (ALT) (r =0.07), AST (r =0.13) and creatinine (r =0.10) but inversely correlated with BMI (r =-0.07), high-density lipoprotein (HDL) (r =-0.09) and eGFR (r =-0.13) in diabetic patients (all values <0.05) (Table S3, model 3). The positive correlation of ANGPTL8 with TG (p =0.001, model 2) was also observed, although it diminished after adjusting for other lipid profiles (p =0.41, model 3).
ANGPTL8 correlates with all-cause mortality and renal dysfunction
As shown in Table 2, increasing quartiles of ANGPTL8 were associated with elevated incidences of death and renal dysfunction in the diabetic patients (all p values <0.05) but not in the control subjects. Furthermore, death due to CVD in diabetic patients also increased numerically in the highest quartile of ANGPTL8 levels (p =0.06, Table 2). Binary logistic regression analyses showed that, compared with the first quartile, non-adjusted RRs (96% CIs) (model 1, Table 3) for the primary outcome (all-cause mortality) were 4.67 (1.00-21.92) and 4.64 (1.86-11.59) for the fourth ANGPTL8 quartile in the control subjects and diabetic patients, respectively. The non-adjusted RRs (96% CIs) (model 1, Table 3) for the secondary outcomes were 2.57 (1.04-6.34) and 1.72 (0.95-3.12), respectively, for the fourth ANGPTL8 quartile compared with the first quartile in the control subjects and diabetic patients. However, the associations of ANGPTL8 with all-cause mortality (model 3) only persisted in the diabetic patients, although they were slightly attenuated after additional adjustment for covariables, including age, sex and BMI (RR, 3.59; 95% CI 1.36-9.51; model 2) and further adjustment for lipid profiles and duration and treatment of diabetes (RR, 3.54; 95% CI 1.32-9.50; model 3). Then, we further analysed the association of ANGPTL8 with any single component of the secondary outcomes and found that elevated ANGPTL8 was associated with an increased risk for renal dysfunction in the diabetic patients (RR in quartile 4 vs quartile 1, 12.43; 95% CI 1.48–104.81; Table 3) after adjusting for covariables.
Multivariable-adjusted restricted cubic spline analyses suggested a linear relationship of ANGPTL8 with all-cause mortality in all of the participants ( for nonlinear trend =0.16, p for linear trend =0.01; Figure 1A). Further analysis indicated a significant linear relationship between ANGPTL8 and all-cause mortality in diabetic patients (p for nonlinear trend =0.99, p for linear trend =0.01; Figure 1B) but not in control subjects (p for nonlinear trend =0.26, p for linear trend =0.80; Figure 1C) after adjusting for age, sex, BMI and lipid profiles.
Predictive values of ANGPTL8 for death
We observed that, when ANGPTL8 levels were combined with QFrailty score, there was improvement for death prediction compared with the QFrailty score alone (Figure 2A-2C, Table S4). The AUC for the ANGPTL8 + QFrailty model was 0.71 versus 0.59 for the QFrailty score alone (p <0.001; Figure 2A) in all of the participants. Consistently, the inclusion of ANGPTL8 improved the predictive performance of QFrailty score in diabetic patients (AUC 0.70 vs 0.59; p <0.001; Figure 2B) and control subjects (AUC 0.71 vs 0.57; p =0.01; Figure 2C).