Bile acid profiles in the discovery cohort
The concentrations of individual bile acids in the good prognosis versus poor prognosis patients in the discovery cohort were presented in Table 1. Eighty-three bile acids were analyzed for each patient (see Materials and Methods). Glyco-hyocholic acid (GHCA) in the good prognosis group showed higher concentrations than that in the poor prognosis group (median and inter-quartile range (IQR): 1168.03 nmol/L, 692.83 ~ 1863.72 nmol/L vs. 557.90 nmol/L, 339.18 ~ 1002.53 nmol/L, P = 0.036), a similar trend was found in tauro‐2β,3α,7α,12α-THBA (91.73 nmol/L, IQR: 52.07 ~ 298.87 nmol/L vs. 51.60 nmol/L, IQR: 34.72 ~ 69.77 nmol/L, P = 0.013). Some other poly-hydroxylated bile acids such as tauro-hyocholic acid (THCA) (P = 0.099), tauro-3α,6α,7α,12α-THBA (P = 0.061), and tauro-3α,6β,7α,12α-THBA (P = 0.099) also showed trends similar to GHCA and tauro‐2β,3α,7α,12α-THBA, with borderline significance. No statistical difference was observed in the concentrations of other bile acids except 3-oxo-CA.
To explore the overall metabolic process of bile acids, concentrations of individual bile acids were summed according to their different categories (Table S2). It was found that the concentration of total tauro-THBAs in the good prognosis group (3607.11 nmol/L, 1851.66 ~ 4506.49 nmol/L) was significantly higher than that in the poor prognosis group (1022.25 nmol/L, 749.59 ~ 1629.08 nmol/L; P = 0.001). No significant differences were observed in other categories, as well the molar ratios of tauro-BAs to glyco-BAs, and the secondary BAs to the primary BAs between these two patient groups.
To analyze in more detail the role of bile acid modification in these two groups of patients, the respective molar ratios of individual bile acids, conjugated versus unconjugated bile acids and some atypical modifications versus unmodified forms were examined (Table 2). The process of hydroxylation (GHCA: GCDCA, THCA: TCDCA) was significantly enhanced in patients with good prognosis compared to the patients with poor prognosis (P = 0.013 and 0.010 respectively). No significant differences were observed in the processes of sulfonation, taurine or glycine conjugation, glucuronidation, or oxide reduction between the two groups.
Bile acid profiles in the validation cohort
To determine whether the results observed in the discovery cohort could be reproduced, the same set of bile acids was profiled in a validation cohort of another 25 JAG1-variant confirmed patients. The difference in the poly-hydroxylated bile acids including GHCA, THCA, three tauro-THBAs (tauro-3α,6α,7α,12α-THBA, tauro-3α,6β,7α,12α-THBA and tauro-2β,3α,7α,12α-THBA) between the two different prognostic groups was confirmed and even more pronounced in the validation cohort (Table 3). Also, the molar ratios of GHCA to GCDCA and THCA to TCDCA as indicators of the bile acids metabolism process via hydroxylation were significantly higher in the good prognosis group than in the poor prognosis group. However, no significant difference was observed for 3-oxo-CA between the two prognosis groups in the validation cohort.
Selection and validation of ALGS prognostic biomarkers
We then focused on the poly-hydroxylated bile acids to determine if they could be used as biomarkers to predict the outcomes of young (one-year-old or less) ALGS patients. The variables with P-value < 0.05 and AUC > 0.7, both in the discovery and validation cohorts, were included as the candidates. Poly-hydroxylated bile acids, GHCA and tauro-2β,3α,7α,12α-THBA, and the molar ratios of GHCA to GCDCA and THCA to TCDCA were initially enrolled.
Optimal cutoffs (GHCA: 607.69 nmol/L, tauro-2β,3α,7α,12α-THBA: 79.88 nmol/L, GHCA: GCDCA: 0.0220, and THCA: TCDCA: 0.0762) were determined using the Youden index in the discovery cohort (Table 4) and these values were applied to predict prognostic outcomes in the validation cohort. The results are seen in Table 5, where, tauro‐2β,3α,7α,12α-THBA achieved an accuracy of 88.00% (92.31% sensitivity and 83.33% specificity), and the molar ratio of THCA to TCDCA achieved a prediction accuracy of 84.00% (100% sensitivity and 67.67% specificity) in the validation cohort.
Univariate and multivariate Cox proportional hazard model
Next, statistical tests of the poly-hydroxylated bile acids (GHCA, THCA, three tauro-THBAs) by Cox proportional hazard model analysis were used to assess their associations with the native liver survivability in the two cohorts using the optimal cutoff values determined in Table 4. Univariate analysis showed that the concentrations of GHCA, THCA, tauro‐3α,6β,7α,12α-THBA, and tauro-2β,3α,7α,12α-THBA affected the native liver survival (Fig. 2), while multivariate analysis indicated that the GHCA concentration was the single independent factor influencing native liver survival (hazard ratio: 6.456, 95%CI: 1.173 - 35.545, P=0.032) (Table 6). The ALGS patients with blood GHCA concentrations of lower than 607.69 nmol/L had a significantly higher death and/or transplantation rate (7/13 died or received liver transplantation at a median age of one year) compared with patients with GHCA concentrations higher than 607.69 nmol/L (2/33 received liver transplantation at 1 year 5 months old and 2 year 2 months old, respectively).