Reduction and stabilization of bilirubin with obeticholic acid treatment in patients with primary biliary cholangitis

Abstract Background & Aims Total bilirubin is a predictor of survival in primary biliary cholangitis, with the main elevated component being direct bilirubin. The purpose of this post hoc analysis was to assess the efficacy and safety of obeticholic acid across quartiles of varying baseline levels of direct bilirubin in the phase 3, randomized, placebo‐controlled Primary Biliary Cholangitis Obeticholic Acid International Study of Efficacy. Methods This analysis assessed patients on the basis of their baseline direct bilirubin level (divided by quartile). Biochemistry and safety outcomes were evaluated within each quartile over time. Results In the quartile with the highest baseline direct bilirubin (>5.47 µmol/L), there was a significant reduction in both direct and total bilirubin at Month 12 compared with placebo. Least squares mean (standard error) change from baseline in direct bilirubin at Month 12 was 4.17 (1.42) µmol/L for placebo, −3.48 (1.63) µmol/L for obeticholic acid 5‐10 mg and −3.66 (1.51) µmol/L for obeticholic acid 10 mg (P < .0001, obeticholic acid vs placebo); the corresponding values for total bilirubin at Month 12 were 4.38 (1.55) µmol/L for placebo, −4.53 (1.83) µmol/L for obeticholic acid 5‐10 mg and −5.06 (1.64) µmol/L for obeticholic acid 10 mg (P < .0001, obeticholic acid vs placebo). Conclusions Obeticholic acid treatment was associated with significant reductions in total and direct bilirubin, particularly in patients with high baseline direct bilirubin. Because raised direct bilirubin levels, even within the normal range, are predictive of survival in primary biliary cholangitis, these results suggest substantial benefits of obeticholic acid in at‐risk patients.


| INTRODUC TI ON
Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease characterized by inflammation and the progressive destruction of bile ducts, cholestasis, eventual cirrhosis and death. 1,2 The prognostic significance of several liver chemistries has been evaluated and found to be associated with disease progression, including alkaline phosphatase (ALP), aspartate aminotransferase (AST) and albumin, with bilirubin being identified as one of the key predictors of survival and prognosis in patients with PBC. [3][4][5] Rising total bilirubin levels are a late-stage feature of PBC and are associated with negative long-term outcomes in patients with the disease. 6,7 In an analysis of liver chemistries associated with longterm outcomes in patients with PBC, a total bilirubin level >1x the upper limit of normal (ULN) was a key inverse predictor of transplant-free survival (hazard ratio: 5.06); 86% of patients with a total bilirubin level ≤1xULN survived for 10 years after enrolment compared with 41% of patients with levels >1xULN. 7 In addition, it has been found that total bilirubin values, even within the normal range, may have prognostic significance; for example, Trivedi et al showed that the optimum cut-off value for total bilirubin in predicting liver transplantation or death was 0.70xULN. 5 The Global PBC Study Group similarly established that rising total bilirubin levels, even within the normal range, are predictive of the 5-year risk of liver transplantation or death. 8 In fact, multiple guidelines, response criteria and risk score calculators used for PBC agree that the stabilization or reduction in total bilirubin levels corresponds to reduced risk for disease progression, highlighting the need for PBC treatment options that can stabilize or reduce bilirubin levels in patients with PBC. 4,6,[9][10][11][12][13][14][15][16][17] Most studies and prognostic scores report on only total bilirubin, although a key disease-related component of total bilirubin is direct or conjugated bilirubin. [6][7][18][19][20] Tahtaci et al evaluated various haematological and biochemical parameters in patients with advanced or early-stage PBC and found that, of total and direct bilirubin, only direct bilirubin level was significantly higher in patients with latestage disease. 21 Although fractionation of total bilirubin is not a routine clinical laboratory assessment at this time, the American College of Gastroenterology's clinical guidelines for the evaluation of abnormal liver chemistries recommends that total serum bilirubin levels be separated into direct and indirect fractions. 22 These guidelines state that direct bilirubin elevations, and not indirect elevations, are often present in cholestatic disorders with impairment in bile flow. 22 In PBC, the levels of bilirubin are elevated mainly by its direct fraction.20,23 Taken together, these data and recommendations suggest that direct bilirubin may be a more sensitive marker for PBC severity than total bilirubin. However, given that total bilirubin is more commonly evaluated, it has emerged as the dominant prognostic marker in various multivariate analyses assessing treatment response and natural history of PBC.
Obeticholic acid (OCA) is a potent and selective farnesoid X receptor agonist that is indicated for PBC as second-line therapy in combination with ursodeoxycholic acid (UDCA) in adults with an inadequate response to UDCA or as a monotherapy in those unable to tolerate UDCA. [24][25][26] While the approval of OCA is based largely on reduction in ALP, beneficial effects in bilirubin have also been noted.
A phase 2, international, randomized, double-blind, placebo-controlled study of OCA as monotherapy showed a decrease from baseline in direct bilirubin levels in patients treated for 3 months with OCA 10 mg and OCA 50 mg compared with placebo. 27 A phase 2, randomized, double-blind, placebo-controlled trial of patients with PBC who had an inadequate response to UDCA also showed decreases in direct bilirubin levels in response to OCA 25 mg and OCA 50 mg compared with placebo. 28 In the pivotal, phase 3 PBC OCA International Study of Efficacy (POISE) trial, daily doses of OCA 5-10 mg resulted in a significantly greater number of patients achieving the primary endpoint (ALP<1.67xULN with a ≥15% reduction in ALP from baseline and a total bilirubin level ≤ULN at Month 12) compared with placebo. 25 Compared with a progressive increase in total bilirubin in the placebo group at Month 12 (2 ± 0.70 μmol/L), patients in the OCA 5 mg Although total bilirubin is predictive of outcomes, direct bilirubin is the main elevated component in PBC. As such, this post hoc analysis assessed the efficacy and safety of OCA across quartiles of varying baseline levels of direct bilirubin in POISE.

| Study design
Detailed methods for POISE, including a CONSORT diagram, were previously published (ClinicalTrials.gov, NCT01473524). 25 Briefly, patients with PBC and an inadequate response to or intolerance of UDCA were randomly assigned to placebo, OCA 5-10 mg, or OCA 10 mg in the 12-month, double-blind, placebo-controlled, phase 3 study. 25 The primary composite endpoint in POISE was ALP<1.67xULN with a ≥15% reduction in ALP from baseline and a total bilirubin level ≤ULN at Month 12. 25 The ULN for total bilirubin was defined as 19.32 μmol/L for women and 25.48 μmol/L for men, and the ULN for direct bilirubin was defined as 3.42 μmol/L for all

Key points
Treatment with obeticholic acid for 12 months improved or stabilized biochemical markers associated with negative long-term outcomes in patients with primary biliary cholangitis, especially in patients who were considered to be at risk of disease progression.
patients. After the double-blind phase, patients could enrol in the open-label extension (OLE) phase, in which all patients were treated with OCA.
In this post hoc analysis, patients in the POISE intent-to-treat population (N = 216) were pooled across treatment groups and equally divided into quartiles by baseline direct bilirubin levels (as this is the main elevated component in PBC) to investigate whether there was a relationship between baseline direct bilirubin level and laboratory measures throughout the course of the study. 20,25 Efficacy and safety analyses were evaluated by direct baseline bilirubin quartiles and treatment groups (Table 1). For comparison with results from direct bilirubin quartiles, efficacy was also evaluated by total bilirubin quartiles. For the assessment of efficacy response rate, discontinuations were considered non-responders as a conservative form of imputation. Analyses were performed for the double-blind phase (initial 12 months); long-term evaluation was performed for the OLE of POISE for up to 36 months of OCA treatment and is presented in the supplemental material. For the OLE analyses, patients were evaluated from the time they initiated OCA treatment; for patients randomly assigned to placebo during the double-blind phase, the baseline value was the visit immediately prior to OCA initiation.
The POISE protocol was approved by local and national ethics and regulatory agencies and was conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki (Seoul, South Korea, October 2008 amendment). 27 Written informed consent was obtained from each patient included in the study.

| Baseline characteristics
Baseline values for most demographic characteristics, UDCA use/ dose and albumin were generally similar across direct bilirubin quartiles ( Table 2). Of the patients who had direct bilirubin levels above the ULN (quartiles 3 and 4), most (83%) had total bilirubin levels within the normal range. The number of male patients and ALP and total bilirubin levels increased progressively by direct bilirubin quartile, whereas platelet count progressively decreased within increasing direct bilirubin quartiles. Baseline values for AST, ALT and GGT did not show clear patterns across quartiles, although the mean value of each of these markers was highest in quartile 4.

| Efficacy
In a comparison between quartiles, direct bilirubin levels remained stable in quartiles 1 and 2 across all treatment groups ( Figure 1A

| Safety and tolerability
In patients receiving OCA 5-10 mg during the double-blind phase, similar incidences of pruritus were observed in each baseline direct bilirubin quartile, and they remained generally similar to placebo in quartiles 1 and 2; however, the incidence of pruritus generally increased with increasing quartiles in the OCA 10 mg group compared with placebo (Table S1). One death unrelated to OCA occurred in a patient receiving OCA 5-10 mg; the patient was in direct bilirubin quartile 4. During the OLE, the exposure-adjusted treatment-emergent adverse event rate for the total OCA group generally increased with increasing direct bilirubin quartile for overall adverse events, pruritus, serious adverse events and hepatobiliary disorders (Table S2). Hyperbilirubinemia was reported in 1 patient during the OLE in quartile 4 (data not shown). One death occurred in the OLE that was deemed unrelated to OCA.29 In direct bilirubin quartiles 1 and 2, there were no statistical differences between treatment groups in pruritus VAS scores; pruritus VAS scores were statistically higher in the OCA 10 mg group relative to placebo during the first 3-6 months of OCA treatment in direct bilirubin quartiles 3 and 4 ( Figure S13). The median change from baseline in pruritus VAS scores for all treatment groups was ≤1 at all time points in the double-blind phase in quartiles 1 and 2 (data not shown).
After 36 months of the OLE, a general increase in pruritus VAS scores was observed in direct bilirubin quartiles 3 and 4 ( Figure S14).

| Summary of the results and their implications
These results suggest that high baseline direct as well as total bilirubin levels identify the risk for worsening of biochemistry in patients bile flow, altered bile ductular integrity or reduced production of bile because of defective activity of bile efflux transporters. 20,32 Results from this study support previous data showing that OCA may improve total and direct bilirubin levels 25 ; however, the novelty of the analyses performed in this study resides in the in-depth evaluation of the effect of OCA across various baseline direct and total bilirubin levels. The demonstrated benefits of OCA in the analyses shown here are expected to be clinically significant, as UDCA-treated patients with PBC who had higher total bilirubin levels, even within the normal range, were shown to have an increased risk of liver transplantation or death compared with patients with lower total bilirubin levels. 5,8,33 Our finding that OCA reduces both total and direct bilirubin in patients with elevated direct bilirubin (quartile 4) supports the potential for OCA to delay the occurrence of outcome events, as a bilirubin level of 1.60xULN is associated with an accelerated increase in bilirubin and a median time of 19 months to an outcome event.34 Even with total bilirubin levels well within the normal range, the data presented here indicate that direct bilirubin levels may be significantly elevated.
Although many guidelines and established risk criteria include total bilirubin, lower thresholds within the normal range may need to be considered for clinical use. 4,6,[9][10][11][12][13][14][15][16][17] This is further exemplified by the inclusion of total bilirubin as a continuous variable within the UK-PBC risk score and Global PBC risk score, suggesting that lower total bilirubin levels within any range contribute to a lower risk of liver-related/all-cause mortality and liver transplantation. 9,16 These findings support the use of direct bilirubin measurements as a potentially more distinct marker of disease progression, which may shape the standards currently used in the field. However, in clinical practice, direct bilirubin levels are typically measured only when total bilirubin level is above the ULN, a fact that may attenuate this proposal.

| Limitations of the study
The analyses performed here are post hoc; therefore, this study was not specifically powered to detect differences within quartiles. In addition, data presented from the OLE did not include a placebo group for comparison to account for natural disease progression. The study population was not representative of one with a high incidence of jaundice; jaundice occurs at total bilirubin levels above 51.30 μmol/L, and the highest total bilirubin quartile in POISE showed a mean level of 19.12 μmol/L. 35

| Strengths of the study
The analyses presented here support the benefits of OCA for various PBC liver chemistries, including total and direct bilirubin levels, even in at-risk patient populations. The data used for these analyses were collected prospectively as part of an international, randomized, placebo-controlled, phase 3 study.

ACK N OWLED G EM ENTS
Technical and editorial support for this manuscript was provided by

E TH I C A L A PPROVA L S TATE M E NT
The POISE protocol was approved by local and national ethics and regulatory agencies and was conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki (Seoul, South Korea, October 2008 amendment).

PATI E NT CO N S E NT S TATE M E NT
Written informed consent was obtained from each patient included in the study.