Obeticholic acid and resveratrol in nonalcoholic fatty liver disease: All that is gold does not glitter, not all those who wander are lost
Authors: Giovanni Musso
Journal: Hepatology (2015)

Article 1: One hundred forty-one patients without cirrhosis with NASH were randomized to 72 weeks of obeticholic acid (OCA) or placebo. At the end of treatment, OCA significantly improved histological features of NASH. Article 2: Twenty overweight/obese NAFLD patients were randomized to 3 g of resveratrol or placebo for 8 weeks. At end of treatment, resveratrol did not significantly improved any liver-related or metabolic feature. Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the Western world; nonalcoholic steatohepatitis (NASH), the progressive form of NAFLD, is the third-leading cause of end-stage liver disease and is projected to become the most common indication for liver transplantation in the next decade. Despite these premises, there are no approved pharmacological therapies for NASH, highlighting the urgent need to develop effective therapeutic strategies for this condition. The results of two long-awaited randomized, placebo-controlled trials (RCTs), targeting two putative mechanisms of liver injury in NAFLD, have been recently published: The multicenter Farnesoid X Receptor Ligand Obeticholic Acid in NASH Treatment (FLINT) trial evaluated the effect of 72 weeks of obeticholic acid (OCA), a potent semisynthetic bile acid agonist of farnesoid X nuclear receptor (FXR) on liver histology in 283 biopsy-proven NASH patients.1 The second smaller, placebo-controlled, proof-of-mechanism RCT assessed the impact of the natural polyphenol, resveratrol, on radiological/biochemical markers of liver disease and on multiple, thoroughly assessed metabolic parameters in 20 overweight/obese patients with NAFLD.2 Although the FLINT trial reported an improvement in liver histology in NASH, high-dose resveratrol supplementation did not ameliorate any liver-related or metabolic parameter. However, some issues warrant clarification to more correctly interpret the results from these RCTs. In the FLINT trial, there was a striking difference between the effect of OCA on the primary outcome (2-point improvement in NAFLD activity score [NAS]) and on definite NASH resolution (Table 1, panel A): Among patients on OCA, 45% met the primary endpoint of NAS improvement, but only 22% of patients showed NASH resolution (P = 0.08 vs. placebo). The discrepancy between the primary endpoint and NASH resolution observed in the FLINT trial could also be observed, but in the opposite direction, in the Pioglitazone versus Vitamin E versus Placebo for the Treatment of Nondiabetic Patients with Nonalcoholic Steatohepatitis (PIVENS) trial (clinicaltrials.gov: NCT00063622), the other large RCT with histological endpoints in NASH, where, among patients treated with pioglitazone, 34% showed NAS improvement and 47% patients had NASH resolution (Table 1). ↔ Liver enzymes ↔ Steatosis (MRS) ↔ s-CK18 ↔ Serum IL-1, IL-6, IL-8, CRP, and TNF-α ↔ Peripheral/hepatic/adipose IR (clamp) ↔ Body/visceral fat ↔ Oxidative stress markers ↔ REE/RQ ↓ Liver enzymes ↓ Steatosis (US) ↓ s-CK18 ↓ Serum IL-6, CRP, and TNF-α ↓ Blood NF-κB activity ↓ ALT ↓ Steatosis (MRS) ↓ HOMA-IR ↓ Serum IL-1, TNF-α, and leptin ↑ AMPK activation ↑ SIRT-1/PGC-1α ↔Liver enzymes ↔Steatosis (MRS) ↔Body/visceral fat ↔Peripheral/hepatic/adipose IR (clamp) ↔REE/RQ ↔AMPK activation ↔SIRT-1/PGC-1α The different impact of active treatment on these two histological endpoints between the PIVENS and the FLINT trials is attributable to the different primary outcome definitions specified in these two RCTs: Both RCTs targeted a 2-point improvement in NAS score as the primary outcome, but in the FLINT trial, the 2-point NAS improvement could occur in any histological feature of NAS (steatosis, ballooning, and lobular inflammation), whereas the PIVENS trial required an improvement in either ballooning or lobular inflammation to occur. Consequently, in the FLINT trial, 78% of patients treated with OCA and 51% of those meeting the primary outcome at the end of treatment still had NASH (Table 1, panel A). These observations raise two questions: How do we determine endpoints of effectiveness in NASH therapy? And, extending this issue to future trial design, which endpoint should we target when evaluating strategies aiming at preventing liver disease progression in NAFLD? Within this context, data from follow-up studies indicate that, unlike a diagnosis of NASH, the NAS score does not predict fibrosis progression. On this basis, it seems questionable to continue to pursue NAS improvement as the primary outcome definition in future trials in NASH. Furthermore, OCA did not significantly improve advanced fibrosis, which has been consistently associated with liver-related complications and is a more important endpoint than improvement in earlier stages of fibrosis. Another remarkable feature in the FLINT trial was the different histological response between diabetic (53% of participants) and nondiabetic individuals: Among diabetic patients, liver histology improved in 53% patients with OCA versus 19% with placebo (odds ratio [OR] for improvement with OCA: 4.6; 95% confidence interval [CI] = 2.0-10.6; P = 0.0003), whereas in nondiabetic participants, liver histology improved in 37% patients with OCA versus 23% with placebo (OR, 2.0; 95% CI = 0.8-4.7; P = 0.12). The positive association of histological response to OCA with increasing severity of glucose intolerance emerged also across progressive stages of pancreatic ß-cell dysfunction (as estimated by homeostasis model assessment [HOMA] B-cell index), a key feature leading to the development of diabetes (online Appendix Table S2 of the original article).1 Therefore, the evidence for effectiveness of OCA in nondiabetic individuals, who account for 47% of this trial population and for a substantial proportion of patients with NASH, is lacking. Putting the results of RCTs with OCA in the context of the other RCTs conducted in NAFLD, it should be noted that the percentage of responders to different therapeutic options for NASH approaches 50%-60%, leaving many patients without an effective treatment. This may suggest that NASH is a heterogeneous condition and diverse mechanisms of liver injury may cooperate in different patient populations to promote liver disease progression. Regarding OCA, an altered bile acid metabolism, which is the rationale for using semisynthetic bile acids and FXR agonists, has been demonstrated more extensively in diabetes, thereby possibly explaining the discrepant results between diabetic and nondiabetic individuals in the FLINT trial. Clearly, this hypothesis needs to be confirmed, refined, and extended by future research, and an individualized profiling of NASH patients, targeting multiple metabolic pathways, may be required to tackle liver disease progression in this population. In the RCTs by Chachay et al.,2 8 weeks of high-dose resveratrol supplementation did not benefit radiological and biochemical features of NAFLD nor any metabolic parameter.2 Resveratrol acts mainly, but not exclusively, as a calorie restriction mimicker by activating cellular Sirtuin (SIRT)−1 and 5′ adenosine monophosphate-activated protein kinase (AMPK) pathways, and a wealth of preclinical data demonstrate its benefits in metabolic disorders, including obesity, metabolic syndrome, diabetes, and NAFLD. To get a balanced, thorough view of resveratrol potentials for NAFLD treatment, we should consider the trial by Chachay et al.2 together with the three other RCTs assessing the effects of this agent on liver and metabolic parameters (Table 1, panel B)3-5 Resveratrol improved radiological/biochemical features of NAFLD and inflammatory/metabolic profile in two RCTs,3, 4 but was ineffective in the other two RCTs2, 5 (Table 1, panel B). Intriguingly, in the two negative RCTs, resveratrol did not improve liver disease, insulin resistance (IR), or inflammatory parameters and failed to trigger its core cellular mechanism of action, that is, did not evoke a calorie-restriction–like response, as indicated by the unaffected resting energy expenditure, respiratory quotient, and SIRT-1/AMPK activity observed in these trials.2, 5 On the contrary, when resveratrol mimicked calorie restriction, liver and metabolic indices improved substantially.3, 4 What are the reason(s) for the divergent response to this agent among the four RCTs? Patient characteristics and treatment duration were similar across the trials (Table 1, panel B). Rather, resveratrol dose ranges strikingly differ between negative and positive RCTs: Perhaps to caution against the low bioavailability of this polyphenol, the researchers of the negative trials used the highest doses, equivalent to those used in rodent models (i.e., 200-300 mg/kg body weight), but obtained substantially lower plasma resveratrol concentrations (mean ± standard deviation [SD]: 29 ± 12 ng/mL) than those observed in the positive trials (mean ± SD resveratrol concentration: 231 ± 30 ng/mL), where much lower doses of resveratrol were used (Table 1, panel B). Therefore, a key point to understand is why the doses administrated were inversely related to the plasma levels and to the biological effectiveness of this polyphenol. Resveratrol has a low bioavailability owing to extensive conjugation by intestinal and hepatic glucuronidases and sulfatases to glucuronide and sulfate metabolites with unclear biological activity, and only a small proportion of the parent compound reaches plasma and tissues. Because glucuronidases and sulfatases are potently inducible phase II enzymes, prolonged administration of high resveratrol doses may have induced these enzymes and enhanced the metabolism of the parent compound to less-active metabolites: Consistent with this hypothesis, whereas daily 150-mg administration yielded persistently elevated resveratrol concentrations throughout the trial by Trimmers et al.,4 in the trial by Chachay et al.,2 plasma resveratrol concentration rapidly declined after 1.5-g resveratrol ingestion (Fig. 3 of the original article2). Unfortunately, plasma resveratrol concentration was measured only at the end of the trial as an index of patient compliance, whereas the comparison of concentration curves of resveratrol and its conjugate metabolites at the beginning and the end of the trial would have allowed estimation of induction effect on drug-metabolizing enzymes. If that was the case, then pharmacological conjugation of resveratrol, with carriers such as phosphatidylcholine, might overcome first-pass effect and enhance its bioavailability, similarly to what has been achieved with other polyphenols. Perhaps future studies simultaneously assessing blood and tissue kinetics of resveratrol and its conjugates over a long treatment period may provide the basis for explaining discrepant results of available trials and help increase bioavailability and effectiveness of resveratrol, rather than disregarding this agent on the basis of the scarce and incomplete human data available. Quoting J.R.R. Tolkien, to summarize the results of RCTs with OCA and reservatrol, all that is gold does not glitter for NASH, and not all agents that wander in search of evidence of effectiveness are lost. Giovanni Musso, M.D. Gradenigo Hospital Torino, Italy