Structure-based rational design of peptide hydroxamic acid inhibitors to target tumor necrosis factor-α converting enzyme as potential therapeutics for hepatitis

The human tumor necrosis factor-α converting enzyme (TACE) has recently been raised as a new and promising therapeutic target of hepatitis and other inflammatory diseases. Here, we reported a successful application of the solved crystal structure of TACE complex with a peptide-like ligand INN for rational design of novel peptide hydroxamic acid inhibitors with high potency and selectivity to target and inhibit TACE. First, the intermolecular interactions between TACE catalytic domain and INN were characterized through an integrated bioinformatics approach, with which the key substructures of INN that dominate ligand binding were identified. Subsequently, the INN molecular structure was simplified to a chemical sketch of peptide hydroxamic acid compound, which can be regarded as a linear tripeptide capped by a N-terminal carboxybenzyl group (chemically protective group) and a C-terminal hydroxamate moiety (coordinated to the Zn(2+) at TACE active site). Based on the sketch, a virtual combinatorial library containing 180 peptide hydroxamic acids was generated, from which seven samples were identified as promising candidates by using a knowledge-based protein-peptide affinity predictor and were then tested in vitro with a standard TACE activity assay protocol. Consequently, three designed peptide hydroxamic acids, i.e. Cbz-Pro-Ile-Gln-hydroxamic acid, Cbz-Leu-Ile-Val-hydroxamic acid and Cbz-Phe-Val-Met-hydroxamic acid, exhibited moderate or high inhibitory activity against TACE, with inhibition constants Ki of 36 ± 5, 510 ± 46 and 320 ± 26 nM, respectively. We also examined the structural basis and non-bonded profile of TACE interaction with a designed peptide hydroxamic acid inhibitor, and found that the inhibitor ligand is tightly buried in the active pocket of TACE, forming a number of hydrogen bonds, hydrophobic forces and van der Waals contacts at the interaction interface, conferring both stability and specificity for TACE-inhibitor complex architecture.

Probiotics for patients with hepatic encephalopathy

BACKGROUND

Hepatic encephalopathy is a disorder of brain function as a result of liver failure and/or portosystemic shunt. Both hepatic encephalopathy (clinically overt) and minimal hepatic encephalopathy (not clinically overt) significantly impair patient's quality of life and daily functioning and represent a significant burden on health care resources. Probiotics are live microorganisms, which when administered in adequate amounts may confer a health benefit on the host.

OBJECTIVES

To quantify the beneficial and harmful effects of any probiotic in any dosage, compared with placebo or no intervention, or with any other treatment for patients with any grade of acute or chronic hepatic encephalopathy as assessed from randomised trials.

SEARCH METHODS

We searched the The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE, EMBASE, Science Citation Index Expanded, conference proceedings, reference lists of included trials and the WHO international clinical trials registry until April 2011 registry platform to identify new and ongoing trials.

SELECTION CRITERIA

We included randomised trials that compared probiotics in any dosage with placebo or no intervention, or with any other treatment in patients with hepatic encephalopathy.

DATA COLLECTION AND ANALYSIS

Three authors independently assessed the risk of bias of the included trials and extracted data on relevant outcomes, with differences resolved by consensus. We conducted random-effects model meta-analysis due to obvious heterogeneity of patients and interventions. A P value of 0.05 or less was defined as significant. Dichotomous outcomes are expressed as risk ratio (RR) and continuous outcomes as mean difference (MD) with 95% confidence intervals (CI).

MAIN RESULTS

We included seven trials of which 550 participants were randomised. Four of the seven trials compared a probiotic with placebo or no treatment in 245 participants, another trial compared a probiotic with lactulose in 40 participants , and the remaining two trials compared a probiotic with both placebo and lactulose in 265 participants. Each trial used different types of probiotics. Duration of administration of the experimental intervention varied from 10 days to 180 days. Two trials were industry funded, and five were unclear about origin of funding. All trials had high risk of bias. When probiotics were compared with no treatment, there was no significant difference in all-cause mortality (2 trials, 105 participants; 1/57 (2%) versus 1/48 (2%): RR 0.72; 95% CI 0.08 to 6.60), lack of recovery (4 trials, 206 participants; 54/107 (50%) versus 68/99 (69%): RR 0.72; 95% CI 0.49 to 1.05), adverse events (3 trials, 145 participants; 2/77 (3%) versus 6/68 (9%): RR 0.34; 95% CI 0.08 to 1.42), quality of life (1 trial, 20 participants contributed to the physical quality of life measurement, 20 participants contributed to the mental quality of life: MD Physical 0.00; 95% CI -5.47 to 5.47; MD Mental 4.00; 95% CI -1.82 to 9.82), or change of/or withdrawal from treatment (3 trials, 175 participants; 11/92 (12%) versus 7/83 (8%): RR 1.28; 95% CI 0.52 to 3.19). No trial reported sepsis or duration of hospital stay as an outcome. Plasma ammonia concentration was significantly lower for participants treated with probiotic at one month (3 trials, 226 participants: MD -2.99 μmol/L; 95% CI -5.70 to -0.29) but not at two months (3 trials, 181 participants: MD -1.82 μmol/L; 95% CI -14.04 to 10.41). Plasma ammonia decreased the most in the participants treated with probiotic at three months (1 trial, 73 participants: MD -6.79 μmol/L; 95% CI -10.39 to -3.19). When probiotics were compared with lactulose no trial reported all-cause mortality, quality of life, duration of hospital stay, or septicaemia. There were no significant differences in lack of recovery (3 trials, 173 participants; 47/87 (54%) versus 44/86 (51%): RR 1.05; 95% CI 0.75 to 1.47), adverse events (2 trials, 111 participants; 3/56 (5%) versus 6/55 (11%): RR 0.57; 95% CI 0.06 to 5.74), change of/or withdrawal from treatment at one month (3 trials, 190 participants; 8/95 (8%) versus 7/95 (7%): RR 1.10; 95% CI 0.40 to 3.03), plasma ammonia concentration (2 trials, 93 participants: MD -6.61 μmol/L; 95% CI -30.05 to 16.84), or change in plasma ammonia concentration (1 trial, 77 participants: MD 1.16 μmol/L; 95% CI -1.96 to 4.28).

AUTHORS' CONCLUSIONS

The trials we located suffered from a high risk of systematic errors ('bias') and high risk of random errors ('play of chance'). While probiotics appear to reduce plasma ammonia concentration when compared with placebo or no intervention, we are unable to conclude that probiotics are efficacious in altering clinically relevant outcomes. Demonstration of unequivocal efficacy is needed before probiotics can be endorsed as effective therapy for hepatic encephalopathy. Further randomised clinical trials are needed.