Diet-induced mouse model of fatty liver disease and nonalcoholic steatohepatitis reflecting clinical disease progression and methods of assessment

Shortcomings of previously reported preclinical models of nonalcoholic steatohepatitis (NASH) include inadequate methods used to induce disease and assess liver pathology. We have developed a dietary model of NASH displaying features observed clinically and methods for objectively assessing disease progression. Mice fed a diet containing 40% fat (of which ∼18% was trans fat), 22% fructose, and 2% cholesterol developed three stages of nonalcoholic fatty liver disease (steatosis, steatohepatitis with fibrosis, and cirrhosis) as assessed by histological and biochemical methods. Using digital pathology to reconstruct the left lateral and right medial lobes of the liver, we made comparisons between and within lobes to determine the uniformity of collagen deposition, which in turn informed experimental sampling methods for histological, biochemical, and gene expression analyses. Gene expression analyses conducted with animals stratified by disease severity led to the identification of several genes for which expression highly correlated with the histological assessment of fibrosis. Importantly, we have established a biopsy method allowing assessment of disease progression. Mice subjected to liver biopsy recovered well from the procedure compared with sham-operated controls with no apparent effect on liver function. Tissue obtained by biopsy was sufficient for gene and protein expression analyses, providing the opportunity to establish an objective method of assessing liver pathology before subjecting animals to treatment. The improved assessment techniques and the observation that mice fed the high-fat diet exhibit many clinically relevant characteristics of NASH establish a preclinical model for identifying pharmacological interventions with greater likelihood of translating to the clinic.

2-arachidonoylglycerol signaling in forebrain regulates systemic energy metabolism

The endocannabinoid system plays a critical role in the control of energy homeostasis, but the identity and localization of the endocannabinoid signal involved remain unknown. In the present study, we developed transgenic mice that overexpress in forebrain neurons the presynaptic hydrolase, monoacylglycerol lipase (MGL), which deactivates the endocannabinoid 2-arachidonoyl-sn-glycerol (2-AG). MGL-overexpressing mice show a 50% decrease in forebrain 2-AG levels but no overt compensation in other endocannabinoid components. This biochemical abnormality is accompanied by a series of metabolic changes that include leanness, elevated energy cost of activity, and hypersensitivity to β(3)-adrenergic-stimulated thermogenesis, which is corrected by reinstating 2-AG activity at CB(1)-cannabinoid receptors. Additionally, the mutant mice are resistant to diet-induced obesity and express high levels of thermogenic proteins, such as uncoupling protein 1, in their brown adipose tissue. The results suggest that 2-AG signaling through CB(1) regulates the activity of forebrain neural circuits involved in the control of energy dissipation.

Biphenyl-3-yl alkylcarbamates as fatty acid amide hydrolase (FAAH) inhibitors: steric effects of N-alkyl chain on rat plasma and liver stability

Secondary alkylcarbamic acid biphenyl-3-yl esters are a class of Fatty Acid Amide Hydrolase (FAAH) inhibitors, which include the reference compounds URB597 and URB694. Given the intrinsic reactivity of the carbamate group, the in vivo potency of these molecules in rats is strongly affected by their hydrolysis in plasma or hepatic metabolism. In the present study, in vitro chemical and metabolic stability assays (rat plasma and rat liver S(9) fraction) were used to investigate the structure-property relationships (SPRs) for a focused series of title compounds, where lipophilicity and steric hindrance of the carbamate N-substituent had been modulated. The resulting degradation rates indicate that a secondary or tertiary alkyl group at the carbamate nitrogen atom increases hydrolytic stability towards rat plasma esterases. The calculated solvent accessible surface area (SASA) of the carbamate fragment was employed to describe the differences observed in rate constants of hydrolysis in rat plasma (log k(plasma)), suggesting that stability in plasma increases if the substituent exerts a shielding effect on the carbamate carbonyl. Stability in rat liver S(9) fraction is increased when a tertiary carbon is bound to the carbamate nitrogen atom, while other steric effects showed complex relationships with degradation rates. The SPRs here described may be applied at the pharmacokinetic optimization of other classes of carbamate FAAH inhibitors.

A second generation of carbamate-based fatty acid amide hydrolase inhibitors with improved activity in vivo

The fatty acid ethanolamides are a class of signaling lipids that include agonists at cannabinoid and alpha type peroxisome proliferator-activated receptors (PPARalpha). In the brain, these compounds are primarily hydrolyzed by the intracellular serine enzyme fatty acid amide hydrolase (FAAH). O-aryl carbamate FAAH inhibitors such as URB597 are being evaluated clinically for the treatment of pain and anxiety, but interactions with carboxylesterases in liver might limit their usefulness. Here we explore two strategies aimed at overcoming this limitation. Lipophilic N-terminal substitutions, which enhance FAAH recognition, yield potent inhibitors but render such compounds susceptible to attack by broad-spectrum hydrolases and inactive in vivo. By contrast, polar electron-donating O-aryl substituents, which decrease carbamate reactivity, yield compounds, such as URB694, that are highly potent FAAH inhibitors in vivo and less reactive with off-target carboxylesterases. The results suggest that an approach balancing inhibitor reactivity with target recognition produces FAAH inhibitors that display significantly improved drug-likeness.

Synthesis and quantitative structure-activity relationship of fatty acid amide hydrolase inhibitors: modulation at the N-portion of biphenyl-3-yl alkylcarbamates

Alkylcarbamic acid biphenyl-3-yl esters are a class of fatty acid amide hydrolase (FAAH) inhibitors that comprises cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester (URB597), a compound with analgesic, anxiolytic-like and antidepressant-like properties in rat and mouse models. Here, we extended the structure-activity relationships (SARs) for this class of compounds by replacing the cyclohexyl ring of the parent compound cyclohexylcarbamic acid biphenyl-3-yl ester (URB524) (FAAH IC50 = 63 nM) with a selected set of substituents of different size, shape, flexibility, and lipophilicity. Docking experiments and linear interaction energy (LIE) calculations indicated that the N-terminal group of O-arylcarbamates fits within the lipophilic region of the substrate-binding site, mimicking the arachidonoyl chain of anandamide. Significant potency improvements were observed for the beta-naphthylmethyl derivative 4q (IC50 = 5.3 nM) and its 3'-carbamoylbiphenyl-3-yl ester 4z (URB880, IC50 = 0.63 nM), indicating that shape complementarity and hydrogen bonds are crucial to obtain highly potent inhibitors.

Identification of a bioactive impurity in a commercial sample of 6-methyl-2-p-tolylaminobenzo[d][1,3]oxazin-4-one (URB754)

The compound URB754 was recently identified as a potent inhibitor of the endocannabinoid-deactivating enzyme monoacylglycerol lipase (MGL) by screening of a commercial chemical library. Based on HPLC/MS, NMR and EI/MS analyses, the present paper shows that the MGL-inhibitory activity attributed to URB754 is in fact due to a chemical impurity present in the commercial sample, identified as bis(methylthio)mercurane. Although this organomercurial compound is highly potent at inhibiting MGL (IC50 = 11.9 +/- 1.1 nM), its biological use is prohibited by its toxicity and target promiscuity.

The fatty-acid amide hydrolase inhibitor URB597 does not affect triacylglycerol hydrolysis in rat tissues

The O-arylcarbamate URB597 (cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester; also referred to as KDS-4103) is a potent inhibitor of fatty-acid amide hydrolase (FAAH), an intracellular serine hydrolase responsible for the inactivation of the endogenous cannabinoid anandamide. URB597 demonstrates a remarkable degree of selectivity for FAAH over other serine hydrolases (e.g. cholinesterases) or other components of the endocannabinoid system (e.g. cannabinoid receptors). However, in a proteomic-based selectivity screen based on the displacement of fluorophosphonate-rhodamine (FPR) from mouse brain proteins, it was recently shown that URB597 prevents FPR binding to triacylglycerol hydrolase (TGH) with a median inhibitory concentration of 192nM. To determine whether this effect correlates with inhibition of TGH activity, we investigated the ability of URB597 to inhibit triolein hydrolysis in rat liver and heart tissues, which are rich in TGH, as well as white adipose tissue (WAT), which is rich in adipose triacylglycerol lipase (TGL) and hormone-sensitive lipase. The results show that URB597 does not affect triolein hydrolysis in any of these tissues at concentrations as high as 10microM, whereas it inhibits FAAH activity at low nanomolar concentrations. Moreover, intraperitoneal (i.p.) administration of URB597 at doses that maximally inhibit FAAH in vivo (0.3-3mgkg(-1)) exerts no effect on triolein hydrolysis and tissue triacylglycerol (TAG) levels in rat liver, heart or WAT. The results indicate that URB597, while potent at inhibiting FAAH, does not affect TGH and TGL activities in rat tissues.