Brimijoin, Stephen

SummaryWeight loss is an effective intervention for diminishing disease burden in obese older adults. Pharmacological interventions that reduce food intake and thereby promote weight loss may offer effective strategies to reduce age‐related disease. We previously reported that 17α‐estradiol (17α‐E2) administration elicits beneficial effects on metabolism and inflammation in old male mice. These observations were associated with reduced calorie intake. Here, we demonstrate that 17α‐E2 acts through pro‐opiomelanocortin (Pomc) expression in the arcuate nucleus (ARC) to reduce food intake and body mass in mouse models of obesity. These results confirm that 17α‐E2 modulates appetite through selective interactions within hypothalamic anorexigenic pathways. Interestingly, some peripheral markers of metabolic homeostasis were also improved in animals with near complete loss of ARC Pomc transcription. This suggests that 17α‐E2 might have central and peripheral actions that can beneficially affect metabolism cooperatively or independently.

Significance Obesity is a major public health problem affecting physical and emotional well-being. Although lifestyle-based programs can help with weight loss, avoiding weight regain is nearly impossible because of persistent hormonal adaptations. Here, in mouse models, we explored a more effective strategy using viral gene transfer of butyrylcholinesterase (BChE) to control the appetite-mediating hormone acyl-ghrelin. We found that a single injection of BChE vector led to a lifetime high enzyme expression and lower circulating acyl-ghrelin. This same treatment suppressed postdieting hyperphagia, corrected metabolic lesions, and lowered weight regain. This outcome confirms the impact of the BChE-ghrelin axis on body weight and indicates that BChE gene transfer could be a successful strategy for long-term control of obesity and the “metabolic syndrome.”

Recent research shows that butyrylcholinesterase (BChE) is not simply a liver enzyme that detoxifies bioactive esters in food and medications. In fact, in pursuing other goals, we recently found that it has an equally important role in regulating the peptide hormone ghrelin and its impact on hunger, obesity, and emotions. Here, we present and examine means of manipulating brain BChE levels by viral gene transfer, either regionally or globally, to modulate ghrelin signaling for long-term therapeutic purposes and to set the stage for exploring the neurophysiological impact of such an intervention.

Despite numerous reports of relationships between weight gain and butyrylcholinesterase (BChE), this enzyme's role in the genesis of obesity remains unclear, but recent research points to strong links with ghrelin, the “hunger hormone.” The availability of BChE knockout (KO) mice provides an opportunity to clarify the causal relationship between BChE and obesity onset. We now find that young KO mice have abnormally high plasma ghrelin levels that slowly decline during long-term high-fat feeding and ultimately drop below those in wild-type mice. On such a diet, the KO mice gained notably more weight, more white fat, and more hepatic fat than wild-type animals. In addition to a greater burden of hepatic triglycerides, the livers of these KO mice show distinctly higher levels of inflammatory markers. Finally, their energy expenditure proved to be lower than in wild-type mice despite similar activity levels and increased caloric intake. A gene transfer of mouse BChE with adeno-associated virus vector restored nearly all aspects of the normal phenotype. Our results indicate that BChE strongly affects fat metabolism, has an important impact on fat accumulation, and may be a promising tool for combating obesity.

Significance Butyrylcholinesterase (BChE), a common plasma enzyme, has been known for decades but its real physiological roles are just beginning to emerge. Although BChE eliminates the neurotransmitter acetylcholine, it is not vital for locomotion, cognition, or other cholinergic functions. Nevertheless, we now find that circulating BChE has a large impact on aggressive behavior in mice that is attributable to its ability to inactivate ghrelin, a peptide hormone involved in hunger, feeding, and stress. A key observation was decreased fighting among group-housed male mice overexpressing BChE after viral gene transfer. In contrast, BChE knockout mice exhibited increased fighting. These effects mirrored changes in plasma levels of active ghrelin. Controlling them might offer therapeutic potential for certain behavioral disorders.

Mouse butyrylcholinesterase (mBChE) and an mBChE-based cocaine hydrolase (mCocH, i.e. the A199S/S227A/S287G/A328W/Y332G mutant) have been characterized for their catalytic activities against cocaine, i.e. naturally occurring (−)-cocaine, in comparison with the corresponding human BChE (hBChE) and an hBChE-based cocaine hydrolase (hCocH, i.e. the A199S/F227A/S287G/A328W/Y332G mutant). It has been demonstrated that mCocH and hCocH have improved the catalytic efficiency of mBChE and hBChE against (−)-cocaine by ~8- and ~2000-fold respectively, although the catalytic efficiencies of mCocH and hCocH against other substrates, including acetylcholine (ACh) and butyrylthiocholine (BTC), are close to those of the corresponding wild-type enzymes mBChE and hBChE. According to the kinetic data, the catalytic efficiency (kcat/KM) of mBChE against (−)-cocaine is comparable with that of hBChE, but the catalytic efficiency of mCocH against (−)-cocaine is remarkably lower than that of hCocH by ~250-fold. The remarkable difference in the catalytic activity between mCocH and hCocH is consistent with the difference between the enzyme–(−)-cocaine binding modes obtained from molecular modelling. Further, both mBChE and hBChE demonstrated substrate activation for all of the examined substrates [(−)-cocaine, ACh and BTC] at high concentrations, whereas both mCocH and hCocH showed substrate inhibition for all three substrates at high concentrations. The amino-acid mutations have remarkably converted substrate activation of the enzymes into substrate inhibition, implying that the rate-determining step of the reaction in mCocH and hCocH might be different from that in mBChE and hBChE.