C75, a Fatty Acid Synthase Inhibitor, Reduces Food Intake via Hypothalamic AMP-activated Protein Kinase

Abstract

Energy homeostasis and feeding are regulated by the central nervous system. C75, a fatty acid synthase (FAS) inhibitor, causes weight loss and anorexia, implying a novel central nervous system pathway(s) for sensing energy balance. AMP-activated protein kinase (AMPK), a sensor of peripheral energy balance, is phosphorylated and activated when energy sources are low. Here, we identify a role for hypothalamic AMPK in the regulation of feeding behavior and in mediating the anorexic effects of C75. 5-Aminoimidazole-4-carboxamide-1-␤-D-ribofuranoside (AICAR), an activator of AMPK, increased food intake, whereas compound C, an inhibitor of AMPK, decreased food intake. C75 rapidly reduced the level of the phosphorylated AMPK ␣ subunit (pAMPK␣) in the hypothalamus, even in fasted mice that had elevated hypothalamic pAMPK␣ levels. Furthermore, AICAR reversed both the C75-induced anorexia and the decrease in hypothalamic pAMPK␣ levels. C75 elevated hypothalamic neuronal ATP levels, which may contribute to the mechanism by which C75 decreased AMPK activity. C75 reduced the levels of pAMPK␣ and phosphorylated cAMP response element-binding protein (pCREB) in the arcuate nucleus neurons of the hypothalamus, suggesting a mechanism for the reduction in NPY expression seen with C75 treatment. These data indicate that modulation of FAS activity in the hypothalamus can alter energy perception via AMPK, which functions as a physiological energy sensor in the hypothalamus.Despite significant advances in the understanding of appetite and satiety at molecular levels (1-3), practical therapies for weight loss remain elusive. We and others (4 -8) have demonstrated that C75, a synthetic fatty acid synthase (FAS) 1 inhibitor, caused profound weight loss and anorexia in lean, dietinduced obese (DIO) and genetically obese (ob/ob) mice. In addition to FAS inhibition, C75 also stimulates carnitine palmitoyltransferase-1 (CPT-1) activity, increasing fatty acid oxidation and ATP levels (8). Since enzymes of the fatty acid metabolic pathways are highly expressed in hypothalamic neurons that regulate feeding behavior (9), we hypothesize that C75-induced alterations in fatty acid metabolism may affect neuronal energy flux, which could signal a change in energy status, leading to changes in feeding behavior.AMPK (AMP-activated protein kinase) is activated by metabolic stresses such as nutrient starvation (10) and ischemiahypoxia (11) and by physiological processes such as vigorous exercise (12, 13). Specifically, increases in the AMP/ATP ratio, decreases in cellular pH, and increases in the creatine/phosphocreatine ratio are known to activate AMPK via allosteric activation of AMPK by AMP and by phosphorylation of AMPK by AMPKK (14 -19). Once activated, AMPK switches off ATPconsuming biosynthetic pathways such as fatty acid synthesis and switches on ATP-generating metabolic pathways such as fatty acid oxidation to preserve ATP levels (20, 21). The central roles of AMPK in both energy sensing and the control of fatty acid metabolism (16,22) and its r...

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“…AMP‐activated protein kinase (AMPK) serves as a cellular energy sensor and is activated in response to a series of metabolic stresses, such as hypoxia, oxidative stress, and glucose deprivation 21, 22. Once activated, AMPK promotes catabolic pathways to generate more ATP, and inhibits anabolic pathways, thus allowing for adaptive changes in growth and metabolism under low energy conditions 23.…”

AMP-activated protein kinase in the brain

“…2,3 We and other laboratories have shown that hypothalamic AMPK plays a major role in the regulation of organism's energy balance. [4][5][6] Our interest in hypothalamic AMPK grew from our work with C75, a synthetic molecule that inhibits fatty acid synthase (FAS) 7 and stimulates carnitine palmitoyltransferase-1 (CPT-1) and beta-oxidation of fatty acids. [8][9][10] Fatty acid metabolic pathways are poised at a crossroads of energy deficit and energy surplus, with the potential to either use or make the high-energy molecule ATP.…”

“…We have shown that C75 increases cellular ATP, and decreases the phosphorylation status and activity of AMPK. 4,8 By increasing the local energy level in energy-sensing hypothalamic neurons, C75 elicits mechanisms that decrease the organism's energy intake and likely also serve to increase wholebody energy expenditure. In our other work, we have also determined that C75 is neuroprotective.…”

“…2,31 Hormones and pharmacological agents modulate AMPK activity in muscle, liver and hypothalamus to promote fatty acid oxidation, glucose utilization and feeding responses. [4][5][6]36,37 Physiological stimuli can activate AMPK to promote tissue-specific responses such as skeletal muscle glucose uptake and glycolysis through glucose transporter translocation and 6-phosphofructo-2-kinase kinase activity, respectively, and fatty acid oxidation. 32,33,38 Liver AMPK inhibits fatty acid and cholesterol biosynthesis by phosphorylating and inactivating ACC and 3-hydroxy-3-methylglutaryl-coenzyme A reductase.…”

“…Our interest in hypothalamic AMPK grew from our work with C75. General brain injection of C75 in rodents decreases food intake and body weight, 4,26,40,41 so C75 exerts some of its weight loss effects by acting in CNS. Once we knew that C75 altered pAMPK in neurons in vitro, 8 we altered the brain and hypothalamic AMPK in mice using well-known pharmacological tools, and fed and fasted states, to demonstrate that AMPK was a physiological mediator of C75's effects.…”