Recent Research Summaries
Courtesy of the Foundation for Prader Willi Research http://pwsresearch.org.
Here's a new article trying to sort out how C75 acts. For those of you who have tried to read any of the medical literature on appetite/feeding/satiety, you have probably realized that there are many hormones and neurotransmitters that influence food intake and energy expenditure. These neuropeptides are made in the brain and/or in the GI tract. Figuring out how these systems overlap, interact and influence each other is a major focus of research in this area. Specifically, integrating the information to determine the pathways that regulate hunger/satiety is an area of active research. One part of this is to determine which peptides (small proteins) are 'upstream' or 'downstream' of the others, so as to figure out who influences whom. Here, the researchers look at that with respect to C75, a molecule that inhibits the enzyme Fatty Acid Synthase (FAS), and causes animals to stop eating and lose weight. They find that administering C75 causes a decrease in ghrelin release, and they propose that this leads to a change in expression of other neuropeptides (NPY, AgRP, POMC, etc) that ultimately results in less food intake. They propose a model for how this is all integrated. The abstract is below. If you want to look at the paper in detail, it is freely available: http://www.pnas.org/cgi/content/short/102/11/3972
As far as I know, levels of Mal-CoA, which they propose as a central part of the 'energy-sensing system' has not yet been studied in PWS -- but several companies are looking at this part of the pathway as a therapeutic target in obesity.
Remember: orexigenic means stimulates food intake (examples: ghrelin, NPY, AgRP), while anorexigenic means inhibits food intake (PYY, orexin, POMC); c-fos expression is just a way these guys look at which neurons get 'turned on'.
Proceedings of the National Academy of Sciences, March 15, 2005 Effect of centrally administered C75, a fatty acid synthase
inhibitor, on ghrelin secretion and its downstream effects Zhiyuan Hu, Seung Hun Cha, Goedelle van Haasteren, Jing Wang and M. Daniel Lane * Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
The central administration of the fatty acid synthase (FAS)
inhibitor, C75, rapidly suppresses the expression of orexigenic neuropeptides [neuropeptide Y (NPY) and agouti-related protein (AgRP)] and activates expression of anorexigenic neuropeptides [proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART)] in the hypothalamus. The combined actions of these changes inhibit food intake and decrease body weight. Intracerebroventricular injection of C75 appears to rapidly inhibit the secretion of ghrelin by hypothalamic explants ex vivo and by the stomach in vivo. Ghrelin administered intracerebroventricularly reverses the anorexic effect of C75, suggesting that C75 acts upstream of ghrelin. Because ghrelin-producing neurons are known to form synapses onto NPY/AgRP neurons, we suggest that the reversal of C75-induced anorexia by ghrelin may be mediated by NPY/AgRP neurons. This hypothesis is supported by the finding that ghrelin reverses the C75-induced inactivation (assessed by c-Fos expression) of neurons in the arcuate nucleus that express NPY (assessed by immunohistochemical costaining). These effects closely correlate with appropriate changes downstream in the expression of the hypothalamic neuropeptides that regulate feeding behavior, i.e., down-regulation of the expression of NPY and AgRP and up-regulation of the expression of proopiomelanocortin/-melanocyte-stimulating hormone, provoked by C75 and reversed by ghrelin. We propose a model in which ghrelin secretion plays an intermediary role between malonyl-CoA, the substrate of fatty acid synthase, and the neural circuitry regulating energy homeostasis.
I saw this new article which looked like a good follow up to the discussion of 'acquired' or hypothalamic obesity (HO), and how it is the same/different than PWS. Based on this paper (abstract below) it looks like the molecular basis for obesity in this population (individuals who have had their hypothalamus damaged, leading to obesity) is at least somewhat different than in PWS. The authors found that unlike PWS, individuals with HO do not have elevated ghrelin levels. It's not entirely clear why this is, but an interesting possibility has to do with insulin. Normally, insulin negatively regulates ghrelin (so if you take in a lot of food, you release insulin and that causes ghrelin to go down so you'll stop eating). One potentially important difference between HO and PWS is that HO is associated with high insulin levels, whereas it has been noted that individuals with PWS have low levels of insulin (may be consistent with the observation that there is less diabetes than you might expect in the PWS population). So, low insulin may contribute to the high ghrelin levels found in individuals with PWS. Note that HO is not consistently associated with hyperphagia like PWS. All of this suggests that HO and PWS are not exactly the same in how they lead to obesity, but comparing the two groups to define what is the same and what is different can give important clues about the underlying causes of obesity in both populations.
The insulin angle is very intruiging to me also in light of the project Rob Nicholls in undertaking (supported by FPWR funds, by the way : ) ). He has seen pancreatic defects in his mouse model of PWS (the pancreas secretes insulin), which might be consistent with the finding of low insulin levels in patients with PWS.
J Clin Endocrinol Metab. 2005 Mar 15; Fasting ghrelin levels are not elevated in children with hypothalamic obesity. Kanumakala S, Greaves R, Pedreira C, Donath S, Warne G, Zacharin M, Harris M. Department of Paediatrics, Royal Alexandra Hospital, Brighton, UK; Department of Complex Biochemistry, The Royal Children's Hospital, Melbourne, Australia; Department of Endocrinology & Diabetes, The Royal Children's Hospital, Melbourne, Australia; Clinical Epidemiology and Biostatistics Unit, MCRI, The Royal Children's Hospital, Melbourne, Australia; and Department of Endocrinology, Mater Children's Hospital, Brisbane, Australia. Morbid obesity is a common problem after damage to the hypothalamus. Hypothalamic dysfunction is also thought to underlie the obesity that is typical of Prader Willi syndrome (PWS). Elevated fasting levels of the appetite stimulating hormone ghrelin have been reported in PWS. The aim of this study was to determine whether fasting ghrelin levels are increased in children with hypothalamic obesity. Fasting total ghrelin levels were compared in three groups; normal weight controls (n = 16), obese controls (n = 16), and patients with hypothalamic obesity (n = 16). Obese children had lower fasting total ghrelin levels than normal controls but there was no difference between the fasting total ghrelin level in obese controls and children with hypothalamic obesity (P = 0.88). These data suggest it is unlikely that an elevation in fasting total ghrelin is responsible for the obesity that occurs after hypothalamic damage. Therapeutic interventions aimed at reducing fasting total ghrelin may prove ineffective in controlling weight gain in this group.
I think this is important. Maybe really important.
The CB-1 receptor in the brain is the receptor that marijuana binds to.
See the current Scientific American, Dec 2004, The Brain's own marijuana, Roger A. Nicoll and Bradley E. Alger. THC (component of marijuana) stimulates the CB1 receptor, whose natural ligands are 2 short fatty acids, anandamide and 2-arachidonyl glycerol (2-AG). 2-AG is a neurotransmitter that causes retrograde signaling at synapses. This dampens inhibition and enhances long-term potentiation. Depolarized-induced suppression of inhibition "enables individual neurons to disconnect briefly from their neighbors and encode information.
If CB1 knockout mice (mice who do not have the CB-1 reptor due to genetic deletion) are conditioned to a sound followed by an electric shock, they are unable to experience extinction after the sound and shock are uncoupled. "Endocannabinoids are important in extinguishing the bad feelings and pain triggered by reminders of past experiences."
Anatomy: Cannabinoid receptors in the hypothalamus are involved in appetite, hormones and sexual behavior; in the basal ganglia, in planning, initiation and termination of action; in the cerebellum, in motor control; in the neocortex, in higher cognitive functions and integration of sensory information; in the hippocampus, in memory and learning of facts, sequences and place; in the brain stem and spinal cord, in vomiting reflex and pain."
You may have seen posts on this list about an obesity drug that is currently in phase 3 trials called rimonabant. It is made by Sanofi-Synthelabo. It binds to this receptor. I am trying to stir up interest on CB-1 and PWS with CB-1 researchers. I can find nothing on CB-1 and PWS on Medline, but doesn't this receptor seem to hit a lot of the same problems or kids have? And, CB-1's natural ligand are two short fatty acids (fat metabolism??).
Alcohol Alcohol. 2004 Nov 18; [Epub ahead of print] Related Articles, Links  THE ENDOCANNABINOID SYSTEM: PHYSIOLOGY AND PHARMACOLOGY.
DE Fonseca FR, Del Arco I, Bermudez-Silva FJ, Bilbao A, Cippitelli A, Navarro M.
Unidad de Investigacion, Fundacion IMABIS, Avenida Carlos Haya 82, 29010 Malaga, Spain; Departamento de Psicobiologia, Facultad de Psicologia, Universidad Complutense, Campus de Somosaguas, 28040 Madrid, Spain. The endogenous cannabinoid system is an ubiquitous lipid signalling system that appeared early in evolution and which has important regulatory functions throughout the body in all vertebrates. The main endocannabinoids (endogenous cannabis-like substances) are small molecules derived from arachidonic acid, anandamide (arachidonoylethanolamide) and 2-arachidonoylglycerol. They bind to a family of G-protein-coupled receptors, of which the cannabinoid CB1 receptor is densely distributed in areas of the brain related to motor control, cognition, emotional responses, motivated behaviour and homeostasis. Outside the brain, the endocannabinoid system is one of the crucial modulators of the autonomic nervous system, the immune system and microcirculation. Endocannabinoids are released upon demand from lipid precursors in a receptor-dependent manner and serve as retrograde signalling messengers in GABAergic and glutamatergic synapses, as well as modulators of postsynaptic transmission, interacting with other neurotransmitters, including dopamine. Endocannabinoids are transported into cells by a specific uptake system and degraded by two well-characterized enzymes, the fatty acid amide hydrolase and the monoacylglycerol lipase. Recent pharmacological advances have led to the synthesis of cannabinoid receptor agonists and antagonists, anandamide uptake blockers and potent, selective inhibitors of endocannabinoid degradation. These new tools have enabled the study of the physiological roles played by the endocannabinoids and have opened up new strategies in the treatment of pain, obesity, neurological diseases including multiple sclerosis, emotional disturbances such as anxiety and other psychiatric disorders including drug addiction. Recent advances have specifically linked the endogenous cannabinoid system to alcoholism, and cannabinoid receptor antagonism now emerges as a promising therapeutic alternative for alcohol dependence and relapse.
J Biol Chem. 2004 Jul 2;279(27):27849-54. Epub 2004 Apr 26. Related Articles, Links
Oleoylethanolamide stimulates lipolysis by activating the nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR-alpha).
Guzman M, Lo Verme J, Fu J, Oveisi F, Blazquez C, Piomelli D.
Department of Pharmacology, University of California, Irvine, CA 92697-4260, USA.
Amides of fatty acids with ethanolamine (FAE) are biologically active lipids that participate in a variety of biological functions, including the regulation of feeding. The polyunsaturated FAE anandamide (arachidonoylethanolamide) increases food intake by activating G protein-coupled cannabinoid receptors. On the other hand, the monounsaturated FAE oleoylethanolamide (OEA) reduces feeding and body weight gain by activating the nuclear receptor PPAR-alpha (peroxisome proliferator-activated receptor alpha). In the present report, we examined whether OEA can also influence energy utilization. OEA (1-20 microm) stimulated glycerol and fatty acid release from freshly dissociated rat adipocytes in a concentration-dependent and structurally selective manner. Under the same conditions, OEA had no effect on glucose uptake or oxidation. OEA enhanced fatty acid oxidation in skeletal muscle strips, dissociated hepatocytes, and primary cardiomyocyte cultures. Administration of OEA in vivo (5 mg kg(-1), intraperitoneally) produced lipolysis in both rats and wild-type mice, but not in mice in which PPAR-alpha had been deleted by homologous recombination (PPAR-alpha(-/-)). Likewise, OEA was unable to enhance lipolysis in adipocytes or stimulate fatty acid oxidation in skeletal muscle strips isolated from PPAR-alpha mice. The synthetic PPAR-alpha agonist Wy-14643 produced similar effects, which also were dependent on the presence of PPAR-alpha. Subchronic treatment with OEA reduced body weight gain and triacylglycerol content in liver and adipose tissue of diet-induced obese rats and wild-type mice, but not in obese PPAR-alpha(-/-) mice. The results suggest that OEA stimulates fat utilization through activation of PPAR-alpha and that this effect may contribute to its anti-obesity actions.
Neuropharmacology. 2004 Jun;46(7):966-73. Related Articles, Links
Impaired action of anxiolytic drugs in mice deficient in cannabinoid CB1 receptors.
Uriguen L, Perez-Rial S, Ledent C, Palomo T, Manzanares J.
Servicio de Psiquiatria y Unidad de Investigacion, Pabellon de Medicina Comunitaria, Hospital Universitario 12 de Octubre, Avda Cordoba s/n, 28041 Madrid, Spain.
The role of cannabinoid CB(1) receptors in the action of anxiolytics was examined. Deletion of CB(1) receptors resulted in increased anxiety-like behaviours in light/dark box, elevated plus maze and social interaction tests. Mutant mice presented basal low corticosterone concentrations and low proopiomelanocortin gene expression in the anterior lobe of the pituitary gland compared to wild-type mice. Ten minutes of restraint stress resulted in a twofold increase in corticosterone concentrations in the plasma of mutant mice, compared to wild-type mice. Bromazepam (50 or 100 microg/kg) markedly increased the time spent in light area in wild-type animals, though both doses were without effect in mutant mice. Administration of buspirone (1 or 2 mg/kg) produced anxiolytic effects in wild-type mice. In contrast, only the highest dose of buspirone had anxiolytic results in mutant mice. Our findings reveal that CB(1) receptors are involved in the regulation of emotional responses, and play a pivotal role in the action mechanism of anxiolytics. They suggest that alterations in the functional activity of the CB(1) receptor may be related to the emergence of anxiety disorders, and may affect treatment with anxiolytics.
2002 International Symposium
I am currently reading the book Prader Willi Syndrome as a Model of Obesity edited by Eiholzer, l'allemand, and Zipf (available from Amazon). This is the summary of the 2002 International Symposium held in Zurich. It is expensive ($120), but well worth it if you like to read the science stuff.
Dr. Lee has an article in there where he proposes that the metabolic problem is not actually a problem with the hypothalamus, but rather is a problem in the periphery. I found his arguments quite convincing. "The peripheral model relies on disordered regulation of substrate- or tissue-generated signaling, an area which is even more poorly understood than central appetite regulation."
Also, some quotes from the Eiholzer article that I found interesting: "From this viewpoint, the onset of obesity represents the external manifestation of insufficient satiety and, at the same time, is an expression of increasing physical strength, health an the children's ability to get their way." (p.2) Does that make sense to any of you? Once the child becomes strong enough to eat well, then they keep eating and gaining weight?? "... children with PWS had decreased muscle mass in absolute terms (as opposed to children with nonsyndromal obesity, who had an increased muscle mass)..."
"Even after long-term growth hormone treatment, muscle mass remained distinctly decreased and fat mass was increased." While I doubt this sentence incorporates any data about infants given GH, it still underscores to me that while GH seems to be able to fix the problem (at least partly) it does not really get at the underlying cause.
In one spot he refers to hypoactivity as insufficient muscle mass. Does that mean that once our kids get enough muscle mass they become more active? Is there something wrong with their muscle or is it just that they don't have enough muscle? Is it a quality problem or just a quantity problem? Why are they low tone? Is it because their muscle to fat ratio is off? But that ratio stays off throughout their life and yet their tone improves with time.
Also, I've discussed PWS and diabetes and the value of a low glycemic index diet for our kids? Eiholzer writes: "The insulin levels, however, are low, at least in children and adolescents. In the periphery, insulin sensitivity is increased, in contrast to most individuals with non- syndromal obesity. Whether the low insulin levels centrally play a role in energy regulation is open."
Also, Eiholzer makes reference to daily training programs to augment GH therapy in the effort to achieve normal muscle mass. Does anyone know anything about this? He seems to discount it by saying: "The downside of a daily training programme, however, is that it requires an additional time investment on part of the parents and other caretakers."
Starvation or Obesity?
This interesting article argues that PWS is more a model of starvation than it is a model of obesity.
The paradox of Prader-Willi syndrome: a genetic model of starvation
Holland A, Whittington J, Hinton E.
Section of Developmental Psychiatry, Douglas House, CB2 2AH, Cambridge, UK. email@example.com
The neurodevelopmental disorder, Prader-Willi syndrome, is generally regarded as a genetic model of obesity. Although the values of some hypothalamic neuropeptides are as expected in obesity, and should result in satiety, we propose that abnormal hypothalamic pathways mean that these are ineffective. We postulate that the body incorrectly interprets the absence of satiation as starvation, and therefore, paradoxically, this syndrome should be redefined as one of starvation that manifests as obesity in a food-rich environment. Also, this syndrome is generally believed to be a contiguous gene disorder, which results from the absence of expression of the paternally derived alleles of maternally imprinted genes on chromosome 15 (15q11-13). We argue, however, that the whole phenotype can be explained by one mechanism and, by implication, the failure of expression of the paternal allele of a single maternally imprinted gene that controls energy balance. We suggest clinical and laboratory approaches to test our hypotheses.
Purchase article ($30)
I want to look into this more later.
SNRPN is involved in RNA processing. Interestingly, the SNRPN gene is located next to several groups of imprinted genes coding for small nucleolar RNAs (snoRNAs); a cluster labeled HBII-85 is particularly interesting since it seems to be in the "minimal coding region" for the PWS phenotype. The function of snoRNAs are not completely defined, but they appear to be involved in processing of m and t RNAs. A German group has been somewhat active in investigating this area in relation to PWS (Maren Runte, Bernhard Horsthemke, etc.)
- Research on Behavior Differences When Related to Food University of North Carolina graduate student is conducting a parental survey-based research project on behavior differences between the three types of Prader-Willi syndrome when related to food versus non-food items. Your participation will be greatly appreciated!
- Genetics and Behavior: Compulsive Behavior in Prader-Willi Syndrome Researchers at the University of Kansas Medical Center and the Division of Genetics and Molecular Medicine at Children’s Mercy Hospital have embarked on a study to better understand compulsive behavior in individuals with Prader‑Willi syndrome (PWS).
- Research On Behavior And Development In Prader-Willi Syndrome Dr. Elisabeth Dykens. Seeking persons with Prader-Willi syndrome aged 4 years through adulthood, and their families to come participate at the Kennedy Center at Vanderbilt University in Nashville, TN.
- Understanding childhood obesity and specifically, the mechanism of development of obesity Andrea Haqq, MD, pediatric endocrinologist at Duke University Medical Center is conducting a study and needs your help.
- Appetite and Prader–Willi Syndrome B.C. Women's and Childrens Hospital Endocrinologist is studying the effect of somatostatin on levels of Ghrelin and appetite in persons with PWS. Your child must be 10–18 years of age and overweight to participate in this study. For further information about the trial, please contact Dr. Jean-Pierre Chanoine at 604-875-2624.