Metabolic dysfunction following weight cycling in male mice.

BACKGROUND: Combatting overweight or obesity can lead to large fluctuations in an individual's body weight, often referred to as weight cycling or 'yo-yo' dieting. Current evidence regarding the potentially damaging effects of these changes is conflicting. METHODS: Here, we assess the metabolic effects of weight cycling in a murine model, comprising three dietary switches to normal or high-fat diets at 6 week intervals; male C57BL/6 mice were fed either a control (C) or high-fat (F) diet for 6 weeks (n=140/group). C and F groups were then either maintained on their initial diet (CC and FF, respectively) or switched to a high-fat (CF) or control (FC) diet (n=35/group). For the final 6 week interval, CC and CF groups were returned to the control diet (CCC and CFC groups), while FC and FF groups were placed on a high-fat diet (FCF and FFF) (n=28/group). RESULTS: For the majority of metabolic outcomes changes aligned with dietary switches; however, assessment of neuropeptides and receptors involved in appetite regulation and reward signalling pathways reveal variable patterns of expression. Furthermore, we demonstrate that multiple cycling events leads to a significant increase in internal fat deposition, even when compared with animals maintained on a high-fat diet (internal fat: FCF: 7.4±0.2 g vs FFF: 5.6±0.2 g; P<0.01). CONCLUSIONS: Increased internal adipose tissue is strongly linked to the development of metabolic syndrome associated conditions such as type 2 diabetes, cardiovascular disease and hypertension. Although further work will be required to elucidate the mechanisms underlying the neuronal control of energy homoeostasis, these studies provide a causative link between weight cycling and adverse health.

Sexual dimorphism in relation to adipose tissue and intrahepatocellular lipid deposition in early infancy.

Sexual dimorphism in adiposity is well described in adults, but the age at which differences first manifest is uncertain. Using a prospective cohort, we describe longitudinal changes in directly measured adiposity and intrahepatocellular lipid (IHCL) in relation to sex in healthy term infants. At median ages of 13 and 63 days, infants underwent quantification of adipose tissue depots by whole-body magnetic resonance imaging and measurement of IHCL by in vivo proton magnetic resonance spectroscopy. Longitudinal data were obtained from 70 infants (40 boys and 30 girls). In the neonatal period girls are more adipose in relation to body size than boys. At follow-up (median age 63 days), girls remained significantly more adipose. The greater relative adiposity that characterises girls is explained by more subcutaneous adipose tissue and this becomes increasingly apparent by follow-up. No significant sex differences were seen in IHCL. Sex-specific differences in infant adipose tissue distribution are in keeping with those described in later life, and suggest that sexual dimorphism in adiposity is established in early infancy.

Peptide YY 3-36 and pancreatic polypeptide differentially regulate hypothalamic neuronal activity in mice in vivo as measured by manganese-enhanced magnetic resonance imaging.

Peptide YY (PYY) and pancreatic polypeptide (PP) are two appetite suppressing hormones, released post-prandially from the ileum and pancreas, respectively. PYY(3-36) , the major circulating form of the peptide, is considered to reduce food intake in humans and rodents via high affinity binding to the auto-inhibitory neuropeptide Y receptor Y2R, whereas PP is considered to act through the Y4R. Current evidence indicates the anorexigenic effects of both peptides occur via signalling in the brainstem and arcuate nucleus (ARC) of the hypothalamus. Manganese-enhanced magnetic resonance imaging (MEMRI) has previously been used to track hypothalamic neuronal activity in vivo in response to both nutritional interventions and gut hormone treatment. In the present study, we used MEMRI to demonstrate that s.c. administration of PP results in a significant reduction in signal intensity (SI) in the ARC, ventromedial hypothalamus and paraventricular nucleus of fasted mice. Subcutaneous delivery of PYY(3-36) resulted in a nonsignificant trend towards decreased SI in the hypothalamus of fasted mice. We found no SI change in the area postrema of the brainstem after s.c. injection of either peptide. These differences in hypothalamic SI profile between PP and PYY(3-36) occurred despite both peptides producing a comparable reduction in food intake. These results suggest that separate central pathways control the anorexigenic response for PP and PYY(3-36) , possibly via a differential effect of Y4 receptor versus Y2 receptor signalling. In addition, we performed a series of MEMRI scans at 0-2, 2-4 and 4-6 h post-injection of PYY(3-36) and a potent analogue of the peptide; PYY(3-36) (LT). We recorded a significant reduction in the ARC SI 2-4 h after PYY(3-36) (LT) injection compared to both saline and PYY(3-36) in fasted mice. The physiological differences between PYY(3-36) and its analogue were also observed in the long-term effects on food intake, with PYY(3-36) (LT) producing a more sustained anorexigenic effect. These data suggest that MEMRI can be used to investigate the long-term effects of gut peptide delivery on activity within the hypothalamus and brainstem.

Coordinated changes in energy intake and expenditure following hypothalamic administration of neuropeptides involved in energy balance.

OBJECTIVE: The hypothalamic control of energy balance is regulated by a complex network of neuropeptide-releasing neurons. Although the effect of these neuropeptides on individual aspects of energy homoeostasis has been studied, the coordinated response of these effects has not been comprehensively investigated. We have simultaneously monitored a number of metabolic parameters following intracerebroventricular (ICV) administration of 1 and 3 nmol of neuropeptides with established roles in the regulation of feeding, activity and metabolism. Ad libitum- fed rats received the orexigenic neuropeptides neuropeptide Y (NPY), agouti-related protein (AgRP), melanin-concentrating hormone (MCH) or orexin-A. Overnight-food-deprived rats received an ICV injection of the anorectic peptides alpha-melanocyte-stimulating hormone (MSH), corticotrophin-releasing factor (CRF) or neuromedin U (NMU). RESULTS: Our results reveal the temporal sequence of the effects of these neuropeptides on both energy intake and expenditure, highlighting key differences in their function as mediators of energy balance. NPY and AgRP increased feeding and decreased oxygen consumption, with the effects of AgRP being more prolonged. In contrast, orexin-A increased both feeding and oxygen consumption, consistent with an observed increase in activity. The potent anorexigenic effects of CRF were accompanied by a prolonged increase in activity, whereas NMU injection resulted in significant but short-lasting inhibition of food intake, ambulatory activity and oxygen consumption. alpha-MSH injection resulted in significant increases in both ambulatory activity and oxygen consumption, and reduced food intake following administration of 3 nmol of the peptide. CONCLUSION: We have for the first time, simultaneously measured several metabolic parameters following hypothalamic administration of a number of neuropeptides within the same experimental system. This work has shown the interrelated effects of these neuropeotides on activity, energy expenditure and food intake, thus facilitating comparison between the different hypothalamic systems.

The importance of acclimatisation and habituation to experimental conditions when investigating the anorectic effects of gastrointestinal hormones in the rat.

OBJECTIVE: Peptide YY3-36 (PYY(3-36)), glucagon-like peptide-1 (GLP-1), oxyntomodulin and cholecystokinin (CCK) are gastrointestinal-derived hormones that are released postprandially in proportion to the amount of calories ingested. All significantly reduce food intake following peripheral administration to rodents. We have investigated the effect of handling, exposure to a novel environment or to environmental enrichment on the anorectic effect of these gut hormones. RESULTS: Results suggest that the transfer of a rat into a novel environment (cage change) inhibits the anorectic response to peripherally administered PYY(3-36) and oxyntomodulin (1 h food intake reduction (% saline control): PYY/home cage 82.3 +/- 5.9%, P < 0.05; PYY/clean cage 103.4 +/- 9.7%; oxyntomodulin/home cage 71.6 +/- 12.1%, P < 0.05; oxyntomodulin/clean cage 103.0 +/- 8.5%) and attenuates the anorectic response to GLP-1 and CCK (1 h food intake reduction (% saline control): GLP-1/home cage 68.8 +/- 6.4%, P < 0.01; GLP-1/clean cage 80.0 +/- 9.3%; CCK/home cage 49.8 +/- 6.2%, P < 0.001; CCK/clean cage 69.4 +/- 10.6%, P < 0.05). We have also observed that exposure to a novel environment does not alter anorectic effect of peripherally administered melanocortin 3/4 receptor agonist, melanotan II (MTII) (1 h food intake reduction (% saline control): MTII/home cage 32.0 +/- 6.3%, P < 0.001; MTII/clean cage 24.8 +/- 4.2%, P < 0.001). The attenuation in food intake observed following exposure to a novel environment can be attributed, in part, to a significant reduction in the food intake of the saline treated animals. In a further study, the anorectic effect of peripherally administered PYY(3-36) is attenuated in unhandled rats (88 +/- 4.2% saline control, P = ns) or rats exposed to environmental enrichment (103.3 +/- 9.7% saline control, P = ns), but not in animals that were handled extensively prior to the study (80.1 +/- 7.3% saline control, P < 0.05). CONCLUSION: These studies highlight the importance of handling, acclimatisation and habituation of rodents to experimental conditions prior to investigating the ability of gut hormones to alter food intake.

Large-scale studies of the association between variation at the TNF/LTA locus and susceptibility to type 2 diabetes.

AIMS/HYPOTHESIS: The proinflammatory cytokine TNF-alpha has been implicated in the pathogenesis of insulin resistance and type 2 diabetes, and variation in the gene encoding TNF-alpha (TNF) has shown inconsistent associations with susceptibility to both conditions. Additionally, the coding non-synonymous variant T60N in the neighbouring LTA gene has been reported to be associated with type 2 diabetes. The present study aimed to obtain a robust assessment of the role of variation in the tightly linked TNF/LTA region in diabetes susceptibility by genotyping TNF and LTA variants in large case-control resources. MATERIALS AND METHODS: The G-308A and G-238A TNF promoter variants and the LTA T60N polymorphism were genotyped in two UK case samples that were ascertained for positive family history and/or early onset of type 2 diabetes (combined n=858) and in 1,257 ethnically matched controls. RESULTS: There were no significant associations between the T60N, G-308A or G-238A genotype and type 2 diabetes in the combined analysis (exact Cochran-Mantel-Haenszel statistic for ordered genotypes for T60N, p=0.69; for G-308A, p=0.51; for G-238A, p=0.16). CONCLUSIONS/INTERPRETATION: The present study, one of the largest association analyses yet reported at this locus, provides no evidence that the specific TNF or LTA variants examined influence susceptibility to type 2 diabetes. More comprehensive studies of the TNF/LTA locus in substantially larger sample sets are required to establish whether genome sequence variation at this locus truly influences susceptibility to type 2 diabetes.

Examining the relationships between the Pro12Ala variant in PPARG and Type 2 diabetes-related traits in UK samples.

AIMS: The Pro12Ala polymorphism in the PPARG gene alters amino acid sequence and has shown consistent association with susceptibility to Type 2 diabetes in several populations. The present study makes use of large, well-characterized case-control resources to enhance understanding of this susceptibility effect by examining related traits, such as body mass index (BMI), waist-hip ratio and age at diagnosis. METHODS: The Pro12Ala variant was genotyped in two UK case samples, ascertained for positive family history and/or early onset of Type 2 diabetes (combined n=971); and in 1257 ethnically matched control subjects. RESULTS: There were significant associations of the Pro12Ala single nucleotide polymorphism (SNP) genotypes with diabetes in both case-control comparisons (P=0.025 and P=0.039). Comparing individuals homozygous for the Pro allele, with those carrying an Ala allele, the combined odds ratio for diabetes was 1.40 (95% CIs, 1.12-1.76, P=0.0031). There was no association between the variant and either waist-hip ratio or age at diagnosis. Proline homozygosity was associated with increased BMI in one patient group (P=0.013) and decreased BMI in the other (P=0.038). CONCLUSIONS: This study confirms that variation within PPARG influences susceptibility to Type 2 diabetes in UK samples. However, the relationship between PPARG variation and BMI is more complex, and studies in much larger sample sets will be required to more precisely characterize the effect of this variant on adiposity.