Validation of whole-body magnetic resonance spectroscopy as a tool to assess murine body composition

Effects of thermoneutrality on food intake, body weight, and body composition in a Prader-Willi syndrome mouse model

OBJECTIVE

Prader-Willi syndrome (PWS) is a multisystem genetic disorder. Unfortunately, none of several mouse models carrying PWS mutations emulates the entirety of the human PWS phenotype, including hyperphagia plus obesity.

METHODS

To determine whether housing at thermoneutrality (TN, 30 °C) permits the development of hyperphagia and obesity in the Snord116del PWS mouse model, the effects of housing three different ages of Snord116del and wild-type (WT) littermates at TN versus room temperature (RT, 22-24 °C) for 8 weeks were compared.

RESULTS

Snord116del mice born and maintained at TN exhibited lower body weight curves, lower percentage fat mass, and lower food intake than WT mice at RT. In 4- to 6-month-old high-fat diet-fed female mice, TN raised the Snord116del body weight curve closer to that of RT-housed WT mice although the TN-housed Snord116del mice did not gain more adiposity or exhibit greater food intake. In 6- to 8-month-old high-fat diet-fed male mice, body weight, adiposity, and food intake of TN-housed Snord116del mice remained far below levels in RT-housed WT mice. TN elicited hypotonia in Snord116del adults and exacerbated mortality of Snord116del newborns.

CONCLUSIONS

In none of three tested TN protocols were greater food intake, body weight, or adiposity induced in Snord116del mice compared with RT-housed WT mice.

Uncovering the effect and mechanism of Panax notoginseng saponins on metabolic syndrome by network pharmacology strategy

ETHNOPHARMACOLOGICAL RELEVANCE

Metabolic syndrome (MetS) is a cluster of disease centered on obesity, which is the result of stagnation of liver qi according to traditional Chinese medicine. Panax notoginseng is a traditional Chinese herbal medicine, entering liver and stomach meridians and dissipating blood stasis, in which panax notoginseng saponins (PNS) are the main active components. However, its effects and mechanism on metabolic syndrome has not been revealed yet.

AIM OF STUDY

To evaluate the anti-MetS effect of PNS, including body weight and adiposity, glucose metabolism and non-alcoholic fatty liver disease (NAFLD), as well as to explore the mechanism and signaling pathway of PNS on MetS effect.

MATERIALS AND METHODS

HPLC was utilized to affirm the percentages of saponins in PNS. In vivo, normal C57BL/6J mice and high-fat diet (HFD)-induced MetS mice were used to evaluate anti-MetS effect of PNS. Body weight, food and water intake were recorded. NMR imager was used for NMR imaging and lipid-water analysis. Blood glucose detection, glucose and insulin tolerance test were performed to evaluate glucose metabolism. Biochemical indexes analysis and histopathological staining were used to evaluate the effect on NAFLD. The expressions of mRNA and proteins related to thermogenesis in adipose tissue were determined using real-time PCR and Western blot. In silico, network pharmacology was utilized to predict potential mechanism. In vitro, matured 3T3-L1 adipocyte was used as subject to confirm the signaling pathway by Western blot.

RESULTS

We determined the content of PNS component by HPLC. In vivo, PNS could improve metabolic syndrome with weight loss, reduction of adiposity, improvement of adipose distribution, correction of glucose metabolism disorder and attenuation of NAFLD. Mechanismly, PNS boosted energy exhaustion and dramatically enhanced thermogenesis in brown adipose tissue (BAT), induced white adipose tissue (WAT) browning. In silico, utilizing network pharmacology strategy, we identified 307 candidate targets which were enriched in MAPK signaling pathway specifically in liver tissue and adipocyte. In vitro validation confirmed ERK and p38MAPK mediated anti-MetS effects of PNS, not JNK signaling pathway.

CONCLUSION

PNS exerted protective effect on metabolic syndrome through MAPK-mediated adipose thermogenic activation, which may serve as a prospective therapeutic drug for metabolic syndrome.

Dietary fructose improves intestinal cell survival and nutrient absorption

Fructose consumption is linked to the rising incidence of obesity and cancer, which are two of the leading causes of morbidity and mortality globally1,2. Dietary fructose metabolism begins at the epithelium of the small intestine, where fructose is transported by glucose transporter type 5 (GLUT5; encoded by SLC2A5) and phosphorylated by ketohexokinase to form fructose 1-phosphate, which accumulates to high levels in the cell3,4. Although this pathway has been implicated in obesity and tumour promotion, the exact mechanism that drives these pathologies in the intestine remains unclear. Here we show that dietary fructose improves the survival of intestinal cells and increases intestinal villus length in several mouse models. The increase in villus length expands the surface area of the gut and increases nutrient absorption and adiposity in mice that are fed a high-fat diet. In hypoxic intestinal cells, fructose 1-phosphate inhibits the M2 isoform of pyruvate kinase to promote cell survival5-7. Genetic ablation of ketohexokinase or stimulation of pyruvate kinase prevents villus elongation and abolishes the nutrient absorption and tumour growth that are induced by feeding mice with high-fructose corn syrup. The ability of fructose to promote cell survival through an allosteric metabolite thus provides additional insights into the excess adiposity generated by a Western diet, and a compelling explanation for the promotion of tumour growth by high-fructose corn syrup.

A noninvasive method to study the evolution of extracellular fluid volume in mice using time-domain nuclear magnetic resonance

Maintaining water homeostasis is fundamental for cellular function. Many diseases and drugs affect water balance and plasma osmolality. Water homeostasis studies in small animals require the use of invasive or terminal methods that make intracellular fluid volume and extracellular fluid volume (ECF) monitoring over time stressful and time consuming. We examined the feasibility of monitoring mouse ECF by a noninvasive method using time-domain nuclear magnetic resonance (TD-NMR). This technique allows differentiation of protons in a liquid environment (free fluid) from protons in soft tissues containing a majority of either small molecules (lean) or large molecules (fat). Moreover, this apparatus enables rapid, noninvasive, and repeated measurements on the same animal. We assessed the feasibility of coupling TD-NMR analysis to a longitudinal metabolic cage study by monitoring mice daily. We determined the effect of 24-h water deprivation on mouse body parameters and detected a sequential and overlapping decrease in free fluid and lean mass during water deprivation. Finally, we studied the effect of mineralocorticoids that are known to induce a transient increase in ECF but for which no direct measurements have been performed in mice. We showed, for the first time, that mineralocorticoids induced a transient ~15% increase in free fluid in conscious mice. TD-NMR is, therefore, the first method to allow direct measurement of discrete changes in ECF in conscious small animals. This method allows analysis of kinetic changes to stimuli before investigating with terminal methods and will allow further understanding of fluid disorders.

High-fructose corn syrup enhances intestinal tumor growth in mice

Excessive consumption of beverages sweetened with high-fructose corn syrup (HFCS) is associated with obesity and with an increased risk of colorectal cancer. Whether HFCS contributes directly to tumorigenesis is unclear. We investigated the effects of daily oral administration of HFCS in adenomatous polyposis coli (APC) mutant mice, which are predisposed to develop intestinal tumors. The HFCS-treated mice showed a substantial increase in tumor size and tumor grade in the absence of obesity and metabolic syndrome. HFCS increased the concentrations of fructose and glucose in the intestinal lumen and serum, respectively, and the tumors transported both sugars. Within the tumors, fructose was converted to fructose-1-phosphate, leading to activation of glycolysis and increased synthesis of fatty acids that support tumor growth. These mouse studies support the hypothesis that the combination of dietary glucose and fructose, even at a moderate dose, can enhance tumorigenesis.

The endocannabinoid anandamide during lactation increases body fat content and CB1 receptor levels in mice adipose tissue

Type 1 cannabinoid receptors (CB₁R) modulate energy balance; thus, their premature activation may result in altered physiology of tissues involved in such a function. Activation of CB₁R mainly occurs after binding to the endocannabinoid Anandamide (AEA). The objective of this study was to evaluate the effects of AEA treatment during lactation on epididymal and body fat content, in addition to CB₁R protein level at weaning. With this purpose, male mice pups were orally treated with AEA (20 μg g⁻¹ body weight) or vehicle during lactation. Mice (21 days old) were killed and epididymal fat was extracted to evaluate its amount, adipocyte size and CB₁R protein levels by western blot analysis. Total body fat percentage was also evaluated. Anandamide-treated mice showed an increased body fat content at 21 and 150 days of age. Moreover, epididymal adipose tissue amount, adipocyte size and CB₁R protein levels were higher in the AEA-treated group. This in vivo study shows for the first time that a progressive increase in body fat accumulation can be programmed in early stages of life by oral treatment with the endocannabinoid AEA, a fact associated with an increased amount of epididymal fat pads and a higher expression of CB₁R in this tissue.

Granulocyte/Macrophage Colony-stimulating Factor-dependent Dendritic Cells Restrain Lean Adipose Tissue Expansion

The physiological roles of macrophages and dendritic cells (DCs) in lean white adipose tissue homeostasis have received little attention. Because DCs are generated from bone marrow progenitors in the presence of granulocyte/macrophage colony-stimulating factor (GM-CSF), we used GM-CSF-deficient (Csf2(-/-)) mice fed a low fat diet to test the hypothesis that adipose tissue DCs regulate the development of adipose tissue. At 4 weeks of age, Csf2(-/-) mice had 75% fewer CD45(+)Cd11b(+)Cd11c(+)MHCII(+) F4/80(-) DCs in white adipose tissue than did wild-type controls. Furthermore, the Csf2(-/-) mice showed a 30% increase in whole body adiposity, which persisted to adulthood. Adipocytes from Csf2(-/-) mice were 50% larger by volume and contained higher levels of adipogenesis gene transcripts, indicating enhanced adipocyte differentiation. In contrast, adipogenesis/adipocyte lipid accumulation was inhibited when preadipocytes were co-cultured with CD45(+)Cd11b(+)Cd11c(+)MHCII(+)F4/80(-) DCs. Medium conditioned by DCs, but not by macrophages, also inhibited adipocyte lipid accumulation. Proteomic analysis revealed that matrix metalloproteinase 12 and fibronectin 1 were greatly enriched in the medium conditioned by DCs compared with that conditioned by macrophages. Silencing fibronectin or genetic deletion of matrix metalloproteinase 12 in DCs partially reversed the inhibition of adipocyte lipid accumulation. Our observations indicate that DCs residing in adipose tissue play a critical role in suppressing normal adipose tissue expansion.

Macrophage metalloelastase (MMP12) regulates adipose tissue expansion, insulin sensitivity, and expression of inducible nitric oxide synthase

Macrophage metalloelastase, a matrix metallopeptidase (MMP12) predominantly expressed by mature tissue macrophages, is implicated in pathological processes. However, physiological functions for MMP12 have not been described. Because mRNA levels for the enzyme increase markedly in adipose tissue of obese mice, we investigated the role of MMP12 in adipose tissue expansion and insulin resistance. In humans, MMP12 expression correlated positively and significantly with insulin resistance, TNF-α expression, and the number of CD14(+)CD206(+) macrophages in adipose tissue. MMP12 was the most abundant matrix metallopeptidase detected by proteomic analysis of conditioned medium of M2 macrophages and dendritic cells. In contrast, it was detected only at low levels in bone marrow derived macrophages and M1 macrophages. When mice received a high-fat diet, adipose tissue mass increased and CD11b(+)F4/80(+)CD11c(-) macrophages accumulated to a greater extent in MMP12-deficient (Mmp12(-/-)) mice than in wild-type mice (Mmp12(+/+)). Despite being markedly more obese, fat-fed Mmp12(-/-) mice were more insulin sensitive than fat-fed Mmp12(+/+) mice. Expression of inducible nitric oxide synthase (Nos2) by Mmp12(-/-) macrophages was significantly impaired both in vivo and in vitro, suggesting that MMP12 might mediate nitric oxide production during inflammation. We propose that MMP12 acts as a double-edged sword by promoting insulin resistance while combatting adipose tissue expansion.

Transgenic mice overexpressing amyloid precursor protein exhibit early metabolic deficits and a pathologically low leptin state associated with hypothalamic dysfunction in arcuate neuropeptide Y neurons

Weight loss is a prominent early feature of Alzheimer's disease (AD) that often precedes the cognitive decline and clinical diagnosis. While the exact pathogenesis of AD remains unclear, accumulation of amyloid-β (Aβ) derived from the amyloid precursor protein (APP) in the brain is thought to lead to the neuronal dysfunction and death underlying the dementia. In this study, we examined whether transgenic mice overexpressing the Swedish mutation of APP (Tg2576), recapitulating selected features of AD, have hypothalamic leptin signaling dysfunction leading to early body weight deficits. We found that 3-month-old Tg2576 mice, before amyloid plaque formation, exhibit decreased weight with markedly decreased adiposity, low plasma leptin levels, and increased energy expenditure without alterations in feeding behavior. The expression of the orexigenic neuropeptide Y (NPY) in the hypothalamus to the low leptin state was abnormal at basal and fasting conditions. In addition, arcuate NPY neurons exhibited abnormal electrophysiological responses to leptin in Tg2576 hypothalamic slices or wild-type slices treated with Aβ. Finally, the metabolic deficits worsened as Tg2576 mice aged and amyloid burden increased in the brain. These results indicate that excess Aβ can potentially disrupt hypothalamic arcuate NPY neurons leading to weight loss and a pathologically low leptin state early in the disease process that progressively worsens as the amyloid burden increases. Collectively, these findings suggest that weight loss is an intrinsic pathological feature of Aβ accumulation and identify hypothalamic leptin signaling as a previously unrecognized pathogenic site of action for Aβ.

Different types of soluble fermentable dietary fibre decrease food intake, body weight gain and adiposity in young adult male rats

BACKGROUND

Dietary fibre-induced satiety offers a physiological approach to body weight regulation, yet there is lack of scientific evidence. This experiment quantified food intake, body weight and body composition responses to three different soluble fermentable dietary fibres in an animal model and explored underlying mechanisms of satiety signalling and hindgut fermentation.

METHODS

Young adult male rats were fed ad libitum purified control diet (CONT) containing 5% w/w cellulose (insoluble fibre), or diet containing 10% w/w cellulose (CELL), fructo-oligosaccharide (FOS), oat beta-glucan (GLUC) or apple pectin (PECT) (4 weeks; n = 10/group). Food intake, body weight, and body composition (MRI) were recorded, final blood samples analysed for gut satiety hormones, hindgut contents for fermentation products (including short-chain fatty acids, SCFA) and intestinal tissues for SCFA receptor gene expression.

RESULTS

GLUC, FOS and PECT groups had, respectively, 10% (P < 0.05), 17% (P < 0.001) and 19% (P < 0.001) lower food intake and 37% (P < 0.01), 37% (P < 0.01) and 45% (P < 0.001) lower body weight gain than CONT during the four-week experiment. At the end they had 26% (P < 0.05), 35% (P < 0.01) and 42% (P < 0.001) less total body fat, respectively, while plasma total glucagon-like peptide-1 (GLP-1) was 2.2-, 3.2- and 2.6-fold higher (P < 0.001) and peptide tyrosine tyrosine (PYY) was 2.3-, 3.1- and 3.0-fold higher (P < 0.001). There were no differences in these parameters between CONT and CELL. Compared with CONT and CELL, caecal concentrations of fermentation products increased 1.4- to 2.2-fold in GLUC, FOS and PECT (P < 0.05) and colonic concentrations increased 1.9- to 2.5-fold in GLUC and FOS (P < 0.05), with no consistent changes in SCFA receptor gene expression detected.

CONCLUSIONS

This provides animal model evidence that sustained intake of three different soluble dietary fibres decreases food intake, weight gain and adiposity, increases circulating satiety hormones GLP-1 and PYY, and increases hindgut fermentation. The presence of soluble fermentable fibre appears to be more important than its source. The results suggest that dietary fibre-induced satiety is worthy of further investigation towards natural body weight regulation in humans.

Metabolic effects of a high-fat diet post-weaning after low maternal dietary folate during pregnancy and lactation

SCOPE

Investigate the influence of low-folate supply during pregnancy and lactation on obesity and markers of the metabolic syndrome in offspring, and how provision of a high-fat diet post weaning may exacerbate the resultant phenotype.

METHODS AND RESULTS

Female C57Bl/6 mice were randomized to low or normal folate diets (0.4 or 2 mg folic acid/kg diet) prior to and during pregnancy and lactation. At 4 wk of age, offspring were randomized to high- or low-fat diets, weighed weekly and food intake assessed at 9 and 18 wk old. Adiposity was measured at 3 and 6 months. Plasma glucose and triacylglycerol (TAG) concentrations were measured at 6 months. Maternal folate supply did not influence adult offspring body weight or adiposity. High-fat feeding post weaning increased body weight and adiposity at 3 and 6 months (p > 0.001). Maternal low folate lowered plasma glucose (p = 0.010) but increased plasma TAG (p = 0.048). High-fat feeding post weaning increased plasma glucose and TAG (p = 0.023, p = 0.049 respectively). Offspring from folate-depleted (but not folate-adequate) dams had 30% higher TAG concentration when fed the high-fat diet from weaning (p = 0.005 for interaction).

CONCLUSION

Inadequate maternal folate intake has long-term effects on offspring metabolism, manifested as increased circulating TAG, particularly in offspring with high-fat intake post weaning.

Quantitative Body Composition Analysis in Awake Mice and Rats by Magnetic Resonance Relaxometry

OBJECTIVE

Magnetic resonance (MR) relaxometry has recently been introduced for noninvasive body composition analysis in awake mice. The purpose of the present study was to extend the method to rats and to introduce calibration procedures that render MR relaxometry fully quantitative.

RESEARCH METHODS AND PROCEDURES

Proton T(2) MR relaxometry at 4.7 Tesla was used for body composition analyses in 700 awake mice and 400 rats of different strains and conditions. Relaxograms calculated from the signal decays observed with multi-spin-echo acquisition provided well-separated contributions of tissue water and fat. Analysis of fat composition was carried out in vivo using (13)C-MR spectroscopy. Evolution of body composition in rats was assessed during drug treatment.

RESULTS

MR relaxometry for noninvasive body composition analysis in laboratory rodents was implemented on a standard MR scanner, and a throughput of >30 animals per hour was achieved. Excellent linearity and reproducibility with coefficients of variance as low as 2.5% and 1.7% were obtained in mice and rats, respectively. The lean mass-to-water ratio (mice, 1.35 +/- 0.03; rats, 1.39 +/- 0.04) and the proton density of fat (mice, 8.1 +/- 0.2; rats, 8.9 +/- 0.2 g/mol) were determined from cross-sectional data. Fat composition analysis by (13)C-MR spectroscopy corroborated these findings and yielded information on the average acyl chain length (16.3 +/- 1.6) and contributions of saturated (27 +/- 3%), monounsaturated (22 +/- 2%), and polyunsaturated (51 +/- 3%) fatty acids. Longitudinal assessments in rats treated with sibutramine and dexfenfluramine showed dose-related changes in body composition.

DISCUSSION

T(2) MR relaxometry backed by solid calibration provides a powerful means for rapid quantitative body composition analysis in awake mice and rats that is suitable for serial investigations in pharmaceutical research.

Fermentable carbohydrate alters hypothalamic neuronal activity and protects against the obesogenic environment

Obesity has become a major global health problem. Recently, attention has focused on the benefits of fermentable carbohydrates on modulating metabolism. Here, we take a system approach to investigate the physiological effects of supplementation with oligofructose-enriched inulin (In). We hypothesize that supplementation with this fermentable carbohydrate will not only lead to changes in body weight and composition, but also to modulation in neuronal activation in the hypothalamus. Male C57BL/6 mice were maintained on a normal chow diet (control) or a high fat (HF) diet supplemented with either oligofructose-enriched In or corn starch (Cs) for 9 weeks. Compared to HF+Cs diet, In supplementation led to significant reduction in average daily weight gain (mean ± s.e.m.: 0.19 ± 0.01 g vs. 0.26 ± 0.02 g, P < 0.01), total body adiposity (24.9 ± 1.2% vs. 30.7 ± 1.4%, P < 0.01), and lowered liver fat content (11.7 ± 1.7% vs. 23.8 ± 3.4%, P < 0.01). Significant changes were also observed in fecal bacterial distribution, with increases in both Bifidobacteria and Lactobacillius and a significant increase in short chain fatty acids (SCFA). Using manganese-enhanced MRI (MEMRI), we observed a significant increase in neuronal activation within the arcuate nucleus (ARC) of animals that received In supplementation compared to those fed HF+Cs diet. In conclusion, we have demonstrated for the first time, in the same animal, a wide range of beneficial metabolic effects following supplementation of a HF diet with oligofructose-enriched In, as well as significant changes in hypothalamic neuronal activity.

Deficiency of lymphotoxin-α does not exacerbate high-fat diet-induced obesity but does enhance inflammation in mice

Lymphotoxin-α (LTα) is secreted by lymphocytes and acts through tumor necrosis factor-α receptors and the LTβ receptor. Our goals were to determine whether LT has a role in obesity and investigate whether LT contributes to the link between obesity and adipose tissue lymphocyte accumulation. LT deficient (LT(-/-)) and wild-type (WT) mice were fed standard pelleted rodent chow or a high-fat/high-sucrose diet (HFHS) for 13 wk. Body weight, body composition, and food intake were measured. Glucose tolerance was assessed. Systemic and adipose tissue inflammatory statuses were evaluated by quantifying plasma adipokine levels and tissue macrophage and T cell-specific gene expression in abdominal fat. LT(-/-) mice were smaller (20%) and leaner (25%) than WT controls after 13 wk of HFHS diet feeding. LT(-/-) mice showed improved glucose tolerance, suggesting that, in WT mice, LT may impair glucose metabolism. Surprisingly, adipose tissue from rodent chow- and HFHS-fed LT(-/-) mice exhibited increased T lymphocyte and macrophage infiltration compared with WT mice. Despite the fact that LT(-/-) mice exhibited an enhanced inflammatory status at the systemic and tissue level even when fed rodent chow, they were protected from enhanced diet-induced obesity and insulin resistance. Thus, LT contributes to body weight and adiposity and is required to modulate the accumulation of immune cells in adipose tissue.

Validation of longitudinal DXA changes in body composition from pre- to mid-adolescence using MRI as reference

Dual-energy X-ray absorptiometry (DXA) has been used extensively for bone mineral density and body composition assessments. Surprisingly, the role of DXA in monitoring changes in children's body composition, using direct imaging methods such as magnetic resonance imaging (MRI) as reference, is still yet to be validated. We aimed at validating the use of DXA in monitoring change in the thigh lean soft tissue mass (LSTM) and fat mass (FM) when compared with thigh skeletal muscle mass (SM) and FM, measured using MRI as the reference standard, from childhood to midadolescence. At baseline, 22 healthy children (16 boys and 6 girls) aged 8-11yr were included, and then recalled at pubertal stage Tanner2-Tanner4. LSTM-DXA and FM-DXA of the mid-third femur and SM-MRI and FM-MRI of the same region were measured on the same day. The same protocol was repeated 26-48mo later. At baseline, DXA overestimated LSTM-DXA on average by 222g (95% confidence interval [CI]: 33-410g) with a concordance C-LSTM=0.576. FM-MRI and FM-DXA were not significantly different (95% CI=213 to 199g, the C-FM=0.907). At follow-up, change in LSTM-DXA and FM-DXA were not significantly different to change in SM-MRI and FM-MRI, respectively (95% CI of the difference was -278 to 208g for LSTM, and -148 to 236g for FM). The coefficient of concordance between the 2 techniques was 0.88 for both LSTM and FM. This study validates the use of DXA in monitoring changes in LSTM and FM in children, confirming its significant potential in clinical and research roles in pediatric body composition.

Two-year body composition analyses of long-lived GHR null mice

Growth hormone receptor gene-disrupted (GHR-/-) mice exhibit increased life span and adipose tissue mass. Although this obese phenotype has been reported extensively for young adult male GHR-/- mice, data for females and for other ages in either gender are lacking. Thus, the purpose of this study was to evaluate body composition longitudinally in both male and female GHR-/- mice. Results show that GHR-/- mice have a greater percent fat mass with no significant difference in absolute fat mass throughout life. Lean mass shows an opposite trend with percent lean mass not significantly different between genotypes but absolute mass reduced in GHR-/- mice. Differences in body composition are more pronounced in male than in female mice, and both genders of GHR-/- mice show specific enlargement of the subcutaneous adipose depot. Along with previously published data, these results suggest a consistent and intriguing protective effect of excess fat mass in the subcutaneous region.

Receptors for tumor necrosis factor-alpha play a protective role against obesity and alter adipose tissue macrophage status

TNF-alpha signals through two receptors, TNFR1 and TNFR2. Our goals were: 1) determine the role of TNFRs in obesity and metabolic disease and 2) investigate whether TNFRs contribute to the link between obesity and adipose tissue macrophage infiltration and polarization. R1(-/-)R2(-/-) (RKO) and wild-type (WT) mice were fed standard chow or a high-fat/high-sucrose diet (HFHS) over 14 wk. Body composition, food intake, and energy expenditure were measured. Oral glucose tolerance and insulin sensitivity tests assessed glucose homeostasis. Adipose tissue and systemic inflammatory status were evaluated by quantifying plasma adipokine levels and macrophage-specific gene expression in fat. RKO mice were heavier (10%) and fatter (18%) than WT controls at 4 wk of age and were 26% heavier and 50% fatter than WT after 14 wk of HFHS diet feeding. Age- and diet-adjusted 24-h oxygen consumption, activity, and respiratory exchange ratio were significantly reduced in RKO mice. Obese RKO mice were markedly insulin resistant, suggesting that intact TNFR signaling is not required for the effect of obesity to impair glucose metabolism. Adipose tissue from HFHS-fed RKO mice exhibited increased macrophage infiltration, but compared with WT mice, macrophage phenotypic markers featured a predominance of antiinflammatory M2 over proinflammatory M1 cells. TNFRs play a physiological role to limit body weight and adiposity by modestly increasing metabolic rate and fatty acid oxidation, and they are required for obesity-induced activation of adipose tissue macrophages. Despite these effects, TNFRs are not required for obesity-induced insulin resistance.

Pegylated leptin antagonist is a potent orexigenic agent: preparation and mechanism of activity

Leptin, a pleiotropic adipokine, is a central regulator of appetite and weight and a key immunomodulatory protein. Although inborn leptin deficiency causes weight gain, it is unclear whether induced leptin deficiency in adult wild-type animals would be orexigenic. Previous work with a potent competitive leptin antagonist did not induce a true metabolic state of leptin deficiency in mice because of a short circulating half-life. In this study, we increased the half-life of the leptin antagonist by pegylation, which resulted in significantly increased bioavailability and retaining of antagonistic activity. Mice administered the pegylated antagonist showed a rapid and dramatic increase in food intake with weight gain. Resulting fat was confined to the mesenteric region with no accumulation in the liver. Serum cholesterol, triglyceride, and hepatic aminotransferases remained unaffected. Weight changes were reversible on cessation of leptin antagonist treatment. The mechanism of severe central leptin deficiency was found to be primarily caused by blockade of transport of circulating leptin across the blood-brain barrier with antagonisms at the arcuate nucleus playing a more minor role. Altogether we introduce a novel compound that induces central and peripheral leptin deficiency. This compound should be useful in exploring the involvement of leptin in metabolic and immune processes and could serve as a therapeutic for the treatment of cachexia.

Vascular inflammation, insulin resistance, and reduced nitric oxide production precede the onset of peripheral insulin resistance

OBJECTIVE

Obesity causes inflammation and insulin resistance in the vasculature as well as in tissues involved in glucose metabolism such as liver, muscle, and adipose tissue. To investigate the relative susceptibility of vascular tissue to these effects, we determined the time course over which inflammation and insulin resistance develops in various tissues of mice with diet-induced obesity (DIO) and compared these tissue-based responses to changes in circulating inflammatory markers.

METHODS AND RESULTS

Adult male C57BL/6 mice were fed either a control low-fat diet (LF; 10% saturated fat) or a high-fat diet (HF, 60% saturated fat) for durations ranging between 1 to 14 weeks. Cellular inflammation and insulin resistance were assessed by measuring phospho-IkappaBalpha and insulin-induced phosphorylation of Akt, respectively, in extracts of thoracic aorta, liver, skeletal muscle, and visceral fat. As expected, HF feeding induced rapid increases of body weight, fat mass, and fasting insulin levels compared to controls, each of which achieved statistical significance within 4 weeks. Whereas plasma markers of inflammation became elevated relatively late in the course of DIO (eg, serum amyloid A [SAA], by Week 14), levels of phospho-IkappaBalpha in aortic lysates were elevated by 2-fold within the first week. The early onset of vascular inflammation was accompanied by biochemical evidence of both endothelial dysfunction (reduced nitric oxide production; induction of intracellular adhesion molecule-1 and vascular cell adhesion molecule-1) and insulin resistance (impaired insulin-induced phosphorylation of Akt and eNOS). Although inflammation and insulin resistance were also detected in skeletal muscle and liver of HF-fed animals, these responses were observed much later (between 4 and 8 weeks of HF feeding), and they were not detected in visceral adipose tissue until 14 weeks.

CONCLUSIONS

During obesity induced by HF feeding, inflammation and insulin resistance develop in the vasculature well before these responses are detected in muscle, liver, or adipose tissue. This observation suggests that the vasculature is more susceptible than other tissues to the deleterious effects of nutrient overload.

Body composition and metabolic changes associated with massive intestinal resection in mice

BACKGROUND

The specific changes in body composition and metabolism during the adaptation response to massive intestinal loss are presently unclear. The present study was designed to determine alterations in these parameters using an established mouse model.

METHODS

Male C57/Bl6 mice underwent either 50% small bowel resection (SBR) or transection with reanastomosis (Sham) operation. Oxygen consumption per unit time, carbon dioxide production per unit time, respiratory quotient, and energy expenditure were measured by indirect calorimetry along with body composition determination by nuclear magnetic resonance at postoperative days 1, 3, 7, 14, 21, and 28.

RESULTS

The mice that underwent SBR had lower rates of metabolism as measured by decreased energy expenditure, carbon dioxide production per unit time and oxygen consumption per unit time when compared with the Sham group throughout the study period. During adaptation, SBR mice had restoration of body fat at two weeks after the operation while the lean mass and body weight remained lower throughout.

CONCLUSION

Without supplemental parenteral nutrition, the adaptation response to massive SBR is characterized by reduced energy metabolism and an inappropriate replenishment of fat stores over lean mass. Futures studies will be needed to determine the metabolic effects of various growth factors designed to enhance structural features of adaptation.

Impact of resistant starch on body fat patterning and central appetite regulation

BACKGROUND

Adipose tissue patterning has a major influence on the risk of developing chronic disease. Environmental influences on both body fat patterning and appetite regulation are not fully understood. This study was performed to investigate the impact of resistant starch (RS) on adipose tissue deposition and central regulation of appetite in mice.

METHODOLOGY AND PRINCIPLE FINDINGS

Forty mice were randomised to a diet supplemented with either the high resistant starch (HRS), or the readily digestible starch (LRS). Using (1)H magnetic resonance (MR) methods, whole body adiposity, intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL) were measured. Manganese-enhanced MRI (MEMRI) was used to investigate neuronal activity in hypothalamic regions involved in appetite control when fed ad libitum. At the end of the interventional period, adipocytes were isolated from epididymal adipose tissue and fasting plasma collected for hormonal and adipokine measurement. Mice on the HRS and LRS diet had similar body weights although total body adiposity, subcutaneous and visceral fat, IHCL, plasma leptin, plasma adiponectin plasma insulin/glucose ratios was significantly greater in the latter group. Adipocytes isolated from the LRS group were significantly larger and had lower insulin-stimulated glucose uptake. MEMRI data obtained from the ventromedial and paraventricular hypothalamic nuclei suggests a satiating effect of the HRS diet despite a lower energy intake.

CONCLUSION AND SIGNIFICANCE

Dietary RS significantly impacts on adipose tissue patterning, adipocyte morphology and metabolism, glucose and insulin metabolism, as well as affecting appetite regulation, supported by changes in neuronal activity in hypothalamic appetite regulation centres which are suggestive of satiation.

Challenge by the murine brain: multi-pinhole SPECT of 123I-labelled pharmaceuticals

This protocol presents an improved method for SPECT imaging based on multi-pinhole techniques, applied to the visualisation of neurotracers in small animal models. Three types of collimators with 6-pinhole apertures adapted to special requirements for the imaging of the brain of mice and rats and to full body imaging in mice are employed in the experiments. A conventional triple-headed TRIAD/Trionix SPECT system was upgraded with pyramidal supports and shieldings onto the multi-pinhole collimators were installed. The system was employed for the assessment of the uptake of [123I]FP-CIT and [123I]IBZM, well known tracers of dopamine transport and dopamine D2/D3 receptors, respectively. Requirements regarding the applied radioactivity are reported, as well as further conditions determining the effectiveness of the detection of the uptake of [123I]FP-CIT and [123I]IBZM. The measurements in mice required only 20-25% of the activity described in previous studies. Dynamic measurements are presented, with a time resolution as high as 10 min in the brain of rats. Due to the lower signal intensity obtained for mice, the time resolution was 42min for [123I]FP-CIT, with a ratio ROI/background of 5.4, and 17 min for [123I]IBZM, with the ratio ROI/background of 4.5 (1.6-7.4).

In vivo mouse imaging and spectroscopy in drug discovery

Imaging modalities such as micro-computed tomography (micro-CT), micro-positron emission tomography (micro-PET), high-resolution MRI, optical imaging, and high-resolution ultrasound have become invaluable tools in preclinical pharmaceutical research. They can be used to non-invasively investigate, in vivo, rodent biology and metabolism, disease models, and pharmacokinetics and pharmacodynamics of drugs. The advantages and limitations of each approach usually determine its application, and therefore a small-rodent imaging laboratory in a pharmaceutical environment should ideally provide access to several techniques. In this paper we aim to illustrate how these techniques may be used to obtain meaningful information for the phenotyping of transgenic mice and for the analysis of compounds in murine models of disease.

Intra-abdominal fat burden discriminated in vivo using proton magnetic resonance spectroscopy

OBJECTIVE

To assess proton magnetic resonance spectroscopy (1H-MRS) as a means to distinguish among mice with disparate intra-abdominal body fat compositions, and to measure changes in intra-abdominal fat burden during weight loss and regain.

RESEARCH METHODS AND PROCEDURES

Intra-abdominal fat burden was analyzed as a ratio of integrated areas under the curves of fat to water (1)H-MRS signals collected from a region of interest standardized across B6.V-Lep(ob), C57BL/6, and A-ZIP/F mice that exhibited various genotypically related body fat compositions, ranging from obese (B6.V-Lep(ob)) to minimal body fat (A-ZIP/F). 1H-MRS analysis of fat burden was compared with intra-abdominal fat volume and with a single cross-sectional intra-abdominal fat area calculated from segmented magnetic resonance images. Similar measurements were made from obese B6.V-Lep(ob) mice before, during, and after they were induced to lose weight by leptin administration.

RESULTS

Relative amounts of intra-abdominal fat analyzed by 1H-MRS differed significantly according to body composition and genotype of the three strains of mice (p < 0.05). Intra-abdominal fat assessed by 1H-MRS correlated with both intra-abdominal fat volume (r = 0.88, p < 0.001) and body weight (r = 0.82, p < 0.001) among, but not within, all three genotypes. During weight loss and regain, there was a significant overall pattern of changes in intra-abdominal fat quantity that occurred, which was reflected by 1H-MRS (p = 0.006).

DISCUSSION

Results support the use of localized 1H-MRS for assessing differences in intra-abdominal fat. Refinements in 1H-MRS voxel region of interest size and location as well as instrument precision may result in improved correlations within certain body compositions.

Long-term treatment with rosiglitazone and metformin reduces the extent of, but does not prevent, islet amyloid deposition in mice expressing the gene for human islet amyloid polypeptide

Islet amyloid deposition in type 2 diabetes is associated with reduced beta-cell mass. Therefore, interventions aimed at reducing islet amyloid formation may help preserve beta-cell mass in type 2 diabetes. Rosiglitazone and metformin act by different mechanisms to improve insulin sensitivity and thereby reduce beta-cell secretory demand, resulting in decreased release of insulin and islet amyloid polypeptide (IAPP), the unique constituent of islet amyloid deposits. We hypothesized that this reduced beta-cell secretory demand would lead to reduced islet amyloid formation. Human IAPP (hIAPP) transgenic mice, a model of islet amyloid, were treated for 12 months with rosiglitazone (1.5 mg.kg(-1).day(-1), n = 19), metformin (1 g.kg(-1).day(-1), n = 18), or control (n = 17). At the end of the study, islet amyloid prevalence (percent islets containing amyloid) and severity (percent islet area occupied by amyloid), islet mass, beta-cell mass, and insulin release were determined. Islet amyloid prevalence (44 +/- 8, 13 +/- 4, and 11 +/- 3% for control, metformin-, and rosiglitazone-treated mice, respectively) and severity (9.2 +/- 3.0, 0.22 +/- 0.11, and 0.10 +/- 0.05% for control, metformin-, and rosiglitazone-treated mice, respectively) were markedly reduced with both rosiglitazone (P < 0.001 for both measures) and metformin treatment (P < 0.001 for both measures). Both treatments were associated with reduced insulin release assessed as the acute insulin response to intravenous glucose (2,189 +/- 857, 621 +/- 256, and 14 +/- 158 pmol/l for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin vs. control and P < 0.005 for rosiglitazone vs. control), consistent with reduced secretory demand. Similarly, islet mass (33.4 +/- 7.0, 16.6 +/- 3.6, and 12.2 +/- 2.1 mg for control, metformin-, and rosiglitazone-treated mice, respectively) was not different with metformin treatment (P = 0.06 vs. control) but was significantly lower with rosiglitazone treatment (P < 0.05 vs. control). When the decreased islet mass was accounted for, the islet amyloid-related decrease in beta-cell mass (percent beta-cell mass/islet mass) was ameliorated in both rosiglitazone- and metformin-treated animals (57.9 +/- 3.1, 64.7 +/- 1.4, and 66.1 +/- 1.6% for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin or rosiglitazone vs. control). In summary, rosiglitazone and metformin protect beta-cells from the deleterious effects of islet amyloid, and this effect may contribute to the ability of these treatments to alleviate the progressive loss of beta-cell mass and function in type 2 diabetes.

Pancreatic beta-cell failure and diabetes in mice with a deletion mutation of the endoplasmic reticulum molecular chaperone gene P58IPK

The endoplasmic reticulum (ER) transmits apoptotic signals in the pancreas during ER stress, implicating ER stress-mediated apoptosis in the development of diabetes. P58(IPK) (DNAJC3) is induced during ER stress and functions as a negative feedback component to inhibit eIF-2alpha signaling and attenuate the later phases of the ER stress response. To gain insight into a more comprehensive role of P58(IPK) function, we generated deletion mutant mice that showed a gradual onset of glucosuria and hyperglycemia associated with increasing apoptosis of pancreatic islet cells. Lack of P58(IPK) had no apparent effect on the functional integrity of viable beta-cells. A set of genes associated with apoptosis showed altered expression in pancreatic islets from P58(IPK)-null mice, further substantiating the apoptosis phenotype. The data provide in vivo evidence to support the concept that P58(IPK) functions as a signal for the downregulation of ER-associated proteins involved in the initial ER stress response, thus preventing excessive cell loss by degradation pathways. Insulin deficiency associated with the absence of P58(IPK) mimics beta-cell failure associated with type 1 and late-stage type 2 diabetes. P58(IPK) function and activity may therefore provide a novel area of investigation into ER-mediated mechanistic and therapeutic approaches for diabetes.

Insulin hypersensitivity and resistance to streptozotocin-induced diabetes in mice lacking PTEN in adipose tissue

In adipose tissue, insulin controls glucose and lipid metabolism through the intracellular mediators phosphatidylinositol 3-kinase and serine-threonine kinase AKT. Phosphatase and a tensin homolog deleted from chromosome 10 (PTEN), a negative regulator of the phosphatidylinositol 3-kinase/AKT pathway, is hypothesized to inhibit the metabolic effects of insulin. Here we report the generation of mice lacking PTEN in adipose tissue. Loss of Pten results in improved systemic glucose tolerance and insulin sensitivity, associated with decreased fasting insulin levels, increased recruitment of the glucose transporter isoform 4 to the cell surface in adipose tissue, and decreased serum resistin levels. Mutant animals also exhibit increased insulin signaling and AMP kinase activity in the liver. Pten mutant mice are resistant to developing streptozotocin-induced diabetes. Adipose-specific Pten deletion, however, does not alter adiposity or plasma fatty acids. Our results demonstrate that in vivo PTEN is a potent negative regulator of insulin signaling and insulin sensitivity in adipose tissue. Furthermore, PTEN may be a promising target for nutritional and/or pharmacological interventions aimed at reversing insulin resistance.

Adiposity induced by adenovirus 5 inoculation

OBJECTIVE

To investigate the effect of viral inoculation by adenovirus 5 (Ad5) on body composition in a mouse model.

DESIGN

Longitudinal monitoring before and after a single injection of virus or saline.

SUBJECTS

Two groups of CD1 mice, one group given a single intraperitoneal dose of Ad5 and the control group, saline.

MEASUREMENTS

Bodyweights and food intake were recorded before and up to 21 weeks after inoculation. At the end of the study, whole-body 1H magnetic resonance spectroscopy (MRS) and localised in vivo 1H MRS spectroscopy of the liver was performed to assess whole-body adiposity and intrahepatic lipid content, respectively.

RESULTS

Ad5-treated animals gained significantly more weight over a period of 21 weeks after inoculation than the controls, 21.8 g (18.8-25.0) and 18.8 g (17.3-19.8) respectively, (P<0.05). The gain in bodyweight in the former animals arises from increased deposition of adipose tissue as measured by whole-body 1H MRS. Adiposity was 6.7% (3.10-11.20%), and 2.40% (0.85-5.65%) for the Ad5-treated and control animals, respectively (P<0.05). No significant difference in intrahepatic lipid content or food intake was observed between the two groups.

CONCLUSION

The significantly higher percentage of adipose tissue in the Ad5-treated mice suggest viral infection may play a contributory role to a predisposition to obesity, although its contribution relative to other factors remains to be determined.

Chronic C75 treatment of diet-induced obese mice increases fat oxidation and reduces food intake to reduce adipose mass

Obesity and its attendant disorders, such as type 2 diabetes, are global health problems. We previously reported that C75, an inhibitor of fatty acid synthase (FAS) and stimulator of carnitine palmitoyltransferase I (CPT I), caused anorexia and profound weight loss in lean and genetically obese mice. To approximate human obesity, we utilized a chronic C75 treatment model for diet-induced obese (DIO) mice. Chronic C75 treatment decreased food consumption and increased energy expenditure due to increased fatty acid oxidation in both DIO and lean mice. There was a substantial loss of adipose tissue and resolution of hepatic steatosis in C75-treated DIO mice. Analysis of changes in the expression of hypothalamic neuropeptides demonstrated that the reduced food consumption in C75-treated DIO mice was accompanied by an increase in cocaine and amphetamine-related transcript expression but not by changes in neuropeptide Y such as seen with acute C75 treatment of lean mice. Inhibition of FAS and stimulation of CPT I provide a means to achieve stable, sustained weight loss in DIO mice.

Evaluation of a quantitative magnetic resonance method for mouse whole body composition analysis

OBJECTIVE

To evaluate applicability, precision, and accuracy of a new quantitative magnetic resonance (QMR) analysis for whole body composition of conscious live mice.

RESEARCH METHODS AND PROCEDURES

Repeated measures of body composition were made by QMR, DXA, and classic chemical analysis of carcass using live and dead mice with different body compositions. Caloric lean and dense diets were used to produce changes in body composition. In addition, different strains of mice representing widely diverse populations were analyzed.

RESULTS

Precision was found to be better for QMR than for DXA. The coefficient of variation for fat ranged from 0.34% to 0.71% compared with 3.06% to 12.60% for DXA. Changes in body composition in response to dietary manipulation were easily detected using QMR. An increase in fat mass of 0.6 gram after 1 week (p < 0.01) was demonstrated in the absence of hyperphagia or a change in mean body weight.

DISCUSSION

QMR and DXA detected similar fat content, but the improved precision afforded by QMR compared with DXA and chemical analysis allowed detection of a significant difference in body fat after 7 days of consuming a diet rich in fat even though average body weight did not significantly change. QMR provides a very precise, accurate, fast, and easy-to-use method for determining fat and lean tissue of mice without the need for anesthesia. Its ability to detect differences with great precision should be of value when characterizing phenotype and studying regulation of body composition brought about by pharmacological and dietary interventions in energy homeostasis.

Increased hypothalamic melanin concentrating hormone gene expression during energy restriction involves a melanocortin-independent, estrogen-sensitive mechanism

Increased expression of melanin concentrating hormone (MCH), an orexigenic neuropeptide produced by neurons in the lateral hypothalamic area (LHA), is implicated in the effect of energy restriction to increase food intake. Since melanocortins inhibit Mch gene expression, this effect of energy restriction to increase Mch signaling may involve reduced hypothalamic melanocortin signaling. Consistent with this hypothesis, we detected increased hypothalamic Mch mRNA levels in agouti (Ay) mice (by 102%; P < 0.05), a model of genetic obesity resulting from impaired melanocortin signaling, compared to wild-type controls. If reduced melanocortin signaling mediates the effect of energy restriction, hypothalamic Mch gene expression in Ay mice should not be increased further by energy restriction, since melanocortin signaling is impaired in these animals regardless of nutritional state. We therefore investigated the effects of energy restriction on hypothalamic Mch gene expression in both Ay mice and in wild-type mice with diet-induced obesity (DIO). Responses in these mice were compared to those induced by administration of 17beta-estradiol (E2) at a dose previously shown to reduce food intake and Mch expression in rats. In both Ay and DIO mice, energy restriction increased hypothalamic Mch mRNA levels (P < 0.05 for each) via a mechanism that was fully blocked by E2. However, E2 did not lower levels of Mch mRNA below basal values in Ay mice, whereas it did so in DIO mice. Thus, the effect of energy restriction to increase hypothalamic Mch gene expression involves an E2-sensitive mechanism that is not altered by impaired melanocortin signaling. By comparison, impaired melanocortin signaling increases hypothalamic Mch gene expression via a mechanism that is insensitive to E2. These findings suggest that while both energy restriction and reduced melanocortin signaling stimulate hypothalamic Mch gene expression, they do so via distinct mechanisms.

Validation and calibration of DEXA body composition in mice

Validated methods of determining murine body composition are required for studies of obesity in mice. Dual-energy X-ray absorptiometry (DEXA) provides a noninvasive approach to assess body fat and lean tissue contents. Similar to DEXA analyses in other species, body fat measurements in mice show acceptable precision but suffer from poor accuracy. Because fat and lean tissues each contain various components, these inaccuracies likely result from selection of inappropriate calibration standards. Analysis of solvents showed that the PIXImus2 DEXA gave results consistent with theoretical calculations. Male mice weighing 26-60 g and having body fat percentages ranging from 3 to 49% were analyzed by both PIXImus2 DEXA and chemical carcass analysis. DEXA overestimated mouse fat content by an average of 3.3 g, and algorithms were generated to calculate body fat from both measured body fat values and the measured ratio of high- to low-energy X-ray attenuations. With calibration to mouse body fat content measured by carcass analysis, the PIXImus2 DEXA gives accurate body composition values in mice.

Melanocortin signaling and anorexia in chronic disease states

Data from both rodent models and humans suggest that intact neuronal melanocortin signaling is essential to prevent obesity, as mutations that decrease the melanocortin signal within the brain induce hyperphagia and excess body fat accumulation. Melanocortins are also involved in the pathogenesis of disorders at the opposite end of the spectrum of energy homeostasis, the anorexia and weight loss associated with inflammatory and neoplastic disease processes. Studies using melanocortin antagonists (SHU9119 or agouti-related peptide) or genetic approaches (melanocortin-4 receptor null mice) suggest that intact melanocortin tone is required for anorexia and weight loss induced by injected lipopolysaccharide (an inflammatory gram-negative bacterial cell wall product) or by implantation of prostate or lung cancer cells. Although the precise mechanism whereby peripheral inflammatory/neoplastic factors activate the melanocortin system remains unknown, the proinflammatory cytokines (interleukin-1, interleukin-6, and tumor necrosis factor-alpha) that are produced in the hypothalamus of rodents during both inflammatory and neoplastic disease processes likely play a role. The data presented in this paper summarize findings that implicate neuronal melanocortin signaling in inflammatory anorexia.

High-resolution magnetic resonance imaging tracks changes in organ and tissue mass in obese and aging rats

Magnetic resonance imaging (MRI) has the ability to discriminate between various soft tissues in vivo. Whole body, specific organ, total adipose tissue (TAT), intra-abdominal adipose tissue (IAAT), and skeletal muscle (SM) weights determined by MRI were compared with weights determined by dissection and chemical analysis in two studies with male Sprague-Dawley rats. A 4.2-T MRI machine acquired high-resolution, in vivo, longitudinal whole body images of rats as they developed obesity or aged. Weights of the whole body and specific tissues were determined using computer image analysis software, including semiautomatic segmentation algorithms for volume calculations. High correlations were found for body weight (r = 0.98), TAT (r = 0.99), and IAAT (r = 0.98) between MRI and dissection and chemical analyses. MRI estimated the weight of the brain, kidneys, and spleen with high accuracy (r > 0.9), but overestimated IAAT, SM, and liver volumes. No differences were detected in organ weights using MRI and dissection measurements. Longitudinal MRI measurements made during the development of obesity and aging accurately represented changes in organ and tissue mass.

Attenuation of diabetic hyperphagia in neuropeptide Y--deficient mice

The combined effects of increased hypothalamic signaling by neuropeptide Y (NPY) and decreased signaling by melanocortins are hypothesized to stimulate food intake when body fat stores are depleted. To investigate NPY's role in the hyperphagic response to uncontrolled diabetes, streptozotocin (STZ) (200 mg/kg intraperitoneally) or saline vehicle was given to NPY-deficient (Npy(--/--)) and wild-type (Npy(+/+)) mice. In Npy(+/+) mice, STZ-induced diabetes increased mean daily food intake to plateau values 50% above baseline intake (+2.0 +/- 0.6 g/day; P < or = 0.05), an effect that was not seen in STZ-treated Npy(--/--) mice (+0.8 +/- 0.1 g/day; NS), despite comparably elevated levels of plasma glucose and comparably decreased levels of body weight, fat content, and plasma leptin. Unlike the impaired feeding response to uncontrolled diabetes, Npy(--/--) mice exhibit intact hyperphagic responses to fasting (Erickson et al. [1], Nature 381:415-418, 1996). To investigate whether differences in hypothalamic melanocortin signaling can explain this discrepancy, we used in situ hybridization to compare the effects of STZ-diabetes and fasting on pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP) mRNA levels in the hypothalamic arcuate nucleus (ARC) of Npy(--/--) and Npy(+/+) mice. AgRP mRNA levels were increased by both fasting and STZ-diabetes, but the increase in STZ-diabetes was small (50-80%) compared with the effect of fasting (approximately 20-fold increase of AgRP mRNA). STZ-diabetes also lowered POMC mRNA levels by 65% in the ARC of Npy(+/+) mice (P less-than-or-equal 0.05) but by only 11% in Npy(--/--) mice (NS); fasting significantly lowered POMC mRNA levels in both genotypes. We conclude that NPY is required for both the increase of food intake and the decrease of hypothalamic POMC gene expression induced by uncontrolled diabetes. In contrast, NPY is not required for either of these responses when the stimulus is food deprivation. Moreover, fasting is a more potent stimulus to hypothalamic AgRP gene expression than is STZ-diabetes. Therefore, central nervous system melanocortin signaling appears to be suppressed more effectively by fasting than by uncontrolled diabetes, which provides a plausible explanation for differences in the feeding response to these two stimuli in mice lacking NPY.

LDL receptor but not apolipoprotein E deficiency increases diet-induced obesity and diabetes in mice

The aim of this study was to determine whether phenotypes associated with type 2 diabetes are altered in dyslipidemic obese mice. C57BL/6 wild-type, low-density lipoprotein (LDL) receptor-deficient (LDLR-/-), and apolipoprotein E-deficient (apoE-/-) mice were fed a high-fat, high-carbohydrate diet (diabetogenic diet), and the development of obesity, diabetes, and hypertriglyceridemia was examined. Wild-type mice became obese and developed hyperglycemia, but not hypertriglyceridemia, in response to this diet. LDLR-/- mice fed the diabetogenic diet became more obese than wild-type mice and developed severe hypertriglyceridemia and hyperleptinemia. Surprisingly, glucose levels were only modestly higher and insulin levels and insulin-to-glucose ratios were not strikingly different from those of wild-type mice. In contrast, diabetogenic diet-fed apoE-/- mice were resistant to changes in glucose and lipid homeostasis despite becoming obese. These data suggest that modifications in lipoprotein profiles associated with loss of the LDL receptor or apoE function have profound and unique consequences on susceptibility to diet-induced obesity and type 2 diabetic phenotypes.