Susanne Klaus

Epigallocatechin gallate attenuates diet-induced obesity in mice by decreasing energy absorption and increasing fat oxidation

OBJECTIVE:To examine the antiobesity effect of epigallocatechin gallate (EGCG), a green tea bioactive polyphenol in a mouse model of diet-induced obesity.METHODS:Obesity was induced in male New Zealand black mice by feeding of a high-fat diet. EGCG purified from green tea (TEAVIGO™) was supplemented in the diet (0.5 and 1%). Body composition (quantitative magnetic resonance), food intake, and food digestibility were recorded over a 4-week period. Animals were killed and mRNA levels of uncoupling proteins (UCP1–3), leptin, malic enzyme (ME), stearoyl-CoA desaturase-1 (SCD1), glucokinase (GK), and pyruvate kinase (PK) were analysed in different tissues. Also investigated were acute effects of orally administered EGCG (500 mg/kg) on body temperature, activity (transponders), and energy expenditure (indirect calorimetry).RESULTS:Dietary supplementation of EGCG resulted in a dose-dependent attenuation of body fat accumulation. Food intake was not affected but faeces energy content was slightly increased by EGCG, indicating a reduced food digestibility and thus reduced long-term energy absorption. Leptin and SCD1 gene expression in white fat was reduced but SCD1 and UCP1 expression in brown fat was not changed. In liver, gene expression of SCD1, ME, and GK was reduced and that of UCP2 increased. Acute oral administration of EGCG over 3 days had no effect on body temperature, activity, and energy expenditure, whereas respiratory quotient during night (activity phase) was decreased, supportive of a decreased lipogenesis and increased fat oxidation.CONCLUSIONS:Dietary EGCG attenuated diet-induced body fat accretion in mice. EGCG apparently promoted fat oxidation, but its fat-reducing effect could be entirely explained by its effect in reducing diet digestibility.

Absence of intestinal microbiota does not protect mice from diet-induced obesity.

The gut microbiota has been implicated in host nutrient absorption and energy homeostasis. We studied the influence of different diets on body composition in germ-free (GF) and conventional (CV) mice. GF and CV male adult C3H mice were fed ad libitum a semi-synthetic low-fat diet (LFD; carbohydrate-protein-fat ratio: 41:42:17; 19.8 kJ/g), a high-fat diet (HFD; 41:16:43; 21.4 kJ/g) or a commercial Western diet (WD; 41:19:41; 21.5 kJ/g). There was no difference in body weight gain between GF and CV mice on the LFD. On the HFD, GF mice gained more body weight and body fat than CV mice, and had lower energy expenditure. GF mice on the WD gained significantly less body fat than GF mice on the HFD. GF mice on both HFD and WD showed increased intestinal mRNA expression of fasting-induced adipose factor/angiopoietin-like protein 4 (Fiaf/Angptl4), but they showed no major changes in circulating Fiaf/Angptl4 compared with CV mice. The faecal microbiota composition of the CV mice differed between diets: the proportion of Firmicutes increased on both HFD and WD at the expense of the Bacteroidetes. This increase in the Firmicutes was mainly due to the proliferation of one family within this phylum: the Erysipelotrichaceae. We conclude that the absence of gut microbiota does not provide a general protection from diet-induced obesity, that intestinal production of Fiaf/Angptl4 does not play a causal role in gut microbiota-mediated effects on fat storage and that diet composition affects gut microbial composition to larger extent than previously thought.

CB(1) signaling in forebrain and sympathetic neurons is a key determinant of endocannabinoid actions on energy balance.

The endocannabinoid system (ECS) plays a critical role in obesity development. The pharmacological blockade of cannabinoid receptor type 1 (CB(1)) has been shown to reduce body weight and to alleviate obesity-related metabolic disorders. An unsolved question is at which anatomical level CB(1) modulates energy balance and the mechanisms involved in its action. Here, we demonstrate that CB(1) receptors expressed in forebrain and sympathetic neurons play a key role in the pathophysiological development of diet-induced obesity. Conditional mutant mice lacking CB(1) expression in neurons known to control energy balance, but not in nonneuronal peripheral organs, displayed a lean phenotype and resistance to diet-induced obesity. This phenotype results from an increase in lipid oxidation and thermogenesis as a consequence of an enhanced sympathetic tone and a decrease in energy absorption. In conclusion, CB(1) signaling in the forebrain and sympathetic neurons is a key determinant of the ECS control of energy balance.

Short photoperiod reduces leptin gene expression in white and brown adipose tissue of Djungarian hamsters

Leptin gene expression in white (WAT) and brown adipose tissue (BAT) of the Djungarian hamster (Phodopus sungorus) was analyzed during seasonal acclimatization. Leptin gene expression in WAT was markedly reduced during winter, independent of changes in environmental temperature. Exposure to artificial short photoperiod also decreased leptin gene expression in WAT as well as in BAT. Although specific leptin gene expression was lower in BAT, total depot expression was as high as in WAT depots, due to higher RNA content of BAT. Our results indicate that there is significant leptin synthesis in brown fat and that leptin might be involved in photoperiod mediated seasonal adaptations of mammals independent of food deprivation or overfeeding.

PYY3-36 as an anti-obesity drug target.

The neuropeptide Y (NPY)/peptide YY (PYY) system has been implicated in the physiology of obesity for several decades. More recently, Batterham et al. 2002 ignited enormous interest in PYY3‐36, an endogenous Y2‐receptor agonist, as a promising anti‐obesity compound. Despite this interest, there have been remarkably few subsequent reports reproducing or extending the initial findings, while at the same time studies finding no anti‐obesity effects have surfaced. Out of 41 different rodent studies conducted (in 16 independent labs worldwide), 33 (83%) were unable to reproduce the reported effects and obtained no change or sometimes increased food intake, despite use of the same experimental conditions (i.e. adaptation protocols, routes of drug administration and doses, rodent strains, diets, drug vendors, light cycles, room temperatures). Among studies by authors in the original study, procedural caveats are reported under which positive effects may be obtained. Currently, data speak against a sustained decrease in food intake, body fat, or body weight gain following PYY3‐36 administration and make the previously suggested role of the hypothalamic melanocortin system unlikely as is the existence of PYY deficiency in human obesity. We review the studies that are in the public domain which support or challenge PYY3‐36 as a potential anti‐obesity target.

Effects of long-term soluble vs. insoluble dietary fiber intake on high-fat diet-induced obesity in C57BL/6J mice

Although most of the proposed beneficial effects of fiber consumption have been attributed to viscous and gel-forming properties of soluble fiber, it is mainly insoluble cereal fiber and whole grains that are strongly associated with reduced diabetes risk in prospective cohort studies, indicating that other unknown mechanisms are likely to be involved. We performed a long-term study investigating potential protective effects of adding soluble guar fiber (10% w/w) vs. insoluble cereal fiber (10% w/w) to an isoenergetic and macronutrient matched high-fat diet in obesity-prone C57BL/6J mice. After 45 weeks, mice fed soluble vs. insoluble fiber showed both significantly increased body weight (41.8+/-3.0 vs. 33.6+/-1.5 g, P=.03) and elevated markers of insulin resistance. In mice fed soluble fiber, energy loss via the feces was significantly lower and colonic fermentation with production of short chain fatty acids (SCFA) was markedly increased. Gene expression analysis in white adipose tissue showed significantly increased levels of the fatty acid target G-protein coupled receptor-40 in soluble fiber-fed mice. Liver gene expression in the insoluble fiber group showed a pattern consistent with increased fatty acid oxidation. The present results show that soluble vs insoluble dietary fiber added to a high-fat, Western-style diet differently affected body weight and estimates of insulin sensitivity in obesity-prone mice. Soluble fiber intake with increased SCFA production significantly contributed to digested energy, thereby potentially outweighing the well known short-term beneficial effects of soluble fiber consumption.

Seasonal acclimation of bank voles and wood mice: nonshivering thermogenesis and thermogenic properties of brown adipose tissue mitochondria

SummarySeasonal acclimation of nonshivering thermogenesis and brown adipose tissue was studied in wild bank voles (Clethrionomys glareolus), yellow necked field mice and wood mice (Apodemus flavicollis, A. sylvaticus). Both, voles and mice increased their capacity for nonshivering thermogenesis during winter. Thermogenic properties of brown fat (cytochrome c oxidase activity, mitochondrial protein content, GDP-binding of brown fat mitochondria) showed similar changes during seasonal acclimation;Clethrionomys andApodemus spp. both showed lowest thermogenic properties in the summer during August, a rapid increase during fall, and highest levels of thermogenic activity in the winter months. With regard to changes in body weight and brown fat mass these species show different strategies for seasonal acclimation. InClethrionomys a reduction of body mass in the winter was found, both in the wild population as well as in individual animals housed in the laboratory.A. flavicollis showed a reduction of body weight during fall, whereasA. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in theApodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas inClethrionomys brown fat mass and cellularity remained seasonally constant. These species live in the same habitat and were trapped in the same area. It is concluded that seasonal improvements of in vivo and in vitro thermogenesis are very similar in these species, although the physiological basis for this improvement is different inClethrionomys andApodemus.

Skeletal muscle mitochondrial uncoupling drives endocrine cross-talk through the induction of FGF21 as a myokine

UCP1-Tg mice with ectopic expression of uncoupling protein 1 (UCP1) in skeletal muscle (SM) are a model of improved substrate metabolism and increased longevity. Analysis of myokine expression showed an induction of fibroblast growth factor 21 (FGF21) in SM, resulting in approximately fivefold elevated circulating FGF21 in UCP1-Tg mice. Despite a reduced muscle mass, UCP1-Tg mice showed no evidence for a myopathy or muscle autophagy deficiency but an activation of integrated stress response (ISR; eIF2α/ATF4) in SM. Targeting mitochondrial function in vitro by treating C2C12 myoblasts with the uncoupler FCCP resulted in a dose-dependent activation of ISR, which was associated with increased expression of FGF21, which was also observed by treatment with respiratory chain inhibitors antimycin A and myxothiazol. The cofactor required for FGF21 action, β-klotho, was expressed in white adipose tissue (WAT) of UCP1-Tg mice, which showed an increased browning of WAT similar to what occurred in altered adipocyte morphology, increased brown adipocyte markers (UCP1, CIDEA), lipolysis (HSL phosphorylation), and respiratory capacity. Importantly, treatment of primary white adipocytes with serum of transgenic mice resulted in increased UCP1 expression. Additionally, UCP1-Tg mice showed reduced body length through the suppressed IGF-I-GH axis and decreased bone mass. We conclude that the induction of FGF21 as a myokine is coupled to disturbance of mitochondrial function and ISR activation in SM. FGF21 released from SM has endocrine effects leading to increased browning of WAT and can explain the healthy metabolic phenotype of UCP1-Tg mice. These results confirm muscle as an important endocrine regulator of whole body metabolism.

Impairment of fat oxidation under high- vs. low-glycemic index diet occurs before the development of an obese phenotype

Exposure to high vs. low glycemic index (GI) diets increases fat mass and insulin resistance in obesity-prone C57BL/6J mice. However, the longer-term effects and potentially involved mechanisms are largely unknown. We exposed four groups of male C57BL/6J mice (n = 10 per group) to long-term (20 wk) or short-term (6 wk) isoenergetic and macronutrient matched diets only differing in starch type and as such GI. Body composition, liver fat, molecular factors of lipid metabolism, and markers of insulin sensitivity and metabolic flexibility were investigated in all four groups of mice. Mice fed the high GI diet showed a rapid-onset (from week 5) marked increase in body fat mass and liver fat, a gene expression profile in liver consistent with elevated lipogenesis, and, after long-term exposure, significantly reduced glucose clearance following a glucose load. The long-term high-GI diet also led to a delayed switch to both carbohydrate and fat oxidation in the postprandial state, indicating reduced metabolic flexibility. In contrast, no difference in carbohydrate oxidation was observed after short-term high- vs. low-GI exposure. However, fatty acid oxidation was significantly blunted as early as 3 wk after beginning of the high-GI intervention, at a time where most measured phenotypic markers including body fat mass were comparable between groups. Thus long-term high-GI feeding resulted in an obese, insulin-resistant, and metabolically inflexible phenotype in obesity-prone C57BL/6J mice. Early onset and significantly impaired fatty acid oxidation preceded these changes, thereby indicating a potentially causal involvement.

Physiology of transgenic mice with brown fat ablation : obesity is due to lowered body temperature

We investigated the physiological basis for development of obesity in uncoupling protein-diphtheria toxin A chain (UCP-DTA) transgenic mice. In these mice the promoter of the brown adipose tissue (BAT)-specific UCP was used to drive expression of DTA, resulting in decreased BAT function and development of obesity and insulin resistance (Lowell, B. B., S. V. Susulic, A. Hamann, J. A. Lawitts, J. Himms-Hagen, B. B. Boyer, L. Kozak, and J. S. Flier. Nature 366: 740-742, 1994). In adult UCP-DTA mice, we measured food intake and food assimilation, locomotor activity, metabolic rate, and body temperature in comparison to control animals. No differences could be observed in food intake or assimilation and locomotor activity. Weight-specific metabolic rates at temperatures between 20 and 37°C, however, were consistently lower in transgenic mice. Continuous telemetric recording of core body temperature showed that transgenic mice displayed a downshift in body temperature levels of ∼0.9°C. In summary, we provide evidence that attenuated body temperature levels alone can be responsible for development of obesity and that BAT thermogenesis is a major determinant of body temperature levels in rodents.