Developmental changes of lipogenic enzyme activities and lipogenesis in brown adipose tissue and liver of the rat.

1. Brown adipose tissue (BAT) and liver lipogenesis in vivo estimated by using 3H2O as tracer was very low and did not change significantly between 10 and 20 days after birth. Lipogenesis increased dramatically in both tissues by weaning at 20 days, peaking between 25 and 30 days of age. Since that time the rate of fatty acid synthesis in BAT decreased gradually to reach adult level after 2 months, whereas in the liver there was a sharp decrease of lipogenesis. 2. The activities of fatty acid synthase, citrate cleavage enzyme, malic enzyme and glucose 6-phosphate dehydrogenase essentially followed a similar course of developmental changes as lipogenesis. 3. In contrast to the enzymes listed above NADP-linked isocitrate dehydrogenase remained unaltered over the period studied, whereas lactate and malate dehydrogenases exhibited very high activity at 10 days after birth and from then decreased to reach adult level at the age of about 20 days. 4. The data obtained indicate that no substantial differences could be detected in the developmental pattern of lipogenesis and lipogenic enzyme activities between BAT and liver up to 30 days of age but after this time these processes were not co-ordinated in both tissues. Beyond this time the BAT was characterized by a much higher rate of lipogenesis than the liver. 5. The results are discussed in terms of the nutrient changes and the relationship between thermogenesis and lipogenesis in BAT.     

Changes in the lipogenic response to feeding of liver, white adipose tissue and brown adipose tissue during the development of obesity in the gold-thioglucose-injected mouse.

Lipogenic response to feeding was measured in vivo in liver, epididymal white adipose tissue (WAT) and interscapular brown adipose tissue (BAT), during the development of obesity in gold-thioglucose (GTG)-injected mice. The fatty acid synthesis after a meal was higher in all tissues of GTG-treated mice on a total-tissue basis, but the magnitude of this increase varied, depending on the tissue and the time after the initiation of obesity. Lipogenesis in BAT from GTG mice was double that of control mice for the first 2 weeks, but subsequently decreased to near control values. In WAT, lipogenesis after feeding was highest 2-4 weeks after GTG injection, and in liver, lipid synthesis in fed obese mice was greatest at 7-12 weeks after the induction of obesity. The post-prandial insulin concentration was increased after 2 weeks of obesity, and serum glucose concentration was higher in fed obese mice after 4 weeks. These results indicate that increased lipogenesis in GTG-injected mice may be due to an increase in insulin concentration after feeding and that insulin resistance (assessed by lipogenic response to insulin release) is apparent in BAT before WAT and liver.     

Effect of metformin on adipose tissue resistin expression in db/db mice

Resistin, a novel adipose-derived protein, has been proposed to cause insulin-resistant states in obesity. To evaluate whether an insulin-sensitizing drug, metformin, regulates adipose tissue resistin expression, murine models of obesity and diabetes, db/db mice, were treated with metformin (metformin group), insulin (insulin group), and vehicle (control group) for 4 weeks, followed by analyzing resistin protein expression in their adipose tissues. Unexpectedly, resistin protein expression was increased by 66% in the metformin group relative to the control group, while it did not differ between the insulin and control groups. Hyperinsulinemia was improved in the metformin group, while the insulin group exhibited severe hyperinsulinemia, similar to the control group. Furthermore, in comparison between obese mice (db/db mice) and age-matched lean controls, resistin protein expression was reduced by 58% in the obese mice with severe hyperinsulinemia. These data collectively suggest that resistin expression may be suppressed by hyperinsulinemia and that metformin may upregulate resistin expression via the improvement of hyperinsulinemia in obesity.     

Impairment of adipsin expression is secondary to the onset of obesity in db/db mice

The nature of the primary biochemical lesions in genetically obese mice, which might prove to be useful models for human obesity, remains totally obscure. The recent finding that the expression of adipsin was virtually suppressed in both db/db and ob/ob adult mice has opened new perspectives, suggesting a potential role for this defect in the pathogenesis of obesity. To be of etiological significance, adipsin deficiency must be present very early in life when excess fat storage starts to develop. We show here that at 10 days of age db/db pups exhibit significantly overdeveloped adipose tissue as compared with lean (+/db) pups but similar levels of both adipose tissue adipsin mRNA and serum adipsin. Adipsin expression was still normal in obese mice 15 days old but frankly deficient at 30 days of age when hyperinsulinemia has developed. Thus the defect in adipsin expression in db/db mice is a secondary feature which cannot be ascribed a role in the onset of obesity.     

Adrenalectomy in genetically obese ob/ob and db/db mice increases the proton conductance pathway

Adrenalectomy (ADX) prevents the excessive weight gain in the genetically obese ob/ob and db/db mice. To test the possibility that this results from increased energy expenditure due to increased thermogenesis in brown adipose tissue (BAT), we measured GDP binding to mitochondria from interscapular brown adipose tissue (BAT) in db/db and ob/ob mice and their lean controls after adrenalectomy, with and without corticosterone replacement. Both the vehicle treated and corticosterone treated db/db and ob/ob mice had lower body weights than the sham-operated mice GDP binding to mitochondria from IBAT was significantly lower in both the db/db and ob/ob mice than in their lean controls. Adrenalectomy significantly increased GDP binding in all mice compared to the respective sham-operated mice, but, the percentage increase was always greater in the db/db and ob/ob mice. Corticosterone treatment of adrenalectomized db/db, ob/ob or lean mice lowered GDP binding to sham levels. Our data confirm previous findings that adrenalectomy results in increased GDP binding to mitochondria from IBAT. Injections of corticosterone into adrenalectomized mice results in a decrease in GDP binding to values which are similar to values in sham-operated mice. Thus adrenalectomy may inhibit the development of obesity by increasing the thermic activity in IBAT.     

Adrenalectomy and steroid treatment in obese (ob/ob) and diabetic (db/db) mice

Adrenalectomy in young obese (ob/ob) and the diabetic (db/db) mouse slowed body weight gain. Treatment of adrenalectomized ob/ob mice with cortisone or deoxycorticosterone acetate (DOCA) significantly increased weight gain in a dose-related manner. Cortisone had no effect on weight gain on lean mice and treatment with dehydroepiandrosterone sulfate was without effect on either ob/ob or lean mice. The increment in body weight of adrenalectomized ob/ob mice treated with corticosterone and DOCA was associated with an increase in body weight and an increase in food intake. When adrenalectomy was performed at twenty-three days of age (five days before weaning), animals carrying the (db/db) genotype remained lighter than their normal littermates. These data document the importance of the adrenal gland and its steroids for the development and maintenance of many features of the obese or diabetes mouse.     

Lipogenesis at the suckling-weaning transition in liver and brown adipose tissue of the rat

The responses of rat hepatic and brown adipose tissue in vivo lipogenesis to premature (15 days) and normal (21 days) weaning have been correlated to changes in the activities of acetyl-CoA carboxylase and two NADPH-producing enzymes, malic enzyme and glucose-6-phosphate dehydrogenase. Both tissues show an induction of lipogenesis in response to weaning. In the liver, lipogenic flux is closely linked to the activity of acetyl-CoA carboxylase, but not necessarily that of malic enzyme or glucose-6-phosphate dehydrogenase, whereas no such dissociation between enzyme activity and flux rate occurs in brown adipose tissue. Thyroid hormones, implicated in many physiological changes around weaning, do not seem to play a primary role in the adaptation of lipogenesis to the dietary change at this time, although a permissive role in both tissues is possible.     

Diabetes (db/db) mutation-induced ovarian involution: progressive hypercytolipidemia

Ovarian atrophy and reproductive tract incompetence are recognized consequences of the progressive expression of the overt, diabetes-obesity syndrome (DOS) in C57BL/KsJ (db/db) mutant mice. The present studies evaluated the progressive changes in ovarian cytoarchitecture, endocrine expression, and reproductive tract cytolipidemic parameters that promote reproductive failure and ovarian involution during the pre-onset, initial, progressive, and chronic expression stages of the DOS. Paired littermate control (normal: +/?) and diabetic (mutant: db/db) C57BL/KsJ females were selected for analysis of ovarian parameters at 2 weeks (pre-onset expression of DOS), 4 weeks (initial DOS expression), 8 weeks (progressive DOS: hyper-glycemic/lipidemic), and 16 weeks (overt/chronic DOS expression) of age. All 4- to 16-week-old (db/db) groups were obese, hyperglycemic, and hyperinsulinemic as compared with age-matched (+/?) controls. Prior to phenotypic expression of the DOS (2 week groups), ovarian interstitial cytolipidemia characterized the perifollicular and cortical regions of db/db tissue samples relative to +/? indices, while comparable body weight, blood glucose, as well as serum insulin and ovarian steroid hormone concentrations characterized both the +/? and db/db groups. Overt DOS expression in the 4-week-old db/db groups was characterized by body obesity, systemic hyperglycemia-hyperinsulinemia, and extensive hypercytolipidemia of ovarian folliculothecal compartments, as well as enhanced tissue lipase activities. By 8 weeks of age, progressive hypercytolipidemia characterized interstitial, thecal, and follicular granulosa cell layers of db/db tissue samples concurrent with suppressed ovarian steroid hormone production, enhanced lipid sequestration, and exacerbation of systemic hyper-glycemia/insulinemia. By 16 weeks of age, the chronic-DOS was characterized by extensive ovarian follicular involution, cortical perivascular hyperlipidemic infiltration, thecal cell atrophy, and follicular granulosa lipid imbibition. These data indicate that db/db mutation-induced ovarian structural and functional involution is a direct reflection of the cellular metabolic shift towards lipogenesis, indicated by the progressive cytoarchitectural transformation into adipocyte-like entities. The cytological indications of cellular metabolic compromise, which precede the phenotypic expression of the DOS indices, suggests that correction of these abnormal shifts in ovarian endocrine and cellular metabolism may restore, delay, or prevent the further compromise of ovarian function by db/db mutation expression.     

The LXR ligand T0901317 induces severe lipogenesis in the db/db diabetic mouse

Liver X receptor (LXR) ligands are currently being evaluated as potential therapeutic agents for the treatment of low HDL. The LXR ligand T0901317 elevates ATP binding cassette transporter A1 (ABCA1) and HDL levels in animal models and induces moderate lipogenesis through upregulation of sterol regulatory element binding protein 1c (SREBP1c). Because insulin may also regulate lipogenesis through SREBP1c and fatty acid synthase (FAS), we investigated the effect of an LXR ligand in hyperinsulinemic mice. Administration of T0901317 to male db/db mice for 12 days resulted in a more severe hypertriacylglycerolemia and hepatic triacylglycerol accumulation than observed in nondiabetic mice. The LXR target genes ABCA1, SREBP1c, FAS, and stearoyl-CoA desaturase 1 were upregulated by T0901317 treatment in both diabetic db/db and nondiabetic C57BLKS mice. Changes in lipogenic gene expression were independent of mouse strain, indicating that the severe lipogenesis observed in LXR ligand-treated db/db mice was not due to additive effects of insulin on lipogenic gene expression. Phosphoenolpyruvate carboxykinase expression was suppressed, suggesting that a shift from gluconeogenesis toward lipogenesis could partially explain our observations in db/db mice. Our data suggest that LXR ligands that have effects on both fatty acid and carbohydrate metabolism should be carefully evaluated in obesity, insulin, and leptin resistance.     

乳源性复合益生菌促进db/db糖尿病小鼠白色脂肪棕色化的研究

目的 研究乳源性复合益生菌对db/db糖尿病小鼠白色脂肪棕色化细胞因子解偶联蛋白1(UCP1)、过氧化物酶体增殖物激活受体γ共激活因子1α(PGC1α)、R结构域蛋白16(PRDM16)表达的影响。 方法 将6周龄的SPF级db/db糖尿病雄性小鼠适应性喂养1周,随机分为糖尿病模型组、罗格列酮组及复合益生菌高剂量组和低剂量组,SC57BL/Ks雄性小鼠为正常对照组,每组8只。血糖仪检测不同时段空腹血糖(FBG)水平,ELISA法检测糖化血红蛋(HbA1c)含量,取各组小鼠皮下白色脂肪组织,HE染色观察脂肪组织形态,用Real time PCR检测各组白色脂肪组织中UCP1、PGC1α、PRDM16 mRNA表达水平以及Western Blot检测各组脂肪组织中UCP1的表达。 结果 与模型组相比,复合益生菌组FBG、HbA1c水平明显下降,并且复合益生菌能够明显增加脂肪组织多室脂肪细胞数量,具有棕色化的趋向,并能够显著提高UCP1、PGC1α、PRDM16的mRNA表达和UCP1表达量。 结论 本研究发现乳源性复合益生菌能够促进白色脂肪棕色化从而改善胰岛素抵抗。     

Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats

This study was designed to monitor the developmental changes in insulinemia and lipogenic enzyme activities in both inguinal adipose tissue and liver during suckling (7, 9, 14, and 17 days of age) and weaning (22 and 30 days of age) on to either a low-fat or a high-fat diet in lean (Fa/fa) and obese (fa/fa) rats. Tissues were removed through surgery and genotypes were retrospectively determined. During suckling, there was no difference in liver enzyme activities between the two groups. In contrast, adipose tissue fatty acid synthetase was increased by 50% and citrate cleavage enzyme and malic enzyme by 30% by 9 days of age. By 17 days of age, there was a threefold elevation in these enzyme activities and 6-phosphogluconic dehydrogenase and a twofold increase in glucose-6-phosphate dehydrogenase per inguinal fat pad in fa/fa versus Fa/fa. Consistent with these results, fat pad weight was increased by 20%, 50%, and 100% at 9, 14, and 17 days of age, respectively, in obese as compared to lean pups. However only by 17 days of age could a slight but significant increase in insulin level be detected in obese pups. Enlargement of inguinal fat pad accelerated after weaning on to a low-fat diet and still more after weaning on to a high-fat diet. Weaning on to a low-fat diet elicited an induction of hepatic lipogenic enzymes two or three times greater in fa/fa than in lean pups, while weaning on to a high-fat diet blunted the differences between genotypes. The lipogenic enzyme activities displayed per total inguinal fat were three to ten times greater in obese than in lean pups, regardless of the diet. However, adipose tissue lipogenic enzyme activities were much lower after weaning on to a high-fat than on to a low-fat diet in obese pups. The high-fat diet was as effective as the low-fat diet in triggering hyperinsulinemia in obese pups. The increased adipose tissue capacity for lipogenesis, starting during the suckling period, could play an important etiologic role in the development and maintenance of obesity in the Zucker rat.-Bazin, R., and M. Lavau. Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats.     

Development of fatty acid-synthetic capacity in interscapular brown adipose tissue during suckling in genetically obese Zucker rats.

The development of the lipogenic capacity in brown adipose tissue was studied in suckling lean (Fa/fa) and obese (fa/fa) Zucker pups aged from 7 to 22 days. In both lean and obese pups, activities of the two key lipogenic enzymes, fatty acid synthetase and acetyl-CoA carboxylase, and of citrate cleavage enzyme rose from the early to the late suckling period. Compared with lean pups, 7-day-old fa/fa pups showed a 35% increase in fat accumulation in interscapular brown adipose tissue and a 25% increase in fatty acid synthetase activity. By 10 days of age, fat deposition, lipogenesis in vivo (assessed by the incorporation of 3H from 3H2O into fatty acids) and fatty acid synthetase activity were 1.5-2-fold higher in pre-obese than in lean pups. Compared with lean pups, the increased lipogenesis in vivo observed in brown adipose tissue of 10-day-old pre-obese pups could not entirely account for the difference in fat deposition observed in this tissue, suggesting that additional mechanisms are at play to explain the increased fat content of this tissue.     

Enlargement of interscapular brown adipose tissue in growth hormone antagonist transgenic and in growth hormone receptor gene-disrupted dwarf mice

Growth hormone (GH) acts on adipose tissue by accelerating fat expenditure, preventing triglyceride accumulation, and facilitating lipid mobilization. To investigate whether GH is involved in the development and metabolism of interscapular brown adipose tissue (BAT), a site of nonshivering thermogenesis, we employed three lines of transgenic mice. Two of the lines are dwarf due to expression of a GH antagonist (GHA) or disruption of the GH receptor/binding-protein gene. A third mouse line is giant due to overexpression of a bovine GH (bGH) transgene. We have found that the body weights of those animals are proportional to their body lengths at 10 weeks of age. However, GHA dwarf mice tend to catch up with the nontransgenic (NT) littermates in body weight but not in body length at 52 weeks of age. The increase of body mass index (BMI) for GHA mice accelerates rapidly relative to controls as a function of age. We have also observed that BAT in both dwarf mouse lines but not in giant mice is enlarged in contrast to nontransgenic littermates. This enlargement occurs as a function of age. Northern analysis suggests that BAT can be a GH-responsive tissue because GHR/BP mRNAs were found there. Finally, the level of uncoupling protein-1 (UCP1) RNA was found to be higher in dwarf mice and lower in giant animals relative to controls, suggesting that GH-mediated signaling may negatively regulate UCP1 gene expression in BAT.     

Reduced maximum capacity of glycolysis in brown adipose tissue of genetically obese, diabetic (db/db) mice and its restoration following treatment with a thermogenic beta-adrenoceptor agonist

The maximal activities of the key glycolytic enzymes hexokinase and 6-phosphofructokinase, were reduced in brown adipose tissue in db/db mice compared to their lean littermates. Treatment of db/db mice with the thermogenic beta-adrenoceptor agonist, BRL 26830, restored normoglycaemia. The only significant increase in activity of hexokinase and 6-phosphofructokinase in the BRL 26830-treated db/db mice occurred in brown adipose tissue where the total tissue activity increased 10- and 11-fold respectively. These changes together with increased 2-deoxyglucose uptake in vivo suggest that brown adipose tissue can play a quantitatively important role in the removal of glucose from the blood.     

Gut microbiota modulate the metabolism of brown adipose tissue in mice

A two by two experimental study has been designed to determine the effect of gut microbiota on energy metabolism in mouse models. The metabolic phenotype of germ-free (GF, n = 20) and conventional (n = 20) mice was characterized using a NMR spectroscopy-based metabolic profiling approach, with a focus on sexual dimorphism (20 males, 20 females) and energy metabolism in urine, plasma, liver, and brown adipose tissue (BAT). Physiological data of age-matched GF and conventional mice showed that male animals had a higher weight than females in both groups. In addition, conventional males had a significantly higher total body fat content (TBFC) compared to conventional females, whereas this sexual dimorphism disappeared in GF animals (i.e., male GF mice had a TBFC similar to those of conventional and GF females). Profiling of BAT hydrophilic extracts revealed that sexual dimorphism in normal mice was absent in GF animals, which also displayed lower BAT lactate levels and higher levels of (D)-3-hydroxybutyrate in liver, plasma, and BAT, together with lower circulating levels of VLDL. These data indicate that the gut microbiota modulate the lipid metabolism in BAT, as the absence of gut microbiota stimulated both hepatic and BAT lipolysis while inhibiting lipogenesis. We also demonstrated that (1)H NMR metabolic profiles of BAT were excellent predictors of BW and TBFC, indicating the potential of BAT to fight against obesity.     

Glycerokinase activity in human brown adipose tissue

Brown adipose tissue (BAT) is known to be responsible for heat production in newborn and adult hibernating mammals. In rats and mice, BAT has been demonstrated to possess a much higher glycerokinase activity than white adipose tissue (WAT). It has been speculated that this high activity may cause the futile cycle of triglyceride breakdown and resynthesis to be activated, thus contributing to heat production. However, at present very little information is available regarding the location, function, and quantitative importance of BAT in adult human subjects. Our objective in this study was to locate BAT in human subjects and to characterize it biochemically, especially with respect to the enzyme glycerokinase. We have looked for histologically identifiable BAT in 32 human subjects and found it in 12 subjects. Most of the BAT samples were obtained from perirenal adipose depots in children undergoing surgery. Some of the samples were almost totally comprised of BAT cells, whereas others were a mixture of BAT cells and WAT cells. The glycerokinase activity per gram of tissue was higher in BAT than in WAT in all the subjects where the above comparison was made. The activity per mg protein or per microgram DNA was higher in most BAT samples. In one pure BAT specimen, the basal lipolytic rate and the lipoprotein lipase activity were measured and they were both higher in BAT than in the WAT obtained from the same patient. These results show that human brown adipose tissue possesses an enzymatic profile very similar to that of rodent brown adipose tissue.     

Astaxanthin protects beta-cells against glucose toxicity in diabetic db/db mice

Oxidative stress induced by hyperglycemia possibly causes the dysfunction of pancreatic beta-cells and various forms of tissue damage in patients with diabetes mellitus. Astaxanthin, a carotenoid of marine microalgae, is reported as a strong anti-oxidant inhibiting lipid peroxidation and scavenging reactive oxygen species. The aim of the present study was to examine whether astaxanthin can elicit beneficial effects on the progressive destruction of pancreatic beta-cells in db/db mice--a well-known obese model of type 2 diabetes. We used diabetic C57BL/KsJ-db/db mice and db/m for the control. Astaxanthin treatment was started at 6 weeks of age and its effects were evaluated at 10, 14, and 18 weeks of age by non-fasting blood glucose levels, intraperitoneal glucose tolerance test including insulin secretion, and beta-cell histology. The non-fasting blood glucose level in db/db mice was significantly higher than that of db/m mice, and the higher level of blood glucose in db/db mice was significantly decreased after treatment with astaxanthin. The ability of islet cells to secrete insulin, as determined by the intraperitoneal glucose tolerance test, was preserved in the astaxanthin-treated group. Histology of the pancreas revealed no significant differences in the beta-cell mass between astaxanthin-treated and -untreated db/db mice. In conclusion, these results indicate that astaxanthin can exert beneficial effects in diabetes, with preservation of beta-cell function. This finding suggests that anti-oxidants may be potentially useful for reducing glucose toxicity.     

Concordant mRNA expression of UCP-3, but not UCP-2, with mitochondrial thioesterase-1 in brown adipose tissue and skeletal muscle in db/db diabetic mice

A recent hypothesis concerning the function of uncoupling protein-3 (UCP-3) depends upon a positive relationship with mitochondrial thioesterase (MTE-1) in situations where fatty acid beta-oxidation is increased. MTE-1 mRNA levels are raised in transgenic mice overexpressing UCP-3 in skeletal muscle and we sought to extend these findings by quantifying in vivo expression of endogenous MTE-1, UCP-1, UCP-2, and UCP-3 mRNA levels in white adipose tissue, interscapular brown adipose tissue, and skeletal muscle in db/db mice. In this study we show that changes in MTE-1 mRNA levels as a result of differences between db/db vs db/+ mice or following long-term treatment of db/db mice with rosiglitazone or Wy-14,643 were more closely correlated with changes in UCP-3 than either UCP-1 or UCP-2 mRNA levels in the tissues examined. The present data contribute to the argument that UCP-3 and MTE-1 are linked within the same metabolic pathway either in response to, or as regulators of, fatty acid beta-oxidation.     

Hepatic and adipose tissue lipogenesis as related to age and thyroid status in the rat

We have previously reported that, in the rat, chronic thyroxine (T4) treatment induced a transient adipose tissue hyperplasia and that, in preadipocytes cultures, lipogenesis as well as adipose conversion were enhanced by triiodothyronine. Therefore we looked for the possibility of a relationship between in vivo stimulation of adipose tissue lipogenesis and the stimulation of fat cell recruitment by thyroid hormones. Hepatic and adipose tissue de novo lipogenesis were estimated by the incorporation of 3H2O into lipids in rats of various ages made slightly hyperthyroid by daily injections of T4 (0.2 microgram/g/day) from birth. Hepatic and adipose tissue lipogenesis were increased at 3 and 6 weeks of age, no stimulation being observed when animals get older. 21 week-old animals were therefore acutely treated with 0.2 or 2 micrograms T4/g/day. In this case, only the high T4 dose was able to induce a consistent lipogenesis stimulation in liver and in retroperitoneal adipose tissue and failed to induce it in epididymal adipose tissue. These results pointed out that thyroid hormones can stimulate lipogenesis both in liver and adipose tissue. However, there is an age related fall in the sensitivity to thyroid hormones for lipogenesis stimulation, not only in the liver, but also and more pronounced in adipose tissue, in parallel to that observed in vivo for adipose differentiation; moreover, this decreased sensitivity seems to be accelerated by a long lasting hyperthyroidal state.