Weight loss in tumour-bearing mice is not associated with changes in resistin gene expression in white adipose tissue.

Resistin, a product of white adipose tissue, is postulated to induce insulin resistance in obesity and regulate adipocyte differentiation. The aim of this study was to examine resistin gene expression in adipose tissue from mice bearing the MAC16 adenocarcinoma, which induces cancer cachexia with marked wasting of adipose tissue and skeletal muscle mass. MAC16-bearing mice lost weight progressively over the period following tumour transplantation, while the weight of control mice remained stable. Leptin mRNA in gonadal fat was 50 % lower in MAC16 mice than in controls (p < 0.05). Plasma insulin concentrations were also significantly lower in the MAC16 group (p < 0.05). However, resistin mRNA level in gonadal fat in MAC16 mice was similar to controls (94 % of controls). Thus, despite severe weight loss and significant falls in leptin expression and insulin concentration, resistin gene expression appears unchanged in white adipose tissue of mice with MAC16 tumour. Maintenance of resistin production may help inhibit the formation of new adipocytes in cancer cachexia.     

Resistin expression in different adipose tissue depots during rat development

Resistin is a hormonal factor synthesised by adipocytes that was first thought to be related with the resistance to insulin in obesity, but whose function is not yet completely established. Here we have studied the ontogenic pattern of resistin mRNA expression in different white adipose tissue depots (WAT) – epididymal, inguinal, mesenteric and retroperitoneal – and in brown adipose tissue (BAT), as well as the circulating resistin levels, in rats of different ages (from the suckling period to one year of age). Resistin mRNA was determined by Northern blotting, and serum levels by enzyme immunoassay. In WAT, resistin expression remains almost constant with age, except in early development, where there is a peak of expression in the epididymal and retroperitoneal depots, and a decrease in the inguinal one, while the expression remains constant for the mesenteric depot. Moreover, there is a site-specific difference regarding resistin expression: all the depots express characteristic levels of mRNA, especially at the age of 2 months, the moment when resistin mRNA levels are significantly higher in the epididymal and the retroperitoneal than in the inguinal and mesenteric WAT and than in the BAT. The transient increased resistin expression in the epididymal and the retroperitoneal WAT at a period of time in which there is a change in diet (from milk to chow) suggests a common nutritional regulation of the resistin gene. Circulating resistin levels increase with age probably reflecting the increase in the body fat content.     

Influence of thyroid dysfunction on serum concentrations of adipocytokines

Thyroid hormones act on several aspects of metabolic and energy homeostasis influencing body weight, thermogenesis, and lipolysis in adipose tissue. Adipocytokines are biologically active substances produced by adipocyte with different physiological functions. These substances have multiple effects on several tissues acting on the intermediate and energy metabolism. For these reasons, attention has recently been focused on the possible relationship between adipocytokines, thyroid status, and thyroid dysfunction. Leptin, a signal of satiety to the brain and regulator of insulin and glucose metabolism, reflects the amount of fat storage and is considered as a pro-inflammatory adipocytokine. Adiponectin is inversely related to the degree of adiposity, increases insulin sensitivity, and may have antiatherogenic and anti-inflammatory properties. Resistin impairs glucose homeostasis and insulin action in mice but not in humans. Resistin might be considered a pro-inflammatory adipocytokine and participate in obesity-associated inflammation. Several reports indicate that leptin regulates thyroid function at hypothalamic-hypophyseal level and, conversely, thyroid hormones might control leptin metabolism at least in some animals studies. Both adiponectin and thyroid hormones share some physiological actions as reduction of body fat by increasing thermogenesis and lipid oxidation. Resistin also seems to be regulated by thyroid hormones, at least in rats. Thyroid dysfunction does not significantly affect serum leptin concentrations. Serum levels of adiponectin are no influenced by thyroid hypofunction; however, hyperthyroidism is associated with normal or elevated adiponectin levels. Finally, discordant results in resistin levels in thyroid dysfunction have been reported in humans.     

Plasma resistin levels in patients with type 1 and type 2 diabetes mellitus and in healthy controls.

Resistin is a recently discovered hormone that is exclusively expressed in adipose tissue. Its expression in rodents was reported to be elevated or suppressed in genetic and diet-induced obesity, respectively. Resistin treatment impaired glucose tolerance and insulin action. Immunoneutralization of resistin improved insulin sensitivity, while thiazolidinedione treatment reduced resistin expression. Therefore, resistin could play a critical role in the development of obesity and type 2 diabetes. In this study were determined resistin plasma levels in humans suffering from type 1 and type 2 diabetes and in healthy controls. Plasma levels of resistin in healthy controls were 38.78 ng/ml. They were not statistically different in individuals with a broad BMI range. Resistin plasma levels in type 2 diabetes were 38.7 ng/ml, and 39.4 ng/ml in type 1 diabetes. Thiazolidinedione treatment did not influence resistin plasma levels. We conclude from our data: 1. resistin can be detected in human plasma, 2. plasma resistin levels are not different in type 1 and type 2 diabetes.     

Increased plasma levels of adipokines in preeclampsia: relationship to placenta and adipose tissue gene expression

Adipokines are predominantly secretory protein hormones from adipose tissue but may also originate in placenta and other organs. Cross-sectionally, we monitored maternal plasma concentration of adiponectin, resistin, and leptin and their mRNA expression in abdominal subcutaneous adipose tissue and placenta from preeclamptic (PE; n = 15) and healthy pregnant (HP; n = 23) women undergoing caesarean section. The study groups were similar in age and BMI, whereas HOMA-IR tended to be higher in the PE group. In fasting plasma samples, the PE group had higher concentrations of adiponectin (18.3 +/- 2.2 vs. 12.2 +/- 1.1 microg/ml, P = 0.011), resistin (5.68 +/- 0.41 vs. 4.65 +/- 0.32 ng/ml, P = 0.028), and leptin (34.4 +/- 3.2 vs. 22.7 +/- 2.1 ng/ml, P = 0.003) compared with the HP group. Adiponectin and leptin concentrations were still different between PE and HP after controlling for BMI and HOMA-IR, whereas resistin concentrations differed only after controlling for BMI but not HOMA-IR. We found similar mean mRNA levels of adiponectin, resistin, and leptin in abdominal subcutaneous adipose tissue in PE and HP women. When data were pooled from PE and HP women, resistin mRNA levels in adipose tissue also correlated with HOMA-IR (r = 0.470, P = 0.012) after controlling for BMI and pregnancy duration. Resistin mRNA levels in placenta were not significantly different between PE and HP, whereas leptin mRNA levels were higher in PE placenta compared with HP. Thus increased plasma concentrations of adiponectin and resistin in preeclampsia may not relate to altered expression levels in adipose tissue and placenta, whereas both plasma and placenta mRNA levels of leptin are increased in preeclampsia.     

Changes in adipocyte hormones leptin, resistin, and adiponectin in thyroid dysfunction

Thyroid hormones as well as the recently discovered secretory products of adipose tissue adiponectin and resistin take part in energy metabolism. To study the changes in the adipocyte hormones with changes in the thyroid functional status, we measured adiponectin, resistin, and leptin in 69 subjects with Graves' disease before and 32 patients at follow up after treatment for hyperthyroidism at hypothyroid state. Concentrations of serum adiponectin and resistin were higher in hyperthyroid state than in hypothyroid state (adiponectin: 5.73 +/- 1.1 vs. 3.0 +/- 0.5 ng/ml, P = 0.03) (resistin: 6.378 +/- 0.6 vs. 5.81 +/- 0.57 ng/ml, P < 0.0001). Resistin levels correlate positively with free t4(r = 0.37, P < 0.01), free t3 levels(r = 0.33, P < 0.01) and negatively with TSH(r = -0.22, P < 0.05). Adiponectin levels correlate with free t4(r = 0.33, P < 0.01) and free t3 (r = 0.44, P < 0.01). Though the adiponectin levels did not correlate with leptin or resistin levels, strong positive correlation of both resistin and adiponectin with thyroid hormones is noted. Serum levels of leptin did not change with change in the thyroid functional status (leptin: 53.38 +/- 2.47 vs. 55.10 +/- 2.58 NS). Leptin levels did not correlate with resistin and adiponectin. We conclude that thyroid function has effect on adipocyte hormones adiponectin and resistin but not leptin.     

Octylphenol stimulates resistin gene expression in 3T3-L1 adipocytes via the estrogen receptor and extracellular signal-regulated kinase pathways

Resistin is known as an adipocyte-specific secretory hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by sexual hormones. Whether environmental estrogens regulate the production of resistin is still not clear. Using 3T3-L1 adipocytes, we found that octylphenol upregulated resistin mRNA expression in dose- and time-dependent manners. The concentration of octylphenol that increased resistin mRNA levels by 50% was approximately 100 nM within 6 h of treatment. The basal half-life of resistin mRNA induced by actinomycin D was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin mRNA degradation. In addition, octylphenol stimulated resistin protein expression and release. The basal half-life of resistin protein induced by cycloheximide was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin protein degradation. While octylphenol was shown to increase activities of the estrogen receptor (ER) and MEK1, signaling was demonstrated to be blocked by pretreatment with either ICI-182780 (an ERalpha antagonist) or U-0126 (a MEK1 inhibitor), in which both inhibitors prevented octylphenol-stimulated phosphorylation of ERK. These results imply that ERalpha and ERK are necessary for the octylphenol stimulation of resistin mRNA expression. Moreover, U-0126 antagonized the octylphenol-increased resistin protein expression and release. These data suggest that the way octylphenol signaling increases resistin protein levels is similar to that by which it increases resistin mRNA levels; it is likely mediated through an ERK-dependent pathway. In vivo, octylphenol increased adipose resistin mRNA expression and serum resistin and glucose levels, supporting its in vitro effect.     

Resistin mRNA levels are downregulated by estrogen in vivo and in vitro

Resistin, a hormone secreted by adipocytes, is suggested to be an important link between obesity and diabetes. The aim of this study was to evaluate the regulatory effect of estrogen on adipocyte resistin gene expression in ovariectomized (OVX) rats and in isolated rat adipocytes in vitro. Subcutaneous injection of estradiol benzoate reduced resistin mRNA levels in adipocytes isolated from the inguinal, parametrial, perirenal, retroperitoneal, or periovarian fat deposits of OVX rats, while an in vitro study showed that estradiol treatment decreased resistin mRNA levels in cultured rat periovarian fat adipocytes. Results of Western blotting analysis also showed that estrogen decreased adipose resistin contents in vivo and in vitro. These data suggest that estrogen is a pivotal negative regulator of resistin gene expression.     

Increased resistin expression in the adipose tissue of male prolactin transgenic mice and in male mice with elevated androgen levels.

The aim of this study was to investigate the regulation of resistin, a recently identified adipocyte-secreted peptide, in the adipose tissue of prolactin (PRL)-transgenic (tg) mice using ribonuclease protection assay. The level of resistin mRNA increased 3.5-fold in the adipose tissue of untreated male PRL-tg mice compared to controls. However, there was no difference in resistin expression in the adipose tissue of female PRL-tg mice compared to control mice. PRL-tg male mice have elevated serum testosterone levels and we therefore analyzed the effects of testosterone alone on resistin mRNA expression. Furthermore, the effects of elevated androgen levels on PRL receptor (PRLR) mRNA expression in the adipose tissue were investigated. Resistin mRNA increased 2.6-fold in the adipose tissue of control male mice with elevated serum androgen levels. In addition, PRLR mRNA expression was increased in the adipose tissue of male mice with elevated testosterone. These results suggest testosterone to be a regulator of resistin and PRLR mRNA expression in the adipose tissue of male mice.     

Identification of variables influencing resistin serum levels in patients with type 1 and type 2 diabetes mellitus.

BACKGROUND: Resistin, a peptide hormone, has been discussed controversially as a missing link between obesity and insulin resistance. In contrast to resistin mRNA expression in adipose tissue, data on human serum levels in obesity and diabetes mellitus is scarce. The physiological range of serum resistin levels, reference values or adjusted percentiles have not yet been determined, making the interpretation of serum resistin concentrations quite difficult. METHODS: Resistin serum concentrations were measured systematically by ELISA in 216 healthy controls, 555 patients with type 2 diabetes and 114 patients with type 1 diabetes. Mean values, median, and range were determined, and BMI-, gender-, and disease-adapted percentiles were calculated for all subgroups. RESULTS: Age and gender did not have any influence on resistin levels. BMI and resistin levels were positively correlated in healthy controls (p = 0.02), albeit with a weak correlation coefficient. This correlation was absent in patients with type 1 and type 2 diabetes. In both genders, healthy controls had significantly higher resistin levels than patients with type 1 and type 2 diabetes (7.9 +/- 0.2 ng/ml vs. 5.7 +/- 0.2 ng/ml and 5.5 +/- 0.1 ng/ml, respectively; p < 0.0001). There was no correlation between resistin levels and occurrence of diabetic retinopathy or nephropathy. CONCLUSIONS: Serum resistin levels can be measured by ELISA over a broad range from 0.6 ng/ml up to 27.7 ng/ml, suggesting that percentiles might be helpful in the interpretation of an individuals resistin value. While age and gender do not influence resistin levels, BMI and occurrence of diabetes have to be considered.     

Sexual Dimorphism and Regulation of Resistin,Adiponectin, and Leptin Expression in the Mouse

Objective: To examine gender differences and hormonal regulation of resistin, adiponectin, and leptin. Research Methods and Procedures: Plasma levels were measured, and mRNA expression in perigonadal fat was quantified by RNase protection assays. Results: Plasma resistin declined with age despite an increase in adiposity in both genders. In male mice, plasma leptin increased, whereas adiponectin levels were constant. In females, both adiponectin and leptin levels increased with age. Resistin mRNA levels were significantly higher in female than male mice at all ages, whereas leptin and adiponectin mRNA levels were similar in fat from 6‐week‐old male and female mice, and sexual dimorphism was apparent only in the older mice, with higher levels apparent in females. Castration did not abolish gender differences in plasma levels or resistin, adiponectin, or leptin mRNAs. Castration of male mice did not significantly change adipokine mRNA levels or plasma levels of resistin or leptin; however, adiponectin was significantly increased. Dihydrotestosterone treatment had no effect on adipokine mRNA expression or resistin and adiponectin levels but increased leptin levels. In contrast, ovariectomy significantly increased resistin mRNA abundance and decreased leptin and adiponectin mRNAs. Plasma leptin levels were also increased by ovariectomy, whereas resistin and adiponectin levels were unchanged. Estrogen replacement significantly reduced resistin mRNA and increased leptin and adiponectin mRNA levels but had no effect on plasma adipokine levels. Discussion: The gender differences in adipokine mRNA expression and plasma levels were not ablated by castration and seem to be dependent on other factors in addition to gonadal steroids.     

Resistin overexpression impaired glucose tolerance in hepatocytes

Resistin is a 12.5-kDa cysteine-rich protein secreted from adipose tissue and is an important factor linking obesity with insulin resistance. Here, we investigated the effect of resistin on glucose tolerance in adult human hepatocytes (L-02 cells). In this study, resistin cDNA was transfected into L-02 cells, and glucose concentration and glucokinase activity were determined subsequently. The data indicated resistin impaired, insulin-stimulated glucose utilization, which implied liver was a target tissue of resistin. To understand its molecular mechanism, mRNA levels of key genes in glucose metabolism and insulin signaling pathway were analyzed. The results demonstrated resistin-stimulated expression of glucose-6-phosphatase (G6Pase), sterol regulatory element-binding protein 1c (SREBP1c) and suppressor of cytokine signaling 3 (SOCS-3), repressed expression of peroxisome proliferator-activated receptor gamma (PPARgamma) as well as insulin receptor substrate 2 (IRS-2). Given that glucokinase (GK) activity and glucose transporter 2 (GLUT2) expression were not altered, we presumed that resistin did not effect them. Moreover, resistin lowered mRNA levels of IRS-2 while stimulating SOCS-3 expression, which suggests it impairs glucose tolerance by blocking the insulin signal transduction pathway.     

Resistin concentrations in murine adipose tissue and serum measured by a new enzyme immunoassay

Objective: In an attempt to clarify the conflicting data on resistin mRNA expression and protein analysis by western blotting in adipose tissue and serum, we developed a sensitive enzyme‐linked immunosorbent assay (ELISA) for direct measurement of mouse resistin. Research Methods and Procedures: We developed polyclonal antibodies directed to the N (21 to 40) and C (79 to 91) termini of mouse resistin. Then, affinity‐purified anti‐C‐terminal resistin immunoglobin G (IgG) was biotinylated. ELISA was based on the sandwiching of antigen between antibody IgG coated on polystyrene plates and biotinylated antibody IgG. The bound biotinylated antibody was quantified with streptavidin‐linked horseradish peroxidase. Results: New ELISA can measure a concentration as low as 0.5 ng/mL of recombinant mouse resistin and is sensitive and specific enough to measure resistin protein in various adipose tissues and in sera. In normal mice, decreases in resistin concentrations in both white adipose tissue and serum were age dependent during 6 to 24 weeks of development. Resistin concentrations were significantly higher in omental adipose tissue in comparison with perirenal and abdominal adipose tissues and were 2‐ to 5‐fold higher in females than males during the growth period. ob/ob mice had significantly lower resistin concentrations than the control mice in both sera and the white adipose tissues, particularly in the omental fat. The treatment by testosterone, but not progesterone or β‐estradiol, in cultured adipocytes reduces resistin protein levels in a dose‐dependent manner. Discussion: New sensitive ELISA for mouse resistin clarified that the resistin concentrations in normal mice were markedly elevated in the omental adipose depots as compared with the perirenal and abdominal adipocyte depots and significantly elevated compared with adipose tissues in genetically obese mice.     

Regulation of Peptide YY Levels by Age,Hormonal, and Nutritional Status

Objective: Peptide YY (PYY) 3‐36 has recently been recognized as an important gut hormone that influences food intake. Peripheral injections of PYY 3‐36 in rats inhibit food intake in experimental animals as well as in lean and obese human subjects. This hormone has been suggested as an attractive therapeutic option for obesity. The aim of this study was to assess the influence of age, sex, thyroid status, growth hormone (GH), pregnancy, and food restriction on PYY levels in rat. Research Methods and Procedures: We determined plasma PYY levels in all experimental sets. Results: PYY levels were influenced by age, with the highest hormone levels achieved in early postnatal life (day 10) and decreasing thereafter. PYY levels were also dependent on thyroid hormone status being decreased in hyperthyroid rats. Exogenous GH administration led to a clear‐cut decrease in PYY levels in both normal and GH‐deficient rats. Acute food deprivation or chronic food restriction led to decreased PYY levels in virgin and pregnant rats. In pregnant rats with food available ad libitum, PYY levels were enhanced at late gestation. Discussion: Our observations indicate that PYY levels are influenced by age, thyroid hormones, and GH. These data indicate that PYY could be involved in the changes of food intake associated with these conditions. The PYY levels observed in acute and chronic food‐restricted rats indicate that, in situations of decreased energy intake, the lower PYY levels could serve to disinhibit central pathways and facilitate food intake.     

Low resistin levels in adipose tissues and serum in high-fat fed mice and genetically obese mice: development of an ELISA system for quantification of resistin

Obesity is a major risk factor for insulin resistance. Resistin, an adipocyte-derived hormone-like molecule, is considered to serve as an important link between obesity and insulin resistance. However, the physiological role of resistin and the mechanism by which it neutralizes insulin action are still unclear. There are also conflicting reports that cast doubt on the cause of insulin resistance. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) system for quantification of mouse resistin levels, analyzed in relation to insulin resistance. C57BL/6J mice fed high-fat diet compared with normal diet had low resistin levels (by 70%, P<0.01) in epididymal adipose tissues. Genetically obese mice, db/db and KK-A(y), had hyperinsulinemia and hyperglycemia but low resistin levels (decreases by 83 and 90%, both P<0.01) compared with C57/BL6J mice in epididymal adipose tissues. Serum resistin levels determined by Western blotting showed a similar pattern to those in adipose tissues. Resistin levels in adipose tissues correlated with serum adiponectin concentrations positively (r=0.49). Our results indicate that the novel ELISA system is suitable for measurement of resistin levels in adipose tissues. The results do not support a role for resistin in insulin resistance.