Brown adipose tissue redox status in response to dietary-induced obesity-associated oxidative stress in male and female rats

Obesity is linked to systemic oxidative stress and, although brown adipose tissue (BAT) plays a crucial role in energy balance, BAT redox status effects on obesity have not been studied previously. Female rats exhibit a greater BAT thermogenic capacity, attributed to enhanced mitochondrial differentiation, than males. The aim of this study was to investigate whether the mitochondrial sexual dimorphism is related to differences in BAT redox status and to assess its role in the regulation of body weight gain in response to chronic high fat diet (HFD) feeding. Ten-week-old Wistar rats of both genders were fed a pelleted control diet or HFD for 26 weeks. Although mitochondria of female rats produced higher levels of hydrogen peroxide than those of males, females exhibited lower oxidative damage, attributed to greater glutathione peroxidase activity and higher glutathione content. In response to HFD, body weight increased markedly in females, but oxidative capacity increased only in males, thus maintaining improved BAT redox status compared with females. In conclusion, the sexual dimorphism in BAT redox status found in control animals is attenuated by the HFD. The enhanced oxidative capacity of HFD males can be related to their greater resistance to body weight gain.

Expression of mitochondrial biogenesis-signaling factors in brown adipocytes is influenced specifically by 17beta-estradiol, testosterone, and progesterone

Control of mitochondrial biogenesis in brown adipose tissue (BAT), as part of the thermogenesis program, is a complex process that requires the integration of multiple transcription factors to orchestrate mitochondrial and nuclear gene expression. Despite the knowledge of the role of sex hormones on BAT physiology, little is known about the effect of these hormones on the mitochondrial biogenic program. The aim of this study was to determine the effect of testosterone, 17beta-estradiol, and progesterone on the expression of nuclear factors involved in the control of mitochondrial biogenesis and thermogenic function such as ppargamma, pgc1alpha, nrf1, gabpa, and tfam, and also an inhibitor of PI3K-Akt pathway, recently found to be involved in the control of mitochondrial recruitment (pten). For this purpose, an in vitro assay using cell-cultured brown adipocytes was used to address the role of steroid hormones, progesterone, testosterone, and 17beta-estradiol on the mRNA expression of these factors by real-time PCR. Thus 17beta-estradiol seemed to exert a dual effect, activating the PI3K-Akt pathway by inhibiting pten mRNA expression and also inhibiting nrf1 and tfam mRNA expression. Progesterone seemed to positively stimulate mitochondriogenesis and BAT differentiation by increasing the mRNA expression of the gabpa-tfam axis and ppargamma, respectively, but also exerted a negative output by increasing pten mRNA levels. Finally, testosterone inhibited the transcription of pgc1alpha, the master factor involved in UCP1 expression and mitochondrial biogenesis. In conclusion, our results support the idea that sex hormones have direct effects on different mediators of the mitochondriogenesis program.

Sex steroid receptor expression in different adipose depots is modified during midpregnancy

Sex hormone signalling is key in the understanding of adipose tissue metabolism during pregnancy. Sex hormones play an important role in adipose tissue metabolism by activating specific receptors that alter several steps of lipolysis and lipogenesis. We analyze steroid receptor mRNA levels in different rat adipose depots and mammary fat pad, as well as the sex hormone profile during midpregnancy, coinciding with the placentation process. Thus, progesterone and estradiol plasma levels were increased as well as testosterone levels. This hormonal profile was accompanied by low glucose to insulin ratio. PR-B, ERalpha and AR receptor densities during midpregnancy were dependent on adipose depot location. In mammary fat pad, the mRNA levels of sex hormone receptors were correlated with the growth of the depot. These results demonstrate that sex steroid hormone receptor mRNA expression during midpregnancy is tissue-specific. Our results agree with the idea that the increased estrogenic and androgenic signalling could be addressed to reducing the lipogenic state in early pregnancy exerted mainly by progesterone and to prepare adipose tissue for the beginning of the catabolic phase in late pregnancy in a depot-specific manner.

Depot differences in steroid receptor expression in adipose tissue: possible role of the local steroid milieu

Sex hormones play an important role in adipose tissue metabolism by activating specific receptors that alter several steps of the lipolytic and lipogenic signal cascade in depot- and sex-dependent manners. However, studies focusing on steroid receptor status in adipose tissue are scarce. In the present study, we analyzed steroid content [testosterone (T), 17beta-estradiol (17beta-E2), and progesterone (P4)] and steroid receptor mRNA levels in different rat adipose tissue depots. As expected, T levels were higher in males than in females (P = 0.031), whereas the reverse trend was observed for P4 (P < 0.001). It is noteworthy that 17beta-E2 adipose tissue levels were higher in inguinal than in the rest of adipose tissues for both sexes, where no sex differences in 17beta-E2 tissue levels were noted (P = 0.010 for retroperitoneal, P = 0.005 for gonadal, P = 0.018 for mesenteric). Regarding steroid receptor levels, androgen (AR) and estrogen receptor (ER)alpha and ERbeta densities were more clearly dependent on adipose depot location than on sex, with visceral depots showing overall higher mRNA densities than their subcutaneous counterparts. Besides, expression of ERalpha predominated over ERbeta expression, and progesterone receptor (PR-B form and PR-A+B form) mRNAs were identically expressed regardless of anatomic depot and sex. In vitro studies in 3T3-L1 cells showed that 17beta-E2 increased ERalpha (P = 0.001) and AR expression (P = 0.001), indicating that estrogen can alter estrogenic and androgenic signaling in adipose tissue. The results highlighted in this study demonstrate important depot-dependent differences in the sensitivity of adipose tissues to sex hormones between visceral and subcutaneous depots that could be related to metabolic situations observed in response to sex hormones.

The glutamine 27 glutamic acid polymorphism of the beta2-adrenoceptor gene is associated with abdominal obesity and greater risk of impaired glucose tolerance in men but not in women: a population-based study in Spain

OBJECTIVE

Given the important role of the beta2-adrenoceptor (beta2-AR) in lipid mobilization and the lack of studies in Southern European countries, the aim of this study was to investigate the role of the glutamine 27 glutamic acid (Gln27Glu) beta2-AR polymorphism in the susceptibility to obesity and its metabolic complications in a population-based nationwide multicentre study in Spain, especially focusing on the hypothetical influence of gender.

DESIGN

Cross-sectional population-based study.

PATIENTS

We studied 666 nonrelated adults (47.9% men and 52.1% women), aged 35-64 years, chosen randomly from a nationwide population-based survey of obesity, and related conditions including insulin resistance and cardiovascular risk factors.

MEASUREMENTS

Body mass index (BMI), waist-to-hip ratio (WHR), sagittal abdominal diameter (SAD), systolic and diastolic blood pressure, fasting and 2-h post-glucose load glycaemic levels, total cholesterol, high density lipoprotein (HDL)- and low density lipoprotein (LDL)-cholesterol, triglycerides, insulin, proinsulin and leptin plasma levels were measured. Beta2-AR Gln27Glu genotypes were determined by restriction fragment length polymorphism (RFLP)-polymerase chain reaction (PCR).

RESULTS

Glu27 homozygous obese men had significantly higher BMI and SAD mean values than both heterozygous and Gln27 homozygous obese men. Two-hour post-load plasma glucose concentration was higher in Glu27 homozygous than in Gln27 homozygous in the whole population and only in men when stratified by gender. No differences according to the genotype were found for the rest of the parameters studied, including homeostasis model assessment (HOMA), insulin, proinsulin and leptin levels, but for total and LDL-cholesterol these increased in men. We did not find differences in the anthropometrical and biochemical parameters according to the genotype in women. Multivariate logistic regression analysis showed that Glu27 homozygosity after adjustment for SAD was associated with type 2 diabetes mellitus.

CONCLUSIONS

Our results suggest that the glutamic acid 27 allele of the beta2-adrenoceptor may be a risk factor in men but not in women for the accumulation of visceral fat and for its association with the development of type 2 diabetes mellitus.

[Genetic polymorphisms and new perspectives in the prevention and treatment of obesity]

The prevalence of obesity has increased to an extraordinary degree, especially over the last three decades, so that if these trends persist, practically all of the adult population would be obese in the course of only two generations. On the basis of family and adoption studies, it has been estimated that the genetic component in obesity ranges from 20% to 80%. Thus, the most common forms of obesity would depend on the interaction of multiple genes as well as on the influence of various environmental factors, such as eating behaviour and lifestyle. Although none of these genes potentially involved in the control of body weight seems to be directly responsible for the syndrome, there have been reports of interesting associations between polymorphisms of certain candidate genes and obesity or its metabolic complications. The studies into associations between genotypes and obese phenotype have increased over the last few years and have basically focussed on the genes involved in the control of the energy balance, giving rise to a whole series of results which might constitute the basis for extremely interesting strategies for the prevention and treatment of this serious problem.

Association of sets of alleles of genes encoding beta3-adrenoreceptor, uncoupling protein 1 and lipoprotein lipase with increased risk of metabolic complications in obesity

OBJECTIVE

To investigate the relationship between the polymorphisms of the beta3-AR (Trp64Arg), UCP1 (A-->G) and LPL (HindIII and PvuII) loci and the metabolic complications associated with obesity in a Turkish population.

SUBJECTS

271 unrelated individuals of Turkish origin including obese (body mass index, BMI>30 kg¿m2) and lean (BMI< or =25 kg¿m2) subjects.

MEASUREMENTS

Anthropometric (weight, height and blood pressure) and metabolic measurements (plasma levels of glucose, cholesterol and triglycerides), and determination of beta3-AR, UCP1 and LPL genotypes by polymerase chain reaction followed by enzymatic digestion.

RESULTS

The distributions of genotypes for each candidate gene (beta3-AR, UCP1 and LPL) were similar between the obese and the lean subjects. The Arg64 allele of the beta3-AR gene was absent from massively obese men. GG carriers of the A-->G variant of the UCP1 gene showed BMI-associated increases of cholesterol levels which were more marked than both AA (P=0.027) and AG (P=0.039) carriers. Obese P+ carriers of the LPL PvuII variant had significantly higher levels of glucose than non-carriers (P=0.011), whereas obese P+P+ carriers did not have significantly different levels of triglycerides than non-carriers (P=0.087). Moreover, carriers of both alleles (G&P+) had higher levels of glucose than non-carriers (P=0.048), but did not have significantly different levels of triglycerides than non-carriers (P=0.125). However, the BMI-associated increase of triglycerides of P+&G carriers was significantly more marked than that of P+ carriers (P=0.0085).

CONCLUSION

Our data support the idea that alleles of specific genes (UCP1, LPL and beta3-AR) might play a role in the development of certain metabolic complications of obesity and might have additive effects when combined with each other (as in the case of UCP1 and LPL). International Journal of Obesity (2000)24, 93-100

Sex differences in the effect of obesity on human plasma tryptophan/large neutral amino acid ratio

BACKGROUND

The neurotransmitter serotonin (5-HT) contributes to the regulation of food intake and appetite behavior, and its rate of synthesis depends upon brain tryptophan (TRP) availability in relation to the large neutral amino acids (LNAAs). Thus, the ratio of TRP to the sum of LNAA (TRP/LNAA) will be representative of the 5-HT brain levels. Differences between men and women in the obesity-linked alterations in whole blood amino acid levels and compartmentation have been described. The aim of this work was to study the effect of obesity on brain TRP availability in men and women and to determine whether there are sex-linked differences.

METHODS

The plasma levels of TRP and LNAAs in 42 men and 46 women (classified according to their body mass index (BMI) into lean, overweight and obese) have been determined by HPLC.

RESULTS

The TRP/LNAA ratio shows a significant drop which is even more pronounced in men than in women as BMI increases. Moreover, the comparison of the values between the 3 BMI groups revealed that the drop in the TRP/LNAA ratio appears with overweight in men but only with obesity in women.

CONCLUSION

These sex differences could affect hypothetical behavioral differences of feeling hunger when facing voluntary food restriction for weight loss in individuals of different genders and with varying degrees of obesity.

Estrogen effects on blood amino acid compartmentation

The present paper focuses on the study of blood amino acid compartmentation in healthy men (lean and obese) and women, with special emphasis on the estimation of the recently described blood-cell adsorbed amino acid pool. The wide range of changes found in this pool on comparing different physiological situations may be attributable to its proposed characteristic high dynamism on the one hand, but also to the influence of other factors such as hormones. Along these lines, the sex- and obesity-linked variations found here in human blood led to the speculation as to whether these differences could be related to the influence of estrogens. This hypothesis was further tested by chronically treating a group of male rats with estrone and checking their subsequent blood amino acid compartment changes (which yielded a greater difference in the adsorbed pool). From the overall results obtained it may be concluded that the higher production of estrogens in women and obese men affects amino acid availability to the tissues by modulating the blood-cell adsorbed amino acid pool through a mechanism that is, at present, unknown.

Amino acid distribution in human blood. A significant pool of amino acids is adsorbed onto blood cell membranes

The recently published existence of a pool of amino acids absorbed onto the blood cell membranes in the rat has provided a new insight into the role of the blood cell amino acid pools, in the context of tissue-blood amino acid transport and their metabolic relationships. In the present study, this pool has been measured in a large (n = 40) representative healthy human population. This pool represents 9% of the blood cell amino acids, which is somewhat lower but in the same order as that previously measured in the rat. The inside-erythrocyte and plasma pools have also been quantified, giving an inside to outside ratio of 1.32 for the combined total amino acids. Statistically significant age related changes in the different blood compartments were detected for some amino acids (aspartate, asparagine, glutamine, tyrosine, methionine, phenylalanine, tryptophan and lysine) as well as for the ratio of tryptophan to the large neutral amino acids. The results obtained emphasize the importance of the amino acid red blood cell pool and assign to it the same order as the plasma pool. The results also feature the membrane-attached pool of some specific amino acids, ie taurine, glutamine, glutamate, aspartate and valine.

Tissue composition in persistent dietary obesity after early and adulthood overfeeding in the rat

The objective of this study was to assess the effects of prolonged cafeteria-diet feeding on tissue composition in adult rats comparing those that had been overfed in early life and then in adulthood with a group that was only overfed in adulthood, and to determine whether any alterations were related to the high energy diet per se or to obesity. In addition to following the body weight changes in detail, tissue masses and composition were determined at selected points of this long term dietary experiment. The marked changes in body weight and tissue composition of cafeteria-fed obese rats were sustained for at least 84 days after returning to the standard diet, and the obesity was exaggerated if these animals were pre-exposed to the palatable diet in early life. Three patterns of tissue composition in response to cafeteria feeding could be discerned: Liver and brown adipose tissue developed cell hypertrophy without apparent hyperplasia. In contrast, the retroperitoneal white adipose depot developed hyperplasia whereas the intestine and kidneys were not associated with marked changes in lipid composition. These adaptations were not recovered to control levels by prolonged standard diet feeding. Previous obesity influenced the adaptations in adipose tissue during the subsequent return to standard diet feeding, and differences between cafeteria-induced obese animals became more apparent when the cafeteria diet was removed. These results indicated the important effects of early dietary experience in subsequent responses to overfeeding.

Dietary-induced permanent changes in brown and white adipose tissue composition in rats

We have previously observed that feeding rats a cafeteria diet causes excess weight gain and changes in tissue composition. The object of this study was to assess whether these alterations were sustained after withdrawal of the palatable diet in the rat. The results showed that the obesity was not reversed by feeding a standard diet ad libitum for five months after withdrawal of the cafeteria diet. Body weight was 26 per cent greater than in control rats and tissue composition showed permanent alterations. The excess weight of lumbar white adipose tissue was due mainly to lipid content (86 per cent) and this was also true, but to a less extent, for interscapular brown fat (59 per cent). Increased brown fat mass was a result of hyperplasia and hypertrophy, whereas increased lumbar white fat was mainly a result of hyperplasia alone. In conclusion, changes in tissue composition, particularly in fat depots, were permanent and could be ascribed to the obesity per se, and not to the diet composition.