Tumour necrosis factor, a key role in obesity?

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.

Vaccinium virgatum Aiton Leaves Extract Suppressed Lipid Accumulation and Uric Acid Production in 3T3-L1 Adipocytes

Blueberry (Vaccinium virgatum Aiton; Kinisato 35 Gou) leaves have recently attracted increasing attention as a useful material for the prevention of lifestyle diseases. Here, we examined the effects of the hot water extract of blueberry leaves (BLEx) on lipogenesis and uric acid production in 3T3-L1 adipocytes. The results showed that BLEx suppressed lipid accumulation and the mRNA expression of differentiation markers in 3T3-L1 adipocytes. A fractionation study showed that the highly polymerized proanthocyanidin-rich fraction was responsible for this effect. Upon maturation to adipocytes, 3T3-L1 cells produced uric acid and tumor necrosis factor-α, and hypoxia stimulated the production of uric acid and xanthine oxidoreductase activity. BLEx suppressed the production of uric acid under these conditions. Although BLEx inhibited the enzymatic activity of xanthine oxidase, this activity was observed in several fractions containing catechin, epicatechin, chlorogenic acid, rutin, and low molecular weight proanthocyanidins. Taken together, these results indicate that BLEx contains various compounds with the ability to suppress lipid accumulation and uric acid production in adipocytes.

Association of hypertriglyceridemic waist-to-height ratio and its dynamic status with risk of type 2 diabetes mellitus: The Rural Chinese Cohort Study

AIMS

To evaluate the risk of type 2 diabetes mellitus (T2DM) in a prospective study with hypertriglyceridemic waist-to-height ratio (HWHtR) and its dynamic status.

METHODS

We collected data for 12,248 participants ≥18 years in this study. Cox's proportional-hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for T2DM risk by baseline HWHtR. Multiple logistic regression analysis was used to estimate odds ratios (ORs) and 95% CIs for T2DM risk by transformation in HWHtR.

RESULTS

We identified 839 T2DM cases during a median follow-up of 5.92 years. Compared with normal TG level and normal WHtR, T2DM risk was increased with high TG level and high WHtR (aHR 2.04, 95% CI 1.49-2.79). Similar results were observed in subgroup analyses by sex and age. During follow-up, T2DM risk was increased with stable high TG level and high WHtR (aOR 4.45, 95% CI 2.76-7.17) compared with stable normal TG level and normal WHtR. The results above were robust in sensitivity analyses.

CONCLUSIONS

HWHtR phenotype and its dynamic status were associated with risk of T2DM. Our study suggests that primary prevention and avoiding the appearance of the HWHtR phenotype in the rural Chinese population may reduce the T2DM risk.

Association of the TNF-α -308G/A polymorphism with lipid profile changes in response to aerobic training program

Promoter polymorphism of the tumor necrosis factor-α (TNF-α) gene is associated with obesity-related traits, although the role of its potential modifying effect on changes in obesity-related parameters achieved through a training program is still unknown. The aim of the present study was to examine whether the TNF-α-308G/A polymorphism (rs1800629) influences the effects of a training program. Accordingly, we studied the alleles and genotypes distribution in a group of 168 Polish Caucasian women measured for selected body mass and composition, as well as biochemical parameters before and after the realization of a 12-week aerobic training program. Our results showed that TNF-α genotypes can modulate training-induced biochemical parameter changes such as lipid profile. We demonstrated that carriers of the GG genotype are associated with decreases in post-training high-density lipoprotein cholesterol (HDL-C) levels (p<0.001). Additionally, we revealed that participants with the GG genotype had a higher low-density lipoprotein cholesterol (LDL-C) level (p=0.046) during the entire study period. It could be concluded that harboring the GG genotype of rs1800629 may be considered to be a disadvantageous factor in the context of training-induced effects on lipid profile changes in young female participants.

Association of visceral adiposity and its longitudinal increase with the risk of diabetes in Chinese adults: A prospective cohort study

OBJECTIVE

A Chinese visceral adiposity index (CVAI) was recently established to estimate the visceral fat area in Chinese adults. This study aimed to investigate the risk of incident prediabetes and diabetes in relation to visceral adiposity calculated by CVAI.

METHODS

A total of 2558 subjects with normal plasma glucose levels from the Shanghai Changfeng Study were enrolled in a prospective cohort study. The independent associations of basal visceral fat area by CVAI and its longitudinal change with incident prediabetes and diabetes were identified using Cox regression analyses.

RESULTS

During an average of 4.4 years of follow-up, 546 (21.3%) and 99 (3.9%) of 2558 nondiabetic subjects developed prediabetes and diabetes, respectively. Visceral fat area by CVAI and its longitudinal increase were independently associated with incident prediabetes and diabetes in Chinese adults. In a multivariable-adjusted regression model, CVAI, as well as its annual change, was the strongest independent predictor of incident prediabetes (HR, 1.383 [1.162-1.647]) and diabetes (HR, 1.607 [1.092-2.364]) compared with other estimates of obesity (BMI and waist circumference). Receiver operating characteristic curve analyses showed that CVAI had better performance than BMI and waist circumference for the prediction of prediabetes and diabetes in Chinese adults.

CONCLUSIONS

Visceral adiposity plays a pivotal role in the pathogenesis of diabetes, and the visceral adiposity estimated by CVAI is superior to the traditional estimates of obesity for the prediction of incident prediabetes and diabetes in Chinese adults.

Convergence between biological, behavioural and genetic determinants of obesity

Multiple biological, behavioural and genetic determinants or correlates of obesity have been identified to date. Genome-wide association studies (GWAS) have contributed to the identification of more than 100 obesity-associated genetic variants, but their roles in causal processes leading to obesity remain largely unknown. Most variants are likely to have tissue-specific regulatory roles through joint contributions to biological pathways and networks, through changes in gene expression that influence quantitative traits, or through the regulation of the epigenome. The recent availability of large-scale functional genomics resources provides an opportunity to re-examine obesity GWAS data to begin elucidating the function of genetic variants. Interrogation of knockout mouse phenotype resources provides a further avenue to test for evidence of convergence between genetic variation and biological or behavioural determinants of obesity.

Serum Levels of Interleukin-6 and C-Reactive Protein Correlate With Body Mass Index Across the Broad Range of Obesity

BACKGROUND

It has been noted that elevated inflammatory markers, such as tumor necrosis factor-alpha (TNF), soluble TNF receptor II (sTNF-RII), interleukin 6 (IL-6) and C-reactive protein (CRP), are characteristically found in the serum in obese patients. In this study, we examined the correlation of these markers with BMI in nonobese, obese, and morbidly obese individuals to explore this relationship across the broad range of obesity.

METHODS

A total of 9 nonobese, including normal and overweight (body mass index [BMI] <30 kg/m2) and 41 obese (BMI > or =30 kg/m2) adults were included in this study. Among obese subjects, 11 subjects were grade I or II obese (BMI > or =30 and <40 kg/m2), and 30 subjects were morbidly obese (grade III obese, BMI > or =40 kg/m2). Serum levels of glucose, insulin, TNF, sTNF-RII, IL-6, and CRP were measured.

RESULTS

Obese subjects (BMI > or =30 kg/m2) had significantly higher serum levels of TNF, sTNF-RII, IL-6, and CRP compared with nonobese subjects. Serum levels of sTNF-RII, IL-6, and CRP, but not TNF, were positively correlated with BMI in obese subjects. However, in morbidly obese subjects, only the serum concentrations of IL-6 and CRP remained correlated with BMI, primarily because of this relationship in men.

CONCLUSIONS

The present results support evidence that obesity represents an inflammatory state. In morbid obesity, the correlation of only IL-6 and CRP with BMI, particularly in males, suggests that IL-6 may be secreted in an endocrine manner in proportion to the expansion of fat mass particularly in the abdominal region, with a corresponding increase in hepatic production of CRP.

Exercise and osteoarthritis: cause and effects

Osteoarthritis (OA) is a common chronic joint condition predominantly affecting the knee, hip, and hand joints. Exercise plays a role in the development and treatment of OA but most of the literature in this area relates to knee OA. While studies indicate that exercise and physical activity have a generally positive effect on healthy cartilage metrics, depending upon the type of the activity and its intensity, the risk of OA development does appear to be moderately increased with sporting participation. In particular, joint injury associated with sports participation may be largely responsible for this increased risk of OA with sport. Various repetitive occupational tasks are also linked to greater likelihood of OA development. There are a number of physical impairments associated with OA including pain, muscle weakness and altered muscle function, reduced proprioception and postural control, joint instability, restricted range of motion, and lower aerobic fitness. These can result directly from the OA pathological process and/or indirectly as a result of factors such as pain, effusion, and reduced activity levels. These impairments and their underlying physiology are often targeted by exercise interventions and evidence generally shows that many of these can be modified by specific exercise. There is currently little clinical trial evidence to show that exercise can alter mechanical load and structural disease progression in those with established OA, although a number of impairments, that are amenable to change with exercise, appears to be associated with increased mechanical load and/or disease progression in longitudinal studies.

Dexamethasone-induced lipolysis increases the adverse effect of adipocytes on osteoblasts using cells derived from human mesenchymal stem cells

The increased bone marrow lipid deposition in steroid-associated bone loss diseases indicates that abnormalities in fat metabolism are associated with disease development. Recent studies have suggested that bone marrow adipocytes are secretory cells and that they may release substances that have an inhibitory effect on the differentiation and function of osteoblasts. We hypothesized that exposure of bone-marrow-derived adipocytes to corticosteroids exacerbates their deleterious effects on osteoblast metabolism and function. Adipocytes and osteoblasts derived from a human mesenchymal stem cell line (240L) were co-cultured in the absence of direct cell contact with or without dexamethasone treatment. After 6days of co-culture, osteoblasts demonstrated significantly lower levels of function based on lower mineralization, alkaline phosphatase activity and expression of osteogenic (Runx2, osteocalcin) mRNA marker. Dexamethasone treatment resulted in significantly lower levels of osteoblastic function compared with co-cultured cells without dexamethasone. Furthermore, conditioned media from dexamethasone-treated adipocytes induced a similar toxic effect and increased apoptosis involving activation of caspases 3/7 compared with conditioned media without dexamethasone treatment. Within the conditioned media, a substantial increase in the levels of leptin and two saturated fatty acids (FAs; stearate and palmitate) was observed after dexamethasone treatment. Although leptin supplementation failed to induce the inhibitory effect on osteoblasts, similar toxic results were produced with stearate and palmitate treatment, and an increase in intracellular reactive oxygen species was observed. Stearate- and palmitate-induced apoptosis was blocked by a reactive oxygen species scavenger pyrrolidine dithiocarbamate. These data show that saturated FAs secreted from adipocytes induce lipotoxic effects via mechanisms that may involve reactive oxygen species accumulation in osteoblasts. Our results suggest that inhibition of saturated FA secretion would protect osteoblasts against adipocytes in corticosteroid-associated bone loss diseases.

Body composition and its association with cardiometabolic risk factors in the elderly: a focus on sarcopenic obesity

Important changes in body composition with aging are a progressive loss of muscle mass and increase of fat mass. Despite their enormous clinical importance, body composition changes such as sarcopenic obesity in the elderly are under-recognized. This study aimed to examine the relationship of body composition with a wide variety of cardiometabolic risk factors among 2943 subjects (1250 men and 1693 women) aged 60 years or older from Korean National Health Examination and Nutrition Survey (KNHANES). Sarcopenia was defined as an appendicular skeletal muscle mass (ASM) divided by weight (%) of < 1 SD below the sex-specific mean for young adults. Obesity was defined as a body mass index (BMI) ≥ 25 kg/m(2). Body composition was categorized into four non-overlapping groups: the sarcopenic obese, sarcopenic nonobese, nonsarcopenic obese, and nonsarcopenic nonobese groups. A wide variety of cardiometabolic risk factors, including blood pressure (BP), glucose tolerance indices, lipid profiles, inflammatory markers, and vitamin D level, were compared according to body composition group. The prevalence of sarcopenic obesity was 18.4% in men and 25.8% in women. In both sexes, the prevalence of vitamin D deficiency and metabolic syndrome was highly prevalent in the sarcopenic obese group. Serum insulin level, homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride levels, and ferritin levels were the highest in the sarcopenic obese group in both men and women, whereas HDL-cholesterol and 25-hydroxyvitamin D (25(OH)D) levels were the lowest in the sarcopenic obese group. The sarcopenic obese group was more closely associated with insulin resistance, metabolic syndrome, and cardiovascular disease (CVD) risk factors than any other group in this elderly population.

Effect of ration size on fillet fatty acid composition, phospholipid allostasis and mRNA expression patterns of lipid regulatory genes in gilthead sea bream (Sparus aurata)

The effect of ration size on muscle fatty acid (FA) composition and mRNA expression levels of key regulatory enzymes of lipid and lipoprotein metabolism have been addressed in juveniles of gilthead sea bream fed a practical diet over the course of an 11-week trial. The experimental setup included three feeding levels: (i) full ration until visual satiety, (ii) 70 % of satiation and (iii) 70 % of satiation with the last 2 weeks at the maintenance ration. Feed restriction reduced lipid content of whole body by 30 % and that of fillet by 50 %. In this scenario, the FA composition of fillet TAG was not altered by ration size, whereas that of phospholipids was largely modified with a higher retention of arachidonic acid and DHA. The mRNA transcript levels of lysophosphatidylcholine acyltransferases, phosphatidylethanolamine N-methyltransferase and FA desaturase 2 were not regulated by ration size in the present experimental model. In contrast, mRNA levels of stearoyl-CoA desaturases were markedly down-regulated by feed restriction. An opposite trend was found for a muscle-specific lipoprotein lipase, which is exclusive of fish lineage. Several upstream regulatory transcriptions were also assessed, although nutritionally mediated changes in mRNA transcripts were almost reduced to PPARα and β, which might act in a counter-regulatory way on lipolysis and lipogenic pathways. This gene expression pattern contributes to the construction of a panel of biomarkers to direct marine fish production towards muscle lean phenotypes with increased retentions of long-chain PUFA.

Genetic association between TNF-alpha -308 G>A polymorphism and longitudinal weight change during clozapine treatment

OBJECTIVE

The aim of the study was to investigate the association between genetic variation in the tumor necrosis factor-alpha (TNF-alpha) gene and longitudinal weight change during long-term clozapine treatment.

METHODS

Fifty-five patients with refractory schizophrenia treated with clozapine for 8 years were recruited. Gender, age, treatment response to clozapine in the first 14 months, baseline BMI, clozapine dose, concomitant use of mood stabilizers and other antipsychotics, and -308 G > A polymorphism in the human TNF-alpha gene were analyzed using generalized estimating equations.

RESULTS

In addition to having a lower baseline BMI (p = 0.0013) and a longer treatment time (p = 0.050), the -308 GG carriers gained significantly more weight than the -308 A allele carriers (p = 0.0084) during 8 years of clozapine treatment, after controlling for other non-genetic factors.

CONCLUSIONS

The -308 G > A genetic variant of the TNF-alpha gene is associated with longitudinal weight change during clozapine treatment. Follow-up duration is an important factor to consider when performing pharmacogenetic study of clozapine-induced weight gain.

Production of Serum Amyloid a in Response to Inflammatory Cytokines by Human Adipocytes

Serum amyloid A (SAA) is a major acute-phase protein in humans, and elevated plasma levels represent a risk factor for cardiovascular diseases. SAA was thought to be produced by hepatocytes only in response to inflammatory stimuli; moreover, recent studies have shown that adipose tissue can secrete several proinflammatory factors. Therefore, we investigated whether cells in adipose tissue can synthesize SAA in response to inflammatory stimuli. Adipocytes and preadipocytes isolated from abdominal adipose tissue were incubated with IL-1, IL-6, TNF-α, LPS, or resistin at different concentrations. After 48 hours, the supernatants were analyzed by ELISAs for human SAA. Preadipocytes did not show any production in SAA. In contrast, in adipocytes, incubation with TNF-α led to a significant increase in SAA production, peaking after LPS or resistin (∼3 times greater vs unstimulated adipocytes). The greatest increase in SAA occurred with all stimuli combined (∼5 times greater vs control cells). Subsequently, we investigated whether treatment with some drugs could modulate SAA production in adipocytes, and observed that fluvastatin led to a significant inhibition of SAA release, whereas a larger modulation of SAA release was observed after treatment with troglitazone or aspirin. These results show for the first time that human adipocytes, and not preadipocytes, can produce SAA in response to inflammatory cytokines and that this process can be modulated.

Adipose tissue-mediated inflammation: the missing link between obesity and cardiovascular disease?

Until relatively recently, the role of adipose tissue in the development of obesity and its consequences was considered to be a passive one. Mounting evidence highlights the role of adipose tissue in the development of a systemic inflammatory state that contributes to obesity-associated vasculopathy and cardiovascular risk. It is now clear that, in addition to storing calories as triglycerides, adipocytes secrete a large variety of cytokines, chemokines and hormone-like factors, such as leptin, resistin, and acute-phase proteins. In addition, insulin resistance, both in nondiabetic and diabetic subjects, is frequently associated with obesity, particularly with an excess of intraabdominal fat. This production of pro-atherogenic substances is of particular interest since an increase in the plasma levels of these mediators may provide a novel mechanistic link between obesity and its vascular complications.

The role of adiposity as a determinant of an inflammatory milieu

With the growing prevalence of obesity, scientific interest in the biology of adipose tissue has been extended to the secretory products of adipocytes, since they have been shown increasingly to affect several aspects of the pathogenesis of obesity-related diseases. Until relatively recently, the role of adipose tissue itself in the development of obesity and its consequences was considered to be a passive one. It is now clear that, in addition to storing energy in the form of triglycerides, adipocytes also secrete a large variety of proteins, including cytokines, chemokines and hormone-like factors. This production of proatherogenic chemokines by adipose tissue is of particular interest, since their local secretion, for example by perivascular adipose depots, may provide a novel mechanistic link between obesity and associated vascular complications.

Atherogenecity of LDL and unfavorable adipokine profile in metabolically obese, normal-weight woman

OBJECTIVE

The relationship of visceral adiposity with adipocytokines and low-density lipoprotein (LDL) particle distribution and oxidation in Asian metabolically obese, normal-weight (MONW) individuals has not been evaluated. We aimed to investigate the association between visceral adiposity and adipocytokines and cardiovascular disease (CVD) risk factors in MONW Korean women with normal glucose tolerance.

METHODS AND PROCEDURES

We examined the metabolic characteristics of 135 non-obese (BMI <25 kg/m(2)) women aged 25-64 years. Twenty-five women (BMI <25 kg/m(2) and visceral fat adiposity (VFA) > or =100 cm(2)) were classified as MONW and 25 women (BMI <25 kg/m(2) and VFA <100 cm(2)), pair-matched for age, weight, height, and menopausal status, as control group. Plasma lipid profiles and adipocytokines were evaluated in these two groups.

RESULTS

MONW subjects had higher systolic (P < 0.05) and diastolic blood pressure (P < 0.005) and higher concentrations of triacylglycerol (TG) (P < 0.005), insulin (P < 0.01), and free fatty acid (FFA) (P < 0.05) than control subjects. There was no significant difference between two groups in LDL-cholesterol (LDL-C) concentrations; however, MONW subjects had smaller LDL particles (P < 0.01) and higher concentrations of oxidized LDL (ox-LDL) (P < 0.05) compared with controls. Moreover, MONW subjects had higher concentrations of tumor necrosis factor-alpha (TNF-alpha) (P < 0.05), interleukin-6 (IL-6) (P < 0.05) and leptin (P < 0.05), and lower plasma adiponectin concentrations (P < 0.05). Higher intake of saturated fat with lower ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFA) and lower fiber intake than normal subjects were found in MONW women.

DISCUSSION

We found an unfavorable inflammatory profile and a more atherogenic LDL profile in MONW female subjects even in the absence of a known CVD risk factors. Moreover, MONW consumed more saturated fat and less fiber than the control group.

Inflammation, obesity and comorbidities: the role of diet

The adipocyte metabolism has been shown to change during the fat enlargement process associated to obesity. Several procoagulant proteins such as plasminogen activator inhibitor type 1, tissue factor or factor VII and also inducible nitric oxide synthase show higher expression in adipose tissue of obese people in comparison to lean. This overexpression could explain at least a part of the atherogenic and cardiovascular risk associated with obesity. In addition to cytokine secretion, many other features have been observed to be common to adipocyte and monocyte/macrophage lines: for example, phagocytic and microbicidal activities, and possibly a cellular plasticity of adipose precursors. Overweight and obesity are associated with an increased risk of such metabolic abnormalities as dyslipidemia, hypertension or type 2 diabetes mellitus and cardiovascular diseases, common features of the metabolic syndrome. Initially, insulin resistance or hyperinsulinemia was suggested as the origin of these abnormalities. More recent studies indicate that adipokynes have an important role in obesity-associated metabolic complications, and suggest that chronically elevated local or systemic concentrations of adipokynes contribute to the development of complications associated with obesity and metabolic syndrome. Considering all the evidence relating to diet and inflammation, the best diet for protecting against the metabolic derangements associated with obesity and metabolic syndrome would be high in fibre-rich cereals, fruit, vegetables, fish, virgin olive oil and nuts; moderate in wine; and low in meat, processed meat foods and trans-fatty acids.

High-fat diets promote insulin resistance through cytokine gene expression in growing female rats

To determine if tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6). IL-6 gene expression is influenced by amount and source of dietary fat, 30 weanling female rats were randomly assigned to a moderate-fat soybean oil (MFS; 22% of total energy fed as fat), high-fat (HF) soybean oil (HFS; 39% of total energy fed as fat), or HF tallow (HFT; 39% of total energy fed as fat) diet treatments. Oral glucose tolerance tests (OGTT) were conducted serially over 10 weeks of treatment. HFT and HFS rats gained more weight and had greater body fat than the MFS rats fed similar amounts of energy. Both groups of HF-fed rats had greater (P<.05) insulin resistance (homeostasis model assessment) than MFS-fed rats. TNF-alpha mRNA abundance quantified by real-time reverse transcriptase-polymerase chain reaction was greater (P<.05) in liver and lower (P<.05) in adipose tissue in HFT compared to HFS and MFS rats. There were positive correlations (P<.05) between hepatic TNF-alpha mRNA and insulin resistance, and negative correlations between insulin sensitivity and hepatic TNF-alpha mRNA and hepatic IL-6 mRNA. During Week 3 and Week 6 OGTTs, hyperinsulinemic responses were observed in the HFT group, after which, on Week 9, insulin secretion was diminished in response to the OGTT, suggesting impaired pancreatic insulin secretion. HFS rats exhibited insulin resistance on Week 9 OGTT. In summary, an HFT diet fed to growing female rats caused insulin resistance associated with increased hepatic TNF-alpha mRNA leading to pancreatic insufficiency. Early-onset insulin resistance related to the inflammatory process in obesity is influenced by the amount and type of fat in the diet.

Sarcopenic obesity and inflammation in the InCHIANTI study

The aging process is often paralleled by decreases in muscle and increases in fat mass. At the extreme these two processes lead to a condition known as "sarcopenic obesity" (Roubenoff R. Ann NY Acad Sci 904: 553-557, 2000). Research suggests that inflammatory cytokines produced by adipose tissue, especially visceral fat, accelerate muscle catabolism and thus contribute to the vicious cycle that initiates and sustains sarcopenic obesity. We tested the hypothesis that obesity and poor muscle strength, hallmarks of sarcopenic obesity, are associated with high circulating levels of proinflammatory cytokines in a random sample of the residents of two municipalities in the Chianti geographic area (Tuscany, Italy). The study sample consisted of 378 men and 493 women 65 yr and older with complete data on anthropometrics, handgrip strength, and inflammatory markers. Participants were cross-classified according to sex-specific tertiles of waist circumference and grip strength and according to a cut point for obesity of body mass index > or =30 kg/m(2). After adjusting for age, sex, education, smoking history, physical activity, and history of comorbid diseases, components of sarcopenic obesity were associated with elevated levels of IL-6, C-reactive protein, IL-1 receptor antagonist, and soluble IL-6 receptor (P < 0.05). Our findings suggest that global obesity and, to a greater extent, central obesity directly affect inflammation, which in turn negatively affects muscle strength, contributing to the development and progression of sarcopenic obesity. These results suggest that proinflammatory cytokines may be critical in both the development and progression of sarcopenic obesity.

Tumour necrosis factor (TNF)α as a regulator of fat tissue mass in the Mediterranean gilthead sea bream (Sparus aurata L.)

The study was undertaken to analyze the lipolytic effect and transcriptional regulation of tumour necrosis factor (TNF)alpha in gilthead sea bream (Sparus aurata L.). The study was also focused on the transcriptional regulation and analysis of the 5-flanking region of lipoprotein lipase (LPL) in an attempt to identify cis-regulatory elements that would support the TNFalpha-mediated effects. The lipolytic effect of TNFalpha was evidenced by the increased release of glycerol in the culture medium of freshly isolated adipocytes. This observation, in addition to the summer up-regulation of TNFalpha transcripts in liver and mesenteric adipose tissue, supported a key role of TNFalpha as a fish limiting factor of tissue fat mass. Accordingly, TNFalpha expression in liver and mesenteric adipose tissue was reduced by fasting. Furthermore, the up-regulated expression of TNFalpha in the skeletal muscle of older fish can represent an adaptive response to limit the enhanced lipid influx towards muscle. A close positive association between LPL and TNFalpha transcripts supported the contribution of TNFalpha as a part of a regulatory network that exerts an inhibitory tonus upon the expression of LPL, which in turns limits the tissue uptake of fatty acids and the ultimate increase of tissue lipid reservoirs. The precise mechanism for the inhibition of LPL gene expression by TNFalpha remains to be established in fish, but analysis of the 5'-flanking region evidenced the conservation through vertebrate evolution of a functional OCT-1/NF-Y site that would mediate the TNFalpha effects on LPL expression.

Regulation of hypothalamic NPY by diet and smoking

Appetite is regulated by a number of hypothalamic neuropeptides including neuropeptide Y (NPY), a powerful feeding stimulator that responds to feeding status, and drugs such as nicotine and cannabis. There is debate regarding the extent of the influence of obesity on hypothalamic NPY. We measured hypothalamic NPY in male Sprague-Dawley rats after short or long term exposure to cafeteria-style high fat diet (32% energy as fat) or laboratory chow (12% fat). Caloric intake and body weight were increased in the high fat diet group, and brown fat and white fat masses were significantly increased after 2 weeks. Hypothalamic NPY concentration was only significantly decreased after long term consumption of the high fat diet. Nicotine decreases food intake and body weight, with conflicting effects on hypothalamic NPY reported. Body weight, plasma hormones and brain NPY were investigated in male Balb/c mice exposed to cigarette smoke for 4 days, 4 and 12 weeks. Food intake was significantly decreased by smoke exposure (2.32+/-0.03g/24h versus 2.71+/-0.04g/24h in control mice (non-smoke exposed) at 12 weeks). Relative to control mice, smoke exposure led to greater weight loss, while pair-feeding the equivalent amount of chow caused an intermediate weight loss. Chronic smoke exposure, but not pair-feeding, was associated with decreased hypothalamic NPY concentration, suggesting an inhibitory effect of cigarette smoking on brain NPY levels. Thus, consumption of a high fat diet and smoke exposure reprogram hypothalamic NPY. Reduced NPY may contribute to the anorexic effect of smoke exposure.

Subcutaneous adipose tissue cytokine production is not responsible for the restoration of systemic inflammation markers during weight loss

CONTEXT

It has been suggested that weight loss can improve systemic inflammation associated with obesity by decreasing the adipose production of pro-inflammatory cytokines. This suggestion, however, remains controversial.

OBJECTIVE

To analyse the effect of weight loss on peripheral inflammatory markers and subcutaneous adipocytokine production.

DESIGN

Patients were studied at baseline, at the end of the weight loss period, and after 2 weeks of weight stabilisation.

SUBJECTS

Nineteen morbid obese non-diabetic patients and 20 lean control subjects.

INTERVENTION

During the weight loss period patients followed a 6-week low-calorie diet.

MEASUREMENTS

Plasma levels of inflammatory markers, maximal in vitro whole-blood cytokine production, subcutaneous adipose tissue expression and content of several cytokines.

RESULTS

Obese subjects had higher circulating levels of C reactive protein (CRP), serum amyloid A (SAA), interleukin IL-6, IL-1 and soluble tumor necrosis factor receptors (sTNFR). Weight loss was associated with a significant decrease in CRP, SAA, leucocytes and plasma IL-6. Maximal in vitro cytokine production of IL-1 and sTNFR1 increased during this period. Weight loss did not induce significant changes in the adipose concentrations of IL-6, IL-1 or sTNF-receptors. However, adipose expression of IL-6, IL-1, TNFalpha, membrane cofactor protein-1 and adiponectin increased at the end of the weight loss period. During weight maintenance, circulating inflammatory parameters increased and in some cases returned to baseline.

CONCLUSIONS

A low-calorie diet is associated with an improvement in the systemic inflammatory status. This seems to be due to energy restriction rather than to adipose mass loss, since inflammatory levels return to baseline soon after weight stabilisation. Furthermore, a negative energy balance and fat mobilisation are associated with increased subcutaneous cytokine adipose expression.

Family and case-control association study of the tumor necrosis factor-alpha (TNF-alpha) gene with schizophrenia and response to antipsychotic medication

BACKGROUND

Dysregulation of the immune system has been suggested to play a role in the etiology of schizophrenia (SCZ). In this context, the tumor necrosis factor-alpha (TNF-alpha) is considered an interesting candidate for genetic studies as overproduction of TNF-alpha, which may be genetically modulated, can influence neuron growth and proliferation. Moreover, the TNF-alpha gene is located on chromosome 6p21.3, a region that has been found to be associated with SCZ in numerous linkage studies. One functional polymorphism, G-308A, has been studied for association with SCZ yielding inconsistent findings.

RESULTS AND DISCUSSIONS

In our study, we investigated the G-308A polymorphism with SCZ including 95 nuclear families and 149 pairs of cases/controls matched by age, gender, and ethnicity. Furthermore, we examined BPRS change scores (after 6 weeks, 3 months, and 6 months) and weight changes (after 6 weeks) with this polymorphism in 153 and 247 patients, respectively, after clozapine treatment. We did not observe biased transmission using family-based association test (P=0.752) or significant differences in case/control studies (P=0.839). However, patients with allele A showed significant improvement on BPRS change score after 3 months (t=2.000, P=0.049) and 6 months (t=2.481, P=0.015) of clozapine treatment when compared with patients without allele A. Moreover, trends were observed for genotype A/A with clinical improvement in BPRS change score after 6 months (F=2.834, P=0.065) using ANCOVA, and for allele G with weight gain (t=-1.702, P=0.091).

CONCLUSION

Overall, the G-308A polymorphism of the TNF-alpha gene does not appear to play a major role in SCZ but might be involved in antipsychotic response.

Genetic and environmental contributions to plasma C-reactive protein and interleukin-6 levels – a study in twins

Elevated baseline levels of acute-phase proteins such as C-reactive protein (CRP) or cytokines like interleukin-6 (IL-6) are known risk factors for atherosclerosis and cardiovascular disease (CVD) events. However, until today, there is only controversial information about the contribution of genetic and environmental factors. Therefore, we performed an open prospective study in 108 monozygotic (MZ) and 60 same-sex dizygotic (DZ) twin pairs to analyse the genetic and environmental contributions to plasma CRP and IL-6 levels. Heritability of IL-6 was 0.61, indicating that plasma IL-6 levels are to a major part influenced by genetic determinants; however, for CRP, heritability was only 0.22, pointing to a moderate genetic influence. Plasma CRP levels were strongly influenced by female gender, older age and especially the body mass index. Our data underline the central role of IL-6 in low-grade inflammation contributing to atherosclerosis and CVD.

Cigarette Smoke Exposure Reprograms the Hypothalamic Neuropeptide Y Axis to Promote Weight Loss

RATIONALE

Despite irrefutable epidemiologic evidence, cigarette smoking remains the major preventable cause of lung disease morbidity worldwide. The appetite-suppressing effect of tobacco is a major behavioral determinant of smoking, but the underlying molecular and neuronal mechanisms are not understood. Neuropeptide Y (NPY) is an orexigenic neuropeptide, whose activity in the hypothalamic paraventricular nucleus governs appetite.

OBJECTIVES

To compare the effects of smoke exposure and equivalent food restriction on body weight, organ mass, cytokines, and brain NPY in Balb/c mice.

METHODS

A pair-feeding study design compared smoke exposure (4 wk; 1 cigarette, 3 x /d, 5 d/wk) to equivalent food restriction (pair-fed) and sham-exposed control mice.

RESULTS

Smoke exposure rapidly induced mild anorexia. After 4 wk, smoke-exposed and pair-fed groups were lighter than control mice (22.0 +/- 0.2, 23.2 +/- 0.5, 24.9 +/- 0.4 g, respectively; p < 0.05). Brown and white fat masses were only reduced by smoke exposure, relative to control mice. NPY concentration in the paraventricular nucleus was significantly and paradoxically reduced by smoke exposure, despite lower plasma leptin concentrations; this was not observed in the pair-fed group experiencing 19% food restriction. Adipose mRNA expression of uncoupling proteins, inflammatory cytokines interleukin 6 and tumor necrosis factor alpha, and adipose triglyceride lipase was decreased by smoke exposure, and even lower in pair-fed mice.

CONCLUSIONS

In contrast to food restriction, smoke exposure caused a reduction in hypothalamic NPY and fat mass, and regulated adipose cytokines. These findings may contribute to understanding weight loss in smoking-related lung disease and in the design of more effective smoking cessation strategies.

Decreased splenic mRNA expression levels of TNF-alpha and IL-6 in diet-induced obese animals

Obesity could be considered as a systemic low-grade inflammatory condition affecting inflammation markers. Adipose tissue synthesizes cytokines whose degree of elevation may depend on the obesity status. Recently, new information is collected on the cross-talking between immune system and adipose tissue in obesity. We report hereby that tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) gene expression in spleen of diet-induced obese animals were markedly decreased (more than 50%) as a consequence of the high fat feeding during five weeks. Interestingly, a very significant negative correlation was found between splenic TNF-alpha mRNA levels and total fat pads (r = -0.806, p = 0.000). These findings support the hypothesis that TNF-alpha gene expression may follow different trends in obese animals adipocytes and splenocytes.

Increased aortic stiffness in the insulin-resistant Zuckerfa/farat

Accumulating clinical evidence indicates increased aortic stiffness, an independent risk factor for cardiovascular and all-cause mortality, in type 2 diabetic and glucose-intolerant individuals. The present study sought to determine whether increased mechanical stiffness, an altered extracellular matrix, and a profibrotic gene expression profile could be observed in the aorta of the insulin-resistant Zucker fa/fa rat. Mechanical testing of Zucker fa/fa aortas showed increased vascular stiffness in longitudinal and circumferential directions compared with Zucker lean controls. Unequal elevations in developed strain favoring the longitudinal direction resulted in a loss of anisotropy. Real-time quantitative PCR and immunohistochemistry revealed increased expression of fibronectin and collagen IVα3in the Zucker fa/fa aorta. In addition, expression of transforming growth factor-β and several Smad proteins was increased in vessels from insulin-resistant animals. In rat vascular smooth muscle cells, 12–18 h of exposure to insulin (100 nmol/l) enhanced transforming growth factor-β1 mRNA expression, implicating a role for hyperinsulinemia in vascular stiffness. Thus there is mechanical, structural, and molecular evidence of arteriosclerosis in the Zucker fa/fa rat at the glucose-intolerant, hyperinsulinemic stage.

Effect of short-term cigarette smoke exposure on body weight, appetite and brain neuropeptide Y in mice

Although nicotinic receptors have been demonstrated in hypothalamic appetite-regulating areas and nicotine administration alters food intake and body weight in both animals and humans, the mechanisms underlying the effects of smoking on appetite circuits remain unclear. Conflicting effects of nicotine on the major orexigenic peptide, neuropeptide Y (NPY), have been observed in the brain, but the effects of smoking are unknown. Thus, we aimed to investigate how cigarette smoking affects body weight, food intake, plasma leptin concentration, hypothalamic NPY peptide, adipose mass and mRNA expression of uncoupling proteins (UCP), and tumor necrosis factor (TNF) alpha. Balb/C mice (8 weeks) were exposed to cigarette smoke (three cigarettes, three times a day for 4 consecutive days) or sham exposed. Body weight and food intake were recorded. Plasma leptin and brain NPY were measured by radioimmunoassay. UCPs and TNF alpha mRNA were measured by real-time PCR. Food intake dropped significantly from the first day of smoking, and weight loss became evident within 2 days. Brown fat and retroperitoneal white fat masses were significantly reduced, and plasma leptin concentration was decreased by 34%, in line with the decreased fat mass. NPY concentrations in hypothalamic subregions were similar between two groups. UCP1 mRNA was decreased in white fat and UCP3 mRNA increased in brown fat in smoking group. Short-term cigarette smoke exposure led to reduced body weight, food intake, and fat mass. The reduction in plasma leptin concentration may have been too modest to increase NPY production; alternatively, change in NPY or its function might have been offset by nicotine or other elements in cigarette smoke.

Metabolic syndrome and robustness tradeoffs

The metabolic syndrome is a highly complex breakdown of normal physiology characterized by obesity, insulin resistance, hyperlipidemia, and hypertension. Type 2 diabetes is a major manifestation of this syndrome, although increased risk for cardiovascular disease (CVD) often precedes the onset of frank clinical diabetes. Prevention and cure for this disease constellation is of major importance to world health. Because the metabolic syndrome affects multiple interacting organ systems (i.e., it is a systemic disease), a systems-level analysis of disease evolution is essential for both complete elucidation of its pathophysiology and improved approaches to therapy. The goal of this review is to provide a perspective on systems-level approaches to metabolic syndrome, with particular emphasis on type 2 diabetes. We consider that metabolic syndromes take over inherent dynamics of our body that ensure robustness against unstable food supply and pathogenic infections, and lead to chronic inflammation that ultimately results in CVD. This exemplifies how trade-offs between robustness against common perturbations (unstable food and infections) and fragility against unusual perturbations (high-energy content foods and low-energy utilization lifestyle) is exploited to form chronic diseases. Possible therapeutic approaches that target fragility of emergent robustness of the disease state have been discussed. A detailed molecular interaction map for adipocyte, hepatocyte, skeletal muscle cell, and pancreatic beta-cell cross-talk in the metabolic syndrome can be viewed at http://www.systems-biology.org/001/003.html.

The metabolic syndrome in obese postmenopausal women: relationship to body composition, visceral fat, and inflammation

The purpose of this study was to investigate whether aerobic fitness, body composition, body fat distribution, and inflammation are different in obese postmenopausal women with and without the metabolic syndrome (MS), and whether the severity of MS is associated with these characteristics. Fifty-eight women (age, 59 +/- 1 yr; body mass index, 33.0 +/- 0.6 kg/m2)completed testing of maximal aerobic capacity, body composition (fat mass, lean mass, and percent body fat), body fat distribution (sc and visceral fat areas, and regional adipocyte sizes), and inflammation (C-reactive protein, IL-6, and TNF-alpha,and their soluble receptors). Lean mass (44.4 +/- 0.9 vs. 41.2 +/- 0.9 kg; P < 0.05), visceral fat area (180 +/- 10 vs. 135 +/- 7 cm2; P <0.001), and plasma soluble TNF receptor 1 (sTNFR1; 860 +/- 25 vs. 765 +/- 42 pg/ml; P < 0.05) were higher in women with the MS(n = 27) than in those without the MS (n = 31). The number of MS components was directly related to weight, body mass index, fat mass, lean mass, visceral fat area, and plasma sT-NFR1. We conclude that obese older women with the MS are characterized by high lean mass, high visceral fat, and elevated sTNFR1, and the severity of the MS is associated with body composition, visceral adiposity, and inflammation.

The role of TNF-alpha in insulin resistance

Insulin resistance is an important component of the metabolic syndrome associated with obesity. Early-stage insulin-resistance and related mild glucose intolerance may be compensated by increased insulin secretion. When combined with impaired insulin secretion, insulin resistance plays an important role in type 2 diabetes (1). Insulin-resistance is also associated with a variety of pathological conditions, including trauma, infection, and cancer. Obesity and type 2 diabetes are the most common metabolic diseases in Western societies, together affecting as much as half of the adult population (2). The prevalence of these conditions is not only high, but continues to increase. We have only recently come to appreciate the role of fat, especially visceral fat, as an endocrine organ. Visceral fat is the source of a number of substances which might play a role in the development of insulin resistance. Among the latter are tumor necrosis factor-alpha (TNF-alpha), adiponectin, IL-6, resistin and free fatty acids. This review will discuss the regulation of insulin responses by TNF-alpha and evidence supporting the hypothesis that over expression of TNF-alpha plays a role in the pathophysiology of insulin resistance.

Reductions in plasma cytokine levels with weight loss improve insulin sensitivity in overweight and obese postmenopausal women

OBJECTIVE

The purpose of this study was to determine whether improvements in insulin sensitivity with weight loss are mediated by changes in inflammation in obese, postmenopausal women.

RESEARCH DESIGN AND METHODS

We studied 58 sedentary, overweight, and obese (BMI 33 +/- 1 kg/m(2), means +/- SEM) postmenopausal (58 +/- 1 year) women at baseline and 37 women who completed 6 months of weight loss induced by diet and exercise. The women underwent 3-h hyperinsulinemic-euglycemic clamps (40 mU x m(-2) x min(-1)) to determine glucose utilization (M). Insulin sensitivity was determined as M/I, the amount of glucose metabolized per unit of plasma insulin (I). Visceral adipose tissue (VAT) and plasma concentrations of C-reactive protein (CRP), cytokines interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha, as well as their soluble receptors, were measured.

RESULTS

At baseline, CRP concentration was a predictor of both glucose utilization and insulin sensitivity, independent of adiposity, race, and aerobic fitness (M: partial r = -0.30, P = 0.03, and M/I: partial r = -0.32, P = 0.02). Weight loss resulted in significant reductions in body weight, fat mass, VAT, and fasting glucose and insulin levels (P < 0.05). Both glucose utilization and insulin sensitivity increased by 16% (P < 0.05). CRP, IL-6, and soluble TNF receptor (sTNFR)-1 concentrations decreased (P < 0.05), but concentrations of TNF-alpha, sTNFR-2, and soluble IL-6 receptor (IL-6sR) did not change. In stepwise regression models to predict changes in glucose homeostasis, changes in VAT and sTNF-R1 independently predicted changes in glucose utilization (r = -0.49 and cumulative r = -0.64, P < 0.01), while changes in VAT and IL-6 were both independent predictors of changes in insulin sensitivity (r = -0.57 and cumulative r = -0.68, P < 0.01).

CONCLUSIONS

Improvements in glucose metabolism with weight loss programs are independently associated with decreases in cytokine concentrations, suggesting that a reduction in inflammation is a potential mechanism that mediates improvements in insulin sensitivity.

The role of TNF-alpha in insulin resistance

Insulin resistance is an important component of the metabolic syndrome associated with obesity. Early-stage insulin-resistance and related mild glucose intolerance may be compensated by increased insulin secretion. When combined with impaired insulin secretion, insulin resistance plays an important role in type 2 diabetes (1). Insulin-resistance is also associated with a variety of pathological conditions, including trauma, infection, and cancer. Obesity and type 2 diabetes are the most common metabolic diseases in Western societies, together affecting as much as half of the adult population (2). The prevalence of these conditions is not only high, but continues to increase. We have only recently come to appreciate the role of fat, especially visceral fat, as an endocrine organ. Visceral fat is the source of a number of substances which might play a role in the development of insulin resistance. Among the latter are tumor necrosis factor-alpha (TNF-alpha), adiponectin, IL-6, resistin and free fatty acids. This review will discuss the regulation of insulin responses by TNF-alpha and evidence supporting the hypothesis that over expression of TNF-alpha plays a role in the pathophysiology of insulin resistance.

Stimulation of lipolysis by tumor necrosis factor-alpha in 3T3-L1 adipocytes is glucose dependent: implications for long-term regulation of lipolysis

Tumor necrosis factor-alpha (TNF-alpha) and hyperglycemia both impair insulin sensitivity in vivo. This may be secondary to stimulation of adipose tissue lipolysis and consequent increased circulating free fatty acids (FFAs). Here we report that neither TNF-alpha nor glucose alone has a pronounced effect on lipolysis in 3T3-L1 adipocytes. However, the combination of TNF-alpha plus glucose markedly stimulates lipolysis. Glucose does not affect the ability of isoproterenol to stimulate lipolysis. Alternative substrates such as acetate, pyruvate, and lactate do not allow the TNF-alpha effect. Mannose was almost as effective as glucose; fructose was marginally effective, but galactose was ineffective. The effectiveness of the sugars corresponded with production of lactate, i.e., the cells readily produced lactate from glucose or mannose, slightly from fructose, and not at all from galactose. The ability of TNF-alpha to phosphorylate extracellular signal-regulated kinase 1 (ERK1) and ERK2 and to downregulate perilipin (which has been implicated in the lipolytic effect of TNF-alpha) was not affected by glucose. We conclude that the lipolytic action of TNF-alpha is influenced by glucose in 3T3-L1 adipocytes. The findings suggest that glucose metabolism is required for the lipolytic response to TNF-alpha but not for early signaling events. These findings suggest novel mechanisms by which TNF-alpha and hyperglycemia raise FFA levels and induce insulin resistance.

TNFalpha expression of subcutaneous adipose tissue in obese and morbid obese females: relationship to adipocyte LPL activity and leptin synthesis

INTRODUCTION

Tumor necrosis factor (TNFalpha) has been invoked as an adipostat. Accordingly, the adipose tissue expression of TNFalpha has been shown to be proportional to the degree of adiposity. The regulatory role of TNFalpha in obesity may be controlled by several mechanisms. These include the inhibitory effect on LPL activity, the mediation on glucose homeostasis or the effect on leptin. To assess the role of TNFalpha in obesity we measured adipocyte TNFalpha expression in 96 females with a wide range of adiposity and with or without type 2 diabetes. We analysed the relationship between TNFalpha expression, adipocyte LPL activity, insulin resistance and leptin in this population.

RESULTS

The TNFalpha and leptin expression of the adipose tissue in obese and morbid obese patients were significantly higher than in controls. Obese and morbid obese patients had slightly higher levels of LPL activity, but these differences were not significant. We observed a significant relationship between adipose TNFalpha expression and body mass index (r=0.35, P<0.001). TNFalpha expression was negatively related to LPL activity (r=-0.28, P<0.05) and positively related to leptin expression (r=0.35, P<0.001).

CONCLUSION

Our results indicate that obese women, even those with morbid obesity, over-express TNFalpha in subcutaneous adipose tissue in proportion to the magnitude of the fat depot and independently of the presence of type 2 diabetes. The TNFalpha system may be a homeostatic mechanism that prevents further fat deposition by regulating LPL activity and leptin production.

Signals of adiposity

Adipose tissue, a reserve of energy, has played an essential role in mammalian evolution. Adipose tissue differs from other tissues in that its mass has considerable capacity to expand, which while beneficial in decreasing the risk of starvation, increases the risk of predation. Adipose tissue mass is thus under tight control in nondomestic species. Adipose tissue secretes a variety of factors, some of which (leptin, tumor necrosis factor (TNF) alpha, resistin) are thought to be involved in modulation of adipose mass. Leptin has a variety of functions, primarily targetting the hypothalamus where it acts to decrease appetite and increase energy expenditure. Leptin is also involved in the adaptations to fasting, and leptin is also required for normal reproductive and immune function. TNF alpha and resistin appear to have key paracrine roles, attenuating the anabolic effects of insulin on adipose tissue metabolism.

The metabolic puzzle during the evolution of HIV infection

Abnormalities in energy, protein, lipid and glucose metabolism have been described in HIV patients since the beginning of the epidemic. With the new antiretroviral agents, nutritional status and survival have improved dramatically. However, since these therapies were introduced, there have been more descriptions of metabolic abnormalities, some of which were similar to and others of which were in conflict with those reported in previous years. This paper reviews the complexity of the metabolic abnormalities in HIV infections before and after the introduction of highly active antiretroviral therapy, and discusses such etiopathogenic mechanisms as secondary infections, antiretroviral drugs and persistent immune activation, which may be involved in these derangements.

Chemokines control fat accumulation and leptin secretion by cultured human adipocytes

In addition to their role in inflammation, cytokines like TNFalpha have been reported to regulate the adipose tissue function suggesting a role for these soluble mediators in metabolism. However, it is not known whether adipocytes have the capacity to secrete chemokines, a group of low molecular weight inflammatory mediators that control leukocyte migration into tissues. Here we show that primary cultures of human preadipocytes constitutively produce three chemokines, interleukin-8 (IL-8), macrophage inflammatory protein-1alpha (MIP-1alpha) and monocyte chemotactic protein-1 (MCP-1), while their level of expression is low in mature adipocytes. Upon TNFalpha treatment, the expression of all the three chemokines is upregulated in adipocytes differentiated in vitro. In addition, we describe the presence of seven different chemokine receptors, mainly in mature adipocytes, both in vitro and in human fat tissue sections. Prolonged stimulation of cultured human adipocytes with exogenous chemokines leads to a decrease in lipid content in association with the downregulation of PPARgamma mRNA expression. Moreover, chemokines positively control the secretion of leptin, a hormone that regulates appetite, by a post-transcriptional mechanism. These findings reveal a new role for chemokines in the regulation of adipose tissue and suggest a novel therapeutic basis for the treatment of obesity, diabetes and cachexia.

Protein kinase B (PKB/Akt)--a key regulator of glucose transport?

The serine/threonine kinase protein kinase B (PKB/Akt) has been shown to play a crucial role in the control of diverse and important cellular functions such as cell survival and glycogen metabolism. There is also convincing evidence that PKB plays a role in the insulin-mediated regulation of glucose transport. Furthermore, states of cellular insulin resistance have been shown to involve impaired PKB activation, and this usually coincides with a loss of glucose transport activation. However, evidence to the contrary is also available, and the role of PKB in the control of glucose transport remains controversial. Here we provide an overview of recent findings, discuss the potential importance of PKB in the regulation of glucose transport and metabolism, and comment on future directions.

Cancer cachexia: from experimental models to patient management

Cachexia is frequently associated with advanced or terminal cancer states, but it can also develop early during the course of neoplastic disease. This syndrome, which is characterized by body weight loss and negative nitrogen balance, significantly affects patient survival and quality of life. Studies on experimental models have shown that a complex interplay of different factors, such as anorexia, classical hormones, cytokines and other less well defined factors, concur in causing tissue wasting. On the basis of these results, it has been possible to prevent the onset of experimental cachexia by targeting therapeutic interventions at the underlying metabolic perturbations. Anticytokine treatments, either acting centrally or peripherally, have received particular attention, and are currently reaching the stage of clinical trials.