Adiposity induced by adenovirus 5 inoculation

Dogs are a susceptible species to human adenovirus 36 infection: New insights into the host range of the virus causing infectious obesity

The prevalence of obesity within the human population is escalating globally yearly. Obesity constitutes a complex ailment with diverse etiological factors. Recently, the infectious side of obesity aetiology, implicating pathogens such as human adenovirus 36 (HAdV-D36), has gained attention. Research indicates that HAdV-D36 can infect humans and various animal species, including mice, monkeys, and chickens, inducing obesity in the animals. The present study aimed to confirm whether companion animals, like dogs, can also host HAdV-D36 and which biochemical markers can be helpful to indicate its presence. The blood of 118 canine subjects was analysed using serological techniques for determining the presence of antibodies and screened for biochemical parameters like leptin, cholesterol, and triglycerides. The presence of anti-HAdV-D36 antibodies was confirmed in 80 of the 118 tested individuals. The investigation of the relationship between antibody levels and the concentrations of cholesterol, triglycerides, and leptin in blood serum revealed a positive correlation between antibody titers and triglyceride levels in the tested samples. Furthermore, utilizing cell cultures facilitated successful isolation of HAdV-D36 from the adipose tissue of 14 dogs under investigation. Our study adds to general knowledge of the range of hosts susceptible to the pathogen in question and highlights the discrepancies in the virus mechanisms found in the existing literature. Given the diverse host range of the virus, which extends to companion animals, a zoonotic potential cannot be ruled out, which, however, requires further extensive research.

E4orf1: The triple agent of adenovirus - Unraveling its roles in oncogenesis, infectious obesity and immune responses in virus replication and vector therapy

Human Adenoviruses (HAdV) are nearly ubiquitous pathogens comprising numerous sub-types that infect various tissues and organs. Among many encoded proteins that facilitate viral replication and subversion of host cellular processes, the viral E4orf1 protein has emerged as an intriguing yet under-investigated player in the complex interplay between the virus and its host. E4orf1 has gained attention as a metabolism activator and oncogenic agent, while recent research is showing that E4orf1 may play a more important role in modulating cellular pathways such as PI3K-Akt-mTOR, Ras, the immune response and further HAdV replication stages than previously anticipated. In this review, we aim to explore the structure, molecular mechanisms, and biological functions of E4orf1, shedding light on its potentially multifaceted roles during HAdV infection, including metabolic diseases and oncogenesis. Furthermore, we discuss the role of functional E4orf1 in biotechnological applications such as Adenovirus (AdV) vaccine vectors and oncolytic AdV. By dissecting the intricate relationships between HAdV types and E4orf1 proteins, this review provides valuable insights into viral pathogenesis and points to promising areas of future research.

Development of Adenovirus-Based Covid-19 Vaccine Candidate in Indonesia

Covid-19 pandemic has struck worldwide by end of 2019 and the use of various vaccine platforms was one of the main strategies to end this. To meet the needs for vaccine technology equality among many countries, we developed adenovirus-based Covid-19 vaccine candidate in Indonesia. SARS-CoV-2 Spike gene (S) was constructed into pAdEasy vector. The recombinant serotype 5 Adenovirus (AdV_S) genome was transfected into AD293 cells to produce recombinant adenovirus. Characterization using PCR confirmed the presence of spike gene. Transgene expression analysis showed the expression of S protein in AdV_S infected AD293 and A549 cells. Optimization of viral production showed the highest titer was obtained at MOI of 0.1 and 1 at 4 days. The in vivo study was performed by injecting Balb/c mice with 3.5 × 107 ifu of purified adenovirus. The result showed that S1-specific IgG was increased up to 56 days after single-dose administration of AdV_S. Interestingly, significant increase of S1 glycoprotein-specific IFN-γ ELISpot was observed in AdV_S treated Balb/c mice. In conclusion, the AdV_S vaccine candidate was successfully produced at laboratory scale, immunogenic, and did not cause severe inflammation in Balb/c mice. This study serves as initial step towards manufacturing of adenovirus-based vaccine in Indonesia.

Case Series of Disseminated Xanthogranulomatosis in Red-crowned Parakeets (Cyanoramphus novaezelandiae) with Detection of Psittacine Adenovirus 2 (PsAdV-2)

Simple Summary

Lipometabolic disorders, such as xanthogranulomatosis, are common diseases in avian medicine. Various manifestations of lipometabolic disorders and risk factors for acquiring lipometabolic diseases have been described in the past years. Xanthogranulomas are usually limited to the skin and supposed to be associated with traumatic or inflammatory injuries in that area. Disseminated xanthogranulomatosis, appearing simultaneously in several internal organs, has been recently described in psittacine birds, the cause of the diseases was not known. Here, we describe a case series of disseminated xanthogranulomatosis in another psittacine species, the Red-crowned Parakeet (Cyanoramphus novaezelandiae) and a possible association with a concurrent psittacine adenovirus 2 (PsAdV-2) infection. Viral infections that trigger lipometabolic diseases have been described in human medicine in some species of small animals and in chickens. PsAdV-2- infections are widely distributed in avian species. A possible association between PsAdV-2- infections and lipometabolic diseases in the Red-crowned Parakeet should be considered. Individual birds and flocks with both or either of these diseases should be carefully examined and monitored.

Abstract

Xanthogranulomatosis is a common dermatological disease in birds. This form of inflammation, possibly associated with lipometabolic disorders, can also be seen in visceral organs, which as yet has only rarely been described in avian medicine. In general, diseases related to impaired lipid metabolism are frequently reported in avian medicine, with hepatic steatosis and atherosclerosis being the most common. In human medicine, infectious agents—especially some strains of adenovirus—were implicated in contributing to lipometabolic disorders; this has also been described for chicken. Here, a case series of six Red-crowned Parakeets (Cyanoramphus novaezelandiae) is presented, all cases being characterized by psittacine adenovirus 2 (PsAdV-2) infection with or without disseminated xanthogranulomatosis. The affected individuals were examined alive by clinical examination. Total body radiographs were taken of two birds, haematology and blood biochemistry results were achieved in one bird. The birds either died immediately after clinical presentation or within two days, two individuals were euthanized due to worsening of their clinical condition. All birds underwent a post-mortem examination. While four birds were finally diagnosed with disseminated xanthogranulomatosis, all six individuals had large eosinophilic intranuclear inclusion bodies in the epithelial cells of the collecting ducts of the kidney and tested positive for PsAdV-2. Further examinations are needed to clarify to what extent PsAdV-2 might elicit lipometabolic disease in birds, or psittacines in general, and, in particular, the Red-crowned Parakeet.

Adenovirus 36 infection and obesity risk: current understanding and future therapeutic strategies

INTRODUCTION

Obesity, a multifactorial disease caused by the interaction between genetic characteristics, metabolism, lifestyle, and environmental factors, is a major global health problem and is currently defined as a pandemic phenomenon. This disease is determined by an interaction of several factors, but the imbalance between energy consumption and expenditure seems to be the crucial point. In some cases, there is no linearity between exposure to those factors that cause the onset of obesity. A striking example of the occurrence of obesity despite no obvious risk factors is that of obesity induced by viral infections. The most important of such viruses appears to be human adenovirus 36 (Adv36).

AREAS COVERED

This review covers the relation between obesity and infection by Adv36 in humans. Also, discussed are the opportunities of prevention or treatment for the effects of Adv36 in human body.

EXPERT OPINION

The role of Ad36 in the development of obesity has already been established. Future research should focus on the development of vaccines against this agent, drug discovery for infected individuals, and effective therapeutic uses of E4orf1 gene protein for diabetes and other diseases in clinical practice.

Findings from Studies Are Congruent with Obesity Having a Viral Origin, but What about Obesity-Related NAFLD?

Infection has recently started receiving greater attention as an unusual causative/inducing factor of obesity. Indeed, the biological plausibility of infectobesity includes direct roles of some viruses to reprogram host metabolism toward a more lipogenic and adipogenic status. Furthermore, the probability that humans may exchange microbiota components (virome/virobiota) points out that the altered response of IFN and other cytokines, which surfaces as a central mechanism for adipogenesis and obesity-associated immune suppression, is due to the fact that gut microbiota uphold intrinsic IFN signaling. Last but not least, the adaptation of both host immune and metabolic system under persistent viral infections play a central role in these phenomena. We hereby discuss the possible link between adenovirus and obesity-related nonalcoholic fatty liver disease (NAFLD). The mechanisms of adenovirus-36 (Ad-36) involvement in hepatic steatosis/NAFLD consist in reducing leptin gene expression and insulin sensitivity, augmenting glucose uptake, activating the lipogenic and pro-inflammatory pathways in adipose tissue, and increasing the level of macrophage chemoattractant protein-1, all of these ultimately leading to chronic inflammation and altered lipid metabolism. Moreover, by reducing leptin expression and secretion Ad-36 may have in turn an obesogenic effect through increased food intake or decreased energy expenditure via altered fat metabolism. Finally, Ad-36 is involved in upregulation of cAMP, phosphatidylinositol 3-kinase, and p38 signaling pathways, downregulation of Wnt10b expression, increased expression of CCAAT/enhancer binding protein-beta, and peroxisome proliferator-activated receptor gamma 2 with consequential lipid accumulation.

Adenovirus 36 prevalence and association with human obesity: a systematic review

INTRODUCTION

Obesity has numerous etiologies and includes biological factors. Studies have demonstrated that the human adenovirus subtype 36 (Adv36) is an adipogenic agent and causes metabolic alterations. Study results on the prevalence of Adv36 and clinical effects in humans vary substantially. This was a systematic review to summarize the studies on the prevalence of Adv36 infection and its association with human obesity.

METHODS

A systematic literature review was conducted using the preferred reporting items for systematic reviews and meta-analysis (PRISMA). Observational or experimental studies found in the Medline, Embase, LILACS, Science Direct and SciELO databases that presented results on the prevalence of Adv36 in humans were included.

RESULTS

Thirty-seven studies were screened. A total of 10,300 adults aged 18-70 years and 4585 children and adolescents aged 3-18 years were assessed. The average prevalence of Adv36 among adults was 22.9%, ranging from 5.5% to 49.8%. Among children and adolescents, the average prevalence of Adv36 was 28.9%, ranging from 7.5% to 73.9%. There was a positive statistical relationship between Adv36 and weight gain, obesity, or metabolic changes in 31 studies. However, in four studies there was no association with obesity, and in one, no association was described. One of the studies showed an inverse correlation, i.e., Adv36 was a protective factor against obesity.

CONCLUSION

Strong evidence suggested a positive association between viral infection and obesity. However, due to the multi-causality of obesity and heterogeneity of studies, diagnostic tests should be standardized and easily accessible by the population to estimate the overall prevalence of Adv36 infection and its association with obesity.

Twenty-five years of research about adipogenic adenoviruses: A systematic review

Infectious etiology is implicated in chronic diseases such as gastric ulcer or atherosclerosis. However, "infection" is a recent term in the field of obesity. Since the first report in 1982 of obesity due to infection, several microbes have been linked to obesity. Among the adipogenic microbes, avian adenovirus SMAM-1 and human adenovirus Ad36 have been studied most extensively for the past 25 years. Here, we present a systematic review of literature about SMAM-1 and Ad36. Reports from North America, Europe, and Asia reveal strong evidence that Ad36 causes obesity in animals and paradoxically improves glycemic control, and in vitro data provides mechanistic explanation. Considering that experimental Ad36 infection of humans is unlikely, its causative role in human obesity or glycemic control has not been demonstrated unequivocally. Nonetheless, most, but not all, observational studies in children and adults link Ad36 infection to obesity and improvement in glycemic control. The E4orf1 gene of Ad36 was identified as responsible for better glycemic control. Overall, 25 years have considerably advanced knowledge about the role of infection in obesity. Potential translational benefits include the development of vaccines to prevent Ad36-induced obesity and drug development based on the E4orf1 protein to improve glycemic control.

Adenovirus 5 produces obesity and adverse metabolic, morphological, and functional changes in the long term in animals fed a balanced diet or a high-fat diet: a study on hamsters

Adenovirus 5 (Ad-5) infection is a common cause of acute respiratory infections and the main vector used in gene therapy. There are few studies on the relationship of Ad-5 to obesity. In the present study, we evaluated the chronic effects of Ad-5 infection on golden (Syrian) hamsters fed either a balanced diet (BD) or a high-fat diet (HFD). After a single inoculation with Ad-5 (1 × 10⁷ pfu), the body weight of the animals was measured weekly. Medium-term (22 weeks) serum biochemical analyses and long-term (44 weeks) liver morphology, adiposity, and locomotive functionality (movement velocity) assessments were carried out. In the animals fed the BD, adenovirus infection produced hyperglycemia and hyperlipidemia. In the long term, it produced a 57% increase in epididymal pad fat and a 30% body weight gain compared with uninoculated animals. In addition, morphological changes related to non-alcoholic fatty liver disease (NAFLD) were observed. The animals fed the HFD had similar but more severe changes. In addition, the hamsters presented an obesity paradox: at the end of the study, the animals that had the most morphological and functional changes (significantly reduced movement velocity) had the lowest body weight. Despite the fact that an HFD appears to be a more harmful factor in the long term than adenovirus infection alone, infection could increase the severity of harmful effects in individuals with an HFD. Epidemiological studies are needed to evaluate the effect of adenovirus as a precursor of chronic liver and cardiovascular diseases, including the chronic effects of gene therapy.

Adipocyte biology: It is time to upgrade to a new model

Globally, the obesity pandemic is profoundly affecting quality of life and economic productivity, but efforts to address this, especially on a pharmacological level, have generally proven unsuccessful to date, serving as a stark demonstration that our understanding of adipocyte biology and pathophysiology is incomplete. To deliver better insight into adipocyte function and obesity, we need improved adipocyte models with a high degree of fidelity in representing the in vivo state and with a diverse range of experimental applications. Adipocyte cell lines, especially 3T3-L1 cells, have been used extensively over many years, but these are limited in terms of relevance and versatility. In this review, I propose that primary adipose-derived stromal/stem cells (ASCs) present a superior model with which to study adipocyte biology ex vivo. In particular, ASCs afford us the opportunity to study adipocytes from different, functionally distinct, adipose depots and to investigate, by means of in vivo/ex vivo studies, the effects of many different physiological and pathophysiological factors, such as age, body weight, hormonal status, diet and nutraceuticals, as well as disease and pharmacological treatments, on the biology of adipocytes and their precursors. This study will give an overview of the characteristics of ASCs and published studies utilizing ASCs, to highlight the areas where our knowledge is lacking. More comprehensive studies in primary ASCs will contribute to an improved understanding of adipose tissue, in healthy and dysfunctional states, which will enhance our efforts to more successfully manage and treat obesity.

Viral Infections and Obesity

PURPOSE OF REVIEW

Obesity is a multifactorial disease that is now endemic throughout most of the world. Although addressing proximate causes of obesity (excess energy intake and reduced energy expenditure) have been longstanding global health priorities, the problem has continued to worsen at the global level.

RECENT FINDINGS

Numerous microbial agents cause obesity in various experimental models-a phenomena known as infectobesity. Several of the same agents alter metabolic function in human cells and are associated with human obesity or metabolic dysfunction in humans. We address the evidence for a role in the genesis of obesity for viral agents in five broad categories: adenoviridae, herpesviridae, phages, transmissible spongiform encephalopathies (slow virus), and other encephalitides and hepatitides. Despite the importance of this topic area, there are many persistent knowledge gaps that need to be resolved. We discuss factors motivating further research and recommend that future infectobesity investigation should be more comprehensive, leveraged, interventional, and patient-centered.

Obesity and Infection: Reciprocal Causality

Associations between different infectious agents and obesity have been reported in humans for over thirty years. In many cases, as in nosocomial infections, this relationship reflects the greater susceptibility of obese individuals to infection due to impaired immunity. In such cases, the infection is not related to obesity as a causal factor but represents a complication of obesity. In contrast, several infections have been suggested as potential causal factors in human obesity. However, evidence of a causal linkage to human obesity has only been provided for adenovirus 36 (Adv36). This virus activates lipogenic and proinflammatory pathways in adipose tissue, improves insulin sensitivity, lipid profile and hepatic steatosis. The E4orf1 gene of Adv36 exerts insulin senzitizing effects, but is devoid of its pro-inflammatory modalities. The development of a vaccine to prevent Adv36-induced obesity or the use of E4orf1 as a ligand for novel antidiabetic drugs could open new horizons in the prophylaxis and treatment of obesity and diabetes. More experimental and clinical studies are needed to elucidate the mutual relations between infection and obesity, identify additional infectious agents causing human obesity, as well as define the conditions that predispose obese individuals to specific infections.

Role of adenoviruses in obesity

Five human adenovirus subtypes, Ad5, Ad9, Ad31, Ad36, and Ad37, and a non-human adenovirus, SMAM1, are linked to increased adiposity in vitro or in vivo. Experimental infection with Ad5, Ad36, and Ad37 produced excess adiposity or weight gain in animals. Ad9 and Ad31 increase fat storage in tissue culture but are not associated with animal or human obesity. Ad36 is the most extensively studied adipogenic adenovirus and is correlated with some measure of overweight/obesity in humans from multiple countries. The correlation is strongest and most consistent in children, but some studies have been negative in both children and adults. About 30% of overweight/obese children and adults and about 15-20% of lean individuals have Ad36 antibodies in epidemiologic studies. The mechanisms of action of Ad36 are due to the early gene 4, open reading frame 1 (E4-ORF1). Blocking E4-ORF1 with siRNA prevents the effects of Ad36, and transfection of lentivirus with E4-ORF1 reproduces the Ad36 effects. Increased adiposity is caused by stimulation of at least three pathways by Ad36. Cell membrane glucose receptors are increased via the Ras pathway, leading to increased intracellular glucose. Fatty acid synthase is increased, which converts the glucose to fatty acids. Finally, peroxisome proliferator-activated receptor-γ is increased, resulting in differentiation of adult stem cells into adipocytes.

CONCLUSIONS

several adenoviruses increase adiposity in animals and are associated with obesity in humans. There are critical gaps in the literature needing further investigation including evaluation of other adenovirus subtypes and better research designs to improve the strength of causal inferences.

The aetiology of obesity beyond eating more and exercising less

Although recent increases in availability of energy dense, processed foods and reductions in institutionally driven physical activity have created an environment that is permissible for obesity to occur, several other factors may contribute to the development of obesity in this context. We review evidence for eleven such factors: endocrine disruptors, intrauterine effects, epigenetics, maternal age, differential fecundity and assortative mating by body mass index, microorganisms, reduction in variability of ambient temperatures, smoking cessation, sleep debt, and pharmaceutical iatrogenesis. Evidence for the role of endocrine disruptors, microorganisms, ambient temperatures, sleep and reproductive factors is accumulating, but additional research is needed to confirm the causative role of these factors in human obesity. However, the role of certain pharmaceuticals and smoking cessation in development of human obesity is clear. Practice points for consideration and future research needed are highlighted for each factor.

Preterm nutritional intake and MRI phenotype at term age: a prospective observational study

OBJECTIVE

To describe (1) the relationship between nutrition and the preterm-at-term infant phenotype, (2) phenotypic differences between preterm-at-term infants and healthy term born infants and (3) relationships between somatic and brain MRI outcomes.

DESIGN

Prospective observational study.

SETTING

UK tertiary neonatal unit.

PARTICIPANTS

Preterm infants (<32 weeks gestation) (n=22) and healthy term infants (n=39) MAIN OUTCOME MEASURES: Preterm nutrient intake; total and regional adipose tissue (AT) depot volumes; brain volume and proximal cerebral arterial vessel tortuosity (CAVT) in preterm infants and in term infants.

RESULTS

Preterm nutrition was deficient in protein and high in carbohydrate and fat. Preterm nutrition was not related to AT volumes, brain volume or proximal CAVT score; a positive association was noted between human milk intake and proximal CAVT score (r=0.44, p=0.05). In comparison to term infants, preterm infants had increased total adiposity, comparable brain volumes and reduced proximal CAVT scores. There was a significant negative correlation between deep subcutaneous abdominal AT volume and brain volume in preterm infants (r=-0.58, p=0.01).

CONCLUSIONS

Though there are significant phenotypic differences between preterm infants at term and term infants, preterm macronutrient intake does not appear to be a determinant. Our preliminary data suggest that (1) human milk may exert a beneficial effect on cerebral arterial vessel tortuosity and (2) there is a negative correlation between adiposity and brain volume in preterm infants at term. Further work is warranted to see if our findings can be replicated and to understand the causal mechanisms.

Investigation of adipogenic effects of human adenovirus serotypes 36 and 5 in a Colo-320 cell line

Aim: We aimed to investigate the adipogenic effects of adenovirus (Ad) serotypes 5, 36 and 8 in a Colo-320 cell line using histochemical, immunohistochemical and electron microscopic methods. Materials & methods: Ad serotypes were inoculated in a Colo-320 cell line and were cultured for 14 days. They were then collected and fixed with 4% paraformaldehyde to analyze their adipogenic effects using histochemistry, immunohistochemistry and electron microscopic methods. Intracellular lipid droplets were detected in the Colo-320 cells inoculated with Ad36 and Ad5 by electron microscopic analyses. Results: After Oil Red O staining, the pink–orange staining was positive intracellularly in Colo-320 cells infected with Ad36 and Ad5. In addition, the leptin immunoreactivity was also positive in these cells. Conclusion: Our results suggested that intracellular lipid accumulation occured after infection with Ad36 and Ad5. The positive staining of Oil Red O and leptin also supported the electron microscopic results; therefore, we conclude that this accumulation occurred due to adipogenic effects of Ad36 and Ad5.

Apolipoprotein A5 deficiency aggravates high-fat diet-induced obesity due to impaired central regulation of food intake

Mutations in apolipoprotein A5 (APOA5) have been associated with hypertriglyceridemia in humans and mice. This has been attributed to a stimulating role for APOA5 in lipoprotein lipase-mediated triglyceride hydrolysis and hepatic clearance of lipoprotein remnant particles. However, because of the low APOA5 plasma abundance, we investigated an additional signaling role for APOA5 in high-fat diet (HFD)-induced obesity. Wild-type (WT) and Apoa5(-/-) mice fed a chow diet showed no difference in body weight or 24-h food intake (Apoa5(-/-), 4.5±0.6 g; WT, 4.2±0.5 g), while Apoa5(-/-) mice fed an HFD ate more in 24 h (Apoa5(-/-), 2.8±0.4 g; WT, 2.5±0.3 g, P<0.05) and became more obese than WT mice. Also, intravenous injection of APOA5-loaded VLDL-like particles lowered food intake (VLDL control, 0.26±0.04 g; VLDL+APOA5, 0.11±0.07 g, P<0.01). In addition, the HFD-induced hyperphagia of Apoa5(-/-) mice was prevented by adenovirus-mediated hepatic overexpression of APOA5. Finally, intracerebroventricular injection of APOA5 reduced food intake compared to injection of the same mouse with artificial cerebral spinal fluid (0.40±0.11 g; APOA5, 0.23±0.08 g, P<0.01). These data indicate that the increased HFD-induced obesity of Apoa5(-/-) mice as compared to WT mice is at least partly explained by hyperphagia and that APOA5 plays a role in the central regulation of food intake.

Insulin sparing action of adenovirus 36 and its E4orf1 protein

Additional drugs are required to effectively manage diabetes and its complications. Recent studies have revealed protective effects of Ad36, a human adenovirus, and its E4orf1 protein on glucose disposal, which may be creatively harnessed to develop novel anti-diabetic agents. Experimental Ad36 infection improves hyperglycemia in animal models and natural Ad36 infection in humans is associated with better glycemic control. Available data indicate distinctive advantages for a drug that may mimic the action of Ad36/E4orf1. The key features of such a potential drug include the ability to increase glucose uptake by adipose tissue and skeletal muscle, to reduce hepatic glucose output independent of proximal insulin signaling, and to up-regulate adiponectin and its hepatic action. The effect of Ad36/E4orf1 on hepatocyte metabolism suggests a role for treating hepatic steatosis. Despite these potential advantages, considerable research is required before such a drug is developed. The in vivo efficacy and safety of E4orf1 in improving hyperglycemia remain unknown, and an appropriate drug delivery system is required. Nonetheless, Ad36 E4orf1 offers a research opportunity to develop a new anti-diabetic agent with multiple potential advantages and conceptually advances the use of a rather unconventional source, microbial proteins, for anti-diabetic drug development.

Aetiological factors behind adipose tissue inflammation: an unexplored research area

OBJECTIVE

Despite extensive research into the biological mechanisms behind obesity-related inflammation, knowledge of environmental and genetic factors triggering such mechanisms is limited. In the present narrative review we present potential determinants of adipose tissue inflammation and suggest ways ahead for future research in the field.

DESIGN

We searched the literature for potential determinants of obesity with inflammation through MEDLINE by applying the MeSH headings 'obesity' and 'inflammation' in combination with specific terms for a series of environmental and genetic factors.

RESULTS

Numerous articles reported on the association between environmental or genetic factors and respectively obesity and inflammation, whereas only a few studies assessed obesity and inflammation as a combined outcome. Among suggested determinants for obesity with inflammation were Adenovirus-36, the gut microbiota, trans-fatty acids, and the four genes FTO, MC4R, TNF-α and LEPR.

CONCLUSIONS

We present a limited number of factors potentially contributing to the development of obesity with inflammation, while concluding that overall the area is indeed sparsely investigated. We present ideas for future studies that can identify relevant aetiological factors. This identification is essential for targeted prevention of obesity with inflammation and the clinical consequences thereof.

A framework for identification of infections that contribute to human obesity

WHO has declared obesity to be a global epidemic. Obesity management strategies mainly target behavioural components of the disorder, but are only marginally effective. A comprehensive understanding of the causative factors of obesity might provide more effective management approaches. Several microbes are causatively and correlatively linked with obesity in animals and human beings. If infections contribute to human obesity, then entirely different prevention and treatment strategies and public health policies could be needed to address this subtype of the disorder. Ethical reasons preclude experimental infection of human beings with candidate microbes to unequivocally determine their contribution to obesity. As an alternative, the available information about the adipogenic human adenovirus Ad36 has been used to create a template that can be used to examine comprehensively the contributions of specific candidate microbes to human obesity. Clinicians should be aware of infectobesity (obesity of infectious origin), and its potential importance in effective obesity management.

Increased energy expenditure in gastric bypass rats is not caused by activated brown adipose tissue

OBJECTIVE

To investigate whether gastric bypass induces a higher activity of brown adipose tissue and greater levels of the brown adipose tissue-specific protein uncoupling protein-1 (UCP-1) in rats.

METHODS

Gastric bypass rats and sham-operated controls (each n = 8) underwent whole body (1)H-MR spectroscopy for analysis of body composition and (18)F-fluorodeoxyglucose positron emission tomography combined with computed tomography ((18)F-FDG PET/CT) imaging for measurement of the metabolic activity of brown adipose tissue. Brown adipose tissue was harvested and weighed, and UCP-1 mRNA content was measured by Northern Blot technique.

RESULTS

Gastric bypass rats had a significantly lower percentage of whole body adipose tissue mass compared to sham-operated rats (p = 0.001). There was no difference in brown adipose tissue activity between the two groups (standardised uptake value sham 2.81 ± 0.58 vs. bypass 2.56 ± 0.46 ; p = 0.73). Furthermore, there was no difference in the UCP-1 mRNA content of brown adipose tissue between the two groups (sham 49.5 ± 13.2 vs. bypass 43.7 ± 13.1; p = 0.77).

CONCLUSION

Gastric bypass does not increase the activity of brown adipose tissue in rats suggesting that other mechanisms are involved to explain the increased energy expenditure after bypass surgery. Our results cannot justify the radiation dose of (18)F-FDG PET/CT studies in humans to determine potential changes in brown adipose tissue after gastric bypass surgery.

Infectivity period of mice inoculated with human adenoviruses

Due to non-productive infections, mice are not a good model to study some human adenoviruses. However, mice provide an excellent model to study the metabolic effects of human adenovirus, Ad36. Research interest in Ad36 is increasing rapidly, and consequently an increase in the use of mice as a model is anticipated. However, little is known about the transmission potential of Ad36 from infected mice to other laboratory animals or personnel. While underestimating the infectivity could promote inadvertent spread of Ad36, overstating it could drain valuable laboratory resources and animals. Therefore, we determined the duration of infectivity in female C57BL/6J mice that were experimentally infected with human adenoviruses Ad36 or Ad2. Other uninfected mice were co-housed for one week with the experimentally-infected animals, four or eight weeks postinfection. Additionally, uninfected mice were housed in the cages of mice that were infected with Ad36, 12 weeks earlier. The presence of viral DNA in tissues was used to indicate infection of mice. Although experimentally-infected mice harboured viral DNA at least up to 12 weeks, the horizontal transmission of infection was observed in co-housed mice only up to four weeks postinfection. Thus, Ad36-infected mice should be considered potentially infective for eight weeks and appropriate handling and barrier containment should be used. After eight week postinfection, horizontal transmission appears unlikely. This information may provide guidelines for animal handling, and experimental design using Ad36, which may increase safety for laboratory personnel and reduce the number of mice required for experiments.

Human obesity relationship with Ad36 adenovirus and insulin resistance

OBJECTIVES

Infection with specific pathogens may lead to increased adiposity: a specific adiposity-promoting effect of Ad36 human adenovirus, without the involvement of neurological mechanisms, was reported. The aim of this study is to investigate whether non-diabetic patients with earlier Ad36 infection show greater degrees of overweight obesity, of Insulin Resistance (IR), assessed by homoeostasis-model assessment (HOMA), and/or of other related factors. Moreover, the relationship, if any, among these factors and an earlier Ad36 infection, and the hypothesis of a mechanism involving IR are investigated.

SUBJECTS

Ad36 seropositivity is assessed in 68 obese and 135 non-obese subjects, along with body composition, HOMA and laboratory investigations.

RESULTS

Age, body mass index (BMI), waist-hip ratio, blood pressure, insulin, HOMA and triglycerides are significantly greater in the Ad36 seropositive group. Ad36 seropositivity, along with HOMA and total cholesterol, explains BMI variance. No Ad36 seropositivity effect to HOMA could be envisaged by the same statistical model.

CONCLUSION

A significant association of Ad36 seropositivity with obesity and with essential hypertension in human beings is suggested by our study; this association is mostly significant in women. Our results do not support that any Ad36 adipogenic adenovirus effect is operating in human obesity through an insulin-resistance-related mechanism. Ad36 seropositive status could also be a hallmark of a clinical-metabolic profile possibly preceding obesity and diabetes in non-obese patients.

Adenovirus infection results in alterations of insulin signaling and glucose homeostasis

Recombinant adenovirus (Ad) vectors can initiate an inflammatory response, limiting its use in gene therapy and basic research. Despite increased efforts to better understand Ad infection, little is known about how it affects cellular metabolic responses. In the current studies, we explored the effects of Ad vectors on insulin signaling molecules and glucose homeostasis. Nonreplicative Ad vectors were injected into rats through the tail vein, and at 4-13 days postinjection insulin signaling and glucose tolerance were examined. Ad vector infection significantly reduced total levels of the insulin receptor (IR), and insulin receptor substrates 1 and 2 (IRS-1, IRS-2) in the liver of rats, resulting in decreased insulin-induced tyrosine phosphorylation of IR, IRS-1, and IRS-2, and decreased interaction of IRS-1 and IRS-2 with phosphoinositide 3-kinase (PI3K). In addition, Ad infection resulted in impaired systemic glucose homeostasis, which recovered by 13 days, after the protein levels of IR, IRS-1, and IRS-2 had started to normalize. Expression of a TNF inhibitor or Kupffer cell depletion attenuated the Ad vector-induced decreases of insulin signaling molecules, indicating a potential role of Kupffer cell activation in this process. These studies provide evidence that systemic administration of Ad vectors can impair insulin signaling in liver, resulting in altered systemic glucose metabolism. Thus, effects of Ad vector infection on insulin action and glucose metabolism need to be considered when Ad vectors are used in research or gene therapy and may be more broadly applicable to other viral agents.

Exacerbation of chronic inflammatory diseases by infectious agents: Fact or fiction?

Chronic inflammatory diseases caused by obesity represent critical public health concerns worldwide. In these diseases such as metabolic syndrome, diabetes and atherosclerosis, adipose tissue acts as an endocrine organ that releases large quantities of inflammatory mediators into circulation. Besides classically recognized effectors on the development of obesity and resultant conditions, infection has attracted attention as an enhancer of chronic inflammatory diseases. Infectious diseases have long been associated with obesity, metabolic syndrome, diabetes and atherosclerosis. However, the infectious hypothesis for chronic inflammatory diseases has been challenged by inconclusive clinical trials. Nevertheless, the large body of evidence accumulated over decades on the association of infectious diseases with obesity, diabetes and cardiovascular disease should not be disregarded. Instead, re-formulation of hypotheses of the mechanisms by which microbes affect obesity-associated diseases may be required with an emphasis on the early events in the progression of such diseases and the multifactorial nature of pathogen-host interactions. This review focuses on pathogens that directly promote obesity and on pathogens that cause chronic infections and thereby enhance metabolic diseases in obese patients. A new perspective on the interaction between infections and obesity-related diseases may improve management of chronic inflammatory diseases that rank high among global threats to human health.

Viral obesity: fact or fiction?

The aetiology of obesity is multifactorial. An understanding of the contributions of various causal factors is essential for the proper management of obesity. Although it is primarily thought of as a condition brought on by lifestyle choices, recent evidence shows there is a link between obesity and viral infections. Numerous animal models have documented an increased body weight and a number of physiologic changes, including increased insulin sensitivity, increased glucose uptake and decreased leptin secretion that contribute to an increase in body fat in adenovirus-36 infection. Other viral agents associated with increasing obesity in animals included canine distemper virus, rous-associated virus 7, scrapie, Borna disease virus, SMAM-1 and other adenoviruses. This review attempted to determine if viral infection is a possible cause of obesity. Also, this paper discussed mechanisms by which viruses might produce obesity. Based on the evidence presented in this paper, it can be concluded that a link between obesity and viral infections cannot be ruled out. Further epidemiologic studies are needed to establish a causal link between the two, and determine if these results can be used in future management and prevention of obesity.

Ten putative contributors to the obesity epidemic

The obesity epidemic is a global issue and shows no signs of abating, while the cause of this epidemic remains unclear. Marketing practices of energy-dense foods and institutionally-driven declines in physical activity are the alleged perpetrators for the epidemic, despite a lack of solid evidence to demonstrate their causal role. While both may contribute to obesity, we call attention to their unquestioned dominance in program funding and public efforts to reduce obesity, and propose several alternative putative contributors that would benefit from equal consideration and attention. Evidence for microorganisms, epigenetics, increasing maternal age, greater fecundity among people with higher adiposity, assortative mating, sleep debt, endocrine disruptors, pharmaceutical iatrogenesis, reduction in variability of ambient temperatures, and intrauterine and intergenerational effects as contributing factors to the obesity epidemic are reviewed herein. While the evidence is strong for some contributors such as pharmaceutical-induced weight gain, it is still emerging for other reviewed factors. Considering the role of such putative etiological factors of obesity may lead to comprehensive, cause specific, and effective strategies for prevention and treatment of this global epidemic.

Intracellular infections enhance interleukin-6 and plasminogen activator inhibitor 1 production by cocultivated human adipocytes and THP-1 monocytes

Obesity is associated with a chronic inflammatory state, and adipocyte dysfunction is thought to play a crucial role in this. Infection of adipose tissue may trigger the production of inflammatory cytokines, leading to increased recruitment of macrophages into adipose tissue, which in turn may exacerbate the inflammatory state in obesity. Low-grade inflammation was mimicked in an in vitro coculture model with human adipocytes and THP-1 monocytes. Adipocytes and monocytes were infected with adenovirus, cytomegalovirus (CMV), or influenza A virus. After 48 h, transinfection was evaluated and interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), adiponectin, and plasminogen activator inhibitor 1 (PAI-1) were measured. IL-6 production was upregulated in cocultures of uninfected adipocytes and THP-1 macrophages in a THP-1 cell number-dependent fashion. IL-6 production by CMV-infected adipocytes was increased relative to that of uninfected adipocytes (P < 0.01). IL-6 production by CMV-infected cocultures was 16- to 37-fold higher than that of uninfected adipocytes (P < 0.001). IL-6 production in influenza A virus-infected cocultures was increased 12- to 20-fold (P < 0.05). Only CMV infection increased levels of PAI-1 in cocultures (fourfold; P < 0.05). Soluble factors produced by THP-1 macrophages rather than by adipocytes were responsible for the increased production of IL-6 in cocultures. Infection of cocultivated human adipocytes and THP-1 monocytes with CMV or influenza A virus led to increased production of IL-6 and PAI-1. Thus, infection of adipose tissue evokes an inflammatory response, leading to adipose tissue dysfunction and subsequent overproduction of IL-6 and PAI-1. This may further compound the atherogenic effects of obesity.

Adipogenic cascade can be induced without adipogenic media by a human adenovirus

Several metabolic abnormalities are associated with relative excess or deficiency of adipose tissue. Identifying the regulators of adipogenic differentiation is critical for its successful manipulation. Ad36, a human adenovirus, is a novel factor that promotes adipogenesis. We exploited the adipogenic potential of Ad36 to reveal exogenous modifiers of adipogenesis in rodent preadipocyte cell line in the presence or absence of differentiation inducers methyl-isobutyl-xanthine, dexamethasone, and insulin (M, D, and I; MDI). A nonadipogenic human adenovirus Ad2 was used as a negative control for viral infection. First, we confirmed that, Ad36, but not Ad2, increases lipid accumulation in the presence or absence of MDI. Time-course studies for expression of key genes of adipogenic cascade showed that it is Ad36, but not Ad2, which downregulated preadipocyte marker gene Wnt10b, and upregulated expression of early (C/EBPDelta and C/EBPbeta), intermediate (PPARgamma2), and late genes (aP2 and G3PDH) of adipogenic cascade even in the absence of MDI. In the presence of MDI, onset of expression of adipogenic genes coincided for Ad36 and control groups, but the expressions were significantly greater for the Ad36 group. Next, we observed that attenuation of Ad36 mRNA expression by an antiadenoviral agent reduced 3T3-L1 differentiation, indicating that viral mRNA expression is required for the process. Furthermore, with or without MDI or its components, Ad36 significantly increased lipid accumulation in 3T3-L1 cells. Cell confluency at the time of Ad36 infection positively influenced lipid accumulation. The results reveal that Ad36 is an MDI-independent exogenous regulator of the adipogenic process. Elucidating the molecular pathways involved may reveal novel regulatory controls of adipogenesis.

Infeccions as the etiology for obesity

The role of infection on obesity development has been questioned since the early 1980's. Several studies on animals have shown that fisiopathologic mechanisms through which infections can produce obesity do exist. At least eight types of obesity-inducing viruses have been identified in animals, especially poultry and mice. Studies on humans are far less convincing; however, two adenoviruses, Ad-36 and SMAM-1, have shown adipogenic properties. In vitro studies with 3T3-L1 cells stated the activation of the enzymatic pathway that leads to fatty tissue accumulation; in vivo studies have also detected higher levels of antibodies against such viruses on obese subjects. Although most known infections nowadays cause obesity through central nervous system lesions, the Ad-36 adenovirus infection affects fatty tissue directly, raising doubts regarding central role component in this case.

Chlamydial LPS and high-sensitivity CRP levels in serum are associated with an elevated body mass index in patients with cardiovascular disease

OBJECTIVE

Seropositivity for Chlamydia pneumoniae has been associated with an elevated body mass index (BMI). Our aim was to study if serum chlamydial lipopolysaccharide (cLPS), C. pneumoniae antibodies and high-sensitivity C-reactive protein (hsCRP) levels are associated with BMI.

PATIENTS AND METHODS

The study population consisted of 174 patients with symptomatic carotid stenosis, abdominal aortic aneurysm or occlusive aortic disease. Information on BMI, diabetes, smoking, hypercholesterolemia, and statin medication was available. Serum C. pneumoniae IgG and IgA antibodies, cLPS, hsCRP and total endotoxin activity (totLPS) were measured.

RESULTS

BMI correlated with cLPS (r = 0.197; P < 0.01) and with hsCRP (rho = 0.195; P < 0.01); in addition, there was a positive correlation between cLPS and hsCRP (rho = 0.499; P < 0.01). A trend of an increasing proportion of C. pneumoniae IgG positivity (titre > or = 64; P = 0.018) and higher serum cLPS (P = 0.01) and hsCRP (P = 0.01) concentrations was observed across the BMI groups (BMI < or = 24.9 kg/m(2), BMI = 25.0-29.9 kg/m(2), and BMI > or = 30.0 kg/m(2)). Among the three BMI groups, 24.6%, 38.8%, and 48.3% were C. pneumoniae IgG-positive and the median (IQR) cLPS concentrations (ng/ml) of the groups were: 92.6 (50.8-167.0), 128.9 (76.4-163.9), and 146.4 (105.8-175.8), respectively. The median (IQR) hsCRP (mg/l) concentrations of the groups were: 1.70 (0.70-3.05) 1.70 (0.80-5.20), and 3.40 (1.45-8.55), respectively. These associations remained statistically significant in a multivariate analysis.

CONCLUSIONS

Elevated serum cLPS levels were associated with an elevated BMI. This is a novel finding and it strengthens the link between chlamydial infection and obesity. A lack of association between totLPS and BMI suggests that the association between infection and an elevated BMI may be specific to certain pathogens.

Infections and obesity: A multinational epidemiological study

Viral infections have been associated with the aetiology of obesity in animal models. This study investigates the association between 7 serological markers of infections and body mass index (BMI) in a population based sample. Individuals (n=985, mean age 42+/-97 (28-55) y, mean BMI 25.594.2) from Iceland, Sweden and Estonia underwent a structured interview and blood sampling. IgG antibodies were measured against Helicobacter pylori and the cagA protein, hepatitis A virus, Toxoplasma gondii, herpes simplex virus 1, Chlamydia pneumoniae, Epstein-Barr virus and cytomegalovirus. High-sensitive C-reactive protein (CRP) was measured as a marker of systemic inflammation. A significant positive association between being overweight (BMI25 kg/m2) and IgG antibodies was found for Helicobacter pylori (OR 1.86, CI 1.34-2.60) and Chlamydia pneumoniae (OR 1.39, CI 1.03-1.88) and combined seropositivity had synergistic effect (OR 2.54 (1.62-3.97)). CRP was positively related to BMI (pB0.0001), whereas no significant association was found between CRP and IgG antibodies against Helicobacter pylori and/or Chlamydia pneumoniae and CRP. The results suggest that infections with Chlamydia pneumoniae and Helicobacter pylori are both significantly and synergistically associated with overweight and this association is not related to indicators of systemic inflammation.

Adipogenic human adenovirus Ad-36 induces commitment, differentiation, and lipid accumulation in human adipose-derived stem cells

Human adenovirus Ad-36 is causatively and correlatively linked with animal and human obesity, respectively. Ad-36 enhances differentiation of rodent preadipocytes, but its effect on adipogenesis in humans is unknown. To indirectly assess the role of Ad-36-induced adipogenesis in human obesity, the effect of the virus on commitment, differentiation, and lipid accumulation was investigated in vitro in primary human adipose-derived stem/stromal cells (hASC). Ad-36 infected hASC in a time- and dose-dependent manner. Even in the presence of osteogenic media, Ad-36-infected hASC showed significantly greater lipid accumulation, suggestive of their commitment to the adipocyte lineage. Even in the absence of adipogenic inducers, Ad-36 significantly increased hASC differentiation, as indicated by a time-dependent expression of genes within the adipogenic cascade-CCAAT/Enhancer binding protein-beta, peroxisome proliferator-activated receptor-gamma, and fatty acid-binding protein-and consequentially increased lipid accumulation in a time- and viral dose-dependent manner. Induction of hASC to the adipocyte state by Ad-36 was further supported by increased expression of lipoprotein lipase and the accumulation of its extracellular fraction. hASC from subjects harboring Ad-36 DNA in their adipose tissue due to natural infection had significantly greater ability to differentiate compared with Ad-36 DNA-negative counterparts, which offers a proof of concept. Thus, Ad-36 has the potential to induce adipogenesis in hASC, which may contribute to adiposity induced by the virus.

Infection-induced inflammatory response of adipocytes in vitro

BACKGROUND

Abdominal obesity plays an important role in the development of insulin resistance, diabetes mellitus and atherosclerosis. The exact pathophysiological mechanisms are unclear but adipocyte dysfunction is thought to be crucial. Infections are associated with the development of atherosclerosis as well as diabetes. In this study we investigated whether adipocytes can be infected and whether this results in production of inflammatory cytokines relevant for the development of atherosclerosis and diabetes.

METHODS

Pre-adipocytes were cultured and differentiated into mature adipocytes in vitro. Adipocytes and pre-adipocytes were incubated with infective and heat-inactivated Chlamydia pneumoniae, cytomegalovirus (CMV), adenovirus (Ad) subtypes 2 and 36, influenza A and respiratory syncitial virus (RSV). After 48 h, adiponectin, interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) and plasminogen activator inhibitor-1 (PAI-1) were measured in supernatants.

RESULTS

Infection of adipocytes with Ad-36, CMV and RSV resulted in increased IL-6 production from 192+/-22 pg ml(-1) (uninfected) to 1030+/-86 pg ml(-1), 838+/-59 pg ml(-1) and 1241+/-191 pg ml(-1), respectively (all P<0.01 vs control). In addition, Ad-36 infection slightly reduced PAI production in adipocytes (285+/-26.8 ng ml(-1) vs uninfected: 477+/-71.2 ng ml(-1); P=0.05) and pre-adipocytes (709+/-43.3 ng ml(-1) vs uninfected: 1071+/-71.8 ng ml(-1); P<0.01). In contrast, human Ad type 2 did not exert any effect on IL-6 or PAI production. None of the microorganisms induced significant changes in adiponectin and/or TNF-alpha production.

CONCLUSIONS

Adipocytes can be infected with several microorganisms in vitro. Infection of adipocytes with Ad-36, but not Ad-2 leads to increased production of IL-6 which might contribute to chronic low-grade inflammation, a process known to be involved in the development of cardiovascular diseases and type 2 diabetes.

Impact of resistant starch on body fat patterning and central appetite regulation

BACKGROUND

Adipose tissue patterning has a major influence on the risk of developing chronic disease. Environmental influences on both body fat patterning and appetite regulation are not fully understood. This study was performed to investigate the impact of resistant starch (RS) on adipose tissue deposition and central regulation of appetite in mice.

METHODOLOGY AND PRINCIPLE FINDINGS

Forty mice were randomised to a diet supplemented with either the high resistant starch (HRS), or the readily digestible starch (LRS). Using (1)H magnetic resonance (MR) methods, whole body adiposity, intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL) were measured. Manganese-enhanced MRI (MEMRI) was used to investigate neuronal activity in hypothalamic regions involved in appetite control when fed ad libitum. At the end of the interventional period, adipocytes were isolated from epididymal adipose tissue and fasting plasma collected for hormonal and adipokine measurement. Mice on the HRS and LRS diet had similar body weights although total body adiposity, subcutaneous and visceral fat, IHCL, plasma leptin, plasma adiponectin plasma insulin/glucose ratios was significantly greater in the latter group. Adipocytes isolated from the LRS group were significantly larger and had lower insulin-stimulated glucose uptake. MEMRI data obtained from the ventromedial and paraventricular hypothalamic nuclei suggests a satiating effect of the HRS diet despite a lower energy intake.

CONCLUSION AND SIGNIFICANCE

Dietary RS significantly impacts on adipose tissue patterning, adipocyte morphology and metabolism, glucose and insulin metabolism, as well as affecting appetite regulation, supported by changes in neuronal activity in hypothalamic appetite regulation centres which are suggestive of satiation.

Viruses as an etiology of obesity

Obesity is a serious chronic disease that has numerous etiologies. The prevalence of obesity has increased dramatically since about 1980 in the United States and worldwide in both developed and developing countries. This rapid spread is compatible with an infectious origin. This review discusses the 5 animal viruses and 3 human viruses that have been shown to cause obesity and examines the evidence to date for virus-induced obesity. The obesogenic animal viruses include canine distemper virus, Rous-associated virus type 7, Borna disease virus, scrapie agent, and SMAM-1. The first 4 viruses attack the central nervous system to produce obesity. SMAM-1, an avian adenovirus from India, acts directly on adipocytes and is the only animal virus that is associated with human obesity. The 3 human adenoviruses, adenovirus (Ad) 36, Ad-37, and Ad-5, that are associated with obesity also affect adipocytes directly. These viruses stimulate enzymes and transcription factors that cause accumulation of triglycerides and differentiation of preadipocytes into mature adipocytes. Ad-5 and Ad-37 have been shown to cause obesity in animals. Ad-36 has been studied the most and is the only human adenovirus to date that has been linked with human obesity. Ad-36 causes obesity in chickens, mice, rats, and monkeys and was present in 30% of obese humans and 11% of nonobese humans. In twins discordant for infection with Ad-36, the infected twins were heavier and fatter than their cotwins. The growing body of evidence demonstrating that viruses produce human obesity supports the concept that at least some of the worldwide epidemic of obesity in the past 25 years is due to viral infections.

Could a virus contribute to weight gain?

OBJECTIVE

Obesity is a serious public health problem associated with increased morbidity and mortality. Although the causes for obesity are unclear, it seems that environmental, genetic, neural and endocrine factors contribute to its development. However, the rapid global spread of obesity resembles epidemiologically the spread of an infectious disease. Thus far, little consideration has been given to the possibility that the epidemic of obesity could be due to an infectious agent. Seven viruses and a scrapie agent have been implicated in obesity.

DESIGN

This review evaluates the infectious pathogens and the evidence that these viruses are associated with obesity and concludes that a strong evidence base is emerging that associates certain viruses with obesity.

CONCLUSION

More work is however required to elucidate the mechanisms of weight gain after viral infection. In the mean time, discounting viruses as a contributing factor to obesity would deprive us of a potential new avenue of investigating and treating the ever increasing epidemic of obesity.

Infectobesity: Obesity of Infectious Origin

The rapid increase in obesity and the associated health care costs have prompted a search for better approaches for its prevention and management. Such efforts may be facilitated by better understanding the etiology of obesity. Of the several etiological factors, infection, an unusual causative factor, has recently started receiving greater attention. In the last two decades, 10 adipogenic pathogens were reported, including human and nonhuman viruses, scrapie agents, bacteria, and gut microflora. Some of these pathogens are associated with human obesity, but their causative role in human obesity has not been established. This chapter presents information about the natural hosts, signs and symptoms, and pathogenesis of the adipogenic microorganisms. If relevant to humans, "Infectobesity" would be a relatively novel, yet extremely significant concept. A new perspective about the infectious etiology of obesity may stimulate additional research to assess the contribution of hitherto unknown pathogens to human obesity and possibly to prevent or treat obesity of infectious origins.

Human adenovirus 36 induces adiposity, increases insulin sensitivity, and alters hypothalamic monoamines in rats

OBJECTIVE

Human adenovirus 36 (Ad-36) increases adiposity and reduces serum lipids in chicken, mouse, and non-human primate models, and it is linked to obesity in sero-epidemiological studies in humans. Involvement of the central nervous system (CNS) or adipose tissue in the mechanism of Ad-36-induced adiposity is unknown. The effects of Ad-36 on adiposity and on the neuroendocrine system were investigated in a rat model.

RESEARCH METHODS AND PROCEDURES

Five-week-old male Wistar rats were inoculated intraperitoneally with Ad-36 or medium.

RESULTS

Despite similar food intakes, infected rats attained significantly greater body weight and fat pad weight by 30 weeks post-inoculation. Epididymal-inguinal, retroperitoneal, and visceral fat pad weights of the infected group were greater by 60%, 46%, and 86%, respectively (p < 0.00001). The fasting serum insulin level and homeostasis model assessment index indicated greater insulin sensitivity in the infected group. Visceral adipose tissue expression of glycerol 3-phosphate dehydrogenase, peroxisome proliferator-activated receptor gamma, and CCAAT/enhancer-binding protein alpha and beta was markedly increased in the infected animals compared with controls. Ad-36 decreased norepinephrine levels significantly in the paraventricular nucleus in infected vs. control rats (mean +/- standard error, 8.9 +/- 1.1 vs. 12.8 +/- 1.2 pg/microg protein; p < 0.05). Ad-36 markedly decreased serum corticosterone in infected vs. control rats (mean +/- standard error, 97 +/- 41.0 vs. 221 +/- 111 ng/mL; p < 0.005).

DISCUSSION

The results suggest that the pro-adipogenic effect of Ad-36 may involve peripheral as well as central effects. The male Wistar rat is a good model for the elucidation of metabolic and molecular mechanisms of Ad-36-induced adiposity.

Adipogenic human adenovirus-36 reduces leptin expression and secretion and increases glucose uptake by fat cells

OBJECTIVE

Human adenovirus Ad-36 causes adiposity in animal models and enhances differentiation and lipid accumulation in human and 3T3-L1 preadipocytes, which may, in part, explain the adipogenic effect of Ad-36. We determined the consequences of Ad-36 infection on leptin and glucose metabolism in fat cells.

DESIGN

3T3-L1 preadipocytes were used to determine the effect of infection by human adenoviruses Ad-36, Ad-2, Ad-9 and Ad-37 on leptin secretion and lipid accumulation. Rat primary adipocytes were used to determine the effect of Ad-36 infection on leptin secretion and glucose uptake in vitro. Furthermore, the effect of Ad-36 on expressions of leptin and selected genes of de novo lipogenesis pathway of visceral adipose tissue were compared ex vivo, between Ad-36 infected and uninfected control rats.

RESULTS

Ad-36 suppressed the expression of leptin mRNA in 3T3-L1 cells by approximately 58 and 52% on days 3 and 5 post-infection, respectively. Leptin release normalized to cellular lipid content was 51% lower (P<0.002) in the Ad-36 infected 3T3-L1 cells. Lipid accumulation was significantly greater and leptin secretion was lower for the 3T3-L1 cells infected with other human adenoviruses Ad-9, Ad-36, or Ad-37. Whereas, human adenovirus Ad-2 did not influence cellular lipid accumulation or the leptin release. In rat primary adipocytes, Ad-36 reduced leptin release by about 40% in presence of 0.48 (P<0.01) or 1.6 nM insulin (P<0.05) and increased glucose uptake by 93% (P<0.001) or 18% (P<0.05) in presence of 0 or 0.48 nM insulin, respectively. Next, the adipose tissue of Ad-36 infected rats showed two to fivefold lower leptin mRNA expression, and 1.6- to 21-fold greater expressions for acetyl Co-A carboxylase-1 and 1.2- to 6.3-fold greater expressions for fatty acid synthase, key genes of de novo lipogenesis, compared to the uninfected weight and adiposity matched controls.

CONCLUSION

The in vitro and ex vivo studies show that Ad-36 modulates adipocyte differentiation, leptin production and glucose metabolism. Whether such a modulation contributes to enhanced adipogenesis and consequent adiposity in Ad-36 infected animals or humans needs to be determined.

Viral mRNA expression but not DNA replication is required for lipogenic effect of human adenovirus Ad-36 in preadipocytes

OBJECTIVE

Human adenovirus Ad-36 causes adiposity in animal models and shows association with human obesity. Ad-36 enhances differentiation of 3T3-L1 and human preadipocytes, without cell lysis, a characteristic that may contribute to its adipogenic effect observed in vivo. Ad-2, another human adenovirus is nonadipogenic in animals and in 3T3-L1 cells and shows no correlation with human obesity. The objective of this study was to determine the adipogenic roles of viral mRNA and DNA, which may explain the differential effects of Ad-36 and Ad-2 on preadipocyte differentiation.

METHODS

This study determined the duration of selected Ad-36 gene expression in 3T3-L1 cells, and the effect on preadipocytes differentiation, when Ad-36 gene expression was attenuated by Cidofovir, an antiadenoviral agent.

RESULTS

The results showed that Ad-36, but not Ad-2, expresses viral mRNA. Ad-36 gene expression peaked at 2-4 days postinoculation and very low levels persisted after day 7. Despite the viral mRNA expression, Ad-36 infection of 3T3-L1 cells was abortive as indicated by a progressive decrease in viral DNA quantity. Attenuation of Ad-36 mRNA expression by Cidofovir reduced the adipogenic effect of the virus.

CONCLUSION

In conclusion, viral mRNA expression, although transient, is a prerequisite for enhancing differentiation of preadipocytes by Ad-36. Viral DNA replication was not required for the effect. This is the first evidence for the role of gene expression of an adipogenic human virus in enhancing preadipocytes differentiation. This study provides the basis for further understanding novel regulatory modulators of preadipocytes differentiation.