Lack of evidence for the role of human adenovirus-36 in obesity in a European cohort

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.

Adipocyte commitment of 3T3-L1 cells is required to support human adenovirus 36 productive replication concurrent with altered lipid and glucose metabolism

Human adenovirus 36 (HAdV-D36) can cause obesity in animal models, induces an adipogenic effect and increased adipocyte differentiation in cell culture. HAdV-D36 infection alters gene expression and the metabolism of the infected cells resulting in increased glucose internalization and triglyceride accumulation. Although HAdV-D36 prevalence correlates with obesity in humans, whether human preadipocytes may be targeted in vivo has not been determined and metabolic reprogramming of preadipocytes has not been explored in the context of the viral replication cycle. HAdV-D36 infection of the mouse fibroblasts, 3T3-L1 cells, which can differentiate into adipocytes, promotes proliferation and differentiation, but replication of the virus in these cells is abortive as indicated by short-lived transient expression of viral mRNA and a progressive loss of viral DNA. Therefore, we have evaluated whether a productive viral replication cycle can be established in the 3T3-L1 preadipocyte model under conditions that drive the cell differentiation process. For this purpose, viral mRNA levels and viral DNA replication were measured by RT-qPCR and qPCR, respectively, and viral progeny production was determined by plaque assay. The lipogenic effect of infection was evaluated with Oil Red O (ORO) staining, and expression of genes that control lipid and glucose metabolism was measured by RT-qPCR. In the context of a viral productive cycle, HAdV-D36 modulated the expression of the adipogenic genes, C/EBPα, C/EBPβ and PPARγ, as well as intracellular lipid accumulation, and the infection was accompanied by altered expression of glucolytic genes. The results show that only adipocyte-committed 3T3-L1 cells are permissive for the expression of early and late viral mRNAs, as well as viral DNA replication and progeny production, supporting productive HAdV-D36 viral replication, indicating that a greater effect on adipogenesis occurs in adipocytes that support productive viral replication.

Next-Generation Sequencing for Confronting Virus Pandemics

Virus pandemics have happened, are happening and will happen again. In recent decades, the rate of zoonotic viral spillover into humans has accelerated, mirroring the expansion of our global footprint and travel network, including the expansion of viral vectors and the destruction of natural spaces, bringing humans closer to wild animals. Once viral cross-species transmission to humans occurs, transmission cannot be stopped by cement walls but by developing barriers based on knowledge that can prevent or reduce the effects of any pandemic. Controlling a local transmission affecting few individuals is more efficient that confronting a community outbreak in which infections cannot be traced. Genetic detection, identification, and characterization of infectious agents using next-generation sequencing (NGS) has been proven to be a powerful tool allowing for the development of fast PCR-based molecular assays, the rapid development of vaccines based on mRNA and DNA, the identification of outbreaks, transmission dynamics and spill-over events, the detection of new variants and treatment of vaccine resistance mutations, the development of direct-acting antiviral drugs, the discovery of relevant minority variants to improve knowledge of the viral life cycle, strengths and weaknesses, the potential for becoming dominant to take appropriate preventive measures, and the discovery of new routes of viral transmission.

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.

Association of adenovirus 36 infection and obesity; An updated meta-analysis of community-based studies

As a health problem, obesity has several risk factors; it has been suggested that human adenovirus type 36 (HAdV-36) infections may possibly be associated with obesity. This updated meta-analysis was designed and conducted with an emphasis on articles published from 2015 to 2020. The PubMed, Web of Science, and Scopus databases were searched up to 1 December 2020. Overall, pooled prevalence and odds ratio of antibodies against HAdV-36 in people with obesity and controls was assessed among different ages. Case-control and cohort studies were included in the analysis. The overall prevalence of HAdV-36 infection in obese population was 31% (CI: 0.24%-0.38%) which was 32% in cases and 27% in controls, respectively; a significant association was found between the cases and the controls (OR, 1.84; 95% CI, 1.39-2.43), especially in children younger than 18 years of age (OR, 2.44; 95% CI, 1.85-3.22). A significant association between adenovirus infection and obesity was found, especially in adolescents.

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.

Presence of Adenovirus-36 DNA in Adipose Tissue of Women: Relationship with Adipocyte Morphology and the Expression of C/EBPβ and HIF-1α

BACKGROUND

Human adenovirus 36 (HAd36) infection has been associated with obesity. Experiments using 3T3-L1 adipocyte cultured cells and human adipose stem cells (hASCc) have shown that HAd36 stimulates the expression of genes implicated in cell differentiation and increased lipid accumulation. The presence of HAd36 in adipose tissue of overweight and obese women has also been confirmed. This study aims to analyze the presence of HAd36 DNA in the adipose tissue of women undergoing surgery for weight reduction and its relationship with obesity through changes in adipocyte morphology as well as the expression of C/EBPβ and HIF-1α.

METHODS

Fifty-two subcutaneous adipose tissue biopsies were collected. The anthropometric parameters measured were weight, height, skin folds, body circumferences, and body fat percentage. Biochemical measures were performed for glucose, cholesterol, triglycerides, cholesterol HDL-c, and LDL-c. The presence of HAd36 DNA was performed by conventional PCR. Adipocyte morphology was analyzed in H&E-stained sections using ImageJ/Fiji software. The expression of genes C/EBPβ, HIF-1α and β-actin was determined using TaqMan probes.

RESULTS

HAd36 DNA was detected in 31% of adipose tissue samples. The presence of viral DNA was not significantly associated with anthropometric, clinical, or metabolic measurements, or with changes in adipose tissue morphology. The levels of mRNA expression for C/EBPβ and HIF-1α did not show significant differences between positive and negative samples for HAd36 (p>0.05).

CONCLUSION

The presence of HAd36 DNA in adipose tissue was identified, but it was not related to morphological changes of adipocytes, or the expression of C/EBPβ and HIF-1α. Further studies are needed to confirm these findings.

Obesity and Diabetes in an Arab population: Role of Adenovirus 36 Infection

Prior infection with adenovirus 36 (Adv36) has been associated with increased adiposity, improved insulin sensitivity, and a lower prevalence of diabetes. This study investigated the prevalence of Adv36 seropositivity and its association with obesity and diabetes among adults attending a diabetes centre in the UAE.Participants (N = 973) with different weight and glucose tolerance categories were recruited. Adv36 seropositivity (Adv36 + ) was assessed using ELISA. Differences among groups were analyzed using statistical tests as appropriate to the data. Prevalence of Adv36+ in the study population was 47%, with no significant difference in obese and non-obese subgroups (42.5% vs 49.6% respectively; p=non-significant). Females were more likely to be Adv36+ compared to males (odds ratio 1.78; 95% CI 1.36–2.32, p < 0.001). We found no significant association between Adv36 seropositivity and different BMI categories, or glucose tolerance status. In our population, the effect of Adv36 infection on lipid profile varied between healthy individuals and individuals with obesity. Adv36 infection is more prevalent in the UAE than in other countries but has no association with obesity. Our study found that females were more likely to be Adv36 positive regardless of weight or diabetes status.

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.

Ileal transcriptome analysis in obese rats induced by high-fat diets and an adenoviral infection

BACKGROUND

Obesity has become a worldwide epidemic affecting millions of people. Obesity and associated health consequences tend to be complicated by diverse causes and multi-systemic involvement. Previous studies have investigated obesity induced by a single factor, such as a high-fat diet (HF) of typical energy-dense food and infection by an adipogenic virus, such as a widely studied human adenovirus serotype 36 (Ad-36). In this study, we hypothesized and investigated the synergistic effect of two causal factors, HF and Ad-36, in obesity induction.

METHODS

The 7-week-old Wistar rats (n = 1214/group) were randomly divided into weight-matched groups and induced for obesity with mock-control, HF, Ad-36, or HF + Ad-36 for 8-30 weeks, and compared for obesity phenotype. A global transcriptomic RNA-Seq analysis was used to profile signature gene response pathways in ileal tissues from 8-week control and obese animals during this early phase of obesity induction.

RESULTS

HF only and particularly co-administration of Ad-36 and HF (HF + Ad-36) induced significant obesity in rats (p < 0.05 or p < 0.005). Compared with either Ad-36 or HF alone, HF + Ad-36 treatment significantly aggravates obesity in rats regarding body weight (n = 12-14/group) and adiposity index (n = 6-7). Genome-wide transcriptomic analyses of intestinal tissues revealed signature genes on an inter-systemic scale, including many genes in the pathways of circadian rhythm and antiviral immunity focusing on IFN signaling.

CONCLUSIONS

Ad-36 exacerbated the induction of obesity in rats compared with those treated with HF alone. Gene-responsive pathways involved in circadian rhythm and antiviral immunity in ileal tissues were significantly (p < 0.05, and FDR < 0.01) regulated during the early phase of obesity induction. This study provided a co-factorial model for obesity induction and profiled molecular targets for further validation and molecular manipulation.

Adenovirus 36 seropositivity is related to obesity risk, glycemic control, and leptin levels in Chilean subjects

BACKGROUND

Adenovirus 36 (Ad-36) has been associated to adiposity in animal and in vitro studies. Ad-36 seropositivity has also been reported to contribute to obesity risk in children and adult populations. We investigated the relationship of Ad-36 serology with obesity and metabolic parameters in a Chilean population.

SUBJECTS AND METHODS

Clinical and anthropometric data were obtained and blood samples were drawn from 99 lean (BMI: 18.5-24.9 kg/m²) and 151 obese (BMI > 30 kg/m²) subjects. Laboratory tests included lipid profile as well as glucose, insulin, leptin, and adiponectin levels. Ad-36 seropositivity was evaluated in serum samples by enzyme-linked immunosorbent assay.

RESULTS

Seroprevalence of Ad-36 was higher in the obese group (58%) than in lean controls (34%) demonstrating that individuals previously infected with Ad-36 have higher risk of obesity in the study population (OR: 2.67, 95%CI: 1.58-4.51, p < 0.001). Interestingly, Ad-36 was related to lower concentrations of triglycerides and VLDL cholesterol in lean subjects (p = 0.049) and lower leptin in obese individuals (p = 0.014). Previous Ad-36 infection was also related to lower glycemia, insulinemia, and HOMA-IR (p < 0.05) in obese subjects who were not under antidiabetic drugs.

CONCLUSIONS

Our results provide evidence of the contribution of previous Ad-36 infection to an increased risk of obesity in adult Chilean population. Ad-36 seropositivity was also associated to lipid profile, glycemic control, and leptin levels in adult Chilean population.

High adenovirus 36 seroprevalence among a population of Hispanic American youth

Infection with adenovirus 36 (Ad36) has been associated with risk of obesity in youth in some studies, but the seroprevalence of this virus has not been examined among all populations. As Hispanic-American youth are of greater risk for obesity than other American youth, we sought to determine the proportion of Ad36 seropositive (Ad36+) students in an urban middle school serving a Hispanic population. We further examined if Ad36+ students were more likely to have obesity, and if Ad36 serostatus impacted changes in weight status following a health intervention. We determined body mass index (BMI) at the beginning and end of a 16-week health intervention among 40 Hispanic-American middle-school students. Ad36 serostatus was determined by enzyme-linked immunsorbent assay (ELISA). Seventy percent of the students were Ad36+. Ad36+ and Ad36 seronegative (Ad36-) did not differ before or after the intervention in body weight measures. The odds of being classified as obese was 1.4 times greater among Ad36+ than Ad36- at baseline, and 2.4 times greater post-intervention, but these were not statistically significant. We report a high seroprevalence of Ad36 among a population of Hispanic-American students. Ad36 seropositivity was associated with a trend for a greater likelihood of having obesity, but did not impact response to a health intervention.

The relationship between human adenovirus 36 and obesity in Chinese Han population

The study aimed to explore the prevalence of human adenovirus-36 (HAdV-36) infection and the association of HAdV-36 with obesity in Chinese Han population. A qualitative determination using ELISA was performed to determine by duplication of the antibodies to HAdV-36 in the serum samples. Logistic regression analysis was used to analyze the association between HAdV-36 seropositivity and obesity. The overall HAdV-36 seroprevalence was 49.8% amongst 824 participants. The prevalence of HAdV-36 seropositive was 42.9 and 51.4% in the obese and non-obese participants, respectively, which was not statistically significant (P=0.05). There were significant differences in the anthropometric and biochemical parameters observed between the two groups except for height (P=0.067) and total cholesterol (TC) (P<0.29). After the adjustment for age and gender, HAdV-36 seropositivity was a protective factor for obesity (odds ratio (OR) = 0.69, 95% confidence intervals (95% CI) = 0.48-0.97, P=0.03). In the male population, the adjusted OR for AD-36 antibody-positive status was statistically decreased for obese adults (OR = 0.59; 95% CI = 0.39-0.91; P=0.02). However, the similar result was not obtained in the female population (OR = 0.90; 95% CI = 0.48-1.67; P=0.73). We found a high prevalence of HAdV-36 infection in China and significant association between HAdV-36 infection and obesity or weight gain after the adjustment for age and gender. The HAdV-36 infection may be related to the weight loss in Chinese Han population, especially in the male group, which needs to be further confirmed.

Using rats as a research model to investigate the effect of human adenovirus 36 on weight gain

BACKGROUND

Recent evidence has shown a positive correlation between obesity and viral infections with a particular emphasis on the human adenovirus-36 (Ad-36). Ad-36 is the first human virus that may increase adiposity in animals, and it is considered as a possible risk factor for obesity in humans; however, the results were not consistent across all the studies. The present study was conducted to examine the influence of Ad-36 infection on obesity in a rat model.

METHODS

Eight-week-old male Wistar rats weighing 170-240 gram (g), were randomly divided into two groups, infection group (48 rats) and a control group (12 rats). The rats in the infection group were infected with human Ad-36. All rats were given free access to a normal chow diet and water. They were weighed weekly.

RESULTS

The mean ± standard deviation (SD) body weights were 229.0 ± 25.9 g and 232.3 ± 16.6 g in the infection and control groups, respectively at the time of infection. The mean ± SD body weight of the infection group (304.0 ± 39.0 g) was higher than the control group (301.0 ± 36.5 g) at 12 weeks post-infection (P = 0.82). Although two groups had approximately same food intakes, the mean change in body weight was greater in the infection group than the control group (75.8 ± 27.9 g vs. 70.8 ± 24.5 g) but it was not significant (P = 0.57).

CONCLUSION

We did not find a statistically significant association between weight gain and Ad-36 infection in the rat model. It seems that longer follow-up duration is needed to develop a significant weight gain in the infected rats. Rats can be used as a good animal model for further investigations about Ad-36-induced obesity, provided not to rely merely on weight measurements. Evaluating body composition or histopathological assessments are suggested.

Adenovirus 36 antibody detection: Improving the standard serum neutralization assay

Adenovirus 36 (AdV36) causes weight gain in animal models, including non-human primates. In humans, AdV36-neutralizing antibodies are associated with adiposity; however, longitudinal studies in large populations are needed to clarify AdV36's contribution. The current gold standard for detection of AdV36-specific antibody is the serum neutralization assay (SNA), which requires long incubation times and highly trained personnel. The standard SNA was modified using an immunocytochemical (ICC) approach, which allows for a more rapid and objective assessment of AdV36 antibodies. Using the ICC assay, virus-infected cells were detected as early as day 1 (D1) and by D5 were detected in 100% of microtiter wells versus 20.3% of wells detected by observing the cytopathic effect. Further, human sera tested with the ICC assay at D5 had a sensitivity and specificity of 80.0% and 95.7%, respectively, when compared to the standard SNA read at D11. Thus, the ICC assay decreased assay incubation time, provided a more objective and easily interpreted assessment, and had a high degree of sensitivity and specificity in determining serological status. The more rapid and objective ICC method will make large population studies feasible, improve comparability among laboratories, and contribute to understanding the role of AdV36 in obesity.

Infectious and Environmental Influences on the Obesity Epidemic

Over the last two decades, the prevalence of obesity has increased rapidly. While it is intuitively appealing to believe that the causes of obesity are manifestly related to excess dietary intake, combined with a reduced expenditure of energy via a decrease in physical activity, it is also been noted that the evidence for these as the sole causes of the obesity epidemic is incomplete. This has led to the search for other causes of obesity, particularly those which stem from the environment we live in. This review will explore two putative causes of obesity: infections and environmental pollutants. It will focus on the key human infection associated with obesity-human adenovirus 36 (Ad36) and will discuss several environmental pollutants which have been postulated to be involved in the development of obesity: bisphenol A, phthalates and persistent organic pollutants. For each of these, the epidemiology and biological mechanisms underpinning the association of these agents with obesity will be reviewed.

Infectobesity: the evaluation of adenovirus-36 infection and obesity

Obesity, which causes some cancer types and other diseases, is not only a global public health problem, but also a factor that affects country's economy. Endocrinal, environmental, neuronal and genetic factors have important roles on the etiology of obesity. When the possibility that SMAM‐1 animal virus could have a relationship with obesity was observed, obesity studies focused on human adenoviruses. Adenovirus‐36 was first isolated in 1978 and was the first human adenovirus to be tested in terms of infectobesity. Both in vivo and in vitro studies proved the strong relationship between adenovirus‐36 presence and obesity. Therefore, a large-scale study incorporating various ethnicities and age groups is required to investigate the worldwide epidemic of obesity and its links with viruses.

Interaction of obesity and infections

There is evidence that certain infections may induce obesity. Obese persons may also have more severe infections and have compromised response to therapies. The objective of this study is to review the available literature identifying infections that potentially contribute to greater body mass index (BMI) and differential responses of overweight and obese persons to infections. A systematic literature review of human studies examining associations between infections and weight gain, differential susceptibility, severity, and response to prevention and treatment of infection according to BMI status (January 1980-July 2014) was conducted. Three hundred and forty-three studies were eligible for inclusion. Evidence indicated that viral infection by human adenovirus Ad36 and antibiotic eradication of Helicobacter pylori were followed by weight gain. People who were overweight or obese had higher susceptibility to developing post-surgical infections, H1N1 influenza and periodontal disease. More severe infections tended to be present in people with a larger BMI. People with a higher BMI had a reduced response to vaccinations and antimicrobial drugs. Higher doses of antibiotics were more effective in obese patients. Infections may influence BMI, and BMI status may influence response to certain infections, as well as to preventive and treatment measures. These observations have potential clinical implications.

Human Adenovirus 36 Infection Increased the Risk of Obesity: A Meta-Analysis Update

Human adenovirus 36 (HAdV-36), as the key pathogen, was supposed and discussed to be associated with obesity. We searched the references on the association between HAdV-36 infection and obesity with the different epidemiological methods, to explore the relationship with a larger sample size by meta-analysis and compare the differences of epidemiological methods and population subsets by the subgroup analyses.We conducted literature search on the association between HAdV-36 infections and obesity in English or Chinese published up to July 1, 2015. The primary outcome was the HAdV-36 infection rate in the obese and lean groups; the secondary outcomes were the BMI level and BMI z-score in the HAdV-36 positive and negative groups. The pooled odds ratio (OR) was calculated for the primary outcome; the standardized mean differences (SMDs) were calculated for the secondary and third outcomes. Prediction interval (PI) was graphically presented in the forest plot of the random effect meta-analyses. Metaregression analysis and subgroup analysis were performed.Finally 24 references with 10,191 study subjects were included in the meta-analysis. The obesity subjects were more likely to be infected with HAdV-36 compared to the lean controls (OR = 2.00; 95%CI: 1.46, 2.74; PI: 0.59, 6.76; P < 0.001) with a high heterogeneity (I = 80.1%; P < 0.001) estimated by the random effect model. Subgroup analysis demonstrated that the pooled OR of HAdV-36 infection for obesity were 1.77 (95%CI: 1.19, 2.63; PI: 0.44, 7.03; P = 0.005) and 2.26 (95%CI: 1.67, 3.07; PI: 1.45, 3.54; P < 0.001) in the adults and children, respectively. Compared to the HAdV-36 negative subjects, the SMD of BMI was 0.28 (95% CI: 0.08, 0.47; PI: -0.53, 1.08; P = 0.006) in the HAdV-36 positive subjects with a high heterogeneity (I = 86.5%; P < 0.001). The BMI z-score in the children with HAdV-36 infection was higher than those without HAdV-36 infection (SMD = 0.19; 95%CI: -0.31, 0.70; PI: -2.10, 2.49), which had no significantly statistical difference (P = 0.453).HAdV-36 infection increased the risk of obesity. HAdV-36 also increased the risk of weight gain in adults, which was not observed in children.

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.

Adenovirus 36 and Obesity: An Overview

There is an epidemic of obesity starting about 1980 in both developed and undeveloped countries definitely associated with multiple etiologies. About 670 million people worldwide are obese. The incidence of obesity has increased in all age groups, including children. Obesity causes numerous diseases and the interaction between genetic, metabolic, social, cultural and environmental factors are possible cofactors for the development of obesity. Evidence emerging over the last 20 years supports the hypothesis that viral infections may be associated with obesity in animals and humans. The most widely studied infectious agent possibly linked to obesity is adenovirus 36 (Adv36). Adv36 causes obesity in animals. In humans, Adv36 associates with obesity both in adults and children and the prevalence of Adv36 increases in relation to the body mass index. In vivo and in vitro studies have shown that the viral E4orf1 protein (early region 4 open reading frame 1, Adv) mediates the Adv36 effect including its adipogenic potential. The Adv36 infection should therefore be considered as a possible risk factor for obesity and could be a potential new therapeutic target in addition to an original way to understand the worldwide rise of the epidemic of obesity. Here, the data indicating a possible link between viral infection and obesity with a particular emphasis to the Adv36 will be reviewed.

The relationship between adenovirus-36 seropositivity, obesity and metabolic profile in Turkish children and adults

Obesity potentially arising from viral infection is known as 'infectobesity'. The latest reports suggest that adenovirus-36 (Adv36) is related to obesity in adults and children. Our aim was not only to determine the Adv36 seropositivity in both obese and non-obese children and adults, but also to investigate correlations between antibody positivity and serum lipid profiles. Both Adv36 positivity and tumour-necrosis-factor-alpha, leptin and interleukin-6 levels were detected in blood samples collected from 146 children and 130 adults by ELISA. Fasting plasma triglycerides, total cholesterol and low-density lipoprotein levels were also measured. Adv36 positivity was determined to be 27·1% and 6% in obese and non-obese children and 17·5% and 4% in obese and non-obese adults, respectively. There was no difference with regard to total cholesterol, low-density lipoprotein, triglyceride, tumour-necrosis-factor-alpha and interleukin-6 levels (P > 0·05). However, there was a significant difference between groups in terms of leptin levels (P < 0·05). We determined the prevalence of Adv36 positivity in obese children and adults. Our results showed that Adv36 may be an obesity agent for both adults and children, parallel with current literature data. However, the available data on a possible relationship between Adv36 infection and obesity both in children and adults do not completely solve the problem.

The role of adenovirus 36 as a risk factor in obesity: the first clinical study made in the fatty tissues of adults in Turkey

Obesity which developes due to multifactorial reasons, was associated recently with human Adenovirus-36 (Ad-36). The aim of this study was to investigate the prevalence of Ad-36 antibodies in obese adults and also to investigate the DNA of Ad-36 in their adipose tissue. In this cross-sectional and case-control based study, 49 obese adults, with BMI ≥ 30 kg/m(2), and 49 non-obese adults, with BMI ≤ 25 kg/m(2), applied for esthetic purposes and were included in this study as patient and control groups, respectively. Adipose tissue samples, obtained by the lipoaspiration method, were studied by single-step PCR and nested-PCR methods. Simultaneously, the presence of Ad-36 antibodies and serum leptin and adiponectin levels were assessed by serum neutralization assay (SNA) and ELISA, respectively. Serum samples which didn't cause a cytopathic effect at ≥ 1:8 were accepted as positive. Ad-36 antibody was detected in 6 (12.2%) of 49 patients by SNA and was statistically significant (p < 0.05). Ad-36 DNA was not detected in any of the adipose tissue samples of the patient or control groups. Mean BMI and leptin levels were higher in the Ad-36-positive group, while adiponectin levels were found to be lower in the Ad-36-positive group. Although no statistically significant difference was found in cholesterol and triglyceride levels between the two groups (p > 0.05), lower mean serum cholesterol and triglyceride levels were found in the Ad-36-positive patients. In conclusion, we couldn't detect Ad-36 DNA in adipose tissue; however, we detected significantly higher Ad-36 antibody levels in the obese group compared to the non-obese group, according to the both univariant and multivariant analyses, suggesting that Ad-36 may play a role in obesity. There is a need for new and extended serial, particularly cohort and human-based, studies in order to have a clear understanding of the Ad-36-obesity relationship.

Association of adenovirus 36 infection with adiposity and inflammatory-related markers in children

CONTEXT

Although animal studies suggest that adenovirus 36 (Ad36) infection is linked to obesity and systemic inflammation, human data are scant and equivocal.

OBJECTIVE

Associations of Ad36 infection with total body adiposity and inflammatory-related markers were determined in 291 children aged 9-13 years (50% female, 49% black).

DESIGN

Fasting blood samples were measured for presence of Ad36-specific antibodies and TNF-α, IL-6, vascular endothelial growth factor (VEGF), and monocyte chemoattractant protein-1 (MCP-1). Fat mass and fat-free soft tissue mass were measured by dual-energy X-ray absorptiometry.

RESULTS

The overall prevalence of Ad36 seropositivity [Ad36(+)] was 42%. There was a higher percentage of Ad36(+) children in the highest tertiles of TNF-α and IL-6 compared with their respective middle and lowest tertiles (both P < .03). There was also a trend toward a higher prevalence of Ad36(+) children in the highest tertile of VEGF compared with tertiles 1 and 2 (P = .05). Multinomial logistic regression, adjusting for age, race, sex, and fat-free soft tissue mass, revealed that compared with children with the lowest TNF-α, IL-6, and VEGF levels (tertile 1), the adjusted odds ratios for Ad36(+) were 2.2 [95% confidence interval (CI) 1.2-4.0], 2.4 (95% CI 1.4-4.0), and 1.8 (95% CI 1.0-3.3), respectively, for those in the highest TNF-α, IL-6, and VEGF levels (tertile 3). No association was observed between Ad36(+) and greater levels of fat mass or MCP-1 (all P > .05).

CONCLUSIONS

In children, our data suggest that Ad36(+) may be associated with biomarkers implicated in inflammation but not with greater levels of fat mass.

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.

Serological data analyses show that adenovirus 36 infection is associated with obesity: a meta-analysis involving 5739 subjects

OBJECTIVE

Serological studies on the relationship between adenovirus 36 (Ad36) and an increased risk of obesity development have shown conflicting results. We reviewed the published studies and carried out a meta-analysis to explore this relationship.

METHODS

PubMed was searched until December 2012 for the relative references with sufficient information to estimate odds ratios (ORs) and 95% confidence intervals (CIs). A total of 11 case-control studies, including 2508 obese subjects and 3005 controls, were selected.

RESULTS

Compared with nonobese controls, Ad36 infection significantly increased the obesity risk by a pooled OR of 1.60 (95% CI = 1.14-2.25; P < 0.01). Meta-regression showed that the types of subject and obesity assessments were potential risk factors. In the subgroup analysis, a significantly increased risk was found in children (OR = 1.95; 95% CI = 1.34-2.85; z = 3.45; P < 0.01) and those with an obesity assessment of BMI ≥ 30 kg/cm2 (OR = 1.89; 95% CI = 1.15-3.10; P < 0.05).

CONCLUSIONS

Ad36 infection is associated with an increased risk of obesity development. To our knowledge, this is the first report to reveal the significant relationship in children with a serological data analysis.

Obesity and infection: two sides of one coin

The prevalence of obesity has exponentially risen worldwide. The etiology of obesity is multifactorial, and genetic inheritance and behavioral/environmental causes are considered the main etiological factors. Moreover, evidence that specific infections might promote the development of obesity has steadily accumulated. Only a few works investigate the impact of obesity on the immune response to infections and the risk of infections in the obese population. The aim of this paper was to review the available data regarding the various aspects of the association between obesity and infections and to highlight the possibility that infectious agents may have an etiological role in obesity, an idea known as "infectobesity". Several microbes have been considered as possible promoter of obesity, but most of the data concern adenovirus-36 that exerts an adipogenic action mainly via a direct effect on adipose tissue leading to weight gain, at least in animal models.Obesity affects the immune response leading to an increased susceptibility to infections. Obese adults and children show an increased incidence of both nosocomial and community-acquired infections. Furthermore, obesity may alter the pharmacokinetics of antimicrobial drugs and impact on vaccine response. However, the various aspects of the association of obesity infections remain poorly studied, and a call to research is necessary to better investigate the problem.In conclusion, obesity impacts millions globally, and greater understanding of its etiology and its effects on immunity, infections, and prevention and management strategies is a key public health concern.

Lack of adenovirus DNA in mediastinal adipose tissue of obese/overweight adults with cardiovascular disorders?

Mediastinal adipose tissue can be found on the anterior surface of pericardial sac below the remnants of the thymus. On the basis of previous studies describing adenoviruses (AdVs) as a causative factor of obesity, the causative relation between the presence of AdVs and an increased accumulation of mediastinal adipose tissue was studied. The study included 25 obese/overweight subjects with cardiac disorders. Specimens from fat deposits from the anterior mediastinum were collected during cardiac surgery procedures. Afterwards, PCR was used to detect AdV-DNA. No AdV-DNA could be detected in adipose tissue. An association between an excessive accumulation of mediastinal adipose tissue and an AdV-infection in the development of accompanying cardiac disorders was excluded.

Effect of adenovirus and influenza virus infection on obesity

The purpose of this review is to provide an overview of the effects of adenovirus and influenza virus infections on obesity in various experimental models. We reviewed studies that were conducted within the past 10 years and were related to virus infection and obesity prevalence. Here, we discuss a different causal relationship between adenovirus and influenza infections with obesity. Adenovirus infection can cause obesity, whereas obesity can be a risk factor for increasing influenza virus infection and increases the risk of morbidity and mortality. The prevalence of obesity due to adenovirus infections may be due to an increase in glucose uptake and reduction in lipolysis caused by an increase in corticosterone secretion. Adenovirus infections may lead to increases in appetite by decreasing norepinephrine and leptin levels and also cause immune dysfunction. The relationship between obesity and influenza virus infection could be summarized by the following features: decreases in memory T-cell functionality and interferon (IFN)-α, IFN-β, and IFN-γ mRNA expression, increases in viral titer and infiltration, and impaired dendritic cell function in obese individuals. Moreover, leptin resistance may play an important role in increasing influenza virus infections in obese individuals. In conclusion, prevention of adenovirus infections could be a good approach for reducing obesity prevalence, and prevention of obesity could reduce influenza virus infections from the point of view of viral infections and obesity.

Clinical and laboratory characteristics of 1179 Czech adolescents evaluated for antibodies to human adenovirus 36

BACKGROUND

Human adenovirus 36 (Adv36) is associated with obesity in children. Most prior studies have been small and the association of Adv36 status with markers of metabolic risks has been inconsistent.

OBJECTIVES

To determine the prevalence of Adv36 antibodies in different weight categories of adolescents and to evaluate the association of Adv36 infection with anthropometric parameters and cardiometabolic health risks.

SUBJECTS AND METHODS

In 1179 Czech adolescents (85 underweight, 506 normal weight, 160 overweight and 428 obese), the following variables were evaluated: anthropometric (body weight, height, body mass index, circumferences, fat mass), blood pressure, biochemical and hormonal (lipid profile, glucose, insulin, liver enzymes, adiponectin) and Adv36 antibodies (enzyme-linked immunosorbent assay).

RESULTS

Of the total cohort, 26.5% were positive for Adv36 antibodies (underweight: 22.3%; normal weight: 21.5%; overweight: 40.0% and obese: 28.0%). The odds ratio for Adv36 antibody positivity evaluated vs normal weight was 2.61 for overweight (95% confidence interval (CI): 1.77-3.86, P<0.001) and 1.46 for obesity (95% CI: 1.07-1.99, P=0.016). A significantly higher prevalence of Adv36 infection was observed in female subjects (32.5%) in comparison to male subjects (19.7%; P<0.001). Adv36 positivity of the whole cohort was significantly related to body weight (P=0.042), body mass index (P=0.015), hip circumference (P=0.004), body height z-score (P=0.029), and total body fat (P=0.000) and trunk fat (P=0.000). Adv36 antibody-positive girls demonstrated significantly higher body height (167.8 vs 165.0 cm, P=0.01) and waist circumference (77.0 vs 72.0 cm, P=0.01). Infected adolescents exhibited significantly higher levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C), but lower levels of blood glucose. Liver enzymes were significantly increased only in Adv36-positive boys.

CONCLUSION

These results demonstrated an association of Adv36 antibodies with obesity and an even greater association with overweight. Adv36 positivity was related to increased fat mass, levels of TC and LDL-C, but to decreased level of blood glucose. No relation to adiponectin levels was revealed.

Adenovirus-36 seropositivity and its relation with obesity and metabolic profile in children

The human adenovirus 36 (Ad-36) is causally and correlatively associated in animals and humans, respectively, with increased adiposity and altered metabolic profile. In previous studies, the relationship between Ad-36 seropositivity with obesity was established in adults and children. We evaluated the association of positive antibodies to Ad-36 with obesity and metabolic profile in Mexican children. Seventy-five children with normal-weight and 82 with obesity were studied in this research. All children had a clinic assessment which included weight, height, body circumferences, and skinfold thickness. Laboratory analyzes included triglycerides, total cholesterol, high-density lipoprotein, low-density lipoprotein, and glucose and insulin levels. An enzyme-linked immunosorbent assay (ELISA) was used to determine the antibodies to Ad-36 in the serum samples. The overall Ad-36 seroprevalence was 73.9%. Ad-36 seropositivity had a higher prevalence in obese children than in normal weight group (58.6 versus 41.4%, P = 0.007). Ad-36 seropositivity was associated with obesity (OR = 2.66, P = 0.01) and high-density lipoprotein <40 mg/dL (OR = 2.85, P = 0.03). The Ad-36 seropositive group had greater risk of 4 metabolic abnormalities compared with those children without none alteration. In summary, Ad-36 seropositivity was associated with obesity and low HDL-c levels in the sample of children studied.

An observational study of the association between adenovirus 36 antibody status and weight loss among youth

OBJECTIVE

Although the human adenovirus 36 (Ad-36) is associated with obesity and relative hypolipidemia, its role in pediatric weight loss treatment response is uncertain. Therefore, the primary study objective was to determine whether Ad-36 antibody (AB) status was associated with response to a pediatric weight loss program. The secondary objective was to assess the association between Ad-36 AB status and baseline lipid values.

METHODS

Participants included 73 youth aged 10-17 years in a residential camp-based weight loss program. The study examined differences in baseline lipid values between Ad-36 AB+ and AB- youth as well as differences in response to treatment, including indices of body size and fitness.

RESULTS

At baseline, results showed that Ad-36 AB+ youth evidenced significantly lower levels of total cholesterol and triglycerides than Ad-36 AB- youth (all p < 0.05). After 4 weeks of treatment, the Ad-36 AB+ youth showed a smaller reduction in BMI percentile than the Ad-36 AB- youth (p < 0.05), a difference of about 0.48 kg.

CONCLUSION

Ad-36 AB status showed a weak association with treatment response, but was associated with a better lipid profile. Ad-36 AB status should be assessed in studies of pediatric obesity treatment and prevention.

Obesity and the gut microbiome: Striving for causality

The gut microbiome has been proposed to play a causal role in obesity. Here, we review the historical context for this hypothesis, highlight recent key findings, and critically discuss issues central to further progress in the field, including the central epistemological problem for the field: how to define causality in the relationship between microbiota and obesity phenotypes. Definition of such will be critical for the field to move forward.

Adenovirus-36 is associated with obesity in children and adults in Sweden as determined by rapid ELISA

BACKGROUND

Experimental and natural human adenovirus-36 (Adv36) infection of multiple animal species results in obesity through increasing adipogenesis and lipid accumulation in adipocytes. Presence of Adv36 antibodies detected by serum neutralization assay has previously been associated with obesity in children and adults living in the USA, South Korea and Italy, whereas no association with adult obesity was detected in Belgium/The Netherlands nor among USA military personnel. Adv36 infection has also been shown to reduce blood lipid levels, increase glucose uptake by adipose tissue and skeletal muscle biopsies, and to associate with improved glycemic control in non-diabetic individuals.

PRINCIPAL FINDINGS

Using a novel ELISA, 1946 clinically well-characterized individuals including 424 children and 1522 non-diabetic adults, and 89 anonymous blood donors, residing in central Sweden representing the population in Stockholm area, were studied for the presence of antibodies against Adv36 in serum. The prevalence of Adv36 positivity in lean individuals increased from ∼7% in 1992-1998 to 15-20% in 2002-2009, which paralleled the increase in obesity prevalence. We found that Adv36-positive serology was associated with pediatric obesity and with severe obesity in females compared to lean and overweight/mildly obese individuals, with a 1.5 to 2-fold Adv36 positivity increase in cases. Moreover, Adv36 positivity was less common among females and males on antilipid pharmacological treatment or with high blood triglyceride level. Insulin sensitivity, measured as lower HOMA-IR, showed a higher point estimate in Adv36-positive obese females and males, although it was not statistically significant (p = 0.08).

CONCLUSION

Using a novel ELISA we show that Adv36 infection is associated with pediatric obesity, severe obesity in adult females and lower risk of high blood lipid levels in non-diabetic Swedish individuals.

Association of adenovirus 36 infection with obesity and metabolic markers in humans: a meta-analysis of observational studies

Background

Several studies have shown that Adenovirus 36 (Ad36) influences the risk of obesity in humans. Clarifying the relationship between Ad36 infection and obesity could lead to more effective approaches for the management of obesity. The objective of this study was to conduct a meta-analysis to confirm the influence of Ad36 infection on obesity and metabolic markers.

Methodology/Principal Findings

We searched MEDLINE and the Cochrane Library for pertinent articles (including their references) published between 1951 and April 22, 2012. Only English language reports of original observational studies were included in this meta-analysis. Data extraction was performed independently by two reviewers. Weighted mean differences (WMDs) and pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated using the random effects model. Of 237 potentially relevant studies, 10 cross-sectional studies (n = 2,870) conformed to the selection criteria. Pooled analysis showed that the WMD for BMI of Ad36 infection compared with non-infection was 3.19 (95% CI 1.44–4.93; P<0.001). Sensitivity analysis restricted to studies of adults yielded a similar result of 3.18 (95% CI 0.78–5.57; P = 0.009). The increased risk of obesity associated with Ad36 infection was also significant (OR: 1.9; 95% CI: 1.01–3.56; P = 0.047). No significant differences were found in relation to total cholesterol (P = 0.83), triglycerides (P = 0.64), HDL (P = 0.69), blood glucose (P = 0.08), waist circumstance (P = 0.09), and systolic blood pressure (P = 0.25).

Conclusion/Significance

Ad36 infection was associated with the risk of obesity and weight gain, but was not associated with abnormal metabolic markers including waist circumstance. It suggests that Ad36 infection is more associated with accumulation of subcutaneous fat than that of visceral fat. The relationship between Ad36 and obesity should be assessed by further studies, including well-designed prospective studies, to gain a better understanding of whether Ad36 plays a role in the etiology of human obesity.

Adenovirus 36 infection and obesity

The most important factors leading to fat accumulation in children are genetic inheritance, endocrine alterations, and behavioural/environmental causes. In addition, experimental animal studies have shown that infections due to various pathogens can lead to overweight and obesity conditions, and studies of humans have found that the incidence of seroconversion against some of these may be significantly more frequent in obese adults and children than in normal subjects. However, the results of these studies are not conclusive and, in some cases, have raised more questions than answers. We reviewed the literature concerning the role of adenovirus 36 (AD-36), the most widely studied infectious agent in animals and humans, because of its potential association with childhood obesity. The available evidence suggests that more studies are needed to evaluate whether or not the association between the presence of AD-36 antibodies and obesity is simply unrelated, and to verify whether there are subjects that have greater tendency to become obese because more easily susceptible to AD-36 infection or with a predisposition to suffer from persistent viral infection more easily leading to the development of obesity. If it is demonstrated that AD-36 does play a role in obesity, it will be important to investigate possible vaccines against the infection itself or antiviral drugs capable of inhibiting disease progression.

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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.