New human adenovirus (candidate adenovirus 36), a novel member of subgroup D

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.

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.

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.

Potential role of E4orf1 protein in aging-associated impairment in glycemic control

Aging constitutes a major risk factor for the development of type-2 diabetes (T2D) where glucose tolerance declines with age, resulting in a high prevalence of T2D and impaired glucose tolerance in the elderly population. Currently more than half of the 20 million U.S. adults with T2D are above the age of 60, and the largest increase in T2D prevalence is expected in the elderly. Obesity is a causative factor for T2D associated insulin resistance and hyperglycemia. Furthermore, the aging process is accelerated by hyperglycemia and effective treatment options are limited for the vulnerable aging population. One of the mechanisms contributing to aging associated hyperglycemia is resistance to insulin-mediated glucose disposal. Chronic hyperglycemia also accelerates aging by increasing pro-inflammatory milieu leading to impaired immune function. Although currently available anti-diabetic agents improve glycemic control, they have potential serious side effects in some cases. Therefore, additional and better drugs are urgently needed for treatment of insulin resistance and aging associated health risk factors. This review presents the novel use of a microbial protein, E4orf1 as a potential anti-diabetic agent, which functions independent of insulin and obesity, highlighting the role of unique sources for future drug development.

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.

Metformin Is Associated With Higher Relative Abundance of Mucin-Degrading Akkermansia muciniphila and Several Short-Chain Fatty Acid-Producing Microbiota in the Gut

The global obesity epidemic, dubbed “globesity” by the World Health Organisation, is a pressing public health issue. The aetiology of obesity is multifactorial incorporating both genetic and environmental factors. Recently, epidemiological studies have observed an association between microbes and obesity. Obesity-promoting microbiome and resultant gut barrier disintegration have been implicated as key factors facilitating metabolic endotoxaemia. This is an influx of bacterial endotoxins into the systemic circulation, believed to underpin obesity pathogenesis. Adipocyte dysfunction and subsequent adipokine secretion characterised by low grade inflammation, were conventionally attributed to persistent hyperlipidaemia. They were thought of as pivotal in perpetuating obesity. It is now debated whether infection and endotoxaemia are also implicated in initiating and perpetuating low grade inflammation. The fact that obesity has a prevalence of over 600 million and serves as a risk factor for chronic diseases including cardiovascular disease and type 2 diabetes mellitus is testament to the importance of exploring the role of microbes in obesity pathobiology. It is on this basis that Massachusetts General Hospital is sponsoring the Faecal Microbiota Transplant for Obesity and Metabolism clinical trial, to study the impact of microbiome composition on weight. The association of microbes with obesity, namely, adenovirus infection and metabolic endotoxaemia, is 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.

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.

An infection of human adenovirus 31 affects the differentiation of preadipocytes into fat cells, its metabolic profile and fat accumulation

The primary issue undertaken in this study was to test the hypothesis that preadipocytes would have intrinsically elevated propensity to differentiate into mature adipocytes due to HAdV31 infection. To prove that, the metabolic and molecular mechanisms responsible for HAdV31-induced adipogenesis were examined. 3T3L1 cells (mouse embryonic fibroblast, adipose like cell line) were used as a surrogate model to analyze an increased proliferation, differentiation, and maturation of preadipocytes infected with human adenovirus. An expression of E4orf1, C/EBP-β, PPAR-γ, GAPDH, aP2, LEP, and fatty acid synthase genes, intracellular lipid accumulation as well as cytokine release from the fat cells were assessed. Data showed that HAdV31 increased an expression of C/EBP-β and PPAR-γ genes leading to an enhanced differentiation of preadipocytes into fat cells. Besides, overexpression of GAPDH and fatty acid synthase, and decreased expression of leptin caused an increased accumulation of intracellular lipids. Secretion of TNF-α and IL-6 from HAdV31-infected cells was strongly decreased, leading to unlimited virus replication. The results obtained from this study provided the evidences that HAdV31, likewise previously documented HAdV36, is a subsequent human adenovirus affecting the differentiation and lipid accumulation of 3T3L1 cells.

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.

Accurate identification of neutralizing antibodies to adenovirus Ad36, -a putative contributor of obesity in humans

BACKGROUND

In children and adults, human adenovirus serotype 36 (Ad36) is linked with increased adiposity, and important metabolic alterations. Since this property is not shared by many other human adenovirus serotypes, it is imperative to specifically identify exposure to Ad36. Although serum neutralization assay (SNA) is the gold standard to specifically detect neutralizing antibodies (NA) to Ad36, it requires 2-weeks to complete and considerable training to interpret the results. Whereas, an enzyme-immuno assay (EIA) may provide a quicker and objective determination.

OBJECTIVES

Evaluate the accuracy of commercially available EIA kits to detect NA to Ad36. Modify SNA to reduce time and increase objectivity.

STUDY DESIGN

Sera of 15 seropositive or 16 seronegative subjects confirmed by SNA were used to test: 1) reproducibility of SNA to detect Ad36 exposure, by repeating assays twice; 2) an EIA that detects antibodies to all human adenovirus serotypes (NS-EIA) (Abcam-108705); 3) an EIA supposedly specific for Ad36 antibody (Ad36-EIA) (MyBioSource,#MBS705802), and 4) the concordance of SNA with a novel combination of SNA and immune-staining (SN-IS) kit (Cell BioLabs,#VPK-111).

RESULTS

The SNA showed exact reproducibility. NS-EIA detected adenovirus antibodies in 94% samples, confirming the non-specificity of the assay for Ad36 serotype. All seronegative samples (as determined by SNA) were false positive by Ad36-EIA. In 97% samples, SN-IS showed fidelity with Ad36-antibody status as determined by SNA.

CONCLUSIONS

The available EIA kits are not specific for detecting NA to Ad36. The modified SNA with immune-staining reduces assay time and increases accuracy of detecting by reducing subjectivity.

Human adenovirus-36 is uncommon in type 2 diabetes and is associated with increased insulin sensitivity in adults in Sweden

BACKGROUND

Human adenovirus-36 (Adv36) increases adiposity, but also upregulates distal insulin signaling in vitro in human adipose and muscle tissue and in vivo in the rodent independently of adiposity. Accordingly, healthy adults and children with antibodies against Adv36 had increased insulin sensitivity and reduced hepatic lipid accumulation. We hypothesized that Adv36 infection would be less frequent in individuals with type 2 diabetes or impaired glycemic control.

METHODS

Presence of antibodies against Adv36 was analyzed for association to type 2 diabetes or impaired glycemic control in a two-wave population-based sample of well-characterized adults (n = 1734). Indices of impaired glycemic control included oral glucose tolerance, and circulating fasting levels of glucose, insulin, and insulin-like growth factor binding protein-1 (IGFBP-1).

RESULTS

Adv36 seropositivity was more common in those with normal glucose tolerance (NGT) than in those with diabetes (females: OR 17.2, 95% CI 4.0-74.3; males: OR 3.5, 95% CI 1.8-6.7). Also, females with NGT had higher frequency of Adv36 seropositivity than females with prediabetes (impaired glucose tolerance and/or impaired fasting glucose; OR 1.8, 95% CI 1.1-3.1). Within the female prediabetes group Adv36 seropositivity was associated with higher insulin sensitivity reflected by reduced HOMA-IR and increased IGFBP-1.

CONCLUSION

Adv36 infection is associated with lower occurrence of type 2 diabetes and better insulin sensitivity in adults, particularly among females.

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.

Harnessing the beneficial properties of adipogenic microbes for improving human health

Obesity is associated with numerous metabolic comorbidities. Weight loss is an effective measure for alleviating many of these metabolic abnormalities. However, considering the limited success of most medical weight-management approaches in producing a sustained weight loss, approaches that improve obesity-related metabolic abnormalities independent of weight loss would be extremely attractive and of practical benefit. Metabolically healthy obesity supports the notion that a better metabolic profile is possible despite obesity. Moreover, adequate expansion of adipose tissue appears to confer protection from obesity-induced metabolic comorbidities. To this end, the 10th Stock conference examined new approaches to improve metabolic comorbidities independent of weight loss. In particular, human adenovirus 36 (Ad36) and specific gut microbes were examined for their potential to influence lipid and glucose homeostasis in animals and humans. While these microbes possess some undesirable properties, research has identified attributes of adenovirus Ad36 and gut microbes that may be selectively harnessed to improve metabolic profile without the obligatory weight loss. Furthermore, identifying the host signalling pathways that these microbes recruit to improve the metabolic profile may offer new templates and targets, which may facilitate the development of novel treatment strategies for obesity-related metabolic conditions.

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.

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.

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.

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.

Patent Highlights

A snapshot of recent key developments in the patent literature of relevance to the advancement of pharmaceutical and medical R&D

Insulin receptor-independent upregulation of cellular glucose uptake

BACKGROUND

Cellular glucose uptake can be enhanced by up-regulating Ras signaling in either insulin dependent or independent manner. In presence of insulin and intact insulin signaling, Ras plays a negligible role in glucose uptake. Conversely, when insulin signaling is impaired in obesity or diabetes, the insulin-independent Ras pathway may be valuable for enhancing glucose disposal. We previously reported that Ad36, a human adenovirus, enhances cellular glucose uptake by up-regulating the Ras/Glut4 pathway. Here, we investigated if Ad36-up-regulated Ras via the insulin-independent pathway, to enhance glucose uptake. Furthermore, uncontrolled up-regulation of Ras is linked with oncogenic cell transformation, if the tumor suppressor gene p53 is also down regulated. Hence, we determined if up-regulation of Ras by Ad36 would induce oncogenic cell transformation. Finally, we determined the relevance of Ad36 to insulin resistance in humans.

METHODS

Insulin receptor (IR) was knocked down with siRNA in 3T3-L1 adipocytes, to determine if Ad36 increases the Ras/Glut4 pathway and glucose uptake without IR-signaling. Next, the effects of Ad36 on cell transformation and p53 abundance were determined. Finally, overweight or obese women were screened for seropositivty to Ad36, as an indicator of natural Ad36 infection. Associations of Ad36 infection with adiposity and C-Reactive proteins (CRP) –two key markers of insulin resistance, and with glucose disposal, were determined.

RESULTS

Unaffected by IR knock-down, Ad36 significantly increased the Ras pathway, Glut4 translocation, and glucose uptake in 3T3-L1 adipocytes. Despite Ras up-regulation, Ad36 did not transform 3T3-L1 cells. This may be because Ad36 significantly increased p53 protein in 3T3-L1 cells or mice adipose tissue. Ad36 seropositivity was associated with greater adiposity and CRP levels, yet a significantly higher systemic glucose disposal rate.

CONCLUSIONS

Overall, the study offers Ras/Glut4 pathway as an alternate to enhance glucose disposal when insulin signaling is impaired, and, importantly, provides Ad36 as a tool to understand the modulation of that pathway.

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.

Adenovirus 36 as an obesity agent maintains the obesity state by increasing MCP-1 and inducing inflammation

BACKGROUND

Although it is well known that adenovirus 36 (Ad36) is associated with obesity in humans as well as in animals, the detailed cellular mechanism is unclear.

METHODS

Wild-type (WT) mice and monocyte chemoattractant protein-1 knockout (MCP-1(-/-)) mice were infected with Ad36, and their weights and inflammatory status were measured. Macrophage infiltration was examined in their reproductive fat pads and in a coculture system. The correlation between Ad36 antibody presence and MCP-1 levels was tested in human samples.

RESULTS

We have shown that Ad36 infection stimulated an inflammatory state by increasing the level of MCP-1 through the activation of nuclear factor κB, which in turn induced the infiltration of macrophages into adipocytes. This induced inflammation resulted in viral obesity, which caused chronic inflammation and affected lipid metabolism. In contrast to WT mice, MCP-1(-/-) mice were protected from Ad36-induced inflammation and obesity. The MCP-1 levels in Ad36-antibody-positive human group were higher than those in the antibody-negative group.

CONCLUSIONS

These findings support the proposition that virus-induced inflammation is the cellular mechanism underlying Ad36-induced obesity. These results also suggest that MCP-1 plays a critical role in Ad36-induced obesity and that MCP-1 may be a therapeutic target in preventing virus-induced obesity.

PPARgamma-independent increase in glucose uptake and adiponectin abundance in fat cells

Although thiazolidinediones (TZD) effectively improve hyperglycemia and increase adiponectin, a proinsulin-sensitizing adipokine, they also increase adipogenesis via peroxisome proliferator-activated receptor (PPAR)γ induction, which may be undesirable. Recent safety concerns about some TZD have prompted the search for next generation agents that can enhance glycemic control and adiponectin independent of PPARγ or adipogenesis. Reminiscent of TZD action, a human adenovirus, adenovirus 36 (Ad36), up-regulates PPARγ, induces adipogenesis, and improves systemic glycemic control in vivo. We determined whether this effect of Ad36 requires PPARγ and/or adipogenesis. Glucose uptake and relevant cell signaling were determined in mock-infected or human adenoviruses Ad36 or Ad2-infected cell types under the following conditions: 1) undifferentiated human-adipose-tissue-derived stem cells (hASC), 2) hASC differentiated as adipocytes, 3) hASC in presence or absence of a PPARγ inhibitor, 4) NIH/3T3 that have impaired PPARγ expression, and 5) PPARγ-knockout mouse embryonic fibroblasts. Mouse embryonic fibroblasts with intact PPARγ served as a positive control. Additionally, to determine natural Ad36 infection, human sera were screened for Ad36 antibodies. In undifferentiated or differentiated hASC, or despite the inhibition, down-regulation, or the absence of PPARγ, Ad36 significantly enhanced glucose uptake and PPARγ, adiponectin, glucose transporter 4, and glucose transporter 1 protein abundance, compared with mock or Ad2-infected cells. This indicated that Ad36 up-regulates glucose uptake and adiponectin secretion independent of adipogenesis or without recruiting PPARγ. In humans, natural Ad36 infection predicted greater adiponectin levels, suggesting a human relevance of these effects. In conclusion, Ad36 provides a novel template to metabolically remodel human adipose tissue to enhance glycemic control without the concomitant increase in adiposity or PPARγ induction associated with TZD actions.

Template to improve glycemic control without reducing adiposity or dietary fat

Drugs that improve chronic hyperglycemia independently of insulin signaling or reduction of adiposity or dietary fat intake may be highly desirable. Ad36, a human adenovirus, promotes glucose uptake in vitro independently of adiposity or proximal insulin signaling. We tested the ability of Ad36 to improve glycemic control in vivo and determined if the natural Ad36 infection in humans is associated with better glycemic control. C57BL/6J mice fed a chow diet or made diabetic with a high-fat (HF) diet were mock infected or infected with Ad36 or adenovirus Ad2 as a control for infection. Postinfection (pi), systemic glycemic control, hepatic lipid content, and cell signaling in tissues pertinent to glucose metabolism were determined. Next, sera of 1,507 adults and children were screened for Ad36 antibodies as an indicator of past natural infection. In chow-fed mice, Ad36 significantly improved glycemic control for 12 wk pi. In HF-fed mice, Ad36 improved glycemic control and hepatic steatosis up to 20 wk pi. In adipose tissue (AT), skeletal muscle (SM), and liver, Ad36 upregulated distal insulin signaling without recruiting the proximal insulin signaling. Cell signaling suggested that Ad36 increases AT and SM glucose uptake and reduces hepatic glucose release. In humans, Ad36 infection predicted better glycemic control and lower hepatic lipid content independently of age, sex, or adiposity. We conclude that Ad36 offers a novel tool to understand the pathways to improve hyperglycemia and hepatic steatosis independently of proximal insulin signaling, and despite a HF diet. This metabolic engineering by Ad36 appears relevant to humans for developing more practical and effective antidiabetic approaches.

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.

Genomic characterization of human adenovirus 36, a putative obesity agent

Increased levels of serum antibody titers against human adenovirus 36 (HAdV-D36) are associated with human obesity and experimental obesity in laboratory animals. While HAdV-D36 has been studied as an infectious agent implicated in obesity for over a decade, the complete genome sequence and its analysis have yet to be reported. A detailed analysis of the genome sequence of HAdV-D36 may be important to understand its role in obesity. Genomic and bioinformatic comparisons with other HAdVs identified differences that suggested unique functions. Global pairwise genome alignment with all sequenced human adenovirus D (HAdV-D) genomes revealed areas of nonconserved sequences in the hexon, E3 CR1 beta, E3 CR1 gamma, and fiber genes. Phylogenetic analysis of all HAdV-D36 proteins confirmed that this virus belongs to species Human adenovirus D. This genomic analysis of HAdV-D36 provides an important tool for comprehending the role that this unique adenovirus may play in human obesity. Low amino acid sequence identity in the E3 CR1 beta and CR1 gamma genes may suggest distinctive roles for these proteins. Furthermore, the predicted molecular models of the HAdV-D36 fiber protein seem to implicate a unique tissue tropism for HAdV-D36.

Adenovirus 36 seropositivity is strongly associated with race and gender, but not obesity, among US military personnel

BACKGROUND

Although several studies have shown a positive association between evidence of anti-adenovirus 36 (Ad-36) antibodies (Ad-36 exposure) and (1) obesity and (2) serum cholesterol in animals, there is limited research demonstrating this association in humans. There is also limited research on transmission, presentation and demographics of Ad-36 infection.

DESIGN

(1) Body mass (body mass index (BMI)), (2) fasting serum cholesterol and triglyceride levels and (3) demographic characteristics were compared between Ad-36 seropositive and seronegative groups. The majority of subjects were matched as cases versus controls on a number of demographic variables.

SUBJECTS

A total of 150 obese and 150 lean active-duty military personnel were studied.

MEASUREMENTS

Subjects completed a questionnaire regarding demographic and behavioral characteristics. Subject serum samples were tested by serum neutralization assay for the presence of anti-Ad-36 antibodies.

RESULTS

In all, 34% of obese and 39% of lean subjects had Ad-36 exposure, an insignificant difference. Serum cholesterol and triglyceride levels were significantly higher among the obese subjects than among the lean, but there were no associations between serum cholesterol and triglyceride levels and Ad-36 exposure. Positive associations were found between Ad-36 exposure and age, race and gender.

CONCLUSION

The study stands in contrast to previous work that has shown a positive relationship between Ad-36 exposure and (1) obesity, and (2) levels of serum cholesterol and triglycerides. In this study there was no association in either case. Unanticipated relationships between Ad-36 exposure and age, race and gender were found, and this is the first time that such a link between Ad-36 exposure and demographics has been found.

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.

Acute effect of infection by adipogenic human adenovirus Ad36

Human adenovirus Ad36 is causally and correlatively associated in animals and humans, respectively, with increased adiposity and altered metabolic profile. We inoculated rats with Ad36 or UV-inactivated Ad36, or mock-infected them. Four days later, Ad36-infected rats showed 23% greater epididymal fat pad weight and viral mRNA; the viral DNA could also be detected in tissues viz. the liver, brain, and adipose tissue. Intranasal or intra-peritoneal routes of viral inoculation showed similar tissue affinity. The serum cytokine response was markedly down-regulated. Ad36 acutely suppresses the systemic immune response and spreads widely. This information will help to determine Ad36 tissue tropism and its metabolic consequences.

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.

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.

Adipogenic potential of multiple human adenoviruses in vivo and in vitro in animals

Human adenovirus-36 (Ad-36) increases adiposity in chickens, mice, and nonhuman primates and is associated with human obesity. Ad-36 paradoxically reduces serum cholesterol and triglycerides in animal models. Ad-36 increases adipocyte differentiation and triglyceride accumulation in 3T3-L1 cells in vitro. This study evaluated whether three other human adenoviruses increase adiposity in chickens and in 3T3-L1 cells in vitro. We inoculated chickens with human Ad-2, Ad-31, Ad-37, or media at age 3 wk. Food intake and weights were recorded for 3.5 wk, and then chickens were killed and visceral fat, body composition, serum lipids, and viral antibody status were determined. Visceral fat and total body fat were significantly elevated ( P < 0.001) in the Ad-37 group compared with all other groups. Final body weights were higher in chickens inoculated with Ad-37 compared with Ad-2, but not significantly higher than in control or Ad-31 groups. Food intake did not differ among groups. Serum cholesterol was elevated in Ad-37 chickens compared with control ( P < 0.01) but was not affected by other viruses. Triglycerides were reduced in Ad-37 chickens ( P < 0.0001) but were not affected by other viruses. In 3T3-L1 cells in vitro, Ad-31, Ad-36, and Ad-37, but not Ad-2, increased adipocyte differentiation and triglycerides accumulation. In summary, Ad-37 is another human adenovirus that increases adiposity and reduces serum triglycerides in an animal model. However, the response of serum cholesterol is opposite that of Ad-36. Evaluation of other human adenoviruses to determine their effects on adiposity and serum lipids is warranted, but in vitro assays may not be definitive for this purpose.

Human adenovirus-36 is associated with increased body weight and paradoxical reduction of serum lipids

BACKGROUND

Human adenovirus-36 (Ad-36) increases adiposity and paradoxically lowers serum cholesterol and triglycerides in chickens, mice, and non-human primates. The role of Ad-36 in human obesity is unknown.

OBJECTIVES

To determine the prevalence of Ad-36 antibodies in obese and nonobese humans. To evaluate the association of Ad-36 antibodies with body mass index (BMI) and serum lipids.

DESIGN

Cohort study. Volunteers from obesity treatment programs, communities, and a research study.

SUBJECTS

Obese and nonobese volunteers at the University of Wisconsin, Madison, WI, and the Bowen Center, Naples, Florida. Obese and thin volunteer research subjects and 89 twin pairs at Columbia University, New York.

INTERVENTIONS

Study 1: 502 subjects; serum neutralization assay for antibodies to Ad-2, Ad-31, Ad-36, and Ad-37; serum cholesterol and triglycerides assays. Study 2: BMI and %body fat in 28 twin pairs discordant for Ad-36 antibodies.

MAIN OUTCOME MEASURES

Presence of antibodies to adenoviruses, BMI, serum cholesterol and triglycerides levels.

RESULTS

Significant (P < 0.001) association of obesity and positive Ad-36 antibody status, independent of age, sex, and collection site. Ad-36 antibodies in 30% of obese, 11% of nonobese. Lower serum cholesterol and triglycerides (P < 0.003) in Ad-36 antibody-positive vs -negative subjects. Twin pairs: antibody-positive twins had higher BMIs (24.5+/-5.2 vs 23.1+/-4.5 kg/m2, P < 0.03) and %body fat (29.6+/-9.5% vs 27.5+/-9.9%, P < 0.04). No association of Ad-2, Ad-31, or Ad-37 antibodies with BMI or serum lipids.

CONCLUSIONS

Ad-36 is associated with increased body weight and lower serum lipids in humans. Prospective studies are indicated to determine if Ad-36 plays a role in the etiology of human obesity.

Human adenovirus Ad-36 promotes weight gain in male rhesus and marmoset monkeys

Although obesity has multiple etiologies, an overlooked possibility is an infectious origin. We previously identified two viruses, SMAM-1, an avian adenovirus (Ad), and Ad-36, a human adenovirus, that produce a syndrome of visceral obesity, with paradoxically decreased serum cholesterol and triglycerides in chickens and mice. In the two studies presented in this paper, we used nonhuman primates to investigate the adiposity-promoting potential of Ad-36. In study 1, we observed spontaneously occurring Ad-36 antibodies in 15 male rhesus monkeys, and a significant longitudinal association of positive antibody status with weight gain and plasma cholesterol lowering during the 18 mo after viral antibody appearance. In study 2, which was a randomized controlled experiment, three male marmosets inoculated with Ad-36 had a threefold body weight gain, a greater fat gain and lower serum cholesterol relative to baseline (P <0.05) than three uninfected controls at 28 wk postinoculation. These studies illustrate that the adiposity-promoting effect of Ad-36 occurs in two nonhuman primate species and demonstrates the usefulness of nonhuman primates for further evaluation of Ad-36-induced adiposity.

Infectobesity: obesity of infectious origin

In the U.S., the prevalence of obesity increased by 30% from 1980 to 1990, and this increase appears to be continuing. Although obesity has multiple etiologies, an overlooked possibility is obesity of an infectious origin. Six pathogens are reported to cause obesity in animals. Canine distemper virus was the first virus reported to cause obesity in mice, followed by Rous-associated virus-7, an avian retrovirus, which has been shown to cause stunting, obesity and hyperlipidemia in chickens. Next, the obesity-promoting effect of Borna disease virus was demonstrated in rats. Scrapie agents were reported to induce obesity in mice and hamsters. The final two reports were of SMAM-1, an avian adenovirus, and Ad-36, a human adenovirus that caused obesity in animals. Additionally, an association with human obesity is the unique feature of SMAM-1 and Ad-36. Although the exact mechanism of pathogen-induced obesity is unclear, infection attributable to certain organisms should be included in the long list of potential etiological factors for obesity. In addition, the involvement of some pathogens in etiology of obesity suggests the possibility of a similar role for additional pathogens.

Transmissibility of adenovirus-induced adiposity in a chicken model

BACKGROUND

We previously reported that human adenovirus Ad-36 induces adiposity and paradoxically lower levels of serum cholesterol (CHOL) and triglycerides (TG) in animals.

OBJECTIVE

To evaluate the transmissibility of Ad-36 and Ad-36 induced adiposity using a chicken model.

DESIGN

Experiment 1--four chickens were housed (two per cage) and one from each cage was inoculated with Ad-36. Duration of presence of Ad-36 DNA in the blood of all chickens was monitored. Experiment 2--two groups of chickens were intranasally inoculated with Ad-36 (infected donors, I-D) or media (control donors, C-D). Blood drawn 36 h later from I-D and C-D groups was inoculated into wing veins of recipient chickens (infected receivers, I-R, and control receivers, C-R, respectively). On sacrifice, 5 weeks post-inoculation, blood was drawn, body weight noted and visceral fat was separated and weighed.

RESULTS

Experiment 1--Ad-36 DNA appeared in the blood of the inoculated chickens and that of uninoculated chickens (cage mates) within 12 h of inoculation and the viral DNA persisted up to 25 days in the blood. Experiment 2--compared with C-D, visceral and total body fat were significantly greater and CHOL significantly lower for the I-D and I-R. TG were significantly lower for the I-D. Ad-36 was isolated from 12 out of 16 blood samples of the I-D that were used for inoculating I-R chickens. Ad-36 DNA was present in the blood and the adipose tissue of the I-D and I-R but not in the skeletal muscles of animals selected randomly for testing.

CONCLUSION

As seen in experiment 1, Ad-36 infection can be transmitted horizontally from an infected chicken to another chicken sharing the cage. Additionally, experiment 2 demonstrated blood-borne transmission of Ad-36-induced adiposity in chickens. Transmissibility of Ad-36-induced adiposity in chicken model raises serious concerns about such a possibility in humans that needs further investigation.

Increased adiposity in animals due to a human virus

BACKGROUND

Four animal models of virus-induced obesity including adiposity induced by an avian adenovirus have been described previously. This is the first report of adiposity induced in animals by a human virus.

OBJECTIVE

We investigated the adiposity promoting effect of a human adenovirus (Ad-36) in two different animal models.

DESIGN

Due to the novel nature of the findings we replicated the experiments using a chicken model three times and a mammal model once. In four separate experiments, chickens and mice were inoculated with human adenovirus Ad-36. Weight matched groups inoculated with tissue culture media were used as non-infected controls in each experiment. Ad-36 inoculated and uninfected control groups were housed in separate rooms under biosafety level 2 or better containment. The first experiment included an additional weight matched group of chickens that was inoculated with CELO (chick embryo lethal orphan virus), an avian adenovirus. Food intakes and body weights were measured weekly. At the time of sacrifice blood was drawn and visceral fat was carefully separated and weighed. Total body fat was determined by chemical extraction of carcass fat.

RESULTS

Animals inoculated with Ad-36 developed a syndrome of increased adipose tissue and paradoxically low levels of serum cholesterol and triglycerides. This syndrome was not seen in chickens inoculated with CELO virus. Sections of the brain and hypothalamus of Ad-36 inoculated animals did not show any overt histopathological changes. Ad-36 DNA could be detected in adipose tissue, but not skeletal muscles of randomly selected animals for as long as 16 weeks after Ad-36 inoculation.

CONCLUSIONS

Data from these animal models suggest that the role of viral disease in the etiology of human obesity must be considered.

Determination of the size of HIV using adenovirus type 2 as an internal length marker

The size of a virion is a key criterion to its proper classification and may have implications in many practical aspects. Size determinations by thin section electron microscopy often result in length aberrations of more than 10% because of a number of preparative and instrumental inaccuracies, e.g. specimen shrinkage or swelling and unreliable calibration. Using adenovirus type 2 as an isometric size marker for internal calibration, we have determined the diameters of mature and immature HIV-1 to be 110 to 128 and 132 to 146 nm, respectively. The marker had been used either as a purified particle suspension added to the HIV producing culture, or adenovirus had been propagated together with HIV by infecting HIV producing cells. Using well characterized isometric markers, e.g. an icosahedral virus, in thin section electron microscopy appears to be a suitable technique for viral size determinations.

Antigenic relationships among the 47 human adenoviruses determined in reference horse antisera

Reference equine antisera to all 47 serotypes of human adenoviruses presently described have been prepared and evaluated by reciprocal neutralization and hemagglutination-inhibition tests. All tests were carried to endpoint dilutions a minimum of five times in each direction to give accurate values for homologous and heterologous antibody titers. Significant cross-reactions in the horse antisera were compared to similar data obtained from rabbit antisera. Using this analysis, major antigenic relationships exist among types 12-18-31 of subgenus A, types 7-11-14 and 34-35 of subgenus B, types 8-9-10, 10-19-37, 13-38-39, 15-22-42, 20-47, 24-32-33-46, and 29-45 of subgenus D, types 16-4 between subgenera B and E, and types 40-41 of subgenus F. Across all subgenera, types 8, 10, 13, 15, 17, 19, 26, 29, 39, 40, and 43 have antigenic moieties found most frequently in other types, averaging 12 heterologous reactions per type when summing both tests in both directions. Types 20, 30, 32, and 45 exhibit shared determinants slightly less often, with a mean of 8 heterologous reactions per type.

Analysis of antigenically intermediate strains of subgenus B and D adenoviruses from AIDS patients

We carried out detailed antigenic and restriction enzyme (RE) analyses on the subgenus B and D adenovirus isolates from 48 AIDS patients. These isolates were unusual both in the diversity of serotypes and in the number of intermediate strains identified. All unusual isolates were strain-purified and tested by serum neutralization (SN) and hemagglutination-inhibition (HI) tests with reference horse and rabbit antisera to all the prototype human adenoviruses; conversely, rabbit antisera were prepared to 16 selected strains from this study and tested by SN and HI with all prototype viruses. Among subgenus B strains, 6 DNA variants of Ad 11 isolates were distinguished by endonucleases BamHI, BglII, BstEII, HindIII, and SmaI. The D 2 variant of Ad 11 was prominent with 5 isolates, and 7 other isolates differed from D 2 in only 1 or 2 enzymes. HindIII was the most discriminative endonuclease for Ad 11 and related strains. Within subgenus D, there were 16 isolates of intermediate strains, including 4 intermediate types related to new Ad types 43-47. The RE patterns of subgenus D strains showed fragment distributions typical of subgenus D, with various unique patterns. Particular care was taken to analyze multiple strains from the same patient, recovered as much as 8 months apart, for evidence of genetic changes. The possible long-term infections with these viruses may provide the opportunity for mutations and recombination to occur, with the resultant generation of a variety of new strains of adenoviruses.