Nikhil V. Dhurandhar

Putative contributors to the secular increase in obesity: exploring the roads less traveled

Objective:To investigate plausible contributors to the obesity epidemic beyond the two most commonly suggested factors, reduced physical activity and food marketing practices.Design:A narrative review of data and published materials that provide evidence of the role of additional putative factors in contributing to the increasing prevalence of obesity.Data:Information was drawn from ecological and epidemiological studies of humans, animal studies and studies addressing physiological mechanisms, when available.Results:For at least 10 putative additional explanations for the increased prevalence of obesity over the recent decades, we found supportive (although not conclusive) evidence that in many cases is as compelling as the evidence for more commonly discussed putative explanations.Conclusion:Undue attention has been devoted to reduced physical activity and food marketing practices as postulated causes for increases in the prevalence of obesity, leading to neglect of other plausible mechanisms and well-intentioned, but potentially ill-founded proposals for reducing obesity rates.

Ten Putative Contributors to the Obesity Epidemic

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

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.

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.

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.

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.

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.

Short-Term Effect of Eggs on Satiety in Overweight and Obese Subjects

Objective: To test the hypotheses that among overweight and obese participants, a breakfast consisting of eggs, in comparison to an isocaloric equal-weight bagel-based breakfast, would induce greater satiety, reduce perceived cravings, and reduce subsequent short-term energy intake. Subjects: Thirty women with BMI’s of at least 25 kg/M2 between the ages of 25 to 60 y were recruited to participate in a randomized crossover design study in an outpatient clinic setting. Design: Following an overnight fast, subjects consumed either an egg or bagel-based breakfast followed by lunch 3.5 h later, in random order two weeks apart. Food intake was weighed at breakfast and lunch and recorded via dietary recall up to 36 h post breakfast. Satiety was assessed using the Fullness Questionnaire and the State-Trait Food Cravings Questionnaire, state version. Results: During the pre-lunch period, participants had greater feelings of satiety after the egg breakfast, and consumed significantly less energy (kJ; 2405.6 ± 550.0 vs 3091.3 ± 445.5, Egg vs Bagel breakfasts, p < 0.0001), grams of protein (16.8 ± 4.2 vs 22.3 ± 3.4, Egg vs Bagel breakfasts, p < 0.0001), carbohydrate 83.1 ± 20.2 vs 110.9 ± 18.7, Egg vs Bagel breakfasts, p < 0.0001), and fat 19.4 ± 5.1 vs 22.8 ± 3.2, Egg vs Bagel breakfasts, p < 0.0001) for lunch. Energy intake following the egg breakfast remained lower for the entire day (p < 0.05) as well as for the next 36 hours (p < 0.001). Conclusions: Compared to an isocaloric, equal weight bagel-based breakfast, the egg-breakfast induced greater satiety and significantly reduced short-term food intake. The potential role of a routine egg breakfast in producing a sustained caloric deficit and consequent weight loss, should be determined.

Adipogenic Human Adenovirus Ad-36 Induces Commitment, Differentiation, and Lipid Accumulation in Human Adipose-Derived Stem Cells

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

Human adenovirus Ad-36 induces adipogenesis via its E4 orf-1 gene.

Objective:Understanding the regulation of adipocyte differentiation by cellular and extracellular factors is crucial for better management of chronic conditions such as obesity, insulin resistance and lipodystrophy. Experimental infection of rats with a human adenovirus type 36 (Ad-36) improves insulin sensitivity and promotes adipogenesis, reminiscent of the effect of thiozolinediones. Therefore, we investigated the role of Ad-36 as a novel regulator of the adipogenic process.Design and Results:Even in the absence of adipogenic inducers, infection of 3T3-L1 preadipocytes and human adipose-derived stem cells (hASC) by Ad-36, but not Ad-2 that is another human adenovirus, modulated regulatory points that spanned the entire adipogenic cascade ranging from the upregulation of cAMP, phosphatidylinositol 3-kinase and p38 signaling pathways, downregulation of Wnt10b expression, and increased expression of CCAAT/enhancer binding protein-β and peroxisome proliferator-activated receptor γ2 and consequential lipid accumulation. Next, we identified that E4 open reading frame (orf)-1 gene of the virus is necessary and sufficient for Ad-36-induced adipogenesis. Selective knockdown of E4 orf-1 by RNAi abrogated Ad-36-induced adipogenic signaling cascade in 3T3-L1 cells and hASC. Compared to the null vector, selective expression of Ad-36 E4 orf-1 in 3T3-L1 induced adipogenesis, which was abrogated when the PDZ-binding domain of the protein was deleted.Conclusion:Thus, Ad-36 E4 orf-1 is a novel inducer of rodent and human adipocyte differentiation process.