predictors of emerging childhood obesity

RESEARCH ARTICLE Open Access

Salivary epigenetic biomarkers as predictors of emerging childhood obesity Amanda Rushing1, Evan C. Sommer2, Shilin Zhao3, Eli K. Po’e4 and Shari L. Barkin5*

Abstract

Background: Epigenetics could facilitate greater understanding of disparities in the emergence of childhood obesity. While blood is a common tissue used in human epigenetic studies, saliva is a promising tissue. Our prior findings in non-obese preschool-aged Hispanic children identified 17 CpG dinucleotides for which differential methylation in saliva at baseline was associated with maternal obesity status. The current study investigated to what extent baseline DNA methylation in salivary samples in these 3–5-year-old Hispanic children predicted the incidence of childhood obesity in a 3-year prospective cohort.

Methods: We examined a subsample (n = 92) of Growing Right Onto Wellness (GROW) trial participants who were randomly selected at baseline, prior to randomization, based on maternal phenotype (obese or non-obese). Baseline saliva samples were collected using the Oragene DNA saliva kit. Objective data were collected on child height and weight at baseline and 36 months later. Methylation arrays were processed using standard protocol. Associations between child obesity at 36 months and baseline salivary methylation at the previously identified 17 CpG dinucleotides were evaluated using multivariable logistic regression models.

Results: Among the n = 75 children eligible for analysis, baseline methylation of Cg1307483 (NRF1) was significantly associated with emerging childhood obesity at 36-month follow-up (OR = 2.98, p = 0.04), after adjusting for child age, gender, child baseline BMI-Z, and adult baseline BMI. This translates to a model-estimated 48% chance of child obesity at 36-month follow-up for a child at the 75th percentile of NRF1 baseline methylation versus only a 30% chance of obesity for a similar child at the 25th percentile. Consistent with other studies, a higher baseline child BMI-Z during the preschool period was associated with the emergence of obesity 3 years later, but baseline methylation of NRF1 was associated with later obesity even after adjusting for child baseline BMI-Z.

Conclusions: Saliva offers a non-invasive means of DNA collection and epigenetic analysis. Our proof of principle study provides sound empirical evidence supporting DNA methylation in salivary tissue as a potential predictor of subsequent childhood obesity for Hispanic children. NFR1 could be a target for further exploration of obesity in this population.

Keywords: Obesity, Hispanic children, Epigenetics, Methylation, Saliva

Background The prevalence of pediatric obesity has been increasing at an alarming rate in the last forty years [1, 2]. Although pediatric obesity prevalence is a global issue, the United States is facing epidemic levels of pediatric obesity [3, 4]. The Center for Disease Control and Prevention indicates that the prevalence of obesity among children aged 2– 19 years old has risen from 13.9% in 2000 to 18.5% in

2016 [5]. However, some ethnic groups have an even higher obesity prevalence [1, 6]. For example, the 2015– 2016 National Health and Nutrition Examination Survey (NHANES) reported 25.8% of Hispanic 2–19 year-olds were obese compared to 14.1% of their non-Hispanic white counterparts [7]. Identifying what influences dif- ferent populations is critical to successfully reducing obesity-related health disparities. Childhood is a particularly sensitive period for neuro-

logical, endocrine, and metabolic development. For ex- ample, obesity at a young age contributes to an

© The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

* Correspondence: shari.barkin@vumc.org 5Department of Pediatrics, Vanderbilt University School of Medicine, 2200 Children’s Way, Doctor’s Office Tower 8232, Nashville, TN 37232-9225, USA Full list of author information is available at the end of the article

Rushing et al. BMC Medical Genetics (2020) 21:34 https://doi.org/10.1186/s12881-020-0968-7

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increased risk of diabetes, hypertension, and cardiovas- cular disease in adulthood [8–10]. Recent literature indi- cates that susceptibility to obesity within an “obesogenic” environment differs among individuals [11, 12]. It is not clear what mechanisms are responsible for obesity variation, but many studies identify a dynamic interaction of genetic and environmental exposures at sensitive periods of development [13, 14]. While mono- genic DNA mutations exist and are associated with obesity, common forms of childhood obesity have frus- trated the scientific community with the so-called prob- lem of missing heritability. It appears that obesity is a multi-trait, multi-state phenotype. The field of epigenet- ics, modifications that affect transcriptional plasticity, might offer insights into the emerging phenotype of childhood obesity. Epigenetic patterns, often measured by DNA methylation, change rapidly in response to en- vironmental factors such as nutrition and physical activ- ity and are specifically vulnerable to changes during early childhood development. Moreover, epigenetic pat- terns vary between ethnic groups and could explain dif- fering susceptibility to early emerging obesity and its commonly associated later chronic diseases [15–18]. Epigenetic patterns are tissue-dependent. While blood

is a common tissue used in studies of human epigenetic changes, saliva is also a promising tissue. Saliva could be particularly valuable in studying pediatric populations given the ease of tissue access, cost-efficiency, and the ability to collect it in multiple settings [19, 20]. Abraham and colleagues illustrated that when comparing DNA fragmentation, quality, and genotype concordance, saliva is comparable to blood samples [21]. When examining methylation patterns, both saliva and blood reliably as- sess epigenetic modifications [22]. In comparing the col- lection of blood and saliva samples, saliva collection is associated with lower infection rates, decreased cost, in- creased patient acceptance,