Although obesity is associated with increased risks from development of metabolic and cardiovascular disease, among other sequelae, there is a subpopulation that remains in good health. Termed metabolically healthy obesity (MHO), these individuals do not progress into disease states such as type 2 diabetes and cardiovascular dysfunction that lead to disability and premature death. Doumatey et al. (2016) examined the serum proteome for prognostic biomarkers that might guide clinicians in providing health advice to their obese patients.1
Using a shotgun proteomics approach with label-free quantitation, the researchers characterized the serum proteomes of 20 African American individuals classified as obese. This group comprised 10 MHO individuals and 10 obese controls diagnosed as unhealthy (metabolically abnormal obesity [MAO]). The MAO individuals presented with hypertension, elevated blood glucose in the absence of overt type 2 diabetes, high homeostatic model assessment insulin resistance values, and raised levels of C-reactive protein (CRP) and lipid parameters (triglyceride and high-density lipoprotein). In contrast, MHO individuals showed no hypertension, diabetes, lipid abnormalities or CRP elevation.
Following collection, researchers depleted abundant proteins from the serum with a commercial immunoaffinity spin column protocol. They then digested the proteins with trypsin before fractionating the peptides by strong cation exchange chromatography. The team then characterized serum proteomes using reverse-phase liquid chromatography–tandem mass spectrometry (RPLC-MS/MS) on an LTQ ion trap mass spectrometer (Thermo Scientific) operated in data-dependent acquisition mode. They searched spectral data by interrogating the UniProt human proteomic database with SEQUEST.
The initial MS/MS scans found 16,553 proteins. However, Doumatey et al. refined this data set by excluding those not represented in both MAO and MHO serum proteomes. They conducted further analysis on the remaining proteins, finding that 56 showed differential expression between the two groups (33 increased in MHO individuals, while 23 decreased). With statistical testing, the researchers concentrated on a subset of 20 proteins, showing that 12 increased in expression and eight decreased in the MHO subjects.
Doumatey et al. then employed ingenuity pathway analysis to concentrate on signaling pathways affected by the altered protein expression. They found that individuals with MHO showed a reduction in the harmful pathways that are usually upregulated in obesity. These included lipid handling and inflammation pathways, with specific reference to the acute phase response.
In this exploratory study, the authors conducted a search for prognostic biomarkers with a high-throughput –omics approach. The data suggest that individuals with MHO show downregulation of harmful pathways usually exacerbated by obesity. Since 10–40% of obese individuals fit this category, with many of them retaining this health status for life, a prognostic serum biomarker could aid clinical management to prevent later conversion into MAO.
However, the researchers strongly suggest that the results from this discovery study be verified by exploring proteome characterization in a larger and more diverse population before they are taken as genuinely reflective of MHO. Furthermore, Doumatey et al. make no claims for causality in their interpretation and note that the study design did not take potential influence of external factors such as physical activity and diet on the serum proteome into consideration.
1. Doumatey, A.P., et al. (2016) “Proinflammatory and lipid biomarkers mediate metabolically healthy obesity: A proteomics study,” Obesity, 24(6) (pp. 1257–1265), doi:10.1002/oby.21482.