The proteome is defined as the set of all expressed
proteins in a cell, tissue or organism.9 Proteomics
aims to characterise information flow within the
cell and the organism, through protein pathways
and networks,10 with the eventual aim of
understanding the functional relevance of
proteins.11While we can gain much information
from proteomic investigation, it is complicated by
its domain size (>100 000 proteins) and the
inability to detect accurately low-abundance
proteins. The proteome is a dynamic reflection of
both genes and the environment and is thought to
hold special promise for biomarker discovery
because proteins are most likely to be ubiquitously
affected in disease and disease response.12 This is
reflected in the many protein disease biomarkers
already available (e.g. CA125 and alpha-fetoprotein).
Metabolomics can generally be defined as the study
of global metabolite profiles in a system (cell, tissue
or organism) under a given set of conditions.13
Metabolomics has a number of theoretical
advantages over the other omic approaches. The
metabolome is the final downstream product of
gene transcription and, therefore, changes in the
metabolome are amplified relative to changes in the
transcriptome and the proteome.14Additionally, as
the downstream product, the metabolome is closest
to the phenotype of the biological system studied.
Although the metabolome contains the smallest
domain (~5000 metabolites), it is more diverse,
containing many different biological molecules,
making it more physically and chemically complex
than the other ‘omes’.