Case Studies
The following case studies illustrate the application of metabolomics in bioprocess optimization.
Case Study 1: Biochemical Marker Discovery
Figure 2. The results of heat mapping generated through metabolomic analysis and the relevant changes discovered. A heat
map demonstrates the changes over time in metabolites from both the cells and the media (red areas reflect increases over
time; green areas depict decreases). The expanded center section of the heat map shows critical changes, demonstrating that
the sorbitol pathway of glucose use changed during the run.
|
In this study, investigators suspected cells were in an energy- deficient state and were not using glucose efficiently as
the culture progressed. Glucose levels in the media were marginally informative of this suspicion. One goal of the study was
to discover markers that are more robust and descriptive than glucose. Figure 2 shows the results of heat mapping generated
through metabolomic analysis and the relevant changes discovered.
A heat map with a subset of metabolites detected in this study, shown at the left in Figure 2, demonstrates the changes over
time from both the cells and the media (red areas reflect an increase over time; green areas depict a decrease). The expanded
center section of the heat map shows critical changes, demonstrating that the sorbitol pathway of glucose use changed during
the run.
Figure 3. Top: A simplified illustration describing how the sorbitol pathway is another route of glucose use. Sorbitol production
can be induced in times of osmotic stress; at high levels, it can induce apoptosis in some cell types. However, sorbitol is
generally thought to be produced in the presence of elevated glucose levels. Bottom: Sorbitol may be a marker of reduced glucose
use by glycolytic pathways.
|
Figure 3 (top) is a simplified illustration describing how the sorbitol pathway is another route of glucose use. Sorbitol
production can be induced in times of osmotic stress, and at high levels, it can induce apoptosis in some cell types. However,
sorbitol is generally thought to be produced in the presence of elevated glucose levels. Consistent with this idea, the bottom
of Figure 3 shows that sorbitol may be a marker of reduced glucose use by glycolytic pathways (this is not to say that a large
proportion of glucose likely entered the sorbitol pathway, just that a reduced proportion may not be entering glycolysis).
Figure 4. Changes over time in the heat map for data from the cells and the media (red reflects increases over time; green
reflects decreases). The biochemical pathway on the bottom demonstrates that many lipid metabolites changed over time.
|
In contrast to measuring glucose in the experimental media, the sorbitol signal is more pronounced with time. Thus, whether
a marker of reduced glucose use by glycolysis or an indicator of osmotic changes, this metabolomic analysis demonstrated that
sorbitol can be used as a robust marker of cellular changes. It may be possible to use sorbitol levels, in conjunction with
glucose and lactate levels, as a measure of glucose-use efficiency. Clearly, measuring only standard markers would not have
provided a conclusive view of what was actually occurring in the experiment.
|
