Diagnosing unhealthy animal cell cultures — if large amounts of lactic acid accumulate in the culture fluid, what is the most likely underlying problem?

Introduction / Context:
Elevated lactate in mammalian culture indicates reliance on glycolysis with pyruvate reduction to lactate instead of mitochondrial oxidation. This often signals oxygen limitation or excessive glycolytic feeding, both of which can harm culture performance.

Given Data / Assumptions:

• Observation: substantial lactic acid accumulation in spent media.
• We are dealing with animal cells, not yeast (so ethanol is not expected).
• We assume typical glucose-containing media.

Concept / Approach:

Under low DO, pyruvate from glycolysis is reduced to lactate to regenerate NAD+, sustaining ATP production via glycolysis. This shift leads to acidification, reduced productivity, and potential apoptosis if prolonged. Therefore oxygen limitation is the most probable root cause.

Step-by-Step Solution:

Verification / Alternative check:

Monitoring DO, OUR/OUR to KLa balance, and pH profiles typically confirms oxygen limitation coinciding with lactate spikes.

Why Other Options Are Wrong:

Mammalian cells do not produce ethanol; hyperoxia would favor oxidation and lower lactate; glycolysis inhibition would decrease, not increase, lactate; glutamine does not force “only oxidative” metabolism.

Common Pitfalls:

Attributing lactate solely to overfeeding rather than also considering oxygen transfer limits; ignoring mixing and KLa constraints in larger vessels.

Final Answer:

Cells do not have enough oxygen, driving anaerobic glycolysis