HEPES in Cell Culture: Properties, Advantages, and Limitations

figure 1 the utility and drawbacks of using HEPES as a supplemental buffering agent in laboratory cell cultures. This chemical is primarily valued for its ability to stabilize pH levels during experiments conducted outside of controlled carbon dioxide environments, maintaining effectiveness across various temperatures. While it offers high solubility and chemical stability, the source emphasizes that it should complement rather than replace the traditional bicarbonate system to ensure healthy cell growth.

HEPES – 4-(2-hydroxyethyl)-1-piperazinetanesulfonic acid – is zwitterionic sulfonic acid commonly used as a buffering agent.

It is added to the culture medium as an auxiliary buffer compared to NaHCO3-/CO2 system, to increase buffering capacity during cell manipulation in ambient air. In atmospheric conditions (CO₂ ≈ 0.03–0.04%), culture media tend to become more alkaline. The addition of HEPES helps counteract this effect and stabilize pH.

HEPES: properties and advantages

HEPES has two dissociation constants:

pKa₁ (25°C) ≈ 3

pKa₂ (25°C) ≈ 7.5

Therefore, its effective buffering ranges are:

– pH 2.5–3.5

– pH 6.8–8.2

Like other “Good’s buffers“, HEPES has properties that make it particularly suitable for cell culture:

High water solubility
Low membrane permeability
Stable acid–base dissociation constants
Low metal chelation
High chemical stability
(resistant to enzymatic and non-enzymatic degradation)
Low absorbance in the UV and visible spectrum
(minimal absorbance between 240–700 nm)
Buffer capacity only minimally affected by:
- concentration
- temperature
- ionic strength

HEPES has a dissociation constant that changes only slightly with temperature.

For example pKa is ≈ 7.55 at 20°C, ≈ 7.48 at 25°C and ≈ 7.31 at 37°C

This limited variation makes HEPES suitable for maintaining stable pH under different temperature conditions.

Can bicarbonate be omitted if HEPES is in the culture medium?

One might assume that adding HEPES makes the bicarbonate–CO₂ buffering system unnecessary.

This is incorrect. Although HEPES can maintain pH, the absence of bicarbonate can limit cell growth in many cell types, particularly at low cell density. (see here and here).

HEPES can complement the bicarbonate–CO₂ system, but it should not replace it under standard cell culture conditions.

Recommended concentrations

HEPES is typically used at concentrations between 10 and 20 mM.

If bicarbonate is also present in the medium, the concentration of HEPES must be about double that of bicarbonate to have maximum buffering capacity.

Limitations

HEPES is not totally biologically inert and you must be aware of the fact that it can influence cellular physiological behavior.

1. Photo-induced toxicity

HEPES can generate reactive oxygen species (ROS) when exposed to light, particularly in the presence of tryptophan and other medium components (Zigler et al., 1985).

To reduce this risk you should store media protected from light (e.g. aluminum foil) and minimize light exposure during handling

2. Cellular uptake

Contrary to early assumptions, HEPES can be taken up by cells (see this pubblication).

Studies have shown uptake in cell lines such as MCF-7, U2OS and HeLa, where HEPES may remain intracellularly for up to 48 hours after medium replacement.

3. Effects on cellular processes

HEPES has been associated with several biological effects, including:

altered uptake of organic molecules (see here or here)
induction or modulation of oxidative stress (see here and here)
inhibition of ion channels (see here)

It has also been observed that:

HEPES can influence the differentiation of certain cell types (e.g. monocyte-derived dendritic cells)
in prion-infected cells, it may inhibit the accumulation of abnormal prion protein (PrPSc) in a concentration-dependent manner (see here)

Conclusion

HEPES is a widely used buffering agent that provides effective pH stabilization, particularly during manipulation outside CO₂-controlled environments.

However, its use should be applied with awareness. HEPES is not a fully physiological buffer and, as discussed above, it presents several limitations that may affect cellular behavior.

For this reason, it is important to consider both its advantages and its potential side effects, while carefully monitoring cell growth, morphology, and overall condition during its use.

In practice, HEPES should be considered a valuable complementary tool rather than a complete replacement for the bicarbonate–CO₂ buffering system.