Might cyclodextrin uptake mask antimicrobial activity?

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Could excipients mask a bioactive effect? The team of López-Nicolás J.M. (University of Murcia, Spain) has recently published a curious case involving cyclodextrins (CDs). As antimicrobial resistance is a problem of our society, the use of new drugs or improve current drugs is desirable. Studying the encapsulation profile of citronellal essential oil to establish the basis for new hydrophilic antimicrobial products with good organoleptic properties, the case was found out.

First of all, the group studied the critical micellar concentration of citronellal, data used to calculate the complexation constant with different CDs. In addition, a GC-MS release profile was carried out which, in combination with a sensory analysis, demonstrated that the complex would be interesting for costumers and the odor remained longer than free citronellal oil.

When these authors started to study the antimicrobial combination, the results were surprising because the addition of CDs masked the antimicrobial activity of citronellal. A possible explanation of this could be the use of CDs as carbon source; then, growth rate would be higher than death rate, masking the antimicrobial effect. For that reason, they used acarbose (used here as Glucobay®, an amylase inhibitor) to stop its degradation and the results were an almost complete inhibition of the growth. Even the combination of citronellal with acarbose was better than only citronellal sample.

Fig 1. (A) Effect of the presence of citronellal, HP-β-CD and a mix of both on E. coli and (B) B. subtilis cultures (LB medium at 37 and 30 ºC, respectively). (C) Effect of the presence of Glucobay® with citronellal, HP-β-CD and a mix of both on E. coli and (D) B. subtilis cultures (LB medium at 37 and 30 ºC, respectively).

These results confirmed that growth caused by CD digestion may sometimes be greater than the antimicrobial effect of some agents, and suggest an easy protocol to solve it with approved drugs.

References

Abril-Sánchez C, Matencio A, Navarro-Orcajada S, García-Carmona F,López-Nicolás JM. Evaluation of the properties of the essential oil citronellal nanoencapsulated by cyclodextrins. Chem Phys Lipids. 2019 Mar;219:72-78. doi:10.1016/j.chemphyslip.2019.02.001.