The effect of botulinum toxin type A in different dilution on the contraction of fibroblast-In vitro study

Botulinum toxin type A (BoNT-A) may directly remodel dermal tissues or induce a loss of normal morphology and cytoplasmic retraction and spread. Intradermal injection was claimed to produce a dermo-lifting effect, including midface lifting by using low concentration with variable dilution.

To understand how intradermal BoNT-A achieves tissue lifting, we examined different type of BoNT-A and their effects on dermal fibroblast contraction.

Normal human dermal fibroblasts were treated with onabotulinumtoxin (ONA), abobotulinumtoxin (ABO), prabotulinumtoxinA (PRABO), incobotulinumtoxinA (INCO), and letibotulinumtoxin A (LETI) in dilutions used in real-world practice. Fifty fibroblasts per dilution were photographed and measured the length to demonstrate their contraction every 2 hours from baseline (0 hours) to 12 hours post-treatment.

ONA did not significantly decrease fibroblast lengths, at any timepoint or dilution. At 1:7 dilution ratios, ABO decreased fibroblast lengths after 2 hours and significantly after 10-12 hours. At 1:7, 1:8, 1:9, and 1:10 dilution, PRABO decreased length, and most rapidly at 1:7 and 1:8. At 1:6, 1:8, 1:9, and 1:10 dilution, INCO decreased lengths almost immediately. At 1:6 dilution, INCO decreased lengths almost immediately. At 1:7 dilution, INCO decreased lengths after 2-4 hours, while at 1:8, 1:9, and 1:10 dilution, INCO decreased lenghts nearly imediately. LETI decreased lengths at all dilutions except 1:9, with near-immediate effects at 1:6, 1:7, 1:8, and 1:10. At 1:4 dilution, LETI decreased lengths from 1 hour.

Different commercial preparations of BoNT-A toxins cause different fibroblast contractions in vitro. Product selection and dilution used may affect the clinical outcome of intradermal injection of BoNT-A for face lifting.