The activity of Aloe arborescens Miller varieties on wound-associated pathogens, wound healing and growth factor production

Various Aloe L. species have been used worldwide to soothe and treat dermal wounds and burns. However, there is a lack of substantiative research on the efficacy of Aloe L. species for wound healing. The aim of this study was to investigate the differences in biological activities of the gel and ethanolic (EtOH) leaf extracts of seven Aloe arborescens Miller varieties. The extracts were investigated for their antibacterial activity against wound-associated bacteria, Staphylococcus aureus (ATCC 6538 and ATCC 25293) and Pseudomonas aeruginosa (ATCC 9027), as well as their nitric oxide (NO) scavenging potential. Varieties with antibacterial activity were further evaluated for wound closure and growth factor stimulation in human keratinocytes (HaCaT). The EtOH leaf extract of the ‘Eloff’ and ‘Jack Marais’ varieties displayed antibacterial activity against S. aureus ATCC 25293 (MIC of 500 and 250 μg/mL, respectively). The EtOH leaf extract of ‘Jack Marais’ displayed an MIC of 500 μg/mL against S. aureus ATCC 6538. The gel extract of ‘Le Roux’ exhibited antioxidant activity with a half maximal inhibitory concentration (IC₅₀ of 2696 ± 582.66 μg/mL). The EtOH leaf extracts of ‘Eloff’ and ‘Jack Marais’ showed significant (p < 0.05) wound closure of 56.06 ± 1.47 and 73.72 ± 0.65%, respectively at 50 μg/mL and the ‘Jack Marais’ gel extract significantly stimulated wound closure (p < 0.05) by 77.02 ± 1.97 and 71.51 ± 1.11% at 50 and 100 μg/mL, respectively. Both the ‘Jack Marais’ gel extract (at 50 and 100 μg/mL) and the EtOH leaf extract (50 μg/mL), significantly (p < 0.05) increased platelet-derived growth factor (PDGF-AA) secretion to 601.09 ± 97.77, 1035.00 ± 913.98 and 559.43 ± 112.52 pg/mL, respectively. The ‘Jack Marais’ EtOH leaf extract exhibited the highest antibacterial activity, whereas the gel extract displayed the greatest potential to stimulate wound closure. This not only suggests a difference in biological activity among varieties but also between the type of extract (gel or leaf).