Abstract:
The Gram-positive bacterium Cutibacterium acnes (previously Propionibacterium acnes),
plays an important role in the pathogenesis and progression of the dermatological skin
disorder acne vulgaris. The methanolic extract of Helichrysum odoratissimum (L.) Sweet
(HO-MeOH) was investigated for its ability to target bacterial growth and pathogenic
virulence factors associated with acne progression. The gas chromatography–mass
spectrometry (GC-MS) analysis of HO-MeOH identified a-humulene (3.94%), acurcumene (3.74%), and caryophyllene (8.12%) as major constituents, which correlated
with previous reports of other Helichrysum species. The HO-MeOH extract exhibited
potent antimicrobial activity against C. acnes (ATCC 6919) with a minimum inhibitory
concentration (MIC) of 7.81 µg/ml. It enhanced the antimicrobial activity of benzoyl
peroxide (BPO). The extract showed high specificity against C. acnes cell aggregation
at sub-inhibitory concentrations, preventing biofilm formation. Mature C. acnes biofilms
were disrupted at a sub-inhibitory concentration of 3.91 µg/ml. At 100 µg/ml, HO-MeOH
reduced interleukin-1a (IL-1a) cytokine levels in C. acnes-induced human keratinocytes
(HaCaT) by 11.08%, highlighting its potential as a comedolytic agent for the treatment of
comedonal acne. The extract exhibited a 50% inhibitory concentration (IC50) of 157.50 µg/
ml against lipase enzyme activity, an enzyme responsible for sebum degradation,
ultimately causing inflammation. The extract’s anti-inflammatory activity was tested
against various targets associated with inflammatory activation by the bacterium. The
extract inhibited pro-inflammatory cytokine levels of IL-8 by 48.31% when compared to C.
acnes-induced HaCaT cells at 7.81 µg/ml. It exhibited cyclooxygenase-II (COX-II) enzyme
inhibition with an IC50 of 22.87 µg/ml. Intracellular nitric oxide (NO) was inhibited by
40.39% at 7.81 µg/ml when compared with NO production in lipopolysaccharide (LPS)-
induced RAW264.7 cells. The intracellular NO inhibition was potentially due to the 2.14
fold reduction of inducible nitric oxide synthase (iNOS) gene expression. The HO-MeOH
extract exhibited an IC50 of 145.45 µg/ml against virulent hyaluronidase enzyme activity, which is responsible for hyaluronan degradation and scar formation. This study provides
scientific validation for the traditional use of H. odoratissimum as an ointment for pimples,
not only due to its ability to control C. acnes proliferation but also due to its inhibitory
activity on various targets associated with bacterial virulence leading to acne progression.
