Antibacterial and anti-inflammatory activity of Syzygium jambos and Leucosidea sericea in addressing acne vulgaris

Abstract

Acne is a common universal condition which affects all ages and can have a significant impact on psychosocial and physical aspects of a person’s life. Etiologically, it is a multifactorial skin disorder which is associated with pilosebaceous unit of the skin. Production of increased amount of sebum by the sebaceous gland is accompanied by the thickening of epidermis at the outlet to the pilosebaceous follicles. As a result, there is an obstruction to the flow of sebum outwards, and a comedo develops. Propionibacterium acnes, the causative agent plays a crucial role in the pathogenesis. Their colonization triggers the host’s inflammatory response and leads to the production of inflammatory cytokines like interleukin-8 (IL-8) and tumour necrosis factor-α (TNF-α). Simultaneously, in anaerobic environment, the bacteria secrete various hydrolytic enzymes such as, nucleases, nuraminidases, hyaluronidases, acid phosphatases lecithinases and other lipases. Due to action of these enzymes, the sebum content changes and reactive oxygen species (ROS) may be released from the impacted damaged follicular walls. All these events result in the progression of inflammation and the pathogenesis of disease. Ethnobotanical studies have documented the use of plants by local people for the treatment of various skin ailments. Also, plants contain numerous biological active compounds, many of which have been shown to possess antimicrobial activity. The current study focuses on the high potency of two plants namely, Syzygium jambos and Leucosidea sericea for their future use as an alternative treatment of acne. From an in vitro antibacterial evaluation of 51 ethanol plant extracts against P. acnes, the aforesaid two plants were found to be the most active, with minimum inhibitory concentration (MIC) values of 31.25 (S. jambos) and 15.62 μg/ml (L. sericea). Subsequent fractionation of S. jambos extract resulted in the isolation of squalene, an anacardic acid analogue and ursolic acid for the first time from this plant. Similarly, fractionation of L. sericea extract resulted in the isolation of phytol acetate, triacontanol, phytol, (E)-3,7,11,15-tetramethylheptadec-2-ene-1,17-diol and alpha kosin for the first time form this plant. Of all the isolated compounds, anacardic acid analogue and alpha kosin were found to be the only active compounds against P. acnes (MIC 7.81 and 1.95 μg/ml, respectively). The transmission electron microscopy (TEM) confirmed the lethality of plant extracts and bioactive compounds on the cells of P. acnes. The extract of S. jambos was found to be non-toxic to mouse melanoma B16-F10 cells and human macrophage U937 cell lines with EC50 (concentration at which 50% cells are viable) values of 450 and 60 μg/ml, respectively. Whereas, L. sericea extract exhibited moderate toxicity to B16-F10 cells (EC50 55 μg/ml) and a comparatively higher toxicity to U937 cells (EC50 26 μg/ml). Of all the isolated compounds, only alpha kosin and a commercially acquired compound, ‘myricetin’, were found to be toxic to both cell lines with EC50 values of <20 μg/ml. The significant antioxidant activity was shown by the extracts of S. jambos, L. sericea, isolated compound alpha kosin, commercially acquired compounds- myricetin, myricitrin and gallic acid with EC50 (concentration at which 50% free radical is scavenged) values varying from 0.9-5.1 μg/ml, comparable to vitamin C (EC50 2 μg/ml), a known antioxidant agent. A significant inhibition of IL-8 and TNF-α was observed for S. jambos, L. sericea, ursolic acid and myricitrin. The aqueous extract of S. jambos and L. sericea in 1:1 combination showed synergism and inhibited the growth of P. acnes at 0.7% (650 μg/ml), comparable to Cytobiol Iris A2, a commercial anti-acne ingredient. The aqueous extract of L. sericea and S. jambos+L. sericea (1:1) showed hydrating potential for 24 h in an in vivo study performed at Future Cosmetics, Pretoria.