Pharmacological screening of traditional medicinal plants used against skin ailments in the Free State, South Africa
Xaba, Valeria Makhosazana
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The skin is the largest organ of the body and it is protected by a composition of layers. It consists of three main protective layers namely epidermis, dermis and subcutaneous layer, also known as a fat layer. Its most crucial function is playing a key immunity role in protecting the body by forming a part of a defence and mechanical barrier to the surrounding environment, and thereby preventing invasion by pathogens. The skin is colonized by indigenous microbial flora which comprises of a broad variety of species, among them are Staphylococccus sp., Propionibacteria, Diptheroids, Micrococcus, Bacillus species and some fungal species which sustain the health of the skin. The skin can still be susceptible to injuries that allow opportunistic microbial agents to enter the skin. Skin diseases vary from mild conditions which are likely to have an effect on the skin’s appearance and can lead to severe conditions which cause disfigurement, disability, and distress or even lead to death. An ethnobotanical survey was conducted and plants used against skin infections were collected and documented. Bark, stem, roots, rhizomes, corms and bulbs were reported to be the most commonly used plant parts. The survey indicated an oral intake of the decoction or concoction preparation. The study documented 22 plant species used by the traditional healers and herbalists of the Free State Province of South Africa for the treatment of wounds and skin infections. Eight frequently used plants, namely Pentanisia prunelloides, Cotyledon orbiculata, Hermannia depressa, Dioscorea sylvatica, Lycopodium clavatum, Merwilla plumbea, Eucomis bicolar, Eucomis autumnalis and Xysmalobium undulatum were investigated for the presence of secondary metabolites, antimicrobial, antioxidant and anti-inflammatory properties. Most plant species tested positive for the presence of saponins, flavonoids, tannins and terpenoids. Saponins were detected in Pentanisia prunelloides extracts, Hermannia depressa and Cotyledon orbiculata aqueous stem extracts, and Xysmalobium undulatum aqueous and ethanol extracts. Flavonoids were present in almost all plants, particularly P. prunelloides aqueous and ethanol extracts, and aqueous extracts prepared from H. depressa, X. undulatum, and C. orbiculata stem. Tannins were detected in aqueous, ethanol, methanol and acetone extracts prepared from C. orbiculata stem, P. prunelloides and H. depressa. P. prunelloides showed a high content of total flavonoids (40.43%), total alkaloids (84.8%), and saponins (19%). Tannins had an absorbance value of 16.54 mg. Total contents found in H. depressa were flavonoids (9.70%), alkaloids (7.0%) and saponins (5%). X. undulatum showed small and limited amounts of total content values, flavonoids (4.50%), alkaloids (6.7%), and saponins (9%). The presence of most general phytochemicals might be responsible for the plants’ therapeutic and pharmacological effects. P. prunelloides ethanolic extract showed the best activity against Bacillus pumilus and Staphyloccocus aureus (0.098-0.52 mg/ml). Methanol extracts showed the least activity, but a progressive inhibition of 0.325 mg/ml against P. aeruginosa was observed. H. depressa acetone extract showed the best activity against B. pumilus at 0.098 mg/ml. Aqueous extract displayed good activity against E. coli, S. aureus and P. aeruginosa with the MIC values of 0.098, 0.36 and 0.195 mg/ml, respectively. Lycopodium clavatum acetone extract displayed good minimum inhibition against S. aureus (0.39 mg/ml), and against P. aeruginosa (0.098 mg/ml). Concerning antifungal activity, the best inhibition was observed with P. prunelloides organic solvents (0.049 mg/ml). H. depressa extracts also showed low MIC values (0.049 mg/ml-0.33 mg/ml). The total phenolic content was determined and recorded as gallic acid equivalents. Extracts that showed the highest phenolic content were H. depressa, C. orbiculata, Dioscorea slyvatica, Eutumnalis bicolar and L. clavatum. H. depressa methanolic extract had the highest phenolic content at 2.09±0.07 mg GAE/g, followed by C. orbiculata acetone extract at 1.48±0.64 mg GAE/g. Acetone and ethanol extracts of E. bicolar and L. clavatum displayed good total phenolic content ranging from 0.92±0.13 to 1.50±0.13 mg GAE/g. For DPPH scavenging activity, C. orbiculata methanol extract with an IC50 value of 0.10±0.03 μg/ml, followed by D. slyvatica aqueous extract (0.12±0.03 μg/ml). The total capacity of antioxidant using Phosphomolybdenum assay was also investigated with gallic acid as a frame of reference. The best activity was found in D. sylvatica ethanol extracts with an IC50 value of 0.04±0.03 μg/ml. Concerning anti-inflammatory activity using 5- Lipoxygenase assay, L. clavatum and C. orbiculata exhibited a higher antiinflammatory activity than that of NDGA and inhibited 5-LOX. L. clavatum ethanol extract displayed the best activity (0.02±0.08 μg/ml). C. orbiculata ethanol extract also exhibited great activity at 0.09±0.02 μg/ml.