Pharmacological screening of traditional medicinal plants used against skin ailments in the Free State, South Africa

[摘要] The skin is the largest organ of the body and it is protected by a composition oflayers. It consists of three main protective layers namely epidermis, dermis andsubcutaneous layer, also known as a fat layer. Its most crucial function is playing akey immunity role in protecting the body by forming a part of a defence andmechanical barrier to the surrounding environment, and thereby preventing invasionby pathogens. The skin is colonized by indigenous microbial flora which comprises ofa broad variety of species, among them are Staphylococccus sp., Propionibacteria,Diptheroids, Micrococcus, Bacillus species and some fungal species which sustainthe health of the skin. The skin can still be susceptible to injuries that allowopportunistic microbial agents to enter the skin. Skin diseases vary from mildconditions which are likely to have an effect on the skin's appearance and can leadto severe conditions which cause disfigurement, disability, and distress or even leadto death. An ethnobotanical survey was conducted and plants used against skininfections were collected and documented. Bark, stem, roots, rhizomes, corms andbulbs were reported to be the most commonly used plant parts. The survey indicatedan oral intake of the decoction or concoction preparation. The study documented 22plant species used by the traditional healers and herbalists of the Free StateProvince of South Africa for the treatment of wounds and skin infections. Eightfrequently used plants, namely Pentanisia prunelloides, Cotyledon orbiculata,Hermannia depressa, Dioscorea sylvatica, Lycopodium clavatum, Merwilla plumbea,Eucomis bicolar, Eucomis autumnalis and Xysmalobium undulatum wereinvestigated for the presence of secondary metabolites, antimicrobial, antioxidantand anti-inflammatory properties.Most plant species tested positive for the presence of saponins, flavonoids, tanninsand terpenoids. Saponins were detected in Pentanisia prunelloides extracts,Hermannia depressa and Cotyledon orbiculata aqueous stem extracts, andXysmalobium undulatum aqueous and ethanol extracts. Flavonoids were present inalmost all plants, particularly P. prunelloides aqueous and ethanol extracts, andaqueous extracts prepared from H. depressa, X. undulatum, and C. orbiculata stem.Tannins were detected in aqueous, ethanol, methanol and acetone extractsprepared from C. orbiculata stem, P. prunelloides and H. depressa. P. prunelloidesshowed a high content of total flavonoids (40.43%), total alkaloids (84.8%), andsaponins (19%). Tannins had an absorbance value of 16.54 mg. Total contentsfound 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 generalphytochemicals might be responsible for the plants' therapeutic and pharmacologicaleffects.P. prunelloides ethanolic extract showed the best activity against Bacillus pumilusand Staphyloccocus aureus (0.098-0.52 mg/ml). Methanol extracts showed the leastactivity, but a progressive inhibition of 0.325 mg/ml against P. aeruginosa wasobserved. H. depressa acetone extract showed the best activity against B. pumilusat 0.098 mg/ml. Aqueous extract displayed good activity against E. coli, S. aureusand 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. prunelloidesorganic 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 methanolicextract 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 ofE. bicolar and L. clavatum displayed good total phenolic content ranging from0.92±0.13 to 1.50±0.13 mg GAE/g. For DPPH scavenging activity, C. orbiculatamethanol extract with an IC50 value of 0.10±0.03 μg/ml, followed by D. slyvaticaaqueous extract (0.12±0.03 μg/ml). The total capacity of antioxidant usingPhosphomolybdenum assay was also investigated with gallic acid as a frame ofreference. The best activity was found in D. sylvatica ethanol extracts with an IC50value of 0.04±0.03 μg/ml. Concerning anti-inflammatory activity using 5-Lipoxygenase assay, L. clavatum and C. orbiculata exhibited a higher antiinflammatoryactivity than that of NDGA and inhibited 5-LOX. L. clavatum ethanolextract displayed the best activity (0.02±0.08 μg/ml). C. orbiculata ethanol extractalso exhibited great activity at 0.09±0.02 μg/ml.

[发布机构] University of the Free State