Comparative Impact of Seasonal Variation on The Skin Depigmentation Activity, Antioxidant Capacities and Phytochemical Constituents of Aspilia Africana (Compositae) And Melanthera Scanden

Medicinal plants are natural sources of affordable, safe and efficient oxidative stress and skin degenerative enzymes inhibitors. Thus, exploring their medicinal properties becomes a great importance and interests to researchers in the field of biomedicine. The present study investigates the comparative impacts of seasonal variation on the medicinal properties of aerial parts of Aspilia africana (Compositae) and Melanthera scanden with an insight of providing clues to further aid the ethnomedicinal applications and traditional uses of the plants. Samplings were carried out in both dry (January and October) and raining (April and July) seasons in Nigeria in the year 2018. Quantitative phytochemical determination of the plant materials includes the in-vitro battery of assays including: phenolics, flavonol and flavanol. Total antioxidant properties of the plants assayed include trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant potential (FRAP). Fe (II)-induced microsomal lipid peroxidation (LPO) assay as well as the tyrosinase inhibition activities of the plants was also evaluated in an in-vtro system. The results of this study showed that the phytochemicals were more concentrated in both plants during dry season than in raining season; both the antioxidant capacities, anti-lipid peroxidation and skin depigmentation inhibitory activities were higher for both plants in the dry than the wet season, The outcome of this study therefore becomes an added value to existing data on Aspilia africana (Compositae) and Melanthera scande. It also showed the best possible time for harvesting the plants for ethnomedicinal applications most especially in terms of their antioxidants and tyrosinase enzyme skin depigmentation activities which can possibly serve as raw materials for cosmetics product formulation. al., Comparative Impact of Seasonal Variation on The Skin Depigmentation Activity, Antioxidant Capacities and Phytochemical Constituents of Aspilia Africana (Compositae) And Melanthera Scanden. Biomed


Introduction
Medicinal plants are cheap sources of antioxidants with the ability to scavenge free radicals, thereby mitigating body exposure to cellular oxidative stress disorders [1]. Free radicals have gained importance in clinical medicine and biological science because of their logical consequences and health implications. Diverse chronic physiological disorders (e.g. skin hyperpigmentation) and degenerative heart related diseases such as early skin aging, coronary heart, inflammation, stroke, diabetes mellitus and cancer are often associated with the presence of free radicals and reactive oxygen species in the body systems [2,3]. The health implications and deleterious effects of free radicals as well as other oxidizing agents have been shown to rescind by plants containing phytochemicals such as flavanol, glycosides flavonoids, flavonol and phenolics [4][5][6]. The free radical scavenging capacity and antioxidant properties of medicinal plants depend largely on their phytochemical constituents while the potential use of plants with these properties for treating human ailments and oxidative stress related diseases have been reported in past and recent literatures [1], [7][8][9]. Some medicinal plants characterized with antioxidant properties have been shown to inhold enzymes inhibition properties. For instance, strong alpha amylase and alpha glucosidase inhibition activities of Triclisia subcordata Oliv was documented [1]. In another study, Hanh et al. showed the Inhibition activity of some Vietnamese folk plants which were aimed to be used in skin-whitening cosmetics [10]. A recent research showed that fermented South African Rooibos (Aspalathus linearis) has significant inhibitory effect on the enzyme tyrosinase present in the skin and they concluded that the plant may be essential in solving problems relating to skin hyperpigmentation [6]. Tyrosinase is a copper-containing enzyme which catalyzes the first two stages of melanin formation [11]. Over accumulation of melanin in the skin result in undesirable dark macromolecular pigment called skin hyperpigmentation [12]. The search for effective and efficient source of natural antioxidants, that can protect the human body from oxidative damage and retard the progress of many chronic oxidative stress related diseases with high safety margins, has therefore focused on the use of plant.
Plants like Aspilia africana (Compositae) and Melanthera scanden are one of medicinal plants considered of great biological importance. Aspilia africana (Compositae) is a semi-woody herb from a perennial woody root that grows up to 2 meters high and widely distributed across tropical Africa including Nigeria [13].
Melanthera scanden is a scandent or scrambling herb of waste thickets, commonly dispersed in the forested areas and extending widely across tropical Africa. The plant is often confused with Aspilia africana and has similar medicinal uses. It is known to provide forage for all stock in thicket edges around villages. On the other hand, both Aspilia africana (Compositae) and Melanthera scanden are fast-growing weeds of cultivation becoming troublesome in the southern Nigeria and in the western Cameroon where there are deemed a pest on oil-palm plantations. With haemostatic preparations they are used on cuts and wounds [14].
They are said to possess the ability to draw up exudations from open sores and promote healing as well as curbing inflammation [15,16]. Antidiabietic, antimicrobial, antioxidant, hypolipidemic, anti-inflammatory and antiplasmodial activities of the plants have been reported [14] [17][18][19][20]. The present study therefore focus on

A. Total Polyphenol
The total polyphenolic content of the plants extract was determined using the Folin-Ciocalteu method as described with little modification [1]. Folin-Ciocalteu reagent and Distilled water were added to a 125μL of each solvent extract. Each mixture was allowed to stand for 10 min before the addition of sodium carbonate solution (7.0 % w/v). The resultant mixture was allowed to stand for 120 min; absorbance was thereafter read at 760 nm on a SpectrumLab70 Spectrophotometer. A gallic acid standard curve was obtained for the calculation of polyphenolic content and the result was expressed in terms of gallic acid in mg/mL of extract. The experiment was carried out in triplicate.

Determination of Flavanol
The Flavanol content of each extract was determined in accordance to a previously described [21]. A 0.05%

4-dimethylaminocinnamaldehyde (DMACA) solution (25 mL) was
added to 50 mg of each solvent extract. Each mixture was allowed to stand for 30 min; absorbance was read at 640 nm. The result was expressed in terms of catechin equivalents in mg CE/g of extract.
The determination was carried out in triplicate.

Determination of Flavonol
The flavonol content of the samples was determined by adopting the method described [22].

Statistical Analysis
The data presented in all the experiments are means ± SD    In Table 2 (Table 2). These results may be justified by concentration values of the evaluated phytochemicals;

Results and Discussion
such that the higher the concentration of the phytochemicals in the plant, the higher the antioxidant capacities of the plants tend to be and vice versa. This trend was also observed in the works reported [1]. Overall, the results this study thus confirm the potency of the plant materials to scavenge free radicals, while the properties also vary with season. In Table 3

Conclusion
In support of previous studies, the present study has confirmed the presence of phenolics, flavanol and flavonol in the evaluated