Searching for new natural bioactive capping agents represent an urgent priority in the green synthesis of metal nanoparticles. Additionaly, the biosaftey of metal nanparticles is a major concern especially in medical applications. Recently, the use of pharmacollogicaly active natural products as capping agents has been deployed to avoid toxic effects during the nanoparticles preparation and to enhance their drugability compared with convential drugs. Helichrysum foetidum is a South African medicinal plant used in folk medicine for the treatment of different human pathologies, and it is known to contain a variety of bioactive compounds. Herein, the total extract and two pure chalcones, helichrysetin and helichrysin, isolated from the same plant were successfully used to synthesize quasi-monodispersed gold nanoparticles in the size range of 2-12 nm. The bio-evaluation of samples indicated that the AuNP/capping agent conjugates are biostable, and have different biological profiles from the total extract/pure compounds. The enzymatic inhibition assays showed significant inhibition by the total extract, helichrysetin and their gold nanoparticles. Interestingly, a similar activity was observed for glucose uptake in HEK293 treated cells. On the other hand, all the tested samples relatively demonstrated no cytotoxicity when tested against the HaCaT keratinocytes. In conclusion, the study demonstrated potential enhancement of glucose uptake in mammalian kidney cells, and inhibition of carbohydrate-hydrolysing enzymes by green synthesized gold nanoparticles of H. foetidum. It also provides a therapeutic appraisal of AuNPs/chalcones conjugate towards the development of antidiabetes drugs derived from H. foetidum and its gold nanoparticles.

The global management of diabetes mellitus (DM) involves the administration of recommended anti-diabetic drugs in addition to a non-sedentary lifestyle upon diagnosis. Despite the success recorded from these synthetic drugs, the traditional method of treatment using medicinal plants is increasingly accepted by the locals due to its low cost and the perceived no side effects. Helichrysum species are used in folk medicine and are documented for the treatment of DM in different regions of the world. This study reviews Helichrysum species and its compounds’ activities in the management of DM. An extensive literature search was carried out, utilizing several scientific databases, ethnobotanical books, theses, and dissertations. About twenty-two Helichrysum species were reported for the treatment of diabetes in different regions of the world. Among these Helichrysum species, only fifteen have been scientifically investigated for their antidiabetic activities, and twelve compounds were identified as bioactive constituents for diabetes. This present review study will be a useful tool for scientists and health professionals working in the field of pharmacology and therapeutics to develop potent antidiabetic drugs that are devoid of side effects.

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Skin cells suffer continuous damage from chronic exposure to ultraviolet light (UV) that may result in UV-induced oxidative stress and skin thinning. This has necessitated the formulation of cosmeceutical products rich in natural antioxidants and free radical scavengers. Aspalathus linearis (rooibos) is an endemic South African fynbos plant growing naturally in the Western Cape region. The plant is rich in phenolics and other bioactives with a wide spectrum of health benefits. The chemical study of an acetonic extract of green A. linearis afforded a novel compound named linearthin (1) and two known dihydrochalcones, aspalathin (2) and nothofagin (3). The chemical structure of the novel compound was elucidated based on spectroscopic data analysis. The bio-evaluation of the isolated chalcones in vitro for protection against UVB-induced oxidative stress were systematically assessed by examining cell viability, metabolic activity, apoptosis, and cytotoxicity using HaCaT and SK-MEL-1 skin cells models. It was observed that pre-treatment with tested samples for 4- and 24 h at low concentrations were sufficient to protect skin cells from UVB-induced damage in vitro as evidenced by higher cell viability and improved metabolic activity in both keratinocytes (HaCaT) and melanocytes (SK-MEL-1). The results further show that the pre-treatment regimen employed by this study involved some degree of cellular adaptation as evidenced by higher levels of reduced glutathione with a concomitant decrease in lipid peroxidation and lowered caspase 3 activity. Furthermore, compound 1 was most cytoprotective against UVB irradiation of HaCaT cell line (over 24 h) with an IC50 of 282 µg/mL and SK-MEL-1 cell line with IC50 values of 248.3 and 142.6 µg/mL over 4 and 24 h, respectively. On the other hand, HaCaT cells exposed to 2 over 4 h before UVB irradiation showed the highest degree of cytoprotection with an IC50 of 398.9 µg/mL among the four studied samples. These results show that linearthin (1) and the two glycoside dihydrochalcone of A. linearis have the potential to be further developed as antioxidant cosmeceutical ingredients that may protect skin against UVB-induced damage.

The green chemistry approach has continuously been applied for the synthesis of functional nanomaterials to reduce waste, environmental hazards, and the use of toxic chemicals among other reasons. Bioactive natural compounds have been found great potential in this regard and are used to improve the stability, activity, and biodistribution of metal nanoparticles (MNPs). Aspalathin (ASP) from Aspalathus linearis (rooibos) has a well-defined pharmacological profile and functional groups capable of both reducing and capping agents in the synthesis of metallic nanoparticles (NP). This study provides the first report of the phytomediated synthesis of gold and silver nanoparticles (AuNPs/AgNPs) via ASP and the green rooibos (GR) extract. The study demonstrated a green chemistry approach to the biosynthesis of nanoparticles of GR-AuNPs, ASP-AuNPs, GR-AgNPs, and ASP-AgNPs. The results showed that GR and ASP could act both as reducing and stabilising agents in the formation of crystalline, with different shapes and dispersity of NPs in the ranges of 1.6–6.7 nm for AgNPs and 7.5–12.5 nm for the AuNPs. However, the ASP NPs were less stable in selected biogenic media compared to GR NPs and were later stabilised with polyethene glycol. The cytotoxicity studies showed that GR-AgNPs were the most cytotoxic against SH-SY5Y and HepG2 with IC50 108.8 and 183.4 μg/mL, respectively. The cellular uptake analysis showed a high uptake of AuNPs and indicated that AgNPs of rooibos at a lower dose (1.3–1.5 μg/mL) is favourable for its anticancer potential. This study is a contribution to plant-mediated metallic nanoparticles using a pure single compound that can be further developed for targeted drug delivery for cancer cells treatments in the coming years.