Investigating and Identifying Traditional Medicinal Plant Antioxidants– New Frontiers in Treating Age-related Maladies Associated with Oxidative Stress

ABSTRACT Oxidative stress is regarded as an imbalance between pro-oxidant and antioxidant species that can result in cellular inflammation associated with illnesses including cancers and cognitive decline. This study investigated medicinal plant extracts for the presence of natural bioactive compounds to explore their antioxidant properties and potential therapeutic relevance in conditions related to oxidative stress. Extracts were created using water as a solvent and compared in triplicate to the positive control quercetin (1 mg/mL) in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay; all extracts were serially diluted from 10 mg/mL creating 8 distinct concentrations. Absorbance readings were compared before and after DPPH administration. At the highest concentration, all extracts demonstrated absorbance change factors <10% relative to the DPPH negative control. This result clearly demonstrated antioxidant activity, as lesser relative absorbance changes indicated greater neutralization of violet DPPH into lighter diphenylpicryl hydrazine via free radical scavenging. Most notably, at lowest concentration, Averrhoa carambola and Psidium guajava represented the least relative absorbance changes at 14.17% and 10.39%, rivaling quercetin’s antioxidant activity– a statistically significant result (p < 0.05). LC-MS/MS analysis of these most potent extracts identified quercetin and kaempferol in Psidium guajava and vitexin-2’’-O-rhamnoside, isovitexin, saponarin, and an additional flavonoid glycoside in Averrhoa carambola . Such compounds may offer potential pharmacological effects, for example, vitexin-2’’-O-rhamnoside and isovitexin have demonstrated anticancer, antidiabetic, neuroprotective, and cardioprotective properties in part through oxidative stress reduction. Future research should corroborate compound effects in human cell culture models, as prior studies are often limited to non-human tissues. INTRODUCTION A medicinal plant is a plant that “contains substances that can be used for therapeutic purposes or which are precursors for the synthesis of useful drugs.” 1 Medicinal plants contain different classes of potentially bioactive compounds, including, but not limited to peptides, alkaloids, phenylpropanoids, polyketides, and terpenoids. 2 Such compounds have alleged and in certain cases documented anticancer, anti-inflammatory, antioxidant, antibacterial, antipyretic, vasodilatory, stimulant, and/or more properties that have been historically used in traditional medicine. 1,3 Evidence suggests that medicinal plants have been used for at least 60,000 years in places including what would be modern-day Iraq. 4 Medicinal plants are still used all around the world today; Dr. Tedros Adhanom Ghebreyesus of the WHO says “For many millions of people around the world, traditional medicine is the first port of call to treat many diseases.” 5 In addition, the prevalence of medicinal plants is evident in developed countries too, with the medicinal plant trade between India and China accounting for two to five billion dollars annually. 1 However, many of these traditional treatments receive significant scrutiny from modern medicine and society’s decreasing reliance on plant-derived drugs. While such scrutiny proves accurate in many cases, several traditional medicinal plants have been shown to offer bioactive compounds that are used as a standard medical practice. This includes morphine, “a natural alkaloid that is derived from resin extracts from the seeds of the opium poppy,” 3 which is utilized in clinical settings for its profound analgesic effects, 3 and quinine, an antimalarial drug derived from Cinchona officinalis bark. 6 The current research project presented herein will serve to test traditional medicinal plant compounds to determine if their claims of relevance can be substantiated and to explore their potential effects on biological organisms, specifically regarding their antioxidant properties and ability to eliminate free radicals. Free radicals are unstable molecular species with unpaired electrons, 7 and can contribute to oxidative stress in organisms. Oxidative stress “is considered as an imbalance between pro- and antioxidant species, which results in molecular and cellular damage.” 8 Examples of known antioxidants include the polyphenol quercetin, which is often used as a positive control for its relative strength in reducing free radicals. 9 Demonstrated efficacy of these medicinal plants could provide potential preventative therapies for age-related illnesses and other maladies associated with oxidative stress, including cancers and cognitive decline. 8,9 RESEARCH QUESTIONS AND PURPOSE Do the traditional medicinal plants under investigation contain bioactive compounds with antioxidant properties capable of neutralizing free radicals in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay? How does the efficacy of the plant extracts compare to the positive control, quercetin, and the associated samples in terms of antioxidant activity as measured by the DPPH assay? Do the extract compounds identified via LC-MS/MS analysis offer potential therapeutic relevance in modern medicine? With our research, we aimed to identify bioactive compounds within medicinal plants, determine if such medicinal plants and their bioactive compounds have applications in modern medical treatments, and ensure medicinal plants are being used safely and accurately under the support of sound scientific evidence.