In-vitro Antioxidant Activity Of Certain Desert Plants

Introduction

Free radicals are highly reactive molecular species that possess unpaired electron. They stay for very short time before they react with another molecule and either abstract or donate an electron in order to achieve stability. By doing so, they generate a new radical from the molecule that they reacted with. The most damaging radicals in biological system are the oxygen radicals (known as reactive oxygen species “ROS”) superoxide •O2−, hydroxyl •OH , and hydroperoxyl •O2H . (1)

ROS are produced physiologically in the body by Numerous cellular systems . The major source that produces ROS in the cell is the mitochondrial respiratory chain . Another major source is the cytochrome P450 , which are group of enzymes located in liver , responsible for detoxifying a variety of compounds present in our environment including drugs , food ,and alcohol . Also they are important for metabolizing substances that naturally present in the body, such as bile acid , fatty acids , steroid , and cholesterol. These biochemical reactions catalyzed by the cytochrome P450 molecules use molecular oxygen, and small amounts of ROS are generated during these reactions.

Other major sources for ROS in the body can be of two types of immune cells known as macrophage and neutrophils , that help in protecting the body from foreign microorganisms by generation of ROS , through a group of enzymes called the NADPH oxidase complex which , when activated , they generate superoxide radicals and hydrogen peroxide. These radicals then interact with chloride ions present in the cells to produce hypochlorite , which in turn destroys the pathogen . Due to that , these ROS are beneficial and even essential to the organism as it plays a primary role in destroying foreign pathogens so helping the body to defense against many kinds of diseases .

Besides the ROS generation that occurs normally in the body, humans are constantly exposed to environmental free radicals , in the form of radiation , UV light , tobacco smoke , and certain compounds referred to as redox cycling agents , which include some pesticides, also certain medications used for cancer treatment. (2)(3)

Excessive exposure to free radicals might become greater than the ability of the body to detoxify them , and as a result oxidative stress appears , which can contributes in the pathogenesis of more than one hundred diseases including cardiovascular diseases that happen when the reactive oxygen species (ROS) induce Ca+2 ion , leading to changes in membrane permeability, membrane lipid bilayer disruption , and functional modification of many cellular proteins. Also Diabetes as the reactive species production are stimulated by cytochrome P450 monooxygenases, glucose auto-oxidation, NADPH-oxidase, lipooxygenase, nitric oxide synthase , and oxidative phosphorylation. In addition , they can cause gastrointestinal diseases that arises probably from the enzymatic processes in gastrointestinal tract (GIT) necessary to form large amounts of oxygen radicals. The reactive oxygen species (ROS) can also damage the renal system causing renal system disorders , and inflammation of the airways , stimulation of histamine release from the mast cells which contribute in the pathogenesis of pulmonary diseases such as chronic obstructive pulmonary disease (COPD) and asthma .

Invariably, to maintain a healthy biological system the balance between oxidation and anti-oxidation is an essential requirement achieved by antioxidants . Antioxidants are any substances that Significantly delay, prevent or inhibit oxidative damage to target molecules , (4) and they are classified based on their source to synthetic and natural antioxidants .

The synthetic antioxidants are mainly polyphenolic compounds chemically synthesized since they do not exist in nature and act mainly by capturing the free radicals and stop the chain reactions , These compounds because they possess antioxidant activity they are commonly used in pharmaceuticals , preservatives for cosmetics and to stabilize the fat, oil, and lipid in food . The most common ones are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), ethylenediaminetetraacetic acid (EDTA) , propyl gallate (PG) , and many more .(5)

Also a significant number of vitamins and minerals that show antioxidant activity are made synthetically through chemical processes, rather than derived directly from plants or other materials . However, some Natural health authorities claim that synthetic vitamins are useless and ineffective . (6)

For instance , Beta-carotene that can be converted into vitamin A by the body the most abundant rotation in nature is “cis-” , and with less extent “trans-“ . The cis- rotated molecules have more anti-oxidation capacity than the trans- , but unfortunately, synthetic beta-carotene has a lot less cis- than trans- molecules.(7) Also a study made on adult male guinea pigs were orally dosed with 50 mg of ascorbate with serum levels measurements shows That both forms of ascorbic acid (synthetic,natural form) gave similar peak concentrations of serum ascorbate but the natural vitamin C peaked later and remained in the serum for a longer period of time , as well as , the bioavailability of the natural vitamin C was significantly greater than that of the synthetic ascorbic acid .(8) furthermore , vitamin E is also present in synthetic and natural forms . The natural forms usually labelled with d letter as ( d-gamma-tocopherol) , while the synthetic forms are labelled with dl letter as ( dl-alpha-tocopherol ) , but this dl -alpha form is less bioavailable than the natural d-alpha natural form , and is only half as potent as the d-alpha form .(9)

On the other hand , The natural antioxidants are either synthesized in the human body through metabolic processes (endogenous) as glutathione peroxidase, catalase, and superoxide dismutase which are considered as enzymatic antioxidants, or the ones which can be consumed from natural sources (exogenous) including minerals (iron, copper, selenium, zinc, etc ..), vitamins ( as vitamin C, A, B, E), carotenoids (β-carotene, lycopene, lutein, and zeaxanthin), and polyphenols (phenolic acids, flavonoids, gingerol, curcumin, etc..) . These Antioxidants can be obtained from natural sources such as fruits, vegetables, cereals, legumes, beverages, spices, and animals. (10)(11)

Plants synthesize and accumulate several non-enzymatic antioxidants such as ascorbic acid, glutathione and phenolics , these natural antioxidant are widely distributed in medicinal plants that exhibit a wide range of biological effects as anti-inflammatory , antiaging , anticancer , anti-atherosclerosis , etc .. (12) So Recently there has been an great interest in the therapeutic potentials of medicinal plants as antioxidants in reducing the free radical induced tissue injuries as the currently used synthetic antioxidants have been suspected to promote negative health effects hence stronger restrictions have been placed on their application and there is a trend to substitute them with naturally occurring antioxidants.(13)

Thus , many different plants are used because of their potent antioxidant activity such as Cocculus hirsutus , the ethanolic extract was investigated for its free radical scavenging that shows promising free radical scavenging activity in dose dependent manner , this antioxidant activity may be related to the presence of antioxidant vitamins and phenolic compounds present in the extract . Also the rhizome of the herb Zingiber officinale (ginger) , which belongs to the family Zingiberaceae . Various studies have demonstrated its anti-oxidant, anti-inflammatory, anti-cancer and anti-microbial properties related to its high polyphenol content . Licorice extract , as well , was tested by studying the inhibition of radiation induced lipid peroxidation in rat liver microsomes. The Chemical constituents are glycyrrhizin, flavones, coumarins that show its activity through free radical scavenging property . (14)

Moreover , Many desert plants have shown antioxidant and free radical scavenging properties upon doing certain tests The first plant is known as Mentha longifolia Linn. Hudson. growing in cold desert region of Ladakh, Jammu and Kashmir, India. Different methods were done to the methanolic extract of this plant such as DPPH, ABTS, FRAP, and Reducing power assay. Upon assessment of the total polyphenolic content (TPC) and total flavonoid content of the plant, they show a potential and beneficial antioxidant activity. (15) Other four desert plants like Fagonia indica Burm. F. , Calotropis procera R.Br. , Zygophylum hamiense Schweinf. , and Salsola imbricate Forssk were tested for the total polyphenolic content and total flavonoid content by using RP-HPLC. And the results show that all the four plants have free radical scavenging properties for the ethanolic and methanolic extracts. (16) Also Solenostemma arghel (Del.) Hayne plant found in Sinai proper; south El Tih desert and the Islamic desert. It is used in folk medicine for many diseases and it is found to have antioxidant properties due to presence of high quantity of flavonoid. (17) In addition , a four desert plants were found in Egypt show antioxidant activity where a polar extract of Panicum turgidum (PTPE), alkaloid (WSAIK) and ethanol extract of Withania somnifera (WSEE), and ethanol extract of Leptadenia pyrotechnica (LPEE) and the DPPH radical scavenging activity were compared among these four plant extract and it shows that WSEE showed the highest DPPH radical scavenging activity followed by PTPE and WSEE, and then WSEE which had the strongest radical scavenging activity. (18)

Our phytochemical study is designed to investigate and evaluate the antioxidant activity by assessing the DPPH scavenging activity, quantification of total polyphenolics and flavonoid compounds of certain desert plants in UAE related to Plantago and Prosopis families were many studies were done believe that they possess potent antioxidant activity . for example the Prosopis species as P.Cinerari , an in- vitro study were done to evaluate the antioxidant activity of methanolic extract on goat liver slice and confirmed that it can improves the antioxidant status of the tissue by enhancing the activity of both enzymatic and non-enzymatic antioxidant(19) . Also a study conducted on Prosopis juliflora plant leaves suggests that it could be a potential source of natural antioxidant that could be utilized as therapeutic agent (20) While the plantago species as (P. afra, P. coronopus, P. lagopus, P. lanceolata, and P. serraria) were also characterized by different methods and all shows antioxidatant activities (21).

References :

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