African Natural Products with Potential Antioxidants and Hepatoprotectives Properties: a Review Bashir Lawal1* , Oluwatosin K
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Lawal et al. Clinical Phytoscience (2016) 2:23 DOI 10.1186/s40816-016-0037-0 REVIEW Open Access African natural products with potential antioxidants and hepatoprotectives properties: a review Bashir Lawal1* , Oluwatosin K. Shittu1,2, Florence I. Oibiokpa1, Eustace B. Berinyuy3 and Hadiza Mohammed1 Abstract Free radicals are highly reactive molecules generated during oxidation reactions which in turn initiate chain reactions resulting to cellular damage. There is substantial evidence implicating free radicals especially reactive oxygen species (ROS) in the etiology of more than one hundred degenerative disorders in humans including, arthritis, atherosclerosis, ischemia and reperfusion injury of many tissues, gastritis, diabetics, central nervous system injury, acquired immunodeficiency syndrome (AIDS) and cancer. Scientific evidence postulates that bioactive compounds especially from natural products are capable of providing protection against free radicals. Consequently, few decades have witnessed a surfeit of research geared towards validating the antioxidant and hepatoprotective potential of the natural products. In this review, African natural products whose antioxidants activities were scientifically validated either in their crude extracts and/or derived products have been discussed. A total 1076 plants species representing 287 family, 132 isolated compounds and 7 insect/mollusk secreation were found. The plant species from the following families; Fababceae, Asteraceae, Lamiaceae, Moraceae, Euphorbiaceae, Combretaceae and Malvaceae have received more scientific attention than others. Analysis of the reports revealed that Combretum apiculatum, Telfaria occidentalis, Acalypha racemosa, Garcinia lucida were the most active plant extracts from African flora. The most active ROS-detoxifying phytochemicals were moracin T, U, S and R (84–87), oleanolic acid (54), 5,7,4′–trihydroxy–3,8,3′,5′–tetramethoxyflavone (89), 5,7,3′–trihydroxy-3,8,4′,5′–trimethoxyflavone (88), luteolin (3′,4′,5,7–tetrahydroxy flavone) (117) and genistein (4′,5,7–trihydroxyisoflavone) (116). The significant antioxidant potential demonstrated by some crude extracts and their constituent compounds render them good candidates for the development of new drugs. Although, the study of the mechanisms of actions as well as clinical validation of some of these isolated compounds is lacking. It is hoped that pertinent scientist and stakeholders will look further into some of these compounds for detailed authentification and subsequent commercialization. Keywords: Antioxidants, DPPH, Hepatoprotective, Africa, Plants, Natural products Introduction further oxidation reactions [2]. They include reducing Oxidation is a chemical reaction that transfers electrons agents such as β-carotene, vitamin C, E and ascorbic or hydrogen from a substance to an oxidizing agent. acid, as well as enzymes like superoxide dismutase Free radicals are generated during this oxidation reaction (SOD), catalase (CAT), glutathione and peroxidases [3], especially during oxidative respiration when there is a and therefore exert their protective role by being oxi- mitochondria leakage of activated oxygen [1], which in dized themselves. Furthermore, many antioxidants turn initiate a chain of reactions that results in cellular compounds have been characterized form plants in- damage. Antioxidants terminate this chain of reactions cluding flavonoids. Flavonoids are phenolic compounds by removing free radical intermediates, thus inhibiting with importants roles in scavenging free radicals and thus play vital roles in preventing oxidative stress asso- * Correspondence: [email protected] ciated disorders [4]. Among the common ROS are ·− 1Department of Biochemistry, Tropical Disease Research Unit, Federal superoxide (O2 ), hydroxyl (OH), and peroxyl (OOH, University of Technology, P.M.B. 65 Minna, Nigeria ROO) radicals [5]. Enzymes capable of producing Full list of author information is available at the end of the article © The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Lawal et al. Clinical Phytoscience (2016) 2:23 Page 2 of 66 superoxide are xanthine oxidase, reduced nicotinamide However, available reviews on the antioxidant potencies adenine dinucleotide phosphate oxidases and cytochrome of African natural products; focused only on medicinal P450 [1]. The imbalance between the production of plants [21], published decade ago with emphasis only on these free radicals and the detoxifying capacity of the 38 plants [22], others are limited to Cameroonian medi- antioxidants results in oxidative stress which is among cinal plants, [23], few African vegetables, fruits and mush- the major implicative factors in etiology of certain de- rooms [24], and hepatoprotective activities of medicinal generative and chronic diseases including diabetes, ath- plants [25]. This review is intended to serve as scientific erosclerosis, parkinson’s disease [6], renal disorders [7], baseline information for the documented African natural cardiovascular, inflammatory, cancer, autoimmune, products with antioxidants and hepatoprotectve reputa- neurodegenerative diseases [8], and several other tion as well as a starting point for future studies. human ailments [9]. The liver is the major regulatory organ responsible for Methodology (Search strategy) the metabolism, storage, detoxification, secretions and ex- To identify natural products from African flora and cretions of various exogenous and endogenous molecules fauna with antioxidant and hepatoprotective potentials, including xenobiotics [10]. It plays a vital role in maintain- a review was compiled based on scientific literature from ing cellular homeostasis and protects the body against various sources including; Google Scholar, Science Direct, deleterious effect of chemicals, drugs, toxin, organism and PubMed, Medline, Science domain [19, 22, 26, 27]. The parasite [5]. Therefore, the healthy performance of the keywords used for identification of relevant data included organ reflects the health status of human [11, 12]. How- the following terms; antioxidant, radical scavenging ac- ever, during these protective roles this organ is susceptible tivities, anti-aging principles, reactive oxygen species, to a numbers of diseases and disorders [13], from chem- free radicals, African medicinal plants, natural product, ical drugs and other agents due to its distinctive metabolic 2,2-Diphenyl-1–picrylhydrazyl radical scavenging assay roles and the proximal affiliation with the gastrointestinal (DPPH), reducing properties and lipid peroxidations. All tract (GIT) [14]. Hepatic injury may also results from ex- relevant data previously published in English were re- cessive alcohol and paracetamol consumptions, exposure trieved. However, data for natural products from sources to infectious agents, xenobiotics and over the-counter other than African countries were completely excluded drugs in western countries [15]. from this review paper. Using the specified procedure Hepatic diseases are a worldwide predicament often for acquisition of necessary data, 641 articles were re- involving free radicals induced oxidative stress which if trieved, out of which 315, mainly in the form of journal left untreated may advance from steatosis to chronic articles, books and reviews; were used for compilation of hepatitis, fibrosis and hepatocellular carcinoma [16]. The the current review. conventional drugs commonly used to combat the dis- The information obtained from these research articles, eases and disorders associated with the liver are beset captured in the current review paper includes; scientific with different undesirable effects on biological systems names, that is the family, genus and specific names, [17]. As a result considerable attentions has been geared parts of plants or mollusk used, solvent system used for towards finding alternative, less toxic and effective anti- the extraction procedure, the bioassay test carried out, oxidants and hepatocurative agents from Africa natural whether in vitro or in vivo, as well as the antioxidant product for the prevention, managements and treatment and hepatoprotective potencies of natural products ori- of diseases and disorders associated with the liver [18]. ginating from African flora and fauna (Tables 1, 2, 3, 4, 5 The natural products with medicinal reputation could and 6). Information was also obtained from authenti- serve as lead sources of natural antioxidants for develop- cated post graduate theses, conference proceedings with ment of novel drugs [12]. literature on antioxidant and hepatoprotective assay re- Africa is blessed with enormous biodiversity of natural sults of flora and fauna endemic or naturalized in Africa. product for healing practices [19]. From time immemorial Africa medicinal plants have been used by virtually all Results and discussion cultures to meet their health care needs. Evolutions A total 1076 plants species representing 287 family and have made plants to harbor a numbers of antioxidant 7 other natural products were identified. Previous phyto- chemicals (phytochemical or secondary metabolites) as chemical studies of ethnomedicinal plants