Anti-inflammatory, anticholinesterase, antioxidant and phytochemical properties of medicinal plants used for pain-related ailments in South Africa
Introduction
Many degenerative diseases such as rheumatoid arthritis, shoulder tendonitis, gouty arthritis, polymyalgia rheumatica, heart disease, asthma, cancer, and inflammatory bowel disease are often associated with inflammatory processes (Polya, 2003, Iwalewa et al., 2007). During inflammatory responses, the activation of phospholipase A2 induces the mobilization of fatty acids, in particular arachidonic acid from the membrane lipid pool (Fiorucci et al., 2001). Arachidonic acid is then oxidized by constitutive cyclooxygenase-1 (COX-1) or inducible cyclooxygenase-2 (COX-2) enzymes, leading to the production of prostaglandins (Fiorucci et al., 2001, Polya, 2003). Prostaglandins are a group of inflammatory mediators, implicated in many pain-related ailments (Rang and Dale, 1987).
In addition, oxidants such as reactive oxygen species (ROS) generated from activated neutrophils and macrophages have been reported to play an important role in the pathogenesis of various pain-related diseases, including neurodegenerative disorders, cancer and atherosclerosis (Winrow et al., 1993, Confortia et al., 2007). Furthermore, oxidative and inflammatory processes are among the pathological features associated with the central nervous system in Alzheimer's disease (AD) (Howes and Houghton, 2003). The brain of patients suffering from AD is said to be under oxidative stress as a result of perturbed ionic calcium balances within their neurons and mitochondria (Emilien et al., 2000, Tabet, 2006). Moreover, there is evidence that acetylcholinesterase (AChE) inhibitors have an anti-inflammatory role through action against free radicals and amyloid toxicity, as well as through decreasing release of cytokines from activated microglia in the brain and blood (Tabet, 2006). There is an established link between the cholinergic system and inflammation as acetylcholine, the principle neurotransmitter, is reported to attenuate the release of cytokines in the parasympathetic anti-inflammatory pathway by which the brain modulates systemic inflammatory responses to endotoxin (Borovikova et al., 2000).
Anti-inflammatory medications such as non-steroidal anti-inflammatory drugs often relieve inflammation and associated pain by inhibiting specific enzymes that the body needs in order to produce pro-inflammatory eicosanoids (Rang and Dale, 1987). According to Howes and Houghton (2003), the use of anti-inflammatory drugs has been proposed as a therapy for AD due to their ability to delay the advancement or reduce the risk of AD. In addition, the intake of anti-inflammatory drugs, oestrogenic steroids and a high level of antioxidants have been reported to result in lower incidences of AD (Houghton et al., 2007).
Due to the fast growing interest in the anti-inflammatory activity of medicinal plants by pharmaceutical companies and scientific research on the discovery of novel anti-inflammatory compounds, medicinal plants could potentially serve as leads in the production of new drugs for treating pain-related ailments with reduced or no side-effects. A variety of chemical types are often present in a plant extract, each having different biological or pharmacological activities such as anthelminthic, antioxidant, antimicrobial, anti-inflammatory and anticholinesterase properties. These chemical types possibly act in a synergistic manner resulting in the overall clinical effect. It is thus important to screen medicinal plant extracts in different in vitro assays because there is a possibility of losing other potentially useful bioactive compounds when only a single biological activity is investigated (Rates, 2001, Houghton et al., 2007).
The study was aimed at evaluating medicinal and therapeutic potentials of seven traditional medicinal plants used for pain-related ailments. The anti-inflammatory, anticholinesterase and antioxidant properties of the medicinal plant extracts were investigated. Phytochemical analysis, for the total phenolic, condensed tannin, gallotannin and flavonoid contents, was also carried out using spectrophotometric methods.
Section snippets
Plant selection and preparation
The selection of medicinal plants was based on indigenous ethnopharmacological records. Medicinal plants (Table 1) were collected from the University of KwaZulu-Natal Botanical Garden, Pietermaritzburg, South Africa. Voucher specimens were prepared, identified and were lodged in the University of KwaZulu-Natal herbarium for record purposes. Plant materials were oven-dried at 50 °C and ground into fine powders through a 1 mm ring sieve using a Retsch® ZM200 ultracentrifugal mill (Rheinische straße
Cyclooxygenase enzyme inhibition
Table 3 shows the percentage inhibitory activity of COX-1 and COX-2 enzymes by the extracts. Some degree of COX-inhibitory activity was observed in all the evaluated extracts. Considering plant extracts with a minimum percentage inhibition of 50% as showing good activity (Eldeen and Van Staden, 2008), at the screening assay concentration of 0.25 μg/μl, out of 28 plant extracts evaluated against both enzymes (COX-1 and -2), 13 showed good COX-1 inhibitory activity, while good activity was
Discussion
All the evaluated medicinal plants in this study are used traditionally for the treatment of pain-related ailments in South Africa. Some of the evaluated plant extracts showed COX-inhibitory activity and other pharmacological activities. A variety of bioactive compounds that could be responsible for the observed bioactivities have been reported in some of the screened medicinal plants. Aloe ferox leaf (DCM and EtOH) showed good anti-inflammatory activity while a moderate antioxidant activity
Acknowledgements
The authors thank Mrs Alison Young (Horticulturist) of the University of KwaZulu-Natal Botanical Garden, for her assistance in plant collection. The National Research Foundation and the University of KwaZulu-Natal are gratefully acknowledged for financial assistance.
References (32)
- et al.
Effects of naturally occurring prenylated flavonoids on enzymes metabolizing arachidonic acid: cyclooxygenases and lipoxygenases
Biochemical Pharmacology
(2001) - et al.
A new and rapid colorimetric determination of acetylcholinesterase activity
Biochemical Pharmacology
(1961) - et al.
Anti-inflammatory and phytochemical properties of twelve medicinal plants used for treating gastro-intestinal ailments in South Africa
Journal of Ethnopharmacology
(2009) - et al.
Dual inhibitors of cyclooxygenase and 5-lipoxygenase. A new avenue in anti-inflammatory therapy?
Biological Pharmacology
(2001) - et al.
Uses and abuses of in vitro tests in ethnopharmacology: visualizing an elephant
Journal of Ethnopharmacology
(2007) - et al.
Plants used in Chinese and Indian traditional medicine for improvement of memory and cognitive function
Pharmacology, Biochemistry and Behavior
(2003) - et al.
Evaluation of antioxidant properties of pomegranate peel extract in comparison with pomegranate pulp extract
Food Chemistry
(2006) - et al.
Evaluation of antioxidant, antibacterial and anti-tyrosinase activities of four Macaranga species
Food Chemistry
(2009) - et al.
Limonoids from Turraea floribunda (Meliaceae)
Phytochemistry
(2004) - et al.
Limonoids from Turraea holstii and Turraea floribunda
Phytochemistry
(1998)