Chapter 3: Inhibition of cyclooxygenase enzyme as an evaluation of anti-inflammatory
3.7. Results and discussions
A total of 68 extracts from 10 plants used for the treatment of tuberculosis and related symptoms in South Africa were screened for their ability to inhibit the COX-2 enzyme.
Table 3.1 shows the results as percentage inhibition of prostaglandin synthesis by the extracts in the COX-2 assay. For inhibition of the enzyme by extracts, four different levels of activity were defined; inhibition below 20% was considered insignificant, between 20% to 40% low, between 40% to 70% moderate and between 70% and 100% as high (TUNÓN et al., 1995).
The highest COX-2 inhibition was exhibited by PE extract from the roots of Pentanisia prunelloides (86.9%). In studies done by YFF et al. (2002) and LINDSEY et al. (1999), the EtOH, ethyl acetate and water extracts of Pentanisia prunelloides (leaves and roots) demonstrated high inhibition of COX enzyme. The roots of Pentanisia prunelloides are reported to be used to relieve chest pain and bacterial infection (YFF et al., 2002). The root EtOH extract of Pentanisia prunelloides exhibited remarkable antimicrobial activity against bacterial strains associated with respiratory ailments (Chapter 2, Table 2.3), and in the present study PE extracts of the same plant part demonstrated high COX-2 inhibition, thus, these findings supports the use of this plant in South African TM for treatment of inflammation associated diseases like pulmonary tuberculosis.
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The DCM extracts of Abrus precatorius subsp. africanus (leaves) and Ficus sur (bark) exhibited high COX-2 inhibition with percentages of 77.9 and 73.9, respectively. In previous research by KUO et al. (1995) on potent antiplatelet, anti-inflammatory and antiallergic properties of isoflavanquinones from the roots of Abrus precatorius subsp. africanus, abruquinones A, B, D and F exhibited remarkable anti-inflammatory effects. Therefore, the noteworthy anti-inflammatory activity exhibited by the extract from Abrus precatorius subsp.
africanus in the present study could be from these abruquinones.
Both the roots and bark of Ficus sur are used by the Zulu people of South Africa for traditionally treating pulmonary tuberculosis. These plant parts showed high COX-1 inhibitory activity in a study by ELDEEN et al. (2005b) and low COX-2 inhibition. In this study a different solvent (DCM) from the ones used by ELDEEN et al. (2005b) (ethyl acetate, EtOH and water) showed the bark of Ficus sur to have high COX-2 inhibition.
Out of a total of 68 extracts tested, only three exhibited high COX-2 inhibition, 14 moderate, 20 low and the remaining 31 showed insignificant inhibition. Of 17 DCM extracts tested, two exhibited high COX-2 inhibition, five showed moderate and the rest showed low to insignificant activity. For PE extracts, only one showed high COX-2 inhibition, four showed moderate and the rest had low to insignificant activity. For EtOH extracts only Abrus precatorius subsp. africanus (leaves), Asparagus africanus (leaves), Ficus sur (roots), and Leonotis intermedia showed moderate COX-2 activity with percentage inhibition ranging from 41.4 to 50.6. The other EtOH extracts exhibited low to insignificant activity. The majority of the water extracts showed insignificant to low COX-2 inhibition with the exception of that of Asparagus africanus that showed moderate activity (56.6%). In the case of water extracts showing weak or no activity in these assays, it is worth mentioning that high dosages are frequently used in TM (McGAW et al., 1997). According to JÄGER et al.
(1996), a species with an anti-inflammatory compound has a potential to be developed into an anti-inflammation product. Cyclooxygenase-2 inhibition is beneficial in clinical conditions as it provides therapeutic effects and its high activity is desirable (BLOBAUM and MARNETT, 2007). However, COX-2 inhibitors are currently regarded as dangerous, as their prolonged use may cause side effects in humans (BLOBAUM and MARNETT, 2007).
All plant species that were evaluated in this study for inhibition of COX- 2 are frequently used for the treatment of tuberculosis and related symptoms. The inhibition of the tested
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COX enzyme shown by some of the evaluated plants supports their use in South African TM for the treatment of pain-related ailments. Additionally, anti-inflammatory property observed by some of the investigated plant extracts in this study indicates the presence of bioactive agents that warrant further investigation. The extracts that exhibited weak or no activity might be active when concentrations higher than those evaluated are used. Since lipophilic compounds are more extractable by non-polar solvents and have far better resorption through the cell membrane, activity exhibited by polar solvents specifically at low concentrations is noteworthy (ZSCHOCKE and VAN STADEN, 2000). The high COX-2 inhibitory activity exhibited by the DCM leaf extracts of Abrus precatorius subsp. africanus is important for medicinal plant species conservation, as the leaves can be sustainable harvested while using the plants for medicine without threat to their survival. When treating inflammation, targeting the desired area is not easy as the process has many mediators and pathways that can lead to many pathological changes. The results obtained in this study are depended strongly on the test system used, therefore additional systems are needed to evaluate anti-inflammatory activity. Anti-inflammatory drugs with low COX-1 and high COX-2 inhibition properties are required. Therefore, it would be ideal to evaluate further the DCM extract of Abrus precatorius subsp. africanus (leaves) and Ficus sur (bark) as well as the PE extract of Pentanisia prunelloides (roots) for their COX-1, LOX inhibition, and to check if these plants inhibit these other enzymes, because high inhibition of both enzymes (COX-1 and COX-2) is associated with adverse effects.
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Table 3.1: Anti-inflammatory activity (COX-2) of extracts from plants that are used for the treatment of tuberculosis and related symptoms in South Africa
Plant species Plant part
used
Percentage inhibition of cyclooxygenase-2
PE DCM EtOH Water
Abrus precatorius subsp. africanus Leaves 11.9±0 77.9±0 42.3±0 0±0 Abrus precatorius subsp. africanus Seeds 39.0±0 26.7±1.6 8.8±0 11.8±0
Asparagus africanus Leaves 9.3±0 29.6±0 50.6±0 56.6±0
Asparagus falcatus Leaves 9.2±0 34.0±0 35.2±0 32.2±0
Brunsvigia grandiflora Bulbs 23.4±0 42.5±0 0±0 12.7±0.03
Ficus sur Bark 12.4±0 73.9±0 9.9±0 0±0
Ficus sur Roots 44.9±0.5 55.0±0 56.3±0 0±0
Indigofera arrecta Leaves 24.7±2.6 28.9±1.6 0.8±0 0±0
Indigofera arrecta Roots 52.2±0 29.3±0 0±0 12.2±0
Leonotis intermedia Leaves 36.9±0 13.4±0 41.4±0 0±0
Leonotis intermedia Stems 0.0±0 6.3±0.8 34.6±0 22.6±0
Pentanisia prunelloides Leaves 2.5±0 48.4±0 16.5±0 39.4±0 Pentanisia prunelloides Roots 86.9±0 9.1±0.7 26.2±0 0±0 Polygala fruticosa Whole plant 54.7±0 20.1±0 31.2±0 0±0 Terminalia phanerophlebia Leaves 29.0±1.1 41.9±0 0±0 0±0 Terminalia phanerophlebia Roots 23.9±0 58.0 ±0 0±0 0±0 Terminalia phanerophlebia Twigs 67.8±0.05 17.9±0 4.4±0 21.1±0
Indomethacin - 79.2 - - -
DCM: dichloromethane, PE: petroleum ether, EtOH: ethanol. The concentration of plant extracts was 250 µg/ml.
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