Agriculture Reference
In-Depth Information
Constituents —
Both commercially important species of
Agathosma
yield essential oils (1-2%
w/w).
A. betulina
is characterized by the dominant presence of diosphenol in the oil (ca. 40% of
total oil) with limonene, menthone, l-pulegone (<5%), and (ψ)-diosphenol (anisomer of diosphenol),
whereas
A. crenulata
elaborates a high pulegone content of about 50% with near total absence of the
diosphenol found in
A. betulina
. Buchu also contains flavonoids, diosmin, diosmetin, quercetin-3,
7-diglucosides, and rutin. It has been reported that the characteristic black currant smell and flavor
of buchu oil is due to the presence of sulfur-containing minor compounds (8-mercapto-p-menthan-
3-one).
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The two species can be standardized and qualitatively differentiated easily by liquid and
gas chromatographic (GC) techniques with or without coupling to mass spectroscopy (MS) based
on the analysis of the composition of the oils. The use of vibrational spectroscopy has also been
reported for the quality assessment of the two commercially important species.
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Pharmacological Studies —
The essential oil obtained from
A. betulina
has been shown to
inhibit 5-lipoxygenase (5-LOX) enzyme, which is involved in the inflammatory process (IC
50
= 35.2
µg/ml).
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The data clearly indicate that the
Agathosma
essential oil blocks the synthesis of 5-LOX
products
in vitro
. Since leukotrienes, for which 5-LOX is the key enzyme, are considered to be
involved in the initiation and maintenance of a variety of inflammatory diseases, it may be reason-
able to state that the inhibition of leukotriene synthesis may, at least in part, be responsible for the
anti-inflammatory action of these species. The spasmolytic activity on guinea pig ileum by the same
species has been demonstrated, which is indicative of apparent blockage of calcium channels.
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Although buchu contains flavonoids, studies have shown that the plant has only weak antioxidant
activity in the DPPH (2,2-diphenyl-β-picrylhydrazyl) assay, both species having IC
50
values greater
than 100 µg/ml. Neither was found to exhibit radical scavenging activity equivalent to that of the
standard, ascorbic acid (IC
50
value of 2.47 ± 0.178 µg/ml).
The antimicrobial activity of various extracts of buchu has been investigated by several schol-
ars who showed that buchu possesses moderate antimicrobial properties.
In vitro
antimicrobial
studies of
A. betulina
extracts (water, dichloromethane: methanol, and methanol) of seven patho-
genic microorganisms (
Listeria monocytogenes
,
Pseudomonas aeruginosa
,
Candida albicans
,
Escherichia coli
,
Proteus vulgaris
,
Staphylococcus aureus,
and
Enterococcus faecalis)
using the
MIC microplate assay showed that the dichloromethane:methanol extracts had the greatest activ-
ity, with MIC values ranging between 3 and 6 mg/ml.
70
The study also evaluated the effect of
buchu extracts on the growth and development of biofilms using the crystal violet (CV) assay. The
dichloromethane:methanol extracts prevented attachment of bacteria to the polyvinyl chloride sur-
face; however, exposure of
Candida albicans
to the extracts enhanced attachment and subsequent
biofilm formation. The growth and development of a preformed biofilm was also inhibited, but to a
lesser extent.
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An evaluation of the efficacy of buchu oil applied topically to treat pain resulting from muscle
damage has been conducted by the Research Unit of Exercise and Sports Medicine, University
of Cape Town (South Africa). In the study, 30 male participants did a bout of exercise using their
nondominant arm with the intention of causing exercise-induced muscle damage. The results from
the double-blind, placebo-controlled trail indicated that the group treated three times daily with
buchu gel showed a reduction in swelling that may be ascribed to the anti-inflammatory properties
of buchu.
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Toxicity —
The extracts of
A. betulina
and
A. crenulata
were shown to be nontoxic at the
concentrations tested (IC
50
values > 100 µg/ml) using the MTT (3-[4, 5-dimethyl-2-thiazol-yl]-2,
5-diphenyl-2H-tetrazoliumbromide) cellular viability assay. In the same assay, the essential oils
exhibited higher toxicity at the concentration tested, both having IC
50
values less than 0.0001 µg/ml
when compared to the control.
71
The compound cis-isopulegone present in both species may con-
tribute to the observed toxicity. R-(+)-Pulegone is known to be a hepatotoxic compound; large oral
doses have been shown to deplete glutathione (GSH), which is needed in one of several biological
