INTRODUCTION
Boswellia dalzielii (Burseraceae) is a tree plant, abundantly found
in north-western Nigeria, where the Hausa speaking people refer to it as Hano
or Harrabi. This plant is very popular among the locals as a potent source
of ethnomedicine. The extract from its leaves is used for the treatment of diarrhea
in poultry. The root decoction of B. dalzielii and Daniella oliveri
is used for wound healing (Etuk et al., 2006a). The fresh bark is eaten
to induce vomiting and relieve symptoms of giddiness and palpitations. The root
decoction of the plant boiled along with Hibiscus sabdariffa is used
for the treatment of syphilis. The fragrant gum resin from the plant is used
locally for fumigation of clothes and houses and as a deodorant (Etuk et
al., 2006a). Oil from the leaves of B. dalzielii was found to exhibit
significant activity against S. aureus, B. subtilis and C.
albicans (Nwinyi et al., 2004). Also, the aqueous stem bark extract
of B. dalzielii was reported to show anti-ulcer activity and reduced
gastrointestinal motility (Nwinyi et al., 2004) and to possess anti-diarrhoeal
effect, which may be related to anticholinergic mechanisms (Etuk et al.,
2006b). Crude extracts of the stem bark of this plant have been found to show
antibacterial activity against both Gram-positive and Gram-negative bacteria
(Olukemi et al., 2005). Despite the widespread uses of this plant in
treating a plethora of human and animal diseases in this environment, little
work has been done on its phytochemistry and its effects on some major organs
in the body.
This study was undertaken to investigate the effects of the aqueous bark extract of B. dalzielii on the liver function. This was with a view to assessing the possible cytotoxic side effect that might arise as a result of consumption of this plant extract, since liver is the major organ of drug metabolism.
MATERIALS AND METHODS
Collection of Plant Sample
The stem bark of Boswellia dalzielii was collected from Unguwan
Hakimi-Dengi, Plateau State, Nigeria, during the dry season (in the month of
January 2004). The plant was identified by Ibrahim Muazzam, a plant taxonomist
in the Department of Medicinal Plant Research and Traditional Medicine, National
Institute for Pharmaceutical Research and Development (NIPRD), Abuja, Nigeria.
A voucher specimen (No. 4592) is deposited at NIPRD herbarium.
Preparation of Plant Extract
One gram of the dried pulverised bark of B. dalzielii was steeped
in 100 mL of hot distilled water (60°C) and kept at room temperature for
30 min with occasional stirring. Thereafter, the mixture was filtered using
Whatman No. 1 filter paper and the filtrate (extract) was transferred into dark-brown
bottle and used soon after. The extract was prepared fresh each time required.
The actual amount of solubles extracted from 1 g of the sample was determined
after evaporating the solvent and weighing the residue (462.5 mg g-1).
Experimental Animals
Thirty female Wistar albino rats, between 7 and 8 weeks old, weighing between
180 and 200 g, were obtained from the Small Laboratory Animal House, National
Institute for Trypanosomiasis Research (NITR), Vom, Jos and transferred to the
University of Jos Animal House where they were allowed to acclimatised for 7
days and where the work was carried out. They were maintained in the experimental
facility, provided standard feed for laboratory rodents and regular tap water
ad libitum. Six animals were housed together until the commencement of
the experiment.
Treatment of Animals
Five groups (A-E) of 6 rats each were used for the study. Group A (control
group) did not receive any dose of the extract. Group B received the normal,
recommended daily dose of 50 mg kg-1 body weight (extrapolated from
human dose), whereas groups C, D and E received 100, 150 and 200 mg kg-1,
respectively, through gastric intubation, for 5 consecutive days. Six hours
after the last dose of the extract, all the animals in the five groups were
sacrificed by decapitation. Blood from each animal was collected separately
in labelled centrifuge tubes. They were spun at 5,000 x g for 15 min using MSE
Minor centrifuge at room temperature. The serum samples were obtained and stored
at -4°C in labelled sample bottles until required.
Quantitative Estimation of Serum Total Protein
Serum total protein was determined by the biuret method, a described by
Gornall et al. (1949).
Serum Albumin Determination
Serum albumin concentration was determined by the bromocresol green (BCG)
binding method, as described by Cheesbrough (1991).
Serum Bilirubin Determination
The serum total bilirubin was estimated by colorimetric method based on
that developed by Jendrassik and Grof, as described by Willard and Meites (1982).
Conjugated bilirubin was determined by the direct Van den Bergh’s reaction.
Unconjugated bilirubin was determined by subtracting conjugated from total bilirubin.
Measurement of Serum Alkaline Phosphatase (ALP) Activity
The serum activity of ALP was determined by the Bessey Lowry and Brock method,
as described by Cheesbrough (1991).
Determination of Serum Aspartate Aminotransferase (AST) Activity
The serum activity of AST was determined by the Reitman-Frankel method,
as described by Cheesbrough (1991).
Determination of Serum Alanine Aminotransferase (ALT) Activity
The serum activity of ALT was determined by the Reitman-Frankel method,
as described by Cheesbrough (1991).
Phytochemical Analysis
The phytochemical screening of the bark extract was carried out using standard
qualitative procedures as described by Trease and Evans (1989) and Sofowora
(1993). The extract was screened for alkaloids (Mayer’s test and Dragendorff’s
test), flavonoids (NaOH test, FeCl3 test and lead acetate test),
glycosides (Salkowski test and Keller-Killiani test), saponins (Frothing test),
tannins (FeCl3 test), steroids and triterpenoids (Lieberman-Burchard
test).
Statistical Analysis
Statistical analysis of data was performed using Stat-view for Mackintosh
software programme (Release 7.0). Group comparisons were done using the analysis
of variance (ANOVA). A p-value of <0.05 was considered statistically significant.
Ethics
This study was carried out with respect for the welfare of animals, as recommended
by WHO (1992). Moreover, all procedures involving animals were carried out in
strict compliance with the Animal Ethics Committee rules and regulations of
the University.
RESULTS
The effect of Boswellia dalzielii bark extract on the serum levels of
total protein, albumin, bilirubin, alkaline phosphatase and transaminases (AST,
ALT) are given in Table 1. A slight decrease was observed
in serum total protein concentration, but this was not statistically significant
(p>0.05). The administration of extract did not have any significant (p>0.05)
effect on the albumin component of serum.
Boswellia dalzielii extract had no detectable effect on the conjugated
bilirubin. However, it did have significant (p<0.05) effects on the total
and the unconjugated bilirubin, at high doses (150 and 200 mg kg-1).
The extract did not have any significant (p>0.05) effect on ALP activity
in general. However, at 150 mg kg-1 ALP activity showed a decrease,
which still was not statistically significant (p>0.05). There were significant
(p<0.001) decreases in the activities of serum transaminases (AST and ALT)
in the treated groups as compared to the control group. This effect appeared
to be dose dependent.
| Table 1: |
Effect of Boswellia dalzielii bark extract on some
biochemical parameters of liver function test |
 |
| Tabulated values are mean±SD of six determinations,
a p<0.05 vs control, b p<0.001 vs control |
The result of phytochemical analysis of B. dalzielii bark extract is as shown in Table 2. As can be seen from the table, glycosides, triterpenoids, steroids and hydrolysable tannins were not detected, while saponins, flavonoids, alkaloids and pseudotannins were detected in the plant bark extract.
DISCUSSION
Generally, a significant increase in serum or plasma total protein is an indication of tissue injury (Emerson et al., 1993). In the present study, a slight decrease was observed in serum total protein concentration, following administration of Boswellia dalzielii extract, but this was not statistically significant. This decrease may, however, suggest that the extract had rather a protective effect on tissues.
A rise in the level of bilirubin in the blood can be as a result of overproduction of bilirubin caused by an excessive breakdown of red blood cells; the bilirubin being of the unconjugated type (Awad, 1997). Also, a rise in the blood total bilirubin level can be caused by liver cell damage (Cheesbrough, 1991; Awad, 1997). In this study, a marked decrease in total and unconjugated bilirubin levels was observed, suggesting that the extract may have a protective effect on both the red blood cells and the liver. Moreover, a progressive decrease was observed in unconjugated bilirubin concentration as the dose of extract increased. Also, at the dose of 200 mg kg-1 unconjugated was completely converted into conjugated bilirubin, i.e., the concentration of conjugated became equal to that of the total bilirubin. These data suggest that the extract may enhance the conjugation of bilirubin in the liver.
The presence of flavonoids further gives credence to the hepato-strengthening effect of Boswellia dalzielii extract. In fact, natural flavonoids and polyphenolic compounds have been reported to exhibit protective and strengthening activities on liver cells (Adzet et al., 1987; Akamatsu et al., 2004; Oh et al., 2004).
Whenever there is liver cell damage the serum or plasma levels of AST and ALT rise. In general, the higher the activities of both enzymes the greater the degree of liver damage (Cheesbrough, 1991; Gatsing et al., 2005; Garba et al., 2006). The decrease in the activities of these transaminases (AST and ALT) observed in the study corroborates the serum total protein and bilirubin contents, thus suggesting the strengthening action of the extract on the liver and other organs having significant quantities of these enzymes.
In the light of the foregoing, it appears that Boswellia dalzielii aqueous bark extract, at the doses used, may rather significantly strengthen the liver. This plant extract may therefore be used in the management of hepatic disorders. However, Etuk et al. (2006a) reported significant reductions in the packed cell volume and red blood cell count and significant increase in the serum urea level of the rats treated with a high dose (2700 mg kg-1) of the aqueous stem bark extract of Boswellia dalzeilii. These findings suggest that prolonged oral administration of very high doses of the aqueous stem bark extract of Boswellia dalzielii may be associated with increased risk of toxicity.
