Ethanolic
extraction of the homogenized dried cloves of A. sativum and A. barbadensis
gave a relatively low percentage yield 6.8 and 11.8 % respectively. This may suggest that most of the chemical components
of the plants have low solubility in ethanol (Table 1 ).This could explain the
use of aqueous extract of most medicinal plants by traditional medicine
practitioners for the sole purpose of achieving high yield and potency as
documented by Sofowora (1993).
Paracetamol induced oxidative stress
and hepatotoxicity in all the treated animals,as reflected by significant
increase (p < 0.05) in TBARS, AST, ALT, ALP and Bilirubin levels and a
significant decrease (p < 0.05 ) in GSH, SOD, CAT and Protein. This
analgesic and antipyretic drug (paracetamol) is quite safe at therapeutic doses
and normally undergoes glucuronidation and sulfation to the corresponding
conjugates.
When acetaminophen intake far exceeds therapeutic doses, the
glucuronidation and sulfation pathways are saturated and the cytochrome P 450 pathways
become increasingly important. However, with time hepatic glutathione is depleted
faster than it can be regenerated and accumulation of a reactive and toxic
metabolite occurs. In the absence of intracellular antioxidants such as glutathione,
this reactive metabolite (N – acetyl-P- benzoquinone imine, NAPQI) reacts with
nucleophilic groups present on cellular macromolecules such as protein or
lipids and alter the homeostasis of calcium resulting in hepatotoxicity
(Katzung, 1998).
The significant increase (p <
0.05) in glutathione level observed after treatment of animals with extracts of
A. sativum and A. barbadensis suggests hepatoprotection.The
actual mechanism of hepatoprotection of these extracts is not well understood;
however chemical constituents of plant extracts have been shown to exhibit
antioxidant properties. For example, flavonoids have been reported to contain
antioxidant properties (Gosh et al, 2007).These antioxidant properties of
extracts may have contributed to hepatoprotection displayed in this work.
Further, cells have a number of mechanisms to protect themselves from the toxic
effect of reactive oxygen species (ROS). Glutathione is an intracellular
reductant, widely distributed in cells and plays major role in catalysis,
metabolism and transport. It protects cells against free radicals, peroxides
and other toxic compounds (Fairhust et al, 1982).In the present study, the
effectiveness of these extracts were demonstrated using paracetamol induced
rats which is a known model for both hepatic glutathione depletion and injury.
Therefore, the level of glutathione is of crucial importance in liver injury
caused by paracetamol. Our results are in line with a research work by Gosh et
al (2007), because we found that after A. sativum and A.
barbadensis supplementation, the GSH level increased significantly (p < 0.05)
in a dose dependent manner as compared with paracetamol treated showing that
exogenous ethanolic extracts might provide a means to recover reduced GSH levels
and to prevent tissue disorders and injuries (Gosh et al, 2007).
From the results, a significant
decrease ( p < 0.05 ) was observed in the level of TBARS, the end products
of lipid peroxidation in the liver of rats treated with extracts of A.
sativum and A. barbadensis as compared to paracetamol treated (Appendix
I).The increase in TBARS levels in liver suggests enhanced lipid peroxidation
leading to tissue damage. Pretreatment with ethanolic extracts of A. sativum
and A. barbadensis significantly reversed these changes in a dose
dependent pattern. Hence it maybe possible that the mechanism of
hepatoprotection of the extracts is due to their ability to reduce or prevent
lipid preoxidations.
The result on super oxide dismutase
(SOD)) showed a significant decrease (P < 0.05) in the
concentration of SOD in the rats treated with paracetamol in comparison with
the control group. This reduced significantly after treatment of animals with extracts
of A. sativum and A. barbadensis in a dose dependent
manner, showing a reversal in the toxicity effect and antioxidant action.
phenols are very important plant constituents because of their free radical
scavenging ability and antioxidant action due to their hydroxyl groups. These
extracts according to the works of sofowora, 1993 is found to contain phenolic
compounds in significant amount, which attributes to its rationality of
possessing antioxidant activity.
Significant increase (p < 0.05)
in the level of catalase (CAT) after treatment of animals with extracts was observed.
This implies that the extracts poses antioxidant activity. Hydrogen peroxide is
a harmful by product of many normal metabolic processes, to prevent damage; it
must be quickly converted into other less dangerous substances. To this end, catalase
is frequently used by cells to rapidly catalyze the decomposition of hydrogen
peroxide into less reactive gaseous
oxygen and water molecules. The was a significant difference (p< 0.05)
produced between the lowest dosage (200 µg/ml) and the highest dosage of (800
µg/ml) of the extracts showing that the extracts are more effective at high
concentration, of which A. sativum
was more effective. Our result is in line with the work of Gosh et al, 2007
were he worked on hepatoprotection and antioxidant activity of some medicinal
plants.
The significant increase (p <
0.05) of AST in rats treated with paracetamol overdose show that the paracetamol
affected the liver hepatocytes causing the enzymes to leak into the blood
stream. However, treatment with ethanolic extracts of A. sativum and A. barbadensis, caused a significant
decrease (p< 0.05) in a dose dependant manner showing that the extracts
contains compounds that can be effective in the protection and treatment of
liver damage. Serum transaminase AST is an important liver enzyme because it
indicates the condition of the liver (Nelson et al, 2000). Liver degeneration
due to drug toxicity is accompanied by leakage of liver enzymes from injured
hepatocytes into the blood. These transaminases are most useful for monitoring
the degree of recovery of a damaged liver. This is in line with the work of
Sorimuthu et al, 2005 where the antioxidant property of A. barbadensis was
observed in streptozotocin – induced diabetes in rats.
The significant decrease (p < 0.05) in serum
ALT as compared with the paracetamol treated group observed after treatment
with extracts suggests hepatoprotective activity of the extracts. Serum ALT
catalysis the conversion of alanine to pyruvate and glutamate, and is released in
a similar manner. Therefore, ALT is more specific to the liver and thus an
important parameter for detecting liver injury (Nelson et al, 2000 From the
results, it shows that both extracts have high medicinal value but A.
sativum was more effective.
Our result demonstrated that the
ethanolic extracts of A. sativum and A. barbadensis caused
significant inhibition (p < 0.05) in the level of serum alkaline phosphatase
in a dose dependent manner.
Alkaline
phosphatase is another liver marker enzyme that is used to check liver dysfunction.
Serum ALP and bilirubin levels are related to the function of hepatic cell.
Increase in serum level of ALP is due to increased synthesis, in the presence
of increasing biliary pressure (Gosh et al, 2007).
Bilirubin, the end product of heme
metabolism is essential in diagnosis of liver damage. The normal range is 0.1 –
0.5 mg / dl in animals. When the level reaches above 2 mg / dl, Jaundice
becomes clinically obvious. From the results obtained, the extracts decreased
bilirubin level significantly (p< 0. 05)as compared with the control group (Appendix
II).Effective control of alkaline phosphatase activity and bilirubin level
points towrds an early improvement in secretory mechanism of hepatic cells.
From the results, the level of
albumin decreased due to its increased catabolism with little effect on
globulin level. The administration of the extracts of A. sativum and A.
barbadensis reduced this abnormality to an extent (with extract of A.
sativum showing a higher effect. plasma proteins are very important in the
body and provide a useful diagnostic aid. Albumin performs an important
function in binding many substances, reducing their availability and toxic
actions. Thus the binding (conjugation) of bilirubin protects the newborn child
against the toxic action of this substances, preventing it from penetrating the
blood-brain–barrier. The binding ability of albumin to drugs is reduced in
hypoalbuminaemia when binding sites are blocked by various metabolites.
In the
histology result, the photomicrograph shows that the liver has necrosis
characterized by distortion of the liver pattern (Walter et al, 1996). Necrosis
is known as death of liver hepatic cells and paracetamol over dose is known to
cause bridge necrosis a type of necrosis caused from extensive damage of
adjacent liver cells and Central portal vein. This could be seen clearing and
cells regenerating after administration of extracts of A. sativum and A.
barbadensis showing that the extracts contains some components capable of
protecting the liver from drug toxicity.