الفهرس 
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Abstract
recent years. It is an inflammatory response that can worsen tissue damage, cause nerve cell
death, and potentially affect the structure and function of the brain or spinal cord. During the
current century, researchers pointed out that exposure to Diacetyl (2, 3-butanedione; DA)
might induce neurotoxicity because of its capability to easily cross the blood brain barrier.
DA is a flavouring agent found in a variety of human foods, including dairy products, roasted
coffee, and caramel. Silymarin (Sily), as a flavonoid, has received a lot of attention in
preserving neuronal function, although it is well known as a hepatoprotective. Accordingly,
the present study was designated to clarify the potential protective and therapeutic efficacy of
Sily against DA-induced neuroinflammation and to explore the underlying mechanisms.
Neuroinflammation was induced in rats via administrating 25 mg diacetyl
(DA)/kg/day orally for 15 or 30 days. A total of 105 male rats were used and randomly
arranged into seven groups according to the treatment. Each group was consisted of 15 rats as
follows; Normal control (C) group (receiving 0.15 mL DW as a vehicle), Diacetyl-15
(DA1) group (receiving 52 mg DA/kg/day for 15 days), Diacetyl-30 (DA2) group
(receiving 25 mg DA/kg/day for 30 days), Silymarin (Sily) group (receiving 50 mg
Silymarin/kg/day for 15 days), Protected (P) group (receiving 50 mg Silymarin/kg/day on
hour before administring 25 mg DA/kg/day for 15 days), Treated-15 (T1) group (25 mg
DA/kg/day for 15 days, followed by 50 mg Silymarin/kg/day for another consecutive 15
days), and Treated-30 (T2) group (receiving 25 mg DA/kg/day for 30 days and started 50
mg Silymarin/kg/day at day 16th parallel with DA for the next 15 days)
Twenty-four hours following the end of experiment, each group was randomly
divided into two sets:
- The first set included 5 rats that was used for evaluating the cognitive and
behavioral testing by using four tasks, including Morris water maze task, Y-maze task,
Climbing pole test, and Open field test starting after 24 hours from the end of experiment
with a delay interval of 48 h in between.
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- The second set included 10 rats which were sacrificed and their brain were isolated, collected and divided into two parts and used for determination of:
- Oxidant / antioxidant status; MDA and NO levels, as well as TAC
- Neuroprotective biomarkers; IL-10, GDNF, and Dyn
- Inflammatory cytokines; IFN-γ, TNFα, and IL-1β
- Acetyl choline esterase activity
- Western immunoblotting determination of p44/42 MAPK (ERK 1/2)/Phospho p44/42 MAPK (ERK1/2), JNK/Phospho-pJNK, and p38MAPK/Phospho-p38MAPK
- Immunohistochemical detection of GFAP and EGFR
- Histopathologic examination with H&E staining
Diacetyl-treated group for 15 days showed a significant increase in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK as compared with control group. However, a significant decrease in % of correct arm choice, motor coordination score, ambulation frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels following the treatement with DA as compared with control group.
Treatment with DA for 15 days also showed moderate positive immunostaining signals for GFAP and EGFR in the brain tissues. These findings were further confirmed significant changes in the normal histological architecture as compared to the normal control group. It revealed scattered neuronal edema and few aggregations of inflammatory cells.
Diacetyl-treated group for 30 days showed a significant increase in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK as compared to control and DA-15 groups. On the contrary, a significant decrease in % of correct arm choice, motor coordination score, ambulation
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frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels was observed in DA-30 group compared with control and DA-15 groups.
Moreover, treatment with DA for 30 days also showed strong positive immunostaining signals for GFAP and EGFR in the brain tissues, as well as revealed severe neuronal edema and heavy infiltration of inflammatory cells within the brain tissue.
Pretreatment with silymarin (50 mg/kg) 2 h before diacetyl for 15 days showed a significant decrease in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK as compared to DA-15 group. However, a significant increase in % of correct arm choice, motor coordination score, ambulation frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels was observed in P group compared with control and DA-15 groups.
Additionally, protected group also showed weak positive immunostaining signals for GFAP and EGFR in the brain tissues and revealed normal histological picture of the brain tissue.
Silymarin treatment (50 mg/kg) for 15 days after stopping diacetyl showed a significant decrease in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK as compared to DA-15 group. However, a significant increase in % of correct arm choice, motor coordination score, ambulation frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels was observed in treated-15 group compared with DA-15 group.
Furthermore, treated-15 group also showed weak positive immunostaining signals for GFAP and EGFR in the brain tissues and revealed normal histological architecture, but with mild neuronal edema.
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Silymarin treatment (50 mg/kg) for 15 days along with diacetyl showed a significant increase in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK, but with a significant decrease in % of correct arm choice, motor coordination score, ambulation frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels as compared to control, silymarin and treated-15 groups.
Moreover, treated-30 group also showed moderate positive immunostaining signals for GFAP and EGFR in the brain tissues and revealed focal aggregates of inflammatory cells in brain tissue.
Silymarin treatment (50 mg/kg) for 15 days parallel with diacetyl showed a significant decrease in escape latency time, % of exploring time, T-turned latency time, grooming frequency, latency time in open field test, MDA and NO levels, IFN-γ, TNFα, and IL-1β concentrations, AChE activity, as well as expression ratio of p-ERK1/2/total ERK1/2, p-c-JNK/total c-JNK, and p-p38-MAPK/total p38-MAPK, but with a significant increase in % of correct arm choice, motor coordination score, ambulation frequency, frequency of rearing behavior, TAC, IL-10, GDNF, and Dyn levels as compared to DA-30 group.
Concllusiions
Silymarin provided preventive and therapeutic efficacies against neuroinflammation caused by DA in the brain, but only to a lesser extent when DA was still given. The anti-inflammatory and antioxidant properties of silymarin might be attributed to its ability to suppress ROS production and stimulate IL-10-mediated M2 neuroprotective state of microglia. Moreover, silymarin enhanced the secretion of neuroprotective markers as GDNF and Dyn, inhibited the release of IFN-γ and other inflammatory mediators (TNF–α, IL-1β, and NO), as well as the activity of AChE. In addition, silymarin could protect neurons from damages by down-regulating the expression of EGFR and GFAP and depressing the phosphorylation of ERK1/2, JNK, and p38 MAPK (Figure VI.1).
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Recommendattiions
- Silymarin would be valuable for protection against diacetyl-prompted oxidative stress and neuroinflammation
- Further clinical studies are required for emphasizing the protective and therapeutic role of silymarin against neuroinflammation
- Recent research should focus on the favorable neuroprotective role of Dyn/GDNF in neurodegenerative disorders