Amelioration of Neurochemical Alteration and Memory and Depressive Behavior in Sepsis by Allopurinol, a Tryptophan 2,3-Dioxygenase Inhibitor

BACKGROUND

In response to inflammation and other stressors, tryptophan is catalyzed by Tryptophan 2,3-Dioxygenase (TDO), which leads to activation of the kynurenine pathway. Sepsis is a serious condition in which the body responds improperly to an infection, and the brain is the inflammation target in this condition.

OBJECTIVE

This study aimed to determine if the induction of TDO contributes to the permeability of the Blood-Brain Barrier (BBB), mortality, neuroinflammation, oxidative stress, and mitochondrial dysfunction, besides long-term behavioral alterations in a preclinical model of sepsis.

METHODS

Male Wistar rats with two months of age were submitted to the sepsis model using Cecal Ligation and Perforation (CLP). The rats received allopurinol (Allo, 20 mg/kg, gavage), a TDO inhibitor, or a vehicle once a day for seven days.

RESULTS

Sepsis induction increased BBB permeability, IL-6 level, neutrophil infiltrate, nitric oxide formation, and oxidative stress, resulting in energy impairment in 24h after CLP and Allo administration restored these parameters. Regarding memory, Allo restored short-term memory impairment and decreased depressive behavior. However, no change in survival rate was verified.

CONCLUSION

In summary, TDO inhibition effectively prevented depressive behavior and memory impairment 10 days after CLP by reducing acute BBB permeability, neuroinflammation, oxidative stress, and mitochondrial alteration.

Memantine Improves Memory and Neurochemical Damage in a Model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is a metabolic disease characterized by the accumulation of branched-chain amino acids (BCAA) in different tissues due to a deficit in the branched-chain alpha-ketoacid dehydrogenase complex. The most common symptoms are poor feeding, psychomotor delay, and neurological damage. However, dietary therapy is not effective. Studies have demonstrated that memantine improves neurological damage in neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Therefore, we hypothesize that memantine, an NMDA receptor antagonist can ameliorate the effects elicited by BCAA in an MSUD animal model. For this, we organized the rats into four groups: control group (1), MSUD group (2), memantine group (3), and MSUD + memantine group (4). Animals were exposed to the MSUD model by the administration of BCAA (15.8 µL/g) (groups 2 and 4) or saline solution (0.9%) (groups 1 and 3) and treated with water or memantine (5 mg/kg) (groups 3 and 4). Our results showed that BCAA administration induced memory alterations, and changes in the levels of acetylcholine in the cerebral cortex. Furthermore, induction of oxidative damage and alterations in antioxidant enzyme activities along with an increase in pro-inflammatory cytokines were verified in the cerebral cortex. Thus, memantine treatment prevented the alterations in memory, acetylcholinesterase activity, 2',7'-Dichlorofluorescein oxidation, thiobarbituric acid reactive substances levels, sulfhydryl content, and inflammation. These findings suggest that memantine can improve the pathomechanisms observed in the MSUD model, and may improve oxidative stress, inflammation, and behavior alterations.