Análise da expressão de citocinas inflamatórias em hipocampo de pacientes com epilepsia mesial do lobo temporal: sugestões para a aplicabilidade de testes de memória pós-cirurgia

Abstract

Neuroinflammation is a major secondary event of the pathophysiology of acute and chronic neural disorders. It contains humoral and cellular components of the innate and adaptive immune systems. Microglial activation is a crucial event in chronic neuronal disorders with deleterious and/or beneficial consequences. Alzheimer's disease (AD) microglia can be beneficial by phagocytizing as amyloid plaques, but may contribute to neuronal damage and a pro-inflammatory phenotype, depending on the disease progression. In epilepsy, an intense and long-lasting microglial reaction has been described using experimental models of status epilepticus, which indicates an important role of microgliosis in neuronal damage. However, microglial activation patterns were not systematically investigated in the brains of human patients with different degrees of hippocampal sclerosis due to temporal lobe epilepsy (TLE). In this study, we explored the pattern of microglial reaction in the hippocampus of TLE patients with different clinical histories and submitted to unilateral hipocampectomy for treatment of refractory TLE. Hippocampal samples were obtained through the resection of this hippocampus. The tissue of a patient who presented the first seizure in childhood, which became continuous (P4) and a patient with latency of decades after the first seizure (P5) was used. Tissue samples removed during surgery were collected in sterile saline solution and then placed in 4% paraformaldehyde for 24 hours. After this time, tissue samples from patients P4 and P5 were cryoprotect in different gradients of glycerol and sucrose solution for two weeks and cut using a 40 μm thick cryostat. The sections were submitted to immunohistochemistry for microglia (anti-Iba1), proinflammatory cytokine (IL-1β) and anti-inflammatory cytokine (TGF-β). Generalized microglial activation with different degrees of microgliosis was present in the hippocampus of patients P4 and P5. However, the microglial reaction was intense in P4, characterized by a considerable number of degenerative and dystrophic microglia and rod cells. TGF-β positive cells were conspicuously present in the hippocampus of both patients in clusters-like cavities and sparsely distributed over the parenchyma of the hippocampus. IL-1β positive cells were not present. The clinical history of each patient, with more or less convulsions over time, seems to induce differential patterns of microglial response during TLE. In the present study, the patient with continuous seizures for many years, without latency, presented intense microglial activation, dystrophy and degeneration that resemble the pathological findings present in AD. Anti-inflammatory reactions by non-microglial cells were also present, as suggested by the generalized presence of TGF-β-positive cells on the hippocampus parenchyma.