“Chemo-brain”- Doxorubicin-Induced Neurotoxicity in Acute Experiment (Histopathology, Immunohistochemistry)

Abstract

Chemotherapy is an effective conventional and widely used treatment for cancer patients, that can significantly prolong the survival of patients with different types of cancer, but, unfortunately, it is associated with serious short- and long-term neurological side effects. Neurotoxicity manifests with a wide range of symptoms including fatigue, emotional instability, anxiety, difficulty concentrating, and issues with learning, reasoning, attention, and memory and syndromes such as acute, subacute and chronic encephalopathies, acute brain dysfunction, numerous cognitive disorders, myelopathy, meningitis, peripheral neuropathies. The phenomenon of chemotherapy-induced cognitive decline is termed as post-chemotherapy cognitive impairment (PCCI), chemotherapy-related cognitive impairment (CRCI), chemotherapy-induced cognitive impairment (CICI) or chemo-brain.

PCCI is a common complaint that dramatically impairs the quality of life of survivors and prevents them from returning to their pre-cancer lives among patients with various types of cancer, such as breast or lung cancer. The exact nature of chemotherapy appears complex, but a clear understanding of the mechanisms involved in PCCI, which could provide important information for potential treatments or therapies, is still unclear.

Doxorubicin (DOX) is commonly used in adjuvant chemotherapy for a variety of tumors, but its efficacy against brain tumors is limited due to its poor penetration across the blood–brain barrier (BBB). Despite this barrier, DOX has been shown to be involved in intense central neurotoxicity despite being almost entirely restricted to the periphery. DOX has been detected in the brain following peripheral administration and has caused severe neurotoxicity. However, the exact morphological mechanisms underlying brain chemotherapy remain unclear.

We study the effects of doxorubicin (DOX) in an acute experiment on the cerebral cortex and cerebellum, which would enable us to contribute to the definition of the functional and morphological basis of DOX-induced neurotoxicity.

The experiment involved adult male Wistar rats (m=170-200 g). A control group of intact animals followed standard vivarium protocols (GALS regulation 2023), and four experimental groups received different doses of DOX (5-15 mg/kg) with varying numbers of injections. Histological and immunohistochemical studies were conducted.

We focused on structural changes in the cortex and cerebellum, observing a significantly reduced number of intact neurons, along with phenomena such as swelling, shrinkage, eosinophilia, and "red neurons." Other findings included chromatolysis, neuronophagia, "crystal-like" cells, massive coagulative necrosis, and expanded Virchow-Robin spaces. Marked reactive gliosis, formation of neuritic plaques (β-amyloid protein), and "neurofibrillary tangles" (microtubule-associated tau-protein) showed progressive tendencies over a 15-day period. Additionally, we noted degeneration of astrocytic glial cytoskeletal elements, hypertrophy-hyperplasia of astrocytes with high expression of anti-GFAP, and in the cerebellum, swelling and disorganization of the Purkinje cell layer with strong positive anti-GFAP reactions. In the choroid plexus, findings included hyperemia, hemolysis, hemo- and plasmorrhagia, and marked swelling of the ependyma with a high positive anti-GFAP reaction.

Thus, a study of doxorubicin (DOX) effect showed significant changes in all neural elements of cytoarchitecture causing reactive astrogliosis and the formation of glial scars in the area of inflammation. These changes can be considered as a significant basis of chemo-brain and subsequent cognitive impairment.