Doxorubicin-induced, Tnf-α- Mediated Brain Oxidative Stress, Neurochemical Alterations, and Cognitive Decline: Insights into Mechanisms of Chemotherapy Induced Cognitive Impairment and Its Prevention

OF DISSERTATION DOXORUBICIN-INDUCED, TNF-α -MEDIATED BRAIN OXIDATIVE STRESS, NEUROCHEMICAL ALTERATIONS, AND COGNITIVE DECLINE: INSIGHTS INTO MECHANISMS OF CHEMOTHERAPY INDUCED COGNITIVE IMPAIRMENT AND ITS PREVENTION The works presented in this dissertation provide insights into the mechanisms of chemotherapy-induced cognitive impairment (CICI or “ChemoBrain”) and take steps toward outlining a preventive strategy. CICI is now widely recognized as a complication of cancer chemotherapy experienced by a large percentage of cancer survivors. Approximately fifty percent of existing FDA-approved anticancer drugs generate reactive oxygen species (ROS). Doxorubicin (Dox), a prototypical ROS-generating chemotherapeutic agent, produces the reactive superoxide radical anion (O2•) in vivo. Dox treatment results in oxidation of plasma proteins, including ApoA-I, leading to TNF-α-mediated oxidative stress in plasma and brain. TNF-α elevation in brain leads to further central nervous system toxicity including mitochondrial dysfunction, neuronal death, and cognitive impairment. Co-administration of the antioxidant drug, 2-mercaptoethane sulfonate sodium (MESNA), prevents Dox-induced protein oxidation and subsequent TNF-α elevation in plasma without interfering with the cancer-killing ability of Dox. In studies presented in this dissertation, we measured oxidative stress in both brain and plasma of Dox-treated mice both with and without MESNA. MESNA ameliorated Dox-induced oxidative protein damage in plasma, confirming our prior studies, and in a new finding led to decreased oxidative stress in brain. Using novel object recognition (NOR), we demonstrated the Dox administration resulted in memory deficits. Using hydrogen magnetic resonance imaging spectroscopy (H-MRS) techniques, we demonstrated that Dox administration led to a dramatic decrease in choline(phosphocholine)/creatine (Cho/Cr) ratios in mouse hippocampus. The activities of both phosphatidylcholine-specific phospholipase C (PC-PLC) and phospholipase D(PLD) were severely diminished following Dox administration. The activity of PC-PLC was preserved when MESNA was co-administered with Dox. In the absence of TNF-α, MRS-indexed Cho/Cr ratio, PLD activity, and mitochondrial oxygen consumption are preserved in brain, and markers of oxidative stress are reduced. Together with results from our previous studies, these results provide strong evidence that TNF-α is strongly associated, if not responsible for CICI. We also tested the notion that O2• is responsible for Dox-induced plasma protein oxidation and TNF-α release. O2• resulted in increased oxidative damage to proteins when added to plasma and increased levels of TNF-α in macrophage culture, providing strong evidence that O2• is responsible for these Dox-induced toxicities.