By Gail Hairston and Allison Perry
Of the 14 million cancer survivors in the United States, a significant number experience a serious side effect called chemotherapy-induced cognitive impairment (CICI). While easily recognized, little is known about the etiology of this condition, also known informally as “chemo brain.” CICI can significantly reduce patients’ quality of life with serious, even devastating, symptoms such as memory lapses, difficulty concentrating, negative impacts on multitasking, confusion and fatigue.
Three University of Kentucky Markey Cancer Center researchers are tackling this problem head-on, serving as principal investigators on a new $2.3 million grant awarded by the National Institutes of Health:
- Allan Butterfield, professor in the UK College of Arts and Sciences' Department of Chemistry, is renowned for his work in neurochemistry and Alzheimer’s research. Previously he has demonstrated that mitochondrial injury, mediated by reactive oxygen species, is an important mechanism of CICI.
- Daret St. Clair, professor in the UK College of Medicine's Department of Toxicology and Cancer Biology, is a leading collaborator with Butterfield on CICI research. The primary research focus of her laboratory is in the area of the mitochondrial antioxidant defense system and its response to oxidative stress, which may induce CICI.
- Subbarao Bondada, professor in the UK College of Medicine's Department of Microbiology, Immunology and Molecular Genetics, focuses primarily on B cell biology, blood cancers and myelodysplastic syndromes. His expertise in B cell biology has led the team into the investigation of the contribution of immune responses to CICI.
The new award, titled "A redox-mediated mechanism of chemotherapy-induced cognitive impairment,” theorizes a novel mechanism of CICI and identifies strategies for its prevention. The research is designed to gain an understanding of damage mechanisms and to identify the cells that produce agents during chemotherapy that lead to cognitive impairment.
The team of three researchers will test the proof-of-concept in an experimental cancer therapy setting using two prototype chemotherapy agents. They have been collaborating with clinical investigators in the Markey Cancer Center, including Dr. Rachel Miller, an associate professor in UK Gynecologic Oncology Services. If successful, the project will generate new insights required to develop effective clinical approaches specifically designed to prevent CICI without reducing chemotherapeutic efficacy, and will significantly improve the quality of life for millions of cancer survivors.
To learn more about research in this area, we asked Chemistry Prof. Butterfield to discuss his research projects. Here we provide some relevance from three of the more than 45 such papers published in 2015-2017 that address his group’s near-term goals.
In a paper published in 2015 , Butterfield showed for the first time that that the metabolic-dependent pathway called mTOR is activated in brains of persons with MCI, long before dementia occurs in this likely prodromal stage of AD. Activated mTOR in the brain is caused by defective glucose metabolism (which Butterfield and others previously described in AD and MCI) or amyloid beta-peptide (a neurotoxic peptide that accumulates in brain in MCI and AD and is associated with oxidative stress). mTOR activation leads to blockage of autophagy and development of insulin resistance. Autophagy in the neuron is a key part of the proteostasis network in cells, processes used to degrade the accumulated intracellular detritus resulting from oxidative damage and other mechanisms. Autophagy therefore normally prevents clogging the machinery of the neuron. However, even in PCAD (patients characterized as having normal cognition but whose brains have extensive pathology reminiscent of AD) as well as brains in MCI (memory loss but no dementia and no alterations of activities of daily living), Butterfield found defective autophagy in brains. Insulin resistance is characterized by the inability of insulin binding to its receptor to have information transduced to intracellular targets. Such signaling is vital to proper brain function that relies heavily on glucose for its energy source. Butterfield demonstrated for the first time that in MCI brain insulin resistance, which as noted above results from a downstream consequence of mTOR activation, is present. Others had reported insulin resistance in AD brain. This paper identifies a key pathway (mTOR) that is inhibited by a known FDA-approved agent that may show promise in slowing progression of AD. Moreover, insulin resistance may be related to type 2 diabetes mellitus (T2DM), a condition that is almost epidemic in Kentucky, and may contribute to the known increased risk of developing AD by those with T2DM.
In a 2016 paper , Butterfield reported the results of the first phospho-proteomics study of brains from persons with PCAD, MCI, and AD to identify pro-survival and cell death pathways. By comparison of the brains at each stage of AD, Butterfield found two key proteins that are inhibited by phosphorylation, suggesting that the phosphorylation status of these two proteins may contribute to the progression of AD from its earliest stages. These proteins are regucalcin and gelsolin. Both proteins are involved in remodeling synaptic membranes upon receipt of action potentials, a process this is key to mechanisms of learning and memory. Since both learning and memory are highly negatively affected in the progression of AD, these two proteins may be critically important in the loss of cognition as the disease progresses.
In a 2017 publication , Butterfield outlined his studies in brain of persons with PCAD, MCI, and AD using redox proteomics that led to new insights into three major processes that are involved in the progression of AD, processes he calls “the triangle of death for neurons.” These processes include: the proteostasis network (which includes autophagy described above; the ubiquitin proteasome system; and the unfolded protein response); defects in glucose metabolism and the presence of insulin resistance; and the phosphorylation status of key proteins involved in learning and memory.
In addition to the recently funded NIH project, Butterfield is part of four other federal grants, which focus on three major scientific questions:
a) Does overexpression of Pin-1 protect brain in Alzheimer’s Disease? Butterfield’s laboratory first reported that a regulatory protein that was oxidatively dysfunctional and of lower level in Alzheimer’s disease and its earlier stage. This protein, Pin-1, is directly involved in the molecular functions of proteins that, when dysfunctional, lead to the two major pathological hallmarks in brain of Alzheimer’s disease subjects. Butterfield reasoned that overexpression of the protein would overcome its oxidized intrinsic form and thereby lead to less oxidative stress, and will measure this along with histopathological indices of one of the major pathological hallmarks of Alzheimer’s disease. Success here will identify Pin-1 as a promising therapeutic target for slowing or stopping progression of Alzheimer’s disease.
b) Are ceria nanoparticles protective or toxic to brain? This is the subject of one of his NIH-funded studies. Butterfield’s prior studies demonstrated that nanoceria, chemical formula CeO2, causes oxidative damage in brain and liver. These observations raise serious concerns about the use of ceria nanoparticles as potential therapeutic agents in disorders such as Alzheimer disease. This NIH grant emanated from in vitro studies by others of cell cultures treated with an oxidative stress-inducing agent like hydrogen peroxide that showed these cells were protected if ceria nanoparticles were also administered to the cultures. Consequently, Butterfield, along with other UK colleagues, proposed to NIH and were funded to address the “Jekyl and Hyde” nature of ceria nanoparticles: are they toxic to brain in naïve rats but protective to brain in rats treated with a prior agent to induce oxidative stress? Ongoing studies will address this point.
c) Is the Pink-1 knockout a good model of Parkinson’s disease? Pink-1 is a mitochondrial-relevant kinase (an enzyme that phosphorylates proteins) that monitors heath of mitochondria. Mutations in Pink-1 are known to cause inherited Parkinson’s disease. Professor Butterfield is funded by a NIH grant to use new molecular biological techniques knock our genes. He presently is completing an age-dependent study of Pink-1 Knockout: 1) magnetic resonance spectroscopy (MRS) in vivo to determine brain neurochemical changes in living rodents; 2) analyses of behavior and motor functions reminiscent of Parkinson’s disease; and 3) Measure oxidative stress in brain, since PD is well known to be associated with oxidative stress, particularly that associated with mitochondria.
1. A. Tramutola, J. Triplett, F. Di Domenico, D.M. Niedowicz, M.P. Murphy, R. Coccia, M. Perluigi, and D.A. Butterfield (2015) Alteration of mTOR Signaling Occurs Early in the Progression of Alzheimer Disease: Analysis of Brain from Subjects with Preclinical AD, Amnestic Mild Cognitive Impairment and Late-Stage AD. Journal of Neurochemistry 133, 739-749.
2. M. Perluigi, F. Di Domenico, E. Barone, and D. A. Butterfield (2016) Aberrant Protein Phosphorylation in Alzheimer Disease Brain Disturbs Pro-Survival and Cell Death Pathways. Biochimica et Biophysica Acta-Molecular Basis of Disease 1862, 1871-1882.
3. F. Di Domenico, E. Barone, M. Perluigi, and D.A. Butterfield (2017), The Triangle of Death in Alzheimer Disease Brain: The Aberrant Cross Talk Among Energy Metabolism, mTOR Signaling and Protein Homeostasis Revealed by Redox Proteomics. Antioxidants and Redox Signaling 26, 364-387.