Methodological shortcomings of preclinical research on chemotherapy-induced cognitive impairment

Risk of Dementia in Different Types of Cancer Survivors: A Nationwide Cohort Study

OBJECTIVES

The association between specific types of malignancies and the subsequent risk of dementia remains unknown.

DESIGN

A retrospective population-based cohort study based on data from Taiwan National Health Insurance Research Database.

SETTING AND PARTICIPANTS

We recruited 32,250 patients who survived malignancies and 322,500 controls between 1998 and 2011 and followed them up until the end of 2013.

MEASUREMENTS

Diagnoses of dementia (including Alzheimer's disease (AD), vascular dementia (VaD), and unspecified dementia) was made during the follow-up period. Cox regression analyses were performed after adjusting for potential confounders. A sensitivity analysis was conducted to exclude patients with prodromal dementia.

RESULTS

Cancer survivors were more likely to develop AD (hazard ratio [HR]: 1.68, 95% confidence interval [CI]: 1.38-2.06), unspecified dementia (HR: 1.19, 95% CI: 1.07-1.32), and any dementia (HR: 1.26, 95% CI: 1.16-1.37) compared with controls after adjusting for potential confounders. Importantly, cancers of the digestive and genitourinary organs seem to be associated with AD, unspecified dementia, and any dementia, whereas only malignant neoplasms of the brain are more likely to develop into VaD. Sensitivity analyses after exclusion of the first three or five years of observation and after exclusion of case enrollment before 2009 or 2007 showed consistent findings.

CONCLUSION

Cancer survivors are at higher risk of subsequent dementia. Different types of cancer survivors may contribute to variable risks of specific dementias. Further studies are necessary to investigate the underlying mechanisms in cancer survivors and patients with dementia.

Systemic and targeted activation of Nrf2 reverses doxorubicin-induced cognitive impairments and sensorimotor deficits in mice

While cancer survivorship has increased due to advances in treatments, chemotherapy often carries long-lived neurotoxic side effects which reduce quality of life. Commonly affected domains include memory, executive function, attention, processing speed and sensorimotor function, colloquially known as chemotherapy-induced cognitive impairment (CICI) or "chemobrain". Oxidative stress and neuroimmune signaling in the brain have been mechanistically linked to the deleterious effects of chemotherapy on cognition and sensorimotor function. With this in mind, we tested if activation of the master regulator of antioxidant response nuclear factor E2-related factor 2 (Nrf2) alleviates cognitive and sensorimotor impairments induced by doxorubicin. The FDA-approved systemic Nrf2 activator, diroximel fumarate (DRF) was used, along with our recently developed prodrug 1c which has the advantage of specifically releasing monomethyl fumarate at sites of oxidative stress. DRF and 1c both reversed doxorubicin-induced deficits in executive function, spatial and working memory, as well as decrements in fine motor coordination and grip strength, across both male and female mice. Both treatments reversed doxorubicin-induced loss of synaptic proteins and microglia phenotypic transition in the hippocampus. Doxorubicin-induced myelin damage in the corpus callosum was reversed by both Nrf2 activators. These results demonstrate the therapeutic potential of Nrf2 activators to reverse doxorubicin-induced cognitive impairments, motor incoordination, and associated structural and phenotypic changes in the brain. The localized release of monomethyl fumarate by 1c has the potential to diminish unwanted effects of fumarates while retaining efficacy.

Cisplatin induces BDNF downregulation in middle-aged female rat model while BDNF enhancement attenuates cisplatin neurotoxicity

Cancer-related cognitive impairments (CRCI) are neurological complications associated with cancer treatment, and greatly affect cancer survivors' quality of life. Brain-derived neurotrophic factor (BDNF) plays an essential role in neurogenesis, learning and memory. The reduction of BDNF is associated with the decrease in cognitive function in various neurological disorders. Few pre-clinical studies have reported on the effects of chemotherapy and medical stress on BDNF levels and cognition. The present study aimed to compare the effects of medical stress and cisplatin on serum BDNF levels and cognitive function in 9-month-old female Sprague Dawley rats to age-matched controls. Serum BDNF levels were collected longitudinally during cisplatin treatment, and cognitive function was assessed by novel object recognition (NOR) 14 weeks post-cisplatin initiation. Terminal BDNF levels were collected 24 weeks after cisplatin initiation. In cultured hippocampal neurons, we screened three neuroprotective agents, riluzole (an approved treatment for amyotrophic lateral sclerosis), as well as the ampakines CX546 and CX1739. We assessed dendritic arborization by Sholl analysis and dendritic spine density by quantifying postsynaptic density-95 (PSD-95) puncta. Cisplatin and exposure to medical stress reduced serum BDNF levels and impaired object discrimination in NOR compared to age-matched controls. Pharmacological BDNF augmentation protected neurons against cisplatin-induced reductions in dendritic branching and PSD-95. Ampakines (CX546 and CX1739) and riluzole did not affect the antitumor efficacy of cisplatin in vitro. In conclusion, we established the first middle-aged rat model of cisplatin-induced CRCI, assessing the contribution of medical stress and longitudinal changes in BDNF levels on cognitive function, although future studies are warranted to assess the efficacy of BDNF enhancement in vivo on synaptic plasticity. Collectively, our results indicate that cancer treatment exerts long-lasting changes in BDNF levels, and support BDNF enhancement as a potential preventative approach to target CRCI with therapeutics that are FDA approved and/or in clinical study for other indications.

More than a small adult brain: Lessons from chemotherapy-induced cognitive impairment for modelling paediatric brain disorders

Childhood is recognised as a period of immense physical and emotional development, and this, in part, is driven by underlying neurophysiological transformations. These neurodevelopmental processes are unique to the paediatric brain and are facilitated by augmented rates of neuroplasticity and expanded neural stem cell populations within neurogenic niches. However, given the immaturity of the developing central nervous system, innate protective mechanisms such as neuroimmune and antioxidant responses are functionally naïve which results in periods of heightened sensitivity to neurotoxic insult. This is highly relevant in the context of paediatric cancer, and in particular, the neurocognitive symptoms associated with treatment, such as surgery, radio- and chemotherapy. The vulnerability of the developing brain may increase susceptibility to damage and persistent symptomology, aligning with reports of more severe neurocognitive dysfunction in children compared to adults. It is therefore surprising, given this intensified neurocognitive burden, that most of the pre-clinical, mechanistic research focuses exclusively on adult populations and extrapolates findings to paediatric cohorts. Given this dearth of age-specific research, throughout this review we will draw comparisons with neurodevelopmental disorders which share comparable pathways to cancer treatment related side-effects. Furthermore, we will examine the unique nuances of the paediatric brain along with the somatic systems which influence neurological function. In doing so, we will highlight the importance of developing in vitro and in vivo paediatric disease models to produce age-specific discovery and clinically translatable research.

Cellular senescence in brain aging and cognitive decline

Cellular senescence is a biological aging hallmark that plays a key role in the development of neurodegenerative diseases. Clinical trials are currently underway to evaluate the effectiveness of senotherapies for these diseases. However, the impact of senescence on brain aging and cognitive decline in the absence of neurodegeneration remains uncertain. Moreover, patient populations like cancer survivors, traumatic brain injury survivors, obese individuals, obstructive sleep apnea patients, and chronic kidney disease patients can suffer age-related brain changes like cognitive decline prematurely, suggesting that they may suffer accelerated senescence in the brain. Understanding the role of senescence in neurocognitive deficits linked to these conditions is crucial, especially considering the rapidly evolving field of senotherapeutics. Such treatments could help alleviate early brain aging in these patients, significantly reducing patient morbidity and healthcare costs. This review provides a translational perspective on how cellular senescence plays a role in brain aging and age-related cognitive decline. We also discuss important caveats surrounding mainstream senotherapies like senolytics and senomorphics, and present emerging evidence of hyperbaric oxygen therapy and immune-directed therapies as viable modalities for reducing senescent cell burden.

Cyclosporin A-mediated translocation of HuR improves MTX-induced cognitive impairment in a mouse model via NCOA4-mediated ferritinophagy

Chemotherapy-induced cognitive impairment (CICI) is a subject that requires critical solutions in neuroscience and oncology. However, its potential mechanism of action remains ambiguous. The aim of this study was to investigate the vital role of HuR in the neuroprotection of cyclosporin A (CsA) during methotrexate (MTX)-induced cognitive impairment. A series of Hu-antigen R (HuR) gain and loss experiments were used to examine cyclosporin A (CsA)-mediated translocation of HuR's ability to improve MTX-induced cognitive impairment through NCOA4-mediated ferritinophagy in vitro and in vivo. Obtained results show that the administration of CsA alleviated MTX-induced cognitive impairment in mice. The presence of MTX promoted the shuttling of HuR from the cytoplasm to the nucleus, whereas treatment with CsA increased cytoplasmic HuR expression levels and the levels of ferritinophagy-related proteins, such as NCOA4 and LC3II, compared to the MTX group. However, applying KH-3, an inhibitor of HuR, reversed CsA's impact on the expression of ferritinophagy-related proteins in the hippocampus and in vitro. Also, treatment with CsA attenuated microglial activation by altering Iba-1 expression and decreased TNF-α and IL-1β levels in mice hippocampi. Moreover, KH-3 neutralized CsA's effects on the expression of both Iba-1 and HuR in vivo and in vitro. In summary, CsA was confirmed to have a neuroprotective role in CICI. Its possible underlying mechanisms may be involved in the translocation of HuR. Mediating the translocation of HuR during CICI could mitigate neruoinflammation and neuronal apoptosis via NCOA4-mediated ferritinophagy and, thus, alleviate cognitive impairment in mice with CICI.