Plasma cholesterol level determines in vivo prion propagation

Neutrophil to High-density Lipoprotein ratio (NHR) as a potential predictor of disease severity and survival time in Creutzfeldt-Jakob disease

INTRODUCTION

Creutzfeldt-Jakob disease (CJD) is a fatal and irreversible neurodegenerative disease. Identification of inexpensive and easy-to-implement biomarkers of CJD which could predict disease severity and patient survival is important for improving disease management. The aim of this study was to assess the predictive value of peripheral neutrophil to lymphocyte ratio (NLR), high-density lipoprotein (HDL), monocyte to HDL ratio (MHR) and neutrophil to HDL ratio (NHR) for CJD.

METHODS

Patients with definite or probable CJD admitted to the Neurology Department of Xuanwu Hospital from 2014 to 2021 were enrolled and followed up until April 2022. Clinical information including sex, age, Barth Index, survival time and results of auxiliary examination were collected, and NLR, HDL, NHR and MHR were measured for all enrolled patients. The associations between NLR, HDL, NHR and MHR, and disease severity (evaluated by Barth Index), survival time and auxiliary examinations were evaluated.

RESULTS

A total of 88 CJD patients were enrolled and all were deceased. NLR (r = -0.341, p = 0.001), NHR (r = -0.346, p = 0.001) and MHR (r = -0.327, p = 0.002) were significantly associated with disease severity. Higher NHR (HR = 2.344, 95% CI = 1.277-4.303 p = 0.006) and lower HDL (HR = 0.567, 95% CI = 0.346-0.930, p = 0.025) were associated with shorter survival time in the CJD patients.

CONCLUSIONS

Peripheral inflammatory biomarkers, especially NHR, were associated with disease severity and survival duration. These findings provide new insights into the mechanisms and treatment strategies of CJD.

Prion therapeutics: Lessons from the past

Prion diseases are a group of incurable zoonotic neurodegenerative diseases (NDDs) in humans and other animals caused by the prion proteins. The abnormal folding and aggregation of the soluble cellular prion proteins (PrPC) into scrapie isoform (PrPSc) in the Central nervous system (CNS) resulted in brain damage and other neurological symptoms. Different therapeutic approaches, including stalling PrPC to PrPSc conversion, increasing PrPSc removal, and PrPC stabilization, for which a spectrum of compounds, ranging from organic compounds to antibodies, have been explored. Additionally, a non-PrP targeted drug strategy using serpin inhibitors has been discussed. Despite numerous scaffolds being screened for anti-prion activity in vitro, only a few were effective in vivo and unfortunately, almost none of them proved effective in the clinical studies, most likely due to toxicity and lack of permeability. Recently, encouraging results from a prion-protein monoclonal antibody, PRN100, were presented in the first human trial on CJD patients, which gives a hope for better future for the discovery of other new molecules to treat prion diseases. In this comprehensive review, we have re-visited the history and discussed various classes of anti-prion agents, their structure, mode of action, and toxicity. Understanding pathogenesis would be vital for developing future treatments for prion diseases. Based on the outcomes of existing therapies, new anti-prion agents could be identified/synthesized/designed with reduced toxicity and increased bioavailability, which could probably be effective in treating prion diseases.

Cholesterol and its reciprocal association with prion infection

Prion diseases are incurable, infectious and fatal neurodegenerative diseases that affect both humans and animals. The pathogenesis of prion disease involves the misfolding of the cellular prion protein, PrP^C, to a disease-causing conformation, PrP^Sc, in the brain. The exact mechanism of conversion of PrP^C to PrP^Sc is not clear; however, there are numerous studies supporting that this process of misfolding requires the association of PrP^C with lipid raft domains of the plasma membrane. An increase in the cellular cholesterol content with prion infection has been observed in both in vivo and in vitro studies. As cholesterol is critical for the formation of lipid rafts, on the one hand, this increase may be related to, or aiding in, the process of prion conversion. On the other hand, increased cholesterol levels may affect neuronal viability. Here, we discuss current literature on the underlying mechanisms and potential consequences of elevated neuronal cholesterol in prion infection and advancements in prion disease therapeutics targeting brain cholesterol homeostasis.

Oral administration of repurposed drug targeting Cyp46A1 increases survival times of prion infected mice

Prion diseases are fatal, infectious, and incurable neurodegenerative disorders caused by misfolding of the cellular prion protein (PrP^C) into the infectious isoform (PrP^Sc). In humans, there are sporadic, genetic and infectious etiologies, with sporadic Creutzfeldt-Jakob disease (sCJD) being the most common form. Currently, no treatment is available for prion diseases. Cellular cholesterol is known to impact prion conversion, which in turn results in an accumulation of cholesterol in prion-infected neurons. The major elimination of brain cholesterol is achieved by the brain specific enzyme, cholesterol 24-hydroxylase (CYP46A1). Cyp46A1 converts cholesterol into 24(S)-hydroxycholesterol, a membrane-permeable molecule that exits the brain. We have demonstrated for the first time that Cyp46A1 levels are reduced in the brains of prion-infected mice at advanced disease stage, in prion-infected neuronal cells and in post-mortem brains of sCJD patients. We have employed the Cyp46A1 activator efavirenz (EFV) for treatment of prion-infected neuronal cells and mice. EFV is an FDA approved anti-HIV medication effectively crossing the blood brain barrier and has been used for decades to chronically treat HIV patients. EFV significantly mitigated PrP^Sc propagation in prion-infected cells while preserving physiological PrP^C and lipid raft integrity. Notably, oral administration of EFV treatment chronically at very low dosage starting weeks to months after intracerebral prion inoculation of mice significantly prolonged the lifespan of animals. In summary, our results suggest that Cyp46A1 as a novel therapeutic target and that its activation through repurposing the anti-retroviral medication EFV might be valuable treatment approach for prion diseases.