May CSF beta-amyloid and tau proteins levels be influenced by long treatment duration and stable medication in narcolepsy?

Cerebrospinal fluid biomarkers of neurodegeneration in narcolepsy type 1

STUDY OBJECTIVES

To measure the levels of five neurodegenerative biomarkers in the cerebrospinal fluid (CSF) of patients with narcolepsy type 1 (NT1) with variable disease duration.

METHODS

Following a standardized protocol of CSF collection and storage, we measured CSF total- and phosphorylated-tau, amyloid-beta 1-40 and 1-42, and neurofilament light chain (NfL) proteins in 30 nonneurological controls and 36 subjects with NT1, including 14 patients with recent disease onset (i.e. ≤12 months, short disease duration group).

RESULTS

CSF levels of all biomarkers were similar in NT1 subjects and controls. The comparison between NT1 with short and long disease duration only revealed slightly higher levels of CSF amyloid-beta 1-40 in the former group (median 9,549.5, interquartile range [IQR] 7,064.2-11,525.0 vs. 6,870.0, IQR 5,133.7-9,951.2, p = 0.043). CSF storage time did not influence the levels of the tested biomarkers.

CONCLUSIONS

The measurement of CSF total-tau, phosphorylated-tau, amyloid-beta 1-40 and 1-42, and NfL proteins is not informative in NT1.

Dysregulation of the orexin/hypocretin system is not limited to narcolepsy but has far-reaching implications for neurological disorders

Neuropeptides orexin A and B (OX-A/B, also called hypocretin 1 and 2) are released selectively by a population of neurons which projects widely into the entire central nervous system but is localized in a restricted area of the tuberal region of the hypothalamus, caudal to the paraventricular nucleus. The OX system prominently targets brain structures involved in the regulation of wake-sleep state switching, and also orchestrates multiple physiological functions. The degeneration and dysregulation of the OX system promotes narcoleptic phenotypes both in humans and animals. Hence, this review begins with the already proven involvement of OX in narcolepsy, but it mainly discusses the new pre-clinical and clinical insights of the role of OX in three major neurological disorders characterized by sleep impairment which have been recently associated with OX dysfunction, such as Alzheimer's disease, stroke and Prader Willi syndrome, and have been emerged over the past 10 years to be strongly associated with the OX dysfunction and should be more considered in the future. In the light of the impairment of the OX system in these neurological disorders, it is conceivable to speculate that the integrity of the OX system is necessary for a healthy functioning body.

CSF Levels of the Endocannabinoid Anandamide are Reduced in Patients with Untreated Narcolepsy Type 1: A Pilot Study

BACKGROUND

Endocannabinoids (ECs) modulate both excitatory and inhibitory components in the CNS. There is a growing body of evidence that shows ECs influence both hypothalamic orexinergic and histaminergic neurons involved in narcolepsy physiopathology. Therefore, ECs may influence sleep and sleep-wake cycle.

OBJECTIVE

To evaluate EC levels in the CSF of untreated narcoleptic patients to test whether ECs are dysregulated in Narcolepsy Type 1 (NT1) and Type 2 (NT2).

METHODS

We compared CSF Anandamide (AEA), 2-Arachidonoylglycerol (2-AG) and orexin in narcoleptic drug-naïve patients and in a sample of healthy subjects.

RESULTS

We compared NT1 (n=6), NT2 (n=6), and healthy controls (n=6). We found significantly reduced AEA levels in NT1 patients compared to both NT2 and controls. No differences were found between AEA levels in NT2 versus controls and between 2-AG levels in all groups, although a trend toward a decrease in NT1 was evident. Finally, the CSF AEA level was related to CSF orexin levels in all subjects.

CONCLUSION

We demonstrated that the EC system is dysregulated in NT1.

Reduced brain amyloid burden in elderly patients with narcolepsy type 1

OBJECTIVE

To determine whether brain amyloid burden in elderly patients with narcolepsy type 1 (NT1) is lower than in controls, and to assess in patients with NT1 the relationships between amyloid burden, cerebral spinal fluid (CSF) markers of Alzheimer disease (AD), CSF orexin-A, and cognitive profile.

METHODS

Cognitive and ¹⁸ F-florbetapir positron emission tomography (PET) data were compared in patients with NT1 aged ≥ 65 years (n = 23) and in age- and sex-matched controls free of clinical dementia selected from the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 69) and the Multi-Domain Intervention Alzheimer's Prevention Trial (MAPT-18F AV45-PET; n = 23) cohorts. The standardized uptake values (SUVs) of the cortical retention index for 6 regions of interest were computed and averaged to create a mean SUV ratio normalized to 3 subcortical reference regions (cerebellum, pons, and a composite region). A cortical/cerebellum SUV ratio ≥ 1.17 defined positive PET amyloid.

RESULTS

Lower cortical amyloid burden was observed in the NT1 than in the ADNI and MAPT-AV45 groups (mean cortical/cerebellum SUV ratios = 0.95 ± 0.15, 1.11 ± 0.18 [p < 0.0001], and 1.14 ± 0.17 [p = 0.0005], respectively). Similar results were obtained with all subcortical reference regions and for all cortical regions of interest, except cingulum. Only 1 patient with NT1 (4.4%) had positive PET amyloid compared with 27.5% in the ADNI and 30.4% in the MAPT-AV45 group. In the NT1 group, cortical or regional amyloid load was not associated with CSF orexin-A, CSF AD biomarkers, or neuropsychological profile.

INTERPRETATION

Lower brain amyloid burden, assessed by ¹⁸ F-florbetapir PET, in patients with NT1 suggests delayed appearance of amyloid plaques. ANN NEUROL 2019;85:74-83.