Biomarkers in Alzheimer's Disease: Are Olfactory Neuronal Precursors Useful for Antemortem Biomarker Research?

Alzheimer's disease (AD), as the main cause of dementia, affects millions of people around the world, whose diagnosis is based mainly on clinical criteria. Unfortunately, the diagnosis is obtained very late, when the neurodegenerative damage is significant for most patients. Therefore, the exhaustive study of biomarkers is indispensable for diagnostic, prognostic, and even follow-up support. AD is a multifactorial disease, and knowing its underlying pathological mechanisms is crucial to propose new and valuable biomarkers. In this review, we summarize some of the main biomarkers described in AD, which have been evaluated mainly by imaging studies in cerebrospinal fluid and blood samples. Furthermore, we describe and propose neuronal precursors derived from the olfactory neuroepithelium as a potential resource to evaluate some of the widely known biomarkers of AD and to gear toward searching for new biomarkers. These neuronal lineage cells, which can be obtained directly from patients through a non-invasive and outpatient procedure, display several characteristics that validate them as a surrogate model to study the central nervous system, allowing the analysis of AD pathophysiological processes. Moreover, the ease of obtaining and harvesting endows them as an accessible and powerful resource to evaluate biomarkers in clinical practice.

Antidepressant Low Doses of Ketamine and Melatonin in Combination Produce Additive Neurogenesis in Human Olfactory Neuronal Precursors.

Melatonin (MEL), an indolamine with diverse functions in the brain, has been shown to produce antidepressant-like effects, presumably through stimulating neurogenesis. We recently showed that the combination of MEL with ketamine (KET), an NMDA receptor antagonist, has robust antidepressant-like effects in mice, at doses that, by themselves, are non-effective and have no adverse effects. Here, we show that the KET/MEL combination increases neurogenesis in a clone derived from human olfactory neuronal precursors, a translational pre-clinical model for effects in the human CNS. Neurogenesis was assessed by the formation of cell clusters > 50 µm in diameter, positively stained for nestin, doublecortin, BrdU and Ki67, markers of progenitor cells, neurogenesis, and proliferation. FGF, EGF and BDNF growth factors increased the number of cell clusters in cultured, cloned ONPs. Similarly, KET or MEL increased the number of clusters in a dose-dependent manner. The KET/MEL combination further increased the formation of clusters, with a maximal effect obtained after a triple administration schedule. Our results show that the combination of KET/MEL, at subeffective doses that do not produce adverse effects, stimulate neurogenesis in human neuronal precursors. Moreover, the mechanism by which the combination elicits neurogenesis is meditated by melatonin receptors, CaM Kinase II and CaM antagonism. This could have clinical advantages for the fast treatment of depression.

Potential Use of Exfoliated and Cultured Olfactory Neuronal Precursors for In Vivo Alzheimer's Disease Diagnosis: A Pilot Study.

Histopathological hallmarks of dementia have been described postmortem in the brain of patients with Alzheimer's disease (AD). Tau, a microtubule associated protein, is abnormally arranged in neurofibrillary tangles. In living AD patients, total tau (t-tau) and hyperphosphorylated tau (p-tau) levels are increased in the cerebrospinal fluid obtained by lumbar puncture. Herein, we studied the t-tau and p-tau levels as well as the subcellular distribution of t-tau in olfactory neuronal precursors obtained by exfoliation of the nasal cavity of AD patients and control participants. Data showed that t-tau and p-tau levels were increased in cell homogenates from AD patients. Also, t-tau immunoreactivity was arranged in a punctate pattern in olfactory neuronal precursors derived from an AD participant with 5 years of evolution and in the oldest participants, either control subjects or those with Alzheimer's disease. Results support that exfoliated neuronal precursors have tau alterations demonstrated in postmortem brain and in the cerebrospinal fluid. This evidence and because the obtainment of olfactory neuronal precursors is a noninvasive procedure, detection of tau alterations shown here might be useful for an early diagnosis of AD-type dementia.

Primary cilia formation is diminished in schizophrenia and bipolar disorder: A possible marker for these psychiatric diseases.

Primary cilium (PC) is a microtubule-rich organelle that protrudes from the plasma membrane and acts as a cellular antenna sensing extracellular signals during brain development. DISC1 (Disrupted-in-Schizophrenia-1) is involved in PC formation and is considered a risk factor for neuropsychiatric disorders. We have previously described altered subcellular distribution of DISC1 and an aberrant microtubule organization in olfactory neuronal precursors (ONP) obtained from schizophrenia (SCZ) and bipolar disorder (BD) patients. Herein, we analyzed in vitro PC formation in healthy control subjects, SCZ and BD patients. The results indicated that 66.73±4.33% of ONP from control subjects showed immunostaining for the PC marker, acetylated α-tubulin. By contrast, only a small percentage of cells in culture from paranoid SCZ and BD patients showed PC staining (SCZ, 12.8±4.43%; BD, 12.32±5.86%). However, cells from an affected proband with disorganized SCZ and a subject with BD displayed a higher percentage of cells with cilia (SCZ, 42.20%; BD, 38.59%). Additionally, cilia elongation was observed in lithium-treated ONP derived from all groups, with a more evident response in cells from the BD group. The present study provides novel evidence that the molecular pathways involved in PC formation are defective in SCZ and BD, and impairment in these processes may be involved in the physiopathology of both diseases. Our observations also suggest that ONP is a patient-derived cell model with a potential use for diagnosis and high-throughput drug screening for brain diseases.

Abnormally Increased Secretion in Olfactory Neuronal Precursors from a Case of Schizophrenia Is Modulated by Melatonin: A Pilot Study.

The alterations that underlie the pathophysiology of schizophrenia (SCZ) include the dysregulation of structural and functional properties of neurons. Among these, the secretion of neurotransmitters and hormones, which plays a key role for neuronal communication and development, is altered. Neuronal precursors from the human olfactory epithelium have been recently characterized as a reliable model for studying the etiopathogenesis of neuropsychiatric diseases. Our previous work has shown that melatonin enhances the development of morphological and functional features of cloned olfactory neuronal precursors (ONPs) from a healthy subject. In this work we found that primary cultures of ONPs obtained from a schizophrenic patient display an increased potassium-evoked secretion, when compared with ONPs from an age- and gender-matched healthy control subject (HCS). Secretion was evaluated by FM1-43 fluorescence cumulative changes in response to depolarization. Interestingly, a 12 h-melatonin treatment modulated the abnormally increased secretion in SCZ ONPs and brought it to levels similar to those found in the HCS ONPs. Our results suggest that the actin cytoskeleton might be a target for melatonin effects, since it induces the thickening of actin microfilament bundles. Further research will address the mechanisms by which melatonin modulates neurochemical secretion from ONPs.