Biomarker identification in neurologic diseases: improving diagnostics and therapeutics

Biomarkers for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common form of motor neuron disease. ALS is a fatal neurodegenerative disease and clinical diagnosis typically takes many months to complete. Early disease diagnosis through the use of biomarkers may aid in correct clinical management of patients and possibly delay time to ventilator and morbidity. This review explores the progress of biomarker discovery efforts for ALS and the many challenges that remain. Included are different technologies utilized in biomarker discovery efforts (proteomic, genomic and metabolomic) and putative biomarkers uncovered using these techniques. These studies have discovered genetic mutations leading to familial forms of ALS, and specific protein alterations that occur in biological fluids (cerebrospinal fluid and blood) and/or tissues of ALS subjects. More recent high-throughput technologies have revealed panels of proteomic or metabolic biomarkers that can discriminate between ALS and control groups. The identification of disease-specific biomarkers will provide opportunities to develop early diagnostic measures as well as surrogate markers to monitor disease progression and test drug efficacy in clinical trials.

Cerebrospinal fluid proteomics reveals potential pathogenic changes in the brains of SIV-infected monkeys

The HIV-1-associated neurocognitive disorder occurs in approximately one-third of infected individuals. It has persisted in the current era of antiretroviral therapy, and its study is complicated by the lack of biomarkers for this condition. Since the cerebrospinal fluid is the most proximal biofluid to the site of pathology, we studied the cerebrospinal fluid in a nonhuman primate model for HIV-1-associated neurocognitive disorder. Here we present a simple and efficient liquid chromatography-coupled mass spectrometry-based proteomics approach that utilizes small amounts of cerebrospinal fluid. First, we demonstrate the validity of the methodology using human cerebrospinal fluid. Next, using the simian immunodeficiency virus-infected monkey model, we show its efficacy in identifying proteins such as alpha-1-antitrypsin, complement C3, hemopexin, IgM heavy chain, and plasminogen, whose increased expression is linked to disease. Finally, we find that the increase in cerebrospinal fluid proteins is linked to increased expression of their genes in the brain parenchyma, revealing that the cerebrospinal fluid alterations identified reflect changes in the brain itself and not merely leakage of the blood-brain or blood-cerebrospinal fluid barriers. This study reveals new central nervous system alterations in lentivirus-induced neurological disease, and this technique can be applied to other systems in which limited amounts of biofluids can be obtained.

Comparative proteomic profiling of cerebrospinal fluid between living and post mortem ALS and control subjects

Neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), lack definitive diagnostic tests or biomarkers of disease progression. Most studies that investigate protein abnormalities in ALS have used biofluids such as blood or cerebrospinal fluid (CSF), while some have used post mortem tissue or CSF samples. Since ALS disease progression and post mortem effects probably induce significant alterations to protein modifications or proteolysis, we directly examined the CSF proteome from ALS subjects at various lengths of time from symptom onset and at autopsy by mass spectrometry based proteomics. CSF was also obtained from both healthy age-matched control subjects and at autopsy from healthy and Alzheimer's disease (AD) controls. We identified significant differences in the CSF proteome between living and post mortem ALS subjects, as well as living and post mortem control subjects. We also noted differences in the CSF proteome of ALS subjects that have exhibited symptoms for varying lengths of time and between ALS and AD subjects at end-stage of disease. This is the first study describing differences in the CSF proteome from post mortem and living ALS subjects using a mass spectrometric approach. These differences highlight the importance of utilizing CSF from living ALS subjects near the time of symptom onset for the identification of early protein biomarkers, although some protein alterations that occur early in the disease process are maintained throughout the course of disease and in post mortem samples.

A generic research paradigm for identification and validation of early molecular diagnostics and new therapeutics in common disorders

Genetically complex disorders continue to confound investigators because of their many underlying factors, both genetic and environmental. In order to tease apart the heritable from the non-heritable contributions to disease, clinicians are relying on researchers in the rapidly expanding fields of high-throughput genomics to identify surrogate clinical endpoints, called biomarkers, that provide a measure of the probability that an individual will succumb to the disease in question. The goals of current biomedical research into complex disorders are to identify and utilize these biomarkers, not only for early detection, but also for personalized treatment with knowledge-guided therapeutics. As the identification of these biomarkers is basically a problem of discovery, we discuss new insights into biomarker detection utilizing the most current genomic technologies available. Additionally, we present here a generic paradigm for the validation of such molecular diagnostics as well as new treatment modalities for complex and increasingly common diseases. Lastly, we delve into the ways genomic biomarkers might be implemented in a clinical setting to allow the subsequent application of targeted therapeutics, which can help the ever expanding groups of individuals experiencing these insidious diseases.