Date Published: December 22, 2013
Publisher: Impact Journals LLC
Author(s): Kira S. Sheinerman, Vladimir G. Tsivinsky, Laila Abdullah, Fiona Crawford, Samuil R. Umansky.
A minimally invasive test for early detection and monitoring of Alzheimer’s and other neurodegenerative diseases is a highly unmet need for drug development and planning of patient care. Mild Cognitive Impairment (MCI) is a syndrome characteristic of early stages of many neurodegenerative diseases. Recently, we have identified two sets of circulating brain-enriched miRNAs, the miR-132 family (miR-128, miR-132, miR-874) normalized per miR-491-5p and the miR-134 family (miR-134, miR-323-3p, miR-382) normalized per miR-370, capable of differentiating MCI from age-matched control (AMC) with high accuracy. Here we report a biomarker validation study of the identified miRNA pairs using larger independent sets of age- and gender- matched plasma samples. The biomarker pairs detected MCI with sensitivity, specificity and overall accuracy similar to those obtained in the first study. The miR-132 family biomarkers differentiated MCI from AMC with 84%-94% sensitivity and 96%-98% specificity, and the miR-134 family biomarkers demonstrated 74%-88% sensitivity and 80-92% specificity. When miRNAs of the same family were combined, miR-132 and miR-134 family biomarkers demonstrated 96% and 87% overall accuracy, respectively. No statistically significant differences in the biomarker concentrations in samples obtained from male and female subjects were observed for either MCI or AMC. The present study also demonstrated that the highest sensitivity and specificity are achieved with pairs of miRNAs whose concentrations in plasma are highly correlated.
The importance of early diagnosis, treatment and prevention of Alzheimer’s disease attracts the attention of scientific and medical communities, regulatory agencies, such as the US Food and Drug Administration (FDA), and industry and government leaders in many countries [1-3]. The number of AD patients and those in high risk populations grows quickly, especially in developed countries, due to increased lifespan. A number of investigational anti-AD drugs, targeting various processes characteristic of AD pathogenesis, have failed in recent clinical trials [1,4-6], likely due to massive neuronal loss and advanced stages of the disease in the enrolled patients [3-5]. It has been demonstrated that AD dementia is preceded by 10-20 years of the disease development, initially without clinical symptoms (pre-symptomatic AD), and then manifested as MCI [7-9]. It is important to note that the detailed analysis of failed clinical trials has demonstrated a therapeutic benefit in the sub-groups of patients with mild and moderate symptoms of AD [6, see also https://investor.lilly.com/releaseDetail.cfm?ReleaseID=702211 and http://www.alzforum.org/new/detail.asp?id=3288%5D. The high need for development of new methods for early AD detection is also emphasized in recent publications from the FDA [10, see also http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM338287.pdf%5D and the U.S. Department of Health and Human Services (“National Alzheimer’s Project Act”, available at: http://aspe.hhs.gov/daltcp/napa/). Since cognitive testing cannot identify patients in pre-symptomatic stages of AD, effective biomarkers are necessary for successful patient stratification and treatment monitoring [3-5].
The main objective of the present work was to validate previously identified sets of plasma biomarker miRNA pairs  in a larger study with clinical samples collected at sites different from the one used in the original study. The data have validated miRNAs of the miR-132 and miR-134 families, paired with miR-491-5p and miR-370 respectively, as highly sensitive biomarkers for detection of MCI. The overall accuracy for differentiating MCI from AMC is 90%-96% and 83%-87% for the biomarker miRNA pairs of miR-132 and miR-134 sets, respectively. The corresponding values obtained in the first feasibility study were 86% – 92% and 82% – 89%. Since a large number of MCI patients will progress to AD dementia [24-26], it is reasonable to suggest that these biomarker pairs detect early stages of AD as well, although they do not differentiate AD from MCI caused by other conditions. As was the case in the feasibility study, the miR-132 family biomarkers detected MCI with higher accuracy than the miR-134 family biomarkers. Although the roles of most miRNAs tested in this study in neuronal differentiation, function and pathology have not been elucidated yet, it has been demonstrated that miR-132 and miR-134 have opposite effect on neurons: miR-132 stimulates [27,28] and miR-134  inhibits neurite growth. Also, the level of miR-132 has been shown to be lower in the hippocampus and temporal neocortex of AD patients [30,31]. Lau et al.  have demonstrated that downregulation of miR-132 occurs at Braak stages III and IV, prior to loss of neuron specific miRNAs. They have also found that deregulation of miR-132-3p in the AD brain appears to occur mainly in neurons displaying Tau hyper-phosphorylation and that the transcription factor FOX01a is a key target of miR-132 in the Tau network. Interestingly, the concentration of miR-128, which promotes neuronal maturation , has been shown to increase in the hippocampus in an intermediate stage and to decrease in a late stage of AD [34,35]. Aging-associated increase in the concentrations of miR-134 and miR-874 in serum has been demonstrated . We plan to further analyze the utility of both sets of biomarker miRNA pairs for MCI detection in larger longitudinal studies.