Our previous studies have demonstrated that stable microRNAs (miRNAs) in mammalian serum and plasma are actively secreted from tissues and cells and can serve as a novel class of biomarkers for diseases, and act as signaling molecules in intercellular communication. Here, we report the surprising finding that exogenous plant miRNAs are present in the sera and tissues of various animals and that these exogenous plant miRNAs are primarily acquired orally, through food intake. MIR168a is abundant in rice and is one of the most highly enriched exogenous plant miRNAs in the sera of Chinese subjects. Functional studies in vitro and in vivo demonstrated that MIR168a could bind to the human/mouse low-density lipoprotein receptor adapter protein 1 (LDLRAP1) mRNA, inhibit LDLRAP1 expression in liver, and consequently decrease LDL removal from mouse plasma. These findings demonstrate that exogenous plant miRNAs in food can regulate the expression of target genes in mammals.

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Exogenous plant MIR168a specifically targets mammalian LDLRAP1: Evidence of cross-kingdom regulation by microRNA

Efficient patient management relies on early diagnosis of disease and monitoring of treatment. In this regard, much effort has been made to find informative, blood-based biomarkers for patients with cancer. Owing to their attributes-which are specifically modulated by the tumour-circulating cell-free microRNAs found in the peripheral blood of patients with cancer may provide insights into the biology of the tumour and the effects of therapeutic interventions. Moreover, the role of microRNAs in the regulation of different cellular processes points to their clinical utility as blood-based biomarkers and future therapeutic targets. MicroRNAs are optimal biomarkers owing to high stability under storage and handling conditions and their presence in blood, urine and other body fluids. In particular, detection of levels of microRNAs in blood plasma and serum has the potential for an earlier cancer diagnosis and to predict prognosis and response to therapy. This Review article considers the latest developments in the use of circulating microRNAs as prognostic and predictive biomarkers and discusses their utility in personalized medicine.

Clinical relevance of circulating cell-free microRNAs in cancer

Circulating, cell-free microRNAs (miRNAs) hold great promise as a new class of cancer biomarkers due to their surprisingly high stability in plasma, association with disease states, and ease of sensitive measurement. Yet little is known about the origin of circulating miRNAs in either healthy or sick people, or what factors influence levels of circulating miRNA biomarkers. Of 79 solid tumor circulating miRNA biomarkers reported in the literature, we found that fifty-eight percent (47/79) are highly expressed in one or more blood cell type. Plasma levels of miRNA biomarkers expressed by myeloid (e.g., miR-223, miR-197, miR-574-3p, let-7a) and lymphoid (e.g., miR-150) blood cells tightly correlated with corresponding white blood cell counts. Plasma miRNA biomarkers expressed by red blood cells (e.g., miR-486-5p, miR-451, miR-92a, miR-16) could not be correlated to red cell counts due to limited variation in hematocrit in the cohort studied, but were significantly increased in hemolyzed specimens (20-30 fold plasma increase; p<0.0000001). Finally, in a patient undergoing autologous hematopoietic cell transplantation, plasma levels of myeloid- and lymphoid-expressed miRNAs (miR-223 and miR-150, respectively) tracked closely with changes in corresponding blood counts. We present evidence that blood cells are a major contributor to circulating miRNA, and that perturbations in blood cell counts and hemolysis can alter plasma miRNA biomarker levels by up to 50-fold. Given that a majority of reported circulating miRNA cancer biomarkers are highly expressed in blood cells, we suggest caution in interpretation of such results as they may reflect a blood cell-based phenomenon rather than a cancer-specific origin.

https://cancerpreventionresearch.aacrjournals.org/content/canprevres/5/3/492.full.pdf

Blood cell origin of circulating microRNAs: a cautionary note for cancer biomarker studies.

The highly conserved RNAs, microRNAs (miRNAs), are a class of small single stranded noncoding RNAs that function through translational repression of specific target mRNAs. miRNAs exhibit a wide range of involvement regulating gene expressions. miRNA expression dysregulated in cancer cells and damaged tissues from different diseases implicates a functional role of miRNAs in the disease development. More recently miRNAs have been detected in cell-free serum, and these circulating miRNAs can distinguish diseased individuals from healthy controls. The noninvasive nature of circulating miRNA collection and their sensitivity and specificity in diseases has encouraged a pursuit of miRNA biomarker research. As a result, approximately 100 circulating miRNAs have been identified as biomarkers for different diseases, and the number is growing. Here we review recently reported circulating miRNA biomarkers and discuss their values and challenges for the disease biomarkers.

Small RNAs have a large impact: circulating microRNAs as biomarkers for human diseases

Purpose: The use of circulating tumor cells (CTC) as a prognostic marker in metastatic breast cancer (MBC) has been well established. However, their efficacy and accuracy are still under scrutiny mainly because of methods of their enrichment and identification. We hypothesized that circulating miRNAs can predict the CTC status of patients with MBC, and tested for the same. Furthermore, we aimed at establishing a panel of circulating miRNAs capable of differentiating MBC cases from healthy controls. Experimental Design: Circulating miRNAs from plasma of CTC-positive and CTC-negative patients with MBC, and healthy controls, were profiled by TaqMan Human MicroRNA arrays. Candidates from the initial screen were validated in an extended cohort of 269 individuals (61 CTC-positive, 72 CTC-negative, 60 CTC-low MBC cases, and 76 controls). Results: CTC-positive had significantly higher levels of miR-141, miR-200a, miR-200b, miR-200c, miR-203, miR-210, miR-375, and miR-801 than CTC-negative MBC and controls ( P P Conclusion: This is the first study to document the capacity of circulating miRNAs to indicate CTC status and their potential as prognostic markers in patients with MBC. Clin Cancer Res; 18(21); 5972–82. ©2012 AACR .

https://clincancerres.aacrjournals.org/content/clincanres/18/21/5972.full.pdf

Circulating miRNAs as Surrogate Markers for Circulating Tumor Cells and Prognostic Markers in Metastatic Breast Cancer

BACKGROUND: Sensitive and specific biomarkers for the early detection of esophageal squamous cell carcinoma (ESCC) are urgently needed to reduce the high morbidity and mortality of the disease. The discovery of serum microRNAs (miRNAs) and their unique concentration profiles in patients with various diseases makes them attractive, novel noninvasive biomarkers for tumor diagnosis. In this study, we investigated the serum miRNA profile in ESCC patients to develop a novel diagnostic ESCC biomarker.

METHODS: Serum samples were taken from 290 ESCC patients and 140 age- and sex-matched controls. Solexa sequencing technology was used for an initial screen of miRNAs in serum samples from 141 patients and 40 controls. A hydrolysis probe–based stem–loop quantitative reverse-transcription PCR (RT-qPCR) assay was conducted in the training and verification phases to confirm the concentrations of selected miRNAs in serum samples from 149 patients and 100 controls.

RESULTS: The Solexa sequencing results demonstrated marked upregulation of 25 serum miRNAs in ESCC patients compared with controls. RT-qPCR analysis identified a profile of 7 serum miRNAs (miR-10a, miR-22, miR-100, miR-148b, miR-223, miR-133a, and miR-127-3p) as ESCC biomarkers. The area under the ROC curve for the selected miRNAs ranged from 0.817 to 0.949, significantly higher than for carcinoembryonic antigen (0.549; P < 0.0005). More importantly, this panel of 7 miRNAs clearly distinguished stage I/II ESCC patients from controls.

CONCLUSIONS: This panel of 7 serum miRNAs holds promise as a novel blood-based biomarker for the diagnosis of ESCC.

Hong Qiu

Papers

Expression Profile of MicroRNAs in Serum: A Fingerprint for Esophageal Squamous Cell Carcinoma