Real-time quantitative PCR and droplet digital PCR for plant miRNAs in mammalian blood provide little evidence for general uptake of dietary miRNAs Limited evidence for general uptake of dietary plant xenomiRs

In 2012 L. Zhang et al. presented the hypothesis that plant miRNAs are transferred into blood and then tissue from dietary sources. Not only did the authors report detection of plant miRNA in animals, they also provided evidence that one specific, abundant plant miRNA, miR168, regulated the expression of low-density lipoprotein receptor-associated protein 1 (LDLRAP1) in mice. Plant miRNAs, then, might be capable of performing the same gene regulatory functions as endogenous animal miRNAs. Furthermore, plant miRNAs appeared to exert this function in tissue after entering from the circulation. Endogenous animal miRNAs are known agents of intercellular communication and are carried and protected in a diverse array of biofluids by extracellular vesicles, protein complexes and other vehicles. The hypothesis of L. Zhang et al., which we have elsewhere called the dietary “xenomiR” hypothesis, has understandably provoked considerable attention, and the implications of evidence that exogenous dietary miRNAs enter the bloodstream and tissues of ingesting animals has been accompanied by an indication that at least one plant miRNA, miR168, participates in “cross-kingdom” regulation of a mammalian transcript. if confirmed, these findings would support investigation of miRNA-based dietary interventions in disease. Here, blood was obtained preand post-prandially (1, 4, 12 h) from pigtailed macaques that received a miRNA-rich plantbased substance. Plant and endogenous miRNAs were measured by Rt-qPCR. Although low-level amplification was observed for some plant miRNA assays, amplification was variable and possibly non-specific, as suggested by droplet digital PCR. A consistent response to dietary intake was not observed. While our results do not support general and consistent uptake of dietary plant miRNAs, additional studies are needed to establish whether or not plant or animal xenomiRs are transferred across the gut in sufficient quantity to regulate endogenous genes. Real-time quantitative PCR and droplet digital PCR for plant miRNAs in mammalian blood provide little evidence for general uptake of dietary miRNAs Limited evidence for general uptake of dietary plant xenomiRs