Table 4.

Contradicting evidence of cross-kingdom communication by diet/plant-derived miRNAs (Adapted with permission from Li et al., 2018, an Open access article distributed under the terms of the Creative Commons Attribution 4.0 International License).

Year	Contents	miRNAs involved	Source origin	miRNA levels	Refuting points	Detectionmethods	Conclusion	Reference
2013	Little or no plant miRNAs or miR168a were detected in blood or liver of mice fed with rice-containing diets	miR168a	Rice	Unmeasurable	The observed changes in LDL levels might be due to the release of endogenous cholesterol stores in response to negligible dietary cholesterol intake in mice fed with only rice	HTS, RT-qPCR, ELISA	Dietary exposure to miR168a did not affect plasma LDL levels. Plasma LDL changes reported by Zhang resulted from nutritional imbalances between test and control groups rather than an RNAi mediated effect of consuming miR168a in rice	Dickinson et al., 2013
2013	Plant miRNAs were not detectable in the plasma from healthy human subjects after intake of a western diet containing fruits.	miR156a miR159a miR169a	Plant material	Undetectable	Low measurable uptake	RT-qPCR	Horizontal delivery of miRNAs via oral ingestion of a typical diet was neither a frequent nor a prevalent event across multiple recipient animal organisms	Snow et al., 2013
	Negligible expression of miR21 in plasma or organ tissue in miR21 knockout mice after oral diets replete with endogenous miR21	miR21	Animal lard diet replete With miR21	Undetectable in plasma; less than one copy per cell in the liver, lungs, kidneys and stomach
	Negligible expression of miR156a, miR159a and miR169a in plasma or organs in mice after diets replete with these miRNAs.	miR156a miR159a miR169a	Vegetariandiets replete with these miRNAs	miR156a: far less than one copy of miRNA per cell in liver, lungs, kidneys and stomach; miR159a and miR169a: undetectable in either plasma and/or organs.
	Negligible expression of plant-derived miRNAs in recipient honeybee tissues.	miR156a miR159a miR169a	Plant derived miRNA	Only miR156a but not miR159a or miR169a, was detected in abdominal tissue derived from nurses and foragers, but again at exceptionally low levels.
2012	Predominant monocot miR168 sequence was present as a result of contamination from a non-plant source	miR168a	Plant	Not available	Contamination	HTS, NB	The observed plant miRNAs in animal sRNA datasets could originate in the process of sequencing, and accumulation of plant miRNAs via dietary exposure was not universal in animals.	Zhang et al., 2012b
2014	Cross-contamination during library preparation was a source of exogenous RNAs	miR168a miR156a miR167a	Plant	Not available	Contamination	HTS	Variable amounts of plant miRNAs were found in publicly available sRNA-seq data sets of human tissues.	Tosar et al., 2014
2014	Failed to observe a postprandial increase in the brassica-specific miR824 or miR167a in broccoli sprouts feeding study	miR167a miR824	Broccoli sprouts	Below detection limit	Low measurable uptake	RT-qPCR	Skeptical of the bioavailability and biologic activity of plant-borne miRNAs	Baier et al., 2014
2013	Nonhuman primates failed to uptake dietary plant miRNAs	miR156 miR160 miR166 miR167 miR168 miR172	Fruit	Not available	The concentrations were too low to be specific and reliable.	RT-qPCR, Droplet digital PCR	The level of miRNAs was too low to be true and/or amplification was non–specific	Witwer et al., 2013
2018	Corn miRNA was extensively degraded in the GI tract and that the uptake into circulation and tissues was minimal	miR156a miR164a miR167a	Corn	No corn miRNAs could be detected in whole blood, fecal or liver of animals	Significant degradation of corn miRNAs occurred during digestion	—	No evidence of increased levels of corn miRNAs in whole blood or tissues after supplementation of corn miRNAs in the diet was observed in a mouse model.	Huang et al., 2018

MVs microvesicles, HTS high-throughput sequencing, NB Northern blot, WB Western blot, ELISA enzyme-linked immunosorbent assay, LDL low-density lipoprotein, sRNA small RNA