Flavanol (flavan-3-ol)-rich lychee fruit extract (FRLFE) is a mixture of oligomerized polyphenols primarily derived from lychee fruit and is rich in flavanol monomers, dimers, and trimers. Supplementation with this functional food has been shown to suppress inflammation and tissue damage caused by high-intensity exercise training. However, it is unclear whether FRLFE has in vitro anti-inflammatory effects, such as suppressing the production of the proinflammatory cytokine tumor necrosis factor α (TNF-α) and the proinflammatory mediator nitric oxide (NO), which is synthesized by inducible nitric oxide synthase (iNOS). Here, we analyzed the effects of FRLFE and its constituents on the expression of inflammatory genes in interleukin 1β (IL-1β)-treated rat hepatocytes. FRLFE decreased the mRNA and protein expression of the iNOS gene, leading to the suppression of IL-1β-induced NO production. FRLFE also decreased the levels of the iNOS antisense transcript, which stabilizes iNOS mRNA. By contrast, unprocessed lychee fruit extract, which is rich in flavanol polymers, and flavanol monomers had little effect on NO production. When a construct harboring the iNOS promoter fused to the firefly luciferase gene was used, FRLFE decreased the luciferase activity in the presence of IL-1β, suggesting that FRLFE suppresses the promoter activity of the iNOS gene at the transcriptional level. Electrophoretic mobility shift assays indicated that FRLFE reduced the nuclear transport of a key regulator, nuclear factor κB (NF-κB). Furthermore, FRLFE inhibited the phosphorylation of NF-κB inhibitor α (IκB-α). FRLFE also reduced the mRNA levels of NF-κB target genes encoding cytokines and chemokines, such as TNF-α. Therefore, FRLFE inhibited NF-κB activation and nuclear translocation to suppress the expression of these inflammatory genes. Our results suggest that flavanols may be responsible for the anti-inflammatory and hepatoprotective effects of FRLFE and may be used to treat inflammatory diseases.

Accumulating data indicate the existence of natural antisense transcripts (asRNAs), frequently transcribed from eukaryotic genes and do not encode proteins in many cases. However, their importance has been overlooked due to their heterogeneity, low expression level, and unknown function. Genes induced in responses to various stimuli are transcriptionally regulated by the activation of a gene promoter and post-transcriptionally regulated by controlling mRNA stability and translatability. A low-copy-number asRNA may post-transcriptionally regulate gene expression with cis-controlling elements on the mRNA. The asRNA itself may act as regulatory RNA in concert with trans-acting factors, including various RNA-binding proteins that bind to cis-controlling elements, microRNAs, and drugs. A novel mechanism that regulates mRNA stability includes the interaction of asRNA with mRNA by hybridization to loops in secondary structures. Furthermore, recent studies have shown that the functional network of mRNAs, asRNAs, and microRNAs finely tunes the levels of mRNA expression. The post-transcriptional mechanisms via these RNA–RNA interactions may play pivotal roles to regulate inducible gene expression and present the possibility of the involvement of asRNAs in various diseases.

Licorice (Glycyrrhizae radix) is the roots and stolons of Glycyrrhiza uralensis Fischer or Glycyrrhiza glabra Linnaeus in the Japanese Pharmacopoeia. Glycyrrhizae radix has been widely used as a sweetener and a traditional medicine. A Glycyrrhizae radix extract contains many constituents and has antispasmodic, antitussive, anti-ulcer, and anti-inflammatory effects. However, reports comparing the anti-inflammatory effects of these constituents are very few. Here, we purified several constituents from the roots and stolons of G. uralensis and examined and compared their anti-inflammatory effects by monitoring the levels of the inflammatory mediator, nitric oxide (NO), in interleukin (IL)-1β-treated rat hepatocytes. From the G. uralensis extract, we purified the main constituent glycyrrhizin and the constituents that are characteristic of G. uralensis (chalcones and flavanones). These constituents suppressed NO production in IL-1β-treated rat hepatocytes, and isoliquiritigenin showed the greatest suppression activity. Isoliquiritigenin, isoliquiritin, and liquiritigenin significantly decreased both protein and mRNA for the inducible nitric oxide synthase. These constituents reduced the levels of mRNAs encoding tumor necrosis factor α and IL-6. In contrast, although glycyrrhizin is abundant, it showed a 100-fold lower potency in NO suppression. Therefore, both glycyrrhizin and the minor constituents (isoliquiritigenin, isoliquiritin, and liquiritigenin) may be responsible for the anti-inflammatory effects of G. uralensis. It is also implied that these constituents may have a therapeutic potential for inflammatory hepatic disorders.

Natural antisense transcripts are frequently transcribed from many genes in eukaryotes. Although natural antisense transcripts have been recognized for a long time, their importance has been overlooked due to their heterogeneity, low expression level, and unknown function. Genes induced in responses to various external stimuli are transcriptionally regulated by the activation of a gene promoter and post-transcriptionally regulated by controlling mRNA stability and translatability. Recent studies have shed light on the functions of natural antisense transcripts at the post-transcriptional level. An antisense transcript may regulate gene expression with cis-controlling elements on the mRNA, and the antisense transcript itself may act in concert with trans-acting factors, including various proteins that bind to cis-controlling elements, drugs, and microRNAs. A novel mechanism recently reported to regulate mRNA stability includes the interaction of the antisense transcript with mRNA by hybridization to single-stranded loops in secondary structures. This antisense transcript-mediated post-transcriptional regulation may be one of the general mechanisms for the regulation of inducible gene expression and presents the possibility of the involvement of natural antisense transcripts in disease.