A smartphone-based electrochemical sensing platform for the portable and simultaneous determination of flavonoids in Citri Reticulatae Pericarpium

BACKGROUND

The efficient and timely determination of polymethoxylated flavones (PMFs, primarily nobiletin and tangeretin) and flavanone glycosides (primarily hesperidin) in Citri Reticulatae Pericarpium (CRP) is of paramount importance for the production of CRP and the evaluation of its efficacy. Conventional analytical methods including chromatography-based approaches commonly provide high sensitivity and selectivity, but require bulky equipment and complicated procedures performed by professional technicians and are thus inconvenient in practical applications. Therefore, there is a clear need for portable and miniaturized sensing platforms that can rapidly and simultaneously detect PMFs and hesperidin in CRP product.

RESULTS

A state-of-the-art three-dimensional porous graphene electrode was first fabricated by direct laser scribing of a poly(ether-ether-ketone) (PEEK) film for electrocatalysis of nobiletin, tangeretin and hesperidin. Kinetic analysis was conducted to investigate the reaction mechanisms of these three flavonoids at such prepared PEEK-laser induced graphene (PEEK-LIG) electrodes. Since the as-prepared PEEK-LIG electrodes exhibited high electrocatalytic efficiency towards these three flavonoids, a portable electrochemical sensing platform assembled with a smartphone, a miniatured electrochemical workstation, and an integrated PEEK-LIG microchip was developed. Consequently, the developed portable electrochemical sensing platforms exhibited great sensitivity and low detection limits for both PMFs and hesperidin. More importantly, tests conducted on real CRP extract samples demonstrated that the developed portable electrochemical sensing platform exhibited high validity, high reliability, as well as excellent reproducibility.

SIGNIFICANCE

This is the inaugural report on the portable and simultaneous determination of PMFs and hesperidin in the pericarp of Citrus Reticulata, which may be utilized for differentiating CRP products. Furthermore, the portable and powerful electrochemical sensing platforms developed could also potentially be applied for a wide range of analytes, thanks to their simple and rapid fabrication and determination processes.

Nobiletin enhances plasma Interleukin-6 and C-X-C motif chemokine ligand 1 levels that are increased by treadmill running

Exercise increases the muscular secretion of Interleukin-6 (IL-6), which is partially regulated by β2-adrenergic receptor signaling. Nobiletin is a polymethoxyflavone (PMF) found in citrus fruits that induces the secretion of IL-6 from C2C12 myotubes, but it remains unclear whether nobiletin promotes IL-6 secretion during exercise. The aim of this study was to clarify the effects of nobiletin on IL-6 secretion during exercise. Nobiletin and epinephrine were found to synergistically increase IL-6 secretion from differentiated C2C12 cells, which was suppressed by the inhibition of adenylyl cyclase (AC) or protein kinase A (PKA). Treadmill running for 60 min increased plasma levels of IL-6, epinephrine, and norepinephrine in rats. Nobiletin (5 mg/kg) orally administered 30 min before running increased plasma IL-6 levels further, although it did not increase plasma epinephrine and norepinephrine. In a similar manner to IL-6, nobiletin and epinephrine synergistically increased the secretion of C-X-C motif chemokine ligand 1 (CXCL-1) from C2C12 cells, or the increase in plasma CXCL-1 was enhanced by nobiletin after treadmill running of rats. Our results suggest that nobiletin promotes IL-6 and CXCL-1 secretion from skeletal muscle by synergistic enhancement of the PKA pathway in β2-adrenergic receptor signaling.

Citrus peel flavonoid nobiletin alleviates lipopolysaccharide-induced inflammation by activating IL-6/STAT3/FOXO3a-mediated autophagy

Nobiletin, a polymethoxyflavone widely present in the peel of citrus fruits, has significant anti-inflammatory activity. Autophagy plays a critical role in maintaining cell homeostasis by promoting the degradation of intracellular structures in response to various stress. Recent research suggests the involvement of autophagy in the inflammatory process and therefore some inflammation-related diseases. However, the "cross-talk" between autophagy and nobiletin's anti-inflammation response remains not well elucidated. Therefore, this study was initiated with the aim of investigating the role of autophagy in nobiletin's protective effect against inflammation in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Results showed that nobiletin significantly (P < 0.05) inhibited the release of nitric oxide (NO) and decreased the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in a dose-dependent manner. Moreover, nobiletin significantly (P < 0.05) promoted autophagy as evidenced by the appearance of more autophagosomes, up-regulated LC3II protein, low-regulated p62 protein, and increased autophagy-related (Atg) genes' expression compared with the control treated with LPS alone. Addition of chloroquine, an autophagy inhibitor, alleviated nobiletin's anti-inflammatory effect, further supporting the requirement of an active autophagy process for the citrus peel flavonoid's biological activity. Mechanistically, we found that nobiletin treatment leads to activation of the IL-6/STAT3/FOXO3a signal pathway through the down-regulation of IL-6 and STAT3 phosphorylation and the upregulation of FOXO3a phosphorylation in the cell nucleus, which is responsible for induction of macrophage autophagy. Taken together, our study provides evidence that nobiletin suppresses inflammatory response through enhancing autophagy through activating the IL-6/STAT3/FOXO3a pathway in macrophage cells.

Orange peel extract reduces the inflammatory state of skeletal muscle after downhill running via an increase in IL-1RA

It has been reported that orange peel extract (OPE) and the 4 major polymethoxyflavones (PMFs) in OPE have a protective effect against downhill running (DR)-induced skeletal muscle inflammation. However, the mechanism is not well understood. We investigated the potential of OPE and PMF compounds for increasing anti-inflammatory cytokine levels. The plasma interleukin-1 receptor antagonist (IL-1RA) level was increased 1 and 8 h after OPE administration in rats. Nobiletin induced the secretion of IL-1RA from C2C12 myotubes. In the inflammatory state of skeletal muscle after DR, OPE administration reduced nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) expression, NF-κB-DNA binding, and monocyte chemotactic protein-1 mRNA levels, but these effects were all abrogated by the intravenous administration of IL-1RA neutralizing antibody. These results indicated that OPE reduces skeletal muscle inflammatory state after DR via an increase in IL-1RA, and that IL-1 receptor signaling is important for skeletal muscle inflammation after DR.