Bioactivity and Application of Representative Plant-derived Cyclic Peptides

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Cyclic peptides are one of the hot concepts in recent years. Compared with linear peptides, some special cyclic peptide structures have the characteristics of high stability and strong targeting, so as to exert stronger efficacy. In addition to synthetic cyclic peptides, plant-derived cyclic peptides are also increasingly appearing in front of the public. Let's take a look at what are the interesting plant cyclic peptide ingredients at present.

Pseudostellaria heterophylla

There is a Pseudostellaria heterophylla cyclopeptide product, a cyclopeptide structure derived from the Pseudostellaria heterophylla, a very Asian adaptogen that also caters to Asian consumers. The plant itself has many functions such as resisting external stress and delaying aging. Pseudostellaria heterophylla contains a variety of cyclic peptide structures. It has been reported that A total of 19 cyclic peptide compounds have been isolated from Pseudostellaria heterophylla, of which 9 compounds are heterophyllin A~H, J (11~19). There are 10 compounds in pseudostellarin A~H, K, L (20~29). In this Pseudostellaria heterophylla cyclic peptide raw material, Heterophyllin B is mainly taken.

Fig.1 Chemical structure of cyclopeptide Heterophyllin B.Fig.1 Structure of cyclic peptide Heterophyllin B.

Table 1 Representative cyclic peptides at Creative Peptides.

CAT# Product Name M.W Molecular Formula Inquiry
R2241Viomycin685.69C25H43N13O10Inquiry
R2242Colistin1169.5C53H100N16O13 (for E1)Inquiry
R2243Micafungin1270.27C56H71N9O23SInquiry
R2244Anidulafungin1140.24C58H73N7O17Inquiry
R2245Fostamatinib580.46C23H26FN6O9PInquiry
R2246Paritaprevir765.88C40H43N7O7SInquiry
R2247Grazoprevir766.9C38H50N6O9SInquiry
Z10-101-154Daptomycin1620.69C72H101N17O26Inquiry
Z10-101-157Caspofungin1093.31C52H88N10O15Inquiry
R2052Zilucoplan (C2H4O)nC126H186N24O32Inquiry
R2238Telavancin1755.6C80H106Cl2N11O27PInquiry
R2239Oritavancin1793.1C86H97Cl3N10O26Inquiry
R2240Bacitracin1422.69C66H103N17O16SInquiry

Returning to the ingredient itself, it has been verified from multiple perspectives at the gene level, protein level, tissue level, and phenotypic level. At the gene level, the expression of COL1A1, COL3A1, COL5A1, COL6A1, SPARC and FN1 genes related to collagen synthesis and tissue increased significantly. The expression of FBLNS, FBN1, FBN2 and ELN genes related to elastin synthesis and tissue was significantly increased. The expression of CASP14 and FLG genes associated with skin hydration was significantly increased. The expression of ITGB4, HSPG2, and FBN1 genes associated with basement membrane increased. The expression of ABCA12, DSG-1, CLDN-1, TGM1 and other genes related to barrier function increased. and HBEGF, TGF-β1, TGFA, IGFIR, IGFBP3, FGF2 genes associated with fibroblast stimulation were significantly increased. Genetically, the data of Pseudostellaria heterophylla cyclic peptide suggests that it has a role in improving aging, skin hydration, barrier function, and many other areas.

Looking further into the anti-aging field, what is the efficacy of Pseudostellaria heterophylla extract?

At the protein level, Pseudostellaria heterophylla cyclic peptide is a good way to increase collagen content. Under the experimental conditions, the promoting effect of cyclic peptide was still very obvious. At very low concentrations, the effect is comparable to retinol, and even more than bakuchiol.

Fig.2 Data on anti-aging effects of Pseudostellaria heterophylla extract.Fig.2 Anti-aging effect of Pseudostellaria heterophylla extract.

In organ models, Pseudostellaria heterophylla cyclic peptide has been found to be well suited to maintain skin structural integrity. As mentioned earlier, this cyclic peptide can upregulate the level of the protein SPARC gene, and this gene can participate in ECM remodeling and tissue repair, so it has achieved good results in experiments.

Fig.3 Pseudostellaria heterophylla is responsible for maintaining the complete sexual function of the skin.Fig.3 Pseudostellaria heterophylla helps maintain skin structural integrity.

Of course, clinical effect is also an important characterization dimension. According to the available clinical results, Pseudostellaria heterophylla cyclic peptide has a good effect on improving wrinkles, firmness, radiance and other dimensions.

Linosorbs(LO)

Linosorbs is also an interesting cyclic peptide ingredient, which has been validated for its application in whitening. LO cyclic peptides are composed of 8 or 9 amino acids, including phenylalanine, proline, leucine, isoleucine, valine, and tryptophan, in an end-to-end structure. In the study, a mixture of LO cyclic peptides derived from flaxseed oil was used, which contained these different cyclic peptide structures.

Fig.4 The Structure of several Linosorbs.Fig.4 Structure diagram of LO. (Yoon Ji Hye, et al., 2022)

Functionally, this Linosorbs inhibits the secretion and synthesis of melanin in the B16F10 melanoma cell model. According to the experimental results, the concentration of cyclic peptide below 100 μg/mL has no cytotoxicity and can significantly inhibit the secretion and synthesis of melanin. Interestingly, there was no significant change in tyrosinase activity, but the mRNA expression levels of MITF, tyrosinase, and TYRP1 were down-regulated in the presence of Linosorbs, suggesting that this cyclic peptide combination regulates melanin from a more upstream position.

Fig.5 Inhibitory effect of LO cyclic peptide on melanin synthesis in B16F10 cells.Fig.5 LO cyclic peptide can inhibit the secretion and synthesis of melanin in B16F10. (Yoon Ji Hye, et al., 2022)

The researchers further verified the pathway and found that LO is likely to have an effect by downregulating the mRNA expression in the CREB pathway. LO1 in the LO panel inhibits phosphorylation not only of CREB but also of PKA. Phosphorylation at CREB serine 133 is blocked by LO2. LO1 and LO2 in its family further inhibit melanin production by targeting the CREB pathway.

Fig.6 LO inhibits the signaling pathway of melanin production.Fig.6 LO inhibits melanin production. (Yoon Ji Hye, et al., 2022)

Citrusin XI

This is derived from citrus fruit cyclic peptides, which mainly play an anti-inflammatory and soothing effect. From citrus fruits, a structure was extracted: Citrusin XI, which contains 7 standard amino acids.

Fig.7 Structure of citrusin 11 with anti-inflammatory activity.Fig.7 Anti-inflammatory activity of Citrusin XI. (Noh Hyung Jun, et al., 2015)

In the efficacy verification, the anti-inflammatory properties of this citrus fruit cyclic peptide are mainly reflected. In LPS-induced macrophage RAW264.7 cells, this component inhibits NO production by decreasing iNOS expression, and also slightly inhibits the expression of COX-2, another inflammation-related factor.

Fig.8 Citrusin 11 plays an anti-inflammatory role.Fig.8 Mechanism of anti-inflammatory activity of Citrusin XI. (Noh Hyung Jun, et al., 2015)

Further study of its mechanism of action revealed that this compound may act through the classical pathway of NF-κB. NF-κB is a transcription factor encoding a variety of pro-inflammatory genes, such as cytokines, chemokines, and inducible enzymes (including iNOS and COX-2), and in the absence of stimulation, NF-κB is inactivated by inhibitory κB (IκB). In response to pro-inflammatory signals such as LPS or cytokines, NF-κB is activated. The cyclic peptide in the study can block IκBα degradation and NF-κB phosphorylation, thereby inhibiting the activation of NF-κB.

Fig.9 Mechanism of Citrusin XI through NF-κB signaling pathway.Fig.9 Citrusin XI exerts anti-inflammatory activity through the NF-κB pathway. (Noh Hyung Jun, et al., 2015)

At present, there are many components of cyclic peptides. As more and more cyclic peptide ingredients appear on the market, we should also look at these ingredients with both optimism and rationality. On the one hand, structures such as cyclic peptides greatly expand our range of options. Cyclic peptides have lower polarity, making them transdermal and more resistant to enzymatic degradation. At the same time, the larger molecular weight and spatial structure of cyclic peptides can also well target hot spots on proteins, forming a more robust protein-protein interaction and activating many biological processes.

On the other hand, this is not the case for all cyclic peptides. Many reports have also mentioned that when linear peptides are modified into cyclic peptides, many times it will affect the change of its configuration, resulting in the loss of many functions. The hydrophilic and hydrophobic nature of cyclic peptides changes upon entry into the membrane, while some cyclic peptides do not change back to their original appearance after a configuration transition. Therefore, multi-angle characterization and in-depth study of mechanisms are important preconditions for cyclic peptides. Again, cyclic peptides are a new option and do not mean they are a substitute for linear peptides.

In addition, when there are many cyclic peptide candidates on the market, multi-angle validation can also increase its credibility. In addition to the conventional protein-level verification of skin efficacy, a small genetic level and a large clinical level may be more essential.

In any case, the new weapon of cyclic peptide is a good thing. But whether the final effect is good or not has to be verified by time.

References

  1. Noh, Hyung Jun, et al., Anti-inflammatory activity of a new cyclic peptide, citrusin XI, isolated from the fruits of Citrus unshiu. Journal of ethnopharmacology 163 (2015): 106-112.
  2. Yoon, Ji Hye, et al., Anti-melanogenesis effects of a cyclic peptide derived from flaxseed via inhibition of creb pathway. International Journal of Molecular Sciences 24.1 (2022): 536.
* Please kindly note that our products and services can only be used to support research purposes (Not for clinical use).
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