Papain

Papain is a cysteine protease with wide specificity, cleaving peptide bonds of basic amino acids, leucine, or glycine. It also hydrolyzes esters and amides.

Papain did not induce proteolysis or cell detachment of HUVEC in a concentration range between 0 and 25 µg/mL. Four hours treatment with 10 µg/mL papain resulted in a reduced susceptibility of endothelial cells to activation by VEGF as determined by phosphorylation levels of Akt, MEK1/2, SAPK/JNK. Papain exerted a distinct inhibitory effect on cell growth, cell migration and tube formation with inhibition of tube formation detectable at concentrations as low as 1 µg/mL^[4]. Papain Activates Human Mast Cells to Release Proinflammatory Mediators via its Enzymatic Activity, papain is a direct activator of both human skin MCs (connective tissue) and CBMCs (mucosal type) via its protease activity and partly via PAR-2 ^[5]. While the affinity to cGMP, I-V relation, channel kinetics, and single-channel current amplitude were almost the same in both papain-treated and the control preparations, the total current flowing through the patch membrane of the papain-treated cells was reduced to about 20% of the control, suggesting that papain reduced the density of cGMP-activated channels^[2]. A significant increase in cell viability when papain was used for RPC isolation^[3].

Papain is a cysteine protease allergen with inherent adjuvant activity, induces potent IL-4 expression by T cells in the popliteal lymph nodes of mice following footpad immunization. B cells subsequently regulate the adaptive immune response by enhancing ICOS expression on CD4(+) T cells and amplifying Th2 and follicular helper T cell induction. Ab blockade of ICOS ligand, expressed by popliteal lymph node B cells, but not dendritic cells, at the peak of the response inhibits IL-4 responses in wild-type mice but not B cell-deficient mice. Thus, B cells play a critical role in amplifying adjuvant-dependent Th2 polarization following noncanonical acquisition and internalization of the cysteine protease papain^[1]. purified papain from C. papaya were effective against S. venezuelensis eggs and larvae in vitro, suggesting their potential use as an alternative treatment for strongyloidiasis^[7]. Rapidly progressing joint disease can be produced in the rabbit by intra-articular injection of concentrated papain^[9]. Enzymatically active papain preferentially induces an IgG1 response and results in mast cell degranulation, both features typical of an allergic reaction in mice^[8].

References:
[1]. Dwyer DF, Woodruff MC, et,al. B cells regulate CD4+ T cell responses to papain following B cell receptor-independent papain uptake. J Immunol. 2014 Jul 15;193(2):529-39. doi: 10.4049/jimmunol.1303247. Epub 2014 Jun 13. PMID: 24928991; PMCID: PMC4203309.
[2]. Shen J, Watanabe S, et,al. Cell dissociation with papain reduces the density of cGMP-activated channels of the retinal rod. Jpn J Physiol. 1995;45(1):151-64. doi: 10.2170/jjphysiol.45.151. PMID: 7544417.
[3]. Scruggs BA, Jiao C, et,al. Optimizing Donor Cellular Dissociation and Subretinal Injection Parameters for Stem Cell-Based Treatments. Stem Cells Transl Med. 2019 Aug;8(8):797-809. doi: 10.1002/sctm.18-0210. Epub 2019 Apr 19. PMID: 31004408; PMCID: PMC6646699.
[4]. Mohr T, Desser L. Plant proteolytic enzyme papain abrogates angiogenic activation of human umbilical vein endothelial cells (HUVEC) in vitro. BMC Complement Altern Med. 2013 Sep 21;13:231. doi: 10.1186/1472-6882-13-231. PMID: 24053149; PMCID: PMC3849051.
[5]. Seaf M, Ben-Zimra M, et,al. Papain Activates Human Mast Cells to Release Proinflammatory Mediators via its Enzymatic Activity. J Invest Dermatol. 2016 Jul;136(7):1523-1525. doi: 10.1016/j.jid.2016.03.030. Epub 2016 Apr 7. PMID: 27060447.
[6]. Moraes D, Levenhagen MA, et,al. In vitro efficacy of latex and purified papain from Carica papaya against Strongyloides venezuelensis eggs and larvae. Rev Inst Med Trop Sao Paulo. 2017 Apr 3;59:e7. doi: 10.1590/S1678-9946201759007. PMID: 28380118; PMCID: PMC5441158.
[7]. Moraes D, Levenhagen MA, et,al. In vitro efficacy of latex and purified papain from Carica papaya against Strongyloides venezuelensis eggs and larvae. Rev Inst Med Trop Sao Paulo. 2017 Apr 3;59:e7. doi: 10.1590/S1678-9946201759007. PMID: 28380118; PMCID: PMC5441158.
[8]. Chambers L, Brown A, et,al. Enzymatically active papain preferentially induces an allergic response in mice. Biochem Biophys Res Commun. 1998 Dec 30;253(3):837-40. doi: 10.1006/bbrc.1998.9862. PMID: 9918815.
[9]. Havdrup T, Telhag H. Papain-induced changes in the knee joints of adult rabbits. Acta Orthop Scand. 1977;48(2):143-9. doi: 10.3109/17453677708985125. PMID: 868495.