Isosilybin A
Isosilybin A is a partial PPARγ agonist, it significantly induced ABCA1 protein expression, it inhibited both monophenolase (IC50 = 1.7-7.6 µM) and diphenolase (IC50 = 12.1-44.9 µM) of tyrosinase. Isosilybin A shows anti-angiogenic efficacy, it has anti-prostate cancer (PCA) activity that is mediated via cell cycle arrest and apoptosis induction.
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Providing storage is as stated on the product vial and the vial is kept tightly sealed, the product can be stored for up to
24 months(2-8C).
Wherever possible, you should prepare and use solutions on the same day. However, if you need to make up stock solutions in advance, we recommend that you store the solution as aliquots in tightly sealed vials at -20C. Generally, these will be useable for up to two weeks. Before use, and prior to opening the vial we recommend that you allow your product to equilibrate to room temperature for at least 1 hour.
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The packaging of the product may have turned upside down during transportation, resulting in the natural compounds adhering to the neck or cap of the vial. take the vial out of its packaging and gently shake to let the compounds fall to the bottom of the vial. for liquid products, centrifuge at 200-500 RPM to gather the liquid at the bottom of the vial. try to avoid loss or contamination during handling.
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Chem Biol Interact. 2017 Jun 1;271:24-29.
The effect of milk thistle (Silybum marianum) and its main flavonolignans on CYP2C8 enzyme activity in human liver microsomes.[Pubmed:
28457856 ]
Milk thistle is a widely-consumed botanical used for an array of purported health benefits. The primary extract of milk thistle is termed silymarin, a complex mixture that contains a number of structurally-related flavonolignans, the flavonoid, taxifolin, and a number of other constituents. The major flavonolignans present in most extracts are silybin A, silybin B, Isosilybin A and isosilybin B, silydianin, silychristin and isosilychristin. Silymarin itself has been reported to inhibit CYP2C8 activity in vitro, but the effect of the individual flavonolignans on this enzyme has not been studied.
METHODS AND RESULTS:
To investigate the effects of milk thistle extract and its main flavonolignans (silybin A, silybin B, Isosilybin A and isosilybin B) on CYP2C8 activity at relevant concentrations, the effect of milk thistle extract and the flavonolignans on CYP2C8 enzyme activity was studied in vitro using human liver microsomes (HLM) incorporating an enzyme-selective substrate for CYP2C8, amodiaquine. Metabolite formation was analyzed using liquid chromatography-tandem mass spectrometry (LC/MS-MS). The concentration causing 50% inhibition of enzyme activity (IC50) was used to express the degree of inhibition. Isosilibinin, a mixture of the diastereoisomers Isosilybin A and isosilybin B, was found to be the most potent inhibitor, followed by isosilybin B with IC50 values (mean ± SE) of 1.64 ± 0.66 μg/mL and 2.67 ± 1.18 μg/mL, respectively. The rank order of observed inhibitory potency after isosilibinin was silibinin > Isosilybin A > silybin A > milk thistle extract > and silybin B.
CONCLUSIONS:
These in vitro results suggest a potentially significant inhibitory effect of isosilibinin and isosilybin B on CYP2C8 activity. However, the observed IC50 values are unlikely to be achieved in humans supplemented with orally administered milk thistle extracts due to the poor bioavailability of flavonolignans documented with most commercially available formulations.
Molecules. 2015 Dec 31;21(1):E55.
Silymarin Constituents Enhance ABCA1 Expression in THP-1 Macrophages.[Pubmed:
26729088 ]
Silymarin is a hepatoprotective mixture of flavonolignans and flavonoids extracted from the seeds of milk thistle (Silybum marianum L. Gaertn). This study investigates the effect of major bioactive constituents from silymarin, silybin A, silybin B, Isosilybin A, isosilybin B, silydianin, silychristin, isosilychristin, and taxifolin, on the expression of ABCA1, an important cholesterol efflux transporter, in THP-1-derived macrophages.
METHODS AND RESULTS:
Four of the studied compounds, Isosilybin A, silybin B, silychristin and isosilychristin, were found to significantly induce ABCA1 protein expression without affecting cell viability. Moreover, Isosilybin A, a partial PPARγ agonist, was found to promote cholesterol efflux from THP-1 macrophages in a concentration-dependent manner.
CONCLUSIONS:
These findings first show ABCA1 protein up-regulating activity of active constituents of silymarin and provide new avenues for their further study in the context of cardiovascular disease.
PLoS One. 2012;7(4):e34630.
Angiopreventive efficacy of pure flavonolignans from milk thistle extract against prostate cancer: targeting VEGF-VEGFR signaling.[Pubmed:
22514647 ]
The role of neo-angiogenesis in prostate cancer (PCA) growth and metastasis is well established, but the development of effective and non-toxic pharmacological inhibitors of angiogenesis remains an unaccomplished goal. In this regard, targeting aberrant angiogenesis through non-toxic phytochemicals could be an attractive angiopreventive strategy against PCA.
METHODS AND RESULTS:
The rationale of the present study was to compare the anti-angiogenic potential of four pure diastereoisomeric flavonolignans, namely silybin A, silybin B, Isosilybin A and isosilybin B, which we established previously as biologically active constituents in Milk Thistle extract. Results showed that oral feeding of these flavonolignans (50 and 100 mg/kg body weight) effectively inhibit the growth of advanced human PCA DU145 xenografts. Immunohistochemical analyses revealed that these flavonolignans inhibit tumor angiogenesis biomarkers (CD31 and nestin) and signaling molecules regulating angiogenesis (VEGF, VEGFR1, VEGFR2, phospho-Akt and HIF-1α) without adversely affecting the vessel-count in normal tissues (liver, lung, and kidney) of tumor bearing mice. These flavonolignans also inhibited the microvessel sprouting from mouse dorsal aortas ex vivo, and the VEGF-induced cell proliferation, capillary-like tube formation and invasiveness of human umbilical vein endothelial cells (HUVEC) in vitro. Further studies in HUVEC showed that these diastereoisomers target cell cycle, apoptosis and VEGF-induced signaling cascade. Three dimensional growth assay as well as co-culture invasion and in vitro angiogenesis studies (with HUVEC and DU145 cells) suggested the differential effectiveness of the diastereoisomers toward PCA and endothelial cells.
CONCLUSIONS:
Overall, these studies elucidated the comparative anti-angiogenic efficacy of pure flavonolignans from Milk Thistle and suggest their usefulness in PCA angioprevention.
Carcinogenesis. 2007 Jul;28(7):1533-42.
Isosilybin B and isosilybin A inhibit growth, induce G1 arrest and cause apoptosis in human prostate cancer LNCaP and 22Rv1 cells.[Pubmed:
17389612]
Silymarin and, one of its constituents, silibinin exert strong efficacy against prostate cancer (PCA); however, anticancer efficacy and associated mechanisms of other components of silymarin, which is a mixture of flavonolignans, are largely unknown.
METHODS AND RESULTS:
Here we have assessed the anticancer efficacy of two pure compounds isosilybin B and Isosilybin A, isolated from silymarin, in human prostate carcinoma LNCaP and 22Rv1 cells. Isosilybin B and Isosilybin A treatment resulted in growth inhibition and cell death together with a strong G(1) arrest and apoptosis in both the cell lines. In the studies examining changes in cell cycle and apoptosis regulators, isosilybin B and Isosilybin A resulted in a decrease in the levels of both cyclins (D1, D3, E and A) and cyclin-dependent kinases (Cdk2, Cdk4 and cell division cycle 25A), but caused an increase in p21, p27 and p53 levels, except in 22Rv1 cells where isosilybin B caused a decrease in p21 protein level. Isosilybin B- and Isosilybin A-induced apoptosis was accompanied with an increase in the cleavage of poly (ADP-ribose) polymerase, caspase-9 and caspase-3 and a decrease in survivin levels. Compared with LNCaP and 22Rv1 cells, the antiproliferative and cytotoxic potentials of isosilybin B and Isosilybin A were of much lesser magnitude in non-neoplastic human prostate epithelial PWR-1E cells suggesting the transformation-selective effect of these compounds.
CONCLUSIONS:
Together, this study for the first time identified that isosilybin B and Isosilybin A, two diastereoisomers isolated from silymarin, have anti-PCA activity that is mediated via cell cycle arrest and apoptosis induction.
Bioorg Med Chem. 2019 Jun 15;27(12):2499-2507.
Tyrosinase inhibitory study of flavonolignans from the seeds of Silybum marianum (Milk thistle).[Pubmed:
30871862 ]
Anti-melanogenesis effects of silymarin from milk thistle have been reported recently, but detailed tyrosinase inhibition properties of individual components have not been investigated. This study purported to substantiate tyrosinase inhibition and its mechanism based on a single metabolite.
METHODS AND RESULTS:
The responsible components for tyrosinase inhibition of target source were found out as flavonolignans which consist of Isosilybin A (1), isosilybin B (2), silydianin (3), 2,3-dihydrosilychristin (4), silychristin A (5), silychristin B (6) and silybin (7), respectively. The isolated flavonolignans (1-7) inhibited both monophenolase (IC50 = 1.7-7.6 µM) and diphenolase (IC50 = 12.1-44.9 µM) of tyrosinase significantly. Their inhibitions were 10-fold effective in comparison with their mother skeletons (8-10). Inhibitory functions were also proved by HPLC analysis using N-acetyl-l-tyrosine as substrate. The predominant formation of Emet·I was confirmed from a long prolongation of lag time and a decrease of the static state activity of the enzyme.
CONCLUSIONS:
All tested compounds had a significant binding affinity to tyrosinase with KSV values of 0.06-0.27 × 104 L·mol-1, which are well correlated with IC50s. In kinetic study, all flavonolignan (1-7) were mixed type I (KI < KIS) inhibitors, whereas their mother skeletons (8-10) were competitive ones. The UPLC-ESI-TOF/MS analysis showed that the isolated inhibitors are the most abundant metabolites in the target plant.
Mol Carcinog. 2010 Oct;49(10):902-12.
Isosilybin A induces apoptosis in human prostate cancer cells via targeting Akt, NF-κB, and androgen receptor signaling.[Pubmed:
20721970]
Prostate cancer (PCA) is the second most malignancy in American men. Advanced stage PCA cells possess unlimited replication potential as well as resistance to apoptosis. Therefore, targeting survival mechanisms and activating apoptotic machinery in PCA cells using nontoxic phytochemicals is suggested as an attractive strategy against this deadly malignancy.
METHODS AND RESULTS:
In the present study, we assessed the effect of one such botanical agent, namely Isosilybin A, on apoptotic machinery and key members of cell survival signaling [Akt, NF-κB, and androgen receptor (AR)] in different PCA cells. Results showed that Isosilybin A (90-180 µM) treatment significantly induces apoptotic death by activating both extrinsic (increased level of DR5 and cleaved caspase 8) and intrinsic pathways (caspase 9 and 3 activation) of apoptosis in three different human PCA cell lines namely 22Rv1, LAPC4, and LNCaP. Further, Isosilybin A treatment decreased the levels of phospho-Akt (serine-473), total Akt, and the nuclear levels of NF-κB constituents (p50 and p65). Isosilybin A treatment also decreased the AR and PSA level in 22Rv1, LAPC4, and LNCaP cells. Employing pan-caspase inhibitor (Z-VAD.fmk), we confirmed that Isosilybin A-mediated decreased AR is independent of caspases activation. Temporal kinetics analysis showed that the primary effect of Isosilybin A is on AR, as decrease in AR was evident much earlier (4 h) relative to caspase activation and apoptosis induction (12 h).
CONCLUSIONS:
Overall, our results demonstrated that Isosilybin A activates apoptotic machinery in PCA cells via targeting Akt-NF-κB-AR axis; thereby, indicating a promising role for this phytochemical in the management of clinical PCA.