Rhein-13C4 is intended for use as an internal standard for the quantification of rhein by GC- or LC-MS. Rhein is an anti-inflammatory anthraquinone found in rhubarb and is the bioactive derivative of its prodrug diacerein . At 10 μM, rhein inhibits IL-1β signaling, suppressing signaling through NF-κB, and reduces the expression of the matrix metalloproteases MMP-1 and MMP-13.1 It inhibits IKKβ (IC50 = 11.8 μM), decreasing iNOS and IL-6 expression in LPS-stimulated macrophages but paradoxically increasing TNF-α, IL-1β, and HMBG1 expression.2 Rhein shows efficacy against pancreatic fibrosis, chronic pancreatitis, and hyperglycemia-induced pancreatic β-cell apoptosis.3,4 It also inhibits angiogenesis of breast cancer cells under normoxic and hypoxic conditions.5

|1. Domagala, F., Martin, G., Bogdanowicz, P., et al. Inhibition of interleukin-1β-induced activation of MEK/ERK pathway and DNA binding of NF-κB and AP-1: Potential mechanism for Diacerein effects in osteoarthritis. Biorheology 43(3-4), 577-587 (2006).|2. Gao, Y., Chen, X., Fang, L., et al. Rhein exerts pro- and anti-inflammatory actions by targeting IKKβ inhibition in LPS-activated macrophages. Free Radic. Biol. Med. 72, 104-112 (2014).|3. Tsang, S.W., Zhang, H., Lin, C., et al. Rhein, a natural anthraquinone derivative, attenuates the activation of pancreatic stellate cells and ameliorates pancreatic fibrosis in mice with experimental chronic pancreatitis. PLoS One 8(12), 1-15 (2013).|4. Sayre, L.M., Larson, D.L., Takemori, A.E., et al. Design and synthesis of naltrexone-derived affinity labels with nonequilibrium opioid agonist and antagonist activities. Evidence for the existence of different μ receptor subtypes in different tissues. Journal of Medicinal Chemistry 27(10), 1325-1335 (1984).|5. Fernand, V.E., Losso, J.N., Traux, R.E., et al. Rhein inhibits angiogenesis and the viability of hormone-dependent and -independent cancer cells under normoxic or hypoxic conditions in vitro. Chem. Biol. Interact. 192(3), 220-232 (2011).