Cantharidin-binding protein: identification as protein phosphatase 2A. (25/89)

The toxic effects of cantharidin from blister beetles and its analogs, including the herbicide endothall, are attributable to their high affinity and specificity for a cantharidin-binding protein (CBP). An ammonium sulfate precipitate of mouse liver cytosol was purified by five chromatographic steps to isolate CBP in 14% yield and > 99% purity as monitored by [3H]cantharidin-binding activity. The purification factor of 2230-fold corresponds to a CBP content of 0.045% of the liver cytosolic protein. CBP is a heterodimer consisting of a 61-kDa alpha subunit and a 39-kDa beta subunit. Amino acid sequences of four peptides from CBP-alpha and three peptides from CBP-beta are identical with deduced amino acid sequences for the A alpha regulatory and C beta catalytic subunits, respectively, of protein phosphatase 2A (PP2A). This assignment of CBP as PP2A-AC from structural evidence is supported by biochemical studies with selective substrates and inhibitors. CBP dephosphorylation of phosphorylase alpha is sensitive not only to okadaic acid, as with PP2A, but also to cantharidin and its analogs, consistent with their potency in blocking the radioligand binding site of CBP. Okadaic acid is a potent inhibitor of [3H]cantharidin binding to CBP. PP2A is present in many mammalian tissues and in plants and is involved in regulatory phosphorylation-dephosphorylation events which modulate multiple cellular functions. Inhibition of PP2A activity may account for the diverse effects and toxicity of cantharidin and its analogs, including the herbicide endothall, in mammals and possibly plants.  (+info)

Cantharidin treatment of digital and periungual warts. (26/89)

Seventy-six digital and periungual warts in 40 patients were treated topically with cantharidin, a potent blistering agent. The material, dissolved in equal parts of acetone and collodion, was applied directly to the warts. Occlusion facilitated blistering. No pretreatment was required. The warts were re-treated at weekly intervals until clinically cured.Fifty-six per cent of digital warts and 33 per cent of periungual warts cleared after a single application of cantharidin. Few required more than three treatments. Observation was continued for more than six months in more than half of the cases. Cure was lasting in about 70 per cent of the cases in which the long term result was known. Cantharidin ranks with liquid nitrogen in effectiveness, but it is painless to apply and does not cause scarring. For these reasons it is especially useful in children.The main disadvantage is pain and tenderness at the treated site for two to four days in some patients. This can be avoided by careful application of the drug. Occasionally new warts appear at the edge of the cantharidin blister. They are best treated by curettage and desiccation.  (+info)

Effects of cantharidin on interleukin-2 and interleukin-1 production in mice in vivo. (27/89)

After cantharidin (0.75, 1.5 mg.kg-1) was given ip 3 times every other day in mice, Con A-induced spleen lymphocyte proliferation, as measured by [3H]TdR incorporation assay, was enhanced from 7,978 +/- 1,780 to 36,631 +/- 8,467 and 29,997 +/- 3,788 dpm in both doses. Interleukin-2 and interleukin-1 production were also increased from 11 +/- 4 to 52 +/- 18, 23 +/- 6 U.ml-1 and from 7,628 +/- 1,477 to 14,532 +/- 2,272, 11,515 +/- 2,862 dpm, respectively. These results suggest that cantharidin potentiates immune response through the release of interleukin-2 and interleukin-1.  (+info)

Macrophage release of transforming growth factor beta1 during resolution of monosodium urate monohydrate crystal-induced inflammation. (28/89)

OBJECTIVE: It has previously been shown that as monocytes differentiate into macrophages, they lose the ability to secrete proinflammatory cytokines in response to monosodium urate monohydrate (MSU) crystals. The purpose of this study was to investigate whether MSU crystals induce macrophages to secrete antiinflammatory factor instead. METHODS: Human monocyte or macrophage isolates were prepared from samples obtained from healthy volunteer donors either by differentiation of blood monocytes in vitro or by collecting cells from skin blisters during the early or late phase of the dermal inflammatory response to cantharidin. Monocyte or macrophage isolates were then incubated with MSU crystals for 24 hours, and culture supernatants were assayed for candidate antiinflammatory mediators (by enzyme-linked immunosorbent assay) and for the capacity to activate or suppress endothelial cell E-selectin expression and secondary neutrophil recruitment under shear flow. RESULTS: Analysis of supernatants from in vitro-differentiated macrophages revealed that transforming growth factor beta1 (TGFbeta1) was induced following MSU crystal stimulation (mean +/- SEM 1.50 +/- 0.24 ng/ml/10(6) cells), but there was no evidence of interleukin-10 (IL-10), IL-1 receptor antagonist, or tumor necrosis factor (TNF) receptor p55 release. Macrophage TGFbeta1 significantly suppressed endothelial cell E-selectin expression and secondary neutrophil capture on endothelial monolayers stimulated with supernatants from MSU-treated monocytes. Leukocytes isolated from resolving (40-hour) skin blisters similarly elaborated TGFbeta1 when challenged with MSU crystals (0.66 +/- 1.3 ng/ml/10(5) CD14+ cells). In contrast, cells isolated from acute (16-hour) skin blisters secreted TNFalpha (0.49 +/- 0.08 ng/ml/10(5) CD14+ cells) but no detectable TGFbeta1. CONCLUSION: These data provide further support for the concept that differentiated macrophages play a protective role in the pathophysiology of gout, and they identify macrophage TGFbeta1 as a mediator of paracrine suppression during the resolution phase of inflammation.  (+info)

Three novel cantharidin-related compounds from the Chinese blister beetle, Mylabris phalerata Pall. (29/89)

Three novel cantharidin analogues were isolated from the Chinese blister beetle, Mylabris phalerata PALL. (Meloidae), which has been used in traditional Chinese medicine for the treatment of cancer. Their structures were determined on the basis of heteronuclear multiple-bond connectivity and nuclear Overhauser effect spectroscopy experiments, and chemical data confirmed them to be so-called cantharimides, in which the anhydride oxygen atoms are replaced by the basic amino acid L-lysine, L-ornithine, and L-arginine moieties.  (+info)

Effects of cantharidinimides on human carcinoma cells. (30/89)

Modification of the cantharidinimide structure led to the discovery of a novel class of antitumor compounds. These cantharidinimide derivatives containing aliphartic, aryl, and pyridyl groups showed some effect in vitro against HepG2 and HL-60 cells.  (+info)

Flavin-containing polyamine oxidase is a hydrogen peroxide source in the oxidative response to the protein phosphatase inhibitor cantharidin in Zea mays L. (31/89)

In this study, the specific contribution of polyamine oxidase (PAO), a hydrogen peroxide (H2O2)-producing enzyme, to the oxidative burst induced in maize mesocotyl by the phosphatase inhibitor cantharidin was examined. For this purpose, a pharmacological approach was applied using, either in vitro or in vivo, two strong inhibitors of maize PAO (MPAO), N-prenylagmatine (G3) and its structural analogue Ro5, as well as diphenyleneiodonium (DPI), an inhibitor of the phagocyte NAD(P)H oxidase. DPI was shown to be a good MPAO inhibitor in vitro. G3, Ro5, and DPI were very effective in inhibiting in vivo the extracellular accumulation of H2O2 that is released by mesocotyl segments upon spermidine supply. G3 and Ro5 did not show any inhibition in vitro of either horseradish peroxidase or barley oxalate oxidase. Moreover, G3 and Ro5 did not inhibit the extracellular accumulation of superoxide radical that is released in vivo upon NADH supply. G3, Ro5, and DPI strongly affected H2O2 production induced in maize mesocotyl by cantharidin. Histochemical localization of H2O2 in cantharidin-treated mesocotyl cross-sections revealed an increase of H2O2-specific staining in the epidermal and subepidermal tissues. The effect was also inhibited by G3 and DPI. Moreover, an increase in MPAO activity was observed in the same tissues upon cantharidin treatment. All these data suggest that G3 and Ro5 behave as powerful and selective inhibitors of MPAO activity either in vitro or in vivo and that MPAO activity contributes to a major part of the cantharidin-induced H2O2 synthesis in the apoplastic milieu of maize mesocotyl.  (+info)

The alpha4 regulatory subunit exerts opposing allosteric effects on protein phosphatases PP6 and PP2A. (32/89)

The protein Ser/Thr phosphatase family contains three enzymes called PP2A, PP4, and PP6 with separate biological functions inferred from genetics of the yeast homologues Pph21/22, Pph3, and Sit4. These catalytic subunits associate with a common subunit called alpha4 (related to yeast Tap42). Here, we characterized recombinant PP6 and PP2A catalytic monomers and alpha4.phosphatase heterodimers. Monomeric PP6 and PP2A showed identical kinetics using either p-nitrophenyl phosphate (pNPP) or 32P-myelin basic protein (MBP) as substrates, with matching Km and Vmax values. Using pNPP as substrate, PP6 and PP2A gave the same IC50 with active site inhibitors okadaic acid, microcystin-LR, calyculin A, and cantharidin. However, with MBP as substrate, PP6 was inhibited at 5-fold lower concentrations of toxins relative to PP2A, suggesting PP6 might be a preferred in vivo target of toxins. Heterodimeric alpha4.PP6 and alpha4.PP2A were starkly different. With MBP as substrate the alpha4.PP2A heterodimer had a 100-fold higher Vmax than alpha4.PP6, and neither heterodimer was active with pNPP. Thus, these phosphatases are distinguished by their different responses to allosteric binding of the common regulatory subunit alpha4. Transient expression of alpha4 differentially increased or decreased phosphorylation of endogenous phosphoproteins, consistent with opposing effects on PP2A and PP6.  (+info)