Ceruloplasmin-induced aggregation of P19 neurons involves a serine protease activity and is accompanied by reelin cleavage

The cytoarchitectural organization of the nervous system depends partly on extracellular serine proteases, including reelin. This 400K protein, which also exists as the N-terminally-derived 300K and 180K fragments, acts through binding to the lipoprotein receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VLDLR). Ceruloplasmin (CP), a multifunctional protein found in the circulation and also expressed on glial cells, was shown to bind to, and induce aggregation of neurons newly differentiated from P19 embryonic stem cells. This indicated a potential developmental role of CP in neuronal organization, possibly in relation with reelin and other extracellular serine proteases. Therefore, we analysed the effect of cell-impermeant, large spectrum, serine protease inhibitors on CP-induced neuroaggregation and studied reelin expression. Soybean trypsin inhibitor and aprotinin (SBTI+Apro) inhibited CP neuroaggregative action. Undifferentiated and neurally-differentiating cultures secreted the 400K reelin. The 180K fragment was present during and after differentiation whereas the 300K species was barely detectable. However, CP stimulated generation of the 300K in the differentiated neuronal cultures, and SBTI+Apro abolished this CP effect. Time course profiles and function-blocking antibody indicated that neuroaggregation does not depend on the generation of the 300K fragment or on reelin action. CP neuroaggregative action thus involves a pericellular serine protease, different from reelin. On the other hand, the CP stimulation of reelin cleavage is in line with a possible role of CP in nervous system development. Since P19 cells express ApoER2 and VLDLR, they can help understanding relationships existing between CP, reelin and intervening protease(s).

Gamma-irradiated ceruloplasmin affords antifibrillatory protection against ischemia/reperfusion damage in the isolated rat heart

PURPOSE

Ceruloplasmin (CP), an important serum antioxidant, was previously found to reduce the incidence of ventricular fibrillation (VF) induced by ischemia and reperfusion in isolated rat hearts. The present study investigated whether CP sterilized by gamma-irradiation maintains its antiarrhythmic capacity and in vitro antioxidant properties.

MATERIALS AND METHODS

Isolated rat hearts submitted to regional ischemia (15 min), were reperfused (10 min) with native CP or with CP irradiated at various doses (1-3 kGy) in the absence or presence of tyrosine (Tyr).

RESULTS

All untreated hearts showed VF at reperfusion, which were all irreversible ventricular fibrillation (IVF). No IVF were found in hearts treated with native CP or gamma-irradiated CP. Cardioprotection afforded by irradiated CP (with or without Tyr) was slightly higher than that obtained with native CP. No VF at all (100% prevention) was found in hearts treated with CP irradiated alone or in the presence of tyrosine at 3 kGy. Tyrosine and irradiated tyrosine had no cardiotoxic or protective effects on reperfusion-induced arrhythmias. The Oxygen Radical Absorbing Capacity (ORAC), measured in vitro with beta-phycoerythrin (beta-PE) fluorescent indicator, was slightly higher for gamma-irradiated CP in the presence of Tyr.

CONCLUSIONS

Ceruloplasmin sterilized by gamma-irradiation maintains antioxidant and antiarrhythmic effects in the post-ischemia reperfused isolated rat heart.

Suitability of commonly used excipients for electrophysiological in-vitro safety pharmacology assessment of effects on hERG potassium current and on rabbit Purkinje fiber action potential

INTRODUCTION

Regulatory guidelines require investigation of the liability for delayed ventricular repolarization by new chemical entities within a broad concentration range in-vitro. However, investigation can be limited by poor drug aqueous solubility, and by solvent physicochemical attributes that disrupt cell membrane integrity. Although excipients or solubilizing agents may aid to achieve the necessary high concentrations, no comprehensive overview on the suitability of solvents for in-vitro electrophysiological safety studies exists.

METHODS

Excipients were tested for potential interference with the hERG (human ether-a-go-go-related gene) K(+) current (whole-cell voltage-clamp, 23+/-2 degrees C), and the shape of rabbit Purkinje fiber action potentials (conventional glass microelectrode technique, 37+/-1 degrees C).

RESULTS AND DISCUSSION

Water-soluble complexation builders/carriers had little effect on hERG K(+) current at up to 50 mg/ml (BSA, bovine serum albumin) and 11 mg/ml (HP-beta-CD, hydroxypropyl-beta-cyclodextrin; IC(20), concentration of 20% inhibition). Water-soluble organic (co)solvents inhibited hERG K(+) currents (IC(20), %/mM): 0.7/152, ethanol; 0.9/67, Transcutol; 1.2/154, DMSO (dimethylsulfoxide); 1.6/389, acetonitrile; 1.9/48, polyethylene glycol 400; 2.1/660, methanol. Part of their inhibitory effect is attributed to the osmolality of extracellular solutions, because hERG IC(20) and extrapolated osmolality at the hERG IC(20) strongly correlate. Water-soluble non-ionic solubilizers/surfactants are potent inhibitors of hERG K(+) current with IC(20) concentrations of 0.07% (Cremophor EL) or lower (Tween 20, Tween 80: approximately 0.001%). Part of this inhibitory effect is attributed to their interaction with lipid membranes, because hERG inhibition occurs close to critical micelle concentrations (Cremophor, approximately 0.009%; Tween 20, approximately 0.007%). Purkinje fiber action potentials are little affected by HP-beta-CD at up to 2 mg/ml, while DMSO tends to shorten the action potential duration at 1%.

CONCLUSION

When conducting electrophysiological in-vitro assessments of drug effects, solubilizers/surfactants (Cremophor EL, Tween 20, Tween 80) should be avoided. Instead, water-soluble organic (co)solvents (methanol, acetonitrile, DMSO) or complexation builders/carriers (HP-beta-CD, BSA) appear to be more favorable.

Aminoacetone Induces Oxidative Modification to Human Plasma Ceruloplasmin

Aminoacetone (AA), a putative endogenous source of cytotoxic methylglyoxal, and ceruloplasmin (CP), the antioxidant plasma copper transporter, are known to increase in diabetes. AA was recently shown in vitro to act as a pro-oxidant toward ferritin and isolated mitochondria. We now report AA oxidative effects on CP mediated by AA-generated reactive oxygen species (ROS). Incubation of 1.5 microM human CP with 0.05-1 mM AA resulted in extensive protein aggregation. That ROS-driven thiol cross-linking underlies the CP aggregation was evidenced by the inhibitory effects of added superoxide dismutase, catalase, mannitol, and dithiothreitol. The addition of CP to AA (mM) solutions accelerated oxygen consumption by AA and caused CP copper ion release and loss of ferroxidase and aminoxidase activities. If operative in vivo, this reaction would impair the antioxidant role of CP and iron uptake by ferritin and hence contribute to intracellular iron-induced oxidative stress during AA accumulation in diabetes mellitus.

The blue copper ceruloplasmin induces aggregation of newly differentiated neurons: a potential modulator of nervous system organization

Ceruloplasmin (CP) is a copper-dependent ferroxidase. It regulates iron metabolism and is involved in inflammation, angiogenesis, and protection against oxidative stress. CP also modulates K(+) channel activity in neuroblastoma cells and affects cardiodynamics of isolated hearts. Considering the presence of CP in the nervous system and the importance of iron ions and K(+) channels in neuronal activity, we postulated a role of CP in neuronal development. This hypothesis was tested using the P19 mouse embryonal carcinoma cell line, a model of neuronal differentiation. Addition of CP to the culture medium of newly differentiated P19 neurons induced cell aggregation within 24 h. This effect was concentration-dependent half-maximal at 50 nM, and not associated with necrosis, apoptosis or changes in secretory function. Deglycosylated CP was aggregative but not denatured CP, copper salts, His(2)Cu complex, or other copper enzymes or serum proteins. CP-induced aggregation was less pronounced with aging neurons and seemed not to involve K(+) channels. Immunocytofluorescence analysis demonstrated that digoxigenin-labeled CP bound to P19 neurons and the proportion of responding neurons decreased with aging. The interaction of digoxigenin-labeled CP with neurons was half-maximal at 120 nM by enzyme-linked immunosorbent assay and displaced by unlabeled CP. Our data indicate a specific aggregative action of CP on young neurons in vitro, possibly involving CP receptors. A potential developmental role of CP in nervous system organization is thus demonstrated.