Oxidative behaviour of apomorphine and its metabolites

Potentiometric detection of apomorphine in human plasma using a 3D printed sensor

Apomorphine is a dopamine agonist that is used for the management of Parkinson's disease and has been proven to effectively decrease the off-time duration, where the symptoms recur, in Parkinson's disease patients. This paper describes the design and fabrication of the first potentiometric sensor for the determination of apomorphine in bulk and human plasma samples. The fabrication protocol involves stereolithographic 3D printing, which is a unique tool for the rapid fabrication of low-cost sensors. The solid-contact apomorphine ion-selective electrode combines a carbon-mesh/thermoplastic composite as the ion-to-electron transducer and a 3D printed ion-selective membrane, doped with the ionophore calix[6]arene. The sensor selectively measures apomorphine in the presence of other biologically present cations - sodium, potassium, magnesium, and calcium - as well as the commonly prescribed Parkinson's pharmaceutical, levodopa (L-Dopa). The sensor demonstrated a linear, Nernstian response, with a slope of 58.8 mV/decade over the range of 5.0 mM-9.8 μM, which covers the biologically (and pharmaceutically) relevant ranges, with a limit of detection of 2.51 μM. Moreover, the apomorphine sensor exhibited good stability (minimal drift of just 188 μV/hour over 10 h) and a shelf-life of almost 4 weeks. Experiments performed in the presence of albumin, the main plasma protein to which apomorphine binds, demonstrate that the sensor responds selectively to free-apomorphine (i.e., not bound or complexed forms). The utility of the sensor was confirmed through the successful determination of apomorphine in spiked human plasma samples.

Mechanistic analyses of the suppression of amyloid β42 aggregation by apomorphine

(R)-Apomorphine (1) has the potential to reduce the accumulation of amyloid β-protein (Aβ42), a causative agent of Alzheimer's disease (AD). Although the inhibition of Aβ42 aggregation by 1 is ascribable to the antioxidative effect of its phenol moiety, its inhibitory mechanism at the molecular level remains to be fully elucidated. LC-MS and UV analyses revealed that 1 is autoxidized during incubation to produce an unstable o-quinone form (2), which formed a Michael adduct with Lys 16 and 28 of Aβ42. A further autoxidized form of 1 (3) with o-quinone and phenanthrene moieties suppressed Aβ42 aggregation comparable to 1, whereas treating 1 with a reductant, tris(2-carboxyethyl)phosphine diminished its inhibitory activity. ¹H-¹⁵N SOFAST-HMQC NMR studies suggested that 1 interacts with Arg5, His13,14, Gln15, and Lys16 of the Aβ42 monomer. These regions form intermolecular β-sheets in Aβ42 aggregates. Since 3 did not perturb the chemical shift of monomeric Aβ42, we performed aggregation experiments using 1,1,1,3,3,3-hexafluoro-2-propanol-treated Aβ42 to investigate whether 3 associates with Aβ42 oligomers. Compounds 1 and 3 delayed the onset of the oligomer-driven nucleation phase. Despite their cytotoxicity, they did not exacerbate Aβ42-mediated neurotoxicity in SH-SY5Y neuroblastoma cells. These results demonstrate that extension of the conjugated system in 1 by autoxidation can promote its planarity, which is required for intercalation into the β-sheet of Aβ42 nuclei, thereby suppressing further aggregation.

Prolonged modulation of FGF-2 expression in astrocytic cultures induced by O,O'-diacetyl-apomorphine

Apomorphine (APO) is an anti-parkinsonian drug currently in use, which provides relief of Parkinson's symptoms. However, the utility of APO is greatly hampered by its poor bioavailability and rapid metabolism. In the present study, O,O'-diacetyl-apomorphine, a prodrug of apomorphine, was synthesized and its biological activity was examined. The prodrug induced fibroblast growth factor-2 production in astrocytic cultures similarly to apomorphine. However, its duration of action was significantly prolonged, and its resistance to oxidation was markedly enhanced compared to APO. O,O'-Diacetyl-apomorphine also induced MEK/MAPK signaling. These results suggest that O,O'-diacetyl-apomorphine can efficiently counteract oxidation and thereby enhance FGF-2 production in astrocytes.