Novel 1-hydroxypyridin-2-one metal chelators prevent and rescue ubiquitin proteasomal-related neuronal injury in an in vitro model of Parkinson’s disease

Abstract

Ubiquitin proteasome system (UPS) impairment, excessive cellular oxidative stress, and iron dyshomeostasis are key to substantia nigra dopaminergic neuronal degeneration in Parkinson's disease (PD); however, a link between these features remains unconfirmed. Using the proteasome inhibitor lactacystin we confirm that nigral injury via UPS impairment disrupts iron homeostasis, in turn increasing oxidative stress and promoting protein aggregation. We demonstrate the neuroprotective potential of two novel 1-hydroxy-2(1H)-pyridinone (1,2-HOPO) iron chelators, compounds C6 and C9, against lactacystininduced cell death. We demonstrate that this cellular preservation relates to the compounds' iron chelating capabilities and subsequent reduced capacity of iron to form reactive oxygen species (ROS), where we also show that the ligands act as antioxidant agents. Our results also demonstrate the ability of C6 and C9 to reduce intracellular lactacystin-induced α-synuclein burden. Stability constant measurements confirmed a high affinity of C6 and C9 for Fe 3+ and display a 3:1 HOPO:Fe 3+ complex formation at physiological pH. Reducing iron reactivity could prevent the demise of nigral dopaminergic neurons. We provide evidence that the lactacystin model presents with several neuropathological hallmarks of PD related to iron dyshomeostasis and that the novel chelating compounds C6 and C9 can protect against lactacystin-related neurotoxicity.

(5-Hydroxy-4-oxo-2-styryl-4H-pyridin-1-yl)-acetic Acid Derivatives as Multifunctional Aldose Reductase Inhibitors

“…The derivatives 7c, 7g and 7k-l which already had exhibited good selectivity toward to ALR2 inhibition were tested for DPPH radical scavenging activity, as well as compound 7a serving as comparison. Interestingly, much superior to well-known antioxidant Trolox and reported deferiprone (3-hydroxy-1,2-dimethyl-1H-pyridin-4-one) [36], phenolic derivatives 7k-l showed excellent DPPH radical scavenging ability, revealing that the phenolic substituents might be a key structure enhancing DPPH free radical scavenging activity (Table 2). Particularly, at a concentration of 1 µM, compound 7l had most favorable antioxidant properties, achieving 41.48% of inhibition rate.…”

Synthesis, physicochemical characterization and neuroprotective evaluation of novel 1-hydroxypyrazin-2(1H)-one iron chelators in an in vitro cell model of Parkinson's disease

“…The kinetics of reaction suggested that these ligands can be classified as being slow radical scavengers, just like the 1-hydroxypyridin-2(1H)-ones 2 and 3. 28,43 The calculated EC 50 values (Table 2) showed that ligands 6a, 6c, 6d and 11a have a similar radical scavenging capability, while ligand 10a exhibited a 4 to 5 times lower EC 50 value, which is slightly better than the commercial ligand DFP 1 (EC 50 = 0.008 mg mL −1 = 5.8 × 10 −5 M) and comparable to multifunctional metal chelators containing phenol antioxidant moieties. 44 Somewhat surprisingly, ligand 6d was no better than the other ligands in this assay despite its added phenol moiety.…”

“…1) are also promising iron chelators in cell culture models of PD in vitro. 27,28 Compounds 2 and 3 reduced intracellular labile iron levels in both the 6-OHDA 27 and lactacystin 28 models of PD, and restored labile iron and iron-responsive protein expression to normal levels in the 6-OHDA model of PD. 27 More recently, we showed that both compounds also reduced α-synuclein accumulation induced by the potent ubiquitin proteasomal inhibitor lactacystin.…”

“…: log D 7.4 of 6a = −1.73, log D 7.4 of 2 = −1.71). 28 Although this suggests a relatively poor ability of 1-hydroxypyrazin-2(1H)-ones to penetrate cell membranes by passive diffusion, the possibility that they can penetrate cell membranes by active transport mechanisms cannot be discounted. In addition, the distribution coefficients of the Fe 3+ complexes of 6a and 11a are higher than that of 2 (log D 7.4 = −0.18).…”

“…27 More recently, we showed that both compounds also reduced α-synuclein accumulation induced by the potent ubiquitin proteasomal inhibitor lactacystin. 28 A closely related family of chelators to the 1,2-HOPOs are the 1-hydroxypyrazin-2(1H)-ones (1,2-HOPYs, Fig. 1).…”