Showing papers by "Paul S. Donnelly published in 2022"

Copper bis(thiosemicarbazone) complexes modulate P‐glycoprotein expression and function in human brain microvascular endothelial cells

Abstract: P‐glycoprotein (P‐gp) is an efflux transporter at the blood–brain barrier (BBB) that hinders brain access of substrate drugs and clears endogenous molecules such as amyloid beta (Aβ) from the brain. As biometals such as copper (Cu) modulate many neuronal signalling pathways linked to P‐gp regulation, it was hypothesised that the bis(thiosemicarbazone) (BTSC) Cu‐releasing complex, copper II glyoxal bis(4‐methyl‐3‐thiosemicarbazone) (CuII[GTSM]), would enhance P‐gp expression and function at the BBB, while copper II diacetyl bis(4‐methyl‐3‐thiosemicarbazone) (CuII[ATSM]), which only releases Cu under hypoxic conditions, would not modulate P‐gp expression. Following treatment with 25–250 nM CuII(BTSC)s for 8–48 h, expression of P‐gp mRNA and protein in human brain endothelial (hCMEC/D3) cells was assessed by RT‐qPCR and Western blot, respectively. P‐gp function was assessed by measuring accumulation of the fluorescent P‐gp substrate, rhodamine 123 and intracellular Cu levels were quantified by inductively coupled plasma mass spectrometry. Interestingly, CuII(ATSM) significantly enhanced P‐gp expression and function 2‐fold and 1.3‐fold, respectively, whereas CuII(GTSM) reduced P‐gp expression 0.5‐fold and function by 200%. As both compounds increased intracellular Cu levels, the effect of different BTSC backbones, independent of Cu, on P‐gp expression was assessed. However, only the Cu‐ATSM complex enhanced P‐gp expression and this was mediated partly through activation (1.4‐fold) of the extracellular signal‐regulated kinase 1 and 2, an outcome that was significantly attenuated in the presence of an inhibitor of the mitogen‐activated protein kinase regulatory pathway. Our findings suggest that CuII(ATSM) and CuII(GTSM) have the potential to modulate the expression and function of P‐gp at the BBB to impact brain drug delivery and clearance of Aβ.

An icosanuclear silver(I) cluster supported by bis(thiosemicarbazonato) ligands†

Abstract: The synthesis and structural characterisation of an icosanuclear silver(I) cluster complex is reported here. The complex includes twenty silver(I) ions supported by eighteen bis(thiosemicarbazonato) ligands. The cluster of silver(I) ions involves several close Ag⋯Ag contacts suggesting some degree of argentophilic interactions and the bis(thiosemicarbazonato) ligands are present in three different conformations highlighting the ability of thiosemicarbazone ligands to coordinate to metal ions in different modes.

Synthesis of acyloin natural products by Mukaiyama hydration.

Abstract: The acyloin natural products are a family of bioactive compounds isolated from fungi and myxobacteria. The total synthesis of 7 members of the acyloin family was achieved via a HWE reaction followed by Mukaiyama-Isayama hydration, using novel Co(II) and Co(III) Schiff base SALPN complexes as catalysts for the key enone hydration step. Furthermore, we have shown that a mild acyloin rearrangement is possible under Mukaiyama hydration conditions, which was crucial in the success of this approach.

Microglial ferroptotic stress causes non-cell autonomous neuronal death

Abstract: Background Ferroptosis is a form of regulated cell death characterised by lipid peroxidation as the terminal endpoint and a requirement for iron. Although it protects against cancer and infection, ferroptosis is also implicated in causing neuronal death in degenerative diseases of the central nervous system (CNS). The precise role for ferroptosis in causing neuronal death is yet to be fully resolved. Methods To elucidate the role of ferroptosis in neuronal death we utilised co-culture and conditioned medium transfer experiments involving microglia, astrocytes and neurones. We ratified clinical significance of our cell culture findings via assessment of human CNS tissue from cases of the fatal, paralysing neurodegenerative condition of amyotrophic lateral sclerosis (ALS). Finally, we utilised the SOD1G37R mouse model of ALS and a novel CNS-permeant ferroptosis inhibitor to verify pharmacological significance in vivo. Results We found that sublethal ferroptotic stress selectively affecting microglia triggers an inflammatory cascade that results in non-cell autonomous neuronal death. Central to this cascade is the conversion of astrocytes to a neurotoxic state. We show that spinal cord tissue from cases of ALS exhibits a signature of ferroptosis that encompasses atomic, molecular and biochemical features. Moreover, a molecular correlation between ferroptosis and neurotoxic astrocytes evident in ALS-affected spinal cord is recapitulated in the SOD1G37R mouse model where treatment with the novel, CNS-permeant ferroptosis inhibitor, CuII(atsm), ameliorated these markers and was neuroprotective. Conclusions By showing that microglia responding to sublethal ferroptotic stress culminates in non-cell autonomous neuronal death, our results implicate microglial ferroptotic stress as a rectifiable cause of neuronal death in neurodegenerative disease. As ferroptosis is currently primarily regarded as an intrinsic cell death phenomenon, these results introduce an entirely new pathophysiological role for ferroptosis in disease.

The role of silver carbonate as a catalyst in the synthesis of N-phenylbenzamide from benzoic acid and phenyl isocyanate: a mechanistic exploration

Abstract: The gas-phase extrusion–insertion (ExIn) reactions of a silver complex [(BPS)Ag(O2CC6H5)]2− ([BPS]2− = 4,7-diphenyl-1,10-phenanthroline-disulfonate), generated via electrospray ionisation was investigated by Multistage Mass Spectrometry (MSn ) experiments in a linear ion trap combined with density functional theory (DFT) calculations. Extrusion of carbon dioxide under collision-induced dissociation (CID) generates the organosilver intermediate [(BPS)Ag(C6H5)]2−, which subsequently reacts with phenyl isocyanate via insertion to yield [(BPS)Ag(NPhC(O)C6H5)]2−. Further CID of the product ion resulted in the formation of [(BPS)Ag(C6H5)]2−, [(BPS)Ag]− and C6H5C(O)NPh−. The formation of a coordinated amidate anion is supported by DFT calculations. Heating a mixture of benzoic acid, phenyl isocyanate, silver carbonate (5 mol%) and phenanthroline (20 mol%) in DMSO and heating by microwave irradiation led to the formation N-phenyl-benzamide in an isolated yield of 89%. The yield decreased to 74% without the addition of phenanthroline, while replacing silver carbonate with sodium carbonate gave an isolated yield of 84%, suggesting that the ExIn reaction may not operate in solution. This was confirmed using benzoic acid with a 13C-isotopic-label at the carboxylate carbon as the starting material, which, under microwave heating in the presence of phenyl isocyanate, silver carbonate (5 mol%) and phenanthroline (20 mol%) gave N-phenyl-benzamide with retention of the 13C isotopic label based on GC-MS experiments under electron ionisation (EI) conditions. DFT calculations using a solvent continuum reveal that the barriers associated with the pathway involving direct attack by the non-coordinated benzoate are below the ExIn pathways for the coordinated silver benzoate.

Novel Anti-Neuroinflammatory Properties of a Thiosemicarbazone–Pyridylhydrazone Copper(II) Complex

Abstract: Neuroinflammation has a major role in several brain disorders including Alzheimer’s disease (AD), yet at present there are no effective anti-neuroinflammatory therapeutics available. Copper(II) complexes of bis(thiosemicarbazones) (CuII(gtsm) and CuII(atsm)) have broad therapeutic actions in preclinical models of neurodegeneration, with CuII(atsm) demonstrating beneficial outcomes on neuroinflammatory markers in vitro and in vivo. These findings suggest that copper(II) complexes could be harnessed as a new approach to modulate immune function in neurodegenerative diseases. In this study, we examined the anti-neuroinflammatory action of several low-molecular-weight, charge-neutral and lipophilic copper(II) complexes. Our analysis revealed that one compound, a thiosemicarbazone–pyridylhydrazone copper(II) complex (CuL5), delivered copper into cells in vitro and increased the concentration of copper in the brain in vivo. In a primary murine microglia culture, CuL5 was shown to decrease secretion of pro-inflammatory cytokine macrophage chemoattractant protein 1 (MCP-1) and expression of tumor necrosis factor alpha (Tnf), increase expression of metallothionein (Mt1), and modulate expression of Alzheimer’s disease-associated risk genes, Trem2 and Cd33. CuL5 also improved the phagocytic function of microglia in vitro. In 5xFAD model AD mice, treatment with CuL5 led to an improved performance in a spatial working memory test, while, interestingly, increased accumulation of amyloid plaques in treated mice. These findings demonstrate that CuL5 can induce anti-neuroinflammatory effects in vitro and provide selective benefit in vivo. The outcomes provide further support for the development of copper-based compounds to modulate neuroinflammation in brain diseases.

Assessment of the epi-pericardial fibrotic substrate by collagen-targeted probes

Abstract: The identification of the fibrotic arrhythmogenic substrate as a means of improving the diagnosis and prediction of atrial fibrillation has been a focus of research for many years. The relationship between the degree of atrial fibrosis as a major component of atrial cardiomyopathy and the recurrence of arrhythmia after AF ablation can correlate. While the focus in identification and characterisation of this substrate has been centred on the atrial wall and the evaluation of atrial scar and extracellular matrix (ECM) expansion by late gadolinium-enhancement (LGE) on cardiac magnetic resonance imaging (CMRI), LGE cannot visualise diffuse fibrosis and diffuse extravasation of gadolinium. The atrial pericardium is a fine avascular fibrous membranous sac that encloses the atrial wall, which can undergo remodelling leading to atrial disease and AF. Nevertheless, little attention has been given to the detection of its fibrocalcification, impact on arrhythmogenesis and, most importantly, on the potential prothrombotic role of epi-pericardial remodelling in generation of emboli. We have recently reported that tracers against collagen I and IV can provide a direct assessment of the ECM, and thus can estimate fibrotic burden with high sensitivity. Here, we show the ability of these optical tracers to identify epi-pericardial fibrosis, as well as to demonstrate subtle interstitial fibrosis of the atrial wall in a mouse model of beta-2-adrenergic receptor (β2-AR) cardiac overexpression.

Hexadentate technetium-99m bis(thiosemicarbazonato) complexes: synthesis, characterisation and biodistribution.

Abstract: The syntheses of non-oxido/non-nitrido bis(thiosemicarbazonato)technetium(V) complexes featuring a series of alkyl and ether substituents is presented. The bis(thiosemicarbazones) were radiolabelled with technetium-99m using an optimised one-pot synthesis from [99mTc][TcO4]-. Mass spectrometry and computational chemistry data suggested a distorted trigonal prismatic coordination environment for the bis(thiosemicarbazonato)technetium(V) complexes by way of a bis(thiosemicarbazone)technetium(V)-oxido intermediate complex. The lipophilicities of the complexes were estimated using distribution ratios and three of the new complexes were investigated in mice using kinetic planar imaging and ex vivo biodistribution experiments and were compared to [99mTc][TcO4]-. Modification of the technetium complexes with various lipophilic functional groups altered the biodistributions of the complexes in mice despite evidence suggesting limited stability of the complexes to biologically relevant conditions. The most hydrophilic complex had higher uptake in the kidneys compared to the most lipophilic, which had higher liver uptake, suggesting modification of the excretion pathways.