The effect of compounds on copper homeostasis in plasmodium falciparum and neuroblastoma cells

Abstract

Adverse changes in copper ion homeostasis can be harmful to living organisms, where an excess of copper can cause oxidative damage leading to carcinogenesis, neurogenerative diseases and the conditions such as Wilson’s and Parkinson’s disease. However, copper is a crucial metal required for metabolism and growth, as in the malaria parasite. Malaria is a global health problem that is further amplified by resistance to antimalarials and insecticides. Consequently, novel copper chelators that diminish metal ion redox effects and inhibit malaria metabolism are required to prevent disease progression. Two potential groups selected for investigation included 8-hydroxyquinoline (8-OH) derivatives and essential oils constituents (EOCs), which are known antioxidants, metal chelators, with antimicrobial properties. Thus, the aim of the study was to determine the interaction of twenty one 8-OHs and fifty-five EOCs with copper and to determine their chemotherapeutic effect on Plasmodium falciparum (3D7), Anopheles gambiae (KGB) and neuroblastoma cells (SHSY5Y), as well as the toxicological effects on human red blood cells and Artemia. The most potent 8-OH derivative, N-butyl-2,2-imino-di-(8-OH) preferentially chelated Cu(I) (IC50: 12.90  0.80 µM) over Cu(II) (IC50: 44.37  2.52 µM), compared to tetrathiomolybdate (IC50 Cu(I): 44.37  2.52 µM; IC50 Cu(II): 45.79  10.54 µM). It interacted synergistically with tetrathiomolybdate to chelate Cu(I) (FIC = 0.40) and in an additive manner to chelate Cu(II) (FIC = 0.75); whilst retaining its ability to chelate copper in vitro. This 8-OH derivative had notable in vitro antimalarial activity (IC50: 0.58 ± 0.03 µM) affecting the progression of trophozoites to schizonts by inhibiting haemozoin formation comparable to chloroquine and interacted synergistically with chloroquine in vitro. N-butyl-2,2-imino-di-(8-OH) possessed larvicidal activity, but not as potently as 2-benzyl-8-OH and DDT. It was twice as cytotoxic to neuroblastoma cells compared to camptothecin, but not as toxic to Artemia as potassium dichromate. Furthermore, 8-OH derivatives with functional groups at positions 5 and 7 displayed improved copper chelating, antioxidant, anticancer, antimalarial and larvicidal activity. The EOCs displayed a diverse pharmacological profile, with the widest range of activity belonging to (±)- menthone. It effectively chelated Cu(II) in preference to Cu(I) (IC50: 12.69  3.69 µM; 10.78  2.00 µM, respectively) compared to trientine (30.97  0.64 µM; 27.34  5.96 µM, respectively); along with promising copper reducing ability. However, this promising chelating ability did not correspond to its ability to inhibit malaria (51.22  8.21 µM). (±)-Menthone possessed significant larvicidal activity (73.00  5.70%) compared to DDT (100.00  0.00%), but was not as active as carvacrol (93.0  5.70%). Although (+)-α-pinene had poor copper chelating activity, it potently inhibited parasite growth (IC50: 0.009  0.002 µM) by inhibiting haemozoin formation, whilst interacting synergistically in vitro with chloroquine (FIC =0.45). The diverse properties of 8-OH derivatives and EOCs give rise to the potential that these compounds may be useful in the management of diseases caused by copper excess, oxidative stress, the malaria parasite and cancer