Azman Abdullah

A review of NAD(P)H: Quinone oxidoreductase 1 (NQO1); A multifunctional antioxidant enzyme

NAD(P)H:quinone-oxidoreductase-1 (NQO1) is a cytosolic enzyme that catalyses two- or four-electron reduction of many endogenous and environmental quinones using flavin adenine dinucleotide (FAD) as a cofactor. It is a cytosolic enzyme exists as a homodimer and is biochemically distinguished by its prominent ability to use either NADH or NADPH as reducing cofactors and by its suppression by the anticoagulant dicumarol. This enzyme generally considered as a detoxification enzyme due to of its ability to diminish reactive quinones and quinone-imines to its less reactive and less toxic hydroquinones forms. NQO1 is a substantially inducible enzyme that is controlled by the Nrf2-Keap1/ARE pathway. Evidence for the significance of the antioxidant functions of NQO1 in suppression of oxidative stress is provided by manifestations that induction of NQO1 levels or their reduction are associated with reduced and raised susceptibilities to oxidative stress, respectively. The gene coding for NQO1 has two common polymorphisms at nucleotide position 609(C-T) and 465 (C-T) of the human cDNA. C465T causes reduction in enzyme activity, whereas the C609T results in complete loss of enzymatic activity due to protein instability. In this review, we discuss the protective functions of NQO1 and present its possible transcriptional pathways regulating its induction by Nrf2-Keap1/ARE pathway.

The Effects of Cosmos caudatus (Ulam Raja) on Detoxifying Enzymes in Extrahepatic Organs in Mice

‘Ulam Raja’ or Cosmos caudatus is a common appetizer (ulam) consumed by the Malay community in Malaysia. However, in vivo studies pertaining to its antioxidant and chemoprotective properties are lacking. This study was done to determine the effects of Cosmos caudatus on detoxifying enzymes in extrahepatic organs (lungs, kidneys and stomach) in mice. Thirty adult male white mice were treated orally for 21 days with different doses of ‘Ulam Raja’ aqueous extract (UR) (100, 500, 1000mg/kg). The control group was given normal saline by oral gavage. Mice fed with diet containing 0.5% butylated hydroxyanisole (BHA) were used as positive control. After 21 days, the mice were sacrificed and extrahepatic organs were harvested. The activities of several detoxifying enzymes [catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), DT-diaphorase (DTD)] were measured. Lipid peroxidation level was determined by measuring malondialdehyde (MDA) concentration. In lungs, 100, 500 & 1000 mg/kg UR oral supplementation resulted in significant increases in CAT, SOD and GST activities. DTD activity in lungs was significantly increased in mice treated with 1000mg/kg UR. MDA levels in lungs were significantly decreased in mice treated with 100mg/kg & 500 mg/kg UR but was significantly increased in mice treated with 1000mg/kg UR. In kidneys, DTD activity was significantly increased in mice treated with 1000mg/kg UR. In stomach, CAT activity was significantly increased in mice treated with 1000mg/kg UR. The results showed that Cosmos caudatus supplementation in mice could protect extrahepatic organs from xenobiotic and oxidative injury. This indicates that consumption of ‘Ulam Raja’ might be a useful chemoprotective measure.

The Effects of Cosmos caudatus (Ulam Raja) on the Levels of Expression of Nrf2 Target Genes in Mice Liver

Background : Cosmos caudatus (Ulam Raja) is an appetizer (ulam) eaten with rice in Malaysia. Previous studies showed that Cosmos caudatus possess high antioxidant content. Nrf2 is a transcription factor which regulates the expression of phase II enzymes and antioxidant proteins. The aim of this study is to investigate the effects of Cosmos caudatus aqueous extract (UR) on the expression of Nrf2 target genes in mice liver. Methods : ICR white mice were treated for 21 days with different doses of UR (100, 500, 1000 mg/kg) through oral gavage. Control mice were only given distilled water. After 21 days, the mice were sacrificed and their livers harvested. Total RNA was extracted, reverse transcribed and subjected to qPCR to detect Nrf2 target genes expression. Results : Administration of 100 mg/kg UR significantly increased NQO1 expression in mice liver. Administration of 500 mg/kg UR significantly increased HO-1 liver expression. Administration of 100 and 500 mg/kg UR significantly increased GSTA1 liver expression. Administration of 500 and 1000 mg/kg UR significantly increased GSTM3 liver expression, whereas GSTP and GSTM1 liver expression was significantly decreased at similar doses . Administration of all doses of UR significantly decreased the expression of GSTA3 , SOD3 and GCLC in mice liver. Conclusion : UR administration mostly resulted in downregulation of Nrf2 target genes. However, conclusive evidence can only be made through the use of Nrf2 knockout mice or by performing Nrf2 nuclear translocation studies.

Tocotrienol-rich Palm Oil Extract Induces NAD(P)H:quinone Oxidoreductase 1 (NQO1) Expression in Mice Liver -

A diet rich in tocotrienols has been shown to be beneficial for health. However, its detailed mechanism of action is still not fully understood. NAD(P)H:quinone oxidoreductase 1 (NQO1) is important in cellular defence due to its ability to detoxify reactive quinones and quinoneimines to their less toxic hydroquinones forms. The objective of this study is to investigate the effects of different doses of palm oil-derived tocotrienol rich fraction (palm TRF) supplementation on NQO1 gene and protein expression in mice livers. Western blot and qPCR assays were used to detect NQO1 expression levels. It was found that palm TRF significantly induced NQO1 expression at all doses given. In conclusion, palm TRF treatment increased NQO1 gene and protein expression in mice liver dose dependently, with the highest expression seen in mice treated with 1000 mg/kg palm TRF, followed by 500 and 200 mg/kg respectively.