N-butanol extracts of Morinda citrifolia suppress advanced glycation end products (AGE)-induced inflammatory reactions in endothelial cells through its anti-oxidative properties

Abstract

Background: Advanced glycation end products (AGEs), senescent macroprotein derivatives formed during a normal aging process and acceleratedly under diabetic conditions, play a role in atherosclerotic cardiovascular disease. AGEs cause endothelial cell (EC) damage, an initial trigger for atherosclerosis through the interaction with a receptor for AGEs (RAGE). We have previously shown that n-butanol extracts of Morinda citrifolia (noni), a plant belonging to the family Rubiaceae, block the binding of AGEs to RAGE in vitro. In this study, we examined the effects of n-butanol extracts of noni on reactive oxygen species (ROS) generation and inflammatory reactions on AGE-exposed human umbilical vein ECs (HUVECs).

Methods: HUVECs were treated with 100 μg/ml AGE-bovine serum albumin (AGE-BSA) or non-glycated BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni for 4 h. Then ROS generation and inflammatory and gene expression in HUVECs were evaluated by dihydroethidium staining and real-time reverse transcription-polymerase chain reaction analyses, respectively. THP-1 cell adhesion to HUVECs was measured after 2-day incubation of AGE-BSA or BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni.

Results: N-butanol extracts of noni at 670 ng/ml significantly inhibited the AGE-induced ROS generation and RAGE, intercellular adhesion molecule-1 and plasminogen activator inhibitor-1 gene expressions in HUVECs. AGEs significantly increased monocytic THP-1 cell adhesion to HUVECs, which was also prevented by 670 ng/ml n-butanol extracts of noni.

Conclusions: The present study demonstrated for the first time that N-butanol extracts of noni could suppress the AGE-induced inflammatory reactions in HUVECs through its anti-oxidative properties via blocking of the interaction of AGEs with RAGE. Inhibition of the AGE-RAGE axis by n-butanol extracts of noni may be a novel nutraceutical strategy for the treatment of cardiovascular disease.

Keywords: AGEs; Atherosclerosis; Oxidative stress; RAGE.

Fig. 1

Effects of noni extracts on ROS generation in AGE-exposed HUVECs. HUVECs were treated with 100 μg/ml AGE-BSA or non-glycated BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni for 4 h. Then superoxide generation was evaluated by intensity of DHE staining. Upper panels show the representative photos of DHE stainings. Lower panel shows the quantitative data. N = 3 per group. *, p < 0.05 compared to the value with AGEs alone

Fig. 2

Effects of noni extracts on RAGE (a), ICAM-1 (b), and PAI-1 (c) mRNA levels in AGE-exposed HUVECs. HUVECs were treated with 100 μg/ml AGE-BSA or non-glycated BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni for 4 h. Then total RNAs were transcribed and amplified by real-time PCR. Data were normalized by the intensity of β-actin (a) or 18S mRNA-derived signals (b and c) and then related to the value obtained with non-glycated BSA treatment alone. a N = 4 per group. b and c N = 8 per group. * and **, p < 0.05 and p < 0.01 compared to the value with AGEs alone, respectively

Fig. 3

Effects of noni extracts on THP-1 cell adhesion to AGE-exposed HUVECs. HUVECs were treated with 100 μg/ml AGE-BSA or non-glycated BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni for 24 h. Then HUVECs were incubated with BCECF-AM-labeled THP-1 cells for 4 h. Non-adherent THP-1 cells were removed. Fluorescent intensities of the adherent THP-1 cells were measured. N = 6 per group. **, p < 0.01 compared to the value with AGEs alone