Mustapha, Sagir
(2022)
Role of endoplasmic reticulum
stress, oxidative stress and
inflammation on early aortic
vasculopathy of Type 2 Diabetic rat
model.
PhD thesis, Universiti Sains Malaysia.
Abstract
Endoplasmic reticulum (ER) stress contributes to other pathological conditions
such as insulin resistance, macro- and microvascular complications associated with
diabetes. The aim of this study was to elucidate the role of ER stress, endothelial
insulin resistance, oxidative stress and inflammation on early vasculopathy in aorta of
type 2 diabetic rats (T2DM). The male Sprague-Dawley rats of 8 – 10 weeks old,
weighing about 250 to 300 g were employed for this study. The rats were divided into
two groups: control group (n=9) and diabetic group (n=18). The diabetic group were
placed on high-fat diet (HFD) for 4 weeks. They were then injected intraperitoneally
(i.p) with 40 mg/kg of single dose streptozotocin dissolved in 0.1 M sodium citrate
buffer of pH 4.5. Rats with fasting blood glucose greater than 11.1 mmol/l were
considered to be diabetic. The control rats were on the normal diet and injected with
equal volume of sodium citrate. Blood pressure was monitored in a warm, conscious
and restrained state using the non- invasive tail-cuff method via a blood pressure
monitoring system. At the 13th week, the diabetic rats were randomly divided into two
groups: diabetic rats (n= 9) and diabetic rats receiving tauroursodeoxycholic acid
(TUDCA) 150 mg/kg/day i.p for two weeks duration (n= 9). At the 15th week, all rats
were sacrificed using a mixture of ketamine (300 mg/kg, i.p) and xylazine (30 mg/kg,
i.p). After sacrifice, aortas were isolated and mounted on the organ bath to determine
acetylcholine- and insulin- mediated relaxations as well as the relaxation mechanisms
using pharmacological inhibitors. ER stress marker, regulators and associated relaxation signaling pathways proteins were assessed using Western blotting. In the
aorta of control rats, acetylcholine- and insulin-mediated relaxation through activation
of eNOS/PI3K, NAD(P)H oxidase and KATP channels pathways. In diabetic rats,
acetylcholine- mediated relaxation through activation of eNOS/PI3K and NAD(P)H
oxidase pathways, whereas insulin-mediated the relaxation through eNOS/PI3K
pathway only. Interestingly, treatment with TUDCA in diabetic rats showed that the
relaxation mediated by acetylcholine and insulin were reverted through activation of
eNOS/PI3K, NAD(P)H oxidase and KATP channels pathways. The functional study
was supported with an enhanced expression of vascular proteins (IRS-1, Akt and
eNOS) with corresponding downregulation of ER stress proteins (IRE-1, BiP and
PERK) in the diabetic rats receiving TUDCA. Therefore, these data suggested that the
inhibition of ER stress could be a potential target for the management of T2DM
vasculopathy.
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