Basic ScienceGLP-1 analog liraglutide protects against oxidative stress and albuminuria in streptozotocin-induced diabetic rats via protein kinase A-mediated inhibition of renal NAD(P)H oxidases
Introduction
Diabetic nephropathy is a leading cause of end-stage renal failure worldwide. Establishment of therapeutic strategies targeting the causative mechanisms of diabetic nephropathy has become increasingly urgent. In recent years, evidence has suggested that oxidative stress may play an important role in the development of diabetic nephropathy [1], [2], [3], [4]. Among the possible sources of reactive oxygen species (ROS) production, we and other investigators have shown that NAD(P)H oxidase may be a major source in diabetic renal tissues [5], [6], [7], [8], [9]. NAD(P)H oxidase may therefore be a therapeutic target for attenuating ROS production in diabetic kidneys, thereby preventing the development of diabetic nephropathy.
Glucagon-like peptide-1 (GLP-1) is an incretin hormone produced by intestinal L cells in response to food intake. It is considered as an effective therapeutic agent for type 2 diabetes mellitus because it regulates plasma glucose levels by stimulating insulin secretion and inhibiting glucagon secretion in a glucose-dependent manner. It may also have other beneficial effects, such as stimulating beta cell proliferation, protecting against beta cell apoptosis, inducing satiety, and delaying gastric emptying [10], [11]. Currently, the GLP-1 receptor agonist exendin-4 [12] and the GLP-1 analog liraglutide [13] are used to treat type 2 diabetes mellitus. GLP-1 acts through the GLP-1 receptor, which is abundantly expressed in pancreatic islet cells, neuronal cells, and gastrointestinal cells; but it has also been found in the heart, vascular smooth cells, and endothelial cells [14], [15], [16]. In fact, GLP-1 receptor agonists have been reported to have direct beneficial effects, such as improving left ventricular performance after myocardial infarction [17] and protecting against cardiac ischemia [18] and the progression of atherosclerosis [19].
The major downstream pathway of GLP-1 receptor activation is generation of the second messenger cAMP followed by activation of PKA or Epac2 [20], [21]. We hypothesized that GLP-1 receptor agonists may have a direct beneficial effect on the development of diabetic nephropathy through inhibition of renal NAD(P)H oxidases because NAD(P)H oxidases have been reported to be inhibited by PKA activation in phagocytes [22], [23]. In the present study, we show that the GLP-1 analog liraglutide may protect against increased oxidative stress and albuminuria in rats with streptozotocin-induced type 1 diabetes mellitus through cAMP-PKA pathway-mediated inhibition of renal NAD(P)H oxidases.
Section snippets
Ethical approval
The experimental procedures were approved by The Animal Care and Use Committee, Kyushu University.
Experimental animals
Male Wistar rats were purchased from Japan SLC (Shizuoka, Japan) and given standard rat chow and water ad libitum. Diabetes was induced in 7-weeks-old rats by injecting streptozotocin (STZ) (Sigma-Aldrich, St. Louis, MO, USA) in 0.1 mol/L citrate buffer pH 4.5 at a dose of 80 mg/kg body weight. Rats with fasting blood glucose levels > 250 mg/dL were considered diabetic. Rats given injections of
Urinary oxidative stress marker and albumin excretion
Administration of liraglutide (0.3 mg/kg/12 h) was started 1 week after the onset of diabetes. Characteristics of the experimental rats are summarized in Table 1. Liraglutide significantly decreased body weight by day 28 in control rats, but not in diabetic rats. It did not affect the plasma glucose level in either group. Liraglutide also decreased food intake significantly in control rats, but not in diabetic rats. It decreased the systolic blood pressure in diabetic rats slightly but
Discussion
A previous study showed that long-term treatment with GLP-1 analog, exendin-4, ameliorated diabetic nephropathy in db/db mice with type 2 diabetes mellitus [30]. However, the underlying mechanism was not fully understood, because exendin-4 treatment ameliorated various metabolic abnormalities in db/db mice, including body weights, adipose tissue weights, circulating free fatty acid and triglyceride concentrations, and improved insulin sensitivity [30]. Therefore, in the present study, we used
Author contributions
H. Hendarto, T. Inoguchi, R. Takayanagi designed the experiments; H. Hendarto, Y. Maeda, N. Ikeda, J. Zheng, R. Takei, H. Yokomizo, E. Hirata performed and analysed data of experiments; H. Hendarto, T. Inoguchi, Y. Maeda, N. Sonoda interpreted results of experiments; H. Hendarto, T. Inoguchi, Y. Maeda prepared figures and drafted manuscript; H. Hendarto, T. Inoguchi, Y. Maeda, N. Sonoda, R. Takayanagi edited and revised manuscript.
Funding
This work was supported in part by the Special Coordination Funds for Promoting Science and Technology (SCF funding program “Innovation Center for Medical Redox Navigation”).
Conflict of interest
The authors reported no potential conflict of interest.
Acknowledgment
We appreciate the technical support from the Research Support Center, Graduate School of Medical Sciences, Kyushu University.
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