Ginsenoside Rg1 ameliorates glomerular fibrosis during kidney aging by inhibiting NOX4 and NLRP3 inflammasome activation in SAMP8 mice

https://doi.org/10.1016/j.intimp.2020.106339Get rights and content

Highlights

  • NOX4 and NLRP3 inflammasome activation play an important role in aging-related renal fibrosis in SAMP8 mice.

  • Rg1 treatment significantly decreased ROS accumulation and NOX4 expression in renal cortex in SAMP8 mice.

  • Rg1 treatment significantly inhibited NLRP3 inflammasome expression in renal cortex in SAMP8 mice.

  • Rg1 treatment may be a potential strategy for delaying the kidney aging.

Abstract

Aging is closely related to the progress of renal fibrosis, which eventually results in renal dysfunction. Ginsenoside Rg1 (Rg1) has been reported to have an extensive anti-aging effect. However, the role and mechanism of Rg1 in aging-related renal fibrosis remain unclear. The present study aimed to evaluate the protective effect and mechanism of Rg1 in renal fibrosis during kidney aging in a model of SAMP8 mice. Taking SAMR1 mice as the control group, SAMP8 mice were administered Apocynin (50 mg/kg), Tempol (50 mg/kg), or Rg1 (5, 10 mg/kg) intragastrically for 9 weeks as treatment groups. The results showed that the elevated levels of blood urea nitrogen, serum creatinine and senescence-associated β-galactosidase (β-Gal) were markedly decreased, the glomerular mesangial proliferation was significantly alleviated and the increased levels of collagen IV and TGF-β1 were significantly downregulated by Rg1 in SAMP8 mice. In addition, the generation of ROS and the expression of NADHP oxidase 4 (NOX4) in the renal cortex were significantly reduced by Rg1 treatment. The expression levels of NLRP3 inflammasome-related proteins and the inflammation-related cytokine IL-1β were also inhibited by Rg1 treatment in the SAMP8 mice. These results suggested that Rg1 could delay kidney aging and inhibit aging-related glomerular fibrosis by reducing NOX4-derived ROS generation and downregulating NLRP3 inflammasome expression.

Introduction

Due to advances in modern medicine, life expectancy is increasing, which leads to an obvious increase in the population of older people. Aging can lead to significant alterations in structure and function in many organs; among them, the kidney is particularly susceptible to aging [1]. Many abnormalities of renal structure and function have been reported to be accompanied by aging, including increase of the mesangial matrix, thickening of the basement membrane, glomerular fibrosis and tubulointerstitial fibrosis [2]. Aberrant fibrogenesis impairs the homeostasis of architecture and function in the kidneys and may contribute to many end-stage renal diseases [3], which eventually results in renal failure and is harmful to health. Accordingly, it is highly important to study kidney aging and related mechanisms for the prevention of aging-related glomerular fibrosis.

The pathogenesis of aging is complicated. Overproduction of reactive oxygen species (ROS)-related oxidative stress is a main characteristic of aging. Numerous studies have shown that oxidative stress is closely associated with many age-related diseases, such as cancer [4], [5], respiratory diseases [6], skeletal muscle abnormalities [7] and chronic kidney disease [8], [9], [10]. Oxidative stress occurs when the oxidant/antioxidant balance is disrupted and excessive ROS synthesis occurs, leading to an oxidative status [11], which usually induces harmful effects, such as oxidative modification of proteins and nucleic acids and lipid peroxidation in cells [12]. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), which consists of a membrane subunit (NOX1, 2, 3, 4, or 5) and catalytic subunits of p22phox, p47phox, p67phox [13], is one of the main sources of ROS generation in many organs [14]. Studies have found that NOX4 localizes in glomerular mesangial cells, renal tubules, renal fibroblasts and podocytes and is closely involved in renal oxidative stress in kidney diseases, such as diabetic nephropathy and renal carcinoma [10], [15]. Based on the above data, we speculated that NOX4-derived ROS oxidative stress may play important roles in the development of glomerular fibrosis during kidney aging.

Inflammation is another major cause for cell aging and contributes to human diseases. Inflammation plays important roles in both mortality and morbidity in aging individuals, and almost all aging-related diseases share an inflammatory pathogenesis [16], which may also play an important role in aging-related renal damage. Inflammasomes, which have a central role in the inflammatory response, can usually be activated by diverse irritants and initiate inflammatory responses via activation of caspase-1, eventually resulting in the generation of pro-inflammatory factors [17]. Inflammasome complexes are composed of a cytosolic pattern-recognition receptor of caspase-1 and an adapter protein of apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), which enables interactions between the components. As the cytosolic receptors, proteins of the NOD-like (nucleotide-binding oligomerization domain) receptor (NLR) family are the major sensor proteins to form inflammasomes [18]. The NLRP3 inflammasome, due to its crucial roles in sterile and infection-triggered inflammation [18], [19], has been reported to play important roles in the evolution of renal fibrosis and contributes to the pathogenesis of acute kidney injury, chronic kidney disease and diabetic kidney disease [20], [21]. It has been reported that excessive ROS is a key signaling molecule in the progression of inflammatory disorders and plays an important role during the process of aging [22], leading to chronic inflammation [23]. In the present study, we hypothesized that NOX4 and NLRP3 inflammasome activation may induce glomerular fibrosis in the kidney with aging.

At present, there are few medicines and methods that are effective in delaying kidney aging. Ginseng has been used for more than 2000 years and is believed to be a panacea to promote longevity. There are many active components in ginseng, and numerous studies have reported that ginseng does have many beneficial effects [24], [25]. Ginsenoside Rg1 (Rg1) is the major active extract in ginseng, with anti-aging, rejuvenating, immune-potentiating and antioxidant activities [25], [26]. Currently, many studies have reported the protective effects of Rg1; for example, Rg1 can obviously suppress renal interstitial fibrosis in unilateral ureteral obstruction (UUO) rats [27] and can improve inflammation and cardiac oxidative stress in streptozotocin-induced diabetic rats [28]. However, few studies have demonstrated the protective effects of Rg1 on aging-related glomerular fibrosis by inhibiting NOX4 and NLRP3 inflammasome activation during kidney aging. In the current study, we hypothesized that Rg1 ameliorates renal fibrosis by inhibiting the activation of NOX4 and NLRP3 inflammasomes in SAMP8 mice. Additionally, because tempol can promote the metabolism of many ROS, it is often used as an ROS scavenger. Apocynin can attenuate the activity of NADPH oxidase by interfering with the intracellular translocation of p47phox and p67phox and is often used as an NOX inhibitor [29]. In this study, we observed the effects of tempol, apocynin and Rg1 on aging-related glomerular fibrosis in old SAMP8 mice and detected the activation of NOX4 and NLRP3 inflammasomes in the renal cortex during aging.

Section snippets

Animals and treatment

Six-month-old male senescence-accelerated resistant mouse 1 (SAMR1) mice and male senescence-accelerated mouse prone 8 strain (SAMP8) mice (30–40 g) were provided by the Department of Laboratory Animal Science, Peking University Health Science Center. Animals were housed in an environment free from specific pathogens under the condition of 22 ± 2℃ and a 12:12 h light/dark cycle with ample food and water. The animals were divided randomly into six groups (n = 9): (1) SAMR1 control group; (2)

Effect of Rg1 treatment on renal function parameters in serum from SAMP8 mice

To investigate the protective effect of Rg1 on aging-related renal damage, biochemical parameters, including BUN and Scr, were observed in this study. After 9 weeks of drug treatment, the serum BUN and Scr levels in the SAMP8 model group were significantly higher than those in the SAMR1 control group (P < 0.01; Fig. 1A & B). Treatment with Rg1 (5, 10 mg/kg), tempol and apocynin resulted in remarkable reductions in these indexes compared with the SAMP8 group, especially in the Rg1

Discussion

Aging is the most important risk factor in many common human diseases. It has been reported that approximately half of human deaths are ascribed to chronic aging-related diseases, such as heart disease, Alzheimer’s disease (AD), cancer and chronic kidney disease (CKD) [34]. CKD has become an increasing problem across the world because it can lead to end-stage renal disease (ESRD) due to renal fibrosis, which is the principal pathological process that underlies CKD progression and ultimately

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was supported by the National Natural Science Foundation of China (81970630, 81671384). We would like to thank Zhirui Fang in the Department of Pharmacology and Bao Li and Dake Huang in the Synthetic Laboratory of Basic Medicine College for their technical assistance.

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