The SSLepR mutant rat represents a novel model to study obesity-induced renal injury before puberty

Does Sex Matter in Obesity-Induced Periodontal Inflammation in the SSLepR Mutant Rats?

Introduction: The incidence of obesity has dramatically increased worldwide. Obesity has been shown to exacerbate the progression of periodontal disease. Studies suggest a sex difference in periodontitis, whereby males are more sensitive to periodontal inflammation compared to females. Aim: In the current study, it was hypothesized that obesity drives periodontal inflammation and bone loss in both sexes. Methodology: Utilizing leptin receptor mutant (SSLepR mutant) rats as a genetic model of obesity, 11-12-week-old male and female lean Dahl salt-sensitive (SS) rats and obese SSLepR mutant rats were used to investigate sex differences in obesity-induced periodontal inflammation. Results: Body weight, insulin, hemoglobin A1c and cholesterol levels were significantly elevated in the obese SSLepR mutant strain vs. the lean SS strain within the same sex. Sex differences in body weight and plasma hemoglobin A1c were only observed in obese SSLepR mutant rats, with males having significantly greater body weight and hemoglobin A1c vs. females. Plasma thiobarbituric acid reactive substances (TBARs) and monocyte chemoattractant protein-1 (MCP-1), markers of systemic oxidative stress and inflammation, respectively, were significantly elevated in obese SSLepR mutant rats vs. lean SS rats, with no sex differences in these parameters in either rat strains. Although micro-CT analyses of the maxillary first molar alveolar bone from obese SSLepR mutant rats revealed no evidence of bone loss and/or sex differences, immuno-histochemical analysis revealed significant elevations in periodontal IL-6 and decreases in IL-10 in obese SSLepR mutant rats vs. lean SS rats, with no apparent sex differences in these parameters. Conclusions: Obesity increases systemic and periodontal inflammation, without evidence of bone loss or apparent sex differences in SSLepR mutant rats.

Abatacept Decreases Renal T-cell Infiltration and Renal Inflammation and Ameliorates Progressive Renal Injury in Obese Dahl Salt-sensitive Rats Before Puberty

ABSTRACT

Prepubertal obesity is growing at an alarming rate and is now considered a risk factor for renal injury. Recently, we reported that the early development of renal injury in obese Dahl salt-sensitive (SS) leptin receptor mutant (SS LepR mutant) rats was associated with increased T-cell infiltration and activation before puberty. Therefore, the current study investigated the effect of inhibiting T-cell activation with abatacept on the progression of renal injury in young obese SS LepR mutant rats before puberty. Four-week-old SS and SS LepR mutant rats were treated with IgG or abatacept (1 mg/kg; ip, every other day) for 4 weeks. Abatacept reduced the renal infiltration of T cells by almost 50% in SS LepR mutant rats. Treatment with abatacept decreased the renal expression of macrophage inflammatory protein-3 alpha while increasing IL-4 in SS LepR mutant rats without affecting SS rats. While not having an impact on blood glucose levels, abatacept reduced hyperinsulinemia and plasma triglycerides in SS LepR mutant rats without affecting SS rats. We did not observe any differences in the mean arterial pressure among the groups. Proteinuria was markedly higher in SS LepR mutant rats than in SS rats throughout the study, and treatment with abatacept decreased proteinuria by about 40% in SS LepR mutant rats without affecting SS rats. We observed significant increases in glomerular and tubular injury and renal fibrosis in SS LepR mutant rats versus SS rats, and chronic treatment with abatacept significantly reduced these renal abnormalities in SS LepR mutant rats. These data suggest that renal T-cell activation contributes to the early progression of renal injury associated with prepubertal obesity.

Metformin reduces insulin resistance and attenuates progressive renal injury in prepubertal obese Dahl salt-sensitive rats

Prepubertal obesity is currently an epidemic and is considered as a major risk factor for renal injury. Previous studies have demonstrated that insulin resistance contributes to renal injury in obesity, independent of diabetes. However, studies examining the relationship between insulin resistance and renal injury in obese children are lacking. Recently, we reported that progressive renal injury in Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) rats was associated with insulin resistance before puberty. Therefore, the aim of the present study was to examine whether decreasing insulin resistance with metformin will reduce renal injury in SSLepRmutant rats. Four-wk-old SS and SSLepRmutant rats were separated into the following two groups: 1) vehicle and 2) metformin (300 mg/kg/day) via chow diet for 4 wk. Chronic administration of metformin markedly reduced insulin resistance and dyslipidemia in SSLepRmutant rats. We did not detect any differences in mean arterial pressure between vehicle and metformin-treated SS and SSLepRmutant rats. Proteinuria was significantly greater in SSLepRmutant rats versus SS rats throughout the study, and metformin administration significantly reduced proteinuria in SSLepRmutant rats. At the end of the protocol, metformin prevented the renal hyperfiltration observed in SSLepRmutant rats versus SS rats. Glomerular and tubular injury and renal inflammation and fibrosis were significantly higher in vehicle-treated SSLepRmutant rats versus SS rats, and metformin reduced these parameters in SSLepRmutant rats. These data suggest that reducing insulin resistance with metformin prevents renal hyperfiltration and progressive renal injury in SSLepRmutant rats before puberty and may be therapeutically useful in managing renal injury during prepubertal obesity.NEW & NOTEWORTHY Childhood/prepubertal obesity is a public health concern that is associated with early signs of proteinuria. Insulin resistance has been described in obese children. However, studies investigating the role of insulin resistance during childhood obesity-associated renal injury are limited. This study provides evidence of an early relationship between insulin resistance and renal injury in a rat model of prepubertal obesity. These data also suggest that reducing insulin resistance with metformin may be renoprotective in obese children.

Chronic treatment with IL-25 increases renal M2 macrophages and reduces renal injury in obese Dahl salt-sensitive rats during the prepubescent stage

Recently, we have reported that the early progression of proteinuria in the obese Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) strain was associated with increased renal macrophage infiltration before puberty. Macrophages can be divided into two distinct phenotypes: M1 (proinflammatory) and M2 (anti-inflammatory). Moreover, previous studies have demonstrated that interleukin (IL)-25 converts resting macrophages and M1 into M2. Therefore, the present study examined whether treatment with IL-25 would reduce the early progression of renal injury in SSLepRmutant rats by increasing renal M2. We also investigated the impact of IL-25 on M2 subtypes: M2a (wound healing/anti-inflammatory), M2b (immune mediated/proinflammatory), M2c (regulatory/anti-inflammatory), and M2d (tumor associated/proangiogenic). Four-wk-old SS and SSLepRmutant rats were treated with either control (IgG) or IL-25 (1 µg/day ip every other day) for 4 wk. The kidneys from SSLepRmutant rats displayed progressive proteinuria and renal histopathology versus SS rats. IL-25 treatment had no effect on these parameters in SS rats. However, in the SSLepRmutant strain, proteinuria was markedly reduced after IL-25 treatment. Chronic treatment with IL-25 significantly decreased glomerular and tubular injury and renal fibrosis in the SSLepRmutant strain. Although the administration of IL-25 did not change total renal macrophage infiltration in both SS and SSLepRmutant rats, IL-25 increased M2a by >50% and reduced M1 by 60% in the kidneys of SSLepRmutant rats. Overall, these data indicate that IL-25 reduces the early progression of renal injury in SSLepRmutant rats by inducing M2a and suppressing M1 and suggest that IL-25 may be a therapeutic target for renal disease associated with obesity. NEW & NOTEWORTHY For the past few decades, immune cells and inflammatory cytokines have been demonstrated to play an important role in the development of renal disease. The present study provides strong evidence that interleukin-25 slows the early progression of renal injury in obese Dahl salt-sensitive rats before puberty by increasing systemic anti-inflammatory cytokines and renal M2a macrophages.

Neutralizing MIP3α Reduces Renal Immune Cell Infiltration and Progressive Renal Injury in Young Obese Dahl Salt-Sensitive Rats

Recently, we reported that the early progression of renal injury in obese Dahl salt-sensitive leptin receptor mutant (SSLepRmutant) rats was associated with increased macrophage inflammatory protein 3-α (MIP3α) expression prior to puberty. Therefore, this study tested the hypothesis that MIP3α plays a role in recruiting immune cells, thereby triggering renal inflammation and early progressive renal injury in SSLepRmutant rats prior to puberty. Four-week-old Dahl salt-sensitive (SS) and SSLepRmutant rats either served as control (IgG; intraperitoneal, every other day) or received MIP3α-neutralizing antibody (MNA; 100 µg/kg) for 4 weeks. MNA reduced circulating and renal MIP3α levels and proinflammatory immune cells by 50%. Although MNA treatment did not affect blood glucose and plasma cholesterol levels, MNA markedly decreased insulin resistance and triglyceride levels in SSLepRmutant rats. We observed no differences in mean arterial pressure (MAP) between SS and SSLepRmutant rats, and MNA had no effect on MAP in either strain. Proteinuria was significantly increased in SSLepRmutant rats versus SS rats over the course of the study. Treatment with MNA markedly decreased proteinuria in SSLepRmutant rats while not affecting SS rats. Also, MNA decreased glomerular and tubular injury and renal fibrosis in SSLepRmutant rats while not affecting SS rats. Overall, these data indicate that MIP3α plays an important role in renal inflammation during the early progression of renal injury in obese SSLepRmutant rats prior to puberty. These data also suggest that MIP3α may be a novel therapeutic target to inhibit insulin resistance and prevent progressive proteinuria in obese children. SIGNIFICANCE STATEMENT: Childhood obesity is increasing at an alarming rate and is now being associated with renal disease. Although most studies have focused on the mechanisms of renal injury associated with adult obesity, few studies have examined the mechanisms of renal injury involved during childhood obesity. In the current study, we observed that the progression of renal injury in obese Dahl salt-sensitive leptin receptor mutant rats was associated with an increase in MIP3α, a chemokine, before puberty, and inhibition of MIP3α markedly reduced renal injury.

Differentially Expressed Genes Analysis in the Human Small Airway Epithelium of Healthy Smokers Shows Potential Risks of Disease Caused by Oxidative Stress and Inflammation and the Potentiality of Astaxanthin as an Anti-Inflammatory Agent

Cigarette smoke (CS) was known for its effect of increasing oxidative stress that could trigger tissue injury and endothelial dysfunction mediated by free radicals and reactive oxygen species (ROS). ROS itself is a key signaling molecule that plays a role in the development of inflammatory disorders. Nuclear factor erythroid2 related factor2 (Nrf2) is the main regulator of antioxidant cellular response to cell and tissue-destroying components caused by CS. Nrf2 protein that is significantly activated in the smokers' small airway epithelium is followed by a series of gene expression changes in the same cells. This study aims to observe differentially expressed genes (DEGs) in the human small airway epithelium of smokers compared to genes whose expression changes due to astaxanthin (AST) treatment, an antioxidant compound that can modulate Nrf2. Gene expression data that was stored in the GEO browser (GSE 11952) was analyzed using GEO2R to search for DEG among smokers and nonsmokers subject. DEG was further compared to those genes whose expression changes due to astaxanthin treatment (AST) that were obtained from the Comparative Toxicogenomics Database (CTD; https://ctdbase.org/). DEG (p < 0.05) analysis result shows that there are 23 genes whose expression regulation is reversed compared to gene expression due to AST treatment. The gene function annotations of the 23 DEGs showed the involvement of some of these genes in chemical and oxidative stress, reactive oxygen species (ROS), and apoptotic signaling pathways. All of the genes were involved/associated with chronic bronchitis, adenocarcinoma of the lung, non-small-cell lung carcinoma, carcinoma, small cell lung carcinoma, type 2 diabetes mellitus, emphysema, ischemic stroke, lung diseases, and inflammation. Thus, AST treatment for smokers could potentially decrease the development of ROS and oxidative stress that leads to inflammation and health risks associated with smoking.