Animal models of pediatric chronic kidney disease. Is adenine intake an appropriate model?

Resveratrol Propionate Ester Supplement Exerts Antihypertensive Effect in Juvenile Rats Exposed to an Adenine Diet via Gut Microbiota Modulation

Resveratrol, acting as a prebiotic, and propionate, functioning as a postbiotic, hold promise for preventing hypertension in chronic kidney disease (CKD). Previously, we employed propionate to enhance the bioavailability of resveratrol through esterification, resulting in the production of a resveratrol propionate ester (RPE) mixture. In this study, we purified 3-O-propanoylresveratrol (RPE2) and 3,4'-di-O-propanoylresveratrol (RPE4) and investigated their protective effects in a juvenile rat adenine-induced CKD model. To this end, male Sprague Dawley rats aged three weeks (n = 40) were divided into five groups: control; CKD (rats fed adenine); CKRSV (CKD rats treated with 50 mg/L resveratrol); CDRPE2 (CKD rats treated with 25 mg/L RPE2); and CKRPE4 (CKD rats treated with 25 mg/L RPE 4). RPE2 and PRE4 similarly exhibited blood pressure-lowering effects comparable to those of resveratrol, along with increased nitric oxide (NO) availability. Furthermore, RPE2 and RPE4 positively influenced plasma short-chain fatty acid (SCFA) levels and induced distinct alterations in the gut microbial composition of adenine-fed juvenile rats. The supplementation of RPE2 and RPE4, by restoring NO, elevating SCFAs, and modulating the gut microbiota, holds potential for ameliorating CKD-induced hypertension.

Is resveratrol really effective in kidney disease?: A different perspective than ever before

BACKGROUND

Chronic kidney disease (CKD) is a global health problem and it is stated that the use of resveratrol supplement contributes to the protection of kidney health. In this study, it was aimed to evaluate the effect of resveratrol supplementation on kidney function, inflammation and histopathological findings in rats with experimental adenine-induced kidney damage.

METHODS

Three different groups of 10 randomly selected rats were formed. The first group was the negative control group, the second group was the uremic control group (KDG), and the third group was the group in which uremia was created and resveratrol was applied (RG). Kidney damage was induced by administration of 200 mg/kg adenine. Resveratrol supplementation was administered at 20 mg/kg after kidney damage. Serum urea, creatinine, indoxyl sulfate (IS), p-cresol, glomerular filtration rate, C-reactive protein (CRP); interleukin (IL)-6 and tumor necrosis factor (TNF)-α gene expression levels and histopathological findings were evaluated.

RESULTS

It was determined that resveratrol supplement applied after the formation of connective tissue in renal failure didn't have an improvement effect on the urine amount, kidney function and inflammatory parameters and histopathological changes (p > 0.05). Just, the increase in the CRP value of KDG (p < 0.05) was not observed in RG.

CONCLUSION

The findings suggest that resveratrol administered after kidney damage with adenine has no effect on kidney disease.

Endogenous adenine mediates kidney injury in diabetic models and predicts diabetic kidney disease in patients

Diabetic kidney disease (DKD) can lead to end-stage kidney disease (ESKD) and mortality; however, few mechanistic biomarkers are available for high-risk patients, especially those without macroalbuminuria. Urine from participants with diabetes from the Chronic Renal Insufficiency Cohort (CRIC) study, the Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in Type 2 Diabetes (SMART2D), and the American Indian Study determined whether urine adenine/creatinine ratio (UAdCR) could be a mechanistic biomarker for ESKD. ESKD and mortality were associated with the highest UAdCR tertile in the CRIC study and SMART2D. ESKD was associated with the highest UAdCR tertile in patients without macroalbuminuria in the CRIC study, SMART2D, and the American Indian study. Empagliflozin lowered UAdCR in nonmacroalbuminuric participants. Spatial metabolomics localized adenine to kidney pathology, and single-cell transcriptomics identified ribonucleoprotein biogenesis as a top pathway in proximal tubules of patients without macroalbuminuria, implicating mTOR. Adenine stimulated matrix in tubular cells via mTOR and stimulated mTOR in mouse kidneys. A specific inhibitor of adenine production was found to reduce kidney hypertrophy and kidney injury in diabetic mice. We propose that endogenous adenine may be a causative factor in DKD.

Functional and histological effects of Anthurium schlechtendalii Kunth extracts on adenine-induced kidney damage of adult Wistar rats

Anthurium schlechtendalii Kunth is used by the Zoque group in southeastern Mexico for kidney and urinary diseases, but its safety and effectiveness are unproven, therefore a model of adenine-induced renal failure in rats was performed. The rats were fed with solid and aqueous plant extracts for 4 weeks to study its effects on kidney histological morphology. Kidneys were examined, and statistical analysis was performed. The adenine-containing diet caused renal failure, characterized by crystal deposits, cystic dilatation of tubules, and micro-abscesses. Both extracts caused tubular damage and collagen increase without inflammation. However, when combined with adenine, the extracts showed some protective effects, although cystic dilatation and granulomatous inflammation were observed. The extracts at the tested doses resulted in glomerular and tubular damage, aggravating cystic degeneration, therefore, its indiscriminate use in Humans is not safe. Additionally, the extracts can serve as a model for studying renal damage without crystal deposits.

Role of endogenous adenine in kidney failure and mortality with diabetes

Diabetic kidney disease (DKD) can lead to end-stage kidney disease (ESKD) and mortality, however, few mechanistic biomarkers are available for high risk patients, especially those without macroalbuminuria. Urine from participants with diabetes from Chronic Renal Insufficiency Cohort (CRIC), Singapore Study of Macro-Angiopathy and Reactivity in Type 2 Diabetes (SMART2D), and the Pima Indian Study determined if urine adenine/creatinine ratio (UAdCR) could be a mechanistic biomarker for ESKD. ESKD and mortality were associated with the highest UAdCR tertile in CRIC (HR 1.57, 1.18, 2.10) and SMART2D (HR 1.77, 1.00, 3.12). ESKD was associated with the highest UAdCR tertile in patients without macroalbuminuria in CRIC (HR 2.36, 1.26, 4.39), SMART2D (HR 2.39, 1.08, 5.29), and Pima Indian study (HR 4.57, CI 1.37-13.34). Empagliflozin lowered UAdCR in non-macroalbuminuric participants. Spatial metabolomics localized adenine to kidney pathology and transcriptomics identified ribonucleoprotein biogenesis as a top pathway in proximal tubules of patients without macroalbuminuria, implicating mammalian target of rapamycin (mTOR). Adenine stimulated matrix in tubular cells via mTOR and stimulated mTOR in mouse kidneys. A specific inhibitor of adenine production was found to reduce kidney hypertrophy and kidney injury in diabetic mice. We propose that endogenous adenine may be a causative factor in DKD.

Upacicalcet, a positive allosteric modulator of the calcium-sensing receptor, prevents vascular calcification and bone disorder in a rat adenine-induced secondary hyperparathyroidism model

Secondary hyperparathyroidism (SHPT) is a major comorbidity of chronic kidney disease (CKD). Chronic elevation of PTH levels is associated with cortical bone deterioration and increase in the risk of fractures in CKD patients. Here, we evaluated the effect of repeated administration of upacicalcet, a novel positive allosteric modulator of the calcium-sensing receptor, in a rat model of adenine-induced renal failure, by determining serum levels of intact PTH (iPTH), calcium, phosphorus, creatinine, and urea nitrogen. Furthermore, parathyroid hyperplasia (parathyroid gland weight and Ki-67-positive cell density), ectopic calcification (calcium content in the thoracic aorta, kidney and heart and positive von Kossa staining in the thoracic aorta), and bone morphometry parameters (cortical porosity and fibrosis volume) were evaluated. Rats treated with either 0.2 mg/kg or 1 mg/kg upacicalcet exhibited significantly lower serum iPTH levels than CKD-control rats, as early as 7 days after the first dose. Repeated administration of upacicalcet reduced serum iPTH levels and inhibited parathyroid hyperplasia in rats with adenine-induced severe renal failure. Moreover, it suppressed ectopic calcification and cortical pore formation. In contrast, serum calcium and phosphorus levels were not significantly affected, suggesting a low risk of hypocalcemia, which often occurs with SHPT treatment. In conclusion, repeated administration of upacicalcet decreased serum iPTH levels and suppressed parathyroid hyperplasia in the adenine-induced CKD rat model of SHPT. Furthermore, ectopic calcification and cortical pore formation were suppressed without significant changes in blood mineral parameters. Upacicalcet safely inhibited the progression of SHPT in an adenine-induced CKD rat model.

Dietary Resveratrol Butyrate Monoester Supplement Improves Hypertension and Kidney Dysfunction in a Young Rat Chronic Kidney Disease Model

Chronic kidney disease (CKD) remains a public health problem. Certain dietary supplements can assist in the prevention of CKD progression. In this regard, resveratrol is a polyphenol and has a potential therapeutic role in alleviating CKD. We previously utilized butyrate in order to improve the bioavailability of resveratrol via esterification and generated a resveratrol butyrate monoester (RBM). In this study, the hypothesis that RBM supplementation is able to protect against kidney dysfunction and hypertension was tested by using an adenine-induced CKD model. For this purpose, three-week-old male Sprague Dawley rats (n = 40) were equally categorized into: group 1-CN (sham control); group 2-CKD (adenine-fed rats); group 3-REV (CKD rats treated with 50 mg/L resveratrol); group 4-MEL (CKD rats treated with 25 mg/L RBM); and group 5-MEH (CKD rats treated with 50 mg/L RBM). At the end of a 12-week period, the rats were then euthanized. The adenine-fed rats displayed hypertension and kidney dysfunction, which were attenuated by dietary supplementation with RBM. The CKD-induced hypertension coincided with: decreased nitric oxide (NO) bioavailability; augmented renal protein expression of a (pro)renin receptor and angiotensin II type 1 receptor; and increased oxidative stress damage. Additionally, RBM and resveratrol supplementation shaped distinct gut microbiota profiles in the adenine-treated CKD rats. The positive effect of high-dose RBM was shown together with an increased abundance of the genera Duncaniella, Ligilactobacillus, and Monoglobus, as well as a decrease in Eubacterium and Schaedierella. Importantly, the mechanism of action of the RBM supplementation may be related to the restoration of NO, rebalancing of the RAS, a reduction in oxidative stress, and alterations to the gut microbiota. Moreover, RBM supplementation shows promise for the purposes of improving CKD outcomes and hypertension. As such, further translation to human studies is warranted.

Treatment of Chronic Kidney Disease with Extracellular Vesicles from Mesenchymal Stem Cells and CD133+ Expanded Cells: A Comparative Preclinical Analysis

Chronic kidney disease (CKD) is characterized by structural abnormalities and the progressive loss of kidney function. Extracellular vesicles (EVs) from human umbilical cord tissue (hUCT)-derived mesenchymal stem cells (MSCs) and expanded human umbilical cord blood (hUCB)-derived CD133⁺ cells (eCD133⁺) maintain the characteristics of the parent cells, providing a new form of cell-free treatment. We evaluated the effects of EVs from hUCT-derived MSCs and hUCB-derived CD133⁺ cells on rats with CDK induced by an adenine-enriched diet. EVs were isolated by ultracentrifugation and characterized by nanoparticle tracking analysis (NTA) and electron microscopy. The animals were randomized and divided into the MSC-EV group, eEPC-EV group and control group. Infusions occurred on the seventh and 14th days after CKD induction. Evaluations of kidney function were carried out by biochemical and histological analyses. Intense labeling of the α-SMA protein was observed when comparing the control with MSC-EVs. In both groups treated with EVs, a significant increase in serum albumin was observed, and the increase in cystatin C was inhibited. The results indicated improvements in renal function in CKD, demonstrating the therapeutic potential of EVs derived from MSCs and eCD133⁺ cells and suggesting the possibility that in the future, more than one type of EV will be used concurrently.

Resveratrol Butyrate Ester Protects Adenine-Treated Rats against Hypertension and Kidney Disease by Regulating the Gut–Kidney Axis

Despite recent advances in pharma-nutritional management, chronic kidney disease (CKD) remains an increasingly prevalent disorder. Resveratrol, a pleiotropic phytochemical, has been found to reduce the risk for several chronic diseases. Considering the low bioavailability of resveratrol, we recently synthesized resveratrol butyrate ester (RBE) via the esterification of resveratrol with butyrate. The aim of this study was to examine the effectiveness of RBE as regards protection from hypertension and kidney damage and explore the underlying mechanisms using a young rat adenine-induced CKD model. Three-week-old male Sprague Dawley rats received regular or 0.5% adenine chow for three weeks. Three groups of adenine-fed CKD rats (N = 8/group) received resveratrol (50 mg/L), or a low dose (25 mg/L) or high dose (50 mg/L) of RBE in drinking water from week 6 to week 12. As compared with the controls, adenine-treated rats had markedly increased creatinine levels and blood pressure, which was associated with renal hypertrophy and decreased creatinine clearance. Treatment with resveratrol or a low or high dose of RBE, similarly protected adenine-fed rats against hypertension and kidney damage. CKD-induced hypertension is associated with an altered gut microbiota profile, dysregulated renal short chain fatty acid (SCFA) receptor expression, activation of the aryl hydrocarbon receptor (AhR) signaling pathway, and reduced nitric oxide bioavailability. We found gut microbiota compositions were shaped differentially by resveratrol and RBE treatment in adenine-treated CKD rats. The beneficial effect of high-dose RBE was associated with reduced renal expression of SCFA G protein-coupled receptor 41 (GPR41) and olfactory receptor 78 (Olfr78), antagonizing the AhR signaling pathway, and increased abundance of beneficial bacteria such as genera Akkermansia, Blautia, and Enterococcus. Our study provided the first evidence documenting RBE as a novel phytochemical supplement targeting the gut–kidney axis to protect against adenine-induced kidney damage and hypertension.

Melatonin Prevents Chronic Kidney Disease-Induced Hypertension in Young Rat Treated with Adenine: Implications of Gut Microbiota-Derived Metabolites

Melatonin, a signaling hormone with pleiotropic biofunctions, has shown health benefits. Trimethylamine-N-oxide (TMAO) and asymmetric dimethylarginine (ADMA) are uremic toxins involved in the development of hypertension. TMAO originates from trimethylamine (TMA), a gut microbial product. ADMA is an endogenous nitric oxide (NO) synthase inhibitor. We examined whether melatonin therapy could prevent hypertension and kidney disease by mediating gut microbiota-derived metabolites and the NO pathway using an adenine-induced chronic kidney disease (CKD) young rat model. Six-week-old young Sprague Dawley rats of both sexes were fed a regular diet (C group), a diet supplemented with 0.5% adenine (CKD group), or adenine plus 0.01% melatonin in their drinking water (CKD + M group) for three weeks (N = 8/group). Adenine-fed rats developed renal dysfunction, hypertension, renal hypertrophy and increased uremic toxin levels of TMAO and ADMA. Melatonin therapy prevented hypertension in both sexes and attenuated kidney injury in males. Melatonin reversed the changes to the plasma TMAO-to-TMA ratio induced by CKD in both sexes. Besides, the protective effects of melatonin were associated with restoration of gut microbiota alterations, including increased α-diversity, and enhancement of the abundance of the phylum Proteobacteria and the genus Roseburia in male rats. Melatonin therapy also partially prevented the increases in ADMA in male CKD rats. Melatonin sex-specifically protected young rats against hypertension and kidney injury induced by CKD. The results of this study contribute toward a greater understanding of the interaction between melatonin, gut microbiota-derived metabolites, and the NO pathway that is behind CKD, which will help to prevent CKD-related disorders in children.

Erlotinib can halt adenine induced nephrotoxicity in mice through modulating ERK1/2, STAT3, p53 and apoptotic pathways

Renal fibrosis is a failed regenerative process that facilitates chronic kidney disease progression. The current study was designed to study the effect of erlotinib, a receptor tyrosine kinase inhibitor, on the progression of renal fibrosis. The study included four groups of mice: control group; adenine group: received adenine (0.2% w/w) daily with food for 4 weeks; erlotinib group: received 80 mg/kg/day erlotinib orally (6 ml/kg/day, 1.3% w/v suspension in normal saline 0.9%) for 4 weeks; adenine + erlotinib group: received adenine and erlotinib concurrently. Kidney function and antioxidant biomarkers were measured. Renal expression of Bcl2 and p53 and histopathological changes (tubular injury and renal fibrosis) were scored. Renal tissue levels of transforming growth factor-β₁, p-ERK1/2 and p-STAT3 were measured. Results obtained showed significant decrease (P < 0.001) in serum creatinine, urea and uric acid in erlotinib + adenine group. Level of malondialdehyde was decreased significantly (P < 0.001) while reduced glutathione and catalase levels were increased (P < 0.01) by erlotinib concurrent administration. Erlotinib markedly reduced fibrosis and tubular injury and decreased TGF-β1, p-ERK1/2 and p-STAT3 (P < 0.5). In addition, expression level of Bcl-2 was elevated (P < 0.001) while that of p53-was reduced compared to adenine alone. Erlotinib can attenuate renal fibrosis development and progression through anti-fibrotic, antioxidant and anti-apoptotic pathways.

Innovative Three-Dimensional Microscopic Analysis of Uremic Growth Plate Discloses Alterations in the Process of Chondrocyte Hypertrophy: Effects of Growth Hormone Treatment

Chronic kidney disease (CKD) alters the morphology and function of the growth plate (GP) of long bones by disturbing chondrocyte maturation. GP chondrocytes were analyzed in growth-retarded young rats with CKD induced by adenine intake (AD), control rats fed ad libitum (C) or pair-fed with the AD group (PF), and CKD rats treated with growth hormone (ADGH). In order to study the alterations in the process of GP maturation, we applied a procedure recently described by our group to obtain high-quality three-dimensional images of whole chondrocytes that can be used to analyze quantitative parameters like cytoplasm density, cell volume, and shape. The final chondrocyte volume was found to be decreased in AD rats, but GH treatment was able to normalize it. The pattern of variation in the cell cytoplasm density suggests that uremia could be causing a delay to the beginning of the chondrocyte hypertrophy process. Growth hormone treatment appears to be able to compensate for this disturbance by triggering an early chondrocyte enlargement that may be mediated by Nkcc1 action, an important membrane cotransporter in the GP chondrocyte enlargement.

Growth plate alterations in chronic kidney disease

Growth retardation is a major feature of chronic kidney disease (CKD) of onset in infants or children and is associated with increased morbidity and mortality. Several factors have been shown to play a causal role in the growth impairment of CKD. All these factors interfere with growth by disturbing the normal physiology of the growth plate of long bones. To facilitate the understanding of the pathogenesis of growth impairment in CKD, this review discusses cellular and molecular alterations of the growth plate during uremia, including structural and dynamic changes of chondrocytes, alterations in their process of maturation and hypertrophy, and disturbances in the growth hormone signaling pathway.

A Novel Model of Chronic Kidney Disease in Rats: Dietary Adenine in Combination with Unilateral Nephrectomy

Background

Adenine at 0.75% in the diet (AD) triggers renal impairment in rats. This model of kidney disease is largely reversible when AD feeding is stopped. Testing of novel drugs parallel to AD administration may result in unwanted interference.

Objectives

We hypothesized that combining AD with unilateral nephrectomy (UNx) would result in progressive chronic kidney disease (CKD) even after cessation of AD.

Methods

In an explorative study, 16 rats with UNx (AD-1K rats) and 10 sham-operated rats (AD-2K rats) received AD-supplemented feed for 3 weeks, followed by 4 weeks of standard chow. Ten sham-operated rats receiving only standard chow served as controls. Laboratory parameters in blood and urine were frequently assessed during and after cessation of AD feeding. Comprehensive pathological examinations were performed in all rats at the end of the experiment.

Results

Rats with UNx were more affected by impaired glomerular filtration rate, anemia, hyperphosphatemia, and hypocalcemia. After cessation of AD feeding, recovery was poorest in AD-1K rats, paralleled by increased proteinuria indicative of progressive CKD. Scores in histopathological damage of the kidneys indicative of CKD were seen in both AD-fed groups, with key parameters being more affected in AD-1K rats. Histopathological changes in the heart were most prominent in AD-1K rats.

Conclusions

Combining AD feeding with UNx provides a time window after cessation of AD feeding for the testing of drugs without interference. Our findings in rats may have implications for research in other target animal species as well.

Metabolomic Signatures of Chronic Kidney Disease of Diverse Etiologies in the Rats and Humans

Chronic kidney disease (CKD) has emerged as a major public health problem worldwide. It frequently progresses to end-stage renal disease, which is related to very high cost and mortality. Novel biomarkers can provide insight into the novel mechanism, facilitate early detection, and monitor progression of CKD and its response to therapeutic interventions. To identify potential biomarkers, we applied an UPLC-HDMS together with univariate and multivariate statistical analyses using plasma samples from patients with CKD of diverse etiologies (100 sera in discovery set and 120 sera in validation set) and two different rat models of CKD. Using comprehensive screening and validation workflow, we identified a panel of seven metabolites that were shared by all patients and animals regardless of the underlying cause of CKD. These included ricinoleic acid, stearic acid, cytosine, LPA(16:0), LPA(18:2), 3-methylhistidine, and argininic acid. The combination of these seven biomarkers enabled the discrimination of patients with CKD from healthy subjects with a sensitivity of 83.3% and a specificity of 96.7%. In addition, these biomarkers accurately reflected improvements in renal function in response to the therapeutic interventions. Our results indicated that the identified biomarkers may improve the diagnosis of CKD and provide a novel tool for monitoring of the progression of disease and response to treatment in CKD patients.