Animal Models of Diabetes-Associated Renal Injury

Melatonin at repeated doses alleviates hyperglycemia-exacerbated cerebral ischemia-reperfusion injury at 72 h via anti-inflammation and anti-apoptosis

Objective

We aimed to investigate how hyperglycemia would exacerbate cerebral ischemia-reperfusion injury (CIRI) in a rat model of type 1 diabetes mellitus (T1DM) and explore the beneficial effects of multiple doses of melatonin in T1DM induced CIRI.

Method

The T1DM rat model was induced with streptozocin, and melatonin (10 mg/kg) was injected at 0.5 h before ischemia as well as at 24 and 48 h after reperfusion.

Results

When compared to normoglycemic (NG) rats, T1DM rats had hyperglycemia with weight loss before CIRI. Despite comparable degrees of ischemia and initial reperfusion, T1DM rats tended to have greater weight loss and had worse neurological deficits and larger infarct volume than NG rats up to 72 h after CIRI. Persistent activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway but not of apoptosis or calpains was a crucial factor in T1DM-mediated exacerbation of CIRI at 72 h. Despite lacking effects on baseline hyperglycemia, ischemia and initial reperfusion, melatonin at multiple doses lessened post-CIRI weight loss, neurological deficits and infarct volume in T1DM rats at 72 h. when compared to vehicle-treated T1DM rats with CIRI. Beneficial effects of melatonin treatment included decreased activation of NF-κB pathway, apoptosis and calpains, leading to reduced expression of inducible nitric oxide synthase and enhanced neuronal density.

Conclusion

Melatonin at multiple doses can alleviate T1DM-mediated exacerbation of CIRI at 72 h through anti-inflammation and anti-apoptosis.

GRP78 Contributes to the Beneficial Effects of SGLT2 Inhibitor on Proximal Tubular Cells in DKD

The beneficial effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on kidney function are well-known; however, their molecular mechanisms are not fully understood. We focused on 78-kDa glucose-regulated protein (GRP78) and its interaction with SGLT2 and integrin-β1 beyond the chaperone property of GRP78. In streptozotocin (STZ)-induced diabetic mouse kidneys, GRP78, SGLT2, and integrin-β1 increased in the plasma membrane fraction, while they were suppressed by canagliflozin. The altered subcellular localization of GRP78/integrin-β1 in STZ mice promoted epithelial mesenchymal transition (EMT) and fibrosis, which were mitigated by canagliflozin. High-glucose conditions reduced intracellular GRP78, increased its secretion, and caused EMT-like changes in cultured HK2 cells, which were again inhibited by canagliflozin. Urinary GRP78 increased in STZ mice, and in vitro experiments with recombinant GRP78 suggested that inflammation spread to surrounding tubular cells and that canagliflozin reversed this effect. Under normal glucose culture, canagliflozin maintained sarco/endoplasmic reticulum (ER) Ca2+-ATPase (SERCA) activity, promoted ER robustness, reduced ER stress response impairment, and protected proximal tubular cells. In conclusion, canagliflozin restored subcellular localization of GRP78, SGLT2, and integrin-β1 and inhibited EMT and fibrosis in DKD. In nondiabetic chronic kidney disease, canagliflozin promoted ER robustness by maintaining SERCA activity and preventing ER stress response failure, and it contributed to tubular protection.

ARTICLE HIGHLIGHTS

Rodent models of AKI and AKI-CKD transition: an update in 2024

Despite known drawbacks, rodent models are essential tools in the research of renal development, physiology, and pathogenesis. In the past decade, rodent models have been developed and used to mimic different etiologies of acute kidney injury (AKI), AKI to chronic kidney disease (CKD) transition or progression, and AKI with comorbidities. These models have been applied for both mechanistic research and preclinical drug development. However, current rodent models have their limitations, especially since they often do not fully recapitulate the pathophysiology of AKI in human patients, and thus need further refinement. Here, we discuss the present status of these rodent models, including the pathophysiologic compatibility, clinical translational significance, key factors affecting model consistency, and their main limitations. Future efforts should focus on establishing robust models that simulate the major clinical and molecular phenotypes of human AKI and its progression.

Monocytes Release Pro-Cathepsin D to Drive Blood-to-Brain Transcytosis in Diabetes

BACKGROUND

Microvascular complications are the major outcome of type 2 diabetes progression, and the underlying mechanism remains to be determined.

METHODS

High-throughput RNA sequencing was performed using human monocyte samples from controls and diabetes. The transgenic mice expressing human CTSD (cathepsin D) in the monocytes was constructed using CD68 promoter. In vivo 2-photon imaging, behavioral tests, immunofluorescence, transmission electron microscopy, Western blot analysis, vascular leakage assay, and single-cell RNA sequencing were performed to clarify the phenotype and elucidate the molecular mechanism.

RESULTS

Monocytes expressed high-level CTSD in patients with type 2 diabetes. The transgenic mice expressing human CTSD in the monocytes showed increased brain microvascular permeability resembling the diabetic microvascular phenotype, accompanied by cognitive deficit. Mechanistically, the monocytes release nonenzymatic pro-CTSD to upregulate caveolin expression in brain endothelium triggering caveolae-mediated transcytosis, without affecting the paracellular route of brain microvasculature. The circulating pro-CTSD activated the caveolae-mediated transcytosis in brain endothelial cells via its binding with low-density LRP1 (lipoprotein receptor-related protein 1). Importantly, genetic ablation of CTSD in the monocytes exhibited a protective effect against the diabetes-enhanced brain microvascular transcytosis and the diabetes-induced cognitive impairment.

CONCLUSIONS

These findings uncover the novel role of circulatory pro-CTSD from monocytes in the pathogenesis of cerebral microvascular lesions in diabetes. The circulatory pro-CTSD is a potential target for the intervention of microvascular complications in diabetes.

Apigenin ameliorates genitourinary dysfunction in a type 1 diabetic rat model via Drp1 modulation

The present study aimed to explore the potential ameliorative effect of apigenin (APG) against diabetes-associated genitourinary complications in rats. A diabetic rat model was induced by the intraperitoneal injection of streptozotocin (STZ). All experimental animals were treated with vehicle or vehicle plus APG at a dose of 0.78 mg/kg/day for 10 days, either once diabetes was confirmed or at the end of the 3rd week after confirmation of diabetes. Rats were sacrificed at the end of the fifth week. In addition to the histological assessment, an analysis of kidney function tests and serum testosterone was performed to assess diabetic genitourinary complications. Gene expression of the mitochondrial fission protein, dynamin related protein 1 (Drp1), was measured in renal and testicular tissues using qRT PCR. APG can increase body weight, reduce blood glucose levels, and improve renal and testicular functions in diabetic rats. APG decreased Drp1 overexpression in diabetic animals' kidneys and testes. In summary, our current work discloses that APG attenuates diabetic genitourinary lesions in rats via suppressing Drp1 overexpression.

Targeting ROCK1 in diabetic kidney disease: Unraveling mesangial fibrosis mechanisms and introducing myricetin as a novel antagonist

Diabetic kidney disease (DKD) stands as a pressing health challenge, with mesangial cell fibrosis identified as a pivotal hallmark leading to glomerular sclerosis. Gaining a deeper grasp on the molecular dynamics behind this can potentially introduce groundbreaking therapeutic avenues. Recent revelations from studies on ROCK1-deficient mice, which displayed resilience against high-fat diet (HFD)-induced glomerulosclerosis and mitochondrial fragmentation, spurred our hypothesis regarding ROCK1's potential role in mesangial cell fibrosis. Subsequent rigorous experiments corroborated our theory, highlighting the critical role of ROCK1 in orchestrating mesangial cell proliferation and fibrosis, especially in high-glucose settings. Mechanistically, ROCK1 inhibition led to a notable hindrance in the high-glucose-triggered MAPK signaling pathway, particularly emphasizing the ROCK1/ERK/P38 axis. To translate this understanding into potential therapeutic interventions, we embarked on a comprehensive drug screening journey. Leveraging molecular modeling techniques, Myricetin surfaced as an efficacious inhibitor of ROCK1. Dose-dependent in vitro assays substantiated Myricetin's prowess in curtailing mesangial cell proliferation and fibrosis via ROCK1/ERK/P38 pathway. In vivo verifications paralleled these findings, with Myricetin treatment resulting in significant renal function enhancements and diminished DKD pathological markers, all pivoted around the ROCK1/ERK/P38 nexus. These findings not only deepen our comprehension of DKD molecular underpinnings but also elevate ROCK1 to the pedestal of a promising therapeutic beacon. Concurrently, Myricetin is spotlighted as a potent natural contender, heralding a new era in DKD therapeutic design.

The Combinational Effect of Inulin and Resveratrol on the Oxidative Stress and Inflammation Level in a Rat Model of Diabetic Nephropathy

Background

Using inulin can enhance resveratrol's effects by improving the intestinal microbiome and the stability of resveratrol.

Objectives

We aimed to investigate the effect of therapeutic intervention with combined inulin and resveratrol on kidney function in diabetic rats.

Methods

Diabetic model was induced by intraperitoneal injection of streptozotocin. Afterward, rats were divided into 6 groups: control, diabetic without treatment, diabetic treated with insulin, diabetic treated with resveratrol, diabetic treated with inulin, and diabetic treated with a combination of inulin and resveratrol. After 10 wk, the creatinine, urea, insulin, urinary proteins, and inflammatory and oxidative stress markers were evaluated. Pathologic changes were examined in kidney tissues.

Results

Renal dysfunction, accompanied by increased inflammation and oxidative stress, was observed. Our results showed that treatment with resveratrol and inulin had antidiabetic effects and was associated with reduced renal dysfunction, oxidative stress, and kidney inflammation. In addition, it was observed that combined treatment with inulin and resveratrol outperformed monotherapies in improving kidney function and reducing oxidative stress and inflammation.

Conclusions

Treatment with resveratrol and inulin can have renoprotective effects by improving oxidative stress and inflammation in kidney tissues. Therefore, employing these 2 compounds is suggested as an inexpensive and available method for diabetic nephropathy.

IL-33/ST2L signaling alleviates diabetic nephropathy by regulating endoplasmic reticulum stress and apoptosis

OBJECTIVE

Diabetic nephropathy (DN) is a serious chronic complication of diabetes mellitus (DM). Endoplasmic reticulum (ER) stress is an important factor in the regulation of pathological processes in DN, and excessive ER stress can lead to apoptosis. Although the IL-33/ST2 axis is known to be involved in diabetic kidney disease or related nephropathy, its role and molecular mechanisms remain poorly understood in terms of DN. The purpose of this study was to investigate the effects of IL-33/ST2 signaling on DN and to characterize the roles that ER stress and apoptosis play in DN.

METHODS

To investigate this study, mice were randomly assigned into DN (induced by 0.1% STZ) and Control groups. Biochemical indices (FBG, BUN, UPR, UCE) were measured in serum and urine samples to reflect blood glucose and kidney damage. Quantitative real-time PCR, western blot, and immunofluorescence were used to assess gene and protein expression of the IL-33/ST2 axis and ER stress relative signaling molecule. Apoptosis was analyzed by flow cytometry.

RESULTS

IL-33 levels are significantly increased in the kidneys of patients and mice with DN. Double immunofluorescence staining showed that IL-33 colocalized with CD31-positive endothelial cells. Treatment with IL-33 attenuated kidney injury in Streptozotocin (STZ)-treated mice. In vitro, we showed that IL-33 attenuated ER stress and apoptosis in glomerular endothelial cells. However, sST2 treatment significantly reversed these effects of IL-33.

CONCLUSION

Together, these data suggest that IL-33/ST2 signaling mitigates STZ-induced renal damage, partly at least, by suppressing ER stress and apoptosis. Therefore, IL-33 may be an effective therapeutic target in DN.

Galantamine improves glycemic control and diabetic nephropathy in Leprdb/db mice

Galantamine, a centrally acting acetylcholinesterase inhibitor, has been shown to attenuate inflammation and insulin resistance in patients with metabolic syndrome. We investigated the effects of galantamine on glycemic control and development of diabetic nephropathy (DN) in Leprdb/db mice. Galantamine significantly reduced food intake, body weight, blood glucose and HbA1c levels. Insulin resistance (HOMA-IR, QUICKI), HOMA-β and elevations in plasma inflammatory cytokine levels (TNF-α, IL-6 and HMGB-1) were all attenuated by galantamine. Galantamine also ameliorated diabetes-induced kidney injury as evidenced by improvements in renal function (BUN, creatinine, albuminuria), histologic injury and apoptosis. Improved glycemic control and nephropathy were associated with increased circulating GLP-1, decreased renal P-38 MAPK and caspase-1 activation and reduced SGLT-2 expression. These findings provide insights into the mechanisms by which galantamine improves glycemic control and attenuates DN in the Leprdb/db mouse model.

Rodent models to study type 1 and type 2 diabetes induced human diabetic nephropathy

INTRODUCTION

Diabetic nephropathy (DN), an outcome of prolonged diabetes, has affected millions of people worldwide and every year the incidence and prevalence increase substantially. The symptoms may start with mild manifestations of the disease such as increased albuminuria, serum creatinine levels, thickening of glomerular basement membrane, expansion of mesangial matrix to severe pathological symptoms such as glomerular lesions and tubulointerstitial fibrosis which may further proceed to cardiovascular dysfunction or end-stage renal disease.

PERSPECTIVE

Numerous therapeutic interventions are being explored for the management of DN, however, these interventions do not completely halt the progression of this disease and hence animal models are being explored to identify critical genetic and molecular parameters which could help in tackling the disease. Rodent models which mostly include mice and rats are commonly used experimental animals which provide a wide range of advantages in understanding the onset and progression of disease in humans and also their response to a wide range of interventions helps in the development of effective therapeutics. Rodent models of type 1 and type 2 diabetes induced DN have been developed utilizing different platforms and interventions during the last few decades some of which mimic various stages of diabetes ranging from early to later stages. However, a rodent model which replicates all the features of human DN is still lacking. This review tries to evaluate the rodent models that are currently available and understand their features and limitations which may help in further development of more robust models of human DN.

CONCLUSION

Using these rodent models can help to understand different aspects of human DN although further research is required to develop more robust models utilizing diverse genetic platforms which may, in turn, assist in developing effective interventions to target the disease at different levels.

Nicotine exacerbates diabetic nephropathy through upregulation of Grem1 expression

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes mellitus. Clinical reports indicate that smoking is a significant risk factor for chronic kidney disease, and the tobacco epidemic exacerbates kidney damage in patients with DN. However, the underlying molecular mechanisms remain unclear.

METHOD

In the present study, we used a diabetic mouse model to investigate the molecular mechanisms for nicotine-exacerbated DN. Twelve-week-old female mice were injected with streptozotocin (STZ) to establish a hyperglycemic diabetic model. After four months, the control and hyperglycemic diabetic mice were further divided into four groups (control, nicotine, diabetic mellitus, nicotine + diabetic mellitus) by intraperitoneal injection of nicotine or PBS. After two months, urine and blood were collected for kidney injury assay, and renal tissues were harvested for further molecular assays using RNA-seq analysis, real-time PCR, Western blot, and immunohistochemistry. In vitro studies, we used siRNA to suppress Grem1 expression in human podocytes. Then we treated them with nicotine and high glucose to compare podocyte injury.

RESULT

Nicotine administration alone did not cause apparent kidney injury, but it significantly increased hyperglycemia-induced albuminuria, BUN, plasma creatinine, and the kidney tissue mRNA expression of KIM-1 and NGAL. Results from RNA-seq analysis, real-time PCR, Western blot, and immunohistochemistry analysis revealed that, compared to hyperglycemia or nicotine alone, the combination of nicotine treatment and hyperglycemia significantly increased the expression of Grem1 and worsened DN. In vitro experiments, suppression of Grem1 expression attenuated nicotine-exacerbated podocyte injury.

CONCLUSION

Grem1 plays a vital role in nicotine-exacerbated DN. Grem1 may be a potential therapeutic target for chronic smokers with DN.

Probiotic Formula Ameliorates Renal Dysfunction Indicators, Glycemic Levels, and Blood Pressure in a Diabetic Nephropathy Mouse Model

One-third of patients with end-stage chronic kidney disease (CKD) experience diabetic nephropathy (DN), which worsens the progression of renal dysfunction. However, preventive measures for DN are lacking. Lactobacillus acidophilus TYCA06, Bifidobacterium longum subsp. infantis BLI-02, and Bifidobacterium bifidum VDD088 probiotic strains have been demonstrated to delay CKD progression. This study evaluated their biological functions to stabilize blood-glucose fluctuations and delay the deterioration of renal function. The db/db mice were used to establish a DN animal model. This was supplemented with 5.125 × 10⁹ CFU/kg/day (high dose) or 1.025 × 10⁹ CFU/kg/day (low dose) mixed with probiotics containing TYCA06, BLI-02, and VDD088 for 8 weeks. Blood urea nitrogen (BUN), serum creatinine, blood glucose, and urine protein were analyzed. Possible mechanisms underlying the alleviation of DN symptoms by probiotic strains were evaluated through in vitro tests. Animal experiments revealed that BUN, serum creatinine, and blood glucose upon probiotic administration were significantly lower than in the control group. The rate of change of urine protein decreased significantly, and blood pressure, glucose tolerance, and renal fibrosis were improved. In vitro testing indicated that TYCA06 and BLI-02 significantly increased acetic acid concentration. TYCA06, BLI-02, and VDD088 were associated with better antioxidation, anti-inflammation, and glucose consumption activities relative to the control. A combination of the probiotics TYCA06, BLI-02, and VDD088 attenuated renal function deterioration and improved blood-glucose fluctuation in a diabetes-induced CKD mouse model.

Sex-Related Aspects in Diabetic Kidney Disease-An Update

Differences between the sexes exist in many diseases, and in most cases, being a specific sex is considered a risk factor in the development and/or progression. This is not quite so clear in diabetic kidney disease (DKD), the development and severity of which depends on many general factors, such as the duration of diabetes mellitus, glycemic control, and biological risk factors. Similarly, sex-specific factors, such as puberty or andro-/menopause, also determine the microvascular complications in both the male and female sex. In particular, the fact that diabetes mellitus itself influences sex hormone levels, which in turn seem to be involved in renal pathophysiology, highlights the complexity of the question of sex differences in DKD. The major objective of this review is to summarize and simplify the current knowledge on biological sex-related aspects in the development/progression but also treatment strategies of human DKD. It also highlights findings from basic preclinical research that may provide explanations for these differences.

Development of a novel angiotensin converting enzyme 2 stimulator with broad implications in SARS-CoV2 and type 1 diabetes

Angiotensin-converting enzyme 2 (ACE2) is protective in cardiovascular disease, lung injury and diabetes yet paradoxically underlies our susceptibility to SARs-CoV2 infection and the fatal heart and lung disease it can induce. Furthermore, diabetic patients have chronic, systemic inflammation and altered ACE2 expression resulting in increased risk of severe COVID-19 and the associated mortality. A drug that could increase ACE2 activity and inhibit cellular uptake of severe acute respiratory syndrome coronavirus 2 (SARs-CoV2), thus decrease infection, would be of high relevance to cardiovascular disease, diabetes and SARs-CoV2 infection. While the need for such a drug lead was highlighted over a decade ago receiving over 600 citations,1 to date, no such drugs are available.2 Here, we report the development of a novel ACE2 stimulator, designated '2A'(international PCT filed), which is a 10 amino acid peptide derived from a snake venom, and demonstrate its in vitro and in vivo efficacy against SARs-CoV2 infection and associated lung inflammation. Peptide 2A also provides remarkable protection against glycaemic dysregulation, weight loss and disease severity in a mouse model of type 1 diabetes. No untoward effects of 2A were observed in these pre-clinical models suggesting its strong clinical translation potential.

Increased Renal Medullary NOX-4 in Female but Not Male Mice during the Early Phase of Type 1 Diabetes: Potential Role of ROS in Upregulation of TGF-β1 and Fibronectin in Collecting Duct Cells

Chronic diabetes mellitus (DM) can lead to kidney damage associated with increased reactive oxygen species (ROS), proteinuria, and tubular damage. Altered protein expression levels of transforming growth factor-beta 1 (TGF-β1), fibronectin, and renal NADPH oxidase (NOX-4) are associated with the profibrotic phenotype in renal tubular cells. NOX-4 is one of the primary sources of ROS in the diabetic kidney and responsible for the induction of profibrotic factors in collecting duct (CD) cells. The renal medulla is predominantly composed of CDs; in DM, these CD cells are exposed to high glucose (HG) load. Currently there is no published literature describing the expression of these markers in the renal medulla in male and female mice during the early phase of DM, or the role of NOX-4-induced ROS. Our aim was to evaluate changes in transcripts and protein abundances of TGF-β1, fibronectin, and NOX-4 along with ROS levels in renal medullary tissues from male and female mice during a short period of streptozotocin (STZ)-induced type 1 DM and the effect of HG in cultured CD cells. CF-1 mice were injected with or without a single dose of STZ (200 mg/kg) and euthanized at day 6. STZ females showed higher expression of fibronectin and TGF-β1 when compared to control mice of either gender. Interestingly, STZ female mice showed a >30-fold increase on mRNA levels and a 3-fold increase in protein levels of kidney medullary NOX-4. Both male and female STZ mice showed increased intrarenal ROS. In primary cultures of inner medullary CD cells exposed to HG over 48 h, the expression of TGF-β1, fibronectin, and NOX-4 were augmented. M-1 CD cells exposed to HG showed increased ROS, fibronectin, and TGF-β1; this effect was prevented by NOX-4 inhibition. Our data suggest that at as early as 6 days of STZ-induced DM, the expression of profibrotic markers TGF-β1 and fibronectin increases in renal medullary CD cells. Antioxidants mechanisms in male and female in renal medullary tissues seems to be differentially regulated by the actions of NOX-4.

Comparison of Local Metabolic Changes in Diabetic Rodent Kidneys Using Mass Spectrometry Imaging

Understanding the renal region-specific metabolic alteration in different animal models of diabetic nephropathy (DN) is critical for uncovering the underlying mechanisms and for developing effective treatments. In the present study, spatially resolved metabolomics based on air flow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) was used to compare the local metabolic changes in the kidneys of HFD/STZ-induced diabetic rats and db/db mice. As a result, a total of 67 and 59 discriminating metabolites were identified and visualized in the kidneys of the HFD/STZ-induced diabetic rats and db/db mice, respectively. The result showed that there were significant region-specific changes in the glycolysis, TCA cycle, lipid metabolism, carnitine metabolism, choline metabolism, and purine metabolism in both DN models. However, the regional levels of the ten metabolites, including glucose, AMP, eicosenoic acid, eicosapentaenoic acid, Phosphatidylserine (36:1), Phosphatidylserine (36:4), Phosphatidylethanolamine (34:1), Phosphatidylethanolamine (36:4), Phosphatidylcholine (34:2), Phosphatidylinositol (38:5) were changed in reversed directions, indicating significant differences in the local metabolic phenotypes of these two commonly used DN animal models. This study provides comprehensive and in-depth analysis of the differences in the tissue and molecular pathological features in diabetic kidney injury in HFD/STZ-induced diabetic rats and db/db mice.

Apolipoprotein M/sphingosine 1-phosphate protects against diabetic nephropathy

Diabetic nephropathy remains a common cause of end-stage renal failure and its associated mortality around the world. Sphingosine 1-phosphate (S1P) is a multifunctional lipid mediator and binds to HDL via apolipoprotein M (ApoM). Since HDL has been reported to be epidemiologically associated with kidney disease, we attempted to investigate the involvement of the ApoM/S1P axis in the pathogenesis/progression of diabetic nephropathy. In type 2 diabetic patients, the serum ApoM levels were inversely correlated with the clinical stage of diabetic nephropathy. The decline in the eGFR over a 5-year observation period proceeded more rapidly in subjects with lower serum ApoM levels. In a mouse model of streptozotocin-induced diabetes, deletion of ApoM deteriorated the phenotypes of diabetic nephropathy: the urinary albumin and plasma creatinine levels increased, the kidneys enlarged, and renal fibrosis and thickening of the basement membrane progressed. On the other hand, overexpression of ApoM ameliorated these phenotypes. These protective effects of ApoM were partially inhibited by treatment with VPC23019, an antagonist of S1P1 and S1P3, but not by treatment with JTE013, an antagonist of S1P2. ApoM/S1P axis attenuated activation of the Smad3 pathway, while augmented eNOS phosphorylation through the S1P1 pathway. Moreover, ApoM/S1P increased the SIRT1 protein levels and enhanced mitochondrial functions by increasing the S1P content of the cell membrane, which might cause selective activation of S1P1. ApoM might be a useful biomarker for predicting the progression of diabetic nephropathy, and the ApoM/S1P-S1P1 axis might serve as a novel therapeutic target for preventing the development/progression of diabetic nephropathy.

A Review of Medicinal Plants with Renoprotective Activity in Diabetic Nephropathy Animal Models

Diabetic nephropathy (DN), also recognized as diabetic kidney disease, is a kidney malfunction caused by diabetes mellitus. A possible contributing factor to the onset of DN is hyperglycemia. Poorly regulated hyperglycemia can damage blood vessel clusters in the kidneys, leading to kidney damage. Its treatment is difficult and expensive because its causes are extremely complex and poorly understood. Extracts from medicinal plants can be an alternative treatment for DN. The bioactive content in medicinal plants inhibits the progression of DN. This work explores the renoprotective activity and possible mechanisms of various medicinal plant extracts administered to diabetic animal models. Research articles published from 2011 to 2022 were gathered from several databases including PubMed, Scopus, ProQuest, and ScienceDirect to ensure up-to-date findings. Results showed that medicinal plant extracts ameliorated the progression of DN via the reduction in oxidative stress and suppression of inflammation, advanced glycation end-product formation, cell apoptosis, and tissue injury-related protein expression.

Diabetic Nephropathy: Pathogenesis to Cure

Diabetic nephropathy (DN) is a leading cause of end-stage renal disorder (ESRD). It is defined as the increase in urinary albumin excretion (UAE) when no other renal disease is present. DN is categorized into microalbuminuria and macroalbuminuria. Factors like high blood pressure, high blood sugar levels, genetics, oxidative stress, hemodynamic and metabolic changes affect DN. Hyperglycemia causes renal damage through activating protein kinase C (PKC), producing advanced end glycation products (AGEs) and reactive oxygen species (ROS). Growth factors, chemokines, cell adhesion molecules, inflammatory cytokines are found to be elevated in the renal tissues of the diabetic patient. Many different and new diagnostic methods and treatment options are available due to the increase in research efforts and progression in medical science. However, until now, no permanent cure is available. This article aims to explore the mechanism, diagnosis, and therapeutic strategies in current use for increasing the understanding of DN.

Evaluation of N-(6-[18F]Fluoropyridin-3-yl)glycine PET renography to detect renal function progression in a rat model of diabetic nephropathy

OBJECTIVE

Given the limitation of biomarkers to predict the renal function progression in diabetic nephropathy, N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine (6-[¹⁸F]FPyGly) was used to evaluate renal function progression in a rat model of diabetic nephropathy.

METHODS

Twenty male Sprague-Dawley rats were randomly divided into four groups, including the healthy control group (HC group), diabetic nephropathy group (DNM group), routine diet treated diabetic nephropathy group (RDNM group), and high fat/high sucrose -diet-fed diabetic nephropathy group (HDNM group). All renal function parameters were determined from animal PET renograms. P and T_max represent the curve peak counts and the time to the curve peak counts of 6-[¹⁸F]FPyGly in kidneys after injection, C_1/2 and the 15 min/Peak ratio represent the time from peak to 1/2 peak in the clearance phase, and the ratio of the curve counts at 15 min to the curve peak counts.

RESULTS

P, T_max, C_1/2, and 15 min/peak ratio of each rat were significantly correlated with S-Cr, BUN. There were significant differences in T_max, P, serum creatinine (SCr), and blood urea nitrogen (BUN) levels between HC and DNM groups. P and the 15 min/Peak ratio were significantly different among DNM, RDNM, and HDNM groups, while T_max and C_1/2 were only significantly different between DNM and RDNM or HDNM groups. There only was a significant difference in BUN between the DNM and HDNM groups.

CONCLUSION

The renal function parameters P, T_max, C_1/2 and 15 min/peak value obtained by dynamic renal imaging based on 6-[¹⁸F]FPyGly could reflect changes of renal function in rats, which had a good correlation with SCr and BUN, and showed more efficient in the diagnosis of diabetic nephropathy and renal function classification than SCr and BUN.

Evaluation and Screening of Hypoglycemic Activity of Total Ginsenosides GBE-5 Fraction From Panax Ginseng Berry Based on UHPLC-MS Metabolomics

Objective

Ginseng berry (GB) was the mature fruit of medicinal and edible herb, Panax ginseng C.A. Meyer, with significant hypoglycemic effect. Ginsenoside was the main hypoglycemic active component of GB. Evaluating and screening the effective components of GB was of great significance to further develop its hypoglycemic effect.

Methods

The polar fractions of ginseng berry extract (GBE) were separated by a solvent extraction, and identified by ultra-high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-MS). The insulin resistance model of HepG2 cells was established, and the hypoglycemic active fraction in GBE polar fractions were screened in vitro. Rat model of type 2 diabetes mellitus (T2DM) was established to verify the hypoglycemic effect of the GBE active fraction. The metabolomic study based on UHPLC-MS was used to analyze the differential metabolites in the serum of T2DM rats after 30 days of intervention with hypoglycemic active GBE fraction. The kyoto encyclopedia of genes and genomes (KEGG) metabolic pathway enrichment analysis was used to study the main metabolic pathways involved in the regulation of hypoglycemic active parts of GBE.

Results

It was found that GBE-5 fraction had better hypoglycemic activity than other GBE polar fractions in vitro cell hypoglycemic activity screening experiment. After 30 days of treatment, the fasting blood glucose value of T2DM rats decreased significantly by 34.75%, indicating that it had significant hypoglycemic effect. Eighteen differential metabolites enriched in KEGG metabolic pathway were screened and identified in the rat serum from T2DM vs. GBE-5 group, and the metabolic pathways mainly involved in regulation include arachidonic acid (AA) metabolism, linoleic acid (LA) metabolism, unsaturated fatty acid biosynthesis, and ferroptosis.

Conclusions

The hypoglycemic effect of GBE-5 fraction was better than that of total ginsenoside of GB. The AA metabolism, LA metabolism, unsaturated fatty acid biosynthesis, and ferroptosis were the potential metabolic pathways for GBE-5 fraction to exert hypoglycemic regulation.

Loss of urotensin II receptor diminishes hyperglycemia and kidney injury in streptozotocin-treated mice

Beyond the CNS, urotensin II (UII) and its receptor (UT) are functionally expressed in peripheral tissues of the endocrine, cardiovascular, and renal systems. The expression levels of UII and UT in the kidney and circulating UII levels are increased in diabetes. UII also promotes mesangial proliferation and matrix accumulation in vitro. Here, we evaluate the effect of UT deletion on the development of hyperglycemia and diabetic kidney disease (DKD) in streptozotocin (STZ)-treated mice. Ten-week-old WT and UT knockout (KO) mice were injected with STZ for 5 days to induce diabetes. Blood glucose levels were measured weekly, and necropsy was performed 12 weeks after STZ injection. UT ablation slowed hyperglycemia and glucosuria in STZ-treated mice. UT KO also ameliorated STZ-induced increase in HbA1c, but not STZ-induced decrease in plasma insulin levels. However, STZ-induced increases in plasma glucagon concentration and immunohistochemical staining for glucagon in pancreatic islets were lessened in UT KO mice. UT ablation also protected against STZ-induced kidney derangements, including albuminuria, mesangial expansion, glomerular lesions, and glomerular endoplasmic reticulum stress. UT is expressed in a cultured pancreatic alpha cell line, and its activation by UII triggered membrane depolarization, T- and L-type voltage-gated Ca2+channel-dependent Ca2+influx, and glucagon secretion. These findings suggest that apart from direct action on the kidneys to cause injury, UT activation by UII may result in DKD by promoting hyperglycemia via induction of glucagon secretion by pancreatic alpha cells.

Overexpression of growth hormone improved hepatic glucose catabolism and relieved liver lipid deposition in common carp (Cyprinus carpio L.) fed a high-starch diet

Growth hormone (GH) is important for regulating insulin secretion and carbohydrate metabolism, and its role in mammalian models of diabetes is relatively worked out. Although some fish species were used as models for diabetes research, the effects of GH on insulin and glucose catabolism and anabolism in these models remain to be clarified. In this study, we investigated the effect of GH on insulin and glucose catabolism and anabolism in an omnivorous fish using GH transgenic (T) common carp that consistently overexpressed GH and wild-type (WT) common carp. We compared the intestinal morphology, and digestive and absorptive capacity of fish fed commercial feed. We also analyzed the growth performance, insulin level, glucose catabolism and anabolism, lipid deposition, and lipid catabolism and anabolism in T carp and WT carp fed diets containing either 30% or 40% starch. In the intestine of T carp, α-amylase activity was enhanced, the number of goblet cells and intestinal villi surface area was increased, and the expression level of glucose transport protein-related genes (glut2 and sglt1) was upregulated when compared to these indicators in WT carp. When fed either a normal or high-starch diet, the growth performance of T carp was better than that of WT carp. Compared with WT carp, serum insulin was increased and glucose was decreased, hepatic expression level of igf-1 and glycolysis-related genes was increased, and the activity level of a hepatic enzyme related to glycolysis was enhanced in T carp. When fed with a high-starch diet, the serum alanine aminotransferase activity, hepatic lipid content, and malondialdehyde content were significantly lower in T carp than in WT carp. These results indicated that overexpression of GH (1) enhanced carbohydrate digestion and absorption in the carp intestine, (2) did not induce insulin resistance and improved glucose catabolism and utilization in carp, and (3) relieved liver lipid deposition. Our data might provide new insights into potential ways to improve glucose utilization in fish and diabetes treatments.

The succinoglycan riclin restores beta cell function through the regulation of macrophages on Th1 and Th2 differentiation in type 1 diabetic mice

Bacterial succinoglycan is found suitable as a viscosifying and emulsifying agent in the food industry. Riclin is a de-succinyl succinoglycan from an Agrobacterium isolate. Our previous study has revealed that riclin exerts special anti-inflammatory effects in vitro and in vivo. This study aims to determine the effects of riclin on preventing against immunological injury of beta cells in a type 1 diabetic model. We found that orally riclin effectively restores beta-cell function and improves the complications of streptozotocin (STZ)-induced diabetes. Riclin also reduces STZ-induced liver and kidney damage, and balances the inappropriate ratio of T helper type 1 cell (Th1)/type 2 cell (Th2) in the spleen and pancreatic draining lymph nodes of the STZ-induced diabetic mice. In a co-culture system with the islet β cell MIN6 and macrophage RAW 264.7, riclin reduces the levels of IFN-γ and IL-1β, protecting against STZ-caused MIN6 cell injury. We identified that riclin specifically binds to the membrane of macrophages and regulates the ratio of IL-10 and IL-12, thereby inhibiting the macrophage-mediated polarization of Th1 cells and promoting the differentiation of Th2 cells, which depends on the dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) receptor. Moreover, orally riclin significantly decreases the incidence of STZ-induced hyperglycemia (7.1% in riclin vs. 92.9% in STZ), and prevents autoimmune diabetes in non-obese diabetic (NOD) mice, with 87.5% of mice free of diabetes compared to 46.6% of the control mice. These results suggest that riclin has potential to be a functional food to prevent and improve autoimmune diabetes and related diseases.

Vitexin, a fenugreek glycoside, ameliorated obesity-induced diabetic nephropathy via modulation of NF-κB/IkBα and AMPK/ACC pathways in mice

Obesity is one of the most critical risk factors for diabetes mellitus and plays a significant role in diabetic nephropathy (DN). The present investigation aimed to evaluate the possible mechanism of action of vitexin on obesity-induced DN in a high-fat diet (HFD)-fed experimental C57BL/6 mice model. Obesity was induced in male C57BL/6 mice by chronic administration of HFD, and mice were concomitantly treated with vitexin (15, 30, and 60 mg/kg, p.o.). HFD-induced increased renal oxido-nitrosative stress and proinflammatory cytokine levels were significantly inhibited by vitexin. The Western blot analysis suggested that alteration in renal NF-κB, IκBα, nephrin, AMPK, and ACC phosphorylation levels was effectively restored by vitexin treatment. Histological aberration induced in renal tissue after chronic administration of HFD was also reduced by vitexin. In conclusion, vitexin suppressed the progression of obesity-induced DN via modulation of NF-κB/IkBα and AMPK/ACC pathways in an experimental model of HFD-induced DN in C57BL/6J mice.

Tetrahydrocurcumin Ameliorates Kidney Injury and High Systolic Blood Pressure in High-Fat Diet-Induced Type 2 Diabetic Mice

BACKGROUND

Activation of the intrarenal renin-angiotensin system (RAS) is implicated in the pathogenesis of kidney injury and hypertension. We aimed to investigate the protective effect of tetrahydrocurcumin (THU) on intrarenal RAS expression, kidney injury, and systolic blood pressure (SBP) in high-fat diet (HFD)-induced type 2 diabetic mice.

METHODS

Eight-week-old male mice were fed a regular diet (RD) or HFD for 12 weeks, and THU (50 or 100 mg/kg/day) was intragastrically administered with HFD. Physiological and metabolic changes were monitored and the expression of RAS components and markers of kidney injury were assessed.

RESULTS

HFD-fed mice exhibited hyperglycemia, insulin resistance, and dyslipidemia compared to those in the RD group (P<0.05). Kidney injury in these mice was indicated by an increase in the ratio of albumin to creatinine, glomerular hypertrophy, and the effacement of podocyte foot processes. Expression of intrarenal angiotensin-converting enzyme, angiotensin II type I receptor, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4, and monocyte chemoattractant protein-1 was also markedly increased in HFD-fed mice. HFD-fed mice exhibited elevated SBP that was accompanied by an increase in the wall thickness and vascular cross-sectional area (P<0.05), 12 weeks post-HFD consumption. Treatment with THU (100 mg/kg/day) suppressed intrarenal RAS activation, improved insulin sensitivity, and reduced SBP, thus, attenuating kidney injury in these mice.

CONCLUSION

THU alleviated kidney injury in mice with HFD-induced type 2 diabetes, possibly by blunting the activation of the intrarenal RAS/nicotinamide adenine dinucleotide phosphate oxidase IV (NOX4)/monocyte chemoattractant protein 1 (MCP-1) axis and by lowering the high SBP.

α-Ketoglutarate Upregulates Collecting Duct (Pro)renin Receptor Expression, Tubular Angiotensin II Formation, and Na+ Reabsorption During High Glucose Conditions

Diabetes mellitus (DM) causes high glucose (HG) levels in the plasma and urine. The (pro)renin receptor (PRR) is a key regulator of renal Na+ handling. PRR is expressed in intercalated (IC) cells of the collecting duct (CD) and binds renin to promote angiotensin (Ang) II formation, thereby contributing to Na+ reabsorption. In DM, the Kreb's cycle is in a state of suppression in most tissues. However, in the CD, expression of glucose transporters is augmented, boosting the Kreb's cycle and consequently causing α-ketoglutarate (αKG) accumulation. The αKG receptor 1 (OXGR1) is a Gq-coupled receptor expressed on the apical membrane of IC cells of the CD. We hypothesize that HG causes αKG secretion and activation of OXGR1, which increases PRR expression in CD cells. This effect then promotes intratubular AngII formation and Na+ reabsorption. To test this hypothesis, streptozotocin (STZ)-induced diabetic mice were treated with or without montelukast (ML), an OXGR1 antagonist, for 6 days. STZ mice had higher urinary αKG and PRR expression along with augmented urinary AngII levels and Na+ retention. Treatment with ML prevented all these effects. Similarly, primary cultured inner medullary CD cells treated with HG showed increased PRR expression, while OXGR1 antagonist prevented this effect. αKG increases PRR expression, while treatments with ML, PKC inhibition, or intracellular Ca2+ depletion impair this effect. In silico analysis suggested that αKG binds to mouse OXGR1. These results indicate that HG conditions promote increased levels of intratubular αKG and OXGR1-dependent PRR upregulation, which impact AngII formation and Na+ reabsorption.

Effect of suramin on urinary excretion of diabetes-induced glomerular and tubular injury parameters in rats

Diabetes mellitus causes changes in metabolism of extracellular nucleotides acting through P2 receptors (P2Rs). This affects renal function and may lead to glomerular and tubular disturbances. We measured urinary excretion of nucleotides (ATP, ADP, AMP, UTP, UDP, UMP) in streptozotocin-induced diabetic rats (65 mg/kg, i.p., day 0) and the effects of P2Rs' blockade by suramin (10 mg/kg, i.p., days +7, +14) on glomerular P2×7R expression and urinary excretion of glomerular (albumin, nephrin) and tubular (KIM-1, NGAL) injury markers, electrolytes, and oxidative stress markers (TBARS, 8-OHdG). Concentrations of nucleotides, specific proteins, electrolytes, and oxidative stress markers in 24-h urine samples collected in metabolic cages at days -1, +6 and +20 were measured using ion-paired reversed-phase HPLC, immunoenzymatic and fluorometric methods, and flame photometry, respectively. Expression of KIM-1 and P2×7R was examined by immunohistochemistry or immunoblotting. Diabetes was associated with increased urinary excretion of ATP, ADP, UTP, UDP and glomerular P2×7R expression. Suramin attenuated P2×7R expression but did not affect urinary excretion of nucleotides. Urinary excretion of albumin, nephrin, NGAL, and 8-OHdG were increased in diabetic rats and were not affected by suramin. TBARS was higher in diabetic rats and suramin attenuated the excretion dynamics in this group. KIM-1 excretion was higher in diabetic rats and suramin further increased excretion of KIM-1 in both diabetic and non-diabetic rats. Furthermore, suramin attenuated the diabetes-induced natriuresis and kaliuresis. It is possible that suramin affects both glomerular and tubular functions in diabetic rats.

Induction of PDCD4 by albumin in proximal tubule epithelial cells potentiates proteinuria-induced dysfunctional autophagy by negatively targeting Atg5

The precise molecular mechanism of autophagy dysfunction in type 1 diabetes is not known. Herein, the role of programmed cell death 4 (PDCD4) in autophagy regulation in the pathogenesis of diabetic kidney disease (DKD) in vivo and in vitro was described. It was found that Pdcd4 mRNA and protein was upregulated in the streptozotocin (STZ)-induced DKD rats. In addition, a unilateral ureteral obstruction mouse model displayed an upregulation of PDCD4 in the disease group. kidney biopsy samples of human DKD patients showed an upregulation of PDCD4. Furthermore, western blotting of the STZ-induced DKD rat tissues displayed a low microtubule-associated protein 1A/1B-light chain 3 (LC3)-II, as compared to the control. It was found that albumin overload in cultured PTEC could upregulate the expression of PDCD4 and p62, and decrease the expression of LC3-II and autophagy-related 5 (Atg5) proteins. The knockout of Pdcd4 in cultured PTECs could lessen albumin-induced dysfunctional autophagy as evidenced by the recovery of Atg5 and LC3-II protein. The forced expression of PDCD4 could further suppress the expression of crucial autophagy-related gene Atg5. Herein, endogenous PDCD4 was shown to promote proteinuria-induced dysfunctional autophagy by negatively regulating Atg5. PDCD4 might therefore be a potential therapeutic target in DKD.

The hepatoprotective effects of fennel seeds extract and trans-Anethole in streptozotocin-induced liver injury in rats

Hypoglycemic, anti-inflammatory, and antioxidant activities of fennel have been recorded in numerous investigations. The study aimed to evaluate the protective effects of fennel or its active component trans-Anethole (TA) on streptozotocin-induced liver injury in rats. Rats were injected with a single dose of STZ (65 mg/kg) and treated with fennel (200 and 400 mg/kg), TA (80 mg/kg), or metformin (300 mg/kg) for 35 days. Serum lipid profile and liver enzyme activity (aminotransferases), oxidative stress markers, and the degree of fibrosis in the liver tissue were assessed. Both fennel and TA decreased blood glucose levels, reduced liver enzyme activity, food, and water intake, and intensity of weight loss, reduced serum triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), and increased high-density lipoprotein cholesterol (HDL-c). Additionally, fennel and TA significantly reduced MDA concentration while increased CAT activity and thiol content and reduced the degree of injury and fibrosis in the liver of diabetic rats. Our results suggest that fennel seed extract and its active compound TA are able to protect the liver against diabetes-induced hepatic injury in rats, probably via hypoglycemic and antioxidant effects.

Diffusion Tensor Imaging in Rat Models of Preclinical Diabetic Nephropathy: A Preliminary Study

PURPOSE

This study aimed to investigate the value of diffusion tensor imaging to assess renal injury in a rat model of preclinical diabetic nephropathy.

METHODS

Twenty-eight male Sprague Dawley rats were divided into two groups: the normal control (NC) group of 10 rats and the diabetic nephropathy (DN) group of 18 rats. Eight weeks after diabetes induction by streptozotocin, 3.0-T magnetic resonance (MR) imaging (b = 0 and 600 s/mm², 15 diffusion directions) using a 32-channel knee coil was performed. After MR imaging, we measured serum creatinine, and collected double kidney tissues for pathology. The apparent diffusion coefficients(ADC) and fractional anisotropy(FA) values of the renal cortex and medulla were calculated for all kidneys. Physiological parameters, laboratory parameters, and imaging results were compared between the two groups.

RESULTS

All DN group animals developed hyperglycemia, polyuria, and emaciation. Serum creatinine was not significantly different between the groups (P > 0.05). Urinary albumin at 2, 4, and 8 weeks was higher in the DN group than in the NC group but <20 µg/min (P < 0.05). Pathologically, renal damage in the DN rats was observed. The ADC value was significantly increased in DN animals in the cortex (1.75×10^-3mm²/s),medulla(1.53×10^-3mm²/s)compared with NC group(cortex, 1.52×10^-3mm²/s; medulla,1.35×10^-3mm²/s). The FA value was significantly reduced in DN animals in the cortex (0.21),medulla(0.25)compared with NC group(cortex,0.26;medulla,0.3).

CONCLUSIONS

Increased apparent diffusion coefficients and decreased fractional anisotropy values on diffusion tensor imaging were associated with preclinical DN. Diffusion tensor imaging may be useful in early, non-invasive, quantitative detection, and therapy monitoring of DN.