Animal models of diabetic microvascular complications: Relevance to clinical features

Zinc oxide nanoparticles prevent the onset of diabetic nephropathy by inhibiting multiple pathways associated with oxidative stress

BACKGROUND

Zinc deficiency is strongly correlated with prolonged diabetes mellitus and diabetic nephropathy (DN). Previously, glucose-lowering, insulinomimetic, and β-cell proliferative activities of zinc oxide nanoparticles (ZON) have been reported. Considering these pleiotropic effects, we hypothesized that ZON modulates multiple cellular pathways associated with necroptosis, inflammation, and renal fibrosis, which are involved in progressive loss of renal function.

AIM

This study evaluated the effect of ZON on renal function, leading to the alleviation of DN in streptozotocin (STZ)-induced type 1 diabetic Wistar rats and proposed a probable mechanism for its activity.

METHODS

Wistar rats (n = 6/group) were used as healthy controls, diabetic controls, diabetic rats treated with ZON (1, 3, and 10 mg/kg), and insulin controls. Urine and serum biochemical parameters, glomerular filtration rate (GFR), and renal histology were also evaluated. Cultured E11 podocytes were evaluated in vitro for markers of oxidative stress, proteins associated with the loss of renal function, and genes associated with renal damage.

KEY FINDINGS

STZ-treated rats receiving oral doses of ZON showed enhanced renal function, with no histological alterations in the kidney tissue. ZON inhibited the TGF-β/Samd3 pathway in renal fibrosis; blocked Ripk1/Ripk3/Mlkl mediated necroptosis and protected against hyperglycemia-induced pyroptosis. In E11 podocytes, ZON reduced oxidative stress under high glucose conditions and retained podocyte-specific proteins.

SIGNIFICANCE

A probable mechanism by which ZON prevents DN has been proposed, suggesting its use as a complementary therapeutic agent for the treatment of diabetic complications. To the best of our knowledge, this is the first study to demonstrate the in vitro effects of ZON in cultured podocytes.

Progress in experimental models to investigate the in vivo and in vitro antidiabetic activity of drugs

Diabetes mellitus is one of the world's most prevalent and complex metabolic disorders, and it is a rapidly growing global public health issue. It is characterized by hyperglycemia, a condition involving a high blood glucose level brought on by deficiencies in insulin secretion, decreased activity of insulin, or both. Prolonged effects of diabetes include cardiovascular problems, retinopathy, neuropathy, nephropathy, and vascular alterations in both macro- and micro-blood vessels. In vivo and in vitro models have always been important for investigating and characterizing disease pathogenesis, identifying targets, and reviewing novel treatment options and medications. Fully understanding these models is crucial for the researchers so this review summarizes the different experimental in vivo and in vitro model options used to study diabetes and its consequences. The most popular in vivo studies involves the small animal models, such as rodent models, chemically induced diabetogens like streptozotocin and alloxan, and the possibility of deleting or overexpressing a specific gene by knockout and transgenic technologies on these animals. Other models include virally induced models, diet/nutrition induced diabetic animals, surgically induced models or pancreatectomy models, and non-obese models. Large animals or non-rodent models like porcine (pig), canine (dog), nonhuman primate, and Zebrafish models are also outlined. The in vitro models discussed are murine and human beta-cell lines and pancreatic islets, human stem cells, and organoid cultures. The other enzymatic in vitro tests to assess diabetes include assay of amylase inhibition and inhibition of α-glucosidase activity.

The regulatory role of miRNA and lncRNA on autophagy in diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes that causes glomerular sclerosis and end-stage renal disease, leading to ascending morbidity and mortality in diabetic patients. Excessive accumulation of aberrantly modified proteins or damaged organelles, such as advanced glycation end-products, dysfunctional mitochondria, and inflammasomes is associated with the pathogenesis of DN. As one of the main degradation pathways, autophagy recycles toxic substances to maintain cellular homeostasis and autophagy dysregulation plays a crucial role in DN progression. MicroRNA (miRNA) and long non-coding RNA (lncRNA) are non-coding RNA (ncRNA) molecules that regulate gene expression and have been implicated in both physiological and pathological conditions. Recent studies have revealed that autophagy-regulating miRNA and lncRNA have been involved in pathological processes of DN, including renal cell injury, mitochondrial dysfunction, inflammation, and renal fibrosis. This review summarizes the role of autophagy in DN and emphasizes the modulation of miRNA and lncRNA on autophagy during disease progression, for the development of promising interventions by targeting these ncRNAs in this disease.

Current advancement in the preclinical models used for the assessment of diabetic neuropathy

Diabetic neuropathy is one of the prevalent and debilitating microvascular complications of diabetes mellitus, affecting a significant portion of the global population. Relational preclinical animal models are essential to understand its pathophysiology and develop effective treatments. This abstract provides an overview of current knowledge and advancements in such models. Various animal models have been developed to mimic the multifaceted aspects of human diabetic neuropathy, including both type 1 and type 2 diabetes. These models involve rodents (rats and mice) and larger animals like rabbits and dogs. Induction of diabetic neuropathy in these models is achieved through chemical, genetic, or dietary interventions, such as diabetogenic agents, genetic modifications, or high-fat diets. Preclinical animal models have greatly contributed to studying the intricate molecular and cellular mechanisms underlying diabetic neuropathy. They have shed light on hyperglycemia-induced oxidative stress, neuroinflammation, mitochondrial dysfunction, and altered neurotrophic factor signaling. Additionally, these models have allowed for the investigation of morphological changes, functional alterations, and behavioral manifestations associated with diabetic neuropathy. These models have also been crucial for evaluating the efficacy and safety of potential therapeutic interventions. Novel pharmacological agents, gene therapies, stem cell-based approaches, exercise, dietary modifications, and neurostimulation techniques have been tested using these models. However, limitations and challenges remain, including physiological differences between humans and animals, complex neuropathy phenotypes, and the need for translational validation. In conclusion, preclinical animal models have played a vital role in advancing our understanding and management of diabetic neuropathy. They have enhanced our knowledge of disease mechanisms, facilitated the development of novel treatments, and provided a platform for translational research. Ongoing efforts to refine and validate these models are crucial for future treatment developments for this debilitating condition.

Current updates on metabolites and its interlinked pathways as biomarkers for diabetic kidney disease: A systematic review

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes mellitus (DM) that poses a serious risk as it can lead to end-stage renal disease (ESRD). DKD is linked to changes in the diversity, composition, and functionality of the microbiota present in the gastrointestinal tract. The interplay between the gut microbiota and the host organism is primarily facilitated by metabolites generated by microbial metabolic processes from both dietary substrates and endogenous host compounds. The production of numerous metabolites by the gut microbiota is a crucial factor in the pathogenesis of DKD. However, a comprehensive understanding of the precise mechanisms by which gut microbiota and its metabolites contribute to the onset and progression of DKD remains incomplete. This review will provide a summary of the current scenario of metabolites in DKD and the impact of these metabolites on DKD progression. We will discuss in detail the primary and gut-derived metabolites in DKD, and the mechanisms of the metabolites involved in DKD progression. Further, we will address the importance of metabolomics in helping identify potential DKD markers. Furthermore, the possible therapeutic interventions and research gaps will be highlighted.

Plasma thrombin-activatable fibrinolysis inhibitor and the 1040C/T polymorphism are risk factors for diabetic kidney disease in Chinese patients with type 2 diabetes

Background

Inflammatory and hemostatic disorders in diabetic microangiopathy (DMA) can be linked to thrombin-activatable fibrinolysis inhibitor (TAFI) and its own gene polymorphisms. Thus, the study aimed to investigate the associations of plasma TAFI and gene polymorphisms with DMA in Chinese patients with type 2 diabetes (T2D).

Methods

Plasma TAFI of 223 patients with T2D was measured, and the genotypes and alleles of the 1040C/T, 438G/A, and 505G/A polymorphisms of the TAFI gene were analyzed. A ROC curve was constructed to evaluate the identifying power of TAFI between patients with T2D and DMA, and logistic regression analysis was used to observe the correlation of plasma TAFI and gene polymorphisms with the risk for DMA.

Results

Plasma TAFI was higher in patients with DMA than in patients with only T2D (p < 0.05). TAFI exhibited the largest area under ROC in identifying diabetic kidney disease (DKD) from only T2D (0.763, 95% CI [0.674-0.853], p < 0.01), and adjusted multivariate analysis showed a high odds ratio (OR: 15.72, 95% CI [4.573-53.987], p < 0.001) for DKD. Higher frequencies of the CT genotype and T allele of the 1040C/T polymorphism were found in DKD compared with only T2D (respectively p < 0.05), and the CT genotype exhibited a high OR (1.623, 95% CI [1.173-2.710], p < 0.05) for DKD. DKD patients with the CT genotype had higher plasma TAFI levels, while T2D and DKD patients with CC/TT genotypes had lower plasma TAFI levels.

Conclusion

Plasma TAFI and the CT genotype and T allele of the 1040C/T polymorphism are independent risk factors for DKD in Chinese T2D patients.

Animal Models of Human Disease

The use of animal models of human disease is critical for furthering our understanding of disease mechanisms, for the discovery of novel targets for treatment, and for translational research. This Special Topic entitled "Animal Models of Human Disease" aimed to collect state-of-the-art primary research studies and review articles from international experts and leading groups using animal models to study human diseases. Submissions were welcomed on a wide range of animal models and pathologies, including infectious disease, acute injury, regeneration, cancer, autoimmunity, degenerative and chronic disease. Seven participating MDPI journals supported the Special Topic, namely: Biomedicines, Cells, Current Issues in Molecular Biology, Diagnostics, Genes, the International Journal of Molecular Sciences, and the International Journal of Translational Medicine. In total, 46 papers were published in this Special Topic, with 37 full length original research papers, 2 research communications and 7 reviews. These contributions cover a wide range of clinically relevant, translatable, and comparative animal models, as well as furthering understanding of fundamental sciences, covering topics on physiological processes, on degenerative, inflammatory, infectious, autoimmune, neurological, metabolic, heamatological, hormonal and mitochondrial disorders, developmental processes and diseases, cardiology, cancer, trauma, stress, and ageing.

Protective effects of GuanXinNing tablet (GXNT) on diabetic encephalopathy in zucker diabetic obesity (ZDF) rats

BACKGROUND

Diabetic encephalopathy (DE) is a complication of diabetes that leads to cognitive and behavioral decline. Utilizing safe and effective complementary and alternative medications for its management is a wise choice. Previous studies have shown that GuanXinNing Tablet (GXNT), an oral preparation primarily derived from two Chinese herbs, Salvia miltiorrhiza Bge. and Ligusticum chuanxiong Hort., exerts a beneficial neuroprotective effect. In this study, we explored the protective effects of GXNT on DE in male Zucker diabetic fatty (ZDF) rats induced by a high-fat diet, aiming to ascertain its significance and potential mechanisms.

METHODS

ZDF rats were induced to develop type 2 diabetes (T2DM) with DE by a high-fat diet and treated with GXNT for 8 weeks until they were 20 weeks old. Throughout the experiment, the animals' vital parameters, such as body weight, were continuously monitored. Cognitive function was evaluated using the Y maze test. Biochemical kits were employed to analyze blood glucose, lipids, and vascular endothelial-related factors. Cerebrovascular lesions were assessed using magnetic resonance angiography (MRA) imaging. Brain lesions were evaluated using hematoxylin and eosin (H&E) staining and ultrastructure observation. IgG and albumin (ALB) leakage were detected using immunofluorescence.

RESULTS

GXNT demonstrated an enhancement in the overall well-being of the animals. It notably improved cognitive and behavioral abilities, as demonstrated by extended retention time in the novel heterogeneous arm during the Y-maze test. GXNT effectively regulated glucose and lipid metabolism, reducing fasting and postprandial blood glucose, glycated hemoglobin (HbA1c), and total cholesterol (TC) levels. Additionally, it exhibited a protective effect on the vascular endothelium by reducing the serum TXB2/PGI2 ratio while elevating NO and PGI2 levels. Moreover, GXNT ameliorated stenosis and occlusion in cerebral vessel branches, increased the number of microvessels and neurons around the hippocampus, and improved microvascular occlusion in the cerebral cortex, along with addressing perivascular cell abnormalities. Immunofluorescence staining showed a decrease in the fluorescence intensity of IgG and ALB in the cerebral cortex.

CONCLUSIONS

GXNT demonstrated a highly satisfactory protective effect on DE in ZDF rats. Its mechanism of action could be based on the regulation of glucolipid metabolism and its protective effect on the vascular endothelium.

Ultra-high performance liquid chromatography coupled to tandem mass spectrometry-based metabolomics study of diabetic distal symmetric polyneuropathy

AIMS/INTRODUCTION

Distal symmetric polyneuropathy (DSPN) is a common complication of type 2 diabetes mellitus, but the underlining mechanisms have not yet been elucidated. The current study was designed to screen the feature metabolites classified as potential biomarkers, and to provide deeper insights into the underlying distinctive metabolic changes during disease progression.

MATERIALS AND METHODS

Plasma metabolite profiles were obtained by the ultra-high liquid chromatography coupled to tandem mass spectrometry method from healthy control participants, patients with type 2 diabetes mellitus and patients with DSPN. Potential biomarkers were selected through comprehensive analysis of statistically significant differences between groups.

RESULTS

Overall, 938 metabolites were identified. Among them, 12 metabolites (dimethylarginine, N6-acetyllysine, N-acetylhistidine, N,N,N-trimethyl-alanylproline betaine, cysteine, 7-methylguanine, N6-carbamoylthreonyladenosine, pseudouridine, 5-methylthioadenosine, N2,N2-dimethylguanosine, aconitate and C-glycosyl tryptophan) were identified as the specific biomarkers. The content of 12 metabolites were significantly higher in the DSPN group compared with the other two groups. Additionally, they showed good performance to discriminate the DSPN state. Correlation analyses showed that the levels of 12 metabolites might be more closely related to the glucose metabolic changes, followed by the levels of lipid metabolism.

CONCLUSIONS

The finding of the 12 signature metabolites might provide a novel perspective for the pathogenesis of DSPN. Future studies are required to test this observation further.

Vascular endothelial growth factor levels in diabetic peripheral neuropathy: a systematic review and meta-analysis

Objective

Vascular endothelial growth factors (VEGFs, including VEGF-A, VEGF-B, VEGF-C, VEGF-D and PLGF) have important roles in the development and function of the peripheral nervous system. Studies have confirmed that VEGFs, especially VEGF-A (so called VEGF) may be associated with the diabetic peripheral neuropathy (DPN) process. However, different studies have shown inconsistent levels of VEGFs in DPN patients. Therefore, we conducted this meta-analysis to evaluate the relationship between cycling levels of VEGFs and DPN.

Methods

This study searched 7 databases, including PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), VIP Database, WanFang Database, and Chinese Biomedical Literature (CBM), to find the target researches. The random effects model was used to calculate the overall effect.

Results

14 studies with 1983 participants were included, among which 13 studies were about VEGF and 1 was VEGF-B, so only the effects of VEGF were pooled. The result showed that there were obviously increased VEGF levels in DPN patients compared with diabetic patients without DPN (SMD:2.12[1.34, 2.90], p<0.00001) and healthy people (SMD:3.50[2.24, 4.75], p<0.00001). In addition, increased circulating VEGF levels were not associated with an increased risk of DPN (OR:1.02[0.99, 1.05], p<0.00001).

Conclusion

Compared with healthy people and diabetic patients without DPN, VEGF content in the peripheral blood of DPN patients is increased, but current evidence does not support the correlation between VEGF levels and the risk of DPN. This suggests that VEGF may play a role in the pathogenesis and repairment of DPN.

Piceatannol promotes neuroprotection by inducing mitophagy and mitobiogenesis in the experimental diabetic peripheral neuropathy and hyperglycemia-induced neurotoxicity

Piceatannol (PCN), a SIRT1 activator, regulates multiple oxidative stress mechanism and has anti-inflammatory potential in various inflammatory conditions. However, its role in Diabetic insulted peripheral neuropathy (DN) remains unknown. Oxidative stress and mitochondrial dysfunction are major contributing factors to DN. Myriad studies have proven that sirtuin1 (SIRT1) stimulation convalesce nerve functions by activating mitochondrial functions like mitochondrial biogenesis and mitophagy. Diabetic neuropathy (DN) was provoked by injecting streptozotocin (STZ) at a dose of 55 mg/kg, i.p to male Sprague Dawley (SD) rats. Mechanical, thermal hyperalgesia was evaluated by using water immersion, Vonfrey Aesthesiometer, and Randall Sellito Calipers. Motor, sensory nerve conduction velocity was measured using Power Lab 4sp system whereas The Laser Doppler system was used to evaluate nerve blood flow. To induce hyperglycemia for the in vitro investigations, high glucose (HG) (30 mM) conditions were applied to Neuro2a cells. At doses of 5 and 10 µM, PCN was examined for its role in SIRT1 and Nrf2 activation. HG-induced N2A cells, reactive oxygen exposure, mitochondrial superoxides and mitochondrial membrane potentials were restored by PCN exposure, and their neurite outgrowth was enhanced. Peroxisome proliferator activated receptor-gamma coactivator-1α (PGC-1α) directed mitochondrial biogenesis was induced by increased SIRT1 activation by piceatannol. SIRT1 activation also enhanced Nrf2-mediated antioxidant signalling. Our study results inferred that PCN administration can counteract the decline in mitochondrial function and antioxidant activity in diabetic rats and HG-exposed N2A cells by increasing the SIRT1 and Nrf2 activities.

Moderate-Intensity Exercise Maintains Redox Homeostasis for Cardiovascular Health

It is well known that exercise is beneficial for cardiovascular health. Oxidative stress is the common pathological basis of many cardiovascular diseases. The overproduction of free radicals, both reactive oxygen species and reactive nitrogen species, can lead to redox imbalance and exacerbate oxidative damage to the cardiovascular system. Maintaining redox homeostasis and enhancing anti-oxidative capacity are critical mechanisms by which exercise protects against cardiovascular diseases. Moderate-intensity exercise is an effective means to maintain cardiovascular redox homeostasis. Moderate-intensity exercise reduces the risk of cardiovascular disease by improving mitochondrial function and anti-oxidative capacity. It also attenuates adverse cardiac remodeling and enhances cardiac function. This paper reviews the primary mechanisms of moderate-intensity exercise-mediated redox homeostasis in the cardiovascular system. Exploring the role of exercise-mediated redox homeostasis in the cardiovascular system is of great significance to the prevention and treatment of cardiovascular diseases.

Chrysin improves diabetic nephropathy by regulating the AMPK-mediated lipid metabolism in HFD/STZ-induced DN mice

Diabetic nephropathy (DN) is a highly prevalent and severe diabetic complication. It is urgent to explore high efficiency and minor side effects therapy for DN. Chrysin is a natural flavonoid with various biological activities found in honey and propolis, and has considerable potential to improve DN. The study was designed to explore the effects and the specific underlying mechanism of chrysin for DN in high-fat-diet (HFD) and streptozotocin (STZ) induced DN mice. Firstly, the study revealed that chrysin effectively improved obesity, insulin resistance (IR), renal function, and pathological injury in DN mice. Secondly, the study found that chrysin improved the key indices and markers of lipid accumulation, oxidative stress, and inflammation which are closely related to the development or progression of DN. Moreover, chrysin markedly modulated lipid metabolism by regulating Adenosine 5' monophosphate-activated protein kinase (AMPK) and essential downstream proteins. Furthermore, AMPK inhibitor (Dorsomorphin) intervention partially suppressed the positive effects of chrysin on all testing indicators, indicating that activated AMPK is crucial for chrysin action on DN. The present study demonstrated that chrysin may improve DN by regulating lipid metabolism, and activated AMPK plays a critical role in the regulation of chrysin. PRACTICAL APPLICATIONS: The study verified the positive effects of chrysin on obesity, insulin resistance, kidney injury, renal function, lipid accumulation, inflammation, and oxidative stress, which are closely related to the development or progression of diabetic nephropathy (DN). Moreover, we explored that chrysin improves DN by regulating AMPK-mediated lipid metabolism. Furthermore, the AMPK inhibitor was used to confirm that activated AMPK plays a critical role in the effects of chrysin. These results could offer a full explanation and a potential option for adjuvant therapy of DN diabetes with chrysin.

Activation of SIRT1 by silibinin improved mitochondrial health and alleviated the oxidative damage in experimental diabetic neuropathy and high glucose-mediated neurotoxicity

BACKGROUND

Silibinin (SBN), a sirtuin 1 (SIRT1) activator, has been evaluated for its anti-inflammatory activity in many inflammatory diseases. However, its role in diabetes-induced peripheral neuropathy (DPN) remains unknown. The SIRT1 activation convalesces nerve functions by improving mitochondrial biogenesis and mitophagy.

METHODS

DPN was induced by streptozotocin (STZ) at a dose of 55 mg/kg, i.p. in the male SD rats whereas neurotoxicity was induced in Neuro2A cells by 30 mM (high glucose) glucose. Neurobehavioural (nerve conduction velocity and nerve blood flow) western blot, immunohistochemistry, and immunocytochemistry were performed to evaluate the protein expression and their cellular localisation.

RESULTS

Two-week SBN treatment improved neurobehavioural symptoms, SIRT1, PGC-1α, and TFAM expression in the sciatic nerve and HG insulted N2A cells. It has also maintained the mitophagy by up-regulating PARL, PINK1, PGAM5, LC3 level and provided antioxidant defence by upregulating Nrf2.

CONCLUSION

SBN has shown neuroprotective potential in DPN through SIRT1 activation and antioxidant mechanism.

Pharmacological evaluation of Thuja occidentalis for the attenuation of neuropathy via AGEs and TNF-α inhibition in diabetic neuropathic rats

When diabetes neuropathy occurs, the oxidative stress caused by chronic hyperglycemia may result in chronic neuronal damage. To mitigate the effects of hyperglycemia-induced neuronal damage, it may be beneficial to address oxidative stress and inflammation in the body. The current study evaluated the neuroprotective efficacy of Thuja occidentalis in streptozotocin (STZ)-nicotinamide (NAD)-induced diabetic neuropathy in male Wistar rats. A single dose of STZ (65 mg/kg, i.p.) was used to induce diabetic neuropathy in Wistar rats. Serum insulin, glucose, hyperalgesia, oxidative stress, inflammatory markers, and histopathology of the sciatic nerve were evaluated for neuropathy. Wistar rats were treated with varying doses of hydroalcoholic extracts of Thuja occidentalis (HAETO) and gabapentin for 30 days. Thuja occidentalis considerably corrected the levels of inflammatory markers and oxidative stress caused by hyperglycemia; also, it led to the restoration of neuronal functions, indicating that it is effective in treating diabetic neuropathy. Furthermore, the molecular docking of thujone at the active pockets of various inflammatory mediators (IL-1β, IL-6, TGF-β1, and TNF-α) has shown good interactions with critical amino acid residues. These findings indicate that the hydroalcoholic extract of Thuja occidentalis effectively inhibits the development of diabetic neuropathy. The hypoglycemic, antioxidant, anti-hyperalgesia, and anti-inflammatory properties of Thuja occidentalis are thought to be responsible for the neuroprotective benefit.

The Problem of Wound Healing in Diabetes—From Molecular Pathways to the Design of an Animal Model

Chronic wounds are becoming an increasingly common clinical problem due to an aging population and an increased incidence of diabetes, atherosclerosis, and venous insufficiency, which are the conditions that impair and delay the healing process. Patients with diabetes constitute a group of subjects in whom the healing process is particularly prolonged regardless of its initial etiology. Circulatory dysfunction, both at the microvascular and macrovascular levels, is a leading factor in delaying or precluding wound healing in diabetes. The prolonged period of wound healing increases the risk of complications such as the development of infection, including sepsis and even amputation. Currently, many substances applied topically or systemically are supposed to accelerate the process of wound regeneration and finally wound closure. The role of clinical trials and preclinical studies, including research based on animal models, is to create safe medicinal products and ensure the fastest possible healing. To achieve this goal and minimize the wide-ranging burdens associated with conducting clinical trials, a correct animal model is needed to replicate the wound conditions in patients with diabetes as closely as possible. The aim of the paper is to summarize the most important molecular pathways which are impaired in the hyperglycemic state in the context of designing an animal model of diabetic chronic wounds. The authors focus on research optimization, including economic aspects and model reproducibility, as well as the ethical dimension of minimizing the suffering of research subjects according to the 3 Rs principle (Replacement, Reduction, Refinement).