Leptin- and leptin receptor-deficient rodent models: relevance for human type 2 diabetes

Proteomics Analysis Provides Insights into the Role of Lipid Metabolism in T2DM-Related Sarcopenia

Sarcopenia has been recognized as an emerging complication of type 2 diabetes mellitus (T2DM). Currently, the pathogenesis of T2DM-related sarcopenia remains unclear. The aim of this study was to investigate the molecular mechanisms and potential therapeutic targets for T2DM-related sarcopenia. In this study, a T2DM-related sarcopenia mouse model was established using db/db mice. Proteins extracted from the gastrocnemius muscles of db/db mice and littermate control db/m mice were analyzed by a 4D label-free quantitative proteomics approach. A total of 131 upregulated and 68 downregulated proteins were identified as differentially expressed proteins (DEPs). Bioinformatics analysis revealed that DEPs were significantly enriched in lipid metabolism. Protein-protein interaction network analysis revealed that six hub proteins, including ACOX1, CPT2, ECI2, ACADVL, ACADL, and ECH1, were involved in the fatty acid oxidation. The hub protein-transcription factor-miRNA network was also constructed using the NetworkAnalyst tool. Finally, the hub proteins were validated by Western blotting and immunohistochemistry and further confirmed to be significantly negatively correlated with muscle mass and grip strength. Our study suggested that lipid metabolism, especially excessive fatty acid oxidation, may be a crucial contributor to the progression of T2DM-related sarcopenia and a common cause of the inter-relationship between T2DM and sarcopenia. Targeting lipid metabolism may be a promising therapeutic strategy for T2DM-related sarcopenia.

Secreted chemokines reveal diverse inflammatory and degenerative processes in the intervertebral disc of the STZ-HFD mouse model of Type 2 diabetes

The chronic inflammation present in type 2 diabetes causes many chronic inflammatory comorbidities, including cardiovascular, renal, and neuropathic complications. Type 2 diabetes is also associated with a number of spinal pathologies, including intervertebral disc (IVD) degeneration and chronic neck and back pain. Although confounding factors such as obesity are thought to increase the loads to the musculoskeletal system and subsequent degeneration, studies have shown that even after adjusting age, body mass index, and genetics (e.g. twins), patients with diabetes suffer from disproportionately more IVD degeneration and back pain. Yet the tissue-specific responses of the IVD during diabetes remains relatively unknown. We hypothesize that chronic diabetes fosters a proinflammatory microenvironment within the IVD that accelerates degeneration and increases susceptibility to painful disorders. To test this hypothesis, we evaluated two commonly used mouse models of diabetes - the leptin-receptor deficient mouse (db/db) and the chronic high-fat diet in mice with impaired beta-cell function (STZ-HFD). The db/db is a genetic model that spontaneous develop diabetes through hyperphagia, while the STZ-HFD mouse first exhibits rapid obesity development under HFD and pronounced insulin resistance following streptozotocin administration. Both animal models were allowed to develop sustained diabetes for at least twelve weeks, as defined by elevated hemoglobin A1C, hyperglycemia, and glucose intolerance. Following the twelve-week period, the IVDs were extracted in quantified in several measures including tissue-specific secreted cytokines, viscoelastic mechanical behavior, structural composition, and histopathologic degeneration. Although there were no differences in mechanical function or the overall structure of the IVD, the STZ-HFD IVDs were more degenerated. More notably, the STZ-HFD model shows a significantly higher fold increase for eight cytokines: CXCL2, CCL2, CCL3, CCL4, CCL12 (monocyte/macrophage associated), IL-2, CXCL9 (T-cell associated), and CCL5 (pleiotropic). Correlative network analyses revealed that the expression of cytokines differentially regulated between the db/db and the STZ-HFD models. Moreover, the STZ-HFD contained a fragmented and modular cytokine network, indicating greater complexities in the regulatory network. Taken together, the STZ-HFD model of type 2 diabetes may better recapitulate the complexities of the chronic inflammatory processes in the IVD during diabetes.

Increased Permeability of the Blood-Brain Barrier in a Diabetic Mouse Model (Leprdb/db Mice)

Type 2 Diabetes Mellitus (T2DM) is linked to multiple complications, including cognitive impairment, and the prevalence of memory-related neurodegenerative diseases is higher in T2DM patients. One possible theory is the alteration of the microvascular and macrovascular environment of the blood-brain barrier (BBB). In this study, we employed different approaches, including RT-PCR, functional pharmacokinetic studies using sodium fluorescein (NaFL), and confocal microscopy, to characterize the functional and molecular integrity of the BBB in a T2DM animal model, leptin receptor-deficient mutant mice (Leprdb/db mice). As a result, VCAM-1, ICAM-1, MMP-9, and S100b (BBB-related markers) dysregulation was observed in the Leprdb/db animal model compared to littermate wild-type mice. The brain concentration of sodium fluorescein (NaFL) increased significantly in Leprdb/db untreated mice compared to insulin-treated mice. Therefore, the permeability of NaFL was higher in Leprdb/db control mice than in all remaining groups. Identifying the factors that increase the BBB in Leprdb/db mice will provide a better understanding of the BBB microvasculature and present previously undescribed findings of T2DM-related brain illnesses, filling knowledge gaps in this emerging field of research.

The Obesogenic Gut Microbiota as a Crucial Factor Defining the Depletion of Predicted Enzyme Abundance for Vitamin B12 Synthesis in the Mouse Intestine

Currently, obesity is a critical global public health burden. Numerous studies have demonstrated the regulation of the pathogenesis of obesity and metabolic abnormalities by the gut microbiota and microbial factors; however, their involvement in the various degrees of obesity is not yet well understood. Previously, obesity has been shown to be associated with decreased levels of vitamin B12. Considering exclusive microbial production of vitamin B12, we hypothesized that a decrease in cobalamin levels in obese individuals may be at least partially caused by its depleted production in the intestinal tract by the commensal microbiota. In the present study, our aim was to estimate the abundance of enzymes and metabolic pathways for vitamin B12 synthesis in the gut microbiota of mouse models of alimentary and genetically determined obesity, to evaluate the contribution of the obesogenic microbiome to vitamin B12 synthesis in the gut. We have defined a significantly lower predicted abundance of enzymes and metabolic pathways for vitamin B12 biosynthesis in obese mice compared to non-obese mice, wherein enzyme depletion was more pronounced in lepr(-/-) (db/db) mice, which developed severe obesity. The predicted abundance of enzymes involved in cobalamin synthesis is strongly correlated with the representation of several microbes in high-fat diet-fed mice, while there were almost no correlations in db/db mice. Therefore, the degree of obesity and the composition of the correspondent microbiota are the main contributors to the representation of genes and pathways for cobalamin biosynthesis in the mouse gut.

(-)-Gallocatechin Gallate Mitigates Metabolic Syndrome-Associated Diabetic Nephropathy in db/db Mice

Metabolic syndrome (MetS) significantly predisposes individuals to diabetes and is a prognostic factor for the progression of diabetic nephropathy (DN). This study aimed to evaluate the efficacy of (-)-gallocatechin gallate (GCG) in alleviating signs of MetS-associated DN in db/db mice. We administered GCG and monitored its effects on several metabolic parameters, including food and water intake, urinary output, blood glucose levels, glucose and insulin homeostasis, lipid profiles, blood pressure, and renal function biomarkers. The main findings indicated that GCG intervention led to marked improvements in these metabolic indicators and renal function, signifying its potential in managing MetS and DN. Furthermore, transcriptome analysis revealed substantial modifications in gene expression, notably the downregulation of pro-inflammatory genes such as S100a8, S100a9, Cd44, Socs3, Mmp3, Mmp9, Nlrp3, IL-1β, Osm, Ptgs2, and Lcn2 and the upregulation of the anti-oxidative gene Gstm3. These genetic alterations suggest significant effects on pathways related to inflammation and oxidative stress. In conclusion, GCG demonstrates therapeutic efficacy for MetS-associated DN, mitigating metabolic disturbances and enhancing renal health by modulating inflammatory and oxidative responses.

Physiological and psychological determinants of long-term diet-induced type 2 diabetes (T2DM) remission: A narrative review

Type 2 diabetes mellitus (T2DM) is a highly prevalent metabolic disease, causing a heavy burden on healthcare systems worldwide, with related complications and anti-diabetes drug prescriptions. Recently, it was demonstrated that T2DM can be put into remission via significant weight loss using low-carbohydrate diets (LCDs) and very low-energy diets (VLEDs) in individuals with overweight and obesity. Clinical trials demonstrated remission rates of 25-77%, and metabolic improvements such as improved blood lipid profile and blood pressure were observed. In contrast, clinical trials showed that remission rate declines with time, concurrent with weight gain, or diminished weight loss. This review aims to discuss existing literature regarding underlying determinants of long-term remission of T2DM including metabolic adaptations to weight loss (e.g., role of gastrointestinal hormones), type of dietary intervention (i.e., LCDs or VLEDs), maintaining beta (β)-cell function, early glycemic control, and psychosocial factors. This narrative review is significant because determining the factors that are associated with challenges in maintaining long-term remission may help in designing sustainable interventions for type 2 diabetes remission.

3D culture models to study pathophysiology of steatotic liver disease

Steatotic liver disease (SLD) refers to a spectrum of diseases caused by hepatic lipid accumulation. SLD has emerged as the leading cause of chronic liver disease worldwide. Despite this burden and many years, understanding the pathophysiology of this disease is challenging due to the inaccessibility to human liver specimens. Therefore, cell-based in vitro systems are widely used as models to investigate the pathophysiology of SLD. Culturing hepatic cells in monolayers causes the loss of their hepatocyte-specific phenotype and, consequently, tissue-specific function and architecture. Hence, three-dimensional (3D) culture models allow cells to mimic the in vivo microenvironment and spatial organization of the liver unit. The utilization of 3D in vitro models minimizes the drawbacks of two-dimensional (2D) cultures and aligns with the 3Rs principles to alleviate the number of in vivo experiments. This article provides an overview of liver 3D models highlighting advantages and limitations, and culminates by discussing their applications in pharmaceutical and biomedical research.

The signaling pathways in obesity-related complications

Obesity, a rapidly expanding epidemic worldwide, is known to exacerbate many medical conditions, making it a significant factor in multiple diseases and their associated complications. This threatening epidemic is linked to various harmful conditions such as type 2 diabetes mellitus, hypertension, metabolic dysfunction-associated steatotic liver disease, polycystic ovary syndrome, cardiovascular diseases (CVDs), dyslipidemia, and cancer. The rise in urbanization and sedentary lifestyles creates an environment that fosters obesity, leading to both psychosocial and medical complications. To identify individuals at risk and ensure timely treatment, it is crucial to have a better understanding of the pathophysiology of obesity and its comorbidities. This comprehensive review highlights the relationship between obesity and obesity-associated complications, including type 2 diabetes, hypertension, (CVDs), dyslipidemia, polycystic ovary syndrome, metabolic dysfunction-associated steatotic liver disease, gastrointestinal complications, and obstructive sleep apnea. It also explores the potential mechanisms underlying these associations. A thorough analysis of the interplay between obesity and its associated complications is vital in developing effective therapeutic strategies to combat the exponential increase in global obesity rates and mitigate the deadly consequences of this polygenic condition.

Possible retinotoxicity of long-term vardenafil treatment

Phosphodiesterase (PDE) inhibitors - such as vardenafil - are used primarily for treating erectile dysfunction via increasing cyclic guanosine monophosphate (cGMP) levels. Recent studies have also demonstrated their significant cardioprotective effects in several diseases, including diabetes, upon long-term, continuous application. However, PDE inhibitors are not specific for PDE5 and also inhibit the retinal isoform. A sustained rise in cGMP in photoreceptors is known to be toxic; therefore, we hypothesized that long-term vardenafil treatment might result in retinotoxicity. The hypothesis was tested in a clinically relevant animal model of type 2 diabetes mellitus. Histological experiments were performed on lean and diabetic Zucker Diabetic Fatty rats. Half of the animals were treated with vardenafil for six months, and the retinal effects were evaluated. Vardenafil treatment alleviated rod outer segment degeneration but decreased rod numbers in some positions and induced changes in the interphotoreceptor matrix, even in control animals. Vardenafil treatment decreased total retinal thickness in the control and diabetic groups and reduced the number of nuclei in the outer nuclear layer. Müller cell activation was detectable even in the vardenafil-treated control animals, and vardenafil did not improve gliosis in the diabetic group. Vardenafil-treated animals showed complex retinal alterations with improvements in some parameters while deterioration in others. Our results point towards the retinotoxicity of vardenafil, even without diabetes, which raises doubts about the retinal safety of long-term continuous vardenafil administration. This effect needs to be considered when approving PDE inhibitors for alternative indications.

Mogroside Ⅴ Inhibits M1 Polarization and Inflammation of Diabetic Mouse Macrophages via p38 MAPK/NF-Κb Signaling Pathway

BACKGROUND

Mogroside V (MV) has anti-inflammatory properties. However, its impact on macrophage polarization under diabetic condition is yet unclear. This study aimed to investigate effects and underlying mechanisms of MV on inflammatory response and M1 polarization of bone marrow-derived macrophages (BMDMs) from diabetic mice.

METHODS

BMDMs were isolated from normal and diabetic C57BL/6 mice. LPS and IFN-γwere used to produce M1-polarized BMDMs. MV treatment was administered throughout the M1 polarization process with or without SB203580 or PDTC. Surface markers CD11b, F4/80 and CD86 of macrophages were identified using flow cytometry or immunofluorescence staining. Inflammatory cytokines IL-1β and IL-6 and phosphorylation levels of p65 and p38 were examined by western blot.

RESULTS

High glucose increased proportion of CD11b+F4/80+CD86+ cells, protein levels of inflammatory cytokines IL-1β and IL-6 and phosphorylation levels of p65 and p38 in LPS+IFN-γ-induced BMDMs, while they were decreased upon MV treatment. Additionally, these effects were further downregulated when MV was co-added with SB203580 or PDTC.

CONCLUSIONS

MV suppressed M1 macrophage polarization and inflammatory response, which was partially through NF-κB and p38 MAPK in LPS+IFN-γ induced BMDMs under high glucose condition, implying the potential of MV in treatment for inflammatory complications of diabetes.

Induction of diabetes by Tacrolimus in a phenotypic model of obesity and metabolic syndrome

Introduction

The pathogenesis of Post-Transplant Diabetes Mellitus (PTDM) is complex and multifactorial and it resembles that of Type-2 Diabetes Mellitus (T2DM). One risk factor specific to PTDM differentiates both entities: the use of immunosuppressive therapy. Specifically, Tacrolimus interacts with obesity and insulin resistance (IR) in accelerating the onset of PTDM. In a genotypic model of IR, the obese Zucker rats, Tacrolimus is highly diabetogenic by promoting the same changes in beta-cell already modified by IR. Nevertheless, genotypic animal models have their limitations and may not resemble the real pathophysiology of diabetes. In this study, we have evaluated the interaction between beta-cell damage and Tacrolimus in a non-genotypic animal model of obesity and metabolic syndrome.

Methods

Sprague Dawley rats were fed a high-fat enriched diet during 45 days to induce obesity and metabolic dysregulation. On top of this established obesity, the administration of Tacrolimus (1mg/kg/day) during 15 days induced severe hyperglycaemia and changes in morphological and structural characteristics of the pancreas.

Results

Obese animals administered with Tacrolimus showed increased size of islets of Langerhans and reduced beta-cell proliferation without changes in apoptosis. There were also changes in beta-cell nuclear factors such as a decrease in nuclear expression of MafA and a nuclear overexpression of FoxO1A, PDX-1 and NeuroD1. These animals also showed increased levels of pancreatic insulin and glucagon.

Discussion

This model could be evidence of the relationship between the T2DM and PTDM physiopathology and, eventually, the model may be instrumental to study the pathogenesis of T2DM.

Differential sex-dependent susceptibility to diastolic dysfunction and arrhythmia in cardiomyocytes from obese diabetic HFpEF model

AIM

Sex-differences in heart failure with preserved ejection fraction (HFpEF) are important, but key mechanisms involved are incompletely understood. While animal models can inform about sex-dependent cellular and molecular changes, many previous preclinical HFpEF models have failed to recapitulate sex-dependent characteristics of human HFpEF. We tested for sex-differences in HFpEF using a two-hit mouse model (leptin receptor-deficient db/db mice plus aldosterone infusion for 4 weeks; db/db+Aldo).

METHODS AND RESULTS

We performed echocardiography, electrophysiology, intracellular Ca2+ imaging, and protein analysis. Female HFpEF mice exhibited more severe diastolic dysfunction in line with increased titin N2B isoform expression and PEVK element phosphorylation, and reduced troponin-I phosphorylation. Female HFpEF mice had lower BNP levels than males despite similar comorbidity burden (obesity, diabetes) and cardiac hypertrophy in both sexes. Male HFpEF mice were more susceptible to cardiac alternans. Male HFpEF cardiomyocytes (versus female) exhibited higher diastolic [Ca2+], slower Ca2+ transient decay, reduced L-type Ca2+ current, more pronounced enhancement of the late Na+ current, and increased short-term variability of action potential duration (APD). However, male and female HFpEF myocytes showed similar downregulation of inward rectifier and transient outward K+ currents, APD prolongation, and frequency of delayed afterdepolarizations. Inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII) reversed all pathological APD changes in HFpEF in both sexes, and empagliflozin pretreatment mimicked these effects of CaMKII inhibition. Vericiguat had only slight benefits, and these effects were larger in HFpEF females.

CONCLUSION

We conclude that the db/db+Aldo preclinical HFpEF murine model recapitulates key sex-specific mechanisms in HFpEF and provides mechanistic insights into impaired excitation-contraction coupling and sex-dependent differential arrhythmia susceptibility in HFpEF with potential therapeutic implications. In male HFpEF myocytes, altered Ca2+ handling and electrophysiology aligned with diastolic dysfunction and arrhythmias, while worse diastolic dysfunction in females may depend more on altered myofilaments properties.

Potential Role of Pig UCP3 in Modulating Adipocyte Browning via the Beta-Adrenergic Receptor Signaling Pathway

Adipose tissue plays an important role in regulating body temperature and metabolism, with white adipocytes serving as storage units for energy. Recent research focused on the browning of white adipocytes (beige adipocytes), causing thermogenesis and lipolysis. The process of browning is linked to the activation of uncoupling protein (UCP) expression, which can be mediated by the β3 adrenergic receptor pathway. Transcriptional factors, such as peroxisome proliferator activated receptor γ (PPARγ) and PPARγ coactivator 1 alpha, play vital roles in cell fate determination for fat cells. Beige adipocytes have metabolic therapeutic potential to combat diseases such as obesity, diabetes mellitus, and dyslipidemia, owing to their significant impact on metabolic functions. However, the molecular mechanisms that cause the induction of browning are unclear. Therefore, research using animal models and primary culture is essential to provide an understanding of browning for further application in human metabolic studies. Pigs have physiological similarities to humans; hence, they are valuable models for research on adipose tissue. This study demonstrates the browning potential of pig white adipocytes through primary culture experiments. The results show that upregulation of UCP3 gene expression and fragmentation of lipid droplets into smaller particles occur due to isoproterenol stimulation, which activates beta-adrenergic receptor signaling. Furthermore, PPARγ and PGC-1α were found to activate the UCP3 promoter region, similar to that of UCP1. These findings suggest that pigs undergo metabolic changes that induce browning in white adipocytes, providing a promising approach for metabolic research with potential implications for human health. This study offers valuable insights into the mechanism of adipocyte browning using pig primary culture that can enhance our understanding of human metabolism, leading to cures for commonly occurring diseases.

Metabolic Syndrome and Tendon Disease: A Comprehensive Review

Metabolic syndrome (MS) is a multifaceted pathological condition characterized by the atypical accumulation of various metabolic components such as central obesity or excess weight, hyperlipidemia, low-density lipoprotein (LDL), hypertension, and insulin resistance. Recently, MS has been recognized as a notable contributor to heart and circulatory diseases. In addition, with increasing research, the impact of MS on tendon repair and disease has gradually emerged. Recent studies have investigated the relationship between tendon healing and diseases such as diabetes, dyslipidemia, obesity, and other metabolic disorders. However, diabetes mellitus (DM), hypercholesterolemia, obesity, and various metabolic disorders often coexist and together constitute MS. At present, insulin resistance is considered the major pathological mechanism underlying MS, central obesity is regarded as the predominant factor responsible for it, and dyslipidemia and other metabolic diseases are known as secondary contributors to MS. This review aims to evaluate the current literature regarding the impact of various pathological conditions in MS on tendon recovery and illness, and to present a comprehensive overview of the effects of MS on tendon recovery and diseases, along with the accompanying molecular mechanisms.

Protein neddylation and its role in health and diseases

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

AGO2 Protects Against Diabetic Cardiomyopathy by Activating Mitochondrial Gene Translation

BACKGROUND

Diabetes is associated with cardiovascular complications. microRNAs translocate into subcellular organelles to modify genes involved in diabetic cardiomyopathy. However, functional properties of subcellular AGO2 (Argonaute2), a core member of miRNA machinery, remain elusive.

METHODS

We elucidated the function and mechanism of subcellular localized AGO2 on mouse models for diabetes and diabetic cardiomyopathy. Recombinant adeno-associated virus type 9 was used to deliver AGO2 to mice through the tail vein. Cardiac structure and functions were assessed by echocardiography and catheter manometer system.

RESULTS

AGO2 was decreased in mitochondria of diabetic cardiomyocytes. Overexpression of mitochondrial AGO2 attenuated diabetes-induced cardiac dysfunction. AGO2 recruited TUFM, a mitochondria translation elongation factor, to activate translation of electron transport chain subunits and decrease reactive oxygen species. Malonylation, a posttranslational modification of AGO2, reduced the importing of AGO2 into mitochondria in diabetic cardiomyopathy. AGO2 malonylation was regulated by a cytoplasmic-localized short isoform of SIRT3 through a previously unknown demalonylase function.

CONCLUSIONS

Our findings reveal that the SIRT3-AGO2-CYTB axis links glucotoxicity to cardiac electron transport chain imbalance, providing new mechanistic insights and the basis to develop mitochondria targeting therapies for diabetic cardiomyopathy.

Improving the Effects of Mulberry Leaves and Neochlorogenic Acid on Glucotoxicity-Induced Hepatic Steatosis in High Fat Diet Treated db/db Mice

There are many complications of type 2 diabetes mellitus. Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are two complications related to the increased lipid accumulation in the liver. Previous studies have shown that mulberry leaf water extract (MLE) has the effect of lowering lipid levels in peripheral blood, inhibiting the expression of fatty acid synthase (FASN) and increasing the activity of liver antioxidant enzymes superoxide dismutase (SOD) and catalase. Our study aimed to investigate the role of MLE and its main component, neochlorogenic acid (nCGA), in reducing serum lipid profiles, decreasing lipid deposition in the liver, and improving steatohepatitis levels. We evaluated the antioxidant activity including glutathione (GSH), glutathione reductase (GRd), glutathione peroxidase (GPx), glutathione S-transferase (GST), and superoxide dismutase (SOD), and catalase was tested in mice fed with MLE and nCGA. The results showed a serum lipid profile, and fatty liver scores were significantly increased in the HFD group compared to the db/m and db mice groups, while liver antioxidant activity significantly decreased in the HFD group. When fed with HFD + MLE or nCGA, there was a significant improvement in serum lipid profiles, liver fatty deposition conditions, steatohepatitis levels, and liver antioxidant activity compared to the HFD group. Although MLE and nCGA do not directly affect the blood sugar level of db/db mice, they do regulate abnormalities in lipid metabolism. These results demonstrate the potential of MLE/nCGA as a treatment against glucotoxicity-induced diabetic fatty liver disease in animal models.

Fish oil minimises feed intake and improves insulin sensitivity in Zucker fa/fa rats

Long-chain n-3 PUFA (LC n-3 PUFA) prevent, in rodents, insulin resistance (IR) induced by a high-fat and/or fructose diet but not IR induced by glucocorticoids. In humans, contrasting effects have also been reported. We investigated their effects on insulin sensitivity, feed intake (FI) and body weight gain in genetically insulin resistant male obese (fa/fa) Zucker (ZO) rats during the development of obesity. ZO rats were fed a diet supplemented with 7 % fish oil (FO) + 1 % corn oil (CO) (wt/wt) (ZOFO), while the control group was fed a diet containing 8 % fat from CO (wt/wt) (ZOCO). Male lean Zucker (ZL) rats fed either FO (ZLFO) or CO (ZLCO) diet were used as controls. FO was a marine-derived TAG oil containing EPA 90 mg/g + DHA 430 mg/g. During an oral glucose tolerance test, glucose tolerance remained unaltered by FO while insulin response was reduced in ZOFO only. Liver insulin sensitivity (euglycaemic-hyperinsulinaemic clamp + 2 deoxyglucose) was improved in ZOFO rats, linked to changes in phosphoenolpyruvate carboxykinase expression, activity and glucose-6-phosphatase activity. FI in response to intra-carotid insulin/glucose infusion was decreased similarly in ZOFO and ZOCO. Hypothalamic ceramides levels were lower in ZOFO than in ZOCO. Our study demonstrates that LC n-3 PUFA can minimise weight gain, possibly by alleviating hypothalamic lipotoxicity, and liver IR in genetically obese Zucker rats.

Remodelling of cAMP dynamics within the SERCA2a microdomain in heart failure with preserved ejection fraction caused by obesity and type 2 diabetes

AIMS

Despite massive efforts, we remain far behind in our attempts to identify effective therapies to treat heart failure with preserved ejection fraction (HFpEF). Diastolic function is critically regulated by sarcoplasmic/endoplasmic reticulum (SR) calcium ATPase 2a (SERCA2a), which forms a functional cardiomyocyte (CM) microdomain where 3',5'-cyclic adenosine monophosphate (cAMP) produced upon β-adrenergic receptor (β-AR) stimulation leads to phospholamban (PLN) phosphorylation and facilitated Ca2+ re-uptake.

METHODS AND RESULTS

To visualize real-time cAMP dynamics in the direct vicinity of SERCA2a in healthy and diseased myocytes, we generated a novel mouse model on the leprdb background that stably expresses the Epac1-PLN Förster resonance energy transfer biosensor. Mice homozygous for the leprdb mutation (db/db) developed obesity and type 2 diabetes and presented with a HFpEF phenotype, evident by mild left ventricular hypertrophy and elevated left atria filling pressures. Live cell imaging uncovered a substantial β2-AR subtype stimulated cAMP response within the PLN/SERCA2a microdomain of db/db but not healthy control (db/+) CMs, which was accompanied by increased PLN phosphorylation and accelerated calcium re-uptake. Importantly, db/db CMs also exhibited a desensitization of β1-AR stimulated cAMP pools within the PLN/SERCA2a microdomain, which was accompanied by a blunted lusitropic effect, suggesting that the increased β2-AR control is an intrinsic compensatory mechanism to maintain PLN/SERCA2a-mediated calcium dynamics and cardiac relaxation. Mechanistically, this was due to a local loss of cAMP-degrading phosphodiesterase 4 associated specifically with the PLN/SERCA2a complex.

CONCLUSION

These newly identified alterations of cAMP dynamics at the subcellular level in HFpEF should provide mechanistic understanding of microdomain remodelling and pave the way towards new therapies.

Zn-Fe primary battery-enabled controlled hydrogen release in stomach for improving insulin resistance in obesity-associated type 2 diabetes

Chronic systemic inflammation in obesity-associated type 2 diabetes (T2D) is a key inducing factor of insulin resistance (IR). Hydrogen molecule (H2) has been proved to be a safe and effective anti-inflammatory agent, but conventional H2 administration methods cannot provide a high dosage and a long duration of H2 treatment in IR-related tissues and thus lead to limited therapeutic efficacies. We here propose a new strategy of controlled H2 release to match the time window of gastric emptying for maximizing the bioavailability and therapeutic outcome of H2. This work enhances the hydrolysis rate of Zn by constructing a Zn-Fe primary-battery micro-/nano-structure, and the H2-releasing rate is adjusted by tuning the ratio of Zn to Fe. The Zn-Fe micro-/nano-structure is orally administrated once daily to alleviate obesity-associated T2D in a leptin-deficient (ob/ob) mouse model. The H2 generation time of the Zn-Fe primary-battery micro-/nano-structure with the Fe/Zn ratio of 1:100 in gastric acid is about 3 h, just matching with the time window of gastric emptying in mice. In vivo monitoring results show that H2 generated by Zn-Fe micro-/nano-structure in stomach can effectively accumulate in major IR-sited tissues including liver, adipose tissue, and skeletal muscle at a high dose for a relatively long time compared to H2-rich water drinking. Oral administration of Zn-Fe micro-/nano-structure at 200 mg/kg body weight has realized an efficient IR improvement and remarkably ameliorated systemic inflammation in ob/ob mice. In addition, a high-dose administration of Zn-Fe shows no visible toxicity in mice. This work provides a new strategy to maximize the outcome of hydrogen therapy.

A Narrative Review of Diabetic Macroangiopathy: From Molecular Mechanism to Therapeutic Approaches

Diabetic macroangiopathy, a prevalent and severe complication of diabetes mellitus, significantly contributes to the increased morbidity and mortality rates among affected individuals. This complex disorder involves multifaceted molecular mechanisms that lead to the dysfunction and damage of large blood vessels, including atherosclerosis (AS) and peripheral arterial disease. Understanding the intricate pathways underlying the development and progression of diabetic macroangiopathy is crucial for the development of effective therapeutic interventions. This review aims to shed light on the molecular mechanism implicated in the pathogenesis of diabetic macroangiopathy. We delve into the intricate interplay of chronic inflammation, oxidative stress, endothelial dysfunction, and dysregulated angiogenesis, all of which contribute to the vascular complications observed in this disorder. By exploring the molecular mechanism involved in the disease we provide insight into potential therapeutic targets and strategies. Moreover, we discuss the current therapeutic approaches used for treating diabetic macroangiopathy, including glycemic control, lipid-lowering agents, and vascular interventions.

Efficacy of Hot Tea Infusion vs. Ethanolic Extract of Moringa oleifera for the Simultaneous Treatment of Nonalcoholic Fatty Liver, Hyperlipidemia, and Hyperglycemia in a Murine Model Fed with a High-Fat Diet

Moringa oleifera (MO) is a native tree of Asia and is cultivated in some areas of Mexico as part of traditional horticulture. The aim of the present study was to compare the efficacy of MO infusion vs. MO ethanolic extract for the simultaneous treatment of nonalcoholic fatty liver (NAFLD), hyperlipidemia, and hyperglycemia in a murine model fed with a high-fat diet (HFD). BALB/c mice were fed a balanced diet (healthy control) or an HFD for 6 months. With this, the NAFLD model was established before starting a therapeutic intervention with MO for two months. The phytochemical analysis by nuclear magnetic resonance in 1H and 13C experiments showed signals for pyrrole alkaloids and triterpenes as the main constituents of the extract and infusion preparation. A significant reduction of SGPT, SGOT, lipids, urea, and glucose in blood among NAFLD groups treated with MO (infusion or extract) was found, when compared to the NAFLD-placebo group. Steatosis and liver inflammation were found to be decreased in the MO groups, as infusion or ethanolic extract. Infusion produced a better therapeutic effect than the extract in all parameters, except glycemic control, where the extract was better. As an additional finding, it is noteworthy that treatment with MO, particularly through infusion, resulted in improved motor activity. Moreover, a reduction in anxiety-like behavior was observed exclusively with the administration of infusion. These observations provide valuable insights into the potential broader effects of Moringa oleifera beyond the primary aim of the study.

Considerations for choosing an optimal animal model of cardiovascular disease

The decision to use the optimal animal model to mimic the various types of cardiovascular disease is a critical one for a basic scientist. Clinical cardiovascular disease can be complex and presents itself as atherosclerosis, hypertension, ischemia/reperfusion injury, myocardial infarcts, and cardiomyopathies, amongst others. This may be further complicated by the simultaneous presence of two or more cardiovascular lesions (for example, atherosclerosis and hypertension) and co-morbidities (i.e., diabetes, infectious disease, obesity, etc). This variety and merging of disease states creates an unusually difficult situation for the researcher who needs to identify the optimal animal model that is available to best represent all of the characteristics of the clinical cardiovascular disease. The present manuscript reviews the characteristics of the various animal models of cardiovascular disease available today, their advantages and disadvantages, with the goal to allow the reader access to the most recent data available for optimal choices prior to the initiation of the study. The animal species that can be chosen, the methods of generating these models of cardiovascular disease, as well as the specific cardiovascular lesions involved in each of these models are reviewed. A particular focus on the JCR:LA-cp rat as a model of cardiovascular disease is discussed.

Genetically modified mice as a tool for the study of human diseases

Modeling a human disease is an essential part of biomedical research. The recent advances in the field of molecular genetics made it possible to obtain genetically modified animals for the study of various diseases. Not only monogenic disorders but also chromosomal and multifactorial disorders can be mimicked in lab animals due to genetic modification. Even human infectious diseases can be studied in genetically modified animals. An animal model of a disease enables the tracking of its pathogenesis and, more importantly, to test new therapies. In the first part of this paper, we review the most common DNA modification technologies and provide key ideas on specific technology choices according to the task at hand. In the second part, we focus on the application of genetically modified mice in studying human diseases.

The Intervention of Probiotics on Type 2 Diabetes Mellitus in Animal Models

Type 2 diabetes accounts for more than 90% of diabetes patients with the incidence and prevalence continuously rising globally. As a prospective therapy strategy for type 2 diabetes, probiotics have shown beneficial effects both in animal experiments and human clinical trials. This review summarizes the commonly used animal models in probiotic intervention research and presents the evidence and mechanism of diabetes intervention with probiotics in these animal models. Probiotics can help maintain glucose homeostasis, improve lipid metabolism, promote the production of short-chain fatty acids, and reduce inflammatory reactions in animal models. However, the clinical translation of benefits from probiotics is still challenged by intrinsic differences between experimental animal models and humans, and the application of humanized non-rodent diabetic animal models may contribute to the clinical translation of probiotics in the future.

A high-fat and fructose diet in dogs mirrors insulin resistance and β-cell dysfunction characteristic of impaired glucose tolerance in humans

This study examined the impact of a hypercaloric high-fat high-fructose diet (HFFD) in dogs as a potential model for human impaired glucose tolerance (IGT) and type 2 diabetes mellitus (T2DM). The HFFD not only led to weight gain but also triggered metabolic alterations akin to the precursors of human T2DM, notably insulin resistance and β-cell dysfunction. Following the HFFD intervention, the dogs exhibited a 50% decrease in insulin sensitivity within the first four weeks, paralleling observations in the progression from normal to IGT in humans. Calculations of the insulinogenic index using both insulin and C-peptide measurements during oral glucose tolerance tests revealed a significant and sustained decrease in early-phase insulin release, with partial compensation in the later phase, predominantly stemming from reduced hepatic insulin clearance. In addition, the Disposition Index, representing the β-cell's capacity to compensate for diminished insulin sensitivity, fell dramatically. These results confirm that a HFFD can instigate metabolic changes in dogs akin to the early stages of progression to T2DM in humans. The study underscores the potential of using dogs subjected to a HFFD as a model organism for studying human IGT and T2DM.

A systematic review of preclinical studies exploring the role of insulin signalling in executive function and memory

Beside its involvement in somatic dysfunctions, altered insulin signalling constitutes a risk factor for the development of mental disorders like Alzheimer's disease and obsessive-compulsive disorder. While insulin-related somatic and mental disorders are often comorbid, the fundamental mechanisms underlying this association are still elusive. Studies conducted in rodent models appear well suited to help decipher these mechanisms. Specifically, these models are apt to prospective studies in which causative mechanisms can be manipulated via multiple tools (e.g., genetically engineered models and environmental interventions), and experimentally dissociated to control for potential confounding factors. Here, we provide a narrative synthesis of preclinical studies investigating the association between hyperglycaemia - as a proxy of insulin-related metabolic dysfunctions - and impairments in working and spatial memory, and attention. Ultimately, this review will advance our knowledge on the role of glucose metabolism in the comorbidity between somatic and mental illnesses.

Obesity amplifies influenza virus-driven disease severity in male and female mice

Influenza virus-induced respiratory pneumonia remains a major public health concern. Obesity, metabolic diseases, and female sex are viewed as independent risk factors for worsened influenza virus-induced lung disease severity. However, lack of experimental models of severe obesity in female mice limits discovery-based studies. Here, via utility of thermoneutral housing (30 °C) and high-fat diet (HFD) feeding, we induced severe obesity and metabolic disease in female C57BL/6 mice and compared their responses to severely obese male C57BL/6 counterparts during influenza virus infection. We show that lean male and female mice have similar lung edema, inflammation, and immune cell infiltration during influenza virus infection. At standard housing conditions, HFD-fed male, but not female, mice exhibit severe obesity, metabolic disease, and exacerbated influenza disease severity. However, combining thermoneutral housing and HFD feeding in female mice induces severe obesity and metabolic disease, which is sufficient to amplify influenza virus-driven disease severity to a level comparable to severely obese male counterparts. Lastly, increased total body weights of male and female mice at time of infection correlated with worsened influenza virus-driven disease severity metrics. Together, our findings confirm the impact of obesity and metabolic disease as key risk factors to influenza disease severity and present a novel mouse experimental model suitable for future mechanistic interrogation of sex, obesity, and metabolic disease traits in influenza virus-driven disease severity.

Preclinical study of diabetic foot ulcers: From pathogenesis to vivo/vitro models and clinical therapeutic transformation

Diabetic foot ulcer (DFU), a common intractable chronic complication of diabetes mellitus (DM), has a prevalence of up to 25%, with more than 17% of the affected patients at risk of amputation or even death. Vascular risk factors, including vascular stenosis or occlusion, dyslipidemia, impaired neurosensory and motor function, and skin infection caused by trauma, all increase the risk of DFU in patients with diabetes. Therefore, diabetic foot is not a single pathogenesis. Preclinical studies have contributed greatly to the pathogenesis determination and efficacy evaluation of DFU. Many therapeutic tools are currently being investigated using DFU animal models for effective clinical translation. However, preclinical animal models that completely mimic the pathogenesis of DFU remain unexplored. Therefore, in this review, the preparation methods and evaluation criteria of DFU animal models with three major pathological mechanisms: neuropathy, angiopathy and DFU infection were discussed in detail. And the advantages and disadvantages of various DFU animal models for clinical sign simulation. Furthermore, the current status of vitro models of DFU and some preclinical studies have been transformed into clinical treatment programs, such as medical dressings, growth factor therapy, 3D bioprinting and pre-vascularization, Traditional Chinese Medicine treatment. However, because of the complexity of the pathological mechanism of DFU, the clinical transformation of DFU model still faces many challenges. We need to further optimize the existing preclinical studies of DFU to provide an effective animal platform for the future study of pathophysiology and clinical treatment of DFU.

Thermoneutral Housing Enables Studies of Vertical Transmission of Obesogenic Diet-Driven Metabolic Diseases

Vertical transmission of obesity is a critical contributor to the unabated obesity pandemic and the associated surge in metabolic diseases. Existing experimental models insufficiently recapitulate "human-like" obesity phenotypes, limiting the discovery of how severe obesity in pregnancy instructs vertical transmission of obesity. Here, via utility of thermoneutral housing and obesogenic diet feeding coupled to syngeneic mating of WT obese female and lean male mice on a C57BL/6 background, we present a tractable, more "human-like" approach to specifically investigate how maternal obesity contributes to offspring health. Using this model, we found that maternal obesity decreased neonatal survival, increased offspring adiposity, and accelerated offspring predisposition to obesity and metabolic disease. We also show that severe maternal obesity was sufficient to skew offspring microbiome and create a proinflammatory gestational environment that correlated with inflammatory changes in the offspring in utero and adulthood. Analysis of a human birth cohort study of mothers with and without obesity and their infants was consistent with mouse study findings of maternal inflammation and offspring weight gain propensity. Together, our results show that dietary induction of obesity in female mice coupled to thermoneutral housing can be used for future mechanistic interrogations of obesity and metabolic disease in pregnancy and vertical transmission of pathogenic traits.

SUMOylation Modulates Reactive Oxygen Species (ROS) Levels and Acts as a Protective Mechanism in the Type 2 Model of Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is the prevalent type of peripheral neuropathy; it primarily impacts extremity nerves. Its multifaceted nature makes the molecular mechanisms of diabetic neuropathy intricate and incompletely elucidated. Several types of post-translational modifications (PTMs) have been implicated in the development and progression of DPN, including phosphorylation, glycation, acetylation and SUMOylation. SUMOylation involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target proteins, and it plays a role in various cellular processes, including protein localization, stability, and function. While the specific relationship between high blood glucose and SUMOylation is not extensively studied, recent evidence implies its involvement in the development of DPN in type 1 diabetes. In this study, we investigated the impact of SUMOylation on the onset and progression of DPN in a type 2 diabetes model using genetically modified mutant mice lacking SUMOylation, specifically in peripheral sensory neurons (SNS-Ubc9-/-). Behavioural measurement for evoked pain, morphological analyses of nerve fibre loss in the epidermis, measurement of reactive oxygen species (ROS) levels, and antioxidant molecules were analysed over several months in SUMOylation-deficient and control mice. Our longitudinal analysis at 30 weeks post-high-fat diet revealed that SNS-Ubc9-/- mice exhibited earlier and more pronounced thermal and mechanical sensation loss and accelerated intraepidermal nerve fibre loss compared to control mice. Mechanistically, these changes are associated with increased levels of ROS both in sensory neuronal soma and in peripheral axonal nerve endings in SNS-Ubc9-/- mice. In addition, we observed compromised detoxifying potential, impaired respiratory chain complexes, and reduced levels of protective lipids in sensory neurons upon deletion of SUMOylation in diabetic mice. Importantly, we also identified mitochondrial malate dehydrogenase (MDH2) as a SUMOylation target, the activity of which is negatively regulated by SUMOylation. Our results indicate that SUMOylation is an essential neuroprotective mechanism in sensory neurons in type 2 diabetes, the deletion of which causes oxidative stress and an impaired respiratory chain, resulting in energy depletion and subsequent damage to sensory neurons.

Obesity Duration and Cardiometabolic Disease

Cardiovascular disease risk is known to be influenced by both the severity of a risk factor and the duration of exposure (eg, LDL [low-density lipoprotein] cholesterol, tobacco smoke). However, this concept has been largely neglected within the obesity literature. While obesity severity has been closely linked with cardiometabolic diseases, the risk of developing these conditions among those with obesity may be augmented by greater obesity duration over the life span. Few longitudinal or contemporary studies have investigated the influence of both factors in combination-cumulative obesity exposure-instead generally focusing on obesity severity, often at a single time point, given ease of use and lack of established methods to encapsulate duration. Our review focuses on what is known about the influence of the duration of exposure to excess adiposity within the obesity-associated cardiometabolic disease risk equation by means of summarizing the hypothesized mechanisms for and evidence surrounding the relationships of obesity duration with diverse cardiovascular and metabolic disease. Through the synthesis of the currently available data, we aim to highlight the importance of a better understanding of the influence of obesity duration in cardiovascular and metabolic disease pathogenesis. We underscore the clinical importance of aggressive early attention to obesity identification and intervention to prevent the development of chronic diseases that arise from exposure to excess body weight.

Effect of Tangshen formula on the remodeling of small intestine and colon in Zucker diabetic fatty rats

Background and aim

Previous study have demonstrated that Tangshen Formula (TSF) could attenuate colonic histomorphological remodeling in the diabetic rat model induced by high fat diet plus low dosage streptozotocin (STZ). However, it is not clear whether TSF has same effect on small intestine and the effect on biomechanical properties of bowel. The aim of this study is to investigate the effect of TSF on histomorphological and biomechanical remodeling of small intestine and colon by using Zucker Diabetic Fatty (ZDF) Rat model.

Materials and methods

ZDF rats (obese fa/fa) with blood glucose higher than 11.7 mmol/L were divided into ZDF group (diabetic control group) and ZDF + TSF group (TSF treatment group), the later were intragastrically administered TSF. The ZDF rats (lean fa/+) were served as normal control (ZL) group. The rats in the ZL and ZDF groups were administered with saline. The experimental period covered from 8 weeks to 24 weeks. At the end of experiment, the ileal and colonic segments were studied in vitro. The histomorphometry and biomechanical parameters were measured.

Results

Compared with ZL group histomorphologically, the wet weight per unit length, wall thickness, wall area and fractions of total and type I and type III collagen in different layers for both ileum and colon increased in ZDF group. Those increasing parameters were partially inhibited in ZDF + TSF group. Compared with ZL group biomechanically, ZDF and ZDF + TSF groups had smaller opening angle and residual strain in ileum, and bigger opening angle and residual strain in colon. Whereas the wall became softer in circumferential direction and stiffer in longitudinal direction for both ileum and colon. However, no difference of biomechanical parameters was found between ZDF and ZDF + TSF groups.

Conclusion

The histomorphological and biomechanical remodeling of ileum and colon were happened in ZDF rats （obese fa/fa）. TSF could partly attenuate ileal and colonic histomorphological remodeling rather than biomechanical remodeling.

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.

Sex Modifies the Impact of Type 2 Diabetes Mellitus on the Murine Whole Brain Metabolome

Type 2 diabetes mellitus (T2DM) leads to the development of cardiovascular diseases, cognitive impairment, and dementia. There are sex differences in the presentation of T2DM and its associated complications. We sought to determine the impact of sex and T2DM on the brain metabolome to gain insights into the underlying mechanisms of T2DM-associated cognitive complications. Untargeted metabolomic analysis was performed, using liquid chromatography-mass spectrometry, on whole brain tissue from adult male and female db/db mice (a T2DM model) compared to wild-type (WT) C57Bl6/J mice. Regardless of sex, T2DM increased free fatty acids and decreased acylcarnitines in the brain. Sex impacted the number (103 versus 65 in males and females, respectively), and types of metabolites shifted by T2DM. Many choline-containing phospholipids were decreased by T2DM in males. Female-specific T2DM effects included changes in neuromodulatory metabolites (γ-aminobutyric acid, 2-linoleoyl glycerol, N-methylaspartic acid, and taurine). Further, there were more significantly different metabolites between sexes in the T2DM condition as compared to the WT controls (54 vs. 15 in T2DM and WT, respectively). T2DM alters the murine brain metabolome in both sex-independent and sex-dependent manners. This work extends our understanding of brain metabolic sex differences in T2DM, cognitive implications, and potential sex-specific metabolic therapeutic targets.

Contribution of animal models to diabetes research: Its history, significance, and translation to humans

Diabetes mellitus is still expanding globally and is epidemic in developing countries. The combat of this plague has caused enormous economic and social burdens related to a lowered quality of life in people with diabetes. Despite recent significant improvements of life expectancy in patients with diabetes, there is still a need for efforts to elucidate the complexities and mechanisms of the disease processes to overcome this difficult disorder. To this end, the use of appropriate animal models in diabetes studies is invaluable for translation to humans and for the development of effective treatment. In this review, a variety of animal models of diabetes with spontaneous onset in particular will be introduced and discussed for their implication in diabetes research.

Fucoidan derived from Sargassum pallidum alleviates metabolism disorders associated with improvement of cardiac injury and oxidative stress in diabetic mice

Type 2 diabetes mellitus (T2DM) and its complications have become a serious global health epidemic. Cardiovascular complications have considered as a major cause of high mortality in diabetic patients. Fucoidans from brown algae have diverse medicinal activities, however, few studies reported pharmacological activity of Sargassum. pallidum fucoidan (Sp-Fuc). Therefore, the aim of this study was to investigate the effects of Sp-Fuc on diabetic symptoms and cardiac injury in spontaneous diabetic db/db mice. SP-Fuc at 200 mg/(kg/d) was administered intragastrically to db/db mice for 8 weeks, the effects on hyperlipidemia, hyperglycemia, insulin resistance, and cardiac damage, as well as oxidative stress, inflammation, Nrf2/ARE, and NF-κB signaling pathways, were investigated. Our data demonstrated that Sp-Fuc significantly (p < 0.05) decreased body weights, hyperlipidemia, and hyperglycemia in db/db mice, along with improved insulin sensitivity. Additionally, Sp-Fuc significantly (p < 0.05) alleviated cardiac dysfunction and pathological morphology of cardiac tissue. Sp-Fuc also significantly (p < 0.05) decreased lipid peroxidation, increased antioxidant function, as well as reduced cardiac inflammation, possibly through Nrf2/ARE and NF-κB signaling. Sp-Fuc can ameliorate the metabolism disorders of glucose and lipid in diabetic mice by activating Nrf2/ARE antioxidant signaling, simultaneously reducing cardiac redox imbalance and inflammatory damage. The present findings provide a perspective on the therapy strategy for T2DM and its complications.

Leptin deficiency impairs adipogenesis and browning response in mouse mesenchymal progenitors

Although phenotypically different, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) are able to produce heat through non-shivering thermogenesis due to the presence of mitochondrial uncoupling protein 1 (UCP1). The appearance of thermogenically active beige adipocytes in iWAT is known as browning. Both brown and beige cells originate from mesenchymal stem cells (MSCs), and in culture conditions a browning response can be induced with hypothermia (i.e. 32 °C) during which nuclear leptin immunodetection was observed. The central role of leptin in regulating food intake and energy consumption is well recognised, but its importance in the browning process at the cellular level is unclear. Here, immunocytochemical analysis of MSC-derived adipocytes established nuclear localization of both leptin and leptin receptor suggesting an involvement of the leptin pathway in the browning response. In order to elucidate whether leptin modulates the expression of brown and beige adipocyte markers, BAT and iWAT samples from leptin-deficient (ob/ob) mice were analysed and exhibited reduced brown/beige marker expression compared to wild-type controls. When MSCs were isolated and differentiated into adipocytes, leptin deficiency was observed to induce a white phenotype, especially when incubated at 32 °C. These adaptations were accompanied with morphological signs of impaired adipogenic differentiation. Overall, our results indicate that leptin supports adipocyte browning and suggest a potential role for leptin in adipogenesis and browning.

Detecting fa leptin receptor mutation in Zucker rats with tetra-primer amplification-refractory mutation system (ARMS)-PCR

Due to the genetic mutation (fa) in the gene encoding for leptin receptor, homozygous Zucker rats (fa-/-) develop excessive adiposity and become an experimental animal model in obesity and metabolic-related diseases research. Based on tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR), we developed a method to quickly genotype Zucker rats with a mutated fa allele from their wildtype littermates. The three genotypes are clearly discriminated on 2.0% agarose gel. Our method can be used as a reliable tool to set up and maintain the breeding colony in animal facilities as well as assign animals to control and treatment groups based on their genotypes for animal studies.

Antidiabetic Effect of Fermented Mesembryanthemum crystallinum L. in db/db Mice Involves Regulation of PI3K-Akt Pathway

Type 2 diabetes (T2D) is a serious health issue with increasing incidences worldwide. However, current medications have limitations due to side effects such as decreased appetite, stomach pain, diarrhea, and extreme tiredness. Here, we report the effect of fermented ice plant (FMC) in the T2M mouse model of db/db mice. FMC showed a greater inhibition of lipid accumulation compared to unfermented ice plant extract. Two-week oral administration with FMC inhibited body weight gain, lowered fasting blood glucose, and improved glucose tolerance. Serum parameters related to T2D including insulin, glycosylated hemoglobin, adiponectin, and cholesterols were improved as well. Histological analysis confirmed the protective effect of FMC on pancreas and liver destruction. FMC treatment significantly increased the expression and phosphorylation of IRS-1, PI3K, and AKT. Additionally, AMP-activated protein kinase phosphorylation and nuclear factor erythroid 2-related factor 2 were also increased in the liver tissues of db/db mice treated with FMC. Overall, our results indicate the anti-diabetic effect of FMC; therefore, we suggest that FMC may be useful as a therapeutic agent for T2D.

NAFLD-Related HCC: Focus on the Latest Relevant Preclinical Models

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and one of the deadliest cancers worldwide. Despite extensive research, the biological mechanisms underlying HCC's development and progression remain only partially understood. Chronic overeating and/or sedentary-lifestyle-associated obesity, which promote Non-Alcoholic Fatty Liver Disease (NAFLD), have recently emerged as worrying risk factors for HCC. NAFLD is characterized by excessive hepatocellular lipid accumulation (steatosis) and affects one quarter of the world's population. Steatosis progresses in the more severe inflammatory form, Non-Alcoholic Steatohepatitis (NASH), potentially leading to HCC. The incidence of NASH is expected to increase by up to 56% over the next 10 years. Better diagnoses and the establishment of effective treatments for NAFLD and HCC will require improvements in our understanding of the fundamental mechanisms of the disease's development. This review describes the pathogenesis of NAFLD and the mechanisms underlying the transition from NAFL/NASH to HCC. We also discuss a selection of appropriate preclinical models of NAFLD for research, from cellular models such as liver-on-a-chip models to in vivo models, focusing particularly on mouse models of dietary NAFLD-HCC.

PRDM16 exerts critical role in myocardial metabolism and energetics in type 2 diabetes induced cardiomyopathy

BACKGROUND

The prevalence of type 2 diabetes mellitus (T2DM) has increased over the past decades. Diabetic cardiomyopathy (DCM) is the leading cause of death in T2DM patients, however, the mechanism underlying DCM remains largely unknown. Here, we aimed to investigate the role of cardiac PR-domain containing 16 (PRDM16) in T2DM.

METHODS

We modeled mice with cardiac-specific deletion of Prdm16 by crossing the floxed Prdm16 mouse model with the cardiomyocyte-specific Cre transgenic mouse. The mice were continuously fed a chow diet or high-fat diet combining with streptozotocin (STZ) for 24 weeks to establish a T2DM model. DB/DB and adequate control mice were given a single intravenous injection of adeno-associated virus 9 (AAV9) carrying cardiac troponin T (cTnT) promoter-driven small hairpin RNA targeting PRDM16 (AAV9-cTnT-shPRDM16) from the retro-orbital venous plexus to knockout Prdm16 in the myocardium. There were at least 12 mice in each group. Mitochondrial morphology and function were detected using transmission electron microscopy, western blot determining the protein level of mitochondrial respiratory chain complex, mitotracker staining and Seahorse XF Cell Mito Stress Test Kit. Untargeted metabolomics analysis and RNA-seq analysis were performed to determine the molecular and metabolic changes associated with Prdm16 deficiency. BODIPY and TUNEL staining were used to detect lipid uptake and apoptosis. Co-immunoprecipitation and ChIP assays were conducted to examine the potential underlying mechanism.

RESULTS

Prdm16 cardiac-specific deficiency accelerated cardiomyopathy and worsened cardiac dysfunction in mice with T2DM, aggravating mitochondrial dysfunction and apoptosis both in vivo and in vitro, while PRDM16 overexpression the deterioration. Prdm16 deficiency also caused cardiac lipid accumulation resulting in metabolic and molecular alterations in T2DM mouse models. Co-IP and luciferase assays confirmed that PRDM16 targeted and regulated the transcriptional activity, expression and interaction of PPAR-α and PGC-1α, while the overexpression of PPAR-α and PGC-1α reversed Prdm16 deficiency-induced cellular dysfunction in T2DM model. Moreover, PRDM16 regulated PPAR-α and PGC-1α and affected mitochondrial function by mainly depending on epigenetic regulation of H3K4me3.

CONCLUSIONS

These findings suggest that PRDM16 exerted its protective role in myocardial lipid metabolism and mitochondrial function in T2DM in a histone lysine methyltransferase activity-dependent manner by regulating PPAR-α and PGC-1α.

Diabetes and cognitive decline: Challenges and future direction

There is growing evidence that diabetes can induce cognitive decline and dementia. It is a slow, progressive cognitive decline that can occur in any age group, but is seen more frequently in older individuals. Symptoms related to cognitive decline are worsened by chronic metabolic syndrome. Animal models are frequently utilized to elucidate the mechanisms of cognitive decline in diabetes and to assess potential drugs for therapy and prevention. This review addresses the common factors and pathophysiology involved in diabetes-related cognitive decline and outlines the various animal models used to study this condition.

AGER1 deficiency-triggered ferroptosis drives fibrosis progression in nonalcoholic steatohepatitis with type 2 diabetes mellitus

Hyperglycemia is an independent risk factor for the rapid progression of nonalcoholic steatohepatitis (NASH) to liver fibrosis with an incompletely defined mechanism. Ferroptosis is a novel form of programmed cell death that has been identified as a pathogenic mechanism in various diseases. However, the role of ferroptosis in the development of liver fibrosis in NASH with type 2 diabetes mellitus (T2DM) is unclear. Here, we observed the histopathological features of the progression of NASH to liver fibrosis as well as hepatocyte epithelial-mesenchymal transition (EMT) in a mouse model of NASH with T2DM and high-glucose-cultured steatotic human normal liver (LO2) cells. The distinctive features of ferroptosis, including iron overload, decreased antioxidant capacity, the accumulation of reactive oxygen species, and elevated lipid peroxidation products, were confirmed in vivo and in vitro. Liver fibrosis and hepatocyte EMT were markedly alleviated after treatment with the ferroptosis inhibitor ferrostatin-1. Furthermore, a decrease in the gene and protein levels of AGE receptor 1 (AGER1) was detected in the transition from NASH to liver fibrosis. Overexpression of AGER1 dramatically reversed hepatocyte EMT in high-glucose-cultured steatotic LO2 cells, whereas the knockdown of AGER1 had the opposite effect. The mechanisms underlying the phenotype appear to be associated with the inhibitory effects of AGER1 on ferroptosis, which is dependent on the regulation of sirtuin 4. Finally, in vivo adeno-associated virus-mediated AGER1 overexpression effectively relieved liver fibrosis in a murine model. Collectively, these findings suggest that ferroptosis participates in the pathogenesis of liver fibrosis in NASH with T2DM by promoting hepatocyte EMT. AGER1 could reverse hepatocyte EMT to ameliorate liver fibrosis by inhibiting ferroptosis. The results also suggest that AGER1 may be a potential therapeutic target for the treatment of liver fibrosis in patients with NASH with T2DM. Chronic hyperglycemia is associated with increased advanced glycation end products, resulting in the downregulation of AGER1. AGER1 deficiency downregulates Sirt4, which disturbs key regulators of ferroptosis (TFR-1, FTH, GPX4, and SLC7A11). These lead to increased iron uptake, decreasing the antioxidative capacity and enhanced lipid ROS production, ultimately leading to ferroptosis, which further promotes hepatocyte epithelial-mesenchymal transition and fibrosis progression in NASH with T2DM.

Enhancement of Sphingomyelinase-Induced Endothelial Nitric Oxide Synthase-Mediated Vasorelaxation in a Murine Model of Type 2 Diabetes

Sphingolipids are important biological mediators both in health and disease. We investigated the vascular effects of enhanced sphingomyelinase (SMase) activity in a mouse model of type 2 diabetes mellitus (T2DM) to gain an understanding of the signaling pathways involved. Myography was used to measure changes in the tone of the thoracic aorta after administration of 0.2 U/mL neutral SMase in the presence or absence of the thromboxane prostanoid (TP) receptor antagonist SQ 29,548 and the nitric oxide synthase (NOS) inhibitor L-NAME. In precontracted aortic segments of non-diabetic mice, SMase induced transient contraction and subsequent weak relaxation, whereas vessels of diabetic (Lepr^db/Lepr^db, referred to as db/db) mice showed marked relaxation. In the presence of the TP receptor antagonist, SMase induced enhanced relaxation in both groups, which was 3-fold stronger in the vessels of db/db mice as compared to controls and could not be abolished by ceramidase or sphingosine-kinase inhibitors. Co-administration of the NOS inhibitor L-NAME abolished vasorelaxation in both groups. Our results indicate dual vasoactive effects of SMase: TP-mediated vasoconstriction and NO-mediated vasorelaxation. Surprisingly, in spite of the general endothelial dysfunction in T2DM, the endothelial NOS-mediated vasorelaxant effect of SMase was markedly enhanced.

The Geroprotective Drug Candidate CMS121 Alleviates Diabetes, Liver Inflammation, and Renal Damage in db/db Leptin Receptor Deficient Mice

db/db mice, which lack leptin receptors and exhibit hyperphagia, show disturbances in energy metabolism and are a model of obesity and type 2 diabetes. The geroneuroprotector drug candidate CMS121 has been shown to be effective in animal models of Alzheimer's disease and aging through the modulation of metabolism. Thus, the hypothesis was that CMS121 could protect db/db mice from metabolic defects and thereby reduce liver inflammation and kidney damage. The mice were treated with CMS121 in their diet for 6 months. No changes were observed in food and oxygen consumption, body mass, or locomotor activity compared to control db/db mice, but a 5% reduction in body weight was noted. Improved glucose tolerance and reduced HbA1c and insulin levels were also seen. Blood and liver triglycerides and free fatty acids decreased. Improved metabolism was supported by lower levels of fatty acid metabolites in the urine. Markers of liver inflammation, including NF-κB, IL-18, caspase 3, and C reactive protein, were lowered by the CMS121 treatment. Urine markers of kidney damage were improved, as evidenced by lower urinary levels of NGAL, clusterin, and albumin. Urine metabolomics studies provided further evidence for kidney protection. Mitochondrial protein markers were elevated in db/db mice, but CMS121 restored the renal levels of NDUFB8, UQCRC2, and VDAC. Overall, long-term CMS121 treatment alleviated metabolic imbalances, liver inflammation, and reduced markers of kidney damage. Thus, this study provides promising evidence for the potential therapeutic use of CMS121 in treating metabolic disorders.

Bone structure and composition in a hyperglycemic, obese, and leptin receptor-deficient rat: Microscale characterization of femur and calvarium

Metabolic abnormalities, such as diabetes mellitus and obesity, can impact bone quantity and/or bone quality. In this work, we characterize bone material properties, in terms of structure and composition, in a novel rat model with congenic leptin receptor (LepR) deficiency, severe obesity, and hyperglycemia (type 2 diabetes-like condition). Femurs and calvaria (parietal region) from 20-week-old male rats are examined to probe bones formed both by endochondral and intramembranous ossification. Compared to the healthy controls, the LepR-deficient animals display significant alterations in femur microarchitecture and in calvarium morphology when analyzed by micro-computed X-ray tomography (micro-CT). In particular, shorter femurs with reduced bone volume, combined with thinner parietal bones and shorter sagittal suture, point towards a delay in the skeletal development of the LepR-deficient rodents. On the other hand, LepR-deficient animals and healthy controls display analogous bone matrix composition, which is assessed in terms of tissue mineral density by micro-CT, degree of mineralization by quantitative backscattered electron imaging, and various metrics extrapolated from Raman hyperspectral images. Some specific microstructural features, i.e., mineralized cartilage islands in the femurs and hyper-mineralized areas in the parietal bones, also show comparable distribution and characteristics in both groups. Overall, the altered bone microarchitecture in the LepR-deficient animals indicates compromised bone quality, despite the normal bone matrix composition. The delayed development is also consistent with observations in humans with congenic Lep/LepR deficiency, making this animal model a suitable candidate for translational research.

Neuroendocrine and neuroimmune mechanisms underlying comorbidity of pain and obesity

Pain and obesity, as well as their associated impairments, are major health concerns. Understanding the relationship between the two is the focus of a growing body of research. However, early researches attribute increased mechanical stress from excessive weight as the main factor of obesity-related pain, which not only over-simplify the association, but also fail to explain some controversial outcomes arising from clinical investigations. This review focuses on neuroendocrine and neuroimmune modulators importantly involved in both pain and obesity, analyzing nociceptive and anti-nociceptive mechanisms based on neuroendocrine pathways including galanin, ghrelin, leptin and their interactions with other neuropeptides and hormone systems which have been reported to play roles in pain and obesity. Mechanisms of immune activities and metabolic alterations are also discussed, due to their intense interactions with neuroendocrine system and crucial roles in the development and maintenance of inflammatory and neuropathic pain. These findings have implications for health given rising rates of obesity and pain-related diagnoses, by providing novel weight-control and analgesic therapies targeted on specific pathways.

Association between Organophosphate Ester Exposure and Insulin Resistance with Glycometabolic Disorders among Older Chinese Adults 60-69 Years of Age: Evidence from the China BAPE Study

BACKGROUND

Organophosphate esters (OPEs) are common endocrine-disrupting chemicals, and OPE exposure may be associated with type 2 diabetes (T2D). However, greater knowledge regarding the biomolecular intermediators underlying the impact of OPEs on T2D in humans are needed to understand biological etiology.

OBJECTIVES

We explored the associations between OPE exposure and glycometabolic markers among older Chinese adults 60-69 years of age to elucidate the underlying mechanisms using a multi-omics approach.

METHODS

This was a longitudinal panel study comprising 76 healthy participants 60-69 years of age who lived in Jinan city of northern China. The study was conducted once every month for 5 months, from September 2018 to January 2019. We measured a total of 17 OPEs in the blood, 11 OPE metabolites in urine, and 4 glycometabolic markers (fasting plasma glucose, glycated serum protein, fasting insulin, and homeostatic model assessment for insulin resistance). The blood transcriptome and serum/urine metabolome were also evaluated. The associations between individual OPEs and glycometabolic markers were explored. An adverse outcome pathway (AOP) was established to determine the biomolecules mediating the associations.

RESULTS

Exposure to five OPEs and OPE metabolites (trimethylolpropane phosphate, triphenyl phosphate, tri-iso-butyl phosphate, dibutyl phosphate, and diphenyl phosphate) was associated with increased levels of glycometabolic markers. The mixture effect analysis further indicated the adverse effect of OPE mixtures. Multi-omics analyses revealed that the endogenous changes in the transcriptional and metabolic levels were associated with OPE exposure. The putative AOPs model suggested that triggers of molecular initiation events (e.g., insulin receptor and glucose transporter type 4) with subsequent key events, including disruptions in signal transduction pathways (e.g., phosphatidylinositol 3-kinase/protein kinase B and insulin secretion signaling) and biological functions (glucose uptake and insulin secretion), may constitute the diabetogenic effects of OPEs.

DISCUSSION

OPEs are associated with the elevated risk of T2D among older Chinese adults 60-69 years of age. Implementing OPE exposure reduction strategies may help reduce the T2D burden among these individuals, if the relationship is causal. https://doi.org/10.1289/EHP11896.

Beyond energy balance regulation: The underestimated role of adipose tissues in host defense against pathogens

Although the adipose tissue (AT) is a central metabolic organ in the regulation of whole-body energy homeostasis, it is also an important endocrine and immunological organ. As an endocrine organ, AT secretes a variety of bioactive peptides known as adipokines - some of which have inflammatory and immunoregulatory properties. As an immunological organ, AT contains a broad spectrum of innate and adaptive immune cells that have mostly been studied in the context of obesity. However, overwhelming evidence supports the notion that AT is a genuine immunological effector site, which contains all cell subsets required to induce and generate specific and effective immune responses against pathogens. Indeed, AT was reported to be an immune reservoir in the host's response to infection, and a site of parasitic, bacterial and viral infections. In addition, besides AT's immune cells, preadipocytes and adipocytes were shown to express innate immune receptors, and adipocytes were reported as antigen-presenting cells to regulate T-cell-mediated adaptive immunity. Here we review the current knowledge on the role of AT and AT's immune system in host defense against pathogens. First, we will summarize the main characteristics of AT: type, distribution, function, and extraordinary plasticity. Second, we will describe the intimate contact AT has with lymph nodes and vessels, and AT immune cell composition. Finally, we will present a comprehensive and up-to-date overview of the current research on the contribution of AT to host defense against pathogens, including the respiratory viruses influenza and SARS-CoV-2.