Sustained kidney biochemical derangement in treated experimental diabetes: a clue to metabolic memory

Nicotinamide riboside Induced Energy Stress and Metabolic Reprogramming in BEAS-2B Cells

Nicotinamide riboside (NR), a NAD+ precursor, has received attention due to several health benefits it has induced in experimental models. Studies in cultured cells, animals, and humans consistently show increased NAD+ availability after NR supplementation, which is considered the only mode of NR action that leads to health benefits. In the present study, we show that a persistently low NR concentration (1 μM) in the growth medium of BEAS-2B human cells, grown in a monolayer, induces energy stress, which precedes a cellular NAD+ increase after 192 h. NR concentrations greater than 1 μM under the specified conditions were cytotoxic in the 2D cell culture model, while all concentrations tested in the 3D cell culture model (BEAS-2B cell spheroids exposed to 1, 5, 10, and 50 μM NR) induced apoptosis. Shotgun proteomics revealed that NR modulated the abundance of proteins, agreeing with the observed effects on cellular energy metabolism and cell growth or survival. Energy stress may activate pathways that lead to health benefits such as cancer prevention. Accordingly, the premalignant 1198 cell line was more sensitive to NR cytotoxicity than the phenotypically normal parent BEAS-2B cell line. The role of a mild energy stress induced by low concentrations of NR in its beneficial effects deserves further investigation. On the other hand, strategies to increase the bioavailability of NR require attention to toxic effects that may arise.

Simultaneous attenuation of hyperglycemic memory-induced retinal, pulmonary, and glomerular dysfunctions by proinsulin C-peptide in diabetes

BACKGROUND

Hyperglycemic memory (HGM) is a pivotal phenomenon in the development of diabetic complications. Although coincident diabetic complications are reported, research on their development and treatment is limited. Thus, we investigated whether C-peptide can simultaneously inhibit HGM-induced retinal, pulmonary, and glomerular dysfunctions in diabetic mice supplemented with insulin.

METHODS

Insulin-treated diabetic mice were supplemented with human C-peptide by subcutaneous implantation of K9-C-peptide depots for 4 weeks, and reactive oxygen species (ROS) generation, transglutaminase (TGase) activity, and vascular leakage were examined in the retina, lung, and kidney.

RESULTS

We found hyperglycemia-induced persistent ROS generation and TGase activation after blood glucose normalization in the retina, lung, and kidney of insulin-supplemented diabetic mice. These pathological events were inhibited by systemic supplementation of human C-peptide via subcutaneous implantation of a thermosensitive biopolymer-conjugated C-peptide depot. ROS generation and TGase activation were in a vicious cycle after glucose normalization, and C-peptide suppressed the vicious cycle and subsequent endothelial permeability in human retinal endothelial cells. Moreover, C-peptide supplementation ameliorated HGM-induced retinal vascular leakage and neurodegeneration, pulmonary vascular leakage and fibrosis, and glomerular adherens junction disruption and vascular leakage.

CONCLUSIONS

Overall, our findings demonstrate that C-peptide supplementation simultaneously attenuates vascular and neuronal dysfunctions in the retina, lung, and glomerulus of insulin-supplemented diabetic mice.

Podocyte Bioenergetics in the Development of Diabetic Nephropathy: The Role of Mitochondria

Diabetic nephropathy (DN) is the leading cause of kidney failure, with an increasing incidence worldwide. Mitochondrial dysfunction is known to occur in DN and has been implicated in the underlying pathogenesis of disease. These complex organelles have an array of important cellular functions and involvement in signaling pathways, and understanding the intricacies of these responses in health, as well as how they are damaged in disease, is likely to highlight novel therapeutic avenues. A key cell type damaged early in DN is the podocyte, and increasing studies have focused on investigating the role of mitochondria in podocyte injury. This review will summarize what is known about podocyte mitochondrial dynamics in DN, with a particular focus on bioenergetic pathways, highlighting key studies in this field and potential opportunities to target, enhance or protect podocyte mitochondrial function in the treatment of DN.

AMPK in microvascular complications of diabetes and the beneficial effects of AMPK activators from plants

BACKGROUND

Diabetes mellitus is a multifactorial disorder with the risk of micro- and macro-vascular complications. High glucose-induced derangements in metabolic pathways are primarily associated with the initiation and progression of secondary complications namely, diabetic nephropathy, neuropathy, and retinopathy. Adenosine monophosphate-activated protein kinase (AMPK) has emerged as an attractive therapeutic target to treat various metabolic disorders including diabetes mellitus. It is a master metabolic regulator that helps in maintaining cellular energy homeostasis by promoting ATP-generating catabolic pathways and inhibiting ATP-consuming anabolic pathways. Numerous pharmacological and plant-derived bioactive compounds that increase AMP-activated protein kinase activation has shown beneficial effects by mitigating secondary complications namely retinopathy, nephropathy, and neuropathy.

PURPOSE

The purpose of this review is to highlight current knowledge on the role of AMPK and its activators from plant origin in diabetic microvascular complications.

METHODS

Search engines such as Google Scholar, PubMed, Science Direct and Web of Science are used to extract papers using relevant key words. Papers mainly focusing on the role of AMPK and AMPK activators from plant origin in diabetic nephropathy, retinopathy, and neuropathy was chosen to be highlighted.

RESULTS

According to results, decrease in AMPK activation during diabetes play a causative role in the pathogenesis of diabetic microvascular complications. Some of the plant-derived bioactive compounds were beneficial in restoring AMPK activity and ameliorating diabetic microvascular complications.

CONCLUSION

AMPK activators from plant origin are beneficial in mitigating diabetic microvascular complications. These pieces of evidence will be helpful in the development of AMPK-centric therapies to mitigate diabetic microvascular complications.

Metformin: the updated protective property in kidney disease

Metformin is a frontline hypoglycemic agent, which is mainly prescribed to manage type 2 diabetes mellitus with obesity. Emerging evidence suggests that metformin also exerts protective effects against various kidney diseases. Some postulate that kidney disease is actually a metabolic disease, accompanied by nonresolving pathophysiologic pathways controlling oxidative stress, endoplasmic reticulum stress, inflammation, lipotoxicity, fibrosis, and senescence, as well as insufficient host defense mechanisms such as AMP-activated protein kinase (AMPK) signaling and autophagy. Metformin may interfere with these pathways by orchestrating AMPK signaling and AMPK-independent pathways to protect the kidneys from injury. Furthermore, the United States Food and Drug Administration declared metformin is safe for patients with mild or moderate kidney impairment in 2016, assuaging some conservative attitudes about metformin management in patients with renal insufficiency and broadening the scope of research on the renal protective effects of metformin. This review focuses on the molecular mechanisms by which metformin imparts renal protection and its potential in the treatment of various kidney diseases.

Central Macular Thickness in Diabetic Macular Edema

Context

Retinal microvascular dysfunction differs in macular edema lesions in the two eyes of the same patient with diabetic retinopathy.

Objective

To evaluate the relationship between central macular thickness (CMT) and metabolic/systemic factors including anthropometric and laboratory findings, in patients with regressed diabetic retinopathy and a history of pars plana vitrectomy (PPV) combined with internal limiting membrane peeling in one eye.

Subjects and Methods

Forty-two eyes with PPV and the same patients' fellow 42 eyes (without PPV) included this study. Fasting blood samples of these 42 diabetics were collected to study adiponectin levels and other routine parameters.

Results

The average hemoglobinA1c value was 7.3±1.3%. CMT of the vitrectomized eyes were significantly correlated with atherogenic index of plasma, total cholesterol, low density lipoprotein cholesterol and uric acid (UA). On the other hand, CMT of the nonvitrectomized fellow eyes significantly correlated with glucose levels and diabetes duration. Adiponectin, adiponectin/body mass index, adiponectin/fibrinogen were found significantly higher in the subgroup with CMT≥300μm in the vitrectomized eyes (P<0.05). UA levels were higher in the subgroup with CMT≥300μm in the fellow (nonvitrectomized) eyes (P<0.05).

Conclusions

Although there was no relationship between CMT and hemoglobinA1c values, CMT seemed to be affected by atherogenicity, prooxidant chemical alterations in the course of inflammation, so determination of adiponectin and UA levels may be suggested before surgery to predict the atherosclerotic damage and the postoperative CMT value. Vitrectomy performed at the proper time may be helpful in metabolic remodeling process of the retinal tissue along with life style changes, well control of diabetes, and intraocular treatments.

The role of DNA methylation and hydroxymethylation in immunosenescence

A healthy functioning immune system is critical to stave off infectious diseases, but as humans and other organisms age, their immune systems decline. As a result, diseases that were readily thwarted in early life pose nontrivial harm and can even be deadly in late life. Immunosenescence is defined as the general deterioration of the immune system with age, and it is characterized by functional changes in hematopoietic stem cells (HSCs) and specific blood cell types as well as changes in levels of numerous factors, particularly those involved in inflammation. Potential mechanisms underlying immunosenescence include epigenetic changes such as changes in DNA methylation (DNAm) and DNA hydroxymethylation (DNAhm) that occur with age. The purpose of this review is to describe what is currently known about the relationship between immunosenescence and the age-related changes to DNAm and DNAhm, and to discuss experimental approaches best suited to fill gaps in our understanding.

The redox balance of healthy Brazilian adults is associated with GPX1 Pro198Leu and -602A/G polymorphisms, selenium status, and anthropometric and lifestyle parameters

PURPOSE

Considering that oxidative stress is implicated in the pathogenesis and progression of different health conditions, we aimed to evaluate whether the redox balance of a healthy Brazilian population is associated with GPX1 polymorphisms, selenium status, lipid profile, and anthropometric and lifestyle parameters.

METHODS

343 healthy adults were assessed for redox balance markers [glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity; malondialdehyde (MDA) and oxygen radical absorption capacity (ORAC)]; genotyped for the polymorphisms GPX1 Pro198Leu (rs1050450), -602A/G (rs3811699) and Arg5Pro (rs8179169); evaluated for selenium biomarkers (plasma, erythrocyte, and urine) and intake; and assessed for lipid profile. Anthropometric (BMI) and lifestyle data (physical activity, current smoking habit and alcohol consumption) were collected. Multivariable regression models were applied to investigate the possible associations.

RESULTS

Although there were no differences in GPx activity according to GPX1 Pro198Leu and -602A/G polymorphisms, this redox balance marker was positively associated with erythrocyte selenium and negatively associated with the presence of a minor allele of Pro198Leu. SOD activity was positively associated with the presence of a minor allele for these polymorphisms. ORAC showed the same pattern among Leu and G carriers and was positively associated with Leu allele presence, BMI and alcohol intake. MDA was only associated negatively with the male sex and plasma selenium.

CONCLUSIONS

Our findings suggest that the redox balance of a Brazilian healthy population is associated with GPX1 polymorphisms (Pro198Leu and -602A/G), selenium status, BMI, sex, smoking habit and alcohol consumption.

Urine Tricarboxylic Acid Cycle Metabolites Predict Progressive Chronic Kidney Disease in Type 2 Diabetes

CONTEXT

Metabolites in the tricarboxylic acid (TCA) cycle are not only involved in energy metabolism but also play important roles in non-energy production activities.

OBJECTIVE

To study whether baseline urine key TCA cycle metabolites (lactate, pyruvate, citrate, α-ketoglutaric acid, succinate, fumarate, and malate) independently predict risk of chronic kidney disease (CKD) progression [fast estimated glomerular filtration rate (eGFR) decline] in individuals with type 2 diabetes mellitus (T2DM).

DESIGN

One discovery and one validation nested case-control studies in two independent T2DM cohorts.

SETTING AND PARTICIPANTS

Subjects with T2DM were recruited and followed in a regional hospital and at a primary care facility.

MAIN OUTCOME MEASURES

eGFR trajectory (slope) was estimated by linear regression. Progressive CKD was defined as eGFR decline of ≥5 mL/min/1.73 m2 per year.

RESULTS

As compared with those with stable renal function (n = 271), participants who experienced progressive CKD (n = 116) had a lower level of urine citrate but significantly higher levels of lactate, fumarate, and malate levels at baseline. Both fumarate and malate predicted progressive CKD independent of traditional cardio-renal risk factors, including eGFR and albuminuria. Fumarate interacted with sex (P for interaction = 0.03) and independently predicted progressive CKD in male but not female participants. All these findings were reproducible in a validation study (case n = 96, control n = 402). Exploratory analysis suggested that fumarate might partially mediate the effect of oxidative stress on CKD progression.

CONCLUSIONS

Key TCA cycle metabolites, especially fumarate, may be involved in the pathophysiologic pathway independent of traditional cardio-renal risk factors, leading to CKD progression in patients with T2DM.

Lacking ketohexokinase-A exacerbates renal injury in streptozotocin-induced diabetic mice

OBJECTIVE

Ketohexokinase (KHK), a primary enzyme in fructose metabolism, has two isoforms, namely, KHK-A and KHK-C. Previously, we reported that renal injury was reduced in streptozotocin-induced diabetic mice which lacked both isoforms. Although both isoforms express in kidney, it has not been elucidated whether each isoform plays distinct roles in the development of diabetic kidney disease (DKD). The aim of the study is to elucidate the role of KHK-A for DKD progression.

MATERIALS AND METHODS

Diabetes was induced by five consecutive daily intraperitoneal injections of streptozotocin (50 mg/kg) in C57BL/6J wild-type mice, mice lacking KHK-A alone (KHK-A KO), and mice lacking both KHK-A and KHK-C (KHK-A/C KO). At 35 weeks, renal injury, inflammation, hypoxia, and oxidative stress were examined. Metabolomic analysis including polyol pathway, fructose metabolism, glycolysis, TCA (tricarboxylic acid) cycle, and NAD (nicotinamide adenine dinucleotide) metabolism in kidney and urine was done.

RESULTS

Diabetic KHK-A KO mice developed severe renal injury compared to diabetic wild-type mice, and this was associated with further increases of intrarenal fructose, dihydroxyacetone phosphate (DHAP), TCA cycle intermediate levels, and severe inflammation. In contrast, renal injury was prevented in diabetic KHK-A/C KO mice compared to both wild-type and KHK-A KO diabetic mice. Further, diabetic KHK-A KO mice contained decreased renal NAD+ level with the increase of renal hypoxia-inducible factor 1-alpha expression despite having increased renal nicotinamide (NAM) level.

CONCLUSION

These results suggest that KHK-C might play a deleterious role in DKD progression through endogenous fructose metabolism, and that KHK-A plays a unique protective role against the development of DKD.

Epigenetics in diabetic nephropathy, immunity and metabolism

When it comes to the epigenome, there is a fine line between clarity and confusion-walk that line and you will discover another fascinating level of transcription control. With the genetic code representing the cornerstone of rules for information that is encoded to proteins somewhere above the genome level there is a set of rules by which chemical information is also read. These epigenetic modifications show a different side of the genetic code that is diverse and regulated, hence modifying genetic transcription transiently, ranging from short- to long-term alterations. While this complexity brings exquisite control it also poses a formidable challenge to efforts to decode mechanisms underlying complex disease. Recent technological and computational advances have improved unbiased acquisition of epigenomic patterns to improve our understanding of the complex chromatin landscape. Key to resolving distinct chromatin signatures of diabetic complications is the identification of the true physiological targets of regulatory proteins, such as reader proteins that recognise, writer proteins that deposit and eraser proteins that remove specific chemical moieties. But how might a diverse group of proteins regulate the diabetic landscape from an epigenomic perspective? Drawing from an ever-expanding compendium of experimental and clinical studies, this review details the current state-of-play and provides a perspective of chromatin-dependent mechanisms implicated in diabetic complications, with a special focus on diabetic nephropathy. We hypothesise a codified signature of the diabetic epigenome and provide examples of prime candidates for chemical modification. As for the pharmacological control of epigenetic marks, we explore future strategies to expedite and refine the search for clinically relevant discoveries. We also consider the challenges associated with therapeutic strategies targeting epigenetic pathways.