Aldose reductase inhibitors in the treatment of diabetic peripheral neuropathy: a review

Mitochondrial dysfunction in diabetic neuropathy: Impaired mitophagy triggers NLRP3 inflammasome

Diabetic neuropathy is one of the challenging complications of diabetes and is characterized by peripheral nerve damage due to hyperglycemia in diabetes. Mitochondrial dysfunction has been reported as one of the key pathophysiological factor contributing to nerve damage in diabetic neuropathy, clinically manifesting as neurodegenerative changes like functional and sensorimotor deficits. Accumulating evidence suggests a clear correlation between mitochondrial dysfunction and NLRP3 inflammasome activation. Unraveling deeper molecular aspects of mitochondrial dysfunction may provide safer and effective therapeutic alternatives. This review links mitochondrial dysfunction and appraises its role in the pathophysiology of diabetic neuropathy. We have also tried to delineate the role of mitophagy in NLRP3 inflammasome activation in experimental diabetic neuropathy.

Chemokine CX3CL1 (Fractalkine) Signaling and Diabetic Encephalopathy

Diabetes mellitus (DM) is the most common metabolic disease in humans, and its prevalence is increasing worldwide in parallel with the obesity pandemic. A lack of insulin or insulin resistance, and consequently hyperglycemia, leads to many systemic disorders, among which diabetic encephalopathy (DE) is a long-term complication of the central nervous system (CNS), characterized by cognitive impairment and motor dysfunctions. The role of oxidative stress and neuroinflammation in the pathomechanism of DE has been proven. Fractalkine (CX3CL1) has unique properties as an adhesion molecule and chemoattractant, and by acting on its only receptor, CX3CR1, it regulates the activity of microglia in physiological states and neuroinflammation. Depending on the clinical context, CX3CL1-CX3CR1 signaling may have neuroprotective effects by inhibiting the inflammatory process in microglia or, conversely, maintaining/intensifying inflammation and neurotoxicity. This review discusses the evidence supporting that the CX3CL1-CX3CR1 pair is neuroprotective and other evidence that it is neurotoxic. Therefore, interrupting the vicious cycle within neuron-microglia interactions by promoting neuroprotective effects or inhibiting the neurotoxic effects of the CX3CL1-CX3CR1 signaling axis may be a therapeutic goal in DE by limiting the inflammatory response. However, the optimal approach to prevent DE is simply tight glycemic control, because the elimination of dysglycemic states in the CNS abolishes the fundamental mechanisms that induce this vicious cycle.

Phytochemical composition of aerial parts and roots of Pfaffia glomerata (Spreng.) Pedersen and anticholinesterase, antioxidant, and antiglycation activities

The Pfaffia glomerata, a plant popularly called Brazilian ginseng, is widely used in Brazil for the treatment of various pathologies, including those associated with the Central Nervous System. 20-hydroxyecdysone (20E), a phytosteroid present in this plant, can promote adaptogenic effects in the organism, providing greater body resistance to stressors. This study aimed to evaluate the phytochemical composition and the anticholinesterase, antioxidant, and antiglycation effects of extracts and fractions of aerial parts and roots of P. glomerata, also analyzing their possible cytotoxic effects. The fractions were obtained by partitioning methanol extracts from the aerial part and roots of P. glomerata with hexane, dichloromethane, ethyl acetate, n-butanol, and water. The samples were initially tested in anticholinesterase, antioxidant, and antiglycation assays, and the most promising samples were submitted for cytotoxicity and chromatographic analyses. Mass spectrometry and chromatography methods revealed that 20E was the main compound in the dichloromethane fractions, there being 35% more 20E in the aerial part (APD) than in the roots (RD). Added to the higher concentration of 20E, the APD fraction also presented more promising results than the RD fraction in anticholinesterase and antioxidant analyses, indicating that their effects may be related to the concentration of 20E. These same fractions showed no hemolytic effects but were cytotoxic in high concentrations. These new findings contribute to scientific information about P. glomerata and open more perspectives for the understanding of its therapeutic properties, allowing the association of biological activity with the presence of 20E.

Vitamin C alleviates hyperglycemic stress in retinal pigment epithelial cells

BACKGROUND

Retinal pigment epithelial cells (RPECs) are a type of retinal cells that structurally and physiologically support photoreceptors. However, hyperglycemia has been shown to play a critical role in the progression of diabetic retinopathy (DR), which is one of the leading causes of vision impairment. In the diabetic eye, the high glucose environment damages RPECs via the induction of oxidative stress, leading to the release of excess reactive oxygen species (ROS) and triggering apoptosis. In this study, we aim to investigate the antioxidant mechanism of Vitamin C in reducing hyperglycemia-induced stress and whether this mechanism can preserve the function of RPECs.

METHODS AND RESULTS

ARPE-19 cells were treated with high glucose in the presence or absence of Vitamin C. Cell viability was measured by MTT assay. Cleaved poly ADP-ribose polymerase (PARP) was used to identify apoptosis in the cells. ROS were detected by the DCFH-DA reaction. The accumulation of sorbitol in the aldose reductase (AR) polyol pathway was determined using the sorbitol detection assay. Primary mouse RPECs were isolated from adult mice and identified by Rpe65 expression. The mitochondrial damage was measured by mitochondrial membrane depolarization. Our results showed that high glucose conditions reduce cell viability in RPECs while Vitamin C can restore cell viability, compared to the vehicle treatment. We also demonstrated that Vitamin C reduces hyperglycemia-induced ROS production and prevents cell apoptosis in RPECs in an AR-independent pathway.

CONCLUSIONS

These results suggest that Vitamin C is not only a nutritional necessity but also an adjuvant that can be combined with AR inhibitors for alleviating hyperglycemic stress in RPECs.

Discovery of a Novel Benzothiadiazine-Based Selective Aldose Reductase Inhibitor as Potential Therapy for Diabetic Peripheral Neuropathy

Aldose reductase 2 (ALR2), an activated enzyme in the polyol pathway by hyperglycemia, has long been recognized as one of the most promising targets for complications of diabetes, especially in diabetic peripheral neuropathy (DPN). However, many of the ALR2 inhibitors have shown serious side effects due to poor selectivity over aldehyde reductase (ALR1). Herein, we describe the discovery of a series of benzothiadiazine acetic acid derivatives as potent and selective inhibitors against ALR2 and evaluation of their anti-DPN activities in vivo. Compound 15c, carrying a carbonyl group at the 3-position of the thiadiazine ring, showed high potent inhibition against ALR2 (IC50 = 33.19 nmol/L) and ∼16,109-fold selectivity for ALR2 over ALR1. Cytotoxicity assays ensured the primary biosafety of 15c. Further pharmacokinetic assay in rats indicated that 15c had a good pharmacokinetic feature (t1/2 = 5.60 h, area under the plasma concentration time curve [AUC(0-t)] = 598.57 ± 216.5 μg/mL * h), which was superior to epalrestat (t1/2 = 2.23 h, AUC[0-t] = 20.43 ± 3.7 μg/mL * h). Finally, in a streptozotocin-induced diabetic rat model, 15c significantly increased the nerve conduction velocities of impaired sensory and motor nerves, achieved potent inhibition of d-sorbitol production in the sciatic nerves, and significantly increased the paw withdrawal mechanical threshold. By combining the above investigations, we propose that 15c might represent a promising lead compound for the discovery of an antidiabetic peripheral neuropathy drug.

ARTICLE HIGHLIGHTS

The polyol pathway and nuclear ketohexokinase A signaling drive hyperglycemia-induced metastasis of gastric cancer

Diabetes might be associated with increased cancer risk, with several studies reporting hyperglycemia as a primary oncogenic stimulant. Since glucose metabolism is linked to numerous metabolic pathways, it is difficult to specify the mechanisms underlying hyperglycemia-induced cancer progression. Here, we focused on the polyol pathway, which is dramatically activated under hyperglycemia and causes diabetic complications. We investigated whether polyol pathway-derived fructose facilitates hyperglycemia-induced gastric cancer metastasis. We performed bioinformatics analysis of gastric cancer datasets and immunohistochemical analyses of gastric cancer specimens, followed by transcriptomic and proteomic analyses to evaluate phenotypic changes in gastric cancer cells. Consequently, we found a clinical association between the polyol pathway and gastric cancer progression. In gastric cancer cell lines, hyperglycemia enhanced cell migration and invasion, cytoskeletal rearrangement, and epithelial-mesenchymal transition (EMT). The hyperglycemia-induced acquisition of metastatic potential was mediated by increased fructose derived from the polyol pathway, which stimulated the nuclear ketohexokinase-A (KHK-A) signaling pathway, thereby inducing EMT by repressing the CDH1 gene. In two different xenograft models of cancer metastasis, gastric cancers overexpressing AKR1B1 were found to be highly metastatic in diabetic mice, but these effects of AKR1B1 were attenuated by KHK-A knockdown. In conclusion, hyperglycemia induces fructose formation through the polyol pathway, which in turn stimulates the KHK-A signaling pathway, driving gastric cancer metastasis by inducing EMT. Thus, the polyol and KHK-A signaling pathways could be potential therapeutic targets to decrease the metastatic risk in gastric cancer patients with diabetes.

Diabetic sensory neuropathy and insulin resistance are induced by loss of UCHL1 in Drosophila

Diabetic sensory neuropathy (DSN) is one of the most common complications of type 2 diabetes (T2D), however the molecular mechanistic association between T2D and DSN remains elusive. Here we identify ubiquitin C-terminal hydrolase L1 (UCHL1), a deubiquitinase highly expressed in neurons, as a key molecule underlying T2D and DSN. Genetic ablation of UCHL1 leads to neuronal insulin resistance and T2D-related symptoms in Drosophila. Furthermore, loss of UCHL1 induces DSN-like phenotypes, including numbness to external noxious stimuli and axonal degeneration of sensory neurons in flies' legs. Conversely, UCHL1 overexpression improves DSN-like defects of T2D model flies. UCHL1 governs insulin signaling by deubiquitinating insulin receptor substrate 1 (IRS1) and antagonizes an E3 ligase of IRS1, Cullin 1 (CUL1). Consistent with these results, genetic and pharmacological suppression of CUL1 activity rescues T2D- and DSN-associated phenotypes. Therefore, our findings suggest a complete set of genetic factors explaining T2D and DSN, together with potential remedies for the diseases.

Atlas of fetal metabolism during mid-to-late gestation and diabetic pregnancy

Mounting evidence suggests metabolism instructs stem cell fate decisions. However, how fetal metabolism changes during development and how altered maternal metabolism shapes fetal metabolism remain unexplored. We present a descriptive atlas of in vivo fetal murine metabolism during mid-to-late gestation in normal and diabetic pregnancy. Using 13C-glucose and liquid chromatography-mass spectrometry (LC-MS), we profiled the metabolism of fetal brains, hearts, livers, and placentas harvested from pregnant dams between embryonic days (E)10.5 and 18.5. Our analysis revealed metabolic features specific to a hyperglycemic environment and signatures that may denote developmental transitions during euglycemic development. We observed sorbitol accumulation in fetal tissues and altered neurotransmitter levels in fetal brains isolated from hyperglycemic dams. Tracing 13C-glucose revealed disparate fetal nutrient sourcing depending on maternal glycemic states. Regardless of glycemic state, histidine-derived metabolites accumulated in late-stage fetal tissues. Our rich dataset presents a comprehensive overview of in vivo fetal tissue metabolism and alterations due to maternal hyperglycemia.

Proteomics-based screening of AKR1B1 as a therapeutic target and validation study for sepsis-associated acute kidney injury

Background

Sepsis and sepsis-associated acute kidney injury (SA-AKI) pose significant global health challenges, necessitating the development of innovative therapeutic strategies. Dysregulated protein expression has been implicated in the initiation and progression of sepsis and SA-AKI. Identifying potential protein targets and modulating their expression is crucial for exploring alternative therapies.

Method

We established an SA-AKI rat model using cecum ligation perforation (CLP) and employed differential proteomic techniques to identify protein expression variations in kidney tissues. Aldose reductase (AKR1B1) emerged as a promising target. The SA-AKI rat model received treatment with the aldose reductase inhibitor (ARI), epalrestat. Blood urea nitrogen (BUN) and creatinine (CRE) levels, as well as IL-1β, IL-6 and TNF-α levels in the serum and kidney tissues, were monitored. Hematoxylin-eosin (H-E) staining and a pathological damage scoring scale assessed renal tissue damage, while protein blotting determined PKC (protein kinase C)/NF-κB pathway protein expression.

Result

Differential proteomics revealed significant downregulation of seven proteins and upregulation of 17 proteins in the SA-AKI rat model renal tissues. AKR1B1 protein expression was notably elevated, confirmed by Western blot. ARI prophylactic administration and ARI treatment groups exhibited reduced renal injury, low BUN and CRE levels and decreased IL-1β, IL-6 and TNF-α levels compared to the CLP group. These changes were statistically significant (P < 0.05). AKR1B1, PKC-α, and NF-κB protein expression levels were also lowered in the ARI prophylactic administration and ARI treatment groups compared to the CLP group (P < 0.05).

Conclusions

Epalrestat appeared to inhibit the PKC/NF-κB inflammatory pathway by inhibiting AKR1B1, resulting in reduced inflammatory cytokine levels in renal tissues and blood. This mitigated renal tissue injuries and improved the systemic inflammatory response in the severe sepsis rat model. Consequently, AKR1B1 holds promise as a target for treating sepsis-associated acute kidney injuries.

Ganoderic Acid A: A Potential Natural Neuroprotective Agent for Neurological Disorders: A Review

Ganoderic acid A (GAA) is one of the major triterpenoids in Ganoderma lucidum (GL). Accumulating evidence has indicated that GAA demonstrates multiple pharmacological effects and exhibits treatment potential for various neurological disorders. Here, the effects and mechanisms of GAA in the treatment of neurological disorders were evaluated and discussed through previous research results. By summarizing previous research results, we found that GAA may play a neuroprotective role through various mechanisms: anti-inflammatory, anti-oxidative stress, anti-apoptosis, protection of nerve cells, and regulation of nerve growth factor. Therefore, GAA is a promising natural neuroprotective agent and this review would contribute to the future development of GAA as a novel clinical candidate drug for treating neurological diseases.

The Role of Aldose Reductase in Polyol Pathway: An Emerging Pharmacological Target in Diabetic Complications and Associated Morbidities

The expression of aldose reductase leads to a variety of biological and pathological effects. It is a multifunctional enzyme which has a tendency to reduce aldehydes to the corresponding sugar.alcohol. In diabetic conditions, the aldose reductase enzyme converts glucose into sorbitol using nicotinamide adenine dinucleotide phosphate as a cofactor. It is a key enzyme in polyol pathway which is a surrogate course of glucose metabolism. The polyol pathway has a significant impact on the aetiology of complications in individuals with end-stage diabetes. The exorbitant level of sorbitol leads to the accumulation of intracellular reactive oxygen species in diabetic heart, neurons, kidneys, eyes and other vasculatures, leading to many complications and pathogenesis. Recently, the pathophysiological role of aldose reductase has been explored with multifarious perspectives. Research on aldose reductase suggest that besides implying in diabetic complications, the enzyme also turns down the lipid-derived aldehydes as well as their glutathione conjugates. Although aldose reductase has certain lucrative role in detoxification of toxic lipid aldehydes, its overexpression leads to intracellular accumulation of sorbitol which is involved in secondary diabetic complications, such as neuropathy, cataractogenesis, nephropathy, retinopathy and cardiovascular pathogenesis. Osmotic upset and oxidative stress are produced by aldose reductase via the polyol pathway. The inhibition of aldose reductase alters the activation of transcription factors like NF-ƙB. Moreover, in many preclinical studies, aldose reductase inhibitors have been observed to reduce inflammation-related impediments, such as asthma, sepsis and colon cancer, in diabetic subjects. Targeting aldose reductase can bestow a novel cognizance for this primordial enzyme as an ingenious strategy to prevent diabetic complications and associated morbidities. In this review article, the significance of aldose reductase is briefly discussed along with their prospective applications in other afflictions.

Mushrooms and Fungi and Their Biological Compounds with Antidiabetic Activity: A Review

Mushrooms have been used by humans for centuries as food and medicine because they have been shown to affect certain diseases. Mushrooms for medicinal purposes have been consumed in the form of extracts and/or biomass of the mycelium or fruiting body. The beneficial health effects of mushrooms are due to their content of bioactive compounds (polysaccharides, proteins, ergosterol, lectins, etc.). On the other hand, diabetes is one of the metabolic diseases that affects the population worldwide, characterized by hyperglycemia that involves a defective metabolism of insulin, a hormone secreted by β cells and that mainly stimulates glucose absorption by the cells. However, it also affects the metabolism of carbohydrates, fats and proteins; poor control of this disease leads to serious damage to eyesight, kidneys, bones, heart, skin, blood vessels, nerves, etc. It has been reported that the consumption of some mushrooms helps control and treat diabetes, since among other actions, they promote the secretion of insulin by the pancreas, help reduce blood glucose and have α-glucosidase inhibitory activity which improves glucose uptake by cells, which are effects that prescription medications have for patients with diabetes. In that sense, this manuscript shows a review of scientific studies that support the abilities of some mushrooms to be used in the control and/or treatment of diabetes.

Diabetic retinopathy: emerging concepts of current and potential therapy

Diabetic retinopathy (DR) is one of the leading causes of permanent central blindness worldwide. Despite the complexity and inadequate understanding of DR pathogenesis, many of the underlying pathways are currently partially understood and may offer potential targets for future treatments. Anti-VEGF medications are currently the main medication for this problem. This article provides an overview of the established pharmacological treatments and those that are being developed to cure DR. We firstly reviewed the widely utilized approaches including pan-retinal photocoagulation therapy, anti-VEGF therapy, corticosteroid therapy, and surgical management of DR. Next, we discussed the mechanisms of action and prospective benefits of novel candidate medications. Current management are far from being a perfect treatment for DR, despite mild-term favorable efficiency and safety profiles. Pharmacological research should work toward developing longer-lasting treatments or new drug delivery systems, as well as on identifying new molecular targets in the pathogenetical mechanism for DR. In order to find a treatment that is specifically designed for each patient, it is also necessary to properly characterize patients, taking into account elements like hereditary factors and intraretinal neovascularization stages for effective utilization of drugs. The current and potential approaches for diabetic retinopathy. Image was constructed using Biorender.com.

Aldose Reductase (AR) Mediates and Perivascular Adipose Tissue (PVAT) Modulates Endothelial Dysfunction of Short-Term High-Fat Diet Feeding in Mice

Increased adiposity of both visceral and perivascular adipose tissue (PVAT) depots is associated with an increased risk of diabetes and cardiovascular disease (CVD). Under healthy conditions, PVAT modulates vascular tone via the release of PVAT-derived relaxing factors, including adiponectin and leptin. However, when PVAT expands with high-fat diet (HFD) feeding, it appears to contribute to the development of endothelial dysfunction (ED). Yet, the mechanisms by which PVAT alters vascular health are unclear. Aldose reductase (AR) catalyzes glucose reduction in the first step of the polyol pathway and has been long implicated in diabetic complications including neuropathy, retinopathy, nephropathy, and vascular diseases. To better understand the roles of both PVAT and AR in HFD-induced ED, we studied structural and functional changes in aortic PVAT induced by short-term HFD (60% kcal fat) feeding in wild type (WT) and aldose reductase-null (AR-null) mice. Although 4 weeks of HFD feeding significantly increased body fat and PVAT mass in both WT and AR-null mice, HFD feeding induced ED in the aortas of WT mice but not of AR-null mice. Moreover, HFD feeding augmented endothelial-dependent relaxation in aortas with intact PVAT only in WT and not in AR-null mice. These data indicate that AR mediates ED associated with short-term HFD feeding and that ED appears to provoke 'compensatory changes' in PVAT induced by HFD. As these data support that the ED of HFD feeding is AR-dependent, vascular-localized AR remains a potential target of temporally selective intervention.

Novel citrinin derivatives from fungus Penicillium sp. TW131-64 and their antimicrobial activities

Six new citrinin derivatives (1, 2, 4, 10, 11, and 16), along with fourteen known analogues, were acquired from Penicillium sp. TW131-64, a marine-derived fungus strain. The chemical structures of new compounds were identified through adopting various spectroscopic methods in combination with X-ray diffraction technology and comparison of the experimental electronic circular dichroism (ECD) with calculated ones. Among them, compounds 1-4 were nitrogen-containing citrinin derivatives existing in enantiomers which were resolved by chiral chromatography. A putative biosynthetic pathway for compounds 1-4 was proposed. Additionally, the antimicrobial activities of these compounds were detected by the broth microdilution assays. Citrinin derivatives 1, 2, 4 and their corresponding enantiomers (1a, 2a, 4a, 1b, 2b, and 4b) exhibited potent antimicrobial activities towards Helicobacter pylori standard strains and multidrug-resistant strains (MIC values ranging from 0.25 to 8 μg/mL), which were comparable or even better than metronidazole. Moreover, compounds 1a and 1b also showed remarkable broad antimicrobial effects towards Staphylococcus aureus, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, vancomycin-resistant Enterococcus faecium (VRE), and Candida albicans. In summary, our studies demonstrated that citrinin enantiomers 1a-4a and 1b-4b, especially 1a and 1b, can be lead compounds in the research and development (R & D) of novel antimicrobial drugs. KEY POINTS: • 3 novel nitrogen-containing citrinin derivatives (1, 2, 4) were isolated. • citrinin derivatives 1-4 in enantiomers were resolved by chiral chromatography. • citrinin derivatives 1a and 1b showed broad and significant antimicrobial effects.

New adipate esters from Cunninghamella echinulata: isolation, identification, biosynthesis and in silico prediction of potential opioid/anti-opioid and antidiabetic activities

Metabolites of the fungus Cunninghamella echinulata NRRL 1382 were investigated under the effect of fusidic acid (1) feeding. In addition to ergosterol (2) which is a fungal sterol, two novel adipate esters (3, 4) were isolated, and their structures were fully investigated using various spectroscopic analyses, including 1 D, 2 D NMR and HRESIMS. In silico biological target prediction and molecular docking investigation revealed a potential agonist/antagonist activity for compound 3 by binding to µ opioid receptor and antidiabetic effect by aldose reductase inhibitory activity for compound 4.

Influence of Nitrosyl Iron Complex with Thiosulfate Ligands on Therapeutically Important Targets Related to Type 2 Diabetes Mellitus

The high prevalence of type 2 diabetes mellitus (T2DM), and the lack of effective therapy, determine the need for new treatment options. The present study is focused on the NO-donors drug class as effective antidiabetic agents. Since numerous biological systems are involved in the pathogenesis and progression of T2DM, the most promising approach to the development of effective drugs for the treatment of T2DM is the search for pharmacologically active compounds that are selective for a number of therapeutic targets for T2DM and its complications: oxidative stress, non-enzymatic protein glycation, polyol pathway. The nitrosyl iron complex with thiosulfate ligands was studied in this work. Binuclear iron nitrosyl complexes are synthetic analogues of [2Fe-2S] centers in the regulatory protein natural reservoirs of NO. Due to their ability to release NO without additional activation under physiological conditions, these compounds are of considerable interest for the development of potential drugs. The present study explores the effects of tetranitrosyl iron complex with thiosulfate ligands (TNIC-ThS) on T2DM and its complications regarding therapeutic targets in vitro, as well as its ability to bind liposomal membrane, inhibit lipid peroxidation (LPO), and non-enzymatic glycation of bovine serum albumin (BSA), as well as aldose reductase, the enzyme that catalyzes the reduction in glucose to sorbitol in the polyol pathway. Using the fluorescent probe method, it has been shown that TNIC-ThS molecules interact with both hydrophilic and hydrophobic regions of model membranes. TNIC-ThS inhibits lipid peroxidation, exhibiting antiradical activity due to releasing NO (IC50 = 21.5 ± 3.7 µM). TNIC-ThS was found to show non-competitive inhibition of aldose reductase with Ki value of 5.25 × 10^-4 M. In addition, TNIC-ThS was shown to be an effective inhibitor of the process of non-enzymatic protein glycation in vitro (IC50 = 47.4 ± 7.6 µM). Thus, TNIC-ThS may be considered to contribute significantly to the treatment of T2DM and diabetic complications.

The Effects of Prolonged Treatment with Cemtirestat on Bone Parameters Reflecting Bone Quality in Non-Diabetic and Streptozotocin-Induced Diabetic Rats

Cemtirestat, a bifunctional drug acting as an aldose reductase inhibitor with antioxidant ability, is considered a promising candidate for the treatment of diabetic neuropathy. Our study firstly examined the effects of prolonged cemtirestat treatment on bone parameters reflecting bone quality in non-diabetic rats and rats with streptozotocin (STZ)-induced diabetes. Experimental animals were assigned to four groups: non-diabetic rats, non-diabetic rats treated with cemtirestat, diabetic rats, and diabetic rats treated with cemtirestat. Higher levels of plasma glucose, triglycerides, cholesterol, glycated hemoglobin, magnesium, reduced femoral weight and length, bone mineral density and content, parameters characterizing trabecular bone mass and microarchitecture, cortical microarchitecture and geometry, and bone mechanical properties were determined in STZ-induced diabetic versus non-diabetic rats. Treatment with cemtirestat did not affect all aforementioned parameters in non-diabetic animals, suggesting that this drug is safe. In diabetic rats, cemtirestat supplementation reduced plasma triglyceride levels, increased the Haversian canal area and slightly, but insignificantly, improved bone mineral content. Nevertheless, the insufficient effect of cemtirestat treatment on diabetic bone disease does not support its use in the therapy of this complication of type 1 diabetes mellitus.

Design, Synthesis, Computational Investigations, and Antitumor Evaluation of N-Rhodanine Glycosides Derivatives as Potent DNA Intercalation and Topo II Inhibition against Cancer Cells

Nitrogen and sulfur glycosylation was carried out via the reaction of rhodanine (1) with α-acetobromoglucose 3 under basic conditions. Deacetylation of the protected nitrogen nucleoside 4 was performed with CH₃ONa in CH₃OH without cleavage of the rhodanine ring to afford the deprotected nitrogen nucleoside 6. Further, deacetylation of the protected sulfur nucleoside 5 was performed with CH₃ONa in CH₃OH with the cleavage of the rhodanine ring to give the hydrolysis product 7. The protected nitrogen nucleosides 11a-f were produced by condensing the protected nitrogen nucleoside 4 with the aromatic aldehydes 10a-f in C₂H₅OH while using morpholine as a secondary amine catalyst. Deacetylation of the protected nitrogen nucleosides 11a-f was performed with NaOCH₃/CH₃OH without cleavage of the rhodanine ring to afford the deprotected nitrogen nucleosides 12a-f. NMR spectroscopy was used to designate the anomers' configurations. To examine the electrical and geometric properties derived from the stable structure of the examined compounds, molecular modeling and DFT calculations using the B3LYP/6-31+G (d,p) level were carried out. The quantum chemical descriptors and experimental findings showed a strong connection. The IC₅₀ values for most compounds were very encouraging when evaluated against MCF-7, HepG2, and A549 cancer cells. Interestingly, IC₅₀ values for 11a, 12b, and 12f were much lower than those for Doxorubicin (7.67, 8.28, 6.62 μM): (3.7, 8.2, 9.8 μM), (3.1, 13.7, 21.8 μM), and (7.17, 2.2, 4.5 μM), respectively. Against Topo II inhibition and DNA intercalation, when compared to Dox (IC₅₀ = 9.65 and 31.27 μM), compound 12f showed IC₅₀ values of 7.3 and 18.2 μM, respectively. In addition, compound 12f induced a 65.6-fold increase in the rate of apoptotic cell death in HepG2 cells, with the cell cycle being arrested in the G2/M phase as a result. Additionally, it upregulated the apoptosis-mediated genes of P53, Bax, and caspase-3,8,9 by 9.53, 8.9, 4.16, 1.13, and 8.4-fold change, while it downregulated the Bcl-2 expression by 0.13-fold. Therefore, glucosylated Rhodanines may be useful as potential therapeutic candidates against cancer because of their topoisomerase II and DNA intercalation activity.

Novel acetic acid derivatives containing quinazolin-4(3H)-one ring: Synthesis, in vitro, and in silico evaluation of potent aldose reductase inhibitors

Aldose reductase (AR) is a crucial enzyme of the polyol pathway through which glucose is metabolized under conditions of hyperglycemia related to diabetes. A series of novel acetic acid derivatives containing quinazolin-4(3H)-one ring (1-22) was synthesized and tested for in vitro AR inhibitory effect. All the target compounds exhibited nanomolar activity against the target enzyme, and all compounds displayed higher activity as compared to the reference drug epalrestat. Among them, Compound 19, named 2-(4-[(2-[(4-methylpiperazin-1-yl)methyl]-4-oxoquinazolin-3(4H)-ylimino)methyl]phenoxy)acetic acid, displayed the strongest inhibitory effect with a KI value of 61.20 ± 10.18 nM. Additionally, these compounds were investigated for activity against L929, nontumoral fibroblast cells, and MCF-7, breast cancer cells using the MTT assay. Compounds 16 and 19 showed lower toxicity against the normal L929 cells. The synthesized compounds' (1-22) absorption, distribution, metabolism, and excretion properties were also evaluated. Molecular docking simulations were used to look into the possible binding mechanisms of these inhibitors against AR.

Therapeutic potential and nutritional significance of Ganoderma lucidum - a comprehensive review from 2010 to 2022

With a long history in traditional Asian medicine, Ganoderma lucidum (G. lucidum) is a mushroom species suggested to improve health and extend life. Its medicinal reputation has merited it with numerous attributes and titles, and it is evidenced to be effective in the prevention and treatment of various metabolic disorders owing to its unique source of bioactive metabolites, primarily polysaccharides, triterpenoids, and polyphenols, attributed with antioxidant, anti-inflammatory, anticancer, hepatoprotective, antidiabetic activities, etc. These unique potential pharmaceutical properties have led to its demand as an important resource of nutrient supplements in the food industry. It is reported that the variety of therapeutic/pharmacological properties was mainly due to its extensive prebiotic and immunomodulatory functions. All literature summarized in this study was collated based on a systematic review of electronic libraries (PubMed, Scopus databases, Web of Science Core Collection, and Google Scholar) from 2010-2022. This review presents an updated and comprehensive summary of the studies on the immunomodulatory therapies and nutritional significance of G. lucidum, with the focus on recent advances in defining its immunobiological mechanisms and the possible applications in the food and pharmaceutical industries for the prevention and management of chronic diseases. In addition, toxicological evidence and the adoption of standard pharmaceutical methods for the safety assessment, quality assurance, and efficacy testing of G. lucidum-derived compounds will be the gateway to bringing them into health establishments.

A comprehensive review on the antidiabetic attributes of thiazolidine-4-ones: Synthetic strategies and structure-activity relationships

The thiazolidine-4-one scaffold has recently emerged as a potential pharmacophore having clinical significance for medicinal chemists. This heterocyclic ring has been reported to possess a plethora of biological activities, including antidiabetic activity that has inspired researchers to integrate this core with different pharmacophoric fragments to design novel and effective antidiabetic leads. The antidiabetic activity has been observed due to the ability of the thiazolidine-4-one nucleus to interact with different biological targets, including peroxisome proliferator-activated receptor γ, protein tyrosine phosphatase 1B, aldose reductase, α-glucosidase, and α-amylase. The present review discusses the mode of action of thiazolidine-4-ones through these antidiabetic drug targets. This review attempts to summarize and analyze the recent developments with regard to the antidiabetic potential of thiazolidine-4-ones covering different synthetic strategies, structure-activity relationships, and docking studies reported in the literature. The significance of various structural modifications at C-2, N-3, and C-5 of the thiazolidine-4-one ring has also been discussed in this manuscript. This comprehensive compilation will provide an inevitable scope for the design and development of potential antidiabetic drug candidates having a thiazolidine-4-one core.

Novel aldo-keto reductase AKR2E9 regulates aldehyde content in the midgut and antennae of the silkworm (Bombyx mori)

We studied the effects of green leaf volatiles (including reactive aldehydes) emitted by plants on insects that feed on these plants. The silkworm (Bombyx mori) is a model lepidopteran that eats mulberry leaves. Defense-related enzymes in silkworms can be targeted for developing new pest control methods. The aldo-keto reductase (AKR) superfamily catalyzes aldehyde reduction by converting a carbonyl group into an alcohol group. Here, we characterized a novel silkworm AKR, designated as AKR2E9. Recombinant AKR2E9 was overexpressed in Escherichia coli. The recombinant protein was used, along with nicotinamide adenine dinucleotide phosphate as a coenzyme, to reduce aldehydes present in mulberry (Morus alba) leaves. The catalytic efficiency of AKR2E9 toward various aldehyde substrates and its inhibitor sensitivity was lower than those of AKR2E8. High expression levels of akr2e9 messenger RNA (mRNA) were detected in the midgut and antennae of silkworms. In the antennae of adult silkworms, akr2e9 mRNA was more abundant than akr2e8 mRNA. The catalytic efficiency of AKR2E9 was low because of steric hindrance, due to which its active site is blocked. High expression levels of AKR2E9 in the midgut and antennae suggest that it may regulate the detoxification of toxic aldehydes in silkworms.

Nanoformulations of flavonoids for diabetes and microvascular diabetic complications

Diabetes is a chronic metabolic disease characterized by an excess of glucose in the blood. If the constant sugar level is not managed correctly in diabetic patients, it may lead to microvascular complications such as diabetic retinopathy, neuropathy, and nephropathy. There are several synthetic drugs for the management of diabetes; however, these drugs produce immense adverse effects in long-term use. Flavonoids are naturally occurring substances categorized in various classes. They are known for their diverse pharmacological actions, and one of them is prominent antihyperglycemic action and their activities in diabetic complications. In the last few decades, many research studies emphasized the potential of flavonoids in diabetes management. Nevertheless, most flavonoids are insoluble in water and cannot produce desired therapeutic action when administered in conventional dosage forms. To overcome this issue, flavonoids were formulated into different nanoformulations to enhance solubility, absorption, and therapeutic efficacy. This review article focuses on flavonoid nanoformulations and in vitro and in vivo studies reported to overcome diabetes mellitus and its complications.

Peripheral neuropathy: A neglected cause of disability in COPD - A narrative review

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory syndrome with systemic involvement leading to various cardiovascular, metabolic, and neurological comorbidities. It is well known that conditions associated with oxygen deprivation and metabolic disturbance are associated with polyneuropathy, but current data regarding the relationship between COPD and peripheral nervous system pathology is limited. This review summarizes the available data on the association between COPD and polyneuropathy, including possible pathophysiological mechanisms such as the role of hypoxia, proinflammatory state, and smoking in nerve damage; the role of cardiovascular and metabolic comorbidities, as well as the diagnostic methods and screening tools for identifying polyneuropathy. Furthermore, it outlines the available options for managing and preventing polyneuropathy in COPD patients. Overall, current data suggest that optimal screening strategies to diagnose polyneuropathy early should be implemented in COPD patients due to their relatively common association and the additional burden of polyneuropathy on quality of life.

Synthesis and aldose reductase inhibition effects of celecoxib derivatives containing pyrazole linked-sulfonamide moiety

In this article, we report the synthesis of Celecoxib derivatives containing the pyrazole-linked sulfonamide moiety. The enzyme inhibition effects of these derivatives on aldose reductase (AR) were also investigated. The IC₅₀ values of the pyrazole sulfonamide derivatives were determined to be in the range of 40.76-8.25 µM. Among the synthesized derivatives, the compound 16 showed the strongest inhibition effect against the AR enzyme, with an IC₅₀ value of 8.25 µM. Molecular docking studies were carried out to determine the interactions of the synthesized compounds with the AR enzyme, and ADMET studies were performed to assess the pharmacokinetic and drug-likeness properties.

Advances on Cyclocarya paliurus polyphenols: Extraction, structures, bioactivities and future perspectives

Cyclocaryapaliurus (C. paliurus) is an edible and medicinal plant, distributed in southern China. As a kind of new food raw material, the leaves of C. paliurus are processed as tea products in daily life. C. paliurus is recognized as a good source to polyphenols, showing excellent bioactivities, which has attracted more and more attention. Polyphenols are important functional bioactive components in C. paliurus. C. paliurus polyphenols perform nutritional functions in anti-diabetes, anti-hyperlipidemic, anti-obesity, anti-oxidant, and other activities. In this review, we summarize the research progress of extraction technologies, structural characteristics, and bioactivities of C. paliurus polyphenols. Other potential functions of C. paliurus polyphenols are prospected. This review provides a reference for further research and applications of C. paliurus polyphenols in a field of functional food and medicines.

The attenuation effect of potassium 2-(1-hydroxypentyl)-benzoate in a mouse model of diabetes-associated cognitive decline: The protein expression in the brain

Aims

dl‐PHPB (potassium 2‐(1‐hydroxypentyl)‐benzoate) has been shown to have neuroprotective effects against acute cerebral ischemia, vascular dementia, and Alzheimer's disease. The aim of this study was to investigate the effects of dl‐PHPB on memory deficits and preliminarily explore the underlying molecular mechanism.

Methods

Blood glucose and behavioral performance were evaluated in the KK‐A^y diabetic mouse model before and after dl‐PHPB administration. Two‐dimensional difference gel electrophoresis (2D‐DIGE)‐based proteomics was used to identify differentially expressed proteins in brain tissue. Western blotting was used to study the molecular mechanism of the related signaling pathways.

Results

Three‐month‐old KK‐A^y mice were given 150 mg/kg dl‐PHPB by oral gavage for 2 months, which produced no effect on the level of serum glucose. In the Morris water maze test, KK‐A^y mice treated with dl‐PHPB showed significant improvements in spatial learning and memory deficits compared with vehicle‐treated KK‐A^y mice. Additionally, we performed 2D‐DIGE to compare brain proteomes of 5‐month KK‐A^y mice treated with and without dl‐PHPB. We found 14 altered proteins in the cortex and 11 in the hippocampus; two of the 25 altered proteins and another four proteins that were identified in a previous study on KK‐A^y mice were then validated by western blot to further confirm whether dl‐PHPB can reverse the expression levels of these proteins. The phosphoinositide 3‐kinase/protein kinase B/glycogen synthase kinase‐3β (PI3K/Akt/GSK‐3β) signaling pathway was also changed in KK‐A^y mice and dl‐PHPB treatment could reverse it.

Conclusions

These results indicate that dl‐PHPB may play a potential role in diabetes‐associated cognitive impairment through PI3K/Akt/GSK‐3β signaling pathway and the differentially expressed proteins may become putative therapeutic targets.

New horizons of biomaterials in treatment of nerve damage in diabetes mellitus: A translational prospective review

BACKGROUND

Peripheral nerve injury is a serious concern that leads to loss of neuronal communication that impairs the quality of life and, in adverse conditions, causes permanent disability. The limited availability of autografts with associated demerits shifts the paradigm of researchers to use biomaterials as an alternative treatment approach to recover nerve damage.

PURPOSE

The purpose of this study is to explore the role of biomaterials in translational treatment approaches in diabetic neuropathy.

STUDY DESIGN

The present study is a prospective review study.

METHODS

Published literature on the role of biomaterials in therapeutics was searched for.

RESULTS

Biomaterials can be implemented with desired characteristics to overcome the problem of nerve regeneration. Biomaterials can be further exploited in the treatment of nerve damage especially associated with PDN. These can be modified, customized, and engineered as scaffolds with the potential of mimicking the extracellular matrix of nerve tissue along with axonal regeneration. Due to their beneficial biological deeds, they can expedite tissue repair and serve as carriers of cellular and pharmacological treatments. Therefore, the emerging research area of biomaterials-mediated treatment of nerve damage provides opportunities to explore them as translational biomedical treatment approaches.

CONCLUSIONS

Pre-clinical and clinical trials in this direction are needed to establish the effective role of several biomaterials in the treatment of other human diseases.

Natural Products & Bioactivity Inspired Synthetic Pursuits Interfacing with Carbohydrates: Ongoing Journey with C-Glycosides

Natural products, remains the most important source for the discovery of new drugs for the treatment of human diseases. This has inspired the synthetic community to design and develop mimics of natural products either to answer important questions in biology or to explore their therapeutic potentials. Glycosides present themselves abundantly in nature, right from the cell surface receptors to natural products of any origin. The O-Glycosides are hydrolytically less stable compared to C-glycosides and this feature has presented a great opportunity for drug discovery. The discovery of Dapagliflozin, an SGLT inhibitor and C-glucoside, for the treatment of diabetes is one such example. Aryl acyl-anion chemistry has been explored for the synthesis of 2-deoxy-C-aryl furanoside/pyranoside/septanosides. Besides success, the studies have provided valuable insight into the natural propensities of the architectural framework for the cascade to furan derivatives. The aryl acyl-anion chemistry has also enabled the synthesis of biologically active diaryl heptanoids. Inspired from sucesss of Dapagliflozin, new analogues have been synthesized with pyridine and isocoumarin heterocycle as the proximal ring. C-glucosides of isoliquiritigenin have been synthesized for the first time and evaluated as an efficient aldose reductase inhibitor. The synthesis and evaluation of acyl-C-β-D-glucosides and benzyl-C-β-D-glucoside as glucose-uptake promoters has revealed promise in small molecules. The concept of building blocks has been used to obtain natural oxylipins, D-xylo and L-xylo-configured alkane tetrols and novel lipophilic ketones with erythro/threo configured trihydroxy polar head-group as possible anti-mycobacterial agents.

Aldose Reductase: a cause and a potential target for the treatment of diabetic complications

Diabetes mellitus, a disorder of metabolism, results in the elevation of glucose level in the blood. In this hyperglycaemic condition, aldose reductase overexpresses and leads to further complications of diabetes through the polyol pathway. Glucose metabolism-related disorders are the accumulation of sorbitol, overproduction of NADH and fructose, reduction in NAD⁺, and excessive NADPH usage, leading to diabetic pathogenesis and its complications such as retinopathy, neuropathy, and nephropathy. Accumulation of sorbitol results in the alteration of osmotic pressure and leads to osmotic stress. The overproduction of NADH causes an increase in reactive oxygen species production which leads to oxidative stress. The overproduction of fructose causes cell death and non-alcoholic fatty liver disease. Apart from these disorders, many other complications have also been discussed in the literature. Therefore, the article overviews the aldose reductase as the causative agent and a potential target for the treatment of diabetic complications. So, aldose reductase inhibitors have gained much importance worldwide right now. Several inhibitors, like derivatives of carboxylic acid, spirohydantoin, phenolic derivatives, etc. could prevent diabetic complications are discussed in this article.

The Importance of Rhodanine Scaffold in Medicinal Chemistry: A Comprehensive Overview

After the clinical use of epalrestat that contains a rhodanine ring, in type II diabetes mellitus and diabetic complications, rhodanin-based compounds have become an important class of heterocyclic in the field of medicinal chemistry. Various modifications to the rhodanine ring have led to a broad spectrum of biological activity of these compounds. Synthesis of rhodanine derivatives, depended on advenced throughput scanning hits, frequently causes potent and selective modulators of targeted enzymes or receptors, which apply their pharmacological activities through different mechanisms of action. Rhodanine-based compounds will likely stay a privileged scaffold in drug discovery because of different probability of chemical modifications of the rhodanine ring. We have, therefore reviewed their biological activities and structure activity relationship.

Efficient Electrocatalytic Approach to Spiro[Furo[3,2-b]pyran-2,5′-pyrimidine] Scaffold as Inhibitor of Aldose Reductase

A continuously growing interest in convenient and ‘green’ reaction techniques encourages organic chemists to elaborate on new synthetic methodologies. Nowadays, organic electrochemistry is a new useful method with important synthetic and ecological advantages. The employment of an electrocatalytic methodology in cascade reactions is very promising because it provides the combination of the synthetic virtues of the cascade strategy with the ecological benefits and convenience of electrocatalytic procedures. In this research, a new type of the electrocatalytic cascade transformation was found: the electrochemical cyclization of 1,3-dimethyl-5-[[3-hydroxy-6-(hydroxymethyl)-4-oxo-4H-pyran-2-yl](aryl)methyl]pyrimidine-2,4,6(1H,3H,5H)-triones was carried out in alcohols in an undivided cell in the presence of sodium halides with the selective formation of spiro[furo[3,2-b]pyran-2,5′-pyrimidines] in 59-95% yields. This new electrocatalytic process is a selective, facile, and efficient way to create spiro[furo[3,2-b]pyran-2,5′-pyrimidines], which are pharmacologically active heterocyclic systems with different biomedical applications. Spiro[furo[3,2-b]pyran-2,5′-pyrimidines] were found to occupy the binding pocket of aldose reductase and inhibit it. The values of the binding energy and Lead Finder’s Virtual Screening scoring function showed that the formation of protein–ligand complexes was favorable. The synthesized compounds are promising for the inhibition of aldose reductase. This makes them interesting for study in the treatment of diabetes or similar diseases.

Neuroprotective validation of pectin in T2DM-induced allodynia and hyperalgesia in diabetic peripheral neuropathic pain

AIM

To validate neuroprotective effect of pectin against neuropathic pain in diabetic rodents.

MATERIAL AND METHOD

Pectin was isolated and characterised from different sources to validate its neuroprotective effect against T2DM associated neuropathic pain. The antioxidant activity of pectins was done by the DPPH method. Type-2 diabetes mellitus (T2DM) was induced in Wistar albino rats by high-fat diet and high-fat emulsion feeding for 2 weeks followed by a single i.p. of Sterptozotocin in 3rd week. The animals were grouped as positive control and Citrus sinensis (L.) Osbeck peel pectin (CSL-OP) as test group and treated for the next 4 weeks. Body weight and blood glucose were measured up to 8 weeks; however, behavioural assessment was done at the end of 5th to 8th week.

RESULT

CSL-OP restored the reduced body weight and elevated blood glucose with increased pain threshold and improved walking performance.

CONCLUSION

CSL-OP prevented progression of early diabetic neuropathy with anti-oxidant activity.

(-)-Kusunokinin as a Potential Aldose Reductase Inhibitor: Equivalency Observed via AKR1B1 Dynamics Simulation

(-)-Kusunokinin performed its anticancer potency through CFS1R and AKT pathways. Its ambiguous binding target has, however, hindered the next development phase. Our study thus applied molecular docking and molecular dynamics simulation to predict the protein target from the pathways. Among various candidates, aldo-keto reductase family 1 member B1 (AKR1B1) was finally identified as a (-)-kusunokinin receptor. The predicted binding affinity of (-)-kusunokinin was better than the selected aldose reductase inhibitors (ARIs) and substrates. The compound also had no significant effect on AKR1B1 conformation. An intriguing AKR1B1 efficacy, with respect to the known inhibitors (epalrestat, zenarestat, and minalrestat) and substrates (UVI2008 and prostaglandin H₂), as well as a similar interactive insight of the enzyme pocket, pinpointed an ARI equivalence of (-)-kusunokinin. An aromatic ring and a γ-butyrolactone ring shared a role with structural counterparts in known inhibitors. The modeling explained that the aromatic constituent contributed to π-π attraction with Trp111. In addition, the γ-butyrolactone ring bound the catalytic His110 using hydrogen bonds, which could lead to enzymatic inhibition as a consequence of substrate competitiveness. Our computer-based findings suggested that the potential of (-)-kusunokinin could be furthered by in vitro and/or in vivo experiments to consolidate (-)-kusunokinin as a new AKR1B1 antagonist in the future.

Decreased miR-132 plays a crucial role in diabetic encephalopathy by regulating the GSK-3β/Tau pathway

Diabetic encephalopathy (DE) is a global concern and Gordian knot worldwide. miRNA-132 (miR-132) is a class of negative gene regulators that promote diabetic pathologic mechanisms and its complications. However, the molecular mechanisms of miR-132 in DE are elusive, thus an alternative therapeutic strategy is urgently in demand. The present study explored the protective effect and the underlying mechanism of miR-132 on DE via the GSK-β/Tau signaling pathway. Experimentally, a type 2 DM rat model was developed by incorporating a high-fat diet and streptozotocin injection. Further, the DE model was screened via the Morris Water Maze test. Primary hippocampal neurons and HT-22 cells were used for in vitro analysis. We found that hyperglycemia exacerbates cognitive impairment in T2DM rats. When we isolated the primary hippocampus neurons, the expression of miR-132 RNA was low in both the DE hippocampus and primary neurons. GSK-3β and Tau 404 were highly expressed in injured HT-22 cells and diabetic hippocampal tissues. miR-132 downregulated the expression of GSK-3β. Besides, a binding and colocalized relationship between GSK3β and Tau was also reported. These findings suggest that miR-132 exerts protective effects from DE injury by repressing GSK-3β expression and alleviating Tau hyperphosphorylation in HT-22 cells and hippocampus tissues.

The Glyoxalase System-New Insights into an Ancient Metabolism

The glyoxalase system was discovered over a hundred years ago and since then it has been claimed to provide the role of an indispensable enzyme system in order to protect cells from a toxic byproduct of glycolysis. This review gives a broad overview of what has been postulated in the last 30 years of glyoxalase research, but within this context it also challenges the concept that the glyoxalase system is an exclusive tool of detoxification and that its substrate, methylglyoxal, is solely a detrimental burden for every living cell due to its toxicity. An overview of consequences of a complete loss of the glyoxalase system in various model organisms is presented with an emphasis on the role of alternative detoxification pathways of methylglyoxal. Furthermore, this review focuses on the overlooked posttranslational modification of Glyoxalase 1 and its possible implications for cellular maintenance under various (patho-)physiological conditions. As a final note, an intriguing point of view for the substrate methylglyoxal is offered, the concept of methylglyoxal (MG)-mediated hormesis.

Emerging importance of satellite glia in nervous system function and dysfunction

Satellite glial cells (SGCs) closely envelop cell bodies of neurons in sensory, sympathetic and parasympathetic ganglia. This unique organization is not found elsewhere in the nervous system. SGCs in sensory ganglia are activated by numerous types of nerve injury and inflammation. The activation includes upregulation of glial fibrillary acidic protein, stronger gap junction-mediated SGC-SGC and neuron-SGC coupling, increased sensitivity to ATP, downregulation of Kir4.1 potassium channels and increased cytokine synthesis and release. There is evidence that these changes in SGCs contribute to chronic pain by augmenting neuronal activity and that these changes are consistent in various rodent pain models and likely also in human pain. Therefore, understanding these changes and the resulting abnormal interactions of SGCs with sensory neurons could provide a mechanistic approach that might be exploited therapeutically in alleviation and prevention of pain. We describe how SGCs are altered in rodent models of four common types of pain: systemic inflammation (sickness behaviour), post-surgical pain, diabetic neuropathic pain and post-herpetic pain.

Kaempferol Rhamnosides from Geranium sibiricum as Aldose Reductase Inhibitors and Their Content by HPLC Analysis

The study aimed to assess the aldose reductase (AR) inhibition of selected Geranium species and determine the bioactive flavonoid constituents. Flavonoids are known to be good AR inhibitors. Among the species examined, G. sibiricum exhibited potent inhibition of AR (IC50 value, 2.4 µg/mL). Further examination of G. sibiricum, after solvent extraction and fractionation, revealed that the ethyl acetate fraction (IC50 value, 0.41 µg/mL) had a potent AR inhibitory effect. Kaempferol rhamnosides were the active compounds from this fraction. Moreover, G. sibiricum showed the highest content of kaempferol-7-O-rhamnoside and kaempferol-3,7-O-dirhamnoside among the samples examined with a concentration in the extracts of 28.1 and 2.2 mg/g, respectively. This study shows that G. sibiricum exhibits promising AR inhibitory activity, which can be explored further as a natural therapy for treating and managing complications associated with diabetes.

Neuroprotective Effect of Salvianolic Acid A against Diabetic Peripheral Neuropathy through Modulation of Nrf2

Oxidative stress has been recognized as the contributor to diabetic peripheral neuropathy (DPN). Antioxidant strategies have been most widely explored; nevertheless, whether antioxidants alone prevent DPN still remains inconclusive. In the present study, we established an in vitro DPN cell model for drug screening using Schwann RSC96 cells under high glucose (HG) stimulation, and we found that salvianolic acid A (SalA) mitigated HG-induced injury evidenced by cell viability and myelination. Mechanistically, SalA exhibited strong antioxidative effects by inhibiting 1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing reactive oxygen species (ROS), malondialdehyde (MDA), and oxidized glutathione (GSSG) content, as well as upregulating antioxidative enzyme mRNA expression. In addition, SalA significantly extenuated neuroinflammation with downregulated inflammatory factor mRNA expression. Furthermore, SalA improved the mitochondrial function of HG-injured Schwann cells by scavenging mitochondrial ROS, decreasing mitochondrial membrane potential (MMP), and enhancing ATP production, as well as upregulating oxidative phosphorylation gene expression. More importantly, we identified nuclear factor-E2-related factor 2 (Nrf2) as the upstream regulator which mediated protective effects of SalA on DPN. SalA directly bound to the Kelch domain of Kelch-like ECH-associated protein 1 (Keap1) and thus disrupted the interaction of Nrf2 and Keap1 predicted by LibDock of Discovery Studio. Additionally, SalA significantly inhibited Nrf2 promoter activity and downregulated Nrf2 mRNA expression but without affecting Nrf2 protein expression. Interestingly, SalA upregulated the nuclear Nrf2 expression and promoted Nrf2 nuclear translocation by high content screening assay, which was confirmed to be involved in its antiglucotoxicity effect by the knockdown of Nrf2 in RSC96 cells. In KK-Ay mice, we demonstrated that SalA could effectively improve the abnormal glucose and lipid metabolism and significantly protect against DPN by increasing the mechanical withdrawal threshold and sciatic nerve conduction velocity and restoring the ultrastructural impairment of the injured sciatic nerve induced by diabetes. Hence, SalA protected against DPN by antioxidative stress, attenuating neuroinflammation, and improving mitochondrial function via Nrf2. SalA may be prospective therapeutics for treating DPN.

In vitro studies of potent aldose reductase inhibitors: Synthesis, characterization, biological evaluation and docking analysis of rhodanine-3-hippuric acid derivatives

Inhibitors of aldose reductase are rate-limiting enzymes and could play a key role to prevent the complications of diabetes. In our attempt to develop novel inhibitors of aldose reductase, the derivatives of rhodanine-3-hippuric acid-pyrazole hybrid were synthesized and characterised by spectral data. The biological studies reveal that all the compounds show an excellent activity against ALR2 with IC₅₀ values ranging from 0.04 to 1.36 µM. Among these the synthesised compounds 6a-m, 6g and 6e showed specific inhibitory activity with IC₅₀ values of 0.04 and 0.06 µM respectively against ALR2 and found to be more potent than epalrestat (IC₅₀ = 0.87 μM), the only aldose reductase inhibitor currently used in the therapy. Molecular docking analysis using the AR-NADP⁺ complex as a receptor was performed with all the synthesized compounds. All the compounds exhibit a well-defined binding mode within the AR active site, similarly to previous described AR inhibitors, with the anion head group bound to the catalytic center, blocking thus its activity. By forming hydrogen bonds with Tyr48 and His110 of the protein from ALR2 (PDB ID: 2FZD), the compounds 6g and 6e interrupt the proton donation mechanism, which is necessary for the catalytic activity of ALR2.

Methylglyoxal Metabolism and Aging-Related Disease: Moving from Correlation toward Causation

Methylglyoxal (MG) is a ubiquitous metabolite that spontaneously reacts with biopolymers forming advanced glycation end-products (AGEs). AGEs are strongly associated with aging-related diseases, including cancer, neurodegenerative diseases, and diabetes. As the formation of AGEs is nonenzymatic, the damage caused by MG and AGEs has been regarded as unspecific. This may have resulted in the field generally been regarded as unappealing by many researchers, as detailed mechanisms have been difficult to probe. However, accumulating evidence highlighting the importance of MG in human metabolism and disease, as well as data revealing how MG can elicit its signaling function via specific protein AGEs, could change the current mindset, accelerating the field to the forefront of future research.

Quercetin protects against diabetic encephalopathy via SIRT1/NLRP3 pathway in db/db mice

Epidemiological studies have found that diabetes and cognitive dysfunction are closely related. Quercetin has been certified with the effect on improving diabetes mellitus (DM) and cognitive impairment. However, the effect and related mechanism of quercetin on diabetic encephalopathy (DE) are still ambiguous. In this study, we used the db/db mice (diabetic model) to discover whether quercetin could improve DE through the Sirtuin1/NLRP3 (NOD‐, LRR‐ and pyrin domain‐containing 3) pathway. Behavioural results (Morris water maze and new object recognition tests) showed that quercetin (70 mg/kg) improved the learning and memory. Furthermore, quercetin alleviated insulin resistance and the level of fasting blood glucose. Besides, Western blot analysis also showed that quercetin increased the protein expressions of nerve‐ and synapse‐related protein, including postsynapticdensity 93 (PSD93), postsynapticdensity 95 (PSD95), brain‐derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the brain of db/db mice. Quercetin also increased the protein expression of SIRT1 and decreased the expression of NLRP3 inflammation‐related proteins, including NLRP3, the adaptor protein ASC and cleaved Caspase‐1, the pro‐inflammatory cytokines IL‐1β and IL‐18. In conclusion, the present results indicate that the SIRT1/NLRP3 pathway may be a crucial mechanism for the neuroprotective effect of quercetin against DE.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.