Agmatine protects Müller cells from high-concentration glucose-induced cell damage via N-methyl-D-aspartic acid receptor inhibition

Exploring the clinical connections between epilepsy and diabetes mellitus: Promising therapeutic strategies utilizing agmatine and metformin

PURPOSE

Diabetes mellitus (DM) and epilepsy and the psychological and socio-economic implications that are associated with their treatments can be quite perplexing. Metformin is an antihyperglycemic medication that is used to treat type 2 DM. In addition, metformin elicits protective actions against multiple diseases, including neurodegeneration and epilepsy. Recent studies indicate that metformin alters the resident gut microbiota in favor of species producing agmatine, an arginine metabolite which, in addition to beneficially altering metabolic pathways, is a potent neuroprotectant and neuromodulant.

METHODS

We first examine the literature for epidemiological and clinical evidences linking DM and epilepsy. Next, basing our analyses on published literature, we propose the possible complementarity of agmatine and metformin in the treatment of DM and epilepsy.

RESULTS

Our analyses of the clinical data suggest a significant association between pathogeneses of epilepsy and DM. Further, both agmatine and metformin appear to be multimodal therapeutic agents and have robust antiepileptogenic and antidiabetic properties. Data from animal and clinical studies largely support the use of metformin/agmatine as a double-edged pharmacotherapeutic agent against DM and epilepsy, particularly in their concurrent pathological occurrences.

CONCLUSION

The present review explores the evidences and available data on possible uses of metformin/agmatine as pertinent antidiabetic and antiepileptic agents. Our hope is that this will stimulate further research on the therapeutic actions of these multimodal agents, particularly for subject-specific clinical outcomes.

Neuroprotection by agmatine: Possible involvement of the gut microbiome?

Agmatine, an endogenous polyamine derived from L-arginine, elicits tremendous multimodal neuromodulant properties. Alterations in agmatinergic signalling are closely linked to the pathogeneses of several brain disorders. Importantly, exogenous agmatine has been shown to act as a potent neuroprotectant in varied pathologies, including brain ageing and associated comorbidities. The antioxidant, anxiolytic, analgesic, antidepressant and memory-enhancing activities of agmatine may derive from its ability to regulate several cellular pathways; including cell metabolism, survival and differentiation, nitric oxide signalling, protein translation, oxidative homeostasis and neurotransmitter signalling. This review briefly discusses mammalian metabolism of agmatine and then proceeds to summarize our current understanding of neuromodulation and neuroprotection mediated by agmatine. Further, the emerging exciting bidirectional links between agmatine and the resident gut microbiome and their implications for brain pathophysiology and ageing are also discussed.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Protective Effect of Agmatine Against Cisplatin- Induced Cellular Apoptosis in an Auditory Cell Line

BACKGROUND

The aims of this study were to evaluate the protective effects of agmatine against cisplatin-induced cellular apoptosis in an audi- tory cell line and to prove the protective mechanism of agmatine.

METHODS

The House Ear Institute-Organ of Corti 1 cells were co-treated with agmatine at different concentrations and 15 μM of cisplatin for 48 hours. Cell viability and proliferation were measured. Annexin V-fluorescein isothiocyanate /propidium iodide staining was performed to analyze apoptosis. The levels of intracellular reactive oxygen species were measured using flow cytometry. The expression of BCL2-associated X protein and the enzymatic activity of caspase-3 was measured to examine the pathway of apoptosis induction.

RESULTS

In normal conditions, the maximal protective effect occurred with 10 mM of agmatine. However, in the presence of cisplatin, the maximal protective effect was observed from 8 mM of agmatine. Thus, 8 mM was chosen as the ideal agmatine concentration for the analysis of protective effects against cisplatin-induced cytotoxicity. Agmatine exerted a significant protective effect against 15 μM of cisplatin when applied for 48 hours and reduced the proportion of necrotic and late apoptotic cells. Agmatine did not significantly reduce the cisplatin-induced increase in reactive oxygen species but decreased the expression of BCL2-associated X protein and the activity of caspase-3.

CONCLUSION

Agmatine protected against cisplatin-induced cellular apoptosis in an auditory cell line. These effects were mediated by the pro- tection of mitochondrial function and inhibition of apoptosis.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood–retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Kir4.1 may represent a novel therapeutic target for diabetic retinopathy (Review)

As the major cause of irreversible loss of vision in adults, diabetic retinopathy (DR) is one of the most serious complications of diabetes. The imbalance of the retinal microenvironment and destruction of the blood-retinal barrier have a significant role in the progression of DR. Inward rectifying potassium channel 4.1 (Kir4.1) is located on Müller cells and is closely related to potassium homeostasis, water balance and glutamate clearance in the whole retina. The present review discusses the functions of Kir4.1 in regulating the retinal microenvironment and related biological mechanisms in DR. In the future, Kir4.1 may represent a novel alternative therapeutic target for DR through affecting the retinal microenvironment.

Retinoprotective effect of agmatine in streptozotocin-induced diabetic rat model: avenues for vascular and neuronal protection : Agmatine in diabetic retinopathy

Diabetic retinopathy (DR) is the most common diabetic neurovascular complication, and the leading cause of preventable blindness among working-age individuals. Recently, agmatine, the endogenous decarboxylated L-arginine, has gained attention as a pleiotropic agent that modulates the diabetes-associated decline in quality of life, and exhibited varied protective biological effects. Diabetes was induced by a single streptozotocin (STZ, 50 mg/kg, i.p.) injection. When diabetes was verified, the animals were randomly allocated into three groups (16 rat each); diabetic, agmatine-treated diabetic (1 mg/kg, daily, for 12 weeks), and control group. Blood glucose homeostasis, retinal redox status, apoptotic parameters, nitric oxide synthase (NOS), nitric oxide (NO), vascular endothelial growth factor (VEGF), glutamate, glutamine, glutamine synthase (GS) activity, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), and mitogen-activated protein kinase (MAPKs) pathways were assayed biochemically. Retinal vascular permeability was measured. Retinal morphology was evaluated by hematoxylin and eosin staining. Retinal N-methyl-D-aspartic acid receptor1 (NMDAR1) and glutamate aspartate transporter (GLAST) mRNA were quantified. Glucose transporter 1, pro-caspase3, and glial fibrillary acidic protein (GFAP) expression were quantified by immunohistochemistry. Chronic agmatine treatment abrogated STZ-induced retinal neurodegeneration features including gliosis, and neuronal apoptosis, restored retinal vascular permeability, mostly through antioxidant, anti-apoptotic capacity, abolishing glutamate excitotoxicity, modulating the activity of NMDARs, MAPKs/NFκB, and NOS/NO pathways. By restoring the molecular and functional background of retinal neurovascular homeostatic balance, agmatine would be appropriate therapeutic option acting upstream of the DR, impeding its progression.

Probucol promotes high glucose-induced proliferation and inhibits apoptosis by reducing reactive oxygen species generation in Müller cells

PURPOSE

To explore the protective effect of probucol on human retinal Müller cells cultured in high glucose.

METHODS

Primary Müller cells from human retinas were cultured in complete DMEM. Third-generation Müller cells were identified using glutamine synthetase (GS) antibody and randomly divided into three groups: normoglycemia (NG, 5.5 mmol/L); hyperglycemia (HG, 30 mmol/L); and hyperglycemia (30 mmol/L) with probucol (10 μmol/L; HGPB). After a 24-h intervention, cell proliferation, apoptosis, and cellular reactive oxygen species (ROS) were measured with a CCK-8 kit, flow cytometry, and DCFH-DA probe, respectively. Kelch-like ECH-associated protein 1 (Keap1), NF-E2-related factor 2 (Nrf2), and glutamate cysteine ligase catalytic subunit (GCLC) protein expression were detected by immunofluorescence staining.

RESULTS

For NG, HG, and HGPB, optical density (OD) values for cell proliferation were 0.98 ± 0.23, 0.58 ± 0.11, and 0.73 ± 0.11; apoptotic rates were 2.79 ± 0.52%, 7.70 ± 0.44%, and 4.00 ± 0.95%; and intracellular ROS were 20.89 ± 5.14, 55.17 ± 14.07, and 26.28 ± 4.73, respectively. Compared to NG, OD was markedly decreased (P < 0.01), apoptosis was increased (P < 0.001), and intracellular ROS level was significantly higher than in HG (P < 0.01). Compared to HG, OD was markedly increased (P < 0.01), apoptosis was meaningfully decreased (P < 0.01), and intracellular ROS level was significantly lower than in HGPB (P < 0.01). GS, Keap1, Nrf2, and GCLC had positive expression.

CONCLUSIONS

Probucol could inhibit intracellular ROS generation, promote proliferation, and decrease apoptosis of human retinal Müller cells cultured in high glucose. This might also be associated with Keap1/Nrf2/ARE oxidative stress signaling pathway activation.

High Glucose-Induced Apoptosis in Human Kidney Cells Was Alleviated by miR-15b-5p Mimics

MicroRNAs were involved in a wide range of biological processes of diabetic nephropathy (DN). It is reported that miR-15b-5p was downregulated in the patients with DN. However, the mechanisms underlying the regulatory effects of miR-15b-5p on patients with diabetes remain unclear. Thus, this study aimed to investigate the role of miR-15b-5p during high glucose (HG)-induced apoptosis in human kidney cells. Quantitative real-time (qRT)-PCR was used to detect the level of miR-15b-5p. CCK-8 assay, EdU staining assays and flow cytometry were used to detect cell proliferation, apoptosis respectively in vitro. In addition, Western blotting was used to determine active caspase-3, cleaved poly(ADP-ribose) polymerase (PARP), phosphorylated (p)-AKT, p-mammalian target of rapamycin (mTOR), p-S6, p-c-Jun N terminal kinase (JNK), p-p38 and p-extracellular signal-regulated kinase (ERK) proteins levels. The expression of miR-15b-5p in patients with DN were dramatically decreased compared with health persons. Similarly, HG down-regulated the expression of miR-15b-5p in HK-2 cells. In contrast, miR-15b-5p mimics alleviated HG-induced apoptosis in HK-2 cells via decreasing the expressions of active caspase 3 and cleaved PARP. EdU detection further confirmed that miR-15b-5p mimics attenuated the anti-proliferation effect of HG in HK-2 cells. Furthermore, HG-induced Akt/mTOR pathway downregulation and JNK upregulation were markedly reversed by miR-15b-5p mimics in cells. The data suggested that miR-15b-5p mimics protects HK-2 cells from HG-induced apoptosis. The anti-apoptotic effects of miR-15b-5p may due to the activation of the Akt/mTOR pathway as well as inactivation of JNK. Taken together, miR-15b-5p might be a potential therapeutic target for the treatment of patients with DN.

Bradykinin-potentiating PEPTIDE-10C, an argininosuccinate synthetase activator, protects against H2O2-induced oxidative stress in SH-SY5Y neuroblastoma cells

Bradykinin-potentiating peptides (BPPs - 5a, 7a, 9a, 10c, 11e, and 12b) of Bothrops jararaca (Bj) were described as argininosuccinate synthase (AsS) activators, improving l-arginine availability. Agmatine and polyamines, which are l-arginine metabolism products, have neuroprotective properties. Here, we investigated the neuroprotective effects of low molecular mass fraction from Bj venom (LMMF) and two synthetic BPPs (BPP-10c, <ENWPHPQIPP; BPP-12b, <EWGRPPGPPIPP) in the SH-SY5Y cell line against H₂O₂-induced oxidative stress. The neuroprotective effects against H₂O₂-induced were analyzed by reactive oxygen species (ROS - DCFH) production; lipid peroxidation (TBARS); intracellular GSH; AsS, iNOS, and NF-kB expressions; nitrite levels (Griess); mitochondrial membrane potential (TMRM); and antioxidant activity (DPPH). Analysis of variance followed by Tukey's post hoc test were calculated for statistical comparisons. Pre-treatment with both BPPs significantly reduced cell death induced by H₂O₂, but BPP-10c showed higher protective capacity than BPP-12b. LMMF pretreatment was unable to prevent the reduction of cell viability caused by H₂O₂. The neuroprotective mechanism of BPP-10c against oxidative stress was investigated. BPP-10c reduced ROS generation and lipid peroxidation in relation to cells treated only with H₂O₂. BBP-10c increased AsS expression and was not neuroprotective in the presence of MDLA, a specific inhibitor of AsS. BPP-10c reduced iNOS expression and nitrate levels but decreased NF-kB expression. Furthermore, BPP-10c protected the mitochondrial membrane against oxidation. Overall, we demonstrated for the first time neuroprotective mechanisms of BPPs against oxidative stress, opening new perspectives to the study and application of these peptides for the treatment of neurodegenerative diseases.

Agmatine protects rat liver from nicotine-induced hepatic damage via antioxidative, antiapoptotic, and antifibrotic pathways

Tobacco smoking with its various forms is a global problem with proved hazardous effects to human health. The present work was planned to study the defending role of agmatine (AGM) on hepatic oxidative stress and damage induced by nicotine in rats. Thirty-two rats divided into four groups were employed: control group, nicotine-only group, AGM group, and AGM-nicotine group. Measurements of serum hepatic biochemical markers, lipid profile, and vascular cell adhesion molecule-1 were done. In addition, malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) activity, and nitrate/nitrite (NOx) levels were estimated in the liver homogenates. Immunohistochemistry for Bax and transforming growth factor beta (TGF-β1) and histopathology of the liver were also included. Data of the study demonstrated that nicotine administration exhibited marked liver deterioration, an increase in liver enzymes, changes in lipid profile, and an elevation in MDA with a decline in levels of SOD, GSH, and NOx (nitrate/nitrite). Also, levels of proapoptotic Bax and profibrotic TGF-β1 showed marked elevation in the liver. AGM treatment to rats in nicotine-only group ameliorated all the previous changes. These findings indicate that AGM could successfully overcome the nicotine-evoked hepatic oxidative stress and tissue injury, apoptosis, and fibrosis.

Conformational study and reassessment of the vibrational assignments for Norspermidine

The present study presents and discusses the conformational preferences of Norspermidine (NSpd). The effects of varying the dielectric constant on the conformational preferences are discussed, with a view to infer which conformation will correspond to the most stable in the pure condensed liquid phase. Within the same context, a set of NSpd-NH3 molecular adducts were simulated in order to determine the relevance of intermolecular hydrogen bonding on the overall stability and relative positioning of the respective vibrational frequencies. The calculations presently performed allowed a reassessment of the vibrational assignments for NSpd. A full assignment of the NSpd vibrational spectra is presented, with special emphasis being given to the vibrational modes that proved to be most affected by hydrogen bonding. The various inconsistencies of a prior study found in the literature were identified and rectified.

Agmatine improves renal function in gentamicin-induced nephrotoxicity in rats

The present study was designed to explore the possible protective effects of agmatine, a known nitric oxide (NO) synthase inhibitor, against gentamicin-induced nephrotoxicity in rats. For this purpose, we quantitatively evaluated gentamicin-induced renal structural and functional alterations using histopathological and biochemical approaches. Furthermore, the effect of agmatine on gentamicin-induced hypersensitivity of urinary bladder rings to acetylcholine (ACh) was evaluated. Twenty-four male Wistar albino rats were randomly divided into 3 groups, namely control, gentamicin (100 mg/kg, i.p.), and gentamicin plus agmatine (40 mg/kg, orally). At the end of the study, all rats were sacrificed and then blood and urine samples and kidneys were taken. Administration of agmatine significantly decreased kidney/body mass ratio, serum creatinine, lactate dehydrogenase (LDH), renal malondialdehyde (MDA), myeloperoxidase (MPO), NO, and tumor necrosis factor-alpha (TNF-α) while it significantly increased creatinine clearance and renal superoxide dismutase (SOD) activity when compared with the gentamicin-treated group. Additionally, agmatine ameliorated tissue morphology as evidenced by histological evaluation and reduced the responses of isolated bladder rings to ACh. Our study indicates that agmatine administration with gentamicin attenuates oxidative-stress associated renal injury by reducing oxygen free radicals and lipid peroxidation, restoring NO level and inhibiting inflammatory mediators such as TNF-α.