The role of insulin against hydrogen peroxide-induced oxidative damages in differentiated SH-SY5Y cells

Cell Culture Media, Unlike the Presence of Insulin, Affect α-Synuclein Aggregation in Dopaminergic Neurons

There are several links between insulin resistance and neurodegenerative disorders such as Parkinson’s disease. However, the direct influence of insulin signaling on abnormal α-synuclein accumulation—a hallmark of Parkinson’s disease—remains poorly explored. To our best knowledge, this work is the first attempt to investigate the direct effects of insulin signaling on pathological α-synuclein accumulation induced by the addition of α-synuclein preformed fibrils in primary dopaminergic neurons. We found that modifying insulin signaling through (1) insulin receptor inhibitor GSK1904529A, (2) SHIP2 inhibitor AS1949490 or (3) PTEN inhibitor VO-OHpic failed to significantly affect α-synuclein aggregation in dopaminergic neurons, in contrast to the aggregation-reducing effects observed after the addition of glial cell line-derived neurotrophic factor. Subsequently, we tested different media formulations, with and without insulin. Again, removal of insulin from cell culturing media showed no effect on α-synuclein accumulation. We observed, however, a reduced α-synuclein aggregation in neurons cultured in neurobasal medium with a B27 supplement, regardless of the presence of insulin, in contrast to DMEM/F12 medium with an N2 supplement. The effects of culture conditions were present only in dopaminergic but not in primary cortical or hippocampal cells, indicating the unique sensitivity of the former. Altogether, our data contravene the direct involvement of insulin signaling in the modulation of α-synuclein aggregation in dopamine neurons. Moreover, we show that the choice of culturing media can significantly affect preformed fibril-induced α-synuclein phosphorylation in a primary dopaminergic cell culture.

Diabetes mellitus and Parkinson's disease: dangerous liaisons between insulin and dopamine

The relationship between diabetes mellitus and Parkinson's disease has been described in several epidemiological studies over the 1960s to date. Molecular studies have shown the possible functional link between insulin and dopamine, as there is strong evidence demonstrating the action of dopamine in pancreatic islets, as well as the insulin effects on feeding and cognition through central nervous system mechanism, largely independent of glucose utilization. Therapies used for the treatment of type 2 diabetes mellitus appear to be promising candidates for symptomatic and/or disease-modifying action in neurodegenerative diseases including Parkinson's disease, while an old dopamine agonist, bromocriptine, has been repositioned for the type 2 diabetes mellitus treatment. This review will aim at reappraising the different studies that have highlighted the dangerous liaisons between diabetes mellitus and Parkinson's disease.

Diabetes and Cognitive Impairment: A Role for Glucotoxicity and Dopaminergic Dysfunction

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia, responsible for the onset of several long-term complications. Recent evidence suggests that cognitive dysfunction represents an emerging complication of DM, but the underlying molecular mechanisms are still obscure. Dopamine (DA), a neurotransmitter essentially known for its relevance in the regulation of behavior and movement, modulates cognitive function, too. Interestingly, alterations of the dopaminergic system have been observed in DM. This review aims to offer a comprehensive overview of the most relevant experimental results assessing DA’s role in cognitive function, highlighting the presence of dopaminergic dysfunction in DM and supporting a role for glucotoxicity in DM-associated dopaminergic dysfunction and cognitive impairment. Several studies confirm a role for DA in cognition both in animal models and in humans. Similarly, significant alterations of the dopaminergic system have been observed in animal models of experimental diabetes and in diabetic patients, too. Evidence is accumulating that advanced glycation end products (AGEs) and their precursor methylglyoxal (MGO) are associated with cognitive impairment and alterations of the dopaminergic system. Further research is needed to clarify the molecular mechanisms linking DM-associated dopaminergic dysfunction and cognitive impairment and to assess the deleterious impact of glucotoxicity.

Diabetes Mellitus and Parkinson's Disease: Shared Pathophysiological Links and Possible Therapeutic Implications

Diabetes mellitus (DM) is the most common chronic metabolic disease. Parkinson's disease (PD) is considered one of the most common neurodegenerative diseases. There are many similarities between both conditions. Both disorders are chronic diseases. Both diseases result from a decrease in a specific substance: dopamine in PD, and insulin in DM. Besides, both disorders arise due to the destruction of particular cells, dopaminergic cells in PD, and pancreatic beta-cell in DM. Recently, many epidemiological and experimental studies showed a connection between DM and PD. There are common underlying mechanisms in the pathophysiology of both diseases. These underlying mechanisms include mitochondrial dysfunction, oxidative stress, hyperglycemia, and inflammation. Insulin resistance is indeed the hallmark of DM, especially type 2 diabetes mellitus (T2DM), which plays a significant role in these pathophysiological and molecular mechanisms. Besides, many studies revealed that anti-diabetic drugs have a beneficial effect on PD. In this current literature review, we aim to explore the standard pathophysiological and molecular linkages between these two disorders as well as how DM could affect the incidence and progression of PD. We also review how anti-diabetic drugs impact PD. In the future, further experimental and expanded clinical studies are needed to fully understand the exact pathophysiological connections between the two disorders and the efficacy of insulin and other anti-diabetic drugs in the treatment of PD in diabetic patients. Fully understanding and targeting these pathophysiological and molecular links could result in de novo curative therapy for PD and DM.

The Relevance of Insulin Action in the Dopaminergic System

The advances in medicine, together with lifestyle modifications, led to a rising life expectancy. Unfortunately, however, aging is accompanied by an alarming boost of age-associated chronic pathologies, including neurodegenerative and metabolic diseases. Interestingly, a non-negligible interplay between alterations of glucose homeostasis and brain dysfunction has clearly emerged. In particular, epidemiological studies have pointed out a possible association between Type 2 Diabetes (T2D) and Parkinson’s Disease (PD). Insulin resistance, one of the major hallmark for etiology of T2D, has a detrimental influence on PD, negatively affecting PD phenotype, accelerating its progression and worsening cognitive impairment. This review aims to provide an exhaustive analysis of the most recent evidences supporting the key role of insulin resistance in PD pathogenesis. It will focus on the relevance of insulin in the brain, working as pro-survival neurotrophic factor and as a master regulator of neuronal mitochondrial function and oxidative stress. Insulin action as a modulator of dopamine signaling and of alpha-synuclein degradation will be described in details, too. The intriguing idea that shared deregulated pathogenic pathways represent a link between PD and insulin resistance has clinical and therapeutic implications. Thus, ongoing studies about the promising healing potential of common antidiabetic drugs such as metformin, exenatide, DPP IV inhibitors, thiazolidinediones and bromocriptine, will be summarized and the rationale for their use to decelerate neurodegeneration will be critically assessed.

The Neuroprotective Effect of Conditioned Medium from Human Adipose-Derived Mesenchymal Stem Cells is Impaired by N-acetyl Cysteine Supplementation

Oxidative stress is a common feature in neurodegenerative diseases associated with neuroinflammation, and therefore, has been proposed as a key target for novel therapies for these diseases. Recently, adipose-derived stem cell (ASC)-based cell therapy has emerged as a novel strategy for neuroprotection. In this study, we evaluate the therapeutic role of ASC-conditioned medium (ASC-CM) against H₂O₂-induced neurotoxicity in a new in vitro model of ec23/brain-derived neurotrophic factor (BDNF)-differentiated human SH-SY5Y neuron-like cells (SH-SY5Yd). In the presence of ASC-CM, stressed SH-SY5Yd cells recover normal axonal morphology (with an almost complete absence of H₂O₂-induced axonal beading), electrophysiological features, and cell viability. This beneficial effect of ASC-CM was associated with its antioxidant capacity and the presence of growth factors, namely, BDNF, glial cell line-derived neurotrophic factor, and transforming growth factor β1. Moreover, the neuroprotective effect of ASC-CM was very similar to that obtained from treatment with BDNF, an essential factor for SH-SY5Yd cell survival. Importantly, we also found that the addition of the antioxidant agent N-acetyl cysteine to ASC-CM abolished its restorative effect; this was associated with a strong reduction in reactive oxygen species (ROS), in contrast to the moderate decrease in ROS produced by ASC-CM alone. These results suggest that neuronal restorative effect of ASC-CM is associated with not only the release of essential neurotrophic factors, but also the maintenance of an appropriate redox state to preserve neuronal function.

3-(Naphthalen-2-yl(propoxy)methyl)azetidine hydrochloride attenuates MPP＋-induced cytotoxicity by regulating oxidative stress and mitochondrial dysfunction in SH-SY5Y cells

Parkinson’s disease (PD) is a common chronic neurodegenerative disease mainly caused by the death of dopaminergic neurons. However, no complete pharmacotherapeutic approaches are currently available for PD therapies. 1-methyl-4-phenylpyridinium (MPP⁺)-induced SH-SY5Y neurotoxicity has been broadly utilized to create cellular models and study the mechanisms and critical aspects of PD. In the present study, we examined the role of a novel azetidine derivative, 3-(naphthalen-2-yl(propoxy)methyl)azetidine hydrochloride (KHG26792), against MPP⁺-induced neurotoxicity in SH-SY5Y cells. Treatment of KHG26792 significantly attenuated MPP⁺-induced changes in the protein levels of Bcl-2 and Bax together with efficient suppression of MPP⁺-induced activation of caspase-3 activity. KHG26792 also attenuated mitochondrial potential and levels of ROS, Ca²⁺, and ATP in MPP⁺-treated SH-SY5Y cells. Additionally, KHG26792 inhibited the induced production of nitric oxide and malondialdehyde. Moreover, the protective effect of KHG26792 is mediated through regulation of glutathione peroxidase and GDNF levels. Our results suggest a possibility that KHG26792 treatment significantly protects against MPP⁺-induced neurotoxicity in SH-SY5Y cells and KHG26792 may be a valuable therapeutic agent for the treatment of PD induced by an environmental toxin.

Sodium alginate in oil-poloxamer organogels for intravaginal drug delivery: Influence on structural parameters, drug release mechanisms, cytotoxicity and in vitro antifungal activity

Local administration of antimicrobial agents is the first therapeutic approach for the treatment of Candida albicans infections. The duration of contact of formulations with the vaginal mucosa is critical for therapeutic efficacy. This study describes the development of organogels employing an oil phase composed of oleic acid (OA) and an aqueous phase consisting of the poloxamer PL₄₀₇, alone or in association with PL₁₈₈, together with 0.25-1% sodium alginate (SA), in order to obtain an intravaginal drug delivery system capable of modulating the release of voriconazole (VRC). VRC was solubilized in oleic acid homogenized with the PL-SA aqueous phase, at a final concentration of 5 mg/mL. Physicochemical characterization was performed for evaluation of the influence of SA on organogel structural organization, biopharmaceutical properties, pharmacological efficacy, and cytotoxicity, envisaging use of the formulation for the treatment of vaginal candidiasis. The enthalpy variation values showed greater changes in the presence of PL₁₈₈ and after the incorporation of SA or VRC in the organogels. Rheological analysis showed T_sol-gel values in the ranges 11-39 °C and 27-30 °C for the OA-PL₄₀₇ and OA-PL_407-188 formulations, respectively. Oscillatory analysis of OA-PL_407-188 showed that G' was ~20-fold higher than G″, even after submitting the formulation to temperature variation. VRC-OA-PL₄₀₇ showed fast drug release from 0.5 to 4 h, maintaining total release (~100%) up to 24 h. The incorporation of SA in the organogels enabled modulation of VRC release, with different release percentages for 0.25% SA (~75%), 0.5% SA (~55%), and 1% SA (~35%). The formulation was non-cytotoxic towards HeLa and Vero cell lines. In diffusion tests, it was able to prevent the growth of Candida albicans and Candida krusei. In conclusion, the results suggested that OA-PL_407-188-SA organogels could be possible new systems for VRC delivery, with potential for use in future vaginal applications.

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.

Insulin on activation of autophagy with integrins and syndecans against MPP+-induced α-synuclein neurotoxicity

Parkinson's disease (PD) is the second most common neurodegenerative disease in the elderly caused by dopaminergic neuronal cell death. Human neuroblastoma SH-SY5Y cells differentiated by retinoic acid have been used to study the in vitro PD model induced by 1-methyl-4-phenyl pyridinium (MPP⁺). In this study, pretreatment of insulin inhibited MPP⁺-induced cell membrane damages, which also inhibited the Cox-2 and α-synuclein levels. In addition, MPP⁺ and/or insulin enhanced the autophagy LC3. Furthermore, MPP⁺-induced neurotoxicity diminished the integrins β3, αV and induced the syndecan-1 and -3. Insulin pretreatment enhanced the phosphorylation of integrin-linked kinase and further induced the integrin and syndecan molecules. These findings suggest that insulin prevents MPP⁺-induced α-synuclein apoptosis through the activation of integrin and syndecan pathways in SH-SY5Y+RA cells.

Protective effects of activated signaling pathways by insulin on C6 glial cell model of MPP+-induced Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease (AD) associated with mitochondrial dysfunction mediated by oxidative stress. Astrocytes regulate neuronal function via the modulation of synaptic transmission and plasticity, secretion of growth factors, uptake of neurotransmitters, and regulation of extracellular ion concentrations and metabolic support of neurons. Therefore, this study was undertaken to investigate the mechanism of action of insulin on a 1-methyl-4-phenylpyridinium (MPP⁺)-induced toxicity of events associated in cell viability and toxicity to the expression profile of cell signaling pathway proteins and genes in rat C6 glial cells. The various concentrations of MPP⁺ alone inhibited cell viability in a dose-dependent manner. Pretreatment of insulin prevented the cell death and lowered the intracellular reactive oxygen species and calcium ion influx by MPP⁺. Insulin also suppressed the α-synuclein and elevated the insulin signaling pathway molecules IR, IGF-1R, IRS-1 and IRS-2 in C6 cells through phosphorylation of Akt/ERK survival pathways. Moreover, insulin inhibits MPP⁺-induced Bax to Bcl-2 ratio. These results suggest that insulin has a protective effect on the MPP⁺-toxicity in C6 glial cells.

The Neuroprotective Role of Insulin Against MPP(+) -Induced Parkinson's Disease in Differentiated SH-SY5Y Cells

Parkinson's disease (PD) is a common chronic neurodegenerative disorder associated with aging that primarily caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SN). Retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells (SH-SY5Y+RA) have been broadly utilized in studies of mechanisms of the pathogenesis underlying 1-Methyl-4-phenyl pyridinium (MPP(+))-induced PD models. Here, we investigated the neuroprotective mechanisms of insulin on MPP(+)-induced neurotoxicity on SH-SY5Y+RA cells. Recent studies suggest that insulin has a protective effect against oxidative stress but not been elucidated for PD. In this study, pretreatment of insulin prevented the cell death in a dose dependent manner and lowered nitric oxide (NO) release, reactive oxygen species (ROS), and calcium ion (Ca(2+)) influx induced by MPP(+). Insulin also elevated tyrosine hydroxylase (TH) and insulin signaling pathways in dopaminergic neuron through activating PI3K/Akt/GSK-3 survival pathways which in turn inhibits MPP(+)-induced iNOS and ERK activation, and Bax to Bcl-2 ratio. These results suggest that insulin has a protective effect on MPP(+)-neurotoxicity in SH-SY5Y+RA cells.

Vitis vinifera (Muscat Variety) Seed Ethanolic Extract Preserves Activity Levels of Enzymes and Histology of the Liver in Adult Male Rats with Diabetes

The effect of V. vinifera seeds on carbohydrate metabolizing enzymes and other enzymes of the liver in diabetes is currently unknown. We therefore investigated changes in the activity levels of these enzymes following V. vinifera seed extract administration to diabetic rats. Methods. V. vinifera seed ethanolic extract (250 and 500 mg/kg/day) or glibenclamide (600 μg/kg/day) was administered to streptozotocin-induced male diabetic rats for 28 consecutive days. At the end of treatment, liver was harvested and activity levels of various liver enzymes were determined. Levels of thiobarbituric acid reactive substances (TBARS) were measured in liver homogenates and liver histopathological changes were observed. Results. V. vinifera seed ethanolic extract was able to prevent the decrease in ICDH, SDH, MDH, and G-6-PDH and the increase in LDH activity levels in liver homogenates. The seed extract also caused serum levels of ALT, AST, ALP, ACP, GGT, and total bilirubin to decrease while causing total proteins to increase. Additionally, the levels of ALT, AST, and TBARS in liver homogenates were decreased. Histopathological changes in the liver were reduced. Conclusion. Near normal activity levels of various enzymes and histology of the liver following V. vinifera seed ethanolic extract administration may be due to decrease in liver oxidative stress in diabetes.

Insulin improves osteogenesis of titanium implants under diabetic conditions by inhibiting reactive oxygen species overproduction via the PI3K-Akt pathway

Clinical evidence indicates that insulin therapy improves implant survival rates in diabetic patients; however, the mechanisms responsible for this effect are unknown. Here, we test if insulin exerts anti-oxidative effects, thereby improving diabetes-associated impaired osteoblast behavior on titanium implants. To test this hypothesis, we cultured primary rabbit osteoblasts in the presence of titanium implants and studied the impact of treatment with normal serum (NS), diabetic serum (DS), DS + insulin, DS + tempol (a superoxide dismutase mimetic), DS + insulin + tempol, and DS + insulin + wortmannin. We analyzed cell function, apoptosis, and reactive oxygen species (ROS) production in osteoblasts following the various treatments. Treatment with DS induced osteoblast dysfunction, evidenced by impaired cell attachment and morphology, decreased cell proliferation and ALP activity, and decreased expression of osteogenesis-related genes. We also observed a significant increase in apoptosis. Importantly, treatment with DS resulted in increased production of ROS in osteoblasts. In contrast, treatment with insulin inhibited ROS production, alleviated cell dysfunction, and decreased apoptosis of osteoblasts on the implants. Scavenging ROS with tempol also attenuated cell dysfunction. Compared to insulin treatment alone, the combination of insulin and tempol failed to further improve osteoblast functional recovery. Moreover, the anti-oxidative and pro-osteogenic effects afforded by insulin were almost completely abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. These results demonstrate, for the first time, that insulin treatment alleviates the impaired osteogenesis of titanium implants under diabetic conditions by inhibiting ROS overproduction via a PI3K/Akt-dependent mechanism. Both the anti-oxidative and metabolic properties of insulin should make it a viable therapeutic option to combat diabetic implant failure.