Hippocampal insulin resistance and the Sirtuin 1 signaling pathway in diabetes-induced cognitive dysfunction

The effects of orlistat on oxidative stress, recognition memory, spatial memory and hippocampal tissue in experimentally induced obesity in rats

This study investigates the impact of orlistat on oxidative stress, spatial memory, recognition memory, and hippocampal tissue in obese rats. The study groups were divided into control, high fat diet-induced obese (HFDIO), HFDIO+orlistat (HFDIO+ORL) groups, each consisting of 8 animals. While control fed with standart diet, HFDIO and HFDIO+ORL fed with high-fat diets for 8 weeks to induce obesity. Then, ORL treated 10 mg/kg for 7 weeks, while control and HFDIO get water. At 16th week, novel object recognition (NOR) and Morris water maze (MWM) tests were performed. TNF-alpha, IL-1beta levels in hippocampal tissue, and total/native thiol/disulphide levels in serum were measured. TNF-alpha level of HFDIO was higher than control, while lower in HFDIO+ORL compared to HFDIO as like IL-1beta level. On the contrary, serum total thiol level was lower in HFDIO than control and higher in HFDIO+ORL compared to the HFDIO, while disulphide level was opposite of the total thiol levels. While recognition index was higher in HFDIO+ORL, in MWM, latency of finding platform in HFDIO was higher than control and latency of HFDIO+ORL was very similar to control in 2-4 days. The HFDIO group demonstrated decrease in time spent in platform zone compared to control, whereas time spent of the HFDIO+ORL was higher than HFDIO. Our study demonstrates that orlistat administration exerts beneficial effects on oxidative stress, spatial memory, recognition memory, and hippocampal tissue in obese rats. It shows that orlistat may have potential therapeutic implications for obesity-related cognitive impairments and hippocampal dysfunction.

Emerging roles of SIRT1 activator, SRT2104, in disease treatment

Silent information regulator 1 (SIRT1) is a NAD+-dependent class III deacetylase that plays important roles in the pathogenesis of numerous diseases, positioning it as a prime candidate for therapeutic intervention. Among its modulators, SRT2104 emerges as the most specific small molecule activator of SIRT1, currently advancing into the clinical translation phase. The primary objective of this review is to evaluate the emerging roles of SRT2104, and to explore its potential as a therapeutic agent in various diseases. In the present review, we systematically summarized the findings from an extensive array of literature sources including the progress of its application in disease treatment and its potential molecular mechanisms by reviewing the literature published in databases such as PubMed, Web of Science, and the World Health Organization International Clinical Trials Registry Platform. We focuses on the strides made in employing SRT2104 for disease treatment, elucidating its potential molecular underpinnings based on preclinical and clinical research data. The findings reveal that SRT2104, as a potent SIRT1 activator, holds considerable therapeutic potential, particularly in modulating metabolic and longevity-related pathways. This review establishes SRT2104 as a leading SIRT1 activator with significant therapeutic promise.

Arc regulates brain damage and neuroinflammation via Sirt1 signaling following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) accounts for only 5 % of all stroke cases, but carries a heavy burden of morbidity and mortality. Activity regulated cytoskeleton associated protein (Arc) is an immediate early gene (IEG)-coded postsynaptic protein that is involved in synaptic plasticity. Increasing evidence and our previous studies have shown that Arc might be involved in the pathological mechanism of various neurological diseases, such as traumatic brain injury (TBI). In this study, we investigated the level of Arc in cerebrospinal fluids (CSF) of aSAH patients and its potential role in brain damage following experimental SAH model. We found that the levels of Arc in aSAH patients' CSF positively correlated with Hunt-Hess (H&H) grades. Knockdown of endogenous Arc expression by small interfere RNA (siRNA) significantly increased brain edema and oxidative stress following SAH. The results of immunostaining in brain sections showed that knockdown of Arc enhanced activation of microglia and astrocytes. In congruent, generation of inflammatory cytokines following SAH was increased by Si-Arc transfection. The results of western blot analysis showed that knockdown of Arc inhibited the expression of Sirt1 and Nrf2, which was accompanied by decreased enzymatic activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-px). In addition, activation of sirtuin 1 (Sirt1) via agonist SRT2104 markedly decreased the brain damage and neuroinflammation induced by Arc knockdown. In conclusion, knockdown of endogenous Arc could aggravate brain damage and neuroinflammation following experimental SAH, and Arc levels in aSAH patients' CSF might be a potential indicator of brain damage and prognosis.

Intranasal Insulin Alleviates Traumatic Brain Injury by Inhibiting Autophagy and Endoplasmic Reticulum Stress-mediated Apoptosis Through the PI3K/Akt/mTOR Signaling Pathway

Intranasal insulin reduces lesion size and enhances memory capacity in traumatic brain injury (TBI) models, but the molecular mechanisms behind this neuroprotective action not yet understood. Here we used Feeney's free-falling method to construct TBI mouse models and administrated intranasal insulin, rapamycin, insulin and rapamycin, or normal saline to assess their effects on neurological functions, cerebral edema, and the expression of Iba1 in microglia through immunofluorescence assay. We also measured concentrations of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in the brain using enzyme immunosorbent assay, investigated apoptosis with TUNEL staining and Western blotting, and evaluated autophagy, endoplasmic reticulum (ER) stress, and PI3K/Akt/mTOR signaling pathway with Western blotting. The autophagosome was assessed through transmission electron microscopy. Our findings demonstrated that intranasal insulin promoted neurological recovery, decreased brain swelling, and reduced injury lesions on days 1, 3, and 7 post TBI. Moreover, intranasal insulin reduced microglia activation and the concentration of IL-1β or TNF-α on the same days. Through Western blotting and transmission electron microscopy, we observed that intranasal insulin suppressed autophagy while activating the PI3K/AKT/mTOR signaling pathway on days 1 and 3 post TBI. TUNEL assay and Western blotting also indicated that intranasal insulin inhibited ER stress-mediated apoptosis. Interestingly, the mTOR inhibitor rapamycin partially blocked the pro-autophagy and anti-apoptosis effects of intranasal insulin both on days 1 and 3 post TBI. Our results suggest that intranasal insulin can ameliorate TBI by regulating autophagy and ER stress-mediated apoptosis through the PI3K/AKT/mTOR signaling pathway, providing a promising therapeutic strategy for TBI.

The sirtuin family in health and disease

Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.

Investigation and modulation of interleukin-6 following subarachnoid hemorrhage: targeting inflammatory activation for cerebral vasospasm

Background

Cerebral vasospasm (CV) can contribute to significant morbidity in subarachnoid hemorrhage (SAH) patients. A key unknown is how CV induction is triggered following SAH.

Methods

Human aneurysmal blood and cerebral spinal fluid were collected for evaluation. To confirm mechanism, c57/bl6 wild type and c57/bl6 IL-6 female knockout (KO) mice were utilized with groups: saline injected, SAH, SAH + IL-6 blockade, SAH IL-6 KO, SAH IL-6 KO + IL-6 administration, SAH + p-STAT3 inhibition. Dual-labeled microglia/myeloid mice were used to show myeloid diapedesis. For SAH, 50 μm blood was collected from tail puncture and administered into basal cisterns. IL-6 blockade was given at various time points. Various markers of neuroinflammation were measured with western blot and immunohistochemistry. Cerebral blood flow was also measured. Vasospasm was measured via cardiac injection of India ink/gelatin. Turning test and Garcia’s modified SAH score were utilized. P < 0.05 was considered significant.

Results

IL-6 expression peaked 3 days following SAH (p < 0.05). Human IL-6 was increased in aneurysmal blood (p < 0.05) and in cerebral spinal fluid (p < 0.01). Receptor upregulation was periventricular and perivascular. Microglia activation following SAH resulted in increased caveolin 3 and myeloid diapedesis. A significant increase in BBB markers endothelin 1 and occludin was noted following SAH, but reduced with IL-6 blockade (p < 0.01). CV occurred 5 days post-SAH, but was absent in IL-6 KO mice and mitigated with IL-6 blockade (p < 0.05). IL-6 blockade, and IL-6 KO mitigated effects of SAH on cerebral blood flow (p < 0.05). SAH mice had impaired performance on turn test and poor modified Garcia scores compared to saline and IL-6 blockade. A distinct microglia phenotype was noted day 5 in the SAH group (overlap coefficients r = 0.96 and r = 0.94) for Arg1 and iNOS, which was altered by IL-6 blockade. Day 7, a significant increase in toll-like receptor 4 and Stat3 was noted. This was mitigated by IL-6 blockade and IL-6 KO, which also reduced Caspase 3 (p < 0.05). To confirm the mechanism, we developed a p-STAT3 inhibitor that targets the IL-6 pathway and this reduced NFΚB, TLR4, and nitrotyrosine (p < 0.001). Ventricular dilation and increased Tunel positivity was noted day 9, but resolved by IL-6 blockade (p < 0.05).

Conclusion

Correlation between IL-6 and CV has been well documented. We show that a mechanistic connection exists via the p-STAT3 pathway, and IL-6 blockade provides benefit in reducing CV and its consequences mediated by myeloid cell origin diapedesis.

Graphical abstract

Role of Sirtuins in Diabetes and Age-Related Processes

The practice of intermittent fasting continues to grow as a widely practiced diet trend due to its feasibility and reported high success rate. By practicing intermittent fasting, levels of sirtuin proteins (SIRTs), also known as the longevity protein, rise in the body and bring numerous health benefits. Currently, seven SIRTs have been described in humans in different locations of the cell with a wide variety of corresponding functions including gene transcription, DNA repair, and protection against oxidative damage. SIRT activators, such as resveratrol found in red wine, are also commonly consumed to amplify the health benefits associated with protection against diabetes and age-related disease processes. The purpose of this review is to explore the interaction of intermittent fasting on SIRT levels and how the increase in these proteins impacts age-related disease processes. The understanding of SIRTs is continuously evolving as more interactions and SIRT-specific activators are being revealed. New discoveries are crucial for forming potential therapeutics that delay many common diseases and promote healthy living. 

12/15-Lipoxygenase Regulation of Diabetic Cognitive Dysfunction Is Determined by Interfering with Inflammation and Cell Apoptosis

This study aimed to discuss the role of 12/15-lipoxygenase (12/15-LOX) regulation involved in diabetes cognitive dysfunction. First, Mini Mental State Examination (MMSE) test was used to evaluate cognitive ability in diabetic patients and normal controls. The plasma test showed that the plasma level of 12/15-LOX in patients with MMSE scores below 27 was significantly increased compared with that of the normal group. Second, 12/15-LOX inhibitor was administered to diabetic rats. Behavioral tests, biochemistry, enzyme-linked immunosorbent assays, and Western blotting were used in this study. We found that the levels of fasting and random blood glucose increased rapidly in diabetic rats, the levels of triglycerides and total cholesterol in the diabetic group increased, and insulin levels decreased significantly. In the Morris water maze test, the escape latency was prolonged, and the crossing times decreased in the diabetic group. Under the microscope, the apoptosis of hippocampal neurons in diabetic rats increased significantly. The levels of TNF-α, IL-6 and 12-hydroxyindoleic acid (12(S)-HETE) significantly increased, and the protein expression of 12/15-LOX, p38 MAPK, Aβ_1-42, caspase-3, caspase-9 and cPLA2 increased, while that of Bcl-2 decreased. However, the use of 12/15-LOX inhibitor reversed these results. Third, 12/15-LOX shRNA and p38MAPK inhibitor were administered to HT22 cells in high-glucose medium. The results of the cell experiment were consistent with those of the animal experiment. Our results indicated that the 12/15-LOX pathway participates in diabetic brain damage by activating p38MAPK to promote inflammation and neuronal apoptosis, and intervention 12/15-LOX can improve diabetic cognitive dysfunction.

Metabolic disorders on cognitive dysfunction after traumatic brain injury

Cognitive dysfunction is a common adverse consequence of traumatic brain injury (TBI). After brain injury, the brain and other organs trigger a series of complex metabolic changes, including reduced glucose metabolism, enhanced lipid peroxidation, disordered neurotransmitter secretion, and imbalanced trace element synthesis. In recent years, several research and clinical studies have demonstrated that brain metabolism directly or indirectly affects cognitive dysfunction after TBI, but the mechanisms remain unclear. Drugs that improve the symptoms of cognitive dysfunction caused by TBI are under investigation and treatments that target metabolic processes are expected to improve cognitive function in the future. This review explores the impact of metabolic disorders on cognitive dysfunction after TBI and provides new strategies for the treatment of metabolic disorders.

Advanced Glycosylation End Products Induced Synaptic Deficits and Cognitive Decline Through ROS-JNK-p53/miR-34c/SYT1 Axis in Diabetic Encephalopathy

Background: miR-34c has been found to be implicated in the pathological process of Alzheimer’s disease, diabetes, and its complications. Objective: To investigate the underlying mechanisms of miR-34c in the pathogenesis of diabetic encephalopathy (DE). Methods: Diabetes mellitus rats were developed by incorporating a high-fat diet and streptozotocin injection. Morris water maze test and novel object recognition test were used to assess the cognitive function of rats. Expression of miR-34c were detected by fluorescence in situ hybridization and qRT-PCR. Immunofluorescence and western blot were used to evaluate synaptotagmin 1 (SYT1) and AdipoR2 or other proteins. Golgi staining was performed to investigate dendritic spine density. Results: The increased miR-34c induced by advanced glycation end-products (AGEs) was mediated by ROS-JNK-p53 pathway, but not ROS-Rb-E2F1 pathway, in hippocampus of DE rats or in HT-22 cells. miR-34c negatively regulated the expression of SYT1, but not AdipoR2, in hippocampal neurons. miR-34c inhibitor rescued the AGE-induced decrease in the density of dendritic spines in primary hippocampal neurons. Administration of AM34c by the intranasal delivery increased the hippocampus levels of SYT1 and ameliorated the cognitive function in DE rats. The serum levels of miR-34c were increased in patients with DE comparing with normal controls. Conclusion: These results demonstrated that AGE-induced oxidative stress mediated increase of miR-34c through ROS-JNK-p53 pathway, resulting in synaptic deficits and cognitive decline by targeting SYT1 in DE, and the miR-34c/SYT1 axis could be considered as a novel therapeutic target for DE patients.

Deciphering therapeutic options for neurodegenerative diseases: insights from SIRT1

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD +)-dependent protein deacetylase that exerts biological effects through nucleoplasmic transfer. Recent studies have highlighted that SIRT1 deacetylates protein substrates to exert its neuroprotective effects, including decreased oxidative stress and inflammatory, increases autophagy, increases levels of nerve growth factors (correlated with behavioral changes), and maintains neural integrity (affects neuronal development and function) in aging or neurological disorder. In this review, we highlight the molecular mechanisms underlying the protective role of SIRT1 in modulating neurodegeneration, focusing on protein homeostasis, aging-related signaling pathways, neurogenesis, and synaptic plasticity. Meanwhile, the potential of targeting SIRT1 to block the occurrence and progression of neurodegenerative diseases is also discussed. Taken together, this review provides an up-to-date evaluation of our current understanding of the neuroprotective mechanisms of SIRT1 and also be involved in the potential therapeutic opportunities of AD and related neurodegenerative diseases.

A Systematic Review of Inflammatory Cytokine Changes Following Aneurysmal Subarachnoid Hemorrhage in Animal Models and Humans

Aneurysmal subarachnoid hemorrhage (aSAH) is a severe form of stroke that occurs following rupture of a cerebral aneurysm. Acute inflammation and secondary delayed inflammatory responses, both largely controlled by cytokines, work together to create high mortality and morbidity for this group. The trajectory and time course of cytokine change must be better understood in order to effectively manage unregulated inflammation and improve patient outcomes following aSAH. A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Three different search phrases ("cytokines and subarachnoid hemorrhage," "cytokine levels and subarachnoid hemorrhage," and "cytokine measurement and subarachnoid hemorrhage") were applied across three databases (PubMed, SCOPUS, and the Cochrane Library). Our procedures returned 856 papers. After application of inclusion/exclusion criteria, 95 preclinical animal studies and 41 clinical studies remained. Across studies, 22 different cytokines had been investigated, 5 different tissue types were analyzed, and 3 animal models were utilized. Three main pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) demonstrated reliable increases following aSAH across the included studies. While this is a promising area of research for potential therapeutics, there are gaps in the knowledge base that bar progress for clinical translation of this information. In particular, there is a need for investigations that explore the systemic inflammatory response following injury in a more diverse number of cytokines, the balance of specific pro-/anti- inflammatory cytokines, and how these biomarkers relate to patient outcomes and recovery over time.

Sleeve gastrectomy attenuated diabetes-related cognitive decline in diabetic rats

OBJECTIVE

To investigate the effects of sleeve gastrectomy (SG) on diabetes-related cognitive decline (DCD) in rats with diabetic mellitus (DM).

METHODS AND METHODS

Forty Wistar rats were randomly divided into control (CON) group (n=10), diabetes mellitus (DM) group (n=10), sham operation (SHAM) group (n=10) and SG group (n=10). DM model was established by high-fat diet (HFD) combined with intraperitoneal injection of streptozocin (STZ). Behavioral evaluation was given using Morris water maze test and Y-maze. In addition, PET-CT, TUNEL assay, histological analysis, transmission electron microscopy (TEM), immunohistochemistry (IHC) and Western blot analysis were used to evaluate the alleviating effects and potential mechanisms of SG on DCD in DM rats.

RESULTS

Compared with the sham group, SG induced significant improvement in the metabolic indices such as blood glucose and body weight. Besides, it could attenuate the insulin resistance compared with SHAM group. In addition, SG could improve the cognitive function of DM rats, which were featured by significant decrease in the escape latency (P<0.05), and significant increase in the time in target quadrant and platform crossings (P<0.05) compared with the SHAM group. SG induced significant elevation in the spontaneous alternation compared with SHAM group (P<0.05). Moreover, SG could improve the arrangement and biosynthesis of hippocampus neuron. Moreover, SG triggered the inhibition of apoptosis of hippocampus neurons, and Western blot analysis showed SG induced significant increase in the ratios of Bcl-2/Bax and Caspase3/cleaved Caspase 3. TEM demonstrated SG could significantly improve the microstructure of hippocampus neurons compared with the SHAM group. Western blot and IHC confirmed the significant decrease in the phosphorylation of tau at Ser404 and Ser396 sites in the SG group. Furthermore, SG activated the PI3K signaling pathway by elevating the phosphorylation of PI3K and Akt and GSK3β compared with the SHAM group.

CONCLUSION

SG attenuated the DCD in DM rats, which may be related to the activation of PI3K signaling pathway.