Protective Effects of Liraglutide and Linagliptin in C. elegans as a New Model for Glucose-Induced Neurodegeneration

Linagliptin, a DPP-4 inhibitor, activates AMPK/FOXO3a and suppresses NFκB to mitigate the debilitating effects of diethylnitrosamine exposure in rat liver: Novel mechanistic insights

Accumulating evidence suggests that dysregulation of FOXO3a plays a significant role in the progression of various malignancies, including hepatocellular carcinoma (HCC). FOXO3a inactivation, driven by oncogenic stimuli, can lead to abnormal cell growth, suppression of apoptosis, and resistance to anticancer drugs. Therefore, FOXO3a emerges as a potential molecular target for the development of innovative treatments in the era of oncology. Linagliptin (LNGTN), a DPP-4 inhibitor known for its safe profile, has exhibited noteworthy anti-inflammatory and anti-oxidative properties in previous in vivo studies. Several potential molecular mechanisms have been proposed to explain these effects. However, the capacity of LNGTN to activate FOXO3a through AMPK activation has not been investigated. In our investigation, we examined the potential repurposing of LNGTN as a hepatoprotective agent against diethylnitrosamine (DENA) intoxication. Additionally, we assessed LNGTN's impact on apoptosis and autophagy. Following a 10-week administration of DENA, the liver underwent damage marked by inflammation and early neoplastic alterations. Our study presents the first experimental evidence demonstrating that LNGTN can reinstate the aberrantly regulated FOXO3a activity by elevating the nuclear fraction of FOXO3a in comparison to the cytosolic fraction, subsequent to AMPK activation. Moreover, noteworthy inactivation of NFκB induced by LNGTN was observed. These effects culminated in the initiation of apoptosis, the activation of autophagy, and the manifestation of anti-inflammatory, antiproliferative, and antiangiogenic outcomes. These effects were concomitant with improved liver function and microstructure. In conclusion, our findings open new avenues for the development of novel therapeutic strategies targeting the AMPK/FOXO3a signaling pathway in the management of chronic liver damage.

FOXO and related transcription factors binding elements in the regulation of neurodegenerative disorders

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and others, are characterized by progressive loss of neuronal cells, which causes memory impairment and cognitive decline. Mounting evidence demonstrated the possible implications of diverse biological processes, namely oxidative stress, mitochondrial dysfunction, aberrant cell cycle re-entry, post-translational modifications, protein aggregation, impaired proteasome dysfunction, autophagy, and many others that cause neuronal cell death. The condition worsens as there is no effective treatment for such diseases due to their complex pathogenesis and mechanism. Mounting evidence demonstrated the role of regulatory transcription factors, such as NFκβ, FoxO, Myc, CREB, and others that regulate the biological processes and diminish the disease progression and pathogenesis. Studies demonstrated that forkhead box O (FoxO) transcription factors had been implicated in the regulation of aging and longevity. Further, the functions of FoxO proteins are regulated by different post-translational modifications (PTMs), namely acetylation, and ubiquitination. Various studies concluded that FoxO proteins exert both neuroprotective and neurotoxic properties depending on their regulation mechanism and activity in the brain. Thus, understanding the nature of FoxO expression and activity in the brain will help develop effective therapeutic strategies. Herein, firstly, we discuss the role of FoxO protein in cell cycle regulation and cell proliferation, followed by the regulation of FoxO proteins through acetylation and ubiquitination. We also briefly explain the activity and expression pattern of FoxO proteins in the neuronal cells and explain the mechanism through which FoxO proteins are rescued from oxidative stress-induced neurotoxicity. Later on, we present a detailed view of the implication of FoxO proteins in neurodegenerative disease and FoxO proteins as an effective therapeutic target.

Sulforaphane and Vitamin E Protect From Glucotoxic Neurodegeneration and Lifespan Reduction In C. Elegans

Caenorhabditis elegans is an established model organism in neurodegeneration and aging research. Oxidative stress and formation of advanced glycation endproducts (AGEs), as they occur under hyperglycemic conditions in diabetes mellitus, contribute to neuronal damage and lifespan reduction. Sulforaphane (SFN) is an indirect antioxidant, alpha-tocopherol (vitamin E) is a direct antioxidant that acts as a free radical scavenger. Aim of this study is to investigate the protective effects of SFN and vitamin E against glucotoxic damages to the neuronal system and lifespan in C. elegans. Culture conditions that mimic clinical hyperglycemia increased the formation of reactive oxygen species (ROS) (p<0.001) and the accumulation of methylglyoxal-derived advanced glycation endproducts (MG-derived AGEs) (p<0.01) with subsequent neuronal damage and neuronal dysfunction, ultimately leading to a significant shortening of lifespan (p<0.01). Treatment with both, 20 µmol/l SFN and 200 µg/ml vitamin E, completely prevented the increase in ROS and MG-derived AGEs, abolished the glucotoxic effects on neuronal structure and function, and preserved lifespan, resulting in a life expectancy similar to untreated controls. These data emphasize the relevance of indirect and direct antioxidants as potential therapeutic options for the prevention of glucotoxic pathologies.

A Novel Micronutrient Blend Mimics Calorie Restriction Transcriptomics in Multiple Tissues of Mice and Increases Lifespan and Mobility in C. elegans

Background: We previously described a novel micronutrient blend that behaves like a putative calorie restriction mimetic. The aim of this paper was to analyze the beneficial effects of our micronutrient blend in mice and C. elegans, and compare them with calorie restriction. Methods: Whole transcriptomic analysis was performed in the brain cortex, skeletal muscle and heart in three groups of mice: old controls (30 months), old + calorie restriction and old + novel micronutrient blend. Longevity and vitality were tested in C. elegans. Results: The micronutrient blend elicited transcriptomic changes in a manner similar to those in the calorie-restricted group and different from those in the control group. Subgroup analysis revealed that nuclear hormone receptor, proteasome complex and angiotensinogen genes, all of which are known to be directly related to aging, were the most affected. Furthermore, a functional analysis in C. elegans was used. We found that feeding C. elegans the micronutrient blend increased longevity as well as vitality. Conclusions: We describe a micronutrient supplement that causes similar changes (transcriptomic and promoting longevity and vitality) as a calorie restriction in mice and C. elegans, respectively, but further studies are required to confirm these effects in humans.

The DPP4 Inhibitor Linagliptin Protects from Experimental Diabetic Retinopathy

Background/aims

Dipeptidyl peptidase 4 (DPP4) inhibitors improve glycemic control in type 2 diabetes, however, their influence on the retinal neurovascular unit remains unclear.

Methods

Vasculo- and neuroprotective effects were assessed in experimental diabetic retinopathy and high glucose-cultivated C. elegans, respectively. In STZ-diabetic Wistar rats (diabetes duration of 24 weeks), DPP4 activity (fluorometric assay), GLP-1 (ELISA), methylglyoxal (LC-MS/MS), acellular capillaries and pericytes (quantitative retinal morphometry), SDF-1a and heme oxygenase-1 (ELISA), HMGB-1, Iba1 and Thy1.1 (immunohistochemistry), nuclei in the ganglion cell layer, GFAP (western blot), and IL-1beta, Icam1, Cxcr4, catalase and beta-actin (quantitative RT-PCR) were determined. In C. elegans, neuronal function was determined using worm tracking software.

Results

Linagliptin decreased DPP4 activity by 77% and resulted in an 11.5-fold increase in active GLP-1. Blood glucose and HbA_1c were reduced by 13% and 14% and retinal methylglyoxal by 66%. The increase in acellular capillaries was diminished by 70% and linagliptin prevented the loss of pericytes and retinal ganglion cells. The rise in Iba-1 positive microglia was reduced by 73% with linagliptin. In addition, the increase in retinal Il1b expression was decreased by 65%. As a functional correlate, impairment of motility (body bending frequency) was significantly prevented in C. elegans.

Conclusion

Our data suggest that linagliptin has a protective effect on the microvasculature of the diabetic retina, most likely due to a combination of neuroprotective and antioxidative effects of linagliptin on the neurovascular unit.

Linagliptin, a Dipeptidyl Peptidase-4 Inhibitor, Mitigates Cognitive Deficits and Pathology in the 3xTg-AD Mouse Model of Alzheimer's Disease

Glucagon-like peptide-1 (GLP-1) is an incretin hormone shown to be active in the treatment of type-2 diabetes (T2D) and has also been shown as efficacious in Alzheimer's disease (AD). Dipeptidyl peptidase-4 (DPP-4), an enzyme that is expressed in numerous cells, rapidly inactivates endogenous GLP-1. Therefore, DPP-4 inhibition is employed as a therapeutic avenue to increase GLP-1 levels in the management of T2D. The effectiveness of DPP-4 inhibitors in the treatment of AD has been reported in various animal models of AD. With this background, the present study was designed to examine the effectiveness of linagliptin, a DPP-4 inhibitor in the 3xTg-AD mouse model of Alzheimer's disease. Nine-month-old 3xTg-AD mice were administered linagliptin orally (5, 10, and 20 mg/kg) for 8 weeks. At the end of the linagliptin treatment, mice were evaluated for cognitive ability on the Morris Water Maze and Y-maze. Following cognitive evaluation, mice were sacrificed to determine the effect of the linagliptin on brain incretin levels, amyloid burden, tau phosphorylation, and neuroinflammation. We confirm that linagliptin treatment for 8 weeks mitigates the cognitive deficits present in 3xTg-AD mice. Moreover, linagliptin also improves brain incretin levels and attenuates amyloid beta, tau phosphorylation as well as neuroinflammation. In conclusion, linagliptin possesses neuroprotective properties that may be attributed to the improvement of incretin levels in the brain.

Advanced Glycation End-Products and Their Receptors: Related Pathologies, Recent Therapeutic Strategies, and a Potential Model for Future Neurodegeneration Studies

Advanced glycation end products (AGEs) are the result of a nonenzymatic reaction between sugars and proteins, lipids, or nucleic acids. AGEs are both consumed and endogenously formed; their accumulation is accelerated under hyperglycemic and oxidative stress conditions, and they are associated with the onset and complication of many diseases, such as cardiovascular diseases, diabetes, and Alzheimer's disease. AGEs exert their deleterious effects by either accumulating in the circulation and tissues or by receptor-mediated signal transduction. Several receptors bind AGEs: some are specific and contribute to clearance of AGEs, whereas others, like the RAGE receptor, are nonspecific, associated with inflammation and oxidative stress, and considered to be mediators of the aforementioned AGE-related diseases. Although several anti-AGE compounds have been studied, understanding the underlying mechanisms of RAGE and targeting it as a therapeutic strategy is becoming increasingly desirable. For achieving these goals efficiently and expeditiously, the C. elegans model has been suggested. This model is already used for studying several human diseases and, by expressing RAGE, could also be used to study RAGE-related pathways and pathologies to facilitate the development of novel therapeutic strategies.