Nuclear magnetic resonance spectroscopy reveals biomarkers of stroke recovery in a mouse model of obesity-associated type 2 diabetes.

Obesity and Type 2 diabetes (T2D) are known to exacerbate cerebral injury caused by stroke. Metabolomics can provide signatures of metabolic disease, and now we explored whether the analysis of plasma metabolites carries biomarkers of how obesity and T2D impact post-stroke recovery. Male mice were fed a high-fat diet (HFD) for 10 months leading to development of obesity with T2D or a standard diet (non-diabetic mice). Then, mice were subjected to either transient middle cerebral artery occlusion (tMCAO) or sham surgery and allowed to recover on standard diet for 2 months before serum samples were collected. Nuclear magnetic resonance (NMR) spectroscopy of serum samples was used to investigate metabolite signals and metabolic pathways that were associated with tMCAO recovery in either T2D or non-diabetic mice. Overall, after post-stroke recovery there were different serum metabolite profiles in T2D and non-diabetic mice. In non-diabetic mice, which show full neurological recovery after stroke, we observed a reduction of isovalerate, and an increase of kynurenate, uridine monophosphate, gluconate and N6-acetyllysine in tMCAO relative to sham mice. In contrast, in mice with T2D, which show impaired stroke recovery, there was a reduction of N,N-dimethylglycine, succinate and proline, and an increase of 2-oxocaproate in serum of tMCAO versus sham mice. Given the inability of T2D mice to recover from stroke, in contrast with non-diabetic mice, we propose that these specific metabolite changes following tMCAO might be used as biomarkers of neurophysiological recovery after stroke in T2D.

The SGLT2 inhibitor Empagliflozin promotes post-stroke functional recovery in diabetic mice.

Type-2 diabetes (T2D) worsens stroke recovery, amplifying post-stroke disabilities. Currently, there are no therapies targeting this important clinical problem. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are potent anti-diabetic drugs that also efficiently reduce cardiovascular death and heart failure. In addition, SGLT2i facilitate several processes implicated in stroke recovery. However, the potential efficacy of SGLT2i to improve stroke recovery in T2D has not been investigated. Therefore, we determined whether a post-stroke intervention with the SGLT2i Empagliflozin could improve stroke recovery in T2D mice. T2D was induced in C57BL6J mice by 8 months of high-fat diet feeding. Hereafter, animals were subjected to transient middle cerebral artery occlusion and treated with vehicle or the SGLTi Empagliflozin (10 mg/kg/day) starting from 3 days after stroke. A similar study in non diabetic mice was also conducted. Stroke recovery was assessed using the forepaw grip strength test. To identify potential mechanisms involved in the Empagliflozin-mediated effects, several metabolic parameters were assessed. Additionally, neuronal survival, neuroinflammation, neurogenesis and cerebral vascularization were analyzed using immunohistochemistry/quantitative microscopy. Empagliflozin significantly improved stroke recovery in T2D but not in non-diabetic mice. Improvement of functional recovery was associated with lowered glycemia, increased serum levels of fibroblast growth factor-21 (FGF-21), and the normalization of T2D-induced aberration of parenchymal pericyte density. The global T2D-epidemic and the fact that T2D is a major risk factor for stroke are drastically increasing the number of people in need of efficacious therapies to improve stroke recovery. Our data provide a strong incentive for the potential use of SGLT2i for the treatment of post-stroke sequelae in T2D.

The Pre-Stroke Induction and Normalization of Insulin Resistance Respectively Worsens and Improves Functional Recovery.

Type 2 diabetes (T2D) impairs post-stroke recovery, and the underlying mechanisms are unknown. Insulin resistance (IR), a T2D hallmark that is also closely linked to aging, has been associated with impaired post-stroke recovery. However, whether IR worsens stroke recovery is unknown. We addressed this question in mouse models where early IR, with or without hyperglycemia, was induced by chronic high-fat diet feeding or sucrose supplementation in the drinking water, respectively. Furthermore, we used 10-month-old mice, spontaneously developing IR but not hyperglycemia, where IR was normalized pharmacologically pre-stroke with Rosiglitazone. Stroke was induced by transient middle cerebral artery occlusion and recovery was assessed by sensorimotor tests. Neuronal survival, neuroinflammation and the density of striatal cholinergic interneurons were also assessed by immunohistochemistry/quantitative microscopy. Pre-stroke induction and normalization of IR, respectively, worsened and improved post-stroke neurological recovery. Moreover, our data indicate a potential association of this impaired recovery with exacerbated neuroinflammation and a decreased density of striatal cholinergic interneurons. The global diabetes epidemic and population aging are dramatically increasing the percentage of people in need of post-stroke treatment/care. Our results suggest that future clinical studies should target pre-stroke IR to reduce stroke sequelae in both diabetics and elderly people with prediabetes.

DPP-4 Inhibitor and Sulfonylurea Differentially Reverse Type 2 Diabetes-Induced Blood-Brain Barrier Leakage and Normalize Capillary Pericyte Coverage.

Microvascular pathology in the brain is one of the suggested mechanisms underlying the increased incidence and progression of neurodegenerative diseases in people with type 2 diabetes (T2D). Although accumulating data suggest a neuroprotective effect of antidiabetics, the underlying mechanisms are unclear. Here, we investigated whether two clinically used antidiabetics, the dipeptidyl peptidase-4 inhibitor linagliptin and the sulfonylurea glimepiride, which restore T2D-induced brain vascular pathology. Microvascular pathology was examined in the striatum of mice fed for 12 months with either normal chow diet or a high-fat diet (HFD) to induce T2D. A subgroup of HFD-fed mice was treated with either linagliptin or glimepiride for 3 months before sacrifice. We demonstrate that T2D caused leakage of the blood-brain barrier (BBB), induced angiogenesis, and reduced pericyte coverage of microvessels. However, linagliptin and glimepiride recovered the BBB integrity and restored the pericyte coverage differentially. Linagliptin normalized T2D-induced angiogenesis and restored pericyte coverage. In contrast, glimepiride enhanced T2D-induced angiogenesis and increased pericyte density, resulting in proper vascular coverage. Interestingly, glimepiride reduced microglial activation, increased microglial-vascular interaction, and increased collagen IV density. This study provides evidence that both DPP-4 inhibition and sulfonylurea reverse T2D-induced BBB leakage, which may contribute to antidiabetic neurorestorative effects.

Normalisation of glucose metabolism by exendin-4 in the chronic phase after stroke promotes functional recovery in male diabetic mice.

BACKGROUND AND PURPOSE: Glucagon-like peptide-1 (GLP-1) receptor activation decreases stroke risk in people with Type 2 diabetes (T2D), while animal studies have shown the efficacy of this strategy to counteract stroke-induced acute brain damage. However, whether GLP-1 receptor activation also improves recovery in the chronic phase after stroke is unknown. We investigated whether post-acute, chronic administration of the GLP-1 receptor agonist, exendin-4, improves post-stroke recovery and examined possible underlying mechanisms in T2D and non-T2D mice. EXPERIMENTAL APPROACH: We induced stroke via transient middle cerebral artery occlusion (tMCAO) in T2D/obese mice (8 months of high-fat diet) and age-matched controls. Exendin-4 was administered for 8 weeks from Day 3 post-tMCAO. We assessed functional recovery by weekly upper-limb grip strength tests. Insulin sensitivity and glycaemia were evaluated at 4 and 8 weeks post-tMCAO. Neuronal survival, stroke-induced neurogenesis, neuroinflammation, atrophy of GABAergic parvalbumin+ interneurons, post-stroke vascular remodelling and fibrotic scar formation were investigated by immunohistochemistry. KEY RESULTS: Exendin-4 normalised T2D-induced impairment of forepaw grip strength recovery in correlation with normalised glycaemia and insulin sensitivity. Moreover, exendin-4 counteracted T2D-induced atrophy of parvalbumin+ interneurons and decreased microglia activation. Finally, exendin-4 normalised density and pericyte coverage of micro-vessels and restored fibrotic scar formation in T2D mice. In non-T2D mice, the exendin-4-mediated recovery was minor. CONCLUSION AND IMPLICATIONS: Chronic GLP-1 receptor activation mediates post-stroke functional recovery in T2D mice by normalising glucose metabolism and improving neuroplasticity and vascular remodelling in the recovery phase. The results warrant clinical trial of GLP-1 receptor agonists for rehabilitation after stroke in T2D. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

A High-Fat Diet Increases Activation of the Glucagon-Like Peptide-1-Producing Neurons in the Nucleus Tractus Solitarii: an Effect that is Partially Reversed by Drugs Normalizing Glycemia.

Glucagon-like peptide-1 (GLP-1) is a peripheral incretin and centrally active peptide produced in the intestine and nucleus tractus solitarii (NTS), respectively. GLP-1 not only regulates metabolism but also improves cognition and is neuroprotective. While intestinal GLP-1-producing cells have been well characterized, less is known about GLP-1-producing neurons in NTS. We hypothesized that obesity-induced type 2 diabetes (T2D) impairs the function of NTS GLP-1-producing neurons and glycemia normalization counteracts this effect. We used immunohistochemistry/quantitative microscopy to investigate the number, potential atrophy, and activation (cFos-expression based) of NTS GLP-1-producing neurons, in non-diabetic versus obese/T2D mice (after 12 months of high-fat diet). NTS neuroinflammation was also assessed. The same parameters were quantified in obese/T2D mice treated from month 9 to 12 with two unrelated anti-hyperglycemic drugs: the dipeptidyl peptidase-4 inhibitor linagliptin and the sulfonylurea glimepiride. We show no effect of T2D on the number and volume but increased activation of NTS GLP-1-producing neurons. This effect was partially normalized by both anti-diabetic treatments, concurrent with decreased neuroinflammation. Increased activation of NTS GLP-1-producing neurons could represent an aberrant metabolic demand in T2D/obesity, attenuated by glycemia normalization. Whether this effect represents a pathophysiological process preceding GLP-1 signaling impairment in the CNS, remains to be investigated.

Diet-induced weight loss in obese/diabetic mice normalizes glucose metabolism and promotes functional recovery after stroke.

BACKGROUND: Post-stroke functional recovery is severely impaired by type 2 diabetes (T2D). This is an important clinical problem since T2D is one of the most common diseases. Because weight loss-based strategies have been shown to decrease stroke risk in people with T2D, we aimed to investigate whether diet-induced weight loss can also improve post-stroke functional recovery and identify some of the underlying mechanisms. METHODS: T2D/obesity was induced by 6 months of high-fat diet (HFD). Weight loss was achieved by a short- or long-term dietary change, replacing HFD with standard diet for 2 or 4 months, respectively. Stroke was induced by middle cerebral artery occlusion and post-stroke recovery was assessed by sensorimotor tests. Mechanisms involved in neurovascular damage in the post-stroke recovery phase, i.e. neuroinflammation, impaired angiogenesis and cellular atrophy of GABAergic parvalbumin (PV)+ interneurons were assessed by immunohistochemistry/quantitative microscopy. RESULTS: Both short- and long-term dietary change led to similar weight loss. However, only the latter enhanced functional recovery after stroke. This effect was associated with pre-stroke normalization of fasting glucose and insulin resistance, and with the reduction of T2D-induced cellular atrophy of PV+ interneurons. Moreover, stroke recovery was associated with decreased T2D-induced neuroinflammation and reduced astrocyte reactivity in the contralateral striatum. CONCLUSION: The global diabetes epidemic will dramatically increase the number of people in need of post-stroke treatment and care. Our results suggest that diet-induced weight loss leading to pre-stroke normalization of glucose metabolism has great potential to reduce the sequelae of stroke in the diabetic population.

Estimated glucose disposal rate and risk of stroke and mortality in type 2 diabetes: a nationwide cohort study.

BACKGROUND AND AIMS: Insulin resistance contributes to the development of type 2 diabetes (T2D) and is also a cardiovascular risk factor. The aim of this study was to investigate the potential association between insulin resistance measured by estimated glucose disposal rate (eGDR) and risk of stroke and mortality thereof in people with T2D. MATERIALS AND METHODS: Nationwide population based observational cohort study that included all T2D patients from the Swedish national diabetes registry between 2004 and 2016 with full data on eGDR and categorised as following: < 4, 4-6, 6-8, and ≥ 8 mg/kg/min. We calculated crude incidence rates and 95% confidence intervals (CIs) and used multiple Cox regression to estimate hazard ratios (HRs) to assess the association between the risk of stroke and death, according to the eGDR categories in which the lowest category < 4 (i.e., highest grade of insulin resistance), served as a reference. The relative importance attributed of each factor in the eGDR formula was measured by the R2 (± SE) values calculating the explainable log-likelihoods in the Cox regression. RESULTS: A total of 104 697 T2D individuals, 44.5% women, mean age of 63 years, were included. During a median follow up-time of 5.6 years, 4201 strokes occurred (4.0%). After multivariate adjustment the HRs (95% CI) for stroke in patients with eGDR categories between 4-6, 6-8 and > 8 were: 0.77 (0.69-0.87), 0.68 (0.58-0.80) and 0.60 (0.48-0.76), compared to the reference < 4. Corresponding numbers for the risk of death were: 0.82 (0.70-0.94), 0.75 (0.64-0.88) and 0.68 (0.53-0.89). The attributed relative risk R2 (± SE) for each variable in the eGDR formula and stroke was for: hypertension (0.045 ± 0.0024), HbA1c (0.013 ± 0.0014), and waist (0.006 ± 0.0009), respectively. CONCLUSION: A low eGDR (a measure of insulin resistance) is associated with an increased risk of stroke and death in individuals with T2D. The relative attributed risk was most important for hypertension.

The selective alpha7 nicotinic acetylcholine receptor agonist AR-R17779 does not affect ischemia-reperfusion brain injury in mice.

Inflammation plays a central role in stroke-induced brain injury. The alpha7 nicotinic acetylcholine receptor (α7nAChR) can modulate immune responses in both the periphery and the brain. The aims of the present study were to investigate α7nAChR expression in different brain regions and evaluate the potential effect of the selective α7nAChR agonist AR-R17779 on ischemia-reperfusion brain injury in mice. Droplet digital PCR (ddPCR) was used to evaluate the absolute expression of the gene encoding α7nAChR (Chrna7) in hippocampus, striatum, thalamus and cortex in adult, naïve mice. Mice subjected to transient middle cerebral artery occlusion (tMCAO) or sham surgery were treated with α7nAChR agonist AR-R17779 (12 mg/kg) or saline once daily for 5 days. Infarct size and microglial activation 7 days after tMCAO were analyzed using immunohistochemistry. Chrna7 expression was found in all analyzed brain regions in naïve mice with the highest expression in cortex and hippocampus. At sacrifice, white blood cell count was significantly decreased in AR-R17779 treated mice compared with saline controls in the sham groups, although, no effect was seen in the tMCAO groups. Brain injury and microglial activation were evident 7 days after tMCAO. However, no difference was found between mice treated with saline or AR-R17779. In conclusion, α7nAChR expression varies in different brain regions and, despite a decrease in white blood cells in sham mice receiving AR-R17779, this compound does not affect stroke-induced brain injury.

The Stroke-Induced Increase of Somatostatin-Expressing Neurons is Inhibited by Diabetes: A Potential Mechanism at the Basis of Impaired Stroke Recovery.

Type 2 diabetes (T2D) hampers recovery after stroke, but the underling mechanisms are mostly unknown. In a recently published study (Pintana et al. in Clin Sci (Lond) 133(13):1367-1386, 2019), we showed that impaired recovery in T2D was associated with persistent atrophy of parvalbumin+ interneurons in the damaged striatum. In the current work, which is an extension of the abovementioned study, we investigated whether somatostatin (SOM)+ interneurons are also affected by T2D during the stroke recovery phase. C57Bl/6j mice were fed with high-fat diet or standard diet (SD) for 12 months and subjected to 30-min transient middle cerebral artery occlusion (tMCAO). SOM+ cell number/density in the striatum was assessed by immunohistochemistry 2 and 6 weeks after tMCAO in peri-infarct and infarct areas. This was possible by establishing a computer-based quantification method that compensates the post-stroke tissue deformation and the irregular cell distribution. SOM+ interneurons largely survived the stroke as seen at 2 weeks. Remarkably, 6 weeks after stroke, the number of SOM+ interneurons increased (vs. contralateral striatum) in SD-fed mice in both peri-infarct and infarct areas. However, this increase did not result from neurogenesis. T2D completely abolished this effect specifically in the in the infarct area. The results suggest that the up-regulation of SOM expression in the post-stroke phase could be related to neurological recovery and T2D could inhibit this process. We also present a new and precise method for cell counting in the stroke-damaged striatum that allows to reveal accurate, area-related effects of stroke on cell number.

Western Diet Accelerates the Impairment of Odor-Related Learning and Olfactory Memory in the Mouse.

Olfactory dysfunction could be an early indicator of cognitive decline in type 2 diabetes (T2D). However, whether obesity affects olfaction in people with T2D is unclear. This question needs to be addressed, because most people with T2D are obese. Importantly, whether different contributing factors leading to obesity (e.g., different components of diet or gain in weight) affect specific olfactory functions and underlying mechanisms is unknown. We examined whether two T2D-inducing obesogenic diets, one containing a high proportion of fat (HFD) and one with moderate fat and high sugar (Western diet, WD), affect odor detection/discrimination, odor-related learning, and olfactory memory in the mouse. We also investigated whether the diets impair adult neurogenesis, GABAergic interneurons, and neuroblasts in the olfactory system. Here, we further assessed olfactory cortex volume and cFos expression-based neuronal activity. The WD-fed mice showed declined odor-related learning and olfactory memory already after 3 months of diet intake (p = 0.046), although both diets induced similar hyperglycemia and weight gain compared to those of standard diet-fed mice (p = 0.0001 and p < 0.0001, respectively) at this time point. Eight months of HFD and WD diminished odor detection (p = 0.016 and p = 0.045, respectively), odor-related learning (p = 0.015 and p = 0.049, respectively), and olfactory memory. We observed no changes in the investigated cellular mechanisms. We show that the early deterioration of olfactory parameters related to learning and memory is associated with a high content of sugar in the diet rather than with hyperglycemia or weight gain. This finding could be exploited for understanding, and potentially preventing, cognitive decline/dementia in people with T2D. The mechanisms behind this finding remain to be elucidated.

Regulation of Glycemia in the Recovery Phase After Stroke Counteracts the Detrimental Effect of Obesity-Induced Type 2 Diabetes on Neurological Recovery.

The interplay between obesity and type 2 diabetes (T2D) in poststroke recovery is unclear. Moreover, the impact of glucose control during the chronic phase after stroke is undetermined. We investigated whether obesity-induced T2D impairs neurological recovery after stroke by using a clinically relevant experimental design. We also investigated the potential efficacy of two clinically used T2D drugs: the dipeptidyl peptidase 4 inhibitor linagliptin and the sulfonylurea glimepiride. We induced transient middle cerebral artery occlusion (tMCAO) in T2D/obese mice (after 7 months of high-fat diet [HFD]) and age-matched controls. After stroke, we replaced HFD with standard diet for 8 weeks to mimic the poststroke clinical situation. Linagliptin or glimepiride were administered daily from 3 days after tMCAO for 8 weeks. We assessed neurological recovery weekly by upper-limb grip strength. Brain damage, neuroinflammation, stroke-induced neurogenesis, and atrophy of parvalbumin-positive (PV+) interneurons were quantified by immunohistochemistry. T2D/obesity impaired poststroke neurological recovery in association with hyperglycemia, neuroinflammation, and atrophy of PV+ interneurons. Both drugs counteracted these effects. In nondiabetic mice, only linagliptin accelerated recovery. These findings shed light on the interplay between obesity and T2D in stroke recovery. Moreover, they promote the use of rehabilitative strategies that are based on efficacious glycemia regulation, even if initiated days after stroke.

Dipeptidyl peptidase-4 inhibitors and sulfonylureas prevent the progressive impairment of the nigrostriatal dopaminergic system induced by diabetes during aging.

The nigrostriatal dopaminergic system (NDS) controls motor activity, and its impairment during type 2 diabetes (T2D) progression could increase Parkinson's disease risk in diabetics. If so, whether glycemia regulation prevents this impairment needs to be addressed. We investigated whether T2D impairs the NDS and whether dipeptidyl peptidase-4 inhibition (DPP-4i; a clinical strategy against T2D but also neuroprotective in animal models) prevents this effect, in middle-aged mice. Neither T2D (induced by 12 months of high-fat diet) nor aging (14 months) changed striatal dopamine content assessed by high-performance liquid chromatography. However, T2D reduced basal and amphetamine-stimulated striatal extracellular dopamine, assessed by microdialysis. Both the DPP-4i linagliptin and the sulfonylurea glimepiride (an antidiabetic comparator unrelated to DPP-4i) counteracted these effects. The functional T2D-induced effects did not correlate with NDS neuronal/glial alterations. However, aging itself affected striatal neurons/glia, and the glia effects were counteracted mainly by DPP-4i. These findings show NDS functional pathophysiology in T2D and suggest the preventive use of two unrelated anti-T2D drugs. Moreover, DPP-4i counteracted striatal age-related glial alterations suggesting striatal rejuvenation properties.

Risk of first stroke in people with type 2 diabetes and its relation to glycaemic control: A nationwide observational study.

AIMS: To compare stroke incidence in people with type 2 diabetes (T2D) with that in a matched control group, and to investigate whether glucose exposure in people with T2D can predict a first-time stroke event and mortality. MATERIAL AND METHODS: In a nationwide observational cohort study, individuals with T2D were linked in the Swedish National Diabetes Register and matched with five individual population-based control subjects. We calculated crude incidence rates and 95% confidence intervals (CIs), and used Cox regression and multivariable hazard ratios (HRs), to estimate the risk of stroke and mortality in relation to glycated haemoglobin (HbA1c) levels. RESULTS: A total of 406 271 people with T2D (age 64.1 ± 12.4 years, 45.7% women) and 2086 440 control subjects (age 64.0 ± 12.4 years, 45.7% women) were included. During a median follow-up of 7.3 years, 26 380 people with T2D (6.5%) versus 92 375 control subjects (4.4%) were diagnosed with a stroke. The incidence rate was 10.12 events per 1000 person-years versus 7.26 events per 1000 person-years (HR 1.54, 95% CI 1.52-1.56). In the T2D group after multivariable adjustments, the HRs for stroke stratified by HbA1c level were: 54-64 mmol/mol: 1.27 (95% CI 1.22-1.32); 65-75 mmol/mol: 1.68 (95% CI 1.60-1.76); 76-86 mmol/mol: 1.89 (95% CI, 1.75-2.05); and > 87 mmol/mol: 2.14 (95% CI 1.90-2.42), respectively, compared with the reference category of HbA1c ≤53 mmol/mol. There was a stepwise increased risk of death after stroke, for every 10-mmol/mol categorical increment of HbA1c (HR 1.71; 95% CI 1.47-2.00) for the highest HbA1c category. CONCLUSIONS: An increased risk of stroke and death was associated with poor glycaemic control in people with T2D.

Obesity-induced type 2 diabetes impairs neurological recovery after stroke in correlation with decreased neurogenesis and persistent atrophy of parvalbumin-positive interneurons.

Type 2 diabetes (T2D) hampers stroke recovery though largely undetermined mechanisms. Few preclinical studies have investigated the effect of genetic/toxin-induced diabetes on long-term stroke recovery. However, the effects of obesity-induced T2D are mostly unknown. We aimed to investigate whether obesity-induced T2D worsens long-term stroke recovery through the impairment of brain's self-repair mechanisms - stroke-induced neurogenesis and parvalbumin (PV)+ interneurons-mediated neuroplasticity. To mimic obesity-induced T2D in the middle-age, C57bl/6j mice were fed 12 months with high-fat diet (HFD) and subjected to transient middle cerebral artery occlusion (tMCAO). We evaluated neurological recovery by upper-limb grip strength at 1 and 6 weeks after tMCAO. Gray and white matter damage, stroke-induced neurogenesis, and survival and potential atrophy of PV-interneurons were quantitated by immunohistochemistry (IHC) at 2 and 6 weeks after tMCAO. Obesity/T2D impaired neurological function without exacerbating brain damage. Moreover, obesity/T2D diminished stroke-induced neural stem cell (NSC) proliferation and neuroblast formation in striatum and hippocampus at 2 weeks after tMCAO and abolished stroke-induced neurogenesis in hippocampus at 6 weeks. Finally, stroke resulted in the atrophy of surviving PV-interneurons 2 weeks after stroke in both non-diabetic and obese/T2D mice. However, after 6 weeks, this effect selectively persisted in obese/T2D mice. We show in a preclinical setting of clinical relevance that obesity/T2D impairs neurological functions in the stroke recovery phase in correlation with reduced neurogenesis and persistent atrophy of PV-interneurons, suggesting impaired neuroplasticity. These findings shed light on the mechanisms behind impaired stroke recovery in T2D and could facilitate the development of new stroke rehabilitative strategies for obese/T2D patients.

Dipeptidyl Peptidase-4 Inhibitors for the Potential Treatment of Brain Disorders; A Mini-Review With Special Focus on Linagliptin and Stroke.

Cerebral stroke is a leading cause of death and persistent disability of elderly in the world. Although stroke prevention by targeting several risk factors such as diabetes and hypertension has decreased the stroke incidence, the total number of strokes is increasing due to the population aging and new preventive therapies are needed. Moreover, post-stroke acute pharmacological strategies aimed to reduce stroke-induced brain injury have failed in clinical trials despite being effective in animal models. Finally, approximately 30% of surviving stroke patients do not recover from stroke and remain permanently dependent on supportive care in activities of daily living. Therefore, strategies to improve stroke recovery in the post-acute phase are highly needed. Linagliptin is a dipeptidyl peptidase-4 inhibitor which is clinically approved to reduce hyperglycemia in type 2 diabetes. The regulation of glycemia by dipeptidyl peptidase-4 inhibition is mainly achieved by preventing endogenous glucagon-like peptide-1 (GLP-1) degradation. Interestingly, linagliptin has also shown glycaemia-independent beneficial effects in animal models of stroke, Parkinson's disease and Alzheimer's disease. In some case the preclinical data have been supported with some clinical data. Although potentially very interesting for the development of new strategies against stroke and neurodegenerative disorders, the mode of action of linagliptin in the brain is still largely unknown and seems to occur in a GLP-1R-independent manner. The purpose of this mini-review is to summarize and discuss the recent experimental and clinical work regarding the effects of linagliptin in the central nervous system, with special emphasis on acute neuroprotection, stroke prevention and post-stroke recovery. We also highlight the main questions in this research field that need to be addressed in clinical perspective.

Human Neural Stem Cells for Ischemic Stroke Treatment.

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. It takes place when the brain does not receive sufficient blood supply due to the blood clot in the vessels or narrowing of vessels' inner space due to accumulation of fat products. Apart from thrombolysis (dissolving of blood clot) and thrombectomy (surgical removal of blood clot or widening of vessel inner area) during the first hours after an ischemic stroke, no effective treatment to improve functional recovery exists in the post-ischemic phase. Due to their narrow therapeutic time window, thrombolysis and thrombectomy are unavailable to more than 80% of stroke patients.Many experimental studies carried out in animal models of stroke have demonstrated that stem cell transplantation may become a new therapeutic strategy in stroke. Transplantation of stem cells of different origin and stage of development has been shown to lead to improvement in experimental models of stroke through several mechanisms including neuronal replacement, modulation of cellular and synaptic plasticity and inflammation, neuroprotection and stimulation of angiogenesis. Several clinical studies and trials based on stem cell delivery in stroke patients are in progress with goal of improvements of functional recovery through mechanisms other than neuronal replacement. These approaches may provide therapeutic benefit, but generation of specific neurons for reconstruction of stroke-injured neural circuitry remains ultimate challenge. For this purpose, neural stem cells could be developed from multiple sources and fated to adopt required neuronal phenotype.

The effect of DPP-4 inhibition to improve functional outcome after stroke is mediated by the SDF-1α/CXCR4 pathway.

BACKGROUND: Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are approved drugs for the treatment of hyperglycemia in patients with type 2 diabetes. These effects are mainly mediated by inhibiting endogenous glucagon-like peptide-1 (GLP-1) cleavage. Interestingly, gliptins can also improve stroke outcome in rodents independently from GLP1. However, the underlying mechanisms are unknown. Stromal cell-derived factor-1α (SDF-1α) is a DPP-4 substrate and CXCR4 agonist promoting beneficial effects in injured brains. However, SDF-1α involvement in gliptin-mediated neuroprotection after ischemic injury is unproven. We aimed to determine whether the gliptin linagliptin improves stroke outcome via the SDF-1α/CXCR4 pathway, and identify additional effectors behind the efficacy. METHODS: Mice were subjected to stroke by transient middle cerebral artery occlusion (MCAO). linagliptin was administered for 3 days or 3 weeks from stroke onset. The CXCR4-antagonist AMD3100 was administered 1 day before MCAO until 3 days thereafter. Stroke outcome was assessed by measuring upper-limb function, infarct volume and neuronal survival. The plasma and brain levels of active GLP-1, GIP and SDF-1α were quantified by ELISA. To identify additional gliptin-mediated molecular effectors, brain samples were analyzed by mass spectrometry. RESULTS: Linagliptin specifically increased active SDF-1α but not glucose-dependent insulinotropic peptide (GIP) or GLP-1 brain levels. Blocking of SDF-1α/CXCR4 pathway abolished the positive effects of linagliptin on upper-limb function and histological outcome after stroke. Moreover, linagliptin treatment after stroke decreased the presence of peptides derived from neurogranin and from an isoform of the myelin basic protein. CONCLUSIONS: We showed that linagliptin improves functional stroke outcome in a SDF-1α/CXCR4-dependent manner. Considering that Calpain activity and intracellular Ca2+ regulate neurogranin and myelin basic protein detection, our data suggest a gliptin-mediated neuroprotective mechanism via the SDF-1α/CXCR4 pathway that could involve the regulation of Ca2+ homeostasis and the reduction of Calpain activity. These results provide new insights into restorative gliptin-mediated effects against stroke.