Glutamate Receptor Dysregulation and Platelet Glutamate Dynamics in Alzheimer's and Parkinson's Diseases: Insights into Current Medications.

Two of the most prevalent neurodegenerative disorders (NDDs), Alzheimer's disease (AD) and Parkinson's disease (PD), present significant challenges to healthcare systems worldwide. While the etiologies of AD and PD differ, both diseases share commonalities in synaptic dysfunction, thereby focusing attention on the role of neurotransmitters. The possible functions that platelets may play in neurodegenerative illnesses including PD and AD are becoming more acknowledged. In AD, platelets have been investigated for their ability to generate amyloid-ß (Aß) peptides, contributing to the formation of neurotoxic plaques. Moreover, platelets are considered biomarkers for early AD diagnosis. In PD, platelets have been studied for their involvement in oxidative stress and mitochondrial dysfunction, which are key factors in the disease's pathogenesis. Emerging research shows that platelets, which release glutamate upon activation, also play a role in these disorders. Decreased glutamate uptake in platelets has been observed in Alzheimer's and Parkinson's patients, pointing to a systemic dysfunction in glutamate handling. This paper aims to elucidate the critical role that glutamate receptors play in the pathophysiology of both AD and PD. Utilizing data from clinical trials, animal models, and cellular studies, we reviewed how glutamate receptors dysfunction contributes to neurodegenerative (ND) processes such as excitotoxicity, synaptic loss, and cognitive impairment. The paper also reviews all current medications including glutamate receptor antagonists for AD and PD, highlighting their mode of action and limitations. A deeper understanding of glutamate receptor involvement including its systemic regulation by platelets could open new avenues for more effective treatments, potentially slowing disease progression and improving patient outcomes.

Noncanonical Sonic Hedgehog signaling amplifies platelet reactivity and thrombogenicity.

Sonic Hedgehog (Shh) is a morphogen in vertebrate embryos that is also associated with organ homeostasis in adults. We report here that human platelets, though enucleate, synthesize Shh from preexisting mRNAs upon agonist stimulation, and mobilize it for surface expression and release on extracellular vesicles, thus alluding to its putative role in platelet activation. Shh, in turn, induced a wave of noncanonical signaling in platelets leading to activation of small GTPase Ras homolog family member A and phosphorylation of myosin light chain in activated protein kinase-dependent manner. Remarkably, agonist-induced thrombogenic responses in platelets, which include platelet aggregation, granule secretion, and spreading on immobilized fibrinogen, were significantly attenuated by inhibition of Hedgehog signaling, thus, implicating inputs from Shh in potentiation of agonist-mediated platelet activation. In consistence, inhibition of the Shh pathway significantly impaired arterial thrombosis in mice. Taken together, the above observations strongly support a feed-forward loop of platelet stimulation triggered locally by Shh, similar to ADP and thromboxane A2, that contributes significantly to the stability of occlusive arterial thrombus and that can be investigated as a potential therapeutic target in thrombotic disorders.

Aspirin resistance and blood biomarkers in predicting ischemic stroke recurrence: An exploratory study.

BACKGROUND: Recurrent strokes cause greater complications and worse outcomes by adding to the existing neurological deficit. There is the paucity of data on serum markers of inflammation as predictors of recurrent stroke. This study was planned to analyze the clinico-etiological profile of recurrent noncardioembolic ischemic stroke, estimate aspirin resistance among regular aspirin users and evaluate blood biomarkers high-sensitivity C-reactive protein (hsCRP), Tumor necrosis factor-alpha (TNF-α), Lipoprotein-associated phospholipase A2 (Lp-PLA2) as probable predictors of stroke recurrence. METHODS: Patients of recurrent noncardioembolic ischemic stroke fulfilling the inclusion criteria were enrolled. Detailed history, clinical examination, and investigations were obtained as per protocol. Aspirin resistance was determined by light transmission aggregometry. Serum hsCRP, TNF-α, and Lp-PLA2 levels were estimated. RESULTS: This study included 34 males and 16 females. Majority of the patients were > 60 years (n = 30, 60%). Thirty (60%) cases had a repeat stroke after 1 year of primary event. Thirty-nine (78%) study participants had hypertension, while 15 (30%) had diabetes. Middle cerebral artery (n = 40, 80%) was the most common vascular territory. Thirty-one (62%) cases belonged to TOAST subtype 1 (large artery atherosclerosis). Seventy two percent cases were prescribed aspirin after index stroke, but only 36% were compliant. Median (range) hsCRP level was 7.5 (0.3-155) mg/L with 72% of patients having high hsCRP level (>3 mg/L). Median (range) serum PLA2 level was 11.98 (3.31-87.24) ng/ml in patients and 6.96 (0.15-61.42) ng/ml in controls (P = 0.029). Median (range) serum TNF-α level in patients was significantly higher than controls (68.22 [1.3-287] pg/ml versus 0.098 [0.002-36.31] pg/ml, P < 0.001). Aspirin resistance was found in 41.7% patients while 16.7% were semi-resistant. Mean % platelet aggregation was 34.75 ± 21.58 in patients and 64.75 ± 16.98 for controls (P < 0.001). CONCLUSIONS: Majority of patients with recurrent stroke were elderly (>60 years), hypertensive, and non-compliant with aspirin. Aspirin resistance was an important factor in patients with antiplatelet compliance. Inflammatory biomarkers hsCRP, PLA2, and TNF-α were found to be significantly elevated in patients compared to controls.

Fibrinogen Mitigates Prion-Mediated Platelet Activation and Neuronal Cell Toxicity.

Prion peptide (PrP) misfolds to infectious scrapie isoform, the ß pleat-rich insoluble fibrils responsible for neurodegeneration and fatal conformational diseases in humans. The amino acid sequence 106-126 from prion proteins, PrP(106-126), is highly amyloidogenic and implicated in prion-induced pathologies. Here, we report a novel interaction between PrP(106-126) and the thrombogenic plasma protein fibrinogen that can lead to mitigation of prion-mediated pro-thrombotic responses in human platelets as well as significant decline in neuronal toxicity. Thus, prior exposure to fibrinogen-restrained PrP-induced rise in cytosolic calcium, calpain activation, and shedding of extracellular vesicles in platelets while it, too, averted cytotoxicity of neuronal cells triggered by prion peptide. Interestingly, PrP was found to accelerate fibrin-rich clot formation, which was resistant to plasmin-mediated fibrinolysis, consistent with enhanced thrombus stability provoked by PrP. We propose that PrP-fibrinogen interaction can be clinically exploited further for prevention and management of infectious prion related disorders. Small molecules or peptides mimicking PrP-binding sites on fibrinogen can potentially mitigate PrP-induced cellular toxicity while also preventing the negative impact of PrP on fibrin clot formation and lysis.

Palliative care services for cancer patients in Nepal, a lower-middle-income country.

With the rise in cancer burden, need for palliative care services has increased simultaneously and majority of people requiring services are from low- and middle-income countries where palliative care is in primitive stage. Nepal is also facing similar challenges of dealing with cancer care and end-of-life care. From its initiation in the early 1990s, there has been gradual progress in the development of palliative care with joint effort of government as well as non-governmental organizations. Morphine, a major milestone for pain management, is being manufactured in the country for nearly a decade, yet morphine equivalence mg per capita is far below the global average. Currently, Nepal has been placed under 'Category 3a' with isolated care provision and there are a lot of challenges to overcome to improve the existing services. Majority of hospice and palliative care centres are located in the capital city and only a few in the periphery. Scarcity of treatment centres and expertise, limited finances, lack of awareness among patients and health care workers, and difficult terrain are major barriers for optimal care. Proper implementation of national guidelines, human resource development and integration of palliative care to primary healthcare level would be crucial steps for further improvement.

AMPK inhibition protects against arterial thrombosis while sparing hemostasis through differential modulation of platelet responses.

AMP-activated protein kinase (AMPK) is a metabolic master switch that has critical role in wide range of pathologies including cardiovascular disorders. As AMPK-α2 knockout mice exhibit impaired thrombus stability, we asked whether pharmacological inhibition of AMPK with a specific small-molecule inhibitor, compound C, could protect against arterial thrombosis without affecting hemostasis. Mice pre-administered with compound C exhibited decreased mesenteric arteriolar thrombosis but normal tail bleeding time compared to vehicle-treated animals. Compound C potently restricted platelet aggregation, clot retraction and integrin activation induced by thrombin and collagen. It impaired platelet spreading on both immobilized fibrinogen and collagen matrices; it, however, had no significant effect on thrombin-induced phosphatidylserine exposure that is characteristic of procoagulant platelets. In parallel, compound C brought about significant drop in thrombin-induced phosphorylation of myosin light chain (MLC) and MLC phosphatase (MYPT1) as well as abrogated rise in level of RhoA-GTP in thrombin-stimulated platelets. Thus, effects of compound C on agonist-induced platelet responses could be at least in part attributed to modulation of cytoskeletal changes mediated by RhoA-MYPT1-MLC signaling. An ideal antithrombotic drug would spare hemostatic responses that maintain vascular integrity while preferentially protecting against thrombosis. The present study suggests that AMPK could be one such potential therapeutic target.

Glutamate induces synthesis of thrombogenic peptides and extracellular vesicle release from human platelets.

Platelets are highly sensitive blood cells, which play central role in hemostasis and thrombosis. Platelet dense granules carry considerable amount of neurotransmitter glutamate that is exocytosed upon cell activation. As platelets also express glutamate receptors on their surface, it is pertinent to ask whether exposure to glutamate would affect their signalling within a growing thrombus. In this study we demonstrate that, glutamate per se induced synthesis of thrombogenic peptides, plasminogen activator inhibitor-1 and hypoxia-inducible factor-2α, from pre-existing mRNAs in enucleate platelets, stimulated cytosolic calcium entry, upregulated RhoA-ROCK-myosin light chain/myosin light chain phosphatase axis, and elicited extensive shedding of extracellular vesicles from platelets. Glutamate, too, incited platelet spreading and adhesion on to immobilized matrix under arterial shear, raised mitochondrial transmembrane potential associated with generation of reactive oxygen species and induced activation of AMP-activated protein kinase in platelets. Taken together, glutamate switches human platelets to pro-activation phenotype mediated mostly through AMPA receptors and thus targeting glutamate receptors may be a promising anti-platelet strategy.

Aerobic glycolysis fuels platelet activation: small-molecule modulators of platelet metabolism as anti-thrombotic agents.

Platelets are critical to arterial thrombosis, which underlies myocardial infarction and stroke. Activated platelets, regardless of the nature of their stimulus, initiate energy-intensive processes that sustain thrombus, while adapting to potential adversities of hypoxia and nutrient deprivation within the densely packed thrombotic milieu. We report here that stimulated platelets switch their energy metabolism to aerobic glycolysis by modulating enzymes at key checkpoints in glucose metabolism. We found that aerobic glycolysis, in turn, accelerates flux through the pentose phosphate pathway and supports platelet activation. Hence, reversing metabolic adaptations of platelets could be an effective alternative to conventional anti-platelet approaches, which are crippled by remarkable redundancy in platelet agonists and ensuing signaling pathways. In support of this hypothesis, small-molecule modulators of pyruvate dehydrogenase, pyruvate kinase M2 and glucose-6-phosphate dehydrogenase, all of which impede aerobic glycolysis and/or the pentose phosphate pathway, restrained the agonist-induced platelet responses ex vivo These drugs, which include the anti-neoplastic candidate, dichloroacetate, and the Food and Drug Administration-approved dehydroepiandrosterone, profoundly impaired thrombosis in mice, thereby exhibiting potential as anti-thrombotic agents.

Indole-3-carbinol improves neurobehavioral symptoms in a cerebral ischemic stroke model.

Stroke is one of the most common causes of death worldwide and also responsible for permanent disability. Ischemic stroke has been found to affect 80% of stroke patients. Recombinant tissue plasminogen activator (rtPA) is the widely used drug for the ischemic stroke with narrow therapeutic window. Indole-3-carbinol (I3C) is a natural compound obtained from brassica species having antithrombotic activity. Middle cerebral artery occlusion (MCAO) model was used followed by reperfusion after 2 h of ischemia for the evaluation of the I3C against ischemic stroke. After reperfusion, I3C (12.5, 25, and 50 mg/kg) was given by oral route once daily and continued up to the 14th day. Behavioral studies including postural reflex, forelimb placing, and cylinder tests showed I3C attenuated the MCAO-induced increase in average score and asymmetry score efficiently. Mean cerebral blood flow (CBF) was improved by treatment with I3C (12.5 mg/kg) by 60% of baseline at 6 h. I3C inhibited ADP-induced platelet aggregation and reduced ischemic volume significantly. It also inhibited in vitro the ADP-induced platelet aggregation in healthy human volunteers. I3C improves behavioral scores and mean CBF after focal cerebral ischemia in rats. Furthermore, I3C showed prophylactic anti-thrombotic activity against carrageenan induced tail thrombosis. Therefore, preclinical evidence points to I3C as a potential candidate for use in cerebral ischemic stroke.