L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria

The intersection of host in vivo metabolism and immune responses to infection with kinetoplastid and apicomplexan parasites

SUMMARYProtozoan parasite infection dramatically alters host metabolism, driven by immunological demand and parasite manipulation strategies. Immunometabolic checkpoints are often exploited by kinetoplastid and protozoan parasites to establish chronic infection, which can significantly impair host metabolic homeostasis. The recent growth of tools to analyze metabolism is expanding our understanding of these questions. Here, we review and contrast host metabolic alterations that occur in vivo during infection with Leishmania, trypanosomes, Toxoplasma, Plasmodium, and Cryptosporidium. Although genetically divergent, there are commonalities among these pathogens in terms of metabolic needs, induction of the type I immune responses required for clearance, and the potential for sustained host metabolic dysbiosis. Comparing these pathogens provides an opportunity to explore how transmission strategy, nutritional demand, and host cell and tissue tropism drive similarities and unique aspects in host response and infection outcome and to design new strategies to treat disease.

Advances in nitric oxide regulators for the treatment of ischemic stroke

Ischemic stroke (IS) is a life-threatening disease worldwide. Nitric oxide (NO) derived from l-arginine catalyzed by NO synthase (NOS) is closely associated with IS. Three isomers of NOS (nNOS, eNOS and iNOS) produce different concentrations of NO, resulting in quite unlike effects during IS. Of them, n/iNOSs generate high levels of NO, detrimental to brain by causing nerve cell apoptosis and/or necrosis, whereas eNOS releases small amounts of NO, beneficial to the brain via increasing cerebral blood flow and improving nerve function. As a result, a large variety of NO regulators (NO donors or n/iNOS inhibitors) have been developed for fighting IS. Regrettably, up to now, no review systematically introduces the progresses in this area. This article first outlines dynamic variation rule of NOS/NO in IS, subsequently highlights advances in NO regulators against IS, and finally presents perspectives based on concentration-, site- and timing-effects of NO production to promote this field forward.

The complex role of eicosanoids in the brain: Implications for brain tumor development and therapeutic opportunities

Eicosanoids are a family of bioactive lipids that play diverse roles in the normal physiology of the brain, including neuronal signaling, synaptic plasticity, and regulation of cerebral blood flow. In the brain, eicosanoids are primarily derived from arachidonic acid, which is released from membrane phospholipids in response to various stimuli. Prostaglandins (PGs) and leukotrienes (LTs) are the major classes of eicosanoids produced in the brain, and they act through specific receptors to modulate various physiological and pathological processes. Dysregulation of eicosanoids has been implicated in the development and progression of brain tumors, including glioblastoma (GBM), meningioma, and medulloblastoma. Eicosanoids have been shown to promote tumor cell proliferation, migration, invasion, angiogenesis, and resistance to therapy. Particularly, PGE2 promotes GBM cell survival and resistance to chemotherapy. Understanding the role of eicosanoids in brain tumors can inform the development of diagnostic and prognostic biomarkers, as well as therapeutic strategies that target eicosanoid pathways. Cyclooxygenase (COX)-2 and 5-lipoxygenase (LOX) inhibitors have been shown to reduce the growth and invasiveness of GBM cells. Moreover, eicosanoids have immunomodulatory effects that can impact the immune response to brain tumors. Understanding the role of eicosanoids in the immune response to brain tumors can inform the development of immunotherapy approaches for these tumors. Overall, the complex role of eicosanoids in the brain underscores the importance of further research to elucidate their functions in normal physiology and disease, and highlights the potential for developing novel therapeutic approaches that target eicosanoid pathways in brain tumors.

Perillyl alcohol modulates activation, permeability and integrity of human brain endothelial cells induced by Plasmodium falciparum

BACKGROUND

Cerebral malaria (CM) is a severe immunovasculopathy caused for Plasmodium falciparum infection, which is characterised by the sequestration of parasitised red blood cells (pRBCs) in brain microvessels. Previous studies have shown that some terpenes, such as perillyl alcohol (POH), exhibit a marked efficacy in preventing cerebrovascular inflammation, breakdown of the brain-blood barrier (BBB) and brain leucocyte accumulation in experimental CM models.

OBJECTIVE

To analyse the effects of POH on the endothelium using human brain endothelial cell (HBEC) monolayers co-cultured with pRBCs.

METHODOLOGY

The loss of tight junction proteins (TJPs) and features of endothelial activation, such as ICAM-1 and VCAM-1 expression were evaluated by quantitative immunofluorescence. Microvesicle (MV) release by HBEC upon stimulation by P. falciparum was evaluated by flow cytometry. Finally, the capacity of POH to revert P. falciparum-induced HBEC monolayer permeability was examined by monitoring trans-endothelial electrical resistance (TEER).

FINDINGS

POH significantly prevented pRBCs-induced endothelial adhesion molecule (ICAM-1, VCAM-1) upregulation and MV release by HBEC, improved their trans-endothelial resistance, and restored their distribution of TJPs such as VE-cadherin, Occludin, and JAM-A.

CONCLUSIONS

POH is a potent monoterpene that is efficient in preventing P. falciparum-pRBCs-induced changes in HBEC, namely their activation, increased permeability and alterations of integrity, all parameters of relevance to CM pathogenesis.

Intravenous whole blood transfusion results in faster recovery of vascular integrity and increased survival in experimental cerebral malaria

BACKGROUND

Cerebral malaria is a lethal complication of Plasmodium falciparum infections in need of better therapies. Previous work in murine experimental cerebral malaria (ECM) indicated that the combination of artemether plus intraperitoneal whole blood improved vascular integrity and increased survival compared to artemether alone. However, the effects of blood or plasma transfusion administered via the intravenous route have not previously been evaluated in ECM.

OBJECTIVES

To evaluate the effects of intravenous whole blood compared to intravenous plasma on hematological parameters, vascular integrity, and survival in artemether-treated ECM.

METHODS

Mice with late-stage ECM received artemether alone or in combination with whole blood or plasma administered via the jugular vein. The outcome measures were hematocrit and platelets; plasma angiopoietin 1, angiopoietin 2, and haptoglobin; blood-brain barrier permeability; and survival.

FINDINGS

Survival increased from 54% with artemether alone to 90% with the combination of artemether and intravenous whole blood. Intravenous plasma lowered survival to 18%. Intravenous transfusion provided fast and pronounced recoveries of hematocrit, platelets, angiopoietins levels and blood brain barrier integrity.

MAIN CONCLUSIONS

The outcome of artemether-treated ECM was improved by intravenous whole blood but worsened by intravenous plasma. Compared to prior studies of transfusion via the intraperitoneal route, intravenous administration was more efficacious.

Dissecting the mechanisms of pathogenesis in cerebral malaria

Cerebral malaria (CM) is one of the leading causes of death due to malaria. It is characterised by coma, presence of asexual parasites in blood smear, and absence of any other reason that can cause encephalopathy. The fatality rate for CM is high, and those who survive CM often experience long-term sequelae, including cognitive and motor dysfunctions. It is unclear how parasites sequestered in the lumen of endothelial cells of the blood–brain barrier (BBB), and localised breakdown of BBB can manifest gross physiological changes across the brain. The pathological changes associated with CM are mainly due to the dysregulation of inflammatory and coagulation pathways. Other factors like host and parasite genetics, transmission intensity, and the host’s immune status are likely to play a role in the development and progression of CM. This work focuses on the pathological mechanisms underlying CM. Insights from humans, mice, and in vitro studies have been summarised to present a cohesive understanding of molecular mechanisms involved in CM pathology.

Thromboxane A2 synthase inhibition ameliorates endothelial dysfunction, memory deficits, oxidative stress and neuroinflammation in rat model of streptozotocin diabetes induced dementia

RATIONALE

Vascular dementia (VaD) is the second leading cause of dementia worldwide. It is very important to find the possible pharmacological agents which may be useful in management and therapy of VaD.

OBJECTIVES

The present study investigates the effect of ozagrel, a selective thromboxane A2 (TXA2) synthase inhibitor, in a rat model of VaD.

METHODS

Single intraperitoneal injection of streptozotocin [STZ, (50 mg/kg)] was administered to Wistar rats to induced diabetes-associated vascular endothelial dysfunction and memory impairment. Morris water maze (MWM) test was employed to assess learning and memory. Endothelial dysfunction was assessed in the isolated aorta by observing endothelial-dependent vasorelaxation and levels of serum nitrite. Various biochemical and histopathological estimations were also performed.

RESULTS

STZ treatment produced endothelial dysfunction, impairment of learning and memory, reduction in body weight and serum nitrite/nitrate, and increase in serum glucose, brain oxidative stress (increased brain thiobarbituric acid reactive species and decreased reduced glutathione levels), brain acetylcholinesterase activity and brain myeloperoxidase activity. Further a significant rise in brain tumor necrosis factor-α & interleukin-6 levels and brain neutrophil infiltration were also observed. Treatment of ozagrel (10 & 20 mg/kg, p. o.)/donepezil (0. 5 mg/kg, i.p., serving as standard) ameliorated STZ induced endothelial dysfunction; memory deficits; biochemical and histopathological changes.

CONCLUSIONS

It may be concluded that ozagrel markedly improved endothelial dysfunction; learning and memory; biochemical and histopathological alteration associated with STZ induced dementia and that TXA2 can be considered as an important therapeutic target for the management of VaD.

Polymeric Nanoparticle Based Diagnosis and Nanomedicine for Treatment and Development of Vaccines for Cerebral Malaria: A Review on Recent Advancement

Cerebral malaria occurs due to Plasmodium falciparum infection, which causes 228 million infections and 450,000 deaths worldwide every year. African people are mostly affected with nearly 91% cases, of which 86% are pregnant women and infants. India and Brazil are the other two countries severely suffering from malaria endemicity. Commonly used drugs have severe side effects, and unfortunately no suitable vaccine is available in the market today. In this line, this review is focused on polymeric nanomaterials and nanocapsules that can be used for the development of effective diagnostic strategies, nanomedicines, and vaccines in the management of cerebral malaria. Further, this review will help scientists and medical professionals by updating the status on the development stages of polymeric nanoparticle based diagnostics, nanomedicines, and vaccines and strategies to eradicate cerebral malaria. In addition to this, the predominant focus of this review is antimalarial agents based on polymer nanomedicines that are currently in the preclinical and clinical trial stages, and potential developments are suggested as well. This review further will have an important social and commercial impact worldwide for the development of polymeric nanomedicines and strategies for the treatment of cerebral malaria.

Expression of Endothelial NOX5 Alters the Integrity of the Blood-Brain Barrier and Causes Loss of Memory in Aging Mice

Blood-Brain barrier (BBB) disruption is a hallmark of central nervous system (CNS) dysfunction, and oxidative stress is one of the molecular mechanisms that may underlie this process. NADPH oxidases (NOX) are involved in oxidative stress-mediated vascular dysfunction and participate in the pathophysiology of its target organs. The NADPH oxidase 5 (NOX5) isoform is absent in rodents, and although little is known about the role it may play in disrupting the BBB, it has recently been implicated in experimental stroke. Our aim was to investigate the role of NADPH oxidase 5 (NOX5) in promoting vascular alterations and to identify its impact on the cognitive status of aged mice. No differences were detected in the arterial blood pressure or body weight between knock-in mice expressing endothelial NOX5 and the control mice. The Morris water maze test showed memory impairments in the aged knock-in mice expressing NOX5 compared with their control littermates. For assessing the BBB integrity, we studied the protein expression of two tight junction (TJ) proteins: Zonula occludens-1 (ZO-1) and occludin. Compared to the control animals, Aged NOX5 mice exhibited reduced levels of both proteins, demonstrating an alteration of the BBB integrity. Our data indicate that vascular NOX5 may favor behavioral changes with aging through oxidative stress-mediated BBB breakdown.

Whole blood transfusion improves vascular integrity and increases survival in artemether-treated experimental cerebral malaria

Pathological features observed in both human and experimental cerebral malaria (ECM) are endothelial dysfunction and changes in blood components. Blood transfusion has been routinely used in patients with severe malarial anemia and can also benefit comatose and acidotic malaria patients. In the present study Plasmodium berghei-infected mice were transfused intraperitoneally with 200 μL of whole blood along with 20 mg/kg of artemether. ECM mice showed severe thrombocytopenia and decreases in hematocrit. Artemether treatment markedly aggravated anemia within 24 h. Whole blood administration significantly prevented further drop in hematocrit and partially restored the platelet count. Increased levels of plasma angiopoietin-2 (Ang-2) remained high 24 h after artemether treatment but returned to normal levels 24 h after blood transfusion, indicating reversal to quiescence. Ang-1 was depleted in ECM mice and levels were not restored by any treatment. Blood transfusion prevented the aggravation of the breakdown of blood brain barrier after artemether treatment and decreased spleen congestion without affecting splenic lymphocyte populations. Critically, blood transfusion resulted in markedly improved survival of mice with ECM (75.9% compared to 50.9% receiving artemether only). These findings indicate that whole blood transfusion can be an effective adjuvant therapy for cerebral malaria.

Ozagrel a thromboxane A2 synthase inhibitor extenuates endothelial dysfunction, oxidative stress and neuroinflammation in rat model of bilateral common carotid artery occlusion induced vascular dementia

The present study investigates the potential of ozagrel, a thromboxane A2 (TXA2) synthase inhibitor, in bilateral common carotid artery occlusion (BCCAo) induced vascular dementia (VaD). Wistar rats were subjected to BCCAo procedure under anesthesia to induce VaD. Morris water maze (MWM) test was employed on 7th day post-surgery to determine learning and memory. Endothelial dysfunction was assessed in isolated aorta by observing endothelial dependent vasorelaxation and levels of serum nitrite. A battery of biochemical and histopathological estimations was performed. Expression analysis of inflammatory cytokines TNF-α and IL-6 was carried out by RT-PCR. BCCAo produced significant impairment in endothelium dependent vasorelaxation and decrease in serum nitrite levels indicating endothelial dysfunction along with poor performance on MWM represents impairment of learning and memory. There was a significant rise in brain oxidative stress level (indicated by increase in brain thiobarbituric acid reactive species and decrease in reduced glutathione levels); increase in brain acetylcholinesterase activity; brain myeloperoxidase activity; brain TNF-α & IL-6 levels, brain TNF-α & IL-6 mRNA expression and brain neutrophil infiltration (as marker of inflammation) were also observed. Treatment of ozagrel (10 & 20 mg/kg, p. o.)/donepezil (0. 5 mg/kg, i.p., serving as standard) ameliorated BCCAo induced endothelial dysfunction; memory deficits; biochemical and histopathological changes in a significant manner. It may be concluded that ozagrel markedly improved endothelial dysfunction; learning and memory; biochemical and histopathological alteration associated with BCCAo induced VaD and that TXA2 can be considered as an important therapeutic target for the treatment of VaD.

Amino Acid Metabolism in Apicomplexan Parasites

Obligate intracellular pathogens have coevolved with their host, leading to clever strategies to access nutrients, to combat the host's immune response, and to establish a safe niche for intracellular replication. The host, on the other hand, has also developed ways to restrict the replication of invaders by limiting access to nutrients required for pathogen survival. In this review, we describe the recent advancements in both computational methods and high-throughput -omics techniques that have been used to study and interrogate metabolic functions in the context of intracellular parasitism. Specifically, we cover the current knowledge on the presence of amino acid biosynthesis and uptake within the Apicomplexa phylum, focusing on human-infecting pathogens: Toxoplasma gondii and Plasmodium falciparum. Given the complex multi-host lifecycle of these pathogens, we hypothesize that amino acids are made, rather than acquired, depending on the host niche. We summarize the stage specificities of enzymes revealed through transcriptomics data, the relevance of amino acids for parasite pathogenesis in vivo, and the role of their transporters. Targeting one or more of these pathways may lead to a deeper understanding of the specific contributions of biosynthesis versus acquisition of amino acids and to design better intervention strategies against the apicomplexan parasites.

Ameliorative effect of ozagrel, a thromboxane A2 synthase inhibitor, in hyperhomocysteinemia-induced experimental vascular cognitive impairment and dementia

The present study investigates the effect of ozagrel, a selective thromboxane A2 (TXA2) inhibitor, in rat model of hyperhomocysteinemia (HHcy)-induced vascular cognitive impairment and dementia (VCID). Wistar rats were administered L-methionine (1.7 g/kg/day; p.o. × 8 weeks) to induce VCID. Morris water maze (MWM) test was employed to assess learning and memory. Endothelial dysfunction was assessed in the isolated aorta by observing endothelial-dependent vasorelaxation and levels of serum nitrite. Various biochemical and histopathological estimations were also performed. L-methionine produced significant impairment in endothelium-dependent vasorelaxation and decreases serum nitrite levels indicating endothelial dysfunction. Further, these animals performed poorly on MWM, depicting impairment of learning and memory. Further, a significant rise in brain oxidative stress level (indicated by increase in brain thiobarbituric acid-reactive species and decrease in reduced glutathione levels), brain acetylcholinesterase activity, brain myeloperoxidase activity, brain TNF-α and IL-6 levels, and brain leukocyte (neutrophil) infiltration was also observed. Treatment of ozagrel (10 and 20 mg/kg, p. o.)/donepezil (0.5 mg/kg, i.p., serving as standard) ameliorated L-methionine-induced endothelial dysfunction, memory deficits, and biochemical and histopathological changes. It may be concluded that ozagrel markedly improved endothelial dysfunction, learning and memory, and biochemical and histopathological alteration associated with L-methionine-induced VCID and that TXA2 can be considered as an important therapeutic target for the management of VCID.