Recovered changes in the spleen by agmatine treatment after transient cerebral ischemia

Comparison of immunophenotypes between Rag2 knockout mice derived from two different sources

BACKGROUND

Recombination activating gene2 (Rag2) knockout (KO) mice are used widely in various research fields, including vaccine development, transplantation studies, and hematopoiesis research, but few studies have compared their phenotypes. This study examined whether there were differences in the immunophenotypes between Rag2 KO mice derived from different sources. In particular, the changes in the organ weight, histological structure, and subpopulation of T and B cells were compared in the spleen and thymus of C57BL/6-Rag2^em1hwl/Korl (Rag2/Korl KO) and B6.Cg-Rag2^tm1.1Cgn/J (Rag2/J KO) mice.

RESULTS

The weight of the spleen and thymus similarly decreased in the Rag2/Korl and Rag2/J KO mice compared to their wild type (WT) mice, even though the other organs were kept at the same weight. A slight difference between the Rag2/Korl and Rag2/J KO group were detected in the number of white blood cells (WBC), lymphocytes (LYM), red cell distribution width (RDW), and platelets (PLT). In addition, the white pulp of the spleen and the cortex region of the thymus decreased in both Rag2 KO mice compared to WT mice. On the other hand, significant differences in the number of CD8⁺ T and B cell subpopulations between WT and Rag2 KO mice were observed between Rag2/Korl and Rag2/J KO group, while the CD4⁺ T subpopulation was maintained similarly in both groups.

CONCLUSIONS

These results suggest that Rag2/Korl and Rag2/J KO mice exhibit similar immunophenotypes in the spleen and thymus except for the differences in the number of CD8⁺ T and B cell subpopulations.

Neural Stem Cells Overexpressing Arginine Decarboxylase Improve Functional Recovery from Spinal Cord Injury in a Mouse Model

Current therapeutic strategies for spinal cord injury (SCI) cannot fully facilitate neural regeneration or improve function. Arginine decarboxylase (ADC) synthesizes agmatine, an endogenous primary amine with neuroprotective effects. Transfection of human ADC (hADC) gene exerts protective effects after injury in murine brain-derived neural precursor cells (mNPCs). Following from these findings, we investigated the effects of hADC-mNPC transplantation in SCI model mice. Mice with experimentally damaged spinal cords were divided into three groups, separately transplanted with fluorescently labeled (1) control mNPCs, (2) retroviral vector (pLXSN)-infected mNPCs (pLXSN-mNPCs), and (3) hADC-mNPCs. Behavioral comparisons between groups were conducted weekly up to 6 weeks after SCI, and urine volume was measured up to 2 weeks after SCI. A subset of animals was euthanized each week after cell transplantation for molecular and histological analyses. The transplantation groups experienced significantly improved behavioral function, with the best recovery occurring in hADC-mNPC mice. Transplanting hADC-mNPCs improved neurological outcomes, induced oligodendrocyte differentiation and remyelination, increased neural lineage differentiation, and decreased glial scar formation. Moreover, locomotor and bladder function were both rehabilitated. These beneficial effects are likely related to differential BMP-2/4/7 expression in neuronal cells, providing an empirical basis for gene therapy as a curative SCI treatment option.

The "Dialogue" Between Central and Peripheral Immunity After Ischemic Stroke: Focus on Spleen

The immune response generated by the body after the incidence of ischemic stroke, runs through the comprehensive process of aftermath. During this process of ischemic stroke, the central neuroinflammation and peripheral immune response seriously affect the prognosis of patients, which has been the focus of research in recent years. As this research scenario progressed, the "dialogue" between central nervous inflammation and peripheral immune response after ischemic stroke has become more closely related. It's worth noting that the spleen, as an important peripheral immune organ, plays a pivotal role in this dialogue. Multiple mechanisms have previously been reported for brain-spleen crosstalk after ischemic stroke. Further, neuroinflammation in the brain can affect the peripheral immune state by activating/inhibiting spleen function. However, the activation of the peripheral immune inflammatory response can work reversibly in the spleen. It further affects intracerebral neuroinflammation through the injured blood-brain barrier. Therefore, paying close attention to the role of spleen as the pivot between central and peripheral immunity in ischemic stroke may help to provide a new target for immune intervention in the treatment of ischemic stroke. In the present review, we reviewed the important role of spleen in central neuroinflammation and peripheral immune response after ischemic stroke. We summarized the relevant studies and reports on spleen as the target of immune intervention which can provide new ideas for the clinical treatment of ischemic stroke.

Systemic inflammation in hemorrhagic strokes - A novel neurological sign and therapeutic target?

Growing evidences suggest that stroke is a systemic disease affecting many organ systems beyond the brain. Stroke-related systemic inflammatory response and immune dysregulations may play an important role in brain injury, recovery, and stroke outcome. The two main phenomena in stroke-related peripheral immune dysregulations are systemic inflammation and post-stroke immunosuppression. There is emerging evidence suggesting that the spleen contracts following ischemic stroke, activates peripheral immune response and this may further potentiate brain injury. Whether similar brain-immune crosstalk occurs in hemorrhagic strokes such as intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) is not established. In this review, we systematically examined animal and human evidence to date on peripheral immune responses associated with hemorrhagic strokes. Specifically, we reviewed the impact of clinical systemic inflammatory response syndrome (SIRS), inflammation- and immune-associated biomarkers, the brain-spleen interaction, and cellular mediators of peripheral immune responses to ICH and SAH including regulatory T cells (Tregs). While there is growing data suggesting that peripheral immune dysregulation following hemorrhagic strokes may be important in brain injury pathogenesis and outcome, details of this brain-immune system cross-talk remain insufficiently understood. This is an important unmet scientific need that may lead to novel therapeutic strategies in this highly morbid condition.

Functional and pharmacological analysis of agmatine administration in different cerebral ischemia animal models

Agmatine (AgM, 100 mg/kg i.p.) effect was tested in parallel at two animal models of cerebral ischemia - rat MCAO model (60'/24 h, 60'/48 h, 90'/24 h, 90'/48 h) and gerbil global ischemia (10') model, administrated 5 min after reperfusion. Aim was to evaluate AgM effect on functional outcome 24 and 48 h after MCAO on neurological and sensor-motor function, and coordination in rats. AgM administration significantly reduced infarct volume, improved neurological score and improved post-ischemic oxidative status. Results of behavioral tests (cylinder test, beam walking test, and adhesive removal test) have shown very effective functional recovery after AgM administration. Efficiency of AgM administration in gerbils was observed in forebrain cortex, striatum, hippocampus, and cerebellum at the level of each examined oxidative stress parameter (nitric oxide level, superoxide production, superoxide dismutase activity, and index of lipid peroxidation) measured in four different time points starting at 3 h up to 48 h after reperfusion. The highest levels were obtained 6 h after the insult. The most sensitive oxidative stress parameter to AgM was nitric oxide. Additionally, we performed pharmacological analysis of AgM on rat isolated common carotid arteries. The findings imply that mixed population of potassium channels located on the smooth muscle cells was involved in common carotid artery response to AgM, with predominance of inward rectifying K⁺ channels. In our comparative experimental approach, judged by behavioral, biochemical, as well as pharmacological data, the AgM administration showed an effective reduction of ischemic neurological damage and oxidative stress, hence indicating a direction towards improving post-stroke recovery.

Role of Neurochemicals in the Interaction between the Microbiota and the Immune and the Nervous System of the Host Organism

This work is concerned with the role of evolutionary conserved substances, neurotransmitters, and neurohormones, within the complex framework of the microbial consortium-immune system-nervous system axis in the human or animal organism. Although the operation of each of these systems per se is relatively well understood, their combined effects on the host organism still await further research. Drawing on recent research on host-produced and microbial low-molecular-weight neurochemicals such as biogenic amines, amino acids, and short-chain fatty acids (SCFAs), we suggest that these mediators form a part of a universal neurochemical "language." It mediates the whole gamut of harmonious and disharmonious interactions between (a) the intestinal microbial consortium, (b) local and systemic immune cells, and (c) the central and peripheral nervous system. Importantly, the ongoing microbiota-host interactivity is bidirectional. We present evidence that a large number of microbially produced low-molecular-weight compounds are identical or homologous to mediators that are synthesized by immune or nervous cells and, therefore, can bind to the corresponding host receptors. In addition, microbial cells specifically respond to host-produced neuromediators/neurohormones because they have adapted to them during the course of many millions of years of microbiota-host coevolution. We emphasize that the terms "microbiota" and "microbial consortium" are to be used in the broadest sense, so as to include, apart from bacteria, also eukaryotic microorganisms. These are exemplified by the mycobiota whose role in the microbial consortium-immune system-nervous system axis researchers are only beginning to elucidate. In light of the above, it is imperative to reform the current strategies of using probiotic microorganisms and their metabolites for treating and preventing dysbiosis-related diseases. The review demonstrates, in the example of novel probiotics (psychobiotics), that many target-oriented probiotic preparations produce important side effects on a wide variety of processes in the host organism. In particular, we should take into account probiotics' capacity to produce mediators that can considerably modify the operation of the microecological, immune, and nervous system of the human organism.

Communication Between the Microbiota and Mammalian Immunity

Mammalian immune systems evolved within a diverse world dominated by microbes, making interactions between these two life-forms inevitable. Adaptive immunity protects against microbes through antigen-specific responses. In classical studies, these responses were investigated in the context of pathogenicity; however, we now know that they have significant effects on our resident microbes. In turn, microbes employ an arsenal of mechanisms to influence development and specificity of host immunity. Understanding these complex reactions will be necessary to develop microbiota-based strategies to prevent or treat disease. Here we review the literature detailing the cross talk between resident microbes with a focus on the specificity of host responses and the microbial molecules that influence them.

Metabolic strategies for the degradation of the neuromodulator agmatine in mammals

Agmatine (1-amino-4-guanidinobutane), a precursor for polyamine biosynthesis, has been identified as an important neuromodulator with anticonvulsant, antineurotoxic and antidepressant actions in the brain. In this context it has emerged as an important mediator of addiction/satiety pathways associated with alcohol misuse. Consequently, the regulation of the activity of key enzymes in agmatine metabolism is an attractive strategy to combat alcoholism and related addiction disorders. Agmatine results from the decarboxylation of L-arginine in a reaction catalyzed by arginine decarboxylase (ADC), and can be converted to either guanidine butyraldehyde by diamine oxidase (DAO) or putrescine and urea by the enzyme agmatinase (AGM) or the more recently identified AGM-like protein (ALP). In rat brain, agmatine, AGM and ALP are predominantly localised in areas associated with roles in appetitive and craving (drug-reinstatement) behaviors. Thus, inhibitors of AGM or ALP are promising agents for the treatment of addictions. In this review, the properties of DAO, AGM and ALP are discussed with a view to their role in the agmatine metabolism in mammals.

Agmatine, a potential novel therapeutic strategy for depression

Major depressive disorder is the most common psychiatric disorder with lifetime prevalence of up to 20% worldwide. It is responsible for more years lost to disability than any other disorder. Despite the fact that current available antidepressant drugs are safe and effective, they are far from ideal. In addition to the need to administer the drugs for weeks or months to obtain clinical benefit, side effects are still a serious problem. Agmatine is an endogenous polyamine synthesized by the enzyme arginine decarboxylase. It modulates several receptors and is considered as a neuromodulator in the brain. In this review, studies demonstrating the antidepressant effects of agmatine are presented and discussed, as well as, the mechanisms of action related to these effects. Also, the potential beneficial effects of agmatine for the treatment of other neurological disorders are presented. In particular, we provide evidence to encourage future clinical studies investigating agmatine as a novel antidepressant drug.

Splenic responses in ischemic stroke: new insights into stroke pathology

In the past decade, the significant contribution of the spleen to ischemic brain damage has gained considerable attention in stroke research. As the largest natural reservoir of immune cells, the spleen establishes critical connections with the ischemic brain during the progression of stroke and mobilizes its cells to the site of injury. Multiple "alarm" signals released from the injured brain are essential for the initiation of brain-spleen communication. Spleen-derived cells, including neutrophils, lymphocytes, and monocytes/macrophages, are known to contribute significantly to ischemic brain damage. Understanding the dynamic splenic responses to stroke will not only provide insights into the evolvement of ischemic brain injury but will also identify potential targets for stroke treatment. Here, we review recent studies on the functions of the spleen in ischemic stroke. We have included a discussion of several therapeutic strategies that target splenic responses and reduce acute ischemic brain damage in preclinical studies. Future investigations on the effects of the spleen on long-term stroke recovery are highly warranted.

Retroviral expression of human arginine decarboxylase reduces oxidative stress injury in mouse cortical astrocytes

BACKGROUND

In physiologic and pathologic conditions of the central nervous system (CNS), astrocytes are a double-edged sword. They not only support neuronal homeostasis but also contribute to increases in neuronal demise. A large body of experimental evidence has shown that impaired astrocytes play crucial roles in the pathologic process of cerebral ischemia; therefore, astrocytes may represent a breakthrough target for neuroprotective therapeutic strategies. Agmatine, an endogenous polyamine catalyzed from L-arginine by arginine decarboxylase (ADC), is a neuromodulator and it protects neurons/glia against various injuries.

RESULTS

In this investigation, agmatine-producing mouse cortical astrocytes were developed through transduction of the human ADC gene. Cells were exposed to oxygen-glucose deprivation (OGD) and restored to a normoxic glucose-supplied condition. Intracellular levels of agmatine were measured by high performance liquid chromatography. Cell viability was evaluated by Hoechest/propidium iodide nuclear staining and lactate dehydrogenase assay. Expression of inducible nitric oxide synthase (iNOS) and matrix metalloproteinase s (MMPs) were assessed by a reverse transcription polymerase chain reaction, Western immunoblots, and immunofluorescence. We confirmed that ADC gene-expressed astrocytes produce a great amount of agmatine. These cells were highly resistant to not only OGD but also restoration, which mimicked ischemia-reperfusion injury in vivo. The neuroprotective effects of ADC seemed to be related to its ability to attenuate expression of iNOS and MMPs.

CONCLUSION

Our findings imply that astrocytes can be reinforced against oxidative stress by endogenous agmatine production through ADC gene transduction. The results of this study provide new insights that may lead to novel therapeutic approaches to reduce cerebral ischemic injuries.

The splenic response to ischemic stroke: what have we learned from rodent models?

The majority of promising experimental compounds have failed in clinical trials, highlighting the need for novel approaches to treat stroke. Much research has been devoted to elucidating the signaling pathways involved in delayed neuroinflammation that can be targeted at clinically relevant time points. The field of stroke research has benefited from experiments characterizing the temporal expression profiles of candidate cytokines, chemokines, matrix metalloproteinases, and other putative pro-inflammatory molecules. Yet, these data have offered only a glimpse into the complex pathological sequelae and have not advanced the treatment of neuropathies. Upon recognition that peripheral immune cell activation is involved in penumbral expansion, the spleen has emerged as a novel target that mediates the peripheral immune response and promotes pro-inflammatory injury. Although the precise mechanisms have yet to be elucidated, accumulated evidence demonstrates that focal cerebral ischemia alters cytokine, chemokine, and immune cell profiles in the spleen. Additionally, removal of this peripheral lymphoid organ is neuroprotective, and the efficacy of several protective therapies has been linked to actions at the level of the spleen. Future experiments aimed at identifying the splenic lymphocyte populations that respond to ischemic stroke, as well as their signaling mechanisms, are critical in developing novel therapies.