Recent advances in stress research: Focus on nitric oxide

The effect of nitroglycerin treatment on cerebral ischaemia: A systematic review and meta-analysis of animal studies

BACKGROUND

Nitroglycerin has been of considerable interest as a treatment for ischaemic stroke. Recent clinical trials with nitroglycerin transdermal patches during the acute phase of stroke failed to improve functional outcomes. Systematic review and meta-analysis of the effectiveness of nitroglycerin in preclinical models of ischaemic stroke has not previously been reported, despite several clinical trials.

OBJECTIVE

To conduct a systematic review and meta-analysis of preclinical evidence regarding the effect of nitroglycerin on infarct volume in animal models of ischaemic stroke.

SUMMARY OF REVIEW

The protocol was registered in PROSPERO (CRD42023432644). Our search identified 238 publications. Three publications met inclusion criteria (including 10 comparisons of infarct size). Study quality was modest (median 6 out of 9), with no evidence of publication bias. Nitroglycerin did not significantly reduce infarct volume (NMD point estimate 20.2 % reduction, 95 % CI -1.52-52.7 %, p = 0.068). Subgroup analysis suggested greater efficacy of nitroglycerin with direct intracarotid administration to the ischaemic territory at the time of reperfusion.

CONCLUSIONS

A small number of studies (three) were included in this review. Overall, nitroglycerin did not reduce infarct volume in experimental stroke models. However, nitroglycerin may be of benefit when administered directly into the ischaemic territory. Given nitroglycerin's short half-life, we propose this route may minimise harmful reduction of cerebral perfusion pressure resulting from hypotension following systemic administration.

Amelioration by Withania somnifera of neurobehavioural and immunological markers in time dependent sensitization induced post traumatic stress disorder in rats

AIMS AND OBJECTIVES

Posttraumatic stress disorder (PTSD) is a complex neuropsychiatric pathophysiology with an unmet need for safe, effective, and sustainable therapeutic modalities. Thus, the present study evaluated the effects of Withaniasomnifera (WS, Ashwagandha) on an experimental model of PTSD in rats.

MATERIALS AND METHODS

Wistar rats (200-250 g) were used and time-dependent sensitization (TDS) was used as the experimental model of PTSD. Standardized WS root extract (100 and 300 mg/kg, p.o. for 15 days) was administered with TDS and their effects were observed on neurobehavioral (anxiety) and brain cytokines, corticosterone, and oxidative stress markers.

RESULTS

Exposure to TDS resulted in anxiogenic behavior in the elevated plus maze (EPM) test, i.e., reductions in open arm entries and open arm time, as compared to the control group. Pretreatment with WS extract (100 and 300 mg/kg × 14 days) attenuated the TDS-induced anxiogenic activity in a dose-related manner, and these WS effects were comparable to those seen after the comparator drug fluoxetine (10 mg/kg). Assay of brain homogenates showed that TDS also resulted in elevations in brain interleukin-6 and reduction in corticosterone levels in both the hippocampus and prefrontal cortex (PFC), which were reversed after WS pretreatments. Further, WS pretreatment also reversed the TDS-induced changes in brain oxidative stress markers, namely elevated malondialdehyde and reduced glutathione levels in both the hippocampus and PFC.

CONCLUSION

These results suggest that WS could have potential as a therapeutic agent for treating PTSD by attenuating anxiogenesis, neuroimmune axis activation, and oxidative stress.

The Effectiveness of L-arginine in Clinical Conditions Associated with Hypoxia

The review summarises the data of the last 50 years on the effectiveness of the amino acid L-arginine in therapeutic practice in conditions accompanied by different-origin hypoxia. The aim of this review was to analyse the literature and our research data on the role of nitric oxide in the modulation of individual physiological reactivity to hypoxia. The review considers the possibility of eliminating methodological conflicts in the case of L-arginine, which can be solved by taking into account individual physiological reactivity (or the hypoxia resistance factor). Considerable attention is paid to genetic and epigenetic mechanisms of adaptation to hypoxia and conditions of adaptation in different models. The article presents data on the clinical effectiveness of L-arginine in cardiovascular system diseases (hypertension, atherosclerosis, coronary heart disease, etc.) and stress disorders associated with these diseases. The review presents a generalised analysis of techniques, data on L-arginine use by athletes, and the ambiguous role of NO in the physiology and pathology of hypoxic states shown via nitric oxide synthesis. Data on the protective effects of adaptation in the formation of individual high reactivity in sportsmen are demonstrated. The review demonstrates a favourable effect of supplementation with L-arginine and its application depending on mitochondrial oxidative phosphorylation processes and biochemical indices in groups of individuals with low and high capacity of adaptation to hypoxia. In individuals with high initial anti-hypoxic reserves, these favourable effects are achieved by the blockade of NO-dependent biosynthesis pathways. Therefore, the methodological tasks of physiological experiments and the therapeutic consequences of treatment should include a component depending on the basic level of physiological reactivity.

Stress Gastric Ulcers and Cytoprotective Strategies: Perspectives and Trends

Stress gastric ulceration is a clinical condition leading to morbidity/mortality and complex etiopathological factors are involved. Pharmacotherapy of such gastric mucosal lesions is not consistent and novel strategies are being explored. Targeting gastrointestinal factors have showed equivocal results and there is a possibility of involvement of extra-gastrointestinal factors. Stress is a highly interactive biological response in which the brain plays a key role. The involvement of brain substrates like the limbic system (amygdala, cortex, hippocampus) and behavioral traits has been investigated and research data has shown that the limbic brain-gut axis may be involved in the regulation of gastric mucosal integrity during stressful situations. The amygdaloid complex, its connections with other limbic structures and their neural networks act in tandem to contribute to both stress ulceration and gastroprotection. Complex neurotransmitter interactions in these areas involving biogenic amines and neuropeptides have been shown to modulate stress ulcerogenesis in experimental models. The immune system and brain-immune interactions also appear to play a decisive role in the genesis of such stress gastric lesions and the possibility of a brain-gut-immune axis has been proposed during stress gastric lesions. More recent studies have shown the involvement of oxidative stress and nitric oxide as well as their interactions during such stress gastric pathology, indicating the possible role of antioxidants and NO modulators as gastroprotective agents for stress ulceration. In view of the complex pathophysiology, multiple targets and lack of consistent therapeutic modalities, newer/alternative hypotheses are constantly emerging, which could be explored for effective treatment strategies aimed at gastric cytoprotection. Herbal agents with adaptogenic properties could be worth exploring in this regard as some of these phytopharmaceutical agents used in traditional medicine have been shown to exhibit gastric cytoprotection as part of their anti-stress profile. Further, their interactions with brain neurotransmitters and immune mechanisms and their relative safety could make them prospective leads for stress ulcer prophylaxis and treatment.

Nitrite-Responsive Hydrogel: Smart Drug Release Depending on the Severity of the Nitric Oxide-Related Disease

Nitric oxide (NO) is known as one of the most important biomarkers of many diseases. However, the development of NO-triggered drug releasing platforms is challenging due to the low concentration and short lifetime of NO in vivo. In this work, a novel nitrite (NO₂^-)-responsive hydrogel (DHPL-GEL), which can be used for smart drug release depending on the severity of the NO-related disease, is demonstrated. A dihydropyridine cross-linking agent is designed to construct DHPL-GEL to enable the responsive degradation of the hydrogel triggered by NO₂^-. On-demand release of the drug loaded in DHPL-GEL was observed under the stimulation of various concentrations of NO₂^- at the physiological level both in vitro and in vivo. In the inflammatory arthritis rat model, the DHPL-GEL drug delivery system showed a better therapeutic effect and less side effects than the traditional therapy and nonresponsive hydrogel drug delivery system, demonstrating the promising application of the NO₂^--responsive hydrogel for the treatment of NO-related diseases.

Alzheimer's Disease: A Contextual Link with Nitric Oxide Synthase

Nitric oxide (NO) is a gasotransmitter with pleiotropic effects which has made a great impact on biology and medicine. A multidimensional neuromodulatory role of NO has been shown in the brain with specific reference to neurodegenerative disorders like Alzheimer's disease (AD) and cognitive dysfunction. It has been found that NO/cGMP signalling pathway has an important role in learning and memory. Initially, it was considered that indirectly NO exerted neurotoxicity in AD via glutamatergic excitotoxicity. However, considering the early development of cognitive functions involved in the learning memory process including long term potentiation and synaptic plasticity, NO has a crucial role. Increasing evidence uncovered the above facts that isoforms of NOS viz endothelial NO synthase (eNOS), neuronal NO synthase (nNOS) and inducible NO synthase (iNOS) having a variable expression in AD are mainly responsible for learning and memory activities. In this review, we focus on the role of NOS isoforms in AD parallel to NO. Further, this review provides convergent evidence that NO could provide a therapeutic avenue in AD via modulation of the relevant NOS expression.

PDTC Alleviates Depressive Symptoms and Colon Tissue Injury via Inhibiting NO Overproduction in CUMS Rats

Background

The accumulated evidence demonstrates that stress plays an important role in the pathogenesis of depression that is associated with intestinal dysfunctions. However, the mechanisms remain unresolved.

Methods

A total of 40 male Wistar rats were obtained and randomly divided into four equal-sized group: control, PDTC + chronic and unpredictable mild stress (CUMS), FLX + CUMS, and CUMS. Western blotting and qRT-PCR were used to examine the levels of nitric oxide (NO), nuclear factor kappa beta (NF-κB), inducible nitric oxide synthase (iNOS), and iNOS mRNA in spinal cord L1-2 and colon.

Key Results

Chronic and unpredictable mild stress increased the serum CORT level, decreased body weight and sucrose preference, and altered OFT performance, while increased levels of NO, iNOS mRNA, iNOS and NF-κB protein in colon and spinal cord were accompanied by histopathological changes in colon. Pretreatment with an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC), reversed these effects. Fluoxetine failed to prevent NO increase in both spinal cord and colon, while the iNOS protein level, although not statistically significantly increased compared to control, was not decreased compared to CUMS. Also, fluoxetine failed to prevent histological changes.

Conclusion

In conclusion, the NF-κB/iNOS pathway may be involved in the mechanism of CUMS-induced depressive-like behavior and colon tissue injury.

Sub-acute restraint stress progressively increases oxidative/nitrosative stress and inflammatory markers while transiently upregulating antioxidant gene expression in the rat hippocampus

We have previously demonstrated that acute stress decreases neuronal nitric oxide synthase (NOS) expression in the hippocampus despite increased concentrations of nitric oxide which may indicate feedback inhibition of neuronal NOS expression via inducible NOS-derived nitric oxide. Moreover, the hippocampus undergoes an initial oxidative/nitrosative insult that is rapidly followed by upregulation of protective antioxidants, including the zinc-binding metallothioneins, in order to counter this and restore redox balance following acute stress exposure. In the present study, we have utilized indicators of oxidative/nitrosative stress, members of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway, antioxidant metallothioneins, and neuroinflammatory markers to observe the changes occurring in the hippocampus following short term repeated stress exposure. Male Wistar rats were subjected to control conditions or 6 h of restraint stress applied for 1, 2, or 3 days (n = 8 per group) after which the hippocampus was isolated for redox assays and relative gene expression. The hippocampus showed increased oxidative stress, transient dys-homeostasis of total zinc, and increased expression of the Nrf2 pathway members. Moreover, repeated stress increased nitrosative status, nitric oxide metabolites, and 3-nitrotyrosine, indicative of nitrosative stress in the hippocampus. However, levels of neuronal NOS decreased over all stress treatment groups, while increases were observed in inducible NOS and xanthine dehydrogenase. In addition to inducible NOS, mRNA expression of other inflammatory markers including interleukin-6 and interleukin-1β also increased even in the presence of increased anti-inflammatory glucocorticoids. Together, these results demonstrate that despite increases in antioxidant expression, sub-acute stress causes an inflammatory phenotype in the hippocampus by inducing oxidative/nitrosative stress, zinc dys-homeostasis, and the accumulation of nitrotyrosinated proteins which is likely driven by increased inducible NOS signaling.

Pharmacological augmentation of endocannabinoid signaling reduces the neuroendocrine response to stress

Activation of the hypothalamic-pituitary-adrenal axis (HPA) is critical for survival when the organism is exposed to a stressful stimulus. The endocannabinoid system (ECS) is currently considered an important neuromodulator involved in numerous pathophysiological processes and whose primary function is to maintain homeostasis. In the tissues constituting the HPA axis, all the components of the ECS are present and the activation of this system acts in parallel with changes in the activity of numerous neurotransmitters, including nitric oxide (NO). NO is widely distributed in the brain and adrenal glands and recent studies have shown that free radicals, and in particular NO, may play a crucial role in the regulation of stress response. Our objective was to determine the participation of the endocannabinoid and NOergic systems as probable mediators of the neuroendocrine HPA axis response to a psychophysical acute stress model in the adult male rat. Animals were pre-treated with cannabinoid receptors agonists and antagonists at central and systemic level prior to acute restraint exposure. We also performed in vitro studies incubating adrenal glands in the presence of ACTH and pharmacological compounds that modifies ECS components. Our results showed that the increase in corticosterone observed after acute restraint stress is blocked by anandamide administered at both central and peripheral level. At hypothalamic level both cannabinoid receptors (CB1 and CB2) are involved, while in the adrenal gland, anandamide has a very potent effect in suppressing ACTH-induced corticosterone release that is mainly mediated by vanilloid TRPV1 receptors. We also observed that stress significantly increased hypothalamic mRNA levels of CB1 as well as adrenal mRNA levels of TRPV1 receptor. In addition, anandamide reduced the activity of the nitric oxide synthase enzyme during stress, indicating that the anti-stress action of endocannabinoids may involve a reduction in NO production at hypothalamic and adrenal levels. In conclusion, an endogenous cannabinoid tone maintains the HPA axis in a stable basal state, which is lost with a noxious stimulus. In this case, the ECS dampens the response to stress allowing the recovery of homeostasis. Moreover, our work further contributes to in vitro evidence for a participation of the endocannabinoid system by inhibiting corticosterone release directly at the adrenal gland level.

Modulation of the stress response in wild fish is associated with variation in dissolved nitrate and nitrite

Disruption of non-reproductive endocrine systems in wildlife by chemicals has received little attention but represents a potentially significant problem. Nitrate is a major anthropogenic contaminant in the freshwater aquatic environment and has been identified as a potential disrupter of endocrine function in aquatic animals. This study was conducted to investigate the relationship between the function of the neuroendocrine stress axis in fish and inorganic N loading along reaches of rivers receiving cumulative point source and diffuse chemical inputs. To accomplish this, the responsiveness of the stress axis, quantified as the rate of release of cortisol to water across the gills during exposure to a standardised stressor, was measured in three-spined sticklebacks (Gasterosteus aculeatus L.) resident at three sites on each of four rivers in north-west England. The magnitude of the stress response in fish captured at the sites furthest downstream on all rivers was more than twice that of fish captured at upstream sites. Site-specific variation in stress axis reactivity was better explained by between-site variation in concentrations of dissolved nitrate, nitrite, and ammonia than by the concentration of wastewater treatment works effluent. An increase in the magnitude of the stress response was seen among sticklebacks at sites where long-term averaged concentrations of NH₃-N, NO₃-N and NO₂-N exceeded 0.6, 4.0 and 0.1 mg/L respectively. These data suggest that either (i) inorganic N is a better surrogate than wastewater effluent concentration for an unknown factor or factors affecting stress axis function in fish, or (ii) dissolved inorganic N directly exerts a disruptive influence on the function of the neuroendocrine stress axis in fish, supporting concerns that nitrate is an endocrine-modulating chemical.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Stress, Anxiety, and Immunomodulation: A Pharmacological Analysis

Stress and stressful events are common occurrences in our daily lives and such aversive situations bring about complex changes in the biological system. Such stress responses influence the brain and behavior, neuroendocrine and immune systems, and these responses orchestrate to increase or decrease the ability of the organism to cope with such stressors. The brain via expression of complex behavioral paradigms controls peripheral responses to stress and a bidirectional link exists in the modulation of stress effects. Anxiety is a common neurobehavioral correlate of a variety of stressors, and both acute and chronic stress exposure could precipitate anxiety disorders. Psychoneuroimmunology involves interactions between the brain and the immune system, and it is now being increasingly recognized that the immune system could contribute to the neurobehavioral responses to stress. Studies have shown that the brain and its complex neurotransmitter networks could influence immune function, and there could be a possible link between anxiogenesis and immunomodulation during stress. Physiological and pharmacological data have highlighted this concept, and the present review gives an overview of the relationship between stress, anxiety, and immune responsiveness.

The dichloromethane fraction from Mahonia bealei (Fort.) Carr. leaves exerts an anti-inflammatory effect both in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Mahonia bealei has a long history of medical use in traditional Chinese medicine for the treatment of inflammatory-associated diseases. Despite numerous phytochemical and pharmacological studies, there is a lack of systematic studies to understand the cellular and molecular mechanisms of the anti-inflammatory activity of this plant.

AIM OF STUDY

This study aimed to evaluate the anti-inflammatory activity of the dichloromethane fraction from M. bealei leaves (MBL-CH).

MATERIALS AND METHODS

RAW 264.7 cells were pretreated with different concentrations of MBL-CH for 30min prior to treatment with 1μg/ml of lipopolysaccharide (LPS). The nuclear factor κB (NF-κB) pathway and subsequent production of inflammatory mediators, such as nitric oxide (NO), prostaglandin E2 (PGE2), and tumour necrosis factor (TNF)-α were investigated. Furthermore, the in vivo mouse model of LPS-induced acute lung injury (ALI) was employed to study the anti-inflammatory effects of MBL-CH.

RESULTS

Pre-treatment with MBL-CH significantly inhibited the LPS-stimulated secretion of NO, PGE2, and TNF-α into the culture medium, as well as the mRNA levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and TNF-α, which were associated with a reduction in the phosphorylation of IκBα, Akt, and PI3K and inhibition of the transcriptional activity of NF-κB. Furthermore, in vivo experiments revealed that MBL-CH attenuated LPS-stimulated lung inflammation in mice.

CONCLUSION

Taken together, our findings indicate that MBL-CH attenuates LPS-stimulated inflammatory responses in macrophages by blocking NF-κB activation through interference with activation of the PI3K/Akt pathway, providing scientific evidence that the plant can be employed in traditional remedies.

Urinary nitrite/nitrate ratio measured by isotope-dilution LC-MS/MS as a tool to screen for urinary tract infections

Urinary tract infections (UTIs) are the most common type of nosocomial infection. Traditionally, the presence of white blood cells and microorganisms in the urine provides objective evidence for UTI diagnosis. Here, we describe the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) to measure the nitrite and nitrate levels in urine and investigate the potential of this method for UTI diagnosis. LC-MS/MS analysis was performed in positive electrospray ionization mode. After adding (15)N-labeled internal standards and derivatizing with 2,3-diaminonaphthalene (DAN), the urinary nitrite content was directly analyzed by LC-MS/MS, whereas the urinary nitrate was first reduced to nitrite before derivatization and LC-MS/MS analysis. The derivatization of nitrite and enzymatic reduction of nitrate were optimized. This method was then applied to 241 healthy subjects and 73 UTI patients. Optimization tests revealed that 1 mL of crude urine required at least 6.25 μmol of DAN to completely derivatize nitrite and 2.5 U of nitrate reductase to completely reduce nitrate to nitrite. Urinary analysis showed that the urinary concentration of nitrite and the nitrite/nitrate ratio were higher in UTI patients than in healthy subjects. Compared with the dipstick-based urinary nitrite test and using LC-MS/MS to determine the nitrite concentration (sensitivity: 23-25%), the nitrite/nitrate ratio was significantly more sensitive (95%) and exhibited a satisfactory specificity (91%) in the screening of UTIs. Taken together, the nitrite/nitrate ratio, which reflects the reducing ability of pathogenic bacteria, could be a better method for the diagnosis of UTIs that is not subject to variations in urine specimen quality.