Effects of sex and estrous cycle on the brain and plasma arginine metabolic profile in rats

Association between human blood metabolites and cerebral cortex architecture: evidence from a Mendelian randomization study

Background

Dysregulation of circulating metabolites may affect brain function and cognition, associated with alterations in the cerebral cortex architecture. However, the exact cause remains unclear. This study aimed to determine the causal effect of circulating metabolites on the cerebral cortex architecture.

Methods

This study utilized retrieved data from genome-wide association studies to investigate the relationship between blood metabolites and cortical architecture. A total of 1,091 metabolites and 309 metabolite ratios were used for exposure. The brain cortex surface area and cortex thickness were selected as the primary outcomes in this study. In this study, the inverse variance weighting method was used as the main analytical method, complemented by sensitivity analyses that were more robust to pleiotropy. Furthermore, metabolic pathway analysis was performed via MetaboAnalyst 6.0. Finally, reverse Mendelian randomization (MR) analysis was conducted to assess the potential for reverse causation.

Results

After correcting for the false discovery rate (FDR), we identified 37 metabolites and 9 metabolite ratios that showed significant causal associations with cortical structures. Among these, Oxalate was found to be most strongly associated with cortical surface area (β: 2387.532, 95% CI 756.570-4018.495, p = 0.037), while Tyrosine was most correlated with cortical thickness (β: -0.015, 95% CI -0.005 to -0.025, p = 0.025). Furthermore, pathway analysis based on metabolites identified six significant metabolic pathways associated with cortical structures and 13 significant metabolic pathways based on metabolite ratios.

Conclusion

The identified metabolites and relevant metabolic pathways reveal potential therapeutic pathways for reducing the risk of neurodegenerative diseases. These findings will help guide health policies and clinical practice in treating neurodegenerative diseases.

Neuroprotection by agmatine: Possible involvement of the gut microbiome?

Agmatine, an endogenous polyamine derived from L-arginine, elicits tremendous multimodal neuromodulant properties. Alterations in agmatinergic signalling are closely linked to the pathogeneses of several brain disorders. Importantly, exogenous agmatine has been shown to act as a potent neuroprotectant in varied pathologies, including brain ageing and associated comorbidities. The antioxidant, anxiolytic, analgesic, antidepressant and memory-enhancing activities of agmatine may derive from its ability to regulate several cellular pathways; including cell metabolism, survival and differentiation, nitric oxide signalling, protein translation, oxidative homeostasis and neurotransmitter signalling. This review briefly discusses mammalian metabolism of agmatine and then proceeds to summarize our current understanding of neuromodulation and neuroprotection mediated by agmatine. Further, the emerging exciting bidirectional links between agmatine and the resident gut microbiome and their implications for brain pathophysiology and ageing are also discussed.

Neurobiochemical characteristics of arginine-rich peptides explain their potential therapeutic efficacy in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer̕ s disease (AD), Parkinson̕ s disease (PD), Huntington̕ s disease (HD), and Amyotrophic Lateral Sclerosis (ALS) require special attention to find new potential treatment methods. This review aims to summarize the current knowledge of the relationship between the biochemical properties of arginine-rich peptides (ARPs) and their neuroprotective effects to deal with the harmful effects of risk factors. It seems that ARPs have portrayed a promising and fantastic landscape for treating neurodegeneration-associated disorders. With multimodal mechanisms of action, ARPs play various unprecedented roles, including as the novel delivery platforms for entering the central nervous system (CNS), the potent antagonists for calcium influx, the invader molecules for targeting mitochondria, and the protein stabilizers. Interestingly, these peptides inhibit the proteolytic enzymes and block protein aggregation to induce pro-survival signaling pathways. ARPs also serve as the scavengers of toxic molecules and the reducers of oxidative stress agents. They also have anti-inflammatory, antimicrobial, and anti-cancer properties. Moreover, by providing an efficient nucleic acid delivery system, ARPs can play an essential role in developing various fields, including gene vaccines, gene therapy, gene editing, and imaging. ARP agents and ARP/cargo therapeutics can be raised as an emergent class of neurotherapeutics for neurodegeneration. Part of the aim of this review is to present recent advances in treating neurodegenerative diseases using ARPs as an emerging and powerful therapeutic tool. The applications and progress of ARPs-based nucleic acid delivery systems have also been discussed to highlight their usefulness as a broad-acting class of drugs.

The effect of maternal separation stress-induced depression on ovarian reserve in Sprague Dawley Rats: The possible role of imipramine and agmatine through a mTOR signal pathway

PURPOSE

To examine the possible role of impramine and agmatine through a mTOR signal pathway on rat ovary after maternal separation stress-induced depression.

METHODS

Sprague Dawley neonatal female rats were divided into control, maternal separation (MS), MS+imipramine, and MS+agmatine groups. Rats were subjected to MS for 4 hours daily from postnatal day (PND) 2 to PND 21 and pups were exposed to social isolation (SI) on PND23 for 37 days for model establishment treated with imipramine (30 mg/kg; ip) or agmatine (40 mg/kg; ip) for 15 days. In order to examine behavioral changes rats were all subjected to locomotor activity and forced swimming tests (FST). Ovaries were isolated for morphological evaluation, follicle counting and mTOR signal pathway protein expression levels were detected.

RESULTS

Increased number of primordial follicles and diminished ovarian reserve in the MS groups were detected. Imipramine treatment caused diminished ovarian reserve and atretic follicle; however, agmatine treatment provided the maintenance of ovarian follicular reserve after MS. mTOR signal pathway may have an important role during rat ovarian follicular development in model of MS.

CONCLUSIONS

Our findings suggest that agmatine may help to protect ovarian reserve during follicular development by controlling cell growth.

The hyperthermic response to intra-preoptic area administration of agmatine in male rats

Agmatine is an endogenous biogenic amine that exerts various effects on the central nervous system. The hypothalamic preoptic area (POA, thermoregulatory command center) has high agmatine immunoreactivity. In this study, in conscious and anesthetized male rats, agmatine microinjection into the POA induced hyperthermic responses associated with increased heat production and locomotor activity. Intra-POA administration of agmatine increased the locomotor activity, the brown adipose tissue temperature and rectum temperature, and induced shivering as demonstrated by increased neck muscle electromyographic activity. However, intra-POA administration of agmatine almost had no impact on the tail temperature of anesthetized rats. Furthermore, there were regional differences in the response to agmatine in the POA. The most effective sites for the microinjection of agmatine to elicit hyperthermic responses were localized in the medial preoptic area (MPA). Agmatine microinjection into the median preoptic nucleus (MnPO) and lateral preoptic nucleus (LPO) had a minimal effect on the mean core temperature. Analysis of the in vitro discharge activity of POA neurons in brain slices when perfused with agmatine showed that agmatine inhibited most warm-sensitive but not temperature-insensitive neurons in the MPA. However, regardless of thermosensitivity, the majority of MnPO and LPO neurons were not responsive to agmatine. The results demonstrated that agmatine injection into the POA of male rats, especially the MPA, induced hyperthermic responses, which may be associated with increased BAT thermogenesis, shivering and locomotor activity by inhibiting warm-sensitive neurons.

The evaluation of sea cucumber (Acaudina leucoprocta) peptide on sex hormone regulation in normal and premature ovarian failure female mice

Sea cucumber peptides (SCPs) have various functional activities. However, studies to evaluate the efficacy and safety of SCPs from the perspective of sex hormones are still lacking. In this study, normal and premature ovarian failure (POF) female mice were used to assess the effect of SCPs on the sex hormones. The ovarian and uterine indices were not influenced by SCP both in normal and POF mice. In normal mice, SCP showed no significant impact on the estrous cycle, ovarian, uterine morphology, sex hormone levels, and sex hormone synthesis-related genes of the ovary. However, 0.6 mg per g bw dosage of SCP (SCPH) statistically increased mapk1 expression on normal mice hypothalamus. In POF mice, SCPH played a more positive role than a low dosage of SCP (0.2 mg per g bw). SCP ameliorated POF-induced estrous cycle disturbances and significantly increased serum estradiol, testosterone, and AMH levels. Moreover, SCP increased the synthesis of the sex hormone by upregulating the expression of StAR, Fshr, and Cyp19a1 in the ovary, which might be due to the activation of the cAMP-related signaling pathways. The upregulation of mapk1, Esr1, and Gnrh was also observed in the hypothalamus. Together, SCP is safe for normal female mice and seems to have positive effects on POF mice from sex hormone regulation. However, the risk of excessive supplementation of sex hormones induced by the SCP intake in POF mice needs to be further explored.

Altered Brain Arginine Metabolism and Polyamine System in a P301S Tauopathy Mouse Model: A Time-Course Study

Altered arginine metabolism (including the polyamine system) has recently been implicated in the pathogenesis of tauopathies, characterised by hyperphosphorylated and aggregated microtubule-associated protein tau (MAPT) accumulation in the brain. The present study, for the first time, systematically determined the time-course of arginine metabolism changes in the MAPT P301S (PS19) mouse brain at 2, 4, 6, 8 and 12 months of age. The polyamines putrescine, spermidine and spermine are critically involved in microtubule assembly and stabilization. This study, therefore, further investigated how polyamine biosynthetic and catabolic enzymes changed in PS19 mice. There were general age-dependent increases of L-arginine, L-ornithine, putrescine and spermidine in the PS19 brain (particularly in the hippocampus and parahippocampal region). While this profile change clearly indicates a shift of arginine metabolism to favor polyamine production (a polyamine stress response), spermine levels were decreased or unchanged due to the upregulation of polyamine retro-conversion pathways. Our results further implicate altered arginine metabolism (particularly the polyamine system) in the pathogenesis of tauopathies. Given the role of the polyamines in microtubule assembly and stabilization, future research is required to understand the functional significance of the polyamine stress response and explore the preventive and/or therapeutic opportunities for tauopathies by targeting the polyamine system.

Comparative study of DHEA and letrozole induced polycystic ovary syndrome in post-pubertal rats

AIM

In order to select a suitable rat model for studying polycystic ovary syndrome (PCOS).

METHODS

Post-pubertal Sprague Dawley (SD) rats were allocated to four groups, abbreviated as the control 1 group, DHEA subcutaneous injection (DHEA) group, control 2 group, letrozole intragastric injection (letrozole) group. Body weight and the estrous cycle were monitored during the modeling. Serum stress hormones and reproductive hormones were evaluated by ELISA. The uterus and ovaries were weighed, ovarian follicle counts were calculated, and AR, LHR, FSHR, and AMH expression were assessed by immunohistochemistry.

RESULTS

In both model group subjected to the 30-day protocol of DHEA or letrozole, the mean body weights were significantly increased. Rats from both model group exhibited a significant increase of the mean length of the diestrous phase of the estrous cycle, the DHEA group had a longer diestrous phase. There was also a significant increase of serum T, E2, LH, insulin, and a significant decrease of AMH in both model group. There was a significant decrease of ovarian weight, P, and serum FSH, and a significant increase of uterus weight, serum LH/FSH in DHEA model group. There was no significant difference in serum P, FSH, and LH/FSH in letrozole model group. Both two model groups showed significantly higher AR, LHR, and AMH protein expression in rats' ovaries. FSHR protein expression in DHEA group was lower, and in letrozole model group was not different.

CONCLUSION

Compared with letrozole intragastric injection group, the pathological characteristics of DHEA subcutaneous injection group rats were closer to the characteristics of PCOS.