Oxytocin promotes hepatic regeneration in elderly mice

Liver Neurobiology: Regulation of Liver Functions by the Nervous System

The nervous system plays an important role in the regulation of liver functions during physiological as well as pathological conditions. This regulatory effect is based on the processing of signals transmitted to the brain by sensory nerves innervating the liver tissue and other visceral organs and by humoral pathways transmitting signals from peripheral tissues and organs. Based on these signals, the brain modulates metabolism, detoxification, regeneration, repair, inflammation, and other processes occurring in the liver. The nervous system thus determines the functional and morphological characteristics of the liver. Liver innervation also mediates the influence of psychosocial factors on liver functions. The aim of this review is to describe complexity of bidirectional interactions between the brain and liver and to characterize the mechanisms and pathways through which the nervous system influences liver function during physiological conditions and maintains liver and systemic homeostasis.

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside promotes liver regeneration after partial hepatectomy in mice: The potential involvement of PPARα-mediated fatty acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG) is the principal bioactive compound contained in Polygonum multiflorum Thunb. (PMT), which is traditionally recorded to possess tonic and anti-aging efficacy.

AIM OF THE STUDY

To identify the TSG-provided promotion on liver regeneration (LR) following partial hepatectomy (PHx) in mice and to explicate its involved mechanism.

MATERIALS AND METHODS

The promotion of TSG on LR was evaluated by hematoxylin and eosin (H&E), 5-bromodeoxyuridinc (BrdU) and Ki-67 staining, and measuring the level of proliferating cell nuclear antigen (PCNA) and Cyclin D1 in mice with PHx at different time points. Gene Expression Omnibus (GEO, GSE15239) database and the label-free quantitative proteomics from liver of mice at 24 h after PHx were integrated to identify potential involved critical proteins, which were verified by Western-blot, Real-time polymerase chain reaction (RT-PCR), molecular docking and luciferase activity assay. Primary hepatocytes isolated from mice were used to investigate the TSG-provided promotion on proliferation in vitro.

RESULTS

TSG (20 mg/kg) promoted LR in mice after PHx. Results from RNA expression data from clinical samples and proteomic analysis from liver tissues indicated that peroxisome proliferator-activated receptor α (PPARα)-mediated fatty acid metabolism pathway were crucially associated with the TSG-provided promotion on LR. TSG enhanced the nuclear translocation of PPARα and the mRNA expression of a series of PPARα-regulated downstream genes. In addition, TSG lowered hepatic triglyceride (TG) and non-esterified fatty acid (NEFA) amounts and increased hepatic adenosine triphosphate (ATP) level in mice after PHx. TSG up-regulated the transcriptional activity of PPARα in vitro. Next results displayed that TSG promoted cell proliferation as well as ATP level in mice primary hepatocytes, which were abolished when PPARα was suppressed. Meanwhile, the cell viability was also elevated in mice primary hepatocytes treated with ATP.

CONCLUSION

Activating PPARα-mediated fatty acid β-oxidation (FAO) pathway led to the production of ATP, which contributed to the TSG-provided promotion on LR after PHx in mice.

Oxytocin, the Love Hormone, in Stem Cell Differentiation

Oxytocin (OXT) is a neurohypophysial nonapeptide that exerts its effects mainly through the oxytocin receptor (OXTR). Several studies have pointed out the role of OXT in the modulation of stem cell (SC) fate and properties. SCs are undifferentiated cells characterized by a remarkable ability to self-renew and differentiate into various cell types of the body. In this review, we focused on the role of OXT in SC differentiation. Specifically, we summarize and discuss the scientific research examining the effects of OXT on mesodermal SC-derived lineages, including cardiac, myogenic, adipogenic, osteogenic, and chondrogenic differentiation. The available studies related to the effects of OXT on SC differentiation provide little insights about the molecular mechanism mediated by the OXT-OXTR pathway. Further research is needed to fully elucidate these pathways to effectively modulate SC differentiation and develop potential therapeutic applications in regenerative medicine.

Cell-specific regulation of the circadian clock by BMAL1 in the paraventricular nucleus: Implications for regulation of systemic biological rhythms

Circadian rhythms are internal biological rhythms driving temporal tissue-specific, metabolic programs. Loss of the circadian transcription factor BMAL1 in the paraventricular nucleus (PVN) of the hypothalamus reveals its importance in metabolic rhythms, but its functions in individual PVN cells are poorly understood. Here, loss of BMAL1 in the PVN results in arrhythmicity of processes controlling energy balance and alters peripheral diurnal gene expression. BMAL1 chromatin immunoprecipitation sequencing (ChIP-seq) and single-nucleus RNA sequencing (snRNA-seq) reveal its temporal regulation of target genes, including oxytocin (OXT), and restoring circulating OXT peaks in BMAL1-PVN knockout (KO) mice rescues absent activity rhythms. While glutamatergic neurons undergo day/night changes in expression of genes involved in cell morphogenesis, astrocytes and oligodendrocytes show gene expression changes in cytoskeletal organization and oxidative phosphorylation. Collectively, our findings show diurnal gene regulation in neuronal and non-neuronal PVN cells and that BMAL1 contributes to diurnal OXT secretion, which is important for systemic diurnal rhythms.

Oxytocin alleviates liver fibrosis via hepatic macrophages

Background & Aims

Previous studies demonstrated oxytocin treatment effectiveness in reducing mortality and reversing liver fibrosis in mice. However, the underlying mechanism remains obscure, given the absence of oxytocin receptor expression in hepatic stellate cells, the primary liver fibrosis effector cells.

Methods

A comprehensive map of cell populations in fibrotic liver was generated using single-cell sequencing. The map enabled our study of the target cells of oxytocin action in the liver in more dimensions. Furthermore, we elucidated the mechanism of the oxytocin signaling system in hepatic macrophages using oxytocin receptor-specific knockout mice and liver fibrosis animal models.

Results

The carbon tetrachloride-induced hepatic fibrosis and bile duct ligation hepatic fibrosis mouse models demonstrated that oxytocin reversed hepatic fibrosis in mice. The mapped liver cell populations demonstrated that oxytocin promoted the phenotypic switch from Ly6high to Ly6Clow in myeloid-derived macrophages. The phenotypic control of oxytocin signaling system activation on this phenotypic switch was validated using myeloid-specific oxytocin receptor knockout mice. Subsequent studies demonstrated that the calcium inward flow induced by oxytocin receptor activation activated the key orphan nuclear receptor NR4A1, which controls macrophage phenotypic switching. Specifically, calcium ions activated CREB, a key target regulator of NR4A1 expression.

Conclusions

The findings established hepatic macrophages as a hub responsible for the oxytocin-mediated alleviation of liver fibrosis. This study revealed a novel pathway where oxytocin regulates macrophage phenotype.

Impact and implications

Previous studies revealed for the first time the expression of oxytocin receptors in the liver. The present study shows that oxytocin reverses hepatic fibrosis and that hepatic macrophages are the central hub of oxytocin-mediated alleviation of hepatic fibrosis by promoting a phenotypic switch in hepatic macrophages, transitioning from Ly6high to Ly6Clow expression. The present study reveals a novel pathway by which oxytocin regulates macrophage phenotype. In addition, the potential applications of oxytocin and its analogues, as traditional drugs for clinical application, in the treatment of liver fibrosis deserve to be further explored.

Traditional Japanese medicine Kamikihito ameliorates sucrose preference, chronic inflammation and obesity induced by a high fat diet in middle-aged mice

The high prevalence of obesity has become a pressing global public health problem and there exists a strong association between increased BMI and mortality at a BMI of 25 kg/m2 or higher. The prevalence of obesity is higher among middle-aged adults than among younger groups and the combination of aging and obesity exacerbate systemic inflammation. Increased inflammatory cytokines such as interleukin 6 and tumor necrosis factor alpha (TNFα) are hallmarks of obesity, and promote the secretion of hepatic C-reactive protein (CRP) which further induces systematic inflammation. The neuropeptide oxytocin has been shown to have anti-obesity and anti-inflammation effects, and also suppress sweet-tasting carbohydrate consumption in mammals. Previously, we have shown that the Japanese herbal medicine Kamikihito (KKT), which is used to treat neuropsychological stress disorders in Japan, functions as an oxytocin receptors agonist. In the present study, we further investigated the effect of KKT on body weight (BW), food intake, inflammation, and sweet preferences in middle-aged obese mice. KKT oral administration for 12 days decreased the expression of pro-inflammatory cytokines in the liver, and the plasma CRP and TNFα levels in obese mice. The effect of KKT administration was found to be different between male and female mice. In the absence of sucrose, KKT administration decreased food intake only in male mice. However, while having access to a 30% sucrose solution, both BW and food intake was decreased by KKT administration in male and female mice; but sucrose intake was decreased in female mice alone. In addition, KKT administration decreased sucrose intake in oxytocin deficient lean mice, but not in the WT lean mice. The present study demonstrates that KKT ameliorates chronic inflammation, which is strongly associated with aging and obesity, and decreases food intake in male mice as well as sucrose intake in female mice; in an oxytocin receptor dependent manner.

Elucidating the role of intrinsic adenosine A1 receptors in acute alcoholism using human-induced pluripotent stem cell-derived hepatocytes

Acute alcoholic hepatitis (AAH) from binge drinking is a serious disease. It is associated with a high mortality rate, especially among young adults. Apoptosis is known to be a primary cause of liver damage, and it can be induced by either intrinsic signaling pathways or by reactive oxygen species (ROS). Adenosine A1 receptors (ADORA1) are known to be involved in ethanol metabolism; however, underlying mechanism is not well understood. For investigating how the intrinsic ADORA1 function in ethanol metabolism in normal human hepatocytes without interference by extrinsic molecules, primary hepatocytes pose a challenge, due to unavoidable contamination by other kinds of cells in the liver. Also, they are difficult to culture stably. As a novel alternative, hepatocytes derived from human-induced pluripotent stem cells were employed because they display similar function to primary hepatocytes and they can be stably cultured. The dynamics and integrity of signal transduction mechanisms were investigated by following chronological changes in gene expression. This shed light on how and when the ADORA1 function and on causal relationships between the pathways and clinical symptoms. The findings of the present study shows that ADORA1 are most activated soon after exposure to ethanol, and transfection of small interfering RNA targeting ADORA1-messenger-RNA (ADORA1-siRNA) into the hepatocytes significantly suppresses production of actin protein and ROS. It suggests that ADORA1 in the liver contribute to apoptosis in acute alcoholism through both intrinsic pathway and ROS activity. Also, actin that is abundant in the cells could be an appropriate biomarker evaluating hepatic function status.

Does activation of oxytocinergic reward circuits postpone the decline of the aging brain?

Oxytocin supports reproduction by promoting sexual- and nursing behavior. Moreover, it stimulates reproductive organs by different avenues. Oxytocin is released to the blood from terminals of oxytocinergic neurons which project from the hypothalamus to the pituitary gland. Concomitantly, the dendrites of these neurons discharge oxytocin into neighboring areas of the hypothalamus. At this location it affects other neuroendocrine systems by autocrine and paracrine mechanisms. Moreover, sensory processing, affective functions, and reward circuits are influenced by oxytocinergic neurons that reach different sites in the brain. In addition to its facilitating impact on various aspects of reproduction, oxytocin is revealed to possess significant anti-inflammatory, restoring, and tranquilizing properties. This has been demonstrated both in many in-vivo and in-vitro studies. The oxytocin system may therefore have the capacity to alleviate detrimental physiological- and mental stress reactions. Thus, high levels of endogenous oxytocin may counteract inadequate inflammation and malfunctioning of neurons and supportive cells in the brain. A persistent low-grade inflammation increasing with age-referred to as inflammaging-may lead to a cognitive decline but may also predispose to neurodegenerative diseases such as Alzheimer's and Parkinson. Interestingly, animal studies indicate that age-related destructive processes in the body can be postponed by techniques that preserve immune- and stem cell functions in the hypothalamus. It is argued in this article that sexual activity-by its stimulating impact on the oxytocinergic activity in many regions of the brain-has the capacity to delay the onset of age-related cerebral decay. This may also postpone frailty and age-associated diseases in the body. Finally, oxytocin possesses neuroplastic properties that may be applied to expand sexual reward. The release of oxytocin may therefore be further potentiated by learning processes that involves oxytocin itself. It may therefore be profitable to raise the consciousness about the potential health benefits of sexual activity particularly among the seniors.

The seamless integration of dietary plant-derived natural flavonoids and gut microbiota may ameliorate non-alcoholic fatty liver disease: a network pharmacology analysis

We comprised metabolites of gut microbiota (GM; endogenous species) and dietary plant-derived natural flavonoids (DPDNFs; exogenous species) were known as potent effectors against non-alcoholic fatty liver disease (NAFLD) via network pharmacology (NP). The crucial targets against NAFLD were identified via GM and DPDNFs. The protein interaction (PPI), bubble chart and networks of GM or natural products- metabolites-targets-key signalling (GNMTK) pathway were described via R Package. Furthermore, the molecular docking test (MDT) to verify the affinity was performed between metabolite(s) and target(s) on a key signalling pathway. On the networks of GNMTK, Enterococcus sp. 45, Escherichia sp.12, Escherichia sp.33 and Bacterium MRG-PMF-1 as key microbiota; flavonoid-rich products as key natural resources; luteolin and myricetin as key metabolites (or dietary flavonoids); AKT Serine/Threonine Kinase 1 (AKT1), CF Transmembrane conductance Regulator (CFTR) and PhosphoInositide-3-Kinase, Regulatory subunit 1 (PIK3R1) as key targets are promising components to treat NAFLD, by suppressing cyclic Adenosine MonoPhosphate (cAMP) signalling pathway. This study shows that components (microbiota, metabolites, targets and a key signalling pathway) and DPDNFs can exert combinatorial pharmacological effects against NAFLD. Overall, the integrated pharmacological approach sheds light on the relationships between GM and DPDNFs.

Machine learning-enhanced insights into sphingolipid-based prognostication: revealing the immunological landscape and predictive proficiency for immunomotherapy and chemotherapy responses in pancreatic carcinoma

Background: With a poor prognosis for affected individuals, pancreatic adenocarcinoma (PAAD) is known as a complicated and diverse illness. Immunocytes have become essential elements in the development of PAAD. Notably, sphingolipid metabolism has a dual function in the development of tumors and the invasion of the immune system. Despite these implications, research on the predictive ability of sphingolipid variables for PAAD prognosis is strikingly lacking, and it is yet unclear how they can affect PAAD immunotherapy and targeted pharmacotherapy. Methods: The investigation process included SPG detection while also being pertinent to the prognosis for PAAD. Both the analytical capability of CIBERSORT and the prognostic capability of the pRRophetic R package were used to evaluate the immunological environments of the various HCC subtypes. In addition, CCK-8 experiments on PAAD cell lines were carried out to confirm the accuracy of drug sensitivity estimates. The results of these trials, which also evaluated cell survival and migratory patterns, confirmed the usefulness of sphingolipid-associated genes (SPGs). Results: As a result of this thorough investigation, 32 SPGs were identified, each of which had a measurable influence on the dynamics of overall survival. This collection of genes served as the conceptual framework for the development of a prognostic model, which was carefully assembled from 10 chosen genes. It should be noted that this grouping of patients into cohorts with high and low risk was a sign of different immune profiles and therapy responses. The increased abundance of SPGs was identified as a possible sign of inadequate responses to immune-based treatment approaches. The careful CCK-8 testing carried out on PAAD cell lines was of the highest importance for providing clear confirmation of drug sensitivity estimates. Conclusion: The significance of Sphingolipid metabolism in the complex web of PAAD development is brought home by this study. The novel risk model, built on the complexity of sphingolipid-associated genes, advances our understanding of PAAD and offers doctors a powerful tool for developing personalised treatment plans that are specifically suited to the unique characteristics of each patient.

Oxytocin Modulates Osteogenic Commitment in Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hASCs) are commonly harvested in minimally invasive contexts with few ethical concerns, and exhibit self-renewal, multi-lineage differentiation, and trophic signaling that make them attractive candidates for cell therapy approaches. The identification of natural molecules that can modulate their biological properties is a challenge for many researchers. Oxytocin (OXT) is a neurohypophyseal hormone that plays a pivotal role in the regulation of mammalian behavior, and is involved in health and well-being processes. Here, we investigated the role of OXT on hASC proliferation, migratory ability, senescence, and autophagy after a treatment of 72 h; OXT did not affect hASC proliferation and migratory ability. Moreover, we observed an increase in SA-β-galactosidase activity, probably related to the promotion of the autophagic process. In addition, the effects of OXT were evaluated on the hASC differentiation ability; OXT promoted osteogenic differentiation in a dose-dependent manner, as demonstrated by Alizarin red staining and gene/protein expression analysis, while it did not affect or reduce adipogenic differentiation. We also observed an increase in the expression of autophagy marker genes at the beginning of the osteogenic process in OXT-treated hASCs, leading us to hypothesize that OXT could promote osteogenesis in hASCs by modulating the autophagic process.

Peripherally restricted oxytocin is sufficient to reduce food intake and motivation, while CNS entry is required for locomotor and taste avoidance effects

OBJECTIVES

Oxytocin (OT) has a well-established role in reproductive behaviours; however, it recently emerged as an important regulator of energy homeostasis. In addition to central nervous system (CNS), OT is found in the plasma and OT receptors (OT-R) are found in peripheral tissues relevant to energy balance regulation. Here, we aim to determine whether peripheral OT-R activation is sufficient to alter energy intake and expenditure.

METHODS AND RESULTS

We first show that systemic OT potently reduced food intake and food-motivated behaviour for a high-fat reward in male and female rats. As it is plausible that peripherally, intraperitoneally (IP) injected OT crosses the blood-brain barrier (BBB) to produce some of the metabolic effects within the CNS, we screened, with a novel fluorescently labelled-OT (fAF546-OT, Roxy), for the presence of IP-injected Roxy in CNS tissue relevant to feeding control and compared such with BBB-impermeable fluorescent OT-B₁₂ (fCy5-OT-B_12; BRoxy). While Roxy did penetrate the CNS, BRoxy did not. To evaluate the behavioural and thermoregulatory impact of exclusive activation of peripheral OT-R, we generated a novel BBB-impermeable OT (OT-B₁₂ ), with equipotent binding at OT-R in vitro. In vivo, IP-injected OT and OT-B₁₂ were equipotent at food intake suppression in rats of both sexes, suggesting that peripheral OT acts on peripheral OT-R to reduce feeding behaviour. Importantly, OT induced a potent conditioned taste avoidance, indistinguishable from that induced by LiCl, when applied peripherally. Remarkably, and in contrast to OT, OT-B₁₂ did not induce any conditioned taste avoidance. Limiting the CNS entry of OT also resulted in a dose-dependent reduction of emesis in male shrews. While both OT and OT-B₁₂ proved to have similar effects on body temperature, only OT resulted in home-cage locomotor depression.

CONCLUSIONS

Together our data indicate that limiting systemic OT CNS penetrance preserves the anorexic effects of the peptide and reduces the clinically undesired side effects of OT: emesis, taste avoidance and locomotor depression. Thus, therapeutic targeting of peripheral OT-R may be a viable strategy to achieve appetite suppression with better patient outcomes.

Oxytocin Release: A Remedy for Cerebral Inflammaging

Oxytocin facilitates reproduction both by physiological and behavioral mechanisms. Oxytocinergic neurons emerging from the hypothalamus release oxytocin from the pituitary gland to the blood by axonal discharge to regulate reproductive organs. However, at the same time, oxytocin is secreted into neighboring areas of the hypothalamus from the dendrites of these neurons. Here, the peptide acts by autocrine and paracrine mechanisms to influence other neuroendocrine systems. Furthermore, oxytocinergic neurons project to many different locations in the brain, where they affect sensory processing, affective functions, and reward. Additional to its regulatory role, significant anti-inflammatory and restoring effects of oxytocin have been reported from many invivo and in-vitro studies. The pervasive property of the oxytocin system may enable it generally to dampen stress reactions both peripherally and centrally, and protect neurons and supportive cells from inadequate inflammation and malfunctioning. Animal experiments have documented the importance of preserving immune- and stem cell functions in the hypothalamus to impede age-related destructive processes of the body. Sexual reward has a profound stimulating impact on the oxytocinergic activity, and the present article therefore presents the hypothesis that frequent sexual activity and gratigying social experiance may postpone the onset of frailty and age-associated diseases by neural protection from the bursts of oxytocin. Furthermore, suggestions are given how the neuroplastic properties of oxytocin may be utilized to enhance sexual reward by learning processes in order to further reinforce the release of this peptide.

Oxytocin: An Old Hormone, A Novel Psychotropic Drug And Possible Use In Treating Psychiatric Disorders

BACKGROUND

Oxytocin is a nonapeptide synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Historically, this molecule has been involved as a key factor in the formation of infant attachment, maternal behavior and pair bonding and, more generally, in linking social signals with cognition, behaviors and reward. In the last decades, the whole oxytocin system has gained a growing interest as it was proposed to be implicated in etiopathogenesis of several neurodevelopmental and neuropsychiatric disorders.

METHODS

With the main goal of an in-depth understanding of the oxytocin role in the regulation of different functions and complex behaviors as well as its intriguing implications in different neuropsychiatric disorders, we performed a critical review of the current state of art. We carried out this work through PubMed database up to June 2021 with the search terms: 1) "oxytocin and neuropsychiatric disorders"; 2) "oxytocin and neurodevelopmental disorders"; 3) "oxytocin and anorexia"; 4) "oxytocin and eating disorders"; 5) "oxytocin and obsessive-compulsive disorder"; 6) "oxytocin and schizophrenia"; 7) "oxytocin and depression"; 8) "oxytocin and bipolar disorder"; 9) "oxytocin and psychosis"; 10) "oxytocin and anxiety"; 11) "oxytocin and personality disorder"; 12) "oxytocin and PTSD".

RESULTS

Biological, genetic, and epigenetic studies highlighted quality and quantity modifications in the expression of oxytocin peptide or in oxytocin receptor isoforms. These alterations would seem to be correlated with a higher risk of presenting several neuropsychiatric disorders belonging to different psychopathological spectra. Collaterally, the exogenous oxytocin administration has shown to ameliorate many neuropsychiatric clinical conditions.

CONCLUSION

Finally, we briefly analyzed the potential pharmacological use of oxytocin in patient with severe symptomatic SARS-CoV-2 infection due to its anti-inflammatory, anti-oxidative and immunoregulatory properties.

Small-For-Size Syndrome and Graft Inflow Modulation Techniques in Liver Transplantation

BACKGROUND

Partial liver transplantation has recently been proposed to alleviate organ shortages. However, transplantation of a small-for-size graft is associated with an increased risk of posttransplant hepatic dysfunction, commonly referred to as small-for-size syndrome (SFSS). This review describes the etiology, pathological features, clinical manifestations, and diagnostic criteria of SFSS. Moreover, we summarize strategies to improve graft function, focusing on graft inflow modulation techniques. Finally, unmet needs and future perspectives are discussed.

SUMMARY

In fact, posttransplant SFSS can be attributed to various factors such as preoperative status of the recipients, surgical techniques, donor age, and graft quality, except for graft size. With targeted improvement measures, satisfactory clinical outcomes can be achieved in recipients at increased risk of SFSS. Given the critical role of relative portal hyperperfusion in the pathogenesis of SFSS, various pharmacological and surgical treatments have been established to reduce or partially divert excessive portal inflow, and recipients will benefit from individualized therapeutic regimens after careful evaluation of benefits against potential risks. However, there remain unmet needs for further research into different aspects of SFSS to better understand the correlation between portal hemodynamics and patient outcomes.

KEY MESSAGES

Contemporary transplant surgeons should consider various donor and recipient factors and develop case-specific prevention and treatment strategies to improve graft and recipient survival rates.

Role of circulating molecules in age-related cardiovascular and metabolic disorders

Studies analyzing heterochronic parabiosis mice models showed that molecules in the blood of young mice rejuvenate aged mice. Therefore, blood-based therapies have become one of the therapeutic approaches to be considered for age-related diseases. Blood includes numerous biologically active molecules such as proteins, metabolites, hormones, miRNAs, etc. and accumulating evidence indicates some of these change their concentration with chronological aging or age-related disorders. The level of some circulating molecules showed a negative or positive correlation with all-cause mortality, cardiovascular events, or metabolic disorders. Through analyses of clinical/translation/basic research, some molecules were focused on as therapeutic targets. One approach is the supplementation of circulating anti-aging molecules. Favorable results in preclinical studies let some molecules to be tested in humans. These showed beneficial or neutral results, and some were inconsistent. Studies with rodents and humans indicate circulating molecules can be recognized as biomarkers or therapeutic targets mediating their pro-aging or anti-aging effects. Characterization of these molecules with aging, testing their biological effects, and finding mimetics of young systemic milieu continue to be an interesting and important research topic to be explored.