Prolactin selectively transported to cerebrospinal fluid from blood under hypoxic/ischemic conditions

Effects of Prolactin on Brain Neurons under Hypoxia

The levels and potential role of prolactin (PRL) in the brain under conditions of acute systemic hypoxia were examined, focusing on the accumulation of PRL in cerebrospinal fluid (CSF) and its effects on neuronal activity and injury. The amount of PRL in the brain was investigated using brain tissues from forensic autopsy cases. We counted the number of neurites that formed in human primary neurons (HNs) after the addition of PRL. Furthermore, HNs supplemented with PRL or triiodothyronine (T3) were exposed to hypoxic conditions, and the dead cells were counted. The results showed correlations between brain PRL and CSF PRL levels. Additionally, PRL accumulation in the brain was observed in cases of asphyxia. In vitro experimental findings indicated increased neurite formation in the HNs treated with PRL. Moreover, both PRL and T3 demonstrated neuroprotective effects against hypoxia-induced neuronal cell death, with PRL showing stronger neuroprotective potential than T3. These results suggest that PRL accumulates in the brain during hypoxia, potentially influences neuronal activity, and exhibits neuroprotective properties against hypoxia-induced neuronal injury.

The conceivable role of prolactin hormone in Parkinson disease: The same goal but with different ways

Parkinson disease (PD) is a progressive neurodegenerative disease (NDD) of the brain. It has been reported that prolactin (PRL) hormone plays a differential effect in PD, may be increasing, reduced or unaffected. PRL level is dysregulated in different neurodegenerative disorders including PD. Preclinical and clinical studies pointed out that PRL may has a neuroprotective against PD neuropathology . Though, the mechanistic role of PRL in PD is not fully elucidated. Therefore, the objective of the present review was to clarify the potential role and mechanistic pathway of PRL in PD neuropathology. The present review highlighted that PRL appears to have a neuroprotective effect against PD neuropathology by inhibiting the expression of pro-inflammatory signaling pathways, antioxidant effects and by inhibiting neuroinflammation. Thus, preclinical and clinical studies are warranted in this regard.

Central Nervous System Stimulants Limit Caffeine Transport at the Blood-Cerebrospinal Fluid Barrier

Caffeine, a common ingredient in energy drinks, crosses the blood-brain barrier easily, but the kinetics of caffeine across the blood-cerebrospinal fluid barrier (BCSFB) has not been investigated. Therefore, 127 autopsy cases (Group A, 30 patients, stimulant-detected group; and Group B, 97 patients, no stimulant detected group) were examined. In addition, a BCSFB model was constructed using human vascular endothelial cells and human choroid plexus epithelial cells separated by a filter, and the kinetics of caffeine in the BCSFB and the effects of 4-aminopyridine (4-AP), a neuroexcitatory agent, were studied. Caffeine concentrations in right heart blood (Rs) and cerebrospinal fluid (CSF) were compared in the autopsy cases: caffeine concentrations were higher in Rs than CSF in Group A compared to Group B. In the BCSFB model, caffeine and 4-AP were added to the upper layer, and the concentration in the lower layer of choroid plexus epithelial cells was measured. The CSF caffeine concentration was suppressed, depending on the 4-AP concentration. Histomorphological examination suggested that choroid plexus epithelial cells were involved in inhibiting the efflux of caffeine to the CSF. Thus, the simultaneous presence of stimulants and caffeine inhibits caffeine transfer across the BCSFB.

The brain as a source and a target of prolactin in mammals

Prolactin is a polypeptide hormone associated with an extensive variety of biological functions. Among the roles of prolactin in vertebrates, some were preserved throughout evolution. This is the case of its function in the brain, where prolactin receptors, are expressed in different structures of the central nervous system. In the brain, prolactin actions are principally associated with reproduction and parental behavior, and involves the modulation of adult neurogenesis, neuroprotection, and neuroplasticity, especially during pregnancy, thereby preparing the brain to parenthood. Prolactin is mainly produced by specialized cells in the anterior pituitary gland. However, during vertebrate evolution many other extrapituitary tissues do also produce prolactin, like the immune system, endothelial cells, reproductive structures and in several regions of the brain. This review summarizes the relevance of prolactin for brain function, the sources of prolactin in the central nervous system, as well as its local production and secretion. A highlight on the impact of prolactin in human neurological diseases is also provided.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

Increased Serum Prolactin and Excessive Daytime Sleepiness: An Attempt of Proof-of-Concept Study

The objectives of this study were: (1) to identify subjects with hyperprolactinemia in a clinical sample of patients; (2) to compare the neurologic, psychiatric, and sleep conditions found in patients subgrouped by excessive daytime sleepiness (EDS) and hyperprolactinemia; and (3) to identify patients with hyperprolactinemia and EDS not supported by the presence of any other neurologic, psychiatric, or sleep disorder, or substance/medication use. A retrospective chart review of inpatients was carried out in order to identify all patients in whom the prolactin (PRL) serum levels were determined. A total of 130 subjects were retrieved: 55 had increased levels of PRL, while the remaining 75 participants had normal PRL levels. EDS was reported by 32 (58.2%) participants with increased PRL and 34 (45.3%) with normal PRL. Obstructive sleep apnea or other sleep or neurologic/psychiatric conditions could explain EDS in all participants with normal PRL. Among subjects with increased PRL, eight had no other neurologic/psychiatric or sleep disorder (or drug) potentially causing EDS; these participants, at polysomnography, had time in bed, sleep period time, and total sleep time longer than those with EDS associated to another condition. These findings can be considered as a preliminary indication of a role of hyperprolactinemia in EDS and represent a basis for future controlled studies able to test this hypothesis in a reliable, objective, and methodologically more appropriate way.

Increased Serum Prolactin and Excessive Daytime Sleepiness: An Attempt of Proof-of-Concept Study

The objectives of this study were: (1) to identify subjects with hyperprolactinemia in a clinical sample of patients; (2) to compare the neurologic, psychiatric, and sleep conditions found in patients subgrouped by excessive daytime sleepiness (EDS) and hyperprolactinemia; and (3) to identify patients with hyperprolactinemia and EDS not supported by the presence of any other neurologic, psychiatric, or sleep disorder, or substance/medication use. A retrospective chart review of inpatients was carried out in order to identify all patients in whom the prolactin (PRL) serum levels were determined. A total of 130 subjects were retrieved: 55 had increased levels of PRL, while the remaining 75 participants had normal PRL levels. EDS was reported by 32 (58.2%) participants with increased PRL and 34 (45.3%) with normal PRL. Obstructive sleep apnea or other sleep or neurologic/psychiatric conditions could explain EDS in all participants with normal PRL. Among subjects with increased PRL, eight had no other neurologic/psychiatric or sleep disorder (or drug) potentially causing EDS; these participants, at polysomnography, had time in bed, sleep period time, and total sleep time longer than those with EDS associated to another condition. These findings can be considered as a preliminary indication of a role of hyperprolactinemia in EDS and represent a basis for future controlled studies able to test this hypothesis in a reliable, objective, and methodologically more appropriate way.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

The Choroid Plexus Is an Alternative Source of Prolactin to the Rat Brain

Among the more than 300 functions attributed to prolactin (PRL), this hormone has been associated with the induction of neurogenesis and differentiation of olfactory neurons especially during pregnancy, which are essential for maternal behavior. Despite the original hypothesis that PRL enters the central nervous system through a process mediated by PRL receptors (PRLR) at the choroid plexus (CP), recent data suggested that PRL transport into the brain is independent of its receptors. Based on transcriptomic data suggesting that PRL could be expressed in the CP, this work aimed to confirm PRL synthesis and secretion by CP epithelial cells (CPEC). The secretion of PRL and the distribution of PRLR in CPEC were further characterized using an in vitro model of the rat blood-cerebrospinal fluid barrier. RT-PCR analysis of PRL transcripts showed its presence in pregnant rat CP, in CPEC, and in the rat immortalized CP cell line, Z310. These observations were reinforced by immunocytochemistry staining of PRL in CPEC and Z310 cell cytoplasm. A 63-kDa immunoreactive PRL protein was detected by Western blot in CP protein extracts as well as in culture medium incubated with rat pituitary and samples of rat cerebrospinal fluid and serum. Positive immunocytochemistry staining of PRLR was present throughout the CPEC cytoplasm and in the apical and basal membrane of these cells. Altogether, our evidences suggest that CP is an alternative source of PRL to the brain, which might impact neurogenesis of olfactory neurons at the subventricular zone, given its proximity to the CP.

Morphological and biochemical changes in the pancreas associated with acute systemic hypoxia

This study aimed to investigate the changes associated with acute systemic hypoxia in the endocrine system, particularly in pancreatic tissues. The investigation was based on macroscopic, pathohistological, biochemical, and molecular biological findings in cell lines and human cadavers. The results showed that cases of death due to asphyxia more frequently showed severe subcapsular/interstitial hemorrhage versus the other causes of death. Histological examination showed that asphyxia cases were associated with severe morphological changes. Although measured insulin levels in the asphyxia were higher compared to other causes of death, no differences were noted for the glucagon and amylase levels with regard to the cause of death. Increased blood insulin levels were not associated with macro- and micromorphological changes, and did not show any association with glucose or cortisol levels. The experiment conducted under hypoxic conditions in cultured cells demonstrated that insulin mRNA expression and insulin protein levels peaked at 10 min after hypoxia exposure. However, there were no changes in either the amylase mRNA or protein levels. Corticosterone level peaked at 120 min after exposure to hypoxic conditions. Overall, acute systemic hypoxic conditions can directly affect the mechanisms involved in pancreatic insulin secretion.

The role of prolactin in central nervous system inflammation

Prolactin has been shown to favor both the activation and suppression of the microglia and astrocytes, as well as the release of inflammatory and anti-inflammatory cytokines. Prolactin has also been associated with neuronal damage in diseases such as multiple sclerosis, epilepsy, and in experimental models of these diseases. However, studies show that prolactin has neuroprotective effects in conditions of neuronal damage and inflammation and may be used as neuroprotector factor. In this review, we first discuss general information about prolactin, then we summarize recent findings of prolactin function in inflammatory and anti-inflammatory processes and factors involved in the possible dual role of prolactin are described. Finally, we review the function of prolactin specifically in the central nervous system and how it promotes a neuroprotective effect, or that of neuronal damage, particularly in experimental autoimmune encephalomyelitis and during excitotoxicity. The overall studies indicated that prolactin may be a promising molecule for the treatment of some neurological diseases.

The protective effects of prolactin on brain injury

AIMS

Brain injuries based on their causes are divided into two categories, TBI and NTBI. TBI is caused by damages such as head injury, but non-physical injury causes NTBI. Prolactin is one of the blood factors that increase during brain injury. It has been assumed to play a regenerative role in post-injury recovery.

MATERIALS AND METHODS

In this review, various valid papers from electronic sources (including Web of Science, Scopus, PubMed, SID, Google Scholar, and ISI databases) used, which in them the protective effect of prolactin on brain injury investigated.

KEY FINDINGS

Inflammation following brain injury with the production of pro-inflammatory cytokines in the affected area can even lead to excitotoxicity and cell death in the damaged area. Medical brain damage treatments are long-term, and can have several side effects. Therefore, it is better to consider medication treatments that have fewer side effects and greater efficacy. Research suggests that prolactin has numerous regenerative effects on brain injury, and prevents cell death. Prolactin is one of the hormones produced in the body; therefore it has fewer side effects and may be more effective because it increases during brain injury.

SIGNIFICANCE

Prolactin can be used peripherally and centrally, and exerts its neuro regenerative effects against further damage post-TBI and NTBI.

Prolactin may serve as a regulator to promote vocal fold wound healing

Reduced prolactin (PRL) has been shown to delay wound healing with a limited understanding of the underlying mechanisms. Here, we aim to explore the role of PRL in the repair of vocal fold (VF) injury. A microarray was used to detect the expressed levels of PRL in rat VF tissue at 1, 4, and 8 weeks after VF injury compared with normal uninjured rats. Then, a systematic bioinformatics analysis has been conducted to explore the literature-based biology network and signaling pathways involved in the repair of VF injury. The expression of PRL was significantly decreased in all VF injury groups (week 1, 4, and 8) compared with the control group (F stats = 280.34; P=4.88e-14), with no significant difference among the three VF injury groups (F stats = 1.97; P=0.18). Wounding has been shown to interfere with both PRL-promoting and inhibiting pathways that were involved in wound healing, including 11 PRL inhibitors and 6 PRL promoters. Our results reveal decreased PRL expression levels in VF injury, which is not in favor of the wound healing. The pathways identified may help in understanding the role of PRL as a treatment target for VF wound healing.

Organ Culture and Grafting of Choroid Plexus into the Ventricular CSF of Normal and Hydrocephalic HTx Rats

Choroid plexus (CP) may aid brain development and repair by secreting growth factors and neurotrophins for CSF streaming to ventricular and subventricular zones. Disrupted ventricular/subventricular zone progenitors and stem cells lead to CNS maldevelopment. Exploring models, we organ cultured the CP and transplanted fresh CP into a lateral ventricle of postnatal hydrocephalic (hyHTx) and nonhydrocephalic (nHTx) rats. After 60 days in vitro, the cultured choroid ependyma formed spherical rings with beating cilia. Cultured CP expressed endocytotic caveolin 1 and apical aquaporin 1 and absorbed horseradish peroxidase from medium. Transthyretin secretory protein was secreted by organ-cultured CP into medium throughout 60 days in vitro. Fresh CP, surviving at 1 week after lateral ventricle implantation of nHTx or hyHTx did not block CSF flow. Avascular 1-week transplants in vivo expressed caveolin 1, aquaporin 1, and transthyretin, indicating that grafted CP may secrete trophic proteins but not CSF. Our findings encourage further exploration on CP organ culture and grafting for translational strategies. Because transplanted CP, though not producing CSF, may secrete beneficial molecules for developing brain injured by hydrocephalus, we propose that upon CP removal in hydrocephalus surgery, the fractionated tissue could be transplanted back (ventricular autograft).

Thyroid-related hormones as potential markers of hypoxia/ischemia

This study aimed to investigate the usefulness of the thyroid-related hormones as markers of acute systemic hypoxia/ischemia to identify deaths caused by asphyxiation due to neck compression in human autopsy cases. The following deaths from pathophysiological conditions were examined: mechanical asphyxia and acute/subacute blunt head injury; acute/subacute non-head blunt injury; sharp instrument injury as the hemorrhagic shock condition; drowning as alveolar injury; burn; and death due to cardiac dysfunction. Blood samples were collected from the left and right cardiac chambers and iliac veins, and serum triiodothyronine (T3), thyroxine (T4), thyroglobulin (Tg), and thyroid-stimulating hormone (TSH) levels were measured using electrochemiluminescence immunoassays. Two types of thyroid cell lines were used to confirm independent thyroid function under the condition of hypoxia (3% O₂). The human thyroid carcinoma cell line (HOTHC) cell line derived from human anaplastic thyroid carcinoma and the UD-PTC (sample of the second resection papillary thyroid carcinoma) cell line derived from human thyroid papillary adenoma, which forms Tg retention follicles, were used to examine the secretion levels of T3, T4, and Tg hormones. The results showed a strong correlation between T3 and T4 levels in all blood sampling sites, while the TSH and Tg levels were not correlated with the other markers. Serum T3 and T4 levels were higher in cases of mechanical asphyxia and acute/subacute blunt head injury, representing hypoxic and ischemic conditions of the brain as compared to those in other causes of death. In the thyroid gland cell line, T4, T3, and Tg levels were stimulated after exposure to hypoxia for 10-30 min. These findings suggest that systemic advanced hypoxia/ischemia may cause a rapid and TSH-independent release of T3 and T4 thyroid hormones in autopsy cases. These findings demonstrate that increased thyroid-related hormone (T3 and T4) levels in the pathophysiological field may indicate systemic hypoxia/ischemia.

Cortisol levels after cold exposure are independent of adrenocorticotropic hormone stimulation

We previously showed that postmortem serum levels of adrenocorticotropic hormone (ACTH) were significantly higher in cases of hypothermia (cold exposure) than other causes of death. This study examined how the human hypothalamic-pituitary-adrenal axis, and specifically cortisol, responds to hypothermia. Human samples: Autopsies on 205 subjects (147 men and 58 women; age 15-98 years, median 60 years) were performed within 3 days of death. Cause of death was classified as either hypothermia (cold exposure, n = 14) or non-cold exposure (controls; n = 191). Cortisol levels were determined in blood samples obtained from the left and right cardiac chambers and common iliac veins using a chemiluminescent enzyme immunoassay. Adrenal gland tissues samples were stained for cortisol using a rabbit anti-human polyclonal antibody. Cell culture: AtT20, a mouse ACTH secretory cell line, and Y-1, a corticosterone secretory cell line derived from a mouse adrenal tumor, were analyzed in mono-and co-culture, and times courses of ACTH (in AtT20) and corticosterone (in Y-1) secretion were assessed after low temperature exposure mimicking hypothermia and compared with data for samples collected postmortem for other cases of death. However, no correlation between ACTH concentration and cortisol levels was observed in hypothermia cases. Immunohistologic analyses of samples from hypothermia cases showed that cortisol staining was localized primarily to the nucleus rather than the cytoplasm of cells in the zona fasciculata of the adrenal gland. During both mono-culture and co-culture, AtT20 cells secreted high levels of ACTH after 10-15 minutes of cold exposure, whereas corticosterone secretion by Y-1 cells increased slowly during the first 15-20 minutes of cold exposure. Similar to autopsy results, no correlation was detected between ACTH levels and corticosterone secretion, either in mono-culture or co-culture experiments. These results suggested that ACTH-independent cortisol secretion may function as a stress response during cold exposure.

Evaluation of screening for drug use using postmortem prolactin levels in serum and cerebrospinal fluid

Prolactin (PRL) levels can usually be controlled by PRL-inhibiting psychiatric drugs that include anti-dopamine agents. However, the use of dopamine (DA) antagonists may lead to hyperprolactinemia under certain clinical conditions. The aim of this study was to investigate postmortem PRL levels as potential markers of drug abuse, especially that of DA antagonists, in autopsy cases. We examined 121 autopsy cases, excluding cases involving acute hypoxia/ischemia, such as asphyxia, because PRL concentrations are reportedly increased under acute hypoxic conditions. Detected drugs were classified as either DA antagonists, stimulants, psychotropic drugs other than DA antagonists, or other non-psychotropic drugs, and many cases had no detected drugs. Samples comprised blood collected from the right heart chamber and cerebrospinal fluid (CSF). PRL protein level was measured by chemiluminescent immunoassay, and PRL gene expression in the anterior pituitary of autopsy cases was analyzed by reverse transcription-polymerase chain reaction. The PRL-positive cell ratio in the anterior pituitary gland was also measured by immunohistochemical analysis. The results indicated that PRL levels in the serum and CSF were higher in DA antagonist cases than in other cases. PRL levels in the serum and CSF also correlated with the PRL gene expression in cases with abuse of DA antagonists. However, no significant difference in the PRL-positive cell ratio in the anterior pituitary gland was evident between any of the classes of drug-detected and drug-undetected cases. These results suggest that postmortem measurements of PRL transcription levels may be useful for diagnosing cases of DA antagonist use.