Regulation of bone remodeling by vasopressin explains the bone loss in hyponatremia

Neuroendocrinology of bone

The past decade has witnessed significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone in primary and secondary osteoporosis. Recent breakthroughs have primarily emerged from identifying disease-causing mutations and phenocopying human bone disease in rodents. Notably, using genetically-modified rodent models, disrupting the reciprocal relationship with tropic pituitary hormone and effector hormones, we have learned that pituitary hormones have independent roles in skeletal physiology, beyond their effects exerted through target endocrine glands. The rise of follicle-stimulating hormone (FSH) in the late perimenopause may account, at least in part, for the rapid bone loss when estrogen is normal, while low thyroid-stimulating hormone (TSH) levels may contribute to the bone loss in thyrotoxicosis. Admittedly speculative, suppressed levels of adrenocorticotropic hormone (ACTH) may directly exacerbate bone loss in the setting of glucocorticoid-induced osteoporosis. Furthermore, beyond their established roles in reproduction and lactation, oxytocin and prolactin may affect intergenerational calcium transfer and therefore fetal skeletal mineralization, whereas elevated vasopressin levels in chronic hyponatremic states may increase the risk of bone loss.. Here, we discuss the interaction of each pituitary hormone in relation to its role in bone physiology and pathophysiology.

Association of serum sodium levels with fractures and mortality in patients undergoing maintenance hemodialysis

BACKGROUND

Hyponatremia is implicated in pathological bone resorption and has been identified as a risk factor for bone fracture in the general population. However, there are limited data on the association between serum sodium levels and fracture risk in patients undergoing hemodialysis (HD).

METHODS

We analyzed a historical cohort of 2220 maintenance HD patients to examine the association between serum sodium levels and the risk of fracture and mortality. We also examined the association between serum sodium levels and osteoporosis, based on metacarpal bone mineral density, in a subcohort of 455 patients with available data. In addition, we examined the association between serum sodium levels and bone turnover markers in a separate cross-sectional cohort of 654 maintenance HD patients.

RESULTS

During a median follow-up of 5.4 years, 712 patients died, 113 experienced clinical fractures, and 64 experienced asymptomatic vertebral fractures. Lower serum sodium levels were associated with an increased risk of mortality (HR 1.06 per 1 mEq/L decrease; 95% CI 1.03-1.09) but not with the risk of clinical fracture (HR 1.04 per 1 mEq/L decrease; 95% CI 0.97-1.11). A similar lack of association was observed for asymptomatic vertebral fracture and any fracture. Serum sodium levels were also not associated with osteoporosis in a subcohort with available data (n = 455) or with bone alkaline phosphatase or tartrate-resistant acid phosphatase-5b in a separate cross-sectional cohort.

CONCLUSION

Serum sodium levels were associated with mortality but not with fracture risk, osteoporosis, or bone turnover markers in maintenance HD patients.

Hypopituitarism and bone disease: pathophysiology, diagnosis and treatment outcomes

Hypopituitarism is a rare but significant endocrine disorder characterized by the inadequate secretion of one or more pituitary hormones. The intricate relationship between hypopituitarism and bone health is a topic of growing interest in the medical community. In this review the authors explore associations between hypopituitarism and bone health, with specific examination of the impact of growth hormone deficiency, central hypogonadism, central hypocortisolism, and central hypothyroidism. Pathogenesis, diagnosis, and treatment options as well as challenges posed by osteopenia, osteoporosis, and fractures in hypopituitarism are discussed.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Extracellular sodium regulates fibroblast growth factor 23 (FGF23) formation

The bone-derived hormone fibroblast growth factor-23 (FGF23) has recently received much attention due to its association with chronic kidney disease and cardiovascular disease progression. Extracellular sodium concentration ([Na+]) plays a significant role in bone metabolism. Hyponatremia (lower serum [Na+]) has recently been shown to be independently associated with FGF23 levels in patients with chronic systolic heart failure. However, nothing is known about the direct impact of [Na+] on FGF23 production. Here, we show that an elevated [Na+] (+20 mM) suppressed FGF23 formation, whereas low [Na+] (-20 mM) increased FGF23 synthesis in the osteoblast-like cell lines UMR-106 and MC3T3-E1. Similar bidirectional changes in FGF23 abundance were observed when osmolality was altered by mannitol but not by urea, suggesting a role of tonicity in FGF23 formation. Moreover, these changes in FGF23 were inversely proportional to the expression of NFAT5 (nuclear factor of activated T cells-5), a transcription factor responsible for tonicity-mediated cellular adaptations. Furthermore, arginine vasopressin, which is often responsible for hyponatremia, did not affect FGF23 production. Next, we performed a comprehensive and unbiased RNA-seq analysis of UMR-106 cells exposed to low versus high [Na+], which revealed several novel genes involved in cellular adaptation to altered tonicity. Additional analysis of cells with Crisp-Cas9-mediated NFAT5 deletion indicated that NFAT5 controls numerous genes associated with FGF23 synthesis, thereby confirming its role in [Na+]-mediated FGF23 regulation. In line with these in vitro observations, we found that hyponatremia patients have higher FGF23 levels. Our results suggest that [Na+] is a critical regulator of FGF23 synthesis.

Pituitary crosstalk with bone, adipose tissue and brain

Traditional textbook physiology has ascribed unitary functions to hormones from the anterior and posterior pituitary gland, mainly in the regulation of effector hormone secretion from endocrine organs. However, the evolutionary biology of pituitary hormones and their receptors provides evidence for a broad range of functions in vertebrate physiology. Over the past decade, we and others have discovered that thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotropic hormone, prolactin, oxytocin and arginine vasopressin act directly on somatic organs, including bone, adipose tissue and liver. New evidence also indicates that pituitary hormone receptors are expressed in brain regions, nuclei and subnuclei. These studies have prompted us to attribute the pathophysiology of certain human diseases, including osteoporosis, obesity and neurodegeneration, at least in part, to changes in pituitary hormone levels. This new information has identified actionable therapeutic targets for drug discovery.

Epidemiology and predictors of hyponatremia in a contemporary cohort of patients with malignancy: a retrospective cohort study

Background

Hyponatremia is associated with worse outcomes among patients with malignancy. However, contemporary cohort data on epidemiology and risk factors are lacking.

Methods

In this single-centre, retrospective cohort study, patients who received intravenous antineoplastic agents from 2018 to 2020 at Nagoya City University Hospital were enrolled. Associations of demographics, antineoplastic agents, types of malignancy and concomitant medications with hyponatremia, defined as serum sodium concentration ≤130 mmol/l, were analysed by mixed-effects logistic regression and the machine learning-based LightGBM model artificial intelligence technology.

Results

Among 2644 patients, 657 (24.8%) developed at least one episode of hyponatremia. Approximately 80% of hyponatremia was due to sodium wasting from the kidneys. Variables associated with hyponatremia both by mixed-effects logistic regression and the LightGBM model were older age, hypoalbuminemia and higher estimated glomerular filtration rate. Among antineoplastic agents, cisplatin {odds ratio [OR] 1.52 [95% confidence interval (CI) 1.18-1.96]}, pembrolizumab [OR 1.42 (95% CI 1.02-1.97)] and bortezomib [OR 3.04 (95% CI 1.96-4.71)] were associated with hyponatremia and these variables also had a positive impact on predicted hyponatremia in the LightGBM model.

Conclusions

Hyponatremia was common among patients with malignancy. In addition to older age and poor nutritional status, novel antineoplastic agents, including immune checkpoint inhibitors and bortezomib, should be recognized as risk factors for hyponatremia.

An Increase in Plasma Sodium Levels Is Associated With an Increase in Osteoblast Function in Chronic SIAD

CONTEXT

Hyponatremia is associated with increased risk for osteoporosis. Preclinical studies in untreated hyponatremia suggest osteoclast upregulation, whereas a clinical study showed improved osteoblast function after hyponatremia normalization in hospitalized patients with syndrome of inappropriate antidiuresis (SIAD).

OBJECTIVE

This work aimed to investigate the effect of an increase in sodium on bone turnover, that is, the ratio of the osteoblast marker procollagen type 1 N-terminal propeptide (P1NP) to the osteoclast marker cross-linked C-terminal telopeptide of type 1 collagen (CTX), in outpatients with chronic SIAD.

METHODS

A predefined secondary analysis was conducted of the 2-month double-blind, crossover, placebo-controlled SANDx Trial (NCT03202667) performed from December 2017 to August 2021. Participants included 11 outpatients with chronic SIAD: 6 women, median age 73 years, who received a 4-week treatment with 25-mg empagliflozin or placebo. Main outcome measures included the relationship between the change in bone formation index (BFI), defined as P1NP/CTX, and the change in plasma sodium levels.

RESULTS

Changes in sodium were positively correlated with changes in BFI and P1NP (BFI: ρ=.55; P < .001; P1NP: ρ=.45; P = .004) but not with CTX (P = .184) and osteocalcin (P = .149). A sodium increase of 1 mmol/l was associated with an increase of 5.21 in BFI (95% CI, 1.41-9.00; P = .013) and with an increase of 1.48 µg/l in P1NP (95% CI, .26-2.62; P = .03). The effect of sodium change on bone markers was independent of the study medication empagliflozin.

CONCLUSION

An increase in plasma sodium levels in outpatients with chronic hyponatremia due to SIAD, even when mild, was associated with an increase in bone formation index (P1NP/CTX) triggered by an increase in P1NP, a surrogate marker of osteoblast function.

Association of hyponatremia with bone mineral density and fractures: a narrative review

Recent studies suggest a possible association of hyponatremia with osteoporosis, falls and bone fractures. The objectives of this narrative review were to further explore this association and the related pathophysiological mechanisms and to suggest a practical approach to patients with osteoporosis or chronic hyponatremia in clinical practice. We conducted an extensive PubMed search until October 2022 with the combination of the following keywords: 'hyponatremia' or 'sodium' or 'SIADH' and 'fractures' or 'bone' or 'osteoporosis', as MeSH Terms. Review of numerous observational studies confirms a significant independent association of, even mild, hyponatremia with two- to three-fold increase in the occurrence of bone fractures. Hyponatremia is a risk factor for osteoporosis with a predilection to affect the hip, while the magnitude of association depends on the severity and chronicity of hyponatremia. Chronic hyponatremia also increases the risk for falls by inducing gait instability and neurocognitive deficits. Besides the detrimental impact of hyponatremia on bone mineral density and risk of falls, it also induces changes in bone quality. Emerging evidence suggests that acute hyponatremia shifts bone turnover dynamics towards less bone formation, while hyponatremia correction increases bone formation. The key unanswered question whether treatment of hyponatremia could improve osteoporosis and lower fracture risk highlights the need for prospective studies, evaluating the impact of sodium normalization on bone metabolism and occurrence of fractures. Recommendations for clinical approach should include measurement of serum sodium in all individuals with fracture or osteoporosis. Also, hyponatremia, as an independent risk factor for fracture, should be taken into consideration when estimating the likelihood for future fragility fracture and in clinical decision-making about pharmacological therapy of osteoporosis. Until it is proven that normalization of sodium can lower fracture occurrence, correcting hyponatremia cannot be universally recommended on this basis, but should be decided on a case-by-case basis.

Syndrome of Inappropriate Antidiuresis: From Pathophysiology to Management

Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of hypotonic hyponatremia, mediated by nonosmotic release of arginine vasopressin (AVP, previously known as antidiuretic hormone), which acts on the renal V2 receptors to promote water retention. There are a variety of underlying causes of SIAD, including malignancy, pulmonary pathology, and central nervous system pathology. In clinical practice, the etiology of hyponatremia is frequently multifactorial and the management approach may need to evolve during treatment of a single episode. It is therefore important to regularly reassess clinical status and biochemistry, while remaining alert to potential underlying etiological factors that may become more apparent during the course of treatment. In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines, but there is considerable controversy regarding second-line therapy in instances where FR is unsuccessful, which occurs in around half of cases. We review the epidemiology, pathophysiology, and differential diagnosis of SIAD, and summarize recent evidence for therapeutic options beyond FR, with a focus on tolvaptan, urea, and sodium-glucose cotransporter 2 inhibitors.

Hyponatremia and aging-related diseases: key player or innocent bystander? A systematic review

BACKGROUND

Hyponatremia is frequent in older age; whether it is a key player, a surrogate marker, or an innocent bystander in age-related diseases is still unclear.

OBJECTIVE

To understand the role of hyponatremia in falls, osteoporosis, fractures, and cognitive impairment in old patients.

METHOD

Eligibility criteria for study inclusions were: written in English, peer-reviewed observational and intervention studies, clinical trial, prospective and retrospective controlled cohort studies, and case-controlled studies without limitations regarding the date of publication.

INFORMATION SOURCES

Protocol available on the International Prospective Register of Systematic Reviews (PROSPERO, CRD42021218389). MEDLINE, Embase, and PsycINFO were searched. Final search done on August 8, 2021. Risk-of-bias assessment: Risk-of-Bias Assessment tool for Non-randomized Studies (RoBANS) and the Bradford Hill's criteria for causality.

RESULTS

Includes studies: One-hundred thirty-five articles retained for the revision. Synthesis of results - Falls: Eleven studies were included. Strong association between hyponatremia and falls in all the studies was found. Osteoporosis and fractures: nineteen articles were included. The association between hyponatremia and osteoporosis is unclear. Cognitive impairment: Five articles were included. No association between hyponatremia and cognitive impairment was found.

DISCUSSION

Interpretation: Falls, osteoporosis, and fractures are multifactorial. Hyponatremia is not temporally related with the outcomes; we suggest that hyponatremia may be regarded as a marker of unhealthy aging and a confounder instead of a causal factor or an innocent bystander for falls and fractures. Concerning cognitive impairment, there are no evidence supporting a real role of hyponatremia to be regarded as an innocent bystander in neurodegeneration.

Natural Peptide Toxins as an Option for Renewed Treatment of Type 2 Vasopressin Receptor-Related Diseases

The type 2 vasopressin receptor (V2R) is expressed in the kidneys, and it is the keystone of water homeostasis. Under the control of the antidiuretic hormone vasopressin, the V2R ensures vital functions, and any disturbance has dramatic consequences. Despite decades of research to develop drugs capable of activating or blocking V2R function to meet real medical needs, only one agonist and one antagonist are virtually used today. These two drugs cover only a small portion of patients' needs, leaving millions of patients without treatment. Natural peptide toxins known to act selectively and at low doses on their receptor target could offer new therapeutic options.

Arginine vasopressin hormone receptor antagonists in experimental autoimmune encephalomyelitis rodent models: A new approach for human multiple sclerosis treatment

Multiple sclerosis (MS) is a chronic demyelinating and neurodegenerative disease that affects the central nervous system. MS is a heterogeneous disorder of multiple factors that are mainly associated with the immune system including the breakdown of the blood-brain and spinal cord barriers induced by T cells, B cells, antigen presenting cells, and immune components such as chemokines and pro-inflammatory cytokines. The incidence of MS has been increasing worldwide recently, and most therapies related to its treatment are associated with the development of several secondary effects, such as headaches, hepatotoxicity, leukopenia, and some types of cancer; therefore, the search for an effective treatment is ongoing. The use of animal models of MS continues to be an important option for extrapolating new treatments. Experimental autoimmune encephalomyelitis (EAE) replicates the several pathophysiological features of MS development and clinical signs, to obtain a potential treatment for MS in humans and improve the disease prognosis. Currently, the exploration of neuro-immune-endocrine interactions represents a highlight of interest in the treatment of immune disorders. The arginine vasopressin hormone (AVP) is involved in the increase in blood−brain barrier permeability, inducing the development and aggressiveness of the disease in the EAE model, whereas its deficiency improves the clinical signs of the disease. Therefore, this present review discussed on the use of conivaptan a blocker of AVP receptors type 1a and type 2 (V1a and V2 AVP) in the modulation of immune response without completely depleting its activity, minimizing the adverse effects associated with the conventional therapies becoming a potential therapeutic target in the treatment of patients with multiple sclerosis.

Morbidity Associated with Chronic Hyponatremia

This article will discuss the consequences of chronic hyponatremia. In conditions such as cancer, heart failure, liver cirrhosis, or chronic kidney disease, the presence and magnitude of hypotonic hyponatremia are considered to reflect the severity of the underlying disease and are associated with increased morbidity as well as mortality. Hyponatremia can be acute (<48 h) or chronic (>2-3 days). Chronic hyponatremia is associated with attention deficit, dizziness, tiredness, gait disturbance, falls, sarcopenia, bone fractures, osteoporosis, hypercalciuria (in the syndrome of inappropriate antidiuresis-SIADH), and kidney stones. In vitro studies have shown that cells grown in a low concentration of extracellular sodium have a greater proliferation rate and motility. Patients with chronic hyponatremia are more likely to develop cancer. We will not review the clinical consequences of respiratory arrest and osmotic demyelination syndrome (ODS) of the too-late or excessive treatment of hyponatremia.

Bone circuitry and interorgan skeletal crosstalk

The past decade has seen significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone integrity in disease. Recent breakthroughs have arisen mainly from identifying disease-causing mutations and modeling human bone disease in rodents, in essence, highlighting the integrative nature of skeletal physiology. It has become increasingly clear that bone cells, osteoblasts, osteoclasts, and osteocytes, communicate and regulate the fate of each other through RANK/RANKL/OPG, liver X receptors (LXRs), EphirinB2-EphB4 signaling, sphingolipids, and other membrane-associated proteins, such as semaphorins. Mounting evidence also showed that critical developmental pathways, namely, bone morphogenetic protein (BMP), NOTCH, and WNT, interact each other and play an important role in postnatal bone remodeling. The skeleton communicates not only with closely situated organs, such as bone marrow, muscle, and fat, but also with remote vital organs, such as the kidney, liver, and brain. The metabolic effect of bone-derived osteocalcin highlights a possible role of skeleton in energy homeostasis. Furthermore, studies using genetically modified rodent models disrupting the reciprocal relationship with tropic pituitary hormone and effector hormone have unraveled an independent role of pituitary hormone in skeletal remodeling beyond the role of regulating target endocrine glands. The cytokine-mediated skeletal actions and the evidence of local production of certain pituitary hormones by bone marrow-derived cells displays a unique endocrine-immune-skeletal connection. Here, we discuss recently elucidated mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, crosstalk between bone and vital organs, as well as opportunities for treating diseases of the skeleton.

The Urine Calcium/Creatinine Ratio and Uricemia during Hyponatremia of Different Origins: Clinical Implications

Background: Chronic hyponatremia is known to be associated with osteoporosis. It has been shown that chronic hyponatremia increases bone resorption in an attempt to release body stores of exchangeable sodium by different mechanisms. We wanted to know the calciuria of patients with hyponatremia of different origins. Material and Methods: We made a retrospective study of 114 consecutive patients with asymptomatic hyponatremia of different origins with the usual serum and urine chemistry. Result: In hyponatremia due to SIADH, we had a high urine calcium/creatinine ratio of 0.23 ± 0.096 while in patients with salt depletion the UCa/UCr ratio was low (0.056 ± 0.038), in patients with hyponatremia secondary to thiazide intake the value was also low (0.075 ± 0.047) as in hypervolemic patients (0.034 ± 0.01). In hyponatremia due to polydipsia, the value was high (0.205 ± 0.10). Correction of hyponatremia in the euvolemic patients was associated with a significant decrease in the UCa/UCr ratio. In patients with hyponatremia secondary to thiazide intake, we noted that in the patients with low uric acid levels (<4 mg/dL, suggesting euvolemia) we also observed a low UCa/UCr (<0.10). In nine patients with chronic SIADH (SNa 125.1 ± 3.6 mEq/L), the 24 h urine calcium excretion was 275 ± 112 mg and decreased to 122 ± 77 mg (p < 0.01) after at least 2 weeks of treatment. Conclusions: Patients with chronic hyponatremia due to SIADH usually have a high UCa/UCr ratio (>0.15). This is also observed in hyponatremia secondary to polydipsia. Patients with thiazide-induced hyponatremia usually have low UCa/UCr levels and this is the case even among those with a biochemistry similar to that in SIADH (uric acid < 4 mg/dL).

Association between Serum Oxytocin, Bone Mineral Density and Body Composition in Chinese Adult Females

Background and Objectives: Oxytocin (OT) is a neuropeptide hormone which is known for its classical effects in pregnancy and lactation. Recently, growing evidence demonstrated a close relation between OT and bone. The present study aimed to explore the relationship between OT, bone and osteoporosis risk in Chinese adult females. Materials and Methods: in total, 149 adult females were enrolled. The serum OT levels were measured using ELISA kits. Bone mineral density (BMD) and body composition were measured by dual-energy X-ray absorptiometry (DXA). The study subjects were divided into two groups according to their menopause status and then divided into tertiles based on their serum OT level. Results: Serum OT, serum estradiol and BMD at three skeletal sites were significantly higher in the premenopausal group than in the postmenopausal group (p < 0.001, p = 0.008 and p < 0.001, respectively). In the tertile analysis, relative to tertile 1, significant associations were found for tertile 3 for OT levels and higher BMD in the femoral neck and total hip, in both pre- and postmenopausal groups. Using logistic regression analysis, tertile 3 appeared less likely to have low-BMD osteoporosis than tertile 1 (OR = 0.257, 95% CI = 0.073, 0.910). In multivariate stepwise regression analysis, OT and total lean mass were two positive determinants of BMD in the femoral neck and total hip in the premenopausal group (adjusted R2 for the model = 0.232 and 0.199, respectively; both p < 0.001). Conclusion: Our study demonstrated positive associations between serum OT levels and BMD in a Chinese (non-Caucasian) population. OT appeared to be more strongly associated with hip BMD in premenopausal females. These results may suggest a protective role and potential therapeutic use of OT in osteoporosis, especially for premenopausal women.

Independent Skeletal Actions of Pituitary Hormones

Over the past years, pituitary hormones and their receptors have been shown to have non-traditional actions that allow them to bypass the hypothalamus-pituitary-effector glands axis. Bone cells-osteoblasts and osteoclasts-express receptors for growth hormone, follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin, and vasopressin. Independent skeletal actions of pituitary hormones on bone have been studied using genetically modified mice with haploinsufficiency and by activating or inactivating the receptors pharmacologically, without altering systemic effector hormone levels. On another front, the discovery of a TSH variant (TSH-βv) in immune cells in the bone marrow and skeletal action of FSHβ through tumor necrosis factor α provides new insights underscoring the integrated physiology of bone-immune-endocrine axis. Here we discuss the interaction of each pituitary hormone with bone and the potential it holds in understanding bone physiology and as a therapeutic target.

Interactions between central nervous system and peripheral metabolic organs

According to Descartes, minds and bodies are distinct kinds of "substance", and they cannot have causal interactions. However, in neuroscience, the two-way interaction between the brain and peripheral organs is an emerging field of research. Several lines of evidence highlight the importance of such interactions. For example, the peripheral metabolic systems are overwhelmingly regulated by the mind (brain), and anxiety and depression greatly affect the functioning of these systems. Also, psychological stress can cause a variety of physical symptoms, such as bone loss. Moreover, the gut microbiota appears to play a key role in neuropsychiatric and neurodegenerative diseases. Mechanistically, as the command center of the body, the brain can regulate our internal organs and glands through the autonomic nervous system and neuroendocrine system, although it is generally considered to be outside the realm of voluntary control. The autonomic nervous system itself can be further subdivided into the sympathetic and parasympathetic systems. The sympathetic division functions a bit like the accelerator pedal on a car, and the parasympathetic division functions as the brake. The high center of the autonomic nervous system and the neuroendocrine system is the hypothalamus, which contains several subnuclei that control several basic physiological functions, such as the digestion of food and regulation of body temperature. Also, numerous peripheral signals contribute to the regulation of brain functions. Gastrointestinal (GI) hormones, insulin, and leptin are transported into the brain, where they regulate innate behaviors such as feeding, and they are also involved in emotional and cognitive functions. The brain can recognize peripheral inflammatory cytokines and induce a transient syndrome called sick behavior (SB), characterized by fatigue, reduced physical and social activity, and cognitive impairment. In summary, knowledge of the biological basis of the interactions between the central nervous system and peripheral organs will promote the full understanding of how our body works and the rational treatment of disorders. Thus, we summarize current development in our understanding of five types of central-peripheral interactions, including neural control of adipose tissues, energy expenditure, bone metabolism, feeding involving the brain-gut axis and gut microbiota. These interactions are essential for maintaining vital bodily functions, which result in homeostasis, i.e., a natural balance in the body's systems.

Brain atlas for glycoprotein hormone receptors at single-transcript level

There is increasing evidence that anterior pituitary hormones, traditionally thought to have unitary functions in regulating single endocrine targets, act on multiple somatic tissues, such as bone, fat, and liver. There is also emerging evidence for anterior pituitary hormone action on brain receptors in mediating central neural and peripheral somatic functions. Here, we have created the most comprehensive neuroanatomical atlas on the expression of TSHR, LHCGR, and FSHR. We have used RNAscope, a technology that allows the detection of mRNA at single-transcript level, together with protein level validation, to document Tshr expression in 173 and Fshr expression in 353 brain regions, nuclei and subnuclei identified using the Atlas for the Mouse Brain in Stereotaxic Coordinates. We also identified Lhcgr transcripts in 401 brain regions, nuclei and subnuclei. Complementarily, we used ViewRNA, another single-transcript detection technology, to establish the expression of FSHR in human brain samples, where transcripts were co-localized in MALAT1-positive neurons. In addition, we show high expression for all three receptors in the ventricular region-with yet unknown functions. Intriguingly, Tshr and Fshr expression in the ependymal layer of the third ventricle was similar to that of the thyroid follicular cells and testicular Sertoli cells, respectively. In contrast, Fshr was localized to NeuN-positive neurons in the granular layer of the dentate gyrus in murine and human brain-both are Alzheimer's disease-vulnerable regions. Our atlas thus provides a vital resource for scientists to explore the link between the stimulation or inactivation of brain glycoprotein hormone receptors on somatic function. New actionable pathways for human disease may be unmasked through further studies.

Hyponatremia elicits gene expression changes driving osteoclast differentiation and functions

Growing evidence indicates that chronic hyponatremia represents a significant risk for bone loss, osteoporosis, and fractures in our aging population. Our prior studies on a rat model of the syndrome of inappropriate antidiuretic hormone secretion indicated that chronic hyponatremia causes osteoporosis by increasing osteoclastic bone resorption, thereby liberating stored sodium from bone. Moreover, studies in RAW264.7 pre-osteoclastic cells showed increased osteoclast formation and resorptive activity in response to low extracellular fluid sodium ion concentration (low [Na+]). These studies implicated a direct stimulatory effect of low [Na+] rather than the low osmolality on cultured osteoclastic cells. In the present cellular studies, we explored gene expression changes triggered by low [Na+] using RNA sequencing and gene ontology analysis. Results were confirmed by mouse whole genome microarray, and quantitative RT-PCR. Findings confirmed gene expression changes supporting osteoclast growth and differentiation through stimulation of receptor activator of nuclear factor kappa-B ligand (RANKL), and PI3K/Akt pathways, and revealed additional pathways. New findings on low [Na+]-induced upregulation of lysosomal genes, mitochondrial energy production, MMP-9 expression, and osteoclast motility have supported the significance of osteoclast transcriptomic responses. Functional assays demonstrated that RANL and low [Na+] independently enhance osteoclast functions. Understanding the molecular mechanisms of hyponatremia-induced osteoporosis provides the basis for future studies identifying sodium-sensing mechanisms in osteoclasts, and potentially other bone cells, and developing strategies for treatment of bone fragility in the vulnerable aging population most affected by both chronic hyponatremia and osteoporosis. ISSUE SECTIONS: Signaling Pathways; Parathyroid, Bone, and Mineral Metabolism.

Exploiting Dependence of Castration-Resistant Prostate Cancer on the Arginine Vasopressin Signaling Axis by Repurposing Vaptans

Men with advanced prostate cancer are treated by androgen deprivation therapy but the disease recurs as incurable castration-resistant prostate cancer (CRPC), requiring new treatment options. We previously demonstrated that the G protein-coupled receptor (GPCR) arginine vasopressin receptor type1A (AVPR1A) is expressed in CRPC and promotes castration-resistant growth in vitro and in vivo. AVPR1A is part of a family of GPCR's including arginine vasopressin receptor type 2 (AVPR2). Interrogation of prostate cancer patient sample data revealed that coexpression of AVPR1A and AVPR2 is highly correlated with disease progression. Stimulation of AVPR2 with a selective agonist desmopressin promoted CRPC cell proliferation through cAMP/protein kinase A signaling, consistent with AVPR2 coupling to the G protein subunit alpha s. In contrast, blocking AVPR2 with a selective FDA-approved antagonist, tolvaptan, reduced cell growth. In CRPC xenografts, antagonizing AVPR2, AVPR1A, or both significantly reduced CRPC tumor growth as well as decreased on-target markers of tumor burden. Combinatorial use of AVPR1A and AVPR2 antagonists promoted apoptosis synergistically in CRPC cells. Furthermore, we found that castration-resistant cells produced AVP, the endogenous ligand for arginine vasopressin receptors, and knockout of AVP in CRPC cells significantly reduced proliferation suggesting possible AVP autocrine signaling. These data indicate that the AVP/arginine vasopressin receptor signaling axis represents a promising and clinically actionable target for CRPC.

IMPLICATIONS

The arginine vasopressin signaling axis in CRPC provides a therapeutic window that is targetable through repurposing safe and effective AVPR1A and AVPR2 antagonists.

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

The association between normal serum sodium levels and bone turnover in patients with type 2 diabetes

BACKGROUND

Sodium is a critically important component of bones, and hyponatremia has firmly been established as a risk factor associated with the incidence of fragility fractures. However, researches have also revealed that lower serum sodium are linked to reductions in muscle mass and a higher risk of cardiovascular disease even when these levels are within the normal range. Accordingly, this study was developed to examine the relationships between normal serum sodium concentrations and bone turnover in patients with type 2 diabetes (T2D).

METHODS

Patients with T2D were enrolled in the present study from January 2021 to April 2022. All patients underwent analyses of serum sodium levels, oral glucose tolerance testing (OGTT), bone turnover markers (BTMs), and dual-energy X-ray absorptiometry (DXA) scanning. BTMs included bone formation markers osteocalcin (OC) and N-terminal propeptide of type-I procollagen (PINP), and bone resorption marker C-terminal telopeptide (CTx). Patients were stratified into three subgroups based on the tertiles of their serum sodium concentrations.

RESULTS

In total, 372 patients with T2D and sodium levels in the normal range were enrolled in this study. Serum OC and PINP levels were increased from subgroup with the low sodium tertile to that with the high sodium tertile (p for trend < 0.05), whereas CTx level was comparable among the subgroups. A positive correlation was detected between serum sodium levels and both lnOC (r = 0.210, p < 0.001) and lnPINP (r = 0.196, p < 0.001), with these relationships remaining significant even following adjustment for age, sex, body mass index (BMI), and HbA1c. Only after adjusting for these four factors a positive correlation was detected between serum sodium levels and CTx levels (r = 0.108, p < 0.05). Linear regression analyses revealed that following adjustment for potential covariates, serum sodium level was and positively significantly associated with lnOC level (β = 0.134, t = 2.281, p < 0.05) and PINP level (β = 0.179, t = 3.023, p < 0.01).

CONCLUSION

These results highlight a significant association between low-normal serum sodium levels and low bone turnover.

Exercise-induced hypercalcemia and vasopressin-mediated bone resorption

Our human observational study showed that elevated arginine vasopressin levels by heavy exercise, not catecholamines, were associated with elevated serum tartrate-resistant acid phosphatase 5b (TRACP-5b). The increase in serum calcium was positively associated with percent changes of TRACP-5b, implying the involvement of bone resorption in the pathogenesis of exercise-induced hypercalcemia.

INTRODUCTION

It remains unclear whether enhanced bone resorption explains exercise-induced hypercalcemia. An experimental study demonstrated that arginine vasopressin (AVP) stimulated osteoclast activity.

METHODS

We conducted a prospective observational study, enrolling 65 trained healthy male officers of the Japan Self-Defense Forces (34 and 31 in waves 1 and 2, respectively). Before and after a 5-h heavy exercise, we collected laboratory data including bone markers, symptoms, and ionized calcium (iCa; wave 2 only). As blood calcium levels change after exercise, we estimated calcium (corrected calcium) levels immediately after the exercise using the correlation between blood calcium and time from the end of exercise in another cohort.

RESULTS

Body weight decreased by 6.9% after the exercise. Corrected post-exercise serum total calcium (tCa) and iCa levels were significantly higher than pre-exercise levels, and 18% of participants showed hypercalcemia defined as corrected tCa >10.4 mg/dL or iCa >1.30 mmol/L. Serum tartrate-resistant acid phosphatase 5b (TRACP-5b), plasma three fractions of catecholamines, and AVP elevated significantly (median 14.3 pg/mL), while procollagen type 1 N-terminal propeptide and whole parathyroid hormone showed significant decreases. Corrected tCa increase showed a non-linear positive association with percent changes of TRACP-5b (%ΔTRACP-5b) even after adjustment for confounders. In addition, %ΔTRACP-5b was not associated with catecholamines, but with post-exercise AVP levels after adjustment for pre-exercise TRACP-5b. Symptoms of nausea or vomiting (observed in 20%) were positively associated with corrected post-exercise iCa after adjustment for post-exercise blood pH.

CONCLUSION

AVP elevation may explain bone resorption and the following hypercalcemia in the setting of heavy exercise.

Thyrotropin, Hyperthyroidism, and Bone Mass

Thyrotropin (TSH), traditionally seen as a pituitary hormone that regulates thyroid glands, has additional roles in physiology including skeletal remodeling. Population-based observations in people with euthyroidism or subclinical hyperthyroidism indicated a negative association between bone mass and low-normal TSH. The findings of correlative studies were supported by small intervention trials using recombinant human TSH (rhTSH) injection, and genetic and case-based evidence. Genetically modified mouse models, which disrupt the reciprocal relationship between TSH and thyroid hormone, have allowed us to examine an independent role of TSH. Since the first description of osteoporotic phenotype in haploinsufficient Tshr +/- mice with normal thyroid hormone levels, the antiosteoclastic effect of TSH has been documented in both in vitro and in vivo studies. Further studies showed that increased osteoclastogenesis in Tshr-deficient mice was mediated by tumor necrosis factor α. Low TSH not only increased osteoclastogenesis, but also decreased osteoblastogenesis in bone marrow-derived primary osteoblast cultures. However, later in vivo studies using small and intermittent doses of rhTSH showed a proanabolic effect, which suggests that its action might be dose and frequency dependent. TSHR was shown to interact with insulin-like growth factor 1 receptor, and vascular endothelial growth factor and Wnt pathway might play a role in TSH's effect on osteoblasts. The expression and direct skeletal effect of a biologically active splice variant of the TSHβ subunit (TSHβv) in bone marrow-derived macrophage and other immune cells suggest a local skeletal effect of TSHR. Further studies of how locally secreted TSHβv and systemic TSHβ interact in skeletal remodeling through the endocrine, immune, and skeletal systems will help us better understand the hyperthyroidism-induced bone disease.

Relationship between Oxytocin and Osteoarthritis: Hope or Despair?

Oxytocin (OT) is involved in breastfeeding and childbirth and appears to play a role in regulating the bone matrix. OT is synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and is released in response to numerous stimuli. It also appears to be produced by osteoblasts in the bone marrow, acting as a paracrine–autocrine regulator of bone formation. Osteoarthritis (OA) is a disease of the whole joint. Different tissues involved in OA express OT receptors (OTRs), such as chondrocytes and osteoblasts. This hormone, which levels are reduced in patients with OA, appears to have a stimulatory effect on chondrogenesis. OT involvement in bone biology could occur at both the osteoblast and chondrocyte levels. The relationships between metabolic syndrome, body weight, and OA are well documented, and the possible effects of OT on different parameters of metabolic syndrome, such as diabetes and body weight, are important. In addition, the effects of OT on adipokines and inflammation are also discussed, especially since recent data have shown that low-grade inflammation is also associated with OA. Furthermore, OT also appears to mediate endogenous analgesia in animal and human studies. These observations provide support for the possible interest of OT in OA and its potential therapeutic treatment.

Bone-to-Brain: A Round Trip in the Adaptation to Mechanical Stimuli

Besides the classical ones (support/protection, hematopoiesis, storage for calcium, and phosphate) multiple roles emerged for bone tissue, definitively making it an organ. Particularly, the endocrine function, and in more general terms, the capability to sense and integrate different stimuli and to send signals to other tissues, has highlighted the importance of bone in homeostasis. Bone is highly innervated and hosts all nervous system branches; bone cells are sensitive to most of neurotransmitters, neuropeptides, and neurohormones that directly affect their metabolic activity and sensitivity to mechanical stimuli. Indeed, bone is the principal mechanosensitive organ. Thanks to the mechanosensing resident cells, and particularly osteocytes, mechanical stimulation induces metabolic responses in bone forming (osteoblasts) and bone resorbing (osteoclasts) cells that allow the adaptation of the affected bony segment to the changing environment. Once stimulated, bone cells express and secrete, or liberate from the entrapping matrix, several mediators (osteokines) that induce responses on distant targets. Brain is a target of some of these mediator [e.g., osteocalcin, lipocalin2, sclerostin, Dickkopf-related protein 1 (Dkk1), and fibroblast growth factor 23], as most of them can cross the blood-brain barrier. For others, a role in brain has been hypothesized, but not yet demonstrated. As exercise effectively modifies the release and the circulating levels of these osteokines, it has been hypothesized that some of the beneficial effects of exercise on brain functions may be associated to such a bone-to-brain communication. This hypothesis hides an interesting clinical clue: may well-addressed physical activities support the treatment of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases?

Assocıatıons between mıld hyponatremıa and gerıatrıc syndromes ın outpatıent settıngs

PURPOSE

The impact of mild hyponatremia on geriatric syndromes is not clear. Our aim was to determine associations between mild hyponatremia and results of comprehensive geriatric assessment tools in outpatient settings.

METHODS

We reviewed medical records of 1255 consecutive outpatient elderly subjects and compared results of comprehensive geriatric assessment measures among patients with mild hyponatremia (serum Na⁺ 130-135 mEq/L) versus normonatremia (serum Na⁺ 136-145 mEq/L). The comprehensive geriatric assessment measures included the Basic and Instrumental Activities of Daily Living, Mini Mental State Examination, Geriatric Depression Score, Tinetti Mobility Test, the Timed Up&Go Test, the Mini Nutritional Assessment, the handgrip test, the Insomnia Severity Index, polypharmacy, recurrent falls, urinary incontinence, orthostatic hypotension, and nocturia.

RESULTS

Of the 1255 patients, 855 were female (68.1%), and the mean age was 73.7 ± 8.3 years. Mild hyponatremia was detected in 108 patients (8.6%). The median serum sodium was 140.5 [interquartile range (IQR) 138.4-141.8] versus 133.8 [IQR, 132.3-134.2] in normonatremia and mild hyponatremia groups, respectively (p < 0.001). The only significant difference for comorbidities between normonatremia and mild hyponatremia groups was the frequency of hypertension (66.9% versus 76.7%, respectively (p = 0.041). None of the comprehensive geriatric assessment tools conferred a significant association with mild hyponatremia. Of the 1061 subjects with available survival data, 96 (9.0%) deceased within 3-4 years of follow-up (p = 0.742). Hyponatremia as an independent variable did not have a significant effect on mortality in univariate logistic regression analysis (OR 1.13, 95% CI 0.55-2.33, p = 0.742).

CONCLUSION

Mild hyponatremia does not apparently affect results of geriatric assessments significantly. Whether particular causes of hyponatremia may have different impacts should be tested in further studies.

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Lower Oxytocin Levels Are Associated with Lower Bone Mineral Density and Less Favorable Hip Geometry in Hypopituitary Men

INTRODUCTION

Hypopituitary patients are at risk for bone loss. Hypothalamic-posterior pituitary hormones oxytocin and vasopressin are anabolic and catabolic, respectively, to the skeleton. Patients with hypopituitarism may be at risk for oxytocin deficiency. Whether oxytocin and/or vasopressin contribute to impaired bone homeostasis in hypopituitarism is unknown.

OBJECTIVES

To determine the relationship between plasma oxytocin and vasopressin levels and bone characteristics (bone mineral density [BMD] and hip structural analysis [HSA]) in patients who have anterior pituitary deficiencies only (APD group) or with central diabetes insipidus (CDI group).

METHODS

This is a cross-sectional study. Subjects included 37 men (17 CDI and 20 APD), aged 20-60 years. Main outcome measures were fasting plasma oxytocin and vasopressin levels, and BMD and HSA using dual X-ray absorptiometry.

RESULTS

Mean BMD and HSA variables did not differ between the CDI and APD groups. Mean BMD Z-scores at most sites were lower in those participants who had fasting oxytocin levels below, rather than above, the median. There were positive associations between fasting oxytocin levels and (1) BMD Z-scores at the spine, femoral neck, total hip, and subtotal body and (2) favorable hip geometry and strength variables at the intertrochanteric region in CDI, but not APD, participants. No associations between vasopressin levels and bone variables were observed in the CDI or ADP groups.

CONCLUSIONS

This study provides evidence for a relationship between oxytocin levels and BMD and estimated hip geometry and strength in hypopituitarism with CDI. Future studies will be important to determine whether oxytocin could be used therapeutically to optimize bone health in patients with hypopituitarism.

Update on: effects of anti-diabetic drugs on bone metabolism

INTRODUCTION

Preclinical, clinical, and population-based studies have provided evidence that anti-diabetic drugs affect bone metabolism and may affect the risk of fracture in diabetic patients.

AREAS COVERED

An overview of the skeletal effects of anti-diabetic drugs used in type 2 diabetes is provided. Searches on AdisInsight, PubMed, and Medline databases were conducted up to 1^st July 2020. The latest evidence from randomized clinical trials and population-based studies on the skeletal safety of the most recent drugs (DPP-4i, GLP-1RA, and SGLT-2i) is provided.

EXPERT OPINION

Diabetic patients present with a higher risk of fracture for a given bone mineral density suggesting a role of bone quality in the etiology of diabetic fracture. Bone quality is difficult to assess in human clinical practice and the use of preclinical models provides valuable information on diabetic bone alterations. As several links have been established between bone and energy homeostasis, it is interesting to study the safety of anti-diabetic drugs on the skeleton. So far, evidence for the newest molecules suggests a neutral fracture risk, but further studies, especially in different types of patient populations (patients at risk or with history of cardiovascular disease, renal impairment, neuropathy) are required to fully appreciate this matter.

Beyond bone biology: Lessons from team science

Today, research in biomedicine often requires the knowledge and technologies in diverse fields. Therefore, there is an increasing need for collaborative team science that crosses traditional disciplines. Here, we discuss our own lessons from both interdisciplinary and transdisciplinary teams, which ultimately ushered us to expand our research realm beyond bone biology.

Effects of androgen excess and glucocorticoid exposure on bone health in adult patients with 21-hydroxylase deficiency

CONTEXT

This study aimed to determine the role of modifiable predictors on bone health in congenital adrenal hyperplasia (CAH).

DESIGN

Cross-sectional, single center study, including 97 patients (N = 42 men) with classic CAH due to 21-hydroxylase deficiency (N = 65 salt wasting, N = 32 simple virilizing).

MAIN OUTCOME MEASURES

Treatment-related predictors of bone health.

RESULTS

Average T scores (-0.9 ± 1.4 vs. -0.4 ± 1.4; p = 0.036) as well as Z scores (-1.0 ± 1.3 vs. -0.1 ± 1.4; p = 0.012) at the spine in patients with CAH were significantly lower in men than women. While osteoporosis was rare in women, it was documented in 9.1% of men with CAH. There was a significant positive correlation of Z scores at the spine with advancing age in women with CAH (R² = 0.178; p = 0.003). In multivariate analysis, the intake of conventional hydrocortisone (HC) instead of synthetic glucocorticoids was independently associated with a higher bone mineral density (BMD) at the hip region in both sexes. In women, there was a positive association with vitamin D concentrations. Interestingly, higher sodium levels were associated with a lower BMD independent of renin levels and fludrocortisone dosage. Neither in men nor in women, markers of androgen control were predictive for BMD at any site. Markers of bone turnover indicated low bone turnover. No pathological fractures were documented.

CONCLUSIONS

Men with CAH are particularly prone to low bone density, while women seem to be relatively protected by androgen excess compared to the general female population. The use of HC instead of synthetic GCs for hormone replacement may translate into better bone health.

A snake toxin as a theranostic agent for the type 2 vasopressin receptor

Rationale: MQ1, a snake toxin which targets with high nanomolar affinity and absolute selectivity for the type 2 vasopressin receptor (V2R), is a drug candidate for renal diseases and a molecular probe for imaging cells or organs expressing V2R.

Methods: MQ1's pharmacological properties were characterized and applied to a rat model of hyponatremia. Its PK/PD parameters were determined as well as its therapeutic index. Fluorescently and radioactively labeled MQ1 were chemically synthesized and associated with moderate loss of affinity. MQ1's dynamic biodistribution was monitored by positron emission tomography. Confocal imaging was used to observe the labeling of three cancer cell lines.

Results: The inverse agonist property of MQ1 very efficiently prevented dDAVP-induced hyponatremia in rats with low nanomolar/kg doses and with a very large therapeutic index. PK (plasma MQ1 concentrations) and PD (diuresis) exhibited a parallel biphasic decrease. The dynamic biodistribution showed that MQ1 targets the kidneys and then exhibits a blood and kidney biphasic decrease. Whatever the approach used, we found a T1/2α between 0.9 and 3.8 h and a T1/2β between 25 and 46 h and demonstrated that the kidneys were able to retain MQ1. Finally, the presence of functional V2R expressed at the membrane of cancer cells was, for the first time, demonstrated with a specific fluorescent ligand.

Conclusion: As the most selective V2 binder, MQ1 is a new promising drug for aquaresis-related diseases and a molecular probe to visualize in vitro and in vivo V2R expressed physiologically or under pathological conditions.

AVPR1A distribution in the whole C57BL/6J mouse neonate

The neuropeptide arginine vasopressin (AVP) plays significant roles in maintaining homeostasis and regulating social behavior. In vaginally delivered neonates, a surge of AVP is released into the bloodstream at levels exceeding release during life-threatening conditions such as hemorrhagic shock. It is currently unknown where the potential sites of action are in the neonate for these robust levels of circulating AVP at birth. The purpose of this study is to identify the location of AVP receptor 1a (AVPR1A) sites as potential peripheral targets of AVP in the neonatal mouse. RT-qPCR analysis of a sampling of tissues from the head demonstrated the presence of Avpr1a mRNA, suggesting local peripheral translation. Using competitive autoradiography in wildtype (WT) and AVPR1A knockout (KO) postnatal day 0 (P0) male and female mice on a C57BL/6J background, specific AVPR1A ligand binding was observed in the neonatal mouse periphery in sensory tissues of the head (eyes, ears, various oronasal regions), bone, spinal cord, adrenal cortex, and the uro-anogenital region in the neonatal AVPR1A WT mouse, as it was significantly reduced or absent in the control samples (AVPR1A KO and competition). AVPR1A throughout the neonatal periphery suggest roles for AVP in modulating peripheral physiology and development of the neonate.

Arginine vasopressin receptor 1a is a therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) recurs after androgen deprivation therapy (ADT) and is incurable. Reactivation of androgen receptor (AR) signaling in the low androgen environment of ADT drives CRPC. This AR activity occurs through a variety of mechanisms, including up-regulation of AR coactivators such as VAV3 and expression of constitutively active AR variants such as the clinically relevant AR-V7. AR-V7 lacks a ligand-binding domain and is linked to poor prognosis. We previously showed that VAV3 enhances AR-V7 activity to drive CRPC progression. Gene expression profiling after depletion of either VAV3 or AR-V7 in CRPC cells revealed arginine vasopressin receptor 1a (AVPR1A) as the most commonly down-regulated gene, indicating that this G protein-coupled receptor may be critical for CRPC. Analysis of publicly available human PC datasets showed that AVPR1A has a higher copy number and increased amounts of mRNA in advanced PC. Depletion of AVPR1A in CRPC cells resulted in decreased cell proliferation and reduced cyclin A. In contrast, androgen-dependent PC, AR-negative PC, or nontumorigenic prostate epithelial cells, which have undetectable AVPR1A mRNA, were minimally affected by AVPR1A depletion. Ectopic expression of AVPR1A in androgen-dependent PC cells conferred castration resistance in vitro and in vivo. Furthermore, treatment of CRPC cells with the AVPR1A ligand, arginine vasopressin (AVP), activated ERK and CREB, known promoters of PC progression. A clinically safe and selective AVPR1A antagonist, relcovaptan, prevented CRPC emergence and decreased CRPC orthotopic and bone metastatic growth in mouse models. Based on these preclinical findings, repurposing AVPR1A antagonists is a promising therapeutic approach for CRPC.

Crosstalk of Brain and Bone-Clinical Observations and Their Molecular Bases

As brain and bone disorders represent major health issues worldwide, substantial clinical investigations demonstrated a bidirectional crosstalk on several levels, mechanistically linking both apparently unrelated organs. While multiple stress, mood and neurodegenerative brain disorders are associated with osteoporosis, rare genetic skeletal diseases display impaired brain development and function. Along with brain and bone pathologies, particularly trauma events highlight the strong interaction of both organs. This review summarizes clinical and experimental observations reported for the crosstalk of brain and bone, followed by a detailed overview of their molecular bases. While brain-derived molecules affecting bone include central regulators, transmitters of the sympathetic, parasympathetic and sensory nervous system, bone-derived mediators altering brain function are released from bone cells and the bone marrow. Although the main pathways of the brain-bone crosstalk remain ‘efferent’, signaling from brain to bone, this review emphasizes the emergence of bone as a crucial ‘afferent’ regulator of cerebral development, function and pathophysiology. Therefore, unraveling the physiological and pathological bases of brain-bone interactions revealed promising pharmacologic targets and novel treatment strategies promoting concurrent brain and bone recovery.

Urinary Lithogenic Risk Profile in ADPKD Patients Treated with Tolvaptan

BACKGROUND AND OBJECTIVES

Nephrolithiasis is a common health problem in autosomal dominant polycystic kidney disease (ADPKD) and significantly contributes to patient morbidity. Recently, Tolvaptan has been introduced for the treatment of ADPKD, but whether it is associated with alterations of the urinary lithogenic risk profile remains unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted an analysis of participants enrolled in the Bern ADPKD registry, a prospective observational cohort study. Twenty-four-hour urine analyses were performed at baseline and then at yearly follow-ups. Relative supersaturation ratios for calcium oxalate, brushite, and uric acid were calculated with the program EQUIL2. Unadjusted and multivariable mixed-effects linear regression models, adjusted for age, sex, body mass index, eGFR, net acid excretion, and height-adjusted total kidney volume, were used to assess the association of Tolvaptan with urinary parameters relevant for kidney stone formation. The maximum individual follow-up time was 3 years, median follow-up time 1.9 years, and cumulative follow-up time 169 years.

RESULTS

In total, 125 participants (38 with and 87 without Tolvaptan treatment) were included in the analysis. In multivariable analysis, Tolvaptan treatment was associated [adjusted estimate of the difference between Tolvaptan and no Tolvaptan; 95% confidence interval (CI)] with lower urine relative supersaturation ratios for calcium oxalate (-0.56; 95% CI, -0.82 to -0.3; P<0.001), brushite (-0.33; 95% CI, -0.54 to -0.11; P=0.004), and uric acid (-0.62; 95% CI, -0.88 to -0.37; P<0.001), and with higher urine citrate in mmol/mmol creatinine per day (0.25; 95% CI, 0.05 to 0.46; P=0.02) and calcium in mmol/mmol creatinine per day (0.31; 95% CI, 0.09 to 0.53; P=0.006) excretion. In addition, Tolvaptan treatment was associated with lower net acid excretion in mEq/mmol creatinine per day (-0.54; 95% CI, -0.90 to -0.17; P=0.004) and higher net gastrointestinal alkali absorption in mEq/mmol creatinine per day (0.57; 95% CI, 0.26 to 0.88; P<0.001).

CONCLUSIONS

Tolvaptan treatment is associated with a significantly improved urinary lithogenic risk profile in patients with ADPKD.

Arginine Vasopressin Modulates Ion and Acid/Base Balance by Regulating Cell Numbers of Sodium Chloride Cotransporter and H+-ATPase Rich Ionocytes

Arginine vasopressin (Avp) is a conserved pleiotropic hormone that is known to regulate both water reabsorption and ion balance; however, many of the mechanisms underlying its effects remain unclear. Here, we used zebrafish embryos to investigate how Avp modulates ion and acid–base homeostasis. After incubating embryos in double-deionized water for 24 h, avp mRNA expression levels were significantly upregulated. Knockdown of Avp protein expression by an antisense morpholino oligonucleotide (MO) reduced the expression of ionocyte-related genes and downregulated whole-body Cl⁻ content and H⁺ secretion, while Na⁺ and Ca²⁺ levels were not affected. Incubation of Avp antagonist SR49059 also downregulated the mRNA expression of sodium chloride cotransporter 2b (ncc2b), which is a transporter responsible for Cl⁻ uptake. Correspondingly, avp morphants showed lower NCC and H⁺-ATPase rich (HR) cell numbers, but Na⁺/K⁺-ATPase rich (NaR) cell numbers remained unchanged. avp MO also downregulated the numbers of foxi3a- and p63-expressing cells. Finally, the mRNA expression levels of calcitonin gene-related peptide (cgrp) and its receptor, calcitonin receptor-like 1 (crlr1), were downregulated in avp morphants, suggesting that Avp might affect Cgrp and Crlr1 for modulating Cl⁻ balance. Together, our results reveal a molecular/cellular pathway through which Avp regulates ion and acid–base balance, providing new insights into its function.

Pathophysiological Mechanisms of Nocturia and Nocturnal Polyuria: The Contribution of Cellular Function, the Urinary Bladder Urothelium, and Circadian Rhythm

Alterations to arginine vasopressin (AVP) secretion, the urinary bladder urothelium (UT) and other components of the bladder, and the water homeostasis biosystem may be relevant to the pathophysiology of nocturia and nocturnal polyuria (NP). AVP is the primary hormone involved in water homeostasis. Disruption to the physiological release of AVP or its target effects may relate to several urinary disturbances. Circadian dysregulation and the effects of aging, for example, the development of oxidative stress and mitochondrial dysfunction, may play a role in nocturia voiding symptoms. The urinary bladder UT not only acts as a highly efficient barrier that is maintained during the filling and voiding of the urinary bladder, but is also capable of sensory and transducer function through a network of functional receptors and ion channels that enable reciprocal communication between UT cells and neighboring elements of the bladder mucosa and wall. Functional components of the UT (eg, claudins and receptors or ion channels) play important roles in AVP-mediated water homeostasis. These components and functions involved in water homeostasis, as well as kidney function, may be affected by the aging process, including age-related mitochondrial dysfunction. The characteristics of NP are discussed and the association between NP and circadian rhythm is examined in light of reports that suggest that nocturia should be considered as a type of circadian dysfunction. Many possible pathologic mechanisms that underlie nocturia and NP have been identified. Future studies may provide further insight into pathophysiology with the hope of identifying new treatment modalities.

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

Hyponatremia and metabolic bone disease in patients with epilepsy: A cross-sectional study

AIM

Patients with epilepsy frequently develop hyponatremia due to the treatment with antiepileptic drugs and have an increased risk of developing metabolic bone disease. Hyponatremia is known to be associated with osteoporosis. The aim of the study was to investigate the association between hyponatremia and osteoporosis in patients with epilepsy.

METHOD AND MATERIAL

This cross-sectional study included patients with epilepsy from a tertiary epilepsy out-patient clinic in Denmark, who had a Dual Energy X-ray Absorptiometry scan performed and an accompanying plasma sodium (p-Na) measured prior to or a maximum of 14 days after the scan. Information regarding the patients' health and medical conditions were obtained from their medical reports.

RESULTS

A total of 695 patients (females 53.8%, age 49 (34:63) years (median (quartiles)) were included. 10.4% had hyponatremia (p-Na ≤ 135 mmol/L). The hyponatremic patients had significantly lower T-scores in the lumbar spine, femoral neck and total femur (all p < 0.023) and the odds ratio of osteoporosis (T-score < -2.5) was significantly increased (2.91 (1.61-5.27) (95% confidence interval) (p = 0.001)). When adjusting for potential confounders the patients with moderate and severe hyponatremia (p-Na < 129 mmol/L) had a significantly lower mean T-score in the lumbar spine (p = 0.030).

CONCLUSION

We conclude that hyponatremia is common in patients with epilepsy and that moderate and severe hyponatremia is independently associated with decreased bone mineral density in the lumbar spine. Therefore, hyponatremia in a patient with epilepsy should warrant further examination of the patient for bone loss and osteoporosis.

Chronic hyponatremia and association with osteoporosis among a large racially/ethnically diverse population

Chronic hyponatremia may contribute to decreased bone density. We studied 341,003 men and women who underwent DXA testing and observed that individuals with chronic hyponatremia (sodium < 135 mEq/L) had an 11% greater likelihood of having osteoporosis. There was a dose-dependent effect with lower sodium and stronger association with osteoporosis.

INTRODUCTION

Chronic hyponatremia has been associated with both neurologic deficits and increased risk of gait abnormalities leading to falls and resultant bone fractures. Whether chronic hyponatremia contributes to decreased bone density is uncertain. We evaluated whether chronic, mild hyponatremia based on serial sodium measurements was associated with increased risk of osteoporosis within a large, ethnically diverse population.

METHODS

This is a retrospective cohort study between January 1, 1998 and December 31, 2014 within Kaiser Permanente Southern California, an integrated healthcare delivery system. Men and women were aged ≥ 55 years with ≥ 2 serum sodium measurements prior to dual-energy X-ray absorptiometry (DXA) testing. Time-weighted (TW) mean sodium values were calculated by using the proportion of time (weight) elapsed between sodium measurements and defined as < 135 mEq/L. Osteoporosis defined as any T-score value ≤ - 2.5 of lumbar spine, femoral neck, or hip.

RESULTS

Among 341,003 individuals with 3,330,903 sodium measurements, 11,539 (3.4%) had chronic hyponatremia and 151,505 (44.4%) had osteoporosis. Chronic hyponatremic individuals had an osteoporosis RR (95% CI) of 1.11 (1.09, 1.13) compared to those with normonatremia. A TW mean sodium increase of 3 mEq/L was associated with a lower risk of osteoporosis [adjusted RR (95% CI) 0.95 (0.93, 0.96)]. A similar association was observed when the arithmetic mean sodium value was used for comparison.

CONCLUSIONS

We observed a modest increase in risk for osteoporosis in people with chronic hyponatremia. There was also a graded association between higher TW mean sodium values and lower risk of osteoporosis. Our findings underscore the premise that chronic hyponatremia may lead to adverse physiological effects and responses which deserves better understanding.

THE EFFECTS OF HYPONATREMIA ON BONE DENSITY AND FRACTURES: A SYSTEMATIC REVIEW AND META-ANALYSIS

Objective: Hyponatremia decreases bone mineral density and is a major risk factor for fragility fractures. Objectives of our systematic review and meta-analysis were to analyze the overall effects of hyponatremia on bone fractures, osteoporosis, and mortality. Methods: We extracted data from Medline, Cochrane Central, and EMBASE 1960-2017 and conference abstracts from 2007-2017. We included studies with data on serum sodium, fractures, bone density, or diagnoses of osteoporosis. Studies were independently reviewed by two authors and assessed for bias using the Newcastle-Ottawa scale. Random effect models meta-analysis was used when at least three studies reported the same outcome measures. We reported summary odds ratios (ORs) and 95% confidence intervals (CIs). Results: We included 26 studies for qualitative analysis. Fifteen studies were included in the meta-analysis to evaluate the effects of hyponatremia on fractures, four studies for bone mineral density changes, and six for mortality. Hyponatremia increased the odds of fractures at all sites (summary OR, 2.34 [95% CI, 1.86, 2.96]. There was an increase in the odds of osteoporosis (summary OR, 2.67 [95% CI, 2.07, 3.43]). Mortality risk among the included studies remained high (summary OR, 1.31 [95% CI, 1.16, 1.47]). Conclusion: Our meta-analysis confirms a statistically significant association of hyponatremia with bone fractures and osteoporosis along with higher mortality. Long-term prospective studies evaluating the impact of correcting hyponatremia on bone health, fractures, and mortality are required. Abbreviations: AVP = arginine vasopressin; CI = confidence interval; CKD = chronic kidney disease; OR = odds ratio; SIADH = syndrome of inappropriate antidiuretic hormone.

Hyponatremia Is Associated With Increased Osteoporosis and Bone Fractures in Patients With Diabetes With Matched Glycemic Control

Context

Patients with diabetes mellitus are at increased risk for bone fragility fracture secondary to multiple mechanisms. Hyperglycemia can induce true dilutional hyponatremia. Hyponatremia is associated with gait instability, osteoporosis, and increased falls and bone fractures, and studies suggest that compromised bone quality with hyponatremia may be independent of plasma osmolality. We performed a case-control study of patients with diabetes mellitus matched by median glycated hemoglobin (HbA1c) to assess whether hyponatremia was associated with increased risk of osteoporosis and/or fragility fracture.

Design

Osteoporosis (n = 823) and fragility fracture (n = 840) cases from the MedStar Health database were matched on age of first HbA1c ≥6.5%, sex, race, median HbA1c over an interval from first HbA1c ≥6.5% to the end of the encounter window, diabetic encounter window length, and type 1 vs type 2 diabetes mellitus with controls without osteoporosis (n = 823) and without fragility fractures (n = 840), respectively. Clinical variables, including coefficient of glucose variation and hyponatremia (defined as serum [Na⁺] <135 mmol/dL within 30 days of the end of the diabetic window), were included in a multivariate analysis.

Results

Multivariate conditional logistic regression models demonstrated that hyponatremia within 30 days of the outcome measure was independently associated with osteoporosis and fragility fractures (osteoporosis OR 3.09; 95% CI, 1.37 to 6.98; fracture OR, 6.41; 95% CI, 2.44 to 16.82).

Conclusions

Our analyses support the hypothesis that hyponatremia is an additional risk factor for osteoporosis and fragility fracture among patients with diabetes mellitus.

Sodium loading, treadmill walking, and the acute redistribution of bone mineral content on dual energy X-ray absorptiometry scans

The purpose of this study was to assess relationships between plasma sodium concentration ([Na⁺]) and bone mineral content (BMC) after an acute sodium load plus treadmill walking and then quantify the amount of sodium the dual energy X-ray absorptiometry (DXA) scan could detect. The primary study was a single-blind randomized control crossover trial under two conditions: ingestion of six flour tablets (placebo trial) or six 1-g NaCl tablets (salt intervention trial). The tablets were ingested after baseline blood and urine collection followed immediately by the DXA scan. After 60 min of rest, a 45-min treadmill walk was conducted. Immediately postexercise, blood and urine were collected and the DXA scan was repeated. Main outcomes included changes (∆: post minus pre) in plasma [Na⁺] and BMC. Additionally, six 1-g NaCl tablets were superimposed over a DXA spine phantom for separate quantification of sodium as BMC. Fourteen subjects completed the primary study. Two-way repeated measures ANOVA tests revealed significant interaction ( F = 13.06; P = 0.0007), condition ( F = 21.88; P < 0.001), and time ( F = 6.51; P = 0.014) effects in plasma [Na⁺]. A significant condition ( F = 6.46; P = 0.014) effect was also noted in urine [Na⁺]. Total body BMC∆ was negatively correlated with plasma [Na⁺]∆ ( r = -0.43; P = 0.02) and urine [Na⁺]∆ ( r = -0.47; P = 0.01). Total body BMC∆ in the salt intervention trial [-5.5 (27) g] closely approximated the amount of NaCl ingested and subsequently absorbed into the bloodstream. The DXA scan quantified 67% of NaCl tablets as BMC in spine phantom analyses. Total body BMC∆ was negatively related to plasma and urine [Na⁺]∆ after treadmill walking. Reductions in total body BMC closely approximated the amount of NaCl ingested (~6 g). The DXA scan quantified NaCl as BMC.