Longterm Increased S100B Enhances Hippocampal Progenitor Cell Proliferation in a Transgenic Mouse Model.

(1) The neurotrophic protein S100B is a marker of brain injury and has been associated with neuroregeneration. In S100Btg mice rendering 12 copies of the murine S100B gene we evaluated whether S100B may serve as a treatment option. (2) In juvenile, adult, and one-year-old S100Btg mice (female and male; n = 8 per group), progenitor cell proliferation was quantified in the subgranular zone (SGZ) and the granular cell layer (GCL) of the dentate gyrus with the proliferative marker Ki67 and BrdU (50 mg/kg). Concomitant signaling was quantified utilizing glial fibrillary acidic protein (GFAP), apolipoprotein E (ApoE), brain-derived neurotrophic factor (BDNF), and the receptor for advanced glycation end products (RAGE) immunohistochemistry. (3) Progenitor cell proliferation in the SGZ and migration to the GCL was enhanced. Hippocampal GFAP was reduced in one-year-old S100Btg mice. ApoE in the hippocampus and frontal cortex of male and BDNF in the frontal cortex of female S100Btg mice was reduced. RAGE was not affected. (4) Enhanced hippocampal neurogenesis in S100Btg mice was not accompanied by reactive astrogliosis. Sex- and brain region-specific variations of ApoE and BDNF require further elucidations. Our data reinforce the importance of this S100Btg model in evaluating the role of S100B in neuroregenerative medicine.

Amyloid-ß Processing in Aged S100B Transgenic Mice Is Sex Dependent.

(1) Background: Calcium-binding protein S100B is involved in neuroregeneration but has also been associated with neurodegeneration. These contrasting effects may result from concentration or duration of exposure. We investigated the effect of long-term increased S100B levels on amyloid-ß processing in one-year-old transgenic (tg) mice with 12 copies of the murine S100B gene with specific consideration of sex and specific brain regions. (2) Methods: S100B and amyloid-ß 42 (Aß42) were quantified in serum, cerebrospinal fluid (CSF), adipose tissue, and different brain regions by ELISA in wild-type (wt) and S100Btg mice (each n = 7 per group). Thioflavin T (ThT) and Aß immunostaining were performed for visualization of Aß deposition. (3) Results: S100B in serum, CSF, and brain was significantly increased in S100Btg mice of both sexes. Aß42 was significantly increased in the hippocampus of male S100Btg mice (p = 0.0075), and the frontal cortex of female S100Btg mice (p = 0.0262). ThT and Aß immunostaining demonstrated Aß deposition in different brain regions in S100Btg mice of both sexes and female wt. (4) Conclusion: Our data validate this experimental model for studying the role of S100B in neurodegeneration and indicate that Aß processing is sex-dependent and brain region-specific, which deserves further investigation of signaling pathways and behavioral responses.

Treatment of posttraumatic syringomyelia: evidence from a systematic review.

BACKGROUND: Following spinal cord injury (SCI), the routine use of magnetic resonance imaging (MRI) resulted in an incremental diagnosis of posttraumatic syringomyelia (PTS). However, facing four decades of preferred surgical treatment of PTS, no clear consensus on the recommended treatment exists. We review the literature on PTS regarding therapeutic strategies, outcomes, and complications. METHODS: We performed a systematic bibliographic search on ("spinal cord injuries" [Mesh] AND "syringomyelia" [Mesh]). English language literature published between 1980 and 2020 was gathered, and case reports and articles examining syrinx due to other causes were excluded. The type of study, interval injury to symptoms, severity and level of injury, therapeutic procedure, duration of follow-up, complications, and outcome were recorded. RESULTS: Forty-three observational studies including 1803 individuals met the eligibility criteria. The time interval from SCI to the diagnosis of PTS varied between 42 and 264 months. Eighty-nine percent of patients were treated surgically (n = 1605) with a complication rate of 26%. Symptoms improved in 43% of patients postoperatively and in 2% treated conservatively. Stable disease was documented in 50% of patients postoperatively and in 88% treated conservatively. The percentage of deterioration was similar (surgery 16%, 0.8% dead; conservative 10%). Detailed analysis of surgical outcome with regard to symptoms revealed that pain, motor, and sensory function could be improved in 43 to 55% of patients while motor function deteriorated in around 25%. The preferred methods of surgery were arachnoid lysis (48%) and syrinx drainage (31%). CONCLUSION: Even diagnosing PTS early in its evolution with MRI, to date, no satisfactory standard treatment exists, and the present literature review shows similar outcomes, regardless of the treatment modality. Therefore, PTS remains a neurosurgical challenge. Additional research is required using appropriate study designs for improving treatment options.

Surgery for craniopharyngioma.

Craniopharyngiomas are rare benign sellar region tumors, which are diagnosed either in childhood or adolescence due to local mass effects on visual pathways, pituitary and hypothalamus, or because of an increased intracranial pressure resulting from obstructive hydrocephalus. The neurosurgeons challenge is to achieve tumor control without aggravating the symptoms. There are essentially two different surgical philosophies. Although only gross tumor resection has been proven to provide cure, the accompanying surgical hazard is substantial. Thus, less aggressive operations with partial or subtotal tumor resection or drainage of cystic portions followed by irradiation may relieve the patient's symptoms and benefit the patient more than a heroic tumor resection-since to date several variants of radiation therapy are available which also serve to control tumor progression. In the present brief review, the surgical techniques and outcomes of operations in craniopharyngiomas with special focus on the resulting morbidity and mortality are summarized.

Neuroprotein dynamics in the cerebrospinal fluid: intraindividual concomitant ventricular and lumbar measurements.

OBJECTIVE: The measurement of neuromarker/neuroproteins in the cerebrospinal fluid (CSF) is gaining increased popularity. However, insufficient information is available on the rostrocaudal distribution of neuroproteins in the CSF to guarantee an appropriate interpretation of ventricular versus lumbar concentrations. METHODS: In 10 patients treated with both an external ventricular and a lumbar CSF drain, we collected concomitant CSF samples. We measured CSF concentrations of the glial S100B protein, the neuron-specific enolase (Cobas e411®; Roche Diagnostics), the leptomeningeal ß-trace protein (BN Pro Spec®; Dade Behring/Siemens), and the blood-derived albumin (Immage; Beckman Coulter). Statistical analysis was performed with a paired Wilcoxon signed ranks test. RESULTS: In patients with a free CSF circulation without any recent neurosurgical procedure, S100B and neuron-specific enolase concentrations did not differ between the ventricular and lumbar CSF while ß-trace and albumin levels were significantly higher in the lumbar than in the ventricular CSF (p=0.008 and p=0.005). Following posterior fossa tumor surgery, all proteins accumulate in the lumbar CSF. CONCLUSION: For brain-derived proteins, we could not confirm a rostrocaudal CSF gradient while lepto-meningeal and blood-derived proteins accumulate in the lumbar CSF. We conclude that for the interpretation of protein CSF concentrations, the source of the sample is of crucial importance.

The role of vasopressin V1A receptors in cytotoxic brain edema formation following brain injury.

BACKGROUND: The hormone and neuropeptide arginine-vasopressin is designated to the maintenance of osmotic homoeostasis and blood pressure regulation. While experimental data show vasopressin V(1A) receptors to regulate aquaporin (AQP)4 water channel dependent brain water movement, the specific role in vasogenic and cytotoxic edema formation remains unclear. The present study was designed to quantify the V(1A) receptor mediated regional brain edema formation in two clinically relevant experimental models, brain injury combined with secondary insult and focal ischemia. METHODS: Male Sprague-Dawley rats were randomly assigned to a continuous infusion of vehicle (1 % DMSO) or the selective non-peptide V(1A) antagonist SR49059 (83nM = 1 mg/kg) starting before controlled cortical impact (CCI) injury plus hypoxia and hypotension (HH, 30 min), or middle cerebral artery (MCA) occlusion (2 h + 2 h reperfusion). RESULTS: A global analysis of brain water content by the wet/dry weight method allowed optimizing the SR49059 dosage, and demonstrated the down-regulation of brain AQP4 expression by immunoblotting. Microgravimetrical quantification in 64 one mm(3) samples per animal (n = 6 per group) from bregma +2.7 to -6.3 mm analysis demonstrated brain edema to be reduced at 4 h by SR49059 treatment in the injured and contralateral cortex following CCI + HH (p = 0.007, p < 0.001) and in the infarct area following MCA occlusion (p = 0.013, p = 0.002, p = 0.004). CONCLUSIONS: Our findings demonstrate that an early cytotoxic brain edema component following brain injury plus secondary insult or focal ischemia results from a vasopressin V(1A) receptor mediated response, and occurs most likely through AQP4 up-regulation. The V(1A) antagonist SR49059 offers a new avenue in brain edema treatment and prompts further study into the role of vasopressin following brain injury.

Infection surveillance in transsphenoidal pituitary surgery - comparison of lipopolysaccharide-binding-protein, interleukin 6, C-reactive protein, white blood cell count, erythrocyte sedimentation rate and body temperature.

BACKGROUND: One of the major concerns in transsphenoidal surgery are infections because the approach to the pituitary includes a route of microbial colonization. To minimize the associated morbidity and mortality, a surveillance program is crucial to monitor for perioperative infections. METHODS: For 1 year, we analysed body temperature (BT), erythrocyte sedimentation rate (ESR), white blood cell count (WBC), C-reactive protein (CRP), interleukin 6 (IL-6) and lipopolysaccharide-binding-protein (LBP) following elective transsphenoidal pituitary surgery. Samples were collected on admission, day 1, 3 and 7 as well as 3 months postoperatively. RESULTS: In 116 patients, all data were available. No postoperative infections occurred within the first postoperative week. BT (37.6 ± 0.6, baseline 37.0 ± 0.5 °C), WBC (11,366 ± 2,541, baseline 6,861 ± 2,123/µl), CRP (25.3 ± 22.6, baseline 3.1 ± 6 mg/l), IL-6 (12 ± 13, baseline 2.7 ± 2.6 pg/ml), and LBP (11.3 ± 4.9, baseline 5.7 ± 2.7 µg/ml) peaked on day 1 postoperatively (each p = 0.001), while ESR peaked on day 3 (25 ± 16, baseline 13 ± 11 mm/h, p = 0.001). BT and IL-6 normalized by day 3 and CRP by day 7, while ESR (23 ± 16 mm/h, p = 0.001), WBC (7,807 ± 2,750/µl, p = 0.001) and LBP (7.3 ± 2.6 µg/ml, p = 0.028) were still increased by day 7. CONCLUSION: The present study establishes normative values for an infection surveillance following transsphenoidal pituitary surgery. CRP, a convenient and reasonable priced parameter, is affected by the procedure for the first postoperative week. IL-6 is more robust and allows a close monitoring on the expense of additional pricing. ESR, WBC and LBP are sustained affected by surgery, and do not offer any advantage. Since no infections were observed, we were unable to calculate the respective sensitivity and specificity.

Intraperitoneal treatment with S100B enhances hippocampal neurogenesis in juvenile mice and after experimental brain injury.

BACKGROUND: Neurogenesis is documented in adult mammals including humans, is promoted by neurotrophic factors, and constitutes an innate repair mechanism following brain injury. The glial neurotrophic protein S100B is released following various types of brain injuries, enhances hippocampal neurogenesis and improves cognitive function following brain injury in rats when applied intrathecally. The present study was designed to elucidate whether the beneficial effect of S100B on injury-induced neurogenesis can be confirmed in mice when applied intraperitoneally (i.p.), and whether this effect is dose-dependent. METHODS: Male juvenile mice were subjected to a unilateral parietal cryolesion or sham injury, and treated with S100B at 20nM, 200nM or vehicle i.p. once daily. Hippocampal progenitor cell proliferation was quantified following labelling with bromo-deoxyuridine (BrdU, 50 mg/KG i.p.) in the germinative area of the dentate gyrus, the subgranular zone (SGZ), on day 4 as well as on cell survival and migration to the granular cell layer (GCL) on day 28. Progenitor cell differentiation was assessed following colabelling with the glial marker GFAP and the neuronal marker NeuN. RESULTS: S100B enhanced significantly the early progenitor cell proliferation in the SGZ as well as cell survival and migration to the GCL, and promoted neuronal differentiation. While these effects were predominately dose-dependent, 200nM S100B failed to enhance the proliferation in the SGZ on day 4 post-injury. CONCLUSION: We conclude that S100B participates in hippocampal neurogenesis after injury at lower nanomolar concentrations. Therefore S100B may serve as a potential adjunct treatment to promote neuroregeneration following brain damage.

Safety and Efficacy of Vaptans in the Treatment of Hyponatremia from Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): A Systematic Review and Meta-Analysis.

The utilization of vasopressin receptor antagonists, known as vaptans, in the management of hyponatremia among patients afflicted with the syndrome of inappropriate antidiuretic hormone (SIADH) remains a contentious subject. This meta-analysis aimed to evaluate the safety and efficacy of vaptans for treating chronic hyponatremia in adult SIADH patients. Clinical trials and observational studies were identified by a systematic search using MEDLINE, EMBASE, and Cochrane Database from inception through September 2022. The inclusion criteria were the studies that reported vaptans' safety or efficacy outcomes compared to placebo or standard therapies. The study protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD 42022357307). Five studies were identified, comprising three RCTs and two cohort studies, enrolling a total of 1840 participants. Regarding short-term efficacy on days 4-5, vaptans exhibited a significant increase in serum sodium concentration from the baseline in comparison to the control group, with a weighted mean difference of 4.77 mmol/L (95% CI, 3.57, 5.96; I2 = 34%). In terms of safety outcomes, the pooled incidence rates of overcorrection were 13.1% (95% CI 4.3, 33.6; I2 = 92%) in the vaptans group and 3.3% (95% CI 1.6, 6.6; I2 = 27%) in the control group. Despite the higher correction rate linked to vaptans, with an OR of 5.72 (95% CI 3.38, 9.70; I2 = 0%), no cases of osmotic demyelination syndrome were observed. Our meta-analysis comprehensively summarizes the efficacy and effect size of vaptans in managing SIADH. While vaptans effectively raise the serum sodium concentration compared to placebo/fluid restriction, clinicians should exercise caution regarding the potential for overcorrection.

How S100B crosses brain barriers and why it is considered a peripheral marker of brain injury.

S100B is a 21-kDa protein that is produced and secreted by astrocytes and widely used as a marker of brain injury in clinical and experimental studies. The majority of these studies are based on measurements in blood serum, assuming an associated increase in cerebrospinal fluid and a rupture of the blood-brain barrier (BBB). Moreover, extracerebral sources of S100B are often underestimated. Herein, we will review these interpretations and discuss the routes by which S100B, produced by astrocytes, reaches the circulatory system. We discuss the concept of S100B as an alarmin and its dual activity as an inflammatory and neurotrophic molecule. Furthermore, we emphasize the lack of data supporting the idea that S100B acts as a marker of BBB rupture, and the need to include the glymphatic system in the interpretations of serum changes of S100B. The review is also dedicated to valorizing extracerebral sources of S100B, particularly adipocytes. Furthermore, S100B per se may have direct and indirect modulating roles in brain barriers: on the tight junctions that regulate paracellular transport; on the expression of its receptor, RAGE, which is involved in transcellular protein transport; and on aquaporin-4, a key protein in the glymphatic system that is responsible for the clearance of extracellular proteins from the central nervous system. We hope that the data on S100B, discussed here, will be useful and that it will translate into further health benefits in medical practice.

Shunt-dependent hydrocephalus following subarachnoid hemorrhage correlates with increased S100B levels in cerebrospinal fluid and serum.

Posthemorrhagic hydrocephalus requiring permanent ventriculoperitoneal shunt placement is a major complication of aneurysmal subarachnoid hemorrhage (SAH). High S100B serum and cerebrospinal fluid (CSF) levels are considered to reflect the severity of brain injury. We prospectively assessed whether S100B levels in serum and CSF were predictive parameters for permanent shunt requirement following aneurysmal SAH. In patients suffering from aneurysmal SAH and treated with an external ventricular drain (EVD), S100B levels in serum and CSF were measured daily as long as the EVD was in place. S100B levels of patients who passed their EVD challenge were compared with those patients who required a permanent ventriculoperitoneal shunt placement. Out of 68 patients included in the study, 43 patients (63.2%) passed the EVD challenge and in 25 patients (36.8%) permanent ventriculoperitoneal shunting was performed. Group comparison revealed that in patients who required shunt placement, S100B was significantly higher in CSF (p < 0.05 at days 2, 4, 6, 10; p < 0.005 at days 1, 3, 5, 7, 8, 9) and serum (p < 0.05 at days 4-7) compared with patients who could be weaned from the EVD. Assessment of S100B levels in CSF and serum may be useful as a predictive parameter for shunt dependency in patients with posthemorrhagic hydrocephalus following aneurysmal SAH.

The atrial natriuretic peptide does not serve osmoregulation but predicts outcome following brain injury.

Atrial natriuretic peptide (ANP) plays an important role in body fluid homeostasis. ANP has been established as a marker of cardiac dysfunction and may play a role in brain edema development after traumatic brain injury (TBI). In order to identify its specific assignment following TBI, we related clinical data and treatment variables in 63 patients to longitudinal midregional (MR) proatrail natriuretic peptide (ANP) measurements. ANP correlated significantly to age (p < 0.0001) and vasopressin release (p < 0.001). Following TBI, ANP was increased initially and on day 3 (cut-off 100 pg/L) in 22% of the patients, in 31% on day 7, and was normalized at follow-up examination. The group comparison revealed that ANP levels did not significantly differ with regard to injury severity, but that high ANP levels predicted a worse Glasgow Outcome Score at 6 months (p < 0.05). While the initially intact osmoregulation - a correlation of urine volume and high serum sodium (r = 0.536, p = 0.003) or low urine osmolality (r = -0.556, p = 0.009) - got lost post-injury, the ANP release was triggered by volume load (p < 0.005). High ANP levels correlated with the neuroendocrine stress response, i.e., high cortisol (p = 0.05) and prolactin (p < 0.001) levels. We conclude that MR-proANP measurements reveal a significant predictive function for the prognosis of TBI.

Development of an experimental model to study the pathophysiology of cerebral salt wasting following subarachnoid hemorrhage.

Hyponatremia is frequent following cranial -neurosurgery or acute brain injury like subarachnoid hemorrhage (SAH), and increases mortality by 30%. The patho-physiology is not understood nor does a causal therapy exist. Since clinical trials are potentially dangerous in this very ill population, we examined whether an established rat model allows studying cerebral salt wasting (CSW) following SAH. The daily urine sodium excretion as well as plasma sodium, osmolality and antidiuretic hormone (ADH) levels were measured for 10 days. Following the injection of 300 µl of blood into the great cistern (SAH(severe)), natriuresis peaked twice (days 1 and 3-5, p < 0.05) resulting in a plasma sodium nadir (day 1 - 133.9 mmol/L, day 5 - 132.6 mmol/L), while following the injection of 300 µL saline (ICP(control)), natriuresis occurred delayed on days 4-5 (p < 0.05). Following double SAH (200 µL twice, 24 h apart), a natriuresis on day 4 resulted in a hyponatremia (131.7 mmol/L, p = 0.025). Neither SAH(mild) (100 µL), the injection of hemolyzed blood (100 µL) or hypertonic saline (200 µL) replicated the effect. The immediate release of ADH (32.23 ± 34.87 pg/mL) following SAH(severe) normalized over the next few days. We conclude that first, the rat model of SAH is suitable for studying CSW, second the increase in intracranial pressure generates the delayed hyponatremia, and third, the ADH release does not mediate natriuresis.

Treatment with Cyclic AMP Activators Reduces Glioblastoma Growth and Invasion as Assessed by Two-Photon Microscopy.

(1) Background: Despite progress in surgery and radio-chemotherapy of glioblastoma (GB), the prognosis remains very poor. GB cells exhibit a preference for hypoxia to maintain their tumor-forming capacity. Enhancing oxidative phosphorylation-known as the anti-Warburg effect-with cyclic AMP activators has been demonstrated to drive GB cells from proliferation to differentiation thereby reducing tumor growth in a cell culture approach. Here we re-evaluate this treatment in a more clinically relevant model. (2) Methods: The effect of treatment with dibutyryl cyclic AMP (dbcAMP, 1 mM) and the cAMP activator forskolin (50µM) was assessed in a GB cell line (U87GFP+, 104 cells) co-cultured with mouse organotypic brain slices providing architecture and biochemical properties of normal brain tissue. Cell viability was determined by propidium-iodide, and gross metabolic effects were excluded in the extracellular medium. Tumor growth was quantified in terms of area, volume, and invasion at the start of culture, 48 h, 7 days, and 14 days after treatment. (3) Results: The tumor area was significantly reduced following dbcAMP or forskolin treatment (F2,249 = 5.968, p = 0.0029). 3D volumetric quantification utilizing two-photon fluorescence microscopy revealed that the treated tumors maintained a spheric shape while the untreated controls exhibited the GB typical invasive growth pattern. (4) Conclusions: Our data demonstrate that treatment with a cAMP analog/activator reduces GB growth and invasion.

CRH and SRIF have opposite effects on the Wnt/ß-catenin signalling pathway through PKA/GSK-3ß in corticotroph pituitary cells.

The Wnt/ß-catenin signalling pathway is involved in tumorigenesis including endocrine tumors. We investigated the Wnt/ß-catenin pathway's modulation by corticotropin-releasing hormone (CRH) and somatostatin or somatotropin release-inhibiting factor (SRIF) in mouse pituitary AtT-20 corticotroph cells. The Wnt/ß-catenin signalling pathway was activated by CRH and inhibited by SRIF. We provide evidence that cAMP/PKA signalling is involved affecting the GSK-3ß phosphorylation status at phospho-GSK-3ß (Ser9), thereby altering ß-catenin degradation downstream. Furthermore, CRH and SRIF showed concordant effects on cell proliferation. Our data demonstrate an important role of the Wnt/ß-catenin pathway in the proliferative control of pituitary corticotroph cells and describe a mechanism for its regulation by CRH and SRIF.

Development of pre-syrinx state and syringomyelia following a minor injury: a case report.

BACKGROUND: A generally accepted rule is that posttraumatic syringomyelia (PTS) results from spinal cord injury (SCI). CASE PRESENTATION: Here, we report the development of syringomyelia without SCI in a 54-year-old Caucasian man following a mild motor vehicle accident. The computed tomography on admission excluded an injury of the spine. Because of neck and back pain, magnetic resonance imaging was performed on day 3 post-injury and demonstrated minimal changes from a ligamentous strain at the cervicothoracic transition. Any traumatic affection of the bone, vertebral discs, intraspinal compartment, or spinal cord were excluded. Some limb weakness and neurogenic bladder dysfunction started manifesting within the following weeks. Repeated MRIs following the accident demonstrated arachnoid adhesions at the C1-2 level and spinal cord edema equivalent to a pre-syrinx state at 12 months and syrinx formation at 24 months. Because of further deterioration, decompression was performed at 36 months. CONCLUSIONS: We conclude that even after a minor trauma PTS can occur and that medullary edema (pre-syrinx state) may precede syrinx formation.

Tolvaptan Versus Fluid Restriction in the Treatment of Hyponatremia Resulting from SIADH Following Pituitary Surgery.

CONTEXT: The relevance of hyponatremia has been acknowledged by guidelines from the United States (2013) and Europe (2014). However, treatment recommendations differ due to limited evidence. OBJECTIVE: In hyponatremia following pituitary surgery-caused by the syndrome of inappropriate antidiuretic hormone (SIADH) secretion-we compared fluid restriction with the pharmacological increase of water excretion by blocking the vasopressin 2 receptors with tolvaptan at a low and a moderate dose. DESIGN: Prospective observational study. SETTING: Neurosurgical Department of a University hospital with more than 200 surgical pituitary procedures per year. PATIENTS: Patients undergoing pituitary surgery and developing serum sodium below 136 mmol/L. The diagnosis of SIADH was established by euvolemia (daily measurement of body weight and fluid balance), inappropriately concentrated urine (specific gravity), and exclusion of adrenocorticotropic and thyroid-stimulating hormone deficiency. INTERVENTION: Patients were treated with fluid restriction (n = 40) or tolvaptan at 3.75 (n = 38) or 7.5 mg (n = 48). MAIN OUTCOME MEASURES: Treatment efficacy was assessed by the duration of hyponatremia, sodium nadir, and length of hospitalization. Safety was established by a sodium increment below 10 mmol/L per day and exclusion of side effects. RESULTS: Treatment with 7.5 mg of tolvaptan resulted in a significant attenuation of hyponatremia and in a significant overcorrection of serum sodium in 30% of patients. The duration of hospitalization did not differ between treatment groups. CONCLUSIONS: Tolvaptan at a moderate dose is more effective than fluid restriction in the treatment of SIADH. Overcorrection of serum sodium may be a side effect of tolvaptan even at low doses.