The gadolinium ion: a potent blocker of calcium channels and catecholamine release from cultured chromaffin cells

Effects of gadolinium (Gd) and a Gd-based contrast agent (GBCA) on early life stages of zebrafish (Danio rerio)

Gadolinium (Gd) is one of the rare earth elements (REY) and is widely used in magnetic resonance imaging (MRI) contrast agents. Anthropogenic Gd enrichment has frequently been found in wastewater treatment plant effluents in industrialised countries, rising concerns regarding effects on aquatic biota. This study investigates the acute toxicity and sublethal effects of Gd in two forms, as inorganic salt (GdCl3) and as Gd-based contrast agent (GBCA), on early life stages of zebrafish (Danio rerio). Nominal exposure concentrations ranged from 3 to 3000 μg L-1, with an exposure duration of 96 h. None of the two tested compounds were acutely toxic to embryos and larvae. Similarly, we did not observe any effects on larval development and locomotive behaviour. However, we found significant changes in the brain activity of larvae exposed to the highest concentrations of GdCl3 and the GBCA. Our findings show that Gd can have sublethal effects on developing fish at lower concentrations than reported previously, highlighting the necessity of investigating the long-term fate and effects of GBCAs released into the aquatic environment.

Deletion of TRPC6, an Autism Risk Gene, Induces Hyperexcitability in Cortical Neurons Derived from Human Pluripotent Stem Cells

Autism spectrum disorder (ASD) is a complex and heterogeneous neurodevelopmental disorder linked to numerous rare, inherited, and arising de novo genetic variants. ASD often co-occurs with attention-deficit hyperactivity disorder and epilepsy, which are associated with hyperexcitability of neurons. However, the physiological and molecular mechanisms underlying hyperexcitability in ASD remain poorly understood. Transient receptor potential canonical-6 (TRPC6) is a Ca2+-permeable cation channel that regulates store-operated calcium entry (SOCE) and is a candidate risk gene for ASD. Using human pluripotent stem cell (hPSC)-derived cortical neurons, single-cell calcium imaging, and electrophysiological recording, we show that TRPC6 knockout (KO) reduces SOCE signaling and leads to hyperexcitability of neurons by increasing action potential frequency and network burst frequency. Our data provide evidence that reduction of SOCE by TRPC6 KO results in neuronal hyperexcitability, which we hypothesize is an important contributor to the cellular pathophysiology underlying hyperactivity in some ASD.

Contributions of the Sodium Leak Channel NALCN to Pacemaking of Medial Ventral Tegmental Area and Substantia Nigra Dopaminergic Neurons

We tested the role of the sodium leak channel, NALCN, in pacemaking of dopaminergic neuron (DAN) subpopulations from adult male and female mice. In situ hybridization revealed NALCN RNA in all DANs, with lower abundance in medial ventral tegmental area (VTA) relative to substantia nigra pars compacta (SNc). Despite lower relative abundance of NALCN, we found that acute pharmacological blockade of NALCN in medial VTA DANs slowed pacemaking by 49.08%. We also examined the electrophysiological properties of projection-defined VTA DAN subpopulations identified by retrograde labeling. Inhibition of NALCN reduced pacemaking in DANs projecting to medial nucleus accumbens (NAc) and others projecting to lateral NAc by 70.74% and 31.98%, respectively, suggesting that NALCN is a primary driver of pacemaking in VTA DANs. In SNc DANs, potentiating NALCN by lowering extracellular calcium concentration speeded pacemaking in wildtype but not NALCN conditional knockout mice, demonstrating functional presence of NALCN. In contrast to VTA DANs, however, pacemaking in SNc DANs was unaffected by inhibition of NALCN. Instead, we found that inhibition of NALCN increased the gain of frequency-current plots at firing frequencies slower than spontaneous firing. Similarly, inhibition of the hyperpolarization-activated cyclic nucleotide-gated (HCN) conductance increased gain but had little effect on pacemaking. Interestingly, simultaneous inhibition of NALCN and HCN resulted in significant reduction in pacemaker rate. Thus, we found NALCN makes substantial contributions to driving pacemaking in VTA DAN subpopulations. In SNc DANs, NALCN is not critical for pacemaking but inhibition of NALCN makes cells more sensitive to hyperpolarizing stimuli.SIGNIFICANCE STATEMENT Pacemaking in midbrain dopaminergic neurons (DAN) relies on multiple subthreshold conductances, including a sodium leak. Whether the sodium leak channel, NALCN, contributes to pacemaking in DANs located in the VTA and the SNc has not yet been determined. Using electrophysiology and pharmacology, we show that NALCN plays a prominent role in driving pacemaking in projection-defined VTA DAN subpopulations. By contrast, pacemaking in SNc neurons does not rely on NALCN. Instead, the presence of NALCN regulates the excitability of SNc DANs by reducing the gain of the neuron's response to inhibitory stimuli. Together, these findings will inform future efforts to obtain DAN subpopulation-specific treatments for use in neuropsychiatric disorders.

Quantitative monitoring of paramagnetic contrast agents and their allocation in plant tissues via DCE-MRI

BACKGROUND

Studying dynamic processes in living organisms with MRI is one of the most promising research areas. The use of paramagnetic compounds as contrast agents (CA), has proven key to such studies, but so far, the lack of appropriate techniques limits the application of CA-technologies in experimental plant biology. The presented proof-of-principle aims to support method and knowledge transfer from medical research to plant science.

RESULTS

In this study, we designed and tested a new approach for plant Dynamic Contrast Enhanced Magnetic Resonance Imaging (pDCE-MRI). The new approach has been applied in situ to a cereal crop (Hordeum vulgare). The pDCE-MRI allows non-invasive investigation of CA allocation within plant tissues. In our experiments, gadolinium-DTPA, the most commonly used contrast agent in medical MRI, was employed. By acquiring dynamic T₁-maps, a new approach visualizes an alteration of a tissue-specific MRI parameter T₁ (longitudinal relaxation time) in response to the CA. Both, the measurement of local CA concentration and the monitoring of translocation in low velocity ranges (cm/h) was possible using this CA-enhanced method.

CONCLUSIONS

A novel pDCE-MRI method is presented for non-invasive investigation of paramagnetic CA allocation in living plants. The temporal resolution of the T₁-mapping has been significantly improved to enable the dynamic in vivo analysis of transport processes at low-velocity ranges, which are common in plants. The newly developed procedure allows to identify vascular regions and to estimate their involvement in CA allocation. Therefore, the presented technique opens a perspective for further development of CA-aided MRI experiments in plant biology.

Using ELP Repeats as a Scaffold for De Novo Construction of Gadolinium-Binding Domains within Multifunctional Recombinant Proteins for Targeted Delivery of Gadolinium to Tumour Cells

Three artificial proteins that bind the gadolinium ion (Gd3+) with tumour-specific ligands were de novo engineered and tested as candidate drugs for binary radiotherapy (BRT) and contrast agents for magnetic resonance imaging (MRI). Gd3+-binding modules were derived from calmodulin. They were joined with elastin-like polypeptide (ELP) repeats from human elastin to form the four-centre Gd3+-binding domain (4MBS-domain) that further was combined with F3 peptide (a ligand of nucleolin, a tumour marker) to form the F3-W4 block. The F3-W4 block was taken alone (E2-13W4 protein), as two repeats (E1-W8) and as three repeats (E1-W12). Each protein was supplemented with three copies of the RGD motif (a ligand of integrin αvβ3) and green fluorescent protein (GFP). In contrast to Magnevist (a Gd-containing contrast agent), the proteins exhibited three to four times higher accumulation in U87MG glioma and A375 melanoma cell lines than in normal fibroblasts. The proteins remained for >24 h in tumours induced by Ca755 adenocarcinoma in C57BL/6 mice. They exhibited stability towards blood proteases and only accumulated in the liver and kidney. The technological advantages of using the engineered proteins as a basis for developing efficient and non-toxic agents for early diagnosis of tumours by MRI as well as part of BRT were demonstrated.

The Effect of Magnetic Field Gradient and Gadolinium-Based MRI Contrast Agent Dotarem on Mouse Macrophages

Magnetic resonance imaging (MRI) is widely used in diagnostic medicine. MRI uses the static magnetic field to polarize nuclei spins, fast-switching magnetic field gradients to generate temporal and spatial resolution, and radiofrequency (RF) electromagnetic waves to control the spin orientation. All these forms of magnetic static and electromagnetic RF fields interact with human tissue and cells. However, reports on the MRI technique's effects on the cells and human body are often inconsistent or contradictory. In both research and clinical MRI, recent progress in improving sensitivity and resolution is associated with the increased magnetic field strength of MRI magnets. Additionally, to improve the contrast of the images, the MRI technique often employs contrast agents, such as gadolinium-based Dotarem, with effects on cells and organs that are still disputable and not fully understood. Application of higher magnetic fields requires revisiting previously observed or potentially possible bio-effects. This article focuses on the influence of a static magnetic field gradient with and without a gadolinium-based MRI contrast agent (Dotarem) and the cellular and molecular effects of Dotarem on macrophages.

Gadolinium: pharmacokinetics and toxicity in humans and laboratory animals following contrast agent administration

Gadolinium-based contrast agents (GBCAs) have transformed magnetic resonance imaging (MRI) by facilitating the use of contrast-enhanced MRI to allow vital clinical diagnosis in a plethora of disease that would otherwise remain undetected. Although over 500 million doses have been administered worldwide, scientific research has documented the retention of gadolinium in tissues, long after exposure, and the discovery of a GBCA-associated disease termed nephrogenic systemic fibrosis, found in patients with impaired renal function. An understanding of the pharmacokinetics in humans and animals alike are pivotal to the understanding of the distribution and excretion of gadolinium and GBCAs, and ultimately their potential retention. This has been well studied in humans and more so in animals, and recently there has been a particular focus on potential toxicities associated with multiple GBCA administration. The purpose of this review is to highlight what is currently known in the literature regarding the pharmacokinetics of gadolinium in humans and animals, and any toxicity associated with GBCA use.

Investigation of Effects of Gadolinium-Based Contrast Agents on Uterine Contractility Using Isolated Rat Myometrium

BACKGROUND

Despite concerns about safety, gadolinium-based contrast agents (GBCAs) are still used for abdominal and pelvic imaging during pregnancy. Researchers have mainly focused on teratogenicity, while very little is known about their possible direct effects on uterine contractility, yet free gadolinium potentially impacts contractility through interaction with calcium channels.

PURPOSE

To investigate possible effects of selected GBCAs (namely gadoteridol, gadoversetamide, gadobutrol, gadoterate meglumine, and gadoxetic acid) on the contractility of rat myometrium.

STUDY TYPE

In vitro organ bath study.

ANIMAL MODEL

Myometria were isolated from adult (10-12 weeks old) Sprague Dawley rats, both pregnant (N = 8) and nonpregnant (N = 36).

FIELD STRENGTH/SEQUENCE

NA.

ASSESSMENT

Myometrial strips were suspended in tissue bath containing physiological saline and isometric contractions were recorded. GBCAs were added to the tissue bath cumulatively, and their effects on contractility parameters (quantified by amplitude, frequency, and area under contractility curve [AUC]) were evaluated by 10-minute intervals.

STATISTICAL TESTS

Normality data, checked by Shapiro-Wilk test, were transformed by arcsine when needed. One- or two-way analysis of variance was performed, where appropriate, followed by Student-Newman-Keuls test. A P value of <0.05 was considered statistically significant.

RESULTS

All of the assayed GBCAs elicited some alterations in the myometrial contractility in a concentration-dependent manner. Gadoterate meglumine, gadoxetic acid, and gadoversetamide caused a concentration-dependent significant attenuation in AUC (oxytocin-induced, from 100% during control period to 45.1 ± 9.0% (nonpregnant) and 59.9 ± 8.5% (pregnant), for 90 μM gadoterate meglumine; respectively), and frequency of the spontaneous and oxytocin-induced contractions. Gadobutrol and gadoteridol at highest dose significantly attenuated mean AUC and frequency of oxytocin-induced contractions of nonpregnant myometrium.

DATA CONCLUSION

Results from this in vitro study indicate that GBCAs elicit modulation of myometrial contractions at clinically relevant concentrations. These effects may account, at least partially, for the known potential side effects (rare cases of miscarriages and elective abortion) of these agents.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 5.

Biosorption of different gadolinium (Gd) complexes from water by Eichhornia crassipes (water hyacinth)

Many studies have demonstrated the Eichhornia crassipes (water hyacinth) potency in removing heavy metals, but the plant's potential for sorption of gadolinium (Gd) has not yet been investigated. In this study, water hyacinth was grown in a glass container for 30 days with either GdCl₃ or Gd-based contrast agent (GBCA; gadoterate) with water obtained from the Tone River. On the day 30, the Gd concentration in both the water and the plants was measured by mass spectrometry (ICP-MS). After 30 days, 98.5% of GdCl₃ in the water had been absorbed by the roots, and 3.5% of Gd was transferred to the leaves. On the other hand, the water hyacinth roots absorbed only 12% of the gadoterate. When exposed to 5 mg/L of GdCl₃, the roots of water hyacinth may effectively remove Gd ions in the aquatic environment, with no visible effect on the general health of the plant. However, the water hyacinth roots did not absorb GBCA. This may result in higher accumulation of Gd in the aqueous environment. The GBCA may be broken down by environmental factors and negatively affect the marine ecosystem.

Sodium background currents in endocrine/neuroendocrine cells: Towards unraveling channel identity and contribution in hormone secretion

In endocrine/neuroendocrine tissues, excitability of secretory cells is patterned by the repertoire of ion channels and there is clear evidence that extracellular sodium (Na⁺) ions contribute to hormone secretion. While voltage-gated channels involved in action potential generation are well-described, the background 'leak' channels operating near the resting membrane potential are much less known, and in particular the channels supporting a background entry of Na⁺ ions. These background Na⁺ currents (called here 'I_Nab') have the ability to modulate the resting membrane potential and subsequently affect action potential firing. Here we compile and analyze the data collected from three endocrine/neuroendocrine tissues: the anterior pituitary gland, the adrenal medulla and the endocrine pancreas. We also model how I_Nab can be functionally involved in cellular excitability. Finally, towards deciphering the physiological role of I_Nab in endocrine/neuroendocrine cells, its implication in hormone release is also discussed.

Selective killing of transformed cells by mechanical stretch

Cancer cells differ from normal cells in several important features like anchorage independence, Warburg effect and mechanosensing. Further, in recent studies, they respond aberrantly to external mechanical distortion. Consistent with altered mechano-responsiveness, we find that cyclic stretching of tumor cells from many different tissues reduces growth rate and causes apoptosis on soft surfaces. Surprisingly, normal cells behave similarly when transformed by depletion of the rigidity sensor protein (Tropomyosin 2.1). Restoration of rigidity sensing in tumor cells promotes rigidity dependent mechanical behavior, i.e. cyclic stretching enhances growth and reduces apoptosis on soft surfaces. The mechanism of mechanical apoptosis (mechanoptosis) of transformed cells involves calcium influx through the mechanosensitive channel, Piezo1 that activates calpain 2 dependent apoptosis through the BAX molecule and subsequent mitochondrial activation of caspase 3 on both fibronetin and collagen matrices. Thus, it is possible to selectively kill tumor cells by mechanical perturbations, while stimulating the growth of normal cells.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe , and studied the most important physicochemical properties in vitro. MnLMe displays optimized r1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r1b =21.1 mM-1  s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (Ka =4.2×103  M-1 ). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe, and studied the most important physicochemical properties in vitro. MnLMe displays optimized r 1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r 1 b=21.1 mM-1 s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (K a=4.2×103 M-1). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

Influence Blocking by Gadolinium in Calcium Diffusion on Synapse Model: A Monte Carlo Simulation Study

BACKGROUND

Gadolinium (Gd³⁺) is a chemical element belonging to the lanthanide group and commonly used in magnetic resonance imaging (MRI) as a contrast agent. However, recently, gadolinium has been reported deposition in the body after a patient receives multiple injections. Gadolinium is a potent block and competes with calcium diffusion into the presynaptic. There has not been a precise mechanism of gadolinium blocking calcium channel as a channel of calcium diffusion to presynaptic until now.

OBJECTIVE

This study aims to investigate the mechanism of calcium influx model and the effect of neurotransmitter release to the synaptic cleft influenced by the presence of Gd³⁺.

MATERIAL AND METHODS

Monte Carlo Cell simulation was used to analyze simulation and also Blender was used to create and visualize the model for synapse. The synapse modeled by a form resembling the actual synapse base on a spherical shape.

RESULTS

The presence of gadolinium around the presynaptic has been disturbing diffusion of calcium influx presynaptic. The result shows that the presence of gadolinium around the presynaptic has caused a decrease in the amount of calcium influx presynaptic. These factors contribute to reducing the establishment of the active membrane, then the amount of synaptic vesicle docking and finally the amount of released neurotransmitter.

CONCLUSION

Gadolinium and calcium compete with each other across of calcium channel. The presence of gadolinium has caused a chain effect for signal transmission at the chemical synapse, reducing the amount of active membrane, synaptic vesicle docking, and releasing neurotransmitter.

Fibromyalgia associated with repeated gadolinium contrast-enhanced MRI examinations

We report a case of a fibromyalgia (FM) patient with an history of brain-cancer presenting signs and symptoms of gadolinium toxicity following repeated administrations of a macrocyclic contrast agent, Gadovist. In the present report, we provide evidence supporting the hypothesis of a causal relationship linking gadolinium deposition to a clinical manifestation of disease, namely fibromyalgia. We unravel a role for gadolinium in the still unknown etiology of fibromyalgia as a metal toxicity disorder. Contrast agents are routinely administered in a clinical context. It is thus possible that the patients are mistakenly believed to show complaint of their primary disease, whereas, in some instances, their symptoms are associated with gadolinium deposition.

Ultrasensitive System for Electrophysiology of Cancer Cell Populations: A Review

Bioelectricity is the electrical activity produced by living organisms. Understanding the role of bioelectricity in a disease context is important as it contributes to both disease diagnosis and therapeutic intervention. Electrophysiology tools work well for neuronal cultures; however, they are limited in their ability to detect the electrical activity of non-neuronal cells, wherein the majority of cancers arise. Electronic structures capable of detecting and modulating signaling, in real-time, in electrically quiescent cells are urgently required. One of the limitations to understanding the role of bioelectricity in cancer is the inability to detect low-level signals. In this study, we review our latest advances in devising bidirectional transducers with large electrode areas and concomitant low impedances. The resulting high sensitivity is demonstrated by the extracellular detection of electrical activity in Rat-C6 glioma and prostate cancer (PC-3) cell populations. By using specific inhibitors, we further demonstrated that the large electrical activity in Rat-C6 glioma populations is acidosis driven. For PC-3 cells, the use of a calcium inhibitor together with the slowly varying nature of the signal suggests that Ca²⁺ channels are involved in the cohort electrogenicity.

The gadolinium hypothesis for fibromyalgia and unexplained widespread chronic pain

Fibromyalgia (FM) is a chronic, painful, heterogeneous, and common disorder carrying a substantial socio-economical burden. It lacks effective cures and its aetiology is still unknown. There exists evidence for central and peripheral neurological contribution to the symptoms but grasping the real source of abnormal nervous system sensitization remains an ongoing challenge. There exists an association between an injury/trauma and the onset of the symptoms, but a causal relationship has not been yet sufficiently supported by scientific evidence. I postulate a role for gadolinium-based contrast agents and retention of gadolinium in the body. This conjecture breaks the hypothesis of a direct role for a physical injury/trauma per se in favour of an indirect one by the subsequent diagnostic procedures. It creates a new link between retention of gadolinium in the body and painful conditions as FM and unexplained chronic widespread pain reported after a trauma, surgery, or medical illness. Experimental evidence demonstrates possible retention of gadolinium species in human body, still lacking conclusive answers on their pathological consequences. Notwithstanding, there exist some initial data that report unexplained chronic widespread pain and symptoms of FM in those patients: they are suggestive for pathological consequences associated with gadolinium retention. Besides clear compelling symptoms overlapping, biochemical findings are provided to sustain the hypothesis of a role for gadolinium in the disease process focusing on neurotransmitters, endogenous metal cations, cytokines, and muscle tissue. Experimental findings strongly support the hypothesis of impairment at the cellular, intracellular, and systemic levels in FM. And these data are highly compatible with collateral effects associated with the interference of the gadolinium ion and its pharmaceutical chelates into biochemical pathways in vivo. The hypothesis presented in this article, along with the support of scientific evidence, links FM and unexplained chronic widespread pain reported after a trauma, surgery, or medical illness to retention of gadolinium in the body. If the hypothesis is confirmed, it could improve diagnosis and prevention, while providing a ground for development of new treatments.

Focused ultrasound activates voltage-gated calcium channels through depolarizing TRPC1 sodium currents in kidney and skeletal muscle

Pulsed focused ultrasound (pFUS) technology is being developed for clinical neuro/immune modulation and regenerative medicine. Biological signal transduction of pFUS forces can require mechanosensitive or voltage-gated plasma membrane ion channels. Previous studies suggested pFUS is capable of activating either channel type, but their mechanistic relationship remains ambiguous. We demonstrated pFUS bioeffects increased mesenchymal stem cell tropism (MSC) by altering molecular microenvironments through cyclooxygenase-2 (COX2)-dependent pathways. This study explored specific relationships between mechanosensitive and voltage-gated Ca²⁺ channels (VGCC) to initiate pFUS bioeffects that increase stem cell tropism.

Methods: Murine kidneys and hamstring were given pFUS (1.15 or 1.125 MHz; 4MPa peak rarefactional pressure) under ultrasound or magnetic resonance imaging guidance. Cavitation and tissue displacement were measure by hydrophone and ultrasound radiofrequency data, respectively. Elastic modeling was performed from displacement measurements. COX2 expression and MSC tropism were evaluated in the presence of pharmacological ion channel inhibitors or in transient-receptor-potential-channel-1 (TRPC1)-deficient mice. Immunohistochemistry and co-immunoprecipitation examined physical channel relationships. Fluorescent ionophore imaging of cultured C2C12 muscle cells or TCMK1 kidney cells probed physiological interactions.

Results: pFUS induced tissue deformations resulting in kPa-scale forces suggesting mechanical activation of pFUS-induced bioeffects. Inhibiting VGCC or TRPC1 in vivo blocked pFUS-induced COX2 upregulation and MSC tropism to kidneys and muscle. A TRPC1/VGCC complex was observed in plasma membranes. VGCC or TRPC1 suppression blocked pFUS-induced Ca²⁺ transients in TCMK1 and C2C12 cells. Additionally, Ca²⁺ transients were blocked by reducing transmembrane Na⁺ potentials and observed Na⁺ transients were diminished by genetic TRPC1 suppression.

Conclusion: This study suggests that pFUS acoustic radiation forces mechanically activate a Na⁺-containing TRPC1 current upstream of VGCC rather than directly opening VGCC. The electrogenic function of TRPC1 provides potential mechanistic insight into other pFUS techniques for physiological modulation and optimization strategies for clinical implementation.

Quantitative analysis of Gd in the protein content of the brain following single injection of gadolinium-based contrast agents (GBCAs) by size exclusion chromatography

OBJECTIVE

To investigate the role of transporter proteins in gadolinium (Gd) distribution and retention in the brain after one high-dose injection of Gd-based contrast agent (GBCA).

METHODS AND MATERIALS

30 ddY mice were randomly divided into three treatment groups to be intravenously injected with either Gadodiamide (linear GBCA), Gadobutrol (macrocyclic GBCA), or Gadoterate (macrocyclic GBCA) at a dose of 5 mmol/kg, while five mice in the control group received 250 µL saline. Five minutes (5 min) and ten days (10d) post-injection, the cerebrospinal fluid (CSF), choroid plexus (CP), and meninges and associated vasculature (MAV) were collected. The brain was then dissected to obtain the olfactory bulb, cerebral cortex, hippocampus, cerebellum, and brainstem. Proteins were extracted and separated by a size-exclusion high-performance liquid chromatography (SEC) system, and Gd concentrations were quantified by inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

5 m post-injection, the Gadodiamide group had the highest Gd concentration, while Gadoterate had the lowest Gd concentration in all parts of the brain (p < .05). Gd concentration was highest in the cerebrospinal fluid (CSF) of the Gadodiamide group (578.4 ± 135.3 nmol), while Gd concentration was highest in MAV in the Gadobutrol group (379.7 ± 75.4 nmol) at 5 min post-injection. At 10d, in spite of the significant decrease of Gd from all GBCAs ( p < 0.01), retained Gd from Gadodiamide was detected all over the brain in several molecules that varied in size. Gd from Gadobutrol detected in the olfactory bulb (8.7 ± 4.5 nmol) was significantly higher than in other parts of the brain. Although most Gd from Gadobutrol was found in molecules similar in size to Gadobutrol, it was also found in several protein molecules of molecular size larger than the contrast agents. Only a small amount of Gd from Gadoterate was found in the brain.

CONCLUSION

GBCAs may be able to pass through intact brain barriers, and the chemical structures of GBCAs may affect the penetration capability of Gd into the brain. Retained Gd in the brain tissue from Gadodiamide and Gadobutrol may be bound to some organic molecules, including proteins.

ADVANCES IN KNOWLEDGE

Intact GBCA are able to penetrate a series of brain barrier immediately after administration regardless the type of the chelate. Gd may be bound with macromolecules that may cause Gd retention in the brain.

Intravenous Calcium-/Zinc-Diethylene Triamine Penta-Acetic Acid in Patients With Presumed Gadolinium Deposition Disease: A Preliminary Report on 25 Patients

OBJECTIVES

The aim of this study was to report the use of intravenous calcium (Ca)-/zinc (Zn)-diethylene triamine penta-acetic acid (DTPA) for the treatment of 25 symptomatic patients diagnosed with gadolinium deposition disease (GDD).

MATERIALS AND METHODS

Written informed consent was obtained. Twenty-five patients (18 women; mean age, 46.8 ± 15.3 years) with a diagnosis of GDD were included. All patients had received at least 1 administration of a gadolinium (Gd)-based contrast agent. Patients received 3 treatment sessions with Ca-/Zn-DTPA, 15 with treatments spaced 1 month apart, and 10 with treatments spaced 1 week apart. In all cases, every treatment consisted of an application of Ca-DTPA and Zn-DTPA separated by 24 hours. Measurements of 24-hour urine Gd content before dosing and on the first and second days of therapy were performed. Symptomatic improvement of patients was determined by use of a 10-point scale of patient symptoms. Serum electrolytes were quantified.

RESULTS

Gadolinium content increased in the urine, with an overall mean of 30.3-fold increase in the monthly regimen (P < 0.001) and 12.9-fold in the weekly regimen (P < 0.001). Eleven patients experienced transient worsening of at least some of their symptoms, termed a "flare-up" phenomenon, in most of whom symptoms improved or receded. Overall, symptoms improved in 13 patients, unchanged in 10, and worse in 2. Significant clinical improvement was present for headache, brain fog, and bone pain for the monthly regimen and arm pain and leg pain for the weekly regimen. There were no significant changes in major serum electrolytes.

CONCLUSIONS

Three courses of intravenous Ca-/Zn-DTPA therapy results in significantly increased urine content of Gd after treatment and moderate symptomatic improvement.

The use of a binary chelate formulation: Could gadolinium based linear contrast agents be rescued by the addition of zinc selective chelates?

Tissue and bone retention of gadolinium based contrast agents (GBCAs) has become a clinical concern because of the potential short and long term toxic effects of free gadolinium. This is a critical problem for most open-chain agents that more readily transmetallate in vivo, in comparison to macrocyclic compounds. Gadolinium diethylene tri-aminepentaacetic acid bis-glucosamide (Gd-DTPA-BIGA) is an experimental, open-chain contrast agent which has a significantly increased relaxivity coefficient in comparison to other GBCAs. This results in greater signal intensity and improved contrast enhancement. These superior imaging qualities initiated a search for a solution to the transmetallation of this agent. Plasma zinc is a well-known GBCA transmettalation agent. Since the base chelate of Gadodiamide (Gd-DPTA-Bis-Methylamide or Omniscan), DTPA-Bis-Methylamide (DTPA-BMA), readily transmettalates with and binds serum zinc, we hypothesized that a plasma "zinc sink," may significantly reduce transmetallation of linear agents. 5% DTPA-BMA was added to a formulation of Gd-DTPA-BIGA, which was tested against the original formulation of Gd-DTPA-BIGA with 0.2% of the base chelate DTPA-BIGA. These formulations, including gadodiamide, were labeled with ¹⁵³GdCl₃ followed by infusion into cohorts of Sprague Dawley rats which were sacrificed at 1, 30 and 60 days. Internal organs were harvested, along with blood, skin and femur, and analyzed for residual gadolinium. A subset of tissues were also interrogated with ICP-MS. Labeled Gadodiamide and saline where used as controls. Conclusion: The addition of 5% DTPA-BMA, as a zinc binding agent, reduced the transmetallation of the linear agent Gd-DTPA-BIGA, in comparison to its original formulation supplemented with 0.2% BIGA. This result indicates that supplementing linear GBCAs with ancillary chelates may hold promise for reducing, or eliminating the biological archiving of gadolinium in tissues. In addition, this paper provides valuable animal data on the long term retention of gadolinium from linear based contrast agents.

Gadolinium deposition and the potential for toxicological sequelae - A literature review of issues surrounding gadolinium-based contrast agents

Every year, approximately 30 million magnetic resonance imaging scans are enhanced with gadolinium-based contrast agents (GBCAs) worldwide. Although the development of nephrogenic systemic fibrosis in patients with renal impairment is well-documented, over recent years it has become apparent that exposure to GBCAs can potentially result in gadolinium deposition within human bone and brain tissue even in the presence of normal renal function. This review will address some of the controversies surrounding the safety of GBCA administration based on evidence from in vivo experiments, animal studies and clinical studies. We additionally evaluate the potential risk of toxicity from exposure to gadolinium in light of new guidance published by the US Food and Drug Administration and the European Medicines Agency, and discuss whether gadolinium deposition disease exists as a new diagnosis.

Influence of Mechanical Unloading on Articular Chondrocyte Dedifferentiation

Due to the limited self-repair capacity of articular cartilage, the surgical restoration of defective cartilage remains a major clinical challenge. The cell-based approach, which is known as autologous chondrocyte transplantation (ACT), has limited success, presumably because the chondrocytes acquire a fibroblast-like phenotype in monolayer culture. This unwanted dedifferentiation process is typically addressed by using three-dimensional scaffolds, pellet culture, and/or the application of exogenous factors. Alternative mechanical unloading approaches are suggested to be beneficial in preserving the chondrocyte phenotype. In this study, we examined if the random positioning machine (RPM) could be used to expand chondrocytes in vitro such that they maintain their phenotype. Bovine chondrocytes were exposed to (a) eight days in static monolayer culture; (b) two days in static monolayer culture, followed by six days of RPM exposure; and, (c) eight days of RPM exposure. Furthermore, the experiment was also conducted with the application of 20 mM gadolinium, which is a nonspecific ion-channel blocker. The results revealed that the chondrocyte phenotype is preserved when chondrocytes go into suspension and aggregate to cell clusters. Exposure to RPM rotation alone does not preserve the chondrocyte phenotype. Interestingly, the gene expression (mRNA) of the mechanosensitive ion channel TRPV4 decreased with progressing dedifferentiation. In contrast, the gene expression (mRNA) of the mechanosensitive ion channel TRPC1 was reduced around fivefold to 10-fold in all of the conditions. The application of gadolinium had only a minor influence on the results. This and previous studies suggest that the chondrocyte phenotype is preserved if cells maintain a round morphology and that the ion channel TRPV4 could play a key role in the dedifferentiation process.

Old and emerging concepts on adrenal chromaffin cell stimulus-secretion coupling

The chromaffin cells (CCs) of the adrenal medulla play a key role in the control of circulating catecholamines to adapt our body function to stressful conditions. A huge research effort over the last 35 years has converted these cells into the Escherichia coli of neurobiology. CCs have been the testing bench for the development of patch-clamp and amperometric recording techniques and helped clarify most of the known molecular mechanisms that regulate cell excitability, Ca²⁺ signals associated with secretion, and the molecular apparatus that regulates vesicle fusion. This special issue provides a state-of-the-art on the many well-known and unsolved questions related to the molecular processes at the basis of CC function. The issue is also the occasion to highlight the seminal work of Antonio G. García (Emeritus Professor at UAM, Madrid) who greatly contributed to the advancement of our present knowledge on CC physiology and pharmacology. All the contributors of the present issue are distinguished scientists who are either staff members, external collaborators, or friends of Prof. García.

Gadolinium Deposition in Human Brain Tissues after Contrast-enhanced MR Imaging in Adult Patients without Intracranial Abnormalities

Purpose To determine whether gadolinium deposits in neural tissues of patients with intracranial abnormalities following intravenous gadolinium-based contrast agent (GBCA) exposure might be related to blood-brain barrier integrity by studying adult patients with normal brain pathologic characteristics. Materials and Methods After obtaining antemortem consent and institutional review board approval, the authors compared postmortem neuronal tissue samples from five patients who had undergone four to 18 gadolinium-enhanced magnetic resonance (MR) examinations between 2005 and 2014 (contrast group) with samples from 10 gadolinium-naive patients who had undergone at least one MR examination during their lifetime (control group). All patients in the contrast group had received gadodiamide. Neuronal tissues from the dentate nuclei, pons, globus pallidus, and thalamus were harvested and analyzed with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy with energy-dispersive x-ray spectroscopy, and light microscopy to quantify, localize, and assess the effects of gadolinium deposition. Results Tissues from the four neuroanatomic regions of gadodiamide-exposed patients contained 0.1-19.4 μg of gadolinium per gram of tissue in a statistically significant dose-dependent relationship (globus pallidus: ρ = 0.90, P = .04). In contradistinction, patients in the control group had undetectable levels of gadolinium with ICP-MS. All patients had normal brain pathologic characteristics at autopsy. Three patients in the contrast group had borderline renal function (estimated glomerular filtration rate <45 mL/min/1.73 m²) and hepatobiliary dysfunction at MR examination. Gadolinium deposition in the contrast group was localized to the capillary endothelium and neuronal interstitium and, in two cases, within the nucleus of the cell. Conclusion Gadolinium deposition in neural tissues after GBCA administration occurs in the absence of intracranial abnormalities that might affect the permeability of the blood-brain barrier. These findings challenge current understanding of the biodistribution of these contrast agents and their safety. ^© RSNA, 2017.

Incidence and Risk Factors for Gadolinium-Based Contrast Agent Immediate Reactions

Since their clinical introduction in 1988, gadolinium-based contrast agents (GBCAs) have demonstrated an excellent safety profile with a reported acute adverse reaction rate ranging from 0.01% to 2%. By comparison, the acute adverse reaction rate of low osmolar nonionic computed tomography contrast agents (CTCs) ranges from 0.7% to 3.1%. Many of the risk factors associated with CTC reactions (drug allergies, asthma, atopy, prior contrast reaction) also point toward an increased incidence of acute adverse events to GBCAs. With CTCs, an increased adverse event rate was associated with ionic preparations and high osmolality. In response to concerns for nephrogenic systemic fibrosis, GBCAs are now selected for their augmented chemical stability. These agents possess some combination of macrocyclic chelates or ionic preparations. With their improved chemical stability, these agents also possess higher osmolality and the increased potential to elicit an acute adverse reaction. In light of these concerns, researchers are now focusing greater efforts on reexamining acute adverse reactions to GBCAs and whether there is an increased association with certain agents. In addition to hypersensitivity reactions, this article will also discuss contrast extravasations, safety of GBCAs for pregnant and nursing patients, and the potential nephrotoxic effects of GBCAs.

Bile acids induce necrosis in pancreatic stellate cells dependent on calcium entry and sodium-driven bile uptake

KEY POINTS

Acute biliary pancreatitis is a sudden and severe condition initiated by bile reflux into the pancreas. Bile acids are known to induce Ca2+ signals and necrosis in isolated pancreatic acinar cells but the effects of bile acids on stellate cells are unexplored. Here we show that cholate and taurocholate elicit more dramatic Ca2+ signals and necrosis in stellate cells compared to the adjacent acinar cells in pancreatic lobules; whereas taurolithocholic acid 3-sulfate primarily affects acinar cells. Ca2+ signals and necrosis are strongly dependent on extracellular Ca2+ as well as Na+ ; and Na+ -dependent transport plays an important role in the overall bile acid uptake in pancreatic stellate cells. Bile acid-mediated pancreatic damage can be further escalated by bradykinin-induced signals in stellate cells and thus killing of stellate cells by bile acids might have important implications in acute biliary pancreatitis.

ABSTRACT

Acute biliary pancreatitis, caused by bile reflux into the pancreas, is a serious condition characterised by premature activation of digestive enzymes within acinar cells, followed by necrosis and inflammation. Bile acids are known to induce pathological Ca2+ signals and necrosis in acinar cells. However, bile acid-elicited signalling events in stellate cells remain unexplored. This is the first study to demonstrate the pathophysiological effects of bile acids on stellate cells in two experimental models: ex vivo (mouse pancreatic lobules) and in vitro (human cells). Sodium cholate and taurocholate induced cytosolic Ca2+ elevations in stellate cells, larger than those elicited simultaneously in the neighbouring acinar cells. In contrast, taurolithocholic acid 3-sulfate (TLC-S), known to induce Ca2+ oscillations in acinar cells, had only minor effects on stellate cells in lobules. The dependence of the Ca2+ signals on extracellular Na+ and the presence of sodium-taurocholate cotransporting polypeptide (NTCP) indicate a Na+ -dependent bile acid uptake mechanism in stellate cells. Bile acid treatment caused necrosis predominantly in stellate cells, which was abolished by removal of extracellular Ca2+ and significantly reduced in the absence of Na+ , showing that bile-dependent cell death was a downstream event of Ca2+ signals. Finally, combined application of TLC-S and the inflammatory mediator bradykinin caused more extensive necrosis in both stellate and acinar cells than TLC-S alone. Our findings shed new light on the mechanism by which bile acids promote pancreatic pathology. This involves not only signalling in acinar cells but also in stellate cells.

Gadolinium deposition in the brain: Lessons learned from other metals known to cross the blood-brain barrier

The recent discovery of gadolinium (Gd) deposition in the brains of patients receiving Gd-based contrast agents (GBCAs) raises several important questions including by what mechanism Gd or GBCAs pass through the blood-brain barrier. Decades of research focused on the safety and stability of GBCAs have not identified any mechanism of uptake. Here we review findings of Gd deposition from human and animal data, and how distribution mechanisms elucidated for endogenous and toxic metals may explain entrance of Gd into the central nervous system. Three general uptake mechanisms are considered along with examples of metals known to enter the central nervous system by these routes: (1) carrier-mediated, (2) transporter-mediated and (3) passive. The potential for chelation therapy to reduce deposition is also discussed. The work reported for other metals provides guidance for how the mechanism of Gd deposition in the brain can be determined which is essential information for rational prevention or treatment.

Distribution and clearance of retained gadolinium in the brain: differences between linear and macrocyclic gadolinium based contrast agents in a mouse model

OBJECTIVE

To investigate the distribution and clearance of retained gadolinium (Gd) in various parts of the brain after intravenously administering a Gd-based contrast agent (GBCA) in normal and renal failure mouse models.

METHODS

Two different mouse models: normal (n = 12) and renal failure (n = 12) were used. Clinical GBCAs (Gd-DTPA-BMA, 5 mmol kg(-1), or Gd-DOTA, 5 mmol kg(-1)) were intravenously administered five times per week for 4 weeks. Both groups were divided into two subgroups based on the time point for sample collection: 3 days (3d) and 45 days (45d) after the last injection. Normal saline (5 ml kg(-1)) was intravenously administered to mice of the control groups in the same manner. Samples of the following parts of the mouse brain were obtained on dissection: olfactory bulb, cerebral cortex, hippocampus, thalamus, mid-brain, cerebellum, pons and medulla. (158)Gd concentrations in each sample were quantified using inductively coupled plasma mass spectrometry.

RESULTS

The olfactory bulb had the highest Gd concentration in both Gd-DTPA-BMA and Gd-DOTA groups. Gd retention was higher in the Gd-DTPA-BMA group than in the Gd-DOTA group (p < 0.01). In the Gd-DTPA-BMA group, Gd retention in the 3d subgroups of normal and renal failure models were similar (p = 0.4). At 45d, Gd in the Gd-DTPA-BMA group was not eliminated from the renal failure model (p = 0.1), while that in the Gd-DOTA group was eliminated from both the normal and renal failure mouse models (p < 0.01).

CONCLUSION

Gd distributions in the brain for both groups were similar, regardless of the renal function and GBCA type. The Gd concentration was highest in the olfactory bulb of both groups. In the Gd-DOTA group, Gd was eliminated from the brain in both mouse models, while in the Gd-DTPA-BMA group, Gd clearance was limited.

ADVANCES IN KNOWLEDGE

Gd concentration in the brain was not affected by renal function. The clearance of Gd from linear GBCA was limited in both the normal and impaired renal function mouse models.

Mechanisms underlying turgor regulation in the estuarine alga Vaucheria erythrospora (Xanthophyceae) exposed to hyperosmotic shock

Aquatic organisms are often exposed to dramatic changes in salinity in the environment. Despite decades of research, many questions related to molecular and physiological mechanisms mediating sensing and adaptation to salinity stress remain unanswered. Here, responses of Vaucheria erythrospora, a turgor-regulating xanthophycean alga from an estuarine habitat, have been investigated. The role of ion uptake in turgor regulation was studied using a single cell pressure probe, microelectrode ion flux estimation (MIFE) technique and membrane potential (Em ) measurements. Turgor recovery was inhibited by Gd(3+) , tetraethylammonium chloride (TEA), verapamil and orthovanadate. A NaCl-induced shock rapidly depolarized the plasma membrane while an isotonic sorbitol treatment hyperpolarized it. Turgor recovery was critically dependent on the presence of Na(+) but not K(+) and Cl(-) in the incubation media. Na(+) uptake was strongly decreased by amiloride and changes in net Na(+) and H(+) fluxes were oppositely directed. This suggests active uptake of Na(+) in V. erythrospora mediated by an antiport Na(+) /H(+) system, functioning in the direction opposite to that of the SOS1 exchanger in higher plants. The alga also retains K(+) efficiently when exposed to high NaCl concentrations. Overall, this study provides insights into mechanisms enabling V. erythrospora to regulate turgor via ion movements during hyperosmotic stress.

TRPV4: physiological role and therapeutic potential in respiratory diseases

Members of the family of transient receptor potential (TRP) channels have been implicated in the pathophysiology of a host of lung diseases. The role of these multimodal cation channels in lung homeostasis is thought to stem from their ability to respond to changes in mechanical stimuli (i.e., shear and stretch), as well as to various protein and lipid mediators. The vanilloid subfamily member, TRPV4, which is highly expressed in the majority of lung cell types, is well positioned for critical involvement in several pulmonary conditions, including edema formation, control of pulmonary vascular tone, and the lung response to local or systemic inflammatory insults. In recent years, several pharmacological inhibitors of TRPV4 have been developed, and the current generation of compounds possess high affinity and specificity for TRPV4. As such, we have now entered a time where the therapeutic potential of TRPV4 inhibitors can be systematically examined in a variety of lung diseases. Due to this fact, this review seeks to describe the current state of the art with respect to the role of TRPV4 in pulmonary homeostasis and disease, and to highlight the current and future roles of TRPV4 inhibitors in disease treatment. We will first focus on genera aspects of TRPV4 structure and function, and then will discuss known roles for TRPV4 in pulmonary diseases, including pulmonary edema formation, pulmonary hypertension, and acute lung injury. Finally, both promising aspects and potential pitfalls of the clinical use of TRPV4 inhibitors will be examined.

Clinical and economic impact of falsely decreased calcium values caused by gadoversetamide interference

OBJECTIVE

Gadolinium is administered as a contrast agent in MRI procedures. Two gadolinium-based contrast agents, gadodiamide and gadoversetamide, interfere with colorimetric total serum calcium methods. The purpose of this prospective observational study was to examine the incidence of calcium interference after gadoversetamide procedures, associated clinical outcomes, and costs 20 months after implementation of quality assurance and physician education programs.

MATERIALS AND METHODS

Records of patients who received gadoversetamide from June 24, 2006, to October 7, 2006, were reviewed to determine if a routine calcium test had been performed after the injection. Calcium values were repeated with an alternate method that is less susceptible to gadoversetamide interference. If the difference was > or = 2.0 mg/dL or if the initial test value was < or = 7.0 mg/dL, patient charts were reviewed for any related treatment. Costs associated with this algorithm were tracked.

RESULTS

The initial calcium test was performed after gadoversetamide in 766 of 3,439 instances. The alternate test was performed in 633 of 766. One hundred twenty-five of 633 (20%) showed a difference in calcium values that was > or = 0.7 mg/dL, with 16 showing differences of > or = 1.6 mg/dL. Chart review for 56 instances revealed that calcium supplements were administered in 22 of 56 around the time of gadoversetamide injection. However, none appeared to be related to the spurious hypocalcemia. The total additional cost (reagent and technologist) for following this algorithm for just over 3 months was $6,807.

CONCLUSION

Approximately 20% of patients receiving gadoversetamide exhibited spurious hypocalcemia. No patients were identified who received inappropriate calcium because of this interference. This may be attributable to the quality assurance and physician education programs.

Biochemical safety profiles of gadolinium-based extracellular contrast agents and nephrogenic systemic fibrosis

Gadolinium (Gd)-based paramagnetic contrast agents are relatively safe when used in clinically recommended doses. However, with the rapidly expanding body of literature linking Gd-based paramagnetic contrast agents and nephrogenic systemic fibrosis (NSF), awareness of the potential side effects and adverse reactions from Gd is now an important requirement for practicing radiologists. In addition to the ongoing accumulation and analyses of clinical NSF data, it is also essential for the practicing radiologist to understand the biochemical characteristics of the extracellular Gd-chelates. The purpose of this review is to consolidate and update the available information on known side effects, adverse reactions, and toxicity of the Gd chelates, with particular emphasis on the potential mechanisms of NSF.

Model for Predicting the Impact of Gadolinium on Plasma Calcium Measured by the o-Cresolphthalein Method

Background: Gadolinium formulations, which are administered as contrast agents in magnetic resonance imaging examinations, interfere with colorimetric serum calcium determinations.

Methods: We performed an in vitro study to determine the extent to which three gadolinium formulations—gadodiamide (Omniscan), gadopentetate dimeglumine (Magnevist), and gadoversetamide (OptiMARK)—affect measurements by two methods that use o-cresolphthalein (Dade Behring, Inc. and Roche Diagnostics) and one that uses arsenazo dye (Equal Diagnostics). We also compared values from the o-cresolphthalein methods for 116 samples from patients administered gadodiamide.

Results: Magnevist did not affect any of the methods evaluated, whereas Omniscan and OptiMARK were identical in their effects. For the Dade method, the differences from the control sample were ≤4.0 and 7.0 mg/L at 0.25 and 0.5 mmol/L gadolinium, respectively. For the Roche method, the differences were 19, 9.0, and 5.0 mg/L at 0.5, 0.25, and 0.125 mmol/L gadolinium, respectively. Falsely increased calcium values were seen when samples were measured by the arsenazo-based method: differences were 6.0 and 3.0 mg/L at 1.0 and 0.5 mmol/L gadolinium. Using patient data collected at our institution, we were able to generate a model for predicting, from a patient’s glomerular filtration rate and the time elapsed since administration, the impact of Omniscan on calcium measurements by the o-cresolphthalein method from Roche Diagnostics.

Conclusions: The predictive model can be used to calculate, in patients who have received gadodiamide, the minimum length of time to wait before blood collection to avoid pseudohypocalcemia when the Roche o-cresolphthalein method is used.

Basic experimental studies and clinical aspects of gadolinium salts and chelates

Gadolinium is a lanthanide that has in recent years become more commonly present in our society. Organic chelates of gadolinium are increasingly used as contrast agents for the imaging of body fluids. Although adverse reactions to these agents are uncommon, it is known that gadolinium salts can bring about a wide variety of changes in physiology. Gadolinium chloride is widely used experimentally as an inhibitor of stretch-activated ion channels and physiological responses of tissues to mechanical stimulation. It is also employed as a selective inhibitor of macrophages in vivo. In this review, the known biochemical actions of gadolinium are brought together with its in vivo pharmacology and toxicology.

Effect of Gd3+ on bradykinin-induced catecholamine secretion from bovine adrenal chromaffin cells

1. The effects of Gd3+ on bradykinin- (BK-) induced catecholamine secretion, 45Ca2+ efflux and cytosolic [Ca2+] were studied using bovine adrenal chromaffin cells. 2. BK increased secretion in a Ca2+-dependent manner. From 1 - 100 microM, Gd3+ progressively inhibited secretion induced by 30 nM BK to near-basal levels, however from 0.3 - 3 mM Gd3+ dramatically enhanced BK-induced secretion to above control levels. Gd3+ also increased basal catecholamine secretion by 2 - 3 fold at 1 mM. These effects were mimicked by Eu3+ and La3+. 3. Gd3+ enhanced secretion induced by other agonists that mobilize intracellular Ca2+ stores, but simply blocked the response to K+. 4. Gd3+ still enhanced basal and BK-induced secretion in Ca2+-free solution or in the presence of 30 microM SKF96365, however both effects of Gd3+ were abolished after depleting intracellular Ca2+ stores. 5. Gd3+ (1 mM) reduced the rate of basal 45Ca2+ efflux by 57%. In Ca2+-free buffer, BK transiently increased cytosolic [Ca2+] measured with Fura-2. The [Ca2+] response to BK was substantially prolonged in the presence of Gd3+ (1 mM). 6. The results suggest that Gd3+ greatly enhances the efficacy of Ca2+ released from intracellular stores in evoking catecholamine secretion, by inhibiting Ca2+ extrusion from the cytosol. This suggests that intracellular Ca2+ stores are fully competent to support secretion in chromaffin cells to levels comparable to those evoked by extracellular Ca2+ entry. Drugs that modify Ca2+ extrusion from the cell, such as lanthanide ions, will be useful in investigating the mechanisms by which intracellular Ca2+-store mobilization couples to Ca2+-dependent exocytosis.

Interference of magnetic resonance imaging contrast agents with the serum calcium measurement technique using colorimetric reagents

A possible interaction between either linear (Gd-DTPA-BMA and Gd-DTPA) or macrocyclic (Gd-DOTA) gadolinium complexes used as magnetic resonance imaging (MRI) contrast agents and colorimetric technique reagents for the measurement of serum calcium was evaluated on human serum pools, and its mechanism was investigated by means of UV spectrometry and electro-spray ionization mass spectrometry (ESI-MS). The highest concentration tested was 2.5 mM (corresponding to a putative strictly intravascular distribution of the compound) and the lowest dose was 0.2 mM (i.e. about two elimination half lives). Serum calcium was dosed in duplicate by conventional colorimetric techniques involving o-cresol-phthalein complexone (OCP) or methylthymol blue (MTB) as reagents. No interference was detected when mixing Gd DOTA with serum, whatever the concentration. Gd DTPA (2.5 mM) did not interfere with the colorimetric technique either. Conversely, the Gd DTPA-BMA solution induced a concentration-related variation in apparent calcium levels. In the UV experiments, solutions of 2.5 mM MRI contrast media were mixed with OCP or MTB and UV absorption spectra were recorded between 400 and 800 nm. For Gd-DOTA/OCP and Gd-DOTA/MTB, no significant variations in the absorbance were detected. However, in the presence of Gd DTPA BMA, the absorbance of OCP and MTB showed substantial and immediate variations over time. The ESI-MS studies showed a complete displacement of Gd3+ ion in the case of Gd-DTPA BMA. In the presence of OCP, we observed the disappearance of Gd-DTPA BMA and the formation of the free ligand DTPA BMA and a new complex Gd OCP with an original stoichiometry of 2/2. Such a phenomenon did not occur in the case of Gd DOTA and Gd DTPA. The decomplexation of Gd-DTPA BMA in the presence of OCP can probably be explained by the weaker thermodynamic stability of Gd-DTPA BMA compared to that of Gd-DOTA and Gd DTPA.

ATP-evoked increases in [Ca2+]i and peptide release from rat isolated neurohypophysial terminals via a P2X2 purinoceptor

1. The effect of externally applied ATP on cytosolic free Ca2+ concentration ([Ca2+]i) was tested in single isolated rat neurohypophysial nerve terminals by fura-2 imaging. The release of vasopressin (AVP) and oxytocin (OT) upon ATP stimulation was also studied from a population of terminals using specific radioimmunoassays. 2. ATP evoked a sustained [Ca2+]i increase, which was dose dependent in the 1-100 microM range (EC50 = 4.8 microM). This effect was observed in only approximately 40 % of the terminals. 3. Interestingly, ATP, in the same range (EC50 = 8.6 microM), evoked AVP, but no significant OT, release from these terminals. 4. Both the [Ca2+]i increase and AVP release induced by ATP were highly and reversibly inhibited by suramin, suggesting the involvement of a P2 purinergic receptor in the ATP-induced responses. Pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), another P2 purinergic receptor antagonist, strongly reduced the ATP-induced [Ca2+]i response. 5. To further characterize the receptor, different agonists were tested, with the following efficacy: ATP = 2-methylthio-ATP > ATP-gamma-S > alpha, beta-methylene-ATP > ADP. The compounds adenosine, AMP, beta, gamma-methylene-ATP and UTP were ineffective. 6. The ATP-dependent [Ca2+]i increase was dependent on extracellular Ca2+ concentration ([Ca2+]o). Fluorescence-quenching experiments with Mn2+ showed that externally applied ATP triggered a Mn2+ influx. The ATP-induced [Ca2+]i increase and AVP release were independent of and additive to a K+-induced response, in addition to being insensitive to Cd2+. The ATP-induced [Ca2+]i increase was strongly reduced in the presence of Gd3+. These results suggest that the observed [Ca2+]i increases were elicited by Ca2+ entry through a P2X channel receptor rather than via a voltage-dependent Ca2+ channel. 7. We propose that ATP, co-released with neuropeptides, could act as a paracrine-autocrine messenger, stimulating, via Ca2+ entry through a P2X2 receptor, the secretion of AVP, in particular, from neurohypophysial nerve terminals.

Stretch-induced stimulation of lower airway nitric oxide formation in the guinea-pig: inhibition by gadolinium chloride

The effect of stretch on lower airway nitric oxide formation was studied in normoxic tracheostomized anaesthetized guinea-pigs. Increase of level of positive end-expiratory pressure caused increased lower airway nitric oxide formation, as measured by its presence in exhaled tracheal air. The L-type calcium channel blocker, verapamil, did not decrease lower airway nitric oxide formation. Neither the local anaesthetic xylocaine nor the ganglion blocker trimetaphan affected exhaled nitric oxide, excluding local and centrally-mediated neuronal reflexes. Intravenous administration of gadolinium chloride (GdCl3, 50 mg/kg) induced a rapid and pronounced decrease (75%) in the basal level of exhaled nitric oxide. GdCl3 completely abolished lower airway nitric oxide formation induced by ventilation with positive end-expiratory pressure (7 cm H2O). GdCl3 induced hypoxaemia, but there was no indication for the development of lung oedema. The results indicate that positive end-expiratory pressure stimulates lower airway nitric oxide formation in the guinea-pig. GdCl3 inhibits lower airway nitric oxide formation in the guinea-pig in vivo, perhaps by interference with stretch-induced cellular calcium-influx.

Proliferation of hepatocytes and attenuation from carbon tetrachloride hepatotoxicity by gadolinium chloride in rats

Intravenous injection of gadolinium chloride (GdCl3) at a dose of 10 mg/kg caused an increase in proliferating cell nuclear antigen labeling index and the grade of pyronin positivity (RNA level) in rat liver. In CCl4-exposed rats, pretreatment with GdCl3 also showed a preventive effect of the liver injury both biochemically and histologically. Moreover, the proliferative action preceded the attenuative effect of the liver injury. Results suggest that GdCl3 induces hepatocyte proliferation, and this action of GdCl3 may modify the development of CCl4-induced liver injury.

Modulation of the gating of the transient outward potassium current of rat isolated cerebellar granule neurons by lanthanum

The effects of the trivalent cation, lanthanum (La3+) on voltage-dependent K+ conductances were studied in rat isolated cerebellar granule neurons under whole-cell voltage-clamp conditions. La3+ at low micromolar concentrations caused a pronounced enhancement in the outward current evoked by depolarising steps from -50 mV, with the apparent recruitment of an inactivating component. The steady-state inactivation curve for the transient outward current, evoked by depolarising steps from -140 mV, was shifted by approximately 40 mV in the depolarising direction by 10 microM La3+, with a slight increase in the slope factor. The kinetics of activation and inactivation were slowed in the presence of La3+. A shift of 10 mV in the depolarising direction was seen for the activation curve of the delayed rectifier current in the presence of 10 microM La3+. These results indicate that La3+ has a potent effect on the gating characteristics of voltage-activated K+ currents. This effect cannot be explained by surface charge considerations.

A toxin fraction (FTX) from the funnel-web spider poison inhibits dihydropyridine-insensitive Ca2+ channels coupled to catecholamine release in bovine adrenal chromaffin cells

In adrenal chromaffin cells, depolarization-evoked Ca2+ influx and catecholamine release are partially blocked by blockers of L-type voltage-sensitive Ca2+ channels. We have now evaluated the sensitivity of the dihydropyridine-resistant components of Ca2+ influx and catecholamine release to a toxin fraction (FTX) from the funnel-web spider poison, which is known to block P-type channels in mammalian neurons. FTX (1:4,000 dilution, with respect to the original fraction) inhibited K(+)-depolarization-induced Ca2+ influx by 50%, as monitored with fura-2, whereas nitrendipine (0.1-1 microM) and FTX (3:3), a synthetic FTX analogue (1 mM), blocked the [Ca2+]i transients by 35 and 30%, respectively. When tested together, FTX and nitrendipine reduced the [Ca2+]i transients by 70%. FTX or nitrendipine reduced adrenaline and noradrenaline release by approximately 80 and 70%, respectively, but both substances together abolished the K(+)-evoked catecholamine release, as measured by HPLC. The omega-conotoxin GVIA (0.5 microM) was without effect on K(+)-stimulated 45Ca2+ uptake. Our results indicate that FTX blocks dihydropyridine- and omega-conotoxin-insensitive Ca2+ channels that, together with L-type voltage-sensitive Ca2+ channels, are coupled to catecholamine release.

Changes of quantal transmitter release caused by gadolinium ions at the frog neuromuscular junction

1. The actions of the trivalent cation, gadolinium (Gd3+), were studied on frog isolated neuromuscular preparations by conventional electrophysiological techniques. 2. Gd3+ (450 microM) applied to normal or formamide-treated cutaneous pectoris nerve-muscle preparations induced, after a short delay, a complete block of neuromuscular transmission. The reversibility of the effect was dependent on the time of exposure. 3. Gd3+ (5-450 microM) had no consistent effect on the resting membrane potential of the muscle fibres. 4. Gd3+ (5-40 microM) applied to preparations equilibrated in solutions containing high Mg2+ and low Ca2+ reduced the mean quantal content of endplate potentials (e.p.ps) in a dose-dependent manner. Under those conditions, 3,4-diaminopyridine (10 microM) consistently reversed the depression of evoked quantal release. 5. The calcium current entering motor nerve terminals, revealed after blocking presynaptic potassium currents with tetraethylammonium (10 mM) in the presence of elevated extracellular Ca2+ (8 mM), was markedly reduced by Gd3+ (0.2-0.5 mM). 6. Gd3+ (40-200 microM) increased the frequency of spontaneous miniature endplate potentials (m.e.p.ps) in junctions bathed either in normal Ringer solution or in a nominally Ca(2+)-free medium supplemented with 0.7 microM tetrodotoxin. This effect may be due to Gd3+ entry into the nerve endings since it is not reversed upon removal of extracellular Gd3+ with chelators (1 mM EGTA or EDTA). Gd3+ also enhanced the frequency of me.p.ps appearing after each nerve stimulus in junctions bathed in a medium containing high Mg2+ and low Ca2+. 7. Gd3+, in concentrations higher than 100 microM, decreased reversibly the amplitude of m.e.p.ps suggesting a postsynaptic action. 8. It is concluded that the block of nerve-impulse evoked quantal release caused by Gd3 + is related to its ability to block the calcium current entering the nerve endings, supporting the view that Gd3 + blocks N-type Ca2+ channels; while the enhancement of spontaneous quantal release is probably the result of Gd3 + entry into motor nerve endings. Besides its dual prejunctional effects on quantal release it is suggested that Gd3 + exerts a postsynaptic action on the endplate acetylcholine receptor-channel complex.

Gadolinium blocks low- and high-threshold calcium currents in pituitary cells

The inhibition of L- and T-type Ca2+ currents by Gd3+ was studied in the rat pituitary GH4C1 cell line. In whole cell patch recordings, Gd3+ at concentrations of 50 nM to 5 microM blocked Ca2+ current through L-type channels. Block was promoted by prolonged channel activation. With 4.5-s test pulses to + 10 mV, Gd3+ at concentrations as low as 200 nM produced near-complete block of L current. At higher Gd3+ concentrations (5 microM), complete block occurred with short test pulses and appeared to be independent of channel activation. Gd3+ also blocked current through low-threshold T channels in GH4C1 cells. Two other trivalent elements, La3+ and Y3+, blocked L-type Ca2+ channels in GH4C1 cells with potency similar to Gd3+. These results indicate that these trivalent cations are effective nonselective inhibitors of both low- and high-threshold Ca2+ channels in endocrine cells. In this regard, they are among the most potent inorganic Ca2+ antagonists yet discovered.

Effect of quinine on the release of catecholamines from bovine cultured chromaffin cells

1. The effects of quinine on catecholamine release from cultured bovine chromaffin cells were studied. 2. Quinine (25-400 microM) produced a dose-related inhibition of catecholamine release in response to depolarizing concentrations (12.5-50 mM) of K+. 3. The inhibition of the secretory response to high K+ produced by quinine decreased with the increase in the extracellular concentration of Ca2+. 4. Stimulation of cultured chromaffin cells with 50 mM K+ produced a significant increase in Ca2+ influx. In the presence of 100 microM quinine a 54% inhibition of the K(+)-induced Ca2+ influx was observed. 5. Quinine treatment of chromaffin cell cultures produced a small but significant decrease in membrane resting potential and a less pronounced depolarization in response to 50 mM K+. 6. The results suggest that the inhibition of the K(+)-evoked release of catecholamines produced by quinine is at least partly due to a decrease in Ca2+ influx. Ca2+ influx is lower because quinine reduces the sensitivity of the membrane potential to changes in extracellular K+ but direct effects of quinine on Ca2+ channels cannot be excluded.

Interactions between alpha-latrotoxin and trivalent cations in rat striatal synaptosomal preparations

The interactions between alpha-latrotoxin (alpha-LTx), a neurosecretagogue purified from the venom of the black widow spider, and the trivalent cations Al3+, Y3+, La3+, Gd3+, and Yb3+ were investigated in rat striatal synaptosomal preparations. All trivalent cations tested were inhibitors of alpha-LTx-induced [3H]dopamine [( 3H]DA) release (order of potency: Yb3+ greater than Gd3+ approximately Y3+ greater than La3+ greater than Al3+). Only with Al3+ could inhibition of [3H]DA release be attributed to a block of 125I-alpha-LTx specific binding to synaptosomal preparations. The inhibitory effect of trivalent ions was reversible provided synaptosomes were washed with buffer containing EDTA. Trivalent ions also inhibited alpha-LTx-induced [3H]DA release at times when alpha-LTx-stimulated release was already evident. alpha-LTx-induced synaptosomal membrane depolarization was blocked by La3+, but not affected by Gd3+, Y3+, and Yb3+. alpha-LTx-stimulated uptake of 45Ca2+ was inhibited by all trivalent cations tested. These results demonstrate that there exist at least three means by which trivalent cations can inhibit alpha-LTx action in rat striatal synaptosomal preparations: (1) inhibition of alpha-LTx binding (Al3+); (2) inhibition of alpha-LTx-induced depolarization (La3+); and (3) inhibition of alpha-LTx-induced 45Ca2+ uptake (Gd3+, Y3+, Yb3+, La3+).

Voltage-sensitive calcium flux into bovine chromaffin cells occurs through dihydropyridine-sensitive and dihydropyridine- and omega-conotoxin-insensitive pathways

The fluorescent Ca2+ indicator FURA-2 was used to characterize the depolarization-related intracellular Ca2+ signalling process in bovine adrenal chromaffin cells. Depolarization with high K+ (10-65 mM) gave rise to a very rapid increase in intracellular free Ca2+ concentration, which subsequently decayed slowly towards a "plateau". The size of this initial increase varied sigmoidally with the calculated membrane potential, the relationship being described well by a Boltzmann distribution function for a transition between two states (transition potential, -23 mV). A dihydropyridine calcium channel agonist [(+)202-791, 1 microM] raised intracellular free Ca2+ concentration further in the presence of 30 mM K+, and it enhanced the initial intracellular Ca2+ response to depolarization. Voltage-sensitive calcium channels in chromaffin cells are believed to include the L-type. Several dihydropyridine calcium channel antagonists [(-)202-791, nifedipine, nitrendipine; 1-5 microM], known to be active on L-type channels, caused only modest inhibition of K+ -induced increase in intracellular free Ca2+ concentration: c. 50% (at 30 mM K+) and 25% (at 40-70 mM K+). In addition, omega-conotoxin GVIA (1-10 microM), a blocker of neuronal N- and L-type calcium channels, reduced the initial increase in intracellular free Ca2+ concentration only slightly at 55 mM K+. Further, the dihydropyridine-insensitive component of the intracellular Ca2+ signal was also insensitive to omega-conotoxin, which was otherwise quite active in a central nervous rat in vivo preparation Gd3+ (40 microM), a potent calcium antagonist in the chromaffin cell, blocked the intracellular Ca2+ response to depolarization. When added at different times after K+ stimulation, however, Gd3+ reduced intracellular free Ca2+ concentration to control levels along a slow time course of several minutes. Similar results were obtained when EGTA was added to reduce extracellular Ca2+ concentration to sub-nanomolar levels, in the presence of high K+. We conclude that bovine chromaffin cells are equipped with at least two different classes of voltage-dependent calcium channels, only one of which is likely to be the L-type channel. We also propose that depolarization, in addition to stimulating Ca2+ influx, may also lead to enhancement of Ca2+ release from an intracellular store.

Some properties of the membrane currents underlying the fertilization potential in sea urchin eggs

1. The ionic currents that underly the fertilization potential of sea urchin eggs were studied in Lytechinus pictus using a single-electrode voltage clamp technique. 2. In unfertilized eggs, a transient inward current was activated at membrane potentials more positive than -45 mV. The maximum amplitude of the current was 0.56 +/- 0.35 nA (mean +/- S.D., n = 33) at a membrane potential of -35 to -25 mV. 3. The amplitude of this transient inward current was decreased by reducing the external concentration of calcium ions and by substituting barium or strontium ions for calcium in the external medium. Cobalt (10-20 mM) and gadolinium (200-500 microM) ions reduced the amplitude of this current in the presence of calcium ions. 4. A transient outward current was activated in unfertilized eggs at membrane potentials more positive than -10 mV. This current inactivates with a time constant of 16 ms at a membrane potential of -9 mV and re-activates over a period of several seconds at a membrane potential of -72 mV. 5. When unfertilized eggs were treated with the calcium ionophore A23187 under voltage clamp conditions, an inward current developed. It reached a maximum 30 s after its onset and declined thereafter. By 90 s it had become constant at 10% of its peak value. 6. The inward current induced by A23187 was voltage dependent. It was maximal at -25 mV in the steady state. 7. When eggs were fertilized under voltage clamp conditions, the fertilization current, If, was recorded. At a holding potential of -50 or -70 mV If had the following characteristics: (a) an initial inward shoulder with a duration ranging from 12 to 30 s; (b) an inward current peak that was attained between 40 and 100 s after the onset of the shoulder current and declined over the next 60 s; (c) an outward current that appeared after the inward current had declined. 8. Current-voltage relations obtained during If showed that the late component of the inward current was voltage dependent. It was maximal at -25 mV in the steady state and resembled the late component of the inward current recorded in A23187-activated eggs. 9. These results indicate that the form of the action potential in unfertilized eggs is due to the activation of a transient inward current and an inactivating outward current. The sustained depolarization after fertilization is due to the activation of a voltage-dependent inward current by the increase in intracellular free calcium concentration that occurs at fertilization.