In vivo measurement of lithium in humans by nuclear magnetic resonance spectroscopy

Modulation of Gq/PLC-Mediated Signaling by Acute Lithium Exposure

Although lithium has long been one of the most widely used pharmacological agents in psychiatry, its mechanisms of action at the cellular and molecular levels remain poorly understood. One of the targets of Li+ is the phosphoinositide pathway, but whereas the impact of Li+ on inositol lipid metabolism is well documented, information on physiological effects at the cellular level is lacking. We examined in two mammalian cell lines the effect of acute Li+ exposure on the mobilization of internal Ca2+ and phospholipase C (PLC)-dependent membrane conductances. We first corroborated by Western blots and immunofluorescence in HEK293 cells the presence of key signaling elements of a muscarinic PLC pathway (M1AchR, Gq, PLC-β1, and IP3Rs). Stimulation with carbachol evoked a dose-dependent mobilization of Ca, as determined with fluorescent indicators. This was due to release from internal stores and proved susceptible to the PLC antagonist U73122. Li+ exposure reproducibly potentiated the Ca response in a concentration-dependent manner extending to the low millimolar range. To broaden those observations to a neuronal context and probe potential Li modulation of electrical signaling, we next examined the cell line SHsy5y. We replicated the potentiating effects of Li on the mobilization of internal Ca, and, after characterizing the basic properties of the electrical response to cholinergic stimulation, we also demonstrated an equally robust upregulation of muscarinic membrane currents. Finally, by directly stimulating the signaling pathway at different links downstream of the receptor, the site of action of the observed Li effects could be narrowed down to the G protein and its interaction with PLC-β. These observations document a modulation of Gq/PLC/IP3-mediated signaling by acute exposure to lithium, reflected in distinct physiological changes in cellular responses.

Position sensitive measurement of trace lithium in the brain with NIK (neutron-induced coincidence method) in suicide

Mood disorder is the leading intrinsic risk factor for suicidal ideation. Questioning any potency of mood-stabilizers, the monovalent cation lithium still holds the throne in medical psychiatric treatment. Furthermore, lithium`s anti-aggressive and suicide-preventive capacity in clinical practice is well established. But little is still known about trace lithium distribution and any associated metabolic effects in the human body. We applied a new technique (neutron-induced coincidence method “NIK”) utilizing the ⁶Li(n,α)³H reaction for the position sensitive, 3D spatially resolved detection of lithium traces in post-mortem human brain tissue in suicide versus control. NIK allowed, for the first time in lithium research, to collect a three dimensional high resolution map of the regional trace lithium content in the non lithium-medicated human brain. The results show an anisotropic distribution of lithium, thus indicating a homeostatic regulation under physiological conditions as a remarkable link to essentiality. In contrast to suicide we could empirically prove significantly higher endogenous lithium concentrations in white compared to gray matter as a general trend in non-suicidal individuals and lower lithium concentrations in emotion-modulating regions in suicide.

The role of brain barriers in the neurokinetics and pharmacodynamics of lithium

Lithium (Li) is the most widely used mood stabilizer in treating patients with bipolar disorder. However, more than half of the patients do not or partially respond to Li therapy, despite serum Li concentrations in the serum therapeutic range. The exact mechanisms underlying the pharmacokinetic-pharmacodynamic (PK-PD) relationships of lithium are still poorly understood and alteration in the brain pharmacokinetics of lithium may be one of the mechanisms explaining the variability in the clinical response to Li. Brain barriers such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) play a crucial role in controlling blood-to-brain and brain-to-blood exchanges of various molecules including central nervous system (CNS) drugs. Recent in vivo studies by nuclear resonance spectroscopy revealed heterogenous brain distribution of Li in human that were not always correlated with serum concentrations, suggesting regional and variable transport mechanisms of Li through the brain barriers. Moreover, alteration in the functionality and integrity of brain barriers is reported in various CNS diseases, as a cause or a consequence and in this regard, Li by itself is known to modulate BBB properties such as the expression and activity of various transporters, metabolizing enzymes, and the specialized tight junction proteins on BBB. In this review, we will focus on recent knowledge into the role of the brain barriers as key-element in the Li neuropharmacokinetics which might improve the understanding of PK-PD of Li and its interindividual variability in drug response.

Accumulation of Lithium in the Hippocampus of Patients With Bipolar Disorder: A Lithium-7 Magnetic Resonance Imaging Study at 7 Tesla

BACKGROUND

Lithium (Li) is a first-line treatment for bipolar disorder (BD). To study its cerebral distribution and association with plasma concentrations, we used ⁷Li magnetic resonance imaging at 7T in euthymic patients with BD treated with Li carbonate for at least 2 years.

METHODS

Three-dimensional ⁷Li magnetic resonance imaging scans (N = 21) were acquired with an ultra-short echo-time sequence using a non-Cartesian k-space sampling scheme. Lithium concentrations ([Li]) were estimated using a phantom replacement approach accounting for differential T₁ and T₂ relaxation effects. In addition to the determination of mean regional [Li] from 7 broad anatomical areas, voxel- and parcellation-based group analyses were conducted for the first time for ⁷Li magnetic resonance imaging.

RESULTS

Using unprecedented spatial sensitivity and specificity, we were able to confirm the heterogeneity of the brain Li distribution and its interindividual variability, as well as the strong correlation between plasma and average brain [Li] ([Li]_B ≈ 0.40 × [Li]_P, R = .74). Remarkably, our statistical analysis led to the identification of a well-defined and significant cluster corresponding closely to the left hippocampus for which high Li content was displayed consistently across our cohort.

CONCLUSIONS

This observation could be of interest considering 1) the major role of the hippocampus in emotion processing and regulation, 2) the consistent atrophy of the hippocampus in untreated patients with BD, and 3) the normalization effect of Li on gray matter volumes. This study paves the way for the elucidation of the relationship between Li cerebral distribution and its therapeutic response, notably in newly diagnosed patients with BD.

Multinuclear MRI at Ultrahigh Fields

In this article, an overview of the current developments and research applications for non-proton magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHFs) is given. Due to technical and methodical advances, efficient MRI of physiologically relevant nuclei, such as Na, Cl, Cl, K, O, or P has become feasible and is of interest to obtain spatially and temporally resolved information that can be used for biomedical and diagnostic applications. Sodium (Na) MRI is the most widespread multinuclear imaging method with applications ranging over all regions of the human body. Na MRI yields the second largest in vivo NMR signal after the clinically used proton signal (H). However, other nuclei such as O and P (energy metabolism) or Cl and K (cell viability) are used in an increasing number of MRI studies at UHF. One major advancement has been the increased availability of whole-body MR scanners with UHFs (B0 ≥7T) expanding the range of detectable nuclei. Nevertheless, efforts in terms of pulse sequence and post-processing developments as well as hardware designs must be made to obtain valuable information in clinically feasible measurement times. This review summarizes the available methods in the field of non-proton UHF MRI, especially for Na MRI, as well as introduces potential applications in clinical research.

3D 7Li magnetic resonance imaging of brain lithium distribution in bipolar disorder

Lithium is a major treatment for bipolar disorder and the likelihood of a favourable response may be determined by its distribution in the brain. Lithium can be directly detected by magnetic resonance (MR), but previous 7Li MR spectroscopy studies have demonstrated that this is challenging compared to conventional 1H MR imaging due to the MR properties of the lithium nucleus and its low concentration in brain tissue, as dictated by therapeutic dose. We have tested and implemented a highly efficient balanced steady-state free precession 7Li-MRI method to address these challenges and enable MRI of brain lithium in a short duration scan. We report a 3D 7Li-MRI acquisition with 25 mm isotropic resolution in an 8-min scan that demonstrates heterogeneity in lithium concentration within the brain in subjects with bipolar disorder. This represents the direct imaging of a pharmaceutical agent in its target organ and notably expands the repertoire of techniques available to investigate the effects of lithium in man.

The toxic effect of lithium ion on neurons (PC12 cells) and Aβ42 molecules

In this study, the neurotoxicity of Li ion and its effect on the morphologies of Aβ42 molecules were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, fluorescence (FL), atomic force microscopy (AFM), and circular dichroism (CD) spectroscopy. MTT assays show that Li ion with a dosage level lower than 50 mg/l did not show detectable cytotoxicity on pheochromocytoma (PC12) cells whereas a dosage level higher than 100 mg/l resulted in significant cytotoxicity. The interaction between Aβ42 and Li ion occurs, and the quenching effect of Li ion on the fluorescence emission of AΒ42 is found to be concentration dependent, suggesting that Li ion can bind to the Aβ42 molecules. CD results suggest that a more incompact conformation state will be adopted upon the interaction between Aβ42 and Li ion. According to AFM images, Li ion could induce the formation of the fibrils after incubation for 3 or 5 days. The formation of the oligomer and fibrils originates from the strong interactions between Aβ42 and Li ion. Li ion could accelerate the random coil Aβ42 monomers aggregating into the β-sheet fibrils, which would induce the neurotoxic effect.

Research applications of magnetic resonance spectroscopy to investigate psychiatric disorders

Advances in magnetic resonance spectroscopy (MRS) methodology and related analytic strategies allow sophisticated testing of neurobiological models of disease pathology in psychiatric disorders. An overview of principles underlying MRS, methodological considerations, and investigative approaches is presented. A review of recent research is presented that highlights innovative approaches applying MRS, in particular, hydrogen MRS, to systematically investigate specific psychiatric disorders, including autism spectrum disorders, schizophrenia, panic disorder, major depression, and bipolar disorder.

Pharmacokinetics of lithium in rat brain regions by spectroscopic imaging

Lithium (Li) and its salts have been demonstrated to be the most effective drug in both acute and prophylactic treatment of bipolar disorder. The exact molecular mechanisms and particular target regions accounting for its mood-stabilizing effect remain unknown. Knowledge of Li distribution and its regional pharmacokinetic properties in the living brain is of value in localizing its action in the brain. Pharmacokinetic measurements in different anatomical regions of the human brain are not yet available. Limited pharmacokinetic measurements in rat brain subvolumes have been performed using atomic absorption technique. However, a noninvasive way of estimating the pharmacokinetics in different regions of the brain where the drug exerts its beneficial effects would allow such methods to be used in the study of patients undergoing Li therapy. Earlier (7)Li MR studies on rat brain regions have provided preliminary pharmacokinetic information from the whole brain. Using (7)Li MR spectroscopic imaging (SI) technology, Li distribution in brain regions of the rat at therapeutic dosages has been recently demonstrated by us. Here we report feasibility of local pharmacokinetic measurements on brain regions obtained by magnetic resonance SI technology. Our results suggest that Li is most active in a region stretching from the anterior cingulate cortex and striatum to the caudal midbrain, with greatest activity including the preoptic area and hypothalamic region. Some activity was seen in prefrontal cortex, but only minimal amounts in the region of the cerebellum and metencephalic brainstem.

Lithium and bipolar mood disorder: the inositol-depletion hypothesis revisited

Inositol, a simple six-carbon sugar, forms the basis of a number of important intracellular signaling molecules. Over the last 35 years, a series of biochemical and cell biological experiments have shown that lithium (Li(+)) reduces the cellular concentration of myo-inositol and as a consequence attenuates signaling within the cell. Based on these observations, inositol-depletion was proposed as a therapeutic mechanism in the treatment of bipolar mood disorder. Recent results have added significant new dimensions to the original hypothesis. However, despite a number of clinical studies, this hypothesis still remains to be either proven or refuted. In this review of our current knowledge, I will consider where the inositol-depletion hypothesis stands today and how it may be further investigated in the future.

Lithium spectroscopic imaging of rat brain at therapeutic doses

Since the discovery that lithium (Li) is efficacious for the treatment of manic depressive illness, the brain Li distribution of mammals treated with lithium has been of interest. However, the spatial relationship of lithium in the brain regions to its function remains largely unknown. Knowledge of Li distribution in the brain is necessary to localize its action in the brain. Both the therapeutic and neurotoxic side effects of Li are centered mainly in the central nervous system and hence there is considerable interest in understanding the extent of lithium penetration into the central nervous system. The mechanism by which neurotoxic side effects are generated is not known and may, in part, be related to the particular distribution of lithium in the brain. The regional specificity in lithium's brain distribution could underlie important steps on its action. Li levels in various brain regions for autopsied rats and humans have been reported. However, many results are conflicting due to ion redistribution at death or during sample preparation. A direct nondestructive measurement of Li levels in the brain where the drug exerts its effects is certainly desirable. Because magnetic resonance technique can be used to observe Li, it can be an appropriate method to monitor and map the distribution in the brain. The application of MR technology to rat brain regions has provided information on lithium distribution in a non-invasive manner. The earlier development work at lower field strengths provided brain lithium information at high dose of Li administration. Here we demonstrate the feasibility of quantitative spectroscopic imaging on rat brain under therapeutic doses.

Biological predictors of lithium response in bipolar disorder

In order to prescribe lithium appropriately to patients with bipolar disorder, predictors of lithium response are helpful. The present paper reviews the biological predictors of lithium response. As a positive predictor of lithium response, the following have been reported: strong loudness dependence of the auditory-evoked N1/P2-response; higher brain lithium concentration; lower inositol monophosphatase (IMPase) mRNA expression; higher serotonin-induced calcium mobilization; increased N-acetyl-aspartate peak and decreased myo-inositol peak; white matter hyperintensity; decreased intracellular pH; higher frequency of phospholipase C gamma-1 (PLCG1)-5 repeat and PLCG1-8 repeat; and C973A polymorphism in the inositol polyphosphate 1-phosphatase gene. In contrast the following have been reported as a predictor of negative lithium response: epileptiform abnormality of electroencephalography; human leukocyte antigen type A3; decreased phosphocreatine peak area after photic stimulation; and homozygotes for the short variant of the serotonin transporter gene. Most of the possible biological predictors of better lithium response, such as lower IMPase mRNA levels, white matter hyperintensity, lower brain intracellular pH, enhanced calcium response, and PLCG1-5 repeat had been detected as risk factors for bipolar disorder, suggesting that bipolar disorder responding well to maintenance lithium treatment is a distinct category having a certain neurobiological basis, although these findings need further replication. The search for biological predictors of lithium response is still in its infancy. Most of the laboratory or neuroimaging techniques used in these studies are not easily performed in clinical settings, so the development of an easy and useful laboratory test is needed.

Effect of chronic Li+ treatment on free intracellular Mg2+ in human neuroblastoma SH-SY5Y cells

OBJECTIVES

Previous findings have demonstrated Li+/Mg2+ competition at therapeutic intracellular Li+ levels after acute Li+ treatment in human neuroblastoma SH-SY5Y cells. In the current study, we examined whether Li+/Mg2+ competition exists at therapeutically relevant extra- and intracellular [Li+] after chronic Li+ loading times.

METHODS

In human neuroblastoma cells, intracellular free Mg2+ was determined by fluorescence spectroscopy with the fluorophore furaptra. Intracellular Li+ and Mg2+ were measured by atomic absorption spectrophotometry.

RESULTS

After loading of the neuroblastoma cells with 1-2 mM extracellular Li+ for 24-72 h, the observed, increased intracellular free [Mg2+] levels were significantly higher (p < 0.03) than those in matched Li+ free cells, and intracellular [Li+] was found to be at therapeutic intracellular levels (0.7-1.5 mM).

CONCLUSIONS

The results demonstrate that Li+/Mg2+ competition exists after chronic treatment with Li+ at therapeutically relevant intracellular Li+ levels in neuroblastoma cells. We found differences between acute and chronic Li+ treatment effects on the extent of Li+/Mg2+ competition. Possible reasons for these differences are discussed.

Pharmacokinetic imaging: a noninvasive method for determining drug distribution and action

Advances in positron emission tomography (PET), single photon emission computed tomography (SPECT) and magnetic resonance spectroscopy (MRS), and the ability to label a wide variety of compounds for in vivo use in humans, have created a new technology for making precise physiological and pharmacological measurements. Due to the noninvasive nature of these approaches, repetitive and/or continuous measurements have become possible. Thus far, these techniques have been primarily used for one-time assessments of individuals. However, experience suggests that a major use of this technology will be in the evaluation of new drug therapies. Already, these techniques have been used to measure precisely and noninvasively the pharmacokinetics of a variety of antimicrobial, antineoplastic and CNS agents. In the case of CNS drugs, imaging techniques (particularly PET) have been used to define the classes of neuroreceptors with which the drug interacts. The physiological, pharmacological and biochemical measurements that can be performed noninvasively using modern imaging techniques can greatly facilitate the evaluation of new therapies. These measurements are most likely to be useful during drug development in preclinical studies and in phase I/II human studies. Preclinically, new drugs can be precisely compared with standard therapies, or a series of analogues can be screened for further development on the basis of performance in animal models. In Phase I/II, imaging measurements can be combined with classical pharmacokinetic data to establish optimal administration schedules, evaluate the utility of interventions in specific clinical situations, and aid in the design of Phase III trials.

Can brain-imaging studies provide a 'mood stabilizer signature?'

Brain-imaging investigations have attempted to characterize the neurobiological basis of bipolar disorder. Preliminary studies have also focused on in vivo brain correlates of treatment response with antidepressants, mood stabilizers and other psychotropic medications. A MEDLINE literature search was conducted dating back to 1966. Selected in vivo brain-imaging studies that examined neurobiological correlates of treatment response in mood disorder patients were identified. Discrete anatomical abnormalities in subregions of the prefrontal cortex, medial temporal lobe and cerebellum have been identified in bipolar patients. Functional imaging studies suggested abnormalities in particular brain circuits encompassing these same brain regions and the striatum. However, functional imaging correlates of treatment response with lithium or other mood stabilizers have not yet been characterized. Neurochemical studies suggested a reduction in N-acetyl aspartate levels in prefrontal cortex and abnormalities in membrane phospholipids in frontal and temporal lobes. Preliminary findings suggest that lithium may increase the gray matter content and N-acetyl aspartate levels in various cortical regions, which could reflect its putative neurotrophic effects. Few in vivo receptor-imaging studies have examined brain correlates of treatment response in bipolar patients. The available studies suggest anatomical, neurochemical and functional brain abnormalities in bipolar patients. However, in vivo brain correlates of treatment response with mood stabilizers in bipolar patients have not yet been well characterized.

Magnetic resonance spectroscopy: current and future applications in psychiatric research

Magnetic resonance spectroscopy (MRS) provides a useful method for studying a number of psychotropic medications and metabolites in human brain in vivo. New insights regarding the pharmacokinetic and pharmacodynamic properties of psychotropic medications in the target organ (i.e., brain) have been obtained using lithium-7 MRS and fluorine-19 MRS. Both proton and phosphorus-31 MRS have significantly enhanced our knowledge of the pathophysiology of a number of psychiatric disorders by providing estimates of brain concentrations of several important cerebral metabolites. Efforts are also being made to link MRS measures of cerebral metabolism with neurophysiologic and neurocognitive processes. Ongoing improvement and refinement in MRS techniques, including the installation of scanners with increased magnetic field strength and better methods of data processing, will improve both spatial and temporal resolution. In addition, efforts to develop multisite research studies may result in greater standardization of MRS procedures and methods for interpretation of results. In this review, the current status of MRS applications in psychiatric research is reviewed, and new frontiers and possible future developments are discussed.

7Li 2D CSI of human brain on a clinical scanner

Lithium salts have been widely used in the treatment of mood disorders, but the mechanism of action is still not clear. In this work, a methodology for two-dimensional Lithium-7 imaging on clinical systems is presented. The data were acquired using a phosphorus volume head coil that was re-tuned for the Lithium-7 frequency. A spectroscopic sequence was used to acquire the free induction decay (FID) after volume excitation using a hard pulse. The results obtained on the head of patients undergoing lithium treatment (n = 7, 0.6 mEq/l average serum level) demonstrate that images of adequate signal to noise ratio (100:1) can be obtained in acceptable imaging times (55 min) using the proposed methodology. The distribution of 7Li appears uniform in the brains of the patients studied.

Brain lithium concentrations in bipolar disorder patients: preliminary (7)Li magnetic resonance studies at 3 T

BACKGROUND

This study was conducted to investigate the feasibility of human brain (7)Li MRS investigations at a high magnetic field (3 T), and to further explore the relationship between brain and serum lithium measures in lithium-treated bipolar patients.

METHODS

Eight bipolar disorder type I patients (5 males, 3 females; mean age +/- SD = 33 +/- 9 years) were studied. A 3-T scanner, using a dual-tuned ((1)H and (7)Li) echoplanar imaging (EPI) compatible radiofrequency (RF) birdcage coil was used. (7)Li magnetic resonance spectroscopy (MRS) signal was acquired at the frequency of 49.64 MHz using an imaging selective in vivo spectroscopy (ISIS) sequence (TR = 15 sec, 128 averages), and quantitation was obtained in reference to an external standard.

RESULTS

The mean +/- SD oral lithium dose was 1265 +/- 442 mg/day, and the mean +/- SD 12-hour serum level was 0.69 +/- 0.19 mEq/L. The measured brain lithium concentrations varied from 0.23 to 0.55 mEq/L (mean +/- SD = 0.35 +/- 0.11 mEq/L). The brain-serum ratios varied from 0.30 to 0.80 (mean +/- SD = 0.52 +/- 0.16). Subjects on single daily doses of lithium at bedtime (n = 5) had higher brain-serum lithium ratios compared with those on twice-a-day schedules (n = 3) (0.61 +/- 0.12 and 0.37 +/- 0.07, respectively; Mann--Whitney U test, Z = -2.24, p =.03).

CONCLUSIONS

This study demonstrated for the first time the feasibility of (7)Li MRS human studies at 3 T. Future studies should examine a possible role for this methodology in investigations of lithium refractoriness and prediction of treatment outcome in bipolar patients.

Brain lithium measurements with (7)Li magnetic resonance spectroscopy (MRS): a literature review

7Li magnetic resonance spectroscopy (MRS) has been successfully used in recent years as a new tool to measure brain tissue lithium concentrations in vivo. After demonstration of its feasibility in animal studies over a decade ago, human investigations have characterized the brain pharmacokinetics of lithium. Preliminary studies have investigated brain pharmacokinetic correlates of clinical response in the treatment of bipolar disorder patients, with indication of possible clinical relevance of 7Li MRS measures. In this paper we reviewed the accumulated literature in this area, and discuss possible directions for this research in the context of preliminary studies conducted by our group that demonstrated the feasibility of 7Li MRS at 3 T.

Applications of (7)Li NMR in biomedicine

The applications of (7)Li NMR spectroscopy and imaging in biology and experimental medicine have been progressing steadily. The interest derives primarily from the clinical use of Li salts to treat mania and manic-depressive illness. One area of investigation is ionic transport across the cellular membrane and compartmentation, so as to elucidate the mechanism(s) of therapeutic action and toxicity in clinical practice. The second is the development of a noninvasive, in vivo analytical tool to measure brain Li concentrations in humans, both as an adjunct to treatment and as a mechanistic probe. Here we review progress to date in this area.

Lithium distribution in red blood cells and plasma: NMR studies of rat blood

To understand the interaction of lithium (Li+) with a coadministered drug in both the blood and the brain, we have treated rats with either Li+ alone or Li+ and a codrug. In this paper we address the important problem of quantitation of intra and extracellular Li+ ion contents in blood by the 7Li-NMR technique and the use of a shift reagent (SR). Although Li+ can be studied by atomic absorption techniques, these techniques involve tedious separation of intra- and extracellular components prior to chemical analysis. Magnetic resonance studies on rat blood, in the dose range of 0.5 to 10 meq/kg, indicate that the intracellular red blood cell Li+ predominates in the lower dose range of 0.5-1.0 meq/kg. As the lithium dose increases, a significantly larger amount of Li+ accumulates in the extracellular volume. Our studies on a number of animals at various doses of LiCl indicate that 7Li-NMR of blood samples provide a reliable, noninvasive quantification of red blood cell and plasma Li+ concentrations. The NMR method was further used to study the effect of coadministered drugs such as thioridazine on the intra- and extracellular Li+ concentration of RBCs.

Neuroimaging and neuropsychology of the striatum. Bridging basic science and clinical practice

Neuroimaging and neuropsychology are complementary disciplines that provide powerful means for assessing the structure and function of corticostriatal systems. Findings from four model basal ganglia disorders--OCD, TS, HD, and PD--are reviewed. This survey is intended as a vehicle for illustrating the breadth of current clinical and research applications, as well as the potential for future advances. The perspectives brought by neuroimaging and neuropsychology serve as a natural bridge from the basic neuroscience to the clinical practice articles in this issue.

Duration of lithium treatment and brain lithium concentration in patients with unipolar and schizoaffective disorder--a study with magnetic resonance spectroscopy

Twenty psychiatric patients on lithium medication were examined with 7-Li-magnetic resonance spectroscopy of the brain. Patients on long-term lithium treatment (> 6 months) were compared with a short-term group who had been taking lithium for between 4 and 8 weeks. Patients met DSM-III-R criteria for either recurrent unipolar depressive disorder (DSM-III-R 296.3x) or schizoaffective disorder, depressive type (DSM-III-R 295.70). The brain:serum lithium ratio was 0.76 +/- 0.26; there was no significant difference between short-term and long-term treatment. In the group of long-term treatment patients there was a positive correlation between lithium dose per day and brain lithium concentration (R = .72, p < .01), and between lithium plasma concentration and brain lithium concentration (R = .65, p < .05). In the short-term group, however, there was no significant correlation for these parameters. No differences between unipolar and schizoaffective disorder were found.

Lithium and neuroleptics in combination: is there enhancement of neurotoxicity leading to permanent sequelae?

Neurotoxicity in relation to concomitant administration of lithium and neuroleptic drugs, particularly haloperidol, has been an ongoing issue. This study examined whether use of lithium with neuroleptic drugs enhances neurotoxicity leading to permanent sequelae. The Spontaneous Reporting System database of the United States Food and Drug Administration and extant literature were reviewed for spectrum cases of lithium/neuroleptic neurotoxicity. Groups taking lithium alone (Li), lithium/haloperidol (LiHal) and lithium/ nonhaloperidol neuroleptics (LiNeuro), each paired for recovery and sequelae, were established for 237 cases. Statistical analyses included pairwise comparisons of lithium levels using the Wilcoxon Rank Sum procedure and logistic regression to analyze the relationship between independent variables and development of sequelae. The Li and Li-Neuro groups showed significant statistical differences in median lithium levels between recovery and sequelae pairs, whereas the LiHal pair did not differ significantly. Lithium level was associated with sequelae development overall and within the Li and LiNeuro groups; no such association was evident in the LiHal group. On multivariable logistic regression analysis, lithium level and taking lithium/haloperidol were significant factors in the development of sequelae, with multiple possibly confounding factors (e.g., age, sex) not statistically significant. Multivariable logistic regression analyses with neuroleptic dose as five discrete dose ranges or actual dose did not show an association between development of sequelae and dose. Database limitations notwithstanding, the lack of apparent impact of serum lithium level on the development of sequelae in patients treated with haloperidol contrasts notably with results in the Li and LiNeuro groups. These findings may suggest a possible effect of pharmacodynamic factors in lithium/neuroleptic combination therapy.

Chronic lithium does not alter human myo-inositol or phosphomonoester concentrations as measured by 1H and 31P MRS

Lithium may act by decreasing intracellular concentrations of myo-inositol. The present study measured the effects of chronic lithium on myo-inositol concentrations in volunteers. Eleven subjects received either lithium (n = 7) or placebo (n = 4) for 7 days in a double-blind study. Myo-inositol concentrations at baseline and day 8 were measured in vivo using 1H magnetic resonance spectroscopy (MRS). The results showed that lithium did not alter brain myo-inositol concentrations compared to placebo. In 5 other subjects we used 1H MRS and 31P MRS to measure changes in both myo-inositol and phosphomonoester concentrations. This second study showed that lithium did not alter myo-inositol or phosphomonoester concentrations. Thus, the present studies do not support the hypothesis that lithium significantly affects the brain concentrations of myo-inositol or phosphomonoesters; however, it is possible these findings represent an inability to detect the changes in myo-inositol and phosphomonoester concentrations that may have occurred following lithium administration.

Twelve-hour brain lithium concentration in lithium maintenance treatment of manic-depressive disorder: daily versus alternate-day dosing schedule

The 12-h brain lithium concentration was measured by lithium-7 magnetic resonance spectroscopy in ten manic-depressive patients receiving daily or alternate-day lithium carbonate treatment. The median dose of lithium carbonate was 800 mg in the daily treatment group and 1200 mg in the alternate-day group. Median 12-h serum lithium concentration in the two groups was 0.86 mmol l-1 and 0.55 mmol l-1, respectively, while the corresponding concentration in brain was 0.67 mmol l-1 and 0.52 mmol l-1, respectively. The 12-h brain lithium concentration was independent of lithium dosing schedule (multiple linear regression), but correlated significantly with the 12-h serum lithium concentration (P = 0.003; B = 0.53, 95% c.l. 0.24-0.82; beta = 0.83). Thus at identical 12-h serum lithium concentrations the 12-h brain lithium concentration is similar with both treatment regimes. As the risk of manic-depressive relapse during alternate-day lithium treatment is in our experience 3-fold greater than with daily treatment (at similar mean 12-h serum lithium concentration), the findings suggest that the difference in the prophylactic efficacy of the two dosing schedules is unrelated to differences in the 12-h brain lithium concentration.

Lithium side effects in relation to brain lithium concentration measured by lithium-7 magnetic resonance spectroscopy

1. The relationship between lithium (Li) side effects and brain Li concentration was examined in 17 patients with bipolar disorder treated with Li and other psychotropic drugs. 2. Brain Li concentration was measured by Li-7 magnetic resonance spectroscopy (MRS). Side effects were assessed using the UCLA General Side Effect Rating Scale For Lithium Treatment (GSE). 3. There was no correlation between the total GSE score and the brain, serum, or erythrocyte Li concentrations. Patients with hand tremor had significantly higher brain Li level (0.51 + or - 0.27 mM) than those without apparent tremor (0.36 + or - 0.20 mM), but no significant difference in serum Li level was seen. As far as the patients had hand tremor, they rarely had brain Li concentration less than the therapeutic range (1 of 15 measurement). On the other hand, they often had brain Li levels less than the therapeutic range when they did not have apparent tremor (13 of 52 measurements). 4. This preliminary study suggests that hand tremor is associated with the brain Li concentration.

Variability of brain lithium levels during maintenance treatment: a magnetic resonance spectroscopy study

In vivo magnetic resonance spectroscopy (MRS) was used to determine the relationship between serum and brain lithium levels in bipolar patients (n=25). Over the broad range of serum lithium levels observed, the correlation (r=.68) with brain lithium levels was high. This correlation was much weaker (r=.39) when limited to only those patients with serum lithium levels in the range of 0.6-1.0 mmol/l. This variability may account for failure of lithium prophylaxis in some patients who have serum lithium levels in the therapeutic range.

24-hour lithium concentration in human brain studied by Li-7 magnetic resonance spectroscopy

Brain and serum lithium concentrations were measured every second hour during a 24-hr period following lithium intake, and again 48-hr later in two normal subjects in steady state lithium treatment receiving lithium carbonate (Priadel Synthelabo) once every evening. The brain-lithium concentration was measured by 7Li magnetic resonance spectroscopy (MRS). The brain lithium level was found to undulate in a peak-trough pattern that followed the serum lithium profile, although in an attenuated form. The brain/serum lithium concentration ratio varied considerably during the 48-hr period, ranging from 0.5 to 1.3, but the ratio was independent of the serum-lithium concentration. The median half-life for lithium was 28 hr in the brain, and 16 hr in serum. The brain lithium concentration in the morning was about 75% of the clinically relevant standard 12-hr serum lithium concentration. The finding that brain lithium undulates during the day means that MRS measurements of brain lithium can only be compared if carried out under standard conditions that include a fixed interval following lithium intake and an identical treatment regimen.

In vivo 7Li NMR diffusion studies in rat brain

Lithium (Li) is widely used for the treatment of several psychiatric disorders and is the drug of choice in the treatment of bipolar disorders. The mechanism of action of Li, however, is unknown. A knowledge of brain Li concentration, its distribution in the brain, and its properties in the cellular microenvironments may contribute significantly towards the understanding of its function. We recently demonstrated by in vivo 7Li NMR the distribution and pharmacokinetics of Li ion in rat brain. We have made diffusion measurements of Li in the head and brain regions of anesthetized rats using the localized STEAM (stimulated echo acquisition mode spectroscopy) technique suitably sensitized to diffusion. In this paper we demonstrate for the first time the feasibility of Li diffusion measurements in the mammalian brain model with the ultimate goal of performing such studies on humans under Li therapy.

In vivo 7Li nuclear magnetic resonance study of lithium pharmacokinetics and chemical shift imaging in psychiatric patients

New data are presented on the application of 7Li in vivo nuclear magnetic resonance (NMR) spectroscopy to human studies. The technique was used to monitor the between-dose pharmacokinetics of lithium (Li) in brain for three patients on Li therapy. Brain Li concentrations were at their highest from 0 to 2 hours after the peak occurred in serum concentration. Elimination from brain tissue took longer than elimination from muscle, and no signal could be detected from brain at 10 days after termination of therapy. A birdcage radiofrequency coil for 7Li was constructed and used to measure the 7Li spin-lattice relaxation time of 4.6 seconds in vivo in human head, and to acquire preliminary spectroscopic images of a phantom and human brain.

Brain lithium concentrations measured with lithium-7 magnetic resonance spectroscopy in patients with affective disorders: relationship to erythrocyte and serum concentrations

Brain lithium concentrations were measured in eight patients with affective disorders using lithium-7 magnetic resonance spectroscopy (MRS). Brain lithium concentrations correlated better with serum concentrations (n = 23, r = 0.66, p < 0.001) than with erythrocyte concentrations (r = 0.44, p < 0.05). Because of previous data in animal experiments these results were unexpected, but the differences in cation transport mechanisms between neurons and erythrocytes may account for the results.

Alterations in brain phosphorous metabolism in bipolar disorder detected by in vivo 31P and 7Li magnetic resonance spectroscopy

Phosphorus-31 magnetic resonance spectroscopy (MRS), able to detect membrane metabolism and intracellular pH as well as energy metabolism in vivo, was applied to 17 bipolar patients in the manic state and the euthymic state. In nine of these patients, brain lithium concentration was simultaneously determined by means of lithium-7 MRS in order to clarify the effect of treatment with lithium on brain phosphorous metabolism. Both phosphomonoester (PME) peak area and intracellular pH were found to be higher in the manic state than in the euthymic state. These values in the euthymic state were lower than those in normal controls whose ages and sexes were matched with the patients. However, PME and intracellular pH did not correlate to brain lithium concentration. These findings coincide with a hypothesis that patients with bipolar disorder may have membrane abnormality in their euthymic state and state-dependent alteration of catecholaminergic activity may be a secondary phenomenon.

Relaxation times and concentrations of 7Li in the brain of patients receiving lithium therapy

The present study describes a protocol for the determination of in vivo absolute molar concentrations of Li+ in the human brain using a double tuned 1H/7Li surface coil. The protocol follows the method of Thulborn and Ackerman [J. Mag. Reson. 55, 357-371 (1983)] where the ratio of the signal intensities of 7Li and 1H in the brain is compared to the same ratio in a phantom containing known concentrations of Li+. The 7Li T1 values in the brains of five patients receiving lithium therapy were measured. The average result was T1 = 3.5 +/- 0.25 s. The phantom solution was adjusted to have this T1 value. The protocol was applied for eight bipolar patients receiving lithium therapy. The average ratio of brain to serum lithium molar concentration was found to be 0.59 +/- 0.12.

MRS detection of whole brain lactate rise during 1 M sodium lactate infusion in rats

Proton magnetic resonance spectroscopy (1H MRS) performed in vivo on nine Sprague Dawley rats detected a threefold increase in whole brain lactate during intravenous 1 mol/L sodium lactate infusion. Significant increases in whole brain lactate were detected within 5 min after starting lactate infusion, progressively rose to a maximum level estimated at 3.2 +/- 1.5 mmol/L (all values +/- SD) immediately postinfusion, then decreased towards baseline levels during the next hr. Venous lactate concentration, increasing from 2.3 +/- 2.4 mmol/L to 43.0 +/- 8.0 mmol/L during the infusion, exhibited a steeper rise and then decreased more rapidly in comparison to changes in whole brain lactate. These data suggest MRS can be used in vivo to study acute changes in brain lactate associated with increasing blood lactate concentrations.

Magnetic resonance spectroscopy: a powerful tool for drug metabolism studies

Studies on the metabolism and disposition of drugs using nuclear magnetic resonance spectroscopy (MRS) as the analytical technique are reviewed. An overview of the main studies classed in terms of the observed magnetic nucleus (1H, 2H, 7Li, 13C, 19F, 31P, 77Se) is followed by some typical examples of the way in which 19F and 31P MRS can be profitably employed to gain more understanding about the metabolism and disposition of the anticancer fluoropyrimidines (5-fluorouracil (FU) and its prodrugs) and ifosfamide (IF). The results of three recent studies carried out in our laboratory are developed. They concern the direct quantitative monitoring of the hepatic metabolism of FU in the isolated perfused mouse liver, the elucidation of the origin of the cardiotoxicity of FU and the metabolism of IF from an analysis of biofluids of patients. Finally, the advantages and limitations of MRS for investigations on drug metabolism are discussed.

In vivo 7Li NMR imaging and localized spectroscopy of rat brain

Lithium-7 in vivo NMR spectroscopy and imaging techniques have been developed at 4.7 T for rat head. The pharmacokinetics of lithium (Li) uptake in rat head has been measured using STEAM localized spectroscopy for the whole brain, which showed relatively rapid uptake of Li and a steady level of Li from about 5 to 20 h. Localized spectroscopy on brain sections revealed no differences in Li concentration among the front, middle, and rear of the brain. The spin-lattice relaxation time showed a single exponential decay for the head. The spin-spin relaxation time for head showed a biexponential behavior. Using a 1H-7Li double coil assembly, 7Li images were generated for rat head, as was the corresponding 1H image for anatomic localization. The 7Li image (7-mm slice thickness, 4-mm in-plane resolution) recorded after the last dose in a multiple ip dose protocol shows the Li distribution in the head and neck. Based on 7Li images, the Li level in muscle was about twice that in the brain. Variations of 7Li intensity level across the brain were typically small.

Brain lithium concentration by 7Li- and 1H-magnetic resonance spectroscopy in bipolar disorder

A method was developed to measure lithium concentrations in the human brain using in vivo 7Li- and 1H-magnetic resonance spectroscopy (MRS). Lithium concentrations measured by MRS in 10 lithium-treated bipolar patients were at the half level of those measured in serum. Serial measurements indicated that lithium concentrations in the brain increased markedly during manic episodes, while serum concentrations were unchanged. These findings suggest that in vivo measurements of lithium concentrations in the brain, combined with measurements of concentrations in serum, may be useful in monitoring the effects of therapeutic drugs.

Lithium and the phosphoinositide cycle: an example of uncompetitive inhibition and its pharmacological consequences

The ability of lithium to exert profound and selective psychopharmacological effects to ameliorate manic-depressive psychosis has been the focus of considerable research effort. There is increasing evidence that lithium exerts its therapeutic action by interfering with polyphosphoinositide metabolism in brain and prevention of inositol recycling by an uncompetitive inhibition of inositol monophosphatase. Stefan Nahorski, Ian Ragan and John Challiss discuss this unusual stimulus-dependent form of enzyme inhibition, emphasizing that the selectivity exhibited by lithium depends upon the degree of inositol lipid hydrolysis and polyphosphoinositide dephosphorylation.

A 7Li NMR study of visibility, spin relaxation, and transport in normal human erythrocytes

The behavior of the lithium (Li) ion in normal human erythrocytes has been studied by 7Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular 7Li spin-lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus, T1 may not be useful for separate observation of intra- and extracellular Li in vivo. The intra- and extracellular T2s were substantially shorter than the corresponding T1s. Also, the intracellular T2 was considerably shorter than that for the extracellular compartment, suggesting that T2 may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra- and intracellular 7Li, confirming that dipolar coupling to 1H is a contributing relaxation mechanism. The 7Li NMR visibility was essentially 100% at high Li concentrations, decreasing to about 84% at 1 mM Li. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra- and extracellular compartments for packed cells is the same. Although a 23Na double-quantum signal could be observed for red blood cells, no double-quantum signal was observed for 7Li.

Lithium-induced decrease of brain inositol and increase of brain inositol-1-phosphate is transient

The effects of a single dose of LiCl (2.5 or 10 mEq/kg) on brain inositol and inositol-1-phosphate (Ins1P), intermediates of brain phosphoinositide (PI) turnover, were determined in male Han: Wistar rats. There was a remarkable, 36-58 fold elevation of brain Li+ as the single dose of LiCl was increased 4-fold. Moreover, the accumulation of brain lithium was slow during repeated administration of LiCl. Brain lithium did not correlate with changes in brain PI turnover either after a single or repeated doses. Thus, after a single dose of LiCl the increases in brain Ins1P were much less than the decreases in brain inositol. Also, brain inositol was significantly decreased only with the high dose of LiCl whereas brain Ins1P accumulation was more prominent with the lower dose. Moreover, repeated daily doses of LiCl only transiently increased brain Ins1P at 1 and 7 d whereas inositol remained at control levels throughout the 14 d observation period. Lithium probably caused the transient decrease in brain inositol by inhibiting several enzymes, in addition to the inhibition of myo-inositol mono-phosphates, in the PI cycle. Moreover, a slow dampening down of PI turnover by lithium, possible via an inhibitory action on G-protein-coupling, may also explain the present findings.

Measurement of tissue lithium concentration by lithium magnetic resonance spectroscopy in patients with bipolar disorder

Measurements of the lithium concentration in the occipital pole of the head and calf muscle of nine patients with bipolar disorder in remission were performed using in vivo lithium-7 nuclear magnetic resonance spectroscopy (7Li NMR). 7Li NMR measurements were performed on a 1-m-bore, 1.85-T, superconducting magnet supplemented with a multinuclear spectrometer, using 11.5-cm-diameter surface coils. The average lithium concentration in the occipital pole was 0.36 +/- 0.10 mEq/L, whereas in the muscle it was 0.50 +/- 0.17 mEq/L, both lower than the average serum lithium concentration (0.79 +/- 0.23 mEq/L). The average brain/serum lithium concentration ratio was 0.47 +/- 0.12 whereas the average muscle/serum lithium concentration ratio was 0.66 +/- 0.20. There was a positive correlation between the brain versus serum and brain versus muscle lithium concentrations. The hypothesis is advanced that the minimal effective concentration of brain lithium concentration for maintenance treatment of bipolar disorder is around 0.2-0.3 mEq/L.