Relevance of red blood cell Lithium concentration in the management of Lithium-treated bipolar and unipolar disorders: a systematic narrative review

BACKGROUND

Despite a variability in response and a narrow therapeutic index, Lithium (Li) remains the gold standard treatment for bipolar disorders (BD), and a treatment of choice for unipolar disorders (UD). Red blood cell Li concentration (RBCLiC) and red blood cell/plasma Li ratio (LiR) have been studied in many areas of mood disorders (such as acute or chronic Li efficacy, adherence, side effects (SE), intoxication management) as well as in several research domains. This systematic review aims to synthesize the existing literature.

METHODS

We conducted a systematic review, based on preferred reporting items for systematic reviews and Metanalysis (PRISMA) guidelines, of articles published between 1972 and February 2023, indexed in the following databases: EMBASE, MEDLINE, Cochrane Library. The search terms were combinations of the following headings: "Lithium AND Plasma AND Erythrocyte AND Mood disorders". The systematic review protocol was published to PROSPERO (CRD42023406154).

RESULTS AND CONCLUSION

Out of the 252 identified studies, 57 met the selection criteria. The articles investigated the interest of RBCLiC and other blood parameters (PLiC and LiR) in various areas: (i) disease management (31 articles) (compliance/adherence (5 articles), SE/toxicity (13 articles), prediction of Li response/therapeutic efficacy for acute episode or for relapse prevention (17 articles)), (ii) Li blood parameters as trait markers of mood disorders subtypes (UD, BDI, BDII) (16 articles), (iii) Li blood parameters as state markers of mood episodes (11 articles), (iv) factors influencing Li blood parameters (age, gender, ethnicity, dosage and duration of Li treatment, co-medications with other treatments, seasonality) associated with RBCLiC or LiR (24 articles), and (v) potential pathophysiological mechanisms (30 articles).

CONCLUSION

Overall, this review suggests that RBCLiC or LiR could be of interest for tolerance monitoring. However, the heterogeneity of methods and results, coupled with the limited amount of data, does not allow clear conclusions to be drawn in the other areas explored in this literature review. Given the potential interest in exploring brain Li pharmacokinetics (PK)s, this review calls for further research.

Intracellular effects of lithium in aging neurons

Lithium therapy received approval during the 1970s, and it has been used for its antidepressant, antimanic, and anti-suicidal effects for acute and long-term prophylaxis and treatment of bipolar disorder (BPD). These properties have been well established; however, the molecular and cellular mechanisms remain controversial. In the past few years, many studies demonstrated that at the cellular level, lithium acts as a regulator of neurogenesis, aging, and Ca2+ homeostasis. At the molecular level, lithium modulates aging by inhibiting glycogen synthase kinase-3β (GSK-3β), and the phosphatidylinositol (PI) cycle; latter, lithium specifically inhibits inositol production, acting as a non-competitive inhibitor of inositol monophosphatase (IMPase). Mitochondria and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) have been related to lithium activity, and its regulation is mediated by GSK-3β degradation and inhibition. Lithium also impacts Ca2+ homeostasis in the mitochondria modulating the function of the lithium-permeable mitochondrial Na+-Ca2+exchanger (NCLX), affecting Ca2+ efflux from the mitochondrial matrix to the endoplasmic reticulum (ER). A close relationship between the protease Omi, GSK-3β, and PGC-1α has also been established. The purpose of this review is to summarize some of the intracellular mechanisms related to lithium activity and how, through them, neuronal aging could be controlled.

Patterns of ingestion of rats during chronic oral administration of lithium chloride

Chronic lithium administration to rodents is used to explore the potential neural mechanisms of mood stabilization, as well as to model the side effects of chronic lithium on multiple organ systems. Oral administration of lithium in the maintenance diet or drinking water is convenient, but lithium can acutely affect intake and it can mediate acquisition of conditioned taste aversions (CTA). We compared ad libitum food and fluid intake by male rats with LiCl or NaCl solutions as their sole source of fluid across 20 days, with a commonly used dosage of LiCl (24 mM: 1 g / L LiCl). To quantify the pattern of intake, rats were housed in cages equipped with lickometers to detect licks and infrared photobeams to detect food access with 6-s resolution. To determine if rats formed a CTA to LiCl, they were subsequently tested with access to NaCl. Rats showed an immediate avoidance of the LiCl solution, as seen on the first day of access by an increased latency to initiate drinking and a decreased size of drinking bouts. Rats showed a differential response to LiCl vs. NaCl after as few as 5 licks. Chronic consumption of LiCl solution led to significantly decreased food and fluid intake compared to baseline, with concomitant weight loss. The decreased intake was realized by marked changes in the pattern of drinking and feeding bouts: a decrease in per-lick volume and a decrease in licks per drinking bout, and an increase in feeding bout duration resulting in an overall decrease in eating rate. Conversely, chronic NaCl access led to an increase in drinking bout number and licks/bout. The avoidance of LiCl was likely a combination of toxic effects of ingested LiCl and rapid acquisition of a learned aversion to the taste of LiCl, as shown by an extinguishable generalized aversion to NaCl solution during subsequent NaCl test days. The marked effect of chronic oral LiCl on ingestion may impact the oral dosing of lithium as well as the rat's metabolic status.

Lithium carbonate accelerates the healing of apical periodontitis

Apical periodontitis is a disease caused by bacterial invasions through the root canals. Our previous study reported that lithium chloride (LiCl) had a healing effect on apical periodontitis. The aim of this report is to investigate the healing properties and mechanism of lithium ion (Li+) for apical periodontitis using rat root canal treatment model. 10-week-old male Wistar rat's mandibular first molars with experimentally induced apical periodontitis underwent root canal treatment and were applied lithium carbonate (Li2CO3) containing intracanal medicament. Base material of the medicament was used as a control. Subject teeth were scanned by micro-CT every week and the periapical lesion volume was evaluated. The lesion volume of Li2CO3 group was significantly smaller than that of the control group. Histological analysis showed that in Li2CO3 group, M2 macrophages and regulatory T cells were induced in the periapical lesion. In situ hybridization experiments revealed a greater expression of Col1a1 in Li2CO3 group compared with the control group. At 24 h after application of intracanal medicament, Axin2-positive cells were distributed in Li2CO3 group. In conclusion, Li2CO3 stimulates Wnt/β-catenin signaling pathway and accelerate the healing process of apical periodontitis, modulating the immune system and the bone metabolism.

Does lithium poisoning induce brain injuries?-A histopathological rat study

Due to a narrow therapeutic index, prolonged lithium treatment and overdose may result in neurotoxicity. Neurotoxicity is deemed reversible with lithium clearance. However, echoing the report of syndrome of irreversible lithium-effectuated neurotoxicity (SILENT) in rare severe poisonings, lithium-induced histopathological brain injuries including extensive neuronal vacuolization, spongiosis and ageing-like neurodegenerative changes were described in the rat following acute toxic and pharmacological exposure. We aimed to investigate the histopathological consequences of lithium exposure in rat models mimicking prolonged treatment and all three patterns of acute, acute-on-chronic and chronic poisonings observed in humans. We performed histopathology and immunostaining-based analyses using optic microscopy of brains obtained from male Sprague-Dawley rats randomly assigned to lithium or saline (controls) and treated according to the therapeutic or to the three poisoning models. No lesion was observed in any brain structure in any of the models. Neuron and astrocyte counts did not differ significantly between lithium-treated rats and controls. Our findings support that lithium-induced neurotoxicity is reversible and brain injury not a common feature of toxicity.

Experimental data on lithium salts: From neuroprotection to multi-organ complications

Lithium-salts stand on the first line of therapy for the management of specific psychiatric conditions, mainly bipolar mood disorder. It is also known to protect the brain against neurodegenerative processes such as Alzheimer's disease. Despite the mentioned merits, recent studies have revealed that high dose or prolonged lithium intake deteriorate the function of multiple key organs including heart, ovaries, thyroid gland and kidneys. Mechanistically, both positive and negative effects of lithium are mediated through methylation of β-catenin nuclear-binding proteins which is potentiated by lithium-induced inhibition of GSK-3 or inositol monophosphatase. The current study briefly reviews the recent experimental data on lithium therapy considering both positive (i.e., neuroprotective) and negative aspects. In this regard, the question is that whether doses of lithium administered in experimental research are comparable with the therapeutic doses, as currently prescribed in clinical practice. It should be noted that the experimental data on animal studies, as widely reviewed here, could not be directly generalized to clinic. This is mainly because lithium doses applied in animal models are usually higher than therapeutic doses, however, there are evidence indicating that even animal to human translated doses of lithium, cause serious complications and this has been reported by meta-analyses on human studies. Therefore, we suggest the clinicians to use lithium-salts with precaution particularly in pregnancy and precisely adjust lithium concentration considering the patient's general health status to avoid lithium toxicity. Indeed, alternative approaches are recommended when the subject is pregnant, prolonged therapy is required or specific organ dysfunction is diagnosed.

Management of lithium intoxication

Lithium is a gold standard maintenance treatment in bipolar affective disorder. It has a narrow therapeutic range, and at higher serum lithium levels there is a risk of adverse effects and toxicity. There are three patterns of lithium intoxication: acute, acute-on-chronic and chronic. We describe risk factors for lithium intoxication, mechanisms of toxicity and clinical symptoms seen in lithium intoxication. We describe both the acute and chronic effects of lithium toxicity. Lithium intoxication may be life-threatening and associated with longer-term sequelae. The management of lithium intoxication involves determining the type of intoxication. We discuss treatment strategies aimed at reducing absorption and increasing elimination of lithium. We discuss clinical indications for extracorporeal methods such as dialysis, which are used to limit the time and degree of exposure of the central nervous system to toxic lithium concentrations. Haemodialysis is the most rapid method of eliminating lithium from the body, but careful monitoring is required. Preventive strategies to mitigate the risk for lithium intoxication are discussed.

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.

A Review for Lithium: Pharmacokinetics, Drug Design, and Toxicity

Lithium as a mood stabilizer has been used as the standard pharmacological treatment for Bipolar Disorder (BD) for more than 60 years. Recent studies have also shown that it has the potential for the treatment of many other neurodegenerative disorders, including Alzheimer's, Parkinson's and Huntington's disease, through its neurotrophic, neuroprotective, antioxidant and anti-inflammatory actions. Therefore, exploring its pharmacokinetic features and designing better lithium preparations are becoming important research topics. We reviewed many studies on the pharmacokinetics, drug design and toxicity of lithium based on recent relevant research from PubMed, Web of Science, Elsevier and Springer databases. Keywords used for searching references were lithium, pharmacology, pharmacokinetics, drug design and toxicity. Lithium is rapidly and completely absorbed from the gastrointestinal tract after oral administration. Its level is initially highest in serum and then is evidently redistributed to various tissue compartments. It is not metabolized and over 95% of lithium is excreted unchanged through the kidney, but different lithium preparations may have different pharmacokinetic features. Lithium has a narrow therapeutic window limited by various adverse effects, but some novel drugs of lithium may overcome these problems. Various formulations of lithium have the potential for treating neurodegenerative brain diseases but further study on their pharmacokinetics will be required in order to determine the optimal formulation, dosage and route of administration.

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.

Effects of Long-Term Endurance Exercise and Lithium Treatment on Neuroprotective Factors in Hippocampus of Obese Rats

To investigate the effects of long-term lithium treatment and low intensity endurance exercise on brain-derived neurotrophic factor (BDNF) expression and glycogen synthase kinase 3 beta (GSK3β) activity in the hippocampus of obese rats. Fifty 10-week-old male Sprague-Dawley rats were selected. There was a control group of 10 rats (chow control group) while the other forty rats were fed on a high-fat diet for eight weeks to induce obesity. Rats were then assigned into four random groups. The rats were given 10 mg/kg lithium chloride (LiCl) dissolved in 1 mL sterile distilled water once a day, 5 times a week. The rats did 20 min of treadmill walking with an exercise intensity of 40% maximal oxygen uptake (VO₂ max) (12 m/min, slope 0%). This was performed for 20 min a day, 3 days a week. Twelve weeks of lithium treatment or endurance exercise significantly reduced body weight and body fat mass in obese rats, without showing additive effects when the treatments were given in parallel or significant toxic responses in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in blood and kidney and liver tissues. BDNF expression in the hippocampus was significantly increased both in exercise and lithium groups with synergistic effects found in the group where both exercise and lithium treatments were given in parallel. On the other hand, the decrease in GSK3β activity was shown only in the lithium treatment group, without showing additive effects when the treatments were given in parallel. Lithium and low-intensity endurance exercise for 12 weeks increased the expression of BDNF, a neuroprotective factor in the hippocampus of obese mice. Lithium treatment alone inhibited the activity of GSK3β. This can be interpreted as a positive indication of applicability of the two factors in the prevention of neurodegenerative diseases.

IVIVC Assessment of Two Mouse Brain Endothelial Cell Models for Drug Screening

Since most preclinical drug permeability assays across the blood-brain barrier (BBB) are still evaluated in rodents, we compared an in vitro mouse primary endothelial cell model to the mouse b.End3 and the acellular parallel artificial membrane permeability assay (PAMPA) models for drug screening purposes. The mRNA expression of key feature membrane proteins of primary and bEnd.3 mouse brain endothelial cells were compared. Transwell^® monolayer models were further characterized in terms of tightness and integrity. The in vitro in vivo correlation (IVIVC) was obtained by the correlation of the in vitro permeability data with log BB values obtained in mice for seven drugs. The mouse primary model showed higher monolayer integrity and levels of mRNA expression of BBB tight junction (TJ) proteins and membrane transporters (MBRT), especially for the efflux transporter Pgp. The IVIVC and drug ranking underlined the superiority of the primary model (r² = 0.765) when compared to the PAMPA-BBB (r² = 0.391) and bEnd.3 cell line (r² = 0.019) models. The primary monolayer mouse model came out as a simple and reliable candidate for the prediction of drug permeability across the BBB. This model encompasses a rapid set-up, a fair reproduction of BBB tissue characteristics, and an accurate drug screening.

Lithium-containing surface pre-reacted glass fillers enhance hDPSC functions and induce reparative dentin formation in a rat pulp capping model through activation of Wnt/β-catenin signaling

Surface pre-reacted glass (S-PRG) fillers are new bioactive molecules used in dental clinic work to fill tooth defects. These fillers release various types of ions (Al⁺³, BO^-3, Na⁺, SiO₃^-2, Sr⁺² and F^-) and exhibit high biocompatibility, antibacterial capability, reduced plaque accumulation, and enhanced osteoblast differentiation. We previously showed that cement of S-PRG fillers could induce tertiary dentin formation in rat models. Previous work also showed that lithium ions can activate the Wnt/β-catenin signaling pathway in vitro and induce dentin formation in pulpotomized teeth in vivo. In the current study, we sought to enhance the effect of S-PRG cement by incorporating LiCl. We show that treatment of human dental pulp stem cells with eluates from S-PRG/LiCl combination cements leads to an upregulation in cell migration, differentiation, and mineralization in vitro. In pulp-capping animal trials, we found that S-PRG/LiCl cements could induce tertiary dentin formation 28-days post-capping. At 7 days post-capping, we identified both β-catenin and Axin2 expression using immunofluorescence, indicative of Wnt/β-catenin signaling activity. In conclusion, S-PRG/LiCl cement is highly effective in promoting human dental pulp stem cells profiles and in enhancing reparative dentin formation in rat teeth through activation of the Wnt/β-catenin canonical signaling pathway. STATEMENT OF SIGNIFICANCE: This is the first study to assess the behavior of S-PRG fillers containing lithium ions on human dental pulp stem cells. We show that this new combination cement promotes positive cell responses by activating the endogenous Wnt/β-catenin signaling pathway in the pulp. The Wnt/β-catenin canonical signaling pathway is involved in many developmental and wound healing processes. The released lithium ions from the S-PRG cement were systematically detected <0.01 mmol/L in our rat model. But it was efficient to induce tertiary dentin formation at the defect site. Since this novel bioactive cement is potentially a promising material for clinical pulp regenerative therapy, future human clinical trials will be needed.

Assessment of Extracorporeal Treatments in Poisoning criteria for the decision of extracorporeal toxin removal in lithium poisoning

AIMS

To assess recommendations provided by the EXtracorporeal TReatments In Poisoning (EXTRIP) workgroup on extracorporeal toxin removal (ECTR) in lithium poisoning.

METHODS

Retrospective assessment in a 128 lithium-poisoned patient cohort previously used to identify ECTR initiation criteria that could improve outcome (Paris criteria). ECTR requirement using EXTRIP criteria was compared to the actual practice or if Paris criteria were used. The potential impact on outcome if these different criteria were used was investigated.

RESULTS

Using the recommended (Rec-EXTRIP) or recommended + suggested (All-EXTRIP) EXTRIP criteria, ECTR would have been indicated in more patients than was actually done (P < .001), or if Paris criteria were used (P < .01). The non-actually ECTR-treated patients fulfilling Rec-EXTRIP or All-EXTRIP criteria had shorter intensive care unit stay (P < .05) and no significant increase in fatalities and neurological impairment on discharge in comparison to the actually ECTR-treated patients. ECTR requirements using EXTRIP vs Paris criteria were not concordant (P < .001). In the non-actually ECTR-treated patients, 31/106 and 55/106 patients fulfilled Rec-EXTRIP or All-EXTRIP but not Paris criteria, respectively. Those patients had longer stay (P < .01) but no worse neurological impairment on discharge than the patients not fulfilling any of these criteria (50/106 and 26/106, respectively). In the non-actually ECTR-treated patients, 7/106 fulfilled Paris but not Rec-EXTRIP criteria. Those patients had longer stay (P < .05) and worse neurological impairment on discharge (P < .01) than the 50/106 patients not fulfilling any of these criteria.

CONCLUSION

In this cohort of lithium poisonings, EXTRIP criteria may lead to more ECTR than actually performed or if the Paris criteria were used, with no demonstrated improvement in outcome.

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.

Investigation of lithium distribution in the rat brain ex vivo using lithium-7 magnetic resonance spectroscopy and imaging at 17.2 T

Lithium is the first-line mood stabilizer for the treatment of patients with bipolar disorder. However, its mechanisms of action and transport across the blood-brain barrier remain poorly understood. The contribution of lithium-7 magnetic resonance imaging (⁷ Li MRI) to investigate brain lithium distribution remains limited because of the modest sensitivity of the lithium nucleus and the expected low brain concentrations in humans and animal models. Therefore, we decided to image lithium distribution in the rat brain ex vivo using a turbo-spin-echo imaging sequence at 17.2 T. The estimation of lithium concentrations was performed using a phantom replacement approach accounting for B₁ inhomogeneities and differential T₁ and T₂ weighting. Our MRI-derived lithium concentrations were validated by comparison with inductively coupled plasma-mass spectrometry (ICP-MS) measurements ([Li]_MRI  = 1.18[Li]_MS , R = 0.95). Overall, a sensitivity of 0.03 mmol/L was achieved for a spatial resolution of 16 μL. Lithium distribution was uneven throughout the brain (normalized lithium content ranged from 0.4 to 1.4) and was mostly symmetrical, with consistently lower concentrations in the metencephalon (cerebellum and brainstem) and higher concentrations in the cortex. Interestingly, low lithium concentrations were also observed close to the lateral ventricles. The average brain-to-plasma lithium ratio was 0.34 ± 0.04, ranging from 0.29 to 0.39. Brain lithium concentrations were reasonably correlated with plasma lithium concentrations, with Pearson correlation factors ranging from 0.63 to 0.90.

Neurobehavioral effects of lithium in the rat: Investigation of the effect/concentration relationships and the contribution of the poisoning pattern

Severity of lithium poisoning depends on the ingested dose, previous treatment duration and renal function. No animal study has investigated neurobehavioral differences in relation to the lithium poisoning pattern observed in humans, while differences in lithium pharmacokinetics have been reported in lithium-pretreated rats mimicking chronic poisonings with enhanced brain accumulation in rats with renal failure. Our objectives were: 1)-to investigate lithium-related effects in overdose on locomotor activity, anxiety-like behavior, spatial recognition memory and anhedonia in the rat; 2)-to model the relationships between lithium-induced effects on locomotion and plasma, erythrocyte, cerebrospinal fluid and brain concentrations previously obtained according to the poisoning pattern. Open-field, elevated plus-maze, Y-maze and sucrose consumption tests were used. In acutely lithium-poisoned rats, we observed horizontal (p<0.001) and vertical hypolocomotion (p<0.0001), increased anxiety-like behavior (p<0.05) and impaired memory (p<0.01) but no altered hedonic status. Horizontal (p<0.01) and vertical (p<0.001) hypolocomotion peaked more markedly 24h after lithium injection and was more prolonged in acute-on-chronically vs. acutely lithium-poisoned rats. Hypolocomotion in chronically lithium-poisoned rats with impaired renal function did not differ from acutely poisoned rats 24h after the last injection. Interestingly, hypolocomotion/concentration relationships best fitted a sigmoidal E_max model in acute poisoning and a linear regression model linked to brain lithium in acute-on-chronic poisoning. In conclusion, lithium overdose alters rat behavior and consistently induces hypolocomotion which is more marked and prolonged in repeatedly lithium-treated rats. Our data suggest that differences between poisoning patterns regarding lithium-induced hypolocomotion are better explained by the duration of lithium exposure than by its brain accumulation.

Electroencephalographic patterns of lithium poisoning: a study of the effect/concentration relationships in the rat

OBJECTIVES

Lithium overdose may result in encephalopathy and electroencephalographic abnormalities. Three poisoning patterns have been identified based on the ingested dose, previous treatment duration and renal function. Whether the severity of lithium-induced encephalopathy depends on the poisoning pattern has not been established. We designed a rat study to investigate lithium-induced encephalopathy and correlate its severity to plasma, erythrocyte, cerebrospinal fluid and brain lithium concentrations previously determined in rat models mimicking human poisoning patterns.

METHODS

Lithium-induced encephalopathy was assessed and scored using continuous electroencephalography.

RESULTS

We demonstrated that lithium overdose was consistently responsible for encephalopathy, the severity of which depended on the poisoning pattern. Acutely poisoned rats developed rapid-onset encephalopathy which reached a maximal grade of 2/5 at 6 h and disappeared at 24 h post-injection. Acute-on-chronically poisoned rats developed persistent and slightly fluctuating encephalopathy which reached a maximal grade of 3/5. Chronically poisoned rats developed rapid-onset but gradually increasing life-threatening encephalopathy which reached a maximal grade of 4/5. None of the acutely, 20% of the acute-on-chronically and 57% of the chronically lithium-poisoned rats developed seizures. The relationships between encephalopathy severity and lithium concentrations fitted a sigmoidal E_max model based on cerebrospinal fluid concentrations in acute poisoning and brain concentrations in acute-on-chronic poisoning. In chronic poisoning, worsening of encephalopathy paralleled the increase in plasma lithium concentrations.

CONCLUSIONS

The severity of lithium-induced encephalopathy is dependent on the poisoning pattern, which was previously shown to determine lithium accumulation in the brain. Our data support the proposition that electroencephalography is a sensitive tool for scoring lithium-related neurotoxicity.

Lithium Poisoning

Lithium is a commonly prescribed treatment for bipolar affective disorder. However, treatment is complicated by lithium’s narrow therapeutic index and the influence of kidney function, both of which increase the risk of toxicity. Therefore, careful attention to dosing, monitoring, and titration is required. The cause of lithium poisoning influences treatment and 3 patterns are described: acute, acute-on-chronic, and chronic. Chronic poisoning is the most common etiology, is usually unintentional, and results from lithium intake exceeding elimination. This is most commonly due to impaired kidney function caused by volume depletion from lithium-induced nephrogenic diabetes insipidus or intercurrent illnesses and is also drug-induced. Lithium poisoning can affect multiple organs; however, the primary site of toxicity is the central nervous system and clinical manifestations vary from asymptomatic supratherapeutic drug concentrations to clinical toxicity such as confusion, ataxia, or seizures. Lithium poisoning has a low mortality rate; however, chronic lithium poisoning can require a prolonged hospital length of stay from impaired mobility and cognition and associated nosocomial complications. Persistent neurological deficits, in particular cerebellar, are described and the incidence and risk factors for its development are poorly understood, but it appears to be uncommon in uncomplicated acute poisoning. Lithium is readily dialyzable, and rationale support extracorporeal treatments to reduce the risk or the duration of toxicity in high-risk exposures. There is disagreement in the literature regarding factors that define patients most likely to benefit from treatments that enhance lithium elimination, including specific plasma lithium concentration thresholds. In the case of extracorporeal treatments, there are observational data in its favor, without evidence from randomized controlled trials (none have been performed), which may lead to conservative practices and potentially unnecessary interventions in some circumstances. More data are required to define the risk–benefit of extracorporeal treatments and their use (modality, duration) in the management of lithium poisoning.