Staying at the crossroads: assessment of the potential of serum lithium monitoring in predicting an ideal lithium dose

Pharmacokinetics of intravenous lithium chloride and assessment of agreement between two methods of lithium concentration measurement in the horse

BACKGROUND

Pharmacokinetics of lithium chloride (LiCl) administered as a bolus, once i.v. have not been determined in horses. There is no point-of-care test to measure lithium (Li⁺ ) concentrations in horses in order to monitor therapeutic levels and avoid toxicity.

OBJECTIVES

To determine the pharmacokinetics of LiCl in healthy adult horses and to compare agreement between two methods of plasma Li⁺ concentration measurement: spectrophotometric enzymatic assay (SEA) and inductively coupled plasma mass spectrometry (ICP-MS).

STUDY DESIGN

Nonrandomised, single exposure with repeated measures over time.

METHODS

Lithium chloride was administered (0.15 mmol/kg bwt) as an i.v. bolus to eight healthy adult horses. Blood samples were collected pre-administration and at multiple times until 48 h post-administration. Samples were analysed by two methods (SEA and ICP-MS) to determine plasma Li⁺ concentrations. Pharmacokinetics were determined based on the reference ICP-MS data.

RESULTS

Adverse side effects were not observed. The SEA showed linearity, R² = 0.9752; intraday coefficient of variation, 2.5%; and recovery, 96.3%. Both noncompartmental and compartmental analyses (traditional two-stage and nonlinear mixed-effects [NLME] modelling) were performed. Geometric mean values of noncompartmental parameters were plasma Li⁺ concentration at time zero, 2.19 mmol/L; terminal elimination half-life, 25.68 h; area under the plasma concentration-time curve from time zero to the limit of quantification, 550 mmol/L min; clearance, 0.273 mL/min/kg; mean residence time, 31.22 h; and volume of distribution at steady state, 511 mL/kg. Results of the traditional two-stage analysis showed good agreement with the NLME modelling approach. Bland-Altman analyses demonstrated poor agreement between the SEA and ICP-MS methods (95% limits of agreement = 0.14 ± 0.13 mmol/L).

MAIN LIMITATIONS

Clinical effects of LiCl have not been investigated.

CONCLUSIONS

The LiCl i.v. bolus displayed pharmacokinetics similar to those reported in other species. The SEA displayed acceptable precision but did not agree well with the reference method (ICP-MS). The Summary is available in Spanish - see Supporting Information.

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.

Lithium protects against oxidative stress-mediated cell death in α-synuclein-overexpressing in vitro and in vivo models of Parkinson's disease

Lithium has recently been suggested to have neuroprotective properties in relation to several neurodegenerative diseases. In this study, we examined the potential cytoprotective effect of lithium in preventing oxidative stress-induced protein accumulation and neuronal cell death in the presence of increased α-synuclein levels in vitro and in vivo. Specifically, lithium administration was found to protect against cell death in a hydrogen peroxide-treated, stable α-synuclein-enhanced green fluorescent protein (EGFP)-overexpressing dopaminergic N27 cell line. Lithium feeding (0.255% lithium chloride) of 9-month-old pan-neuronal α-synuclein transgenic mice over a 3-month period was also sufficient to prevent accumulation of oxidized/nitrated α-synuclein as a consequence of chronic paraquat/maneb administration in multiple brain regions, including the glomerular layer, mitral cells, and the granule cell layer of the olfactory bulb (OB), striatum, substantia nigra pars compacta (SNpc) and Purkinje cells of the cerebellum. Lithium not only prevented α-synuclein-mediated protein accumulation/aggregation in these brain regions but also protected neuronal cells including mitral cells and dopaminergic SNpc neurons against oxidative stress-induced neurodegeneration. These results suggest that lithium can prevent both α-synuclein accumulation and neurodegeneration in an animal model of PD, suggesting that this drug, already FDA-approved for use in bipolar disorder, may constitute a novel therapy for another human disease.