lithium 
 salts have a long history of human consumption beginning 
 in the 1800s . in psychiatry , they have been used to treat mania and 
 as a prophylactic for depression since the mid-20th century . today , lithium salts are used as a mood stabilizer 
 for the treatment of bipolar disorder and also , off - label , for other 
 psychiatric indications . for example , lithium is the only drug that 
 consistently reduces suicidality in patients with neuropsychiatric 
 disorders . despite these effective medicinal uses , current united 
 states food and drug administration ( fda)-approved lithium pharmaceutics 
 ( lithium carbonate and lithium citrate ) are plagued with a narrow 
 therapeutic window that requires regular monitoring of plasma lithium 
 levels and blood chemistry by a clinician to mitigate adverse events . still , many patients undergoing lithium therapy find the side effects 
 to be unbearable , which negatively affects compliance and discourages 
 physicians from utilizing lithium . these problems arise because lithium s 
 site of action is the brain , and current lithium salts cross the blood - brain - barrier 
 slowly . as a result , there is unnecessary accumulation 
 of lithium ions in peripheral organs , particularly in the kidneys 
 and heart , where side effects can arise . thus , multiple administrations 
 throughout the day are required to safely reach therapeutic concentrations . further , the patient must remain keenly aware of their hydration status 
 as dehydration promotes a more rapid serum chemical imbalance with 
 renal and cardiac toxicity . unfortunately , the serum concentrations 
 required to maintain therapeutic efficacy often lead to metabolic 
 adverse effects such as hypothyroidism , hyperparathyroidism , weight 
 gain , and nephrogenic diabetes insipidus . if supratherapeutic serum concentrations of lithium are achieved , 
 lithium intoxication ensues . patients with lithium poisoning can exhibit 
 loss of consciousness , muscle tremor , epileptic seizures , and pulmonary 
 complications . because lithium is so effective 
 at reducing manic episodes and 
 suicidality in patients with bipolar disorder , it is still used clinically 
 despite its narrow therapeutic index and serious side effects . nevertheless , recent studies have identified many important 
 bioactivities of lithium that may be responsible for its therapeutic 
 efficacy in its current fda - approved indications and beyond . for example , 
 lithium exerts neuroprotective effects , in part , by increasing brain - derived 
 neurotrophic factor ( bdnf ) . chronic lithium treatment has been shown 
 to increase the expression of bdnf in rats and humans . this increase in bdnf activity 
 can lead to restoration of learning and memory deficits through promotion 
 of neurogenesis and long - term potentiation ( ltp ) . another neuroprotective 
 mechanism of lithium is attenuation of the production of inflammatory 
 cytokines like il-6 and nitric oxide ( no ) in activated microglia . this is particularly important since aberrant 
 microglial function is a common finding in a number of neuropsychiatric 
 diseases . moreover , recent lines of evidence 
 have implicated bdnf and no in novel mechanisms for lithium s antidepressant 
 effects . lithium has also been found to inhibit certain enzymes 
 in a noncompetitive 
 manner by displacing the required divalent cation , magnesium . two of these enzymes that have important implications 
 in bipolar disorder are glycogen synthase kinase-3 beta ( gsk-3 ) 
 and inositol monophosphatase ( impase ) . gsk-3 was first identified 
 as the molecular target of lithium by klein and melton . it functions by phosphorylating glycogen synthase , 
 the rate - limiting enzyme of glycogen biosynthesis . gsk-3 inhibitors like lithium generally produce 
 antidepressant - like and antimania - like effects in animal models , which 
 have been used to explain lithium s efficacy for bipolar disorder . gsk-3 is expressed in all tissues , with 
 particularly abundant levels in the brain . therefore , this enzyme is thought to have tremendous potential as 
 a therapeutic target for the treatment of a variety of neurological 
 diseases that are characterized by dysregulated gsk-3 such 
 as alzheimer s disease , hiv associated neurocognitive disorders , 
 and autism spectrum disorders . in addition to inhibiting 
 gsk-3 , lithium also inhibits inositol 
 monophosphatase ( impase ) leading to cerebral inositol depletion . lithium , valproic acid , and carbamazepine , which are all used for 
 stabilization of mood , have been shown to lead to the depletion of 
 inositol . this has bolstered support 
 for the inositol depletion hypothesis of lithium therapy and has highlighted 
 this molecular target in the search for  lithium mimetics  . however , given the frequency of suicidality 
 as a comorbidity in patients with bipolar disorder and that only lithium consistently reduces suicidality in these 
 patients , it is doubtful that selective impase inhibitors will produce 
 the desired clinical outcome that can be achieved with lithium . these 
 lines of evidence imply that the antisuicidality effects of lithium 
 are not solely attributable to impase inhibition / inositol depletion . that the solid - state structure and composition of an active pharmaceutical 
 ingredient ( api ) critically impacts its drug delivery performance , 
 especially its physicochemical properties , means that materials science 
 plays a critical role in enabling the development of bioactive molecules 
 as drug products . in this contribution , we report that a materials 
 science strategy based upon crystal engineering can enable improvement 
 of the therapeutic window of lithium while retaining the bioactivities 
 of current fda - approved lithium solid forms . our approach is based 
 upon cocrystallization , which has gained the attention of both academia 
 and industry in the past decade . indeed , the fda has recently released 
 regulatory guidelines for industry on pharmaceutical cocrystals . almarsson and zaworotko have defined pharmaceutical 
 cocrystals as  co - crystals that are formed between a molecular 
 or ionic active pharmaceutical ingredient ( api ) and a co - crystal former 
 that is a solid under ambient conditions  . cocrystallization is of growing interest because these 
 multicomponent materials that are based upon two or more further , they represent novel solid forms of apis that can improve 
 the physicochemical properties ( e.g. , solubility and stability ) , improve 
 efficacy ( e.g. , bioavailability ) , and provide a means for extending 
 the life cycle of existing apis . previously , we successfully used cocrystallization of two molecular 
 coformers to improve the solubility and consequent bioavailability 
 of the poorly soluble bioflavonoid quercetin and to conversely lower the pharmacokinetics of the highly soluble 
 antioxidant epigallocatechin-3-gallate , egcg . the molecular cocrystals of quercetin and egcg that we studied were 
 stabilized by hydrogen bonded supramolecular synthons , which are assumed 
 to dissociate in vivo leaving therapeutically bioactive 
 quercetin and egcg . ionic cocrystals ( iccs ) have even more recently 
 emerged as another class of multicomponent pharmaceutical materials 
 ( mpms ) of scientific and practical interest . the general formula 
 of iccs is therefore abn , where a is a cation , b is an anion , and n is neutral 
 molecule or another salt . if one of the components of the icc is a 
 pharmaceutical compound then there is considerable opportunity to 
 modulate the physicochemical and biological efficacy of the pharmaceutical 
 compound because there are two components that can be changed . this 
 contrasts with single component crystals of pharmaceutical compounds , 
 which have very limited opportunities for fine - tuning of materials 
 properties , and other mpms such as simple salts , ab , and molecular cocrystals , ab , for which there is 
 only variable component besides the pharmaceutical compound . reported iccs of inorganic lithium salts , lib , with a series of amino acids , zwitterionic 
 molecules , n , by exploiting the strength of lithium carboxylate bonds . in these iccs , the lithium cation ( api ) forms 
 coordination bonds to the amino acid coformers and the inorganic anions 
 remain in the composition to balance charge . given that coordination 
 bonds are stronger than hydrogen bonds we became interested in determining 
 if the stronger bonding would affect the in vivo speciation 
 of lithium and thereby modulate its therapeutic bioactivity and pharmacokinetics . we herein describe the synthesis of two novel iccs of organic anion 
 salts of lithium with the amino acid coformer , proline . we assessed 
 the blood and brain pharmacokinetics of this new speciation of lithium 
 in rats and their therapeutic activities at several established targets 
 of lithium therapy . lithium salicylate ( 98% 
 purity ) , lithium hydroxide ( 98% purity ) , nicotinic acid ( 98% 
 purity ) , and proline ( 99% purity ) were purchased from sigma - aldrich 
 corporation ( st . louis , mo ) and used as such without further purification . lithium salicylate ( 98% 
 pure , anhydrous , 
 used as received from sigma aldrich , 1 mmol ) and l - proline 
 ( 99% pure , used as received from sigma aldrich , 1 mmol ) were 
 dissolved in 2.0 ml of hot deionized water . the resulting solution 
 was maintained on a hot plate ( 7590 c ) to allow slow 
 evaporation of solvent until crystals had formed . lithium hydroxide ( 98% 
 pure , anhydrous , 
 used as received from sigma aldrich , 1 mmol ) , nicotinic acid ( 98% 
 pure , anhydrous , used as received from sigma aldrich , 1 mmol ) , and l - proline ( 99% pure , used as received from sigma aldrich , 
 2 mmol ) were dissolved in 3.0 ml of deionized water and left to stand 
 on a hot plate until block shape colorless crystals had emerged from 
 solution . the x - ray diffraction 
 data were collected using a bruker - axs smart - apexii 
 ccd diffractometer ( cu k ,  = 1.54178  ) . the structure was solved using 
 shelxs-97 ( direct methods ) and refined using shelxl-97 ( full - matrix 
 least - squares on f ) contained in olex2 and wingx v1.70.01 programs . all non - hydrogen atoms , except 
 disordered c29a 
 and c29b , were refined anisotropically . hydrogen atoms of ch , 
 ch2 , nh2 , and oh groups were placed in geometrically 
 calculated positions and included in the refinement process using 
 riding model with isotropic thermal parameters : uiso(h ) = 1.2ueq ( ch , 
 ch2 , nh2 ) , uiso(h ) = 1.5ueq(oh ) . one of the l - proline rings is disordered over two positions in a 1:1 ratio . the crystal was a twin , and refinement was conducted with an 
 hkl5 type file generated using the [ 1/0/0;0/1/0;0.14/0/1 ] 
 twin law . the structure with probability 
 ellipsoids is available in the supporting information ( figure s4 ) . hydrogen atoms of the ch and ch2 groups 
 were placed in geometrically calculated positions and included in 
 the refinement process using riding model with isotropic thermal parameters : 
 uiso(h ) = 1.2ueq ( ch , ch2 , nh2 ) . hydrogen atoms of the nh2 group were 
 found from difference fourier map inspection and were freely refined . the l - proline ring was found to be disordered 
 over two positions with an approximate ratio of 0.7:0.3 . crystallographic 
 data is available in the cambridge structural database ( ccdc 962324 ) . the structure with probability ellipsoids is available in the supporting information ( figure s2 ) . powder x - ray diffraction ( pxrd ) 
 and differential scanning calorimetry ( dsc ) were used to confirm the 
 purity of the cocrystal preparations . pxrd patterns ( from bulk samples ) 
 were compared to the calculated pattern ( from the single crystal ) 
 and indicated that phase purity had been obtained ( figure 3 ) . dsc indicated a clean single 
 endotherm corresponding to the cocrystals . prior to bioactivity and 
 pharmacokinetics evaluation , purity was confirmed by preparing equimolar 
 lithium solutions of lispro and lis and measuring lithium concentration 
 using atomic absorption spectrometry . the dsc ( figure s1 ) for lnapro 
 is available in the supporting information . the dsc ( figure s3 ) and aas ( figure s5 ) data for lispro are available 
 in the supporting information . square grid network exhibited 
 by lispro ( a ) and lnapro ( b ) . experimental 
 versus calculated pxrd of lispro ( a ) and lnapro ( b ) . adult rat hippocampal 
 neural stem 
 cells ( nsc , millipore ) were treated with lispro or lis at 0 , 1 , and 
 5 mm for 40 h in a differentiation media . cells were lysed using ripa 
 buffer with protease inhibitors cocktail and subjected to immunoblotting 
 analysis using an antibody against phosphorylated phospho - gsk-3ser9 
 ( inactive form ) or total gsk-3. densitometry analysis was represented 
 by ratio of phospho - gsk-3ser9 to total gsk-3 band intensity 
 under wb from two independent experiments . t - tests 
 were used to assess statistical significance in the ratio of phospho - gsk-3ser9 
 to total gsk-3. mouse neuroblastoma 
 ( n2a ) cells were grown 
 in dulbecco s modified eagle s medium ( dmem ) supplemented 
 with 10% fetal bovine serum ( fbs ) and 1% penicillin - streptomycin . cells were plated in 24-well plate at a density 5  10 cells per well in dmem supplemented with 5% fbs and 1% penicillin - streptomycin . twenty - four hours later , 1 and 10 mm of lithium as lithium salicylate 
 ( lis ) or cocrystal ( lispro ) were added to each well and incubated 
 for 48 h. after treatment , media were collected for brain derived 
 neurotrophic factor ( bdnf ) enzyme linked immunosorbent assay ( elisa ) 
 and cells were lysed for bicinchoninic acid assay ( bca ) . bdnf levels 
 were measured in collected media with a bdnf sandwich elisa kit ( millipore , 
 cat . shortly , samples were incubated in a mouse anti - bdnf 
 monoclconal antibody coated 96-well immunoassay plate at 4 c , 
 overnight on a shaker . the plates were thoroughly washed at least 
 four times , and a biotinylated mouse anti - human bdnf monoclonal antibody 
 was added to each well and incubated for 2.5 h at room temperature 
 on a shaker . after washing , a streptavidin - enzyme conjugate solution 
 was added and incubated at room temperature for 1 h on a shaker . after 
 washing , a tmb / e substrate solution was added to the plates and inactivated 
 after 7 min by adding the stop solution . the bdnf was detected immediately 
 by measuring absorbance at 450 nm using a microplate reader . bdnf 
 concentration was analyzed based on the bdnf standard curve and normalized 
 to total protein concentration as determined using a bca protein assay 
 kit ( pierce , rockford , il ) . bv2 microglia cells 
 were grown in dmem supplemented with 10% fbs and 1% penicillin - streptomycin . cells were plated in 24-well plate at a density 5  10 cells per well in dmem with 10% fbs and 1% penicillin - streptomycin . twenty - four hours later , 25 and 12.5 mm of lithium in dmem as lis 
 or lispro were added to each wells and incubated for 30 min . the microglia 
 were activated by the addition of 100 ng / ml or lps . six hours later , 
 media was collected and no was measured using a griess reagent system 
 ( promega , madison , wi ) per the manufacturer s instructions . adult rat hippocampal 
 neural stem cells were obtained from millipore ( billerica , ma ) and 
 grown in expansion media that contained 1 b-27 supplement minus 
 vitamin a , 2 mm gibco glutamax , and 20 ng / ml bfgf in neurobasal a 
 medium ( all from gibco , carlsbad , ca ) . after neurospheres formed , 
 cells were plated on 12 mm poly - l - lysine coated coverslips 
 ( bd biocoat , bedford , ma ) at density 5  10 cells / well 
 in 3 mm lis and lispro containing neurobasal a medium only . differentiation 
 was induced for 5 days at 37 c with 5% co2 , and equal 
 amounts of media was added to each well at day 3 . cells were fixed with 4% paraformaldehyde 
 ( pfa , sigma - aldrich , st . louis , mo ) for 15 min at room temperature 
 and washed with pbs for 5 min three times . cells were then permeabilized 
 with 1% triton x-100 in pbs for 10 min at room temperature . after 
 washing with pbs for 5 min three times , cells were blocked with 1% 
 bovine serum albumin ( bsa , sigma - aldrich , st . louis , mo ) in 0.02% 
 tween 20 containing pbs ( pbst ) for 10 min at room temperature with 
 gentle shaking . mouse monoclonal anti - tuj1 ( covance , mms 435p , 1:2000 ) 
 and rabbit polyclonal anti - gfap ( abcam , ab7260 , 1:1000 ) antibodies 
 were diluted in the blocking buffer and incubated for overnight at 
 4 c with gentle shaking . after washing with 0.02% pbst 5 min 
 for three times , goat anti - mounse alexa fluor 488 ( 1:250 , green ) and 
 goat anti - rabbit alexa fluor conjugated 555 ( 1:250 , red ) ( both from 
 abcam , cambridge , ma ) in blocking buffer nuclei were visualized by mounting with vectasheild 
 hardset mounting media with dapi ( vector laboratory , burlingame , ca ) . the animals 
 were housed at the moffitt cancer center vivarium ( tampa , fl ) with 
 a 12 h light  dark cycle . the rats were allowed to acclimate 
 for a period of one week before any experiments are carried out . the rats were dosed via oral gavage with 4 meq / kg elemental lithium 
 as lispro or li2co3 dissolved in deionized water 
 or suspended in 1% methylcellulose , respectively . animals in each 
 treatment group were euthanized at 2 , 24 , 48 , and 72 h ( n = 3/time point ) , and blood was collected by cardiac puncture and 
 carefully perfused with a pressure - controlled pump to maintain microvasculature 
 integrity before removing brain tissue . blood was centrifuged at 1600 g at room temperature for 10 min , and plasma was separated . a 500 l aliquot was diluted 10-fold in a 5% tca and 10% ipa 
 solution , vortexed , and allowed to sit for 10 min in order to precipitate 
 proteins . these aliquots were centrifuged at 3000 g for 30 min , and the supernatant was transferred to clean tubes prior 
 to measuring lithium content using atomic absorption spectroscopy 
 ( aas ) . brains were rinsed with pbs and weighed , and then an equal 
 volume of concentrated hno3 was added . the brains were 
 heated in this nitric acid solution for 1 h , allowed to cool to room 
 temperature , and then centrifuged at 3000 g for 1 
 h. the supernatant was removed and diluted 10-fold in 10% ipa prior 
 to measuring lithium content using aas ( shimadzu aa-6200 ) . peak height 
 measurements were carried out referring to values obtained for standards 
 of known concentrations . single crystal x - ray 
 structural analysis reveals that lispro contains four lithium cations , 
 four salicylate anions , and four l - proline molecules in the 
 unit cell . each 
 lithium cation is linked to adjacent lithium cations by four bridging 
 carboxylate moieties , two from salicylate and two from l - proline 
 ( li  o distances : 1.916(1 ) , 1.915(1 ) and 1.875(1 ) , 1.905(1 ) 
  ) . the overall network can be described as square grids and 
 is illustrated in figure 2a . the hydroxyl group 
 of salicylate and protonated nitrogen of l - proline are involved 
 in intramolecular and intermolecular hydrogen bonds ( o  ho : 2.558(1 ) and 2.641(1 ) ; n  ho : 2.751(1 ) , 2.745(1 ) and 2.874(1 ) ) ( table 2 ) . the single crystal x - ray diffraction parameters 
 of this and the other crystal structures reported herein are tabulated 
 in table 1 . the crystal structure 
 of lnapro reveals that the 1:1 icc crystallized in space group p21212 and that it contains four lithium 
 cations , four nicotinate anions , and four l - proline molecules 
 in the unit cell . two carboxylate moieties of nicotinate and two carboxylate moieties 
 of proline molecules bridge adjacent lithium cations ( li  o 
 distances : 1.897(3 ) , 1.897(3 ) and 1.920(3 ) , 2.920(3 )  ) . the protonated nitrogen atoms of proline form 
 hydrogen bonds with carboxylate moieties ( n  ho : 2.779(2 ) and 2.762(2 )  ) ( table 3 ) . 1/2 
  x , 1/2 + y , 1  z. adult rat hippocampal neural stem cells 
 ( nsc , millipore ) were treated with lispro or lis at 0 , 1 , and 5 mm 
 for 40 h in a differentiation media and lysates subjected to immunoblotting 
 analysis using an antibody against phosphorylated gsk-3 ser9 
 ( phosph - gsk-3ser9 ) or total gsk-3. the results from 
 this experiment are shown in figure 4 . densitometry 
 analysis was represented by ratio of phosph - gsk-3ser9 to total 
 gsk-3 band intensity under western blot . the results of two 
 independent experiments are shown in figure 4b as mean  sem . t - tests revealed significant 
 differences in ratio of phosph - gsk-3ser9 to total gsk-3 
 in 1 and 5 mm of both lispro and lis compared to control ( * p < 0.05 , * * * p < 0.001 ) . however , 
 there were no significant differences in the ratio of lispro and lis 
 at equivalent concentrations , suggesting that iccs of lithium remain 
 bioactive and are bioequivalent to inorganic salts of lithium . lispro treatment 
 increases phosphorylation of gsk-3 in adult 
 rat hippocampal neural stem cells . adult rat hippocampal neural stem 
 cells ( nsc , millipore ) were treated with lispro or lis for 40 h in 
 a differentiated media . ( a ) cells were lysed by ripa buffer with protease 
 cocktails and subjected to immunoblotting ( wb ) analysis using an antibody 
 against phosphorylated gsk-3 ser9 ( phosph - gsk-3 ser9 ) 
 or total gsk-3. ( b ) densitometry analysis from two independent 
 experiments is represented by ratio of phosph - gsk-3 ser9 to 
 total gsk-3 band intensity under wb . t - tests 
 revealed significant differences in ratio of phosph - gsk-3 ser9 
 to total gsk-3 for 1 and 5 mm of both lispro and lis compared 
 to control ( * p < 0.05 , * * * p < 
 0.001 ) . these results are representative of two independent experiments 
 with n = 2 for each condition . mouse neuroblastoma ( n2a ) cells were treated with lis and lispro 
 at 5 and 25 mm in dmem supplemented with 5% fbs for 48 h. bdnf quantification 
 was determined via elisa kit . we found that both lis and lispro produced 
 dose dependent increases in bdnf ( figure 5 ) . this provides further evidence 
 that the lithium remains bioactive despite being in the icc form , 
 lispro . neuroblastoma 
 cells were treated with lis and lispro for 48 h. bdnf was quantified 
 in the media by elisa and normalized to total protein in the cell 
 lysate by bca . t - tests revealed significant differences 
 at 1 and 10 mm for lispro compared to the no treatment control ( * p < 0.05 ) and only at 10 mm for lis ( * * p < 0.01 ) . there were no statistically significant differences 
 between lis and lispro at either concentration ( p > 0.05 ) . bv2 microglia cells were treated 
 with lis and lispro at 12.5 and 
 25 mm in dmem for 30 min prior to activation of microglia by 100 ng / ml 
 lps . no was measured in the media 6 h later using a griess reagent 
 system . further , lithium 
 treatment ( both as lis and lispro ) attenuated this proinflammatory 
 response . at 25 mm , both lithium forms completely inhibited no production . 
 at 12.5 mm , we found lispro to be more effective than lis at attenuating 
 no production in these lps - activated microglia . this supports the 
 bioactivity of lispro and suggests that , in some instances , it may 
 be advantageous to the parent salt form , lis . bv2 microglia were pretreated with lis and lispro at 25 and 12.5 mm 
 for 1 h prior to being activated by the addition of 100 ng / ml lps . the 
 no treatment , no lps control group produced very low ( basal ) levels 
 of no . the lithium treatments abolished no production at 25 
 mm and reduced it at 12.5 mm with lispro being advantageous at this 
 concentration . statistical significance from the no treatment with 
 lps control was assessed by t - tests ( * p < 0.05 , * * p < 0.01 , * * * p < 0.001 ) . lithium has been shown to promote 
 neuronal differentiation of hippocampal 
 progenitor cells . to test whether lispro 
 possessed this bioactivity , we treated adult rat hippocampal neural 
 stem cells with lithium as lis and lispro at 3 mm for 5 days . immunocytochemistry 
 studies indicated that , compared to the no treatment control group 
 ( figure 7a ) , both lis ( figure 7b ) and lispro ( figure 7c ) did indeed 
 promote differentiation of the progenitor cells into neurons over 
 the course of the experiment . adult rat 
 hippocampal neural stem cells were cultured with neurobasal media 
 only ( a ) , neurobasal media with 3 mm lis ( b ) , and neurobasal media 
 with 3 mm lispro ( c ) . blue dapi staining indicates nuclei , red gfap 
 staining indicates astrocytes , and green tuj1 indicates neurons . dawley 
 rats weighing 200250 g were dosed via oral gavage with 4 meq / kg 
 elemental lithium as the icc lispro dissolved in deionized water or 
 lithium carbonate ( li2co3 ) suspended in 1% methylcellulose . animals in each treatment group were euthanized at 2 , 24 , 48 , and 
 72 h ( n = 3/time point ) , and blood and brain were 
 collected . the plasma pharmacokinetics of li2co3 produced a sharp peak and rapid elimination with nearly undetectable 
 levels at 48 h ( figure 8a ) . this produced a 
 concomitant spike in brain lithium levels at 24 h ( figure 8b ) . lispro produced elevated lithium plasma levels 
 at the earliest time point ( 2 h ) ( figure 8c ) . the plasma lithium levels peaked at 24 h and remained elevated at 
 48 h before becoming almost undetectable at 72 h. lispro produced 
 steady brain levels of lithium at 24 and 48 h ( figure 8d ) . the compilation of lispro versus li2co3 plasma ( figure 8e ) and brain ( figure 8f ) pharmacokinetics reveals some distinct differences 
 between the icc and salt forms . although lispro produced very steady 
 lithium plasma and brain levels out to 48 h , it was at the cost of 
 bioavailability , which was clearly reduced compared to li2co3 in both the plasma and brain compartments . male rats ( n = 
 3 per formulation per time point ) were dosed with 4 meq / kg of lithium 
 via oral gavage as lispro or li2co3 . plasma 
 and brain lithium levels were determined at 2 , 24 , 48 , and 72 h by 
 atomic absorption spectrometry . ( a ) li2co3 plasma 
 lithium concentration versus time ( mean  sem ) . ( b ) li2co3 brain lithium per gram of wet weight versus time ( mean 
  sem ) . ( c ) lispro plasma lithium concentration versus time ( mean 
  sem ) . ( d ) lispro brain lithium per gram of wet weight versus 
 time ( mean  sem ) . ( e ) compilation plasma lithium concentration 
 versus time ( mean  sem ) . ( f ) compilation brain lithium concentration 
 versus time ( mean  sem ) . in regard to the therapeutic activity of 
 various lithium salts 
 for the treatment of bipolar disorder , equivalence is often assumed 
 because the lithium cation is regarded as the api . our bioactivity 
 assessments of a new lithium icc compared to the parent lithium salt 
 supports this assumption only for the clinically relevant end points 
 that we evaluated in vitro . importantly , because 
 the molecular ideology of bipolar disorder is not fully understood , 
 we can not conclude that various forms of lithium will be equally effective 
 at treating bipolar disorder in vivo . however , in 
 this regard , we note that certain lithium salts alone might offer 
 significant benefits from an efficacy and/or toxicity standpoint . to our knowledge , there have been no side - by - side clinical evaluations 
 of the therapeutic efficacy of the lithium salts that we utilized 
 here . however , empirical evidence suggests that some of the anions 
 might be therapeutically synergistic with lithium for the treatment 
 of bipolar disorder . for example , a recent pharmacoepidemiological 
 study suggests that acetylsalicylic acid ( aspirin ) might be beneficial 
 as an adjunct treatment with lithium salts for the treatment of bipolar 
 disorder . the anion in lispro , salicylic 
 acid , is the primary bioactive metabolite of aspirin . reported that low - dose aspirin produced significant reduction in the 
 relative risk of clinical deterioration in subjects on lithium and 
 that this was not the case with other nsaids and glucocorticoids . the authors hypothesize that this is due to 
 synergistic anti - inflammatory actions of lithium and acetylsalicylic 
 acid by increasing the brain concentrations of 17-oh - dha , an anti - inflammatory 
 brain dha metabolite . this hypothesis is supported by previous studies 
 that demonstrated neuroinflammation in bd , that aspirin increases 17-oh - dha , and 
 that lithium reduces neuroinflammation . lithium nicotinate has 
 been used in russia for the treatment of alcoholism and stress . this lithium salt is distinguished by low toxicity and good tolerance . collectively , these findings suggest that lithium 
 salicylate and lithium nicotinate might be advantageous to current 
 fda - approved lithium salts from efficacy and toxicity standpoints , 
 respectively . as such , they are ideal as building blocks for the next 
 generation of lithium therapeutics . conversely , other lithium salts 
 should probably be avoided for pharmaceutical applications . in two 
 recent communications , wouters et al . and braga et al . reported new 
 iccs of lithium chloride and lithium bromide with racetams . although racetams generally possess good toxicity profiles and might 
 prove to act synergistically with lithium , bromide salts have been 
 known to cause serious side effects that were coined bromism . this illustrates the importance of considering the safety of all 
 components during crystal engineering studies that involve pharmaceutical 
 materials . development of multicomponent salt forms as apis 
 for the treatment 
 of bipolar disorder would require high monetary investment and development 
 of such drug products would therefore have to be enabled through exclusive 
 intellectual property protection . moreover , they are known to modify the physicochemical 
 properties and pharmacokinetics of an api . in our experiments , we 
 synthesized and characterized novel iccs of lithium salicylate and 
 lithium nicotinate with the amino acid proline . lispro was selected 
 for efficacy and pharmacokinetic evaluations due to the likelihood 
 for additive or possibly even synergistic effects in treating neuropsychiatric 
 diseases due to the biologically noninert anion , salicylic acid . to our knowledge , this represents the first biological assessment 
 of what is likely to become a very important class of pharmaceutical 
 materials ( iccs ) . our findings suggest that this change in speciation 
 did not negatively affect the in vitro bioactivity 
 of lithium at established targets for the treatment of neuropsychiatric 
 disorders relative to the corresponding parent lithium salt . furthermore , 
 this is the first report of the pharmacokinetics of a cocrystal of 
 a suspected bcs class i api as defined by amidon et al . compared to an fda - approved lithium salt , lithium 
 carbonate ( li2co3 ) , in addition to 
 being more efficacious by exploiting potential synergies , lispro may 
 also offer a better safety profile due to unexpected pharmacokinetic 
 changes . we found that a 4 meq / kg dose of lispro to rats provided 
 consistently elevated levels of lithium in the plasma and brain out 
 to 48 h. conversely , li2co3 was almost undetectable 
 at 48 h in the plasma and produced a large spike in the plasma and 
 brain at 24 h post dose . this type of pharmacokinetic profile can 
 contribute to the toxicity of lithium given its narrow therapeutic 
 window . indeed , lippman and evans suggested that an ideal lithium 
 preparation would attenuate high blood level peaks and exhibit gradually 
 declining blood concentrations . this 
 has been the driving logic behind the development and evaluation of 
 many controlled release formulations . recently , emami et al . 
 evaluated the pharmacokinetics of a proprietary sustained - release 
 li2co3 formulation compared to eskalith cr , 
 the fda approved controlled - release li2co3 formulation , 
 and conventional li2co3 in man . they found that the plasma spike produced by conventional 
 lithium carbonate was greatly reduced in their proprietary formulation 
 and eskalith cr and conclude that this could be used to reduce the 
 frequency of dosing and improve patient compliance . the pharmacokinetics 
 exhibited by our icc of lithium salicylate , lispro , is very similar 
 to those in controlled release formulations . this apparent pharmacokinetic 
 advantage of lispro compared to conventional lithium carbonate was 
 unexpected . although serendipitous in nature , this finding could be 
 key in creating the next generation of lithium therapeutics . if these 
 pharmacokinetic changes can be used to modify the dosing regimen for 
 lithium therapy , this could improve patient compliance and reduce 
 toxicity . future studies are required to evaluate potential toxicity 
 and efficacy advantages in vivo during maintenance 
 lithium therapy conditions . since we have attained a more attractive in vivo pharmacokinetic profile and equivalent in 
 vitro bioactivity at key therapeutic points , it would be 
 quite significant 
 if we could alleviate side effects in vivo or exploit 
 synergistic activities with these or other lithium iccs . specifically , 
 future studies are required to assess safety and efficacy advantages 
 of lithium iccs in vivo . indeed , these findings represent 
 an important initial step in the crystal engineering enabled development 
 of the next generation of lithium therapeutics .
current 
 united states food and drug administration ( fda)-approved 
 lithium salts are plagued with a narrow therapeutic window . 
 recent 
 attempts to find alternative drugs have identified new chemical entities , 
 but lithium s polypharmacological mechanisms for treating neuropsychiatric 
 disorders are highly debated and are not yet matched . 
 thus , re - engineering 
 current lithium solid forms in order to optimize performance represents 
 a low cost and low risk approach to the desired therapeutic outcome . 
 in this contribution , we employed a crystal engineering strategy to 
 synthesize the first ionic cocrystals ( iccs ) of lithium salts with 
 organic anions . 
 we are unaware of any previous studies that have assessed 
 the biological efficacy of any iccs , and encouragingly we found that 
 the new speciation did not negatively affect established bioactivities 
 of lithium . 
 we also observed that lithium iccs exhibit modulated pharmacokinetics 
 compared to lithium carbonate . 
 indeed , the studies detailed herein 
 represent an important advancement in a crystal engineering approach 
 to a new generation of lithium therapeutics .