Lithium: a versatile tool for understanding renal physiology

Many kinases for controlling the water channel aquaporin-2

Aquaporin-2 (AQP2) is a member of the aquaporin water channel family. In the kidney, AQP2 is expressed in collecting duct principal cells where it facilitates water reabsorption in response to antidiuretic hormone (arginine vasopressin, AVP). AVP induces the redistribution of AQP2 from intracellular vesicles and its incorporation into the plasma membrane. The plasma membrane insertion of AQP2 represents the crucial step in AVP-mediated water reabsorption. Dysregulation of the system preventing the AQP2 plasma membrane insertion causes diabetes insipidus (DI), a disease characterised by an impaired urine concentrating ability and polydipsia. There is no satisfactory treatment of DI available. This review discusses kinases that control the localisation of AQP2 and points out potential kinase-directed targets for the treatment of DI.

Bipolar mania and epilepsy pathophysiology and treatment may converge in purine metabolism: A new perspective on available evidence

Decreased ATPergic signaling is an increasingly recognized pathophysiology in bipolar mania disease models. In parallel, adenosine deficit is increasingly recognized in epilepsy pathophysiology. Under-recognized ATP and/or adenosine-increasing mechanisms of several antimanic and antiseizure therapies including lithium, valproate, carbamazepine, and ECT suggest a fundamental pathogenic role of adenosine deficit in bipolar mania to match the established role of adenosine deficit in epilepsy. The depletion of adenosine-derivatives within the purine cycle is expected to result in a compensatory increase in oxopurines (uric acid precursors) and secondarily increased uric acid, observed in both bipolar mania and epilepsy. Cortisol-based inhibition of purine conversion to adenosine-derivatives may be reflected in observed uric acid increases and the well-established contribution of cortisol to both bipolar mania and epilepsy pathology. Cortisol-inhibited conversion from IMP to AMP as precursor of both ATP and adenosine may represent a mechanism for treatment resistance common in both bipolar mania and epilepsy. Anti-cortisol therapies may therefore augment other treatments both in bipolar mania and epilepsy. Evidence linking (i) adenosine deficit with a decreased need for sleep, (ii) IMP/cGMP excess with compulsive hypersexuality, and (iii) guanosine excess with grandiose delusions may converge to suggest a novel theory of bipolar mania as a condition characterized by disrupted purine metabolism. The potential for disease-modification and prevention related to adenosine-mediated epigenetic changes in epilepsy may be mirrored in mania. Evaluating the purinergic effects of existing agents and validating purine dysregulation may improve diagnosis and treatment in bipolar mania and epilepsy and provide specific targets for drug development.

Is There a Need for a Dedicated Pharmacokinetic Trial for a Drug in Obese Populations? A Drug Prioritization Decision Tree Framework

Obesity is a growing global health concern associated with high comorbidity rates, leading to an increasing number of patients who are obese requiring medication. However, clinical trials often exclude or under-represent individuals who are obese, creating the need for a methodology to adjust labeling to ensure safe and effective dosing for all patients. To address this, we developed a 2-part decision tree framework to prioritize drugs for dedicated pharmacokinetic studies in obese subjects. Leveraging current drug knowledge and modeling techniques, the decision tree system predicts expected exposure changes and recommends labeling strategies, allowing stakeholders to prioritize resources toward the drugs most in need. In a case study evaluating 30 drugs from literature across different therapeutic areas, our first decision tree predicted the expected direction of exposure change accurately in 73% of cases. We conclude that this decision tree system offers a valuable tool to advance research in obesity pharmacology and personalize drug development for patients who are obese, ensuring safe and effective medication.

Reimagining safe lithium applications in the living environment and its impacts on human, animal, and plant system

Lithium's (Li) ubiquitous distribution in the environment is a rising concern due to its rapid proliferation in the modern electronic industry. Li enigmatic entry into the terrestrial food chain raises many questions and uncertainties that may pose a grave threat to living biota. We examined the leverage existing published articles regarding advances in global Li resources, interplay with plants, and possible involvement with living organisms, especially humans and animals. Globally, Li concentration (<10-300 mg kg^-1) is detected in agricultural soil, and their pollutant levels vary with space and time. High mobility of Li results in higher accumulation in plants, but the clear mechanisms and specific functions remain unknown. Our assessment reveals the causal relationship between Li level and biota health. For example, lower Li intake (<0.6 mM in serum) leads to mental disorders, while higher intake (>1.5 mM in serum) induces thyroid, stomach, kidney, and reproductive system dysfunctions in humans and animals. However, there is a serious knowledge gap regarding Li regulatory standards in environmental compartments, and mechanistic approaches to unveil its consequences are needed. Furthermore, aggressive efforts are required to define optimum levels of Li for the normal functioning of animals, plants, and humans. This review is designed to revitalize the current status of Li research and identify the key knowledge gaps to fight back against the mountainous challenges of Li during the recent digital revolution. Additionally, we propose pathways to overcome Li problems and develop a strategy for effective, safe, and acceptable applications.

Atorvastatin lowers serum calcium levels in lithium-users: results from a randomized controlled trial

BACKGROUND

Although lithium is considered the gold-standard treatment for bipolar disorder (BD), it is associated with a variety of major endocrine and metabolic side effects, including parathyroid hormone (PTH) dependent hypercalcemia. Aside from surgery and medication discontinuation, there are limited treatments for hypercalcemia. This paper will assess data from a randomized controlled trial (RCT).

METHODS

This is a secondary analysis of an RCT that explored the effects of atorvastatin (n = 27) versus placebo (n = 33) on lithium-induced nephrogenic diabetes insipidus (NDI) in patients with BD and major depressive disorder (MDD) using lithium (n = 60), over a 12-week period. This secondary analysis will explore serum calcium levels and thyroid stimulating hormone (TSH) measured at baseline, week 4, and week 12.

RESULTS

At 12-weeks follow-up while adjusting results for baseline, linear regression analyses found that corrected serum calcium levels were significantly lower in the treatment group (mean (M) = 2.30 mmol/L, standard deviation (SD) = 0.07) compared to the placebo group (M = 2.33 mmol/L, SD = 0.07) (β = - 0.03 (95% C.I.; - 0.0662, - 0.0035), p = 0.03) for lithium users. There were no significant changes in TSH.

CONCLUSION

In lithium users with relatively normal calcium levels, receiving atorvastatin was associated with a decrease in serum calcium levels. Although exciting, this is a preliminary finding that needs further investigation with hypercalcemic patients. Future RCTs could examine whether atorvastatin can treat PTH dependent hypercalcemia due to lithium and other causes.

Lithium Chloride and GSK3 Inhibition Reduce Aquaporin-2 Expression in Primary Cultured Inner Medullary Collecting Duct Cells Due to Independent Mechanisms

Lithium chloride (LiCl) is a widely used drug for the treatment of bipolar disorders, but as a side effect, 40% of the patients develop diabetes insipidus. LiCl affects the activity of the glycogen synthase kinase 3 (GSK3), and mice deficient for GSK3β showed a reduction in the urine concentration capability. The cellular and molecular mechanisms are not fully understood. We used primary cultured inner medullary collecting duct cells to analyze the underlying mechanisms. LiCl and the inhibitor of GSK3 (SB216763) induced a decrease in the aquaporin-2 (Aqp2) protein level. LiCl induced downregulation of Aqp2 mRNA expression while SB216763 had no effect and TWS119 led to increase in expression. The inhibition of the lysosomal activity with bafilomycin or chloroquine prevented both LiCl- and SB216763-mediated downregulation of Aqp2 protein expression. Bafilomycin and chloroquine induced the accumulation of Aqp2 in lysosomal structures, which was prevented in cells treated with dibutyryl cyclic adenosine monophosphate (dbcAMP), which led to phosphorylation and membrane localization of Aqp2. Downregulation of Aqp2 was also evident when LiCl was applied together with dbcAMP, and dbcAMP prevented the SB216763-induced downregulation. We showed that LiCl and SB216763 induce downregulation of Aqp2 via different mechanisms. While LiCl also affected the mRNA level, SB216763 induced lysosmal degradation. Specific GSK3β inhibition had an opposite effect, indicating a more complex regulatory mechanism.

Chloroquine attenuates lithium-induced NDI and proliferation of renal collecting duct cells

Lithium is widely used in psychiatry as the golden standard for more than 60 yr due to its effectiveness. However, its adverse effect has been limiting its long-term use in clinic. About 40% of patients taking lithium develop nephrogenic diabetes insipidus (NDI). Lithium can also induce proliferation of collecting duct cells, leading to microcyst formation in the kidney. Lithium was considered an autophagy inducer that might contribute to the therapeutic benefit of neuropsychiatric disorders. Thus, we hypothesized that autophagy may play a role in lithium-induced kidney nephrotoxicity. To address our hypothesis, we fed mice with a lithium-containing diet with chloroquine (CQ), an autophagy inhibitor, concurrently. Lithium-treated mice presented enhanced autophagy activity in the kidney cortex and medulla. CQ treatment significantly ameliorated lithium-induced polyuria, polydipsia, natriuresis, and kaliuresis accompanied with attenuated downregulation of aquaporin-2 and Na⁺-K⁺-2Cl^- cotransporter protein. The protective effect of CQ on aquaporin-2 protein abundance was confirmed in cultured cortical collecting duct cells. In addition, we found that lithium-induced proliferation of collecting duct cells was also suppressed by CQ as detected by proliferating cell nuclear antigen staining. Moreover, both phosphorylated mammalian target of rapamycin and β-catenin expression, which have been reported to be increased by lithium and associated with cell proliferation, were reduced by CQ. Taken together, our study demonstrated that CQ protected against lithium-induced NDI and collecting duct cell proliferation possibly through inhibiting autophagy.

Systematic review and practical guideline for the prevention and management of the renal side effects of lithium therapy

Lithium is the first line therapy of bipolar mood disorder. Lithium-induced nephrogenic diabetes insipidus (Li-NDI) and lithium nephropathy (Li-NP, i.e., renal insufficiency) are prevalent side effects of lithium therapy, with significant morbidity. The objective of this systematic review is to provide an overview of preventive and management strategies for Li-NDI and Li-NP. For this, the PRISMA guideline for systematic reviews was used. Papers on the prevention and/or treatment of Li-NDI or Li-NP, and (influenceable) risk factors for development of Li-NDI or Li-NP were included. We found that the amount of evidence on prevention and treatment of Li-NDI and Li-NP is scarce. To prevent Li-NDI and Li-NP we advise to use a once-daily dosing schedule, target the lowest serum lithium level that is effective and prevent lithium intoxication. We emphasize the importance of monitoring for Li-NDI and Li-NP, as early diagnosis and treatment can prevent further progression and permanent damage. Collaboration between psychiatrist, nephrologist and patients themselves is essential. In patients with Li-NDI and/or Li-NP cessation of lithium therapy and/or switch to another mood stabilizer should be considered. In patients with Li-NDI, off label therapy with amiloride can be useful.

Extracellular Nucleotides and P2 Receptors in Renal Function

The understanding of the nucleotide/P2 receptor system in the regulation of renal hemodynamics and transport function has grown exponentially over the last 20 yr. This review attempts to integrate the available data while also identifying areas of missing information. First, the determinants of nucleotide concentrations in the interstitial and tubular fluids of the kidney are described, including mechanisms of cellular release of nucleotides and their extracellular breakdown. Then the renal cell membrane expression of P2X and P2Y receptors is discussed in the context of their effects on renal vascular and tubular functions. Attention is paid to effects on the cortical vasculature and intraglomerular structures, autoregulation of renal blood flow, tubuloglomerular feedback, and the control of medullary blood flow. The role of the nucleotide/P2 receptor system in the autocrine/paracrine regulation of sodium and fluid transport in the tubular and collecting duct system is outlined together with its role in integrative sodium and fluid homeostasis and blood pressure control. The final section summarizes the rapidly growing evidence indicating a prominent role of the extracellular nucleotide/P2 receptor system in the pathophysiology of the kidney and aims to identify potential therapeutic opportunities, including hypertension, lithium-induced nephropathy, polycystic kidney disease, and kidney inflammation. We are only beginning to unravel the distinct physiological and pathophysiological influences of the extracellular nucleotide/P2 receptor system and the associated therapeutic perspectives.

Using Lithium in Older Age Bipolar Disorder: Special Considerations

Lithium is the gold-standard treatment for bipolar disorder, and is effective in the management of manic, depressive, and maintenance phases of bipolar disorder treatment. Despite this, the implications of lithium use in the older population remain less understood. This critical narrative review aims to better understand the impact of lithium in older age bipolar disorder (OABD), including tolerability and efficacy, based on up-to-date evidence. Relevant studies of efficacy, effectiveness, and tolerability published any time prior to May 2018 were identified using the PubMed keyword search "lithium older adult bipolar disorder" and references from recent international bipolar disorder guidelines. One randomized controlled trial was identified, the GERI-BD (Acute Pharmacotherapy in Late-Life Mania) study. This study found lithium to be effective in late-life mania and hypomania. The remaining literature examining lithium in OABD was reviewed, comprising of a number of small open-label and retrospective studies, with special considerations highlighted. In summary, there is a small yet increasing geriatric evidence base that lithium is effective in OABD. Although there can be adverse effects with lithium, it is generally well tolerated, and there are methods to minimize these risks. Further research would strengthen the evidence base for lithium therapy in OABD. In the meantime, lithium remains the gold-standard treatment for OABD.

Genetic deletion of ADP-activated P2Y12 receptor ameliorates lithium-induced nephrogenic diabetes insipidus in mice

AIM

Therapeutic use of lithium in bipolar disorder is limited by the development of nephrogenic diabetes insipidus (NDI). We reported that pharmacological blockade of P2Y₁₂ receptor (R) with clopidogrel or prasugrel significantly ameliorated lithium-induced NDI in rodents. Using mice genetically lacking P2Y₁₂ -R we evaluated whether the observed amelioration is mediated through P2Y₁₂ -R METHODS: P2ry12^-/- mouse line (C57/BL6) was rederived from cryopreserved embryos of the knockout (KO) mice generated by Deltagen Inc. Syngeneic wild type (WT) mice obtained by heterozygous crossing were inbred. Groups of adult WT and KO mice were fed lithium-added (40 mmol LiCl/kg food) or regular diet, and euthanized after 2 or 4 weeks. Twenty-four hour urine samples and terminal blood and kidney samples were analyzed.

RESULTS

At both time points, lithium-induced polyuria and decrease in aquaporin-2 (AQP2) protein abundance in the kidney medulla were less marked in KO vs WT mice. Immunofluorescence microscopy revealed that lithium-induced alterations in the cellular disposition of AQP2 protein in the medullary collecting ducts of WT mice were blunted in KO mice. Serum lithium, sodium and osmolality were similar in both genotypes after lithium treatment. After 2 weeks, lithium induced marked increases in urinary excretion of Na, K, and arginine vasopressin in WT mice but not in KO mice.

CONCLUSION

Taken together, our data show that similar to pharmacological blockade, deletion of P2Y₁₂ -R significantly ameliorates lithium-induced NDI, without reducing serum lithium levels. Hence, targeting P2Y₁₂ -R with currently available drugs in the market offers a novel and safer method for treating NDI.

[Renal toxicity of lithium]

Besides its efficiency, lithium has a narrow therapeutic index and can result in considerable toxicity. Among the potential side effects, two types of renal toxicity are observed: a decreased renal concentrating ability and a chronic renal failure. Lithium-induced polyuria is frequent, estimated to affect up to 40% of patients, and develops usually early. It may be irreversible, especially if the treatment has been prescribed for more than 15 years. A chronic renal failure is observed in patients treated for more than 10 to 20 years. Its prevalence is estimated at 12% after 19 years of treatment. Some patients (0.5%) may reach end stage renal disease. The major risk factor is the duration of exposure to lithium. Discussion about stopping or not lithium in case of renal failure needs multidisciplinary expertise and depends on psychiatric status and renal function.

Genetic Deletion of P2Y2 Receptor Offers Long-Term (5 Months) Protection Against Lithium-Induced Polyuria, Natriuresis, Kaliuresis, and Collecting Duct Remodeling and Cell Proliferation

Chronic lithium administration for the treatment of bipolar disorder leads to nephrogenic diabetes insipidus (NDI), characterized by polyuria, natriuresis, kaliuresis, and collecting duct remodeling and cell proliferation among other features. Previously, using a 2-week lithium-induced NDI model, we reported that P2Y2 receptor (R) knockout mice are significantly resistant to polyuria, natriuresis, kaliuresis, and decrease in AQP2 protein abundance in the kidney relative to wild type mice. Here we show this protection is long-lasting, and is also associated with significant amelioration of lithium-induced collecting duct remodeling and cell proliferation. Age-matched wild type and knockout mice were fed regular (n = 5/genotype) or lithium-added (40 mmol/kg chow; n = 10/genotype) diet for 5 months and euthanized. Water intake, urine output and osmolality were monitored once in every month. Salt blocks were provided to mice on lithium-diet to prevent sodium loss. At the end of 5 months mice were euthanized and serum and kidney samples were analyzed. There was a steady increase in lithium-induced polyuria, natriuresis and kaliuresis in wild type mice over the 5-month period. Increases in these urinary parameters were very low in lithium-fed knockout mice, resulting in significantly widening differences between the wild type and knockout mice. Terminal AQP2 and NKCC2 protein abundances in the kidney were significantly higher in lithium-fed knockout vs. wild type mice. There were no significant differences in terminal serum lithium or sodium levels between the wild type and knockout mice. Confocal immunofluorescence microscopy revealed that lithium-induced marked remodeling of collecting duct with significantly increased proportion of [H+]-ATPase-positive intercalated cells and decreased proportion of AQP2-positive principal cells in the wild type, but not in knockout mice. Lithium-induced collecting duct cell proliferation (indicated by Ki67 labeling), was significantly lower in knockout vs. wild type mice. This is the first piece of evidence that purinergic signaling is potentially involved in lithium-induced collecting duct remodeling and cell proliferation. Our results demonstrate that genetic deletion of P2Y2-R protects against the key structural and functional alterations in Li-induced NDI, and underscore the potential utility of targeting this receptor for the treatment of NDI in bipolar patients on chronic lithium therapy.

Bile Acid G Protein-Coupled Membrane Receptor TGR5 Modulates Aquaporin 2-Mediated Water Homeostasis

BACKGROUND

The bile acid-activated receptors, including the membrane G protein-coupled receptor TGR5 and nuclear farnesoid X receptor (FXR), have roles in kidney diseases. In this study, we investigated the role of TGR5 in renal water handling and the underlying molecular mechanisms.

METHODS

We used tubule suspensions of inner medullary collecting duct (IMCD) cells from rat kidneys to investigate the effect of TGR5 signaling on aquaporin-2 (AQP2) expression, and examined the in vivo effects of TGR5 in mice with lithium-induced nephrogenic diabetes insipidus (NDI) and Tgr5 knockout (Tgr5 ^-/-) mice.

RESULTS

Activation of TGR5 by lithocholic acid (LCA), an endogenous TGR5 ligand, or INT-777, a synthetic TGR5-specific agonist, induced AQP2 expression and intracellular trafficking in rat IMCD cells via a cAMP-protein kinase A signaling pathway. In mice with NDI, dietary supplementation with LCA markedly decreased urine output and increased urine osmolality, which was associated with significantly upregulated AQP2 expression in the kidney inner medulla. Supplementation with endogenous FXR agonist had no effect. In primary IMCD suspensions from lithium-treated rats, treatment with INT-767 (FXR and TGR5 dual agonist) or INT-777, but not INT-747 (FXR agonist), increased AQP2 expression. Tgr5 ^-/- mice exhibited an attenuated ability to concentrate urine in response to dehydration, which was associated with decreased AQP2 expression in the kidney inner medulla. In lithium-treated Tgr5 ^-/- mice, LCA treatment failed to prevent reduction of AQP2 expression.

CONCLUSIONS

TGR5 stimulation increases renal AQP2 expression and improves impaired urinary concentration in lithium-induced NDI. TGR5 is thus involved in regulating water metabolism in the kidney.

Chronic lithium treatment induces novel patterns of pendrin localization and expression

Prolonged lithium treatment is associated with various renal side effects and is known to induce inner medullary collecting duct (IMCD) remodeling. In animals treated with lithium, the fraction of intercalated cells (ICs), which are responsible for acid-base homeostasis, increases compared with renal principal cells (PCs). To investigate the intricacies of lithium-induced IMCD remodeling, male Sprague-Dawley rats were fed a lithium-enriched diet for 0,1, 2, 3, 6, 9, or 12 wk. Urine osmolality was decreased at 1 wk, and from 2 to 12 wk, animals were severely polyuric. After 6 wk of lithium treatment, approximately one-quarter of the cells in the initial IMCD expressed vacuolar H⁺-ATPase, an IC marker. These cells were localized in portions of the inner medulla, where ICs are not normally found. Pendrin, a Cl^-/[Formula: see text] exchanger, is normally expressed only in two IC subtypes found in the convoluted tubule, the cortical collecting duct, and the connecting tubule. At 6 wk of lithium treatment, we observed various patterns of pendrin localization and expression in the rat IMCD, including a novel phenotype wherein pendrin was coexpressed with aquaporin-4. These observations collectively suggest that renal IMCD cell plasticity may play an important role in lithium-induced IMCD remodeling.

Use of acetazolamide in lithium-induced nephrogenic diabetes insipidus: a case report

Lithium-induced nephrogenic diabetes insipidus (Li-NDI) is a rare and difficult-to-treat condition. A study in mice and two recent papers describe the use of acetazolamide in Li-NDI in 7 patients (a case report and a 6 patient series). We describe the case of a 63-year-old woman with bipolar disorder treated with lithium and no previous history of diabetes insipidus. She was hospitalized due to a bowel obstruction and developed severe dehydration after surgery when she was water deprived. After desmopressin administration and unsuccessful thiazide and amiloride treatment, acetazolamide was administrated to control polyuria and hydroelectrolytic disorders without significant side effects. To our knowledge, this is the third publication on acetazolamide use in Li-NDI patients.

The soluble (Pro) renin receptor does not influence lithium-induced diabetes insipidus but does provoke beiging of white adipose tissue in mice

Earlier we reported that the recombinant soluble (pro) renin receptor sPRR-His upregulates renal aquoporin-2 (AQP2) expression, and attenuates polyuria associated with nephrogenic diabetes insipidus (NDI) induced by vasopressin type 2 receptor (V2R) antagonism. Patients that receive lithium therapy develop polyuria associated NDI that might be secondary to downregulation of renal AQP2. We hypothesized that sPRR-His attenuates indices of NDI associated with lithium treatment. Eight-week-old male C57/BL6 mice consumed chow supplemented with LiCl (40 mmol/kg diets) for 14 days. For the last 7 days mice received either sPRR-His [30 μg/(kg day), i.v.; sPRR] or vehicle (Veh) via minipump. Control (Con) mice consumed standard chow for 14 days. Compared to Con mice, 14-d LiCl treatment elevated water intake and urine volume, and decreased urine osmolality, regardless of sPRR-His or Veh administration. These data indicate that sPRR-His treatment does not attenuate indices of NDI evoked by lithium. Unexpectedly, epididymal fat mass was lower, adipocyte UCP1 mRNA and protein expression were higher, and multilocular lipid morphology was enhanced, in LiCl-fed mice treated with sPRR-His versus vehicle. The beiging of white adipose tissue is a novel metabolic benefit of manipulating the sPRR in the context of lithium-induced NDI.

Drug Interactions with Lithium: An Update

Lithium has been used for the management of psychiatric illnesses for over 50 years and it continues to be regarded as a first-line agent for the treatment and prevention of bipolar disorder. Lithium possesses a narrow therapeutic index and comparatively minor alterations in plasma concentrations can have significant clinical sequelae. Several drug classes have been implicated in the development of lithium toxicity over the years, including diuretics and non-steroidal anti-inflammatory compounds, but much of the anecdotal and experimental evidence supporting these interactions is dated, and many newer medications and medication classes have been introduced during the intervening years. This review is intended to provide an update on the accumulated evidence documenting potential interactions with lithium, with a focus on pharmacokinetic insights gained within the last two decades. The clinical relevance and ramifications of these interactions are discussed.

Prasugrel suppresses development of lithium-induced nephrogenic diabetes insipidus in mice

Previously, we localized ADP-activated P2Y12 receptor (R) in rodent kidney and showed that its blockade by clopidogrel bisulfate (CLPD) attenuates lithium (Li)-induced nephrogenic diabetes insipidus (NDI). Here, we evaluated the effect of prasugrel (PRSG) administration on Li-induced NDI in mice. Both CLPD and PRSG belong to the thienopyridine class of ADP receptor antagonists. Groups of age-matched adult male B6D2 mice (N = 5/group) were fed either regular rodent chow (CNT), or with added LiCl (40 mmol/kg chow) or PRSG in drinking water (10 mg/kg bw/day) or a combination of LiCl and PRSG for 14 days and then euthanized. Water intake and urine output were determined and blood and kidney tissues were collected and analyzed. PRSG administration completely suppressed Li-induced polydipsia and polyuria and significantly prevented Li-induced decreases in AQP2 protein abundance in renal cortex and medulla. However, PRSG either alone or in combination with Li did not have a significant effect on the protein abundances of NKCC2 or NCC in the cortex and/or medulla. Immunofluorescence microscopy revealed that PRSG administration prevented Li-induced alterations in cellular disposition of AQP2 protein in medullary collecting ducts. Serum Li, Na, and osmolality were not affected by the administration of PRSG. Similar to CLPD, PRSG administration had no effect on Li-induced increase in urinary Na excretion. However, unlike CLPD, PRSG did not augment Li-induced increase in urinary arginine vasopressin (AVP) excretion. Taken together, these data suggest that the pharmacological inhibition of P2Y12-R by the thienopyridine group of drugs may potentially offer therapeutic benefits in Li-induced NDI.

Role of adenylyl cyclase 6 in the development of lithium-induced nephrogenic diabetes insipidus

Psychiatric patients treated with lithium (Li⁺) may develop nephrogenic diabetes insipidus (NDI). Although the etiology of Li⁺-induced NDI (Li-NDI) is poorly understood, it occurs partially due to reduced aquaporin-2 (AQP2) expression in the kidney collecting ducts. A mechanism postulated for this is that Li⁺ inhibits adenylyl cyclase (AC) activity, leading to decreased cAMP, reduced AQP2 abundance, and less membrane targeting. We hypothesized that Li-NDI would not develop in mice lacking AC6. Whole-body AC6 knockout (AC6^-/-) mice and potentially novel connecting tubule/principal cell-specific AC6 knockout (AC6^loxloxCre) mice had approximately 50% lower urine osmolality and doubled water intake under baseline conditions compared with controls. Dietary Li⁺ administration increased water intake and reduced urine osmolality in control, AC6^-/-, and AC6^loxloxCre mice. Consistent with AC6^-/- mice, medullary AQP2 and pS256-AQP2 abundances were lower in AC6^loxloxCre mice compared with controls under standard conditions, and levels were further reduced after Li⁺ administration. AC6^loxloxCre and control mice had a similar increase in the numbers of proliferating cell nuclear antigen-positive cells in response to Li⁺. However, AC6^loxloxCre mice had a higher number of H⁺-ATPase B1 subunit-positive cells under standard conditions and after Li⁺ administration. Collectively, AC6 has a minor role in Li-NDI development but may be important for determining the intercalated cell-to-principal cell ratio.

Involvement of ENaC in the development of salt-sensitive hypertension

Salt-sensitive hypertension is associated with renal and vascular dysfunctions, which lead to impaired fluid excretion, increased cardiac output, and total peripheral resistance. It is commonly accepted that increased renal sodium handling and plasma volume expansion are necessary factors for the development of salt-induced hypertension. The epithelial sodium channel (ENaC) is a trimeric ion channel expressed in the distal nephron that plays a critical role in the regulation of sodium reabsorption in both normal and pathological conditions. In this mini-review, we summarize recent studies investigating the role of ENaC in the development of salt-sensitive hypertension. On the basis of experimental data obtained from the Dahl salt-sensitive rats, we and others have demonstrated that abnormal ENaC activation in response to a dietary NaCl load contributes to the development of high blood pressure in this model. The role of different humoral factors, such as the components of the renin-angiotensin-aldosterone system, members of the epidermal growth factors family, arginine vasopressin, and oxidative stress mediating the effects of dietary salt on ENaC are discussed in this review to highlight future research directions and to determine potential molecular targets for drug development.

Gsk3 Signalling and Redox Status in Bipolar Disorder: Evidence from Lithium Efficacy

Objective. To discuss the link between glycogen synthase kinase-3 (GSK3) and the main biological alterations demonstrated in bipolar disorder (BD), with special attention to the redox status and the evidence supporting the efficacy of lithium (a GSK3 inhibitor) in the treatment of BD. Methods. A literature research on the discussed topics, using Pubmed and Google Scholar, has been conducted. Moreover, a manual selection of interesting references from the identified articles has been performed. Results. The main biological alterations of BD, pertaining to inflammation, oxidative stress, membrane ion channels, and circadian system, seem to be intertwined. The dysfunction of the GSK3 signalling pathway is involved in all the aforementioned “biological causes” of BD. In a complex scenario, it can be seen as the common denominator linking them all. Lithium inhibition of GSK3 could, at least in part, explain its positive effect on these biological dysfunctions and its superiority in terms of clinical efficacy. Conclusions. Deepening the knowledge on the molecular bases of BD is fundamental to identifying the biochemical pathways that must be targeted in order to provide patients with increasingly effective therapeutic tools against an invalidating disorder such as BD.

Sex-specific effects of LiCl treatment on preservation of renal function and extended life-span in murine models of SLE: perspective on insights into the potential basis for survivorship in NZB/W female mice

Considerable research effort has been invested in attempting to understand immune dysregulation leading to autoimmunity and target organ damage. In systemic lupus erythematosus (SLE), patients can develop a systemic disease with a number of organs involved. One of the major target organs is the kidney, but patients vary in the progression of the end-organ targeting of this organ. Some patients develop glomerulonephritis only, while others develop rapidly progressive end organ failure. In murine models of SLE, renal involvement can also occur. Studies performed over the past several years have indicated that treatment with LiCl of females, but not males of the NZB/W model, at an early age during the onset of disease, can prevent development of end-stage renal disease in a significant percentage of the animals. While on Li treatment, up to 80 % of the females can exhibit long-term survival with evidence of mild glomerulonephritis which does not progress to renal failure in spite of on-going autoimmunity. Stopping the treatment led to a reactivation of the disease and renal failure. Li treatment of other murine models of SLE was less effective and decreased survivorship in male BxSB mice, exhibited little effect on male MRL-lpr mice, and only modestly improved survivorship in female MRL-lpr mice. This perspective piece discusses the findings of several related studies which support the concept that protecting target organs such as the kidney, even in the face of continued immune insults and some inflammation, can lead to prolonged survival with retention of organ function. Some possible mechanisms for the effectiveness of Li treatment in this context are also discussed. However, the detailed mechanistic basis for the sex-specific effects of LiCl treatment particularly in the NZB/W model remains to be elucidated. Elucidating such details may provide important clues for development of effective treatment for patients with SLE, ~90 % of which are females.

The AQP-3 water channel is a pivotal modulator of glycerol-induced chloride channel activation in nasopharyngeal carcinoma cells

Aquaporin (AQP) and chloride channels are ubiquitous in virtually all living cells, playing pivotal roles in cell proliferation, migration and apoptosis. We previously reported that AQP-3 aquaglyceroporin and ClC-3 chloride channels could form complexes to regulate cell volume in nasopharyngeal carcinoma cells. In this study, the roles of AQP-3 in their hetero-complexes were further investigated. Glycerol entered the cells via AQP-3 and induced two different Cl(-) currents through cell swelling-dependent or -independent pathways. The swelling-dependent Cl(-) current was significantly inhibited by pretreatment with CuCl2 and AQP-3-siRNA. After siRNA-induced AQP-3 knock-down, the 140 mM glycerol isoosmotic solution swelled cells by 22% (45% in AQP-3-intact cells) and induced a smaller Cl(-) current; this current was smaller than that activated by 8% cell volume swelling, which induced by the 140 mM glycerol hyperosmotic solution in AQP-3-intact cells. This suggests that the interaction between AQP-3 and ClC-3 plays an important role in cell volume regulation and that AQP-3 may be a modulator that opens volume-regulated chloride channels. The swelling-independent Cl(-) current, which was activated by extracellular glycerol, was reduced by CuCl2 and AQP-3-siRNA pretreatment. Dialyzing glycerol into cells via the pipette directly induced the swelling-independent Cl(-) current; however this current was blocked by AQP-3 down-regulation, suggesting AQP-3 is essential for the opening of chloride channels. In conclusion, AQP-3 is the pathway for water, glycerol and other small solutes to enter cells, and it may be an essential modulator for the gating of chloride channels.

Clopidogrel attenuates lithium-induced alterations in renal water and sodium channels/transporters in mice

Lithium (Li) administration causes deranged expression and function of renal aquaporins and sodium channels/transporters resulting in nephrogenic diabetes insipidus (NDI). Extracellular nucleotides (ATP/ADP/UTP), via P2 receptors, regulate these transport functions. We tested whether clopidogrel bisulfate (CLPD), an antagonist of ADP-activated P2Y(12) receptor, would affect Li-induced alterations in renal aquaporins and sodium channels/transporters. Adult mice were treated for 14 days with CLPD and/or Li and euthanized. Urine and kidneys were collected for analysis. When administered with Li, CLPD ameliorated polyuria, attenuated the rise in urine prostaglandin E2 (PGE2), and resulted in significantly higher urinary arginine vasopressin (AVP) and aldosterone levels as compared to Li treatment alone. However, urine sodium excretion remained elevated. Semi-quantitative immunoblotting revealed that CLPD alone increased renal aquaporin 2 (AQP2), Na-K-2Cl cotransporter (NKCC2), Na-Cl cotransporter (NCC), and the subunits of the epithelial Na channel (ENaC) in medulla by 25-130 %. When combined with Li, CLPD prevented downregulation of AQP2, Na-K-ATPase, and NKCC2 but was less effective against downregulation of cortical α- or γ-ENaC (70 kDa band). Thus, CLPD primarily attenuated Li-induced downregulation of proteins involved in water conservation (AVP-sensitive), with modest effects on aldosterone-sensitive proteins potentially explaining sustained natriuresis. Confocal immunofluorescence microscopy revealed strong labeling for P2Y(12)-R in proximal tubule brush border and blood vessels in the cortex and less intense labeling in medullary thick ascending limb and the collecting ducts. Therefore, there is the potential for CLPD to be directly acting at the tubule sites to mediate these effects. In conclusion, P2Y(12)-R may represent a novel therapeutic target for Li-induced NDI.

Medical comorbidity, acute medical care use in late-life bipolar disorder: a comparison of lithium, valproate, and other pharmacotherapies

OBJECTIVE

Bipolar disorder is associated with high rates of medical comorbidity, particularly in late life. Little is known about medical health service utilization and potential effects of bipolar pharmacotherapy. We hypothesized that lithium use would not be associated with higher rates of medical hospitalization.

METHODS

Population-based retrospective cohort study of 1388 bipolar disorder patients aged ≥66years discharged from a psychiatric hospitalization in Ontario, Canada, between 2006 and 2012. Patients were divided into lithium users, valproate users, and non-lithium/non-valproate users. The main outcome was acute non-psychiatric, medical/surgical hospitalization during 1-year follow-up.

RESULTS

The rate of medical hospitalizations was 0.22 per patient-year. Time-to-medical hospitalization did not differ among lithium, valproate, and non-lithium/non-valproate users after adjusting for age, sex, past medical hospitalization, and antipsychotic use. Lithium, valproate, and non-lithium/non-valproate users did not differ markedly in terms of reason for medical hospitalization, 1-year acute medical health utilization outcomes, and medical comorbidity rates.

CONCLUSION

There were high rates of health service use for medical conditions among older adults with bipolar disorder, but this did not appear to be associated with lithium use, compared to valproate and other medication use (e.g., antipsychotics). A proactive collaborative care approach may prevent medical service utilization in severe late-life bipolar disorder.

Targeting renal purinergic signalling for the treatment of lithium-induced nephrogenic diabetes insipidus

Lithium still retains its critical position in the treatment of bipolar disorder by virtue of its ability to prevent suicidal tendencies. However, chronic use of lithium is often limited by the development of nephrogenic diabetes insipidus (NDI), a debilitating condition. Lithium-induced NDI is due to resistance of the kidney to arginine vasopressin (AVP), leading to polyuria, natriuresis and kaliuresis. Purinergic signalling mediated by extracellular nucleotides (ATP/UTP), acting via P2Y receptors, opposes the action of AVP on renal collecting duct (CD) by decreasing the cellular cAMP and thus AQP2 protein levels. Taking a cue from this phenomenon, we discovered the potential involvement of ATP/UTP-activated P2Y2 receptor in lithium-induced NDI in rats and showed that P2Y2 receptor knockout mice are significantly resistant to Li-induced polyuria, natriuresis and kaliuresis. Extension of these studies revealed that ADP-activated P2Y12 receptor is expressed in the kidney, and its irreversible blockade by the administration of clopidogrel bisulphate (Plavix(®)) ameliorates Li-induced NDI in rodents. Parallel in vitro studies showed that P2Y12 receptor blockade by the reversible antagonist PSB-0739 sensitizes CD to the action of AVP. Thus, our studies unravelled the potential beneficial effects of targeting P2Y2 or P2Y12 receptors to counter AVP resistance in lithium-induced NDI. If established in further studies, our findings may pave the way for the development of better and safer methods for the treatment of NDI by bringing a paradigm shift in the approach from the current therapies that predominantly counter the anti-AVP effects to those that enhance the sensitivity of the kidney to AVP action.

P2Y12 Receptor Localizes in the Renal Collecting Duct and Its Blockade Augments Arginine Vasopressin Action and Alleviates Nephrogenic Diabetes Insipidus

P2Y12 receptor (P2Y12-R) signaling is mediated through Gi, ultimately reducing cellular cAMP levels. Because cAMP is a central modulator of arginine vasopressin (AVP)-induced water transport in the renal collecting duct (CD), we hypothesized that if expressed in the CD, P2Y12-R may play a role in renal handling of water in health and in nephrogenic diabetes insipidus. We found P2Y12-R mRNA expression in rat kidney, and immunolocalized its protein and aquaporin-2 (AQP2) in CD principal cells. Administration of clopidogrel bisulfate, an irreversible inhibitor of P2Y12-R, significantly increased urine concentration and AQP2 protein in the kidneys of Sprague-Dawley rats. Notably, clopidogrel did not alter urine concentration in Brattleboro rats that lack AVP. Clopidogrel administration also significantly ameliorated lithium-induced polyuria, improved urine concentrating ability and AQP2 protein abundance, and reversed the lithium-induced increase in free-water excretion, without decreasing blood or kidney tissue lithium levels. Clopidogrel administration also augmented the lithium-induced increase in urinary AVP excretion and suppressed the lithium-induced increase in urinary nitrates/nitrites (nitric oxide production) and 8-isoprostane (oxidative stress). Furthermore, selective blockade of P2Y12-R by the reversible antagonist PSB-0739 in primary cultures of rat inner medullary CD cells potentiated the expression of AQP2 and AQP3 mRNA, and cAMP production induced by dDAVP (desmopressin). In conclusion, pharmacologic blockade of renal P2Y12-R increases urinary concentrating ability by augmenting the effect of AVP on the kidney and ameliorates lithium-induced NDI by potentiating the action of AVP on the CD. This strategy may offer a novel and effective therapy for lithium-induced NDI.

Collecting duct intercalated cell function and regulation

Intercalated cells are kidney tubule epithelial cells with important roles in the regulation of acid-base homeostasis. However, in recent years the understanding of the function of the intercalated cell has become greatly enhanced and has shaped a new model for how the distal segments of the kidney tubule integrate salt and water reabsorption, potassium homeostasis, and acid-base status. These cells appear in the late distal convoluted tubule or in the connecting segment, depending on the species. They are most abundant in the collecting duct, where they can be detected all the way from the cortex to the initial part of the inner medulla. Intercalated cells are interspersed among the more numerous segment-specific principal cells. There are three types of intercalated cells, each having distinct structures and expressing different ensembles of transport proteins that translate into very different functions in the processing of the urine. This review includes recent findings on how intercalated cells regulate their intracellular milieu and contribute to acid-base regulation and sodium, chloride, and potassium homeostasis, thus highlighting their potential role as targets for the treatment of hypertension. Their novel regulation by paracrine signals in the collecting duct is also discussed. Finally, this article addresses their role as part of the innate immune system of the kidney tubule.

Association between bipolar episodes and fluid and electrolyte homeostasis: a retrospective longitudinal study

OBJECTIVES

Imbalance of fluid and electrolyte homeostasis has been suggested to be associated with the neuropathological processes underlying bipolar disorder. However, longitudinal data regarding the association of bipolar episodes with fluid balance are still lacking. We hypothesized that mania may be associated with a relative fluid retention and hemodilution, and depression with a relative hemoconcentration.

METHODS

Patients with bipolar disorder (n = 43) admitted to a mental health center, both with depressive and manic episodes, were retrospectively followed between 2005 and 2013. Fluid balance and electrolyte serum indices were compared between their manic and depressive episodes. We adjusted for physical and psychiatric comorbidities and for psychotropic treatment, using two-way analysis of variance with repeated measures.

RESULTS

There was a significant reduction in serum fluid balance indices during mania compared to depression: mean hemoglobin concentration 13.9 ± 1.4 g/dL versus 14.5 ± 1.4 g/dL, paired t = -4.2, p < 0.0005; mean hematocrit 41.1 ± 4.1% versus 42.3 ± 3.7%, paired t = -3.0, p < 0.005; mean albumin concentration 4.2 ± 0.3 g/dL versus 4.5 ± 0.3 g/dL, paired t = -4.5, p < 0.0001; and mean sodium concentration 140.3 ± 2.0 mEq/L versus 141.0 ± 2.0 mEq/L, paired t = -2.1, p = 0.04, respectively. Controlling for physical and psychiatric comorbidities and psychotropic treatment did not alter these associations.

CONCLUSIONS

Our results support the notion of an imbalance of fluid and electrolyte homeostasis among bipolar episodes, which is suggestive for relative hemoconcentration during depressive episodes and relative hemodilution during manic episodes. These findings may eventually lead to novel therapeutic targets.

Absence of PKC-alpha attenuates lithium-induced nephrogenic diabetes insipidus

Lithium, an effective antipsychotic, induces nephrogenic diabetes insipidus (NDI) in ∼40% of patients. The decreased capacity to concentrate urine is likely due to lithium acutely disrupting the cAMP pathway and chronically reducing urea transporter (UT-A1) and water channel (AQP2) expression in the inner medulla. Targeting an alternative signaling pathway, such as PKC-mediated signaling, may be an effective method of treating lithium-induced polyuria. PKC-alpha null mice (PKCα KO) and strain-matched wild type (WT) controls were treated with lithium for 0, 3 or 5 days. WT mice had increased urine output and lowered urine osmolality after 3 and 5 days of treatment whereas PKCα KO mice had no change in urine output or concentration. Western blot analysis revealed that AQP2 expression in medullary tissues was lowered after 3 and 5 days in WT mice; however, AQP2 was unchanged in PKCα KO. Similar results were observed with UT-A1 expression. Animals were also treated with lithium for 6 weeks. Lithium-treated WT mice had 19-fold increased urine output whereas treated PKCα KO animals had a 4-fold increase in output. AQP2 and UT-A1 expression was lowered in 6 week lithium-treated WT animals whereas in treated PKCα KO mice, AQP2 was only reduced by 2-fold and UT-A1 expression was unaffected. Urinary sodium, potassium and calcium were elevated in lithium-fed WT but not in lithium-fed PKCα KO mice. Our data show that ablation of PKCα preserves AQP2 and UT-A1 protein expression and localization in lithium-induced NDI, and prevents the development of the severe polyuria associated with lithium therapy.

Regulation of mineral metabolism by lithium

Lithium, an inhibitor of glycogen synthase kinase 3 (GSK3), is widely used for the treatment of mood disorders. Side effects of lithium include nephrogenic diabetes insipidus, leading to renal water loss. Dehydration has in turn been shown to downregulate Klotho, which is required as co-receptor for the downregulation of 1,25(OH)2D3 formation by fibroblast growth factor 23 (FGF23). FGF23 decreases and 1,25(OH)2D3 stimulates renal tubular phosphate reabsorption. The present study explored whether lithium influences renal Klotho expression, FGF23 serum levels, 1,25(OH)2D3 formation, and renal phosphate excretion. To this end, mice were analyzed after a 14-day period of sham treatment or of treatment with lithium (200 mg/kg/day subcutaneously). Serum antidiuretic hormone (ADH), FGF23, and 1,25(OH)2D3 concentrations were determined by ELISA or EIA, renal Klotho protein abundance and GSK3 phosphorylation were analyzed by Western blotting, and serum phosphate and calcium concentration by photometry. Lithium treatment significantly increased renal GSK3 phosphorylation, enhanced serum ADH and FGF23 concentrations, downregulated renal Klotho expression, stimulated renal calcium and phosphate excretion, and decreased serum 1,25(OH)2D3 and phosphate concentrations. In conclusion, lithium treatment upregulates FGF23 formation, an effect paralleled by substantial decrease of serum 1,25(OH)2D3, and phosphate concentrations and thus possibly affecting tissue calcification.

Rapamycin inhibition of mTORC1 reverses lithium-induced proliferation of renal collecting duct cells

Nephrogenic diabetes insipidus (NDI) is the most common renal side effect in patients undergoing lithium therapy for bipolar affective disorders. Approximately 2 million US patients take lithium of whom ∼50% will have altered renal function and develop NDI (2, 37). Lithium-induced NDI is a defect in the urinary concentrating mechanism. Lithium therapy also leads to proliferation and abundant renal cysts (microcysts), commonly in the collecting ducts of the cortico-medullary region. The mTOR pathway integrates nutrient and mitogen signals to control cell proliferation and cell growth (size) via the mTOR Complex 1 (mTORC1). To address our hypothesis that mTOR activation may be responsible for lithium-induced proliferation of collecting ducts, we fed mice lithium chronically and assessed mTORC1 signaling in the renal medulla. We demonstrate that mTOR signaling is activated in the renal collecting ducts of lithium-treated mice; lithium increased the phosphorylation of rS6 (Ser240/Ser244), p-TSC2 (Thr1462), and p-mTOR (Ser2448). Consistent with our hypothesis, treatment with rapamycin, an allosteric inhibitor of mTOR, reversed lithium-induced proliferation of medullary collecting duct cells and reduced levels of p-rS6 and p-mTOR. Medullary levels of p-GSK3β were increased in the renal medullas of lithium-treated mice and remained elevated following rapamycin treatment. However, mTOR inhibition did not improve lithium-induced NDI and did not restore the expression of collecting duct proteins aquaporin-2 or UT-A1.