Dysregulation of Renal Cyclooxygenase-2 in Rats with Lithium-induced Nephrogenic Diabetes Insipidus

LISPRO mitigates β-amyloid and associated pathologies in Alzheimer's mice

Lithium has been marketed in the United States of America since the 1970s as a treatment for bipolar disorder. More recently, studies have shown that lithium can improve cognitive decline associated with Alzheimer’s disease (AD). However, the current United States Food and Drug Administration-approved lithium pharmaceutics (carbonate and citrate chemical forms) have a narrow therapeutic window and unstable pharmacokinetics that, without careful monitoring, can cause serious adverse effects. Here, we investigated the safety profile, pharmacokinetics, and therapeutic efficacy of LISPRO (ionic co-crystal of lithium salicylate and l-proline), lithium salicylate, and lithium carbonate (Li₂CO₃). We found that LISPRO (8-week oral treatment) reduces β-amyloid plaques and phosphorylation of tau by reducing neuroinflammation and inactivating glycogen synthase kinase 3β in transgenic Tg2576 mice. Specifically, cytokine profiles from the brain, plasma, and splenocytes suggested that 8-week oral treatment with LISPRO downregulates pro-inflammatory cytokines, upregulates anti-inflammatory cytokines, and suppresses renal cyclooxygenase 2 expression in transgenic Tg2576 mice. Pharmacokinetic studies indicated that LISPRO provides significantly higher brain lithium levels and more steady plasma lithium levels in both B6129SF2/J (2-week oral treatment) and transgenic Tg2576 (8-week oral treatment) mice compared with Li₂CO₃. Oral administration of LISPRO for 28 weeks significantly reduced β-amyloid plaques and tau-phosphorylation. In addition, LISPRO significantly elevated pre-synaptic (synaptophysin) and post-synaptic protein (post synaptic density protein 95) expression in brains from transgenic 3XTg-AD mice. Taken together, our data suggest that LISPRO may be a superior form of lithium with improved safety and efficacy as a potential new disease modifying drug for AD.

Ginsenoside-Rb1 ameliorates lithium-induced nephrotoxicity and neurotoxicity: Differential regulation of COX-2/PGE2 pathway

To investigate the effect of Ginsenoside-Rb1 (GRb1) on lithium (Li⁺)-induced toxicity, GRb1 was given to rats orally (100mg/kg) for 14days. In independent groups, lithium chloride (4meq/kg/day i.p.) was administered at day 4 of the experiment for 10days, with or without GRb1. Li⁺ caused significant deterioration of behavioral responses including righting reflex, spontaneous motor activity and catalepsy. Li⁺ also caused distortion in normal renal, cerebral and cerebellum architecture and significantly worsened all kidney functional parameters tested compared to control. In addition, Li caused oxidative stress in both kidney and brain, evident by significant increase in malondialdehyde and nitric oxide levels, with decrease in reduced glutathione and catalase activity. Administration of GRb1 prior to Li⁺ significantly improved behavioral responses, renal and brain histopathological picture, kidney function tests and oxidative stress markers compared to sole Li⁺-treated group. Concomitant administration of GRb1 decreased Li⁺ levels by about 50% in serum, urine and brain and by 35% in the kidney. Interestingly, Li⁺ had a differential effect on cyclooxygenase (COX)-2/prostaglandin E₂ (PGE₂) pathway, as it significantly increased COX-2 expression and PGE₂ level in the kidney, while decreasing them in the brain compared to control. On the other hand, administering GRb1 with Li⁺ suppressed COX-2/PGE₂ pathway in both kidney and brain compared to Li⁺ alone. In conclusion, GRb1 can alter Li⁺ pharmacokinetics resulting in extensively decreasing its serum and tissue concentrations. Furthermore, COX-2/PGE₂ pathway has a mechanistic role in the nephro- and neuro-protective effects of GRb1 against Li⁺-induced toxicity.

Acetazolamide Attenuates Lithium-Induced Nephrogenic Diabetes Insipidus

To reduce lithium-induced nephrogenic diabetes insipidus (lithium-NDI), patients with bipolar disorder are treated with thiazide and amiloride, which are thought to induce antidiuresis by a compensatory increase in prourine uptake in proximal tubules. However, thiazides induced antidiuresis and alkalinized the urine in lithium-NDI mice lacking the sodium-chloride cotransporter, suggesting that inhibition of carbonic anhydrases (CAs) confers the beneficial thiazide effect. Therefore, we tested the effect of the CA-specific blocker acetazolamide in lithium-NDI. In collecting duct (mpkCCD) cells, acetazolamide reduced the cellular lithium content and attenuated lithium-induced downregulation of aquaporin-2 through a mechanism different from that of amiloride. Treatment of lithium-NDI mice with acetazolamide or thiazide/amiloride induced similar antidiuresis and increased urine osmolality and aquaporin-2 abundance. Thiazide/amiloride-treated mice showed hyponatremia, hyperkalemia, hypercalcemia, metabolic acidosis, and increased serum lithium concentrations, adverse effects previously observed in patients but not in acetazolamide-treated mice in this study. Furthermore, acetazolamide treatment reduced inulin clearance and cortical expression of sodium/hydrogen exchanger 3 and attenuated the increased expression of urinary PGE2 observed in lithium-NDI mice. These results show that the antidiuresis with acetazolamide was partially caused by a tubular-glomerular feedback response and reduced GFR. The tubular-glomerular feedback response and/or direct effect on collecting duct principal or intercalated cells may underlie the reduced urinary PGE2 levels with acetazolamide, thereby contributing to the attenuation of lithium-NDI. In conclusion, CA activity contributes to lithium-NDI development, and acetazolamide attenuates lithium-NDI development in mice similar to thiazide/amiloride but with fewer adverse effects.

Lithium causes G2 arrest of renal principal cells

Vasopressin-regulated expression and insertion of aquaporin-2 channels in the luminal membrane of renal principal cells is essential for urine concentration. Lithium affects urine concentrating ability, and approximately 20% of patients treated with lithium develop nephrogenic diabetes insipidus (NDI), a disorder characterized by polyuria and polydipsia. Lithium-induced NDI is caused by aquaporin-2 downregulation and a reduced ratio of principal/intercalated cells, yet lithium induces principal cell proliferation. Here, we studied how lithium-induced principal cell proliferation can lead to a reduced ratio of principal/intercalated cells using two-dimensional and three-dimensional polarized cultures of mouse renal collecting duct cells and mice treated with clinically relevant lithium concentrations. DNA image cytometry and immunoblotting revealed that lithium initiated proliferation of mouse renal collecting duct cells but also increased the G2/S ratio, indicating G2/M phase arrest. In mice, treatment with lithium for 4, 7, 10, or 13 days led to features of NDI and an increase in the number of principal cells expressing PCNA in the papilla. Remarkably, 30%-40% of the PCNA-positive principal cells also expressed pHistone-H3, a late G2/M phase marker detected in approximately 20% of cells during undisturbed proliferation. Our data reveal that lithium treatment initiates proliferation of renal principal cells but that a significant percentage of these cells are arrested in the late G2 phase, which explains the reduced principal/intercalated cell ratio and may identify the molecular pathway underlying the development of lithium-induced renal fibrosis.

Inhibition of glycogen synthase kinase-3β prevents NSAID-induced acute kidney injury

Clinical use of nonsteroidal anti-inflammatory drugs (NSAIDs) like diclofenac (DCLF) is limited by multiple adverse effects, including renal toxicity leading to acute kidney injury. In mice with DCLF-induced nephrotoxicity, TDZD-8, a selective glycogen synthase kinase (GSK)3β inhibitor, improved acute kidney dysfunction and ameliorated tubular necrosis and apoptosis associated with induced cortical expression of cyclooxygenase-2 (COX-2) and prostaglandin E2. This renoprotective effect was blunted but still largely preserved in COX-2-null mice, suggesting that other GSK3β targets beyond COX-2 functioned in renal protection. Indeed, TDZD-8 diminished the mitochondrial permeability transition in DCLF-injured kidneys. In vitro, GSK3β inhibition reinstated viability and suppressed necrosis and apoptosis in DCLF-stimulated tubular epithelial cells. DCLF elicited oxidative stress, enhanced the activity of the redox-sensitive GSK3β, and promoted a mitochondrial permeability transition by interacting with cyclophilin D, a key component of the mitochondrial permeability transition pore. TDZD-8 blocked GSK3β activity and prevented GSK3β-mediated cyclophilin D phosphorylation and the ensuing mitochondrial permeability transition, concomitant with normalization of intracellular ATP. Conversely, ectopic expression of a constitutively active GSK3β abolished the effects of TDZD-8. Hence, inhibition of GSK3β ameliorates NSAID-induced acute kidney injury by induction of renal cortical COX-2 and direct inhibition of the mitochondrial permeability transition.

Renal effects of prostaglandins and cyclooxygenase-2 inhibitors

Prostaglandins (PGs) with best-defined renal functions are PGE₂ and prostacyclin (PGI₂). These vasodilatory PGs increase renal blood flow and glomerular filtration rate under conditions associated with decreased actual or effective circulating volume, resulting in greater tubular flow and secretion of potassium. Under conditions of decreased renal perfusion, the production of renal PGs serves as an important compensatory mechanism. PGI₂ (and possibly PGE₂) increases potassium secretion mainly by stimulating secretion of renin and activating the renin-angiotensin system, which leads to increased secretion of aldosterone. In addition, PGE₂ is involved in the regulation of sodium and water reabsorption and acts as a counterregulatory factor under conditions of increased sodium reabsorption. PGE₂ decreases sodium reabsorption at the thick ascending limb of the loop of Henle probably via inhibition of the Na⁺-K⁺-2Cl^- cotransporter type 2 (NKCC2). Cyclooxygenase inhibitors may enhance urinary concentrating ability in part through effects to upregulate NKCC2 in the thick ascending limb of Henle's loop and aquaporin-2 in the collecting duct. Thus, they may be useful to treat Bartter's syndrome and nephrogenic diabetes insipidus.