Pharmacokinetics and pharmacodynamics of intravenous bumetanide in mutant Nagase analbuminemic rats: importance of globulin binding for the pharmacodynamic effects

Pharmacology of Compounds Targeting Cation-Chloride Cotransporter Physiology

Transporters of the solute carrier family 12 (SLC12) carry inorganic cations such as Na+ and/or K+ alongside Cl across the plasma membrane of cells. These tightly coupled, electroneutral, transporters are expressed in almost all tissues/organs in the body where they fulfil many critical functions. The family includes two key transporters participating in salt reabsorption in the kidney: the Na-K-2Cl cotransporter-2 (NKCC2), expressed in the loop of Henle, and the Na-Cl cotransporter (NCC), expressed in the distal convoluted tubule. NCC and NKCC2 are the targets of thiazides and "loop" diuretics, respectively, drugs that are widely used in clinical medicine to treat hypertension and edema. Bumetanide, in addition to its effect as a loop diuretic, has recently received increasing attention as a possible therapeutic agent for neurodevelopmental disorders. This chapter also describes how over the past two decades, the pharmacology of Na+ independent transporters has expanded significantly to provide novel tools for research. This work has indeed led to the identification of compounds that are 100-fold to 1000-fold more potent than furosemide, the first described inhibitor of K-Cl cotransport, and identified compounds that possibly directly stimulate the function of the K-Cl cotransporter. Finally, the recent cryo-electron microscopy revolution has begun providing answers as to where and how pharmacological agents bind to and affect the function of the transporters.

Inhibition mechanism of NKCC1 involves the carboxyl terminus and long-range conformational coupling

The Na-K-2Cl cotransporter-1 (NKCC1) is an electroneutral Na⁺-dependent transporter responsible for simultaneously translocating Na⁺, K⁺, and Cl^- ions into cells. In human tissue, NKCC1 plays a critical role in regulating cytoplasmic volume, fluid intake, chloride homeostasis, and cell polarity. Here, we report four structures of human NKCC1 (hNKCC1), both in the absence and presence of loop diuretic (bumetanide or furosemide), using single-particle cryo-electron microscopy. These structures allow us to directly observe various novel conformations of the hNKCC1 dimer. They also reveal two drug-binding sites located at the transmembrane and cytosolic carboxyl-terminal domains, respectively. Together, our findings enable us to delineate an inhibition mechanism that involves a coupled movement between the cytosolic and transmembrane domains of hNKCC1.

A Wholistic View of How Bumetanide Attenuates Autism Spectrum Disorders

The specific NKCC1 cotransporter antagonist, bumetanide, attenuates the severity of Autism Spectrum Disorders (ASD), and many neurodevelopmental or neurodegenerative disorders in animal models and clinical trials. However, the pervasive expression of NKCC1 in many cell types throughout the body is thought to challenge the therapeutic efficacy of bumetanide. However, many peripheral functions, including intestinal, metabolic, or vascular, etc., are perturbed in brain disorders contributing to the neurological sequels. Alterations of these functions also increase the incidence of the disorder suggesting complex bidirectional links with the clinical manifestations. We suggest that a more holistic view of ASD and other disorders is warranted to account for the multiple sites impacted by the original intra-uterine insult. From this perspective, large-spectrum active repositioned drugs that act centrally and peripherally might constitute a useful approach to treating these disorders.

Natriuresis guided therapy in acute heart failure: rationale and design of the Pragmatic Urinary Sodium-based Treatment algoritHm in Acute Heart Failure (PUSH-AHF) trial

Aims

Insufficient diuretic response frequently occurs in patients admitted for acute heart failure (HF) and is associated with worse clinical outcomes. Recent studies have shown that measuring natriuresis early after hospital admission could reliably identify patients with a poor diuretic response during hospitalization who might require enhanced diuretic treatment. This study will test the hypothesis that natriuresis‐guided therapy in patients with acute HF improves natriuresis and clinical outcomes.

Methods

The Pragmatic Urinary Sodium‐based treatment algoritHm in Acute Heart Failure (PUSH‐AHF) is a pragmatic, single‐centre, randomized, controlled, open‐label study, aiming to recruit 310 acute HF patients requiring treatment with intravenous loop diuretics. Patients will be randomized to natriuresis‐guided therapy or standard of care. Natriuresis will be determined at set time points after initiation of intravenous loop diuretics, and treatment will be adjusted based on the urinary sodium levels in the natriuresis‐guided group using a pre‐specified stepwise approach of increasing doses of loop diuretics and the initiation of combination diuretic therapy. The co‐primary endpoint is 24‐h urinary sodium excretion after start of loop diuretic therapy and a combined endpoint of all‐cause mortality or first HF rehospitalization at 6 months. Secondary endpoints include 48‐ and 72‐h sodium excretion, length of hospital stay, and percentage change in N‐terminal pro brain natriuretic peptide at 48 and 72 h.

Conclusion

The PUSH‐AHF study will investigate whether natriuresis‐guided therapy, using a pre‐specified stepwise diuretic treatment approach, improves natriuresis and clinical outcomes in patients with acute HF.

Contribution of Monocarboxylate Transporter 6 to the Pharmacokinetics and Pharmacodynamics of Bumetanide in Mice

Bumetanide, a sulfamyl loop diuretic, is used for the treatment of edema in association with congestive heart failure. Being a polar, anionic compound at physiologic pH, bumetanide uptake and efflux into different tissues is largely transporter-mediated. Of note, organic anion transporters (SLC22A) have been extensively studied in terms of their importance in transporting bumetanide to its primary site of action in the kidney. The contribution of one of the less-studied bumetanide transporters, monocarboxylate transporter 6 (MCT6; SLC16A5), to bumetanide pharmacokinetics (PK) and pharmacodynamics (PD) has yet to be characterized. The affinity of bumetanide for murine Mct6 was evaluated using Mct6-transfected Xenopus laevis oocytes. Furthermore, bumetanide was intravenously and orally administered to wild-type mice (Mct6^+/+) and homozygous Mct6 knockout mice (Mct6^-/-) to elucidate the contribution of Mct6 to bumetanide PK/PD in vivo. We demonstrated that murine Mct6 transports bumetanide at a similar affinity compared with human MCT6 (78 and 84 μM, respectively, at pH 7.4). After bumetanide administration, there were no significant differences in plasma PK. Additionally, diuresis was significantly decreased by ∼55% after intravenous bumetanide administration in Mct6^-/- mice. Kidney cortex concentrations of bumetanide were decreased, suggesting decreased Mct6-mediated bumetanide transport to its site of action in the kidney. Overall, these results suggest that Mct6 does not play a major role in the plasma PK of bumetanide in mice; however, it significantly contributes to bumetanide's pharmacodynamics due to changes in kidney concentrations. SIGNIFICANCE STATEMENT: Previous evidence suggested that MCT6 transports bumetanide in vitro; however, no studies to date have evaluated the in vivo contribution of this transporter. In vitro studies indicated that mouse and human MCT6 transport bumetanide with similar affinities. Using Mct6 knockout mice, we demonstrated that murine Mct6 does not play a major role in the plasma pharmacokinetics of bumetanide; however, the pharmacodynamic effect of diuresis was attenuated in the knockout mice, likely because of the decreased bumetanide concentrations in the kidney.

Bumetanide: A review of its neuroplasticity and behavioral effects after stroke

Stroke often leads to neuronal injury and neurological functional deficits. Whilst spontaneous neurogenesis and axon regeneration are induced by ischemic stroke, effective pharmacological treatments are also essential for the improvement of neuroplasticity and functional recovery after stroke. However, no pharmacological therapy has been demonstrated to be able to effectively improve the functional recovery after stroke. Bumetanide is a specific Na+-K+-Cl- co-transporter inhibitor which can maintain chloride homeostasis in neurons. Therefore, many studies have focused on this drug's effect in stroke recovery in recent years. Here, we first review the function of Na+-K+-Cl- co-transporter in neurons, then how bumetanide's role in reducing brain damage, promoting neuroplasticity, leading to functional recovery after stroke, is elucidated. Finally, we discuss current limitations of bumetanide's efficiency and their potential solutions. These results may provide new avenues for further exploring mechanisms of post-stroke functional recovery as well as promising therapeutic targets for functional disability rehabilitation after ischemic stroke.

A microsensing system for the in vivo real-time detection of local drug kinetics

Real-time recording of the kinetics of systemically administered drugs in in vivo microenvironments may accelerate the development of effective medical therapies. However, conventional methods require considerable analyte quantities, have low sampling rates and do not address how drug kinetics correlate with target function over time. Here, we describe the development and application of a drug-sensing system consisting of a glass microelectrode and a microsensor composed of boron-doped diamond with a tip of around 40 μm in diameter. We show that, in the guinea pig cochlea, the system can measure-simultaneously and in real time-changes in the concentration of bumetanide (a diuretic that is ototoxic but applicable to epilepsy treatment) and the endocochlear potential underlying hearing. In the rat brain, we tracked the kinetics of the drug and the local field potentials representing neuronal activity. We also show that the actions of the antiepileptic drug lamotrigine and the anticancer reagent doxorubicin can be monitored in vivo. Our microsensing system offers the potential to detect pharmacological and physiological responses that might otherwise remain undetected.

A combined clinical and biomarker approach to predict diuretic response in acute heart failure

Background

Poor diuretic response in acute heart failure is related to poor clinical outcome. The underlying mechanisms and pathophysiology behind diuretic resistance are incompletely understood. We evaluated a combined approach using clinical characteristics and biomarkers to predict diuretic response in acute heart failure (AHF).

Methods and results

We investigated explanatory and predictive models for diuretic response—weight loss at day 4 per 40 mg of furosemide—in 974 patients with AHF included in the PROTECT trial. Biomarkers, addressing multiple pathophysiological pathways, were determined at baseline and after 24 h. An explanatory baseline biomarker model of a poor diuretic response included low potassium, chloride, hemoglobin, myeloperoxidase, and high blood urea nitrogen, albumin, triglycerides, ST2 and neutrophil gelatinase-associated lipocalin (r² = 0.086). Diuretic response after 24 h (early diuretic response) was a strong predictor of diuretic response (β = 0.467, P < 0.001; r² = 0.523). Addition of diuretic response after 24 h to biomarkers and clinical characteristics significantly improved the predictive model (r² = 0.586, P < 0.001).

Conclusions

Biomarkers indicate that diuretic unresponsiveness is associated with an atherosclerotic profile with abnormal renal function and electrolytes. However, predicting diuretic response is difficult and biomarkers have limited additive value. Patients at risk of poor diuretic response can be identified by measuring early diuretic response after 24 h.

Electronic supplementary material

The online version of this article (doi:10.1007/s00392-015-0896-2) contains supplementary material, which is available to authorized users.

Diuretic response in acute heart failure-pathophysiology, evaluation, and therapy

The administration of loop diuretics to achieve decongestion is the cornerstone of therapy for acute heart failure. Unfortunately, impaired response to diuretics is common in these patients and associated with adverse outcomes. Diuretic resistance is thought to result from a complex interplay between cardiac and renal dysfunction, and specific renal adaptation and escape mechanisms, such as neurohormonal activation and the braking phenomenon. However, our understanding of diuretic response in patients with acute heart failure is still limited and a uniform definition is lacking. Three objective methods to evaluate diuretic response have been introduced, which all suggest that diuretic response should be determined based on the effect of diuretic dose administered. Several strategies have been proposed to overcome diuretic resistance, including combination therapy and ultrafiltration, but prospective studies in patients who are truly unresponsive to diuretics are lacking. An enhanced understanding of diuretic response should ultimately lead to an improved, individualized approach to treating patients with acute heart failure.

Ion transporters in brain endothelial cells that contribute to formation of brain interstitial fluid

Ions and water transported across the endothelium lining the blood–brain barrier contribute to the fluid secreted into the brain and are important in maintaining appropriate volume and ionic composition of brain interstitial fluid. Changes in this secretion process may occur after stroke. The present study identifies at transcript and protein level ion transporters involved in the movement of key ions and examines how levels of certain of these alter following oxidative stress. Immunohistochemistry provides evidence for Cl⁻/HCO₃⁻ exchanger, AE2, and Na⁺, HCO₃⁻ cotransporters, NBCe1 and NBCn1, on brain microvessels. mRNA analysis by RT-PCR reveals expression of these transporters in cultured rat brain microvascular endothelial cells (both primary and immortalized GPNT cells) and also Na⁺/H⁺ exchangers, NHE1 (primary and immortalized) and NHE2 (primary cells only). Knock-down using siRNA in immortalized GPNT cells identifies AE2 as responsible for much of the Cl⁻/HCO₃⁻ exchange following extracellular chloride removal and NHE1 as the transporter that accounts for most of the Na⁺/H⁺ exchange following intracellular acidification. Transcript levels of both AE2 and NHE1 are increased following hypoxia/reoxygenation. Further work is now required to determine the localization of the bicarbonate transporters to luminal or abluminal membranes of the endothelial cells as well as to identify and localize additional transport mechanisms that must exist for K⁺ and Cl⁻.

The effect of organic anion transporter 3 inhibitor probenecid on bumetanide levels in the brain: an integrated in vivo microdialysis study in the rat

Objectives

Recent data highlight the potential of bumetanide as a treatment for neonatal seizures and autism, as it facilitates the excitatory to inhibitory switch in gamma-aminobutyric acid signalling. This study examines the extent of blood-brain barrier (BBB) permeation of bumetanide, a key determinant of the efficacy of centrally acting drugs. Furthermore, the impact of efflux transporter organic anion transporter 3 (oat3) inhibition on bumetanide pharmacokinetics was investigated.

Methods

Bumetanide levels in extracellular fluid (ECF) and plasma in the presence and absence of oat3 inhibitor probenecid were monitored using integrated microdialysis.

Key findings

Following a bumetanide bolus/continuous infusion of 10 mg/kg and 6 mg/kg/h, bumetanide was detected in hippocampal ECF at the estimated concentration of 131 ± 55 ng/ml. Plasma bumetanide levels were ∼20 mg/l at steady state. Coadministration of probenecid resulted in an increase in bumetanide levels in both ECF and plasma, indicating that oat3 inhibition influences the pharmacokinetics of bumetanide primarily in the periphery.

Conclusion

Although bumetanide reached detectable levels in hippocampal ECF, bumetanide concentration in ECF was low relative to systemic concentration. Oat3 inhibition by probenecid resulted in increased bumetanide concentrations in brain and plasma. As an acute treatment in neonatal seizures, the bumetanide/probenecid combination may hold therapeutic potential.

Pharmacotherapeutic targeting of cation-chloride cotransporters in neonatal seizures

Seizures are a common manifestation of acute neurologic insults in neonates and are often resistant to the standard antiepileptic drugs that are efficacious in children and adults. The paucity of evidence-based treatment guidelines, coupled with a rudimentary understanding of disease pathogenesis, has made the current treatment of neonatal seizures empiric and often ineffective, highlighting the need for novel therapies. Key developmental differences in γ-aminobutyric acid (GABA)ergic neurotransmission between the immature and mature brain, and trauma-induced alterations in the function of the cation-chloride cotransporters (CCCs) NKCC1 and KCC2, probably contribute to the poor efficacy of standard antiepileptic drugs used in the treatment of neonatal seizures. Although CCCs are attractive drug targets, bumetanide and other existing CCC inhibitors are suboptimal because of pharmacokinetic constraints and lack of target specificity. Newer approaches including isoform-specific NKCC1 inhibitors with increased central nervous system penetration, and direct and indirect strategies to enhance KCC2-mediated neuronal chloride extrusion, might allow therapeutic modulation of the GABAergic system for neonatal seizure treatment. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Consequences of inhibition of bumetanide metabolism in rodents on brain penetration and effects of bumetanide in chronic models of epilepsy

The diuretic bumetanide, which acts by blocking the Na-K-Cl cotransporter (NKCC), is widely used to inhibit neuronal NKCC1, particularly when NKCC1 expression is abnormally increased in brain diseases such as epilepsy. However, bumetanide poorly penetrates into the brain and, in rodents, is rapidly eliminated because of extensive oxidation of its N-butyl sidechain, reducing the translational value of rodent experiments. Inhibition of oxidation by piperonyl butoxide (PBO) has previously been reported to increase the half-life and diuretic activity of bumetanide in rats. Here we studied whether inhibition of bumetanide metabolism by PBO also increases brain levels of bumetanide in rats, and whether this alters pharmacodynamic effects in the kindling model of epilepsy. Furthermore, we studied the effects of PBO in mice. Mice eliminated bumetanide less rapidly than rats (elimination half-life 47 min vs. 13 min). Pretreatment with PBO increased the half-life in mice to average values (70 min) previously determined in humans, and markedly elevated brain levels of bumetanide. In rats, the increase in plasma and brain levels of bumetanide by PBO was less marked than in mice. PBO significantly increased the diuretic activity of bumetanide in rats and, less effectively, in mice. In epileptic mice, bumetanide (with PBO) did not suppress spontaneous seizures. In the rat kindling model, bumetanide (with or without PBO) did not exert anticonvulsant effects on fully kindled seizures, but dose-dependently altered kindling development. These data indicate that PBO offers a simple means to enhance the translational properties of rodent experiments with bumetanide, particularly when using mice.

Pharmacokinetics of drugs in mutant Nagase analbuminemic rats and responses to select diuretics

OBJECTIVES

To report (1) the pharmacokinetics of drugs that are mainly metabolized via hepatic cytochrome P450s (CYPs) or mainly excreted via the urine and bile, (2) the mechanism for the urinary excretion of drugs (such as glomerular filtration or renal active secretion or re-absorption), and (3) the diuretic effect of some loop diuretics in mutant Nagase analbuminaemic rats (NARs), an animal model for human familial analbuminaemia based on the pharmacokinetics of drugs reported in the literatures.

KEY FINDINGS

In NARs, the changes in the time-averaged non-renal clearances (CL(NR)s) of drugs that are mainly metabolized via CYPs were explained in terms of changes in the hepatic intrinsic clearance (mainly because of changes in CYPs), free (unbound) fractions of drugs in the plasma (fp) and hepatic blood-flow rate (QH) depending on the hepatic excretion ratios of drugs.

SUMMARY

The CL(NR) changes of drugs mainly metabolized via hepatic CYPs can be sufficiently explained by the three earlier mentioned factors. The plasma albumin (furosemide) or globulin (azosemide, bumetanide and torasemide) binding affects their diuretic effects.

Co-administration of furosemide with albumin for overcoming diuretic resistance in patients with hypoalbuminemia: a meta-analysis

PURPOSE

To systematically review clinical studies of co-administration of albumin and loop diuretics in hypoalbuminemic patients as a strategy to overcome diuretic resistance.

MATERIALS AND METHODS

Systematic search of electronic databases up to October 2012. We included randomized clinical trials of adults with hypoalbuminemia, comparing co-administration of loop diuretics and albumin versus loop diuretics alone. Quantitative data were synthesized with meta-analytic techniques for clinical, surrogate (urinary volume and urinary sodium excretion) and intermediate (pharmacokinetic and hemodynamic parameters) outcomes.

RESULTS

Ten studies were included, of which 8 trials with crossover design were synthesized with meta-analysis. A statistically significant increase in the amount of urine volume (increment of 231 mL [95% confidence interval 135.5-326.5]) and sodium excreted (15.9 mEq [4.9-26.8]) at 8 hours were found in favor of co-administration of albumin and furosemide. These differences were no longer statistically significant at 24 hours. Meta-analyses for intermediate outcomes (ie, furosemide excretion, distribution volume etc.) did not reveal statistically significant differences.

CONCLUSIONS

Synthesis of a heterogeneous body of evidence shows transient effects of modest clinical significance for co-administration of albumin with furosemide in hypoalbuminemic patients. Pragmatic, large-scale randomized studies are needed to delineate the role of this strategy.

Pharmacokinetics of drugs in spontaneously or secondary hypertensive rats

1. Spontaneously hypertensive rats (SHRs) and deoxycorticosterone acetate-salt-induced hypertensive rats (DOCA-salt rats) have been developed as animal models for human essential (idiopathic or primary) and secondary hypertensions, respectively. 2. In order to identify pharmacokinetic changes (mainly non-renal clearance, CLNR) in 16-week-old SHRs due to hereditary characteristics and/or neither the hypertensive state itself, we reviewed the pharmacokinetics of drugs in 6- (blood pressure within a normotensive range) and 16-week-old SHRs and 16-week-old DOCA-salt rats compared with respective control rats. 3. We reviewed changes in CLNRs of drugs which are primarily metabolized via hepatic microsomal cytochrome P 450 enzymes (CYPs) based mainly on data from hypertensive rats, and present the data in terms of changes in in vitro hepatic intrinsic clearance (CLint), free fraction in plasma (fp) and hepatic blood flow rate (QH) depending on the hepatic excretion ratios of drugs. In general, changes in the CLNRs of drugs in this category were well-explained by the above-described factors. 4. We also reviewed and discussed the mechanism of urinary excretion of drugs (i.e. glomerular filtration and active renal secretion or reabsorption) in hypertensive rats.

Disease-modifying effects of phenobarbital and the NKCC1 inhibitor bumetanide in the pilocarpine model of temporal lobe epilepsy

Accumulating evidence suggests that changes in neuronal chloride homeostasis may be involved in the mechanisms by which brain insults induce the development of epilepsy. A variety of brain insults, including status epilepticus (SE), lead to changes in the expression of the cation-chloride cotransporters KCC2 and NKCC1, resulting in intracellular chloride accumulation and reappearance of immature, depolarizing synaptic responses to GABA(A) receptor activation, which may critically contribute to the neuronal hyperexcitability underlying epileptogenesis. In the present study, it was evaluated whether prolonged administration of the selective NKCC1 inhibitor, bumetanide, after a pilocarpine-induced SE modifies the development of epilepsy in adult female rats. The antiepileptic drug phenobarbital, either alone or in combination, was used for comparison. Based on pharmacokinetic studies with bumetanide, which showed extremely rapid elimination and low brain penetration of this drug in rats, bumetanide was administered systemically with different dosing protocols, including continuous intravenous infusion. As shown by immunohistochemistry, neuronal NKCC1 expression was markedly upregulated shortly after SE. Prophylactic treatment with phenobarbital after SE reduced the number of rats developing spontaneous seizures and decreased seizure frequency, indicating a disease-modifying effect. Bumetanide did not exert any significant effects on development of spontaneous seizures nor did it enhance the effects of phenobarbital. However, combined treatment with both drugs counteracted several of the behavioral consequences of SE, which was not observed with single drug treatment. These data do not indicate that bumetanide can prevent epilepsy after SE, but the disease-modifying effect of this drug warrants further studies with more lipophilic prodrugs of bumetanide.

Prediction of human pharmacokinetics — renal metabolic and excretion clearance

The kidneys have the capability to both excrete and metabolise drugs. An understanding of mechanisms that determine these processes is required for the prediction of pharmacokinetics, exposures, doses and interactions of candidate drugs. This is particularly important for compounds predicted to have low or negligible non-renal clearance (CL). Clinically significant interactions in drug transport occur mostly in the kidneys. The main objective was to evaluate methods for prediction of excretion and metabolic renal CL (CLR) in humans. CLR is difficult to predict because of the involvement of bi-directional passive and active tubular transport, differences in uptake capacity, pH and residence time on luminal and blood sides of tubular cells, and limited knowledge about regional tubular residence time, permeability (Pe) and metabolic capacity. Allometry provides poor predictions of excretion CLR because of species differences in unbound fraction, urine pH and active transport. The correlation between fraction excreted unchanged in urine (fe) in humans and animals is also poor, except for compounds with high passive Pe (extensive/complete tubular reabsorption; zero/negligible fe) and/or high non-renal CL. Physiologically based in-vitro/in-vivo methods could potentially be useful for predicting CLR. Filtration could easily be predicted. Prediction of tubular secretion CL requires an in-vitro transport model and establishment of an in-vitro/in-vivo relationship, and does not appear to have been attempted. The relationship between passive Pe and tubular fraction reabsorbed (freabs) for compounds with and without apparent secretion has recently been established and useful equations and limits for prediction were developed. The suggestion that reabsorption has a lipophilicity cut-off does not seem to hold. Instead, compounds with passive Pe that is less than or equal to that of atenolol are expected to have negligible passive freabs. Compounds with passive Pe that is equal to or higher than that of carbamazepine are expected to have complete freabs. For compounds with intermediate Pe the relationship is irregular and freabs is difficult to predict. Tubular cells are comparably impermeable (for passive diffusion), and show regional differences in enzymatic and transporter activities. This limits the usefulness of microsome data and makes microsome-based predictions of metabolic CLR questionable. Renal concentrations and activities of CYP450s are comparably low, suggesting that CYP450 substrates have negligible metabolic CLR. The metabolic CLR of high-Pe UDP-glucuronyltransferase substrates could contribute to the total CL.

Pharmacokinetics of 5-fluorouracil in mutant Nagase analbuminemic rats: faster metabolism of 5-fluorouracil via CYP1A

It has been reported that plasma albumin concentrations were significantly lower in cancer patients than those in the healthy volunteers, and the expression and mRNA level of hepatic microsomal cytochrome P450 (CYP) 1A2 increased in mutant Nagase analbuminemic rats (NARs). After intravenous administration of 5-fluorouracil at a dose of 30 mg/kg to NARs, the time-averaged nonrenal clearance (Clnr) of the drug was significantly faster than the controls (51.3 versus 28.8 ml/min/kg), possibly due to an increase in the expression and mRNA level of CYP1A2 in NARs. In order to determine whether 5-fluorouracil is metabolized via CYP1A2 in male Sprague-Dawley rats, the rats were pretreated with 3-methylcholanthrene (a main inducer of CYP1A1/2 in rats). The Clnr of 5-fluorouracil was significantly faster (34.3 versus 27.3 ml/min/kg) in rats pretreated with 3-methylcholanthrene. The aforementioned data indicate that CYP1A is involved in the metabolism of 5-fluorouracil in rats.

Pharmacokinetics of Oltipraz in Mutant Nagase Analbuminemic Rats

Pharmacokinetic parameters of oltipraz were compared after intravenous (10 mg/kg) and oral (50 mg/kg) administration to control male Sprague-Dawely rats and mutant Nagase analbuminemic rats (NARs). In NARs, the expression and mRNA level of CYP1A2 increased, and oltipraz was mainly metabolized via CYP1A1/2, 2B1/2, 2C11, 201, and 3A1/2 in male rats. Hence, it may be expected that the CL of oltipraz would be significantly faster in NARs. This was proven by the following results. After intravenous administration, the CL of oltipraz was significantly faster in NARs (125% increase) than controls due to significantly greater free fractions (unbound to plasma proteins) of oltipraz (197% increase) and significantly faster CL(int) for the disappearance of oltipraz (11.4% increase) in NARs, since oltipraz is an intermediate hepatic extraction ratio drug in rats. The V(ss) was significantly larger in NARs (109% increase) and this could be due to significant increase in free fractions of oltipraz in NARs. After oral administration, the AUC of oltipraz was also significantly smaller in NARs (61.9% decrease). This could also be due to significant increase in free fractions of oltipraz and significantly faster CL(int) in NARs. However, this was not due to decrease in absorption in NARs.

Pharmacokinetics and pharmacodynamics of intravenous azosemide in mutant Nagase analbuminemic rats

This paper reports 1) the increase in expression of CYP1A2 in mutant Nagase analbuminemic rats (NARs), 2) the role of globulin binding of azosemide in circulating blood in its urinary excretion and hence its diuretic effects in NARs, and 3) the significantly faster renal (CL(R)) and nonrenal (CL(NR)) clearances of azosemide in NARs. Azosemide (mainly metabolized via CYP1A2 in rats), 10 mg/kg, was intravenously administered to control rats and NARs. Northern and Western blot analyses revealed that the expression of CYP1A2 increased approximately 3.5-fold in NARs as compared with control. The plasma protein binding of azosemide in control rats and NARs was 97.9 and 84.6%, respectively. In NARs, plasma protein binding (84.6%) was due to binding to alpha- (82.6%) and beta- (68.9%) globulins. In NARs, the amount of unchanged azosemide excreted in 8-h urine was significantly greater (37.7 versus 21.0% of intravenous dose) than that in control rats due to an increase in intrinsic renal active secretion of azosemide. Accordingly, the 8-h urine output was significantly greater in NARs. The area under the plasma concentration-time curve of azosemide was significantly smaller (505 versus 2790 microg. min/ml) in NARs because of markedly faster CL(R) (7.36 versus 0.772 ml/min/kg, secondary to a significant increase in urinary excretion of azosemide and intrinsic renal active secretion). Additionally, CL(NR) was significantly faster (12.4 versus 3.05 ml/min/kg, because of approximately 3.5 fold increase in CYP1A2) in NARs compared with control. Based on in vitro hepatic microsomal studies, the intrinsic M1 [a metabolite of azosemide; 5-(2-amino-4-chloro-5-sulfamoylphenyl)-tetrazole] formation clearance was significantly faster (67.0% increase) in NARs than that in control rats, and this supports significantly faster CL(NR) in NARs. Renal sensitivity to azosemide was significantly greater in NARs than in control rats with respect to 8-h urine output (385 versus 221 ml/kg) and 8-h urinary excretions of sodium, potassium, and chloride. This study supports that in NARs, binding of azosemide to alpha- and beta-globulins in circulating blood play an important role in its diuretic effects.

Pharmacokinetics of intravenous theophylline in mutant Nagase analbuminemic rats

It was obtained from our laboratories that the expression of hepatic microsomal cytochrome P450 (CYP) 1A2 increased approximately 3.5 times in mutant Nagase analbuminemic rats (NARs, an animal model for human familial analbuminemia), and theophylline was reported to be metabolized to 1,3-dimethyluric acid (1,3-DMU) and 1-methylxanthine (which was further metabolized to 1-methyluric acid, 1-MU, via xanthine oxidase) via CYP1A2 in rats. Hence, the pharmacokinetic parameters of theophylline, 1,3-DMU and 1-MU were compared after intravenous administration of aminophylline, 5 mg/kg as theophylline, to control Sprague-Dawley rats and NARs. In NARs, the total area under the plasma concentration-time curve from time zero to time infinity (AUC) of theophylline was significantly smaller (1,040 versus 1,750 microg min/ml) than that in control rats and this could be due to significantly faster renal clearance (CL(R), 1.39 versus 0.571 ml/min/kg, due to inhibition of renal reabsorption of unchanged theophylline) and nonrenal clearance (CL(NR), 3.36 versus 2.25 ml/min/kg, due to 3.5-fold increase in CYP1A2) than those in control rats. Based on in vitro hepatic microsomal studies, the intrinsic 1,3-DMU formation clearance was significantly faster in NARs than that in control rats (267 versus 180 x 10(-6) ml/min). After intravenous administration of 1,3-DMU, the renal secretion of 1,3-DMU was inhibited in NARs. Inhibition of renal secretion or reabsorption of various compounds in NARs was also discussed.

Pharmacokinetics and pharmacodynamics of intravenous trasemide in mutant Nagase analbuminemic rats

The importance of plasma protein binding of intravenous furosemide in circulating blood for its urinary excretion and hence its diuretic effects in mutant Nagase analbuminemic rats (NARs, an animal model for human familial analbuminemia) was reported. Based on the furosemide report, the diuretic effects of another loop diuretic, torasemide, could be expected in NARs if plasma protein binding of torasemide is considerable in the rats. This was proven by this study. After intravenous administration of torasemide, 10 mg/kg, to NARs, the plasma protein binding of torasemide was 23.3% in the rats due to binding to alpha- and beta-globulins (this value, 23.3%, was greater than only 12% for furosemide), and hence the percentages of intravenous dose of torasemide excreted in 8-h urine as unchanged drug was 14.9% in the rat (this value was considerably greater than only 7% for furosemide). After intravenous administration of torasemide to NARs, the AUC (301 versus 2680 microg/min/ml) was significantly smaller [due to significantly faster both Cl(r) (4.81 versus 0.386 ml/min/kg) and Cl(nr) (28.3 versus 3.33 ml/min/kg)], terminal half-life (18.3 versus 73.5 min) and mean residence time (6.97 versus 61.8 min) were significantly shorter (due to faster Cl, 33.2 versus 3.74 ml/min/kg), and amount of 8-h urinary excretion of unchanged torasemide (446 versus 323 microg, due to increase in intrinsic renal excretion) was significantly greater than those in control rats. The 8-h urine output and 8-h urinary excretions of sodium and chloride were comparable between two groups of rats although the 8-h urinary excretion of torasemide was significantly greater in NARs. This could be explained by the following. The amount of urinary excretion of torasemide was significantly greater in NARs than that in control rats only between 0 and 30 min urine collection. In both groups of rats, the urinary excretion rate of torasemide during 0-30 min reached an upper plateau with respect to urine flow rate as well urinary excretion rates of sodium and chloride. Therefore, the diuretic effects (8-h urine output and 8-h urinary excretions of sodium and chloride) were not significantly different between the two groups of rats.