Non-ionic diffusion and the excretion of weak acids and bases

Benthic macroinvertebrate assemblages in relation to high ammonia loading: A 5-year fertilization experiment in 5 subtropical ponds

Nitrogen pollution, especially ammonia, and its impacts on aquatic ecosystems are always hot topics worldwide. Evaluating the toxicity effect of ammonia on aquatic organisms is the essential basis for nitrogen management. Benthic macroinvertebrates are widely used to evaluate ammonia toxicity based on acute and chronic lab tests. In comparison, responses of macroinvertebrates under field and controlled conditions were rarely studied. To explore the effect of ammonia on macroinvertebrate assemblages and the underlying mechanisms under field conditions, a 5-year fertilization experiment was conducted in 5 quasi-natural ponds located in the Yangtze River floodplain. One control (TN0, no artificial ammonia loading) and four treatments (TN2, TN10, TN20, TN100; ordered by artificial ammonia loading from low to high) were set. The results showed that (1) species number of macroinvertebrates differed little among the ponds, while total density and biomass were positively correlated with unionized ammonia concentration (NH3), indicating that increased ammonia loading had no adverse impact on macroinvertebrate abundance; (2) all ponds were dominated by gathering collectors and the biomass was higher in the ponds with higher ammonia loading resulting from the more phytoplankton promoted by ammonia loading and improved internal phosphorus release; (3) the biomass of predators also increased with the increasing NH3 which may be due to the bottom-up effect through their prey; (4) some species, such as Limnodrilus hoffmeisteri, survived and were dominant species in the ponds with higher NH3 compared with 96 h median lethal concentration from acute lab test. The results suggested that higher ammonia loading increased macroinvertebrate abundance, mainly contributed by gathering collectors and predators. Unlike previous acute and chronic lab tests, macroinvertebrates showed extremely high tolerance to NH3 in field conditions. This study supported that ammonia toxicity to aquatic organisms was scale-dependent and should be evaluated at multiple scales.

Decreasing toxicity of un-ionized ammonia on the gastropod Bellamya aeruginosa when moving from laboratory to field scale

Along with a steady increasing use of artificial nitrogen fertilizer, concerns have been raised about the effects that high nitrogen loading may have on ecosystems. Due to the toxicity of unionized ammonia (NH₃), tolerance criteria have been proposed for ambient water management in many countries; however, these are mainly based on acute or chronic tests carried out under lab conditions run with purified water. Aiming at understanding the responses of organisms to natural exposure to high ammonia concentrations, a Viviparidae gastropod, Bellamya aeruginosa, was tested at three experimental scales: standard 96-h lab test, one-month cage test in 6 experimental ponds with continuous nitrogen inputs, and intensive investigation of the B. aeruginosa from these ponds in spring and winter. The results were: 1) 96-h LC₅₀ in the standard lab test was 0.56 mg NH₃-N/L and 343.3 mg TAN/L (total ammonia expressed as N, standardized at pH 7 and 20 ℃). 2) In the one-month cage test, the survival rate was 97% when NH₃-N was 0.61 mg/L (i.e., a higher concentration than the lab 96-h LC₅₀) and the body size of the gastropods actually increased with increasing NH₃-N concentrations. 3) In the winter-spring investigation, little effect of ammonia on the standing crops of gastropods was found, and the body size of the gastropods tended to increase with increasing ammonia concentrations (NH₃-N concentration range of 0.05 ~ 2.06 mg/L). Thus, B. aeruginosa showed higher tolerance to ammonia exposure (NH₃-N concentration < 0.81 mg/L) in the field than under laboratory conditions. Our study points to the necessity of considering the relevant scale when determining criteria for ammonia toxicity in water management.

Mechanistic PBPK Modeling of Urine pH Effect on Renal and Systemic Disposition of Methamphetamine and Amphetamine

The effect of urine pH on renal excretion and systemic disposition has been observed for many drugs and metabolites. When urine pH is altered, tubular ionization, passive reabsorption, renal clearance, and systemic exposure of drugs and metabolites may all change dramatically, raising clinically significant concerns. Surprisingly, the urine pH effect on drug disposition is not routinely explored in humans, and regulatory agencies have neither developed guidance on this issue nor required industry to conduct pertinent human trials. In this study, we hypothesized that physiologically based pharmacokinetic (PBPK) modeling could be used as a cost-effective method to examine potential urine pH effect on drug and metabolite disposition. Our previously developed and verified mechanistic kidney model was integrated with a full-body PBPK model to simulate renal clearance and area under the plasma concentration-time curve (AUC) with varying urine pH statuses using methamphetamine and amphetamine as model compounds. We first developed and verified drug models for methamphetamine and amphetamine under normal urine pH condition [absolute average fold error (AAFE) < 1.25 at study level]. Then, acidic and alkaline urine scenarios were simulated. Our simulation results show that the renal excretion and plasma concentration-time profiles for methamphetamine and amphetamine could be recapitulated under different urine pH (AAFE < 2 at individual level). The methamphetamine-amphetamine parent-metabolite full-body PBPK model also successfully simulated amphetamine plasma concentration-time profiles (AAFE < 1.25 at study level) and amphetamine/methamphetamine urinary concentration ratios (AAFE < 2 at individual level) after dosing methamphetamine. This demonstrates that our mechanistic PBPK model can predict urine pH effect on systemic and urinary disposition of drugs and metabolites. SIGNIFICANCE STATEMENT: Our study shows that integrating mechanistic kidney model with full-body physiologically based pharmacokinetic model can predict the magnitude of alteration in renal excretion and area under the plasma concentration-time curve (AUC) of drugs and metabolites when urine pH is changed. This provides a cost-effective method to evaluate the likelihood of renal and systemic disposition changes due to varying urine pH. This is important because multiple drugs and diseases can alter urine pH, leading to quantitatively and clinically significant changes in drug and metabolite disposition that may require adjustment of therapy.

Ultrastructural evaluation of urine alkalinization versus hydration on colistin-induced nephrotoxicity

OBJECTIVES

Colistin is a vital antibiotic used in multidrug-resistant infections. Its most important side effect is nephrotoxicity. Colistin is a weak acid. This study aims to evaluate whether urine alkalinization is protective in the nephrotoxicity of colistin.

METHODS

Twenty-eight male Sprague-Dawley rats were divided into groups. Group I (n = 4) was injected with intramuscular distilled water twice a day for 7 days. Group II (n = 8) was injected with 750,000 IU/kg/day colistin for 7 days. Group III (n = 8) was injected with the same dose of colistin after their urinary pH was ≥7 through the addition of bicarbonate in their drinking water. Group IV (n = 8) was injected with the same dose of colistin after their urine density fell below 1010 through the addition of NaCl molds in their food and 12.6 mg/L NaCl in their drinking water.

RESULTS

According to tubular degenerations (scored 0-5), group I scored 0, group II scored 4.25, group III scored 2, and group IV scored 1.5. In groups III and IV, protection was achieved (p = 0.001). The bicarbonate group was not superior to the NaCl group (p = 0.789). In transmission electron microscopy, group III had more microvilli integrity and autophagic vacuoles compared to group IV. Group IV had mitochondrial swelling and cristae lysis. A lower urine density was related to lower tubular scores (p = 0.001).

CONCLUSIONS

Colistin was highly nephrotoxic without protection. Light microscopy findings revealed that urinary alkalinization and NaCl hydration were similarly protective. Urine alkalinization further prevents ultrastructural changes as revealed by electron microscopy.

Pharmacodynamic Evaluation of Fosfomycin against Escherichia coli and Klebsiella spp. from Urinary Tract Infections and the Influence of pH on Fosfomycin Activities

Fosfomycin is widely used for the treatment of uncomplicated urinary tract infection (UTI), and it has recently been recommended that fosfomycin be used to treat infections caused by multidrug-resistant (MDR) Gram-negative bacilli. Whether urine acidification can improve bacterial susceptibility to fosfomycin oral dosing regimens has not been analyzed. The MIC of fosfomycin for 245 Gram-negative bacterial isolates, consisting of 158 Escherichia coli isolates and 87 Klebsiella isolates which were collected from patients with urinary tract infections, were determined at pH 6.0 and 7.0 using the agar dilution method. Monte Carlo simulation of the urinary fosfomycin area under the concentration-time curve (AUC) after a single oral dose of 3,000 mg fosfomycin and the MIC distribution were used to determine the probability of target attainment (PTA). Fosfomycin was effective against E. coli (MIC₉₀ ≤ 16 μg/ml) but not against Klebsiella spp. (MIC₉₀ > 512 μg/ml). Acidification of the environment increased the susceptibility of 71% of the bacterial isolates and resulted in a statistically significant decrease in bacterial survival. The use of a regimen consisting of a single oral dose of fosfomycin against an E. coli isolate with an MIC of ≤64 mg/liter was able to achieve a PTA of ≥90% for a target pharmacodynamic index (AUC/MIC) of 23 in urine; PTA was not achieved when the MIC was higher than 64 mg/liter. The cumulative fractions of the bacterial responses (CFR) were 99% and 55% against E. coli and Klebsiella spp., respectively, based on simulated drug exposure in urine with an acidic pH of 6.0. A decrease of the pH from 7.0 to 6.0 improved the PTA and CFR of the target pharmacodynamic index in both E. coli and Klebsiella isolates.

Subcellular Partitioning and Intramacrophage Selectivity of Antimicrobial Compounds against Mycobacterium tuberculosis

The efficacy of antimicrobial drugs against Mycobacterium tuberculosis, an intracellular bacterial pathogen, is generally first established by testing compounds against bacteria in axenic culture. However, inside infected macrophages, bacteria encounter an environment which differs substantially from broth culture and are subject to important host-dependent pharmacokinetic phenomena which modulate drug activity. Here, we describe how pH-dependent partitioning drives asymmetric antimicrobial drug distribution in M. tuberculosis-infected macrophages. Specifically, weak bases with moderate activity against M. tuberculosis (fluoxetine, sertraline, and dibucaine) were shown to accumulate intracellularly due to differential permeability and relative abundance of their ionized and nonionized forms. Nonprotonatable analogs of the test compounds did not show this effect. Neutralization of acidic organelles directly with ammonium chloride or indirectly with bafilomycin A1 partially abrogated the growth restriction of these drugs. Using high-performance liquid chromatography, we quantified the degree of accumulation and reversibility upon acidic compartment neutralization in macrophages and observed that accumulation was greater in infected than in uninfected macrophages. We further demonstrate that the efficacy of a clinically used compound, clofazimine, is augmented by pH-based partitioning in a macrophage infection model. Because the parameters which govern this effect are well understood and are amenable to chemical modification, this knowledge may enable the rational development of more effective antibiotics against tuberculosis.

Clinical pharmacokinetics of the nicotinic channel modulator dexmecamylamine (TC-5214) in subjects with various degrees of renal impairment

BACKGROUND AND OBJECTIVE

Dexmecamylamine (TC-5214) is a nicotinic channel modulator that was evaluated as a potential adjunct treatment to an antidepressant for patients with major depressive disorder. Dexmecamylamine is almost completely eliminated via the kidneys, with more than 90 % of a given dose excreted unchanged in urine. The aim of this study was to assess the single-dose pharmacokinetics of dexmecamylamine in subjects with various degrees of renal impairment and subjects undergoing hemodialysis.

METHODS

A single-dose, open-label, parallel-group study was conducted at two study centers in the USA. There were four treatment groups with eight subjects in each, receiving a single dose of dexmecamylamine 8 mg (subjects with normal renal function and mild renal impairment) or TC-5412 2 mg [subjects with moderate renal impairment and end-stage renal disease (ESRD)]. The pharmacokinetics of dexmecamylamine in plasma, urine, and dialysate were evaluated using non-compartmental analysis.

RESULTS

The plasma pharmacokinetics of dexmecamylamine were influenced by renal function. The increase in dose-normalized area under the plasma concentration-time curve (AUC) was statistically significant with an approximately doubled exposure in subjects with moderate renal impairment compared with subjects with normal renal function. The maximum plasma concentration was not impacted by renal function. Plasma clearance of dexmecamylamine in ESRD subjects appeared negligible, with flat plasma concentration-time profiles. Hemodialysis had a relatively modest effect on reduction of dexmecamylamine plasma concentrations. There was no discernable relationship between renal clearance and urinary pH.

CONCLUSION

Renal impairment increased the AUC, prolonged the elimination half-life, and decreased the clearance of dexmecamylamine following administration as a single oral dose. It is likely that renal function would need to be taken into account when setting the dose. Dexmecamylamine administration should be avoided or the dose significantly reduced in patients with severe renal impairment and ESRD.

Clinical pharmacokinetics of the nicotinic channel modulator dexmecamylamine (TC-5214) in subjects with various degrees of renal impairment

BACKGROUND AND OBJECTIVE

Dexmecamylamine (TC-5214) is a nicotinic channel modulator that was evaluated as a potential adjunct treatment to an antidepressant for patients with major depressive disorder. Dexmecamylamine is almost completely eliminated via the kidneys, with more than 90 % of a given dose excreted unchanged in urine. The aim of this study was to assess the single-dose pharmacokinetics of dexmecamylamine in subjects with various degrees of renal impairment and subjects undergoing hemodialysis.

METHODS

A single-dose, open-label, parallel-group study was conducted at two study centers in the USA. There were four treatment groups with eight subjects in each, receiving a single dose of dexmecamylamine 8 mg (subjects with normal renal function and mild renal impairment) or TC-5412 2 mg [subjects with moderate renal impairment and end-stage renal disease (ESRD)]. The pharmacokinetics of dexmecamylamine in plasma, urine, and dialysate were evaluated using non-compartmental analysis.

RESULTS

The plasma pharmacokinetics of dexmecamylamine were influenced by renal function. The increase in dose-normalized area under the plasma concentration-time curve (AUC) was statistically significant with an approximately doubled exposure in subjects with moderate renal impairment compared with subjects with normal renal function. The maximum plasma concentration was not impacted by renal function. Plasma clearance of dexmecamylamine in ESRD subjects appeared negligible, with flat plasma concentration-time profiles. Hemodialysis had a relatively modest effect on reduction of dexmecamylamine plasma concentrations. There was no discernable relationship between renal clearance and urinary pH.

CONCLUSION

Renal impairment increased the AUC, prolonged the elimination half-life, and decreased the clearance of dexmecamylamine following administration as a single oral dose. It is likely that renal function would need to be taken into account when setting the dose. Dexmecamylamine administration should be avoided or the dose significantly reduced in patients with severe renal impairment and ESRD.

Urinary excretion kinetics of methylamphetamine in man

The urinary excretion of methylamphetamine and its metabolite, amphetamine, was studied after oral administration of (+)- and (–)-methylamphetamine hydrochloride to three male subjects. Fluctuations in the excretion rate of both amines occurred and were associated with changes in urinary pH. The fluctuations were abolished when the urine was maintained either acid or alkaline, by administration of ammonium chloride and sodium bicarbonate respectively. The total amount of both amines excreted was lower under alkaline than acid urine conditions. N-Demethylation of methylamphetamine was small, but greater for the (+)- than the (–)-isomer.

Intracellular pharmacokinetics of telithromycin, a ketolide antibiotic, in alveolar macrophages

OBJECTIVES

Telithromycin, a ketolide antibiotic, has an antibacterial range that covers intracellular parasitic pathogens that survive or multiply intracellularly in alveolar macrophages. The intracellular pharmacokinetics of TEL in alveolar macrophages was evaluated in vitro.

METHODS

Telithromycin (50 microm) was applied to NR8383 as cultured alveolar macrophages, followed by incubation at 37 degrees C or 4 degrees C. After incubation, the amount of telithromycin in cells was determined.

KEY FINDINGS

Telithromycin exhibited high accumulation in NR8383 and its intracellular accumulation was temperature dependent. Also, telithromycin distributed to the organelles and cytosol in NR8383 and, in particular, it accumulated in the acidic organelle compartments.

CONCLUSIONS

This study suggests that the high accumulation of telithromycin in NR8383 is due to its high influx via active transport systems and trapping in acidic organelles, such as lysosomes. Moreover, this study provides important information for optimizing the treatment of respiratory intracellular parasitic infections based on the intracellular pharmacokinetics of antibiotics and parasitic sites.

Cell handling, membrane-binding properties, and membrane-penetration modeling approaches of pivampicillin and phthalimidomethylampicillin, two basic esters of ampicillin, in comparison with chloroquine and azithromycin

PURPOSE

The purpose of this work was to examine and understand the cellular pharmacokinetics of two basic esters of ampicillin, pivaloyloxymethyl (PIVA) and phthalimidomethyl (PIMA), in comparison with lysosomotropic drugs (chloroquine, azithromycin).

METHODS

Cell culture studies (J774 macrophages) were undertaken to study uptake and release kinetics and to assess the influence of concentration, pH, proton ionophore (monensin), and MRP and P-gp inhibitors (probenecid, gemfibrozil, cyclosporin A, GF 120918). Equilibrium dialysis with liposomes were performed to directly asses the extent of drug binding to bilayers. Conformational analysis modeling of the drug penetration in bilayers was conducted to rationalize the experimental observations.

RESULTS

PIVA and PIMA showed properties in almost complete contrast with those of chloroquine and azithromycin, i.e., fast apparent accumulation and fast release at 4 degrees C as well as at 37 degrees C, saturation of uptake (apparent Kd 40 microM), no influence of monensin, MRP, or P-gp inhibitors; tight binding to liposomes (Kd approx. 40 microM); and sharp increase in calculated free energy when forced in the hydrophobic domain.

CONCLUSIONS

Although they are weak organic bases, PIVA and PIMA show none of the properties of lysosomotropic agents. We hypothesize that they remain locked onto the pericellular membrane and may never penetrate cells as such in significant amounts.

Absorption, distribution, metabolism and excretion of daily oral doses of [14C]methyl parathion in hens

Adult hens were given oral daily doses of 2 mg (2 microC(i))/kg/day (14% of oral LD(50) in male rats) of [14C]methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate) for 10 consecutive days. Five treated hens were sacrificed at 1, 2, 4, 8, 12, 24, and 48 h after the last dose. Methyl parathion was absorbed from the gastrointestinal tract and distributed rapidly. Maximum radioactivity was detected in tissues within 8 h of dosing, (ng methyl parathion equivalent/g fresh tissue or ml plasma): Plasma (189.2), liver (94.7), kidney (146.2), brain (61.4), gastrointestinal tissues (106.7). Methyl parathion was detected in the plasma, kidney and liver, while methyl parathion metabolite p-nitrophenol was detected in the liver and in the kidney. Elimination of methyl parathion from plasma was monophasic with a terminal half-life of 17.5 h, corresponding to an elimination rate constant of 0.039 ng/hr. Most of the absorbed radioactivity was excreted in the combined fecal-urine excreta (98%). Analysis of the metabolites in the excreta revealed that non-conjugated metabolites accounted for 13% of the total excretion. Conjugated metabolites accounted for 87% of the total excretion; of that, 6% as p-nitrophenyl-glucoronide conjugate, 7% as p-nitrophenyl-sulfate conjugate, 23% as bound hot sulfuric acid hydrolyzable residues, and 51% as water soluble metabolites. The presence of majority of radioactivity in the excreta as conjugated metabolites indicates that determining only unbound p-nitrophenol as a biological marker for methyl parathion exposure underestimates total fecal-urine excretion of p-nitrophenol. The slow elimination rate of methyl parathion is significant, since hens are more comparable to humans with respect to their cytochrome P450 activities.

The resting membrane potential of white muscle from brown trout (Salmo trutta) exposed to copper in soft, acidic water

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=−52.2+/−4.9 mV) and compared with that of unexposed, control animals (E(M)=−86.5+/−2.9 mV) (means +/− s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

Partial pressure of ammonia versus ammonia in hepatic encephalopathy

Ammonia is considered the major pathogenetic factor of cerebral dysfunction in hepatic failure. The correlation between total plasma ammonia and the severity of hepatic encephalopathy (HE), however, is variable. Because ammonia that is present in gaseous form readily enters the brain, the correlation with the grade of HE of the pH-dependent partial pressure of gaseous ammonia (pNH(3)) could be better than that of total arterial ammonia levels. To test this hypothesis, 56 cirrhotic patients with acute episodes of clinical HE (median age, 54 years; range, 21-75) were studied by clinical examination and by long-latency median-nerve sensory-evoked potentials (SEPs) N70 peak, an objective and sensitive electrophysiological measure of HE. pNH(3) was calculated from arterial blood according to published methods. The clinical grade of HE correlated (P <.001) with both pNH(3) and total ammonia, but correlation was stronger with pNH(3) (r =.79 vs.69, P =.01). A similar correlation was found for N70 peak latency (r =.71 with pNH(3) vs.64 with total ammonia, respectively, P =.08). In summary, arterial pNH(3) correlates more closely than total ammonia with the degree of clinical and electrophysiological abnormalities in HE. These findings support the ammonia hypothesis of HE and suggest that pNH(3) might be superior to total ammonia in the pathophysiological evaluation of HE.

Valproate-induced biochemical abnormalities in pregnancy corrected by vitamins: a case report

PURPOSE

Valproate (VPA) is a teratogenic anticonvulsant (AED), but vitamin supplementation has been suggested to limit the effect of VPA on the fetus. Maternal urinary metabolites were monitored to assess the metabolic effects of VPA before and after vitamin supplementation.

METHODS

A pregnant woman with epilepsy receiving VPA and ethosuximide (ESM) was given high-dose multivitamins from 13 to 28 weeks' gestation. Maternal urinary metabolites were measured throughout the pregnancy by gas chromatography/mass spectrometry.

RESULTS

Before multivitamin supplementation began, the patient had significantly increased excretion rates of alpha-ketoglutarate, beta-lactate, pyruvate, lactate, methylmalonate, and other metabolites compared with normal pregnant women. During multivitamin supplementation, many previously increased excretion rates decreased significantly. Fetal head growth was normal up to 30 weeks, but then lagged. Bitemporal narrowing was noted at birth.

CONCLUSIONS

VPA may cause metabolic abnormalities in pregnancy. Many biochemical abnormalities attributable to VPA in this patient were corrected with high-dose multivitamin supplementation. The specific relation between biochemical abnormalities and VPA teratogenesis remains to be determined.