Occurrence of male-specific and somatic coliphages and relationship with rainfall in privately-owned wells from peri‑urban and rural households

Privately-owned drinking water wells serving fewer than 25 people (private wells) are prevalent and understudied across most of the US. Private wells primarily serve rural households located outside of municipal drinking water and sewerage service coverage areas. These wells are not regulated by United States Environmental Protection Agency (EPA) under the Safe Drinking Water Act, are not regularly monitored by any public agency or utility, and generally do not undergo disinfection treatment. Coliphages are a group of viruses that infect coliform bacteria and are useful viral surrogates for fecal contamination in water systems in much the same way that fecal indicator bacteria (FIB), such as E. coli and to a lesser extent total coliforms, are used to quantify fecal contamination. Coliphages are approved by the EPA for regulatory monitoring in groundwater wells in the USA, but are not routinely used for this purpose. The present study characterizes the occurrence of male-specific and somatic coliphages, along with FIB, in private wells (n = 122) across two different counties in North Carolina. While occurrences of E. coli were rare and frequency of total coliform was generally low (~20%), male-specific and somatic coliphages were detectable in 66% and 54% of samples, respectively. Concentrations of male-specific coliphages were higher than somatics at each county and on a monthly basis. Rainfall appears to be partly influencing higher coliphage concentrations in December, January and February. This research underscores the need for increased surveillance in private wells and consideration of using coliphages in order to better characterize occurrence of fecal contamination at the time of sampling, especially during rainier months.

Occurrence of Lead and Other Toxic Metals Derived from Drinking-Water Systems in Three West African Countries

BACKGROUND

Exposure to toxic metals (TMs) such as lead can cause lifelong neurodevelopmental impairment and other adverse outcomes. TMs enter drinking water from human activity, geogenic contamination, and corrosion of water system components. Several studies report TM contamination in piped systems and private wells in high-income countries (HICs). However, few robust studies report on TM contamination in low- and middle-income countries (LMICs).

OBJECTIVES

We characterized the occurrence and investigated sources of TM contamination in 261 rural water systems in three West African LMICs to inform prevention and management.

METHODS

Water samples were collected from 261 community water systems (handpumps and public taps) across rural Ghana, Mali, and Niger. Scrapings were collected from accessible components of a subset of these systems using a drill with acid-washed diamond-tipped bits. Samples were analyzed by inductively coupled plasma (ICP) mass spectrometry or ICP optical emission spectroscopy.

RESULTS

Of the TMs studied, lead most frequently occurred at levels of concern in sampled water system components and water samples. Lead mass fractions exceeded International Plumbing Code (IPC) recommended limits (0.25% wt/wt) for components in 82% (107/130) of systems tested; brass components proved most problematic, with 72% (26/36) exceeding IPC limits. Presence of a brass component in a water system increased expected lead concentrations in drinking-water samples by 3.8 times. Overall, lead exceeded World Health Organization (WHO) guideline values in 9% (24/261) of drinking-water samples across countries; these results are broadly comparable to results observed in many HICs. Results did not vary significantly by geography or system type.

DISCUSSION

Ensuring use of lead-free (<0.25%) components in new water systems and progressively remediating existing systems could reduce drinking-water lead exposures and improve health outcomes for millions. However, reflexive decommissioning of existing systems may deprive users of sufficient water for health or drive them to riskier sources. Because supply chains for many water system components are global, TM monitoring, prevention, and management may be warranted in other LMICs beyond the study area as well. https://doi.org/10.1289/EHP7804.

WaSH CQI: Applying continuous quality improvement methods to water service delivery in four districts of rural northern Ghana

Continuous, safely managed water is critical to health and development, but rural service delivery faces complex challenges in low- and middle-income countries (LMICs). We report the first application of continuous quality improvement (CQI) methods to improve the microbial quality of household water for consumption (HWC) and the functionality of water sources in four rural districts of northern Ghana. We further report on the impacts of interventions developed through these methods. A local CQI team was formed and trained in CQI methods. Baseline data were collected and analyzed to identify determinants of service delivery problems and microbial safety. The CQI team randomized communities, developed an improvement package, iteratively piloted it in intervention communities, and used uptake survey data to refine the package. The final improvement package comprised safe water storage containers, refresher training for community WaSH committees and replacement of missing maintenance tools. This package significantly reduced contamination of HWC (p<0.01), and significant reduction in contamination persisted two years after implementation. Repair times in both intervention and control arms decreased relative to baseline (p<0.05), but differences between intervention and control arms were not significant at endline. Further work is needed to build on the gains in household water quality observed in this work, sustain and scale these improvements, and explore applications of CQI to other aspects of water supply and sanitation.

Indinavir Increases Midazolam N-Glucuronidation in Humans: Identification of an Alternate CYP3A Inhibitor Using an In Vitro to In Vivo Approach

Midazolam is a widely used index substrate for assessing effects of xenobiotics on CYP3A activity. A previous study involving human hepatocytes showed the primary route of midazolam metabolism, 1'-hydroxylation, shifted to N-glucuronidation in the presence of the CYP3A inhibitor ketoconazole, which may lead to an overprediction of the magnitude of a xenobiotic-midazolam interaction. Because ketoconazole is no longer recommended as a clinical CYP3A inhibitor, indinavir was selected as an alternate CYP3A inhibitor to evaluate the contribution of the N-glucuronidation pathway to midazolam metabolism. The effects of indinavir on midazolam 1'-hydroxylation and N-glucuronidation were first characterized in human-derived in vitro systems. Compared with vehicle, indinavir (10 μM) inhibited midazolam 1'-hydroxylation by recombinant CYP3A4, human liver microsomes, and high-CYP3A activity cryopreserved human hepatocytes by ≥70%; the IC₅₀ obtained with hepatocytes (2.7 μM) was within reported human unbound indinavir C_max (≤5 μM). Midazolam N-glucuronidation in hepatocytes increased in the presence of indinavir in both a concentration-dependent (1-33 μM) and time-dependent (0-4 hours) manner (by up to 2.5-fold), prompting assessment in human volunteers (n = 8). As predicted by these in vitro data, indinavir was a strong inhibitor of the 1'-hydroxylation pathway, decreasing the 1'-hydroxymidazolam/midazolam area under the plasma concentration versus time curve (AUC)_0-12h ratio by 80%. Although not statistically significant, the midazolam N-glucuronide/midazolam AUC_0-12h ratio increased by 40%, suggesting a shift to the N-glucuronidation pathway. The amount of midazolam N-glucuronide recovered in urine increased 4-fold but remained <10% of the oral midazolam dose (2.5 mg). A powered clinical study would clarify whether N-glucuronidation should be considered when assessing the magnitude of a xenobiotic-midazolam interaction.

Carrying water may be a major contributor to disability from musculoskeletal disorders in low income countries: a cross-sectional survey in South Africa, Ghana and Vietnam

Background

The Sustainable Development Goals include commitments to end poverty, and promote education for all, gender equality, the availability of water and decent work for all. An important constraint is the fact that each day, many millions of women and children, and much less frequently men, carry their household’s water home from off-plot sources. The burden of fetching water exacerbates gender inequality by keeping women out of education and paid employment. Despite speculation about the potential health impacts of fetching water, there is very little empirical evidence. We report the first large study of the health impacts of carrying water on women and children.

Methods

A cross-sectional survey was conducted in South Africa, Ghana and Vietnam during 2012. It investigated water carrying methods and health status. Because areas of self-reported pain were correlated we undertook factor analysis of sites of reported pain, to interpret patterns of pain reporting. Regression analysis using Generalised Estimating Equations (GEE) investigated water carrying as a risk factor for general health and self-reported pain.

Results

People who previously carried water had increased relative risk of reporting pain in the hands (risk ratio RR 3.62, 95% confidence interval CI 1.34 to 9.75) and upper back (RR 2.27, 95% CI 1.17 to 4.40), as did people who currently carry water (RR hand pain 3.11, 95% CI 1.34 to 7.23; RR upper back pain 2.16, 95% CI 1.25 to 3.73). The factor analysis results indicate that factor 1, ‘axial compression’, which is correlated with pain in the head and upper back, chest/ribs, hands, feet and abdomen/stomach, is associated with currently (0.30, 95% CI 0.17 to 0.43) or previously (0.21, 95% CI 0.01 to 0.42) carrying water. Factor 2, ‘soft tissue strain’, which is correlated with pain in the neck, shoulders/arms, lower back and hips/pelvis or legs, is marginally negatively associated with currently (-0.18, 95% CI -0.32 to -0.04) carrying water. The factor ‘axial compression’ was more strongly associated with carrying water containers on the head.

Conclusions

Participants who reported a history of current or past water carrying more frequently reported pain in locations most likely to be associated with sustained spinal axial compression in the cervical region. Given the fact that cervical spinal conditions are globally one of the more common causes of disability, our findings suggest that water carrying, especially by head loading is a major contributing factor in musculoskeletal disease burden in low income countries. Our findings support the proposed indicator for monitoring SDG6.1: “Percentage of population using safely managed drinking water services at home.”

Evaluating Mobile Survey Tools (MSTs) for Field-Level Monitoring and Data Collection: Development of a Novel Evaluation Framework, and Application to MSTs for Rural Water and Sanitation Monitoring

Information and communications technologies (ICTs) such as mobile survey tools (MSTs) can facilitate field-level data collection to drive improvements in national and international development programs. MSTs allow users to gather and transmit field data in real time, standardize data storage and management, automate routine analyses, and visualize data. Dozens of diverse MST options are available, and users may struggle to select suitable options. We developed a systematic MST Evaluation Framework (EF), based on International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) software quality modeling standards, to objectively assess MSTs and assist program implementers in identifying suitable MST options. The EF is applicable to MSTs for a broad variety of applications. We also conducted an MST user survey to elucidate needs and priorities of current MST users. Finally, the EF was used to assess seven MSTs currently used for water and sanitation monitoring, as a validation exercise. The results suggest that the EF is a promising method for evaluating MSTs.

A Systematic Review and Meta-Analysis of Fecal Contamination and Inadequate Treatment of Packaged Water

BACKGROUND

Packaged water products provide an increasingly important source of water for consumption. However, recent studies raise concerns over their safety.

OBJECTIVES

To assess the microbial safety of packaged water, examine differences between regions, country incomes, packaged water types, and compare packaged water with other water sources.

METHODS

We performed a systematic review and meta-analysis. Articles published in English, French, Portuguese, Spanish and Turkish, with no date restrictions were identified from online databases and two previous reviews. Studies published before April 2014 that assessed packaged water for the presence of Escherichia coli, thermotolerant or total coliforms were included provided they tested at least ten samples or brands.

RESULTS

A total of 170 studies were included in the review. The majority of studies did not detect fecal indicator bacteria in packaged water (78/141). Compared to packaged water from upper-middle and high-income countries, packaged water from low and lower-middle-income countries was 4.6 (95% CI: 2.6-8.1) and 13.6 (95% CI: 6.9-26.7) times more likely to contain fecal indicator bacteria and total coliforms, respectively. Compared to all other packaged water types, water from small bottles was less likely to be contaminated with fecal indicator bacteria (OR = 0.32, 95%CI: 0.17-0.58) and total coliforms (OR = 0.10, 95%CI: 0.05, 0.22). Packaged water was less likely to contain fecal indicator bacteria (OR = 0.35, 95%CI: 0.20, 0.62) compared to other water sources used for consumption.

CONCLUSIONS

Policymakers and regulators should recognize the potential benefits of packaged water in providing safer water for consumption at and away from home, especially for those who are otherwise unlikely to gain access to a reliable, safe water supply in the near future. To improve the quality of packaged water products they should be integrated into regulatory and monitoring frameworks.

Understanding handpump sustainability: Determinants of rural water source functionality in the Greater Afram Plains region of Ghana

Safe drinking water is critical to human health and development. In rural sub-Saharan Africa, most improved water sources are boreholes with handpumps; studies suggest that up to one third of these handpumps are nonfunctional at any given time. This work presents findings from a secondary analysis of cross-sectional data from 1509 water sources in 570 communities in the rural Greater Afram Plains (GAP) region of Ghana; one of the largest studies of its kind. 79.4% of enumerated water sources were functional when visited; in multivariable regressions, functionality depended on source age, management, tariff collection, the number of other sources in the community, and the district. A Bayesian network (BN) model developed using the same data set found strong dependencies of functionality on implementer, pump type, management, and the availability of tools, with synergistic effects from management determinants on functionality, increasing the likelihood of a source being functional from a baseline of 72% to more than 97% with optimal management and available tools. We suggest that functionality may be a dynamic equilibrium between regular breakdowns and repairs, with management a key determinant of repair rate. Management variables may interact synergistically in ways better captured by BN analysis than by logistic regressions. These qualitative findings may prove generalizable beyond the study area, and may offer new approaches to understanding and increasing handpump functionality and safe water access.

Microbiological and Chemical Quality of Packaged Sachet Water and Household Stored Drinking Water in Freetown, Sierra Leone

Packaged drinking water (PW) sold in bottles and plastic bags/sachets is widely consumed in low- and middle-income countries (LMICs), and many urban users in sub-Saharan Africa (SSA) rely on packaged sachet water (PSW) as their primary source of water for consumption. However, few rigorous studies have investigated PSW quality in SSA, and none have compared PSW to stored household water for consumption (HWC). A clearer understanding of PSW quality in the context of alternative sources is needed to inform policy and regulation. As elsewhere in SSA, PSW is widely consumed in Sierra Leone, but government oversight is nearly nonexistent. This study examined the microbiological and chemical quality of a representative sample of PSW products in Freetown, Sierra Leone at packaged water manufacturing facilities (PWMFs) and at points of sale (POSs). Samples of HWC were also analyzed for comparison. The study did not find evidence of serious chemical contamination among the parameters studied. However, 19% of 45 PSW products sampled at the PWMF contained detectable Escherichia coli (EC), although only two samples exceeded 10 CFU/100 mL. Concentrations of total coliforms (TC) in PSW (but not EC) increased along the supply chain. Samples of HWC from 60 households in Freetown were significantly more likely to contain EC and TC than PSW at the point of production (p<0.01), and had significantly higher concentrations of both bacterial indicators (p<0.01). These results highlight the need for additional PSW regulation and surveillance, while demonstrating the need to prioritize the safety of HWC. At present, PSW may be the least unsafe option for many households.

Global monitoring of water supply and sanitation: history, methods and future challenges

International monitoring of drinking water and sanitation shapes awareness of countries' needs and informs policy, implementation and research efforts to extend and improve services. The Millennium Development Goals established global targets for drinking water and sanitation access; progress towards these targets, facilitated by international monitoring, has contributed to reducing the global disease burden and increasing quality of life. The experiences of the MDG period generated important lessons about the strengths and limitations of current approaches to defining and monitoring access to drinking water and sanitation. The methods by which the Joint Monitoring Programme (JMP) of WHO and UNICEF tracks access and progress are based on analysis of data from household surveys and linear regression modelling of these results over time. These methods provide nationally representative and internationally comparable insights into the drinking water and sanitation facilities used by populations worldwide, but also have substantial limitations: current methods do not address water quality, equity of access, or extra-household services. Improved statistical methods are needed to better model temporal trends. This article describes and critically reviews JMP methods in detail for the first time. It also explores the impact of, and future directions for, international monitoring of drinking water and sanitation.

Inactivation of Escherichia coli by polychromatic simulated sunlight: evidence for and implications of a fenton mechanism involving iron, hydrogen peroxide, and superoxide

Sunlight inactivation of Escherichia coli has previously been shown to accelerate in the presence of oxygen, exogenously added hydrogen peroxide, and bioavailable forms of exogenously added iron. In this study, mutants unable to effectively scavenge hydrogen peroxide or superoxide were found to be more sensitive to polychromatic simulated sunlight (without UVB wavelengths) than wild-type cells, while wild-type cells grown under low-iron conditions were less sensitive than cells grown in the presence of abundant iron. Furthermore, prior exposure to simulated sunlight was found to sensitize cells to subsequent hydrogen peroxide exposure in the dark, but this effect was attenuated for cells grown with low iron. Mutants deficient in recombination DNA repair were sensitized to simulated sunlight (without UVB wavelengths), but growth in the presence of iron chelators reduced the degree of sensitization conferred by this mutation. These findings support the hypothesis that hydrogen peroxide, superoxide, and intracellular iron all participate in the photoinactivation of E. coli and further suggest that the inactivation rate of enteric bacteria in the environment may be strongly dependent on iron availability and growth conditions.

Solar water disinfection (SODIS) of Escherichia coli, Enterococcus spp., and MS2 coliphage: effects of additives and alternative container materials

The use of alternative container materials and added oxidants accelerated the inactivation of MS2 coliphage and Escherichia coli and Enterococcus spp. bacteria during solar water disinfection (SODIS) trials. Specifically, bottles made from polypropylene copolymer (PPCO), a partially UVB-transparent plastic, resulted in three-log inactivation of these organisms in approximately half the time required for disinfection in bottles made from PET, polycarbonate, or Tritan(®), which absorb most UVB light. Furthermore, the addition of 125 mg/L sodium percarbonate in combination with either citric acid or copper plus ascorbate tended to accelerate inactivation by factors of 1.4-19. Finally, it was observed that the inactivation of E. coli and enterococci derived from local wastewater was far slower than the inactivation of laboratory-cultured E. coli and Enterococcus spp., while the inactivation of MS2 was slowest of all. These results highlight the importance of UVB in SODIS under certain conditions, and also the greater sunlight resistance of some viruses and of bacteria of fecal origin, as compared to the laboratory-cultured bacteria commonly used to model their inactivation. Furthermore, this study illustrates promising new avenues for accelerating the inactivation of bacteria and viruses by solar disinfection.

Time-dependent inhibition and estimation of CYP3A clinical pharmacokinetic drug-drug interactions using plated human cell systems

The current studies assessed the utility of freshly plated hepatocytes, cryopreserved plated hepatocytes, and cryopreserved plated HepaRG cells for the estimation of inactivation parameters k(inact) and K(I) for CYP3A. This was achieved using a subset of CYP3A time-dependent inhibitors (fluoxetine, verapamil, clarithromycin, troleandomycin, and mibefradil) representing a range of potencies. The estimated k(inact) and K(I) values for each time-dependent inhibitor were compared with those obtained using human liver microsomes and used to estimate the magnitude of clinical pharmacokinetic drug-drug interaction (DDI). The inactivation kinetic parameter, k(inact), was most consistent across systems tested for clarithromycin, verapamil, and troleandomycin, with a high k(inact) of 0.91 min(-1) observed for mibefradil in HepaRG cells. The apparent K(I) estimates derived from the various systems displayed a range of variability from 3-fold for clarithromycin (5.4-17.7 μM) to 6-fold for verapamil (1.9-12.6 μM). In general, the inactivation kinetic parameters derived from the cell systems tested fairly replicated what was observed in time-dependent inhibition studies using human liver microsomes. Despite some of the observed differences in inactivation kinetic parameters, the estimated DDIs derived from each of the tested systems generally agreed with the clinically reported DDI within approximately 2-fold. In addition, a plated cell approach offered the ability to conduct longer primary incubations (greater than 30 min), which afforded improved ability to identify the weak time-dependent inhibitor fluoxetine. Overall, results from these studies suggest that in vitro inactivation parameters generated from plated cell systems may be a practical approach for identifying time-dependent inhibitors and for estimating the magnitude of clinical DDIs.

Simulated sunlight action spectra for inactivation of MS2 and PRD1 bacteriophages in clear water

Action spectra for simulated sunlight were measured in clear water for two viruses: PRD1, a double-stranded DNA bacteriophage, and MS2, a single-stranded RNA bacteriophage. Viruses were diluted into phosphate buffered saline (20 mM PBS, pH 7.5) and exposed for 22 h to simulated sunlight either directly or through one of six glass filters with 50% cutoff wavelengths ranging from 280 to 350 nm. Virus survival was measured using the double agar layer plaque method. Both UVA (320-400 nm) and UVB (280-320 nm) light were found to contribute to PRD1 inactivation, while only UVB inactivated MS2. A computational model was developed for interpreting these action spectra with 3-nm resolution. Using these methods, we provide detailed estimates of the sensitivity of MS2 and PRD1 to photoinactivation from 285 to 345 nm. The resulting sensitivity coefficients can be combined with solar spectra to estimate inactivation rates in clear water under different sunlight conditions. This approach will be useful for modeling the inactivation of viruses and other microorganisms in sunlit natural and engineered systems.

Characterization of aldehyde oxidase enzyme activity in cryopreserved human hepatocytes

Substrates of aldehyde oxidase (AO), for which human clinical pharmacokinetics are reported, were selected and evaluated in pooled mixed-gender cryopreserved human hepatocytes in an effort to quantitatively characterize AO activity. Estimated hepatic clearance (Cl(h)) for BIBX1382, carbazeran, O⁶-benzylguanine, zaleplon, and XK-469 using cryopreserved hepatocytes was 18, 17, 12, <4.3, and <4.3 ml · min⁻¹ · kg⁻¹, respectively. The observed metabolic clearance in cryopreserved hepatocytes was confirmed to be a result of AO-mediated metabolism via two approaches. Metabolite identification after incubations in the presence of H₂¹⁸O confirmed that the predominant oxidative metabolite was generated by AO, as expected isotope patterns in mass spectra were observed after analysis by high-resolution mass spectrometry. Second, clearance values were efficiently attenuated upon coincubation with hydralazine, an inhibitor of AO. The low exposure after oral doses of BIBX1382 and carbazeran (∼5% F) would have been fairly well predicted using simple hepatic extraction (f(h)) values derived from cryopreserved hepatocytes. In addition, the estimated hepatic clearance value for O⁶-benzylguanine was within ∼80% of the observed total clearance in humans after intravenous administration (15 ml · min⁻¹ · kg⁻¹), indicating a reasonable level of quantitative activity from this in vitro system. However, a 3.5-fold underprediction of total clearance was observed for zaleplon, despite the 5-oxo metabolite being clearly observed. These data taken together suggest that the use of cryopreserved hepatocytes may be a practical approach for assessing AO-mediated metabolism in discovery and potentially useful for predicting hepatic clearance of AO substrates.

Discovery of CP-690,550: a potent and selective Janus kinase (JAK) inhibitor for the treatment of autoimmune diseases and organ transplant rejection

There is a critical need for safer and more convenient treatments for organ transplant rejection and autoimmune disorders such as rheumatoid arthritis. Janus tyrosine kinases (JAK1, JAK3) are expressed in lymphoid cells and are involved in the signaling of multiple cytokines important for various T cell functions. Blockade of the JAK1/JAK3-STAT pathway with a small molecule was anticipated to provide therapeutic immunosuppression/immunomodulation. The Pfizer compound library was screened against the catalytic domain of JAK3 resulting in the identification of a pyrrolopyrimidine-based series of inhibitors represented by CP-352,664 (2a). Synthetic analogues of 2a were screened against the JAK enzymes and evaluated in an IL-2 induced T cell blast proliferation assay. Select compounds were evaluated in rodent efficacy models of allograft rejection and destructive inflammatory arthritis. Optimization within this chemical series led to identification of CP-690,550 1, a potential first-in-class JAK inhibitor for treatment of autoimmune diseases and organ transplant rejection.

Recent advances in high throughput screening for ADME properties

With the increase in the numbers of molecules synthesized in a typical drug discovery program, as well as the large amount of information utilized in the selection of a drug candidate, there is a need for a plethora of drug metabolism and pharmacokinetic (DMPK) information to be regularly generated in discovery. Over the past decade, many in vitro, and even in vivo, DMPK screens have been developed and routinely deployed to generate this information in support of drug discovery efforts. In the past few years, newer methods, or adaptations to methods, have been published, and this review attempts to summarize these advances. In particular, advances have been reported for experimental approaches to metabolic clearance, CYP inhibition, in vivo exposure, and distribution, as well as in silico determinations of absorption, distribution, metabolism, and excretion (ADME) properties. Bioanalytical approaches aimed at optimizing analyte method development, sample preparation, and analyte detection, have also been reported. Future advances will further improve the ability to make decisions on molecules earlier in drug discovery.

Speeding up solar disinfection (SODIS): effects of hydrogen peroxide, temperature, pH, and copper plus ascorbate on the photoinactivation of E. coli

Solar disinfection, or SODIS, shows tremendous promise for point-of-use drinking water treatment in developing countries, but can require 48 h or more for adequate disinfection in cloudy weather. In this research, we show that a number of low-cost additives are capable of accelerating SODIS. These additives included 100-1000 muM hydrogen peroxide, both at room temperature and at elevated temperatures, 0.5 - 1% lemon and lime juice, and copper metal or aqueous copper plus ascorbate, with or without hydrogen peroxide. Laboratory and field experiments indicated that additives might make SODIS more rapid and effective in both sunny and cloudy weather, developments that could help make the technology more effective and acceptable to users.

The role of the intestine in drug metabolism and pharmacokinetics: an industry perspective

Over the past decade, our knowledge concerning the importance of intestinal metabolism in the disposition of xenobiotics has significantly improved. Compounds such as midazolam can be extensively extracted in the intestine upon first-pass metabolism after oral dosing. Conversely, the intestine plays a less important, albeit less characterized role in systemic metabolism. This manuscript is meant to review the published examples of pharmaceutical industry research on the intestinal metabolism of xenobiotics, including the various in vitro and in vivo models used. While it is clear that some examples exist of published characterization of the role of intestinal metabolism in drug disposition from the pharmaceutical industry, the majority of industry literature ignores its contribution. The opportunity exists to increase the examination of intestinal metabolism of drugs and drug candidates in industry.

Piperazinyl CCR1 antagonists--optimization of human liver microsome stability

The synthesis, biological activity, and pharmacokinetic profile of CCR1 antagonists are described.

In vivo use of the P450 inactivator 1-aminobenzotriazole in the rat: varied dosing route to elucidate gut and liver contributions to first-pass and systemic clearance

The small intestine is regarded as an absorptive organ in the uptake of orally administered drugs, but also has the ability to metabolize drugs by both phase 1 and phase 2 reactions. The amount of drug that reaches the systemic circulation can be reduced by both intestinal and hepatic metabolism. 1-Aminobenzotriazole (ABT) is an irreversible inhibitor of cytochrome P450s. Through in vivo and in vitro studies, ABT has been evaluated for its utility in studying intestinal metabolism in rats. Rats have been exposed to ABT through varied routes of administration followed by p.o. and i.v. administration of midazolam (MDZ), a CYP3A substrate. The MDZ bioavailablity in rats dosed orally and in rats dosed intravenously with ABT is 58.5% and 0.7%, respectively (%F = 2.3% w/o ABT). The approximately 80-fold difference between the two groups suggests the majority of the extraction occurs in the intestine following an oral dose. To further study the utility of ABT, the antihistamine fexofenadine (Fex), which is not significantly metabolized and is a substrate for the uptake and efflux transporters, OATP and P-gp, was tested in rat. There was no change in oral or systemic exposure of Fex when animals were predosed with ABT, suggesting that ABT does not affect these transporters. These findings may lead to a better understanding of the interdependent role of absorption and metabolism and the specificity of ABT. This method should have utility in drug discovery for the identification of factors limiting oral bioavailability.

The complexities inherent in attempts to decrease drug clearance by blocking sites of CYP-mediated metabolism

Oxidative metabolism by the cytochromes P450 (CYPs) is the most common metabolic pathway of drug clearance. Medicinal chemists in drug discovery often synthesize analogs of lead molecules to reduce clearance due to metabolism. One method generally used when attempting to reduce CYP metabolism is to identify the site of modification to 'block' it. Substituting fluorine in the place of hydrogen at metabolically labile positions, for example, is a common approach, although deuterium can also be considered here for simplicity. In this case, the rate of metabolism via a specific pathway is attenuated, but the rate of overall substrate consumption or overall clearance is not significantly altered, due to a compensatory increase in the rate of formation of an alternate metabolite. The concepts and evidence behind this phenomenon as it relates to complexities in blocking metabolic clearance are presented herein.

A streamlined method to predict hepatic clearance using human liver microsomes in the presence of human plasma

INTRODUCTION

Human liver microsomal incubations are often used to predict the metabolic lability of new chemical entities. The clearance values are scaled-up from in vitro data and mathematically corrected for plasma protein binding, or in some cases the free fraction ratio of plasma to microsomes, using well-established scaling methods such as the well-stirred model. This can be time consuming for multiple compounds since it requires separate experiments to determine in vitro lability, and free fraction.

METHODS

We attempted to streamline clearance predictions by combining experiments into one. Firstly, we combined the free fraction experiments into one free fraction ratio by measuring the partitioning of compound between plasma and microsomes, and by applying this experimental ratio to clearance predictions found that it performed at least as well as free fractions determined separately. We also incubated compounds with plasma added to the incubation mixture and compared the predicted clearances to values determined using traditional mathematical protein binding corrections.

RESULTS

Consistently, incubations with added plasma resulted in CL predictions closer to literature values than incubations only mathematically corrected for protein binding. For example, incorporating plasma into a ketamine incubation resulted in a CL value of 15.1 mL/min/kg, compared with a value of 10.2 using mathematical binding corrections. The literature value is 16.4 mL/min/kg.

DISCUSSION

This work characterizes this new method and compares it to the traditional microsomal incubation method using several literature compounds, and suggests that streamlining the methods may generate quality data faster and with less resource investment.

ALTERED AZT (3′-AZIDO-3′-DEOXYTHYMIDINE) GLUCURONIDATION KINETICS IN LIVER MICROSOMES AS AN EXPLANATION FOR UNDERPREDICTION OF IN VIVO CLEARANCE: COMPARISON TO HEPATOCYTES AND EFFECT OF INCUBATION ENVIRONMENT

Human liver microsomes are a reagent commonly used to predict human hepatic clearance of new chemical entities via phase 1 metabolism. Another common metabolic pathway, glucuronidation, can also be observed in human liver microsomes, although the scalability of this process has not been validated. In fact, several groups have demonstrated that clearance estimated from liver microsomes with UDP-glucuronic acid typically underpredicts the actual in vivo clearance more than 10-fold for compounds that are predominantly glucuronidated. In contrast, clearance predicted using human hepatocytes, for these same compounds, provides a more accurate assessment of in vivo clearance. We sought to characterize the kinetics of glucuronidation of the selective UGT2B7 substrate AZT (3'-azido-3'-deoxythymidine), a selective UGT2B7 substrate, in human liver microsomes (HLMs), recombinant UGT2B7, and human hepatocytes. Apparent Km values in these three preparations were 760, 490, and 87 microM with apparent Vmax values highest in hepatocytes. The IC50 for ibuprofen against AZT glucuronidation, when run at its Km concentration in HLMs and hepatocytes, was 975 and 170 microM respectively. Since incubation conditions have been shown to modulate glucuronidation rates, AZT glucuronidation was performed in various physiological and nonphysiological buffer systems, namely Tris, phosphate, sulfate, carbonate, acetate, human plasma, deproteinized human liver cytosol, and Williams E medium. The data showed that carbonate and Williams E medium, more physiologically relevant buffers, yielded the highest rates of AZT glucuronidation. Km observed in HLM/carbonate was 240 microM closer to that found in hepatocytes, suggesting that matrix differences might cause the kinetic differences observed between liver preparations. Caution should be exercised when extrapolating metabolic lability via glucuronidation or inhibition of UGT enzymes from human liver microsomes, since this system appears to underpredict the degree of lability or inhibition, respectively, due in part to an apparent decrease in substrate affinity.

Assessment of UDP-glucuronosyltransferase catalyzed formation of ethyl glucuronide in human liver microsomes and recombinant UGTs

While ethanol is primarily metabolized to acetaldehyde and acetic acid via alcohol dehydrogenase, a minor but increasingly important pathway in the field of forensic science involves the conjugation of glucuronic acid to form an ethyl glucuronide (EtG) metabolite. The kinetics of ethyl glucuronide formation were examined in human liver microsomes (HLM) and recombinant UDP-glucuronosyltransferases (UGTs). The metabolite exhibited a relatively slow rate of formation in a human liver microsome mix of 75.4 pmol/(min/mg). Further investigation identified multiple UGT isoforms to be responsible for catalyzing the addition of glucuronic acid to ethanol, with UGT1A1 and 2B7 being the two most prevalent isoforms. Co-incubation with bilirubin or 3'-azido-3'-deoxythymidine (UGT1A1 and 2B7 inhibitors, respectively) inhibited the greatest amount of ethyl glucuronide formation, though other UGT inhibitors also showed some effect. Enzyme kinetics were performed in human liver microsomes and recombinant UGT enzymes. The apparent Km (Km app) and Vmax values were determined to be 0.17+/-0.08 mM and 75.98+/-5.63 pmol/(min/mg) (human liver microsomes), 0.03+/-0.01 mM and 25.22+/-3.45 pmol/(min/mg) (UGT1A1), and 0.11+/-0.04 mM and 52.03+/-9.8 pmol/(min/mg) (UGT2B7). Thus, it appears that multiple UGTs are responsible for the formation of ethyl glucuronide and that any functional differences in the enzymology underlying ethyl glucuronide formation would most likely be masked by a combination of other enzymatic pathways.

Impact of incubation conditions on bufuralol human clearance predictions: enzyme lability and nonspecific binding

Human liver microsomes (HLMs) are frequently utilized in drug discovery to predict the human clearance of a compound. The extent to which the incubation conditions affect the accuracy of a human clearance prediction was determined for bufuralol. HLMs were preincubated at 37 degrees C for varying times (5-120 min) with and without NADPH, and the remaining enzyme activity was determined by incubating compounds that have been characterized to be selective for individual cytochromes P450 or flavin-containing monooxygenase 3. CYP2D6, the high-affinity component of bufuralol metabolism, was shown to be the least stable of the isoforms studied. The loss of CYP2D6 activity was further examined by determining the kinetics of 1'-hydroxybufuralol formation after different preincubation time periods, by using reactive oxygen species (ROS) scavengers, and by utilizing Western blotting techniques. A 3-fold decrease in Vmax was observed over 2 h, whereas the Km remained constant. ROS scavengers were able to block enzyme lability, and Western blots revealed no apparent loss of immunoreactive enzyme. The protein binding of bufuralol was determined in HLMs, recombinant CYP2D6, and human plasma. A prediction of theoretical bufuralol concentrations over a 120-min incubation that incorporated enzyme lability was performed and shown to be closer to actual data than if enzyme lability were ignored. Finally, a similar prediction using literature bufuralol data, coupled with the observed protein binding data, was used to illustrate that the most accurate predictions of bufuralol clearance are obtained when the amount of protein in the incubation is kept to a minimum and the overall incubation time is less than 20 min.

Prevention of organ allograft rejection by a specific Janus kinase 3 inhibitor

Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings.

Flavin-containing monooxygenase activity in hepatocytes and microsomes: in vitro characterization and in vivo scaling of benzydamine clearance

Liver microsomes, and more recently cryopreserved hepatocytes, are commonly used in the in vitro characterization of the metabolism of new xenobiotics. The flavin-containing monooxygenases (FMO) are a major non p450 oxidase present in liver microsomes and hepatocytes. Since FMO is known to be thermally labile, and this enzyme may be involved in the metabolic clearance of some drugs, we sought to more completely characterize the metabolic competency of this enzyme in cryopreserved hepatocytes and in liver microsomes preincubated under various conditions using benzydamine as an in vitro and in vivo probe. The metabolism of benzydamine to its major metabolite, the N-oxide, is mediated by FMO3 in humans. We found that the in vitro microsomal t(1/2) was 70% longer when incubations were prewarmed at 37 degrees C in the absence of NADPH compared with prewarming in the presence of an NADPH-regenerating system, and N-oxide formation was inhibited >99%. Interestingly, the in vivo clearance predicted from these incubations and from human hepatocytes overpredicted the observed clearance of benzydamine in humans (>10.5 versus 2.4 ml/min/kg). In contrast, rat hepatocytes successfully predicted rat in vivo benzydamine clearance to within approximately 30% (>68 versus 48 ml/min/kg). Benzydamine N-oxidation in liver microsomes from all common preclinical species demonstrated heat sensitivity. This information should be considered when extrapolating metabolism data of xenobiotics from these in vitro systems.

Characterization by liquid chromatography-nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry of two coupled oxidative-conjugative metabolic pathways for 7-ethoxycoumarin in human liver microsomes treated with alamethicin

The microsomal metabolism of 7-ethoxycoumarin (7-EC) was investigated using liquid chromatography (LC)-NMR and liquid chromatography-mass spectrometry (LC-MS) to characterize the coupling of oxidative-conjugative metabolism events. Within microsomes, cytochromes P450 (P450s) and UDP-glucuronosyltransferases (UGTs) are spatially disparate, each having surface and luminal localization, respectively. To optimize cofactor and substrate transit to UGT without compromising P450 activity, the pore-forming peptide alamethicin was used for microsomal perforation. Aqueous extracts of microsomal incubations containing NADPH and UDP-glucuronic acid were injected for LC-NMR and LC-MS analysis. The analytical complementarity of LC-NMR and LC-MS permitted the identification of four metabolites (M1 to M4). The metabolites M1 and M2 are novel microsomal metabolites for 7-EC, consistent with 3-hydroxylation and subsequent glucuronidation, respectively. Metabolites M3 and M4 were 7-hydroxycoumarin (7-HC) and 7-HC glucuronide, respectively. Viewed collectively, these results illustrate the utility of alamethicin in the examination of coupled oxidative-conjugative metabolism and the synergy of LC-NMR and LC-MS in metabolite identification.

The role of hepatic and extrahepatic UDP-glucuronosyltransferases in human drug metabolism

At present, the methods and enzymology of the UDP-glucuronosyltransferases (UGTs) lag behind that of the cytochromes P450 (CYPs). About 15 human UGTs have been identified, and knowledge about their regulation, substrate selectivity, and tissue distribution has progressed recently. Alamethicin has been characterized as a treatment to remove the latency of microsomal glucuronidations. Most UGT isoforms appear to have a distinct hepatic and/or extrahepatic expression, resulting in significant expression in kidney, intestine, and steroid target tissues. The gastrointestinal tract possesses a complex expression pattern largely containing members of the UGT1A subfamily. Thus, these forms are poised to participate in the first pass metabolism of oral drugs. The authors and others have identified a significant expression of UGT1A1 in human small intestine, an enzyme possessing considerable allelic variability and a polymorphic expression pattern in intestine. Intestinal glucuronidation therefore plays a major role not only in first pass metabolism, but also in the degree of interindividual variation in overall oral bioavailability. Due to issues such as significant genetic variability and tissue localization in first-pass organs, clearance due to UGT1A1 should be minimized for new drugs.

Active site characteristics of CYP4B1 probed with aromatic ligands

The active site topography of rabbit CYP4B1 has been studied relative to CYP2B1 and CYP102 using a variety of aromatic probe substrates. Oxidation of the prochiral substrate cumene by CYP4B1, but not CYP2B1 or CYP102, resulted in the formation of the thermodynamically disfavored omega-hydroxy metabolite, 2-phenyl-1-propanol, with product stereoselectivity for the (S)-enantiomer. Reaction of CYP4B1, CYP2B1, and CYP102 with phenyldiazene produced spectroscopically observable sigma-complexes for each enzyme. Subsequent oxidation of the CYP2B1 and CYP102 complexes followed by LC/ESI--MS analysis yielded heme pyrrole migration patterns similar to those in previous literature reports. Upon identical treatment, no migration products were detected for CYP4B1. Intramolecular deuterium isotope effects for the benzylic hydroxylation of o-xylene-alpha-(2)H(3), p-xylene-alpha-(2)H(3), 2-(2)H(3),6-dimethylnaphthalene, and 4-(2)H(3),4'-dimethylbiphenyl were determined for CYP4B1 and CYP2B1 to further map their active site dimensions. These probes permit assessment of the ease of equilibration, within P450 active sites, of oxidizable methyl groups located between 3 and 10 A apart [Iyer et al. (1997) Biochemistry 36, 7136--7143]. Isotope effects for the CYP4B1-mediated benzylic hydroxylation of o- and p-xylenes were fully expressed (k(H)/k(D) = 9.7 and 6.8, respectively), whereas deuterium isotope effects for the naphthyl and biphenyl derivatives were both substantially masked (k(H)/k(D) approximately equal to 1). In contrast, significant suppression of the deuterium isotope effects for CYP2B1 occurred only with the biphenyl substrate. Therefore, rapid equilibration between two methyl groups more than 6 A apart is impeded within the active site of CYP4B1, whereas for CYP2B1, equilibration is facile for methyl groups distanced by more than 8 A. Collectively, all data are consistent with the conclusion that the active site of CYP4B1 is considerably restricted relative to CYP2B1.

Tissue distribution and interindividual variation in human UDP-glucuronosyltransferase activity: relationship between UGT1A1 promoter genotype and variability in a liver bank

The variability in a liver bank and tissue distribution of three probe UDP-glucuronosyltransferase (UGT) activities were determined as a means to predict interindividual differences in expression and the contribution of extrahepatic metabolism to presystemic and systemic clearance. Formation rates of acetaminophen-O-glucuronide (APAPG), morphine-3-glucuronide (M3G), and oestradiol-3-glucuronide (E3G) as probes for UGT1A6, 2B7, and 1A1, respectively, were determined in human kidney, liver, and lung microsomes, and in microsomes from intestinal mucosa corresponding to duodenum, jejunum and ileum. While formation of E3G and APAPG were detectable in human kidney microsomes, M3G formation rates from kidney microsomes approached the levels seen in liver, indicating significant expression of UGT2B7. Interestingly, rates of E3G formation in human intestine exceeded the hepatic rates by several fold, while APAPG and M3G formation rates were low. The intestinal apparent Km value for E3G formation was essentially identical to that seen in liver, consistent with intestinal UGT1A1 expression. No UGT activities were observed in lung. Variability in APAPG and M3G activity across a bank of 20 human livers was modest (< or = 7-fold), compared to E3G formation, which varied approximately 30-fold. The E3G formation rates were found to segregate by UGT1A1 promoter genotype, with wild-type (TA)6 rates significantly greater than homozygous mutant (TA)7 individuals. Kinetic analyses were performed to demonstrate that the promoter mutation altered apparent Vmax without significantly affecting apparent Km. These results suggest that glucuronidation, and specifically UGT1A1 activity, can profoundly contribute to intestinal first pass metabolism and interindividual variability due to the expression of common allelic variants.

Immunochemical identification of UGT isoforms in human small bowel and in caco-2 cell monolayers

Previous work had suggested the presence of significant levels of UDP-glucuronosyltransferase 1A1 (UGT1A1) catalytic activity in human small intestinal microsomes, with undetectable to low UGT1A6 and 2B7 activities. To confirm the presence of UGT1A1 isoform in human small bowel, to explore the possible absence of UGT1A6 and 2B7 in the organ, and to examine induced Caco-2 cells as a potential model for human intestinal metabolism, Western blot analysis was performed using specific antibodies to the relevant UGT isoforms. Significant expression of UGT1A1 protein was observed in all samples of human small intestinal microsomes, while UGT1A6 expression was undetectable to faint and UGT2B7 immunoreactivity was faint to detectable. Caco-2 cells treated with typical enzyme-inducing agents resulted in low UGT2B7 expression but failed to mimic the UGT1A1 levels found in human small bowel. Further work needs to be performed to develop a comprehensive in vitro model for human small intestinal first-pass metabolism.

In vitro glucuronidation using human liver microsomes and the pore-forming peptide alamethicin

The UDP-glucuronosyltransferases (UGTs) are a superfamily of membrane-bound enzymes whose active site is localized inside the endoplasmic reticulum. Glucuronidation using human liver microsomes has traditionally involved disruption of the membrane barrier, usually by detergent treatment, to attain maximal enzyme activity. The goals of the current work were to develop a universal method to glucuronidate xenobiotic substrates using microsomes, and to apply this method to sequential oxidation-glucuronidation reactions. Three assays of UGT catalytic activity estradiol-3-glucuronidation, acetaminophen-O-glucuronidation, and morphine-3-glucuronidation, which are relatively selective probes for human UGT1A1, 1A6, and 2B7 isoforms, respectively, were developed. Treatment of microsomes with the pore-forming peptide alamethicin (50 microg/mg protein) resulted in conjugation rates 2 to 3 times the rates observed with untreated microsomes. Addition of physiological concentrations of Mg(2+) to the alamethicin-treated microsomes yielded rates that were 4 to 7 times the rates with untreated microsomes. Optimized assay conditions were found not to detrimentally affect cytochrome P450 activity as determined by effects on testosterone 6beta-hydroxylation and 7-ethoxycoumarin deethylation. Formation of estradiol-3-glucuronide displayed atypical kinetics, and data best fit the Hill equation, yielding apparent kinetic parameters of K(m)(app) = 0.017 mM, V(max)(app) = 0.4 nmol/mg/min, and n = 1.8. Formation of acetaminophen-O-glucuronide also best fit the Hill equation, with K(m)(app) = 4 mM, V(max)(app) = 1.5 nmol/mg/min, and n = 1.4. Alternatively, morphine-3-glucuronide formation displayed Michaelis-Menten kinetics, with K(m)(app) = 2 mM and V(max)(app) = 2. 5 nmol/mg/min. Finally, alamethicin treatment of microsomes was found to be effective in facilitating the sequential oxidation-glucuronidation of 7-ethoxycoumarin.

Enzymatic determinants of the substrate specificity of CYP2C9: role of B'-C loop residues in providing the pi-stacking anchor site for warfarin binding

Previous modeling efforts have suggested that coumarin ligand binding to CYP2C9 is dictated by electrostatic and pi-stacking interactions with complementary amino acids of the protein. In this study, analysis of a combined CoMFA-homology model for the enzyme identified F110 and F114 as potential hydrophobic, aromatic active-site residues which could pi-stack with the nonmetabolized C-9 phenyl ring of the warfarin enantiomers. To test this hypothesis, we introduced mutations at key residues located in the putative loop region between the B' and C helices of CYP2C9. The F110L, F110Y, V113L, and F114L mutants, but not the F114Y mutant, expressed readily, and the purified proteins were each active in the metabolism of lauric acid. The V113L mutant metabolized neither (R)- nor (S)-warfarin, and the F114L mutant alone displayed altered metabolite profiles for the warfarin enantiomers. Therefore, the effect of the F110L and F114L mutants on the interaction of CYP2C9 with several of its substrates as well as the potent inhibitor sulfaphenazole was chosen for examination in further detail. For each substrate examined, the F110L mutant exhibited modest changes in its kinetic parameters and product profiles. However, the F114L mutant altered the metabolite ratios for the warfarin enantiomers such that significant metabolism occurred for the first time on the putative C-9 phenyl anchor, at the 4'-position of (R)- and (S)-warfarin. In addition, the Vmax for (S)-warfarin 7-hydroxylation decreased 4-fold and the Km was increased 13-fold by the F114L mutation, whereas kinetic parameters for lauric acid metabolism, a substrate which cannot interact with the enzyme by a pi-stacking mechanism, were not markedly affected by this mutation. Finally, the F114L mutant effected a greater than 100-fold increase in the Ki for inhibition of CYP2C9 activity by sulfaphenazole. These data support a role for B'-C helix loop residues F114 and V113 in the hydrophobic binding of warfarin to CYP2C9, and are consistent with pi-stacking to F114 for certain aromatic ligands.

Identification of a meander region proline residue critical for heme binding to cytochrome P450: implications for the catalytic function of human CYP4B1

Alignment of xenobiotic-metabolizing P450 protein sequences highlights an invariant proline residue in the meander region two amino acids N-terminal to the distal arginine of the putative ERR triad thought to be important for heme binding. This occurs as a serine in the sequences derived from human CYP4B1 gDNA and both human lung and placental CYP4B1 cDNAs. Reversion of this serine to the conserved proline residue (Ser427 --> Pro) by site-directed mutagenesis conferred the ability to incorporate heme on the human placental enzyme. Mutation of the corresponding proline in rabbit CYP4B1 (Pro422 --> Ser) abolished heme incorporation. Membrane preparations of human CYP4B1(Pro) and rabbit CYP4B1(Pro), but not the corresponding CYP4B1(Ser) variants, supported lauric acid hydroxylation preferentially at the omega-position. Purified, reconstituted human CYP4B1(Pro) and rabbit CYP4B1(Pro) formed 12-hydroxylauric acid at rates of 17-21 min-1, and both enzymes were also C-8 to C-10 fatty acid omega-hydroxylases preferentially, with total rates of hydroxylation decreasing in the order C-12 > C-10 > C-9 > C-8. Finally, neither human nor rabbit CYP4B1(Pro) formed detectable levels of any hydroxylated testosterone metabolites. Therefore, the presence of a consensus Pro-X-Arg motif is critical for incorporation of the heme prosthetic group in human and rabbit CYP4B1 proteins expressed in insect cells. Native human CYP4B1, expressed in vivo, is likely to be functionally impaired if Pro427 is required for holoenzyme expression in mammalian cells.

P450-catalyzed in-chain desaturation of valproic acid: isoform selectivity and mechanism of formation of Delta 3-valproic acid generated by baculovirus-expressed CYP3A1

The mechanism of formation of the in-chain, unsaturated fatty acid metabolite, Delta3-valproic acid (Delta3-VPA) by rat liver microsomes was examined. Microsomal rates of formation of Delta3-VPA were below quantifiable limits in reactions catalyzed by control female rat liver microsomes, but were induced more than 20-fold following pretreatment with triacetyloleandomycin and pregnenolone-16alpha-carbonitrile. Microsomal incubations conducted with 3-hydroxy-VPA or [2-2H1]VPA demonstrated that Delta3-VPA did not arise by dehydration of preformed alcohol nor was it reversibly isomerized to Delta2-VPA. CYP3A1 expression was optimized in the baculovirus expression vector system, and infected insect cell membranes which were supplemented with P450 reductase catalyzed formation of 3-OH-, 4-OH-, 5-OH-, Delta3-, and Delta4-VPA in ratios of 160:35:6:3:1. Intramolecular deuterium isotope effects on metabolite formation, determined with cDNA-expressed CYP3A1 and either [3,3-2H2]VPA or [4,4-2H2]VPA, yielded kH/kD values for Delta3-VPA of 2.00 +/- 0.06 and 2.36 +/- 0.08, respectively. These values were significantly lower than the isotope effects observed in the same incubations for 3-OH-VPA formation from 3,3-D2-VPA (kH/kD = 6.04 +/- 0.08), or for 4-OH- and Delta4-VPA formation from 4, 4-D2-VPA (kH/kD > 5). Collectively, these data demonstrate the existence of a microsomal P450-dependent in-chain fatty acid desaturase system distinct from the well-documented cytochrome b5-linked CoA desaturases and suggest further that CYP3A1-dependent formation of Delta3-VPA arises via nonselective, initial hydrogen atom abstraction from either the C-3 or the C-4 position.

Positional specificity of rabbit CYP4B1 for omega-hydroxylation1 of short-medium chain fatty acids and hydrocarbons

Rabbit CYP4B1 was incubated with a series of fatty acid and hydrocarbon substrates and metabolites were identified by gas chromatography and gas chromatography/mass spectrometry. C-7 to C-10 n-alkyl fatty acids were preferentially hydroxylated at the terminal carbon (omega/omega-1 = 1.1-7.4) with turnover numbers of 1-11 min-1. The C-7 to C-10 n-alkyl hydrocarbons exhibited turnover numbers of 11-33 min-1 for the corresponding reactions and even higher regioselectivities for hydroxylation at the thermodynamically disfavored site (omega/omega-1 = 1.6-23). These results demonstrate a functional link between CYP4B1 and other CYP4 fatty acid hydroxylases, and show further that CYP4B1's unusual positional specificity is not dictated by the presence of a carboxylate (or polar) anchor on the substrate. This suggests the presence of a dominant hydrocarbon binding site which effectively restricts the access of short-medium chain n-alkyl substrates to the perferryl species in the active site of rabbit CYP4B1.

Cytochrome P450-dependent desaturation of lauric acid: isoform selectivity and mechanism of formation of 11-dodecenoic acid

Cytochrome P450-catalyzed desaturation reactions have been reported infrequently in the literature. Previously, we documented the formation of the terminal olefinic metabolite of valproic acid by various members of the CYP2B and CYP4B sub-families. However, despite the extensive use of fatty acid substrates in drug metabolism studies, other examples of terminal desaturation at non-activated carbon centers are lacking. The goals of the present studies were to determine whether the archetypal P450 substrate, lauric acid (dodecanoic acid; DDA), also undergoes desaturation reactions, identify specific rabbit P450 isoforms which catalyze this reaction and examine its mechanism. A highly sensitive, capillary GC/MS assay was developed to separate and quantitate the trimethylsilyl derivatives of 11-ene-DDA, cis- and trans-10-ene-DDA and cis- and trans-9-ene-DDA. Among all of these potential olefinic metabolites, only 11-ene-DDA was formed at a significant rate by rabbit liver microsomes. The formation of 11-ene-DDA was NADPH-dependent, and was induced markedly by acetone pre-treatment, but not by phenobarbital, rifampin or Arochlor 1254. Studies with seven purified, reconstituted rabbit P450 isoforms showed that the most rapid rates of desaturation were obtained with CYP2E1, CYP4A5/7 and CYP4B1. Non-competitive, intermolecular isotope effect experiments, conducted with [12,12,12-2H3]DDA and [11,11-2H2]DDA, demonstrated further that CYP4B1-mediated terminal desaturation of DDA is initiated by removal of a hydrogen atom from the omega-1 rather than the omega position.

Human CYP2C9 and CYP2A6 mediate formation of the hepatotoxin 4-ene-valproic acid

Cytochrome P450-dependent desaturation of the anticonvulsant drug valproic acid (VPA) results in formation of the hepatotoxin, 4-ene-VPA. Polytherapy with other anticonvulsants which are known P450 inducers increases the flux through this bioactivation pathway. The aim of the present study was to identify specific, inducible forms of human liver P450 which catalyze terminal desaturation of VPA. Oxidized VPA metabolites formed in an NADPH-dependent manner by human liver microsomes were quantified by gas-chromatography/mass spectrometry. In vitro reaction conditions were established which reflected the product profile found in vivo. Production of 4-ene-VPA by microsomal P450s could be inhibited significantly by coumarin, sulfaphenazole and diethyldithiocarbamate, but not by triacetyloleandomycin, quinidine or furafylline. Recombinant human CYP3A4 did not form detectable levels of 4-ene-VPA and, of nine additional isoforms expressed in either HepG2 or lymphoblastoid cells which were screened for VPA desaturase activity, only CYP2C9 and CYP2A6 formed detectable levels of metabolite. Consequently, CYP3A4, the isoform usually associated with induction by anticonvulsants cannot be responsible for the enhanced 4-ene-VPA formation that occurs during polytherapy. Instead, enhanced activity in vivo likely results from induction of CYP2A6 and/or CYP2C9.

Lisinopril versus placebo in the treatment of heart failure: the Lisinopril Heart Failure Study Group

Lisinopril, a long-acting, angiotensin-converting enzyme inhibitor, was compared with placebo in a randomized, parallel, double-blind, 12-week study of 193 patients with heart failure. All patients were New York Heart Association Functional Class II, III, or IV and had remained symptomatic despite optimal dosing with digoxin and diuretics. After 12 weeks of therapy, the improvement in treadmill exercise duration was greater in the lisinopril group (113 seconds) compared with the placebo group (86 seconds). This improvement in exercise duration was particularly evident in patients with left ventricular ejection fractions less than 35% (lisinopril = 130 seconds; placebo = 94 seconds). In patients receiving lisinopril, the increase in exercise duration was accompanied by an improvement in quality of life as measured by the Yale Scale Dyspnea/Fatigue Index and in signs and symptoms of heart failure. In addition, the lisinopril group had a larger mean increase (3.7%) in left ventricular ejection fraction when compared with the placebo group (1.3%). Thus, lisinopril, administered once daily for 12 weeks, was well tolerated and efficacious in the treatment of heart failure when used concomitantly with diuretics and digoxin.

Formation, characterization, and immunoreactivity of lysine thioamide adducts from fluorinated nephrotoxic cysteine conjugates in vitro and in vivo

Fluorinated nephrotoxic cysteine conjugates undergo bioactivation via the beta-lyase pathway to thionoacetyl fluorides (TAF), the putative reactive intermediates. The TAF derived from S-(1,1,2,2,-tetrafluoroethyl)-L-cysteine (TFEC) difluorothionoacetylates amine nucleophiles found in proteins and lipids. A specific antisera, raised against (trifluoroacetamido)lysine adducts formed in vivo after halothane treatment, has previously been used to localize TFEC-derived protein adducts immunohistochemically, and a good correlation between adduction and toxicity was demonstrated. Interestingly, thioamide formation is facilitated by acyl-transfer catalysts such as imidazoles and phenols. However, although putative lysine adducts have been reported to be formed from the related TAF derived from S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC), protein adducts derived from CTFC metabolism have not been completely characterized. In the present investigation we characterize (chlorofluorothionacetamido)lysine (CFTAL) adduct formation during S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC) metabolism, both in vitro and in vivo. Our data indicate that formation of CTFC-derived lysine thioamides was not as dependent on nucleophilic catalysis as observed for TFEC, and this appears to be due to an apparent greater reactivity of the TAF resulting in a higher trapping efficiency in the absence of catalyst. Also, qualitative and quantitative differences in the structures and time course of CTFC versus TFEC adduct breakdown were observed. Antibodies raised against the halothane metabolite protein adduct (trifluoroacetamido)lysine cross-react with specific mitochondrial proteins from the kidneys of TFEC-treated rats. Using this antibody, we have found that the pattern of adducted proteins from TFEC- and CTFC-treated Fischer rats was similar, but the intensity was considerably lower after treatment with equimolar concentrations of CTFC in vivo.

Changes in dyspnea-fatigue ratings as indicators of quality of life in the treatment of congestive heart failure

A new clinical index of dyspnea and fatigue has been applied to rate the condition of patients with congestive heart failure. The index has 3 components, each rated on a scale from 0 to 4, for the magnitude of the task that evokes dyspnea or fatigue, the magnitude of the pace (or effort) with which the task is performed and the associated functional impairment in general activities. The ratings for each component are added to form an aggregated score, which can range from 0, for the worst condition, to 12, for the best. Because dyspnea and fatigue are prime symptoms and sources of clinical distress, the index helps reflect the quality of life in patients with congestive heart failure. In double-blind trials of therapy, changes in the index showed good correlations with patients' self-selected ratings of improvement. The posttherapeutic changes in the index ratings were significantly higher with a new active agent (lisinopril) than with placebo or another active agent (captopril).

Lisinopril and captopril in the treatment of heart failure in older patients. Comparison of a long- and short-acting angiotensin-converting enzyme inhibitor

Heart failure is a common cardiovascular disorder that increases in prevalence with age. Older patients may respond differently than younger patients to the various classes of drugs used in the treatment of congestive heart failure (CHF). The responses of older patients (at least 65 years of age) were evaluated as part of a large multicenter trial utilizing angiotensin-converting enzyme (ACE) inhibitors in the treatment of CHF. A prospectively planned subgroup analysis of older CHF patients' therapeutic response to the long-acting (approximately 24-hour) ACE inhibitor lisinopril was compared with their response to captopril, a short-acting (less than eight-hour) ACE inhibitor. Symptomatic improvement occurred in both the lisinopril and captopril groups. Exercise duration also improved for patients treated with both agents. However, there was a tendency for lisinopril to be more effective than captopril (p = 0.08). Thus, the low level of renin activity often found in the plasma of older patients did not decrease the ability of the ACE inhibitors to improve effort tolerance. Left ventricular ejection fraction increased in patients treated with lisinopril but not in those treated with captopril. The improvement in left ventricular ejection fraction with lisinopril may be indicative of a more favorable prognosis in patients with CHF, since another long-acting ACE inhibitor, enalapril, reduces the rate of mortality associated with CHF. ACE inhibitors were generally well-tolerated by the older patients in the study. Therefore, ACE inhibitors appear to offer a useful therapeutic approach to the management of CHF in the older age group.

Immunological characterization of maize starch branching enzymes

Highly purified fractions of three starch branching enzymes from developing maize (Zea mays L.) endosperm were used to prepare antisera in rabbits. In double diffusion experiments, no immunoprecipitate was observed when branching enzyme IIa or IIb was tested against branching enzyme I antiserum. No immunoprecipitate was formed when branching enzyme I was tested against branching enzyme IIa or IIb antiserum. Increasing amounts of antisera in the above combinations also failed to inhibit enzyme activity. Branching enzyme IIa antiserum cross-reacted and formed spurs with branching enzyme IIb when compared with branching enzyme IIa antigen. Comparison of branching enzyme IIb antiserum with branching enzyme IIa also resulted in an immunoprecipitate. Increasing levels of branching enzyme IIa antiserum inhibited branching enzyme IIb as did the reciprocal combination. The data indicated that branching enzymes IIa and IIb are immunologically similar while branching enzyme I is distinct. The data supports the classification of starch branching enzymes based on genetic, kinetic, and chromatographic properties.

Myocardial revascularization in patients with chronic renal failure

Symptomatic coronary artery disease in patients with chronic renal failure can complicate their management in a dialysis program. Hypotension associated with hemodialysis and the anemia of chronic renal disease can produce anginal episodes refractory to medical management. Untreated coronary artery disease may be a contraindication to renal transplantation in an otherwise acceptable candidate. We have encountered three cases of coronary artery disease severe enough to necessitate coronary bypass in patients from our long-term hemodialysis program. All three patients had uncomplicated postoperative courses, none had perioperative infarction, and in all three patients postoperative angiography demonstrated patency of all grafts. One patient subsequently underwent successful renal transplantation; the other two patients have continued in hemodialyses since bypass. We believe our experience and the reported experience of others confirm the feasibility of coronary bypass grafting in patients with chronic renal failure.