Turbulent Flow Over Large Roughness Elements: Effect of Frontal and Plan Solidity on Turbulence Statistics and Structure.

Wind-tunnel experiments were carried out on fully-rough boundary layers with large roughness ( δ / h ≈ 10 , where h is the height of the roughness elements and δ is the boundary-layer thickness). Twelve different surface conditions were created by using LEGO™ bricks of uniform height. Six cases are tested for a fixed plan solidity ( λ P ) with variations in frontal density ( λ F ), while the other six cases have varying λ P for fixed λ F . Particle image velocimetry and floating-element drag-balance measurements were performed. The current results complement those contained in Placidi and Ganapathisubramani (J Fluid Mech 782:541-566, 2015), extending the previous analysis to the turbulence statistics and spatial structure. Results indicate that mean velocity profiles in defect form agree with Townsend's similarity hypothesis with varying λ F , however, the agreement is worse for cases with varying λ P . The streamwise and wall-normal turbulent stresses, as well as the Reynolds shear stresses, show a lack of similarity across most examined cases. This suggests that the critical height of the roughness for which outer-layer similarity holds depends not only on the height of the roughness, but also on the local wall morphology. A new criterion based on shelter solidity, defined as the sheltered plan area per unit wall-parallel area, which is similar to the 'effective shelter area' in Raupach and Shaw (Boundary-Layer Meteorol 22:79-90, 1982), is found to capture the departure of the turbulence statistics from outer-layer similarity. Despite this lack of similarity reported in the turbulence statistics, proper orthogonal decomposition analysis, as well as two-point spatial correlations, show that some form of universal flow structure is present, as all cases exhibit virtually identical proper orthogonal decomposition mode shapes and correlation fields. Finally, reduced models based on proper orthogonal decomposition reveal that the small scales of the turbulence play a significant role in assessing outer-layer similarity.

Elastic Properties of Few Nanometers Thick Polycrystalline MoS2 Membranes: A Nondestructive Study.

The performance gain-oriented nanostructurization has opened a new pathway for tuning mechanical features of solid matter vital for application and maintained performance. Simultaneously, the mechanical evaluation has been pushed down to dimensions way below 1 µm. To date, the most standard technique to study the mechanical properties of suspended 2D materials is based on nanoindentation experiments. In this work, by means of micro-Brillouin light scattering we determine the mechanical properties, that is, Young modulus and residual stress, of polycrystalline few nanometers thick MoS2 membranes in a simple, contact-less, nondestructive manner. The results show huge elastic softening compared to bulk MoS2, which is correlated with the sample morphology and the residual stress.

Wind resource assessment in heterogeneous terrain.

High-resolution particle image velocimetry data obtained in rough-wall boundary layer experiments are re-analysed to examine the influence of surface roughness heterogeneities on wind resource. Two different types of heterogeneities are examined: (i) surfaces with repeating roughness units of the order of the boundary layer thickness (Placidi & Ganapathisubramani. 2015 J. Fluid Mech.782, 541-566. (doi:10.1017/jfm.2015.552)) and (ii) surfaces with streamwise-aligned elevated strips that mimic adjacent hills and valleys (Vanderwel & Ganapathisubramani. 2015 J. Fluid Mech.774, 1-12. (doi:10.1017/jfm.2015.228)). For the first case, the data show that the power extraction potential is highly dependent on the surface morphology with a variation of up to 20% in the available wind resource across the different surfaces examined. A strong correlation is shown to exist between the frontal and plan solidities of the rough surfaces and the equivalent wind speed, and hence the wind resource potential. These differences are also found in profiles of [Formula: see text] and [Formula: see text] (where U is the streamwise velocity), which act as proxies for thrust and power output. For the second case, the secondary flows that cause low- and high-momentum pathways when the spacing between adjacent hills is beyond a critical value result in significant variations in wind resource availability. Contour maps of [Formula: see text] and [Formula: see text] show a large difference in thrust and power potential (over 50%) between hills and valleys (at a fixed vertical height). These variations do not seem to be present when adjacent hills are close to each other (i.e. when the spacing is much less than the boundary layer thickness). The variance in thrust and power also appears to be significant in the presence of secondary flows. Finally, there are substantial differences in the dispersive and turbulent stresses across the terrain, which could lead to variable fatigue life depending on the placement of the turbines within such heterogeneous terrain. Overall, these results indicate the importance of accounting for heterogeneous terrain when siting individual turbines and wind farms.This article is part of the themed issue 'Wind energy in complex terrains'.

Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors.

AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

Seasonality of births and conceptions in a pastoral community of the province of l'Aquila (Abruzzo, Italy), 1802-1965.

Natality rates and seasonality of births and conceptions were analyzed from 6,116 birth records in the pastoral community of Roio (Abruzzo, Italy) from 1802 to 1965. Gross natality rates averaged 25.5 x 1000 in the past, lower than those reported for agricultural groups. Seasonality of births showed a marked pattern: 807-67% of births occurred in the first six months of the year. The monthly distribution of conceptions was compared to that of marriages. The results show a high correlation in the 19th century and a lower one in the 20th century. These findings suggest that pastoralism acted as a primary regulator of reproduction in this community.

Kinetics of plasma and tissue distribution of 9-cis-retinoic acid in rat.

The biotransformation and tissue distribution of 9-cis-retinoic acid was investigated in hairless rats. Indeed, only limited information is available about the pharmacokinetics of 9-cis-retinoic acid. Assuming that the target site for retinoids is the skin, tissue distribution study is therefore particularly justified. Following single oral administration of 30 mg/kg of 9-cis-retinoic acid, the parent drug and five metabolites were detected in plasma. Additionally, concentrations of 9-cis-retinoic acid and metabolites were determined in the skin and seven other tissues. The distribution of 9-cis-retinoic acid was rapid in all of the organs studied (T(max)

A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology.

Ethical, economic and technical reasons hinder regular supply of freshly isolated hepatocytes from higher mammals such as monkey for preclinical evaluation of drugs. Hence, we aimed at developing optimal and reproducible protocols to cryopreserve and thaw parenchymal liver cells from this major toxicological species. Before the routine use of these protocols, we validated them through a multi-laboratory study. Dissociation of the whole animal liver resulted in obtaining 1-5 billion parenchymal cells with a viability of about 86%. An appropriate fraction (around 20%) of the freshly isolated cells was immediately set in primary culture and various hepato-specific tests were performed to examine their metabolic, biochemical and toxicological functions as well as their ultrastructural characteristics. The major part of the hepatocytes was frozen and their functionality checked using the same parameters after thawing. The characterization of fresh and thawed monkey hepatocytes demonstrated the maintenance of various hepato-specific functions. Indeed, cryopreserved hepatocytes were able to survive and to function in culture as well as their fresh counterparts. The ability for synthesis (proteins, ATP, GSH) and conjugation and secretion of biliary acids was preserved after deep freeze storage. A better stability of drug metabolizing activities than in rodent hepatocytes was observed in monkey. After thawing, Phase I and Phase II activities (cytochrome P450, ethoxycoumarin-O-deethylase, aldrin epoxidase, epoxide hydrolase, glutathione transferase, glutathione reductase and glutathione peroxidase) were well preserved. The metabolic patterns of several drugs were qualitatively and quantitatively similar before and after cryopreservation. Lastly, cytotoxicity tests suggested that the freezing/thawing steps did not change cell sensitivity to toxic compounds.

A glycoprotein from rat liver endoplasmic reticulum promotes both aggregation and fusion of liposomes at acidic pH.

Low-pH-induced fusion of liposomes with rat liver endoplasmic reticulum was evidenced. Fusion was inactivated by treatment of microsomes with trypsin or EEDQ (N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline), indicating the involvement of a protein. The protein was purified 555-fold by chromatographic steps. The identification and purification to homogeneity was obtained by electroelution from a slab gel, which gave a still active protein of about 50 kDa. The protein promoted the fusion of liposomes; laser light scattering showed an increase of mean radius of vesicles from 60 up to about 340 nm. Fusion was studied as mass action kinetics, describing the overall fusion as a two-step sequence of a second order aggregation followed by a first order fusion of liposomes. For phosphatidylcholine containing liposomes aggregation was not rate-limiting at pH 5.0 and fusion followed first order kinetics with a rate constant of 13 . 10(-3) sec-1. For phosphatidylethanolamine/phosphatidic acid liposomes aggregation was rate-limiting; however, the overall fusion was first order process, suggesting that fusogenic protein influences both aggregation and fusion of liposomes. The protein binds to the lipid bilayer of liposomes, independently of pH, probably by a hydrophobic segment. Exposed carboxylic groups might be able to trigger pH-dependent aggregation and fusion. It is proposed that the protein inserted in the lipid bilayer bridges with an adjacent liposome forming a fused doublet. Since at endoplasmic reticulum level proton pumps are operating to generate a low-pH environment, the membrane bound fusogenic protein may be responsible for both aggregation and fusion of neighboring membranes and therefore could operate in the exchange of lipidic material between intracellular membranes.

Interspecies variability of TNP-470 metabolism, using primary monkey, rat, and dog cultured hepatocytes.

The biotransformation of TNP-470 [O-(chloroacetylcarbamoyl)fumagillol; AGM 1470], a potent in vitro inhibitor of angiogenesis, was investigated in primary cultured hepatocytes isolated from different species, including monkey, dog, and rat, as well as in microsomal fractions of various monkey tissues. Previous metabolic studies by our group using human hepatocytes in primary culture demonstrated that TNP-470 was primarily metabolized to M-IV through an ester cleavage, with subsequent conversion of M-IV to M-II by microsomal epoxide hydrolase. Additional studies using monkey liver microsomes demonstrated that M-II was then glucuronidated by uridine-5'-diphosphoglucuronyl transferase, leading to the formation of M-III. Three other, as yet unidentified, metabolites, labeled M-I, M-V, and M-VI, were also detected. Similarly to findings in human hepatocytes, the predominant extracellular metabolite was M-II in all species studied. Minor interspecies variability was observed in the total amount of drug biotransformed by hepatocytes, but some variability was detected in the metabolic pattern of TNP-470 in monkey hepatocytes, compared with rat or dog hepatocytes. In monkey hepatocytes, as previously observed in human cells, TNP-470 was metabolized to six derivatives, labeled M-I, M-II, M-III, M-IV, M-V, and M-VI, whereas the latter metabolite was not observed in dog or rat extracellular medium. Extrahepatic metabolism of TNP-470 was also studied using monkey intestine, kidney, and lung microsomes, which demonstrated that, under these experimental conditions, TNP-470 was extensively metabolized to four derivatives, i.e. M-I, M-II, M-III, and M-IV, with M-III being detected only in liver samples. These studies suggest that the metabolism of TNP-470 in monkeys appears to be most closely related to that observed in humans. Although the individual quantitative metabolic profiles were quite different in various animal species, only one metabolite, namely M-VI, was not detected in either dog or rat hepatocytes in vitro.

Increase of cytochrome P-450 1A and glutathione transferase transcripts in cultured hepatocytes from dogs, monkeys, and humans after cryopreservation.

The study was designed to investigate the effects of phenobarbital (PB), 3-methylcholanthrene (3-MC), and oltipraz (OPZ), a synthetic derivative of 1,2-dithiole-3-thione, on the levels of cytochrome P450 1A1/2 and gluthathione transferase (GST) mRNAs in both fresh and cryopreserved human, monkey, and dog hepatocytes in primary culture. GST alpha mRNAs were demonstrated in liver parenchymal cells from the three species: after 4 days of culture, their basal levels were decreased, but were strongly higher in PB- and OPZ-treated cells from the three species. In contrast 3-MC was mostly effective on human hepatocytes. The increased levels of GST alpha mRNAs in the presence of PB or OPZ were not observed in all cell populations. GST mu mRNAs, which were detected in both dog and monkey hepatocytes, were induced only in the presence of OPZ. GST pi mRNAs were expressed in dog hepatocytes but did not respond to any of the inducers. In all cases, similar effects were observed in fresh and thawed hepatocytes. Similarly, CYP1A1/2 transcripts were induced by 3-MC in both fresh and cryopreserved cells from the three species but also after OPZ treatment for monkey hepatocytes. These findings demonstrate that enzymes which play a major role in bioactivation/detoxication of xenobiotics remain expressed and inducible in hepatocytes from various species after cryopreservation and thawing.

Excretion of oral 9-cis-retinoic acid in the rat.

We have studied excretion of oral 9-cis-retinoic acid in urine and feces in vigil rats and in bile in anesthetized rats. A proportion of 53 +/- 13% of the dose of 9-cis-retinoic acid administered was eliminated through the feces in 72 hr, and the urinary excretion was negligible. The prevalent form of elimination in feces and urine was the unchanged compound. Low biliary excretion was, for the most part, composed of metabolites.

Disposition and metabolism of the angiogenic moderator O-(chloroacetyl-carbamoyl) fumagillol (TNP-470; AGM-1470) in human hepatocytes and tissue microsomes.

The biotransformation of O-(chloroacetyl-carbamoyl) fumagillol (TNP-470; AGM 1470), a potent in vitro inhibitor of angiogenesis, was investigated in primary cultured human hepatocytes and microsomal fractions of various human tissues. Exposure of human hepatocytes to 5 microM [3H]TNP-470 led to a rapid metabolism of unchanged drug to six metabolic derivatives within 30 min. The predominant extracellular metabolites were M-II and M-IV, attaining a maximum level of 3.23 +/- 0.34 and 0.88 +/- 0.10 microM, respectively. M-II leveled off, while M-IV rapidly declined to 0.06 +/- 0.05 microM by 3 h. TNP-470 was undetectable after 60 min. M-V and M-VI slowly reached maximal concentrations of 0.26 +/- 0.12 and 0.32 +/- 0.16 microM, respectively. M-I only reached a concentration of 0.18 +/- 0.07 microM at 60 min and leveled at 0.13 +/- 0.06 microM for the remaining time of the experiment. The intracellular profile was different, with M-III and M-V representing the major metabolites detected. Studies using human liver microsomes demonstrated that M-IV formation was associated with an esterase-like enzymatic cleavage of TNP-470 and that this metabolite was then further metabolized by microsomal epoxide hydrolase to M-II, as evidenced by inhibition of this metabolic step by cyclohexene oxide, a microsomal epoxide hydrolase inhibitor. Extrahepatic metabolism of TNP-470 was also demonstrated using different sites of human intestinal, stomach, and kidney microsomes, with metabolite M-IV as the principal derivative detected in these tissues. Hepatic microsomal samples from seven different donors demonstrated large interindividual variations in the formation of both M-II and M-IV. In summary, this study demonstrates a rapid and extensive metabolism of TNP-470 in human tissues. The data emphasize the need to evaluate the in vivo formation and extent of TNP-470 metabolites to adequately assess the pharmacodynamic effects of this novel anticancer drug with a novel mechanism of action.

Comparative metabolism of 3'-azido-3'-deoxythymidine in cultured hepatocytes from rats, dogs, monkeys, and humans.

3'-Azido-3'-deoxythymidine (AZT), the main antiretroviral drug used against Human Immunodeficiency Virus, was approved by the Food and Drug Administration in 1987 with only little knowledge concerning its metabolism. The aim of our study was to evaluate the interspecies variability of AZT metabolism in primary cultures of hepatocytes, freshly isolated from rats, dogs, monkeys, and humans. Cultures were exposed to 10 or 100 microM [3H]AZT. Extracellular and intracellular compartments were analyzed using a HPLC method. Intracellular and extracellular metabolic patterns were qualitatively similar, but very low amounts of AZT and metabolites were detected within hepatocytes. In all species, the 3'-azido-3'-deoxy-5'-O-beta-D-glucopyranuronosylthymidine (GAZT) was identified as the major metabolite of AZT. In addition to this glucuronide, two minor peaks were detected: one coeluting with 3'-amino-3'-deoxythymidine(AMT); and the other with a retention time corresponding, on the basis of the publications in this field, to 3'-amino-3'-deoxythymidine glucuronide. However, further investigation allowed this compound to be characterized as tritiated water, possibly representing a catabolic endproduct of AZT. Although glucuronidation was the main metabolic pathway in the four species studied, AZT biotransformation rate was much lower in rat and dog hepatocytes than in monkey and human ones. Finally, an excellent correlation was obtained between in vivo and in vitro metabolic data.

In vitro evaluation of donor liver preservation fluids on human hepatocyte function.

Successful liver transplantation depends on adequate preservation of cellular function. We therefore tested the effects of two currently used liver preservation fluids, Euro-Collins (EC) solution and University of Wisconsin (UW) solution, on the viability and some functional activities of hepatocytes isolated from human livers. Cells in primary culture were maintained under hypoxic (95% N2/5% CO2) and hypothermic (4 degrees C) conditions for 24 h, either in EC or UW solution. This treatment did not result in significant hepatocyte damage, as judged by phase contrast microscopy, intracellular LDH release, and the MTT mitochondrial test. However, neutral red uptake indicated that lysosomal functions were slightly affected (35% decrease) when compared to control conditions. At the end of the hypoxia/hypothermia period, hepatocyte monolayers were incubated at 37 degrees C under normoxic conditions for 24 h, in order to simulate the reperfusion of a transplanted liver. Three drugs--midazolam, diazepam, zidovudine--were used as diagnostic substrates to check the metabolic abilities of human hepatocytes replaced in normal conditions. Both phase I (hydroxylation, demethylation) and phase II (glucuronidation) metabolic reactions were affected by the hypoxia/hypothermia shock. Indeed, a 30%-50% decrease in these activities was observed as compared to values obtained in control hepatocytes. No difference could, however, be found at the cellular level regarding the solution used for cold storage. These results suggest that the superiority of UW over EC solution, already reported in clinical practice after transplantation of preserved human livers, was not due to a better preservation of the hepatocytes.

Tissue-specific expression and methylation of the human CYP2E1 gene.

The level and number of CYP2E1 gene transcripts were investigated by northern blot analysis in various human adult tissues including liver, lung, placenta, skin and neurinoma. Three transcripts of 1.8, 2.6 and 4 Kb were expressed in a tissue-specific manner. The origin of the various transcripts was studied and showed that both 4 and 2.6 Kb mRNAs contained sequences from the 3' non-translated region of the gene and that the 4 Kb also contained region localized in the 5' non-translated region. Furthermore, it clearly appeared that a catalytically active CYP2E1 enzyme (as proved by NDMA demethylase activity) was only detected in tissues expressing the 1.8 Kb. The human CYP2E1 was also identified through immunohistochemical techniques. Finally, we observed a relation between the hypomethylation of the human CYP2E1 gene and the hypoexpression of the corresponding protein.

Uptake and metabolism of vinca alkaloids by freshly isolated human hepatocytes in suspension.

A study was carried out to evaluate the uptake, release and metabolism of four currently used vinca alkaloids, including vinblastine, vincristine, vindesine and navelbine, using freshly isolated human hepatocytes in suspension. The drugs were rapidly taken up and intensely metabolised by the cells, giving a number of yet unidentified biotransformation products. Navelbine was the most rapidly and intensely accumulated drug followed by vinblastine, vindesine and vincristine. The extent of cell uptake appeared to parallel the lipophilicities of these compounds. Interestingly, we found a significant correlation between the mean uptake rates of the vinca alkaloids into the cells, which were 0.279, 0.343, 0.568 and 0.834 pmol/min/10(6) cells for vincristine, vindesine, vinblastine and navelbine, respectively, and the in vivo plasma clearances of the drugs (r = 0.9995, p < 0.001). This finding is of great importance as regards a better understanding of the structure-activity relationship among this class of antitumour drugs, as well as a reliable extrapolation of in vitro results to the in vivo situation.

Human hepatic uptake of two vinca alkaloids: navelbine and vincristine.

A human liver plasma membrane model for the evaluation of the specific binding and transport processes of drugs presenting high hepatic clearance such as vinca alkaloids was developed. Uptake of the two structural antitumor analogs, navelbine (NVB) and vincristine (VCR), which exhibit wide variabilities in their respective pharmacokinetic parameters and antitumor spectra, was investigated. The high yield, the enzymatic profile and the retention of physiologic transport capacities, as demonstrated by taurocholate uptake, revealed that this membrane preparation was well suited for studies of hepatic drug transport systems. For both drugs two distinct processes were observed: mainly membrane binding and transport. NVB was found to bind to the membrane vesicles more intensively than VCR, but the transport processes were almost identical. However only NVB uptake seems to involve Na(+)-dependent processes. These significant differences may be related to the respective lipophilicity of the drugs. The more lipophilic molecule (NVB) presents the highest uptake, which is presumably at the origin of its greatest distribution volume in vivo.

Involvement of human liver cytochrome P450 3A in vinblastine metabolism: drug interactions.

Vinblastine biotransformation was investigated by using a human liver microsomes library. The drug was converted into one major metabolite (M) upon incubation with the microsomes. A large interindividual variation in vinblastine metabolism was observed among the samples tested, with a 4.4 ratio between the lowest and the highest metabolic rates. The biotransformation of vinblastine followed Michaelis-Menten kinetics (Km = 6.82 +/- 0.27 microM and Vmax = 0.64 +/- 0.06 nmol/min/mg protein). The involvement of the cytochrome P450 3A subfamily in vinblastine metabolism was demonstrated by the following body of evidence: (a) the competitive inhibition of vinblastine biotransformation by cytochrome P450 3A specific probes with Ki values of 0.17, 22.5, 14.8, and 35.3 microM for ketoconazole, erythromycin, troleandomycin, and vindesine, respectively; (b) the immunoinhibition of vinblastine metabolism by polyclonal anti-cytochrome P450 3A antibodies; (c) the highly significant correlation between the level of cytochrome P450 3A determined by Western blots and vinblastine metabolism (r = 0.759, P < 0.001); (d) the highly significant correlation between erythromycin N-demethylase activity (mediated by cytochrome P450 3A) and vinblastine metabolism (r = 0.83, P < 0.001); (e) the significant correlation between the CYP3A4 mRNA level and vinblastine metabolism (r = 0.60, P < 0.1). Although vincristine and navelbine (members of the Vinca alkaloid family) also inhibit the metabolism of vinblastine, suggesting the involvement of the cytochrome subfamily in their respective metabolisms, other anticancer drugs currently associated with vinblastine in chemotherapy (etoposide, Adriamycin, lomustine, and teniposide) also interfere with vinblastine biotransformation. These metabolic drug interactions may alter the antitumor activity and/or toxicity of the drug during anticancer chemotherapy.

Reduction of 3'-azido-3'-deoxythymidine to 3'-amino-3'-deoxythymidine in human liver microsomes and its relationship to cytochrome P450.

The formation of 3'-amino-3'-deoxythymidine (AMT) in patients receiving 3'-azido-3'-deoxythymidine (zidovudine) and the potential role of this metabolite in zidovudine-induced toxicity was recently demonstrated by our laboratory. This study evaluated the formation of AMT versus cytochrome P450 (P450) content, cytochrome B5 (B5) content and the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase activity in human liver microsomes obtained from 24 different donors. Significant interindividual differences in total P450 content and P450 reductase activity were observed, whereas no variation was observed in B5 content. Of particular importance, metabolism of zidovudine to AMT varied widely and correlated with P450 content but not with B5 content or P450 reductase activity. The apparent values for the Michaelis-Menten constant and the maximum rate of metabolism of the reaction were 46.1 mmol/L and 3.5 nmol/min/mg microsomal protein. These large variations of AMT levels as a function of P450 suggest that major interindividual differences may be observed in the pharmacokinetics and formation of this metabolite that may affect the pharmacodynamic properties of zidovudine. Potential drug-drug interactions may occur with therapeutic agents that interact with or induce P450 (zidovudine).