Comparative analyses of multi-species sequences from targeted genomic regions

The systematic comparison of genomic sequences from different organisms represents a central focus of contemporary genome analysis. Comparative analyses of vertebrate sequences can identify coding and conserved non-coding regions, including regulatory elements, and provide insight into the forces that have rendered modern-day genomes. As a complement to whole-genome sequencing efforts, we are sequencing and comparing targeted genomic regions in multiple, evolutionarily diverse vertebrates. Here we report the generation and analysis of over 12 megabases (Mb) of sequence from 12 species, all derived from the genomic region orthologous to a segment of about 1.8 Mb on human chromosome 7 containing ten genes, including the gene mutated in cystic fibrosis. These sequences show conservation reflecting both functional constraints and the neutral mutational events that shaped this genomic region. In particular, we identify substantial numbers of conserved non-coding segments beyond those previously identified experimentally, most of which are not detectable by pair-wise sequence comparisons alone. Analysis of transposable element insertions highlights the variation in genome dynamics among these species and confirms the placement of rodents as a sister group to the primates.

Kinetics of metabolism and degradation of mometasone furoate in rat biological fluids and tissues

Mometasone furoate (MF) is a potent glucocorticoid developed for the treatment of glucocorticoid-responsive inflammatory disorders. The in-vitro and ex-vivo kinetics of the degradation and metabolism of MF were studied in selected biological fluids of rat and subcellular fractions of different rat tissues. In-vitro, MF was found to degrade slowly into four products in serum and urine, and metabolized rapidly and extensively in rat liver, minimally in extrahepatic tissues, including intestine, stomach, lung and kidney. Further investigation found that the microsomal fraction was the major intracellular site of MF 6 beta-hydroxylation in rat liver. Using chemical inhibitors, CYP3A was found to be the major enzyme involved in the in-vitro MF 6 beta-hydroxylation in rat liver microsomes. Enzyme kinetic studies in rat liver microsomes showed that the overall metabolic process of MF followed biphasic Michaelis-Menten kinetics, while 6 beta-hydroxylation obeyed monophasic Michaelis-Menten kinetics. The kinetic parameters derived from the kinetic models along with the enzyme inhibition studies suggest that MF is mainly metabolized via 6 beta-hydroxylation mediated by CYP3A primarily, and also biotransformed via other pathway(s) catalysed by other enzymes in rat liver in-vitro.

The roles of vasoactive intestinal polypeptide in the mammalian circadian clock

Biological oscillations with an endogenous period of near 24 h (circadian rhythms) are generated by the master circadian pacemaker or clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. This clock is synchronised to recurring environmental signals conveyed by selective neural pathways. One of the main chemical constituents of SCN neurones is vasoactive intestinal polypeptide (VIP). Such neurones are retinorecipient and activated by light. Exogenous application of VIP resets the SCN circadian clock in a light-like manner, both in vivo and in vitro. These resetting actions appear to be mediated through the VPAC2 receptor (a type of receptor for VIP). Unexpectedly, genetically ablating expression of the VPAC2 receptor renders the circadian clock arrhythmic at the molecular, neurophysiological and behavioural levels. These findings indicate that this intrinsic neuropeptide acting through the VPAC2 receptor participates in both resetting to light and maintenance of ongoing rhythmicity of the SCN.

Effects of vasoactive intestinal polypeptide on neurones of the rat suprachiasmatic nuclei in vitro

The suprachiasmatic nuclei (SCN) of the hypothalamus house the main circadian pacemaker in mammals. Vasoactive intestinal polypeptide (VIP) is the most abundant neuropeptide in the SCN and has been shown to phase-shift the electrical activity rhythm of SCN cells in vitro. However, the effects of VIP on the cellular activity of rat SCN neurones are unknown. In this study, we examined the acute effects of VIP on the extracellularly recorded spontaneous firing rate of SCN neurones in an in-vitro hypothalamic slice preparation. Furthermore, with the use of receptor-selective agonists and antagonists, we determined which receptors might mediate the effects of VIP in the SCN. Approximately 50% of cells responded to VIP; the main type of response was suppression in firing rate, although a few cells were activated. Suppression responses to VIP were mimicked by the VPAC(2) receptor agonist Ro 25-1553 and blocked by the selective VPAC(2) receptor antagonist PG 99-465. The PAC(1) receptor agonist maxadilan evoked responses from 40% of SCN cells, and activations to this agonist were not altered by PG 99-465. Responses to VIP were not blocked by antagonists to ionotropic glutamate receptors, but the duration of suppression was modulated by the GABA(A) receptor antagonist bicuculline. Our data indicate that VIP alters the electrical activity of rat SCN neurones in vitro, via both VPAC(2) and PAC(1) receptors.

Patterns of genetic variation in Mendelian and complex traits

This review discusses the prospects for understanding the genetic basis of complex traits in humans. We take the view that work done on Drosophila melanogaster can serve as a model for understanding complex traits in humans, and the literature on this model system, as well as on humans, is reviewed. The prospects for success in understanding the genetic basis of complex traits depend, in part, on the nature of the forces acting on genetic variation. We suggest that different experimental approaches should be undertaken for traits caused by common genetic variants versus those arising from rare genetic variants.

High-throughput variation detection and genotyping using microarrays

The genetic dissection of complex traits may ultimately require a large number of SNPs to be genotyped in multiple individuals who exhibit phenotypic variation in a trait of interest. Microarray technology can enable rapid genotyping of variation specific to study samples. To facilitate their use, we have developed an automated statistical method (ABACUS) to analyze microarray hybridization data and applied this method to Affymetrix Variation Detection Arrays (VDAs). ABACUS provides a quality score to individual genotypes, allowing investigators to focus their attention on sites that give accurate information. We have applied ABACUS to an experiment encompassing 32 autosomal and eight X-linked genomic regions, each consisting of approximately 50 kb of unique sequence spanning a 100-kb region, in 40 humans. At sufficiently high-quality scores, we are able to read approximately 80% of all sites. To assess the accuracy of SNP detection, 108 of 108 SNPs have been experimentally confirmed; an additional 371 SNPs have been confirmed electronically. To access the accuracy of diploid genotypes at segregating autosomal sites, we confirmed 1515 of 1515 homozygous calls, and 420 of 423 (99.29%) heterozygotes. In replicate experiments, consisting of independent amplification of identical samples followed by hybridization to distinct microarrays of the same design, genotyping is highly repeatable. In an autosomal replicate experiment, 813,295 of 813,295 genotypes are called identically (including 351 heterozygotes); at an X-linked locus in males (haploid), 841,236 of 841,236 sites are called identically.

Distribution of substance P and neurokinin-1 receptor immunoreactivity in the suprachiasmatic nuclei and intergeniculate leaflet of hamster, mouse, and rat

The circadian pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) receives photic information directly via the retinohypothalamic tract (RHT) and indirectly from retinally innervated cells in the thalamic intergeniculate leaflet (IGL) that project to the SCN. Using standard immunohistochemical methods, we examined the presence and distribution of substance P (SP) and the neurokinin-1 receptor (NK-1) in the SCN and IGL of rat and determined whether the patterns of immunostaining generalized to the SCN and IGL of Syrian hamster, Siberian hamster, and mouse. Terminals immunoreactive for SP were sparse within the SCN of Siberian and Syrian hamsters and mouse but were intense in the ventral, retinally innervated portion of the rat SCN. Immunostaining for the NK-1 receptor was mainly absent from the SCN of hamster and mouse. In contrast, a plexus of NK-1-ir cells and processes that was in close proximity to SP-ir terminals was found in the ventral SCN of the rat. Substance P-ir terminals were observed in the IGL of all four species, as were NK-1-ir cells and fibres. Double-labelled IGL sections of hamster or rat revealed SP-ir terminals in close apposition to NK-1-immunostained cells and/or fibres. These data indicate that SP could be a neurotransmitter of the RHT in rat, but not in hamster or in mouse, and they highlight potential species differences in the role of SP within the SCN circadian pacemaker. Such species differences do not appear to exist at the level of the IGL, where SP-ir and NK-1-ir were similar in all species studied.

High-performance liquid chromatographic analysis of mometasone furoate and its degradation products: application to in vitro degradation studies

A method of analysis of mometasone furoate in pharmaceutical formulations and biological fluids is necessary to study the degradation kinetics and determine its stability. A simple high-performance liquid chromatographic method was developed for simultaneous determination of mometasone furoate and its degradation products in human plasma. Plasma (0.5 ml) was extracted with dichloromethane after addition of the internal standard, dexamethasone 21-acetate. Separation was achieved on a Beckman C(8) column with UV detection at 248 nm. The calibration curve was linear ranging from 0.2 to 100 microg/ml. The mean extraction efficiency was >86%. Precision of the assay was <10% (CV), and was within 10% at the limit of quantitation (0.2 microg/ml). Bias of the assay was lower than 7%. The limit of detection was 50 ng/ml for a 0.5-ml sample. The assay was applied successfully to the in vitro kinetic study of degradation of mometasone furoate in human plasma and simulated biological fluids.

Vasoactive intestinal polypeptide (VIP) phase-shifts the rat suprachiasmatic nucleus clock in vitro

In mammals, the principal circadian pacemaker is housed in the hypothalamic suprachiasmatic nuclei (SCN). The SCN exhibit high levels of vasoactive intestinal polypeptide (VIP) immunoreactivity and two of the three VIP receptors, VPAC(2) and PAC(1), are found in the rat SCN. However, the role of VIP in the SCN remains unclear. In this study, we examined the phase-resetting actions of VIP and selective VIP receptor agonists on the electrical activity rhythm of rat SCN neurons in vitro. Application of VIP during the subjective day did not shift the peak in the firing rate rhythm. However, VIP treatment during the early or late subjective night evoked a small phase delay or a large phase advance, respectively. The phase-advancing effect of VIP was reproduced by the novel VPAC(2) receptor agonist RO 25-1553, but not by pituitary adenylate cyclase-activating peptide (a potent PAC(1) receptor agonist), or by [K15,R16,L27]VIP(1-7)/GRF(8-27), a novel, selective VPAC(1) receptor agonist. These data show that VIP phase-dependently phase-resets the rodent SCN pacemaker in vitro, presumably via the VPAC(2) receptor. As the pattern of phase-shifting evoked by VIP and RO 25-1553 resembles the phase-resetting actions of light on rodent behavioural rhythms, these data support a role for VIP and the VPAC(2) receptor in photic entrainment of the rodent circadian pacemaker.

Orexin-A immunoreactive neurons in the rat hypothalamus do not contain neuronal nitric oxide synthase (nNOS)

The lateral hypothalamic area (LHA), a key site involved in the central control of feeding and energy homeostasis, contains populations of neurons that produce the orexin peptides or nitric oxide, two chemical factors that increase food intake. In this study, we used immunohistochemistry to investigate the possibility that rat LHA neurons co-express orexin-A and neuronal nitric oxide synthase (nNOS). The orexin-A and nNOS cell populations in the LHA showed extensive overlap without co-localization, and no evidence of direct anatomic contact was found. The finding that LHA neurons do not co-localize orexin-A and nNOS may suggest that the actions of the orexins and nitric oxide on food intake are mediated via independent mechanisms, however, nitric oxide is a diffusible molecule and could potentially affect the activity of orexin neurons via a non-synaptic mechanism.

Estimating divergence times in the presence of an overdispersed molecular clock

Molecular loci that fail relative-rate tests are said to be "overdispersed." Traditional molecular-clock approaches to estimating divergence times do not take this into account. In this study, a method was developed to estimate divergence times using loci that may be overdispersed. The approach was to replace the traditional Poisson process assumption with a more general stationary process assumption. A probability model was developed, and an accompanying computer program was written to find maximum-likelihood estimates of divergence times under both the Poisson process and the stationary process assumptions. In simulation, it was shown that confidence intervals under the traditional Poisson assumptions often vastly underestimate the true confidence limits for overdispersed loci. Both models were applied to two data sets: one from land plants, the other from the higher metazoans. In both cases, the traditional Poisson process model could be rejected with high confidence. Maximum-likelihood analysis of the metazoan data set under the more general stationary process suggested that their radiation occurred well over a billion years ago, but confidence intervals were extremely wide. It was also shown that a model consistent with a Cambrian (or nearly Cambrian) origination of the animal phyla, although significantly less likely than a much older divergence, fitted the data well. It is argued that without an a priori understanding of the variance in the time between substitutions, molecular data sets may be incapable of ever establishing the age of the metazoan radiation.

Metabolism kinetics of beclomethasone propionate esters in human lung homogenates

PURPOSE

The purposes of this study were to characterize the kinetics of beclomethasone dipropionate (BDP) and its 17-monopropionate ester (17-BMP) in human lung 1000g supernatant (HLu) at 37 degrees C, and to analyze the interindividual variability in the metabolism of BDP in HLu.

METHODS

The concentrations of BDP and its metabolites were determined by HPLC with UV detection at 242 nm. Kinetics of BDP and 17-BMP decomposition were characterized by least-squares fitting of rate equations.

RESULTS

The active metabolite 17-BMP was rapidly formed following the incubation of BDP in HLu. Kinetics of BDP and 17-BMP in HLu were nonlinear owing to product inhibition and enzyme saturation. A model taking into account the product inhibition provides a kinetic basis for understanding the in vivo behavior of BDP and its metabolites in human lung. There was approximately a 3.5-fold difference in the initial half-life of BDP in HLu observed in seven subjects.

CONCLUSIONS

An effective activation of BDP was demonstrated in HLu through the rapid formation of 17-BMP. Kinetics of BDP and 17-BMP in HLu were well characterized by the nonlinear kinetic model. Interindividual difference in the initial half-life of BDP was due mainly to esterase metabolizing activity rather than binding affinity.

The hypothalamus and the regulation of energy homeostasis: lifting the lid on a black box

The hypothalamus is the focus of many peripheral signals and neural pathways that control energy homeostasis and body weight. Emphasis has moved away from anatomical concepts of 'feeding' and 'satiety' centres to the specific neurotransmitters that modulate feeding behaviour and energy expenditure. We have chosen three examples to illustrate the physiological roles of hypothalamic neurotransmitters and their potential as targets for the development of new drugs to treat obesity and other nutritional disorders. Neuropeptide Y (NPY) is expressed by neurones of the hypothalamic arcuate nucleus (ARC) that project to important appetite-regulating nuclei, including the paraventricular nucleus (PVN). NPY injected into the PVN is the most potent central appetite stimulant known, and also inhibits thermogenesis; repeated administration rapidly induces obesity. The ARC NPY neurones are stimulated by starvation, probably mediated by falls in circulating leptin and insulin (which both inhibit these neurones), and contribute to the increased hunger in this and other conditions of energy deficit. They therefore act homeostatically to correct negative energy balance. ARC NPY neurones also mediate hyperphagia and obesity in the ob/ob and db/db mice and fa/fa rat, in which leptin inhibition is lost through mutations affecting leptin or its receptor. Antagonists of the Y5 receptor (currently thought to be the NPY 'feeding' receptor) have anti-obesity effects. Melanocortin-4 receptors (MC4-R) are expressed in various hypothalamic regions, including the ventromedial nucleus and ARC. Activation of MC4-R by agonists such as alpha-melanocyte-stimulating hormone (a cleavage product of pro-opiomelanocortin which is expressed in ARC neurones) inhibits feeding and causes weight loss. Conversely, MC4-R antagonists such as 'agouti' protein and agouti gene-related peptide (AGRP) stimulate feeding and cause obesity. Ectopic expression of agouti in the hypothalamus leads to obesity in the AVY mouse, while AGRP is co-expressed by NPY neurones in the ARC. Synthetic MC4-R agonists may ultimately find use as anti-obesity drugs in human subjects Orexins-A and -B, derived from prepro-orexin, are expressed in specific neurones of the lateral hypothalamic area (LHA). Orexin-A injected centrally stimulates eating and prepro-orexin mRNA is up regulated by fasting and hypoglycaemia. The LHA is important in receiving sensory signals from the gut and liver, and in sensing glucose, and orexin neurones may be involved in stimulating feeding in response to falls in plasma glucose.

Concentration-effect relationship of hydroxychloroquine in patients with rheumatoid arthritis--a prospective, dose ranging study

OBJECTIVE

A 6 month prospective randomized double blind study was conducted to investigate hydroxychloroquine dose concentration-effect relationships in people with rheumatoid arthritis.

METHODS

Patients were randomized in 2 groups: one group received 200 mg hydroxychloroquine sulfate daily (A) and one group received 400 mg daily (B). Each month, 8 disease variables were assessed, adverse events recorded, and hydroxychloroquine blood concentrations determined.

RESULTS

Twenty-three patients were included: 10 in group A and 13 in group B. After 6 months of therapy, a significant improvement in disease activity was noted for 6 criteria with no statistical differences between groups: pain (assessed by a visual analog scale), joint scores (swelling and tenderness), impairment in daily living activity (18 activities graded 0 to 8), patient assessment of disease state, and erythrocyte sedimentation rate. Hydroxychloroquine steady-state blood concentrations (Month 6) were significantly different between groups (mean +/- SD): 450.6 +/- 285.3 ng/ml (A) vs 870.3 +/- 329.3 ng/ml (B) (p = 0.0001). Steady-state concentrations were correlated with the daily dose (r = 0.63, p = 0.005), the improvement in activity of daily living (r = 0.49, p = 0.03), and the improvement in joint tenderness score (r = 0.47, p = 0.038).

CONCLUSION

The data indicate that hydroxychloroquine is an effective therapy, but there were no further improvements observed in the group receiving 400 mg daily compared to those receiving 200 mg. There were some correlations between hydroxychloroquine steady-state blood concentrations and effects.

The evolution of an alpha-esterase pseudogene inactivated in the Drosophila melanogaster lineage

Previous analyses of the alpha-esterase cluster of Drosophila melanogaster revealed 10 active genes and the DmalphaE4a-Psi pseudogene. Here, we reconstruct the evolution of the pseudogene from the sequences of 12 alleles from widely scattered D. melanogaster populations and single alleles from Drosophila simulans and Drosophila yakuba. All of the DmalphaE4a-Psi alleles contain numerous inactivating mutations, suggesting that pseudogene alleles are fixed in natural populations. Several lines of evidence also suggest that DmalphaE4a is now evolving without selective constraint in the D. melanogaster lineage. There are three polymorphic indels which result in frameshifts; a key nucleotide of the intron splice acceptor is polymorphic; the neutral mutation parameter is the same for replacement and silent sites; one of the nonsilent polymorphisms results in a stop codon; only 1 of the 13 replacement polymorphisms is biochemically conservative; residues that are conserved among active esterases have different states in DmalphaE4a-Psi; and there are about half as many transitional polymorphisms as transversional ones. In contrast, the D. simulans and D. yakuba orthologs DsalphaE4a and DyalphaE4a do not have the inactivating mutations of DmalphaE4a-Psi and appear to be evolving under the purifying selection typical of protein- encoding genes. For instance, there have been more substitutions in the introns than in the exons, and more in silent sites than in replacement sites. Furthermore, most of the amino acid substitutions that have occurred between DyalphaE4a and DsalphaE4a are located in sites that typically vary among active alpha-esterases rather than those that are usually conserved. We argue that the original alphaE4a gene had a function which it has lost since the divergence of the D. melanogaster and D. simulans lineages.

Understanding the overdispersed molecular clock

Rates of molecular evolution at some protein-encoding loci are more irregular than expected under a simple neutral model of molecular evolution. This pattern of excessive irregularity in protein substitutions is often called the "overdispersed molecular clock" and is characterized by an index of dispersion, R(T) > 1. Assuming infinite sites, no recombination model of the gene R(T) is given for a general stationary model of molecular evolution. R(T) is shown to be affected by only three things: fluctuations that occur on a very slow time scale, advantageous or deleterious mutations, and interactions between mutations. In the absence of interactions, advantageous mutations are shown to lower R(T); deleterious mutations are shown to raise it. Previously described models for the overdispersed molecular clock are analyzed in terms of this work as are a few very simple new models. A model of deleterious mutations is shown to be sufficient to explain the observed values of R(T). Our current best estimates of R(T) suggest that either most mutations are deleterious or some key population parameter changes on a very slow time scale. No other interpretations seem plausible. Finally, a comment is made on how R(T) might be used to distinguish selective sweeps from background selection.

The index of dispersion of molecular evolution: slow fluctuations

The most simple neutral model of molecular evolution predicts that the number of substitutions within a lineage in T generations ought to be Poisson distributed. Therefore, the variance in the number of substitutions ought to equal the mean number. The ratio of the variance to the mean number of substitutions is called the index of dispersion, R(T). Assuming infinite sites, no recombination model of the gene, and a haploid, Moran population structure, R(T) is derived for a general stationary model of molecular evolution. R(T) is shown to be affected by fluctuations in parameters only when they occur on a very slow time scale. In order for parameter fluctuations to cause R(T) to deviate significantly from one, the time between parameter changes must be roughly as large, or larger, than the time between substitutions.

Differential distribution of orexin-A and orexin-B immunoreactivity in the rat brain and spinal cord

The orexins are recently identified appetite-stimulating hypothalamic peptides. We used immunohistochemistry to map orexin-A and orexin-B immunoreactivity in rat brain, spinal cord, and some peripheral tissues. Orexin-A- and orexin-B-immunoreactive cell bodies were confined to the lateral hypothalamic area and perifornical nuclei. Orexin-A-immunoreactive fibers were densely distributed in the hypothalamus, septum, thalamus, locus coeruleus, spinal cord, and near the ventricles, but absent from peripheral sites investigated. In contrast, orexin-B-immunoreactive fibers were distributed sparsely in the hypothalamus. Orexin cells are strategically sited to contribute to feeding regulation, but their widespread projections suggest that orexins have other physiological roles.

Electrophysiological effects of opioid receptor activation on Syrian hamster suprachiasmatic nucleus neurones in vitro

Entrainment of the dominant circadian pacemaker localised to the hypothalamic suprachiasmatic nuclei (SCN) is mediated partially via the indirect retino-geniculo-hypothalamic projection to the SCN, which is presumed to utilise enkephalin and other neurotransmitters, to modulate circadian rhythmicity. In the present study, we have investigated electrophysiologically the currently unknown functional effects of enkephalin, and another opioid receptor agonist morphine, on hamster SCN neuronal activity in vitro. Basal or N-methyl-D-aspartate-evoked firing rates of SCN neurones were generally unresponsive (86%) to the opioid receptor agonists leucine-enkephalin, methionine-enkephalin, or morphine. Washout of the enkephalins or morphine resulted in a rebound excitatory response ("withdrawal activation") in 39% of neurones tested. Withdrawal activation was also elicited by administration of the opioid receptor antagonist naloxone, following pre-exposure to morphine, in 59% of neurones tested. These withdrawal responses were blocked or attenuated by the alpha2-adrenoceptor agonist clonidine, results which suggest a functional interaction exists between opioid receptors and alpha2-adrenoceptors in the SCN. Our observations show that opioid receptor agonists are largely devoid of actions on normal hamster SCN circadian pacemaker activity, while the occurrence of withdrawal responses may have implications on circadian function during withdrawal from opiate abuse.

Classic Weinstein: tetrad analysis, genetic variation and achiasmate segregation in Drosophila and humans

A maximum-likelihood method for the estimation of tetrad frequencies from single-spore data is presented. The multilocus exchange with interference and viability (MEIV) model incorporates a clearly defined model of exchange, interference, and viability whose parameters define a multinomial distribution for single-spore data. Maximum-likelihood analysis of the MEIV model (MEIVLA) allows point estimation of tetrad frequencies and determination of confidence intervals. We employ MEIVLA to determine tetrad frequencies among 15 X chromosomes sampled at random from Drosophila melanogaster natural populations in Africa and North America. Significant variation in the frequency of nonexchange, or E(0) tetrads, is observed within both natural populations. Because most nondisjunction arises from E(0) tetrads, this observation is quite unexpected given both the prevalence and the deleterious consequences of nondisjunction in D. melanogaster. Use of MEIVLA is also demonstrated by reanalyzing a recently published human chromosome 21 dataset. Analysis of simulated datasets demonstrates that MEIVLA is superior to previous methods of tetrad frequency estimation and is particularly well suited to analyze samples where the E(0) tetrad frequency is low and sample sizes are small, conditions likely to be met in most samples from human populations. We discuss the implications of our analysis for determining whether an achiasmate system exists in humans to ensure the proper segregation of E(0) tetrads.

Stability of finite difference deconvolution II: simulation studies

Theoretical analysis of the stability of finite difference deconvolution (FDD) indicates that if the cumulative amount function is used to characterize the drug input the method is stable for any sampling schedule for an intravenous unit impulse response function. The analysis also indicates that the method is stable for an oral unit impulse response only for well designed sampling schedules. This article confirms these results through numerical simulation experiments. It is shown that the assumption that the unit impulse response is error-free has an influence on the performance of FDD which is generally of no practical significance, except possibly for the first few points estimated. It is also shown that there is no significant interaction between the statistical error due to data noise and the deterministic algorithm error. The major source of error in practice is likely to be the data noise in the input response function. The simulations confirm that, with the estimated cumulative amount function as the quantity estimated and, with a well designed sampling schedule for the case of an oral unit impulse response, FDD is in practice an accurate and stable method with acceptable precision under a typical error disturbance.

Stability of finite difference deconvolution I: theoretical analysis

Analysis of the stability of finite difference deconvolution (FDD) shows that it is dependent on the characteristics of the unit impulse response function and the sampling schedule of the input response function, and that stability properties are improved when the cumulative amount function is directly estimated rather than the rate function. The estimated input rate for an intravenous (iv) unit impulse response function and the release rate for an oral solution unit impulse response function are unstable for any sampling schedule of the input response function. However, for an iv unit impulse response function, the estimated cumulative amount absorbed is stable for any sampling schedule of the response function. For an oral unit impulse response function, the estimated cumulative amount released is unstable for all the sampling points of the input response function located before the time of the maximum of the oral unit impulse response function, but it can be made stable if an appropriately designed sampling schedule of the input response function is used. In addition, the theoretical basis for choosing a sampling schedule to overcome the instability of FDD has been established.

Responses to neuropeptide Y in adult hamster suprachiasmatic nucleus neurones in vitro

We investigated the effects of neuropeptide Y and related analogues on the extracellularly recorded spontaneous firing rate activity of adult Syrian hamster suprachiasmatic nucleus neurones in vitro. Sixty-seven neurones were tested with neuropeptide Y: 45% were suppressed, 4% were activated, and the remaining 51% were unresponsive. These responses were not blocked by the GABA receptor antagonist bicuculline, indicating that neuropeptide Y-evoked responses did not appear to be dependent on GABA(A) receptor activation. We tested the effects of the neuropeptide Y Y1 receptor agonist [Leu31, Pro34]neuropeptide Y and the neuropeptide Y Y2 receptor agonist neuropeptide Y-(13-36) on nine cells suppressed by neuropeptide Y in order to determine the receptor subtype(s) mediating the effects of neuropeptide Y. Four of nine cells were suppressed by [Leu31, Pro34]neuropeptide Y only, one of nine was suppressed by neuropeptide Y-(13-36) only, two of nine were suppressed by both compounds, while the remaining two cells did not respond to either compound. These data suggest that neuropeptide Y can modulate suprachiasmatic nucleus function directly, without recruitment of GABA(A) interneurones. Further, our results indicate that neuropeptide Y may act on more than one receptor subtype within the adult hamster suprachiasmatic nucleus.

Pharmacokinetics of dexamethasone and its relationship to dexamethasone suppression test outcome in depressed patients and healthy control subjects

The pharmacokinetics of dexamethasone (DEX) were studied in 9 drug-free melancholically depressed patients and 10 healthy control subjects matched by sex and age. Each subject received 1 mg of DEX administered orally and by the (i.v.) route at 11:00 PM and serial blood samples were collected over the next 17 hours until 4:00 PM. There were no significant differences between the diagnostic groups and DEX bioavailability, peak plasma level, time to maximum concentration, or in elimination half-life after oral administration. Bioavailability estimates indicated that DEX absorption was incomplete and variable mean = 61%, SD = 14) in controls as well as depressed patients. In both groups there was a wide interindividual variability in plasma DEX levels following both oral and i.v. routes of administration. This variability could not be reliably predicted by differences in age, sex, or weight between subjects. The factors that accounted for most the variability in 4:00 PM plasma DEX levels after oral administration were clearance, bioavailability, and time to reach maximum concentration. Plasma DEX levels were lower in 3 depressed nonsuppressors compared to 3 matched controls who suppressed. No single pharmacokinetic factor was shown to be responsible for the lower DEX levels in the depressed nonsuppressors. These results indicate that plasma DEX levels need to be measured in each individual during the DST procedure so that this information may be taken into consideration when interpreting DST results.

Ionophoretically applied substance P activates hamster suprachiasmatic nucleus neurons

ionophoretic ejection of substance P (SP) activated 31% and suppressed 9% of hamster suprachiasmatic nucleus (SCN) cells in vitro. Hamster SCN cells did not demonstrate variation in sensitivity to SP across the circadian phases tested. SP modulated the response of 47% of hamster SCN cells to the excitatory amino acid (EAA) agonists glutamate and N-methyl-D-aspartate (NMDA). The results indicate that SP can alter both the spontaneous and EAA-evoked firing rate characteristics of hamster SCN neurons.

Effects of ionophoretically applied bombesin-like peptides on hamster suprachiasmatic nucleus neurons in vitro

Ionophoresis of the smaller bombesin-like peptides (gastrin releasing peptide [GRP]-(18-27), neuromedin B, and bombesin) evoked responses from 30-60% of hamster suprachiasmatic nucleus cells recorded in a hypothalamic slice preparation, depending on the circadian phase. We also demonstrated for the first time that the putative bombesin-like peptide receptor antagonists [D-F5,D-Phe6,D-Ala11]bombesin-(6-13)methyl ester (BIM 26226) and [D-Phe6,Des-Met14]bombesin-(6-14)ethyl amide can be applied ionophoretically to block physiological responses to bombesin-like peptides. Together with earlier findings, these results show that bombesin-like peptides administered by several methods can potently alter the firing rates of hamster suprachiasmatic nucleus neurons in vitro. These results indicate that bombesin-like peptides affect suprachiasmatic nucleus cells and could play a role in modulating suprachiasmatic nucleus-mediated circadian rhythm entrainment.

Bioavailability of hydroxychloroquine tablets in patients with rheumatoid arthritis

Nine patients with RA received two doses of 155 mg racemic hydroxychloroquine each, as a tablet and by i.v. infusion, in a randomized cross-over design study. Blood concentrations over the first 32 h following each dose were determined. Bioavailability was estimated using a sequential exponential least squares deconvolution method. The mean fraction absorbed from the tablet was 0.79 (range 0.39 to 1.27). The mean absorption lag-time was 1.3 h (range 0.5 to 3.7 h) and the mean time for 50% absorption was 4.3 h (range 1.9 to 10.3 h). Mean rate and extent of hydroxychloroquine absorption were not significantly different from that previously reported for healthy volunteers, although the interindividual variability in absorption parameters was greater in the patient group. Variability in the extent of absorption would lead to differences in steady-state hydroxychloroquine concentrations between patients, potentially contributing to the variability in response observed in clinical practice.

Disposition and absorption of hydroxychloroquine enantiomers following a single dose of the racemate

The disposition of hydroxychloroquine enantiomers has been investigated in nine patients with rheumatoid arthritis following administration of a single dose of the racemate. Blood concentrations of (-)-(R)-hydroxychloroquine exceed those of (+)-(S)-hydroxychloroquine following both an oral and intravenous dose of the racemate. Maximum blood concentrations of (-)-(R)-hydroxychloroquine were higher than (+)-(S)-hydroxychloroquine after oral dosing (121 +/- 56 and 99 +/- 42 ng/ml, respectively, P = 0.009). The time to maximum concentration and the absorption half-life, calculated using deconvolution techniques, were similar for both enantiomers. The fractions of the dose of each enantiomer absorbed were similar, 0.74 and 0.77 for (-)-(R)- and (+)-(S)-hydroxychloroquine, respectively (P = 0.77). The data suggest that absorption of hydroxychloroquine is not enantioselective. The stereoselective disposition of hydroxychloroquine appears to be due to enantioselective metabolism and renal clearance, rather than stereoselectivity in absorption and distribution.

Pharmacokinetics and pharmacodynamics of hydroxychloroquine enantiomers in patients with rheumatoid arthritis receiving multiple doses of racemate

Hydroxychloroquine, a slow acting antirheumatic drug, is administered as the racemic mixture. Blood concentrations of the two enantiomers of hydroxychloroquine were measured in two studies, one study of eight patients, in whom blood and urine concentrations were measured during the first 6 months of therapy with rac-hydroxychloroquine, and one of 43 patients who had received rac-hydroxychloroquine therapy for at least 6 months. In the latter study rheumatoid disease activity was also measured. The pharmacokinetics of hydroxychloroquine were found to be enantioselective. The concentrations of (-)-(R)-hydroxychloroquine were higher than those of the (+)-(S)-antipode in all patients at all time points, although the ratios of the two enantiomers did display a two to three fold variability between patients. Both total and renal clearance were greater for the (+)-(S)-enantiomer. From the observational, cross-sectional study design used, it was not possible to differentiate concentration-effect relationships of the two enantiomers. The 11-fold range of drug concentrations swamped any effect of variability between patients in enantiomer proportions. Blood concentrations of both enantiomers were significantly higher in groups of patients with less active disease.

Concentration-effect relationship of hydroxychloroquine in rheumatoid arthritis--a cross sectional study

OBJECTIVE

To determine the relationship between hydroxychloroquine concentration and effect in patients with rheumatoid arthritis (RA).

METHODS

Using a cross sectional study design, drug concentration and effect were measured at one time. Forty-three patients with RA, receiving hydroxychloroquine therapy for at least 6 months and not receiving glucocorticosteroids, gold or penicillamine therapy were enrolled. The main outcome measures were hydroxychloroquine concentration and disease activity measured as degree of synovitis, pain, duration and intensity of morning stiffness, impairment of activities of daily living, patients' and physicians' subjective assessment of disease, erythrocyte sedimentation rate, and rheumatoid factor (RF). Hemoglobin and albumin concentrations were also recorded.

RESULTS

Patients with none or mild intensity of morning stiffness, those with stiffness lasting less than 0.5 h and those with negative RF had significantly higher hydroxychloroquine blood concentrations than those in whom these measures indicated a more active disease (Mann-Whitney U test, p < 0.05). Similar trends were recorded for 3 other disease activity measures (p = 0.12-0.24). Analysis of all 9 individual disease activity measures indicated that the groups with less active disease had higher mean blood concentrations of hydroxychloroquine than those with measures indicating more active disease (p < 0.01).

CONCLUSION

Our data provide the first evidence of a concentration-response relationship for hydroxychloroquine in RA for individual disease activity measures. However, an unweighted summed score of disease activity did not correlate significantly with drug blood concentrations. A prospective study is necessary to confirm the relationship and to determine a therapeutic concentration range.

Absorption and in vivo dissolution of hydroxycholoroquine in fed subjects assessed using deconvolution techniques

1. Nine healthy subjects each received three doses of 155 mg rac-hydroxychloroquine, as a tablet, an oral solution and by intravenous infusion, in a randomised cross-over design study, 30 min after a standard high fat breakfast. 2. Four methods of deconvolution were used to assess the absolute bioavailability of the tablet and oral solution doses. These were the delta function method, the staircase approximation method, and two least squares methods using a single first-order input and a sequential first-order input. The mean (+/- s.d.) fraction absorbed estimated by the four methods was 0.64 +/- 0.14 after the tablet and 0.87 +/- 0.30 after the oral solution. Wide intersubject variability was observed (0.50-0.91 for the tablet; 0.30-1.37 for the solution). 3. The mean (+/- s.d.) absorption half-life was 3.7 +/- 2.0 h for the tablet and 3.3 +/- 1.6 h for the solution, suggesting that absorption following the tablet dose was not rate-limited by dissolution. 4. The in vivo dissolution rate, extent of release and lag-time were determined using cube-root law and first-order input functions. Dissolution was found to be rapid, after a significant lag-time, but incomplete in some subjects. 5. The rate and extent of absorption was similar to that reported previously for fasted subjects. The lag-time before absorption commenced in fed subjects (1.65 +/- 0.46 h) showed a significant three-fold increase over that reported previously in fasting subjects (0.63 +/- 0.33 h), but this difference is not likely to be of clinical significance.

Disposition of the enantiomers of hydroxychloroquine in patients with rheumatoid arthritis following multiple doses of the racemate

In eight patients with rheumatoid arthritis receiving racemic hydroxychloroquine, blood and urine concentrations of the enantiomers of hydroxychloroquine and its major metabolites were measured each month over the first 6 months of therapy. Plasma concentrations of hydroxychloroquine enantiomers were measured in five of these patients. In all patients, the blood concentration of (R)-hydroxychloroquine exceeded that of the (S)-enantiomer, the mean (R)/(S) ratio being 2.2 (range 1.6-2.9). A similar excess of (R)-hydroxychloroquine was found in the plasma, the mean (R)/(S) ratio being 1.6 (range 1.2-1.9). The mean enantiomer blood concentration ratio (R)/(S) for the metabolite desethylhydroxychloroquine was 0.45 (range 0.34-0.58) and for desethylchloroquine it was 0.56 (range 0.35-0.86) suggesting stereoselective metabolism of hydroxychloroquine. (S)-hydroxychloroquine had a mean (+/- s.d.) renal clearance from blood of 41 +/- 11 ml min-1, approximately twice that of (R)-hydroxychloroquine. The predicted unbound renal clearance was also higher for (S)-hydroxychloroquine. The clinical implications of enantioselective disposition of hydroxychloroquine are currently not known.

Kinetics of chloroquine uptake into isolated rat hepatocytes

The kinetics of uptake of chloroquine into isolated rat hepatocytes were studied to further investigate whether they are consistent with accumulation of chloroquine at therapeutic concentrations that is predominantly due to lysosomal trapping. A mathematical model describing the disposition of weak bases in isolated hepatocytes was developed and fitted to the chloroquine uptake data, allowing estimation of permeability coefficients for un-ionized chloroquine transport across rate-limiting membranes (p0 = 5.9 +/- 0.5 cm. s-1). The results of these studies suggest that the lysosomal membrane is the rate-limiting membrane in uptake of chloroquine in isolated hepatocytes. The rate and extent of accumulation of chloroquine in isolated hepatocytes in the presence of 10 mM NH4Cl were decreased. These results are consistent with a reduction in lysosomal pH caused by NH4Cl. The kinetics of uptake of hydroxychloroquine, which is structurally similar to chloroquine, were also investigated. The results of these studies were also consistent with lysosomal trapping, although the p0 value for un-ionized hydroxychloroquine (p0 = 0.28 +/- 0.02 cm.s-1) was much lower than that for un-ionized chloroquine. The estimated p0 value for un-ionized chloroquine and hydroxychloroquine transport across the lysosomal membrane are of a similar magnitude to those reported for transport of these compounds across human erythrocyte membranes, suggesting a similar transport mechanism.

Plasma protein binding of the enantiomers of hydroxychloroquine and metabolites

The in vitro binding of the enantiomers of hydroxychloroquine and its three major metabolites in pooled plasma obtained from four healthy volunteers and the binding of the enantiomers of hydroxychloroquine to purified plasma proteins has been investigated. The plasma protein binding of hydroxychloroquine was found to be stereoselective. The (S)-enantiomer of hydroxychloroquine was 64% bound in plasma, while (R)-hydroxychloroquine was 37% bound. Fifty% of (S)-hydroxychloroquine was bound to a 40 g.l-1 solution of human serum albumin, while only 29% of the (R)-enantiomer was bound. The enantioselectivity of hydroxychloroquine binding was reversed in a 0.7 g.l-1 solution of alpha 1-acid glycoprotein with (R)-hydroxychloroquine being bound to a greater extent than its optical antipode (41% versus 29%). The enantiomers of the metabolites of hydroxychloroquine were bound to a similar extent to plasma and purified plasma proteins. Binding of hydroxychloroquine to plasma and purified proteins was found to be linear over the racemic concentration range of 50 to 1000 ng.ml-1 and hydroxychloroquine metabolite binding to plasma was linear over the range 25 to 500 ng.ml-1.

Blood to plasma ratio of mefloquine: interpretation and pharmacokinetic implications

The blood to plasma ratio of the antimalarial mefloquine has been reported to be close to 1, while other reports indicate extensive accumulation in erythrocytes. This apparent contradiction has been resolved by a quantitative examination of the compensating effects of plasma protein binding of mefloquine which almost exactly matches the extent of mefloquine accumulation in erythrocytes. The observed blood to plasma ratio of about 1 arises as the result of a balance between extensive red cell uptake and extensive plasma protein binding. Some pharmacokinetic implications of the distribution of mefloquine within blood are outlined.

Gentamicin clearance during continuous arteriovenous hemodiafiltration

OBJECTIVE

To investigate the feasibility of predicting gentamicin dosing requirements during continuous arteriovenous hemodiafiltration (CAVHD).

DESIGN

Prospective study.

SETTING

General intensive therapy unit in a university teaching hospital.

PATIENTS

Five adult patients with acute renal failure in whom both dialytic and gentamicin therapy were indicated.

MEASUREMENTS AND MAIN RESULTS

CAVHD clearance and total body clearance of gentamicin were estimated from serial gentamicin concentrations in the blood and the combined ultrafiltrate and dialysate. Results (mean +/- SD) were: CAVHD clearance of gentamicin 5.2 +/- 1.8 mL/min; total body clearance of gentamicin 20.5 +/- 6.9 mL/min; ultrafiltrate flow rate 7.0 +/- 2.4 mL/min (420 +/- 146 mL/hr). CAVHD clearance of gentamicin was small and represented approximately 25% of total body clearance of gentamicin, although significant interpatient variation existed in these measurements and in the proportion of total gentamicin clearance attributable to CAVHD. CAVHD clearance of gentamicin was related to the ultrafiltrate flow rate (r2 = .81).

CONCLUSIONS

CAVHD clearance of gentamicin may be predicted for variable ultrafiltrate flow rates. However, due to its minor and variable contribution to total body clearance of gentamicin, prediction of gentamicin dosing requirements based on estimates of CAVHD clearance of gentamicin would be precluded and close monitoring of circulating gentamicin concentrations during CAVHD is necessary.

Chloride-37 nuclear magnetic resonance spectroscopic study of binding of salicylic acid and other hydroxybenzoic acids to the band 3 anion transport protein of human erythrocytes

Chloride-37 nuclear magnetic resonance spectroscopy was used to investigate the displacement of chloride (Cl-) from binding sites on band 3 anion transport protein in human erythrocytes by salicylic acid and five other hydroxybenzoic acids (HAs). All the HAs studied displaced Cl- from these binding sites. The association constants for binding of the HAs to band 3 anion transport protein were larger than that for Cl- and dependent on the specific structural features of the molecule, rather than general physicochemical characteristics.

A kinetic study of the role of band 3 anion transport protein in the transport of salicylic acid and other hydroxybenzoic acids across the human erythrocyte membrane

The mechanism of transport of salicylic acid and five other hydroxybenzoic acids across the human erythrocyte membrane was investigated. The specific anion transport inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, reduced but did not totally abolish transport of these acids. This observation suggests that these acids are transported by two parallel processes, one involving the band 3 anion transport protein channel and the other probably involving passive diffusion of the un-ionized molecule. The activation energies for membrane transport were large (99-127 kJ.mol-1), an observation that is consistent with the rate-limiting step for anion transport being the conformational change of the band 3 anion transport protein.

Sensitive stereospecific assay of warfarin in plasma: reversed-phase high-performance liquid chromatographic separation using diastereoisomeric esters of (-)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-hept-5- ene-2-carboxylic acid

A stereospecific reversed-phase high-performance liquid chromatographic (HPLC) assay for warfarin in plasma has been developed. The assay involves a rapid, simple clean-up procedure which separates warfarin from plasma constituents and warfarin metabolites. Warfarin enantiomers were assayed as their (-)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene -2- carboxylic acid diastereoisomeric esters by reversed-phase HPLC. Excellent resolution of the diastereoisomers was achieved in less than 10 min. Sensitivity of the assay was approximately 5-10 ng/ml for each isomer.

Bioavailability of hydroxychloroquine tablets assessed with deconvolution techniques

Four deconvolution methods (staircase, delta function, and least squares methods using single and sequential first-order input functions) were used to assess the absolute bioavailability of hydroxychloroquine tablets in nine healthy fasting volunteers. The volunteers received, in a random crossover design, a 155-mg oral tablet and a 155-mg iv infusion of racemic hydroxychloroquine. The mean fractions of the dose absorbed, calculated using the four deconvolution methods, were not statistically different (p = 0.70). The mean fraction absorbed (+/- SD) was 0.67 +/- 0.12, which was not significantly different from that reported previously in a conventional bioavailability study (p = 0.22). The mean absorption half-life was calculated to be 4.0 +/- 1.3 h. The mean lag time before absorption commenced was 0.57 +/- 0.30 h. The fraction of the dose absorbed ranged from 0.44 to 0.86. Low and/or variable bioavailability of hydroxychloroquine may be a cause of therapeutic failure in some patients. Validation of the deconvolution methods means that these techniques may now be used to assess the bioavailability of hydroxychloroquine in patients. An advantage of these methods is that samples need only be collected over the expected time period of absorption, rather than the whole time drug can be detected in the body, as is required in conventional area under the concentration-time curve ratio methods. Deconvolution studies may be completed in 2 weeks rather than the 10 months required for a conventional bioavailability study of hydroxychloroquine.

Simulation of kinetic data on the influx and efflux of chloroquine by erythrocytes infected with Plasmodium falciparum. Evidence for a drug-importer in chloroquine-sensitive strains

Literature data on influx and efflux kinetics of chloroquine (CQ) with erythrocytes infected with the malaria parasite Plasmodium falciparum were simulated using a four-compartment model with first-order exchange between the compartments. The four compartments represent (1) the buffer surrounding the infected erythrocyte; (2) the cytosol of the host erythrocyte; (3) the parasite cytosol; and (4) the food vacuole. Simulations showed that basal membrane transport of CQ, estimated from data on influx of CQ into uninfected red cells, largely accounts for uptake and release of CQ by erythrocytes infected with two different CQ-resistant (CQ-R) parasite strains. In contrast, the rate of uptake of CQ by erythrocytes infected with a CQ-sensitive (CQ-S) strain is substantially higher than predicted by uptake with membrane transfer by basal diffusion of CQ. Simulations also indicate that the difference in kinetics of CQ uptake by erythrocytes infected with the CQ-S and CQ-R strains can be explained by a net increase in the inward permeability coefficient at the host erythrocyte membrane, the composite membrane surrounding the parasite or the food vacuole membrane. The results are consistent with the presence of a drug-importer for CQ in erythrocytes infected with sensitive strains, which is absent in those infected with resistant strains. They are not consistent with the hypothesis that CQ resistance is attributable to a drug-exporter in resistant cells which is lacking in sensitive cells.

High-performance liquid chromatographic separation of the enantiomers of hydroxychloroquine and its major metabolites in biological fluids using an alpha 1-acid glycoprotein stationary phase

An enantioselective two-stage off-line assay has been developed for the analysis of hydroxychloroquine and its three major metabolites in biological fluids. The first non-stereoselective stage of the assay (PRP-1 column) separates and quantitates parent drug and metabolites. Fractions containing hydroxychloroquine and each of the metabolites are collected manually, evaporated, reconstituted in mobile phase and re-injected onto an alpha 1-acid glycoprotein column to separate and determine proportions of individual enantiomers. Preliminary results from patients samples indicate that the disposition of hydroxychloroquine and its major metabolites is enantioselective. p6

Kinetics and thermodynamics of chloroquine and hydroxychloroquine transport across the human erythrocyte membrane

Chloroquine (CQ) and hydroxychloroquine (HCQ) have almost identical molecular volumes but showed very different permeability characteristics. The permeability coefficient for the unionised species of CQ (2.0 cm/sec at 25 degrees) was about fifty times that of HCQ (0.039 cm/sec at 25 degrees), but the apparent activation energy for transport (85 kJ/mol for CQ, 81 kJ/mol for HCQ) was almost identical for the two drugs. The partition coefficient of CQ into various organic solvents was much higher than for HCQ, but the different permeability behaviour cannot be quantitatively explained by partitioning behaviour into hexane or octanol, two solvents commonly used to mimic the membrane interior. A comparison of permeability and partitioning characteristics suggests that the barrier phase for these drugs within the membrane can be modelled by a mixed solvent of 5% octanol in hexane. The results suggest that interactions with hydrogen bonding groups within the membrane are important in the membrane transport of these drugs, and that the membrane does not behave functionally as a simple hydrocarbon barrier.

Uptake of chloroquine by human erythrocytes

Analysis of studies of the pH dependence of the kinetics of chloroquine (CQ) uptake by human erythrocytes indicates that the unionised CQ species is the major membrane permeant at physiological pH even though the concentration of this species as a fraction of the total CQ concentration in solution is extremely small (0.01% at pH 7.4). CQ concentration-dependence studies and studies performed in the presence of various substrates and inhibitors of erythrocyte membrane transport failed to provide evidence of saturation or inhibition of CQ transport, which suggests that the likely mechanism of CQ transport across human erythrocyte membranes is by passive diffusion. Results of equilibrium binding studies of CQ to intact and lysed human erythrocytes indicated that the mechanism of CQ accumulation in intact human erythrocytes appears to be by a combination of ion trapping (a consequence of the basic nature of the drug and the pH gradient across the human erythrocyte membrane) and binding of CQ to cell components.

Bioavailability of hydroxychloroquine tablets in healthy volunteers

1. Five healthy volunteers received, in a randomised crossover design study, a 155 mg oral tablet and an intravenous infusion of 155 mg racemic hydroxychloroquine (200 mg hydroxychloroquine sulphate) to assess the bioavailability of the commercially available tablet (Plaquenil, Winthrop Laboratories, Australia). 2. The terminal elimination half-life of hydroxychloroquine is more than 40 days, thus blood and urine samples were collected for 5 months following each dose to characterise adequately the terminal elimination phase and obtain accurate estimates of the areas under the concentration-time curves. 3. The mean (+/- s.d.) fraction of the oral dose absorbed, estimated from the blood and urine data, was 0.74 (+/- 0.13). A wide range of estimates of the fraction of the oral dose absorbed was calculated from the plasma data (0.41 - 1.53), reflecting the difficulties of accurate measurement of hydroxychloroquine in plasma. 4. A period of 6 months is required to achieve 96% of steady-state levels of hydroxychloroquine with the usual once daily, oral dosage regimen. Pharmacokinetic factors may thus be partly responsible for the delayed action of the drug in rheumatic conditions. 5. Haemodialysis will not aid in the case of oral overdose with hydroxychloroquine. Although the proportionate increase in clearance may be large, the increase in the fraction of the dose excreted will be negligible. The extensive sequestration of the drug by tissues limits effectiveness of haemodialysis.

Thrombosis: the major Hickman catheter complication in patients with solid tumor

Major complications of Hickman catheter placement (thrombosis and infection) were determined in 168 patients with solid tumor (lung, 79; head and neck, 56; esophagus, 24; and miscellaneous, 9). Catheter-related thrombosis was clinically detected in 22 individuals and was detected at autopsy in six (total 17 percent). The 17 percent figure underestimates the true incidence of thrombosis since only 25 percent of study patients had autopsies. Patients with adenocarcinoma of the lung constituted a high risk group. Nine of 20 (45 percent) of these patients had thrombosis compared to 25, 9, and 16 percent of patients with squamous cell cancers of lung, head and neck and esophagus, respectively (p less than 0.002). Three patients with thrombosis had pulmonary emboli and two died. Thrombosis occurred despite daily heparin catheter flushing. INfections occurred in 11 patients. One had suspected endocarditis, one had a subcutaneous tunnel infection, and nine had exit site infections. All responded to local or systemic antibiotics. Better methods to prevent thrombosis are needed.

The potential role of lysosomes in tissue distribution of weak bases

The potential importance of lysosomes as a site of accumulation of weak bases in tissues is discussed. A simple mathematical treatment predicts the quantitative significance of lysosomal trapping for monoacidic and diacidic weak bases. The features which are characteristics of lysosomal trapping are discussed, particularly in comparison with active transport and intracellular binding mechanisms. These features include: linear accumulation at low concentrations; nonlinearity at higher concentrations; dependence on structural integrity of tissue; energy dependence and competition with other weak bases. Subcellular distribution studies have previously shown that weak bases accumulate extensively in membranes; however, the dependence of accumulation on the structural integrity of tissue suggests that this is not the only significant mechanism of accumulation. The results of a range of studies of tissue distribution of weak bases are discussed to illustrate that these findings are consistent with accumulation in lung and liver being attributable to a combination of lysosomal trapping and accumulation in membranes whereas, in muscle, accumulation in membranes is the predominant mechanism of accumulation. The possible pharmacokinetic significance of lysosomal trapping of weak bases is also discussed.

A dose-ranging study of the pharmacokinetics of hydroxy-chloroquine following intravenous administration to healthy volunteers

1. The pharmacokinetics of hydroxychloroquine were studied in five healthy volunteers following an intravenous infusion of 155 mg (2.47 +/- 0.25 mg kg-1) racemic hydroxychloroquine. Four of these volunteers also received a further 310 mg (4.92 +/- 0.45 mg kg-1) infusion of hydroxychloroquine and evidence of nonlinearities in the pharmacokinetics of hydroxychloroquine were sought. 2. No nonlinear elimination or distribution processes appeared to be operating at the doses of hydroxychloroquine used in this study, supporting the hypothesis that in the therapeutic dosing range the pharmacokinetics of hydroxychloroquine are linear. 3. Half-life and mean residence time were long (around 40 days) and large volumes of distribution were calculated (5,522 l from blood, 44,257 l from plasma). Sequestration into the tissues is an important feature of the disposition of hydroxychloroquine. The persistence of hydroxychloroquine in the body is due primarily to this extensive tissue distribution, rather than to low clearance (667 ml min-1 based on plasma data, 96 ml min-1 based on blood data). 4. Plasma data were more variable than blood data. Blood to plasma concentration ratios were not constant (mean +/- s.d.: 7.2 +/- 4.2). The data indicate that it is preferable to measure whole blood concentrations of hydroxychloroquine, rather than plasma concentrations, in pharmacokinetic studies. 5. The pharmacokinetics of hydroxychloroquine are similar to those of chloroquine.