Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Enhanced oral bioavailability of 2'- beta-fluoro-2',3'-dideoxyadenosine (F-ddA) through local inhibition of intestinal adenosine deaminase

PURPOSE

Intestinal enzyme inhibition may be an effective tool to increase the oral bioavailability of compounds that undergo first-pass intestinal metabolism. However, systemic enzyme inhibition may be undesirable and therefore should be minimized. 2-Beta-fluoro-2',3'-dideoxyadenosine (F-ddA) is an adenosine deaminase (ADA) activated prodrug of 2-beta-fluoro-2',3'-dideoxyinosine (F-ddI) with enhanced delivery to the central nervous system (CNS) that has been tested clinically for the treatment of AIDS. Unfortunately, intestinally localized ADA constitutes a formidable enzymatic barrier to the oral absorption of F-ddA. This study explores various factors involved in inhibitor selection and dosage regimen design to achieve local ADA inhibition with minimal systemic inhibition.

METHODS

In situ intestinal perfusions with mesenteric vein cannulation were performed in the rat ileum to determine the lumenal disappearance and venous blood appearance of F-ddA and F-ddI. Coperfusions with the ADA inhibitor erythro9-(2-hydroxy-3-nonyl)adenine [(+)-EHNA] over a range of concentrations were used to monitor inhibitor effects on F-ddA absorption and metabolism.

RESULTS

High concentrations of EHNA in coperfusions with F-ddA completely inhibited intestinal ADA, increasing the permeability coefficient of F-ddA by nearly threefold but producing high systemic inhibition of ADA. Mathematical models were utilized to show that in full-length intestinal perfusions an optimal log mean lumenal EHNA perfusate concentration of 0.5 microg/ml could achieve an intestinal bioavailability of 80% with <20% systemic inhibition.

CONCLUSIONS

Optimizing local enzyme inhibition may require careful selection of a suitable inhibitor, the dose of the inhibitor, and the inhibitor vs. drug absorption profiles.

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Dynamics of the 16O(e, e'p) reaction at high missing energies

We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25<E(m)<50 MeV and P(m) approximately 60 MeV/c, the reaction is dominated by a single 1s(1/2) proton knockout. At larger P(m), the single-particle aspects are increasingly masked by more complicated processes. Calculations which include pion exchange currents, isobar currents, and short-range correlations account for the shape and the transversity, but for only half of the magnitude of the measured cross section.

Prospective evaluation of propofol anesthesia in the pediatric intensive care unit for elective oncology procedures in ambulatory and hospitalized children

OBJECTIVES

To evaluate our experience with propofol anesthesia delivered by pediatric intensivists in the pediatric intensive care unit (PICU) to facilitate elective oncology procedures in children performed by pediatric oncologists.

METHODS

Elective oncology procedures performed with propofol anesthesia in our multidisciplinary, university-affiliated PICU were prospectively evaluated over a 7-month period. Ambulatory and hospitalized children were prescheduled for their procedure, underwent a medical evaluation, and met fasting requirements before the start of anesthesia. Continuous cardiorespiratory and neurologic monitoring was performed by a pediatric intensivist and a PICU nurse, while the procedure was performed by a pediatric oncologist. Propofol was delivered in intermittent boluses to achieve the desired level of anesthesia. Information studied included patient demographics, procedures performed, induction and total doses of propofol used, the duration of the different phases of the patient's PICU stay, the occurrence of side effects, the need for therapeutic interventions, and the incidence of recall of the procedure.

RESULTS

Fifty procedures in 28 children (mean age: 7.5 +/- 4.3 years) were evaluated. Sixty-one percent of patients had established diagnoses. Fifty-four percent of procedures were lumbar puncture with intrathecal chemotherapy administration and 26% of procedures were bone marrow aspirations with biopsy. Induction propofol doses were 2. 0 +/-.8 mg/kg for ambulatory and hospitalized patients, while total propofol doses were 6.6 +/- 2.3 mg/kg and 7.9 +/- 2.4 mg/kg for ambulatory and hospitalized patients, respectively. Induction time was 1.5 +/-.7 minutes, recovery time was 23.4 +/- 11.5 minutes, and total PICU time was 88.8 +/- 27.7 minutes. Transient decreases in systolic blood pressure less than the fifth percentile for age occurred in 64% of procedures, with a mean decrease of 25% +/- 10%. Intravenous fluids were administered in 31% of these cases. Hypotension was more common in ambulatory patients but was not predicted by propofol dose, anesthesia time, or age. Partial airway obstruction was noted in 12% of procedures while apnea requiring bag-valve-mask ventilation occurred in 2% of procedures. Neither was associated with age, propofol dose, or the duration of anesthesia. All procedures were successfully completed and there were no incidences of recall of the procedure.

CONCLUSIONS

Propofol anesthesia is effective in achieving patient comfort and amnesia, while optimizing conditions for elective oncology procedures in children. Although transient hypotension and respiratory depression may occur, propofol anesthesia seems to be safe to use for these procedures in the PICU setting. Recovery from anesthesia was rapid and total stay was brief. Under the proper conditions, propofol anesthesia delivered by pediatric intensivists in the PICU is a reasonable option available to facilitate invasive oncology procedures in children.

Retrospective analysis of ingestions of iron containing products in the united states: are there differences between chewable vitamins and adult preparations?

Iron is the one of the leading causes of pediatric poisoning deaths in the United States. Most cases of serious iron overdose reported in the medical literature have resulted from adult formulations of iron. To begin evaluating the possibility that differences in toxicity exist between iron preparations, we performed a retrospective evaluation of all exposures to pediatric and adult iron products reported to the American Association of Poison Control Centers' (AAPCC) Toxic Exposure Surveillance System (TESS) from 1983 to 1998. We attempted to determine the incidence of fatal iron poisoning for each group. A total of 195,780 ingestions of children's vitamins containing iron were reported to the TESS between 1983 and 1998 with no resulting fatalities. During the same twelve-year study period, 147,079 exposures to adult forms of iron were reported with 60 fatalities (p < 0.0001). A prospective study is required to assess whether differences may exist in the toxicity of these two iron preparations.

A quantitative model for the dependence of solute permeability on peptide and cholesterol content in biomembranes

The influence of varying concentrations of a transmembrane peptide, gramicidin A (gA), and cholesterol (Chol) on the passive permeation of p-methylhippuric acid (MHA) and alpha-carbamoyl-p-methylhippuric acid (CMHA) across egg-lecithin membranes (EPC) has been investigated in vesicle efflux experiments. Incorporation of 0.25 volume fraction of gA in its nonchannel conformation increased the permeability coefficient (Pm) for CMHA by a factor of 6.0 +/- 1.8 but did not alter Pm for MHA, a more lipophilic permeant. In contrast, incorporation of 0.26 volume fraction Chol with no added protein decreased the Pm values for both CMHA and MHA by similar factors of 4.2 +/- 1.1 and 3.5 +/- 1.2, respectively. A quantitative structure-transport model has been developed to account for the dependence of Pm on the membrane concentrations of gA and Chol in terms of induced changes in both membrane chain ordering and hydrophobicity. Chain ordering is assumed to affect Pm for both permeants similarly since they are comparable in molecular size, while changes in Pm ratios in the presence of gA or Chol are attributed to alterations in membrane hydrophobicity. Changes in lipid chain ordering were detected by monitoring membrane fluidity using fluorescence anisotropy of 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene incorporated into the membranes. The influence of additives on membrane hydrophobicity, which governs Pm ratios through effects on solute partitioning into the barrier domain, were rationalized within the framework of regular solution theory using solubility parameters as a measure of membrane hydrophobicity. Fits of the Pm ratios using the theoretical model yielded solubility parameters for gA and Chol in EPC membranes of 13.2 and 7.7 (cal/ml)(1/2), respectively, suggesting that gA decreases the barrier domain hydrophobicity while Chol has a minimal effect on barrier hydrophobicity. After correcting for barrier domain hydrophobicity, permeability decrements due to membrane ordering induced by gA or Chol were found to exhibit a strong correlation with membrane order as predicted by free-surface-area theory, regardless of whether gA or Chol is used as the ordering agent.

Use of cultured cerebral capillary endothelial cells in modeling the central nervous system availability of 2',3'-dideoxyinosine

The biochemical and physiological mechanisms responsible for the limited central nervous system (CNS) uptake of dideoxynucleoside reverse transcriptase inhibitors currently used to treat HIV-1 infection in humans are poorly understood. In vitro models of the blood-brain barrier (BBB) offer an attractive alternative to in vivo or in situ animal studies for understanding the role of the blood-brain barrier in regulating brain tissue concentrations of these agents. In the present study, the kinetics of 2', 3'-dideoxyinosine (ddI) uptake and purine nucleoside phosphorylase (PNP) mediated catabolism in primary cultures of bovine brain microvessel endothelial cells (BBMECs) were determined in order to ascertain the importance of both transport and metabolism governing the CNS availability of this purine dideoxynucleoside. Initial rates of ddI uptake as a function of ddI donor concentration suggest the involvement of both passive diffusion and carrier-mediated processes. These studies confirm earlier in vivo findings that transporters may play a role in regulating the CNS concentration of ddI. Analysis of ddI uptake and metabolite accumulation in BBMECs over longer time intervals (beyond the intial rate region) provide substantial in vitro evidence for an enzymatic BBB for ddI. Simulations of the CNS availability of ddI derived from in vitro estimates of parameters for passive diffusion, carrier-mediation, and metabolism indicate that the fraction of ddI entering the BBB cells which actually reaches the brain parenchyma may be quite low (< 2%) due to metabolism by PNP localized within the BBB, consistent with the low CNS delivery of ddI observed in vivo. Transporters and metabolic enzymes within the BBB may function in coordinated fashion to reduce the CNS concentrations of both rapidly metabolized and poorly metabolized dideoxynucleosides.

Influence of a transmembrane protein on the permeability of small molecules across lipid membranes

The influence of the nonchannel conformation of the transmembrane protein gramicidin A on the permeability coefficients of neutral and ionized alpha-X-p-methyl-hippuric acid analogues (XMHA) (X = H, OCH(3), CN, OH, COOH, and CONH(2)) across egg-lecithin membranes has been investigated in vesicle efflux experiments. Although 10 mol% gramicidin A increases lipid chain ordering, it enhances the transport of neutral XMHA analogues up to 8-fold, with more hydrophilic permeants exhibiting the greatest increase. Substituent contributions to the free energies of transfer of both neutral and anionic XMHA analogues from water into the bilayer barrier domain were calculated. Linear free-energy relationships were established between these values and those for solute partitioning from water into decadiene, chlorobutane, butyl ether, and octanol to assess barrier hydrophobicity. The barrier domain is similar for both neutral and ionized permeants and substantially more hydrophobic than octanol, thus establishing its location as being beyond the hydrated headgroup region and eliminating transient water pores as the transport pathway for these permeants, as the hydrated interface or water pores would be expected to be more hydrophilic than octanol. The addition of 10 mol% gramicidin A alters the barrier domain from a decadiene-like solvent to one possessing a greater hydrogen-bond accepting capacity. The permeability coefficients for ionized XMHAs increase with Na(+) or K(+) concentration, exhibiting saturability at high ion concentrations. This behavior can be quantitatively rationalized by Gouy-Chapman theory, though ion-pairing cannot be conclusively ruled out. The finding that transmembrane proteins alter barrier selectivity, favoring polar permeant transport, constitutes an important step toward understanding permeability in biomembranes.

Exon skipping in IVD RNA processing in isovaleric acidemia caused by point mutations in the coding region of the IVD gene

Isovaleric acidemia (IVA) is a recessive disorder caused by a deficiency of isovaleryl-CoA dehydrogenase (IVD). We have reported elsewhere nine point mutations in the IVD gene in fibroblasts of patients with IVA, which lead to abnormalities in IVD protein processing and activity. In this report, we describe eight IVD gene mutations identified in seven IVA patients that result in abnormal splicing of IVD RNA. Four mutations in the coding region lead to aberrantly spliced mRNA species in patient fibroblasts. Three of these are amino acid altering point mutations, whereas one is a single-base insertion that leads to a shift in the reading frame of the mRNA. Two of the coding mutations strengthen pre-existing cryptic splice acceptors adjacent to the natural splice junctions and apparently interfere with exon recognition, resulting in exon skipping. This mechanism for missplicing has not been reported elsewhere. Four other mutations alter either the conserved gt or ag dinucleotide splice sites in the IVD gene. Exon skipping and cryptic splicing were confirmed by transfection of these mutations into a Cos-7 cell line model splicing system. Several of the mutations were predicted by individual information analysis to inactivate or significantly weaken adjacent donor or acceptor sites. The high frequency of splicing mutations identified in these patients is unusual, as is the finding of missplicing associated with missense mutations in exons. These results may lead to a better understanding of the phenotypic complexity of IVA, as well as provide insight into those factors important in defining intron/exon boundaries in vivo.

In vitro models of the blood-brain barrier to polar permeants: comparison of transmonolayer flux measurements and cell uptake kinetics using cultured cerebral capillary endothelial cells

Given that the cerebral microvasculature within the brain constitutes the rate-limiting barrier to drug entry, primary cultures of cerebral capillary endothelial cells would appear to offer a potentially useful model system for predicting drug delivery to the central nervous system. In the present study, the predictive capabilities of two potential models of the in vivo blood-brain barrier (BBB) to the passive diffusion of polar permeants were assessed. A comparison of the logarithms of the in vitro transmonolayer permeability coefficients (Pmonolayer) for several polar permeants varying in lipophilicity (from this study and literature data) with the well-established relationship between the logarithms of the in vivo BBB permeability coefficients (log PBBB) and permeant lipophilicity as measured by the logarithm of the octanol/water partition coefficient (log PCoctanol/water) demonstrated that in vitro permeation across these monolayers is largely insensitive to polar permeant lipophilicity as a result of the predominance of the paracellular component in the transmonolayer flux. Conversely, kinetic studies of uptake of the same compounds into monolayers yielded transfer rate constants (kp) reflecting membrane permeability coefficients ranging over several orders of magnitude, similar to the variation in permeant lipophilicity. Furthermore, a linear relationship could be demonstrated between the logarithms of kp and in vivo BBB log P (slope = 1.42 +/- 0.35; r = 0. 92). In conclusion, this preliminary investigation suggests that monitoring the kinetics of cell uptake into cerebral capillary endothelial cell monolayers may be superior to transmonolayer flux measurements for predicting the passive diffusion of polar permeants across the BBB in vivo.

Influence of chain ordering on the selectivity of dipalmitoylphosphatidylcholine bilayer membranes for permeant size and shape

The effects of lipid chain packing and permeant size and shape on permeability across lipid bilayers have been investigated in gel and liquid crystalline dipalmitoylphosphatidylcholine (DPPC) bilayers by a combined NMR line-broadening/dynamic light scattering method using seven short-chain monocarboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, and trimethylacetic acid) as permeants. The experimental permeability coefficients are compared with the predictions of a bulk solubility diffusion model in which the bilayer membrane is represented as a slab of bulk hexadecane. Deviations of the observed permeability coefficients (Pm) from the values predicted from solubility diffusion theory (Po) lead to the determination of a correction factor, the permeability decrement f (= Pm/Po), to account for the effects of chain ordering. The natural logarithm of f has been found to correlate linearly with the inverse of the bilayer free surface area with slopes of 25 +/- 2, 36 +/- 3, 45 +/- 8, 32 +/- 12, 33 +/- 4, 49 +/- 12, and 75 +/- 6 A2 for formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, and trimethylacetic acid, respectively. The slope, which measures the sensitivity of the permeability coefficient of a given permeant to bilayer chain packing, exhibits an excellent linear correlation (r = 0.94) with the minimum cross-sectional area of the permeant and a poor correlation (r = 0.59) with molecular volume, suggesting that in the bilayer interior the permeants prefer to move with their long principal axis along the bilayer normal. Based on these studies, a permeability model combining the effects of bilayer chain packing and permeant size and shape on permeability across lipid membranes is developed.

Neutron yields from 435 MeV/nucleon Nb stopping in Nb and 272 MeV/nucleon Nb stopping in Nb and Al

Neutron fluences were measured from 435 MeV/nucleon Nb ions stopping in a Nb target and 272 MeV/nucleon Nb ions stopping in targets of Nb and Al for neutrons above 20 MeV and at laboratory angles between 3 degrees and 80 degrees. The resultant spectra were integrated over angles to produce neutron energy distributions and over energy to produce neutron angular distributions. The total neutron yields for each system were obtained by integrating over the angular distributions. The angular distributions from all three systems are peaked forward, and the energy distributions from all three systems show an appreciable yield of neutrons with velocities greater than the beam velocity. Comparison of the total neutron yields from the two Nb + Nb systems suggests that the average neutron multiplicity decreases with decreasing projectile energy. Comparison of the total yields from the two 272 MeV/nucleon systems suggests that the total yields show the same dependence on projectile and target mass number as do total inclusive neutron cross sections. The data are compared with Boltzmann-Uehling-Uhlenbeck model calculations.

The barrier domain for solute permeation varies with lipid bilayer phase structure

The chemical selectivities of the transport barriers in lipid bilayers varying in composition and phase structure (gel-phase DPPC and DHPC bilayers and liquid-crystalline DPPC/CHOL/50:50 mol% bilayers) have been investigated by determining functional group contributions to transport of a series of alpha-substituted p-toluic acid analogs obtained in vesicle efflux experiments. Linear free energy relationships are established between the free energies of transfer for this series of compounds from water to the barrier domain and corresponding values for their transfer from water into six model bulk solvents (hexadecane, hexadecene, decadiene, chlorobutane, butyl ether, and octanol) determined in partitioning experiments to compare the barrier microenvironment to that in these model solvents. The barrier microenvironment in all bilayers studied is substantially more hydrophobic than octanol, thus establishing the location of the barrier beyond the hydrated headgroup interfacial region, as the interface is expected to be more hydrophilic than octanol. The chemical nature of the barrier domain microenvironment varies with bilayer phase structure. The barrier regions in non-interdigitated DPPC and interdigitated DHPC gel-phase bilayers exhibit some degree of hydrogen-bond acceptor capacity as may occur if these domains lie in the vicinity of the ester/ether linkages between the headgroups and the acyl chains. Intercalation of 50 mol% cholesterol into DPPC bilayers, which induces a phase transition to a liquid-crystalline phase, substantially increases the apparent barrier domain hydrophobicity relative to gel-phase bilayers to a nonhydrogen bonding, hydrocarbonlike environment resembling hexadecene. This result, combined with similar observations in liquid-crystalline egg-PC bilayers (J. Pharm. Sci. (1994), 83:1511-1518), supports the notion that the transition from the gel-phase to liquid-crystalline phase shifts the barrier domain further into the bilayer interior (i.e., deeper within the ordered chain region).

Characterization of molecular defects in isovaleryl-CoA dehydrogenase in patients with isovaleric acidemia

Isovaleryl-CoA dehydrogenase (IVD) is a homotetrameric mitochondrial flavoenzyme which catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA. PCR of IVD genomic and complementary DNA was used to identify mutations occurring in patients with deficiencies in IVD activity. Western blotting, in vitro mitochondrial import, prokaryotic expression, and kinetic studies of IVD mutants were conducted to characterize the molecular defects caused by the amino acid replacements. Mutations leading to Arg21Pro, Asp40Asn, Ala282Val, Cys328Arg, Val342Ala, Arg363Cys, and Arg382Leu replacements were identified. Western blotting of fibroblast extracts and/or in vitro mitochondrial import experiments indicate that the seven precursor IVD mutant peptides, and a previously identified IVD Leu13Pro mutant, are synthesized and imported into mitochondria. While the IVD Leu13Pro, Arg21Pro, and Cys328Arg mutant peptides are rapidly degraded following mitochondrial import, the other mutant peptides exhibit greater mitochondrial stability, though less than the wild-type enzyme. Active IVD Ala282Val, Val342Ala, Arg363Cys, and Arg382Leu mutants were less stable than wild type when produced in Escherichia coli. The Km values of purified IVD Ala282Val, Val342Ala, and Arg382Leu mutants are 27.0, 2. 8, and 6.9 microM isovaleryl-CoA, respectively, compared to 3.1 microM for the wild type, using the electron-transfer flavoprotein (ETF) fluorescence quenching assay. The catalytic efficiency per mole of FAD content of these three mutants is 4.8, 17.0, and 17.0 microM-1*min-1, respectively, compared to 170 microM-1*min-1 for wild type.

Diversion of 911 poisoning calls to a poison center

OBJECTIVE

To determine the impact and safety of diverting poisoning calls from 911 to a regional poison center.

METHODS

A prospective six-month review was performed of all calls transferred from 911 dispatchers to a regional poison center for management. Recommendations for management and transport were made by the poison center using existing protocols. Patients were followed with telephone contact by poison center staff until symptoms resolved or until hospital discharge. Medical outcomes were categorized using the American Association of Poison Control Center guidelines for medical outcome.

RESULTS

A total of 262 cases were reviewed; four were excluded. The poison center was contacted prior to ambulance dispatch in 210 cases (81%). An ambulance was sent before the poison center was contacted 48 times (19%). The majority of patients originally calling 911 were managed at home (175/258; 68%). Patients experienced either no effect or minor effects in 254 cases (98%). Two patients developed moderate effects (0.8%), one developed a major effect (0.4%), and one died (0.04)%. No adverse effects or treatment delays resulted from diversion of calls to the poison center.

CONCLUSIONS

Appropriate poisoning and toxic exposure cases may be diverted safely from emergency medical services dispatch to a regional poison center for management, reducing unnecessary responses, with substantial cost savings.

Compositional heterogeneity in parenteral lipid emulsions after sedimentation field flow fractionation

This study examines the size and compositional heterogeneity of particles in a commercial lipid emulsion (Intralipid) before and after equilibration with penclomedine, a highly lipophilic cytotoxic agent. Emulsions were fractionated by sedimentation field-flow fractionation (sedFFF), and particle sizes of the monodisperse fractions were determined by photon correlation spectroscopy. The triglyceride (TG), phosphatidylcholine (PC), and penclomedine (in drug loaded emulsions) contents in each fraction were determined by HPLC. The aqueous-entrapped volume within Intralipid was determined to be approximately 10% by size-exclusion chromatography using [3H]mannitol. Thirteen sedFFF fractions collected from the drug free emulsions yielded particles ranging in size from 154 to 423 nm. Total channel recoveries were 89% and 95% for TG and PC, respectively. Apparent particle densities varied significantly with size, suggesting heterogeneity in composition as confirmed by PC/TG mass ratios which varied dramatically. Computer fits of the distribution profiles suggested populations of phospholipid vesicles and oil droplets containing excess phospholipid in addition to classical emulsion droplets. Drug loading induced a significant shift of the predominant triglyceride containing population to a larger particle size. The penclomedine distribution profile closely mimicked that of the TG rather than the PC fraction. These studies suggest the need to consider not only size distribution but also compositional distribution in characterizing parenteral emulsions.

Pharmacokinetics of the protease inhibitor KNI-272 in plasma and cerebrospinal fluid in nonhuman primates after intravenous dosing and in human immunodeficiency virus-infected children after intravenous and oral dosing

KNI-272 is a human immunodeficiency virus (HIV) protease inhibitor with potent activity in vitro. We studied the pharmacokinetics of KNI-272 in the plasma and cerebrospinal fluid (CSF) of a nonhuman primate model and after intravenous and oral administration to children with HIV infection. Plasma and CSF were sampled over 24 h after the administration of an intravenous dose of 50 mg of KNI-272 per kg of body weight (approximately 1,000 mg/m2) to three nonhuman primates. The pharmacokinetics of KNI-272 were also studied in 18 children (9 males and 9 females; median age, 9.4 years) enrolled in a phase I trial of four dose levels of KNI-272 (100, 200, 330, and 500 mg/m2 per dose given four times daily). The plasma concentration-time profile of KNI-272 in the nonhuman primate model was characterized by considerable interanimal variability and rapid elimination (clearance, 2.5 liters/h/kg; terminal half-life, 0.54 h). The level of drug exposure achieved in CSF, as measured by the area under the KNI-272 concentration-time curve, was only 1% of that achieved in plasma. The pharmacokinetics of KNI-272 in children were characterized by rapid elimination (clearance, 276 ml/min/m2; terminal half-life, 0.44 h), limited (12%) and apparently saturable bioavailability, and limited distribution (volume of distribution at steady state, 0.11 liter/kg). The concentrations in plasma were maintained above a concentration that is active in vitro for less than half of the 6-h dosing interval. There was no significant increase in CD4 cell counts or decrease in p24 antigen or HIV RNA levels. The pharmacokinetic profile of KNI-272 may limit the drug's efficacy in vivo. It appears that KNI-272 will play a limited role in the treatment of HIV-infected children.

Optimization of the local inhibition of intestinal adenosine deaminase (ADA) by erythro-9-(2-hydroxy-3-nonyl)adenine: enhanced oral delivery of an ADA-activated prodrug for anti-HIV therapy

Previous in situ perfusion studies in rat ileal segments have demonstrated that high concentrations (>40 microg/mL) of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), a semitight binding inhibitor of adenosine deaminase (ADA), are effective in completely inhibiting the intestinal metabolism of 6-chloro-2',3'-dideoxypurine (6-Cl-ddP), an ADA activated prodrug of the anti-HIV agent 2', 3'-dideoxyinosine (ddI) designed for improved targeting to the central nervous system. However, the intestinal absorption of EHNA results in complete inhibition of the ADA activity in the mesenteric blood draining the isolated intestinal segment being perfused and may lead to complete inhibition of ADA present in the systemic circulation and other sites, an unacceptable outcome since bioconversion in the target tissue is required for prodrug efficacy. This study examines the feasibility of locally inhibiting ADA present in the intestinal wall using EHNA to increase the intestinal absorption of 6-Cl-ddP. Transport experiments conducted in isolated ileal segments from mesenteric cannulated rats using perfusate containing prodrug and various concentrations of EHNA demonstrated that a 0.1 microg/mL logarithmic mean lumenal concentration of EHNA was effective in increasing the intestinal bioavailability of Cl-ddP to > 90%. Intestinal uptake parameters for EHNA and pharmacokinetic parameters generated in vivo in chronically catheterized rats given intravenous infusions ranging from 12.5 to 310 microg/kg/min were used to demonstrate that <10% of systemic ADA would be inhibited at steady state using the optimal perfusate concentration of EHNA. Thus, in continuous perfusions it is possible to increase the intestinal bioavailability of 6-Cl-ddP to >90% with minimal (<10%) inhibition of systemic ADA. Local inhibition of enzymes may be an effective strategy to increase the oral bioavailability of tissue enzyme-activated prodrugs or other drugs which may also be substrates for intestinal enzymes.

Absorption and intestinal metabolism of purine dideoxynucleosides and an adenosine deaminase-activated prodrug of 2',3'-dideoxyinosine in the mesenteric vein cannulated rat ileum

This study investigates the mechanisms of absorption and the role of intestinally localized purine salvage pathway enzymes on the ileal availabilities of 2',3'-dideoxyinosine (ddI), a substrate for purine nucleoside phosphorylase (PNP); 2'-fluoro-2',3'-dideoxyinosine (F-ddI), a non-PNP substrate; and 6-chloro-2',3'-dideoxypurine (6-Cl-ddP), an adenosine deaminase (ADA) activated prodrug of ddI. The potential for increasing the intestinal availability of 6-Cl-ddP through the use of ADA inhibitors, namely, 2'-deoxycoformycin (DCF) and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), is also explored. Drug permeability coefficients across the intestinal epithelium were determined in in situ perfusions in the mesenteric vein cannulated rat ileum based on both drug appearance in blood (Pblood) and disappearance from the lumen (Plumen) and their paracellular and transcellular components were estimated by comparison to the permeabilities of two paracellular markers, mannitol and urea. Values of Pblood for ddI were determined to be (1.1 +/- 0.3) x 10(-6) cm/s, in close agreement with the value of (1.0 +/- 0.3) x 10(-6) cm/s obtained for F-ddI, a PNP resistant analogue of ddI having virtually the same molecular size and lipophilicity as ddI. This indicates that PNP may not play an important role in the low intestinal absorption of ddI. The Pblood for 6-Cl-ddP, (19 +/- 2) x 10(-6) cm/s, was 4.5-fold lower than Plumen, (84 +/- 12) x 10(-6) cm/s, which means that 77 +/- 6% of 6-Cl-ddP was metabolized during its intestinal transport, thus qualitatively accounting for the low oral bioavailability (7%) of 6-Cl-ddP observed in vivo in rats. Extensive intracellular metabolism of 6-Cl-ddP by ADA was confirmed by the high concentrations of ddI found both in the intestinal lumen and blood during 6-Cl-ddP perfusions and by a rate of ddI appearance in blood which was approximately 10-fold higher than ddI controls. Co-perfusion of the potent, hydrophilic ADA inhibitor DCF (Ki = 0. 001-0.05 nM) with 6-Cl-ddP led to only partial inhibition of intestinal ADA, while complete inhibition was obtained using the less potent but more lipophilic inhibitor EHNA (Ki = 1-20 nM). Hence, EHNA may be used to improve intestinal absorption of 6-Cl-ddP in vivo.

Phase structures of binary lipid bilayers as revealed by permeability of small molecules

The effects of changes in bilayer phase structure on the permeability of acetic acid and trimethylacetic acid were studied in large unilamellar vesicles (LUVs) composed of dipalmitoylphosphatidylcholine (DPPC)/cholesterol (CHOL), dihexadecylphosphatidylcholine (DHPC)/CHOL, or DPPC/dimyristoylphosphatidylcholine (DMPC) using an NMR line-broadening method. Phase transitions were induced by changes in temperature and lipid composition (i.e., XCHOL was varied from 0.0 to 0.5 and XDMPC from 0.0 to 1.0). In DPPC/CHOL and DHPC/CHOL bilayers, the addition of CHOL induces only a modest change in the permeability coefficient (Pm) of acetic acid in the gel-phase (Pbeta') but significantly reduces Pm in ordered and disordered liquid-crystalline phases (Lo and Lalpha). Abrupt changes in slopes in semi-logarithmic plots of Pm vs. XCHOL occur at specific values of XCHOL and temperature corresponding to the boundaries between Pbeta' and Lo or between Lalpha and Lo phases. In most respects, phase diagrams generated from the break points in plots of Pm vs. XCHOL obtained at various temperatures in DHPC/CHOL and DPPC/CHOL bilayers closely resemble those constructed previously for DPPC/CHOL bilayers using NMR and DSC methods. Above Tm, the phase diagrams generated from permeability data reveal the presence of both the disordered (Lalpha) and the ordered (Lo) liquid-crystalline phases, as well as the two-phase coexistence region. In DPPC/DMPC bilayers, the addition of DMPC increases Pm dramatically in the gel phase but only slightly in the liquid-crystalline phase. Abrupt changes in slopes in semi-logarithmic plots of Pm vs. XDMPC also occur at specific values of XDMPC and temperature, from which a phase diagram can be constructed which closely resembles diagrams obtained previously by other methods. These correlations indicate that trans-bilayer permeability measurements can be used to construct lipid bilayer phase diagrams. Positive deviations of Pm from predicted values based on the phase lever rule are observed in the two-phase coexistence regions with the degree of the deviation depending on bilayer chemical composition and temperature. These results may reflect a specific contribution of the interfacial region between two phases to higher solute permeability or may be due to the higher lateral compressibility of lipid bilayers in the two-phase coexistence region.

Microscale titrimetric and spectrophotometric methods for determination of ionization constants and partition coefficients of new drug candidates

This study describes the adaptation of conventional titrimetric and spectrophotometric techniques to a microscale for the determination of drug ionization constants (pKa) and partition coefficients (log P). The apparatus for determining pKa and compound purity (or equivalent weight) consists of a three-port conical glass microvial maintained at 25 degrees C, a pH microelectrode, and a microinjection pump equipped with a 10 microL gastight syringe for titrant delivery. Sample mixing and protection from atmospheric CO2, which is particularly important at the microscale, is accomplished using a fine stream of water-saturated N2 bubbles. Simple titrimetric procedures combined with ionic equilibria models which allow the accurate determination of pKa and purity (or equivalent weight) using sample sizes in the microgram range and solution volumes of 10-100 microL were developed and validated using acetic acid and tromethamine. Simultaneous determinations of pKa, purity or equivalent weight, and octanol/water partition coefficient were shown to be possible from a single sample of a test solute by adapting the pH-metric technique to a microscale. Using benzoic acid as a model compound, a pKa of 4.24 and octanol/water partition coefficient of 64 were obtained, in close agreement with the literature values. The principles employed in titrimetric analysis were also applied to demonstrate the spectrophotometric determination of benzoic acid's pKa and partition coefficient using only 6 micrograms of compound. The microscale titration method was then used to determine the two pKa values of an "unknown" diprotic acid containing a carboxyl and an aromatic SH group. The phenyl thiol pKa was confirmed using the microscale spectrophotometric procedure.

Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.