An extended pharmacokinetic/pharmacodynamic model describing quantitatively the influence of plasma protein binding, tissue binding, and receptor binding on the potency and time course of action of drugs

An extended pharmacokinetic/pharmacodynamic (PK/PD) model is presented, in which the effect of binding of the drug to plasma proteins and to tissue binding sites in a peripheral compartment, and nonspecific and receptor binding in the effect compartment are taken into account. It represents an extension of the classical Sheiner model, and the model proposed by Donati and Meistelman. The present model is characterized by the following parameters: Kue (exit rate constant of unbound drug from the effect compartment), Pue (ratio of the unbound clearances to and from the effect compartment), fue (fraction of drug in effect compartment that is not bound to nonspecific binding sites), Kd (equilibrium dissociation constant of drug-receptor binding), and Rtot (concentration of receptor binding sites in effect compartment). The rate of association and dissociation of the drug-receptor complex can be incorporated in the model. The influence of the pharmacokinetic parameters (V1, V2, fu, fu2, CLu10, CLu20, CLu12, CLu21) and the PK/PD model parameters (kue, Pue, fue, Kd, Rtot) on various dynamic parameters is analyzed. These include potency (single dose needed to produce 90% effect, ED90), constant infusion dosing rate needed to maintain a constant effect of 90%, time to maximum effect (onset time), and duration to 90% recovery. The neuromuscular blocking agent vecuronium is used as an example. It is shown that both potency and time course of action are strongly dependent on the ratio V1/fu, CLu10, kue, Pue (at equipotent doses the time course is not affected by Pue), fue, Kd, and Rtot (only if Rtot is high), whereas they are less affected by the ratio V2/fu2, CLu20, CLu12, and CLu21. In general, the model parameters affect the ED90 and the time course of action in the same direction, e.g., an increase of V1 results in an increase of ED90 and an increase of onset time and duration. However, the unbound clearance CLu10, the intercompartmental unbound clearance CLu12 and the receptor affinity Kd have an opposite effect on ED90 and the time course parameters, e.g., an increase of CLu10 results in an increase of ED90 and a decrease of onset time and duration. This effect may be responsible for the inverse relationship between onset time and potency of neuromuscular blocking drugs observed in animal experiments and clinical studies. We demonstrate that PK/PD analysis using the traditional effect compartment model (Sheiner model) results in an apparent value of keo, which is a function of kue, fue, Kd, Rtot, as well as the unbound drug concentration in the effect compartment Cue. On the other hand, the model proposed by Donati and Meistelman gives correct values of keo (equal to the product fue.kue), but the receptor affinity Kd and the receptor density Rtot obtained by this method are apparent values, which depend on fu, fue, and Pue.     

Local Strain Measurement within Tendon

Abstract:  Tendon is a dense connective tissue, responsible for transmitting the forces generated by muscles to the skeleton. It is composed of a hierarchical arrangement of crimped collagen fibres, interspersed with proteoglycan matrix and cells, known as tenocytes. During physiological loading, tendons are subjected to strains in the region of 5–6%, which result in the straightening and realignment of the collagen fibres, generating variable local strain fields within the tendon. This study demonstrates a technique for analysing local strains within viable tendon explants, during both loading and unloading of the tissue. Samples were strained in a custom-designed rig, allowing real-time visualisation of cell nuclei, used as local discrete markers, on a confocal microscope. Results indicated that local strains within the fascicle are smaller than the applied strains, never exceeding 1.2%, even at 8% gross applied strain. By contrast, the sliding of adjacent collagen units was recorded at each strain increment in this study, reaching a mean maximum of 3.9% of the applied displacement. Loading–unloading studies indicated that sliding behaviour is reversible up to strains of 5%, and provides the major extension mechanism within the rat-tail tendon. This technique can be extended to further analyse shearing behaviour within the matrix.     

Superconductivity and magnetism in niobium doped YBa2Cu3O7 Related high Tc ceramics

Magnetic characterization has been performed on the members of the cuprateniobate RBa₂Cu₂NbO₈ (R = Pr, Nd, and La) series and R_1.5Ce_0.5Sr₂Cu₂NbO₁₀ (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K. The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.     

Childhood sexual abuse and current suicidality in college women and men

The effects of retinoic acid (RA) on osteoblastic differentiation and activity were studied in fetal rat calvaria cells cultured for up to 24 days. Fetal bovine serum used for the experiments was treated with an anion-exchange resin to remove endogenous RA. The depletion of RA in the treated serum was confirmed by high-performance liquid chromatography and tritiated RA tracing. Under the culture conditions employed, the continuous presence of RA for 14 days at 10(-9) mol/l or higher decreased both alkaline phosphatase (ALP) activity on day 12 and the number of bone nodules on day 14 in a dose-dependent manner. Short-term (24 h) exposure to RA at 10(-8) mol/l, which is a physiological concentration, decreased and increased the levels of ALP and osteopontin mRNA on day 6, respectively. Retinoic acid at 10(-8) mol/l also increased the level of osteocalcin mRNA on day 12. However, these effects were not obvious at later stages (days 18 and 24). At a high concentration (10(-6) mol/l), RA increased the level of osteopontin mRNA on day 6 and decreased the levels of ALP and osteocalcin mRNA irrespective of culture period. These results suggest that, at physiological concentrations, RA suppresses the differentiation of osteoprogenitor cells and regulates osteoblastic functions.     

Dynamic thermographic imaging for estimation of regional perfusion in the tuberculin reaction in healthy adults

A sensitive method for measurement of the volume of blood flow through the skin, based on the kinetics of reheating after localised cooling, is described in this paper. This method has been used to study the tuberculin reaction as a model of cutaneous delayed-type hypersensitivity (DHS) in man. Over the positive reaction there is accelerated reheating similar in kinetics and extent to that seen after maximal hyperaemia induced by intradermal injection of histamine or prostaglandin E2. The earlier phase of reheating (10-100 s) is more dependent on blood flow, whereas the later phase (100-300 s) is apparently more dependent on non-perfusion heat exchange mechanisms, including conduction. The reheat kinetic method is largely dependent on blood flow in the deep dermal vessels (diameter > 50 microns), whereas the alternative approach of measurement of the velocity of flow of erythrocytes in the microcirculation by laser Doppler (LD) flowmetry gives results biased towards the most superficial dermal circulation. Previous studies with LD flowmetry have shown that the blood velocity is greatest at the centre of weak and strong reactions, while in the most intense reactions it is raised at the centre but maximal at the periphery (central relative slowing, CRS) raising the possibility of central ischaemia. The reheat kinetics approach has now indicated that the deep dermal circulation is not impaired in CRS reactions. It is concluded that there must be partial obstruction of the parts of the microcirculation communicating between the deep and superficial dermal plexuses, presumably from the accumulation of exudate oedema in the most intense tuberculin reactions.     

A unique property of a plasma proteoglycan, the C1q inhibitor. An anticoagulant state resulting from its binding to fibrinogen

The C1q inhibitor, C1qI, an approximately 30-kD circulating chondroitin-4 sulfate proteoglycan, displayed concentration-dependent prolongation of plasma and fibrinogen solution clotting times. Under factor XIIIa catalyzed cross-linking conditions and maximum C1qI concentrations, minor amounts of clot formed displaying complete gamma-gamma dimer formation but virtually no alpha-polymer formation. The anticoagulant effect was undiminished by its binding to C1q, by increased ionic strength, and by CaCl2, but was abolished by incubation of C1qI with chondroitinase ABC. 125I-labeled C1qI bound to immobilized fibrinogen, fibrin monomer, fibrinogen plasmic fragments D1 and E, and fibrin polymers. Occupancy on the E domain required uncleaved fibrinopeptides together with another structure(s), and it did not decrease binding of thrombin to fibrinogen. Occupancy on the D domain did not decrease the fibrinogen binding to fibrin monomer. We conclude that the E domain occupancy impaired fibrinopeptide cleavage, and occupancy on the D domain impaired polymerization, both steric hindrance effects. C1qI binding to fibrinogen explains at least in part the well-known fibrin(ogen) presence in immune complex-related lesions, and the fibrinogen presence in vascular basement membranes and atheromata. We postulate that fibrin binding by resident basement membrane proteoglycans provides dense anchoring of thrombus, substantially enhancing its hemostatic function.     

Lysis of human monocytic leukemia cells by extracellular adenosine triphosphate: mechanism and characterization of the adenosine triphosphate receptor

The present study shows that extracellular adenosine triphosphate (ATP) has the capacity to mediate dose-dependent lysis of the monocytic leukemia cell line THP-1. The lysis, assessed by 51Cr release, was found to be selective for ATP, because adenosine diphosphate (ADP) or other nucleotides were less effective in their ability to lyse the cells. The amount of 51Cr released was particularly enhanced by the stimulation of the cells with 1,000 U/mL of interferon gamma (IFN-gamma) for 3 days, and the sensitivity was time and dose dependent. Analysis of the mechanism of lysis indicated that the fully ionized form, ATP4-, mediated the lysis, because the addition of cation chelators or the absence of the divalent cations, Ca2+ and Mg2+, in the culture medium of a 6-hour 51Cr release assay increased the percent specific lysis. Therefore, the ATP receptors on THP-1 cells were classified as P2Z purinoceptors. Moreover, it is shown here that the Ca2+/calmodulin complex plays a role in the regulation of the lysis by extracellular ATP of THP-1 cells, because antagonists of this complex, such as trifluoperazine or KN-62, were found to inhibit the ATP-mediated cell lysis.     

Preexercise meal composition alters plasma large neutral amino acid responses during exercise and recovery

This study was designed to determine metabolic and physical performance responses to ingestion of pre-exercise meals with different macronutrient and fiber profiles. Twelve physically active subjects (6 males and 6 females) were used to investigate the metabolic and physical performance consequences of consuming pre-exercise meals consisting of oat, corn, or wheat cereals. A fasting trial served as the control, and all subjects received each treatment in a Latin-square design. Blood samples were drawn before and 85 min after meal ingestion, during 90 min of cycling exercise (60% VO2peak), after a 6.4 km performance ride, and during 60 min of recovery. Expired air samples were collected to determine nutrient utilization. Resting carbohydrate oxidation rates and plasma insulin concentrations after oat ingestion were less than after wheat, and corn and wheat ingestion, respectively (P < 0.05). During exercise, the change in plasma glucose from pre-exercise was greater after consuming wheat and corn compared with oat (P < 0.05), and it was inversely related to pre-exercise plasma insulin concentration (r = -0.55, P = 0.0001). Plasma free fatty acid concentrations were inversely related to plasma lactate concentrations (r = -0.58, P = 0.0001). Free fatty acid concentrations and fat oxidation were greater in fasting trials than all others, but performance ride times did not differ among treatments. Plasma branched-chain amino acid concentrations resembled their respective meal profiles throughout exercise, the performance ride, and recovery. These results indicate that pre-exercise meal composition can influence glucose homeostasis during early exercise and plasma branched-chain amino acid concentrations over a substantial range of metabolic demands.