Solubilization and controlled release of a hydrophobic drug using novel micelle-forming ABC triblock copolymers

Amphiphilic ABC triblock copolymers composed of monomethoxy-capped poly(ethylene glycol) (MPEG), poly(2-(dimethylamino)ethyl methacrylate) (DMA), and poly(2-(diethylamino)ethyl methacrylate) (DEA) have been synthesized by atom transfer radical polymerization (ATRP). These copolymers dissolve molecularly in acidic aqueous media at room temperature due to protonation of the tertiary amine groups on the DMA and DEA residues. On adjusting the pH with base, micellization occurred at pH 8, with the water-insoluble, deprotonated DEA block forming the hydrophobic cores and the MPEG and DMA blocks forming the hydrophilic micellar coronas and inner shells, respectively. This pH-induced micellization has been exploited to develop a solvent-free protocol for drug loading. A model hydrophobic drug, dipyridamole (DIP), which dissolves in acid but is insoluble above pH 5.8, was incorporated into the micelles by increasing the pH of an aqueous drug/copolymer mixture to 9. Both the empty and the drug-loaded micelles were characterized by dynamic light scattering and fluorescence studies. The interaction of both pyrene and DIP with the MPEG-DMA-DEA micelles was studied by fluorescence; both compounds had relatively high partition coefficients into the micelles, 4.5 x 10(5) and 1.5 x 10(4), respectively. Intensity-average micelle diameters ranged from 20 to 90 nm, depending on the polymer composition and concentration. Shorter MPEG blocks (Mn = 2000) produced larger micelles than longer MPEG blocks (Mn = 5000) due to the shift in the hydrophilic-hydrophobic balance of the copolymer. Transmission electron microscopy studies of the drug-loaded micelles indicated spherical morphologies and reasonably uniform particle size distributions, which is in marked contrast to the needlelike morphology observed for pure DIP in the absence of the copolymer. Experiments on controlled release demonstrated that DIP-loaded MPEG-DMA-DEA micelles act as a drug carrier, giving slow release to the surrounding solution over a period of days. Rapid release can be triggered by reducing the pH to reverse the micellization.     

Synthesis of biocompatible,stimuli-responsive,physical gels based on ABA triblock copolymers

ABA triblock copolymers [A = 2-(diisopropylamino)ethyl methacrylate), DPA or 2-(diethylamino)ethyl methacrylate), DEA; B = 2-methacryloyloxyethyl phosphorylcholine, MPC] prepared using atom transfer radical polymerization dissolve in acidic solution but form biocompatible free-standing gels at around neutral pH in moderately concentrated aqueous solution (above approximately 10 w/v % copolymer). Proton NMR studies indicate that physical gelation occurs because the deprotonated outer DPA (or DEA) blocks become hydrophobic, which leads to attractive interactions between the chains: addition of acid leads to immediate dissolution of the micellar gel. Release studies using dipyridamole as a model hydrophobic drug indicate that sustained release profiles can be obtained from these gels under physiologically relevant conditions. More concentrated DPA-MPC-DPA gels give slower release profiles, as expected. At lower pH, fast, triggered release can also be achieved, because gel dissolution occurs under these conditions. Furthermore, the nature of the outer block also plays a role; the more hydrophobic DPA-MPC-DPA triblock gels are formed at lower copolymer concentrations and retain the drug longer than the DEA-MPC-DEA triblock gels.     

Fine tuning micellar core-forming block of poly(ethylene glycol)-block-poly(ε-caprolactone) amphiphilic copolymers based on chemical modification for the solubilization and delivery of doxorubicin

This study aimed to optimize poly(ethylene glycol)-b-poly(ε-caprolactone) (PEG-b-PCL)-based amphiphilic block copolymers for achieving a better micellar drug delivery system (DDS) with improved solubilization and delivery of doxorubicin (DOX). First, the Flory-Huggins interaction parameters between DOX and the core-forming segments [i.e., poly(ε-caprolactone) (PCL) and poly[(ε-caprolactone-co-γ-(carbamic acid benzyl ester)-ε-caprolactone] (P(CL-co-CABCL))] was calculated to assess the drug-polymer compatibility. The results indicated a better compatibility between DOX and P(CL-co-CABCL) than that between DOX and PCL, motivating the synthesis of monomethoxy-poly(ethylene glycol)-b-poly[(ε-caprolactone-co-γ-(carbamic acid benzyl ester)-ε-caprolactone] (mPEG-b-P(CL-co-CABCL)) block copolymer. Second, two novel block copolymers of mPEG-b-P(CL-co-CABCL) with different compositions were prepared via ring-opening polymerization of CL and CABCL using mPEG as a macroinitiator and characterized by (1)H NMR, FT-IR, GPC, WAXD, and DSC techniques. It was found that the introduction of CABCL decreased the crystallinity of mPEG-b-PCL copolymer. Micellar formation of the copolymers in aqueous solution was investigated with fluorescence spectroscopy, DLS and TEM. mPEG-b-P(CL-co-CABCL) copolymers had a lower critical micelle concentration (CMC) than mPEG-b-PCL and subsequently led to an improved stability of prepared micelles. Furthermore, both higher loading capacity and slower in vitro release of DOX were observed for micelles of copolymers with increased content of CABCL, attributed to both improved drug-core compatibility and favorable amorphous core structure. Meanwhile, DOX-loaded micelles facilitated better uptake of DOX by HepG2 cells and were mainly retained in the cytosol, whereas free DOX accumulated more in the nuclei. However, possibly because of the slower intracellular release of DOX, DOX-loaded micelles were less potent in inhibiting cell proliferation than free DOX in vitro. Taken together, the introduction of CABCL in the core-forming block of mPEG-b-PCL resulted in micelles with superior properties, which hold great promise for drug delivery applications.     

Micellization phenomena of amphiphilic block copolymers based on methoxy poly(ethylene glycol) and either crystalline or amorphous poly(caprolactone-b-lactide)

This study focuses on the aggregation behavior of the biodegradable amphiphilic block copolymers based on methoxy poly(ethylene glycol) (mPEG) as a hydrophilic block and either crystalline poly(caprolactone-b-l-lactide) (P(CL-LLA)) or amorphous poly(caprolactone-b-D,L-lactide) (P(CL-DLLA)) as a hydrophobic block. These block copolymers have a strong tendency to form micelles in aqueous medium, with very low critical micelle concentrations (CMCs). The CMC of P(CL-LLA)-b-mPEG is higher than that of P(CL-DLLA)-b-mPEG when the mPEG block has the same molecular weight. Furthermore, the partition equilibrium coefficient (K(v)) of pyrene in the micellar solution of P(CL-LLA)-b-mPEG copolymer was lower than that of P(CL-DLLA)-b-mPEG copolymer when the mPEG block was the same length. These differences were believed to be related to the physical state of the core-forming blocks, i.e., the crystalline P(CL-LLA) block and the amorphous P(CL-DLLA) block. The TEM images showed that micelles formed by P(CL-LLA)-b-mPEG assembled in a cylindrical morphology, whereas those formed by P(CL-DLLA)-b-mPEG took a classical spherical shape. In addition, with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses, it is believed that the crystallization tendency of the core-forming blocks is the main factor governing the morphology of micelles in water. A possible mechanism for the cylindrical assembly morphology was discussed.     

Hydrotropic polymeric micelles for enhanced paclitaxel solubility: in vitro and in vivo characterization

The purpose of this investigation was to characterize the in vitro stability and in vivo disposition of paclitaxel in rats after solubilization of paclitaxel into hydrotropic polymeric micelles. The amphiphilic block copolymers consisted of a micellar shell-forming poly(ethylene glycol) (PEG) block and a core-forming poly(2-(4-vinylbenzyloxy)-N,N-diethylnicotinamide) (P(VBODENA)) block. N,N-Diethylnicotinamide (DENA) in the micellar inner core resulted in effective paclitaxel solubilization and stabilization. Solubilization of paclitaxel using polymeric micelles of poly(ethylene glycol)-b-P(D,L-lactide) (PEG-b-PLA) served as a control for the stability study. Up to 37.4 wt % paclitaxel could be loaded in PEG-b-P(VBODENA) micelles, whereas the maximum loading amount for PEG-b-PLA micelles was 27.6 wt %. Thermal analysis showed that paclitaxel in the polymeric micelles existed in the molecularly dispersed amorphous state even at loadings over 30 wt %. Paclitaxel-loaded hydrotropic polymeric micelles retained their stability in water for weeks, whereas paclitaxel-loaded PEG-b-PLA micelles precipitated in a few days. Hydrotropic polymer micelles were more effective than PEG-PLA micelle formulations in inhibiting the proliferation of human cancer cells. Paclitaxel in hydrotropic polymer micelles was administered orally (3.8 mg/kg), intravenously (2.5 mg/kg), or via the portal vein (2.5 mg/kg) to rats. The oral bioavailability was 12.4% of the intravenous administration. Our data suggest that polymeric micelles with a hydrotropic structure are superior as a carrier of paclitaxel due to a high solubilizing capacity combined with long-term stability, which has not been accomplished by other existing polymeric micelle systems.     

Interaction of dipyridamole with micelles of lysophosphatidylcholine and with bovine serum albumin: fluorescence studies.

The interaction of the coronary vasodilator dipyridamole with biological systems, protein and membranes has been studied through optical absorption and fluorescence spectroscopies. Using the analysis of the spectra and fluorescence intensity of dipyridamole (DIP) in solution, the interaction of this compound with the transport protein albumin (BSA) and with a model of cell membranes, namely micelles of lysophosphatidylcholine (L-PC), was investigated. Measurements were performed at pH 5.0 and pH 7.0 where the molecule of DIP is fully protonated and partially protonated, respectively. The quenching of fluorescence with nitroxide-stable radicals 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as well as with acrylamide and iodide allowed the localization of the drug in the polar interface of micelles. Quenching by acrylamide and iodide in L-PC micelles demonstrated the effect of micelle protonation which increased the accessibility of iodide to the chromophore. An effective association constant was obtained both at pH 7.0 (7.5 x 10(3) M-1) and pH 5.0 (2.5 x 10(3) M-1) and a very good agreement with the proposed binding model was observed. The quantum yields of fluorescence data agree very well with the fluorescence lifetimes. The measurement of lifetimes was important to understand the kinetic data obtained from Stern-Volmer plots both of radical, acrylamide and iodide quenching of fluorescence. It was observed that, in the presence of micelles, the kq value increased for TEMPO while decreased for TEMPOL. This result, together with the vanishing solubility of DIP in saturated hydrocarbons and the preferential partition of TEMPO in micelles, suggested the localization of DIP in the polar micellar interface. This is also supported by the enhanced iodide quenching at pH 5.0, constancy of acrylamide quenching in the range of pH 7.0-5.0 and the partition of TEMPO and TEMPOL in SDS micelles. The association constant of DIP to BSA was also estimated both at pH 7.0 (2 x 10(4) M-1) and pH 5.0 (4 x 10(3) M-1). Quenching studies with nitroxide radicals, acrylamide and iodide also suggested the binding of the drug to a hydrophobic region of the protein. At pH 5.0, the protein undergo a conformational change which leads to a loosening of the overall structure so that the accessibility of the nitroxide radicals for DIP is increased at this pH. The differences in kq values at pH 7.0 and pH 5.0 suggested that at pH 7.0 the chromophore is protected in the protein site.(ABSTRACT TRUNCATED AT 400 WORDS)     

Enhanced cardioprotection against ischemia-reperfusion injury with a dipyridamole and low-dose atorvastatin combination

Atorvastatin (ATV) limits infarct size (IS) by activating Akt and ecto-5-nucleotidase, which generates adenosine. Activated Akt and adenosine activate endothelial nitric oxide synthase (eNOS). When given orally, high doses (10 mg/kg) are needed to achieve full protection. We determined whether dipyridamole (DIP), by preventing the reuptake of adenosine, has a synergistic effect with ATV in reducing myocardial IS. In this study, rats received 3-days of the following: water, ATV (2 mg.kg(-1).day(-1)), DIP (6 mg.kg(-1).day(-1)), or ATV + DIP. In addition, rats received 3-days of the following: aminophylline (Ami; 10 mg.kg(-1).day(-1)) or Ami + ATV + DIP. Rats underwent 30 min of myocardial ischemia followed by 4 h of reperfusion (IS protocol), or hearts were explanted for immunoblotting. As a result, IS in the controls was 34.0 +/- 2.8% of the area at risk. ATV (33.1 +/- 2.1%) and DIP (30.5 +/- 1.5%) did not affect IS, whereas ATV + DIP reduced IS (12.2 +/- 0.5%; P < 0.001 vs. each of the other groups). There was no difference in IS between the Ami alone (48.1 +/- 0.8%) and the Ami + ATV + DIP (45.8 +/- 2.9%) group (P = 0.422), suggesting that Ami completely blocked the protective effect. Myocardial adenosine level in the controls was 30.6 +/- 3.6 pg/microl. ATV (51.0 +/- 4.9 pg/microl) and DIP (51.5 +/- 6.8 pg/microl) caused a small increase in adenosine levels, whereas ATV + DIP caused a greater increase in adenosine levels (66.4 +/- 3.1 pg/microl). ATV and DIP alone did not affect myocardial Ser473 phosphorylated-Akt and Ser1177 phosphorylated-eNOS levels, whereas ATV + DIP significantly increased them. In conclusion, low-dose ATV and DIP had synergistic effects in reducing myocardial IS and activation of Akt and eNOS. This combination may have a potential benefit in augmenting the eNOS-mediated pleiotropic effects of statins.     

Novel fast degradable thermosensitive polymeric micelles based on PEG-block-poly(N-(2-hydroxyethyl)methacrylamide-oligolactates)

The aim of this study was to design a thermosensitive polymeric micelle system with a relatively fast degradation time of around 1 day. These micelles are of interest for the (targeted) delivery of biologically active molecules. Therefore, N-(2-hydroxyethyl)methacrylamide-oligolactates (HEMAm-Lac(n)()) were synthesized and used as building blocks for biodegradable (block co) polymers. p(HEMAm-Lac(2)) is a thermosensitive polymer with a cloud point (CP) of 22 degrees C which could be lowered by copolymerization with HEMAm-Lac(4). The block copolymer PEG-b-((80%HEMAm-Lac(2))-(20%HEMAm-Lac(4))) self-assembled into compact spherical micelles with an average size of 80 nm above the CP of the thermosensitive block (6 degrees C). Under physiological conditions (pH 7.4; 37 degrees C), the micelles started to swell after 4 h and were fully destabilized within 8 h due to hydrolysis of the lactate side chains. Rapidly degrading thermosensitive polymeric micelles based on PEG-b-((80%HEMAm-Lac(2))-(20%HEMAm-Lac(4))) have attractive features as a (targeted) drug carrier system for therapeutic applications.     

Folding of apocytochrome c in lipid micelles: formation of alpha-helix precedes membrane insertion.

Apocytochrome c, which in aqueous solution is largely unstructured, acquires a highly alpha-helical structure upon interaction with lipid. The alpha-helix content induced in apocytochrome c depends on the lipid system, and this folding process is driven by both electrostatic and hydrophobic lipid-protein interactions. The folding kinetic mechanism of apocytochrome c induced by zwitterionic micelles of lysophosphatidylcholine (L-PC), predominantly driven by hydrophobic lipid-protein interactions, was investigated by fluorescence stopped-flow measurements of Trp 59 and fluorescein-phosphatidylethanolamine-(FPE) labeled micelles, in combination with stopped-flow far-UV circular dichroism. It was found that formation of the alpha-helical structure of apocytochrome c precedes membrane insertion. The unfolded state in solution (U(W)) binds to the micelle surface in a helical conformation (I(S)) and is followed by insertion into the lipid micelle, i.e., formation of the final helical state H(L). Binding of apocytochrome c to the lipid micelle (U(W) --> I(S)) is concurrent with formation of a large fraction (75-100%, depending on lipid concentration) of the alpha-helical structure of the final lipid-inserted state H(L). The highly helical intermediate I(S) is formed on the time scale of 3-12 ms, depending on lipid concentration, and inserts into the lipid micelle (I(S) --> H(L)) in the time range of approximately 200 ms to >1 s, depending on lipid-to-protein ratio. The final lipid-inserted helical state H(L) in L-PC micelles has an alpha-helix content approximately 65% of that of cytochrome c in solution and has no compact stable tertiary structure as revealed by circular dichroism results.     

Alterations in liver, muscle, and adipose tissue insulin sensitivity in men with HIV infection and dyslipidemia

Dyslipidemia is common in patients with HIV infection. In this study, a two-stage euglycemic hyperinsulinemic clamp, with infusion of stable isotopically labeled tracers, was used to evaluate insulin action in skeletal muscle, liver, and adipose tissue in HIV-infected men with dyslipidemia (HIV-DL; plasma triglyceride >250 mg/dl and HDL <45 mg/dl; n=12), HIV-infected men without dyslipidemia (HIV w/o DL; n=12), and healthy men (n=6). Basal rates of glucose production (glucose R(a)), glucose disposal (glucose R(d)), and lipolysis (palmitate R(a)) were similar between groups. The relative suppression of glucose R(a) (63+/- 4, 77+/- 2, and 78+/- 3%, P=0.008) and palmitate R(a) (49+/-4, 63+/-3, and 68+/-3%, P=0.005) during ow-dose insulin infusion (plasma insulin approximately 30 microU/ml), and the relative stimulation of glucose R(d) (214+/-21, 390+/-25, and 393+/-46%, P=0.001) during high-dose insulin infusion (plasma insulin approximately 75 microU/ml) were lower in HIV-DL than in HIV w/o DL and healthy volunteers, respectively. Suppression of basal glucose R(a) correlated with plasma adiponectin (r=0.44, P=0.02) and inversely with plasma IL-6 (r=-0.49, P<0.001). Stimulation of glucose R(d) correlated directly with adiponectin (r=0.48, P<0.01) and inversely with IL-6 (r=-0.49, P=0.02). We conclude that dyslipidemia in HIV-infected men is indicative of multiorgan insulin resistance, and circulating adipokines may be important in the pathogenesis of impaired insulin action.     

Inhibitory Effect of Dipyridamole and its Derivatives on Lipid Peroxidation in Mitochondria

Dipyridamole (DIP), 2,6-bis(diethanolamino)-4,8-dipiperidino-[5,4-d]pyrimidine, is a coronary vasodilator widely used in clinics. It has also been reported to have coactivator activity for a number of antitumour drugs and antioxidant activity in membrane systems. In recent years we have been studying the spectroscopic properties of this drug and several of its derivatives as well as their interaction with charged micelles and phospholipid monolayers. A strong interaction of DIP and DIP derivatives with these model membrane systems and a dependence of the strength of the interaction upon the chemical structure of the DIP derivative was observed. Here, the antioxidant effect of DIP and the derivatives, RA14, RA47, and RA25, was compared. We observed that although it strongly inhibits the iron-induced lipoperoxidation on mitochondria (IC₅₀ = 1 μM), it shows no protection against an organic oxidant, cumene hydroperoxide. The order of hydrophobicity of the DIP derivatives, DIP > RA14 > RA47 > RA25, correlates very well with both the values of the association constants of these derivatives to micelles, their localization in the micelles, and phospholipid films and their antioxidant effect on mitochondria. So, a very good correlation of the structure of the drug in regarded to the nature of its substituents with the biological activity is observed. Essentially the same result was observed either measuring the lipid peroxidation or the membrane fluidity by ESR, suggesting that the effect of DIP and DIP derivatives is probably associated to their binding to the lipid bilayer and not to interaction with membrane proteins.     

Analysis of the productivity of a continuous algal culture system

We describe a first-principles analysis of a system for the continuous culture of the green alga Scenedesmus obliquus under light-limiting conditions. According to this analysis, the productivity of the algal culture is given by the relation Y = E(m)I(0)AK(1 - e(-alphacl)) - GRcV, where Y = yield (g cells/h), E(m) = 0.20 (the maximum attainable photosynthetic conversion on an energy basis), A = illuminated area (m(2)), K = 0.156[(g cells/h/W), the energy equivalent of the algae], I(0) = light intensity (W/m(2)), alpha = extinction coefficient (L/cm/g),c = cell concentration (g/L), I = light path (cm), R = respiration rate (g carbon/g cells/h), V = culture volume (L), and G = ratio of g cells to g carbon (2.04). This formula is completely determined and has no free adjustable parameters. Using parameter values determined independently, the model accurately predicted the relationship of productivity to cell density in the culture system.     

Effects of hypoxia on the venous circulation in rainbow trout (Oncorhynchus mykiss)

Hypoxia in fish is generally associated with bradycardia while cardiac output (Q) remains unaltered or slightly increased due to a compensatory increase in stroke volume (SV). Rainbow trout (Oncorhynchus mykiss) were subjected to severe (P(W)O2=7.3+/-0.2 kPa) or mild (P(W)O2=11.5+/-0.2 kPa) hypoxia. Central venous pressure (P(ven)), dorsal aortic pressure (P(da)), heart rate (f(H)) and Q, were recorded in vivo. Both levels of hypoxia triggered a significant increase in P(ven). Severe hypoxia was associated with bradycardia and unaltered Q, whereas mild hypoxia was associated with a small but significant increase in Q and no bradycardia. These findings indicate that an increase in P(ven) promotes an increase in SV during hypoxia. Since mild hypoxia increased P(ven), Q and SV without bradycardia or reduced systemic resistance (R(sys)), we hypothesize that an active increase in venous tone serving to mobilize blood to the central venous compartment in order to increase cardiac preload and consequently SV, is an important cardiovascular trait associated with hypoxia. Pharmacological pre-treatment with prazosin (1 mg kg(-1)) did not conclusively reveal the underlying mechanisms to the observed changes in P(ven). This study discusses the influence of venous pooling, reduced R(sys) and altered venous tone on changes in P(ven) observed during hypoxia.     

Multifunctional polymeric micelles with folate-mediated cancer cell targeting and pH-triggered drug releasing properties for active intracellular drug delivery

A new type of multifunctional polymeric micelle drug carrier for active intracellular drug delivery was prepared and characterized in this study. The micelle is a nano-supramolecular assembly with a spherical core-shell structure, and its surface and core were modified with piloting molecules for cancer cells and pH-sensitive drug binding linkers for controlled drug release, respectively. In order to prepare such micelles, self-assembling amphiphilic block copolymers, folate-poly(ethylene glycol)-poly(aspartate hydrazone adriamycin) [Fol-PEG-P(Asp-Hyd-ADR)], were specially designed and synthesized by installing a molecular promoter to enhance intracellular transport, folate (Fol), at the end of the shell-forming PEG chain and conjugating the anticancer drug, adriamycin (ADR), to the side chain of the core-forming PAsp segment through an acid-sensitive hydrazone bond. Because folate-binding proteins (FBP) are selectively overexpressed on the cancer cell membranes, the folate-bound micelles (FMA) can be guided to the cancer cells in the body, and after the micelles enter the cells, hydrazone bonds are cleaved by the intracellular acidic environment (pH 5-6) so that the drug release profile of the micelles is controlled pH-dependently. In this regard, FBP-binding selectivity of the prepared FMA was evaluated by surface plasmon resonance (SPR) measurements. The tetrazolium dye method (MTT assay) using human pharyngeal cancer cells (KB cell) revealed that FMA significantly improved cell growth inhibitory activity in spite of a short exposure time due to the selective and strong interaction between folate molecules and their receptors. Subsequent flow cytometric analysis showed that cellular uptake of FMA significantly increased. Consequently, these findings would provide one of the most effective approaches for cancer treatment using intracellular environment-targeting supramolecular drug carriers.     

Hydroxyzine, promethazine and thioridazine interaction with phospholipid monomolecular layers at the air-water interface

In this work the interaction of Hydroxyzine, Promethazine and Thioridazine with Langmuir films of dipalmitoylphosphatidylcholine (dpPC) and dipalmitoylphosphatidic acid (dpPA), is studied. Temporal variations in lateral surface pressure (pi) were measured at different initial pi (pi(i)), subphase pH and drug-concentration. Drugs with the smallest (PRO) and largest (HYD) molecular size exhibited the lowest adsorption (k(a)) and the highest desorption (k(d)) rate constant values, respectively. The affinity binding constants (K(b)) obtained in monolayers followed the same profile (K(b,PRO) < K(b,HYD) < K(b,THI)) of the egg-PC/water partition coefficients (P) determined in bilayers. The drug concentration required to reach the half-maximal Deltapi at pi(i) = 14 mN/m (K(0.5)), was very sensitive to pH. The maximal increment in pi upon drug incorporation into the monolayer (deltapi(max)) will depend on the phospholipid collapse pressure (pi(c)), the monolayers's compressibility and drug's size, shape and charge. The higher pi(c) of dpPC lead to higher pi(cut-off) values (maximal pi allowing drug penetration), if compared with dpPA. In dpPC and dpPA pi(cut-off) decreased as a function of the molecular size of the uncharged drugs. In dpPA, protonated drugs became electrostatically trapped at the monolayer surface hence drug penetration, monolayer deformation and pi increase were impaired and the correlation between pi(cut-off) and drug molecular size was lost.     

Pharmacokinetics and tissue distribution of novel traditional Chinese medicine-platinum anticancer agents in rats

The pharmacokinetics and tissue distribution profiles of a novel series of traditional Chinese medicine-platinum (TCM-Pt) compounds [Pt(C(8)H(8)O(5))(NH(2)R)(2)]: 1 (where R=H), 3 (R=CH(3)) and 5 (R=C(6)H(10)), were studied in Sprague-Dawley rats following a single bolus intravenous (i.v.) injection. Platinum concentrations in total plasma, plasma ultrafiltrate, urine and tissues were measured by flameless atomic absorption spectroscopy. Pharmacokinetic studies showed that plasma concentrations of total and free platinum for the novel TCM-Pt compounds as well as cisplatin and carboplatin declined in a biexponential manner with a short distribution half-life (t(1/2alpha): 0.12-0.34h). Compared with cisplatin, the novel TCM-Pt compounds had a longer elimination half-life (t(1/2beta)), larger dose normalized area under the curve (AUC/D), larger volume of distribution at steady-state (V(ss)), slower clearance (CL) of free platinum and higher percentage of cumulative urinary excretion (CUE), which can be attributed to their lower chemical reactivities. In tissues, the highest Pt concentrations were found in the kidney, followed by the liver and the lowest in the heart; no Pt was detected in the brain. Twenty-four hours after drug administration, platinum concentrations in tissues were significantly lower for the novel TCM-Pt compounds. These findings suggest that the novel compounds might afford higher clinical efficacy and reduced systemic side effects, when compared with cisplatin.     

Physiological responses to interval training sessions at velocities associated with VO2max

Previous research has indicated that short-duration, high-intensity work intervals performed at velocities associated with maximal oxygen uptake (vVO2max) combined with active recovery intervals may be effective in eliciting improvements in endurance performance. This study was designed to characterize selected physiological responses to short-duration (< or = 60 seconds) interval work performed at velocities corresponding to 100% of vVO2max. Twelve men participated in 3 randomized trials consisting of treadmill running using work (W)/recovery (R) intervals of 15 seconds W/15 seconds R (15/15); 30 seconds W/15 seconds R (30/15); and 60 seconds W/15 seconds R (60/15). Work intervals were performed at 100% of vVO2max, whereas R intervals were performed at 50% of vVO2max. A fourth trial consisting of continuous work (C) at 100% of vVO2max was also performed. All subjects completed the 15/15 and 30/15 trials; however, only 5 of the 12 completed the 60/15 trial. The percentage of VO2max (mean +/- SD) during 15/15 (71.6 +/- 4.2%) was significantly lower (p < or = 0.05) than the percentages during 30/15 (84.6 +/- 4.0%), 60/15 (89.2 +/- 4.2%), or C (87.9 +/- 5.0%). Similar results were found for heart rate and perceived exertion. Blood lactate concentrations following exercise were significantly lower (p < or = 0.05) in 15/15 (7.3 +/- 2.4 mmol x L(-1)) than in the other trials. No significant differences (p > 0.05) existed among 30/15 (11.5 +/- 1.8 mmol x L(-1)), 60/15 (12.5 +/- 1.8 mmol x L(-1)) or C (12.1 +/- 1.8 mmol x L(-1)). High intensity, short-duration 2:1 W/R intervals appear to produce responses that may benefit both aerobic and anaerobic energy system development. A 4:1 W/R ratio may be an upper limit for individuals in the initial phases of interval training.     

Cooperativity of phospholipid reorganization upon interaction of dipyridamole with surface monolayers on water

Results from various surface sensitive characterization techniques suggest a model for the interaction of the piperidinopyrimidine dipyridamole (DIP)--known as a vasodilator and inhibitor of P-glycoprotein associated multidrug resistance of tumor cells--with phospholipid monolayers in which the drug is peripherally associated with the membrane, binding (up to) five phospholipids at a time. These multiple interactions are responsible for a very strong association of the drug with the lipid monolayer even at exceedingly low concentrations (approximately 0.2 mol%). Electrostatic interactions and hydrogen bonding are likely involved in the binding of DIP to DPPC. Cooperative effects among the lipids are invoked to explain the macroscopically measurable changes of lipid monolayer properties even when only one out of 100 DPPC molecules is directly associated with a DIP molecule. A reversal of the observed changes upon drug association with the membrane as the DIP concentration surpasses a threshold concentration (c(crit)approximately 0.5 mol%) may be explained by cooperativity in a different context, the self-aggregation of drug molecules. With its implications for the interaction of DIP with phospholipid films, this work provides a first approach to the explanation of the high sensitivity of cell membranes to piperidinopyrimidine drugs on a molecular level.     

The influence of biomass temperature on biostabilization-biodrying of municipal solid waste

A laboratory study was carried out to obtain data on the influence of biomass temperature on biostabilization-biodrying of municipal solid waste (initial moisture content of 410 g kg wet weight (w.w.)(-1)). Three trials were carried out at three different biomass temperatures, obtained by airflow rate control (A = 70 degrees C, B = 60 degrees C and C = 45 degrees C). Biodegradation and biodrying were inversely correlated: fast biodrying produced low biological stability and vice versa. The product obtained from process A was characterized by the highest degradation coefficient (166 g kg TS0(-1); TS0(-1) = initial total solid content) and lowest water loss (409 g kg W0(-1); W0 = initial water content). Due to the high reduction of easily degradable volatile solid content and preservation of water, process A produced the highest biological stability (dynamic respiration index, DRI = 141 mg O2 kg VS(-1); VS = volatile solids) but the lowest energy content (EC = 10,351 kJ kg w.w.(-1)). Conversely, process C which showed the highest water elimination (667 g kg W0(-1)), and lowest degradation rate (18 g kg TS0(-1)) was optimal for refuse-derived fuel (RDF) production having the highest energy content (EC = 14,056 kJ kg w.w.(-1)). Nevertheless, the low biological stability reached, due to preservation of degradable volatile solids, at the end of the process (DRI = 1055 mg O2 kg VS(-1)), indicated that the RDF should be used immediately, without storage. Trial B showed substantial agreement between low moisture content (losses of 665 g kg W0(-1)), high energy content (EC = 13,558 kJ kg w.w.(-1)) and good biological stability (DRI = 166 mg O2 kg VS(-1)), so that, in this case, the product could be used immediately for RDF or stored with minimum pollutant impact (odors, leaches and biogas production).     

Intracellular singlet oxygen generation by phagocytosing neutrophils in response to particles coated with a chemical trap.

To determine if singlet oxygen (O2(1 delta g)) is produced by neutrophils (PMNs) during the process of phagocytosis, glass beads were coated with a specific chemical trap for O2(1 delta g), 9,10-diphenylanthracene (DPA). Singlet oxygen, but not other reactive oxygen species, reacts rapidly with DPA at a rate of kr = 1.3 x 10(6) M-1 s-1 to form a stable product, DPA-endoperoxide (Corey, E. J., and Taylor, W. C. (1964) J. Am. Chem. Soc. 86, 3881-3882; Wasserman, H. H., Scheffer, J. R., and Cooper, J. L. (1972) J. Am. Chem. Soc. 94, 4991-4996; Turro, N. J., Chow, M.-F., and Rigaudy, J. (1981) J. Am. Chem. Soc. 103, 7218-7224). The production of DPA-endoperoxide was determined by ultraviolet spectroscopy as a decrease in DPA absorbance at 355 nm. The absorbance of DPA was normalized to the absorbance of perylene, which was included in the coating on the beads as a nonreactive, internal standard. In the present study, DPA- and perylene-coated beads were initially allowed to adhere to fibronectin-coated coverslips. PMNs were then added to the bead-coated coverslips and allowed to adhere and phagocytose the beads for 1 h at 37 degrees C. In some experiments, 4B-phorbol-12-myristate-13-acetate (PMA) (1 ng/2.5 x 10(7) cells/ml), a known activator of the PMN NADPH-oxidase, was added as a co-stimulant. The amount of O2(1 delta g) produced by phagocytically stimulated PMNs was calculated to be 11.3 +/- 4.9 nmol of O2(1 delta g)/1.25 x 10(6) cells. Low dose PMA co-stimulation increased the production of O2(1 delta g) to 14.1 +/- 4.1 nmol/1.25 x 10(6) cells. Averaged together these amounts represent approximately 19 +/- 5.0% of the total oxygen consumed by PMNs in response to DPA- and perylene-coated beads. The specificity of the DPA reaction with O2(1 delta g) was confirmed by warming to 120 degrees C, which releases O2(1 delta g) from the DPA-endoperoxide, regenerating the parent DPA compound (Wasserman et al., 1972; Turro et al., 1981) and the absorbance at 355 nm. In addition, beta-carotene, an avid quencher of O2(1 delta g), was included in the coating of some bead preparations; assays in which these beads were used showed no change in the absorbance at 355 nm. Singlet oxygen production by myeloperoxidase was also measured using the coated bead assay and the results suggest that this is a major pathway by which singlet oxygen is generated in phagocytically stimulated PMNs.(ABSTRACT TRUNCATED AT 400 WORDS)