Use of in vitro critical inhibitory concentration, a novel approach to predict in vivo synergistic bactericidal effect of combined amikacin and piperacillin against pseudomonas aeruginosa in a systemic rat infection model

PURPOSE: This study was undertaken to explore the use of in vitro critical inhibitory concentration (CIC) as a surrogate marker relating the pharmacokinetic (PK) parameters to in vivo bactericidal synergistic effect [pharmacodynamic (PD)] of amikacin + piperacillin combination against Pseudomonas aeruginosa in a systemic rat infection model. METHODS: The in vitro antibacterial activities of amikacin and piperacillin, alone and in combinations at various ratios of the concentrations, were tested against a standard [5 x 10(5) colony-forming units (CFU)/ml] and a large (1.5 x 10(8) CFU/ml) inoculum of P. aeruginosa ATCC 9027 using a modified survival-time method. The CIC of each individual antibiotic for the different combinations was determined using a cup-plate method. In vivo studies were performed on Sprague-Dawley rats using a systemic model of infection with P. aeruginosa ATCC 9027. PK profiles and in vivo killing effects of the combination at different dosing ratios were studied. RESULTS: An inoculum effect was observed with the antibiotics studied. Synergy was seen against both the inocula at the following concentration ratios: 70% C(ami) + 30% C(pip) and 75% C(ami) + 25% C(pip), where C(ami) and C(pip) are the concentrations of amikacin and piperacillin to produce a 1000-fold decrease in bacterial population over 5 h, respectively. The CIC values determined corroborated with the order of in vitro bacterial killing observed for the antibiotic combinations. The dosing ratio of 12.6 mg/kg amikacin + 36 mg/kg piperacillin (a 70:30 ratio of the individual doses) exhibited the greatest killing in vivo when compared to the other ratios. The PK-PD relationships were described by simple, linear regression equations using the area under the in vivo killing curve as a PD marker and the AUCIC(ami)/CIC(ami) + AUCIC(pip)/CIC(pip), AUC(ami)/CIC(ami) + AUC(pip)/CIC(pip), C(max,ami)/CIC(ami) + C(max,pip)/CIC(pip), and AUCIC(ami)/MIC(ami) + AUCIC(pip)/MIC(pip) as PK markers for the amikacin + piperacillin combination. CONCLUSION: The combination of amikacin and piperacillin exhibited synergistic killing effect on P. aeruginosa that could be modeled using CIC as a surrogate marker relating the PK parameters to in vivo bactericidal effect.

Determination of thalidomide by high performance liquid chromatography: plasma pharmacokinetic studies in the rat

A sensitive and simple high performance liquid chromatography (HPLC) method was developed and validated for the determination of thalidomide in rat plasma. Chromatography was accomplished with a reversed-phase Hypersil C18 column. Mobile phase consisted of acetonitrile-10 mM ammonium acetate buffer (pH 5.50) (28:72, v/v), at a flow rate of 0.8 ml/min. Thalidomide was monitored by ultraviolet detector at 220 nm and it gave a linear response as a function of concentration over 0.02–50 μM. The limit of quantitation in rat plasma was 0.50 ng (0.02 μM plasma concentration) with an aliquot of 20 μl. Results from a 3-day validation study indicated that this method allows for simple and rapid quantitation of thalidomide with excellent accuracy and reliability. Using this validated assay, the effect of coadministered irinotecan (CPT-11) on the plasma pharmacokinetics of thalidomide in rats was determined. Coadministration of CPT-11 (intravenously, 60 mg/kg) increased the maximum plasma concentration (C_max) and area under the plasma concentration–time curve (AUC_{0–10 h}) of thalidomide by 32.29 and 11.66%, respectively, as compared to the control, but none of the effect of CPT-11 was of statistical significance (P > 0.05). Concomitant CPT-11 also caused a 10.04% decrease in plasma clearance (CL) and 14.51% decrease in volume of distribution (V_d) (P > 0.05). These results suggest that coadministered CPT-11 did not significantly alter the plasma pharmacokinetics of thalidomide in rats. Further studies are warranted to explore the pharmacokinetic and pharmacodynamic interactions between CPT-11 and thalidomide.

High strain mechanical loading rapidly induces tendon apoptosis : an ex vivo rat tibialis anterior model

Background: The role of apoptosis, or programmed cell death, has only recently been explored in tendon.

Objective: To investigate the development of apoptosis after high strain loading of rat tendon.

Methods: The right tibialis anterior tendons of three rats were prepared for mechanical loading, and left tendons were prepared identically as non-loaded controls. Tendon was loaded with 20% strain for six hours using a 1 Hz longitudinal sine wave signal. The following were used to assess apoptosis: (a) a monoclonal mouse antibody (F7-26) to label single stranded DNA breaks; (b) a rabbit polyclonal antibody that specifically recognises the cleaved form of caspase-3.

Results: Light microscopy confirmed that the high strain protocol induced a stretch overload injury. Control tendons showed little or no staining with the F7-26 antibody, but the loaded tendons displayed numerous apoptotic cells. The percentage of apoptotic cells (20%) in the loaded tendon was significantly greater than in the control tendon (1%) (p = 0.000). The labelled cells colocalised with abnormal nuclear morphology, including nuclear fragmentation. The staining against cleaved caspase-3 was positive in loaded tendons only, and localised both to nucleus and cytoplasm.

Conclusion: This experiment extends knowledge of human tendon apoptosis by showing that apoptosis can occur in response to short term, high strain mechanical loading. This is the first report of mechanical loading of intact tendon causing excessive apoptosis.

Effect of dietary fatty acids on the intestinal permeability of marker drug compounds in excised rat jejunum

The aim of this study was to explore the effects of diets containing saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and ω-3 and ω-6 polyunsaturated fatty acids (ω-3 and ω-6 PUFA, respectively) on the passive and active transport properties of rat jejunum using marker compounds. Rats were fed diets supplemented with 18.4% (w/w) lipid (4 groups) or standard rat chow (1 group) for a period of 30 days. At the end of the dietary period, mucosal scrapings were taken for the determination of membrane phospholipids, and the apparent jejunal permeability of radiolabelled marker compounds was determined using modified Ussing chambers. Changes in the phospholipid content of the brush border membrane reflected the different lipid content of the diets. The passive paracellular permeability of mannitol was not significantly affected by the fatty acid composition of the diet, although there was a trend toward decreased mannitol permeability in the rats fed both the ω-3 and ω-6 PUFA diets. In comparison, the transcellular diffusion of diazepam was reduced by 20% (P < 0.05) in rats fed diets supplemented with ω-3 and ω-6 PUFA. In the lipid-fed rats, the serosal to mucosal flux of digoxin, an intestinal P-glycoprotein substrate, was reduced by 20% (P < 0.05) relative to the chow-fed group, however there were no significant differences between the different lipid groups. The active absorption of D-glucose via the Na+-dependent transport pathway was highest in the SFA, MUFA and PUFA ω-3 dietary groups, intermediate in the low-fat chow group and lowest in the PUFA ω-6 group, and was positively correlated with short-circuit current. These studies indicate that dietary fatty acid changes can result in moderate changes to the active and passive transport properties of excised rat jejunum.

Management of power line easement vegetation for small mammal conservation in Australia : a case study of the broad-toothed rat (Mastacomys fuscus)

Within Australia, very little attention has been given to the potential biodiversity benefits of power line easements, if ecologically sensitive management regimes are developed. This study examined the potential power line easements may have for the conservation of small mammals, and in particular the near threatened, Broad-toothed Rat Mastacomys fuscus, in Australia. Easement vegetation was found to support a diverse small mammal community, including M. fuscus if the vegetation was allowed to develop some structural complexity. M. fuscus was one of the first species to recolonize the easement habitat, provided that the areas had regenerated to a sufficient level. Results suggests; however, that the current management technique used, where the entire easement is managed at one time via mass slashing, on short rotation times, is most likely limiting M. fuscus to low abundances, and causing isolation of the current M. fuscus populations. To ensure that power line easements supply functional, usable habitat for small mammals and other species and to minimize their potential to fragment small mammal populations, it is recommended that current management techniques be reassessed. In an effort to develop more appropriate management regimes, it was recommended that rotation times be increased between management, that mass slashing of the easement at one time be reassessed, especially in naturally low growing areas and that rotational type slashing be implemented. Other techniques such as spot spraying, may be all that is needed within some areas to control emergent saplings. This study highlights that potential biodiversity values do exist for Australian power line easements, if some changes occur to the current management practices.

Characterization of the drug binding specificity of rat liver fatty acid binding protein

Liver-fatty acid binding protein (L-FABP) is found in high levels in enterocytes and is involved in the cytosolic solubilization of fatty acids during fat absorption. In the current studies, the interaction of L-FABP with a range of lipophilic drugs has been evaluated to explore the potential for L-FABP to provide an analogous function during the absorption of lipophilic drugs. Binding affinity for L-FABP was assessed by displacement of a fluorescent marker, 1-anilinonaphthalene-8-sulfonic acid (ANS), and the binding site location was determined via nuclear magnetic resonance chemical shift perturbation studies. It was found that the majority of drugs bound to L-FABP at two sites, with the internal site generally having a higher affinity for the compounds tested. Furthermore, in contrast to the interaction of L-FABP with fatty acids, it was demonstrated that a terminal carboxylate is not required for specific binding of lipophilic drugs at the internal site of L-FABP.

Characterization of lipophilic drug binding to rat intestinal fatty acid binding protein

Intestinal fatty acid binding protein (I-FABP) is present at high levels in the absorptive cells of the intestine (enterocytes) where it plays a role in the intracellular solubilization of fatty acids (FA). However, I-FABP has also been shown to bind to a range of non-FA ligands, including some lipophilic drug molecules, albeit with generally lower affinity than FA. The significance of these lower affinity interactions with exogenous compounds is not known. In this manuscript, we describe further characterization of drug-rat I-FABP binding interactions using a thermal-shift assay. A structural explanation of the observed affinity of rat I-FABP for different drugs based on spectroscopic data and modeling experiments is presented. In addition, immunocytochemistry has been used to probe the expression of I-FABP in a cell culture model reflective of the absorptive cells of the small intestine. Taken together, these data suggest a possible role for I-FABP in the disposition of some lipophilic drugs within the enterocyte.

Probing the fibrate binding specificity of rat liver fatty acid binding protein

Liver-fatty acid binding protein (L-FABP) is found in high levels in enterocytes and is involved in cytosolic solubilization of fatty acids. In addition, L-FABP has been shown to bind endogenous and exogenous lipophilic compounds, suggesting that it may also play a role in modulating their absorption and disposition within enterocytes. Previously, we have described binding of L-FABP to a range of drugs, including a series of fibrates. In the present study, we have generated structural models of L-FABP-fibrate complexes and undertaken thermodynamic analysis of the binding of fibrates containing either a carboxylic acid or ester functionality. Analysis of the current data reveals that both the location and the energetics of binding are different for fibrates that contain a carboxylate compared to those that do not. As such, the data presented in this study suggest potential mechanisms that underpin molecular recognition and dictate specificity in the interaction between fibrates and L-FABP.

An improved method for the purification of rat liver-type fatty acid binding protein from Escherichia coli

We have developed expedient and reliable methods to isolate cyclosporin synthetase for in vitro biosynthesis of cyclosporins. We have examined enzyme purification strategies suited to large-scale processing and present a chromatographic sequence that serves as a pilot model for industrial scale preparation of cyclosporin synthetase from cyclosporin producing fungi. A chromatographic sequence consisting of ammonium sulfate precipitation → gel filtration → hydrophobic interaction chromatography → anion exchange chromatography, yielded an electrophoretically homogeneous cyclosporin synthetase preparation (Coomassie G-250 brilliant blue staining). Furthermore, a native polyacrylamide gel electrophoresis system was developed for the isolation of active cyclosporin synthetase enzyme from crude extracts of cyclosporin producing fungi. The environmental factors affecting enzyme stability and the continuity of the in vitro cyclosporin biosynthetic reaction-temperature, pH, and substrate depletion were assessed and manageable conditions have been defined for sustainable cyclosporin biosynthesis with enzyme isolates. Cyclosporin synthetase exhibited an optimal temperature range of 24–29 °C and a pH optimum of 7.6. The native enzyme displayed a pI of 5.7, as determined by isoelectric focusing. The industrial implementation of an in vitro biosynthetic approach could potentially prove useful for the production of important therapeutic cyclosporins which occur as only minor fermentation by-products.

Uteroplacental insufficiency and reducing litter size alters skeletal muscle mitochondrial biogenesis in a sex-specific manner in the adult rat

Uteroplacental insufficiency has been shown to impair insulin action and glucose homeostasis in adult offspring and may act in part via altered mitochondrial biogenesis and lipid balance in skeletal muscle. Bilateral uterine vessel ligation to induce uteroplacental insufficiency in offspring (Restricted) or sham surgery was performed on day 18 of gestation in rats. To match the litter size of Restricted offspring, a separate cohort of sham litters had litter size reduced to five at birth (Reduced Litter), which also restricted postnatal growth. Remaining litters from sham mothers were unaltered (Control). Offspring were studied at 6 mo of age. In males, both Restricted and Reduced Litter offspring had reduced gastrocnemius PPAR γ coactivator-1α (PGC-1 α) mRNA and protein, and mitochondrial transcription factor A (mtTFA) and cytochrome oxidase (COX) III mRNA (P < 0.05), whereas only Restricted had reduced skeletal muscle COX IV mRNA and protein and glycogen (P < 0.05), despite unaltered glucose tolerance, homeostasis model assessment (HOMA) and intramuscular triglycerides. In females, only gastrocnemius mtTFA mRNA was lower in Reduced Litter offspring (P < 0.05). Furthermore, glucose tolerance was not altered in any female offspring, although HOMA and intramuscular triglycerides increased in Restricted offspring (P < 0.05). It is concluded that restriction of growth due to uteroplacental insufficiency alters skeletal muscle mitochondrial biogenesis and metabolic characteristics, such as glycogen and lipid levels, in a sex-specific manner in the adult rat in the absence of impaired glucose tolerance. Furthermore, an adverse postnatal environment induced by reducing litter size also restricts growth and alters skeletal muscle mitochondrial biogenesis and metabolic characteristics in the adult rat.

Effect of nitric oxide synthase inhibition on mitochondrial biogenesis in rat skeletal muscle

The purpose of this study was to determine whether nitric oxide synthase (NOS) inhibition decreased basal and exercise-induced skeletal muscle mitochondrial biogenesis. Male Sprague-Dawley rats were assigned to one of four treatment groups: NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, ingested for 2 days in drinking water, 1 mg/ml) followed by acute exercise, no L-NAME ingestion and acute exercise, rest plus L-NAME, and rest without L-NAME. The exercised rats ran on a treadmill for 53 ± 2 min and were then killed 4 h later. NOS inhibition significantly (P < 0.05; main effect) decreased basal peroxisome proliferator-activated receptor-{gamma} coactivator 1beta (PGC-1beta) mRNA levels and tended (P = 0.08) to decrease mtTFA mRNA levels in the soleus, but not the extensor digitorum longus (EDL) muscle. This coincided with significantly reduced basal levels of cytochrome c oxidase (COX) I and COX IV mRNA, COX IV protein and COX enzyme activity following NOS inhibition in the soleus, but not the EDL muscle. NOS inhibition had no effect on citrate synthase or beta-hydroxyacyl CoA dehydrogenase activity, or cytochrome c protein abundance in the soleus or EDL. NOS inhibition did not reduce the exercise-induced increase in peroxisome proliferator-activated receptor-{gamma} coactivator 1{alpha} (PGC-1{alpha}) mRNA in the soleus or EDL. In conclusion, inhibition of NOS appears to decrease some aspects of the mitochondrial respiratory chain in the soleus under basal conditions, but does not attenuate exercise-induced mitochondrial biogenesis in the soleus or in the EDL.