A re-evaluation of the HSA-piroxicam interaction

Piroxicam binding to HSA was studied using equilibrium dialysis and fluorescence methods. It was shown that this drug, like its analogs isoxicam and tenoxicam, binds to the apazone locus (site I area) and to a lesser extent to the diazepam site (site II). The piroxicam binding to HSA can be modulated by various specific ligands--apazone, warfarin, diazepam, ibuprofen--and these drug interactions have to be considered not only as potential displacement from the HSA binding sites but also in terms of induced allosteric effects.

Blood distribution of tenoxicam in humans: a particular HSA drug interaction

Blood binding of tenoxicam was studied in vitro by equilibrium dialysis. Isolated human plasma proteins and blood cells were checked, and the distribution of the bound form was then calculated. The results showed that tenoxicam is mainly bound to HSA and that binding percentages are not different when measured in plasma (98.4%) and in an HSA solution at physiological concentration (704 microM, 98.15%). In these conditions, within the range of 1-150 microM, the tenoxicam binding percentage remained constant, evidence of a nonsaturable process. When a lower HSA concentration (10 microM) was used, the binding parameters of the tenoxicam interaction were calculated by using the same equilibrium dialysis data, by 3 methods of analysis- a stoichiometric method and site-oriented methods, fixing or not the number of HSA binding sites (n) as integer values. The best fit was observed with the first method, suggesting that two main interactions occurred. The site-oriented method gave lesser fits, the better being observed when n was not fixed. Its value, 1.77, suggest the possibility of two binding sites, one of them not preformed. The effects of known markers of site I, warfarin and apazone, of site II, diazepam and ibuprofen and of palmitic acid showed that tenoxicam is bound simultaneously to both sites I and II. The binding capacity of site I for tenoxicam is enhanced by diazepam: as this compound alone is bound to site II, this result suggests that the two HSA binding sites are not independent.

Evidence for isoxicam binding to site I as a primary site and to site II as a secondary site of human serum albumin

Isoxicam binding to HSA was studied using equilibrium dialysis and fluorescence methods. It was shown that this drug binds to or near site I (warfarin or azapropazone site) and to site II (the diazepam site) as a secondary site, although it is generally considered that their respective drug structural requirements are often exclusive. The binding parameters were calculated with different mathematical models; a site oriented model with or without fixing the number of binding sites as integer values and a stoichiometric model. The relevant results are in good agreement under the selected experimental conditions. The stoichiometric method indicates that no positive cooperativity occurred during the binding process but other interactions between the two sites cannot be excluded.

Prolonged exposure of neutrophils to saline or bronchoalveolar lavage fluid does not alter superoxide anion generation

The role played by neutrophils (PMNs) in the genesis of lung injury in diverse clinical situations, such as bronchial asthma, idiopathic pulmonary fibrosis, and the adult respiratory distress syndrome, is an area of intensive investigation. Functional studies of PMNs, particularly those obtained from the alveoli by bronchoalveolar lavage, should shed light on their contribution to lung injury. However, it has not been demonstrated whether procedures used to harvest cells from the lung (bronchoalveolar lavage), particularly the potentially prolonged exposure to saline, commonly used to perform lavage, and other components of lavage fluid, can alter the functional characteristics of PMNs. In this report we demonstrate that a 2- to 3-hour exposure of neutrophils to saline from both humans and sheep in vitro does not alter the functional characteristics of PMNs as determined by superoxide anion generation after activation with phorbol myristate acetate (PMA; 6.96 +/- 0.44 vs. 7.60 +/- 0.32 nmol O2-/250,000 PMNs for control and saline-treated human cells, respectively, after a 45-min incubation with 10(-7) M PMA, and 4.73 +/- 0.30 vs. 4.50 +/- 0.42 nmol O2-/250,000 PMNs for control and saline-treated sheep cells). In a second series of experiments, we studied the effect of exposure of human PMNs to bronchoalveolar lavage fluid supernatants obtained from normal volunteers on superoxide anion generation by neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of enucleation-induced metastasis in intraocular melanoma by periorbital irradiation

The optimum treatment of malignant choroidal melanoma remains controversial. Some authors have hypothesized that enucleation promotes metastatic disease. This hypothesis has been demonstrated in the B16F10 melanoma mouse model. The present study used this model to examine the effect of external beam irradiation as a means of reducing metastases induced by enucleation. The results show a dose-dependent reduction in the DNA synthesis of irradiated melanoma cells. Administration of 800 cGy (800 rad) of radiation produced a 90% reduction in DNA synthesis; however, higher levels of radiation failed to produce further depression of cell proliferation. Irradiation of melanoma cells before intravenous injection resulted in a significant dose-dependent reduction in the number of lung metastases. While there was no effect with 100 cGy (100 rad) of radiation, 1000 cGy (1000 rad) produced a 95% reduction in metastases. In the animal model of enucleation-induced metastasis, 2000 cGy (2000 rad) delivered to the orbit either before or after enucleation produced a significant reduction in the number of lung tumors, compared with animals that did not undergo irradiation; 1000 cGy (1000 rad) delivered before enucleation did not have such an effect. These studies provide evidence that periorbital external beam irradiation is useful in reducing metastases following enucleation of a malignant melanoma in this animal model.

Binding of 8-methoxypsoralen to human serum proteins and red blood cells

Serum binding of 8-methoxypsoralen (8-MOP) was studied by equilibrium dialysis. In therapeutic concentrations, 8-MOP binding in serum was high, 91.4%, and constant, indicating concentration-independent kinetics. This binding involved the two main proteins, human serum albumin and alpha 1-acid glycoprotein, in a saturable process with one class of binding sites (n) and affinity constants (Ka) of 1.295 X 10(4) mol/l and 2.115 X 10(4) mol/l, respectively. Binding to lipoproteins and gamma globulins was negligible and non-saturable in therapeutic concentrations, with nKa values of 0.35, 0.024, 0.013 and 0.0004 mumol/l for VLDL, LDL, HDL and gamma globulins, respectively. Inhibition of 8-MOP serum binding was observed with salicylic acid and indomethacin, but not with diazepam, warfarin or erythromycin. Over a range of therapeutic concentrations, the ration of 8-MOP concentration in red blood cells (RBCs) and in serum was constant at 20.3% and three times higher than would be expected if a simple diffusion of the 8-MOP plasma free fraction (fu) occurred. According to the measured and calculated parameters, simulations of 8-MOP blood binding in pathological states (hypoalbuminaemia with or without inflammation) showed variations of fu which were partially 'buffered' by RBCs. Simulation of 8-MOP protein binding at cutaneous interstitial fluid level showed that fu is approximately 30% and permitted prediction of a decrease of fu available to the epidermis in case of local or systemic inflammation. This may imply an increase in the minimum phototoxic dose relevant for PUVA and explain some cases of 'poor' responsiveness of psoriatic patients to PUVA therapy.

Intrathecal diazepam suppresses nociceptive reflexes and potentiates electroacupuncture effects in pentobarbital-anesthetized rats

Using noxious heat-evoked tail flick in rats anesthetized with pentobarbital infusion, we studied the effects of diazepam applied intrathecally. This drug caused a marked suppression of nociceptive reflexes in a dose-dependent manner. In addition, a small non-suppressive dose of diazepam potentiated electroacupuncture effects. These results are discussed in terms of gamma-aminobutyric acid (GABA) since it is known that diazepam enhances binding of GABA to its receptor and hence potentiates inhibitory effects of GABA in the spinal cord. The possible synergism of diazepam and pentobarbital is also discussed.

Management of anti-thrombin III deficiency during pregnancy without administration of anti-thrombin III

We report a patient with hereditary antithrombin III deficiency who was successfully treated with heparin throughout pregnancy. Functional antithrombin III levels fell to 0.32 U/ml during heparin treatment, but it was possible to achieve a heparin effect, measured by the activated partial thromboplastin time, thrombin clotting time and heparin assay with subcutaneous heparin in doses of 30,000 U to 35,000 U/24 hours. This achieve an long term heparin effect was obtained without the need for antithrombin III infusions.

Stability of thiamin in parenteral nutrition solutions

Since the vitamin thiamin is sensitive to degradation in the presence of stoichiometric concentrations of sulfite ions, the stability of thiamin in parenteral nutrition solutions containing sulfite as an antioxidant and preservative has been questioned. The usual clinical practice of mixing amino acids, dextrose, and other solutions for administration in total parenteral nutrition significantly dilutes the concentration of sulfite. We have measured the thiamin concentration in total parenteral nutrition solutions sampled from containers after administration to patients. We have also determined the time course of thiamin degradation in solutions containing two concentrations of sulfite. Thiamin content exceeded labeled amounts in total parenteral nutrition bags containing amino acid, dextrose, and multivitamin solutions. However, when multivitamins were added directly to amino acid solutions containing 0.1% (9.6 mM) sulfite, significant degradation occurred by 5 hr. Thiamin was stable for at least 22 hr when added to total parenteral nutrition solutions containing less than 0.05% (4.8 mM) sulfite.