gamma-Irradiation of PEGd,lPLA and PEG-PLGA multiblock copolymers. I. Effect of irradiation doses.

To evaluate the effects of different gamma irradiation doses on PEGd,lPLA and PEG-PLGA multiblock copolymers. The behaviour of the multiblock copolymers to irradiation was compared to that of PLA, PLGA polymers. PEGd,lPLA, PEG-PLGA, PLA and PLGA polymers were irradiated by using a (60)Co irradiation source at 5, 15, 25 and 50 kGy total dose. Characterization was performed on all samples before and after irradiation, by nuclear magnetic resonance (NMR), infrared absorption spectrophotometry (FTIR) and gel permeation chromatography (GPC). The effect of gamma irradiation on polymer stability was also evaluated. Results of NMR and FTIR suggest an increase in -OH and -COOH groups, attributed to scission reactions induced by irradiation treatment. Data of GPC analysis showed that the weight average molecular weight (Mw) of polymer samples decreased with increasing irradiation dose. The extent of Mw degradation expressed as percentage of Mw reduction was more prominent for polymers with high molecular weight as PEGd,lPLA and PLA. The dominant effect of gamma-irradiation on both polymer samples was chain scission. The multiblock copolymer PEGd,lPLA presented higher sensitivity to irradiation treatment with respect to PLA, likely due to the presence of PEG in the matrix. The effect of gamma irradiation continues over a much longer period of time after gamma irradiation has been performed. It is suggested that the material reacts with oxygen to form peroxyl free radicals, which may further undergo degradation reactions during storage after irradiation.

Biodegradable microspheres of poly(DL-lactic acid) containing piroxicam as a model drug for controlled release via the parenteral route.

Poly(DL-lactic acid), synthesized in this laboratory from DL-lactic acid, was used to prepare microspheres containing piroxicam, using a solvent evaporation technique. The microspheres obtained were characterized for their surface characteristics (by SEM), surface charge, density, particle size distribution, glass transition temperature, drug incorporation and encapsulation efficiency, IR spectroscopy and in vitro drug release. The suspension of microspheres was evaluated for its syringeability. The effect of channelling agents such as PVP and PEG 6000 on in vitro drug release was studied. The effect of gamma-radiation on poly(DL-lactic acid) and on the in vitro release of piroxicam from the microspheres was also studied.

Poly(L-lactic acid) microspheres containing neutron-activatable holmium-165: a study of the physical characteristics of microspheres before and after irradiation in a nuclear reactor.

The solvent evaporation technique was employed to prepare poly(L-lactic acid) (PLA) microspheres with 165Ho acetylacetonate (Ho-AcAc). Particle size, percentage Ho-165, percent residual solvent, and retentive ability of the spheres were found to be strongly affected by preparatory conditions. Differential scanning calorimetry (DSC) thermograms suggested that the Ho-AcAc existed in the PLA matrix as a molecular dispersion. High neutron flux irradiations of the PLA spheres in a nuclear reactor produced Ho-166, a therapeutic radionuclide that emits high-energy negatrons (Emax = 1.84 MeV; half-life = 26.9 hr). The gamma radiation dose (53-75 Mrad) from the core of the reactor provided an overkill of all bioburdens in the PLA spheres. Gel permeation chromatography (GPC) analysis showed that these irradiations caused a reduction in PLA molecular weight. Infrared spectra, 13C NMR spectra, 1H NMR spectra, and DSC thermograms further confirmed the presence of lower molecular weight PLA but proved the overall maintenance of PLA structure.

[Effect of low-energy laser radiation on the levels of cyclic nucleotides and lactic acid of the mucous membranes in gastric and duodenal ulcers]. / Vliianie nizkoenergeticheskogo lazernogo izlucheniia na uroven' tsiklicheskikh nukleotidov i molochnoi kisloty v slizistoi obolochke pri iazvennoi bolezni zheludka i dvenadtsatiperstnoi kishki.

The level of cyclic nucleotides in biological material undergoes changes due to endoscopic treatment of gastric and duodenal ulcers with the help of helium-neon laser radiation which, in addition to dynamics of the clinical picture and gastroduodenoscopic data, makes it possible to diagnose the disease remission and in certain cases to predict the course of peptic ulcer.

Substrate irradiation stimulation of the in vitro lactate-pyruvate interconversion reactions mediated by lactic dehydrogenase.

Experimental studies of the Comorosan effect are presented for the LDH-mediated interconversions of lactate and pyruvate. Consistent with the findings of the Comorosan group, the rate of the lactate/LDH reaction was found increased for crystalline lithium lactate irradiated with green light for times t comprising the manifold t = 15+30n sec, n = 0,1,2... However, no upper limit to the number of activating times was encountered although the Comorosan group has always obtained only six such activations. The pyruvate/LDH reaction rate was found enhanced for crystalline sodium pyruvate irradiated t = 5+30n sec. Sharpness of activations for 5-sec and 65-sec irradiated samples was investigated and found to occur only within approximately +/- 0.5 sec of 5.0 and 65.0 sec, slightly broader than the +/- 0.15-sec peak reported by Comorosan for the 5-sec signal. The data contribute to the credibility of the phenomenon but reveal sensitivity of some properties to individual laboratory or procedural factors. The first support is provided for the "discriminating function" component of Comorosan's metabolic control hypothesis.