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PubMed1989

In vivo characteristics of low molecular weight copoly (D,L-lactic acid) formulations with controlled release of LH-RH agonist.

Amorphous and crystalline copolymers with a relatively low molecular weight of 1800 were synthesized by direct copolycondensation of D-lactic acid and L-lactic acid in the absence of a catalyst, to evaluate their in vivo capabilities as biodegradable carriers for drug delivery systems. A luteinizing hormone-releasing hormone agonist, des-Gly10-(D-Leu6)-LH-RH ethylamide, was incorporated in a fine cylindrical copolymer formulation, under melt-pressing technique, a mild heat-pressure condition. This formulation was implanted subcutaneously in the back of male rats. The rate of in vivo degradation of amorphous copolymer was much faster than that of crystalline copolymer. Contrary to this tendency, the in vivo release of the drug from this amorphous formulation was held constant over a longer period, compared with the crystalline formulation. This can be closely related to the difference in dispersion of the drug in the formulation.

Animals↗
PubMed2000

Similar increases in extracellular lactic acid in the limbic system during epileptic and/or olfactory stimulation.

Previous studies have shown that physiological stimulation of brain activity increases anaerobic glucose consumption, both in humans and in experimental animals. To investigate this phenomenon further, we measured extracellular lactate levels within different rat brain regions, using microdialysis. Experiments were performed comparing the effects of natural, physiological olfactory stimulation of the limbic system with experimental limbic seizures. Olfactory stimulation was carried out by using different odors (i.e. both conventional odors: 2-isobutyl-3-methoxypyrazine, green pepper essence; thymol; and 2-sec-butylthiazoline, a sexual pheromone). Limbic seizures were either induced by systemic injection of pilocarpine (200-400 mg/kg) or focally elicited by microinfusions of chemoconvulsants (bicuculline 118 pmol and cychlothiazide 1.2 nmol) within the anterior piriform cortex. Seizures induced by systemic pilocarpine tripled lactic acid within the hippocampus, whereas limbic seizures elicited by focal microinfusion of chemoconvulsants within the piriform cortex produced a less pronounced increase in extracellular lactic acid. Increases in extracellular lactate occurring during olfactory stimulation with the sexual pheromone (three times the baseline levels) were non-significantly different from those occurring after systemic pilocarpine. Increases in lactic acid following natural olfactory stimulation were abolished both by olfactory bulbectomy and by the focal microinfusion of tetrodotoxin, while they were significantly attenuated by the local application of the N-methyl-D-aspartate antagonist AP-5. Increases in hippocampal lactate induced by short-lasting stimuli (olfactory stimulation or microinfusion of subthreshold doses of chemoconvulsants, bicuculline 30 pmol) were reproducible after a short delay (1 h) and cumulated when applied sequentially. In contrast, limbic status epilepticus led to a long-lasting refractoriness to additional lactate-raising stimuli and there was no further increase in lactate levels when the olfactory stimulation was produced during status epilepticus. Increases in lactic acid following olfactory stimulation occurred with site specificity in the rhinencephalon (hippocampus, piriform and entorhinal cortex) but not in the dorsal striatum. Site specificity crucially relied on the quality of the stimulus. For instance, other natural stimuli (i.e. tail pinch) produced a similar increase in extracellular lactate in all brain areas under investigation. The major conclusion of this work is that the presentation of an odor known to be a rat pheromone results in lactate production as great as that induced by the systemic convulsant pylocarpine (maximum: 2.286+/-0.195 mM and 1.803+/-0.108 mM, respectively). This supports the notion that the great magnitude of lactate production known to accompany seizures can result from the intensified neural activity per se ("aerobic gycolysis"), not merely from local anoxia or other pathological changes.

2-Amino-5-phosphonovalerate↗
PubMed2000

Biodegradable poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether diblock copolymers: structures and surface properties relevant to their use as biomaterials.

To obtain biodegradable polymers with variable surface properties for tissue culture applications, poly(ethylene glycol) blocks were attached to poly(lactic acid) blocks in a variety of combinations. The resulting poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether (Me.PEG-PLA) diblock copolymers were subject to comprehensive investigations concerning their bulk microstructure and surface properties to evaluate their suitability for drug delivery applications as well as for the manufacture of scaffolds in tissue engineering. Results obtained from 1H-NMR, gel permeation chromatography, wide angle X-ray diffraction and modulated differential scanning calorimetry revealed that the polymer bulk microstructure contains poly(ethylene glycol)-monomethyl ether (Me.PEG) domains segregated from poly(D,L-lactic acid) (PLA) domains varying with the composition of the diblock copolymers. Analysis of the surface of polymer films with atomic force microscopy and X-ray photoelectron spectroscopy indicated that there is a variable amount of Me.PEG chains present on the polymer surface, depending on the polymer composition. It could be shown that the presence of Me.PEG chains in the polymer surface had a suppressive effect on the adsorption of two model peptides (salmon calcitonin and human atrial natriuretic peptide). The possibility to modify polymer bulk microstructure as well as surface properties by variation of the copolymer composition is a prerequisite for their efficient use in the fields of drug delivery and tissue engineering.

Biocompatible Materials↗
PubMed2000

Dynamic changes of intracellular pH in individual lactic acid bacterium cells in response to a rapid drop in extracellular pH.

We describe the dynamics of changes in the intracellular pH (pH(i)) values of a number of lactic acid bacteria in response to a rapid drop in the extracellular pH (pH(ex)). Strains of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, and Lactococcus lactis were investigated. Listeria innocua, a gram-positive, non-lactic acid bacterium, was included for comparison. The method which we used was based on fluorescence ratio imaging of single cells, and it was therefore possible to describe variations in pH(i) within a population. The bacteria were immobilized on a membrane filter, placed in a closed perfusion chamber, and analyzed during a rapid decrease in the pH(ex) from 7.0 to 5.0. Under these conditions, the pH(i) of L. innocua remained neutral (between 7 and 8). In contrast, the pH(i) values of all of the strains of lactic acid bacteria investigated decreased to approximately 5.5 as the pH(ex) was decreased. No pronounced differences were observed between cells of the same strain harvested from the exponential and stationary phases. Small differences between species were observed with regard to the initial pH(i) at pH(ex) 7.0, while different kinetics of pH(i) regulation were observed in different species and also in different strains of S. thermophilus.

Hydrogen-Ion Concentration↗
PubMed2003

Using banana to generate lactic acid through batch process fermentation.

We evaluated the usefulness of waste banana for generating lactic acid through batch fermentation, using Lactobacillus casei under three treatments. Two treatments consisted of substrates of diluted banana purée, one of which was enriched with salts and amino acids. The control treatment comprised a substrate suitable for L. casei growth. When fermentation was evaluated over time, significant differences (P<0.05) were found in the three treatments for each of five variables analyzed (generation and productivity of lactic acid, and consumption of glucose, fructose, and sucrose). Maximum productivity was (in g l(-1) h(-1)) 0.13 for the regular banana treatment, 1.49 for the enriched banana, and 1.48 for the control, with no significant differences found between the latter two treatments. Glucose consumption curves showed that L. casei made greater use of the substrate in the enriched banana and control treatments than in the regular banana treatment. For fructose intake, the enriched banana treatment showed significantly better (P<0.05) results than the regular one. Sucrose consumption was insignificant (P<0.05), probably because fermentation time was too short. Even when enriched, diluted banana purée is an ineffective substrate for L. casei, probably because it lacks nutrients.

Bioreactors↗
PubMed1997

Lactic acid bacteria of foods and their current taxonomy.

Application of molecular genetic techniques to determine the relatedness of food-associated lactic acid bacteria has resulted in significant changes in their taxonomic classification. During the 1980s the genus Streptococcus was separated into the three genera Enterococcus, Lactococcus and Streptococcus. The lactic acid bacteria associated with foods now include species of the genera Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus and Weissella. The genus Lactobacillus remains heterogeneous with over 60 species (ymol% G+C content ranging from 33 to 55), of which about one-third are strictly heterofermentative. However, many changes have been made and reorganization of the genus along lines that do not follow previous morphological or phenotypic differentiation from Leuconostoc and Pediococcus is being studied. Phylogenetically belonging to the Actinomyces branch of the bacteria, Lactobacillus bifidus has been moved to the genus Bifidobacterium also on account of its greater than 50 mol% G+C content. It is therefore no longer considered one of the lactic acid bacteria senso strictu, which form part of the Clostridium branch of the bacteria. The new genus Weissella has been established to include one member of the genus Leuconostoc (Leuc, paramesenteroides) and heterofermentative lactobacilli with unusual interpeptide bridges in the peptidoglycan. Contrary to the clear-cut division of the streptococci, morphological and physiological features of Weissella do not directly support this grouping which now incorporates species that produce D(-)- as well as DL-lactate. The new genus Carnobacterium is morphologically similar to the lactobacilli, but it shares some physiological similarities (e.g. growth at pH 9.5) and a common phylogenetic branch with the genus Enterococcus. The review includes information on the taxonomic changes and the relationship of the bacteria of food fermentation and spoilage.

Enterococcus↗
PubMed1990

Spinal angiomas. The meaning of cerebrospinal fluid lactic acid in the etiology and differential diagnosis of transverse myelopathy.

We report five out of eleven patients with transverse myelopathy due to spinal angiomas. Transverse myelopathy can be caused by a number of disorders. The formation of lactic acid points to ischaemia within the spinal cord, due to altered haemodynamics as in spinal angiomas. The meaning of cerebrospinal fluid lactic acid is discussed with respect to etiology and differential diagnosis of transverse myelopathy. The combined finding of CSF lactic acid and protein elevation in the absence of cell count and immunological and/or serological abnormalities points to an isolated vascular cause of the transverse myelopathy.

Adolescent↗
PubMedDate not supplied

Development of metabolically engineered Saccharomyces cerevisiae cells for the production of lactic acid.

Interesting challenges from metabolically engineered Saccharomyces cerevisiae cells arise from the opportunity to obtain yeast strains useful for the production of chemical(s). In this paper, we describe the accumulation of lactic acid in the culture medium of growing, engineered yeast cells expressing a mammalian lactate dehydrogenase gene (LDH-A). High and reproducible productions (20 g/L) and productivities (up to 11 g/L/h) of lactic acid have been obtained by modulating the physiological growth conditions. Since yeast cells are acid tolerant and survive at very low pH values, the production of lactate can be avoided. In perspective, the approaches described could be useful for the production of lactic acid, outflanking the problems related to the synthesis from bacteria cells. In fact, during industrial productions, there is an inhibitory effect on the metabolic activities of the growing bacteria (i.e., Lactobacillus spp.) caused by the acid produced and by the low pH value. Thus, strategies to prevent the lowering of pH are conventional operations. These processes allow the production of lactate(s) and require the purification of the acid from its salt. The biotechnological implications of this study are also discussed.

Animals↗
PubMed2005

The genetic diversity of lactic acid producing bacteria in the equine gastrointestinal tract.

Seventy-two lactic acid producing bacterial isolates (excluding streptococci) were cultured from the gastrointestinal tract of six horses. Two of the horses were orally dosed with raftilose to induce lactic acidosis and laminitis while the remaining four were maintained on a roughage diet. Near complete 16S rDNA was amplified by PCR from the genomic DNA of each isolate. Following RFLP analysis with the restriction enzymes MboI, HhaI and HinfI, the PCR products from the 18 isolates that produced L- and/or D-lactate were subsequently cloned and sequenced. DNA sequence analysis indicated that the majority of the isolates were closely related to species within the genus Lactobacillus, including Lactobacillus salivarius, Lactobacillus mucosae and Lactobacillus delbrueckii. Four isolates were closely related to Mitsuokella jalaludinii. Lactic acid producing bacteria (LAB) from the equine gastrointestinal tract was dominated by representatives from the genus Lactobacillus, but also included D-lactate-producing bacteria closely related to M. jalaludinii. Identification and characterization of LAB from the equine gastrointestinal tract should contribute to our understanding and management of fermentative acidosis, ulceration of the stomach and laminitis.

Acidosis↗
PubMed2004

[Preparation and toxicity of triptolide-loaded poly (D,L-lactic acid) nanoparticles].

AIM: Investigations on reducing the toxicity of triptolide through poly(D, L-lactic acid) nanoparticles as a drug carrier by oral administration to Wistar rats. METHODS: Triptolide-loaded poly (D, L-lactic acid) nanoparticles (TP-PLA-NPs) were prepared by modified spontaneous emulsification solvent diffusion (modified-SESD). The shape of nanoparticles was observed by transmission electron microscope (TEM). The size distribution and mean diameter were measured by laser light scattering technique. The entrapment efficiency and contents of drug loading were determined by RP-HPLC. The physical state of drug loaded in nanopartiles were primarily investigated by X-ray powder diffractometry. TP-PLA-NPs release behavior in vitro was carried out. After oral administration of the nanoparticles to Wistar rats in 15d, the toxicity for liver and kidney were studied by determining aspartate transaminase (AST), alanine transaminase (ALT) and blood urea nitrogen in serum and concentration of protein in urine. RESULTS: The preparation process adapted to the formulation was as follows: the volume ratio of the aqueous and organic phases was 40/15; the surfactant concentration was 1%; the drug concentration was 0.3%; triptolide-PLA was 1:15 (w/w). The mean diameter was 149.7 nm and the polydispersity index was 0. 088 for the nanoparticles prepared by above conditions. The entrapment efficiency and content of drug loading were 74.27% and 1.36%, respectively. The release behavior of drug in vitro showed an initial burst effect, subsequently a slower rate stage. The results indicated that the liver toxicity (P < 0.01) and kidney toxicity (P < 0.05) caused by triptolide could be decreased significantly by nanoparticles carrier. CONCLUSION: PLA-NPs might be used as a new oral carrier for triptolide.

Alanine Transaminase↗
PubMed2006

Scale-up of L-lactic acid production by mutant strain Rhizopus sp. MK-96-1196 from 0.003 m3 to 5 m3 in airlift bioreactors.

In order to study the feasibility of commercial-scale L-lactic acid production by Rhizopus sp. MK-96-1196 using large scale airlift bioreactors (ALBs), a scale-up study from 0.003 m3 to 5 m3 ALB was carried out using oxygen transfer rate (OTR) as the scale-up criterion. Enhanced L-lactic acid production was achieved at OTRs higher than 0.28 (g-O2/l/h) irrespective of the scale of the bioreactor in question: in the range of 0.003 m3 to 5 m3, more than 90 g/lL-lactic acid was produced with a yield of approximately 80%, based on the initial glucose concentration. In future research, we plan to design an ALB greater than 3000 m3 (working volume: 2000 m3) for further studies on the production of L-lactic acid in large quantities.

Bioreactors↗
PubMed2002

Shear-load carrying capacities of the distal rat femora after osteotomy fixed with self-reinforced polyglycolic acid and poly-L-lactic acid pins.

Distal femora of 40 rats were osteotomized and fixed with self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) pin 2.0 mm in diameter and 15 mm in length. The shear-load carrying capacities of the osteotomized bones were compared with each other and with the intact control rat distal femora of the same age of 20 pairs. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities reached their highest values at 24 weeks in the SR-PGA-fixed specimens, after that decreasing to the level where they remained. In the SR-PLLA-fixed specimens the strength values of the pins increased after three weeks, but there was a decrease at 24 weeks. After that the shear-load carrying capacities started to raise because of the influence of the healed osteotomy. In the control bones the shear-load carrying capacities were weaker than in the SR-PGA-and SR-PLLA-fixed specimens except at three weeks, as the osteotomies had not yet healed. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA-fixed specimens was 199.1 N, in the SR-PLLA-fixed specimens 214.6 N, the corresponding value of the control specimens being 148.2 N.

Journal Article↗