PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Models, Biological”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMed2000

Modeling of biological processes using self-cycling fermentation and genetic algorithms.

Self-cycling fermentation (SCF) was coupled with a genetic algorithm (GA) to provide a simple system for evaluating biological models. The SCF provided the necessary system excitation and data "richness" required to completely define the fitted biological models. The solution scheme based on the GA avoided the computational difficulties often associated with calculus-based nonlinear regression techniques, resulting in rapid and accurate convergence. After validating the mathematical approach, data from the SCF obtained under denitrifying conditions were fitted successfully to an established model using the GA. Finally, data obtained in the SCF for the removal of phenol were used to compare multiple models. This work suggests that the SCF, in conjunction with the GA, provides a coherent system that can facilitate the characterization of biological systems.

Algorithms↗
PubMed2003

Fluorescence imaging of multiple myeloma cells in a clinically relevant SCID/NOD in vivo model: biologic and clinical implications.

The in vivo preclinical testing of investigational therapies for multiple myeloma (MM) is hampered by the fact that models generated to recapitulate the development of diffuse skeletal lesions after i.v. injections of tumor cells do not allow for ready detection of the exact site(s) of lesions or for comprehensive monitoring of their progression. We therefore developed an in vivo MM model in severe combined immunodeficient/nonobese diabetic mice in which diffuse MM lesions developed after tail vein i.v. injection of human RPMI-8226/S MM cells stably transfected with a construct for green fluorescent protein (GFP). Using whole-body real-time fluorescence imaging to detect autofluorescent GFP(+) MM cells (and confirming the sensitivity and specificity of these findings both histologically and by flow cytometric detection of GFP(+) cells), we serially monitored, in a cohort of 75 mice, the development and progression of MM tumors. Their anatomical distribution and pathophysiological manifestations were consistent with the clinical course of MM in human patients, i.e., hallmarked by major involvement of the axial skeleton (e.g., spine, skull, and pelvis) and frequent development of paralysis secondary to spinal lesions without significant tumor spread to lungs, liver, spleen, or kidney. This model both recapitulates the diffuse bone disease of human MM and allows for serial whole-body visualization of its spatiotemporal progression. It therefore provides a valuable in vivo system to elucidate the molecular mechanisms underlying the marked osteotropism of MM, particularly for the axial skeleton, and for assessment of in vivo activity of novel anti-MM therapeutics.

Animals↗
PubMed2005

Modeling biologic soft tissues for haptic feedback with an hybrid multiresolution method.

The simulation of realistic surgical procedures requires specialized optimized algorithms for the models of organs and tissues, which should comply both with accuracy of results and run-time computation. This paper provides a numerical method for implementing deformation of soft tissues for haptic feedback that makes use of a hybrid pre-computation scheme.

Algorithms↗
PubMed1981

[Transport of cytidinediphosphocholine in different biological models. I - Synthesis and characterization of (5 3H, Met 14 C) cytidinediphosphocholine].

In order to investigate the transport of CDP-choline across the biological membranes we have synthesized the double labeled CDP-choline. The (5 3H, methyl 14C) CDP-choline is synthesized by a crossed condensation of (5 3H) CMP and methyl 14C) p-choline using DCC as condensing agent. The product of the reaction is identified by chromatographics and spectroscopics methods.

Carbon Radioisotopes↗
PubMed2003

Modelling biological nutrient removal activated sludge systems - a review.

The external nitrification (EN) biological nutrient removal (BNR) activated sludge (ENBNRAS) system shows considerable promise for full-scale implementation. As an aid for this implementation, a mathematical simulation model would be an invaluable tool. To develop such a model, a study was conducted to select the most suitable simulation model to serve as a starting point for further development. For this, the existing available simulation models for BNRAS systems are compared with one another and evaluated against experimental observations in the literature and on ENBNRAS systems. One process immediately apparent to be crucially important is the anoxic growth of phosphorus accumulating organisms (PAOs), with associated PAO denitrification and anoxic P uptake for polyP formation. These linked processes are lacking in the earlier kinetic simulation models for BNRAS systems, which were based on aerobic PAO growth and P uptake only, but have been incorporated into the more recent kinetic models. This provides a substantive body of information on modelling this aspect. Other processes of significance identified to require consideration are anaerobic slowly biodegradable COD (SBCOD) hydrolysis to readily biodegradable COD (RBCOD), and COD loss. Both processes have significant impact on the predicted BEPR performance. Due to the uncertainties associated with the mechanisms and quantification of these two processes, it is concluded that the most extensively validated kinetic simulation model should be selected for development, and that the omissions in this model should be addressed progressively, using the relevant information drawn from the existing models, the literature and observations on ENBNRAS systems.

Bioreactors↗
PubMed1993

Diagnostic tools and biologic models for studying osteoporosis and oral bone loss: tissue sampling.

Study of oral tissues to understand the mechanisms of osteoporosis and oral bone loss includes histologic, biochemical, and molecular assessments of the tissue itself, as well as in vivo analysis of the biology of resident cells. Tissue sampling is limited by the nature of the defect and the use of appropriate controls (contralateral site vs same site, different subjects vs repeated measures of the same sites). Experimental parameters may include histomorphometrics, histochemistry, immunohistochemistry, and in situ hybridization. Molecular and biochemical technology also can be used to study the tissue in vivo. The presence of mineral is a confounding variable. To understand the underlying mechanisms of oral bone loss, cell culture is a powerful tool. The location in the oral cavity, the type of tissue (periosteum/cortical bone/trabecular bone), and the presence of pathology (periodontal disease) affect the biology of the cultured cells. Enzymatic release of cells from their extracellular matrix yields heterogeneous cell populations. Migratory cells from explant cultures are more homogeneous but less differentiated. Fibroblastic and bacterial contamination may be problems. Although cell culture data must be considered in the context of the intact tissue, the potential exists for developing bone cell function tests with diagnostic use in the treatment of bone disease.

Alveolar Bone Loss↗
PubMed1991

Characterization of calcium channel forming activity of Entamoeba histolytica in model biological membranes.

Entamoeba histolytica is an invasive enteric protozoan parasite whose cytolytic activity is associated with irreversible increases in target cell intracellular calcium. We studied the effect of homogenates of virulent E. histolytica on calcium permeability of bovine chromaffin granules and rat liver mitochondria, model membrane systems whose mechanisms of ion transport and permeability are well characterized. Treatment of chromaffin granules, with an extract of E. histolytica resulted in a dose-dependent increase in calcium uptake. These effects were similar to that seen with the calcium ionophore A23187 and indicate that the homogenate acts as a divalent cation ionophore. However, unlike what is observed with A23187, the Ca2+ uptake was greater in the presence of the permeable anion Cl- than in its absence. Also, in contrast to the calcium ionophore A23187, a homogenate of E. histolytica caused no calcium release from rat liver mitochondria but resulted in a dramatic increase in the rate of calcium accumulation. The amebic homogenate did not bind calcium in the absence of mitochondria. The increase in mitochondria calcium uptake occurred only in the presence of respiration and with normal state 3 and 4 oxygen consumption. Calcium accumulation occurred both in the presence and absence of 5 mM Pi. Substitution of NaCl or KCl for sucrose in the medium did not alter the enhanced mitochondria calcium uptake. Most data are consistent with the hypothesis that the E. histolytica homogenate is acting as a calcium ionophore transporting charged calcium electrophoretically across the chromaffin granules and the mitochondria inner membrane. This activity may contribute to the cytopathogenicity by E. histolytica.

Animals↗
PubMed1993

Childhood cross-gender behavior and adult homosexuality: the resurgence of biological models of sexuality.

Research on the causes of homosexuality frequently treat it as a matter of disturbed gender identity and/or gender role. Recently, attempts have been made to link cross-gender behavior among boys with adult homosexuality. Often this research presumes a common biological determinant to both the childhood behavior patterns and homosexuality in adulthood. Authors have described such childhood cross-gender behavior in boys as part of a "prehomosexual" configuration. This paper argues that the research to date suffers from (1) a failure to differentiate such concepts as gender identity, gender role and sexual orientation, (2) a reliance upon potentially inappropriate dichotomies in describing such concepts, (3) problematic interpretations of research that makes few distinctions between human sexual behavior and sexual behavior among rodents, and (4) the contradictions implicit in seeking simple biological determinants of constructs (such as cross-gender behavior) that are culturally determined. The author argues that any potential biological factors contributing to sexual orientation must be mediated by a complex sequence of experiences and psychosocial factors. Therefore, the essentialists' search for a simple congruence between physiological or biological traits and homosexuality may be expected to fail.

Female↗
PubMed2005

Binding of gaseous Fe(III)-heme cation to model biological molecules: direct association and ligand transfer reactions.

The binding of a variety of ligands with Fe(III)-heme(+) ion, prosthetic group of heme proteins, has been studied in the gas phase by ESI-FT-ICR mass spectrometry. The ligands have been selected among substrate molecules of heme proteins (e.g., NO, nitroso compounds) or among model compounds acting for the functional groups that are present in the protein backbone (e.g., amines, thioethers, nitriles, ketones, amides, etc.). Both the kinetic and the thermodynamic features of the addition reactions are reported. Fe(III)-heme(+) ions react faster with lone pair donor ligands as the reaction becomes increasingly thermodynamically favored (higher heme cation basicity of the ligand, HCB, namely -DeltaG degrees for the ligand addition reaction). In turn HCBs correlate in general with the gas phase basicity toward the proton of the various ligands. A ligand addition equilibrium is established with weaker ligands, methanol, acetonitrile and acetone, yielding absolute HCB values, whereas ligand transfer equilibriums allowed a scale of relative (and absolute) HCBs to be constructed. NO displays exceptional binding properties towards Fe(III)-heme(+), unrelated to the low gas phase basicity toward the proton of this molecule, which is clearly the basis for the paramount role of heme proteins in NO binding and regulation.

Cations↗
PubMed2000

[Macrodiolides--chemical properties and activity in a biological model].

Diolides, often classified into a group of macrolides, represent a heterogenous group of microbial metabolites whose common feature is the presence of a cyclic diester moiety in their structure. These compounds have cytotoxic, antiviral, anthelmintic or immunosuppressive activities and they were effective agents against some autoimmune diseases. Diolides, contrary to macrolides, showed a substantially lower antibacterial activity. The current data on the chemical properties and biological activity of diolides are presented in this paper.

Anti-Bacterial Agents↗
PubMed1984

Beyond the biological model: new directions in bisexual and homosexual research.

Past research on homosexuality has been based on two assumptions: one, that gender is the critical determinant of a sexual relationship, and two, that sexual orientation is an essential condition. This paper argues that investigation of sexual relationships on these bases tests only within, rather than between, paradigms of possible relationships. It assumes that choice of partners is based on a number of physical and psychological characteristics apart from their biological sex and that different meanings of sexuality and of the contexts of sexual encounters will determine which characteristics are chosen. It is also suggested that comparisons between groups of exclusive homosexuals and exclusive heterosexuals will not cast light on preferred partner characteristics. It is therefore necessary to look at the preferred partner characteristics of bisexuals in order to understand the bases and significance of homosexual or heterosexual partner choice. Finally, it is concluded that the meanings of homosexuality in different contexts may be so varied that the possibility of establishing a unified theory of the homosexual identity is precluded.

Female↗
PubMed2006

Modeling biological motor control for human locomotion with functional electrical stimulation.

This paper develops a novel control system for functional electrical stimulation (FES) locomotion, which aims to generate normal locomotion for paraplegics via FES. It explores the possibility of applying ideas from biology to engineering. The neural control mechanism of the biological motor system, the central pattern generator, has been adopted in the control system design. Some artificial control techniques such as neural network control, fuzzy logic, control and impedance control are incorporated to refine the control performance. Several types of sensory feedback are integrated to endow this control system with an adaptive ability. A musculoskeletal model with 7 segments and 18 muscles is constructed for the simulation study. Satisfactory simulation results are achieved under this FES control system, which indicates a promising technique for the potential application of FES locomotion in future.

Electric Stimulation Therapy↗
PubMedDate not supplied

[A biological model study of the effect of Aerococcus viridans on pathogenic bacteria].

Morphological researches studies showed that the treatment of infected skin wounds with Aerobact quickly eliminated inflammation, promoted regeneration of damaged tissues, that actively stimulated formation of granulations. A decrease of S. aureus virulence which completely or partially loose lethal and necrotic activity is one of the reasons of the observed phenomenon. On the model of S. typhimurium infection the expressed protective action of bacteria of Aerococcus genus was shown; this gives us a good prospect in the expansion of the indications for application of probiotic Aerobact.

Animals↗
PubMed2000

ESR study on the antioxidant activity of TAK-218 in biological model membranes.

TAK-218 has a 2,3-dihydrobenzofuran-5-amine (coumaran) structure which resembles alpha-tocopherol, and is a promising candidate as an agent for central nervous system (CNS) trauma and ischemia. The radical scavenging activity of TAK-218 was studied using electron spin resonance (ESR) spectroscopy. TAK-218 exhibited a more potent scavenging activity towards the hydroxyl radical than did the well-known hydroxyl radical scavengers, mannitol and dimethylsulfoxide. Towards the superoxide radical, TAK-218 showed equal potency to glutathione. TAK-218 reacted rapidly with stable radicals, such as galvinoxyl and 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH), and gave the quinone as a two-electron oxidized product in analogy with alpha-tocopherol. To exhibit an excellent antioxidative activity in living systems, the compounds should not only have the intrinsic radical scavenging activity but also good distribution in the biological lipid-bilayer membrane. To examine the antioxidant activity of TAK-218, the inhibition of lipid peroxidation by alpha-tocopherol and TAK-218 in liposomal membranes was studied using an ESR spin-label technique. Both alpha-tocopherol and TAK-218 completely inhibited lipid peroxidation by radicals generated in an aqueous layer using a water-soluble radical initiator, 2,2'-azobis-(2-amidinopropane) hydrochloride (AAPH). At a high incubation temperature (45 degrees C), alpha-tocopherol scavenged radicals more effectively than TAK-218 on the surface of the membrane, while TAK-218 scavenged radicals more effectively in the interior of the membrane. The difference between TAK-218 and alpha-tocopherol for radical scavenging in the membrane system derives from the different distribution pattern of these compounds. TAK-218 can penetrate the membrane freely and can scavenge the radical in the membrane interior. Furthermore, TAK-218 was shown to inhibit lipid peroxidation initiated by a lipid soluble radical initiator, 2,2'-azobis-(2,4-dimethylvaleronitrile) (AMVN), in a membrane more effectively than alpha-tocopherol.

Antioxidants↗
PubMedDate not supplied

[A study of water autodiffusion in model biological membranes, oriented lipid bilayers].

The autodiffusion of water in a multibilayer structure formed by dipalmitoyl phosphatidylcholine and oriented on glass plates was studied by the method of NMR with magnetic field pulse gradient. It was shown that water molecules occur in several states differing in the degree of interaction with lipid molecules. A spectrum of the coefficients of water autodiffusion in a direction transversal to bilayers was found. The use of samples with different distances between the plates and an analysis of the dependence of the mode of diffuse decay of spin echo on diffusion time and the orientation of the sample, as well as measurements at temperatures above and below the gel-liquid crystal phase transition in cholesterol-containing samples enabled one to discriminate the diffuse decay component responsible for the transbilayer movement of water. The coefficient of bilayer permeability was estimated using the Tanner model. It was shown that the formation of mechanical defects ("cracks") in plane oriented bilayers is the most probable reason for the presence of the water component with the relatively high coefficient of diffusion.

1,2-Dipalmitoylphosphatidylcholine↗