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Optimizing Reporter Gene Expression for Molecular Magnetic Resonance Imaging
Published in Shoogo Ueno, Bioimaging, 2020
Qin Sun, Frank S. Prato, Donna E. Goldhawk
Magnetosome synthesis is a protein-directed process, beginning with expression of structural genes that encode the required magnetosome components. While the nature of these components is still incompletely understood, progress has been made in many areas. The genomes of numerous MTB have now been sequenced, permitting comparison of conserved gene sequences and synteny.42,43 Despite the breadth of MTB species, there are common genes that specify the main magnetosome structure and approximately two-thirds of these are clustered on a magnetosome genomic island.44 Removal of this cluster of DNA prevents magnetotaxis in the microorganism but is not lethal, demonstrating that magnetosomes likely confer selective advantage(s) rather than compulsory function(s).
Static Magnetic Therapy for Pain
Published in Mark V. Boswell, B. Eliot Cole, Weiner's Pain Management, 2005
Michael J. McLean, Stefan Engström
The conceptually simplest way to detect a magnetic field is with another magnet, as described above for the interaction between two dipole magnets. Some birds have a type of magnetite in specialized receptor cells in their beaks (Hanzlik et al., 2000). But, the presence of magnetic material in animal tissues does not reveal how sensing the field is transduced. Magnetotaxis may be the result of physical attraction between an external magnetic field and magnetite in bacteria, like some physical tractor beam (Blakemore, 1975). In the absence of magnetic material, the dipole moment of unpaired electrons or dipoles within diamagnetic cell components, such as enzymes or ion channels, might be targets. In these cases, the external magnetic field can be viewed as inducing a weak magnetic field in certain cell structures and then interacting with the induced field. Altering biological dipoles intrinsic to proteins could be coupled directly to function, e.g., by modulating enzyme activity. For example, two different static magnetic fields increased calcium-calmodulin dependent myosin phosphorylation in a cell free system to different degrees (Engström et al., 2002; Markov & Pilla, 1997). Altering calcium binding to calmodulin could provide control of amplification of the phosphorylation step. Removal of the magnetic field would be expected to result in return to the baseline level of activity because diamagnetic substances do not store magnetic energy permanently. Both magnetic flux density (the number of magnetic flux lines per unit area) and field gradients (changes of field strength with distance) were implicated in these results. Thus, the sensor, or magnetoceptor, may not be very different from a pharmacological receptor, in which the agonist binding site is a peptide sequence gating an ion channel or coupled to a G protein. The “agonist” for the magnetoceptor is distinctly different, however, and operates from a distance in the form of non-ionizing radiation instead of a ligand binding to a receptor. Also, the magnetoceptor may respond to one or more characteristics of the imposed magnetic field. Put a different way, different components of an external magnetic field may modulate the magnetoceptor, suggesting that magnetic fields might be designed to have specific influences on target tissues.
Bioengineered smart bacterial carriers for combinational targeted therapy of solid tumours
Published in Journal of Drug Targeting, 2020
Siamak Alizadeh, Abolghasem Esmaeili, Abolfazl Barzegari, Mohammad A. Rafi, Yadollah Omidi
Bacterial microrobots (BMRs), so-called bacteriobots, have been developed based on the intrinsic features of bacteria, including chemotaxis, phototaxis and magnetotaxis [128]. They can be engineered to be responsive to various stimuli, including the external chemical attractants, ultraviolet light and electromagnetic actuation stimuli [63]. Bacteriobots are fabricated through the vigorous attachment of various biocompatible and biodegradable ingredients to appropriate bacteria to create stimuli-responsive bacterial-based microrobots from which the loaded drugs can be released in a controlled manner [128]. As shown in Figure 7, BMRs are mainly composed of bacteria as a sensor and microbead containing therapeutic agents and an actuator to direct them to their target sites and induce the intended biological impacts [63]. In comparison with other passive and active targeted DDSs as well as controlled-release and pulsatile delivery systems, owing to their advantages, various types of biomedical microrobots have recently been developed [129]. Several bacterial strains with high motility have been used for microrobot actuation, including Escherichia coli, Serratia marcescens, Salmonella typhimurium and magnetotactic bacteria (MTB) such as Magnetospirillum gryphiswaldense strain MSR-1 [129,130]. The success paradigm was the use of paclitaxel-loaded liposomal micro-cargo in combination with tumour-targeting Salmonella typhimurium bacteria for targeting the breast cancer cell line (4T1). Based on this finding, the drug-loaded bacteriobots revealed strong tumour targeting and killing potentials [131].