© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

10.4.1 Biochemical Cytocide and Virucide

Biochemical cytocide involves the killing of pathogenic cells using biochemical, cytochemical, or other means which cause the cell to die a "natural," though perhaps highly accelerated, death. Any agent or set of conditions that stresses the metabolism or normal response mechanisms of a cell may trigger the process of apoptosis, or programmed cell death, but the level of stress is crucial.²⁰⁶⁰

At high stress levels, including sharp pH changes or high toxin levels (Section 10.4.1.4), or high agitation rates,²⁰⁶¹ cells may die instantly by necrosis,^2291,2292 largely because they have no time to respond to the stimulus. In necrotic cytocide, neighboring cells are showered with cellular debris as the necrotic cell swells and lyses, an event likely to cause wider injury and a process to be avoided in nanomedical situations wherever possible.

At intermediate levels of cell stress, the cell is injured but not killed, and so has time to activate its own suicide program.²⁰⁶⁰ The contents of the dying cell are retained within sealed vesicles until removed through phagocytosis, thus the cell dies in a controlled and tissue-friendly way.

At low levels of environmental stress, cells can, for example, switch on the production of heat shock proteins which helps them to survive until the stress is removed,²⁰⁶⁰ largely by accelerating the refolding of proteins which have been damaged by heat and some other insults. Similarly, UV radiation activates a DNA damage response, cell starvation activates the proteasome protein-recycling response, and glucocorticoids might activate responses to eliminate all nonessential functions.

Of course, once a certain stress threshold is passed and survival is deemed impossible, death by apoptosis ensues. Nanomedical biocytocidal instrumentalities should seek to dispose of cells by apoptotic methods (Section 10.4.1.1), or by functionally equivalent techniques such as phagocytic flagging (Section 10.4.1.2) or cell division arrest (Section 10.4.1.3).

Last updated on 24 February 2003