Page 23 - Veterinary Laser Therapy in Small Animal Practice

Light is just the catalyst 9

a given time period (say, as the hand-piece is being Wow. That’s three ways light inside the cell helps
moved over the treatment area), the more ATP can be the cells function better. It enhances the redox cycle
produced in cells. This phenomenon is what people call of cytochrome oxidase, which produces more ATP
photobiomodulation, the increase in natural cellular for cells to utilize in their natural functions. It helps
function via the use of light. produce NO within the cell, which facilitates cell
signaling. And at the same time it forces the cells to
1.5.2 Nitric oxide: a not-so-secondary effect use O more efficiently, for things the body needs O 2
2
for (respiration), and makes available more NO for
There is slightly more to the story inside the cell. Nitric things the cells need NO for (cell signaling). Pretty
oxide (NO) plays a very important role in cell signaling, cool.
both within the cell and between cells. An abundance So this is how light can enhance the usage of oxygen
of NO leads mostly to positive cellular function. There once it gets into the cell. But that is only the tail end
is, of course, a ceiling to this effect, where too much of the circuit. This is akin to squeezing really hard on
NO leads to nitrosative stress, but studies on several the nozzle of your garden hose in the hope of hosing
different cell lines show that light therapy enhances the down your burning trashcan without first opening the
production of NO, and within levels that lead to pre- spigot past a slow drip. Without a plentiful supply
dominantly positive results. [17] This is the “causal” effect of oxygen, the heightened efficiency of the cell will
that has been well documented: laser promotes the have little effect on the clinical outcome. There must
production of NO by somehow enhancing the conver- be some way to increase local oxygenation with laser
sion of nitrosyls (molecules containing the NO+ ion) to therapy …
NO. [17, 18] But there is also a “resultant” theory. (NOTE:
you can read more about NO in Chapter 3.)
N-O and O-O look very similar at the molecular
level; the N is only slightly smaller than the O, and so Summary from a
the molecules tend to bind to similar things. This can be different perspective
very bad, in the same way that C-O (carbon monoxide)
binds to similar things as O-O, which will cause the cells Light can have a therapeutic effect if it penetrates
to suffocate. If NO binds to things in the cells that need the skin and gets absorbed by certain molecules.
to (and normally do) bind to O , cells are inhibited. But For light to penetrate the skin, wavelength is the
2
the fact that light therapy increases the amount of NO first limiting factor. The therapeutic window is
available for the cell (all things being equal), means that around 700–1000 nm. Melanin acts as a barrier
it is making better use of the O , which is a VERY good by absorbing light in the visible to 750 nm range,
2
thing for the body. but is more transparent to longer wavelengths.
Remember that the cell needs O as the final elec- Light is absorbed by molecules such as H O,
2
2
tron capture agent in the respiratory cycle. Well, NO melanin, hemoglobin, and cytochrome c oxidase.
competes with O for this last electron capture. But The right type and amount of light can have
2
again, amounts of extracellular NO have been shown the effect of increasing temperature, metabolic
to increase with laser, which means O is being better efficiency, and O delivery.
2
utilized in more efficient ATP production. 2

While this is true, certain clinical situations can be
particularly susceptible to NO
production. For instance, ischemia –
reperfusion injury. In a model in which
blood flow from the cranial mesenteric
artery was occluded for an hour, LT increased tissue
damage, at least in the first few hours. [19]

REDONDO PRINT (4-COL BLEED).indd 9 08/08/2019 09:46