Page 35 - Veterinary Laser Therapy in Small Animal Practice

Anti-inflammatory effect 21

histomorphometric analysis, and polymerase chain anti-inflammatory than those at the high end of
reaction (PCR) for pro-inflammatory and pro-fibrotic the range. For instance, in a rat model of induced
molecules, LT-treated animals showed a decreased arthritis, 4.5 J/cm applied with 0.4 W/cm had a
2
2
inflammatory and fibrotic response compared to con- strong anti-inflammatory effect, decreasing the
trols. In a rat model of crescentic glomerulonephri- levels of inflammatory cells and mediators, but 72 J/
tis, [72] transcutaneous LT (daily for 14 days) decreased cm with the same power density lacked effect. [78] In
2
the expression of inflammatory mediators in the renal a model of muscle injury (muscle damage induced
2
2
cortex, the infiltration of macrophages and lympho- by freezing), using 0.5 W/cm , 10 J/cm was more
cytes, and the morphological damage to glomeruli. effective than 50 J/cm in decreasing COX-2 expres-
2
In an experimental model of acute muscle injury, sion. [37] Remember this is a rat model and we are not
LT was more effective than topically applied diclofenac transposing this figures straight into a dog; however,
or cryotherapy in decreasing the release of pro-in- at some intuitive level it makes sense to think that
flammatory cytokines. Higher doses did not seem to strong stimulation is not the point when working
help. It decreased COX-2 expression while improving with acutely inflamed tissue. But then think how
muscle injury healing, increasing collagen synthesis, little of the energy delivered to the surface can reach
and improving its organization to be more similar to the tissues; the good news is that in the deep tissues,
the unharmed tissue. [37] In osteoarthritis models, LT where less of the light penetrates, the effect is more
decreased polymorphonuclear cell numbers in the likely to be anti-inflammatory.
synovial fluid and capsule. [41, 73] Tendinitis models also
showed a decrease in inflammation with LT (together Don’t forget that a certain degree of inflammation
with better collagen repair and other effects). [47, 74] For is part of the healing process, even if we describe these
most tissues you will find some scientific evidence of effects separately. The other big effect of LT is anal-
the anti-inflammatory effect of LT. For instance, vascu- gesia. Of course, inflammation and pain are not inde-
lar inflammation and abnormal metabolism are patho- pendent either; after all, pain is one of the classical signs
logical components of several neurodegenerative and of inflammation.
arterial diseases. LT was able to decrease abdominal
aortic aneurysm progression in a mouse model. [75] Or
in an experimental model of rat mastitis, LT decreased Summary from a
the number of neutrophils entering the mammary different perspective
alveoli. [76]
Finally, let’s consider two facts with potential clinical Inflammation is part of the healing process, and
consequences.
the “soup” of mediators is a very complicated
network of real-time balancing acts. Most of these
• Steroids seem to play a role in the anti-inflammatory molecules don’t absorb light directly, but even
effect of LT. A study in rats found the anti-inflam- minor changes in the soup, caused by the external
matory effect was lost in adrenalectomized individ- stimulus of light, can initiate a cascade of events.
uals. [24] Interestingly, in that study they compared Mysteriously enough, the vast majority of these
doses of 1, 2.5, and 5 J/cm , and 5 J/cm seemed not types of cascade that have been studied lead to a
2
2
to work. But the same author, years later, described positive effect. This supports a major theme in this
an anti-inflammatory effect with an even higher book: laser doesn’t determine the direction of the
dose, 7.5 J/cm , using the same animal model. [77] effect; the body (by and large) wants to heal itself,
2
• In some reports, lower doses were found to be more
and laser simply enables it to do so.

REDONDO PRINT (4-COL BLEED).indd 21 08/08/2019 09:47