Nitric
Oxide and Its Role in Health and Diabetes.
Thomas
Burke Ph.D.
Part 9. How Light
(Photo Energy) May Increase Local NO and Vasodilation
Light mediated
vasodilation was first described by R F Furchgott, in his nitric oxide
research that lead to his receipt of a Nobel Prize in 1998. Later
studies conducted by other researchers confirm and extend
Furchgott’s early work and demonstrate the ability of light or photo
energy to influence the localized production or release of NO and
stimulate vasodilation through NO’s effect on cGMP (as discussed in
detail in Part 4). This finding suggests that properly designed
illumination devices may be effective, noninvasive therapeutic agents
for patients who would benefit from increased localized NO
availability.
At first blush,
some might question that something as simple as light can have such a
profound biological effect. However, the biological importance of light has been
recognized for quite some time. Various wavelengths of light are
absorbed by chemical compounds, which then lead to biologic responses.
Sunlight absorbed by chloroplasts in plant cells permits formation of
starch. Sunlight absorbed by human skin generates vitamin D. Blue
light applied to the back of the knee will alter human circadian
rhythm. Some wavelengths of light, including near infrared and
ultraviolet (UV) light cannot be seen with the human eye, and yet UV
causes biologic effects, especially in the skin. Near infrared photo
energy also exerts biologic effects
All light, visible
or invisible, consists of photons. The size or mass of the photons is
dependent on the specific wavelength of the light. Considerable
research has been conducted about light (photo energy).
This research shows that the target tissues must first absorb
light in order to have a biological effect. Additionally, absorption
is best achieved when the light is 1) directed perpendicular to the
skin, and 2) placed in direct contact with the skin. Moreover, photo
energy emitted from a source that produces of a homogenous wavelength
is often more effective therapeutically than light composed of several
wavelengths (for example white light)
Recent research
supports the hypothesis that some wavelengths of photo energy are
absorbed by hemoglobin and that intense illumination can release the
NO from hemoglobin (specifically from the nitrosothiols in the beta
chain of the hemoglobin molecule) in red blood cells (RBCs). This
finding provides the basis of a potentially profound noninvasive
therapeutic device for patients who would benefit from increased
localized NO availability. Since RBCs are continuously delivered to
the area of treatment, there is a natural supply of NO that can be
released from each new RBC that passes under the light source and is
exposed to the appropriate wavelength of photo energy. Since the half
life of the NO released under the area of illumination is only 2 to 3
seconds, NO release is very local, preventing the effect of increased
NO from being manifested in other portions of the body.
What’s more, dosage is taken care of the body itself. As you
will recall, vasodilation from NO is based its effect on the enzyme
Guanylate Cyclase (GC), which forms cGMP to phosphorylate myosin and
relax smooth muscle cells in the vascular system. Once available levels of GC are saturated with NO, or once
maximum levels of cGMP are achieved, further vasodilation through
illumination will not occur until these biologic compounds return to
their pre-illumination status.
One device that
employs illumination to apparently increase the localized levels of NO
is The Anodyne Therapy System. This
FDA cleared medical device delivers near infrared (890 nm) photo
energy from 60 super luminous diodes mounted on flexible pads that can
be placed in direct skin contact; in addition, the flexible pads
assure that the photo energy is delivered perpendicular to the skin to
maximize absorption. Tests
conducted with a scanning laser Doppler (Moor Instruments) demonstrate
that the near infrared photo thermal energy delivered by the Anodyne
Therapy system can increase localized microcirculation by as much as
3200% after just 30 minutes. Further
tests show that increased microcirculation achieved by the Anodyne
Therapy System on neuropathic feet is 10 times more than that achieved
with warmth alone.
In summary, intense
illumination of the skin may non-invasively increase the localized
release of NO from hemoglobin. The
effectiveness of the illumination is dependent upon absorption by the
targeted tissues, which is based on wavelength, skin contact, and
perpendicular delivery. The potential net effects of skin contact
illumination are those we have previously discussed in relation to NO,
i.e., better blood flow via stimulation of GC, acute delivery of
growth factors and white blood cells, fibroblastic differentiation and
proliferation, angiogenesis, reduced edema, and mediation of pain.
The next article
will be a summary of the biology of NO, as outlined in previous parts
of this series; in addition, we will discuss how this very important
molecule regulates so many other important biologic functions which
are important for the health of diabetic patients.
Dr.
Tom Burke received his PhD in Physiology from University of Houston,
Post Doctoral Training at Duke Medical School, He was an Associate
Professor of Medicine and Physiology at the University of Colorado
Medical School. He has authored more than 70 published scientific
clinical articles and has been a visiting scientist at the Mayo
Clinic, Yale University, University of Alabama, and University of
Florida. He is a recognized international lecturer on cell injury and
nephrology.
View Part
1, Part 2, Part
3, Part 4, Part
5, Part 6, Part
7, Part 8
View
Dr. Burke's Archive
Printer
Friendly Version
|