Mea culpa. Yesterday, our gourmet club had its annual
September picnic. My wife and I were the planners, with the
responsibility of creating the menu, distributing the food
preparation assignments and bringing the various libations for
some 32 picnickers. When my wife, who hates wasting food,
showed me her assignments I maintained vigorously that she
wasn”t planning enough food. My opinion was taken to heart,
reluctantly, and she increased the quantities accordingly. In my
defense, five people didn”t show up, making the dining total 27.
Nevertheless, I was completely wrong and we literally had
enough food left over for another 27 people! In the beverage
area, I insisted that we take 38 bottles of Heineken with another
10 bottles at home in case of emergency. Needless to say, I was
shocked to find our total consumption of beer to be 12 bottles.
Brian Trumbore would be ashamed of us! My only explanation
is that our club does tend to be in large measure in or close to the
senior citizen category and (a) our appetites and metabolisms are
markedly decreased and (b) it takes too much energy to get up
and walk over for seconds.
Unfortunately, another thing that slows down as you get older is
the osteoblast. Osteoblasts, let”s call them OBs for short, are the
cells in our bodies that are responsible for making new bone.
These OBs certainly have their work cut out for them as we grow
from infancy to our final skeletal size in young adulthood. The
amount of material placed upon that skeletal framework
thereafter has become the object of concern for an increasing
number of members of our society. Actually, our OBs don”t call
it quits after we reach adulthood, but continue to manufacture
bone even in our senior years. Otherwise my broken leg,
suffered while pacing off the distance to reproduce my hole-in-
one on that hole, would not have healed.
You might question at this point why, if the OBs continue
working, we all don”t just get taller and taller as we age? It”s the
osteoclasts, or OCs for short. These OCs are cells that chew up
or resorb old bone. Throughout our lives the OBs and OCs are
making and destroying bone tissue and it”s mostly a harmonious,
beneficial relationship between the two activities. Just as so
many in our area are remodeling their homes, so too is your bone
structure undergoing continual remodeling. In the September 1
issue of Science there is a collection of papers describing the
current status of bone remodeling and repair. This bone
remodeling, if I interpret these papers correctly, goes something
like this. The OC attaches to the bone and manages with some
neat chemistry to dig out a pit (bone types call it a lacuna). When
the OC is finished, along comes the OB to put bone back in the
pit. The OCs are relatively fast workers, finishing their
excavation of their pits in around 3 weeks. The OBs, on the
other hand, are derived from bone marrow cells and take 3 to 4
months to fill in those pits! It”s estimated that your skeleton is
completely remodeled every decade.
Osteoporosis is certainly the skeletal problem that gets most
attention as we age. At age 30, the balance of power begins to
shift to the OCs, i.e., the OBs don”t put as much bone back in the
pits as the OCs take out. One of the leaders in the field of
biomedical materials is Larry Hench, Chair of Ceramic Materials
at Imperial College in London. On the occasion of his receiving
the Von Hippel Award of the Materials Research Society (MRS)
in 1998, he presented two figures I saw in the May 1999 issue of
the MRS Bulletin. One figure was a graph of human
survivability in 1900 compared to estimates for 2000. I presume
this was a global figure but he didn”t give a reference. The
shocking thing to me was that in 1900 only about 40% of us
humans lived to be 10 years old. Of those who lived to be 10,
only half were alive at 50 and very few made it to 60 or 70. In
contrast, today almost everyone survives to age 20 and over 60%
survive to 60, with a quarter or so getting to 80. And Willard
Scott, of the Today show, certainly doesn”t lack for pictures of
centenarians to put on those Smuckers jars.
The other Hench figure deals with the decay in bone strength in
men and women after age 30. Hench cites the structure of the
hipbone and its change with age. The hipbone consists of an
outer compact bone layer but the interior is so-called trabecular
bone. This inner material has a porous spongy type of structure
that is lightweight but structurally strong and also provides a
large surface area for metabolism of the body as a whole. It is
this open structure that deteriorates and the result is that women
eventually lose 40 to 50% of their bone strength. With men, it”s
more like 10 to 20%. Too often, the result is the shearing off of
parts of the hip, fractures of the longer bones and collapse of
vertebrae. Combining the two figures, Hench points out that the
at-risk population in the world for these types of problems is
catastrophic and that hundreds of thousands of people suffer
these problems.
What about prevention of bone damage, particularly that caused
by osteoporosis? You”ve all heard of or may be using hormone
replacement therapy, notably estrogen replacement therapy, with
all its pros and cons. In reading these various articles and
searching the Web, I”ve learned that the simvastatin I take for my
cholesterol and the thiazide diuretic for my blood pressure both
appear to favor bone formation over bone loss. It”s too late,
however, for my broken leg with its stainless steel plate. I asked
one graduate student in our bone-healing group at Robert Wood
Johnson Medical School about getting the plate removed. Her
reply was that I should do it before I”m 80. I think I may have
found her reason for this suggestion. It”s stem cells.
There”s currently a lot of talk about the ethics of using stem cells
from embryos for research and treatment of diseases. It seems
that stem cells from embryos can be induced to form virtually
any type of cell in the body. However, when it comes to bone
repair, there”s a problem. Bone marrow stem cells aren”t as
versatile but are committed to end up as cells devoted to bone,
cartilage, tendon, heart, muscle and neural tissues. The hitch is
that these stem cells drop from 1 in 10,000 bone marrow cells at
birth to 1 in 400,000 at age 50 and at age 80 there are only 1 in 1
to 2 million cells. I guess that at 80 there just won”t be enough
cells available for recruiting to fill the holes left by the screws
holding my steel plate.
What to do when severe bone damage has occurred? The
approach of Larry Hench, his wife June Wilson-Hench and their
colleagues has been to come up with ceramic materials that not
only the gaps in the damaged bone but also interact with and
bond to the bone. In addition, they have found materials that
will bond both to bone and to soft tissues. The materials are
marketed under the trade name of Bioglass. One application in
the field of hearing impairment has been in use in human patients
for 14 years. Bioglass has been implanted to replace missing
middle-ear bones in children. The Bioglass served to bridge the
space between the eardrum and the bones remaining in the ear.
With hearing restored, in 14 years there had not been a case of
penetration of the implants through the eardrum. This was a
primary cause of failure in previous implants.
This bioactive ceramic material has had its most extensive use in
the dental arena. According to Hench, about a million teeth have
been saved from the ravages of periodontal disease, in which
microorganisms attack the bone around a tooth. By filling the
resulting eroded regions of the bone with finely powdered
Bioglass, the bone regrows rapidly and the periodontal ligament
reattaches. This ligament turns out to be an important player in
promoting healthy bones. When we bite down on something we
are compressing the bone heavily, or would be without the
ligament. The ligament takes the brunt of the compressive load
and stretches, pulling on the bone so the bone feels more of a
tensile (lengthwise) load. Why is this important? Compressive
loads tell those OCs to get cracking and the bone is resorbed at a
rate of a millimeter a year. A few years go by and no more bone!
In contrast, tensile loads signal the OBs to counteract the OCs
destructive ways.
Back to the gourmet picnic. Now my wife tells me that she has
found the reason why her pina (tilde over the n) colada cake
maintained its thickness quite well, while the other two gals”
cakes both fell substantially on removal from the oven. It”s my
fault again! In reproducing the recipes for distribution, I copied
1/2 rather than the recipe”s 1/3 cup of Bacardi dark rum! This
50% error seems to have led to the densification of the cakes, as
well as their more pronounced rum flavor. I can only plead
failing eyesight. And this was before I ran over my glasses with
a golf cart last week!
Allen F. Bortrum
