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Research Program Summary
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David N. Herndon, MD
Chief of
Staff and Director of Research
Shriners Burns Hospital - Galveston
Director,
Combined Burn Service
University of Texas Medical Branch in Galveston
Research efforts at the Shriners Hospital for Children in Galveston, Texas
continue to be directed at understanding one of the most severe and complex
injuries a child can sustain. Burn investigators, both clinical and basic
science, are focusing their efforts on clinical problems pertinent to
improving survival and the quality of life for all burned children. We
continue to direct our interest in the areas of cardiopulmonary
pathophysiology, metabolism, responses to thermal injury at the molecular
level, infection, wound healing, and integrated long term outcomes of burned
children.
Cardiopulmonary
Pathophysiology
Traumatized
acute lung injury is responsible for a great deal of the mortality which we
see in thermally injured patients, in fact, few of our children die from
their burn wounds who do not have a concomitant inhalation injury.
Investigators at the Shriners Burns Institute have demonstrated that there
is a marked increase in systemic blood flow to the airways following
inhalation injury. Most recently we have accumulated evidence that
hyperemia is mediated by a neural inflammatory response. In addition to
these studies, we have demonstrated that if the airway and one lung are
subjected to inhalation injury, the opposite lung, although not exposed to
smoke, develops edema and evidence of tissue damage. These studies confirm
the neural influence in the response. These studies demonstrate that the
treatment of the airway may prevent life threatening changes that occur in
the gas exchange areas of the lung.
Back to
TOC
Acute Lung Injury
Recently, smoke inhalation studies
have focused on airway damage as the major cause of lung injury.
Investigators have determined that blood from injured airway flows through
the gas exchange area. This broncho-pulmonary shunt transports toxic
mediators from the injured airway to the areas where gas exchange takes
place. It is now possible to determine if the reduction of blood flow
through the shunt minimizes injury to the gas exchange areas. This
discovery is important since drugs applied to the airway by nebulization
would be absorbed into the brochial circulation and carried to the
parenchyma to prevent or minimize damage. Thus far, two compounds appear
successful in treating the inhalation injury by nebulization into the
airway.
Mediators released from the
bronchial circulation cause white blood cells called neutrophils to stick in
the pulmonary microvasculature and to release cytotoxins, such as free
oxygen radicals and proteases, which in turn damage the air exchange areas
of the lung. We have been studying this phenomenon and now show that a
different mechanism is involved for the adherence and movement of
neutrophils into the air exchange areas of the lung that is seen in systemic
tissues.
Burned patients frequently
must be placed on a ventilator since their lungs may be damaged to the
extent that they cannot support life. This support ventilation itself can
cause damage to the lung. We have continued to work in the development of a
catheter, which can be placed in the circulation and act as a gas exchanger.
We are further investigating
the morphological and physiological alternations in alveolar macrophage
function after smoke inhalation. These abnormalities may contribute to
diminished pulmonary host defense during smoke inhalation injury. In order
for survival to take place following inhalation injury the cellular damage
to the airway must heal. We are now studying techniques that accelerate the
healing process. Investigations have demonstrated that the healing can be
accelerated by 30% with the combination of epidermal and platelet derived
growth factors and a 40% increase if the growth factor was combined with
Vitamin A. This study is important since acceleration of the healing
process may minimize scarring processes, which may cause chronic lung
disease.
The healing process can also
be delayed by infection. Our research team has studied the effects of
Pseudomonas aeruginosa; bacteria commonly associated with airway infections
and have determined that these organisms adhere to airway epithelial cells.
The understanding of this adherence has led to investigating compounds that
can block or reverse infections caused by these bacteria.
Back to TOC
Thermal
Injury and Resuscitation
Data show that large numbers of
severely burned patients have a poor outcome because of inadequate
resuscitation. Much of the misunderstanding with resuscitation results from
the fact that research has used models with full-thickness burns that cover
approximately 40% of the animal’s body surface. Many thermally injured
patients, however, have larger burns that are partial thickness. We have
been studying large animals given an 80% second degree (partial thickness)
thermal injury. Our findings in relation to fluid resuscitation techniques
show that the combination of high concentration salt mixtures and high
molecular weight starch may be superior to the more traditional technique of
resuscitation with balanced salt solutions.
Back to TOC
Metabolism
Severely injured patients are
often metabolically hyperactive. In the past, investigators at the Shriners
Burns Hospital-Galveston have established that there is an increase in two
of the major glucose regulatory hormones, glucagon and insulin. They have
further reported that the elevation of these two hormones contribute to the
elevation of blood glucose as well as the transport of the sugar into the
cells of the various body organs. The elevation in intracellular glucose
then drives the metabolism of this sugar in a more rapid fashion to the end
product of the major glucose metabolic pathway, the pyruvate. This latter
compound can be metabolized in three different ways. It can be converted
into lactate and be released into the blood where it circulates to the liver
to be resynthesized into glucose. This occurs in burn patients but this
cycle will not account for all of the elevated pyruvate formed. It can go
into a cycle called the Krebs cycle that breaks it down into water and
carbon dioxide. The rate with which this cycle operates is determined by
the body’s energy expenditure. Energy utilization of the thermal injured
patient is minimally increased in comparison to the total pyruvate load
elevation. Consequently, the overabundance of this material must go
into the other two pathways. The amino acid glutamine can donate an amine
to the pyruvate to convert it into the amino acid alanine. It has been
determined that this latter is the phenomenon that occurs in thermally
injured patients. It is unfortunate for this depletes the body of its
glutamine stores. There are many cells such as the epithelial cells of the
gastrointestinal tract, which are dependent upon this particular amino acid
for their viability. Consequently, as a result of its depletion, these
cells may atrophy. Glutamine is also an important substrate for metabolism
in white blood cells. Thus, a deficiency of the amino acid may result in a
compromised immune function. This is a major accomplishment by our
metabolism group. Preliminary data suggests that this phenomenon may be
reduced by the administration of propranolol.
Normal subjects on typical
diets are able to break down 20 to 50% of the urea that would otherwise be
excreted in urine and they can re-use the nitrogen contained in the urea for
synthesis of the amino acid building blocks of proteins. Studies this year
have shown that this metabolic process is absent in burned children
maintained on clinical diets. A failure to recycle this nitrogen may thus
contribute to the muscle wasting that accompanies burn injury.
It has previously been
reported that thermally injured patients experience bone demineralization.
This causes them to easily fracture their bones, a problem that can greatly
prolong their hospitalization. Burned patients remain immobile for long
periods of time. This can likewise result in demineralization. Burned
sheep, however, are not immobile and thus it is easy to determine the
affects of burn injury on bone demineralization. Investigators at the
Shriners Burns Hospital-Galveston have evidence from preliminary studies
that the demineralization can occur from thermal injury alone.
Back to TOC
Molecular Responses to Injury
A strong focus on the
molecular mechanism underlying cellular responses to injury has been
developed at Shriners Burns Hospital-Galveston, Texas. These investigators
are examining the molecular mechanisms that regulate changes in gut and
hepatic gene expression following injury and following septic challenge.
The hepatic acute phase response is an example of the alteration in liver
function that occurs during the systemic inflammatory response. Also, gut
mucosal injury is a prominent feature of a large burn injury and in the
response to endotoxin it is important to determine the molecular mechanisms
underlying the gut injury and repair sequence. A better understanding of
these mechanisms may provide novel targets for pharmacologic therapy aimed
at preventing complications such as overwhelming sepsis and multiple organ
failure that are determinants of mortality in burn patients.
This group has also shown that
heavy metals such as Hg, Pb, and Cd induce a subset of genes belonging to
the family of acute phase reactants. The proteins that are induced are
important for protection against further tissue damage during the
inflammatory response. During the past year we concentrated on elucidation
of how heavy metals induce the expression of these genes. Our studies have
shown that Hg causes an increase in proteins in the nucleus that activate
these genes. These transactivators belong to the C/EBPa family of
regulatory proteins. Our studies also suggest that activation of the acute
phase reactant by heavy metals proceeds via a unique pathway that differs
from the pathway activated by the bacterial endotoxin, lipopolysaccharide.
These acute phase reactant genes are also activated by thermal injury. Our
goal is to elucidate the similarities and differences in the response to
various inflammatory agents including thermal injury, heavy metals and
endotoxins. An understanding of these pathways is essential for development
of clinically important treatment protocols.
Our researchers have
identified, for the first time, functional neurotensin receptors on
T-lymphocytes and, in addition, have found that the amino acid glutamine
serves as an important nutritional component to increase the expression of
the heat shock gene. These findings have important implications in the
management of patients who have sustained traumatic injuries. They have
also demonstrated changes in the expression of liver genes and their protein
products that occur during the systemic inflammatory response to sepsis or
to massive trauma such as major burns. The toxic bacterial product called
endotoxin causes rapid induction of a set of liver genes whose induction was
previously associated with liver regeneration. Proteins induced by
endotoxin are regulators of gene transcription and may have important roles
in altered hepatic function following systemic inflammation.
Back to TOC
Sepsis
Ultimately, the major cause of
death in thermally injured trauma patients is gram-negative sepsis. With
this syndrome, several of the organs fail to function. Researchers at this
institute have determined, in a model of sepsis, that there is a failure of
the kidneys, the heart and the lung. They have been accomplishing studies
for several years in an effort to determine the mediation of this response.
Most recently they have discovered that a thromboxane synthetase inhibitor,
an aspirin-like compound, would prevent this multi-organ failure seen with
endotoxin.
Many of the thermally injured
patients develop blood borne infections or sepsis, yet the source of the
organisms cannot be determined. Some investigators have speculated that the
gastrointestinal tract is the source of these organisms. Recently, a group
of investigators at the Galveston Unit have demonstrated that following
thermal injury, smoke inhalation or the administration of bacterial toxins
causes a constriction of the blood vessels that go to the intestine. The
lack of blood flow, or ischemia, which results is associated with the
appearance of bacteria from the GI tract and several other systemic areas of
the body suggesting that the hypoxia has compromised the barrier which
prevents bacteria from entering the body. They have demonstrated that
vasodilator agents will reverse this phenomenon, and more recently they have
demonstrated that the same agent that was being studied by the endotoxin
group, the thromboxane synthetase inhibitor, would likewise reverse the
vascular constriction seen after thermal injury and prevent the bacterial
translocation. This is a most important finding which may have some life
saving results in the future.
The researchers at the
Shriners Burn Hospital-Galveston have developed an animal preparation that
mimics the phenomena of sepsis (blood born infection or blood poisoning)
observed in our patients. This syndrome is responsible for severe
complications in the majority of burn patients and is the case of death in
the majority of burned children. Dilators released in the syndrome cause
vasodilatation and diverts the life giving blood from vital tissues to those
that are not metabolically active. This shunt leads to the failure of many
organs and the death of the patient. At Shriners Burns Hospital-Galveston
investigators have determined that a drug that blocks a natural dilator,
reported to be released in sepsis, would reverse this process. The results
of these investigations have led to multiple clinical trails of this agent
in Europe and soon in the U.S. Preliminary results indicate that the
compound will prevent morbidity and mortality in septic humans in the same
manner that it worked in sheep.
Back to TOC
Blood Borne
Infections (Sepsis)
The mechanism by which
bacteria enter into the body in burned patients has been a mystery in many
situations. Dr. David Herndon and his research team have determined that
bacteria enter the circulation from the gastrointestinal tract following
thermal injury. This action is accentuated in the septic animal model.
Thus, thermal injury causes bacteria to enter into the circulation and this
in turn results in many more bacteria and their toxins entering into the
circulation, a phenomena called a positive feedback loop. This group has
demonstrated that this phenomenon can be blocked by the administration of
aspirin-like drugs and a compound that blocks a constrictor material
produced by the kidney. Dr. Herndon has also established a collaborative
arrangement with Dr. Wolfe’s group to study protein metabolism in these
animals and Dr. Papconstantinou, who is evaluating the role of acute phase
reactant proteins.
Other research teams have been
able to produce antibodies against L-selectin, E-selectin, and P-selectin
for use in blocking neutrophil emigration into the lungs of the sheep. They
have cloned a near full-length cDNA for sheep P-selectin and have expressed
a recombinant protein fragment from this DNA in E. coli. This material is
essential for producing antibodies against both P and E selectin. In
addition this group has identified a cross-reacting antibody against sheep
L-selectin.
Back to TOC
Wound
Healing
Growth factors released by
traumatized cells promote cell migration into the wound, epithelial cell
growth, growth of blood vessels, matrix formation and remodeling. KC is a
protein that regulates the replication of certain cells and the synthesis of
proteins essential for wound healing. During the past year, Dr.
Papaconstantinou has shown that the production of KC is significantly
increased in rat thermal injury models and that many tissues produce KC, but
the liver is the major site of its synthesis. Their studies suggest that KC
may play a key role in the early phases of wound healing and have cloned the
KC gene and are in the process of transferring the gene into cells that are
involved in wound healing. This group has also determined that the cytokine
KC is secreted by burned animals. More surprising is the finding that
animals, which secrete KC in large quantities, have a greater ability to
survive the response to thermal injury than low secretors. The primary
goals are to devise gene therapy techniques that would accelerate wound
healing and reduce scar formation.
Wound healing has likewise
been studied by our research team. They have developed techniques for
evaluating the tensile and breaking strength of wounds and have recently
begun studying the relationship of Fibrinogen, one of the major components
of a clot and hyaluronan, the basic component of the intercellular matrix.
It further has been determined
that growth hormone stimulates wound healing in burned children. These
studies have continued with the addition of the growth promoting material,
insulin-like growth factor-one.
Back to TOC
Longitudinal Psychological Adaptation to Trauma
Trauma significantly impacts
not only the patient but also the patient’s family and community as well.
Focusing on the burned child/family as a model, a team of investigators at
Shriners Burns Hospital-Galveston has conducted a series of studies to
identify outcome sequelae and factors that enhance positive long-term
adaptation. These studies reveal an incidence of 20 to 40% of each sample
of the population, regardless of size or severity of the injury, to exhibit
moderate psychological problems. The data indicate that, although most
burned children do not develop serious behavioral pathology, many may fail
to develop positive adaptive behaviors that would enhance their psychosocial
adjustment.
Characteristics of the family
of the patient have been found in several studies to be the primary factors
contributing to positive psychosocial recovery for this pediatric burn
population. Family values of cohesion, autonomy, organization, and
achievement have been identified as most important to the child’s positive
adjustment. A strong relationship exists between disturbance of a parent
and disturbance attributed to the patient by that parent. No causal
relationship is yet clear, but the findings emphasize the need for including
the family unit in studies and treatment of the burned child.
Although most of the work of
this group has focused on pediatric burn patients, they recently concluded a
study comparing a sample of burned children/families to head-injured
children/families. Results for both trauma populations suggest that family
characteristics most significantly contribute to psychosocial outcome for
the child. Families of resilient children in both groups were significantly
more cohesive and emphasized moral-religious values to a significantly
greater degree than the normative reference groups of non-clinical
families. The traumatized children, both head-injured and burn injured, who
did not make positive adjustments had families that did not differ from the
norm. These findings suggest that an adaptive familial response to
traumatic injury to a child can promote successful long-term adjustment of
that child for even the most severely injured children and regardless of the
visibility of the child’s impairment.
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