THE SYSTEMIC RESPONSE TO INJURY

THE SYSTEMIC RESPONSE TO INJURY

INTRODUCTION:

Injury :

Surgical

Traumatic

Infectious

Host response:

Endocrine

Metabolic

Immunologic

Minor Injury:

Limited duration

Healing and restoration of metabolic and immune homeostasis readily occurs

Major Injury:

Deterioration of host regulatory response

Precludes full restoration of function

Results to death

Initial Response to Injury

Inherently inflammatory

Activation of cellular processes

Restore or maintain function in tissues

Promoting eradication or repair of dysfunctional cells.

Dynamic process: presence of counter-regulatory processes

ENDOCRINE RESPONSE TO INJURY

Hormone Response Pathways

Mediators released by the injured tissues

Neural and nociceptive input from the site of injury.

Baroreceptor stimulation from intravascular volume depletion

Hormones released:

Hypothalamopituitary controlAutonomic nervous system control

Primary stimuli of neuroendocrine reflexes:

1. Effective circulating volume

2. Oxygen, carbon dioxide and hydrogen ion concentration

3. Pain

4. Emotional stimuli ( fear and anxiety )

5. Energy substrates

6. Temperatures

7. wounds

Hormone-Mediated Receptor Activity

Central to the mediated response at the cellular level:

Hormone-receptor interaction

Post-receptor activity

Mechanisms of Signal Transduction:

1. Receptor kinases e.g. insulin and IGF

2. Guanine nucleotide-binding or G protein-coupled receptors( activated by peptide hormones, neurotransmitters, prostaglandins)

3. Ligand-gated ion channels

Hormone-Mediated Intracellular Pathways

caAMP: most common intracellular second messenger.Hormone Receptor Cell membrane alteration Activation of Adenylate Cyclase ATP cAMP

/

Activation of various intracellular protein KinasesADRENOCORTICOTROPIC HORMONE (ACTH)

In non-stressed healthy human being- Release is circadian

- Peaks at late night and last just before sunrise

In injured subjects

Elevated CRH and ACTH

Pain and anxiety are prominent mediators for release in conscious patients.

ACTH-promoting mediators active in injury:Vasopressin

Angiotensin II

Cholecystokinin

VIP

Catecholamines

Oxytocin

Proinflammatory cytokines

ACTH zona fasciculata adenylate cyclase cAMP protein kinases, cytochrome P450 desmolase-catalyzed side-chain cleavage of cholesterol glucocorticoid production

CORTISOL/GLUCOCORTICOIDS

Cortisol- the major human glucocorticoid

Essential for survival after significant physiological stress.

In injury:

Not under diurnal variation

May remain elevated depending upon the type of systemic stress

In burns = 4 weeks

In hemorrhage = 1 week

Return to normal levels after restitution of blood volume after hemorrhage.

Co-existing systemic stress (e.g. infection) can prolong elevation

Effect on Host Metabolism:

Potentiates the actions of glucagon and epinephrine

Hyperglycemia

Stimulates enzymatic activities favoring gluconeogenesis

=Induction of phosphoenol pyruvate carboxykinase=Induction of transaminases

Decreases insulin binding to insulin receptors in muscles and adipose tissues

Induces proteolysis and augments release of lactate in muscles

Shifts substrates for hepatic gluconeogenesis

Stimulates lipolysis and inhibits glucose uptake by adipose tissues.

Increases the lipolytic activity of ACTH, GH, glucagon, and epinephrine

Rise in plasma free fatty acids, triglycerides and glycerol

10% in active form

90% bound to cortisol-binding globulin (CBG) and albumin

With injury:

Increase total cortisol level

Decrease CBG and albumin to about 50%

Increase free cortisol of as much as 10X the normal level

ACUTE ADRENAL INSUFFICIENCY

Life threatening

Usually due to atrophy of the adrenal gland from indiscriminate use of exogenous glucocorticoid.

Symptoms:

Weakness

Nausea and vomiting

Fever

Hypotension

Signs:

Hypoglycemia due to decreased gluconeogenesis

Hyponatremia due to impaired Na resorption

Hyperkalemia due to diminished kaliuresis

IMMUNOSUPPRESION

EFFECTS:

Rapid lymphopenia

Monocytopenia

Eosinopenia

Neutrophilia

IMMUNOLOGIC CHANGES:

Thymic involution

Decrease T killer and natural killer cell function

Decrease T lymphocyte blastogenesis

Decrease mixed lymphocyte responsiveness

Impaired graft-versus-host reaction

Delayed hypersensitivity responses

Immunologic changes

Monocytes lose capacity for intracellular killing but maintain normal chemotactic and phagocytic properties.

Neutrophil decreases its chemotactic activity

Inhibits immunocyte proinflammatory cytokine synthesis and secretion.

Important negative regulatory function in the inflammatory response to injury.

MACROPHAGE INHIBITORY FACTOR A glucocorticoid antagonist produced by the anterior pituitary.

Can reverse the immunosuppressive effects of glucocorticoid

Systemically via anterior pituitary secretion

Locally via T lymphocyte secretion

TRH ( Thyrotropin-Releasing Hormone )

Primary stimulant for the synthesis, storage and release of TSH.

TSH (Thyroid Stimulating Hormone)

Secreted by the anterior pituitary thru TRH stimulation.

Stimulates the production of thyroxine(T4) in all its phases of synthesis, storage and release.

Corticosteroid, GH, somatostatin, fasting, T4 and T3 can inhibit secretion

Estrogens can also stimulate TSH release.

THYROID HORMONES (T4 & T3)

T4 is converted to T3 in peripheral tissues.

T3 is more potent that T4.

Transported intracellularly and bind to cytosolic receptors.

Thyronine-receptor complex binds with DNA which mediate transcription of protein products.

Free T4 and T3 inhibit both TRH and TSH secretion in a negative feedback loop.

INFLUENCES ON CELLULAR METABOLISM AND FUNCTION:

Enhance membrane transport of glucose

Increase glucose oxidation.

Increase the formation and storage of fat when carbohydrate is in excess.

Elevation in overall oxygen consumption

Heat production

IN INJURY

Decrease T3 levels

Decreased TSH without compensatory rise.

Peripheral conversion of T4 to T3 is impaired.

Increased conversion of T4 to biologically inactive rT3( reverse T3 ).

Euthyroid sick syndrome/non-thyroidal illness.

Free T4 remain relatively constant despite reduced total T4 level.

Reduced free T4 in severely injured patients is predictive of mortality.

Immunologic effects:

Lymphoid cells have high-affinity nuclear and cytoplasmic binding sites for thyronine.

Increase amino acids and glucose uptake into cells.

In Hyperthyroid:

= Increased oxygen consumption

= Enhanced in both types of immunity

In Thyroid hormone depletion: Significantly decreased cellular and humoral immunity

GROWTH HORMONE

GHRH from the hypothalamus stimulates the release in the anterior pituitary in a pulsatile fashion mostly during sleeping hours.

Other factors that influence release:

Autonomic stimul

Thyroxine

AVP

ACTH

-melanocyte SH

Glucagon

Sex hormone

Physical exercise, sleep, stress, hypovolemia, fasting hypoglycemia, decreased circulating fatty acids, increased amino acid levels.

Factors that inhibit GH release:

Hyperglycemia

Hypertriglyceridemia

Somatostatin

Beta-adrenergic stimulation

cortisol

DURING STRESS/INJURY:

Promote protein synthesis

Mediated by a secondary release of IGF-1

Promotes amino acid incorporation

Promotes cellular proliferation

Attenuates proteolysis in the skeletal muscles and liver

Enhance mobilization of fat stores

Potentiates adrenergic lipolytic effects on adipose stores.

Promote hepatic ketogenesis

Inhibit insulin release

Decrease glucose oxidation causing elevation of blood glucose levels.

IGF ( insulin-like growth factor )

Mediators of hepatic protein synthesis and glycolysis

Increase glucose uptake and lipid synthesis in adipose tissues.

Increase glucose uptake and protein synthesis in skeletal muscles

Promotes incorporation of sulfate and proteoglycans into cartilage resulting to skeletal growth.

Inhibited by:IL-1TNF-IL-6

In injury, major surgery and anesthesia circulating GH levels increases but associated decrease in protein synthesis and negative nitrogen balance is due to decreased IGF.

Liver is the predominant source of IGF-1

Preexisting liver dysfunction leads to negative nitrogen balance

IGF-binding protein

Necessary for effective binding of IGF to the cells

Attenuates the catabolic effects after surgery

Effects on the Immune System:

Leukocytes have high affinity surface receptors for GH.

GH & IGF are immunostimulatory

Promote tissue proliferation

Augments proliferation of T lymphocytes it mitogens.

Augments the cytotoxicity of T killer cells to allogenic stimuli.

GH deficient human being do not demonstrate immunologic abnormalities.

SOMATOSTATIN

14 amino acid polypeptide

Produced by gastric antral cells and pancreatic islet D cells.

Inhibits release of:GHTSHReninInsulinGlucagon

Regulates excessive nutrient absorption and activities of GH and IGF during convalescence from injury.

GONADOTROPHINS AND SEX HORMONES

LHRH/GnRH (hypothalamus) anterior pituitary FSH/LH androgens/estrogens

RELEASE OF THESE HORMONES ARE BLOCKED BY:CRH

Prolactin

Estrogen

Progestins

Androgens

IN STRESS AND INJURY

LH and FSH are suppressed

Reduced estrogen and androgen secretion

Due to the inhibitory effect of CRH

Menstrual irregularity

Decreased libido

Estrogens:

Inhibits cell-mediated immunity

Inhibit natural killer cell activity

Inhibit neutrophil function

Stimulates antibody-mediated immunity

High estrogen states predispose patients to increased infectious complications.

ANDROGENS:

= Predominantly immunosuppressive

= Castration can enhance immune function

PROLACTIN

LHRH/GnRH and Dopamine from the hypothalamus suppresses prolactin secretion of the ant. pituitary.

Stimulants for release: *VIP=vasoactive intestinal polypeptide

CRH

TRH

GHRH

Serotonin

VIP

In injury:

Adults elevation

Children reduced

Has immunostimulatory properties

Reduced/depressed Prolactin levels:

Increased susceptibility to infection

Decreased lymphocyte proliferation

Decreased lymphocyte production and receptor expression.

Decrease interferon- production

Macrophage dysfunction

Also synthesized and secreted by T lymphocyte in an autocrine or paracrine fashion.

Elevated after major operation or insults

Activation of opioid receptors in the GIT reduces peristaltic activity and suppresses fluid secretion.

-endorphins

Attenuates pain perception

Induce hypotension thru serotonin-mediated pathway.

Induce hyperglycemia

Increase insulin and glucagon release by the pancreas

Modulates vasopressin and oxytocin secretion

Regulates catecholamine release

Anti-nociceptive

Increase natural killer cell cytotoxicity and T cell blastogenesis

ENDOGENOUS OPIOIDS

IL-1 activates the release of POMC, precursor of opioids, from the pituitary gland.

Mediates their effects through delta, kappa and mu receptors.

Inhibit proliferation and differentiation of lymphocytes and monocytes/macrophages

Immunoinhibitory effects are dose dependent and sensitive to the state of activation of the immune system.

HORMONES UNDER POSTERIOR PITUITARY REGULATION: ARGININE VASOPRESSIN & OXYTOCIN

ARGININE VASOPRESSIN

Also called Antidiuretic hormone

Synthesized in the anterior pituitary

Transported into the posterior pituitary for storage

Stimulus for release:

Elevated plasma osmolality detected by sodium sensitive hypothalamic osmoreceptors.

Beta adrenergic agents

Pain

Elevated glucose concentrations

Changes in effective circulating volume (10% or more) sensed by:

= Baroreceptors

= Left atrial stretch receptors

= chemoreceptors

Inhibits release:

alpha-adrenergic agonists

atrial natriuretic peptides

Effects:

Kidneys:

promotes reabsorption of water in the distal tubules and collecting ducts

Peripheral circulation:

vasoconstriction

- splanchnic circulation = trauma induces ishcemia/reperfusion phenomena = gut barriers impairment

Glucose metabolism:

stimulates hepatic glycogenolysis and gluconeogenesis more potently that glucagon

cause hyperglycemia

increases the osmotic effect which contributes to the restoration of the circulation.

In Stress/injury/surgery:

= elevated secretion

= elevation last for 1 week after the insult.

SIADH (syndrome of inappropriate antidiuretic hormone) secretion:

excessive vasopressin release

effect:

low urine output, highly concentrated urine, dilutional hyponatremia

diagnosis:

can only be made in euvolemic patients

plasma osmolality = < 275mOsm/kg H20

urine osmolality = > 100 mOsm/kg H20

commonly seen after head trauma and burns

Central Diabetes Insipidus:

absence of AVP

effects:

= voluminous output of dilute urine= precipitate hypernatremia= hypovolemic shock

frequently seen in comatose patients

Treatment:

free water

exogenous vasopressin ( desmopressin )

OXYTOCIN

Structurally similar to AVP

Stimulus for secretion:

= suckling

= nipple stimulation in lactating woman

Effects:

= contraction of lactating mammary glands

= contraction of the uterus

unknown role in injury response

no known function and stimulants for section in males.

HORMONES OF THE AUTONOMIC SYSTEM

CATHECOLAMINES

ALDOSTERONE

RENIN-ANGIOTENSIN

INSULIN

GLUCAGON

CATECHOLAMINES

Significant influence in the physiologic response to stress and injury.

Severe injury activates the adrenergic system

hypermetabolic state.

Increase plasma level after injury

average 3 - 4 times the baseline right after injury

peak level is attained at 24 to 48 hours

Major Cathecolamines:

norepinephrine

elevation results from synaptic leakage during sympathetic nervous activity.

Epinepherine

derived from the secretion of chromaffin cells of the adrenal medulla

EFFECTS:

METABOLIC

In the Liver, promotes: glycogenolysis, gluconeogenesis, lypolysis, ketogenesis

In the Skeletal muscles:

inhibits insulin facilitated glucose uptake

Peripheral Tissues:

increases lipolysis in adipose tissues

Generally promote stress induced hyperglycemia

EFFECTS:

HORMONAL

In the Pancreas:

decrease insulin secretion

increase glucagon secretion

In the Thyroid Gland

increase thyroid hormone secretionincrease parathyroid secretion

In the Adrenals

inhibits the release of aldosterone

EFFECT:

IMMUNOLOGIC:

EPINEPHRINE:

increases intracellular cAMP by occupying the beta receptors of lymphocytes

decrease in immune responsiveness.

Enhances leukocyte demargination

neutrophilia

lymphocytosis

lowers the ratio of CD4 to CD8 T lymphocytes.

Depressed mitogen-induced T lymphocyte proliferation

ALDOSTERONE

A mineralocorticoid

synthesized, stored, and released in the zona glomerulosa of the adrenal gland

Stimuli for release:

ACTH (most potent)

angiotensin II

hyperkalemia

aldosterone stimulating factor (pituitary)

Major Function:

= maintain intravascular volume= conservation of sodium= elimination of potassium and hydrogen

Effects:

early convoluted tubule

= increase sodium and chloride reabsorption

= increase excretion of hydrogen ions.

Late distal convoluted tubule

further sodium reabsorptionexcretion of potassium

with vasopressin, it increases osmotic water flux into the tubules

Aldosterone deficiency

hypotensionhyperkalemia

Aldosterone excess

edema

hypertension

hypokalemia

metabolic alkalosis

In Injury:

ACTH stimulates brief burst of aldosterone release

Angiotensin II induces protracted release

loss of circadian cycle release of the hormone

RENIN

Synthesized and stored primarily within the renal juxtaglomerular apparatus

juxtaglomerular neurogenic receptor

juxtaglomerular cell

baroreceptors

sensitive to low blood pressure

increase renin secretion

macula densa=detect changes in chloride concentration

initially exist as an inactive form = Prorenin

activation and release:

ACTH

AVP

glucagon

prostaglandins

potassium

magnesium

calcium

ANGIOTENSIN

kidneyreninpulmonary endothelial cells ACE(angiontensin converting enzyme

\

/

liverangiotensinogen angiotensin I angiotensin II

ANGIOTENSIN II

potent vasoconstrictor

stimulates synthesis of aldosterone and vasopressin

capable of regulating thirst

stimulates heart rate and myocardial contractility

potentiates the release of epinephrine

increases CRH release

activates the sympathetic system

induce glycogenolysis and gluconeogenesis

maintains volume homeostasis in injury

INSULIN

From the beta cells of the islet of Langerhans of the pancreas

Factors for release:

certain substrate:

glucose = major stimulant

amino acids

free fatty acids

ketone bodies

Autonomic neural inputs:

epinephrine and sympathetic stimulation (inhibits insulin release)

Factor for release:

Hormonal factors: diminish release

glucagonsomatostatingastrointestinal hormonesbeta-endorphinsinterleukin 1Peripherally: interfere with glucose uptake(cortisol,estrogen, progesterone)

In Injury:

impaired insulin production & function

stress-induced hyperglycemia

bi-phasic pattern of release:

first phase:

few hours after injury

relative suppression of release

influence of cathecolamines and sympathetic stimulation

late phase:

return to normal or excessive production

persistent hyperglycemia

peripheral resistance to insulin

ration between insulin to glucose: predictor of mortality and survival

Effects:

global anabolic effect

promotes hepatic glycogenesis and glycolysis

increase glucose transport into the cells

promotes adipose tissue lipogenesis

promotes protein synthesis

enhances T lymphocyte proliferation and cytotoxicity

increase B and T lymphocyte population

GLUCAGON

A pancreatic islet cell secretion

is a catabolic hormone

primary stimulants for secretion are plasma glucose concentration and exercise

stimulates hepatic glycogenolysis and gluconeogenesis

75% of glucose produced by the liver

promotes hepatic ketogenesis

promotes lipolysis in adipose tissues

In injury:

initially decreased release

at 12 hour post injury returns to normal

at 24 hours, at supernormal level which will persist up to 3 days.

IMMUNE RESPONSE TO INJURY

CYTOKINES

small proteins or lipids

synthesized and secreted by immunocytes

effects:

persistence of systemic inflammation

progression of organ failure

late mortality

indispensable in tissue healing and in the immune response generated against microbial invasion

CYTOKINE MEDIATED RESPONSE

CYTOKINES:

Responses:

hemodynamic

metabolic

immunologic

Produced by:

diverse cells at the site of injury

systemic immune cells

Primary activity: paracrine

characteristics:

small polypeptides or glycoproteins

exert effect at very low concentrations

mostly are about less than 30 kilodaltons

not stored in their pre-formed molecules

appears rapidly after injury

active gene transcription and translation by the injured or stimulated cells.

MODE OF ACTION

cytokine specific cell receptor intracellular signaling pathway gene transcription

immune influence:

immune cell production

immune cell differentiation

immune cell proliferation

immune cell survival

regulate the production and actions of other cytokines

exhibits inflammatory pleotrophism

capacity to activate diverse cell types

capacity to diverse immune responses

proinflammatory

anti-inflammatory

overlapping of activities of different cytokines

Manifestations of response:

fever

leukocytosis

hyperventilation

tachycardia

In septic shock:

exaggerated acute production of pro-inflammatory cytokines

hemodynamic instability

In Chronic illnesses

excessive production of cytokines

metabolic derangement

debilitating muscle wasting and cachexia

In severely injured or infected patients:

presence of pre-existing cytokines

end-organ injury

multiple organ failure and high mortality

Anti-inflammatory cytokines may serve to attenuate exaggerated pro-inflammatory responses.

Excessive release of anti-inflammatory cytokines may also render patients immunocompromised and increase susceptibility to infection.

KINDS OF CYTOKINES

TUMOR NECROSIS FACTOR - alpha

earliest to rise in injury, short lived and mono- phasic

peaks at 90 minutes

return to undetectable levels in 4 hours

half life of 15 - 18 minutes

one of the most potent

induce marked metabolic and hemodynamic changes

activate cytokines distally in the cascade

sources of synthesis:

monocytes

T cells

macrophages

Kupffer cells = single largest population in the body

Endogenous modulators

cause the abbreviated production

prevent any propagation of unregulated activity

Endogenous Inhibitors:

cleaved extracellular domains of the transmembrane TNF receptors:

soluble TNF receptors and sTNFRs

detectable in the circulation

serve a protective role

competitively sequestering excess circulating TNF Effects:

muscle catabolism and cachexia during stress

amino acids are mobilized from skeletal muscles

amino acids shunted to the liver for fuel substrates

through ubiquitin-proteasome proteolytic pathway

increased expression of ubiquitin gene

coagulation activation

promotes release of prostaglandin E2

promotes release of platelet activating factor

promotes release of glucocorticoids

promotes the release of eicosanoids

INTERLEUKIN - 1

synthesis and release is induced by TNF-( sources:

macrophages

endothelial cells

two known pro-inflammatory species:

IL - 1( cell membrane associated

effects via cell contact

lesser quantity than IL-1( IL-1( a more detectable form

produced in greater quantities

capable of inducing systemic derangements after injury TNF-( influence:

potency and effects

similar physiologic and metabolic alterations

initiate hemodynamic decompensation

acts synergistically

initiates the inflammatory cascade by the release of the distal cytokines mediators:

IL-2, IL-4, IL-6, IL-8

granulocyte/macrophage colony stimulating factor(GM-CSF)

interferon-( (IFN-()

half-life is 6 minutes

primary role: local inflammatory mediator

Effects:

stimulates local prostaglandin activity in the anterior hypothalmus

inflammatory febrile response to injury

induction of anorexia ( effect on the satiety center)

enhance the production of IL-2

augments T cell proliferation

skeletal muscle proteolysis

promotes the release of (-endophins and increase the number of central opioid -like receptors

attenuated pain perception after surgery

potent stimulant to ACTH and glucocorticoid release via actions on the hypothalamus and pituitary gland.

Regulator of activity:

IL-1receptor antagonist ( IL-1ra )

a non-agonist IL-1 species

released also during injury

competes with binding to IL-1 receptors without signal transduction

potent regulator of IL-1 activity

INTERLEUKIN - 2

Characteristics:

secreted by lymphocytes, short half life: < 10 minutes, barely detectable in the circulation

Effects:

promotes T lymphocyte proliferation

promotes immunoglobulin production

preserve gut integrity

Factors diminishing expression/release/activity:

Acute Injury

several disease states:

cancer

AIDS

Peri-operative blood transfusion

surgery

major injuries

In injury/stress:

attenuated IL-2 expression

immunocompromised state of the surgical patients

diminished gut barrier IL-2 activity

enteric activation of the inflammatory cytokine cascade

accelerated lymphocyte programmed cell death ( apoptosis )

with diminished IL-2 activity contribute to the immunocompromised phenotype of an injured patient.

A population shift from type 1 T helper cell to type 2 T helper cells

type1 T helper cell ( cell-mediated and opsonizing antibody immune response, IL-2,IL-12, IFN-( production)

type2 T helper cell ( IgG antibody mediated immune response; IL-4, IL-6, IL-10, IL-13 production )

type 2 T helper cell immune response is less effective against microorganisms

increase risk of post-operative infectionsINTERLEUKIN 4

A glycoprotein

produced by activated type 2 T helper cells

effects:

diverse biologic hematopoitic effect

induce B lymphocyte proliferation

enhance macrophage major histocompatibility complex class II ( HLA-DR & HLA-DP ) expression and adhesion molecules

antigen presenting cells

differentiation of B cells to produce IgG4 and IgE

allergic and anti-helminthic response

potent anti-inflammatory cytokine:

down regulates functions of activated macrophage

IL-1(, IL-6, IL-8, TNF-(, superoxide production

not seen in resting monocytes

induce programmed cell death in inflammatory macrophage

opposed by IFN-( increase macrophage susceptibility to the anti-inflammatory effects of glucocorticoids

INTERLEUKIN 6

Produced by all cell types

production is induced by TNF-( and IL-1

elevated levels after acute injury and stress

indicator of inflammatory response

predictor of pre-operative morbidity

detectable in the circulation 60 minutes after injury

peaks at 4-6 hours

persists for as long as 10 days

levels are proportional to the extent of tissue injury

Effects:

mediator for the hepatic acute-phase protein response to injury.

Enhance production of the ff:

C-reactive protein

fibrinogen

haptoglobin

amyloid A

(-1-antitrypsin

complement system

induces PMN activation during injury

delay phagocytic disposal of senescent or dysfunctional PMNs

cause persistence of inflammatory cell after injury

injurious effects to distant tissues (lungs and kidneys)

mediates anti-inflammatory pathways

attenuates TNF and IL-1 activity

promotes the release of sTNFRs and IL-1ra

in prolonged and persistent expression:

immunosuppression

post-operative infections

impair glutaminase activity

reduction in plasma glutamine

INTERLEUKIN 8

Temporarily associated with IL-6

additional bio-marker for the risk of multiple organ failure.

Effects:

= PMN activator

= potent chemoattractant= major contributor to organ injury(acute lung injury)

INTERLEUKIN 10

Important endogenous regulatory mediator during inflammatory response

modulates TNF-( activity

absence result to increase TNF-( production and increase in mortality

promotes IL-1ra and sTNFR production

protective role after injury-induced inflammatory response

may abrogate the proinflammatory response necessary for local clearance of invading organisms.

INTERLEUKIN 12

Promote differentiation of type 1 T helper cells.

Promotes production of IFN-( prevent programmed cell death( apoptosis ) in certain T lymphocyte populations.

INTERLEUKIN 13

A pleotrophic cytokine

produced during type 2 T helper cell response

modulate macrophage function

no effect on T lymphocyte

has influence on sub-population of B lymphocyte only.

Up regulate macrophage major histocompatibility complex class I and II antigens and other surface antigens ( CD 23)

inhibits:

nitric oxide production

expression of pro-inflammatory cytokines

enhance production of IL-1ra

net effect is anti-inflammatory

INTERFERON-( Produced from T helper cells activated by IL-2 or IL-12

induce production of IL-2 and IL-12 from T helper cells

half life : 30 mins.

Detectable 6 hours after injury

peaks at 48 to 72 hours

persist for 7-8 days

Effects:

activate circulating and tissue macrophages

activates alveolar macrophages after major surgery

acute lung inflammation

GRANULOCYTE/MACROPHAGE-COLONY STIMULATING FACTOR Production is induced by IL-2 and endotoxin

delays apoptosis of macrophages and PMN

promotes maturation and recruitment of functional lymphocytes for normal inflammatory cytokine response

promotes wound healing

suppress IL-10 production

augment neutrophil population and function

REGULATION OF INFLAMMATORY CELL DEATH

PROGRAMMED CELL DEATH

TNF RECEPTOR-MEDIATED PROGRAMMED CELL DEATH

Fas/CD95 RECEPTOR-MEDIATED PROGRAMMED CELL DEATH

PROGRAMMED CELL DEATH

Host response to injury and infection

Collective activities of circulating and tissue fixed immunocytes and endothelial cell population.

In normal host:

The principal mechanism by which senescent or dysfunctional cells as systematically disposed

Without immunocyte activation

No release of proinflammatory contents.

Signals inducing apoptosis differ from cell to cell which arises from the extracellualr environment

Hormonal activities

Paracrine activities

In Inflammation:

Disruption of normal apoptosis

Delayed disposal of activated macrophages and PMN

TNF

IL-1, IL-3, IL-6

GM-CSF

G-CSF

IFN-( Accelerated apoptosis in activated monocyte: IL-4 and IL-10

Purpose:

Without programmed apoptosis

Prolonged survival of immunocytes

Perpetuates and augment inflammatory response to injury and infection

Precipitate multiple organ failure

Eventual death in severely injured and critically ill patients.

TNF RECEPTOR-MEDIATED PROGRAMMED CELL DEATH

Tumor necrosis factor receptors (TNFRs)

Belong to a family of 15 transmembrane proteins that are virtually present in all cells

other members include:

Lymphotoxin- receptor

Fas/CD95 ( APO-1 )

Nerve growth factor receptor ( NGFR )

CD 27, CD 30, OX40, 4-IBB

DR3 ( WSL-1, APO-3, TRAMP ), DR4 ( APO-2 )

Receptor induction may initiate programmed cell death

Two specific trans-membrane TNFRs

Type 1, p55

Induces:

Apoptosis

Cytotoxicity

Expression of adhesion molecules on endothelial cells

Activation of sphingomyelin pathway

Activation of nuclear factor-kappa B ( NF-( B )

Dominant role in apoptosis

Participation of type II TNFRs is necessary

p75 protein transducers are shared by p55 signaling complex

Similar cytoplasmic sequence motif with Fas known as death domain

Propagate downstream signaling for programmed cell death

Type II,p75

Induces:

Proliferation of T cells

Proliferation of fibroblast

Proliferation of natural T killer cells

Proliferation of proinflammatory cytokines

During sepsis and endotoximia

Down regulation of macrophage and PMN TNFR activity

Delayed apoptosis of inflammatory macrophages and PMN

Prolongation of inflammatory response

Found in virtually all cell types

Fas/CD95 Receptor-Mediated Programmed Cell Death

Tissue specific

Liver, lungs, heart, intestines, skin, lymphocytes.

FasL = specific ligand for Fas

Only known role: initiate programmed cell death

Induce apoptosis via similar mechanism with p55

Fas/FasL cross-linking in activated immunocytes

Advantageous in systemic inflammation

Detrimental to the host at the tissue level:

In the liver:

Precipitate or exacerbate ongoing hepatic injury

Up-regulation of Fas receptors with acute toxic injury simultaneously enhanced by FasL expression in infiltrating lymphocytes

In the thyroid gland

Thyroiditis

Thyroid gland destruction

IMMUNOCYTE RECEPTOR ACTIVITY IN INFLAMMATION

Membrane TNFR

In Human endotoximia

In Macrophage:

Down regulation

Reaches to low levels at 2 hours after endotoxin infusion

Recovers to normal levels at 6 hours

The most sensitive correlate identified for human response to endotoxin exposure

In PMN

More sustained decrease in surface TNFRs under same condition

Signs:

Fever,

chills

leukocytosis

Membrane TNFR

In Sepsis:

Reduction of cell-surface TNFRs

Non-survivors : immediate reduction of cell surface TNFRs expression

Survivors : almost normal receptor levels from the outset.

Used as an indicator of outcome in patients with severe sepsis

Soluble TNFR

Proteolytically cleaved extracellular domains of membrane-associated TNFRs

Elevated in severe sepsis

Retain affinity to TNF

Compete with the cellular receptors for binding of free TNF

A counter-regulatory response to excessive systemic TNF activity

HORMONE AND CYTOKINE INTERACTIONS

CORTISOL/GLUCOCORTICOID

Given before or concomitantly with endotoxin infusion

Attenuate symptoms, cathecolamine response and acute phase response.

Increase release of IL-10

Anti-inflammatory effect

Given 6 hours or more before infusion of endotoxin

No attenuation of responses

Given for more than 12 hours infusion

Increase TNF and IL-6 release (IL-1)

Activate hypothalamo-pituitary adrenal axis

Release of CRH and ACTH

Increase glucocorticoid levels

Inhibit endotoxin induced production of TNF at the level of mRNA translation

Glucocorticoid/Cortisol

Regulate T lymphocyte proliferation or Cell death

CD8 T cells are more sensitive than CD4 cells

Requires elevation of cAMP

IL-2, IL-4 and IL-10 protects T lymphocytes from glucocorticoid-induced apoptosis

Dexamethasone inhibits neutrophil apoptosis and prolongs their functional responsiveness

Detrimental to patients

Delay of clearance of inflammatory cells from tissues perpetuate the injurious effect of activated neutrophils.

Cathecolamines

inhibit endotoxin-induced macrophage production of TNF-( short term exposure to epinephrine

increase production of anti-inflammatory cytokine IL-10

Longer pre-exposure to epinephrine (24 hr.)

less pronounced anti-inflammatory effect

limit excessive proinflammatory effects of cytokine network during the early phase of systemic infection

attenuates endotoxin-induced down regulation of TNFR expression on human monocytes

beta-receptor mediated

cAMP dependent

OTHER MEDIATORS OF INJURY RESPONSE

ENDOTHELIAL CELL MEDIATORS

stimulants:

TNF-(IL-1

endotoxin

thrombin

histamine

IFN-( released mediators:

IL-1

Platelet-activating Factor (PAF)

Prostaglandins ( PGI2 and PGE2)

GM-CSF

Growth Factors

endothelin

nitric oxide

thromboxane A2

Endothelial Cell Function

modulates coagulation and vasomotor activities

contributes to the inflammatory process

releases Collagenase

autodigest their own basement membrane

permits neovascularization and vascular re-modeling

facilitate adequate oxygen supply and immunocyte transport

Angiotensin-converting enzyme (ACE)

convert angiotensin I to angiotensin II

potent regulator of vascular tone

released mediators modulates cardiovascular and renal function

influence the hypothalmus-pituitary-adrenal axis

Up-regulates expression of leukocyte adhesion receptor molecules

E-selectin (ELAM-1)

expression during inflammation requires the stimulation of TNF-( and IL-1

detectable mRNA activity for E-selectin in 1 hour and maximal at 4-6 hours

P-selectin

intercellular adhesion molecules (ICAM-1, ICAM-2)

internalization of adhesion molecules within the endothelial cell after recovery from the inflammatory process

In non-stressed state:

little capacity to recognize and bind circulation leukocytes

In injury:

neutrophil adhesion to the endothelium

increase vascular permeability

passage of leukocytes to injured tissues

margination of circulating PMNs to the endothelial surfaces

Rolling = marginated deformable PMN traveling along the endothelial surfaces at markedly reduced velocity.

Process of transient attachment and detachment between receptors of PMNs and the endothelium diapedesis:

factors:

development of strong receptor adhesions

PMN activation by endothelial mediators

release of PMN proteinases at endothelial junctions

migration of PMNs out of the vascular compartment

Acute Lung injury:

capillary leakage and post-ischemic injury

caused by:

activated PMN

inflammatory mediators

release of reactive oxygen metabolites

ENDOTHELIAL CELL MEDIATORS

ENDOTHELIUM-DERIVED NITRIC OXIDE

known also as Relaxing Factor ( EDNO or EDRF )

Release:

Acetylcholine stimulation

hypoxia

endotoxin

cellular injury

mechanical shear stress from circulation blood

readily diffusible

half-life : few seconds;spontaneously decompose into nitrate and nitrite

formed from oxidation of l-arginine

catalyzed by nitric oxide synthase (NO-synthase)

co-factors: calmodulin, ionized calcium, NADPH

formation is also found in PMN, macrophages, renal cells, Kupffer cells, cerebellar neurons.

Vasodilatory Activity

induction of smooth muscle relaxation

requires activation of soluble Guanylate Cyclase

increase cytosolic cGMP in monocytes

increased cytosolic cGMP in platelets reduced adhesion and aggregation

induces vasodilatation and platelet deactivation

mediates protein synthesis in hepatocytes

mediates electron transport in hepatocyte mitochondria In septic shock and trauma

elevated

measured by its nitrite and nitrate metabolites

low systemic vascular resistance and elevated endotoxin levels

agents that block EDNO induces a state of vasoconstriction readily reversed by l-arginine administration

basal release of endogenous EDNO (responsible for constant state of vasodilatation)

PROSTACYLCLIN ( PGI2 )

secreted by endothelial cells

synthesized from arachidonic acid

stimulation for synthesis and release:

vascular shear stress

hypoxia

Effects:

potent vasodilator

increase platelet cAMP

relaxation and platelet deactivation

used to reduce pulmonary hypertension esp. in pediatric patients

ENDOTHELINS

secreted in response to:

injury

thrombin

transforming growth factor-(IL-1

angiotensin II

arginine vasopressin

cathecolamines

anoxia

21 amino acid polypeptide

Potent Vasocontrictor

3 members in the peptide family( ET1, ET2, ET3 )

ET-1

only ET produced by endothelial cell

most biologically active and potent vasoconstrictor

10X more potent that angiotensin II

3 ET receptors (ETA, ETB, ETC )

function by the G- protein-coupled receptor mechanism

ETB receptor are linked to the formation of EDNO and PGI2

transient vasodilatation with low doe ET-1 administration

need for EDNO and ET to maintain physiologic vascular tone

Acetylcholine

reverses vasoconstrictor activity of ET

stimulates EDNO production

increased ET levels correlates with severity of injury

trauma

surgery

cardiogenic shock

septic shock

PLATELET-ACTIVATING FACTOR a Phospholipid constituent of cell membrane

Release is induced by:

TNF

IL-1AVPangiotensin II

Effects:

potent inflammatory mediator

stimulates TxA2

potent vasoconstrictor

increase glucagon activity

increase cathecolamine activity

induce hypotension

increase vascular permeability

hemoconcentration

primed PMN activity

eosinophil chemotaxis/degranulation

thrombocytopenia

induces a general leukocytopenia by margination

cause contraction of endothelial cells

increase permeability

permits passage of macromolecules e.g. albumin

Chemotactant

leukocytes adhere to vascular walls

facilitate migration out of vascular compartment

Other cells that secret PAF

macrophagePMNbasophils

mast cells

eosinophils

ATRIAL NATRIURETIC PEPTIDES

released by:

central nervous system

specialized endothelium found in the atrial tissues

induction of release:

vascular wall tension

Effect:

potent inhibitor for aldosterone secretion

prevents absorption of sodium

unknown role in human response to injuryINTRACELLULAR MEDIATORS:

Heat-Shock Proteins

induction of production:

heat

hypoxia

trauma

heavy metals

local traumahemorrhage

production:

require gene induction by heat-shock transcription factor

in parallel with activity of the hypothalamo-pituitary-adrenal axis

ACTH sensitive

declines with age

Effects:

protects cells from deleterious effects traumatic stress

assembly, disassembly, stability and transport of proteins (e.g. glucocorticoids)

Reactive Oxygen Metabolites:

short-lived, highly reactive molecular oxygen species with an unpaired outer orbit

production processes:

anaerobic glucose oxidation

reduction of oxygen to superoxide anion

potent ROM

metabolized to other reactive species ( hydrogen peroxide and hydroxyl radicals )

produced by activated leukocytes

Effects:

cause tissue injury by peroxidation of cell membrane unsaturated fatty acids.

Induce apoptosis

depletion of intracellular glutathione or ROM scavengers

activation of Fas/CD95 receptors leads to depletion of GSH

induce reperfusion injury:

ischemia fully activated production of ROM oxygen lack non-functional ROM restoration of blood flow and oxygen large quantities of ROM tissue injury

In normal subjects:

cells are not immune to the effects of their own ROM

protected by oxygen scavengers:glutathione & catalases

OTHER INFLAMMATORY MEDIATORS

EICOSANOIDS

class of mediators:

prostaglandins (PG)

thromboxanes (Tx)

leukotrines (LT)

hydroxyeicosatetraenoic acids (HETE)

Lipoxins (Lx)

oxidation derivatives of the membrane phospholipid Arachidonic Acid

secreted by virtually all nucleated cells except lymphocytes

the formation of prostacyclines (PGI2) requires further enzymatic activity by prostacyclin synthetase.

Activates Phospholipase A2 :

epinephrine

angiotensin II

bradykinin

histamine

thrombin

phospholipase A2 inhibitor

lipocortin

secretion is induced by cortisol

inhibits production of arachidonic acids metabolites

not stored in cells

synthesized rapidly by cells upon stimulation by:

hypoxia and ischemia

direct tissue injury

endotoxin

histamine

norepinephrine

acetylcholine

AVP,

serotonin

angiotensin II

Bradykinin

COX-2

stimuli that induce synthesis of eicosanoids also induce this 2nd cyclooxygenase enzyme

enhances the production of Arachidonic acids

activity is inhibited by glucocorticoids

specific inhibition of cyclooxygenase metabolites

Products of arachidonic acids metabolism are functionally cell/tissue specific

Vascular endothelium

= PGI2

=vasodilatation and platelet deactivator

Platelets

thromboxane synthetase converts platelet prostaglandins to TxA2

potent vasoconstrictor

platelet aggregator

Macrophages

synthesize cyclooxygenase and lipooxygenase products

Second Messengers

PGE

activates adenylate cyclase

increase intracellular cAMP inhibit AVP activity and hormone -stimulated lipolysis

Thromboxanes and leukotrienes

increase intracellular free calcium via phosphatidylinositol pathway

opposite effect to PGE

Effects:

deleterious effects implicated in

acute lung injury

pancreatitis

renal failure

vascular permeability

leukocyte migration

vasodilatation

Effects:

Leukotrienes:

produced by cell in the lungs, connective tissues, smooth muscles, macrophages and mast cells

mediate anaphylactic reactions

1,000 X more potent than histamines in promoting capillary permeability

promotes leukocyte adherence

neutrophil activation

bronchoconstriction

vasoconstriction

Lipoxins

induce neutrophil activation

production of superoxides

neutrophil degranulation

Effects:

Metabolic

products of cyclooxygenase pathways inh insulin release pancreatic B-cell

products of lipooxygenase pathway promote beta cell activity

Hepatocytes

have specific receptors for PGE2

inhibit gluconeogenesis

inhibit hormone-stimulated lipolysis

Immune Response

PGE2 suppress proliferation of human T lymphocytes by mitogens mediated by down-regulation of IL-2 production

LTB4 released by PMN during phagocytosis serves as chemoattractants for other leukocytes

OTHER INFLAMMATORY MEDIATORS

Kallikrein-Kinin System

Kinins:

ex: Bradykinin (potent vasodilator)

produced through kininogen degradation by the serine protease KALLIKREINE

Pro-enzyme: Prekallikreine

activated by: Hageman Factor, trypsin, plasmin, Factor XI, glass surfaces, kaolin, collagen

rapidly metabolized by:

Kinase I - degrades the anaphylatoxins C3a, C4a and C5a

Kinase II - identical with angiotensin converting enzyme

ACE inhibitors block kinin degradation and enhance the kinin-induced injurious effect of the bronchial tree.

Effects:

increase capillary permeability

increase edema

evoke pain

increase bronchoconstriction

increase renal vasodilatation - reduce renal blood flow - increase renin - sodium and water retention via renin-angiotensin system.

Increase glucose clearance by inhibiting gluconeogenesis

increase nitrogen retention

Stimulus for Kinin Release:

Bradykinin:

hypoxia & ischemia

hemorrhage

sepsis

endotoximia

tissue injury

OTHER INFLAMMATORY MEDIATORS

Serotonin:

5-hydroxytryptamine, 5-HT

tryptophan derivative neurotransmitter

found in entero-chromaffin cell and in platelets

Effects:

= vasoconstriction

= bronchoconstriction

= platelet aggregation

= myocardial chronotrophe and = inotrophe

role in injury response is unclear

OTHER INFLAMMATORY MEDIATORS

Histamine (derived from Histidine)

Stored in :

neurons, skin, gastric mucusa

mast cells, basophils, platelets

induction of release : increase Calcium levels

two receptor types for histamine binding:

H1 binding :

increase histamine precursor uptake ( l-histidine )

two receptor types for histamine binding

H1 binding:

bronchoconstriction

stimulates intestinal motility

stimulates myocardial contractility

H2 binding:

inhibits histamine release

H1 and H2 receptor activation induces vasodilatation and increased vascular permeability

Effects:

hypotension

peripheral pooling of blood

increased capillary permeability

decreased venous return

myocardial failure

Released:

hemorrhagic shock, trauma, thermal injury, endotoximia and sepsis

Histamine levels are correlated with mortality from septic shock

METABOLIC RESPONSE TO INJURY

Cuthbertson Model: two phases

Ebb phase:

earliest moments to hours after injury

hemodynamic instability/reduction in effective circulating blood volume

reduction in total body energy expenditure

losses of urinary nitrogen

early enhancement of neuroendocrine hormone appearance ( cathecolamines and cortisol )

Flow phase:

initiated by tissue reperfusion and reoxygenation resulting from fluid or volume resuscitation

cessation of the initial injury conditions

metabolic response:

direct energy and protein substrates

= preserve critical organ function= repair of damaged tissues

increase in whole body oxygen consumption

increase metabolic rate

enhancement of critical enzyme pathways for readily oxidizable substrates ( glucose )

stimulation of immune system functions

repair of tissue destruction

protection from additional breaks in epithelial barriers

reprioritization of substrate processing

production of acute-phase reactants, immunoreactive proteins and coagulation factors

biologic priority of wound healing established

SUBSTRATE METABOLISM

an average healthy adult 70 kg. BW

expends 1700 to 1800 kcal/day of energy

from lipid, carbohydrate and protein sources

obligate glycolytic cells:

neurons, leukocytes and erythrocytes

spends 180 gms. Of glucose /24hr. For basal energy needs

In Acute Starvation:

glucose is derived from existing storage pools

75 gm. As hepatic glycogen

reduction of circulating glucose

primary stimulus for hormonal release that modulates gluconeogenesis

substrate substitution for tissues that require glucose for energy

fall within hours after onset of fasting

decrease in insulin release

increase in circulating glucagon

elevations of GH, Cathecolamines, AVP, angiotensin II

In Acute Fasting:

glucagon and epinephrine

enhance cAMP

glycogenolysis

cortisol and glucagon

promote gluconeogenesis

norepinephrine, AVP and Angiotensin II

promote glycogenolysis

mediated by intracellular signals of phosphatidylinositol and calcium

Liver:

sustained glucose production depends on supply of amino acids, glycerol and fatty acids

Primary gluconeogenic precursosrs:

lactate - converted back to glucose by the Cori cycle

glycerol

amino acids ( alanine and glutamine )

skeletal muscle:

releases lactate

cannot directly release free glucose due to lack of G-6-phosphatase

breakdown of glycogen stores

glycolysis of transported glucose

not sufficient to maintain glucose homeostasis

75 gms of protein must be degraded daily

proteolysis

decreased insulin and increased cortisol

associated with increased urinary nitrogen excretion ( N = 6-8 g/day to 8-11 g within the initial 5 days of fasting)

Kidneys

increased urinary ammonia excretion

deamination of amino acids for gluconeogenesis

primary route of elimination of alpha-amino nitrogen during starvation

active hepatic enzymes are diminished

increased renal gluconeogenesis

increase metabolism of glutamine and glutamate

account for up to 45% of glucose production during late starvation

After 5 days of Fasting

whole body proteolysis diminishes to 15-20g/day

urinary nitrogen excretion stabilizes at 2-5 g/day

nervous system and other glucose utilizing tissues adapt to ketone oxidation as source of energy

Brain:

blood brain barrier increases the rate of ketone body transport

increase ketone body metabolism

reduced amount of protein required for gluconeogenesis

reduced anabolic growth factors (IGF-1)

reduces the important signals for transcellular amino acid transport

Tissue protein synthesis also falls

energy requirements for gluconeogenesis and basal enzymatic and muscular function

160 g of triglyceride from adipose tissue (fatty acid and glycerol)

fatty acid release

reduced serum insulin concentration

increased glucagon and cathecolamines

used for energy by the heart, kidney, muscle and liver

lipid stores provide up to 40% of the caloric expenditure during starvation

Lipid Oxidation

diminishes absolute glucose requirement

ketone body spares glucose

inhibition of pyruvate dehydrogenase in most tissues

decreases the amount of mandatory glycolysis

diminishes protein degradation

reduction of the initial obligatory neuroendocrine stress hormone response

whole body energy expenditure decrease

decreased sympathetic activity

reduced skeletal muscle activity

decreased secretory enzyme production

decreased intestinal metabolic demands

METABOLISM AFTER INJURY

sustained activities of macroendocrine hormones and immune cell activation differentiates injury metabolism from unstressed starvation

Energy Balance:

increase energy expenditure

increased activity of the sympathetic nervous system

increased circulating cathecolamine concentration

regulation of cell membrane sodium permeability

energy required for ion pump action to maintain normal transmembrane concentration

account for over 40% of total body expenditure

increase oxygen consumption

Lipid Metabolism

Primary sources of energy following injury

Lipolysis

enhanced by:

1.)immediate elevation in ACTH, cortisol,

catecholamines, glucagon, and GH

2.)reduction in insulin

3.)increased sympathetic nervous system activity.

Hormone sensitive lipase = chief stimulus are the catecholamines (kinase hormone sensitive lipase)PAGE 20