Systemic Response to Injury & Metabolic Support

1. Systemic Response to Injury & Metabolic Support a review of Schwartz’s Principles of Surgery- Chapter 1 L. Coughlin, M.D. July 7, 2008

2. Introduction • Inflammatory response to injury • to restore tissue function • Eradicate invading microorganisms • Local- limited duration, restores function • Major • overwhelming inflammatory response • Potential multi-organ failure • Adversely impacts patient survival

3. Infection Identifiable source of microbial insult SIRS = 2 or more: Temp ≥38˚C or ≤36˚C HR ≥ 90 bpm RR ≥ 20 breaths/min or PaCO2 ≤ 32 mmHg or mechanical ventilation WBC ≥ 12,000/µL or ≤ 4000/µL or ≥ 10% band forms Sepsis Infection + SIRS Severe Sepsis Sepsis + Organ Dysfunction Septic Shock Sepsis + Cardiovascular Collapse (requires vasopressors) Clinical Spectrum of SIRS

4. Signaling • Humoral – inflammatory mediators in the circulation can induce fever and anorexia i.e. TNF-α • Neural – parasympathetic vagal stimulation attenuates the inflammatory response via Ach release • Reduces HR, increases gut motility, dilates arterioles, constricts pupils, and decreases inflammation • Reduces macrophage activation • Reduces macrophage release of pro-inflammatory mediators (TNF-α, IL-1, IL-18)

5. Hormone Signaling • Hormone classifications • polypeptide (cytokine, insulin) • amino acid (epinephrine, serotonin, or histamine) • fatty acid (cortisol, leukotrienes) • Pathways • Receptor Kinases – insulin • Guanine nucleotide binding (G-protein) - prostaglandins • Ligand Gated ion channels

6. Adrenocorticotropic Hormone • Synthesized anterior pituitary • Regulated by circadian signals • Pattern is dramatically altered in injured patients • Elevation is proportional to injury severity • Released by: pain, anxiety, vasopressin, angiotensin II, cholecystokinin, catecholamines, and pro-inflammatory cytokines • ACTH signals increase glucocorticoid production

7. Glucocorticoids • Cortisol – elevated following injury, • duration of elevation depends on severity of injury • Potentiates hyperglycemia • Hepatic gluconeogenesis • Muscle and adipose tissue –> induces insulin resistance • Skeletal m.–> protein degradation, lactate release • Adipose -> reduces release of TG, FFA, glycerol

8. Exogenous administration • Adrenal suppression in the acutely ill • Acute Adrenal Insufficiency • Atrophy of the adrenal glands • Weakness, n/v, fever, hypotension • Hypoglycemia, hyponatremia, hyperkalemia • Immunosuppression • Thymic involution, decreased T-killer and NK fcn, graft vs host rxns, delayed hypersensitivity responses, inability of monocyte intracellular killing, inhibition of superoxide reactivity and chemotaxis in neutrophils • Down regulates pro-inflammatory cytokine production (TNF-α, IL-1, IL-6) • Increases anti-inflammatory mediator IL-10 • Useful in septic shock, surgical trauma, and CABG

9. Macrophage Inhibitory Factor • Glucocorticoid antagonist • produced by anterior pituitary & T-lymphocytes • Reverses immunosuppressive effects of glucocorticoids • Potentiates G- and G+ septic shock • Experimentally improves survival

10. Growth Hormone • During stress -> protein synth, fat mobilization, and skeletal cartilage growth • 2˚ to release of insulin-like growth factor (IGF1) • Injury reduces IGF1 levels • IGF1 inhibited by pro-inflammatory cytokines • TNF-α, IL-1α, IL-6 • GH admin to pediatric burn patients shows improvement in their clinical course

11. Catecholamines • Severe injury activates the adrenergic system • Norepi and Epi immed. increase 3-4 fold and remain elevated 24-48hrs after injury • Epinephrine • hepatic glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis • Decreases insulin and glucagon secretion • Peripheral- lipolysis, insulin resistance in skeletal m. • = stress induced hyperglycemia

12. Epinephrine – other effects • Increase secretion of T3, T4, and renin • Reduces release of aldosterone • Enhances leukocyte demargination and lymphocytosis

13. Aldosterone • Synthesized, stored, released from the adrenal zona glomerulosa • Maintains intravascular volume • Conserves sodium • Eliminates potassium and hydrogen ions • Acts on the early distal convoluted tubules • Deficiency- hypotension, hyperkalemia • Excess- edema, HTN, hypokalemia, metab alkalosis

14. Insulin • Stress inhibited release + peripheral insulin resistance = hyperglycemia • Injury has 2 phases of insulin release • Within hours- release is suppressed • Later- normal/xs insulin production with peripheral insulin resistance • Activated lymphocytes have insulin receptors -> enhanced Tcell proliferation and cytotoxicity • Tight control of glucose levels esp. in diabetics significantly reduces mortality after injury

15. Acute Phase Proteins • Nonspecific markers • Produced by hepatocytes • Response to injury, infection, inflammation • Induced by IL-6 • C-reactive protein best reflects inflammation • No diurnal variation, not affected by feeding • Affected only by preexisting hepatic failure • Accuracy surpasses that of ESR

16. Inflammatory Mediators • Heat Shock Proteins • Reactive Oxygen Metabolites • Eicosanoids • Fatty Acid Metabolites • Kallikrein-Kinin System • Serotonin • Histamine • Cytokines

17. Heat Shock Proteins • Induced by hypoxia, trauma, heavy metals, and hemorrhage • Intracellularly modify and transport proteins • Steroids • Requires gene induction by a transcription factor • ACTH sensitive • Production seems to decline with age

18. Reactive Oxygen Metabolites • Short-lived • Cause tissue injury by oxidation of unsaturated fatty acids within cell membranes • Produced by anaerobic glucose oxidation and reduction to superoxide anion in leukocytes • Further metabolized to hydrogen peroxide and hydroxyl radicals • Cells are protected by oxygen scavengers – glutathione and catalases • In ischemia- production of oxygen metabolites are activated but nonfunctional due to no oxygen supply. After reperfusion, large amounts are produced causing injury

19. Glucocorticoids (Cortisol) Corticosteroids Eicosanoids

20. Eicosanoids • Secreted by nucleated cells (not lymphocytes) • Induced by hypoxic injury, direct tissue injury, endotoxin, norepinephrine, vasopressin, ang II, bradykinin, serotonin, ACh, cytokines, histamine • Diverse systemic effects • Adverse effects include acute lung injury, pancreatitis, renal failure • NSAIDs acetylate COX which reduce prostaglandin levels

21. Pancreas – glucagon secretion- PGD2, PGE2 Liver – glucagon stimulated glucose production- PGE2 Adipose – lipolysis- PGE2 Bone – resorption- PGE2, PGF2α, PGI2 Parathyroid – PTH secretion- PGE2 Pulmonary – Bronchoconstriction- PGF2α, TXA2, LTC4, LTD4, LTE4 Immune – suppress lymphocytes- PGE2 Hematologic platelet aggregation- TXA2 Capillary leakage- PGE2, LT PMN adherence and activation- LT Pituitary Prolactin- PGE1 LH- PGE1, PGE2, 5-HETE TSH- PGA1, PGB1, PGE1, PGE1α GH- PGE1 Renal – renin secretion- PGE2, PGI2 GI – cytoprotective- PGE2 Eicosanoid Effects

22. Fatty Acid Metabolites • Omega 6 FA – precursors of inflammatory mediators (LT, PG, platelet activating, factor) • found in enteral nutrition formulas • Substituting Omega 3 FA attenuate the inflammatory response • Reduces TNFα, IL6, PGE2 • Reduces the metabolic rater, normalizes glucose metabolism, attenuates weight loss, improves nitrogen balance, reduces endotoxin induced acute lung injury, minimizes reperfusion injury to the myocardium, small intestine, and skeletal muscles.

23. Kallikrein-Kinin System • Bradykinins are potent vasodilators • Stimulated by hypoxic and ischemic injury • Hemorrhage, sepsis, endotoxemia, tissue injury • Magnitude proportional to severity of injury • Produced by kininogen degradation by kallikrein • Kinins increase capillary permeability (edema), pain, inhibit gluconeogenesis, renal vasodilation, incr bronchoconstriction • In clinical trials, bradykinin antagonists help reverse G- sepsis, but do not improve survival

24. Serotonin • Present in intestinal chromaffin cells & platelets • Vasoconstriction, bronchoconstriction, platelet aggregation • Myocardial chronotrope and ionotrope • Unclear role in inflammation

25. Histamine • Stored in neurons, skin, gastric mucosa, mast cells, basophils, and platelets • H1 – bronchoconstriction, increases intestinal motility and myocardial contractility • H2 – inhibits histamine release • H1/H2 – hypotension, decreased venous return/peripheral blood pooling, increased capillary permeability, myocardial failure.

26. Cytokines • Most potent mediators of inflammation • Local- eradicate microorganisms, promote wound healing • Overwhelming response- hemodynamic instability (septic shock) or metabolic derangements (muscle wasting) • Uncontrolled- end-organ failure, death • Self-regulatory production of anti-inflammatory cytokines, but inappropriate release may render the patient immunocompromised and susceptible to infection

27. Tumor Necrosis Factor α • Secreted from monocytes, macrophages, Tcells • Responds early, T ½ < 20min • Potent evocation of cytokine cascade • Induces muscle catabolism/cachexia, coagulation, PGE2, PAF, glucocorticoids, eicosanoids • Circulating TNF receptors compete with cellular receptors and may act as a counter regulatory system to prevent excessive TNF-α activity

28. Interleukin-1 • Released by activated macrophages, endothelial cells • IL1α- cell membrane associated • IL1β- circulation • Synergistic with TNF- α • T ½ = 6 min • Induces febrile response by stimulating PG activity in the anterior hypothalamus • Release of β-endorphins after surgery reduce perception of pain

29. Interleukin-2 • Promotes T-lymphocyte proliferation, Ig production, gut barrier integrity • T ½ < 10 min • Major injury or perioperative blood transfusions reduce IL-2 activity leading to a transient immunocompromised state • Regulates lymphocyte apoptosis

30. Interleukin-4 • Produced by type 2 T Helper lymphocytes • Important in antibody-mediated switching and antigen presentation • Induces class switching to promote IgE & IgG4 • Important in allergic and antihelmintic responses • Anti-inflammatory- downregulates IL-1, TNF-α, IL-6, IL-8 and oxygen radical production • Increases macrophage susceptibility to anti-inflammatory effects of glucocorticoids

31. Interleukin-5 • Released from T lymphocytes, eosinophils, mast cells and basophils • Promotes eosinophil proliferation and airway inflammation

32. Interleukin-6 • Induced by IL-1 and TNF-α • Levels are detectable within 60 min of injury, peak 4-6 hours, and persist up to 10 days • Levels are proportional to extent of tissue injury • Pro-inflammatory • Mediates hepatic acute phase response during injury and convalescence • Induces and prolongs neutrophil activity • Anti-inflammatory • Attenuate TNF-α and IL-1 activity • Promote release of circulating TNF- α receptors & IL-1 antagonists

33. Interleukin-8 • Released from monocytes, macrophages, T lymphocytes • Activity similar to IL-6 • Chemoattractant for PMNs, basophils, eosinophils, and lymphocytes, activates PMNs • Proposed biomarker for risk of multiple organ failure

34. Interleukin-10 • Anti-inflammatory • Released from T lymphocytes • Down-regulates TNF-α activity • Also attenuates IL-18 mRNA in monocytes • Studies in animal sepsis and ARDS models suggest induced IL-10 decreases the systemic inflammatory response and reduces mortality

35. Interleukin-12 • Promotes differentiation of type 1 T Helper cells • Promotes PMN and coagulation activation • In primate studies, IL-12 induces inflammatory responses independent of TNF-α and IL-1 • In animal studies of fecal peritonitis and burns, IL-12 administration increases survival, whereas IL-12 neutralization increases mortality

36. Interleukin-13 • Similar to IL-4, overall anti-inflammatory • Modulates macrophage function • Unlike IL-4, has no effect on T lymphocytes • Inhibits NO production • Inhibits pro-inflammatory cytokines • Attenuates leukocyte interaction with activated endothelial surfaces

37. Interleukin-15 • Derived from macrophages • Shares receptor components with IL-2, and shares promoting lymphocyte activation/prolif. • In neutrophils, it induces IL-8 and nuclear factor кB -> enhanced phagocytosis against fungal infections

38. Interleukin-18 • Formerly IFN-γ-inducing factor • Produced by macrophages • Pro-inflammatory, similar to IL-12 • Increased levels are pronounced (especially in G- sepsis) and can last up to 21 days

39. Interferon-γ • Helper T lymphocytes activated by bacterial antigens, IL-2, IL-12, or IL-18 produce IFN-γ • IFN-γ can induce IL-2, IL-12, or IL-18 • Detectable in circulation by 6 hrs and remain elevated for up to 8 days • Activate circulating and tissue macrophages • Induces acute lung inflammation by activating alveolar macrophages after surgery or trauma

40. Granulocyte-Macrophage Colony-Stimulating Factor • Delays apoptosis of macrophages and PMNs • Promotes the maturation and recruitment of PMNs in inflammation and perhaps wound healing • May contribute to organ injury such as ARDS • Peri-operative GM-CSF undergoing major oncologic procedures and burn patients demonstrate enhances neutrophil counts and fcn

41. High Mobility Group Box 1 • DNA transcription factor • Expressed 24-48 hrs after injury • Associated with weight loss, food aversion, shock, SIRS and Sepsis • Peak levels are associated with ARDS and death

42. Cell Signaling Pathways • Heat Shock Proteins • produced in response to ischemia/injury • HS Factors are activated upon injury, undergo conformational changes, translocate into the nucleus, and bind HSP promoter regions • Attenuate inflammatory response • Ligand Gated Ion Channels • When activated by a ligand, a rapid influx of ions cross the cell membrane. i.e. neurotransmitters

43. Cell Signaling Pathways • G-protein receptors • Largest family of signaling receptors • Adjacent effector protein activated receptor • Second messengers – cAMP or calcium • Can result in gene transcription or activation of phospholipase C • Tyrosine Kinases • When activated, receptors dimerize, phosphorylate, and recruit secondary signaling molecules • Used in gene transcription and cell proliferation • i.e. insulin, PGDF, IGF-1

44. Cell Signaling Pathways • Janus Kinase/Signal Transduction and Activator of Transcription (JAK-STAT) • IL-6, IL-10, IL-12, IL-13, IFN-γ • Ligand binds to the receptor, receptor dimerizes, enzymatic activation via phosphorylation propagates through the JAK domain and recruits STAT to the cytosolic receptor portion. • STAT dimerizes and translocates into the nucleus as a transcription factor • Suppressors of cytokine signaling (SOCS) block JAK-STAT

45. Tumor Necrosis Factor • Apoptosis - normal fcn of cellular disposal w/o activating the immune/inflammatory system • 2 receptors • TNFR-1 : inflammation, apoptosis, circulatory shock • TNFR-2 : no inflammation or shock • CD95 (Fas) receptor similar structure to TNFR-1 • Initiates apoptosis

46. Cell Mediated Inflammation • Platelets • Source of eicosanoids and vasoactive mediators • Clot is a chemoattractant for PMNs/monocytes • Modulate PMN endothelium adherence • Migration occurs within 3 hrs of injury • Mediated by serotonin, PAF, PGE2 • Eosinophils • Migrate to parasitic infection and allergen challenge to release cytotoxic granules • Reside in the GI, lung, and GU tissues • Activated by IL-3, GM-CSF, IL-5, PAF, and anaphylatoxins C3a and C5a

47. Cell Mediated Inflammation • Lymphocytes • T-helpers produce IL-3, TNF-α, GM-CSF • TH1: IFN-γ, IL-2, IL-12 • TH2: IL-4, IL-5, IL-6, IL-9, IL-10, IL-13 • Severe infection – shift toward more TH2 • Mast Cells • First responders to injury • Produce histamine, cytokines, eicosanoids, proteases, chemokines, TNF-α (stored in granules) • Cause vasodilation, capillary leakage, and recruit immunocytes

48. Cell Mediated Inflammation • Monocytes • Downregulation of receptor TNFR is clinically and experimentally correlated with CHF, nonsurvival in sepsis • Neutrophils • Modulate acute inflammation • Maturation is stimulated by G-CSF • Rolling (L-selectin (fast), P-selectin (slow) • Adhesion/transmigration – ICAM 1, 2, PECAM 1, VCAM 1, CD18

49. Endothelium-Mediated Injury • Neutrophil-Endothelium Interaction • Increased vascular permeability – facilitate oxygen delivery and immunocyte migration • Accumulation of neutrophils at injury sites can cause cytotoxicity to vital organs • Ischemia-reperfusion injury potentiates this response by releasing oxygen metabolites and lysosomal enz. • Neutrophils – rolling 10-20min (p-selectin), >20min

50. Nitric Oxide • Derived from endothelial surfaces responding to Ach, hypoxia, endotoxin, cellular injury, or shear stresses of circulating blood • T ½ = seconds • Reduces microthrombosis, mediates protein synthesis in hepatocytes • Formed from oxidation of L-arginine via NOS (+calmodulin, Ca2+, NADPH)