Aki pathophysiology chaken maniyan

Acute Kidney injury Pathophysiology

and Novel biomarker

CHAKEN MANIYAN M.D.Nephrology fellow ,

Phramongkutklao hospital 19 Aug 2016

Scope : Part I

• Pathophysiology

• Pre-renal AKI

• Post-renal AKI

• Renal (focus on acute tubular necrosis) AKI

• Hemodynamic / endothelium injury

• Inflammatory response

• Tubular injury

• Cell death and regeneration

Pathophysiology of prerenal AKI

A physiologic response to mild-moderate renal hypoperfusion

Rapid reversible upon restoration of RBF and glomerular filtration pressure

More severe hypoperfusion lead to ischemic injury and intrinsic renal AKI

Thus, prerenal AKI and intrinsic renal AKI due to ischemia are part of a spectrum of manifestations of renal hypoperfusion.

Compensatory mechanisms

A physiologic response to mild-moderate renal hypoperfusion

EXTRINSIC: Neurohormonal mechanisms Pituitary response

INTRINSIC: RAAS activation Tubuloglomerular feedback Afferent arteriolar dilatation Efferent arteriolar constriction

Homeostasis to maintain RBF

Critical Care Medicine: Principles of Diagnosis and Management in the Adult .4th edition

RAASactivation

Regulation of renal perfusion pressure

J. Gary Abuelo,N Engl J Med 2007; 357:797-805

Pathophysiology of Post renal AKI

Obstruction can affect hemodynamic variables and GFR

GFR = Kf x (PGC-PT- ΠGC)

Kf - glomerular ultrafiltration coeffecient (related to surface area and permeability of capillary membrane)

PGC- glomerular capillary pressure (influenced by RBF and resistance of afferent and efferent arterioles)

PT - hydraulic pressure of fluid in tubuleΠGC- oncotic pressure of proteins in glomerular capillary

RBF = (aortic pressure - renal venous pressure) renal vascular resistance

Influences PGC constriction of afferent arteriole will result in a decrease of PGC and GFR

An increase in efferent arteriolar resistance will increase PGC

Campbell-Walsh Urology, 11th Edition, 2016 Elsevier Inc.

Summary of renal hemodynamic change UUO and BUO

Campbell-Walsh Urology, 11th Edition, 2016 Elsevier Inc.

Triphasic pattern of UUO

Smith's Textbook of endourology 3rd edition vol I

Pre-glomerular vasodilatation

Post-glomerular vasoconstriction

Pre and Post-glomerular vasoconstriction

Regulation of GFR in Response to Obstruction

• After release of obstruction

• RBF is increased

• GFR remains low because of nonperfusion or underperfusion of many glomeruli

• Intense afferent vasoconstriction reduces PGC, so that even though PT also falls with release of the obstruction

• Macula densa likely senses dramatic change in rate of flow, and this may lead to intense vasoconstriction

Nevo A, et al. Urology. 2014 Dec. 84 (6):1475-9

Recovery of Glomerular Function

after Relief of Obstruction

• Depends on several factors,

• Duration and extent of obstruction

• Presence of functioning contralateral kidney

• Presence of associated infection

• Level of pre obstruction RBF

Nevo A, et al. Urology. 2014 Dec. 84 (6):1475-9

Pathophysiology of ATN

Morphologic changes

• Classical hallmark of ATN is loss of apical brush border of proximal tubular cell

• Detached tubular cell , denuded tubular basement and focal proximal tubular dilatation

• Sloughed tubule cells, brush border vesicle remnants, and cellular debris in combination with Tamm-Horsfall protein form classical muddy-brown granular casts

J Am Soc Nephrol. 2011 Mar;22(3):416-25

Major biochemical change

• Intracellular calcium accumulation

• ⬆ROS

• Activation of phospholipases and proteases

• ATP depletion

• The net effect result in

• Cell death

• Sloughing of viable cells into tubule lumen by impairment of normal cell-to-basement membrane adhesion

• Activation of inflammatory response


Destiny of injury

Insult Inju

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NECRO

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APOP

TOSIS

REGENE

RATE

Conceptual pathophysiology of AKI

Hemodynamic andEndothelial TubularInflammation effect

Activation Dysfunction ApoptosisCytokine release⬆Permeability⬇RBF

Lethal : Cell deathSublethal: - cytoskeleton disruption - loss of polarity - loss off tight junction - tubular obstruction - backleak phenomenon

WBC aggregationDendritic activationCytokine release Tissue margination

Reduced GFR/Function loss

Adapted from: Nature review of Nephrology 2012

Injury








Injury

Hemodynamic factor in development of ATN

Comprehensive clinical nephrology 5th edition : Section XIV Acute Kidney Injury

Effect of endothelial disruption

• ↑vascular permeability

• Leukocyte recruitment and activation.

• Activated endothelium ➪ up regulation of intracellular adhesion molecule 1 (ICAM-1) and P- selectin

K J Kelly. J Clin Invest. 1996 Feb 15; 97(4): 1056–1063

Model of leukocyte extravasation

Robbins and Cotran Pathologic Basis of Disease. 7th ed. Philadelphia: Elsevier Saunders

Effects of renal ischemia on histopathology

in ICAM-1–deficient and control mice

K J Kelly. J Clin Invest. 1996 Feb 15; 97(4): 1056–1063

ICAM-1–deficientICAM-1–present

Coagulation

• Injured endothelial cell interact with protein C through endothelial cell protein C receptor (EPCR) and thrombomodulin

• Activated protein C

• antithrombotic actions

• antiinflammatory

• cytoprotective pathways to restore normal homeostasis

• During inflammatory response, protein C, are consumed along with downregulation EPCR and thrombomodulin expression

Bernard GR, et al.. N Engl J Med. 2001;344:699–709.

Multiple protective effect of activated protein C

Adapted from Bernard GR, et al.. N Engl J Med. 2001;344:699–709.

Activation of protein C

Faust el al. NEJM 2001; 345:408-16 27

Endothelial cell activation and injury

Sharfuddin, A.Nat. Rev. Nephrol. doi:10.1038/nrneph.2011.16








Injury

Inflammatory response in AKI

• Dendritic cells and macrophages respond to bacterial structures called pathogen-associated molecular patterns (PAMPs),

• Tissue damage (eg IRI) is recognized intracellular proteins (heat shock proteins, and HMBG1.) released by dead cells called alarmin

• Danger model = Endogenous alarmins and exogenous PAMPs can be considered subgroups of damage-associated molecular patterns (DAMPs).

Matzinger P, Science. 2002;296(5566):301Rosin DL, J Am Soc Nephrol. 2011 Mar;22(3):416-25

Danger & Stranger model


Key Inflammatory response after IRI

• Initiated by endothelial dysfunction with leukocyte extravasation

• Macrophage release of proinflammatory

cytokines (TNF-𝛼, IL-8,IL-1)

• Chemotactic cytokines (e.g., monocyte chemoattractant protein-1 [MCP-1] IL-8, RANTES)

• Powerful recruits other inflammatory cells and complement activation

Alterations in microvasculature and

inflammation in ischemic AKI

P.Devarajan et al ; J Am Soc Nephrol 17: 1503–1520, 2006

Complement activation

• Complement system generates number of inflammatory signals that lead to ongoing injury

• Induce recruitment of neutrophils and directly damages endothelium and surrounding cells.

• Activation of alternative and lectin pathway (forms membrane attack complex (C5-C9) may contribute to renal injury

Thurman JM, Kidney Int. 2005;67(2):524.B.Vries,Am J Pathol. 2004 Nov; 165(5): 1677–1688.

Three pathways of complement activation

B.Vries,Am J Pathol. 2004 Nov; 165(5): 1677–1688.

Ischemia followed by reperfusion leads to

renal deposition of MBL(mannose binding lectin)

B.Vries,Am J Pathol. 2004 Nov; 165(5): 1677–1688.

Complement activation in kidneys with ATN

occurs via the alternative complement pathway.

P.Devarajan et al ,Kidney Int. 2005;67(2):524.




Sublethal: - cytoskeleton disruption - loss of polarity - loss off tight junction - tubular obstruction - backleak phenomenon Lethal : Cell death




Injury

Sites of tubular injury

in acute tubular necrosis

• S3 segment and medullary TAL

is most damaged area during ischemic injury

• Limited anaerobic glycolysis

• Marked hypoperfusion and congestion area

• Highly metabolised due to reabsorption

Comprehensive clinical nephrology 5th edition : Section XIV Acute Kidney Injury

Regional blood flow is altered

following injury in ischemic AKI

Karlberg L. Acta Physiologica Scandinavica. 1983;118:11–17.

IRI leads to loss of polarity

• Ischemia-induced redistribution of membrane proteins

• Disrupts beta-1 integrins protein which regulate actin–spectrin cytoskeleton cytoskeleton that anchors the Na-K-ATPase pump lead to redistribution

• This redistribution of pump results in loss of bidirectional transport of Na and water resulting high FeNa in ATN

Schrier RW et al , J Clin Invest. 2006;116(2):357.

Tubular Epithelial Cell Injury and the

Development of Acute Tubular Necrosis

Adapted from Schrier RW. J Clin Invest. 2004;114:5-14.

Backleak Phenomenon

• ATP depletion induces rapid disruption of actin cytoskeleton result in loss of tight junctions

• Increased paracellular permeability producing backleak of the glomerular filtrate into interstitial

• Interstitial edema play major role in decreased blood flow and exacerbating tubular injury during extension phase

Asif A et al, Nature Reviews Nephrology 7, 189-200 April 2011

CYTOSKELETAL AND INTRACELLULAR

STRUCTURAL CHANGES

Sharfuddin A: Encyclopedia of intensive care medicine, New York, 2012, Springer

Loss of filamentous F-actin (Proximal tubule microvilli)

Loss of tight junction paracellular transport

(Backleak Phenomenon)

Loss of polarity

Disruption of integrins with ECM

Intratubular obstruction

• Tubular cells bind to beta1-integrin ligands on basement membrane

• minimize tubule cell detachment and intratubular obstruction

• Intraluminal casts and Tamm-Horsfall protein, converted to gel-like polymer in high local luminal sodium concentrations

J Am Soc Nephrol. 2005;16(2):374

Kidney Int. 2001;59(3):932J Am Soc Nephrol. 2005;16(2):374

Classical muddy brown granular casts.

Endothelial-tubular interaction in

ATN

J. Gary Abuelo,N Engl J Med 2007; 357:797-805

Cell death and regeneration

Alterations in tubule cell structure

after Ischemic reperfusion injury

initiation phase

P.Devarajan et al. J Am Soc Nephrol 17: 1503–1520, 2012

extension phaseinitiation phase sublethal injury

maintenance phasestem cells and progenitor cells?

Inhibition of apoptosis and inflammation at extension stage may represent a powerful therapeutic approach

recovery phase

Apoptotic pathway

A. Linkermann, J Am Soc Nephrol. 2014 Dec; 25(12): 2689–2701.

Four-phase model of necrosis

A. Linkermann, J Am Soc Nephrol. 2006 Dec; 25(12): 2689–2701.

Necrosis : is it really unprogrammed?

• Necrosis

• cytoplasmic and organelle swelling

• loss of cell membrane integrity

• release of cellular contents into extracellular space

• inflammatory response within the tissue

• Believed form of accidental uncontrolled cell death w/o signal

• Nowadays general agreement that necrosis can occur in a regulated manner

• Two special forms of regulated necrosis are necroptosis and parthanatos.

Sandra M., Clinical Kidney Journal, 2015, vol. 8, no. 5, 548–559

Necroptosis : New pathway of death

Signalling pathways of different cell death modes

Sandra M., Clinical Kidney Journal, 2015, vol. 8, no. 5, 548–559

Programmed Cell Death ≠ Apoptosis

A.Linkermann, N Engl J Med 2014;370:455-65.

Necroptosis• Consequence of death receptor

• Signal 1 : signalling upon formation of RIPK1

• Regulated necrosis, started by TNFR1 ligation (inhibited by RIP1-targeting chemical necrostatin-1)

• Triggers: FAS/CD95, TRAILR (TNF-related apoptosis-inducing ligand receptor), TLR3/4 (Toll-like receptor), etoposide and IRI (ischaemia-reperfusion injury)

• RIPK3/mixed lineage kinase domain-like protein (MLKL) containing necroptosome

• Signal 2 : Opening mitochondria permeability transition (MPT) pore

• Upon MPT pore opening and apoptosome-forming proteins

• Induce apoptotic phenotype in a caspase-independent mannere

Allam R, J Am Soc Nephrol 2012; 23: 1375–1388 Sandra M., Clinical Kidney Journal, 2015, vol. 8, no. 5, 548–559

Major signal in Necroptosis

A.Linkermann, Kidney International (2016) 89, 46–57

Difference between apoptosis, necroptosis and necrosis

Apoptosis Necroptosis Necrosis

Type of cell death Controlled Controlled Uncontrolled

Trigger Trauma, toxic stress, self-renew, aging, development. Trauma, toxic stress, infection Trauma, toxic stress,

infection

MorphologyExtensive membrane blebbing, condensation and fragmentation of the nucleus

Cytoplasmic swelling, rupture of the plasma membrane and spilling of the intracellular content

Extensive organelle and cell swelling, loss of membrane integrity, release of extracellular contents

Signalling pathway Specific, intrinsic or extrinsic pathways Specific, e.g TNFR1 pathway Unspecific

Executioner Caspase, (caspase-3, -6, -7, -8 and -9) RIP kinase (RIPK1 and RIPK3) -

Inhibitor Z-VAD fmk Necrostatin-1 -

Adapted from A. Linkermann et al. Cell Death Dis. 2015 Nov; 6(11): e1975.

Promising intervention to control regulated necrosis

A.Linkermann, Kidney International (2016) 89, 46–57

Take home

Thank you for your attention

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Aki pathophysiology chaken maniyan