Post on 07-Oct-2018
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The role of microcirculatory and mitochondrial dysfunction in sepsis-induced acute kidney injury (AKI): a model of sepsis-induced organ dysfunction
Hernando Gomez, MD
Mentors: Michael R. Pinsky, MDJohn A. Kellum, MDBrian Zuckerbraun, MD
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A Unifying Theory of Sepsis-Induced Acute Kidney Injury
Work in progress…
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The classic conceptual model
AKI
Hypovolemia Heart failure Major surgery Sepsis
“Classic conception”
Hypoperfusion Ischemia/hypoxia
Shock
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•Exposure to warm ischemia (cardiac arrest) doesn’t always result in AKI
AKI and warm ischemia
Chua, et al. Resuscitation 2012
No PRCSPRCS*
RIFLE I or F 31.4% 51.7%
ALL
*PRCS = Post-resuscitation cardiogenic shock
6.4%
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•Sepsis-induced AKI can occur in the absence of shock
AKI in the absence of overt shock
CAP AKINon severe CAP 20.3%Non severe sepsis 23.8%Not requiring ICU 25%
1Murugan Kidney Int 2010
AKI (n=302)
No AKI (n=962)
AKI (n=386)
No AKI (n=1158)
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•AKI is independent of renal blood flow2
1Langenberg, Bellomo Crit Care 2005, 2Langenberg et al. Kidney Int 2006
Systematic review of studies measuring Renal Blood Flow (RBF) in sepsis1
Species Studies (n,%) RBF n(%) ~ or RBF n(%)Human 3 - 3Animals 159 99 (62%) 60 (38%)
Small 65 (41%) 19 (29%) 46 (71%)Large 94 (59%) 53 (56%) 41 (44%)
AKI can occur in the setting of increased RBF2
Baseline
Sepsis
Baseline
Sepsis
Sepsis-induced AKI
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•Exposure to septic plasma causes AKI-like changes in tubular epithelial cells in vitro1
Podocytes and Proximal tubular epithelial cells
Burned septic patient
Sepsis-induced AKI
a. Alteration in cell polarity
Vehi
cle
Hea
lthy
Bur
n+se
ptic
AK
I
b. Decreased cell-cell interactions(tight junction ZO-1 protein)
No stimuli Healthy plasma
Burned+ Septic AKI plasma
c. Increased apoptosis (TUNEL)
Seps
is(S
)
S+A
KI
Bur
n+S
Bur
n+S+
AK
I
1Mariano Crit Care 2008
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Sepsis-induced AKIConsistent histology findings
Tiwari et al
2. Apical tubular epithelial cell vacuolization and loss of brush border
4. Paucity of apoptosis/necrosis
1. Microvascular dysfunction
Wu et al. JASN 2007
3. Inflammation and oxidative stress
Wu et al. JASN 2007
Sepsis-induced AKI
(S-AKI) is NOT
ATN
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Sepsis-induced AKI… is there anything else out there?
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Sepsis-induced AKI
Microvascular dysfunction
InflammationMetabolic response
Lack of functionLack of cell death
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Sepsis-induced AKIUnifying theory model
DAMPs/PAMPs and other inflammatory mediators gain access to the tubular epithelial cell through filtration and peritubular capillary-TEC interactions – The “danger alarm signal”
1
2
1. El-Achkar 20082. Wu 2007
Reference
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Sepsis-induced AKIUnifying theory modelSluggish microvascular flow amplifies the “danger alarm signal” on the capillary side, and TLR-4-mediates recognition of DAMPs/PAMPs on the tubular side
= Amplification H1
1 2
4
H1
1. Tiwari 2005, Wu 20072. Goddard 1995, Holthoff 20123. Singbartl 20114. Kalakeche 2011, El-Achkar 2008
Reference
HypothesisH1
3
1
1 TNFα 4
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Sepsis-induced AKITEC response: 1. Prioritization of energy consumption, 2. quality control, and 3. cell cycle arrest
Tubular Lumen
NHE1
Cl-Endocytosis
Mitochondria
Protein synthesis
Regulation of energy metabolism• Prioritization of
utilization• Mitophagy• Cell cycle arrest
G1
G2
S
M
G0
Tubular epithelial cellS2 segment and beyond
Cl-
Inflammatory mediators from blood
• Altered energy balance: AMP:ATP
• Uncoupled respiration
• ROS/RNS• ѱ
Apoptosis
Nucleus
1
1
2
H1
H1
1
S1 Tubular epithelial cell
Signal from S1 cells Filtered mediators
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Sepsis-induced AKI
DAMPs
NaCl
Afferent arteriole Efferent arteriole
Peritubular capillary
TAL
Loop of Henle
PT
Macula Densa
DT
CD
GFR
Inju
red
tubu
lar c
ells
The Tubulo-glomerular feedback (TGF) may be the link between tubular injury and decline in GFR
* *
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Sepsis-induced AKIPreliminary data
Sepsis = Alteration in energy metabolism
How is energy metabolism regulated in the cell?
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Sepsis-induced AKIPreliminary data
AMP activated protein kinase (AMPK)
AutophagyInflammation
AnabolismCatabolism
Over-Activation(AICAR)
Organ Protection
Cytokines Sepsis
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Sepsis-induced AKIPreliminary data
• Model: Rodent (mice) Cecal Ligation and Puncture (CLP).• 22 gauge needle / 2 perforations
• 4 Groups and interventions (n=5-8/group):
• CLP • Sham• CLP+AICAR (100mg/kg) • Sham + AICAR
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Sepsis-induced AKIPreliminary data
0
0.1
0.2
0.3
0.4
0.5
0.6
mg/
dL
Groups
Creatininep<0.05
0500
1000150020002500300035004000
pg/m
L
Groups
Cystatin C
0102030405060708090
mg/
dL
Groups
BUNp<0.05
p<0.05p<0.05 p<0.05
Activation of AMPK by AICAR protects against cecal ligation and puncture-induced kidney injury
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Sepsis-induced AKIPreliminary data
Activation of AMPK by AICAR reverses cecal ligation and puncture-induced increases in serum cytokine levels
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Sepsis-induced AKI: K12 developmentAims
Aim 1: To determine the role of microvascular dysfunction on activation of energy regulating pathways in the tubular endothelial cell (TEC), namely, AMPK activation and induction of mitophagy.
Approach: Animal model (rat CLP) and TEC culture.
1. Determine the differences in microvascular dysfunction, AMPK activation and mitophagy in animals with and without AKI. (CLP rat model)
H1: Microvascular dysfunction, and activation of AMPK and mitophagy in AKI > Non AKI
2. Determine the temporal and spatial relationship between microvascular dysfunction and activation of AMPK and mitophagy. (CLP rat model)
H11: Microvascular dysfunction precedes AMPK and mitophagy activationH12: Microvascular dysfunction is associated with AMPK and mitophagy activation
3. Determine if microcirculatory dysfunction is associated with energy failure in the TEC. (CLP rat model)
H1: Microvascular dysfunction is associated with an increase in AMP/ATP ratio
Microvascular dysfunction
Metabolic response
Lack of functionLack of cell death
Microvascular dysfunction
Metabolic responseLack of function
Lack of cell death
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Sepsis-induced AKI: K12 developmentAims
Aim 2: To determine the signaling mechanisms regulating recognition and response of the TEC to inflammatory mediators
Approach: Animal model (rat CLP) and TEC culture.Focus: AMPK signaling, mitophagy activation, energy failure
1. Determine the role of inflammation on AMPK and mitophagy activation, and on energy balance in the TEC (CLP rat model: TLR+/+, TLR4 -/-, Leukocyte depletion model; TEC culture with exposure to septic serum)
H11: AMPK and mitophagy will not be activated in TLR4-/- TEC
H12: TLR4-/- mice will not develop microvascular dysfunction after CLPH13: CLP after leukocyte depletion will be associated with a lack of AKI
2. Determine the role of AMPK over-activation on TEC response to inflammation (CLP rat model and TEC culture)
H11: AMPK over-activation is associated with higher AMP:ATP ratio and less oxidative stress
3. Determine the effect of sera from animals subjected to different severities of CLP (low, moderate, severe) on TEC AMPK and mitophagy activation, and on AMP:ATP ratio in vitro (TEC culture exposed to septic sera from different severity models of AKI)
H12: Activation of AMPK and mitophagy will increase with increasing CLP severity sera.
Microvascular dysfunction
InflammationMetabolic response
Lack of functionLack of cell death
Microvascular dysfunction
Inflammation
Metabolic response
Lack of functionLack of cell death
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Sepsis-induced AKI: K12 developmentAims
Aim 3: To define the different clinical/biochemical phenotypes of presentation of sepsis, and their relation to sepsis-induced AKI.
Approach: Database exploration – HiDenIC and Astute.
1. Determine S-AKI subpopulations based on clinical variables – refinement of prior epidemiologic descriptions
2. Determine S-AKI subpopulations using biochemical variables such as urine NGAL, TIMP-2 and IGFBP-7
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Thank you
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Thoughts??