Mechanisms of intervention to reduce proteinuria

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Mechanisms of intervention to reduce
proteinuriaBiomarkers beyond proteinuria

• Jeffrey Kopp, MD
• Kidney Disease Section
• NIDDK, NIH

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Possible mechanisms of proteinuria reduction

• Reduction in glomerular capillary hydrostatic
  pressure
• Restoring glomerular filtration barrier
• - Cytoprotection podocyte, endothelium
• - Restoration of glomerular basement membrane
  pore size distribution
• Restoring proximal tubule protein reabsorption
  cytoprotection

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Hydrostatic mechanisms
Reducing efferent arteriolar tone - ACEI, ARB
Treating systemic hypertension - all agents
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Podocyte injury
Mitochondrial dysfunction

• Loss of filtration slits and slit diaphragms
• - Mutations
• Transcription
• - ER processing
• Signaling
• Actin cytoskeleton

Detachment, loss of adhesion
Apoptosis
Loss of anionic charge podocalyxin (glucose)
Replenishment failure (?)
Dysregulation (collapsing glomerulopathy)
IC, C5b-9
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Protecting and restoring podocyte phenotype
Preventing IC deposition

• Glucocorticoids
• Transcription
• Actin stabilization
• Ransom KI 2005
• Anti-apoptotic
• Wada JASN 2005
• Transport from ER
• Fuji KI 2006

Mizoribine - Transport from ER via
energetics Nakajo JASN 2007

• Retinoids
• reverse FPE
• ?nephrin, podocin
• Vaughan KI 2005

Cyclosporine
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Glomerular basement membrane

• Collagen IV
• Mutations
• - Isoform shift
• ? synthesis by glucose, Ang 2
• ?degradation

• Loss of heparan sulfate (?) and HSPG agrin
• production,
• ? degradation
• Glucose, Ang2

Jefferson, KI 2008
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Endothelium
Haraldsson, Physiol Rev 2008
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Injury to endothelial cell and endothelial
surface layer
Hyperglycemia, AGE
Free fatty acids
ROS, oxidative stress, mitochondrial dysfunction
Proinflammatory cytokines (TNF?) Adiponectin
VEGF antagonism
Haraldsson, Physiol Rev 2008 Rask- Madsen, Nature
Clin Pract 2007
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Pima diabetics Macroproteinuria but not
microproteinuria is associated with shunt
Macro
Micro

• Shunt magnitude correlates with FPE

Lemley, JASN 2000
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Proximal tubule albumin reabsorption
Birn, KI 2006
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Impaired albumin reabsorption by proximal tubule
in PAN nephrosis
0
40 s
14 min

• CON

PAN
Russo, KI 2007
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Gene therapy reduces tubulointerstitial injury in
rat overload proteinuria model
MCP-1 antagonist (7ND)

• I?B?

Shimizu, JASN 2003
Takase, KI 2005
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Does macroalbuminuria cause tubulointerstitial
damage?

• Pro
• Overload albuminuria models
• Exposure to albumin (or cytokines of FA on
  albumin) induces RANTES, MCP-1, IL8, fractalkine,
  TNF-?, ET, TGF-? alters integrins, may induce
  apoptosis
• Other proteins iron carriers, complement, Ig,
  growth factors
• Gene therapy to PTC (MCP-1 reduction, I?B)
  protects

• Con
• Minimal change nephropathy proteinuria for years
  without progression
• Role of selectivity

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Biomarkers

• Biomarkers measures that predict clinical
  outcome
• NIH biomarker working group a characteristic
  that is objectively measured and evaluated as an
  indicator of normal biologic processes,
  pathogenic processes, or pharmacologic responses
• Clinical end point a variable that reflects how
  a patient feels or functions or how long a
  patient survives
• Surrogate end point a biomarker that can
  substitute for an observed clinically meaningful
  end point
• Intermediate end point a characteristic that is
  intermediate in the causal pathway between an
  intervention and the clinical endpoint

Clinical end point
Treatment
Stevens, CJASN 2006
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Biomarkers in drug development and use

• Pre-clinical/animal
• Clinical studies identify pathways
• Animal studies screening for leads, rank
  candidates
• Clinical studies
• Identify pathways
• Early detection
• Differential diagnosis, identify subpopulations
• Prognosis
• Surrogate end point for trials
• Assess drug effect, dose-ranging, more efficient
  trial design
• Clinical therapy drug dosing

Hewitt, JASN 2004
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Biomarkers and CKD

• Increased interest, increased funding
• Needed more systematic searches, validation in
  prospective observational studies (CRIC, CKID)
  and interventional trials

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Biomarkers can address different issues across
the course of disease
Hewitt, JASN 2004
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Biomarker discovery approaches
SELDI-TOF
MALDI-TOF
2D gel
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Two biomarkers are better than one
Hewitt, JASN 2004
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Cystatin C

• Cystatin C 13.3 kDa, product of all nucleated
  cells, freely filtered and readily reabsorbed
• May have advantages over serum creatinine (MDRD
  eGFR) in monitoring GFR over time vs iothalamate
  r0.77, 0.31) (Perkins JASN 2005)

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Podocyturia

• Evidence that podocyte depletion characterizes
  most progressive CKD
• Direct counting of urinary podocytes is
  impractical
• Enumeration with FACS has proven difficult
• Podocyte proteins total, exosomes

Kuusniemi, KI
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Podocyturia correlates more closely than
proteinuria with disease activity in animal models

• PAN

Thy-1
5/6 Nx
Yu JASN 2005
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Diabetic nephropathy Nephrinuria
Men
Women

• Increased urine nephrin in diabetes, but
  unrelated to proteinuria

Pätäri, Diabetes 2003
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Lupus nephritis urinary cytokines
Li Autoimmunity Rev 2006
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Treatment reduces urinary TGF-? in diabetic
nephropathy

• Ruboxistaurin

ACEI ARB
Gilbert Diabetes Care 2007
Song NDT 2006
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Urinary exosomes

• Derived from podocytes, RTEC, and lower tract
  cells
• Sample various cellular compartments, including
  nucleus

Zhou KI in press
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Conclusions

• Diverse mechanisms of proteinuria and of
  proteinuria reduction
• Non-albumin protein biomarkers are not yet
  validated surrogates, demonstrated to lie within
  the causal pathway to CKD across multiple
  diseases and multiple interventions

Strength of association
Glomerular microalbuminuria diabetic vs metabolic
Glomerular hypertension
Endothelial injury
Glomerular macroalbuminuria
GBM abnormalities
CKD progression
Podocyte injury
Tubular microalbuminuria
Proximal tubule dysfunction
Tubular macroproteinnuria
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