Transcript Mechanisms of intervention to reduce proteinuria

Mechanisms of intervention to
reduce proteinuria
&
Biomarkers: beyond proteinuria
Jeffrey Kopp, MD
Kidney Disease Section
NIDDK, NIH
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
Hydrostatic mechanisms
Reducing efferent
arteriolar tone
- ACEI, ARB
Treating systemic
hypertension
- all agents
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)
Dysregulation (collapsing
glomerulopathy)
IC, C5b-9
Replenishment
failure (?)
Protecting and restoring podocyte phenotype
Glucocorticoids
-Transcription
- Actin stabilization
Ransom KI 2005
- Anti-apoptotic
Preventing IC
deposition
Mizoribine
- Transport from ER via
energetics
Nakajo JASN 2007
Wada JASN 2005
- Transport from ER
Fuji KI 2006
Cyclosporine
Retinoids
-reverse FPE
- nephrin, podocin
Vaughan KI 2005
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
Endothelium
Haraldsson, Physiol Rev 2008
Injury to endothelial cell and
endothelial surface layer
Hyperglycemia, AGE
ROS, oxidative stress,
mitochondrial
dysfunction
Free fatty acids
Proinflammatory
cytokines (TNF)
Adiponectin
VEGF
antagonism
Haraldsson, Physiol Rev 2008
Rask- Madsen, Nature Clin Pract 2007
Pima diabetics: Macroproteinuria but not
microproteinuria is associated with shunt
Macro
Micro
 Shunt magnitude
correlates with FPE
Lemley, JASN 2000
Proximal tubule albumin reabsorption
Birn, KI 2006
Impaired albumin reabsorption by
proximal tubule in PAN nephrosis
0
40 s
14 min
CON
PAN
Russo, KI 2007
Gene therapy reduces tubulointerstitial injury in
rat overload proteinuria model
MCP-1 antagonist
(7ND)
IB
Takase, KI 2005
Shimizu, JASN 2003
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
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
Treatment
B
I
B
S
Clinical end
point
Stevens, CJASN 2006
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
Biomarkers and CKD

Increased interest, increased funding

Needed: more systematic searches, validation in
prospective observational studies (CRIC, CKID) and
interventional trials
Biomarkers can address different issues
across the course of disease
Hewitt, JASN 2004
Biomarker discovery approaches
SELDI-TOF
MALDI-TOF
2D gel
Two biomarkers are better than one
Hewitt, JASN 2004
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 r=0.77, 0.31)
(Perkins JASN 2005)
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
Podocyturia correlates more closely than
proteinuria with disease activity in animal models
PAN
Thy-1
5/6 Nx
Yu JASN 2005
Diabetic nephropathy: Nephrinuria
Men
Women
 Increased urine nephrin in diabetes, but unrelated to proteinuria
Pätäri, Diabetes 2003
Lupus nephritis: urinary cytokines
Li Autoimmunity Rev 2006
Treatment reduces urinary TGF- in
diabetic nephropathy
ACEI + ARB
Song NDT 2006
Ruboxistaurin
Gilbert Diabetes Care 2007
Urinary exosomes
 Derived from podocytes,
RTEC, and lower tract cells
 Sample various cellular
compartments, including
nucleus
Normal
FSGS
WT-1
Male
2.2 2.8
Normal
4.0
6.4 8.4
20 g/day proteinuria
FSGS
Female
6.1
WT-1
8.4 10.9 15.0 g/day proteinuria
Zhou KI in press
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
Glomerular hypertension
Glomerular
microalbuminuria
diabetic vs metabolic
Strength of
association
Endothelial injury
GBM abnormalities
Glomerular
macroalbuminuria
Podocyte injury
Proximal tubule
dysfunction
Tubular
microalbuminuria
Tubular
macroproteinnuria
CKD
progression