Post on 29-Jan-2016
Mechanisms of intervention to reduce proteinuria
&Biomarkers: beyond proteinuria
Jeffrey Kopp, MDKidney 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
Treating systemic hypertension
- all agents
Reducing efferent arteriolar tone
- ACEI, ARB
Podocyte injury
Detachment, loss of adhesion
Apoptosis
Loss of filtration slits and slit diaphragms
- Mutations-Transcription
- ER processing- Signaling
- Actin cytoskeleton
Dysregulation (collapsing glomerulopathy)
Replenishment failure (?)
Loss of anionic charge: podocalyxin (glucose)
IC, C5b-9
Mitochondrial dysfunction
Protecting and restoring podocyte phenotype
Glucocorticoids-Transcription
- Actin stabilizationRansom KI 2005
- Anti-apoptoticWada JASN 2005
- Transport from ERFuji KI 2006
Retinoids-reverse FPE
- nephrin, podocinVaughan KI 2005
Mizoribine
- Transport from ER via energetics
Nakajo JASN 2007
Cyclosporine
Preventing IC deposition
Glomerular basement membrane
Jefferson, KI 2008
Collagen IV - Mutations
- Isoform shift- synthesis by glucose,
Ang 2- degradation
Loss of heparan sulfate (?) and HSPG agrin:
production, degradation
- Glucose, Ang2
Injury to endothelial cell and endothelial surface layer
Haraldsson, Physiol Rev 2008Rask- Madsen, Nature Clin Pract 2007
Hyperglycemia, AGE
VEGF antagonism
ROS, oxidative stress, mitochondrial dysfunction
Proinflammatory cytokines (TNF)
Adiponectin
Free fatty acids
Pima diabetics: Macroproteinuria but not microproteinuria is associated with shunt
Lemley, JASN 2000
Macro Micro
Shunt magnitude correlates with FPE
Impaired albumin reabsorption by proximal tubule in PAN nephrosis
CON
Russo, KI 2007
PAN
0 40 s 14 min
Gene therapy reduces tubulointerstitial injury in rat overload proteinuria model
IB
Takase, KI 2005Shimizu, JASN 2003
MCP-1 antagonist(7ND)
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, IB) 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
Stevens, CJASN 2006
TreatmentClinical end
point
B
B SI
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
CKD and biomarkers
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 20070
250
500
750
1000
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)
Cystatin and kidney function
1998 1999 2000 2001 2002 2003 2004 2005 2006 20070
50
100
150
200
250
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
Yu JASN 2005
Thy-1
5/6 Nx
Diabetic nephropathy: Nephrinuria
Increased urine nephrin in diabetes, but unrelated to proteinuria
Men
Women
Pätäri, Diabetes 2003
Treatment reduces urinary TGF- in diabetic nephropathy
Ruboxistaurin
Gilbert Diabetes Care 2007Song NDT 2006
ACEI + ARB
Urinary exosomes
Derived from podocytes, RTEC, and lower tract cells
Sample various cellular compartments, including nucleus
Zhou KI in press
6.1 8.4 10.9 15.0 g/day proteinuria
Female
Normal FSGS
WT-1
2.2 2.8 4.0 6.4 8.4 20 g/day proteinuria
Male
Normal FSGS
WT-1
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
CKD progression
Glomerular microalbuminuria
diabetic vs metabolic
Glomerular macroalbuminuria
Tubular microalbuminuria
Glomerular hypertension
Endothelial injury
Podocyte injury
GBM abnormalities
Proximal tubule dysfunction Tubular
macroproteinnuria
Strength of association