autosomal dominant polycystic kidney disease (adpkd)
TRANSCRIPT
Autosomal Dominant Polycystic Kidney Disease (ADPKD)
Molecular targets of therapy in
Rupin KumarMedical Student, 5th Year Rabindra Nath Tagore Government Medical College,UdaipurIndia
Definition
ADPKD is a multisystem disorder characterized by multiple, bilateral renal cysts associated with cysts in other organs, such as liver, pancreas, and arachnoid membranes.
Incidence: 1 in every 400 to 1000 live births.
Typically leads to renal failure mainly due to continued enlargement of cysts.
A Gross Comparison!
Markedly enlarged polycystic kidneys in comparison to a normal kidney in the middle.
The Nephro’s Concerns!
Renal manifestations
Decline in urine
concentrating ability
manifesting clinically as
polyuria, polydipsia,
nocturia (60%)
Hypertension(60-100%)
Nephrolithiasis, mainly uric acid
(25%)
Proteinuria(>300mg/day, 48%)Flank and
abdominal pain
The Genetics of ADPKD
PKD1
Located on Chromosome 16
Codes for Polycystin 1 protein (PC1)
Associated with more severe phenotype
Incidence: 85%
PKD2
Located on Chromosome 4
Codes for Polycystin 2 protein (PC2)
Less severe phenotype
Incidence: 15%*PKD1 mutation maybe associated with deletion of TSC2 gene in 2/3rd, CONTIGUOUS GENE SYNDROME
Wilson, P. D. N Engl J Med 2004;350:151-164
Age
(in
yea
rs)
Role of PC1 and PC2
N-terminal
GPCR, proteolytic site
C-terminal, binds to β-catenin
Locations:
PC1: Cilia, Basolateral membranes, inter-membrane junctions.Helps in cell-cell adhesions.
PC2: non-selective cation channel, permeable to Calcium.Located mainly in SER.S
ite o
f in
tera
cti
on
Why only certain areas affected?
Genetic defects + in all cells; cysts only in <10% tubules Focal Cystic Dilation.
The concept of loss of heterozygosity:
Timing of
inactivation of PKD1
Second Hit Mutations
Loss of Heterozygosit
y
Threshold Model of Cyst Formation
Gallagher et al, Adv Chronic Kidney Disease 2010 March; 17(2): 118-130
Timing of inactivation of PKD1
Gallagher et al, Adv Chronic Kidney Disease 2010 March; 17(2): 118-130
A, Kidneys of Pkd1cond/cond;tamoxifen-Cre+ mice with inactivation of Pkd1 induced atpostnatal day 12 (P12) became cystic within 3 weeks (left panel), whereas if Pkd1 inactivationoccurs at P14, they remained normal 3 months later (right panel) B,C, Pkd1inactivation in adult kidneys results in late-onset renal cystic disease. Kidneys fromPkd1cond/cond;tamoxifen-Cre+ mice harvested 3 months (B) or 6 months (C) after Pkd1inactivation was induced at 6 weeks of age
Cellular Pathways of Cyst Formation
Translocation of Na-K ATPase pumpsRole of cAMP and intracellular
calciumMammalian target of rapamycin
(mTOR)Role of ciliaTubular hyperplasiaCell planarity changes
Translocation of Na-K ATPase pumps**Avner et al, Proc. Natl. Acad. Sci. 1992: 89, 7447-7451
Apical-lateral distribution of Na-K ATPase is a normal transient feature of early collecting tubule development.
But, apical membrane distribution PERSISTS in cystic kidneys.
Maybe due to cellular dedifferentiation or cellular immaturity.
Trans-tubular import of fluid into cysts.
Histological evidenceExpression of Na+/K+-ATPase subunits during control and cystic CPK renal tubular development. [Immunoperoxidase stain(brown), counterstained with hematoxylin. A and C, x 165; B and D, x 130.] (A) Control day 3 proximal tubules demonstrate basal-lateralexpression of Na+/K+-ATPase al subunit. (31 subunit expression was identical. (B) CPK day 3 cystic proximal tubules, as well as unaffectedproximal tubules in the field, demonstrate basal-lateral Na+/K+-ATPase al subunit expression. (31 subunit expression was identical. (C) Controlday 8 outer cortical collecting tubule demonstrates apical, as well as lateral, (31 subunit expression. Note the purely basal-lateral staining ofother collecting tubules in the field. al subunit expression was identical. (D) CPK day 8 cystic outer cortical collecting tubule demonstratesapical, as well as lateral, (81 subunit expression. Note the purely basal-lateral staining of no cystic tubules in the field. al subunit expressionwas identical.
Role of cAMP and intracellular calcium
PC2 overexpression aided by PC1
Increases intracellular
calcium
Reduced intracellular calcium
Inhibits calcium dependent phosphodiesterases
Stimulates Adenyl Cyclase
Increased cAMP
Increased cAMP
CFTR dependent fluid and chloride secretion
Increases aquaporin expression (?)
Cell proliferation through activation of MAP-kinases
Calcimimetics, increased CaSR activation
Increasing GsPCR antagonist, e.g. Vasopressin or GiPCR agonist, eg. Octreotide
Activated by 2-acylamino-3-thiophenecarboxylase
Cystic Fibrosis
Mammalian target of rapamycin (mTOR) *Nephrol Dial Transplant 2006; 1752-57
Growth Factors
PI3K
AKT
Phosphorylates TSC1/TSC2
GTPase action of Rheb
+mTOR Complex
Cell Proliferation
and angiogenesis
mTOR inhibitors
Role of Cilia
• Located on renal tubular epithelial cells.
• Senses fluid flow-mediated deflection of
ciliary axoneme by increased influx of calcium.• But PC1 inactivation causes
defective sensory perception of flow.
• Reduced intracellular calcium, increased cAMP!
Cell Planarity Loss
Summing up targets!!
Clinical Trials and OutcomesVasopressin Receptor Antagonists:OPC 31260, Tolvaptan Multicenter, placebo-controlled, double-blinded trial
(TEMPO 3:4) Inclusion: 18 to 50 years, GFR >60ml/min, TKV >750ml. Dose: 60 to 120mg daily, 2:1 Drug: Placebo Results after 3 years:Tovalptan Placebo
Increase in TKV 2.8% 5.5%
Decline in kidney function
-2.61 mg/ml -3.81mg/ml
Adverse effects noted with Tolvaptan:1. Increased liver enzymes (4.9%)2. Chest pain (0.8%)3. Headache (0.5%) Torres VE, Chapman AB, Devuyst O et al. Tolvaptan in patients with autosomal dominant polycystic kidney disease.
NEJM 2012; 367:407
Clinical Trials and OutcomesIncreased fluid intake: Suppresses vasopressin levels. Pilot study to compare acute and chronic (atleast 3L/day)
water loading on urine osmolality and cAMP concentrations in 13 subjects with ADPKD, 10 healthy controls.
Excluded: Antidiuretic use, GFR <60.
Results: Chronic water load increased urine volume to mean of
3.1L/day and decreased osmolality to 270 mosm/day in ADPKD subjects.
Acute water load reduced 24-hr cAMP excretion. Less practical feasibility, monitor Na levels.
Barash I et al, A pilot study to evaluate changes in the urine osmolality and urine cAMP in response to acute and chronic water loading in ADPKD. Clin J Am Nephrol 2010; 5:563.
Clinical Trials and OutcomesSomatostatin:
RCT on 34 patients with ADPKD with Somatostatin or placebo.
Large multicentric trials required. Results after one year:
Somatostatin Placebo
Mean kidney volume
Stable, 0.25% increase
8.60% increase
GFR Reduced to same degree
Reduced to same degree
Hogan et al. Randomized Clinical Trial of long-acting Somatostatin for ADPKD and liver disese. J Am Soc Nephro 2010; 21: 1052
Clinical Trials and Outcomes* Walz et al. Evrolimus in patients with ADPKD. NEJM 2010; 262:820** Novalic et al. Dose-dependent effects of Sirolimus on mTOR signaling and polycystic kidney diasese J Am Soc Nephrol. 23: 182 *** Shullingford et al. Folate conjugated rapamycin slows progression of polycystic kidney disease. J Am. Soc Nephrol. 2012. 23: 1674
mTOR inhibitors: *Double blind, two year. 431 patients with PKD (mean GFR 55
ml/min/1.73m2) with placebo or everolimus. Increase in protein: creatinine in Everolimus group. S/e: Leukopenia, thrombocytopenia, hyperlipidemia.
**Trial 2: Open-label RCT, 18 months. 100 patients with PKD (mean GFR 70 ml/min)
with placebo or sirolimus. NO CHANGE IN TKV OR GFR after 18 months. Albumin: creatinine 38% increased in Sirolimus group.***Novel strategy:Kidney-targeted folate-conjugated form of rapamycin inhibited mTOR activity
in the kidney but not in other organs in a mouse model.
Everolimus Placebo
Increase in TKV
230ml 310ml
Decrease in GFR
8.9ml/min 7.7 ml/min
Other approaches attempted
PPAR agonistsMAP kinase inhibitorsEDGF inhibitorsLovastatinMethylprednisoloneAmiloride and caffeine restriction
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