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

Thank you for giving me this opportunity!