Renal Pathophysiology Iain MacLeod, Ph.D Iain MacLeod 23 November 2009

Renal Anatomy 800,000 to 1 million nephrons / kidney initial filtering component – renal corpuscle tubule extending from renal corpuscle to collecting ducts Renal corpuscle forms filtrate of blood free of cells and protein Filtrate leaves and enters tubule – as it flows through the tubule, substances are exchanged Fluid remaining at the end of each nephron combines in collecting ducts – leaves as urine Renal corpuscle: interconnected capillary loops – glomerulus supplied with blood from afferent arteriole glomerulus protrudes into Bowman’s capsule as blood flows through glomerulus, 1/5 of plasma filters into Bowman’s capsule remaining blood leaves through efferent arteriole

A – Renal corpuscle B – Proximal tubule C – Distal convoluted tubule D – Juxtaglomerular apparatus 1. Basement membrane (Basal lamina) 2. Bowman's capsule – parietal layer 3. Bowman's capsule – visceral layer 3a. Pedicels (podocytes) 3b. Podocyte 4. Bowman's space (urinary space) 5a. Mesangium – Intraglomerular cell 5b. Mesangium – Extraglomerular cell 6. Granular cells (Juxtaglomerular cells) 7. Macula densa 8. Myocytes (smooth muscle) 9. Afferent arteriole 10. Glomerulus Capillaries 11. Efferent arteriole Renal Corpuscle

A.The endothelial cells of the glomerulus B.Glomerular basement membrane C.Podocytes Renal Corpuscle

Membranous Glomerulonephritis Progressive disease thought to occur as a result of autoimmunity – 85% of cases are idiopathic Disease can also occur secondary to other autoimmune diseases (eg. systemic lupus erythematosus) or through inflammation in response to bacterial / viral infection. Symptoms: Edema Foamy appearance of urine Frequent urination High blood pressure Membranous glomerulonephritis is the most common cause of nephrotic syndrome in Caucasians (20- 35%).

Membranous Glomerulonephritis - Pathology Characterized by subepithelial immune deposits - presence of immunoglobulins, complement, and membrane attack complex (MAC) (C5b-9) Immune complexes serve as a trigger for the complement cascade and formation of the MAC – but what triggers Ab formation ?

Membranous Glomerulonephritis - Pathology Characterized by subepithelial immune deposits - presence of immunoglobulins, complement, and membrane attack complex (MAC) (C5b-9) Immune complexes serve as a trigger for the complement cascade and formation of the MAC – but what triggers Ab formation ? Serum samples from 26 of 37 patients (70%) with idiopathic but not secondary membranous nephropathy specifically identified a 185-kD glycoprotein in nonreduced glomerular extract. Reactive serum specimens recognized recombinant PLA 2 R and bound the 185-kD glomerular protein. PLA 2 R was expressed in podocytes in normal human glomeruli and colocalized with IgG4 in immune deposits in glomeruli of patients with membranous nephropathy. IgG eluted from such deposits in patients with idiopathic membranous nephropathy, but not in those with lupus membranous or IgA nephropathy, recognized PLA 2 R. (N Engl J Med Jul 2;361(1):11-21)

Membrane Attack Complex (MAC)

Membrane Attack Complex What happens ? Lysis of glomerular epithelial cells Stimulates release of proteases and reactive O 2 species that induce further cell damage Capillary walls become more porous, increasing the amount of fluid that can enter Bowman’s capsule Inhibitor of nephrin is released, decreasing the selectivity of filtration through podocytes.

Membranous Glomerulonephritis – Clinical Features Any thoughts on clinical / laboratory features?

Membranous Glomerulonephritis – Clinical Features Any thoughts on clinical / laboratory features? Proteinuria is generally in nephrotic range and can be massive (>10 g/24h) (corresponding hypoproteinemia) Hypoalbuminemia Hypercholesterolemia Microhematuria is common and macrohematuria is unusual No hypocomplementemia (at least in idiopathic forms) and in many cases increased levels of MAC (C5b-C9)

Membranous Glomerulonephritis – Clinical Features Any thoughts on clinical / laboratory features? Proteinuria is generally in nephrotic range and can be massive (>10 g/24h) (corresponding hypoproteinemia) Hypoalbuminemia Hypercholesterolemia Microhematuria is common and macrohematuria is unusual No hypocomplementemia (at least in idiopathic forms) and in many cases increased levels of MAC (C5b-C9) The reason for most of these changes should be obvious – why do patients present with hypercholesterolemia ? triglycerides are normally cleared by the liver and other organs not the kidney mechanism is unknown but enzymes involved in fatty acid metabolism are not as active one route could be that an enzyme inhibitor that is normally cleared by the kidney can accumulate

Membranous Glomerulonephritis – Outcomes Prognosis ~25% of patients have partial or complete remission (with 1/3 of those having recurrence) 50% will lack any proteinuria or impairment of renal function A small percentage will have rapid loss of renal function, possibly leading to death. Varying outcomes with no obvious differences in pathology make treatment options difficult.

Membranous Glomerulonephritis – Outcomes Prognosis ~25% of patients have partial or complete remission (with 1/3 of those having recurrence) 50% will lack any proteinuria or impairment of renal function A small percentage will have rapid loss of renal function, possibly leading to death. Varying outcomes with no obvious differences in pathology make treatment options difficult. Treatment Corticosteroids and other immunosuppresants – limited use with variable data on the effectiveness Side effects of immunosuppresants may be more dangerous than the underlying disease Calcineurin inhibitors (CNIs) induce remission of proteinuria in most nephrotic patient 60% of patients become treatment dependent and are at risk of chronic nephrotoxicity

Membranous Glomerulonephritis – Outcomes Is Rituximab the answer? - Humanized monoclonal antibody designed to target the cellular protein, CD20 - CD20 is found on the surface of all mature B cells – involved in the progression of B cells in to plasma cells, which produce high quantities of antibodies (but actual role is unknown) - Rituixmab causes B cells to undergo programmed cell death, allowing new, less-reactive B cells to develop in the bone marrow. - Destroys memory B cells, those responsible for recognising previous exposure to an antigen.

Membranous Glomerulonephritis – Outcomes Is Rituximab the answer? Design: Thirteen patients with membranous glomerulonephritis, normal renal function, and proven dependence on calcineurin inhibitors, despite previous treatment with other immunosuppressant drugs, received a single trial of four weekly doses of rituximab (375 mg/m 2 ).

Membranous Glomerulonephritis – Outcomes Is Rituximab the answer? Design: Thirteen patients with membranous glomerulonephritis, normal renal function, and proven dependence on calcineurin inhibitors, despite previous treatment with other immunosuppressant drugs, received a single trial of four weekly doses of rituximab (375 mg/m 2 ). Outcome measures: the percentage of patients with CNI withdrawal and no evidence of relapse and the percentage of patients with complete or partial remission 30 mo after CNI withdrawal.

Membranous Glomerulonephritis – Outcomes Is Rituximab the answer? Clin J Am Soc Nephrol Jun;4(6): Epub 2009 May 28 Design: Thirteen patients with membranous glomerulonephritis, normal renal function, and proven dependence on calcineurin inhibitors, despite previous treatment with other immunosuppressant drugs, received a single trial of four weekly doses of rituximab (375 mg/m 2 ). Outcome measures: the percentage of patients with CNI withdrawal and no evidence of relapse and the percentage of patients with complete or partial remission 30 mo after CNI withdrawal. Results: After rituximab, proteinuria decreased significantly (2.5 ± 0,76 basal versus 0.85 ± 0.17 at 6 mo; p =.0003) CNIs and other immunosuppressant drugs could be withdrawn in all patients with no evidence of relapse. After CNI withdrawal, glomerular filtration rate increased significantly (90.3 ± 15 basal to ± 20 at 3 mo with a mean increase of 15.3% [range 0–20]). Three patients suffered a relapse of nephrotic proteinuria 19, 23, and 28 mo after rituximab treatment; all were successfully treated with a second course of rituximab. At 30 mo, all patients were in remission.