Richard J. Glassock

Permselectivity of the Glomerular Capillary Wall: FACILITATED FILTRATION OF CIRCULATING POLYCATIONS

To examine the electrostatic effects of fixed negative charges on the glomerular capillary wall, polydisperse [(3)H]DEAE dextran, a polycationic form of dextran, was infused into 10 Munich-Wistar rats. Fractional clearances of DEAE ranging in radius from 18 to 44A were determined in these rats, together with direct measurements of the forces and flows governing the glomerular filtration rate of water. These results were compared with data previously obtained in Munich-Wistar rats receiving tritiated neutral dextran (D) and polyanionic dextran sulfate (DS). Measured values for the determinants of the glomerular filtration rate of water in rats given DEAE were found to be essentially identical to those in rats given either D or DS. In addition, DEAE was shown to be neither secreted nor reabsorbed. Fractional clearances of polycationic DEAE were increased relative to both D and DS, the increase relative to D being significant for effective molecular radii ranging from 24 to 44A. Fractional DEAE clearances were also measured in a separate group of six Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN). Fractional DEAE clearances in NSN rats were reduced significantly, relative to values measured in normal rats, for effective DEAE radii ranging from 18 to 42A. Moreover, in NSN rats, fixed negative charges on the glomerular capillary wall were greatly reduced, relative to non-NSN rats, as evidenced by a reduction in intensity of colloidal iron staining. Thus, in NSN rats, DEAE clearances were essentially indistinguishable from values obtained with both neutral D and polyanionic DS.

Acute Interstitial Nephritis Due to Methicillin

Fourteen patients are described with a syndrome of methicillin-induced interstitial nephritis. In all patients severe renal dysfunction developed with an average peak serum creatinine of 8 mg/100 ml. An increased total peripheral eosinophil count was found in all patients. All patients had sterile pyuria and each of nine patients studied by Wrights stain of urine sediment had marked eosinophiluria. These findings are suggestive of methicillin-induced interstitial nephritis, although proteinura was a variable finding in our patients. Eight of 14 patients in our study received prednisone therapy for their interstitial nephritis, and the time lapse between maximal and final base line serum creatinine levels was statistically less in the prednisone-treated compared to the nontreated groups. Clinical manifestations of this syndrome are discussed, and the light and electron microscopic and immunofluorescent findings on renal biospy are described.

Left Ventricular Mass in Chronic Kidney Disease and ESRD

Chronic kidney disease (CKD) and ESRD, treated with conventional hemo- or peritoneal dialysis are both associated with a high prevalence of an increase in left ventricular mass (left ventricular hypertrophy [LVH]), intermyocardial cell fibrosis, and capillary loss. Cardiac magnetic resonance imaging is the best way to detect and quantify these abnormalities, but M-Mode and 2-D echocardiography can also be used if one recognizes their pitfalls. The mechanisms underlying these abnormalities in CKD and ESRD are diverse but involve afterload (arterial pressure and compliance), preload (intravascular volume and anemia), and a wide variety of afterload/preload independent factors. The hemodynamic, metabolic, cellular, and molecular mediators of myocardial hypertrophy, fibrosis, apoptosis, and capillary degeneration are increasingly well understood. These abnormalities predispose to sudden cardiac death, most likely by promotion of electrical instability and re-entry arrhythmias and congestive heart failure. Current treatment modalities for CKD and ESRD, including thrice weekly conventional hemodialysis and peritoneal dialysis and metabolic and anemia management regimens, do not adequately prevent or correct these abnormalities. A new paradigm of therapy for CKD and ESRD that places prevention and reversal of LVH and cardiac fibrosis as a high priority is needed. This will require novel approaches to management and controlled interventional trials to provide evidence to fuel the transition from old to new treatment strategies. In the meantime, key management principles designed to ameliorate LVH and its complications should become a routine part of the care of the patients with CKD and ESRD.

An epidemic of chronic kidney disease: fact or fiction?

The publication of the Kidney Disease Outcomes and Quality Initiative (KDOQI) clinical practice guidelines for the evaluation, classification and stratification of chronic kidney disease (CKD) in February of 2002 was a landmark event [1]. This effort has profoundly impacted clinical practice, helped bring some order to a chaotic system of nomenclature and stimulated a resurgence of interest in this longneglected domain of clinical nephrology [2]. The nephrology community is now using a definition of the five stages of CKD, based on the presence of ‘kidney damage’ and/or reduced estimated glomerular filtration rate (eGFR) for 3 months or more [1,3]. However, it is noteworthy that three of the five stages of CKD (stages 3, 4 and 5) were arbitrarily defined and based solely on the absolute threshold of eGFR (standardized to 1.73 m2 body surface area) without any requirement for concomitant evidence of ‘kidney damage’, such as proteinuria or adjustment for age and gender [2]. These levels of eGFR, combined with the similarly arbitrary selection of a time dimension (≥3 months) for their persistence to establish ‘chronicity’, became the ‘gold-standard’ for definition of a ‘disease’. The abbreviated modification of diet in renal disease (MDRD) equation for deriving an estimate of true glomerular filtration rate (GFR) from values of serum creatinine (calibrated to the standard used to derive the formula) quickly became the most widely used method for determination of eGFR, despite its lack of validation in subjects without CKD or across a wide spectrum of ages, body habitus, diet, ethnicity and geographic location [4]. Because of inaccuracies, relative to true GFR, when eGFR is >60 ml/min/1.73 m2 reporting of specific values of eGFR was recommended only when calculated values of <60 ml/min/1.73 m2 were obtained [5]. Despite

Human Immunodeficiency Virus (HIV) Infection and the Kidney

Since the first report on the acquired immunodeficiency syndrome (AIDS) in 1981, organ involvement of AIDS has increased. We discuss the effect of human immunodeficiency virus (HIV) infection, the causative agent of AIDS, on the field of nephrology. Hyponatremia, the commonest fluid and electrolyte abnormality, is caused by various pathophysiologic mechanisms, including adrenal insufficiency. The renal parenchymal complications are diverse, but a new entity, HIV-associated nephropathy, is becoming recognized because of its characteristic clinical and pathologic features, including the fact that it causes irreversible renal failure. HIV infection in patients with end-stage renal failure, both before and after initiation of maintenance dialysis, is a significant problem. The present methods of preventing spread of virus in dialysis units seem successful. Few patients who are infected with HIV or who have AIDS have had renal transplantation, although unsuspected viral infection of cadaveric organs remains a concern.

Posttransplant Recurrence of Primary Glomerulonephritis

All forms of primary GN may recur after kidney transplantation and potentially jeopardize the survival of the graft. IgA nephritis (IgAN) may recur in approximately one third of patients, more frequently in younger patients and in those with a rapid progression of the original disease. However, with the exception of few patients with rapid progression, there is no evidence that recurrence of IgAN has a deleterious effect on graft survival at least up to 10 years. Recurrence of focal segmental glomerulosclerosis (FSGS) is often associated with nephrotic proteinuria and is more frequent in children, in patients with rapid progression of the original disease, and in those who lost a previous transplant from recurrence. The natural course of recurrent FSGS is usually unfavorable. Early and intensive plasmapheresis may obtain complete or partial response in several patients. Good results have also been reported with rituximab. Idiopathic membranous nephropathy (IMN) may recur in 30% to 40% of patients. The graft survival in patients with IMN is not different than that of patients with other renal diseases. Good results with rituximab have been reported. Membranoproliferative GN (MPGN) may recur in 27% to 65% of patients. The recurrence is more frequent and the prognosis is more severe in type II MPGN. Although recurrent GN is relatively frequent and may worsen the outcome of renal allografts in some patients, its effect is diluted by several other risk-factors that may have a greater effect than recurrent GN on the long-term graft survival.

The implications of anatomical and functional changes of the aging kidney: with an emphasis on the glomeruli

Aging is both a natural and inevitable biological process. With advancing age, the kidneys undergo anatomical and physiological changes that are not only the consequences of normal organ senescence but also of specific diseases (such as atherosclerosis or diabetes) that occur with greater frequency in older individuals. Disentangling these two processes, one pathologic and the other physiologic, is difficult. In this review we concentrate on the glomerular structural and functional alterations that accompany natural aging. We also analyze how these changes affect the identification of individuals of advancing age as having chronic kidney disease (CKD) and how these changes can influence prognosis for adverse outcomes, including all-cause mortality, end-stage renal disease, cardiovascular events and mortality, and acute kidney injury. This review describes important shortcomings and deficiencies with our current approach and understanding of CKD in the older and elderly adult.

Diagnosis and natural course of membranous nephropathy

Membranous nephropathy is a relatively common glomerular disease found to underlie both nonnephrotic and nephrotic proteinuria. In adults, about 75% of cases are primary (idiopathic) and 25% are secondary to a wide variety of causes, including neoplasia, infections, autoimmunity, and drugs. Presenting features are not distinctive enough to permit a diagnosis without a renal biopsy examination. Serologic studies are normal in the idiopathic disorder. The morphologic features are characteristic and include gradual thickening of the capillary wall caused by the in situ deposition of immune complexes accompanied by new basement membrane synthesis. The natural history of the untreated disorder is variable. Spontaneous remissions (complete and partial) of proteinuria, usually accompanied by stable renal function, eventually occur in 40% to 50% of patients and the remainder slowly progress to end-stage renal disease (ESRD) or die of complications or from unrelated disease after 5 to 15 years. Factors associated with a progressive course include older age at onset, male gender, persisting hypertension, hyperlipidemia and/or hypoalbuminemia, reduced renal function at discovery, persisting nephrotic range glomerular proteinuria, concomitant tubular proteinuria, and advanced glomerular damage with chronic tubulointerstitial fibrosis.

The pathogenesis of idiopathic membranous nephropathy: a 50-year odyssey.

Ever since its first delineation as a distinct clinicopathologic entity in 1957, idiopathic membranous nephropathy (MN) has been the subject of intense laboratory and clinical investigation. The availability of laboratory models (particularly active and passive Heymann nephritis) of this disorder has been a boon to investigators. Concepts regarding the fundamental mechanisms of immune deposit formation, a sine qua non of idiopathic MN, have evolved and now are firmly established. Circulating autoantibodies (immunoglobulin G4 and immunoglobulin G1 subclasses) interacting with antigens native to or planted in the glomerular capillary wall at the podocyte cell membrane-basement membrane interface generally are regarded as the fundamental pathobiological mechanism. Thus, MN now is regarded as a podocytopathy. The immune deposits evoke an alteration in glomerular capillary permeability, probably through complement-mediated injury of the podocyte and its slit-pore membrane; however, cell-mediated immunity also may have a role, and the physical presence of immune deposits and basement membrane alterations also may participate. The exact nature of the autoantibody systems operative in human idiopathic MN is being uncovered rapidly. It is hoped that this 50-year odyssey will culminate in real progress in the diagnosis, prognosis, and therapy for the human disease.

Determinants of glomerular filtration in experimental glomerulonephritis in the rat.

Pressures and flows were measured in surface glomerular capillaries, efferent arterioles, and proximal tubules of 22 Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN). Linear deposits of rabbit and rat IgG and C3 component of complement were demonstrated in glomerular capillary walls by immunofluorescence microscopy. Light microscopy revealed diffuse proliferative glomerulonephritis, and proteinuria was present. Although whole kidney and single nephron glomerular filtration rate (GFR) in NSN (0.8 plus or minus 0.04 SE2 ml/min and 2 plus or minus 2 nl/min, respectively) remained unchanged from values in 16 weight-matched NORMAL HYDROPENIC control rats (0.8 plus or minus 0.08 and 28 plus or minus 2), important alterations in glomerular dynamics were noted. Mean transcapillary hydraulic pressure difference (deltaP) averaged 41 plus or minus 1 mm Hg in NSN versus 32 plus or minus 1 in controls (P LESS THAN 0.005). Oncotic pressures at the afferent (piA) end of the glomerular capillary were similar in both groups ( 16 mm /g) but increased much less by the efferent end (piE) in NSN (to 29 plus or minus 1 mm Hg) than in controls (33 plus or minus 1, P less than 0.025). Hence, equality between deltaP and piE, denoting filtration pressure equilibrium, obtained in control but not in NSN rats. While glomerular plasma flow rate was slightly higher in NSN (88 plus or minus 8 nl/min) than in controls (76 plus or minus 6, P greater than 0.2), the failure to achieve filtration equilibrium in NSN rats was primarily the consequence of a marked fall in the glomerular capillary ultrafiltration coefficient, Kf, to a mean value of 0.03 nl/(s times mm Hg), considerably lower than that found recently for the normal rat, 0.08 nl/(s times mm Hg). Thus, despite extensive glomerular injury, evidenced morphologically and by the low Kf, GFR remained normal. This maintenance of GFR resulted primarily from increases in deltaP, which tended to increase the net driving force for filtration, and thereby compensate for the reduction in Kf.