IgA nephropathy: markers of progression and clues to pathogenesis.

The unpredictable progression of IgA nephropathy hinders its treatment. The correlation of renal dysfunction with the immunophenotype of leukocytic infiltrates revealed interstitial CD20(+) cells and tubular NKG7(+)(GMP-17(+))/CD8(+) intraepithelial cells as predictive markers of progression in early-phase IgA nephropathy. This suggests that adaptive and innate immune responses mediate progression.

Glycogen synthase kinase 3beta: a novel marker and modulator of inflammatory injury in chronic renal allograft disease.

One key cell-signaling event central to inflammation in kidney diseases, including chronic renal allograft dysfunction or disease (CRAD), is the activation of NF-kappaB, which controls transcription of numerous proinflammatory mediators. Glycogen synthase kinase (GSK) 3beta is an indispensable element of NF-kappaB activation, however, the exact role of GSK3beta in the pathogenesis of inflammatory kidney diseases like CRAD is uncertain and was examined. Immunohistochemistry staining of GSK3beta was weak in normal kidneys, but was markedly induced in inflamed allograft kidneys, with prominent cytoplasmic staining of tubular cells in areas of inflammation. Net GSK3beta activity is regulated by inhibitory phosphorylation of its serine 9 residue, and this occurred in CRAD. Thus, the magnitude of GSK3beta inactivation was inversely correlated with the degree of injury as assessed by Banff criteria. In vitro in cultured human tubular epithelial cells, GSK3beta overexpression augmented, while GSK3beta silencing diminished proinflammatory cellular responses to TNF-alpha stimulation, including NF-kappaB activation and expression of chemokines MCP-1 and RANTES. These inflammatory responses were obliterated by GSK3beta inhibitors. Collectively, GSK3beta plays an important role in mediating proinflammatory NF-kappaB activation and renal inflammation. Suppression of GSK3beta activity might represent a novel therapeutic strategy to treat CRAD.

Glomerular injury in uninephrectomized spontaneously hypertensive rats. A consequence of glomerular capillary hypertension.

Micropuncture and/or morphologic studies were performed in intact Wistar-Kyoto rats (WKY) (group 0), intact spontaneously hypertensive rats (SHR) (groups 1 and 5), uninephrectomized (UNX) WKY (groups 2 and 6), and UNX SHR (groups 3 and 4, 7 and 8). UNX was performed when rats were 5 wk of age. Groups 0-4 were observed for 34 wk after which whole kidney clearance and morphologic studies were performed. Groups 5-8 underwent micropuncture study at 10 wk of age. Groups 4 and 8 were fed a diet containing 6% protein. All other rats ingested standard laboratory diet. 5 wk after UNX, normotensive group 6 had higher single nephron glomerular filtration rate (SNGFR) and initial glomerular plasma flow rate (QA) than intact, hypertensive group 5. Glomerular transcapillary hydraulic pressure difference (delta P) was similar in these two groups. Hypertensive group 7 exhibited less elevation in SNGFR and QA than group 6, but delta P was significantly increased. The presence of glomerular capillary hypertension in UNX SHR at 10 wk was associated with the development of significant proteinuria and an increased incidence of mesangial expansion and glomerular sclerosis at 7 mo (group 3) as compared with groups 0, 1, and 2. Protein restriction prevented the development of increased delta P in UNX SHR (group 8) and also conferred long-term protection from increased urinary protein excretion and glomerular injury (group 4). These studies suggest that glomerular capillary hypertension predisposes to glomerular injury in this model of hypertension with reduced renal mass.

Hemodynamic basis for glomerular injury in rats with desoxycorticosterone-salt hypertension.

Micropuncture and/or morphologic studies were performed in seven groups of uninephrectomized (UNX) adult male Munich-Wistar rats. Control groups 1, 3, and 6 received standard (24% protein) chow and tap water. Groups 2, 4, and 5 received weekly injections of desoxycorticosterone pivilate (DOC) and 1% saline for drinking, groups 2 and 4 were fed standard chow, and Group 5 a diet containing 6% protein. Group 7 received DOC, salt, and standard chow for 3 wk followed by withdrawal of DOC and salt for an additional 6 wk. 10-14 d after UNX, groups 1 and 2 exhibited similar single nephron glomerular filtration rates (SNGFR) and initial glomerular plasma flow rates (QA). Group 2 had higher mean arterial pressure (AP) and glomerular capillary hydraulic pressure (PGC) than group 1. 3-4 wk after UNX, group 4 exhibited further elevations in AP and PGC as compared with groups 2 and 3. SNGFR and QA were similar in groups 3 and 4, but these average values were greater than typical for normal rats. Group 4 also demonstrated increased urinary protein excretion. Morphologic evaluation of glomeruli in groups 2 and 4 revealed mesangial expansion and focal intraglomerular hemorrhage whereas glomeruli of groups 1 and 3 were essentially normal. Values for AP and PGC in group 5 were not different than group 3 but significantly lower than group 4. QA and SNGFR were lower in group 5 (low protein) than in groups 3 and 4. Furthermore, proteinuria and glomerular structural lesions were abolished in group 5. Morphologic studies performed in groups 6 and 7 showed that early DOC-SALT lesions progress to focal glomerular sclerosis. These studies suggest that continued elevations in glomerular capillary flows and pressures predispose to glomerular injury in this model of systemic arterial hypertension.

Excess risk of renal allograft loss and early mortality among elderly recipients is associated with poor exercise capacity.

BACKGROUND: Successful renal transplantation in the elderly offers substantial benefits in quality and life expectancy. However, in this group of patients there is an early increased risk of death compared with those remaining on dialysis. MATERIALS AND METHODS: Graft and patient outcomes in 64 older transplant recipients were compared with 338 patients aged 18 - 59 years. We identified potential risk factors that may predict clinical outcomes in older transplant recipients. A log-rank test and Cox regression analyses were performed to assess the impact of various patient characteristics on graft and patient survival. RESULTS: Among older patients, graft survival was 76.6% and 67% at 1 and 3 years, respectively. When graft survival was censored for death with functioning graft, the 1- and 3-year graft survival was 83% and 82%, respectively. Patient survival was 78% and 71% at 1 and 3 years, respectively. These survival rates were significantly lower than those of younger recipients. Pretransplant inactivity, delayed graft function, smoking history and longer waiting time predicted poor graft and patient survival. A history of chronic obstructive pulmonary disease, and peripheral vascular disease also predicted a higher mortality among older recipients. CONCLUSION: Older kidney transplant recipients are at high risk for allograft failure and early death. Poor functional capacity predicts a poor outcome for older patients undergoing renal transplantation. Therefore, careful patient selection is paramount, and every effort should be made to initiate timely interventions aimed at increasing physical activity in those with low fitness level.

Cryptosporidium infection in renal transplant patients.

Cryptosporidium parvum, an intracellular protozoan parasite, is a significant cause of gastrointestinal disease worldwide. Transmission can occur from an infected person, animal or fecally contaminated environment. The clinical manifestations of cryptosporidiosis are dependent on the immunologic state of the host. Infection among immunocompetent hosts results in diarrhea that is typically self-limited. In immunocompromised hosts, however, the infection may be protracted and life-threatening with no reliable antimicrobial therapy. In transplant patients, a course of antimicrobial therapy along with concurrent reduction in immunosuppression optimize immunologic status and may potentially lead to resolution of the infection.

Current strategies for management of hypertensive renal disease.

The incidence of hypertensive end-stage renal disease continues to increase annually. To reduce this incidence, it is necessary to control systolic and diastolic hypertension. Reversible causes should always be sought in any hypertensive patient who develops renal insufficiency. Blood pressure should be reduced to 130/85 mm Hg, and in African Americans with hypertensive renal failure, reducing the blood pressure to 120/75 mm Hg may be beneficial. Any antihypertensive treatment regimen that effectively lowers blood pressure will help slow progressive renal failure. Whenever possible, an angiotensin-converting enzyme inhibitor should be part of the treatment, since these drugs have been shown to be renoprotective beyond their antihypertensive effect in certain renal disease categories.

Effects of amlodipine on glomerular filtration, growth, and injury in experimental hypertension.

The objective of this study was to determine whether the calcium antagonist amlodipine could slow the progression of chronic renal disease. We examined the effects of amlodipine on kidney structure and function in two experimental models of hypertension. In the first study, adult, male Munich Wistar rats underwent uninephrectomy and were given weekly injections of desoxycorticosterone and 1% saline for drinking. Rats ingested normal chow or chow containing amlodipine for 8 weeks. The drug reduced systemic blood pressure, but glomerular filtration rate, kidney weight, proteinuria, and morphological evidence of glomerular injury were not affected. In the second study, male spontaneously hypertensive rats underwent uninephrectomy at 5 weeks of age and were followed for 6 months, during which they received no therapy or amlodipine. The drug dose was determined in preliminary studies to be the highest dose not associated with marked growth retardation. Again, although systemic blood pressure was significantly reduced by amlodipine, proteinuria and the prevalence of glomerulosclerosis were similar in amlodipine-treated and control spontaneously hypertensive rats. Micropuncture studies revealed that glomerular pressure remained elevated in amlodipine-treated spontaneously hypertensive rats. Kidney weight and glomerular volume were also similar in amlodipine-treated and control rats. Amlodipine also failed to inhibit platelet aggregation. Therefore, antihypertensive therapy with amlodipine fails to reduce glomerular pressure in spontaneously hypertensive rats as well as glomerular size and injury in spontaneously hypertension rats and desoxycorticosterone-salt hypertension. Although other dihydropyridine calcium antagonists have been found to reduce experimental glomerular injury, these data suggest that amlodipine may not prevent hypertensive nephrosclerosis.

Pathogenesis of systemic hypertension and glomerular injury in the spontaneously hypertensive rat.

Weanling and young spontaneously hypertensive rats (SHRs) demonstrate higher plasma renin activity and plasma aldosterone concentration than age-matched normotensive Wistar-Kyoto (WKY) control rats. In addition, this age group exhibits a salt-retaining tendency not seen in WKYs. Nevertheless, when they reach adulthood, these differences between SHRs and WKYs are all but abolished, yet hypertension persists in SHRs. The possible mechanisms leading to these changes in SHRs and to the differences seen with advancing age are discussed. Results of micropuncture studies that help elucidate the glomerular hemodynamic adaptations to elevation in systemic blood pressure in young SHRs are also presented. Evidence is advanced suggesting that increased intraglomerular pressure is responsible for the histologic lesions characteristic of untreated severe hypertension. The salutary effects of treatment with vasodilator drugs that reduce intraglomerular pressure are emphasized.

Antihypertensive drugs, dietary salt, and renal protection: how low should you go and with which therapy?

Although it is clear that hypertension accelerates the rate of progression of most forms of chronic renal disease, many unanswered questions remain concerning how to optimally preserve kidney function in patients with hypertension and renal insufficiency. The mechanisms by which hypertension accelerates progression of renal disease have been extensively studied in experimental models. Glomerular capillary hypertension, consequent to an increase in systemic blood pressure combined with a reduction in preglomerular resistance and/or an increase in postglomerular resistance, results in increased hydraulic stress to the glomerular capillary wall. This and other mechanisms result in the release of growth-promoting cytokines and soluble mediators of fibrosis that stimulate cellular proliferation and matrix accumulation, ultimately leading to glomerular sclerosis and interstitial fibrosis. Almost without exception, studies in animals demonstrate that blood pressure reduction reduces the rate of progression of experimental renal disease. Angiotensin-converting enzyme inhibitors and, possibly, calcium antagonists may have a therapeutic advantage compared with other antihypertensive drugs in preventing kidney damage. This has been linked to both blood pressure-dependent and -independent actions. However, most experimental studies have failed to reduce blood pressure to a level sufficient to establish the clinical relevance of potential blood pressure-independent effects. Experimental studies comparing various types of antihypertensive drugs in which a mean arterial pressure (MAP) of approximately 92 mm Hg is achieved are necessary to determine whether clinically important differences in the effects of these drugs on the rate of progression of renal disease exist. Clinical experience with high blood pressure and kidney disease in humans suggests that the risk of developing hypertension-associated renal disease is a continuous variable across the entire range of systolic and diastolic blood pressures. Logically, optimal protection of kidney function may therefore be a continuous function of declining systemic blood pressure. Consistent with this view, recent clinical trials suggest that reducing MAP to 92 mm Hg, corresponding to a blood pressure reading of 125/75 mm Hg, provides more optimal stabilization of renal function in patients with nondiabetic proteinuric kidney disease (>1 g/d) compared with more conventional therapy with a blood pressure goal of 140/90 mm Hg (MAP 107 mm Hg). Clinical trials in patients with diabetes mellitus and renal insufficiency also demonstrate the benefits of reducing blood pressure to approximately 95 mm Hg MAP. Dietary salt consumption may be another important variable affecting the rate of progression of renal disease due to both direct, salt-dependent effects on renal growth and the action of decreased salt intake to augment the antihypertensive and antiproteinuric properties of many drugs. The precise role of alterations in dietary salt consumption on progression of renal disease directly as well as on the effectiveness of various antihypertensive drugs has yet to be examined in clinical trials.

Residual renal function and mortality risk in hemodialysis patients.

Residual renal function, defined as the urinary clearance of urea and creatinine, is minimal in many patients treated with hemodialysis (HD) and tends to be ignored in most outcome studies involving HD patients. Recent studies showed that residual renal function, even at a low level, is influential in preventing mortality in the minority of patients with end-stage renal disease treated with peritoneal dialysis. This issue generally has not been examined in patients treated with HD. This prospective observational study of all 114 patients at a single community-based freestanding HD center is designed to examine the impact of residual renal function (defined as renal urea clearance and renal creatinine clearance derived from 24-hour urinary volumes) on mortality over a 2-year period. During that period, 50 deaths occurred in 114 patients. The presence of residual renal function was protective against mortality (odds ratio for death, 0.44; 95% confidence interval, 0.24 to 0.81; P = 0.008), even after adjustment for duration of dialysis treatment, age, smoking, presence of diabetes, presence of cardiovascular disease, serum albumin level, and urea reduction rate. In conclusion, the presence of residual renal function, even at a low level, is associated with a lower mortality risk in HD patients.

Impact of antihypertensive therapy on progressive kidney damage.

Our ability to measure precisely the pressures and flows within the glomerular microcirculation has enabled us to begin to unravel the complex relationship between systemic hypertension and kidney disease. Although a number of factors have been implicated in the development of glomerular sclerosis, one consistent finding has been that glomerular injury occurs when elevated pressures are transmitted to the glomerular capillaries. Intrarenal hypertension, in conjunction with renal hypertrophy, and, possibly, disturbances in lipid metabolism and blood coagulation constitute secondary processes through which those nephrons not severely injured by the primary renal disease are eventually destroyed. Ultimately, all renal function is lost. Clinically, increased glomerular pressure is likely to contribute to glomerular injury in those patients in whom hypertension and renal insufficiency coexist. In patients with diabetes, as yet unidentified factors cause preglomerular resistance to fall so that glomerular hypertension develops even in the absence of elevation in systemic blood pressure. Although no therapy has been proven to slow the rate of progression to end stage renal failure in humans, a number of promising interventions have been identified. These include dietary protein or salt restriction, and medication, with either converting enzyme inhibitors or calcium channel blockers.

Renal vascular effects of calcium channel blockers in hypertension.

Recent evidence suggests that calcium channel blockers have specific effects on renal hemodynamics in patients with hypertension and may also slow the progression of chronic renal failure. When these agents are studied in vitro, their predominant effect is to reverse afferent arteriolar vasoconstriction induced by catecholamines or angiotensin II. Because efferent resistance may remain high, glomerular filtration rate rises while renal blood flow remains low. The effects in vivo are less consistent. In human hypertension, calcium channel blockers lower renal resistance and may raise both renal blood flow and glomerular filtration rate. In experimental models of chronic renal disease, calcium channel blockers slow the progression of renal damage; however, variable effects on renal hemodynamics have been found. Other factors implicated in the progression of renal damage, including compensatory renal hypertrophy, platelet aggregation, and calcium deposition, may also be favorably influenced by these agents. Recent studies suggest that calcium channel blockers may have similar protective effects in patients with hypertension and chronic renal disease.

Calcium carbonate exacerbates glomerular capillary hypertension and injury in rats with desoxycorticosterone-salt hypertension.

To examine the effects of dietary calcium supplementation on systemic and renal hemodynamics and glomerular injury in experimental hypertension, rats with desoxycorticosterone-salt hypertension were fed either standard chow, containing 1% calcium by weight, or chow supplemented with calcium carbonate to achieve a calcium content of 2% by weight. Ingestion of calcium carbonate failed to reduce systemic blood pressure, but was associated with increased proteinuria and morphologic evidence of glomerular injury. Micropuncture studies revealed that afferent arteriolar resistance was reduced and glomerular capillary pressure further increased in the high calcium group. Thus, calcium carbonate, in moderate amounts, not only failed to ameliorate systemic hypertension but, paradoxically, worsened intrarenal hypertension and injury in rats with mineralocorticoid-induced hypertension.

Does essential hypertension cause end-stage renal disease?

The number of patients developing end-stage renal disease (ESRD) as a consequence of hypertension is increasing and accounts for 25% of new cases of ESRD in the United States. However, the diagnosis of hypertensive ESRD is one of exclusion and no pathologic data corroborate this classification. Undoubtedly, these patients suffer from a variety of diseases, including accelerated hypertension and atherosclerotic disease of the large arteries. Also included are patients with an undiagnosed primary renal disease. The prevalence of these conditions in the hypertensive population is unknown. It is also proposed that mild to moderate hypertension can lead to ESRD. In support of this view, early investigators noted that nephrosclerosis was correlated with hypertension and/or left ventricular hypertrophy. More recently, in the Hypertension Detection and Follow-up Program, renal function was found to decline in some patients despite treatment. Data from the Baltimore Longitudinal Study of Aging indicate that the rate at which creatinine clearance declines with aging is correlated with blood pressure. A recent retrospective study reported that serum creatinine increased significantly in approximately 15% of treated hypertensive patients. However, in none of these studies was the presence of intrinsic renal disease definitively excluded. Furthermore, although an increase in serum creatinine or decline in clearance has been reported, progression to end-stage renal disease has not been documented. Therefore, additional studies are necessary to determine the frequency with which essential hypertension leads to end-stage renal disease.

Impact of antihypertensive therapy on progression of experimental renal disease.

Hypertension is common in patients with renal disease and, when uncontrolled, accelerates the rate of progression to end stage renal failure. There is considerable evidence that antihypertensive therapy can slow the rate of decline in kidney function in these patients. However, controversy exists regarding the mechanisms by which antihypertensive agents prevent kidney damage as well as the relative utility of different classes of drugs. This paper will focus on a series of studies, including several conducted in our laboratory, in which the impact of antihypertensive agents on kidney structure and function have been examined in experimental models of progressive kidney failure. Taken together, these studies suggest that most drugs that reduce systemic blood pressure will also lessen kidney damage, albeit to varying degrees and by different mechanisms.

Antihypertensive agents that limit ventricular hypertrophy inhibit cardiac expression of insulin-like growth factor-I.

BACKGROUND: Left ventricular hypertrophy (LVH) is a generalized adaptation to altered myocardial load. Hypertension induces significant increases in ventricular IGF-I gene expression that occur coordinately with development of LVH. To test whether IGF-I promotes initiation of LVH, we examined ventricular IGF-I mRNA content in spontaneously hypertensive rats (SHRs) treated with antihypertensive drugs that limit or permit LVH. METHODS: Prehypertensive SHRs were left untreated or treated with enalapril, nifedipine, or hydralazine. Systolic blood pressure (SBP), hypertrophy index (ventricular weight/body weight), and ventricular IGF-I mRNA levels were examined 2, 4, and 6 weeks after beginning therapy in the experimental groups. RESULTS: Systolic blood pressure reached hypertensive levels after 2 weeks in untreated animals, and was controlled in the treated animals. The hypertrophy index in untreated animals was significantly elevated at 4 weeks. By 6 weeks, the hypertrophy indices of both the enalapril- and nifedipine-treated groups were significantly lower than that of the untreated group. In contrast, the hypertrophy index of the hydralazine-treated animals remained comparable to that of the untreated animals. By 4 weeks, IGF-I mRNA levels in the enalapril- and nifedipine-treated groups were significantly lower than those in the untreated and hydralazine-treated groups. CONCLUSIONS: We conclude that: (1) antihypertensive drugs that reduce LVH blunt ventricular IGF-I mRNA content; and (2) the hemodynamic effects of antihypertensives may be dissociated from their ability to promote or limit a hypertrophic response. The clear association of LVH with ventricular IGF-I mRNA content suggests that IGF-I is an important determinant of ventricular growth. Our data also suggest that angiotensin-converting enzyme inhibitors and calcium channel blockers may reduce LVH by inhibiting cardiac IGF-I gene expression.

Increase urinary hepatocyte growth factor excretion in human acute renal failure.

Studies in animals suggest that hepatocyte growth factor (HGF) is an important mediator of kidney development, compensatory growth and tubule repair following acute injury, however, evidence for HGF action in human renal disease is scant. To determine whether increased renal production of HGF occurs in man, urine HGF excretion rate was measured in normals and in patients with a variety of acute and chronic renal diseases. Urine samples were collected from 9 healthy individuals, 25 individuals with acute tubular necrosis (ATN), 20 individuals with chronic glomerular disease, 9 patients with polycystic kidney disease and 10 individuals with severe chronic renal failure not yet receiving renal replacement therapy. Samples were initially frozen and then HGF content measured by ELISA and factored for creatinine concentration measured by autoanalyzer. Detectable but low levels of HGF were found in the urine of normals and in patients with chronic glomerular or polycystic disease. Levels were also not increased in patients with advanced, chronic renal insufficiency. In contrast, a marked increase in urine HGF was observed in patients with acute renal failure. In addition, HGF excretion tended to correlate with disease severity as higher levels were observed in patients with oliguric ATN. Urine HGF levels declined to control values in patients recovering from ATN, generally within one week. These findings are consistent with a role for HGF in promoting tubule cell proliferation, differentiation and recovery from acute tubular injury in man.