The role of apoptosis in the development of renal cortical tubular atrophy associated with healed experimental renal papillary necrosis

Apoptosis of tubulointerstitial chronic inflammatory cells in progressive renal fibrosis after cancer therapies

Progressive renal fibrosis is an unwanted and limiting side effect of cancer treatments, whether they are systemic (for example, chemotherapy), local (for example, radiotherapy), or total body irradiation for allogenic bone marrow transplants. The relative roles of macrophages, myofibroblasts, and lymphocytes and the apoptotic deletion of renal functional or inflammatory cell populations in the pathogenesis of renal fibrosis are yet unclear. In this study, rat models of 2 renal cancer treatments: cis-platinum-(II)-diammine dichloride (cisplatin, 6-mg/kg body weight) and radiation (single dose of 20 Gy) were used. Kidneys were analyzed 4 days to 3 months after treatment. The extent of renal fibrosis was compared with number and localization of chronic inflammatory cell populations, cell death (apoptosis and necrosis), and expression and localization of profibrotic growth factors transforming growth factor-beta1 (TGF-beta1) and tumor necrosis factor-alpha (TNF-alpha). The models provided contrasting rates of fibrogenesis: After cisplatin, development of fibrosis was rapid and extensive (up to 50% fibrosis at 3 months); in comparison, radiation-induced fibrosis was slowly progressive (approximately 10% fibrosis at 3 months). The extent of fibrosis was associated spatially and temporally with increasing numbers of myofibroblasts with TGF-beta1 or macrophages with TNF-alpha. Tubular epithelial apoptosis was highest with high TNF-alpha (P<0.05). A significant inverse correlation existed between extent of tubulointerstitial fibrosis and interstitial cell apoptosis for cisplatin and a similar nonsignificant result for radiation (r(2)=0.8671 for cisplatin, P<0.05; r(2)=0.2935 for radiation, NS). The latter result suggests a role for inflammatory cell apoptosis in minimizing development of renal fibrosis.

A comparison of pathomolecular markers of fibrosis and morphology in kidney from autopsies of African Americans and whites

African Americans have an increased incidence of chronic kidney disease (CKD) due to hypertension and arteriosclerosis and increased death due to coronary artery disease, compared with whites. The pathogenesis of CKD involves the increased presence and activation of myofibroblasts and macrophages, promotion of tubulointerstitial fibrosis, and effects of tubulointerstitial cell mitosis and apoptosis. We hypothesized that increased risk of hypertensive vascular disease may be identified by renal pathomolecular markers that are associated with progressive CKD. Renal sections were available from 50 autopsies of 33 African Americans (55% males) and 17 whites (76% males) undergoing forensic autopsy for unexpected death. Sclerotic glomeruli, severity of cortical fibrosis, and renal arteriolosclerosis, total glomerular number (N (glom)), average glomerular volume (V (glom)), birth weights, and blood pressure were known. Presence and locality of markers for myofibroblasts (alpha-SMA), macrophages (CD68), collagen, pro-fibrotic transforming growth factor-beta1 were scored in renal autopsies, and tubulointerstitial apoptosis was recorded. The results demonstrated a strong positive correlation between age, cortical fibrosis and alpha-SMA (p<0.05), and between CD68 and hypertension and coronary artery disease (p<0.05). The findings confirm the role of myofibroblasts and macrophages in pathogenesis of human CKD. However, the markers showed no significant relationships to V (glom), N (glom), birth weight, or race.

Cell death in toxic nephropathies

Toxic nephropathies cause acute and chronic renal failure, primarily as a result of injury to renal tubular epithelium. There is a well-known capacity in the renal nephron for the synchronous occurrence of both apoptosis and necrosis in toxic nephropathies. This has engendered interest in the differing or complementary roles of these modes of cell death. Once thought to be mutually exclusive in incidence and morphologic and biochemical features, recent evidence in renal and other diseases indicates some blurring in the features of apoptosis and necrosis, particularly in the situations in which they are identified, in their molecular pathways, and in the role of inflammation in the processes. Definition of the heterogenic pathophysiologic response of the nephron should provide information useful for promoting the health of the kidney after injury, particularly in relation to controlling the extent and modalities of cell death via the associated renal-specific molecular features. This article indicates the significance and some problems of defining the types of cell death in toxic nephropathies.

Regular use of analgesics is a risk factor for renal cell carcinoma

Phenacetin-based analgesics have been linked to the development of renal pelvis cancer and renal cell carcinoma (RCC). The relationship between non-phenacetin types of analgesics and kidney cancer is less clear, although laboratory evidence suggests that these drugs possess carcinogenic potential. A population-based case-control study involving 1204 non-Asian RCC patients aged 25-74 and an equal number of sex-, age- and race-matched neighbourhood controls was conducted in Los Angeles, California, to investigate the relationship between sustained use of analgesics and risk of RCC according to major formulation categories. Detailed information on medical and medication histories, and other lifestyle factors was collected through in-person interviews. Regular use of analgesics was a significant risk factor for RCC in both men and women (odds ratio (OR) = 1.6, 95% confidence interval (CI) = 1.4-1.9 for both sexes combined). Risks were elevated across all four major classes of analgesics (aspirin, non-steroidal anti-inflammatory agents other than aspirin, acetaminophen and phenacetin). Within each class of analgesics, there was statistically significant increasing risk with increasing level of exposure. Although there was some minor variability by major class of formulation, in general individuals in the highest exposure categories exhibited approximately 2.5-fold increase in risk relative to non- or irregular users of analgesics. Subjects who took one regular-strength (i.e. 325 mg) aspirin a day or less for cardiovascular disease prevention were not at an increased risk of RCC (OR = 0.9, 95% CI = 0.6-1.4).

Apoptosis in the kidney

Apoptosis is a highly regulated mechanism of cell death. Although apoptosis has a functional role in normal development and tissue homeostasis, aberrant triggering of the process by toxicants may lead to abnormal function or disease. Low level exposures to toxicants that induce apoptosis in kidney may therefore create a critical disturbance in kidney homeostasis, contributing to renal neoplasia or renal disease. In this report, we review the involvement of apoptosis in normal kidney development and in renal disease and discuss some of the toxicants and molecular factors involved in regulation of the process in renal cells.

Renal papillary necrosis--40 years on

Analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) are well recognized as a major class of therapeutic agent that causes renal papillary necrosis (RPN). Over the last decade a broad spectrum of other therapeutic agents and many chemicals have also been reported that have the potential to cause this lesion in animals and man. There is consensus that RPN is the primary lesion that can progress to cortical degeneration; and it is only at this stage that the lesion is easily diagnosed. In the absence of sensitive and selective noninvasive biomarkers of RPN there is still no clear indication of which compound, under what circumstances, has the greatest potential to cause this lesion in man. Attempts to mimic RPN in rodents using analgesics and NSAIDs have not provided robust models of the lesion. Thus, much of the research has concentrated on those compounds that cause an acute or subacute RPN as the basis by which to study the pathogenesis of the lesion. Based on the mechanistic understanding gleaned from these model compounds it has been possible to transpose an understanding of the underlying processes to the analgesics and NSAIDs. The mechanism of RPN is still controversial. There are data that support microvascular changes and local ischemic injury as the underlying cause. Alternatively, several model papillotoxins, some analgesics, and NSAIDs target selectively for the medullary interstitial cells, which is the earliest reported aberration, after which there are a series of degenerative processes affecting other renal cell types. Many papillotoxins have the potential to undergo prostaglandin hydroperoxidase-mediated metabolic activation, specifically in the renal medullary interstitial cells. These reactive intermediates, in the presence of large quantities of polyunsaturated lipid droplets, result in localized and selective injury of the medullary interstitial cells. These highly differentiated cells do not repair, and it is generally accepted that continuing insult to these cells will result in their progressive erosion. The loss of these cells is thought to be central to the degenerative cascade that affects the cortex. There is still a need to understand better the primary mechanism and the secondary consequences of RPN so that the risk of chemical agents in use and novel molecules can be fully assessed.

Normal ultrastructure of the kidney and lower urinary tract

The mammalian urinary tract includes the kidneys, ureters, urinary bladder, and urethra. The renal parenchyma is composed of the glomeruli and a heterogeneous array of tubule segments that are specialized in both function and structure and are arranged in a specific spatial distribution. The ultrastructure of the glomeruli and renal tubule epithelia have been well characterized and the relationship between the cellular structure and the function of the various components of the kidney have been the subject of intense study by many investigators. The lower urinary tract, the ureters, urinary bladder, and urethra, which are histologically similar throughout, are composed of a mucosal layer lined by transitional epithelium, a tunica muscularis, and a tunica serosa or adventitia. The present manuscript reviews the normal ultrastructural morphology of the kidney and the lower urinary tract. The normal ultrastructure is illustrated using transmission electron microscopy of normal rat kidney and urinary bladder preserved by in vivo perfusion with glutaraldehyde fixative and processed in epoxy resin.

Apoptosis in the mammalian kidney: incidence, effectors, and molecular control in normal development and disease states

In the preceding sections we have emphasized the current status of our knowledge concerning the involvement of apoptosis in normal and abnormal renal developmental processes, in control of the adult kidney size and capacity, in the development of renal disease states and in renal oncogenesis. At several points, we noted that studies of apoptosis in the kidney and in renal cells lag behind those in other organ systems. Even with the rudimentary knowledge now available, however, it is apparent that apoptosis is an extremely important process in the kidney. Recent observations lend credence to the view that continued study of this unique cell death process might enable the generation of novel and more effective therapies to treat renal diseases and renal malignancies. We wish to highlight several areas that require particular attention. First, the relationship between blood supply and apoptosis in the kidney requires further investigation. Benign human renal diseases are common in our population; and we now know that most of these diseases are associated with abnormal rates of apoptosis. Although the initiating agents for the various renal diseases vary, there is good reason to believe that much of the apoptosis that occurs in these adult diseases is the end result of reduced renal blood flow initiated by the causative agent. Cytokines or other extrinsic agents that can reduce the apoptotic loss of renal cells under these conditions hold theoretical promise in treating these diseases. Second, there is an urgent need to define the endocrine, paracrine, or autocrine roles of cytokines in normal renal physiology and in the pathogenesis of various renal syndromes. As indicated above, elaboration of fibrous extracellular material by fibroblasts in the tubulointerstitial regions of the kidney appears to be part of the final common pathway leading to end-stage renal disease. It is important to understand how the function of these fibroblasts is controlled. Conversely, apoptosis of glomerular or renal tubular cells also appears to play a role in the development of many of these syndromes. There is already experimental and clinical evidence showing that IGF-1 and hepatocyte growth factor therapies can be useful in renal diseases [57, 58]. It remains to be determined how much of the usefulness of these cytokines is related to their ability to suppress apoptosis as opposed to their ability to promote true growth. Finally, the analysis of apoptotic regulation during renal oncogenesis is critical. Maligant renal cell cancers are difficult to detect in adults before their metastases cause symptoms; and by this late stage renal tumors are almost invariably fatal. The ability of these tumors to regress spontaneously indicates that most apoptotic pathways are retained in these cells, yet their disappointing response to chemotherapy indicates that we have much to learn about how to trigger these pathways. Hopefully a better understanding of the control of these pathways will lead to improved therapy for this devastating group of neoplasms.

Cell apoptosis and proliferation in experimental chronic obstructive uropathy

Cell proliferation and apoptosis in kidneys with chronic obstructive uropathy (COU) have not been adequately studied. Whether these fundamental cellular processes play any role in the pathogenesis and evolution of COU remains undetermined. Sprague-Dawley rats with COU induced by unilateral ureteral ligation were sacrificed at postoperative days 1, 6, 9, 15, 34, 43, 60, 75, and 90, and were compared with control, sham-operated rats sacrificed at days 0, 15, 43, and 90. The kidneys with ureteral ligation, the contralateral kidneys, and the control kidneys were submitted to in situ end-labeling of fragmented DNAs for the detection of apoptotic cells, and to immunostaining with many monoclonal antibodies directed against the nuclear antigens associated with cell proliferation for the detection of proliferating cells. Additional rats with COU were also submitted to BrdU labeling to detect proliferating cells. The tubular, interstitial, and glomerular cells showing either apoptosis or proliferation were separately quantitated and the obtained data were correlated with dry kidney weight, tubular diameter, glomerular surface area and interstitial volume. Apoptotic tubular cells in kidney with COU increased rapidly, reaching 30-fold that of control at day 25, which was followed by an equally rapid decrease to the control level. During the same period, both the dry kidney weight and the mean tubular diameter decreased markedly. These data suggest that apoptosis may play a significant role in tubular atrophy and renal weight loss. The rapid increase in tubular cell apoptosis was immediately preceded by a 37% gain in the dry kidney weight over the control; just before that increase, there was also an approximate 60-fold increase in the proliferation rate of tubular cells detected by immunostaining for proliferating nuclear antigen or by BrdU labeling. The significance of this intriguing temporal relationship of tubular cell apoptosis and proliferation remains to be elucidated, but it may have pathogenetic implications. In contrast to the rise and fall of the frequency of tubular cell apoptosis and proliferation, the frequency of interstitial cell apoptosis and proliferation displayed continuous increase toward the end of the experiment, with a roughly parallel increase in the interstitial damage. Apoptosis and proliferation of glomerular cells in kidneys with COU did not show any significant changes throughout the experiment. In conclusion, the obtained data suggest that tubular cell apoptosis may be pathogenetically related to the tubular atrophy and renal tissue loss in COU, and that proliferation and apoptosis of interstitial cells may play a role in the observed interstitial changes in this model. This study should provide the impetus for further exploration of the mechanisms of cell death and cell proliferation as a novel venue for understanding the pathogenesis of COU.

Characterization of a renal epithelial cell model of apoptosis using okadaic acid and the NRK-52E cell line

Apoptotic cell death plays an important role in the pathogenesis of renal tubular epithelial damage and repair following tubular injury. Presently, the cellular factors involved in regulating apoptotic pathways in the kidney are unknown. To address the possibility that protein phosphorylation may regulate apoptosis in kidney cells, okadaic acid (OKA), a specific inhibitor of protein phosphatases 1A and 2A, was tested for its morphologic and biochemical effects on normal rat kidney epithelial cells (NRK-52E) in culture. As revealed by the DNA-specific stain DAPI, nuclei of cells treated with 1.0 microM okadaic acid contained irregular clumps of dense chromatin. Additional morphologic alterations typical of apoptosis were apparent within 2 hr after treatment with 1.0 microM OKA, including marked cellular rounding, cytoplasmic condensation, and cytoplasmic blebs. Ultrastructurally, 1.0 microM OKA caused cytoplasmic bleb formation, cellular fragmentation, condensation of heterochromatin into clumps, and segregation of nucleoli. At this stage, the cytoplasmic fragments and blebs contained many normal mitochondria. The attached, rounded cells also effectively excluded propidium iodide, demonstrating maintenance of membrane integrity despite pronounced morphologic alterations. A 2-fold increase in intracellular free Ca2+ was apparent 90 min after treatment with 1.0 microM okadaic acid. Transverse alternating field electrophoresis revealed the appearance of large DNA fragments of approximately 300-kbp. The appearance of these 300-kbp fragments correlated temporally with the observed elevation in intracellular calcium and the onset of morphologic alterations. However, preloading cells with EGTA-AM, an intracellular calcium chelator, obliterated the calcium elevation and had no effect on OKA-induced morphology, DNA fragmentation, or cell death. Detectable internucleosomal fragmentation occurred much later than the onset of morphologic changes (24-hr treatment time) and did not correlate with elevations in cellular calcium. These studies support the hypothesis that during apoptosis, chromatin condensation reflects chromatin cleavage at nuclease-sensitive sites between hexameric rosettes. These results also suggest that morphologic and nuclear alterations in the pathway of OKA-induced apoptosis occur independent of observed increases in intracellular calcium.

Effects of hypoxia on morphological and biochemical characteristics of renal epithelial cell and tubule cultures

Apoptotic cell death plays an important role in the pathogenesis of renal atrophy in diseases of the kidney involving chronic mild ischemia. The present study constitutes an in vitro model of these diseases and assesses the modes of cell death involved after hypoxic treatment of renal epithelium. Cultures of MDCK cells or primary cultures of rat renal parenchymal tubules were treated in either a physiological or a hypoxic atmosphere. Cultures were collected before treatment and at 24 h and 48 h, for morphological and biochemical studies. Both apoptosis and necrosis were observed at significantly increased levels by 48 h of hypoxia in the MDCK cell cultures. DNA gel electrophoresis patterns supported these findings. Experiments using tubule cultures demonstrated that, during the 48 h of study, tubular epithelial cells in the center of the control tubule structures died by apoptosis, possibly as a result of mild oxygen and/or nutrient depletion. With added hypoxic treatment, however, the entire tubule structure became necrotic. Results are similar to those found during in vivo studies, thus providing in vitro models that may be developed further to define factors in the pathogenesis of some renal diseases.