Role of amount and nature of carbohydrates in the course of experimental renal failure

The effect of energy restriction on development and progression of chronic kidney disease: review of the current evidence

Energy restriction (ER) has anti-ageing effects and probably protects from a range of chronic diseases including cancer, diabetes and chronic kidney disease (CKD). Specifically, ER has a positive impact on experimental kidney ageing, CKD (diabetic nephropathy, polycystic kidney disease) and acute kidney injury (nephrotoxic, ischaemia-reperfusion injury) through such mechanisms as increased autophagy, mitochondrial biogenesis and DNA repair, and decreased inflammation and oxidative stress. Key molecules contributing to ER-mediated kidney protection include adenosine monophosphate-activated protein kinase, sirtuin-1 and PPAR-γ coactivator 1α. However, CKD is a complex condition, and ER may potentially worsen CKD complications such as protein-energy wasting, bone-mineral disorders and impaired wound healing. ER mimetics are drugs, such as metformin and Na-glucose co-transporter-2 which mimic the action of ER. This review aims to provide comprehensive data regarding the effect of ER on CKD progression and outcomes.

Dietary restriction regimens for fighting kidney disease: Insights from rodent studies

This review critically discusses the research findings on the effects of various dietary restriction regimens in rodent models of kidney disease. Long-term caloric restriction executed at both early and progressive stages of kidney disease was found to exert beneficial effects in rodents. Moreover, some studies have also demonstrated the efficacy of short-term caloric restriction in treating the kidney disease of variable aetiologies possibly by improving mitochondrial dysfunction, autophagy process and suppression of inflammation. However, the mechanisms underlying these short-term caloric restriction mediated protective effects in rodent models of kidney disease are not completely understood. Importantly, few available evidences have also suggested that carbohydrate restriction can exert beneficial effects in aging and experimentally induced renal injury models, but the mechanisms are not explored yet. Interestingly, the benefits of low protein diet in kidney disease models are extensively reported in literature. However, in most of these studies implementation of the low protein dietary regimen was found to associated with increased high carbohydrate and caloric intake (non-isocaloric). Thus, testing the effects of low protein diet under isocaloric conditions might further help to particularly understand the role of dietary protein content in pathology of kidney disease. Moreover, the direct evidences comparing the efficacy of various dietary restriction regimens in rodent models of kidney diseases are also scarce at present.

Invited Review: A Contemporary Overview of Chronic Progressive Nephropathy in the Laboratory Rat, and Its Significance for Human Risk Assessment

CPN (chronic progressive nephropathy) is a spontaneous age-related disease that occurs in high incidence in the strains of rat commonly used in preclinical toxicology studies, exhibiting a male predisposition. Although increasing in incidence and severity with age, evidence indicates that CPN should be regarded as a specific disease entity and not just a manifestation of the aging process. A number of factors, mainly dietary manipulations, have been shown to modify the expression of CPN. Amongst these, restriction of caloric intake is the most effective for inhibiting the disease process. The precise etiology of CPN and the mechanism(s) underlying its pathogenesis remain unknown, but the long-standing assumption that glomerular dysfunction is the primary basis is challenged in the light of contemporary developments in understanding filtration and postglomerular cellular processing of albumin. CPN is not only a degenerative disease, but also has regenerative aspects with a high cell proliferative rate in affected tubules. Accordingly, evidence is emerging that advanced, particularly end-stage CPN, is a risk factor for a marginal increase in the background incidence of renal tubule tumors. Many chemicals are known to exacerbate the severity of CPN to an advanced stage, and this interaction between chemical and CPN can result in a small increase in the incidence of renal adenomas in 2-year carcinogenicity bioassays. Review of the pathological entities associated with chronic renal failure in man emphasizes that this rodent condition has no strict human counterpart. Because CPN is a rodent-specific entity, the finding of a small, statistically significant increase in renal tubule tumors, linked to exacerbation of CPN by a test chemical in a preclinical study for carcinogenicity, can be regarded as having no relevance for extrapolation in human risk assessment.

Aging in the glomerulus

Kidney function declines with age in the majority of the population. Although very few older people progress to end stage, the consequences of doing so are burdensome for the patient and very expensive for the society. Although some of the observed decline is likely due to changes in the vasculature, much is associated with the development of age-associated glomerulosclerosis. This article will review the well-established structural and functional changes in the glomerulus with age. The role of calorie restriction in modifying age-related pathology will be discussed. The importance of the podocyte as a critical cell in the aging process is considered using animal models and human biopsy material. Newer data on changes in gene expression driven by nuclear factor kappa beta (NFkB) and possible changes in biology in the glomerulus are discussed. The relationship between pathways involved in aging and the decline in kidney function is reviewed. There is speculation on the significance of these changes in relation to normal and pathological aging.

NFkappaB promotes inflammation, coagulation, and fibrosis in the aging glomerulus

The peak prevalence of ESRD from glomerulosclerosis occurs at 70 to 79 years. To understand why old glomeruli are prone to failure, we analyzed the Fischer 344 rat model of aging under ad libitum-fed (rapid aging) and calorie-restricted (slowed aging) conditions. All glomerular cells contained genes whose expression changed "linearly" during adult life from 2 to 24 months: mesangial cells (e.g., MMP9), endothelial cells (e.g., ICAM and VCAM), parietal epithelial cells (e.g., ceruloplasmin), and podocytes (e.g., nephrin and prepronociceptin). Patterns of aging glomerular gene expression closely resembled atherosclerosis, including activation of endothelial cells, epithelial cells, and macrophages, as well as proinflammatory pathways related to cell adhesion, chemotaxis, blood coagulation, oxidoreductases, matrix metalloproteinases, and TGF-beta activation. We used a nonbiased data-mining approach to identify NFkappaB as the likely transcriptional regulator of these events. We confirmed NFkappaB activation by two independent methods: translocation of NFkappaB p50 to glomerular nuclei and ChIP assays demonstrating NFkappaB p50 binding to the kappaB motif of target genes in old versus young glomeruli. These data suggest that old glomeruli exhibit NFkappaB-associated up-regulation of a proinflammatory, procoagulable, and profibrotic phenotype compared with young glomeruli; these distinctions could explain their enhanced susceptibility to failure. Furthermore, these results provide a potential mechanistic explanation for the close relationship between ESRD and atherosclerotic organ failure as two parallel arms of age-associated NFkappaB-driven processes.

Podocytes and glomerular function with aging

Kidney function declines with age in association with the development of age-associated glomerulosclerosis. The well-established structural and functional changes with age are reviewed briefly. The modification of aging pathology by calorie restriction is discussed. The role of the podocyte as a critical cell in the aging process is considered, using animal models and human biopsy material. Newer data on changes in gene expression and possible changes in biology in the glomerulus are discussed. There is speculation on the implications of this change in biology for human disease and progression.

The spectrum of podocytopathies: a unifying view of glomerular diseases

Glomerular diseases encompass a broad array of clinicopathologically defined syndromes which together account for 90% of end-stage kidney disease costing $20 billion per annum to treat in the United States alone. Recent insights have defined the central role of the podocyte as both the regulator of glomerular development as well as the determinant of progression to glomerulosclerosis. We can now place all glomerular diseases within this spectrum of podocytopathies with predictable outcomes based on podocyte biology impacted by temporal, genetic, and environmental cues. This simplified construct is particularly useful to rationalize clinical effort toward podocyte preservation and prevention of progression as well as to focus basic research effort on understanding podocyte biology and for clinical research toward development of practical monitoring strategies for podocyte injury, dysfunction, and loss.

Podocyte hypertrophy, "adaptation," and "decompensation" associated with glomerular enlargement and glomerulosclerosis in the aging rat: prevention by calorie restriction

Whether podocyte depletion could cause the glomerulosclerosis of aging in Fischer 344 rats at ages 2, 6, 17, and 24 mo was evaluated. Ad libitum-fed rats developed proteinuria and glomerulosclerosis by 24 mo, whereas calorie-restricted rats did not. No evidence of age-associated progressive linear loss of podocytes from glomeruli was found. Rather, ad libitum-fed rats developed glomerular enlargement over time. To accommodate the increased glomerular volume, podocytes principally underwent hypertrophy, whereas other glomerular cells underwent hyperplasia. Stages of hypertrophy through which podocytes pass en route to podocyte loss and glomerulosclerosis were identified: Stage 1, normal podocyte; stage 2, nonstressed podocyte hypertrophy; stage 3, "adaptive" podocyte hypertrophy manifest by changes in synthesis of structural components (e.g., desmin) but maintenance of normal function; stage 4, "decompensated" podocyte hypertrophy relative to total glomerular volume manifest by reduced production of key machinery necessary for normal podocyte function (e.g., Wilms' tumor 1 protein [WT1], transcription factor pod1, nephrin, glomerular epithelial protein 1, podocalyxin, vascular endothelial growth factor, and alpha5 type IV collagen) and associated with widened foot processes and decreased filter efficiency (proteinuria); and stage 5, podocyte numbers decrease in association with focal segmental glomerulosclerosis. In contrast, in calorie-restricted rats, glomerular enlargement was minor, significant podocyte hypertrophy did not occur, podocyte machinery was unchanged, there was no proteinuria, and glomerulosclerosis did not develop. Glomerular enlargement therefore was associated with podocyte hypertrophy rather than hyperplasia. Hypertrophy above a certain threshold was associated with podocyte stress and then failure, culminating in reduced podocyte numbers in sclerotic glomeruli. This process could be prevented by calorie restriction.

A low-iron-available, polyphenol-enriched, carbohydrate-restricted diet to slow progression of diabetic nephropathy

Diabetic nephropathy has become the leading cause of uremia. Several lines of evidence suggest dietary factors other than protein intake have a substantial role in the progression of diabetic nephropathy to end-stage renal disease. The present investigation was initiated to evaluate whether a carbohydrate-restricted, low-iron-available, polyphenol-enriched (CR-LIPE) diet may delay and improve the outcome of diabetic nephropathy to a greater extent than standard protein restriction. To this aim, 191 diabetic patients, all with type 2 diabetes, were randomized to either CR-LIPE or standard protein restriction and the following outcomes monitored: doubling of serum creatinine, cumulative incidence of end-stage renal disease, and all cause mortality. Over a mean follow-up interval of 3.9 +/- 1.8 years, serum creatinine concentration doubled in 19 patients on CR-LIPE (21%) and in 31 control subjects (39%) (P < 0.01). Renal replacement therapy or death occurred in 18 patients on CR-LIPE (20%) and in 31 control subjects (39%) (P < 0.01). These differences were independent from follow-up interval, sex, mean arterial blood pressure, HbA(1c), initial renal dysfunction, and angiotensin system inhibitor use. In conclusion, CR-LIPE was 40-50% more effective than standard protein restriction in improving renal and overall survival rates.

Nutrition and chronic renal failure in rats: what is an optimal dietary protein?

In chronic uremia (CRF), malnutrition is an important determinant of morbidity in adults and impaired growth in children. Causes of malnutrition include anorexia and abnormal protein and amino acid metabolism. To determine how different levels of dietary protein and CRF interact to influence growth and nutritional status, CRF and sham-operated, pair-fed control rats were fed isocaloric diets containing 8, 17, or 30% protein for 21 d to mimic dietary regimens recommended for CRF patients: the minimum daily requirement; the recommended daily allowance; or an excess of dietary protein. Serum creatinine did not differ between groups of CRF rats but blood urea nitrogen was lowest in CRF rats fed 8% protein (P < 0.001). CRF rats eating 30% protein gained less weight and length compared to their controls or CRF rats fed 8 or 17% protein (P < 0.05); they also had acidemia. CRF rats fed 8% protein had the highest efficiency of utilization of protein for growth, while 17% protein promoted the highest efficiency of utilization of food and calories for growth. Notably, CRF rats eating 30% protein had the lowest protein efficiency; their calorie intake was also the lowest because of anorexia. Plasma branched-chain amino acids were progressively higher in control rats eating 8, 17, or 30% protein. CRF rats fed 8 or 17% protein had lower branched-chain amino acid concentrations compared with CRF rats fed 30% protein. In CRF, it is concluded that excessive dietary protein impairs growth but a low-protein diet does not impair nutritional responses and permits utilization of protein for growth if calories are sufficient.

Role of fermentable carbohydrate supplements with a low-protein diet in the course of chronic renal failure: experimental bases

During the past few years, considerable attention has been given to the impact of nutrition on kidney disease. The question arises of whether the effect of a moderate dietary protein restriction could be reinforced by enrichment of the diet with fermentable carbohydrates. Feeding fermentable carbohydrates may stimulate the extrarenal route of nitrogen (N) excretion through the fecal route. Such an effect has been reported in several species, including healthy humans and patients with chronic renal failure (CRF). Furthermore, studies of these subjects show that the greater fecal N excretion during the fermentable carbohydrate supplementation period was accompanied by a significant decrease in plasma urea concentration. In animal models of experimental renal failure, the consumption of diets containing fermentable carbohydrates results in a greater rate of urea N transfer from blood to the cecal lumen, where it is hydrolyzed by bacterial urease before subsequent microflora metabolism and proliferation. Therefore, this results in a greater fecal N excretion, coupled with a reduction in urinary N excretion and plasma urea concentration. Because elevated concentrations of serum urea N have been associated with adverse clinical symptoms of CRF, these results suggest a possible usefulness of combining fermentable carbohydrates with a low-protein diet to increase N excretion through the fecal route. Further investigations in this population of patients of whether fermentable carbohydrates in the diet may be beneficial in delaying or treating the symptoms and chronic complications of CRF will certainly emerge in the future. This should be realized without adversely affecting nutritional status and, as far as possible, by optimizing protein intake for the patients without being detrimental to renal function.

Food preferences and food habits of patients with chronic renal failure undergoing dialysis

OBJECTIVE

To examine and compare the food preferences of patients undergoing maintenance hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) with those of age- and sex-matched controls.

DESIGN

We administered two questionnaires, one assessing preferences for 88 food items (according to a nine-point hedonic scale) and the other assessing factors influencing dietary habits.

SUBJECTS

Thirty-three patients on HD, 17 patients on CAPD, and 30 control subjects with normal renal function.

MAIN OUTCOME MEASURES

The 88 foods were grouped into 14 classes to compare preferences. Taste aversions, food preparation details, and psychological and social determinants of food intake were also compared.

STATISTICAL ANALYSIS

The preference ratings of the HD, CAPD, and control groups were compared using analysis of variance. The dietary habits results were examined using a chi 2 analysis.

RESULTS

Sweet foods (P = .002), vegetables (P = .003), red meats (P = .010), and fish and poultry (P = .015) were less pleasant for patients on HD than for control subjects. Red meats (P = .019), fish and poultry (P = .032), and eggs (P = .005) were less pleasant for patients on HD than for patients on CAPD. Red meat was the most unpopular food group for all dialysis patients. The most common factor affecting dietary intake was a loss of interest in food and/or cooking.

CONCLUSION

We conclude that chronic renal failure influences patients' food preferences and food habits. Knowledge of these preferences will help dietitians plan more adequate and enjoyable diets for such patients.

Low calorie unrestricted protein diet attenuates renal injury in hypertensive rats

In the present investigation we researched the effects of low calorie diet without protein restriction on the renal function and glomerular injury of uninephrectomized spontaneously hypertensive rats. We compared the findings with those that occurred in two different groups of uninephrectomized spontaneously hypertensive rats: one treated with oral hydralazine (10 mg/kg per day) and a second fed regular food. The low calorie diet and hydralazine treatment significantly reduced intra-arterial blood pressure in each group (p < 0.05 and p < 0.001, respectively). The control group showed at the end of the experiment a slight but not significantly different increase in the intra-arterial blood pressure. Low calorie diet was more effective in protecting the kidney function. Creatinine clearance after treatment was significantly higher in uninephrectomized spontaneously hypertensive rats on a low calorie diet than in either the hydralazine-treated or control groups (p < 0.01). The 24-hour urinary protein excretion in the low calorie diet group was significantly lower than in the control group (p < 0.05) and lower but not statistically different from the hydralazine-treated group. The mean glomerular injury index of the remaining kidney in the low calorie diet group was lower than in either the hydralazine-treated or control groups (p < 0.05), and the mean mesangial expansion index in the low calorie diet group was significantly lower than in the control group (p < 0.05). The favorable effect of low calorie diet on renal function was independent of protein restriction or sodium and potassium content.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of calorie restriction on glomeruli and tubules of the remnant kidney

We have previously shown that 40% calorie restriction (CR) prevents renal injury 21 weeks after 5/6 nephrectomy (Nx) in rats, regardless of whether protein intake was concurrently restricted or not. Growth retardation appeared to be a necessary prerequisite for the protective effects of CR. To further study these mechanisms, we performed 5/6 Nx in male F344 rats and pair-fed them with a control diet (ad lib group) or a high protein diet restricted by 40% so that protein intake was similar, but calorie consumption was reduced (CR group). Four weeks after 5/6 Nx, when glomerulosclerosis had not yet developed, we compared various parameters as follows in both dietary groups and sham operated rats: urinary protein excretion (uPr), GFR (14C inulin clearance), mean nephron GFR (MNGFR; GFR divided by total number of glomeruli), glomerular volume (VG), tubulointerstitial index (TII), a measure of tubular damage kidney weight (kidney wt), kidney IGF-I content by RIA, and IGF-I immunohistochemistry. CR ameliorated the increase of MNGFR, but not glomerular hypertrophy. TII, kidney wt and kidney IGF-I content were increased in the ad lib Nx group; these changes were alleviated by CR. Two weeks after 5/6 Nx, immunohistochemistry for IGF-I showed increased staining in superficial distal nephrons in the ad lib group, and this was also suppressed by CR. The occurrence of tubulointerstitial pathology prior to glomerulosclerosis, and the beneficial effects of CR on all parameters except Vg indicate a dissociation of mechanisms which result in tubular versus glomerular hypertrophy and damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Can the rate of progression of chronic renal failure be altered?

The cost of renal replacement therapy for end-stage renal disease in the United States exceeds three billion dollars per year. Nonimmunologic mechanisms may contribute to progressive renal injury in renal failure of diverse etiologies. Based on the potential adverse renal effects of these processes, a number of dietary and pharmacologic interventions have been proposed as being potentially beneficial in slowing the rate of progression of chronic renal failure to end-stage renal disease. This article reviews current evidence in animal models and humans supporting the efficacy of each of the proposed interventions.

On the natural tendency to progressive loss of remaining kidney function in patients with impaired renal function

Patients who lose more than 50% of their functioning renal mass are at risk to develop progressive deterioration of their remaining kidney function, even though the process that caused the original loss of kidney function may no longer be present. The glomerular capillary hyperperfusion, hypertension, and hyperfiltration that occur in the surviving nephrons may play an important role in the natural tendency for renal function to deteriorate. Nevertheless, recent studies suggest that these glomerular hemodynamic events may not be the final common pathway for the natural deterioration of renal function, as was once thought. With regard to the general management of patients with impaired renal function, recent evidence suggests that controlling systemic blood pressure, reducing dietary protein and phosphorus intake, and controlling hyperlipidemia may be effective in slowing the loss of renal function.

Pathogenesis and significance of nonprimary focal and segmental glomerulosclerosis

Injury of the glomerular microvasculature by nonimmunologic processes is often the underlying mechanism of progressive deterioration of renal function in patients with a variety of renal disorders. The structural hallmark of this injury is focal and segmental glomerulosclerosis, often accompanied by entrapment of hyalin. Although such lesions are quite characteristic for diseases that primarily affect the glomerular podocyte, similar damage occurs in association with functional and structural adaptive changes that develop as a consequence of a significant loss of functioning nephrons or other systemic disorders. Experimental studies have revealed that such functional adaptations include intrarenal vasodilatation that through increases in glomerular capillary pressure and plasma flow leads to a significant compensatory hyperfiltration. This functional state is accompanied by a parallel increase in glomerular volume, attained chiefly by expansion of matrix components and an increase in the number of endothelial and mesangial cells, but not of podocytes. The persistence of the adaptive changes results in endothelial, mesangial, and epithelial cell dysfunction revealed clinically by proteinuria and structurally by the development of microthrombosis, microaneurysms, mesangial expansion, and occlusion of capillaries by hyalin accumulation. Although all these pathologic processes can lead to segmental collapse of the capillary tuft, it is the progressive hyalin deposition in capillaries with defective or detached podocytes that represents the major mechanism in the development of segmental and eventually global glomerulosclerosis. The inability of the highly differentiated podocyte to replicate in response to systemic or locally released trophic factors ultimately results in imperfections of the capillary wall that set the stage for permeability defects amplified and accentuated by greatly augmented hydrodynamic forces. These structural and functional microvascular changes acting in concert not only facilitate the transcapillary convection of macromolecules that results in albuminuria, but can also be anticipated to play a key role in the entrapment and accumulation of larger macromolecules in front of the lamina densa in the form of hyalin material. Continuing damage to the glomerular microvasculature exacerbates the adaptive changes in surviving nephrons, closing a positive-feedback loop that culminates in end-stage renal failure.