The aging kidney: a review--part II

[Research Progress in Stress-Induced Senescence of Renal Tubular Cells in Diabetic Nephropathy]

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Renal tubulointerstitial injury is an important pathophysiological basis that contributes to the progression of DN to end-stage renal disease. Stress-induced senescence of renal tubular epithelial cells (RTECs) forms a key link that causes tubulointerstitial injury. In recent years, it has been reported that organelles, such as endoplasmic reticulum, mitochondria, and lysosomes, in RTECs are damaged to varying degrees in DN, and that their functional imbalance may lead to stress-induced senescence of RTECs, thereby causing sustained cellular and tissue-organ damage, which in turn promotes the progression of the disease. However, the core mechanism underlying changes in the senescence microenvironment caused by stress-induced senescence of RTECs in DN is still not understood. In addition, the mechanism by which organelles lose homeostasis also needs to be further investigated. Herein, we described the specific pathophysiological mechanisms of renal tubular injury, stress-induced senescence of RTECs, and their association with organelles in the context of DN in order to provide reference for the next-step research, as well as the development of new therapeutic strategies.

Newer Glucose-Lowering Therapies in Older Adults with Type 2 Diabetes

Diabetes is prevalent in older adults and older adults with diabetes are more likely to have multiple comorbidities. It is, therefore, important to personalize diabetes management in this group. Newer glucose-lowering drugs, including dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists can be safely used in older patients and are preferred choices in many cases due to their safety, efficacy, and low risk of hypoglycemia.

Structural and Functional Changes in Aging Kidneys

The renal condition is one of the crucial predictors of longevity; therefore, early diagnosis of any dysfunction plays an important role. Kidneys are highly susceptible to the aging process. Unfavorable conditions may lead to a significant disturbance of the body's homeostasis. Apart from physiological changes, there are some conditions such as hypertension, diabetes or obesity which contribute to the acceleration of the aging process. A determination of macroscopic and microscopic changes is essential for assessing the progression of aging. With age, we observe a decrease in the volume of renal parenchyma and an increase in adipose tissue in the renal sinuses. Senescence may also be manifested by the roughness of the kidney surface or simple renal cysts. The main microscopic changes are a thickening of the glomerular basement membrane, nephrosclerosis, an accumulation of extracellular matrix, and mesangial widening. The principal aspect of stopping unfavorable changes is to maintain health. Studies have shown many useful ways to mitigate renal aging. This review is focused especially on medications such as renin-angiotensin-aldosterone system blockers or resveratrol, but even eating habits and lifestyle.

The ageing kidney: Molecular mechanisms and clinical implications

As human life expectancy keeps increasing, ageing populations present a growing challenge for clinical practices. Human ageing is associated with molecular, structural, and functional changes in a variety of organ systems, including the kidney. During the ageing process, the kidney experiences progressive functional decline as well as macroscopic and microscopic histological alterations, which are accentuated by systemic comorbidities like hypertension and diabetes mellitus, or by preexisting or underlying kidney diseases. Although ageing per se does not cause kidney injury, physiologic changes associated with normal ageing processes are likely to impair the reparative capacity of the kidney and thus predispose older people to acute kidney disease, chronic kidney disease and other renal diseases. Mechanistically, cell senescence plays a key role in renal ageing, involving a number of cellular signaling mechanisms, many of which may be harnessed as international targets for slowing or even reversing kidney ageing. This review summarizes the clinical characteristics of renal ageing, highlights the latest progresses in deciphering the role of cell senescence in renal ageing, and envisages potential interventional strategies and novel therapeutic targets for preventing or improving renal ageing in the hope of maintaining long-term kidney health and function across the life course.

Clinical characteristics and cost of hospital stay of octogenarians and nonagenarians in intensive care nephrology unit

PURPOSE

As the population gets older, the elderly and very elderly patients are increasingly been treated in nephrology intensive care units (ICU). In this study we evaluated the characteristics and outcomes of the octogenarians (80-89 years old), nonagenarians (≥ 90 years old) and compared them with elderly (65-79 years old) patients treated in nephrology ICU.

METHODS

Eighteen nonagenarians, 70 octogenarians and 88 elderly patients were included in the study. Indication for hospitalization, presence of comorbid diseases, and requirement for acute dialysis treatment were investigated. Need for mechanical ventilation, vasopressors, central venous catheterization, urinary catheterization, anticoagulation, and transfusion of blood products were evaluated. Mortality rate and hospital cost were calculated. Data about survival at 1 month after discharge was collected.

RESULTS

Causes of hospitalization, need for dialysis treatment, mechanical ventilation, vasopressors, central venous catheterization, urinary catheterization, anticoagulation, and transfusion of blood products were not different between age groups. Diabetes mellitus and malignancy were more frequent in elderly, whereas dementia/Alzheimer's disease was more common in nonagenarians. Although, mortality in ICU was increased as the age increased, it was statistically insignificant. However, 1 month mortality rate after discharge from hospital was increased especially in nonagenarians. In nonagenarians infection, whereas in octogenarians need for dialysis treatment, were related with mortality. Length of intensive care stay and hospital cost did not differ between age groups.

CONCLUSION

Length of nephrology intensive care stay, mortality rate and hospital cost did not differ for very elderly age groups, but mortality risk was higher for nonagenarians after discharge from hospital.

Geriatric Pharmacology: An Update

An aging worldwide population demands that anesthesiologists consider geriatrics a unique subset of patients requiring customization of practice. This article reviews the current literature investigating physiologic changes of the elderly that affect pharmacokinetics and pharmacodynamics. Changes in drug absorption, distribution, metabolism, and excretion are discussed as well as the ultimate effects of medications. Implications for practice regarding specific anesthetic and analgesic drugs are addressed. Despite the immense body of research that contributes to understanding of geriatric pharmacology, elderly patients often are excluded from rigorous research trials, and further scientific investigation to inform best practices for this group of patients is needed.

Aging Kidney and Aging-Related Disease

With the development of society and improvement of health care, the life span is much longer than before, which brings serious aging problems. Among all the aging problems, renal aging grows to be nonnegligible issue. The aging process of kidney is always accompanied with structural and functional changes. Molecular changes, including Klotho and Sirtuins, are the basic causes of phenotypical changes. Cell senescence and cell autophagy play fundamental roles in the process of renal aging. To effectively intervene in the process of renal aging, different methods have been tried separately, which could produce different effects. Effective intervention of renal aging could be meaningful for healthy state of the whole body.

Quantitative analysis of the renal aging in rats. Stereological study

PURPOSE

To evaluate the renal function and the renal histological alterations through the stereology and morphometrics in rats submitted to the natural process of aging.

METHODS

Seventy two Wistar rats, divided in six groups. Each group was sacrificed in a different age: 3, 6, 9, 12, 18 and 24 months. It was performed right nephrectomy, stereological and morphometric analysis of the renal tissue (renal volume and weight, density of volume (Vv[glom]) and numerical density (Nv[glom]) of the renal glomeruli and average glomerular volume (Vol[glom])) and also it was evaluated the renal function for the dosage of serum creatinine and urea.

RESULTS

There was significant decrease of the renal function in the oldest rats. The renal volume presented gradual increase during the development of the rats with the biggest values registered in the group of animals at 12 months of age and significant progressive decrease in older animals. Vv[glom] presented statistically significant gradual reduction between the groups and the Nv[glom] also decreased significantly.

CONCLUSIONS

The renal function proved to be inferior in senile rats when compared to the young rats. The morphometric and stereological analysis evidenced renal atrophy, gradual reduction of the volume density and numerical density of the renal glomeruli associated to the aging process.

The aging kidney and the nephrotoxic effects of mercury

Owing to advances in modern medicine, life expectancies are lengthening and leading to an increase in the population of older individuals. The aging process leads to significant alterations in many organ systems, with the kidney being particularly susceptible to age-related changes. Within the kidney, aging leads to ultrastructural changes such as glomerular and tubular hypertrophy, glomerulosclerosis, and tubulointerstitial fibrosis, which may compromise renal plasma flow (RPF) and glomerular filtration rate (GFR). These alterations may reduce the functional reserve of the kidneys, making them more susceptible to pathological events when challenged or stressed, such as following exposure to nephrotoxicants. An important and prevalent environmental toxicant that induces nephrotoxic effects is mercury (Hg). Since exposure of normal kidneys to mercuric ions might induce glomerular and tubular injury, aged kidneys, which may not be functioning at full capacity, may be more sensitive to the effects of Hg than normal kidneys. Age-related renal changes and the effects of Hg in the kidney have been characterized separately. However, little is known regarding the influence of nephrotoxicants, such as Hg, on aged kidneys. The purpose of this review was to summarize known findings related to exposure of aged and diseased kidneys to the environmentally relevant nephrotoxicant Hg.

Frailty in elderly people with chronic kidney disease

In recent years, the concept of frailty as a "state of pre-disability" has been widely accepted by those involved in the care of the elderly. Its importance lies not only in its high prevalence - more than 25% in people over 85 years of age - but it is also considered an independent risk factor of disability, institutionalisation and mortality amongst the elderly. The study of renal function is relevant in patients with major comorbidities. Studies have shown a significant association between chronic kidney disease and the development of adverse clinical outcomes such as heart disease, heart failure, end-stage renal disease, increased susceptibility to infections and greater functional impairment. Frailty can be reversed, which is why a study of frailty in patients with chronic kidney disease is of particular interest. This article aims to describe the association between ageing, frailty and chronic kidney disease in light of the most recent and relevant scientific publications.

Physiology Considerations in Geriatric Patients

Physiology changes at the structural, functional, and molecular levels as people age, and every major organ system experiences physiologic change with time. The changes to the nervous system result mostly in cognitive impairments, the cardiovascular system develops higher blood pressures with lower cardiac output, the respiratory system undergoes a reduction of arterial oxyhemoglobin levels, the gastrointestinal system experiences delayed gastric emptying and reduction of hepatic metabolism, and the renal system experiences a diminished glomerular filtration rate. Combined, these changes create a complex physiologic condition. This unique physiology must be taken into consideration for geriatric patients undergoing general anesthesia.

Distinguishing age-related from disease-related glomerulosclerosis on kidney biopsy: the Aging Kidney Anatomy study

BACKGROUND

Global glomerulosclerosis is characteristic of chronic kidney disease and also occurs with normal aging. Our goal was to determine the upper limit of normal for number of globally sclerotic glomeruli.

METHODS

Core-needle biopsies of the renal cortex were obtained at the time of living kidney transplantation at three centers between 1998 and 2011. The number of globally sclerotic glomeruli was averaged across two biopsy sections. Quantile regression was used to estimate the 95th percentile for globally sclerotic glomeruli as the upper reference limit. There were 2052 donors (mean age 43 years, 41% male, 10% hypertensive), with a mean (SD) of 16.0 (9.7) glomeruli and 0.47 (0.99) globally sclerotic glomeruli on biopsy; only 2.6% had >5% fibrosis.

RESULTS

In a multivariable model excluding hypertensive donors, independent predictors of the number of globally sclerotic glomeruli were age, total number of glomeruli and cortex area. A simplified model was used to estimate the 95th percentile for number of globally sclerotic glomeruli by total number of glomeruli and age. For a biopsy section with 17-32 total glomeruli, the 95th percentile ranged from 1 for a 20-year old to 5.5 for a 70-year old donor. Hypertensive donors were more likely to have an abnormal number of globally sclerotic glomeruli (OR = 1.79, P = 0.035).

CONCLUSIONS

We have derived the 95% reference limit for number of globally sclerotic glomeruli in ostensibly healthy individuals accounting for age and the biopsy characteristics. Numbers of globally sclerotic glomeruli in a kidney biopsy that exceed these thresholds suggest chronic pathological injury in excess of that expected with normal aging.

Spatial distribution of end-stage renal disease (ESRD) and social inequalities in mixed urban and rural areas: a study in the Bretagne administrative region of France

Background

Several studies have investigated the implication of biological and environmental factors on geographic variations of end-stage renal disease (ESRD) incidence at large area scales, but none of them assessed the implication of neighbourhood characteristics (healthcare supply, socio-economic level and urbanization degree) on spatial repartition of ESRD. We evaluated the spatial implications of adjustment for neighbourhood characteristics on the spatial distribution of ESRD incidence at the smallest geographic unit in France.

Methods

All adult patients living in Bretagne and beginning renal replacement therapy during the 2004–09 period were included. Their residential address was geocoded at the census block level. Each census block was characterized by socio-economic deprivation index, healthcare supply and rural/urban typology. Using a spatial scan statistic, we examined whether there were significant clusters of high risk of ESRD incidence.

Results

The ESRD incidence was non-randomly spatially distributed, with a cluster of high risk in the western Bretagne region (relative risk, RR = 1.28, P-value = 0.0003). Adjustment for sex, age and neighbourhood characteristics induced cluster shifts. After these adjustments, a significant cluster (P = 0.013) persisted.

Conclusions

Our spatial analysis of ESRD incidence at a fine scale, across a mixed rural/urban area, indicated that, beyond age and sex, neighbourhood characteristics explained a great part of spatial distribution of ESRD incidence. However, to better understand spatial variation of ESRD incidence, it would be necessary to research and adjust for other determinants of ESRD.

Effect of aging on renal function plus monitoring and support

Several anatomic changes and physiologic alterations occur in the aging kidney, awareness of which is essential for the early recognition of acute kidney injury (AKI) to improve outcomes in hospitalized geriatric patients. There are no unique diagnostic methods or treatment modalities in the care of the geriatric patient with AKI. Therapy is mainly supportive, and the full spectrum of treatment options, including renal replacement therapy (RRT), should not be withheld from a patient based on age. More studies need to be performed to determine the optimal timing, intensity, and modality of RRT in the geriatric population.

Acute kidney injury, sodium disorders, and hypercalcemia in the aging kidney: diagnostic and therapeutic management strategies in emergency medicine

This article summarizes the current literature regarding the structural and functional changes of the aging kidney and describes how these changes make the older patient more susceptible to acute kidney injury and fluid and electrolyte disorders. It discusses the clinical manifestations, evaluation, and management of hyponatremia and shows how the management of hypernatremia in geriatric patients involves addressing the underlying cause and safely correcting the hypernatremia. The current literature regarding evaluation and management of hypercalcemia in older patients is summarized. The management of severe hypercalcemia is discussed in detail. The evaluation and management of acute kidney injury is described.

The chronic kidney disease “epidemy”

Chronic kidney disease is a general term for heterogenous disorders with >3 months duration affecting kidney structure and function. Nowadays, involving 10–16% of the adult population worldwide, chronic kidney disease is recognised as a major global public health problem. The number of cases is continuously increasing. In this review, epidemiology, definition, new classification and a conceptual model for development, progression and complications of chronic kidney disease as well as strategies to improve outcome are summarized. Orv. Hetil., 2013, 154, 43–51.

Risk score for the prediction of contrast-induced nephropathy in elderly patients undergoing percutaneous coronary intervention

We developed a risk score for contrast-induced nephropathy (CIN) in elderly patients (n = 668) before percutaneous coronary intervention (PCI). Another 277 elderly patients were studied for validation. Based on the odds ratio, risk factors were assigned a weighted integer; the sum of the integers was the risk score. Among the 668 elderly patients, 105 (15.7%) experienced CIN. There were 9 risk factors for CIN (with weighted integer): estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) (4), diabetes (3), left ventricular ejection fraction <45% (3), hypotension (2), age >70 years (2), myocardial infarction (2), emergency PCI (2), anemia (2), and contrast agent volume >200 mL (2). The incidence of CIN was 3.4%, 11.9%, 36.9%, and 69.8% in the low-risk (≤4), moderate risk (5-8), high-risk (9-12), and very-high-risk groups (≥13). The model demonstrated good discriminative power in the validation population (c statistic = 0.79). This score can be used to plan preventative measures.

Renal function and morphology in aged Beagle dogs before and after hydrocortisone administration

Objectives of this study were to evaluate glomerular filtration rate (GFR), renal structural changes and proteinuria in aged Beagle dogs before and after hydrocortisone (HC) administration. Eleven Beagle dogs ≥10 years old were treated with either hydrocortisone (HC group, n = 6) or placebo (control group, n = 5). Urinary markers, GFR and kidney biopsies were evaluated before (T0), during (T16 wks) and after discontinuing HC administration (T24 wks). Results indicate that HC administration causes a significant increase in GFR. At all time points except T16 wks, proteinuria was higher in the control group than in the HC group, and there was no significant difference in urinary markers between groups. At T16 wks, proteinuria, urinary albumin-to-creatinine (c) ratio, immunoglobulin G/c and retinol-binding protein/c were higher compared to baseline in the HC group. At T0, rare to mild renal lesions were detected in all HC dogs and rare to moderate changes in all control dogs. Glomerulosclerosis progressed in both groups until T24 wks. Tubular atrophy was detected in three HC dogs at T16 wks and T24 wks, but also in five control dogs throughout the study. At every time point, five HC dogs and all control dogs had rare to moderate interstitial inflammation. Rare to mild interstitial fibrosis was found in up to three HC dogs at T16 wks and T24 wks, and severe fibrosis in one HC dog at T24 wks. Up to four control dogs had rare to mild fibrosis at all time points. These findings indicate that clinically healthy, aged Beagle dogs may have considerable renal lesions and proteinuria, which could have implications for experimental or toxicological studies. Additional research is needed to elucidate glucocorticoid effects on renal structure, but functional changes such as hyperfiltration and proteinuria warrant attention to kidney function of canine patients with Cushing's syndrome or receiving exogenous glucocorticoids.

Chronic kidney disease

Chronic kidney disease is a general term for heterogeneous disorders affecting kidney structure and function. The 2002 guidelines for definition and classification of this disease represented an important shift towards its recognition as a worldwide public health problem that should be managed in its early stages by general internists. Disease and management are classified according to stages of disease severity, which are assessed from glomerular filtration rate (GFR) and albuminuria, and clinical diagnosis (cause and pathology). Chronic kidney disease can be detected with routine laboratory tests, and some treatments can prevent development and slow disease progression, reduce complications of decreased GFR and risk of cardiovascular disease, and improve survival and quality of life. In this Seminar we discuss disease burden, recommendations for assessment and management, and future challenges. We emphasise clinical practice guidelines, clinical trials, and areas of uncertainty.

Aging and physiological changes of the kidneys including changes in glomerular filtration rate

In addition to the structural changes in the kidney associated with aging, physiological changes in renal function are also found in older adults, such as decreased glomerular filtration rate, vascular dysautonomia, altered tubular handling of creatinine, reduction in sodium reabsorption and potassium secretion, and diminished renal reserve. These alterations make aged individuals susceptible to the development of clinical conditions in response to usual stimuli that would otherwise be compensated for in younger individuals, including acute kidney injury, volume depletion and overload, disorders of serum sodium and potassium concentration, and toxic reactions to water-soluble drugs excreted by the kidneys. Additionally, the preservation with aging of a normal urinalysis, normal serum urea and creatinine values, erythropoietin synthesis, and normal phosphorus, calcium and magnesium tubular handling distinguishes decreased GFR due to normal aging from that due to chronic kidney disease.

Hypertension and angiogenesis in the aging kidney: a review

With advanced aging, main components of the kidney are altered, including blood vessels, glomeruli and tubulointerstitium. Disruption in these 3 elements is interconnected and associated with several modifications, such as loss of kidney mass and systemic, metabolic and immunologic diseases. In this review we focus on renal blood vessels, the key role of hypertension and angiogenesis in the elderly kidney, the hemodynamic and molecular mechanisms underlying this aging process and the main factors involved. So far, the present data suggests a strong association between renal disease and hypertension and the impairment of regulatory mechanisms, such as angiogenesis in the aging kidney. The endothelium is a key player in vascular control and appears to be also disrupted in many compensatory functions (i.e., vasodilation). Perspectives for the management of the dysfunctional aging kidney are also addressed.

The association between age and nephrosclerosis on renal biopsy among healthy adults

BACKGROUND

Chronic kidney disease is common with older age and is characterized on renal biopsy by global glomerulosclerosis, tubular atrophy, interstitial fibrosis, and arteriosclerosis.

OBJECTIVE

To see whether the prevalence of these histologic abnormalities in the kidney increases with age in healthy adults and whether histologic findings are explained by age-related differences in kidney function or chronic kidney disease risk factors.

DESIGN

Cross-sectional study.

SETTING

Mayo Clinic, Rochester, Minnesota, from 1999 to 2009.

PATIENTS

1203 adult living kidney donors.

MEASUREMENTS

Core-needle biopsy of the renal cortex obtained during surgical implantation of the kidney, and medical record data of kidney function and risk factors obtained before donation.

RESULTS

The prevalence of nephrosclerosis (> or =2 chronic histologic abnormalities) was 2.7% (95% CI, 1.1% to 6.7%) for patients aged 18 to 29 years, 16% (CI, 12% to 20%) for patients aged 30 to 39 years, 28% (CI, 24% to 32%) for patients aged 40 to 49 years, 44% (CI, 38% to 50%) for patients aged 50 to 59 years, 58% (CI, 47% to 67%) for patients aged 60 to 69 years, and 73% (CI, 43% to 90%) for patients aged 70 to 77 years. Adjustment for kidney function and risk factor covariates did not explain the age-related increase in the prevalence of nephrosclerosis.

LIMITATION

Kidney donors are selected for health and lack the spectrum or severity of renal pathologic findings in the general population.

CONCLUSION

Kidney function and chronic kidney disease risk factors do not explain the strong association between age and nephrosclerosis in healthy adults.

PRIMARY FUNDING SOURCE

National Institutes of Health, U.S. Public Health Service.

The association between age and nephrosclerosis on renal biopsy among healthy adults

BACKGROUND

Chronic kidney disease is common with older age and is characterized on renal biopsy by global glomerulosclerosis, tubular atrophy, interstitial fibrosis, and arteriosclerosis.

OBJECTIVE

To see whether the prevalence of these histologic abnormalities in the kidney increases with age in healthy adults and whether histologic findings are explained by age-related differences in kidney function or chronic kidney disease risk factors.

DESIGN

Cross-sectional study.

SETTING

Mayo Clinic, Rochester, Minnesota, from 1999 to 2009.

PATIENTS

1203 adult living kidney donors.

MEASUREMENTS

Core-needle biopsy of the renal cortex obtained during surgical implantation of the kidney, and medical record data of kidney function and risk factors obtained before donation.

RESULTS

The prevalence of nephrosclerosis (> or =2 chronic histologic abnormalities) was 2.7% (95% CI, 1.1% to 6.7%) for patients aged 18 to 29 years, 16% (CI, 12% to 20%) for patients aged 30 to 39 years, 28% (CI, 24% to 32%) for patients aged 40 to 49 years, 44% (CI, 38% to 50%) for patients aged 50 to 59 years, 58% (CI, 47% to 67%) for patients aged 60 to 69 years, and 73% (CI, 43% to 90%) for patients aged 70 to 77 years. Adjustment for kidney function and risk factor covariates did not explain the age-related increase in the prevalence of nephrosclerosis.

LIMITATION

Kidney donors are selected for health and lack the spectrum or severity of renal pathologic findings in the general population.

CONCLUSION

Kidney function and chronic kidney disease risk factors do not explain the strong association between age and nephrosclerosis in healthy adults.

PRIMARY FUNDING SOURCE

National Institutes of Health, U.S. Public Health Service.

Omega-3 and renal function in older adults

Chronic kidney disease (CKD) is a major public health problem and can result in end-stage renal disease with need for dialysis or transplantation. In Europe up to 12% of the adult population had some renal impairment, while in the United States the end stage of CKD has increased dramatically from 209.000 in 1991 to 472.000 in 2004. Diabetes and hypertension are major causes of kidney pathology. Infection, particularly ascending infection, is more common with increasing age, as both immune function declines and associated pathology predisposing to infection, such as obstructive uropathy, becomes more common. Most pathological changes in the kidney appear to be initiated by oxidative stress, followed by an inflammatory reaction. Oxidative stress results from an imbalance between free radicals and their detoxification by endogenous and exogenous scavengers, including polyunsaturated fatty acids (PUFA). Recent studies showed that PUFA supplementation slowed the rate of loss of renal function in patients with IgA nephropathy. Then, studies of omega-3 supplementation in dialysis patients describe salutary effects on triglyceride levels and dialysis access patency. We examined the relationship between total plasma PUFA levels and change in creatinine clearance over a three-year follow-up in the older persons enrolled in the InCHIANTI study, a population-based epidemiology study conducted in Tuscany, Italy. This study showed that older adults with low total plasma PUFA levels have a greater decline in creatinine clearance over three years of follow-up. These findings suggest that a higher dietary intake of PUFA may be protective against progression to chronic kidney disease.

Conceptual model of CKD: applications and implications

The conceptual model of chronic kidney disease (CKD) was developed by the National Kidney Foundation's Kidney Disease Quality Outcome Initiative (NKF-KDOQI) in 2002 and subsequently revised and adopted by an international consensus under the auspices of KDIGO (Kidney Disease: Improving Global Outcomes) in 2005. This model includes concepts of definition, staging, outcomes, and treatment, as well as risk factors for the development, progression, and complications of CKD. Treatments are available for patients with risk factors and for each stage of CKD; these include slowing the progression of kidney disease, preventing and treating the complications of decreased glomerular filtration rate, and reducing cardiovascular disease risk factors and treating cardiovascular disease. In principle, measures to improve the prevention, detection, and treatment could reduce adverse outcomes, improve the quality of life, and prolong the survival of individuals with CKD. The conceptual model for CKD is now being applied to a public health approach for the prevention of the development, progression, and complications of CKD. Primary prevention is defined as prevention of CKD; secondary and tertiary prevention are defined as improving outcomes of patients with CKD stages 1 to 4 and kidney failure (CKD stage 5), respectively. The conceptual model has also fostered debate about important questions: Is CKD a disease or a cardiovascular disease risk-factor condition? Do all patients with CKD need to be referred to a nephrologist? What does CKD care include? Should the classification be modified to include cause of disease and prognosis? Can CKD evolve from acute kidney disease, and is CKD reversible? Is albuminuria a manifestation of a kidney disease or systemic endothelial dysfunction? Is the age-related decrease in glomerular filtration rate normal or abnormal, and should we change the definition of CKD in the elderly? A combination of immediate action, data gathering, and research to establish the efficacy, effectiveness, and costs related to CKD are needed to respond to CKD as a public health problem.

Creatinine reabsorption by the aged kidney

AIM

The handling of renal creatinine in human beings has classically been described as the result of two particular physiological processes: glomerular filtration and proximal tubular secretion. However, there are particular physiological situations in which tubular creatinine reabsorption has been documented, such as in the case of healthy newborns and premature babies. We performed a prospective study in order to evaluate if there is tubular creatinine reabsorption in healthy elderly people.

PATIENTS AND METHOD

We studied prospectively nine healthy volunteers, four of them young (20-33 years old) and the remaining five, old (65-73 years old). Since creatinine is secreted in the proximal tubules, and its secretion can be completely blocked by cimetidine administration, a creatinine clearance with cimetidine reliably represents the glomerular filtration rate. Therefore, if the ratio creatinine clearance (Ccr)/creatinine clearance with cimetidine (CcrWC) is higher than one, this would indicate net creatinine secretion, whereas a ratio lower than one would indicate a net renal creatinine tubular reabsorption; a ratio equal to one indicates creatinine filtration. Finally, the Ccr, CcrWC, and Ccr/CcrWC ratios were compared between the young and old group.

STATISTICAL TESTS

Mann-Whitney and Wilcoxon tests were used.

RESULTS

As expected, creatinine clearance in the elderly was significantly lower than in the young [Ccr: 74.4 ml/min (47.9-100.9) (old) vs. 153.8 ml/min (108.3-199.2) (young), p = 0.014]. Similarly, the creatinine clearance with cimetidine (CcrWC) was significantly lower in the elderly compared to the young [CcrWC: 81.8 ml/min (69.2-94.5) (old) vs. 122.5 ml/min (82.6-162.4) (young), p = 0.028]. The ratio of Ccr/CcrWC was 0.9 in the elderly vs. 1.26 in the young (p = 0.014), indicating net creatinine reabsorption in the elderly and net creatinine secretion in the young.

CONCLUSION

Our findings indicate that there seems to be a net reabsorption of creatinine in the renal tubules of healthy old persons.

[Old age and the kidneys]

Age-related changes in renal morphology and function cannot be regarded physiological. The number of glomeruli falls, sclerotic glomeruli and aglomerular arterioles develop. Besides tubular atrophy interstitial fibrosis is often seen, and the age-related vascular changes strongly affect the kidneys. Renal blood flow and GFR decrease, without concomitant changes in se-creatinine. Disorders of tubular transport manifest mainly in salt- and water-excretion and lead to hyposthenuria. The pathogenesis of these age-related changes is not fully understood. Nevertheless, such changes impair the excretory functions and the pharmacokinetics of drugs. In real chronic renal failure other functions (erythropoietin production, vitamin-D, Ca and P metabolism) are also impaired. Due to more frequent occurrence of systemic diseases (diabetes, hypertension, etc.) in the elderly, real chronic renal failure is also more common, and various forms of acute renal failure develop more easily.

The normal ageing kidney – morphology and physiology

This paper will review some fundamentals of normal renal physiology necessary to understand the changes occurring with age and enable the reader to distinguish between chronic renal insufficiency and the consequences of normal ageing on kidney function.

Renal senescence in 2008: progress and challenges

Kidneys are significantly affected by profound anatomic and functional changes with senescence. These changes lead to decline in glomerular filtration rate, decreased urinary concentrating and diluting ability, diminished urinary acidification, and impaired potassium clearance, to list a few. Such changes make the elderly prone to drug toxicity and serious fluid and electrolyte imbalance. While the entire mystery of aging is far from being clear, the role of oxidative stress, telomere length, Klotho gene expression, and the renin angiotensin system seem to be the key mechanisms involved in aging. Aging, being a complex process, involves an array of intertwined molecular pathways. Simultaneous study of multiple molecular pathways in parallel could provide invaluable information in understanding the clinical course of kidney aging and elucidating mechanisms that play key roles in the aging process. A better understanding of these mechanisms may help to preserve renal function, improve morbidity and mortality, and hopefully reduce healthcare costs for the aging population.

Renal ageing

The function of the kidney, as well as its morphology, changes markedly with age. The glomerular filtration rate falls progressively, independent of overt pathology. Glomerular, vascular and accompanying parenchymal changes occur and other disorders associated with ageing, such as diabetes and hypertension, have a stochastic deleterious effect on both form and function. Declining renal function with age has important implications, not only for individual homeostasis but also for the use of drug therapy and for the receipt and donation of organs for transplantation. Molecular mechanisms and cellular changes underlying some of the functional and structural changes associated with ageing are becoming clearer, as are some of the ways in which genetic background, age and disease can combine to produce functional damage.

Does renal ageing affect survival?

The effects of ageing on progressive deterioration of renal function, both in human and experimental animals, are described elsewhere, but the effect of renal damage on overall survival and longevity is not yet clearly established. The wild-type animals of various genetic backgrounds, fed with regular diet, overtime develop severe age-associated nephropathy, that include but not limited to inflammatory cell infiltration, glomerulosclerosis, and tubulointerstitial fibrosis. Such renal damage significantly reduces their survival. Reducing renal damage, either by caloric restriction or by suppressing growth hormone (GH)/insulin-like growth factor-1 (IGF-1) activity could significantly enhance the longevity of these animals. Available survival studies using experimental animals clearly suggest that kidney pathology is one of the important non-neoplastic lesions that could affect overall survival, and that restoration of renal function by preventing kidney damage could significantly extend longevity. Careful long-term studies are needed to determine the human relevance of these experimental studies.

Increased susceptibility of aging kidney to ischemic injury: identification of candidate genes changed during aging, but corrected by caloric restriction

Aging is associated with an increased incidence and severity of acute renal failure. However, the molecular mechanism underlying the increased susceptibility to injury remains undefined. These experiments were designed to investigate the influence of age on the response of the kidney to ischemic injury and to identify candidate genes that may mediate this response. Renal slices prepared from young (5 mo), aged ad libitum (aged-AL; 24 mo), and aged caloric-restricted (aged-CR; 24 mo) male Fischer 344 rats were subjected to ischemic stress (100% N(2)) for 0-60 min. As assessed by biochemical and histological evaluation, slices from aged-AL rats were more susceptible to injury than young counterparts. Importantly, caloric restriction attenuated the increased susceptibility to injury. In an attempt to identify the molecular pathway(s) underlying this response, microarray analysis was performed on tissue harvested from the same animals used for the viability experiments. RNA was isolated and the corresponding cDNA was hybridized to CodeLink Rat Whole Genome Bioarray slides. Subsequent gene expression analysis was performed using GeneSpring software. Using two-sample t-tests and a twofold cut-off, the expression of 92 genes was changed during aging and attenuated by caloric restriction, including claudin-7, kidney injury molecule-1 (Kim-1), and matrix metalloproteinase-7 (MMP-7). Claudin-7 gene expression peaked at 18 mo; however, increased protein expression in certain tubular epithelial cells was seen at 24 mo. Kim-1 gene expression was not elevated at 8 or 12 mo but was at 18 and 24 mo. However, changes in Kim-1 protein expression were only seen at 24 mo and corresponded to increased urinary levels. Importantly, these changes were attenuated by caloric restriction. MMP-7 gene expression was decreased at 8 mo, but an age-dependent increase was seen at 24 mo. Increased MMP-7 protein expression in tubular epithelial cells at 24 mo was correlated with the gene expression pattern. In summary, we identified genes changed by aging and changes attenuated by caloric restriction. This will facilitate investigation into the molecular mechanism mediating the age-related increase in susceptibility to injury.