Food restriction prevents advanced glycation end product accumulation and retards kidney aging in lean rats

A Role for Advanced Glycation End Products in Molecular Ageing

Ageing is a composite process that involves numerous changes at the cellular, tissue, organ and whole-body levels. These changes result in decreased functioning of the organism and the development of certain conditions, which ultimately lead to an increased risk of death. Advanced glycation end products (AGEs) are a family of compounds with a diverse chemical nature. They are the products of non-enzymatic reactions between reducing sugars and proteins, lipids or nucleic acids and are synthesised in high amounts in both physiological and pathological conditions. Accumulation of these molecules increases the level of damage to tissue/organs structures (immune elements, connective tissue, brain, pancreatic beta cells, nephrons, and muscles), which consequently triggers the development of age-related diseases, such as diabetes mellitus, neurodegeneration, and cardiovascular and kidney disorders. Irrespective of the role of AGEs in the initiation or progression of chronic disorders, a reduction in their levels would certainly provide health benefits. In this review, we provide an overview of the role of AGEs in these areas. Moreover, we provide examples of lifestyle interventions, such as caloric restriction or physical activities, that may modulate AGE formation and accumulation and help to promote healthy ageing.

Dietary Restriction for Kidney Protection: Decline in Nephroprotective Mechanisms During Aging

Dietary restriction (DR) is believed to be one of the most promising approaches to extend life span of different animal species and to delay deleterious age-related physiological alterations and diseases. Among others, DR was shown to ameliorate acute kidney injury (AKI) and chronic kidney disease (CKD). However, to date, a comprehensive analysis of the mechanisms of the protective effect of DR specifically in kidney pathologies has not been carried out. The protective properties of DR are mediated by a range of signaling pathways associated with adaptation to reduced nutrient intake. The adaptation is accompanied by a number of metabolic changes, such as autophagy activation, metabolic shifts toward lipid utilization and ketone bodies production, improvement of mitochondria functioning, and decreased oxidative stress. However, some studies indicated that with age, the gain of DR-mediated positive remodeling gradually decreases. This may be an obstacle if we seek to translate the DR approach into a clinic for the treatment of kidney diseases as most patients with AKI and CKD are elderly. It is well known that aging is accompanied by impairments in a huge variety of organs and systems, such as hormonal regulation, stress sensing, autophagy and proteasomal activity, gene expression, and epigenome profile, increased damage to macromolecules and organelles including mitochondria. All these age-associated changes might be the reasons for the reduced protective potential of the DR during aging. We summarized the available mechanisms of DR-mediated nephroprotection and described ways to improve the effectiveness of this approach for an aged kidney.

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.

Umbilical cord mesenchymal stem cell conditioned medium restored the expression of collagen II and aggrecan in nucleus pulposus mesenchymal stem cells exposed to high glucose

Diabetes can cause intervertebral disc degeneration by accelerating apoptosis and senescence of nucleus pulposus mesenchymal stem cells (NPMSCs). The aim of this study was to determine the effect of umbilical cord mesenchymal stem cells (UCMSCs) conditioned medium on high glucose (HG) induced degradation of NPMSCs produced extracellular matrix. NPMSCs were isolated from the inner intervertebral disc tissue using type XI collagenase digestion. According to Annexin V/propidium iodide (PI) flow cytometry analysis; HG leads to an increase in the rate of NPMSCs apoptosis. HG injury also resulted in a marked decrease in the percentage of cells in G0/G1 phase and an increase in cells in S and G2/M phases, indicating that HG induces cell cycle arrest of NPMSCs. Treatment with MSC-CM abolished the effect of HG on cell senescence. HG also significantly inhibited collagen II and aggrecan expression in NPMSCs. After MSC-CM treatment, the expression of these two extracellular matrix components was restored. Exposure to HG resulted in phosphorylation of p38 MAPK, while the levels of total p38 MAPK were not affected. When treated with MSC-CM, phosphorylated p38 MAPK levels of NPMSCs were lower than those without CM treatment. Our data also showed that p38 MAPK inhibitor SB203580 can attenuated phosphorylation of p38 MAPK and resumed the collagen II and aggrecan expression in NPMSCs. In summary, this study demonstrated that MSC-CM has the potential to alleviate HG induced extracellular matrix degradation via the p38 MAPK pathway.

MMP2-A2M interaction increases ECM accumulation in aged rat kidney and its modulation by calorie restriction

Age-associated renal fibrosis is related with renal function decline during aging. Imbalance between accumulation and degradation of extracellular matrix is key feature of fibrosis. In this study, RNA-sequencing (RNA-Seq) results based on next-generation sequencing (NGS) data were analyzed to identify key proteins that change during aging and calorie restriction (CR). Among the changed genes, A2M and MMP2, which are known to interact, exhibited the highest between centrality (BC) and degree values when analyzed by protein–protein interaction (PPI). Both mRNA and protein levels of MMP2 and A2M were increased during aging. Furthermore, the interaction between MMP2 and A2M was verified by immunoprecipitation and immunohistochemistry. MMP2 activity was further measured under the presence or absence of A2M-MMP2 interaction. MMP2 activity, which was increased under the absence of A2M-MMP2 interaction, was significantly decreased under the presence of interactions in aged kidney. We further hypothesized that the interaction between A2M-MMP2 played a role in the inactivation of MMP2 leading to accumulation of ECM including collagen type I and IV. Aged kidney showed highly accumulated MMP2 substrate proteins despite of increased MMP2 protein expression and CR blunted these accumulation. Additional in vivo analysis revealed that the signal transducer and activator of transcription (STAT) 3 transcriptional factor was significantly increased thus increasing A2M expression during aging. STAT3 activating cytokines were also highly increased in aged kidney. In conclusion, the results of the present study indicate that A2M-MMP2 interaction has a role in age-associated renal ECM accumulation and in the suppression such fibrosis by CR.

Advanced Glycation End Products: Link between Diet and Ovulatory Dysfunction in PCOS?

PCOS is the most common cause of anovulation in reproductive-aged women with 70% experiencing ovulatory problems. Advanced glycation end products are highly reactive molecules that are formed by non-enzymatic reactions of sugars with proteins, nucleic acids and lipids. AGEs are also present in a variety of diet where substantial increase in AGEs can result due to thermal processing and modifications of food. Elevation in bodily AGEs, produced endogenously or absorbed exogenously from high-AGE diets, is further exaggerated in women with PCOS and is associated with ovulatory dysfunction. Additionally, increased expression of AGEs as pro-inflammatory receptors in the ovarian tissue has been observed in women with PCOS. In this review, we summarize the role of dietary AGEs as mediators of metabolic and reproductive alterations in PCOS. Once a mechanistic understanding of the relationship between AGEs and anovulation is established, there is a promise that such knowledge will contribute to the subsequent development of targeted pharmacological therapies that will treat anovulation and improve ovarian health in women with PCOS.

Advanced glycation end products: A link between metabolic and endothelial dysfunction in polycystic ovary syndrome?

Polycystic ovary syndrome (PCOS), a heterogeneous syndrome of reproductive and metabolic alterations, is associated with increased long-term risk of cardiovascular complications. This phenomenon has been linked to an increase in oxidative stress and inflammatory markers. Advanced glycation end products (AGEs) are pro-inflammatory molecules that trigger a state of intracellular oxidative stress and inflammation after binding to their cell membrane receptors RAGE. The activation of the AGE-RAGE axis has been well known to play a role in atherosclerosis in both men and women. Women with PCOS have systemic chronic inflammatory condition even at the ovarian level as represented by elevated levels of serum/ovarian AGEs and increased expression of the pro-inflammatory RAGE in ovarian tissue. Data also showed the presence of sRAGE in the follicular fluid and its potential protective role against the harmful effect of AGEs on ovarian function. Thus, whether AGE-RAGE axis constitutes a link between metabolic and endothelial dysfunction in women with PCOS is addressed in this review. Additionally, we discuss the role of hormonal changes observed in PCOS and how they are linked with the AGE-RAGE axis in order to better understand the nature of this complex syndrome whose consequences extend well beyond reproduction.

miR-184 and miR-150 promote renal glomerular mesangial cell aging by targeting Rab1a and Rab31

The molecular mechanism of kidney aging is not well understood, but the abnormal expression of miRNAs with aging is considered to be an important contributor. miR-184 and miR-150 were screened using a miRNA microarray and qRT-PCR and found to be significantly upregulated in 24-month-old rats. Rat renal primary glomerular mesangial cells (GMCs) were isolated from 3-month and 24-month-old rats for the in vitro analysis of the roles of miR-184 and miR-150 in kidney aging. Bioinformatics analyses suggested that Rab1a and Rab31, which are associated with cell autophagy, were targeted by both miR-184 and miR-150. miR-184 and miR-150 were increased significantly in aging GMCs versus young cells, while Rab1a and Rab31 were significantly lower in aging cells. Furthermore, dual luciferase reporter assays revealed that miR-184 and miR-150 bound to the 3'-UTR of Rab1a and Rab31 mRNAs. Transfection of miR-184 and miR-150 mimics into young GMCs suppressed the expression of Rab1a and Rab31. Transfected cells showed lower autophagy activities and higher levels of cellular oxidative products, leading to the aging of young GMCs. However, miR-184 and miR-150 inhibitors promoted autophagy and reduced oxidative damage by upregulating Rab1a and Rab31 in old GMCs. In conclusion, miR-184 and miR-150 inhibited autophagy, promoting GMC aging.

Alterations in intervertebral disc composition, matrix homeostasis and biomechanical behavior in the UCD-T2DM rat model of type 2 diabetes

Type 2 diabetes (T2D) adversely affects many tissues, and the greater incidence of discogenic low back pain among diabetic patients suggests that the intervertebral disc is affected too. Using a rat model of polygenic obese T2D, we demonstrate that diabetes compromises several aspects of disc composition, matrix homeostasis, and biomechanical behavior. Coccygeal motion segments were harvested from 6-month-old lean Sprague-Dawley rats, obese Sprague-Dawley rats, and diabetic obese UCD-T2DM rats (diabetic for 69 ± 7 days). Findings indicated that diabetes but not obesity reduced disc glycosaminoglycan and water contents, and these degenerative changes correlated with increased vertebral endplate thickness and decreased endplate porosity, and with higher levels of the advanced glycation end-product (AGE) pentosidine. Consistent with their diminished glycosaminoglycan and water contents and their higher AGE levels, discs from diabetic rats were stiffer and exhibited less creep when compressed. At the matrix level, elevated expression of hypoxia-inducible genes and catabolic markers in the discs from diabetic rats coincided with increased oxidative stress and greater interactions between AGEs and one of their receptors (RAGE). Taken together, these findings indicate that endplate sclerosis, increased oxidative stress, and AGE/RAGE-mediated interactions could be important factors for explaining the greater incidence of disc pathology in T2D.

Effect of advanced glycation end product intake on inflammation and aging: a systematic review

Aging is associated with a chronic low-grade inflammatory status that contributes to chronic diseases such as age-related muscle wasting, kidney disease, and diabetes mellitus. Since advanced glycation end products (AGEs) are known to be proinflammatory, this systematic review examined the relation between the dietary intake of AGEs and inflammatory processes. The PubMed and Web of Science databases were screened systematically. Seventeen relevant studies in humans or animals were included. The intervention studies in humans showed mainly a decrease in inflammation in subjects on a low-AGE diet, while an increase in inflammation in subjects on a high-AGE diet was less apparent. About half of the observational studies found a relationship between inflammatory processes and AGEs in food. When the results are considered together, the dietary intake of AGEs appears to be related to inflammatory status and the level of circulating AGEs. Moreover, limiting AGE intake may lead to a decrease in inflammation and chronic diseases related to inflammatory status. Most of the trials were conducted in patients with chronic kidney disease or diabetes, and thus additional studies in healthy individuals are needed. Further investigation is needed to elucidate the effects of lifetime exposure of dietary AGEs on aging and health.

Reducing mitochondrial decay with mitochondrial nutrients to delay and treat cognitive dysfunction, Alzheimer's disease, and Parkinson's disease

Mitochondrial decay due to oxidative damage is a contributor to brain aging and age-related neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). One type of mitochondrial decay is oxidative modification of key mitochondrial enzymes. Enzyme dysfunction, that is due to poor binding of substrates and coenzymes may be ameliorated by supplementing adequate levels of substrates or coenzyme precursors. Such supplementation with mitochondrial nutrients (mt-nutrients) may be useful to prevent or delay mitochondrial decay, thus prevent or treat AD and PD. In the present review, we survey the literature to identify mt-nutrients that can (1) protect mitochondrial enzymes and/or stimulate enzyme activity by elevating levels of substrates and cofactors; (2) induce phase-2 enzymes to enhance antioxidant defenses; (3) scavenge free radicals and prevent oxidant production in mitochondria, and (4) repair mitochondrial membrane. Then, we discuss the relationships among mt-nutrient deficiency, mitochondrial decay, and cognitive dysfunction, and summarize available evidence suggesting an effect of mt-nutrient supplementation on AD and PD. It appears that greater effects might be obtained by longer-term administration of combinations of mt-nutrients. Thus, optimal doses of combinations of mt-nutrients to delay and repair mitochondrial decay could be a strategy for preventing and treating cognitive dysfunction, including AD and PD.

Kidney aging--inevitable or preventable?

The aging process affects all organs, including the kidneys. As part of this process, progressive scarring and a measurable decline in renal function occur in most people over time. The improved understanding of the processes that can lead to and/or hasten scarring and loss of renal function over time parallels advances in our understanding of the aging process. Clinical factors, including hypertension, diabetes mellitus, obesity, abnormal lipid levels and vitamin D deficiency, have been associated with increasing renal sclerosis with age. In addition, tissue factors such as angiotensin II, advanced glycation end products, oxidative stress and Klotho are associated with renal aging. These associations and possible interventions, including the control of blood pressure, blood sugar, weight, diet and calorie restriction might make renal aging more preventable than inevitable.

Dietary interventions to extend life span and health span based on calorie restriction

The societal impact of obesity, diabetes, and other metabolic disorders continues to rise despite increasing evidence of their negative long-term consequences on health span, longevity, and aging. Unfortunately, dietary management and exercise frequently fail as remedies, underscoring the need for the development of alternative interventions to successfully treat metabolic disorders and enhance life span and health span. Using calorie restriction (CR)-which is well known to improve both health and longevity in controlled studies-as their benchmark, gerontologists are coming closer to identifying dietary and pharmacological therapies that may be applicable to aging humans. This review covers some of the more promising interventions targeted to affect pathways implicated in the aging process as well as variations on classical CR that may be better suited to human adaptation.

Advanced glycation end-products induce tubular CTGF via TGF-beta-independent Smad3 signaling

Advanced glycation end-products (AGEs) can induce expression of connective tissue growth factor (CTGF), which seems to promote the development of diabetic nephropathy, but the exact signaling mechanisms that mediate this induction are unknown. Here, AGEs induced CTGF expression in tubular epithelial cells (TECs) that either lacked the TGF-beta1 gene or expressed dominant TGF-beta receptor II, demonstrating independence of TGF-beta. Furthermore, conditional knockout of the gene encoding TGF-beta receptor II from the kidney did not prevent AGE-induced renal expression of CTGF and collagen I. More specific, AGEs induced CTGF expression via the receptor for AGEs-extracellular signal-regulated kinase (RAGE-ERK)/p38 mitogen-activated protein kinase-Smad cross-talk pathway because inhibition of this pathway by several methods (anti-RAGE antibody, specific inhibitors, or dominant negative adenovirus to ERK1/2 and p38) blocked this induction. Overexpressing Smad7 abolished AGE-induced Smad3 phosphorylation and CTGF expression, demonstrating the necessity for activation of Smad signaling in this process. More important, knockdown of either Smad3 or Smad2 demonstrated that Smad3 but not Smad2 is essential for CTGF induction in response to AGEs. In conclusion, AGEs induce tubular CTGF expression via the TGF-beta-independent RAGE-ERK/p38-Smad3 cross-talk pathway. These data suggest that overexpression of Smad7 or targeting Smad3 may have therapeutic potential for diabetic nephropathy.

Oral glycotoxins determine the effects of calorie restriction on oxidant stress, age-related diseases, and lifespan

We previously showed that the content of advanced glycation end products (AGEs) in the diet correlates with serum AGE levels, oxidant stress (OS), organ dysfunction, and lifespan. We now show that the addition of a chemically defined AGE (methyl-glyoxal-BSA) to low-AGE mouse chow increased serum levels of AGEs and OS, demonstrating that dietary AGEs are oxidants that can induce systemic OS. OS predisposes to the development of cardiovascular and chronic kidney diseases; calorie restriction (CR) is the most studied means to decrease OS, increase longevity, and reduce OS-related organ damage in mammals. Because reduction of food intake also decreases oxidant AGE s intake, we asked whether the beneficial effects of CR in mammals are related to the restriction of oxidants or energy. Pair-fed mice were provided either a CR diet or a high-AGE CR diet in which AGEs were elevated by brief heat treatment (CR-high). Old CR-high mice developed high levels of 8-isoprostanes, AGEs, RAGE, and p66(shc), coupled with low AGER1 and GSH/GSSG levels, insulin resistance, marked myocardial and renal fibrosis, and shortened lifespan. In contrast, old CR mice had low OS, p66(shc), RAGE, and AGE levels, but high AGER1 levels, coupled with longer lifespan. Therefore, the beneficial effects of a CR diet may be partly related to reduced oxidant intake, a principal determinant of oxidant status in aging mice, rather than decreased energy intake.

Neuroendocrine factors in the regulation of inflammation: excessive adiposity and calorie restriction

Acute inflammation is usually a self-limited life preserving response, triggered by pathogens and/or traumatic injuries. This transient response normally leads to removal of harmful agents and to healing of the damaged tissues. In contrast, unchecked or chronic inflammation can lead to persistent tissue and organ damage by activated leukocytes, cytokines, or collagen deposition. Excessive energy intake and adiposity cause systemic inflammation, whereas calorie restriction without malnutrition exerts a potent anti-inflammatory effect. As individuals accumulate fat and their adipocytes enlarge, adipose tissue undergoes molecular and cellular alterations, macrophages accumulate, and inflammation ensues. Overweight/obese subjects have significantly higher plasma concentrations of C-reactive protein and several cytokines, including IL-6, IL-8, IL-18, and TNF-alpha. Experimental animals on a chronic CR regimen, instead, have low levels of circulating inflammatory cytokines, low blood lymphocyte levels, reduced production of inflammatory cytokines by the white blood cells in response to stimulation, and cortisol levels in the high normal range. Recent data demonstrate that CR exerts a powerful anti-inflammatory effect also in non-human primates and humans. Multiple metabolic and neuroendocrine mechanisms are responsible for the CR-mediated anti-inflammatory effects, including reduced adiposity and secretion of pro-inflammatory adipokines, enhanced glucocorticoid production, reduced plasma glucose and advanced glycation end-product concentrations, increased parasympathetic tone, and increased ghrelin production. Measuring tissue specific effects of CR using genomic, proteomic, and metabolomic techniques in humans will foster the understanding of the complex biological processes involved in the anti-inflammatory and anti-aging effects of CR.

Vieillissement: rôle et contrôle de la glycation

PURPOSE

Advanced glycation end-products (AGEs) accumulate in aging tissues and organs during rheumatoid arthritis and Alzheimer disease. These aging toxins are especially involved in cell alteration during diabetes mellitus (glycotoxin) and renal failure (uremic toxin). AGEs participate to the endothelial dysfunction leading to diabetic macro but also micro-angiopathy. AGEs binding to cell receptors are critical steps in the deleterious consequences of AGE excess. AGE-receptor activation altered cell and organ functions by a pro-inflammatory, pro-coagulant and pro-fibrosis factors cell response.

CURRENT KNOWLEDGE AND KEY POINTS

Non-enzymatic glycation and glycoxidation with glucose auto-oxidation represent the two main pathways resulting in AGE formation. No exclusive AGE classification is actually available. Pathophysiological mechanisms are described to explain AGE toxicity. AGEs bind to cell receptors inducing deleterious consequences such as endothelial dysfunction after endothelial RAGE activation. AGEs can also have deleterious effects through glycated protein accumulation or in situ protein glycation.

FUTURE PROSPECTS AND PROJECTS

Many in vitro or animal studies demonstrated that AGE deleterious effects can be prevented by glycation inhibitors, AGE cross-link breakers or AGE-RAGE interaction inhibition. New molecules are actually studied as new strategy to prevent or treat the deleterious effects of these aging toxins.

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.

Metabolism of a Heterocyclic Amine Colon Carcinogen in Young and Old Rats

The incidence of colon cancer increases with age, and this may be related to altered metabolism and disposition of carcinogens. One such carcinogen implicated in colon cancer is the heterocyclic amine found in well done meat, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). The purpose of these studies was to determine whether the disposition and metabolism of IQ changes with age, comparing young (3-month) and old (22- to 24-month) male F344 rats. Animals were treated with vehicle or beta-naphthoflavone (BNF), an inducer of drug-metabolizing cytochromes P450. Disposition and metabolism of IQ were determined after i.p. injection of radiolabeled IQ. Urinary IQ metabolites were identified and quantitated by high-performance liquid chromatography and mass spectroscopy. In BNF-treated animals, total radiolabeled IQ excretion by old rats was less than half that of young rats. Binding of radiolabeled IQ metabolites by the old kidney was 10 times higher than that of the young. There were no age differences in intestinal and hepatic binding. There was a significant age-related increase in IQ conjugation to glucuronic acid and a decrease in conjugation to sulfate regardless of treatment. The induction of renal CYP1A1, a major P450 involved in IQ metabolism, by BNF did not change with age. Changes in IQ metabolism with age along with altered renal function may contribute to the decreased urinary excretion and increased renal binding of IQ and/or its metabolites seen in the old animals.

Changing prescribing practice in CAPD patients in Korea: increased utilization of low GDP solutions improves patient outcome

BACKGROUND

Novel, biocompatible peritoneal dialysis (PD) solutions have become available in recent years. In 2001, low glucose degradation products (GDP), neutral pH solutions became commercially available in Korea. To date, there are no reports regarding the large scale adoption of these solutions in clinical practice and regarding what, if any, impact these solutions have on patient outcomes.

METHODS

Using a database of almost 4000 patients treated by PD in Korea, we conducted a prospective, longitudinal observational study documenting the patterns of use of one novel low GDP solution (balance, Fresenius Medical Care, St Wendel, Germany) in 1909 PD incident patients between 1 January 2002 and midyear 2005. Outcomes including patient and technique survival and peritonitis rates were analysed using univariate and multivariate analysis.

RESULTS

Prescription of low GDP solutions reached between 70 and 80% by the year 2003 and persisted at this level. Patients prescribed low GDP PD solution tended to be younger and were more likely to be treated in centres with larger enrollment in the database. Survival of diabetic patients treated with the new PD solution was identical to that of the non-diabetic patients treated with standard PD fluids (PDF) and treatment with low GDP PDF independently reduced the relative risk (RR) of death (RR = 0.613; CI 0.50-0.74; P < 0.00001) in a proportional hazards model which included age, diabetes and centre experience. In a univariate analysis, low GDP PD solution was associated with a longer technique survival (P = 0.049) but this effect was not significant in multivariate analysis. No significant differences in peritonitis-free interval or peritonitis rate could be attributed to the prescribed PDF.

CONCLUSION

Prescription of low GDP, pH-neutral PD solutions has rapidly increased in Korea. This change has resulted in a significant improvement in patient and technique survival without any measurable change in peritonitis incidence or rate. Reasons for the improved patient survival cannot be determined from this analysis and require further study.

In a type 2 diabetic nephropathy rat model, the improvement of obesity by a low calorie diet reduces oxidative/carbonyl stress and prevents diabetic nephropathy

BACKGROUND

The present study has been undertaken to unravel the critical factors involved in the progression of diabetic nephropathy (DN).

METHODS

A unique type 2 diabetic rat model with a wide range of metabolic derangements and hypertension has been utilized, the spontaneously hypertensive/NIH-corpulent rat SHR/NDmcr-cp(cp/cp). It develops histologically evident glomerular injury and tubulointerstitial damage, including mesangial activation, podocyte injury, and inflammatory cell infiltration in the tubulointerstitium.

RESULTS

A low calorie diet for 22 weeks significantly improves obesity, proteinuria and renal morphological alterations. The correction of renal injury is independent of blood pressure control. Obesity correction, although partial, normalizes the renal content of pentosidine taken as a marker of oxidative stress and advanced glycation end products (AGEs). This occurs despite the fact that, in this model, improvement of glucose control and hyperlipidaemia is limited. Proteinuria and body weight are highly correlated with renal pentosidine content, while proteinuria and body weight are also correlated with each other. Diabetic renal injury is thus inhibited by a low calorie diet with an attendant reduction of oxidative stress and AGE formation, despite sustained hypertension.

CONCLUSION

The present findings suggest a direct role of obesity in the generation of a localized oxidative stress and AGE formation, directly responsible for DN.

Calorie restriction modulates renal expression of sterol regulatory element binding proteins, lipid accumulation, and age-related renal disease

Sterol regulatory element binding proteins (SREBP) are major regulators of fatty acid and cholesterol synthesis. This study found that age-related renal matrix deposition and proteinuria were associated with increased renal expression of SREBP-1 and SREBP-2 and increased renal accumulation of triglyceride and cholesterol. Because calorie restriction (CR) modulates age-related renal disease, it then was determined whether the effects of CR are mediated partially by modulation of renal lipid metabolism. Compared with ad libitum (AL)-fed 24-month-old (24 m) F344BN rats, CR resulted in significant decreases in extracellular matrix accumulation (periodic acid-Schiff staining and immunofluorescence of type IV collagen and fibronectin) and proteinuria. A significant decrease was also observed in the renal expression of growth factors (connective tissue growth factor and vascular endothelial growth factor) and matrix metalloproteinase inhibitor (plasminogen activator inhibitor-1). These structural and functional changes were associated with significant decreases in renal nuclear SREBP-1 (5.2 in 24 m AL versus 3.3 densitometry units in 24 m CR; P < 0.01) and SREBP-2 (7.1 in 24 m AL versus 4.1 densitometry units in 24 m CR; P < 0.01) protein abundance and renal triglyceride and cholesterol contents. It is interesting that serum leptin level was significantly increased as a function of aging, and CR resulted in significant reduction in serum leptin level. Because it was shown previously that increased renal expression of SREBP-1a per se caused renal lipid accumulation, glomerulosclerosis, and proteinuria, the results suggest that CR modulates age-related renal disease in part by modulation of renal SREBP expression and renal lipid accumulation.

Physical Exercise Retards the Development of Chronic Nephropathy in the Ageing Rat as Efficiently as Food Restriction Does

BACKGROUND

Obesity combined with decreasing physical fitness in the ageing Western populations promotes a number of degenerative diseases, including chronic kidney disease. It has further been shown in rodent models that prevention of obesity by food restriction mitigates development of kidney lesions. Whether lifelong physical activity also has a positive effect is not known.

OBJECTIVE

To compare the effects of physical exercise and food restriction on the development of chronic kidney lesions in ageing rats.

METHODS

Male Sprague-Dawley rats were divided into groups: voluntarily running in wheels (RW), food restriction to the degree necessary to attain pair weight to RW rats (PW), forced running in treadmills (TM) and sedentary controls housed individually (S1) or 4 in each cage (S4). The interventions began at the age of 5 months and kidneys were sampled and analysed histologically at the ages of 15, 19 and 23 months.

RESULTS

Total score for kidney lesions (sum of the scores for glomerular changes, interstitial non-purulent inflammation, proteinaceous casts in tubules and increased amount of connective tissue, the possible maximum being 10.0) increased from 0.5 +/- 0.2 at 5 months of age to 1.6 +/- 0.3 for RW, 2.3 +/- 0.4 for PW, 4.5 +/- 0.4 for TM, 3.6 +/- 0.5 for S1 and 5.4 +/- 0.6 for S4 at the age of 23 months. The increase from 5 months of age was gradual for all groups through 15, 19 and 23 months. The patterns for the various lesions followed the same pattern with the exception of connective tissue, which did not increase.

CONCLUSION

Voluntary running in wheels is as effective in mitigating kidney lesions as is food restriction, while forced running in a treadmill is not effective in this respect.

Aging biology and geriatric clinical pharmacology

Population aging evokes doomsday economic and sociological prognostication, despite a minority of older people suffering significant dependency and the potential for advances in therapeutics of age-related disease and primary aging. Biological aging processes are linked mechanistically to altered drug handling, altered physiological reserve, and pharmacodynamic responses. Parenteral loading doses need only be adjusted for body weight as volumes of distribution are little changed, whereas oral loading doses in some cases may require reduction to account for age-related increases in bioavailability. Age-related reduction of hepatic blood flow and hepatocyte mass and primary aging changes in hepatic sinusoidal endothelium with effects on drug transfer and oxygen delivery reduce hepatic drug clearance. Primary renal aging is evident, although renal clearance reduction in older people is predominantly disease-related and is poorly estimated by standard methods. The geriatric dosing axiom, "start low and go slow" is based on pharmacokinetic considerations and concern for adverse drug reactions, not from clinical trial data. In the absence of generalizable dosage guidelines, individualization via effect titration is required. Altered pharmacodynamics are well documented in the cardiovascular system, with changes in the autonomic system, autacoid receptors, drug receptors, and endothelial function to modify baseline cardiovascular tone and responses to stimuli such as postural change and feeding. Adverse drug reactions and polypharmacy represent major linkages to avoidable morbidity and mortality. This, combined with a deficient therapeutic evidence base, suggests that extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Even so, therapeutic advances generally may convert healthy longevity from an asset of fortunate individuals into a general social benefit.

Predictors of baseline peritoneal transport status in Australian and New Zealand peritoneal dialysis patients

BACKGROUND

Factors that predict peritoneal transport status in peritoneal dialysis (PD) patients are poorly understood. The aim of the present study is to determine these factors in Australian and New Zealand incident PD patients.

METHODS

The study included all patients on the Australian and New Zealand Dialysis and Transplant Registry who started PD therapy between April 1, 1991, and March 31, 2002, and underwent a peritoneal equilibration test (PET) within the first 6 months. Predictors of peritoneal transport category and dialysate-plasma creatinine ratio at 4 hours (D-P Cr 4h) were assessed by multivariate ordinal logistic regression and multiple linear regression, respectively.

RESULTS

A total of 3,188 patients were studied. Mean D-P Cr 4h was 0.69 +/- 0.13. High transport status was associated with older age (adjusted odds ratio [OR], 1.08 for each 10 years; 95% confidence interval [CI], 1.03 to 1.13), Maori and Pacific Islander racial origin (OR, 1.48; 95% CI, 1.13 to 1.94), and normal body mass index (BMI; < 18.5 kg/m2: OR, 0.90; 95% CI, 0.65 to 1.24; BMI of 18.5 to 25 kg/m2: OR, 1 [reference]; BMI of 25 to 30 kg/m2: OR, 0.81; 95% CI, 0.70 to 0.95; BMI > 30 kg/m2: OR, 0.71; 95% CI, 0.58 to 0.86), but was not independently predicted by sex, diabetes, other comorbid diseases, smoking, previous hemodialysis therapy or transplantation, or residual renal function. Similar results were found when peritoneal permeability was modeled as a continuous variable (D-P Cr 4h).

CONCLUSION

In Australian and New Zealand PD patients, higher peritoneal transport status is independently associated with racial origin, older age, and lower BMI. The diversity of peritoneal transport characteristics in different ethnic populations suggests that additional validation of PET measurements in various racial groups and study of their relationship to patient outcomes are warranted.

Increased level of glycoxidation product N(epsilon)-(carboxymethyl)lysine in rat serum and urine proteins with aging: link with glycoxidative damage accumulation in kidney

Accumulation of carboxymethylated proteins (CML-proteins) is taken as a biomarker of glycoxidative stress which is thought to contribute to the age-related impairment in tissue and cell function. To investigate the occurrence and extent of glycoxidative damage with aging in rat kidney, serum and urine, we have prepared a polyclonal antibody against CML-modified bovine serum albumin. We subsequently used it for immunolocalization and in enzyme-linked immunosorbent assays to evaluate CML-protein content. In the serum, CML-protein level was 1.43+/-0.14 pmol CML/micrograms protein at 3 months and significantly increased by 50% from 10 to 27 months (1.50+/-0.14 pmol CML/micrograms protein vs 2.27+/-0.26 pmol CML/micrograms protein), albumin and transferrin being the main modified proteins. In the urine, CML-protein level was 2.50+/-0.14 pmol CML/micrograms protein at 3 months and markedly increased from 10 months (2.99+/-0.24 pmol CML/micrograms protein) to 27 months (3.76+/-0.25 pmol CML/micrograms protein), with albumin as the main excreted modified protein. Immunolocalization of CML-proteins in kidney provided evidence for an age-dependent increased accumulation in extracellular matrices. Intense staining of the glomerular basement membrane (GBM), Bowman's capsule, and the tubular basement membrane was found. Additionally, the CML content for collagen from GBM was 195.85+/-28.95 pmol CML/microgrms OHPro at 3 months and significantly increased from 10 months (187.61+/-21.99 pmol CML/micrograms OHPro) to 27 months (334.55+/-62.21 pmol CML/micrograms OHPro). These data show that circulating CML-protein level in serum and urine and CML accumulation in nephron extracellular matrices with aging are increasing in parallel. The CML-protein measurement in serum and urine may thus be used as an index for the assessment of age-associated glycoxidative kidney damage.

Age-related increase of protein glycation in peripheral blood lymphocytes is restricted to preferential target proteins

Advanced glycation end products (AGE) have been analyzed in aging human peripheral blood lymphocytes since protein glycation and glycoxidation are believed to contribute to the intracellular age-related accumulation of damaged proteins, a process that has been associated with the cellular functional deficits that occur with age. The appearance of AGE in cell lysates was monitored with an enzyme-linked immunosorbent assay using an anti-AGE antibody raised against glycated RNAse. When lymphocyte cytosolic extracts from old donors (86-91 years old) were compared with those from young donors (20-25 years old), a small but significant 40% increase of protein glycation was observed. In both age groups, further analysis of the pattern of glycated proteins by two-dimensional gel electrophoresis followed by western blotting with the same anti-AGE antibody, showed that the protein silver stain and the immunoblot patterns were not superimposable indicating that glycoxidative modifications are targeting only a restricted set of proteins. Among these preferential protein targets, seven of them exhibited a significant age-related increased immunoreactivity with the anti-AGE antibody suggesting that the corresponding modified proteins might serve as biomarkers of aging lymphocytes.

Oxidative, glycoxidative and lipoxidative damage to rat heart mitochondrial proteins is lower after 4 months of caloric restriction than in age-matched controls

In this investigation the effect of 4 months of 40% restriction of calories on defined markers of oxidative, glycoxidative or lipoxidative damage to heart mitochondrial proteins was studied. The protein markers assessed were N(epsilon)-(carboxyethyl)lysine (CEL), N(epsilon)-(carboxymethyl)lysine (CML), N(epsilon)-(malondialdehyde)lysine (MDA-lys), and the recently described (PNAS 98:69-74, 2001) main constituents of protein carbonyls glutamic and aminoadipic semialdehydes. All these markers were measured by gas chromatography/mass spectrometry. The results showed that glutamic semialdehyde was present in rat heart mitochondria at levels 20-fold higher than aminoadipic semialdehyde. After 4 months of caloric restriction, the levels of CEL, CML, MDA-lys and glutamic semialdehyde were significantly lower in the mitochondria from caloric restricted animals than in the controls. These decreases were not due to a lower degree of oxidative attack to mitochondrial proteins, since the rate of mitochondrial oxygen radical generation was not modified by 4 months of caloric restriction. The decreases in MDA-lys and CML were not due either to changes in the sensitivity of mitochondrial lipids to peroxidation since measurements of the fatty acid composition showed that the total number of fatty acid double bonds and the peroxidizability index were not changed by caloric restriction. The results globally indicate that caloric restriction during 4 months decreases oxidative stress-derived damage to heart mitochondrial proteins. They also suggest that these decreases are due to an increase in the capacity of the restricted mitochondria to decompose oxidatively modified proteins.

Cellular signaling, AGE accumulation and gene expression in hepatocytes of lean aging rats fed ad libitum or food-restricted

The effects of food restriction on liver glucagon and vasopressin V1a receptors, on AGE accumulation and on gene expression were investigated in 10- and 30-month-old WAG/Rij female rats fed ad libitum or chronically food-restricted by 30%. The age-related increase in glucagon and vasopressin V1a receptor density, as well as the rise in glucagon-induced cAMP generation was prevented by the restriction. AGE accumulation, characteristic of the aging process, was normalized in food-restricted animals. Gene expression determined with rat Atlas cDNA Expression Arrays containing 1176 cDNA indicates that a few genes exhibited a greater than twofold change in mRNA ratios with age. Most down-regulated genes were related to oxidative metabolism of lipids, and most of the up-regulated genes were concerned with the cell cycle and transcription factors. Chronic food restriction partially prevents these changes in gene expression and induces up- and down-regulation of several mRNAs which are not modified with age in ad libitum fed rats.

Effect of drinking green tea on age-associated accumulation of Maillard-type fluorescence and carbonyl groups in rat aortic and skin collagen

Tea catechins and other flavonoids have been shown to potentially protect against chronic cardiovascular diseases such as coronary heart disease and atherosclerosis. In this study, 6-month-old female Sprague-Dawley rats were fed green tea extract (50 mg/100 ml in drinking water) up to the age of 22 months, and the age-associated changes in Maillard-type fluorescence and carbonyl groups in the aortic and skin collagen were compared with those occurring in the water-fed control animals. Collagen-linked Maillard-type fluorescence was found to increase in both the aortic and skin tissues as animals aged. The age-associated increase in the fluorescence in the aortic collagen was remarkably inhibited by the green tea extract treatment, while that occurring in the skin collagen was not significantly inhibited by the treatment. The collagen carbonyl content also increased in both the aortic and skin tissues as animals aged. In contrast with the case of Maillard-type fluorescence, however, the age-associated increase in the carbonyl content was not inhibited by the green tea extract treatment either in the aortic or skin collagen. These results suggest that the inhibition of AGE formation in collagen is an important mechanism for the protective effects of tea catechins against cardiovascular diseases.

Food restriction prevents age-related polyuria by vasopressin-dependent recruitment of aquaporin-2

The mechanisms underlying the prevention of age-related polyuria by chronic food restriction were investigated in female WAG/Rij rats. The decreased osmolality of renal papilla observed in senescent rats was not corrected by food restriction. A reduced urea content in the inner medulla of senescent rats, fed ad libitum or food-restricted, was suggested by the marked decrease in expression of UT-A1 and UT-B1 urea transporters. Aquaporin-2 (AQP2) downregulation in the inner medulla of senescent rats was partially prevented by food restriction. Both AQP2 and the phosphorylated form of AQP2 (p-AQP2), the presence of which was diffuse within the cytoplasm of collecting duct principal cells in normally fed senescent rats, were preferentially targeted at the apical region of the cells in food-restricted senescent animals. Plasma vasopressin (AVP) was similar in 10- and 30-mo-old rats fed ad libitum, but was doubled in food-restricted 30-mo-old rats. This study indicates that 1) kidney aging is associated with a marked decrease in AQP2, UT-A1, and UT-B1 expression in the inner medulla and a reduced papillary osmolality; and 2) the prevention of age-related polyuria by chronic food restriction occurs through an improved recruitment of AQP2 and p-AQP2 to the apical membrane in inner medulla principal cells, permitted by increased plasma AVP concentration.

Glucagon and vasopressin V1a receptor signaling in hepatocytes from aging rats

Glucose tolerance is reduced with age. The relationship between this change in glucose homeostasis and signaling of glucagon and vasopressin V1a receptors was investigated in hepatocytes isolated from 10- and 30-month-old female WAG/Rij rats. Binding capacity of hepatocytes for 125I glucagon and 3H vasopressin increased 2- and 1.8-fold, respectively, between 10 and 30 months. Intracellular cAMP accumulation induced by glucagon was 40% greater in hepatocytes of aging rats than of adults, although EC(50) were similar in the two groups. Conversely, phosphodiesterases activity and nucleotides leakage out of the cells were unchanged with age. The rise in intracellular calcium consecutive to the stimulation of V1a receptor was comparable in adult and senescent animals. Finally, glucose release by hepatocyte suspensions was greater in senescent than in adult animals in absence as in presence of glucagon. These experiments suggest that increase in glucagon receptor expression and cAMP generation would contribute to the impaired glucose tolerance characteristic of the aging process.