Calorie restriction in obesity: prevention of kidney disease in rodents

Diabetic Kidney Disease: Contribution of Phenyl Sulfate Derived from Dietary Tyrosine upon Gut Microbiota Catabolism

Deranged gut microbiota can release increased levels of uremic toxins leading to exacerbated kidney injury. In diabetic kidney disease (DKD), phenyl sulfate (PS) derived from tyrosine catabolism by gut microbiota has been demonstrated to be both an early diagnostic marker and a therapeutic target. In this perspective article, we summarize PS generation pathways and recent findings on PS and kidney injury in DKD. Increasing evidence has shown that the underlying mechanisms of PS-induced kidney injury mainly involve oxidative stress, redox imbalance, and mitochondrial dysfunction, which all may be targeted to attenuate PS-induced kidney injury. For future research directions, we think that a deeper understanding of the pathogenic role of PS in kidney injury using a variety of diabetic animal models should be investigated. Moreover, we also suggest beneficial approaches that could be used to mitigate the deleterious effect of PS on the kidney. These approaches include caloric restriction, tyrosine restriction, and administration of ketogenic drugs, ketogenic diets or natural products; all of which should be conducted under obese and diabetic conditions.

Diet Change Improves Obesity and Lipid Deposition in High-Fat Diet-Induced Mice

The number of obese people is increasing dramatically worldwide, and one of the major causes of obesity is excess energy due to high-fat diets. Several studies have shown that reducing food and energy intake represents a key intervention or treatment to combat overweight/obesity. Here, we conducted a 12-week energy-restricted dietary intervention for high-fat diet-induced obese mice (C57BL/6J) to investigate the effectiveness of diet change in improving obesity. The results revealed that the diet change from HFD to NFD significantly reduced weight gain and subcutaneous adipose tissue weight in high-fat diet-induced obese mice, providing scientific evidence for the effectiveness of diet change in improving body weight and fat deposition in obese individuals. Regarding the potential explanations for these observations, weight reduction may be attributed to the excessive enlargement of adipocytes in the white adipose tissue of obese mice that were inhibited. Diet change significantly promoted lipolysis in the adipose tissue (eWAT: Adrb3, Plin1, HSL, and CPTA1a; ingWAT: CPT1a) and liver (reduced content of nonesterified fatty acids), and reduced lipogenesis in ingWAT (Dgat2). Moreover, the proportion of proliferative stem cells in vWAT and sWAT changed dramatically with diet change. Overall, our study reveals the phenotypic, structural, and metabolic diversity of multiple tissues (vWAT and sWAT) in response to diet change and identifies a role for adipocyte stem cells in the tissue specificity of diet change.

Simultaneous SGLT2 inhibition and caloric restriction improves insulin resistance and kidney function in OLETF rats

SGLT2 inhibitors (SGLT2i) are emerging as a novel therapy for type 2 diabetes due to their effective hypoglycemic and potential cardio- and nephroprotective effects, while caloric restriction (CR) is a common behavioral modification to improve adiposity and insulin resistance. Therefore, both interventions simultaneously may potentially further improve metabolic syndrome by enhancing carbohydrate metabolism. To test this hypothesis, cohorts of 10-week old, male Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were treated with SGLT2i (10 mg luseoglifozin/kg/day x 4 wks) (OLETF only) and/or 30% CR (2 wks at 12 weeks of age). CR maintained body mass in both strains while SGLT2i alone did not have any effect on body mass. Simultaneous treatments decreased SBP in OLETF vs SGLT2i alone, decreased insulin resistance index (IRI), and increased creatinine clearance vs OLETF ad lib. Conversely, CR decreased albuminuria independent of SGLT2i. In conclusion, SGLT2i treatment by itself did not elicit significant improvements in insulin resistance, kidney function or blood pressure. However, when combined with CR, these changes where more profound than with CR alone without inducing chronic hypoglycemia.

Prospective Pharmacological Potential of Resveratrol in Delaying Kidney Aging

Aging is an unavoidable part of life. The more aged we become, the more susceptible we become to various complications and damages to the vital organs, including the kidneys. The existing drugs for kidney diseases are mostly of synthetic origins; thus, natural compounds with minimal side-effects have attracted growing interest from the scientific community and pharmaceutical companies. A literature search was carried out to collect published research information on the effects of resveratrol on kidney aging. Recently, resveratrol has emerged as a potential anti-aging agent. This versatile polyphenol exerts its anti-aging effects by intervening in various pathologies and multi-signaling systems, including sirtuin type 1, AMP-activated protein kinase, and nuclear factor-κB. Researchers are trying to figure out the detailed mechanisms and possible resveratrol-mediated interventions in divergent pathways at the molecular level. This review highlights (i) the causative factors implicated in kidney aging and the therapeutic aspects of resveratrol, and (ii) the effectiveness of resveratrol in delaying the aging process of the kidney while minimizing all possible side effects.

NADH/NAD+ Redox Imbalance and Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common and severe complication of diabetes mellitus. If left untreated, DKD can advance to end stage renal disease that requires either dialysis or kidney replacement. While numerous mechanisms underlie the pathogenesis of DKD, oxidative stress driven by NADH/NAD⁺ redox imbalance and mitochondrial dysfunction have been thought to be the major pathophysiological mechanism of DKD. In this review, the pathways that increase NADH generation and those that decrease NAD⁺ levels are overviewed. This is followed by discussion of the consequences of NADH/NAD⁺ redox imbalance including disruption of mitochondrial homeostasis and function. Approaches that can be applied to counteract DKD are then discussed, which include mitochondria-targeted antioxidants and mimetics of superoxide dismutase, caloric restriction, plant/herbal extracts or their isolated compounds. Finally, the review ends by pointing out that future studies are needed to dissect the role of each pathway involved in NADH-NAD⁺ metabolism so that novel strategies to restore NADH/NAD⁺ redox balance in the diabetic kidney could be designed to combat DKD.

Methionine restriction delays aging-related urogenital diseases in male Fischer 344 rats

Dietary methionine restriction (MR) has been found to enhance longevity across many species. We hypothesized that MR might enhance longevity in part by delaying or inhibiting age-related disease processes. To this end, male Fischer 344 rats were fed control (CF, 0.86% methionine) or MR (0.17% methionine) diets throughout their life until sacrifice at approximately 30 months of age, and histopathology was performed to identify the incidence and progression of two important aging-related pathologies, namely, chronic progressive nephropathy (CPN) and testicular tumorigenesis. Although kidney pathology was observed in 87% CF rats and CPN in 62% of CF animals, no evidence of kidney disease was observed in MR rats. Consistent with the absence of renal pathology, urinary albumin levels were lower in the MR group compared to controls throughout the study, with over a six-fold difference between the groups at 30 months of age. Biomarkers associated with renal disease, namely, clusterin, cystatin C, and β-2 microglobulin, were reduced following 18 months of MR. A reduction in testicular tumor incidence from 88% in CF to 22% in MR rats was also observed. These results suggest that MR may lead to metabolic and cellular changes providing protection against age-related diseases.

Twist2 Is Upregulated in Early Stages of Repair Following Acute Kidney Injury

The aging kidney is a marked by a number of structural and functional changes, including an increased susceptibility to acute kidney injury (AKI). Previous studies from our laboratory have shown that aging male Fischer 344 rats (24 month) are more susceptible to apoptosis-mediated injury than young counterparts. In the current studies, we examined the initial injury and early recovery phases of mercuric chloride-induced AKI. Interestingly, the aging kidney had decreased serum creatinine compared to young controls 1 day following mercuric chloride injury, but by day 4, serum creatinine was significantly elevated, suggesting that the aging kidney did not recover from injury. This conclusion is supported by the findings that serum creatinine and kidney injury molecule-1 (Kim-1) gene expression remain elevated compared to young controls at 10 days post-injury. To begin to elucidate mechanism(s) underlying dysrepair in the aging kidney, we examined the expression of Twist2, a helix-loop-helix transcription factor that may mediate renal fibrosis. Interestingly, Twist2 gene expression was elevated following injury in both young and aged rats, and Twist2 protein expression is elevated by mercuric chloride in vitro.

Effect of Long-Term Somatotropin Treatment on Body Composition and Life Span in Aging Obese Zucker Rats

The objective of this work was to test the hypothesis that a somatotropin (STH)-induced reduction in body fat would prolong the life span of the obese Zucker rat. Two experiments were conducted. In the first experiment, male and female, lean and obese Zucker rats were treated with STH (0 or 2 mg/d bovine STH) for 4 weeks, beginning at 7 months of age. Across phenotypes, STH treatment increased the growth rate by 159%, muscle weights by 14%, and circulating insulin-like growth factor (IGF)-1 by 23%, and decreased carcass fat by 21% (P < 0.05). The second experiment was a longevity trial to determine whether these changes in body composition would increase the life span of the obese rat. Beginning at 7 months of age, individually housed, male and female, lean and obese rats were assigned to daily STH treatments (0 or 2 mg/d). Rats were monitored daily, and sick or moribund rats were euthanized and necropsied to determine existing pathologies. The average life span of the lean rats was 661 days and was unaffected by STH treatment (639 days, NS) or gender. Average life span of the vehicle-injected obese rats (435 days) was less than that of the lean group (P < 0.001). STH treatment of the obese rats resulted in a further reduction of life span (349 days, P < 0.02). The predominant pathology observed across the treatment groups was renal disease, characterized by progressive glomerulonephropathy. Thus, although exogenous STH was able to reduce carcass lipid and to increase lean tissue mass in obese rats, there was no improvement in longevity. In contrast to the hypothesis, STH actually reduced the life span of the obese rat. It is likely that STH treatment accelerated the development of progressive glomerulonephropathy in the obese rat.

Ageing and obesity similarly impair antibody responses

Ageing is characterized by increased low-grade chronic inflammation, which is a significant risk factor for morbidity and mortality of elderly individuals. Similar to ageing, obesity is considered to be an inflammatory predisposition associated with chronic activation of immune cells and consequent local and systemic inflammation. Both ageing and obesity are characterized by reduced innate and adaptive immune responses. This review focuses on B cells, how they may contribute, at least locally, to low-grade chronic inflammation in ageing and obesity and on the mechanisms involved.

SIRT1 and Kidney Function

BACKGROUND

SIRT1 is a nicotinamide adenine dinucleotide-dependent deacetylase belonging to the class III histone deacetylases. Abundantly expressed in the kidney, especially in the renal medulla, SIRT1 is closely involved in renal physiology and pathology.

SUMMARY

SIRT1 targets both histone and nonhistone proteins, participates in many important signaling pathways and mediates the regulation of longevity, metabolic homeostasis, acute stress response and DNA integrity. With regard to the kidney, SIRT1 attenuates diabetic albuminuria, reduces blood pressure and related cardiovascular diseases, resists acute kidney injury, delays kidney fibrogenesis, promotes cyst formation and benefits renal ageing.

KEY MESSAGES

This review summarizes the biology of SIRT1 and focuses on the latest studies concerning SIRT1 as a potential therapeutic target for kidney diseases.

Obesity-induced changes in kidney mitochondria and endoplasmic reticulum in the presence or absence of leptin

We investigated obesity-induced changes in kidney lipid accumulation, mitochondrial function, and endoplasmic reticulum (ER) stress in the absence of hypertension, and the potential role of leptin in modulating these changes. We compared two normotensive genetic mouse models of obesity, leptin-deficient ob/ob mice and hyperleptinemic melanocortin-4 receptor-deficient mice (LoxTB MC4R-/-), with their respective lean controls. Compared with controls, ob/ob and LoxTB MC4R-/- mice exhibit significant albuminuria, increased creatinine clearance, and high renal triglyceride content. Renal ATP levels were decreased in both obesity models, and mitochondria isolated from both models showed alterations that would lower mitochondrial ATP production. Mitochondria from hyperleptinemic LoxTB MC4R-/- mice kidneys respired NADH-generating substrates (including palmitate) at lower rates due to an apparent decrease in complex I activity, and these mitochondria showed oxidative damage. Kidney mitochondria of leptin-deficient ob/ob mice showed normal rates of respiration with no evidence of oxidative damage, but electron transfer was partially uncoupled from ATP synthesis. A fourfold induction of C/EBP homologous protein (CHOP) expression indicated induction of ER stress in kidneys of hyperleptinemic LoxTB MC4R-/- mice. In contrast, ER stress was not induced in kidneys of leptin-deficient ob/ob mice. Our findings show that obesity, in the absence of hypertension, is associated with renal dysfunction in mice but not with major renal injury. Alterations to mitochondria that lower cellular ATP levels may be involved in obesity-induced renal injury. The type and severity of mitochondrial and ER dysfunction differs depending upon the presence or absence of leptin.

Sirtuin1 Maintains Actin Cytoskeleton by Deacetylation of Cortactin in Injured Podocytes

Recent studies have highlighted the renoprotective effect of sirtuin1 (SIRT1), a deacetylase that contributes to cellular regulation. However, the pathophysiologic role of SIRT1 in podocytes remains unclear. Here, we investigated the function of SIRT1 in podocytes. We first established podocyte-specific Sirt1 knockout (SIRT1(pod-/-)) mice. We then induced glomerular disease by nephrotoxic serum injection. The increase in urinary albumin excretion and BUN and the severity of glomerular injury were all significantly greater in SIRT1(pod-/-) mice than in wild-type mice. Western blot analysis and immunofluorescence showed a significant decrease in podocyte-specific proteins in SIRT1(pod-/-) mice, and electron microscopy showed marked exacerbation of podocyte injury, including actin cytoskeleton derangement in SIRT1(pod-/-) mice compared with wild-type mice. Protamine sulfate-induced podocyte injury was also exacerbated by podocyte-specific SIRT1 deficiency. In vitro, actin cytoskeleton derangement in H2O2-treated podocytes became prominent when the cells were pretreated with SIRT1 inhibitors. Conversely, this H2O2-induced derangement was ameliorated by SIRT1 activation. Furthermore, SIRT1 activation deacetylated the actin-binding and -polymerizing protein cortactin in the nucleus and facilitated deacetylated cortactin localization in the cytoplasm. Cortactin knockdown or inhibition of the nuclear export of cortactin induced actin cytoskeleton derangement and dissociation of cortactin from F-actin, suggesting the necessity of cytoplasmic cortactin for maintenance of the actin cytoskeleton. Taken together, these findings indicate that SIRT1 protects podocytes and prevents glomerular injury by deacetylating cortactin and thereby, maintaining actin cytoskeleton integrity.

Overexpression of MMP-7 Increases Collagen 1A2 in the Aging Kidney

The percentage of the U.S. population over 65 is rapidly increasing, as is the incidence of chronic kidney disease (CKD). The kidney is susceptible to age-dependent alterations in structure, specifically tubulointerstitial fibrosis that leads to CKD. Matrix metalloproteinases (MMPs) were initially characterized as extracellular matrix (ECM) proteinases; however, it is clear that their biological role is much larger. We have observed increased gene expression of several MMPs in the aging kidney, including MMP-7. MMP-7 overexpression was observed starting at 16 months, with over a 500-fold upregulation in 2-year-old animals. Overexpression of MMP-7 is not observed in age-matched, calorically restricted controls that do not develop fibrosis and renal dysfunction, suggesting a role in the pathogenesis. In order to delineate the contributions of MMP-7 to renal dysfunction, we overexpressed MMP-7 in NRK-52E cells. High-throughput sequencing of the cells revealed that two collagen genes, Col1a2 and Col3a1, were elevated in the MMP-7 overexpressing cells. These two collagen genes were also elevated in aging rat kidneys and temporally correlated with increased MMP-7 expression. Addition of exogenous MMP-7, or conditioned media from MMP-7 overexpressing cells also increased Col1A2 expression. Inhibition of protein kinase A (PKA), src, and MAPK signaling at p38 and ERK was able to attenuate the MMP-7 upregulation of Col1a2. Consistent with this finding, increased phosphorylation of PKA, src, and ERK was seen in MMP-7 overexpressing cells and upon exogenous MMP-7 treatment of NRK-52E cells. These data suggest a novel mechanism by which MMP-7 contributes to the development of fibrosis leading to CKD.

Effects of weight reduction regimens and bariatric surgery on chronic kidney disease in obese patients

Increasing evidence nowadays is showing that obesity by itself, independent of other comorbidities like diabetes and hypertension, is associated with renal functional changes and structural damage. Intentional weight loss demonstrates beneficial reduction in proteinuria and albuminuria in patients with mild to moderate chronic kidney disease, particularly those whose renal damage is likely induced by obesity. The safety of some weight loss interventions, particularly the use of high-protein diets and/or medications, is questionable in this population due to the lack of well-designed randomized controlled studies reporting on their efficacy or harm. Bariatric surgery showed the most promising results with regards to ameliorating glomerular hyperfiltration and albuminuria albeit with a modest risk of increased perioperative complications with advanced stages of chronic kidney disease (CKD).

Mitochondrial autophagy involving renal injury and aging is modulated by caloric intake in aged rat kidneys

BACKGROUND

A high-calorie (HC) diet induces renal injury and promotes aging, and calorie restriction (CR) may ameliorate these responses. However, the effects of long-term HC and CR on renal damage and aging have been not fully determined. Autophagy plays a crucial role in removing protein aggregates and damaged organelles to maintain intracellular homeostasis and function. The role of autophagy in HC-induced renal damage is unknown.

METHODS

We evaluated the expression of LC3/Atg8 as a marker of the autophagosome; p62/SQSTM1; polyubiquitin aggregates as markers of autophagy flux; Ambra1, PINK1, Parkin and Bnip3 as markers of mitophagy; 8-hydroxydeoxyguanosine (8-OHdG) as a marker of DNA oxidative damage; and p16 as a marker of organ aging by western blot and immunohistochemical staining in the kidneys of 24-month-old Fischer 344 rats. We also observed mitochondrial structure and autolysosomes by transmission electron microscopy.

RESULTS

Expression of the autophagosome formation marker LC3/Atg8 and markers of mitochondrial autophagy (mitophagy) were markedly decreased in the kidneys of the HC group, and markedly increased in CR kidneys. p62/SQSTM1 and polyubiquitin aggregates increased in HC kidneys, and decreased in CR kidneys. Transmission electron microscopy demonstrated that HC kidneys showed severe abnormal mitochondrial morphology with fewer autolysosomes, while CR kidneys exhibited normal mitochondrial morphology with numerous autolysosomes. The level of 8-hydroxydeoxyguanosine was increased in HC kidneys and decreased in CR kidneys. Markers of aging, such as p16 and senescence-associated-galactosidase, were increased significantly in the HC group and decreased significantly in the CR group.

CONCLUSION

The study firstly suggests that HC diet inhibits renal autophagy and aggravates renal oxidative damage and aging, while CR enhances renal autophagy and ameliorates oxidative damage and aging in the kidneys.

Obesity and kidney disease: potential mechanisms

Assessment of adiposity should include measurements of both body mass index and waist circumference. The prevalence of obesity, based on a body mass index of 30 kg/m(2) or greater, has increased substantially over the past 2 decades in Western societies. Obesity remains the number one preventable risk factor for chronic kidney disease because obesity largely mediates diabetes and hypertension, the 2 most common etiologies for end-stage kidney disease. However, obesity itself likely has independent effects on renal hemodynamics and individuals with a low number of nephrons are likely to be the most susceptible to these changes. Multiple mechanisms have been postulated whereby obesity directly impacts kidney disease including hyperfiltration, increased glomerular capillary wall tension, and podocyte stress. Weight loss reduces glomerular filtration rate and effective renal plasma flow along with proteinuria, but these changes are most notable after bariatric surgery in adults with morbid obesity. Aside from adiposity itself, the high caloric intake that leads to obesity also may heighten chronic kidney disease risk via the circuitous loop between Sirt1 and adiponectin and podocyte effacement. Sirt1 is a nicotinamide adenine dinucleotide+dependent deacteylase that is up-regulated in the setting of caloric restriction. Sirt1 expression modulates adiponectin levels that in turn appear to influence podocyte effacement. Clinical trials are needed to assess the benefits and risks of intentional weight loss on kidney disease measures and progression.

Dietary patterns, calories, and kidney disease

Specific nutritional factors that mediate obesity or CKD remain very difficult to quantify in any population. That being said, several macronutrients, including protein intake, have been examined as risk factors for CKD progression. Given the correlation of micro- and macronutrients within a particular diet and the consistency of an individual's dietary habits over time for most individuals, dietary patterns may have a greater impact on CKD risk and progression. This review focuses on dietary patterns and their association with CKD. To date, studies examining dietary patterns and CKD risk remain very limited, and more studies are needed. However, the follow-up period may need to be fairly long to detect any association. Caloric intake itself may also affect CKD risk. This may be due to the influence of caloric intake on sirtuin1, which modulates adiponectin gene expression and nitric oxide bioavailability.

Inflammation and oxidative stress in obesity-related glomerulopathy

Obesity-related glomerulopathy is an increasing cause of end-stage renal disease. Obesity has been considered a state of chronic low-grade systemic inflammation and chronic oxidative stress. Augmented inflammation in adipose and kidney tissues promotes the progression of kidney damage in obesity. Adipose tissue, which is accumulated in obesity, is a key endocrine organ that produces multiple biologically active molecules, including leptin, adiponectin, resistin, that affect inflammation, and subsequent deregulation of cell function in renal glomeruli that leads to pathological changes. Oxidative stress is also associated with obesity-related renal diseases and may trigger the initiation or progression of renal damage in obesity. In this paper, we focus on inflammation and oxidative stress in the progression of obesity-related glomerulopathy and possible interventions to prevent kidney injury in obesity.

Structural equation modeling highlights the potential of Kim-1 as a biomarker for chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a major public health problem, and despite continued research in the field, there is still a need to identify both biomarkers of risk and progression, as well as potential therapeutic targets. Structural equation modeling (SEM) is a family of statistical techniques that has been utilized in the fields of sociology and psychology for many years; however, its utilization in the biological sciences is relatively novel. SEM's ability to investigate complex relationships in an efficient, single model could be utilized to understand the progression of CKD, as well as to develop a predictive model to assess kidney status in the patient.

METHODS

Fischer 344 rats were fed either an ad libitum diet or a calorically restricted diet, and a time-course study of kidney structure and function was performed. EQS, a SEM software package, was utilized to generate five CKD models of the Fisher 344 rat and identify relationships between measured variables and estimates of kidney damage and kidney function.

RESULTS

All models identified strong relationships between a biomarker for CKD, kidney injury molecule-1 (Kim-1) and kidney damage, in the Fischer 344 rat CKD model. Models also indicate a strong relationship between age and renal damage and dysfunction.

CONCLUSION

SEM can be used to model CKD and could be useful to examine biomarkers in CKD patients.

Alternate-day fasting reverses the age-associated hypertrophy phenotype in rat heart by influencing the ERK and PI3K signaling pathways

The age-related increased impedance in large arteries overloads the senescent heart, and the myocardial phenotype is hypertrophic. Together with qualitative changes observed in the senile heart, this can be responsible for impaired diastolic function. A restricted diet providing adequate nutrient intake, e.g. alternate-day fasting (ADF), has been shown to extend life-span and decrease incidence and progression of age-associated diseases in laboratory rodents, and to ameliorate some metabolic markers of aging in rhesus monkeys and humans. This study reports an age-related increase of some biological and morphological hypertrophy markers in the rat heart, together with increased plasma BNP, a well known marker of heart failure. The tissue modifications might likely be related to hyper-activation of two of the signaling pathways associated with myocardial pathological hypertrophy: ERK1/2 and PI3Kγ. Increased ERK1/2 activation might be in part related to the disturbance of STAT3, with a consequent decrease of SOCS3. In this context, the down-modulation of ERK1/2 and PI3Kγ signaling, together with the restoration of STAT3 activity and SOCS3 content, both observed with ADF, might help to reduce pathological hypertrophy stimuli and to rescue an important cardioprotective pathway, possibly opening new preventive and therapeutic perspectives in age-related heart failure.

Aging increases oxidative stress and renal expression of oxidant and antioxidant enzymes that are associated with an increased trend in systolic blood pressure

The aim of this study was to investigate whether the effects of aging on oxidative stress markers and expression of major oxidant and antioxidant enzymes associate with impairment of renal function and increases in blood pressure. To explore this, we determined age-associated changes in lipid peroxidation (urinary malondialdehyde), plasma and urinary hydrogen peroxide (H₂O₂) levels, as well as renal H₂O₂ production, and the expression of oxidant and antioxidant enzymes in young (13 weeks) and old (52 weeks) male Wistar Kyoto (WKY) rats. Urinary lipid peroxidation levels and H₂O₂ production by the renal cortex and medulla of old rats were higher than their young counterparts. This was accompanied by overexpression of NADPH oxidase components Nox4 and p22^phox in the renal cortex of old rats. Similarly, expression of superoxide dismutase (SOD) isoforms 2 and 3 and catalase were increased in the renal cortex from old rats. Renal function parameters (creatinine clearance and fractional excretion of sodium), diastolic blood pressure and heart rate were not affected by aging, although slight increases in systolic blood pressure were observed during this 52-week period. It is concluded that overexpression of renal Nox4 and p22^phox and the increases in renal H₂O₂ levels in aged WKY does not associate with renal functional impairment or marked increases in blood pressure. It is hypothesized that lack of oxidative stress-associated effects in aged WKY rats may result from increases in antioxidant defenses that counteract the damaging effects of H₂O₂.

Sirtuins and their relevance to the kidney

Sirtuins (silent information regulator 2 [Sir2] proteins) belong to an ancient family of evolutionary conserved nicotinamide adenine dinucleotide (NAD)(+)-dependent enzymes with deacetylase and/or mono-ADP-ribosyltransferase activity. They regulate DNA repair and recombination, chromosomal stability, and gene transcription, and most importantly mediate the health-promoting effects of caloric restriction (CR), which includes the retardation of aging. At least seven Sir2 homologs, sirtuins (SIRT) 1 to 7 have been identified in mammals. Mammalian SIRT1, the most extensively studied family member, couples protein deacetylation with NAD(+) hydrolysis and links cellular energy and redox state to multiple signaling and survival pathways. Cell-type and context-specific activation of sirtuins increases resistance to metabolic, oxidative, and hypoxic stress in different tissues. In particular, SIRT1 plays a central role in mediating the beneficial effects of CR, and its activation associates with longevity and the attenuation of metabolic disorders. SIRT1 in the kidney is cytoprotective and participates in the regulation of BP and sodium balance. Here, we review sirtuin biology and discuss how CR-triggered sirtuin-dependent pathways affect renal physiology and the pathogenesis of kidney diseases and related disorders.

The effect of calorie restriction on growth and development in silkworm, Bombyx mori

Caloric restriction (CR) is known to extend the life span in different species from yeast to mammals. In this report, a simple organism silkworm (Bombyx mori) was used to study the effect of moderate CR on the growth and development processes of insects. Here we show that an extension of life span upon moderate CR was observed in the silkworm. The total protein level in the 5th instar larvae hemolymph appeared to decline significantly under CR. SDS-PAGE analysis showed that the influence of CR was sex-dependent. The CR effects on female animals were much more significant than on the males. The MALDI-TOF MS study identified 16 proteins that expressed differentially among six groups of the male or female larvae fed at different time frequencies. Four of them, storage protein 1 (SP1), arylphorin (SP2), imaginal disk growth factor (IDGF), and 30-kDa lipoprotein, showed significant differences. It was demonstrated that these four proteins were up-regulated when the larvae were over-fed and down-regulated when the larvae were less-fed.

Neurochemistry, neuropathology, and heredity in SAMP8: a mouse model of senescence

The SAMP8 strain spontaneously develops learning and memory deficits with characteristics of aging, and is a good model for studying the mechanism of cognitive dysfunction with age. Oxidative stress occurs systemically in SAMP8 from early on in life and increases with aging. Neuropathological changes such as the deposition of A beta, hyperphosphorylation of tau, impaired development of dendritic spines, and sponge formation, and neurochemical changes were found in the SAMP8 brain. These changes may be partially mediated by oxidative stress. Oxidative damage is a major factor in neurodegenerative disorders and aging. A decline in the respiratory control ratio suggesting mitochondrial dysfunction was found in the brain of SAMP8. The rise in oxidative stress following mitochondrial dysfunction may trigger neuropathological and neurochemical changes, disrupting the development of neural networks in the brain in SAMP8.

Calpain 10 is required for cell viability and is decreased in the aging kidney

Aging is associated with abnormalities in kidney function, but the exact mechanisms are unknown. We examined calpains 1, 2, and 10 protein levels in kidneys from rats, mice, and humans of various ages and determined whether calpain 10 is required for cell viability. Calpain 10 protein expression decreased in the kidney, but not in the liver, of aging Fischer 344 rats, and this decrease was attenuated with caloric restriction. There was no change in calpains 1 or 2 levels in the kidney or liver in control and caloric-restricted aging rats. Aging mice also exhibited decreased calpain 10 protein levels. Calpain 10 protein and mRNA levels decreased linearly in human kidney samples with age in the absence of changes in calpains 1 or 2. Our laboratory previously found calpain 10 to be expressed in both the cytosol and mitochondria of rabbit renal proximal tubular cells (RPTC). Adenoviral-delivered shRNA to rabbit RPTC decreased mitochondrial calpain 10 expression below detectable levels by 3 days while cytosolic calpain 10 levels remained unchanged at 3 days and decreased to approximately 20% of control by 5 days. Knockdown of mitochondrial calpain 10 resulted in nuclear condensation and cleaved procaspase 3, markers of apoptosis. In summary, mitochondrial calpain 10 is required for cell viability and calpain 10 levels specifically decrease in aging rat, mice, and human kidney tissues when renal function decreases, suggesting that calpain 10 is required for renal function and is a biomarker of the aging kidney.

Effect of drastic weight loss after bariatric surgery on renal parameters in extremely obese patients: long-term follow-up

Obesity is a health problem that is reaching epidemic proportions. Extreme obesity (body mass index [BMI] > or =40 kg/m2) is a type of obesity that usually does not respond to medical treatment, with surgery being the current treatment of choice. Extreme obesity is associated with cardiovascular disease, type 2 diabetes, dyslipidemia, and hypertension. Recently, obesity has been related with high rate of renal lesions, but renal function and renal parameters in extreme obesity scarcely are documented. The objective of this study was to evaluate the effect of weight loss after bariatric surgery (BS) on BP, renal parameters, and renal function in 61 extremely obese (EO) patients after 24 mo of follow-up. A total of 61 EO adults (37 women) were studied prospectively before and 24 mo after surgery. Control subjects were 24 healthy, normal-weight adults (15 women). Anthropometric, BP, and renal parameters were determined. Presurgery weight, BMI, GFR, 24-h proteinuria, and 24-h albuminuria were higher in the EO patients than in control subjects (P < 0.001). All parameters improved at 12 mo after BS. However, during the second year of follow-up, only 24-h albuminuria (P = 0.006) and BMI (P = 0.014) continued to improve. At 24 mo after BS, obesity-related renal alterations considerably improved. This improvement was observed mainly in the first year after surgery, when the majority of weight loss occurred. However, 24-h albuminuria still improves during the second year of follow-up. It is possible that this decrease in 24-h albuminuria is not GFR related but rather is attributable to the persistence of the decrease in BMI and to the improvement of other weight-related metabolic factors.

Endocrine regulation of ageing

Over the past 15 years it has become clear that mutations in genes that regulate endocrine signalling pathways can prolong lifespan. Lifespan can be increased by altered endocrine signalling in a group of cells or a single tissue, which indicates that crosstalk between tissues functions to coordinate ageing of the organism. These endocrine pathways might serve as targets for the manipulation of the ageing process and prevention of age-related diseases.

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.

Caloric restriction increases learning consolidation and facilitates synaptic plasticity through mechanisms dependent on NR2B subunits of the NMDA receptor

One of the main focal points of aging research is the search for treatments that will prevent or ameliorate the learning and memory deficiencies associated with aging. Here we have examined the effects of maintaining mature mice on a long-term intermittent fasting diet (L-IFD). We found that L-IFD enhances learning and consolidation processes. We also assessed the long-term changes in synaptic efficiency in these animals. L-IFD mice showed an increase in low-theta-band oscillations, paired-pulse facilitation, and facilitation of long-term synaptic plasticity in the hippocampus with respect to mice fed ad libitum. In addition, we found an increase in the expression of the NMDA receptor subunit NR2B in some brain areas of L-IFD mice. Specific antagonism of this subunit in the hippocampus reversed the beneficial effects of L-IFD. These data provide a molecular and cellular mechanism by which L-IFD may enhance cognition, ameliorating some aging-associated cognitive deficits.

Low auxotrophy-complementing amino acid concentrations reduce yeast chronological life span

In the yeast Saccharomyces cerevisiae, interventions resembling caloric restriction, either by reduction of glucose or non-essential amino acid content in the medium, prolong life span and retard aging. Here we have examined the role of auxotrophy-complementing amino acid supplementation of S. cerevisiae strains in determining yeast chronological life span and stress resistance. The results obtained from cells cultured in standard amino acid concentrations revealed a reduced final biomass yield and premature aging phenotypes. These included shorter life span and indicators of oxidative stress, together with a G2/M cell cycle arrest and the appearance of a sub-G0/G1 population pointing to the occurrence of a specific cell death programme under starvation of essential amino acids. In order to overcome this starvation, five times higher amino acid concentrations were supplied to the medium as has already been commonly used by few laboratories. Such cultures reached more than five-fold higher final biomass yield in stationary phase and the early aging phenotypes were abrogated. Furthermore, in a long-lived yeast strain lacking TOR1, there was no positive effect of amino acid supplementation on longevity. On the contrary, amino acid supply had a positive effect on chronological life span of RAS2 deleted cells. This study may provide novel insights into the role of essential nutrients and their effect on aging process and raises the warning that the positive effects of caloric restriction on life span maybe restricted to non-essential nutrients. Moreover, the severe consequences on cell physiology, life span and stress resistance induced by essential amino acid imbalances presents a note of caution for those still using standard amino acid concentrations for studies with auxotrophic yeast strains.

Adult-onset calorie restriction delays the accumulation of mitochondrial enzyme abnormalities in aging rat kidney tubular epithelial cells

Adult-onset calorie restriction (A-CR) is an experimental model of life extension and healthy aging less explored, compared with calorie restriction begun at early ages, but one more realistic for human application. We examined the effect of A-CR on the aging rat kidney with respect to common structural age-dependent changes and the accumulation of mitochondrial enzyme abnormalities in tubular epithelial cells. A 40% calorie restriction was initiated in middle-aged rats, before the onset of significant age-related changes in the Fischer x Brown Norway rat kidney. This dietary intervention effectively reduced glomerulosclerosis and tubular atrophy within 6 mo and changed the rate of interstitial fibrosis formation within 1 yr and vascular wall thickening and the expression cytochrome c oxidase (COX)-deficient tubular epithelial cells in 18 mo compared with age-matched ad libitum-fed rats. Our histological approach (histochemical staining for mitochondrial enzyme activity and laser capture microdissection) coupled with mitochondrial DNA (mtDNA) PCR analyses demonstrated that COX-deficient renal tubular epithelial cells accumulated mtDNA deletion mutations and that these cells contained unique, clonally expanded mtDNA deletion mutations. Renal tubular epithelial cells with mitochondrial abnormalities presented cellular characteristics indicative of physiological dysfunction.

Effect of food restriction on the insulin signalling pathway in rat skeletal muscle and adipose tissue

We tried to elucidate the effects of a brief and severe model of food restriction on insulin sensitivity in female rats, focusing on key proteins involved in the insulin signalling pathway in skeletal muscle and adipose tissue after 5, 10 and 15 days of food restriction. Using euglycemic clamp, we detected that food-restricted rats are significantly less sensitive to insulin action than control rats. However, the time of restriction promotes a progressive increase on insulin sensitivity. The analysis of the insulin signalling pathway showed a tissue-specific regulation of several proteins involved in insulin signalling. In skeletal muscle, insulin receptor substrate 1 and Glut4 are up-regulated at the end of the food restriction period, just the opposite of what we found in adipose tissue. In conclusion, a 50% reduction of food intake modulates insulin sensitivity through a tissue-specific regulation of the insulin signalling pathway in the main target tissues for this hormone.

Calorie restriction and SIR2 genes--towards a mechanism

Calorie restriction is the first and most compelling example of life extension in mammals. Much speculation about how CR works has focused on ideas of what causes aging. Since these causes themselves are much disputed, I have instead focused my thinking on lessons from simple model organisms, which have emerged from recent genetic studies. These findings can now be integrated with numerous, elegant studies on CR over the decades, which provide a treasure trove of information about physiological changes that are elicited by this regimen. In this paper, I present data showing that the SIR2 gene is a strong candidate to regulate CR in the simple model organisms, such as yeast and Drosophila. I then summarize what is known about the mammalian Sirt1 as it relates to physiological changes during CR, and discuss how this mechanism may impact on life span, as well as diseases of aging.

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.

Ageing and metabolism: drug discovery opportunities

There has recently been significant progress in our understanding of the mechanisms that regulate ageing, and it has been shown that changes in single genes can dramatically extend lifespan and increase resistance to many diseases. Furthermore, many of these genes belong to evolutionarily conserved pathways that also control energy metabolism. In this review, we describe the shared molecular machinery that regulates ageing and energy metabolism. Although drugs to slow ageing face severe regulatory hurdles, it is likely that an understanding of ageing pathways will help to identify novel drug targets to treat metabolic disorders and other age-related diseases.

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.

Calorie restriction, SIRT1 and metabolism: understanding longevity

Calorie restriction (CR) is the only experimental manipulation that is known to extend the lifespan of a number of organisms including yeast, worms, flies, rodents and perhaps non-human primates. In addition, CR has been shown to reduce the incidence of age-related disorders (for example, diabetes, cancer and cardiovascular disorders) in mammals. The mechanisms through which this occurs have been unclear. CR induces metabolic changes, improves insulin sensitivity and alters neuroendocrine function in animals. In this review, we summarize recent findings that are beginning to clarify the mechanisms by which CR results in longevity and robust health, which might open new avenues of therapy for diseases of ageing.

Calorie restriction--the SIR2 connection

A nutritious diet low in calories improves the health and extends the life span of rodents. Recent studies identified a gene, SIR2, which encodes an NAD-dependent deacetylase and may mediate the effects of calorie restriction. In this review, we discuss SIR2 genes and calorie restriction in the lower organisms yeast and Drosophila. We then describe the physiological changes in mammals during calorie restriction and how they may lead to the observed health benefits. We summarize the roles of mammalian Sirt1 in mediating these changes in tissues and endocrine systems and propose that Sirt1 regulates calorie restriction by sensing low calories and triggering physiological changes linked to health and longevity.

Loss of N-cadherin and alpha-catenin in the proximal tubules of aging male Fischer 344 rats

Aging is associated with a loss of renal reserve, and increased sensitivity to either xenobiotic or physiologic insult. Given the critical role of the cadherin/catenin complex in establishing and maintaining the integrity and polarity of tubular epithelial cells, it was hypothesized that aging was associated with alterations in renal cadherin/catenin complexes. Histological assessment of aged (24 months) kidneys harvested from male Fischer 344 rats demonstrates mild degeneration of proximal tubules, multifocal chronic lymphocytic infiltration, moderate development of protein casts inside tubules, and tubular dilatation or degeneration. Western blot analysis revealed that N-cadherin protein expression is not constant over 24 months. N-cadherin expression increased from 4 to 9 months, with peak levels at 9 and 13 months. A decrease in expression was seen at 19 months and an almost complete loss of expression was seen at 24 months. In contrast, the expression of E- and Ksp-cadherin was constant over 24 months. A loss of alpha-catenin at was seen at 19 and 24 months in the absence of changes in beta-, gamma-, and p120-catenin. This pattern of N-cadherin expression (increase followed by decrease) was confirmed by real-time PCR analysis, which demonstrated a similar pattern as the Western blot, suggesting that the loss of N-cadherin protein was due to decreased gene expression. The loss of N-cadherin was specific for the kidney, as no changes in N-cadherin expression in the liver, brain, or testes were seen during aging. The conclusion that loss of N-cadherin expression is a critical component of the renal dysfunction associated with aging is supported by the finding that caloric restriction attenuates the loss of N-cadherin, as well as the finding that a significant loss of N-cadherin is seen in the kidneys of ZDF x SHHF rats, a genetic model of end-stage renal disease. Cadherin and catenin expression was further analyzed by immunofluorescence. A significant loss of staining of both N-cadherin and alpha-catenin was seen in the proximal tubules of rats at 24 months. Interestingly, this corresponded with delocalization of the alpha-1 subunit of the Na+K+-ATPase, i.e. aberrant staining on cell-cell borders and some indication of apical staining in proximal tubules. Taken together, these data suggest that aging is associated with decreased expression of N-cadherin and alpha-catenin and is associated with a loss of cell polarity.

Is obesity a major cause of chronic kidney disease?

Excess weight gain is a major risk factor for essential hypertension and for end-stage renal disease (ESRD). Obesity raises blood pressure by increasing renal tubular sodium reabsorption, impairing pressure natriuresis, and causing volume expansion because of activation of the sympathetic nervous system and renin-angiotensin system and by physical compression of the kidneys, especially when visceral obesity is present. Obesity also causes renal vasodilation and glomerular hyperfiltration that initially serve as compensatory mechanisms to maintain sodium balance in the face of increased tubular reabsorption. In the long-term, however, these changes, along with the increased systemic arterial pressure, create a hemodynamic burden on the kidneys that causes glomerular injury. With prolonged obesity, there is increasing urinary protein excretion and gradual loss of nephron function that worsens with time and exacerbates hypertension. With the worsening of metabolic disturbances and the development of type II diabetes in some obese patients, kidney disease progresses much more rapidly. Weight reduction is an essential first step in the management of obesity, hypertension, and kidney disease. Special considerations for the obese patient, in addition to adequately controlling the blood pressure, include correction of the metabolic abnormalities and protection of the kidneys from further injury.

Is there a rationale for angiotensin blockade in the management of obesity hypertension?

Obesity, currently affecting >20% of the adult population in most Western countries, is a major risk factor for the development of hypertension. Hypertension in obese patients is, in the majority of instances, further complicated by the concomitant presence of dyslipidemia and insulin resistance. The latter is reflected by derangement of glucose homeostasis, ranging from hyperinsulinemia to frank type 2 diabetes. Hypertension in obese patients is also associated with an increased risk for left ventricular hypertrophy, endothelial dysfunction, renal hyperfiltration, microalbuminuria, and elevated markers of inflammation. Sodium retention, volume expansion, and increased cardiac output are common findings in obese individuals. These changes are largely attributable to increased activity of the sympathetic nervous system and insufficient suppression of the renin-angiotensin system. Recent data show increased expression of angiotensin II-forming enzymes in adipose tissue, and increased activity of the renin-angiotensin system has recently been implicated in the development of insulin resistance and type 2 diabetes. Accordingly, antihypertensive agents that block the renin-angiotensin system might be a beneficial strategy for treatment of obesity-related hypertension. Both angiotensin-converting enzyme inhibitors and angiotensin type-1 receptor blockers have been associated with favorable metabolic properties and end-organ protection in addition to their antihypertensive effects. Data from ongoing large trials will provide an indication of the protective and preventive effects of these treatment strategies while offering insights into the mechanisms linking obesity, hypertension, and other facets of the metabolic syndrome.

Model of nonalcoholic steatohepatitis

BACKGROUND

Obesity and diabetes are frequently associated with nonalcoholic steatohepatitis (NASH), but studies have been hampered by the absence of a suitable experimental model.

OBJECTIVE

Our objective was to create a rat model of NASH.

DESIGN

Sprague-Dawley rats were fed a high-fat, liquid diet (71% of energy from fat, 11% from carbohydrates, 18% from protein) or the standard Lieber-DeCarli diet (35% of energy from fat, 47% from carbohydrates, 18% from protein). The diets were given ad libitum or as two-thirds of the amount consumed ad libitum.

RESULTS

Rats fed the high-fat diet ad libitum for 3 wk developed panlobular steatosis, whereas those fed the standard diet had few fat droplets. Accordingly, total lipid concentrations with the high-fat and standard diets were 129.9 +/- 9.1 ( +/- SEM) and 66.7 +/- 4.6 mg/g liver, respectively (P < 0.001). The high-fat diet caused abnormal mitochondria and mononuclear inflammation, which were accompanied by increased hepatic tumor necrosis factor alpha (TNF-alpha; P < 0.001), TNF-alpha messenger RNA (mRNA) (P < 0.001), collagen type 1, and alpha1(I) procollagen mRNA (P < 0.001). In addition, these rats had increased cytochrome P4502E1 (CYP2E1) mRNA (P < 0.001), which was accompanied by CYP2E1 induction (P < 0.001) and oxidative stress with increased 4-hydroxynonenal (P < 0.001). Plasma insulin was elevated, which reflected insulin resistance, a NASH pathogenic factor. Rats fed a restricted high-fat diet developed only mild steatosis with attenuated biochemical changes, whereas those given a restricted standard diet had normal livers.

CONCLUSION

This rat model reproduces the key features of human NASH and provides a realistic experimental model for elucidating its treatment.

Obesity and hypertension

This article has discussed some of the mechanisms involved in the causal relation between obesity and hypertension. Obesity causes a constellation of maladaptive disorders that individually and synergistically contribute to hypertension, among other cardiovascular morbidities. Well-designed population-based studies are needed to assess the individual contribution of each of these disorders to the development of hypertension. In addition, because the control of obesity may eliminate 48% of the hypertension in whites and 28% in blacks, this article has offered an up-to-date on the management of this problem. It is hoped that this article will help scientists formulate a thorough understanding of obesity hypertension and form the basis for more research in this field, which has a huge impact on human life.

Impact of the obesity epidemic on hypertension and renal disease

Excess weight gain is a major cause of increased blood pressure in most patients with essential hypertension, and also greatly increases the risk for renal disease. Obesity raises blood pressure by increasing renal tubular reabsorption, impairing pressure natriuresis, causing volume expansion due to activation of the sympathetic nervous system and renin-angiotensin system, and by physical compression of the kidneys, especially when visceral obesity is present. The mechanisms of sympathetic nervous system activation in obesity may be due, in part, to hyperleptinemia that stimulates the hypothalamic pro-opiomelanocortin pathway. With prolonged obesity, there may be a gradual loss of nephron function that worsens with time and exacerbates hypertension. Weight reduction is an essential first step in the management of obesity hypertension and renal disease. Special considerations for the obese patient, in addition to adequately controlling the blood pressure, include correction of the metabolic abnormalities and protection of the kidneys from further injury.

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

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