Age-related changes in rat glomerular basement membrane

Clinical aspects of changes in water and sodium homeostasis in the elderly

The population of elderly individuals is increasing worldwide. With aging, various hormonal and kidney changes occur, both affecting water homeostasis. Aging is a risk factor for chronic kidney disease (CKD) and many features of CKD are reproduced in the aging kidney. Dehydration and hyperosmolarity can be triggered by diminished thirst perception in this population. Elderly with dementia are especially susceptible to abnormalities of their electrolyte and body water homeostasis and should be (re-)assessed for polypharmacy. Hypo- and hypernatremia can be life threatening and should be diagnosed and treated promptly, following current practice guidelines. In severe cases of acute symptomatic hyponatremia, a rapid bolus of 100 to 150 ml of intravenous 3% hypertonic saline is appropriate to avert catastrophic outcomes; for asymptomatic hyponatremia, a very gradual correction is preferred. In summary, the body sodium (Na+) balance is regulated by a complex interplay of environmental and individual factors. In this review, we attempt to provide an overview on this topic, including dehydration, hyponatremia, hypernatremia, age-related kidney changes, water and sodium balance, and age-related changes in the vasopressin and renin-angiotensin-aldosterone system.

A Scavenger Role for Nitric Oxide in the Aged Rat Kidney

Progressive ageing is associated with an increment of biomolecules modified through oxidation as a result of the action of free radicals deriving from reactive oxygen species that attack biomolecules. During ageing many alterations of renal functions have been reported. Renal ageing is associated with a progressive decline of glomerular filtration, renal blood flow and augmented vascular resistance. The kidney is a very important source of inducible nitric oxide synthase (iNOS) in both epithelial and vascular structures. In this study we have investigated mRNA and protein iNOS expression and localization and nitric oxide (NO) production in young and aged rats. An increased expression of iNOS occurs in rat kidney during ageing. In the aged rat, an increase in the values of both iNOS-RNA and iNOS protein was observed through rtPCR and Western blot analysis. The activities of three isoforms of NOS were also seen. In the aged rat kidney the production of NO decreased, due to the reduction of the activities of the three NOS. This suggests that in the aged rat a progressive increase of superoxide anion does not imply an increase in the production of NO which functions as a scavenger molecule, causing oxidative stress with accumulation of reactive oxygen species (ROS).

An active role for basement membrane assembly and modification in tissue sculpting

Basement membranes are a dense, sheet-like form of extracellular matrix (ECM) that underlie epithelia and endothelia, and surround muscle, fat and Schwann cells. Basement membranes separate tissues and protect them from mechanical stress. Although traditionally thought of as a static support structure, a growing body of evidence suggests that dynamic basement membrane deposition and modification instructs coordinated cellular behaviors and acts mechanically to sculpt tissues. In this Commentary, we highlight recent studies that support the idea that far from being a passive matrix, basement membranes play formative roles in shaping tissues.

Fluid and electrolyte homeostasis in the elderly: physiological changes of ageing and clinical consequences

Characteristic of the normal ageing process are changes in the renal, hormonal and thirst regulatory systems involved in the control of sodium and water balance. In the presence of disease or drug use, the ageing changes put the elderly person at increased risk of either sodium retention or loss and of water retention or loss. Clinically, these alterations in water and sodium balance are commonly expressed as either hyponatraemia or hypernatraemia with central nervous system dysfunction as the symptomatic expression. Thus, the impaired homeostasis of the many systems affecting fluid balance in the elderly is readily influenced by many of the disease states and medications which are often present in the elderly with resultant adverse clinical consequences. Awareness of these age-associated circumstances can allow the physician to anticipate the impact of illnesses and drugs and to implement a rational approach to therapeutic intervention and management.

Renal function in aging

A variety of age-related anatomic and functional alterations in the kidney have been described. Anatomic abnormalities in the aging kidney include a decrease in kidney size, increased glomerular sclerosis, altered tubular structure, and an altered pattern of vascular flow. These anatomic abnormalities are associated with renal functional abnormalities, including decreased renal blood flow, and glomerular filtration rate. Altered renal tubular function, including impaired handling of water, sodium, acid, and glucose, may also be present. Impaired "endocrinologic" functioning manifested by changes in the renin-angiotensin system, vitamin D metabolism, and antidiuretic hormone responsiveness have been reported. The kidney is constantly exposed to the effects of a variety of potentially toxic processes. These range from environmental toxins and drugs, to a variety of chronic medical illnesses including hypertension, diabetes, and atherosclerotic disease. In this context, differentiation of "aging" effects from nephrotoxic effects resulting from these other processes is difficult. It has been argued that hypertension is an important factor in the development and progression of renal insufficiency in the elderly. The relationship between hypertension, glomerular hyperfiltration, atherosclerosis, and progressive renal dysfunction needs further study. Further research may allow the rational recommendation of interventions designed to control age-associated changes in renal function.

Effect of age and diabetes on type IV collagen and laminin in human kidney cortex

Specific radioimmunoassays for the 7-S domain of type IV collagen and the fragment P1 of laminin were used to quantify these basement membrane proteins in human kidney cortex at different ages and in some patients with diabetes mellitus. The antigens were solubilized by treating the tissue samples with the proteolytic enzymes collagenase, trypsin and pepsin. Total collagen content (as indicated by hydroxyproline concentration) increased with age, and the proportion of the collagen that could be solubilized by any enzyme treatment decreased. The type IV collagen concentration increased significantly with age, whereas the laminin concentration tended to decrease. In the one case of a type I diabetic the amounts of both antigens exceeded those in the age matched controls. In four type II diabetics the results were comparable with those for other aged cases. The distribution of the proteins was studied using the peroxidase-antiperoxidase method. The staining intensity and thickness of both antigens increased with age in the mesangium and Bowmans capsules, the change in type IV collagen staining being more evident. In diabetic patients these changes were more pronounced and other basement membranes appeared thicker in the stainings. These results indicate that basement membrane material accumulates in the kidney cortex during aging and that an alteration takes place in the composition of the basement membranes, the proportion of type IV collagen increasing and that of laminin decreasing.

Differential solubility of subcomponents of rat glomerular basement membrane

Marked differences were found in the electrophoretic profiles and amino-acid compositions of components prepared from rat glomerular basement membrane (GBM) by a number of different solubilization procedures. Treatment with reducing agent resulted in a simplified electrophoretic pattern which was characterized by the presence of a major collagenous component with a mol.wt. of 150 000. In contrast, detergent solubilized mainly lower-mol.-wt. material which had a more polar amino-acid composition. When both reagents were used together the majority of the basement-membrane material was solubilized within 2 h and components with mol.wts. of 170 000 and 135 000 were predominant in the pro-alpha region of the gel. Treatment for a further 16 h was required to solubilize higher-mol.-wt. material and to achieve maximum solubility of components in the pro-alpha region with mol.wts. of 185 000 and 150 000. These methods provide a means of separating subcomponents of rat GBM while avoiding the problems of degradation inherent in enzymatic procedures.

Chemical composition and solubility of human glomerular and tubular basement membranes of adult and senescent men

The effect of aging on the composition of human renal basement membranes was studied in persons aged 22-90 years. The relative proportion of cortex in kidney appears to decrease with aging. Twenty pairs of GBM and TBM preparations were isolated using the detergent method. Protein content of the basement membrane preparations amounts to about 66% and is independent of type of membrane or age. Amino acid and carbohydrate analyses of both GBM and TBM revealed that the extents of hydroxylation of proline at the C4 position and of lysine decrease with aging. In the case of lysine this occurred from the seventh of life onwards. The decreases are probably not caused by a change of the collagen content. The extent of glycosylation of hydroxylysine is similar for all basement membrane preparations. An adapted protein assay is presented for solutions containing SDS and dithiothreitol. In the presence of these two compounds, solubility of GBM and TBM from adult and aged persons is similar and amounts to about 55 and 85% after 10 and 60 min, respectively, of heating at 95 degrees C. In SDS-polyacrylamide gels, no differences were observed for the major peptide bands between the preparations, irrespective of basement membrane type or age.

Effect of D-penicillamine on glomerular basement membrane, urinary N-acetyl-beta-D-glucosaminidase and protein excretion in rats

The administration of D-penicillamine (450 mg/kg) to young rats resulted in an immediate increase in urinary NAG and volume, as well as mild proteinuria of a predominently low molecular weight type. Doses less than 400 mg/kg failed to alter the urinary profile. Analysis of glomerular basement membrane prepared from rats injected with D-penicillamine (450 mg/kg) failed to show any abnormalities in amino acid and sugar composition. In contrast, glomerular basement membrane prepared from D-penicillamine injected rats was more soluble than membrane prepared from normal rats in SDS and 2-mercaptoethanol. The solubilised components of the membrane were resolved on SDS-polyacrylamide gel electrophoresis. An increase in the low molecular weight, and a concomitant fall in the higher molecular weight components present in the membrane was demonstrated. D-penicillamine therefore affects glomerular basement membrane directly in young rats, possibly by interfering with cross-link formation. These studies may provide a further basis for the study of D-penicillamine toxicity in man.

Age-related changes in non-enzymatic glycosylation of human basement membranes

Age and diabetes-related changes in the extent of non-enzymatic glycosylation of two anatomically distinct human basement membranes were examined. The amount of glucose in ketoamine linkage to glomerular basement membrane, measured by the thiobarbituric acid reaction, correlated positively and significantly with age. For analysis of lens capsule basement membrane, adsorption to agarose-linked phenylboronate was used. The ability of this resin to completely discriminate non-glycosylated from glycosylated residues was first documented by separating synthetic preparations of radioactive glucitol-lysine and glucitol-hydroxylysine, the glucosylamines formed with non-enzymatic glycosylation of collagen, from the respective free amino acids by affinity chromatography on and batch adsorption to phenylboronate. The extent of non-enzymatic glycosylation of lens capsule basement membranes correlated with age in both non-diabetic and diabetic samples, and the slopes of the lines for age versus glycosylation were similar in both groups. The calculated line for diabetic specimens, however, was displaced about 15 years to the left, compatible with premature aging. The results indicate that non-enzymatic glycosylation can be accurately assessed in minute amounts of tissue by phenylboronate adsorption, and provide evidence that human basement membrane is subject to increased glycosylation with aging and diabetes.

Age-related changes in sulfation of basement membrane glycosaminoglycans

Alterations in heparan sulfate, the principal glycosaminoglycan species in glomerular basement membrane, have been proposed as contributory to permeability changes in nephropathic disorders. In the present study, the extent of sulfation of glycosaminoglycans isolated from pronase digests of human glomerular basement membrane, obtained from subjects 15-89 years old, was examined. The sulfate to hexuronic acid ratio significantly diminished as a function of increasing age. These results suggest that decreased sulfation of glycosaminoglycans and consequent reduction in net negative charge alters permselective properties of the glomerular basement membrane with aging.