Age-related changes in the amino acid composition of human glomerular basement membrane

Relationship between hypertension and renal function and its therapeutic implications in the elderly

The kidney is an important target of hypertension-induced organ damage. Recent long-term observation studies have documented that in individuals, without primary chronic renal disease, a very significant relationship exists between hypertension and impaired renal function, elderly hypertensives having a particularly worse prognosis. The hallmark of hypertensive renal injury is thought to be a progressive increase in intrarenal vascular resistance. The alterations in renal hemodynamics are accentuated in elderly patients with essential hypertension, pointing to a greater vulnerability of the senescent kidney to superimposed injury such as high blood pressure. Treatment of elevated blood pressure in the elderly therefore not only reduces cardiovascular morbidity and mortality, but also reduces the incidence of renal failure as a consequence of hypertension-induced damage.

Anatomic and physiologic age changes in the kidney

Cross-sectional studies of renal function in man indicate there is a progressive decline with age after the age of 40 years. The blood vessels, glomeruli, tubules and interstitium are all potential sites of primary involvement in the aging process as well as for renal disease. Regardless of the anatomic structure initially affected, most chronic renal conditions evolve with destruction of the entire nephron. Whether the observed decrease in renal function associated with aging is the result of intervening pathologic processes, e.g. ischemia (vascular obliteration) or infection, or is the result of a more insidious involutional process, it has generated much discussion but few answers. The purpose of this report is to review the descriptive studies documenting the changes in renal morphology and physiology with age and to focus on what is known about the mechanisms involved in these losses of renal substances and function.

[Nonessential amino acid content in early weaned piglets following qualitatively and quantitively different protein supplies]

A total of 60 piglets of German Landrace weaned at the age of 2 weeks were fed ad libitum with isoenergetic diets of different proteins (casein + dried skim milk, soybean protein + dried skim milk, only soybean protein) and different protein levels in the diet (20, 27, 34, 40% in D.M.). After 4 weeks the piglets were homogenized and examined for their content of non essential amino acids in the whole body mass by ion exchange chromatography. On the fresh and dried material the content of the non essential amino acids Asx, Ser, Glx, Pro, Gly and Ala increased with the higher protein contents of the diet. Decreasing protein quality reduced the content of serine, whereas coincidently the concentration of glycine, especially on the protein levels of 20 and 27% in the diet increased. On the contrary the protein quality had no effect on the concentration of Asx, Glx, Pro and Ala. Related to the whole body protein the highest contents of the non essential amino acids, excepting serine, were found in piglets which got few protein of low quality. Influenced by the different protein supply the proportion of glycine to lysine varied from 1.28 to 2.17. The mentioned changes in the amino acid composition of the piglets are mainly discussed as shiftings in the proportion of organs and tissues and their protein composition.

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.

Age-related changes in rat glomerular basement membrane

1. The yield of GBM from rat kidney increased with rat age and the membrane became more collagen-like, as judged by the glycine, hydroxyproline, hydroxylysine content and the degree of glycosylation. 2. GBM became progressively less soluble in sodium dodecyl sulphate (SDS) and 2-mercaptoethanol with age. An increase in the lower molecular weight subunits of membranes prepared from older rats was demonstrated by polyacrylamide gel electrophoresis.

Chemical characterization of glomerular and tubular basement membranes of men of different age

Pairs of glomerular and tubular basement membrane preparations were obtained from kidneys of individuals of premature age up to 80 years. The purity of the preparations was established with light and electron microscopy and by estimating the total phosphorus content. The amino acid and carbohydrate composition was determined and statistically evaluated for 33 to 38 preparations divided over five age groups. Comparison of glomerular and tubular basement membranes from the same kidneys showed that regardless of age glomerular basement membranes contain more 3-hydroxyproline and more of the heteropolysaccharide constituents neuraminic acids and mannose. These differences cannot be ascribed solely to the presence of a minor amount of interstitial collagen. The chemical composition of the two types of basement membranes changes with age. For the first few years after birth the contents of glycine and total imino acids increase and those of collagen-nonspecific amino acids decrease, whereas constituents of the heteropolysaccharide units do not change markedly. These results suggest that proportions of collagenous and noncollagenous peptide moieties gradually change with age in both glomerular and tubular basement membranes. In addition, the extent of hydroxylation of proline and lysine increases significantly with age, reaching an adult level for glomerular basement membranes after 4 to 7 months of age and for tubular basement membranes during late childhood. The contents of glucose and galactose rise with age to an extent comparable with that of hydroxylysine. The age-related changes in basement membrane composition may influence functional properties of these extracellular renal structures.