Changes in the proteolytic activity of human erythrocyte membrane during red cell aging

Calpain from rat intestinal epithelial cells: age-dependent dynamics during cell differentiation

Micromolar and millimolar Ca(2+)-requiring neutral protease (calpain I and calpain II) along with their endogenous inhibitor calpastatin were isolated and partially purified from the same preparation of rat intestinal epithelial cells. Calpain I and II were partially purified by 1300 and 900-fold with 57 and 53 per cent yield, respectively. The optimum assay conditions revealed pH 7.5, 20 min incubation at 25 degrees C and 0.24% casein substrate for both calpains. The optimum calcium concentration obtained for calpain I and II were 25 microM and 4 mM, respectively. Distribution of rat intestinal epithelial cells calpain I and II along with calpastatin during cell differentiation stages in weanling to senescence age were studied. Calpain I in weanling rats was in an increasing order from villus to crypt regions. Adult rats indicated well expressed consistent calpain I throughout the differentiation stages. Whereas, significant lowering towards crypt region cells were evident in old rats. Calpain II in weanling and adult rats was found to be consistent throughout the differentiation stages. Old animals revealed an increasing trend from villus to crypt region with insignificant activity present in upper villus cells. Concomitantly, different concentrations of calpastatin were observed throughout the differentiation stages in all the age groups. Moreover, the levels of calpains exceeded that of calpastatin in most of the epithelial cell populations during developmental stages. In addition to casein, intestinal epithelial cell membranes were found to be equally good substrates for calpains. Proteolytic susceptibility of weanling, adult and old rat membrane proteins varied significantly all along the ageing process in rats. Simultaneous age-dependent calpastatin response were also evident. Taken together the results obtained provided strong evidence that calpain plays significant role in rat intestinal cell differentiation and ageing process with calpastatin as its specific regulatory protein.

Reduction of the in vitro hemolytic activity of soybean lecithin liposomes by treatment with a block copolymer

The in vitro hemolytic activity of liposomes made of soybean L-alpha-lecithin towards diluted (0.0086 v/v) human erythrocytes was used to investigate the effect of surface coating on the interaction of liposomes with cells. The increase in apparent volume of the block copolymer of ethylene glycol and propylene glycol, Pluronic F-127, in the presence of liposomes supports the hypothesis of either adsorption or penetration of the copolymer at the surface of the liposomes. When the liposomes are pre-incubated with Pluronic F-127, their lytic activity towards fresh erythrocytes is significantly reduced while it remains unchanged towards erythrocytes aged in vitro. It is also found that aging the liposomes has little effect on their lytic activity while aging of the erythrocytes makes them more fragile towards the liposomes. The results are discussed in terms of steric hindrance.

Persistent protein damage despite reduced oxygen radical formation in the aging rat brain

The relation between cerebral oxygen radicals and the aging process was investigated in crude synaptosomal (P2) fractions from rats. The rate of formation of oxygen radicals was measured using the probe 2',7'-dichlorofluorescein diacetate (DCFH-DA), which is de-esterified and subsequently oxidized by oxygen radicals to a fluorescent product 2',7'-dichlorofluorescein (DCF). There was a significant age-dependent decrease in the formation rate of oxygen radicals, observed by decreased formation of DCF. No difference in oxygen radical formation was apparent between age groups following an in vitro challenge with an ascorbate/FeSO4 mixture. This age-dependent decrease in cerebral oxygen radical generation coincided with age-dependent increases in superoxide dismutase. No age-related alterations in lipid order in either the hydrophilic or lipophilic membrane regions were observed using fluorescence polarization analysis. Age-dependent losses in cerebral P2 tryptophan fluorescence (a measure of protein degradation), and increased liberation of [14C]protein fragments into the acid-soluble fraction (a measure of overall proteolytic activity) were observed. Results suggest that aging does not proceed as a result of elevated rates of generation of oxygen radicals, a finding that does not support the proposed free radical theory of aging. The observed age-dependent decrease in the formation of oxygen radicals does not effect membrane lipid order. These findings implicate modifications in proteins and activated protein catabolic pathways as major contributing factors in the normal physiological process of senescence.

Erythrocyte endogenous proteinase activity during blood bank storage

We studied proteolytic alterations of membrane proteins in ghosts derived from human red blood cells, preserved up to 35 days in the liquid state either as whole blood or with additive solution. The study was carried out by performing sodium dodecyl sulfate polyacrylamide gel electrophoresis of stromal proteins from erythrocytes, either previously treated with proteinase inhibitors or previously incubated in conditions promoting proteolysis. To differentiate the effect of erythrocyte from granulocyte proteinases, the investigation was also carried out in leukocyte-free red cell preparations. The results show: (1) the effects of endogenous proteinases on membrane proteins derived from red cells stored under blood bank conditions; (2) a decrease of proteolytic effects in ghosts derived from red cells which have been submitted to a longer storage; (3) a relevant influence of the red cell resuspending medium before lysis on the time-dependent onset and exhaustion of proteolysis in ghosts. The presence of increased proteolysis in ghosts could be regarded as a marker of molecular lesions induced in red cells by storage under blood bank conditions.

Proteolytic activity of human erythrocyte membrane during ghosts preparation

1. Proteins in human erythrocyte membranes after red blood cells hemolysis revealed relatively high rate of self-digestion. 2. This indicates hemolysis as a critical moment for membrane proteases activation. 3. The detailed pattern of band 3 protein and spectrin degradation during ghosts preparation was more complicated and reflected both the changes in proteolytic susceptibility and extraction of some proteases. 4. Further extraction of membrane proteins by alkali stripping resulted in an increase in the self-digestion rate and decrease in the degradation rate of an exogenous substrate.