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Biomedical subjects

F X Maquart

Publications and source records attributed to F X Maquart.

At least 73 records · Page 4Linked to original sources
PubMed1989

Does oxygen free radical increased formation explain long term complications of diabetes mellitus?

Oxygen free radicals (OFR) can form by reaction of glycated proteins with molecular oxygen. We hypothesize that this mechanism operates in tissues of diabetic patients when their content of glycated proteins is significantly increased. OFR are harmful to polyunsaturated fatty acids of lipid membranes, proteins, sugars and DNA. The most significant complications of diabetes, for example polyneuritis, retinopathy, microangiopathy, perforating ulcers, impaired healing, may depend on the excessive production of OFR by glycated proteins. Clues to these effects may be deduced from the decrease of glutathione stores in red blood cells, and the increases of lipid peroxidation and malondialdehyde formation, all of which have been documented to occur in the course of diabetes mellitus.

Diabetes Complications↗
PubMed1988

Stimulation of collagen synthesis in fibroblast cultures by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+.

Glycyl-L-histidyl-L-lysine (GHK) is a tripeptide with affinity for copper(II) ions and was isolated from human plasma. This peptide appears to play a physiological role in wound healing. We report the stimulating effect of GHK-Cu on collagen synthesis by fibroblasts. The stimulation began between 10(-12) and 10(-11) M, maximized at 10(-9) M, and was independent of any change in cell number. The presence of a GHK triplet in the alpha 2(I) chain of type I collagen suggests that the tripeptide might be liberated by proteases at the site of a wound and exert in situ healing effects.

Cells, Cultured↗
PubMed1986

Fibronectin dependence of the contraction of collagen lattices by human skin fibroblasts.

The role of fibronectin in the contraction of collagen lattices by human skin fibroblasts has been investigated. Incubation of lattice cultures in Dulbecco's modified Eagle's medium supplemented with increasing concentrations of non-dialysed or dialysed fetal calf serum demonstrated that the rate of contraction was dependent on non-dialysable serum components. The suppression of contraction observed when fibronectin was eliminated from serum, either by affinity chromatography on gelatin-agarose columns or by precipitation with anti-fibronectin antibodies, showed that fibronectin is critical for the contraction. When collagen lattices were incubated in a serum-free culture medium totally devoid of fibronectin, no contraction occurred. When fibronectin was added to this medium, their contraction was correlated with the concentration of fibronectin added. The contraction was inhibited by cycloheximide, tunicamycin, and monensin. These results demonstrate that the contraction of collagen lattices by human skin fibroblasts is dependent on fibronectin, and that other protein factors synthesized by the cells or contained in serum are also necessary.

Blood↗
PubMed1986

[Increased retraction of collagen lattices by fibroblasts from patients with scleroderma].

Skin fibroblasts from eight scleroderma patients were seeded in collagen lattices, and their capacity of retraction was compared to that of fibroblasts from normal volunteers. In all cases, pathological fibroblasts retracted collagen lattices earlier and more intensively than controls. This in vitro feature may be related to the cutaneous retraction which characterizes scleroderma lesions in vivo.

Adult↗
PubMed1985

Inhibition of collagen production in scleroderma fibroblast cultures by a connective tissue glycoprotein extracted from normal dermis.

It was shown in a previous paper that a connective tissue glycoprotein (CTGP) extracted from normal rabbit dermis was able to inhibit total protein and collagen syntheses by normal dermis fibroblast cultures. In the present study, the effects of CTGP on scleroderma fibroblasts were investigated. [14C]Proline incorporation into total proteins of the supernatant was not significantly different from that found in controls. By contrast, the amount of collagen, expressed as percentage of total secreted protein, was far higher in scleroderma cultures than in normal ones (14.4% +/- 6.0% vs 4.6% +/- 0.9%). Addition of CTGP to the medium induced a concentration-dependent inhibition of [14C]proline incorporation into proteins from both control and scleroderma cells. In control cultures, no significant decrease of the percentage of collagen was observed, but over 60 micrograms/ml, both cytotoxic effects and inhibition of protein synthesis occurred. In scleroderma cultures, the inhibition was twice as effective on collagen as on noncollagen protein synthesis. The inhibition of collagen secretion was not related either to changes in collagen hydroxylation or to the intracellular catabolism of newly synthesized procollagen.

Animals↗
PubMed1984

A glucose transfer from membrane glycoconjugates to haemoglobin in isolated young red blood cells: another biosynthetic way for glycosylated haemoglobins.

Human red blood cells (RBC) are separated by centrifugation into young and old ones, as demonstrated by lower enzymatic activities and lower potassium content of the older ones. The young RBC fraction represents 5% of total RBC. After incubation for 24 h in a neutral buffer, the young RBC HbA1c content increases significantly from 4.2 to 5.2% of total Hb. No increase is found in the case of old RBC. When young RBC have been extracted for 1 h by a neutral buffer prior to incubation, there is no more increase of HbA1c. The extract contains a glycoconjugate that is both soluble in neutral buffers and in chloroform. A glycolipid extractable from the young RBC membrane contributes to HbA1c formation but disappears from old RBC, in which glycosylation by free glucose occurs. These processes are stereospecific.

Blood Glucose↗
PubMed1984

[Hormonal control of the metabolism of collagen].

This paper summarizes the results of hormonal studies applying to collagen metabolism that were published during the last 10 years. This general review demonstrates that most of the hormones, when they act on this metabolism, either decrease the amount of synthesized collagen or increase its catabolism. This effect is demonstrated on whole living animals, in isolated organs, in pathological cases such as corticosteroid induced osteoporosis, and more directly in cell cultures. At physiological levels, some of the effects may be slight or biphasic but at pharmacological levels glucocorticoids and estrogens are strongly inhibiting. These inhibiting effects may be ascribed to various stages of collagen biosynthesis: transcription of the genes, translation of mRNA, post-translational reactions, that are particularly developed in the case of collagen and particularly sensitive to the hormone action. Intracellular degradation of collagen represents an important way of control for this biosynthesis and is noticeably activated by the system of cAMP and some prostaglandins. Finally, collagenases acting on the extracellular fibrils are stimulated by several groups of hormones such as thyroid hormone, testosterone, parathyroid hormone. This increase in catabolism acts in the sense of a fast decrease in the amount of collagen, confirming that most of the hormonal systems are aimed at decreasing both the synthesis of new collagen and the number of mature fibers existing in a given connective tissue. On the other hand, many growth factors and several hormones such as insulin and somatomedins are able to activate the mitoses in the cells that are know to produce collagen, and for this reason, indirectly stimulate the synthesis of this fibrous protein. It is of interest to point out that every time the organism needs depositing more collagen in any zone of the extracellular matrix, it has to send mobile cells from other tissues or to activate the divisions of the cells already present in the concerned tissue. This process is particularly conspicuous in the case of inflamed tissues. It is proposed as a general rule that decreases in the collagen amounts may be triggered by very fast hormonal mechanisms acting both to stop biosynthesis and to activate degradation, whereas the increase in collagen layering depends on indirect and slow mechanisms in which cell divisions represent the first event.

Animals↗
PubMed1984

[Methods of biochemical diagnosis of connective tissue involvement in diabetes].

During the course of diabetes mellitus, several lines of evidence demonstrate that connective matrix is involved. This relationship is still ambiguous and the biological techniques of study are more related to research than to routine. Skin biopsy followed by cultivation of the fibroblasts permits to demonstrate that the diabetic cells divide more slowly than the normal ones. The collagens of the diabetic patients do not seem to be modified according to any genetical abnormality. The evaluation of serum collagens and procollagens by radioimmunological techniques recently showed that the type IV collagen, which derivates from basement membranes, should be in increased amount. In the case of experimental diabetes, in animals, the skin collagen concentration is decreased whereas the amount of intermediate degradation products increases. The method of skin collagen evaluation is not used for clinical purposes and the degradation products found in human diabetic urine are not in increased amounts. The thickening of basement membrane is a well established phenomenon in the diabetes mellitus patients, but the chemical nature of the lesions is not well understood. A non-enzymatic hyperglycosylation of collagen and the other molecules of the basement membrane is possible but does not explain completely this thickening on a quantitative basis, inasmuch that hemoglobin glycosylation, that serves as a model for all the nonenzymatic glycosylations, is presently under discussion as regards its mechanism and seems more complicated than previously suggested.(ABSTRACT TRUNCATED AT 250 WORDS)

Basement Membrane↗
PubMed1983

[Effect of somatomedin A and its serum cofactor on human fibroblasts in culture. Relation between mitogenic activity and effects on the biosynthesis of collagen and other proteins].

It was demonstrated in a previous paper that the sulfation activity of somatomedin A (SM-A) depends on the presence of a low molecular weight cofactor (CoF) present in human serum. In this paper, the effects of the two factors on human dermis fibroblast proliferation and syntheses of proteins and collagen were studied. The addition of SM-A alone to the culture medium had no mitogenic effect but modified the distribution of newly synthesized proteins, since 14C-proline incorporation was increased into proteins of the cell layer and decreased into proteins of the medium. The addition of CoF alone had no significant effect. Simultaneous addition of SM-A and CoF restarted cell divisions and increased the inhibiting activity of SM-A on the secretion of proteins into cell supernatant.

Cell Cycle↗
PubMed1982

A glucose-containing fraction extracted from the young erythrocyte membrane is capable of transferring glucose to hemoglobin in vitro.

Red blood cell (RBC) membranes are rich in a glycoconjugate that is extractable in chloroform/methanol solutions (2/1, v/v) and contains several hexoses, such as glucose. Old and young RBC are separated and their respective glycoconjugates are prepared. HbA0 is purified by column chromatography and incubated with solutions of this conjugate. After 24-h incubation, Hb is dialyzed and the amount of glycosylated Hb is measured by a method of column chromatography adapted from Trivelli. A very significant amount of HBAlc is formed when young RBC extracts are incubated: 3.6% of total Hb becomes HBAlc with the extracts, versus 3.2% with free glucose, and only 2.5% for controls. No increase in HbAlc is obtained when extracts of old RBC are incubated. Another difference between the action of the glycoconjugate and free glucose is that the former induces the increase of only the HBAlc fraction, whereas glucose induces the increase of all the minor Hb fractions. The evaluation of glucose contained in the conjugate before and after the glycosylation reaction demonstrates that it is due to an exchange of glucose units from the conjugate to Hb. The reaction is stereospecifically inhibited by p-nitrophenyl-beta-D-glucoside. The nature of the formed HbAlc is demonstrated by isoelectric focusing. A slight increase of HbAlc observed in the incubated controls may be due to an internal migration of some residues of glucose primitively bound to lysyl residues in an unstable form and also to some degree of denaturation during the incubation.

Erythrocyte Membrane↗
PubMed1982

[Glycosylated hemoglobin and diabetes mellitus].

Properly estimated glycosylated hemoglobin A1c (HbA1c) is a good objective indicator of diabetic control over the previous eight weeks. It is essential to eliminate the labile fraction (pre-HbA1c). A valuable tool in diabetes research, prospectives studies using this index will permit clarification of the relationships between the complications of diabetes and chronic hyperglycemia. Glycosylation of hemoglobin is an example of a reaction secondary to hyperglycemia which can also occur with numerous circulating or tissue proteins. This may explain pathogenesis of some diabetic complications. Its value as a prognostic indicator depends critically upon methodology and this report summarises the current'state of the art in this respect.

Chromatography, Ion Exchange↗