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Biomedical subjects

G Siegenthaler

Publications and source records attributed to G Siegenthaler.

At least 55 records · Page 3Linked to original sources
PubMed1990

Regulation of metabolism of retinol-binding protein by vitamin A status in children with biliary atresia.

Regulation of retinol-binding protein (RBP) by vitamin A status was studied in 43 children; 25 had biliary atresia and vitamin A deficiency, 15 had biliary atresia treated by vitamin A, and 9 control children had normal liver and vitamin A status. Vitamin A and RBP were assayed and the two forms of RBP, holo-RBP and apo-RBP, were separated in both liver and plasma. No difference in liver RBP concentrations was found between the three groups; apo-RBP was the most abundant form. Plasma RBP concentrations and the ratio of retinol to RBP were lower for vitamin A-deficient than for vitamin A-treated children. Two models could be proposed: 1) a preferential secretion of holo-RBP with variations in RBP catabolism or synthesis in vitamin A-deficient liver and 2) a continuous secretion of RBP by the liver with a rapid clearance of plasma apo-RBP in vitamin A deficiency.

Biliary Atresia↗
PubMed1990

Metabolism of natural retinoids in psoriatic epidermis.

Synthetic retinoids that have distinct therapeutic activity on psoriatic plaques act at least in part through the metabolic pathways of natural retinoids. The metabolism of retinol, retinal, and retinoic acid in human epidermis in general and psoriatic plaques in particular has not been previously analyzed. This appears to be an important issue, because enzymatic formation of retinoic acid from retinol within target cells is thought to be the source of biologically active retinoic acid therein and might be subjected to regulation. We found chat the enzymatic system that transforms (3H)retinol into (3H)retinoic acid is detectable in psoriatic plaques (0.33 +/- 0.07 pmol/h/mg protein) but only in trace amounts in normal epidermis. The activity due to alcohol deshydrogenase seems not to be involved in this process. (3H)retinal was found to be either reduced into retinol or oxidized into retinoic acid, depending on the ratio of NAD to NADH (the oxidized arid reduced nicotinamide-adenine dinucleotide, respectively); the former reaction was higher in psoriatic plaques than in normal epidermis.

Humans↗
PubMed1990

Total removal of craniopharyngiomas. Approaches and long-term results in 144 patients.

The clinical features, perioperative course, and postoperative outcomes of 144 patients who underwent microsurgical resection of craniopharyngioma were reviewed. Overall, 90% of the tumors were completely resected and 7% recurred. Evaluation of those patients who underwent primary resection revealed much better results. The operative techniques and approaches are reviewed in detail. The results of this series suggest that primary total removal of craniopharyngiomas yields the best long-term outcome for the patient. Experience has shown that the larger the tumor the greater will be the damage, both preoperatively and intraoperatively, to vital intracranial structures. Consequently, early diagnosis, at a stage when the tumor is still small, improves the chances of accomplishing complete removal and of achieving good operative results. The early diagnosis of craniopharyngioma, before it can produce devastating neurological defects, continues to be the principal goal of our medical and pediatric colleagues.

Adolescent↗
PubMed1989

Retinoid binding proteins and human skin.

New techniques for the analysis of proteins with specific binding for natural retinoids in human plasma and skin extracts have been developed. Polyacrylamide gel electrophoresis (PAGE), followed by protein blotting with an antiserum specific to retinol-binding protein (RBP), the plasma carrier of retinol, showed that: (1) retinoic acid induced striking conformational changes when bound to RBP, and (2) none of the several synthetic retinoids used in human therapy were found to bind to RBP. This directly confirms and extends previous indirect observations that synthetic retinoids are not delivered to the target organs through RBP. Human skin extracts incubated with either [3H]retinol or [3H]retinoic acid and analyzed by PAGE is a novel technique for the study of cellular retinol-(CRBP) and retinoic acid-(CRABP) binding proteins; it allows one to more specifically analyse these binding proteins and differentiate them from RBP. This technique confirmed and extended our previous observations: (1) CRABP is present in much higher amounts in the epidermis than in the dermis, whereas CRBP is detectable in very low amounts in both tissues, (2) a dramatic increase of CRABP is found in psoriatic plaques and (3) there is an up-modulation of epidermal CRABP during systemic or topical synthetic retinoid therapy. When the ability of some synthetic analogs of retinoic acid to compete with [3H]retinoic acid binding on human skin CRABP was studied, two important observations were made: (1) the analogs that, when given to human subjects were pharmacologically active, were found to be good competitors and vice-versa, (2) no strict correlation was found between the IC50 and the pharmacological potency of the retinoid.

Biological Transport↗
PubMed1989

Localization and characterization of the interleukin 1 immunoreactive pool (IL-1 alpha and beta forms) in normal human epidermis.

A panel of polyclonal antisera and monoclonal antibodies (MoAb) raised against recombinant human interleukin 1 alpha (rh IL-1 alpha) and beta (rh IL-1 beta) was used to localize IL-1 pools within epidermal compartments and to characterize the immunoreactive species. Interleukin 1 alpha and beta immunoreactive species were detected by Western blot analysis only when epidermal extracts were obtained in extraction buffers containing dithiothreitol (DTT), sodium dodecyl sulfate (SDS), or 2 mercaptoethanol. Together with the 31-kD (intracellular precursor molecule) and the 17-kD (mature, secreted form) species, most of the antisera and MoAb reacted with a protein of 52-kD that was not found in several internal organs, and from which a 31-kD form could be released upon reelectrophoresis. Interleukin 1 beta immunoreactivity was consistently found by immunohistology at the level of the stratum granulosum, where IL-1 alpha immunoreactivity, although less consistently, also localized. Several monoclonal antibodies to IL-1 beta reacted intensively and specifically with epidermal basal cells. At the electron microscopical level, IL-1 beta immunoreactivity was detected in the upper layers of the stratum granulosum; it appeared to be membrane associated and suggested an exocytosis process similar to that involving lamellar bodies. These observations 1) confirm the presence of IL-1 species in the normal unstimulated human epidermis, 2) show that both IL-1 alpha and beta are detectable herein, 3) identify 52-kD IL-1 alpha and beta immunoreactive bands that appear special to the epidermis, and 4) suggest a link between epidermal IL-1 and the differentiation process of the keratinocyte.

Antibodies, Monoclonal↗
PubMed1989

Isotretinoin differs from other synthetic retinoids in its modulation of human cellular retinoic acid binding protein (CRABP).

Isotretinoin differs from acitretin and Ro137410 by its striking sebostatic effect in acne after oral, but not topical, administration. The reason for this is not yet understood. Previous studies indicate that cellular retinoic acid binding protein (CRABP) might be implicated in the action of synthetic retinoids. We, therefore, compared the three retinoids for their ability to increase epidermal CRABP levels after systemic and topical treatment. Oral treatment with acitretin and Ro137410 led to a striking increase of epidermal CRABP (from 2.6 +/- 0.9 to 16.2 +/- 2.9, P less than 0.004 and from 2.5 +/- 1.2 to 21.5 +/- 3.4 pmol/mg protein, P less than 0.004, respectively), while isotretinoin failed to induce a comparable rise (3.2 +/- 1.6 before and 3.7 +/- 0.7 pmol/mg protein after treatment), although it displayed in all patients a striking sebostatic effect. After topical application, the increase of CRABP was comparable for all three compounds. The interaction of isotretinoin with the epidermis seems to be different from other synthetic retinoids only after systemic treatment, a finding that parallels clinical observations.

Acitretin↗
PubMed1989

Ligand-specific and non-specific in vivo modulation of human epidermal cellular retinoic acid binding protein (CRABP).

Retinoic acid (RA) is bound intracellularly by a specific, low molecular weight protein (CRABP), that is unrelated to its nuclear receptor and whose function and regulation are still unknown. In the present study we were able to obtain an in vivo modulation of CRABP by different stimuli in one of the major target organs of RA: the human skin. We found increased CRABP after daily application during 4 days of natural or synthetic retinoids (RA, acitretin, isotretinoin, Ro137410, retinol), that have either a high affinity to CRABP or can be transformed into RA. Only Ro150778 with no affinity and no reported transformation had no effect. No macro- or microscopical changes could be observed with any of the tested compounds. Induction of inflammatory and hyperproliferative changes in the skin by topical dithranol treatment, UVB irradiation or scotch tape stripping also induced a significant increase of CRABP 3 days after exposure. Topical diflucortolone showed not only a tendancy to decrease intrinsic CRABP levels, but significantly reduced the retinoid stimulated rise of CRABP. Thus we conclude that the increase of CRABP in a fully differentiated adult tissue seems to be a biological phenomenon following processes of inflammation and proliferation with a lag of several days, while retinoids seem to be able to induce such a rise independently of, or before, the appearance of such processes. Corticosteroids seem to be inhibitors of this reaction. We discuss the hypothesis that CRABP might function as an intracellular 'buffer' in the case of RA overload.

Acitretin↗
PubMed1988

Terminal differentiation in cultured human keratinocytes is associated with increased levels of cellular retinoic acid-binding protein.

The control of normal epithelial cell growth and differentiation by retinoids (vitamin A and its analogs) may involve, at least in part, cellular retinoid-binding proteins. In the present study the levels of cellular retinoic acid (CRABP)- and retinol (CRBP)-binding proteins were measured in cultured normal human epidermal keratinocytes. To this end cells were cultured under either low calcium (nondifferentiating) or normal calcium (differentiating) conditions; in the latter culture the cells were also separated into nondifferentiated, attached cells, and differentiating, shed, cell populations. Two different techniques [gel filtration and polyacrylamide gel electrophoresis (PAGE)] were used, for both the qualitative and the quantitative determinations of retinoid-binding proteins. Gel filtration analysis on Sephadex G75 columns showed the presence of high-molecular-weight binding sites for retinol and retinoic acid in both nondifferentiated and the differentiating keratinocytes; the nature of these binding proteins is unclear. Free CRABP was found in the cytosol of differentiating cells, but was undetectable in nondifferentiated cells. Using a more sensitive PAGE technique, very low levels of CRABP and CRBP could be detected in nondifferentiated keratinocytes. By this technique it was possible to demonstrate very high levels of CRABP only in differentiating keratinocytes; the CRBP levels were found to be very low in differentiating cells and comparable to the amount found in nondifferentiated cells. On the basis of molecular weight determinations by gel exclusion and by electrophoretic mobility, the CRABP and CRBP of cultured keratinocytes were found to be identical to CRBP and CRABP from human epidermis.

Carrier Proteins↗
PubMed1988

Retinoid-binding proteins in human oral mucosa.

Vitamin A affects epithelial differentiation and growth via at least 3 different binding proteins. The specific delivery of extracellular retinol to target cells is performed by plasma retinol-binding protein (RBP) while cellular retinol- and retinoic acid-binding proteins (CRBP and CRABP) are implicated in the cellular action of the 2 natural retinoids. We have studied the levels of these 3 binding proteins by gel filtration and polyacrylamide electrophoresis in human oral mucosa, epithelium and chorion and compared it to those found in keratinizing human epidermis. The levels of CRABP in oral epithelium were markedly higher (about 4 times) than that of epidermis whereas CRBP was in a similar amount in epithelium chorion, dermis and epidermis. RBP with preserved affinity for retinol, was present in the epithelium of oral mucosa whereas only degraded RBP was detected in epidermis. These results suggest (i) a higher specific retinol delivery and (ii) a distinct cellular metabolism of retinoic acid in the oral epithelium as compared with epidermis. Since cornification occurs when keratinocytes are deprived of retinol, it might be that our observations are linked to the absence of cornification in the human oral mucosa. Further, high levels of CRABP in mucosal epithelium might have therapeutical implications because the synthetic retinoids used in human therapy bind to CRABP.

Adolescent↗
PubMed1987

A slab gel electrophoresis technique for measurement of plasma retinol-binding protein, cellular retinol-binding and retinoic-acid-binding proteins in human skin.

At least four different proteins that bind retinoids could be present in a vitamin A target tissue like the skin. In order to separate cellular retinoid-binding proteins (CRBP and CRABP) from serum retinol-binding protein (RBP) and albumin, a one-step procedure was devised. The technique is based on slab polyacrylamide gel electrophoresis (PAGE) of the extracted proteins incubated with tritiated retinoids. The procedure was used to study binding proteins in the skin. The results show that epidermal extracts (the epithelial part of the skin) contain no RBP activities whereas dermal extracts (the mesenchymal part of the skin) contain 1.6 +/- 0.81 pmol/mg protein of RBP. This technique further showed higher levels of CRABP in both epidermal (9.05 +/- 1.16 pmol/mg protein) and dermal (1.5 +/- 0.54 pmol/mg protein) extracts than those previously determined by other less specific techniques. On the other hand CRBP levels were found to be lower in the two tissues (epidermis 0.2 +/- 0.1 pmol/mg and dermis 0.12 +/- 0.05 pmol/mg protein). New conditions to measure specifically CRABP with the charcoal/dextran technique could be developed and analyzed by the PAGE technique; a dissociation constant of 13.7 nM was then calculated for epidermal CRABP. This PAGE technique appears to be the most appropriate method for the study of retinoid-binding proteins including RBP in human skin.

Carrier Proteins↗
PubMed1987

Retinol-binding protein in human serum: conformational changes induced by retinoic acid binding.

Polyacrylamide gel electrophoresis and isoelectrofocusing followed by immunoblotting technique with an anti-human retinol-binding protein (RBP) serum were used to study holo-RBP and apo-RBP in human plasma. Three observations were made the technique allowed for the first time to directly and quantitatively analyse holo- and apo-RBP. Holo-RBP represented 97.86 +/- 0.78% and apo-RBP 1.94 +/- 0.73% of the total RBP. All-trans-retinoic acid (RA) was found to bind to apo-RBP and to significantly modify the tertiary structure of the protein; this raises the question of RBP involvement in the transport of RA. reconstitution of holo-RBP using apo-RBP from delipidized serum was achieved only after its incubation with natural all-trans-retinoids such as retinol, 3-dehydroretinol and retinoic acid but not with synthetic analogs of retinoic acid (13-cis-retinoic acid, TMMP, 13-cis-TMMP, TTNPB). It appears that RBP has a structure specificity for natural retinoids.

Apoproteins↗
PubMed1987

A receptor binding assay for endoxin in human urine.

Endoxin is an endogenous substance known to participate in the regulation of the sodium balance and hypertension. Its chemical nature remains elusive. Based on its capacity to specifically bind to Na-K ATPase receptors we describe a receptor assay for its measurement in human urine. The endoxin was extracted by methanol and desalted on a silicagel column with a mixture of chloroform-ethanol. Calibration curves have been established by the transformation of the weight of crude extract in actual content of active material expressed in nmol/l as calculated from Scatchard plots analysis. Normal values are given for subjects on regular salt diet. Changes in endoxin urinary elimination after an oral salt load are outlined.

Binding, Competitive↗
PubMed1987

Loss of retinol-binding properties for plasma retinol-binding protein in normal human epidermis.

Terminal differentiation of the keratinocytes (cornification) has been linked to a restricted supply of retinol. Retinol is distributed to target cells by the retinol-binding protein (RBP), which circulates in the plasma in complex with transthyretin (TTR). In this study we have addressed the question of retinol delivery to the epidermis via RBP. Retinol radiobinding assays, affinity chromatography with TTR coupled to Sepharose beads, polyacrylamide gel electrophoresis, and immunoblotting techniques were used to show that epidermal extracts contain retinol binding sites with no affinity for TTR. Immunoreactive RBP was detected in the epidermal extracts. The RBP in the epidermis was in the apoform (without retinol) in contrast to serum where the majority of RBP is in the holoform (with retinol). Epidermal RBP was converted in vitro into the holoform only after addition of 20 times more retinol, which was needed to reconstitute holoforms of RBP in dermal extracts, human buccal mucosal extracts, and delipidized normal serum or purified delipidized RBP. Moreover, several immunoreactive RBP bands (possibly degradation products) were identified in the epidermal but not in dermal extracts. Retinol-binding protein from nonkeratinizing human oral mucosa showed different immunoblotting patterns when compared to epidermal RBP. These results suggest that degradation of RBP within the epidermis may result in a decreased retinol supply to the keratinocytes, and may lead to the cornification of the epidermis.

Binding Sites↗
PubMed1987

Human skin retinoid-binding proteins and therapy with synthetic retinoids: a still unexplained link.

Human skin contains several proteins that could bind retinoids. One is the retinol-binding protein (RBP, the plasma carrier of natural vitamin A, retinol, which was found to also bind retinoic acid (RA) in vitro. A polyacrylamide gel electrophoresis technique followed by protein immunoblot analysis with an antiserum specific against RBP was developed. This technique allowed us to study the binding of several natural and synthetic retinoids to the plasma RBP; it was found that only natural retinoids bind to RBP in vitro; RA binding was found to induce major conformational changes in the protein. The technique was then used for the study of RBP in human epidermal and dermal extracts; this showed that RBP degradation with loss of binding properties for retinol occurred within the epidermis. A polyacrylamide gel electrophoresis binding assay was developed for studying cellular retinol-(CRABP) and retinoic acid-(CRABP) binding protein in human skin cytosolic extracts. CRABP was (1) found at much higher levels in normal epidermis than in the dermis (2); dramatically elevated in psoriatic plaques and in some retinoid-responsive dermatoses, and (3) up-modulated by both topical and systemic administration of natural and synthetic retinoids. Such alterations were not observed for CRBP. From these and other observations presented here, it appears that CRABP should be one of the first candidates to be carefully analyzed in the search of the cellular receptor for the mediation of the synthetic retinoids pharmacological effects.

Benzoates↗