Biomedical subjects
A B Roberts
Publications and source records attributed to A B Roberts.
Biological activity and metabolism of the retinoid axerophthene (vitamin A hydrocarbon).
Biological properties of axerophthene, the hydrocarbon analog of retinol, have been studied both in vitro and in vivo. In tracheal organ culture axerophthene reversed keratinization caused by deficiency of retinoid in the culture medium; its potency was of the same order of magnitude as that of retinyl acetate. Axerophthene supported growth in hamsters fed vitamin A-deficient diets although less effectively than did retinyl acetate. Axerophthene was considerably less toxic than was retinyl acetate when administered repeatedly in high doses to rats. Administration of an equivalent p.o. dose of axerophthene caused much less deposition of retinyl palmitate in the liver than did the same dose of retinyl acetate, while a greater level of total retinoid was found in the mammary gland after administration of axerophthene.
Assay of retinoids in biological samples by reverse-phase high-pressure liquid chromatography.
A separation procedure for retinoids based on reversephase high-pressure liquid chromatography with solvent mixtures of acetonitrile and water is described. The method may be applied to the screening of synthetic retinoids, which have potential for use in the prevention of cancer. It is easily adapted to a variety of biological samples and can be applied to other conventional retinoid assays in liver and plasma, detecting as little as 1 nmol retinyl esters and less than 0.3 nmol retinol per g tissue. The one-step chromatography results in separation and simultaneous determination of many of the synthetic retinoids and all of the natural retinoids, including the retinyl esters that are separated into their major fatty acid components. The method has been applied to the analysis of retinoid levels in the liver and intestine of vitamin A-deficient hamsters following a p.o. dose (0.5 mg/day for 2 days) of retinyl acetate or of a synthetic vitamin A analog and is predictive of the degree to which various synthetic retinoids can be converted to retinol and stored in the liver as retinyl esters. Because of its speed, excellent recoveries, and high resolution, the method offers significant advantages over previous, more lengthy procedures.
Late recurrence of thrombotic thrombocytopenic purpura after splenectomy.
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Synthesis of cyclic AMP and phosphodiesterase in various species of cellular slime molds and its bearing on chemotaxis and differentiation.
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The effect of DPPD on the decarboxylation of retinoic acid in vitro and in vivo.
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Pathways of retinoic acid and retinol metabolism.
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Decarboxylation of retinoic acid in tissue slices from rat kidney and liver.
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Oxidative decarboxylation of retinoic acid in microsomes of rat liver and kidney.
Liver and kidney microsomes have been found to catalyze a rapid decarboxylation of retinoic acid in vitro. The reaction requires NADPH and Fe(2+), and is further stimulated by the presence of pyrophosphate. Thiamine pyrophosphate contained sufficient iron as an impurity to provide strong enhancement of the reaction in the absence of added iron. The decarboxylation could also be shown to occur nonenzymatically in the presence of ascorbate, Fe(2+), and boiled microsomes, but there was little autoxidation resulting in decarboxylation. The reaction was strongly inhibited by chelating agents, N,N'-diphenyl-p-phenylene diamine, phenazine methosulfate, and ferricyanide, and resembled lipid peroxidation in both its cofactor requirements and response to inhibitors. The product of the reaction appeared to lack only the C-15 of the original retinoic acid molecule. It was not retained by diethylaminoethyl cellulose, was more polar than retinoic acid upon silicic acid chromatography, had a lower UV absorption maximum (295 m micro ) than the starting product, and seemed to have an aldehyde group at C-14. The physiological significance of the decarboxylation remains to be assessed, but its rapidity makes it important to in vitro work on retinoic acid.
Pathways of retinol and retinoic acid metabolism in the rat.
1. The metabolism of retinoic acid and retinyl acetate labelled with (14)C in various positions was studied after intravenous injection of physiological amounts of these compounds into retinol-deficient rats. 2. Analysis of the resultant radio-activity in the urine, carbon dioxide and faeces led to a postulation of the existence of three major pathways for the metabolism of these two compounds. 3. Evidence is presented that retinoic acid and retinol are metabolized by either the same or at least similar pathways and that retinol becomes oxidized to the carboxyl state before any degradation of the isoprenoid side chain occurs. 4. It is not possible to decide from these data whether retinoic acid is an intermediate in the retinol pathway. 5. Possible sites for the regulation of retinol metabolism are discussed.
Impact of diabetes mellitus on infrainguinal bypass grafting.
The purpose of this study was to examine the role of diabetes mellitus (DM) in infrainguinal bypass graft outcome. One hundred forty-four patients who underwent 170 infrainguinal bypass grafts from 1990 to 1995 were reviewed retrospectively. Seventy-eight patients (94 bypasses) had DM and were followed for an average of 15.4 months; 13 patients were lost to follow up. The mean age was 68 years; 44 (56.4%) were men. The major indication for intervention was limb salvage for the DM (87/94, 92.6%) and non-DM (56/76, 73.7%) groups. No significant difference was found for perioperative wound complications, hematoma, myocardial infarction, or deep venous thrombosis between the DM and non-DM groups. Early mortalities were three for DM and one for non-DM patients. No significant difference was found between primary patency (p = 0.71), secondary patency (p = 0.32), limb salvage (p = 0.99), and survival (p = 0.72) between DM and non-DM groups. DM patients were more likely to have significant tissue loss (p = 0.009) and a longer hospital stay (p = 0.01). In conclusion, infrainguinal vein bypass grafting can be performed successfully in diabetic patients with comparable patency and limb-salvage rates to those without DM.
Loss of Smad3 modulates wound healing.
TGF-beta plays a central and critical role in tissue repair. The recent identification of TGF-beta signal transduction pathways involving Smad proteins has now made it possible to explore their contribution to the activities of TGF-beta in vivo. Both Smad3 and its closely related homolog Smad2 act as latent nuclear transcriptional activators and mediate intracellular signaling by TGF-betas and activin, each of which regulates cellular functions pivotal to cutaneous wound healing. Mice null for Smad3 (Smad3(ex8/ex8)) survive into adulthood and show accelerated cutaneous wound healing characterized by an increased rate of re-epithelialization and a reduced local inflammatory infiltrate. These data implicate Smad3 in specific pathways of tissue repair and suggest that it could be a target for the development of therapeutic strategies to modulate wound healing.
Autocrine growth factors and cancer.
The ability of cancer cells to produce and to respond to their own growth factors (autocrine secretion) has become a central concept linking oncogene and growth factor research. Oncogenes confer growth factor autonomy on cells not only by coding directly for autocrine peptide growth factors or their receptors, but also by amplifying the mitogenic signals generated by a growth factor at its receptor. Antagonists of positive autocrine growth factors can inhibit growth of cancer cells in experimental animals. Recently identified negative autocrine growth factors might themselves control aberrant cell growth.
Selective inhibition of the anchorage-independent growth of myc-transfected fibroblasts by retinoic acid.
Fischer rat 3T3 (FR3T3) fibroblasts transfected with a cellular myc gene can be induced to grow and form colonies in soft agar by treatment either with epidermal growth factor (EGF) alone or with the combination of platelet-derived growth factor (PDGF) and type-beta transforming growth factor (TGF-beta). We now show that induction of anchorage-independent growth by each of these sets of growth factors involves different cellular pathways which can be distinguished by their sensitivity to retinoic acid. Colony formation induced by the combined action of PDGF and TGF-beta is 100-fold more sensitive to inhibition by retinoic acid than is colony formation induced by treatment of the myc-transfected cells with EGF. Moreover, retinoic acid (10(-8) M) is inhibitory for colony growth whenever TGF-beta is present, regardless of whether the effects of TGF-beta are stimulatory, as occurs in the presence of PDGF, or inhibitory, as found in the presence of EGF.
Human transforming growth factor-alpha causes precocious eyelid opening in newborn mice.
Both murine and human epidermal growth factors (EGFs) are known to cause precocious opening of the eyelids in newborn mice. Another set of peptides that are structurally and functionally homologous to murine and human EGFs are the murine and human type-alpha transforming growth factors (TGF-alpha s), TGF-alpha s have been found in many cancer cells and it has been suggested that their autocrine action may play an important part in malignant transformation. In several in vitro systems murine and human TGF-alpha s are functionally interchangeable with murine and human EGFs. However, the in vivo activity of the TGF-alpha s has not been characterized, as only small amounts of these peptides were available until recently. The cloning of the gene for human TGF-alpha and its expression in Escherichia coli now allow us to demonstrate that human TGF-alpha is as active as murine EGF in promoting eyelid opening in newborn mice. Furthermore, we show in a dose-dependent eyelid opening assay that human EGF is as potent as its murine homologue with respect to this biological property.
Human transforming growth factor-beta complementary DNA sequence and expression in normal and transformed cells.
The partial amino-acid sequence of purified human transforming growth factor-beta (TGF-beta) was used to identify a series of cDNA clones encoding the protein. The cDNA sequence indicates that the 112-amino acid monomeric form of the natural TGF-beta homodimer is derived proteolytically from a much longer precursor polypeptide which may be secreted. TGF-beta messenger RNA is synthesized in various normal and transformed cells.
Wound healing in the fetus. Possible role for inflammatory macrophages and transforming growth factor-beta isoforms.
Macrophages are believed to play a crucial role in wound healing by synthesizing and secreting numerous cytokines. Some of these cytokines, such as transforming growth factor-beta and tumor necrosis factor-alpha, promote fibrosis and repair. We have shown that macrophages are recruited to sterile fetal wounds and have the potential to regulate repair by synthesizing transforming growth factor-beta(1), transforming growth factor-beta(2), and tumor necrosis factor-alpha. Transforming growth factor-beta was present in fetal lamb wounds in higher amounts than in adult sheep wounds. Furthermore, the concentrations and ratios of the transforming growth factor-beta isoforms in wounds that healed without scarring were different from those in wounds that scarred; transforming growth factor-beta(2) was highest in fetal wounds that did not scar and lowest in adult wounds. These data suggest that concentrations of transforming growth factor-beta isoforms rather than total transforming growth factor-beta concentration may be important in the regulation of fibrosis in prenatal and postnatal wound healing.
Transforming growth factor-beta: activity and efficacy in animal models of wound healing.
Of the myriad of growth factors examined for their ability to accelerate or improve tissue repair, none has as broad a spectrum of action as that of TGF-beta. In the 10 years since the first description of its ability to enhance wound healing, tremendous advances have been made in understanding the basis of its action in tissue repair. It is released from activated platelets and can both act on and be secreted by each of the diverse cell types which participate in the healing process. Actions of TGF-beta to stimulate chemotaxis, fibrogenesis, angiogenesis, and autoinduction of its expression are mediated by signalling through a unique set of serine-threonine kinase receptors which distinguish it mechanistically from other growth factors with activities in wound healing. Both topical and systemic administration of TGF-beta have been shown to improve healing in a variety of animal models of both normal and impaired healing at dermal as well as nondermal sites such as bone, intestine, the eye, or the mouth.