Oxygen-18 studies on the conversion of proline to collagen hydroxyproline

Fluorinated methacrylamide chitosan hydrogel dressings enhance healing in an acute porcine wound model

Wound healing involves multiple interrelated processes required to lead to successful healing outcomes. Phagocytosis, inflammation, cell proliferation, angiogenesis, energy production, and collagen synthesis are all directly or indirectly dependent on oxygen. Along with other critical factors, such as nutrition and comorbidities, availability of oxygen is a key determinant of healing success. Previously, we have presented a novel oxygenated hydrogel material that can be made into dressings for continuous localized oxygen delivery to wounds. In this study, an acute porcine wound model was used to test the healing benefits of these oxygenated MACF (MACF + O₂) hydrogel dressings compared to controls, which included commercial Derma-Gel^TM hydrogel dressings. Wound closure and histological analyses were performed to assess re-epithelialization, collagen synthesis, angiogenesis, and keratinocyte maturation. Results from these assays revealed that wounds treated with MACF + O₂ hydrogel dressings closed faster as compared to Derma-Gel (p<0.05). Targeted metabolomics via liquid chromatography separation and mass spectrometric detection (LC-MS/MS) and a biochemical assay determined the concentration of hydroxyproline in wound samples at days 14 and 21, showing that MACF + O₂ hydrogel dressings improved wound healing via an upregulated collagen synthesis pathway as compared to Derma-Gel (p<0.05). Histological evidence showed that MACF + O₂ hydrogel dressings improve new blood vessel formation and keratinocyte maturation over all other treatments.

Oxygen and animal evolution: did a rise of atmospheric oxygen "trigger" the origin of animals?

Recent studies challenge the classical view that the origin of animal life was primarily controlled by atmospheric oxygen levels. For example, some modern sponges, representing early-branching animals, can live under 200 times less oxygen than currently present in the atmosphere - levels commonly thought to have been maintained prior to their origination. Furthermore, it is increasingly argued that the earliest animals, which likely lived in low oxygen environments, played an active role in constructing the well-oxygenated conditions typical of the modern oceans. Therefore, while oxygen is still relevant to understanding early animal evolution, the relationships between the two might be less straightforward than previously thought.

Oxygen-18 tracer studies of enzyme reactions with radical/cation diagnostic probes

This review considers reactions of enzymes with the cyclopropanoid radical/cation diagnostic probes norcarane, 1,1-dimethylcyclopropane, and 1,1-diethylcyclopropane as elaborated by the use of 18O2 and 18OH2 to trace the origin of O-atoms incorporated during catalysis. The reactions of soluble and integral membrane diiron enzymes are summarized and compared to results obtained from cytochrome P450 studies. Norcarane proved to be an excellent substrate for the diiron enzyme toluene 4-monooxygenase and its engineered isoforms, with kcat and coupling between NADH utilization and total hydroxylated products comparable to that determined for toluene, the natural substrate. Results obtained with toluene 4-monooxygenase show that the un-rearranged and radical-rearranged alcohol products have a high percentage of O-atom incorporation (>80-95%) from O2, while the cation-derived ring-expansion products have O-atom incorporation primarily derived from solvent water. Mechanistic possibilities accounting for this difference are discussed.

The effect of pulsed expansion of subfascially placed expanders on the extent and duration of mitosis in the capsule and rat integument

This study investigated the mitotic activity in the subdermally induced capsule and the epithelium surrounding tissue expanders maintained by pulsed expansions. Tissue expanders were placed into the fascial plane beneath the panniculus muscle of the rat and expanded sequentially. The volume in the expander was rapidly increased to a constant level and maintained for 48 hours; this was followed by a total decrease of volume for 48 hours. The procedure was repeated with volumes of 20, 30, and 40 mL. At the conclusion of each cycle of expander inflation, a group of rats was killed, and biopsy specimens of the induced capsule and epithelium were obtained. The developing capsule exhibited a significant increase in the mitotic index in the layers adjacent to the expander. The highest mitotic index was obtained with an inflation of 30 mL. These observations suggest that cellular proliferation, growth, and development of the extracellular matrix in the induced subdermal capsule can be sustained by pulsed volume changes in the expander.

Gas chromatography-mass spectrometry determination of 18O2 in 18O-labelled 4-hydroxyproline for measurement of collagen synthesis and intracellular degradation

The use of gas chromatography-mass spectrometry (GC-MS) and 18O2, a stable isotope which is incorporated into collagen during the post-translational conversion of proline to hydroxyproline, offers the potential advantages of high levels of sensitivity and specificity as compared to other techniques for measuring rates of collagen synthesis and degradation in vitro and vivo. Trifluoracetylation and methanol esterification of hydroxyproline yields two derivatives of hydroxyproline: N,O-trifluoroacetyl methyl 4-hydroxy-L-proline (N,O-TFA-Hyp) and N-trifluoroacetyl methyl 4-hydroxy-L-proline (N-TFA-Hyp). In the past, N-TFA-Hyp, which yields the 16O/18O-containing m/z 182/184 ion pair [M-COOH3]+ when analyzed by electron impact ionization GC-MS, has been proposed for analysis of 18O-enriched collagen. Although N,O-TFA-Hyp can be converted to N-TFA-Hyp by solvolysis, we find that this leads to degradation of the chromatography in GC-MS and demonstrate here that this extra chemical step is unnecessary if the m/z 278/280 ion pair (representing the [M-COOCH3]+. fragment) is measured by selected ion monitoring. By labelling fibroblasts in culture with 18O2, a sample of isotope-enriched collagen was obtained which was used to calibrate the GC-MS over the range 0.5-49% atom percent enrichment (APE). The greater sensitivity of 18O2 versus [15N]proline for labelling newly synthesized collagen was demonstrated by the finding of a ten-fold higher enrichment in the former isotope when administered to cell cultures at the same precursor APE. Thus, the approach described herein permits the determination of total hydroxyproline and APE on the same sample avoiding additional processing steps while maintaining the quality of chromatography and the sensitivity of detection. Measurement of absolute rates of both collagen synthesis and intracellular degradation of newly synthesized collagen in cell cultures is thus possible. Preliminary results comparing collagen metabolism in pairs of fibroblasts from hypertrophic scars and normal skin in post-burn patients are presented.

The influence of different levels of PEEP on peripheral tissue perfusion measured by subcutaneous and transcutaneous oxygen tension

OBJECTIVE

To compare subcutaneous (PscO2) and transcutaneous (PtcO2) oxygen tension measurements in relation to hemodynamic variables at different levels of PEEP, and to evaluate the usefulness of these measurements as monitors of peripheral tissue perfusion.

DESIGN

Prospective trial.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Seven patients with gastric cancer who where undergoing total gastrectomy.

INTERVENTIONS

Silicone catheter was placed in the upper arm and transcutaneous oxygen monitor was placed on the upper part of the chest. A pulmonary artery catheter was placed in the right pulmonary artery.

MEASUREMENTS AND RESULTS

PscO2 and PtcO2 together with hemodynamic variables were measured at different levels of PEEP. Progressive increase of PEEP reduced cardiac index (CI) (p < 0.05) with a concomitant decrease of PscO2 (p < 0.05) and oxygen delivery (DO2) (p < 0.05). Changes in PtcO2 paralleled changes in arterial oxygen tension (PaO2), but no correlation was found between PtcO2, CI and DO2.

CONCLUSION

PscO2 is a sensitive indicator of subcutaneous tissue perfusion, which can be used to identify the PEEP level, with optimum peripheral perfusion. PscO2 seems to be a more reliable indicator of tissue perfusion than PtcO2.

The source of oxygen in the reaction catalysed by collagen lysyl hydroxylase

The synthetic peptides (Pro-Pro-Gly)5 and (Ile-Lys-Gly)5-Phe were hydroxylated with collagen prolyl hydroxylase and lysyl hydroxylase in an 18O2 atmosphere. The oxygen atoms in the hydroxy groups of hydroxyproline and hydroxylysine were 87% and 6.5% respectively derived from the atmospheric 18O2. The results are consistent with those reported previously for proline hydroxylation in vivo [Fujimoto & Tamiya (1962) Biochem. J. 84, 333-335; Prockop, Kaplan & Udenfriend (1962) Biochem. Biophys. Res. Commun. 9, 192-196; Fujimoto & Tamiya (1963) Biochem. Biophys. Res. Commun. 10, 498-501; Prockop, Kaplan & Udenfriend (1963) Arch. Biochem. Biophys. 101, 499-503] and in vitro [Cardinale, Rhoads & Udenfriend (1971) Biochem. Biophys. Res. Commun. 43, 537-543] and for lysine hydroxylation in vivo [Fujimoto & Tamiya (1963) Biochem. Biophys. Res. Commun. 10, 498-501]. In view of the similarities of these two oxygenase-type hydroxylation reactions the participation of intermediates is proposed, the oxygen atoms of which are exchangeable with those of water. The atmospheric oxygen atoms incorporated into the intermediate must be equilibrated with water oxygen atoms in the slower lysyl hydroxylase reaction.

Lactate dehydrogenase isoenzymes in macrophages and serum during the development of pulmonary silicosis in the rat

The lactate dehydrogenase (LDH) isoenzyme pattern in macrophages (peritoneal and alveolar) in the rat was studied on polyacrylamide gel electrophoresis. Further, the release of LDH isoenzymes from cultured macrophages exposed to silica dust and also the pattern of serum LDH isoenzymes in silica exposed animals were investigated. The isoenzyme pattern of the alveolar macrophages showed all the five bands, contrary to peritoneal macrophages in which two bands, viz. LDH1 and LDH2, were missing. Silica-exposed macrophages liberated LDH5 in the supernatant culture medium. This LDH isoenzyme also increased in the serum of silicotic rats during the early stages of the development of the disease.

Inhibition of lysyl hydroxylase by catechol analogs

Catechol analogs inhibit the activity of lysyl hydroxylase (peptidyllysine, 2-oxyglutarate: oxygen 5-oxidoreductase, EC 1.14.11.4), a microsomal enzyme which catalyzes the transformation of certain lysyl residues in collagen to hydroxylysine. Chick embryo lysyl hydroxylase activity was measured by specific tritium release as tritiated water from an L-[4,5-3H]lysine-labelled unhydroxylated collagen substrate prepared from chick calvaria. Catechol analogs did not bind irreversibly to either enzyme or substrate, as full activity was restored with dialysis. Addition of excess cofactor, Fe2+, ascorbic acid, or alpha-ketoglutarate, did not affect inhibition. Kinetic analysis revealed that with respect to collagen substrate, catechol demonstrated a noncompetitive type of inhibition with a Ki of 15 muM.

Proline recycling during collagen metabolism as determined by concurrent 18O2-and 3H-labeling

In a previous study where rat skin collagen was labeled with 180 in the hydroxyl group of the collagen hydroxyproline we noticed that the decat rate of this label was much faster than had been observed when the skin collagen hydroxyproline was labeled with oH in the prolyl ring. In this study a ratwas labeled concurrently with [1802] and [3H] proline and the rate of decline of both labels was determined in rat skin collagen hydroxyproline. After correction for growth dilution of the skin collagen the [180] hydroxyproline was found to have a half-life of 27 days while the [3H] hydroxyproline had a half-life of 53 days. The decay rate of the [180] hydroxyproline represents the true turnover rate of collagen since there is no possibility of recycling this label. Hence, the difference between this and the [3H] hydroxyproline decay rate is due to recycling of L-[3H] proline into new collagen. The efficiency of recycling of proline from catabolized collagen into new collagen was about 93%.

Molecular-orbital study of hydroxylation of collagenous proline and lysine

EHT and CNDO/2 types of calculations permit the interpretation of the course of hydroxylation of collagenous proline and lysine. Calculations were performed for the models of proline (I), zwitterion of proline (II), proline-containing peptide (III), and lysine (IV). The theoretical results are consistent with an electrophilic mechanism.

Effect of amobarbital on oxygen consumption in bovine dental pulp

Respiratory inhibition by amobarbital, and by the combined action of amobarbital and cyanide, was measured in bovine dental pulp slices. The oxygen consumption rate was depressed by approximately 85% under both conditions, and it is believed that this represents almost the entire portion devoted to respiratory processes. Since a prior study showed that approximately 59% of pulpal oxygen consumption was used in cyanide-sensitive respiration, it is concluded that approximately 26% is consumed in cyanide-stable respiration. A significant portion of the remaining 15% may be involved in the hydroxylation of proline necessary for collagen synthesis in dentinogenesis.

Endogenous oxygen consumption rates of bovine alveolar mucosa

Oxygen consumption rates were determined for bovine whole alveolar mucosa, alveolar mucosal connective tissue, and alveolar mucosal epithelium. The mean oxygen quotients were 0.88, 0.39, and 2.08, respectively. Because inclusion of connective tissue in epithelial slices was unavoidable, a histometric technique for estimating the connective tissue volume for correcting the raw QO2 of the epithelium was used. Of the fibers in alveolar mucosal connective tissue, 27.7% were collagenous and 72.3% were elastic. Those of attached gingiva were completely collagenous. The QO2 0.39 for alveolar mucosal connective tissue is lower than the previously reported QO2 0.69 for attached gingival connective tissue because of the additional oxygen required for hydroxylation of proline and lysine in collagen synthesis.

Oxygen-collagen priority and the early metazoan fossil record

The thesis is developed that a low oxygen level Precambrian atmosphere presented early-evolving metazoan organisms with physiological connective tissue priorities resulting from the important molecular oxygen requirements in the biosynthesis of collagen hydroxyproline. Shells, cuticles, and carapaces which are not mandatory metazoan prerequisites but which directly or indirectly demand substantial connective tissue collagen are oxygen expensive, low priority features. A marked increase in atmospheric oxygen level near the beginning of the Paleozoic would eliminate oxygen-collagen priorities simultaneously and on a world-wide basis in all metazoan stocks providing evolutionary pressure for enlarged musculatures and associated "hard parts." This could explain the sudden presence in the fossil record of the early Cambrian of advanced and diversified metazoans, the earlier forms of which were essentially unpreservable.

Metabolic phases during the development of granulation tissue

1. The metabolism of incubated slices of sponge-induced granulation tissue, harvested 4-90 days after the implantation, was studied with special reference to the capacity of collagen synthesis and to the energy metabolism. Data are also given on the nucleic acid contents during the observation period. Three metabolic phases were evident. 2. The viability of the slices for the synthesis of collagen was studied in various conditions. Freezing and homogenization destroyed the capacity of the tissue to incorporate proline into collagen. 3. Consumption of oxygen reached the maximum at 30-40 days. There was evidence that the pentose phosphate cycle was important, especially during the phases of the proliferation and the involution. The formation of lactic acid was maximal at about 20 days. 4. The capacity to incorporate proline into collagen hydroxyproline in vitro was limited to a relatively short period at 10-30 days. 5. The synthesis of collagen was dependent on the supply of oxygen and glucose, which latter could be replaced in the incubation medium by other monosaccharides but not by the metabolites of glucose or tricarboxylic acid-cycle intermediates.

Partial characterization of protocollagen from embryonic cartilage

1. Attempts were made to isolate and characterize the protocollagen that accumulates in connective tissue when the hydroxylation of proline and lysine is inhibited. The term protocollagen has been used to describe the proline-rich and lysine-rich polypeptide or polypeptides that serve as substrates for the formation of hydroxyproline and hydroxylysine during the synthesis of collagen. 2. Both protocollagen and newly synthesized collagen from embryonic cartilage were isolated as complex aggregates, which contained sulphated mucopolysaccharides and other proteins or polypeptides from the same tissue. The complexes containing protocollagen were similar to those containing newly synthesized collagen when examined with several different techniques. 3. After the complexes were denatured and disaggregated, zone centrifugation and gel filtration indicated that the denatured protocollagen was similar to the denatured newly synthesized collagen obtained from cartilage in which the hydroxylation was not inhibited, and it was also similar to purified alpha-collagen. The results suggest that, when the hydroxylation is inhibited, most of the protocollagen polypeptides that accumulate are as large as complete alpha-chains of collagen. 4. Significant purification of the protocollagen polypeptides was obtained with a new technique for DEAE-Sephadex chromatography in which urea was used to prevent aggregation of the samples and the column was eluted with guanidine thiocyanate. 5. Protocollagen polypeptides were completely hydrolysed to diffusible peptides by a specific collagenase. 6. It is not entirely clear whether the hydroxylation normally begins while relatively short protocollagen molecules are still attached to polysomes, or whether protocollagen molecules of the size of alpha-collagen are synthesized even when the hydroxylation is not inhibited. 7. Results obtained with puromycin suggest that some hydroxylation occurs with smaller polypeptides, but polypeptide chains approaching the size of alpha-collagen are required to obtain complete hydroxylation of the appropriate amino acid residues of protocollagen.