Retention of bone cell viability in mouse calvarial explants after cryopreservation

Newborn mouse calvaria, cyropreserved at -196 degrees C in serum-free medium containing dimethyl-sulfoxide, were compared to unpreserved explants for bone cell viability by [3H]thymidine uptake. Other explants were studied using autoradiography to compare the histological appearance of the cryopreserved and control unpreserved explant sites of cellular localization of [3H]thymidine. After short-term cryopreservation, calvarial bone cells, including less differentiated osteoprogenitor cells, survived as indicated by their incorporation of the DNA precursor. With culture continuing for up to 24 hr after thawing and in the continuous presence of [3H]thymidine, additional labeled thymidine was incorporated, indicating that the proliferative ability of explant cells persists after cryopreservation. Cryopreserved bone explants did not, however, incorporate the same amount of labeled thymidine as did controls at each time point studied. These events, as measured quantitatively and observed by autoradiography of the tissue, indicate that newborn calvarial bone cell proliferation in vitro continues after cryopreservation. The large surface:mass ratio of the tissue and its proportionate volume of calcified matrix apparently permits it to behave as an isolated cell population with regard to the diffusion of the cryoprotectant and thermal conductivity, thus permitting the retention of explant viability.     

DIFFERENTIAL INCORPORATION OF [3H]LYSINE INTO VISUAL CORTEX PROTEIN FRACTIONS DURING FIRST EXPOSURE TO LIGHT

—A resolution of the enhancement of protein synthesis in the visual cortex of rats during first exposure to light (Richardson and Rose , 1972) was achieved by polyacrylamide gel electrophoresis using a double-labelling technique. Differential incorporation of lysine was established between exposed and control animals in two fractions of the soluble proteins and seven fractions of the insoluble proteins. This suggests that exposure to a new experience of this type involves a specific effect on protein synthesis, rather than a general stimulation across all fractions.     

Determination of plasma leukotrienes in antigen-induced bronchoconstrictive guinea pigs.

Convenient extraction and radioimmunoassay methods for measurement of leukotrienes C4 and D4 (LTC4 and LTD4) in biological fluids are described. LTC4 or LTD4 in plasma was extracted with acetonitrile, and the extract was washed with dichloromethane then adjusted to pH 3.5 or 6.0, respectively. Each leukotriene was partially purified by using a C18-bonded silica cartridge and quantitated by radioimmunoassay. Amounts of LTC4 and LTD4 in the range of 0.025-1.6 ng could be assayed in plasma. This procedure was employed to examine the increase in plasma LTC4 (0.249 +/- 0.036 ng/ml) and LTD4 (1.399 +/- 0.235 ng/ml) of guinea pigs during intravenous challenge-induced anaphylactic bronchoconstriction, and the suppression of the increase of bronchoconstriction and leukotrienes by the administration of 5-lipoxygenase inhibitors such as E6080 (6-hydroxy-2-(4-sulfamoylbenzyl-amino)- 4,5,7-trimethylbenzothiazole hydrochloride), AA861 (2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone ) and phenidone. On the other hand, LTC4 and LTD4 were not detected in plasma after an inhaled challenge, though significant bronchoconstriction was provoked. It was concluded that the present study validates a new technique for quantitating plasma leukotrienes on the basis of pH and a suitable method for evaluating the pharmacological efficacy of 5-lipoxygenase inhibitors.     

Continuous spectrophotometric assays for dopamine beta-monooxygenase based on two novel electron donors: N,N-dimethyl-1,4-phenylenediamine and 2-aminoascorbic acid.

Based on the novel chromophoric electron donors, N,N-dimethyl-1,4-phenylenediamine (DMPD) and 2-amino-2-deoxy-L-ascorbic acid (2-aminoascorbic acid), two sensitive, convenient, and continuous spectrophotometric assays for dopamine beta-monooxygenase (EC 1.14.17.1) are described. Both, DMPD and 2-aminoascorbic acid are kinetically and stoichiometrically well-behaved electron donors for dopamine beta-monooxygenase with kinetic parameters comparable to the most efficient physiological electron donor, ascorbic acid. During dopamine beta-monooxygenase turnover, DMPD is converted to its chromophoric cation radical which is stable under the standard assay conditions. The rate of the enzyme-dependent formation of DMPD cation radical under standard assay conditions could easily be followed at 515 nm with high accuracy and reproducibility. Similarly, dopamine beta-monooxygenase-mediated oxidation of 2-aminoascorbic acid results in the formation of the known, stable chromophoric product, 2,2'-nitrilodi-2(2')-deoxy-L-ascorbic acid (red pigment), which has a very strong absorption maximum at 385 nm. Both the above assays are superior to the existing assays in their convenience, reproducibility, and sensitivity for routine kinetic analysis of dopamine beta-monooxygenase and may be adopted as a simple color test for the enzyme. We propose that the above assays could also be adopted to design continuous and sensitive spectrophotometric assays for ascorbate oxidase, peptidyl alpha-amidating monooxygenase, and the chromaffin granule electron transport protein, cytochrome b561, due to their remarkable similarity to dopamine beta-monooxygenase in the chemistry of catalysis with regard to the electron donor.     

Preparation of eumelanin-related metabolites 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their O-methyl derivatives

5,6-Dihydroxyindole (5,6DHI) and 5,6-dihydroxyindole-2-carboxylic acid (5,6DHI2C) are ultimate precursors of the black melanin, eumelanin. These indolic metabolites and their O-methyl derivatives are excreted in urine of melanoma patients at high levels and of healthy persons at low levels. We describe here a simplified procedure for preparing milligram to subgram quantities of 5,6DHI and 5,6DHI2C and their O-methyl derivatives. Dopachrome generated in situ by ferricyanide oxidation of dopa at pH 6.5 underwent spontaneous decarboxylation to give 5,6DHI in 40% isolation yield, while treatment of dopachrome with alkali at pH 13 afforded 5,6DHI2C in 38% isolation yield. Two isomeric O-methyl derivatives of 5,6DHI were prepared by treatment with diazomethane, while those of 5,6DHI2C were prepared by treatment with diazomethane followed by alkaline hydrolysis of the methyl esters. 5,6DHI and 6-hydroxy-5-methoxyindole were also obtained by heating the corresponding carboxylic acids in decalin. 5-Hydroxy-6-methoxyindole and 6-hydroxy-5-methoxyindole-2-carboxylic acid could also be prepared by debenzylation of the commercially available O-benzyl derivatives.