PubMed · 5221981
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J F Woodbury. 1966. Experiences with dimethylsulfoxide.. https://pubmed.ncbi.nlm.nih.gov/5221981/
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Free radicals are well-established transient intermediates in chemical and biological processes. Singlet oxygen, though not a free radical, is also a fairly common reactive chemical species. It is rare that singlet oxygen is studied with the electron spin resonance (ESR) technique in biological systems, because there are few suitable detecting agents. We have recently researched some semiquinone radicals. Specifically, our focus has been on bipyrazole derivatives, which slowly convert to semiquinone radicals in DMSO solution in the presence of potassium tert-butoxide and oxygen. These bipyrazole derivatives are dimers of 3-methyl-1-phenyl-2-pyrazolin-5-one and have anti-ischemic activities and free radical scavenging properties. In this work, we synthesized a new bipyrazole derivative, 4,4'-bis(1p-carboxyphenyl-3-methyl-5-hydroxyl)-pyrazole, DRD156. The resulting semiquinone radical, formed by reaction with singlet oxygen, was characterized by ESR spectroscopy. DRD156 gave no ESR signals from hydroxyl radical, superoxide, and hydrogen peroxide. DRD156, though, gives an ESR response with hypochlorite. This agent, nevertheless, has a much higher ability to detect singlet oxygen than traditional agents with the ESR technique.
The mutagenicity of isomers and homologs of diphenylmethanediisocyanate (4,4'-diisocyanatodiphenylmethane, 2,4'-diisocyanatodiphenylmethane, a mixture of monomeric MDI isomers, and polymeric MDI), containing 55-100% of monomeric MDI, was determined in the Salmonella/microsome test using dimethylsulfoxide (DMSO) and ethyleneglycoldimethylether (EGDE) as solvents. Positive results were obtained for DMSO solutions of all four diisocyanates in the presence of S9 mix containing 30% S9 fraction. Uniformly negative results were found when the diisocyanates were dissolved in EDGE. These results correspond to those of analytical investigations. A small amount of diaminodiphenylmethane (MDA) is one of the reaction products formed when MDI is dissolved in commercial DMSO. No MDA could be detected in solutions of MDI in EGDE. It is therefore concluded that the positive results obtained with diisocyanates in DMSO solutions are due to the formation of MDA. This is artificially formed through the hydrolysis of MDI, caused by traces of water that are always present in DMSO. These findings indicate that DMSO is an inappropriate solvent and should therefore not be used in any in vitro study with diisocyanates. EGDE may be a suitable replacement. The positive test results reported so far for DMSO solutions of MDI are thus only of limited relevance for risk evaluation.
Thrombopoietin (TPO, c-Mpl ligand) is considered to play an important role in the regulation of megakaryocytopoiesis and platelet production by activating the cytokine receptor c-Mpl. We have examined the binding of 125I-TPO to the human megakaryocytic cell line, CMK, and to primary human megakaryocytes. Scatchard analysis of TPO binding to its cognate receptor in megakaryocytic cells suggested the existence of a single class of c-Mpl receptors. CMK cells exhibited 1223 receptors per cell with a dissociation constant (Kd) of Kd = 223 pM, whereas primary human megakaryocytes exhibited 12140 receptors per cell and a dissociation constant of Kd = 749 pM. The pretreatment of CMK cells and primary bone marrow megakaryocytes with TPO resulted in a decreased binding of TPO to the c-Mpl receptors. This down-regulation was observed within 3 h and was not inhibited by cycloheximide. Phorbol ester, an activator of protein kinase C, also inhibited TPO binding to the c-Mpl receptors by reducing the number of these receptors. The pretreatment of CMK cells with IL-3, IL-6 and DMSO, all of which induced the differentiation of CMK cells, did not affect the binding of TPO to the c-Mpl receptors. These results suggest an additional mechanism, where protein kinase C may help to regulate the binding of TPO to these cells.