2,3-Dimercaptopropanol is a substance able to re-activate sulfhydryl groups of enzymes and has the property to form temporary complexes with metals, including zinc. It is also known that certain amino acids, particu- larly cysteine and glutathione also contain in its composition mole coli SH-groups. Administration of these amino acids in to animals result prevention developing of experimental diabetes caused zinkbinding diabetogenic chemicals. It is confirmed that this effect is determined by their ability to form non-toxic tempo- rary complexes with zinc in B-cells of pancreatic islets that protect cells of the destruction caused by diabetogenic chelating agents. The authors have shown that 2,3-dimercaptopropanol at doses of 60 and 120 mg/kg is able to prevent the development of diabetes in almost all experimental animals. Authors found that this ability 2,3-dimercaptopropanol is explained by its property through SH-groups included in its com- position, to form non-toxic complexes with zinc in pancreatic cells that protect cells of death.
2,3-Dimercaptopropanol (DMP) is known as re-activator of SH-group of enzymes and possess ability to form stable complexes with metals. However it is known that some aminoacids contains SH-groups in mole- cule as Cystein and Glutathuone reduced form protect developing of diabetes caused by chelat active chemi- cals. This effect determined by high affinity of SH-group for zinc and cadmium [1]. 2,3-Dimercaptopropanol is able in added to destroy other complexes, previously formed with zinc by chelators, that accompanied by re-placing atom of chelator from complex [2] and formation of complex DMT-metal via SH-group.
Aim of work: to investigate state of histostructure of pancreatic islets and possible interaction of Zn+2- ions in B-cells with DMP and Dithizon, a diabetogenic chelator.
Material and methods
Animals: 10 rabbits 2,200–2,650 g were used. Group 1: control intact animals: A-injection of Dithizon, 48,9 mg/kg; B-intact rabbit; Group 2: injection of DMP («SIGMA») in doses 60 and 120 mg/kg to 8 animals; 30 min later water solution of Dithizon 46,6–49,7 mg/kg was injected to 6 animals; animals killed 10 min past injection of DZ. Group 3: injection of DMP, 60 and 120 mg/kg to 2 animals; animals killed 10 min past injection. Group 4: injection of DMP, 60 and 120 mg/kg to 2 animals; 30 min later injection of Dithizon 48 mg/kg; animals killed 5 days past injection of DZ.
Frozen sections of pancreas were investigated using dark microscopy for revealing of DZ-Zn+2-complex in B-cells. The high specific fluorescent method revealing of free Zn+2-ions in B-cells by fluorochrom 8-para(toluenesulphonylamino)quinolin [8PTSQ] was used [3, 4]. 3 animals were killed 5 days past injec- tions of DMP and DZ. Pancreas was fixed in alcohol 70º + H2S. Staining of sections by aldehyde-fucshine [5–7] and 8PTSQ.
Results
Group 1. Control intact animals section o pancreas. 20 frozen sections of pancreas tissue were investi- gated using dark microscopy. Cytoplasm of all investigated islets contain a large amount of red chelat com- plex Zn+2-Dithizon [1] which concentrated on the all surface of cytoplasm, maximally around blood islet’s capillaries (fig. 1.1). Reaction for Zn+2-ions: intensive fluorescence of B-cells (fig. 1.2). Group 2. Admin- istration of 2,3-dimercaptopropropanol and of Dithizon result prevention of formation in majority of B-cells of Zn+2-Dithizon complex which is partially formed in cells located around blood capillaries (fig. 1.3). Protective effect determined by not diabetogenic binding of Zn+2-ions by DMT. It is known that DMT possess high affinity for Zn+2-ions.
- Intact rabbit. Injection of Dithizon, 48,9 mg/kg; dark microscopy; red granules of complex zinc-DZ in B-cells; [×280]
- Intact Positive fluorescent reaction for Zn in B-cells: intensive green fluorescence of Zn in cytoplasm of B-cells; [×140]
- Injection of DMP 60 mg/kg + DZ; dark microscopy; only B-cells contacted with capillaries contain complex zinc-DZ; [×280]
- Injection of DMP 60 mg/kg + DZ; negative fluorescent reaction for Zn in B-cells: only a few cells contain a small amount of Zn; [×140]
- Dithizon, 48 mg/kg. Aldehyde-fucshine staining; destruction of B-cells; degranulation, decreasing of insulin content in B-cells; [×280]
- Injection of DMP + DZ; Aldehyde-fucshine staining; histostructure of islets and insulin content in B-cells without changes; [×280]
Figure 1. Pancreas tissue
Group 3. Investigation of free Zn+2-ions content in B-cells past injection of DMT showed a negative re- action for Zn+2 in islets (fig. 1.4). A few B-cells contains minimal amount of Zn+2 in cytoplasm. This result determined by forming by DMT of not visible Zn+2-DMT complex.
Group 4. Investigation of effect of DMT on diabetogenic property of Dithizon showed that administra- tion of it accompanied by absence of any histological changes in pancreatic islets (fig. 1.5; 1.6).
Results of investigation of blood glucose level
T a b l e
Results of investigation of blood glucose level (table 1) demonstrated that injection of Dithizon accom- panied by marked decreasing of blood glucose level that is determined by release of a large amount of insu- lin as result of destruction within short time of majority B-cells. In other animals, past injections of DMT and followed past 1, 2 and 3 h injections of diabetogenic doses of Dithizon not accompanied by hyperglycemia in animals. We observed only not reliable increasing of blood glucose level until 5,6–5,8 mmol/l (Table).
Discussion
Molecule of 2,3-Dimercaptopropanol (C3H8OS2 m.m. 124,22) contains two SH-groups. It is known that some metals (Me) as mercury, arsenic, cadmium, lead, zinc interacted with chemicals contains SH-groups and formed stable cyclic mercaptide:
As bivalent metal Zn+2-ions interacts with 2 SH-groups of molecule of 2,3-Dimercaptopropanol with forming of cyclic mercaptide which are more stable in compared with some chelat active chemicals. It is known that 2,3-Dimercaptopropanol is able to destroy complexes previously formed with chelators accom- panied by replace atom of chelator from complex [2].
Thus, obtained results showed that 2,3-Dimercaptopropanol protect B-cells of destruction caused by Dithizon and of developing of diabetes. Investigation of interaction in B-cells between Zn+2-ions and 2,3-Dimercaptopropanol evidently showed that DMT protect B-cells of formation of toxic Dithizon-Zn+2 complex by interseption of Zn+2-ions and forming new complex DMT-Zn+2.
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