On the role of oxygen in dehydrogenase reactions using tetrazolium salts

Sex-specific biotransformation and detoxification after xenobiotic exposure of primary cultured hepatocytes of European flounder (Platichthys flesus L.)

Sex-specific effects of sublethal concentrations of known effective pro-oxidants such as 100,200 and 400 microM benzo[a]pyrene (B[a]p), 50 microM nitrofurantoin (NF) and 100 microM hydrogen peroxide (H2O2) on biotransformation pathways were studied in isolated hepatocytes of immature female and male European flounder (Platichthys flesus L.). Cell responses were assessed at the level of: (1) stress induction as measured by formation of reactive oxygen species (ROS), mainly superoxide radicals, and induction of cytochrome P450 (CYP450) biotransformation activity; (2) cellular antioxidant defences, both non-enzymatic (reduced glutathione) and enzymatic (DT-diaphorase (DTD) or quinone oxidoreductase, EC 1.6.99.2); (3) detoxification (aldehyde dehydrogenase (ALDH), EC 1.2.1.3); and (4) cellular damage as measured by reduced lysosomal membrane stability and cell death. As there is increasing evidence that 17-beta-estradiol interferes with certain pathways of xenobiotic biotransformation, we additionally tested the effects of different concentrations of 17-beta-estradiol (0.2-10 microM) alone and 17-beta-estradiol (1 microM) in combination with 100 microM B[a]p. Parameters were monitored after 1 and 9 days of exposure by quantitative image analysis of chromogenic or fluorogenic reaction products. Our study revealed sex-dependent differences in cellular stress responses. In hepatocytes of female flounder, biotransformation was slower and the capacity of non-enzymatic antioxidant defences and detoxification of toxic aldehydes was lower than in males. Additional administration of 17-beta-estradiol enlarged these differences between the sexes with respect to biotransformation activity and antioxidant defence in xenobiotic-induced injury. These findings may explain the higher susceptibility of female flounder to toxic and carcinogenic compounds in the marine environment.

Enzyme cytochemical techniques for metabolic mapping in living cells, with special reference to proteolysis

Specific enzymes play key roles in many pathophysiological processes and therefore are targets for therapeutic strategies. The activity of most enzymes is largely determined by many factors at the post-translational level. Therefore, it is essential to study the activity of target enzymes in living cells and tissues in a quantitative manner in relation to pathophysiological processes to understand its relevance and the potential impact of its targeting by drugs. Proteases, in particular, are crucial in every aspect of life and death of an organism and are therefore important targets. Enzyme activity in living cells can be studied with various tools. These can be endogenous fluorescent metabolites or synthetic chromogenic or fluorogenic substrates. The use of endogenous metabolites is rather limited and nonspecific because they are involved in many biological processes, but novel chromogenic and fluorogenic substrates have been developed to monitor activity of enzymes, and particularly proteases, in living cells and tissues. This review discusses these substrates and the methods in which they are applied, as well as their advantages and disadvantages for metabolic mapping in living cells.

The use of silicon microfabrication technology in painless blood glucose monitoring

A unique minimally invasive system for painless blood testing is now being commercialized for measurement of blood glucose concentration by diabetics. The novel component of this system, a consumable microsampling and assay device, consists of a tough, flexible silicon microneedle comparable in cross-section to a human hair integrated with a silicon microcuvette. This microneedle is capable of reliably taking a very small sample of whole blood completely painlessly, unlike sticks with the much larger metal lancet that must be used in all other current systems. The device permits a one-step process that avoids the need to transfer blood from a skin puncture to a test strip, thus minimizing blood required and possible mess. The small hand-held instrument containing the consumable is touched to the skin of the arm or any other part of the body, not necessarily the tip of the finger, and held there for one second. During this time, the microneedle is advanced and then withdrawn under microprocessor control, puncturing the skin and drawing less than 200 nanoliters of blood into the microcuvette, where the assay is performed automatically. The instrument calculates the blood glucose concentration, displays the result, and holds it in memory for recall. The consumable is produced by silicon microelectromechanical systems technology and can be produced in high volume at low unit cost. This technology shows promise of being extended to other analytes and to continuous monitoring.

Oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase activity for the discrimination between nonmalignant and malignant cells

We review here the oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase (G6PDH) activity to detect cancer cells. This inexpensive and rapid assay can be performed within half an hour. Discrimination between cancerous and noncancerous cells is based on a combination of elevated G6PDH activity, decreased superoxide dismutase (SOD) activity, and decreased lipid peroxidation in cancer cells. The test discriminates between adenomas and carcinomas of the colon with a certainty of >80% and has a high prognostic value for survival of colon cancer patients. Pancreatitis and pancreatic cancer are discriminated with a certainty of 100%. Therefore, the test can be applied by pathologists to provide additional information in difficult cases of diagnosis of cancer and for prognosis.

On the mechanism of the multistep reduction of tetrazolium salts with special reference to the involvement of tetrazolium radicals

Thin layer chromatography (TLC) was performed to analyze which products are formed when unstable tetrazolinyl radicals are generated during the reduction of tetrazolium salts under physiological conditions of biochemical and histochemical assays. It was found in aqueous media that irrespective the assay conditions, reduction of 2,3-di(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (p-DNTTC) or 2,3-di(4-nitrophenyl)-5-t-butyl-2H-tetrazolium chloride (t-butyl-DNTC) always lead to production of formazan and never to generation of the corresponding 2(4-nitrophenyl)-5-phenyl- (respectively t-butyl-) tetrazoles by splitting off a nitrophenyl side chain from the tetrazolium ring as a cation. This reaction is known to occur in non-aqueous media (Neugebauer, 1973). Because p-DNTTC is analogous to tetrazolium salts that are used in biochemical and histochemical assays, it is concluded that reduction of tetrazolium salts leads to formation of formazans only under these conditions.

Radical intermediates in the redox reactions of tetrazolium salts in aprotic solvents (cyclovoltammetric, EPR and UV-VIS study)

Tetrazolium Blue (TBCl2) and Nitrotetrazolium Blue (NTBCl2) cathodically reduced in non aqueous solvents form radicals with the center of unpaired electron on the tetrazolyl ring (TBH., NTBH.) as detected by EPR spectroscopy. After prolonged reduction, formazans (TBH2, NTBH2) are formed and are then further reduced to the nitro-centered anion radical (from NTBH2) and the azogroup-centered anion radical (from TBH2). The first cathodic peak in the cyclovoltammetric study in the region from -0.3 to -0.6 V vs. SCE (saturated calomel electrode) is irreversible and indicates an adsorption and diffusion process on the platinum and mercury electrodes. Formation of TBH+ and NTBH+ is assumed. The second peak, in the region from -0.8 to -1.3 V vs. SCE, is nearly reversible and coupled with the formation of TBH. and NTBH. radicals. UV-VIS spectra measured during the reduction show isosbestic points at the conversions: TB++-->TBH+, NTB++-->NTBH+; further, TBH+-->TBH2 and NTBH+-->NTBH2. The characteristic colours of the solutions observed can be used to characterise the reduction state of tetrazolium salts.

Factors affecting the selection and use of tetrazolium salts as cytochemical indicators of microbial viability and activity

The reduction of four tetrazolium cations (TCs), nitroblue tetrazolium (NBT), neotetrazolium (NT), methylthiazolyldiphenyltetrazolium (MTT) and iodonitrophenyltetrazolium (INT), by viable micro-organisms, immobilized on glass cover slips, was examined by light microscopy with a view to determining a systematic basis for applying these reagents as cytochemical indicators of microbial viability and activity. The potential value of histochemical information about TC reactions for developing their microbiological applications was also assessed. INT and MTT detected viable cells more readily than NBT and NT. In order to obtain cell-localized formazan, MTT required cobalt ions in the reaction mixture and INT reactions had to be assessed soon after mounting. In general, formazan deposition could be accelerated by the addition of glucose and an intermediate electron carrier (IEC) to the reaction mixture, although inhibitory effects of IECs were also detected. Cultures in exponential phase, in stationary phase and inhibited by chloramphenicol could be differentiated with MTT but not with INT. For some organisms, notably Candida albicans, Pseudomonas aeruginosa and Enterococcus faecalis. TC reactions proved to be a relatively insensitive means of demonstrating viability. Two parameters used in selecting TCs for histochemical reactions, lipophilicity and reducibility appeared to be predictive for the relative sensitivity of these reagents as indicators of cell viability. The concepts of substantivity, a measure of non-specific interactions between reagents and staining substrates, and TC oxygen sensitivity, the effect of competition between oxygen and TCs for electrons, were found to be relevant to formazan deposition in live microbes. These findings support the use of TCs as cytochemical probes of microbial activity in defined settings and the use of histochemical knowledge to support further development of these techniques.

The tetrazolium-formazan system: design and histochemistry

Our increasing knowledge about the chemistry and the correlations between chemical structure and histochemical properties of the tetrazolium/formazan system is resulting in: a better understanding of existing histochemical tetrazolium techniques; the selection of optimal tetrazolium salts for qualified use in histochemistry, cytochemistry and biochemistry; both qualitative and quantitative improvements in histochemical techniques for purposes demonstrating the activities of various dehydrogenating enzymes; an extended insight into the "state" of the tested biological object by means of tetrazolium indicators with special properties; and the combination of histochemical enzyme determination with further morphological techniques. This article has attempted to illustrate the progress in the use of the tetrazolium/formazan-system for histochemical purposes.

Cytophotometric analysis of reaction rates of succinate and lactate dehydrogenase activity in rat liver, heart muscle and tracheal epithelium

Reaction rates of succinate and lactate dehydrogenase activity in cryostat sections of rat liver, tracheal epithelium and heart muscle were monitored by continuous measurement of formazan formation by cytophotometry at room temperature. Incubation media contained polyvinyl alcohol as tissue protectant and Tetranitro BT as final electron acceptor. Control media lacked either substrate or substrate and coenzyme. Controls were also performed by adding malonate (a competitive inhibitor of succinate dehydrogenase), pyruvate (a non-competitive inhibitor of lactate dehydrogenase), oxalate (a competitive inhibitor of lactate dehydrogenase) or N-ethylmaleimide (a blocker of SH groups). A specific malonate-sensitive linear test minus control response for succinate dehydrogenase activity was obtained in liver (1.6 mumol H2cm-3 min-1) and tracheal epithelium (0.8 mumol H2cm-3 min-1) but not in heart muscle. All variations in the incubation conditions tested did not result in a linear test minus control response in the latter tissue. Because the reaction was sensitive to malonate, it was concluded that the initial reaction rate was the specific rate of succinate dehydrogenase activity in heart muscle (9.1 mumol H2 cm-3 min-1). Test minus control reactions for lactate dehydrogenase activity were distinctly non-linear for all tissues tested. This appeared to be due to product inhibition by pyruvate generated during the reaction and therefore it was concluded that the appropriate control reaction was the test reaction in the presence of 20 mM pyruvate. The initial rate of the test minus this control was the true rate of lactate dehydrogenase activity. The lactate dehydrogenase activity thus found in liver parenchyma was 5.0 mumol of H2 generated per cm3 liver tissue per min.