An electron microscopic study of the permeability of iris capillaries to horseradish peroxidase in the vervet monkey (Cercopithecus aethiops)

Summary Anesthetized vervets were given intravenous injections of horseradish peroxidase. Subsequent studies of iris capillaries with the electron microscope showed peroxidase reaction product within the lumen of the vessels and in endothelial vesicles, but no peroxidase had penetrated the vascular endothelium. The normal ultrastructure of the vascular wall was retained.     

A comparison of the fine-structural localization of nucleoside phosphatase activity in large intracranial blood vessels and the thoracic aorta of rabbits

Summary Nucleoside phosphatase activity was localized in rabbit intracranial blood vessels, namely cerebral and basilar arteries and veins, and in the thoracic aorta using the electron microscope. In the intracranial vessels the same ultrastructural localization of reaction product was found when ATP or ADP was used as substrate in a modified Wachstein-Meisel procedure using Mg ions as the enzyme activator. No reaction product was seen when using AMP or -glycero-phosphate as substrates, or in controls without any substrate. Reaction product was sparsely localized within cell membrane invaginations on all sides of endothelial and, to a lesser extent, of smooth muscle cells. Pinocytotic vesicles occasionally contained reaction product. The greatest amount of lead phosphate (reaction product) precipitate was found in the basement membranes of both endothelial and smooth muscle cells, particularly intense in the former case. A diffuse precipitate of reaction product was observed in the cytoplasm of adventitial fibroblasts.The thoracic aorta demonstrated the same localization with the following exceptions: generally greater concentrations of reaction product were found using ATP as substrate, than in the corresponding intracranial vessels; interendothelial gaps and the cell membrane invaginations of these gaps were completely filled with reaction product; there was no specific localization of reaction product in the basement membranes; and reaction product could also be demonstrated using AMP and glycero-phosphate as substrates. Acid phosphatase activity was localized in lysosomes in endothelial and smooth muscle cells from both types of vessels. The differences in enzyme localization between aorta and intracranial vessels were discussed, particularly in light of the differences in nucleoside phosphatase activity and transport functions between brain and somatic capillaries.     

Localization of adenosine deaminase and adenosine deaminase complexing protein in rabbit brain

Adenosine deaminase and adenosine deaminase complexing protein have been localized in rabbit brain. Brains fixed in paraformaldehyde or in Clarke's solution were blocked coronally. Blocks from brains fixed in paraformaldehyde were either frozen in liquid nitrogen or embedded in paraffin. Tissue fixed in Clarke's solution was embedded in paraffin. Sections from each block were stained by the peroxidase-antiperoxidase method for adenosine deaminase or complexing protein using affinity-purified goat antibodies. Adenosine deaminase and complexing protein did not co-localize. Adenosine deaminase was detected in oligodendroglia and in endothelial cells lining blood vessels, whereas complexing protein was concentrated in neurons. The subcellular location and appearance of the peroxidase reaction product associated with individual cells was also quite distinctive. The cell bodies of adenosine deaminase-positive oligodendroglia were filled with intense deposits of peroxidase reaction product. In contrast to oligodendroglia, the reaction product associated with most neurons stained for complexing protein was concentrated in granular-appearing cytoplasmic deposits. In some instances, these deposits were clustered about the nuclear membrane. Staining of neurons in the granular layer of cerebellum was an exception. Granule cells were lightly outlined by peroxidase reaction product. Cerebellar islands, also referred to as glomeruli, were stained an intense uniform brown. These results raise the possibility that oligodendroglia and blood vessel endothelia, through the action of adenosine deaminase, might play a role in controlling the concentration of extracellular adenosine in brain. They do not, however, support the suggestion that complexing protein aids in adenosine metabolism by positioning adenosine deaminase on the plasma membrane.     

FINE STRUCTURAL LOCALIZATION OF A BLOOD-BRAIN BARRIER TO EXOGENOUS PEROXIDASE

Horseradish peroxidase was administered to mice by intravenous injection, and its distribution in cerebral cortex studied with a recently available technique for localizing peroxidase with the electron microscope. Brains were fixed by either immersion or vascular perfusion 10–60 min after administration of various doses of peroxidase. Exogenous peroxidase was localized in the lumina of blood vessels and in some micropinocytotic vesicles within endothelial cells; none was found beyond the vascular endothelium. Micropinocytotic vesicles were few in number and did not appear to transport peroxidase while tight junctions between endothelial cells were probably responsible for preventing its intercellular passage. Our findings therefore localize, at a fine structural level, a "barrier" to the passage of peroxidase at the endothelium of vessels in the cerebral cortex. The significance of these findings is discussed, particularly with reference to a recent study in which similar techniques were applied to capillaries in heart and skeletal muscle.     

Tropolone as a substrate for horseradish peroxidase

Tropolone (2,4,6-cycloheptatrien-1-one), in the presence of hydrogen peroxide but not in its absence, can serve as a donor for the horseradish peroxidase catalysed reaction. The product formed is yellow and is characterized by a new peak at 418 nm. The relationship between the rate of oxidation of tropolone (ΔA at 418 nm/min) and various concentrations of horseradish peroxidase, tropolone and hydrogen peroxide is described. The yellow product obtained by the oxidation of tropolone by horseradish peroxidase in the presence of hydrogen peroxide was purified by chromatography on Sephadex G-10 and its spectral properties at different pHs are presented. The M, of the yellow product was estimated to be ca 500, suggesting that tropolone, in the presence of horseradish peroxidase and hydrogen peroxide is converted to a tetratropolone.     

The role of porcine thyroid peroxidase and FAD-containing monooxygenase in the metabolism of 1-methyl-2-thioimidazole (methimazole)

The peroxidase and FAD-containing monooxygenase activities of porcine thyroid subcellular preparations were measured and it was observed that FAD-containing monooxygenase activity was considerably lower than that of peroxidase. The end product of 1-methyl-2[14C]thioimidazole oxidation catalysed by thyroid peroxidase was confirmed to be 1-methylimidazole by mass spectrometry. In the presence of thyroid peroxidase 1-methyl-2-thioimidazole would appear initially to be oxidised to bis(1-methylimidazole)-2,2'-disulphide. The extent of oxidation was dependent on the iodide concentration in the reaction mixture.     

Time course of angiogenesis in solid pineal autografts

Angiogenesis and reperfusion of blood vessels were analysed qualitatively, at the light- and electron-microscopical levels, in solid pineal autografts placed intracerebrally in adult rats (post-transplantation survival times: 1, 3, 7, 10, 14 and 28 days). Reperfusion of blood vessels was studied in sections from immersion-fixed brains incubated to demonstrate the endogenous peroxidase activity of erythrocytes within the lumen of blood vessels. The possible presence of the blood-brain barrier (BBB) within the grafts was also investigated by injecting native horseradish peroxidase (HRP) intravenously into the rats. Angiogenesis, the morphological and functional properties of blood vessels vascularizing the grafts and the survival of pineal tissue were analysed ultrastructurally following transplantation. Revascularization of pineal autografts placed into the adult host central nervous system occurred very slowly, requiring 7–10 days to establish anastomoses between graft and host blood vessels. During this process, signs of angiogenesis in pineal and cerebral capillaries were evident, suggesting that both contributed to graft revascularization. Morphological and functional studies with HRP revealed that, following transplantation, blood vessels at the graft-host interface or within pineal autografts maintained their morphological and functional properties: they were fenestrated and did not present a BBB to blood-borne peroxidase. Thus, after grafting, the presence or absence of the BBB is graft-determined. Revascularized pineal tissue showed good survival and pinealocytes revealed structural features of active secretory cells.     

Horseradish peroxidase catalyzed hydroxylations: mechanistic studies

The hydroxylation of phenol to hydroquinone and catechol in the presence of dihydroxyfumaric acid and oxygen catalyzed by horseradish peroxidase was studied under conditions where the product yield was high and the side reactions were minimal. The reaction is partially uncoupled with a molar ratio of dihydroxyfumaric acid consumed to hydroxylated products of 12:1. Hydrogen peroxide does not participate in the reaction as evidenced by the lack of effect of catalase and by the direct addition of hydrogen peroxide. Conversely, superoxide and hydroxyl radicals are involved as their scavengers are potent inhibitors. Experiments were all consistent with the involvement of compound III (oxygenated ferrous complex) of peroxidase in the reaction. Compound III is stable in the presence of phenol alone but decomposes rapidly in the presence of both phenol and dihydroxyfumaric acid with the concomitant formation of product. Therefore, phenol and dihydroxyfumaric acid must be present with compound III in order for the hydroxylation reaction to occur. A mechanism consistent with the experimental results is proposed.     

The effect of prostaglandin E1 and noradrenaline on the tone of cerebral vessels and arterial pressure]

Acute experiments were conducted on cats; it was found that prostaglandine (PG) E1 produced a contrary effect on the tone of the cerebral vessels and on systemic arterial pressure depending on the presence of ethanol in its solution. Blocking of PG biosynthesis with indometacine promoted a marked increase in the vasoconstrictor reaction of the cerebral vessels and aided elevation of arterial pressure in response to noradrenaline administration. It is supposed that disturbance of PG biosynthesis in the organism could play a definite role in the genesis of hypertension and cerebrovascular disturbances.     

Diffusion artefacts and tissue fixation in thyroperoxidase cytochemistry

The distribution of endogenous peroxidase activity in rat, mouse and human thyroid follicle cells was studied with electron microscopic cytochemistry after incubation in 3-3'-diaminobenzidine (DAB). In all three species enzyme activity was found at the apical plasma membrane (facing the follicle lumen) as well as in intracellular compartments. The enzyme activity in the apical plasma membrane was more sensitive to changes in fixation conditions than the activity in intracellular compartments. Under optimal conditions more than 90% of the follicle cells in normal rat thyroids displayed a cytochemical reaction at the apical plasma membrane. In all three species the reaction product at the apical plasma membrane formed a gradient which extended into the colloid which otherwise was unreactive. Evidence obtained indicated that this gradient was not due to the presence of soluble peroxidase in the lumen but most likely signified the diffusion of the reaction product from the membrane-bound enzyme.     

Erythrocyte-mediated microinjection of horseradish peroxidase into BHK cells

In order to establish the distribution with time of proteins microinjected into mammalian cells, horseradish peroxidase (HRP) was microinjected into baby hamster kidney (BHK) cells using chicken erythrocyte ghosts. At time intervals following initiation of fusion between ghosts and target cells, samples were fixed with aldehydes and the peroxidase visualized by reaction with diaminobenzidine and viewing by light and electron microscopy. At 10 min, the reaction product was observed within the cytoplasm of 60% of the microinjected cells, but was excluded from the nucleus and membranous organelles. In the other 40% of microinjected cells, the reaction product was also observed within the nucleus. At 30 min, the reaction product was observed to be evenly distributed throughout the cell, including the nucleus but excluded from organelles. By 6 h, the reaction product was present almost exclusively within the nucleus of 63% of microinjected cells. At all time points, 20–30% of the erythrocytes ghosts appear to have been taken up by cells by phagocytosis rather than fusion, as evidenced by the presence of peroxidase reaction product within intact and fragmented erythrocyte ghosts in the cytoplasm of target cells. Cells incubated with a lanthanum solution following fusion excluded this electron dense tracer, indicating that the cytoplasmic compartment is not opened during exposure to polyethylene glycol.     

Studies on Phyto-peroxidase

Both crystalline Japanese-radish peroxidase a and c could catalyze the aerobic destruction of indole-3-acetic acid in the presence of a small amount of hydrogen peroxide as an inducer. The pH dependences of the enzymic activities of peroxidase a and c were different from each other. The optimum pH of peroxidase a was found at 3.6, while that of peroxidase c lied in a broad range over 3 to 4.8. In lower concentrations of both peroxidases at pH 3.8 and 6.0, the major product of the reaction was identical with that presented by Ray with using an Omphalia enzyme, which would probably be methyldioxindole, while, in higher concentrations of both peroxidases at pH 3.8, the major product was found to be indole-aldehyde.     

A reliable method combining horseradish peroxidase histochemistry with immuno-beta-galactosidase staining

A sensitive combination of horseradish peroxidase (HRP) tracing and immunohistochemistry was used by Rye et al. [J Histochem Cytochem (1984) 32:1145] in a search for the origins of neurotransmitter- and neuromodulator-containing nerve fibers in brain. In this combination, peroxidase as a marker in immunohistochemistry was thought to yield a homogeneous brown immunoreaction product of diaminobenzidine, different from the black granular reaction product of retrogradely transported HRP, which is visualized by the tetramethylbenzidine (TMB) reaction and subsequent stabilization. A neuron that exhibits both kinds of reaction products in its cytoplasm in sections subjected to combination staining is referred to as a double-labeled cell. With a combined HRP and corticotropin-releasing factor (CRF) immunoperoxidase-antiperoxidase (PAP) method, the first set of experiments showed "false" double-labeled cells in the pyramidal cell layer of rat cerebral cortex, but only rarely in the subcortical areas, possibly because of the use of one enzyme system in two different histochemical procedures. This limitation of the double-staining technique prompted us to demonstrate an alternate combination of HRP tracing and immunohistochemistry in the second set of experiments by employing two previously described independent enzyme systems: HRP as a retrograde tracer and beta-galactosidase as a marker for immunohistochemical demonstration of CRF. A homogeneous blue reaction product indicated immuno-beta-galactosidase staining, and a granular black or brown reaction product labeled retrogradely transported HRP in double-labeled cells in subcortical regions. Neither double labeling nor "false" double labeling was seen in pyramidal cells of cerebral cortex. These findings suggest that application of two independent enzyme systems in a combined HRP and immunohistochemical method may be useful for investigating in origins of peptidergic fibers in brain when the combination of HRP histochemistry and the PAP method appears to be inappropriate.     

Ultrastructural localization of cholesterol by enzyme histochemistry

Summary The histochemical localization of cholesterol using oxidized diaminobenzidine as the final reaction product was studied at the electron microscopical level and compared with the digitonin method of cholesterol localization based on cholesterol digitonide as the final reaction product. Tissue chopper sections of fixed rat adrenal glands were incubated at 37° C in a medium consisting of 0.8 units/ml cholesterol oxidase, 1.4 units/ml cholesterol ester hydrolase, 50 units/ml horseradish peroxidase, 0.5 mg/ml diaminobenzidine, 0.1% v/v Triton X-100 (or Surfal) and an endogenous peroxidase inhibitor in 0.1m phosphate buffer, pH 7.0. An electron-dense osmiophilic reaction product was observed in many lipid droplets, intracellular vesicles and focally around mitochondria. Appropriate control experiments indicated that deposition of reaction product depended on the presence of cholesterol and the necessary enzymes. Comparison studies using digitonin confirmed the presence of cholesterol in the lipid droplets, but ultrastructural distortion limited the resolution of the more discrete deposits of cholesterol such as around mitochondria. The enzyme method permits finer resolution of these discrete deposits of cholesterol than the digitonin method because it does not cause distortion of cellular ultrastructure attributed to the formation of cholesterol digitonide. The enzyme method or a combination of enzyme and digitonin enables localization of free, esterified or total cholesterol.     

NADPH oxidation catalyzed by the peroxidase/H2O2 system. Iodide-mediated oxidation of NADPH to iodinated NADP

Oxidation of NADPH catalyzed by the peroxidase/H2O2 system is known to require the presence of mediating molecules. Using either lactoperoxidase or horseradish peroxidase, we demonstrated that in the peroxidase/H2O2 system, NADPH oxidation was mediated by iodide. The oxidation product was the iodinated NADP. This product was shown to possess spectral characteristics different from those of NADP+ and NADPH, since for iodinated NADP, increased absorbance was observed in the 280-nm region and was directly proportional to the rate of iodination. It is suggested that oxidation and iodination of NADPH proceed via a single reaction between the intermediary iodide oxidation species and NADPH. Experiments with different molecules of NADPH analogues indicated that iodination occurred in the nicotinamide part of the NADPH molecule.     

Trypanosoma cruzi: experimental Chagas' disease in rhesus monkeys. II. Ultrastructural and cytochemical studies of peroxidase and acid phosphatase activities

Ultrastructural and cytochemical studies of peroxidase and acid phosphatase were performed in skin, lymph node and heart muscle tissue of rhesus monkeys with experimental Chagas' disease. At the site of inoculation there was a proliferative reaction with the presence of immature macrophages revealed by peroxidase technique. At the lymph node a diffuse inflammatory exudate with mononuclear cells, fibroblasts and immature activated macrophages reproduces the human pattern of acute Chagas' disease inflammatory lesions. The heart muscle cells present different degrees of degenerative alterations and a striking increase in the number of lysosomal profiles that exhibit acid hydrolase reaction product. A strong inflammatory reaction was present due to lymphocytic infiltrate or due to eosinophil granulocytes associated to ruptured cells. The present study provides some experimental evidences that the monkey model could be used as a reliable model to characterize histopathological alterations of the human disease.     

Cytochemical localization of peroxidase activity in the mitochondria of Hymenolepis diminuta.

A cytochemical study of mitochondria of Hymenolepis diminuta indicates the presence of a mitochondrial peroxidase. Utilizing a 3,3'-diaminobenzidine (DAB) medium at pH 9.7, the reaction product is localized in the intracristal space, and between the inner and outer membranes of the mitochondria. No inhibitory effects are exerted on the peroxidase reaction by cyanide, azide, or aminotriazole. In addition, the mitochondria appear to have an enzyme which is cytochemically similar to vertebrate cytochrome c-oxidase. The possible physiological significance of the peroxidase is discussed.     

Endogenous peroxidase in the lacrimal gland of the rat and its differentiation against injected catalase and horseradish-peroxidase

Summary The localization of endogenous peroxidase was studied in the glandula orbitalis (lacrimalis) externa of the rat by the method of Graham and Karnovsky (1966). Reaction product is visible in all cisternae of the rough endoplasmic reticulum including the perinuclear cisternae, in condensing vacuoles, and in all secretion granules. The Golgi cisternae seldom are peroxidase positive. Intercalated duct cells rarely contain reaction product in a few scattered cisternae of the rough endoplasmic reticulum and in secretion granules.After the injection of beef liver catalase reaction product is found in the capillary lumen. Both the injected catalase and the endogenous peroxidase are completely inhibited by 10^–2M aminotriazole, while the pseudoperoxidatic activity within the erythrocytes persists. After injection of horseradish-peroxidase reaction product is visible within the capillary lumen and also in the intercellular spaces between lacrimal gland cells. 10^–2M aminotriazole completely inhibits the endogenous peroxidase while the exogenous horseradish-peroxidase remains unaffected. The inhibitory effect of aminotriazole is not specific for catalase since lacrimal gland peroxidase is also inhibited.     

Electron cytochemistry of developing and mature eosinophils in the bone marrow of the fowl and the duck

Synopsis Enzyme cytochemical studies have been carried out on eosinophils in the fowl and the duck. Peroxidase was found in all regions of the Golgi apparatus, the rough endoplasmic reticulum and the perinuclear cisternae of the early cells. In fowl eosinophil granules irregular deposits of peroxidase and arylsulphatase final reaction product were found, but the acid phosphatase deposits were even. In the duck in contrast, peroxidase was demonstrated in the external part of the granule only. Acid phosphatase and arylsulphatase were found in both the interna and the externa of the duck eosinophil granules. An ammoniacal silver nitrate reaction for the presence of the histone arginine was also studied. Silver deposits were found occupying all regions of the granules of eosinophils from both species of bird.The presence of the hydrolytic enzymes acid phosphatase and arylsulphatase in avian eosinophil granules supports the theory that these structures are lysosomal in nature and that they correspond with mammalian eosinophils in this respect.     

1-Naphthol basic dye (1-NBD). An alternative to diaminobenzidine (DAB) in immunoperoxidase techniques

The usefulness of 1-naphthol as substrate for horseradish peroxidase (HRP) in immunohistochemistry was studied using the peroxidase-antiperoxidase (PAP) and avidin-biotin-complex (ABC) methods in the demonstration of glial fibrillary acidic protein (GFAP), vimentin, carbonic anhydrase C (CA.C), and factor VIII-related antigen (FVIII/RAg) in central nervous tissue and cerebral tumors. In the presence of ammonium carbonate, 1-naphthol is oxidized by HRP and hydrogen peroxide, producing a fine gray-violet precipitate. The oxidation product of 1-naphthol proved capable of binding a great number of basic dyes. For each stain the final reaction product had a characteristic color that was different from the spontaneous color of the dye and from the color displayed by nuclei. The final color obtained with this procedure was alcohol resistant and could be mounted in solvent-based mounting media. The results obtained with the 1-naphthol basic dye (1-NBD) method were compared with those obtained using the diaminobenzidine (DAB) reaction in the demonstration of GFAP-positive astrocytes. The DAB reaction produced a more intense staining but also a coarser precipitate than the 1-NBD reaction. The 1-NBD procedure showed more morphological detail of fine structures and did not obscure nuclei and mitosis. The very low toxicity of 1-naphthol compared with DAB (a suspected carcinogen) is an important advantage of the 1-NBD method, as is its high specificity and sensitivity.