A quantitative histochemical study of dipeptidylpeptidase IV (DPP IV)

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

Comparison of the activity levels and localization of dipeptidyl peptidase IV in normal and tumor human lung cells

Dipeptidyl peptidase IV (DPPIV) was studied in three human lung cells - P (fetal lung-derived cells), A549 (lung adenocarcinoma) and SK-MES-1 (squamous cell carcinoma) using a fluorescent cytochemical procedure developed on the basis of the substrate 4-(glycyl-L-prolyl hydrazido)-N-hexyl-1,8-naphthalimide. The observed differences in the enzyme expression were confirmed by measuring the enzyme hydrolysis of glycyl-L-prolyl-para-nitroanilide. The surface and total dipeptidyl peptidase activities of P cells were correspondingly 7-8 and 3-10 times higher than those of SK-MES-1 and A549 cells. The ratio surface per total activity showed that in P (95%) and A549 (93%) cells the enzyme is associated with the plasmalemma while in SK-MES-1 cells (35%) it is bound to intracellular membranes. In order to compare the results from cell cultures with those in human tumor, the enzyme activity was investigated in cryo-sections of three cases of diagnosed squamous lung carcinoma. DPPIV activity was restricted to the connective tissue stroma surrounding the DPPIV-negative tumor foci.

The need for metabolic mapping in living cells and tissues

The ultimate activity of an enzyme depends on many regulatory steps from transcription of the gene up to complex formation of the enzyme. Therefore, gene expression (mRNA levels) or protein expression (protein levels) are not reliable parameters to predict the functional activity of an enzyme. Activity measurements in cell homogenates or in frozen or fixed (and thus dead) cell preparations are not appropriate either because post-translational regulation mechanisms that exist in living cells may be lost by homogenization or freezing or chemical fixation of cells. Therefore, metabolic mapping in living cells or, in other words, visualization and quantification using microscopy and image analysis of enzyme reactions in living cells is the approach of choice to understand the functional role of enzymes in vivo as is demonstrated here with a number of examples in recent literature.

Screening of stimulatory effects of dietary risk factors on mouse intestinal cell kinetics

AIM

Although epidemiological and experimental studies validate influence of genetic, environmental and dietary factors in the causation of various types of cancers including colon, results from all these sources are inconclusive. Hypothesizing that high fat diet and obesity are among the major predisposing factors in the incidence of colon cancer, we evaluated the role of diet constituted with food material derived from a tropical plant, Tamarindus indica Linn (TI).

METHODS

A two part randomized double-blind study was conducted employing inbred Swiss albino mice from a single generation for the whole investigation. One day-old neonates (n = 12) were subcutaneously administered with monosodium glutamate (MSG) to induce obesity (OB). At weaning these animals were maintained on modified AIN-76 diet supplemented with 10% TI and 10% fat bolus (w/w, TIFB) for 8 wk. Subsequently, in the second part of study, four groups of animals belonging to the same generation, age and gender (n = 12 per group), were maintained on: AIN-76 control diet (CD); AIN-76 mixed with 10% TI extract (TI); and, mixed with 10% TI and 10% FB (TIFB) for 8 wk, to determine intestinal crypt cell proliferation, functionally-specific enzyme activities, fermentation profile, and energy preferences.

RESULTS

We observed a significant increase in the crypt cell production rate in distal colonic segment of experimental animals when compared with the controls. This segment also contained significantly low butyrate levels compared to control and TIFB groups. All the experimental groups showed a gross decrease in the enzyme activities viz., succinate dehydrogenase, acid-galactosidase and dipeptidyl amino peptidase IV demonstrating pathological stress caused by the test regimens, and an altered metabolic flux in the cellular environment.

CONCLUSION

We have demonstrated a cumulative response to the three dietary factors, one of which (TI) is reported, herein, for the first time to modulate kinetics of large intestinal mucosa, contributing to total risk posed by these test agents.

Developmental regulation of intestinal epithelial hydrolase activity in human fetal jejunal xenografts maintained in severe-combined immunodeficient mice

Intestinal epithelial brush border hydrolases are important and sensitive enzyme markers of gastrointestinal development and function. Little is know about the mechanisms that regulate the induction of these enzymes during human fetal development, as these events occur primarily in utero. The present work used ectopically grafted human fetal jejunal xenografts (median age,13.3 wk of gestation), maintained in severe-combined immunodeficient mice, to study the differential expression of five different hydrolases after 10 wk of xenotransplantation. The spatio-temporal distribution of brush border alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, lactase-phlorizin hydrolase, and dipeptidyl peptidase IV enzyme activities were measured quantitatively using scanning microdensitometry along the crypt-villus axes of fetal, xenograft, and pediatric (median age, 34 mo) biopsies. Ectopic grafting of fetal jejunum closely recapitulated the development of these enzymes in utero, with alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, and dipeptidyl peptidase IV enzyme activities closely matching the spatio-temporal distribution and levels recorded in pediatric duodenal biopsies. Lactase-phlorizin hydrolase was the only enzyme not to reach values recorded in pediatric brush border membranes, although activities were significantly (5.6-fold) higher than in pretransplanted fetal bowel. Human jejunal xenografts therefore demonstrate an appropriate developmental induction of brush border hydrolase activity and may represent a useful model to study trans-acting factors that promote human epithelial differentiation and function in vivo. Characterization of such agents may be of potential therapeutic use in the treatment of diseases associated with gastrointestinal immaturity, notably necrotizing enterocolitis.

Heterogeneity of kinetic parameters of enzymes in situ in rat liver lobules

In the present review, metabolic compartmentation in liver lobules is discussed as being dynamic and more complex than thus far assumed on the basis of numbers of mRNA or protein molecules or the capacity (zero-order activity) of enzymes. Isoenzyme distribution patterns and local kinetic parameters of enzymes may vary over the different zones of liver lobules. As a consequence, metabolic fluxes in vivo at physiological substrate concentrations may be completely different from those that are assumed on the basis of the number of molecules or the capacity of enzymes present in zones of liver lobules. For a more correct estimation of the levels of metabolic processes in the different compartments of liver tissue, local kinetic parameters and substrate concentrations have to be determined to calculate local metabolic fluxes. Direct measurements of metabolic fluxes in vivo with the use of noninvasive techniques is a promising alternative and the techniques will become increasingly important in future metabolic research.

Analysis of enzyme reactions in situ

Estimations of metabolic rates in cells and tissues and their regulation on the basis of kinetic properties of enzymes in diluted solutions may not be applicable to intact living cells or tissues. Enzymes often behave differently in living cells because of the high cellular protein content that can lead to homologous and heterologous associations of protein molecules. These associations often change the kinetics of enzymes as part of post-translational regulation mechanisms. An overview is given of these interactions between enzyme molecules or between enzyme molecules and structural elements in the cell, such as the cytoskeleton. Biochemical and histochemical methods are discussed that have been developed for in vivo and in situ analyses of enzyme reactions, particularly for the study of effects of molecular interactions. Quantitative (histochemical) analysis of local enzyme reactions or fluxes of metabolites has become increasingly important. At present, it is possible to calculate local concentrations of substrates in cells or tissue compartments and to express local kinetic parameters in units that are directly comparable with those obtained by biochemical assays of enzymes in suspensions. In situ analysis of the activities of a number of enzymes have revealed variations in their kinetic properties (Km and Vmax) in different tissue compartments. This stresses the importance of in vivo or in situ analyses of cellular metabolism. Finally, histochemical determinations of enzyme activity in parallel with immunohistochemistry for the detection of the total number of enzyme molecules and in situ hybridization of its messenger RNA allow the analysis of regulation mechanisms at all levels between transcription of the gene and post-translational activity modulation.

The evolution of proteinase substrates with special reference to dipeptidylpeptidase IV

The design and development of specific substrates for proteolytic enzymes is reviewed. Particular attention is given to substrates containing the leaving groups 4-methoxy-2-naphthylamide (MNA) and 7-amino-4-trifluoromethylcoumarin (AFC). The MNA substrates are used for histochemical and cytochemical purposes, and they yield a coloured final reaction product when azo-coupled with a diazonium salt, an osmiophilic product for electron microscopy when coupled with hexazotized Pararosaniline, or a fluorescent final reaction product when coupled with 5-nitrosalicylaldehyde. AFC substrates are considerably more sensitive, and they yield the fluorescent product AFC after enzymatic cleavage of the substrate. AFC is not sufficiently water-insoluble to allow (intra)cellular localization, but AFC substrates are successfully used for incubations in microwells (Immu-Probe technique) and for the demonstration of banding patterns after gel electrophoresis (enzyme-directed overlay membrane technique). The methods are discussed with the example of the elucidation of the role of dipeptidylpeptidase IV in autoimmune diseases.

Altered zonal expression of the CD26 antigen (dipeptidyl peptidase IV) in human cirrhotic liver

Dipeptidyl peptidase IV is a cell surface ectopeptidase with widespread tissue distribution. Recently it was shown to display extracellular matrix-binding properties; therefore its role in cirrhosis is of interest. The aim of this study was to use monoclonal antibodies directed against the human CD26 antigen (which has been shown to be dipeptidyl peptidase IV) to study the distribution of this molecule in normal human and cirrhotic liver. Identical staining was obtained with the three monoclonal antibodies (TaI, 1F7 and TS145) and enzyme histochemistry. In normal liver (n = 11) intense staining of hepatic acinar zones 2 and 3 was present, but little staining was seen in zone I. Hepatocyte staining was confined to the bile canalicular domain. In cirrhotic livers (n = 23) obtained at transplantation, staining of regenerating nodules without a zonal pattern was present. In addition, we saw staining of the lymphoid cell infiltrate and proliferating bile ductules. In a minority of cirrhotic biopsy specimens (four) staining of the basolateral hepatocyte domain in regenerating nodules was seen. Biopsy specimens from hepatic allografts (n = 28) were used as disease controls. These samples all showed preferential staining of zones 2 and 3, similar to that in normal biopsy specimens. Eleven of these samples showed staining of the basolateral and bile canalicular domains. In conclusion, the normal acinar distribution of dipeptidyl peptidase IV (zones 2 and 3) is lost in cirrhotic nodules. Furthermore, the altered membrane distribution of this molecule in cirrhosis and allograft rejection may allow increased hepatocyte extracellular matrix interactions during organ remodeling.

Galactose effects on enterocyte differentiation in the mouse jejunum

The present work investigates the ability of galactose to affect enterocyte differentiation during normal development in vivo. Energy intake has also been varied to take account of the fact that galactose is poorly metabolized in mice. Brush-border lactase, alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N, alkaline phosphatase and microvillus length were measured as markers of enterocyte differentiation in mice fed diets containing galactose (G diet), corn oil (E diet) or galactose + corn oil (G + E diet). Maintaining mice on a G instead of E diet reduced brush-border lactase activity and enterocyte migration rates; alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N and microvillus length expression increased and alkaline phosphatase activity remained unchanged. Feeding the G + E diet restored enterocyte migration rates, lactase, aminopeptidase N and dipeptidylpeptidase-IV activities to values found in mice fed the E diet. Galactose stimulation of alpha-glucosidase and microvillus length expression was, however, fully maintained in mice fed the G + E diet. Present results show that enterocyte differentiation is affected independently by varying dietary galactose and energy levels; that galactose effects always increase and energy effects usually decrease expression of enterocyte components and that energy stimulation of lactase activity is exceptional.

Identification of the bile canalicular cell surface molecule GP110 as the ectopeptidase dipeptidyl peptidase IV: an analysis by tissue distribution, purification and N-terminal amino acid sequence

This paper describes the tissue distribution, purification and N-terminal amino acid sequence of the bile canalicular cell surface molecule dipeptidyl peptidase IV. Immunoperoxidase staining of cryostat sections of rat liver with a monoclonal antibody, Medical Research Council OX-61, indicated specific binding to hepatocyte bile canalicular domains and brush borders of bile ducts. Additional staining was seen in other epithelial brush borders (small intestine, kidney, colon, pancreatic duct); acinar structures in salivary glands; endothelial structures and T cell areas in thymus, spleen and lymph node. The tissue distribution suggested that monoclonal antibody OX-61 binds to the ectoenzyme dipeptidyl peptidase IV. This was confirmed by depletion of dipeptidyl peptidase IV activity from tissue homogenates by monoclonal antibody OX-61 coupled to Sepharose. The molecule recognized by OX-61 was then purified from liver and kidney by monoclonal antibody affinity chromatography. The molecule had a molecular weight of 110 kD under reducing conditions. The purified molecule was subsequently analyzed for amino acid composition and N-terminal amino acid sequence. Thirty-one N-terminal amino acids were sequenced and indicated identity with part of the predicted N-terminus of the previously cloned bile canalicular molecule GP110. On review, other similarities between dipeptidyl peptidase IV and GP110 were detected: molecular weight, deglycosylated form and metabolic half-life. Finally, the recent cloning of dipeptidyl peptidase IV permitted a comparison between the molecule recognized by monoclonal antibody OX-61, GP110 and dipeptidyl peptidase IV. It is concluded that these three molecules are almost certainly identical.

Reaction rate measurements of proteases and glycosidases with chromogenic methods

Simultaneous azo-coupling and indigogenic methods were evaluated for the quantitative histochemical assay of the plasma membrane proteases gamma-glutamyl transpeptidase (EC 2.3.2.2) and dipeptidyl peptidase IV (EC 3.4.14.5) and the glycosidases maltase-glucoamylase and glucoamylase (EC 3.2.1.20) in decidual cells, jejunal enterocytes and renal proximal tubulocytes. Using kinetic (continuous) microdensitometry, a linear increase in the final reaction product was found from 3 up to 10 min, depending on the substrate concentration and the plasma membrane glycosidase or protease under investigation. Combined continuous and end point (static) microdensitometry revealed a linear relationship between the section thickness (enzyme concentration) and final reaction product up to 12 microns for the proteases and up to 16 microns for the glycosidases. Apparent Km and Vmax values were calculated with a computerized version of the direct linear plot and compared with the results obtained with the linear transformations according to Lineweaver-Burk, Eadie-Hofstee and Hanes. Apparent Km and Vmax values for the proteases were calculated separately for each animal and were 1.82 mM and 1.02 mM and 2.43 arbitrary units (a.u.) and 1.67 a.u. (gamma-glutamyl transpeptidase, decidua) and 0.42 mM and 0.38 mM and 0.29 and 0.26 a.u. (dipeptidyl peptidase IV, decidua). For the alpha-D-glucosidases, the corresponding values were 0.23 mM and 0.15 a.u. (kidney) and 0.55 mM and 0.20 a.u. (jejunum). The results show the suitability of the indigogenic methods for quantitative histochemical measurements of plasma membrane alpha-D-glucosidases, whereas the simultaneous azo-coupling procedures seemed to be less suitable for the quantification of surface membrane proteases, due to, for example, interactions of diazonium salts with amino acid or peptide substrates, reaction products and peptide activators.

Cytochemical analysis of single villus peptidase activities in pig intestine during neonatal development

The present work uses a new technique of whole tissue cytochemistry and automated scanning to obtain measurements of peptidase activity and surface structure in intact villi microdissected from the jejunum of newborn and 28-day-old pigs. Intact villi from 28-day-old pigs are shown by this method to contain 30% more aminopeptidase N and 400% more dipeptidylpeptidase IV activity than is found on villi taken from newborn pig intestine. Villi taken from 28-day-old pig intestine are also half as long and twice as wide at their base as those taken from newborn animals. These changes in shape take place without significantly affecting the total surface area of the villus. Increases in peptidase activities occurring during postnatal development can be further subdivided into those dependent upon induced changes in enterocyte biochemistry and those dependent upon the changing geometry of villi. Over 90% of the total increase in peptidase activities occurring during neonatal development was shown, by this analysis, to involve enterocyte reprogramming of enzyme production. The present method of whole tissue cytochemistry appears to combine successfully the ability to measure peptidase activities at the cellular level in undisrupted tissue with a facility to relate these results to the overall shape of a single villus. These and more general applications of the method now provide new ways to analyse a variety of changes taking place in intestinal structure and function in a quantitative manner.

Kinetic and end-point microdensitometry (section biochemistry) of gamma-glutamyl transpeptidase and dipeptidyl peptidase IV in the mature mouse decidua and visceral yolk sac

gamma-Glutamyl transpeptidase (EC 2.3.2.2) and dipeptidyl peptidase IV (EC 3.4.14.5) were measured in mature mouse decidual and visceral yolk sac epithelial cells by means of kinetic (continuous) and end-point (static) microdensitometry (section biochemistry). For continuous measurements a new device for starting the enzyme reaction allowed the first readings to be made already during its very early phase. Since the initial reaction rates of both peptidases were very different in the plasma membrane of decidual and also in the visceral yolk sac epithelial cells, it was difficult to select a sufficient number of cells of the same activity for representative measurements on the basis of kinetic microdensitometry. Static section biochemistry was performed also for statistical reasons, i.e., in order to obtain information about the distribution of the activities of the decidual and visceral epithelial cells and the number of measurements required to guarantee valid data. Various groups of decidual and visceral yolk sac epithelial cells with different gamma-glutamyl transpeptidase and dipeptidyl peptidase IV activities were formed. In this way, different activities of gamma-glutamyl transpeptidase were measured in the plasma membrane of the cells of the antimesometrial, intermediate, and mesometrial decidua. Compared with dipeptidyl peptidase IV, gamma-glutamyl transpeptidase was significantly more active in the plasma membrane of the antimesometrial decidual cells and microvillous zone of the visceral yolk sac epithelial cells.

Characterization of stereomicroscopically identified preneoplastic lesions during dimethylhydrazine-induced colonic carcinogenesis

Preneoplastic mucosal changes were studied at six different time-points during dimethylhydrazine (DMH)-induced colorectal carcinogenesis in the rat. After 40 weeks of treatment, seven of 10 animals were bearing a total of 11 colorectal adenocarcinomas. The crypt cell production rate in the normal mucosa of DMH-treated animals was greatly increased in the left colon and rectum and further rose with the duration of the experiment. Focal disturbances of the mucosal architecture could be detected as early as 4 weeks after the initiation of DMH-treatment using a stereomicroscope. Their incidence was greatest in the left colon and rectum and increased strongly with the duration of carcinogen exposure. Characterization of these mucosal alterations, by means of conventional histology, morphometry after microdissection, cell kinetics, mucin histochemistry and quantitative enzyme histochemistry performed with serial sections, revealed mild epithelial dysplasia, a considerable elongation and dilatation of the crypts and a marked increase of the crypt cell production, including a shift of the main proliferative compartment from the basal to the medial crypt segment as well as the occurrence of mitotic figures in the luminal epithelium. In affected crypts, the goblet cells completely lacked sulphomucins and exclusively contained sialomucins. The activities of the enzymes diaminopeptidase IV (brush-border), succinate dehydrogenase (mitochondria) and acid beta-galactosidase (lysosomes) were markedly reduced. We conclude that these early mucosal alterations are indeed preneoplastic lesions and indicate the existence of the adenoma-carcinoma sequence in this animal model.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of alkaline phosphatase activity after conventional isoelectric focusing by an indoxyl-tetrazolium salt technique

Alkaline phosphatase was solubilized from human and rat tissues using papain in the presence of TRITON X-100 and subjected to isoelectric focusing (IEF) in polyacrylamide or agarose gels. Up till now, usually 1- and 2-naphthylphosphates have been used as substrates in order to specifically stain molecular forms of this enzyme by the azo-dye technique. In this paper, the use of another histochemical substrate, 5-bromo-4-chloro-3-indoxyl phosphate, in combination with tetrazolium salts [McGadey, J. (1970) Histochemie 23, 180-184] is presented. After hydrolysis, the released indoxyl moieties reduce tetrazolium salts to insoluble formazans at the zones of alkaline phosphatase activity. Zymogrammes showing molecular forms of alkaline phosphatase from 20 rat organs and the application of this staining technique for the detection of alkaline phosphatase activity in non-dialyzed human plasma after IEF are presented.

The alkali burned cornea: electron microscopical, enzyme histochemical, and biochemical observations

The early phase of wound healing after small central alkali burns of the guinea pig cornea was studied using electron microscopical, enzyme histochemical, and biochemical techniques. In the first phase, which was morphologically characterized by the destruction of the epithelium and keratocytes and by the infiltration of the cornea with polymorphonuclear leukocytes, an increase in the activity of lysosomal phosphatases and glycosidases (beta-D-glucuronidase, acid beta-D-galactosidase, beta-D-N-acetylglucosaminidase) was noticed. In the second phase, the cornea was invaded by capillaries and fibroblasts. In this phase, the activity of proteases (aminopeptidase M, dipeptidyl peptidase IV) increased intra- and extracellularly, suggesting that these enzymes may be involved in the turnover of the collagenous matrix and the ground substance. Using synthetic 4-methoxy-2-naphthylamine substrates and fluorescence-band detection techniques after isoelectric focusing, an increase in the activity of endopeptidases was demonstrated. The decreased activity of gamma-glutamyl transpeptidase may be linked with the activation of latent collagenase.

Cytochemistry of membrane proteases

Membrane proteases that are detectable by cytochemical means are the classified exopeptidases, aminopeptidases A and M (or N), gamma-glutamyl transpeptidase (which also acts as transferase), dipeptidyl peptidase IV and the endopeptidase, enteropeptidase (also known as enterokinase). Not yet classified are the possible exopeptidase, tripeptidyl peptidase and endopeptidases I (Ala-endopeptidase) and II (Arg-endopeptidase). All these membrane proteases can be investigated with either chromogenic or fluorogenic procedures using synthetic peptide substrates. The most useful substrates are 4-methoxy-2-naphthylamine amino acids and peptides for cytochemical localizations at the light and electron microscope levels, for cytophotometric quantification and the study of membrane protease isoenzymes after analytical isoelectric focusing. Amino acid or peptide derivatives of naphthylamine AS can be recommended for light microscopical localization and cytofluorometric quantification, and 7-amino-4-methylcoumarin and 7-amino-4-trifluoromethylcoumarin amino acids and peptides for the development of enzyme bands after isoelectric focusing. Cytochemistry reveals the heterogeneity in the distribution and species differences of membrane proteases in adult cells, tissues and organs and during development. It also reveals some common localizations, such as in small intestinal enterocytes and proximal tubule cells. The species and organ differences are substantiated and extended considerably by isoelectric focusing in combination with methods for the cytochemical detection of proteases. In addition, continuous cytophotometry or cytofluorometry (section and cultured cell biochemistry) allows the kinetic characteristics, initial reaction rates and maximum activities of all membrane proteases to be determined. The physiological functions of the endopeptidases and exopeptidases are still a matter of debate. However, from cytochemical inhibition studies with natural peptide substrates, e.g. peptide hormones, there is increasing evidence that the proteases detected with synthetic peptides play a decisive role in many physiological circumstances, e.g. in endocrine regulation mechanisms or the regulation of blood pressure. In this respect, capillary endothelium-linked surface membrane proteases may be especially important.

Quantitative histochemistry of the angiotensinase A (APA) in the renal glomeruli of rats after stimulation of the renin-angiotensin system

Quantitative histochemical measurements of aminopeptidase A (APA, angiotensinase A) were done kinetically in the kidney glomeruli of rats after short-term experiments (treatment with furosemide as well as captopril for 2, 4, and 6 h). The APA activities increased after treatment with furosemide or captopril. Highest activities were determined after 4 h using furosemide and 6 h using captopril. It is concluded that glomerular APA activities correspond to the renin/angiotensin plasma levels and that the fast changes of APA activities are well demonstrable by kinetic densitometric measurements in situ.

[Has dipeptidyl peptidase IV an effect on blood pressure and coagulation?]

Dipeptidyl peptidase IV is a very specific protease that attracts growing scientific interest during the last few years. The enzyme has been purified to homogeneity from various human tissues. Histochemically, this protease is found at certain border lines of many organ compartments, as in the proximal tubuli of kidney, in the bile canaliculi of liver, in the capillary endothel, or in the myofibroblasts of placenta. In the blood, especially T-helper lymphocytes contain this enzyme. Dipeptidyl peptidase IV seems to be predestinated for regulatory functions, because it is located on the outer membranes of these cells. The peptidase very specifically degrades substance P. Thus, it is discussed whether the system substance P/dipeptidyl peptidase IV is involved in the regulation of blood pressure, especially in the placenta. On the other hand, the specific attack of the peptidase on the alpha-chain of monomeric fibrin considerably reduces the clotting potency of these molecules. Therefore, dipeptidyl peptidase IV may also be involved in the regulation of blood coagulation in intact vessels, especially because the capillary endothel is lined with this enzyme. The plasma zinc concentration seems to influence the peptidase activity. An increase in plasma zinc stimulates various factors that promote blood clotting.

Isoelectric focusing (IEF) and band detection with fluorogenic protease substrates

In a previous paper, combined dye histochemistry and analytical isoelectric focusing (IEF) of supernatants from organ homogenates have been shown to yield good results for the detection of protease isoenzymes. Difficulties arise when the protease to be studied is partially or completely inhibited by diazonium salts and when synthetic peptide substrates different from 4-methoxy-2-naphthylamine (MNA) amino acids and peptides are to be used. In this paper a technique is described in which cellulose acetate foils impregnated with MNA, 7-amino-4-methyl-coumarin (AMC) and 7-amino-4-trifluoromethylcoumarin (AFC) substrates are overlaid on electrophoresis strips after IEF. After incubation, the foils are viewed with an UV-lamp and photographed. The MNA, AMC and AFC peptides are equally suitable for fluorescence band detection. Using this technique, occasionally protease isoenzymes are found which are more sensitive towards diazonium salts, e.g. aminopeptidase A and M. Sometimes it is also possible to detect thiolproteases which is not the case when employing dye histochemistry.

Positional dependence of enterocyte membrane potential in hamster and rabbit enterocytes

A technique is described allowing microelectrode impalement of enterocytes located at known positions along intestinal villi from rabbits and hamsters. Using this technique a 5 mV hyperpolarization in membrane potential is shown to occur as enterocytes migrate over the basal third of intestinal villi. The villus structure of the hamster ileum is similar to the rabbit, but the enterocyte lifespan in these two tissues differs considerably (enterocyte migration rates of 17.6 and 6.3 microns hr-1 for hamster and rabbit respectively). A correlation was found between the position an enterocyte occupied on the crypt-villus axis and the developmental state of the membrane potential. No such correlation existed when making comparisons on a time basis. These results are discussed both in terms of what is now known concerning different aspects of enterocyte development and in relation to what type of control mechanism might be generally responsible for initiating differentiation in this tissue.

Recent advances in protease research using synthetic substrates

2-Naphthylamine, 4-methoxy-2-naphthylamine, 7-amino-4-methylcoumarin and 7-amino-4-trifluoromethylcoumarin and X peptides have become a useful tool to study proteases by a battery of complementary methods; they now include biochemistry, section biochemistry, location cytochemistry, ultracytochemistry and isoelectric focusing. By the use of these procedures we hope that more insight will be possible in the functional role of proteases in health and disease in the near future.

Fluorescence detection of proteases with AFC, AMC and MNA peptides using isoelectric focusing

The fluorescence detection of proteases is not only possible with MNA but also with AFC and AMC peptides which were used up till now only for biochemical protease investigations. The MNA method is more sensitive due to the coupling capability of MNA with NSA than the AMC and AFC procedure. In comparison with the simultaneous azo-dye method the fluorescence technique may be inferior as far as the sharpness of the bands is concerned. The fluorescence staining is superior, however, if proteinases have to be investigated that are inhibited by diazonium salts, or where interference of diazonium salts and activators or inhibitors occurs; finally, it is a simple procedure to elucidate the value of MNA, AFC and AMC peptides for one and the same protease. In the field of applied isoelectric focusing the azo-dye and fluorescence procedure are now used together by us to detect possible differences in protease isoenzyme patterns in normal and diseased human biopsies, e.g. from liver, kidney and small intestine.

Effect of diet upon enterocyte differentiation in the rat jejunum

Positional and temporal correlates for the development of microvillus membranes and for two of the hydrolytic enzymes they contain have been determined and compared with the ability of enterocytes to transport valine during migration from crypt base to villus tip in jejunal tissue taken from rats maintained on diets containing different amounts of protein. Microvillus elongation and the appearance of both aminopeptidase N (APN) and isomaltase (IM) activities reached maximal rates of expression in enterocytes located 16 +/- 5 micron from the crypt-villus junction. This close positional correlation was not found for the later development of the valine transport function. Feeding rats isoenergetic diets containing 20% instead of 5% protein caused significant increases in both villus height and crypt depth without changing the positional correlations described above. The maximal rates for microvillus elongation and APN and IM appearance were greater and occurred earlier in enterocytes taken from rats fed a high-protein diet. The time of onset and capacity to transport valine were found to be closely correlated for rats maintained on high- and low-protein diets. The ratio of APN to IM activity in fully differentiated enterocytes was either 0.7 or 1.2 depending on whether rats had been fed a low- or high-protein diet. The maximal length of microvillus membranes in fully differentiated enterocytes from rats on a low-protein diet was 1.4 times that found in rats maintained on a high-protein diet. Possible ways in which the microvillus membrane structure of enterocytes, enzyme activity and the ability to transport amino acids might be controlled are discussed. Relative estimates are also made of the probable effects that changes in diet will have on the capacity of the intestine to digest and absorb nutrients.