SAR443809: a selective inhibitor of the complement alternative pathway, targeting complement factor Bb

Dysregulated activation of the complement system is implicated in the onset or progression of several diseases. Most clinical-stage complement inhibitors target the inactive complement proteins present at high concentrations in plasma, which increases target-mediated drug disposition and necessitates high drug levels to sustain therapeutic inhibition. Furthermore, many efforts are aimed at inhibiting only terminal pathway activity, which leaves opsonin-mediated effector functions intact. We describe the discovery of SAR443809, a specific inhibitor of the alternative pathway C3/C5 convertase (C3bBb). SAR443809 selectively binds to the activated form of factor B (factor Bb) and inhibits alternative pathway activity by blocking the cleavage of C3, leaving the initiation of classical and lectin complement pathways unaffected. Ex vivo experiments with patient-derived paroxysmal nocturnal hemoglobinuria erythrocytes show that, although terminal pathway inhibition via C5 blockade can effectively inhibit hemolysis, proximal complement inhibition with SAR443809 inhibits both hemolysis and C3b deposition, abrogating the propensity for extravascular hemolysis. Finally, intravenous and subcutaneous administration of the antibody in nonhuman primates demonstrated sustained inhibition of complement activity for several weeks after injection. Overall, SAR443809 shows strong potential for treatment of alternative pathway-mediated disorders.

Unwinding the Role of the CMG Helicase in Inborn Errors of Immunity

Inborn errors of immunity (IEI) are a collection of diseases resulting from genetic causes that impact the immune system through multiple mechanisms. Natural killer cell deficiency (NKD) is one such IEI where natural killer (NK) cells are the main immune lineage affected. Though rare, the deficiency of several genes has been described as underlying causes of NKD, including MCM4, GINS1, MCM10 , and GINS4 , all of which are involved in the eukaryotic CMG helicase. The CMG helicase is made up of C DC45 – M CM – G INS and accessory proteins including MCM10. The CMG helicase plays a critical role in DNA replication by unwinding the double helix and enabling access of polymerases to single-stranded DNA, and thus helicase proteins are active in any proliferating cell. Replication stress, DNA damage, and cell cycle arrest are among the cellular phenotypes attributed to loss of function variants in CMG helicase proteins. Despite the ubiquitous function of the CMG helicase, NK cells have an apparent susceptibility to the deficiency of helicase proteins. This review will examine the role of the CMG helicase in inborn errors of immunity through the lens of NKD and further discuss why natural killer cells can be so strongly affected by helicase deficiency.

Nek2 Kinase Signaling in Malaria, Bone, Immune and Kidney Disorders to Metastatic Cancers and Drug Resistance: Progress on Nek2 Inhibitor Development

Cell cycle kinases represent an important component of the cell machinery that controls signal transduction involved in cell proliferation, growth, and differentiation. Nek2 is a mitotic Ser/Thr kinase that localizes predominantly to centrosomes and kinetochores and orchestrates centrosome disjunction and faithful chromosomal segregation. Its activity is tightly regulated during the cell cycle with the help of other kinases and phosphatases and via proteasomal degradation. Increased levels of Nek2 kinase can promote centrosome amplification (CA), mitotic defects, chromosome instability (CIN), tumor growth, and cancer metastasis. While it remains a highly attractive target for the development of anti-cancer therapeutics, several new roles of the Nek2 enzyme have recently emerged: these include drug resistance, bone, ciliopathies, immune and kidney diseases, and parasitic diseases such as malaria. Therefore, Nek2 is at the interface of multiple cellular processes and can influence numerous cellular signaling networks. Herein, we provide a critical overview of Nek2 kinase biology and discuss the signaling roles it plays in both normal and diseased human physiology. While the majority of research efforts over the last two decades have focused on the roles of Nek2 kinase in tumor development and cancer metastasis, the signaling mechanisms involving the key players associated with several other notable human diseases are highlighted here. We summarize the efforts made so far to develop Nek2 inhibitory small molecules, illustrate their action modalities, and provide our opinion on the future of Nek2-targeted therapeutics. It is anticipated that the functional inhibition of Nek2 kinase will be a key strategy going forward in drug development, with applications across multiple human diseases.

Arginase as a Potential Biomarker of Disease Progression: A Molecular Imaging Perspective

Arginase is a widely known enzyme of the urea cycle that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. The action of arginase goes beyond the boundaries of hepatic ureogenic function, being widespread through most tissues. Two arginase isoforms coexist, the type I (Arg1) predominantly expressed in the liver and the type II (Arg2) expressed throughout extrahepatic tissues. By producing L-ornithine while competing with nitric oxide synthase (NOS) for the same substrate (L-arginine), arginase can influence the endogenous levels of polyamines, proline, and NO•. Several pathophysiological processes may deregulate arginase/NOS balance, disturbing the homeostasis and functionality of the organism. Upregulated arginase expression is associated with several pathological processes that can range from cardiovascular, immune-mediated, and tumorigenic conditions to neurodegenerative disorders. Thus, arginase is a potential biomarker of disease progression and severity and has recently been the subject of research studies regarding the therapeutic efficacy of arginase inhibitors. This review gives a comprehensive overview of the pathophysiological role of arginase and the current state of development of arginase inhibitors, discussing the potential of arginase as a molecular imaging biomarker and stimulating the development of novel specific and high-affinity arginase imaging probes.

Accumulating insights into the role of phospholipase D2 in human diseases

Phospholipase D2 (PLD2) is a lipid-signaling enzyme that produces the signaling molecule phosphatidic acid (PA) by catalyzing the hydrolysis of phosphatidylcholine (PC). The molecular characteristics of PLD2, the mechanisms of regulation of its activity, its functions in the signaling pathway involving PA and binding partners, and its role in cellular physiology have been extensively studied over the past decades. Although several potential roles of PLD2 have been proposed based on the results of molecular and cell-based studies, the pathophysiological functions of PLD2 in vivo have not yet been fully investigated at the organismal level. Here, we address accumulated evidences that provide insight into the role of PLD2 in human disease. We summarize recent studies using animal models that provide direct evidence of the function of PLD2 in several pathological conditions such as vascular disease, immunological disease, and neurological disease. In light of the use of recently developed PLD2-specific inhibitors showing potential in alleviating pathological conditions, improving our understanding of the role of PLD2 in human disease would be necessary to target the regulation of PLD2 activity as a therapeutic strategy.

Synergy in activating class I PI3Ks

The class I phosphoinositide 3-kinases (PI3Ks) are lipid kinases that transduce a host of cellular signals and regulate a broad range of essential functions including growth, proliferation, and migration. As such, PI3Ks have pivotal roles in diseases such as cancer, diabetes, primary immune disorders, and inflammation. These enzymes are activated downstream of numerous activating stimuli including receptor tyrosine kinases, G protein-coupled receptors (GPCRs), and the Ras superfamily of small G proteins. A major challenge is to decipher how each PI3K isoform is able to successfully synergize these inputs into their intended signaling function. This article highlights recent progress in characterizing the molecular mechanisms of PI3K isoform-specific activation pathways, as well as novel roles for PI3Ks in human diseases, specifically cancer and immune diseases.

[The role of glycosylases of the base excision DNA repair in pathogenesis of hereditary and infectious human diseases]

DNA glycosylases are enzymes that initiate base excision repair, a process of removal of damaged bases from the cellular DNA. Recent data show that variants of two human DNA glycosylases, MUTYH and OGG1, are associated with an increased risk of cancer. In addition, activities of various DNA glycosylases have been implicated in protection of humans from neurodegenerative diseases, immune disorders and viral infections. On the other hand, DNA glycosylases from pathogenic microorganisms help them to avoid the host defensive systems. Thus, DNA glycosylases represent both potential therapeutic agents and drug targets.

CD26/dipeptidyl peptidase IV as a novel therapeutic target for cancer and immune disorders

CD26 is a 110 kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV) activity that is expressed on numerous cell types and has a multitude of biological functions. An important aspect of CD26 biology is its peptidase activity and its functional and physical association with molecules with key roles in various cellular pathways and biological programs. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its linkage with signaling pathways and structures involved in T-lymphocyte activation as well as antigen presenting cell-T-cell interaction. Recent work also suggests that CD26 has a significant role in tumor biology, being both a marker of disease behavior clinically as well as playing an important role in tumor pathogenesis and development. In this paper, we will review emerging data that suggest CD26 may be an appropriate therapeutic target for the treatment of selected neoplasms and immune disorders. Through the use of various experimental approaches and agents to influence CD26/DPPIV expression and activity, such as anti-CD26 antibodies, CD26/DPPIV chemical inhibitors, siRNAs to inhibit CD26 expression, overexpressing CD26 transfectants and soluble CD26 molecules, our group has shown that CD26 interacts with structures with essential cellular functions. Its association with such key molecules as topoisomerase IIalpha, p38 MAPK, and integrin beta1, has important clinical implications, including its potential ability to regulate tumor sensitivity to selected chemotherapies and to influence tumor migration/metastases and tumorigenesis. Importantly, our recent in vitro and in vivo data support the hypothesis that CD26 may indeed be an appropriate target for therapy for selected cancers and immune disorders.

Emerging roles of cysteine cathepsins in disease and their potential as drug targets

The general view on cysteine cathepsins, which were long believed to be primarily involved in intracellular protein turnover, has dramatically changed in last 10 to 15 years. The discovery of new cathepsins, such as cathepsins K, V, X, F and O, and their tissue distribution suggested that at least some of them are involved in very specific cellular processes. Moreover, gene ablation experiments revealed that cathepsins play a vital role in numerous physiological processes, such as antigen processing and presentation, bone remodelling, prohormone processing and wound healing. Their involvement in several pathologies, including osteoporosis, rheumatoid arthritis, osteoarthritis, bronchial asthma and cancer have also been confirmed and today several of them have been validated as relevant targets for therapies. Compounds targeting cathepsins S and K are already in clinical evaluation, whereas others are in experimental phases. The cathepsin K inhibitor AAE-581 (balicatib) as the most advanced of them passed Phase II clinical trials in 2005. In this review, we discuss the current view on cathepsins as an emerging group of targets for several diseases and the development of cathepsin K and S inhibitors for treatment of osteoporosis and various immune disorders.

Telomerase induction in T cells: a cure for aging and disease?

Cells of the immune system are unique among normal somatic cells in that they have the capacity to upregulate the telomere-extending enzyme, telomerase, albeit in a precisely controlled fashion. Kinetic analysis of telomerase activity in long-term T cell cultures has documented that the high level of telomerase induced in concert with activation reaches a peak at 3-5 days, then declines by 3 weeks. The process is recapitulated during secondary antigenic stimulation, but by the third, and all subsequent stimulations in vitro, CD8 T cells are unable to upregulate telomerase. Cell division in the absence of telomerase activity results in progressive telomere shortening, and ultimately, the DNA damage/cell cycle arrest that is signaled by critically short telomeres. Cultures of senescent CD8 T cells show altered cytokine patterns, resistance to apoptosis, and absence of expression of the CD28 costimulatory receptor. CD8 T cells with these and other features of replicative senescence accumulate progressively with age, and at an accelerated rate, during chronic infection with HIV-1. Clinical studies have shown that high proportions of CD8 T cells with the senescent phenotype correlate with several deleterious physiologic outcomes, including poor vaccine responses, bone loss, and increased proinflammatory cytokines. CD8(+)CD28(-) T cells have also been shown to exert suppressive activity on other immune cells. Based on the central role of telomere shortening in the replicative senescence program, we are developing several telomerase-based approaches as potential immunoenhancing treatments for aging and HIV disease. Gene therapy of HIV-specific CD8 T cells with the telomerase catalytic component (hTERT) results in enhanced proliferative capacity, increased anti-viral functions, and a delay in the loss of CD28 expression, with no changes in karyotype or growth kinetics. These proof-of-principle studies have led to screening for pharmacological approaches that might mimic the gene therapy effects, in a more clinically suitable formulation.

The role of iNOS in chronic inflammatory processes in vivo: is it damage-promoting, protective, or active at all?

The expression of the inducible nitric oxide synthase (iNOS) is one of the direct consequences of an inflammatory process. Early studies have focused on the potential toxicity of the ensuing high-output NO-synthesis serving as a means to eliminate pathogens or tumor cells but also contributing to local tissue destruction during chronic inflammation. More recently, however, data are accumulating on a protective effect of high-output NO synthesis and - equally important - on a gene-regulatory function that helps to mount a protective stress response and simultaneously aids in down-regulating the proinflammatory response. These findings appear to contrast to the often observed sustained iNOS-expression during chronic inflammatory diseases, as for instance in Psoriasis vulgaris and other conditions with a chronic Th1-like reactivity. We here pose the question as to whether the iNOS is really active in these diseases. We review the data accumulated on iNOS expression in chronic diseases. We also report on the various factors that potentially interfere with proper NO formation by the expressed enzyme. We also highlight the recent findings of how, why and where evidences emerge that impeded NO formation contributes to chronic disease processes and finally present details on our current understanding of such abnormally low NO synthesis and its contribution to the pathophysiological processes of the human proinflammatory skin disease Psoriasis vulgaris.

Artemis sheds new light on V(D)J recombination

V(D)J recombination represents one of the three mechanisms that contribute to the diversity of the immune repertoire of B lymphocytes and T lymphocytes. It also constitutes a major checkpoint during the development of the immune system. Indeed, any V(D)J recombination deficiency leads to a block of B-cell and T-cell maturation in humans and animal models, leading to severe combined immunodeficiency (T-B-SCID). Nine factors have been identified so far to participate in V(D)J recombination. The discovery of Artemis, mutated in a subset of T-B-SCID, provided some new information regarding one of the missing V(D)J recombinase activities: hairpin opening at coding ends prior to DNA repair of the recombination activating genes 1/2-generated DNA double-strand break. New conditions of immune deficiency in humans are now under investigations and should lead to the identification of additional V(D)J recombination/DNA repair factors.

CD26/dipeptidyl peptidase IV: a regulator of immune function and a potential molecular target for therapy

CD26 is a 110 kDa surface-bound ectopeptidase with intrinsic dipeptidyl peptidase IV (DPP IV) activity, which has multiple biological functions. In this review, we will focus specifically on work demonstrating that CD26 has a key role in immune function as a T cell activation molecule and a regulator of the functional effect of selected biological factors through its DPP IV enzyme activity. As further evidence of the important role played by this multifaceted molecule in immune regulation, we will also discuss experimental attempts from our laboratory and others to influence immune-mediated conditions through CD26 monoclonal antibodies and DPP IV activity with various agents, including anti-CD26 monoclonal antibodies and DPP IV chemical inhibitors. Of special significance from a clinical perspective is also CD26 effect on glucose metabolism through its DPP IV activity and its potential role as a therapeutic target in diabetes. In addition, we will review recent studies that describe the physical and functional interaction of CD26 with other essential cellular structures and the biological consequences of their association. In particular, we will present recent data from our laboratory that demonstrates the correlation between CD26, especially its DPP IV activity, and the key nuclear protein topoisomerase II alpha, an interaction that has important clinical implications. In summary, we will examine the biology of the multifaceted CD26/DPP IV molecule, focusing particularly on its function in immune regulation and its potential role as a molecular target for novel treatment modalities for a number of disease states, ranging from autoimmune diseases, diabetes to malignancies.

Myeloperoxidase in kidney disease

In glomerular and tubulointerstitial disease, polymorphonuclear- and monocyte-derived reactive oxygen species may contribute to oxidative modification of proteins, lipids, and nucleic acids. In part, the processes instigated by reactive oxygen species parallel events that lead to the development of atherosclerosis. Myeloperoxidase (MPO), a heme protein and catalyst for (lipo)protein oxidation is present in these mononuclear cells. The ability of MPO to generate hypochlorous acid/hypochlorite (HOCl/OCl-) from hydrogen peroxide in the presence of chloride ions is a unique and defining activity for this enzyme. The MPO-hydrogen peroxide-chloride system leads to a variety of chlorinated protein and lipid adducts that in turn may cause dysfunction of cells in different compartments of the kidney. The aim of this article is to cover and interpret some experimental and clinical aspects in glomerular and tubulointerstitial diseases in which the MPO-hydrogen peroxide-chloride system has been considered an important pathophysiologic factor in the progression but also the attenuation of experimental renal disease. The colocalization of MPO and HOCl-modified proteins in glomerular peripheral basement membranes and podocytes in human membranous glomerulonephritis, the presence of HOCl-modified proteins in mononuclear cells of the interstitium and in damaged human tubular epithelia, the inflammation induced and exacerbated by MPO antibody complexes in necrotizing glomerulonephritis, and the presence of HOCl-modified epitopes in urine following hyperlipidemia-induced renal damage in rodents suggest that MPO is an important pathogenic factor in glomerular and tubulointerstitial diseases. Specifically, the interaction of MPO with nitric oxide metabolism adds to the complexity of actions of oxidants and may help to explain bimodal partly detrimental partly beneficial effects of the MPO-hydrogen peroxide-chloride system in redox-modulated renal diseases.

Proteinases and their inhibitors in the immune system

The most important roles of proteinases in the immune system are found in apoptosis and major histocompatibility complex (MHC) class II-mediated antigen presentation. A variety of cysteine proteinases, serine proteinases, and aspartic proteinases as well as their inhibitors are involved in the regulation of apoptosis in neutrophils, monocytes, and dendritic cells, in selection of specific B and T lymphocytes, and in killing of target cells by cytotoxic T cells and natural killer cells. In antigen presentation, endocytosed antigens are digested into antigenic peptides by both aspartic and cysteine proteinases. In parallel, MHC class II molecules are processed by aspartic and cysteine proteinases to degrade the invariant chain that occupies the peptide-binding site. Proteinase activity in these processes is highly regulated, particularly by posttranslational activation and the balance between active proteinases and specific endogenous inhibitors such as cystatins, thyropins, and serpins. This article discusses the regulation of proteolytic processes in apoptosis and antigen presentation in immune cells and the consequences of therapeutic interference in the balance of proteinases and their inhibitors.

Growing significance of myeloperoxidase in non-infectious diseases

Myeloperoxidase (MPO) is a glycoprotein released by activated polymorphonuclear neutrophils, which takes part in the defense of the organism through production of hypochlorous acid (HOCl), a potent oxidant. Since the discovery of MPO deficiency, initially regarded as rare and restricted to patients suffering from severe infections, MPO has attracted clinical attention. The development of new technologies allowing screening for this defect has permitted new advances in the comprehension of underlying mechanisms. Apart from its implications for host defense, the expression of MPO restricted to myeloid precursors makes MPO mRNA a good marker of acute myeloid leukemia. In addition, during the last few years, involvement of MPO has been described in numerous diseases such as atherosclerosis, lung cancer, Alzheimer's disease and multiple sclerosis. Both strong oxidative activity and MPO genetic polymorphism have been involved. This review summarizes the broad range of diseases involving MPO and points out the possible use of this protein as a new clinical marker and a future therapeutic target.

[The ubiquitin-proteasome system: the relationship between protein degradation and human diseases]

The ubiquitin-proteasome system is the major machinery in the cell for specific intracellular degradation. Degradation of a protein via the ubiquitin-proteasome pathway involves two successive steps: 1. Covalent attachment of multiple ubiquitin molecules to the substrate, and 2. Degradation of the tagged protein by the 26S proteasome complex. Via targeting of many substrates, the system regulates a broad array of basic cellular processes such as cell cycle, differentiation and signal transduction. Therefore, it is not surprising that aberrations in the system underlie the pathogenesis of many human diseases, among them malignancies, neurodegenerative diseases and many disorders of the immune and inflammatory response. In some pathologies the involvement of the system is direct, whereas in others the mechanistic linkage is less clear. It is expected that the ongoing extensive research in this area will shed light on the underlying pathogenetic mechanisms of the ubiquitin system-related diseases, and will lead to the development of mechanism-based therapeutic modalities.

Ectopeptidases in pathophysiology

Ectopeptidases are transmembrane proteins present in a wide variety of tissues and cell types. Dysregulated expression of certain ectopeptidases in human malignancies suggests their value as clinical markers. Ectopeptidase interaction with agonistic antibodies or their inhibitors has revealed that these ectoenzymes are able to modulate bioactive peptide responses and to influence growth, apoptosis and differentiation, as well as adhesion and motility, all functions involved in normal and tumoral processes. There is evidence that ectopeptidase-mediated signal transduction frequently involves tyrosine phosphorylation. Combined analyses of gene organization and regulation of ectopeptidases by various physiological factors have provided insights into their structure-function relationships. Understanding the roles of ectopeptidases in pathophysiology may have implications in considering them as therapeutic targets.

Serum angiotensin-converting enzyme as a marker for the chronic fatigue-immune dysfunction syndrome: a comparison to serum angiotensin-converting enzyme in sarcoidosis

PURPOSE

To study the reliability of a serum angiotensin-converting enzyme (ACE) assay as a marker for the chronic fatigue-immune dysfunction syndrome (CFIDS), and to compare some enzyme characteristics of ACE in CFIDS with that in sarcoidosis.

PATIENTS AND METHODS

Forty-nine patients with CFIDS and 56 endemic control subjects from Lyndonville, New York, and Charlotte, North Carolina; plus 23 untreated patients with active sarcoidosis, 24 with sarcoidosis receiving corticosteroid therapy, and 32 patient controls without sarcoidosis from California. Serum ACE levels were determined with a spectrophotometric method. The effect of freezing and thawing and the effect of storage at 4 degrees C were compared between CFIDS and sarcoidosis samples.

RESULTS

Serum ACE levels were elevated in 80% of patients with CFIDS and 30% of endemic control subjects as compared with 9.4% of nonendemic California control subjects. The ACE activity in CFIDS differed from that in sarcoidosis because of its lability with storage at 4 degrees C in CFIDS and its partial activation with freezing and thawing. Thus, ACE activity was elevated in the majority of CFIDS patients either upon initial assay or upon a subsequent assay after refreezing. ACE activity was elevated in 87% of patients with active sarcoidosis and was not affected by storage or freezing and thawing.

CONCLUSIONS

Serum ACE elevations may be a useful marker for CFIDS, especially if a method can be developed to distinguish ACE in CFIDS from that in sarcoidosis. The sensitivity for CFIDS was 80%, with 68% specificity in an endemic area. The increased prevalence of serum ACE elevations in endemic controls as compared with nonendemic controls suggests that an ACE increase may be an early manifestation of CFIDS and supports the concept that CFIDS is a definite disease state.

Characterization of specific proteases associated with the surface of human skin fibroblasts, and their modulation in pathology

Human skin fibroblasts were probed for cell surface protease activity. One activity removing dipeptides from the NH2-terminal end of Gly-Pro-pNA was specifically inhibited by di-isopropyl-fluorophosphate (DFP), phenylmethanesulphony fluoride (PMSF), and diprotin A, and thus was identified as dipeptidyl peptidase IV (DPP IV). A group of bestatin-sensitive N-exoaminopeptidase activities was also characterized when Ala-, Leu-, and Arg-pNA were used as chromogenic substrates. Using human monoclonal antibodies anti-CD 13 and anti-CD 26 that recognized, respectively, an N-Ala-aminopeptidase and DPP IV, it was found that human dermal fibroblasts expressed the CD 13 and CD 26 antigen on their surface. In addition, both peptidases were specifically immunoprecipitated by monoclonal antibodies anti-CD 13 and anti-CD 26 from plasma membranes. Cell surface proteolytic activities were also investigated in human fibroblasts derived from dermatological and rheumatic diseases (i.e., psoriasis, rheumatoid arthritis, and lichen planus). It was found that these fibroblasts also expressed both types of proteinases initially identified on normal skin fibroblasts and that the levels of Ala-aminopeptidase activities were similar in all cases. In contrast, the levels of Arg-, Leu-exoaminopeptidase, and DPP IV activities were significantly higher (up to 6.6-fold) in the three pathological fibroblast populations than in their normal counterparts. These proteolytic enzymes, therefore, can potentially serve as markers in dermatological diseases. Taken together, our results suggest that skin fibroblast-derived proteinases associated with both serine and N-aminopeptidase activities may play an important role by participating in the extracellular events associated with fibroblast behaviour.

Phosphodiesterase and immune dysfunction in atopic dermatitis

Atopic dermatitis and the other atopic conditions occur as a result of direct or indirect influences from cells of hematopoietic origin. Cellular immune abnormalities have been described, but appear to be secondary to cutaneous inflammation in atopic dermatitis. Pharmacophysiologic abnormalities are numerous and may relate to defective cyclic nucleotide metabolism in circulating and infiltrating leukocytes. A consistent leukocyte abnormality is elevated cyclic AMP-phosphodiesterase. This enzyme abnormality results in reduced intracellular cyclic AMP, creating a net permissive effect upon cell function. Phosphodiesterase inhibitors have been demonstrated to reduce abnormal histamine release and IgE production by cultured leukocytes. Studies of phosphodiesterase and associated defects in atopic leukocytes may lead to delineation of basic pathogenetic mechanisms as well as providing the potential for therapeutic targeting.

Microassay for adenosine deaminase, the enzyme lacking in some forms of immunodeficiency, in mouse preimplantation embryos

A highly sensitive biochemical microassay has been developed for adenosine deaminase (ADA; EC 3.5.4.4), the enzyme deficient in approximately 20% of cases of severe combined immuno-deficiency disease (SCID). The microassay is capable of detecting femtomolar amounts of reaction product in a single blastomere from a mouse 8-cell embryo and thus is sensitive enough to be considered for the possible preimplantation diagnosis of SCID in human embryos.

Enzyme activities in the rabbit cornea during immunogenic keratitis

In rabbits inflammation of the cornea was induced by intrastromal injection of horse serum. Between 2 and 4 weeks after injection, infiltration of the cornea with leukocytes and neovascularization could be observed. During this period, the rabbits were killed and their corneas analyzed for protein, alkaline phosphatase, acid phosphatase, N-acetyl-beta-D-glucosaminidase, and lactate dehydrogenase. The enzyme activities in the inflamed corneal stroma reflect the high lysosomal activity, which probably originates from the leukocytes. The enzyme activities in the epithelium indicate that the tissue is abnormal and undergoing repair processes.

Retrospective demonstration of endogenous peroxidase activity in plastic-embedded tissues conventionally prepared for electron microscopy

A procedure is described that permits retrospective demonstration of intracellular endogenous peroxidase activity in tissue conventionally prepared for electron microscopy, i.e., doubly fixed with aldehydes and osmium tetroxide, "stained" in block with uranyl acetate, and embedded in epoxy resins. Using sodium ethoxide, plastic was removed from 1 micrometer sections; subsequently, the sections were incubated for 20 min in diaminobenzidine solution (44 mg/100 ml) made in acetate-citric acid buffer, pH 5.6, with 0.01% hydrogen peroxide. After this treatment, the sections were rinsed, dehydrated, and mounted. Cell types known to have endogenous peroxidase activity (red blood cells, macrophages, and retinal pigment epithelium cells in our preparations) show positive granules in their cytoplasm--control sections were uniformly negative. This method, which could also be used prospectively, cytochemically demonstrates endogenous peroxidase activity upon optical microscopical examination of the treated tissues; correlative electron microscopic studies may be performed on the same tissue block, or even adjacent sections.

Purine nucleoside phosphorylase deficiency: altered kinetic properties of a mutant enzyme

Erythrocyte purine nucleoside phosphorylase from two brothers had 0.5% of normal activity. It differed from the normal enzyme by a tenfold increase in the Michaelis constant for inosine, an inability of inosine to protect against thermal lability, and a more positive net charge. The altered kinetic properties may account for the milder disease in the patients compared to the previously described cases. The data provide evidence for a structural gene mutation and genetic heterogeneity in the new disease of purine nucleoside phosphorylase deficiency and T cell dysfunction.