Epacadostat stabilizes the apo-form of IDO1 and signals a pro-tumorigenic pathway in human ovarian cancer cells

The tryptophan-degrading enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is a plastic immune checkpoint molecule that potently orchestrates immune responses within the tumor microenvironment (TME). As a heme-containing protein, IDO1 catalyzes the conversion of the essential amino acid tryptophan into immunoactive metabolites, called kynurenines. By depleting tryptophan and enriching the TME with kynurenines, IDO1 catalytic activity shapes an immunosuppressive TME. Accordingly, the inducible or constitutive IDO1 expression in cancer correlates with a negative prognosis for patients, representing one of the critical tumor-escape mechanisms. However, clinically trialed IDO1 catalytic inhibitors disappointed the expected anti-tumor efficacy. Interestingly, the non-enzymatic apo-form of IDO1 is still active as a transducing protein, capable of promoting an immunoregulatory phenotype in dendritic cells (DCs) as well as a pro-tumorigenic behavior in murine melanoma. Moreover, the IDO1 catalytic inhibitor epacadostat can induce a tolerogenic phenotype in plasmacytoid DCs, overcoming the catalytic inhibition of IDO1. Based on this recent evidence, IDO1 plasticity was investigated in the human ovarian cancer cell line, SKOV-3, that constitutively expresses IDO1 in a dynamic balance between the holo- and apo-protein, and thus potentially endowed with a dual function (i.e., enzymatic and non-enzymatic). Besides inhibiting the catalytic activity, epacadostat persistently stabilizes the apo-form of IDO1 protein, favoring its tyrosine-phosphorylation and promoting its association with the phosphatase SHP-2. In SKOV-3 cells, both these early molecular events activate a signaling pathway transduced by IDO1 apo-protein, which is independent of its catalytic activity and contributes to the tumorigenic phenotype of SKOV-3 cells. Overall, our findings unveiled a new mechanism of action of epacadostat on IDO1 target, repositioning the catalytic inhibitor as a stabilizer of the apo-form of IDO1, still capable of transducing a pro-tumorigenic pathway in SKOV-3 tumor. This mechanism could contribute to clarify the lack of effectiveness of epacadostat in clinical trials and shed light on innovative immunotherapeutic strategies to tackle IDO1 target.

Membrane Localization and Phosphorylation of Indoleamine 2,3-Dioxygenase 2 (IDO2) in A549 Human Lung Adenocarcinoma Cells: First Steps in Exploring Its Signaling Function

Indoleamine 2,3-dioxygenase 2 (IDO2) is a paralog of Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan-degrading enzyme producing immunomodulatory molecules. However, the two proteins are unlikely to carry out the same functions. IDO2 shows little or no tryptophan catabolic activity and exerts contrasting immunomodulatory roles in a context-dependent manner in cancer and autoimmune diseases. The recently described potential non-enzymatic activity of IDO2 has suggested its possible involvement in alternative pathways, resulting in either pro- or anti-inflammatory effects in different models. In a previous study on non-small cell lung cancer (NSCLC) tissues, we found that IDO2 expression revealed at the plasma membrane level of tumor cells was significantly associated with poor prognosis. In this study, the A549 human cell line, basally expressing IDO2, was used as an in vitro model of human lung adenocarcinoma to gain more insights into a possible alternative function of IDO2 different from the catalytic one. In these cells, immunocytochemistry and isopycnic sucrose gradient analyses confirmed the IDO2 protein localization in the cell membrane compartment, and the immunoprecipitation of tyrosine-phosphorylated proteins revealed that kinase activities can target IDO2. The different localization from the cytosolic one and the phosphorylation state are the first indications for the signaling function of IDO2, suggesting that the IDO2 non-enzymatic role in cancer cells is worthy of deeper understanding.

A back-door insights into the modulation of Src kinase activity by the polyamine spermidine

Src is a protein tyrosine kinase commonly activated downstream of transmembrane receptors and plays key roles in cell growth, migration and survival signaling pathways. In conventional dendritic cells (cDCs), Src is involved in the activation of the non-enzymatic functions of indoleamine 2,3-dioxygenase 1 (IDO1), an immunoregulatory molecule endowed with both catalytic activity and signal transducing properties. Prompted by the discovery that the metabolite spermidine confers a tolerogenic phenotype on cDCs that is dependent on both the expression of IDO1 and the activity of Src kinase, we here investigated the spermidine mode of action. We found that spermidine directly binds Src in a previously unknown allosteric site located on the backside of the SH2 domain and thus acts as a positive allosteric modulator of the enzyme. Besides confirming that Src phosphorylates IDO1, here we showed that spermidine promotes the protein-protein interaction of Src with IDO1. Overall, this study may pave the way toward the design of allosteric modulators able to switch on/off the Src-mediated pathways, including those involving the immunoregulatory protein IDO1.

GLP-1 receptor agonists as promising disease-modifying agents in WFS1 spectrum disorder

WFS1 spectrum disorder (WFS1-SD) is a rare monogenic neurodegenerative disorder whose cardinal symptoms are childhood-onset diabetes mellitus, optic atrophy, deafness, diabetes insipidus, and neurological signs ranging from mild to severe. The prognosis is poor as most patients die prematurely with severe neurological disabilities such as bulbar dysfunction and organic brain syndrome. Mutation of the WFS1 gene is recognized as the prime mover of the disease and responsible for a dysregulated ER stress signaling, which leads to neuron and pancreatic β-cell death. There is no currently cure and no treatment that definitively arrests the progression of the disease. GLP-1 receptor agonists appear to be an efficient way to reduce elevated ER stress in vitro and in vivo, and increasing findings suggest they could be effective in delaying the progression of WFS1-SD. Here, we summarize the characteristics of GLP-1 receptor agonists and preclinical and clinical data obtained by testing them in WFS1-SD as a feasible strategy for managing this disease.

The signaling function of IDO1 incites the malignant progression of mouse B16 melanoma

Indoleamine 2,3 dioxygenase 1 (IDO1), a leader tryptophan-degrading enzyme, represents a recognized immune checkpoint molecule. In neoplasia, IDO1 is often highly expressed in dendritic cells infiltrating the tumor and/or in tumor cells themselves, particularly in human melanoma. In dendritic cells, IDO1 does not merely metabolize tryptophan into kynurenine but, after phosphorylation of critical tyrosine residues in the non-catalytic small domain, it triggers a signaling pathway prolonging its immunoregulatory effects by a feed-forward mechanism. We here investigated whether the non-enzymatic function of IDO1 could also play a role in tumor cells by using B16-F10 mouse melanoma cells transfected with either the wild-type Ido1 gene (Ido1^WT ) or a mutated variant lacking the catalytic, but not signaling activity (Ido1^H350A ). As compared to the Ido1^WT -transfected counterpart (B16^WT), B16-F10 cells expressing Ido1^H350A (B16^H350A) were characterized by an in vitro accelerated growth mediated by increased Ras and Erk activities. Faster growth and malignant progression of B16^H350A cells, also detectable in vivo, were found to be accompanied by a reduction in tumor-infiltrating CD8⁺ T cells and an increase in Foxp3⁺ regulatory T cells. Our data, therefore, suggest that the IDO1 signaling function can also occur in tumor cells and that alternative therapeutic approach strategies should be undertaken to effectively tackle this important immune checkpoint molecule.

The catalytic inhibitor epacadostat can affect the non-enzymatic function of IDO1

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1.

Unrevealing the Role of TLRs in the Pathogenesis of Autoimmune Disease by Using Mouse Model of Diabetes

Toll-like receptors (TLRs) are receptors of the innate immune system specialized in recognizing conserved molecular pattern of pathogens and initiating an appropriate immune response. Along with the recognition of foreign materials, TLRs have also been shown to respond to endogenous molecules, thus mediating the development of autoimmune diseases. Type 1 diabetes (T1D) is a prototypic autoimmune disease in which TLRs play a pathogenic role. We here describe a protocol to study the role of TLRs in the development and progression of T1D by resorting to the nonobese diabetic (NOD) mouse model.

Unconventional Pathways of Protein Secretion: Mammals vs. Plants

In eukaryotes, many proteins contain an N-terminal signal peptide that allows their translocation into the endoplasmic reticulum followed by secretion outside the cell according to the classical secretory system. However, an increasing number of secreted proteins lacking the signal peptide sequence are emerging. These proteins, secreted in several alternative ways collectively known as unconventional protein secretion (UPS) pathways, exert extracellular functions including cell signaling, immune modulation, as well as moonlighting activities different from their well-described intracellular functions. Pathways for UPS include direct transfer across the plasma membrane, secretion from endosomal/multivesicular body-related components, release within plasma membrane-derived microvesicles, or use of elements of autophagy. In this review we describe the mammals and plants UPS pathways identified so far highlighting commonalities and differences.

The [1,2,4]Triazolo[4,3-a]pyridine as a New Player in the Field of IDO1 Catalytic Holo-Inhibitors

Inhibitors of indoleamine 2,3-dioxygenase 1 (IDO1) are considered a promising strategy in cancer immunotherapy as they are able to boost the immune response and to work in synergy with other immunotherapeutic agents. Despite the fact that no IDO1 inhibitor has been approved so far, recent studies have shed light on the additional roles that IDO1 mediates beyond its catalytic activity, conferring new life to the field. Here we present a novel class of compounds originated from a structure-based virtual screening made on IDO1 active site. The starting hit compound is a novel chemotype based on a [1,2,4]triazolo[4,3-a]pyridine scaffold, so far underexploited among the heme binding moieties. Thanks to the rational and in silico-guided design of analogues, an improvement of the potency to sub-micromolar levels has been achieved, with excellent in vitro metabolic stability and exquisite selectivity with respect to other heme-containing enzymes.

Human Indoleamine 2,3-dioxygenase 1 (IDO1) Expressed in Plant Cells Induces Kynurenine Production

Genetic engineering of plants has turned out to be an attractive approach to produce various secondary metabolites. Here, we attempted to produce kynurenine, a health-promoting metabolite, in plants of Nicotiana tabacum (tobacco) transformed by Agrobacterium tumefaciens with the gene, coding for human indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme responsible for the kynurenine production because of tryptophan degradation. The presence of IDO1 gene in transgenic plants was confirmed by PCR, but the protein failed to be detected. To confer higher stability to the heterologous human IDO1 protein and to provide a more sensitive method to detect the protein of interest, we cloned a gene construct coding for IDO1-GFP. Analysis of transiently transfected tobacco protoplasts demonstrated that the IDO1-GFP gene led to the expression of a detectable protein and to the production of kynurenine in the protoplast medium. Interestingly, the intracellular localisation of human IDO1 in plant cells is similar to that found in mammal cells, mainly in cytosol, but in early endosomes as well. To the best of our knowledge, this is the first report on the expression of human IDO1 enzyme capable of secreting kynurenines in plant cells.

Novel mutations in the WFS1 gene are associated with Wolfram syndrome and systemic inflammation

Mutations in the WFS1 gene, encoding wolframin (WFS1), cause endoplasmic reticulum (ER) stress and are associated with a rare autosomal-recessive disorder known as Wolfram syndrome (WS). WS is clinically characterized by childhood-onset diabetes mellitus, optic atrophy, deafness, diabetes insipidus and neurological signs. We identified two novel WFS1 mutations in a patient with WS, namely, c.316-1G > A (in intron 3) and c.757A > T (in exon 7). Both mutations, located in the N-terminal region of the protein, were predicted to generate a truncated and inactive form of WFS1. We found that although the WFS1 protein was not expressed in peripheral blood mononuclear cells (PBMCs) of the proband, no constitutive ER stress activation could be detected in those cells. In contrast, WS proband’s PBMCs produced very high levels of proinflammatory cytokines (i.e. TNF-α, IL-1β, and IL-6) in the absence of any stimulus. WFS1 silencing in PBMCs from control subjects by means of small RNA interference also induced a pronounced proinflammatory cytokine profile. The same cytokines were also significantly higher in sera from the WS patient as compared to matched healthy controls. Moreover, the chronic inflammatory state was associated with a dominance of proinflammatory T helper 17 (Th17)-type cells over regulatory T (Treg) lymphocytes in the WS PBMCs. The identification of a state of systemic chronic inflammation associated with WFS1 deficiency may pave the way to innovative and personalized therapeutic interventions in WS.

Class IA PI3Ks regulate subcellular and functional dynamics of IDO1

Knowledge of a protein's spatial dynamics at the subcellular level is key to understanding its function(s), interactions, and associated intracellular events. Indoleamine 2,3-dioxygenase 1 (IDO1) is a cytosolic enzyme that controls immune responses via tryptophan metabolism, mainly through its enzymic activity. When phosphorylated, however, IDO1 acts as a signaling molecule in plasmacytoid dendritic cells (pDCs), thus activating genomic effects, ultimately leading to long-lasting immunosuppression. Whether the two activities-namely, the catalytic and signaling functions-are spatially segregated has been unclear. We found that, under conditions favoring signaling rather than catabolic events, IDO1 shifts from the cytosol to early endosomes. The event requires interaction with class IA phosphoinositide 3-kinases (PI3Ks), which become activated, resulting in full expression of the immunoregulatory phenotype in vivo in pDCs as resulting from IDO1-dependent signaling events. Thus, IDO1's spatial dynamics meet the needs for short-acting as well as durable mechanisms of immune suppression, both under acute and chronic inflammatory conditions. These data expand the theoretical basis for an IDO1-centered therapy in inflammation and autoimmunity.

Effect of Probiotic Administration on Serum Tryptophan Metabolites in Pediatric Type 1 Diabetes Patients

Type 1 diabetes (T1D) is characterized by anomalous functioning of the immuno regulatory, tryptophan-catabolic enzyme indoleamine 2,3 dioxygenase 1 (IDO1). In T1D, the levels of kynurenine-the first byproduct of tryptophan degradation via IDO1-are significantly lower than in nondiabetic controls, such that defective immune regulation by IDO1 has been recognized as potentially contributing to autoimmunity in T1D. Because tryptophan catabolism-and the production of immune regulatory catabolites-also occurs via the gut microbiota, we measured serum levels of tryptophan, and metabolites thereof, in pediatric, diabetic patients after a 3-month oral course of Lactobacillus rhamnosus GG. Daily administration of the probiotic significantly affected circulating levels of tryptophan as well as the qualitative pattern of metabolite formation in the diabetic patients, while it decreased inflammatory cytokine production by the patients. This study suggests for the first time that a probiotic treatment may affect systemic tryptophan metabolism and restrain proinflammatory profile in pediatric T1D.

Engagement of Nuclear Coactivator 7 by 3-Hydroxyanthranilic Acid Enhances Activation of Aryl Hydrocarbon Receptor in Immunoregulatory Dendritic Cells

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the first step in the kynurenine pathway of tryptophan (Trp) degradation that produces several biologically active Trp metabolites. L-kynurenine (Kyn), the first byproduct by IDO1, promotes immunoregulatory effects via activation of the Aryl hydrocarbon Receptor (AhR) in dendritic cells (DCs) and T lymphocytes. We here identified the nuclear coactivator 7 (NCOA7) as a molecular target of 3-hydroxyanthranilic acid (3-HAA), a Trp metabolite produced downstream of Kyn along the kynurenine pathway. In cells overexpressing NCOA7 and AhR, the presence of 3-HAA increased the association of the two molecules and enhanced Kyn-driven, AhR-dependent gene transcription. Physiologically, conventional (cDCs) but not plasmacytoid DCs or other immune cells expressed high levels of NCOA7. In cocultures of CD4⁺ T cells with cDCs, the co-addition of Kyn and 3-HAA significantly increased the induction of Foxp3⁺ regulatory T cells and the production of immunosuppressive transforming growth factor β in an NCOA7-dependent fashion. Thus, the co-presence of NCOA7 and the Trp metabolite 3-HAA can selectively enhance the activation of ubiquitary AhR in cDCs and consequent immunoregulatory effects. Because NCOA7 is often overexpressed and/or mutated in tumor microenvironments, our current data may provide evidence for a new immune check-point mechanism based on Trp metabolism and AhR.

IL-35Ig-expressing dendritic cells induce tolerance via Arginase 1

The cytokine interleukin IL‐35 is known to exert strong immunosuppressive functions. Indoleamine 2,3‐dioxygenase 1 (IDO1) and Arginase 1 (Arg1) are metabolic enzymes that, expressed by dendritic cells (DCs), contribute to immunoregulation. Here, we explored any possible link between IL‐35 and the activity of those enzymes. We transfected a single chain IL‐35Ig gene construct in murine splenic DCs (DC₃₅) and assessed any IDO1 and Arg1 activities as resulting from ectopic IL‐35Ig expression, both in vitro and in vivo. Unlike Ido1, Arg1 expression was induced in vitro in DC₃₅, and it conferred an immunosuppressive phenotype on those cells, as revealed by a delayed‐type hypersensitivity assay. Moreover, the in vivo onset of a tolerogenic phenotype in DC₃₅ was associated with the detection of CD25⁺CD39⁺, rather than Foxp3⁺, regulatory T cells. Therefore, Arg1, but not Ido1, expression in DC₃₅ appears to be an early event in IL‐35Ig–mediated immunosuppression.

Polyunsaturated fatty acids of germ cell membranes, glutathione and blutathione-dependent enzyme-PHGPx: from basic to clinic

The lipid metabolism in sperm cells is important both for energy production and for cell structure. A special composition of membrane phospholipids, rich in polyunsaturated fatty acids (PUFA), and the different composition of sperm and immature germ cell membrane are described and discussed. Testis germ cells as well as epididymal maturing spermatozoa are endowed with enzymatic and non-enzymatic scavenger systems to prevent lipoperoxidative damage. Catalase, superoxide dismutase, and glutathione-dependent oxidoreductases are present in variable amounts in the different developmental stages. Phospholipid hydroperoxide glutathione peroxidase (PHGPx) activity and roles in caput and cauda epididymal sperm cells are discussed. Also seminal plasma has a highly specialized scavenger system that defends the sperm membrane against lipoperoxidation and the degree of PUFA insaturation acts to achieve the same goal. Systemic predisposition and a number of pathologies can lead to an anti-oxidant/pro-oxidant disequilibrium. Scavengers, such as glutathione can be used to treat these cases as they can restore the physiological constitution of PUFA in the cell membrane.

Guinea pig transglutaminase immunolinked assay does not predict coeliac disease in patients with chronic liver disease

BACKGROUND

It has been suggested that serological screening for coeliac disease (CD) should be performed in patients with chronic unexplained hypertransaminasaemia.

AIMS

To evaluate the specificity for CD diagnosis of serum IgA antitissue transglutaminase (tTG) determination in consecutive patients with chronic hypertransaminasaemia using the most widely utilised ELISA based on tTG from guinea pig as the antigen.

PATIENTS AND METHODS

We studied 98 patients with chronic hypertransaminasaemia, evaluated for the first time in a hepatology clinic. Serum anti-tTG and antiendomysial (EmA) assays were performed. Patients positive for EmA and/or anti-tTG were proposed for intestinal biopsy. Finally, all sera were reassayed for anti-tTG using an ELISA based on human recombinant tTG as the antigen.

RESULTS

A total of 94/98 hypertransaminasaemic patients were positive for hepatitis virus markers, with 82/98 (83%) positive for anti-hepatitis C virus. Liver histology showed that most patients had mild or moderate chronic hepatitis while severe fibrosis or overt liver cirrhosis was found in 20/98. CD screening showed that 15/98 (16%) hypertransaminasaemic subjects had anti-tTG values in the same range as CD patients; however, IgA EmA were positive in only 2/98 (2%). Distal duodenal biopsy, performed in nine patients, showed subtotal villous atrophy in the two EmA+/anti-tTG+ patients but was normal in 7/7 EmA-/anti-tTG+ subjects. The presence of anti-tTG+ values in EmA- patients was unrelated to particular gastrointestinal symptoms, other associated diseases, severity of liver histology, or distribution of viral hepatitis markers. There was a significantly higher frequency of positive serum autoantibodies (antinuclear, antimitochondrial, antismooth muscle, and anti-liver-kidney microsomal antibodies) in anti-tTG+/EmA- patients than in the other subjects (9/13 v 10/83; p<0.003). Also, a correlation was found between serum gamma globulin and anti-tTG values (p<0.01). When sera were tested with the ELISA based on human tTG as the antigen, no false positive results were observed: only the two EmA+ patients with atrophy of the intestinal mucosa were positive for anti-tTG while all others were negative, including those false positive in the ELISA based on guinea pig tTG as the antigen.

CONCLUSIONS

In patients with elevated transaminases and chronic liver disease there was a high frequency of false positive anti-tTG results using the ELISA based on tTG from guinea pig as the antigen. Indeed, the presence of anti-tTG did not correlate with the presence of EmA or CD. These false positives depend on the presence of hepatic proteins in the commercial tTG obtained from guinea pig liver and disappear when human tTG is used as the antigen in the ELISA system. We suggest that the commonly used tTG ELISA based on guinea pig antigen should not be used as a screening tool for CD in patients with chronic liver disease.

Efficacy of long-term treatment with thalidomide in children and young adults with Crohn disease: preliminary results

BACKGROUND

Several proinflammatory cytokines are involved in the pathogenesis of inflammatory bowel diseases. A significant role has been given to tumor necrosis factor alpha (TNF-alpha) as a guide proinflammatory cytokine. Thalidomide selectively reduces TNF-alpha production by inflammatory cells. The aim of the study was to assess the efficacy of thalidomide to induce and maintain remission in refractory Crohn disease.

METHODS

The decision to administer thalidomide was made on the basis of patient intolerance or resistance to conventional medical treatment or as the last medical resort before surgical intervention. Only 5 of 96 patients with inflammatory bowel disease satisfied these criteria. All five patients had Crohn disease (male: mean age, 17 years). Thalidomide was administered at night at a dose of 1.5-2 mg/kg/day. The Pediatric Crohn Disease Activity Index, modified Harvey-Bradshaw scores, and steroids reduction were used to assess clinical response.

RESULTS

Disease activity decreased consistently in four patients with a reduction of mean Pediatric Crohn Disease Activity Index from 36,9 to 2,5 and the mean Harvey-Bradshaw from 8.5 to 0.75 after 3 months of treatment. Steroid treatment (mean dose, 35 mg/day before treatment) was tapered and then discontinued, in four patients, within 1-3 months. Four patients are in remission after 19-24 months of treatment. The fifth patient discontinued thalidomide after 1 week because of distal paresthesia.

CONCLUSION

Thalidomide seems to be an effective and safe treatment in patients with refractory Crohn disease. This is the first report of long-term use of thalidomide in refractory Crohn disease in pediatric patients.

Interaction with Borrelia burgdorferi causes increased expression of the CR3 integrin and increased binding affinity to fibronectin via CR3

We have previously demonstrated that the alphaMbeta2 integrin (known as CR3 or Mac-1) expressed on neutrophils (PMNs) and/or on CHO Mac-1 transfected cells,in the presence of serum complement binds B. burgdorferi and promotes an increased non -opsonic adhesion, in the presence of serum complement. In this study we demonstrate that: 1) living motile B. burgdorferiand recombinant lipidated OspA and OspC, up-regulate CR3 expression on PMNs; 2) in the absence of serum, B. burgdorferi induces increased adhesion of CHO cells expressing CR3 to fibronectin, an extracellular matrix protein. Both the I-domain and the lectin-like domain of CR3 are involved in the binding recognition and activation because mAb anti I-domain and N-acetyl-glucosamine inhibit cell adhesion to fibronectin. These data indicate that B. burgdorferi whole cells, but not Osps, activate CR3 integrin; since this receptor plays a key role in priming neutrophils to important inflammatory events, the interaction of B. burgdorferi with neutrophils via the CR3 may enhance their role both in defence and in disease.

Lipoperoxidation damage of spermatozoa polyunsaturated fatty acids (PUFA): scavenger mechanisms and possible scavenger therapies

The lipid metabolism in sperm cells is important both as one of the main sources for energy production and for cell structure. The double leaflets of the membrane should be considered not simply as a passive lipid film, but as a very specialized structure. The complete maturation of the sperm cell membrane is attained after testicular lipid biosynthetic processes and after passage through the epididymis. A special composition of membrane phospholipids, rich in polyunsaturated fatty acids (PUFA), and the different composition of sperm and immature germ cell membrane are described and discussed. Testis germ cells as well as epididymal maturing spermatozoa are endowed with enzymatic and non-enzymatic scavenger systems to prevent lipoperoxidative damage. Catalase, superoxide dismutase and GSH-dependent oxidoreductases are present in variable amounts in the different developmental stages. Phospholipid hydroperoxide GSH peroxidase (PHGPx) activity and alpha tochopherol of epididymal spermatozoa are considered in detail. Their distribution and roles in caput and cauda epididymal sperm cells are discussed. Seminal plasma also has a highly specialized scavenger system that defends the sperm membrane against lipoperoxidation and the degree of PUFA insaturation acts to achieve the same goal. Systemic predisposition and a number of pathologies can lead to an anti-oxidant/pro-oxidant disequilibrium. Scavengers, such as GSH, can be used to treat these cases as they can restore the physiological constitution of PUFA in the cell membrane. The results of GSH therapy are presented and discussed.

Antioxidant systems in rat epididymal spermatozoa

Mammalian caput and cauda epididymidal spermatozoa exhibit diverse stages of maturation, and their plasma membrane shows diverse composition and stability levels, thus enabling these spermatozoa to undergo the acrosomal reaction after transit through the epididymis. As a result, the study of antiperoxidative mechanisms is quite relevant, since epididymal spermatozoa must be properly protected against agents such as reactive oxygen species, which can impair the complex maturation process. We considered activities of certain enzymes (glutathione peroxidase [GPx], phospholipid hydroperoxide glutathione peroxidase [PHGPx], glutathione reductase [GR], superoxide dismutase [SOD], and catalase [CAT]) and the vitamin E content in isolated rat caput and cauda epididymidal spermatozoa. The results indicate that caput epididymidal sperm have significantly greater PHGPx (3.5x), GPx (2.4x), and SOD (1.7x) activities, as well as a greater amount of vitamin E (3.8x). There were no detectable differences in the GR and CAT activities of caput and cauda epididymidal spermatozoa. The substantial drop in PHGPx activity during epididymal transit is discussed in relation to an additional function of this enzyme: the use of caput sperm protamines as a sulfhydryl substrate. In vitro peroxidation of the two sperm populations by the free radical generator (azo-initiator) 2,2'-azobis(2-amidinopropane) dihydrochloride revealed that only about 13% of the vitamin E content of the caput epididymidal spermatozoa was consumed, which contrasts with the greater consumption (about 70%) of the vitamin in cauda epididymidal spermatozoa. Selective inhibition of PHGPx, SOD, or CAT did not change this picture. The higher susceptibility of cauda epididymidal spermatozoa to radicals is discussed in relation to the diverse enzymatic activities, vitamin E content, and peroxidative response. These factors are correlated with the different stages of sperm cell maturation, which are characterized-from caput to cauda epididymidis-by progressive destabilization of the plasma and acrosomal membranes.

Distribution and possible novel role of phospholipid hydroperoxide glutathione peroxidase in rat epididymal spermatozoa

The selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PHGPx, EC 1.11.1.12) is present, in both free and membrane-bound form, in several mammalian tissues. It utilizes thiols such as glutathione to specifically scavenge phospholipid hydroperoxides. The testis exhibits the highest PHGPx-specific activity so far measured, and interest in the presence and function of the enzyme in this tissue has recently grown. Here we report the localization of PHGPx in rat epididymal spermatozoa and its distribution in subfractions obtained by sucrose density gradient centrifugation. Immunochemical evidence and enzymatic activity revealed for the first time that PHGPx is present in sperm heads and tail midpiece mitochondria. The binding of the enzyme to spermatozoa, head, and mitochondria was barely affected by ionic strength or thiols or detergents, as compared to the detachment of PHGPx obtained from testis nuclei. Moreover, we demonstrated that pure PHGPx exhibits a higher thiol-oxidase activity toward isolated epididymal caput protamines than toward protamines from epididymal cauda. These results suggest a role for the enzyme in the maturation of spermatozoa through the metabolism of hydroperoxides and sperm thiol oxidation, in addition to its serving as an antioxidant protector.

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) in rat testis nuclei is bound to chromatin

In rat testis nuclei the activity of the selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PHGPx, EC 1.11.1.12) is much higher than in other tissues and subcellular compartments, with the sole exception of mitochondria. In nuclei, the bound enzyme is solubilized by DNase I treatment, thus suggesting a binding to chromatin. Treatment with ionic strength releases about 70% of bound PHGPx, suggesting that electrostatic bonds are involved. Immunogold electron microscopy indicates the association of PHGPx with chromatin structures in isolated nuclei. A possible interpretation of these data is a PHGPx protective role against DNA peroxidative damage. Furthermore, in agreement with kinetic and structural information, PHGPx-chromatin binding could suggest an hypothetical thiol oxidase activity toward specific thiol bearing proteins which could substitute for GSH as alternative donor substrates. Such activity could give to the enzyme a new important function which is not only protective but also has a specific regulatory function in chromatin condensation.

Rat testis mitochondrial phospholipid hydroperoxide glutathione peroxidase does not protect endogenous vitamin E against Fe2+-induced (lipo)peroxidation

Rat testis mitochondria contain large amounts of both seleno-enzyme phospholipid hydroperoxide glutathione peroxidase (EC 1.11.1.12, PHGPx) and alpha-tocopherol. The scavenger role of vitamin E consists of transforming the lipoperoxyl radicals into lipid hydroperoxides, thus interrupting the peroxidative cascade. These hydroperoxides are in turn substrates of the PHGPx, which is considered one of the most important specific enzymes capable of protecting, in situ, the membranes from lipid peroxidation. A connection or synergism could, therefore, be envisaged between vitamin and enzyme opposing lipid damage in the mitochondria. Here we present data concerning the HPLC evaluation of vitamin E consumption in rat testis mitochondria and mitochondrial membranes, under different conditions of PHGPx activity, after Fe2+-induced lipid peroxidation. We have found that the enzyme activity, under the conditions tested, does not spare vitamin E from its peroxidation, therefore indicating that the postulated synergism between PHGPx and alpha-tocopherol can be excluded in rat testis mitochondria.

Distribution of phospholipid hydroperoxide glutathione peroxidase (PHGPx) in rat testis mitochondria

The distribution of phospholipid hydroperoxide glutathione peroxidase (PHGPx) in isolated rat testis mitochondria was investigated, using a reverse sucrose density gradient centrifugation procedure for the separation of the inner and outer membranes and the contact sites between the two membranes. The results indicate that PHGPx is largely localized in the contact sites fraction. This finding might therefore suggest that the enzyme has more than just an antioxidant function.

Characterization of a voltage-dependent anionic channel in fused synaptosomes isolated from rat hippocampi

The inside out configuration of the patch-clamp technique was used to study single-channel anionic currents from purified hippocampal synaptosomes fused into liposomes to form giant proteoliposomes. At least six different anionic channels with unitary conductances of 22-150 pS were found. The most frequently observed was the 32-pS conductance channel. This was voltage-dependent; the open probability increased from 0.20 at -40 mV to 0.46 at 40 mV. This channel may be involved in the repolarization of nerve terminal membranes after an action potential, thus, limiting the duration of the spike and the transmitter release.

Ionic permeability of the mitochondrial outer membrane

The ionic permeability of the outer mitochondrial membrane (OMM) was studied with the patch clamp technique. Electrical recording of intact mitochondria (hence of the outer membrane (OM], derived from mouse liver, showed the presence of currents corresponding to low conductances (less than 50 pS), as well as of four distinct conductances of 99 pS, 152 pS, 220 pS and 307 pS (in 150 mM KCl). The latter were voltage gated, being open preferentially at positive (pipette) potentials. Very similar currents were found by patch clamping liposomes containing the isolated OM derived from rat brain mitochondria. Here a conductance of approximately 530 pS, resembling in its electrical characteristics a conductance already attributed to mitochondrial contact sites (Moran et al. 1990), was also detected. Immunoblot assays of mitochondria and of the isolated OM with antibodies against the outer membrane voltage-dependent anion channel (VDAC) (Colombini 1979), showed the presence of the anion channel in each case. However, the typical electrical behaviour displayed by such a channel in planar bilayers could not be detected under our experimental conditions. From this study, the permeability of the OMM appears different from what has been reported hitherto, yet is more in line with that multifarious and dynamic structure which apparently should belong to it, at least within the framework of mitochondrial biogenesis (Pfanner and Neupert 1990).

Distribution of glutathione peroxidases and glutathione reductase in rat brain mitochondria

The distribution of glutathione reductase (GR), glutathione peroxidase (GPx) and phospholipid hydroperoxide glutathione peroxidase (PHGPx) in isolated rat brain mitochondria was investigated, using a fractionation procedure for the separation of inner and outer membranes, contact sites between the two membranes and a soluble fraction mainly originating from the mitochondrial matrix. The data indicate that GR and GPx are concentrated in the soluble fraction, with a minor portion of the two enzymes being associated with the contact sites. PHGPx is localized largely in the inner membrane. The possible functional significance of these findings is discussed.

Evidence for (lipo) oligosaccharides in Borrelia burgdorferi and their serological specificity

SDS-PAGE and Western immunoblot profiles have been determined for different strains of Borrelia burgdorferi. Major proteins of 60 kDa, 41 kDa corresponding to flagellin, 34-36 kDa and 30-31 kDa corresponding to OspB and OspA respectively, and 18-20 kDa corresponding to 'pC' fractions were detected. A "rough" lipopolysaccharide which we called lipooligosaccharide (LOS) of 8-11 kDa appeared to be present, being detected by specific silver staining, as in crude Borrelia lysates as in proteinase K digested Borrelia strains, quite similar in shape among the different strains examined. The LOS reacted in Western blotting with immune anti-B. burgdorferi rabbit serum and also with sera collected from humans affected by Lyme borreliosis. The LOS did not react with sera positive for syphilis or leptospirosis, and their immunological specificity is discussed.

Hydrogen peroxide production by monoamine oxidase in isolated rat-brain mitochondria: its effect on glutathione levels and Ca2+ efflux

H2O2 production and accumulation during incubation of isolated rat-brain mitochondria with substrates of monoamine oxidase A and B were investigated. All substrates gave rise to an accumulation of H2O2 which was inhibited by malate + pyruvate or isocitrate, consistent with a need for mitochondrial NADPH to maintain glutathione in the reduced state. However, in the absence of these additions the level of reduced glutathione decreased only by about 30%, indicating that only a fraction of the mitochondrial glutathione pool was accessible to the glutathione peroxidase and glutathione reductase activities responsible for the continuous removal of H2O2 generated by monoamine oxidase. The H2O2 accumulation was also inhibited by externally added reduced glutathione or NADPH but not NADH. External NADPH was oxidized by added oxidized glutathione but not alpha-ketoglutarate + NH4+. These results suggest that the removal of H2O2 generated by monoamine oxidase proceeds by way of special fractions of glutathione peroxidase and glutathione reductase that are located in the intermembrane space of mitochondria in such a way that they can react with both intra- and extra-mitochondrial glutathione and NADPH, possibly at the contact sites between the inner and outer mitochondrial membranes. Evidence is also presented that H2O2 generated by monoamine oxidase enhances Ca2+ release from mitochondria and may thus function as a regulator of mitochondrial Ca2+ efflux.

Electrophysiological characterization of contact sites in brain mitochondria

From morphological and biochemical studies it has been recognized that the regions where the outer and inner membranes of mitochondria come in close contact (contact sites) can be the route mechanism through which mitochondria interact directly with the cytoplasm. We have studied these regions electrophysiologically with the patch clamp technique, with the aim of understanding if this direct interaction is mediated by high conductance ion channels similar to the channel already detected in the inner membrane of mitochondria (Sorgato M. C., Keller, B. U., and Stühmer, W. (1987) Nature 330, 498-500). Contact sites isolated from rat brain mitochondria were thus incorporated into liposomes subsequently enlarged sufficiently to be patch clamped. This study shows that these particular fractions contain ion channels with conductances ranging from approximately 5 picosiemens to 1 nanosiemens (in symmetrical 150 mM KCl). Most of these channels are not voltage-dependent and can be open at physiological potentials sustained by respiring mitochondria. The lack of voltage sensitivity seems not to be the outcome of methodological artifacts, as voltage-gated channels are detected in giant liposomes containing either the outer mitochondrial membrane or a partially purified fraction of the inner mitochondrial membrane. These data therefore indicate that channels present in mitochondrial contact sites have properties which render them amenable to perform several of the functions hypothesized for these regions, particularly that of translocating macromolecules from the cytoplasm to the matrix of mitochondria.

Leptospiral lipopolysaccharide presence in the outer envelope: electrophoretic evidence and immunological specificity

Purified preparations of lipopolysaccharides (LPS) extracted from two different strains of Leptospira interrogans have been electrophoretically analyzed in order to determine their location at the level of outer envelope (OE). Evidence has been collected for the presence of some LPS fractions in the OE, suggesting that a part of this molecule is embedded in the membrane structure. The serological specificity of the LPS has been in addition tested by means of monoclonal antiserovar antibodies (Moabs); the results indicated that the LPS structure is endowed of the immunodeterminants of the serovar. The remarkable relevance of this finding for the Leptospira taxonomy is discussed.

Mitochondrial boundary membrane contact sites in brain: points of hexokinase and creatine kinase location, and control of Ca2+ transport

The location of hexokinase at the surface of brain mitochondria was investigated by electron microscopy using immuno-gold labelling techniques. The enzyme was located where the two mitochondrial limiting membranes were opposed and contact sites were possible. Disruption of the outer membrane by digitonin did not remove bound hexokinase and creatine kinase from brain mitochondria, although the activity of outer membrane markers and adenylate kinase decreased, suggesting a preferential location of both enzymes in the contact sites. In agreement with that, a membrane fraction was isolated from osmotically lysed rat brain mitochondria in which hexokinase and creatine kinase were concentrated. The density of this kinase-rich fraction was specifically increased by immuno-gold labelling of hexokinase, allowing a further purification by density gradient centrifugation. The fraction was composed of inner and outer limiting membrane components as shown by the specific marker enzymes, succinate dehydrogenase and NADH-cytochrome-c-oxidase (rotenone insensitive). As reported earlier for the enriched contact site fraction of liver mitochondria the fraction from brain mitochondria contained a high activity of glutathione transferase and a low cholesterol concentration. Moreover, the contacts showed a higher Ca2+ binding capacity in comparison to outer and inner membrane fractions. This finding may have regulatory implications because glucose phosphorylation via hexokinase activated the active Ca2+ uptake system and inhibited the passive efflux, resulting in an increase of intramitochondrial Ca2+.

Influence of Ca2+ on the isolation from rat brain mitochondria of a fraction enriched of boundary membrane contact sites

Data have been obtained suggesting that the complex porin-hexokinase of brain mitochondria may be related to the contact sites between the outer and inner membrane. In the attempt to isolate from brain mitochondria the inner and outer membranes and the boundary membrane contacts, a procedure was developed based on swelling and shrinking of the organelles, followed by sonication and reverse discontinuous density gradient centrifugation. Three fractions were obtained by this technique, which were identified by measuring the relative specific activities of marker enzymes, namely succinate-cytochrome c reductase; NADH-cytochrome c reductase (rotenone insensitive); hexokinase and glutathione transferase, for the inner and outer membranes and contact sites, respectively. The fraction which contains the contact sites is characterized by the highest specific activity of hexokinase and glutathione transferase and by the highest calcium binding capacity; physiological concentrations of this cation produces a sharper separation of this fraction. Results indicate that both the porin-hexokinase gating system of the outer membrane and the calcium transporting complex of the inner membrane are present in the fraction which contains the contact sites.

Biochemical and immunohistochemical evidence that in cartilage an alkaline phosphatase is a Ca2+-binding glycoprotein

A glycoprotein that exhibits alkaline phosphatase activity and binds Ca2+ with high affinity has been extracted and purified from cartilage matrix vesicles by fast protein liquid chromatography. Antibodies against this glycoprotein were used to analyze its distribution in chondrocytes and in the matrix of calcifying cartilage. Under the light microscope, using immunoperoxidase or immunofluorescence techniques, the glycoprotein is localized in chondrocytes of the resting zone. At this level, the extracellular matrix does not show any reaction. In the cartilage plate, between the proliferating and the hypertrophic region, a weak immune reactivity is seen in the cytoplasm, whereas in the intercolumnar matrix the collagen fibers appear clearly stained. Stained granular structures, distributed with a pattern similar to that of matrix vesicles, are also visible. Calcified matrix is the most stained area. These results were confirmed under the electron microscope using both immunoperoxidase and protein A-gold techniques. In parallel studies, enzyme activity was also analyzed by histochemical methods. Whereas resting cartilage, the intercellular matrix of the resting zone, and calcified matrix do not exhibit any enzyme activity, the zones of maturing and hypertrophic chondrocytes are highly reactive. Some weak reactivity is also shown by chondrocytes of the resting zone. The observation that this glycoprotein (which binds Ca2+ and has alkaline phosphatase activity) is synthesized in chondrocytes and is exported to the extracellular matrix at the time when calcification begins, suggests that it plays a specific role in the process of calcification.

Heterogeneity of lipopolysaccharide banding patterns in Leptospira spp

Strains of Leptospira interrogans and Leptospira biflexa, examined by electrophoresis after whole cell lysis and protein digestion, revealed the presence of 2-keto-3-deoxyoctonate and an heterogeneous lipopolysaccharide electrophoretic banding pattern, which was characteristic of the species.

The role of hexokinase as a possible modulator of Ca2+ movements in isolated rat brain mitochondria

The present study shows that in brain mitochondria the active calcium uptake and the sodium-dependent calcium efflux are modulated by the porin-bound enzyme hexokinase. The release of the enzyme, promoted by glucose-6-phosphate (G-6-P), under conditions which do not affect mitochondrial functions, is accompanied by a decrease of the rates of fluxes of the cation. This phenomenon is discussed and correlated with the formation of microcompartments between the inner and outer mitochondrial membranes, where the hexokinase-porin complex may constitute a regulating gate system for calcium.

[Immunoglobulinic fragments of urinary proteins in patients affected by acute pneumonopathies, lung cancer and tuberculosis (author's transl)]

This study reports the immunoelectrophoretic analysis performed on 95 samples of urinary proteins. This analysis shows that in the majority of cases the migrant proteins in gamma position are F(ab) and Fc fragments, and free light chains with a molecular weight between 70,000 and 10,000. There is evidence of an increase in the immunoglobulinic fragments during inflammatory processes and their disappearance afterwards. This phenomenon proves that the elimination of these fragments evidences an increased synthesis of immunoglobulins and consequently also an increased catabolism.

The Ca2+-binding glycoprotein as the site of metabolic regulation of mitochondrial Ca2+ movements

A change in the redox state of pyridine nucleotides such as that evoked by addition of oxaloacetate has been shown to promote Ca2+ efflux from Ca2+ pre-loaded respiring mitochondria. An affinity-chromatography-purified antibody preparation obtained against the mitochondrial Ca2+-binding glycoprotein inhibits the phenomenon. This finding suggests that the glycoprotein is involved also in the oxaloacetate-induced Ca2+ release. This conclusion is reinforced by the finding that Ca2+-binding glycoprotein shows four sites per molecule where the pyridine nucleotides may be bound. Binding of NAD+ occurs preferentially over the others and the binding shows positive cooperativity, indicating that the glycoprotein undergoes an allosteric change upon NAD+ binding. Interestingly, in addition, NAD+ lowers the affinity of the glycoprotein for Ca2+. The effect cannot be induced by NADH. Pyridine nucleotide phosphates, NADP+ and NADPH, are essentially not bound. The results are consistent with the view that the glycoprotein is the site of regulation of Ca2+ equilibration across the mitochondrial membrane and make it possible to conclude that the effector in the phenomenon is NAD+.

The ability of the mitochondrial Ca2+-binding glycoprotein to restore Ca2+ transport in glycoprotein-depleted rat liver mitochondria

Rat liver mitochondria may be subfractionated in sediment and supernatant fractions by swelling in the presence of EDTA and oxaloacetate. The sediment is largely depleted of the Ca2+-binding glycoprotein and its Ca2+-transporting activity may be as low as 10--20% of the starting value. Both the rate of Ca2+ uptake and the capacity to maintain a high Ca2+ concentration gradient across the membrane are depressed. Addition of an osmotic supernatant to the assay mixture may partially restore the original Ca2+-transporting ability. The active component in the supernatant is the Ca2+-binding glycoprotein. This is shown by the following facts: (a) the effect is enhanced by the addition of the purified glycoprotein to the supernatant; (b) precipitation of the glycoprotein from the supernatant by affinity chromatography-purified antibodies abolishes the stimulatory effect, and (c) in the presence of 130 microM Mg2+, the glycoprotein alone may restore fully the Ca2+-transporting ability of the particles. The maximal velocity is already reached at 0.1 microgram glycoprotein/mg mitochondrial protein.

The immunoglobulins response in rabbit to single antigenic factors of leptospira. Investigations with two serovars from saprophytic leptospira

The agglutinating antibodies formed after immunization of rabbits with viable leptospira consist of 19S and 7S immunoglobulins. IgM and IgG are formed already earlier in the course of immunization. after a lapse of one month more IgG is found than IgM. The specificity of agglutination with the main antigenic factors is due mainly to IgG.

Isolation of a sulfobromophthalein-binding protein from hepatocyte plasma membrane

This paper deals with the isolation and partial characterization of a protein capable of high affinity sulfobromophthalein-binding from liver plasma membrane. The purification involves acetone powder of a crude preparation of rat liver plasma membrane, salt extraction and purification through two chromatographic steps. Based on sulfobromophthalein binding, the process gives a yield of approximately 40%, with a purification of about 300 times with respect to the starting homogenate. The best preparation can bind more than 100 nmol sulfobromophthalein/mg protein. The protein behaves as a single species in dodecyl sulphate polyacrylamide gel electrophoresis, with an apparent molecular weight of 1.7 . 10(5). The molecule does not contain sugars. The dissociation constant of the protein . sulfobromophthalein complex has been found to be 4. 10(-6) M, a value in agreement with that of high affinity binding sites described on isolated liver plasma membrane.