Dipeptidyl peptidase IV (DP IV) activity in serum and on lymphocytes of MRL/Mp-lpr/lpr mice correlates with disease onset

Proteolysis and Oxidation of Therapeutic Proteins After Intradermal or Subcutaneous Administration

The intradermal (ID) and subcutaneous (SC) routes are commonly used for therapeutic proteins (TPs) and vaccines; however, the bioavailability of TPs is typically less than small molecule drugs given via the same routes. Proteolytic enzymes in the dermal, SC, and lymphatic tissues may be responsible for the loss of TPs. In addition, the TPs may be exposed to reactive oxygen species generated in the SC tissue and the lymphatic system in response to injection-related trauma and impurities within the formulation. The reactive oxygen species can oxidize TPs to alter their efficacy and immunogenicity potential. Mechanistic understandings of the dominant proteolysis and oxidative routes are useful in the drug discovery process, formulation development, and to assess the potential for immunogenicity and altered pharmacokinetics (PK). Furthermore, in vitro tools representing the ID or SC and lymphatic system can be used to evaluate the extent of proteolysis of the TPs after the injection and before systemic entry. The in vitro clearance data may be included in physiologically based pharmacokinetic models for improved PK predictions. In this review, we have summarized various physiological factors responsible for proteolysis and oxidation of TPs after ID and SC administration.

A comprehensive autoantigen-ome of autoimmune liver diseases identified from dermatan sulfate affinity enrichment of liver tissue proteins

BACKGROUND

Autoimmune diseases result from aberrant immune attacks by the body itself. It is mysterious how autoantigens, a large cohort of seemingly unconnected molecules expressed in different parts of the body, can induce similar autoimmune responses. We have previously found that dermatan sulfate (DS) can form complexes with molecules of apoptotic cells and stimulate autoreactive CD5+ B cells to produce autoantibodies. Hence, autoantigenic molecules share a unique biochemical property in their affinity to DS. This study sought to further test this uniform principle of autoantigenicity.

RESULTS

Proteomes were extracted from freshly collected mouse livers. They were loaded onto columns packed with DS-Sepharose resins. Proteins were eluted with step gradients of increasing salt strength. Proteins that bound to DS with weak, moderate, or strong affinity were eluted with 0.4, 0.6, and 1.0 M NaCl, respectively. After desalting, trypsin digestion, and gel electrophoresis, proteins were sequenced by mass spectrometry. To validate whether these proteins have been previously identified as autoantigens, an extensive literature search was conducted using the protein name or its alternative names as keywords. Of the 41 proteins identified from the strong DS-affinity fraction, 33 (80%) were verified autoantigens. Of the 46 proteins with moderate DS-affinity, 27 (59%) were verified autoantigens. Of the 125 proteins with weak DS-affinity, 44 (35%) were known autoantigens. Strikingly, these autoantigens fell into the classical autoantibody categories of autoimmune liver diseases: ANA (anti-nuclear autoantibodies), SMA (anti-smooth muscle autoantibodies), AMA (anti-mitochondrial autoantibodies), and LKM (liver-kidney microsomal autoantigens).

CONCLUSIONS

This study of DS-affinity enrichment of liver proteins establishes a comprehensive autoantigen-ome for autoimmune liver diseases, yielding 104 verified and 108 potential autoantigens. The liver autoantigen-ome sheds light on the molecular origins of autoimmune liver diseases and further supports the notion of a unifying biochemical principle of autoantigenicity.

Dipeptidyl peptidase in autoimmune pathophysiology

CD26 is a 110-kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV) activity that is expressed on various cell types and has many biological functions. An important aspect of CD26 biology is its peptidase activity and its functional and physical association with molecules with key roles in human immunological programs. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its link age with signaling pathways and structures involved in T cell activation a well as antigen-presenting cell-T cell interaction, being a marker of diseas behavior clinically as well as playing an important role in autoimmune pathogenesis and development. 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, soluble CD26 molecules and proteomic approach, we have shown that CD26 interacts with structures with essential cellular functions in T cell responses. We will review emerging data that suggest CD26 may be an appropriate therapeutic target for the treatment of selected immune disorders.

Discovery of a new biomarker for the mucopolysaccharidoses (MPS), dipeptidyl peptidase IV (DPP-IV; CD26), by SELDI-TOF mass spectrometry

Surface enhanced laser desorption/ionisation time of flight (SELDI-TOF) mass spectrometry has been used to search for new protein biomarkers in the plasma of patients with mucopolysacharidoses (MPS). Differences in the levels of some plasma proteins, particularly the apolipoprotein ApoCI, were observed between MPS patients and normal controls, using the different chromatographic surfaces (ProteinChips). ApoCI was identified by both its mass and by immunological techniques. In plasma, it exists in two forms, ApoCI and a truncated form which lacks two N-terminal amino acids, ApoCI'. In controls, the ratio of ApoCI':ApoCI observed using the cation-exchange surface (CM10) was approximately 1:2 whereas in most MPS patients it varied from 1:1 to 1:0.8. The ratio of ApoCI':ApoCI in plasma is determined by the activity of dipeptidyl peptidase IV, DPP-IV (also known as the leucocyte antigen CD26), which was found to be elevated up to 3-fold in MPS patients. The DPP-IV activity decreased in MPS I patients undergoing enzyme replacement therapy, indicating that it could be a useful biomarker for monitoring the efficacy of treatment in MPS disease. As DPP-IV has an important regulatory role in metabolism, it is possible that its elevation could cause some of the secondary pathology in MPS, and inhibition of DPP-IV might have a role in MPS therapy.

The anti-inflammatory effect of neuropeptide Y (NPY) in rats is dependent on dipeptidyl peptidase 4 (DP4) activity and age

Neuropeptide Y (NPY)-induced modulation of the immune and inflammatory responses is regulated by tissue-specific expression of different receptor subtypes (Y1-Y6) and the activity of the enzyme dipeptidyl peptidase 4 (DP4, CD26) which terminates the action of NPY on Y1 receptor subtype. The present study investigated the age-dependent effect of NPY on inflammatory paw edema and macrophage nitric oxide production in Dark Agouti rats exhibiting a high-plasma DP4 activity, as acknowledged earlier. The results showed that NPY suppressed paw edema in adult and aged, but not in young rats. Furthermore, plasma DP4 activity decreased, while macrophage DP4 activity, as well as macrophage CD26 expression increased with aging. The use of NPY-related peptides and Y receptor-specific antagonists revealed that anti-inflammatory effect of NPY is mediated via Y1 and Y5 receptors. NPY-induced suppression of paw edema in young rats following inhibition of DP4 additionally emphasized the role for Y1 receptor in the anti-inflammatory action of NPY. In contrast to the in vivo situation, NPY stimulated macrophage nitric oxide production in vitro only in young rats, and this effect was mediated via Y1 and Y2 receptors. It can be concluded that age-dependant modulation of inflammatory reactions by NPY is determined by plasma, but not macrophage DP4 activity at different ages.

Effects of dipeptidyl peptidase IV on the satiety actions of peptide YY

AIMS/HYPOTHESIS

Dipeptidyl peptidase IV (DP IV) inhibitors are currently being developed to prolong the biological activity of insulinotropic peptides as a novel approach in the treatment of diabetes. We hypothesised that DP IV inhibition could attenuate the satiety actions of peptide YY (PYY) by altering the conversion of PYY(1-36) to PYY(3-36).

MATERIALS AND METHODS

The effects of PYY delivered by osmotic mini-pumps were assessed in rats treated with a DP IV inhibitor and in a rat model deficient in DP IV.

RESULTS

Pharmacological levels of total PYY were found in the circulation after the exogenous administration of PYY(3-36). While both PYY(1-36) and PYY(3-36) reduced food intake in normal rats, PYY(1-36) was ineffective in rats deficient in DP IV. When re-fed after a 24-h fast, DP IV-deficient rats exhibited higher food intake and weight gain than normal rats. Moreover, unlike controls, there was no postprandial increase in PYY levels in DP IV-deficient rats. Despite these findings, administration of a DP IV inhibitor, Pro-boroPro, did not alter the acute anorectic effects of exogenous PYY(1-36) in normal rats. This could be the result of the protection of other appetite regulatory peptides or the generation of PYY(3-36) by remaining DP IV activity or other dipeptidyl peptidases.

CONCLUSIONS/INTERPRETATION

Although DP IV inhibition with Pro-boroPro attenuated the generation of PYY(3-36), our results indicate that short-term DP IV inhibition does not eliminate the satiety actions of exogenously administered PYY(1-36) at the doses tested.

CD26/DPP IV in experimental and clinical organ transplantation

The T-cell activation-Ag CD26 possesses dipeptidyl peptidase IV (DPP IV) enzymatic activity. Costimulatory efficacy and immunocompetence are associated with the enzymatic activity.

GOALS

In models of experimental cardiac allograft transplantation (HTx), we analyzed the role of CD26/DPP IV during organ rejection. Also, we investigated CD26 enzymatic and cellular expression in human recipients of kidney transplants (Tx).

MATERIAL AND METHODS

Heterotopic HTx in rats, models of acute and accelerated rejection. Monitoring of DPP IV serum levels and humoral immunity. Propro-diphenyl phosphonate was employed to inhibit DPP IV activity during rejection. In a prospective study, surface expression of CD26, 3, 4, 8, 45, 122 and ADA on PBL and DPP IV serum activity were measured in kidney recipients for 24 months post-transplantation.

RESULTS

Acute rejection was . associated with increased serum DPP IV activity (p < 0.005). Specific inhibition abrogated acute (p < 0.0001) and accelerated (p < 0.01) rejection, impairing cytotoxicity and allospecific Ig-synthesis. Kidney recipients displayed a significant drop in CD26 expression on PBL for up to 18 months postoperatively (p < 0.001). CD4, 8, 45, 122 and ADA expression kinetics were only briefly affected. DPP IV enzymic activity stayed depressed for at least 12 months (p < 0.001).

CONCLUSION

CD26/DPP IV is pivotal in T-cell mediated immune responses toward allo-Ag. In clinical transplantation, engraftment/immunosuppression are reflected by CD26 cellular and enzymatic expression posttransplantation and may serve as an indicator for immunomodulation.

The multifunctional or moonlighting protein CD26/DPPIV

CD26/DPPIV can be considered a moonlighting protein because it is a multifunctional protein that exerts its different functions depending on cell type and intra- or extracellular conditions in which it is expressed. In the present review, we summarize all its known functions in relation to physiological and pathophysiological conditions. The protein is a proteolytic enzyme, receptor, costimulatory protein, and is involved in adhesion and apoptosis. The CD26/DPPIV protein plays a major role in immune response. Abnormal expression is found in the case of autoimmune diseases, HIV-related diseases and cancer. Natural substrates for CD26/DPPIV are involved in immunomodulation, psycho/neuronal modulation and physiological processes in general. Therefore, targeting of CD26/ DPPIV and especially its proteolytic activity has many therapeutic potentials. On the other hand, there are homologous proteins with overlapping proteolytic activity, which thus may prevent specific modulation of CD26/DPPIV. In conclusion, CD26/DPPIV is a protein present both in various cellular compartments and extracellularly where it exerts different functions and thus is a true moonlighting protein.

CD26: a multifunctional integral membrane and secreted protein of activated lymphocytes

CD26 has proved interesting in the fields of immunology, endocrinology, cancer biology and nutrition owing to its ubiquitous and unusual enzyme activity. This dipeptidyl aminopeptidase (DPP IV) activity generally inactivates but sometimes alters or enhances the biological activities of its peptide substrates, which include several chemokines. CD26 costimulates both the CD3 and the CD2 dependent T-cell activation and tyrosine phosphorylation of TCR/CD3 signal transduction pathway proteins. CD26 in vivo has integral membrane protein and soluble forms. Soluble CD26 is at significant levels in serum, these levels alter in many diseases and soluble CD26 can modulate in vitro T-cell proliferation. CD26, being an adenosine deaminase binding protein (ADAbp), functions as a receptor for ADA on lymphocytes. The focus of this review is the structure and function of CD26 and the influence of its ligand binding activity on T-cell proliferation and the T cell costimulatory activity of CD26.

Activation of autoreactive T cells that help nucleobindin-injected mice produce anti-DNA antibodies

Nucleobindin (Nuc) is a DNA- and calcium-binding protein that was originally identified as an anti-DNA antibody-enhancing factor in MRL/MpJ-lpr/lpr (MRL/lpr) mice. In MRL/lpr mice, both expression of Nuc mRNA in enlarged lymph nodes and serum concentration of Nuc protein are shown to increase as disease progresses. Administration of recombinant (r) Nuc to young MRL/MpJ-+/+ and normal BALB/c mice leads to augmentation or induction of IgG anti-double-stranded (ds) DNA autoantibodies. In this study, spleen cells prepared from MRL/lpr mice were found to show a proliferative response to rNuc, indicating existence of T cells that are specific to this autoantigen in peripheral lymphoid tissues. Furthermore, CD4+ T cell lines were generated from a BALB/c mouse that had been producing anti-dsDNA antibodies as a result of repeated injections of rNuc. These T cell lines were confirmed to be autoreactive, because they proliferated in culture with syngeneic but not with allogeneic spleen cells without addition of any exogenous antigens. Their proliferation was enhanced by rNuc, and inhibited by an anti-MHC class II monoclonal antibody. Upon in vivo inoculation, these T cells provided help for rNuc-injected BALB/c mice to produce anti-DNA antibodies. These results suggest that Nuc is able to activate autoreactive peripheral T cells through an MHC-class II pathway leading to acceleration or induction of anti-DNA antibody production when it is excessively produced in lupus-prone mice or experimentally administered into normal mice.

CD26, let it cut or cut it down

The costimulatory properties of CD26 have been studied extensively and significant progress has been made in unravelling the complex nature of this molecule. Here, we summarize recent findings on molecular and functional characteristics of CD26. We argue that a multidisciplinary approach might reveal the molecular events underlying the role of CD26 in HIV infection and immune, inflammatory and endocrine responses.

Inhibition of CD26/dipeptidyl peptidase IV activity in vivo prolongs cardiac allograft survival in rat recipients

The CD26 antigen, one of the major costimulatory molecules in T cell activation, was shown to possess dipeptidyl peptidase IV (DPP IV) activity. Previously, we demonstrated that immunosuppressed kidney transplant patients exhibit lower DPP IV serum activity as compared with healthy individuals. In the present study, we analyzed the role of CD26/DPP IV in the immune cascade triggered by organ transplantation and leading to acute rejection of cardiac allografts in rat recipients. Transplantation of hearts from (Lewis x Brown Norway)F1 donors into Lewis hosts resulted in an early (24 hr) increase in cellular CD26 expression, followed by a rise in DPP IV serum activity, which peaked at day 6, i.e., before the time of actual graft loss. Specific targeting of DPP IV activity with a novel, low-molecular-weight inhibitor of the diphenyl-phosphonate group (prodipine) abrogated acute rejection and prolonged cardiac allograft survival to 14.0+/-0.9 days (P<0.0001). Prodipine treatment prevented the early peak of cellular CD26 expression and thoroughly suppressed systemic DPP IV activity. The inhibition of DPP IV was associated with severely impaired host cytotoxic T lymphocyte responses in vitro. These results demonstrate the role of CD26/DPP IV in alloantigen-mediated immune regulation in vivo and provide the first direct evidence that CD26/DPP IV plays an important role in the mechanism of allograft rejection. The model of targeting CD26/DPP IV may reveal essential interactions on the level of costimulatory alternate T cell activation pathways, allowing a more subtle approach for more selective immunosuppression in transplant recipients.

Suppression of arthritis by the inhibitors of dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DP IV, CD26) is a serine exoprotease which selectively cleaves the penultimate proline residue of polypeptides. This enzyme is also expressed as a surface marker on activated T cells. In order to assess the relevance of DP IV in immunological disorders, we evaluated the in vivo effects of specific DP IV inhibitors using two arthritis models, one which was induced by collagen one by alkyldiamine. These animal models share several pathological features associated with rheumatoid arthritis. The transition state substrate analog of DP IV, (S)-Alanylpyrrolidine-boronic Acid (Ala-boroPro), suppressed hind paw swelling, which was associated with collagen-induced and alkyldiamine-induced arthritis. A competitive inhibitor of DP IV, Lys(Z(NO2))-thiazolidide and an irreversible inhibitor, Ala-Pro-nitrobenzoylhydroxylamine also suppressed alkyldiamine-induced arthritis dose-dependently. We also analyzed the pharmacological effects of Lys(Z(NO2))-thiazolidide on several immune responses in vitro, in order to determine its mode of action. This inhibitor suppressed mitogen-induced and antigen-induced proliferation of T cells. However, studies using splenic cells from DP IV deficient rats showed that the inhibition of lymphocyte proliferation was not exerted through the inhibition of DP IV.

Expression of CD26/dipeptidyl peptidase IV in adult T cell leukemia/lymphoma (ATLL)

The association of CD26/dipeptidyl peptidase IV (DPPIV) and human T lymphotropic virus type I (HTLV-I) was studied by two approaches. First, we examined the expression of CD26 in peripheral blood mononuclear cells (PBMC) from the patients with adult T cell leukemia/lymphoma (ATLL), an HTLV-I-related malignancy. The expression of CD26 on the surface of PBMC was decreased in all 20 patients with ATLL compared with those from normal individuals (P < 0.01) and the expression of the CD26 gene transcript was not detectable in seven out of eight patients with ATLL. Then we compared the quantity of viral DNA in CD26-negative (CD26-) and CD26-positive (CD26+) cells obtained from 17 HTLV-I healthy carries by using a polymerase chain reaction method. The CD26-cells had a higher copy number of viral DNA than CD26+ cells. These findings indicate that HTLV-I has in vivo tropism to CD26- cells, suggesting that some phenotypes of ATLL cells reflect the in vivo cellular tropism of HTLV-I.