Cellular and Structural Characterization of VP1 and VP2 Knockout Mutants of AAV3B Serotype and Implications for AAV Manufacturing

AAV virion biology is still lacking a complete understanding of the role that the various structural subunits (VP1, 2, and 3) play in virus assembly, infectivity, and therapeutic delivery for clinical indications. In this study, we focus on the less studied adeno-associated virus AAV3B and generate a collection of AAV plasmid substrates that assemble virion particles deficient specifically in VP1, VP2, or VP1 and 2 structural subunits. Using a collection of biological and structural assays, we observed that virions devoid of VP1, VP2, or VP1 and 2 efficiently assembled virion particles, indistinguishable by cryoelectron microscopy (cryo-EM) from that of wild type (WT), but unique in virion transduction (WT > VP2 > VP1 > VP1 and 2 mutants). We also observed that the missing structural subunit was mostly compensated by additional VP3 protomers in the formed virion particle. Using cryo-EM analysis, virions fell into three classes, namely full, empty, and partially filled, based on comparison of density values within the capsid. Further, we characterize virions described as "broken" or "disassembled" particles, and provide structural information that supports the particle dissolution occurring through the two-fold symmetry sites. Finally, we highlight the unique value of employing cryo-EM as an essential tool for release criteria with respect to AAV manufacturing.

c-Fos induces chondrogenic tumor formation in immortalized human mesenchymal progenitor cells

Mesenchymal progenitor cells (MPCs) have been hypothesized as cells of origin for sarcomas, and c-Fos transcription factor has been showed to act as an oncogene in bone tumors. In this study, we show c-Fos is present in most sarcomas with chondral phenotype, while multiple other genes are related to c-Fos expression pattern. To further define the role of c-Fos in sarcomagenesis, we expressed it in primary human MPCs (hMPCs), immortalized hMPCs and transformed murine MPCs (mMPCs). In immortalized hMPCs, c-Fos expression generated morphological changes, reduced mobility capacity and impaired adipogenic- and osteogenic-differentiation potentials. Remarkably, immortalized hMPCs or mMPCs expressing c-Fos generated tumors harboring a chondrogenic phenotype and morphology. Thus, here we show that c-Fos protein has a key role in sarcomas and that c-Fos expression in immortalized MPCs yields cell transformation and chondrogenic tumor formation.

IFNγ Regulates Activated Vδ2+ T Cells through a Feedback Mechanism Mediated by Mesenchymal Stem Cells

γδ T cells play a role in a wide range of diseases such as autoimmunity and cancer. The majority of circulating human γδ T lymphocytes express a Vγ9Vδ2+ (Vδ2+) T cell receptor (TCR) and following activation release pro-inflammatory cytokines. In this study, we show that IFNγ, produced by Vδ2+ cells, activates mesenchymal stem cell (MSC)-mediated immunosupression, which in turn exerts a negative feedback mechanism on γδ T cell function ranging from cytokine production to proliferation. Importantly, this modulatory effect is limited to a short period of time (<24 hours) post-T cell activation, after which MSCs can no longer exert their immunoregulatory capacity. Using genetically modified MSCs with the IFNγ receptor 1 constitutively silenced, we demonstrate that IFNγ is essential to this process. Activated γδ T cells induce expression of several factors by MSCs that participate in the depletion of amino acids. In particular, we show that indolamine 2,3-dioxygenase (IDO), an enzyme involved in L-tryptophan degradation, is responsible for MSC-mediated immunosuppression of Vδ2+ T cells. Thus, our data demonstrate that γδ T cell responses can be immuno-modulated by different signals derived from MSC.

The RING ubiquitin E3 RNF114 interacts with A20 and modulates NF-κB activity and T-cell activation

Accurate regulation of nuclear factor-κB (NF-κB) activity is crucial to prevent a variety of disorders including immune and inflammatory diseases. Active NF-κB promotes IκBα and A20 expression, important negative regulatory molecules that control the NF-κB response. In this study, using two-hybrid screening we identify the RING-type zinc-finger protein 114 (RNF114) as an A20-interacting factor. RNF114 interacts with A20 in T cells and modulates A20 ubiquitylation. RNF114 acts as negative regulator of NF-κB-dependent transcription, not only by stabilizing the A20 protein but also IκBα. Importantly, we demonstrate that in T cells, the effect of RNF114 is linked to the modulation of T-cell activation and apoptosis but is independent of cell cycle regulation. Altogether, our data indicate that RNF114 is a new partner of A2O involved in the regulation of NF-κB activity that contributes to the control of signaling pathways modulating T cell-mediated immune response.

Human mesenchymal stromal cells modulate T-cell responses through TNF-α-mediated activation of NF-κB

Although mesenchymal stromal cells (MSCs) possess the capacity to modulate immune responses, little is known about the mechanisms that underpin these processes. In this study, we show that immunosupression is mediated by activation of nuclear factor kappa B (NF-κB) in human MSCs. This pathway is activated by TNF-α that is generated following TCR stimulation of T cells. Inhibition of NF-κB through silencing of IκB kinase β or the TNF-α receptor abolishes the immunosuppressive capacity of MSCs. Our data also indicate that MSC-associated NF-κB activation primarily leads to inhibition of T-cell proliferation with little effect on expression of the activation markers CD69 and CD25. Thus, our data support the hypothesis that the TNF-α/NF-κB signalling pathway is required for the initial priming of immunosuppressive function in human MSCs. Interestingly, drugs that interfere with NF-κB activation significantly antagonise the immunoregulatory effect of MSCs, which could have important implications for immunosuppression regimens in the clinic.

Podocalyxin-like protein 1 is a relevant marker for human c-kit(pos) cardiac stem cells

Cardiac progenitor cells (CPCs) from adult myocardium offer an alternative cell therapy approach for ischaemic heart disease. Improved clinical performance of CPCs in clinical trials requires a comprehensive definition of their biology and specific interactions with the environment. In this work we characterize specific human CPC surface markers and study some of their related functions. c-kit(pos) human CPCs (hCPCs) were characterized for cell surface marker expression, pluripotency, early and late cardiac differentiation markers and therapeutic activity in a rat model of acute myocardial infarction. The results indicate that hCPCs are a mesenchymal stem cell (MSC)-like population, with a similar immunoregulatory capacity. A partial hCPC membrane proteome was analysed by liquid chromatography-mass spectrometry/mass spectrometry and 36 proteins were identified. Several, including CD26, myoferlin and podocalyxin-like protein 1 (PODXL), have been previously described in other stem-cell systems. Suppression and overexpression analysis demonstrated that PODXL regulates hCPC activation, migration and differentiation; it also modulates their local immunoregulatory capacity. Therefore, hCPCs are a resident cardiac population that shares many features with hMSCs, including their capacity for local immunoregulation. Expression of PODXL appears to favour the immature state of hCPCs, while its downregulation facilitates their differentiation. Copyright © 2016 John Wiley & Sons, Ltd.

Hypoxia-inducible factor 1 alpha contributes to cardiac healing in mesenchymal stem cells-mediated cardiac repair

Mesenchymal stem cells (MSC) are effective in treating myocardial infarction (MI) and previous reports demonstrated that hypoxia improves MSC self-renewal and therapeutics. Considering that hypoxia-inducible factor-1 alpha (HIF-1α) is a master regulator of the adaptative response to hypoxia, we hypothesized that HIF-1α overexpression in MSC could mimic some of the mechanisms triggered by hypoxia and increase their therapeutic potential without hypoxia stimulation. Transduction of MSC with HIF-1α lentivirus vectors (MSC-HIF) resulted in increased cell adhesion and migration, and activation of target genes coding for paracrine factors. When MSC-HIF were intramyocardially injected in infarcted nude rats, significant improvement was found (after treatment of infarcted rats with MSC-HIF) in terms of cardiac function, angiogenesis, cardiomyocyte proliferation, and reduction of fibrotic tissue with no induction of cardiac hypertrophy. This finding provides evidences for a crucial role of HIF-1α on MSC biology and suggests the stabilization of HIF-1α as a novel strategy for cellular therapies.

Histone deacetylase 3 modulates the expansion of human hematopoietic stem cells

Epigenetic changes are regarded as emerging major players for hematopoietic stem cell (HSC) biology. Although some histone deacetylase (HDAC) inhibitors, such as valproic acid (VA), induce differentiation and apoptosis in a variety of leukemic cells in vitro, they produce a favorable effect on the expansion of normal HSCs. In this study, we have identified the VA target HDAC3 as a negative regulator of umbilical cord blood HSC expansion. We demonstrate that knockdown of the transcript dramatically improves CD34+ cell expansion, which correlates with a higher potential to generate colony-forming units in functional assays. We show that this effect is mediated at the level of primitive hematopoietic cells and that it is not due to negative effects on specific cell commitment or alterations in the cell cycle. HDAC3 inhibition does not block commitment to the monocytic lineage and the maturation of monocyte precursors, which are the main inhibited pathways in the presence of VA. Therefore, our results identify HDAC3 as a promising target for therapies aiming to expand HSCs.

Regulation of human bone marrow stromal cell proliferation and differentiation capacity by glucocorticoid receptor and AP-1 crosstalk

Although marrow adipocytes and osteoblasts derive from a common bone marrow stromal cells (BMSCs), the mechanisms that underlie osteoporosis-associated bone loss and marrow adipogenesis during prolonged steroid treatment are unclear. We show in human BMSCs (hBMSCs) that glucocorticoid receptor (GR) signaling in response to high concentrations of glucocorticoid (GC) supports adipogenesis but inhibits osteogenesis by reducing c-Jun expression and hBMSC proliferation. Conversely, significantly lower concentrations of GC, which permit hBMSC proliferation, are necessary for normal bone mineralization. In contrast, platelet-derived growth factor (PDGF) signaling increases both JNK/c-Jun activity and hBMSC expansion, favoring osteogenic differentiation instead of adipogenesis. Indeed, PDGF antagonizes the proadipogenic qualities of GC/GR signaling. Thus our results reveal a novel c-Jun-centered regulatory network of signaling pathways in differentiating hBMSCs that controls the proliferation-dependent balance between osteogenesis and adipogenesis.

Mesenchymal stem cells provide better results than hematopoietic precursors for the treatment of myocardial infarction

OBJECTIVES

The purpose of this study was to compare the ability of human CD34(+) hematopoietic stem cells and bone marrow mesenchymal stem cells (MSC) to treat myocardial infarction (MI) in a model of permanent left descendent coronary artery (LDA) ligation in nude rats.

BACKGROUND

Transplantation of human CD34(+) cells and MSC has been proved to be effective in treating MI, but no comparative studies have been performed to elucidate which treatment prevents left ventricular (LV) remodelling more efficiently.

METHODS

Human bone marrow MSC or freshly isolated CD34(+) cells from umbilical cord blood were injected intramyocardially in infarcted nude rats. Cardiac function was analyzed by echocardiography. Ventricular remodelling was evaluated by tissue histology and electron microscopy, and neo-formed vessels were quantified by immunohistochemistry. Chronic local inflammatory infiltrates were evaluated in LV wall by hematoxylin-eosin staining. Apoptosis of infarcted tissue was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

RESULTS

Both cell types induced an improvement in LV cardiac function and increased tissue cell proliferation in myocardial tissue and neoangiogenesis. However, MSC were more effective for the reduction of infarct size and prevention of ventricular remodelling. Scar tissue was 17.48 +/- 1.29% in the CD34 group and 10.36 +/- 1.07% in the MSC group (p < 0.001 in MSC vs. CD34). Moreover, unlike MSC, CD34(+)-treated animals showed local inflammatory infiltrates in LV wall that persisted 4 weeks after transplantation.

CONCLUSIONS

Mesenchymal stem cells might be more effective than CD34(+) cells for the healing of the infarct. This study contributes to elucidate the mechanisms by which these cell types operate in the course of MI treatment.

Mesenchymal stem cells and their use as cell replacement therapy and disease modelling tool

Mesenchymal stem cells (MSCs) from adult somatic tissues may differentiate in vitro and in vivo into multiple mesodermal tissues including bone, cartilage, adipose tissue, tendon, ligament or even muscle. MSCs preferentially home to damaged tissues where they exert their therapeutic potential. A striking feature of the MSCs is their low inherent immunogenicity as they induce little, if any, proliferation of allogeneic lymphocytes and antigen-presenting cells. Instead, MSCs appear to be immunosuppressive in vitro. Their multi-lineage differentiation potential coupled to their immuno-privileged properties is being exploited worldwide for both autologous and allo-geneic cell replacement strategies. Here, we introduce the readers to the biology of MSCs and the mechanisms underlying immune tolerance. We then outline potential cell replacement strategies and clinical applications based on the MSCs immunological properties. Ongoing clinical trials for graft-versus-host-disease, haematopoietic recovery after co-transplantation of MSCs along with haematopoietic stem cells and tissue repair are discussed. Finally, we review the emerging area based on the use of MSCs as a target cell subset for either spontaneous or induced neoplastic transformation and, for modelling non-haematological mesenchymal cancers such as sarcomas.

An endoplasmic reticulum retention function for the cytoplasmic tail of the human pre-T cell receptor (TCR) alpha chain: potential role in the regulation of cell surface pre-TCR expression levels

The pre-T cell receptor (TCR), which consists of a TCR-beta chain paired with pre-TCR-alpha (pTalpha) and associated with CD3/zeta components, is a critical regulator of T cell development. For unknown reasons, extremely low pre-TCR levels reach the plasma membrane of pre-T cells. By transfecting chimeric TCR-alpha-pTalpha proteins into pre-T and mature T cell lines, we show here that the low surface expression of the human pre-TCR is pTalpha chain dependent. Particularly, the cytoplasmic domain of pTalpha is sufficient to reduce surface expression of a conventional TCR-alpha/beta to pre-TCR expression levels. Such reduced expression cannot be attributed to qualitative differences in the biochemical composition of the CD3/zeta modules associated with pre-TCR and TCR surface complexes. Rather, evidence is provided that the pTalpha cytoplasmic tail also causes a reduced surface expression of individual membrane molecules such as CD25 and CD4, which are shown to be retained in the endoplasmic reticulum (ER). Native pTalpha is also observed to be predominantly ER localized. Finally, sequential truncations along the pTalpha cytoplasmic domain revealed that removal of the COOH-terminal 48 residues is sufficient to release a CD4-pTalpha chimera from ER retention, and to restore native CD4 surface expression levels. As such a truncation in pTalpha also correlates with enhanced pre-TCR expression, the observed pTalpha ER retention function may contribute to the regulation of surface pre-TCR expression on pre-T cells.

Beta-selection is associated with the onset of CD8beta chain expression on CD4(+)CD8alphaalpha(+) pre-T cells during human intrathymic development

T-cell precursors that undergo productive rearrangements at the T-cell receptor (TCR) beta locus are selected for proliferation and further maturation, before TCRalpha expression, by signaling through a pre-TCR composed of the TCRbeta chain paired with a pre-TCRalpha (pTalpha) chain. Such a critical developmental checkpoint, known as beta-selection, results in progression from CD4(-) CD8(-) double negative (DN) to CD4(+) CD8(+) double positive (DP) TCRalphabeta(-) thymocytes. In contrast to mice, progression to the DP compartment occurs in humans via a CD4(+) CD8(-) intermediate stage. Here we show that the CD4(+) CD8(-) to CD4(+) CD8(+) transition involves the sequential acquisition of the alpha and beta chains of CD8 at distinct maturation stages. Our results indicate that CD8alpha, but not CD8beta, is expressed in vivo in a minor subset of DP TCRalphabeta(-) thymocytes, referred to as CD4(+) CD8alphaalpha(+) pre-T cells, mostly composed of resting cells lacking cytoplasmic TCRbeta chain (TCRbeta(ic)). In contrast, expression of CD8alphabeta heterodimers was selectively found on DP TCRalphabeta(-) thymocytes that express TCRbeta(ic) and are enriched for cycling cells. Interestingly, CD4(+) CD8alphaalpha(+) pre-T cells are shown to be functional intermediates between CD4(+) CD8(-) TCRbeta(ic)(-) and CD4(+) CD8alphabeta(+) TCRbeta(ic)(+) thymocytes. More importantly, evidence is provided that onset of CD8beta and TCRbeta(ic) expression are coincident developmental events associated with acquisition of CD3 and pTalpha chain on the cell surface. Therefore, we propose that the CD4(+) CD8alphaalpha(+) to CD4(+) CD8alphabeta(+) transition marks the key control point of pre-TCR-mediated beta-selection in human T-cell development.

Identification of a late stage of small noncycling pTalpha- pre-T cells as immediate precursors of T cell receptor alpha/beta+ thymocytes

During thymocyte development, progression from T cell receptor (TCR)beta to TCRalpha rearrangement is mediated by a CD3-associated pre-TCR composed of the TCRbeta chain paired with pre-TCRalpha (pTalpha). A major issue is how surface expression of the pre-TCR is regulated during normal thymocyte development to control transition through this checkpoint. Here, we show that developmental expression of pTalpha is time- and stage-specific, and is confined in vivo to a limited subset of large cycling human pre-T cells that coexpress low density CD3. This restricted expression pattern allowed the identification of a novel subset of small CD3(-) thymocytes lacking surface pTalpha, but expressing cytoplasmic TCRbeta, that represent late noncycling pre-T cells in which recombination activating gene reexpression and downregulation of T early alpha transcription are coincident events associated with cell cycle arrest, and immediately preceding TCRalpha gene expression. Importantly, thymocytes at this late pre-T cell stage are shown to be functional intermediates between large pTalpha+ pre-T cells and TCRalpha/beta+ thymocytes. The results support a developmental model in which pre-TCR-expressing pre-T cells are brought into cycle, rapidly downregulate surface pre-TCR, and finally become small resting pre-T cells, before the onset of TCRalpha gene expression.

Enhanced green fluorescent protein as an efficient reporter gene for retroviral transduction of human multipotent lymphoid precursors

Owing to its autofluorescence properties, green fluorescent protein (GFP) has aroused increasing interest as a marker system for many research applications. In this study we investigated the suitability of the "enhanced" GFP (EGFP), a mutant version of GFP optimized for flow cytometry and microscopy detection, as a reporter gene for retroviral transduction protocols. EGFP was shown to display a bright and stably maintained emission pattern in transfected GP+envAm12 packaging cells. Stable fluorescent emission was observed as well after transduction in NIH 3T3 fibroblasts and in the human Jurkat T cell line, in which EGFP was shown to confer no deleterious effect or growth disadvantage on the expressing cells. Moreover, EGFP expression could be detected after short-term retroviral exposure, thus allowing a rapid and quantitative retroviral titering assay, alternative to the standard colony-formation procedure. Most importantly, we showed the feasibility of EGFP as a marker gene in retroviral-mediated transduction of primary lymphoid precursors. In particular, transduction of CD34+CD1- human thymocytes by short-term cocultivation yielded up to 30% of EGFP-expressing cells, while maintaining CD34 expression levels. Finally, when cultured under multicytokine-supported conditions, such transduced intrathymic progenitors were shown to efficiently generate lymphoid-related dendritic cells, which displayed a distinct EGFP expression. Therefore, because of its rapid and easy detectability and its nontoxic characteristics, EGFP proves itself to be a valuable reporter gene by allowing the transduction of multipotential progenitors and by being compatible with the developmental programs of lymphoid lineage generation.

Identification of a common developmental pathway for thymic natural killer cells and dendritic cells

Current data support the notion that the thymus is seeded by a yet uncommitted progenitor cell able to generate T cells, B cells, natural killer (NK) cells, and dendritic cells (DCs). We assess in this report the developmental relationship of DCs and NK cells derived from a small subset of CD34(+) human postnatal thymocytes that, like the earliest precursors in the fetal thymus, display low CD33 surface expression. Culture of these isolated CD34(+) CD33(lo) thymic progenitors with a mixture of cytokines, including interleukin-7 (IL-7), IL-1alpha, IL-6, granulocyte-macrophage colony-stimulating factor, and stem cell factor, results in predominant generation of DCs. However, the addition of IL-2 to the cytokine mixture leads to the simultaneous development of DCs and NK cells. Both developmental pathways progress through a transient population of CD34(+)CD44(bright) CD5(lo/-)CD33(+) large-sized cells, distinct from small-sized T-lineage precursors, that contain bipotential NK/DC progenitors. These data provide evidence of linked pathways of NK cell and DC development from intrathymic precursors and suggest that NK cells and DCs branch off the T lineage through a common intermediate progenitor.

Herpesvirus saimiri immortalization of alpha beta and gamma delta human T-lineage cells derived from CD34+ intrathymic precursors in vitro

Herpesvirus saimiri (HVS), an agent that can infect many human cell types, has been shown to immortalize selectively TCR alpha beta + CD3+ T lymphocytes. Human T cell precursors defined as CD34+CD3-CD4-CD8- were isolated from thymic samples and exposed to HVS in the presence of either IL-2 or IL-7. Cultures lacking the virus were non-viable by day 15. Test cultures, in contrast, showed a sustained proliferative activity lasting > 5 months, allowing the phenotypical and molecular analysis of the cellular progeny. In the presence of IL-7, TCR alpha beta + cells with three different phenotypes (mainly CD4+CD8-, but also CD4+CD8+ and CD4-CD8+) were immortalized, whereas no TCR gamma delta + cells were recovered. Kinetic studies showed that the expansion of immortalized TCR alpha beta + cells was preceded by a gradual loss of CD34+ cells followed by a transient accumulation of two distinct cell subsets: first CD1+CD4+CD3- cells and then CD4+CD8+ thymocytes. This resembles early phenotypic changes occurring during normal intrathymic T cell development. In the presence of IL-2, in contrast, only TCR gamma delta + cells were immortalized (mainly CD4-CD8+, but also CD4-CD8-). The results show that HVS can be used to read the CD3+ cellular outcome of T cell differentiation assays, including gamma delta + CD4-CD8+, gamma delta + CD4-CD8-, alpha beta + CD4+CD8-, alpha beta + CD4-CD8+ and alpha beta + CD4+CD8+ T cells. A clear role for different cytokines (IL-2 for gamma delta + cells, IL-7 for alpha beta + cells) in early T cell commitment was also apparent.

Regulation of pre-T cell receptor (pT alpha-TCR beta) gene expression during human thymic development

In murine T cell development, early thymocytes that productively rearrange the T cell receptor (TCR) beta locus are selected to continue maturation, before TCR alpha expression, by means of a pre-TCR alpha- (pT alpha-) TCR beta heterodimer (pre-TCR). The aim of this study was to identify equivalent stages in human thymocyte development. We show here that variable-diversity-joining region TCR beta rearrangement and the expression of full-length TCR beta transcripts have been initiated in some immature thymocytes at the TCR alpha/beta- CD4+CD8- stage, and become common in a downstream subset of TCR alpha/beta- CD4+CD8+ thymocytes that is highly enriched in large cycling cells. TCR beta chain expression was hardly detected in TCR alpha/beta- CD4+CD8- thymocytes, whereas cytoplasmic TCR beta chain was found in virtually all TCR alpha/beta- CD4+CD8+ blasts. In addition, a TCR beta complex distinct from the mature TCR alpha/beta heterodimer was immunoprecipitated only from the latter subset. cDNA derived from TCR alpha/beta- CD4+CD8+ blasts allowed us to identify and clone the gene encoding the human pT alpha chain, and to examine its expression at different stages of thymocyte development. Our results show that high pT alpha transcription occurs only in CD4+CD8- and CD4+CD8+ TCR alpha/beta- thymocytes, whereas it is weaker in earlier and later stages of development. Based on these results, we propose that the transition from TCR alpha/beta- CD4+CD8- to TCR alpha/beta- CD4+CD8+ thymocytes represents a critical developmental stage at which the successful expression of TCR beta promotes the clonal expansion and further maturation of human thymocytes, independent of TCR alpha.

The development of T and non-T cell lineages from CD34+ human thymic precursors can be traced by the differential expression of CD44

In addition to T-lineage cells, a small proportion of hematopoietic non-T cells are present in the human postnatal thymus. However, the origin of this minor non-T cell thymic compartment is presently unknown. In this study we have analyzed the developmental potential of the earliest human intrathymic precursors, characterized as CD34+ cells expressing intermediate levels of CD44. We show that these CD34+CD44int thymocytes cultured with interleukin 7 were able to develop simultaneously into both T- and non-T (monocytes and dendritic cells) -lineage cells. Both developmental pathways progress through a CD1+CD4+ intermediate stage, currently believed to be the immediate precursor of double positive thymocytes. However, separate progenitors for either T or non-T cells could be characterized within CD1+CD4+ thymocytes by their opposite expression of CD44. Downregulated levels of CD44 identified CD1+CD4+ T-lineage precursors, whereas CD44 upregulation occurred on CD1+CD4+ intermediates that later differentiated into non-T cells. Therefore, commitment of human early intrathymic precursors to either T or non-T cell lineages can be traced by the differential expression of the CD44 receptor.

Induced photolysis of rabbit red blood cells by several photosensitizers

The photolysis of rabbit red blood cells induced by several photosensitizers has been studied. Membrane photohemolysis was found to be dependent on light dose (J/cm2) for hematoporphyrin (HP), methylene blue (MB) and toluidine blue (TB). No significant hemolysis was detected when mesotetra (4N-methylpyridyl) porphine (T4MPyP) plus light was used. Sodium azide inhibited, whereas deuterium oxide potentiated membrane lysis with HP, MB and TB. In the case of T4MPyP no differences were observed when using sodium azide or deuterium oxide.

Photodynamic induction of DNA-protein cross-linking in solution by several sensitizers and visible light

The combined effect of several sensitizers and light on H2O or D2O solutions of DNA-histone complexes, as well as the significance of singlet oxygen (1O2), in this photosensitizing reaction has been studied. On H2O solutions, the production of 1O2, as well as the formation of DNA-protein cross-links (DPCs), were found to be dependent on light dose for all the sensitizers. Mesotetra (4N-methylpyridyl) porphine (T4MPyP), methylene blue (MB), and toluidine blue (TB) were the best photosensitizers with regard to tryptophan photolysis, followed by hematoporphyrin (HP), thioflavine T (TT), and pyronin G (PG). The formation of DPCs showed high initial rates, reaching a plateau at doses over 90 J/cm2. Under these irradiation conditions, the percentage of DPCs induced by the sensitizers decreases in the order T4MPyP > MB > TB >> HP approximately TT >> PG (approximately 0). These DPCs were totally destroyed with proteinase K (15 micrograms/ml). The irradiation of the DNA-histone-sensitizer solutions in the presence of L-carnosine (5 x 10(-4) M) produced approximately a 50% of DPCs inhibition for T4MPyP, MB, and TB, and a total inhibition for HP, TT, and PG. The substitution of H2O by D2O as solvent significantly increased the photodegradation of tryptophan, as well as the photoinduction of DPCs by the sensitizers. The results obtained indicate that singlet oxygen is the main agent responsible in the DNA-protein cross-linking formation.