Purine nucleoside phosphorylase activity and expression are upregulated in sites affected by periodontal disease

A nucleoside-based supramolecular hydrogel integrating localized self-delivery and immunomodulation for periodontitis treatment

Periodontitis is a highly prevalent oral disease characterized by bacterial-induced hyperactivation of the host immune system, leading to a sustained inflammatory response and osteoclastic activity, which ultimately results in periodontal destruction. In this work, an immunomodulatory supramolecular hydrogel for the topical treatment of periodontitis was synthesized using a simple one-pot method. This phenylboronate ester-based 8AGPB hydrogel exhibited excellent stability, self-healing properties, injectability, and biocompatibility. During degradation, the 8AGPB hydrogel releases immunomodulatory agent 8-aminoguanosine (8AG), which regulates MAPK and NF-κB signaling pathways by modulation of second messengers in macrophages. In combination with 1,4-phenylenediboronic acid (PBA), which possesses antioxidant properties, 8AG effectively inhibits ROS production and oxidative damage in LPS-stimulated macrophages, lowering the M1/M2 macrophage polarization ratio and reducing the secretion of pro-inflammatory factors. In an experimental periodontitis model using C57BL/6 mice, periodontal injection of the 8AGPB hydrogel reduced inflammatory infiltration and osteoclastic activity through immunomodulation and inhibition of osteoclast differentiation, thereby ameliorating periodontal destruction during periodontitis progression. Overall, the 8AGPB supramolecular hydrogel, serving as an injectable self-delivery platform for 8AG, may represent a promising novel strategy for periodontitis treatment and offer insights for the development of future topical anti-inflammatory systems.

Perspectives and challenges in developing small molecules targeting purine nucleoside phosphorylase

As a cytosolic enzyme involved in the purine salvage pathway metabolism, purine nucleoside phosphorylase (PNP) plays an important role in a variety of cellular functions but also in immune system, including cell growth, apoptosis and cancer development and progression. Based on its T-cell targeting profile, PNP is a potential target for the treatment of some malignant T-cell proliferative cancers including lymphoma and leukemia, and some specific immunological diseases. Numerous small-molecule PNP inhibitors have been developed so far. However, only Peldesine, Forodesine and Ulodesine have entered clinical trials and exhibited some potential for the treatment of T-cell leukemia and gout. The most recent direction in PNP inhibitor development has been focused on PNP small-molecule inhibitors with better potency, selectivity, and pharmacokinetic property. In this perspective, considering the structure, biological functions, and disease relevance of PNP, we highlight the recent research progress in PNP small-molecule inhibitor development and discuss prospective strategies for designing additional PNP therapeutic agents.

Osteopontin interacts with dendritic cells and macrophages in pulp inflammation: Comprehensive transcriptomic analysis and laboratory investigations

AIM

To investigate novel diagnostic markers for pulpitis and validate by clinical samples from normal and inflamed pulp. To explore the relationship between diagnostic markers and immune cells or their phenotypes during pulp inflammation.

METHODOLOGY

Two microarray datasets, GSE77459 and GSE92681, and identified differential expression genes were integrated. To understand immune features, gene functions, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), Disease Ontology (DO) and ImmuneSigDB Gene Set Enrichment Analysis (GSEA) were analysed. For predictive purposes, machine learning techniques were applied to detect diagnostic markers. Immune infiltration in inflamed pulp was studied using CIBERSORT. The relationship between diagnostic markers and immune cells was investigated and validated their gene expression in clinical samples from the normal or inflamed pulp by qRT-PCR. Finally, the correlation between one marker, secreted phosphoprotein 1 (SPP1), encoding osteopontin (OPN), and dendritic cells (DCs)/macrophages was identified via HE staining and multiplex immunohistochemistry. An in vitro inflammatory dental pulp microenvironment model of THP-1 macrophages cocultured with dental pulp cells derived conditioned media (DPCs-CM) to investigate OPN production and macrophage phenotypes was established.

RESULTS

Analysis revealed unique immunologic features in inflamed pulp. Three diagnostic markers for pulpitis: endothelin-1 (EDN1), SPP1, and purine nucleoside phosphorylase (PNP), and validated them using qRT-PCR were predicted. Multiplex immunohistochemistry demonstrated OPN co-localized with activated DCs and M2 macrophages during pulp inflammation. In vitro experiments showed that THP-1 macrophages produced the highest levels of OPN when stimulated with DPCs-CM derived from the 20 μg/mL LPS pre-conditioned group, suggesting an M2b-like phenotype by increasing surface marker CD86 and expression of IL6, TNFα, IL10, and CCL1 but not CCL17 and MerTK. Levels of CCL1 and IL10 elevated significantly in the macrophages' supernatant from the 20 μg/mL LPS pre-conditioned CM group. OPN was proven co-localizing with CD86 in the inflamed pulp by immunofluorescence.

CONCLUSIONS

The current findings suggest that OPN can serve as a promising biomarker for pulpitis, correlated with DCs and macrophages. OPN+ macrophages in the inflamed pulp are associated with M2b-like phenotypes. These insights offer the potential for improved diagnosis and targeted therapy.

Multi-omics study of key genes, metabolites, and pathways of periodontitis

OBJECTIVE

This study aimed to explore the key genes, metabolites, and pathways that influence periodontitis pathogenesis by integrating transcriptomic and metabolomic studies.

DESIGN

Gingival crevicular fluid samples from periodontitis patients and healthy controls were collected for liquid chromatography/tandem mass-based metabolomics. RNA-seq data for periodontitis and control samples were obtained from the GSE16134 dataset. Differential metabolites and differentially expressed genes (DEGs) between the two groups were then compared. Based on the protein-protein interaction (PPI) network module analysis, key module genes were selected from immune-related DEGs. Correlation and pathway enrichment analyses were performed for differential metabolites and key module genes. A multi-omics integrative analysis was performed using bioinformatic methods to construct a gene-metabolite-pathway network.

RESULTS

From the metabolomics study, 146 differential metabolites were identified, which were mainly enriched in the pathways of purine metabolism and Adenosine triphosphate binding cassette transporters (ABC transporters). The GSE16134 dataset revealed 102 immune-related DEGs (458 upregulated and 264 downregulated genes), 33 of which may play core roles in the key modules of the PPI network and are involved in cytokine-related regulatory pathways. Through a multi-omics integrative analysis, a gene-metabolite-pathway network was constructed, including 28 genes (such as platelet derived growth factor D (PDGFD), neurturin (NRTN), and interleukin 2 receptor, gamma (IL2RG)); 47 metabolites (such as deoxyinosine); and 8 pathways (such as ABC transporters).

CONCLUSION

PDGFD, NRTN, and IL2RG may be potential biomarkers of periodontitis and may affect disease progression by regulating deoxyinosine to participate in the ABC transporter pathway.

Sphingosine kinase activity and sphingosine-1-phosphate in the inflamed human periodontium

OBJECTIVES

This study evaluated changes in the levels of Sphingosine-1-Phosphate (S1P) and Sphingosine Kinase (SPHK) activity in response to non-surgical periodontal treatment in humans.

METHODS

Diseased (n = 65) and healthy sites (n = 72) were screened in 18 patients with localized periodontitis stage II or III. Periodontal clinical parameters were recorded, and the gingival crevicular fluid (GCF) collected at baseline, 30 and 90 days of non-surgical treatment. Internal control sites without attachment loss/bleeding were sampled at baseline and after 90 days of treatment. SPHK activity and S1P levels and SPHK 1/2 isoforms were determined in the GCF at different time points using ELISA.

RESULTS

Non-surgical treatment caused significant improvement in all periodontal clinical parameters (p < 0.01). Activity of SPHK and S1P levels was decreased (p < 0.05) 30 days after treatment and continued up to 90 days (p < 0.01); control sites remained unchanged throughout the study and resembled treated sites at 3 months (p > 0.05). SPHK1 levels presented decrease after periodontal treatment (p < 0.001). SPHK2 levels were lower than SPHK1 (p < 0.001) and remained unchanged.

CONCLUSIONS

S1P levels and SPHK activity decreased within 3 months of non-surgical periodontal treatment, which were correlated with improvements in periodontal parameters. Only SPHK1 levels varied significantly in the states of health and disease.

Purinergic Signaling in Oral Tissues

The role of the purinergic signal has been extensively investigated in many tissues and related organs, including the central and peripheral nervous systems as well as the gastrointestinal, cardiovascular, respiratory, renal, and immune systems. Less attention has been paid to the influence of purines in the oral cavity, which is the first part of the digestive apparatus and also acts as the body’s first antimicrobial barrier. In this review, evidence is provided of the presence and possible physiological role of the purinergic system in the different structures forming the oral cavity including teeth, tongue, hard palate, and soft palate with their annexes such as taste buds, salivary glands, and nervous fibers innervating the oral structures. We also report findings on the involvement of the purinergic signal in pathological conditions affecting the oral apparatus such as Sjögren’s syndrome or following irradiation for the treatment of head and neck cancer, and the use of experimental drugs interfering with the purine system to improve bone healing after damage. Further investigations are required to translate the results obtained so far into the clinical setting in order to pave the way for a wider application of purine-based treatments in oral diseases.

Gingival fibroblasts dynamically reprogram cellular metabolism during infection of Porphyromonas gingivalis

OBJECTIVE

The purpose of the present study was to explore the sequential changes in the cellular metabolism in gingival fibroblasts (GFs) in response toPorphyromonas gingvalis (P. gingivalis) ATCC33277 infection.

DESIGN

GFs were treated withP. gingivalis at the MOI of 50 for 4, 24 and 48 h to mimic the early, medium, and late phase in the bacterial infection. LDH assay and cell counting kit-8 were utilized to explore cell death and proliferation. Real-time PCR was utilized to explore the gene transcription of pro-inflammatory genes. The relative levels of biomolecules in GFs were measured by gas chromatography-mass spectrometry. Principal component analysis and orthogonal partial least-squares-discriminant analysis were performed to visualize the metabolic difference among experimental groups. In addition, pathway analysis was conducted regarding differential metabolites in GFs.

RESULTS

P. gingivalis infection triggered significant gene transcription of IL-1β, IL 6, MCP 1, and MMP 1 in GFs. In addition, P. gingivalis stimulated cell proliferation of GFs at MOI of 10, 50 and 250. Moreover, P. gingivalis triggered significant cell death at higher MOI. 69, 173 and 148 metabolites were qualitatively detected at 4, 24 and 48 h after P. gingivalis infection respectively in GFs, showing a sequential change of different phase. Kyoto Encyclopedia of Genes and Genomes pathway analysis demonstrated that ATP-binding cassette transporters, glutathione, purine and pyrimidine metabolism was significantly altered in different phase.

CONCLUSIONS

Human GFs may sequentially rewire metabolomics to shape the inflammatory responses and support the proliferation of host cells during P. gingivalis infection.

Release of soluble and vesicular purine nucleoside phosphorylase from rat astrocytes and microglia induced by pro-inflammatory stimulation with extracellular ATP via P2X7 receptors

Purine nucleoside phosphorylase (PNP), a crucial enzyme in purine metabolism which converts ribonucleosides into purine bases, has mainly been found inside glial cells. Since we recently demonstrated that PNP is released from rat C6 glioma cells, we then wondered whether this occurs in normal brain cells. Using rat primary cultures of microglia, astrocytes and cerebellar granule neurons, we found that in basal condition all these cells constitutively released a metabolically active PNP with Km values very similar to those measured in C6 glioma cells. However, the enzyme expression/release was greater in microglia or astrocytes that in neurons. Moreover, we exposed primary brain cell cultures to pro-inflammatory agents such as lipopolysaccharide (LPS) or ATP alone or in combination. LPS alone caused an increased interleukin-1β (IL-1β) secretion mainly from microglia and no modification in the PNP release, even from neurons in which it enhanced cell death. In contrast, ATP administered alone to glial cells at high micromolar concentrations significantly stimulated the release of PNP within 1 h, an effect not modified by LPS presence, whereas IL-1β secretion was stimulated by ATP only in cells primed for 2 h with LPS. In both cases ATP effect was mediated by P2X₇ receptor (P2X₇R), since it was mimicked by cell exposure to Bz-ATP, an agonist of P2X₇R, and blocked by cell pre-treatment with the P2X₇R antagonist A438079. Interestingly, ATP-induced PNP release from glial cells partly occurred through the secretion of lysosomal vesicles in the extracellular medium. Thus, during inflammatory cerebral events PNP secretion promoted by extracellular ATP accumulation might concur to control extracellular purine signals. Further studies could elucidate whether, in these conditions, a consensual activity of enzymes downstream of PNP in the purine metabolic cascade avoids accumulation of extracellular purine bases that might concur to brain injury by unusual formation of reactive oxygen species.

Development of a new HPLC method using fluorescence detection without derivatization for determining purine nucleoside phosphorylase activity in human plasma

Purine nucleoside phosphorylase (PNP) activity is involved in cell survival and function, since PNP is a key enzyme in the purine metabolic pathway where it catalyzes the phosphorolysis of the nucleosides to the corresponding nucleobases. Its dysfunction has been found in relevant pathological conditions (such as inflammation and cancer), so the detection of PNP activity in plasma could represent an attractive marker for early diagnosis or assessment of disease progression. Thus the aim of this study was to develop a simple, fast and sensitive HPLC method for the determination of PNP activity in plasma. The separation was achieved on a Phenomenex Kinetex PFP column using 0.1% formic acid in water and methanol as mobile phases in gradient elution mode at a flow rate of 1ml/min and purine compounds were detected using UV absorption and fluorescence. The analysis was fast since the run was achieved within 13min. This method improved the separation of the different purines, allowing the UV-based quantification of the natural PNP substrates (inosine and guanosine) or products (hypoxanthine and guanine) and its subsequent metabolic products (xanthine and uric acid) with a good precision and accuracy. The most interesting innovation is the simultaneous use of a fluorescence detector (excitation/emission wavelength of 260/375nm) that allowed the quantification of guanosine and guanine without derivatization. Compared with UV, the fluorescence detection improved the sensitivity for guanine detection by about 10-fold and abolished almost completely the baseline noise due to the presence of plasma in the enzymatic reaction mixture. Thus, the validated method allowed an excellent evaluation of PNP activity in plasma which could be useful as an indicator of several pathological conditions.

Elucidating the evolutionary history and expression patterns of nucleoside phosphorylase paralogs (vegetative storage proteins) in Populus and the plant kingdom

BACKGROUND

Nucleoside phosphorylases (NPs) have been extensively investigated in human and bacterial systems for their role in metabolic nucleotide salvaging and links to oncogenesis. In plants, NP-like proteins have not been comprehensively studied, likely because there is no evidence of a metabolic function in nucleoside salvage. However, in the forest trees genus Populus a family of NP-like proteins function as an important ecophysiological adaptation for inter- and intra-seasonal nitrogen storage and cycling.

RESULTS

We conducted phylogenetic analyses to determine the distribution and evolution of NP-like proteins in plants. These analyses revealed two major clusters of NP-like proteins in plants. Group I proteins were encoded by genes across a wide range of plant taxa while proteins encoded by Group II genes were dominated by species belonging to the order Malpighiales and included the Populus Bark Storage Protein (BSP) and WIN4-like proteins. Additionally, we evaluated the NP-like genes in Populus by examining the transcript abundance of the 13 NP-like genes found in the Populus genome in various tissues of plants exposed to long-day (LD) and short-day (SD) photoperiods. We found that all 13 of the Populus NP-like genes belonging to either Group I or II are expressed in various tissues in both LD and SD conditions. Tests of natural selection and expression evolution analysis of the Populus genes suggests that divergence in gene expression may have occurred recently during the evolution of Populus, which supports the adaptive maintenance models. Lastly, in silico analysis of cis-regulatory elements in the promoters of the 13 NP-like genes in Populus revealed common regulatory elements known to be involved in light regulation, stress/pathogenesis and phytohormone responses.

CONCLUSION

In Populus, the evolution of the NP-like protein and gene family has been shaped by duplication events and natural selection. Expression data suggest that previously uncharacterized NP-like proteins may function in nutrient sensing and/or signaling. These proteins are members of Group I NP-like proteins, which are widely distributed in many plant taxa. We conclude that NP-like proteins may function in plants, although this function is undefined.

The transition state analog inhibitor of Purine Nucleoside Phosphorylase (PNP) Immucillin-H arrests bone loss in rat periodontal disease models

Purine nucleoside phosphorylase (PNP) is a purine-metabolizing enzyme that catalyzes the reversible phosphorolysis of 6-oxypurine (deoxy)nucleosides to their respective bases and (deoxy)ribose-1-phosphate. It is a key enzyme in the purine salvage pathway of mammalian cells. The present investigation sought to determine whether the PNP transition state analog inhibitor (Immucillin-H) arrests bone loss in two models of induced periodontal disease in rats. Periodontal disease was induced in rats using ligature or LPS injection followed by administration of Immucillin-H for direct analysis of bone loss, histology and TRAP staining. In vitro osteoclast differentiation and activation of T CD4+ cells in the presence of Immucillin-H were carried out for assessment of RANKL expression, PNP and Cathepsin K activity. Immucillin-H inhibited bone loss induced by ligatures and LPS, leading to a reduced number of infiltrating osteoclasts and inflammatory cells. In vitro assays revealed that Immucillin-H could not directly abrogate differentiation of osteoclast precursor cells, but affected lymphocyte-mediated osteoclastogenesis. On the other hand, incubation of pre-activated T CD4+ with Immucillin-H decreased RANKL secretion with no compromise of cell viability. The PNP transition state analog Immucillin-H arrests bone loss mediated by T CD4+ cells with no direct effect on osteoclasts. PNP inhibitor may have an impact in the treatment of diseases characterized by the presence of pathogens and imbalances of bone metabolism.