Cytidine deaminase activity in synovial fluid of patients with rheumatoid arthritis: relation to lactoferrin, acidosis, and cartilage proteoglycan release

Unveiling cytokine charge disparity as a potential mechanism for immune regulation

Cytokines are small signaling proteins that regulate the immune responses to infection and tissue damage. Surface charges of cytokines determine their in vivo fate in immune regulation, e.g., half-life and distribution. The overall negative charges in the extracellular microenvironment and the acidosis during inflammation and infection may differentially impact cytokines with different surface charges for fine-tuned immune regulation via controlling tissue residential properties. However, the trend and role of cytokine surface charges has yet to be elucidated in the literature. Interestingly, we have observed that most pro-inflammatory cytokines have a negative charge, while most anti-inflammatory cytokines and chemokines have a positive charge. In this review, we extensively examined the surface charges of all cytokines and chemokines, summarized the pharmacokinetics and tissue adhesion of major cytokines, and analyzed the link of surface charge with cytokine biodistribution, activation, and function in immune regulation. Additionally, we identified that the general trend of charge disparity between pro- and anti-inflammatory cytokines represents a unique opportunity to develop precise immune modulation approaches, which can be applied to many inflammation-associated diseases including solid tumors, chronic wounds, infection, and sepsis.

Stimuli-Sensitive Nanotherapies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common chronic inflammatory disease in the joints. It is one of the leading causes of disability with increasing morbidity, which has become one of the serious clinical issues. Current treatments would only provide temporary relief due to the lack of early diagnosis and effective therapy, and thus the replacement of joints may be needed when the OA deteriorates. Although the intra-articular injection and oral administration of drugs are helpful for OA treatment, they are suffering from systemic toxicity, short retention time in joint, and insufficient bioavailability. Nanomedicine is potential to improve the drug delivery efficiency and targeting ability. In this focused progress review, the particle-based drug loading systems that can achieve targeted and triggered release are summarized. Stimuli-responsive nanocarriers that are sensitive to endogenous microenvironmental signals such as reactive oxygen species, enzymes, pH, and temperature, as well as external stimuli such as light for OA therapy are introduced in this review. Furthermore, the nanocarriers associated with targeted therapy and imaging for OA treatment are summarized. The potential applications of nanotherapies for OA treatment are finally discussed.

Extracellular Acidosis and mTOR Inhibition Drive the Differentiation of Human Monocyte-Derived Dendritic Cells

During inflammation, recruited monocytes can differentiate either into macrophages or dendritic cells (DCs); however, little is known about the environmental factors that determine this cell fate decision. Low extracellular pH is a hallmark of a variety of inflammatory processes and solid tumors. Here, we report that low pH dramatically promotes the differentiation of monocytes into DCs (monocyte-derived DCs [mo-DCs]). This process is associated with a reduction in glucose consumption and lactate production, the upregulation of mitochondrial respiratory chain genes, and the inhibition of mTORC1 activity. Interestingly, we also find that both serum starvation and pharmacological inhibition of mTORC1 markedly promote the differentiation of mo-DCs. Our study contributes to better understanding the mechanisms that govern the differentiation of monocytes into DCs and reveals the role of both extracellular pH and mTORC1 as master regulators of monocyte cell fate.

Acid-sensing ion channel 1a mediates acid-induced pyroptosis through calpain-2/calcineurin pathway in rat articular chondrocytes

The pyroptosis is a causative agent of rheumatoid arthritis, a systemic autoimmune disease merged with degenerative articular cartilage. Nevertheless, the precise mechanism of extracellular acidosis on chondrocyte pyroptosis is largely unclear. Acid-sensing ion channels (ASICs) belong to an extracellular H⁺ -activated cation channel family. Accumulating evidence has highlighted activation of ASICs induced by extracellular acidosis upregulate calpain and calcineurin expression in arthritis. In the present study, to investigate the expression and the role of acid-sensing ion channel 1a (ASIC1a), calpain, calcineurin, and NLRP3 inflammasome proteins in regulating acid-induced articular chondrocyte pyroptosis, primary rat articular chondrocytes were subjected to different pH, different time, and different treatments with or without ASIC1a, calpain-2, and calcineurin, respectively. Initially, the research results showed that extracellular acidosis-induced the protein expression of ASIC1a in a pH- and time-dependent manner, and the messenger RNA and protein expressions of calpain, calcineurin, NLRP3, apoptosis-associated speck-like protein, and caspase-1 were significantly increased in a time-dependent manner. Furthermore, the inhibition of ASIC1a, calpain-2, or calcineurin, respectively, could decrease the cell death accompanied with the decreased interleukin-1β level, and the decreased expression of ASIC1a, calpain-2, calcineurin, and NLRP3 inflammasome proteins. Taken together, these results indicated the activation of ASIC1a induced by extracellular acidosis could trigger pyroptosis of rat articular chondrocytes, the mechanism of which might partly be involved with the activation of calpain-2/calcineurin pathway.

Unravelling the Interplay between Extracellular Acidosis and Immune Cells

The development of an acidic tissue environment is a hallmark of a variety of inflammatory processes and solid tumors. However, little attention has been paid so far to analyze the influence exerted by extracellular pH on the immune response. Tissue acidosis (pH 6.0 to 7.0) is usually associated with the course of infectious processes in peripheral tissues. Moreover, it represents a prominent feature of solid tumors. In fact, values of pH ranging from 5.7 to 7.0 are usually found in a number of solid tumors such as breast cancer, brain tumors, sarcomas, malignant melanoma, squamous cell carcinomas, and adenocarcinomas. Both the innate and adaptive arms of the immune response appear to be finely regulated by extracellular acidosis in the range of pH values found at inflammatory sites and tumors. Low pH has been shown to delay neutrophil apoptosis, promoting their differentiation into a proangiogenic profile. Acting on monocytes and macrophages, it induces the activation of the inflammasome and the production of IL-1β, while the exposure of conventional dendritic cells to low pH promotes the acquisition of a mature phenotype. Overall, these observations suggest that high concentrations of protons could be recognized by innate immune cells as a danger-associated molecular pattern (DAMP). On the other hand, by acting on T lymphocytes, low pH has been shown to suppress the cytotoxic response mediated by CD8+ T cells as well as the production of IFN-γ by TH1 cells. Interestingly, modulation of tumor microenvironment acidity has been shown to be able not only to reverse anergy in human and mouse tumor-infiltrating T lymphocytes but also to improve the antitumor immune response induced by checkpoint inhibitors. Here, we provide an integrated view of the influence exerted by low pH on immune cells and discuss its implications in the immune response against infectious agents and tumor cells.

Low pH impairs complement-dependent cytotoxicity against IgG-coated target cells

Local acidosis is a common feature of allergic, vascular, autoimmune, and cancer diseases. However, few studies have addressed the effect of extracellular pH on the immune response. Here, we analyzed whether low pH could modulate complement-dependent cytotoxicity (CDC) against IgG-coated cells. Using human serum as a complement source, we found that extracellular pH values of 5.5 and 6.0 strongly inhibit CDC against either B lymphoblast cell lines coated with the chimeric anti-CD20 mAb rituximab or PBMCs coated with the humanized anti-CD52 mAb alemtuzumab. Suppression of CDC by low pH was observed either in cells suspended in culture medium or in whole blood assays. Interestingly, not only CDC against IgG-coated cells, but also the activation of the complement system induced by the alternative and lectin pathways was prevented by low pH. Tumor-targeting mAbs represent one of the most successful tools for cancer therapy, however, the use of mAb monotherapy has only modest effects on solid tumors. Our present results suggest that severe acidosis, a hallmark of solid tumors, might impair complement-mediated tumor destruction directed by mAb.

ASIC2a overexpression enhances the protective effect of PcTx1 and APETx2 against acidosis-induced articular chondrocyte apoptosis and cytotoxicity

Acid hydrarthrosis is another important pathological character in rheumatoid arthritis (RA), and acid-sensing ion channel 1a (ASIC1a) plays a destructive role in acidosis-induced articular chondrocyte cytotoxicity. Recently, ASIC2a has been reported to possess neuroprotective effect on acidosis-induced injury of neuronal cells. However, whether ASIC2a has an enhanced effect on the protective effect of blocking ASIC1a and ASIC3 against acid-induced chondrocyte apoptosis is still unclear. The aim of present study was to investigate the chondroprotective effect of ASIC2a with PcTx1 (ASIC1a specific blocker) and APETx2 (ASIC3 specific blocker) on acidosis-induced chondrocyte apoptosis. Our results revealed that acid (pH 6.0) decreased the cell viability and induced apoptosis of articular chondrocytes. PcTx1 and APETx2 combination significantly attenuated acidosis-induced chondrocyte cytotoxicity due to inhibit apoptosis, and this role could be enhanced by ASIC2a overexpression compared with the PcTx1 and APETx2 combination alone group. Moreover, both the [Ca²⁺]_i levels and the levels of phosphorylated ERK1/2 as well as p38 were further reduced in acidosis-induced chondrocytes after ASIC2a overexpression in the presence of PcTx1 and APETx2. Furthermore, ASIC2a overexpression also reduced acid-induced the expression of ASIC1a. In addition, ASIC2a overexpression further promoted the PcTx1 and APETx2-increased levels of type II collagen in acidosis-induced chondrocytes. Taken together, the current data suggested that ASIC2a overexpression might enhance the anti-apoptotic and protective role of PcTx1 and APETx2 against acid-induced rat articular chondrocyte apoptosis by regulating ASIC1a expression and the [Ca²⁺]_i levels and at least in part, suppressing p38 and ERK1/2 MAPK signaling pathways.

ASIC1a Promotes Acid-Induced Autophagy in Rat Articular Chondrocytes through the AMPK/FoxO3a Pathway

Acid-sensing ion channel 1a (ASIC1a) is a member of the extracellular H⁺-activated cation channels family. Our previous studies suggested that ASIC1a contributed to acid-induced rat articular chondrocytes autophagy. However, its potential mechanisms remain unclear. The present study demonstrated the effect of ASIC1a on rat articular chondrocytes autophagy and explored the underlying molecular mechanisms. The results demonstrated that ASIC1a contributed to acid-induced autophagy in rat articular chondrocytes, and which was associated with an increase in (Ca2+)i, as indicated that acid-induced increases in mRNA and protein expression of LC3B-II and other autophagy-related markers were inhibited by ASIC1a-specific blocker, PcTx1 and calcium chelating agent, BAPTA-AM. Furthermore, the results showed that extracellular acid increased level of Forkhead box O (FoxO) 3a, but was reversed by inhibition of ASIC1a and Ca2+ influx. Moreover, gene ablation of FoxO3a prevented acid-induced increases in mRNA and protein expression of LC3B-II, Beclin1 and the formation of autophagosome. Finally, it also showed that ASIC1a activated adenine nucleotide (AMP)-activated protein kinase (AMPK). In addition, suppression of AMPK by Compound C and its small interfering RNA (siRNA) prevented acid-induced upregulation of total and nuclear FoxO3a and increases in mRNA and protein expression of LC3B-II, Beclin1, and ATG5. Taken together, these findings suggested that AMPK/FoxO3a axis plays an important role in ASIC1a-mediated autophagy in rat articular chondrocytes, which may provide novel mechanistic insight into ASIC1a effects on autophagy.

Acidosis exacerbates in vivo IL-1-dependent inflammatory responses and neutrophil recruitment during pulmonary Pseudomonas aeruginosa infection

Acidic microenvironments commonly occur at sites of inflammation and bacterial infections. In the context of a Pseudomonas aeruginosa infection, we previously demonstrated that acidosis enhances the cellular proinflammatory interleukin (IL)-1β response in vitro. However, how pH alterations affect in vivo IL-1β responses and subsequent IL-1-driven inflammation during infection with P. aeruginosa is unclear. Here, we report that acidosis enhances in vivo IL-1β production and downstream IL-1 receptor-dependent responses during infection with P. aeruginosa in models of acute pneumonia and peritonitis. Importantly, we demonstrate that infection with P. aeruginosa within an acidic environment leads to enhanced production of a subset of proinflammatory cytokines, including chemokine (C-X-C) motif ligand 1, IL-6, and chemokine (C-C motif) ligand 2, and increased neutrophil recruitment. Furthermore, with the use of IL-1 receptor type 1-deficient mice, we identify the contribution of the IL-1 signaling pathway to the acidosis-enhanced inflammatory response and pathology. These data provide insights into the potential benefit of pH regulation during bacterial infections to control disease progression and immunopathology.

Acidosis increases the susceptibility of respiratory epithelial cells to Pseudomonas aeruginosa-induced cytotoxicity

Bacterial infection can lead to acidosis of the local microenvironment, which is believed to exacerbate disease pathogenesis; however, the mechanisms by which changes in pH alter disease progression are poorly understood. We test the hypothesis that acidosis enhances respiratory epithelial cell death in response to infection with Pseudomonas aeruginosa Our findings support the idea that acidosis in the context of P. aeruginosa infection results in increased epithelial cell cytotoxicity due to ExoU intoxication. Importantly, enforced maintenance of neutral pH during P. aeruginosa infection demonstrates that cytotoxicity is dependent on the acidosis. Investigation of the underlying mechanisms revealed that host cell cytotoxicity correlated with increased bacterial survival during an acidic infection that was due to reduced bactericidal activity of host-derived antimicrobial peptides. These findings extend previous reports that the activities of antimicrobial peptides are pH-dependent and provide novel insights into the consequences of acidosis on infection-derived pathology. Therefore, this report provides the first evidence that physiological levels of acidosis increase the susceptibility of epithelial cells to acute Pseudomonas infection and demonstrates the benefit of maintaining pH homeostasis during a bacterial infection.

Acidosis potentiates the host proinflammatory interleukin-1β response to Pseudomonas aeruginosa infection

Infection by Pseudomonas aeruginosa, and bacteria in general, frequently promotes acidification of the local microenvironment, and this is reinforced by pulmonary exertion and exacerbation. However, the consequence of an acidic environment on the host inflammatory response to P. aeruginosa infection is poorly understood. Here we report that the pivotal cellular and host proinflammatory interleukin-1β (IL-1β) response, which enables host clearance of the infection but can produce collateral inflammatory damage, is increased in response to P. aeruginosa infection within an acidic environment. Synergistic mechanisms that promote increased IL-1β release in response to P. aeruginosa infection in an acidic environment are increased pro-IL-1β induction and increased caspase-1 activity, the latter being dependent upon a functional type III secretion system of the bacteria and the NLRC4 inflammasome of the host. Using an in vivo peritonitis model, we have validated that the IL-1β inflammatory response is increased in mice in response to P. aeruginosa infection within an acidic microenvironment. These data reveal novel insights into the regulation and exacerbation of inflammatory responses to P. aeruginosa.

Oxygen and pH-sensitivity of human osteoarthritic chondrocytes in 3-D alginate bead culture system

OBJECTIVE

To identify the effect of alterations in physical parameters such as oxygen and pH on processes associated with cellular redox balance in osteoarthritic chondrocytes.

METHOD

Human osteoarthritic chondrocytes (HOAC) were isolated from total knee arthroplasty samples and cultured in 3-D alginate beads in four different oxygen tensions (<1%, 2%, 5% and 21% O2), at pH 7.2 and 6.2 and in the presence or absence of 10 ng/ml, interleukin-1β (IL-1β). Cell viability, media glycosaminoglycan (GAG) levels, media nitrate/nitrate levels, active matrix metalloproteinase (MMP)-13 and intracellular adenosine triphosphate (ATPi) were measured over a 96-h time course. Intracellular reactive oxygen species (ROS), mitochondrial membrane potential, intracellular pH and reduced/oxidised glutathione (GSH/GSSG) were additionally measured after 48-h incubation under these experimental conditions.

RESULTS

Hypoxia (2% O2) and anoxia (<1% O2), acidosis (pH 6.2) and 10 ng/ml IL-1β reduced HOAC cell viability and increased GAG media levels. Acidosis and IL-1β increased nitrite/nitrate release, but increases were moderate at 2% O2 and significantly reduced at <1% O2. ATPi was significantly reduced following hypoxia and anoxia and acidosis. At 48 h cellular ROS levels were increased by acidosis and IL-1β but reduced in hypoxia and anoxia. Mitochondrial membrane potential was reduced in low oxygen, acidosis and IL-1β. Anoxia also resulted in intracellular acidosis. GSH/GSSG ratio was reduced in low oxygen conditions, acidosis and IL-1β.

CONCLUSIONS

This study shows that oxygen and pH affect elements of the redox system in HOAC including cellular anti-oxidants, mitochondrial membrane potential and ROS levels.

Gene expression profiling of articular cartilage reveals functional pathways and networks of candidate genes for osteochondrosis in pigs

Osteochondrosis (OC) is a joint disorder that frequently causes leg weakness in growing pigs, resulting in welfare problems and economic losses. We aimed to detect molecular pathways relevant to the emergence of the disease and to identify candidate genes for the liability to the disorder. Therefore, we compared microarray-based expression patterns of articular cartilage with (n=11) and without (n=11) histologically diagnosed OC lesions obtained from discordant sib-pairs. A total of 1,564 genes were found with different transcript abundance [differentially expressed (DE) genes] at q≤0.05. To further identify candidate genes, we integrated data from quantitative trait loci (QTL) and genome-wide association (GWA) studies with the expression analysis. We detected 317 DE genes within the QTL confidence intervals, of which 26 DE genes also overlapped GWA regions. Ingenuity Pathway Analysis suggests a pathogenic role of immune response, angiogenesis, and synthesis of extracellular matrix pathways for OC. These processes could facilitate the emergence of defects. But they may also promote the degradation of articular cartilage and the worsening of the disease. A functional network was derived that comprised genes with functional and positional clues of their role in bone and cartilage metabolisms and development, including extracellular matrix genes (e.g., LOX, OGN, and ASPN), angiogenesis genes (e.g., ANGPTL4 and PDGFA), and immune response genes (e.g., ICAM1, AZGP1, C1QB, C1QC, PDE4B, and CDA). The study identified molecular processes linked to OC and several genes with positional, genetic-statistical, and functional evidence for their role in the emergence of articular cartilage lesions and the liability to OC.

Low extracellular pH stimulates the production of IL-1β by human monocytes

The development of acidic environments is a hallmark of inflammatory processes of different etiology. We have previously shown that transient exposure to acidic conditions, similar to those encountered in vivo, induces the activation of neutrophils and the phenotypic maturation of dendritic cells. We here report that extracellular acidosis (pH 6.5) selectively stimulates the production and the secretion of IL-1β by human monocytes without affecting the production of TNF-α, IL-6 and the expression of CD40, CD80, CD86, and HLA-DR. Stimulation of IL-1β production by pH 6.5-treated monocytes was shown to be dependent on caspase-1 activity, and it was also observed using peripheral blood mononuclear cells instead of isolated monocytes. Contrasting with the results in monocytes, we found that pH 6.5 did not stimulate any production of IL-1β by macrophages. Changes in intracellular pH seem to be involved in the stimulation of IL-1β production. In fact, monocytes cultured at pH 6.5 undergo a fall in the values of intracellular pH while the inhibitor of the Na+/H+ exchanger, 5-(N-ethyl-N-isopropyl)amiloride induced both, a decrease in the values of intracellular pH and the stimulation of IL-1β production. Real time quantitative PCR assays indicated that monocytes cultured either at pH 6.5 or in the presence of 5-(N-ethyl-N-isopropyl)amiloride expressed higher levels of pro-IL-1β mRNA suggesting that low values of intracellular pH enhance the production of IL-1β, at least in part, by stimulating the synthesis of its precursor.

Acid-sensing ion channels contribute to the effect of acidosis on the function of dendritic cells

As an H(+)-gated subgroup of the degenerin/epithelial Na(+) channel family, acid-sensing ion channels (ASICs) were reported to be involved in various physiological and pathological processes in neurons. However, little is known about the role of ASICs in the function of dendritic cells (DCs). In this study, we investigated the expression of ASICs in mouse bone marrow-derived DCs and their possible role in the function of DCs. We found that ASIC1, ASIC2, and ASIC3 are expressed in DCs at the mRNA and protein levels, and extracellular acid can evoke ASIC-like currents in DCs. We also demonstrated that acidosis upregulated the expression of CD11c, MHC class II, CD80, and CD86 and enhanced the Ag-presenting ability of DCs via ASICs. Moreover, the effect of acidosis on DCs can be abolished by the nonsteroidal anti-inflammatory drugs ibuprofen and diclofenac. These results suggest that ASICs are involved in the acidosis-mediated effect on DC function.

Extracellular acidosis triggers the maturation of human dendritic cells and the production of IL-12

Although the development of an acidic tissue environment or acidosis is a hallmark of inflammatory processes, few studies analyze the effect of extracellular pH on immune cells. We have previously shown that exposure of murine dendritic cells (DCs) to pH 6.5 stimulates macropinocytosis and cross-presentation of extracellular Ags by MHC class I molecules. We report that the transient exposure of human DCs to pH 6.5 markedly increases the expression of HLA-DR, CD40, CD80, CD86, CD83, and CCR7 and improves the T cell priming ability of DCs. Incubation of DCs at pH 6.5 results in the activation of the PI3K/Akt and the MAPK pathways. Using specific inhibitors, we show that the maturation of DCs induced by acidosis was strictly dependent on the activation of p38 MAPK. DC exposure to pH 6.5 also induces a dramatic increase in their production of IL-12, stimulating the synthesis of IFN-gamma, but not IL-4, by Ag-specific CD4(+) T cells. Interestingly, we find that suboptimal doses of LPS abrogated the ability of pH 6.5 to induce DC maturation, suggesting a cross-talk between the activation pathways triggered by LPS and extracellular protons in DCs. We conclude that extracellular acidosis in peripheral tissues may contribute to the initiation of adaptive immune responses by DCs, favoring the development of Th1 immunity.

Compatibility in the Biomphalaria glabrata/Echinostoma caproni model: Potential involvement of proteins from hemocytes revealed by a proteomic approach

As an approach to investigate the suspected involvement of cellular factors in Biomphalaria glabrata resistance/susceptibility to Echinostoma caproni, we compared protein patterns from hemocytes collected from susceptible and resistant snails. This proteomic approach revealed that twelve hemocytic proteins exhibited significant differences in their apparent abundance. The genes corresponding to five of them were characterized by a combination of mass spectrometry and molecular cloning. They encode an aldolase, an intermediate filament protein, a cytidine deaminase, the ribosomal protein P1 and the histone H4. Furthermore, we investigated their expression in parasite-exposed or -unexposed snails. These last experiments revealed changes in transcript levels corresponding to intermediate filament and histone H4 proteins post-infection.

Antimicrobial peptides are expressed and produced in healthy and inflamed human synovial membranes

The objective of this study was to determine the expression and production of antimicrobial peptides by healthy and inflamed human synovial membranes. Deposition of the antimicrobial peptides lysozyme, lactoferrin, secretory phospholipase A(2) (sPA(2)), matrilysin (MMP7), human neutrophil alpha-defensins 1-3 (HNP 1-3), human beta-defensin 1 (HBD-1), and human beta-defensin 2 (HBD-2) was determined by immunohistochemistry. Expression of mRNA for the antimicrobial peptides bactericidal permeability-increasing protein (BPI), heparin binding protein (CAP37), human cationic antimicrobial protein (LL37), human alpha-defensin 5 (HD5), human alpha-defensin 6 (HD6), HBD-1, HBD-2, and human beta-defensin 3 (HBD-3) was analysed by reverse transcription polymerase chain reaction (RT-PCR). RT-PCR revealed CAP37 and HBD-1 mRNA in samples of healthy synovial membrane. Additionally, HBD-3 and/or LL37 mRNA was detected in synovial membrane samples from patients with pyogenic arthritis (PA), osteoarthritis (OA) or rheumatoid arthritis (RA). BPI, HD5, HD6, and HBD-2 mRNAs were absent from all samples investigated. Immunohistochemistry identified lysozyme, lactoferrin, sPA(2), and MMP7 in type A synoviocytes of all samples. HBD-1 was only present in type B synoviocytes of some of the samples. Immunoreactive HBD-2 peptide was only visible in some inflamed samples. HNP1-3 was detected in both healthy and inflamed synovial membranes. The data suggest that human synovial membranes produce a broad spectrum of antimicrobial peptides. Under inflammatory conditions, the expression pattern changes, with induction of HBD-3 in PA (LL37 in RA; HBD-3 and LL37 in OA) as well as down-regulation of HBD-1. HBD-3 holds therapeutic potential in PA as it has a broad spectrum of antimicrobial activity and accelerates epithelial healing. However, caution is appropriate since defensins also promote fibrin formation and cell proliferation - key elements in joint infection. Clarification of the role of antimicrobial peptides in OA and RA will require further investigation.

Growth Inhibition of Granulocyte-Macrophage Colony-Forming Cells by Human Cytidine Deaminase Requires the Catalytic Function of the Protein

Previous studies have indicated that cytidine deaminase (CDD) is a potent growth inhibitor of granulocyte-macrophage colony-forming cells (GM-CFC). In this study, we have undertaken molecular cloning and purification of recombinant human CDD to elucidate the growth regulatory potential and mechanism behind the growth suppressive effect. The purified protein had a specific activity of 1.35 × 105 U/mg and a Km value of 30 μmol/L. In the GM-CFC assay, the recombinant protein was shown to reduce colony formation to 50% at 16 pmol/L concentration. Similarly, as was observed with CDD derived from granulocyte extract, the effect depended on the presence of thymidine (≥ 4 × 10-5 mol/L). These results imply that CDD is an extremely potent inhibitor of GM-CFC and that no additional factor from the granulocyte extract is required for the growth inhibitory effect. Modification of CDD by truncation from the C-terminal end, or by amino acid substitution of an active site glutamate residue, eliminated both the enzyme activity and the growth regulatory potential of CDD. Furthermore, CDD fromEscherichia coli was found to be even more effective than human CDD in growth suppression of GM-CFC, with 10-fold higher inhibitory activity corresponding to a 10-fold higher enzymatic activity. Taken together, these results show that the catalytic nucleoside deaminating function of the protein is essential for the growth suppressive effect of CDD. Most probably, CDD exerts growth inhibition by depleting the cytidine and deoxycytidine pool required for DNA synthesis, as addition of deoxycytidine monophosphate, which is not a substrate for CDD, neutralizes the inhibiting effect.

Growth Inhibition of Granulocyte-Macrophage Colony-Forming Cells by Human Cytidine Deaminase Requires the Catalytic Function of the Protein

Previous studies have indicated that cytidine deaminase (CDD) is a potent growth inhibitor of granulocyte-macrophage colony-forming cells (GM-CFC). In this study, we have undertaken molecular cloning and purification of recombinant human CDD to elucidate the growth regulatory potential and mechanism behind the growth suppressive effect. The purified protein had a specific activity of 1.35 × 105 U/mg and a Km value of 30 μmol/L. In the GM-CFC assay, the recombinant protein was shown to reduce colony formation to 50% at 16 pmol/L concentration. Similarly, as was observed with CDD derived from granulocyte extract, the effect depended on the presence of thymidine (≥ 4 × 10-5 mol/L). These results imply that CDD is an extremely potent inhibitor of GM-CFC and that no additional factor from the granulocyte extract is required for the growth inhibitory effect. Modification of CDD by truncation from the C-terminal end, or by amino acid substitution of an active site glutamate residue, eliminated both the enzyme activity and the growth regulatory potential of CDD. Furthermore, CDD fromEscherichia coli was found to be even more effective than human CDD in growth suppression of GM-CFC, with 10-fold higher inhibitory activity corresponding to a 10-fold higher enzymatic activity. Taken together, these results show that the catalytic nucleoside deaminating function of the protein is essential for the growth suppressive effect of CDD. Most probably, CDD exerts growth inhibition by depleting the cytidine and deoxycytidine pool required for DNA synthesis, as addition of deoxycytidine monophosphate, which is not a substrate for CDD, neutralizes the inhibiting effect.

Host tissue damage by phagocytes

Evidence continues to accumulate on the importance of neutrophils (PMNs) and phagocytes in the causation of tissue and endothelial injury that frequently accompanies the inflammatory response. Increased production of superoxide anions in combination with decreased endothelial antioxidant activity may contribute to the development of vascular disease including atherosclerosis, vasospasm, diabetic vascular complications, tissue damage in ischemia-reperfusion, and hypotension. Free radicals generated in the vascular wall may act directly on smooth muscle or interact with each other thus producing biologically active endogenous mediators. Derangement of macrophage function may occur in conditions characterized by protein malnutrition, thus leading to failure to develop a specific immunoresponse and to an increase in the production of oxygen intermediate radicals, which may cause tissue damage. A local inflammatory response followed by endothelial cell activation could also facilitate migration of immunocompetent cells into the parenchyma of grafted organs and stimulate dendritic cells in the graft. There is now convincing evidence that excessive and prolonged production of NO contributes to tissue damage in septicemia, ischemia/reperfusion injury, and other inflammatory conditions. There is also increasing evidence that the complement system plays an important role in tissue damage in association with phagocytes, e.g., in ischemia/reperfusion injury, carcinogenesis, and aging. It can therefore be surmised that phagocytic cells may act both as "friends" and as "foes" and that they are important mediators of tissue damage in a variety of conditions.

Predictors of joint damage in rheumatoid arthritis

Rheumatoid arthritis (RA) is the dominant form of destructive chronic arthritis with the potential to cause substantial disability and permanent functional impairment. The final extent and progression rate with time, however, varies markedly. In order to study effects of intervention and to support early aggressive and atoxic therapy in selected cases, predictive disease markers are needed. Recent advances regarding joint tissue composition and pathophysiology have defined a number of biological marker candidates which need to be explored for possible prognostic information. Some markers are characteristic for RA, such as rheumatoid factors and certain autoantibodies, which although they are more prevalent among patients with aggressive disease are not sensitive as predictors in early disease. Genetic susceptibility markers have been claimed to be good predictors of persisting arthritis in early synovitis clinics, but their role as severity markers in established disease is limited. Unspecific markers of inflammation, notably ESR or CRP when persistently elevated, are useful to monitor disease course and newer markers need to document their superiority over these. Another group of markers are attractive because of enriched or exclusive occurrence in joint tissue, and altered metabolism in joint disease. Thus, collagen type III propeptides, hyaluronates, and neopterin originating in the synovium could be useful, and, in particular, hyaluronate levels indeed do provide some predictive information. Highly tissue-specific cartilage metabolites include aggrecan fragments, collagen II fragments, cartilage oligomeric matrix protein (COMP) and the extraarticular cartilage matrix protein (CMP). When used alone or in combination in early disease some information can be obtained which may in the future facilitate prognostication. Bone metabolism can be monitored and there are different markers for synthesis and resorption. Meanwhile, whilst the new markers are essential research tools, their routine clinical usefulness remains to be proven.

Interleukin-6 in relation to other proinflammatory cytokines, chemotactic activity and neutrophil activation in rheumatoid synovial fluid

OBJECTIVE

To evaluate the relation between synovial fluid (SF) concentrations of interleukin-6 (IL-6) and other mediators of inflammation which are responsible for joint degradation in rheumatoid arthritis (RA).

METHODS

We measured IL-6, IL-1 beta, tumour necrosis factor alpha (TNF alpha), granulocyte macrophage colony stimulating factor, IL-8, and polymorphonuclear leucocyte (PMNL) chemotaxis and degranulation in SF from patients with RA (n = 30) in the early phase of the disease.

RESULTS

In a cross-sectional study IL-6 concentrations correlated with those of IL-1 beta, IL-8 and with PMNL activation as reflected by lactoferrin concentrations. In a longitudinal study, changes in IL-6 concentrations correlated with changes in TNF alpha, IL-8 and lactoferrin concentrations.

CONCLUSION

IL-6 in SF appears to reflect the local proinflammatory, potentially erosive activity in RA. This supports the use of acute phase proteins, which are mainly induced by IL-6, as variables to monitor the course of RA.

Re-evaluation of the colorimetric assay for cytidine deaminase activity

This study re-evaluated the colorimetric assay for cytidine deaminase (CTD), and showed that the optimum conditions were pH 7.5, 37 degrees C, and up to 24 h. In addition, this method was found to require protein precipitation. Following these modifications, intra-assay and inter-assay coefficients of variation were below 5 per cent, indicating that the assay was highly reliable. CTD activity was determined in 282 serum samples from 206 normal pregnant women by the incubation of 100 microliters of serum and 400 microliters of 1.4 mmol/l cytidine substrate for 16 h at 37 degrees C. Following protein precipitation, the ammonia liberated during conversion was measured by a colorimetric procedure. The mean (+/- SD) CTD activity was 7.31 +/- 2.50 U at 3-12 weeks of gestation, 8.70 +/- 2.12 U at 13-24 weeks, 7.59 +/- 2.25 U at 25-36 weeks, and 7.29 +/- 2.16 U at 37-42 weeks. High levels of CTD activity were found in patients with abruptio placentae and amnionitis associated with intrauterine fetal death (IUFD). The increase in CTD activity was noted from 3 days to 1 week before the confirmation of IUFD. The placenta contains extremely high levels of CTD, but cord serum does not. Thus, the excessive elevation of CTD activity was probably derived from progressive placental damage. This modified CTD assay was concluded to be simple and reliable, and may perhaps be useful in detecting pregnancy disorders.

Lactoferrin regulates the release of tumour necrosis factor alpha and interleukin 6 in vivo

The effects of bovine lactoferrin on the serum cytokine levels, induced by lipopolysaccharide (LPS) in mice, are described. Bovine lactoferrin (BLF) introduced intravenously, 24 hours before i.v. injection of 50 micrograms of LPS, significantly lowered the serum concentration of TNF-alpha. Doses of BLF lower than 100 micrograms as well as pretreatment of mice with BLF on days 6-2 or 12-2 hours before LPS challenge, were not effective. Moreover, BLF induces by itself a relatively high level of IL-6, peaking at 1 hour following injection. Pretreatment of LPS-injected mice with BLF causes, in addition, a small but statistically significant drop in IL-6 level. Human albumin, used as a control protein, did not cause any changes in the cytokine levels. The data reported herein provide a satisfactory explanation with regard to preventive activity of LF in infection.

Cytidine deaminase activity in abnormal pregnancy

OBJECTIVE

To determine the usefulness of cytidine deaminase (CTD) activity in the prediction of abnormal pregnancy and the prognosis of fetal outcome.

METHOD

The CTD activities in 367 pregnant women and 17 placentas and their cord sera were determined. The CTD activity was estimated to determine the amount of ammonia liberated during conversion of cytidine into uridine. The Kruskal-Wallis test and paired t-test were employed for statistical comparisons.

RESULT

The placentas contained extremely high levels of CTD activity, but the cord serum did not. The mean value of CTD activity in abnormal pregnancy women was significantly higher than in normal pregnancy women. The two cases with a CTD activity of 40 U or more had the worst infant prognosis.

CONCLUSION

The CTD activity in abnormal pregnancies was excessively elevated due to a damaged placenta under progressive deterioration. This CTD assay was simple and had predictive value for the prognosis of an infant of an abnormal pregnancy.

The search for laboratory measures of outcome in rheumatoid arthritis

A large number of laboratory tests have been developed within the past decade to measure factors involved in the immune inflammation of RA. These can be divided into genetic markers, general measures of inflammation, autoantibodies and tissue-specific markers. In general, it is simpler to prove the power of a certain test to measure the disease process than to predict outcome. Apart from RF positivity and CRP/ESR, few, if any, tests have proven to be of importance in independent studies from different centres. Among the promising candidates for future work are detailed analysis of the HLA-D region genes, sulphoxidation status, the autoantibody against RA33 nuclear antigen, soluble IL-2 receptor measuring lymphocyte activity, hyaluronate/hyaluronan or PIIINP from synovial tissue, the combined use of COMP and proteoglycan epitope tests for cartilage matrix, and pyrodinoline cross-linking for collagen from bone and cartilage. The ideal setting for testing such markers are prospective cohort studies starting early in the disease, and since many such studies have been initiated recently, one can expect much new information in coming years. Attention needs to be devoted to the kinetics of marker metabolism, since many are degraded or removed at very fast rates from the circulation, making serum assays less informative.