Increased circulating fibronectin, depletion of natural IgM and heightened EBV, HSV-1 reactivation in ME/CFS and long COVID

Myalgic Encephalomyelitis/ Chronic Fatigue syndrome (ME/CFS) is a complex, debilitating, long-term illness without a diagnostic biomarker. ME/CFS patients share overlapping symptoms with long COVID patients, an observation which has strengthened the infectious origin hypothesis of ME/CFS. However, the exact sequence of events leading to disease development is largely unknown for both clinical conditions. Here we show antibody response to herpesvirus dUTPases, particularly to that of Epstein-Barr virus (EBV) and HSV-1, increased circulating fibronectin (FN1) levels in serum and depletion of natural IgM against fibronectin ((n)IgM-FN1) are common factors for both severe ME/CFS and long COVID. We provide evidence for herpesvirus dUTPases-mediated alterations in host cell cytoskeleton, mitochondrial dysfunction and OXPHOS. Our data show altered active immune complexes, immunoglobulin-mediated mitochondrial fragmentation as well as adaptive IgM production in ME/CFS patients. Our findings provide mechanistic insight into both ME/CFS and long COVID development. Finding of increased circulating FN1 and depletion of (n)IgM-FN1 as a biomarker for the severity of both ME/CFS and long COVID has an immediate implication in diagnostics and development of treatment modalities.

Endogenous Retroviral Elements Generate Pathologic Neutrophils in Pulmonary Arterial Hypertension

Rationale: The role of neutrophils and their extracellular vesicles (EVs) in the pathogenesis of pulmonary arterial hypertension is unclear. Objectives: To relate functional abnormalities in pulmonary arterial hypertension neutrophils and their EVs to mechanisms uncovered by proteomic and transcriptomic profiling. Methods: Production of elastase, release of extracellular traps, adhesion, and migration were assessed in neutrophils from patients with pulmonary arterial hypertension and control subjects. Proteomic analyses were applied to explain functional perturbations, and transcriptomic data were used to find underlying mechanisms. CD66b-specific neutrophil EVs were isolated from plasma of patients with pulmonary arterial hypertension, and we determined whether they produce pulmonary hypertension in mice. Measurements and Main Results: Neutrophils from patients with pulmonary arterial hypertension produce and release increased neutrophil elastase, associated with enhanced extracellular traps. They exhibit reduced migration and increased adhesion attributed to elevated β1-integrin and vinculin identified by proteomic analysis and previously linked to an antiviral response. This was substantiated by a transcriptomic IFN signature that we related to an increase in human endogenous retrovirus K envelope protein. Transfection of human endogenous retrovirus K envelope in a neutrophil cell line (HL-60) increases neutrophil elastase and IFN genes, whereas vinculin is increased by human endogenous retrovirus K deoxyuridine triphosphate diphosphatase that is elevated in patient plasma. Neutrophil EVs from patient plasma contain increased neutrophil elastase and human endogenous retrovirus K envelope and induce pulmonary hypertension in mice, mitigated by elafin, an elastase inhibitor. Conclusions: Elevated human endogenous retroviral elements and elastase link a neutrophil innate immune response to pulmonary arterial hypertension.

EBV/HHV-6A dUTPases contribute to Myalgic Encephalomyelitis/Chronic-Fatigue-Syndrome pathophysiology by enhancing TFH cell differentiation and extrafollicular activities

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic, debilitating multisystem illness of unknown etiology for which there is no cure and no diagnostic tests available. Despite increasing evidence implicating EBV and human herpesvirus-6A (HHV-6A) as potential causative infectious agents in a subset of ME/CFS patients, there are few mechanistic studies to address a causal relationship. In this study we examined a large ME/CFS cohort (n=351) and 77 controls and demonstrate a significant increase in activin A and IL-21serum levels, which correlated with seropositivity for antibodies to the EBV and HHV-6 protein deoxyuridine-triphosphate nucleotidohydrolase (dUTPase), but not CXCL13. These cytokines are critical for T follicular helper (TFH) cell differentiation, generation of high-affinity antibodies and long-lived plasma cells. Notably, ME/CFS serum was sufficient to drive TFH cell differentiation via an activin A-dependent mechanism. The lack of simultaneous CXCL13 increase with IL-21 indicates impaired TFH-function in ME/CFS. In vitro studies revealed that virus-dUTPases strongly induced activin A secretion while in vivo, EBV-dUTPase induced the formation of splenic marginal zone B and invariant NKTFH cells. Altogether, our data indicate abnormal germinal center (GC) activity in ME/CFS subjects and highlight a mechanism by which EBV and HHV6-dUTPases may alter GC and extrafollicular Ab responses.

Examination of control asymptomatic cohorts reveals heightened anti-EBV and HHV-6 A/B dUTPase antibodies in the aging populations

Members of the human Herpesviridae are found in high prevalence in the human virome. While these viruses are known to cause numerous disease pathologies in symptomatic individuals little is known concerning the role that these viruses may have in modulating the host immune system in asymptomatic “healthy” individuals, especially during the aging process. Examination of three cohorts of “healthy asymptomatic” individuals (n = 255) for the presence of antibodies against the herpesviruses deoxyuridine triphosphate nucleotidohydrolase (dUTPase) as a marker for lytic/abortive‐lytic replication demonstrated that all cohorts exhibited differential anti‐herpesvirus dUTPase antibodies positivity frequencies ranging from 40.4% to 84% with some individuals in these cohorts expressing antibodies to the dUTPases of multiple herpesviruses (17.2%–56%). Furthermore, our results demonstrate that there was a statistically significant difference in anti‐human herpesvirus 6 A and 6B (HHV‐6 A/B) dUTPase antibodies in Cohort 3 (age = 66.2 ± 15.02 years) versus Cohort 1 (age 46.88 ± 8.61 years), suggesting that reactivation of HHV‐6 A/B is not attenuated by aging. It is well established/documented that herpesvirus dUTPases induce immune dysfunction, as such it is of critical importance that additional studies be performed to determine how these viral proteins alter immune responses in asymptomatic individuals.

Monocyte-released HERV-K dUTPase engages TLR4 and MCAM causing endothelial mesenchymal transition

We previously reported heightened expression of the human endogenous retroviral protein HERV-K deoxyuridine triphosphate nucleotidohydrolase (dUTPase) in circulating monocytes and pulmonary arterial (PA) adventitial macrophages of patients with PA hypertension (PAH). Furthermore, recombinant HERV-K dUTPase increased IL-6 in PA endothelial cells (PAECs) and caused pulmonary hypertension in rats. Here we show that monocytes overexpressing HERV-K dUTPase, as opposed to GFP, can release HERV-K dUTPase in extracellular vesicles (EVs) that cause pulmonary hypertension in mice in association with endothelial mesenchymal transition (EndMT) related to induction of SNAIL/SLUG and proinflammatory molecules IL-6 as well as VCAM1. In PAECs, HERV-K dUTPase requires TLR4-myeloid differentiation primary response–88 to increase IL-6 and SNAIL/SLUG, and HERV-K dUTPase interaction with melanoma cell adhesion molecule (MCAM) is necessary to upregulate VCAM1. TLR4 engagement induces p-p38 activation of NF-κB in addition to p-pSMAD3 required for SNAIL and pSTAT1 for IL-6. HERV-K dUTPase interaction with MCAM also induces p-p38 activation of NF-κB in addition to pERK1/2-activating transcription factor-2 (ATF2) to increase VCAM1. Thus in PAH, monocytes or macrophages can release HERV-K dUTPase in EVs, and HERV-K dUTPase can engage dual receptors and signaling pathways to subvert PAEC transcriptional machinery to induce EndMT and associated proinflammatory molecules.

Upregulation of Human Endogenous Retrovirus-K Is Linked to Immunity and Inflammation in Pulmonary Arterial Hypertension

BACKGROUND

Immune dysregulation has been linked to occlusive vascular remodeling in pulmonary arterial hypertension (PAH) that is hereditary, idiopathic, or associated with other conditions. Circulating autoantibodies, lung perivascular lymphoid tissue, and elevated cytokines have been related to PAH pathogenesis but without a clear understanding of how these abnormalities are initiated, perpetuated, and connected in the progression of disease. We therefore set out to identify specific target antigens in PAH lung immune complexes as a starting point toward resolving these issues to better inform future application of immunomodulatory therapies.

METHODS

Lung immune complexes were isolated and PAH target antigens were identified by liquid chromatography tandem mass spectrometry, confirmed by enzyme-linked immunosorbent assay, and localized by confocal microscopy. One PAH antigen linked to immunity and inflammation was pursued and a link to PAH pathophysiology was investigated by next-generation sequencing, functional studies in cultured monocytes and endothelial cells, and hemodynamic and lung studies in a rat.

RESULTS

SAM domain and HD domain-containing protein 1 (SAMHD1), an innate immune factor that suppresses HIV replication, was identified and confirmed as highly expressed in immune complexes from 16 hereditary and idiopathic PAH versus 12 control lungs. Elevated SAMHD1 was localized to endothelial cells, perivascular dendritic cells, and macrophages, and SAMHD1 antibodies were prevalent in tertiary lymphoid tissue. An unbiased screen using metagenomic sequencing related SAMHD1 to increased expression of human endogenous retrovirus K (HERV-K) in PAH versus control lungs (n=4). HERV-K envelope and deoxyuridine triphosphate nucleotidohydrolase mRNAs were elevated in PAH versus control lungs (n=10), and proteins were localized to macrophages. HERV-K deoxyuridine triphosphate nucleotidohydrolase induced SAMHD1 and proinflammatory cytokines (eg, interleukin 6, interleukin 1β, and tumor necrosis factor α) in circulating monocytes, pulmonary arterial endothelial cells, and also activated B cells. Vulnerability of pulmonary arterial endothelial cells (PAEC) to apoptosis was increased by HERV-K deoxyuridine triphosphate nucleotidohydrolase in an interleukin 6-independent manner. Furthermore, 3 weekly injections of HERV-K deoxyuridine triphosphate nucleotidohydrolase induced hemodynamic and vascular changes of pulmonary hypertension in rats (n=8) and elevated interleukin 6.

CONCLUSIONS

Our study reveals that upregulation of the endogenous retrovirus HERV-K could both initiate and sustain activation of the immune system and cause vascular changes associated with PAH.

Current and potential immune therapies and vaccines in the management of psoriasis

Psoriasis is a chronic, immune skin disease associated with significant morbidity. Development of psoriasis is influenced by numerous genes, one allele is HLA-CW*0602. Other genes and single nucleotide polymorphisms affect immunologic pathways and antimicrobial peptide synthesis. Dendritic cells initiate psoriasis by activating T-cells toward a Th1 and Th17 response, with increased cytokines including TNF-α, IL-6, -12, -17, -22, and -23. IL-22 appears to promote keratinocyte dedifferentiation and increased antimicrobial peptide synthesis while TNF-α and IL-17 induce leukocyte localization within the psoriatic plaque. These recent insights identifying key cytokine pathways have led to the development of inhibitors with significant efficacy in the treatment of psoriasis. While a strategy for vaccine modulation of the immune response in psoriasis is in progress, with new technology they may provide a cost-effective long-term treatment that may induce tolerance or targeted self-inhibition for patients with autoimmune disorders, such as psoriasis.

Evidence for the role of Epstein Barr Virus infections in the pathogenesis of acute coronary events

BACKGROUND

The role of viral infections in the pathogenesis of atherosclerosis remains controversial largely due to inconsistent detection of the virus in atherosclerotic lesions. However, viral infections elicit a pro-inflammatory cascade known to be atherogenic and to precipitate acute ischemic events. We have published in vitro data that provide the foundation for a mechanism that reconciles these conflicting observations. To determine the relation between an early viral protein, deoxyuridine triphosphate nucleotidohydrolase (dUTPase), produced following reactivation of Epstein Barr Virus (EBV) to circulating pro-inflammatory cytokines, intercellular adhesion molecule-1 (ICAM-1) and acute coronary events.

METHODOLOGY/PRINCIPAL FINDINGS

Blood samples were obtained from 299 patients undergoing percutaneous coronary intervention for stable angina (SA), unstable angina (UA), or acute myocardial infarction (AMI). Plasma concentrations of pro-inflammatory cytokines and neutralizing antibody against EBV-encoded dUTPase were compared in the three patient groups. AMI was associated with the highest measures of interleukin-6 (ANOVA p<0.05; 4.6 ± 2.6 pg/mL in patients with AMI vs. 3.2 ± 2.3 pg/mL in SA). ICAM-1 was significantly higher in patients with AMI (ANOVA p<0.05; 304 ± 116 pg/mL in AMI vs. 265 ± 86 pg/mL SA). The highest values of ICAM-1 were found in patients having an AMI and who were antibody positive for dUTPase (ANOVA p=0.008; 369 ± 183 pg/mL in AMI and positive for dUTPase vs. 249 ± 70 pg/mL in SA negative for dUTPase antibody).

CONCLUSIONS/SIGNIFICANCE

These clinical data support a model, based on in vitro studies, by which EBV may precipitate AMI even under conditions of low viral load through the pro-inflammatory action of the early protein dUTPase that is produced even during incomplete viral replication. They further support the putative role of viral infections in the pathogenesis of atherosclerosis and coronary artery events.

Antibody to Epstein-Barr virus deoxyuridine triphosphate nucleotidohydrolase and deoxyribonucleotide polymerase in a chronic fatigue syndrome subset

BACKGROUND

A defined diagnostic panel differentiated patients who had been diagnosed with chronic fatigue syndrome (CFS), based upon Fukuda/Carruthers criteria. This diagnostic panel identified an Epstein-Barr virus (EBV) subset of patients (6), excluding for the first time other similar "clinical" conditions such as cytomegalovirus (CMV), human herpesvirus 6 (HHV6), babesiosis, ehrlichiosis, borreliosis, Mycoplasma pneumoniae, Chlamydia pneumoniae, and adult rheumatic fever, which may be mistakenly called CFS. CFS patients were treated with valacyclovir (14.3 mg/kg q6h) for ≥ 12 months. Each patient improved, based upon the Functional Activity Appraisal: Energy Index Score Healthcare Worker Assessment (EIPS), which is a validated (FSS-9), item scale with high degree of internal consistency measured by Cronbach's alpha.

METHODS

Antibody to EBV viral capsid antigen (VCA) IgM, EBV Diffuse Early Antigen EA(D), and neutralizing antibodies against EBV-encoded DNA polymerase and EBV-encoded dUTPase were assayed serially approximately every three months for 13-16 months from sera obtained from patients with CFS (6) and from sera obtained from twenty patients who had no history of CFS.

RESULTS

Antibodies to EBV EA(D) and neutralizing antibodies against the encoded-proteins EBV DNA polymerase and deoxyuridine triphosphate nucleotidohydrolase (dUTPase) were present in the EBV subset CFS patients. Of the sera samples obtained from patients with CFS 93.9% were positive for EA(D), while 31.6% of the control patients were positive for EBV EA(D). Serum samples were positive for neutralizing antibodies against the EBV-encoded dUTPase (23/52; 44.2%) and DNA polymerase (41/52; 78.8%) in EBV subset CFS patients, but negative in sera of controls.

CONCLUSIONS

There is prolonged elevated antibody level against the encoded proteins EBV dUTPase and EBV DNA polymerase in a subset of CFS patients, suggesting that this antibody panel could be used to identify these patients, if these preliminary findings are corroborated by studies with a larger number of EBV subset CFS patients.

Silver nanocolloids disrupt medaka embryogenesis through vital gene expressions

Silver nanomaterials are the major components of healthcare products largely because of their antimicrobial effects. However, their unintended toxicity to biological organisms and its mechanism are not well understood. Using medaka fish embryo model, the toxic effects and corresponding mechanisms of silver nanocolloids (SNC, particle size 3.8 ± 1.0-diameter nm) were investigated. SNC caused morphological changes in embryos including cardiovascular malformations, ischemia, underdeveloped central nervous system and eyes, and kyphosis at exposures of 0.5 mg/L. Interestingly, SNC were observed inside the eggs at a level of 786.1 ± 32.5 pg/mg egg weight, and TEM analysis showed that SNC adhered to the surface and inside of the chorion. Meanwhile, medaka oligo DNA microarray and qRT-PCR were used for gene expression analysis in the embryos exposed to 0.05 mg/L SNC for 48 h. As a result, expressions of six of the oxidative stress-, embryogenesis- and morphogenesis-related genes, ctsL, tpm1, rbp, mt, atp2a1, and hox6b6, were affected by the SNC exposure, and these genes' involvement in those malformations was implied. Thus, SNC could potentially cause malformations in the cardiovascular and central nervous systems in developing medaka embryo through SNC-induced differential expression of the genes related to oxidative stress, embryonic cellular proliferation, and morphological development.

Depletion of uracil-DNA glycosylase activity is associated with decreased cell proliferation

Uracil-DNA glycosylase (UNG) is the primary enzyme responsible for removing uracil residues from DNA. Increasing evidence suggests that UNG may be a potential target for the development of novel antiviral and/or anticancer agents. To determine whether the uracil-DNA glycosylase inhibitor protein (UGI) could be used to specifically target UNGs intracellularly, we developed a construct that expresses UGI as a fusion protein with the TAT-protein transduction domain and described a novel method for the purification of recombinant TAT-UGI. Treatment of several cell types with TAT-UGI resulted in a dose- and time-dependent decrease in UNG activity. A somewhat surprising effect of TAT-UGI treatment was the decrease in cell proliferation, but not in cell viability. The results of this study support the premise that UNG can be used as a potential therapeutic target and also demonstrate that protein transduction can be used to modulate UNG activity.

Detection of three novel translocations and specific common chromosomal break sites in malignant melanoma by spectral karyotyping

Chromosomal aberrations in malignant melanoma cells have been reported using standard chromosome banding analysis and comparative genomic hybridization. To identify marker chromosomes and translocations that are difficult to characterize by standard banding analysis, 15 early passage malignant melanoma cell lines were examined using spectral karyotyping. All 15 tumor cell lines had lost all or part of 1p and 10q. Losses of material on chromosome arms 4p (12/15), 6q (12/15), 9p (15/15), 12p (13/15), 12q (13/15), 13q (11/15), and 19q (14/15) were the next most frequent events. Gain of chromosome arms 1q (11/15), 6p (13/15), and 20q11 (14/15) was also observed. Interestingly, we identified translocations der(12)t(12;20)(q15;q11), der(19)t(10;19)(q23;q13), and der(12)t(12;19)(q13;q13) in 4/15 tumors. Three recurring translocations involving four of the most frequent break points were detected. The identification of recurring translocations and unique chromosome break points in melanoma will aid in the identification of the genes that are important in the neoplastic process.

Lead and mercury mutagenesis: type of mutation dependent upon metal concentration

Lead and mercury are toxic metals that are widely distributed in the atmosphere, soil, and groundwater. It is estimated that 2-4 x 10(4) tons of these metals are released annually into the environment by natural and industrial processes. Therefore, human exposure to low relatively nontoxic concentrations of these metals is unavoidable. However, the possible health effects of such exposure remain controversial. We have previously reported that low, subthreshold concentrations (0.1-1 microM) of these metals are mutagenic in the transgenic Chinese hamster ovary cell line AS52. The purpose of the present study is to determine the types of mutations induced in the gpt gene in AS52 cells. Using multiplex polymerase chain reaction and southern blot analyses, we characterized the 138 lead-induced, 192 mercury-induced, 29 reactive oxygen radical-induced, and 20 spontaneously arising mutants for point and deletion mutations in the gpt gene. Similar levels of point mutations were observed in the lead- and mercury-induced populations (47.8 and 53.6, respectively), which was significantly less than that occurring in the spontaneously arising and reactive oxygen intermediate-induced mutants. However, further examination of the data revealed that at concentrations of the metals of equal to or less than 0.4 microM, the majority of the mutations in the gpt gene were point mutations, while at higher concentrations, deletions (partial and complete) were the predominant type of mutation. These results are consistent with the hypothesis that lead and mercury induce mutations in eukaryotic cells by at least two distinct mechanisms.

Fas-induced apoptosis in human malignant melanoma cell lines is associated with the activation of the p34(cdc2)-related PITSLRE protein kinases

The Cdc2L locus encoding the PITSLRE protein kinases maps to chromosome band 1p36 and consists of two duplicated and tandemly linked genes. The purpose of the present study was to determine whether diminution of PITSLRE kinases leads to deregulation of apoptosis. The human melanoma cell lines A375 (Cdc2L wild-type alleles) and UACC 1227 (mutant Cdc2L alleles) were tested with agonist anti-Fas monoclonal antibody. We found that exposure of these cells to anti-Fas for 24, 48, or 72 h resulted in differential sensitivity to Fas-induced apoptosis. In A375, cell death started at 24-48 h post-treatment, and it was maximal by 72 h. Conversely, UACC 1227 cells were resistant to Fas-mediated apoptosis. Induction of PITSLRE histone H1 kinase activity was observed in A375 anti-Fas treated but not in UACC 1227 cells. Also, the PITSLRE protein kinase activity in A375 anti-Fas-treated cells preceded maximal levels of apoptosis. Finally, fluorescence confocal microscopy revealed a nuclear localization of PITSLRE proteins in normal melanocytes and A375 cells but a cytoplasmic localization in UACC 1227 cells. The differences in PITSLRE protein and cellular localization between A375 and UACC 1227 cells appear to account for the differences in sensitivity of the two cells lines to anti-Fas and staurosporine. These observations suggest that alterations in PITSLRE gene expression and protein localization may result in the loss of apoptotic signaling.

Abnormalities in the p34cdc2-related PITSLRE protein kinase gene complex (CDC2L) on chromosome band 1p36 in melanoma

The two genes encoding the PITSLRE protein kinase isoforms, CDC2L1 and CDC2L2, are localized to human chromosome band 1p36. The PITSLRE protein kinases are a part of the p34cdc2 supergene family. Several protein products of the CDC2L locus may be effector(s) in apoptotic signaling. The larger PITSLRE p110 isoforms appear to regulate some aspect of RNA splicing/transcription during the cell cycle. One or more of these genes may function as tumor suppressor genes in melanoma. Using fluorescence in situ hybridization, one allele of the CDC2L gene complex on chromosome 1 was either deleted or translocated in 8 of 14 different melanoma cell lines. We also observed mutations in the 5' promoter region of the CDC2L1 gene in four different cell lines relative to normal melanocytes using PCR-SSCP analysis and direct DNA sequencing. Western blot analysis revealed decreased level of PITSLRE protein expression in several cell lines, as well as in four surgical malignant melanoma specimens relative to normal melanocytes. Thus, the decreased PITSLRE protein expression appears to result from deletion of the CDC2L alleles and possibly by mutations within the 5' promoter region. We propose that aberrations in the CDC2L genes may contribute to the pathogenesis or progression of melanoma.

Lead and mercury mutagenesis: role of H2O2, superoxide dismutase, and xanthine oxidase

It has been suggested that reactive oxygen intermediates (ROIs) may have a role in the genotoxic effects of lead (Pb2+) and mercury (Hg2+), but there have not been any definitive studies demonstrating a causal relationship between the induction of ROIs by these metals and mutagenesis. We previously demonstrated, using the transgenic Chinese hamster ovary cell line AS52, that low concentrations (0.1-1 microM) of Pb2+ and Hg2+ are mutagenic. In the present study, using a novel histochemical computer-enhanced image analysis technique, we demonstrate that Pb2+ and Hg2+ induce the formation of H2O2 in AS52 cells by at least two distinct mechanisms. One is characterized by the rapid induction of H2O2 following treatment of cells with concentrations of Pb2+ or Hg2+ below 0.8 and 1 microM, respectively, while the second occurs in AS52 cells treated with concentrations of Pb2+ or Hg2+ greater than 0.8 and 1 microM, respectively. Pb2+ and Hg2+ (0.1-1 microM) had no effect on the activities of partially purified catalase, glutathione peroxidase, or glutathione reductase, important enzymes involved with antioxidant defense, but these metals stimulated the activities of copper-zinc superoxide dismutase (CuZn-SOD) and xanthine oxidase (XO). Allopurinol (50 microM), a specific inhibitor of xanthine oxidase, inhibited the induction of H2O2 by Pb2+ (0.8-1 microM) and Hg2+ (1 microM) and also inhibited Pb2+- and Hg2+-induced mutagenesis. These results demonstrate that Pb2+ and Hg2+ disrupt the redox status of AS52 cells by enhancing the activities of CuZn-SOD and XO. Furthermore, the results of these studies also demonstrate that there is a causal relationship between the induction of H2O2 by these metals and mutagenesis.

Antimutagenic and promutagenic activity of ascorbic acid during oxidative stress

Ascorbic acid (AA) has both antioxidant and prooxidant activities. However, there have not been any studies to elucidate the molecular mechanisms that determine whether AA functions as an anti- or a prooxidant during oxidative stress. The results of this study, using the Chinese hamster ovary cell line AS52 as a model system, demonstrate that there is a temporal relationship between the anti- and prooxidant activities of a physiologically relevant concentration of AA (50 microM) and oxidative stress. Treatment of cells with AA (50 microM) 24 hr prior to treatment of the cells with a radical generating system (RGS) results in a statistically significant inhibition of the cytotoxicity and mutagenicity associated with exposure of AS52 cells to oxidative stress. Conversely, cotreatment of cells with AA and the RGS results in a statistically significant increase in both the cytotoxic and mutagenic effects of oxidative stress when compared to cell populations exposed only to the RGS. The results, using a novel histochemical-computer image analysis system to detect hydrogen peroxide (H2O2), also demonstrate that there is a direct correlation between the ability of AA to decrease the levels of H2O2 in cells and the cytotoxic and mutagenic effects of oxidative stress. This study suggests that the time at which AA is administered in relation to exposure to oxidative stress has an impact on AA antimutagenic activity, and this may explain the conflicting results concerning the effectiveness of AA as a cancer chemopreventive agent.

Mutagenic potential of peripheral blood leukocytes: in vivo exposure to the carcinogen 7,12-dimethylbenz[a]anthracene, and the tumor promoter 12-O-tetradecanoylphorbol acetate followed by in vitro co-culture with AS52 cells

Co-culture of AS52 cells with peripheral blood leukocytes (PBLs), obtained from SENCAR mice topically treated with either tetradecanoyl-phorbol-13-acetate (TPA) or 7,12-dimethylbenz[a]anthracene (DMBA)-TPA, resulted in a 7-160-fold increase in the mutation frequency of the gpt gene in AS52 cells when compared to that induced by PBLs isolated from mice treated with either acetone or DMBA. This increase in mutation frequency was inhibited by the anti-oxidant (-)epigallocatechin gallate (EGCG). These results demonstrate that the AS52 cell line can be used as a mammalian mutagenesis model for the study of in vivo mechanism(s) of mutagenesis by leukocytes and also as a model for in vivo chemoprevention studies.

Mutagenesis of AS52 cells by low concentrations of lead(II) and mercury(II)

Little is known at the molecular level concerning the genotoxic effects following the acute exposure of eukaryotic cells to low concentrations of lead (II) or mercury (II). There have been conflicting reports concerning the mutagenic potential of these heavy metals, and there have not been any studies performed to determine the molecular mechanism(s) by which these metals are mutagenic. The Chinese hamster ovary cell line, AS52, contains a stably integrated single functional copy of the Escherichia coli xanthine-guanine phosphoribosyltransferase (gpt) gene. Mutations in the gpt gene confer resistance to 6-thioguanine (TG). There was little effect on viability, as measured by relative cloning efficiency, of AS52 cells exposed to lead (II) or mercury (II) up to concentrations of 0.5 microM and 0.3 microM, respectively. However, higher concentrations of the metals caused a significant increase in cell death. There was also a dose-dependent increase in the isolation of mutants resistant to TG in treated cells when compared to non-treated controls. Concentrations of the metals as low as 0.1 microM caused a significant increase in the number of mutants resistant to TG when compared to the number of spontaneous mutants obtained in nontreated controls. While the molecular mechanism(s) by which lead and mercury (II) are genotoxic is unknown, the results of this study demonstrate that low concentrations of lead (II) and mercury (II) are mutagenic in eukaryotic cells.

Mutagenic effect of mercury (II) in eukaryotic cells

Acute exposure of KB and Chinese hamster ovary cells (AS52) to low concentrations of mercury (II) results in a dose dependent binding of mercury to DNA. This binding of mercury (II) to the DNA occurs at concentrations of mercury that have little if any effect on glutatione levels or on superoxide dismutase activity. Mutational studies with AS52 cells demonstrated that concentrations (0.1 to 0.4 microM) of mercury (II) which were not cytotoxic caused an increase (1.7 to 3.1) in the frequency of mutations in the gpt gene when compared to non-treated controls. These results suggest that there may be risks associated with exposure to non-cytotoxic levels of mercury (II).