Pathogenesis of cytomegalovirus-associated pneumonitis in ICR mice: possible involvement of superoxide radicals

Detecting free radicals post viral infections

Free radical generation plays a key role in viral infections. While free radicals have an antimicrobial effect on bacteria or fungi, their interplay with viruses is complicated and varies greatly for different types of viruses as well as different radical species. In some cases, radical generation contributes to the defense against the viruses and thus reduces the viral load. In other cases, radical generation induces mutations or damages the host tissue and can increase the viral load. This has led to antioxidants being used to treat viral infections. Here we discuss the roles that radicals play in virus pathology. Furthermore, we critically review methods that facilitate the detection of free radicals in vivo or in vitro in viral infections.

Management of the virulent influenza virus infection by oral formulation of nonhydrolized carnosine and isopeptide of carnosine attenuating proinflammatory cytokine-induced nitric oxide production

Inducible nitric oxide synthase (iNOS) plays an important role in mediating inflammation. In our studies, we found that iNOS-derived NO was significantly increased in the serum samples of 150 patients infected with influenza A virus in comparison with samples of 140 healthy individuals. In human lung epithelial cells, infection with influenza A virus or stimulation with poly(I:C) + interferon-gamma resulted in increased mRNA and protein levels of both interleukin-32 and iNOS, with subsequent release of NO. Activated macrophages are also a source of nitric oxide (NO), which is largely produced by iNOS in response to proinflammatory cytokines. In this review article, the presented findings have many important implications for understanding the Influenza A (H1N1) viral pathogenesis, prevention, and treatment. The direct viral cytotoxicity (referred cytopathic effect) is only a fraction of several types of events induced by virus infection. Nitric oxide and oxygen free radicals such as superoxide anion (O₂⁻˙) are generated markedly in influenza A (including H1N1) virus-infected host boosts, and these molecular species are identified as the potent pathogenic agents. The mutual interaction of NO with O₂⁻˙ resulting in formation of peroxynitrite is operative in the pathogenic mechanism of influenza virus pneumonia. The toxicity and reactivity of oxygen radicals, generated in excessive amounts mediate the overreaction of the host's immune response against the organs or tissues in which viruses are replicating, and this may explain the mechanism of tissue injuries observed in influenza virus infection of various types. The authors revealed the protection that carnosine and its bioavailable nonhydrolized forms provide against peroxynitrite damage and other types of viral injuries in which immunologic interactions are usually involved. Carnosine (beta-alanyl-L-histidine) shows the pharmacologic intracellular correction of NO release which might be one of the important factors of natural immunity in controlling the initial stages of influenza A virus infection (inhibition of virus replication) and virus-induced regulation of cytokine gene expression. The protective effects of orally applied nonhydrolized formulated species of carnosine include at least direct interaction with nitric oxide, inhibition of cytotoxic NO-induced proinflammatory condition, and attenuation of the effects of cytokines and chemokines that can exert profound effects on inflammatory cells. These data are consistent with the hypothesis that natural products, such as chicken soup and chicken breast extracts rich in carnosine and its derivative anserine (beta-alanyl-1-methyl-L-histidine) could contribute to the pathogenesis and prevention of influenza virus infections and cold but have a limitation due to susceptibility to enzymatic hydrolysis of dipeptides with serum carnosinase and urine excretion after oral ingestion of a commercial chicken extract. The developed and patented by the authors formulations of nonhydrolized in digestive tract and blood natural carnosine peptide and isopeptide (gamma-glutamyl-carnosine) products have a promise in the Influenza A (H1N1) virus infection disease control and prevention.

Beneficial actions of melatonin in the management of viral infections: a new use for this "molecular handyman"?

Melatonin (N‐acetyl‐5‐methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein. Copyright © 2012 John Wiley & Sons, Ltd.

Therapeutic effects of xanthine oxidase inhibitors: renaissance half a century after the discovery of allopurinol

The prototypical xanthine oxidase (XO) inhibitor allopurinol, has been the cornerstone of the clinical management of gout and conditions associated with hyperuricemia for several decades. More recent data indicate that XO also plays an important role in various forms of ischemic and other types of tissue and vascular injuries, inflammatory diseases, and chronic heart failure. Allopurinol and its active metabolite oxypurinol showed considerable promise in the treatment of these conditions both in experimental animals and in small-scale human clinical trials. Although some of the beneficial effects of these compounds may be unrelated to the inhibition of the XO, the encouraging findings rekindled significant interest in the development of additional, novel series of XO inhibitors for various therapeutic indications. Here we present a critical overview of the effects of XO inhibitors in various pathophysiological conditions and also review the various emerging therapeutic strategies offered by this approach.

Oxidative injury to endothelial cells due to Epstein-Barr virus-induced autoantibodies against manganese superoxide dismutase

During the course of acute Epstein-Barr virus (EBV) infection, there is a rise of oxygen radical production. As a consequence, the production of the oxygen radical scavenger manganese superoxide dismutase (MnSOD) is increased. Patients with acute EBV infections regularly develop autoantibodies against MnSOD that are able to inhibit the enzyme activity in vitro. To elucidate the origin of the autoantibodies, the epitopes on MnSOD were determined. The entire sequence of MnSOD was synthesized as overlapping pentadecapeptides, which were scanned for their reactivity with sera of patients with acute EBV infections. Sera as well as affinity-purified anti-MnSOD antibodies reacted with the peptides p(no15) (amino acids 47-61) and p(no30) (amino acids 122-136) lying in crucial parts of the MnSOD tetramer. The two main epitopes p(no15) and p(no30) showed sequence homologies with EBV-encoded proteins. Reactivity of affinity-purified antibodies with a peptide of the homologous BGLF4 points to a molecular mimicry causing the occurrence of anti-MnSOD antibodies. Anti-MnSOD antibodies were able to block the protective effects of MnSOD in a model for oxidative damage produced by xanthine/xanthine oxidase in EAhy926 endothelial cells. Thus, these autoantibodies may contribute in vivo to the clinical symptoms by accumulation of toxic oxygen radicals.

Xanthine oxidoreductase activity in human liver disease

OBJECTIVES

The aim of this study was to investigate the level and the form of xanthine oxidoreductase (XOR) in severely diseased human livers, to ascertain whether the modifications of the enzyme activity reported in experimental pathology also occur in human liver disease.

METHODS

Total, dehydrogenase, and oxidase activities of XOR were measured in samples of human liver removed for transplantation or partial hepatectomy. Samples included four groups: 1) histologically normal liver tissue, adjacent to metastases from extrahepatic tumors (controls), 2) liver with virus-related cirrhosis; 3) liver with virus-negative cirrhosis, and 4) hepatocellular carcinoma tissue (HCC).

RESULTS

The level of total XOR was significantly higher in liver with virus-related cirrhosis, but not in virus-negative cirrhosis, than in controls. In virus-positive cirrhosis, the total XOR activity correlated positively with the level of ALT. The percentage of XOR oxidase activity in cirrhotic liver, regardless of virus infection, correlated positively with aspartate amino-transferase, bilirubin concentration, and partial thromboplastin time, and negatively with prothrombin time. The activity of XOR was significantly lower in HCC than in control tissue or in a nonneoplastic area of the same liver.

CONCLUSIONS

Consistent with previous reports in experimental pathology, the level of XOR was increased in cirrhotic liver, in association with viral infection. This increment correlated with ALT, suggesting a relationship between XOR activity and the extent of liver injury caused by viral replication. The percentage of oxidase activity seems to be correlated with tissue damage and consequent liver impairment. The low XOR activity observed in HCC is consistent with reported experimental pathology.

Marked elevation in cortical urate and xanthine oxidoreductase activity in experimental bacterial meningitis

Experimental bacterial meningitis due to Streptococcus pneumoniae in infant rats was associated with a time-dependent increase in CSF and cortical urate that was approximately 30-fold elevated at 22 h after infection compared to baseline. This increase was mirrored by a 20-fold rise in cortical xanthine oxidoreductase activity. The relative proportion of the oxidant-producing xanthine oxidase to total activity did not increase, however. Blood plasma levels of urate also increased during infection, but part of this was as a consequence of dehydration, as reflected by elevated ascorbate concentrations in the plasma. Administration of the radical scavenger alpha-phenyl-tert-butyl nitrone, previously shown to be neuroprotective in the present model, did not significantly affect either xanthine dehydrogenase or xanthine oxidase activity, and increased even further cortical accumulation of urate. Treatment with the xanthine oxidoreductase inhibitor allopurinol inhibited CSF urate levels earlier than those in blood plasma, supporting the notion that urate was produced within the brain. However, this treatment did not prevent the loss of ascorbate and reduced glutathione in the cortex and CSF. Together with data from the literature, the results strongly suggest that xanthine oxidase is not a major cause of oxidative stress in bacterial meningitis and that urate formation due to induction of xanthine oxidoreductase in the brain may in fact represent a protective response.

Role of free radicals in viral pathogenesis and mutation

Oxygen radicals and nitric oxide (NO) are generated in excess in a diverse array of microbial infections. Emerging concepts in free radical biology are now shedding light on the pathogenesis of various diseases. Free-radical induced pathogenicity in virus infections is of great importance, because evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. Although oxygen radicals and NO have an antimicrobial effect on bacteria and protozoa, they have opposing effects in virus infections such as influenza virus pneumonia and several other neurotropic virus infections. A high output of NO from inducible NO synthase, occurring in a variety of virus infections, produces highly reactive nitrogen oxide species, such as peroxynitrite, via interaction with oxygen radicals and reactive oxygen intermediates. The production of these various reactive species confers the diverse biological functions of NO. The reactive nitrogen species cause oxidative tissue injury and mutagenesis through oxidation and nitration of various biomolecules. The unique biological properties of free radicals are further illustrated by recent evidence showing accelerated viral mutation by NO-induced oxidative stress. NO appears to affect a host's immune response, with immunopathological consequences. For example, NO is reported to suppress type 1 helper T cell-dependent immune responses during infections, leading to type 2 helper T cell-biased immunological host responses. NO-induced immunosuppression may thus contribute to the pathogenesis of virus infections and help expansion of quasispecies population of viral pathogens. This review describes the pathophysiological roles of free radicals in the pathogenesis of viral disease and in viral mutation as related to both nonspecific inflammatory responses and immunological host reactions modulated by NO.

Generation of reactive oxygen species and formation and membrane lipid peroxides in cells infected with Chlamydia trachomatis

OBJECTIVES

Chlamydiae are obligate intracellular pathogens that cause many diseases for which the pathogenic mechanisms are largely unknown. Because reactive oxygen species (ROS) have been implicated in pathogenesis of many viral and bacterial infections, the authors assessed the release of ROS in selected host cells (monocytes, Sup-T1 cells, and Hep-2 cells) infected with Chlamydia trachomatis.

METHODS

Infected cell cultures demonstrated a dramatic depletion of uric acid from culture media that was not seen in uninfected cultures. Reactive oxygen species generated in infected cultures were associated with the formation of lipid peroxides in host cell membrane.

RESULTS

There was a significant increase in lipid peroxide levels in infected cells compared to uninfected controls. Ascorbic acid treatment of infected cell cultures reduced the formation of membrane lipid peroxides.

CONCLUSIONS

These results suggest that ROS produced during chlamydial replication cause membrane lipid peroxidation. The role of ROS-induced membrane damage in chlamydial pathogenesis is discussed.

Superoxide generation by monocytes following infection with human cytomegalovirus

A significant level of superoxide (O2-) generation was observed in a U937-derived subclone following infection with human cytomegalovirus (HCMV). Although there were no detectable levels of viral mRNA and/or protein expression, HCMV DNA content transiently increased immediately before O2- generation. Similarly, O2- generation was also observed in peripheral blood monocytes derived from healthy donors.

Induction of nitric oxide synthesis and xanthine oxidase and their roles in the antimicrobial mechanism against Salmonella typhimurium infection in mice

The role of superoxide anion (O2-) and nitric oxide (NO) in the host defense mechanism against Salmonella typhimurium (LT-2) was examined by focusing on xanthine oxidase (XO) as an O2(-)-generating system and on inducible NO synthase (iNOS). When ICR mice were infected with a 0.1 50% lethal dose (2 x 10(5) CFU) of S. typhimurium, bacterial growth in the liver reached a peak value 3 days after infection (10(4.32) CFU/g of liver) and decreased thereafter. XO activity in the liver became maximum at 7 days after infection; the value was 34.6 +/- 1.4 mU/g of liver at 7 days (compared with 11.0 +/- 1.3 mU/g of liver before infection). The time profile of NO production in the liver as determined by electron spin resonance spectroscopy was consistent with that of XO activity. Histological examination of infected liver showed the formation of multiple microabscesses with granulomatous lesions consisting of polymorphonuclear cells and mononuclear cells, and iNOS-expressing cells were localized in the confined areas of the microabscesses. When XO inhibitors such as allopurinol and 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP) were administered to the infected mice, the mortality of the mice was significantly increased (10 of 21 and 11 of 20 for the allopurinol- and AHPP-treated groups, respectively, versus 2 of 20 for control mice), and bacterial growth was significantly enhanced. A similar exacerbation of the infection was obtained with N(omega)-monomethyl-L-arginine (L-NMMA) treatment of the mice. Of considerable importance is that granuloma formation in the liver was poorly developed by treatment with either XO inhibitors or L-NMMA. These results suggest that XO and NO play an important role in the antimicrobial mechanism against S. typhimurium in mice.

Pathogenesis of influenza virus-induced pneumonia: involvement of both nitric oxide and oxygen radicals

The role of nitric oxide (NO) in the pathogenesis of influenza virus-induced pneumonia in mice was investigated. Experimental influenza virus pneumonia was produced with influenza virus A/Kumamoto/Y5/67(H2N2). Both the enzyme activity of NO synthase (NOS) and mRNA expression of the inducible NOS were greatly increased in the mouse lungs; increases were mediated by interferon gamma. Excessive production of NO in the virus-infected lung was studied further by using electron spin resonance (ESR) spectroscopy. In vivo spin trapping with dithiocarbamate-iron complexes indicated that a significant amount of NO was generated in the virus-infected lung. Furthermore, an NO-hemoglobin ESR signal appeared in the virus-infected lung, and formation of NO-hemoglobin was significantly increased by treatment with superoxide dismutase and was inhibited by N(omega)-monomethyl-L-arginine (L-NMMA) administration. Immunohistochemistry with a specific anti-nitrotyrosine antibody showed intense staining of alveolar phagocytic cells such as macrophages and neutrophils and of intraalveolar exudate in the virus-infected lung. These results strongly suggest formation of peroxynitrite in the lung through the reaction of NO with O2-, which is generated by alveolar phagocytic cells and xanthine oxidase. In addition, administration of L-NMMA resulted in significant improvement in the survival rate of virus-infected mice without appreciable suppression of their antiviral defenses. On the basis of these data, we conclude that NO together with O2- which forms more reactive peroxynitrite may be the most important pathogenic factors in influenza virus-induced pneumonia in mice.

Granulation in livers of mice infected with Salmonella typhimurium is caused by superoxide released from host phagocytes

The pathophysiological roles of superoxide (O2.-) at the site of infection of facultative intracellular bacteria were examined in this study. To evaluate the actual in vivo generation of the superoxide, an ex vivo chemiluminescence assay was newly developed. When ICR mice were infected with a sublethal dose (8 x 10(4) CFU) of Salmonella typhimurium, the number of bacteria in the liver reached its peak at 5 days after infection (10(5.05) CFU/g of liver) and decreased thereafter. At 21 days after infection, the bacteria became undetectable. On the other hand, phorbol myristate 13-acetate-stimulated O2.- generation reached a maximum at 7 days after infection (mean photon count, 1,249 cps versus 28.8 cps before infection; n = 4) and decreased thereafter to a level similar to that before infection at 21 days after infection (28.8 cps). Histological examinations revealed that the total area of the lesions reached a peak at 7 days after infection (7.2 x 10(4) microns 2/10 visual fields). In the early phase, a microabscess with infiltration of polymorphonuclear cells was noted, and then, in the late stage, the lesion was replaced by granulation with mononuclear cell infiltration. When microscopic lesions were measured histologically, a significant correlation between the area of the lesions and phorbol myristate 13-acetate-stimulated O2.- generation was observed, which suggested that superoxide was responsible for the generation of the lesions. Modified superoxide dismutase, i.e., alpha-4-([6-(N-maleimido)hexanoyloxymethyl] cumyl)half-butyl-esterified poly(stylrene-co-malelic acid)-conjugated superoxide dismutase (SM-SOD), was then applied. When SM-SOD was administered to suppress the O2.- generation in vivo, the number of bacteria increased (10(6.1) CFU). However, the lesion formation was inhibited (total lesion area, 0.3 x 10(4) microns 2). These results suggest that the establishment of the microabscess and granuloma formation after S. typhimurium infection is not due to the bacteria per se but rather to the O2.- from the host's phagocytes. Two aspects of the O2.-, i.e., the bactericidal role and the tissue-injurious effect, were clearly demonstrated in this study. Therefore, the information obtained from these results is useful in designing treatment strategy for similar kinds of infection.

Prolonged infection of mouse brain neurons with murine cytomegalovirus after pre- and perinatal infection

The susceptibility of mice at different developmental stages to a relatively low titer of cell culture-passaged murine cytomegalovirus (MCMV) infection was compared in terms of the urinary excretion of MCMV examined by plaque assay and in terms of the distribution of viral infection, determined by immunohistochemistry, using antibodies specific to the early nuclear antigen of MCMV. Viral infection on day 8.5 of gestation (E8.5) into the conceptus and intraperitoneal infection on day 15.5 of gestation (E15.5), postnatal day 2 (P2), postnatal day 11 (P11), and 30 days after birth (P30), respectively, were performed. Embryonal and perinatal mice were more susceptible to MCMV in terms of urinary excretion of the virus and the presence of viral antigen-positive cells in the brain, lungs, and kidneys. In the embryonal and perinatal infection, the viral antigen-positive cells in the neurons of the cerebral cortex and hippocampus were retained late after birth, even though the positive cells in the lungs and kidneys had disappeared. In the mice infected on E8.5, small clusters of viral antigen-positive cells were detected only in the cortex and hippocampus late after birth, without the urinary excretion of virus. These results suggest that when mice are infected with MCMV at the embryonal and perinatal stages, elimination of the infected neurons is delayed compared with that of the other cells in the lungs and kidneys. These findings provide a model for the analysis of pathogenesis of the subclinical congenital CMV infection that manifested clinically late after birth in humans as brain disorders.

The antiviral activity of tumour necrosis factor on herpes simplex virus type 1: role for a butylated hydroxyanisole sensitive factor

We have previously shown that specific antibodies (Mab 32/Ab 301) against tumour necrosis factor (TNF) enhance its antiviral activity in vaccinia virus-infected mice. In the present study, TNF alone was found to have antiviral activity against herpes simplex virus-1 (HSV-1). Antibody enhancement was found, both in vivo and in vitro, at lower TNF doses. The magnitude of the TNF-induced antiviral response was dependent upon the genetic background of the mouse. C57BL/6 mice were very sensitive to the antiviral activity of TNF, which was inhibited by the free radical scavenger butylated hydroxyanisole (BHA). TNF plus Mab 32 induced a significant antiviral effect in L929 cells which was associated with pronounced CPE. The CPE was largely reversed in the presence of BHA, and furthermore, TNF antiviral activity was significantly reversed in the presence of BHA. Specific inhibitors of nitric oxide synthetase, lipoxygenase or cyclo-oxygenase did not influence either the CPE or growth kinetics of HSV-1, suggesting that neither reactive nitrogen intermediates nor arachidonic acid metabolites were involved in the antiviral mechanism of TNF. This, together with observed increases in Cu/Zn SOD levels in virus infected cells, suggests that reactive oxygen intermediates may have a role in the direct control of HSV-1 growth and that free radicals may play a part in the antiviral activity induced by TNF.

Studies of the pathogenesis of wild-type virus and six temperature-sensitive mutants of mouse cytomegalovirus

A comparison of six temperature-sensitive (ts) mutants with the parental wild-type (wt) virus showed that, when 1-week-old BALB/c mice were inoculated intraperitoneally with 300 pfu of mouse passaged virus, the viruses could be broadly categorized into two groups. Two viruses (wt and tsm6) were lethal at this dose (10 and 2 LD50 respectively); animals died within 4-6 days of inoculation and the virus became generalized infecting heart, lung, liver, spleen, kidney, and salivary glands to high titre (> 4.3 log10 pfu/g). In contrast, for viruses (tsm1, tsm3, and tsm4) not lethal at this dose (300 pfu = 0.1 to 0.25 LD50), viral replication was poor (< 3.4 log10 pfu/g) except in the salivary glands (5.6 to 7.5 log10 pfu/g). Mutant tsm5 failed to replicate in any tissue while mutant tsm2, lethal at this dose (300 pfu = 1 LD50), produced levels of virus similar to those found with tsm1, tsm3, and tsm4. Comparison of all viruses at sub-lethal doses (0.1 to 0.25 LD50) did show minor differences in their replication in heart, and in levels of virus and duration of infection in kidney and salivary glands. More marked differences were evident between the viruses in their ability to be reactivated from the latent state during immunosuppression. Wild-type virus was most easily reactivated in that 67% of animals exhibited virus in salivary glands, heart, lung, spleen, and kidney. Mutants tsm1, tsm2, tsm3 and tsm6 could be reactivated but from fewer animals (33%, 33%, 18%, and 38% respectively) and fewer tissues. Mutants tsm4 and tsm5 could not be reactivated. Differences in the ability of the viruses to replicate in the lungs and to cause pneumonitis in intranasally-inoculated immunosuppressed mice were also seen. Although immunosuppression was necessary for the induction of severe pneumonitis, differences in severity of pneumonitis resulted from differences in the ability of the mutants to replicate in the lung in vivo. These different mutants should prove useful for examining the viral and host factors involved in CMV-induced pneumonitis, and for examining mechanisms involved in latency and reactivation.