Bactericidal and cytotoxic effects of hypothiocyanite-hydrogen peroxide mixtures

Antibacterial and antiplaque efficacy of a lactoperoxidase-thiocyanate-hydrogen-peroxide-system-containing lozenge

Background

Antimicrobial agents are considered valuable adjuncts to mechanical methods of plaque control. However, their long-term use can be limited because of side effects.

Therefore, using physiological substances is promising due to no risk of development, for example, of microbial resistances, allergies or DNA damaging. The lactoperoxidase-thiocyanate-hydrogen peroxide system (LPO-system) is a highly effective antimicrobial system. This study aimed to evaluate in a randomized study with a four-replicate cross-over design the effectiveness of two oral hygiene lozenges containing LPO-system in oral hygiene.

Results

After using the mouth rinse as positive control (A) and allocated test lozenges (B) (0.083% H₂O₂) & (C) (0.04% H₂O₂) for 4 days instead of the normal oral hygiene procedures (tooth brushing etc.), Listerine rinse (A) was statistically significantly more effective than the LPO-system-lozenge with 0.083% H₂O₂, the LPO-system-lozenge with 0.04% H₂O₂, and the placebo lozenge (D) in inhibiting plaque. Lozenges B and C were statistically significantly more effective than the placebo lozenge, but no statistically significant differences could be observed between them.

The LPO-system-lozenge (B) reduced statistically significantly more S. mutans than the LPO-system-lozenge with (C) and the placebo lozenge (D). The LPO-system-lozenge (C) reduced statistically significantly more Lactobacilli than Listerine (A), the LPO-system-lozenge (B) and the placebo lozenge (D). There were no statistically significant differences in the total CFUs between Listerine rinse, the LPO-system-lozenge with 0.083% H₂O₂ (B), the LPO-system-lozenge with 0.04% H₂O₂ (C), and the placebo lozenge (D). On day 5 there were no differences of the OSCN⁻-values between all A, B, C, and D. However, the SCN⁻-values increased over the days in both LPO-system-lozenges (B/C). The statistically significant differences between B/C and A/D on day 5 were as followed: A to B p = 0.0268; A to C p = 0.0035; B to D p = 0.0051; C to D p = 0.0007. Only in the group of Listerine (A) increased the NO₃⁻/NO₂⁻-quotient over the test time, which indicates a reduction of nitrate-reducing bacteria. On Day 5 the statistically significant difference between A and B was p = 0.0123.

Conclusions

The results indicate that lozenges containing a complete LPO-system, inhibiting plaque regrowth and reducing cariogenic bacteria, may be used in the daily oral hygiene.

Reverse Ordered Sequential Mechanism for Lactoperoxidase with Inhibition by Hydrogen Peroxide

Lactoperoxidase (LPO, Fe^III in its resting state in the absence of substrates)—an enzyme secreted from human mammary, salivary, and other mucosal glands—catalyzes the oxidation of thiocyanate (SCN⁻) by hydrogen peroxide (H₂O₂) to produce hypothiocyanite (OSCN⁻), which functions as an antimicrobial agent. The accepted catalytic mechanism, called the halogen cycle, comprises a two-electron oxidation of LPO by H₂O₂ to produce oxoiron(IV) radicals, followed by O-atom transfer to SCN⁻. However, the mechanism does not explain biphasic kinetics and inhibition by H₂O₂ at low concentration of reducing substrate, conditions that may be biologically relevant. We propose an ordered sequential mechanism in which the order of substrate binding is reversed, first SCN⁻ and then H₂O₂. The sequence of substrate binding that is described by the halogen cycle mechanism is actually inhibitory.

Nasal disinfection for the prevention and control of COVID-19: A scoping review on potential chemo-preventive agents

BACKGROUND

Neither pre-exposure nor post-exposure chemo-prophylaxis agents are currently available to prevent COVID-19. On the other hand, high loads of SARS-CoV-2 are shed from the nasal cavity before and after symptoms onset.

OBJECTIVE

To conduct a scoping review on the available evidence on tolerable nasal disinfectants with encouraging health outcomes against SARS-CoV-2, i.e., agents effective against at least two different viruses beyond SARS-CoV-2.

METHODS

Online databases were searched to identify papers published during 2010-2020. Publications were selected if they were relevant to the scoping review. The review was narrative, describing for each treatment the mechanism(s) of action, tolerability, in vitro and in vivo evidence of the effects against SARS-CoV-2 and whether the product had been marketed.

RESULTS

Eight treatments were scrutinized: hypothiocyanite, lactoferrin, N-chlorotaurine, interferon-alpha, povidone-iodine, quaternary ammonium compounds, alcohol-based nasal antiseptics and hydroxychloroquine. In vitro viricidal effect against SARS-CoV-2 was reported for ethanol, alcohol-based hand sanitizers and povidone-iodine. Inhibition of other coronaviruses was described for lactoferrin, ethanol, hydroxychloroquine and quaternary ammonium compound. No treatment has been tested against SARS-CoV-2 in randomized controlled clinical trials thus far. However, interferon-alpha, lactoferrin and hydroxychloroquine were tested in one-arm open label uncontrolled clinical trial. Oxidant activity (hypothiocyanite, N-chlorotaurine and povidone-iodine), enhancement of endocytic and lysosomal pH (quaternary ammonium compounds and hydroxychloroquine) and destruction of the viral capsid (quaternary ammonium compounds, alcohol-based nasal antiseptics) were the main mechanisms of action. Lactoferrin and interferon-alpha have subtle biological mechanisms. With the exception of N-chlorotaurine, all other products available on the market.

CONCLUSIONS

Effective and safe chemo-prophylactic drugs against SARS-CoV-2 do not exist yet but most eligible candidates are already in the market. Whilst the human nasal cavity is the port of entry for SARS-CoV-2, the mouth is involved as exit site through emission of respiratory droplets. The well-known hand-to-nose-to-hand cycle of contamination requires appropriate additional strategies for infection control. To narrow down the subsequent laboratory and clinical investigations, a case-control approach could be employed to compare the use of candidate drugs among individuals testing positive and negative to COVID-19 swabs.

Antibacterial and mechanical properties of arginine-containing glass ionomer cements

OBJECTIVE

The study investigated the effect of incorporating l-arginine (Arg) in a glass ionomer cement (GIC) on its mechanical properties and antibacterial potential.

METHODS

Pre-determined proportions (1%, 2%, and 4% by wt.) of Arg were incorporated in GIC powder; while GIC without Arg served as control. The flexural strength, nanohardness, surface roughness, elemental analysis using SEM-EDX (n = 6) and F/Arg/Ca/Al/Si release in deionized water for 21 days were assessed. The antibacterial potential was evaluated in a multi-species biofilm model with Streptococcus mutans, Streptococcus sanguinis, Streptococcus gordonii, and Lactobacillus acidophilus for 72 h. Real-time qPCR was used to analyse biofilm bacterial concentrations. Propidium monoazide modification of real-time qPCR was performed to quantify viable/dead bacteria. The pH, lactic acid, ADS activity, and H₂O₂ metabolism were measured. Confocal microscopy was used to investigate the biofilm bacterial live/dead cells, density, and thickness.

RESULTS

There was no difference in flexural strength among the different groups (p > 0.05). No significant difference in nanohardness and surface roughness was observed between 4% Arg + GIC and control (p > 0.05). The 4% Arg + GIC showed significantly higher F/Arg/Al/Si release than the other groups (p < 0.05), reduced total bacterial concentration and growth inhibition of viable S. mutans and S. sanguinis (p < 0.05). Lactic acid formation for 4% Arg + GIC was significantly higher than 1% Arg + GIC (p < 0.05). The spent media pH of 4% Arg + GIC was higher than the other groups (p < 0.05), with proportionately lower ammonia and higher H₂O₂ released (p < 0.05).

SIGNIFICANCE

Addition of 4% l-arginine in GIC enhanced its antibacterial activity via a biofilm modulatory effect for microbial homeostasis, with no detrimental effect on its mechanical properties.

Antimicrobial actions of dual oxidases and lactoperoxidase

The NOX/DUOX family of NADPH oxidases are transmembrane proteins generating reactive oxygen species as their primary enzymatic products. NADPH oxidase (NOX) 1-5 and Dual oxidase (DUOX) 1 and 2 are members of this family. These enzymes have several biological functions including immune defense, hormone biosynthesis, fertilization, cell proliferation and differentiation, extracellular matrix formation and vascular regulation. They are found in a variety of tissues such as the airways, salivary glands, colon, thyroid gland and lymphoid organs. The discovery of NADPH oxidases has drastically transformed our view of the biology of reactive oxygen species and oxidative stress. Roles of several isoforms including DUOX1 and DUOX2 in host innate immune defense have been implicated and are still being uncovered. DUOX enzymes highly expressed in the respiratory and salivary gland epithelium have been proposed as the major sources of hydrogen peroxide supporting mucosal oxidative antimicrobial defenses. In this review, we shortly present data on DUOX discovery, structure and function, and provide a detailed, up-to-date summary of discoveries regarding antibacterial, antiviral, antifungal, and antiparasitic functions of DUOX enzymes. We also present all the literature describing the immune functions of lactoperoxidase, an enzyme working in partnership with DUOX to produce antimicrobial substances.

A randomised clinical study to determine the effect of a toothpaste containing enzymes and proteins on plaque oral microbiome ecology

The numerous species that make up the oral microbiome are now understood to play a key role in establishment and maintenance of oral health. The ability to taxonomically identify community members at the species level is important to elucidating its diversity and association to health and disease. We report the overall ecological effects of using a toothpaste containing enzymes and proteins compared to a control toothpaste on the plaque microbiome. The results reported here demonstrate that a toothpaste containing enzymes and proteins can augment natural salivary defences to promote an overall community shift resulting in an increase in bacteria associated with gum health and a concomitant decrease in those associated with periodontal disease. Statistical analysis shows significant increases in 12 taxa associated with gum health including Neisseria spp. and a significant decrease in 10 taxa associated with periodontal disease including Treponema spp. The results demonstrate that a toothpaste containing enzymes and proteins can significantly shift the ecology of the oral microbiome (at species level) resulting in a community with a stronger association to health.

Co-operative inhibitory effects of hydrogen peroxide and iodine against bacterial and yeast species

BACKGROUND

Hydrogen peroxide and iodine are powerful antimicrobials widely used as antiseptics and disinfectants. Their antimicrobial properties are known to be enhanced by combining them with other compounds. We studied co-operative inhibitory activities (synergism, additive effects and modes of growth inhibition) of hydrogen peroxide and iodine used concurrently against 3 bacterial and 16 yeast species.

RESULTS

Synergistic or additive inhibitory effects were shown for hydrogen peroxide and iodine mixtures against all 19 species used in the study. Both biocides were mostly cidal individually and in mixtures against Pseudomonas aeruginosa and Staphylococcus aureus. Both compounds manifested static inhibitory effects individually, but their mixtures were synergistically cidal for Saccharomyces cerevisiae and Escherihia coli. Cells of S. cerevisiae treated with hydrogen peroxide and iodine-hydrogen peroxide mixture produced increased numbers of respiratory deficient mutants indicating genotoxic effects.

CONCLUSION

Iodine and hydrogen peroxide used concurrently interact synergistically or additively against a range of prokaryotic and eukaryotic microorganisms. The study provides an insight as to how these traditional antimicrobials could be used more effectively for disinfection and antisepsis. In addition, a simple approach is proposed for scoring genotoxicity of different biocides by using the budding yeast system.

Hypothiocyanous acid: benign or deadly?

Hypothiocyanous acid (HOSCN) is produced in biological systems by the peroxidase-catalyzed reaction of thiocyanate (SCN(-)) with H(2)O(2). This oxidant plays an important role in the human immune system, owing to its potent bacteriostatic properties. Significant amounts of HOSCN are also formed by immune cells under inflammatory conditions, yet the reactivity of this oxidant with host tissue is poorly characterized. Traditionally, HOSCN has been viewed as a mild oxidant, which is innocuous to mammalian cells. Indeed, recent studies show that the presence of SCN(-) in airways has a protective function, by preventing the formation of other, more damaging, inflammatory oxidants. However, there is an increasing body of evidence that challenges this dogma, showing that the selectivity of HOSCN for specific thiol-containing cellular targets results in the initiation of significant cellular damage. This propensity to induce cellular dysfunction is gaining considerable interest, particularly in the cardiovascular field, as smokers have elevated plasma SCN(-), the precursor for HOSCN. This review will outline the beneficial and detrimental aspects of HOSCN formation in biological systems.

The role of hypothiocyanous acid (HOSCN) in biological systems

Hypohalous acids (HOX), produced by peroxidase-catalysed reactions of halide and pseudohalide ions with H(2)O(2), play an important role in the human immune system. However, there is compelling evidence that these oxidants also mediate host tissue damage and contribute to the progression of a number of inflammatory diseases. Although it is well established that significant amounts of hypothiocyanous acid (HOSCN) are formed under physiological conditions, the reactions of this oxidant with host biological systems are relatively poorly characterized. It is generally accepted that HOSCN is a mild oxidant that reacts selectively with thiols. However, it is becoming increasingly recognized that this selectivity can result in the induction of significant cellular damage, which may contribute to disease. This review will outline the formation and reactivity of HOSCN and the role of this oxidant in biological systems.

Inorganic chemistry of defensive peroxidases in the human oral cavity

The innate host response system is comprised of various mechanisms for orchestrating host response to microbial infection of the oral cavity. The heterogeneity of the oral cavity and the associated microenvironments that are produced give rise to different chemistries that affect the innate defense system. One focus of this review is on how these spatial differences influence the two major defensive peroxidases of the oral cavity, salivary peroxidase (SPO) and myeloperoxidase (MPO). With hydrogen peroxide (H(2)O(2)) as an oxidant, the defensive peroxidases use inorganic ions to produce antimicrobials that are generally more effective than H(2)O(2) itself. The concentrations of the inorganic substrates are different in saliva vs. gingival crevicular fluid (GCF). Thus, in the supragingival regime, SPO and MPO work in unison for the exclusive production of hypothiocyanite (OSCN(-), a reactive inorganic species), which constantly bathes nascent plaques. In contrast, MPO is introduced to the GCF during inflammatory response, and in that environment it is capable of producing hypochlorite (OCl(-)), a chemically more powerful oxidant that is implicated in host tissue damage. A second focus of this review is on inter-person variation that may contribute to different peroxidase function. Many of these differences are attributed to dietary or smoking practices that alter the concentrations of relevant inorganic species in the oral cavity (e.g.: fluoride, F(-); cyanide, CN(-); cyanate, OCN(-); thiocyanate, SCN(-); and nitrate, NO(3)(-)). Because of the complexity of the host and microflora biology and the associated chemistry, it is difficult to establish the significance of the human peroxidase systems during the pathogenesis of oral diseases. The problem is particularly complex with respect to the gingival sulcus and periodontal pockets (where the very different defensive stratagems of GCF and saliva co-mingle). Despite this complexity, intriguing in vitro and in vivo studies are reviewed here that reveal the interplay between peroxidase function and associated inorganic chemistry.

Hypothiocyanous acid is a more potent inducer of apoptosis and protein thiol depletion in murine macrophage cells than hypochlorous acid or hypobromous acid

Hypohalous acids are generated by activated leucocytes, via the formation of H(2)O(2) and the release of peroxidase enzymes (myeloperoxidase and eosinophil peroxidase). These species are important bactericidal agents, but HOCl (hypochlorous acid) and HOBr (hypobromous acid) have also been implicated in tissue damage in a number of inflammatory diseases. HOSCN (hypothiocyanous acid; cyanosulfenic acid) is a milder, more thiol-specific, oxidant than HOCl or HOBr and as such may be a more potent inducer of cellular dysfunction due to selective targeting of critical thiol residues on proteins. In the present study, HOCl and HOBr are shown to react rapidly with macrophage (J774A.1) cells, resulting in a greater extent of cell lysis compared with HOSCN. However, HOSCN induces apoptosis and necrosis with greater efficacy, and at lower concentrations, than HOCl or HOBr. Apoptosis occurs in conjunction with an increased release of cytochrome c into the cytosol, but no associated increase in caspase activity. Similarly, apoptosis is observed on treating the cells in the presence of a caspase inhibitor, suggesting that it is mediated by a caspase-independent pathway. HOSCN oxidized protein thiols more efficiently than either HOCl or HOBr. The greater efficacy of HOSCN in inducing apoptosis is attributed to selective damage to critical mitochondrial membrane protein thiol groups, resulting in increased permeability and subsequent leakage of cytochrome c into the cytosol. This induction of damage by HOSCN may be of critical importance in people with elevated levels of SCN(-) (thiocyanate ions) arising from cigarette smoking, and plays a role in the pathologies associated with this biological insult.

How to prevent immunological reactions in leprosy patients and interrupt transmission of Mycobacterium leprae to healthy subjects: two hypotheses

The basis of World Health Organization strategy for leprosy elimination is that the only source and reservoir for infection are patients with the disease. It was assumed that multi drug therapy (MDT) would reduce transmission of Mycobacterium leprae, but there is no convincing evidence for this. Furthermore, even if MDT has been proved to be extremely effective against the infectious disease, a noticeable proportion of leprosy patients can suffer from immunologic hypersensitivity reactions which are now the most significant issue in the managements of the disease. In endemic areas it was found that: M. leprae survives outside human body; healthy individuals harbor M. leprae bacilli in nasal cavity and shed micro-organisms in environment; there is widespread subclinical transmission of M. leprae with transient infection of the nose resulting in the development of a mucosal immune response. This disparate clinical, epidemiologic, and microbiologic evidence leads to the first hypothesis: that antigenic load in local tissues, sufficient to trigger the immune response, comes from external supply of M. leprae organisms. The hypothiocyanite anion (OSCN-) is generated in vivo by the reaction of thiocyanate with hydrogen peroxide catalyzed by lactoperoxidase. OSCN- is an antimicrobial oxidizing agent that prevents growth of bacteria, fungi, and viruses. OSNC- exists in lower airway secretions and lung has never been reported to be affected by leprosy. There is a sufficient concentration of OSCN- in the saliva, and accordingly mouth is rarely affected by leprosy. By contrast, the concentration of this compound is low or nil in nasal and lacrimal secretions and leprosy very often affects nose and eyes. The second hypothesis is that OSCN- may also protect from leprosy. Recently a method of OSCN- production, not involving enzymatic steps or use of toxic heavy-metal salts, has been patented. Studies on the susceptibility of M. leprae to hypothiocyanite could be carried out and, in case of positive results, the substance might be used in order to sterilize the nasal cavity of healthy carriers and prevent transmission of M. leprae to healthy subjects and to leprosy patients in whom it may trigger an immune response.

Autocatalytic Modification of the Prosthetic Heme of Horseradish but Not Lactoperoxidase by Thiocyanate Oxidation Products. A Role for Heme−Protein Covalent Cross-Linking

The mammalian peroxidases eosinophil peroxidase, lactoperoxidase (LPO), and myeloperoxidase oxidize thiocyanate to the antimicrobial agents hypothiocyanous acid (HOSCN) and (SCN)2 and are part of a defense system that protects the host from infections. Horseradish peroxidase (HRP), a plant enzyme, also oxidizes thiocyanate. We report here that the prosthetic heme vinyl groups of HRP react with the catalytically generated HOSCN and (SCN)2 to form at least nine vinyl-modified heme adducts. Mass spectrometry combined with analysis of the equivalent reactions of HRP reconstituted with 2- or 4-cyclopropylheme, or mesoheme-d4, shows that all of the prosthetic heme modifications result from addition of oxidized thiocyanate to the heme vinyl groups. No delta-meso-substitution of the heme was observed, in contrast to what is observed with radical agents. Model studies show that incubation of either HRP with preformed HOSCN or a solution of heme with preformed (SCN)2 gives rise to the same products obtained in the HRP-catalyzed reaction. Model studies also demonstrate that the SCN* radical, if formed, should add to a meso-carbon. These findings implicate an electrophilic addition mechanism. In contrast, oxidation by LPO of thiocyanate, the normal substrate of this enzyme, does not result in heme modification. In view of the demonstrated intrinsic reactivity of the heme group, LPO must actively suppress heme modification. As the key difference between LPO (and other mammalian peroxidases) and HRP is the presence of two covalent ester links between the heme and the protein, we propose that these links contribute to steric protection of the adjacent heme vinyl groups.

Redox buffering of hypochlorous acid by thiocyanate in physiologic fluids

The major antimicrobial products of neutrophilic myeloperoxidase (MPO) in physiologic fluids are hypochlorous acid (HOCl) and hypothiocyanite (OSCN-), and the former is generally believed to be the killing agent. However, we have determined that HOCl oxidizes SCN- in a facile nonenzymic reaction. The observed kinetics and computational models substantiate the hypothesis that SCN- serves to moderate the potential autotoxicity of HOCl by restricting its lifetime in physiologic fluids. Furthermore, the oxidizing equivalents of HOCl are preserved in OSCN-, a more discriminate biocide that is not lethal to mammalian cells.

Do folic acid and thiocyanate have a preventive effect on exogenously induced disturbances of embryonic cranial development?

The preventive influence of folic acid and thiocyanate on procarbazine-induced disturbances of embryonic cranial development was investigated on experimental animals. Low dosages of folic acid or thiocyanate demonstrated no prophylactic effect. When thiocyanate was administered alone, an increased cleft rate was unexpectedly found for the secondary palate. The combined application of folic acid and thiocyanate showed a cleft-prophylactic effect in the secondary palate in addition to growth protection in the primary palate. It can be assumed that thiocyanate has a positive effect on chondral and osseous growth of the palate during the post-sensitive phase of embryogenesis, while in the sensitive phase, it can function as a carrier for teratogenous and toxic substances.

Effect of local application of delmopinol hydrochloride on developing and early established supragingival plaque in humans

The aim of the study was to investigate the effect of delmopinol hydrochloride on the development of dental plaque and on newly established plaque. In addition, the influence of this compound on the composition of the microbiota colonizing the gingival mucous membrane was studied. 14 healthy male volunteers took part. After a 3 week pre-experimental period of intense oral hygiene, the participants refrained from all oral hygiene for 14 days. The buccal surfaces of cuspids and bicuspids on one side of the jaws were treated with a 1% aqueous solution of delmopinol hydrochloride (applied with a paint brush) 2 x a day for 7 days, while the contralateral side received placebo solution. On day 7, the application procedures were changed in that the test compound was applied on the teeth previously treated with placebo and vice versa. Plaque development was assessed clinically and by photo-based planimetric determination. The clinical recordings revealed that 89.3% of the placebo-treated surfaces displayed visible plaque on day 7, compared to 6.0% of the delmopinol hydrochloride treated surfaces. Delmopinol hydrochloride treatment of the previously placebo-treated surfaces resulted in a decrease in the number of surfaces with visible plaque from 89.3% on day 7 to 6% on day 14. These results were confirmed by the planimetric data. No significant change in the composition of the mucosal flora was observed during the experimental period. The present results indicate that delmopinol hydrochloride markedly reduces the formation of dental plaque on a clean tooth surface exposed to conditions which favour bacterial colonization. Furthermore, the substance appears to possess plaque-dissolving properties.

The influence of different fluoride salts on fluoride-mediated inhibition of peroxidase activity in human saliva

Fluoride-mediated inhibition of peroxidase potential activity in human saliva was investigated using NaF, NH4F, CaF2, Na2PO3F (MFP), SnF2 and TiF4. At pH 5.5 and for a 20 mM F concentration, the inhibition percentages increased from 2% for MFP and 5% for CaF2 to 61% for NaF and 65% for NH4F, while a 100% inhibition was observed at 10 mM for TiF4 and at 5 mM for SnF2. The inhibition was enhanced at acid pH and removed at pH 7. The inhibition could be attributed to ionized F-, except for SnF2 and TiF4, in which part of the inhibition could be imputed to the cations.

Effects of a lactoperoxidase-system-containing toothpaste on dental plaque and whole saliva in vivo

The effects of a lactoperoxidase-system-containing toothpaste. Biotene, on saliva and dental plaque were studied. In a double-blind crossover study 20 healthy volunteers used an experimental (comprising the complete peroxidase system) or a placebo (without lactoperoxidase, KSCN, and glucose oxidase) toothpaste twice daily for 2 weeks separated by a 2-week washout period. At base lines and at the end of both test periods saliva and plaque samples were collected, and plaque pH changes were monitored. Saliva was analyzed for hypothiocyanite (HOSCN/OSCN-) and thiocyanate (SCN-) concentrations and salivary peroxidase activity. The amount of total streptococci, mutans streptococci, lactobacilli, and total anaerobic flora was determined both in saliva and in plaque samples. The accumulation and the acidogenicity of plaque were also quantitated. A 2-week daily use of Biotene had no effect on salivary flow rate, peroxidase activity, HOSCN/OSCN-, SCN-, or any of the monitored bacterial counts compared with the placebo toothpaste. The accumulation of dental plaque was not affected by the lactoperoxidase-system-containing toothpaste. The acidogenicity of plaque did not change significantly, nor did the two test dentifrices differ in their ability to inhibit the plaque pH drop caused by sucrose in subjects with normal salivary flow rate.

Peroxidase activities in bull spermatozoa

The present study was carried out to determine the localization of peroxidase activity in bull spermatozoa. 3,3'-Diaminobenzidine (DAB) was used as a substrate for revealing peroxidase activity, and light and electron microscopic analysis of the results obtained was performed. Peroxidase activity was detected in the mitochondria of the middle piece and the outer acrosomal membrane. Catalase was excluded as an enzyme, catalyzing the detected peroxidase activity. Concerning the biochemical properties of bull sperm peroxidases, peroxidase activity was found to be manifested in a large pH range, 4-10.5. Bull sperm peroxidase activity appeared to be temperature sensitive and azide sensitive and could be readily inhibited by phenylhydrazine. Electrophoretic analysis of the proteins from bull sperm extracts separated in a Davis-Ornstein system of 7% polyacrylamide gel, followed by the determination of peroxidase activity on the polyacrylamide gels, revealed that all 14 sperm protein fractions available on the gel possessed peroxidase when benzidine was used as a substrate. The possible reasons for the electrophoretic heterogeneity of bull sperm peroxidases are discussed.

Lethal oxidative damage to human immunodeficiency virus by human recombinant myeloperoxidase

Human recombinant myeloperoxidase was evaluated in a cell-free system for its inactivation properties on the replication of human immunodeficiency virus, HTLV-IIIB. In the presence of a hydrogen peroxide generating system (glucose and glucose oxidase) and sodium thiocyanate, the recombinant enzyme inhibited virus-induced syncytium formation and viral replication without causing any cytopathic effects on SupT1 reporter cells. In addition, U937 monocytoid cells, chronically infected with HIV1, were exposed to recombinant myeloperoxidase (10 U/ml) and monitored during 48 h for the accumulation of intracellular p24 viral antigen. Under these conditions, the recombinant enzyme significantly reduced intracellular viral replication without affecting cell viability.

Sorbitol adaptation of dental plaque in people with low and normal salivary-secretion rates

Caries-related bacteriological and biochemical factors were studied in 12 persons with low and 11 persons with normal salivary-secretion rates before and after a four-week period of frequent mouthrinses with 10% sorbitol solution (adaptation period). After the adaptation period, an increase in total numbers of sorbitol-fermenting bacteria and mutans streptococci was found in plaque samples from both groups. The pH drop in dental plaque in situ after a mouthrinse with sorbitol was more pronounced after the adaptation period, especially in the group with the low salivary-secretion rate. Increased acid production in plaque from sorbitol was also observed in the two groups in vitro. The composition of the fermentation end-products was affected by the sorbitol exposure. It is suggested that in subjects with diminished natural protection against caries development, such as patients with low salivary-secretion rate, a cariogenic potential of sorbitol should be considered when this polyol is included in products that might be used frequently.

Cytotoxic properties of salivary oxidants

Salivary peroxidase and to a lesser extent myeloperoxidase are present in significant concentrations in saliva and catalyze the oxidation of thiocyanate anion (SCN-) by H2O2 to yield the potent oxidants hypothiocyanous acid (HOSCN) and its conjugate base hypothiocyanite anion (OSCN-). The objective of this study was to characterize the cytotoxic potential of peroxidase-generated HOSCN/OSCN- toward human erythrocytes. We found that HOSCN/OSCN- (0.25 mM) generated by the peroxidase-H2O2-SCN- system caused significant hemolysis at pH 6.0 but not at pH 6.5, 7.0, or 7.4. Erythrocyte hemoglobin (OxyHb) was oxidized to methemoglobin (MetHb) at all pH values tested; however, the rate of MetHb formation was dramatically increased at low pH and was not affected by inosine hexaphosphate, suggesting that hemoglobin was oxidized primarily by HOSCN. Concurrent with oxidation of hemoglobin (Hb), there was a pH-dependent consumption of HOSCN/OSCN- with more of the oxidant consumed at pH 6.0 compared with pH 6.5, 7.0, or 7.4. The enhanced oxidation of Hb at acidic pH was not due simply to increased membrane permeability by the uncharged species (HOSCN), since both erythrocyte lysate Hb and purified Hb were oxidized to the same extent at low pH as were intact erythrocytes. It is concluded that both OSCN- and HOSCN enter human erythrocytes where the protonated oxidant (HOSCN) mediates hemolysis and oxidizes OxyHb to MetHb, whereas both HOSCN and OSCN- oxidize glutathione (GSH). These data suggest that the extracellular pH may play an important role in modulating the cytotoxic properties of salivary oxidants.

Peroxidase activities in the hamster bronchoalveolar lining fluid: modifications induced by exposure to silica dust

The modifications of peroxidase (Po) activity have been studied in bronchoalveolar lavage fluid (BALF) from hamsters exposed to silica dust. In silica-treated animals, the mean total BALF-Po activity was significantly increased compared to control animals. This increased activity was accompanied by an influx of polymorphonuclear neutrophils in airways. HPLC gel filtration of BALF from control animals separated 5 peaks with Po activity. They had an apparent molecular weight of 140, 110, 80, 57, and 42 kDa. In BALF from silica-exposed animals, with the exception of the 57-kDa fraction, the same peaks were found. Additional fractions with an apparent molecular weight of greater than 200, 180, 92, 65, and 20 kDa were detected. All the fractions but those at 57 and 92 kDa were detectable in a whole-blood homogenate. Exposing hamsters to silica induced both quantitative modifications and a different pattern of BALF proteins having Po activity in the alveolar lining fluid.

Susceptibility of Plasmodium falciparum to a peroxidase-mediated oxygen-dependent microbicidal system

The viability of Plasmodium falciparum in culture was assessed by [3H]hypoxanthine incorporation during 24 h of incubation with lactoperoxidase, glucose-glucose oxidase, hydrogen peroxide, halides, or thiocyanate, alone or in combination. Synergistic inhibition was produced by the following combinations: lactoperoxidase plus hydrogen peroxide, lactoperoxidase plus glucose-glucose oxidase, and lactoperoxidase plus hydrogen peroxide plus halides or thiocyanate. These inhibitory effects were reversed by catalase and glutathione. The presence of plasmodial crisis forms inside the erythrocytes suggests that the oxygen-dependent microbicidal system of phagocytes has a killing effect.

Improved selective culture media for Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

By modifying the previously described media tryptic soy-serum-bacitracin-vancomycin (TSBV) agar and tryptic soy-serum-bacitracin-vancomycin-fluoride (TSBVF) agar, two improved selective culture media were developed for isolation and enumeration of Actinobacillus actinomycetemcomitans (A medium) and Haemophilus aphrophilus (H medium) in oral specimens. Both media were supplemented with fusidic acid and spiramycin, and carbenicillin was also added to A medium. The growth yields of pure cultures of A. actinomycetemcomitans on A medium and of H. aphrophilus on H medium were comparable with those on the reference media. Compared with blood agar, the selective media inhibited these species about 10-fold or less. In addition, A and H media suppressed the growth of pure cultures of Capnocytophaga spp. and Neisseria spp., commonly found as contaminants on TSBV and TSBVF, 10(5) times or more compared with that on blood agar. In samples from diseased periodontal pockets, the recoveries of A. actinomycetemcomitans on A medium and H. aphrophilus on H medium equaled those on TSBV and TSBVF, respectively. In about 50% of the cultures on the reference media, contaminating bacteria were detected at levels higher than 10(4) CFU/ml of sample. The corresponding value for both A and H media was about 2%.

Is thiocyanate peroxidation at equilibrium in vivo?

The peroxidase-catalyzed oxidation of SCN- by H2O2 is an important in vivo reaction because it limits the accumulation of toxic H2O2 and provides significant concentrations of the antimicrobial agents, HOSCN and OSCN-. Data presented in this report suggest that the reaction: (Formula: see text) is in a state of dynamic equilibrium in vivo. Since OSCN- can form the weak acid HOSCN (pKa = 5.3), the equilibrium constant expression (Kox) for thiocyanate peroxidation is dependent on the concentration of hydrogen ions as well as the concentrations of H2O2, SCN-, HOSCN, OSCN- and water, and on the HOSCN ionization constant, Ka: (Formula: see text). The concentration of water is assumed to be constant and unaffected by the other components and is omitted from the Kox equation. The value of Kox was estimated from in vitro data to be 3.7 X 10(3) M-1 (S.D. = 0.8 X 10(3) M-1, n = 8). Using this value for Kox and observations of salivary concentrations of SCN- and HOSCN + OSCN- from several previous reports, the equilibrium concentrations of H2O2 in whole saliva were calculated to range from 8 to 13 microM. This range is consistent with reported estimates of 10 microM as the hydrogen peroxide tolerance limit for human cells.

The role of H2O2 and the lactoperoxidase-SCN(-)-H2O2 system on the interaction between two bacteria originating from human dental plaque, Streptococcus rattus (mutans) BHT and Streptococcus mitior LPA-1, grown on human teeth in an artificial mouth

Teeth were inoculated with either the organisms separately or with a freshly-prepared mixture of both. The apparatus was swept with 5 per cent (v/v) CO2 in either air or N2, and incubated for 90 h. A nutrient supplement containing 1 per cent (w/v) glucose was supplied for 1 h in every 6 h. Both organisms achieved similar numbers when grown aerobically in pure culture, yet in mixed culture there was pronounced inhibition of BHT (p less than 0.001). When the synthetic saliva was supplemented with catalase the strain BHT count in mixed culture was much higher (p less than 0.001). It was concluded, therefore, that the strain LPA-1 produced inhibitory levels of hydrogen peroxide (H2O2) on the tooth surface under aerobic conditions. This was supported by finding that a lower viable count of LPA-1 in pure culture was attained when lactoperoxidase (LPO) was included in the saliva (p less than 0.005), as all components of the LPO-SCN-H2O2 system were presumably present. With the N2-CO2 mixture, conditions were not strictly anaerobic and both catalase and LPO increased all viable counts. Under these conditions, therefore, when H2O2 was limiting, LPO protected bacteria against its bactericidal effect.