Theta-burst rTMS in schizophrenia to ameliorate negative and cognitive symptoms: study protocol for a double-blind, sham-controlled, randomized clinical trial

BACKGROUND

Treatment effects of conventional approaches with antipsychotics or psychosocial interventions are limited when it comes to reducing negative and cognitive symptoms in schizophrenia. While there is emerging clinical evidence that new, augmented protocols based on theta-burst stimulation can increase rTMS efficacy dramatically in depression, data on similar augmented therapies are limited in schizophrenia. The different patterns of network impairments in subjects may underlie that some but not all patients responded to given stimulation locations.

METHODS

Therefore, we propose an augmented theta-burst stimulation protocol in schizophrenia by stimulating both locations connected to negative symptoms: (1) the left dorsolateral prefrontal cortex (DLPFC), and (2) the vermis of the cerebellum. Ninety subjects with schizophrenia presenting negative symptoms and aging between 18 and 55 years will be randomized to active and sham stimulation in a 1:1 ratio. The TBS parameters we adopted follow the standard TBS protocols, with 3-pulse 50-Hz bursts given every 200 ms (at 5 Hz) and an intensity of 100% active motor threshold. We plan to deliver 1800 stimuli to the left DLPFC and 1800 stimuli to the vermis daily in two 9.5-min blocks for 4 weeks. The primary endpoint is the change in negative symptom severity measured by the Positive and Negative Syndrome Scale (PANSS). Secondary efficacy endpoints are changes in cognitive flexibility, executive functioning, short-term memory, social cognition, and facial emotion recognition. The difference between study groups will be analyzed by a linear mixed model analysis with the difference relative to baseline in efficacy variables as the dependent variable and treatment group, visit, and treatment-by-visit interaction as independent variables. The safety outcome is the number of serious adverse events.

DISCUSSION

This is a double-blind, sham-controlled, randomized medical device study to assess the efficacy and safety of an augmented theta-burst rTMS treatment in schizophrenia. We hypothesize that social cognition and negative symptoms of patients on active therapy will improve significantly compared to patients on sham treatment.

TRIAL REGISTRATION

The study protocol is registered at "ClinicalTrials.gov" with the following ID: NCT05100888. All items from the World Health Organization Trial Registration Data Set are registered. Initial release: 10/19/2021.

Low Functional network integrity in cognitively unimpaired and MCI subjects with depressive symptoms: results from a multi-center fMRI study

Evidence suggests that depressive symptomatology is a consequence of network dysfunction rather than lesion pathology. We studied whole-brain functional connectivity using a Minimum Spanning Tree as a graph-theoretical approach. Furthermore, we examined functional connectivity in the Default Mode Network, the Frontolimbic Network (FLN), the Salience Network, and the Cognitive Control Network. All 183 elderly subjects underwent a comprehensive neuropsychological evaluation and a 3 Tesla brain MRI scan. To assess the potential presence of depressive symptoms, the 13-item version of the Beck Depression Inventory (BDI) or the Geriatric Depression Scale (GDS) was utilized. Participants were assigned into three groups based on their cognitive status: amnestic mild cognitive impairment (MCI), non-amnestic MCI, and healthy controls. Regarding affective symptoms, subjects were categorized into depressed and non-depressed groups. An increased mean eccentricity and network diameter were found in patients with depressive symptoms relative to non-depressed ones, and both measures showed correlations with depressive symptom severity. In patients with depressive symptoms, a functional hypoconnectivity was detected between the Anterior Cingulate Cortex (ACC) and the right amygdala in the FLN, which impairment correlated with depressive symptom severity. While no structural difference was found in subjects with depressive symptoms, the volume of the hippocampus and the thickness of the precuneus and the entorhinal cortex were decreased in subjects with MCI, especially in amnestic MCI. The increase in eccentricity and diameter indicates a more path-like functional network configuration that may lead to an impaired functional integration in depression, a possible cause of depressive symptomatology in the elderly.

Psychometric validation of the Reported and Intended Behaviour Scale (RIBS) in Hungary with a particular focus on 'Don't know' responses and further scoring recommendations

AIMS

Reported and Intended Behaviour Scale (RIBS) was designed to measure mental health stigma-related behaviors in the general public. We aimed to examine its psychometric properties and validate the scale in a Hungarian non-clinical community sample. The secondary aim of this study was to assess the appropriateness of the current scoring recommendations of 'Don't know' responses being coded as neutral, which had never been investigated before. In addition, we provide an overview of the results of already existing studies on the scale.

METHODS

Hungarian participants completed the RIBS within this cross-sectional online survey study and were considered non-clinical individuals based on a cut-off point of the Global Severity Index T score of 63 on the Symptom Checklist-90-Revised. Confirmatory factor analysis, reliability measures, and comparative analyses were performed.

RESULTS

Of the n = 5,701, n = 5,141 participants were included in the analysis. The mean age was 27.8 ± 11.1 years, and 89.2% (n = 4,587) of the sample were female. The unidimensional structure was supported by good model fit indices (RMSEA = 0.031, CFI = 0.999, TLI = 0.996, and WRMR = 0.006). Internal consistency of the RIBS and its test-retest reliability with a 5-month follow-up period were found to be good (Cronbach's alpha = 0.88 and ICC = 0.838). We found statistically significant differences between the total scores when the 'Don't know' responders were excluded from the sample or when they were coded as neutral as recommended by the scale authors (16 (IQR:13-18) vs. 15 (IQR:13-18) p < 0.0001). There were also statistically significant differences between 'Neither agree nor disagree' and 'Don't know' participants in several aspects of lived experiences of mental health problems.

CONCLUSIONS

The RIBS demonstrated good psychometric properties and can be transferred to the Hungarian context. It will be a valuable tool in assessing stigmatizing behavior and testing the efficacy of antistigma programs. Our results suggest that 'Neither agree nor disagree' and 'Don't know' responses bear different meanings, and coding should account for this.

Virtual reality-based theory of mind intervention in schizophrenia: Preliminary efficacy results

BACKGROUND

In recent years, a growing body of literature has supported the core nature and functional significance of Theory of Mind (ToM) deficit in schizophrenia. These findings have made ToM impairment a promising treatment target. However, despite the encouraging results, its complexity makes it difficult to develop new interventions and even to understand the exact nature and scope of the deficit. Yet, further investigation has suggested that using modern technology and multilevel assessment may help solve the problem.

METHODS

Virtual Reality-based Theory of Mind Intervention (VR-ToMIS) is a recently developed structured method using the combination of cognitive and behavioral therapeutic techniques and the advantages of Virtual Reality (VR) technology. A controlled study with a three-month follow-up was conducted with 42 patients (suffering from schizophrenia or schizo-affective disorder) randomly assigned to either an experimental (VR-ToMIS) or control group (passive-VR). Repeated two-way factorial analysis of covariance was used to evaluate the effects of VR-ToMIS on symptoms, neuro- and social cognition, pragmatic skills, and quality of life when the effect of IQ was controlled.

RESULTS

Patients participating in VR-ToMIS showed significant improvements in all types of ToM tasks (except for hyper-ToM task, based on the results of Cartoon test, Faux pas test and and Baron-Cohen Minds in the Eyes Test) compared to the control group with moderate to large effect sizes. In the case of negative and cognitive symptoms, significant between-group differences were also supported. Improvement was moderated by IQ in the case of higher-order ToM, manner, and relevance implicatures. Results were proved to be sustainable three months after the treatment.

CONCLUSION

Although the presented results are considered preliminary, they support the potential of the integration of modern technology and traditional methods for future interventions.

Regrouping scalets: Psychometric properties of the theory of mind picture stories task in a schizophrenic sample

Theory of mind is one of the most intensively studied phenomena in the development of schizophrenic symptoms and impairments in social adjustment. Complex theory of mind processing requires both visual and verbal aspects of the social-perceptual and social-cognitive components of mind reading. Reliable assessment methods are considered essential for the proper conduct of research. The current study aims at investigating the psychometric properties of the Theory of Mind Picture Stories Task (ToM PST). Forty-seven patients with schizophrenia were enrolled in the study from three sites. Data from ToM PST were used for computing the consistency, reliability, and internal and construct validity of the test.Our preliminary findings showed less appropriate consistency. Therefore, we attempted to carry out structural changes on the task while preserving its scales and subscales, which measure crucial factors of ToM. The newly structured task has four scales. They show proper consistency (Sequencing: Cronbach's α = 0.70, Theory of a Single Person's Mind: α = 0.74, Switching Between Minds: α = 0.70, Comprehension of Misleading Behaviour: α = 0.67, Total: α = 0.80) with appropriate internal and construct validity, a moderate test-retest reliability over a four-month-course, and a proper inter-rater reliability.

The Development of a Complex FEP Program at Semmelweis University

Introduction First episode psychosis (FEP) programs target the first 3-5 years after the first manifestation of a psychotic episode. Although follow-up results after 10-15 years are mixed, reported results of the first 5-10 years are promising in improving relapse prevention, functional outcomes and reducing mental health care costs, compared to treatment as usual. Objectives Our objective was to develop the first complex FEP program in Hungary. Methods Male and female inpatients, (age:17-40years), hospitalized due to a first psychotic episode and consenting to participate, were included, since 2019 October. Drug induced psychosis and organic background in the etiology of the psychotic episode were excluded. Duration of the program is 2-3 years, based on the individual needs of the patients. The program provides detailed clinical and neuropsychological examinations, MRI, pharmacotherapy, various psychosocial interventions, and support group for relatives. Results Twenty-eight patients [15 male,13 female, mean age=22,4 (18-40)years] were included. The program has been repeatedly limited by COVID-19 pandemic. Psychiatric control, pharmacotherapy, psychoeducation and supportive therapy, however could be continously provided via telepsychiatry, even during the lockdown. During the first 2 years, 90% of the patients remained in treatment, showed good compliance with pharmacotherapy; 10% of the patients were rehospitalized due to relapse. In the presentation, besides clinical experiences, preliminary clinical outcome data will also be presented. Conclusions The first complex FEP program in Hungary, although limited repeatedly by the pandemic, show promising clinical results with low relapse rates and high level of adherence to therapy in the first 2 years after a first psychotic episode.

Efficacy of metacognitive training on symptom severity, neurocognition and social cognition in patients with schizophrenia: A single-blind randomized controlled trial

Over the past decades, a number of complementary treatments for schizophrenia have emerged. One of these is metacognitive training (MCT), which combines the principles of cognitive‐behavioral therapies, cognitive remediation, and psychoeducation into a hybrid approach placing emphasis on increasing metacognitive awareness. The aim of our study was to investigate the efficacy of MCT on symptom severity, and neurocognitive and social cognitive functioning in schizophrenia; also, attention was paid to the assessment of subjective acceptability. Forty‐six patients diagnosed with schizophrenia were included in our single‐blind randomized controlled trial, who were assigned to the intervention or control group. The intervention group was provided standard MCT, while the control group received treatment as usual. We assessed symptom severity and cognitive functions before and after the training, as well as after a 6‐month follow‐up period. Compared to the control group, the intervention group showed improvement in overall symptom severity, and positive and disorganized symptoms. Training participans showed further improvement at the follow‐up assessment. Regarding neurocognitive functions, improvement in visuospatial functions was observed between pre‐ and post‐intervention assessments compared to the control group. Patients showed excellent adherence, and evaluated the training as useful and interesting. In line with the results of previous studies, our results demonstrate the efficacy of MCT on symptom severity in schizophrenia. Improvements in cognitive functions that are closely related to the onset and prevalence of symptoms of schizophrenia were also found.

Verbal manifestations of metacognitive and social cognitive operations in patients with schizophrenia who received metacognitive training

The study investigates with inductive content analysis the verbal manifestations of schizophrenia patients, their utterances within the theory of mind modules of Metacognitive Training. Participants were recruited via psychiatrists’ verbal referrals. Four small groups were formed, two of which consented to the audio recording of their sessions. Only the sessions of these two groups of five and four patients respectively were investigated. As two participants dropped out, the verbalisations of seven participants were eventually analysed. All patients had schizophrenia diagnosis (mean age: 43 years, male: two, female: five). The verbal contents were transcribed, then two independent coders did the categorisation of the content; investigator triangulation ensured the reliability and validity of the study. As a result, a five-level hierarchy of cognitive operations was revealed in a bottom-up way. Patients attempted to interpret not only facial expressions but expressive movements, too, during emotion recognition. When deducing the state of others, patients sought contextual information; moreover, the burden of the illness and stigmatisation became easy to share. No signs of awareness of the consequences of the inferred states were found regarding future adjustment. Our hierarchical structure was consistent with related literature, and the specificities of cognitive operations of participants were also revealed.

[What makes someone a troll? The psychology of trolling: Systematic literature review]

BACKGROUND

The World Wide Web along with online social media has significantly changed the dynamics of communication. Information is easier and faster to access, but at the same time the relevance of the content often remains questionable, often confronting users with half-truths and untruths. Information consumption patterns have also changed a lot, allowing more room for the emergence of deviant, provocative behaviors through anonymity. The latter form of behavior can have different effects depending on its intensity and content, including, the polarization of opinions or the negative influence on users 'psychological wellbeing'. In our current article the literature on the pheno menon known as trolling in Internet slang was reviewed in order to better understand its nature and its possible effects.

METHOD

Our systematic literature review was based on a computer search of the PubMed and ScienceDirect databases framed by the PRISMA guideline. The following keywords were used: "Internet" OR "Facebook" OR "Twitter" OR "Instagram" AND "troll" OR "trolling".

RESULT

Based on the mentioned methon, a total number of 4575 articles were identified. Based on the inclusion and exclusion criteria 24 articles were included in the final sample. The results and experiences of the published papers were presented according to the subgroups formed on the basis of the purpose of the studies.

CONCLUSION

Included articles focused primarily on understanding the motivation of trolling behavior and their impact on online behavior. However, the possible impact of trolls on individuals was left out of focus, leaving many open questions behind.

Case Report: Feasibility of a Novel Virtual Reality-Based Intervention for Patients With Schizophrenia

Schizophrenia is a severe and disabling mental illness, associated with persistent difficulties in social functioning. While gaining and retaining a job or staying socially integrated can be very difficult for the patients, the treatment of poor functionality remains challenging with limited options in pharmacotherapy. To address the limitations of medical treatment, several interesting and innovative approaches have been introduced in the field of psychotherapy. Recent approaches incorporate modern technology as well, such as virtual reality. A potential therapeutic benefit of virtual reality is particularly significant when an interpersonal dimension of the problem needs to be addressed. One example is a Virtual Reality based Theory of Mind Intervention (VR-ToMIS), a novel method, which enables patients to practice complex social interactions without the burden of real-life consequences. Our paper presents a case report showing promising results of VR-ToMIS. Ms. Smith is a 50- year-old patient who has been suffering from schizophrenia for 20 years. Although in her case there was no problem with compliance throughout the years, she had severe problems regarding social functionality. With VR-ToMIS, she improved in ToM and communicative-pragmatic skills. The effects of the intervention went beyond the increased scores of the tests. Before the intervention there was a risk of the patient becoming unemployed as she was unable to follow the main principles of communicative exchange. Usually, her contribution was more informative than was required. After the intervention her communication became more balanced and she could retain her job. This case suggests that VR-ToMIS may be a promising tool for treating social disfunction in schizophrenia.

[Virtual Reality in psychiatry and psychotherapy]

The use of virtual reality (VR) technology in psychiatry and psychotherapy has spread continiously over the last two decades. Researches has mainly focused on the VR-based therapy of anxiety disorders, but encouraging results have also been published in the field of diagnosis and therapy of eating disorders, addictions, autism, and ADHD. There have been fewer reports on the therapy of schizophrenia yet. In these cases VR interventions cover a wide range of symptoms. VR based interventions have already been developed for cognitive and social abilities that are more difficult to alleviate by medication. Among positive symptoms, the developed methods mainly focus on auditory hallucinations and delusions. In general, the current results confirm the effectiveness of VR-based therapeutic interventions and justify the need for further research. Research and therapy on this fieed at the VR Laboratory of the Department of Psychi - atry and Psychotherapy, Semmelweis University also support literature data. However, the widespread use of VRbased interventions requires further well-designed, blinded, randomized, long-term follow-up studies.

A novel virtual reality-based theory of mind intervention for outpatients with schizophrenia: A proof-of-concept pilot study

Schizophrenia is a severe and highly disabling mental illness. Although several pharmacological solutions are available to alleviate symptoms of schizophrenia, they do not seem to provide solution for accompanying social dysfunctions. To handle this unmet clinical need, many innovative interventions have been developed recently. Considering the promising results on this field and the development trend, characterized by the growing proportion of included interactive technology, our research team developed a novel virtual reality (VR)-based targeted theory of mind (ToM) intervention (VR-ToMIS) for stable outpatients with schizophrenia. VR-ToMIS is a nine-session long structured and individualized method that uses cognitive and behavioural therapeutic techniques in an immersive VR environment. Our study was a randomized, controlled pilot study. Twenty-one patients have been recruited and randomly allocated to either VR-ToMIS or passive VR condition. Patients assigned to passive VR condition could use the same VR software as the VR-ToMIS group, but without any interventions. Effects on psychiatric symptoms, neurocognitive and social cognitive functions, pragmatic language skills and quality of life were evaluated by using analysis of covariance. According to our results, VR-ToMIS was associated with improvements in negative symptoms, in one neurocognitive field (immediate memory), ToM and pragmatic language skills, but no significant change in quality of life scores was detected. Significant changes in VR-ToMIS group were associated with moderate to large therapeutic effects (η_p ²  = .24-.46, φ = .55-.67). On the background of the presented pilot results, VR-ToMIS is concluded to be feasible and tolerable.

[The concept and characteristics of metacognition and its role in schizophrenia]

Schizophrenia research in the last decades led to rapid development of our knowledge regarding the cogni - tive deficits in the disease. Presence of neurocognitive and social cognitive deficits in schizophrenia is widely confirmed by empirical studies. Metacognition is one of the most recent and relatively less studied field of schizophrenia. Our lite rature review aims to introduce the concept and characteristics of metacognition. Then we overview the relation - ship between schizophrenia associated neurocognitive and social cognitive impairments and metacognitive deficits. Associations between the metacognitive deficits and the symptomatology will also be discussed. Finally, a method for the treatment of metacognitive deficits in schizophrenia will be suggested. The results of the overviewed studies sup - port, that the umbrella term of metacognition encompassing the neurocognitive and social cognitive deficits, may provide a comprehensive model to better understand how cognitive deficits contribute to the development and main - tanance of symptoms, and schizophrenia-associated serious social dysfunctions.

[Treatment of Theory of Mind deficits in schizophrenia by using Virtual Reality, the VR-ToMIS training (Virtual Reality based Theory of Mind Intervention in Schizophrenia)]

Rapid development in information technology has been observed recently and has led to valuable developments also in healthcare. 3D-bio-printing or the virtual simulations that help the acquisition of anatomical and pathological knowledge and testing the acquired knowledge are just some of the examples. This progress can be recognized also in psychiatry. One of the most spectacular ways of using these technologies in psychiatry might be the therapeutic techniques associated with Virtual Reality (VR) simulations, which are currently available for anxiety disorders, eating disorders and addictions. A research team of the Psychiatric and Psychotherapeutic Department of the Semmelweis University has developed a Virtual Reality-based intervention that fits in with this perspective. The intervention mainly aims at Theory of Mind deficit and pragmatic language impairment in schizophrenia. In this article the current status of our research team's work will be presented. The article reviews the literature that provides the basis for the development, leads the reader through the main stages of the development process, and finally the program itself will be introduced. Process and mechanism of change associated with the intervention and the potential risks of the use of VR will also be discussed.

Interventions for the treatment of theory of mind deficits in schizophrenia: Systematic literature review

Theory of Mind (ToM) plays a central role in regulating social interactions and its impairment is consistently reported in schizophrenia. Regarding schizophrenia, ToM is usually discussed as a sub-domain of social cognition. Since social cognitive deficits have drawn the attention of researchers, a variety of novel treatment techniques and approaches targeting social cognitive deficits have been developed. Encouraging results have repeatedly been reported on the modifiability of social cognitive impairment through these techniques. However, emotional perception seems to be over-represented in these approaches at the expense of other areas, such as ToM. This article presents a systematic review on the social cognitive interventions of the last 10 years, which focused on the remediation of ToM or used techniques primarily focusing on one or more social cognitive domains other than ToM, but with hypothetical effects on it. The aim of our systematic review was to compare these intervention techniques in order to see how effective they are in the remediation of ToM, and to find the best techniques to ameliorate ToM deficits in schizophrenia. According to our findings targeted ToM intervention produced more improvement in ToM tasks, while data regarding non-ToM interventions showed contradictory results with limited effects on ToM.

[Treatment of metacognitive impairments in schizophrenia - The Metacognitive Training]

In the recent years plenty of therapeutic treatment methods have been developed, aimed at neurocognitive impairments in schizophrenia. These trainingprograms can hold up promising results in the improvement of neurocognitive functions. Nevertheless the generalisation on the daily life is not perspicuous. A reason for it might be the supposition, that further factors such as metacognition and social cognition may play a mediator role between neurocognition and functional outcomes. As a result, many socialcognitive remediation methods and programs have emerged targeting the impairment of deficits both in the field of neuro- and social cognition and deficits of metacognition. We review the specific impairments in schizophrenia (e.g. deficits of Theory of Mind, disorder of emotional perception, specific cognitive biases or impairment of metamemory), the construction and speciality of the Metacognitive Training, and the findings of studies aimed at the efficacy of the method. In addition to the socialcognitive remediation, the goal of Metacognitive Training is the correction of the cognitive biases playing an important role in the emergence and subsistence of delusions.

Novel, cell-penetrating molecular transporters with flexible backbones and permanently charged side-chains

Various cell-penetrating peptides have been discovered recently that can translocate across plasma membranes and can even carry large cargo molecules into the cells. Because under physiological conditions most of these peptides carry considerable positive charges due to the presence of basic amino acids such as arginine, we decided to investigate whether molecular transporters composed of permanently charged side-chains also possess such cell penetrating ability. Arginine-rich oligomers that have a backbone with increased flexibility due to incorporation of non-α-amino acids (ε-aminocaproic acid) have been found to be effective molecular transporters. Here, we report the preparation of analogue structures by replacing the arginine residues with the quaternary form of a novel redox amino acid (Nys+) that contain a trigonelline moiety; it has already been shown possible to replace the original basic amino acid side-chain of neuropeptides without significant activity-loss due to the sufficiently close steric and electronic analogy between the new Nys+ and the original side-chains (in their protonated form, e.g., Arg+, Lys+). A nonamer analogue showed transporter activity resulting in increased cellular uptake in human carcinoma (HeLa) cells.

Monitoring in situ catalytically active states of Ru catalysts for different methanol oxidation pathways

One of the prerequisites for the detailed understanding of heterogeneous catalysis is the identification of the dynamic response of the catalyst surface under variable reaction conditions. The present study of methanol oxidation on different model Ru pre-catalysts, performed approaching the realistic catalytic reaction conditions, provides direct evidence of the significant effect of reactants' chemical potentials and temperature on the catalyst surface composition and the corresponding catalytic activity and selectivity. The experiments were carried out for three regimes of oxygen potentials in the 10(-1) mbar pressure range, combining in situ analysis of the catalyst surface by synchrotron-based photoelectron core level spectroscopy with simultaneous monitoring of the products released in the gas phase by mass spectroscopy. Metallic Ru with adsorbed oxygen and transient 'surface oxide', RuO(x), with varying x have been identified as the catalytically active states under specific reaction conditions, favouring partial or full oxidation pathways. It has been shown that the composition of catalytically active steady states, exhibiting different activity and selectivity, evolves under the reaction conditions, independent of the crystallographic orientation and the initial pre-catalyst chemical state, metallic Ru or RuO(2).

The effects of parasite-derived immune-suppressive factors on the cellular innate immune and autoimmune responses of Drosophila melanogaster

Immune-suppressive factors (ISFs) introduced into larvae of Drosophila melanogaster during infection by virulent endoparasitic wasps effectively block the innate immune response mediated by blood cells (hemocytes) but have little influence on the autoimmune response made by a tumor strain in which the blood cells manifest a similar response but instead target and destroy endogenous tissues. Quantitative hemocyte analyses indicate that ISFs interfere with the immune effector responses downstream of nonself recognition, hemocyte activation and differentiation, because these responses were manifested by tumor hosts, in which the parasitoids developed. The data suggest that once activated to encapsulate aberrant tissues, the target specificity of the autoimmune-activated hemocytes, and the genetic program underlying tumor formation, cannot be blocked by parasitoid-derived ISFs, which effectively inhibit identical hemocyte-mediated responses during parasitization.

Conformational study of linear and cyclic peptides corresponding to the 276-284 epitope region of HSV gD-1

The results of conformational analysis of linear and cyclic peptides from the 276SALLEDPVG(284) sequence of glycoprotein D of Herpes simplex virus are presented. The epitope peptides were synthesized by SPPS and on resin cyclization was applied for preparation of cyclic compounds. Circular dichroism spectroscopy, Fourier-transform infrared spectroscopy and nuclear magnetic resonance (NMR) were used to determine of the solution structure of both linear and cyclic peptides. The results indicated that the cyclopeptides containing the core of the epitope (DPVG) as a part of the cycle have more stable beta-turn structure than the linear peptides or the cyclic analogues, where the core motif is not a part of the cycle. NMR study of H-SALLc(EDPVGK)-NH(2) confirm presence of a type I beta-turn structure which includes the DPVG epitope core.

A novel strategy for the synthesis of omega-functionalized perfluoroalkyl iodides

[reaction: see text] The applicability of telomeric alcohols, H(CF(2)CF(2))(n)()CH(2)OH, for the synthesis of omega-functionalized F-alkylating reagents, I(CF(2)CF(2))(n-1)CH(2)OAc (6, n = 5), is demonstrated. The key steps of this optimized method are the "activation" of the HCF(2)- terminus in a lithiation process yielding olefin 2 [(Z+E)-BuCF=CF(CF(2)CF(2))(4)CH(2)OH, 86%] and a successive ozonation reaction in trifluoroethanol media affording ester 3b [CF(3)CH(2)O(2)C(CF(2)CF(2))(4)CH(2)OH, 93%]. Highly stereospecific ozone cleavage of the (E)-2 isomer was observed in methanol due to the competitive oxidation of the solvent.

The effects of nitric oxide on the oxidations of l-dopa and dopamine mediated by tyrosinase and peroxidase

The effects of nitric oxide (NO) on both tyrosinase/O(2)- and horseradish peroxidase/H(2)O(2)-mediated oxidations of dopamine and its o-dihydric phenol precursor l-dopa were compared with autoxidative processes and quantitatively assessed by oxidative and reductive electrochemical detection systems. In peroxidase/H(2)O(2)/NO-catalyzed reactions, significantly more substrate was oxidized than in the corresponding control incubations lacking NO. In tyrosinase/O(2)/NO-promoted reactions the total amounts of l-dopa and dopamine oxidized were significantly less than the amounts of the substrates oxidized by enzyme alone. These data indicate that the activity of the heme protein peroxidase was enhanced by NO, whereas tyrosinase, a copper-containing monoxygenase, was inhibited. The NO-mediated reduction of tyrosinase/O(2) activity may be attributed to the formation of an inhibitory copper.nitrosyl complex. An oxidized nitrodopamine derivative, considered to be either the quinone or semiquinone of 6-nitrosodopamine, was generated in peroxidase/H(2)O(2)/NO-mediated reactions with dopamine along with two oxidized melanin precursors, dopamine quinone and dopaminechrome. No corresponding nitroso compound was formed in reactions involving l-dopa or in any of the tyrosinase-mediated reactions. The formation of such a noncyclized nitrosodopamine represents an important alternative pathway in catecholamine metabolism, one that by-passes the formation of cytoprotective indole precursors of melanin. The results of this investigation suggest that cellular integrity and function can be adversely affected by NO-promoted oxidations of dopamine and other catechols, reactions that not only accelerate their conversion to reactive quinones but also form potentially cytotoxic noncyclized nitroso derivatives. Reduced levels of dopamine in the brain through NO-enhanced oxidation of the catecholamine will almost certainly be manifested by diminished levels of the dopamine-derived brain pigment neuromelanin.

Ca(2+)-induced changes of surfactin conformation: a FTIR and circular dichroism study

Previous NMR studies on surfactin proposed two gamma or beta-turn-containing conformers while recent CD studies described beta-sheets and alpha-helices in surfactin. Since these data were not obtained in the same conditions, the conformation of surfactin was reinvestigated by FTIR spectroscopy, a diagnostic method for beta-sheets. In trifluoroethanol, the FTIR spectra of surfactin and its diester are compatible with gamma and/or beta-turn(s) and the differences in their CD spectra show the importance of the Glu(1) and Asp(5) COOH groups in stabilizing the lipopeptide conformation. The calcium-induced spectral changes of both lipopeptides suggest a first binding of the divalent ions to the surfactin COOH groups (until calcium-lipopeptide mole ratio reached 1) followed by bulk conformational changes (at higher mole ratios). In Tris buffer at pH 8.5, the FTIR amide I band shape, without the typical 1610-1628 and 1675-1695 cm(-1) bands, ascertains the absence of beta-sheets.

Developmental and immunological aspects of Drosophila-parasitoid relationships

The Drosophila-parasitic wasp (parasitoid) associations involve integrating adaptations of considerable complexity. This review focuses on some of the factors that influence these interactions including host immunity, nutrition and hormonal changes, and parasitoid virulence and mechanisms of immune suppression.

Spectroscopic evidence of beta-turn in N-glycated peptidomimetics related to leucine-enkephalin

The conformational differences caused by N-glycation of the amide bond in endogenous opioid pentapeptide leucine-enkephalin (Tyr-Gly-Gly-Phe-Leu) have been explored in solution using FTIR spectroscopy, NMR and molecular modelling. The compounds studied include protected and unprotected enkephalin analogues N-alkylated at the second (Gly2) amino acid residue with a 6-deoxy-D-galactose moiety (1-3). Comparison of the amide I component bands in the FTIR spectra, measured in trifluoroethanol (TFE), CHCl3 and DMSO, revealed significant differences in the intensity as well as shifts in component band frequencies for glycopeptides 1-3. We found that only the FTIR spectrum of the fully protected compound 1 indicated the presence of a higher population of beta-turns, while the spectra of the partially protected and unprotected glycopeptides 2 and 3 reflected the dominance of unordered or open structures, with some low population of turns. The observed NOE connectivities in CDCl3 for both isomers of the fully protected compound 1, the all-trans one and another with Tyr1-Gly2 peptide bond in cis conformation, indicate the presence of a beta-like turn conformation. Molecular dynamics simulations of the glycopeptide 1 obtained by unconstrained energy minimization of trans- and cis-1 shows that one of trans form conformations is consistent with beta-turn whereas cis isomer has revealed less-compact turn.

Conformational consequences of coupling bullous pemphigoid antigenic peptides to glutathione-S-transferase and their diagnostic significance

Recombinant epitopic peptides BP1 and BP2 representing the Bullous pemphigoid autoantigens of BP230 and BP180 bound to the fusion partner glutathione-S-transferase (pGEX-4T-2, Pharmacia) have been previously shown to increase the efficacy of diagnosis of the disease. Using glutathione-S-transferase-bound monomer peptides, the sensitivity of the immunological reaction exceeded that of the free synthetic epitopes and was further increased with the number of epitopic blocks in the multimer fusion products. This has been explained by the avidity effect of the fusion partner dimer formation and the high ligand affinity due to the tandem repetitions of epitopic sequences. However, a beneficial conformation of the bound epitopic peptides might also contribute to the above phenomenon. Circular dichroism (CD) and Fourier transform infrared (FTIR) absorption spectroscopic studies revealed the importance of glutathione-S-transferase to induce and stabilize ordered secondary structures of the epitopic peptides. The free monomer and multimer peptides in aqueous buffer were present as a mixture of unordered and beta-sheet conformation, while binding them to the fusion partner the proportion of ordered secondary structures increased in parallel with the number of antigenic epitopes. The most prominent changes in the conformational state of the monomers in the fusion form were the increase of alpha-helical and beta-sheet and the decrease of unordered conformation, while in the case of oligomeric peptides the adoption of a helical conformation was accompanied by the decrease of beta-sheet structure. An outstanding alpha-helix content (46%) was detected in the case of the trimeric BP1 in its recombinant fusion form.

Nitric oxide involvement in Drosophila immunity

The augmented production of nitric oxide (NO) was observed during the hemocyte-mediated melanotic encapsulation responses of Drosophila melanogaster and D. teissieri. When introduced into the hemocoel of D. melanogaster larvae, NO activated the gene encoding the antimicrobial peptide Diptericin. These observations, together with previous studies documenting the production of superoxide anion (O(*-)(2)) and H(2)O(2) in immune-challenged Drosophila, provide evidence that reactive intermediates of both oxygen (ROI) and nitrogen (RNI) constitute a part of the cytotoxic arsenal employed by Drosophila in defense against both microbial pathogens and eukaryotic parasites. These ROI and RNI appear to represent an evolutionarily conserved innate immune response that is mediated by regulatory proteins that are homologous to those of mammalian species.

Effect of D-amino acid substitution in a mucin 2 epitope on mucin-specific monoclonal antibody recognition

We have studied the influence of D-amino acid substitution in the flanking region on the antibody recognition of the 19TGTQ22 epitope core in the tandem repeat of mucin 2 (MUC2) glycoprotein. Analogue peptides corresponding to the optimal epitope sequence (16PTPTGTQ22) have been prepared by the replacement of single or multiple L-amino acid residues at the N-terminal part of the molecule. According to previous studies, this portion of the all-L 16PTPTGTQ22 peptide possesses a beta-turn secondary structure important for efficient monoclonal antibody interaction. The binding properties of sequentially modified peptides (pTPTGTQ, ptPTGTQ, ptpTGTQ, and ptptGTQ) have been analyzed by a MUC2 glycoprotein specific monoclonal antibody (MAb 996) using RIA inhibition assay and characterized by IC50 values. At the same time, we have investigated the secondary structure of the compounds by circular dichroism and Fourier transform infrared spectroscopy in solution. Our data showed that the presence of D-amino acid residue(s) at position(s) 16P, 16PT17, or 16PTP18 resulted in gradually decreasing antibody binding, but the replacement of the L-Thr at position 19 almost abolished activity. Parallel with this reduction, changes in the conformer population have been detected. The propensity of the pTPTGTQ peptide to adopt folded, most probably beta-turn, structure in water can be in correlation with its essentially preserved antibody recognition. After further substitution, the peptide still contained beta- and/or gamma-turn folded secondary structural elements. The conformation of peptide ptptGTQ could be characterized mostly by semiextended (polyproline II) and probably classic gamma-turn conformers built up from D residues.

Iron, metalloenzymes and cytotoxic reactions

There is considerable evidence implicating iron and other redox-active transition metals as progenitors of reactive intermediates of oxygen (ROI), molecules which lead to oxidative stress and contribute to various neurodegenerative processes. An important aspect of such metal-mediated damage to biomolecules is the site-specific nature of such pathological activity. Iron sequestering molecules, such as ferritin, transferrin, lactotransferrin, melanotransferrin, hemosiderin and heme can serve as cytoprotectants against metal-mediated oxidant damage. Metalloenzymes also constitute an important group of iron sequestering molecules. Metalloenzyme-catalyzed reactions in which metal ions at the enzyme active site undergo redox-cycling in association with O2 are site-specific in nature, and may represent a potential source of ROI-mediated damage to biomolecules. Dysregulation of brain iron and alterations in the levels of metalloenzymes involved in reactions with O2 derived molecules can contribute to neuronal damage. Iron may increase the cytotoxicity of neuronal dopamine by increasing its rate of oxidation to quinones and semiquinones, thereby reducing the level of this neurotransmitter. Interestingly, dopamine also may play an important role in the maintenance of transition-metal homeostasis as an iron chelator, since it can form both catecholate and hydroxamate groups, molecules employed by many microorganisms to sequester iron.

Contrasting effects of catecholic and O-methylated tetrahydroisoquinolines on hydroxyl radical production

Tetrahydroisoquinolines (TIQs) are intraneuronal, catecholamine-derived alkaloids that have been implicated in the etiology of Parkinson's disease and in alcohol related disorders. The in vitro production of the cytotoxic hydroxyl radical (*OH) was recorded during the autoxidation of salsolinol (SAL) and salsolinol-1-carboxylic acid (SAL-1C), but not when these two catecholic TIQs were oxidized by tyrosinase. Significantly higher levels of the radical were produced when these catecholic TIQs were incubated with *OH generating complexes, or with chelated iron. In contrast, mono-O-methylated TIQs such as salsoline (SLN) and salsoline-1-carboxylic acid (SLN-1C) did not generate *OH during autoxidation or when incubated with chelated iron or tyrosinase. Radical production by *OH-generating complexes was reduced in the presence of O-methylated TIQs. The neurotoxicity of TIQs may result from their propensity to autoxidize and generate reactive quinoids and ensuing oxygen radicals. The functional significance of the replacement of a hydroxyl group attached to C-7 of SAL or SAL-1C with a methoxyl group remains to be determined. This single structural modification may prevent mono-O-methylated TIQs from participating in catalytic redox cycling reactions that would otherwise augment *OH production. If true, then O-methylation and other cellular mechanisms that circumvent the autoxidation of catecholamine-derived TIQs may reduce the likelihood of these substances forming cytotoxic quinoids and influencing endogenous *OH-generating reactions.

Effect of solution conformation on antibody recognition of a protein core epitope from gastrointestinal mucin (MUC2)

Antibody recognition of the tandem repeat unit of MUC2 glycoprotein was investigated. To clarify the role of secondary structure, the immunoreactivity and conformation of overlapping and truncated peptides were investigated. For this several MUC2 peptides have been synthesized and their secondary structure has been analyzed by circular dichroism and Fourier transform infrared spectroscopical methods. For the binding studies a MUC2 mucin protein core-specific monoclonal antibody was used in competition RIA experiments. The minimal size peptide functioning as epitope was peptide 18PTGTQ22. Within the immunodominant 13TPTPTPTGTQTPTT26 region we found that all peptides recognized by the 996 monoclonal antibody adopted beta-turns secondary structure. Peptides 15TPTPTGTQ22 and 16PTPTGTQ22, containing the most prominent beta-turn(s), had the strongest immunoreactivity. It was also observed that peptides with Pro on their N-termini (16PTPTGTQ22, 18PTGTQ22) adopt a different type of beta-turn in TFE than peptides with Thr at their N-terminal. Based on the antibody binding, molecular dynamics calculations, and secondary structure analysis, we propose a model for the epitope structure of the MUC2 mucin tandem repeat.

Hydrogen peroxide production in immune-reactive Drosophila melanogaster

Upon infection with the wasp parasitoid Leptopilina boulardi, the blood cells or hemocytes of Drosophila melanogaster larvae become activated and manifest a type of communal phagocytosis wherein eggs of the parasitoid are enveloped by multicellular, melanotic capsules. Hemocytes engaged in this collaborative response generate reactive oxygen intermediates (ROI). These molecules, together with melanogenic intermediates, are believed to destroy intrahemocoelic parasites. Cellular uptake of 2',7'-dichlorofluorescin diacetate (DCF-DA) and the oxidation of its deacetylated form (DCF) to yield the fluorescent product dichlorofluorescein (DC) was used as an intracellular probe for oxidant generation. The selective uptake of the fluorescent probe only by activated plasmatocytes from immune-reactive larvae identified these hemocytes as the source of ROI. Inhibition of DCF oxidation by catalase established hydrogen peroxide (H2O2) as 1 of the principal oxidants generated during melanotic encapsulation. A sensitive spectrometric assay for assessing iron oxidation and complex formation with xylenol orange (FOX assay) also was used to document in vitro-enhanced H2O2-mediated oxidations by hemolymph from immune-competent larvae. Cumulative evidence now establishes both superoxide anion (O2-*) and its dismutation product H2O2 in the cellular encapsulation response of D. melanogaster.

Hydroxyl radical formation via iron-mediated Fenton chemistry is inhibited by methylated catechols

The differing effects of O-methylated catecholamines and their dihydroxyphenyl precursors on the production of *OH were quantified using a previously established specific salicylate hydroxylation assay in conjunction with a sensitive electrochemical detection system. The production of *OH by the Fenton reaction was diminished significantly by O-methylated catecholamines (O-methyldopa, O-methyldopamine, O-methyltyrosine, and N-acetyl-O-methyldopamine), whereas radical production was augmented by dihydroxyphenyls (DOPA, dopamine, and N-acetyldopamine), including those with methylated side chains (N-methyldopamine and alpha-methyldopa). Monohydroxyphenyls such as octopamine, tyramine, tyrosine, and alpha-methyltyrosine had little or no effect on radical production. These data show that a methyl group positioned on the side chain of a catecholamine does not alter its pro-oxidant behavior, while a methyl group positioned on the aromatic ring renders the catecholamine sterically or kinetically unfavorable for coordination with transition metals, thus preventing the promotion of Fenton chemistry. These results highlight the importance of O-methylation in forming catechols that are less reactive than their dihydroxyphenyl precursors. Thus, factors regulating the methylation of brain catecholamines may play a crucial role in mediating neuronal integrity during aging and in the pathogenesis of certain neurodegenerative disorders. Competitive side-chain methylation reactions may sustain or perpetuate some dihydroxyphenyls, creating an oxidatively less favorable environment for cells than would result from compounds formed by O-methylation.

Liposome-induced conformational changes of an epitopic peptide and its palmitoylated derivative of influenza virus hemagglutinin

The conformation of synthetic HA317-329-NH2 representing the major B- and T-cell epitopic region of influenza virus hemagglutinin, its palmitoylated derivative (HA317-329-Thr(Pal)-NH2), and the intersubunit peptide (HA317-341-NH2) comprising also the fusion peptide, were studied in aqueous buffer and in the presence of neutral and negatively charged liposomes. The free peptide is unordered in aqueous solution, even in the presence of liposomes. However, grafting the palmitic acid or the fusion peptide onto the C-terminus of the peptide enables the hydrophilic HA317-329 to adopt folded (turn) and beta-strand structure on the surface of neutral and negatively charged liposomes, respectively. The results emphasize the importance of some kind of anchor for achieving a specific conformation of epitopic peptide HA317-329-NH2 on the surface of liposomes.

The effects of dietary yeast on the cellular immune response of Drosophila melanogaster against the larval parasitoid, Leptopilina boulardi

The role of dietary yeast in Drosophila melanogaster cellular immunity was investigated. Host larvae deprived of yeast immediately after parasitization by the cynipid wasp Leptopilina boulardi encapsulated a significantly lower percentage of the parasitoid's eggs than hosts transferred to a medium with yeast. When the transfers of hosts were made 24 hr after exposure to the parasite, diet had no effect on the immune response that had commenced prior to the transfers. This study demonstrates for the first time the effect of a specific dietary component on the immune responsiveness of Drosophila against a larval parasitoid.

Prolonged oviposition decreases the ability of the parasitoid Leptopilina boulardi to suppress the cellular immune response of its host Drosophila melanogaster

The cellular immune response of Drosophila against metazoan parasites is characterized by the production of melanotic capsules comprised mostly of host blood cells (hemocytes). During the latter part of the ovipositional period of the cynipid wasp parasitoid Leptopilina boulardi, eggs are deposited into host larvae of Drosophila melanogaster that are more susceptible to destruction by melanotic encapsulation than are eggs laid earlier. The increase in parasitoid mortality is attributed to a decline in the wasp's ability to suppress the host immune response. The decrease in active immune suppression is dependent on the reproductive physiology of the wasp, and this correlates with the extent of her prior ovipositional experience and not on her chronological age nor on the number of eggs remaining in the ovarioles. Such females with prior ovipositional experience which lack the ability to immune suppress infect far fewer hosts than females with no prior ovipositional experience. The reluctance of experienced wasps to infect hosts is not due to egg depletion, but instead is attributed to a depletion in immune suppressive substances. Perhaps by ovipositional restraints, retaining eggs that would otherwise become encapsulated reduces selection pressure in host populations for specific immune reactivity.

Hydroxyl radical formation resulting from the interaction of nitric oxide and hydrogen peroxide

The highly reactive and cytotoxic hydroxyl radical (OH) was found by electrochemical detection to be produced in reactions involving hydrogen peroxide (H2O2) and the nitric oxide (NO) donor diethylamine- NO complex. Using aromatic hydroxylation of salicylate as a specific indicator of OH, three salicylate hydroxylation products were identified; catechol, 2,3- and 2,5-dihydroxybenzoic acid. Four additional compounds were detected but not identified. The interactions of H2O2 and NO represent a biologically feasible reaction mechanism that can account for OH-induced damage in cellular environments where transition metal ions are unavailable for participation in the superoxide-mediated Fenton reaction. The ability of the NO/H2O2 complex to generate OH independently of iron or other transition metals provides a new focus for studies concerned with the origin of tissue-specific damage caused by oxygen-derived species.

Conformational effect of phosphorylation on T cell receptor/CD3 zeta-chain sequences

The effect of tyrosine-phosphorylation on the conformation of three tyrosine-based immunoreceptor activation motifs, zeta(69-86), zeta(106-126), and zeta(138-155), located in the T cell receptor/CD3 zeta-chain was investigated. Circular dichroism and Fourier-transform infrared spectroscopy of the nonphosphorylated and phosphorylated fragments gave evidence that phosphorylation can alter the secondary structure of the peptides. The most significant--alpha-helix to beta-sheet--conformational change was observed in the case of the zeta(138-155) peptide sequence which may be relevant to recognition by Src homology 2 (SH2) domains of signaling proteins.

Comparative studies of enhanced iron-mediated production of hydroxyl radical by glutathione, cysteine, ascorbic acid, and selected catechols

A sensitive electrochemical detection system was employed together with a specific salicylate hydroxylation assay to comparatively assess the effects of various substances on the iron-mediated generation of the hydroxyl radical (.OH). Hydroxyl radical production was found to be enhanced significantly by reduced glutathione, cysteine, ascorbic acid, and selected catechols, but not by mannitol, melatonin or tyramine. The data showed that over the range of concentrations examined, the augmented effects were linearly proportional to the amount of added reductant for a given amount of iron in the system. The pro-oxidant activity of thiols and ascorbate reduced and recycled iron providing both hydrogen peroxide (H2O2) and catalytic ferrous ions for augmented .OH production by the Fenton reaction. The enhanced production of .OH by catechols resulted from their oxidation either by molecular oxygen or ferric ions, with the accompanying formation of semiquinones, superoxide anion and H2O2. These data caution against therapeutic applications of thiols and ascorbate for ameliorating oxy-radical-induced tissue damage in environments where free redox-active metal ions may be present to function both as foci for site-specific peroxidative activity, and as catalysts to promote the pro-oxidant properties of certain endogenous reductants, thereby elevating rather than diminishing .OH levels.

Ca(2+)- and Al(3+)-induced conformational transitions of amyloid fragment H-Ile-Ile-Gly-Leu-Met-NH2

The effect of Ca2+ and Al3+ binding on the conformation of the neurotoxic amyloid fragment H-Ile-Ile-Gly-Leu-Met-NH2 [betaA(31-35)NH2] was studied in trifluoroethanol solutions and in the presence of liposomes. Comparative circular dichroism and Fourier-transform infrared spectroscopic studies revealed that the peptide forms a specific 1:1 complex with Ca2+ which coordinates the polar amide carbonyl groups of the peptide backbone. The results suggest the importance of a folded structure in the complexation of Ca2+. On the contrary, the increasing Al3+ concentration causes a gradual shift of the conformational equilibrium toward beta-sheet structure reflecting no specific binding site for Al3+. In the presence of liposomes the peptide adopts a conformation similar to that of the Ca(2+)-peptide complex. The relevance of the stabilization of peptide conformation by Ca2+ and liposome binding to the bioactive conformation of betaA(31-35)NH2 is also discussed.

Effect of Ca2+ on the secondary structure of linear and cyclic collagen sequence analogs

To investigate the role of secondary structure in the substrate specificity of human 72 kDa type IV collagenase, we synthesised linear and cyclic collagen sequence analogs. As Ca2+ plays a crucial role in the enzyme activity, the CD and FTIR spectra of the peptides were also measured in the presence of Ca2+. Most of the linear, but none of the cyclic peptides form stable 1:1 Ca2+ complexes. The cyclic hexapeptides adopt significantly different backbone conformations comprising not only beta-turns but also the less frequent gamma-turns. Consequently, in the cyclopeptides the scissile Gly-Ile(Leu) bond is embedded into a different conformational environment, but in spite of that none of them is a substrate or an inhibitor of the enzyme. The best substrate Ac-Pro-Leu-Gly-Leu-Ala-Gly-D-Lys-OH binds Ca2+, but does not form a stable 1:1 Ca2+ complex, which suggests that instead of a folded structure an extended flexible conformation is preferred by the enzyme.

Hydrogen peroxide generation associated with the oxidations of the eumelanin precursors 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid

The ability of iron chelates to promote hydroxyl radical (.OH) formation from hydrogen peroxide (H2O2) via Fenton chemistry was exploited to detect H2O2 produced during the oxidations of the eumelanin precursors 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). H2O2 generation during the autooxidations of DHI and DHICA was confirmed on the basis of the electrochemical detection of three hydroxylation products of salicylate [2,3 and 2,5-dihydroxybenzoic acid (DHBA) and catechol], which was used as an .OH indicator. The oxidations of both 5,6-dihydroxyindoles were augmented by tyrosinase and peroxidase without the addition of H2O2. The partial inhibitions by catalase of the auto-oxidations and tyrosinase- and peroxidase-mediated oxidations of DHI and DHICA provide additional evidence of an endogenous origin of H2O2 during the final stages of eumelanogenesis. The mechanism proposed for the formation of H2O2 involves the semiquinones of DHI and DHICA in the univalent transfer of electrons to molecular oxygen. The observations described in this study support previous reports suggesting that factors modulating the levels of H2O2 in melanocytes and melanoma cells play critical roles in directing the course of melanogenesis and influencing the potential cytotoxicity of the biosynthetic pathways.