A meta-analysis on first-trimester blood count parameters-is the neutrophil-to-lymphocyte ratio a potentially novel method for first-trimester preeclampsia screening?

Objective: Meta-analysis focusing on the role of first-trimester neutrophil-to-lymphocyte ratio (NLR) in the prediction of preeclampsia. Data sources: PubMed, Scopus, Web of Science, Cochrane Library, and Embase databases were queried from inception up to December 31, 2022. Study eligibility criteria: The study included all types of original research that was conducted in humans and values of NLR were measured during the first trimester, among patients who later developed preeclampsia, compared to the values of control groups. Study appraisal and synthesis methods: Two reviewers independently performed data abstraction and quality appraisal, and disagreements were resolved by consensus and, if necessary, by the opinion of a third reviewer. During the analysis, PRISMA and MOOSE guidelines were followed. All statistical analyses were made with R. Results: For the research on the predictive role of NLR values in the first trimester for preeclampsia, a total of 6 studies were selected for analysis, covering 2,469 patients. The meta-analysis revealed a 95% confidence interval (CI) for the effect size of 0.641 to 1.523, with a prediction interval of 0.027 to 2.137. Conclusion: Based on the analysis, NLR is a promising biochemical marker for future pieces of research that try to find new screening methods for first-trimester preeclampsia. We encourage other researchers to examine NLR's predictive value combined with other markers in preeclampsia screening, this way being able to find new and affordable protocols for first-trimester preeclampsia screening. Systematic review registration: identifier CRD42023392663.

Inositol-Exchange Activity in Human Primordial Placenta.

Human placenta is an intensively growing tissue. Phosphatidylinositol (PI) and its derivatives are part of the signaling pathway in the regulation of trophoblast cell differentiation. There are two different enzymes that take part in the direct PI synthesis: phosphatidylinositol synthase (PIS) and inositol exchange enzyme (IE). The presence of PIS is known in the human placenta, but IE activity has not been documented before. In our study, we describe the physiological properties of the two enzymes in vitro. PIS and IE were studied in different Mn2+ and Mg2+ concentrations that enabled us to separate the individual enzyme activities. Enzyme activity was measured by incorporation of 3[H]inositol in human primordial placenta tissue or microsomes. Optimal PIS activity was achieved between 0.5 and 2.0 mM Mn2+ concentration, but higher concentrations inhibit enzyme activity. In the presence of Mg2+, the enzyme activity increases continuously up to a concentration of 100 mM. PIS was inhibited by nucleoside di- and tri-phosphates. PI production increases between 0.1 and 10 mM Mn2+ concentration. The incorporation of [3H]inositol into PI increased by 57% when adding stabile GTP analog. The described novel pathway of inositol synthesis may provide an additional therapeutic approach of inositol supplementation before and during pregnancy.

Robot-assisted laparoscopy does not have demonstrable advantages over conventional laparoscopy in endometriosis surgery: a systematic review and meta-analysis.

BACKGROUND: Endometriosis is a chronic condition affecting 6-10% of women of reproductive age, with endometriosis-related pain and infertility being the leading symptoms. Currently, the gold standard treatment approach to surgery is conventional laparoscopy (CL); however, the increasing availability of robot-assisted surgery is projected as a competitor of CL. This study aimed to compare the perioperative outcomes of robot-assisted laparoscopy (RAL) and CL in endometriosis surgery. OBJECTIVES: We aimed to compare the effectiveness and safety of these two procedures. METHODS: A systematic search was conducted in three medical databases. Studies investigating different perioperative outcomes of endometriosis-related surgeries were included. Results are presented as odds ratios (OR) or mean differences (MD) with 95% confidence intervals (CI). RESULTS: Our search yielded 2,014 records, of which 13 were eligible for data extraction. No significant differences were detected between the CL and RAL groups in terms of intraoperative complications (OR = 1.07, CI 0.43-2.63), postoperative complications (OR = 1.3, CI 0.73-2.32), number of conversions to open surgery (OR = 1.34, CI 0.76-2.37), length of hospital stays (MD = 0.12, CI 0.33-0.57), blood loss (MD = 16.73, CI 4.18-37.63) or number of rehospitalizations (OR = 0.95, CI 0.13-6.75). In terms of operative times (MD = 28.09 min, CI 11.59-44.59) and operating room times (MD = 51.39 min, CI 15.07-87.72;), the RAL technique remained inferior. CONCLUSION: RAL does not have statistically demonstrable advantages over CL in terms of perioperative outcomes for endometriosis-related surgery.

Predicting Potentially Fatal COVID-19 Disease in Pregnant Patients Using the Neutrophil-to-Lymphocyte Ratio (NLR).

OBJECTIVE: To evaluate the neutrophil-to-lymphocyte ratio (NLR) values' possible predictive role in fatal and severe cases of COVID-19 disease in pregnant women. Design and data collection: A case-control study was conducted with the inclusion of 45 pregnant COVID-19 patients. All the data were obtained from the hospital information system of Semmelweis University by two of the authors. RESULTS: Statistical analyses showed that NLR values were significantly higher in patients with fatal COVID-19 compared to those who survived the disease, with or without mechanical ventilation. The study also assessed whether NLR values measured on the first day of hospitalization or at their peak provided better markers of disease severity. While both the first-day and peak NLR values were evaluated in patients who did not survive the disease, only the peak NLR values had predictive value regarding patient death. CONCLUSION: Based on our results, the peak NLR values appear to be useful markers of COVID-19 severity, with a cut-off value of 18.05. However, the authors suggest and hope that larger sample size studies will be conducted to further validate the findings of their research.

Recent Advances in the Prevention and Screening of Preeclampsia.

Throughout the history of medicine, preeclampsia has remained an enigmatic field of obstetrics. In 2023, despite its prevalence and impact, preeclampsia's exact cause and effective treatment remain elusive; the current options are limited to delivery. The purpose of this review is to summarize the knowledge of the possible novel prophylactic therapies and screening methods for preeclampsia, thereby providing valuable insights for healthcare professionals and researchers. Aspirin and LMWH have already been widely used; meanwhile, calcium, vitamin D, and pravastatin show promise, and endothelin receptor antagonists are being explored. Stress reduction, dietary changes, and lifestyle modifications are also being investigated. Another interesting and fast-growing area is AI- and software-based screening methods. It is also key to find novel biomarkers, which, in some cases, are not only able to predict the development of the disease, but some of them hold promise to be a potential therapeutic target. We conclude that, while a definitive cure for preeclampsia may not be eligible in the near future, it is likely that the assessment and enhancement of preventive methods will lead to the prevention of many cases. However, it is also important to highlight that more additional research is needed in the future to clarify the exact pathophysiology of preeclampsia and to thus identify potential therapeutic targets for more improved treatment methods.

Case report: COVID-19 infection in a pregnant 33-year-old kidney transplant recipient.

Patients facing severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infections with comorbidities, especially patients whose immune system is weakened have higher chances to face severe outcomes. One of the main reasons behind the suppression of the immune system is iatrogenic, in patients who have autoimmune diseases and/or had an organ transplant. Although there are studies that are examining immunocompromised and/or transplanted patients with COVID-19 infection, furthermore there is a limited number of studies available which are dealing with COVID-19 in pregnant women; however, it is unique and is worth reporting when these factors are coexisting. In this study, we present the case of a 33-year-old Caucasian pregnant woman, who had a kidney transplant in 2009 and contracted the SARS-CoV-2 virus on the 26th gestational week, in 2021. After her infection, superimposed preeclampsia was diagnosed and due to the worsening flowmetric parameters, she gave birth to a premature male newborn with cesarean section. Our kidney transplant patient's case highlights how COVID-19 disease can lead to preeclampsia and artificial termination of gestation.

Effect of Pravastatin and Simvastatin on the Reduction of Cytochrome C.

Statins are used to treat hypercholesterolemia, with several pleiotropic effects. Alongside their positive effects (for example, decreasing blood pressure), they can also bring about negative effects/symptoms (such as myopathy). Their main mechanism of action is inducing apoptosis, the key step being the release of cytochrome c from the mitochondria. This can be facilitated by oxidative stress, through which glutathione is oxidized. In this research, glutathione was used as a respiratory substrate to measure the mitochondrial oxygen consumption of rat liver with an O2 electrode. The reduction of cytochrome c was monitored photometrically. Hydrophilic (pravastatin) and lipophilic (simvastatin) statins were used for the measurements. Pravastatin reduces the reduction of cytochrome c and the oxygen consumption of the mitochondria, while simvastatin, on the other hand, increases the reduction of cytochrome c and the mitochondrial oxygen consumption. The results make it seem probable that statins influence the mitochondrial oxygen consumption through cytochrome c. Simvastatin could enhance the oxidizing capacity of free cytochrome c, thereby increasing oxidative stress and thus facilitating apoptosis. The observed effects could further the understanding of the mechanism of action of statins and thereby aid in constructing optimal statin therapy for every patient.

Pravastatin in preeclampsia: A meta-analysis and systematic review.

Objective: To review of the efficacy and safety of pravastatin use for prophylaxis and treatment of preeclampsia. Design: Systematic review and meta-analysis of clinical studies evaluating pravastatin for treatment and/or prophylaxis of preeclampsia. Data collection: Two independent reviewers systematically searched data from PubMed, Scopus, Web of Science, Cochrane, Embase, and clinicaltrials.gov databases, for studies evaluating pravastatin for prevention of pre-eclampsia. Results: Fourteen studies were identified, including 1,570 pregnant women who received either pravastatin or placebo, published between 2003 and 2022. From these studies, 5 studies were identified for inclusion in the meta-analysis to evaluate the role of pravastatin use prior to 20 weeks of gestation, to prevent pre-eclampsia, Pravastatin treatment reduced the incidence of preeclampsia by 61% and premature birth by 45%. Among the newborns, there was a 45% reduction in intrauterine growth retardation (IUGR) in the treated group, as well as a 77% reduction in those receiving neonatal intensive care unit (NICU) admissions. Conclusion: Prophylactic treatment with pravastatin appears to reduce risk of developing pre-eclampsia as well as potentially lowering risk of IUGR, preterm birth, and NICU admission in neonates.

[Effect of pravastatin on tetrahydrobiopterin-sensitive and -resistant NO synthase activity of preeclamptic placentas]. / A pravasztatin hatása tetrahidrobiopterin-érzékeny és -rezisztens praeeclampsiás placenták NO-szintáz-aktivitására.

Introduction: The treatment of preeclampsia, which occurs in 3-8% of pregnancies, is not yet resolved. In preeclampsia, NO synthesis is insufficient, which can contribute to hypertension, proteinuria and abnormal vascularization of the placenta. Decreased NO synthesis in the preeclamptic placenta may also be due to a decrease in the affinity of NO synthase for tetrahydrobiopterin (BH4), resulting in BH4 resistance. In recent years, pravastatin has been shown to prevent preeclampsia in animal models and in human studies. One of the known pleiotropic effects of pravastatin is that it increases NO synthase activity. Aim: Description of the effect of pravastatin on BH4-resistant NO synthase activity in the preeclamptic placenta. Method: NO synthase activity in the placental microsome was measured with C14 arginine substrate using healthy (n = 9) and preeclamptic (n = 9) samples. NO synthase activity was measured at 0.02 µM, physiological at 0.20 µM and pharmacological at 50 µM BH4. Results: One of the 9 preeclamptic patients was BH4-resistant; physiologic BH4 concentration did not significantly increase NO synthase activity, whereas healthy placental microsomes showed a mean increase of 60% (p<0.01), and BH4-sensitive preeclamptic specimen showed a 67% (p<0.01) increase. 10 µM pravastatin increased NO synthase activity by 32-38% at each BH4 concentration in healthy, BH4-sensitive and BH4-resistant preeclampsia samples. Conclusion: 10 µM pravastatin increased BH4-resistant placental NO synthase activity to a similar extent as placental physiological BH4 concentration (0.06-0.20 µM) to BH4-sensitive NO synthase activity. The NO synthase activity of BH4-resistant preeclamptic placenta can be increased by pravastatin to physiological level. Orv Hetil. 2020; 161(10): 389-395.

Pravastatin induces NO synthesis by enhancing microsomal arginine uptake in healthy and preeclamptic placentas.

BACKGROUND: Pravastatin, a known inducer of endothelial nitric-oxide synthase (eNOS) was demonstrated in human placenta, however the exact mechanism of it's action is not fully understood. Since placental NO (nitric oxide) synthesis is of primary importance in the regulation of placental blood flow, we aimed to clarify the effects of pravastatin on healthy (n = 6) and preeclamptic (n = 6) placentas (Caucasian participants). METHODS: The eNOS activity of human placental microsomes was determined by the conversion rate of C14 L-arginine into C14 L-citrulline with or without pravastatin and Geldanamycin. Phosphorylation of eNOS (Ser1177) was investigated by Western blot. Microsomal arginine uptake was measured by a rapid filtration method. RESULTS: Pravastatin significantly increased total eNOS activity in healthy (28%, p<0.05) and preeclamptic placentas (32%, p<0.05) using 1 mM Ca2+ promoting the dissociation of a eNOS from it's inhibitor caveolin. Pravastatin and Geldanamycin (Hsp90 inhibitor) cotreatment increased microsomal eNOS activity. Pravastatin treatment had no significant effects on Ser1177 phosphorylation of eNOS in either healthy or preeclamptic placentas. Pravastatin induced arginine uptake of placental microsomes in both healthy (38%, p < 0.05) and preeclamptic pregnancies (34%, p < 0.05). CONCLUSIONS: This study provides a novel mechanism of pravastatin action on placental NO metabolism. Pravastatin induces the placental microsomal arginine uptake leading to the rapid activation of eNOS independently of Ser1177 phosphorylation. These new findings may contribute to better understanding of preeclampsia and may also have a clinical relevance.

[Gynecological aspects of hidradenitis suppurativa]. / A hidradenitis suppurativa nogyógyászati vonatkozásai.

Hidradenitis suppurativa is a chronic inflammatory disease of the hair follicles, usually presenting after puberty on the apocrine gland-bearing areas of the body. It usually flares up periodically and can lead to a severe condition affecting the 20-40-year-old childbearing age group. HS occurs more commonly in women. The main clinical features consist of painful, cicatrizing nodules and abscesses which develop mostly in the axillary, inguinal, genital and perianal regions and also on the breasts. HS is often accompanied by severe pain and malodorous discharge, both of which cause significant psychological stress and social stigma. Our main aim with this review paper is to highlight the gynecological aspects of this disease, as many times - due to the typical localization of the disease - patients seek gynecological care first when they experience the first symptoms of this disease. The most important classification of HS is the Hurley scale, which is based on the severity of the clinical symptoms. In recent years, numerous clinical trials have been conducted to seek optimized care of HS patients. Several drugs are used for the treatment of HS, but in most cases, the treatment has to be switched many times. It is of great importance to carefully follow comorbidities and possible pregnancies as in these cases, careful selection of treatment is required. Thus, HS is not only a dermatological, but also a gynecological disease. With an appropriate treatment and follow-up, the disease can be effectively handled. Orv Hetil. 2019; 160(8): 291-299.

Placental gene expression of transforming growth factor beta 1 (TGF-ß1) in small for gestational age newborns.

OBJECTIVE: The gene expression of transforming growth factor beta-1 (TGF-ß1) in human placental samples obtained from pregnancies with small for gestational age fetuses (SGA) was compared to those of normal pregnancies. METHODS: In 2011 placental samples from 101 pregnancies with SGA and from 140 normal pregnancies were obtained for analysis of TGF-ß1 gene expression. Several clinical parameters were also assessed for correlation between genetic and clinical parameters. RESULTS: There were no significant differences in gene activity of the TGF-ß1 gene between the SGA versus normal pregnancy groups (Ln2α: 0.16; p = 0.07). Within the SGA group, no fetal gender-dependent differences were seen in TGF-ß1 gene expression (Ln2α: −0.11; p = 0.05). Similarly, no significant differences in gene activity were observed by the degree of severity of SGA as assessed by percentile fetal birth-weight (Ln2α: 0.32; p = 0.06). CONCLUSION: We found no change in gene expression of TGF-ß1 in placental samples obtained from SGA pregnancies versus normal pregnancy suggesting an absence of a direct role of the TGF-ß1 gene in the development of SGA. However, the absence of increased gene expression of TGF-ß1 in SGA can be conceptualized as a failure to mount a compensatory response in the SGA environment.

[Screening of trisomy 21 nowadays. Is maternal age so important?]. / A 21-es triszómia szurése napjainkban. Az anyai életkor valóban olyan fontos?

INTRODUCTION: Trisomy 21 is the most common chromosomal abnormality, therefore, screening and diagnosis of this disorder is in the centre of attention worldwide. An efficient screening method is the combined test based on maternal age, ultrasound signs, biochemical markers, and a risk ratio can be calculated based on these data. AIM: The aim of the authors was to determine the causes of missed prenatal diagnosis of Down's syndrome at the 2nd Department of Obstetrics and Gynecology, Semmelweis University. METHOD: A retrospective study was carried out by collecting data from medical records of mothers who had delivered a newborn with Down's syndrome in the Department between 2008 and 2012. Each medical record was analyzed individually. RESULTS: In most cases the missed diagnosis of Down's syndrome occurred when the expectant mother failed to attend the first trimester screening or did not take the risk of invasive diagnostic procedures needed for fetal kariotyping. CONCLUSIONS: Analysis of fetal DNA circulating in maternal plasma can be a solution for those who refuse invasive fetal diagnostics. This test has high sensitivity and very low false positive rate. It has become available since the end of 2011 in the United States and, since the autumn of 2012, in Hungary, too. The test, however, is not reimbursed by national health insurance.

Association between subjective feelings of distress, plasma cortisol, anxiety, and depression in pregnant women.

OBJECTIVE: Psychosocial stressors are consistently associated with antenatal anxiety and depression, while the impact of cortisol has proved inconsistent. Most studies have focused either on psychological or physiological stress indices. We investigated both subjective and endocrinologic indices of distress in the same subjects. STUDY DESIGN: We performed a cross-sectional study in late pregnancy in 79 women to investigate associations between the factors involved in anxiety and depression. Outcome measures were the Beck Depression Inventory (BDI), State-Trait Anxiety Inventory (STAI), Perceived Stress Scale, a Likert-like scale for fear of delivery, a structured interview to assess health and socioeconomic status, and fasting plasma cortisol levels measured in the morning. RESULTS: High BDI and STAI scores were associated with high levels of perceived stress and fear of delivery, but not with levels of plasma cortisol typical of the gestation phase. A multiple regression analysis revealed that subjective feelings of distress explained over 50% of the variation in BDI and STAI scores. Plasma cortisol was not a significant predictor of psychometric scores and did not show significant correlation with them in correlation analyses, and subjects with low and high cortisol levels showed similar psychometric scores. CONCLUSION: Antenatal depression and anxiety were significantly associated with subjective feelings of distress but not with increased cortisol. This finding may be explained by the blunted cortisol stress responses characteristic of pregnancy. The mechanisms mediating the effects of subjective distress remain obscure: likely candidates include monoamine neurotransmission, and/or stress-induced changes in glucocorticoid receptor expression or distribution.

[The pathophysiology of preeclampsia in view of the two-stage model]. / A praeeclampsia kórélettana a kétlépcsos modell tükrében.

Preeclampsia is a common and severe disease in pregnancy, a major cause of maternal and fetal morbidity and mortality. The main features of the disease are de novo hypertension after the 20th gestational week and proteinuria, and it is frequently accompanied by edema and other subjective symptoms. The origin of the disease is the placenta, but its sequelae affect multiple organ systems. According to the two-stage model of preeclampsia, the abnormal and hypoperfused placenta (stage 1) releases factors to the bloodstream, which are responsible for the maternal symptoms (stage 2). Oxidative stress, impaired function of nitric-oxide synthase, cellular and humoral immunological factors play an important role in the pathophysiology of the placenta. Endothelial dysfunction is the common denominator of the clinical symptoms. The theory explains the origins of hypertension, proteinuria, edema and other symptoms as well.

[Ultrasonography in the diagnosis of ovarian and endometrial carcinoma]. / Az ultrahangvizsgálat szerepe a méhtest és a petefészek rosszindulatú daganatainak diagnosztikájában.

Transvaginal sonography has become a crucial part of the routine gynecologic examination. It offers now a great help in the diagnosis of almost all gynecological diseases. Transvaginal ultrasound means the first step in the diagnosis of the first two most common gynecological malignancies, and in many cases we are able to set up a diagnosis of its own. The purpose of this article is to emphasize the significant role of transvaginal ultrasonography in the diagnosis of these two dieseases mentioned above, with summarizing the latest developments regarding the capabilities of sonography (Doppler-technique, three-dimensional ultrasonograpy).

High early uterine vascular resistance values increase the risk of adverse pregnancy outcome independently from placental VEGF and VEGFR1 reactivities.

OBJECTIVE: From data in the literature, we hypothesized that high vascular resistance values in the uterine arteries at the end of the first trimester would increase adverse pregnancy outcomes and therefore might be accompanied by changes in VEGF/VEGFR1 immunoreactivities. STUDY DESIGN: In our university hospital 82 women (Study I n=62 and Study II n=20) were divided into two groups according to their uterine vascular resistance values. Uterine vascular resistance values were measured in the 10-13th weeks of gestation by color-Doppler ultrasonography. Women were divided into low and high vascular resistance groups. In the prospective follow-up study (Study I) the data of the pregnancy outcome were recorded. In cross-sectional study (Study II), VEGF and VEGFR1 immunoreactivities were measured on the tissue samples from women who underwent termination of pregnancy. RESULTS: In the high vascular resistance group (PI>2.3), the probability of adverse pregnancy outcome was significantly higher (40.0% vs. 12.8%). No differences in VEGF and VEGFR1 immunoreactivities were observed between groups. In both groups, intense VEGF immunoreactivity was observed in the maternal glandular epithelium and in the decidual cells. Weak reactivity was observed in the villous trophoblast. VEGFR1 immunoreactivity was intense in all regions. CONCLUSIONS: Our data suggest that high vascular resistance values in the first trimester are independent from VEGF/VEGFR1 immunoreactivities and markedly increase the probability of adverse pregnancy outcomes. This may be used for early screening of pregnant women in the first trimester.

[Nitric oxide and preeclampsia]. / A nitrogén-monoxid-szintézis zavarai praeeclampsiában.

Preeclampsia is one of the leading causes of obstetric morbidity and mortality. The placenta has a crucial role in the development of preeclampsia. Despite intensive researches the cause of disorder is still unknown. Insufficient NO synthesis may have a key role in pathogenesis. Endothelial NO synthesis (eNOS) is the primary isoenzyme expressed in human placenta, its known disturbances are discussed. Deficiency of substrate (arginine), cofactor (tetrahydrobiopterin, BH4) and calcium can decrease the NO synthesis. Serum levels of free fatty acids (FFA), asymmetric dimethylarginine, reactive oxygen species and glucose may increase in preeclamptic pregnancy. These substances decrease NO production by different ways. The reduced affinity of eNOS to the cofactor BH4 may lead to insufficient NO, but increased superoxide production in preeclamptic placentas. Polymorphisms of eNOS gene (D298E, -786T→C) were associated with preeclamptic complications (not adequately documented). Data suggest that smoking has protective role against preeclampsia. The mechanism is not clear, even the actions of smoking on eNOS are ambivalent. The expression of eNOS is decreased, while the phosphorylation of the activator Ser1177 and also the deactivator Thr495 are increased by cigarette smoke. The oxidative stress directly decreases NO levels. Smoking lowers serum FFA levels, thus the activity of eNOS may be increased. CO produced during smoking mimics the effect of NO and can compensate its absence partially.

Activation energy determinations suggest that thiols reverse autooxidation of tetrahydrobiopterin by a different mechanism than ascorbate.

In neutral aqueous solutions tetrahydrobiopterin is oxidized by dioxygen in a reaction that is succinctly described as autooxidation. Ascorbate and thiols moderate this reaction by reversing the oxidative process. In the present study the effect of various thiols on the apparent Arrhenius activation energy of tetrahydrobiopterin autooxidation was characterized and compared to that of ascorbate determined previously. We observed that - in sharp contrast to ascorbate - the efficiency of thiols to protect tetrahydrobiopterin decreased with the elevation of temperature from 22 to 37 degrees C. Accordingly, the apparent Arrhenius activation energies (in kJ/mol) measured in the presence of thiols were consistently greater than the value determined with tetrahydrobiopterin alone (59.6 +/- 1.4) or in the presence of ascorbate (59.9 +/- 2.8). Thus, the energy values were 88.8+/-1.1 with glutathione, 87.6 +/- 2.1 with N-acetylcysteine, 79.2 +/- 1.6 with cysteine, 75.1 +/- 2.4 with dithiotreitol and 70.3 +/- 0.9 with homocysteine. Since thiols are as potent reducing agents as ascorbate, these findings suggest that thiols and ascorbate protect tetrahydrobiopterin from oxidation acting at different steps of the oxidation process. It is likely that thiols reduce quinoidal dihydrobiopterin, whereas ascorbate scavenges the trihydrobiopterin radical to tetrahydrobiopterin. Furthermore, the results indicate that thiols are excellent tools to protect tetrahydrobiopterin from autooxidative decomposition in laboratory experiments conducted at relatively low temperatures, whereas the protective effect diminishes at 37 degrees C, i.e. under physiological conditions.

Spectrophotometric analysis of the protective effect of ascorbate against spontaneous oxidation of tetrahydrobiopterin in aqueous solution: kinetic characteristics and potentiation by catalase of ascorbate action.

Tetrahydrobiopterin (BH(4)) is oxidized by O(2) readily in aqueous solutions and physiological concentrations of ascorbate have been shown to inhibit this reaction. In order to gain insight into the mechanism of ascorbate effect, a spectrophotometric analysis was applied for the study of the time course of BH(4) oxidation in the presence of various concentrations of ascorbate and the effect of various temperatures on the apparent second-order rate constant of BH(4) oxidation (k(ox)) in the presence or absence of catalase. In 100 micromol/l concentration, ascorbate alone prolonged the half-life time of 36 micromol/l BH(4) 1.4-fold whereas in the presence of catalase 1.85-fold. In the presence of catalase ascorbate decreased the value of k(ox) to 51 +/- 0.67%, whereas in the absence of it only to 64 +/- 0.77% of control (P < 0.01). The extent of ascorbate effect was not dependent on temperature, at least between 22 and 37 degrees C, either in the presence or absence of catalase. In the absence of catalase the apparent Arrhenius activation energies: 57.02 +/- 0.09 kJ/mol (-ascorbate) and 56.77 +/- 2.21 kJ/mol (+ascorbate) whereas in the presence of catalase: 62.72 +/- 1.37 kJ/mol (-ascorbate) and 59.93 +/- 2.84 kJ/mol (+ascorbate, mean +/- S.E.M., n=3) were obtained. The study shows that catalase potentiates the BH(4)-stabilizing effect of ascorbate. It is concluded that removal of H(2)O(2) generated from BH(4) during oxidation by O(2) prevents a decrease of ascorbate concentration, and in the presence of ascorbate the pacemaker step in the overall reaction is the oxidation of BH(4) and not the reduction of the quinonoid BH(2) back to BH(4) by ascorbate.