Modern Approach to Melanoma Adjuvant Treatment with Anti-PD1 Immune Check Point Inhibitors or BRAF/MEK Targeted Therapy: Multicenter Real-World Report

BACKGROUND

The landscape of melanoma management changed as randomized trials have launched adjuvant treatment.

MATERIALS AND METHODS

An analysis of data on 248 consecutive melanoma stage III and IV patients given adjuvant therapy in eight centers (February 2019 to January 2021) was conducted.

RESULTS

The analyzed cohort comprised 147 melanoma patients given anti-PD1 (33% nivolumab, 26% pembrolizumab), and 101 (41%) were given dabrafenib plus trametinib (DT). The 2-year overall survival (OS), relapse-free survival (RFS), and distant-metastases-free survival (DMFS) rates were 86.7%, 61.4%, and 70.2%, respectively. The disease stage affected only the RFS rate; for stage IV, it was 52.2% (95% CI: 33.4-81.5%) vs. 62.5% (95% CI: 52.3-74.8%) for IIIA-D, p = 0.0033. The type of lymph node surgery before adjuvant therapy did not influence the outcomes. Completion of lymph node dissection cessation after positive SLNB did not affect the results in terms of RFS or OS. Treatment-related adverse events (TRAE) were associated with longer 24-month RFS, with a rate of 68.7% (55.5-84.9%) for TRAE vs. 56.6% (45.8-70%) without TRAE, p = 0.0031. For TRAE of grade ≥ 3, a significant decline in OS to 60.6% (26.9-100%; p = 0.004) was observed.

CONCLUSIONS

Melanoma adjuvant therapy with anti-PD1 or DT outside clinical trials appears to be effective and comparable with the results of registration studies. Our data support a de-escalating surgery approach in melanoma treatment.

Long-term clinical evidence of comparable efficacy and toxicity of nivolumab and pembrolizumab in advanced melanoma treatment

Pembrolizumab and nivolumab (anty-PD-1 antibody) are commonly used for the treatment of melanoma patients. However, their efficacy and safety have never been directly compared, leaving little guidance for clinicians to select the best therapy. The study included patients with inoperable or metastatic melanoma treated in first line with anti-PD-1 immunotherapy (nivolumab or pembrolizumab). In total 1037 patients were enrolled in the study, 455 (44%) patients were treated with pembrolizumab and 582 (56%) with nivolumab. The estimated median overall survival (OS) in the pembrolizumab and nivolumab groups was 17.4 and 20.0 months [P = 0.2323; hazard ratio (HR), 1.1; 95% confidence interval (CI), 0.94-1.28], respectively, whereas the median progression-free survival (PFS) was 5.6 and 7.5 months (P = 0.0941; HR, 1.13; 95% CI, 0.98-1.29), respectively. The estimated 2- and 3-year OS in the pembrolizumab and nivolumab groups were 42/34% and 47/37%, respectively, and the PFS was 25/21% and 29/23%, respectively. There were 391 (49%) immune-related adverse events (irAEs) of any grade during treatment, including 133 (42%) related to pembrolizumab treatment and 258 (53%) to nivolumab treatment. A total of 72 (9.6%) irAEs were in G3 or G4, including during pembrolizumab 29 (9%) and nivolumab 48 (11%). There were no differences in OS, PFS and overall response rates between nivolumab and pembrolizumab therapy in previously untreated patients with advanced/metastatic melanoma. There were no differences in the frequency of G1/G2 or G3/G4 irAEs. The choice of treatment should be based on the preferences of the patient and the clinician.

Long-Term Real-World Outcomes and Safety of Vemurafenib and Vemurafenib + Cobimetinib Therapy in Patients with BRAF-Mutated Melanoma

BACKGROUND

Combined treatment with BRAFi and/or MEK inhibitors (MEKi) improves outcomes in advanced melanoma patients in comparison with monotherapy.

OBJECTIVE

We aim to report real-world treatment efficacy and safety of vemurafenib (V) and vemurafenib + cobimetinib (V + C) from 10 years of practice.

PATIENTS AND METHODS

A total of 275 consecutive patients with unresectable or metastatic BRAF mutated melanoma started first-line V or V + C treatment between 1 October 2013 and 31 December 2020. Survival analyses were performed using the Kaplan-Meier method, and Log-rank and Chi-square tests were used for comparison between groups.

RESULTS

The estimated median overall survival (mOS) was 10.3 months in the V group, and 12.3 months in the V + C group (p = 0.0005; HR = 1.58, 95% CI 1.2-2.1), although the latter group of patients had lactate dehydrogenase elevated numerically more often. Estimated median progression-free survival (mPFS) was 5.5 months in the V group, and 8.3 months in the V + C group (p = 0.0002; HR = 1.62, 95% CI 1.3-2.1). Complete response, partial response, stable disease, and progressive disease as best responses were recorded in the V/V + C groups in 7%/10%, 52%/46%, 26%/28%, and 15%/16% of patients, respectively. The numbers of patients with any grade of adverse effects were similar in both groups.

CONCLUSIONS

We confirmed significant improvement in the mOS and mPFS of unresectable and/or metastatic BRAF mutated-melanoma patients treated outside clinical trials with V + C as compared with V, with no major increase in toxicity for the combination.

Relevance of admission hyperglycaemia and diabetes mellitus to efficacy and safety of mechanical thrombectomy in stroke patients

INTRODUCTION

The relevance of diabetes mellitus (DM) to the efficacy of mechanical thrombectomy (MT) has been the subject of few studies and with only inconclusive results.

OBJECTIVES

This study aimed to evaluate the effect of DM and admission hyperglycaemia on the efficacy and safety of MT in stroke patients.

MATERIAL AND METHODS

This retrospective study analysis focused on the relevance of admission hyperglyacemia and DM to the functional status of patients treated with MT at the Upper Silesian Medical Centre of the Silesian Medical University in Katowice, Poland.

RESULTS

417 stroke patients (median age 70 years) were qualified for the study. There were 103 patients (24.70%) with DM. Admission hyperglycaemia ≥ 140 mg% was found in 91 patients (21.82%), of whom 69 were diagnosed with DM before or during hospitalisation. The parameters with the strongest effect on the functional status on days 7, 90 and 365 were: age, and neurological status according to the National Institutes of Health Stroke Scale (NIHSS) on the first day of ischaemic stroke before MT. The angiographic effect indirect after MT and patient functional status on days 7, 90 and 365 were comparable between the groups, regardless of the DM burden. The frequency of symptomatic intracranial bleeding 24 hours after MT was comparable between patients with and patients without DM (p = 0.092). Model based on parameters were age, NIHSS on the first day of ischaemic stroke, an when score in Thrombolysis In Cerebral Infarct (TICI) showed good predictive attributes for the functional status of patients in the acute period (day 7). Age, a lack of admission hyperglycaemia, and the neurological state on day 1 of ischaemic stroke (before MT) were the key parameters for a favourable outcome (≤ 2 points on the modified Rankin Scale, mRS) on day 90. Admission hyperglycaemia ≥ 140 mg/dL, regardless of the presence or absence of DM, had a negative effect on achieving a good functional status one week after stroke onset.

CONCLUSIONS

Diabetes mellitus has a neutral effect on the angiographic and clinical outcomes of mechanical thrombectomy in stroke patients. It does not increase the risk of intracranial haemorrhage after instrumental therapy. It is admission hyperglycaemia, rather than diabetes mellitus, that is a predictor of poor functional status in patients treated with thrombectomy. According to our results, the patient's neurological status, age, and the outcome of thrombectomy are relevant to the functional status in the acute ischaemic stroke period.

Long-Term Outcomes of Targeted Therapy after First-Line Immunotherapy in BRAF-Mutated Advanced Cutaneous Melanoma Patients—Real-World Evidence

Background: Currently, limited data on targeted therapy and immunotherapy sequencing in patients with BRAF-mutant melanoma is available. Targeted therapy and immunotherapy are expected to be comparable in terms of overall survival (OS) when used as second-line therapies; therefore, understanding the characteristics of patients who completed sequential treatment is needed. Methods: The primary objective of this study was to analyze the efficacy of BRAFi/MEKi activity as second-line therapy in patients with advanced melanoma. We also aimed to describe the clinical characteristics of patients with advanced melanoma who were treated sequentially with immunotherapy and targeted therapy. We enrolled 97 patients treated between 1st December 2015 and 31st December 2020 with first-line immunotherapy with programmed cell death 1 (PD-1) checkpoint inhibitors; and for the second-line treatment with at least one cycle of BRAFi/MEKi therapy with follow-up through 31 January 2022. Results: Median OS since first-line treatment initiation was 19.9 months and 12.8 months since initiation of BRAFi/MEKi treatment. All BRAFi/MRKi combinations were similarly effective. Median progression free survival (PFS) was 7.5 months since initiation of any BRAFi/MEKi treatment. Conclusions: BRAFi/MEKi therapy is effective in the second-line in advanced and metastatic melanoma patients. For the first time, the efficacy of all BRAFi/MEKi combinations as second-line therapy is shown.

Clinical and Non-Clinical Determinants of the Effect of Mechanical Thrombectomy and Post-Stroke Functional Status of Patients in Short and Long-Term Follow-Up

To date, inconsistent results evaluating the effect of parameters on mechanical thrombectomy (MT) outcomes in stroke-patients have been published. This study aimed to identify the key parameters for functional status after MT in stroke-patients in short and long-term follow-up.

METHOD

The study analysis focused on the relevance of selected clinical and non-clinical parameters to the functional status of the patients after MT.

RESULTS

417 stroke-patients (mean age 67.8 ± 13.2 years) were qualified. Atrial fibrillation, and leukocytosis were significant for the neurological status on the first day of stroke (p = 0.036, and p = 0.0004, respectively). The parameters with the strongest effect on the functional status on day 10 were: age (p = 0.009), NIHSS (p = 0.002), hyperglycemia (p = 0.009), the result in TICI (p = 0.046), and first pass effect (p = 0.043). The parameters with the strongest effect on the functional status on day 365 were: age and NIHSS on the first day of stroke (p = 0.0002 and 0.002, respectively). Leukocytosis and the neurological status at baseline were key parameters associated with ICB after MT (p = 0.007 and p = 0.003, respectively).

CONCLUSIONS

Age and neurological status in the ultra-acute phase of stroke are crucial for the functional status in short and long-term observations of patients treated with mechanical thrombectomy. Atrial fibrillation, hyperglycemia, and inflammatory state are relevant to the short-term post-stroke functional status. First pass effect and the degree of post-interventional reperfusion are important technical parameters to the short-term functional status. Neurological status and white blood count during the acute phase are associated with a high rate of post-procedural intracranial bleeding.

Abstract P4-02-12: Association of nodal stage as assessed by FDG PET/CT with pathological complete response rate after preoperative chemotherapy

Preoperative chemotherapy (preopCT) is gaining importance in management of breast cancer, as it allows to avoid axillary clearance in responders. In case of axillary surgery the pathological complete response (pCR) of involved nodes is required to omit lymphadenectomy. Selecting the patients (pts) for axillary-sparing surgery is a challenging task, as currently it is reserved for N1 stage, but no more detailed criteria exist.

FDG-PET/CT is a valuable tool to assess the extent of systemic disease in breast cancer before chemotherapy, used in stage III and selected stage IIB patients. The axillary nodal burden assessed in PET/CT could potentially affect the chances of pCR, and thus influence the decisions whether to clip the involved LNs and whether to proceed with either SNB or primary lymphadenectomy.

The aim of the study was to assess the sensitivity of PET/CT to diagnose involved axillary LNs and to verify whether FDG-PET/CT axillary staging is associated with the rate of pathological complete response after preopCT.

Material and Methods. The study group consisted of 287 pts with breast cancer with regional lymph node involvement, treated by preopCT, within the prospective trial analyzing the clinical and molecular predictors of response to preopCT, upon the approval of Ethics Committee at our Institution and after patients’ informed consent. Among them 16 (5.6%) had cT1 tumor, 131 (45.6%) T2, 69 (24.0%) T3 and 66 (23.0%) T4. Clinical nodal stage was N1 in 164 pts (57.1%), 94 (32.8%) had N2 and 29 (10.5%) N3 disease. 24 tumors were grade 1 (8.7%), 83 tumors grade 2 (30.1%) and the majority - 157 of tumors (56.9%) - grade 3. There were 81 pts (28.2%) with HER2-positive subtypes, 151 pts with luminal HER2-negative subtypes (52.6%) and 55 pts with TNBC (19.1%). 260 pts (90.6%) showed sufficient tumor regression to undergo surgery.

Results. In 55 pts we observed pCR (21.6%), in 205 pts (78.9%) no pCR was found. When the regional lymph nodes were assessed by PET/CT pre-chemotherapy (data obtained in 259 pts, 90.2%), in 42 patients (16.2%) no uptake was found (despite positive thin-needle biopsy), in 65 pts (25.1%) there was uptake in single lymph node (LN), in 47 pts (18.1%) in two LN, and in 105 (40.5%) uptake was found in three or more LNs - thus, the vast majority (86%) exhibited uptake on PET/CT. Median of maximal SUV in lymph nodes was 4.9 (IQR 2.1-9.8), median of SUV in breast was 7.6 (IQR 4.4-12.0). In 160 patients (70.8%) SUVmax in LNs was lower than in breast (ratio<1), in 66 patients (29.2%) SUVmax in LNs was higher than in breast. Median of breast/axilla SUVmax ratio was 71.4% (IQR 38.1%-110.1%).

pCR rate did not depend on regional nodal burden: in patients with cN1 disease, pCR rate was 21.8%, in cN2 19.8% and in cN3 22.2% (non-significant, n.s.). When number of nodes, as assessed by FDG PET was taken into account, pCR rate in pts with no uptake in LNs was 17,5%, in pts with uptake in 1-2 LNs pCR rate was 20.9% and in pts with 3 and more LNs pCR rate was 20.7% (n.s.). When the ratio of tumor/nodes SUVmax was analyzed, no difference in pCR rate between pts with ratio below 1 (22.2%) and above >=1 (16.4%; n.s.) was found.

However, pCR rate was associated with biological tumor features: higher in G3 tumors, TNBC and HER2 subtypes, as well as in tumors with small diameter (data not shown).

Conclusions. Patients with higher burden of regional lymph node involvement exhibit equal chance of pathological complete response as compared to low-volume/low-uptake individuals. The feasibility of limited surgery in higher stage regional nodal disease with pCR after chemotherapy shall be tested in prospective trials.

The study was supported by the Polish National Center of Research and Development MILESTONE project - Molecular diagnostics and imaging in individualized therapy for breast, thyroid and prostate cancer, grant no. STRATEGMED 2/267398/4/NCBR/2015.

Citation Format: Marcin Kubeczko, Andrea D'Amico, Anna Polakiewicz-Gilowska, Agnieszka Badora-Rybicka, Damian Borys, Izabela Gorczewska, Marco Di Pietro, Olgierd Chrabański, Wiesław Bal, Anna Michalik, Mateusz Raus, Agnieszka Pasierbek, Rafał Tarnawski, Barbara Bobek-Billewicz, Michał Jarząb. Association of nodal stage as assessed by FDG PET/CT with pathological complete response rate after preoperative chemotherapy [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-02-12.

Effectiveness and safety of CyberKnife radiosurgery in treatment of trigeminalgia - experiences of Polish neurological and oncological centres

Trigeminal neuralgia (TN) is one of the most common cranial neuropathies. Pathologies located alongside the long nerve can also cause its mechanical compression or secondary involvement in the inflammatory process, and thus cause pain. TN is characterised by severe paroxysmal unilateral facial pain in the innervation area of branches I-III of the nerve V when provoked by light touch or slight movement. Multiple therapeutic methods are available, but most of them yield unsatisfactory results. According to guidelines (AAN and EFNS) the first-line therapy in trigeminalgia is carbamazepine/oxcarbazepine, and if there is a poor response - surgical treatment [1]. The array of surgical options includes percutaneous retrogasserian glycerol injection, radiofrequency thermocoagulation, balloon decompression, thermal rhizotomy, and stereotactic radiosurgery [2-4]. This paper presents our own experiences with CyberKnife (CK), a new type of radiosurgical (RS) treatment of 64 TN patients. CONCLUSIONS: CyberKnife radiotherapy is characterised by high efficacy in 80% of patients with trigeminalgia, minimal invasiveness, and subsiding mild side effects. Radioablation of nerve V root in patients with neuralgia allows us to entirely stop antiepileptic therapy or reduce its doses, which in turn reduces the risk of potential side effects. CyberKnife can be a therapeutic option in those patients who have been offered ineffective therapies, or treatments with limited efficacy, and/or in older patients with comorbidities.

The Association of SNPs Located in the CDKN2B-AS1 and LPA Genes With Carotid Artery Stenosis and Atherogenic Stroke

Introduction: The aim of this project was to assess the prevalence of four selected SNPs rs4977574 and rs7857345 (CDKN2B-AS1 gene) and rs3798220 and rs10455872 polymorphisms (the LPA gene) in the subpopulation of patients with symptomatic and asymptomatic carotid stenosis.

Material and Methods: This study included 623 individuals (244 patients with symptomatic carotid artery stenosis, 176 patients with asymptomatic carotid artery stenosis and 203 healthy people. All the participants underwent neurological examination, duplex Doppler ultrasound examination and molecular procedures.

Results: In the first part of the analysis the assiociation of SNPs with stroke/TIA was investigated. The association was seen in symptomatic vs. control group for two SNPs: rs4977574 and rs7857345 (CDKN2B-AS1 gene); genotype distributions for rs4977574 and rs7857345 showed the statistically significant differences between patients and controls (p = 0.043 and 0.017, respectively). No association was observed for rs3798220 and rs10455872 located in the LPA gene. There were statistically significant differences between asymptomatic patients vs. control group in genotype distribution for the SNPs located in CDKN2B-AS1: rs4977574 and rs7857345 (p = 0.031 and 0.0099, respectively); and for the rs3798220 (LPA gene; p = 0.003); however, statistically significant differences did not occur for the rs10455872 polymorphism located in the LPA gene. In the next part of the evaluation, a comparison between symptomatic and asymptomatic patients was performed. Significant differences in genotype distribution were seen only for the rs3798220 polymorphism located in the LPA gene (p = 0.0015). The analysis of the prevalence of the polymorphisms in the total group (symptomatic and asymptomatic) patients in comparison with the control group showed significant differences for three polymorphisms: rs4977574 and rs7857345 (CDKN2B-AS1 gene; p = 0.015 and 0.0046, respectively) and rs3798220 (LPA gene, p = 0.044).

Conclusions: The present research on the carotid artery stenosis patient cohort suggests the significant association between the rs4977574, rs7857345 and rs3798220 polymorphisms and carotid artery stenosis as well as between the rs4977574 and rs7857345 polymorphisms and atherogenic stroke. The rs4977574 and rs7857345 polymorphisms in patients with carotid artery stenosis appear to affect a person's susceptibility to atherogenic brain ischemia. Our results need to be replicated in future studies.

The importance of selected markers of inflammation and blood-brain barrier damage for short-term ischemic stroke prognosis

Acute cerebral ischemia triggers local and systemic immune response. The aims of this project was to assess the blood serum concentration of the markers of inflammation and markers of the blood brain barrier damage on the first day of ischemic stroke, and the mutual correlations between these marker levels. Patients with first-in-life stroke were analysed according to: plasma concentration of the following markers on the first day of stroke: interleukin 2 (IL-2) and interleuki 6 (IL-6), S100B, tumor necrosis factor-α (TNF-α), progranulin (GRN), neuron specific enolase (NSE), urokinase-type plasminogen activator (uPA), vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), C-reactive protein (CRP), leucocyte and thrombocyte counts; their neurological status on the first day of stroke (NIHSS) and their functional status at 30 days following stroke (mRS). The study included 138 patients with mean age: 73.11 ± 11.48. Patients with a higher score on the NIHSS showed significantly higher concentrations of TNF-α, white blood cells (WBC), CRP, NSE, IL-6 and S100B. Patients with a higher score on the modified Rankin Score (mRS) showed significantly higher concentrations of WBC, CRP, GRN, IL-6, S100B. Factors with an independent influence on the neurological status on the first day of stroke were: sex, WBC, total blood platelet (PLT) count, CRP, S100B and IL-6 levels. Atrial fibrillation, leukocyte count, CRP, NSA, uPA, IL-6 and S100B showed an independent impact on the functional status on the 30^th day of stroke. Patients with symptomatic atherosclerosis, as compared to others, were older (P = 0.003) and had higher levels of CRP, IL-6, and S100B. In each case, the differences were statistically significant. We conclude that the concentration of Il-6 and S100B on the first day of stroke are important for both the neurological status and the functional status in the acute period of the disease. Increased CRP and leukocyte count are associated with a worse prognosis regarding the course of acute stroke. The expression of pro-inflammatory agents and markers of blood-brain barrier damage in the acute phase of stroke seem to be more prominent in patients with symptomatic atherosclerosis than in patients with no clinical features of atherosclerosis. The expression of inflammatory parameters may indicate the importance of the inflammatory process starting during the early days of ischemic stroke, for the post-stroke neurological deficit.

The presence of Tau protein in blood as a potential prognostic factor in stroke patients

Tau protein is found in the blood of 40 - 50% of patients in the acute phase of a stroke, as a result of the degradation of neurons and damage to the blood-brain barrier. The aim of the study was to assess the incidence of tau protein in the blood of stroke patients, as well as to evaluate the potential impact of tau protein presence in the blood of patients on their neurological state during the first 24 hours, and their functional condition three months after the stroke. Eighty-seven patients aged 39 - 99 (42 females and 45 males) diagnosed with stroke were enrolled in the prospective study (August 2014 - April 2015). The following parameters were analyzed in enrolled participants: the age at which first ischemic stroke occurred, neurological state during the first 24 hours (National Institutes of Health Stroke Scale - NIHSS), blood tau protein and brain derived neurotrophic factor (BDNF) concentrations on day 2 of stroke, the functional condition on day 90 after stroke onset (mRankin). A multifactorial analysis was carried out to establish independent factors for the presence of serum tau protein and to identify independent factors for poor prognosis. Eighty-seven patients of the mean age of 71.7 ± 11.8 years (median 74; min. 39 max. 99 years) took part in the study. The tau protein was found in the serum of 42 (48.27%) patients in the concentrations between 29.56 and 19 023.50 ng/ml. The female sex was the only independent factor for the presence of tau protein in blood (RR 4.49 (1.68 - 11.97), P = 0.003). The mean BDNF concentration in the evaluated group was: 9.96 ± 5.21; median 10.39. Three independent factors for poor functional condition of patients on day 90 after the stroke were identified: the presence of tau protein in blood (RR 3.90 (1.45 - 10.49), P = 0.007), BDNF concentration below the mean value for the study (RR 14.49 (4.60 - 45.45); P = 0.000) and NIHSS score > 4 during the first 24 hours of stroke (RR 1.14; 95% CI: 1.00 - 1.31; P = 0.027). The presence of the tau protein, low BDNF concentrations, and moderate/serious neurological state during the first 24 hours of stroke can be considered as negative prognosis for the patient's functional condition. The coincidence of high BDNF concentrations and absence of tau in blood during the acute phase of an ischemic stroke is a predictor of patient's good state in 3 months after stroke.

Revised stability constant, spectroscopic properties and binding mode of Zn(II) to FluoZin-3, the most common zinc probe in life sciences

2-[2-[2-[2-[bis(carboxylatomethyl)amino]-5-methoxyphenoxy]ethoxy]-4-(2,7-difluoro-3-oxido-6-oxo-4a,9a-dihydroxanthen-9-yl)anilino]acetate (FluoZin-3) is used very broadly in life sciences as intra- and extracellular Zn(II) sensor selective for Zn(II) over Co(II), Ca(II) and Mg(II) ions at their physiological concentrations. It has been used for determination of relative and absolute levels of exchangeable Zn(II) in cells and extracellular fluids. Despite its popularity, the knowledge of its acid/base and Zn(II) coordination abilities and of its spectroscopic properties remained very limited. Also the published conditional dissociation constant ((C)Kd) values at pH7.4 are slightly discrepant, (15nM or 8.9nM). In this work we determined the (C)Kd for Zn(II) complexation by FluoZin-3 at pH7.4 with nitrilotriacetic acid (NTA) as competitor using two independent methods: fluorimetry and UV-Vis spectroscopy. For the first time, we investigated FluoZin-3 alone and complexed with Zn(II) in the wide range of pH, determining the total of eight pKa values from fluorescence spectra and from various regions of UV-Vis spectra. The validated values of (C)Kd (9.1±0.4nM; -log (C)Kd=8.04) and of the absolute (pH-independent) stability constant log βZnL (8.16±0.05) were provided by fluorescence spectroscopy experiments performed at 1μM concentrations. Our experiments demonstrated that both of aminocarboxylate moieties of FluoZin-3 bind the Zn(II) ion synergistically.

Low Concentration of BDNF in the Acute Phase of Ischemic Stroke as a Factor in Poor Prognosis in Terms of Functional Status of Patients

BACKGROUND According to recent studies, brain-derived neurotrophic factor (BDNF) probably plays a role in development of cerebral ischemia and can be significant for the prognosis of improved mobility after stroke. The aim of this prospective study was to evaluate the blood concentration of BDNF during the 1st day of first-ever ischemic stroke and find a potential association between BDNF concentration and the neurological status in the acute period, as well as between BDNF and the functional status in the sub-acute phase of stroke. MATERIAL AND METHODS The prospective study involved 87 patients aged 39-99 years (42 women, 45 men) with first-in-life complete ischemic stroke. All study subjects underwent analysis as follows: BDNF blood concentration and neurological status according to NIHSS on the 1st day of stroke, comorbidities, etiological type of ischemic stroke by ASCOD, and functional status on the 14th and 90th day after the onset according to mRankin scale. RESULTS Mean concentration of BDNF in the study group was 9.96 ng/mL±5.21, median 10.39 ng/mL. Patients aged ≤65 years (25 individuals) had a significantly higher mean concentration of BDNF (11.94 ng/mL±4.46; median 12.34 ng/mL) than the older subjects (62 individuals) with a mean concentration of 9.17 ng/mL±5.32 (median 8.66 ng/mL). The mean score by mRankin scale on the 90th day was significantly higher among patients with lower concentrations of BDNF on the 1st day of stroke, which reflects their poorer functional status. The functional status on the 90th day was significantly worse (3-6 points by Rankin scale) in patients who had BDNF below the mean value in the acute phase of stroke. The independent factors for poor functional status of patients on the 90th day after stroke were a score >4 points by NIHSS (RR 1.14; 95% CI: 1.00-1.31; p=0.027) and the concentration of BDNF below the mean value (assessed on the 1st day of stroke) (RR 14.49; CI 4.60-45.45; p=0.000). CONCLUSIONS The neurological status and concentration of BDNF on the 1st day of ischemic stroke are independent prognostic factors in medium-term observation. Reduction in the concentration of BDNF in the acute phase of stroke is a factor for poor prognosis in terms of the functional status of patients on the 90th day after onset.

Cu(II) complexation potentiates arginine vasopressin action on nonpregnant human myometrium in vitro

Copper may influence in vivo and in vitro uterine activity. Recent evidence has shown that cupric ions can easily form complexes with oligopeptides like arginine vasopressin (AVP). The high complex stability in vitro suggests a possibility of complex formation in vivo, in the uterus of intrauterine device users. In vitro isometric contractions were recorded in uterine tissues from nonpregnant premenopausal women undergoing hysterectomy and the effect of Cu-AVP complex on isolated human nonpregnant myometrium was investigated. The addition of the Cu(II)-AVP complex to the bath medium led to a concentration-dependent increase of the contractile activity. The activity was somewhat lower for the complex (-log EC(50) of 8.5 +/- 0.2, n = 7) than for AVP, but the difference was not statistically significant (p = 0.11). The maximal responses (E(max)) of the myometrium strips treated with AVP and the Cu (II)-AVP complex did not differ significantly. To assess the effect of presence of Cu (II) in the medium on tissue response to AVP, myometrium strips were preincubated for 20 min in the medium containing 10(-6) mol/L Cu(II) prior to the administration of AVP. The chosen Cu (II) concentration was below the threshold of effect on the spontaneous contractile activity in our experiments. The presence of cupric ions in the bath caused a significant leftward shift in the concentration-response curve to AVP.

Molecular mechanism of hydrogen peroxide conversion and activation by Cu(II)-amikacin complexes

The interactions between Cu(II)-amikacin complexes [Cu(II)-Ami] and hydrogen peroxide were studied by spectroscopy (EPR, UV-vis, CD, XAS) and cyclic voltammetry. A monomer-dimer equilibrium was detected at complex concentrations above 5 mM (log K(dim) = 1.84 +/- 0.03). The dimeric complex undergoes easy, although irreversible oxidation (ca. 0.5-0.6 V) to a Cu(III) species on platinum electrode. However, the monomeric complexes are able to catalyze hydrogen peroxide disproportionation reaction at pH 7.4 in a multistep process, mediated by hydroxyl radicals and involving both Cu(I)/Cu(II) and Cu(II)/Cu(III) redox pairs.

Stray Cu(II) may cause oxidative damage when coordinated to the -TESHHK- sequence derived from the C-terminal tail of histone H2A

CH(3)CO-Thr-Glu-Ser-His-His-Lys-NH(2), a hexapeptide representing the 120-125 sequence of histone H2A, coordinates Cu(II) ions efficiently. Monomeric complexes are formed. In the major complex at physiological pH, CuH(-1)L, Cu(II) is coordinated equatorially through the imidazole nitrogen of the His-4 residue and the amide nitrogens of the Ser-3 and His-4 residues, and axially through the imidazole nitrogen of the His-5 residue. This complex reacts with H(2)O(2) and the resulting reactive oxygen intermediate efficiently oxidizes 2'-deoxyguanosine. The underlying mechanism involves the formation of Cu(III) and a metal-bound hydroxyl radical species.

[Use of modern microscopic techniques for examining dialysis membrane properties]

The aim of the study was the microscopic evaluation of internal structure of cuprophane and polysulfone membrane and their surface analysis before and after reprocessing. The investigations were performed using an optical measurement system (Digital Instruments), a scanning electron microscope (SEM) and an atomic force microscope (AFM). We confirmed by SEM that reprocessing completely removed biofilm from both membranes surface. The analysis based on AFM visualized channels in the examined membrane. The diameter of the channels varied from 150 nm for cuprophane to 380 nm for polysulfone. The roughness expressed as root mean square (RMS) was higher for cuprophane than for polysulfone membrane. The physical differences between nanostrucure of the examined membranes might be responsible for lower biocompatibility of cuprophane.

Differential zinc and DNA binding by partial peptides of human protamine HP2

The Zn(II) binding by partial peptides of human protamine HP2: HP2(1-15); HP2(1-25), HP2(26-40), HP2(37-47), and HP2(43-57) was studied by circular dichroism (CD). Precipitation of a 20-mer DNA by these partial peptides and the effects of Zn(II) thereon were investigated using polyacrylamide gel electrophoresis (GE). The results of this study suggest that reduced HP2 (thiol groups intact) can bind Zn(II) at various parts of the molecule. In the absence of DNA, the primary Zn(II) binding site in reduced HP2 is located in the 37-47 sequence (involving Cys-37, His-39, His-43, and Cys-47), while in the presence of DNA, the strongest Zn(II) binding is provided by sequences 12-22 (by His-12, Cys-13, His-19, and His-22) and 43-57 (His-43, Cys-47, Cys-53, and His-57). In its oxidized form, HP2 can bind zinc through His residues of the 7-22 sequence. Zn(II) markedly enhances DNA binding by all partial peptides. These findings suggest that Zn(II) ions may be a regulatory factor for sperm chromatin condensation processes.

The value of flow cytometric crossmatch in cardiac transplantation

One of the major clinical problems in cardiac transplantation is that of moderate rejection of the graft, and over the past few years there is increasing evidence that humoral antibody may be important in graft prognosis. The sensitivity of the conventional cytotoxic crossmatch has been questioned, and an increased significance of there of the flow cytometric crossmatch (FCXM) to detect the presence of antibodies before transplantation has been reported. In this study we have examined the sera of 138 cardiac transplants (1988-1992) for the presence of donor-directed IgG and IgM antibodies using FCXM. Sera were collected immediately before transplantation and before the institution of immunosuppressive therapy. All pretransplant cytotoxic crossmatches were negative. After a minimum follow-up period of 3 months, the performance of the transplants was graded by endomyocardial biopsy: 1, no or mild evidence of rejection; 2, patients showing moderate rejection requiring increased immunosuppression. Of the 138 patients studied, 10 patients were excluded as they died within the first week of transplantation. Eight children were excluded since they were given prophylactic ATG (Merieux). A positive FCXM result was defined as showing values in excess of that found for the AB control sera. A significant association was found between the presence of both IgG to T and B cells and IgM to T cells and graft performance (P = 0.02 and 0.93, respectively). Indeed, IgM-directed T-cell antibodies were only found in patients with moderate rejecton. These two groups were mutually exclusive, so that the FCXM was able to identify the presence of moderate rejection in 55% of the patients. In conclusion, results show that pretransplant FCXM in cardiac transplantation provides a more sensitive assay of antibody status in recipients and has proved to be of prognostic value.

Copper(II)–lincomycin: complexation pattern and oxidative activity

Coordination of Cu(II) to lincomycin was studied by potentiometry, UV-Vis, circular dichroism (CD), EPR, NMR, cyclic voltammetry (CV) and ESI-MS. Only mononuclear complexes of stoichiometries ranging from CuL to CuH(-3)L were found. In the main species present at neutral pH, CuH(-2)L, lincomycin bonds Cu(II) through both of its nitrogen donors, and a deprotonated oxygen donor at C4 of the sugar moiety. High pressure liquid chromatography (HPLC) of products of 2'-deoxyguanosine (dG) oxidation and agarose gel electrophoresis of plasmid DNA confirmed that lincomycin complexes effectively facilitate dG oxidation by H2O2, but are not able to cleave double-stranded plasmid DNA.

Coordination of heavy metals by dithiothreitol, a commonly used thiol group protectant

D,L-Dithiothreitol (DTT), known also as Cleland reagent, is a thiol group protectant, used commonly in peptide and protein chemistry. Therefore, it is often added at high concentrations in preparations of proteins relevant to heavy metal biochemistry. The coordination of five of these metal ions, Zn(II), Cd(II), Pb(II), Ni(II) and Cu(I) to DTT was studied by means of potentiometric titrations, and UV-Vis and NMR spectroscopies. It was found that DTT forms specific and very stable polymeric and monomeric complexes with all of these metal ions, using both of its sulfur donors. The quantitative description of these complexes in solution and the solid state provides the basis for predictions of interference from DTT in studies of metal ion binding of thiol-containing biomolecules.

Induction of a secondary structure in the N-terminal pentadecapeptide of human protamine HP2 through Ni(II) coordination. An NMR study

A solution structure of the Ni(II) complex with the N-terminal pentadecapeptide of human protamine HP2 (HP2(1)(-)(15)) was elucidated with the use of a range of one- and two-dimensional (1)H NMR techniques and molecular modeling. A striking double-loop conformation was found, exhibiting the interactions of the aromatic ring of the Tyr(8) residue with the Ni(II) coordination site at Arg(1), Thr(2), and His(3) residues and the side chain of the Arg(15) residue. In such a conformation, a tendency was found for all five positively charged arginine side chains to locate on one side of the molecule, making possible efficient contacts with the DNA double helix. These structural features, induced indirectly by Ni(II) coordination, are discussed in terms of a possible physiological function of the N-terminus of HP2 as a metal-binding site.

Lead effects on protamine-DNA binding

BACKGROUND

Lead impairs male fertility and may affect offspring of exposed males, but the mechanisms for this impairment are not completely clear. Protamine P1 and P2 families pack and protect mammalian sperm DNA. Human HP2 is a zinc-protein and may have an important role in fertility. As lead has affinity for zinc-containing proteins, we evaluated its ability in vitro to bind to HP2 and its effects on HP2-DNA binding. Methods and Results UV/VIS spectroscopic data indicated that HP2 binds both Pb(2+) and Zn(2+)(as chloride salts). They also provided evidence that thiol groups mainly participate for Zn(2+)-binding; however, HP2 has additional binding sites for Pb(2+). The mobility shift assay showed that lead interaction with HP2 caused a dose-dependent decrease on HP2 binding to DNA, suggesting that lead may alter chromatin stability.

CONCLUSIONS

These in vitro results demonstrate that lead can interact with HP2 altering the DNA-protamine binding. This chemical interaction of lead with protamines may result in chromatin alterations, which in turn may lead to male fertility problems and eventually to DNA damage.

Ni(II) specifically cleaves the C-terminal tail of the major variant of histone H2A and forms an oxidative damage-mediating complex with the cleaved-off octapeptide

The acetyl-TESHHK-amide peptide, modeling a part of the C-terminal "tail" of histone H2A, was found previously by us to undergo at pH 7. 4 a Ni(II)-assisted hydrolysis of the E-S peptide bond with formation of a stronger Ni(II) complex with the SHHK-amide product [Bal, W., et al. (1998) Chem. Res. Toxicol. 11, 1014-1023]. To further characterize the hydrolysis and test the resulting Ni(II) complex for redox activity, bovine histone H2A and three peptides were investigated: acetyl-LLGKVTIAQGGVLPNIQAVLLPKKTESHHKAKGK (H2A(34)), modeling the entire "C-tail" of H2A; SHHKAKGK (H2A(8)), modeling the cutoff product of hydrolysis; and acetyl-KTESHKAKGK (H2A(10)), modeling a putative Ni(II) binding site in a minor variant H2A.4 of human histone H2A. The Ni(II)-assisted hydrolysis of H2A and H2A(34) was found to proceed approximately 7-fold faster than that of the Ni(II)-acetyl-TESHHK-amide complex under comparable conditions. In both cases, the Ni(II) complex with H2A(8) was the smaller product of the hydrolysis, indicating a high site specificity of the reaction. Of three other metals tested with H2A(34), only Cu(II) cleaved the E-S bond, although much less efficiently than Ni(II); Co(II) and Zn(II) had no effect whatsoever. The H2A(10) peptide appeared to be fully resistant to hydrolytic cleavage and did not exhibit any redox activity versus H(2)O(2) in the presence of Ni(II) at pH 7.4. Likewise, redox-inactive was the Ni(II)-H2A(34) complex. In contrast, the Ni(II)-H2A(8) complex promoted oxidative damage of pUC19 DNA by H(2)O(2), evidenced by a significant increase in the number of single strand breaks and nucleobase modifications typical for a hydroxyl radical-like species attack on DNA. Interestingly, instead of 8-oxopurines, the corresponding formamidopyrimidines were the major products of the damage. The difference in redox activity between the Ni(II)-H2A(34) and Ni(II)-H2A(8) complexes is most likely associated with their different geometries: octahedral and square planar, respectively. Incubation of the Ni(II)-H2A(8) complex with H(2)O(2) also resulted in degradation of the peptide ligand, especially at its Ser and His residues. Thus, binding of Ni(II) to the ESHHK motif of the histone H2A C-tail is damaging to the histone C-terminal tail and to histone-associated DNA. The results support a dual mechanism of Ni(II)-induced carcinogenesis, including both genotoxic and epigenetic effects.

Lead interaction with human protamine (HP2) as a mechanism of male reproductive toxicity

During spermatogenesis, histones are replaced by protamines, which condense and protect sperm DNA. In humans, zinc contributes to sperm chromatin stability and binds to protamine P2 (HP2). Chemical interactions with nuclear protamines, which prevent normal sperm chromatin condensation, may induce changes in the sperm genome and thus affect fertility and offspring development. Since lead has a high affinity for zinc-containing proteins, we investigated lead interactions with HP2 as a novel mechanism of its toxicity to sperm. UV/vis and CD spectroscopy results indicated that HP2 binds Pb(2+) at two different sites, causing a conformational change in the protein. They also provided evidence that thiol groups are primarily involved in Zn(2+) and Pb(2+) binding to HP2 and that HP2 may have additional binding sites for Pb(2+) not related to Zn(2+). HP2 affinities for Pb(2+) and Zn(2+) were very similar, suggesting that Pb(2+) can compete with or replace Zn(2+) in HP2 in vivo. This interaction of lead with HP2 resulted in a dose-dependent decrease in the extent of HP2-DNA binding, although lead interaction with DNA also contributed to this effect. Therefore, the ability of lead to decrease the level of HP2-DNA interaction may result in alterations to sperm chromatin condensation, and thus in reduced fertility.

Coordination chemistry of glutathione

The metal ion coordination abilities of reduced and oxidized glutathione are reviewed. Reduced glutathione (GSH) is a very versatile ligand, forming stable complexes with both hard and soft metal ions. Several general binding modes of GSH are described. Soft metal ions coordinate exclusively or primarily through thiol sulfur. Hard ones prefer the amino acid-like moiety of the glutamic acid residue. Several transition metal ions can additionally coordinate to the peptide nitrogen of the gamma-Glu-Cys bond. Oxidized glutathione lacks the thiol function. Nevertheless, it proves to be a surprisingly efficient ligand for a range of metal ions, coordinating them primarily through the donors of the glutamic acid residue.

Molecular models in nickel carcinogenesis

Nickel compounds are known human carcinogens, but the exact molecular mechanisms of nickel carcinogenesis are not known. Due to their abundance, histones are likely targets for Ni(II) ions among nuclear macromolecules. This paper reviews our recent studies of peptide and protein models of Ni(II) binding to histones. The results allowed us to propose several mechanisms of Ni(II)-inflicted damage, including nucleobase oxidation and sequence-specific histone hydrolysis. Quantitative estimations of Ni(II) speciation, based on these studies, support the likelihood of Ni(II) binding to histones in vivo, and the protective role of high levels of glutathione. These calculations indicate the importance of histidine in the intracellular Ni(II) speciation.

Coordination chemistry of glutathione

The metal ion coordination abilities of reduced and oxidized glutathione are reviewed. Reduced glutathione (GSH) is a very versatile ligand, forming stable complexes with both hard and soft metal ions. Several general binding modes of GSH are described. Soft metal ions coordinate exclusively or primarily through thiol sulfur. Hard ones prefer the amino acid-like moiety of the glutamic acid residue. Several transition metal ions can additionally coordinate to the peptide nitrogen of the gamma-Glu-Cys bond. Oxidized glutathione lacks the thiol function. Nevertheless, it proves to be a surprisingly efficient ligand for a range of metal ions, coordinating them primarily through the donors of the glutamic acid residue.

Effects of Ni(II) and Cu(II) on DNA interaction with the N-terminal sequence of human protamine P2: enhancement of binding and mediation of oxidative DNA strand scission and base damage

Epidemiological evidence suggests that certain paternal exposures to metals may increase the risk of cancer in the progeny. This effect may be associated with promutagenic damage to the sperm DNA. The latter is packed with protamines which might sequester carcinogenic metals and moderate the damage. Human protamine P2 has an amino acid motif at its N-terminus that can serve as a heavy metal trap, especially for Ni(II) and Cu(II). We have synthesized a pentadecapeptide modeling this motif, Arg-Thr-His-Gly-Gln-Ser-His-Tyr-Arg-Arg-Arg-His-Cys-Ser-Arg-amide (HP21-15) and described its complexes with Ni(II) and Cu(II), including their capacity to mediate oxidative DNA degradation [Bal et al. (1997) Chem. Res. Toxicol., 10, 906-914 and 915-921]. In the present study, effects of HP21-15 on Ni(II)- and Cu(II)-mediated DNA oxidation by H2O2 at pH 7.4 were investigated in more detail using the circular plasmid pUC19 DNA as a target, and the single/double-strand breaks and production of oxidized DNA bases, as end points. Ni(II) alone was found to promote oxidative DNA strand scission (mostly single strand breaks) and base damage, while Cu(II) alone produced the same effects, but to a much greater extent. Both metals were relatively more damaging to the pyrimidine bases than to purine bases. HP21-15 tended to increase the Ni(II)/H2O2-induced DNA breakage. In sharp contrast, the destruction of DNA strands by Cu(II)/H2O2 was almost completely prevented by HP21-15. The effect of HP21-15 on the oxidative DNA base damage varied from a limited enhancement (5-hydroxyhydantoin and thymine glycol) to slight suppression (5-hydroxycytosine, 5-hydroxyuracil, 8-oxoguanine, 8-oxoadenine, 2-hydroxyadenine, fapyguanine and fapyadenine) toward Ni(II)/H2O2. HP21-15 strongly suppressed the oxidative activity of Cu(II)/H2O2 in regard to all bases in DNA. Consistently with the above, the electron spin resonance/spin trap measurements revealed greater and more persistent generation of OH* and O2-*-like oxidants from H2O2 by the Ni(II)-HP21-15 complex than by the Cu(II)-HP21-15 complex (no O2-* was detected). Both complexes were also found to bind to DNA more strongly than HP21-15 alone. The results indicate that protamine P2 is capable of binding Ni(II) and Cu(II) and, in this way, attenuating the mediation of oxidative DNA damage by Cu(II), but not Ni(II). The effects found may be mechanistically involved in the reproductive toxicity and carcinogenicity of metals.

Interaction of Nickel(II) with histones: in vitro binding of nickel(II) to the core histone tetramer

The absorption spectra of Ni(II) bound to the core histone tetramer, (H3-H4)2, of chicken erythrocytes in 500 mM NaCl + 100 mM phosphate (pH 7.4) were recorded. A charge transfer band was seen at 317 nm, characteristic of a bond between Ni(II) and the sulfur atom of Cys-110 of histone H3. The conditional affinity constants for Ni(II) binding at pH 7.4 for low and high Ni(II) saturation (log Kc = 4.26 +/- 0.02 and 5.26 +/- 0.11 M-1, respectively) were calculated from spectrophotometric titrations with the use of this band. The binding of Ni(II) to (H3-H4)2 is proposed to involve the Cys-110 and His-113 of different H3 molecules within the tetramer. The competition between histones and low-molecular-weight chelators for Ni(II) in the cell nucleus, histidine and glutathione, is discussed on the basis of the above results, indicating that histone H3 is very likely to bind Ni(II) dissolved intracellularly from phagocytosed particulate nickel compounds.

Interactions of Nickel(II) with histones: interactions of Nickel(II) with CH3CO-Thr-Glu-Ser-His-His-Lys-NH2, a peptide modeling the potential metal binding site in the "C-Tail" region of histone H2A

A combined pH-metric and spectroscopic (UV/vis, CD, NMR) study of the Ni(II) binding to CH3CO-Thr-Glu-Ser-His-His-Lys-NH2 (AcTESHHKam), a blocked hexapeptide modeling a part of the C-terminal sequence of the major variant of histone H2A (residues 120-125), revealed the formation of a pseudo-octahedral NiHL complex in weakly acidic and neutral solutions. Ni(II) is bound to the peptide through imidazole nitrogens on both of its histidine residues and the carboxylate of the side chain of glutamic acid. At higher pH, a series of square-planar complexes are formed. This process is accompanied by hydrolytic degradation of the peptide. At pH 7.4, the peptide hydrolyzes in a Ni(II)-assisted fashion, yielding the square-planar Ni(II) complex of SHHKam as the sole product detected by CD, MALDI-TOF MS, and HPLC. Quantitative analysis of complex stabilities indicates that the -TESHHK- motif is a very likely binding site for carcinogenic Ni(II) ions in the cell nucleus. The Ni(II)-assisted hydrolysis of the C-terminal chain of histone H2A may provide a novel mechanism of genotoxicity combining the damage to the nucleosome with the generation of further toxic Ni(II) species.

Multi-metal binding site of serum albumin

Circular dichroism and electron spin resonance spectroscopy are used to investigate the second specific metal binding site on human, bovine and porcine albumins. Ni(II), Zn(II) and Cd(II) can displace Cu(II) from the second Cu(II) site but not from the first strong site of human and bovine albumins (the N-terminal site). The second Cu(II) binds more strongly than the other metal ions to the second site of all three proteins, except Zn(II) binding to porcine albumin which is ca. 10 x stronger than Cu(II). The second Cu(II) site appears to be a tetragonal ¿2N, 4O¿ site.

The impact of the amino-acid sequence on the specificity of copper(II) interactions with peptides having nonco-ordinating side-chains

The review presents specific interactions that occur in complexes of Cu(II) ions with peptides composed only of amino acids with nonco-ordinating side chains. Three classes of such peptides are discussed. The first type (NSFRY analogues) is characterised by the presence of a specific combination of bulky and aromatic residues, leading to a formation of multiple weak interactions around Cu(II) that result in an extremely high stability of complexes. The second class is composed of complexes of vasopressins and oxytocins, achieving superstability through a pre-conformation in the peptide molecule. The third group are oligopeptides containing one or two proline residues. These peptides form exotic macrochelate loops with Cu(II) in a result of the break-point effect of Pro residues. Particular emphasis in the review was given to stability constants of complexes, compared to oligoglycine or oligoalanine peptides.

The impact of the amino-acid sequence on the specificity of copper(II) interactions with peptides having nonco-ordinating side-chains

The review presents specific interactions that occur in complexes of Cu(II) ions with peptides composed only of amino acids with nonco-ordinating side chains. Three classes of such peptides are discussed. The first type (NSFRY analogues) is characterised by the presence of a specific combination of bulky and aromatic residues, leading to a formation of multiple weak interactions around Cu(II) that result in an extremely high stability of complexes. The second class is composed of complexes of vasopressins and oxytocins, achieving superstability through a pre-conformation in the peptide molecule. The third group are oligopeptides containing one or two proline residues. These peptides form exotic macrochelate loops with Cu(II) in a result of the break-point effect of Pro residues. Particular emphasis in the review was given to stability constants of complexes, compared to oligoglycine or oligoalanine peptides.

Binding of nickel(II) and copper(II) to the N-terminal sequence of human protamine HP2

A potentiometric and spectroscopic (UV/vis and CD) study of Cu(II) and Ni(II) binding to the N-terminal pentadecapeptide of human protamine HP2 (HP2(1-15)) was performed. The results indicate that the N-terminal tripeptide motif Arg-Thr-His is the exclusive binding site for both metal ions at a metal to HP2(1-15) molar ratio not higher than 1. The very high value of protonation-corrected stability constant (log *K) for Ni(II)-HP2(1-15) complex, -19.29, indicates that HP2 has the potential to sequester Ni(II) from other peptide and protein carriers, including albumin. The same is likely for Cu(II) (log *K = -13.13). The CD spectra of Cu(II) and Ni(II) complexes of HP2(1-15) indicate that the N-terminal metal binding affects the overall conformation of the peptide that, in turn, may alter interaction of HP2 with DNA. These results imply HP2 as a likely target for the toxic metals Ni(II) and Cu(II).

Mediation of oxidative DNA damage by nickel(II) and copper(II) complexes with the N-terminal sequence of human protamine HP2

The potential of Ni(II) and Cu(II) complexes with Arg-Thr-His-Gly-Gln-Ser-His-Tyr-Arg-Arg-Arg-His-Cys-Ser-Arg-amide (HP2(1-15)), a peptide modeling the N-terminal amino acid sequence of human protamine HP2, to mediate oxidative DNA damage was studied by measurements of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) generation from 2'-deoxyguanosine (dG) and calf thymus DNA and by formation of double-strand breaks in calf thymus DNA. The concentrations of reagents were 0.1 mM dG and the metal-HP2(1-15) complex, 1 mM H2O2, 1.5 mM DNA (per phosphate group), 100 mM phosphate buffer, pH 7.4, ambient O2. Samples were incubated at 37 degrees C for 16-24 h. The Cu(II)-HP2(1-15) complex was found to be an effective promoter of the formation of 8-oxo-dG from both dG and DNA with ambient O2 (approximately 13- and 3-fold increase versus the oxidant alone, respectively) and H2O2 (approximately 25-fold increase in either case). The Ni(II)-HP2(1-15) complex was ineffective with O2 versus 8-oxo-dG production from both substrates but markedly enhanced the attack of H2O2 on dG and DNA (approximately 5-fold increase of 8-oxo-dG production in either case). Both Cu(II)- and Ni(II)-HP2(1-15) equally promoted double-strand scission by H2O2 in calf thymus DNA. The promotion by the complexes of dG and DNA oxidation with H2O2 was accompanied by oxidative damage to the complexes themselves, consisting of decreasing contents of their His (to approximately 50% of control in either complex) and especially Tyr (down to 48% of control in Cu(II)- and 19% in Ni(II)-HP2[1-15]) residues, as well as appearance of aspartic acid, the known oxidation product of His residues in peptides (up to 22% vs Gly for Cu(II)- and 10% for Ni(II)-HP2(1-15)). The above results provide a novel chemical mechanism of Cu(II) and Ni(II) toxicity and may have wide implications for reproductive and transgenerational effects of metal exposure.

Copper(II) interactions with an experimental antiviral agent, I-deoxynojirimycin, and oxygen activation by resulting complexes

1-deoxynojirimycin (DNJ), a 5-imino analog of 1-deoxyglucose, is a potent inhibitor of alpha-glucosidase 1. DNJ and its derivatives have been considered as experimental drugs against human HIV-1 and hepatitis B viruses. Since amino and imino ligands have a high affinity for copper, it seems possible that biological activity of DNJ may be, at least in part, modulated by tissue copper. To test this possibility, potentiometric and spectroscopic studies of the complexation of DNJ by cupric ions were performed in order to obtain thermodynamic and structural background for further pharmacologic investigations. The effect of histidine, a major tissue copper carrier, on coordination equilibria was also studied. Results indicate that DNJ and Cu(II) form two stable complexes at physiological pH, CuH-1(DNJ)2+ and CuH-2(DNJ)2, involving Cu(II) chelation by the N-5 and O-6 donor atoms. In the presence of histidine, ternary complexes are also formed, of which the CuDNJHis+ species is stable in the physiological pH range. Binary Cu(II)-DNJ complexes are extremely effective mediators of in vitro oxidation of the guanine moiety in both 2'-deoxyguanosine (dG) and DNA to 8-oxoguanine (8-oxo-dG) and of DNA double strand scission by ambient O2 or H2O2. This mediation is suppressed by histidine in dG, but not in DNA. The results suggest that tissue Cu(II) may greatly enhance nonspecific cytotoxic effects of systemically administered DNJ through oxidative damage mechanisms, and therefore the prospective use of DNJ for therapeutic purposes must be developed with caution. On the other hand, however, the expected high genotoxic potential of synthetic Cu(II)-DNJ complexes may be used against viruses by means of targeted delivery of these complexes to the infected cells.

Characterization of pNiXa, a serpin of Xenopus laevis oocytes and embryos, and its histidine-rich, Ni(II)-binding domain

A Ni(II)-binding serpin, pNiXa, is abundant in Xenopus oocytes and embryos. Kinetic assays show that purified pNiXa strongly inhibits bovine alpha-chymotrypsin (Ki = 3 mM), weakly inhibits porcine elastase (K1 = 0.5 microM), and does not inhibit bovine trypsin. The reversible, slow-binding inhibition of alpha-chymotrypsin by pNiXa is unaffected by Ni(II). Ovochymase in egg exudates is inhibited by pNiXa, but to a limited extent, even at high pNiXa concentrations. An octadecapeptide that models the His-rich domain (-HRHRHEQQGHHDSAKHGH-) of pNiXa forms six-coordinate, octahedral Ni(II)-complexes when the N-terminus is acetylated, and a square-planar Ni(II)-complex when the N-terminus is unblocked. Spectroscopy reveals two distinct types of octahedral Ni(II)-coordination to the N-acetylated octadecapeptide, involving, respectively, 3-4 and 5-6 imidazole nitrogens; the octadecapeptide undergoes partial, reversible precipitation in pH- and Ni(II)-dependent fashion, suggesting an insoluble, Ni(II)-coupled (Hx)n-dimer. Such (Hx)n-peptide interaction is confirmed by an enzyme-linked biotinavidin assay with N-biotin-KHRHRHE-amide and N-acetyl-KHRHRHE-resin beads, which become coupled after adding Ni(II) or Zn(II). H2O2 oxidation of 2'-deoxyguanosine to mutagenic 8-hydroxy-2'-deoxyguanosine is enhanced by the octahedral Ni(II)-octadecapeptide complex, although the effect is more intense with the square-planar Ni(II)-octadecapeptide complex. Immunoperoxidase staining of whole mounts with pNiXa antibody shows that pNiXa is distributed throughout gastrula-stage embryos and is localized during organogenesis in the brain, eye, spinal cord, myotomes, craniofacial tissues, and other sites of Ni(II)-induced anomalies. Patterns of pNiXa staining are similar in controls and Ni(II)-exposed embryos. Binding of Ni(II) to pNiXa may cause embryotoxicity by enhancing oxidative reactions that produce tissue injury and genotoxicity. Although the natural target proteinases for pNiXa inhibition have not been established, pNiXa may be an important regulator of proteolysis during embryonic development.

Interactions of nickel(II) with histones: enhancement of 2'-deoxyguanosine oxidation by Ni(II) complexes with CH3CO-Cys-Ala-Ile-His-NH2, a putative metal binding sequence of histone H3

Studies of 2'-deoxyguanosine oxidation by hydrogen peroxide in the presence of CH3CO-Cys-Ala-Ile-His-NH2 (CAIH) and/or NiCl2 have been carried out in 100 mM phosphate buffer (pH 7.4) at 37 degrees C. The dimeric CAIH oxidation product, CAIH disulfide, and its weak, octahedral Ni(II) complex, rather than the monomeric CAIH and its strong, square-planar Ni(II) complex, were found to be major catalysts of 8-oxo-2'-deoxyguanosine (8-oxo-dG) formation. The presence of Ni(II) largely enhanced 8-oxo-dG yield, especially at submillimolar concentrations of H2O2. The reaction was found not to involve detectable amounts of free radicals or Ni(III). These results, together with those published previously [Bal, W. et al. (1995) Chem. Res. Toxicol. 8, 683-692], lay a framework for the detailed investigations of the interactions of histone octamer with Ni(II) and other metal ions. They also suggest that molecular mechanisms of nickel carcinogenesis may involve oxidative damage processes catalyzed by weak Ni(II) complexes with cellular components.

Interactions of nickel(II) with histones. Stability and solution structure of complexes with CH3CO-Cys-Ala-Ile-His-NH2, a putative metal binding sequence of histone H3

Nickel(II) compounds are established human carcinogens, but the molecular mechanisms underlying their activity are only partially known. One mechanism may include mediation by nickel of promutagenic oxidative DNA damage that depends on Ni(II) binding to chromatin. To characterize such binding at the histone moiety of chromatin, we synthesized the peptide CH3CO-Cys-Ala-Ile-His-NH2 (L), a model of the evolutionarily conserved motif in histone H3 with expected affinity for transition metals, and evaluated its reactivity toward Ni(II). Combined spectroscopic (UV/vis, CD, NMR) and potentiometric measurements showed that, at physiological pH, mixtures of Ni(II) and L yielded unusual macrochelate complexes, NiL and NiL2, in which the metal cation was bound through Cys and His side chains in a square-planar arrangement. Above pH 9, a NiH-3L complex was formed, structurally analogous to typical square-planar nickel complexes. These complexes are expected to catalyze oxidation reactions, and therefore, coordination of Ni(II) by the L motif in core histone H3 may be a key event in oxidative DNA base damage observed in the process of Ni(II)-induced carcinogenesis.

Cu(II) binding by angiotensin II fragments: Asp-Arg-Val-Tyr-Ile-His and Arg-Val-Tyr-Ile-His. Competition between amino group and imidazole nitrogens in anchoring of metal ions

Potentiometric and spectroscopic (absorption, circular dichroism and electron paramagnetic resonance) study on the coordination of two angiotensin II fragments (Asp-Arg-Val-Tyr-Ile-His and Arg-Val-Tyr-Ile-His) to Cu(II) ions has shown that competition between amino and imidazole nitrogens to anchor metal ions is a complicated process and may lead to formation of macrochelate rings. The important factor that influences this competition is the distance between competing His and N-terminal residues (number of spacer residues in a peptide sequence).