[Type 2 amiodarone-induced thyrotoxicosis: efficacy of glucocorticoid therapy, a retrospective analysis].

BACKGROUND: Type 2 amiodarone-induced thyrotoxicosis remains a significant problem of endocrinology and cardiology. Due to the increase a life expectancy of the population, the prevalence of cardiac arrhythmias and prescribing of amiodarone are increasing. Thyrotoxicosis aggravates the existing cardiovascular disease in patients, leads to the progression of left ventricular dysfunction, relapses of arrhythmias, increasing the risk of adverse outcomes. The tactic of further management of patients is complicated: it is necessary to resolve the issue of canceling or continuing the use of antiarrhythmic drugs necessary for a patient with a history of cardiac arrhythmia, as well as competent therapy of the thyroid pathology that has arisen. Oral glucocorticoids are the first-line drugs for the treatment of patients with moderate and severe type 2  amiodarone-induced thyrotoxicosis. Despite the appearance of clinical recommendations, opinions on the management of patients are differ, both among cardiologists and among endocrinologists. Often thyrostatics are prescribed to patients simultaneously with glucocorticoids, although it doesn't have pathogenetic basis. AIM: To evaluate the efficacy of various therapy options in patients with type 2 amiodarone-induced thyrotoxicosis. MATERIALS AND METHODS: The retrospective study included 38 patients (20 men and 18 women aged 35 to 85 years) with type 2 amiodarone-induced thyrotoxicosis. All patients underwent an analysis of anamnestic, anthropometric data, complex laboratory and instrumental diagnostics. According to the treatment options, 3 groups were retrospectively formed: without therapy (n=19), taking glucocorticoids (n=11) and combination of glucocorticoids and thyrostatics (n=8). The follow-up period was 6-18 months, including the treatment. The efficacy of treatment in the groups was evaluated by the time of reaching euthyroidism on the background of glucocorticoid therapy and duration of thyrotoxicosis; the search was conducted for potential predictors of delayed response to glucocorticoid therapy and long-term course of thyrotoxicosis. RESULTS: The average age was 62.0 [52.9; 66.3] years. The level of free thyroxine was significantly decreased after 1 month from the start of therapy in both groups: from 38.1 [32.1; 58.4] to 23.4 [19.6; 29.3] pmol/l (p<0.001) in the group taking glucocorticoids; from 73.9 [42.2; 75.6] to 39.3 [22.4; 47.2] pmol/l (p<0.001) in the combination therapy group. The time of reaching euthyroidism was longer in the combination therapy group (p=0.047), didn't depend on the dose (p=0.338) and duration of taking thiamazole (p=0.911), the delayed response to therapy correlated with age (p=-0.857; p=0.007) and time interval from the appearance of clinical symptoms of thyrotoxicosis to the start of glucocorticoid therapy (p=0.881; p<0.001). CONCLUSION: The results demonstrate the dependence of glucocorticoid response on the age of the patient and start time of therapy relative to the duration of thyrotoxicosis, inexpediency of additional prescribing thyrostatics in type 2 amiodarone-induced thyrotoxicosis.

[Solitary mediastinal fibrous tumor complicated by hypoglycemic crises (Doege-Potter syndrome)]. / Solitarnaya fibroznaya opukhol' sredosteniya, oslozhnennaya gipoglikemicheskimi krizami (sindrom Doge­Pottera).

Diagnostic and treatment algorithms for large mediastinal tumors are clear. However, long-term results are not always good. They largely depend on early diagnosis and morphological structure of tumor. Neoplasms may be asymptomatic for a long time, especially in case of slow growth. These tumors are usually diagnosed as soon as complications occur (for example, compression syndrome). Routine X-ray screening is rarer situation. Paraneoplastic syndromes are rare, and some ones are casuistic and unknown to surgical community. We describe the diagnosis and treatment of a patient with giant solitary mediastinal tumor complicated by hypoglycemic crises (Doege-Potter syndrome). This complication was life-threatening and required a multidisciplinary approach. Aggressive surgical approach cured the patient and returned her to normal lifestyle. The proposed algorithm for perioperative drug therapy was effective and deserves attention. This report will be useful for surgeons, oncologists, anesthesiologists, intensive care specialists and endocrinologists.

[Hypochondriasis in Graves' disease: the role of pathologic factors and clinical characteristics endocrinopathy]. / Ipokhondricheskie razvitiya pri bolezni Greivsa: rol' patokharakterologicheskikh faktorov i klinicheskikh kharakteristik endokrinopatii.

OBJECTIVE: Clinical qualification of hypochondriasis or illness anxiety disorder (IAD) in Graves' disease (GD) and verification of associated personality and endocrinological factors. MATERIAL AND METHODS: A sample consisted of 27 patients (25 female and 2 male, mean age 48.4 years) with GD and personality disorders (PDs). The patients were examined clinically and with interviews for the assessment of PD according to DSM-IV (SCID-II-PD) and the Short Health Anxiety Inventory (SHAI). RESULTS: IAD was diagnosed in 8 cases (29.6%), of which the main study group was formed. The remaining 19 patients, who did not show signs of IAD, were assigned to the control group. In the main group, the average score on the SHAI «health anxiety¼ subscale was significantly higher (10.2 vs 4.8 points, p<0.05) corresponding to the clinical qualification of the condition as IAD. When assessing the frequency of categorical PDs, it was found that there were no affective PDs in the main group, likewise there were no anxiety cluster PDs in the control group (p<0.05). In turn, in the main group, PDs were characterized by such dimensions as the phenomena of psychopathological diathesis, reactive lability, neuropathy, which were not observed in the control group. The endocrinological factor that differed significantly in main and control groups was the frequency of recurrence of GD (75.0% vs, 40.1%, p<0.05). CONCLUSION: Despite the generally relatively favourable prognosis of GD, there is a significant frequency of IAD, the key role in the formation of which is apparently played by the parameters of the premorbid characteristics, as well as GD recurrence.

[Radioactive iodine in the treatment of Graves' disease: history and modern concept of radionuclide therapy].

Radioactive iodine 131I is a theranostic isotope used both for diagnosis and therapy of benign thyroid diseases and thyroid cancer for 85 years. The formation of nuclear medicine is closely linked with the use of 131I. The history of radioiodine therapy began in 1941, when endocrinologist Saul Hertz for the first time used 131I to treat patients with Graves' disease. Since 1946 radioactive iodine 131I became widely available, and its effectiveness became public knowledge after reports on thyrotoxicosis treatment published in the Journal of the American Medical Association by multidisciplinary groups of scientists - physicists and endocrinologists. In 1951, isotope 131I became the first Food and Drug Administration approved RP for the treatment of thyroid disorders. Around the same time on the basis of the First Moscow Medical Institute studies on the use of radioiodine isotopes in patients with thyrotoxicosis began. The head of the Soviet group on the studying of radioactive iodine was the physician-scientist Vera Georgievna Spesivtseva. The research works of medical physicists Edith Quimby and Leonidas Marinelli in optimizing therapeutic strategies using radioactive substances in the late 1940s and the wording of the ALARA (As Low As Reasonably Achievable) principle of minimizing exposure of ionizing radiation by the International Commission on Radiological Protection in 1954 contributed to the greater introduction of radionuclides into the medicine.

[Time-restricted eating as a novel strategy for treatment of obesity and it's comorbid conditions].

The article provides a review of the current literature about time-restricted eating (TRE) as a new tool for the treatment of obesity and comorbid conditions. The search for new nutritional strategies in obesity, one of which is TRE, is due to the weak adherence of patients to hypocaloric diets in the long term, as well as the available data on the importance of -desynchronization of food intake with natural circadian rhythms in the development and progression of obesity and cardio--metabolic complications. The article describes the main mechanisms that regulate the circadian rhythms of food intake and nutrient absorption, substantiates the importance of adhering to a physiological diet for maintaining metabolic health. The main part of the review is devoted to reviewing the currently available researches on the effectiveness of various strategies of intermittent energy restriction for weight loss and the correction of metabolic parameters. Potential mechanisms of  the -effect of TRE on health are discussed, including those mediated by an unintentional decrease in caloric intake and changes in eating behavior, and differences in the effectiveness of early and late TRE. The article contains a detailed discussion of the potential problems and contradictions associated with the use of time-restricted eating in clinical practice, namely: the limitations and inconsistencies of the available clinical trials, the lack of data on long-term efficacy and safety, social and psychological limitations that impede the widespread use of TRE.

[Survival predictors in patients with ectopic acth syndrome].

AIM: To determine significant factors affecting the survival of patients with ectopic ACTH syndrome (EAS). MATERIALS AND METHODS: A multi-center, observational study with a retrospective analysis of patients with EAS. The end point of the study was the fatal outcome of patients from various causes. In order to identify predictors of survival or mortality, univariate and multifactorial Cox regression analyses were carried out. ROC-analysis was used to determine the prognostic threshold values of individual predictors. The survival analysis was carried out using the Kaplan-Mayer method. Statistical data processing was carried out by using IBM SPSS Statistics 23. RESULTS: The age of patients at the time of diagnosis ranged from 12 to 76 years (Me 40 years [28;54]). The age of the studied population was 55 years [38; 64] for women and 42 years [32; 54] for men. The median period of observation was 50 months [13;91], with a maximum follow-up of 382 months. 92 patients (60,9%) had bronchopulmonary NET, 17 (11,3%) - thymic carcinoid, 8 - pancreatic NET, 5 -pheochromocytoma, 1- cecum NET, 1- appendix carcinoid tumor, 1 - medullary thyroid cancer and 26 (17,2%) patients had an occult NET. The primary tumor was removed in 101 patients (66,9%). Bilateral adrenalectomy was performed in 42 (27,8%) cases. Metastases were revealed in 23,2% (n=35) of patients. Relapse of the disease was observed in 24,4%, long-term remission was preserved in 64 patients (74,4%). Death occurred in 42 patients (28%). The average age of survivors was 47,0±15,2 versus 53,5±15,6 years for the deceased (p=0,022). The average survival time from diagnosis for the deceased was 32 months, Me 16,5 months [7;54]. Multivariate analysis revealed that the following factors have a direct impact on survival: age of diagnosis ≥51 years (OR 4,493; 95% CI 2,056-9,818, p<0,001), bronchopulmonary neuroendocrine tumor (NET) (OR 0,281; 95% CI 0,119-0,665, p=0,004), the presence of distant metastases (OR 2,489; 95% CI 1,141-5,427, p=0,022), late-night salivary cortisol (LNSC) ≥122,2 nmol/L (OR 2,493; 95% CI 1,014-6,128, p=0,047). CONCLUSION: The prognosis of patients with EAS is influenced by the age of diagnosis, NET localization, distant metastases and level of LNSC. The most common cause of ectopic ACTH syndrome was bronchopulmonary NET which was associated with the best survival rate.

Blind source separation of molecular components of the human skin in vivo: non-negative matrix factorization of Raman microspectroscopy data.

Determination of the molecular composition of the skin is crucial for numerous tasks in medicine, pharmacology, dermatology and cosmetology. Confocal Raman microspectroscopy is a sensitive method for the evaluation of molecular depth profiles in the skin in vivo. Since the Raman spectra of most of the skin constituents significantly superimpose, a spectral decomposition by a set of predefined library components is usually performed to disentangle their contributions. However, the incorrect choice of the number and type of components or differences between the spectra of the basic components measured in vitro and in vivo can lead to incorrect results of the decomposition procedure. Here, we investigate an alternative data-driven approach based on a non-negative matrix factorization (NNMF) algorithm of depth-resolved Raman spectra of skin that does not require a priori information of spectral data for the analysis. Using the model and experimentally measured depth-resolved Raman spectra of the upper epidermis in vivo, we show that NNMF provides depth profiles of endogenous molecular components and exogenous agents penetrating through the upper epidermis for the spectra and concentration. Moreover, we demonstrate that this approach is capable of providing new information on the molecular profiles of the skin.

[Endocrine late-effects and bone mineral density after combined treatment of malignant brain tumors in childhood and adolescence].

BACKGROUND: The implementation of standardized protocols for combined treatment of cancer into clinical practice inevitably leads to a long-term consequence. AIMS: To study the prevalence of endocrine disorders, to assess the prevalence and degree of decline of bone mineral density (BMD) in individuals who have undergone combined treatment of malignant brain tumors in childhood and adolescence. MATERIALS AND METHODS: A retrospective study was conducted with 59 young adults (31 men; 28 women) who have undergone surgical treatment of malignant brain tumour followed by radiation treatment (craniospinal radiation in combination with or without polychemotherapy). Group I consisted of 37 patients, who were treated between the ages of 3 and 16 years. Group II included 22 patients who received treatment between the ages of 16 and 38 years. RESULTS: GH deficiency according to the results of the insulin hypoglycemia test was diagnosed in 48 patients (81%), 22 -patients had secondary adrenal insufficiency (37%). The majority of those examined (33 patients (56%)) did not achieve the target growth. Only 5 people from I group was treated with recombinant GH. Correlation analysis demonstrates that age of treatment is the main factor affecting final growth (r=0,619, p<0,001). Many cases of hypothyroidism (n=39 (66%)) and hypogonadism (19 women; 17 men) were detected. According to the DXA, a decrease of BMD ≤-2.0 SD (Z-score) in L1-L4 was found in 35 of 59 patients (59%). The BMD in the I group was significantly lower than in patients treated at an older age (p<0.001). A moderate correlation was discovered between BMD in L1-L4 at the time of examination and the level of estradiol in women (r=0.596, p<0.05) and testosterone in men (r=0.472, p<0.05). Direct correlation between BMD and age of diagnosis was revealed (r=0.781, p<0.01). CONCLUSIONS: The results show that patients need to be monitored annually and for life after the combined treatment of malignant brain tumors in order to detect the long-term effects of the treatment. The high incidence of osteopenic conditions determines the relevance and need for early diagnosis to prevent further bone loss, reduced bone strength and the risk of fractures.

[Clinical and laboratory characteristics and results of treatment of patients with ACTH-producing neuroendocrine tumors of various localization].

AIM: To study the clinical, biochemical characteristics, treatment results and follow-up of patients with ectopic ACTH syndrome EAS (ACTH adrenocorticotropic hormone ). MATERIALS AND METHODS: A retrospective, observational, single-center study of 130 patients with EAS. Demographic information of patients, medical history, results of laboratory and instrumental investigations at the pre- and postoperative stages and follow-up of EAS were analyzed. RESULTS: The mean age at the diagnosis ranged from 12 to 74 years (Me 40 years [28; 54]). The duration of the disease from the onset of symptoms to the verification of the diagnosis varied from 2 to 168 months (Me 17.5 months [7; 46]). Eighty-one (62,3%) patients had bronchopulmonary NET, 9 thymic carcinoid, 7 pancreatic NET, 5 pheochromocytoma, 1 cecum NET, 1 appendix carcinoid tumor, 1 medullary thyroid cancer and 25 (19.2%) had an occult source of ACTH. The median follow-up period of patients was 27 months [9.75; 61.0] with a maximum follow-up of 372 months. Currently, primary tumor was removed in 82 (63.1%) patients, bilateral adrenalectomy was performed in 23 (18%) patients, in 16 of them there was an occult source of ACTH-producing NET and in 7 patients in order to control hypercortisolism after non-successful surgical treatment. Regional and distant metastases were revealed in 25 (19.2%) patients. At the time of the last observation 59 (72%) patients were exhibited a full recovery, 12 (14.6%) had relapse of the disease and 26 (20%) died from multiple organ failure (n=18), pulmonary embolism (n=4), surgical complications (n=2), disseminated intravascular coagulation syndrome (n=1) or COVID-19 (n=1). CONCLUSION: In our cohort of patients bronchopulmonary NET are the most frequent cause of EAS (62.3%). Surgical treatment leads to remission of hypercortisolism in 72% cases; the proportion of relapse (14.6%) and fatal outcome (20%) remains frequent in EAS.

[Primary hyperparathyroidism and vitamin D deficiency].

Primary hyperparathyroidism (PHPT) is the third most common endocrine disease after diabetes mellitus and thyroid pathology. Recent epidemiological and experimental data have shown that long-term maintenance of low vitamin D levels in the blood can lead to the development of hyperplastic processes in the cells of the parathyroid glands, followed by autonomous production of parathyroid hormone. In PHPT vitamin D insufficiency or deficiency according to various sources occurs with a frequency of 5377% of cases. The literature review indicates more severe disease in patients with concomitant vitamin D deficiency. The expediency of preoperative assessment of vitamin D levels in all patients with PHPT in order to minimize the risk of hypocalcemia after parathyroidectomy is discussed. This article presents the relationship between vitamin D deficiency and PHPT, as well as possible methods for correcting vitamin D deficiency in PHPT. Molecular and cellular mechanisms of the occurrence of pathological processes in the parathyroid glands under conditions of low vitamin D levels are presented.

Melanin distribution from the dermal-epidermal junction to the stratum corneum: non-invasive in vivo assessment by fluorescence and Raman microspectroscopy.

The fate of melanin in the epidermis is of great interest due to its involvement in numerous physiological and pathological processes in the skin. Melanin localization can be assessed ex vivo and in vivo using its distinctive optical properties. Melanin exhibits a characteristic Raman spectrum band shape and discernible near-infrared excited (NIR) fluorescence. However, a detailed analysis of the capabilities of depth-resolved confocal Raman and fluorescence microspectroscopy in the evaluation of melanin distribution in the human skin is lacking. Here we demonstrate how the fraction of melanin at different depths in the human skin in vivo can be estimated from its Raman spectra (bands at 1,380 and 1,570 cm-1) using several procedures including a simple ratiometric approach, spectral decomposition and non-negative matrix factorization. The depth profiles of matrix factorization components specific to melanin, collagen and natural moisturizing factor provide information about their localization in the skin. The depth profile of the collagen-related matrix factorization component allows for precise determination of the dermal-epidermal junction, i.e. the epidermal thickness. Spectral features of fluorescence background originating from melanin were found to correlate with relative intensities of the melanin Raman bands. We also hypothesized that NIR fluorescence in the skin is not originated solely from melanin, and the possible impact of oxidized species should be taken into account. The ratio of melanin-related Raman bands at 1,380 and 1,570 cm-1 could be related to melanin molecular organization. The proposed combined analysis of the Raman scattering signal and NIR fluorescence could be a useful tool for rapid non-invasive in vivo diagnostics of melanin-related processes in the human skin.

[Differential diagnosis of normocalcemic hyperparathyroidism and idiopathic hypercalciuria on the example of clinical case].

Idiopathic hypercalciuria is a heterogeneous generalized disorder caused by various defects in calcium transport and increased urinary calcium excretion. The main etiopathogenetic factors are violations of vitamin D metabolism, changes in the sensitivity of calcitriol receptors and violations of the processes of calcium reabsorption in the proximal tubules and in the ascending knee of the Henle loop. This article presents a clinical observation of patient with idiopathic hypercalciuria, initially high levels of parathyroid hormone (PTH) in the absence of hyperparathyroidism. Therapy with thiazide diuretics allowed to achieve normalization of daily urinary calcium excretion and reducing PTH. Despite the low prevalence of idiopathic hypercalciuria, differential diagnosis of this metabolic disorder should be carried out with mandatory consideration of clinical and laboratory data, as well as with diseases that may cause increased PTH production.

[Inluence of osteoporosis and its causative factors on the prevention of recurrence of urinary stone disease].

INTRODUCTION: The aim of postoperative examination, treatment and follow-up of patients with urinary stone disease is a prevention of recurrence. A choice of method of prevention is based on the results of postoperative examination with consideration of etiological factors of urinary stone disease. An analysis of influence of osteoporosis and its causative factors on the recurrence of urinary stone disease is presented in the article. AIM: to clarify the influence of osteoporosis and its causative factors on excretion of calcium, uric acid and recurrence of urinary stone disease. MATERIALS AND METHODS: A total of 86 patients after surgical treatment of urinary stone disease were included in the study. A physicochemical analysis of stones and their fragments, excretion of calcium and uric acid were done postoperatively. The risk factors for osteoporosis were identified using specific questionnaire. Bone mineral density (BMD) was assessed by X-ray densitometry. After X-ray phasic analysis of the stones and studying of the daily excretion of calcium and uric acid, 10 and 7 patients were prescribed to thiazide diuretics and allopurinol, respectively. In 69 patients (80.2%) there were no indications to the treatment and all of them were included in control surveillance group. RESULTS: Calcium oxalate stones were predominated in patients who were under surveillance (=0,0254). A prevalence of risk factors for osteoporosis was similar in all groups (=0,2156), as well as rate of decrease in BMD (=0,64). In patients taking thiazide diuretics, a significant decrease in daily calcium excretion was found (=0,0054) without significant changes in excretion of uric acid and diuresis volume. Among patients receiving allopurinol there was a significant decrease in daily uric acid excretion (=0,021), without significant changes in excretion of calcium and diuresis volume. There were no significant changes of these values in the control group. A recurrence of urinary stone disease in treatment group was detected in 4 patients with a decrease of BMD after 381+/-61 days, while in control group there were 5 recurrences in patients with decreased BMD and I recurrence in patient with normal BMD after 836+/-64 days. CONCLUSION: Treatment aimed at prevention of recurrence of urinary stone disease allows to correct detected metabolic disturbances. However, such factor as the decrease in BMD can influence on the rate and frequency of recurrence of urinary stone disease. A clarifying of risk factors for osteoporosis and diagnosis of osteoporosis allow to give reliable recommendations for its treatment and to decrease risk of recurrence of urinary stone disease.

Label-Free Multiphoton Microscopy: The Origin of Fluorophores and Capabilities for Analyzing Biochemical Processes.

Multiphoton microscopy (MPM) is a method of molecular imaging and specifically of intravital imaging that is characterized by high spatial resolution in combination with a greater depth of penetration into the tissue. MPM is a multimodal method based on detection of nonlinear optical signals - multiphoton fluorescence and optical harmonics - and also allows imaging with the use of the parameters of fluorescence decay kinetics. This review describes and discusses photophysical processes within major reporter molecules used in MPM with endogenous contrasts and summarizes several modern experiments that illustrate the capabilities of label-free MPM for molecular imaging of biochemical processes in connective tissue and cells.

Fluorescence detection of protein content in house dust: the possible role of keratin.

We propose a fluorescence method for protein content assessment in fine house dust, which can be used as an indicator of the hygienic state of occupied rooms. The results of the measurements performed with 30 house dust samples, including ultrafiltration experiments, strongly suggest that the fluorescence emission of house dust extracts excited at 350 nm is mainly due to protein fragments, which are presumably keratin hydrolysates. This suggestion is supported by several facts: (i) Spectral band shapes for all the samples under investigation are close and correspond to that of keratin; (ii) fluorescence intensity correlates with the total protein content as provided by Lowry assay; (iii) treatment of the samples with proteinase K, which induces keratin hydrolysis, results in fluorescence enhancement without changing fluorescence band shape; and (iv) Raman spectra of keratin and fine house dust samples exhibit a very similar structure. Based on the obtained results and literature data, we propose a hypothesis that keratin is a major substrate for fluorescence species in fine house dust, which are responsible for emission at 350-nm excitation.

Tyrosine fluorescence probing of conformational changes in tryptophan-lacking domain of albumins.

We addressed the possibility of using tyrosine (Tyr) fluorescence for monitoring conformational changes of proteins which are undetectable via tryptophan (Trp) fluorescence. The model objects, human (HSA) and bovine (BSA) serum albumins, contain one and two Trp residues, respectively, while Tyr is more uniformly distributed over their structure. The results of the investigation of albumins interaction with ethanol using intrinsic Trp and Tyr steady-state and time-resolved picosecond fluorescence indicated the presence of an intermediate at 10% (v/v) of ethanol in solution, that was supported by the results of extrinsic fluorescence measurements with the Nile Red dye. Based on the comparison of HSA and BSA Trp and Tyr fluorescence, it was suggested that conformational changes at low ethanol concentration are located in the domain III of albumins, which lacks tryptophan residues. The sensitivity of Tyr fluorescence to domain III alterations was further verified by studying albumins interaction with GdnHCl.

Photosystem II Activity of Wild Type Synechocystis PCC 6803 and Its Mutants with Different Plastoquinone Pool Redox States.

To assess the role of redox state of photosystem II (PSII) acceptor side electron carriers in PSII photochemical activity, we studied sub-millisecond fluorescence kinetics of the wild type Synechocystis PCC 6803 and its mutants with natural variability in the redox state of the plastoquinone (PQ) pool. In cyanobacteria, dark adaptation tends to reduce PQ pool and induce a shift of the cyanobacterial photosynthetic apparatus to State 2, whereas illumination oxidizes PQ pool, leading to State 1 (Mullineaux, C. W., and Holzwarth, A. R. (1990) FEBS Lett., 260, 245-248). We show here that dark-adapted Ox(-) mutant with naturally reduced PQ is characterized by slower QA(-) reoxidation and O2 evolution rates, as well as lower quantum yield of PSII primary photochemical reactions (Fv/Fm) as compared to the wild type and SDH(-) mutant, in which the PQ pool remains oxidized in the dark. These results indicate a large portion of photochemically inactive PSII reaction centers in the Ox(-) mutant after dark adaptation. While light adaptation increases Fv/Fm in all tested strains, indicating PSII activation, by far the greatest increase in Fv/Fm and O2 evolution rates is observed in the Ox(-) mutant. Continuous illumination of Ox(-) mutant cells with low-intensity blue light, that accelerates QA(-) reoxidation, also increases Fv/Fm and PSII functional absorption cross-section (590 nm); this effect is almost absent in the wild type and SDH(-) mutant. We believe that these changes are caused by the reorganization of the photosynthetic apparatus during transition from State 2 to State 1. We propose that two processes affect the PSII activity during changes of light conditions: 1) reversible inactivation of PSII, which is associated with the reduction of electron carriers on the PSII acceptor side in the dark, and 2) PSII activation under low light related to the increase in functional absorption cross-section at 590 nm.

Experimental evidence of incomplete fluorescence quenching of pyrene bound to humic substances: implications for Koc measurements.

Fluorescence quenching (FQ) is extensively used for quantitative assessment of partition coefficients (KOC) of polycyclic aromatic hydrocarbons (PAHs) to natural organic materials - humic substances (HS). The presence of bound PAHs with incompletely quenched fluorescence would lead to underestimation of the KOC values measured by this technique. The goal of this work was to prove the validity of this assumption using an original experimental setup, which implied FQ measurements upon excitation into two distinct vibronically coupled electronic states. Pyrene was used as a fluorescent probe, and aquatic fulvic acid (SRFA) and leonardite humic acid (CHP) were used as the humic materials with low and high binding affinity for pyrene, respectively. Excitation of pyrene into the forbidden (S0-S1) and allowed (S0-S2) electronic states yielded two pairs of nonidentical FQ curves. This was indicative of incomplete quenching of the bound pyrene, and the divergence of the two FQ curves was much more pronounced for CHP as compared to SRFA. The two component model of fluorescence response formation was proposed to estimate the KOC values from the data obtained. The resulting pyrene KOC value for CHP (220 ± 20) g L(-1) was a factor 3 higher compared to the KOC value determined with the use of the Stern-Volmer formalism (68 ± 2) g L(-1). At the same time for aquatic FA the difference in FQ curves was almost negligible, which enables the use of the Stern-Volmer formalism for weakly interacting HS and PAHs.

The time course of non-photochemical quenching in phycobilisomes of Synechocystis sp. PCC6803 as revealed by picosecond time-resolved fluorimetry.

As high-intensity solar radiation can lead to extensive damage of the photosynthetic apparatus, cyanobacteria have developed various protection mechanisms to reduce the effective excitation energy transfer (EET) from the antenna complexes to the reaction center. One of them is non-photochemical quenching (NPQ) of the phycobilisome (PB) fluorescence. In Synechocystis sp. PCC6803 this role is carried by the orange carotenoid protein (OCP), which reacts to high-intensity light by a series of conformational changes, enabling the binding of OCP to the PBs reducing the flow of energy into the photosystems. In this paper the mechanisms of energy migration in two mutant PB complexes of Synechocystis sp. were investigated and compared. The mutant CK is lacking phycocyanin in the PBs while the mutant ΔPSI/PSII does not contain both photosystems. Fluorescence decay spectra with picosecond time resolution were registered using a single photon counting technique. The studies were performed in a wide range of temperatures - from 4 to 300 K. The time course of NPQ and fluorescence recovery in darkness was studied at room temperature using both steady-state and time-resolved fluorescence measurements. The OCP induced NPQ has been shown to be due to EET from PB cores to the red form of OCP under photon flux densities up to 1000 µmolphotonsm⁻²s⁻¹. The gradual changes of the energy transfer rate from allophycocyanin to OCP were observed during the irradiation of the sample with blue light and consequent adaptation to darkness. This fact was interpreted as the revelation of intermolecular interaction between OCP and PB binding site. At low temperatures a significantly enhanced EET from allophycocyanin to terminal emitters has been shown, due to the decreased back transfer from terminal emitter to APC. The activation of OCP not only leads to fluorescence quenching, but also affects the rate constants of energy transfer as shown by model based analysis of the decay associated spectra. The results indicate that the ability of OCP to quench the fluorescence is strongly temperature dependent. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

Investigation of OCP-triggered dissipation of excitation energy in PSI/PSII-less Synechocystis sp. PCC 6803 mutant using non-linear laser fluorimetry.

In order to prevent photodestruction by high light, photosynthetic organisms have evolved a number of mechanisms, known as non-photochemical quenching (NPQ), that deactivate the excited states of light harvesting pigments. Here we investigate the NPQ mechanism in the cyanobacterium Synechocystis sp. PCC 6803 mutant deficient in both photosystems. Using non-linear laser fluorimetry, we have determined molecular photophysical characteristics of phycocyanin and spectrally distinct forms of allophycocyanin for the cells in non-quenched and quenched states. Our analysis of non-linear fluorescence characteristics revealed that NPQ activation leads to an ~2-fold decrease in the relaxation times of both allophycocyanin fluorescence components, F660 and F680, and a 5-fold decrease in the effective excitation cross-section of F680, suggesting an emergence of a pathway of energy dissipation for both types of allophycocyanin. In contrast, NPQ does not affect the rates of singlet-singlet exciton annihilation. This indicates that, upon NPQ activation, the excess excitation energy is transferred from allophycocyanins to quencher molecules (presumably 3'hydroxyechinenone in the orange carotenoid protein), rather than being dissipated due to conformational changes of chromophores within the phycobilisome core. Kinetic measurements of fluorescence quenching in the Synechocystis mutant revealed the presence of several stages in NPQ development, as previously observed in the wild type. However, the lack of photosystems in the mutant enhanced the magnitude of NPQ as compared to the wild type, and allowed us to better characterize this process. Our results suggest a more complex kinetics of the NPQ process, thus clarifying a multistep model for the formation of the quenching center.