Analysis of porphyrins and enzymes in porphyrin synthesis in Taenia solium cysticercus from man and pig

Identification by methods of steady-state and kinetic spectrofluorimetry of endogenous porphyrins and flavins sensitizing the formation of reactive oxygen species in cancer cells

The question about acceptor molecules of optical radiation that determine the effects of photobiomodulation in relation to various types of cells still remains the focus of attention of researchers. This issue is most relevant for cancer cells, since, depending on the parameters of optical radiation, light can either stimulate their growth or inhibit them and lead to death. This study shows that endogenous porphyrins, which have sensitizing properties, may play an important role in the implementation of the effects of photobiomodulation, along with flavins. For the first time, using steady-state and kinetic spectrofluorimetry, free-base porphyrins and their zinc complexes were discovered and identified in living human cervical epithelial carcinoma (HeLa) cells, as well as in their extracts. It has been shown that reliable detection of porphyrin fluorescence in cells is hampered by the intense fluorescence of flavins due to their high concentration (micromolar range) and higher (compared to tetrapyrroles) fluorescence quantum yield. Optimization of the spectral range of excitation and the use of extractants that provide multiple quenching of the flavin component while increasing the emission efficiency of tetrapyrroles makes it possible to weaken the contribution of the flavin component to the recorded fluorescence spectra.

Acquiring of photosensitivity by Mycobacterium tuberculosis in vitro and inside infected macrophages is associated with accumulation of endogenous Zn-porphyrins

Mycobacterium tuberculosis (Mtb) is able to transition into a dormant state, causing the latent state of tuberculosis. Dormant mycobacteria acquire resistance to all known antibacterial drugs and can survive in the human body for decades before becoming active. In the dormant forms of M. tuberculosis, the synthesis of porphyrins and its Zn-complexes significantly increased when 5-aminolevulinic acid (ALA) was added to the growth medium. Transcriptome analysis revealed an activation of 8 genes involved in the metabolism of tetrapyrroles during the Mtb transition into a dormant state, which may lead to the observed accumulation of free porphyrins. Dormant Mtb viability was reduced by more than 99.99% under illumination for 30 min (300 J/cm2) with 565 nm light that correspond for Zn-porphyrin and coproporphyrin absorptions. We did not observe any PDI effect in vitro using active bacteria grown without ALA. However, after accumulation of active cells in lung macrophages and their persistence within macrophages for several days in the presence of ALA, a significant sensitivity of active Mtb cells (ca. 99.99%) to light exposure was developed. These findings create a perspective for the treatment of latent and multidrug-resistant tuberculosis by the eradication of the pathogen in order to prevent recurrence of this disease.

Recognition of immune reactive proteins as a potential multiepitope vaccine candidate of Taenia solium cysticerci through proteomic approach

Metacestode, the larva of Taenia solium, is the causative agent for neurocysticercosis (NCC), which causes epilepsy. The unavailability of a vaccine against human NCC is a major cause for its widespread prevalence across the globe. Therefore, the development of a reliable vaccine against NCC is the need of the hour. Employing a combination of proteomics and immunoinformatics, we endeavored to formulate a vaccine candidate. The immune reactive cyst fluid antigens of T. solium were identified by immune-blotting two-dimensional gels with NCC patient's sera, followed by Matrix-assisted laser desorption-ionization analysis. We performed a detailed proteomic study of these immune reactive proteins by utilizing immune-informatics tools, identified the nontoxic, nonallergic, B-cell epitopes, and collected epitopes with the least sequence homology with human and other Taenia species. These epitopes were joined through linkers to construct a multiepitope vaccine. Different physiochemical parameters such as molecular weight (23.82 kDa), instability (39.91), and aliphatic index (49.61) were calculated to ensure the stability of the linked peptides vaccine. The vaccine demonstrated stable interactions with different immune receptors like Toll-like receptor 4 and IgG confirming that it will effectively stimulate the host immune response. We anticipate that our designed B-cell linear epitope-based vaccine will show promising results in in vitro and in vivo assays. This study provides a platform that would be useful to develop other suitable vaccine candidates to prevent helminthic neglected tropical diseases in near future.

5-Aminolevulinic acid fluorescence in brain non-neoplastic lesions: a systematic review and case series

Fluorescence-guided surgery with 5-aminolevulinic acid (5-ALA) is used to assist brain tumor resection, especially for high-grade gliomas but also for low-grade gliomas, metastasis, and meningiomas. With the increasing use of this technique, even to assist biopsies, high-grade glioma-mimicking lesions had misled diagnosis by showing 5-ALA fluorescence in non-neoplastic lesions such as radiation necrosis and inflammatory or infectious disease. Since only isolated reports have been published, we systematically review papers reporting non-neoplastic lesion cases with 5-ALA according with the PRISMA guidelines, present our series, and discuss its pathophysiology. In total, 245 articles were identified and 12 were extracted according to our inclusion criteria. Analyzing 27 patients, high-grade glioma was postulated as preoperative diagnosis in 48% of the cases. Microsurgical resection was performed in 19 cases (70%), while 8 patients were submitted to biopsy (30%). We found 4 positive cases in demyelinating disease (50%), 4 in brain abscess (80%), 1 in neurocysticercosis (33%), 1 in neurotoxoplasmosis, infarction, and hematoma (100%), 4 in inflammatory disease (80%), and 3 in cortical dysplasia (100%). New indications are being considered especially in benign lesion biopsies with assistance of 5-ALA. Using fluorescence as an aid in biopsies may improve procedure time, number of samples, and necessity of intraoperative pathology. Further studies should include this technology to encourage more beneficial uses.

Transient transgenesis of the tapeworm Taenia crassiceps

Human and porcine cysticercosis is caused by the larval stage of the flatworm Taenia solium (Cestoda). Infestation of the human brain, also known as neurocysticercosis, is the most common parasite disease of the central nervous system worldwide. Significant advances in the understanding of the disease have been achieved using the Taenia crassiceps murine model. We describe here a successful transfection protocol of T. crassiceps cysticerci as the first step to approach a number of currently inaccessible biological questions on cysticercosis. T. crassiceps cysticerci (ORF strain) were microinjected with the plasmid pcDNA3.1/NT-GFP-TOPO, encoding the green fluorescent protein (GFP) driven by a cytomegalovirus promoter (CMV). Twelve hours after the microinjection, GFP fluorescence gradually developed in patches associated to bud structures in the bladder wall of cysts. Fluorescence reached a peak at 24-48 h and lasted up to 72 h after the microinjection. Immunohistochemical studies on tissue sections of transfected cysts using an anti-GFP antibody, demonstrated co-localization of the antibody and the GFP fluorescence in the tegumentary cytoplasm and subtegumentary cytons. To validate at the mRNA level the expression of GFP, we carried out RT-PCR using two pairs of nested primers. Results showed expression of GFP-mRNA at 24 h post-transfection. Moreover, western blot assays of crude extracts of transfected cysts, carried out using the anti-GFP specific antibody, showed the expected protein band of 27 kDa, demonstrating that the GFP expression started at 24 after plasmid microinjection and was maintained up to 72 h. These findings will facilitate the development of functional genomics approaches applied to this model of cysticercosis.

Evaluation of the non-catalytic binding function of Ts26GST a glutathione transferase isoform of Taenia solium

Taenia solium glutathione transferase isoform of 26.5 kDa (Ts26GST) was observed to bind non-catalytically to porphyrins, trans-trans-dienals, bile acids and fatty acids, as assessed by inhibition kinetics, fluorescence spectroscopy and competitive fluorescence assays with 8-anilino-1-naphthalene sulfonate (ANS). The quenching of Ts26GST intrinsic fluorescence allowed for the determination of the dissociation constants (KD) for all ligands. Obtained data indicate that Ts26GST binds to all ligands but with different affinity. Porphyrins and lipid peroxide products inhibited Ts26GST catalytic activity up to 100% in contrast with only 20-30% inhibition observed for bile acids and two saturated fatty acids. Non-competitive type inhibition was observed for all enzyme inhibitor ligands except for trans-trans-2,4-decadienal, which exhibited uncompetitive type inhibition. The dissociation constant value KD = 0.7 μM for the hematin ligand, determined by competitive fluorescence assays with ANS, was in good agreement with its inhibition kinetic value Ki = 0.3 μM and its intrinsic fluorescence quenching KD = 0.7 μM. The remaining ligands did not displace ANS from the enzyme suggesting the existence of different binding sites. In addition to the catalytic activity of Ts26GST the results obtained suggest that the enzyme exhibits a ligandin function with broad specificity towards nonsubstrate ligands.

"Triple Observation Method (TOM)" to discriminate optically autofluorescence from porphyrins versus that from copper-metallothioneins

We propose a conclusive difference observed between the excitation conditions required to observe porphyrins and copper-metallothioneins in cells and/or tissues using an ordinary fluorescence microscope. We have emphasized the importance of examining the spectral properties of the emissions to avoid any serious mistakes such as confusing porphyrins with copper-metallothioneins in the liver and kidneys. However, microspectrophotometry is not a conventional method for either histochemical, cytochemical, or pathological studies because microspectrophotometers are both expensive and difficult to operate. Therefore, we demonstrate a simple comparative method using ordinary excitation filter arrangements. When using our technique, it becomes possible to optically discriminate more accurately between the autofluorescence properties arising from porphyrins and those arising from copper-metallothioneins. We would like to name our simple technique "Triple Observation Method (TOM)".

In situ detection of ALA-stimulated porphyrin metabolic products in Escherichia coli B by fluorescence line narrowing spectroscopy

In a recent work [Photochem. Photobiol. B: Biol. 50 (1999) 8] the successful photodynamic inactivation of Escherichia coli bacteria by visible light was reported based on delta-aminolevulinic acid (ALA)-induced endogenous porphyrin accumulation. In this work, the identification of these porphyrin derivatives in intact bacteria was performed by low-temperature conventional fluorescence and fluorescence line narrowing (FLN) techniques. Conventional fluorescence emission spectroscopy at cryogenic temperatures revealed the presence of the free-base porphyrins, identified earlier by high-performance liquid chromatography analysis of disintegrated bacterial cells after ALA induction; however, emission maxima characteristic for metal porphyrins were also observed. We demonstrated that the primary reason for this signal is that metal porphyrins are formed from free-base porphyrins by Mg2+ ions present in the culturing medium. Incorporation of Zn ions originating from the glassware could also be supposed. In the FLN experiment, the energy selection effect could be clearly demonstrated for (0,0) emissions of both the free-base and the metal porphyrins. The comparison of the conventional emission spectra and the bands revealed by the FLN experiment show that the dominant monomeric structural population is that of metal porphyrins. The intensity and the shape of the FLN lines indicate an aggregated population of the free-base porphyrins, beside a small monomeric population.

Abnormal accumulation of porphyrin derivatives in the kidneys of Long-Evans Cinnamon rats, as evidenced by microspectrophotometry

In the study described here we have revealed an abnormal accumulation of porphyrin derivatives in the kidneys of Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. In addition, we have confirmed that the derivatives emitted red-orange light in renal sections under UV excitation. This renal red-orange emission has previously been identified as luminescence from cuprous metallothioneins [Cu(I)-MTs], which also accumulate in both the kidneys and liver of LEC rats. In this study, we measured the emission spectra of the luminescence in the kidneys using microspectrophotometry. The spectra of the renal red-orange emission resembled those of porphyrin derivatives rather than those of Cu(I)-MTs. We then extracted these derivatives from the kidneys. An abundance of porphyrin derivatives was established. A significant increase in the levels of the derivatives in the liver and urine of the LEC rats was also confirmed. These results provide evidence of a heme-metabolism abnormality in LEC rats.

Fluorescence line narrowing spectroscopy: a tool for studying proteins

Perhaps the most important contribution of FLN is that it provides an experimental approach to relate physical changes in the protein to predicted dynamical behavior. It is clear that the sample is inhomogeneously broadened in a continuous manner, consistent with the damped motion of proteins. At the same time configurational substates can be selected, suggesting that there is indeed a hierarchy of protein motion and structure. As yet, identification of the structure, and relating it to the spectra, has not been achieved. It is clear that the electric field exerted by neighboring atoms shifts the electronic transition, and the inhomogeneity is greater when the surrounding disorder is greater. The inhomogeneity for the chromophore in the protein is dependent on the protein conformation and is intermediate between that of a crystal and a glass. The phonon coupling also depends on the chromophore and the protein. Fluorescence line narrowing provides in addition ground- and excited-state vibrational frequencies, thereby allowing for structural differences between the excited-state and the ground-state molecule to be detected.

Laser-induced fluorescence line narrowing of native porphyrins in animal tissue

Using monochromatic laser excitation, narrowing of the porphyrins 0-0 fluorescence line in rat muscle tissue to a width of 50-70 cm-1 at 4.2 K is observed. Fluorescence spectra at different excitation wavelengths and excitation spectra are measured. Fluorescence line peak follows the shift of the excitation frequency. Several of the most prominent vibrational frequencies of porphyrins in the excited electronic state are determined.

Protein conformation monitored by energy-selective optical spectroscopy

Fluctuations in the polypeptide chain lead to disorder in proteins and to a distribution in the parameters that regulate their functions. Using low temperature (to reduce the fluctuations) and narrow-band lasers (to select one substate among the many forms), high-resolution absorption and fluorescence spectra for chromophores in proteins can be obtained. These spectra reveal information on the kind and extent of disorder in proteins and allow for the determination of the vibrational energies of both ground and excited state molecules, true inhomogeneous spectral width, and kinetic studies of individual protein substates.

Native and denatured Zn cytochrome c studied by fluorescence line narrowing spectroscopy

Fluorescence Line Narrowing (FLN) spectroscopy was employed to compare the environment around the porphyrin in folded and unfolded Zn-substituted cytochrome c (Zn cyt c). Parameters of the resolved spectra, including the inhomogeneous energy-distribution function, vibrational energy levels, and phonon coupling, were compared for guanidine-denatured Zn cyt c and native Zn cyt c. The spectra of denatured Zn cyt c showed increased broad background and decreased peak resolution when compared to the native protein, indicating that denaturation results in increased phonon coupling. The energy-distribution function for the unfolded protein was fitted to a single Gaussian centered at 17,230 cm-1 with a width of approx. 360 cm-1, which proved to be blue shifted and much wider than that for native Zn cyt c (approx. 65 cm-1). Vibrational frequencies of the ground-state for Zn cyt c were identified and shown to change upon denaturation. Temperature-dependence of the FLN spectra of native Zn cyt c was analyzed and found to have step-like broadening between 40 K and 50 K. Such discontinuous spectral broadening behavior suggests that a discrete conformational change occurs in the protein at these temperatures.

Development of porphyria cutanea tarda after treatment with cyclophosphamide

Porphyria cutanea tarda, a metabolic disorder of heme biosynthesis, is characterized by cutaneous hyperpigmentation, facial hypertrichosis, dark urine, and a distinctive pattern of excess porphyrin production. Hepatic uroporphyrinogen decarboxylase activity is markedly reduced in patients with this disorder. Although porphyria cutanea tarda may be familial, it is more often sporadic in occurrence, and has been associated with excess alcohol ingestion, estrogen administration, iron overload, and several environmental hepatotoxins. It has also been associated on occasion with malignancy. We report a 46-yr-old woman with ovarian carcinoma who developed porphyria cutanea tarda while undergoing treatment with cisplatin and cyclophosphamide. The temporal course of the porphyrin abnormality suggested that cyclophosphamide was the pathogenic agent, and symptoms regressed after cessation of this drug with continued administration of cisplatin. The pathogenesis of the porphyria is not clear; however, cyclophosphamide is a substrate for cytochrome P450, and may produce metabolites that destroy this protein. The resulting increased turnover of heme might then result in overproduction of porphyrin precursors, resulting in the clinical syndrome. Studies of porphyrin metabolism in patients treated with cyclophosphamide may help to elucidate this possibility.