Phycocyanin Research Articles

Structural characterization and antioxidant potential of phycocyanin from the cyanobacterium Geitlerinema sp. H8DM

We are reporting characterization of phycocyanin (PC), a prime light harvesting pigment, composed of nearly the same molecular weight of alpha- (17.5 kDa) and beta- (18.1 kDa) subunits in Geitlerinema sp. H8DM. Phycocyanin was purified using ammonium sulfate and anionic exchange chromatography. The fluorescence emission spectrum of PC was 637 nm when excited over 589 nm, which denoted integrity and functionality of protein structure. PC was depicted as a single subunit of ~18 kDa based on SDS-PAGE. However, similarity between both subunits was proven by two spots on gel using two dimensional gel electrophoresis. MALDI ToF/ToF showed structure similarities with alpha and beta subunits of PC. Urea induced Gibbs free energy denoted that folding and structural stability of this pigment is similar to phycocyanin of other species. Biophysical properties of peptide sequence were analyzed for several parameters and 3D model for its correlation as antioxidant. Furthermore, verification of in-silico data of PC was done by in vitro anti-oxidant assays. Hence, due to high availability, stability and antioxidant properties it can be used for auxiliary applications as colorant and therapeutic agent against oxidative stress.

Identification and antioxidant activity of synthetic peptides from phycobiliproteins of Pyropia yezoensis

The objective of the present study was to identify peptides, based on active components of the red algae seaweed Pyropia yezoensis, able to inhibit the generation of reactive oxygen species (ROS), which is associated with aging and oxidative activities. Phycobilin, specific to red algae, covalently binds with water-soluble proteins. There are three types of pigment bound proteins, known as phycobiliproteins (PBPs): Phycoerythrin (PE), phycocyanin (PC) and allophycocyanin (APC). In the present study, PBPs reported previously to have antioxidant activities in P. yezoensis were identified and, based on these data, several peptides were synthesized (PBP 1-13) and their inhibition of ROS generation was examined. The existence of PBPs of each type, PE, PC and APC, was established in P. yezoensis and all were analyzed. In addition, PBP 1-2 and 7-9 peptides from PE were synthesized and showed antioxidant activities in HepG2 cells. In HepG2 cells, treatment with PBP2 reduced hydrogen peroxide-mediated oxidative stress and restored the expression of superoxide dismutase (SOD). Furthermore, phosphorylated nuclear factor erythroid-derived 2-like 2 (Nrf2) was elevated by PBP2 treatment. Overall, these results suggested that Nrf2-SOD pathways may be involved in the PBP2-mediated antioxidant effects. Therefore, from the investigations of P. yezoensis, several candidate peptides were identified with promising antioxidant and, potentially, anti-aging properties.

The toxicity of cadmium ion (Cd2+) to phycocyanin: an in vitro spectroscopic study.

The pollution of heavy metals is a severer problem for the ecosystems in waters. The toxicity of Cd2+ on phycocyanin (PC) is studied in molecular level in this work. The fluorescence quenching of PC is observed by the adding Cd2+ from 0 to 500 × 10-7molL-1. From the theoretical calculation and the time-resolved fluorescence decay profiles, the fluorescence quenching of PC by Cd2+ is found to be static. The synchronous fluorescence spectra are used to study the change in amino acid residues of PC molecules, indicating that the effect of Cd2+ on the Trp of PC is more significant than the Tyr. The UV-Vis absorbance of tetrapyrrole decreases from 0.26 to 0.23cps with increasing Cd2+ concentration, suggesting that Cd2+ affects the light adsorption and the photosynthesis function of PC. The circular dichroism spectra reveal that adding Cd2+ also changes the secondary structure (α-helix) of PC.

A Four-Band Semi-Analytical Model for Estimating Phycocyanin in Inland Waters From Simulated MERIS and OLCI Data

Existing remote-sensing algorithms to estimate the phycocyanin (PC) concentration in turbid inland waters have high associated uncertainties, especially at low PC concentrations in diverse phytoplankton communities. This paper provides the theoretical framework for a four-band semi-analytical algorithm (FBA_PC) which isolates PC absorption from second-order variability caused by yellow matter and other phytoplankton pigment absorption. The algorithm suits the band configuration of both the Medium Resolution Imaging Spectrometer (MERIS) and Sentinel-3 Ocean and Land Color Instrument (OLCI). Calibration of the algorithm was based on absorption data from 12 inland water bodies in the USA, The Netherlands, and China, combined with measurements from laboratory-grown cultures, which demonstrated that the assumptions underlying FBA-PC are an improvement over existing three-band approaches. Validation of FBA_PC in seven inland water bodies in the USA, The Netherlands, and China showed good agreement of FBA_PC adjusted to the MERIS/OLCI band configuration with measured PC, with root-mean-square error =27.691 $\text {mg} \cdot \text {m}^{-3}$ , mean absolute percentage error = 172.863%, and coefficient of determination ( $R^{2}) = 0.730$ . FBA_PC outperformed previously proposed PC algorithms that can be applied to MERIS or OLCI data, and is expected to be more robust when applied to a wider range of water bodies.

Cryospectroscopy Studies of Intact Light-Harvesting Antennas Reveal Empirical Electronic Energy Transitions in Two Cyanobacteria Species

Understanding of electronic energy transition (EET) mechanisms from the light-harvesting unit to the reaction center in a natural system has been limited by (a) the use of conventional transient time-resolved spectroscopy at room temperature, which result in high signal-to-noise ratio and (b) examining extracts instead of intact light-harvesting units. Here, we report previously unknown differences and new insight in EET of two cyanobacteria species, Acaryochloris marina and Thermosynechoccocus vulcanus, which have been found only after using UV-vis, hole-burning, and fluorescence spectroscopy at ultralow temperature and examining their intact light-harvesting unit, phycobilisomes (PBS). Although the exciton formation is similarly induced by photoexcitation of chromophore assemblies in phycocyanin (PC) and allophycocyanin (APC) in PBSs of both species, the EET mechanisms are totally different, being adiabatic in A. marina and nonadiabatic in T. vulcanus. The PBS of A. marina has only one APC trimer and energy transfer is through coupling of α84 in APC with β84 in adjacent PC. In T. vulcanus, the PBS has three components: coupling between APC core and the entire PC rod and couplings of β-β18 and of LCM to β in the adjacent APC-like trimer. A total of 80% of the excitation energy is trapped in the coupling β-β18 and regulates the flow of energy from the high- to low-level terminal electronic transition emitter β-LCM. All these details cannot be observed at room temperature and in extracted units.

Mechanistic investigation of transcutaneous protein delivery using solid-in-oil nanodispersion: A case study with phycocyanin

Phycocyanin (PC), a water-soluble protein-chromophore complex composed of hexameric (αβ)6 subunits, has important biological functions in blue-green algae as well as pharmacological activities in biomedicine. We have previously developed a solid-in-oil (S/O) nanodispersion method to deliver biomacromolecules through the skin, although the transcutaneous mechanism has not yet been fully elucidated. To study the mechanism of transcutaneous protein delivery, we therefore enabled S/O nanodispersion by coating PC with hydrophobic surfactants and evaluated how the proteinaceous macromolecules formulated in an oil phase might permeate the skin. The extent of S/O nanodispersion of PC was dependent on the type of surfactant, suggesting that the selection of a suitable surfactant is crucial for encapsulating a large protein having a subunit structure. By measuring the intrinsic fluorescence of PC, we found that S/O nanodispersion facilitated the accumulation of PC in the stratum corneum (SC) of Yucatan micropig skin. Furthermore, after crossing the SC layer, the fluorescent recovery of PC was evident, indicating the release of the biologically active form of PC from the SC into the deeper skin layer.

Composition and functional property of photosynthetic pigments under circadian rhythm in the cyanobacterium Spirulina platensis.

Circadian rhythm is an important endogenous biological signal for sustainable growth and development of cyanobacteria in natural ecosystems. Circadian effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A) and ultraviolet-B (UV-B) radiations on pigment composition have been studied in the cyanobacterium Spirulina platensis under light (L)/dark (D) oscillation with a combination of 4/20, 8/16, 12/12, 16/8, 20/4 and 24/24h time duration. Circadian exposure of PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB) showed more than twofold decline in Chl a, total protein and phycocyanin (PC) in light phase and significant recovery was achieved in dark phase. The fluorescence emission wavelength of PC was shifted towards lower wavelengths in the light phase of PAB in comparison to P and PA whereas the same wavelength was retrieved in the dark phase. The production of free radicals was accelerated twofold in the light phase (24h L) whereas the same was retrieved to the level of control during the dark phase. Oxidatively induced damage was alleviated by antioxidative enzymes such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and ascorbate peroxidase (APX) in the light phase (0-24-h L) whereas the dark phase showed significant inhibition of the same enzymes. Similar characteristic inhibition of free radicals and recovery of PC was observed inside cellular filament after circadian rhythm of 24/24h (L/D). Circadian exposure of P, PA and PAB significantly altered the synthesis and recovery of pigments that could be crucial for optimization and sustainable production of photosynthetic products for human welfare.

A Hybrid EOF Algorithm to Improve MODIS Cyanobacteria Phycocyanin Data Quality in a Highly Turbid Lake: Bloom and Nonbloom Condition

Extensive monitoring of cyanobacterial blooms in lakes and reservoirs can provide important protection for drinking water sources. In most inland waterbodies, phycocyanin (PC) concentrations are the best indicator of cyanobacteria distribution. PC has a characteristic absorption peak near 620 nm; however, reflectance at this wavelength is only available from MEdium Resolution Imaging Spectrometer (MERIS) and Ocean and Land Colour Instrument (OLCI) sensors. MERIS stopped providing data after 2012 and OLCI was only recently launched (February 2016). The Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua is currently the only satellite instrument that can provide well-calibrated top-of-atmosphere radiance data over an extended number of years to the present. In this study, we develop and validate a new approach based on empirical orthogonal function (EOF) to quantify PC concentrations in a turbid inland lake (Lake Chaohu, China). Based on Rayleigh-corrected reflectance data ( $R_{{\rm{rc}}}$ ) at 469, 555, 645, and 859 nm, the concentrations of PC were estimated by regression of 87 concurrent MODIS-field measurements for bloom and nonbloom conditions. The validation ( N = 93) showed R 2 = 0.40 and unbiased RMS = 60.86%. Application of the algorithm from 2000 and 2014 showed spatial distribution patterns and seasonal changes that confirmed in situ and MERIS-based studies of floating algae mats. The spatial information on PC concentrations in Lake Chaohu had a reduced sensitivity to perturbations from thin aerosols and high sediments. This EOF approach allows us for new insights in the long-term dynamics of shallow lakes and reservoirs where having a better understanding of cyanobacterial blooms is important.

Structural characteristics of phycobiliproteins from red alga Mazzaella japonica

We determined the primary structures of phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC) from red alga Mazzaella japonica. The phycobiliproteins consist of α- and β-subunits like other red algae. M. japonica phycobiliproteins all conserved Cys residues for chromophore attachment site. The amino acid sequences of M. japonica phycobiliproteins showed considerably high identities with those of other red algae (81–100%). In addition, the sequences (YRD, LDY, LRY, VY, LF, and FY), which were angiotensin I converting enzyme (ACE) inhibitory peptides from other algae were detected in the primary structures of M. japonica phycobiliproteins. Then, we prepared the protein hydrolysates from M. japonica and measured its ACE inhibitory activity. Consequently, M. japonica protein hydrolysates indicated considerably high ACE inhibitory activity. Practical applications M. japonica is an abundant resource in Japan, which contains a lot of phycobiliproteins. Then, M. japonica protein hydrolysates strongly inhibited the activity of ACE. Therefore, it has the potential to be an ingredient of functional food.

Isolation and purification of phycocyanin from cyanobacteria of a mangrove forest

A cyanobacterium is an ancient group of photosynthetic prokaryotes that are thought to be the first organisms to carry out oxygenic photosynthesis. Phycocyanin (PC) is used to capture light energy for photosynthesis, unique to cyanobacteria. Sundarbans, a mangrove forest, is situated in the delta of Ganges, Meghna and Brahmaputra rivers, India. It has been declared as world heritage centre for its biodiversity. We would be the first to report on the photosynthetic pigment, phycocyanin of any strain of cyanobacteria isolated from a mangrove forest, Sundarbans. We have isolated the photosynthetic pigment from a cyanobacterial strain, AP24. Sequential precipitation of crude extract was done by the use of ammonium sulphate. Dialysis of the protein sample, anion exchange chromatography on a DEAE-cellulose DE 52 column and gel filtration chromatography with Sephadex G-100 column chromatography increased the purity ratio of phycocyanin. The purification was done both by DEAE-cellulose [purity ratio of the eluted cyanobacterial phycocyanin (C-PC) (A620/A280) increased to 4.31] and by Sephadex column. The molecular weight of purified C-PC was found to be 72 kDa, which include two subunits α (17 kDa) and β (19 kDa) in a dimer association (αβ)2. The purified C-PC shows antioxidant activity. It was observed that the rate of haemolysis is decreased with increasing concentration of C-PC.

Evaluating physico-chemical influences on cyanobacterial blooms using hyperspectral images in inland water, Korea

Understanding harmful algal blooms is imperative to protect aquatic ecosystems and human health. This study describes the spatial and temporal distributions of cyanobacterial blooms to identify the relations between blooms and environmental factors in the Baekje Reservoir. Two-year cyanobacterial cell data at one fixed station and four remotely sensed distributions of phycocyanin (PC) concentrations based on hyperspectral images (HSIs) were used to describe the relation between the spatial and temporal variations in the blooms and the affecting factors. An artificial neural network model and a three-dimensional hydrodynamic model were implemented to estimate the PC concentrations using remotely sensed HSIs and simulate the hydrodynamics, respectively. The statistical test results showed that the variations in the cyanobacterial biomass depended significantly on variations in the water temperature (slope = 0.13, p-value < 0.01), total nitrogen (slope = −0.487, p-value < 0.01), and total phosphorus (slope = 20.7, p-value < 0.05), whereas the variation in the biomass was moderately dependent on the variation in the outflow (slope = −0.0097, p-value = 0.065). Water temperature was the main factor affecting variations in the PC concentrations for the three months from August to October and was significantly different for the three months (p-value < 0.01). Hydrodynamic parameters also had a partial effect on the variations in the PC concentrations in those three months. Overall, this study helps to describe spatial and temporal variations in cyanobacterial blooms and identify the factors affecting the variation in the blooms. This study may play an important role as a basis for developing strategies to reduce bloom frequency and severity.

Quantum dots based imprinting fluorescent nanosensor for the selective and sensitive detection of phycocyanin: A general imprinting strategy toward proteins

Molecular imprinting as a versatile technology has gained popularity in various fields for diverse species; however, protein imprinting still remains challenging due to some inherent problems but is potentially rewarding work. Herein, we reported a facile strategy to imprint phycocyanin (PC), as a template, using quantum dots (QDs) co-capped by thioglycollic acid and glutathione directly as functional monomer via dopamine self-polymerization, which effectively simplified the imprinting process and afforded easy accessibility to recognition sites. The resulting QDs based imprinting nanosensor showed significant fluorescence decrease of QDs within less than 16s upon binding PC owing to the ultrathin imprinting layer (ca. 3nm), leading to a high detectability down to 0.075μM. An excellent linearity was found within the wide range of 0.8–8.0μM (R2=0.9935). Good recognition selectivity toward PC was displayed over other possible competing molecules, with a high imprinting factor of 7.3. Seawater and lake water samples spiked with PC were also analyzed, presenting satisfactory recoveries ranging from 90.8–110.1% with precisions below 4.6%, indicating the practicality of the imprinting nanosensor for accurately rapid nanoscale monitoring of algae blooms. By using another protein, bovine haemoglobin (BHb), as a convincing support model, the present study can provide a simple and general imprinting strategy toward various concerned proteins through rationally utilizing diverse functionalization and interactions.

Phycocyanin attenuates pulmonary fibrosis via the TLR2-MyD88-NF-\u03baB signaling pathway

Our aim was to investigate the effects of phycocyanin (PC) on bleomycin (BLM)-induced pulmonary fibrosis (PF). In this study, C57 BL/6 wild-type (WT) mice and toll-like receptor (TLR) 2 deficient mice were treated with PC for 28 days following BLM exposure. Serum and lung tissues were collected on days 3, 7 and 28. Data shows PC significantly decreased the levels of hydroxyproline (HYP), vimentin, surfactant-associated protein C (SP-C), fibroblast specific protein-1 (S100A4) and α-smooth muscle actin (α-SMA) but dramatically increased E-cadherin and podoplanin (PDPN) expression on day 28. Moreover, PC greatly decreased the levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and myeloperoxidase (MPO) at the earlier time. Reduced expression of key genes in the TLR2 pathway was also detected. Compared with WT mice, TLR2-deficient mice exhibited less injury, and the protective effect of PC was partly diminished in this background. These data indicate the anti-fibrotic effects of PC may be mediated by reducing W/D ratio, MPO, IL-6, TNF-α, protecting type I alveolar epithelial cells, inhibiting fibroblast proliferation, attenuating epithelial-mesenchymal transitions (EMT) and reducing oxidative stress. The TLR2-MyD88-NF-κB pathway plays an important role in PC-mediated reduction in pulmonary fibrosis.

Management of toxic cyanobacteria for drinking water production of Ain Zada Dam.

Blooms of toxic cyanobacteria in Algerian reservoirs represent a potential health problem, mainly from drinking water that supplies the local population of Ain Zada (Bordj Bou Arreridj). The objective of this study is to monitor, detect, and identify the existence of cyanobacteria and microcystins during blooming times. Samples were taken in 2013 from eight stations. The results show that three potentially toxic cyanobacterial genera with the species Planktothrix agardhii were dominant. Cyanobacterial biomass, phycocyanin (PC) concentrations, and microcystin (MC) concentrations were high in the surface layer and at 14m depth; these values were also high in the treated water. On 11 May 2013, MC concentrations were 6.3μg/L in MC-LR equivalent in the drinking water. This study shows for the first time the presence of cyanotoxins in raw and treated waters, highlighting that regular monitoring of cyanobacteria and cyanotoxins must be undertaken to avoid potential health problems.

Concentration-based self-assembly of phycocyanin.

Cyanobacteria light-harvesting complexes can change their structure to cope with fluctuating environmental conditions. Studying in vivo structural changes is difficult owing to complexities imposed by the cellular environment. Mimicking this system in vitro is challenging, as well. The in vivo system is highly concentrated, and handling similar in vitro concentrated samples optically is difficult because of high absorption. In this research, we mapped the cyanobacteria antennas self-assembly pathways using highly concentrated solutions of phycocyanin (PC) that mimic the in vivo condition. PC was isolated from the thermophilic cyanobacterium Thermosynechococcus vulcanus and measured by several methods. PC has three oligomeric states: hexamer, trimer, and monomer. We showed that the oligomeric state was changed upon increase of PC solution concentration. This oligomerization mechanism may enable photosynthetic organisms to adapt their light-harvesting system to a wide range of environmental conditions.

Effect of salinity on some physiological and biochemical responses in the cyanobacterium Synechococcus elongatus

In this study, some physiological and biochemical responses of Synechococcus elongatus to salt stress were investigated. The cyanobactrium was grown in BG-11 medium under different concentrations of NaCl (0, 0.5, 1 M). The results indicated that the growth of S. elongatus was significantly inhibited under salt stress on days 5, 9 and 12. Protein content increased in S. elongatus on day 12 in presence of salt. Salinity induced proline accumulation at 1 M NaCl on day 12 and caused a significant enhance in hydrogen peroxide content on day 5. Catalase (CAT) activity continuously increased on day 5. An increasing trend in polyphenol oxidase (PPO) activity was indicated on days 5 and 9. Superoxide dismutase (SOD) activity gradually induced with increasing NaCl concentrations on day 5. Salt stress decreased chlorophyll content compared to that of control in three stages of growth, and carotenoid content declined on days 9 and 12. The contents of phycobiliprotein (PBP), phycoerythrin (PE) and phycocyanin (PC) enhanced significantly under different NaCl concentrations on days 5 and 9. These results show that S. elongatus has limited adaptative potential to salinity, and the optimum medium for its culture should not bear NaCl even at a moderate level, if production of carotenoids is aimed.

Comparative study of thylakoid membranes in terminal heterocysts and vegetative cells from two cyanobacteria, Rivularia M-261 and Anabaena variabilis, by fluorescence and absorption spectral microscopy

Heterocyst is a nitrogen-fixing cell differentiated from a cell for oxygen-evolving photosynthesis (vegetative cell) in some filamentous cyanobacteria when fixed nitrogen (e.g., ammonia and nitrate) is limited. Heterocysts appear at multiple separated positions in a single filament with an interval of 10–20 cells in some genera (including Anabaena variabilis). In other genera, a single heterocyst appears only at the basal terminal in a filament (including Rivularia M-261). Such morphological diversity may necessitate different properties of heterocysts. However, possible differences in heterocysts have largely remained unexplored due to the minority of heterocysts among major vegetative cells. Here, we have applied spectroscopic microscopy to Rivularia and A. variabilis to analyze their thylakoid membranes in individual cells. Absorption and fluorescence spectral imaging enabled us to estimate concentrations and interconnections of key photosynthetic components like photosystem I (PSI), photosystem II (PSII) and subunits of light-harvesting phycobilisome including phycocyanin (PC). The concentration of PC in heterocysts of Rivularia is far higher than that of A. variabilis. Fluorescence quantum yield of PC in Rivularia heterocysts was found to be virtually the same as those in its vegetative cells, while fluorescence quantum yield of PC in A. variabilis heterocysts was enhanced in comparison with its vegetative cells. PSI concentration in the thylakoid membranes of heterocysts seems to remain nearly the same as those of the vegetative cells in both the species. The average stoichiometric ratio between PSI monomer and PC hexamer in Rivularia heterocysts is estimated to be about 1:1.

Excitation energy transfer in phycobiliproteins of the cyanobacterium Acaryochloris marina investigated by spectral hole burning.

The cyanobacterium Acaryochloris marina developed two types of antenna complexes, which contain chlorophyll-d (Chl d) and phycocyanobilin (PCB) as light-harvesting pigment molecules, respectively. The latter membrane-extrinsic complexes are denoted as phycobiliproteins (PBPs). Spectral hole burning was employed to study excitation energy transfer and electron-phonon coupling in PBPs. The data reveal a rich spectral substructure with a total of four low-energy electronic states whose absorption bands peak at 633, 644, 654, and at about 673nm. The electronic states at ~633 and 644nm can be tentatively attributed to phycocyanin (PC) and allophycocyanin (APC), respectively. The remaining low-energy electronic states including the terminal emitter at 673nm may be associated with different isoforms of PC, APC, or the linker protein. Furthermore, the hole burning data reveal a large number of excited state vibrational frequencies, which are characteristic for the chromophore PCB. In summary, the results are in good agreement with the low-energy level structure of PBPs and electron-phonon coupling parameters reported by Gryliuk et al. (BBA 1837:1490-1499, 2014) based on difference fluorescence line-narrowing experiments.

Optimizing Semi-Analytical Algorithms for Estimating Chlorophyll-a and Phycocyanin Concentrations in Inland Waters in Korea

Several semi-analytical algorithms have been developed to estimate the chlorophyll-a (Chl-a) and phycocyanin (PC) concentrations in inland waters. This study aimed at identifying the influence of algorithm parameters on the output variables and searching optimal parameter values. The optimal parameters of seven semi-analytical algorithms were applied to estimate the Chl-a and PC concentrations. The absorption coefficient measurements were coupled with pigment measurements to calibrate the algorithm parameters. For sensitivity analysis, the elementary effect test was conducted to analyze the influence of the algorithm parameters. The sensitivity analysis results showed that the parameters in the Y function and specific absorption coefficient were the most sensitive parameters. Then, the parameters were optimized via a single-objective optimization that involved one objective function being minimized and a multi-objective optimization that contained more than one objective function. The single-objective optimization led to substantial errors in absorption coefficients. In contrast, the multi-objective optimization improved the algorithm performance with respect to both the absorption coefficient estimates and pigment concentration estimates. The optimized parameters of the absorption coefficient reflected the high-particulate content in waters of the Baekje reservoir using an infrared backscattering wavelength and relatively high value of Y. Moreover, the results indicate the value of measuring the site-specific absorption if site-specific optimization of semi-analyical algorithm parameters was envisioned.

Phycocyanin-Functionalized Selenium Nanoparticles Reverse Palmitic Acid-Induced Pancreatic β Cell Apoptosis by Enhancing Cellular Uptake and Blocking Reactive Oxygen Species (ROS)-Mediated Mitochondria Dysfunction.

Accumulation of palmitic acid (PA) in human bodies could cause damage to pancreatic β cells and lead to chronic diseases by generation of reactive oxygen species (ROS). Therefore, it is of great significance to search for nutrition-available agents with antioxidant activity to protect pancreatic islet cells against PA-induced damage. Phycocyanin (PC) and selenium (Se) have been reported to have excellent antioxidant activity. In this study, PC-functionalized selenium nanoparticles (PC-SeNPs) were synthesized to investigate the in vitro protective effects on INS-1E rat insulinoma β cells against PA-induced cell death. A potent protective effect was achieved by regulation of particle size and PC content. Among three PC-SeNPs (165, 235, and 371 nm), PC-SeNPs-235 nm showed the highest cellular uptake and the best protective activities. For cell cycle analysis, PC-SeNPs showed a better protective effect on PA-induced INS-1E cell apoptosis than PC or SeNPs, and PC-SeNPs-235 nm exhibited the best effect. Further mechanistic studies demonstrated that PA induced overproduction of intracellular ROS, mitochondria fragmentation, activation of caspase-3, -8, and -9, and cleavage of PARP. However, pretreatment of the cells with PC-SeNPs effectively blocked these intracellular events, which suggests that PC-SeNPs could protect INS-1E cells against PA-induced cell apoptosis via attenuating oxidative stress and downstream signaling pathways. This finding provides a great promising nutritional approach for protection against diseases related to islet damage.