Vitamin B2 in Nanoscopic Environments under Visible Light: Photosensitized Antioxidant or Phototoxic Drug?

Biomaterial composed of chitosan, riboflavin, and hydroxyapatite for bone tissue regeneration

Biomaterial engineering approaches involve using a combination of miscellaneous bioactive molecules which may promote cell proliferation and, thus, form a scaffold with the environment that favors the regeneration process. Chitosan, a naturally occurring biodegradable polymer, possess some essential features, i.e., biodegradability, biocompatibility, and in the solid phase good porosity, which may contribute to promote cell adhesion. Moreover, doping of the materials with other biocompounds will create a unique and multifunctional scaffold that will be useful in regenerative medicine. This study is focused on the manufacturing and characterization of composite materials based on chitosan, hydroxyapatite, and riboflavin. The resulting films were fabricated by the casting/solvent evaporation method. Morphological and spectroscopy analyses of the films revealed a porous structure and an interconnection between chitosan and apatite. The composite material showed an inhibitory effect on Staphylococcus aureus and exhibited higher antioxidant activity compared to pure chitosan. In vitro studies on riboflavin showed increased cell proliferation and migration of fibroblasts and osteosarcoma cells, thus demonstrating their potential for bone tissue engineering applications.

Spectroscopic studies on a natural biomarker for the identification of origin and quality of tea extracts for the development of a portable and field deployable prototype

Even in the era of smart technologies and IoT enabled devices, tea testing technique continues to be a person specific subjective task. In this study, we have employed optical spectroscopy-based detection technique for the quantitative validation of tea quality. In this regard, we have employed the external quantum yield of quercetin at 450 nm (λ_ex = 360 nm), which is an enzymatic product generated by the activity of β-glucosidase on rutin, a naturally occurring metabolite responsible for tea-flavour (quality). We have found that a specific point in a graph representing Optical Density and external Quantum Yield as independent and dependent variables respectively of an aqueous tea extract objectively indicates a specific variety of the tea. A variety of tea samples from various geographical origin have been analysed with the developed technique and found to be useful for the tea quality assessment. The principal component analysis distinctly showed the tea samples originated from Nepal and Darjeeling having similar external quantum yield, while the tea samples from Assam region had a lower external quantum yield. Furthermore, we have employed experimental and computational biology techniques for the detection of adulteration and health benefit of the tea extracts. In order to assure the portability/field use, we have also developed a prototype which confirms the results obtained in the laboratory. We are of the opinion that the simple user interface and almost zero maintenance cost of the device will make it useful and attractive with minimally trained manpower at low resource setting.

Dual Sensitization via Electron and Energy Harvesting in a Nanohybrid for Improvement of Therapeutic Efficacy

We demonstrate experimental evidence of the effect of surface plasmon resonance of noble metal nanoparticles (NPs) on the activity of a well-known biomedicinal drug in the proximity of a semiconductor having a wide band gap for enhanced photodynamic therapy (PDT) efficacy. We have chosen riboflavin (Rf) (or vitamin B₂) as a model photosensitizer, attached with ZnO NPs and further attached with gold (Au) NP-decorated ZnO to increase the efficiency. The synthesized nanohybrids are characterized with the help of different microscopic, optical spectroscopic, and density functional theory (DFT)-based techniques. The DFT and time-dependent DFT-based calculations validate the experimental findings. A detailed ultrafast spectroscopic study has been carried out further to study the excited-state charge dynamics in the interface of the nanohybrids. The occurrence of a Förster resonance energy transfer (FRET) between Rf and Au has been found to be the key reason for the increased efficiency in the Rf-ZnO-Au nanohybrid over the Rf-ZnO one. The dipolar coupling between Au and Rf in the Rf-ZnO-Au nanohybrid further facilitates the generation of reactive oxygen species (ROS) in comparison to Rf-ZnO under blue-light irradiation. The greater efficiency in ROS generation by the Rf-ZnO-Au nanohybrid has been utilized for antimicrobial action against methicillin-resistant S. aureus (MRSA). Overall, the present study highlights the dual sensitization for achieving enhanced electron injection efficiency in the Rf-ZnO-Au nanohybrid in order to use it as an antibacterial agent that could be translated in PDT.

Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration

The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)^P23H/+ and Prph2^Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in Rho^P23H/+/Rtbdn^−/− and Prph2^Y141C/+/Rtbdn^−/− retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

Combating Essential Metal Toxicity: Key Information from Optical Spectroscopy

Chelation therapy is one of the most effective and widely accepted methods of treatment to reduce metal toxicity caused by an excess amount of essential metals. Essential minerals play an important role in maintaining healthy human physiology. However, the presence of an excess amount of such essential metals can cause cell injury, which finally leads to severe life-threatening diseases. Chelating complexes can efficiently capture the targeted metal and can easily be excreted from the body. Commonly utilized metal chelators have major side effects including long-term damage to some organs, which has pointed out the need of less harmful biocompatible chelating agents. In this work, we have investigated the iron chelating property of curcumin through various spectroscopic tools by synthesizing and characterizing the iron-curcumin (Fe-Cur) complex. We have also investigated whether the synthesized materials are able to retain their antioxidant activity after the chelation of a substantial amount of metal ion. Our study unravels the improved antioxidant activity of the synthesized chelate complex. We further demonstrate that the proposed complex generates no significant reactive oxygen species (ROS) under dark conditions, which makes it a promising candidate for chelation therapy of iron toxicity. Femtosecond-resolved fluorescence studies further provide insight into the mechanism of activity of the new complex where electron transfer from ligand to metal has been observed prominently. Thus, the Fe-Cur complex has a potential to act as a dual activity medicine for excretion of toxic metal ions via chelation and as a therapeutic agent of oxidative stress caused by the metal ion as well.

Reaction-diffusion model as framework for understanding the role of riboflavin in “eye defence” formulations

Analysis of UV-visible spectra, performed on commercial riboflavin-based eye drops, showed that absorbance is a saturating function of vitamin concentration. This implies a threshold concentration, C_t, such that for riboflavin concentration > C_t the absorbance remains constant and the effectiveness of the eye drops is independent of the dose used. These experimental results were combined with a diffusion–reaction model to elucidate the mechanism of action within the cornea. The model predicts that the eye drops have a low effectiveness on UVB and UVC, while they have a good performance for UVA. Indeed, at the center of the cornea the transmittance is significantly reduced and after 1 h it is reduced by about 70% compared to a cornea devoid of eye drops.

Analysis of UV-visible spectra, performed on commercial riboflavin-based eye drops, showed that absorbance is a saturating function of vitamin concentration.

Optical control of mitochondrial reductive reactions in living cells using an electron donor-acceptor linked molecule

It has been known for decades that intracellular redox reactions control various vital functions in living systems, which include the synthesis of biomolecules, the modulation of protein functions, and cell signaling. Although there have been several reports on the control of such functions using DNA and RNA, the non-invasive optical control of biological functions is an important ongoing challenge. In this study, a hybrid of an electron donor-acceptor linked molecule based on a ferrocene(Fc)-porphyrin(ZnP)-fullerene(C₆₀) analogue and an elaborately designed nano-carrier, referred to herein as a MITO-Porter, resulted in a successful photoinduced intermolecular electron transfer reaction via the long-lived intramolecular charge separation, leading to site-specific reductive reactions in the mitochondria of living HeLa cells. A Fc-ZnP-C₆₀ linked molecule, 1-Oct, was designed and prepared for taking advantage of the unique photophysical properties with excellent efficiency (i.e. a long lifetime and a high quantum yield) for photoinduced charge separation. The targeted delivery of 1-Oct to mitochondria was accomplished by using a combination of the Fc-ZnP-C₆₀ molecule and a drug delivery nano-carrier, MITO-Porter, that was recently established by our group for intracellular cargo delivery. The successful delivery of 1-Oct by the MITO-Porter permitted the optically-controlled generation of O₂^- in the mitochondria of HeLa cells and the following induction of apoptosis as a cell signalling response was observed in confocal laser microscopy experiments. The obtained results indicate the use of an electron donor-acceptor system such as this can be a promising tool for the non-invasive triggering of redox-coupled cellular activities in living systems.

Convenient synthesis of deazaflavin cofactor FO and its activity in F(420)-dependent NADP reductase

F420 and FO are phenolic 5-deazaflavin cofactors that complement nicotinamide and flavin redox coenzymes in biochemical oxidoreductases and photocatalytic systems. Specifically, these 5-deazaflavins lack the single electron reactivity with O2 of riboflavin-derived coenzymes (FMN and FAD), and, in general, have a more negative redox potential than NAD(P)(+). For example, F420-dependent NADP(+) oxidoreductase (Fno) is critical to the conversion of CO2 to CH4 by methanogenic archaea, while FO functions as a light-harvesting agent in DNA repair. The preparation of these cofactors is an obstacle to their use in biochemical studies and biotechnology. Here, a convenient synthesis of FO was achieved by improving the redox stability of synthetic intermediates containing a polar, electron-rich aminophenol fragment. Improved yields and simplified purification techniques for FO are described. Additionally, Fno activity was restored with FO in the absence of F420. Investigating the FO-dependent NADP(+)/NADPH redox process by stopped-flow spectrophotometry, steady state kinetics were defined as having a Km of 4.00 ± 0.39 μM and a kcat of 5.27 ± 0.14 s(-1). The preparation of FO should enable future biochemical studies and novel uses of F420 mimics.

Photoinduced Dynamics and Toxicity of a Cancer Drug in Proximity of Inorganic Nanoparticles under Visible Light

Drug sensitization with various inorganic nanoparticles (NPs) has proved to be a promising and an emergent concept in the field of nanomedicine. Rose bengal (RB), a notable photosensitizer, triggers the formation of reactive oxygen species under green-light irradiation, and consequently, it induces cytotoxicity and cell death. In the present study, the effect of photoinduced dynamics of RB upon complexation with semiconductor zinc oxide NPs is explored. To accomplish this, we successfully synthesized nanohybrids of RB with ZnO NPs with a particle size of 24 nm and optically characterized them. The uniform size and integrity of the particles were confirmed by high-resolution transmission electron microscopy. UV/Vis absorption and steady-state fluorescence studies reveal the formation of the nanohybrids. ultrafast picosecond-resolved fluorescence studies of RB-ZnO nanohybrids demonstrate an efficient electron transfer from the photoexcited drug to the semiconductor NPs. Picosecond-resolved Förster resonance energy transfer from ZnO NPs to RB unravel the proximity of the drug to the semiconductor at the molecular level. The photoinduced ROS formation was monitored using a dichlorofluorescin oxidation assay, which is a conventional oxidative stress indicator. It is observed that the ROS generation under green light illumination is greater at low concentrations of RB-ZnO nanohybrids compared with free RB. Substantial photodynamic activity of the nanohybrids in bacterial and fungal cell lines validated the in vitro toxicity results. Furthermore, the cytotoxic effect of the nanohybrids in HeLa cells, which was monitored by MTT assay, is also noteworthy.

Direct Observation of Coupling between Structural Fluctuation and Ultrafast Hydration Dynamics of Fluorescent Probes in Anionic Micelles

The coupling of structural fluctuation and the dynamics of associated water molecules of biological macromolecules is vital for various biological activities. Although a number of molecular dynamics (MD) studies on proteins/DNA predicted the importance of such coupling, experimental evidence of variation of hydration dynamics with controlled structural fluctuation even in model macromolecule is sparse and raised controversies in the contemporary literature. Here, we have investigated dynamics of hydration at the surfaces of two similar anionic micelles sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS) as model macromolecules using coumarin 500 (C500) as spectroscopic probe with femtosecond to picosecond time resolution up to 20 ns time window. The constituting surfactants SDS and SDBS are structurally similar except one benzene moiety in the SDBS may offer additional rigidity to the SDBS micelles through π-stacking and added bulkiness. The structural integrity of the micelles in the aqueous medium is confirmed in dynamic light scattering (DLS) studies. A variety of studies including polarization gated fluorescence spectroscopy and quasielastic neutron scattering (QENS) have been used to confirm differential structural fluctuation of SDS and SDBS micelles. We have also employed femtosecond-resolved Förster resonance energy transfer (FRET) in order to study binding of a cationic organic ligand ethidium bromide (EtBr) salt at the micellar surfaces. The distance distribution of the donor (C500)-acceptor (EtBr) in the micellar media reveals the manifestation of the structural flexibility of the micelles. Our studies on dynamical coupling of the structural flexibility with surface hydration in the nanoscopic micellar media may find the relevance in the "master-slave" type water dynamics in biologically relevant macromolecules.

Modulation of stability and functionality of a phyto-antioxidant by weakly interacting metal ions: curcumin in aqueous solution

Metal exchange process in metallo–curcumin leading to duality in action: enhancement of both aqueous stability and anti-oxidant property.