Influences of polycyclic aromatic hydrocarbon on the epigenome toxicity and its applicability in human health risk assessment.

The existence of polycyclic aromatic hydrocarbons (PAHs) in ambient air is an escalating concern worldwide because of their ability to cause cancer and induce permanent changes in the genetic material. Growing evidence implies that during early life-sensitive stages, the risk of progression of acute and chronic diseases depends on epigenetic changes initiated by the influence of environmental cues. Several reports deciphered the relationship between exposure to environmental chemicals and epigenetics, and have known toxicants that alter the epigenetic states. Amongst PAHs, benzo[a]pyrene (B[a]P) is accepted as a group 1 cancer-causing agent by the International Agency for the Research on Cancer (IARC). B[a]P is a well-studied pro-carcinogen that is metabolically activated by the aryl hydrocarbon receptor (AhR)/cytochrome P450 pathway. Cytochrome P450 plays a pivotal role in the stimulation step, which is essential for DNA adduct formation. Accruing evidence suggests that epigenetic alterations assume a fundamental part in PAH-promoted carcinogenesis. This interaction between PAHs and epigenetic factors results in an altered profile of these marks, globally and locus-specific. Some of the epigenetic changes due to exposure to PAHs lead to increased disease susceptibility and progression. It is well understood that exposure to environmental carcinogens, such as PAH triggers disease pathways through changes in the genome. Several evidence reported due to the epigenome-wide association studies, that early life adverse environmental events may trigger widespread and persistent variations in transcriptional profiling. Moreover, these variations respond to DNA damage and/or a consequence of epigenetic modifications that need further investigation. Growing evidence has associated PAHs with epigenetic variations involving alterations in DNA methylation, histone modification, and micro RNA (miRNA) regulation. Epigenetic alterations to PAH exposure were related to chronic diseases, such as pulmonary disease, cardiovascular disease, endocrine disruptor, nervous system disorder, and cancer. This hormetic response gives a novel perception concerning the toxicity of PAHs and the biological reaction that may be a distinct reliance on exposure. This review sheds light on understanding the latest evidence about how PAHs can alter epigenetic patterns and human health. In conclusion, as several epigenetic change mechanisms remain unclear yet, further analyses derived from PAHs exposure must be performed to find new targets and disease biomarkers. In spite of the current limitations, numerous evidence supports the perception that epigenetics grips substantial potential for advancing our knowledge about the molecular mechanisms of environmental toxicants, also for predicting health-associated risks due to environmental circumstances exposure and individual susceptibility.

Preparation and Characterization of Biomimetic ß-Lens Crystallins Using Single-Chain Polymeric Nanoparticles.

Presbyopia, the inability to focus at arm's length, and cataracts that cloud vision are associated primarily with changes in the mechanical and optical properties of the lens. The optical properties, particularly the refractive index, of the human lens originate from the cytoplasm of the lens fiber, which contains a highly concentrated solution (∼40%) of globular proteins referred to as α, ß, and γ crystallins, of which ß is the most abundant. In this study, we focus on the synthesis and characterization of a ß-crystallin biomimetic in an effort to understand and develop treatments for presbyopia and cataract. Polyacrylamide was used as a protein analogue. The side chains were endowed with aromatic and acidic functionality. Acrylic acid was incorporated into the copolymer and cross-linked with diamines to form nanoparticles. The composition and cross-linking condition of the biomimetic copolymers were optimized to match the hydrodynamic radius (Rh), refractive index, size, density, and intrinsic and dynamic viscosities with those of ßhigh lens crystallins. The refractive indices and densities of the nanoparticles' dispersion at different concentrations matched that of ßhigh lens crystallins, and the viscosity of the nanoparticles approached that of ßhigh lens crystallins. The biocompatibility findings for primary porcine retinal pigment epithelial (ppRPE) cells and porcine lens epithelial (pLE) cells showed both cell types tolerated up to 30 mg/mL of nanoparticles. These materials have the potential for use as replacements for the crystallins in developing an accommodating intraocular lens nanocomposite hydrogel that closely replicates the natural autofocusing ability of the original.

Synthesis and Characterization of Injectable Sulfonate-Containing Hydrogels.

Sulfonate-containing hydrogels are of particular interest because of their tunable mechanical and swelling properties, as well as their biological effects. Polysulfonate copolymers were synthesized by reacting 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), and acrylic acid (AA). We found that the incorporation rate of sulfonate-containing monomer and the molecular weight of the copolymer were significantly enhanced by increasing the ionic strength of the solution. We introduced thiol groups by modifying the pendant carboxylates or copolymerizing along with a disulfide-containing monomer. The thiol-containing copolymers were reacted with a 4-arm acrylamide-terminated poly(ethylene glycol) via a thiol-ene click reaction, which was mediated by a photoinitiator, a redox initiator, or a base-catalyzed Michael-Addition. We were able to tailor the storage modulus (33-1800 Pa) and swelling capacity (1-91 wt %) of the hydrogel by varying the concentration of the copolymers. We determined that the injectable sulfonate-containing hydrogels were biocompatible up to 20 mg/mL, as observed by an electric cell-substrate impedance sensing (ECIS) technique, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using three different cell lines: human retinal pigment epithelial cells (ARPE-19), fibroblasts (NIH 3T3), and Chinese hamster ovary cells (CHO).

Combustion conditions influence toxicity of flame-generated soot to ocular (ARPE-19) cells.

Soot is a prevalent aerosol found both indoors and outdoors that has several sources, such as natural (e.g., wildfires), civilian (e.g., cooking), or military (e.g., burn pit operation). Additionally, within the sources, factors that influence the physicochemical properties of the soot include combustion temperature, oxygen availability, and fuel type. Being able to reproduce soot in the laboratory and systematically assess its toxicity is important in the pursuit of elucidating pathologies associated with its exposure. Of the organs of interest, we targeted the eye given the scant attention received. Yet, air pollution constituents such as soot have been linked to diseases such as age-related macular degeneration and proliferative vitreoretinopathy. We developed a bench-scale system to synthesize different types of soot, that is, soot with a systematically varied physical attributes or chemical composition. We used common analytical techniques to probe such properties, and used statistical analyses to correlate them with toxicity in vitro using ARPE-19 cells. Within the range of flame conditions studied, we find that soot toxicity increases with increasing oxygen concentration in fuel-rich premixed flames, and weakly increases with decreasing flame temperature. Additionally, soot particles produced in premixed flames are generally smaller in size, exhibit a lesser fractal structure, and are considerably more toxic to ARPE-19 cells than soot particles produced in non-premixed flames.

Comparative proteomic analysis identifies age-dependent increases in the abundance of specific proteins after deletion of the small heat shock proteins αA- and αB-crystallin.

Mice with deletion of genes for small heat shock proteins αA- and αB-crystallin (αA/αB(-/-)) develop cataracts. We used proteomic analysis to identify lens proteins that change in abundance after deletion of these α-crystallin genes. Wild-type (WT) and αA/αB(-/-) knockout (DKO) mice were compared using two-dimensional difference gel electrophoresis and mass spectrometric analysis, and protein identifications were validated by Mascot proteomic software. The abundance of histones H2A, H4, and H2B fragment, and a low molecular weight ß1-catenin increased 2-3-fold in postnatal day 2 lenses of DKO lenses compared with WT lenses. Additional major increases were observed in abundance of ßB2-crystallin and vimentin in 30-day-old lenses of DKO animals compared with WT animals. Lenses of DKO mice were comprised of nine protein spots containing ßB2-crystallin at 10-40-fold higher abundance and three protein spots containing vimentin at ≥2-fold higher abundance than in WT lenses. Gel permeation chromatography identified a unique 328 kDa protein in DKO lenses, containing ß-crystallin, demonstrating aggregation of ß-crystallin in the absence of α-crystallins. Together, these changes provide biochemical evidence for possible functions of specific cell adhesion proteins, cytoskeletal proteins, and crystallins in lens opacities caused by the absence of the major chaperones, αA- and αB-crystallins.

Hyaluronic Acid-Based Gold Nanoparticles for the Topical Delivery of Therapeutics to the Retina and the Retinal Pigment Epithelium.

The ocular immune privilege is a phenomenon brought about by anatomical and physiological barriers to shield the eye from immune and inflammation responses. While this phenomenon is beneficial for eyes protection, it is, at the same time, a hindrance for drug delivery to the posterior segment of the eye to treat retinal diseases. Some ocular barriers can be bypassed by intravitreal injections, but these are associated with several side effects and patient noncompliance, especially when frequent injections are required. As an alternative, applying drugs as an eye drop is preferred due to the safety and ease. This study investigated the possible use of topically-applied hyaluronic acid-coated gold nanoparticles as drug delivery vehicles to the back of the eye. The coated gold nanoparticles were topically applied to mouse eyes, and results were compared to topically applied uncoated gold nanoparticles and phosphate-buffered saline (PBS) solution. Retina sections from these mice were then analyzed using fluorescence microscopy, inductively coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy (TEM). All characterization techniques used in this study suggest that hyaluronic acid-coated gold nanoparticles have higher distribution in the posterior segment of the eye than uncoated gold nanoparticles. Electroretinogram (ERG) analysis revealed that the visual function of mice receiving the coated gold nanoparticles was not affected, and these nanoparticles can, therefore, be applied safely. Together, our results suggest that hyaluronic acid-coated gold nanoparticles constitute potential drug delivery vehicles to the retina when applied noninvasively as an eye drop.

Hyaluronan-Conjugated Carbon Quantum Dots for Bioimaging Use.

This work demonstrates the application of hyaluronan-conjugated nitrogen-doped carbon quantum dots (HA-nCQDs) for bioimaging of tumor cells and illustrates their potential use as carriers in targeted drug delivery. Quantum dots are challenging to deliver with specificity, which hinders their application. To facilitate targeted internalization by cancer cells, hyaluronic acid, a natural ligand of CD44 receptors, was covalently grafted on nCQDs. The HA-nCQD conjugate was synthesized by carbodiimide coupling of the amine moieties on nCQDs and the carboxylic acids on HA chains. Conjugated HA-nCQD retained sufficient fluorescence, although with 30% lower quantum efficiency than the original nCQDs. Confocal microscopy showed enhanced internalization of HA-nCQDs, facilitated by CD44 receptors. To demonstrate the specificity of HA-nCQDs toward human tumor cells, patient-derived breast cancer tissue with high-CD44 expression was implanted in adult mice. The tumors were allowed to grow up to 200-250 mm3 prior to the injection of HA-nCQDs. With either local or systemic injection, we achieved a high level of tumor specificity judged by a strong signal-to-noise ratio between the tumor and the surrounding tissue in vivo. Overall, the results show that HA-nCQDs can be used for imaging of CD44-specific tumors in preclinical models of human cancer and potentially used as carriers for targeted drug delivery into CD44-rich cells.

Redox-Responsive Hyaluronic Acid-Based Nanogels for the Topical Delivery of the Visual Chromophore to Retinal Photoreceptors.

Delivering therapeutics to the posterior segment of the eye is challenging due to various anatomical and physical barriers. While significant improvements have been realized by introducing direct injections to diseased sites, these approaches come with potential side effects that can range from simple inflammation to severe retinal damage. The topical instillation of drugs remains a safer and preferred alternative for patients' compliance. Here, we report the synthesis of penetratin-complexed, redox-responsive hyaluronic acid-based nanogels for the triggered release and delivery of therapeutics to the posterior part of the eye via topical application. The synthesized nanogels were shown to release their load only when exposed to a reducing environment, similar to the cytoplasm. As a model drug, visual chromophore analog, 9-cis-retinal, was loaded into nanogels and efficiently delivered to the mouse retina's photoreceptors when applied topically. Electroretinogram measurements showed a partial recovery of photoreceptor function in all treated eyes versus untreated controls. To the best of our knowledge, this report constitutes the first attempt to use a topically applied triggered-release drug delivery system to target the pigmented layer of the retina, in addition to the first attempt to deliver the visual chromophore topically.

Bioinspired Thermosensitive Hydrogel as a Vitreous Substitute: Synthesis, Properties, and Progress of Animal Studies.

In many vitreal diseases, the surgeon removes the natural vitreous and replaces it with silicone oils, gases, or balanced salt solutions to fill the eyeball and hold the retina in position. However, these materials are often associated with complications and have properties that differ from natural vitreous. Herein, we report an extension of our previous work on the synthesis of a biomimetic hydrogel that is composed of thiolated gellan as an analogue of type II collagen and poly(methacrylamide-co-methacrylate-co-bis(methacryloyl)cystamine), a polyelectrolyte, as an analogue of hyaluronic acid. This thermosensitive hydrogel can be injected into the eye as a viscous solution at 45 °C. It then forms a physical gel in situ when it reaches body temperature, and later forms disulfide covalent crosslinks. In this article, we evaluated two different formulations of the biomimetic hydrogels for their physical, mechanical, and optical properties, and we determined their biocompatibility with several cell lines. Finally, we report on the progress of the four-month preclinical evaluation of our bio-inspired vitreous substitute in comparison to silicone oil or a balanced salt solution. We assessed the eyes with a slit-lamp examination, intraocular pressure measurements, electroretinography, and optical coherence tomography. Preliminary results are very encouraging for the continuing evaluation of our bio-inspired hydrogel in clinical trials.

Comparison of the behavior of natural and refilled porcine lenses in a robotic lens stretcher.

The mechanism by which the eye dynamically changes focal distance (accommodation), and the mechanism by which this ability is lost with age (presbyopia), are still contested. Due to inherent confounding factors in vivo, in vitro measurements have been undertaken using a robotic lens stretcher to examine these mechanisms as well as the efficacy of lens refilling - a proposed treatment for presbyopia. Dynamic forces, anterior and posterior curvatures, and lens thickness are all correlated for young natural and refilled porcine lenses. Comparisons are made to lenses refilled with a homogeneous polymer system. The amplitude of accommodation of the young porcine lens is very small such that it may be a suitable model for presbyopia. The behavior of refilled lenses was highly dependent on the refill volume. The volume could be tuned to maximize accommodative amplitude in the refilled lens.

Investigating the Effects of Stove Emissions on Ocular and Cancer Cells.

More than a third of the world's population relies on solid fuels for cooking and heating, with major health consequences. Although solid fuel combustion emissions are known to increase the prevalence of illnesses such as chronic obstructive pulmonary disease and lung cancer, however, their effect on the eyes is underexplored. This study assesses the acute toxicity of solid fuel combustion emissions on healthy ocular cells and a cancer cell line. Three healthy ocular cell lines (corneal, lens, and retinal epithelial cells) and a cancer cell line (Chinese hamster ovary cells) were exposed to liquid and gas phase emissions from applewood and coal combustion. Following the exposure, real-time cell attachment behavior was monitored for at least 120 hours with electrical cell impedance spectroscopy. The viability of the cells, amount of apoptotic cells, and generation of reactive oxygen species (ROS) were quantified with MTT, ApoTox-Glo, and ROS-Glo H2O2 assays, respectively. The results showed that coal emissions compromised the viability of ocular cells more than applewood emissions. Interestingly, the cancer cells, although their viability was not compromised, generated 1.7 to 2.7 times more ROS than healthy cells. This acute exposure study provides compelling proof that biomass combustion emissions compromise the viability of ocular cells and increase ROS generation. The increased ROS generation was fatal for ocular cells, but it promoted the growth of cancer cells.

Bioinspired Fibrillary Hydrogel with Controlled Swelling Behavior: Applicability as an Artificial Vitreous.

The vitreous humor of the eye is mainly composed of fibrillary collagen and semiflexible hyaluronic acid (HA). To mimic this macromolecular composition of the vitreous, we previously developed an injectable two-component hydrogel composed of a fibrillary gellan and a semiflexible polyelectrolyte, poly[methacrylamide-co-(methacrylic acid)], both endowed with thiol cross-linkers. We optimized the hydrogel formulations for optical, physical, mechanical, and transport properties approximating those of the vitreous. Here, we studied 11 hydrogel formulations with varying concentrations of each component, and, as expected, we found that they all swelled in physiological solution. The two formulations that most closely matched the vitreous properties were investigated further. Judged against nonsurgical control and silicone oil, a clinically accepted vitreous replacement, both hydrogel formulations were biocompatible in rabbits for 30 days. Both hydrogels maintained optical clarity, physiological intraocular pressure, and intact retinal layers that displayed normal electroretinography. The swelling behavior of the gel led us to postulate that the native vitreous may also exhibit controlled swelling, where ionic HA's swelling capacity is restricted by fibrillary collagen. In conclusion, the two hydrogels merit further in vivo evaluation as an artificial vitreous for an extended duration and additionally in mini-pigs for their similarity to human eyes in size.

Mechanism of insolubilization by a single-point mutation in alphaA-crystallin linked with hereditary human cataracts.

AlphaA-crystallin is a small heat shock protein that functions as a molecular chaperone and a lens structural protein. The R49C single-point mutation in alphaA-crystallin causes hereditary human cataracts. We have previously investigated the in vivo properties of this mutant in a gene knock-in mouse model. Remarkably, homozygous mice carrying the alphaA-R49C mutant exhibit nearly complete lens opacity concurrent with small lenses and small eyes. Here we have investigated the 90 degrees light scattering, viscosity, refractive index, and bis-ANS fluorescence of lens proteins isolated from the alphaA-R49C mouse lenses and found that the concentration of total water-soluble proteins showed a pronounced decrease in alphaA-R49C homozygous lenses. Light scattering measurements on proteins separated by gel permeation chromatography showed a small amount of high-molecular mass aggregated material in the void volume which still remains soluble in alphaA-R49C homozygous lens homogenates. An increased level of binding of beta- and gamma-crystallin to the alpha-crystallin fraction was observed in alphaA-R49C heterozygous and homozygous lenses but not in wild-type lenses. Quantitative analysis with the hydrophobic fluorescence probe bis-ANS showed a pronounced increase in fluorescence yield upon binding to alpha-crystallin from mutant as compared with the wild-type lenses. These results suggest that the decrease in the solubility of the alphaA-R49C mutant protein was due to an increase in its hydrophobicity and supra-aggregation of alphaA-crystallin that leads to cataract formation. Our study further shows that analysis of mutant proteins from the mouse model is an effective way to understand the mechanism of protein insolubilization in hereditary cataracts.

Material characterization of porcine lenticular soluble proteins.

The soluble proteins present in the ocular lens impart important optical and dynamic mechanical properties on the lens. The short-range order of crystallin proteins grants transparency to a very concentrated protein solution. This unique protein system directly enables proper visual function of the eye. These proteins were investigated in steady and oscillatory shear. Steady shear data were fitted with a modified Herschel-Bulkley yield stress model that allows for a Newtonian plateau at low shear rates. The Cox-Merz rule was used in conjunction with large amplitude oscillatory shear to give insight into the degradation of the fluid structure with increasing strain. The shear thinning viscoelastic behavior of these proteins gives rise to beneficial mechanical properties and results from the same short-range order granting optical transparency.

Hyaluronate coating enhances the delivery and biocompatibility of gold nanoparticles.

For targeted delivery with nanoparticles (NPs) as drug carriers, it is imperative that the NPs are internalized into the targeted cell. Surface properties of NPs influence their interactions with cells. We examined the responses of retinal pigment epithelial cells, NIH 3T3 fibroblast cells, and Chinese hamster ovary cells to gold nanoparticles (Au NPs) in their nascent form as well as coated with end-thiolated hyaluronate (HS-HA). The grafting density of HS-HA on Au NPs was calculated based on total organic carbon measurements and thermal gravimetric analysis. We imaged the intracellular NPs by 3D confocal microscopy. We quantified viability and generation of reactive oxygen species (ROS) of the cells to Au NPs and monitored cell-surface attachment via electrical cell-substrate impedance sensing. The results confirmed that receptors on cell surfaces, for HA, are critical in internalizing HS-HA-Au NPs, and HA may mitigate ROS pathways known to lead to cell death. The 50- and 100-nm HS-HA-Au NPs were able to enter the cells; however, their nascent forms could not. This study shows that the delivery of larger Au NPs is enhanced with HS-HA coating and illustrates the potential of HA-coated NPs as a drug delivery agent for inflamed, proliferating, and cancer cells that express CD44 receptors.

Synthesis and characterization of in situ forming anionic hydrogel as vitreous substitutes.

The natural vitreous is a biological hydrogel consisting primarily of a collagen and anionic hyaluronate. It is surgically removed in many ocular diseases and replaced with fluids, gases, or silicone oils. We have been interested in developing synthetic hydrogels as vitreous substitutes. In this study, we combined the stiffness and hydrophobicity of polymethacrylamide (PMAM) and the anionic nature of polymethacrylate (PMAA) to make copolymers that would mimic the natural vitreous. We used bis-methacryloyl cystamine (BMAC) to introduce thiol groups for reversible crosslink. The Mn of copolymers ranged from ∼100 k to ∼200 k Da (polydisperisty index of 1.47-2.63) and their composition as determined by titration, 1 H NMR and disulfide test were close to the feed ratio. The reactivities of monomers were as follows: MAM > MAA ∼ BMAC. Copolymers with higher MAA contents gelled faster, swelled more, and had higher storage modulus (1.5 to 100 Pa) comparable to that of the natural vitreous. We evaluated the biocompatibility of copolymers by electric cell-substrate impedance sensing (ECIS) using human retinal pigment epithelial cells, primary porcine retinal pigmented epithelial cells, human microvascular endothelial cells adult dermis, and a fibroblast line 3T3. The biocompatibility decreases as the content of BMAC increases. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 977-988, 2017.

Biomimetic hydrogel with tunable mechanical properties for vitreous substitutes.

UNLABELLED: The vitreous humor of the eye is a biological hydrogel principally composed of collagen fibers interspersed with hyaluronic acid. Certain pathological conditions necessitate its removal and replacement. Current substitutes, like silicone oils and perfluorocarbons, are not biomimetic and have known complications. In this study, we have developed an in situ forming two-component biomimetic hydrogel with tunable mechanical and osmotic properties. The components are gellan, an analogue of collagen, and poly(methacrylamide-co-methacrylate), an analogue of hyaluronic acid; both endowed with thiol side groups. We used response surface methodology to consider seventeen possible hydrogels to determine how each component affects the optical, mechanical, sol-gel transition temperature and swelling properties. The optical and physical properties of the hydrogels were similar to vitreous. The shear storage moduli ranged from 3 to 358Pa at 1Hz and sol-gel transition temperatures from 35.5 to 43°C. The hydrogel had the ability to remain swollen without degradation for four weeks in vitro. Three hydrogels were tested for biocompatibility on primary porcine retinal pigment epithelial cells, human retinal pigment epithelial cells, and fibroblast (3T3/NIH) cells, by electric cell-substrate impedance sensing system. The two-component hydrogels allowed for the tuning and optimizing of mechanical, swelling, and transition temperature to obtain three biocompatible hydrogels with properties similar to the vitreous. Future studies include testing of the optimized hydrogels in animal models for use as a long-term substitute, whose preliminary results are mentioned. STATEMENT OF SIGNIFICANCE: Although hydrogels are researched as long-term vitreous substitute, none have advanced sufficiently to reach clinical application. Our work focuses on the development of a novel two component in situ forming hydrogel that bio-mimic the natural vitreous. Our thiol-containing copolymers can be injected as an aqueous solution into the vitreous cavity wherein, at physiological temperature, the rigid component will instantaneously form a physical gel imbedding the random coil copolymer. Upon subsequent oxidation, the two components will form disulfide cross-links and a stable reversible hydrogel capable of providing osmotic pressure to reattach the retina. It may be left in the eye permanently or easily removed by injection of a simple reducing agent to cleave the disulfide bonds, rather than surgery. This contribution is significant because it is expected to provide patients with a much better quality of life by improving surgical outcomes, creating much less post-operative burden, and reducing the need for secondary surgeries.

Biocompatibility of gold nanoparticles in retinal pigment epithelial cell line.

Gold nanoparticles (Au NPs) have been tested as targeted delivery agents because of their high chemical stability and surface plasmon properties. Here, we investigated the biocompatibility of Au spheres (5-, 10-, 20-, 30-, 50-. and 100-nm), cubes (50-nm), and rods (10×90nm) on a retinal pigment epithelial (ARPE-19) cell line. The lethal dose for killing 50% of the cells (LD50) was evaluated using an MTT (3-[4, 5 dimethyl-thiazoly-2-yl] 2-5 diphenyl tetrazolium bromide) assay. At and above LD50, based on mass concentrations, the confluent cell layer began to detach, as shown by real-time measurements of electric impedance. We found that the biocompatibility of spheres improved with increasing nanoparticle size. The Au rods were less biocompatible than 10-nm spheres. Confocal microscopy showed that cubic (50-nm) and spherical NPs (50- and 100-nm) neither had cytotoxic effects nor entered cells. Lethal doses for internalized spherical NPs, which were toxic, were recalculated based on surface area (LD50,A) concentrations. Indeed, when biocompatibility was expressed as the surface area concentration of NPs, the curve was independent of size. The LD50,A of Au nanospheres was 23cm2/ml. Our findings demonstrate that the sole modulation of the surface area would make it possible to use Au NPs for therapeutic purposes.

Investigating thiol-modification on hyaluronan via carbodiimide chemistry using response surface methodology.

Hyaluronan (HA) is a naturally occurring glycosaminoglycan widely researched for its use as a biomaterial in tissue engineering, drug delivery, angiogenesis, and ophthalmic surgeries. The mechanical properties of this biomaterial can be altered to a required extent by chemically modifying the pendant reactive groups. However, derivatizing these polymers to a predetermined extent has been the Achilles heel for this process. In this study, we have investigated the factors controlling the derivatization of the carboxyl moieties of HA with amine containing thiol, cystamine dihydrochloride (Cys), via carbodiimide crosslinking chemistry. We used fractional factorial design to screen and identify the significant factor(s) affecting the reaction, and response surface methodology (RSM) to develop a model equation for predicting the degree of thiolation of HA. Also, we analyzed the reaction mechanism for potential side reactions. We observed that N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) (mole ratio with repeat unit of HA) is the significant factor controlling the degree of amidation. The quadratic equations developed from RSM predict the formulation for a desired degree of amidation of HA and percentage of potential side product. Hence, derivatizing HA to a predetermined extent with minimal side product can be achieved using the statistical design of experiments.

Investigating triazine-based modification of hyaluronan using statistical designs.

Hyaluronan (HA) and its derivatives have been extensively researched for many biomedical applications. To precisely tailor the property of HA by derivatizing it to a pre-determined extent is challenging, yet critical. In this paper, we used 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methylmorpholine (NMM) to derivatize HA via a triazine-based coupling reaction. Using a fractional factorial (FF) design, we observed that water content in the solvent, and molar ratios of CDMT and NaHCO3 to the carboxylate were the significant factors controlling the derivatization. We investigated how the effect of each factor changes as reaction conditions change. Moreover, by altering the amount of CDMT and NaHCO3, we developed a cubic regression model for precise control of the extent of derivatization using a response surface methodology (RSM) with a D-optimal design. No spurious peaks were detected by (1)H NMR spectrum and only 10% decrease of molecular weight of the derivatized HA was determined by GPC. The HA with 6% modification was relatively biocompatible up to 15 mg/mL.