Detection of nanometer-sized particles in living cells using modern fluorescence fluctuation methods

Recent Advances in Nanodrug Delivery Systems Production, Efficacy, Safety, and Toxicity

In the last three decades, the development of nanoparticles or nano-formulations as drug delivery systems has emerged as a promising tool to overcome the limitations of conventional delivery, potentially to improve the stability and solubility of active molecules, promote their transport across the biological membranes, and prolong circulation times to increase efficacy of a therapy. Despite several nano-formulations having applications in drug delivery, some issues concerning their safety and toxicity are still debated. This chapter describes the recent available information regarding safety, toxicity, and efficacy of nano-formulations for drug delivery. Several key factors can influence the behavior of nanoparticles in a biological environment, and their evaluation is crucial to design non-toxic and effective nano-formulations. Among them, we have focused our attention on materials and methods for their preparation (including the innovative microfluidic technique), mechanisms of interactions with biological systems, purification of nanoparticles, manufacture impurities, and nano-stability. This chapter places emphasis on the utilization of in silico, in vitro, and in vivo models for the assessment and prediction of toxicity associated with these nano-formulations. Furthermore, the chapter includes specific examples of in vitro and in vivo studies conducted on nanoparticles, illustrating their application in this field.

Ultra-small micelles together with UTMD enhanced the therapeutic effect of docetaxel on Glioblastoma

Owing to the difficult-to-penetrate blood-brain barrier (BBB), glioblastoma (GBM) doesn't respond well to the current chemical therapeutics. In this study, ultra-small micelles (NMs) self-assembled by RRR-a-tocopheryl succinate-grafted-ε-polylysine conjugate (VES-g-ε-PLL) as the delivery vehicle of chemical therapeutics in conjunction with ultrasound-targeted microbubble destruction (UTMD) to surmount BBB and treat GBM. Docetaxel (DTX) as a hydrophobic model drug was incorporated into NMs. DTX-loaded micelles (DTX-NMs) with 3.08% of drug loading exhibited a hydrodynamic diameter (33.2 nm) and positive Zeta potential (16.9 mV), having a remarkable tumor-permeating capacity. Furthermore, DTX-NMs presented good stability in physiologic condition. The sustained-release release profile of DTX-NMs was also displayed by dynamic dialysis. Treatment of DTX-NMs together with UTMD led to more pronounced apoptosis of C6 tumor cells than DTX-NMs alone. Moreover, compared with the DTX solution or DTX-NMs alone, the combination of DTX-NMs with UTMD had a stronger inhibitory effect on tumor growth for GBM-bearing rats. The median survival period of GBM-bearing rats was extended to 75 days in the DTX-NMs+UTMD group from under 25 days in the control group. The invasive growth of glioblastoma was largely inhibited by the combination of DTX-NMs with UTMD, which was demonstrated by staining of Ki67, caspase-3, and CD31, together with TUNEL assay. In conclusion, the combination of ultra-small micelles (NMs) with UTMD may be a promising strategy to overcome the limitations of the first-line chemotherapeutics against GBM.

Myco-Nanofabrication of Silver Nanoparticles by Penicillium brasilianum NP5 and Their Antimicrobial, Photoprotective and Anticancer Effect on MDA-MB-231 Breast Cancer Cell Line

Currently, the exploration of fungal organisms for novel metabolite production and its pharmacological applications is much appreciated in the biomedical field. In the present study, the fungal strains were isolated from soil of unexplored Yellapura regions. The potent isolate NP5 was selected based on preliminary screening and identified as Penicillium brasilianum NP5 through morphological, microscopic, and molecular characterizations. Synthesis of silver nanoparticles from P. brasilianum was confirmed by the color change of the reaction mixture and UV-visible surface plasmon resonance (SPR) spectra of 420 nm. Fourier transform infrared (FTIR) analysis revealed the functional groups involved in synthesis. Atomic force microscopy (AFM) and transmission electron microscope (TEM) analysis showed aggregation of the NPs, with sizes ranged from 10 to 60 nm, an average particle size of 25.32 nm, and a polydispersity index (PDI) of 0.40. The crystalline nature and silver as the major element in NP5-AgNPs was confirmed by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis. The negative value −15.3 mV in Zeta potential exhibited good stability, and thermostability was recorded by thermogravimetric analysis (TGA). NP5-AgNPs showed good antimicrobial activity on selected human pathogens in a concentration-dependent manner. The MTT assay showed concentration-dependent anticancer activity with an IC50 of 41.93 µg/mL on the MDA-MB-231 cell line. Further, apoptotic study was carried out by flow cytometry to observe the rate of apoptosis. The calculated sun protection factor (SPF) value confirms good photoprotection capacity. From the results obtained, NP5-AgNPs can be used in the pharmaceutical field after successful in vitro clinical studies.

Advances on the early cellular events occurring upon exposure of human macrophages to aluminum oxyhydroxide adjuvant

Aluminum compounds are the most widely used adjuvants in veterinary and human vaccines. Despite almost a century of use and substantial advances made in recent decades about their fate and biological effects, the exact mechanism of their action has been continuously debated, from the initial "depot-theory" to the direct immune system stimulation, and remains elusive. Here we investigated the early in vitro response of primary human PBMCs obtained from healthy individuals to aluminum oxyhydroxide (the most commonly used adjuvant) and a whole vaccine, in terms of internalization, conventional and non-conventional autophagy pathways, inflammation, ROS production, and mitochondrial metabolism. During the first four hours of contact, aluminum oxyhydroxide particles, with or without adsorbed vaccine antigen, (1) were quickly recognized and internalized by immune cells; (2) increased and balanced two cellular clearance mechanisms, i.e. canonical autophagy and LC3-associated phagocytosis; (3) induced an inflammatory response with TNF-α production as an early event; (4) and altered mitochondrial metabolism as assessed by both decreased maximal oxygen consumption and reduced mitochondrial reserve, thus potentially limiting further adaptation to other energetic requests. Further studies should consider a multisystemic approach of the cellular adjuvant mechanism involving interconnections between clearance mechanism, inflammatory response and mitochondrial respiration.

UV Light-Activated GdYVO4:Eu3+ Nanoparticles Induce Reactive Oxygen Species Generation in Leukocytes Without Affecting Erythrocytes In Vitro

Nanoparticles (NPs) have been reported to be promising enhancement agents for radiation therapy. The aim of the study was to assess the cytotoxicity of UV non-treated and UV pretreated GdYVO₄:Eu³⁺ nanoparticles against erythrocytes and leukocytes by detecting eryptosis and reactive oxygen species (ROS) generation. Levels of intracellular ROS in erythrocytes and leukocytes using a ROS-sensitive dye 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA), as well as eryptosis rate utilizing annexin V staining, following direct exposure to UV-activated and nonactivated NPs were detected by flow cytometry. Blood cells were collected from 9 intact WAG rats. Neither the UV light-untreated GdYVO₄:Eu³⁺ NPs nor the treated ones promoted eryptosis and ROS generation in erythrocytes. Low concentrations of UV light-untreated NPs did not induce oxidative stress in leukocytes, evidenced by unaffected intracellular ROS levels. UV light treatment grants prooxidant properties to NPs, confirmed by NP-induced ROS overproduction in leukocytes. High concentrations of both UV light-treated and untreated NPs altered the redox state of leukocytes. UV light treatment imparts prooxidant properties to GdYVO₄:Eu³⁺ NPs, making them promising radiosensitizing agents in cancer radiation therapy.

Current Advances in Lipid and Polymeric Antimicrobial Peptide Delivery Systems and Coatings for the Prevention and Treatment of Bacterial Infections

Bacterial infections constitute a threat to public health as antibiotics are becoming less effective due to the emergence of antimicrobial resistant strains and biofilm and persister formation. Antimicrobial peptides (AMPs) are considered excellent alternatives to antibiotics; however, they suffer from limitations related to their peptidic nature and possible toxicity. The present review critically evaluates the chemical characteristics and antibacterial effects of lipid and polymeric AMP delivery systems and coatings that offer the promise of enhancing the efficacy of AMPs, reducing their limitations and prolonging their half-life. Unfortunately, the antibacterial activities of these systems and coatings have mainly been evaluated in vitro against planktonic bacteria in less biologically relevant conditions, with only some studies focusing on the antibiofilm activities of the formulated AMPs and on the antibacterial effects in animal models. Further improvements of lipid and polymeric AMP delivery systems and coatings may involve the functionalization of these systems to better target the infections and an analysis of the antibacterial activities in biologically relevant environments. Based on the available data we proposed which polymeric AMP delivery system or coatings could be profitable for the treatment of the different hard-to-treat infections, such as bloodstream infections and catheter- or implant-related infections.

Nanoformulations for Drug Delivery: Safety, Toxicity, and Efficacy

This chapter presents an outline of the recent available information regarding safety, toxicity, and efficacy of nano drug delivery systems. Of particular importance is the evaluation of several key factors to design nontoxic and effective nanoformulations. Among them, we focus on nanostructure materials and synthesis methods, mechanisms of interactions with biological systems, treatment of nanoparticles, manufacture impurities, and nanostability. Emphasis is given to in silico, in vitro, and in vivo models used to assess and predict the toxicity of these new formulations. Additionally, some examples of in vitro and in vivo studies of specific nanoderivatives are also presented in this chapter.

An injectable acellular matrix scaffold with absorbable permeable nanoparticles improves the therapeutic effects of docetaxel on glioblastoma

Intratumoral drug delivery (IT) is an inherently appealing approach for concentrating toxic chemotherapies at the site of action. However, for most chemotherapies, poor tumor penetration and short retention at the administration site limit their anti-tumor effects. In this work, we describe permeable nanoparticles (NPs) prepared with a novel amphiphilic polymer, RRR-α-tocopheryl succinate-grafted-ε-polylysine conjugate (VES-g-ε-PLL). The nanoparticles (NPs) of VES-g-ε-PLL exhibited an ultra-small hydrodynamic diameter (20.8 nm) and positive zeta potential (20.6 mV), which facilitate strong glioma spheroid penetration ability in vitro. Additionally, the hydrophobic model drug docetaxel (DTX) could be effectively encapsulated in the nanoparticles with 3.99% drug loading and 73.37% encapsulation efficiency. To prolong the retention time of DTX-loaded nanoparticles (DTX-NPs) in the tumor, intact decellularized brain extracellular matrix (dBECM) derived from healthy rats was used as a drug depot to adsorb the ultra-small DTX-NPs. The intact DTX-NPs-adsorbing dBECM scaffold was further homogenized into an injectable DTX-NPs-dBECM suspension for intratumoral administration. The DTX-NPs-dBECM suspension exhibited slower DTX release than naked DTX-NPs without compromising the tumor penetration ability of DTX-NPs. An antitumor study showed that the DTX-NPs-dBECM suspension exhibited more powerful in vitro inhibition of tumor spheroid growth than free DTX solution or DTX-NPs. Due to strong tumor penetration ability and prolonged retention, DTX-NPs-dBECM led to complete suppression of glioma growth in vivo at 28 days after treatment. The therapeutic mechanism was due to enhanced proliferation inhibition and apoptosis of tumor cells and angiogenesis inhibition of glioma after treatment with DTX-NPs-dBECM. Finally, the safety of DTX-NPs-dBECM at the therapeutic dose was demonstrated via pathological HE assay from heart, liver, spleen, lung and kidney tissues. In conclusion, permeable nanoparticle-absorbing dBECM is a potential carrier for intratumoral delivery of common chemotherapeutics.

Comparative assessment of the apoptotic potential of silver nanoparticles synthesized by Bacillus tequilensis and Calocybe indica in MDA-MB-231 human breast cancer cells: targeting p53 for anticancer therapy

Background

Recently, the use of nanotechnology has been expanding very rapidly in diverse areas of research, such as consumer products, energy, materials, and medicine. This is especially true in the area of nanomedicine, due to physicochemical properties, such as mechanical, chemical, magnetic, optical, and electrical properties, compared with bulk materials. The first goal of this study was to produce silver nanoparticles (AgNPs) using two different biological resources as reducing agents, Bacillus tequilensis and Calocybe indica. The second goal was to investigate the apoptotic potential of the as-prepared AgNPs in breast cancer cells. The final goal was to investigate the role of p53 in the cellular response elicited by AgNPs.

Methods

The synthesis and characterization of AgNPs were assessed by various analytical techniques, including ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The apoptotic efficiency of AgNPs was confirmed using a series of assays, including cell viability, leakage of lactate dehydrogenase (LDH), production of reactive oxygen species (ROS), DNA fragmentation, mitochondrial membrane potential, and Western blot.

Results

The absorption spectrum of the yellow AgNPs showed the presence of nanoparticles. XRD and FTIR spectroscopy results confirmed the crystal structure and biomolecules involved in the synthesis of AgNPs. The AgNPs derived from bacteria and fungi showed distinguishable shapes, with an average size of 20 nm. Cell viability assays suggested a dose-dependent toxic effect of AgNPs, which was confirmed by leakage of LDH, activation of ROS, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells in MDA-MB-231 breast cancer cells. Western blot analyses revealed that AgNPs induce cellular apoptosis via activation of p53, p-Erk1/2, and caspase-3 signaling, and downregulation of Bcl-2. Cells pretreated with pifithrin-alpha were protected from p53-mediated AgNPs-induced toxicity.

Conclusion

We have demonstrated a simple approach for the synthesis of AgNPs using the novel strains B. tequilensis and C. indica, as well as their mechanism of cell death in a p53-dependent manner in MDA-MB-231 human breast cancer cells. The present findings could provide insight for the future development of a suitable anticancer drug, which may lead to the development of novel nanotherapeutic molecules for the treatment of cancers.

Differential nanoreprotoxicity of silver nanoparticles in male somatic cells and spermatogonial stem cells

Background

Silver nanoparticles (AgNPs) possess unique physical, chemical, and biological properties. AgNPs have been increasingly used as anticancer, antiangiogenic, and antibacterial agents for the treatment of bacterial infections in open wounds as well as in ointments, bandages, and wound dressings. The present study aimed to investigate the effects of two different sizes of AgNPs (10 nm and 20 nm) in male somatic Leydig (TM3) and Sertoli (TM4) cells and spermatogonial stem cells (SSCs).

Methods

Here, we demonstrate a green and simple method for the synthesis of AgNPs using Bacillus cereus culture supernatants. The synthesized AgNPs were characterized using ultraviolet and visible absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM). The toxicity of the synthesized AgNPs was evaluated by the effects on cell viability, metabolic activity, oxidative stress, apoptosis, and expression of genes encoding steroidogenic and tight junction proteins.

Results

AgNPs inhibited the viability and proliferation of TM3 and TM4 cells in a dose- and size-dependent manner by damaging cell membranes and inducing the generation of reactive oxygen species, which in turn affected SSC growth on TM3 and TM4 as feeder cells. Small AgNPs (10 nm) were more cytotoxic than medium-sized nanoparticles (20 nm). TEM revealed the presence of AgNPs in the cell cytoplasm and nucleus, and detected mitochondrial damage and enhanced formation of autosomes and autolysosomes in the AgNP-treated cells. Flow cytometry analysis using Annexin V/propidium iodide staining showed massive cell death by apoptosis or necrosis. Real-time polymerase chain reaction and western blot analyses indicated that in TM3 and TM4 cells, AgNPs activated the p53, p38, and pErk1/2 signaling pathways and significantly downregulated the expression of genes related to testosterone synthesis (TM3) and tight junctions (TM4). Furthermore, the exposure of TM3 and TM4 cells to AgNPs inhibited proliferation and self-renewal of SSCs.

Conclusion

Our results suggest that AgNPs exhibit size-dependent nanoreprotoxicity in male somatic cells and SSCs, strongly suggesting that applications of AgNPs in commercial products must be carefully evaluated. Further studies of AgNPs-induced nanoreprotoxicity in animal models are required.

Mesenchymal stromal cells loading curcumin-INVITE-micelles: a drug delivery system for neurodegenerative diseases

This work reports on the formation of a carrier-in-carrier device for the systemic delivery and targeting of hydrophobic drugs mediated by micelle-loaded mesenchymal stromal cells (MSCs) (carrier-in-carrier) to be administered by intravenous injection. The innate ability of MSCs to reach injured tissues such as the central nervous system or other damaged tissues, is the key for the second order delivery and first order targeting. Inulin-D-alfa-tocopherol succinate micelles (INVITE M) are able to incorporate highly hydrophobic drugs and, due to their dimensions (≈7 nm diameter), to penetrate the cell membrane easily and quickly. This study demonstrates that the curcumin loaded micelles (INVITE MC), sterilized by filtration, reached the maximum loading in MSCs in few minutes and that the loading was concentration-dependent. When "naked" curcumin was used, an evident cytotoxicity on MSCs was detected, while INVITE micelles protected them from this effect. Moreover, MSCs loaded with INVITE MC are able to release the entrapped drug. This study strongly supports the feasibility of the carrier-in-carrier approach for the therapy of selected diseases, i.e., this innovative drug delivery system will be proposed for the treatment of the amyotrophic lateral sclerosis (ALS).

Mitochondrial potential (ΔΨm) changes in single rat hepatocytes: the effect of orthovanadate nanoparticles doped with rare-earth elements

Rare-earth-based nanoparticles (NPs) are widely used as fluorescent probes for imaging in vitro and in vivo. One of the challenges that restrain NPs applications in biomedical research is their effect on subcellular structures. In this paper, the ability of lanthanide NPs to affect the cellular oxidative balance and alter the mitochondrial function was analyzed. Since size and shape mutually affect the cellular internalization and intracellular distribution of NPs, the investigations were performed with NPs of spherical (GdYVO4:Eu(3+), spindle-(GdVO4: Eu(3+) and rod-like (LaVO4: Eu(3+) shapes. Quantitative microfluorimetry with JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide) as a mitochondrial probe was used for monitoring of the mitochondrial transmembrane potential (ΔΨ m) in single living cells. Changes in the ratio of the JC-1 probe fluorescence were used to analyze the NPs effect on ΔΨ(m). The fastest suppressive effect (within 1 hour) was found for spherical NPs. Gradual lowering of ΔΨ(m) was observed at the exposure of cells within 24 hours for all types of NPs. Exogenous thiols were required for ΔΨ(m) protection. The protective role of exogenous glutathione (GSH) proves that the increase of reactive oxygen species (ROS) formation with depletion of GSH can mediate NPs toxicity. The dynamics of the shape-dependent effect can be explained by the features of NPs transportation into cells.

Oxidative stress mediated cytotoxicity of biologically synthesized silver nanoparticles in human lung epithelial adenocarcinoma cell line

The goal of the present study was to investigate the toxicity of biologically prepared small size of silver nanoparticles in human lung epithelial adenocarcinoma cells A549. Herein, we describe a facile method for the synthesis of silver nanoparticles by treating the supernatant from a culture of Escherichia coli with silver nitrate. The formation of silver nanoparticles was characterized using various analytical techniques. The results from UV-visible (UV-vis) spectroscopy and X-ray diffraction analysis show a characteristic strong resonance centered at 420 nm and a single crystalline nature, respectively. Fourier transform infrared spectroscopy confirmed the possible bio-molecules responsible for the reduction of silver from silver nitrate into nanoparticles. The particle size analyzer and transmission electron microscopy results suggest that silver nanoparticles are spherical in shape with an average diameter of 15 nm. The results derived from in vitro studies showed a concentration-dependent decrease in cell viability when A549 cells were exposed to silver nanoparticles. This decrease in cell viability corresponded to increased leakage of lactate dehydrogenase (LDH), increased intracellular reactive oxygen species generation (ROS), and decreased mitochondrial transmembrane potential (MTP). Furthermore, uptake and intracellular localization of silver nanoparticles were observed and were accompanied by accumulation of autophagosomes and autolysosomes in A549 cells. The results indicate that silver nanoparticles play a significant role in apoptosis. Interestingly, biologically synthesized silver nanoparticles showed more potent cytotoxicity at the concentrations tested compared to that shown by chemically synthesized silver nanoparticles. Therefore, our results demonstrated that human lung epithelial A549 cells could provide a valuable model to assess the cytotoxicity of silver nanoparticles.

Subtype-specific differences in corticotropin-releasing factor receptor complexes detected by fluorescence spectroscopy

G protein-coupled receptors have been proposed to exist in signalosomes subject to agonist-driven shifts in the assembly disassembly equilibrium, affected by stabilizing membrane lipids and/or cortical actin restricting mobility. We investigated the highly homologous corticotropin-releasing factor receptors (CRFRs), CRFR1 and -2, which are different within their hydrophobic core. Agonist stimulation of CRFR1 and CRFR2 gave rise to similar concentration-response curves for cAMP accumulation, but CRFR2 underwent restricted collision coupling. Both CRFR1 and CRFR2 formed constitutive oligomers at the cell surface and recruited beta-arrestin upon agonist activation (as assessed by fluorescence resonance energy transfer microscopy in living cells). However, CRFR2, but not CRFR1, failed to undergo agonist-induced internalization. Likewise, agonist binding accelerated the diffusion rate of CRFR2 only (detected by fluorescence recovery after photobleaching and fluorescence correlation spectroscopy) but reduced the mobile fraction, which is indicative of local confinement. Fluorescence intensity distribution analysis demonstrated that the size of CRFR complexes was not changed. Disruption of the actin cytoskeleton abolished the agonist-dependent increase in CRFR2 mobility, shifted the agonist concentration curve for CRFR2 to the left, and promoted agonist-induced internalization of CRFR2. Our observations are incompatible with an agonist-induced change in monomer-oligomer equilibrium, but they suggest an agonist-induced redistribution of CRFR2 into a membrane microdomain that affords rapid diffusion but restricted mobility and that is stabilized by the actin cytoskeleton. Our data show that membrane anisotropy can determine the shape and duration of receptor-generated signals in a subtype-specific manner.

Drug delivery and nanoparticles:applications and hazards

The use of nanotechnology in medicine and more specifically drug delivery is set to spread rapidly. Currently many substances are under investigation for drug delivery and more specifically for cancer therapy. Interestingly pharmaceutical sciences are using nanoparticles to reduce toxicity and side effects of drugs and up to recently did not realize that carrier systems themselves may impose risks to the patient. The kind of hazards that are introduced by using nanoparticles for drug delivery are beyond that posed by conventional hazards imposed by chemicals in classical delivery matrices. For nanoparticles the knowledge on particle toxicity as obtained in inhalation toxicity shows the way how to investigate the potential hazards of nanoparticles. The toxicology of particulate matter differs from toxicology of substances as the composing chemical(s) may or may not be soluble in biological matrices, thus influencing greatly the potential exposure of various internal organs. This may vary from a rather high local exposure in the lungs and a low or neglectable exposure for other organ systems after inhalation. However, absorbed species may also influence the potential toxicity of the inhaled particles. For nanoparticles the situation is different as their size opens the potential for crossing the various biological barriers within the body. From a positive viewpoint, especially the potential to cross the blood brain barrier may open new ways for drug delivery into the brain. In addition, the nanosize also allows for access into the cell and various cellular compartments including the nucleus. A multitude of substances are currently under investigation for the preparation of nanoparticles for drug delivery, varying from biological substances like albumin, gelatine and phospholipids for liposomes, and more substances of a chemical nature like various polymers and solid metal containing nanoparticles. It is obvious that the potential interaction with tissues and cells, and the potential toxicity, greatly depends on the actual composition of the nanoparticle formulation. This paper provides an overview on some of the currently used systems for drug delivery. Besides the potential beneficial use also attention is drawn to the questions how we should proceed with the safety evaluation of the nanoparticle formulations for drug delivery. For such testing the lessons learned from particle toxicity as applied in inhalation toxicology may be of use. Although for pharmaceutical use the current requirements seem to be adequate to detect most of the adverse effects of nanoparticle formulations, it can not be expected that all aspects of nanoparticle toxicology will be detected. So, probably additional more specific testing would be needed.

Getting It Right the First Time: Developing Nanotechnology while Protecting Workers, Public Health, and the Environment

Nanotechnology, the design and manipulation of materials at the atomic scale, may well revolutionize many of the ways our society manufactures products, produces energy, and treats diseases. Innovative nanotechnology products are already reaching the market in a wide variety of consumer products. Some of the observed properties of nanomaterials call into question the adequacy of current methods for determining hazard and exposure, and for controlling resulting risks. Given the limitations of existing regulatory tools and policies, two distinct kinds of initiatives are urgently needed: first, a major increase in the federal investment nanomaterial risk research, and second, rapid development and implementation of voluntary standards of care pending development of adequate regulatory safeguards. The U.S. government should increase federal funding for nanomaterial risk research under the National Nanotechnology Initiative to at least $100 million annually for the next several years. Several voluntary programs are currently at various stages of evolution, though the eventual outputs of each of these are still far from clear. Ultimately, effective regulatory safeguards, harmonized globally, are necessary to provide a level playing field for industry while adequately protecting human health and the environment.