Coupled Turbidity and Spectroscopy Problems: A Simple Algorithm for Volumetric Analysis of Optically Thin or Dilute, In Vitro Bacterial Cultures in Various Media.

An approach binary spectronephelometry (BSN) to perform real-time simultaneous noninvasive in situ physical and chemical analysis of bacterial cultures in fluid media is described. We choose to characterize cultures of Escherichia coli (NC), Pseudomonas aeruginosa (PA), and Shewanella oneidensis (SO) in the specific case of complex media whose Raman spectrum cannot be unambiguously assigned. Nevertheless, organism number density and a measure of the chemical makeup of the fluid medium can be monitored noninvasively, simultaneously, and continuously, despite changing turbidity and medium chemistry. The method involves irradiating a culture in fluid medium in an appropriate vessel (in this case a standard 1 cm cuvette) using a near infrared laser and collecting all the backscattered light from the cuvette, i.e., the Rayleigh-Mie line and the inelastically emitted light which includes unresolved Raman scattered light and fluorescence. Complex "legacy" media contain materials of biological origin whose chemical composition cannot be fully delineated. We independently calibrate this approach to a commonly used reference, optical density at 600 nm (OD600) for characterizing the number density of organisms. We suggest that the total inelastically emitted light could be a measure of the chemical state of a biologically based medium, e.g., lysogeny broth (LB). This approach may be useful in a broad range of basic and applied studies and enterprises that utilize bacterial cultures in any medium or container that permits optical probing in the single scattering limit.

In vivo, noncontact, real-time, PV[O]H imaging of the immediate local physiological response to spinal cord injury in a rat model.

We report a small exploratory study of a methodology for real-time imaging of chemical and physical changes in spinal cords in the immediate aftermath of a localized contusive injury. One hundred separate experiments involving scanning NIR images, one-dimensional, two-dimensional (2-D), and point measurements, obtained in vivo, within a 3 × 7 mm field, on spinal cords surgically exposed between T9 and T10 revealed differences between injured and healthy cords. The collected raw data, i.e., elastic and inelastic emission from the laser probed tissues, combined via the PV[O]H algorithm, allow construction of five images over the first 5 h post injury. Within the larger study, a total of 13 rats were studied using 2-D images, i.e., injured and control. A single 830-nm laser (100-µm diameter round spot) was spatially line-scanned across the cord to reveal photobleaching effects and surface profiles possibly locating a near surface longitudinal artery/vein. In separate experiments, the laser was scanned in two dimensions across the exposed cord surface relative to the injury in a specific pattern to avoid uneven photobleaching of the imaged tissue. The 2-D scanning produced elastic and inelastic emission that allowed construction of PV[O]H images that had good fidelity with the visually observed surfaces and separate line scans and suggested differences between the volume fractions of fluid and turbidity of injured and healthy cord tissue.

Optical interference probe of biofilm hydrology: label-free characterization of the dynamic hydration behavior of native biofilms.

Biofilm produced by Escherichia coli (E. coli) or Pseudomonas aeruginosa (P. aeruginosa) on quartz or polystyrene is removed from the culture medium and drained. Observed optical interference fringes indicate the presence of a layer of uniform thickness with refractive index different from air-dried biofilm. Fringe wavelengths indicate that layer optical thickness is < 20 ?? ? m or 1 to 2 orders of magnitude thinner than the biofilm as measured by confocal Raman microscopy or fluorescence imaging of the bacteria. Raman shows that films have an alginate-like carbohydrate composition. Fringe amplitudes indicate that the refractive index of the interfering layer is higher than dry alginate. Drying and rehydration nondestructively thins and restores the interfering layer. The strength of the 1451-nm near infrared water absorption varies in unison with thickness. Absorption and layer thickness are proportional for films with different bacteria, substrates, and growth conditions. Formation of the interfering layer is general, possibly depending more on the chemical nature of alginate-like materials than bacterial processes. Films grown during the exponential growth phase produce no observable interference fringes, indicating requirements for layer formation are not met, possibly reflecting bacterial activities at that stage. The interfering layer might provide a protective environment for bacteria when water is scarce.

Coupled turbidity and spectroscopy problems: a simple algorithm for the volumetric analysis of optically thin or dilute two-phase systems.

We report an algorithm for measuring the phase volume fraction and solute concentration of a two-phase system, applicable to either optically thin or optically dilute spatially homogeneous systems. Probing light is directed into the sample, and the elastically scattered light (EE) is collected as one signal and the inelastically scattered light (IE) collected as another signal. The IE can be pure fluorescence or Raman or an unresolved combination of the two. As the IE and the EE are produced by fundamentally different processes, they are independent. The algorithm, derived from radiation transfer theory, shows that phase volume and concentration are linear functions of the EE and IE. The parameters are derived from a training set. We present examples of how the algorithm performs when the assumption of spatial homogeneity is violated and when light-induced photochemistry causes changes in the IE. Although this is a generally valid algorithm with many potential applications, its use is discussed briefly in the context of blood and tissue analysis since the algorithm was originally designed for noninvasive in vivo probing of human skin.

Size histograms of gold nanoparticles measured by gravitational sedimentation.

Sedimentation curves of gold nanoparticles in water were obtained by measuring the optical density of a suspension over time. The results are not subject to sampling errors, and refer to the particles in situ. Curves obtained simultaneously at several wave lengths were analyzed together to derive the size histogram of the sedimenting particles. The bins in the histogram were 5 nm wide and centered at diameters 60, 65, …, 110 nm. To get the histogram, we weighted previously calculated solutions to the Mason-Weaver sedimentation-diffusion equation for various particle diameters with absorption/scattering coefficients and size (diameter) abundances {c(j)}, and found the {c(j)} which gave the best fit to all the theoretical sedimentation curves. The effects of changing the number of bins and the wave lengths used were studied. Going to smaller bins would mean determining more parameters and require more wave lengths. The histograms derived from sedimentation agreed quite well in general with the histogram derived from TEM. Differences found for the smallest particle diameters are partly due to statistical fluctuations (TEM found only 1-2 particles out of 103 with these diameters). More important is that the TEM histogram indicates 12% of the particles have diameters of 75±2.5 nm, and the sedimentation histogram shows none. We show that this reflects the difference between the particles in situ, which possess a low-density shell about 1 nm thick, and the bare particles on the TEM stage. Correcting for this makes agreement between the two histograms excellent. Comparing sedimentation-derived with TEM-derived histograms thus shows differences between the particles in situ and on the TEM stage.

Cyclodextrin capped gold nanoparticles as a delivery vehicle for a prodrug of cisplatin.

In this work, we explore the use of a quick coupling mechanism for "arming" a cyclodextrin coated gold nanoparticle (AuNP) delivery vehicle, 2, with an adamantane-oxoplatin conjugate that is a prodrug of cisplatin, 3, to produce a cytotoxic nanodrug, 4. The two-part arming system, which utilizes the well-known guest-host interaction between ß-cyclodextrin and adamantane, may be useful for rapidly constituting polyfunctional nanodrugs prior to their application in chemotherapy. The 4.7 ± 1.1 nm delivery vehicle, 2, coated with per-6-thio-ß-cyclodextrin (ßSCD), was characterized using transmission electron microscopy and absorption spectroscopy, and the density of surface-attached ßSCD molecules, ∼210 ßSCD/AuNP, was determined using thermogravimetric analysis. Because (13)C NMR spectra of ßSCD used in the study exhibited disulfide linkages and the observed surface density on the AuNP exceeded that possible for a close-packed mono layer, a fraction of the surface-attached ßSCD molecules on the particle were oligomerized through disulfide linkages. Determination of the binding constant, K, for the 3-ßCD interaction using (1)H NMR chemical shifts was complicated by the self-association of 3 to form a dimer through its conjugated adamantane residue. With a dimerization constant of K2 = 26.7 M(-1), the value of K for the 3-ßCD interaction (1:1 stoichiometry) is 400-800 M(-1), which is lower than the value, K = 1.4 × 10(3) M(-1), measured for the 2-3 interaction using ICP-MS. Optical microscopy showed that when neuroblastoma SK-N-SH cells are treated with the nanodrug, 4 (2+3), clusters of gold nanoparticles are observed in the nuclear regions of living cells within 24 h after exposure, but, at later times when most cells are dying or dead, clustering is no longer observed. Treating the cells with 4 for 72 h gave percent inhibitions that are lower than that of cisplatin, suggesting that the Pt(IV) ions in 4 may be incompletely reduced to cytotoxic Pt(II) species in the cell.

Gravitational sedimentation of gold nanoparticles.

We study the gravitational sedimentation of citrate- or ascorbate-capped spherical gold nanoparticles (AuNP) by measuring the absorption-vs.-time curve produced as the particles sediment through the optical beam of a spectrophotometer, and comparing the results with a calculated sedimentation curve. TEM showed the AuNP had gold-core diameters of 12.1±0.6, 65.0±5.2, 82.5±5.2 or 91.8±6.2 nm, and gave diameter distribution histograms. The Mason-Weaver sedimentation-diffusion equation was solved for various particle diameters and the solutions were weighted with the TEM histogram and the size-dependent extinction coefficient, for comparison with absorbance-vs.-time curve obtained from freshly prepared suspensions of the AuNP. For particles having average gold-core diameters of 12.1±0.6, 65.0±5.2 and 82.5±5.2 nm, very good agreement exists between the theoretical and observed curves, showing that the particles sediment individually and that the diameter of the gold core is the important factor controlling sedimentation. For the largest particles, observed and calculated curves generally agree, but the former shows random effects consistent with non-homogeneous domains in the sample. Unlike TEM, the simple and unambiguous sedimentation experiment detects all the particles in the sample and can in principle be used to derive the true size histogram. It avoids artifacts of TEM sampling and shear forces of ultracentrifugation. We also show how information about the size histogram can be obtained from the sedimentation curve.

Pt(IV) complexes as prodrugs for cisplatin.

The antitumor effects of platinum(IV) complexes, considered prodrugs for cisplatin, are believed to be due to biological reduction of Pt(IV) to Pt(II), with the reduction products binding to DNA and other cellular targets. In this work we used pBR322 DNA to capture the products of reduction of oxoplatin, c,t,c-[PtCl(2)(OH)(2)(NH(3))(2)], 3, and a carboxylate-modified analog, c,t,c-[PtCl(2)(OH)(O(2)CCH(2)CH(2)CO(2)H)(NH(3))(2)], 4, by ascorbic acid (AsA) or glutathione (GSH). Since carbonate plays a significant role in the speciation of platinum complexes in solution, we also investigated the effects of carbonate on the reduction/DNA-binding process. In pH 7.4 buffer in the absence of carbonate, both 3 and 4 are reduced by AsA to cisplatin (confirmed using ((195))Pt NMR), which binds to and unwinds closed circular DNA in a manner consistent with the formation of the well-known 1, 2 intrastrand DNA crosslink. However, when GSH is used as the reducing agent for 3 and 4, ((195))Pt NMR shows that cisplatin is not produced in the reaction medium. Although the Pt(II) products bind to closed circular DNA, their effect on the mobility of Form I DNA is different from that produced by cisplatin. When physiological carbonate is present in the reduction medium, ((13))C NMR shows that Pt(II) carbonato complexes form which block or impede platinum binding to DNA. The results of the study vis-à-vis the ability of the Pt(IV) complexes to act as prodrugs for cisplatin are discussed.

Analyzing near-infrared scattering from human skin to monitor changes in hematocrit.

Probing tissue with near-infrared radiation (NIR) simultaneously produces remitted fluorescence and Raman scattering (IE) plus Rayleigh∕Mie light scattering (EE) that noninvasively give chemical and physical information about the materials and objects within. We model tissue as a three-phase system: plasma and red blood cell (RBC) phases that are mobile and a static tissue phase. In vivo, any volume of tissue naturally experiences spatial and temporal fluctuations of blood plasma and RBC content. Plasma and RBC fractions may be discriminated from each other on the basis of their physical, chemical, and optical properties. Thus, IE and EE from NIR probing yield information about these fractions. Assuming there is no void volume in viable tissue, or that void volume is constant, changes in plasma and RBC volume fractions may be calculated from simultaneous measurements of the two observables, EE and IE. In a previously published analysis we showed the underlying phenomenology but did not provide an algorithm for calculating volume fractions from experimental data. Now, we present a simple analysis that allows monitoring of fluid fraction and hematocrit (Hct) changes by measuring IE and EE, and apply it to some experimental in vivo measurements.

Stability of carboplatin and oxaliplatin in their infusion solutions is due to self-association.

Carboplatin and oxaliplatin are commonly used platinum anticancer agents that are sold as ready-to-use aqueous infusion solutions with shelf lives of 2 and 3 years, respectively. The observed rate constants for the hydrolysis of these drugs, however, are too large to account for their long shelf lives. We here use electrospray-trap mass spectrometry to show that carboplatin and oxaliplatin are self-associated at concentrations in their ready-to-use infusion solutions (~27 mM and 13 mM, respectively) and, as expected, when the drug concentration is reduced to more physiologically relevant concentrations (100 µM and 5 µM, respectively) the association equilibrium is shifted in favor of the monomeric forms of these drugs. Using (1)H NMR we measure the intensity of the NH resonance of the two symmetry-equivalent NH(3) molecules of carboplatin, relative to the intensity of the γ-methylene CH resonance, as a function of total drug concentration. Then, by fitting the data to models of different molecularity, we show that the association complex is a dimer with a monomer-dimer association constant of K (M(-1)) = 391 ± 127. The work presented here shows that carboplatin and oxaliplatin mainly exist as association complexes in concentrated aqueous solution, a property that accounts for the long term stability of their ready-to-use infusion solutions, and that these association complexes may exist, to some extent, in the blood after injection.

Cytotoxicity of Cu(II) and Zn(II) 2,2'-bipyridyl complexes: dependence of IC50 on recovery time.

We measure the cytotoxicity of three metal complexes containing the 2,2'-bypyridine ligand, Cu(bpy)(NCS)(2), 1, [Cu(bpy)(2)(H(2)O)](PF(6))(2), 2, and Zn(bpy)(2)(NCS)(2), 3, toward neuroblastoma cells (SK-N-SH) and ovarian cancer cells (OVCAR-3) using two different cell assays. The cells were exposed to various concentrations of the compounds for 1 h and the percent inhibition of cell growth, I, measured for various times after exposure, i.e., as a function of the recovery time t. After developing the theory showing the relationship between I and t, the cytotoxicity data were analyzed to reveal that the two copper complexes, 1 and 2, cause the cells to divide at a slower rate than the controls during the recovery period, but the zinc complex, 3, had little or no effect on cell division during the recovery period. The usual metric for reporting cytotoxicity is IC(50), which is the concentration of agent required to inhibit cell growth to 50% of the control population. However, since IC(50) can depend on the recovery time, t, as is the case for 1 and 2, reporting IC(50) for a single recovery time can hide important information about the long-time effects of a cytotoxic agent on the health of the cell population. Mechanistic studies with the compounds revealed that the copper complexes, 1 and 2, cleave closed circular pBR322 DNA in the presence of ascorbate, while the zinc complex, 3, does not facilitate DNA cleavage under the same conditions. This difference in DNA cleavage activity may be related to the fact that Cu(II) is redox active and can readily change its oxidation state, while Zn(II) is redox inert and cannot participate in a redox cycle with ascorbate to break DNA.

On probing human fingertips in vivo using near-infrared light: model calculations.

We probe volar-side fingertip capillary beds with near-infrared laser light and collect Raman, Rayleigh, and Mie scattered light and fluorescence. The results are interpreted using radiation transfer theory in the single-scattering approximation. The surface topography of the skin is modeled using the Fresnel equations. The skin is treated as a three-layer material, with a mean-field treatment of tissue composition and related optical properties. The model, with a reasonable choice of tissue parameters, gives a remarkably accurate account of the features of actual measurements. It predicts the optimal values for the incident angle of the laser beam and the distance between beam and detector. It explains the correlated temporal changes in the intensities of elastically and inelastically scattered light caused by heart-driven pulses and why they are out of phase. With appropriate boundary conditions, the model can be used to discuss the scattering from ridged skin extruded conformally into an aperture in a metal surface under constant light pressure. The probing results suggest an inherent regularity and similarity in the anatomy and composition of surface and subsurface tissues of a wide range of skin types.

Mesoporous silica microparticles enhance the cytotoxicity of anticancer platinum drugs.

We report on the endocytosis and the time-dependent enhanced cytotoxicity of anticancer platinum drugs when the drugs are combined with (or loaded into) one of the two most common types of mesoporous silica materials, MCM-41 or SBA-15. The anticancer drug cisplatin and its isomer transplatin, when loaded on MCM-41 and SBA-15 microparticles, were less cytotoxic to leukemia cells than the drugs alone after 12 h exposure. However, the drug-loaded microparticles exhibited unprecedented enhanced cytotoxicity to the cancerous cells after 24 h of exposure. This cytotoxicity of the drug-loaded microparticles was even higher than of the pure drugs in solutions, suggesting that mesoporous silica microparticles loaded with cisplatin or transplatin enabled a localized intracellular release of the platinum compounds and possibly also facilitated the drug's hydrolysis, enhancing the desired cytotoxic effect.

Isomer-dependent adsorption and release of cis- and trans-platin anticancer drugs by mesoporous silica nanoparticles.

We report on adsorption and release of the anticancer drugs cisplatin and transplatin from mesoporous silica nanomaterials, emphasizing the differences between cisplatin and its much less toxic isomer. Two types of particles, MCM-41 and SBA-15, were used, either as just synthesized or after calcination to remove the templates. The particles were characterized by TEM, nitrogen physisorption, and elemental analysis. The UV-vis spectra of cisplatin and transplatin were obtained and the intensities of several bands (205-210 nm, 210-220 nm, 220-235 nm, and 300-330 nm) were found proportional to drug concentrations, allowing their use for measuring drug concentration. To evaluate drug adsorption by nanoparticles, nanoparticles were incubated in drug solutions and removed by centrifugation, after which the supernatants were scanned by spectrometer to determine drug remaining. It was found that calcined MCM adsorbed less cisplatin or transplatin per particle than as-synthesized MCM. SBA nanoparticles adsorbed slightly more cisplatin than MCM, and slightly less transplatin. Measurements of drug adsorption as a function of time show that drug is rapidly adsorbed by all particles studied. This rapid adsorption is probably associated with adsorption of drug on the external surfaces of the particles as well as the possible physisorption within the surfactant assemblies or by replacing the surfactant molecules or ions in the case of the as-synthesized materials. For calcined SBA particles, it is followed by a slow take-up of drug, perhaps due to the internal pores. There is no slow take-up by as-synthesized SBA particles or by either as-synthesized or calcined MCM particles. Measurement of the release of platinum drugs from nanoparticles previously soaked in drug solutions showed a substantial quick release for all particles and both drugs. This was followed by a slow release of Pt species in the case of transplatin in calcined SBA.

Simultaneous, noninvasive observation of elastic scattering, fluorescence and inelastic scattering as a monitor of blood flow and hematocrit in human fingertip capillary beds.

We report simultaneous observation of elastic scattering, fluorescence, and inelastic scattering from in vivo near-infrared probing of human skin. Careful control of the mechanical force needed to obtain reliable registration of in vivo tissue with an appropriate optical system allows reproducible observation of blood flow in capillary beds of human volar side fingertips. The time dependence of the elastically scattered light is highly correlated with that of the combined fluorescence and Raman scattered light. We interpret this in terms of turbidity (the impeding effect of red blood cells on optical propagation to and from the scattering centers) and the changes in the volume percentages of the tissues in the irradiated volume with normal homeostatic processes. By fitting to a model, these measurements may be used to determine volume fractions of plasma and RBCs.

Mesoporosity and functional group dependent endocytosis and cytotoxicity of silica nanomaterials.

We report different mesoporosity-dependent and functional group-dependent cytotoxicity and endocytosis of various silica nanomaterials on suspended and adherent cells. This dependency further varied with incubation time and particle dosage, and appeared to be associated with the particles' endocytotic efficiency and their chemical and physical properties. We studied two common mesoporous nanomaterials (MSNs), MCM-41 and SBA-15, and one type of solid-cored silica microsphere, paralleled by their quaternary amine functionalized counterparts. Compared to SBA-15, MCM-41 has a larger surface area but smaller pore size, whereas SMS exhibits low surface area and poor porosity. In Jurkat cells, SBA-15 and MCM-41 exhibited different cytotoxicity profiles. However, no significant cell death was detected when treated with the aminated MSNs, indicating that the positively charged quaternary amines prevented cellular injury from mesoporous nanoparticles. Furthermore, the effective internalization of MSN but not aminated-MSNs was clearly observed, in line with their consequent cytotoxicity. SK-N-SH (human neuroblastoma) cells were found to be more resistant to the treatment of MSN, whether aminated or not. Incubation with either SBA-15 or MCM-41 over time showed a recovery in cell viability, while exposure to MSN-N particles did not induce a noticeable cell death until longer incubation with high dosage of 200 microg/mL was applied. Both aminated and nonaminated silica spheres exhibited instant and constant toxicity on Jurkat (human T-cell lymphoma) cells. TEM images revealed successful endocytosis of SMS and SMS-N, although SMS-N appeared to accumulate more in the nucleus. For SK-N-SH cells, low dosage of SMS was found to be less toxic, whereas high dosage produced profound cell death.

Accelerated oxidation of epinephrine by silica nanoparticles.

We have measured the influence of mesoporous silica (MCM-41 and SBA-15) nanoparticles and dense silica nanoparticles on epinephrine oxidation, a pH-dependent reaction, whose rate is small in acidic or neutral solutions but much greater at higher pH. The reaction was measured by monitoring adrenochrome at 480 nm, the product of epinephrine oxidation. In distilled water (dH(2)O) with no particles present, the oxidation of epinephrine occurs slowly but more rapidly at higher pH. The presence of MCM-41 or silica spheres does not accelerate the oxidation, but SBA-15 does, showing that the difference in the structures of nanomaterials leads to differing effects on the epinephrine oxidative process. In phosphate buffered saline (PBS, pH = 7.4), epinephrine undergoes a much quicker oxidation, and, in this case, the presence of SBA-15 and MCM-41 makes it even more rapid. Silica spheres have no noticeable influence on the oxidation in PBS or in dH(2)O. The possibility that the catalytic effect of mesoporous silica nanoparticles (MSN) could result from the residue of templating chemicals, however, can be excluded due to the postsynthesis calcinations. Experiments with dithionite, added either earlier than or at the same time as the epinephrine addition, show that fast oxidation takes place only when dithionite and epinephrine are simultaneously added into PBS solution. This confirms a vital role of oxygen radicals (probably *O(2)(-)) in the oxidation of epinephrine. These oxygen radicals are likely to form and accumulate within the phosphate buffer or in the presence of MSN. Comparing the three kinds of silica nanoparticles applied, we note that mesoporous SBA-15 and MCM-41 materials own much larger surface area than solid silica particles do, whereas MCM-41 possesses a much narrower pore size (0.4-fold) than SBA-15. It seems, therefore, that large surface area, characteristic mesoporosity, and surface structures aid in the deposit of oxygen radicals inside MSN particles, which catalyze the epinephrine oxidation in a favorable phosphate environment.

Kinetic studies on enzyme-catalyzed reactions: oxidation of glucose, decomposition of hydrogen peroxide and their combination.

The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 +/- 0.7) x 10(4) M(-1) s(-1) at 37 degrees C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37 degrees C and well above unity at 25 degrees C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s(-1) and 0.090 s(-1) respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain.

Quantitative measure of cytotoxicity of anticancer drugs and other agents.

Many anticancer drugs act on cancer cells to promote apoptosis, which includes impairment of cellular respiration (mitochondrial O(2) consumption). Other agents also inhibit cellular respiration, sometimes irreversibly. To investigate the sensitivity of cancer cells to cytotoxins, including anticancer drugs, we compare the profiles of cellular O(2) consumption in the absence and presence of these agents. Oxygen measurements are made at 37 degrees C, using glucose as a substrate, with [O(2)] obtained from the phosphorescence decay rate of a palladium phosphor. The rate of respiration k is defined as -d[O(2)]/dt in a sealed container. Different toxins produce different profiles of impaired respiration, implying different mechanisms for the drug-induced mitochondrial dysfunction. The decrease in the average value of k over a fixed time period, I, is proposed as a characteristic value to assess mitochondrial injury. The value of I depends on the nature of the toxin, its concentration, and the exposure time as well as on the cell type. Results for several cell types and 10 cytotoxins are presented here.

Mesoporous silica nanoparticles inhibit cellular respiration.

We studied the effect of two types of mesoporous silica nanoparticles, MCM-41 and SBA-15, on mitochondrial O 2 consumption (respiration) in HL-60 (myeloid) cells, Jurkat (lymphoid) cells, and isolated mitochondria. SBA-15 inhibited cellular respiration at 25-500 microg/mL; the inhibition was concentration-dependent and time-dependent. The cellular ATP profile paralleled that of respiration. MCM-41 had no noticeable effect on respiration rate. In cells depleted of metabolic fuels, 50 microg/mL SBA-15 delayed the onset of glucose-supported respiration by 12 min and 200 microg/mL SBA-15 by 34 min; MCM-41 also delayed the onset of glucose-supported respiration. Neither SBA-15 nor MCM-41 affected cellular glutathione. Both nanoparticles inhibited respiration of isolated mitochondria and submitochondrial particles.