Protein conjugation with PAMAM nanoparticles: Microscopic and thermodynamic analysis.

PAMAM dendrimers form strong protein conjugates that are used in drug delivery systems. We report the thermodynamic and binding analysis of polyamidoamine (PAMAM-G4) conjugation with human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. Hydrophobicity played a major role in PAMAM-protein interactions with more hydrophobic b-LG forming stronger polymer-protein conjugates. Thermodynamic parameters showed PAMAM-protein bindings occur via hydrophobic and H-bonding contacts for b-LG, while van der waals and H-bonding interactions prevail in HSA and BSA-polymer conjugates. The protein loading efficacy was 45-55%. PAMAM complexation induced major alterations of protein conformation. TEM images show major polymer morphological changes upon protein conjugation.

Structural modeling for DNA binding to antioxidants resveratrol, genistein and curcumin.

Several models are presented here for the bindings of the antioxidant polyphenols resveratrol, genistein and curcumin with DNA in aqueous solution at physiological conditions. Multiple spectroscopic methods and molecular modeling were used to locate the binding sites of these polyphenols with DNA duplex. Structural models showed that intercalation is more stable for resveratrol and genistein than groove bindings, while curcumin interaction is via DNA grooves. Docking showed more stable complexes formed with resveratrol and genistein than curcumin with the free binding energies of -4.62 for resveratrol-DNA (intercalation), -4.28 for resveratrol-DNA (groove binding), -4.54 for genistein-DNA (intercalation), -4.38 for genistein-DNA (groove binding) and -3.84 kcal/mol for curcumin-DNA (groove binding). The free binding energies show polyphenol-DNA complexation is spontaneous at room temperature. At high polyphenol concentration a major DNA aggregation occurred, while biopolymer remained in B-family structure.

Locating the binding sites of antioxidants resveratrol, genistein and curcumin with tRNA.

We located the binding sites of antioxidants resveratrol, genistein and curcumin on tRNA in aqueous solution at physiological conditions using constant tRNA concentration and various polyphenol contents. FTIR, UV-visible, CD spectroscopic methods and molecular modeling were used to determine polyphenol binding sites, the binding constant and the effects of polyphenol complexation on tRNA conformation and particle formation. Structural analysis showed that polyphenols bind tRNA via G-C and A-U base pairs through hydrophilic, hydrophobic and H-bonding contacts with overall binding constants of K(res-tRNA)=8.95(±0.80)×10(3) M(-1), K(gen-tRNA)=3.07(±0.5)×10(3) M(-1) and K(cur-tRNA)=1.55(±0.3)×10(4) M(-1). Molecular modeling showed the participation of several nucleobases in polyphenol-tRNA adduct formation with free binding energy of -4.43 for resveratrol, -4.26 kcal/mol for genistein and -4.84 kcal/mol for curcumin, indicating that the interaction process is spontaneous at room temperature. While tRNA remains in A-family structure, major biopolymer aggregation and particle formation occurred at high polyphenol contents.

Modelling of vitamin A binding to tRNA.

The binding sites of retinol and retinoic acid with tRNA are located in aqueous solution at physiological conditions using constant tRNA concentration and various retinoid contents. FTIR, CD, fluorescence spectroscopic methods and molecular modelling were used to determine retinoid binding sites, the binding constant and the effects of retinol and retinoic acid complexation on tRNA conformation and aggregation. Structural analysis showed that retinol and retinoic acid bind tRNA via G-C and A-U base pairs with overall binding constants of Kret-tRNA=2.0 (±0.40)×10(4)M(-1) and Kretac-tRNA=6.0 (±1)×10(4)M(-1). The number of binding sites occupied by retinoids on tRNA were 1.4 for retinol-tRNA and 1.7 for retinoic acid-tRNA complexes. Hydrophobic interactions were also observed at high retinol and retinoic acid contents. Molecular modelling showed the participation of several nucleobases in retinoid-tRNA complexation with free binding energy of -4.36 for retinol-tRNA and -4.53kcal/mol for retinoic acid-tRNA adducts.

Probing the binding of cationic lipids with dendrimers.

Polycationic polymers are used extensively in biology to disrupt cell membranes and thus enhance the transport of materials into the cell. We report the bindings of several lipids cholesterol (Chol), 1,2-dioleoyl-3-trimethylammonium-propane(DOTAP), dioctadecyldimethylammoniumbromide (DDAB), and dioleoylphosphatidylethanolamine (DOPE) to dendrimers of different compositions such as mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) under physiological conditions. FTIR, UV-visible spectroscopic, methods and molecular modeling were used to analyze the lipid binding mode, the binding constant, and the effects of lipid complexation on the dendrimer structure. The structural analysis showed that lipids bind dendrimers through both hydrophilic and hydrophobic contacts with overall binding constants of K(chol-mPEG-G3) = 1.7 × 10(3) M(-1), K(chol-mPEG-PAMAM-G4) = 2.7 × 10(3) M(-1), K(chol-PAMAM-G4) = 1.0 × 10(3) M(-1), K(DOPE-mPEG-G3) = 1.5 × 10(3) M(-1), K(DOPE-mPEG-PAMAM-G4) = 1.6 × 10(3) M(-1), K(DOPE-PAMAM-G4) = 5.3 × 10(2) M(-1), K(DDAB-mPEG-G3) = 1.5 × 10(3) M(-1), K(DDAB-mPEG-PAMAM-G4) = 1.9 × 10(2) M(-1), K(DDAB-PAMAM-G4) = 7.0 × 10(2) M(-1), K(DOTAP-mPEG-G3) = 1.9 × 10(3) M(-1), K(DOTAP-mPEG-PAMAM-G4) = 1.5 × 10(3) M(-1), and K(DOTAP-PAMAM-G4) = 5.7 × 10(2) M(-1). Weaker interaction was observed as dendrimer cationic charges increased. The free binding energies from docking were -5.15 (cholesterol), -5.79 (DDAB), and -5.36 kcal/mol (DOTAP) with the order of stability DDAB-PAMAM-G-4 > DOTAP-PAMAM-G4 > cholesterol-PAMAM-G4, consistent with the spectroscopic results. Dendrimers might act as carriers to transport lipids in vitro.

Effect of PEG and mPEG-anthracene on tRNA aggregation and particle formation.

Poly(ethylene glycol) (PEG) and its derivatives are synthetic polymers with major applications in gene and drug delivery systems. Synthetic polymers are also used to transport miRNA and siRNA in vitro. We studied the interaction of tRNA with several PEGs of different compositions, such as PEG 3350, PEG 6000, and mPEG-anthracene under physiological conditions. FTIR, UV-visible, CD, and fluorescence spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the PEG binding mode, the binding constant, and the effects of polymer complexation on tRNA stability, aggregation, and particle formation. Structural analysis showed that PEG-tRNA interaction occurs via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of K(PEG 3350-tRNA)= 1.9 (±0.5) × 10(4) M(-1), K(PEG 6000-tRNA) = 8.9 (±1) × 10(4) M(-1), and K(mPEG-anthracene)= 1.2 (±0.40) × 10(3) M(-1) show stronger polymer-RNA complexation by PEG 6000 and by PEG 3350 than the mPEG-anthracene. AFM imaging showed that PEG complexes contain on average one tRNA with PEG 3350, five tRNA with PEG 6000, and ten tRNA molecules with mPEG-anthracene. tRNA aggregation and particle formation occurred at high polymer concentrations, whereas it remains in A-family structure.

PEG and mPEG-anthracene induce DNA condensation and particle formation.

In this study, we investigated the binding of DNA with poly(ethylene glycol) (PEG) of different sizes and compositions such as PEG 3350, PEG 6000, and mPEG-anthracene in aqueous solution at physiological conditions. The effects of size and composition on DNA aggregation and condensation as well as conformation were determined using Fourier transform infrared (FTIR), UV-visible, CD, fluorescence spectroscopic methods and atomic force microscopy (AFM). Structural analysis showed moderate complex formation for PEG 3350 and PEG 6000 and weaker interaction for mPE-anthracene-DNA adducts with both hydrophilic and hydrophobic contacts. The order of ± stability of the complexes formed is K(PEG 6000) = 1.5 (±0.4) × 10(4) M(-1) > K(PEG 3350) = 7.9 (±1) × 10(3) M(-1) > K(m(PEG-anthracene))= 3.6 (±0.8) × 10(3) M(-1) with nearly 1 bound PEG molecule per DNA. No B-DNA conformational changes were observed, while DNA condensation and particle formation occurred at high PEG concentration.

Bundling and aggregation of DNA by cationic dendrimers.

Dendrimers are unique synthetic macromolecules of nanometer dimensions with a highly branched structure and globular shape. Among dendrimers, polyamidoamine (PAMAM) have received most attention as potential transfection agents for gene delivery, because these macromolecules bind DNA at physiological pH. The aim of this study was to examine the interaction of calf-thymus DNA with several dendrimers of different compositions, such as mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions, using constant DNA concentration and various dendrimer contents. FTIR, UV-visible, and CD spectroscopic methods, as well as atomic force microscopy (AFM), were used to analyze the macromolecule binding mode, the binding constant, and the effects of dendrimer complexation on DNA stability, aggregation, condensation, and conformation. Structural analysis showed a strong dendrimer-DNA interaction via major and minor grooves and the backbone phosphate group with overall binding constants of K(mPEG-G3) = 1.5 (±0.5) × 10(3) M(-1), K(mPEG-G4) = 3.4 (±0.80) × 10(3) M(-1), and K(PAMAM-G4) = 8.2 (±0.90) × 10(4) M(-1). The order of stability of polymer-DNA complexation is PAMAM-G4 > mPEG-G4 > mPEG-G3. Both hydrophilic and hydrophobic interactions were observed for dendrimer-DNA complexes. DNA remained in the B-family structure, while biopolymer particle formation and condensation occurred at high dendrimer concentrations.

Structural analysis of DNA interaction with retinol and retinoic acid.

Dietary constituents of fresh fruits and vegetables may play a relevant role in DNA adduct formation by inhibiting enzymatic activities. Studies have shown the important role of antioxidant vitamins A, C, and E in the protection against cancer and cardiovascular diseases. The antioxidant activity of vitamin A and beta-carotene may consist of scavenging oxygen radicals and preventing DNA damage. This study was designed to examine the interaction of calf-thymus DNA with retinol and retinoic acid in aqueous solution at physiological conditions using a constant DNA concentration and various retinoid contents. Fourier transform infrared (FTIR), circular dichroism (CD), and fluorescence spectroscopic methods were used to determine retinoid binding mode, the binding constant, and the effects of retinol and retinoic acid complexation on DNA conformation and aggregation. Structural analysis showed that retinol and retinoic acid bind DNA via G-C and A-T base pairs and the backbone phosphate groups with overall binding constants of Kret = 3.0 (+/-0.50) x 10(3) (mol.L(-1))(-1) and Kretac = 1.0 (+/-0.20) x 10(4) (mol.L(-1))(-1). The number of bound retinoids per DNA were 0.84 for retinol and 1.3 for retinoic acid. Hydrophobic interactions were also observed at high retinol and retinoic acid contents. At a high retinoid concentration, major DNA aggregation occurred, while DNA remained in the B-family structure.

Complexes of dendrimers with bovine serum albumin.

We report the complexation of bovine serum albumin (BSA) with several dendrimers of different compositions mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions using constant protein concentration and various dendrimer contents. FTIR, CD, and fluorescence spectroscopic methods were used to analyze polymer binding mode, the binding constant, and the effects of dendrimer complexation on BSA stability and conformation. Structural analysis showed that dendrimers bind BSA via hydrophilic and hydrophobic interactions with a number of bound polymers (n): 1.30 for mPEG-PAMAM-G3, 1.30 for mPEG-PAMAM-G4, and 1.0 for PAMAM-G4. The polymer-BSA binding constants were K(mPEG-G3) = 5.0 (+/-0.8) x 10(3) M(-1), K(mPEG-G4) = 1.0 (+/-0.3) x 10(4) M(-1), and K(PAMAM-G4) = 1.1 (+/-0.4) x 10(4) M(-1). Dendrimer binding altered BSA conformation with a major reduction of alpha-helix and an increase in random coil and turn structures, indicating a partial protein unfolding.

Dendrimers bind human serum albumin.

Dendrimers are synthetic, highly branched, spherical macromolecules with nanometer dimensions and potential applications in DNA and drug delivery systems. Human serum albumin (HSA) is a major transporter for delivering several endogenous compounds and drugs in vivo. The aim of this study was to examine the interaction of human serum albumin with several dendrimers such as mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions, using constant protein concentration and various dendrimer compositions. FTIR, UV-visible, CD, and fluorescence spectroscopic methods were used to analyze macromolecule binding mode, the binding constant and the effects of dendrimers complexation on HSA stability and conformation. Structural analysis showed that dendrimers bind HSA via polypeptide polar groups (hydrophilic) with number of bound polymer (n) 1.08 (mPEG-PAMAM-G3), 1.50 (mPEG-PAMAM-G4), and 0.96 (PAMAM-G4). The overall binding constants estimated were of KmPEG-G3=1.3 (+/-0.2)x10(4) M(-1), KmPEG-G4=2.2 (+/-0.4)x10(4) M(-1), and KPAMAM-G4=2.6 (+/-0.5)x10(4) M(-1). HSA conformation was altered by dendrimers with a major reduction of alpha-helix and increase in random coil and turn structures suggesting a partial protein unfolding.

Simultaneous recording of task-induced changes in blood oxygenation, volume, and flow using diffuse optical imaging and arterial spin-labeling MRI.

Increased neural activity in brain tissue is accompanied by an array of supporting physiological processes, including increases in blood flow and the rates at which glucose and oxygen are consumed. These responses lead to secondary effects such as alterations in blood oxygenation and blood volume, and are ultimately the primary determinants of the amplitude and temporal signature of the blood oxygenation level-dependent (BOLD) signal used prevalently to map brain function. We have performed experiments using a combination of optical and MRI-based imaging methods to develop a more comprehensive picture of the physiological events accompanying activation of primary motor cortex during a finger apposition task. Temporal profiles for changes in tissue hemoglobin concentrations were qualitatively similar to those observed for MRI-based flow and oxygenation signals. Quantitative analysis of these signals revealed peak changes of +16 +/- 2% for HbO, -13 +/- 2% for HbR, +8 +/- 3% for total Hb, +83 +/- 9% for cerebral blood flow, and +1.4 +/- 0.1% for the BOLD MRI signal. A mass balance model was used to estimate the change in rate of oxidative metabolism implied by the optical and flow measurements, leading to a computed value of +47 +/- 5%. It should be noted that the optical and MRI observations may in general reflect changes over different volumes of tissue. The ratio of fractional changes in oxidative metabolism to fractional change in blood flow was found to be 0.56 +/- 0.08, in general agreement with previous studies of flow-metabolism coupling.

Can the cerebral metabolic rate of oxygen be estimated with near-infrared spectroscopy?

We have measured the changes in oxy-haemoglobin and deoxy-haemoglobin in the adult human brain during a brief finger tapping exercise using near-infrared spectroscopy (NIRS). The cerebral metabolic rate of oxygen (CMRO2) can be estimated from these NIRS data provided certain model assumptions. The change in CMRO2 is related to changes in the total haemoglobin concentration, deoxy-haemoglobin concentration and blood flow. As NIRS does not provide a measure of dynamic changes in blood flow during brain activation, we relied on a Windkessel model that relates dynamic blood volume and flow changes, which has been used previously for estimating CMRO2 from functional magnetic resonance imaging (fMRI) data. Because of the partial volume effect we are unable to quantify the absolute changes in the local brain haemoglobin concentrations with NIRS and thus are unable to obtain an estimate of the absolute CMRO2 change. An absolute estimate is also confounded by uncertainty in the flow-volume relationship. However, the ratio of the flow change to the CMRO2 change is relatively insensitive to these uncertainties. For the linger tapping task, we estimate a most probable flow-consumption ratio ranging from 1.5 to 3 in agreement with previous findings presented in the literature, although we cannot exclude the possibility that there is no CMRO2 change. The large range in the ratio arises from the large number of model parameters that must be estimated from the data. A more precise estimate of the flow-consumption ratio will require better estimates of the model parameters or flow information, as can be provided by combining NIRS with fMRI.

The tubulointerstitial nephritis and uveitis syndrome.

The world's medical literature on tubulointerstitial nephritis and uveitis (TINU) syndrome was reviewed, and data on 133 patients with TINU syndrome were identified. The median age of onset was 15 years (range 9-74 years) with a 3:1 female-to-male predominance. Common laboratory abnormalities included elevated Westergren erythrocyte sedimentation rates and elevated urinary beta-2-microglobulin levels. Ocular symptoms preceded systemic symptoms in 21% of cases, and followed systemic symptoms by up to 14 months in 65% of cases. Uveitis involved only the anterior segment in 80% of cases. Uveitis was bilateral at presentation in 77% of cases. Patients were treated with systemic corticosteroids in 80% of cases and with immunosuppressive drugs in 9% of cases. Uveitis recurred or followed a chronic course in 56% of patients and persisted for several years in some cases. Ocular complications (including posterior synechiae, cataracts, and elevated intraocular pressure) were reported in 21% of cases. The visual prognosis appears to be good. Persistent renal dysfunction was reported in 11% of cases, including five patients who required renal dialysis. TINU syndrome is a distinct clinical entity that may be under-recognized and may account for some cases of unexplained chronic or recurrent uveitis. It is important for ophthalmologists, nephrologists, and primary care providers to be familiar with this disorder to ensure early diagnosis and appropriate treatment.

Improved mapping of pharmacologically induced neuronal activation using the IRON technique with superparamagnetic blood pool agents.

The use of functional magnetic resonance imaging (fMRI) techniques for evaluation of pharmacologic stimuli has great potential for understanding neurotransmitter dynamics for a number of brain disorders, such as drug abuse, schizophrenia, epilepsy, or neurodegeneration. Unfortunately, blood oxygenation level-dependent (BOLD) imaging at common fields strengths, such as 1.5 or 3 T, has very low sensitivity and contrast-to-noise ratios (CNRs). We demonstrate here the utility of using an intravascular superparamagnetic iron oxide contrast agent with a long plasma half-life for evaluation of hemodynamic changes related to dopaminergic stimuli using amphetamine or the cocaine analog 2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane (CFT). We refer to this technique as increased relaxation with iron oxide nanoparticles (IRON). Results obtained here show that even at field strengths as high as 4.7 T, one can obtain increases in CNR by factors of 2-3 over BOLD imaging that lead to greater than an order of magnitude increase in statistical power with greatly increased sensitivity to hemodynamic changes in brain regions difficult to observe using BOLD imaging. Furthermore, use of the intravascular contrast agent allows for a meaningful physiologic parameter to be measured (relative cerebral blood volume (rCBV)), compared to conventional BOLD imaging.

Visual motion processing investigated using contrast agent-enhanced fMRI in awake behaving monkeys.

To reduce the information gap between human neuroimaging and macaque physiology and anatomy, we mapped fMRI signals produced by moving and stationary stimuli (random dots or lines) in fixating monkeys. Functional sensitivity was increased by a factor of approximately 5 relative to the BOLD technique by injecting a contrast agent (monocrystalline iron oxide nanoparticle [MION]). Areas identified as motion sensitive included V2, V3, MT/V5, vMST, FST, VIP, and FEF (with moving dots), as well as V4, TE, LIP, and PIP (with random lines). These regions sensitive for moving dots are largely in agreement with monkey single unit data and (except for V3A) with human fMRI results. Moving lines activate some regions that have not been previously implicated in motion processing. Overall, the results clarify the relationship between the motion pathway and the dorsal stream in primates.

Functional magnetic resonance imaging of reorganization in rat brain after stroke.

Functional recovery after stroke has been associated with brain plasticity; however, the exact relationship is unknown. We performed behavioral tests, functional MRI, and histology in a rat stroke model to assess the correlation between temporal changes in sensorimotor function, brain activation patterns, cerebral ischemic damage, and cerebrovascular reactivity. Unilateral stroke induced a large ipsilateral infarct and acute dysfunction of the contralateral forelimb, which significantly recovered at later stages. Forelimb impairment was accompanied by loss of stimulus-induced activation in the ipsilesional sensorimotor cortex; however, local tissue and perfusion were only moderately affected and cerebrovascular reactivity was preserved in this area. At 3 days after stroke, extensive activation-induced responses were detected in the contralesional hemisphere. After 14 days, we found reduced involvement of the contralesional hemisphere, and significant responses in the infarction periphery. Our data suggest that limb dysfunction is related to loss of brain activation in the ipsilesional sensorimotor cortex and that restoration of function is associated with biphasic recruitment of peri- and contralesional functional fields in the brain.

Regional sensitivity and coupling of BOLD and CBV changes during stimulation of rat brain.

Functional MRI of rat brain was performed at 2 Tesla following intravenous injection of cocaine in order to 1) determine if changes in CBV and changes in BOLD signal were regionally coupled in brain parenchyma, and 2) compare the sensitivities of these imaging methods across different brain structures. Percent changes in CBV and BOLD relaxation rate were spatially and temporally coupled during this graded brain activation. The use of contrast agent increased functional sensitivity in all parenchymal brain structures, with a strong but predictable dependence on the resting-state blood volume fraction. Magn Reson Med 45:443-447, 2001.

The accuracy of near infrared spectroscopy and imaging during focal changes in cerebral hemodynamics.

Near infrared spectroscopy (NIRS) can detect changes in the concentrations of oxy-hemoglobin ([HbO]) and deoxy-hemoglobin ([Hb]) in tissue based upon differential absorption at multiple wavelengths. The common analysis of NIRS data uses the modified Beer-Lambert law, which is an empirical formulation that assumes global concentration changes. We used simulations to examine the errors that result when this analysis is applied to focal hemodynamic changes, and we performed simultaneous NIRS measurements during a motor task in adult humans and a neonate to evaluate the dependence of the measured changes on detector-probe geometry. For both simulations and in vivo measurements, the wide range of NIRS results was compared to an imaging analysis, diffuse optical tomography (DOT). The results demonstrate that relative changes in [HbO] and [Hb] cannot, in general, be quantified with NIRS. In contrast to that method, DOT analysis was shown to accurately quantify simulated changes in chromophore concentrations. These results and the general principles suggest that DOT can accurately measure changes in [Hb] and [HbO], but NIRS cannot accurately determine even relative focal changes in these chromophore concentrations. For the standard NIRS analysis to become more accurate for focal changes, it must account for the position of the focal change relative to the source and detector as well as the wavelength dependent optical properties of the medium.