White matter abnormalities in the Hdc knockout mouse, a model of tic and OCD pathophysiology.

Introduction: An inactivating mutation in the histidine decarboxylase gene (Hdc) has been identified as a rare but high-penetrance genetic cause of Tourette syndrome (TS). TS is a neurodevelopmental syndrome characterized by recurrent motor and vocal tics; it is accompanied by structural and functional abnormalities in the cortico-basal ganglia circuitry. Hdc, which is expressed both in the posterior hypothalamus and peripherally, encodes an enzyme required for the biosynthesis of histamine. Hdc knockout mice (Hdc-KO) functionally recapitulate this mutation and exhibit behavioral and neurochemical abnormalities that parallel those seen in patients with TS. Materials and methods: We performed exploratory RNA-seq to identify pathological alterations in several brain regions in Hdc-KO mice. Findings were corroborated with RNA and protein quantification, immunohistochemistry, and ex vivo brain imaging using MRI. Results: Exploratory RNA-Seq analysis revealed, unexpectedly, that genes associated with oligodendrocytes and with myelin production are upregulated in the dorsal striatum of these mice. This was confirmed by qPCR, immunostaining, and immunoblotting. These results suggest an abnormality in myelination in the striatum. To test this in an intact mouse brain, we performed whole-brain ex vivo diffusion tensor imaging (DTI), which revealed reduced fractional anisotropy (FA) in the dorsal striatum. Discussion: While the DTI literature in individuals with TS is sparse, these results are consistent with findings of disrupted descending cortical projections in patients with tics. The Hdc-KO model may represent a powerful system in which to examine the developmental mechanisms underlying this abnormality.

High-resolution pH imaging using ratiometric chemical exchange saturation transfer combined with biosensor imaging of redundant deviation in shifts featuring paramagnetic DOTA-tetraglycinate agents.

Chemical exchange saturation transfer (CEST) and biosensor imaging of redundant deviation in shifts (BIRDS) methods differ respectively by detecting exchangeable and nonexchangeable proton signals by magnetic resonance. Because CEST contrast depends on both temperature and pH, simultaneous CEST and BIRDS imaging can be employed to separate these contributions. Here, we test if high-resolution pH imaging in vivo is possible with ratiometric CEST calibrated for temperature variations measured by BIRDS. Thulium- and europium-based DOTA-tetraglycinate agents, TmDOTA-(gly)4- and EuDOTA-(gly)4- , were used for high-resolution pH mapping in vitro and in vivo, using BIRDS for temperature adjustments needed for a more accurate ratiometric CEST approach. Although neither agent showed pH dependence with BIRDS in vitro in the pH range 6 to 8, each one's temperature sensitivity was enhanced when mixed because of increased redundancy. By contrast, the CEST signal of each agent was affected by the presence of the other agent in vitro. However, pH could be measured more accurately when temperature from BIRDS was detected. These in vitro calibrations with TmDOTA-(gly)4- and EuDOTA-(gly)4- enabled high-resolution pH imaging of glioblastoma in rat brains. It was concluded that temperature mapping with BIRDS can calibrate the ratiometric CEST signal from a cocktail of TmDOTA-(gly)4- and EuDOTA-(gly)4- agents to provide temperature-independent absolute pH imaging in vivo.

Methylated tetra-amide derivatives of paramagnetic complexes for magnetic resonance biosensing with both BIRDS and CEST.

Paramagnetic agents that utilize two mechanisms to provide physiological information by magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) are described. MRI with chemical exchange saturation transfer (CEST) takes advantage of the agent's exchangeable protons (e.g., -OH or -NHx , where 2 ≥ x ≥ 1) to create pH contrast. The agent's incorporation of non-exchangeable protons (e.g., -CHy , where 3 ≥ y ≥ 1) makes it possible to map tissue temperature and/or pH using an MRSI method called biosensor imaging of redundant deviation in shifts (BIRDS). Hybrid probes based upon 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate chelate (DOTA4- ) and its methylated analog (1,4,7,10-tetraazacyclododecane-α, α', α″, α‴-tetramethyl-1,4,7,10-tetraacetate, DOTMA4- ) were synthesized, and modified to create new tetra-amide chelates. Addition of several methyl groups per pendent arm of the symmetrical chelates, positioned proximally and distally to thulium ions (Tm3+ ), gave rise to favorable BIRDS properties (i.e., high signal-to-noise ratio (SNR) from non-exchangeable methyl proton peaks) and CEST responsiveness (i.e., from amide exchangeable protons). Structures of the Tm3+ probes elucidate the influence of methyl group placement on sensor performance. An eight-coordinate geometry with high symmetry was observed for the complexes: Tm-L1 was based on DOTA4- , whereas Tm-L2 and Tm-L3 were based on DOTMA4- , where the latter contained an additional carboxylate at the distal end of each arm. The distance of Tm3+ from terminal methyl carbons is a key determinant for sustaining BIRDS temperature sensitivity without compromising CEST pH contrast; however, water solubility was influenced by introduction of hydrophobic methyl groups and hydrophilic carboxylate. Combined BIRDS and CEST detection of Tm-L2, which features two high-SNR methyl peaks and a strong amide CEST peak, should enable simultaneous temperature and pH measurements for high-resolution molecular imaging in vivo.

Dynamic Thermal Mapping of Localized Therapeutic Hypothermia in the Brain.

Although whole body cooling is used widely to provide therapeutic hypothermia for the brain, there are undesirable clinical side effects. Selective brain cooling may allow for rapid and controllable neuroprotection while mitigating these undesirable side effects. We evaluated an innovative cerebrospinal fluid (CSF) cooling platform that utilizes chilled saline pumped through surgically implanted intraventricular catheters to induce hypothermia. Magnetic resonance thermal imaging of the healthy sheep brain (n = 4) at 7.0T provided dynamic temperature measurements from the whole brain. Global brain temperature was 38.5 ± 0.8°C at baseline (body temperature of 39.2 ± 0.4°C), and decreased by 3.1 ± 0.3°C over ∼30 min of cooling (p < 0.0001). Significant cooling was achieved in all defined regions across both the ipsilateral and contralateral hemispheres relative to catheter placement. On cooling cessation, global brain temperature increased by 3.1 ± 0.2°C over ∼20 min (p < 0.0001). Rapid and synchronized temperature fall/rise on cooling onset/offset was observed reproducibly with rates ranging from 0.06-0.21°C/min, where rewarming was faster than cooling (p < 0.0001) signifying the importance of thermoregulation in the brain. Although core regions (including the subcortex, midbrain, olfactory tract, temporal lobe, occipital lobe, and parahippocampal cortex) had slightly warmer (∼0.2°C) baseline temperatures, after cooling, temperatures reached the same level as the non-core regions (35.6 ± 0.2°C), indicating the cooling effectiveness of the CSF-based cooling device. In summary, CSF-based intraventricular cooling reliably reduces temperature in all identified brain regions to levels known to be neuroprotective, while maintaining overall systemic normothermia. Dynamic thermal mapping provides high spatiotemporal temperature measurements that can aid in optimizing selective neuroprotective protocols.

Temozolomide arrests glioma growth and normalizes intratumoral extracellular pH.

Gliomas maintain an acidic extracellular pH (pHe), which promotes tumor growth and builds resistance to therapy. Given evidence that acidic pHe beyond the tumor core indicates infiltration, we hypothesized that imaging the intratumoral pHe in relation to the peritumoral pHe can provide a novel readout of therapeutic influence on the tumor microenvironment. We used Biosensor Imaging of Redundant Deviation in Shifts (BIRDS), which utilizes chemical shifts of non-exchangeable protons from macrocyclic chelates (e.g., DOTP8-) complexed with paramagnetic thulium (Tm3+), to generate pHe maps in rat brains bearing U251 tumors. Following TmDOTP5- infusion, T2-weighted MRI provided delineation of the tumor boundary and BIRDS was used to image the pHe gradient between intratumoral and peritumoral regions (ΔpHe) in both untreated and temozolomide treated (40 mg/kg) rats bearing U251 tumors. Treated rats had reduced tumor volume (p < 0.01), reduced proliferation (Ki-67 staining; p < 0.03) and apoptosis induction (cleaved Caspase-3 staining; p < 0.001) when compared to untreated rats. The ΔpHe was significantly higher in untreated compared to treated rats (p < 0.002), suggesting that temozolomide, which induces apoptosis and hinders proliferation, also normalizes intratumoral pHe. Thus, BIRDS can be used to map the ΔpHe in gliomas and provide a physiological readout of the therapeutic response on the tumor microenvironment.

Network evolution in mesial temporal lobe epilepsy revealed by diffusion tensor imaging.

OBJECTIVE: The objective of the present study is to identify novel, time-indexed imaging biomarkers of epileptogenesis in mesial temporal lobe epilepsy (MTLE). METHODS: We used high-resolution brain diffusion tensor imaging (DTI) of the translationally relevant methionine sulfoximine (MSO) brain infusion model of MTLE. MSO inhibits astroglial glutamine synthetase, which is deficient in the epileptogenic hippocampal formation of patients with MTLE. MSO-infused (epileptogenic) rats were compared with phosphate-buffered saline (PBS)-infused (nonepileptogenic) rats at early (3-4 days) and late (6-9 weeks) time points during epileptogenesis. RESULTS: The epileptogenic rats exhibited significant changes in DTI-measured fractional anisotropy (FA) in numerous brain regions versus nonepileptogenic rats. Changes included decreases and increases in FA in regions such as the entorhinal-hippocampal area, amygdala, corpus callosum, thalamus, striatum, accumbens, and neocortex. The FA changes evolved over time as animals transitioned from early to late epileptogenesis. For example, some areas with significant decreases in FA early in epileptogenesis changed to significant increases late in epileptogenesis. Finally, the FA changes significantly correlated with the seizure load. SIGNIFICANCE: Our results suggest (1) that high-resolution DTI can be used for early identification and tracking of the epileptogenic process in MTLE, and (2) that the process identified by DTI is present in multiple brain areas, even though infusion of MSO is restricted to the unilateral entorhinal-hippocampal region.

Dynamic and Energetic Signatures of Adenine Tracts in a rA-dT RNA-DNA Hybrid and in Homologous RNA-DNA, RNA-RNA, and DNA-DNA Double Helices.

Nuclear magnetic resonance spectroscopy and proton exchange are being used to characterize the opening reactions of individual base pairs in the RNA-DNA hybrid 5'-rGCGAUAAAAAGGCC-3'/5'-dGGCCTTTTTATCGC-3'. The hybrid contains a central tract of five rA-dT base pairs. The rates and the equilibrium constant of the opening reaction for each base pair are determined from the dependence of the exchange rates of imino protons on ammonia concentration, at 10 °C. The results are compared to those previously obtained by our laboratory for three homologous duplexes of the same base sequence (except for the appropriate T/U substitution), containing tracts of dA-rU, rA-rU, or dA-dT base pairs. The rA-dT tract is distinguished by an enhanced propensity of the base pairs to exist in the extrahelical state. The opening rates of rA-dT base pairs also exhibit a strong dependence on the location of the base pair in the structure; namely, as one advances into the tract, the opening rates of rA-dT base pairs gradually decrease. The local stability of each rA-dT base pair within the tract is the same as that of the corresponding rA-rU base pair in the homologous RNA-only duplex but differs from the stabilities of dA-dT and dA-rU base pairs in the other two duplexes (namely, dA-dT > rA-dT > dA-rU). These results demonstrate that, in nucleic acid double helices with the same base sequence, the opening dynamics and the energetics of individual base pairs are strongly influenced by the nature of the strand and by the structural context of the base pair.

Mapping Extracellular pH of Gliomas in Presence of Superparamagnetic Nanoparticles: Towards Imaging the Distribution of Drug-Containing Nanoparticles and Their Curative Effect on the Tumor Microenvironment.

Since brain's microvasculature is compromised in gliomas, intravenous injection of tumor-targeting nanoparticles containing drugs (D-NPs) and superparamagnetic iron oxide (SPIO-NPs) can deliver high payloads of drugs while allowing MRI to track drug distribution. However, therapeutic effect of D-NPs remains poorly investigated because superparamagnetic fields generated by SPIO-NPs perturb conventional MRI readouts. Because extracellular pH (pHe) is a tumor hallmark, mapping pHe is critical. Brain pHe is measured by biosensor imaging of redundant deviation in shifts (BIRDS) with lanthanide agents, by detecting paramagnetically shifted resonances of nonexchangeable protons on the agent. To test the hypothesis that BIRDS-based pHe readout remains uncompromised by presence of SPIO-NPs, we mapped pHe in glioma-bearing rats before and after SPIO-NPs infusion. While SPIO-NPs accumulation in the tumor enhanced MRI contrast, the pHe inside and outside the MRI-defined tumor boundary remained unchanged after SPIO-NPs infusion, regardless of the tumor type (9L versus RG2) or agent injection method (renal ligation versus coinfusion with probenecid). These results demonstrate that we can simultaneously and noninvasively image the specific location and the healing efficacy of D-NPs, where MRI contrast from SPIO-NPs can track their distribution and BIRDS-based pHe can map their therapeutic impact.

Improved specific loss power on cancer cells by hyperthermia and MRI contrast of hydrophilic Fex Co1-x Fe2 O4 nanoensembles.

Ferrite-based ferri/superparamagnetic nanoparticles can be rapidly heated by an external alternating magnetic field (AMF) to induce tissue necrosis of the adjacent microenvironment, but in addition provide magnetic resonance imaging (MRI) contrast utilizing enhanced water relaxivity. Here we characterized nanoensembles of Fe-Co mixed spinel ferrites (i.e. Fex Co1-x Fe2 O4 , where x ranges from 0.2 to 0.8) synthesized by chemical co-precipitation. With nanoensembles of increasing Co content the saturation magnetization improved, while lattice parameter remained relatively constant. MRI water (transverse) relaxivity at 11.7 T was also boosted with increasing Co content. Efficiency of AMF-induced heating was quite comparable for the nanoensembles with either chitosan or polyethylene glycol (PEG) coating except for PEG-coated Fe0.2 Co0.8 Fe2 O4 , which was twice as less efficient as others. While toxicity of the nanoensembles with either coating examined on 9L tumor cell cultures showed no significant differences, upon AMF exposure (i.e. heat-induced necrosis) Fex Co1-x Fe2 O4 composition with different values of x showed quite dramatic effects on cell death of tumor cells with both coatings. This study lays the ground work for further characterization of other mixed spinel ferrites, and in addition we expect that chitosan and PEG coated Fex Co1-x Fe2 O4 of all the compositions will have good potential for preclinical applications in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Excitatory Synaptic Drive and Feedforward Inhibition in the Hippocampal CA3 Circuit Are Regulated by SynCAM 1.

UNLABELLED: Select adhesion proteins control the development of synapses and modulate their structural and functional properties. Despite these important roles, the extent to which different synapse-organizing mechanisms act across brain regions to establish connectivity and regulate network properties is incompletely understood. Further, their functional roles in different neuronal populations remain to be defined. Here, we applied diffusion tensor imaging (DTI), a modality of magnetic resonance imaging (MRI), to map connectivity changes in knock-out (KO) mice lacking the synaptogenic cell adhesion protein SynCAM 1. This identified reduced fractional anisotropy in the hippocampal CA3 area in absence of SynCAM 1. In agreement, mossy fiber refinement in CA3 was impaired in SynCAM 1 KO mice. Mossy fibers make excitatory inputs onto postsynaptic specializations of CA3 pyramidal neurons termed thorny excrescences and these structures were smaller in the absence of SynCAM 1. However, the most prevalent targets of mossy fibers are GABAergic interneurons and SynCAM 1 loss unexpectedly reduced the number of excitatory terminals onto parvalbumin (PV)-positive interneurons in CA3. SynCAM 1 KO mice additionally exhibited lower postsynaptic GluA1 expression in these PV-positive interneurons. These synaptic imbalances in SynCAM 1 KO mice resulted in CA3 disinhibition, in agreement with reduced feedforward inhibition in this network in the absence of SynCAM 1-dependent excitatory drive onto interneurons. In turn, mice lacking SynCAM 1 were impaired in memory tasks involving CA3. Our results support that SynCAM 1 modulates excitatory mossy fiber inputs onto both interneurons and principal neurons in the hippocampal CA3 area to balance network excitability. SIGNIFICANCE STATEMENT: This study advances our understanding of synapse-organizing mechanisms on two levels. First, the data support that synaptogenic proteins guide connectivity and can function in distinct brain regions even if they are expressed broadly. Second, the results demonstrate that a synaptogenic process that controls excitatory inputs to both pyramidal neurons and interneurons can balance excitation and inhibition. Specifically, the study reveals that hippocampal CA3 connectivity is modulated by the synapse-organizing adhesion protein SynCAM 1 and identifies a novel, SynCAM 1-dependent mechanism that controls excitatory inputs onto parvalbumin-positive interneurons. This enables SynCAM 1 to regulate feedforward inhibition and set network excitability. Further, we show that diffusion tensor imaging is sensitive to these cellular refinements affecting neuronal connectivity.

Towards longitudinal mapping of extracellular pH in gliomas.

Biosensor imaging of redundant deviation in shifts (BIRDS), an ultrafast chemical shift imaging technique, requires infusion of paramagnetic probes such as 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis methylene phosphonate (DOTP(8-) ) complexed with thulium (Tm(3+) ) ion (i.e. TmDOTP(5-) ), where the pH-sensitive resonances of hyperfine-shifted non-exchangeable protons contained within the paramagnetic probe are detected. While imaging extracellular pH (pHe ) with BIRDS meets an important cancer research need by mapping the intratumoral-peritumoral pHe gradient, the surgical intervention used to raise the probe's plasma concentration limits longitudinal scans on the same subject. Here we describe using probenecid (i.e. an organic anion transporter inhibitor) to temporarily restrict renal clearance of TmDOTP(5-) , thereby facilitating molecular imaging by BIRDS without surgical intervention. Co-infusion of probenecid with TmDOTP(5-) increased the probe's distribution into various organs, including the brain, compared with infusing TmDOTP(5-) alone. In vivo BIRDS data using the probenecid-TmDOTP(5-) co-infusion method in rats bearing RG2, 9 L, and U87 brain tumors showed intratumoral-peritumoral pHe gradients that were unaffected by the probe dose. This co-infusion method can be used for pHe mapping with BIRDS in preclinical models for tumor characterization and therapeutic monitoring, given the possibility of repeated scans with BIRDS (e.g. over days and even weeks) in the same subject. The longitudinal pHe readout by the probenecid-TmDOTP(5-) co-infusion method for BIRDS adds translational value in tumor assessment and treatment. Copyright © 2016 John Wiley & Sons, Ltd.

Convulsive seizures from experimental focal cortical dysplasia occur independently of cell misplacement.

Focal cortical dysplasia (FCD), a local malformation of cortical development, is the most common cause of pharmacoresistant epilepsy associated with life-long neurocognitive impairments. It remains unclear whether neuronal misplacement is required for seizure activity. Here we show that dyslamination and white matter heterotopia are not necessary for seizure generation in a murine model of type II FCDs. These experimental FCDs generated by increasing mTOR activity in layer 2/3 neurons of the medial prefrontal cortex are associated with tonic-clonic seizures and a normal survival rate. Preventing all FCD-related defects, including neuronal misplacement and dysmorphogenesis, with rapamycin treatments from birth eliminates seizures, but seizures recur after rapamycin withdrawal. In addition, bypassing neuronal misplacement and heterotopia using inducible vectors do not prevent seizure occurrence. Collectively, data obtained using our new experimental FCD-associated epilepsy suggest that life-long treatment to reduce neuronal dysmorphogenesis is required to suppress seizures in individuals with FCD.

Delivery of mesenchymal stem cells in biomimetic engineered scaffolds promotes healing of diabetic ulcers.

AIM: We hypothesized that delivery of mesenchymal stem cells (MSCs) in a biomimetic collagen scaffold improves wound healing in a diabetic mouse model. MATERIALS & METHODS: Rolled collagen scaffolds containing MSCs were implanted or applied topically to diabetic C57BL/6 mice with excisional wounds. RESULTS: Rolled scaffolds were hypoxic, inducing MSC synthesis and secretion of VEGF. Diabetic mice with wounds treated with rolled scaffolds containing MSCs showed increased healing compared with controls. Histologic examination showed increased cellular proliferation, increased VEGF expression and capillary density, and increased numbers of macrophages, fibroblasts and smooth muscle cells. Addition of laminin to the collagen scaffold enhanced these effects. CONCLUSION: Activated MSCs delivered in a biomimetic-collagen scaffold enhanced wound healing in a translationally relevant diabetic mouse model.

Imaging the intratumoral-peritumoral extracellular pH gradient of gliomas.

Solid tumors have an acidic extracellular pH (pHe ) but near neutral intracellular pH (pHi ). Because acidic pHe milieu is conducive to tumor growth and builds resistance to therapy, simultaneous mapping of pHe inside and outside the tumor (i.e., intratumoral-peritumoral pHe gradient) fulfills an important need in cancer imaging. We used Biosensor Imaging of Redundant Deviation in Shifts (BIRDS), which utilizes shifts of non-exchangeable protons from macrocyclic chelates (e.g., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) or DOTP(8-) ) complexed with paramagnetic thulium (Tm(3) (+) ) ion, to generate in vivo pHe maps in rat brains bearing 9L and RG2 tumors. Upon TmDOTP(5-) infusion, MRI identified the tumor boundary by enhanced water transverse relaxation and BIRDS allowed imaging of intratumoral-peritumoral pHe gradients. The pHe measured by BIRDS was compared with pHi measured with (31) P-MRS. In normal tissue, pHe was similar to pHi , but inside the tumor pHe was lower than pHi . While the intratumoral pHe was acidic for both tumor types, peritumoral pHe varied with tumor type. The intratumoral-peritumoral pHe gradient was much larger for 9L than RG2 tumors because in RG2 tumors acidic pHe was found in distal peritumoral regions. The increased presence of Ki-67 positive cells beyond the RG2 tumor border suggested that RG2 was more invasive than the 9L tumor. These results indicate that extensive acidic pHe beyond the tumor boundary correlates with tumor cell invasion. In summary, BIRDS has sensitivity to map the in vivo intratumoral-peritumoral pHe gradient, thereby creating preclinical applications in monitoring cancer therapeutic responses (e.g., with pHe -altering drugs). Copyright © 2016 John Wiley & Sons, Ltd.

Dendrimer-Based Responsive MRI Contrast Agents (G1-G4) for Biosensor Imaging of Redundant Deviation in Shifts (BIRDS).

Biosensor imaging of redundant deviation in shifts (BIRDS) is a molecular imaging platform for magnetic resonance that utilizes unique properties of low molecular weight paramagnetic monomers by detecting hyperfine-shifted nonexchangeable protons and transforming the chemical shift information to reflect its microenvironment (e.g., via temperature, pH, etc.). To optimize translational biosensing potential of BIRDS we examined if this detection scheme observed with monomers can be extended onto dendrimers, which are versatile and biocompatible macromolecules with modifiable surface for molecular imaging and drug delivery. Here we report on feasibility of paramagnetic dendrimers for BIRDS. The results show that BIRDS is resilient with paramagnetic dendrimers up to the fourth generation (i.e., G1-G4), where the model dendrimer and chelate were based on poly(amido amine) (PAMAM) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA(4-)) complexed with thulium ion (Tm(3+)). Temperature sensitivities of two prominent signals of Gn-PAMAM-(TmDOTA(-))x (where n = 1-4, x = 6-39) were comparable to that of prominent signals in TmDOTA(-). Transverse relaxation times of the coalesced nonexchangeable protons on Gn-PAMAM-(TmDOTA(-))x were relatively short to provide signal-to-noise ratio that was comparable to or better than that of TmDOTA(-). A fluorescent dye, rhodamine, was conjugated to a G2-PAMAM-(TmDOTA)12 to create a dual-modality nanosized contrast agent. BIRDS properties of the dendrimer were unaltered with rhodamine conjugation. Purposely designed paramagnetic dendrimers for BIRDS in conjunction with novel macromolecular surface modification for functional ligands/drugs could potentially be used for biologically compatible theranostic sensors.

Lanthanide ion (III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate for dual biosensing of pH with chemical exchange saturation transfer (CEST) and biosensor imaging of redundant deviation in shifts (BIRDS).

Relaxivity-based magnetic resonance of phosphonated ligands chelated with gadolinium (Gd(3+)) shows promise for pH imaging. However instead of monitoring the paramagnetic effect of lanthanide complexes on the relaxivity of water protons, biosensor (or molecular) imaging with magnetic resonance is also possible by detecting either the nonexchangeable or the exchangeable protons on the lanthanide complexes themselves. The nonexchangeable protons (e.g. -CHx, where 3 ≥ x ≥ 1) are detected using a three-dimensional chemical shift imaging method called biosensor imaging of redundant deviation in shifts (BIRDS), whereas the exchangeable protons (e.g. -OH or -NHy , where 2 ≥ y ≥ 1) are measured with chemical exchange saturation transfer (CEST) contrast. Here we tested the feasibility of BIRDS and CEST for pH imaging of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminophosphonate (DOTA-4AmP(8-)) chelated with thulium (Tm(3+) ) and ytterbium (Yb(3+)). BIRDS and CEST experiments show that both complexes are responsive to pH and temperature changes. Higher pH and temperature sensitivities are obtained with BIRDS for either complex when using the chemical shift difference between two proton resonances vs using the chemical shift of a single proton resonance, thereby eliminating the need to use water resonance as reference. While CEST contrast for both agents is linearly dependent on pH within a relatively large range (i.e. 6.3-7.9), much stronger CEST contrast is obtained with YbDOTA-4AmP(5-) than with TmDOTA-4AmP(5-). In addition, we demonstrate the prospect of using BIRDS to calibrate CEST as new platform for quantitative pH imaging.

Characterization of a lanthanide complex encapsulated with MRI contrast agents into liposomes for biosensor imaging of redundant deviation in shifts (BIRDS).

Purposely designed magnetic resonance imaging (MRI) probes encapsulated in liposomes, which alter contrast by their paramagnetic effect on longitudinal (T1) and transverse (T2) relaxation times of tissue water, hold promise for molecular imaging. However, a challenge with liposomal MRI probes that are solely dependent on enhancement of water relaxation is lack of specific molecular readouts, especially in strong paramagnetic environments, thereby reducing the potential for monitoring disease treatment (e.g., cancer) beyond the generated MRI contrast. Previously, it has been shown that molecular imaging with magnetic resonance is also possible by detecting the signal of non-exchangeable protons emanating from paramagnetic lanthanide complexes themselves [e.g., TmDOTP5⁻, which is a Tm³âº -containing biosensor based on a macrocyclic chelate 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate), DOTP5⁻] with a method called biosensor imaging of redundant deviation in shifts (BIRDS). Here, we show that BIRDS is useful for molecular imaging with probes like TmDOTP5⁻ even when they are encapsulated inside liposomes with ultrastrong T1and T2contrast agents (e.g., Magnevist and Molday ION, respectively). We demonstrate that molecular readouts such as pH and temperature determined from probes like TmDOTP5⁻ are resilient, because the sensitivity of the chemical shifts to the probe's environment is not compromised by the presence of other paramagnetic agents contained within the same nanocarrier milieu. Because high liposomal encapsulation efficiency allows for robust MRI contrast and signal amplification for BIRDS, nanoengineered liposomal probes containing both monomers, TmDOTP5⁻ and paramagnetic contrast agents, could allow high spatial resolution imaging of disease diagnosis (with MRI) and status monitoring (with BIRDS).

Intranasal epidermal growth factor treatment rescues neonatal brain injury.

There are no clinically relevant treatments available that improve function in the growing population of very preterm infants (less than 32 weeks' gestation) with neonatal brain injury. Diffuse white matter injury (DWMI) is a common finding in these children and results in chronic neurodevelopmental impairments. As shown recently, failure in oligodendrocyte progenitor cell maturation contributes to DWMI. We demonstrated previously that the epidermal growth factor receptor (EGFR) has an important role in oligodendrocyte development. Here we examine whether enhanced EGFR signalling stimulates the endogenous response of EGFR-expressing progenitor cells during a critical period after brain injury, and promotes cellular and behavioural recovery in the developing brain. Using an established mouse model of very preterm brain injury, we demonstrate that selective overexpression of human EGFR in oligodendrocyte lineage cells or the administration of intranasal heparin-binding EGF immediately after injury decreases oligodendroglia death, enhances generation of new oligodendrocytes from progenitor cells and promotes functional recovery. Furthermore, these interventions diminish ultrastructural abnormalities and alleviate behavioural deficits on white-matter-specific paradigms. Inhibition of EGFR signalling with a molecularly targeted agent used for cancer therapy demonstrates that EGFR activation is an important contributor to oligodendrocyte regeneration and functional recovery after DWMI. Thus, our study provides direct evidence that targeting EGFR in oligodendrocyte progenitor cells at a specific time after injury is clinically feasible and potentially applicable to the treatment of premature children with white matter injury.

Enhanced base-pair opening in the adenine tract of a RNA double helix.

Proton exchange and nuclear magnetic resonance spectroscopy are being used to characterize the kinetics and energetics of base-pair opening in two nucleic acid double helices. One is the RNA duplex 5'-r(GCGAUAAAAAGGCC)-3'/5'-r(GGCCUUUUUAUCGC)-3', which contains a central tract of five AU base pairs. The other is the homologous DNA duplex with a central tract of five AT base pairs. The rates and the equilibrium constants of the opening reaction of each base pair are measured from the dependence of the exchange rates of imino protons on ammonia concentration, at 10 °C. The results reveal that the tract of AU base pairs in the RNA duplex differs from the homologous tract of AT base pairs in DNA in several ways. The rates of opening of AU base pairs in RNA are high and increase progressively along the tract, reaching their largest values at the 3'-end of the tract. In contrast, the opening rates of AT base pairs in DNA are much lower than those of AU base pairs. Within the tract, the largest opening rate is observed for the AT base pair at the 5'-end of the tract. These differences in opening kinetics are paralleled by differences in the stabilities of individual base pairs. All AU base pairs in the RNA are less stable than the AT base pairs in the DNA. The presence of the tract enhances these differences by increasing the stability of AT base pairs in DNA while decreasing the stability of AU base pairs in RNA. Due to these divergent trends, along the tracts, the AU base pairs become progressively less stable than AT base pairs. These findings demonstrate that tracts of AU base pairs in RNA have specific dynamic and energetic signatures that distinguish them from similar tracts of AT base pairs in DNA.

Structural energetics of the adenine tract from an intrinsic transcription terminator.

Intrinsic transcription termination sites generally contain a tract of adenines in the DNA template that yields a tract of uracils at the 3' end of the nascent RNA. To understand how this base sequence contributes to termination of transcription, we have investigated two nucleic acid structures. The first is the RNA-DNA hybrid that contains the uracil tract 5'-rUUUUUAU-3' from the tR2 intrinsic terminator of bacteriophage lambda. The second is the homologous DNA-DNA duplex that contains the adenine tract 5'-dATAAAAA-3'. This duplex is present at the tR2 site when the DNA is not transcribed. The opening and the stability of each rU-dA/dT-dA base pair in the two structures are characterized by imino proton exchange and nuclear magnetic resonance spectroscopy. The results reveal concerted opening of the central rU-dA base pairs in the RNA-DNA hybrid. Furthermore, the stability profile of the adenine tract in the RNA-DNA hybrid is very different from that of the tract in the template DNA-DNA duplex. In the RNA-DNA hybrid, the stabilities of rU-dA base pairs range from 4.3 to 6.5 kcal/mol (at 10 degrees C). The sites of lowest stability are identified at the central positions of the tract. In the template DNA-DNA duplex, the dT-dA base pairs are more stable than the corresponding rU-dA base pairs in the hybrid by 0.9 to 4.6 kcal/mol and, in contrast to the RNA-DNA hybrid, the central base pairs have the highest stability. These results suggest that the central rU-dA/dT-dA base pairs in the adenine tract make the largest energetic contributions to transcription termination by promoting both the dissociation of the RNA transcript and the closing of the transcription bubble. The results also suggest that the high stability of dT-dA base pairs in the DNA provides a signal for the pausing of RNA polymerase at the termination site.