Nephrogenic systemic fibrosis: an emerging entity

Coordination-Regulated Terpyridine-Mn(II) Complexes for Photodynamic Therapy Guided by Multiphoton Fluorescence/Magnetic Resonance Imaging

The synergy of multiphoton fluorescence imaging (MP-FI) and magnetic resonance imaging (MRI) provides an imaging platform with high resolution and unlimited penetration depth for early disease detection. Herein, two kinds of terpyridine-Mn(II) complexes (FD-Mn-O₂NO and FD-Mn-FD) possessing seven and six coordination modes, respectively, were designed rationally for photodynamic therapy (PDT) guided by MP-FI/MRI. The complexes obtain different multiphoton fluorescence/magnetic resonance properties by adjusting the number of terpyridine ligands. Among them, FD-Mn-FD exhibits the following superiorities: (1) The optimal three-photon excitation wavelength of FD-Mn-FD falls at 1450 nm (NIR-II), which brings high sensitivity and deep tissue penetration in MP-FI. (2) FD-Mn-FD has effective longitudinal relaxation efficiency (r₁ = 2.6 m M^-1 s^-1), which can be used for T₁-weighted MRI, overcoming the problems of limited tissue penetration depth and low spatial resolution. (3) FD-Mn-FD generates endogenous ¹O₂ under irradiation by 808 nm light, thereby enhancing the PDT effect in vitro and in vivo. To the best of our knowledge, the complex FD-Mn-FD is the first complex to guide PDT through MP-FI/MRI, providing a blueprint for accurate and effective early detection and timely treatment of the complex in the early stages of cancer.

Mn(II) complexes of phenylenediamine based macrocyclic ligands as T1-MRI contrast agents

The Mn(II) complexes are emerging as alternative T₁-MRI contrast agents (CAs) to the currently available Gd-based CAs. The complexes [Mn(L1)] 1 and [Mn(L2)] 2 of o-phenylenediamine based macrocyclic ligands are reported as T₁-CAs for MRI applications. The high spin state of the Mn(II) complexes (S = 5/2) is confirmed by EPR spectra. The complexes showed an irreversible Mn(II)/Mn(III) redox potential at pH 7.28, which became more and less positive at the acidic and alkaline pHs, respectively. The species [MnL], [Mn(LH_-1), and [Mn(LH_-2) are persisted in solution. Complex 1 is inert towards Ca(II), Mg(II), and Zn(II), whereas complex 2 is inert for Ca(II) and Mg(II) and labile under Zn(II) and Cu(II) ions. Complex 1 showed an r₁-relaxivity of 3.27 and 2.32 mM^-1 s^-1 at 1.41 T, 25, and 37 °C respectively via inner-sphere water relaxation, which is lower than that of 2 (r₁, 5.56, and 4.19 mM^-1 s^-1) at pH 7.28 and 1.41 T. The Mn(II) complexes showed a 2-8% enhancement of r₁-relaxivity while lowering the pH to acidic, which corresponds to the release of free Mn(II) ions. In contrast, the r₁-relaxivity is dropped to 52% and 20% for 1 and 2 respectively under alkaline pH due to the deprotonation of inner-sphere water. Phantom images obtained on Bruker 'BIOSPEC' 47/40 animal research MRI/MRS scanner showed concentration-dependent brightness. The interaction of human serum albumin (HSA) with 1 and 2 exhibited five times higher r₁-relaxivities (11.3 and 22.0 mM^-1 s^-1 at 1.41 T, respectively).

A highly stable l-alanine-based mono(aquated) Mn(ii) complex as a T1-weighted MRI contrast agent

The synthesized lithium (S)-6,6'-(1-carboxyethylazanediyl)bis(methylene)dipicolinate (Li₃cbda) is a new chiral, alanine-based ligand bearing two picolinate functionalities. The trianionic form of the ligand [(cbda)^3-] constitutes a seven-coordinate, water-soluble, pentagonal bipyramidal Mn(ii) complex (1). The structural analysis reveals the presence of a water coordinating site in the complex. The complex is thermodynamically very stable, and the stability is not affected by the presence of physiological anions (HCO₃^-, PO₄^3-, and F^-). The pH of the medium exerts a small effect on the stability of the complex. The r₁ relaxivity of 3.02 mM^-1 s^-1 is exhibited by the complex at 1.41 T, pH ∼7.4, and 25 °C. Phantom images obtained via a clinical MRI BRIVO MR355 system established concentration-dependent signal enhancement by the complex. The cytotoxicity test confirmed complex 1 as a biocompatible potential T₁-weighted MRI contrast agent.

MRI Contrast Agents Based on Conjugated Polyelectrolytes and Dendritic Polymers

Three complexes of gadolinium-based on dentritic molecules are reported as magnetic resonance imaging (MRI) contrast agents. Their ligands feature four carboxylate groups, which contribute to good water solubility and a strong combination with metal ions. As a new attempt, coupling polymerization is carried out to make a combination of conjugated polyelectrolytes and dendrimers for MRI contrast agents. For comparison, mononuclear and binuclear complexes are also reported. The investigation suggests that the contrast agent with the newly designed macromolecular skeleton provides higher longitudinal relaxivity value (36.2 mm -1 s-1 ) and more visible enhancement in in vivo and in vitro MR images than the small molecular ones. In addition, extremely low cytotoxicity and main clearance via hepatobiliary are confirmed, which reduces the deterioration of chronic kidney disease. All the results indicate that these three complexes are generally applicable as promising clinical contrast agents.

A New Bis(aquated) High Relaxivity Mn(II) Complex as an Alternative to Gd(III)-Based MRI Contrast Agent

Disclosed here are a piperazine, a pyridine, and two carboxylate groups containing pentadentate ligand H₂pmpa and its corresponding water-soluble Mn(II) complex (1). DFT-based structural optimization implied that the complex had pentagonal bipyramidal geometry where the axial positions were occupied by two water molecules, and the equatorial plane was constituted by the ligand ON₃O donor set. Thus, a bis(aquated) disc-like Mn(II) complex has been synthesized. The complex showed higher stability compared with Mn(II)-EDTA complex [log K_MnL = 14.29(3)] and showed a very high r₁ relaxivity value of 5.88 mM^-1 s^-1 at 1.41 T, 25 °C, and pH = 7.4. The relaxivity value remained almost unaffected by the pH of the medium in the range of 6-10. Although the presence of 200 equiv of fluoride and bicarbonate anions did not affect the relaxivity value appreciably, an increase in the value was noticed in the presence of phosphate anion due to slow tumbling of the complex. Cell viability measurements, as well as phantom MR images using clinical MRI imager, consolidated the possible candidature of complex 1 as a positive contrast agent.

Impaired Myocardial Oxygenation Response to Stress in Patients With Chronic Kidney Disease

BACKGROUND

Coronary artery disease and left ventricular hypertrophy are prevalent in the chronic kidney disease (CKD) and renal transplant (RT) population. Advances in cardiovascular magnetic resonance (CMR) with blood oxygen level-dependent (BOLD) technique provides capability to assess myocardial oxygenation as a measure of ischemia. We hypothesized that the myocardial oxygenation response to stress would be impaired in CKD and RT patients.

METHODS AND RESULTS

Fifty-three subjects (23 subjects with CKD, 10 RT recipients, 10 hypertensive (HT) controls, and 10 normal controls without known coronary artery disease) underwent CMR scanning. All groups had cine and BOLD CMR at 3 T. The RT and HT groups also had late gadolinium CMR to assess infarction/replacement fibrosis. The CKD group underwent 2-dimensional echocardiography strain to assess fibrosis. Myocardial oxygenation was measured at rest and under stress with adenosine (140 μg/kg per minute) using BOLD signal intensity. A total of 2898 myocardial segments (1200 segments in CKD patients, 552 segments in RT, 480 segments in HT, and 666 segments in normal controls) were compared using linear mixed modeling. Diabetes mellitus (P=0.47) and hypertension (P=0.57) were similar between CKD, RT, and HT groups. The mean BOLD signal intensity change was significantly lower in the CKD and RT groups compared to HT controls and normal controls (-0.89±10.63% in CKD versus 5.66±7.87% in RT versus 15.54±9.58% in HT controls versus 16.19±11.11% in normal controls, P<0.0001). BOLD signal intensity change was associated with estimated glomerular filtration rate (β=0.16, 95% CI=0.10 to 0.22, P<0.0001). Left ventricular mass index and left ventricular septal wall diameter were similar between the CKD predialysis, RT, and HT groups. None of the CKD patients had impaired global longitudinal strain and none of the RT group had late gadolinium hyperenhancement.

CONCLUSIONS

Myocardial oxygenation response to stress is impaired in CKD patients and RT recipients without known coronary artery disease, and unlikely to be solely accounted for by the presence of diabetes mellitus, left ventricular hypertrophy, or myocardial scarring. The impaired myocardial oxygenation in CKD patients may be associated with declining renal function. Noncontrast BOLD CMR is a promising tool for detecting myocardial ischemia in the CKD population.

Myocardial Ischemia Assessment in Chronic Kidney Disease: Challenges and Pitfalls

Coronary artery disease is the leading cause of mortality and morbidity in the chronic kidney disease (CKD) population and often presents with atypical symptoms. Current diagnostic investigations of myocardial ischemia in CKD lack sensitivity and specificity or may have adverse effects. We present a case vignette and explore the challenges of diagnostic myocardial stress investigation in patients with CKD.

Manganese-impregnated mesoporous silica nanoparticles for signal enhancement in MRI cell labelling studies

Mesoporous silica nanoparticles (MSNs) are used in drug delivery and cell tracking applications. As Mn(2+) is already implemented as a "positive" cell contrast agent in preclinical imaging procedures (in the form of MnCl2 for neurological studies), the introduction of Mn in the porous network of MSNs would allow labelling cells and tracking them using MRI. These particles are in general internalized in endosomes, an acidic environment with high saline concentration. In addition, the available MSN porosity could also serve as a carrier to deliver medical/therapeutic substances through the labelled cells. In the present study, manganese oxide was introduced in the porous network of MCM-48 silica nanoparticles (Mn-M48SNs). The particles exhibit a narrow size distribution (~140 nm diam.) and high porosity (~60% vol.), which was validated after insertion of Mn. The resulting Mn-M48SNs were characterized by TEM, N2 physisorption, and XRD. Evidence was found with H2-TPR, and XPS characterization, that Mn(II) is the main oxidation state of the paramagnetic species after suspension in water, most probably in the form of Mn-OOH. The colloidal stability as a function of time was confirmed by DLS in water, acetate buffer and cell culture medium. In NMR data, no significant evidence of Mn(2+) leaching was found in Mn-M48SNs in acidic water (pH 6), up to 96 hours after suspension. High longitudinal relaxivity values of r1 = 8.4 mM(-1) s(-1) were measured at 60 MHz and 37 °C, with the lowest relaxometric ratios (r2/r1 = 2) reported to date for a Mn-MSN system. Leukaemia cells (P388) were labelled with Mn-M48SNs and nanoparticle cell internalization was confirmed by TEM. Finally, MRI contrast enhancement provided by cell labelling with escalated incubation concentrations of Mn-M48SNs was quantified at 1 T. This study confirmed the possibility of efficiently confining Mn into M48SNs using incipient wetness, while maintaining an open porosity and relatively high pore volume. Because these Mn-labelled M48SNs express strong "positive" contrast media properties at low concentrations, they are potentially applicable for cell tracking and drug delivery methodologies.

Nephrogenic systemic fibrosis: concepts and perspectives

Nephrogenic systemic fibrosis is a chronic, progressive condition that develops in some patients with renal impairment after exposure to gadolinium-based contrast agents used in magnetic resonance imaging. Thickening of the skin is typical, usually affecting the extremities. Visceral organs can also be affected. The diagnosis of the disease requires careful clinicopathological correlation. Treatment aims at restoring renal function, which is associated with delayed progression and, eventually, remission of skin changes. Reduction and prevention of nephrogenic systemic fibrosis cases are based on limiting the use of gadolinium-based contrast agents in patients with kidney disorders (especially in patients with advanced renal failure at stages 4 and 5), and restricting their use to situations in which they are essential to diagnosis/follow-up. Other than limiting exposure to gadolinium based contrast agents, no effective preventive methods have been reported. Due to increased awareness about the disease among radiologists and nephrologists, the incidence of nephrogenic systemic fibrosis is declining.

Magnetic resonance imaging of renal masses

The increasing frequency of incidentally detected renal masses supports the need for accurate imaging characterization to avoid unnecessary surgery/interventional procedures. Furthermore, the need for accurate presurgical diagnosis of specific histologic subtypes of renal malignancies is increasingly important as advances in understanding of tumor biology direct targeted courses of therapy. Magnetic resonance imaging is uniquely suited for the evaluation of renal masses because of its ability to provide excellent soft-tissue contrast and demonstration of enhancement, as well as its multiplanar capabilities. Although the spectrum of masses that may occur in the kidneys is broad, specific imaging features may assist in their accurate diagnosis. Examples of the imaging appearance of common and uncommon renal masses are provided along with a protocol for comprehensive magnetic resonance examination of the kidneys.