Trehalose as an alternative to glycerol as a glassing agent for in vivo DNP MRI

Abstract

In dynamic nuclear polarization (DNP), the solution needs to form a glass to attain significant levels of polarization in reasonable time periods. Molecules that do not form glasses by themselves are often mixed with glass forming excipients. Although glassing agents are often essential in DNP studies, they have the potential to perturb the metabolic measurements that are being studied. Glycerol, the glassing agent of choice for in vivo DNP studies, is effective in reducing ice crystal formation during freezing, but is rapidly metabolized, potentially altering the redox and adenosine triphosphate balance of the system. Methods: DNP buildup curves of 13 C urea and alanine with OX063 in the presence of trehalose, glycerol, and other polyol excipients were measured as a function of concentration. T 1 and T m relaxation times for OX063 in the presence of trehalose were measured by EPR. Results: Approximately 15-20 wt% trehalose gives a glass that polarizes samples more rapidly than the commonly used 60%-wt formulation of glycerol and yields similar polarization levels within clinically relevant timeframes. Conclusions: Trehalose may be an attractive biologically inert alternative to glycerol for situations where there may be concerns about glycerol's glucogenic potential and possible alteration of the adenosine triphosphate/adenosine diphosphate and redox balance.

Dynamic Nuclear Polarization for Sensitivity Enhancement in Biomolecular Solid-State NMR

“…Trehalose has shown to be a possible alternative cryoprotectant resulting in similar enhancement factors in dissolution DNP . Furthermore, studies have demonstrated the possibility of using aqueous sucrose solution, which is known to promote the formation of amorphous ice, for structural ribosome studies with DNP .…”

Real-Time insight into in vivo redox status utilizing hyperpolarized [1-13C] N-acetyl cysteine

“…To reduce intermolecular association, [1- 13 C] NAC was titrated to a neutral pH of 7.5 using 5 M NaOH. The resulting solution of 3.2 M [1- 13 C] NAC became a homogenous self-glassing solution when frozen, a particular advantage for in vivo applications which typically require as highly concentrated solution as possible to achieve maximum sensitivity and to avoid complications from additives which may be potentially toxic or interfere with the metabolic processes being studied 31 , 32 . This polarizing solution shows efficient polarization build-up (Fig.…”

“…1 C), reaching half of the equilibrium polarization in 11,000 s, similar to other hyperpolarized probes being considered for clinical use 25 . An improvement in polarization kinetics and equilibrium polarization values may be possible with optimization of polarization and glassing conditions 31 , 33 , 34 . This solution remained stable overtime at both neutral and acidic pH (Fig.…”

Structure-guided design enables development of a hyperpolarized molecular probe for the detection of aminopeptidase N activity in vivo

“…This sample was successfully hyperpolarized without the use of any glassing agents. Because of the concern that common glassing agents, such as DMSO and glycerol, may perturb metabolic systems, methods of hyperpolarization without glassing agents or with alternative glassing agents that are biologically inert have been sought ( 39 ). The property of being hyperpolarized at high concentrations without glassing agents is advantageous for practical hyperpolarization.…”