Metal Species in Biology: Bottom-Up and Top-Down LC Approaches in Applied Toxicological Research

Abstract

Since the inception of liquid chromatography (LC) more than 100 years ago this separation technique has been developed into a powerful analytical tool that is frequently applied in life science research. To this end, unique insights into the interaction of metal species (throughout this manuscript “metal species” refers to “toxic metals, metalloid compounds, and metal-based drugs” and “toxic metals” to “toxic metals and metalloid compounds”) with endogenous ligands can be obtained by using LC approaches that involve their hyphenation with inductively coupled plasma-based element specific detectors. This review aims to provide a synopsis of the different LC approaches which may be employed to advance our understanding of these interactions either in a “bottom-up” or a “top-down” manner. In the “bottom-up” LC-configuration, endogenous ligands are introduced into a physiologically relevant mobile phase buffer, and the metal species of interest is injected. Subsequent “interrogation” of the on-column formed complex(es) by employing a suitable separation mechanism (e.g., size exclusion chromatography or reversed-phase LC) while changing the ligand concentration(s), the column temperature or the pH can provide valuable insight into the formation of complexes under near physiological conditions. This approach allows to establish the relative stability and hydrophobicity of metal-ligand complexes as well as the dynamic coordination of a metal species (injected) to two ligands (dissolved in the mobile phase). Conversely, the “top-down” analysis of a biological fluid (e.g., blood plasma) by LC (e.g., using size exclusion chromatography) can be used to determine the size distribution of endogenous metalloproteins which are collectively referred to as the “metalloproteome”. This approach can provide unique insight into the metabolism and the plasma protein binding of metal species, and can simultaneously visualize the dose-dependent perturbation of the metalloproteome by a particular metal species. The concerted application of these LC approaches is destined to provide new insight into biochemical processes which represent an important starting point to advance human health in the 21st century.

Physiologically relevant plasma d , l -homocysteine concentrations mobilize Cd from human serum albumin

“…Extensive research efforts have been aimed at gaining insight into the mammalian toxicology of Cd, but considerable knowledge gaps remain [17]. The role that the bloodstream plays in the context of distributing Cd to its toxicological target organs [18], for example, is not very well understood. On one hand, the reaction of Cd 2+ with essential ultra-trace elements, such as selenium in the bloodstream, may adversely affect the distribution of the latter to organs and therefore exert systemic toxicity [18,19].…”

“…The role that the bloodstream plays in the context of distributing Cd to its toxicological target organs [18], for example, is not very well understood. On one hand, the reaction of Cd 2+ with essential ultra-trace elements, such as selenium in the bloodstream, may adversely affect the distribution of the latter to organs and therefore exert systemic toxicity [18,19]. On the other hand, this toxic metal is also known to exert selective toxicity to the kidneys [20] and the testes [21].…”

Integrative Metallomics Studies of Toxic Metal(loid) Substances at the Blood Plasma–Red Blood Cell–Organ/Tumor Nexus

“…The bloodstream should not, however, be viewed as a seamless pipe, since it contains up to 10,000 plasma proteins [68], >400 SMW metabolites [69] and ~1600 RBC cytosolic proteins [70] which can engage in a variety of potential chemical reactions with toxic metal(loid) substances. The enormous number of potential binding sites on plasma proteins/SMW metabolites, for example, can result in their reversible vs. irreversible binding [71], while the partial or complete sequestration of toxic metal(loid) substances within RBCs would preclude their influx to target organs. Given the reducing conditions within RBCs, redox reactions of toxic metal(loid) substances within RBCs must also be considered.…”