Chloride concentrations in human hepatic cytosol and mitochondria are a function of age

Abstract

We recently reported that, in a concentration-dependent manner, chloride protects hepatic glutathione transferase zeta 1 from inactivation by dichloroacetate, an investigational drug used in treating various acquired and congenital metabolic diseases. Despite the importance of chloride ions in normal physiology, and decades of study of chloride transport across membranes, the literature lacks information on chloride concentrations in animal tissues other than blood. In this study we measured chloride concentrations in human liver samples from male and female donors aged 1 day to 84 years (n = 97). Because glutathione transferase zeta 1 is present in cytosol and, to a lesser extent, in mitochondria, we measured chloride in these fractions by high-performance liquid chromatography analysis following conversion of the free chloride to pentafluorobenzylchloride. We found that chloride concentration decreased with age in hepatic cytosol but increased in liver mitochondria. In addition, chloride concentrations in cytosol, (105.2 ± 62.4 mM; range: 24.7 – 365.7 mM) were strikingly higher than those in mitochondria (4.2 ± 3.8 mM; range 0.9 – 22.2 mM). These results suggest a possible explanation for clinical observations seen in patients treated with dichloroacetate, whereby children metabolize the drug more rapidly than adults following repeated doses, and also provide information that may influence our understanding of normal liver physiology.

GSTZ1 expression and chloride concentrations modulate sensitivity of cancer cells to dichloroacetate

“…Of note, the non-tumor breast tissue showed higher variability in [Cl − ] between donors than did the non-tumor liver samples. Additionally, both non-tumor and tumor breast tissues had mean Cl − levels that were much higher than the liver samples (Figure 5D), while liver mitochondria had very low [Cl − ], consistent with our previous findings [11]. As a whole, only cytosol from liver tumors had Cl − levels that were different from matched controls.…”

“…chloride concentration ([Cl − ]) was 0.22 ± 0.07 μmol/mg protein in the cytosol. For reference, we have reported the chloride concentration in normal adult liver cytosol to be approximately 75 mM [11]. …”

“…Although small sample size precluded replicate [Cl − ] measurements, we have previously shown the assay to be highly reproducible [11]. …”

“…Chloride concentrations were determined using a HPLC method that measures the derivitization of pentafluorobenzyl bromide to pentafluorobenzyl chloride [10,11]. …”

Pharmacogenetic Considerations with Dichloroacetate Dosing

“…Recent findings of the effect of chloride on GSTZ11 inactivation could explain these discrepancies. It was found that chloride protects GSTZ11 from inactivation by DCA at physio logically relevant concentrations in the liver [62,63], however the GSTZ11 in liver cytosol of those who were heterozygous for GSTZ1A was less protected from inactivation by physiological (38 mM) chloride than those with other GSTZ1 allelic variants (Table 4). The effect of chloride was such that the GSTZ11 enzymes in livers from individuals with the GSTZ1A variant on one allele were inactivated twice as quickly as those with other haplotypes.…”