Inactivation of aldehyde dehydrogenase by disulfiram in the presence and absence of lipoic acid or dihydrolipoic acid : an in vitro study

The inhibition of aldehyde dehydrogenase (ALDH) by disulfiram (DSF) in vitro can be prevented and/or reversed by dithiothreitol (DTT), which is a well-known low molecular weight non-physiological redox reagent commonly used in laboratory experiments. These observations inspired us to ask the question whether the inhibition of ALDH by DSF can be preserved or abolished also by dihydrolipoic acid (DHLA), which is the only currently known low molecular weight physiological dithiol in the body of humans and other animals. It can even be metaphorized that DHLA is an "endogenous DTT". Lipoic acid (LA) is the oxidized form of DHLA. We investigated the inactivation of ALDH derived from yeast and rat liver by DSF in the presence or absence of LA or DHLA. The results clearly show that DHLA is able both to restore and protect ALDH activity blocked by DSF. The proposed mechanism is discussed

The glial Gomori-positive material is sulfane sulpfur.

The Gomori-positive glia are periventricular astrocytes with abundant cytoplasmic granular material, predominantly occupying a periventricular site in the brain. These granular inclusions are strongly stained with chrome hematoxylin in the Gomori's method as well as exhibit red autofluorescence and non-enzymatic peroxidase activity. The glial Gomori-positive material (GGPM) granules are positive in the performic acid Alcian blue method indicating the presence of protein-bound sulfur, what has been shown by our previous studies. The number of cells containing glial Gomori-positive granules dropped after administration of cyanide and increased under the influence of sulfane sulfur donor (diallyl disulfide). This suggests, that sulfur of these granules is a sulfane sulfur, possibly in the form of protein-bound cysteine persulfide. Sulfane sulfur is labile, reactive sulfur atom covalently bound to another sulfur atom. In this paper we present evidence that GGPM exhibit affinity to cyanolysis and its stainability in Gomori's method is due to the presence of protein-bound sulfane sulfur. The biological role of the Gomori-positive glia connected with protective properties of sulfane sulfur has been discussed

Is aldehyde dehydrogenase inhibited by sulfur compounds? In vitro and in vivo studies

Aldehyde dehydrogenase (ALDH) catalyzes the critical step of ethanol metabolism, i.e. transformation of toxic acetaldehyde to acetic acid. It is a redox sensitive protein with the key Cys in its active site. Recently, it has been documented that activity of some proteins can be modified by sulfur-containing molecules called reactive sulfur species leading to the formation of hydro- persulfides. The aim of the present study was to examine whether ALDH activity can be modified in this way. Studies were performed in vitro using yeast ALDH and various reactive sulfur species, including Na2S, GSSH, K2Sx, Na2S2O3, and garlic-derived allyl sulfides. The effect of garlic-derived trisulfide on ALDH activity was also studied in vivo in the rat liver. The obtained results clearly demonstrated that ALDH could be regulated by sulfur species which inhibited its enzymatic activity. The results also suggested that not H2S but polysulfides or hydropersulfides were the oxidizing species responsible for this modification. This process was easily reversible by reducing agents. After the treatment with polysulfides or hydropersulfides the level of protein-bound sulfur increased, while the activity of the enzyme dramatically decreased. Moreover, the study demonstrated that ALDH activity was inhibited in vivo in the rat liver after garlic-derived trisulfide administration. This is the first study reporting the regulation of ALDH activity by sulfane sulfur species and the results suggest that it leads to the inhibition of the enzyme

Plasma levels of total, free and protein bound thiols as well as sulfane sulfur in different age groups of rats

The redox status of plasma thiols can be a diagnostic indicator of different pathological states. The aim of this study was to identify the age dependent changes in the plasma levels of total, free and protein bound glutathione, cysteine and homocysteine. The determination was conducted in plasma of three groups of rats: 1) young (3-month-old), 2) middle aged (19-month-old), and 3) old (31-month-old). Total levels of glutathione, cysteine and homocysteine and their respective free and protein-bound fractions decreased with age. The only exception was a rise in free homocysteine concentration in the middle group, which indicates a different pattern of transformations of this thiol in plasma. The drop in the level of protein-bound thiols suggests that the antioxidant capacity of plasma diminishes with age, which, consequently, leads to impaired protection of -SH groups through irreversible oxidation. The plasma sulfane sulfur level also declines with age, which means that aging is accompanied by inhibition of anaerobic sulfur metabolism

Is the mechanism of nitroglycerin tolerance associated with aldehyde dehydrogenase activity? : a contribution to the ongoing discussion

The aim of the study presented here was an attempt to answer the question posed in the title: Is the mechanism of nitroglycerin tolerance associated with aldehyde dehydrogenase (ALDH) activity? Here, we investigated the effect of administration (separately or jointly) of lipoic acid (LA), nitroglycerin (GTN), and disulfiram (DSF; an irreversible in vivo inhibitor of all ALDH isozymes (including ALDH2)), on the development of tolerance to GTN. We also assessed the total activity of ALDH in the rat liver homogenates. Our data revealed that not only DSF and GTN inhibited the total ALDH activity in the rat liver, but LA also proved to be an inhibitor of this enzyme. At the same time, the obtained results demonstrated that the GTN tolerance did not develop in GTN, DSF and LA jointly treated rats, but did develop in GTN and DSF jointly treated rats. This means that the ability of LA to prevent GTN tolerance is not associated with the total ALDH activity in the rat liver. In this context, the fact that animals jointly receiving GTN and DSF developed tolerance to GTN, and in animals that in addition to GTN and DSF also received LA such tolerance did not develop, is - in our opinion - a sufficient premise to conclude that the nitrate tolerance certainly is not caused by a decrease in the activity of any of the ALDH isoenzymes present in the rat liver, including ALDH2. However, many questions still await an answer, including the basic one: What is the mechanism of tolerance to nitroglycerin

The effect of lipoic acid on cyanate toxicity in different structures of the rat brain

Cyanate is formed mostly during nonenzymatic urea biodegradation. Its active form isocyanate reacts with protein –NH(2) and –SH groups, which changes their structure and function. The present studies aimed to investigate the effect of cyanate on activity of the enzymes, which possess –SH groups in the active centers and are implicated in anaerobic cysteine transformation and cyanide detoxification, as well as on glutathione level and peroxidative processes in different brain structures of the rat: cortex, striatum, hippocampus, and substantia nigra. In addition, we examined whether a concomitant treatment with lipoate, a dithiol that may act as a target of S-carbamoylation, can prevent these changes. Cyanate-inhibited sulfurtransferase activities and lowered sulfide level, which was accompanied by a decrease in glutathione concentration and elevation of reactive oxygen species level in almost all rat brain structures. Lipoate administered in combination with cyanate was able to prevent the above-mentioned negative cyanate-induced changes in a majority of the examined brain structures. These observations can be promising for chronic renal failure patients since lipoate can play a double role in these patients contributing to efficient antioxidant defense and protection against cyanate and cyanide toxicity