GLUCOSAMINE S-ADENOSYLMETHIONINE (SAME)

Safety And Efficacy Of Dietary Supplement Glucosamine S-Adenosylmethionine (SAME)

Table of Contents

Outline3

1. Introduction4

2. Materials and methods8

2.1. Materials8

2.2. Hepatocyte isolation, culture, and treatment8

2.3. Determination of hepatocyte GSH content9

2.4. Determination of hepatocyte toxicity9

2.5. Statistics10

3. Results10

3.1. Effect of GSH depletion on galactosamine toxicity10

3.2. Effect of cysteamine on galactosamine toxicity13

3.3. Effect of GSH-ester on galactosamine toxicity14

3.4. Effect of SAMe on galactosamine toxicity17

4. Discussion19

References24

Safety And Efficacy Of Dietary Supplement Glucosamine S-Adenosylmethionine (SAME)

Outline

A gradual but extensive depletion of hepatic GSH has long been known to accompany development of galactosamine-induced hepatotoxicity in rats, and some protection from liver injury has been observed after administration of sulfhydryl-donating compounds. Although these observations support a key role for GSH in the underlying mechanism, the impact of GSH depletion and repletion on the hepatotoxic response to galactosamine is unclear. To investigate the role of GSH in galactosamine-induced liver injury, we examined the effect of modulating GSH content on galactosamine toxicity in rat primary hepatocyte cultures. Galactosamine (4 mM) cytotoxicity was assessed by release of lactate dehydrogenase into the culture medium, and hepatocellular GSH content was measured by HPLC with electrochemical detection. The data indicated that prior depletion of GSH with either diethyl maleate or buthionine sulfoximine significantly enhanced galactosamine toxicity; however, addition of GSH-ester or alternate sulfur nucleophiles at various times during the incubation did not abrogate toxicity. In contrast, co-addition of S-adenosylmethionine (SAMe) with galactosamine exerted a marked protective effect without significantly altering hepatocyte GSH content. These data suggest that GSH depletion is not directly involved in the sequelae for galactosamine-induced hepatotoxicity, and raise the possibility that SAMe may have hepatoprotective effects that are not dependent on its ability to enhance GSH synthesis.

1. Introduction

Galactosamine has long been used as a model of chemical-induced liver injury because of its ability to induce a diffuse hepatic necrosis in rodents. Hepatotoxicity has been attributed to a rapid (30 min) and extensive loss of uridine nucleotides (<10% of normal levels), leading to inhibition of RNA and protein synthesis (Decker and Keppler, 1972, Decker and Keppler, 1974, Keppler et al., 1969 and Keppler et al., 1970b). Hepatotoxicity can be prevented by co-treatment with uridine or uridine precursors if they are administered within 4 h of exposure to galactosamine (Decker and Keppler, 1974, Farber et al., 1973 and Keppler et al., 1970a).

Accompanying galactosamine toxicity in vivo is a slow but extensive depletion (24 h, <20% of normal) in hepatic reduced glutathione (GSH) (MacDonald et al., 1984, MacDonald et al., 1985a and McMillan and Jollow, 1992). As noted above for uridine nucleotides, the loss of GSH may also contribute to galactosamine toxicity because administration of low molecular weight sulfhydryl compounds (which restore GSH content by stimulating GSH synthesis) up to 12 h after galactosamine has been shown to diminish the toxic response (MacDonald et al., 1984, MacDonald et al., 1985a and MacDonald et al., 1985b).

The mechanism underlying the ability of sulfhydryl-donating compounds to protect against galactosamine-induced liver injury is unclear. Galactosamine does not conjugate with GSH (Maley et al., 1968), so it is unlikely that GSH depletion reflects metabolic utilization of GSH ...