Methamphetamine causes acute hyperthermia-dependent liver damage

Abstract

Methamphetamine-induced neurotoxicity has been correlated with damage to the liver but this damage has not been extensively characterized. Moreover, the mechanism by which the drug contributes to liver damage is unknown. This study characterizes the hepatocellular toxicity of methamphetamine and examines if hyperthermia contributes to this liver damage. Livers from methamphetamine-treated rats were examined using electron microscopy and hematoxylin and eosin staining. Methamphetamine increased glycogen stores, mitochondrial aggregation, microvesicular lipid, and hydropic change. These changes were diffuse throughout the hepatic lobule, as evidenced by a lack of hematoxylin and eosin staining. To confirm if these changes were indicative of damage, serum aspartate and alanine aminotransferase were measured. The functional significance of methamphetamine-induced liver damage was also examined by measuring plasma ammonia. To examine the contribution of hyperthermia to this damage, methamphetamine-treated rats were cooled during and after drug treatment by cooling their external environment. Serum aspartate and alanine aminotransferase, as well as plasma ammonia were increased concurrently with these morphologic changes and were prevented when methamphetamine-induced hyperthermia was blocked. These findings support that methamphetamine produces changes in hepatocellular morphology and damage persisting for at least 24 h after drug exposure. At this same time point, methamphetamine treatment significantly increases plasma ammonia concentrations, consistent with impaired ammonia metabolism and functional liver damage. Methamphetamine-induced hyperthermia contributes significantly to the persistent liver damage and increases in peripheral ammonia produced by the drug.

Keywords: Ammonia; hyperthermia; liver damage; methamphetamine.

Figure 1

Ultrastructural changes in liver 24 h after methamphetamine exposure. Representative images from METH- or saline-treated groups are shown. Hepatocytes of METH-treated rats have increased microvesicular lipid (#), hydropic change (&), increased intracellular glycogen stores (*), and mitochondrial aggregation (arrow) compared to control animals (5200× magnification).

Figure 2

Effect of METH dose on hyperthermia and alterations in hepatocellular morphology. Rats were treated with 2, 5, and 10 mg/kg of METH ×4 injections, every 2 h or saline. (A) During drug treatment temperature was measured and each larger dose of METH produced a trend toward increased hyperthermia throughout treatment. Treatment with 10 mg/kg METH produces significant hyperthermia throughout drug treatment. (B) When changes in hepatocellular morphology were examined 24 h later, increases in METH dose also appeared to dose dependently decrease hepatocellular cytoplasmic staining. *P < 0.05, (n = 3–5 per group).

Figure 3

Effect of environmental cooling on methamphetamine-induced hyperthermia. Rats were treated with METH or saline (arrows denote injections). The external environment of a group of METH-treated rats was cooled throughout drug treatment and for 5 h after the last injection to prevent METH-induced hyperthermia. Cooling was regulated to ensure that the body temperatures of METH-treated cooled rats were similar to that of saline-treated rats. METH produced a significant elevation in body temperature throughout treatment compared to the saline-treated and METH-cooled groups. Body temperature of METH-cooled rats did not differ significantly from saline-treated rats. *P < 0.05 (n = 10 per group).

Figure 4

Effect of hyperthermia on methamphetamine-induced changes in liver morphology. Hepatocellular morphology was evaluated using H&E sections from livers collected at 24 h after the last drug injection. A representative picture from all groups of the hepatic lobule near the central vein is shown (asterisk denotes central vein). The livers of METH-treated rats show less hepatocellular cytoplasmic staining (arrows denote cytoplasm) compared to saline-treated rats. The cytoplasmic clearing was prevented when METH-induced hyperthermia was blocked by cooling the rats to normothermic temperatures.

Figure 5

Effect of hyperthermia on methamphetamine-induced increases in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Serum AST and ALT were measured 24 h after treatment with METH or saline. A group of METH-treated rats were cooled during and after treatment to prevent METH-induced hyperthermia. (A) AST was significantly elevated by 89.1 ± 16.4% (mean ± SEM) in METH-treated rats compared to saline-treated rats and this increase was blocked when hyperthermia was prevented in METH-treated rats (METH cooled). (B) ALT was significantly elevated by 24.3 ± 9.3% (Mean ± SEM) in METH-treated rats compared to saline-treated rats. This increase was blocked when METH-induced hyperthermia was prevented (METH cooled). *P < 0.05 compared to saline-treated rats, †P < 0.05 compared to METH-treated rats (n = 10 per group).

Figure 6

Effect of hyperthermia on methamphetamine-induced persistent increases in plasma ammonia. Plasma ammonia was measured 24 h after treatment with METH or saline. A group of METH-treated rats were cooled to prevent METH-induced hyperthermia. METH treatment significantly elevated plasma ammonia concentrations by 114.8 ± 10.5%. This increase was blocked by preventing METH-induced hyperthermia (METH cooled) *P < 0.05 compared to saline-treated rats, †P < 0.05 compared to METH-treated rats (n = 10 per group).