Toxicological evaluation of chronic oral administration of Melissa officinalis hydro-ethanol extract in Sprague-Dawley rats

Melissa officinalis is a plant that has been widely used as an herbal medicine in many countries. Unfortunately, despite the prevalent medicinal uses of the plant, there are no reports on the possible toxic effects of M. officinalis. This study was designed to evaluate the effect of long-term administration of hydro-alcoholic extract of M. officinalis on some biochemical and hematological parameters and histopathology of organs. Thirty Sprague-Dawley rats were allocated to three equal groups. The animals in groups A and B received 600 and 1200 mg/kg M. officinalis extract, respectively, for 30 days. The rats in group C were given gavaged saline as control. The animals were euthanized at the end of experiment and the blood samples were collected for biochemical and hematology analysis. Additionally, appropriate tissue samples were collected from kidney, liver, spleen, heart and lung for light microscopic examination. M. officinalis caused a significant increase in the alanine aminotransferase level in the treated rats. Although the increase in creatine phosphokinase and lactate dehydrogenase levels were observed in group A and B, respectively, but there were no significant differences. A significant decrease was observed in the total protein and albumin concentrations in serum of treated rats as compared to the control group. The creatinine concentrations were significantly higher in the group B when compared to the other groups. There were no significant differences in cholesterol, triglyceride and urea concentrations between all groups of rats. The main histopathologic findings in the liver were included hepatocyte degeneration, congestion and dilation of sinusoids, proliferation of bile ducts and infiltration of mononuclear cells around the portal area. Histopathologic examination of the kidneys showed a tubular degeneration and necrosis, tubular and glomerular atrophy and congestion. These lesions were more prominent in the high dose treated rats. The findings suggest that long-term administration of M. officinalis extract even at low doses induces hepatic and renal lesions in rats.