The Effect of Waterpipe Tobacco Smoke Exposure on Learning and Memory Functions in the Rat Model

Abstract

Tobacco smoking is a global health hazard that kills about 5 million people annually. Waterpipe smoking is among the most popular methods of tobacco consumption worldwide. In this study, we investigated whether waterpipe smoking impairs learning and memory in the hippocampus, a question of special concern due to the particular popularity of waterpipe use among youth. Additionally, possible molecular targets for expected learning and memory impairment were determined. In this study, rats were exposed to waterpipe smoke (WTS) by whole body exposure 1 h × 5 days/week, for 1 month, and outcomes were compared to a control group exposed only to fresh air. Outcomes included spatial learning and memory using the radial arm water maze (RAWM) and oxidative stress biomarkers (catalase, glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione (GSH), oxidized glutathione (GSSG), GSH/GSSG ratio). We found that WTS exposure led to impaired short- and long-term memory. This impairment was accompanied by reduced hippocampal activity of catalase, SOD, GPx, GSH, and GSH/GSSG, elevated GSSG, thus marked changes in oxidative stress biomarkers. In conclusion, there is reason for concern that WTS exposure may impair cognitive ability.

Keywords: Hippocampus; Maze; Memory; Tobacco; Waterpipe.

Figure 1. Animal learning performance in the radial arm water maze (RAWM)

Comparison of control, and Waterpipe smoking (Waterpipe) groups. Each animal was trained for six consecutive trials separated by 5 min rest, then another six consecutive trials (the learning phase). Performance of animals was compared based on the average number of errors committed in each trial (n=12–14/group).

Figure 2. Memory performance in the RAWM

Short-term memory test at 30 min (A), long-term memory tests at 5 h (B) and at 24 h (C), after the last trial of the learning phase. Chronic exposure to waterpipe smoke impaired short- and long-term memory. Each point is mean ± SEM of the number of errors committed in the corresponding memory test from 12 to 14 rats. * indicates significant difference from all other groups, (P < 0.05).

Figure 3. Changes in glutathione levels in the hippocampus

(A) Levels of reduced glutathione (GSH). (B) Levels of oxidized glutathione (GSSG). (C) Ratio of GSH/GSSG. Both GSH and GSSG were measured using commercially available glutathione assay kit. Each point is the mean ± SEM. * Indicate significant difference from all other groups, (P< 0.05, n=10–12/group).

Figure 4. Activity of GPx, SOD and catalase in the hippocampus

Chronic exposure to waterpipe decreases the activity of (A) GPx, (B) SOD, and (C) catalase in the hippocampus. The activities of various enzymes were measured using commercially available kits according to manufacturer’s instructions. ELISA plates were read using an automated plate reader. Each point is the mean ± SEM of 12 to 14 rats. * indicates significant difference from all other groups, (P < 0.05, n=10–12/group).