Human health is adversely affected by cigarette smoking and exposure to cigarette smoke. One of the most avoidable causes of illness and death is cigarette smoking. Additionally, prior epidemiological research has demonstrated that smoking cigarettes is the primary cause of cancer and the mortality rate associated with cancer [1,2]. High concentrations of free radicals, including superoxide, hydroxyl radicals, reactive oxygen species, hydrogen peroxide, and peroxynitrite, are found in cigarette smoke. These free radicals react with oxygen-containing molecules to propagate and accumulate other free radicals, which may increase the production of oxidants, decrease antioxidant enzymes, and increase oxidative stress and damage [3]. Lipid peroxidation is the process by which oxidants such as free radicals (reactive oxygen species, superoxide, hydroxyl radicals, hydrogen peroxide, and peroxynitrite) or non-free radical species attack lipids that contain carbon carbon double bonds, specifically polyunsaturated fatty acids (PUFAs). In this attack, a carbon atom is attacked by removing hydrogen and then inserting oxygen, which forms hydroperoxides and lipid peroxyl radicals [4,5]. Peroxidative modification frequently targets cholesterol, phospholipids, and glycolipids, which can cause harm and even death. Lipids can also be oxidised by lipoxygenases, cyclooxygenases, and cytochrome P450, a signalling protein, among other enzymatic activities. Depending on their unique metabolic conditions and regenerative abilities, cells can either induce cell death or enhance cell survival in response to membrane lipid peroxidation [6,7]. Lipid oxidation's effects on cell membranes and its role in physiological functions and serious pathological diseases have been thoroughly examined in a wide range of literatures (Catalá, Xiao, Ademowo). It is commonly known that dyslipidemia, which is marked by decreased levels of high-density lipoprotein cholesterol (HDL-C) and elevated levels of serum triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and total cholesterol (TC), is strongly linked to cardiovascular disease (CVD) [8,9]. In fact, some research has shown that low HDL-C levels can be just as dangerous to coronary health as high LDL-C levels, even when there are normal LDL-C and triglyceride levels present. HDL-C lowers the risk of atherosclerosis and is essential for the transfer of cholesterol. Atherosclerosis is a common condition characterised by the formation of fatty deposits in the inner layers of arteries called atheromatous plaques. Hyperlipidemia and lipid oxidation lead to atherosclerosis, which has long been a leading cause of death in affluent nations. It is a vascular intima disease that can affect any part of the vascular system, including the aorta and coronary arteries. It is characterised by intimal plaques [10–13]. In this study, adult male wistar rats' serum lipid profiles—total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and lipid peroxidation (malondialdehyde activity)—will be examined in relation to the protective effects of vitamin C against exposure to cigarette smoke.

Animal Care and Grouping

For this experiment, eighteen (18) adult male Wistar rats in good health that weighed between 150 and 200 grammes were used. In the animal house of the Obafemi Awolowo College of Health Science, Sagamu campus, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria, the rats were kept in wire and plastic gauze cages. The rats were given a standardised pellet meal and unrestricted access to water during their two-week acclimatisation period. The National Research Council's [14] internationally recognised standard criteria for the use of animals in research were followed in the handling and care of the animals. Three groups of six rats each were created by random selection among the rats. Group A received only fresh air exposure, Group B received cigarette smoke exposure, and Group C received cigarette smoke exposure with 300 mg/kg of vitamin C. The rats were placed in a plastic chamber measuring 32.3 by 23.6 by 19.2 cm, and they were exposed to commercially available cigarettes (Benson & Hedges, British American Tobacco (Nigeria) Limited). Six rats were placed in plastic chambers with air inlets, and eighteen cigarettes were allowed to burn (3 pieces per rat/day). The rats were exposed to the smoke from cigarettes for two hours every day for thirty days, with a 10-minute break for fresh air every thirty minutes. The exposure to cigarette smoke was carried out using modified Fan et al. [12] methods. Vitamin C was administered at a body weight of 300 mg/kg two hours after being exposed to cigarette smoke.

Procedure for Blood Collection

Blood was collected from the orbital venous sinus, the rat was restrained, the neck gently scruffed and the eye made to bulge. A capillary tube was inserted dorsally in to the eye and blood was allowed to flow by capillary action through the capillary tube into a plain sample bottle.

Determination of Fasting Lipid Profile

The blood was analysed for serum triglycerides, serum cholesterol, serum high density lipoprotein cholesterol (HDL), and serum low density lipoprotein cholesterol (LDL) by using standard laboratory methods.

Determination of Lipid Peroxidation

The malondialehyde activity of serum was estimated using the method of Stocks and Dormandy [15].

Statistical Analysis

All the values are expressed as mean ± standard error of mean (SEM). Analysis of data was done using GraphPad Prism version 5 for Windows. Differences between groups were analyzed by one-way ANOVA followed by Dunnet post-hoc test. Differences were considered significant when P < 0.05.

The table 1 presents the impact of vitamin C on dyslipidemia induced by cigarette smoke exposure in adult male Wistar rats. The cholesterol levels in Group B, exposed to cigarette smoke, show a increase compared to the control (Group A). However, the vitamin C-treated group (Group C) exhibits a significant reduction in cholesterol levels compared to the smoke-exposed group, and this reduction is statistically significant. Similar to cholesterol, the triglyceride levels in Group B are elevated due to cigarette smoke exposure. In contrast, Group C, treated with vitamin C, demonstrates a significant decrease in triglyceride levels compared to the smoke-exposed group. High-density lipoprotein (HDL), is notably reduced in Group B, indicating a negative impact of cigarette smoke. However, Group C shows a substantial increase in HDL levels compared to the smoke-exposed group, and this improvement is statistically significant. Low-density lipoprotein (LDL), experiences a rise in Group B. Conversely, Group C, treated with vitamin C, demonstrates a marked decrease in LDL levels compared to the smoke-exposed group, and this reduction is statistically significant.

Table 1: Ameliorative effect of vitamin C against exposure to cigarettes smoke induced Dyslipidaemia in adult male wistar rats.

Each value is an expression of mean ± SEM. (P <0.05). #-Values were significant when compared to group B

Figure 1 below shows the ameliorative effect of vitamin C against exposure to cigarette smoke-induced pathological changes in the serum level of lipid peroxidation in adult male Wistar rats. In the test group B (Cigarette Smoke Exposed), the MDA level is significantly increased to 5.226 (p < 0.05 compared to Group A). The test group C (Cigarette Smoke Exposed + Vitamin C): MDA level is reduced to 3.142 ± 0.4381 µmol/ml, and this reduction is significant compared to Group B (p < 0.05). Exposure to cigarette smoke significantly increases the serum level of lipid peroxidation, as indicated by the elevated MDA concentration compared to the control group. Administration of vitamin C to rats exposed to cigarette smoke shows an ameliorative effect. The MDA level is significantly lower in Group C compared to Group B.

Figure 1: Ameliorative effect of vitamin C against exposure to cigarettes smoke induced pathological changes in the serum level of lipid peroxidation in adult male wistar rats. Each bar is an expression of mean ± SEM. (P <0.05). * - Values were significant when compared to group A, #-Values were significant when compared to group B.

Cigarette smoking is a well-known risk factor for cardiovascular diseases, including dyslipidemia, which is characterized by abnormal levels of lipids in the blood. The exposure to cigarette smoke causes dyslipidemia through several factors, including the effects of nicotine, carbon monoxide (CO), oxidant gases, polycyclic aromatic hydrocarbons (PAHs), and other constituents of tobacco smoke on lipid metabolism. Nicotine, a highly addictive substance in cigarettes, is rapidly absorbed from cigarette smoke and can promote the activation of macrophages, leading to endothelial dysfunction, lipid abnormalities, and insulin resistance. Also, CO, another component of cigarette smoke, can also contribute to endothelial dysfunction and lipid abnormalities (United States). Oxidant gases, including superoxide anion (O2-) and hydrogen peroxide (H2O2), are reactive oxygen species (ROS) generated during the exposure to cigarettes smoke. These oxidant gases are known for their ability to induce oxidative stress by promoting the oxidation of cellular components [16,17] Low-density lipoprotein (LDL) cholesterol is a carrier of cholesterol in the bloodstream. However, when exposed to oxidant gases, LDL molecules can undergo oxidative modifications. Superoxide anion and hydrogen peroxide can directly interact with LDL, initiating a process of lipid peroxidation (as seen in figure 1) leading to the formation of oxidized LDL (oxLDL) [18]. OxLDL is characterized by structural modifications, including the oxidation of lipids within its structure. OxLDL exhibits atherogenic properties, meaning it contributes to the development of atherosclerosis, a common manifestation of dyslipidemia. Also, OxLDL stimulates an inflammatory response in the vascular endothelium, attracting immune cells and initiating the formation of atherosclerotic plaques (table 1). Dyslipidemia, characterized by elevated levels of LDL cholesterol, provides an ample substrate for the generation of oxLDL. OxLDL perpetuates a cycle of inflammation, oxidative stress, and lipid accumulation, further exacerbating dyslipidemia [19,20] (as seen in table 1). Cigarette smoking has been shown to alter lipid/lipoprotein levels in serum. Smokers have been found to have higher levels of total cholesterol (TC), triglycerides (TG), very low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) compared to nonsmokers [21], the result of this stusy also correspond with the changes seen in the lipid profile of rats exposed to cigarettes smoke. Research has shown that dyslipidemia is associated with increased oxidative stress, leading to lipid peroxidation and inflammation [22]. A study conducted in Iran found a prevalence of 40% for dyslipidemia, and smokers showed a greater risk of having abnormal total cholesterol and LDL-C levels than non-smokers [23]. Vitamin C, also known as ascorbic acid, is a powerful antioxidant that plays a crucial role in the body's defence against oxidative stress and lipid peroxidation. Vitamin C has been shown to have a protective effect against oxidative stress in both macro and microangiopathy, and it can improve metabolic control. In a systematic review and meta-analysis of clinical trials, vitamin C supplementation was found to reduce lipid peroxidation and insulin resistance in patients with type 2 diabetes mellitus. However, there is no adequate evidence to support vitamin C supplementation for dyslipidemias in diabetic patients, and more research is needed to determine the optimal dose, duration of treatment, and baseline values for this specific group of patients [24]. Vitamin C has been shown to lower serum low-density lipoprotein (LDL) cholesterol and triglycerides. In a meta-analysis of 13 randomized controlled trials, vitamin C supplementation resulted in a significant decrease in serum LDL cholesterol and triglyceride concentrations. This effect is likely due to vitamin C's ability to intercept ROS in the aqueous phase, thereby significantly reducing plasma lipid peroxide levels and inhibiting oxidative acyl–coenzyme A: cholesterol acyltransferase and cholesterol ester transfer protein, the changes noticed here was also seen in our study (table 1 and figure 1). Vitamin C also protects high-density lipoprotein (HDL) cholesterol from lipid oxidation, allowing it to be involved in a process known as reverse cholesterol transport. This process helps remove excess cholesterol from the body and reduces the risk of cardiovascular diseases [25].

In conclusion, the detrimental impact of cigarette smoking on cardiovascular health, particularly its association with dyslipidemia, is evident through various mechanisms. The resulting dyslipidemia sets off a cascade of events, including atherogenic properties and inflammatory responses. The presented study aligns with existing evidence showcasing the alteration of lipid profiles in response to cigarette smoke exposure, reflecting the higher levels of total cholesterol, triglycerides, and LDL observed in smokers. The introduction of vitamin C as a potential therapeutic intervention brings optimism to mitigate the adverse effects of oxidative stress and dyslipidemia in rats exposed to cigarettes smoke. In essence, this study contributes valuable insights into the intricate interplay between cigarette smoke exposure, dyslipidemia, and the potential ameliorative effects of vitamin C, paving the way for future investigations and targeted therapeutic strategies in cardiovascular health.

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