Qualitative analysis of the impact of palm and sesame oil on liver tissue health: can histology aid diagnosis?

Abstract

Aim:

The present study, by examining liver histopathology, provides valuable insights into the changes caused by palm oil and sesame oil.

Background:

Plant-based foods are essential for liver health because they improve liver function and prevent disease. Palm oil can affect liver function and fat metabolism owing to its high saturated fat content, and its consumption can lead to non-alcoholic fatty liver disease (NAFLD), which may advance to non-alcoholic steatohepatitis (NASH). Sesame has potent anti-inflammatory and antioxidant properties that help to reduce oxidative stress and inflammation in the liver. Despite extensive research on the health effects of various oils, studies on liver histopathology are lacking.

Methods:

In a controlled laboratory environment, 18 rats were divided into three groups and treated for 90 days with palm oil (15% w/w), sesame oil (7.5% w/w), or a control diet. Liver tissue was examined by histopathology, including hematoxylin-eosin and Van Gieson staining, as well as histomorphometric changes, such as sinusoid size and liver and body weight.

Results:

The results obtained from tissue staining, examination of sinusoid size, and liver weight measurement showed that palm oil consumption led to liver damage, inflammation, and fibrosis, whereas sesame oil protected the liver.

Conclusion:

Palm oil consumption should be limited as much as possible, and healthier alternatives, such as sesame oil, should be considered.

Introduction

Plant-based foods are crucial for sustaining liver health, as they contain compounds that can enhance liver function and potentially prevent liver disease (1). An unhealthy diet may lead to excessive fat accumulation in the liver, thereby contributing to non-alcoholic fatty liver disease (NAFLD) (2). Certain fats, particularly polyunsaturated fatty acids (PUFAs) such as omega-3 and omega-6, are indispensable for health because the body cannot synthesize them. These fatty acids are vital for cellular functions and the regulation of inflammation (3).

Hepatitis, also known as liver inflammation, is caused by autoimmune diseases, viral infections, excessive alcohol consumption, or metabolic disorders. Approximately one-third of the individuals diagnosed with nonalcoholic fatty liver disease (NAFLD) may progress to nonalcoholic steatohepatitis (NASH), a condition characterized by inflammation and fibrosis, which can ultimately lead to cirrhosis. Nutrient metabolism, drug detoxification, and protein synthesis depend on liver function. These essential processes are disrupted by chronic liver inflammation, which subsequently affects the health and quality of life (4, 5)

Edible palm oil is derived from the mesocarp of oil palm fruit (Elaeis guineensis Jacq) (6). Palm oil consumption may impact liver function and lipid metabolism due to its high saturated fat content (7). The ingestion of palm oil can lead to non-alcoholic steatohepatitis (NASH) by causing hepatocyte swelling and lipid accumulation (8). Structural damage to liver tissue may result from increased liver weight, disorganization of hepatic structure, and abnormal arrangements of hepatocytes (9). Palm oil is widely used as a cooking oil by consumers (10).

Sesame seeds (Sesamum indicum L.) are one of the earliest oilseeds used medicinally and pharmaceutically (11, 12) since sesame oil contains compounds such as sesamol and sesamin (13). It increases fatty acid oxidation, reduces lipid levels, and supports lipid metabolism, particularly in nonalcoholic fatty liver disease (14). The protective effects of sesame oil on liver health have been demonstrated by reducing ALT and AST enzyme levels, reducing the severity of nonalcoholic fatty liver disease, and reducing inflammation and hepatocellular damage in lead-induced liver injury (15).

Despite extensive research into the potential health impacts of various oils, the study of liver histopathology remains limited. This gap is crucial because previous research on the health effects of palm oil, which focused solely on blood factors and liver enzymes, has shown significant variability in results. Some studies indicate that consuming palm oil can cause liver damage, while others suggest it might have positive effects under certain conditions (9, 16). This inconsistency highlights the need for more precise and controlled studies to clarify the impact of palm oil on liver tissue health. Understanding these nuances is essential because palm oil is a prevalent ingredient in numerous processed foods and is widely used in cooking and food products (17). The present study addresses this research gap by investigating the effects of palm and sesame oil on liver tissue, liver weight, and body weight. The present study provides essential results by examining liver histopathology to demonstrate the changes induced by palm and sesame oil, highlighting the importance of dietary fat choices for maintaining liver integrity.

Methods

Laboratory animals

Eighteen male Wistar rats, aged 12–14 weeks and weighing 230 ± 20 g were acquired fro. They hadteur Institute (Tehran, Iran). Animals were housed in special cages at a temperature of 22 ± 2 °C, with a 12-hr light/12-hr dark photoperiod, and had free access to water and food (in accordance with Canadian Council on Animal Care guidelines). All animal treatments have been certified by the Ethics Committee of Kermanshah University of Medical Sciences Ethics Committee of Kermanshah University of Medical Sciences (Ethics number: IR.KUMS.REC.1398.099).

The rats were randomly divided into three groups (six in each) and treated as follows for 90 days after weighing. The groups were as follows: Control (the rats treated with their regular chew), palm oil (PO; the rats treated with 15% weight/weight of palm oil added to their regular chew) (18), and Sesame oil (SO; the rats treated 7/5% weight/weight of Sesame oil into their regular chew) (19). Effective doses were selected based on previous studies. One day after the last treatments, the rats were weighed and anesthetized by intraperitoneal injection of ketamine HCL (100 mg/kg) and xylazine (10 mg/kg) (Merk; Germany). Every effort was made to minimize suffering. The liver was excised, blotted dry, weighed, and placed in 10% formalin. Hematoxylin-eosin (H&E) and van Gieson staining were added for histopathological examination. In this regard, as per our previous study (Chehrei et al., 2017), the diameter of the sinusoids was measured using Motic software and an optical microscope.

Statistical analysis

Data were expressed as Mean±Standard error of the mean (Mean±SEM) and statistically evaluated using analysis of variance (ANOVA) followed by a post-hoc test using IBM SPSS software version 27. A value of p<0.05 was considered statistically significant.

Results

No significant changes were observed in the liver tissue of the group receiving sesame oil compared to the control group (Figure 1). In the samples treated with 15% w/w palm oil, lipid droplets were evident in hepatocytes (Figure 2a). Structural alterations were apparent in the liver tissue, including irregular hepatocyte arrangement, hepatocellular swelling and ballooning, and disruption of liver architecture (Figure 2a). Amas was observed within the endothelium of the central vein, accompanied by the presence of inflammatory cells. A group of cells had abnormally entered the central lobular vein, and the blood vessel walls exhibited increased thickness compared with the control group (Figure 2b). Infiltration of inflammatory cells was observed near the damaged hepatocytes (Figure 2c). The portal triad exhibited abnormalities and was infiltrated by inflammatory cells (Figure 2d). Fibrotic strands were visible surrounding the central vein (Figure 3). The sinusoidal spaces were enlarged and irregular compared with those of the other groups (p<0.001) (Figure 4). Although the group receiving palm oil demonstrated an increase in weight compared with the other groups, this weight gain did not differ significantly (p = 0.94) between the experimental and control rats. The liver weight of rats receiving palm oil increased significantly (p<0.001) compared with the sesame and control groups (Table 1).

Figure 1.

Photomicrograph Showing Essentially Normal Liver Section in control and sesame group. Include clear hepatocyte cords, central vein: SV and normal sinusoid: S (a), and normal portal triad (b) observed under an Olympus light microscope fixed with the camera, at a magnification (40 ×). (H&E staining)

Figure 2.

Histological examinations of liver tissue in the group treated with 15% w/w palm oil. (a) Section showing fat-filled, balloon-shaped hepatocytes: arrows, dilated sinusoids (S), (b) The section shows a central vein with a thick wall: arrowheads, an accumulation of inflammatory cells adjacent to the endothelial area: arrows, the presence of abnormal cell clusters within the vein, and distortion of hepatic architecture, (c) Section showing infiltration of the inflammatory cell, (d) section showing abnormal portal triad with inflammatory cell observed under an Olympus light microscope fixed with the camera, at a magnification (40 ×). (H&E staining).

Figure 3.

Histological examination of fibrosis in experimental and control groups. (a) Section showing the control group without the fibrous strand. (b) Section showing the sesame group without the fibrous strand. (c) section showing fibrous strands around the central vein which also extend around the sinusoids: arrowheads, in the palm oil group observed under an Olympus light microscope fixed with the camera, at a magnification (40 ×). (Van Gieson staining).

Figure 4.

The effect of palm and sesame oils on the diameter of rat liver sinusoids. The data are represented as Mean ± EM. Values are statistically significant at *p <0.001 Vs. control.

Table 1.

The Effect of Palm and sesame oils on Body and Liver Weight (g)

Diet	Control	Palm oil	Sesame oil
Body Weight	256.83±10.22	263.33±17.03	257.16±10.05
Liver Weight	11.81±1.38	15.86±0.79*	11.88±1.39

Results are expressed as mean ± SEM (n=6). *Significant at p< 0.001 compared with control using analysis of variance.

Discussion

These findings suggest that palm oil may have detrimental effects on liver tissue health compared to sesame oil. Prolonged exposure to palm oil may contribute to hepatic damage, as evidenced by increased liver weight, mild steatosis, inflammation, and early fibrosis. Conversely, research has shown that sesame oil has a benign effect on liver tissue, which remains comparable to normal tissue.

Liver steatosis is characterized by the accumulation of neutral lipids within organelles called lipid droplets (LDs) in the hepatocyte cytoplasm. Currently, non-alcoholic fatty liver disease (NAFLD), an umbrella term used to define different conditions in which LDs are present in more than 5% of the hepatocytes and are associated with metabolic diseases (20), has garnered increasing attention. NAFLD is classified based on histological assessment of liver biopsies, which evaluates the degree of steatosis, hepatocyte ballooning, and inflammation in the liver tissue. Non-alcoholic fatty liver (NAFL) refers to simple steatosis, while non-alcoholic steatohepatitis (NASH) requires hepatocyte ballooning and inflammation (21).

Liver inflammation is a complex process involving various cellular and molecular mechanisms. Itemphasizes the crucial role of hepatocytes in this process, particularly their response to liver insults and inflammatory signals (21). Inflammatory pathways involving diverse immune cells, such as T lymphocytes and neutrophils, are activated in NAFLD, contributing to liver damage and fibrosis (22).

Liver fibrosis is a severe condition that can lead to cirrhosis, liver failure, and portal hypertension. It is caused by chronic liver diseases, such as hepatitis B and C, alcoholism, and nonalcoholic fatty liver disease (23). The primary cells involved in the development and progression of liver fibrosis are hepatic stellate cells (HSCs), which secrete fibrogenic factors that promote collagen production (24).

The effects of palm oil and sesame oil on liver tissue have been studied in various contexts, with differing results. Palm oilis high in saturated fats and has both positive and negative impacts on liver health. There is no clear evidence that palm oil benefits or harms health. Some studies, consistent with the present study's results, have shown adverse effects of palm oil consumption on the body, such as fat accumulation in hepatocytes, liver inflammation (25), and body weight gain. Palm oil can increase cholesterol levels and metabolic disorders dueto its high saturated fat content (26). In contrast, the omega-3 and omega-6 fatty acids (27) in a sesame oil-based diet help maintain the standard, typical structure and function of the liver (28). Sesame oil protects the liver from methotrexate toxicity by reducing inflammatory responses and oxidative stress (29). A histopathological examination revealed no significant changes in the liver weight and texture of the treated mice with palm puree compared to the control group (30).‏ This discrepancy in the results may be due to the use of pure palm oil instead of palm oil. Similar to the results of the present study, several studies have investigated the effect of palm oiand sesame supplementation on body weight, showing that this oil does not affect body weight compared with other oils (32). In contrast, one study showed increased rat weight after palm oil consumption (33), and a comprehensive meta-analysis of clinical trials found that sesame oil consumption significantly lowered body weight and BMI (34). This difference in results may be due to the type of samples used, as Atefi et al.’s study samples were affected by NAFLD.

Liver sinusoidal spaces are critical for hepatic function, as they facilitate the exchange of nutrients, waste products, and signaling molecules between hepatocytes and the circulatory system. Alterations in their structure can impair liver function and exacerbate conditions such as fibrosis and inflammation (35). Numerous studies have examined the association between palm oil consumption and the liver sinusoids. Consistent with our findings, these studies have demonstrated that prolonged oil exposure may result in microanatomical damage, such as necrosis and sinusoidal enlargement, in the livers of mice, suggesting potential toxicity (36).

In public discussions, the increasing use of palm oil is often criticized for its health effects. In addition to examining the health effects of palm oil, the environmental impacts associated with palm oil production, deforestation, and the resulting problems for biodiversity are highly debated (37). Many studies have focusedon different types of oils owing to their potential impact on human health. The effects of palm oil and sesame oil on liver tissue appear complex. They may depend on various factors, inclcomponents, oxidation levels, and the overall dietary context. Further research is needed to fully understand the potential impacts of these oils on liver health and to determine their effects in different populations and disease states.

Histopathological markers such as perisinusoidal fibrosis can potentially serve as diagnostic and predictive biomarkers for liver injury associated with high consumption of saturated fatty acid oils, particularly within the context of metabolic dysfunction-associated steatotic liver disease and metabolic dysfunction-associated steatohepatitis (38, 39). The presence and progression of liver fibrosis, including perisinusoidal fibrosis, are significant predictors of MASH advancement and the development of hepatocellular carcinoma (39). Studies have demonstrated that perisinusoidal fibrosis can be staged in NAFLD, indicating its utility in assessing disease severity and progression (40). While sinusoidal dilation is recognized as a hepatic sinusoidal disorder (41), its direct role as a specific diagnostic or predictive biomarker for liver injury linked explicitly to high consumption of saturated fatty acid oil is less explicitly detailed in the provided literature. However, the broader context of NAFLD, which is associated with factors such as obesity, poor diet, and increased hepatic lipogenesis from high-calorie diets, suggests that these histopathological changes reflect the impact of dietary factors on liver health (39).

A limitation of this study was its small sample size (N = 6). While some animal experiments are exploratory and may not always require precise sample size calculations, the challenges of sample size limitations that come with reduced statistical power cannot be ignored because low statistical power increases the likelihood of false-positive and false-negative findings, which can lead to overestimation of effect sizes and compromise the reproducibility of research results. Ethical issues related to working with small numbers in animal research, as well as the associated costs, often contribute to the prevalence of small sample sizes.

Conclusion

This comparative study highlights the potential risks associated with palm oil consumption, including fat accumulation in hepatocytes, and the relative safety of sesame oil on liver health. The results of this study indicate that palm oil consumption should be as limited as possible, and healthier alternatives, such as sesame oil, should be considered. Further research, including long-term studies and human trials, is needed to confirm these findings and understand the underlying mechanisms.

Conflict of interests

There is no conflict of interest for authors of this article.