Aluminum (Al), an environmental toxicant, is considered a potential etiological factor causing neuropathological and neurochemical alterations, together with neurobehavioral abnormalities. Al-based products are used in many fields, including industry, medicine, and agriculture (Klotz et al., 2017). In addition, they are widely involved in food manufacturing and daily necessities, such as food additives, antiperspirants, Al cooking utensils, Al foil, water purifiers, and some vaccines, which largely increase the risk of exposure to Al in humans. Al can negatively impact human health, where it is distributed mainly in the brain, liver, and kidney tissues (Kandimalla et al., 2016; Xu et al., 2017; Alasfar and Isaifan, 2021). Hence, exposure or intake of Al for a long time produces toxic effects in humans and animals and may result in conditions such as neurotoxicity, hepatotoxicity, kidney disease, and Alzheimer’s disease (AD) (Mailloux et al., 2011; Krause et al., 2020).

Researchers have recently found increased levels of Al in the brain tissue of people suffering from epilepsy, autism, or AD (Alasfar and Isaifan, 2021). Thus, Al toxicity may be responsible for neurotoxicity and neurodegenerative disorders, including AD, autism, or multiple sclerosis and their related manifestations, such as memory loss and dementia.

A growing body of evidence suggests that amyloid-beta (Aβ) deposition is not only a central player in the pathogenesis of AD, but it also has a pivotal role in the etiopathogenesis of other neurodegenerative disorders, including multiple sclerosis, autism, and epilepsy (Sokol et al., 2019; Romoli et al., 2021; Lopresti, 2022). Physiologically, there is a balance between the rate of production of Aβ and its rate of degradation (Baranello et al., 2015). The degradation of Aβ occurs mainly through the liver (Maarouf et al., 2018). Actually, the liver, a vital organ for the metabolism of chemicals, metabolizes more than 60% of Aβ, thus limiting Aβ accumulation. Given these facts, upon Al-intoxication, the liver, the major organ for Al accumulation, can be injured, resulting in impairment in liver metabolism that could lead to further Aβ accumulation in the brain and hence fostering the progression of neurodegenerative diseases. Furthermore, liver dysfunction may play a role in the progression of neurodegenerative diseases by acting as a source of pro-inflammatory mediators (Wiseman et al., 2015; Estrada et al., 2019).

It is interesting to note that recent research studies have revealed synergistic interactions between Aβ and the tau protein in several neurodegenerative disorders (Sengupta and Kayed, 2022). Al neurotoxicity and the accumulation of Aβ result in neuroinflammation, neurodegeneration, and neuronal apoptosis. In fact, Aβ further stimulates the expression and production of several pro-inflammatory mediators, such tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6β (IL-6β), by the activated microglia, which in turn trigger the hyperphosphorylation of tau protein in the brain that forms neurofibrillary tangles (NFTs), resulting in neuronal cell death (Ghosh et al., 2013; Meraz-Ríos et al., 2013; González-Domínguez et al., 2015; Calsolaro and Edison, 2016; Cao et al., 2016; Domingues et al., 2017). There is ample evidence that the dysregulation of the Wnt3a/β-catenin/GSK-3β signaling pathway has a crucial role in both the onset and progression of neurodegenerative disorders resulting from the neurotoxic effects of Al (Li et al., 2020), where glycogen synthase kinase-3β (GSK-3β) phosphorylates tau, contributes to the development of Aβ (Hernandez et al., 2013), and initiates neurodegeneration (Jia et al., 2019; Lauretti et al., 2020).

It has been documented that long-term Al exposure is associated with alteration in the gut microbiota, leading to gut dysbiosis that elevates systemic inflammation and disrupts the gut–brain axis, thus triggering neuroinflammation and neurotoxicity and enhancing the progression of neurodegenerative diseases via dysregulation in the gut–brain axis (Zhai et al., 2017).

Several research studies have looked into potential protective measures in light of Al’s significant propensity for neurotoxicity and its role in the emergence of neurodegenerative and neurodevelopmental diseases. As inflammation, oxidative stress, apoptosis, mitochondrial dysfunction, and endoplasmic reticulum stress all play a part in Al neurotoxicity, it is expected that the majority of protective drugs will exert their protective effects by acting as antioxidants and anti-inflammatory agents. The current protective agents include chelators to bind Al; polyphenols; or polyphenol-rich phytoextracts as antioxidants (Skalny et al., 2021).

To date, there is a growing interest in alternative medicine because herbs and herbal-derived products possess myriad actions, such as antioxidant, anti-inflammatory, anti-amyloid, and anti-apoptotic activities (Kumar and Arti Singh, 2017). Among the widely used, potentially editable nutritional and medicinal herbs in most countries are sesame seed. It has various medicinal uses, such as in the dry couch and asthma as a bronchodilator, ulcers as an anti-inflammatory agent, urinary tract diseases and wound healing as an antimicrobial agent, brain diseases such as migraine and vertigo as a neuroprotective agent, congestive heart failure as a cardioprotective agent, and liver diseases as a hepatoprotective agent (Mili et al., 2021). It contains sesame lignans (including sesamol), which have an inhibitory effect on cholesterol 24S-hydroxylase (CYP46A1), which is a brain-specific cytochrome P450 and plays a significant role in the cholesterol catabolism in the brain tissues, preventing cerebral ischemia in the middle cerebral arteries and inhibiting the cerebral apoptotic pathway (Du et al., 2022). Sesamol is a promising candidate to attenuate neurotoxicity and neuroinflammation due to its anti-inflammatory activity (Sachdeva et al., 2015; Castro-González et al., 2020). Sesamol has neuroprotective properties and can help with cognitive deficits and anxiety. Interestingly, sesamol has been documented to prevent Aβ accumulation, change the microbiota of the stomach, and improve the microbial metabolite output (Yuan et al., 2019). Sesamol prevents Al-induced neurotoxicity through its anti-inflammatory, antioxidant, and anti-apoptotic effects (Abou-Zeid et al., 2021; Du et al., 2022).

The gut–brain axis has received a lot of attention for its effect on the healthy function of the central nervous system (Dempsey et al., 2019). Many research studies have shown that probiotic therapy can be used for different organophosphorus toxins, metal toxicity, and many medication toxicities (Feng et al., 2019). The proven molecular mechanisms of such a detoxification process, even in low-concentrations, of the toxins include that probiotics precipitate these compounds (Chen et al., 2022). Improving the gut microbiota with probiotics could be considered a promising therapy for neurodegenerative diseases, especially those triggered by neurotoxicity. Probiotic bacteria modulate the gut–brain axis. Owing to their anti-inflammatory and antioxidant activities, probiotics can help enhance memory functions, improve cognitive functions, and hence halt the development of neurodegenerative diseases, including AD (Arora et al., 2020). Lactobacillus plantarum is an example of probiotic bacteria that is found to restore gut microbiota in the AD model and protect from induced eye neurodegeneration in the AD model (Tan et al., 2020). It has been reported recently that Lactobacillus casei administration prevented neuronal death, decreased the accumulation of Aβ, and hyperphosphorylated p-tau. These probiotic bacteria protect against neuronal death through their antioxidant, anti-inflammatory, and immune-modulating properties and their ability to restore gut microbiota dysbiosis caused by Al neurotoxicity (Qiao et al., 2022). Metal chelation, a classical therapy for metal toxicity such as copper and aluminum, could be achieved through probiotic bacteria, e.g., L. rhamnosus (Lactobacillus rhamnosus) (Gaisawat et al., 2019).

Based on the aforementioned data, the current study aims to evaluate and provide mechanistic insights on the protective effects of sesamol and/or the probiotic bacteria L. rhamnosus against the behavioral, biochemical, and histopathological alterations centrally in the brain and peripherally in the liver of aluminum chloride (AlCl₃)-intoxicated rats.

In this work, the effects of sesamol, L. rhamnosus, and sesamol + L. rhamnosus were studied on the control groups, but none of these three groups showed significant differences from the control group in any of the measured parameters. Thus, these results were not displayed to avoid data complexity.

Despite the hazardous consequences of long-term exposure, Al cookware is still being used in rural areas owing to its low price. Al is highly distributed in the liver and brain tissues, leading to neurotoxicity, neurodegenerative diseases, and liver diseases (Congdon and Sigurdsson, 2018; Zhu et al., 2020). Using probiotics as an add-on therapy with herbal products may be regarded a promising avenue for attenuation of Al-induced neurotoxicity and neurodegenerative diseases. Herein, we investigated the protective effects of sesamol, probiotics, and their combination against Al-induced deleterious effects on the brain and liver, highlighting the mechanistic pathways contributing to their ameliorative effects.

Al neurotoxicity contributes to the accumulation of amyloid-β (Aβ) and the hyperphosphorylated tau (p-tau) protein (Hussien et al., 2018). Consequently, we measured Aβ and the p-tau protein as markers for evaluating the neuroprotective ability of the chosen drugs in order to develop a drug or regimen that can reduce the formation of Aβ or improve its clearance. Treatment with sesamol and/or the probiotic Lactobacillus rhamnosus (L. rhamnosus) showed anti-dementia properties by reducing the elevated dementia markers, and their combination showed the best results among the treatment regimens in comparison with the AlCl₃-intoxicated group. These results are in agreement with previous studies (Ohsawa et al., 2015; Liu et al., 2017b).

In the current study, Al-intoxicated rats revealed impairment in learning and memory, as well as lower activity and exploration, as depicted by MWM and Y-maze tests, respectively. These findings are consistent with publications by John et al. (2015), Thenmozhi et al. (2015), Soubh et al. (2021). Such behavioral disturbance was confirmed by the alteration of inflammatory, pro-inflammatory, and apoptotic biomarkers. The abnormal assemblies of Aβ and excessive phosphorylation of Tau were proven to affect neuronal plasticity and function, which are responsible for long-term behavioral disturbances (Soubh et al., 2021). Our proposed treatment with sesamol and/or L. rhamnosus (i.e., either monotherapy or combination therapy) prevented such deleterious behavioral effects of AlCl₃. Sesamol showed the ability to reduce cognitive impairment caused by environmental pollutants (John et al., 2015) or stress exposure (Kumar et al., 2013), which is consistent with our findings. In addition, previous reports highlighted the potential of certain Lactobacillus strain supplementation as a probiotic in the regulation of emotional behavior in stress-related disorders (Bravo et al., 2011; Karen et al., 2021).

Downregulation of the Wnt signaling balance has been interconnected with the development of Al-induced neurotoxicity (Mohamed et al., 2022). Therefore, upregulation of the Wnt signaling pathway prevents the cytotoxic effects of the accumulated Aβ (Toledo and Inestrosa, 2010). In the current work, AlCl₃ switched off the Wnt pathway as indicated by the upregulation of the level of GSK-3β, leading to the downregulation of free β-catenin. Sesamol alone or in combination with L. rhamnosus restored the basal levels of GSK-3β and β-catenin, halting the effects of AlCl₃. This effect contributed to the behavioral enhancement and reversed the impaired synaptic plasticity and memory deficit, which goes along with the previously reported importance of activation of Wnt signaling for reducing neurological disorders in AD (Vargas et al., 2014). To the best of our knowledge, there are no complete biochemical, histological, and behavioral studies for the effect of sesamol on the Wnt pathway in the AlCl₃-intoxicated rat model. Nonetheless, downregulation of GSK-3β levels and modulation of the Wnt pathway are reported to be protective in many neurodegenerative diseases, including AD (Toledo and Inestrosa, 2010), which adds value to our study by using sesamol.

Additionally, switching off Wnt/β-catenin signaling plays a crucial role in the propagation of neuroinflammatory mediators. It was reported earlier that either Aβ aggregation or increased levels of GSK-3β activate the glial cells, with the subsequent production of inflammatory mediators, such as IL-6 and TNF-α (Majdalawieh and Ro, 2015; Gan et al., 2021). In our study, we found a significant increase in the level of inflammatory mediators both centrally in the brain and peripherally in the liver in rats after AlCl₃ administration compared to the control group. However, sesamol alone or in combination with the chosen probiotic significantly decreased the unfavorable inflammatory condition in comparison to the AlCl₃-intoxicated group. Consistent with our results, sesamol inhibited amyloidogenesis and inflammation-induced memory impairment by inhibiting NF-κB and the production of inflammatory mediators (Liu et al., 2017a). Furthermore, a former study that used a probiotic mixture containing our chosen strain, L. rhamnosus, presented a reduction in inflammatory markers, which evoked improvement in memory function in the AD model of rats (Ohsawa et al., 2015). It has been proven that probiotics have a strong ability to restore the homeostasis of the gut microbiota and ameliorate cognitive impairment through both anti-inflammatory and antioxidant pathways (Gibbs et al., 1999; Consolo et al., 2009; Couto et al., 2014). Our study proved that the use of probiotics showed a superior effect over sesamol as an anti-inflammatory agent both centrally and peripherally.

Neuronal loss in Al-induced neurotoxicity is closely linked with apoptosis, which could induce memory loss and cognitive impairment (Maya et al., 2016). Notably, the accumulation of Aβ and p-tau proteins triggers apoptosis (Maurer et al., 2006; Green and Llambi, 2015; Wang et al., 2018). The accumulation of ROS may also initiate apoptosis (Hsin et al., 2008; Liu et al., 2020; Mesole et al., 2020). AlCl₃ resulted in high levels of apoptotic markers, caspase-3 and Bax, and lower levels of the anti-apoptotic protein Bcl-2 in the brain and liver compared to normal rats. Our histological findings showed that the cerebral neurons of the Al-intoxicated group had undergone extensive neuronal death.

This study showed the ability of sesamol and or L. rhamnosus to prevent programmed cell death in brain and liver tissues, as marked herein by the reduced levels of the apoptotic markers caspase-3 and Bax, together with an elevation in the anti-apoptotic marker Bcl-2, compared to the Al-intoxicated group. The anti-apoptotic power of sesamol has been previously reported (Hou et al., 2006; Gao et al., 2017). Sesamol’s anti-apoptotic effect in nerve cells may be mediated by molecular pathways that upregulate the anti-apoptotic protein Bcl-2 and inhibit the pro-apoptotic protein Bax (Abou-Zeid et al., 2021; Ruankham et al., 2021). As a result of sesamol’s antioxidant, anti-inflammatory, and anti-apoptotic properties, the administration of sesamol dramatically reduced Al-induced toxicity in the liver and brain. Additionally, Lactobacillus helveticus reduced lipopolysaccharide-induced hippocampus apoptosis via modulation of the gut–brain axis, implying that this probiotic and related strains may be useful in some neurodegenerative disorders (Mohammadi et al., 2019). Furthermore, L. rhamnosus has been shown to inhibit ROS release, enhance catalase, SOD, and BDNF levels, and regulate the Bax/Bcl-2 ratio (Tian et al., 2020; Kumar et al., 2022). Our results go along with these data and give the histopathological and behavioral output of these molecular mechanisms. Dubey et al. (2019) showed that some species of Lactobacillus can chelate heavy metals in the intestine of mice, such as cobalt and lead. This may reduce the toxicity of these heavy metals and protect the intestinal microflora. In our model, we administered AlCl₃ through the intraperitoneal route of administration. So, the main protection site is at the tissue level through the Wnt and inflammatory pathways. There is evidence of the ability of L. rhamnosus to chelate Al, a low-molecular-weight heavy metal. It may be an interesting point of research in the near future to study the effect of oral administration of L. rhamnosus on the Al serum and tissue levels.

In view of the notion that the liver is one of the most susceptible organs to the damaging effect induced by AlCl₃, and owing to its essential role in the clearance of circulating Aβ, we chose to investigate the detrimental effects of Al on the liver, with highlights on the effect of this hepatic injury on neurotoxicity induced by AlCl₃. Since the liver is a crucial participant in peripheral Aβ clearance, any disruption in this clearance could tip the delicate Aβ balance toward brain buildup. Moreover, increasing amyloid aggregation, neuroinflammation, apoptosis, and the disturbance in signaling molecules in different brain regions is thought to be connected to signals originating in the liver and gut microbiota; this is known as the gut microbiota–liver–brain axis (Daily et al., 2021). Previous reports showed that elevation in the AST/ALT ratio, a marker of liver function (Giannini et al., 1999), is associated with an elevation in circulating Aβ-40 levels (Wang et al., 2017), results that are quite related to ours.

One of the major pathways for inflammatory cytokine signal transduction is JAK-2/STAT-3 signaling (Nazeam et al., 2021). This cue affects cell proliferation, survival, development, and differentiation (Soubh et al., 2021). The AlCl₃-intoxicated group showed significant stimulation of JAK-2 and its sub-molecule, STAT-3, in our investigation, which was provoked by a large increase in the amount of IL-6β, an inflammatory cytokine, in liver tissue. Our results are in agreement with those of Li et al., 2018. Moreover, the concurrent treatment with sesamol or L. rhamnosus and their combination inhibited this gush and prevented its hepatotoxic effect compared to the AlCl₃-intoxicated group. Formerly, sesame seeds hampered thyroid cell growth via inhibition of STAT-3 translocation. Moreover, probiotics have been shown to reduce Helicobacter pylori infection by inhibiting JAK-2 via their anti-inflammatory properties (Lee et al., 2010).

Nuclear receptors like PPARs control variable pathways such as inflammatory responses and metabolic detoxification (Li and Guo, 2011). Thus, abnormal levels of PPARs are reported in several liver diseases (Peyrou et al., 2012). In the current work, we investigated PPAR-γ as one of the most important functional isoforms in the PPAR family that controls various cellular functions (Li and Guo, 2011; Tyagi et al., 2011; Peyrou et al., 2012), and AlCl₃-intoxicated rats exhibited a marked decline in PPAR-γ expression compared to healthy rats. Previously, sesamol and sesame oil treatments were associated with upregulation of liver PPAR-γ (Majdalawieh and Ro, 2015). This is consistent with our results, which proved that sesamol administration restored the contents of PPAR-γ. In addition, administration of the probiotic L. rhamnosus was reported to increase the expression of PPAR-γ in the liver. Based on our data and previous studies, L. rhamnosus and sesamol alone have significant potential to reduce liver damage by inducing PPAR-γ activity and thus inflating their anti-inflammatory abilities (Lecarpentier and Vallée, 2016).

α-SMA is one of the markers that monitors liver fibrosis in patients with non-alcoholic fatty liver disease (NAFLD) (Di Cerbo et al., 2016; Patel et al., 2020). In this investigation, the administration of sesamol or L. rhamnosus alone or in combination resulted in considerable downregulation of α-SMA protein expression in the AlCl₃-intoxicated group. According to the best of our knowledge, this is the first report on the effect of co-administration of sesamol and L. rhamnosus on α-SMA. The various anti-inflammatory potentials of both sesamol and L. rhamnosus were marked by inhibiting NF-κB, JAK-2/STAT-3 and increasing PPAR-γ hubs, which contributed to α-SMA downregulation; as α-SMA increases with chronic inflammation of the liver, these findings are in line with those of Periasamy et al. (2014) and Elalfy et al. (2019).

MMP-2 is one of the major enzymes that belong to the MMP family, which is a family of endopeptidase-dysregulated enzymes that increase during inflammation. On the other hand, TIMPs control the expression and activity of MMPs (Gibbs et al., 1999; Consolo et al., 2009). MMPs are reported to be found at various stages of hepatic illnesses, ranging from inflammation, liver injury, cirrhosis, fibrosis, and hepatocarcinogenesis to recovery and hepatic regeneration (Geervliet and Bansal, 2020).

In our study, there was a massive increase in liver expression of MMP-2 and TIMP-1, reflecting the inflammatory effect of AlCl₃ on the liver. Administration of sesamol alone or with L. rhamnosus significantly ceased increased expressions of both MMP-2 and TIMP-1. Previous reports documented the ability of sesamol to hamper elevated MMP expression in various tissues (Lu et al., 2011; Periasamy et al., 2014). These findings provided plausible justification for the amelioration of AlCl₃-mediated perturbation in liver function tests (AST, ALT, and bilirubin) by sesamol and/or L. rhamnosus documented herein.

In comparison to the AlCl₃-intoxicated group, the hepatoprotective and neuroprotective powers of sesamol and/or L. rhamnosus were investigated, and they were able to preserve and correct hepatic and brain tissue scores by preventing histological abnormalities. Additionally, this tissue-preserving potential of both sesamol and L. rhamnosus can be attributed to their anti-dementia, anti-inflammatory, and anti-apoptotic properties and the modulation of various signaling molecules in both the brain and liver (Di Cerbo et al., 2016; Khadira Sereen et al., 2017; Ezdini et al., 2020).

Sesamol alone or in combination with the probiotic L. rhamnosus prevented cognitive dysfunction and preserved brain tissue, offering neuroprotection by anti-dementia, anti-inflammatory, and anti-apoptotic properties, modulation of the gut–liver–brain axis, Wnt/β-catenin/GSK-3β, inflammatory, and apoptotic pathways. In addition, these regimens, either single or combined, blocked the peripheral deleterious effect of AlCl₃ on the liver, as exemplified herein by liver probing, where the hepatic expression of inflammatory mediators, apoptotic markers, fibrotic biomarkers, and markers of JAK-2/STAT-3 and PPAR-γ pathways was modulated, and hepatic histopathology was improved. Accordingly, we highly recommend performing clinical trials using sesamol and/or L. rhamnosus as add-on agents in the treatment protocol of Al-induced neurodegenerative diseases.