Ivermectin for Alzheimer’s Disease

Dr. Weeks Comment: None of the FDA-approved drugs for Alzheimer’s disease have been satisfactory. Repurpose drugs are promising. Read a little bit about the recently demonized but historically highly acclaimed medicine Ivermectin, and how it can help people with dementia and Alzheimer’s disease.

 

Article highlights

• Ivermectin is an anti-parasitic drug that has recently received attention for its potential non-parasitic effects and applications.
• Recently, our research team has reported the neuroprotective effects of ivermectin in cerebral ischemia-reperfusion.
• The present study for the first time indicates the protective effect of ivermectin on STZ-induced Alzheimer’s disease in rats.
• Ivermectin administration reduces Aβ plaques and histopathological changes.
• Ivermectin administration reduces acetylcholinesterase enzyme activity, as well as improves memory and learning.

These results highlight the potential of ivermectin as a therapeutic agent in the treatment of Alzheimer’s disease, warranting further studies to elucidate its mechanisms.

 

 

https://www.tandfonline.com/doi/full/10.1080/17582024.2025.2554374#d1e233

 

 

Neuroprotective effects of ivermectin on Alzheimer’s model induced by streptozotocin in rats

Neda Farajpour & Hamid Soraya

 

ABSTRACT

Background

Alzheimer’s disease is a neurodegenerative condition characterized by memory deficits and cognitive decline. Ivermectin, an antiparasitic agent, has shown neuroprotective effects. The present study was conducted to determine the protective effects of ivermectin in a streptozocin-induced Alzheimer’s model in rats.

Methods

Alzheimer’s model was induced by bilateral intracerebroventricular injection of streptozocin (3 mg/kg BW, 2 doses). Ivermectin was administered intraperitoneally at a dose of 2 mg/kg. On day 19, after behavioral memory and learning tests, the samples were collected for histological and enzymatic studies.

Results

Ivermectin reduced the histopathological changes, including pyknotic and dead neurons and the accumulation of Aβ plaques. Ivermectin administration also reduced serum (p < 0.0001) and brain tissue (p < 0.01) acetylcholinesterase activity as well as improved learning (p < 0.05) and spatial memory (p < 0.0001).

Conclusions

Ivermectin demonstrates protective effects in the STZ-induced Alzheimer’s model by reducing pathological changes and Aβ plaques, acetylcholinesterase activity, as well as improving memory and learning.

 

Plain Language Summary

Alzheimer’s disease is a neurological disease and the most common cause of dementia in the elderly. Despite progress in Alzheimer’s research, there is no definitive cure for this disease, and therefore, more research is needed to find new drugs to treat this disease. Our previous study showed the neuroprotective effects of ivermectin in ischemic stroke. Hence, our aim in the present study was to investigate the possible beneficial and therapeutic effects of ivermectin in Alzheimer’s disease. For this purpose, we first induced Alzheimer’s in rats and then treated them with ivermectin at a dose of 2 mg/kg for three days. The results we obtained showed that administration of ivermectin can reduce brain tissue damage and improve memory and learning. Ivermectin also caused a decrease in the activity of the acetylcholinesterase enzyme. This enzyme breaks down acetylcholine, a neurotransmitter that plays a crucial role in memory and learning. Therefore, a decrease in the activity of this enzyme reduces the loss of acetylcholine. This study concludes that ivermectin could be considered as a potential treatment for Alzheimer’s disease. It should be noted that this study was conducted on laboratory animals and further studies are needed to confirm its use in humans.

 

1. Introduction

Alzheimer’s disease is the most prevalent neurodegenerative disorder that is associated with impaired memory and cognitive function and is considered as a phenomenon of the 21st century [Citation1]. It is also the most common reason for dementia in the elderly population [Citation2]. According to the published statistics, about 2% of people in developed countries suffer from Alzheimer’s disease [Citation3]. Nonetheless, there exist no efficacious pharmacological agents capable of halting or reversing the advancement of the disease. Therefore, the search for effective treatment and medication is essential. Alzheimer’s disease pathologically defined by the extracellular accumulation of amyloid β (Aβ) into senile plaques, alongside intracellular deposition of hyperphosphorylated tau (pTau) manifesting as neurofibrillary tangles. In recent years, research has demonstrated that environmental inflammation, which precipitates the activation of the innate immune response and the production of pro-inflammatory cytokines, constitutes one of the detrimental elements that may exacerbate the pathogenesis of Alzheimer’s disease [Citation4]. Clinically, individuals afflicted with Alzheimer’s disease exhibit progressive memory impairment accompanied by diverse cognitive dysfunctions [Citation5]. Extensive studies are being conducted on Alzheimer’s disease, and some studies have shown that reducing the accumulation of Aβ plaques in the brain, has a beneficial effect on the disease and improve the cognitive performance of patients in clinical evaluations. Moreover, these plaques are key in inducing neuroinflammation and neuron death [Citation6,Citation7].

Acetylcholinesterase is a cholinergic enzyme found in neuromuscular postsynaptic junctions, particularly in muscles and nerves. This enzyme hydrolyzes acetylcholine to choline and acetic acid. The main role of acetylcholinesterase is to interrupt neuronal signaling in the synaptic cleft to prevent the activation of surrounding receptors by acetylcholine [Citation8]. In this context, Alzheimer’s disease is also delineated by the degeneration of cholinergic neurons alongside their neural projections originating from the basal forebrain. Consequently, diminished cholinergic activity is associated with cognitive deficits observed in affected individuals and is linked to reduced concentrations of the acetylcholine, choline acetyltransferase (which serves as the rate-limiting enzyme in the biosynthesis of acetylcholine), and the enzyme responsible for the hydrolysis of acetylcholine [Citation9]. Acetylcholinesterase (AChE) hydrolyzes acetylcholine, a neurotransmitter important in learning and memory. In Alzheimer’s disease, the levels and activity of this enzyme are significantly altered. Increased AChE activity is associated with reduced cholinergic transmission, which is one of the main causes of cognitive impairment in the disease. AChE inhibitors are one of the main therapeutic strategies for improving cognitive function in Alzheimer’s patients. By inhibiting this enzyme, these drugs increase the duration of acetylcholine’s residence in the synapse and enhance cholinergic transmission [Citation10,Citation11].

Ivermectin (IVM), or 22,23-dihydro-ivermectin B1, was first isolated from Streptomyces avermitilis [Citation12]. It’s an antiparasitic drug whose mechanism of action involves affecting glutamate-gated chloride channels and gamma-aminobutyric acid (GABA) receptors in the nervous system of parasites. Ivermectin acts as an agonist of GABA receptors, disrupting the transmission of nerve signals associated with this receptor [Citation13,Citation14]. GABA receptors are divided into GABA-A and GABA-B. GABA-A is considered to be involved in fast synaptic inhibition [Citation15]. GABAergic neurons exhibit a broad network of synaptic connections to cholinergic and glutamatergic neurons. Malfunction of the GABAergic system has the potential to induce cognitive deficits. A significant decrease in GABA levels has been reported in severe Alzheimer’s cases, which may underlie its behavioral and psychological symptoms [Citation3]. Moreover, in a study it was observed that ivermectin was effective as a moderate inhibitor in eliminating high doses of nicotine-induced toxins in the hippocampus region [Citation16]. Also, our research team has been reported that three-day administration of ivermectin demonstrates neuroprotective effects in cerebral ischemia-reperfusion [Citation17].

Considering the reported neuroprotective effects of ivermectin in previous studies, as well as the effect of GABA in Alzheimer’s disease, and that one of the mechanisms of ivermectin is the effect on GABA receptors, our hypothesis was that ivermectin could have beneficial effects in Alzheimer’s disease. Therefore, the present study aimed to investigate the effects of ivermectin on the histopathology and number of hippocampal Aβ plaques, activity of acetylcholinesterase enzyme and brain myeloperoxidase enzyme, as well as memory and learning in male Wistar rats with Alzheimer’s disease.

2. Materials and methods

2.1. Animals

In this study, 24 male Wistar rats (weighing 250 to 300 grams, 8 to 10 weeks) were used. The animals were purchased from the animal house of our university and were kept at a standard environment with a free access to food and water. The ethics committee of Urmia University of Medical Sciences approved this study (code: IR.UMSU.AEC.1402.005).

2.2. Experimental design

In this study, male Wistar rats were divided randomly into four groups (n = 6): In group 1 (control group) the animals underwent sham surgery and were left untreated for the entire period of study. In group 2 (IVM group), animals underwent sham surgery and received ivermectin intraperitoneally (ip) at a dose of 2 mg/kg/day for 3 days. Rats in group 3 (Alzheimer’s group) received 3 mg/kg bilateral intracerebroventricular (ICV) injection of streptozocin in two doses, and group 4 (Alzheimer’s group treated with ivermectin), received 3 mg/kg bilateral intracerebroventricular injection of streptozocin in two doses and also ivermectin intraperitoneally at a dose of 2 mg/kg daily for three days after surgery. Overall, 3 rats in the Alzheimer’s group and 2 rats in the ivermectin-treated group died during the study, and were immediately replaced.

Then, on the 19^th day, after performing memory and learning tests with the Barnes Maze test, the blood samples were taken from portal vein and then were euthanized to collect the brain. After isolation, the brain tissues were quickly washed in normal saline to remove blood and other debris, and then were kept frozen at −80°C until further analysis.

2.3. Surgery

After deep anesthesia of the rats with a mixture of ketamine (80 mg/kg) and xylazine (10 mg/kg ip), which is characterized by the disappearance of the pain reflex, the animals were fixed in a stereotactic apparatus and the surface of the skull was cleaned, then an incision is made in the sagittal area of the midline and two holes will be made in the skull. The coordinates for the ICV were determined to be 0.72 mm posterior to the Bregma, 1.5 mm lateral to the sagittal suture, and 3.6 mm ventral to the brain’s cortical surface. A guide cannula was inserted into the perforated region of the skull, and streptozocin (STZ) was administered through a Hamilton syringe utilizing a microinjection pump. The needle was retained in situ for an additional duration of 2 minutes, after which the guide cannula was extracted and the overlying skin was sutured. During this experiment, ICV injection of STZ (3 mg/kg) divided into two 1.5 mg/kg doses and given bilaterally at day 1 and day 3. After the surgery, tetracycline spray was applied topically to their wounds, and penicillin was injected intramuscularly to prevent infection. For the duration of the wound healing period, which lasted approximately two weeks, the rats were maintained in isolation and in separate cages [Citation18,Citation19].

2.4. Barnes test

The Barnes maze test was started 14 days after STZ injection (between days 15 to 18) to examine spatial learning and memory in rats. In this behavioral test, a large circular plate with 20 small circles around it and one of these circles has a special chamber for the rat is placed on four rotating legs at a distance of 89 cm from the floor. Two 120-watt lights are installed in the corners of the room and 8 visual signs are installed on the wall of the room. This test was performed over 4 days, including the habituation day, the first and second days of training, and finally the test day. On the habituation day, the animal is placed under a clear glass cup for 30 seconds and each rat is given a time of 3 minutes to enter the hole independently. If it does not work, we enter it with a tap. It remains in the cage for 1 minute. On the first day of training, the animal is placed in a cardboard box in the center of the maze for 15 seconds, and then a white noise is played when the cardboard is removed. Each rat is given 3-minute opportunities to find the hole independently. It remains in the cage for 1 minute and the buzzer is turned off. The second day of training is similar to the first day, except that each rat has two 2-minute opportunities to find the cage or else it is guided. On the test day, the cage is removed and each rat is given 2 minutes to turn around the maze. Given that the cage has been removed, the time it takes the rat to turn around in the cage and the number of times it dips its head into the cage circle are measured [Citation20].

2.5. Histopathology

At the end of study, the brain tissue was removed rapidly and fixed in 10% formalin for histopathological examination. For this, the brain samples were sectioned at 5 µm slices and hematoxylin and eosin (H&E) staining and also thioflavin S staining were used. Two trained persons (one of which was a pathologist) investigated the histopathological changes including pyknotic, wrinkled and dead neurons for H & E staining and the number of Aβ plaques for thioflavin S staining [Citation21–23].

2.6. Acetylcholinesterase

Acetylcholinesterase (AChE) which hydrolyzes acetylcholine, a neurotransmitter important in learning and memory, was measured in both serum and hippocampus tissue according to the kit’s instruction (Biorexfars B×C0801kit).

2.7. Myeloperoxidase assay

The level of myeloperoxidase activity, as a neutrophil marker, was measured according to the kit’s instruction (Nampox kit NS-15062). In brief, 10 to 20 mg of frontal brain tissue sample was homogenized in 1 ml of sample buffer1X and according to the kit’s instructions, 10 μL of sample was mixed with 80 μL of diluted R1 kit and incubated for 10 minutes at room temperature and away from light. Next, 110 μL of R2 kit was prepared and added to the mixture. Then the plate was measured using a microplate reader at a wavelength of 650 nm at the first (60 seconds) and tenth (600 seconds) minute and then the MPO amount was calculated.

2.8. Statistical analysis

Data are expressed as mean ± standard error of the mean (SEM). The normality of distribution was assessed using the Kolmogorov – Smirnov test. One-way analysis of variance (ANOVA) was applied to identify significant differences, followed by Tukey’s post hoc test for intergroup comparisons. Statistical analyses were performed using GraphPad Prism version 9.0 (GraphPad Software, San Diego, CA, USA), with a significance threshold set at p < 0.05.

3. Results

3.1. The effect of ivermectin on learning and memory

In order to determine the learning and memory, Barnes behavioral test was used. This test was performed for 4 days including the habituation day, the first and second days of training, and the last day of testing. On the second day of evaluation, our results showed that the group receiving ivermectin (IVM) 2 mg/kg had a significantly longer latency time compared to the control group (p < 0.01), but a shorter latency time compared to the ALZ group. Also, the ALZ group had a significantly longer latency time compared to the control group (p < 0.001), which confirms the cognitive deficit of this model. Finally, the ALZ + IVM 2 mg/kg group had a shorter latency time compared to the ALZ group, but this decrease was not significant. On the third day of evaluation, our results showed that, as on the second day, the shortest latency time was for the control group and the longest latency time was for the ALZ group, which also had a statistically significant difference (p < 0.001). The ALZ + IVM 2 mg/kg group had a significantly (p < 0.05) shorter latency compared to the Alzheimer’s group, indicating the protective and beneficial effect of IVM on learning (Figure 1(A)).

Figure 1. The effect of ivermectin on learning and memory in streptozocin-induced Alzheimer’s disease. A: the latency, the time it took each rat to reach the cage location, was recorded for 2 days at specific times of the day. B: time in target quadrant: percentage of time each rat spent in the target quadrant (where the cage was previously located). Data are reported as mean ± standard error of the mean (SEM) (n = 6). One-way ANOVA and Tukey’s post hoc test was used for statistical analysis. ^#p < 0.05, **p < .01, ***p < .001, ****p < .0001; IVM: ivermectin, ALZ: Alzheimer’s disease.

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The percentage of time each rat spent in the target quadrant (where the cage was previously located) was introduced as time spent in target quadrant. Our results showed that the least time spent by rats in the target quadrant was related to the ALZ group and was significantly less than the control group (p < 0.0001). It was also observed that the time in the ALZ + IVM 2 mg/kg group was significantly higher compared to the ALZ group and could indicate an improvement in the spatial memory of rats after treatment (p < 0.05 ((Figure 1(B)).

3.2. The effect of ivermectin on histopathological changes

After sampling, brain tissues were examined using H&E staining and our results showed that in the control group and ivermectin alone treated group, neurons were healthy, and in the Alzheimer group, there were many wrinkled and dead neurons. Administration of ivermectin in rats induced with Alzheimer’s disease improved the histopathological changes and the number of pyknotic and dead neurons were reduced compared to the Alzheimer’s group (Figure 2).

Figure 2. Histopathological changes of rat brain tissues in different experimental groups.

↑ indicates healthy neurons and the ▴ indicates pyknotic, wrinkled and dead neurons. Healthy hippocampus (A) Alzheimer’s group (B) ivermectin alone group (C) Alzheimer group treated with ivermectin (D).

In order to evaluate the effect of ivermectin on Aβ plaques in the brain tissue of rats with streptozocin-induced Alzheimer’s disease, thioflavin S staining was used, as shown in Figure 3. The Analysis of images in each group showed that the highest amount of plaques was observed in the ALZ group and the lowest amount of plaques was observed in the 2 mg/kg IVM group. It was also observed that the amount of Aβ plaques in the brain tissue was reduced in the ALZ + IVM 2 mg/kg group compared to the ALZ group (Figure 4).

Figure 3. Immunofluorescence micrographs of brain tissue in different groups, with arrows indicating positive reactions with thioflavin S.

Figure 4. Fluorescent reaction with thioflavin S in rat brain tissues in different experimental groups.

3.3. The effect of ivermectin on serum and brain tissue acetylcholinesterase (AChE) activity

Serum AChE activity showed that the Alzheimer’s (ALZ) group had a significant increase in comparison to the control group (p < 0.0001). The results showed a significant decrease in AChE activity in the ALZ + IVM 2 mg/kg treated group compared to the ALZ group (p < 0.05) (Figure 5(A)). Examination of AChE activity in hippocampus tissue samples showed that the Alzheimer’s (ALZ) group had a significant increase in the level of this enzyme compared to the control group (p < 0.01) and administration of ivermectin to the STZ-induced Alzheimer’s disease group (ALZ + IVM 2 mg/kg), reduced the AChE activity in comparison to the Alzheimer’s group (p < 0.05) (Figure 5(B)).

Figure 5. Effect of ivermectin on the activity of acetylcholinesterase (AChE) in serum (A) and hippocampus tissue (B). Data are reported as mean ± standard error of the mean (SEM) (n = 6). One-way ANOVA and Tukey’s post hoc test was used for statistical analysis. ^#p < 0.05 **p < .01, ***p < .0001; IVM: Ivermectin, ALZ: Alzheimer’s disease.

3.4. Effect of ivermectin on myeloperoxidase (MPO) enzyme activity

MPO levels in the brain tissue samples showed that the activity of this enzyme was significantly reduced in the Alzheimer’s (ALZ) group (p < 0.05). On the other hand, the IVM 2 mg/kg group was not significantly different from the control group. In the ALZ + IVM 2 mg/kg group, MPO levels increased compared to the Alzheimer’s group (p < 0.05), so that this value was close to the control level (Figure 6).

Figure 6. Effect of ivermectin on the activity of myeloperoxidase (MPO) in brain tissue. Data are presented as mean ± standard error of the mean (SEM) (n = 6). One-way ANOVA and Tukey’s post hoc test was used for statistical analysis. ^#p < 0.05, **p < .05; IVM: ivermectin, ALZ: Alzheimer’s disease.

4. Discussion

Alzheimer’s disease is a neurodegenerative disease determined by the accumulation of Aβ plaques and neurofibrillary tangles, coupled with increased acetylcholinesterase (AChE) activity and chronic inflammation [Citation24]. Recent evidence suggests that the dysfunction of the GABAergic system plays a crucial role in cognitive impairment observed in Alzheimer’s disease, as severe cases have been associated with significant reductions in GABA levels. In this context, ivermectin – a drug traditionally known for its antiparasitic properties – has emerged as a compound of interest due to its ability to modulate GABA receptors [Citation12].

In mammals, ivermectin exhibits a multifaceted mechanism of action. It not only activates several members of the Cys-loop receptor family, including GABA-A, glycine, and nicotinic acetylcholine receptors, but also activates the P2×4receptor [Citation13,Citation14]. Based on these diverse pharmacological actions, our study was designed to evaluate the neuroprotective potential of ivermectin in an STZ-induced Alzheimer’s disease model. The present results showed that ivermectin administration, reduced Aβ plaques, histopathological changes, acetylcholinesterase enzyme activity, as well as improved memory and learning. These indicate the protective and therapeutic effect of ivermectin on STZ-induced Alzheimer’s disease in rats.

Ivermectin is a lipophilic compound characterized by limited permeability to the central nervous system (CNS), where P-glycoprotein in endothelial cells of the blood-brain barrier limits drug uptake into the brain. Consequently, to assess the central nervous system effects of this pharmacological agent, higher doses are administered. Recently, we have elucidated the neuroprotective properties of ivermectin administered at a dose of 2 mg/kg (standard therapeutic dose is about 0.2 mg/kg) in the context of cerebral ischemia, evidenced by a decrease in infarct size, histopathological changes such as the accumulation of cerebral leukocytes and edema, as well as diminished lipid peroxidation and myeloperoxidase activity. Furthermore, an additional investigation has revealed the pronounced anticonvulsant capabilities of ivermectin, thereby corroborating the assertion that ivermectin manifests various inhibitory effects within the mammalian central nervous system, potentially through its interaction with both GABA-sensitive and GABA-insensitive chloride channels. These observations imply that high doses of ivermectin yield adequate therapeutic concentrations in the brain and effectively target the compromised regions [Citation17,Citation25,Citation26].

In a streptozocin (STZ)-induced Alzheimer’s model, there is a notable elevation in acetylcholinesterase (AChE) activity within the hippocampal region, which significantly contributes to the deterioration of cognitive functions. The administration of STZ via intracerebroventricular (icv) methods disrupts the metabolism of glucose in the brain, resulting in deficits within the cholinergic system and an augmentation of AChE activity. The increased activity of AChE hastens the catabolism of acetylcholine, a neurotransmitter vital for cognitive processes such as learning and memory, thereby exacerbating cognitive deficits. Furthermore, oxidative stress and/or the generation of reactive oxygen species (ROS) may be implicated in the heightened AChE activity observed in STZ-induced Alzheimer’s disease [Citation27,Citation28]. Consistent with previous studies by Silva et al. and Ali et al. our Alzheimer’s disease model demonstrated significantly elevated AChE levels in both serum and brain tissue [Citation29,Citation30]. Remarkably, treatment with ivermectin led to a significant reduction in AChE activity in the Alzheimer’s disease group. This reduction might be mediated through different mechanisms. Evidence suggests that ivermectin may inhibit acetylcholinesterase (AChE), particularly when administered at high concentrations or through repeated exposure. Additionally, it functions as a positive allosteric modulator of the alpha7 nicotinic acetylcholine receptor, thereby enhancing receptor activity. Nonetheless, further research is required to fully understand the interplay between ivermectin and STZ in the context of AChE activity and its implications in Alzheimer’s disease [Citation31,Citation32]. The dual mechanism not only enhances cholinergic transmission by increasing acetylcholine availability but also helps mitigate the neurotoxic cascades induced by the excessive generation of AChE-derived peptides [Citation33]. This dual approach is comparable to the mechanism exploited by established treatments like donepezil, which target cholinergic deficits in Alzheimer’s disease [Citation34].

In Alzheimer’s disease, chronic brain inflammation is a critical driver of neurodegeneration. The inflammatory milieu involves the recruitment of peripheral immune cells into the brain [Citation35,Citation36] and the localization of MPO not only in Aβ plaques but also in tau tangles and within neurons, astrocytes, and microglia [Citation37–39]. Ivermectin’s capacity to modulate these inflammatory markers underscores its potential immunomodulatory role in Alzheimer’s disease.

Neutrophil migration toward Aβ plaques in Alzheimer’s disease models has been reported. Moreover, MPO-deficient Alzheimer’s disease model mice show better cognitive outcomes and reduced inflammation [Citation40]. Accumulation of aggregated Aβ plaques is a major cause of cognitive dysfunction in Alzheimer’s disease. The hippocampus and neocortex are the main targets for Aβ aggregates [Citation41]. In Alzheimer’s disease, myeloperoxidase (MPO) is commonly elevated [Citation42]. Contrary to some previous reports, in this study we reported reduced level of MPO activity in Alzheimer’s disease model in rats. In our opinion, the migration of neutrophils and their accumulation in specific parts of the brain in the streptozotocin-induced Alzheimer’s model has caused the level of the myeloperoxidase enzyme to be low in the frontal part of the brain that we sampled. Moreover, ivermectin treatment increased the level of myeloperoxidase enzyme, which may indicate the immunomodulatory effects of ivermectin in this disease model.

Of course, on the other hand it has been reported that in multiple sclerosis disease, serum MPO levels were significantly lower than in healthy controls. Also in some animal models, deletion of MPO has led to the severity of symptoms and increased mortality. MPO-deficient mice developed MS symptoms more frequently and earlier than normal mice, and the severity of the disease and the degree of paralysis of the lower limbs were also greater [Citation43,Citation44].

Behavioral assessments in our study revealed prolonged latency times during learning tasks in Alzheimer’s disease group, indicative of severe cognitive deficits. On the other hand, ivermectin treatment (in ALZ + IVM group) resulted in a notable reduction in these latency times and an improvement in spatial memory performance, although complete restoration to control levels was not achieved. These findings are consistent with observations made by Alavi et al. [Citation45], who reported that levetiracetam, an anticonvulsant drug known to indirectly affect the GABAergic system, enhanced cognitive performance in an STZ-induced Alzheimer’s disease model. Levetiracetam was shown to reduce AChE activity, proinflammatory cytokine levels (IL-1β, IL-6, TNF-α), and tau hyperphosphorylation, thereby improving learning and memory. The similarities between the effects of levetiracetam and ivermectin in modulating the GABA system and cholinergic signaling suggest that ivermectin’s therapeutic potential may be partly mediated through similar indirect mechanisms [Citation46].

Interestingly, it was observed that ivermectin administration (in the IVM group) caused impairment in memory and learning. Purinergic receptors are widely implicated in cognitive processes, both in normal and disease states. Among these, P2XRs are deeply involved in learning processes [Citation47]. Moreover, it was reported that the neuronal A2A receptor, a purinergic receptor, promotes loss of synapses in the hippocampus and worsens spatial memory deficits in mice with no effect on hippocampal Aβ plaque accumulation [Citation48], which is consistent with our results. Ivermectin acts as a positive allosteric modulator of P2X4Rs. Given that ivermectin acts on different receptors, its effects on the CNS are complex. In this case, we believe that in normal (non-Alzheimer’s) conditions, the stimulatory effects of ivermectin on purinergic receptors predominate, causing memory and learning deficits without inducing structural changes in the brain, although further studies are needed to confirm this accurately.

Histopathological examination of brain tissue provides compelling evidence for the neuroprotective effects of ivermectin. In our study, ivermectin-treated rats with Alzheimer’s disease displayed a significantly lower number of pyknotic and dead neurons compared to that received STZ alone (Alzheimer’s disease group). In the study by Seyed Abadi et al. the results showed that treatment with ivermectin resulted in a significant decrease in myeloperoxidase activity and an increase in memory and learning function compared to the control group, and neuroprotective effects were evident [Citation18].

The STZ-induced Alzheimer’s disease model effectively mirrors key pathological features of human Alzheimer’s disease, including oxidative stress, brain atrophy, neuronal loss, and the deposition of Aβ and hyperphosphorylated tau [Citation49]. Consistent with our results, Correia et al. provided evidence that STZ disrupts mitochondrial function, leading to the accumulation of Aβ1–42 and the formation of Aβ in both the hippocampus and cortex [Citation50]. Paidi et al. further reported significant accumulation of Aβ (Aβ1–42) and hyperphosphorylated tau proteins in STZ-treated animals, thereby reinforcing the validity of this model in recapitulating human pathology [Citation51]. The formation and accumulation of Aβ plaques are central to Alzheimer’s disease pathology. In our study, thioflavin S staining revealed that ivermectin-treated rats had a marked reduction in hippocampal Aβ plaques compared to untreated Alzheimer’s disease rats. Biswas et al. [Citation52] showed that STZ-induced increases in AChE activity and Aβ deposition could be significantly mitigated by donepezil. Similarly, Pilipenko et al. [Citation53] found that diazepam not only modulated AChE and GABA biosynthesis but also improved memory and learning functions, thereby supporting the potential of pharmacological interventions that target multiple pathways in Alzheimer’s disease.

Although this study for the first time showed the therapeutic effects of ivermectin in STZ-induced Alzheimer’s disease, but has some limitations. This study focused primarily on biochemical and histopathological markers, and further investigations incorporating molecular analyses could provide deeper insights into the underlying mechanisms of ivermectin’s effects. Also, in vivo imaging has not been performed to demonstrate structural or functional changes. Additionally, we did not measure serum or brain ivermectin levels in this study.

5. Conclusion

In conclusion, our findings demonstrate that ivermectin exerts significant neuroprotective effects in the STZ-induced Alzheimer’s disease model by reducing Aβ plaque deposition, histopathological changes, and AChE enzyme activity and improving learning, memory, and cholinergic signaling. Collectively, these results highlight the potential of ivermectin as a therapeutic agent in the treatment of Alzheimer’s disease, warranting further studies to elucidate its mechanisms and assess its clinical applicability.

Article highlights

• Ivermectin is an anti-parasitic drug that has recently received attention for its potential non-parasitic effects and applications.
• Recently, our research team has reported the neuroprotective effects of ivermectin in cerebral ischemia-reperfusion.
• The present study for the first time indicates the protective effect of ivermectin on STZ-induced Alzheimer’s disease in rats.
• Ivermectin administration reduces Aβ plaques and histopathological changes.
• Ivermectin administration reduces acetylcholinesterase enzyme activity, as well as improves memory and learning.
• These results highlight the potential of ivermectin as a therapeutic agent in the treatment of Alzheimer’s disease, warranting further studies to elucidate its mechanisms.

 

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