Punicic Acid And Its Role in The Prevention Of Neurological Disorders: A Review Part 3

3.2. Punicic Acid Effects on Neurodegenerative Disease

Punicic acid could be related to neurodegeneration prevention through several different pathways, including (1) intracellular mechanisms related to oxidative damage through peroxisome proliferator-activated receptor (PPAR)s and high-density lipoprotein (HDL) associated paraoxonase 1 (PON1); (2) local tissue environment such as synaptic function via calpains, and (3) systemic environment such as inflammation and lipid metabolism via PPARs and glucose metabolism with glucose transporter type 4 (GLUT4) (Table 1). 

Exosomes are substances within cells that play an important role in maintaining the normal physiological functions of cells. Research in recent years has found that peroxisomes are closely related to human memory and play an important role in improving human cognitive abilities.

First, exosomes can promote energy metabolism in cells and increase the body's energy level. This is especially obvious in the human brain because the brain is one of the most complex organs in the human body and requires a large amount of energy to support people's thinking, memory, and other functions. If the level of peroxisomes in the body can be effectively maintained, people's memory will be more stable and long-lasting.

Secondly, exosomes can promote the removal of free radicals in the body and prevent cells from being damaged by free radical attacks. Free radicals are products of cell metabolism. They exist in huge amounts in the human body and can damage the structure and function of molecules within cells. If the peroxisomes in the body can effectively remove these free radicals, the health and stability of cells can be maintained, thereby improving people's memory and cognitive abilities.

Finally, oxisomes can also improve people's antioxidant capacity, thus protecting the body from disease. People's health status is closely related to memory. If the body is in a healthy state, people's memory and cognitive abilities will also be stronger. Oxisosomes are good antioxidants that protect the body from free radicals and prevent the body from becoming weak due to disease.

In short, exosomes have a very significant impact on human memory and cognitive abilities. They can maintain the normal metabolism of cells, protect cells from free radicals, and improve human antioxidant capacity. Therefore, we should actively maintain the levels of peroxisomes in the body to further improve our memory and cognitive abilities. It can be seen that we need to improve memory, and Cistanche deserticola can significantly improve memory, because Cistanche deserticola can also regulate the balance of neurotransmitters, such as increasing the levels of acetylcholine and growth factors. These substances are very important for memory and learning. In addition, Cistanche deserticola can also improve blood flow and promote oxygen delivery, which can ensure that the brain receives sufficient nutrients and energy, thereby improving brain vitality and endurance.

Click know 10 ways to improve memory

Punicic acid can act as an agonist of PPARγ, increasing mRNA expression of PPAR-α, PPAR-β, PPAR-γ, and PPAR- γ, and bind to both PPAR- γ and PPAR-α [83,84]. It increases GLUT4 protein expression [85] and increases the anti-oxidative properties of HDL and PON1 activity [86,87]. 

Finally, punicic acid can act as an inhibitor of calpain, which plays a key role in ROS generation, and calpain may play a role in mitochondrial ROS generation and HDL degradation [88].

3.2.1. Punicic Acid Increases Expression of Peroxisome Proliferators Activated Receptors (PPARs)
There is a relationship between the role of PPARs such as PPAR-α, PPAR-β/δ, and PPAR-γ and neurodegenerative disease, particularly Alzheimer's. Inside the brain, activities attributed to PPAR-α include the reduction in oxidative stress, neuroinflammation, tau hyperphosphorylation, less Aβ formation and aggregation, glucose metabolism, autophagy, neurotransmission, and aspects of lipid metabolism such as fatty acyl-CoA β-oxidation and PUFA biosynthesis. 

Similarly, PPAR-β/δ regulates the central nervous system myelination process, while PPAR-γ is involved in neuron biogenesis, neuroinflammation, and neurodegeneration [89,90]. In patients with neurological diseases, PPARs are down-regulated [91].

The effects of punic acid on PPARs have been studied over time. The evidence shows that punicic acid decreases inflammation induced by pro-inflammatory cytokines Tumor Necrosis Factor Alpha (TNF-α) and Interleukin 6 (IL-6) on 3T3-L1 pre-adipocytes. 

Likewise, punicic acid-enhanced protein expression of PPAR-γ abates transcriptional activity of Nuclear Factor Kappa B (NFκB) p65 subunit, reduced mRNA expression of suppressor of cytokine signaling 3 (SOCS3), and attenuates protein tyrosine phosphatase 1B (PTP1B) induced by TNF-α [83,84]. 

A more recent study in mice liver fed a high-fat diet supplemented with PSO nanoemulsions found that punicic acid increased the expression of lipid metabolism-related genes PPAR-α, PPAR-β and PPAR-γ, fatty acid synthase (Fasn), and sterol regulatory element-binding transcription factor (Srbp1), along with antioxidant genes (aldehyde oxidase 1 (Aox1), glutathione S-transferase A4 (Gst4), NAD(P)H quinone dehydrogenase 1 (Nqo1), Nrf2, and peroxiredoxin 1 (Prdx1), and decreased levels of IL-6 and TNF-α [12]. 

The Punicic acid effect over PPARs is also related to HDL metabolism. Rabbits supplemented with microencapsulated pomegranate showed a modified lipid composition of HDL particles. PPARα and PPARγ can remodel HDL structure through the regulation of the expression of genes related to HDL metabolism [86].

3.2.2. Punicic Acid Participation in Calpain Hyperactivation Inhibition

Calpains are calcium-dependent cysteine proteases that have been implicated in several neurodegenerative diseases such as Alzheimer's and Huntington's Disease. Calpains are important for synaptic function and neuroplasticity, as they exert a neuroprotective effect at base expression, while overactivation leads to neurotoxicity. Calpain-1 and calpain-2 are abundant in the brain, and their hyperactivation is implicated in the late stages of neurodegenerative diseases [92]. 

Calpain-1 is overexpressed in the late stages of Alzheimer's, generating toxic fragments of tau in response to Aβ aggregate treatment. Calpain-2, on the other hand, was found to show increased early activity in the pathogenesis of Alzheimer's in a mouse model and was correlated with decreased cognitive function and increased Aβ in neocortical tissue samples from Alzheimer's patients [92,93]. 

Mice with induced Machado–Joseph Disease (MJD) phenology presented an overactivated calpain system baseline and led to increased cell death in the cerebellum. Elimination of calpain-2 in mice with induced MJD phenology resulted in reduced neurotoxicity and increased survival of the mice [94]. 

Calpain inhibitors are known to have neuroprotective effects; therefore, pharmaceutical companies developed calpain inhibitors as potential therapeutic drugs for Alzheimer's, among other NDs [95]. 

Calpain inhibition effects contributed to the neuroprotective effects exhibited by the PSO-nanoformulation commercialized as the product GranaGard®. The formulation contains high levels of punicic acid and resulted in the detention of Creutzfeldt–Jakob disease (CJD) for 60–80 days, followed by slower disease progression [88]. This same formulation was found to reduce Aβ formation, cyclin-dependent kinase 5 (cdk5) accumulation, and the key mitochondrial enzyme Cytochrome c oxidase in transgenic mice [43]. 

Additionally, ducking studies confirmed that punicic acid's metabolite, CLA, inhibits the active site of µ-calpain, exerting neuroprotective effects against H2O2 and induced Aβ degradation in human neuroblastoma cell lines [96].

3.2.3. Punicic Acid Induced a Higher Expression of GLUT4

Another common occurrence for several neurodegenerative diseases is a disturbance in glucose metabolism and the function and expression of glucose transporters. For example, hypometabolism of glucose due to a decrease in the expression of glucose transporters in the brain occurs in Alzheimer's disease [97]. 

Similarly, energy and glucose metabolism disturbances are suggested to play a role in the development of Huntington's disease pathology [98]. The human brain expresses ten different sodium-independent glucose transporters (GLUTs), which in conjunction with sodium-dependent glucose cotransporters (SGLTs) and uniporter SWEET protein, are responsible for glucose uptake. 

GLUT4 is an insulin-sensitive glucose transporter expressed in the hypothalamus, sensorimotor cortex, cerebellum, hippocampus, and pituitary. Its physiological role is unknown, but some of its suggested functions are its involvement in glucose sensing, the insulin modulation of glucose transport in distinct brain areas, and the transport of glucose, in case of high demand, to the motor neurons [97,98]. 

In Alzheimer's, along with decreased glucose uptake in highly active areas of the brain such as the cortex, hippocampus, and cerebral microvessels, glucose transporters (GLUT) decrease [98,99]. Impaired expression of GLUT-4 in the hippocampal neurons could be related to short-term memory loss and disorientation in Alzheimer's patients [100]. 

Supplementation with three daily capsules of PSO in 52 obese patients with type 2 diabetes showed an increase in the expression of the GLUT-4 gene and a decrease in fasting blood sugar [85]. Likewise, an increase in mRNA and protein expression of GLUT4 was observed in 3T3-L1 adipocytes treated with punic acid [83].

3.2.4. Effect of Punicic Acid over HDL and PON1

Another mechanism related to oxidative stress-related diseases is the alteration of paraoxonase 1 (PON1) in circulatory plasma. The paraoxonase (PON) family of enzymes is a group of polymorphic lactonases with broad substrate specificity that have potent antioxidant, anti-inflammatory, and anti-apoptotic properties. 

They are highly found in HDLs, and PON1 associated with HDL helps prevent LDL oxidation [101,102]. Low levels of PON1 and HDL cholesterol are associated with a high vulnerability to oxidative damage of lipids, proteins, and DNA and elevated immune-inflammatory response. 

Decreased PON1 content is also related to the neurotoxic effects of the immune-inflammatory and nitro-oxidative pathways in people suffering from neuroprogressive disorders such as major depressive disorder, bipolar disorder, and schizophrenia [103]. In NDs, alterations to circulatory plasma PON1 were reported [101]. Additionally, reduction in PON1 levels is common in PD patients compared to healthy people [104]. 

Pomegranate induces modifications of high-density lipoproteins (HDL) lipid composition and functionality. Rabbits were supplemented during 30 days with microencapsulated pomegranate, which induced an increase in HDL cholesterol and HDL phospholipids, decreased non−HDL sphingomyelin levels, and lowered the content of the triglycerides-phospholipids ratio. There was an increase in HDL functionality and improved oxidation resistance, most likely as a result of reduced triglyceride levels of the HDL and an increase in PON1 activity [86]. 

In a similar study, women with acute coronary syndrome were supplemented with microencapsulated pomegranate for 30 days, which shifted the distribution from large HDL to intermediate and small-sized particles, and a decrease in triglyceride values and an increase in PON1 activity was observed. HDL remodeling did not change the affinity of lipoprotein for PON1 since PON1 activity remained constant before or after supplementation. 

This means that the higher PON1 activity after pomegranate supplementation is due to its higher synthesis [87]. Additionally, CLA isomers, particularly c9, and t11, help protect PON1 from oxidative oxidation and stabilization in a concentration-dependent manner by binding to a specific binding site on a PON1 molecule [102]. 

Because microencapsulated pomegranate is composed of many beneficial nutraceutical components, including punicic acid, new studies need to be conducted to explore the direct effect of punicic acid on PON1 and HDL. In summary, punicic acid (PuA) can act as (1) an agonist of PPARs, which reduces neuroinflammation and tau hyperphosphorylation and conducts less Aβ formation and aggregation. 

Punicic acid reduces the Aβ formation by (2) inhibiting activation of calpain and cyclin-dependent kinase 5 (cdk5), limiting the hyperphosphorylation of tau protein. Likewise, (3) PuA increases GLUT4 protein expression regulating the glucose brain metabolism, reducing insulin resistance, and reducing the hyperphosphorylation of tau proteins. As a part of its strong antioxidant effects, (4) PuA increased the anti-oxidative properties of HDL and PON1 activity, reducing ROS generation and lipids peroxidation (Figure 6).

4. Concluding Remarks and Future Perspectives

Punicic acid is an important nutraceutical compound in the prevention and treatment of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's disease. 

Punicic acid can decrease oxidative damage and inflammation by increasing the expression of peroxisome proliferator-activated receptors. In addition, it can reduce beta-amyloid deposit formation and tau hyperphosphorylation by increasing the expression of GLUT4 protein and the inhibition of calpain hyperactivation. Microencapsulated pomegranate, with high levels of punicic acid, increases PON1 antioxidant activity in HDL. 

Likewise, encapsulated pomegranate formulations with high levels of punicic acid have shown an increase in PON1 antioxidant activity in HDL. However, punicic acid shows very low permeability across the blood–brain barrier, resulting in very limited effects on neurological disorders. 

To overcome this challenge, brain-targeted formulations that bypass the BBB have better results at diminishing ND's symptoms, such as decreased amyloid precursor protein gene expression, oxidative stress, and neuroinflammation. Future studies that focus on the effect of punicic acid on neurodegeneration need to be mindful of the effect of the BBB on the brain bioavailability of the bioactive molecule and attempt to develop specific delivery mechanisms that allow the exerting of localized effects.

Author Contributions: Conceptualization, M.A.-R. and D.G.-F.; investigation, C.M.G.-V.; writing- original draft preparation, C.M.G.-V.; writing-review and editing, M.A.-R., M.M.-Á., D.G.-F. and C.M.G.-V.; visualization, M.A.-R., D.G.-F. and M.M.-Á. All authors have read and agreed to the published version of the manuscript.

Funding: This work was supported by the Consejo Nacional de Ciencia y Tecnología (CONACYT) [CVU1078786] Claudia Melissa Guerra Vázquez scholarship, and the School of Engineering and Sciences of the Tecnológico de Monterrey.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Acknowledgments: Authors thank the Consejo Nacional de Ciencia y Tecnología (CONACYT), for Claudia Melissa Guerra Vázquez scholarship [CVU 1078786] and the Nutriomics and Emerging Technologies, and Bioprocess Research Chairs of Tecnológico de Monterrey. Figures were created with BioRender.com.

Conflicts of Interest: The authors declare no conflict of interest.

References

1. Wyss-Coray, T. Ageing, Neurodegeneration and Brain Rejuvenation. Nature 2016, 539, 180–186. [CrossRef] [PubMed] 

2. Checkoway, H.; Lundin, J.I.; Kelada, S.N. Neurodegenerative Diseases. IARC Sci. Publ. 2011, 163, 407–419. 

3. Prince, M.; Bryce, R.; Albanese, E.; Wimo, A.; Ribeiro, W.; Ferri, C.P. The Global Prevalence of Dementia: A Systematic Review and Metaanalysis. Alzheimers Dement. 2013, 9, 63. [CrossRef] [PubMed] 

4. Akbar, M.; Song, B.-J.; Essa, M.M.; Khan, M. Pomegranate: An Ideal Fruit for Human Health. Int. J. Nutr. Pharm. Neurol. Dis. 2015, 5, 141. [CrossRef] 

5. Viuda-Martos, M.; Fernández-López, J.; Pérez-Álvarez, J.A. Pomegranate and Its Many Functional Components as Related to Human Health: A Review. Compr. Rev. Food Sci. Food Saf. 2010, 9, 635–654. [CrossRef] [PubMed] 

6. Jalal, H.; Pal, M.A.; Hamdani, H.; Rovida, M.; Khan, N.N. Antioxidant Activity of Pomegranate Peel and Seed Powder Extracts. J. Pharmacogn. Phytochem. 2018, 7, 992–997. 

7. Kýralan, M.; Gölükcü, M.; Tokgöz, H. Oil and Conjugated Linolenic Acid Contents of Seeds from Important Pomegranate Cultivars (Punica Granatum L.) Grown in Turkey. J. Am. Oil Chem. Soc. 2009, 86, 985–990. [CrossRef] 

8. Peng, Y. Comparative Analysis of the Biological Components of Pomegranate Seed from Different Cultivars. Int. J. Food Prop. 2019, 22, 784–794. [CrossRef] 

9. Kaseke, T.; Opara, U.L.; Fawole, O.A. Effects of Enzymatic Pretreatment of Seeds on the Physicochemical Properties, Bioactive Compounds, and Antioxidant Activity of Pomegranate Seed Oil. Molecules 2021, 26, 4575. [CrossRef] 

10. Shaban, N.Z.; Talaat, I.M.; Elrashidy, F.H.; Hegazy, A.Y.; Sultan, A.S. Therapeutic Role of Punica Granatum (Pomegranate) Seed Oil Extract on Bone Turnover and Resorption Induced in Ovariectomized Rats. J. Nutr. Health Aging 2017, 21, 1299–1306. [CrossRef]

For more information:1950477648nn@gmail.com