Bioactive Compounds and Pharmacological Potential of Pomegranate (Punica granatum) Seeds - A Review

Pomegranate (Punica granatum L.) and its phytochemicals as anxiolytic; an underreported effect with therapeutic potential: A systematic review

Anxiety is a mental disorder characterized by excessive concern about possible future threats that, if prolonged, becomes a pathology that must be controlled through psychotherapy and medication. Currently, the pharmacological treatment for anxiety involves the use of antidepressants and benzodiazepines; however, these treatments often come with adverse effects. Thus, there is a need to seek natural compounds that can help alleviate anxiety and reduce these side effects. On the other hand, pomegranate (PG) fruit is known to have important health benefits, which have been compiled in several reviews. However, its anxiolytic effect has not been thoroughly studied, and clinical research on this topic is lacking. The aim of this work was to conduct a systematic review of studies exploring the anxiolytic-like effect of PG and its phytochemicals. Databases such as Pubmed, ScienceDirect, Springer link, Google scholar, Worldwide science, and Web of science were searched for articles using predetermined terms. Inclusion criteria were established, and original articles that met these criteria were selected. The data collected included information on PG part and variety, species, sample size, anxiety model, dose, route and time of administration, reference drug, main results, and the mechanisms of action. Fifty-nine studies were found that reported the anxiolytic-like effect of PG and its phytochemicals such as anthocyanins, flavonoids, tannins, organic acids, and xanthonoids. The literature suggests that the mechanisms of action behind this effect involved the inhibition of the GABAergic receptor, NMDA, CaMKII/CREB pathway; the reduction of oxidative stress, inhibiting TLR4 and nNOS; modulation of cytokines and the expression of NFkB, GAD67, and iNOS, as well as the activation of Nrf2 and AMPK. PG and some of its phytochemicals could be considered as a novel alternative for the treatment of pathological anxiety. This review is the first to document the anxiolytic-like effect of PG.

Functional Compounds of Cold-Pressed Pomegranate Seed Oil: Fatty Acids and Phytosterols Profile as Quality Biomarkers for Origin Discrimination

Cold-pressed pomegranate seed oil (PSO) is a product of the extraction of non-edible pomegranate seeds. Its unique chemical composition in terms of both polyunsaturated fatty acids, especially punicic acid (PA), and secondary metabolites, such as phytosterols, tocopherols and phenols, make it an interesting functional ingredient for food enrichment. It is not clear if the biomarkers profile of PSO depends to factors connected to the geographical origin of seeds. This work presents a statistical comparative analysis, concerning biomolecules composition and geographical origin of 32 commercial cold-pressed PSOs, performed by principal component analysis. The study discriminates between Turkish and Italian PSOs, on the base of the fatty acid profile and phytosterols, and not on the tocopherols and phenols. These results confirmed PA as the main characteristic biomarker of oil genuineness and, for the first time, disclosed a statistically relevant variability of phytosterols, which can be proposed as quality biomarkers for discrimination of geographical origins.

Discovery of Potent Angiotensin-Converting Enzyme Inhibitors in Pomegranate as a Treatment for Hypertension

Pomegranate (Punica granatum L.) is associated with numerous health benefits due to its high levels of antioxidant polyphenolic substances. Since pomegranate extract has been shown to inhibit angiotensin-converting enzyme (ACE), the potential inhibitory effect of most of its main constituents against ACE is unknown. Therefore, we tested the activities of 24 major compounds, the majority of which significantly inhibited ACE. Notably, pedunculagin, punicalin, and gallagic acid were the most effective ACE inhibitors with IC₅₀ values of 0.91, 1.12, and 1.77 μM, respectively. As demonstrated in molecular docking studies, compounds block ACE by forming multiple hydrogen bonds and hydrophobic interactions with catalytic residues and zinc ions in ACE's C- and N-domains, consequently inhibiting ACE's catalytic activity. Also, the most active pedunculagin stimulated nitric oxide (NO) production, activated the endothelial nitric oxide synthase enzyme (eNOS), and significantly increased eNOS protein expression levels up to 5.3-fold in EA.hy926 cells. Furthermore, pedunculagin increased in cellular calcium (Ca²⁺) concentration promoted eNOS enzyme activation and reduced the production of reactive oxygen species (ROS). In addition, the active compounds improved glucose uptake in insulin-resistant C2C12 skeletal muscle cells in a dose-dependent manner. The results of these computational, in vitro, and cellular experiments provide further evidence to the traditional medicine that involves using pomegranates to treat cardiovascular diseases like hypertension.

In-Depth Chemical Characterization of Punica granatum L. Seed Oil

Fruit seeds belonging to the pomegranate cultivar "Granata" were subjected to extraction and oily component analysis, with the aim of obtaining information about their composition. The presence of conjugated isomers of linolenic acid (CLNA isomers) in the oily phase extracted from the seeds gives a high added value to this part of the fruit, which is too often considered and treated as waste. The separated seeds were subjected to a classic Soxhlet extraction with n-hexane or extraction with supercritical CO₂, assisted by ethanol. The resulting oils were evaluated by ¹H and ¹³C-NMR and AP-MALDI-MS techniques. Differences in the triacylglycerols composition, with particular regard to punicic acid and other CLNA content, were studied in depth. Results showed the prevalence of punicic acid in the triacylglycerol mixture up to the 75%, with clear preponderance in the extract by supercritical fluids. Consequently, other CLNA isomers are, altogether, two-fold less represented in the supercritical extract than in the Soxhlet one. The two oily residues were subjected to solid phase extraction (SPE) and to HPLC-DAD analysis for the polyphenolic isolation and characterization. In addition to HPLC analysis, which showed different content and composition, DPPH analysis to evaluate the antiradical potential showed that the extract obtained with supercritical CO₂ was much more active.

The Therapeutic Wound Healing Bioactivities of Various Medicinal Plants

The skin serves as the body's first line of defense, guarding against mechanical, chemical, and thermal damage to the interior organs. It includes a highly developed immune response that serves as a barrier against pathogenic infections. Wound healing is a dynamic process underpinned by numerous cellular activities, including homeostasis, inflammation, proliferation, and remodeling, that require proper harmonious integration to effectively repair the damaged tissue. Following cutaneous damage, microorganisms can quickly enter the tissues beneath the skin, which can result in chronic wounds and fatal infections. Natural phytomedicines that possess considerable pharmacological properties have been widely and effectively employed forwound treatment and infection prevention. Since ancient times, phytotherapy has been able to efficiently treat cutaneous wounds, reduce the onset of infections, and minimize the usage of antibiotics that cause critical antibiotic resistance. There are a remarkable number of wound-healing botanicals that have been widely used in the Northern Hemisphere, including Achiella millefolium, Aloe vera, Althaea officinalis, Calendula officinalis, Matricaria chamomilla, Curcuma longa, Eucalyptus, Jojoba, plantain, pine, green tea, pomegranate, and Inula. This review addresses the most often used medicinal plants from the Northern Hemisphere that facilitate the treatment of wounds, and also suggests viable natural alternatives that can be used in the field of wound care.

Current Perspective and Mechanistic Insights on Bioactive Plant Secondary Metabolites for the Prevention and Treatment of Cardiovascular Diseases

Cardiovascular diseases (CVDs) are one of the most prevalent medical conditions of modern era and are one of the primary causes of adult mortality in both developing and developed countries. Conventional medications such as use of aspirin, beta-blockers, statins and angiotensin- converting enzyme inhibitors involve use of drugs with many antagonistic effects. Hence, alternative therapies which are safe, effective, and relatively cheap are increasingly being investigated for the treatment and prevention of CVDs. The secondary metabolites of medicinal plants contain several bioactive compounds which have emerged as alternatives to toxic modern medicines. The detrimental effects of CVDs can be mitigated via the use of various bioactive phytochemicals such as catechin, isoflavones, quercetin etc. present in medicinal plants. Current review intends to accumulate previously published data over the years using online databases concerning herbal plant based secondary metabolites that can help in inhibition and treatment of CVDs. An in-depth review of various phytochemical constituents with therapeutic actions such as antioxidant, anti-inflammatory, vasorelaxant, anti-hypertensive and cardioprotective properties has been delineated. An attempt has been made to provide a probable mechanistic overview for the pertinent phytoconstituent which will help in achieving a better prognosis and effective treatment for CVDs.

Protective effects of pomegranate (Punica granatum) and its main components against natural and chemical toxic agents: A comprehensive review

BACKGROUND

Different chemical toxicants or natural toxins can damage human health through various routes such as air, water, fruits, foods, and vegetables.

PURPOSE

Herbal medicines may be safe and selective for the prevention of toxic agents due to their active ingredients and various pharmacological properties. According to the beneficial properties of pomegranate, this paper summarized the protective effects of this plant against toxic substances.

STUDY DESIGN

In this review, we focused on the findings of in vivo and in vitro studies of the protective effects of pomegranate (Punica granatum) and its active components including ellagic acid and punicalagin, against natural and chemical toxic agents.

METHODS

We collected articles from the following databases or search engines such as Web of Sciences, Google Scholar, Pubmed and Scopus without a time limit until the end of September 2022.

RESULTS

P. granatum and its constituents have shown protective effects against natural toxins such as aflatoxins, and endotoxins as well as chemical toxicants for instance arsenic, diazinon, and carbon tetrachloride. The protective effects of these compounds are related to different mechanisms such as the prevention of oxidative stress, and reduction of inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), cyclooxygenase-2(COX-2) and nuclear factor ĸB (NF-ĸB) as well as the modulation of apoptosis, mitogen-activated protein kinase (MAPK) signaling pathways and improvement of liver or cardiac function via regulation of enzymes.

CONCLUSION

In this review, different in vitro and in vivo studies have shown that P. granatum and its active constituents have protective effects against natural and chemical toxic agents via different mechanisms. There are no clinical trials on the protective effects of P. granatum against toxic agents.

Mediterranean Food Industry By-Products as a Novel Source of Phytochemicals with a Promising Role in Cancer Prevention

The Mediterranean diet is recognized as a sustainable dietary approach with beneficial health effects. This is highly relevant, although the production of typical Mediterranean food, i.e., olive oil or wine, processed tomatoes and pomegranate products, generates significant amounts of waste. Ideally, this waste should be disposed in an appropriate, eco-friendly way. A number of scientific papers were published recently showing that these by-products can be exploited as a valuable source of biologically active components with health benefits, including anticancer effects. In this review, accordingly, we elaborate on such phytochemicals recovered from the food waste generated during the processing of vegetables and fruits, typical of the Mediterranean diet, with a focus on substances with anticancer activity. The molecular mechanisms of these phytochemicals, which might be included in supporting treatment and prevention of various types of cancer, are presented. The use of bioactive components from food waste may improve the economic feasibility and sustainability of the food processing industry in the Mediterranean region and can provide a new strategy to approach prevention of cancer.

Pomegranate Peels and Seeds as a Source of Phenolic Compounds: Effect of Cultivar, By-Product, and Extraction Solvent

The nutraceutical properties of Punica granatum L. are not restricted to the edible portion of the fruit but also to the peels and seeds, flowers, leaves, and tree bark. The recovery and valorization of the peel and seeds (ca. 50% of the whole fruit), besides the positive environmental impact, can be viewed as a source of natural bioactive compounds. Thus, the bioactive properties of extracts of pomegranate peel and seeds from Acco and Wonderful known cultivars, as well as of the novel Big Full cultivar, were evaluated. The dried and ground pomegranate by-products were submitted to a conventional solid/liquid extraction with ethanol/water mixtures (0%, 25%, 50%, and 75% of EtOH, v/v). The obtained extracts were characterized in terms of total phenolic compounds (TPC), total flavonoids (TF), and antioxidant activity (AA), determined by the DPPH radical scavenging activity and expressed as IC50 (half maximum inhibitory concentration). With the exception of the Acco cultivar, the extraction yield (EY) was higher for peels, whose extracts showed higher TPC, TF, and IC50 (lower AA). The extracts obtained from the by-products of the Big Full cultivar had a statistically higher overall bioactive potential (TPC: 0.36 mg GAE/mg extract; TF: 0.031 mg CATE/mg extract; IC50: 0.51 mg/mL) compared to the other two studied cultivars. Furthermore, the EY was enhanced by solvents richer in ethanol (50-75%), allowing obtaining extracts richer in TPC and TF with higher AA. Finally, it was shown that EY combined with bioactive data allowed a satisfactory principal component unsupervised differentiation of the pomegranate extracts according to the type of by-product used.

Pomegranate (Punica granatum L.) and Metabolic Syndrome Risk Factors and Outcomes: A Systematic Review of Clinical Studies

Pomegranate (Punica granatum L.) can be considered a multipurpose medicinal and dietary plant due to its anti-inflammatory and antioxidant actions. Pomegranate can be used to prevent or treat metabolic syndrome (MetS) risk factors. Although previously published reviews addressed the effects of pomegranate on different diseases, there is no systematic review that exclusively focuses on clinical trials related to all MetS-related risk factors. In view of this limitation, the objective of this up-to-date, comprehensive, and systematic review is to critically evaluate the potential of pomegranate (P. granatum) on various MetS risk factors on the basis of clinical studies. PubMed, EMBASE, MEDLINE, Google Scholar, COCHRANE, and Clinical Trials.gov databases were searched on 15 October 2021. The Preferred Reporting Items for a Systematic Review and Meta-Analysis guidelines were followed, and the bias risk evaluation was performed according to the Cochrane Handbook for Systematic Reviews of Interventions. We identified 5683 studies in the databases. After removing the duplicates, 3418 studies remained. Of these, 147 studies met the eligibility criteria, and finally, only 20 were included in the qualitative analysis. The included studies suggest that pomegranate can be beneficial to reduce body weight, blood pressure, glycemia, triglycerides, total cholesterol, and low-density lipoprotein cholesterol. Moreover, it can augment high-density lipoprotein cholesterol levels and improve insulin resistance. Although relevant effects were observed, additional well-designed clinical trials are needed to determine the correct formulations and doses to be used to prevent or treat MetS components.

Modifying the diet and gut microbiota to prevent and manage neurodegenerative diseases

The global prevalence of Alzheimer's disease and Parkinson's disease is steadily increasing due to the aging population. The lack of effective drugs against these neurodegenerative disorders makes it imperative to identify new strategies for their prevention and treatment. Recent studies have revealed that harnessing the power of the gut microbiota through modification of diet may be a valuable approach for reducing the risk, modulating the symptoms, and ameliorating the pathophysiological aspects of neurodegenerative diseases. Consuming specific dietary components can alter the prevalence of bacterial communities within the gut to a healthy enterotype, which can influence the production of beneficial metabolites by microbiota. This article focuses on several dietary components, which have been demonstrated to affect the gut microbiota-brain axis and therefore could lead to attenuation of specific pathological processes in neurodegenerative diseases. Published evidence indicates that fermented foods, including kefir, and foods that are high in bioactive polyphenols and complex carbohydrates, such as grapes, pomegranates, and seaweed, may be effective at reducing neuroinflammation, oxidative stress, neurotransmitter dysfunction, and neuronal death associated with Alzheimer's and Parkinson's diseases. Even though experimental evidence supporting the protective properties of the above dietary components in these diseases is emerging, it is evident that further human clinical studies are required to conclusively establish the benefits of any suggested dietary interventions. The translational potential of such research is illustrated by the clinical success of the recently developed Alzheimer's drug, GV-971, which is a seaweed derivative that works by modulating the gut microbiota-brain axis.

Dietary Phytochemicals that Can Extend Longevity by Regulation of Metabolism

Diet provides energy and nutrition for human survival, and also provides various joy of taste. Extensive studies have shown that the major components of diet, such as protein, carbohydrate and fat, play important roles in regulating aging and longevity. Whether other dietary ingredients can help prevent aging and extend longevity is a very interesting question. Here based on recent findings, we discussed dietary plant ingredients that can extend longevity by regulation of metabolism, targeting TRP channels, mitophagy, senescence pathways and circadian rhythms. Better understanding of the detailed effects and mechanisms of dietary ingredients on longevity regulation, would be helpful for developing new intervention tools for preventing aging and aging related diseases.

A New Insight into the Degradation of Anthocyanins: Reversible versus the Irreversible Chemical Processes

The kinetics and thermodynamics of the pH-dependent reversible and irreversible processes leading to color fading of pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, and cyanidin-3-O-glucoside dyes in aqueous solutions are reported. Following the addition of base to the flavylium cation, the quinoidal bases disappear by three distinct steps: (i) in an acidic medium by a biexponential process, in which the faster step is controlled by the hydration reaction and the slower one by cis-trans isomerization; the degradation process occurs essentially from the anionic quinoidal base; (ii) in a basic medium (pH > 9.5), in which the disappearance of the anionic bases is monoexponential, with the rate proportional to the hydroxyl concentration (hydroxyl attack), leading to anionic chalcones (cis and trans) at equilibrium─the slower degradation step occurs from the di- and trianionic chalcones; and (iii) in the pH region circa 7.7 < pH < 9.5, in which hydration and hydroxyl attacks are much slower than anionic quinoidal base degradation (which is the rate-controlling step) and the equilibrium cannot be attained.

Punicalagin Regulates Signaling Pathways in Inflammation-Associated Chronic Diseases

Inflammation is a complex biological defense system associated with a series of chronic diseases such as cancer, arthritis, diabetes, cardiovascular and neurodegenerative diseases. The extracts of pomegranate fruit and peel have been reported to possess health-beneficial properties in inflammation-associated chronic diseases. Punicalagin is considered to be the major active component of pomegranate extracts. In this review we have focused on recent studies into the therapeutic effects of punicalagin on inflammation-associated chronic diseases and the regulatory roles in NF-κB, MAPK, IL-6/JAK/STAT3 and PI3K/Akt/mTOR signaling pathways. We have concluded that punicalagin may be a promising therapeutic compound in preventing and treating inflammation-associated chronic diseases, although further clinical studies are required.

Affinity-Guided Isolation and Identification of Procyanidin B2 from Mangosteen (Garcinia mangostana L.) Rinds and its In Vitro LPS Binding and Neutralization Activities

Garcinia mangostana L. (mangosteen) is a tropical fruit that has been used for medicinal purposes in Southeast Asia for centuries. With an interest in its applications to treat infection, we sought to investigate the bioactive constituents of mangosteen and identified the phenolic compound procyanidin B2 from the mangosteen pericarp by examining lipopolysaccharide (LPS) binding capacity. The LPS binding and neutralization activities of procyanidin B2 were determined by a combination of biophysical and in silico techniques. The affinity of procyanidin B2 to LPS was 1.61 × 10^-5 M. Procyanidin B2 significantly neutralized LPS and selectively inhibited the LPS-induced release of tumor necrosis factor (TNF)-α from RAW264.7 cells in a dose-dependent manner. Binding thermodynamics revealed favorable hydrogen bonding and hydrophobic interactions between procyanidin B2 and LPS. Molecular simulations suggested that hydrogen bonding and hydrophobic interactions were involved in the binding process. These findings have, for the first time, shed light on the anti-inflammatory properties of procyanidin B2 through LPS binding and neutralization and provided a promising lead for the development of antiendotoxin agents.

Anthelmintic activity of pomegranate peel extract (Punica granatum) and synthetic anthelmintics against gastrointestinal nematodes in cattle, sheep, goats, and buffalos: in vivo study

Parasitic gastroenteritis (PGE) is one of the most important parasitic diseases that causes economic losses and health problems in ruminants. PGE causes a drop in milk, meat, and wool production in addition to decreasing animal fertility and sometimes leading to animal death. Conventional anthelmintics used for animal treatment are expensive, especially for farmers in developing countries. Moreover, the concern of anthelmintic resistance to these synthetic drugs is rising. Therefore, this study aimed to evaluate the anthelmintic activity of plant extract pomegranate (Punica granatum L) peel extract (PPE) against PGE infestations among ruminants. A total of 120 ruminants of different species (20 cattle, 12 buffalos, 68 sheep, and 20 goats) were examined for PGE eggs in their fecal samples. The animals under experiment were divided into four groups: the first group (negative control) was not given any drugs, the second group was given ivermectin (0.5 ml/25 kg bwt) (positive control 1), the third group was given albendazole (2.5 mg active principle/kg bwt) (positive control 2), and the fourth group was given PPE (200 mg/kg bwt). Fecal egg count (FEC) was performed on day 0 prior to the 1st dose of treatment. On day 15, an additional treatment (with the same doses) was administered and FEC was performed on days 7 and 21. Our results showed that on the 7th day of the experiment, there was an increase in FEC in the negative control group by 5%, while in the second, third, and fourth groups, there was a decrease in FEC with 95%, 90%, and 85% respectively. On the 21st day (7 days from the second dose), there was an increase in FEC in the control group by a 10% and 100% reduction in FEC in both the second and third groups. While in the fourth group, there was a decrease in FEC by 97%. In conclusion, PPE could be used as a safe, cheap, and effective natural anthelmintic against PGE.

Antiproliferative effects of Turkish pomegranate (Punica granatum L.) extracts on MCF-7 human breast cancer cell lines with focus on antioxidant potential and bioactive compounds analyzed by LC-MS/MS

In this study, eight different pomegranate (Punica granatum L.) cultivars from Turkey were evaluated for their antioxidant and cytotoxic effects on the MCF-7 breast cancer cell lines and MCF-10A breast fibrocystic epithelial cell lines with a focus on their chemical compositions by LC-MS/MS. Cell lines were treated with pomegranate juice extracts in different doses at selected time intervals (24th, 48th, and 72nd hour). Afterwards, WST-1 cell proliferation assay was performed to investigate the cytotoxicity of the extracts. Accordingly, all extracts decreased the cell viability of MCF-7 breast cancer cell lines and had no cytotoxic effect on the cell viability of MCF-10A cell lines. Among eight extracts, P7 (Izmir 1513), which was rich in anthocyanins such as cyanidin chloride (69.76 ± 8.02 μg/g extract), cyanidin-3-O-glucoside (903.66 ± 101.89 μg/g extract), and punicalagin (992.09 ± 174.53 μg/g extract), was found to demonstrate the strongest cytotoxic activity on MCF-7 breast cancer cell lines by decreasing the cell viability in half at 24th hour with an IC₅₀ value of 49.08 µg/ml. PRACTICAL APPLICATIONS: Eight commercially valuable pomegranate (Punica granatum) cultivars from Turkey were examined. Pelargonidin, cyanidin, cyanidin-3-O-gl, callistephin, and delphinidin-3-O-gl were quantified. Two cultivars (P1 and P3) showed comparatively higher antioxidant effects. A cultivar (P7) showed strongest cytotoxic activity against MCF-7 breast cancer cell line. The cultivars have potential to be used as natural antioxidant and anticancer agents.

Targeting Inflammation by Anthocyanins as the Novel Therapeutic Potential for Chronic Diseases: An Update

Low-grade chronic inflammation (LGCI) and oxidative stress act as cooperative and synergistic partners in the pathogenesis of a wide variety of diseases. Polyphenols, including anthocyanins, are involved in regulating the inflammatory state and activating the endogenous antioxidant defenses. Anthocyanins' effects on inflammatory markers are promising and may have the potential to exert an anti-inflammatory effect in vitro and in vivo. Therefore, translating these research findings into clinical practice would effectively contribute to the prevention and treatment of chronic disease. The present narrative review summarizes the results of clinical studies from the last 5 years in the context of the anti-inflammatory and anti-oxidative role of anthocyanins in both health and disease. There is evidence to indicate that anthocyanins supplementation in the regulation of pro-inflammatory markers among the healthy and chronic disease population. Although the inconsistencies between the result of randomized control trials (RCTs) and meta-analyses were also observed. Regarding anthocyanins' effects on inflammatory markers, there is a need for long-term clinical trials allowing for the quantifiable progression of inflammation. The present review can help clinicians and other health care professionals understand the importance of anthocyanins use in patients with chronic diseases.

Preventive Applications of Polyphenols in Dentistry-A Review

Polyphenols are natural substances that have been shown to provide various health benefits. Antioxidant, anti-inflammatory, and anti-carcinogenic effects have been described. At the same time, they inhibit the actions of bacteria, viruses, and fungi. Thus, studies have also examined their effects within the oral cavity. This review provides an overview on the different polyphenols, and their structure and interactions with the tooth surface and the pellicle. In particular, the effects of various tea polyphenols on bioadhesion and erosion have been reviewed. The current research confirms that polyphenols can reduce the growth of cariogenic bacteria. Furthermore, they can decrease the adherence of bacteria to the tooth surface and improve the erosion-protective properties of the acquired enamel pellicle. Tea polyphenols, especially, have the potential to contribute to an oral health-related diet. However, in vitro studies have mainly been conducted. In situ studies and clinical studies need to be extended and supplemented in order to significantly contribute to additive prevention measures in caries prophylaxis.