The Intrinsic Virtues of EGCG, an Extremely Good Cell Guardian, on Prevention and Treatment of Diabesity Complications

Combination of Metformin and Epigallocatechin-3-Gallate Lowers Cortisol, 11β-Hydroxysteroid Dehydrogenase Type 1, and Blood Glucose Levels in Sprague Dawley Rats with Obesity and Diabetes

Background

The combined effects of metformin and epigallocatechin-3-gallate (EGCG) on cortisol, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), and blood glucose levels have not been investigated. This study evaluated the effectiveness of combining EGCG with metformin in regulating those levels in a rat model of diet-induced diabetes and obesity.

Methods

Thirty diabetic and obese rats on a high-fat diet were treated daily for 28 days with EGCG (100 mg/kg of body weight/day), metformin (200 mg/kg of body weight/day), or both. Control groups comprised lean rats, untreated obese diabetic rats, and metformin-only-treated rats. Blood samples were collected to measure cortisol and fasting blood glucose (FBG) levels and liver tissue samples were examined for 11β-HSD1 levels.

Results

Rats receiving combination therapy had significantly reduced cortisol levels (from 36.70±15.13 to 31.25±7.10 ng/mL) compared with the untreated obese diabetic rats but not the rats receiving monotherapy. Rats receiving combination therapy and EGCG monotherapy had significantly lower 11β-HSD1 levels compared with the untreated obese diabetic rats (92.68±10.82 and 93.74±18.11 ng/L vs. 120.66±14.00 ng/L). Combination therapy and metformin monotherapy significantly reduced FBG levels (440.83±133.30 to 140.50±7.36 mg/dL and 480.67±86.32 to 214.17±102.78 mg/dL, respectively) by approximately 68.1% and 55.4% compared with rats receiving EGCG monotherapy and untreated obese diabetic rats.

Conclusion

Combining EGCG with metformin exhibited synergistic effects compared with monotherapy for managing diabetes, leading to improved outcomes in reduction of baseline cortisol levels along with reduction in 11β-HSD1 and blood glucose levels.

Epigallocatechin gallate enhances sympathetic heart rate variability and decreases blood pressure in obese subjects: a randomized control trial

This study aimed to investigate effects of epigallocatechin gallate (EGCG) on blood pressure (BP) and autonomic nervous system, indicated by 5-min heart rate variability (HRV) measurement in obese subjects, and determine correlations of BP with metabolic factors. In a double-blind, randomized controlled trial, obese subjects (n = 30) were randomly allocated to receive 150 mg EGCG (n = 15) or placebo (n = 15) twice a day without dietary restrictions. After 8-week EGCG treatment, systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) significantly decreased, while the low-frequency (LF) to high-frequency power (HF) ratio (LF/HF ratio) significantly increased (P < 0.05 all), indicating a shift toward sympathetic dominance, either directly or indirectly after BP lowering. SBP had positive correlations with obesity parameters, leptin, insulin, and insulin resistance but had a negative correlation with insulin sensitivity. DBP was positively correlated with age and HF in normalized unit, but negatively correlated with height and LF in ms2. High-density lipoprotein cholesterol (HDL-C) was negatively correlated with SBP, DBP, and MAP reflecting its protective effect against elevated BP. In conclusion, the 8-week EGCG treatment decreased BP and increased the LF/HF ratio, reflecting increased sympathetic activity, either a direct EGCG effect or an indirect compensatory response following BP reduction.

Epigenetic modifications in obesity-associated diseases

The global prevalence of obesity has reached epidemic levels, significantly elevating the susceptibility to various cardiometabolic conditions and certain types of cancer. In addition to causing metabolic abnormalities such as insulin resistance (IR), elevated blood glucose and lipids, and ectopic fat deposition, obesity can also damage pancreatic islet cells, endothelial cells, and cardiomyocytes through chronic inflammation, and even promote the development of a microenvironment conducive to cancer initiation. Improper dietary habits and lack of physical exercise are important behavioral factors that increase the risk of obesity, which can affect gene expression through epigenetic modifications. Epigenetic alterations can occur in early stage of obesity, some of which are reversible, while others persist over time and lead to obesity-related complications. Therefore, the dynamic adjustability of epigenetic modifications can be leveraged to reverse the development of obesity-associated diseases through behavioral interventions, drugs, and bariatric surgery. This review provides a comprehensive summary of the impact of epigenetic regulation on the initiation and development of obesity-associated cancers, type 2 diabetes, and cardiovascular diseases, establishing a theoretical basis for prevention, diagnosis, and treatment of these conditions.

Epigallocatechin-3-Gallate and Genistein for Decreasing Gut Dysbiosis, Inhibiting Inflammasomes, and Aiding Autophagy in Alzheimer's Disease

There are approximately 24 million cases of Alzheimer's disease (AD) worldwide, and the number of cases is expected to increase four-fold by 2050. AD is a neurodegenerative disease that leads to severe dementia in most patients. There are several neuropathological signs of AD, such as deposition of amyloid beta (Aβ) plaques, formation of neurofibrillary tangles (NFTs), neuronal loss, activation of inflammasomes, and declining autophagy. Several of these hallmarks are linked to the gut microbiome. The gastrointestinal (GI) tract contains microbial diversity, which is important in regulating several functions in the brain via the gut-brain axis (GBA). The disruption of the balance in the gut microbiota is known as gut dysbiosis. Recent studies strongly support that targeting gut dysbiosis with selective bioflavonoids is a highly plausible solution to attenuate activation of inflammasomes (contributing to neuroinflammation) and resume autophagy (a cellular mechanism for lysosomal degradation of the damaged components and recycling of building blocks) to stop AD pathogenesis. This review is focused on two bioflavonoids, specifically epigallocatechin-3-gallate (EGCG) and genistein (GS), as a possible new paradigm of treatment for maintaining healthy gut microbiota in AD due to their implications in modulating crucial AD signaling pathways. The combination of EGCG and GS has a higher potential than either agent alone to attenuate the signaling pathways implicated in AD pathogenesis. The effects of EGCG and GS on altering gut microbiota and GBA were also explored, along with conclusions from various delivery methods to increase the bioavailability of these bioflavonoids in the body.

Insights into prevention mechanisms of bioactive components from healthy diets against Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease in which senile plaques, neurofibrillary tangles, insulin resistance, oxidative stress, chronic neuroinflammation, and abnormal neurotransmission are the potential mechanisms involved in its onset and development. Although it is still an intractable disorder, diet intervention has been developed as an innovative strategy for AD prevention. Some bioactive compounds and micronutrients from food, including soy isoflavones, rutin, vitamin B1, etc., have exhibited numerous neuronal health-promoting effects in both in vivo and in vitro studies. It is well known that their antiapoptotic, antioxidative, and anti-inflammatory properties prevent the neuronal or glial cells from injury or death, minimize oxidative damage, inhibit the production of proinflammatory cytokines by modulating typical signaling pathways of MAPK, NF-kβ, and TLR, and further reduce Aβ genesis and tau hyperphosphorylation. However, parts of the dietary components trigger AD-related proteins productions and inflammasome as well as inflammatory gene upregulation. This review summarized the neuroprotective or nerve damage-promoting role and underlying molecular mechanisms of flavonoids, vitamins, and fatty acids via the data from library databases, PubMed, and journal websites, which provides a comprehensive analysis of the prevention potential of these dietary components against AD.

Epigallocatechin gallate improves the quality of diabetic oocytes

BACKGROUND

Maternal diabetes compromises the quality and developmental potential of oocytes. Therefore, it is important to study how to ameliorate the adverse effects of diabetes on oocyte quality. Epigallocatechin gallate (EGCG) has a variety of physiological activities, including anti-inflammatory, antioxidant, and anti-diabetes. In the present study, we evaluated the effect of EGCG on the maturation of diabetic oocytes in vitro.

OBJECTIVE

Investigating the role of EGCG in restoring the adverse effects of diabetes on oocyte quality.

METHODS

Diabetes mouse model was established by a single injection of streptozotocin (STZ). Oocytes were collected and matured in vitro with/without EGCG in M16 medium.

RESULTS

Compared with control, diabetic oocytes have a higher frequency of spindle defects and chromosome misalignment, but EGCG effectively reduces the incidence of oocytes with abnormal spindle assembly and chromosome mismatches. Moreover, the abnormal mitochondrial membrane potential (MMP) of diabetic oocytes is significantly alleviated by EGCG, and the reduced expression of genes regulating mitochondrial fusion (Mfn1 and Mfn2) and fission (Drp1) in diabetic oocytes is significantly increased while EGCG is added. EGCG also decreases the higher level of reactive oxygen species (ROS) in diabetic oocytes that may be regulated by the increased expression of superoxide dismutase 1 (Sod1) and superoxide dismutase 2 (Sod2). EGCG can also reduce the DNA damage of diabetic oocytes.

CONCLUSIONS

Our results suggest that EGCG, at least partially, improve the quality of diabetic oocytes.

Therapeutic Effects of Green Tea Polyphenol (‒)-Epigallocatechin-3-Gallate (EGCG) in Relation to Molecular Pathways Controlling Inflammation, Oxidative Stress, and Apoptosis

(‒)-Epigallocatechin-3-gallate (EGCG) is the most abundant polyphenol in green tea. Thanks to multiple interactions with cell surface receptors, intracellular signaling pathways, and nuclear transcription factors, EGCG possesses a wide variety of anti-inflammatory, antioxidant, antifibrotic, anti-remodelation, and tissue-protective properties which may be useful in the treatment of various diseases, particularly in cancer, and neurological, cardiovascular, respiratory, and metabolic disorders. This article reviews current information on the biological effects of EGCG in the above-mentioned disorders in relation to molecular pathways controlling inflammation, oxidative stress, and cell apoptosis.

Green Tea Polyphenol (-)-Epigallocatechin-3-Gallate (EGCG): A Time for a New Player in the Treatment of Respiratory Diseases?

(-)-Epigallocatechin-3-gallate (EGCG) is a major polyphenol of green tea that possesses a wide variety of actions. EGCG acts as a strong antioxidant which effectively scavenges reactive oxygen species (ROS), inhibits pro-oxidant enzymes including NADPH oxidase, activates antioxidant systems including superoxide dismutase, catalase, or glutathione, and reduces abundant production of nitric oxide metabolites by inducible nitric oxide synthase. ECGC also exerts potent anti-inflammatory, anti-fibrotic, pro-apoptotic, anti-tumorous, and metabolic effects via modulation of a variety of intracellular signaling cascades. Based on this knowledge, the use of EGCG could be of benefit in respiratory diseases with acute or chronic inflammatory, oxidative, and fibrotizing processes in their pathogenesis. This article reviews current information on the biological effects of EGCG in those respiratory diseases or animal models in which EGCG has been administered, i.e., acute respiratory distress syndrome, respiratory infections, COVID-19, bronchial asthma, chronic obstructive pulmonary disease, lung fibrosis, silicosis, lung cancer, pulmonary hypertension, and lung embolism, and critically discusses effectiveness of EGCG administration in these respiratory disorders. For this review, articles in English language from the PubMed database were used.

Chemico-biological aspects of (-)-epigallocatechin-3-gallate (EGCG) to improve its stability, bioavailability and membrane permeability: Current status and future prospects

Natural products have been a bedrock for drug discovery for decades. (-)-Epigallocatechin-3-gallate (EGCG) is one of the widely studied natural polyphenolic compounds derived from green tea. It is the key component believed to be responsible for the medicinal value of green tea. Significant studies implemented in in vitro, in cellulo, and in vivo models have suggested its anti-oxidant, anti-cancer, anti-diabetic, anti-inflammatory, anti-microbial, neuroprotective activities etc. Despite having such a wide array of therapeutic potential and promising results in preclinical studies, its applicability to humans has encountered with rather limited success largely due to the poor bioavailability, poor membrane permeability, rapid metabolic clearance and lack of stability of EGCG. Therefore, novel techniques are warranted to address those limitations so that EGCG or its modified analogs can be used in the clinical setup. This review comprehensively covers different strategies such as structural modifications, nano-carriers as efficient drug delivery systems, synergistic studies with other bioactivities to improve the chemico-biological aspects (e.g., stability, bioavailability, permeability, etc.) of EGCG for its enhanced pharmacokinetics and pharmacological properties, eventually enhancing its therapeutic potentials. We think this review article will serve as a strong platform with comprehensive literature on the development of novel techniques to improve the bioavailability of EGCG so that it can be translated to the clinical applications.

Epigallocatechin-3-Gallate Delivery in Lipid-Based Nanoparticles: Potentiality and Perspectives for Future Applications in Cancer Chemoprevention and Therapy

Chemoprevention is a strategy aimed to not only reduce the risk but also delay the development or recurrence of cancer. An ideal chemopreventive agent is not dangerous and ought not to result in side effects or damage to human health. In this context, epigallocatechin-3-gallate (EGCG) is considered a suitable chemopreventive agent, but its clinical use is limited by many factors, namely, the difference in source, administration, individual metabolism, absorption, and distribution. Genetic and dietary differences greatly cause this variability, which has limited the rational use of EGCG in chemoprevention and, particularly, the definition of a safe and efficient concentration. In the present mini review, the main limitations to a complete understanding of the use of EGCG as a chemopreventive agent will be briefly illustrated. This review also indicates the introduction and trialing of lipid-based nanoparticles (NPs) as a proper strategy to deliver EGCG at a well-defined concentration for better investigation of the chemopreventive activity. Finally, some examples of cancers that might benefit from EGCG treatment in different stages of the disease are proposed.

Low dose epigallocatechin-3-gallate revives doxorubicin responsiveness by a redox-sensitive pathway in A549 lung adenocarcinoma cells

Pulmonary cancer confronts the greatest hurdle of resistance against most chemotherapeutic drugs. This may be circumvented with a combination of conventional chemotherapy with bioactive herbal adjuvant. Epigallocatechin-3-gallate (EGCG), was investigated for its chemo-sensitizing property along with doxorubicin (Dox), in an intrinsically nonresponsive lung adenocarcinoma (LAC) cell line, A549. A compromised functionality of Dox was reversed when EGCG was used as an adjuvant. On one hand, Dox (10 μM)-EGCG (0.5 μM) post treatment combination decreased the drug efflux, multidrug-resistance (MDR) signaling, invasiveness while, on the other hand, it increased drug internalization, cell-cycle arrest, stress-induced damage, and finally cell death. The resistant nature of A549 was probably due to constitutive activation of nuclear erythroid 2-related factor 2 (Nrf2) and its upstream/downstream antioxidant effectors, which were also pro-oxidatively coordinated by EGCG. In conclusion low dose EGCG improved Dox-toxicity and imparted oxidative damage-mediated antineoplastic efficacy by reorienting the redox signaling in A549 LAC cells.

Induction of Reactive Oxygen Species Is Necessary for Efficient Onset of Cyprinid Herpesvirus 2 Replication: Implications for Novel Antiviral Strategy With Antioxidants

Cyprinid herpesvirus 2 (CyHV-2) has caused great economic loss to the crucian carp breeding industry. Upon viral stimulation, eukaryotic cells generally activate the expression of anti-oxidative genes to maintain the intracellular oxidative balance and resist viral infection. Here, intracellular reactive oxygen species (ROS) levels in CyHV-2-infected cells were monitored to show that CyHV-2 induced the increase of intracellular ROS during early infection, and intracellular excessive accumulation of ROS was ameliorated during late infection, which was accompanied by activated expression of genes related to Nrf2 signaling pathway. In order to explore the interaction between CyHV-2 infection and ROS production, RyuF-2 cells were treated with either antioxidant epigallocatechin-3-gallate (EGCG) or berberine hydrochloride (BBH) and then infected with CyHV-2. Both BBH and EGCG could effectively inhibit the amplification of CyHV-2 while inhibiting the accumulation of intracellular ROS. Consistent with this, the oxidant stress-related genes were up-regulated by CyHV-2 infection and down-regulated in cells treated with either BBH or EGCG, through which the production of intracellular ROS was modulated. These results collectively demonstrated that early ROS accumulation favored the replication of CyHV-2, while antioxidants (BBH and EGCG) could inhibit the amplification of CyHV-2 by inhibiting ROS induction.

EGCG prevents pressure overload‑induced myocardial remodeling by downregulating overexpression of HDAC5 in mice

Myocardial remodeling is a complex pathological process and its mechanism is unclear. The present study investigated whether epigallocatechin gallate (EGCG) prevents myocardial remodeling by regulating histone acetylation and explored the mechanisms underlying this effect in the heart of a mouse model of transverse aortic constriction (TAC). A TAC mouse model was created by partial thoracic aortic banding (TAB). Subsequently, TAC mice were injected with EGCG at a dose of 50 mg/kg/day for 12 weeks. The hearts of mice were collected for analysis 4, 8 and 12 weeks after TAC. Histopathological changes in the heart were observed by hematoxylin and eosin, Masson trichrome and wheat germ agglutinin staining. Protein expression levels were investigated using western blotting. Cardiac function of mice was detected by echocardiography. The level of histone acetylated lysine 27 on histone H3 (H3K27ac) first increased and then decreased in the hearts of mice at 4, 8 and 12 weeks after TAC. The expression levels of two genes associated with pathological myocardial remodeling, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), also increased initially but then decreased. The expression levels of histone deacetylase 5 (HDAC5) gradually increased in the hearts of mice at 4, 8 and 12 weeks after TAC. Furthermore, EGCG increased acetylation of H3K27ac by inhibiting HDAC5 in the heart of TAC mice treated with EGCG for 12 weeks. EGCG normalized the transcriptional activity of heart nuclear transcription factor myocyte enhancer factor 2A in TAC mice treated for 12 weeks. The low expression levels of myocardial remodeling‑associated genes (ANP and BNP) were reversed by EGCG treatment for 12 weeks in TAC mice. In addition, EGCG reversed cardiac enlargement and improved cardiac function and survival in TAC mice when treated with EGCG for 12 weeks. Modification of the HDAC5‑mediated imbalance in histone H3K27ac served a key role in pathological myocardial remodeling. The present results show that EGCG prevented and delayed myocardial remodeling in TAC mice by inhibiting HDAC5.

Recent insights on tea metabolites, their biosynthesis and chemo-preventing effects: A review

Tea manufactured from the cultivated shoots of Camellia sinensis (L.) O. Kuntze is the most commonly consumed nonalcoholic drink around the world. Tea is an agro-based, environmentally sustainable, labor-intensive, job-generating, and export-oriented industry in many countries. Tea includes phenolic compounds, flavonoids, alkaloids, vitamins, enzymes, crude fibers, protein, lipids, and carbohydrates, among other biochemical constituents. This review described the nature of tea metabolites, their biosynthesis and accumulation with response to various factors. The therapeutic application of various metabolites of tea against microbial diseases, cancer, neurological, and other metabolic disorders was also discussed in detail. The seasonal variation, cultivation practices and genetic variability influence tea metabolite synthesis. Tea biochemical constituents, especially polyphenols and its integral part catechin metabolites, are broadly focused on potential applicability for their action against various diseases. In addition to this, tea also contains bioactive flavonoids that possess health-beneficial effects. The catechin fractions, epigallocatechin 3-gallate and epicatechin 3-gallate, are the main components of tea that has strong antioxidant and medicinal properties. The synergistic function of natural tea metabolites with synthetic drugs provides effective protection against various diseases. Furthermore, the application of nanotechnologies enhanced bioavailability, enhancing the therapeutic potential of natural metabolites against numerous diseases and pathogens.

Prenatal EGCG exposure-induced heart mass reduction in adult male mice and underlying mechanisms

Epigallocatechin-3-gallate (EGCG), which is a major polyphenol in tea, has an unclear effect on cardiac development. In the present study, mice (C57BL/6) were exposed in utero to EGCG dissolved in drinking water (3 μg/ml) for 16 days. A significant decrease in the heart/body weight ratio was observed in adult males but not in adult females. The protein expression levels of TGF-β1 and its downstream transcription factors SMAD3 and SMAD4 were significantly decreased in male hearts. The PI3K/AKT signaling pathway was inhibited, the expression of proapoptotic proteins, such as BAX, Cleaved Caspase3 and Cleaved Caspase9, was elevated, and the level of antiapoptotic proteins, such as BCL-2, was decreased. A reduced heart/body weight ratio may be associated with the loss of cardiac fibers and an increase in myocardial apoptosis. The cardiac levels of aromatic hydrocarbon receptor and androgen receptor were elevated only in males, which may explain the sexual dimorphism in the effects. The promoter methylation levels of pik3r1, tgf-β, smad4 were elevated, and those of ahr were reduced, explaining the mechanism underlying the cardiac histological alteration caused by prenatal exposure to EGCG. The results suggest that ingestion of EGCG during pregnancy may be a risk factor for cardiac development in offspring.

Anti-damage effect of theaflavin-3'-gallate from black tea on UVB-irradiated HaCaT cells by photoprotection and maintaining cell homeostasis

Keratinocytes are rich in lipids and are the main sensitive cells to ultraviolet (UV) rays. Theaflavins are the core functional components of black tea and are known as the "soft gold" in tea. In this study, ultraviolet-B (UVB) irradiation caused apoptosis and necrosis of human epidermal keratinocytes (HaCaT). EGCG and the four theaflavins had anti-UVB damage activity, among which theaflavin-3'-gallate (TF3'G) had the best activity. The results of biophysical and molecular biology experiments showed that TF3'G has anti-damage effects on UVB-irradiated HaCaT cells through the dual effects of photoprotection and maintenance of cell homeostasis. That is, TF3'G preincubation could absorb UV rays, reduce the accumulation of aging-related heterochromatin (SAHF) formation, increase mitochondrial membrane potential, downregulate NF-κB inflammation pathways, inhibit the formation of cytotoxic aggregates, and protect biological macromolecules Structure, etc. The accumulation of conjugated π bonds and the balance benzoquinone are the core functional structure of TF3'G with high efficiency and low toxicity. The study indicates that TF3'G has the potential to inhibit the photoaging and intrinsic aging of skin cells.

Phenolic Compounds of Red Wine Aglianico del Vulture Modulate the Functional Activity of Macrophages via Inhibition of NF-κB and the Citrate Pathway

Phenolic compounds of red wine powder (RWP) extracted from the Italian red wine Aglianico del Vulture have been investigated for the potential immunomodulatory and anti-inflammatory capacity on human macrophages. These compounds reduce the secretion of IL-1β, IL-6, and TNF-α proinflammatory cytokines and increase the release of IL-10 anti-inflammatory cytokine induced by lipopolysaccharide (LPS). In addition, RWP restores Annexin A1 levels, thus involving activation of proresolutive pathways. Noteworthy, RWP lowers NF-κB protein levels, promoter activity, and nuclear translocation. As a consequence of NF-κB inhibition, reduced promoter activities of SLC25A1—encoding the mitochondrial citrate carrier (CIC)—and ATP citrate lyase (ACLY) metabolic genes have been observed. CIC, ACLY, and citrate are components of the citrate pathway: in LPS-activated macrophages, the mitochondrial citrate is exported by CIC into the cytosol where it is cleaved by ACLY in oxaloacetate and acetyl-CoA, precursors for ROS, NO^·, and PGE₂ inflammatory mediators. We identify the citrate pathway as a RWP target in carrying out its anti-inflammatory activity since RWP reduces CIC and ACLY protein levels, ACLY enzymatic activity, the cytosolic citrate concentration, and in turn ROS, NO^·, PGE₂, and histone acetylation levels. Overall findings suggest that RWP potentially restores macrophage homeostasis by suppressing inflammatory pathways and activating proresolutive processes.

Neural Underpinnings of Obesity: The Role of Oxidative Stress and Inflammation in the Brain

Obesity prevalence is increasing at an unprecedented rate throughout the world, and is a strong risk factor for metabolic, cardiovascular, and neurological/neurodegenerative disorders. While low-grade systemic inflammation triggered primarily by adipose tissue dysfunction is closely linked to obesity, inflammation is also observed in the brain or the central nervous system (CNS). Considering that the hypothalamus, a classical homeostatic center, and other higher cortical areas (e.g. prefrontal cortex, dorsal striatum, hippocampus, etc.) also actively participate in regulating energy homeostasis by engaging in inhibitory control, reward calculation, and memory retrieval, understanding the role of CNS oxidative stress and inflammation in obesity and their underlying mechanisms would greatly help develop novel therapeutic interventions to correct obesity and related comorbidities. Here we review accumulating evidence for the association between ER stress and mitochondrial dysfunction, the main culprits responsible for oxidative stress and inflammation in various brain regions, and energy imbalance that leads to the development of obesity. Potential beneficial effects of natural antioxidant and anti-inflammatory compounds on CNS health and obesity are also discussed.