Zapotin (5,6,2',6'-tetramethoxyflavone) Modulates the Crosstalk Between Autophagy and Apoptosis Pathways in Cancer Cells with Overexpressed Constitutively Active PKCϵ

Roles of Neuronal Protein Kinase Cε on Endoplasmic Reticulum Stress and Autophagic Formation in Diabetic Neuropathy

In chronic diabetic neuropathy (DN), the cellular mechanisms of neuropathic pain remain unclear. Protein kinase C epsilon (PKCε) is an intracellular signaling molecule that mediates chronic pain. This paper addresses the long-term upregulated PKCε in DN associated with endoplasmic reticulum (ER) stress and autophagic formation and correlates to chronic neuropathic pain. We found that thermal hyperalgesia and mechanical allodynia course development were associated with PKCε upregulation after DN but not skin denervation. Pathologically, PKCε upregulation was associated with the expression of inositol-requiring enzyme 1α (IRE1α; ER stress-related molecule) and ubiquitin D (UBD), which are involved in the ubiquitin-proteasome system (UPS)-mediated degradation of misfolded proteins under ER stress. Manders coefficient analyses revealed an approximately 50% colocalized ratio for IRE1α(+):PKCε(+) neurons (0.34-0.48 for M1 and 0.40-0.58 for M2 Manders coefficients). The colocalized coefficients of UBD/PKCε increased (M1: 0.33 ± 0.03 vs. 0.77 ± 0.04, p < 0.001; M2: 0.29 ± 0.05 vs. 0.78 ± 0.04; p < 0.001) in the acute DN stage. In addition, the regulatory subunit p85 of phosphoinositide 3-kinase, which is involved in regulating insulin signaling, exhibited similar expression patterns to those of IRE1α and UBD; for example, it had highly colocalized ratios to PKCε. The ultrastructural examination further confirmed that autophagic formation was associated with PKCε upregulation. Furthermore, PKCεv1-2, a PKCε specific inhibitor, reverses neuropathic pain, ER stress, and autophagic formation in DN. This finding suggests PKCε plays an upstream molecule in DN-associated neuropathic pain and neuropathology and could provide a potential therapeutic target.

Using Flavonoid Substitution Status to Predict Anticancer Effects in Human Melanoma Cancers: An In Vitro Study

Skin cancers are a dominant type of cancer that impacts millions per year. Cancer is a heterogeneous disease triggered by the irreversible impairment of cellular homeostasis and function. In this study, we investigated the activity of 37 structurally diverse flavonoids to find potentially active substances using two melanoma cell lines: C32 and A375. First, the cytotoxic potential and DNA biosynthesis inhibition of flavonoids were tested to determine the most active compounds in cancer and normal cells. Second, the molecular mechanism of the anticancer activity of flavonoids was elucidated using Western blot and immunofluorescence analyses. Compounds 1, 6, 15, and 37 reduced the viability of A375 and C32 cell lines via the intrinsic and extrinsic pathways of apoptosis, whereas 16 and 17 acted in a higher degree via the inhibition of DNA biosynthesis. In our experiment, we demonstrated the anticancer activity of compound 15 (5,6-dihydroxyflavone) for the first time. The in vitro studies pointed out the importance of the flavonoid core in hydroxyl groups in the search for potential drugs for amelanotic melanoma.

Two new methoxylated flavones isolated from Casimiroa edulis La Llave and their MMP-9 inhibitory activity

Casimiroa edulis La Llave is known to contain unusual 5,6-dimethoxyflavones bearing a variously oxygenated B-ring. Phytochemical investigation of the leaves and the roots of C. edulis achieved the isolation of two new methoxylated flavones, named casedulones A (1) and B (2), together with 12 known analogues. Their unique structures were established with the aid of spectral analyses and total syntheses. Pre-treatment with 20 µM of 1 and 2 suppressed MMP-9 expression in LPS-mediated THP-1 cells, indicating that the characteristic flavonoids in C. edulis could be potential anti-angiogenics for cancer prevention.

Zapotin, a Polymethoxyflavone, with Potential Therapeutic Attributes

The use of plants as traditional medicines is common and has prevailed in many different cultures over time. Polymethoxyflavones (PMFs) are natural polyphenols from the group of flavonoids. Zapotin, a member of the PMFs, is found mainly in citrus plants and is almost exclusively limited to their peels. The chemical structure of zapotin has been questioned from the very beginning, since the structure of flavonoids with a single oxygen atom in the C2′ position is extremely rare in the plant kingdom. To clarify this, the structural determination and bio-inspired synthesis of zapotin are discussed in detail in this review. Due to the broad biological potential of PMFs, the complication in the isolation process and characterization of PMFs, as well as their purification, have been estimated by adapting various chromatographic methods. According to available data from the literature, zapotin may be a promising curative agent with extensive biological activities, especially as a chemopreventive factor. Apart from that, zapotin acts as an antidepressant-like, anticancer, antifungal, and antioxidant agent. Finally, accessible studies about zapotin metabolism (absorption, distribution, metabolism, excretion, and toxicity) underline its potential in use as a therapeutic substance.

Angiotensin II and hypoxia induce autophagy in cardiomyocytes via activating specific protein kinase C subtypes

Background

The purpose of this study was to explore the role of protein kinase C (PKC) isozymes and reactive oxygen species (ROS) in hypoxia and angiotensin (Ang) II-induced autophagy.

Methods

Primary cardiomyocytes were isolated from Sprague-Dawley (SD) neonatal rats and cultured in hypoxia and/or Ang II conditions. Dihydroethidium fluorescence staining was used to detect the content of ROS. Cardiomyocyte autophagy was determined using Monodansylcadaverine fluorescence staining and Western blot. We also inhibited ROS production to explore the relationship between ROS and autophagy. ELISA was used to detect the contents of PKC δ and PKC ε. After inhibition of PKC δ activation and PKC ε expression by lentiviral siRNA, ROS content and autophagy of cultured cardiomyocytes were detected.

Results

Hypoxia and Ang II stimulation increased autophagy in cardiomyocytes, accompanied by increased intracellular ROS production. Inhibiting ROS following hypoxia or Ang II stimulation significantly suppressed autophagy in comparison with hypoxia or Ang II stimulation group. Inhibiting PKC δ significantly reduced ROS production and autophagy activity following hypoxia or accompanied with Ang II stimulation except Ang II stimulation alone. Knockdown of PKC ε notably decreased ROS production and autophagy in response to Ang II alone and in combination with hypoxia rather than hypoxia alone.

Conclusions

Both hypoxia and Ang II stimulation can induce autophagy in cardiomyocytes through increasing intracellular ROS. However, hypoxia and Ang II stimulation induced myocardial autophagy via PKC δ and PKC ε, respectively.

The subgroup of 2'-hydroxy-flavonoids: Molecular diversity, mechanism of action, and anticancer properties

Flavonoids are abundant in nature, structurally very diversified and largely investigated. However, the subgroup of 2'-hydroxyflavonoids is much less known and not frequently studied. The present review identifies the major naturally-occurring and synthetic 2'-hydroxyflavonoid derivatives and discusses their structural characteristics and biological properties, with a focus on anticancer activities. The pharmacological properties of 2'-hydroxyflavone (2'-HF) and 2'-hydroxyflavanone (2'-HFa) are detailed. Upon binding to the Ral-interacting protein Rlip implicated in the transport of glutathione conjugates, 2'-HFa inhibits tumor cell proliferation and restrict tumor growth, in particular in breast cancer models. Among the synthetic derivatives, the characteristics of the anticancer product 2D08 (2',3',4'-trihydroxy flavone) are detailed to shed light on the molecular mechanism of action of this compound, as a regulator of protein SUMOylation. Inhibition of protein SUMOylation by 2D08 blocks cancer cell migration and invasion, and the compound greatly enhances the anticancer effects of conventional cytotoxic drugs like etoposide. The structural role of the 2'-hydroxyl group on the phenyl C-ring of the flavonoid is discussed, notably the capacity to engage intramolecular H-bonding interactions with the O1 atom on the B-ring of the chromone unit (or the oxygen of a 3-OH group when it is presents). The 2'-hydroxyl group of flavonoid appears as a regulator of the conformational freedom between the bicyclic A-B unit and the appended phenyl C-ring, favoring the planarity of the molecule. It is an essential group accounting for the biological properties of 2'-HF, 2'-HFa and structurally related compounds. This review shed light on 2'-hydroxyflavonoids to encourage their use and chemical development.

Polyphenol-Mediated Autophagy in Cancer: Evidence of In Vitro and In Vivo Studies

One of the hallmarks of cellular transformation is the altered mechanism of cell death. There are three main types of cell death, characterized by different morphological and biochemical features, namely apoptosis (type I), autophagic cell death (type II) and necrosis (type III). Autophagy, or self-eating, is a tightly regulated process involved in stress responses, and it is a lysosomal degradation process. The role of autophagy in cancer is controversial and has been associated with both the induction and the inhibition of tumor growth. Autophagy can exert tumor suppression through the degradation of oncogenic proteins, suppression of inflammation, chronic tissue damage and ultimately by preventing mutations and genetic instability. On the other hand, tumor cells activate autophagy for survival in cellular stress conditions. Thus, autophagy modulation could represent a promising therapeutic strategy for cancer. Several studies have shown that polyphenols, natural compounds found in foods and beverages of plant origin, can efficiently modulate autophagy in several types of cancer. In this review, we summarize the current knowledge on the effects of polyphenols on autophagy, highlighting the conceptual benefits or drawbacks and subtle cell-specific effects of polyphenols for envisioning future therapies employing polyphenols as chemoadjuvants.

The roles of PKCs in regulating autophagy

PURPOSE

Autophagy, as a highly conserved cellular degradation and recycling process, plays an important part in maintaining cellular homeostasis. PKC signaling is involved in multiple pathways including cell cycle progression, tumorigenesis, migration and autophagy.

METHODS

Literatures about PKC and autophagy from PubMed databases were reviewed in this study.

RESULTS

Studies regarding the association of PKC and autophagy remain debatable. Different duration of the stimulation of autophagy and distinct cell contexts result in different function of PKC in regulating autophagy. The subcellular localization of PKCs and their downstream regulators may influence the autophagy regulation as well. As important intracellular components, the mitochondria play an important role in regulating autophagy, by metabolic modulation and structural derangement.

CONCLUSION

Phase II studies regarding PKC-β inhibitor, enzastaurin, showed promising results in MCL, DLBCL and recurrent high-grade gliomas. However, the detailed mechanism is still in need. The mechanism of PKC-β in mediating autophagy in lymphoma and high-grade gliomas remains elusive as well. Moreover, several studies were in agreement that rottlerin enhanced autophagy in breast cancer cells, which warrants further clinical studies to verify PKC-δ as a therapeutic target. Thus, identifying the function of PKC in modulating autophagy and conducting related clinical studies help find novel target for chemotherapy.

Impact of PKCε downregulation on autophagy in glioblastoma cells

Background

Several efforts have been focused on identification of pathways involved in malignancy, progression, and response to treatment in Glioblastoma (GB). Overexpression of PKCε was detected in histological samples from GB, anaplastic astrocytoma, and gliosarcoma and is considered an important marker of negative disease outcome. In multiple studies on GB, autophagy has been shown as a survival mechanism during cellular stress, contributing to resistance against anti-cancer agents. The main object of this research was to determine the influence of PKCε downregulation on the expression of genes involved in autophagy pathways in glioblastoma cell lines U-138 MG and U-118 MG with high PKCε level.

Methods

We conducted siRNA-mediated knockdown of PKCε in glioblastoma cell lines and studied the effects of autophagy pathway. The expression of autophagy-related genes was analyzed using qPCR and Western blot analysis was carried out to assess protein levels. Immunostaining was used to detect functional autophagic maturation process.

Results

We found that these cell lines exhibited a high basal expression of autophagy-related genes. Our results suggest that the loss of PKCε contributes to the downregulation of genes involved in autophagy pathways. Moreover, most of the changes we observed in Western blot analysis and endogenous immunofluorescence experiments confirmed dysfunction of autophagy programs. We found that knockdown of PKCε induced a decrease in the expression of Beclin1, Atg5, PI3K, whereas the expression of other autophagy-related proteins mTOR and Bcl2 was increased. Treatment of control siRNA glioma cells with rapamycin-induced autophagosome formation and increase in LC3-II level and caused a decrease in the expression of p62. Additionally, PKCε siRNA caused a diminution in the Akt phosphorylation at Ser473 and in the protein level in both cell lines. Moreover, we observed reduction in the adhesion of glioblastoma cells, accompanied by the decrease in total FAK protein level and phosphorylation.

Conclusions

Effects of down-regulation of PKCε in glioma cells raised the possibility that the expression of PKCε is essential for the autophagic signal transduction pathways in these cells.

Thus, our results identify an important role of PKCε in autophagy and may, more importantly, identifyit as a novel therapeutic target.

Influence of lipopolysaccharides on autophagy and inflammation in pancreatic islet cells of mice fed by high-fat diet

The aim of this study was to confirm whether chronic low-grade inflammation could induce autophagy and damage in islet cells. The high-fat diet (HF) and low-dose lipopolysaccharides (LPS) were used to simulate chronic inflammation. Islet function was observed, the expression of autophagy-related proteins and the activity of glucose synthase kinase 3β (GSK-3β) were detected, and the role of autophagy in islet injury induced by inflammation was explored. Higher blood glucose was observed in HF group and LPS group compared with control (C) group, and there was no significant difference between LPS group and LiCl group. The apoptotic pancreatic islet cells in the LPS group were higher than in the HF and C groups, and the in the LiCl group they were higher than in the C group and lower than in the LPS group. Compared with the C group, LC3II/I ratio in the HF group was increased ( P < 0.05), in LPS and LiCl groups it was lower than in the HF group, and in LiCl group it was higher than in the LPS group. There was no significant difference between HF group and C group with regard to the ratio of p-GSK-3β/GSK-3β, but in the LiCl group it was higher than in the LPS group. The results demonstrated that low-grade inflammation might cause autophagy flux impaired through activation of GSK-3β, and induced islet cells damage. LiCl could play a role in protecting islet cells through autophagy enhancement.

Chemical Profile and Biological Activity of Casimiroa Edulis Non-Edible Fruit`s Parts

Purpose: the non-edible fruit parts of Casimiroa edulis Llave et were evaluated for their active constituents and their potential as antioxidants, anti-inflammatory and antitumor activity. Methods: Fruits peel (FP) and seeds kernel (SK) of Casimiroa edulis Llave et Lex. were extracted successively with hexane and then methanol. Fatty acids were prepared from hexane extracts and identified by GC. Total flavonoid, phenolic acids and tannins contents in methanol extracts were determined by UV spectrophotometer and identified by HPLC. Antioxidant, in-vitro anti-inflammatory activity and antitumor effect against Caco-2 cell line were determined. Results: GC analysis of hexane extracts showed that oleic acid (47.00%) was the major unsaturated fatty acids in both extracts while lignoceric acid (15.49%) is the most abundant saturated fatty acid in (FP). Total phenolic, flavonoid and tannin contents in (FP) & (SK) methanol extracts were; 37.5±1.5, 10.79±0.66 and 22.28±0.23 for (FP); 53.5±1.5mg/g, 14.44±0.32 mg/g; and 53.73±3.58 mg/g for (SK) respectively. HPLC analysis of methanol extract revealed that; the major phenolic compound was pyrogallol in (FP) and p-hydroxybenzoic acid in (SK), the major flavonoid was luteolin 6-arabinose-8-glucose in (FP) and acacetin in (SK). Conclusion: This study showed that non-edible parts of C. edulis fruit is a rich source of different phenolic compounds and fatty acids which has great antioxidant, anti-inflammatory and antitumor activities; that could be used as a natural source in pharmaceutical industry.