Nrf2 inhibition regulates intracellular lipid accumulation in mouse insulinoma cells and improves insulin secretory function.

High amount of fat in the pancreas is linked to poor functioning of ß-cells and raises the risk of type 2 diabetes. Here we report the putative role of a circulatory glycoprotein Fetuin-A, a known obesity marker, in promoting lipid accumulation in ß-cells and its association with Fatty acid translocase/CD36 for lipid storage culminate in ß-cell dysfunction. Additionally, this work reveals regulation of CD36 via Nrf2, a key regulator of oxidative stress, and reduction of lipid accumulation by suppression of Nrf2 that restores ß-cell function. Palmitate (0.50 mM) and Fetuin-A (100 µg/mL) exposure showed high levels of intracellular lipid in MIN6 (mouse insulinoma cells) with a concomitant decrease in insulin secretion. This also increased the expression of important lipogenic factors, like CD36, PGC1α, PPARγ, and SREBP1. Flow cytometry analysis of CD36 membrane localization has been corroborated with an increased accumulation of lipids as indicated by Oil-Red-O staining. Immunoblotting and immunofluorescence of Nrf2 indicated its high expression in palmitate-fetuin-A incubation and translocation in the nucleus. Suppression of Nrf2 by siRNA showed a reduced expression of lipogenic genes, ablation of lipid droplets, decrease in the number of apoptotic cells, and restoration of insulin secretion with a corresponding increase of Pdx1, BETA2, and Ins1 gene expression. Our study thus suggested an important aspect of lipid accumulation in the pancreatic ß-cells contributing to ß-cell dysfunction and demonstrated the role of Fetuin-A in CD36 expression, with a possible way of restoring ß-cell function by targeting Nrf2.

Fetuin-A excess expression amplifies lipid induced apoptosis and ß-cell damage.

Fetuin-A, a hepato-adipokine, is associated with lipid-mediated islet inflammation and inflicts ß-cell death but the underlying mechanisms are still unclear. In an earlier report, it was shown that fetuin-A promotes lipid-induced insulin resistance by acting as an endogenous ligand of toll like receptor 4. Recently, we have also reported that ß-cells secrete fetuin-A on stimulation by palmitate causing ß-cell dysfunction. The aim of this study was twofold: (a) screening the role of fetuin-A in survival of murine ß-cells, and (b) to validate the effect of fetuin-A release and lipid induced apoptosis in mouse insulinoma cell line MIN6. Excess of lipid and fetuin-A in circulation induced significant deterioration of islet histoarchitecture and impeded insulin secretion by 2.7 ± 0.5-folds in 20 weeks high fat diet mice. Administration of fetuin-A (0.7 mg/g) along with 4 weeks of HFD produced similar results as 20 weeks of high fat feeding. Treating high doses of palmitate alone (0.50 mM) as well as in combination with fetuin-A (100 µg/ml) for 24 h inflicted apoptosis in MIN6 through the mitochondrial pathway. Knockdown of fetuin-A gene partially inhibited palmitate inflicted apoptosis in MIN6 by 1.83 ± 0.25 times, however, fetuin-A when added in the medium caused re-emergence of apoptosis. Notably, apoptosis induced by palmitate conditioned media from MIN6, 3T3L1, and HepG2, was partially inhibited in fetuin-A KD MIN6. These results confirmed the critical role of circulatory fetuin-A and ß-cell secreted fetuin-A in ß-cell dysfunction and apoptosis under hyperlipidemic conditions.

Fetuin-A secretion from ß-cells leads to accumulation of macrophages in islets, aggravates inflammation and impairs insulin secretion.

Elevated fetuin-A levels, chemokines and islet-resident macrophages are crucial factors associated with obesity-mediated type 2 diabetes (T2D). Here, the aim of the study was to investigate the effect of MIN6 (a mouse insulinoma cell line)-derived fetuin-A (also known as AHSG) in macrophage polarization and decipher the effect of M1 type pro-inflammatory macrophages in commanding over insulin secretion. MIN6 and islet-derived fetuin-A induced expression of the M1 type macrophage markers Emr1 (also known as Adgre1), Cd68 and CD11c (Itgax) (∼1.8 fold) along with increased cytokine secretion. Interestingly, suppression of fetuin-A in MIN6 successfully reduced M1 markers by ∼1.5 fold. MIN6-derived fetuin-A also induced chemotaxis of macrophages in a Boyden chamber chemotaxis assay. Furthermore, high-fat feeding in mice showed elevated cytokine and fetuin-A content in serum and islets, and also migration and polarization of macrophages to the islets, while ß-cells failed to meet the increased insulin demand. Moreover, in MIN6 culture, M1 macrophages sharply decreased insulin secretion by ∼2.8 fold. Altogether our results support an association of fetuin-A with islet inflammation and ß-cell dysfunction, owing to its role as a key chemoattractant and macrophage polarizing factor.

Exploring the Propensities of Fluorescent Carbazole Analogs toward the Inhibition of Amyloid Aggregation in Type 2 Diabetes: An Experimental and Theoretical Endeavor.

Amyloid aggregation is a pathological trait observed in many incurable and fatal neurodegenerative and metabolic diseases associated with misfolding and self-assembly of various proteins. Noncovalent interactions between these structural motifs and small molecules can, however, prevent this aggregation. Herein, five structurally different synthetic (Cz1-Cz4) and naturally occurring (Cz5, mahanimbine) fluorescent carbazole analogs are explored for their comparative amyloid aggregation inhibitory activities. Cz3 inhibited the amyloid deposition on the pancreatic ß-cells of diabetic mice. Moreover, Cz3 and Cz5 also showed efficacy as the fluorescent cell (MIN6) imaging agents. Further structural modifications of these carbazoles may lead to development of low-cost and non-toxic therapeutic agents for Type 2 diabetes and other amyloidosis-related diseases.

Blocking TLR4-NF-κB pathway protects mouse islets from the combinatorial impact of high fat and fetuin-A mediated dysfunction and restores ability for insulin secretion.

Lipid mediated pancreatic ß-cell dysfunction during Type 2 diabetes is known to be regulated by activation of TLR4 (Toll Like Receptor 4) and NF-κB (Nuclear factor kappa B). Recently we have reported that MIN6 cells (mouse insulinoma cells) secrete fetuin-A on stimulation by palmitate that aggravates ß-cell dysfunction, but the mechanism involved in-vivo has not been demonstrated and thus remained unclear. Here we attempted to dissect the role of palmitate and fetuin-A on insulin secretion using high fat diet (HFD) fed mice model. HFD islets showed curtailed insulin secretion after 20 weeks of treatment with activated TLR4-NF-κB pathway. Further treatment of islets with palmitate raised fetuin-A expression by ~2.8 folds and cut down insulin secretion by ~1.4 folds. However, blocking the activity of TLR4, fetuin-A and NF-κB using specific inhibitors or siRNAs not only restored insulin secretion by ~2 folds in standard diet fed mice islets and MIN6 cells but also evoke insulin secretory ability by ~2.3 folds in HFD islets. Altogether this study demonstrated that blocking TLR4, fetuin-A and NF-κB protect pancreatic ß-cells from the negative effects of free fatty acid and fetuin-A and restore insulin secretion.

Kaempferol inhibits Nrf2 signalling pathway via downregulation of Nrf2 mRNA and induces apoptosis in NSCLC cells.

Chemoprevention failure is considered to be the most emerging problem that makes non-small cell lung cancer (NSCLC) as one of the deadliest malignancies in the world. In NSCLC cells, Nuclear factor erythroid 2-related factor 2 (Nrf2), a redox sensitive transcription factor, promotes cancer cell survival and fosters mechanism for drug resistance. Here we report identification of Kaempferol, a dietary flavonoid, as a potent Nrf2 inhibitor using Nrf2 reporter assay in NSCLC cells (A549 and NCIH460). Kaempferol selectively reduces Nrf2 mRNA and protein levels and lower level of nuclear Nrf2 downregulates transcription of Nrf2 target genes (NQO1, HO1, AKR1C1 and GST). Kaempferol (25 µM) mediated downregulation of GST, NQO1 and HO1 expression is also observed even after stimulation of Nrf2 by tert-butylhydroquinone (tBHQ). Again, Kaempferol incubation does not change the levels of NFκBp65 and phospho NFκBp65, suggesting it hampers Nrf2 signalling pathway in these cells. Nrf2 inhibition by Kaempferol induces ROS accumulation after 48 h of treatment and makes NSCLC cells sensitive to apoptosis at physiological concentration. Taken together, our study demonstrates that Kaempferol is a potent inhibitor of Nrf2 and can be used as a natural sensitizer and anti-cancer agent for lung cancer therapeutics.

Trigonelline inhibits Nrf2 via EGFR signalling pathway and augments efficacy of Cisplatin and Etoposide in NSCLC cells.

Constitutive high expression of Nrf2 (Nuclear factor erythroid 2-related factor 2) is an important contributor of proliferation and chemoresistance in Non-small cell lung cancer (NSCLC). The aim of this present study was to investigate the Nrf2 inhibitory effect of Trigonelline, its mechanism of action and its possible use in combinatorial treatment with anti- lung cancer drugs, Cisplatin and Etoposide. Our immunofluorescence, western blot and real time PCR data showed that Trigonelline prevented nuclear accumulation of pNrf2 (four folds) and downregulated Nrf2 targeted genes in both A549 and NCIH460 cells. Trigonelline inhibited Nrf2 via reduced activation of EGFR signalling pathway and its downstream effector ERK 1/2 kinase. Trigonelline in combination with Cisplatin/Etoposide abrogated proliferation of NSCLC cells (A549, NCIH460 and NCIH1299) without showing any visible cytotoxicity to the normal lung epithelial cell (L132). Combinatorial treatment of Trigonelline with Cisplatin/Etoposide showed strong synergism at a sufficiently low concentration than the IC50 values of these drugs. Nrf2 knockdown experiment in NSCLC cells obliterated the effect of Trigonelline- Cisplatin and Trigonelline-Etoposide combination, indicating the role of Nrf2 inhibition in augmenting drug sensitivity. Our study demonstrated that Trigonelline blocks Nrf2 activation and its nuclear translocation via inhibition of EGFR signalling pathway. It has improved responsiveness of NSCLC cells for Cisplatin and Etoposide and could be a promising choice for lung cancer therapy.

Unfolding the Role of a Flavone-Based Fluorescent Antioxidant towards the Misfolding of Amyloid Proteins: An Endeavour to Probe Amyloid Aggregation.

4'-N,N-Dimethylamino-3-hydroxyflavone (DMAHF), a synthetic fluorescent flavone analogue with potent antioxidant activity, was explored as a molecular rotor-like fluoroprobe for amyloid aggregations, a causative factor in Alzheimer's disease, Parkinson's disease, type-2 diabetes, etc. During its interactions with (human) insulin amyloid aggregation (IAA), its microenvironment was changed. This instigated a drastic change in its excited-state intramolecular proton transfer-based dual emission behavior, which was tracked to monitor its amyloid probing activity. Thus, the amyloid probing potential of DMAHF was originated from its interactions with IAA, which were studied by various spectroscopic techniques and molecular docking and quantum-mechanical calculations. Morphological changes of the IAA in the presence of DMAHF were studied by scanning electron microscopy. DMAHF also probed efficiently the islet amyloid polypeptide deposition in the pancreatic ß-cells of diabetic mice. DMAHF showed significant sensitivity and specificity towards amyloid aggregation without having any complexity in its photophysical behavior. This indicates its potential as an ideal bio-friendly and cost-effective fluoroprobe for amyloid proteins.

A Nuclear-Localized Naphthalimide-Based Fluorescent Light-Up Probe for Selective Detection of Carbon Monoxide in Living Cells.

A nuclear-localized fluorescent light-up probe, NucFP-NO2, was designed and synthesized that can detect CO selectively in an aqueous buffer (pH 7.4, 37 °C) through the CO-mediated transformation of the nitro group into an amino-functionalized moiety. This probe triggered a more than 55-fold "turn-on" fluorescence response to CO without using any metal ions, e.g., Pd, Rh, Fe, etc. The enhanced response is highly selective over a variety of relevant reactive oxygen, nitrogen, and sulfur species and also various biologically important cationic, anionic, and neutral species. The detection limit of this probe for CO is as low as 0.18 µM with a linear range of 0-70 µM. Also, this fluorogenic probe is an efficient candidate for monitoring intracellular CO in living cells (RAW 264.7, A549 cells), and the fluorescence signals predominantly localize in the nuclear region.

Designed Synthesis of Dual Emitting Silicon Quantum Dot for Cell Imaging: Direct Labeling of Alpha 2-HS-Glycoprotein.

The innocent silicon quantum dots (SQDs) having dual emissive property (blue in VIS and red in NIR), high photostability, and freedom from auto fluorescence are designed and synthesized for the first time using ethylene glycol. A new attempt has been made for direct labeling of Alpha 2-HS-Glycoprotein (Fetuin A) through functionalization of the synthesized dots by EDC coupling. The SQDs were characterized by FTIR, TEM, AFM, XRD, EDX, DLS, and TGA. The chemistry involved in the synthesis and functionalization of dots is elucidated in detail. The synthesized SQDs are suitable for live cell imaging as well as direct labeling of the Fetuin A in the NIR region. The direct labeling technique developed for Fetuin A imaging is robust, more specific, and simple, and reduces the number of incubation and washing steps and produces better quality data compared to the conventional method using Rhodamine B.

Palmitate induced Fetuin-A secretion from pancreatic ß-cells adversely affects its function and elicits inflammation.

Islets of type 2 diabetes patients display inflammation, elevated levels of cytokines and macrophages. The master regulator of inflammation in the islets is free fatty acids (FFA). It has already been reported that FFA and TLR4 stimulation induces pro-inflammatory factors in the islets. In this report we demonstrate that excess lipid triggers Fetuin-A (FetA) secretion from the pancreatic ß-cells. Palmitate treatment to MIN6 cells showed significantly elevated FetA levels in respect to their controls. Fatty acid induces the FetA gene and protein expression in the pancreatic ß-cells via TLR4 and over-expression of NF-κB. In the NF-κB knocked down MIN6 cells palmitate could not trigger FetA release into the incubation medium. These results suggest that NF-κB mediates palmitate stimulated FetA secretion from the pancreatic ß-cells. Blocking the activity of TLR4 by CLI-095 incubation or TLR4 siRNA restored insulin secretion which confirmed the role of TLR4 in FFA-FetA mediated pancreatic ß-cell dysfunction. Palmitate mediated expression of NF-κB enahnced inflammatory response through expression of cytokines such as IL-1ß and IL-6. These results suggest that FFA mediated FetA secretion from pancreatic ß-cells lead to their dysfunction via FFA-TLR4 pathway. FetA thus creates an inflammatory environment in the pancreatic islets that can become a possible cause behind pancreatic ß-cell dysfunction in chronic hyperlipidemic condition.

Antioxidant flavone analog functionalized fluorescent silica nanoparticles: Synthesis and exploration of their possible use as biomolecule sensor.

For the first time, a synthetic fluorescent antioxidant flavone analog was successfully anchored onto the surface of the APTES-modified mesoporous silica nanoparticles (NPs) through sulfonamide linkage. The surface chemistry and morphology of the flavone modified fluorescent silica (FMFS) NPs were studied in detail. The flavone moiety when attached onto the FMFS NP surface, imparted its characteristic fluorescence and antioxidant activities to these NPs. Moreover, the NPs are highly biocompatible as evidenced from their cytotoxicity assay on normal lung cell (L132). The fluorescence activity of these biocompatible NPs was further utilized to study their interaction with a biomolecule, BSA (Bovine Serum Albumin). It was interesting to note that the fluorescence behavior of FMFS NPs completely changed on their binding with BSA. On the other hand, the intrinsic fluorescence activity of BSA was also significantly modified due to its interaction with FMFS NPs. Thus, the sensing and detection of biomolecules like BSA in presence of FMFS NPs can be accomplished by monitoring changes in the fluorescence behavior of either FMFS NPs or BSA. Furthermore, these FMFS NPs retained their intrinsic fluorescence behavior in the cellular medium which opens up their possible use as biocompatible cell imaging agents in future.