Mitochondrially targeted effects of berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo(5,6-a) quinolizinium] on K1735-M2 mouse melanoma cells: comparison with direct effects on isolated mitochondrial fractions

A systematic review of the anticancer properties of berberine, a natural product from Chinese herbs

Natural products represent a rich reservoir of potential small chemical molecules exhibiting antiproliferation and anticancer properties. An example is berberine, a protoberberine alkaloid widely distributed in medical plants used in traditional Chinese prescriptions. Recent advances have shown that berberine exerts anticancer activities both in vitro and in vivo through different mechanisms. Berberine shows inhibitory effects on the proliferation and reproduction of certain tumorigenic microorganisms and viruses, such as Heliobacter pylori and hepatitis B virus. Transcriptional regulation of some oncogene and carcinogenesis-related gene expression and interaction with both DNA and RNA are also well documented. Besides, berberine is a broad spectrum enzyme inhibitor, which affects N-acetyltransferase, cyclooxygenase-2, and topoisomerase activities and gene/protein expression. These actions, together with the regulation of reactive oxygen species production, mitochondrial transmembrane potential, and nuclear factor-kappaB activation might underlie its antiproliferative and proapoptotic effects. More importantly, the suppression of tumor growth and metastasis, the beneficial application in combined medication, and the improvement of multidrug resistance both in vivo and in vitro clearly show its potential as an alternative medicine for tumor chemotherapy.

Acute inhibition of selected membrane-proximal mouse T cell receptor signaling by mitochondrial antagonists

T cells absorb nanometric membrane vesicles, prepared from plasma membrane of antigen presenting cells, via dual receptor/ligand interactions of T cell receptor (TCR) with cognate peptide/major histocompatibility complex (MHC) plus lymphocyte function-associated antigen 1 (LFA-1) with intercellular adhesion molecule 1. TCR-mediated signaling for LFA-1 activation is also required for the vesicle absorption. Exploiting those findings, we had established a high throughput screening (HTS) platform and screened a library for isolation of small molecules inhibiting the vesicle absorption. Follow-up studies confirmed that treatments (1 hour) with various mitochondrial antagonists, including a class of anti-diabetic drugs (i.e., Metformin and Phenformin), resulted in ubiquitous inhibition of the vesicle absorption without compromising viability of T cells. Further studies revealed that the mitochondrial drug treatments caused impairment of specific membrane-proximal TCR signaling event(s). Thus, activation of Akt and PLC-gamma1 and entry of extracellular Ca(2+) following TCR stimulation were attenuated while polymerization of monomeric actins upon TCR triggering progressed normally after the treatments. Dynamic F-actin rearrangement concurring with the vesicle absorption was also found to be impaired by the drug treatments, implying that the inhibition by the drug treatments of downstream signaling events (and the vesicle absorption) could result from lack of directional relocation of signaling and cell surface molecules. We also assessed the potential application of mitochondrial antagonists as immune modulators by probing effects of the long-term drug treatments (24 hours) on viability of resting primary T cells and cell cycle progression of antigen-stimulated T cells. This study unveils a novel regulatory mechanism for T cell immunity in response to environmental factors having effects on mitochondrial function.

Can Drug Safety be Predicted and Animal Experiments Reduced by Using Isolated Mitochondrial Fractions?

Mitochondrial toxicity has resulted in the withdrawal of several drugs from the market. One particular example is nefazodone, an anti-depressant withdrawn in the USA due to hepatoxicity caused by drug-induced mitochondrial dysfunction. Drug development and safety testing can involve the use of large numbers of laboratory animals, which, without a decisive pre-screening for mitochondrial toxicity, are often unable to pre-empt higher mortality rates in some patient groups. The use of isolated mitochondria as a screening tool for drug safety can decrease the number of laboratory animals used in pre-clinical studies, thus improving animal welfare and healthcare outcomes and costs. Novel techniques involving high-throughput methods can be used to investigate whether a molecule is a mitochondrial toxicant. Moreover, these screens are mechanistically-based, since the effects of the drug on oxidative phosphorylation, calcium homeostasis and mitochondrial genetics can be assessed. This review is intended to demonstrate that isolated mitochondrial fractions are suitable for predicting drug and general chemical safety in toxicological screenings, thus contributing to the refinement and reduction of animal use in laboratory research.

Berberine suppresses proinflammatory responses through AMPK activation in macrophages

Berberine (BBR) has been shown to improve several metabolic disorders, such as obesity, type 2 diabetes, and dyslipidemia, by stimulating AMP-activated protein kinase (AMPK). However, the effects of BBR on proinflammatory responses in macrophages are poorly understood. Here we show that BBR represses proinflammatory responses through AMPK activation in macrophages. In adipose tissue of obese db/db mice, BBR treatment significantly downregulated the expression of proinflammatory genes such as TNF-alpha, IL-1beta, IL-6, monocyte chemoattractant protein-1 (MCP-1), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Consistently, BBR inhibited LPS-induced expression of proinflammatory genes including IL-1beta, IL-6, iNOS, MCP-1, COX-2, and matrix metalloprotease-9 in peritoneal macrophages and RAW 264.7 cells. Upon various proinflammatory signals including LPS, free fatty acids, and hydrogen peroxide, BBR suppressed the phosphorylation of MAPKs, such as p38, ERK, and JNK, and the level of reactive oxygen species in macrophages. Moreover, these inhibitory effects of BBR on proinflammatory responses were abolished by AMPK inhibition via either compound C, an AMPK inhibitor, or dominant-negative AMPK, implying that BBR would downregulate proinflammatory responses in macrophages via AMPK stimulation.

The effect of berberine in vitro on tight junctions in human Caco-2 intestinal epithelial cells

Berberine is one of the main alkaloids of Rhizoma coptidis which has been used for patients with gastrointestinal disorders. The major aim of this study was to investigate the effect of berberine on tight junction. Caco-2 cells were treated with various concentration of berberine. We observed the integrity of tight junction by measuring the transepithelial electrical resistance (TEER), and also studied the effect of berberine on morphology of tight junction and tight junction protein. These findings showed the first time that berberine could reduce epithelial gut permeability, and might help explain the possible mechanisms of anti-diarrhea activity of berberine.

Sanguinarine cytotoxicity on mouse melanoma K1735-M2 cells--nuclear vs. mitochondrial effects

Sanguinarine (SANG) is an alkaloid recognized to have anti-proliferative activity against various human tumour cell lines. No data is available on the susceptibility of advanced malignant melanoma to SANG, although this disease has a very poor prognosis if not detected in time due to the resistance to conventional chemotherapy. The present work was designed to study the nuclear and mitochondrial involvement in the pro-apoptotic effect of SANG in an invasive mouse melanoma cell line. The results obtained show that SANG is primarily accumulated by the cell nuclei, causing inhibition of cell proliferation and inducing cell death, as confirmed by an increase in sub-G1 peaks. At low concentrations, SANG induces mitochondrial depolarization in a sub-population of melanoma cells, which also generally displayed strong nuclear labelling of phosphorylated histone H2AX. Western blotting revealed an increase in p53, but not Bax protein, in both whole-cell extracts and in mitochondrial fractions. Isolated hepatic mitochondrial fractions revealed that SANG affects the mitochondrial respiratory chain, and has dual effects on mitochondrial calcium loading capacity. We suggest that SANG is able to induce apoptosis in metastatic melanoma cells. The knowledge of mitochondrial vs. nuclear effects of SANG is important in the development of this promising compound for clinical use against aggressive melanoma.

Mechanisms of berberine (natural yellow 18)-induced mitochondrial dysfunction: interaction with the adenine nucleotide translocator

Berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo (5,6-a) quinolizinium] is an alkaloid present in plants of the Berberidaceae family and used in traditional Chinese and North American medicine. We have previously demonstrated that berberine causes mitochondrial depolarization and fragmentation, with simultaneous increase in oxidative stress. We also demonstrated that berberine causes an inhibition of mitochondrial respiration and a decrease on calcium loading capacity through induction of the mitochondrial permeability transition (MPT). The objective of the present work is to investigate a common target for both induction of the MPT and inhibition of respiration. The hypothesis is that berberine induces the MPT through interacting with the adenine nucleotide translocator (ANT). By measuring induction of the MPT through increased mitochondrial swelling, membrane depolarization and loss of calcium retention, we observed that the effects of berberine were not inhibited by bongkrekic acid although adenosine diphosphate (ADP)/oligomycin completely prevented the MPT. Also, we observed that berberine increased the depolarization effect of oleic acid on liver mitochondria. The initial depolarization observed when berberine is added to mitochondria was not affected by ANT inhibitors. Taken together, we propose that berberine acts on the ANT, altering the binding of the protein to bongkrekic acid but not to cyclosporin A or ADP. It is also clear that the membrane potential is required for berberine effects, most likely for allowing for its mitochondrial accumulation. Mitochondrial effects of berberine can be relevant not only for its proposed antitumor activity but also for the assessment of its organ toxicity, depending on factors such as tissue accumulation or delivery.