R-Lipoic Acid Inhibits Mammalian Pyruvate Dehydrogenase Kinase

Dichloroacetate for Cancer Treatment: Some Facts and Many Doubts

Rarely has a chemical elicited as much controversy as dichloroacetate (DCA). DCA was initially considered a dangerous toxic industrial waste product, then a potential treatment for lactic acidosis. However, the main controversies started in 2008 when DCA was found to have anti-cancer effects on experimental animals. These publications showed contradictory results in vivo and in vitro such that a thorough consideration of this compound's in cancer is merited. Despite 50 years of experimentation, DCA's future in therapeutics is uncertain. Without adequate clinical trials and health authorities' approval, DCA has been introduced in off-label cancer treatments in alternative medicine clinics in Canada, Germany, and other European countries. The lack of well-planned clinical trials and its use by people without medical training has discouraged consideration by the scientific community. There are few thorough clinical studies of DCA, and many publications are individual case reports. Case reports of DCA's benefits against cancer have been increasing recently. Furthermore, it has been shown that DCA synergizes with conventional treatments and other repurposable drugs. Beyond the classic DCA target, pyruvate dehydrogenase kinase, new target molecules have also been recently discovered. These findings have renewed interest in DCA. This paper explores whether existing evidence justifies further research on DCA for cancer treatment and it explores the role DCA may play in it.

Targeting the Metabolic Paradigms in Cancer and Diabetes

Dysregulated metabolic dynamics are evident in both cancer and diabetes, with metabolic alterations representing a facet of the myriad changes observed in these conditions. This review delves into the commonalities in metabolism between cancer and type 2 diabetes (T2D), focusing specifically on the contrasting roles of oxidative phosphorylation (OXPHOS) and glycolysis as primary energy-generating pathways within cells. Building on earlier research, we explore how a shift towards one pathway over the other serves as a foundational aspect in the development of cancer and T2D. Unlike previous reviews, we posit that this shift may occur in seemingly opposing yet complementary directions, akin to the Yin and Yang concept. These metabolic fluctuations reveal an intricate network of underlying defective signaling pathways, orchestrating the pathogenesis and progression of each disease. The Warburg phenomenon, characterized by the prevalence of aerobic glycolysis over minimal to no OXPHOS, emerges as the predominant metabolic phenotype in cancer. Conversely, in T2D, the prevailing metabolic paradigm has traditionally been perceived in terms of discrete irregularities rather than an OXPHOS-to-glycolysis shift. Throughout T2D pathogenesis, OXPHOS remains consistently heightened due to chronic hyperglycemia or hyperinsulinemia. In advanced insulin resistance and T2D, the metabolic landscape becomes more complex, featuring differential tissue-specific alterations that affect OXPHOS. Recent findings suggest that addressing the metabolic imbalance in both cancer and diabetes could offer an effective treatment strategy. Numerous pharmaceutical and nutritional modalities exhibiting therapeutic effects in both conditions ultimately modulate the OXPHOS-glycolysis axis. Noteworthy nutritional adjuncts, such as alpha-lipoic acid, flavonoids, and glutamine, demonstrate the ability to reprogram metabolism, exerting anti-tumor and anti-diabetic effects. Similarly, pharmacological agents like metformin exhibit therapeutic efficacy in both T2D and cancer. This review discusses the molecular mechanisms underlying these metabolic shifts and explores promising therapeutic strategies aimed at reversing the metabolic imbalance in both disease scenarios.

Toxicity of the spike protein of COVID-19 is a redox shift phenomenon: A novel therapeutic approach

We previously demonstrated that most diseases display a form of anabolism due to mitochondrial impairment: in cancer, a daughter cell is formed; in Alzheimer's disease, amyloid plaques; in inflammation cytokines and lymphokines. The infection by Covid-19 follows a similar pattern. Long-term effects include redox shift and cellular anabolism as a result of the Warburg effect and mitochondrial dysfunction. This unrelenting anabolism leads to the cytokine storm, chronic fatigue, chronic inflammation or neurodegenerative diseases. Drugs such as Lipoic acid and Methylene Blue have been shown to enhance the mitochondrial activity, relieve the Warburg effect and increase catabolism. Similarly, coMeBining Methylene Blue, Chlorine dioxide and Lipoic acid may help reduce long-term Covid-19 effects by stimulating the catabolism.

Alpha-lipoic acid supplementation corrects pathological alterations in cellular models of pantothenate kinase-associated neurodegeneration with residual PANK2 expression levels

BACKGROUND

Neurodegeneration with brain iron accumulation (NBIA) disorders are a group of neurodegenerative diseases that have in common the accumulation of iron in the basal nuclei of the brain which are essential components of the extrapyramidal system. Frequent symptoms are progressive spasticity, dystonia, muscle rigidity, neuropsychiatric symptoms, and retinal degeneration or optic nerve atrophy. One of the most prevalent subtypes of NBIA is Pantothenate kinase-associated neurodegeneration (PKAN). It is caused by pathogenic variants in the gene of pantothenate kinase 2 (PANK2) which encodes the enzyme responsible for the first reaction on the coenzyme A (CoA) biosynthesis pathway. Thus, deficient PANK2 activity induces CoA deficiency as well as low expression levels of 4'-phosphopantetheinyl proteins which are essential for mitochondrial metabolism.

METHODS

This study is aimed at evaluating the role of alpha-lipoic acid (α-LA) in reversing the pathological alterations in fibroblasts and induced neurons derived from PKAN patients. Iron accumulation, lipid peroxidation, transcript and protein expression levels of PANK2, mitochondrial ACP (mtACP), 4''-phosphopantetheinyl and lipoylated proteins, as well as pyruvate dehydrogenase (PDH) and Complex I activity were examined.

RESULTS

Treatment with α-LA was able to correct all pathological alterations in responsive mutant fibroblasts with residual PANK2 enzyme expression. However, α-LA had no effect on mutant fibroblasts with truncated/incomplete protein expression. The positive effect of α-LA in particular pathogenic variants was also confirmed in induced neurons derived from mutant fibroblasts.

CONCLUSIONS

Our results suggest that α-LA treatment can increase the expression levels of PANK2 and reverse the mutant phenotype in PANK2 responsive pathogenic variants. The existence of residual enzyme expression in some affected individuals raises the possibility of treatment using high dose of α-LA.

Oxoplatin-Based Pt(IV) Lipoate Complexes and Their Biological Activity

α-Lipoic acid, known for its anti-inflammatory and antioxidant activity, represents a promising ligand for Pt(IV) prodrugs. Three new Pt(IV) lipoate complexes were synthesized and characterized by NMR spectroscopy (1 H, 13 C, 195 Pt), mass spectrometry and elemental analysis. Due to the low solubility of the complex containing two axial lipoate ligands, further experiments to examine the biological activity were performed with two Pt(IV) complexes containing just one axial lipoate ligand. Both complexes exhibit anticancer activity and produce reactive oxygen species (ROS) in the cell lines tested. Especially, the monosubstituted complex can be reduced by ascorbic acid and forms adducts with 9-methylguanine (9MeG), which is favorable for the formation of DNA-crosslinks in the cells.

Decrypting the potential role of α-lipoic acid in Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases with motor disturbances, cognitive decline, and behavioral impairment. It is characterized by the extracellular aggregation of amyloid-β plaques and the intracellular accumulation of tau protein. AD patients show a cognitive decline, which has been associated with oxidative stress, as well as mitochondrial dysfunction. Alpha-lipoic acid (α-LA), a natural antioxidant present in food and used as a dietary supplement, has been considered a promising agent for the prevention or treatment of neurodegenerative disorders. Despite multiple preclinical studies indicating beneficial effects of α-LA in memory functioning, and pointing to its neuroprotective effects, to date only a few studies have examined its effects in humans. Studies performed in animal models of memory loss associated with aging and AD have shown that α-LA improves memory in a variety of behavioral paradigms. Furthermore, molecular mechanisms underlying α-LA effects have also been investigated. Accordingly, α-LA shows antioxidant, antiapoptotic, anti-inflammatory, glioprotective, metal chelating properties in both in vivo and in vitro studies. In addition, it has been shown that α-LA reverses age-associated loss of neurotransmitters and their receptors. The review article aimed at summarizing and discussing the main studies investigating the neuroprotective effects of α-LA on cognition as well as its molecular effects, to improve the understanding of the therapeutic potential of α-LA in patients suffering from neurodegenerative disorders, supporting the development of clinical trials with α-LA.

Hyperosmolarity Triggers the Warburg Effect in Chinese Hamster Ovary Cells and Reveals a Reduced Mitochondria Horsepower

Tumor cells are known to favor a glycolytic metabolism over oxidative phosphorylation (OxPhos), which takes place in mitochondria, to produce the energy and building blocks essential for cell maintenance and cell growth. This phenotypic property of tumor cells gives them several advantages over normal cells and is known as the Warburg effect. Tumors can be treated as a metabolic disease by targeting their bioenergetics capacity. Alpha-lipoic acid (ALA) and calcium hydroxycitrate (HCA) are two drugs known to target the Warburg effect in tumor cells and hence induce the mitochondria for ATP production. However, tumor cells, known to have an increased flux through glycolysis, are not able to handle the activation of their mitochondria by drugs or any other condition, leading to decoupling of gene regulation. In this study, these drug effects were studied by mimicking an inflammatory condition through the imposition of a hyperosmotic condition in Chinese hamster ovary (CHO) cells, which behave similarly to tumor cells. Indeed, CHO cells grown in high osmolarity conditions, using 200 mM mannitol, showed a pronounced Warburg effect phenotype. Our results show that hyperosmolar conditions triggered high-throughput glycolysis and enhanced glutaminolysis in CHO cells, such as during cancer cell proliferation in inflammatory tissue. Finally, we found that the hyperosmolar condition was correlated with increased mitochondrial membrane potential (ΔΨm) but mitochondrial horsepower seemed to vanish (h = Δp/ΔΨm), which may be explained by mitochondrial hyperfusion.

Targeting pyruvate dehydrogenase kinase signaling in the development of effective cancer therapy

Pyruvate is irreversibly decarboxylated to acetyl coenzyme A by mitochondrial pyruvate dehydrogenase complex (PDC). Decarboxylation of pyruvate is considered a crucial step in cell metabolism and energetics. The cancer cells prefer aerobic glycolysis rather than mitochondrial oxidation of pyruvate. This attribute of cancer cells allows them to sustain under indefinite proliferation and growth. Pyruvate dehydrogenase kinases (PDKs) play critical roles in many diseases because they regulate PDC activity. Recent findings suggest an altered metabolism of cancer cells is associated with impaired mitochondrial function due to PDC inhibition. PDKs inhibit the PDC activity via phosphorylation of the E1a subunit and subsequently cause a glycolytic shift. Thus, inhibition of PDK is an attractive strategy in anticancer therapy. This review highlights that PDC/PDK axis could be implicated in cancer's therapeutic management by developing potential small-molecule PDK inhibitors. In recent years, a dramatic increase in the targeting of the PDC/PDK axis for cancer treatment gained an attention from the scientific community. We further discuss breakthrough findings in the PDC-PDK axis. In addition, structural features, functional significance, mechanism of activation, involvement in various human pathologies, and expression of different forms of PDKs (PDK1-4) in different types of cancers are discussed in detail. We further emphasized the gene expression profiling of PDKs in cancer patients to prognosis and therapeutic manifestations. Additionally, inhibition of the PDK/PDC axis by small molecule inhibitors and natural compounds at different clinical evaluation stages has also been discussed comprehensively.

Combining lipoic acid to methylene blue reduces the Warburg effect in CHO cells: From TCA cycle activation to enhancing monoclonal antibody production

The Warburg effect, a hallmark of cancer, has recently been identified as a metabolic limitation of Chinese Hamster Ovary (CHO) cells, the primary platform for the production of monoclonal antibodies (mAb). Metabolic engineering approaches, including genetic modifications and feeding strategies, have been attempted to impose the metabolic prevalence of respiration over aerobic glycolysis. Their main objective lies in decreasing lactate production while improving energy efficiency. Although yielding promising increases in productivity, such strategies require long development phases and alter entangled metabolic pathways which singular roles remain unclear. We propose to apply drugs used for the metabolic therapy of cancer to target the Warburg effect at different levels, on CHO cells. The use of α-lipoic acid, a pyruvate dehydrogenase activator, replenished the Krebs cycle through increased anaplerosis but resulted in mitochondrial saturation. The electron shuttle function of a second drug, methylene blue, enhanced the mitochondrial capacity. It pulled on anaplerotic pathways while reducing stress signals and resulted in a 24% increase of the maximum mAb production. Finally, the combination of both drugs proved to be promising for stimulating Krebs cycle activity and mitochondrial respiration. Therefore, drugs used in metabolic therapy are valuable candidates to understand and improve the metabolic limitations of CHO-based bioproduction.

Role of coenzymes in cancer metabolism

Cancer is a heterogeneous set of diseases characterized by the rewiring of cellular signaling and the reprogramming of metabolic pathways to sustain growth and proliferation. In past decades, studies were focused primarily on the genetic complexity of cancer. Recently, increasing number of studies have discovered several mutations among metabolic enzymes in different tumor cells. Most of the enzymes are regulated by coenzymes, organic cofactors, that function as intermediate carrier of electrons or functional groups that are transferred during the reaction. However, the precise role of cofactors is not well elucidated. In this review, we discuss several metabolic enzymes associated to cancer metabolism rewiring, whose inhibition may represent a therapeutic target. Such enzymes, upon expression or inhibition, may impact also the coenzymes levels, but only in few cases, it was possible to direct correlate coenzymes changes with a specific enzyme. In addition, we also summarize an up-to-date information on biological role of some coenzymes, preclinical and clinical studies, that have been carried out in various cancers and their outputs.

Multi-Acting Mitochondria-Targeted Platinum(IV) Prodrugs of Kiteplatin with α-Lipoic Acid in the Axial Positions

Platinum(II) drugs are activated intracellularly by aquation of the leaving groups and then bind to DNA, forming DNA adducts capable to activate various signal-transduction pathways. Mostly explored in recent years are Pt(IV) complexes which allow the presence of two additional ligands in the axial positions suitable for the attachment of other cancer-targeting ligands. Here we have extended this strategy by coordinating in the axial positions of kiteplatin ([PtCl₂(cis-1,4-DACH)], DACH = Diaminocyclohexane) and its CBDCA (1,1-cyclobutanedicarboxylate) analogue the antioxidant α-Lipoic acid (ALA), an inhibitor of the mitochondrial pyruvate dehydrogenase kinase (PDK). The new compounds (cis,trans,cis-[Pt(CBDCA)(ALA)₂(cis-1,4-DACH)], 2, and cis,trans,cis-[PtCl₂(ALA)₂(cis-1,4-DACH)], 3), after intracellular reduction, release the precursor Pt(II) species and two molecules of ALA. The Pt residue is able to target DNA, while ALA could act on mitochondria as activator of the pyruvate dehydrogenase complex, thus suppressing anaerobic glycolysis. Compounds 2 and 3 were tested in vitro on a panel of five human cancer cell lines and compared to cisplatin, oxaliplatin, and kiteplatin. They proved to be much more effective than the reference compounds, with complex 3 most effective in 3D spheroid tumor cultures. Notably, treatment of human A431 carcinoma cells with 2 and 3 did not determine increase of cellular ROS (usually correlated to inhibition of mitochondrial PDK) and did not induce a significant depolarization of the mitochondrial membrane or alteration of other morphological mitochondrial parameters.

The Long-Term Survival of a Patient With Stage IV Renal Cell Carcinoma Following an Integrative Treatment Approach Including the Intravenous α-Lipoic Acid/Low-Dose Naltrexone Protocol

In this case report, we describe the treatment of a 64-year-old male patient diagnosed with metastatic renal cell carcinoma (RCC) in June of 2008. In spite of a left nephrectomy and the standard oncological protocols, the patient developed a solitary left lung metastasis that continued to grow. He was informed that given his diagnosis and poor response to conventional therapy, any further treatment would, at best, be palliative. The patient arrived at the Integrative Medical Center of New Mexico in August of 2010. He was in very poor health, weak, and cachectic. An integrative program—developed by one of the authors using intravenous (IV) α-lipoic acid, IV vitamin C, low-dose naltrexone, and hydroxycitrate, and a healthy life style program—was initiated. From August 2010 to August 2015, the patient’s RCC with left lung metastasis was followed closely using computed tomography and positron emission tomography/computed tomography imaging. His most recent positron emission tomography scan demonstrated no residual increased glucose uptake in his left lung. After only a few treatments of IV α-lipoic acid and IV vitamin C, his symptoms began to improve, and the patient regained his baseline weight. His energy and outlook improved, and he returned to work. The patient had stable disease with disappearance of the signs and symptoms of stage IV RCC, a full 9 years following diagnosis, with a gentle integrative program, which is essentially free of side effects. As of November 2017 the patient feels well and is working at his full-time job.

Therapeutic Targeting of the Pyruvate Dehydrogenase Complex/Pyruvate Dehydrogenase Kinase (PDC/PDK) Axis in Cancer

The mitochondrial pyruvate dehydrogenase complex (PDC) irreversibly decarboxylates pyruvate to acetyl coenzyme A, thereby linking glycolysis to the tricarboxylic acid cycle and defining a critical step in cellular bioenergetics. Inhibition of PDC activity by pyruvate dehydrogenase kinase (PDK)-mediated phosphorylation has been associated with the pathobiology of many disorders of metabolic integration, including cancer. Consequently, the PDC/PDK axis has long been a therapeutic target. The most common underlying mechanism accounting for PDC inhibition in these conditions is post-transcriptional upregulation of one or more PDK isoforms, leading to phosphorylation of the E1α subunit of PDC. Such perturbations of the PDC/PDK axis induce a "glycolytic shift," whereby affected cells favor adenosine triphosphate production by glycolysis over mitochondrial oxidative phosphorylation and cellular proliferation over cellular quiescence. Dichloroacetate is the prototypic xenobiotic inhibitor of PDK, thereby maintaining PDC in its unphosphorylated, catalytically active form. However, recent interest in the therapeutic targeting of the PDC/PDK axis for the treatment of cancer has yielded a new generation of small molecule PDK inhibitors. Ongoing investigations of the central role of PDC in cellular energy metabolism and its regulation by pharmacological effectors of PDKs promise to open multiple exciting vistas into the biochemical understanding and treatment of cancer and other diseases.

Mechanisms of Vascular Calcification: The Pivotal Role of Pyruvate Dehydrogenase Kinase 4

Vascular calcification, abnormal mineralization of the vessel wall, is frequently associated with aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Vascular calcification is a key risk factor for many adverse clinical outcomes, including ischemic cardiac events and subsequent cardiovascular mortality. Vascular calcification was long considered to be a passive degenerative process, but it is now recognized as an active and highly regulated process similar to bone formation. However, despite numerous studies on the pathogenesis of vascular calcification, the mechanisms driving this process remain poorly understood. Pyruvate dehydrogenase kinases (PDKs) play an important role in the regulation of cellular metabolism and mitochondrial function. Recent studies show that PDK4 is an attractive therapeutic target for the treatment of various metabolic diseases. In this review, we summarize our current knowledge regarding the mechanisms of vascular calcification and describe the role of PDK4 in the osteogenic differentiation of vascular smooth muscle cells and development of vascular calcification. Further studies aimed at understanding the molecular mechanisms of vascular calcification will be critical for the development of novel therapeutic strategies.

The disulfide compound α-lipoic acid and its derivatives: A novel class of anticancer agents targeting mitochondria

The endogenous disulfide α-lipoic acid (LA) is an essential mitochondrial co-factor. In addition, LA and its reduced counterpart dihydro lipoic acid form a potent redox couple with antioxidative functions, for which it is used as dietary supplement and therapeutic. Recently, it has gained attention due to its cytotoxic effects in cancer cells, which is the key aspect of this review. We initially recapitulate the dietary occurrence, gastrointestinal absorption and pharmacokinetics of LA, illustrating its diverse antioxidative mechanisms. We then focus on its mode of action in cancer cells, in which it triggers primarily the mitochondrial pathway of apoptosis, whereas non-transformed primary cells are hardly affected. Furthermore, LA impairs oncogenic signaling and displays anti-metastatic potential. Novel LA derivatives such as CPI-613, which target mitochondrial energy metabolism, are described and recent pre-clinical studies are presented, which demonstrate that LA and its derivatives exert antitumor activity in vivo. Finally, we highlight clinical studies currently performed with the LA analog CPI-613. In summary, LA and its derivatives are promising candidates to complement the arsenal of established anticancer drugs due to their mitochondria-targeted mode of action and non-genotoxic properties.

Pyruvate Dehydrogenase Kinase 4 Promotes Vascular Calcification via SMAD1/5/8 Phosphorylation

Vascular calcification, a pathologic response to defective calcium and phosphate homeostasis, is strongly associated with cardiovascular mortality and morbidity. In this study, we have observed that pyruvate dehydrogenase kinase 4 (PDK4) is upregulated and pyruvate dehydrogenase complex phosphorylation is increased in calcifying vascular smooth muscle cells (VSMCs) and in calcified vessels of patients with atherosclerosis, suggesting that PDK4 plays an important role in vascular calcification. Both genetic and pharmacological inhibition of PDK4 ameliorated the calcification in phosphate-treated VSMCs and aortic rings and in vitamin D₃-treated mice. PDK4 augmented the osteogenic differentiation of VSMCs by phosphorylating SMAD1/5/8 via direct interaction, which enhances BMP2 signaling. Furthermore, increased expression of PDK4 in phosphate-treated VSMCs induced mitochondrial dysfunction followed by apoptosis. Taken together, our results show that upregulation of PDK4 promotes vascular calcification by increasing osteogenic markers with no adverse effect on bone formation, demonstrating that PDK4 is a therapeutic target for vascular calcification.

Interaction of α-Lipoic Acid with the Human Na+/Multivitamin Transporter (hSMVT)

The human Na(+)/multivitamin transporter (hSMVT) has been suggested to transport α-lipoic acid (LA), a potent antioxidant and anti-inflammatory agent used in therapeutic applications, e.g. in the treatment of diabetic neuropathy and Alzheimer disease. However, the molecular basis of the cellular delivery of LA and in particular the stereospecificity of the transport process are not well understood. Here, we expressed recombinant hSMVT in Pichia pastoris and used affinity chromatography to purify the detergent-solubilized protein followed by reconstitution of hSMVT in lipid bilayers. Using a combined approach encompassing radiolabeled LA transport and equilibrium binding studies in conjunction with the stabilized R-(+)- and S-(-)-enantiomers and the R,S-(+/-) racemic mixture of LA or lipoamide, we identified the biologically active form of LA, R-LA, to be the physiological substrate of hSMVT. Interaction of R-LA with hSMVT is strictly dependent on Na(+). Under equilibrium conditions, hSMVT can simultaneously bind ~2 molecules of R-LA in a biphasic binding isotherm with dissociation constants (Kd) of 0.9 and 7.4 μm. Transport of R-LA in the oocyte and reconstituted system is exclusively dependent on Na(+) and exhibits an affinity of ~3 μm. Measuring transport with known amounts of protein in proteoliposomes containing hSMVT in outside-out orientation yielded a catalytic turnover number (kcat) of about 1 s(-1), a value that is well in agreement with other Na(+)-coupled transporters. Our data suggest that hSMVT-mediated transport is highly specific for R-LA at our tested concentration range, a finding with wide ramifications for the use of LA in therapeutic applications.

Lipoic acid induces p53-independent cell death in colorectal cancer cells and potentiates the cytotoxicity of 5-fluorouracil

Alpha-lipoic acid (LA), which plays a pivotal role in mitochondrial energy metabolism, is an endogenous dithiol compound with an array of antioxidative functions. It has been shown that LA triggers cell death in tumor cell lines, whereas non-transformed cells are hardly affected. In the present study, we analyzed the cytotoxicity of LA on colorectal cancer (CRC) cells differing in their p53 status and investigated a putative synergistic effect with the anticancer drug 5-fluorouracil (5-FU). We show that LA induces a dose-dependent decrease in cell viability, which was independent of the p53 status as attested in isogenic p53-proficient and p53-deficient cell lines. This effect was largely attributable to cell death induction as revealed by Annexin-V/PI staining. LA-treated HCT116 cells underwent caspase-dependent and caspase-independent cell death, which was blocked by the pan-caspase inhibitor zVAD and the RIP-kinase inhibitor Necrostatin-1, respectively. In CaCO-2 and HT29 cells, LA induced caspase-dependent cell demise via activation of caspase-9, caspase-3 and caspase-7 with subsequent PARP-1 cleavage as demonstrated by immunoblot analysis, activity assays and pan-caspase inhibition. Interestingly, LA treatment did neither activate p53 nor induced genotoxic effects as shown by lack of DNA strand breaks and phosphorylation of histone 2AX. Finally, we provide evidence that LA increases the cytotoxic effect induced by the anticancer drug 5-FU as revealed by significantly enhanced cell death rates in HCT116 and CaCO-2 cells. Collectively, these findings demonstrate that LA induces CRC cell death independent of their p53 status and potentiates the cytotoxicity of 5-FU without causing DNA damage on its own, which makes it a candidate for tumor therapy.

Adverse effects of high doses of intravenous alpha lipoic Acid on liver mitochondria

Alpha lipoic acid (ALA, thioctic acid), among other actions, is an essential coenzyme in the conversion of pyruvate to acetyl co-enzyme A. Therefore, it is necessary for the production of energy for aerobic organisms. Scientists have found that it can be used medically to help regenerate liver tissue, reverse the complications of diabetes mellitus, slow or stop the growth of cancer cells, and chelate heavy metals, among other actions. In this article, the authors describe the cellular mitochondrial damage from excessively high doses of this beneficial agent.

Regulation of pyruvate metabolism in metabolic-related diseases

Pyruvate is an obligatory intermediate in the oxidative disposal of glucose and a major precursor for the synthesis of glucose, glycerol, fatty acids, and non-essential amino acids. Stringent control of the fate of pyruvate is critically important for cellular homeostasis. The regulatory mechanisms for its metabolism are therefore of great interest. Recent advances include the findings that (a) the mitochondrial pyruvate carrier is sensitive to inhibition by thiazolidinediones; (b) pyruvate dehydrogenase kinases induce the Warburg effect in many disease states; and (c) pyruvate carboxylase is an important determinate of the rates of gluconeogenesis in humans with type 2 diabetes. These enzymes are potential therapeutic targets for several diseases.

Structure-guided development of specific pyruvate dehydrogenase kinase inhibitors targeting the ATP-binding pocket

Pyruvate dehydrogenase kinase isoforms (PDKs 1-4) negatively regulate activity of the mitochondrial pyruvate dehydrogenase complex by reversible phosphorylation. PDK isoforms are up-regulated in obesity, diabetes, heart failure, and cancer and are potential therapeutic targets for these important human diseases. Here, we employed a structure-guided design to convert a known Hsp90 inhibitor to a series of highly specific PDK inhibitors, based on structural conservation in the ATP-binding pocket. The key step involved the substitution of a carbonyl group in the parent compound with a sulfonyl in the PDK inhibitors. The final compound of this series, 2-[(2,4-dihydroxyphenyl)sulfonyl]isoindoline-4,6-diol, designated PS10, inhibits all four PDK isoforms with IC50 = 0.8 μM for PDK2. The administration of PS10 (70 mg/kg) to diet-induced obese mice significantly augments pyruvate dehydrogenase complex activity with reduced phosphorylation in different tissues. Prolonged PS10 treatments result in improved glucose tolerance and notably lessened hepatic steatosis in the mouse model. The results support the pharmacological approach of targeting PDK to control both glucose and fat levels in obesity and type 2 diabetes.

Selective cytotoxicity and combined effects of camptothecin or paclitaxel with sodium-R-alpha lipoate on A549 human non-small cell lung cancer cells

Nonsmall cell lung cancer (NSCLC) is the most common type of lung cancer and remains the deadliest form of cancer in the United States and worldwide. New therapies are highly sought after to improve outcome. The effect of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity was evaluated on A549 NSCLC and BEAS-2B "normal" lung epithelial cells. Combination indices (CI) and dose reduction indices (DRI) were investigated by studying the cytotoxicity of sodium-R-alpha lipoate (0-16 mM), camptothecin (0-25 nM) and paclitaxel (0-0.06 nM) alone and in combination. 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium-bromide (MTT) was used to assess cytotoxicity. The combinational cytotoxic effects of sodium-R-alpha lipoate with camptothecin or paclitaxel were analyzed using a simulation of dose effects (CompuSyn® 3.01). The effects of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity varied based on concentrations and treatment times. It was found that sodium-R-alpha lipoate wasn't cytotoxic toward BEAS-2B cells at any of the concentrations tested. For A549 cells, CIs [(additive (CI = 1); synergistic (CI < 1); antagonistic (CI < 1)] were lower and DRIs were higher for the camptothecin/sodium-R-alpha-lipoate combination (CI = ∼0.17-1.5; DRI = ∼2.2-22.6) than the paclitaxel/sodium-R-alpha-lipoate combination (CI = ∼0.8-9.9; DRI = ∼0.10-5.8) suggesting that the camptothecin regimen was synergistic and that the addition of sodium-R-alpha lipoate was important for reducing the camptothecin dose and potential for adverse effects.

Lipoic acid inhibits cell proliferation of tumor cells in vitro and in vivo

Cancer cells convert glucose preferentially to lactate even in the presence of oxygen (aerobic glycolysis-Warburg effect). New concepts in cancer treatment aim at inhibition of aerobic glycolysis. Pyruvate dehydrogenase converts pyruvate to acetylCoA thus preventing lactate formation. Therefore, the aim of this study was to evaluate compounds that could activate pyruvate dehydrogenase in cancer cells. We investigated the effects of (R)-(+)-α-lipoic acid (LPA) and dichloroacetate (DCA), possible activators of pyruvate dehydrogenase, on suppression of aerobic glycolysis and induction of cell death. The neuroblastoma cell lines Kelly, SK-N-SH, Neuro-2a and the breast cancer cell line SkBr3 were incubated with different concentrations (0.1-30 mM) of LPA and DCA. The effects of both compounds on cell viability/proliferation (WST-1 assay), [18F]-FDG uptake, lactate production and induction of apoptosis (flow cytometric detection of caspase-3) were evaluated. Furthermore, NMRI nu/nu mice that had been inoculated s.c. with SkBr3 cells were treated daily for four weeks with LPA (i.p, 18.5 mg/kg) starting at day 7 p.i.. Tumor development was measured with a sliding caliper and monitored via [18F]-FDG-PET. Residual tumors after therapy were examined histopathologically. These data suggests that LPA can reduce (1) cell viability/proliferation, (2) uptake of [18F]-FDG and (3) lactate production and increase apoptosis in all investigated cell lines. In contrast, DCA was almost ineffective. In the mouse xenograft model with s.c. SkBr3 cells, daily treatment with LPA retarded tumor progression. Therefore, LPA seems to be a promising compound for cancer treatment.

The pyruvate carboxylase-pyruvate dehydrogenase axis in islet pyruvate metabolism: Going round in circles?

Pyruvate is the major product of glycolysis in pancreatic β-cells, and its ultimate metabolic fate depends on the relative activities of two enzymes. The first, pyruvate carboxylase (PC) replenishes oxaloacetate withdrawn from the tricarboxylic acid (TCA) cycle via the carboxylation of pyruvate to form oxaloacetate. Flux via PC is also involved in the formation of NADPH, one of several important coupling factors for insulin secretion. In most tissues, PC activity is enhanced by increased acetyl-CoA. The alternative fate of pyruvate is its oxidative decarboxylation to form acetyl-CoA via the pyruvate dehydrogenase complex (PDC). The ultimate fate of acetyl-CoA carbon is oxidation to CO2 via the TCA cycle, and so the PDC reaction results of the irreversible loss of glucose-derived carbon. Thus, PDC activity is stringently regulated. The mechanisms controlling PDC activity include end-product inhibition by increased acetyl-CoA, NADH and ATP, and its phosphorylation (inactivation) by a family of pyruvate dehydrogenase kinases (PDHKs 1-4). Here we review new developments in the regulation of the activities and expression of PC, PDC and the PDHKs in the pancreatic islet in relation to islet pyruvate disposition and glucose-stimulated insulin secretion (GSIS).

Role of pyruvate dehydrogenase kinase 4 in regulation of blood glucose levels

In the well-fed state a relatively high activity of the pyruvate dehydrogenase complex (PDC) reduces blood glucose levels by directing the carbon of pyruvate into the citric acid cycle. In the fasted state a relatively low activity of the PDC helps maintain blood glucose levels by conserving pyruvate and other three carbon compounds for gluconeogenesis. The relative activities of the pyruvate dehydrogenase kinases (PDKs) and the opposing pyruvate dehydrogenase phosphatases determine the activity of PDC in the fed and fasted states. Up regulation of PDK4 is largely responsible for inactivation of PDC in the fasted state. PDK4 knockout mice have lower fasting blood glucose levels than wild type mice, proving that up regulation of PDK4 is important for normal glucose homeostasis. In type 2 diabetes, up regulation of PDK4 also inactivates PDC, which promotes gluconeogenesis and thereby contributes to the hyperglycemia characteristic of this disease. When fed a high fat diet, wild type mice develop fasting hyperglycemia but PDK4 knockout mice remain euglycemic, proving that up regulation of PDK4 contributes to hyperglycemia in diabetes. These finding suggest PDK4 inhibitors might prove useful in the treatment of type 2 diabetes.

Early lipoic acid intake protects retina of diabetic mice

The aim of this study was to test the effect of lipoic acid treatment on the retina after a short diabetic insult. Diabetes was induced by alloxan and mice were divided into sub-groups; control, diabetic, diabetic+insulin and all groups received+/-lipoic acid (100 mg/kg body weight) for 3 weeks. GSH content, MDA concentration, GPx activity were measured and electroretinograms (ERG) were recorded. Early administration of lipoic acid to diabetic mice prevented the statistically significant decreases of GSH content and GPx activity and normalized MDA concentration. Moreover, lipoic acid restored electroretinogram b-wave amplitude of diabetic animals to control values. Lipoic acid has a protective effect on the diabetic retina.

α-Lipoic acid increases cardiac glucose oxidation independent of AMP-activated protein kinase in isolated working rat hearts

Alpha-lipoic acid (ALA) is a naturally occurring enantiomer of lipoic acid and is a cofactor of key metabolic enzyme complexes catalyzing the decarboxylation of alpha-keto acids. It was recently shown that ALA increases insulin sensitivity by activating AMP-activated protein kinase (AMPK) in skeletal muscle. Also, administration of ALA to obese rats increases insulin-stimulated glucose uptake in the whole body. We investigated the metabolic effects of ALA on isolated working rat hearts. ALA (500 microM) stimulated glucose oxidation (157+/-31 nmol.dry wt(-1).min(-1) in control vs 315+/-63 nmol.dry wt(-1).min(-1) in ALA-treated, p<0.05) without affecting glycolysis, lactate oxidation, or palmitate oxidation. Cardiac work was not affected by ALA treatment. The effect of ALA on glucose oxidation was not associated with an activation of AMPK. AMPK activity was 190+/-14 pmol.mg protein(-1).min(-1) in control vs 190+/-16 pmol.mg protein(-1).min(-1) in ALA-treated hearts. This study shows that ALA stimulates glucose oxidation in isolated working rat hearts independent of AMPK activation. The beneficial effects of ALA treatment in diabetic patients may be at least in part related to its effect on glucose metabolism.

Mechanisms underlying regulation of the expression and activities of the mammalian pyruvate dehydrogenase kinases

The mechanisms that control mammalian pyruvate dehydrogenase complex (PDC) activity include its phosphorylation (inactivation) by a family of pyruvate dehydrogenase kinases (PDKs 1 - 4). Here we review new developments in the regulation of the activities and expression of the PDKs, in particular PDK2 and PDK4, in relation to glucose and lipid homeostasis. This review describes recent advances relating to the acute and long-term modes of regulation of the PDKs, with particular emphasis on the regulatory roles of nuclear receptors including peroxisome proliferator-activated receptor (PPAR) alpha and Liver X receptor (LXR), PPAR gamma coactivator alpha (PGC-1alpha) and insulin, and the impact of changes in PDK activity and expression in glucose and lipid homeostasis. Since PDK4 may assist in lipid clearance when there is an imbalance between lipid delivery and oxidation, it may represent an attractive target for interventions aimed at rectifying abnormal lipid as well as glucose homeostasis in disease states.

Regulation of the pyruvate dehydrogenase complex

The PDC (pyruvate dehydrogenase complex) plays a central role in the maintenance of glucose homoeostasis in mammals. The carbon flux through the PDC is meticulously controlled by elaborate mechanisms involving post-translational (short-term) phosphorylation/dephosphorylation and transcriptional (long-term) controls. The former regulatory mechanism involving multiple phosphorylation sites and tissue-specific distribution of the dedicated kinases and phosphatases is not only dependent on the interactions among the catalytic and regulatory components of the complex but also sensitive to the intramitochondrial redox state and metabolite levels as indicators of the energy status. Furthermore, differential transcriptional controls of the regulatory components of PDC further add to the complexity needed for long-term tuning of PDC activity for the maintenance of glucose homoeostasis during normal and disease states.

Proceedings from the “Third International Conference on Mechanism of Action of Nutraceuticals”

The "Third International Conference on Mechanisms of Action of Nutraceuticals" (ICMAN 3) was held to bring investigators from around the world together to find answers and share experience relevant to the role of nutraceuticals in health and disease. Dietary supplements are currently receiving recognition as being beneficial in coronary heart disease, cancer, osteoporosis and other chronic and degenerative diseases such as diabetes, Parkinson's and Alzheimer's diseases. This gave impetus to investigate the mechanisms of action of nutraceuticals and related bioactive compounds in disease pathologies. Many lines of evidence indicate that the mechanistic actions of natural compounds involve a wide array of biological processes, including activation of antioxidant defenses, signal transduction pathways, cell survival-associated gene expression, cell proliferation and differentiation and preservation of mitochondrial integrity. Furthermore, many of these compounds exert anti-inflammatory actions through inhibition of oxidative stress-induced transcription factors (e.g., NF-kappaB, AP-1), cytotoxic cytokines and cyclooxygenase-2. It appears that these properties play a crucial role in the protection against the pathologies of numerous age-related or chronic diseases. This review summarizes the latest research finding in functional foods and micronutrients in the promotion of health and reduction of risk for major chronic diseases as presented in this symposium.