Large enhancement of skeletal muscle cell glucose uptake and suppression of hepatocyte glucose-6-phosphatase activity by weak uncouplers of oxidative phosphorylation

Diabetes-induced testicular oxidative stress, inflammation, and caspase-dependent apoptosis: the protective role of metformin

Context: Metformin's effect on glycaemic control is well documented, but its effect on diabetes-induced testicular impairment has been scarcely reported.Objective: To investigate the effects of metformin on testicular oxidative stress, inflammation, and apoptosis, which largely contribute to fertility decline in diabetic state.Methods: Male Sprague-Dawley rats were divided into 3 groups (n = 6/group) namely: normal control (NC), diabetic control (DC), and metformin (300 mg/kg b.w./d)-treated diabetic groups. Metformin was administrated for 4 weeks.Results: Decreased mRNA expressions and activities of antioxidant enzymes were seen in the testes of DC group. mRNA and protein expressions of pro-inflammatory and pro-apoptotic markers increased, while interleukin-10 and proliferating cell nuclear antigen (PCNA) decreased in the testes of DC group. Treatment with metformin up-regulated antioxidant enzymes, down-regulated inflammation, and apoptosis and increased PCNA immunoexpression in the testes.Conclusions: Metformin protects the testes from diabetes-induced impairment and may improve male reproductive health in diabetic state.

Mifepristone for Treatment of Metabolic Syndrome: Beyond Cushing's Syndrome

A growing body of research indicates that cortisol, the glucocorticoid product of the activation of the hypothalamic-pituitary-adrenal axis, plays a role in the pathophysiology of metabolic syndrome. In this regard, chronic exposure to cortisol is associated with risk factors related to metabolic syndrome like weight gain, type 2 diabetes, hypertension, among others. Mifepristone is the only FDA-approved drug with antiglucocorticoids properties for improved the glycemic control in patients with type 2 patients secondary to endogenous Cushing’s syndrome. Mifepristone also have been shown positive effects in rodents models of diabetes and patients with obesity due to antipsychotic treatment. However, the underlying molecular mechanisms are not fully understood. In this perspective, we summarized the literature regarding the beneficial effects of mifepristone in metabolic syndrome from animal studies to clinical research. Also, we propose a potential mechanism for the beneficial effects in insulin sensitivity which involved the regulation of mitochondrial function in muscle cells.

Oxidative Stress, NF-κB-Mediated Inflammation and Apoptosis in the Testes of Streptozotocin-Induced Diabetic Rats: Combined Protective Effects of Malaysian Propolis and Metformin

Oxidative stress, inflammation and apoptosis are major complications that trigger organ failure in diabetes mellitus (DM), and are proven to adversely affect the male reproductive system. Clinical and experimental studies have demonstrated the promising protective effects of propolis in DM and its associated systemic effects. Herein, we investigated the effect of Malaysian propolis (MP) on testicular oxidative stress, inflammation and apoptosis in diabetic rats. Further, the possibility of a complementary effect of MP with the anti-hyperglycaemic agent, metformin (Met), was studied with the idea of recommending its use in the event that Met alone is unable to contain the negative effects of DM on the male reproductive system in mind. Male Sprague-Dawley rats were either gavaged distilled water (normoglycaemic control and diabetic control groups), MP (diabetic rats on MP), Met (diabetic rats on Met) or MP+Met (diabetic rats on MP+Met), for 4 weeks. MP decreased oxidative stress by up-regulating (p < 0.05) testicular mRNA levels of nuclear factor erythroid 2-related factor 2, superoxide dismutase, catalase and glutathione peroxidase; increasing (p < 0.05) the activities of antioxidant enzymes; and decreasing (p < 0.05) lipid peroxidation in the testes and epididymis of diabetic rats. Further, MP down-regulated (p < 0.05) testicular mRNA and protein levels of pro-inflammatory mediators (nuclear factor kappa B, inducible nitric oxide synthase, tumour necrosis factor-α and interleukin (IL)-1β), decreased (p < 0.05) the nitric oxide level, and increased (p < 0.05) IL-10 mRNA and protein levels. MP also down-regulated (p < 0.05) Bax/Bcl-2, p53, casapase-8, caspase-9 and caspase-3 genes, and increased (p < 0.05) testicular germ cell proliferation. MP's effects were comparable to Met. However, the best results were achieved following co-administration of MP and Met. Therefore, we concluded that administration of the MP+Met combination better attenuates testicular oxidative stress, inflammation and apoptosis in DM, relative to MP or Met monotherapy, and may improve the fertility of males with DM.

Cytotoxic effects of 4'-hydroxychalcone on human neuroblastoma cells (SH-SY5Y)

Neuroblastoma is an aggressive form of cancer with high mortality. Hydroxychalcones have received considerable attention because of their cytotoxic activities on cancer cells. However, the effect of the 4'-hydroxychalcone on neuroblastoma cells is unknown. The aim of the present study was to characterize the cytotoxicity of 4HC to neuroblastoma and the importance of mitochondrial effects in its action mechanism using an in vitro model of SH-SY5Y cells. Incubation of cultured SHSY5Y cells with 10-60 μM 4HC (24 h) decreased cell confluency, cellular metabolic activity and depleted intracellular ATP relative to the vehicle-treated control. The mechanism of 4HC-induced cell toxicity likely involves mitochondria dysfunctional as judged by inhibition of mitochondrial respiration, depolarization of mitochondria membrane potential and intracellular and morphological alterations. Furthermore, loss of cell viability was accompanied mainly by increase of phosphatidylserine exposure on the surface of cells, suggesting that the flavonoid may induce apoptosis in SH-SY5Y cells. In addition, treatment inhibited SH-SY5Y cell migration/proliferation in a scratch assay and induced significant changes in the cell cycle progression. Our results showed the effects of 4HC in the human neuroblastoma cell line SH-SY5Y are associated with mitochondrial dysfunctional, depletion of intracellular ATP levels, ROS increase, alteration in cell cycle progression and cellular morphology.

Down-regulation of steroidogenesis-related genes and its accompanying fertility decline in streptozotocin-induced diabetic male rats: ameliorative effect of metformin

BACKGROUND

Metformin has long been used for glycemic control in diabetic state. Recently, other benefits of metformin beyond blood glucose regulation have emerged.

OBJECTIVES

To investigate the effect of metformin on the expression of testicular steroidogenesis-related genes, spermatogenesis, and fertility of male diabetic rats.

MATERIALS AND METHODS

Eighteen adult male Sprague Dawley rats were divided into three groups, namely normal control (NC), diabetic control (DC), and metformin-treated (300 mg/kg body weight/day) diabetic rats (D+Met). Diabetes was induced using a single intraperitoneal injection of streptozotocin (60 mg/kg b.w.), followed by oral treatment with metformin for four weeks.

RESULTS

Diabetes decreased serum and intratesticular testosterone levels and increased serum but not intratesticular levels of luteinizing hormone. Sperm count, motility, viability, and normal morphology were decreased, while sperm nuclear DNA fragmentation was increased in DC group, relative to NC group. Testicular mRNA levels of androgen receptor, luteinizing hormone receptor, cytochrome P450 enzyme (CYP11A1), steroidogenic acute regulatory (StAR) protein, 3β-hydroxysteroid dehydrogenase (HSD), and 17β-HSD, as well as the level of StAR protein and activities of CYP11A1, 3β-HSD, and 17β-HSD, were decreased in DC group. Similarly, decreased activities of epididymal antioxidant enzymes and increased lipid peroxidation were observed in DC group. Consequently, decreased litter size, fetal weight, mating and fertility indices, and increased pre- and post-implantation losses were recorded in DC group. Following intervention with metformin, we observed increases in serum and intratesticular testosterone levels, Leydig cell count, improved sperm parameters, and decreased sperm nuclear DNA fragmentation. Furthermore, mRNA levels and activities of steroidogenesis-related enzymes were increased, with improved fertility outcome.

DISCUSSION AND CONCLUSION

Diabetes mellitus is associated with dysregulation of steroidogenesis, abnormal spermatogenesis, and fertility decline. Controlling hyperglycemia is therefore crucial in preserving male reproductive function. Metformin not only regulates blood glucose level, but also preserves male fertility in diabetic state.

Mifepristone enhances insulin-stimulated Akt phosphorylation and glucose uptake in skeletal muscle cells

Mifepristone is the only FDA-approved drug for glycaemia control in patients with Cushing's syndrome and type 2 diabetes. Mifepristone also has beneficial effects in animal models of diabetes and patients with antipsychotic treatment-induced obesity. However, the mechanisms through which Mifepristone produces its beneficial effects are not completely elucidated.

PURPOSE

To determine the effects of mifepristone on insulin-stimulated glucose uptake on a model of L6 rat-derived skeletal muscle cells.

RESULTS

Mifepristone enhanced insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane and Akt Ser⁴⁷³ phosphorylation in L6 myotubes. In addition, mifepristone reduced oxygen consumption and ATP levels and increased AMPK Thr¹⁷² phosphorylation. The knockdown of AMPK prevented the effects of mifepristone on insulin response.

CONCLUSIONS

Mifepristone enhanced insulin-stimulated glucose uptake through a mechanism that involves a decrease in mitochondrial function and AMPK activation in skeletal muscle cells.

Effects of curcumin and ursolic acid on the mitochondrial coupling efficiency and hydrogen peroxide emission of intact skeletal myoblasts

Curcumin may improve blood glucose management, but the mechanism is not fully established. We demonstrated that curcumin (40 μM) reduced the mitochondrial coupling efficiency (percentage of oxygen consumption coupled to ATP synthesis) of intact skeletal muscle cells. A 30-minute pretreatment with curcumin reduced mitochondrial coupling efficiency by 17.0 ± 0.4% relative to vehicle (p < 0.008). Curcumin pretreatment also decreased the rate of hydrogen peroxide emission by 43 ± 13% compared to vehicle (p < 0.05). Analysis of cell respiration in the presence of curcumin revealed a 40 ± 4% increase in the rate of oxygen consumption upon curcumin administration (p < 0.05 compared to vehicle). No difference in mitochondrial coupling efficiency was observed between vehicle- and curcumin-pretreated cells after permeabilization of cell membranes (p > 0.7). The interaction between curcumin and ursolic acid, another natural compound that may improve blood glucose management, was also examined. Pretreatment with ursolic acid (0.12 μM) increased the mitochondrial coupling efficiency of intact cells by 4.1 ± 1.1% relative to vehicle (p < 0.008) and attenuated the effect of curcumin when the two compounds were used in combination. The observed changes to mitochondrial coupling efficiency and hydrogen peroxide emission were consistent with the established effects of curcumin on blood glucose control. Our findings also show that changes to mitochondrial coupling efficiency after curcumin pretreatment may go undetected unless cells are assessed in the intact condition.

Relative Effects of Fluid Oscillations and Nutrient Transport in the In Vitro Growth of Valvular Tissues

Engineered valvular tissues are cultured dynamically, and involve specimen movement. We previously demonstrated that oscillatory shear stresses (OSS) under combined steady flow and specimen cyclic flexure (flex-flow) promote tissue formation. However, localized efficiency of specimen mass transport is also important in the context of cell viability within the growing tissues. Here, we investigated the delivery of two essential species for cell survival, glucose and oxygen, to 3-dimensional (3D) engineered valvular tissues. We applied a convective-diffusive model to characterize glucose and oxygen mass transport with and without valve-like specimen flexural movement. We found the mass transport effects for glucose and oxygen to be negligible for scaffold porosities typically present during in vitro experiments and non-essential unless the porosity was unusually low (<40%). For more typical scaffold porosities (75%) however, we found negligible variation in the specimen mass fraction of glucose and oxygen in both non-moving and moving constructs (p > 0.05). Based on this result, we conducted an experiment using bone marrow stem cell (BMSC)-seeded scaffolds under Pulsatile flow-alone states to permit OSS without any specimen movement. BMSC-seeded specimen collagen from the pulsatile flow and flex-flow environments were subsequently found to be comparable (p > 0.05) and exhibited some gene expression similarities. We conclude that a critical magnitude of fluid-induced, OSS created by either pulsatile flow or flex-flow conditions, particularly when the oscillations are physiologically-relevant, is the direct, principal stimulus that promotes engineered valvular tissues and its phenotype, whereas mass transport benefits derived from specimen movement are minimal.

Butein and Its Role in Chronic Diseases

Natural compounds isolated from various plant sources have been used for therapeutic purpose for centuries. These compounds have been routinely used for the management of various chronic ailments and have gained considerable attention because of their significant efficacy and comparatively low side effects. Butein, a chacolnoid compound that has been isolated from various medicinal plants has exhibited a wide range of beneficial pharmacological effects, such as anti-inflammatory, anticancer, antioxidant, and anti-angiogenic in diverse disease models. This article briefly summarizes the past published literature related to the therapeutic and protective effects of butein, as demonstrated in various models of human chronic diseases. Further analysis of its important cellular targets, toxicity, and pharmacokinetic profile may further significantly expand its therapeutic application.

Effects of phytochemicals on in vitro anti-inflammatory activity of Bifidobacterium adolescentis

Probiotics have been shown to improve the condition of not only the human gastrointestinal tract but also the entire body. We found that quercetin enhances the anti-inflammatory activity of Bifidobacterium adolescentis, which is abundant in human intestines. Here, we assessed whether certain phytochemicals could enhance the anti-inflammatory activity of B. adolescentis. Bifidobacteria were anaerobically cultured with phytochemicals for 3 h, and the anti-inflammatory activity of the supernatants was estimated by testing their ability to inhibit nitric oxide (NO) production by lipopolysaccharide-stimulated RAW264 macrophages. Of the 55 phytochemicals tested, phloretin, (+)-taxifolin, and (-)-epigallocatechin gallate as well as quercetin-3-O-glucoside and quercetin-4'-O-glucoside were similar to quercetin in promoting NO suppression by B. adolescentis. In addition, the phytochemicals excluding quercetin increased the concentrations of lactic and acetic acids in the co-culture supernatants. These results suggest that some phytochemicals may activate the anti-inflammatory function of B. adolescentis.

Metformin and male reproduction: effects on Sertoli cell metabolism

BACKGROUND AND PURPOSE

Metformin is commonly used to treat type 2 diabetes (T2D). While new clinical applications have been ascribed to metformin, including treatment of anovulatory infertility, its effects on male reproduction have not been investigated. The Sertoli cell (SC) is crucial for germ cell development, exerting metabolic control of spermatogenesis, therefore, we investigated the effects of metformin on SC metabolism.

EXPERIMENTAL APPROACH

Rat SCs were cultured in the absence and presence of metformin (5, 50 and 500 μM). mRNA and protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase 1 (PFK 1), lactate dehydrogenase (LDH) and monocarboxylate transporter 4 (MCT4) were determined by quantitative PCR and Western blot respectively. LDH activity was assessed and metabolite production/consumption determined by (1) H-NMR.

KEY RESULTS

Metformin (50 μM) decreased mRNA and protein levels of GLUT1, GLUT3, MCT4 and PFK 1 but did not affect LDH mRNA or protein levels. However, although glucose consumption was maintained in metformin-treated cells, LDH activity, lactate and alanine production were increased, indicating an enhanced glycolytic flux. No metabolic cytotoxicity was detected in SCs exposed to supra-pharmacological concentration of metformin.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that metformin: (i) decreases mRNA and protein levels of glycolysis-related transporters in SCs but increases their activity; and (ii) stimulates alanine production, which induces antioxidant activity and maintains the NADH/NAD(+) equilibrium. The increased lactate in metformin-treated SCs provides nutritional support and has an anti-apoptotic effect in developing germ cells. Thus, metformin can be considered as a suitable antidiabetic drug for male patients of reproductive age with T2D.

Perspectives of mitochondrial medicine

Mitochondrial medicine was established more than 50 years ago after discovery of the very first pathology caused by impaired mitochondria. Since then, more than 100 mitochondrial pathologies have been discovered. However, the number may be significantly higher if we interpret the term "mitochondrial medicine" more widely and include in these pathologies not only those determined by the genetic apparatus of the nucleus and mitochondria, but also acquired mitochondrial defects of non-genetic nature. Now the main problems of mitochondriology arise from methodology, this being due to studies of mitochondrial activities under different models and conditions that are far from the functioning of mitochondria in a cell, organ, or organism. Controversial behavior of mitochondria ("friends and foes") to some extent might be explained by their bacterial origin with possible preservation of "egoistic" features peculiar to bacteria. Apparently, for normal mitochondrial functioning it is essential to maintain homeostasis of a number of mitochondrial elements such as mitochondrial DNA structure, membrane potential, and the system of mitochondrial quality control. Abrogation of these elements can cause a number of pathologies that have become subjects of mitochondrial medicine. Some approaches to therapy of mitochondrial pathologies are discussed.

Antidiabetic plants improving insulin sensitivity

BACKGROUND

Globally, the prevalence of diabetes mellitus is increasing at an alarming rate. This chronic pathology gravely troubled the human health and quality of life. Both insulin deficiency and insulin resistance are involved in the pathophysiology of diabetes mellitus. Moreover, insulin resistance is being diagnosed nowadays in a growing population of diabetic and obese patients, especially in industrialized societies. There are lots of conventional agents available to control and to treat diabetes, but total recovery from this disorder has not been reported up to this date. Plants provided a potential source of hypoglycemic drugs and are widely used in several traditional systems of medicine to prevent diabetes. A few reviews with less attention paid to mechanisms of action have been published on antidiabetic plants.

OBJECTIVES

The present review focuses on the various plants that have been reported to be effective in improving insulin sensitivity associated with diabetes.

KEY FINDINGS

In this work, an updated systematic review of the published literature has been conducted to review the antidiabetic plants improving insulin sensitivity and 111 medicinal plants have been reported to have a beneficial effect on insulin sensitivity using several in-vitro and in-vivo animal models of diabetes.

CONCLUSION

The different metabolic and cellular effects of the antidiabetic plants improving insulin sensitivity are reported indicating the important role of medicinal plants as potential alternative or complementary use in controlling insulin resistance associated with diabetes mellitus.

Potassium channel openers prevent palmitate-induced insulin resistance in C2C12 myotubes

Insulin resistance (IR) of muscle cells is an early symptom of type 2 diabetes. It often results from excessive lipid accumulation in muscle fibers which under in vitro experimental conditions may be induced by incubation of muscle cells with palmitate. IR is manifested as a reduced response of cells to insulin expressed by lowered Akt kinase phosphorylation and decreased insulin-dependent glucose uptake. Stimulation of mitochondrial oxidative metabolism by mild dissipation of the mitochondrial potential is thought to increase fatty acid utilization and thereby prevent insulin resistance. Here it is shown that nicorandil and NS1619, which are openers of two different mitochondrial potassium channels, protect C2C12 myotubes from palmitate-induced insulin resistance. Preincubation of myotubes with 5-hydroxydecanoate abolishes the protective effect of nicorandil. The efficient concentrations of both openers are far below those commonly applied for cytoprotection. This is probably why their effects on the mitochondrial energy metabolism are small. These data suggest that opening of mitochondrial potassium channels could be a promising approach in prevention and therapy of insulin resistance related to dyslipidemia and obesity.

A novel chemical uncoupler ameliorates obesity and related phenotypes in mice with diet-induced obesity by modulating energy expenditure and food intake

AIMS/HYPOTHESIS

Decreasing mitochondrial coupling efficiency has been shown to be an effective therapy for obesity and related metabolic symptoms. Here we identified a novel mitochondrial uncoupler that promoted uncoupled respiration in a cell type-specific manner and investigated its effects on modulation of energy metabolism in vivo and in vitro.

METHODS

We screened a collection of mitochondrial membrane potential depolarising compounds for a novel chemical uncoupler on isolated skeletal muscle mitochondria using a channel oxygen system. The effect on respiration of metabolic cells (L6 myotubes, 3T3-L1 adipocytes and rat primary hepatocytes) was examined and metabolic pathways sensitive to cellular ATP content were also evaluated. The chronic metabolic effects were investigated in high-fat diet-induced obese mice and standard diet-fed (SD) lean mice.

RESULTS

The novel uncoupler, CZ5, promoted uncoupled respiration in a cell type-specific manner. It stimulated fuel oxidation in L6 myotubes and reduced lipid accumulation in 3T3-L1 adipocytes but did not affect gluconeogenesis or the triacylglycerol content in hepatocytes. The administration of CZ5 to SD mice increased energy expenditure (EE) but did not affect body weight or adiposity. Chronic studies in mice on high-fat diet showed that CZ5 reduced body weight and improved glucose and lipid metabolism via both increased EE and suppressed energy intake. The reduced adiposity was associated with the restoration of expression of key metabolic genes in visceral adipose tissue.

CONCLUSIONS/INTERPRETATION

This work demonstrates that a cell type-specific mitochondrial chemical uncoupler may have therapeutic potential for treating high-fat diet-induced metabolic diseases.

Remodeling of oxidative energy metabolism by galactose improves glucose handling and metabolic switching in human skeletal muscle cells

Cultured human myotubes have a low mitochondrial oxidative potential. This study aims to remodel energy metabolism in myotubes by replacing glucose with galactose during growth and differentiation to ultimately examine the consequences for fatty acid and glucose metabolism. Exposure to galactose showed an increased [¹⁴C]oleic acid oxidation, whereas cellular uptake of oleic acid uptake was unchanged. On the other hand, both cellular uptake and oxidation of [¹⁴C]glucose increased in myotubes exposed to galactose. In the presence of the mitochondrial uncoupler carbonylcyanide p-trifluormethoxy-phenylhydrazone (FCCP) the reserve capacity for glucose oxidation was increased in cells grown with galactose. Staining and live imaging of the cells showed that myotubes exposed to galactose had a significant increase in mitochondrial and neutral lipid content. Suppressibility of fatty acid oxidation by acute addition of glucose was increased compared to cells grown in presence of glucose. In summary, we show that cells grown in galactose were more oxidative, had increased oxidative capacity and higher mitochondrial content, and showed an increased glucose handling. Interestingly, cells exposed to galactose showed an increased suppressibility of fatty acid metabolism. Thus, galactose improved glucose metabolism and metabolic switching of myotubes, representing a cell model that may be valuable for metabolic studies related to insulin resistance and disorders involving mitochondrial impairments.

Novel small-molecule PGC-1α transcriptional regulator with beneficial effects on diabetic db/db mice

Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) has been shown to influence energy metabolism. Hence, we explored a strategy to target PGC-1α expression to treat metabolic syndromes. We developed a high-throughput screening assay that uses the human PGC-1α promoter to drive expression of luciferase. The effects of lead compound stimulation on PGC-1α expression in muscle cells and hepatocytes were investigated in vitro and in vivo. A novel small molecule, ZLN005, led to changes in PGC-1α mRNA levels, glucose uptake, and fatty acid oxidation in L6 myotubes. Activation of AMP-activated protein kinase was involved in the induction of PGC-1α expression. In diabetic db/db mice, chronic administration of ZLN005 increased PGC-1α and downstream gene transcription in skeletal muscle, whereas hepatic PGC-1α and gluconeogenesis genes were reduced. ZLN005 increased fat oxidation and improved the glucose tolerance, pyruvate tolerance, and insulin sensitivity of diabetic db/db mice. Hyperglycemia and dyslipidemia also were ameliorated after treatment with ZLN005. Our results demonstrated that a novel small molecule selectively elevated the expression of PGC-1α in myotubes and skeletal muscle and exerted promising therapeutic effects for treating type 2 diabetes.

Mitochondrial inhibitor as a new class of insulin sensitizer

Insulin resistance is a major risk factor for type 2 diabetes. AMP-activated protein kinase (AMPK) is a drug target in the improvement of insulin sensitivity. Several insulin-sensitizing medicines are able to activate AMPK through inhibition of mitochondrial functions. These drugs, such as metformin and STZ, inhibit ATP synthesis in mitochondria to raise AMP/ATP ratio in the process of AMPK activation. However, chemicals that activate AMPK directly or by activating its upstream kinases have not been approved for treatment of type 2 diabetes in humans. In an early study, we reported that berberine inhibited oxygen consumption in mitochondria, and increased AMP/ATP ratio in cells. The observation suggests an indirect mechanism for AMPK activation by berberine. Berberine stimulates glycolysis for ATP production that offsets the cell toxicity after mitochondria inhibition. The study suggests that mitochondrial inhibition is an approach for AMPK activation. In this review article, literature is critically reviewed to interpret the role of mitochondria function in the mechanism of insulin resistance, which supports that mitochondria inhibitors represent a new class of AMPK activator. The inhibitors are promising candidates for insulin sensitizers. This review provides a guideline in search for small molecule AMPK activators in the drug discovery for type 2 diabetes.

Simple thermodynamic model of unassisted proton shuttle uncoupling and prediction of activity from calculated speciation, lipophilicity, and molecular geometry

A mechanistic model of uncoupling of oxidative phosphorylation by lipophilic weak acids (i.e. proton shuttles) was developed for the purposes of predicting the relative activity of xenobiotics of widely varying structure and of guiding the design of optimized derivatives. The model is based on thermodynamic premises not formulated elsewhere that allow for the calculation of steady-state conditions and of rate of energy dissipation on the basis of acid-dissociation and permeability behavior, the later estimated from partitioning behavior and geometric considerations. Moreover, permeability of either the neutral or of the ionized species is proposed to be effectively enhanced under conditions of asymmetrical molecular distribution. Finally, special considerations were developed to accommodate multi-protic compounds. The comparison of predicted to measured activity for a diverse testset of 48 compounds of natural origin spanning a wide range of activity yielded a Spearman's rho of 0.90. The model was used to tentatively identify several novel proton shuttles, as well as to elucidate core structures particularly conducive to proton shuttle activity from which optimized derivatives can be designed. Principles of design were formulated and examples of derivatives projected to be active at concentrations on the order of 10(-7)M are proposed. Among these are di-protic compounds predicted to shuttle two protons per cycle iteration and proposed to maximally exploit the proton shuttle mechanism. This work promotes the design of highly active, yet easily-metabolized uncouplers for therapeutic applications, namely the indirect activation of AMP-kinase, as well as for various industrial applications where low persistence is desirable.