Differences between dietary supplement and prescription drug omega-3 fatty acid formulations: a legislative and regulatory perspective.

The medical management of many diseases and conditions can include either restriction or provision of specific essential nutrients. When such nutrients are needed, there are often both prescription and nonprescription products available, as in the case of nicotinic acid or omega-3 fatty acids. Although they may seem to contain similar ingredients, there may be important differences between the prescription and dietary-supplement preparations. The manufacturing of prescription pharmaceutical products is regulated by the US Food and Drug Administration (FDA), which mandates standards for consistency and quality assurance. Dietary supplements are available to consumers under the provisions of the Dietary Supplement Health and Education Act of 1994, for which the FDA has the burden of proving a dietary supplement is harmful rather than requiring the manufacturer prove that the supplement is safe. Consumers and medical professionals should be aware of the important qualitative and quantitative differences between the FDA-approved prescription formulations and dietary supplements, particularly when an essential nutrient is part of the medical management of a disease or condition.

Botulinum neurotoxins: mechanism of action.

Botulinum neurotoxins are used clinically for conditions characterized by hyperexcitability of peripheral nerve terminals and hypersecretory syndromes. These neurotoxins are synthesized as precursor proteins with low activity, but their effects are mediated by the active form of the neurotoxin through a multistep mechanism. Following a high-affinity interaction with a protein receptor and polysialogangliosides on the synaptic membrane, botulinum neurotoxins enter the neuron and causes a sustained inhibition of synaptic transmission. The active neurotoxin is part of a high-molecular-weight complex that protects the neurotoxin from proteolytic degradation. Although complexing proteins do not affect diffusion of therapeutic neurotoxin, they may lead to the development of neutralizing antibodies that block responsiveness to it. Nerve terminal intoxication is reversible and its duration varies for different BoNT serotypes. Although it was previously assumed that botulinum neurotoxins exert effects only on the peripheral synapses, such as the neuromuscular junction, there is now substantial evidence that these neurotoxins affect neurotransmission at distal central nervous system sites as well.

n-3 Fatty acids and cardiovascular disease: mechanisms underlying beneficial effects.

Dietary n-3 fatty acids, particularly eicosapentaenoic acid and docosahexaenoic acid, are important nutrients through the life cycle. Evidence from observational, clinical, animal, and in vitro studies indicates a beneficial role of n-3 fatty acids in the prevention and management of cardiovascular disease. Although the precise mechanisms are still unclear, clinical and preclinical studies indicate that the cardioprotective effects of n-3 fatty acids may be attributed to a number of distinct biological effects on lipid and lipoprotein metabolism, blood pressure, platelet function, arterial cholesterol delivery, vascular function, and inflammatory responses.

Prescription omega-3 fatty acids and their lipid effects: physiologic mechanisms of action and clinical implications.

Hypertriglyceridemia is a risk factor for atherosclerotic coronary heart disease. Very high triglyceride (TG) levels (> or =500 mg/dl [5.65 mmol/l]) increase the risk of pancreatitis. One therapeutic option to lower TG levels is omega-3 fatty acids, which are derived from the oil of fish and other seafood. The American Heart Association has acknowledged that fish oils may decrease dysrhythmias, decrease sudden death, decrease the rate of atherosclerosis and slightly lower blood pressure, and has recommended fish consumption or fish oil supplementation as a therapeutic strategy to reduce cardiovascular disease. A prescription omega-3-acid ethyl esters (P-OM3) preparation has been available in many European nations for at least a decade, and was approved by the US FDA in 2004 to reduce very high TG levels (> or =500 mg/dl [5.65 mmol/l]). Mechanistically, most evidence suggests that omega-3 fatty acids reduce the synthesis and secretion of very-low-density lipoprotein (VLDL) particles, and increase TG removal from VLDL and chylomicron particles through the upregulation of enzymes, such as lipoprotein lipase. Omega-3 fatty acids differ mechanistically from other lipid-altering drugs, which helps to explain why therapies such as P-OM3 have complementary mechanisms of action and, thus, complementary lipid benefits when administered with statins. Additional human studies are needed to define more clearly the cellular and molecular basis for the TG-lowering effects of omega-3 fatty acids and their favorable cardiovascular effects, particularly in patients with hypertriglyceridemia.

Omega-3 fatty acids and coronary heart disease risk: clinical and mechanistic perspectives.

The most common omega-3 fatty acids contain 18-22 carbons and a signature double bond at the third position from the methyl (or n, or omega) end of the molecule. These fatty acids must be obtained in the diet as they cannot be synthesized by vertebrates. They include the plant-derived alpha-linolenic acid (ALA, 18:3n-3), and the fish-oil-derived eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). Normally, very little ALA is converted to EPA, and even less to DHA, and therefore direct intake of the latter two is optimal. EPA and DHA and their metabolites have important biologic functions, including effects on membranes, eicosanoid metabolism, and gene transcription. Studies indicate that the use of fish oil is associated with coronary heart disease risk reduction. A number of mechanisms may be responsible for such effects. These include prevention of arrhythmias as well as lowering heart rate and blood pressure, decreasing platelet aggregation, and lowering triglyceride levels. The latter is accomplished by decreasing the production of hepatic triglycerides and increasing the clearance of plasma triglycerides. Our focus is to review the potential mechanisms by which these fatty acids reduce cardiovascular disease risk.

Transcriptional activation of the suppressor of cytokine signaling-3 (SOCS-3) gene via STAT3 is increased in F9 REX1 (ZFP-42) knockout teratocarcinoma stem cells relative to wild-type cells.

Rex1 (Zfp42), first identified as a gene that is transcriptionally repressed by retinoic acid (RA), encodes a zinc finger transcription factor expressed at high levels in F9 teratocarcinoma stem cells, embryonic stem cells, and other stem cells. Loss of both alleles of Rex1 by homologous recombination alters the RA-induced differentiation of F9 cells, a model of pluripotent embryonic stem cells. We identified Suppressor of Cytokine Signaling-3 (SOCS-3) as a gene that exhibits greatly increased transcriptional activation in RA, cAMP, and theophylline (RACT)-treated F9 Rex1(-/-) cells (approximately 25-fold) as compared to wild-type (WT) cells ( approximately 2.5-fold). By promoter deletion, mutation, and transient transfection analyses, we have shown that this transcriptional increase is mediated by the STAT3 DNA-binding elements located between -99 to -60 in the SOCS-3 promoter. Overexpression of STAT3 dominant-negative mutants greatly diminishes this SOCS-3 transcriptional increase in F9 Rex1(-/-) cells. This increase in SOCS-3 transcription is associated with a four- to fivefold higher level of tyrosine-phosphorylated STAT3 in the RACT-treated F9 Rex1(-/-) cells as compared to WT. Dominant-negative Src tyrosine kinase, Jak2, and protein kinase A partially reduce the transcriptional activation of the SOCS 3 gene in RACT-treated F9 Rex1 null cells. In contrast, parathyroid hormone peptide enhances the effect of RA in F9 Rex1(-/-) cells, but not in F9 WT. Thus, Rex1, which is highly expressed in stem cells, inhibits signaling via the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, thereby modulating the differentiation of F9 cells.

Dispelling the myths about omega-3 fatty acids.

Although there is an enormous amount of information available on omega-3 fatty acids, it is sometimes misleading, contradictory, and unsupported by scientific fact. Consumers and medical professionals may be confused regarding the potential value of omega-3 fatty acid supplements, despite having either read or heard about fi sh oil consumption and/or omega-3 fatty acid benefits and risks. The availability of a prescription formulation of omega-3-acid ethyl esters (P-OM3) has provided important new information that helps to dispel the myths and alleviate concerns surrounding the use of omega-3 fatty acids in clinical practice. The safety and efficacy of P-OM3, but not dietary-supplement omega-3 fatty acids, are documented in placebo-controlled trials. In general, studies using Food and Drug Administration-approved dosages of P-OM3 have not substantiated various myths surrounding the negative effects of omega-3 fatty acids. Thus, there are now evidence-based clinical guidelines for the use of omega-3 fatty acids in clinical practice.

Patient use of dietary supplements: a clinician's perspective.

BACKGROUND: The estimated prevalence of dietary-supplement use among US adults was 73% in 2002. Appropriate use of dietary supplements within the paradigm of evidence-based medicine may be a challenge for medical doctors and non-physician clinicians. Randomized, controlled, clinical trial data, which are considered the gold standard for evidence-based decision making, are lacking. Standardized guidelines for the use of dietary supplements are lacking, and dietary supplements can bear unsupported claims. OBJECTIVES: This article is intended to review clinically-relevant issues related to the widespread use of dietary supplements, with emphasis on regulatory oversight and safety. METHODS: Review articles and clinical trial articles published up until December 2007 were selected based on a search of the MEDLINE electronic database using PubMed. The Food and Drug Administration (FDA) Website was also used as a resource. We used the search terms dietary supplement(s), vitamin supplements, mineral supplements, and Dietary Supplement and Health Education Act. Articles discussing dietary supplements and their regulation, prevalence of use, prescription and nonprescription formulations, and/or adverse events were selected for review. Articles discussing one or more of these topics in adults were selected for inclusion. RESULTS: New FDA regulations require dietary-supplement manufacturers to evaluate the identity, purity, strength, and composition of their products. However, these regulations are not designed to demonstrate product efficacy and safety, and dietary-supplement manufacturers are not required to submit efficacy and safety data to the FDA prior to marketing. Product contamination and/or mislabeling may undermine the integrity of dietary-supplement formulations. CONCLUSIONS: The use of dietary supplements may be associated with adverse events. Although there are new regulatory requirements for dietary supplements, these products will not require FDA approval or submission of efficacy and safety data prior to marketing under the new regulation. A limitation to the literature used for this review is the lack of prospective, randomized clinical trials on the safety and efficacy of dietary supplements. Clinicians should be aware of all the dietary supplements that their patients consume, and help their patients make informed decisions appropriate to their medical care.

Retinoids arrest breast cancer cell proliferation: retinoic acid selectively reduces the duration of receptor tyrosine kinase signaling.

Retinoic acid (RA) induces cell cycle arrest of hormone-dependent human breast cancer (HBC) cells. Previously, we demonstrated that RA-induced growth arrest of T-47D HBC cells required the activity of the RA-induced protein kinase, protein kinase Calpha (PKCalpha) [J. Cell Physiol. 172 (1997) 306]. Here, we demonstrate that RA treatment of T-47D cells interfered with growth factor signaling to downstream, cytoplasmic and nuclear targets. RA treatment did not inhibit epidermal growth factor (EGF) receptor activation but resulted in rapid inactivation. The lack of sustained EGFR activation was associated with transient rather than sustained association of the EGFR with the Shc adaptor proteins and activation of Erk 1/2 and with compromised induction of expression of immediate early response genes. Inhibiting the activity of PKCalpha, a retinoic acid-induced target gene, prevented the effects of RA on cell proliferation and EGF signaling. Constitutive expression of PKCalpha, in the absence of RA, decreased cell proliferation and decreased EGF signaling. RA treatment increased steady-state levels of the protein tyrosine phosphatase PTP-1C and all measured effects of RA on EGF receptor function were reversed by the tyrosine phosphate inhibitor orthovanadate. These results indicate that RA-induced target genes, particularly PKCalpha, prevent sustained growth factor signaling, uncoupling activated receptor tyrosine kinases and nuclear targets that are required for cell cycle progression.

Retinoic acid inhibits leukemia inhibitory factor signaling pathways in mouse embryonic stem cells.

Retinoic acid (RA) induces the differentiation of murine embryonic stem (ES) cells to cell types resembling those found in the early embryo. When cultured in the presence of leukemia inhibitory factor (LIF), ES cells are maintained in an undifferentiated (self-renewing) state. Addition of RA to the culture media overrides the self-renewing effects of LIF to induce ES cell differentiation. Therefore, we hypothesized that RA-induced differentiation of ES cells may be accomplished by antagonism of LIF-induced signaling pathways. We demonstrate that RA-induced differentiation of CCE ES cells is associated with (1) downregulation of the LIF receptor (LIFR); (2) decreased tyrosine phosphorylation of signal transducer and activator of transcription 3 protein (Stat3); and (3) increased activation of extracellular regulated kinase (Erk1/2). We conclude that RA induces CCE ES cell differentiation in the presence of LIF, in part, by disrupting signaling between the LIFR/gp130 receptor and nuclear targets that are required to prevent ES cell differentiation. Our data indicate that RA-induced inhibition of LIF signaling does not involve Erk1/2-dependent actions.