PREMECO PLUS

Mechanism of action

Cyanocobalamin serves as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase enzymes. Methionine synthase is essential for the synthesis of purines and pyrimidines that form DNA. L-methylmalonyl-CoA mutase is involved in the degradation of propionate, crucial for fat and protein metabolism. The lack of vitamin B12 results in the accumulation of methylmalonyl CoA, contributing to neurological manifestations. Additionally, it is vital for the synthesis of methionine from homocysteine, and its deficiency can lead to functional folate deficiency, which impacts red blood cell formation.

Pharmacodynamics

Cyanocobalamin corrects vitamin B12 deficiency and alleviates symptoms and laboratory abnormalities associated with pernicious anemia, such as megaloblastic indices, gastrointestinal lesions, and neurological damage. It is essential for growth, cell reproduction, hematopoiesis, nucleoprotein, and myelin synthesis. The drug significantly impacts fat and carbohydrate metabolism, as well as protein synthesis. Rapidly dividing cells, such as those in the bone marrow, have a high demand for vitamin B12. Parenteral administration of cyanocobalamin can quickly reverse the anemia and gastrointestinal symptoms of vitamin B12 deficiency, while also preventing the progression of related neurological damage.

Pharmacokinetics

Cyanocobalamin is absorbed in the intestine, primarily in the ileum, via specific transport mechanisms that may be impaired in individuals with intrinsic factor deficiency (as seen in pernicious anemia). Once absorbed, it is widely distributed in body tissues, with significant concentrations found in the liver, kidneys, and heart. The vitamin is stored in the liver, where it can be released into circulation as needed. Cyanocobalamin undergoes conversion to its active forms, methylcobalamin and adenosylcobalamin, which are utilized in various metabolic processes. The elimination half-life is variable, but it is generally excreted via urine as metabolites

Adverse effects

• Abdominal distension
• Decreased appetite
• Flatulence
• Nausea

Interactions

• Folic acid may interact with cyanocobalamin, especially in cases of megaloblastic anemia caused by folate deficiency.

Precautions

• Should not be given alone for pernicious anemia.
• Use caution in patients with Leber's disease, as it may worsen optic atrophy.

Pregnancy

Cyanocobalamin is essential during pregnancy as it helps prevent neural tube defects. It is advised that females of childbearing potential take 5 mg of folic acid daily before conception and throughout pregnancy.

Breast-feeding

Cyanocobalamin is generally considered safe during breastfeeding, but it is advised to monitor the infant for any adverse effects.

Storage

Store in a cool, dry place, away from direct sunlight. Protect from moisture.

Formulations

• Tablet: 1000 micrograms
• Tablet: 500 micrograms
• Tablet: 100 micrograms
• Oral solution: 50 micrograms per ml
• Solution for injection: 1000 micrograms per ml

Indications

• Hypertension
• Heart failure
• Angina pectoris
• Certain arrhythmias

Dosage

Children: Refer to the BNF for Children for appropriate paediatric dosing information.

Adults: Refer to clinical guidelines for specific dosing recommendations based on the condition being treated.

Mechanism of action

Alpa functions as an antagonist of specific receptors in the body, leading to vasodilation and decreased peripheral resistance. This results in lower blood pressure and reduced cardiac workload. By blocking these receptors, Alpa promotes relaxation of blood vessels, improving blood flow and oxygen delivery to tissues.

Pharmacodynamics

The pharmacodynamic effects of Alpa include a decrease in systemic vascular resistance and a reduction in heart rate. These effects are mediated through its action on the sympathetic nervous system, thereby leading to a decrease in cardiac output and overall workload on the heart. The onset of action can vary, with full therapeutic effects often observed over a period of days to weeks.

Pharmacokinetics

Alpa is absorbed through the gastrointestinal tract, with peak plasma concentrations typically reached within several hours post-administration. It has a variable half-life, allowing for once-daily dosing in many cases. Metabolism primarily occurs in the liver through cytochrome P450 enzymes, and elimination is usually via renal pathways. The pharmacokinetic profile may be influenced by factors such as age, liver function, and concurrent medications.

Pregnancy

Alpa should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Consult clinical guidelines and assess individual risk factors.

Breast-feeding

Caution is advised when using Alpa during breastfeeding. Consider the potential effects on the infant and the importance of the drug to the mother.

Storage

Store Alpa in a cool, dry place away from direct sunlight. Keep out of reach of children.

Indications

• Type 2 diabetes mellitus
• Insulin resistance
• Impaired glucose tolerance
• Metabolic syndrome
• Hyperlipidemia

Dosage

Children: Refer to the BNF for Children for specific dosage recommendations suitable for pediatric patients.

Adults: Refer to the BNF for specific dosage recommendations based on the condition being treated.

Mechanism of action

Chromium enhances insulin signaling by upregulating insulin receptor-mediated pathways. It affects downstream effector molecules after insulin binds to its receptor, leading to the activation of phosphatidylinositol 2-kinase (PI3K) and protein kinase B (Akt). This process promotes the translocation of glucose transporter-4 (Glut4) to the cell membrane, facilitating increased glucose uptake. Additionally, chromium can promote GLUT-4 transporter translocation independently of insulin receptor activity under insulin-resistant conditions and aids in cholesterol efflux by increasing membrane fluidity.

Pharmacodynamics

Trivalent chromium is essential for the glucose tolerance factor, which activates insulin-mediated pathways. It enhances insulin binding to cells, increases the density of insulin receptors, and activates insulin receptor kinase, all of which contribute to improved insulin sensitivity. Chromium deficiency can lead to impaired glucose metabolism, and supplementation can normalize glucose tolerance in individuals exhibiting diabetic-like characteristics due to deficiency.

Pharmacokinetics

Chromium absorption occurs primarily in the intestines, but its bioavailability is influenced by various dietary factors, such as the presence of other minerals and vitamins. The mineral is transported in the bloodstream bound to transferrin and is predominantly stored in the liver, spleen, and bone. The elimination of chromium occurs mainly through urine, with small amounts excreted in feces. The half-life and exact metabolic pathways for chromium can vary based on its form and the individual's nutritional status.

Pregnancy

Chromium is generally considered safe during pregnancy when taken in appropriate amounts, but it is advisable to consult a healthcare provider.

Breast-feeding

Chromium is excreted in breast milk, and while it is deemed safe in moderate amounts, consultation with a healthcare provider is recommended.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Indications

• Folate deficiency
• Megaloblastic anemia
• Prevention of neural tube defects in pregnancy
• Supplementation in patients on certain medications (e.g., methotrexate)

Dosage

Children: Refer to the BNF for Children for appropriate pa

Adults: Refer to specific guidelines or the BNF for appropriate adult dosing based on the indication.

Mechanism of action

Folate functions as a coenzyme in the conversion of homocysteine to methionine, a process that is vital for DNA synthesis and repair. It is involved in the one-carbon metabolism pathway, where it acts as a carrier of one-carbon units necessary for the synthesis of purines and thymidylate, thus supporting the production of nucleotides and DNA. This mechanism is particularly important in rapidly dividing cells.

Pharmacodynamics

Folate is critical for the formation of red blood cells and the proper functioning of the nervous system. It aids in the production of nucleic acids, which are essential for cell proliferation. Folate deficiency can lead to impaired DNA synthesis, resulting in megaloblastic anemia characterized by the presence of large, immature red blood cells in the bloodstream. Adequate folate levels are also associated with reduced risk of neural tube defects in developing fetuses.

Pharmacokinetics

Folate is absorbed in the proximal part of the small intestine, primarily in the jejunum, and is transported in the bloodstream bound to plasma proteins. It undergoes hepatic metabolism and is stored mainly in the liver. The elimination half-life varies, but dietary folate can be retained in the body for several weeks. Excess folate is excreted through the urine. The bioavailability of folate from food sources is lower compared to synthetic folic acid found in supplements.

Interactions

• folates+fluorouracil: Severe (increases risk of toxicity)
• folates+antiepileptics: Moderate (decreases concentration)
• folates+fosphenytoin: Moderate (decreases concentration)
• folates+phenobarbital: Moderate (decreases concentration)
• folates+phenytoin: Moderate (decreases concentration)
• folates+primidone: Moderate (decreases concentration)
• sulfasalazine+folates: Unknown (decreases absorption)

Pregnancy

Folate is essential for fetal development and is often recommended to prevent neural tube defects.

Breast-feeding

Folate is generally safe during breastfeeding, as it is important for both maternal and infant health.

Storage

Store in a cool, dry place, away from direct sunlight.

Formulations

• Tablets
• Injection

Indications

• Polycystic ovary syndrome (PCOS)
• Generalized anxiety disorder
• Depression
• Obsessive-compulsive disorder
• Insulin resistance

Dosage

Children: Refer to the BNF for Children for appropriate dosing guidelines for paediatric patients.

Adults: Refer to the BNF for specific dosing recommendations, as doses may vary based on the condition being treated.

Mechanism of action

Inositol functions primarily as a precursor for the synthesis of phosphoinositides, which are key components of cell membranes. These phosphoinositides are involved in various intracellular signaling pathways, particularly those mediated by G-protein coupled receptors. Inositol also influences the action of neurotransmitters such as serotonin and has been shown to enhance insulin sensitivity and glucose metabolism.

Pharmacodynamics

Inositol has been observed to have mood-stabilizing effects and may improve insulin sensitivity. Its role in cell signaling impacts various physiological processes, including cellular communication and metabolic regulation. The therapeutic effects of inositol in psychiatric conditions may be attributed to its ability to modulate neurotransmitter systems, particularly involving serotonin and dopamine.

Pharmacokinetics

Inositol is well-absorbed from the gastrointestinal tract, with peak plasma levels occurring within 1 to 2 hours after ingestion. It is distributed throughout the body and can cross the blood-brain barrier. Inositol is predominantly excreted in the urine, with a half-life that varies based on dosage and individual metabolism. Metabolism occurs primarily through dephosphorylation to form various inositol phosphates.

Pregnancy

Inositol is generally considered safe during pregnancy but should be used under medical supervision.

Breast-feeding

Inositol is likely safe during breastfeeding, but consult a healthcare provider for specific recommendations.

Storage

Store in a cool, dry place, away from direct sunlight. Keep out of reach of children.

Formulations

• Powder
• Capsules

Indications

• Diabetic neuropathy
• Oxidative stress-related disorders
• Metabolic syndrome
• Weight management
• Liver health

Dosage

Children: Refer to specific product guidelines, as safety and efficacy in children have not been established.

Adults: Refer to specific product guidelines, as dosages may vary based on the formulation and indication.

Mechanism of action

Lipoic acid acts as a cofactor for mitochondrial enzyme complexes, particularly those involved in the Krebs cycle, enhancing energy production. It also possesses antioxidant properties, neutralizing free radicals and regenerating other antioxidants such as vitamins C and E. Additionally, lipoic acid can modulate various signaling pathways, including those related to insulin sensitivity and inflammation.

Pharmacodynamics

Lipoic acid has a dual role as a coenzyme and an antioxidant. By participating in the decarboxylation of alpha-keto acids, it aids in energy production. Its antioxidant properties contribute to the protection of cells from oxidative stress, which is implicated in various chronic diseases. Lipoic acid can improve insulin sensitivity, making it beneficial in managing glucose metabolism disorders.

Pharmacokinetics

After oral administration, lipoic acid is absorbed in the gastrointestinal tract, with peak plasma concentrations occurring within 30 to 60 minutes. It undergoes hepatic metabolism, primarily via reduction and conjugation, resulting in various metabolites. The elimination half-life is approximately 30 minutes to 2 hours, and it is excreted primarily in urine. The bioavailability of lipoic acid can be affected by food intake.

Adverse effects

• Nausea
• Vomiting
• Abdominal pain
• Skin rash
• Hypoglycemia

Interactions

• May enhance the effects of insulin and other antidiabetic medications
• May interact with heavy metal chelators

Precautions

• Use with caution in patients with diabetes due to the risk of hypoglycemia
• Monitor blood sugar levels in diabetic patients

Pregnancy

Safety during pregnancy has not been established; use only if clearly needed.

Breast-feeding

It is not known whether lipoic acid is excreted in human breast milk; caution is advised.

Storage

Store in a cool, dry place away from light.

Formulations

• Capsules
• Tablets
• Injectable solutions

Indications

• Cognitive enhancement
• Liver support
• Antioxidant therapy

Dosage

Children: Refer to established guidelines or clinical resources for specific dosing recommendations.

Adults: Refer to established guidelines or clinical resources for specific dosing recommendations.

Mechanism of action

Monomethionine acts as a methyl donor in the transmethylation process, which is vital for the synthesis of various biomolecules, including neurotransmitters and phospholipids. It may help in reducing oxidative stress by scavenging free radicals and enhancing antioxidant defenses, thus protecting cells from damage.

Pharmacodynamics

Monomethionine exhibits antioxidant activity, which helps in mitigating the effects of oxidative stress. Its role in methylation processes is essential for maintaining normal cellular functions and promoting overall metabolic health. The compound may also influence neurotransmitter levels, contributing to cognitive function and mood stabilization.

Pharmacokinetics

Monomethionine is absorbed readily from the gastrointestinal tract, with peak plasma concentrations typically occurring within a few hours post-administration. Its distribution in the body and metabolism involve conversion to other forms of methionine and related metabolites, which can be utilized by various tissues for protein synthesis and other metabolic pathways. The elimination half-life and excretion pathways are not well-defined in the literature.

Pregnancy

There is insufficient evidence regarding the safety of monomethionine in pregnancy. Caution is advised.

Breast-feeding

Limited data is available on the excretion of monomethionine in human milk. Caution is advised.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Indications

• Hyperlipidemia
• Dyslipidemia
• Atherosclerosis
• Peripheral vascular disease

Dosage

Children: Refer to established clinical guidelines or pharmacology references for pediatric dosing, as specific pediatric doses may not be established.

Adults: Refer to established clinical guidelines or pharmacology references for specific dosing information, as dosing can vary based on the specific formulation and indication.

Mechanism of action

Polynicotinate exerts its effects primarily through the activation of nicotinic acid receptors, which leads to increased lipolysis in adipose tissue, resulting in the mobilization of free fatty acids. It also enhances the activity of lipoprotein lipase, aiding in the clearance of triglycerides from the bloodstream. This action contributes to a reduction in total cholesterol and low-density lipoprotein (LDL) levels while potentially increasing high-density lipoprotein (HDL) levels.

Pharmacodynamics

Polynicotinate influences lipid metabolism by modulating the synthesis and breakdown of lipoproteins. Its vasodilatory properties can lead to improved blood flow, which may contribute to its therapeutic effects in conditions related to poor circulation. Additionally, its modulation of lipid levels is beneficial in reducing the risk of cardiovascular diseases.

Pharmacokinetics

Polynicotinate is absorbed from the gastrointestinal tract, with the rate of absorption influenced by the presence of food. It undergoes extensive first-pass metabolism in the liver. The peak plasma concentration is typically reached within a few hours of administration. The elimination half-life is variable but generally ranges around 1 to 2 hours. Excretion primarily occurs via the kidneys, with metabolites being eliminated in urine.

Adverse effects

• Gastrointestinal disturbances
• Headache
• Dizziness
• Flushing
• Nausea

Precautions

• Use with caution in patients with liver or kidney impairment
• Monitor for allergic reactions

Pregnancy

There is limited data on the safety of polynicotinate during pregnancy. It should be used only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Limited information is available on the excretion of polynicotinate in human milk. Caution should be exercised when administering to nursing mothers.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Tablets
• Capsules
• Oral solution

Indications

• Cancer chemoprevention
• Selenium deficiency

Dosage

Children: Refer to the BNF for Children for appropriate dosing information.

Adults: Refer to the BNF for appropriate dosing information.

Mechanism of action

Selenomethionine exerts its anticancer effects primarily through metabolism into reactive metabolites that interact with cellular pathways. Specifically, when combined with methioninase, its anticancer activity is enhanced, leading to increased levels of superoxide and apoptosis in cancer cells expressing wild-type p53. This process involves translocation of p53 to mitochondria, activation of caspase pathways, and modulation of apoptosis-related proteins.

Pharmacodynamics

Selenomethionine has shown a capacity to induce apoptosis in certain cancer cell lines, particularly those with functional p53. The compound appears to increase superoxide production, mitochondrial dysfunction, and activation of apoptotic markers. While it has been investigated for its chemopreventive properties, its weaker efficacy compared to other selenium compounds limits its role as a primary agent in cancer therapy.

Pharmacokinetics

Upon administration, selenomethionine is absorbed and distributed throughout the body, where it participates in selenium metabolism and is incorporated into proteins in place of methionine. The metabolism involves conversion to various selenoamino acids and metabolites, which are then excreted primarily via renal pathways. The pharmacokinetics can be influenced by dietary selenium intake and individual metabolic variations.

Pregnancy

Selenomethionine should only be used in pregnancy if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Caution should be exercised when administering selenomethionine to nursing mothers.

Storage

Store in a cool, dry place, away from direct sunlight and out of reach of children.

Formulations

• Selenomethionine capsules
• Selenomethionine tablets

Indications

• Schizophrenia
• Acute psychosis
• Bipolar disorder
• Severe agitation

Dosage

Children: Refer to BNF for Children for specific paediatric dosing recommendations.

Adults: Refer to official dosing guidelines or BNF for specific adult dosing recommendations.

Mechanism of action

Zine exerts its therapeutic effects primarily through antagonism of dopamine D2 receptors in the central nervous system. This inhibition reduces dopaminergic activity, which is believed to be elevated in psychotic states. Additionally, zine may also interact with serotonin receptors, contributing to its overall antipsychotic effects.

Pharmacodynamics

The pharmacodynamic profile of zine is characterized by its ability to exert sedative and antipsychotic effects. By blocking D2 receptors, zine decreases symptoms of psychosis such as hallucinations and delusions. Its sedative properties can help manage agitation and anxiety, making it useful in acute psychiatric settings. However, the blockade of D2 receptors can also lead to extrapyramidal side effects, which are common with typical antipsychotics.

Pharmacokinetics

Zine is generally well-absorbed following oral administration, with peak plasma concentrations occurring within a few hours. The drug undergoes hepatic metabolism, primarily via cytochrome P450 enzymes, leading to the formation of active metabolites. The elimination half-life of zine allows for once-daily dosing in many cases. Renal excretion plays a role in the elimination of both the parent compound and its metabolites.

Contra-indications

• Hypersensitivity to zine or any of its components
• Severe liver impairment
• Severe renal impairment
• Acute porphyria

Adverse effects

• Drowsiness
• Dizziness
• Dry mouth
• Constipation
• Blurred vision
• Weight gain
• Extrapyramidal symptoms
• Tardive dyskinesia
• Neuroleptic malignant syndrome

Interactions

• CNS depressants (e.g., alcohol, benzodiazepines) may enhance sedation
• Anticholinergic drugs may increase the risk of anticholinergic side effects
• Antidepressants (e.g., MAO inhibitors) may lead to increased side effects

Precautions

• Monitor for signs of extrapyramidal symptoms
• Use with caution in patients with a history of seizures
• Evaluate liver and renal function before initiation
• Gradual discontinuation is recommended to avoid withdrawal symptoms

Pregnancy

Zine should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. Animal studies have shown adverse effects.

Breast-feeding

Zine is excreted in breast milk. Caution should be exercised when administering to nursing mothers, as it may affect the infant.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Oral tablets
• Oral suspension
• Injectable formulations

Mechanism of action

Vitamin B12 serves as a cofactor for _methionine synthase_ and _L-methylmalonyl-CoA mutase_ enzymes. Methionine synthase is essential for the synthesis of purines and pyrimidines that form DNA. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to _succinyl-CoA_ in the degradation of propionate, an important reaction required for both fat and protein metabolism. It is a lack of vitamin B12 cofactor in the above reaction and the resulting accumulation of methylmalonyl CoA that is believed to be responsible for the neurological manifestations of B12 deficiency. Succinyl-CoA is also necessary for the synthesis of hemoglobin. In tissues, vitamin B12 is required for the synthesis of _methionine_ from homocysteine. Methionine is required for the formation of S-adenosylmethionine, a methyl donor for nearly 100 substrates, comprised of DNA, RNA, hormones, proteins, as well as lipids. Without vitamin B12, tetrahydrofolate cannot be regenerated from 5-methyltetrahydrofolate, and this can lead to functional folate deficiency,. This reaction is dependent on methylcobalamin (vitamin B12) as a co-factor and is also dependent on folate, in which the methyl group of methyltetrahydrofolate is transferred to homocysteine to form _methionine_ and _tetrahydrofolate_. Vitamin B12 incorporates into circulating folic acid into growing red blood cells; retaining the folate in these cells. A deficiency of vitamin B12 and the interruption of this reaction leads to the development of megaloblastic anemia.

Pharmacodynamics

**General effects** Cyanocobalamin corrects vitamin B12 deficiency and improves the symptoms and laboratory abnormalities associated with pernicious anemia (megaloblastic indices, gastrointestinal lesions, and neurologic damage). This drug aids in growth, cell reproduction, hematopoiesis, nucleoprotein, and myelin synthesis. It also plays an important role in fat metabolism, carbohydrate metabolism, as well as protein synthesis. Cells that undergo rapid division (for example, epithelial cells, bone marrow, and myeloid cells) have a high demand for vitamin B12. **Parenteral cyanocobalamin effects** The parenteral administration of vitamin B12 rapidly and completely reverses the megaloblastic anemia and gastrointestinal symptoms of vitamin B12 deficiency. Rapid parenteral administration of vitamin B12 in deficiency related neurological damage prevents the progression of this condition. **Nasal spray effects** In 24 vitamin B12 deficient patients who were already stabilized on intramuscular (IM) vitamin B12 therapy, single daily doses of intranasal cyanocobalamin for 8 weeks lead to serum vitamin B12 concentrations that were within the target therapeutic range (>200 ng/L).

Mechanism of action

Chromium is an essential nutrient involved in the metabolism of glucose, insulin and blood lipids. Its role in potentiating insulin signalling cascades has been implicated in several studies. Chromium upregulates insulin-stimulated insulin signal transduction via affecting effector molecules downstream of the insulin receptor (IR). IR-mediated signalling pathway involves phoshorylation of multiple intracellular domains and protein kinases, and downstream effector molecules. Upon activation by ligands, intracellular β-subunit of IR autophosphorylates and activates tyrosine kinase domain of the IR, followed by activation and phosphorylation of regulatory proteins and downstream signalling effectors including phosphatidylinositol 2-kinase (PI3K). PI3K activates further downstream reaction cascades to activate protein kinase B (Akt) to ultimately promote translocation of glucose transporter-4 (Glut4)-vesicles from the cytoplasm to the cell surface and regulate glucose uptake. Chromium enhances the kinase activity of insulin receptor β and increases the activity of downstream effectors, pI3-kinase and Akt. Under insulin-resistant conditions, chromium also promotes GLUT-4 transporter translocation that is independent of activity of IR, IRS-1, PI3-kinase, or Akt; chromium mediates cholesterol efflux from the membranes via increasing fluidity of the membrane by decreasing the membrane cholesterol and upregulation of sterol regulatory element-binding protein. As a result, intracellular GLUT-4 transporters are stimulated to translocate from intracellular to the plasma membrane, leading to enhanced glucose uptake in muscle cells. Chromium attenuates the activity of PTP-1B _in vitro,_ which is a negative regulator of insulin signaling. It also alleviates ER stress that is observed to be elevated the suppression of insulin signaling. ER stress is thought to activate c-Jun N-terminal kinase (JNK), which subsequently induces serine phosphorylation of IRS and aberration of insulin signalling. Transient upregulation of AMPK by chromium also leads to increased glucose uptake. While the toxicity of metals and metalloids, like arsenic, cadmium, mercury, lead and chromium, is undisputed, the underlying molecular mechanisms are not entirely clear. General consensus holds that proteins are the prime targets; heavy metals interfere with the physiological activity of specific, particularly susceptible proteins, either by forming a complex with functional side chain groups or by displacing essential metal ions in metalloproteins. Recent studies have revealed an additional mode of metal action targeted at proteins in a non-native state; certain heavy metals and metalloids have been found to inhibit the in vitro refolding of chemically denatured proteins, to interfere with protein folding in vivo and to cause aggregation of nascent proteins in living cells. Apparently, unfolded proteins with motile backbone and side chains are considerably more prone to engage in stable, pluridentate metal complexes than native proteins with their well-defined 3D structure. By interfering with the folding process, heavy metal ions and metalloids profoundly affect protein homeostasis and cell viability. This review describes how heavy metals impede protein folding and promote protein aggregation, how cells regulate quality control systems to protect themselves from metal toxicity and how metals might contribute to protein misfolding disorders.

Pharmacodynamics

Trivalent chromium is part of glucose tolerance factor, an essential activator of insulin-mediated reactions. Chromium helps to maintain normal glucose metabolism and peripheral nerve function. Chromium increases insulin binding to cells, increases insulin receptor density and activates insulin receptor kinase leading to enhanced insulin sensitivity. In chromium deficiency, intravenous administration of chromium resulted in normalization of the glucose tolerance curve from the diabetic-like curve typical of chromium deficiency.

Mechanism of action

Selenomethionine (SeMet) is the chemical form or major component of selenium used for cancer chemoprevention in several clinical trials. However, evidence from experimental studies indicates that SeMet has weaker anticancer effects than most other forms of selenium. ... The anticancer activity of SeMet can be enhanced by methioninase (METase), indicating that SeMet metabolites are responsible for its anticancer activity. ... Wild-type p53-expressing LNCaP human prostate cancer cells were more sensitive to cotreatment with SeMet and METase than p53-null PC3 human prostate cancer cells. SeMet and METase cotreatment significantly increased levels of superoxide and apoptosis in LNCaP cells. Cotreatment with SeMet and METase resulted in increased levels of phosphorylated p53 (Ser15), total p53, Bax, and p21(Waf1) proteins. LNCaP cells treated with SeMet and METase also showed p53 translocation to mitochondria, decreased mitochondrial membrane potential, cytochrome c release into the cytosol, and activation of caspase-9. The effects of SeMet and METase were suppressed by pretreatment with a synthetic superoxide dismutase mimic or by knockdown of p53 via RNA interference. Reexpression of wild-type p53 in PC3 cells resulted in increases in superoxide production, apoptosis, and caspase-9 activity and a decrease in mitochondrial membrane potential following cotreatment with SeMet and METase. /The/ study shows that apoptosis induced by SeMet plus METase is superoxide mediated and p53 dependent via mitochondrial pathway(s). These results suggest that superoxide and p53 may play a role in cancer chemoprevention by selenium. ... The toxicity of Se is thought to arise from its ability to substitute for sulfur during the assembly of proteins. .../More/ recent studies also indicate that some forms of selenium are capable of generating oxidative stress in an in vitro test system that includes glutathione. L-Selenomethionine, the predominant form of selenium in the eggs of oviparous vertebrates, does not generate oxidative radicals in this system, but lesions consistent with oxidative stress have been identified in fish and birds with high concentrations of Se. /This study reports/ on the ability of rainbow trout embryos to transform L-selenomethionine to a form capable of producing a superoxide radical. Oxidative stress appears to be generated by methioninase enzyme activity in the embryos that liberates methylselenol from l-selenomethionine. Methylselenol redox cycles in the presence of glutathione producing superoxide and likely accounts for oxidative lesions present in fish and birds environmentally exposed to excessive loads of selenomethionine. /L-Selenomethionine/ Primary cultures of porcine aortic endothelial cells were used to test the potential protective effect ... against several types of oxidative stress. The stressors included exposure to hyperoxia, treatment with paraquat, and incubation in the presence of the hypoxanthine/xanthine oxidase system. This protective effect ... of selenomethionine ... is known to increase glutathione peroxidase activity. ... High-selenium containing yeast is being evaluated in clinical trials against colon polyp recurrence. However, the molecular targets for the anticancer effects of selenium remain unclear. Previous studies by our group demonstrated that selenomethionine-induced growth arrest appears to be mediated by activation of ERK and subsequent phosphorylation of RSK and histone H3. These results suggest that selenomethionine can alter gene expression. In the present study, we have used cDNA microarrays to determine whether gene expression differences exist in HCT116 colon cancer cells treated with selenomethionine. These experiments reveal statistically significant expression changes for 50 genes. Genes we found to increase with selenomethionine treatment include KLK6, ATOX1, SGK, GJB2, DAP-1, PLAU, VIM, DPYSL2, STC2 and PXN. Conversely, genes downregulated by selenomethionine include PRKACB,