Relationship between lipid composition and drug metabolizing capacity of human liver

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

Possible Induction of Cholinesterase in Epileptic Patients Treated With Anticonvulsant Drugs: Relationship With Lipoprotein Levels

The effect of enzyme-inducing anticonvulsant drugs on the serum concentrations of lipoproteins has been widely studied. However, there is little agreement between the results with regard to the possible development of a lipoprotein profile related to an increased or decreased cardiovascular risk. It has been suggested that cholinesterase (ChE) could be induced by these drugs, something of undeniable interest as ChE appears to have a relation to the metabolism of lipoproteins. The serum activity of ChE was determined in a group of 90 adult epileptic patients (56 male and 34 female) treated with phenobarbital, phenytoin, and carbamazepine. The liver enzyme induction produced by these drugs was then evaluated by determining serum gamma-glutamyltranspherase activity and urinary excretion of D-glucaric acid. A significant increase of serum ChE (p < 0.005) was found in the group of patients compared to a control group (n = 49) with a similar distribution for age and sex. A significant correlation was found for both male and female patients between ChE and concentrations of triglycerides, phospholipids, cholesterol, low-density lipoprotein (LDL) phospholipids, LDL-cholesterol, and apolipoprotein B (p < 0.01). Similarly, in female patients, ChE had a significant correlation with the total cholesterol/high-density lipoprotein (HDL) cholesterol and LDL-cholesterol/HDL-cholesterol ratios (p < 0.01). The ChE/HDL-cholesterol relationship, which has been proposed as a marker for cardiovascular risk, presented significant correlations with the total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios in patients of both sexes (p < 0.001). In the case of epileptic patients treated with enzyme-inducing anticonvulsant drugs, there may be an association between the possible induction of ChE and the metabolism of lipoproteins containing apolipoprotein B.

Elimination of endoplasmic reticulum stress and cardiovascular, type 2 diabetic, and other metabolic diseases

Multiple factors including unhealthy living habits influence the life-maintaining functions of the endoplasmic reticulum (ER) and induce ER stress and metabolic abnormalities. The ER responds to the disturbances by activating mechanisms that increase the capacity to eliminate ER stress. This article elucidates the effects of ER activation that eliminates both ER stress and associated cardiovascular, type 2 diabetic (DM2), and other metabolic diseases. ER-activating compounds eliminate ER stress by lowering elevated cholesterol, regress atherosclerosis, decrease cardiovascular mortality, reduce blood glucose and insulin, and, together with the normalization of glucose-insulin homeostasis, remove insulin resistance, pancreatic β-cell failure, and DM2. A deficient cytochrome P450 activity in hepatic ER leads to cholesterol accumulation that induces stress and xanthoma formation, whereas P450-activating therapy up-regulates apolipoprotein AI and LDLR genes, down-regulates apolipoprotein B gene, and produces an antiatherogenic plasma lipoprotein profile. The ER activation reduces the stress also by eliminating hepatic fat and converting saturated fatty acids (FAs) to unsaturated FAs. Cognitive processes require gene expression modification, and preclinical studies indicate that ER-activating therapy improves cognition. Promotion of healthy lifestyle choices and indicated therapies are key factors in the prevention and elimination of ER stress and associated global health problems.

Gene-activation mechanisms in the regression of atherosclerosis, elimination of diabetes type 2, and prevention of dementia

Atherosclerotic vascular disease, diabetes mellitus (DM) and dementia are major global health problems. Both endogenous and exogenous factors activate genes functioning in biological processes. This review article focuses on gene-activation mechanisms that regress atherosclerosis, eliminate DM type 2 (DM2), and prevent cognitive decline and dementia. Gene-activating compounds upregulating functions of liver endoplasmic reticulum (ER) and affecting lipid and protein metabolism, increase ER size through membrane synthesis, and produce an antiatherogenic plasma lipoprotein profile. Numerous gene-activators regress atherosclerosis and reduce the occurrence of atherosclerotic disease. The gene-activators increase glucose disposal rate and insulin sensitivity and, by restoring normal glucose and insulin levels, remove metabolic syndrome and DM2. Patients with DM2 show an improvement of plasma lipoprotein profile and glucose tolerance together with increase in liver phospholipid (PL) and cytochrome (CYP) P450. The gene-activating compounds induce hepatic protein and PL synthesis, and upregulate enzymes including CYPs and glucokinase, nuclear receptors, apolipoproteins and ABC (ATP-binding cassette) transporters. They induce reparation of ER structures and eliminate consequences of ER stress. Healthy living habits activate mechanisms that maintain high levels of HDL and apolipoprotein AI, promote health, and prevent cognitive decline and dementia. Agonists of liver X receptor (LXR) reduce amyloid in brain plaques and improve cognitive performance in mouse models of Alzheimer's disease. The gene activation increases the capacity to withstand cellular stress and to repair cellular damage and increases life span. Life free of major health problems and in good cognitive health promotes well-being and living a long and active life.

Gene activation regresses atherosclerosis, promotes health, and enhances longevity

Background

Lifestyle factors and pharmacological compounds activate genetic mechanisms that influence the development of atherosclerotic and other diseases. This article reviews studies on natural and pharmacological gene activation that promotes health and enhances longevity.

Results

Living habits including healthy diet and regular physical activity, and pharmacotherapy, upregulate genes encoding enzymes and apolipoprotein and ATP-binding cassette transporters, acting in metabolic processes that promote health and increase survival. Cytochrome P450-enzymes, physiological factors in maintaining cholesterol homeostasis, generate oxysterols for the elimination of surplus cholesterol. Hepatic CTP:phosphocholine cytidylyltransferase-α is an important regulator of plasma HDL-C level. Gene-activators produce plasma lipoprotein profile, high HDL-C, HDL₂-C and HDL-C/cholesterol ratio, which is typical of low risk of atherosclerotic disease, and also of exceptional longevity together with reduced prevalence of cardiovascular, metabolic and other diseases. High HDL contributes to protection against inflammation, oxidation and thrombosis, and associates with good cognitive function in very old people. Avoiding unhealthy stress and managing it properly promotes health and increases life expectancy.

Conclusions

Healthy living habits and gene-activating xenobiotics upregulate mechanisms that produce lipoprotein pattern typical of very old people and enhance longevity. Lipoprotein metabolism and large HDL₂ associate with the process of living a very long life. Major future goals for health promotion are the improving of commitment to both wise lifestyle choices and drug therapy, and further the developing of new and more effective and well tolerated drugs and treatments.

Lipids and delta6-desaturase activity alterations in rat liver microsomal membranes induced by fumonisin B1

Alterations in the membrane structure and function of hepatocyte membranes by fumonisin B1 (FB1) have been proposed to play an important role in the disruption of growth regulatory effects and hence in the cancer-promoting ability of the mycotoxin. Detailed analyses of lipids in liver microsomal fractions of rats exposed to different dietary levels of FB1 over a period of 21 d indicated an increase in PC, PE, PI, and cholesterol (Chol). These changes decreased the PC/PE and increased the total phospholipid/Chol ratios. When considering FA content, the quantities of total FA increased (P < 0.05) in the major phospholipid fractions as a result of the increased phospholipid levels. However, when considering the relative levels (mg/100 mg of the total FA) of specific FA, the monounsaturated FA (16:1 n-7 and 18:1n-9) and 18:2n-6 increased (P < 0.05), whereas the long-chain PUFA decreased (P < 0.05) in the main phospholipid fractions. Enzyme analyses indicated that the activity of the delta6-desaturase was significantly reduced in liver microsomal preparations in a dose-dependent manner. An increase in the 20:3n-6/20:4n-6 ratio also suggested a decrease in the activity of the delta5-desaturase. Disruption of microsomal lipid metabolism at different levels by FB1 could play an important role in the alteration of growth regulatory effects in the liver.

Membrane insertion of cytochrome P450 1A2 promoted by anionic phospholipids

The role of phospholipids in the membrane binding and subsequent insertion of the microsomal protein rabbit cytochrome P450 (P450) 1A2 into phospholipid bilayers was investigated. The insertion of P450 1A2 into phospholipid bilayers was measured by the quenching of Trp fluorescence of P450 1A2 by pyrene and brominated and doxyl-labeled phospholipids. When the phosphatidylcholine (PC) matrix was replaced with acidic phospholipids [phosphatidic acid (PA), phosphatidylserine, and phosphatidylinositol] and phosphatidylethanolamine (PE), the extent of insertion into lipid bilayers was strictly dependent on the type of acidic phospholipids. All anionic phospholipids caused the penetration of P450 1A2 into lipid bilayers, but PA was the most efficient in facilitating deep penetration of P450 1A2 into bilayers. On the other hand, binding of P450 1A2 to liposomes was increased by acidic phospholipids to the same degree regardless of the type of acidic phospholipids. PE was found to act as an inert matrix phospholipid, similar to PC, as it exerted very little effect on the insertion of P450 1A2 into lipid bilayers and the binding of P450 1A2 to membranes. It was also found that the phospholipid-dependent membrane insertion of P450 1A2 was associated with altered enzyme activity, increased alpha-helix content, and increased Trp fluorescence of P450 1A2. These results indicate that negative charges on the acidic phospholipids are important for the initial binding of P450 1A2 to membranes, but the penetration of P450 1A2 into lipid bilayers is regulated by the type of acidic phospholipids, and that phospholipid-dependent insertion of P450 1A2 is accompanied by a structural change of P450 1A2.

Nutritional factors of microsomal enzymatic induction: influence of lipidic components of the diet

We compared the ability of two different diets containing 6 per cent of maize oil and 6 per cent of fish oil to modify: firstly the enzyme induction by phenobarbital and secondly the phenobarbital hydroxylation by the liver either in vivo or during in vitro perfusions. The presence of fish oil in the diet increased the cyt P 450 content and the bilirubin glucuronosyl transferase activity. The two induction effects promoted by the association of the phenobarbital treatment and the eating of the fish oil were not additive and it was found that the phenobarbital induction effect was decreased by the fish oil consumption. Phenobarbital and p-hydroxyphenobarbital kinetics were different in the two groups of animals. Phenobarbital was more slowly eluted in the fish oil fed than in the maize oil fed rats while p-hydroxyphenobarbital was more slowly eluted by the fish oil-fed rat livers.

Microsomal enzyme induction, lipoproteins and atherosclerosis

The liver is the principal site for the synthesis and elimination of lipoproteins circulating in plasma, and alterations in hepatic function influence plasma lipoprotein levels. High HDL-C/T-C and apo A-I/apo B ratios, which are characteristic of a low coronary risk, have been typical of healthy subjects with high microsomal enzyme activity in the liver. Microsomal enzyme inducing drugs such as phenytoin, phenobarbital and carbamazepine, and also alcohol, influence serum lipid and apoprotein concentrations. The inducers increase the concentrations of hepatic microsomal enzyme and apo A-I mRNA, and also proteins and phospholipids. They similarly increase serum HDL-C and apo A-I levels and the HDL-C/LDL-C ratio, powerful protective factors against coronary heart disease. These parameters parallel hepatic protein and phospholipid concentrations, and microsomal enzyme activity as assessed by liver cytochrome P-450 or antipyrine kinetics. Serum LDL-C levels are inversely proportional to hepatic cytochrome P-450 concentrations. Experimental studies indicate that phenobarbital retards cholesterol accumulation in the arterial wall and the formation of atherosclerotic plaque. A decreased mortality rate from coronary heart disease has been reported for subjects who take enzyme inducers, drugs or alcohol, whereas impairment of hepatic microsomal function may promote atherogenesis. In addition to drugs non-pharmacological factors such as dietary constituents and physical exercise may influence hepatic microsomal function and hence improve the serum lipoprotein profile. These observations, which connect microsomal inducers, liver lipids and proteins, serum lipids and apoproteins characteristic of a low risk of atherosclerotic disease and low incidence of coronary deaths, lead to the conclusion that the activation of liver microsomal function can prevent atherogenesis in man.

A role for dietary lipids and antioxidants in the activation of carcinogens

The ways in which dietary polyunsaturated fats and antioxidants affect the balance between activation and detoxification of environmental precarcinogens is discussed, with particular reference to the polycyclic aromatic hydrocarbon benzo(a)pyrene. The structure and composition of membranes and their susceptibility to peroxidation is dependent on the polyunsaturated fatty acid (PUFA) content of the cell and its antioxidant status, both of which are determined to a large degree by dietary intake of these compounds. An increase in the PUFA content of membranes stimulates the oxidation of precarcinogens to reactive intermediates by affecting the configuration and induction of membrane-bound enzymes (e.g., the mixed-function oxidase system and epoxide hydratase); providing increased availability of substrates (hydroperoxides) for peroxidases that cooxidise carcinogens (e.g., prostaglandin synthetase and P-450 peroxidase); and increasing the likelihood of direct activation reactions between peroxyl radicals and precarcinogens. Antioxidants, on the other hand, protect against lipid peroxidation, scavenge oxygen-derived free radicals and reactive carcinogenic species. In addition some synthetic antioxidants exert specific effects on enzymes, which results in increased detoxification and reduced rates of activation. The balance between dietary polyunsaturated fats, antioxidants and the initiation of carcinogenesis is discussed in relation to animal models of chemical carcinogenesis and the epidemiology of human cancer.

Effect of long-term anticonvulsant therapy on glucose metabolism in humans

This study was undertaken to evaluate the effect of anticonvulsants on glucose metabolism in humans. Tissue sensitivity to insulin (euglycemic clamp technique) and liver microsomal enzyme activity (oral antipyrine test) were measured in six subjects with epilepsy plus type 1 diabetes mellitus. They had received anticonvulsant drugs for greater than 8 years. Three groups--type 1 diabetics, persons with epilepsy, and healthy subjects--matched for sex, and weight, served as controls. Glucose disposal rate (M) was faster in subjects on anticonvulsant therapy as compared with the corresponding control group (p less than 0.01) and in nondiabetics as compared with diabetics (p less than 0.001). Antipyrine metabolism was rapid among patients on anticonvulsants and high normal in diabetics. Liver microsomal enzyme activity and glucose metabolism were related among diabetic (r = 0.593) and nondiabetic (r = 0.649) groups, respectively. Anticonvulsants with liver microsomal enzyme-inducing properties appear to enhance insulin sensitivity. These findings may serve to understand the long-term effect of anticonvulsants on glucose metabolism in humans.

The effect of liver microsomal enzyme inducing and inhibiting drugs on insulin mediated glucose metabolism in man

The effects of hepatic microsomal enzyme inducing (phenobarbitone and flumecinol), and inhibiting (cimetidine) drugs, and placebo treatment on insulin mediated glucose metabolism (M) were investigated in 29 healthy volunteers. Phenobarbitone (50 mg for 10 days) increased M (30%), metabolic clearance rate of glucose (MCRg), and antipyrine clearance rate (33%). Fasting immunoreactive insulin (IRI) decreased while fasting blood glucose (BG) remained unaltered. Flumecinol, another inducer, tested in two doses (200 mg and 600 mg for 6 days), did not alter glucose or antipyrine metabolism. Fasting IRI reduced on treatment with 600 mg of flumecinol, but not with the smaller dose. Cimetidine (600 mg for 6 days) decreased M (19.5%), MCRg (26%), and antipyrine clearance rate (20%). The placebo did not alter glucose or antipyrine metabolism. The results indicate that the insulin mediated glucose disposal rate can be altered by drugs influencing hepatic microsomal enzyme activity.