Achieving and maintaining National Cholesterol Education Program low-density lipoprotein cholesterol goals with five statins.

PURPOSE: Most patients fail to achieve and maintain low-density lipoprotein (LDL) cholesterol goals established by the National Cholesterol Education Program (NCEP). The Atorvastatin Comparative Cholesterol Efficacy and Safety Study (ACCESS) was a randomized study comparing the efficacy and safety of five statins and their ability reduce LDL cholesterol to the NCEP target level. SUBJECTS AND METHODS: Of 7542 patients screened, 3916 hypercholesterolemic patients were randomly assigned to treatment with a statin, beginning with the lowest recommended dose (atorvastatin, pravastatin, and simvastatin, 10 mg; fluvastatin and lovastatin, 20 mg). If the NCEP target was not achieved, the dose was titrated up to the recommended maximum (atorvastatin, fluvastatin, and lovastatin, 80 mg; pravastatin and simvastatin, 40 mg). The total duration of treatment was 54 weeks. RESULTS: Atorvastatin achieved the greatest mean reduction in LDL cholesterol: 36% +/- 11% at 6 weeks (initial dose) and 42% +/- 13% at 54 weeks. More patients receiving atorvastatin at its initial dose (53%, 997 of 1888) achieved their NCEP target levels than patients receiving simvastatin (38%, 174 of 462), lovastatin (28%, 134 of 472), pravastatin (15%, 71 of 461), or fluvastatin (15%, 69 of 474) at the initial dose. Atorvastatin-treated patients were more likely to maintain their target levels from week 6 to week 54. The percent reduction in LDL cholesterol achieved at the initial dose correlated strongly with the proportion of patients who maintained their goals at 54 weeks (r = -0.84). CONCLUSION: For patients treated with statins, providing a greater margin between the NCEP target level and the achieved LDL cholesterol level enhances the likelihood of maintaining NCEP goal levels.

Correlation of non-high-density lipoprotein cholesterol with apolipoprotein B: effect of 5 hydroxymethylglutaryl coenzyme A reductase inhibitors on non-high-density lipoprotein cholesterol levels.

Apolipoprotein B has been shown to be a better predictor of coronary heart disease than low-density lipoprotein (LDL) cholesterol, and non-high-density lipoprotein (non-HDL) cholesterol may also be a better parameter for coronary heart disease risk assessment and as a target for therapy. Data from the Atorvastatin Comparative Cholesterol Efficacy and Safety Study (ACCESS) were used to assess the correlation between lipid and apolipoprotein B levels before and after lipid-lowering therapy and to examine the effects of 5 hydroxymethylglutaryl coenzyme A reductase inhibitors on lipids and apolipoprotein B. The 54-week study randomized 3,916 hypercholesterolemic patients to atorvastatin, fluvastatin, lovastatin, pravastatin, or simvastatin, initiated at recommended starting doses with titrations as needed at weeks 6, 12, and 18 to achieve National Cholesterol Education Program LDL targets. Compared with LDL cholesterol, non-HDL cholesterol correlated better with apolipoprotein B levels at baseline (r = 0.914, p <0.0001) and at week 54 (r = 0.938, p <0.0001), and the correlation was strong across all baseline triglyceride strata. At starting doses, atorvastatin (10 mg) lowered non-HDL cholesterol by 33.3% compared with 26.6% with simvastatin (10 mg), 24.1% with lovastatin (20 mg), 17.2% with fluvastatin (20 mg), and 17.0% with pravastatin (10 mg). Atorvastatin also provided greater reductions in non-HDL cholesterol after dose titration, and a greater percentage of patients taking atorvastatin achieved non-HDL cholesterol targets. Baseline triglyceride did not affect non-HDL cholesterol reductions with any of the 5 hydroxymethylglutaryl coenzyme A reductase inhibitors. Fewer patients achieved non-HDL cholesterol targets than LDL cholesterol targets, particularly among high-risk patients, implying that if non-HDL cholesterol was used as a target for treatment, more patients would need to be treated more aggressively than National Cholesterol Education Program guidelines require.

Cardiovascular diseases in women.

Cardiovascular disease is the leading cause of death in women. Approaches to diagnosis and management of cardiovascular disease in women often differ from those in men. In some instances, these differences are justified by clinical trial and epidemiologic data.

Amino acid-specific ADP-ribosylation. Sensitivity to hydroxylamine of [cysteine(ADP-ribose)]protein and [arginine(ADP-ribose)]protein linkages.

Hydroxylamine stability has been used to classify (ADP-ribose)protein bonds into sensitive and resistant linkages, with the former representing (ADP-ribose)glutamate, and the latter, (ADP-ribose)arginine. Recently, it was shown that cysteine also serves as an ADP-ribose acceptor. The hydroxylamine stability of [cysteine([32P]ADP-ribose)]protein and [arginine([32P] ADP-ribose)]protein bonds was compared. In transducin, pertussis toxin catalyzes the ADP-ribosylation of a cysteine residue, whereas choleragen (cholera toxin) modifies an arginine moiety. The (ADP-ribose)cysteine bond formed by pertussis toxin was more stable to hydroxylamine than was the (ADP-ribose)arginine bond formed by choleragen. The (ADP-ribose)cysteine bond apparently represents a third class of ADP-ribose bonds. Pertussis toxin ADP-ribosylates the inhibitory guanyl nucleotide-binding regulatory protein (Gi) of adenylate cyclase, whereas choleragen modifies the stimulatory guanyl nucleotide-binding regulatory protein (Gs). These (ADP-ribose)protein linkages are identical in stability to those formed in transducin by the two toxins, consistent with the probability that cysteine and arginine are modified in Gi and Gs, respectively. Bonds exhibiting differences in hydroxylamine-stability were found in membranes from various non-intoxicated mammalian cells following incubation with [32P]NAD, which may reflect the presence of endogenous NAD:protein-ADP-ribosyl-transferases.

Heterologous desensitization of adenylate cyclase with prostaglandin E1 alters sensitivity to inhibitory as well as stimulatory agonists.

Adenylate cyclase in cultured human fibroblasts is activated by prostaglandin E1 (PGE1) or beta-adrenergic agonists, e.g., isoproterenol, and inhibited by muscarinic agonists. Incubation with PGE1 reduced adenylate cyclase responsiveness to both PGE1 and isoproterenol; this so-called heterologous desensitization is believed to result from impaired function of the stimulatory guanyl nucleotide-binding protein of the cyclase complex. The effect of heterologous desensitization by PGE1 on inhibition of adenylate cyclase by the muscarinic agonist oxotremorine was examined. Muscarinic inhibition of basal and isoproterenol-stimulated cAMP accumulation was attenuated following exposure to PGE1; the concentration of oxotremorine required for half-maximal inhibition of cAMP accumulation was increased. In both intact cells and membrane preparations the number of binding sites for [3H]scopolamine, a muscarinic antagonist, was unaltered by desensitization. Following exposure to PGE1, receptor affinity for oxotremorine, assessed by competition with [3H] scopolamine, and the guanyl nucleotide sensitivity of agonist binding were reduced. The amount of inhibitory guanyl nucleotide-binding regulatory protein available for [32P]ADP-ribosylation by pertussis toxin was unaltered by desensitization. Thus, heterologous desensitization of adenylate cyclase with the stimulatory agonist PGE1 alters sensitivity to inhibitory as well as stimulatory ligands.

NIH conference. Cyclic nucleotides: mediators of bacterial toxin action in disease.

In several bacterial diseases, the clinical, laboratory, and histologic findings result from the elaboration by the organism of a toxic product that binds to and may enter the host cell to alter its metabolism. In some cases, the intracellular mediators of toxin action are the cyclic nucleotides, cyclic adenosine 5'-monophosphate (cAMP) and cyclic guanosine 5'-monophosphate (cGMP), the ubiquitous second messengers through which numerous hormones, neurotransmitters, and drugs exert their effects. Certain toxins act by enhancing the activity of cellular enzymes that synthesize cAMP or cGMP; and others, by themselves catalyzing cAMP synthesis after entering the cell. Studies of the mechanism of action of these toxins have helped in deciphering the enzymatic components within animal cells that are responsible for cyclic nucleotide synthesis, degradation, and function as well as in understanding the pathogenesis of the diseases in which they are involved.

Requirement for both choleragen and pertussis toxin to obtain maximal activation of adenylate cyclase in cultured cells.

NG108-15 cells contain both the inhibitory and stimulatory guanyl nucleotide-binding regulatory proteins of the cyclase system. Choleragen activates cyclase directly by ADP-ribosylating the stimulatory guanyl nucleotide-binding protein; prostaglandin E1 does not further increase activity of cells treated with maximally effective concentrations of choleragen. Including pertussis toxin during incubation with this concentration of choleragen, however, further augments both cyclase activity and cAMP accumulation by intact cells. These observations suggest that the inhibitory guanyl nucleotide-binding protein exerts basal inhibition on catalytic activity which cannot be overcome by maximally effective concentrations of choleragen, stimulatory hormones, or both.

ADP-ribosylation of adenylate cyclase by pertussis toxin. Effects on inhibitory agonist binding.

Adenylate cyclase in NG108-15 (neuroblastoma X glioma hybrid) cells is responsive to both stimulatory and inhibitory ligands. Bordetella pertussis toxin (PT) catalyzes the ADP-ribosylation of a 41,000-Da peptide believed to be a subunit of the putative guanyl nucleotide-binding protein (Gi) involved in cyclase inhibition and abolishes inhibitory effects of opiate agonists. In studying the effects of PT on opiate receptors, we found that [3H]enkephalinamide binding was reduced by approximately 90% in membranes prepared from cells incubated with PT compared to control membranes. Agonist affinity, assessed by enkephalinamide competition for [3H]diprenorphine-binding sites, was markedly reduced in cells incubated with PT. Furthermore, inhibition by guanylylimidodiphosphate of ligand binding to opiate receptors was reduced following treatment with PT. The number of opiate receptors assessed by [3H]diprenorphine binding was unaltered by PT. These data are consistent with the hypothesis that PT-catalyzed ADP-ribosylation impairs the interaction of Gi with the inhibitory receptor-ligand complex, effectively uncoupling the inhibitory receptor from Gi and the cyclase catalytic unit.

Pertussis toxin-catalyzed ADP-ribosylation: effects on the coupling of inhibitory receptors to the adenylate cyclase system.

The adenylate cyclase system consists of stimulatory and inhibitory hormone and drug receptors coupled through different GTP-binding proteins to a catalytic unit, responsible for the synthesis of cAMP from ATP. Pertussis toxin blocks the effect of inhibitory agonists on the catalytic unit by enzymatically inactivating the inhibitory GTP-binding protein (Gi). Study of the inhibitory arm of the cyclase system has been facilitated by the dissection of the overall process of hormonal inhibition of cAMP formation into a series of reactions characteristic of the individual protein components of this complex system; pertussis toxin has proven to be a useful tool with which to study these individual reactions. Exposure of cells or membranes to pertussis toxin in the presence of NAD results in ADP-ribosylation of a 41,000 Da subunit of Gi. ADP-ribosylation of Gi has a number of effects on the overall and partial reactions of the cyclase system, including a loss of a) hormonal inhibition of cAMP formation, b) hormonal stimulation of GTPase and c) agonist-induced release of membrane-bound guanyl nucleotides. In addition, in toxin-treated membranes, the affinity of inhibitory receptors for agonist but not antagonist is decreased with no significant change in receptor number.

Activation by thiol of the latent NAD glycohydrolase and ADP-ribosyltransferase activities of Bordetella pertussis toxin (islet-activating protein).

Pertussis toxin (islet-activating protein) activates adenylate cyclase in susceptible cells by ADP-ribosylating an inhibitory component of the cyclase system. This toxin, assayed in a cell-free system in the presence of high concentrations of thiol, catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. This NAD glycohydrolase activity co-chromatographed on Sephacryl G-200 in 6.5 M urea, pH 3.2, 0.1 M glycine with the ADP-ribosyltransferase activity of the toxin, as monitored by the transfer of [32P]ADP-ribose from [32P]NAD to a 41,000-Da protein in NG108-15 neuroblastoma X glioma hybrid cells. In the absence of thiol, the native holotoxin was enzymatically inactive. Following addition of 250 mM dithiothreitol to the assay, maximal enzymatic activity was evident after a delay of approximately 1 h; with 20 mM thiol, the delay was longer. The Km for NAD with the fully activated enzyme was 25 microM; the Km did not appear to vary with the extent of activation. Thiol was necessary in a cell-free system to demonstrate NAD glycohydrolase activity. When extensively washed membranes were used as a source of 41,000-Da substrate, thiol was necessary to observe ADP-ribosylation in some cases (human erythrocytes) and significantly stimulated activity in others (NG108-15 cells). In contrast to the bacterial toxins choleragen and Escherichia coli heat-labile enterotoxin that ADP-ribosylate stimulatory components of the cyclase system, pertussis toxin did not transfer ADP-ribose to low molecular weight guanidino compounds, such as arginine or agmatine.