Is age an independent predictor of early and late mortality in patients with acute myocardial infarction?

PURPOSE: To determine whether advancing age is an independent predictor of increased mortality following acute myocardial infarction or simply a marker for more extensive cardiac disease, a higher prevalence of comorbid conditions, and/or differences in therapeutic approach. PATIENTS: A total of 261 consecutive patients with documented acute myocardial infarction admitted to a university teaching hospital during a 1-year interval. METHODS: Seventy-four variables were analyzed to determine univariate predictors of inhospital and 1-year post-discharge mortality. Multiple linear regression models were constructed to determine independent predictors of early and late mortality after adjusting for baseline and therapeutic differences between younger and older patients. RESULTS: Compared with patients less than 70 years (n = 124), patients greater than or equal to 70 years (n = 137) were more likely (all p less than 0.05) to be female and have a prior history of ischemic heart disease. New York Heart Association functional class and Killip class on admission were higher in older patients, as were the admission serum creatinine and blood urea nitrogen levels. Serum albumin and peak creatine kinase levels were lower in older patients, but older patients were more likely to exhibit left ventricular hypertrophy or atrioventricular block on the initial electrocardiogram. Finally, younger patients were three times as likely to receive a thrombolytic agent and 66% more likely to receive intravenous beta-blockade than older patients, and younger patients were also more likely to receive heparin and intravenous nitroglycerin. Hospital mortality was 5.6% in patients less than 70 years versus 16.1% in patients greater than or equal to 70 years (p = 0.013). After adjusting for baseline and therapeutic differences, independent predictors of hospital mortality were systolic blood pressure on admission (inverse correlation, p = 0.0095), beta-blocker therapy (inverse correlation, p = 0.01), age (p = 0.014), peak creatine kinase level (p = 0.015), and Killip class (p = 0.035). Among hospital survivors, 1-year post discharge mortality was 6.8% in patients less than 70 years versus 19.1% in those greater than or equal to 70 years (p = 0.001). Independent predictors of post-discharge mortality after adjusting for age-related baseline and therapeutic differences were admission heart rate (p = 0.0004), age (p = 0.011), left ventricular ejection fraction (inverse correlation, p = 0.012), initial non-Q-wave myocardial infarction (p = 0.026), and the blood urea nitrogen level (p = 0.036). CONCLUSION: After adjusting for multiple baseline and therapeutic differences between older and younger patients, age per se remains a strong independent predictor of both inhospital and 1-year post-discharge mortality rates in patients with acute myocardial infarction.

Prognosis of patients > or = 70 years of age with non-Q-wave acute myocardial infarction compared with younger patients with similar infarcts and with patients > or = 70 years of age with Q-wave acute myocardial infarction.

In this study, 70 patients > or = 70 years of age admitted to the coronary care unit with non-Q-wave acute myocardial infarction (AMI) were followed prospectively for 1 year, and the clinical course in these patients was compared with that in 61 patients < 70 years with non-Q-wave AMI and 56 patients > or = 70 years with Q-wave AMI. Compared with the younger patients with non-Q-wave AMI, older patients were more likely to develop atrial fibrillation (23% vs 8%; p < 0.05) and congestive heart failure (53% vs 30%; p < 0.01), and less likely to receive thrombolytic therapy (9% vs 28%; p < 0.01), cardiac catheterization (41% vs 72%; p < 0.01), and coronary angioplasty (20% vs 39%; p < 0.05). Hospital mortality did not differ significantly between older and younger non-Q-wave AMI patients (10% vs 3%), but 1-year mortality was higher in the elderly (36% vs 16%; p = 0.02). Elderly patients with Q-wave AMI had more in-hospital complications, including death (25% vs 10%; p < 0.05), than elderly patients with non-Q-wave AMI. In contrast, postdischarge mortality was higher in elderly patients with non-Q-wave AMI, so that total mortality at 1 year was similar in the 2 groups. Overall, elderly patients with non-Q-wave AMI accounted for 62% of all deaths occurring during the first year after discharge (relative risk 2.6 compared with other groups; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Stability over time of variables measuring heart rate variability in normal subjects.

Both time and frequency domain measures of heart rate (HR) variability have been used to assess autonomic tone in a variety of clinical conditions. Few studies in normal subjects have been performed to determine the stability of HR variability over time, or the correlation between and within time and frequency domain measures of HR variability. Fourteen normal subjects aged 20 to 55 years were studied with baseline and placebo 24-hour ambulatory electrocardiograms performed 3 to 65 days apart to assess the reproducibility of the following time domain measures of cycle length variability: the standard deviation of all normal cycle intervals; mean normal cycle interval; mean day normal cycle interval; night/day difference in mean normal cycle interval; root-mean-square successive cycle interval difference; percentage of differences between adjacent normal cycle length intervals that are greater than 50 ms computed over the entire 24-hour electrocardiographic recording (proportion of adjacent intervals greater than 50 ms); and the frequency domain measures of high (0.15 to 40 Hz), low (0.003 to 0.15) and total (0.003 to 0.40) power. The mean and standard deviations of these measures were virtually identical between placebo and baseline measurements and within the studied time range. Variables strongly dependent on vagal tone (high-frequency, low-frequency and total power, root-mean-square successive difference, and percentage of differences between adjacent normal cycle intervals greater than 50 ms computed over the entire 24-hour electrocardiographic recording) were highly correlated (r greater than 0.8). It is concluded that measures of HR variability are stable over short periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of digoxin and enalapril on heart period variability and response to head-up tilt in normal subjects.

To test the effects of digitalis and angiotensin-converting enzyme inhibition on the RR interval variability in an electrocardiogram, 20 normal subjects were given digoxin 0.25 mg, enalapril 10 mg, and placebo twice daily in a randomized, double-blind, crossover study. Continuous 24-hour electrocardiographic recordings obtained on day 5 of each treatment were analyzed and several time domain and power spectral measures of heart period variability were calculated. Digoxin markedly increased (up to 51%) indexes of vagal modulation of heart period without changing mean RR interval. Enalapril did not change any measure of heart period variability despite a modest hypotensive effect. To determine the effect of each treatment on the response to orthostatic stress, 10 subjects also underwent 15 minutes of 60 degrees head-up tilt; power spectra were calculated for 15 minutes at 0 degree and at 60 degrees of tilt. Neither active treatment affected the response to head-up tilt.

Life expectancy in the Marfan syndrome.

Data reported in 1972 indicated that lifespan in patients with the Marfan syndrome is markedly shortened, and that most deaths are cardiovascular. This study was performed to determine whether survival in the Marfan syndrome has changed since 1972, and to discern whether treatment (medical or surgical) has altered prognosis. Survival curves were generated on 417 patients from 4 referral centers, with a definite diagnosis of the Marfan syndrome. Birth date, age at death, cardiovascular surgery, or treatment with beta blockers, or any combination of these, were included in the analysis. Forty-seven of 417 patients died. Mean age at death (41 +/- 18 years) was significantly increased compared with age in 1972 (32 +/- 16 years, p = 0.0023). Median (50%) cumulative probability of survival in 1993 was 72 years compared with 48 years in 1972. Of 112 surgically treated patients, 10-year probability of survival was 70%. Patients undergoing surgery after 1980 enjoyed significantly increased survival than patients who had undergone operation before 1980 (p = 0.008). In conclusion, life expectancy for patients with the Marfan syndrome has increased > 25% since 1972. Reasons for this dramatic increase may include (1) an overall improvement in population life expectancy, (2) benefits arising from cardiovascular surgery, and (3) greater proportion of milder cases due to increased frequency of diagnosis. Medical therapy (including beta blockers) was also associated with an increase in probable survival.

Quantification of cholesterol tracers by gas chromatography--negative ion chemical ionization mass spectrometry.

Because of its high sensitivity, gas chromatography negative ion chemical ionization mass spectrometry (GC-NCI-MS) is a potentially valuable analytical tool for the study of cholesterol metabolism. Of several derivatives prepared for potential use in tracer studies pentafluorobenzoyl cholesterol was selected because it formed rapidly at ambient temperature and was stable for long periods, could be detected at a level of 1 fmol, and yielded a mass spectrum in which the molecular ion was the principal component. Hexadeuterated cholesterol tracer ([26,26,26,27,27,27-2H6]cholesterol) could be detected in dilutions up to 2700 in unlabeled cholesterol by selected ion monitoring with a coefficient of variation averaging 3.2%. In seven normal subjects tracer cholesterol was infused intravenously and plasma cholesterol enrichment was determined after 4 h. The measured rapidly miscible cholesterol pool was 391.0 +/- 38.6 mg cholesterol/kg. Negative ion mass spectrometry of pentafluorobenzyol cholesterol will facilitate analysis of both small amounts of natural cholesterol and labeled cholesterol in applications where sensitivity is critical.

Time domain measurements of heart rate variability.

Assessment of HRV through time domain variables is a simple and practical method of assessing autonomic function. In this capacity its utility has been demonstrated in normal subjects and in diverse cardiac and noncardiac pathologic states. It can be used to assess the effects of drugs and other interventions, including exercise and psychological and physical stress on cardiac autonomic tone. Importantly, decreased HRV is almost uniformly associated with adverse outcome. The prognostic information appears to incorporate both alterations in autonomic tone and longer term components and is best assessed using ambulatory ECG recordings. Defining the clinical applicability and physiologic mechanisms of changes in HRV remain active areas of research.

Cholesterol absorption efficiency declines at moderate dietary doses in normal human subjects.

While unphysiologically large cholesterol doses are known to reduce percent cholesterol absorption, smaller amounts are reported to have no effect in human subjects. To determine the dose;-response relation between dietary cholesterol consumed and the efficiency of intestinal cholesterol absorption, we fed 18 normal subjects two test meals containing different amounts of natural cholesterol. In each test pentadeuterated cholesterol tracer was given orally, hexadeuterated cholesterol tracer was given intravenously, and the tracer ratio was measured in plasma 4 days later by gas chromatography/negative ion mass spectrometry. Baseline cholesterol absorption in the presence of 26 mg cholesterol tracer was 40.7 +/- 2.3%. This decreased by 4.9 percentage points (P = 0.05) when a total of 188 mg cholesterol was included in the meal and by 15.6 percentage points (P = 0.006) when 421 mg cholesterol was given, showing that the efficiency of cholesterol absorption declines appreciably even with modest increases in cholesterol dose. Considerable variation was noted in the response of different subjects and, on the higher cholesterol dose, dietary cholesterol absorption varied 5-fold from 40 mg to 212 mg. Fasting plasma insulin was correlated with the ability to absorb higher cholesterol doses without loss of efficiency (r(s) = 0.700, P = 0.036). Percent cholesterol absorption in a single meal is significantly influenced by the amount of cholesterol in that meal, suggesting that acute dietary factors influencing cholesterol absorption need further study.

Lack of effect of cholesterol esterase inhibitor CVT-1 on cholesterol absorption and LDL cholesterol in humans.

Two clinical trials were performed to test the hypothesis that CVT-1, a potent inhibitor of pancreatic cholesterol esterase, reduces percent cholesterol absorption and LDL cholesterol in humans. Measurements of cholesterol absorption were made with deuterated cholesterol tracers given orally and intravenously and detected in plasma by a new technique using negative ion mass spectrometry. Study 1 was a randomized, double-blind parallel study of CVT-1 treatment at doses of 0, 300, 1500, and 3000 mg/day in 19 subjects. Percent cholesterol absorption measured at baseline and again after 2 and 6 weeks showed no treatment effect and LDL cholesterol was unchanged. Study II was a randomized open-label crossover comparison between CVT-1 given as 1000 mg three times daily for 2 weeks and 187.5 mg hourly 16 hours/day for 2 weeks. Percent cholesterol absorption and plasma LDL cholesterol were not different between periods. We conclude that cholesterol esterase is not required for unesterified cholesterol absorption in human subjects.

Receptor-like function of heparin in the binding and uptake of neutral lipids.

Molecular mechanisms regulating the binding, amphipathic stabilization, and metabolism of the major neutral lipids (e.g., cholesteryl esters, triglycerides, and fatty acids) are well studied, but the details of their movement from a binding compartment to a metabolic compartment deserve further attention. Since all neutral lipids must cross hydrophilic segments of plasma membranes during such movement, we postulate that a critical receptor-like site exists on the plasma membrane to mediate a step between binding and metabolism and that membrane-associated heparin is a key part of this mediator. For example, intestinal brush border membranes containing heparin bind homogeneous human pancreatic 125I-labeled cholesterol esterase (100 kDa) and 125I-labeled triglyceride lipase (52 kDa). This interaction is enzyme concentration-dependent, specific, and saturable and is reversed upon addition of soluble heparin. Scatchard analysis demonstrates a single class of receptors with a Kd of 100 nM and a Bmax of approximately 50-60 pmol per mg of vesicle protein. In contrast, enzymes associated with the hydrolysis of hydrophilic compounds such as amylase, phospholipase A2, and deoxyribonuclease do not bind to intestinal membranes in this manner. Human pancreatic cholesterol esterase also binds specifically and saturably to cultured intestinal epithelial cells (CaCo-2), and soluble heparin significantly diminishes the cellular uptake of the resultant hydrophobic reaction products (cholesterol and free fatty acids). We conclude that a physiological role for intestinal heparin is that of a mediator to bind neutral lipolytic enzymes at the brush border and thus promote absorption of the subsequent hydrolyzed nutrients in the intestine. This mechanism may be a generalizable pathway for transport of neutral lipids into endothelial and other cells.

Heparin-modulated binding of pancreatic lipase and uptake of hydrolyzed triglycerides in the intestine.

Utilizing small intestine membranes that contain heparin (50 micrograms/mg protein), binding of triglyceride lipase (homogeneous 52 kDa, specific activity, 70 nmol/mg.h) to membranes was shown to be concentration dependent and saturable, and it was characterized by a single dissociation constant (KD = 86 +/- 16 nM) with a maximal binding capacity of 54 +/- 8 pmol/mg of vesicle protein. Specific binding was decreased in a concentration-dependent manner by the addition of exogenous heparin, and binding was virtually eliminated (less than 6% control values) by pretreatment of membranes with bacterial heparinase. Cultured intestinal epithelial cells (CaCo-2), shown to possess membrane-associated heparin, also bound pancreatic triglyceride lipase in a specific and saturable manner, with KD = 77 +/- 12 nM and Bmax = 13.7 +/- 6 pmol/10(6) cells. Soluble heparin not only decreased binding, but it also diminished the enzyme-mediated cellular uptake of [14C]oleate from [14C]triolein by over 75%. Therefore, intestinal heparin, a component of the brush border membrane, localizes pancreatic triglyceride lipase in a receptor-like manner to the plasma membrane to promote the subsequent absorption of fatty acids derived from hydrolyzed triglycerides.

Heart rate variability: a measure of cardiac autonomic tone.

Analysis of HRV based on routine 24-hour Holter recordings provides a sensitive, noninvasive measurement of autonomic input to the heart. HRV can be measured in the time or frequency domain. Each frequency domain variable correlates at least r = 0.85 with a time domain variable. Thus time domain measures can be used as surrogates for frequency domain measures which may simplify future studies. Abnormalities of autonomic input to the heart, which are indicated by decreased indices of HRV, are associated with increased susceptibility to ventricular arrhythmias. Decreased indices of HRV are also associated with CHF, diabetes, and alcoholic cardiomyopathy. Decreased indices of HRV are an independent risk factor for mortality post MI and in patients with advanced CHF. Medications can also affect HRV, and that effect may become an important clinical consideration, especially in high-risk patients.

Percent cholesterol absorption in normal women and men quantified with dual stable isotopic tracers and negative ion mass spectrometry.

Percent cholesterol absorption was measured in 94 normal subjects aged 17- 80 years while consuming diets generally low in cholesterol (mean intake = 226 +/- 126 mg/day). A new dual stable isotope method was used where a cholesterol tracer containing 6 extra mass units was given intravenously and another tracer with 5 extra mass units was given orally during a standard test meal. The ratio of tracers in plasma was determined by negative ion mass spectrometry of pentafluorobenzoyl sterol esters. Absorption values ranged widely from 29.0% to 80.1% with mean 56.2 +/- 12.1 (SD) %. Cholesterol absorption was significantly increased in African-Americans (63.4 +/- 11.8% vs. 55.1 +/- 11.9%, P = 0.027) but was similar for women (53.3 +/- 11.9%) and men (57.6 +/- 12.1%). It was not related to plasma lipoproteins, age, apoE3/E3 or E3/E4 genotype, or chronic dietary intake of energy, fat, or cholesterol quantitated from 7- day food records. However, dietary cholesterol intake was positively related to plasma cholesterol (P = 0.036) and triglycerides (P = 0.026). The milligram amount of dietary cholesterol absorbed (but not percent absorption) was positively correlated with fasting plasma insulin (r = 0.525, P < 0.0001), C-peptide (r = 0.367, P = 0.0003) and glucagon (r = 0.421, P < 0.0001) independent of gender, body fat percent and age.The efficiency of intestinal cholesterol absorption and the milligram amount of dietary cholesterol absorbed were not related to plasma cholesterol or LDL cholesterol in individuals consuming a low-cholesterol low-fat diet. The dominant factor determining dietary cholesterol absorption was intake rather than absorption efficiency. Dietary cholesterol and fat were strongly and independently related to hormonal measures of insulin resistance.-Bosner, M. S., L. G. Lange, W. F. Stenson, and R. E. Ostlund, Jr. Percent cholesterol absorption in normal women and men quantified with dual stable isotopic tracers and negative ion mass spectrometry.

Cholesterol transport function of pancreatic cholesterol esterase: directed sterol uptake and esterification in enterocytes.

We have recently hypothesized that neutral lipids can, in part, move across biological membranes via a mechanism involving enzymes anchored to membrane proteoglycans such as those found in the brush border of the enterocyte [Bosner, M. S., Gulick, T., Riley, D. J. S., Spilburg, C. A., & Lange, L. G. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7438-7442]. Present results now show a subsequent, essential protein-mediated sorting of neutral lipids for further intracellular metabolism. Thus, in the absence of enzyme, 0.002 pmol of cellular ester appeared after 2 h, and its level increased only 3.5-fold after 12 h. However, in the presence of cholesterol esterase, the level of cholesterol ester increased 39-fold in the same time period, indicating that the enzyme-mediated uptake accounts for 10-fold greater ester synthesis than that from basal absorption. Kinetic analysis reveals that both enzyme-mediated and background absorption depend on taurocholate concentration and are second-order reactions more likely dependent on collision than diffusion. Other lipid-recognizing proteins such as pancreatic triglyceride lipase and the intestinal fatty acid binding protein are not stimulatory to intracellular cholesterol processing. Taken together, these data suggest that pancreatic cholesterol esterase and possibly other proteoglycan-binding extracellular enzymes of neutral lipid metabolism may facilitate movement of neutral lipids into the plasma membrane and direct them into functional intracellular sites.

Sensitive detection of abnormal aortic architecture in Marfan syndrome with high-frequency ultrasonic tissue characterization.

BACKGROUND: Aneurysmal dilation of the aorta with subsequent rupture or dissection occurs frequently in patients with Marfan syndrome and is the primary cause of morbidity. These complications are related to the altered composition and disorganized structure of the aortic media. Our goal was to use high-frequency ultrasonic tissue characterization to identify these structural changes in abnormal aorta from patients with Marfan syndrome. We measured integrated backscatter and anisotropy of backscatter of ultrasound from specimens of aorta from patients with Marfan syndrome undergoing aortic root replacement and compared these values with those from aortic specimens of patients without clinical aortic pathology. METHODS AND RESULTS: Aortic tissue was obtained at the time of surgery from 11 patients with Marfan syndrome undergoing repair of an aortic aneurysm or dissection. Normal tissue was obtained at the time of autopsy from 8 patients without evidence of aortic disease. Acoustic microscopy at 50 MHz was performed to measure integrated backscatter from each specimen. The magnitude of ultrasonic anisotropy of backscatter for each tissue type was determined as an index of the three-dimensional (3D) organization of the vessel matrix. The collagen content of each specimen was determined with a hydroxyproline assay. Marfan aortas exhibited less backscatter than did normal aortas (-40.9 +/- 2.9 versus -32.6 +/- 2.2 dB for patients with Marfan syndrome and healthy subjects, respectively, P < .0001). No significant difference in collagen concentrations was observed between normal and Marfan aorta (262.7 +/- 52.7 versus 282.4 +/- 41.8 mg/g tissue for normal and Marfan aortas, respectively, P = .42), despite the large difference in backscatter. Histological analysis revealed striking differences in both the amount and organization of the elastin in the aortic aneurysm segments from patients with Marfan syndrome compared with normal aorta. Normal aorta was characterized by well-formed elastin fibers arranged in a lamellar pattern. The media from aneurysms in Marfan aorta exhibited a profound decrease in elastin content that was associated with loss of the highly aligned and ordered lamellar arrangement. The directional dependence of scattering, or ultrasonic anisotropy, also differed dramatically between the two tissue types. Backscatter from normal aorta decreased substantially when the media was insonified parallel compared with perpendicular to the principal axis of the elastin fibers. Marfan aorta exhibited a much smaller directional dependence of scattering. Normal aortas manifested a 14-fold greater ultrasonic anisotropy than did Marfan aortas (24.1 +/- 3.7 versus 12.4 +/- 3.3 dB for normal and Marfan aortas, P < .0001), which is indicative of the profound extent of matrix disorganization in Marfan syndrome. CONCLUSIONS: These data show that high-frequency ultrasonic tissue characterization sensitively detects changes in vessel wall composition and organization that occur in the aorta of patients with Marfan syndrome. Aortic segments from these patients manifested a significant decrease in integrated backscatter compared with normal aorta (approximately 8 dB, or greater than a 6-fold decrease in scattering). A 15-fold reduction in the ultrasonic anisotropy of Marfan tissue was observed, which suggests a marked disorganization of the 3D architecture of these aortas. These data support the hypothesis that high-frequency ultrasonic tissue characterization may be useful for identifying abnormalities of vessel wall composition, architecture, and material properties.

Identification of a species specific regulatory site in human pancreatic cholesterol esterase.

All mammalian pancreatic cholesterol esterases (CEase) bind to membrane-associated heparin at a single site on the intestinal brush border membrane with a dissociation constant of 100 nM. While the enzyme is bound to the membrane, the activity of the human and bovine enzymes is enhanced 2-fold when compared to the activity of the enzyme in solution. On the other hand, soluble heparin potently inhibits the human CEase-catalyzed hydrolysis of cholesterol oleate with an IC50 of 2 x 10(-4) mg/mL, a value that is about 10(4) times more potent than that found with the bovine enzyme. The C-terminal portion of the human enzyme contains 16 proline-rich repeats of 11 amino acids each, while that from other species contains only a few of these repeat units. To determine if the unique human C-terminus is responsible for this inhibition, two chimeras containing either the human N-terminus (residues 1-445) and the bovine C-terminus (residues 446-557), HB, or the bovine N-terminus (residues 1-445) and the human C-terminus (residues 446-722), BH, were prepared. The cholesterol oleate hydrolytic activity of these chimeras was similar to that for the recombinant human and bovine enzymes. Importantly, each chimera was inhibited by heparin with IC50 values of 0.03 and 0.1 mg/mL for HB and BH, respectively. These intermediate IC50 values indicate that human CEase has two structural regions that contribute to is unique inhibition by this sulfated glycosaminoglycan, and these could regulate cholesterol uptake in humans.

Assessment of percent cholesterol absorption in humans with stable isotopes.

Dietary cholesterol restriction is a general recommendation for the medical community and emphasizes the importance of intestinal cholesterol absorption and metabolism in humans. However, several methods that may accurately quantify cholesterol absorption utilize radioactive isotopes that are undesirable for younger individuals, women, children, and normal subjects. To eliminate this hazard, we have developed a procedure for measurement of percent cholesterol absorption, based on that of Zilversmit (1972. Proc. Soc. Exp. Med. Biol. 140: 862-865), using stable nonradioactive isotopic tracers of cholesterol. [26,26,26,27,27,27-2H]cholesterol (30 mg) was administered orally and [23,24,25,26,27-13C]cholesterol (15 mg) was administered intravenously on day 0 and percent cholesterol absorption was calculated as the plasma ratio of oral/intravenous isotopic tracer on day 3 as determined by gas chromatography-mass spectrometry with selected ion monitoring. Tracer cholesterol given orally peaked in plasma on day 2 and then slowly declined in parallel with the intravenous tracer. Cholesterol absorption in 16 healthy subjects (on no medication and not ingesting alcohol) consuming a Step One Diet was 53.5% +/- 8.5 SD%. Five subjects underwent repeat testing after 4-6 weeks with excellent replication (SD of difference between tests = 2.8%). No differences in the metabolism of [13C5]cholesterol, [2H6]cholesterol, and [14C]cholesterol were observed. The use of stable isotopes for the study of percent cholesterol absorption is precise and safe, allowing repeated measurements in normal individuals and thus facilitating clinical investigation of this key component of human cholesterol metabolism.

Structure of the human pancreatic cholesterol esterase gene.

The gene for human pancreatic cholesterol esterase consists of 11 exons and 10 introns and is 9.2 kb in length. The last and longest exon (841 nucleotides) is unique to the human gene. Functional amino acids are encoded on separate exons. The leader sequence is encoded by a single exon which carries two additional N-terminal amino acids of the mature functional protein. A positive TATA element is identified 43 nucleotides from the start codon. Pulse-field gel electrophoresis and hybridization with various cDNA probes and direct sequence data revealed the existence of a CEase-like gene. Partial sequence analysis of this gene from a human cosmid library and human genomic DNA showed a premature stop signal in exon 10, shortly after the codon for the active-site histidine. Both the functional gene and the CEase-like gene have a polyadenylation signal in the 3'-untranslated region. Thus, the complex gene structure for this intestinally active enzyme may provide in part a potential molecular explanation for the well-known heterogeneity of the intestinal absorption of cholesterol.