Tacrolimus, cyclosporine and plasma lipoproteins in renal transplant recipients.

To compare the effect of tacrolimus (FK506) and cyclosporine (CsA) on plasma lipoproteins in renal transplant recipients receiving maintainance therapy, the following prospective study was undertaken. Blood from nineteen recipients on tacrolimus (FK group) and from twenty-one on CsA (CsA group) was collected at baseline, 3-, 6-, and 10-month intervals. Plasma lipids, lipoproteins and oxidation properties of lipoproteins were determined. Plasma total cholesterol, low density lipoprotein (LDL) cholesterol, and apolipoprotein B (apoB) were substantially increased in both groups, although only the CsA group showed significant differences at all time intervals and at the baseline. High density lipoprotein cholesterol, triglycerides, and apolipoprotein A varied in both groups at time intervals from the baseline, but not significantly. The susceptibility to oxidation of LDL isolated from the FK group at all times was uninfluenced by the tacrolimus treatment, and values were comparable to those obtained from LDL isolated from healthy individuals. A significantly higher susceptibility to oxidation as indicated by the shorter time required to start the formation of conjugated dienes was observed in LDL isolated from the CsA group at 3 and at 6 months of therapy. Tacrolimus-treated patients appear to have less hyperlipidemic and have LDL less susceptible to oxidation than patients treated with CsA.

Vitamins C and E inhibit O2- production in the pig coronary artery.

BACKGROUND: We previously found in a pig coronary balloon injury model that vitamins C and E as well as probucol had beneficial effects on the vessel response to injury measured by morphometry These effects correlated with an inhibition in the ability to oxidize LDLs ex vivo, suggesting that the morphological response was due to the antioxidant effect of the treatments. METHODS AND RESULTS: In the present study, the production of O2- by vessels 14 days after balloon injury was determined and correlated with circulating and tissue levels of vitamins C and E. Twenty-five domestic pigs were divided into four groups: control (n=7), vitamin C (500 mg/d, group C, n=6), vitamin E (1000 IU/d, group E, n=6), and vitamins C and E (500 mg/d and 1000 IU/d, group C+E, n=6). Vitamins were administered 7 days before oversized balloon injury of the left anterior descending coronary artery (LAD) and continued for 14 days after injury. Vitamin C and E concentrations were determined in plasma and lymphocytes as an index for tissue levels. Vessels were harvested after animals were killed, and O2- production was measured by lucigenin chemiluminescence. O2- production by the injured LAD was 2.5-fold greater than O2- production by the uninjured LAD or right coronary artery (RCA). The increase in O2- was caused primarily by cells present in the media and neointima. All vitamin-treated groups showed significantly decreased O2- production in both the RCA and LAD (approximately 45% inhibition) relative to vessels in the control, untreated group. There was a significant correlation between LAD O2- production and lymphocyte vitamin E levels. CONCLUSIONS: The present study is the first to show increased O2- production in injured vessels and to demonstrate that antioxidant vitamins reduce O2- production. These results suggest that beneficial effects of antioxidant vitamins in coronary artery disease are related, in part, to alterations in vessel redox state.

Oxidized lipoprotein (a) induces cell adhesion molecule Mac-1 (CD 11b) and enhances adhesion of the monocytic cell line U937 to cultured endothelial cells.

Because of structural similarities between low density lipoproteins (LDL) and lipoprotein (a) (Lp(a)), we have investigated the properties and the functional activities of oxidized Lp(a) and focused on whether oxidized Lp(a), like oxidized LDL, can induce monocyte differentiation and adhesion of monocytic cells to endothelial cells grown in culture. Oxidized Lp(a), prepared in vitro by cupric ion oxidation, gave absorption curves of conjugated dienes with a lag-phase of 61.7 +/- 6.6 min (mean +/- S.D.) as compared to 85.2 +/- 7.2 min (n = 6, P < 0.01) for oxidized LDL from the same donors and at equimolar concentrations. Degradation of oxidized 125I Lp(a) by the monocytic cell line U937 at 37 degrees C was 1.6 +/- 0.3 nmol/g of cell protein, significantly (P < 0.01) greater than the degradation of oxidized 125I-LDL, which was 1.15 +/- 0.2 nmol/g of cell protein. Equimolar concentrations of oxidized Lp(a) and LDL inhibited the growth of U937 by 82 +/- 8.2% and 64 +/- 7.1%, respectively, when compared with the effect (negligible) produced by native Lp(a) and LDL. In addition, equimolar concentrations of oxidized Lp(a) and LDL induced adhesion molecule, Mac-1 (CD 11b), expression in U937 by 64 +/- 7.1% and 58 +/- 6.1% (P > 0.05), respectively, of the effect produced by phorbol esters (PMA) (P < 0.01). U937 cells incubated with oxidized Lp(a) and LDL, showed an adherence to cultured endothelial cells at 42 +/- 5.2% and 34 +/- 4.8%, respectively (P < 0.05), of the adherence shown by the same cells activated by PMA (P < 0.01). Our results suggest that oxidized Lp(a) like oxidized LDL plays an important role in the development of atherogenesis by inducing adhesion of monocytes to the arterial intimal and by stimulating intimal monocytes to differentiate into macrophages.

AquaLite bioluminescence assay of thyrotropin in serum evaluated.

We studied a new commercially available thyrotropin (TSH) assay, the AquaLite Bioluminescence TSH-Immunoassay (SeaLite Inc.). This assay has a detection limit of 0.005 mIU/L and a functional sensitivity of 0.017 mIU/L and meets the requirements of a third-generation TSH assay. Using this assay, we measured serum TSH in 153 euthyroid individuals and in the following patients: 32 primary hypothyroids; 38 primary hyperthyroids; 35 with thyroid cancer receiving suppressive therapy with levothyroxine (L-T4); 33 receiving replacement L-T4 aimed at reaching and maintaining a euthyroid status; 23 with subclinical hyperthyroidism; and 52 hospitalized for nonthyroidal illnesses (NTI). The AquaLite TSH assay perfectly discriminated hypothyroid and untreated hyperthyroid patients from euthyroid subjects and clearly discriminated between overtly and mildly hyperthyroid patients. Intermethod comparisons showed that the AquaLite and the Nichols assays were more effective than the ACS-180 and the TOSOH assays in discriminating among hyperthyroid patients, including patients over-treated with L-T4.

Combination of vitamins C and E alters the response to coronary balloon injury in the pig.

Restenosis is the major limitation of the long-term success of percutaneous transluminal coronary angioplasty. The process of restenosis involves repair of vascular injury and remodeling of vessel architecture. Therapeutic interventions that improve vascular function may therefore be beneficial in the treatment of restenosis. Antioxidants such as probucol and vitamins C and E have proved effective in improving endothelial function in hypercholesterolemia, inhibiting lipid accumulation in animal models of atherosclerosis, and decreasing cardiovascular mortality in humans. Forty-two female domestic swine were divided into four study groups: control (n = 12); vitamin C (500 mg/d, group C, n = 9); vitamin E (1000 U/d, group E, n = 10); and vitamins C and E (500 mg/d + 1000 U/d, group C+E, n = 11) before oversized balloon injury of the left anterior descending and circumflex coronary arteries. Vitamins were administered 7 days before balloon injury and continued until the swine were killed 14 days after injury. Significant differences in morphometric parameters were present only in group C+E, with increases in vessel and lumen area in the segment with maximal injury. Although there was no decrease in intima area or in maximal intima thickness, the ratio of intima area to vessel area was significantly reduced, consistent with a positive effect in group C+E. Graphic analysis of the relationship between initial vessel injury (using internal elastic lamina fracture length/lumen perimeter) and vessel response to injury (using intima area/vessel area) for all segments showed improved indices for group C+E (P < .005). The beneficial effect of vitamins correlated with changes in lipid redox state. Low-density lipoprotein (LDL) thiobarbituric acid-reactive substances showed an approximately 70% decrease in all treatment groups, and the lag phase for LDL-conjugated diene formation was significantly increased, with group C+E > group E > group C. The combination of vitamins C and E improved vascular response to injury because of an apparent beneficial effect on vascular remodeling. The fact that the combination of vitamins C+E was better than vitamin E or vitamin C alone is consistent with the ability of vitamin C to improve the antioxidant effect of vitamin E, suggesting that the improved vessel response was due to a change in redox state. This study suggests an important role for oxygen radicals in the vascular response to injury and suggests that vascular remodeling and intimal proliferation are important to the restenotic process.

Cyclosporine increases the oxidizability of low-density lipoproteins in renal transplant recipients.

Blood specimens from twenty-six renal transplant recipients treated with cyclosporine (CsA) were collected at weekly intervals, two months after transplantation. Specimens were grouped according to their CsA concentrations. Group I consisted of ten specimens with CsA concentration of >400 ng/ml; group II consisted of ten specimens with CsA concentrations ranging from 120-300 ng/ml; and group III consisted of six specimens with CsA concentrations of < 100 ng/ml. In addition, specimens from five renal transplant patients who, instead of CsA, received the immunosuppressant FK506 (group IV), and from six healty individuals were included. Plasma low-density lipoproteins (LDL) were isolated and their susceptibility to oxidation was studied by continuously monitoring the formation of conjugated dienes during copper ion-mediated oxidation. Patients with higher blood concentrations of CsA (groups I and II) had significantly higher oxidizability of LDL, as indicated by the shorter time required to start the oxidation (lag phase). The oxidizability of samples with low concentration of CsA (group III) was not significantly different from that of FK506-treated patients or healthy individuals. There was a negative correlation (r = -0702, P < 0.01) between oxidizability (lag phase) and CsA concentration in LDL. No correlation between blood CsA and plasma cholesterol or triglyceride concentration was evident during a three-month period postoperatively. Similarly, no correlation between the degree of oxidizability and plasma cholesterol or triglycerides was found at the time of the experiment. These findings suggest a prooxidant effect of CsA to plasma LDL, and may indicate that CsA is an important risk factor in the accelerated atherosclerosis of renal transplant recipients.

Discordant results for determinations of triglycerides in pig sera.

We recently determined triglyceride concentrations in pig sera by three fully enzymatic methods (Kodak Ektachem 700, Hitachi 707, and Abbott EPx) and obtained significantly lower values than those obtained with chemical or enzymatic methods based on chemical hydrolysis. All methods used involve microbial lipases for liberating glycerol from glycerides and glycerol phosphate dehydrogenases or oxidases for subsequent oxidation. The methods were validated against reference methods by using fresh human sera and survey materials. The discordant results were not from matrix sample-method interaction but from incomplete hydrolysis of pig serum triglycerides by the lipolytic enzymes. When serum triglycerides from 10 pigs showing the highest biases were hydrolyzed by microbial lipases and the reaction mixture was subjected to thin-layer and gas-liquid chromatography, the predominant end products were palmitoyl monoglyceride and a mixture of free fatty acids with the following composition (fatty acid as percent of total +/- SD): 16:0, 7.8 +/- 2; 18:0, 5.4 +/- 2.2; 18:1, 53 +/- 12; 18:2, 31 +/- 4.6; and 18:3, 2.5 +/- 1. Assuming that the lipases exhibit the usual specificity toward the 1 and 3 positions of the triglyceride, the data suggest that, in pig, triglycerides 18:1 and 18:2 occupy the 1 and 3 positions and 16:0 (palmitic acid) predominantly occupies the 2 position. Triglycerides of this structure may not be well hydrolyzed by the typical lipolytic enzymes in clinical assays.

Paradoxical response of plasma lipoprotein(a) in patients undergoing cardiopulmonary bypass.

Plasma lipid, lipoprotein and apolipoprotein levels are known to decrease after major surgery. Coronary artery bypass surgery additionally involves use of extracorporeal circulation by use of a cardiopulmonary bypass pump, which necessitates hemodilution due to saline dextrose infusion to prime the pump. To investigate changes in lipids, lipoproteins and apolipoproteins as well as changes in C-reactive protein and albumin we conducted a study on 22 patients undergoing cardiac surgery involving cardiopulmonary bypass. Timed arterial blood samples were taken before, during and after cardiopulmonary bypass. At the onset and during cardiopulmonary bypass a rapid and significant fall was observed in all lipids and lipoproteins except lipoprotein(a) with recovery to near basal levels by 72 h for cholesterol, triglycerides, high density lipoprotein cholesterol and albumin, while apolipoproteins AI and B remained below basal levels during the postoperative period up to 72 h. In contrast, lipoprotein(a) levels increased at the onset, doubled during cardiopulmonary bypass and remained elevated postoperatively. On the other hand, C-reactive protein levels fell at the onset and during cardiopulmonary bypass but they became markedly elevated postoperatively. When results were corrected for hemodilution, the response patterns remained unchanged. As lipoprotein(a) is both atherogenic and thrombogenic, its elevation during cardiopulmonary bypass may be clinically important.

Effect of freezing and thawing of serum on the immunoassay of lipoprotein(a).

We studied the effect of freezing and thawing of serum on the determination of lipoprotein(a) [Lp(a)] with a commercial enzyme-linked immunosorbent assay (ELISA) and an immunoturbidimetric assay (ITA). Portions of sera from 11 apparently healthy persons and pooled sera, from an additional 10 subjects were frozen at either -20 or -70 degrees C and thawed at room temperature. Cycles of freezing and thawing were repeated during the experiments (1 month). Samples were assayed for Lp(a) after thawing. Pooled sera were subjected to quick freezing at -70 degrees C and thawing at room temperature in cycles. Results show a significant (P less than 0.05) decrease in Lp(a) concentration in sera subjected to freezing and thawing. Samples thawed from -20 degrees C gave concentrations by ELISA that were significantly lower than those of fresh samples after one freeze-thaw cycle. By ITA the decrease was significant only after two cycles. In specimens frozen at -70 degrees C, Lp(a) concentrations determined by ELISA decreased after two cycles, and by ITA after three freeze-thaw cycles. Serum samples subjected to quick freezing at -70 degrees C and thawing did not show significant decreases in Lp(a) immunoreactivity during four cycles. Immunoreactivity of Lp(a) in samples stored at 4 degrees C decreased after 6 days but fell faster in serum samples subjected to freezing and thawing before storage at 4 degrees C.

Effect of lyophilization on determinations of lipoprotein(a) in serum.

We studied the effect of lyophilization of serum on the determination of serum lipoprotein(a) [Lp(a)], using two enzyme-linked immunosorbent assays (ELISAs) and one immunoturbidimetric assay (ITA). After adjusting for the effect of dilution due to the reconstitution of lyophilized serum, Lp(a) values obtained for lyophilized sera were consistently lower than the original values for the corresponding fresh samples, the difference ranging from 17% to 83% for the monoclonal-polyclonal antibody-based ELISAs and from 12% to 49% for the exclusively polyclonal ITA. Statistical analysis showed that differences between either ELISA and the ITA were significant but not the differences between the ELISAs. Moreover, the effect was not qualitatively or quantitatively uniform, which suggested that the effect was serum-source dependent. Addition of sucrose (600 mmol/L) to sera before lyophilization decreased but did not eliminate the effect. Apparently, serum pools in lyophilized form are not a suitable reference material for Lp(a) determination. Because different methods produce different results for Lp(a) in the same common reference material intended for standardization of Lp(a) methodology, any Lp(a) method should be tested for the effect of lyophilization if lyophilized samples are to be analyzed.

Usefulness of serum lipoprotein (a) as a predictor of restenosis after percutaneous transluminal coronary angioplasty.

Serum lipoprotein (a) (Lp[a]) has been associated with coronary artery atherosclerosis. Its association with restenosis after percutaneous transluminal coronary angioplasty (PTCA) has not been previously studied. Serum levels of Lp(a), in addition to other lipoproteins, and their components using standard assays, were determined in subjects undergoing cardiac catheterization within 10 months after PTCA. Clinical (e.g., sex, diabetes, angina class) and angiographic (e.g., PTCA percent diameter reduction) factors were not different between the group without (diameter reduction less than 50%; group A) and the group with (diameter reduction greater than or equal to 50%; Group B) restenosis. Total cholesterol, triglycerides, high- and low-density lipoprotein cholesterol, apolipoprotein A-I, apolipoprotein B and Lp(a) were compared. Univariate predictors of restenosis were serum triglycerides (2.50 +/- 1.07 mmol/liter for group A vs 1.72 +/- 0.79 +/- mmol/litre for group B, p = 0.008), and Lp(a) (median: 7.0 mg/dl [range 0 to 44] for group A vs 19 mg/dl [range 1 to 120] for group B; p = 0.006). Stepwise logistic regression revealed the only significant independent predictor of restenosis to be serum Lp(a) (p = 0.018). Each quintile of Lp(a) was associated with a progressively higher risk of restenosis, with the highest quintile (40 to 120 mg/dl) having an odds ratio of 11 (95% confidence interval 9 to 13) compared with the lowest quintile (0 to 3.9 mg/dl) (p = 0.033). A serum Lp(a) of greater than 19 mg/dl was associated with an odds ratio of 5.9 (95% confidence interval 4.6 to 7.2) (restenosis rates of 58% in the group with 0 to 19 mg/dl and 89% in the group with 19 to 120 mg/dl; p = 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin E supplementation, plasma lipids and incidence of restenosis after percutaneous transluminal coronary angioplasty (PTCA).

To test whether alpha-tocopherol prevents restenosis following percutaneous transluminal coronary angioplasty (PTCA), we enrolled patients in a double-blind, placebo-controlled trial. Patients were randomized after successful PTCA to receive vitamin E in the form of dl-alpha-tocopherol, 1200 IU/day, orally vs an inactive placebo for 4 months. Patients' blood was analyzed at baseline and at 4 months post-PTCA for differences in plasma lipids, lipoproteins, apolipoproteins, alpha-tocopherol, retinol, beta-carotene and lipoperoxide concentrations. One hundred patients completed the protocol. No significant difference was found in any parameter except alpha-tocopherol level between the vitamin E group and the placebo group, verifying compliance. Follow-up cardiac catheterization was obtained in 83% of the patients receiving placebo and in 86% of the patients receiving dl-alpha-tocopherol. Including thallium and exercise stress testing, objective information was obtained for practically all the patients receiving dl-alpha-tocopherol or placebo. Restenosis was defined as the presence of a lesion with greater than or equal to 50% stenosis in a previously dilated artery segment and results were analyzed with respect to pre- and post-PTCA artery diameter, vessel diameter at follow-up, and restenosis rate. Patients receiving dl-alpha-tocopherol had a 35.5% restenosis angiographically documented vs 47.5% restenosis in patients receiving the placebo. The overall incidence of restenosis defined by an abnormal angiogram or thallium test or exercise stress test was 34.6% in patients receiving dl-alpha-tocopherol and 50% in patients receiving the placebo. This difference (p = 0.06) did not reach significance because of an inadequate sample size.

Parallel assays of beta-endorphin and ACTH in Cushing's patients undergoing petrosal sinus sampling.

This study explores the possibility of improving endocrinologic testing during petrosal sinus catheterization by determining both beta-endorphin and corticotropin (ACTH). We studied 14 patients with Cushing's disease, two with adrenal tumor, and three with ectopic tumors secreting ACTH. In patients with Cushing's disease, beta-endorphin concentrations paralleled those of ACTH in all basal plasma samples collected either from petrosal sinuses or peripheral veins. Individual responses of beta-endorphin and ACTH to corticotropin releasing hormone (CRH) were closely related to the presence of a corticotroph adenoma. In such patients, a consistently higher concentration of beta-endorphin over ACTH was observed in all samples collected either from petrosal sinuses or peripheral veins; the ratios were unchanged after the administration of CRH. In patients with ectopic ACTH secretion, the mean ratio of beta-endorphin over ACTH (with both values expressed in pmol/L) was significantly higher (3.5) than that of patients with Cushing's disease (2.9) or Cushing's syndrome due to adrenal tumor (2.7).

Sex steroids and bone density in premenopausal and perimenopausal women.

Bone density begins to decline in women before menopause, and the degree of bone loss is variable. We performed a cross-sectional analysis on the entry data of a 5-yr prospective study of risk factors for osteoporosis to determine the correlation of bone density with serum sex steroid concentrations and body weight. We studied 292 healthy white women, aged 35-50 yr, who were menstruating regularly or had had menses in the past 12 months. Blood samples were drawn in the early follicular phase for estradiol (E2), testosterone (T), dehydroepiandrosterone sulfate, and sex hormone-binding globulin (SHBG). Free levels of E2 (FE2) and T (FT) were calculated based on total T and E2, SHBG, and albumin levels. Women were classified as premenopausal (FSH, less than 12 U/L) and perimenopausal (FSH greater than or equal to 12 U/L; n = 46; 16%). Bone density was measured by dual photon absorptiometry of the lumbar spine (L2-L4) and hip and by single photon absorptiometry of the wrist. Perimenopausal women were older than premenopausal women (45.5 +/- 3.5 and 41.0 +/- 3.9 yr, respectively), but did not differ in height or weight. While bone density did not correlate with age in each group, perimenopausal women had significantly lower bone density at the L2-L4 and femoral neck (L2-L4, 1.18 +/- 0.14 in perimenopausal and 1.24 +/- 0.12 g/cm2 in premenopausal women; femur, 0.84 +/- 0.11 in perimenopausal and 0.90 +/- 0.11 g/cm2 in premenopausal women; P less than 0.005). Body weight showed the strongest positive correlation with bone density. Log FT, percent FT, and FE2 percent correlated positively with bone density, even after controlling for weight. Log SHBG was negatively correlated with bone density in premenopausal women at the hip and wrist after controlling for weight. FSH was inversely correlated with bone density, and E2 and T were lower in perimenopausal than premenopausal women. These data suggest that women who are still menstruating may have relative deficiencies in both E2 and T, with reduced bone densities as a consequence.

Four sensitive thyrotropin assays critically evaluated and compared.

We compared four sensitive procedures for thyrotropin (TSH)--Corning's Magic-Lite, ElectroNucleonics' Delfia, Baxter's Stratus, Nichols' Allegro--for their ability to completely discriminate TSH concentrations in sera in euthyroidism, hyperthyroidism, and hypothyroidism. We evaluated the analytical and clinical performance of these procedures according to previously published criteria. All procedures we examined fulfilled the criterion stipulating less than 1% overlap between the assay variation at the lower normal range limit and the assay sensitivity. Both measurements were made with an interassay CV not exceeding 10% to 15%. All procedures produced results that correlated well for specimens with TSH concentrations of greater than 0.4 milli-int. unit/L, and all four procedures clearly distinguished hypothyroid from euthyroid subjects. In a hyperthyroid-euthyroid comparison, three of the procedures, the Magic-Lite, Delfia, and Allegro, differentiated the two with 97% accuracy, the Stratus procedure with only 90% accuracy. The procedures appeared to differ even more in the measurement of TSH in serum of patients undergoing suppressive treatment with thyroid hormones and in hospitalized nonthyroidally ill patients. The observed differences among procedures were thought to be related in part to a matrix serum effect, which is accentuated in samples from hospitalized patients.

Comparison of specific radioimmunoassays for cyclosporine.

This study compares two recently introduced radioimmunoassay kits involving specific monoclonal antibodies to cyclosporine. One kit (Sandimmun) involved 3H-labeled CsA (3H-CsA) as tracer and the other (CY-CLO-Trac-SP) involved a 125I-labeled conjugated derivative of CsA. The kits were nearly equivalent in method performance characteristics. They produced superimposed standard curves and equivalent values to transplanted patient samples. Concentrations of CsA determined by either kit were apparently equivalent to values measured by high-performance liquid chromatography, suggesting that the specific monoclonal antibodies used with the kits detect in trough blood mainly native CsA. The 125I-labeled CsA, when compared with the 3H-CsA alternative, increased the sensitivity and precision, decreased the turnaround time, and provided a technically efficient and conveniently capable method of replacing HPLC for measuring native CsA.

Marine lipid concentrate and atherosclerosis in the rabbit model.

Twenty-seven New Zealand white rabbits underwent balloon de-endothelialization of the aorta and iliac arteries while consuming a 2% cholesterol, 10% peanut oil rabbit chow. Ten of these rabbits were fed 1 ml of concentrated marine fish lipid (MaxEpaTm) daily. Six weeks after de-endothelialization, angiography of the treated arteries was performed and histologic cross-sections of the terminal aorta were measured with a planimeter. Iliac artery luminal diameters were also measured at consecutive 3-mm divisions from the aortic bifurcation and found to have a mean lumen diameter of 1.60 +/- 0.08 mm in the marine lipid-supplemented group (M) and 1.38 +/- 0.12 mm in the control group (C) (P less than 0.001). Analysis of variance on individual segmental diameters confirmed this difference. However, neither the angiographic diameters nor histologic, cross-sectional, luminal areas of the terminal aorta were different between groups. Instead, the mean cross-sectional area of the terminal aortic wall was significantly greater in the marine lipid-fed group (4.4 +/- 1.2 mm2 in M and 3.1 +/- 0.6 mm2 in C, P less than 0.01). In addition, the vessel wall area showed a positive correlation with red blood cell (RBC) incorporation of docosahexaenoic acid (r = 0.82, P less than 0.005) in both groups. In the M group, RBC eicosapentaenoic acid and docosahexaenoic acids increased 100% and 650%, respectively, over baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of serine palmitoyltransferase activity in rabbit aorta by L-cycloserine.

Serine palmitoyltransferase (EC 2.3.1.50) initiates the biosynthesis of sphingolipids. Its activity is induced in the aortas of rabbits fed a Purina lab chow supplemented with 2% cholesterol (Williams, R. D., D. S. Sgoutas, and G. S. Zaatari. 1986. J. Lipid Res. 27: 763-770). Induction occurs during atherogenesis in parallel with increased arterial sphingomyelin concentrations. In this study, L-cycloserine was shown to be a potent inhibitor of serine palmitoyltransferase in aortas from New Zealand White rabbits. Activity was reduced in vitro by 50% using 5 microM L-cycloserine with 50 micrograms of microsomal protein. To assess in vivo inhibition, L-cycloserine was administered by intraperitoneal injection to rabbits maintained on either a standard Purina laboratory chow or one supplemented with 2% cholesterol. Serine palmitoyltransferase activity was inhibited by 76% in the aortas of rabbits on the standard chow 4 hr after a single 25 mg/kg body weight dose and 52% after a 10 mg/kg dose. Activity was reduced by 36% in animals on the standard chow and by 37% in the cholesterol-fed group after 1 week of daily doses. These experiments demonstrate that L-cycloserine inhibits serine palmitoyltransferase in aorta, and thus may be used to reduce sphingomyelin concentrations during experimental atherogenesis.