Jane L.H.C. Third

The effects of cholestyramine on high density lipoprotein metabolism.

This study on 4 type II hyperlipoproteinaemic subjects examines the effects of pharmacologic doses (8 g twice daily) of the bile acid sequestrant cholestyramine on the plasma distribution and chemical composition of the high density lipoprotein subfractions, HDL2 and HDL3, and describes the influence of the drug on the metabolism of the major HDL aporoteins, apolipoprotein A-I and A-II. Cholestyramine lowered plasma low density lipoprotein cholesterol (32%; P less than 0.05) without affecting the level of that lipid in very low density or high density lipoproteins. However, the plasma HDL2/HDL3 ratio and apolipoprotein A-I concentration rose significantly on treatment, while apolipoprotein A-II remained unchanged. The rise in apolipoprotein A-I derived from an increase in its synthetic rate and produced a relative enrichment of the protein with respect to apolipoprotein A-II in both HDL subfractions. These results demonstrate the cholestyramine treatment affects HDL metabolism in a way which, according to current concepts, may prove beneficial to the recipient.

Low density lipoprotein metabolism in a family of familial hypercholesterolemic patients

A low-density lipoprotein turnover study was performed on six heteroxygous familial hypercholesterolemic subjects and five control subjects. The diagnosis of the condition was clear-cut on biochemical, clinical, and genetic grounds. Kinetic analysis of the plasma decay curves gave the following mean values: (1) The plasma concentration of low density lipoprotein apoprotein (apoLDL) in the affected subjects was 247 mg/dl, a 2.5-fold increase over control values (98 mg/dl). (2) The calculated fractional catabolic rate of the intravascular apoLDL pool in the dyslipo-proteniemics was reduced with respect to control data (16.4%/day versus 31.2%/day), and the half-life of the apolipoprotein was correspondingly increased (6.07 days versus 3.63 days). (3) The absolute catabolic rate of the apoLDL was 15.6 mg/kg/day in contrast to the lower value of 11.6 mg/kg/day in the control group. (4) A strong negative correlation was observed between the plasma apoLDL concentration and the fractional catabolic rate (r = 0.96). We conclude from our data that increased apoLDL synthesis coupled with a defective or saturated catabolic mechanism is implicated in the pathogenesis of familial hypercholesterolemia.

Circadian relationship of serum uric acid and nitric oxide.

To the Editor: Nitric oxide–mediated damage has been implicated in a number of neurological diseases including stroke1, 2 and multiple sclerosis (MS).3 For instance, monocytes expressing high levels of nitric oxide synthetase have been found in plaques from the brains of patients with MS.4 The proximal agent of neuronal cell damage may be peroxynitrite, which is formed in vivo from the synthesis of nitric oxide and superoxide.

Circadian variation in oxidative stress markers in healthy and type II diabetic men

Seven clinically healthy, nondiabetic (ND) and four Type II diabetic (D) men were assessed for circadian rhythms in oxidative “stress markers.” Blood samples were collected at 3h intervals for ∼27 h beginning at 19:00h. Urine samples were collected every 3 h beginning with the 16:00h–19:00h sample. The dark (sleep) phase of the light–dark cycle extended from 22:30h to 06:30h, with brief awakening for sampling at 01:00h and 04:00h. Subjects were offered general hospital meals at 16:30h, 07:30h, and 13:30h (2400 cal in total/24 h). Serum samples were analyzed for uric acid (UA) and nitrite (NO) concentrations, and urine samples were assayed for 8-hydroxydeoxyguanosine (8-OHdG), malondialdehyde (MDA), and 8-isoprostane (ISP). Data were analyzed statistically both by the population multiple-components method and by the analysis of variance (ANOVA). The 24h mean level of UA and NO was greater in D than in ND subjects (424 vs. 338 μmol/L and 39.2 vs. 12.7 μM, respectively). A significant circadian rhythm in UA (p=0.001) and NO (p=0.048) was evident in ND but not in D (p=0.214 and 0.065). A circadian rhythm (p=0.004, amplitude=8.6 pmol/kgbw/3h urine vol.) was also evident in urine 8-OHdG of ND but not of D. The 24h mean levels of ND and D were comparable (76.8 vs. 65.7 pmol/kgbw/3h urine vol.). No circadian rhythm by population multiple-components was evident in MDA and ISP levels of ND subjects, or in 8-OHdG, MDA, and ISP in D. However, a significant time-effect was demonstrated by ANOVA in all variables and groups. The 24h mean of MDA and ISP in D was significantly greater than in ND (214 vs. 119 nmol/3h urine vol. and 622 vs. 465 ng/3h urine vol.). The peak concentrations of the three oxidative “stress markers” in urine, like those of serum NO, occurred early in the evening in both groups of men. This observation suggests a correlation between increased oxidative damage and increased rate of anabolic–catabolic events as evidenced by similarities in the timing of peak NO production and in parameters relevant to metabolic functions.

Primary and familial hypoalphalipoproteinemia

Our specific aim was to assess within-family clustering of high-density lipoprotein cholesterol (HDLC) levels in kindreds identified through probands with primary hypoalphalipoproteinemia, and to determine whether, and to what degree, familial aggregation of HDLC less than or equal to the tenth percentile represents a heritable trait, familial hypoalphalipoproteinemia. Our probands were selected arbitrarily by virtue of HDLC less than or equal to the age-sex-race-specific tenth percentile as the sole dyslipoproteinemia, with an additional requirement that they be normotriglyceridemic (triglyceride levels less than the 90th percentile). The probands were also required to have primary hypoalphalipoproteinemia, not secondary to diseases and/or drugs. Fifteen of the 16 probands were men; 12 were referred because of premature myocardial infarction, angina, or stroke, 2 because of family history of premature myocardial infarction or stroke, and 2 because of low HDLC observed on routine health examinations. Two of the 16 kindreds exhibited three-generation vertical transmission of bottom decile HDLC. In three kindreds, there was also three-generation vertical transmission of bottom decile HDLC, but top decile triglycerides accompanied bottom decile HDLC in one or more generations. Eight kindreds displayed two-generation vertical transmission of bottom decile HDLC. After excluding probands, there were 11 critical matings (bottom decile HDLC by normal), with 30 living offspring, all of whom were sampled. Of these 30 offspring, 13 had bottom decile HDLC, 17 had HDLC greater than tenth percentile. The ratio of offspring with bottom decile HDLC to those of HDLC greater than tenth percentile was 13:17 (0.76/1), not significantly different from the ratio of 1/1, the ratio predictive of a dominant trait, X2(1) = 0.53, P greater than 0.4. The nearly 1:1 segregation ratio for the group of offspring was not due to the aggregation of sibships with, in general, most of the sibs, or none of the sibs affected; within-family expression of low HDLC was also not sex-linked. The 13 hypoalphalipoproteinemic offspring of 11 critical matings included only two subjects whose bottom decile HDLC was accompanied by top decile triglyceride. Our data suggests that not only (by selection) was low HDLC in the probands the sole dyslipoproteinemia, but that the segregation of low HDLC in offspring of critical matings was primarily accounted for by isolated low HDLC, not by hypoalphalipoproteinemia secondary to hypertriglyceridemia. Familial hypoalphalipoproteinemia is a heritable disorder with a pattern of transmission not significantly different from that expected by a hypothesis of mendel

Relation between circadian patterns in levels of circulating lipoprotein(a), fibrinogen, platelets, and related lipid variables in men.

BACKGROUND A correlation has been reported between lipoprotein(a) [Lp(a)] concentration and risk for coronary artery disease. High concentrations of Lp(a) might be markers for vascular or tissue injury or might be associated with other genetic or environmental factors that can cause acute myocardial infarction. METHODS We measured the circadian characteristics of circulating Lp(a), fibrinogen, platelets, cholesterol, triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol for a group of adult male volunteers who had no clinical symptoms. We obtained samples every 3 hours around the clock to assess the normal degree of variation within a 24-hour period and to test for similarities in circadian patterns and correlations with level of Lp(a). RESULTS Each variable displayed a highly significant circadian rhythm. Lp(a), fibrinogen, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol peaked in the morning. Cholesterol and platelets peaked in the late afternoon, and triglycerides peaked in the evening. CONCLUSIONS Although peak levels of Lp(a) and fibrinogen coincide with reported morning peak frequencies of myocardial infarction and stroke, the platelet peak appears to coincide with late afternoon peak frequencies of sudden cardiac death and fatal stroke. The data suggest that proper timing of single samples may improve the usefulness and accuracy of diagnosis, risk assessment, and therapy.

Circadian interrelationships among levels of plasma fibrinogen, blood platelets, and serum interleukin-6.

Circadian (24 h) rhythms of fibrinogen, interleu kin-6 (IL-6), and platelet levels were studied in 11 males ages 46 to 72 years. Since there is a known circadian rhythm for fibrinogen and IL-6, we postulated that the peak level (acro phase) of fibrinogen would follow the acrophase of IL-6, based on the fact that IL-6 is the stimulus for fibrinogen production in the liver. Platelet levels were measured to show whether there was any correlation with the IL-6 acrophase because it has been reported that IL-6 affects megakaryocytes and platelets in dogs. We found that the acrophase for IL-6 occurred at 02:03 h and the acrophase for fibrinogen occurred at 09:16 h. Platelet counts peaked at 16:56 h. Thus, there was a positive correlation between IL-6 and fibrinogen acrophases and a negative corre lation of each with the acrophase for platelets. The positive linkage of IL-6 with fibrinogen in this study suggests that sup pression of IL-6 production would lower those peak fibrinogen levels that occur in the morning in association with arterial ischemic events. This could result in fewer arterial ischemic events, especially in the morning. Key Words: Circadian— Fibrinogen—Interleukin—6 (IL-6)—Platelets—Arterial ischemia.

Day-night variations in blood levels of nitric oxide, T-TFPI, and E-selectin

Circadian (8/24 hours) variations in serum nitric oxide (NO), total tissue factor pathway inhibitor (T-TFPI), and E-selectin levels were studied in healthy adults and in subjects with type II diabetes. We postulated a possibility a functional relationship between them because vascular endothelium is the primary site of their synthesis and functions. NO is released by the action of eNO synthase isoform and modulates physiologic responses (e.g., vascular dilation, relaxation, increasing blood flow, inhibition of platelet and white blood cell adhesion); T-TFPI, a coagulation inhibitor, is also released from endothelial cells, and is bound to plasma lipoproteins and to glycosaminoglycans; E-selectin is expressed on endothelial cells after activation by inflammatory cytokines (interleukin-1β and tumor necrosis factor-α) and elevated levels have been reported in a variety of pathologic conditions, including diabetes. We found that obese diabetic subjects had greater mean concentrations of NO and E-selectin than healthy men, 39.25 versus 12.71 μM and 81.51 versus 26.03 ng/mL, respectively. The T-TFPI levels were essentially similar in both groups of men, 47.10 versus 48.76 ng/mL. We observed that the time of peak concentrations of T-TFPI and E-selectin was similar to the timing of NO trough levels, suggesting a possible functional relationship. It may be hypothesized, therefore, that the higher concentrations of NO, unbalanced by increases in T-TFPI and E-selectin, may result in increased vascular wall uptake of lipoproteins in diabetic subjects, who are at greater risk than healthy men for developing diffuse atherosclerosis.

Effects of nicotinic acid therapy on high-density ldpoprotein metabolism in type II and type IV hyperlipoproteinaemia

Abstract This study investigates the influence of pharmacologie doses of nicotinic acid on HDL metabolism in six type II and four type IV hyperlipoproteinaemic subjects. Although the drug lowered the level of triacylglycerol and VLDL-cholesterol in the type II group, it produced no significant change in the plasma concentrations of LDL-cholesterol, HDL-cholesterol, HDL2, HDL3 and apolipoproteins A-I and A-II. However, separation of the group into IIa and IIb subtypes revealed a marked divergence in their response to treatment. The former exhibited a substantial reduction in plasma triacylglycerol and a striking rise in the HDL2/HDL3 ratio while in the latter these parameters were little affected by the drug. In the type IV subjects nicotinic acid lowered both cholesterol and triacylglycerol levels, the former deriving from a reduction in the level of that lipid associated with VLDL. In contrast, HDL-cholesterol rose significantly in this group, as did both HDL2 and HDL3. These changes were accompanied by an increase in plasma apolipoprotein A-I due to a fall in its fractional rate of catabolism. The plasma apolipoprotein A-II level was unaffected by treatment. These differing responses to nicotinic acid treatment may reflect a differential effect of the drug on triacylglycerol and VLDL metabolism in normoand hypertriglyceridaemic subjects.

Circadian variation of serum leptin in healthy and diabetic men.

Leptin, from the Greek leptos, meaning thin (in reference to its ability to reduce body fat stores), is a hormone secreted primarily by adipocytes. At one time, leptin was portrayed as a potential means of combating obesity. Recently, leptin has been identified as a potent inhibitor of bone formation, acting through the central nervous system. Since numerous studies clearly show that bone remodeling is circadian rhythmic with peak activity during sleep, it is of interest to explore circadian variability in serum leptin. Accordingly, circadian characteristics of serum leptin were examined in 7 clinically healthy men and 4 obese men with type II diabetes. Blood samples were collected for 24h at 3h intervals beginning at 19:00. The dark (sleep) phase of the light-dark cycle extended from 22:30 to 06:30, with brief awakening for sampling at 01:00 and 04:00. Subjects consumed general hospital meals (2400 calories) at 16:30, 07:30, and 13:30. Serum leptin levels were determined by a R&D Systems enzyme immunoassay technique. Data were analyzed by linear least-squares estimation using the population multiple components method. A statistically significant (P <. 018) circadian rhythm modeled by a single 24h cosine curve characterized the data of each group. The 24h mean leptin level was statistically greater (P <. 001) in the obese diabetic men than in the healthy men (9.47 ± 0.66 ng/mL vs. 24.07 ± 1.71 ng/mL, respectively). Higher leptin levels occurred between midnight and roughly 02:30, and lowest leptin levels occurred between noon and the early afternoon. The phasing of this rhythm is similar to the circadian rhythm in bone remodeling previously described. Our results suggest the findings from a single morning blood sampling for leptin may be misleading since it may underestimate the mean 24h and peak concentrations of the hormone. (Chronobiology International, 18(2), 273–283, 2001)