HDL cholesterol and TaqIB cholesteryl ester transfer protein gene polymorphism in renal transplant recipients

Decreased serum levels of high-density lipoprotein cholesterol (HDL-C) are a well-known risk factor for coronary heart disease (CHD) in the general population and have been suggested as one of the best predictor of CHD after renal transplantation. However, very heterogeneous HDL-C levels have been reported in renal transplant recipients. In this patient population, serum HDL-C levels are determined by complex interactions between hormonal, environmental (such as a high amount of abdominal adipose tissue), and genetic factors and drugs (particularly glucocorticoids). We, therefore, evaluated the effects of the cholesteryl ester transfer protein (CETP) gene TaqIB polymorphism as well as of abdominal obesity on HDL-C levels in 78 male renal transplant recipients who were receiving azathioprine and/or ciclosporin A in combination with prednisone as immunosuppression. The patients were classified into genotypic groups according to the presence or absence of the restriction site (B1 allele or B2 allele, respectively). The distribution of CETP genotypes was similar to that previously described in the general population. Overall, HDL-C levels were 19 and 26% higher in B1B2 and B2B2 patients as compared with B1B1 homozygotes (p < 0.05), even after control for other lipid measurements. Patients with abdominal obesity (waist girth >/=93 cm) showed reduced HDL-C levels as compared with lean (waist girth <93 cm) patients (1.20 +/- 0.28 vs. 1.42 +/- 0.41 mmol/l, respectively, p < 0.01). Moreover, the HDL-C levels were markedly affected by the CETP TaqIB polymorphism in lean patients (+28 and +41% in B1B2 and B2B2 as compared with B1B1 patients, p < 0.05), but no significant difference was observed among obese patients. Significantly lower total cholesterol:HDL-C ratios were obtained in lean B2B2 homozygotes, suggesting that these patients could be less susceptible to atherosclerosis than lean B1B1 homozygotes. In addition, patients with the B1B1 genotype had more documented CHD as compared with patients carrying at least one B2 allele, supporting the protective effect of the B2 allele against CHD. In conclusion, considerable variation in HDL-C levels appears to be explained by the CETP TaqIB gene polymorphism in male renal transplant recipients, but this potential protective gene effect appears strongly reduced by concomitant abdominal obesity.

Relationship of adipose tissue cholesteryl ester transfer protein (CETP) mRNA to plasma concentrations of CETP in man

Adipose tissue is an important site of cholesteryl ester transfer protein (CETP) synthesis and CETP plays a local role in adipocyte cholesteryl ester accumulation from high density lipoproteins (HDL). Human adipose tissue maintained in organ culture secretes CETP, but it is not known to what extent adipose tissue CETP contributes to the plasma pool of CETP in man. Aging is associated with changes in adipose tissue composition and function, including impaired adipocyte triglyceride lipolysis. We determined pericardiac adipose tissue CETP mRNA levels and plasma concentrations of CETP and lipoproteins in middle-aged and elderly subjects (47-78 years) with stable coronary heart disease (CHD) undergoing elective coronary artery bypass grafting (CABG). Plasma concentrations of CETP were highly correlated with adipose tissue CETP mRNA abundance (r = 0.85, P < 0.002, n = 13), suggesting that adipose tissue may contribute to the plasma pool of CETP. There was an inverse correlation between age and plasma CETP concentrations in this population (r = -0.70, P <0.008, n = 13). CETP mRNA levels in pericardial adipose tissue were also negatively associated with age (r = -0.70, P < 0.035, n = 10). These relationships were independent of plasma lipids, lipoproteins and body mass index. However, adipose tissue CETP mRNA concentrations levels were related to adipocyte size. CETP mRNA abundance in pericardial adipose tissue was negatively correlated with mean adipocyte size, estimated as adipose tissue triglyceride/mg protein (r = -0.76, P < 0.02, n = 9), in accord with previous studies from this laboratory demonstrating that CETP gene expression is greatest in small lipid-poor adipocytes. A negative relationship between age and adipose tissue CETP mRNA abundance (r = -0.63, P < 0.05, n = 10) was confirmed in a separate population of healthy female subjects, aged 18-63 years, from whom subcutaneous adipose tissue was obtained at the time of reduction mammoplasty. The decrease in plasma concentrations of CETP with age may be explained in part by changes in adipose tissue CETP gene expression.

Preferential expression of cholesteryl ester transfer protein mRNA by stromal-vascular cells of human adipose tissue

Cholesteryl ester transfer protein (CETP) mRNA is more abundantly expressed in small mature adipocytes as compared to large, lipid-rich adipocytes [Radeau et al., J. Lipid Res. 36 (1995) 2552-2561]. In the present study, the stromal vascular fraction (SVF) of human adipose tissue was isolated and the presence of very small fat cells in this fraction confirmed by electron microscopy and by demonstrating the presence of mRNA for adipsin and for CCAAT enhancer binding protein alpha (C/EBPalpha), a marker of adipocyte differentiation. sn-Glycerol 3-phosphate dehydrogenase (GPDH) activity was present in the SVF but not in the preadipocyte fraction. Northern blot analysis of human adipose tissue demonstrated that CETP mRNA expression was significantly greater (+96%, P<0.03) in stromal-vascular cells (SVC) as compared to mature fat cells. By comparison, lipoprotein lipase mRNA expression was lower (-75%, P<0.03) in SVC while apolipoprotein E mRNA expression was not significantly different in SVC as compared to isolated adipocytes. By RT-PCR analysis, we demonstrated that CETP mRNA was expressed by human pre-adipocytes at levels less than those of SVC and adipocytes. The absence of monocytes/macrophages in SVC was confirmed by the absence of FcgammaRIII (CD16) mRNA in these fractions. These data demonstrate that CETP mRNA is most highly expressed in the immature fat cells of human adipose tissue, consistent with other experiments from this laboratory demonstrating that CETP plays an important local role in adipocyte cholesterol accumulation.

Cellular protein kinase C activity in asthma

Protein kinase C (PKC) is a primary group of enzymes mediating signal transduction for a wide variety of functions in many different cell types. Its activation has been implicated in various inflammatory diseases. In asthma, inflammatory cells, such as alveolar macrophages (AM) and polymorphonuclear neutrophils (PMN), are primed and activated compared with those obtained from control subjects. In particular, they release higher amounts of reactive oxygen species. PKC has been known to play an important role in the respiratory burst of human leukocytes. In this study, the PKC activity was measured in blood neutrophils and alveolar macrophages from control (n = 16) and asthmatic subjects (n = 28). In PMN, the total PKC activity was significantly lower in PMN from stable (182.00 +/- 27.20) and unstable (108.40 +/- 14.15) asthmatic patients, compared with control subjects (257.35 +/- 29.70 pmol/10(7) cells/min with p < 0.05 and p < 0.0005, respectively). In AM, PKC activity was 479.50 +/- 71.80 for controls and 254.00 +/- 25.90 pmol/10(7) cells/min for asthmatic patients. Moreover the percentage of membrane PKC was significantly higher in stable asthmatic patients in both cell types. After stimulation of neutrophils with PMA, a significant decrease in total PKC activity was observed in both control and asthmatic subjects. We have found an abnormal regulation of PKC activity in both blood PMNs and AM in asthmatic patients. These findings are consistent with the functional hyperreactivity of inflammatory cells observed in asthma.

Cholesteryl ester transfer protein (CETP) mRNA abundance in human adipose tissue: relationship to cell size and membrane cholesterol content

Cholesteryl ester transfer protein (CETP) has a well-defined role in plasma neutral lipid transport. CETP synthesized by human adipose tissue may contribute to the plasma CETP pool. CETP mRNA abundance increases in subcutaneous adipose tissue in response to cholesterol feeding and we have hypothesized that CETP gene expression is regulated by a specific pool of cellular sterol. In the present study, we have quantified CETP mRNA levels in subcutaneous adipose tissue of 10 female subjects using a solution hybridization RNase protection assay. Particulate (membrane cholesterol) and lipid droplet cholesterol (core cholesterol) were determined by gas chromatography. CETP mRNA abundance in these adipose tissue specimens correlated significantly with membrane cholesterol expressed as a fraction of membrane protein (r = 0.67, P = 0.031). There was also a linear relationship between CETP mRNA abundance and membrane cholesterol to core triglyceride ratio (r = 0.77, P = 0.009) and a strong correlation between the percentage of cellular cholesterol in the membrane fraction (ratio of membrane to core cholesterol) and CETP mRNA abundance (r = 0.91, P = 0.0002). In contrast, there was a negative relationship between each of lipid droplet cholesterol and triglyceride and CETP mRNA levels. Human adipose tissue maintained in organ culture for several days was shown to secrete CETP into the culture medium. Incubation with cholesterol-rich chylomicron remnants elicited a dose-dependent increase in both membrane and core cholesterol and a concomitant increase in the level of CETP mRNA. These studies demonstrate that adipose tissue CETP mRNA abundance is a function of membrane cholesterol concentration rather than lipid droplet cholesterol and that CETP mRNA increases with adipocyte cholesterol enrichment via chylomicron remnants. CETP gene expression is highest in small lipid-poor adipocytes, suggesting that CETP synthesized and secreted by adipocytes may have a role in promoting cellular cholesterol accumulation.

Effect of nedocromil sodium on sulfidopeptide leukotrienes-stimulated human alveolar macrophages in asthma

Alveolar macrophages (AM) may take part in the amplification of the inflammatory mechanism involved in asthma. During an asthma attack, mast cells and eosinophils release arachidonic acid derivative mediators of inflammation such as sulfidopeptide leukotrienes. Among them, LTC4 has been shown to be present in bronchoalveolar fluid. In asthmatic patients, we showed that the ability of AM to transform LTC4 into its derivatives LTD4 and LTE4 was related to the intensity of the local inflammation observed during endoscopy. AM from asthmatics incubated in the presence of LTC4 or LTE4, generated LTB4 and 5-HETE, which are potent chemoattractants. Nedocromil sodium (10(-4) M) decreased LTB4 releasability and intracellular 5-HETE concentrations in zymosan-stimulated AM from asthmatic patients, and was shown to decrease the LTC4 or LTE4-promoted formation of LTB4 and 5-HETE.

Enhanced esterification process of 5-hydroxyeicosatetraenoic acid (5-HETE) in PMN from asthmatic patients

Polymorphonuclear neutrophils (PMN) generate 5-HETE which can be retained within cells as free metabolites or esterified into cellular lipids. Since this metabolite has been shown to have certain inflammatory properties, we compared the generation and distribution profile of 5-HETE in A 23187-stimulated PMN from asthmatic patients (AP) and normal subjects (NS). 5-HETE was analyzed using RP-HPLC. After 5 min, total 5 HETE generation was similar in the two populations. However, esterified 5-HETE was significantly enhanced in AP (72 +/- 3% versus 47 +/- 2% of the total synthesis, p less than 0.005), whereas intracellular free 5-HETE was decreased (13 +/- 3% versus 37 +/- 4%, p less than 0.005) and similar low release was observed. Kinetic studies showed that PMN from AP esterified 5-HETE more rapidly and to a greater extent than PMN from NS. By contrast, more intracellular free 5-HETE was recovered in PMN from NS. Esterification seems to be the major pathway of 5-HETE metabolism in PMN from AP. Moreover, we showed that most of the 5-HETE added exogenously was esterified into cellular lipids. In these experimental conditions, PAF-induced migration of PMN was increased. The enhanced ability of PMN to migrate could be due to the increase of 5-HETE esterification process.

Arachidonate 5-lipoxygenase metabolism in human neutrophils from patients with asthma: in vitro effect of nedocromil sodium

Among the cells which participate in amplification of the local inflammatory reaction in asthma, neutrophils (PMN) are pro-inflammatory cells that can generate inflammatory mediators and arachidonic acid derivatives in particular. In asthmatic patients (AP) with attacks, the capacity of blood PMN to produce 5-lipoxygenase metabolites was investigated and compared to the response in healthy subjects (HS). PMN from 6 AP and from 6 HS were stimulated by calcium ionophore A23187 and arachidonate 5-lipoxygenase metabolites were analyzed by reverse-phase HPLC. LTB4, 6-trans LTB4, omega OH-LTB4 and 5-HETE were identified. In AP, total LTB4 synthesis was enhanced as compared to synthesis with PMN in HS. But the total 5-HETE synthesis by PMN from AP was decreased. Thus, the inflammatory potential of PMN from AP was enhanced in comparison to HS. The anti-inflammatory effect of nedocromil sodium (NS) was studied in the 5-lipoxygenase metabolism of arachidonic acid. NS (10(-4) mol/l) inhibited total LTB4 synthesized by PMN in AP but not in HS. We conclude that NS affects leukotriene synthesis only in cells with enhanced inflammatory potential.

Enhanced arachidonic acid metabolism and human neutrophil migration in asthma

In stable state asthmatic patients (AP) without any airway obstruction, the capacity of peripheral blood polymorphonuclear neutrophils (PMN) to produce 5-lipoxygenase metabolites and to migrate, was investigated and compared with the response in healthy subjects (HS). After calcium-ionophore A23187 stimulation, PMN from AP and HS produced LTB4, its hydroxylated derivatives: omega-OH-and omega-CO2H-LTB4) (omega-LTB4, i.e 6-trans-LTB4 and 5,6-diHETE isomers, and 5-HETE. We found an increase in LTB4 (+59%), omega-LTB4 (+39%), 6-trans-LTB4 (+128%), and free 5-HETE (+63%) generation of AP as compared with HS. Unstimulated migration was enhanced in AP (122 +/- 27 PMN/10 high power fields (hpf) in AP versus 74 +/- 25 PMN/10 hpf in HS, p less than 0.025) and suggested a greater capacity of PMN from AP to migrate. This was confirmed by the PAF-induced chemotaxis studies which showed, in AP, a greater PAF-sensitivity of PMN (10(-6) M versus 10(-5) M in HS) and a greater chemotaxis response (600 +/- 50 PMN versus 200 +/- 35 PMN in HS). In AP, we compared the capacity of PMN to generate LTB4 and 5-HETE with their capacity to migrate. We found an inverse correlation (r = 0.86, p less than 0.007) of intracellular free 5-HETE with chemotaxis to PAF.