Publications

Inflammation induces marked changes in lipid and lipoprotein metabolism. Proprotein convertase subtilisin kexin 9 (PCSK9) plays an important role in regulating LDL receptor degradation. Here, we demonstrate that LPS decreases hepatic LDL receptor protein but at the same time hepatic LDL receptor mRNA levels are not decreased. We therefore explored the effect of LPS on PCSK9 expression. LPS results in a marked increase in hepatic PCSK9 mRNA levels (4h 2.5-fold increase; 38h 12.5-fold increase). The increase in PCSK9 is a sensitive response with 1microg LPS inducing a (1/2) maximal response. LPS also increased PCSK9 expression in the kidney. Finally, zymosan and turpentine, other treatments that induce inflammation, also stimulated hepatic expression of PCSK9. Thus, inflammation stimulates PCSK9 expression leading to increased LDL receptor degradation and decreasing LDL receptors thereby increasing serum LDL, which could have beneficial effects on host defense.

Infection and inflammation affect adipose triglyceride metabolism, resulting in increased plasma free fatty acid (FFA) and VLDL levels during the acute-phase response. Lipin-1, a multifunctional protein, plays a critical role in adipose differentiation, mitochondrial oxidation, and triglyceride synthesis. Here, we examined whether LPS [a Toll-like receptor (TLR)-4 activator], zymosan (a TLR-2 activator), and proinflammatory cytokines regulate lipin-1 in adipose tissue. LPS administration caused a marked decrease in the levels of lipin-1 mRNA and protein in adipose tissue. The decrease in lipin-1 mRNA levels occurred rapidly and lasted for at least 24 h. In contrast, lipin-2 and -3 mRNA levels did not change, suggesting specific repression of lipin-1. Zymosan similarly decreased lipin-1 mRNA without affecting lipin-2 or lipin-3 mRNA levels. To determine the pathways by which LPS repressed lipin-1, we examined the effect of proinflammatory cytokines on cultured adipocytes. In 3T3-L1 adipocytes, TNF-alpha, IL-1beta, and IFN-gamma, but not LPS or IL-6, caused a decrease in lipin-1 mRNA levels. Furthermore, TNF-alpha and IL-1beta administration also decreased mRNA levels of lipin-1 in adipose tissue in mice. Importantly, the LPS-induced decrease in lipin-1 mRNA levels was significantly but not totally blunted in TNF-alpha/IL-1 receptor-null mice compared with controls, suggesting key roles for TNF-alpha/IL-1beta and other cytokines in mediating LPS-induced repression of lipin-1. Together, our results demonstrate that expression of lipin-1, one of the essential triglyceride synthetic enzymes, was suppressed by LPS, zymosan, and proinflammatory cytokines in mouse adipose tissue and in cultured 3T3-L1 adipocytes, which could contribute to a decrease in the utilization of FFA to synthesize triglycerides in adipose tissue, thus promoting the release of FFA into the circulation.

OBJECTIVE

To assess by race/ethnicity long-term changes in metabolic parameters and body composition among treatment-naive persons initiating antiretroviral therapy (ART).

METHODS

We compared changes in 398 participants (African American n = 243, Latino n = 43, white n = 112) initiating ART. At baseline, 1-month (metabolic parameters only) and 4-month follow-up intervals (anthropometric measurements) were performed and fasting metabolic parameters measured. Rates of change over time and overall mean changes from baseline were compared.

RESULTS

Latinos had the greatest increase in glucose and insulin resistance and greatest loss of mid-arm and mid-thigh subcutaneous tissue areas. On average, mid-arm and mid-thigh nonsubcutaneous tissue areas increased in all races. Waist subcutaneous tissue area decreased only for Latinos. Visceral tissue area increased the most for Latinos and whites. For all groups, the initial increase in high-density lipoprotein cholesterol was sustained. The initial increase in low-density lipoprotein cholesterol was followed by a gradual decline in all groups. Triglycerides increased for all groups; the increase being the least for African Americans.

CONCLUSIONS

In this prospective long-term evaluation, changes in metabolic parameters and body composition varied across race groups. Latinos experienced the most unfavorable changes. Such changes should be monitored over time as the identified differences may impact ART selection.

CONTEXT

Leptin deficiency is associated with dyslipidemia and insulin resistance in animals and humans with lipoatrophy; leptin replacement ameliorates these abnormalities.

OBJECTIVE

The objective of the study was to evaluate the effects of leptin therapy in lipoatrophic HIV-infected patients with dyslipidemia and hypoleptinemia.

DESIGN

This was a 6-month, open-label, proof-of-principle pilot study.

SETTING

Metabolic ward studies were performed before and 3 and 6 months after leptin treatment.

PARTICIPANTS

Participants included eight HIV-infected men with lipoatrophy, fasting triglycerides greater than 300 mg/dl, and serum leptin less than 3 ng/ml.

INTERVENTION

Recombinant human leptin was given by sc injection (0.01 mg/kg and 0.03 mg/kg twice daily for successive 3 month periods).

OUTCOME MEASURES

Measures included fat distribution by magnetic resonance imaging and dual-energy X-ray absorptiometry; fasting lipids; insulin sensitivity by euglycemic hyperinsulinemic clamp; endogenous glucose production, gluconeogenesis, glycogenolysis, and whole-body lipolysis by stable isotope tracer studies; oral glucose tolerance testing; liver fat by proton magnetic resonance spectroscopy; and safety.

RESULTS

Visceral fat decreased by 32% (P = 0.001) with no changes in peripheral fat. There were significant decreases in fasting total (15%, P = 0.012), direct low-density lipoprotein (20%, P = 0.002), and non-high-density lipoprotein (19%, P = 0.005) cholesterol. High-density lipoprotein cholesterol increased. Triglycerides, whole-body lipolysis, and free fatty acids decreased during fasting and hyperinsulinemia. Fasting insulin decreased. Endogenous glucose production decreased during fasting and hyperinsulinemia, providing evidence of improved hepatic insulin sensitivity. Leptin was well tolerated but decreased lean mass.

CONCLUSIONS

Leptin treatment was associated with marked improvement in dyslipidemia. Hepatic insulin sensitivity improved and lipolysis decreased. Visceral fat decreased with no exacerbation of peripheral lipoatrophy. Results from this pilot study suggest that leptin warrants further study in patients with HIV-associated lipoatrophy.

ABCA12 (ATP binding cassette transporter, family 12) is a cellular membrane transporter that facilitates the delivery of glucosylceramides to epidermal lamellar bodies in keratinocytes, a process that is critical for permeability barrier formation. Following secretion of lamellar bodies into the stratum corneum, glucosylceramides are metabolized to ceramides, which comprise approximately 50% of the lipid in stratum corneum. Gene mutations of ABCA12 underlie harlequin ichthyosis, a devastating skin disorder characterized by abnormal lamellar bodies and a severe barrier abnormality. Recently we reported that peroxisome proliferator-activated receptor (PPAR) and liver X receptor activators increase ABCA12 expression in human keratinocytes. Here we demonstrate that ceramide (C(2)-Cer and C(6)-Cer), but not C(8)-glucosylceramides, sphingosine, or ceramide 1-phosphate, increases ABCA12 mRNA expression in a dose- and time-dependent manner. Inhibitors of glucosylceramide synthase, sphingomyelin synthase, and ceramidase and small interfering RNA knockdown of human alkaline ceramidase, which all increase endogenous ceramide levels, also increased ABCA12 mRNA levels. Moreover, simultaneous treatment with C(6)-Cer and each of these same inhibitors additively increased ABCA12 expression, indicating that ceramide is an important inducer of ABCA12 expression and that the conversion of ceramide to other sphingolipids or metabolites is not required. Finally, both exogenous and endogenous ceramides preferentially stimulate PPARdelta expression (but not other PPARs or liver X receptors), whereas PPARdelta knockdown by siRNA transfection specifically diminished the ceramide-induced increase in ABCA12 mRNA levels, indicating that PPARdelta is a mediator of the ceramide effect. Together, these results show that ceramide, an important lipid component of epidermis, up-regulates ABCA12 expression via the PPARdelta-mediated signaling pathway, providing a substrate-driven, feed-forward mechanism for regulating this key lipid transporter.

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARalpha and beta/delta, RXRalpha, beta, and gamma, thyroid hormone receptor alpha and beta, and estrogen related receptor alpha (ERRalpha) and their coactivators PGC-1alpha, PGC-1beta, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARalpha deficient mice, baseline CPT-1beta and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARalpha signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis.

OBJECTIVE

To examine the long-term effects of individual antiretroviral drugs on body composition among 416 persons initiating antiretroviral therapy (ART).

METHODS

In a substudy of a clinical trial of persons initiating ART, changes in body composition attributable to individual ART were examined. ARTs assessed were as follows: indinavir, ritonavir, nelfinavir, efavirenz, nevirapine, stavudine (d4T), zidovudine (ZDV), lamivudine (3TC), didanosine, and abacavir. Skinfolds and circumferences were measured at baseline and every 4 months. Mid arm, mid thigh, and waist subcutaneous tissue areas and nonsubcutaneous tissue areas were calculated. Rates of change per year of exposure to each individual ART drug were determined using multivariate longitudinal regression.

RESULTS

d4T and ZDV use was associated with losses in subcutaneous tissue area and skinfold thickness. 3TC use was associated with gains in all subcutaneous tissue areas and skinfold thickness, whereas abacavir use was associated with an increase in waist subcutaneous tissue area. Indinavir was associated with gains in waist subcutaneous tissue area, whereas indinavir, efavirenz, and nevirapine were associated with increases in upper back skinfolds. d4T use was also associated with increases in all nonsubcutaneous tissue areas; 3TC use was associated with the greatest increase in waist nonsubcutaneous tissue area.

CONCLUSION

In this prospective nonrandomized evaluation, the nucleoside reverse transcriptase inhibitors d4T and ZDV were associated with decreases in subcutaneous tissue areas, whereas 3TC use was associated with increased subcutaneous tissue areas and waist nonsubcutaneous tissue area.

OBJECTIVE

C-reactive protein (CRP) levels>3 mg/L and>10 mg/L are associated with high and very high cardiovascular risk, respectively, in the general population. Because rheumatoid arthritis (RA) confers excess cardiovascular mortality, we determined the prevalence of these CRP levels among RA patients stratified on the basis of their RA disease activity.

METHODS

We evaluated physician and patient global assessments of disease activity, tender and swollen 28 joint counts, erythrocyte sedimentation rate (ESR), and CRP measured in a single clinic visit for 151 RA patients. Disease activity was calculated using the Clinical Disease Activity Index (CDAI) and the Disease Activity Score 28 Joints (DAS28-ESR and DAS28-CRP).

RESULTS

Median CRP level was 5.3 mg/L. 68% of patients had CRP>3 mg/L, and 25% had CRP>10 mg/L. Of those with 0-1 swollen joints (n = 56), or 0-1 tender joints (n = 81), 64% and 67%, respectively, had CRP>3 mg/L, and 23% and 20%, respectively, had CRP>10 mg/L. Of those with remission or mildly active disease by CDAI (n = 58), DAS28-ESR (n = 39), or DAS28-CRP (n = 70), 49-66% had CRP>3 mg/L, and 10-14% had CRP>10 mg/L. Of patients with moderate disease activity by CDAI (n = 51), DAS28-ESR (n = 78), or DAS28-CRP (n = 66), 67-73% had CRP>3 mg/L, and 25-33% had CRP>10 mg/L.

CONCLUSION

Even among RA patients whose disease is judged to be controlled by joint counts or standardized disease scores, a substantial proportion have CRP levels that are associated high or very high risk for future cardiovascular events in the general population.