Plasma lipid profiling across species for the identification of optimal animal models of human dyslipidemia

In an attempt to understand the applicability of various animal models to dyslipidemia in humans and to identify improved preclinical models for target discovery and validation for dyslipidemia, we measured comprehensive plasma lipid profiles in 24 models. These included five mouse strains, six other nonprimate species, and four nonhuman primate (NHP) species, and both healthy animals and animals with metabolic disorders. Dyslipidemic humans were assessed by the same measures. Plasma lipoprotein profiles, eight major plasma lipid fractions, and FA compositions within these lipid fractions were compared both qualitatively and quantitatively across the species. Given the importance of statins in decreasing plasma low-density lipoprotein cholesterol for treatment of dyslipidemia in humans, the responses of these measures to simvastatin treatment were also assessed for each species and compared with dyslipidemic humans. NHPs, followed by dog, were the models that demonstrated closest overall match to dyslipidemic humans. For the subset of the dyslipidemic population with high plasma triglyceride levels, the data also pointed to hamster and db/db mouse as representative models for practical use in target validation. Most traditional models, including rabbit, Zucker diabetic fatty rat, and the majority of mouse models, did not demonstrate overall similarity to dyslipidemic humans in this study.     

The plasma concentration of HDL-associated apoM is influenced by LDL receptor-mediated clearance of apoB-containing particles

ApoM is mainly associated with HDL. Nevertheless, we have consistently observed positive correlations of apoM with plasma LDL cholesterol in humans. Moreover, LDL receptor deficiency is associated with increased plasma apoM in mice. Here, we tested the idea that plasma apoM concentrations are affected by the rate of LDL receptor-mediated clearance of apoB-containing particles. We measured apoM in humans each carrying one of three different LDL receptor mutations (n = 9) or the apoB3500 mutation (n = 12). These carriers had increased plasma apoM (1.34 ± 0.13 μM, P = 0.003, and 1.23 ± 0.10 μM, P = 0.02, respectively) as compared with noncarriers (0.93 ± 0.04 μM). When we injected human apoM-containing HDL into Wt (n = 6) or LDL receptor-deficient mice (n = 6), the removal of HDL-associated human apoM was delayed in the LDL receptor-deficient mice. After 2 h, 54 ± 5% versus 90 ± 8% (P < 0.005) of the initial amounts of human apoM remained in the plasma of Wt and LDL receptor-deficient mice, respectively. Finally, we compared the turnover of radio-iodinated LDL and plasma apoM concentrations in 45 normocholesterolemic humans. There was a negative correlation between plasma apoM and the fractional catabolic rate of LDL (r = -0.38, P = 0.009). These data suggest that the plasma clearance of apoM, despite apoM primarily being associated with HDL, is influenced by LDL receptor-mediated clearance of apoB-containing particles.     

Rescue of Mtp siRNA-induced hepatic steatosis by DGAT2 siRNA silencing

Microsomal triglyceride transfer protein (Mtp) inhibitors represent a novel therapeutic approach to lower circulating LDL cholesterol, although therapeutic development has been hindered by the observed increase in hepatic triglycerides and liver steatosis following treatment. Here, we used small interfering RNAs (siRNA) targeting Mtp to achieve target-specific silencing to study this phenomenon and to determine to what extent liver steatosis is induced by changes in Mtp expression. We observed that Mtp silencing led to a decrease in many genes involved in hepatic triglyceride synthesis. Given the role of diacylglycerol O-acyltransferase 2 (Dgat2) in regulating hepatic triglyceride synthesis, we then evaluated whether target-specific silencing of both Dgat2 and Mtp were sufficient to attenuate Mtp silencing-induced liver steatosis. We showed that the simultaneous inhibition of Dgat2 and Mtp led to a decrease in plasma cholesterol and a reduction in the accumulation of hepatic triglycerides caused by the inhibition of Mtp. Collectively, these findings provide a proof-of-principle for a triglyceride synthesis/Mtp inhibitor combination and represent a potentially novel approach for therapeutic development in which targeting multiple pathways can achieve the desired response.     

Significant interaction between LRP2 rs2544390 in intron 1 and alcohol drinking for serum uric acid levels among a Japanese population

A genome-wide association study identified that LRP2 rs2544390 in intron 1 was associated with serum uric acid (SUA) levels among Japanese, as well as polymorphisms of SLC22A12, ABCG2, and SLC2A9. This study aimed to confirm the association of rs2544390 C/T with SUA, as well as another LRP2 polymorphism (rs3755166 G/A) in the promoter. Subjects were 5016 health checkup examinees (3409 males and 1607 females) aged 35 to 69years with creatinine<2.0mg/dL. The subjects with SLC22A12 258WW, SLC2A9 rs11722228C allele, ABCG2 126QQ and 141Q allele (2546 males and 1199 females) were selected for analysis. Mean SUA was 6.03mg/dL for CC, 6.18mg/dL for CT, and 6.19mg/dL for TT among males (p=0.012), and 4.49mg/dL, 4.45mg/dL, and 4.42mg/dL among females (not significant), respectively. No association was observed for rs3755166. The association with rs2544390 was stronger among male drinkers. The odds ratio of drinking ≥5/week relative to no drinking for hyperuricemia (SUA≥7mg/dL and/or under medication for hyperuricemia) was 1.11 (95% confidence interval, 0.67-1.84) among CC males, 1.75 (1.22-2.51) among CT males, and 3.13 (1.80-5.43) among TT males. The interaction terms with drinking ≥5/week were 1.56 (p=0.156) for CT and 2.87 (p=0.005) for TT. This was the first report on the interaction between LRP2 genotype and alcohol drinking for SUA. Since the low density lipoprotein-related protein 2 (megalin) encoded by LRP2 is a multi-ligand endocytic receptor expressed in many tissues including the kidney proximal tubules, the association/interaction remained to be confirmed both epidemiologically and biologically.     

PPARγ2 Pro12Ala polymorphism is associated with improved lipoprotein lipase functioning in adipose tissue of insulin resistant obese women

Lipoprotein lipase (LPL) plays a pivotal role in lipid metabolism, contributes to metabolic disorders related to insulin action and body weight regulation, and is influenced by inflammation. The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPAR)γ2 gene seems to influence LPL functioning, but its role in obesity and insulin resistance status, which usually coexist in the clinical setting, has not been explored. Our aim was to analyze the association of obesity and insulin resistance with adipose LPL activity and expression, and the influence of the PPARγ2 Pro12Ala polymorphism. A cross-sectional study was conducted in 58 reproductive-age women who underwent elective abdominal surgery. Free-fatty acids, glucose, insulin, and selected adipokines were measured in fasting blood samples. DNA was isolated and the polymorphism genotyped. Biopsies of abdominal subcutaneous adipose tissue obtained during surgery were used to determine enzymatic LPL activity and expression; and expression of selected cytokines. Overweight/obese women presented lower LPL activity (P = 0.022) and higher circulating TNF-α (P = 0.020) than controls. Insulin resistant women also showed borderline lower LPL activity than non-resistant (P = 0.052), but adiposity and inflammatory molecules were comparable. Nevertheless, LPL activity was higher in Pro12Ala carriers than in non-carriers after adjusting for obesity, insulin resistance and inflammation. Likewise, adipose LPL expression was increased in carriers while expression of cytokines was decreased. Our data suggest that insulin resistance is associated with low adipose LPL activity independently of obesity, but the PPARγ2 Pro12Ala polymorphism seems to protect the LPL functioning of obese insulin resistant women, likely through regulating inflammation in adipose tissue.     

Delayed luminescence: a novel technique to obtain new insights into water structure

Fully understanding the structure of water is a crucial point in biophysics because this liquid is essential in the operation of the engines of life. Many of its amazing anomalies seem to be tailored to support biological processes and, during about a century, several models have been developed to describe the water structuring. In particular, a theory assumes that water is a mixture of domains constituted by two distinct and inter-converting structural species, the low-density water (LDW) and the high-density water (HDW). According to this theory, by using some particular solutes or changing the water temperature, it should be possible to modify the equilibrium between the two species, changing in this way the water behavior in specific biological processes, as in governing the shape and stability of the structures of proteins. In this work, we assess the possibility of obtaining information on the structures induced in water by specific salts or by temperature by measuring the delayed luminescence (DL) of some salt solutions and of water in the super-cooled regime. Previous works have demonstrated that the delayed luminescence of a system is correlated with its dynamic ordered structures. The results show significant DL signals only when the formation of LDW domains is expected. The measurement reveals a similar activation energy for the domains both in aqueous salt solutions and super-cooled water. It is worth noting that the time trend of DL signals suggests the existence of structures unusually long-lasting in time, up to the microsecond range.     

Increased expression and phosphorylation of the two S100A9 isoforms in mononuclear cells from patients with systemic lupus erythematosus: a proteomic signature for circulating low-density granulocytes

Proteins differentially expressed in peripheral blood mononuclear cells (PBMCs) from systemic lupus erythematosus (SLE) patients versus Normal controls were identified by 2-DE and MALDI-MS. Thus, S100A9 expression was significantly increased in SLE PBMCs relative to Normal PBMCs at both mRNA and protein levels. Increased S100A9 levels in SLE PBMCs correlated positively with the abnormal presence of low-density granulocytes (LDGs) detected by flow-cytometry in the mononuclear cell fractions. Another set of proteins that were differentially expressed in SLE PBMCs formed S100A9-independent clusters, suggesting that these differences in protein expression are in fact reflecting changes in the abundance of specific cell types. In SLE PBMCs spots of the two S100A9 isoforms, S100A9-l and S100A9-s, and their phosphorylated counterparts were identified and confirmed to be phosphorylated at Thr¹¹³ by MS/MS analyses. In addition, the phorbol ester PMA alone or in combination with ionomycin induced a stronger increase in threonine phosphorylation of S100A9 in SLE than in Normal PBMCs, while the same stimuli caused the opposite effect on phosphorylation and activation of Erk1/2, suggesting the existence of an abnormal S100A9 signaling in SLE PBMCs. Therefore, the expansion and activation of LDGs in SLE seems to underlie this prominent S100A9 signature.     

Skeletal muscle damage and impaired regeneration due to LPL-mediated lipotoxicity

According to the concept of lipotoxicity, ectopic accumulation of lipids in non-adipose tissue induces pathological changes. The most prominent effects are seen in fatty liver disease, lipid cardiomyopathy, non-insulin-dependent diabetes mellitus, insulin resistance and skeletal muscle myopathy. We used the MCK(m)-hLPL mouse distinguished by skeletal and cardiac muscle-specific human lipoprotein lipase (hLPL) overexpression to investigate effects of lipid overload in skeletal muscle. We were intrigued to find that ectopic lipid accumulation induced proteasomal activity, apoptosis and skeletal muscle damage. In line with these findings we observed reduced Musculus gastrocnemius and Musculus quadriceps mass in transgenic animals, accompanied by severely impaired physical endurance. We suggest that muscle loss was aggravated by impaired muscle regeneration as evidenced by reduced cross-sectional area of regenerating myofibers after cardiotoxin-induced injury in MCK(m)-hLPL mice. Similarly, an almost complete loss of myogenic potential was observed in C2C12 murine myoblasts upon overexpression of LPL. Our findings directly link lipid overload to muscle damage, impaired regeneration and loss of performance. These findings support the concept of lipotoxicity and are a further step to explain pathological effects seen in muscle of obese patients, patients with the metabolic syndrome and patients with cancer-associated cachexia.     

Increased risk of coronary artery disease in Caucasians with extremely low HDL cholesterol due to mutations in ABCA1, APOA1, and LCAT

Mutations in ABCA1, APOA1, and LCAT reduce HDL cholesterol (HDLc) in humans. However, the prevalence of these mutations and their relative effects on HDLc reduction and risk of coronary artery disease (CAD) are less clear. Here we searched for ABCA1, APOA1, and LCAT mutations in 178 unrelated probands with HDLc < 10th percentile but no other major lipid abnormalities, including 89 with ≥ 1 first-degree relative with low HDLc (familial probands) and 89 where familial status of low HDLc is uncertain (unknown probands). Mutations were most frequent in LCAT (15.7%), followed by ABCA1 (9.0%) and APOA1 (4.5%), and were found in 42.7% of familial but only 14.6% of unknown probands (p = 2.44 ∗ 10^− 5). Interestingly, only 16 of 24 (66.7%) mutations assessed in families conferred an average HDLc < 10th percentile. Furthermore, only mutation carriers with HDLc < 5th percentile had elevated risk of CAD (odds ratio (OR) = 2.26 for 34 ABCA1 mutation carriers vs. 149 total first-degree relative controls, p = 0.05; OR = 2.50 for 26 APOA1 mutation carriers, p = 0.04; OR = 3.44 for 38 LCAT mutation carriers, p = 1.1 ∗ 10^− 3). These observations show that mutations in ABCA1, APOA1, and LCAT are sufficient to explain > 40% of familial hypoalphalipoproteinemia in this cohort. Moreover, individuals with mutations and large reductions in HDLc have increased risk of CAD. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).