Davalintide (AC2307), a novel amylin-mimetic peptide: enhanced pharmacological properties over native amylin to reduce food intake and body weight.

OBJECTIVE: The current set of studies describe the in vivo metabolic actions of the novel amylin-mimetic peptide davalintide (AC2307) in rodents and compares these effects with those of the native peptide. RESEARCH DESIGN AND METHODS: The anti-obesity effects of davalintide were examined after intraperitoneal injection or sustained peripheral infusion through subcutaneously implanted osmotic pumps. The effect of davalintide on food intake after lesioning of the area postrema (AP) and neuronal activation as measured by c-Fos, were also investigated. RESULTS: Similar to amylin, davalintide bound with high affinity to amylin, calcitonin and calcitonin gene-related peptide receptors. Acutely, davalintide displayed greater suppression of dark-cycle feeding and an extended duration of action compared with amylin (23 versus 6 h). Davalintide had no effect on locomotor activity or kaolin consumption at doses that decreased food intake. Davalintide-induced weight loss through infusion was dose dependent, durable up to 8 weeks, fat-specific and lean-sparing, and was associated with a shift in food preference away from high-fat (palatable) chow. Metabolic rate was maintained during active weight loss. Both davalintide and amylin failed to suppress food intake after lesioning of the AP and activated similar brain nuclei, with davalintide displaying an extended duration of c-Fos expression compared with amylin (8 versus 2 h). CONCLUSION: Davalintide displayed enhanced in vivo metabolic activity over amylin while retaining the beneficial properties possessed by the native molecule. In vitro receptor binding, c-Fos expression and AP lesion studies suggest that the metabolic actions of davalintide and amylin occur through activation of similar neuronal pathways.

Effects of PYY[3-36] in rodent models of diabetes and obesity.

BACKGROUND: Peptide YY (PYY) is a 36 amino-acid peptide secreted from ileal L cells following meals. The cleaved subpeptide PYY[3-36] is biologically active and may constitute the majority of circulating PYY-like immunoreactivity. The peptide family that includes PYY, pancreatic peptide and neuropeptide Y is noted for its orexigenic effect following intracerebroventricular administration. OBJECTIVE: To investigate the effects of peripheral (intraperitoneal and chronic subcutaneous) infusions of PYY[3-36] on food intake, body weight and glycemic indices. DESIGN/RESULTS: Food intake was measured in normal mice and in several rodent models of obesity and type II diabetes. In marked contrast to the reported central orexigenic effects, in the present study, PYY[3-36] acutely inhibited food intake by up to 45%, with an ED(50) of 12.5 microg/kg in fasted female NIH/Swiss mice. A 4-week infusion reduced weight gain in female ob/ob mice, without affecting the cumulative food intake. In diet-induced obese male mice, PYY[3-36] infusion reduced cumulative food intake, weight gain and epididymal fat weight (as a fraction of carcass) with similar ED(50)'s (466, 297 and 201 microg/kg/day, respectively) and prevented a diet-induced increase in HbA1c. Infusion at 100 microg/kg/day for 8 weeks in male fa/fa rats reduced the weight gain (288+/-11 vs 326+/-12 g in saline-infused controls; P<0.05), similar to effects in a pair-fed group. In female ob/ob and db/db mice, there was no acute effect of PYY[3-36] on plasma glucose concentrations. In male diabetic fatty Zucker rats, PYY[3-36] infused for 4 weeks reduced HbA1c and fructosamine (ED(50)'s 30 and 44 microg/kg/day). CONCLUSION: Peripheral PYY[3-36] administration reduced the food intake, body weight gain and glycemic indices in diverse rodent models of metabolic disease of both sexes. These findings justify further exploration of the potential physiologic and therapeutic roles of PYY[3-36].

Peroxisome proliferator-activated receptor subtype-specific regulation of hepatic and peripheral gene expression in the Zucker diabetic fatty rat.

Fibrates and thiazolidinediones are used clinically to treat hypertriglyceridemia and hyperglycemia, respectively. Fibrates bind to the peroxisome proliferator-activated receptor (PPAR)-alpha, and thiazolidinediones are ligands of PPAR-gamma. These intracellular receptors form heterodimers with retinoid X receptor to modulate gene transcription. To elucidate the target genes regulated by these compounds, we treated Zucker diabetic fatty rats (ZDF) for 15 days with a PPAR-alpha-specific compound, fenofibrate, a PPAR-gamma-specific ligand, rosiglitazone, and a PPAR-alpha/-gamma coagonist, GW2331, and measured the levels of several messenger RNAs (mRNAs) in liver by real-time polymerase chain reaction. All 3 compounds decreased serum glucose and triglyceride levels. Fenofibrate and GW2331 induced expression of acyl-coenzyme A (CoA) oxidase and enoyl-CoA hydratase and reduced apolipoprotein C-III and phosphoenolpyruvate carboxykinase mRNAs. Rosiglitazone modestly increased apolipoprotein C-III mRNA and had no effect on expression of the other 2 genes in the liver but increased the expression of glucose transporter 4 and phosphoenolpyruvate carboxykinase in adipose tissue. We identified a novel target in liver, mitogen-activated phosphokinase phosphatase 1, whose down-regulation by PPAR-alpha agonists may improve insulin sensitivity in that tissue by prolonging insulin responses. The results of these studies suggest that activation of PPAR-alpha as well as PPAR-gamma in therapy for type 2 diabetes will enhance glucose and triglyceride control by combining actions in hepatic and peripheral tissues.

Design and synthesis of 2-methyl-2-[4-(2-[5-methyl-2-aryloxazol-4-yl]ethoxy)phenoxy]propionic acids: a new class of dual PPARalpha/gamma agonists.

Propionic acid derivative 8, which was designed and synthesized based on putative pharmacophores of known PPARgamma- and PPARalpha-selective compounds, exhibits potent dual PPARalpha/gamma agonist activity as demonstrated by in vitro binding and dose overlap in the newly introduced EOB mouse model for glucose lowering and lipid/cholesterol homeostasis.

Peroxisome proliferator-activated receptor (PPAR) gamma and retinoid X receptor (RXR) agonists have complementary effects on glucose and lipid metabolism in human skeletal muscle.

AIMS/HYPOTHESIS: To determine the independent and potentially synergistic effects of agonists for PPAR gamma and RXR on glucose and lipid metabolism, as well as gene expression, in human skeletal muscle cell cultures. METHODS: Fully differentiated myotubes from non-diabetic subjects and subjects with Type II (non-insulin-dependent) diabetes mellitus were chronically (2 days) treated with LG100268 (4 mumol/l), an RXR agonist, or troglitazone (4.6 mumol/l), a PPAR gamma agonist or both, to determine the effects on glucose uptake, activity of glycogen synthase and palmitate oxidation. RESULTS: The combination of both agents increased glucose uptake (60 +/- 9% compared to control subjects) but not either agent alone (16 +/- 9 and 26 +/- 6% for LG100268 and troglitazone, p < 0.01, respectively). The agent LG100268 alone had little effect on the activity of glycogen synthase but the effect of troglitazone increased with LG100268 (p < 0.05). With chronic exposure, LG100268 upregulated palmitate oxidation (53 +/- 12% increase, p < 0.005), in a way similar to troglitazone (68 +/- 23%, p < 0.005). Synergism was observed when both agonists were combined (146 +/- 38%, p < 0.005 vs either agent alone). Treatment with either agent led to about a twofold increase in the expression of fatty acid transporter (FAT/CD36). Troglitazone upregulated PPAR gamma protein expression, whereas LG100268 had no effect. Furthermore, neither LG100268 nor troglitazone had any effect on the protein expression of RXR isoforms or PPAR alpha. CONCLUSION/INTERPRETATION: Co-activation of PPAR gamma and RXR results in additive or synergistic effects on glucose and lipid metabolism in skeletal muscle, but unlike troglitazone, LG100268 does not alter expression of its own receptor.

Reduction of atherosclerosis in apolipoprotein E knockout mice by activation of the retinoid X receptor.

A common feature of many metabolic pathways is their control by retinoid X receptor (RXR) heterodimers. Dysregulation of such metabolic pathways can lead to the development of atherosclerosis, a disease influenced by both systemic and local factors. Here we analyzed the effects of activation of RXR and some of its heterodimers in apolipoprotein E -/- mice, a well established animal model of atherosclerosis. An RXR agonist drastically reduced the development of atherosclerosis. In addition, a ligand for the peroxisome proliferator-activated receptor (PPAR)gamma and a dual agonist of both PPARalpha and PPARgamma had moderate inhibitory effects. Both RXR and liver X receptor (LXR) agonists induced ATP-binding cassette protein 1 (ABC-1) expression and stimulated ABC-1-mediated cholesterol efflux from macrophages from wild-type, but not from LXRalpha and beta double -/-, mice. Hence, activation of ABC-1-mediated cholesterol efflux by the RXR/LXR heterodimer might contribute to the beneficial effects of rexinoids on atherosclerosis and warrant further evaluation of RXR/LXR agonists in prevention and treatment of atherosclerosis.

Accumulation of cholestatic lipoproteins in ANIT-treated human apolipoprotein A-I transgenic rats is diminished through dose-dependent apolipoprotein A-I activation of LCAT.

Administration of alpha-naphthylisothiocyanate (ANIT) to rats induces changes to plasma lipids consistent with cholestasis. We have previously shown (J. Lipid Res. 37 (1996) 1086) that animals treated with ANIT accumulate large amounts of free cholesterol (FC) and phospholipid (PL)-rich cholestatic lipoproteins in the LDL density range by 48 h. This lipid was cleared by 120 h through apparent movement into HDL with concomitant cholesteryl ester (CE) production. It was hypothesised that the clearance was mediated through the movement of the PL and FC into apolipoprotein A-I (apo A-I) containing lipoproteins followed by LCAT esterification to form CE. To test this hypothesis, rats overexpressing various amounts of human apo A-I (TgR[HuAI] rats) were treated with ANIT (100 mg/kg) and the effect of plasma apo A-I concentration on plasma lipids and lipoprotein distribution was examined. In untreated TgR[HuAI] rats, human apo A-I levels were strongly correlated to plasma PL (r(2)=0. 94), FC (r(2)=0.93) and CE (r(2)=0.90), whereas in ANIT-treated TgR[HuAI] rats, human apo A-I levels were most strongly correlated to CE levels (r(2)=0.80) and an increased CE/FC ratio (r(2)=0.62) and the movement of cholestatic lipid in the LDL to HDL. Since LCAT activity was not affected by ANIT treatment, these results demonstrate that the ability of LCAT to esterify the plasma FC present in cholestatic liver disease is limited by in vivo apo A-I activation of the cholestatic lipid and not by the catalytic capacity of LCAT.

A selective peroxisome proliferator-activated receptor-gamma (PPARgamma) modulator blocks adipocyte differentiation but stimulates glucose uptake in 3T3-L1 adipocytes.

Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists such as the thiazolidinediones are insulin sensitizers used in the treatment of type 2 diabetes. These compounds induce adipogenesis in cell culture models and increase weight gain in rodents and humans. We have identified a novel PPARgamma ligand, LG100641, that does not activate PPARgamma but selectively and competitively blocks thiazolidinedione-induced PPARgamma activation and adipocyte conversion. It also antagonizes target gene activation as well as repression in agonist-treated 3T3-L1 adipocytes. This novel PPARgamma antagonist does not block adipocyte differentiation induced by a ligand for the retinoid X receptor (RXR), the heterodimeric partner for PPARgamma, or by a differentiation cocktail containing insulin, dexamethasone, and 1-methyl-3-isobutylxanthine. Surprisingly, LG100641, like the PPARgamma agonist rosiglitazone, increases glucose uptake in 3T3-L1 adipocytes. Such selective PPARgamma antagonists may help determine whether insulin sensitization by thiazolidinediones is mediated solely through PPARgamma activation, and whether there are PPARgamma-ligand-independent pathways for adipocyte differentiation. If selective PPARgamma modulators block adipogenesis in vivo, they may prevent obesity, lower insulin resistance, and delay the onset of type 2 diabetes.

RXR agonists activate PPARalpha-inducible genes, lower triglycerides, and raise HDL levels in vivo.

Peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors (RXRs) are members of the intracellular receptor superfamily. PPARs bind to peroxisome proliferator-response elements (PPREs) as heterodimers with RXR and as such activate gene transcription in response to activators. Fibrates like gemfibrozil are well-known PPARalpha activators and are used in the treatment of hyperlipidemia. We show that the RXR ligand LGD1069 (Targretin), like gemfibrozil, can activate the PPARalpha/RXR signal-transduction pathway, including transactivation of the bifunctional enzyme or acyl-CoA oxidase response elements in a cotransfection assay. The activation also occurs in vivo, whereby in rats treated with LGD1069 or gemfibrozil, bifunctional enzyme and acyl-CoA oxidase RNA are induced and the combination of LGD1069 and gemfibrozil leads to a greater induction. Importantly, in hypertriglyceridemic db/db mice treated with RXR or PPARalpha agonists, triglyceride levels are lowered, and the combination again has significantly greater efficacy. RXR agonists also raise HDL cholesterol levels without changing apoA-I RNA expression. This observation suggests the use of RXR-selective agonists, "rexinoids," either alone or in combination with a fibrate as a new therapeutic approach to treating patients with high triglyceride and low HDL cholesterol levels.

Skeletal muscle peroxisome proliferator- activated receptor-gamma expression in obesity and non- insulin-dependent diabetes mellitus.

UNLABELLED: The two isoforms of peroxisome proliferator-activated receptor-gamma (PPARgamma1 and PPARgamma2), are ligand-activated transcription factors that are the intracellular targets of a new class of insulin sensitizing agents, the thiazolidinediones. The observation that thiazolidinediones enhance skeletal muscle insulin sensitivity in obesity and in patients with non-insulin-dependent diabetes mellitus (NIDDM), by activating PPARgamma, and possibly by inducing its expression, suggests that PPARgamma expression in skeletal muscle plays a key role in determining tissue sensitivity to insulin, and that PPARgamma expression may be decreased in insulin resistant subjects. We used a sensitive ribonuclease protection assay, that permits simultaneous measurement of the two isoforms, to examine the effects of obesity and NIDDM, and the effects of insulin, on skeletal muscle levels of PPARgamma1 and PPARgamma2 mRNA. We studied seven patients with NIDDM (body mass index, 32+/-1 kg/m2), seven lean (24+/-1 kg/m2), and six obese (36+/-1 kg/m2) normal subjects. Biopsies from the vastus lateralis muscle were taken before and after a 5-h hyperinsulinemic (80 mU/m2 per minute) euglycemic clamp. The obese controls and NIDDM patients were insulin resistant with glucose disposal rates during the last 30 min of the clamp that were 67 and 31%, respectively, of those found in the lean controls. PPARgamma1, but not PPARgamma2 mRNA was detected in skeletal muscle at 10-15% of the level found in adipose tissue. No difference was found in PPARgamma1 levels between the three groups, and there was no change in PPARgamma1 levels after 5 h of hyperinsulinemia. In obese subjects, PPARgamma1 correlated with clamp glucose disposal rates (r = 0.92, P < 0.01). In the lean and NIDDM patients, muscle PPARgamma1 levels correlated with percentage body fat (r = 0.76 and r = 0.82, respectively, both P < 0.05) but not with body mass index. IN CONCLUSION: (a) skeletal muscle PPARgamma1 expression does not differ between normal and diabetic subjects, and is not induced by short-term hyperinsulinemia; (b) skeletal muscle PPARgamma1 expression was higher in subjects whose percent body fat exceeded 25%, and this may be a compensatory phenomenon in an attempt to maintain normal insulin sensitivity.

Regulation of lipoprotein metabolism by thiazolidinediones occurs through a distinct but complementary mechanism relative to fibrates.

Thiazolidinediones are antidiabetic agents, which not only improve glucose metabolism but also reduce blood triglyceride concentrations. These compounds are synthetic ligands for PPAR gamma, a transcription factor belonging to the nuclear receptor subfamily of PPARs, which are important transcriptional regulators of lipid and lipoprotein metabolism. The goal of this study was to evaluate the influence of a potent thiazolidinedione, BRL49653, on serum lipoproteins and to determine whether its lipid-lowering effects are mediated by changes in the expression of key genes implicated in lipoprotein metabolism. Treatment of normal rats for 7 days with BRL49653 decreased serum triglycerides in a dose-dependent fashion without affecting serum total and HDL cholesterol and apolipoprotein (apo) A-I and apo A-II concentrations. The decrease in triglyceride concentrations after BRL49653 was mainly due to a reduction of the amount of VLDL particles of unchanged lipid and apo composition. BRL49653 treatment did not change triglyceride production in vivo as analyzed by injection of Triton WR-1339, indicating a primary action on triglyceride catabolism. Analysis of the influence of BRL49653 on the expression of LPL and apo C-III, two key players in triglyceride catabolism, showed a dose-dependent increase in mRNA levels and activity of LPL in epididymal adipose tissue, whereas liver apo C-III mRNA levels remained constant. Furthermore, addition of BRL49653 to primary cultures of differentiated adipocytes increased LPL mRNA levels, indicating a direct action of the drug on the adipocyte. Simultaneous administration of BRL49653 and fenofibrate, a hypolipidemic drug that acts primarily on liver through activation of PPAR alpha both decreased liver apo C-III and increased adipose tissue LPL mRNA levels, resulting in a more pronounced lowering of serum triglycerides than each drug alone. In conclusion, both fibrates and thiazolidinediones exert a hypotriglyceridemic effect. While fibrates act primarily on the liver by decreasing apo C-III production, BRL49653 acts primarily on adipose tissue by increasing lipolysis through the induction of LPL expression. Drugs combining both PPAR alpha and gamma activation potential should therefore display a more efficient hypotriglyceridemic activity than either compound alone and may provide a rationale for improved therapy for elevated triglycerides.

Sensitization of diabetic and obese mice to insulin by retinoid X receptor agonists.

Retinoic acid receptors (RAR), thyroid hormone receptors (TR), peroxisome proliferator activated receptors (PPARs) and the orphan receptor, LXR, bind preferentially to DNA as heterodimers with a common partner, retinoid X receptor (RXR), to regulate transcription. We investigated whether RXR-selective agonists replicate the activity of ligands for several of these receptors? We demonstrate here that RXR-selective ligands (referred to as rexinoids) function as RXR heterodimer-selective agonists, activating RXR: PPARgamma and RXR:LXR dimers but not RXR:RAR or RXR:TR heterodimers. Because PPARgamma is a target for antidiabetic agents, we investigated whether RXR ligands could alter insulin and glucose signalling. In mouse models of noninsulin-dependent diabetes mellitus (NIDDM) and obesity, RXR agonists function as insulin sensitizers and can decrease hyperglycaemia, hypertriglyceridaemia and hyperinsulinaemia. This antidiabetic activity can be further enhanced by combination treatment with PPARgamma agonists, such as thiazolidinediones. These data suggest that the RXR:PPARgamma heterodimer is a single-function complex serving as a molecular target for treatment of insulin resistance. Activation of the RXR:PPARgamma dimer with rexinoids may provide a new and effective treatment for NIDDM.

Identification, characterization, and tissue distribution of human peroxisome proliferator-activated receptor (PPAR) isoforms PPARgamma2 versus PPARgamma1 and activation with retinoid X receptor agonists and antagonists.

We describe the cloning, characterization, and tissue distribution of the two human peroxisome proliferator activated receptor isoforms hPPARgamma2 and hPPARgamma1. In cotransfection assays the two isoforms were activated to approximately the same extent by known PPARgamma activators. Human PPARgamma binds to DNA as a heterodimer with the retinoid X receptor (RXR). This heterodimer was activated by both RXR agonists and antagonists and the addition of PPARgamma ligands with retinoids resulted in greater than additive activation. Such heterodimer-selective modulators may have a role in the treatment of PPARgamma/RXR-modulated diseases like diabetes. Northern blot analysis indicated the presence of PPARgamma in skeletal muscle, and a sensitive RNase protection assay confirmed the presence of only PPARgamma1 in muscle that was not solely due to fat contamination. However, both PPARgamma1 and PPARgamma2 RNA were detected in fat, and the ratio of PPARgamma1 to PPARgamma2 RNA varied in different individuals. The presence of tissue-specific distribution of isoforms and the variable ratio of PPARgamma1 to PPARgamma2 raised the possibility that isoform expression may be modulated in disease states like non-insulin-dependent diabetes mellitus. Interestingly, a third protected band was detected with fat RNA indicating the possible existence of a third human PPARgamma isoform.

Effect of experimental nephrosis on hepatic lipoprotein secretion and urinary lipoprotein excretion in rats expressing the human apolipoprotein A-I gene.

When human apolipoprotein A-I was expressed in transgenic rats, induction of the nephrotic syndrome resulted in plasma A-I levels exceeding 10 mg/ml. Plasma lipids were no higher than in non-transgenic nephrotic rats. To explain this, the livers from four groups of rats were perfused: wild-type controls (WC), high expressor human apoA-I transgenic controls (TrGC), wild-type nephrotics (WN), and high expressor transgenic nephrotics (TrGN). Compared to the WC group, TrGC rats secreted the same amount of d < 1.063 g/ml lipoproteins but 50% more high density lipoprotein (HDL), with a 5-fold increase in total apoA-I output due to human apoA-I. Compared to the WC group, nephrosis in the WN rats caused a 2-fold increase in both d < 1.063 g/ml lipoproteins and HDL secretion with a 4.6-fold increase in rat apoA-I output. Compared to the TrGC group, nephrosis in the TrGN rats did not increase d < 1.063 g/ml lipoprotein secretion, but caused a 50% increase in HDL secretion and a 6-fold increase in human apoA-I output. The hepatic levels of mRNA for apoB and for HMG-CoA reductase, as well as the degree of apoB mRNA editing, were unchanged. Examination of the perfusate HDL by electron microscopy revealed spherical particles averaging 30 nm in diameter in the WC and WN rats and 17 and 20 nm in the TrGC and TrGN rats. Urinary HDL particles from the TrGN rats did not contain rat apoA-I and averaged 8.2 nm versus 11 nm in the WN rats. We conclude that the size of the nascent HDL, and subsequently of the mature HDL, is determined by the primary structure of apoA-I. In the TrGN rats, the heterogeneous mature HDL has a population of smaller human HDL which is more readily lost in the urine, accounting for the failure of plasma HDL levels to rise above those in TrGC rats. The fact that plasma triglyceride levels in TrGN rats were also not increased may relate to the failure of hepatic apoB secretion to increase, which in turn may have been due to saturation of the protein synthetic capacity by human apoA-I production.

Overexpression of human apolipoprotein A-I in transgenic rats and the hyperlipoproteinemia associated with experimental nephrosis.

Hyperlipoproteinemia contributes both to kidney disease progression and the development of atherosclerosis. Elevated high density lipoprotein cholesterol and apolipoprotein A-I (apoA-I) serum levels are independent factors protective against the atherosclerotic process. We examined the effects in a transgenic rat model of human apoA-I expression on the hyperlipoproteinemia and edema after puromycin aminonucleoside-induced nephrosis in three groups of animals: low line (TgR[hAI]low, human plasma apoA-I = 16.0 mg/dl); high line (TgR[hAI]high, 284 mg/dl); and non-transgenic litter mates (TgR[hAI]non). Nephrosis increased total plasma apoA-I levels 2-fold in TgR[hAI]non rats (75 vs. 162 mg/dl) and 4-fold in the TgR[hAI]low (97 vs. 458 mg/dl) and TgR[hAI]high rats (356 vs. 1,346 mg/dl). In both transgenic lines, this increase was due mainly to elevations of serum human apoA-I. The hepatic steady-state levels of rat apoA-I mRNA increased 5- to 7-fold in all three groups, while human apoA-I mRNA levels increased 21- and 65-fold in the low and high expressing groups, respectively, indicating a different degree of responsiveness of the rat and human genes. While nephrotic TgR[hAI]non and TgR[hAI]low rats showed severe hyperlipoproteinemia and edema, much lower levels of edema and of serum triglycerides, phospholipids, and cholesterol were seen in the TgR[hAI]high group. Urinary excretion of apoA-I, phospholipids, and cholesterol was significantly increased in the TgR[hAI]high group, indicating this as one possible mechanism for the relatively lower serum levels of these lipids. We conclude that the human apoA-I gene is responsive to nephrosis and that human apoA-I-transgenic rats with this syndrome provide an animal model for the study of human high density lipoprotein and apoA-I metabolism.

High level expression of human apolipoprotein A-I in transgenic rats raises total serum high density lipoprotein cholesterol and lowers rat apolipoprotein A-I.

To examine the consequences of increased apolipoprotein A-I production on cholesterol and lipoprotein metabolism, we have produced two lines of transgenic rats; one expressing moderate and one very high levels of human apolipoprotein A-I. The rats were produced by microinjection of a 13 kbp DNA fragment containing the human apolipoprotein A-I gene plus 10 kbp of its 5' flanking sequence and 1 kbp of its 3' flanking sequence. Both lines of transgenic rats express human apolipoprotein A-I mRNA in liver and human apolipoprotein A-I in plasma. Sera from these rats contain significantly higher levels of total apolipoprotein A-I, high density lipoprotein cholesterol and phospholipid than sera from non-transgenic littermates. Transgenic rats expressing high levels of human apolipoprotein A-I have reduced levels of serum rat apolipoprotein A-I suggesting a mechanism exists to down-regulate apolipoprotein A-I production. These transgenic rats provide a unique animal model to examine the effects of increased apolipoprotein A-I production on lipid and lipoprotein metabolism.

Nonimmunochemical quantitation of mammalian apolipoprotein A-I in whole serum or plasma by nonreducing gel electrophoresis.

A rapid and convenient method for the quantitation of mammalian apoA-I has been developed. The method involves nonreducing sodium dodecyl sulfate gel electrophoresis and Coomassie blue staining, and takes advantage of the relative abundance of apoA-I in whole serum or plasma. ApoA-I was sufficiently resolved to allow quantitation by laser densitometry or spectrophotometry. The assay was linear from 0.25 to 4.0 micrograms of apoA-I. Analytic recovery was 98%. Within-assay variability was 3.1% and between-assay variability was 7.5%. A high degree of positive correlative (r = 0.98) was observed with a human apoA-I radioimmunoassay. For several species investigated, the apoA-I values obtained correlated strongly and positively with high density lipoprotein cholesterol values. When applied to a study of nutritional perturbation in the Mongolian gerbil, the method detected sensible and significant changes in serum apoA-I that paralleled changes in HDL cholesterol.

Expression of lipoprotein lipase gene in combined lipase deficiency.

The expression of the gene for lipoprotein lipase (LPL) was studied in brown adipose tissue and the liver of combined lipase deficient (cld/cld) and unaffected mice. The mRNA specific for LPL was detected in both animals. Although the size of LPL mRNA in cld mice was similar to that of unaffected mice, the mRNA concentration in affected animals was higher than in unaffected animals. We also studied the LPL gene mutation in cld mice by Southern blot analysis. No restriction fragment length polymorphisms were observed after digestion with 16 endonucleases. These data indicate that there is no gene insertion or deletion, but do not exclude the possibility of point mutation in the LPL structural gene. However, the present results agree with the hypothesis that the genetic defect in cld is not due to a mutation in the LPL structural gene, but instead involves the defective post-translational processing of LPL or defective cellular function affecting transport and secretion of this enzyme group.

Interaction of lipoprotein lipase with heparin.

The hydrolysis of triglyceride-rich plasma lipoproteins is initiated by lipoprotein lipase (LPL) located at the luminal surface of endothelial cells. We previously reported that LPL binds to cultured endothelial cells with a Km of 2.7 x 10(-7) M and that this binding is inhibited by heparinase, heparin, or heparan sulfate. We and others recently isolated LPL cDNAs from various animals. The deduced amino acid sequence from cDNA sequence is highly conserved among animal species. The structural analysis revealed two regions rich in basic amino acid residues at the carboxyl-terminal region that may interact with the anionic heparin-like molecules. Amino acid residues 292 to 300 of bovine LPL are extremely similar to the reported heparin binding sites on apolipoproteins B-100 (amino acid residues 3359-3367) and E (amino acid residues 142-150).