Onset and development of hypertriglyceridemia in the Zucker rat (fa/fa)

Salmon Fillet Intake Led to Higher Serum Triacylglycerol in Obese Zucker Fa/Fa Rats But Not in Normolipidemic Long-Evans Rats

The triacylglycerol lowering effect of fatty fish and fish oils is well recognized, however we recently showed that salmon intake resulted in higher serum triacylglycerol concentration in obese Zucker fa/fa rats. Since effects of salmon fillet have never before been studied in rats, the objective of this study was to compare effects of salmon intake on serum lipids in hyperlipidemic obese rats with normolipidemic lean rats. Zucker fa/fa rats and Long-Evans rats were fed diets with 25% protein from baked salmon fillet and 75% protein from casein, or casein as sole protein source (control group) for four weeks. Serum triacylglycerol concentration was higher, and cholesterol and apolipoproteinB-100 concentrations were lower in Zucker fa/fa rats fed Baked Salmon Diet compared to Zucker fa/fa rats fed Control Diet, with no differences in serum triacylglycerol, cholesterol and apolipoproteinB-100 between Long-Evans rats fed Baked Salmon Diet or Control Diet. Serum triacylglycerol fatty acid composition showed greater similarities to dietary fatty acids in Zucker fa/fa rats than in Long-Evans rats. To conclude, intake of baked salmon fillet resulted in higher serum triacylglycerol concentration and lower serum cholesterol concentration in hyperlipidemic obese Zucker fa/fa rats but did not affect serum lipids in normolipidemic lean Long-Evans rats.

The Plasmodium liver-stage parasitophorous vacuole: A front-line of communication between parasite and host

The intracellular development and differentiation of the Plasmodium parasite in the host liver is a prerequisite for the actual onset of malaria disease pathology. Since liver-stage infection is clinically silent and can be completely eliminated by sterilizing immune responses, it is a promising target for urgently needed innovative antimalarial drugs and/or vaccines. Discovered more than 65 years ago, these stages remain poorly understood regarding their molecular repertoire and interaction with their host cells in comparison to the pathogenic erythrocytic stages. The differentiating and replicative intrahepatic parasite resides in a membranous compartment called the parasitophorous vacuole, separating it from the host-cell cytoplasm. Here we outline seminal work that contributed to our present understanding of the fundamental dynamic cellular processes of the intrahepatic malarial parasite with both specific host-cell factors and compartments.

Maternal diabetes in pregnancy: early and long-term outcomes on the offspring and the concept of "metabolic memory"

The adverse outcomes on the offspring from maternal diabetes in pregnancy are substantially documented. In this paper, we report main knowledge on impacts of maternal diabetes on early and long-term health of the offspring, with specific comments on maternal obesity. The main adverse outcome on progenies from pregnancy complicated with maternal diabetes appears to be macrosomia, as it is commonly known that intrauterine exposure to hyperglycemia increases the risk and programs the offspring to develop diabetes and/or obesity at adulthood. This “fetal programming”, due to intrauterine diabetic milieu, is termed as “metabolic memory”. In gestational diabetes as well as in macrosomia, the complications include metabolic abnormalities, degraded antioxidant status, disrupted immune system and potential metabolic syndrome in adult offspring. Furthermore, there is evidence that maternal obesity may also increase the risk of obesity and diabetes in offspring. However, women with GDM possibly exhibit greater macrosomia than obese women. Obesity and diabetes in pregnancy have independent and additive effects on obstetric complications, and both require proper management. Management of gestational diabetes mellitus and maternal obesity is essential for maternal and offspring's good health. Increasing physical activity, preventing gestational weight gain, and having some qualitative nutritional habits may be beneficial during both the pregnancy and offspring's future life.

Role of lipids and fatty acids in macrosomic offspring of diabetic pregnancy

Diabetic pregnancy frequently results in macrosomia or fetal obesity. It seems that the anomalies in carbohydrate and lipid metabolism in macrosomic infants of diabetic mothers are due to maternal hyperglycemia, which leads to fetal hyperinsulinemia. We have developed a rat model of macrosomic offspring and assessed the onset of obesity in these animals. The macrosomic offspring born to diabetic mothers are prone to the development of glucose intolerance and obesity as a function of age. It seems that in utero programming during diabetic pregnancy creates a "metabolic memory" which is responsible for the development of obesity in macrosomic offspring. We have demonstrated that the metabolism of lipids, and altered anti-oxidant status and immune system are implicated in the etiopathology of obesity in these animals. We have reported beneficial effects of n-3 polyunsaturated fatty acids (PUFAs) in obese animals, born to diabetic dams.

Modulation of lipid metabolism by n-3 polyunsaturated fatty acids in gestational diabetic rats and their macrosomic offspring

The time course of changes in lipid metabolism by dietary n-3 PUFAs (polyunsaturated fatty acids) in streptozotocin-induced diabetic rats during pregnancy (days 12 and 21) and their macrosomic offspring at birth (day 0) and through adulthood (days 60 and 90) was studied with respect to adipose tissue, liver and serum lipid concentrations, and fatty acid composition. Glucose and insulin levels were also assessed in order to characterize the diabetic state of macrosomic offspring. Pregnant diabetic and control rats were fed either an Isio-4 or EPAX diet (enriched with n-3 PUFA). The same diets were also consumed by pups at weaning. Compared with control rats, during pregnancy diabetic rats had a significant elevation in liver and serum triacylglycerol (triglyceride) and cholesterol concentrations. At birth, macrosomic pups had higher serum insulin and glucose levels than control pups. The macrosomic rats maintained accelerated postnatal growth combined with high adipose tissue weight and lipid content through the first 12 weeks of age. The macrosomic pups from diabetic rats fed the Isio-4 diet also showed a significant enhancement in liver and serum triacylglycerol and cholesterol levels at birth and during adulthood. Feeding the EPAX diet to diabetic mothers as well as their macrosomic pups increased serum and liver levels of EPA (eicospentaenoic acid) and DHA (docosahexaenoic acid) with a reduction in arachidonic acid. The EPAX diet induced a significant decrease in liver and serum triacylglycerol and cholesterol concentrations in mothers during pregnancy and in their macrosomic pups during adulthood. Since the EPAX diet improves lipid anomalies considerably in diabetic mothers and their macrosomic offspring, it may prevent long-term metabolic abnormalities associated with macrosomia.

Impaired lipoprotein metabolism in obese offspring of streptozotocin-induced diabetic rats

The time course of changes in lipoprotein metabolism of obese offspring of mildly diabetic rats was studied with respect to serum lipoprotein composition as well as LCAT and tissue lipoprotein lipase (LPL) activities. Mild hyperglycemia in pregnant rats was induced by intraperitoneal injection of streptozotocin on day 5 of gestation. Control pregnant rats were injected with citrate buffer. At birth, obese pups had higher serum glucose, insulin, and lipoprotein (VLDL, LDL-HDL1, HDL(2-3)) levels than control pups. After 1 mon of life, all of these parameters in obese rats became similar to those of controls. However, LCAT, adipose tissue LPL, and hepatic triacylglycerol lipase activities were high. At 2 mon of age, VLDL-TAG levels were higher in obese females than in controls. By the age of 3 mon, obese offspring had developed insulin resistance with hyperglycemia, hyperinsulinemia, and higher serum lipoprotein concentrations. Indeed, qualitative abnormalities of lipoproteins were seen and were typical of obese and diabetic human beings. Fetal hyperinsulinemia should be considered as a risk factor for later metabolic diseases, including dyslipoproteinemia.

Effect of oral oleoyl-estrone treatment on plasma lipoproteins and tissue lipase activities of Zucker lean and obese female rats

OBJECTIVE

To study the effect of oral oleoyl-estrone on the plasma lipoprotein profile and tissue lipase activities in order to determine the handling of circulating lipids by adipose tissue, liver and muscle of obese female rats.

DESIGN

Lean (Fa/?) and obese (fa/fa) female Zucker rats treated for 10 days with a daily gavage of 0.2 ml sunflower oil containing 0 (controls) or 10 micromol/kg of oleoyl-estrone. After sacrifice, samples of tissues and plasma were taken.

MEASUREMENTS

Plasma lipoprotein classes and composition; lipoprotein lipase and hepatic lipase activities in plasma, liver, skeletal muscle and periovaric and mesenteric white adipose tissue (WAT).

RESULTS

Oleoyl-estrone decreased plasma cholesterol (mainly in HDLs: 76%) of lean rats, but dramatically decreased all lipid classes in obese rats, in which chylomicra and VLDL lost most of their triacylglycerols (95 and 81%, respectively). Hepatic lipase activity decreased markedly with oleoyl-estrone in all groups, both in plasma (79% lean, 100% obese) and liver (62% in both groups). Lipoprotein lipase activity was largely unchanged by oleoyl-estrone in lean rats, but in the obese it decreased in WAT (82% in periovaric, and 49% in mesenteric), and increased in plasma (x4) and in skeletal muscle (x5); liver levels showed no change.

CONCLUSIONS

The shift observed in obese rats from a decrease in liver and WAT lipoprotein lipase and hepatic lipase activities to an increase in muscle lipoprotein lipase is coincident with the hypolipemic effect of oleoyl-estrone, especially in obese rats, and indicates that muscle is a key site for the disposal of endogenous fat mobilized due to oleoyl-estrone treatment.

Developmental changes in adipose and muscle lipoprotein lipase activity in the atherosclerosis-prone JCR:LA-corpulent rat

OBJECTIVE

To characterize the developmental changes in adipose and muscle lipoprotein lipase (LPL) activity in the atherosclerosis-prone JCR:LA-corpulent rat, and to test the hypothesis that tissue-specific abnormalities in LPL activity precede the establishment of obesity.

DESIGN

Lean (+/?) and obese cp/cp male JCR:LA rats were studied at 4, 5 and 8 weeks of age, that is at the onset of obesity, and at a time when obesity is well established. Assessment was made of plasma variables related to glucose and lipid metabolism and of LPL activity in several adipose depots, skeletal muscles and the heart.

RESULTS

At week 4, body weights were identical in both genotypes and began to diverge at week 5. Eight-week-old cp/cp rats weighed 35% more than their lean counterparts. Perirenal and epididymal adipose depot weights were also identical in both genotypes at week 4 and began to increase in cp/cp rats at week 5, whereas the subcutaneous depot of 4-week-old cp/cp rats was slightly enlarged. At week 4, the cp/cp rats were hyperinsulinemic (5-fold), hyperleptinemic (30-fold) and hypertriglyceridemic (3-fold) compared to their lean counterparts, and their liver contained twice as much triglyceride. The 4-week-old cp/cp rats displayed 2-7-fold higher LPL specific activity in the various adipose depots compared to lean rats, and enzyme activity remained higher in obese than in lean rats at all subsequent ages. In contrast, LPL activity in the vastus lateralis, gastrocnemius and heart muscles of 4-week-old obese rats was approximately half that observed in lean animals.

CONCLUSION

Profound, persistent alterations in the tissue-specific modulation of LPL activity are established in the JCR:LA cp/cp rat prior to the development of frank obesity. The increase in adipose tissue LPL activity and its decrease in muscle tissues are likely to be related to the concomitant alterations in insulinemia and triglyceridemia, respectively. The pre-obesity, tissue-specific alterations in LPL activity may be considered as an integrated adaptation to increased lipid flux aimed at driving lipids toward storage sites and limiting their uptake by triglyceride-laden muscles.

Adipose tissue-specific increase in angiotensinogen expression and secretion in the obese (fa/fa) Zucker rat

We investigated angiotensinogen (AGT) expression in adipose tissue and liver of Zucker rats during the onset of obesity. The developmental pattern of AGT expression (protein and mRNA) in liver was similar in both genotypes. In inguinal adipose tissue, AGT cell content was similar in suckling and weaned pups in lean rats, whereas it continuously increased with age in obese rats. AGT amount in adipocytes was unaffected by the genotype until weaning. Thereafter, adipocytes from obese rats displayed a significant increase in AGT content that was strengthened with age. Compared with the cell content, the amount of secreted AGT over 24 h was higher, and a genotype effect was observed as early as 14 days of age. Using fat cell populations differing by size, we showed that this AGT oversecretion was not solely related to adipocyte hypertrophy. Our results demonstrate that the fa genotype exerts a control on the production of AGT in a tissue-specific manner, suggesting a local role of AGT in the overdevelopment of adipose tissue.

Dietary oligofructose lessens hepatic steatosis, but does not prevent hypertriglyceridemia in obese zucker rats

We studied the influence of oligofructose (OFS), a nondigestible fructan, on lipid metabolism in obese fa/fa Zucker rats. The addition of 10 g/100 g OFS to the diet slowed the increase in body weight without modifying serum triglycerides or glucose concentrations after 7 wk of treatment. However, an oral load of 2 g glucose and 5 g corn oil/kg body weight increased triglyceridemia more in OFS-fed rats than in control rats. After 10 wk, OFS decreased the hepatic concentration of triglycerides 57% relative to controls. The less severe steatosis was confirmed by histologic analysis. Among the key enzymes involved in fatty acid synthesis and esterification, only malic enzyme activity was significantly lower in OFS-fed rats than in controls. The epididymal fat mass was significantly lower in OFS-fed rats. In conclusion, dietary enrichment with OFS can counteract both the fat mass development and the hepatic steatosis that occur in obese Zucker rats. Future studies will be designed to clarify in obese animals the influence of dietary OFS on postprandial triglyceridemia, which is an important variable associated with the development of atherosclerosis in humans, and to analyze the biochemical mechanism underlying the "hepatoprotective" effect of OFS.

The db/db mouse, a model for diabetic dyslipidemia: molecular characterization and effects of Western diet feeding

Diabetic dyslipidemia is a major factor contributing to the accelerated atherosclerosis in type 2 diabetes mellitus. Although several mouse models are available, the plasma lipoproteins in response to diet have not been fully characterized in these animals. In this study, we have characterized the plasma lipoproteins and related apolipoproteins, as well as the vascular lipases, in diabetes (db/db) mice and their nondiabetic controls (+/?) in the C57BL/KsJ strain. Within 6 weeks of age, db/db mice developed significant obesity, fasting hyperglycemia, and hyperinsulinemia. By FPLC analysis, db/db mice showed a prominent peak in the low-density lipoprotein (LDL) range that was absent in +/? mice, although high-density lipoprotein (HDL) was the predominant species in both groups of animals. Postheparin lipoprotein lipase (LPL) activity in db/db mice was 28% of the level in +/? mice. Upon feeding a human-like 0.15% (wt/wt) cholesterol and 21% (wt/wt) fat "Western" diet, db/db mice developed elevated plasma cholesterol, accompanied by an exaggerated apolipoprotein E (apoE) response compared with +/? mice. FPLC analysis showed that the marked hypercholesterolemic response in db/db mice was the result of a massive increase in the LDL region, which overshadowed a moderate increase in HDL. We next isolated lipoproteins by ultracentrifugation and characterized them by nondenaturing gradient gel electrophoresis. With regular chow, db/db mice had almost exclusively small dense LDL with a peak size at 21.4 nm, as compared with 26.6 nm in nondiabetic controls. On the Western diet, the small dense LDLs persisted but larger particles also appeared in db/db mice, whereas the size distribution in +/? mice was unchanged by the diet. Our results suggest that db/db mice fed a Western diet have a plasma lipoprotein phenotype that shows some similarities to that in patients with type 2 diabetes mellitus, and that db/db mice are a useful model to study the pathogenesis and treatment of diabetic dyslipidemia.

Dietary fat is shunted away from oxidation, toward storage in obese Zucker rats

Previous measurements of lipoprotein lipase (LPL) activity in adipose tissue (ATLPL) of lean and obese Zucker rats have consistently documented increased activity in obese rats relative to lean. Since LPL is considered to be rate limiting for the delivery of triglyceride fatty acids (TGFA) to muscle and adipose tissue, these data have been used to suggest that the metabolic partitioning of TGFA favors storage over oxidation in obese rats. To document the partitioning of TGFA directly, the fate of 14C labeled oleic acid (42nmols) was fed to lean, obese, and obese Zucker rats fed a hypocaloric diet designed to chronically reduce weight 25% below that of obese controls (reduced-obese). The amount of 14C recovered in CO2 over 6 hours following ingestion was significantly less in obese rats compared to lean (0.45 +/- 0.06 vs. 0.88 +/- 0.09nmols, p = .0004) and less still in the reduced obese group (0.34 +/- 0.06nmols p = .00003). Six hours after ingestion, the quantity of label found in adipose tissue was significantly greater in the obese rats compared to lean (14.51 +/- 1.92 vs. 1.38 +/- 0.29nmols p < .00001), but was intermediate in the reduced-obese group (9.23 +/- 0.98nmols p = .0003). At 2.2 hours there was significantly more label in skeletal muscle of lean rats compared to either obese or reduced-obese (2.33 +/- 0.24; 1.35 +/- 0.04nmols p = .01; 1.41 +/- 0.27nm p = .02). However, at 6 hours these differences between groups were no longer present. These finding Indicate that dietary fat is shunted away from oxidation toward storage in obese Zucker rats. Additionally it appears that there may be a relative block in the oxidation of TGFA that is taken up by skeletal muscle in obese rats. Finally the relative normalization of this partitioning defect in reduced-obese rats is at variance with what was suggested by previous measurements of tissue specific levels of LPL, and suggests an enhanced recirculation of fatty acids from adipose tissue to muscle in reduced-obese rats. This could occur through increased delivery of non-esterified fatty acids (NEFA) to muscle as a result of an increase in net lipolysis.

Evidence for a sustained genetic effect on fat storage capacity in cultured adipose cells from Zucker rats

Using mature adipocytes and preadipocytes from genetically obese Zucker rats, we investigated the cells' ability to maintain abnormal fat storage capacity when withdrawn from their in vivo environment. Long-term adipocyte cultures from obese rats displayed an increase in both glucose consumption (GC) and enzyme activities, including fatty acid synthase (4-fold), glycerol-3-phosphate dehydrogenase (4.5-fold), lipoprotein lipase (LPL; 6-fold), and malic enzyme (2.5-fold). Fully differentiated obese predipocytes exhibited a twofold increase in these enzyme activities, together with higher glucose metabolism. In obese cells, LPL mRNA was increased in both adipocytes (6-fold) and differentiated preadipocytes (2-fold). Insulin mediated an increase in GC and lipogenic enzymes in both adipocytes and preadipocytes regardless of the genotype; this effect was more marked in obese cells. Examining cultured adipocytes from rats fed a high-fat diet, we showed that the nutritional effect upon GC and lipogenic enzymes was abolished after culture. These results demonstrated that fatty mutation may be intrinsically expressed in prolonged cultured mature adipocytes and in newly differentiated adipocytes.

Angiotensin II in brown adipose tissue from young and adult Zucker obese and lean rats

Previous studies demonstrated that interscapular brown adipose tissue (ISBAT) produces angiotensin II (ANG II), which facilitates sympathetic neurotransmission (SN). ANG II content and regulation of SN were examined in young (17 days) and adult (16 wk) Zucker obese and lean rats. ANG II content in ISBAT from preobese rats was decreased compared with lean littermates. Evoked 3H overflow in ISBAT slices preloaded with [3H]NE was greater in preobese rats compared with control. ANG II increased evoked 3H overflow in ISBAT slices to a greater extent in preobese rats compared with control. [3H]NE uptake in ISBAT slices from preobese rats was decreased compared with control. In adult obese rats, plasma renin activity was decreased compared with control. ISBAT ANG II content was increased in adult obese rats compared with control. Evoked 3H overflow in ISBAT slices preloaded with [3H]NE was not different between obese and control. ANG II did not increase evoked 3H overflow in obese rats; however, ANG II increased evoked 3H overflow in lean rats. [3H]NE uptake in ISBAT slices from obese rats was decreased compared with control. These results suggest that ANG II modulation of SN activity is decreased in ISBAT from adult obese rats. In contrast, in young obese rats, increased SN activity and ANG II regulation of SN were evident in brown adipose tissue.

Marked enhancement of acyl-CoA synthetase activity and mRNA, paralleled to lipoprotein lipase mRNA, in adipose tissues of Zucker obese rats (fa/fa)

To clarify the role of acyl-CoA synthetase in development of obesity, the mRNA levels and activities were studied in Zucker fatty rats (fa/fa). In Zucker fatty rats compared with their lean littermates, marked enhancement of ACS were observed in adipose tissues. Obese/lean rats ratio of ACS activity and mRNA in abdominal subcutaneous fat (3.3- and 3.9-fold, respectively) were greater than in mesenteric fat (2.0- and 2.2-fold). The enhancement of ACS activity and mRNA in the liver of fatty rats (1.2- and 1.8-fold) were less than those in the adipose tissues. There were no enhancement of ACS activities and mRNA levels in heart tissue of the obese rats. LPL mRNA levels were also enhanced in adipose tissue of fatty rats and obese/lean ratio of LPL mRNA was also higher in abdominal subcutaneous fat than mesenteric fat (6.2- vs 3.1-fold). The larger obese/lean rats ratio of LPL and ACS parameters in abdominal subcutaneous fat than mesenteric fat may be related to the observation that the increase of subcutaneous fat weight was larger than that of mesenteric fat weight in fatty rats (21.1- vs 4.9-fold). Integrated enhancement of LPL and ACS gene expression in adipose tissue may play an important role in the development of obesity.

Gene expression of lipid storage-related enzymes in adipose tissue of the genetically obese Zucker rat. Co-ordinated increase in transcriptional activity and potentiation by hyperinsulinaemia

The genetically obese Zucker rat displays excessive fat storage capacity which is due to a tissue-specific increase in the activities of a number of lipid storage-related enzymes in adipose tissue. The aim of this study was to investigate the molecular mechanism responsible for this phenomenon. Lean (Fa/fa) and obese (fa/fa) Zucker rats were studied during the early stages of adipose tissue overdevelopment, both before (at 16 days of age) and after (at 30 days of age) the emergence of hyperinsulinaemia, in order to delineate the effects of the fatty genotype independently of those of hyperinsulinaemia. Lipoprotein lipase (LPL), glycerophosphate dehydrogenase (GPDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and malic enzyme (ME) mRNA levels in the adipose tissue of lean and obese rats were assessed by Northern blot analysis, and the relative transcription rates of the corresponding genes were compared in the two genotypes by a nuclear run-on assay. In normoinsulinaemic 16-day-old pre-obese rats, mRNA levels were increased over control values (LPL, 5-fold; ME, 2-fold; GAPDH, 3-fold), in close correlation with genotype-mediated differences in enzyme activities. Stimulation of the transcription rates of the ME and GAPDH genes was observed in obese rats, which could fully account for differences in steady-state mRNA levels. At this age, GPDH activity, mRNA level and transcription rate were similar in the two genotypes. In hyperinsulinaemic 30-day-old obese rats, a 6-7-fold increase in both mRNA and the transcription rate of GPDH emerged, together with an amplification of the genotype-mediated differences observed in younger animals (GAPDH, 6-fold; ME, 7.9-fold; LPL, 10-fold). These results demonstrate that the obese genotype exerts a co-ordinated control on the expression of these genes in adipose tissue, mainly at the transcriptional level. This genotype effect is greatly amplified by the development of hyperinsulinaemia.

Computation of the effective body mass for metabolic studies of lean and obese rats

The whole-animal metabolic rates of lean and obese rats cannot be directly compared because obese rats have much greater body mass than lean rats. Expressing the results as metabolic rate per unit of body mass is also not satisfactory because lean and obese rats of the same size have different body compositions. To make possible comparisons between the two types of rats, metabolic rate must be expressed per unit of effective body mass. Effective body mass for lean and obese Zucker rats can be calculated as 1.00 M0.75 and 0.82 M0.75, respectively, where M is the mass of the animal.

Postnatal recruitment of brown adipose tissue is induced by the cold stress experienced by the pups. An analysis of mRNA levels for thermogenin and lipoprotein lipase

In order to investigate the postnatal recruitment process, gene expression in the brown adipose tissue of rat pups was followed during the first 20 h of life. In normal pups, the level of mRNA coding for the uncoupling protein thermogenin increased markedly but gradually within the first 24 h. Lipoprotein lipase and actin mRNA levels were relatively low and remained constant. In pups exposed to thermoneutral temperature (35 degrees C) for the first 12 h after birth, no increase in thermogenin mRNA or lipoprotein lipase mRNA was observed, whereas in pups exposed to 28 degrees C a clear increase in both thermogenin and lipoprotein lipase mRNA levels was found. Actin mRNA levels were not affected by the environmental temperature under these circumstances. It was concluded that the postnatal recruitment in brown adipose tissue is a consequence of the cold stress experienced by the newborn pups. Thus, postnatal recruitment is not ontogenically predetermined.

Effects of reduced renal mass on tissue lipids and renal injury in hyperlipidemic rats

Increasing evidence from experimental models of chronic renal failure suggests that abnormalities in lipid metabolism may contribute to progressive renal injury. In the present study, hyperlipidemic obese, and normolipemic lean Zucker rats were subjected to unilateral nephrectomy or sham surgery at eight weeks of age. After 32 weeks, renal injury was greater in obese than in lean rats, and injury was made worse by nephrectomy. Among the major lipid classes, increased renal cortical cholesteryl esters were positively correlated with the degree of renal injury, suggesting that mechanisms analogous to those thought to be important in the pathogenesis of atherosclerosis may cause renal injury. Among phospholipid fatty acids, the ratio of oleic to linoleic acids (18:1/18:2) was strongly linked to both glomerular (r = 0.83, P less than 0.01) and tubulo-interstitial (rr = 0.80, P less than 0.01) injury, suggesting a possible role for a relative essential fatty acid deficiency in renal injury. There were also strong, negative associations between eicosapentaenoic acid levels and glomerular (r = -0.63, P less than 0.01) and tubulointerstitial (r = -0.71, P less than .01) injury. Altogether, these results suggest that specific abnormalities in renal lipid metabolism may be important in the pathogenesis of chronic, progressive renal injury.

Intestinal very-low-density lipoprotein secretion in the genetically obese Zucker rat

The objectives of this study were to measure intestinal very-low-density lipoprotein (VLDL) production in obese Zucker rats and to assess an eventual effect of a high-fat diet. VLDL secretion was specifically inhibited by orotic acid, and intestinal VLDL output was measured following the Triton WR-1339 method. After a control diet, total VLDL secretion (without orotic acid) was 4.8 +/- 0.3 and 1.4 +/- 0.1 mg triacylglycerol/ml in obese and lean rats, respectively, decreasing by 30% in obese rats after fat-feeding. Intestinal VLDL production was similar in obese and lean rats fed the control diet (0.32 +/- 0.05 and 0.27 +/- 0.05 mg triacylglycerol/ml, respectively), increasing 2.5-fold after fat-feeding in both genotypes. Thus, intestine contributed 21 and 60% of total VLDL in lean but only 7 and 24% in obese rats with the control and high-fat diets, respectively. These results show that the intestine of obese Zucker rats does not contribute to their hypertriglyceridemia, suggesting that it originates solely from liver. Moreover, their intestinal VLDL production was stimulated by fat-feeding to the same extent as in lean animals.

Lipoprotein secretion in lean and obese Zucker female rats in vivo and in a single-pass-perfused liver preparation

The plasma lipoprotein composition as well as lipoprotein synthesis and secretion were studied in vivo and in a single-pass-perfused liver preparation in lean and obese Zucker rats. Compared with their lean littermates the levels in the plasma of very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) + low density lipoprotein (LDL) and high density lipoprotein (HDL) were increased 4-, 2- and 2.5 fold, respectively, in obese rats. In these rats both VLDL and IDL + LDL were enriched in triglycerides, while the HDL were enriched in cholesterol. Although the VLDL and IDL + LDL protein concentrations were the same in lean and obese rats, the HDL protein concentration was 3-fold greater in the obese rats. Both the lean and obese rats incorporated similar amounts of [14C]leucine into total liver protein. However, obese rats incorporated 2.5-fold and 6-fold more [14C]leucine into VLDL and HDL in vivo, 2.7-fold and 1.7 fold more [35S]methionine in VLDL and HDL present in the perfusate, than did lean rats. The perfusate [35S]S-labelled apoproteins (apo-B100, B48; apo-E, apo-AI, apo-AIV and apo-C) were separated by gel electrophoresis and identified by autoradiography. Incorporation of [3H]glycerol into liver, VLDL, IDL + LDL and HDL triglycerides was 2-, 48-, 13- and 1.5-fold higher in obese than in lean rats, respectively. The [3H]-labelled triglycerides in VLDL and IDL + LDL present in the perfusate was 5.4-fold and 4.4-fold more in obese rat. There was no difference in the incorporation of [3H]glycerol into triglycerides of perfusate HDL between the two genotypes of rats. Thus, the hypertriglyceridaemia observed in obese Zucker rats results from very high synthetic rates of both the lipid and protein moieties of plasma lipoproteins. Before this study, no report of the simultaneous triglycerides and protein synthesis in vivo and in a single-pass-perfused liver preparations had been reported.

Effect of long-term clofibric acid treatment on serum and tissue lipid and cholesterol levels in obese Zucker rats

The long-term effects of clofibric acid (200 mg/kg body weight) injected subcutaneously from 6-36 weeks of age were assessed in obese, hyperlipemic Zucker rats. At 18 and 36 weeks of age, treated rats had significantly lower fasted serum cholesterol levels but triacylglycerol levels were not affected. Rats were killed at 36 weeks of age at which time there were no differences in body and kidney weights between control and clofibric acid-treated rats. Liver, spleen and heart weights were lowered by clofibric acid treatment. In liver there was an elevation of lipid/g due to treatment but there were no effects on cholesterol/g or on either total liver lipid or cholesterol levels. In the epididymal fat pad of clofibric acid-treated rats, there was a 21% elevation of cholesterol level on a per pad basis. In the other organs, there were no effects of treatment on lipid or cholesterol levels except for lowered total cholesterol in kidney. Several liver lipogenic enzymes were lowered by treatment but malic enzyme was two times higher.

Pharmacologic action of L-carnitine on hypertriglyceridemia in obese Zucker rats

Administration of pharmacologic amounts of L-carnitine was studied in the hypertriglyceridemic Zucker rat. When administered subcutaneously, doses from 250 to 2,000 mg/kg/d significantly decreased plasma triglycerides in obese rats over eight to 12 weeks, with no effect on plasma triglycerides in lean rats. Oral doses at the same high levels were not effective in decreasing plasma triglycerides. Triglyceride secretion rate was reduced from 367 micrograms/min to 168 micrograms/min in treated obese rats. Concurrently, liver lipid was increased twofold in obese treated rats, and the livers of these rats showed significant fatty infiltration. The mechanism of action of carnitine in decreasing plasma triglycerides appeared to be via decreased secretion of triglycerides by the liver of obese rats. There was no effect of L-carnitine in lean or obese rats on the following variables: carnitine palmitoyltransferase-A kinetics or malonyl CoA inhibition, mitochondrial or peroxisomal oxidative capacity, lipoprotein lipase in heart, muscle, and adipose, or fecal lipids. The effect of pharmacologic L-carnitine thus appears to be an inhibition of triglyceride synthesis and/or secretion by the liver.

Effects of cold acclimation on the activity of lipoprotein lipase in adipose tissues of genetically obese Zucker rats

The activity of lipoprotein lipase (LPL) was studied in interscapilar brown adipose tissue (BAT), epididymal white adipose tissue (WAT) and in the heart of lean and obese adult Zucker rats maintained at 22 degrees C or adapted to cold (10 degrees C). In WAT the specific activity per gram of tissue was lower in obese than in lean rats but the total activity within the tissue was three-fold higher. Cold acclimation did not modify total activity in either lean or obese rats. In BAT, but not in the heart, both specific and total activities were lower in obese than in lean animals. They were enhanced in both tissues following cold acclimation. Six-hour fasting led to a decrease in specific activity in WAT of lean rats but had no effect in obese animals; an increase was observed in BAT and heart of both genotypes. Insulin administration has no effect on activities in WAT in either 22 or 10 degrees C adapted obese rats. Norepinephrine administration stimulates LPL activity in BAT and heart of all groups. It is concluded that the lack of development of obesity previously observed in obese rats following cold acclimation is not due to a decreased capacity of lipid uptake by WAT. It might in part be due to an increased lipid oxidation in BAT.

Development of fatty acid-synthetic capacity in interscapular brown adipose tissue during suckling in genetically obese Zucker rats

The development of the lipogenic capacity in brown adipose tissue was studied in suckling lean (Fa/fa) and obese (fa/fa) Zucker pups aged from 7 to 22 days. In both lean and obese pups, activities of the two key lipogenic enzymes, fatty acid synthetase and acetyl-CoA carboxylase, and of citrate cleavage enzyme rose from the early to the late suckling period. Compared with lean pups, 7-day-old fa/fa pups showed a 35% increase in fat accumulation in interscapular brown adipose tissue and a 25% increase in fatty acid synthetase activity. By 10 days of age, fat deposition, lipogenesis in vivo (assessed by the incorporation of 3H from 3H2O into fatty acids) and fatty acid synthetase activity were 1.5-2-fold higher in pre-obese than in lean pups. Compared with lean pups, the increased lipogenesis in vivo observed in brown adipose tissue of 10-day-old pre-obese pups could not entirely account for the difference in fat deposition observed in this tissue, suggesting that additional mechanisms are at play to explain the increased fat content of this tissue.

Evidence of a defect in energy expenditure in 7-day-old Zucker rat (fa/fa)

The aim of the investigation was to see whether a defect in energy expenditure could be found in the Zucker rat at the onset of obesity. Obese (fa/fa) and lean (Fa/fa) 7-day-old pups were studied at three ambient temperatures. At 33 degrees C fa/fa pups showed a reduction in oxygen consumption, respiratory CO2 production, in vivo oxidation of injected [1-14C]palmitic acid, as well as in core temperature. When the pups were kept at 28 degrees C, the difference between genotypes was considerably accentuated, thus indicating a subnormal thermogenic response of the fa/fa pups to a mildly cold environment. At 20 degrees C, however, the metabolic rates dropped to the same low level, and the core temperature equilibrated with ambient temperature in both genotypes. The results demonstrate that the 1-wk-old fa/fa pup has a defect in thermoregulatory thermogenesis. The magnitude of the deficit in energy expenditure was more than adequate to account for the 50% greater fat content of 7-day-old fa/fa pups.

Lipogenesis in primary cultures of adipoblasts derived from genetically obese Zucker rats

Adipocyte precursor cultures prepared from the epididymal fat pads of genetically obese (fa/fa) and lean (Fa/Fa) Zucker rats grow similarly in culture. Addition of enriched medium (EM) containing human serum, insulin, and glucose stimulated lipid filling of the adipocyte precursors in both cultures. However, [3H] H2O incorporation into total lipids, fatty acid synthetase and lipoprotein lipase activities, and cytosolic protein contents are all decreased in the fa/fa compared with the Fa/Fa cultures. Substitution of lean or obese rat serum for human serum in the enriched medium does not alter the decreased lipogenic capacity of the fa/fa adipocyte precursor cultures.

Changes in the activities of lipoprotein lipase and the lipogenic enzymes in tumor-bearing rats

The effects of tumor growth on lipid metabolism were investigated by evaluating serum lipids, lipoprotein lipase activity (LPLA), the lipogenic enzymes, urinary catecholamines along with serum insulin and glucagon levels. We injected 1.5 X 10(6) cells of rat mammary tumor, AC33, and killed the rats on the 18th day. Serum triglycerides and free fatty acids of the tumor-bearing (TB) rats increased 4 and 5 times, respectively, more than the control (C) rats. Total liver lipids were not significantly different between the two groups. Tumor growth produced a 70% decrease in total epididymal fat pad LPLA; there were no changes in soleus muscle LPLA. Serum insulin levels of the TB rats were 49% less than the C rats. The TB rats had significantly lighter epididymal fat pads and lower activities of adipose fatty acid synthetase and citrate cleavage enzyme. Urinary catecholamines of the TB rats were reduced over 30% compared with the C rats. These results show that the hypertriglyceridemia of the TB rats may be due, in part, to a deficiency of adipose tissue LPLA. The data also suggest that the effects of the tumor on lipid metabolism may be mediated through insulin.

Evidence for a high fatty acid synthesis activity in interscapular brown adipose tissue of genetically obese Zucker rats

Obese (fa/fa) rats (30 days old) exhibited a 50% increase in the weight of interscapular brown adipose tissue compared with their lean (Fa/fa) littermates. The tissue weight increase was accounted for by an increased fat content. Lipogenesis in vivo, as assessed by the incorporation of 3H from 3H2O into lipid, was increased 5-fold in brown adipose tissue of obese as compared with lean rats. Accordingly, acetyl-CoA carboxylase, fatty acid synthetase, citrate-cleavage enzyme and malic enzyme in this tissue were 4-8 times more active in obese than in lean rats.