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J Peinado-Onsurbe

Publications and source records attributed to J Peinado-Onsurbe.

17 recordsLinked to original sources
PubMed1997

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.

Adipose Tissue↗
PubMed1996

PPARalpha and PPARgamma activators direct a distinct tissue-specific transcriptional response via a PPRE in the lipoprotein lipase gene.

Increased activity of lipoprotein lipase (LPL) may explain the hypotriglyceridemic effects of fibrates, thiazolidinediones and fatty acids, which are known activators (and/or ligands) of the various peroxisome proliferator-activated receptors (PPARs). Treatment with compounds which activate preferentially PPARalpha, such as fenofibrate, induced LPL expression exclusively in rat liver. In contrast, the antidiabetic thiazolidinedione BRL 49653, a high affinity ligand for PPARgamma, had no effect on liver, but induced LPL expression in rat adipose tissue. In the hepatocyte cell line AML-12, fenofibric acid, but not BRL 49653, induced LPL mRNA, whereas in 3T3-L1 preadipocytes, the PPARgamma ligand induced LPL mRNA levels much quicker and to a higher extent than fenofibric acid. In both the in vivo and in vitro studies, inducibility by either PPARalpha or gamma activators, correlated with the tissue distribution of the respective PPARs: an adipocyte-restricted expression of PPARgamma, whereas PPARalpha was expressed predominantly in liver. A sequence element was identified in the human LPL promoter that mediates the functional responsiveness to fibrates and thiazolidinediones. Methylation interference and gel retardation assays demonstrated that a PPARalpha or gamma and the 9-cis retinoic acid receptor (RXR) heterodimers bind to this sequence -169 TGCCCTTTCCCCC -157. These data provide evidence that transcriptional activation of the LPL gene by fibrates and thiazolidinediones is mediated by PPAR-RXR heterodimers and contributes significantly to their hypotriglyceridemic effects in vivo. Whereas thiazolidinediones predominantly affect adipocyte LPL production through activation of PPARgamma, fibrates exert their effects mainly in the liver via activation of PPARalpha.

3T3 Cells↗
PubMed1996

Hepatic regeneration induces changes in lipoprotein lipase activity in several tissues and its re-expression in the liver.

We examined the expression of lipoprotein lipase (LPL) gene and LPL activity following a two-thirds hepatectomy and during liver regeneration. In most of the tissues studied, LPL activity increased a few hours after partial hepatectomy, but soon returned to normal levels. The greatest increase was found in the adrenal glands, plasma and liver. This increase in LPL activity in the liver could be partially due to an increase in the influx of the enzyme from extrahepatic tissues. There is, however, also a re-expression of LPL mRNA in the liver after partial hepatectomy (during the first hours). It is well known that LPL is expressed in the liver of neonatal animals, but progressively decreases during post-natal development, to reach adult levels around the time of weaning. Our results show by the first time that the remaining liver re-expresses LPL gene during the regeneration process and that the hepatocytes de-differentiate and acquire some of the neonatal characteristics. The increase in LPL mRNA will contribute to the rise in LPL activity after hepatectomy. This presence of LPL could enable the liver to take up fatty acids from the circulating triacylglycerols, which are needed as energetic and plastic substrates during the process of hepatic regeneration.

Adipose Tissue↗
PubMed1996

Decrease in the expression of hepatic lipase activity following partial hepatectomy.

Variations in hepatic lipase (HL) activity were studied for the first time in liver, plasma and adrenal glands of partially hepatectomized (70%), sham-operated and intact rats. Activity profiles performed during 7 days in liver, plasma and adrenal glands of sham-operated rats were similar to those obtained in intact animals. However, HL activity in intact animals appeared to be slightly higher during the first 24 hours. Following surgery, hepatectomized animals showed a reduction of about 300 U in liver HL activity which persisted for 7 days. Plasma HL activity of hepatectomized rats was undetectable at 6 hours post-surgery but in increased afterwards. A high correlation between liver and adrenal gland HL activity was found in hepatectomized but not in sham-operated animals. HL mRNA levels in hepatectomized rats showed a 40% decrease during the first 24 hours after surgery, but they returned to the normal range later. On the other hand, HL mRNA values increased in sham-operated rats but no increase in HL activity was detected in these animals. To conclude, our results show that HL activity decreases dramatically during hepatic regeneration due to a concomitant decrement in the expression of the gene that encodes the enzyme and to other undetermined factors.

Adrenal Glands↗
PubMed1996

Expression and regulation of the lipoprotein lipase gene in human adrenal cortex.

Lipoprotein lipase (LPL), an enzyme which hydrolyzes triglycerides and participates in the catabolism of remnant lipoproteins, plays a crucial role in energy and lipid metabolism. The goal of this study was to analyze the expression and regulation of the LPL gene in human adrenals. Reverse transcriptase-polymerase chain reaction amplification and sequence analysis demonstrated the presence of LPL mRNA in fetal and adult human adrenal cortex. Furthermore, the human adrenocortical carcinoma cell line, NCI-H295, expresses LPL mRNA and protein, which is localized to the outer cellular membrane as demonstrated by immunofluorescence confocal microscopy and can be released in the medium by heparin addition. To asses whether the LPL gene is regulated by agents regulating adrenal steroidogenesis, NCI-H295 cells were treated with activators of second messenger systems. Whereas the calcium-ionophore A23187 did not affect LPL gene expression, treatment with phorbol 12-myristate 13-acetate decreased LPL mRNA levels in a time- and dose-dependent manner. This decrease after phorbol 12-myristate 13-acetate was associated with diminished heparin-releasable LPL mass and activity in the culture medium. Addition of the cAMP analog 8-Br-cAMP to NCI-H295 cells resulted in a rapid, but transient dose-dependent induction of LPL mRNA. Treatment with the protein synthesis inhibitor cycloheximide gradually induced, whereas simultaneous addition of cAMP and cycloheximide superinduced LPL mRNA levels. Nuclear run-on analysis indicated that the effects of cAMP and cycloheximide occurred at the transcriptional and post-transcriptional level, respectively. Transient co-transfection assays demonstrated that the first 230 base pairs of the proximal LPL promoter contain a cAMP-responsive element activated by protein kinase A and transcription factors belonging to the CREB/CREM family. These data indicate that LPL is expressed in human adrenal cortex and regulated in NCI-H295 adrenocortical carcinoma cells by activators of the protein kinase A and protein kinase C second messenger pathways in a manner comparable to P450scc, which catalyzes the first step in adrenal steroidogenesis. These observations suggest a role for LPL in adrenal energy and/or lipid metabolism and possibly in steroidogenesis.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Hormonal regulation of lipoprotein lipase activity from 5-day-old rat hepatocytes.

Lipoprotein lipase (LPL) activity is known to be synthesized, active and functional in the 1-day-old rat liver: it peaks just at birth triggered by parturition. During suckling LPL mRNA, LPL synthesis and LPL activity are still high at 5 days and then fade reaching adult values at weaning. How LPL expression is gradually extinguished is not known. Therefore we studied the effect of different doses of several hormones on LPL activity released by incubated hepatocytes from 5-day-old rats. In the presence of heparin the release of LPL activity in the medium was linear until 3 h and was always significantly increased vs. without heparin. At 3 h in the presence of heparin the main hormonal effects were: dose-dependent increase (30-60%) with dexamethasone; dose-dependent increase (20-60%) with glucagon; dose-independent decrease (50-60%) with ethinylestradiol, testosterone, progesterone and prolactin; no effect with insulin; 20-40% increase with adrenaline < 1 mM but 40-50% decrease with noradrenaline < 10 microM. Increase of LPL release by glucagon and adrenaline agrees with the increased LPL expression we previously found in an undifferentiated hepatoma cell line when the adenylate cyclase/protein kinase A pathway was activated. The effect of glucagon is concordant with our previous observations that fasting increases liver LPL activity in neonatal rats. The high estradiol levels known to be present in male and female 9-19-day-old rats might contribute to liver LPL extinction during suckling.

Animals↗
PubMed1996

Lipoprotein lipase in highly vascularized structures of the eye.

Ocular tissues are highly dependent on lipid turnover and metabolism, which requires an uptake mechanism for fatty acids from lipoproteins. We studied the activity and expression of lipoprotein lipase (LPL), which catalyzes the hydrolysis of plasma triglycerides, in different ocular regions. Human and bovine eyes were dissected and various specialized anatomical areas were assayed for LPL activity, mRNA, and immunoreactivity. Variable levels of LPL activity were detected in all structures in human and bovine eyes. LPL activity was much higher in vascularized structures, such as ciliary body, iris, and retina than in avascular eye structures, such as vitreous body, lens, and cornea. In both human and bovine eyes, ciliary body contained the highest LPL lipolytic activity. LPL mRNA was detected by reverse transcription followed by polymerase chain reaction (RT-PCR) in all regions of human eyes. By RT-PCR analysis it was shown that bovine eyes contained high levels of LPL mRNA in ciliary body and iris, lower levels were found in retina, optic nerve, and lens, whereas no LPL mRNA could be found in bovine cornea. RT-PCR data, obtained in bovine eyes, agree with the results obtained by Northern blot experiments, confirming the high levels of LPL mRNA in iris and ciliary body. Immunofluorescence experiments performed on human eye samples indicated that the LPL protein is mostly distributed on the choroides, the choriocapillaris, and on the vessels of ciliary body, iris, optic nerve, and retina. The present study demonstrates that active LPL protein is synthesized, secreted, and located among microvessels in several specialized regions of the eye, and suggests that LPL could be involved in the uptake of fatty acids by the ocular tissues.

Adolescent↗
PubMed1995

Na+,K(+)-ATPase expression during the early phase of liver growth after partial hepatectomy.

Na+,K(+)-ATPase expression has been studied in the early phase of liver growth after partial hepatectomy to ascertain whether its increased activity is due to stable effects, involving de novo synthesis and insertion of pumps into the plasma membrane. Na+,K(+)-ATPase activity progressively increases after partial hepatectomy, reaching a three-fold induction above basal values 12 h after surgery. mRNA amounts of both alpha 1 and beta 1 subunits are rapidly increased up to two-fold for alpha 1 and nearly three-fold for beta 1, at 9 and 12 h post-hepatectomy, respectively. This correlates with increased abundance of both subunit proteins. The results prove that the increase of Na+,K(+)-ATPase activity correlates with higher expression of both subunit proteins and mRNAs, although the characteristics of the induction suggest that some translational and post-translational events may be equally involved in the increased activity of the pump.

Animals↗
PubMed1995

Lipoprotein lipase activity in developing rat brain areas.

Lipoprotein lipase (LPL) is a key extracellular enzyme that enables tissue to import fatty acids from triacylglyceride-rich lipoproteins. LPL is present in most tissues of the body, but in the brain its functional significance remains unclear. Lipids constitute the main components of myelin and undergo significant changes during maturation. However, nothing is known of the postnatal evolution of LPL activity in the brain areas during postnatal development. Here we found that LPL activity is relatively high in the newborn brain and peaks between the 5th and the 10th days after birth, reaching activities 5 times higher than in the adult brain. In all the areas studied (olfactory bulbs, cortex, thalamus, cerebellum, hippocampus, striatum, brain-stem and spinal cord) LPL also increases sharply during postnatal development. Hippocampus shows the highest LPL activity levels, which are between 5 and 11 times higher than in the other regions. The significance of these high LPL activity levels is discussed.

Aging↗
PubMed1993

Epidermal growth factor interferes with the effect of adrenaline on glucose production and on hepatic lipase secretion in rat hepatocytes.

We studied the interaction of epidermal growth factor (EGF) and adrenaline in the control of several metabolic functions in isolated hepatocytes from fed rats. EGF did not modulate glucose release, urea production or hepatic lipase secretion, but interfered with the stimulatory effect of adrenaline on both glucose and urea production and also with the inhibitory effect of this hormone on hepatic lipase secretion. EGF also interfered with the effect of both angiotensin II and vasopressin on glucose release and on hepatic lipase secretion. While the effect of EGF interfering with the action of adrenaline on glucose release was potentiated in the absence of extracellular calcium, the effect on the inhibition of hepatic lipase secretion was abolished. These results suggest that EGF interfered with catecholamine actions in the liver at a site distal from the generation of the calcium signal.

Animals↗
PubMed1993

Effects of sex steroids on hepatic and lipoprotein lipase activity and mRNA in the rat.

In humans, sex steroids have been implicated in the regulation of hepatic and lipoprotein lipase activity. Therefore, the effects of orchidectomy and subsequent androgen or estrogen administration on hepatic lipase (HL) and adipose tissue and heart lipoprotein lipase (LPL) were examined. Relative to intact controls, orchidectomy of male rats resulted in no significant change in HL activity and mRNA, or in heart and adipose tissue LPL activity and mRNA levels. Subsequently, a subcutaneous silastic tubing, delivering either testosterone, dihydrotestosterone, nandrolone, or 17 beta-estradiol, was implanted for 5 weeks. All substitution treatments had a tendency to reduce HL activity and to induce HL mRNA levels. This effect was, however, only significant for testosterone which resulted in a decrease in HL activity (238 +/- 15 vs. 328 +/- 31 mU/g tissue; p vs. control < 0.05) and an increase in HL mRNA (166 +/- 11 vs. 100 RAU; p vs. control < 0.01). No significant effects of androgens on LPL expression either in heart or adipose tissue were observed. Adipose tissue LPL activity (20 +/- vs. 35 +/- 4 mU/g; p vs. control < 0.05) and mRNA (28 +/- 4 vs. 100 RAU; p vs. control < 0.001) levels, but not heart LPL, however, were diminished substantially after 17 alpha-estradiol treatment. In conclusion, rat HL is influenced by testosterone, while adipose tissue, but not heart LPL, is reduced after estrogen administration.

Adipose Tissue↗
PubMed1992

Lipoprotein lipase expression in undifferentiated hepatoma cells is regulated by progesterone and protein kinase A.

Recently, it was shown that lipoprotein lipase (LPL) was produced in neonatal but not in adult rat liver. In an attempt to further define the mechanism involved in liver LPL expression, we identified a neonatal mouse hepatoma cell line, BWTG3, capable of producing LPL. The regulation of LPL expression by various extracellular stimuli was investigated in this cell line. Progesterone caused a rise in LPL production by BWTG3 cells. Other hormones tested, such as insulin, glucagon, adrenalin, testosterone, and thyroid hormone, had no effect on LPL production. The effects of progesterone on LPL production showed slow kinetics reaching a maximum 24 h after addition. Cotransfection of a progesterone receptor expression vector with a 5'-LPL-CAT reporter construct resulted in an induction of CAT activity, suggesting that the increase in LPL accumulation after progesterone was linked to transcriptional induction of the LPL gene. Stimuli causing an elevation of protein kinase A activity in the cells also increased LPL production. Three agents capable of elevating intracellular cAMP levels, i.e., forskolin, dBcAMP, and choleratoxin, caused an elevation of LPL production. The increase in LPL activity caused by forskolin and choleratoxin was paralleled by an elevation of LPL mRNA levels, while dBcAMP only induced a small elevation of LPL mRNA levels. The increase in LPL production was shown to be linked to the stimulation of the PKA signal transduction pathway and was apparently transmitted via the transcription factor CREB. No effect of the stimulation of protein kinase C or calcium/calmodulin-dependent kinase on LPL production was detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Neonatal extinction of liver lipoprotein lipase expression.

In contrast to the complete absence of lipoprotein lipase (LPL) mRNA in adult rat liver, fetal and neonatal rat liver contain substantial amounts of LPL mRNA, which is translated in active LPL protein as can be deduced from the presence of LPL activity in this organ. At this neonatal stage, both the relative abundance of LPL mRNA and LPL activity increased with starvation. During the suckling period, LPL mRNA and LPL activity gradually decreased until both parameters were undetectable. While the administration of L-thyroxine or hydrocortisone enhanced the disappearance of LPL mRNA, induced hypothyroidism delayed its disappearance. In adult animals induced hypothyroidism could not reactivate LPL mRNA production in the liver. The data presented suggest that liver LPL production responds to changes in the nutritional state and becomes extinguished during development, in a fashion reminiscent to the extinction of alpha-fetoprotein. This extinction of LPL gene expression is influenced by hormonal factors.

Animals↗
PubMed1992

Lipoprotein lipase and hepatic lipase activities are differentially regulated in isolated hepatocytes from neonatal rats.

Lipoprotein lipase and hepatic lipase are members of the lipase gene family sharing a high degree of homology in their amino acid sequences and genomic organization. We have recently shown that isolated hepatocytes from neonatal rats express both enzyme activities. We show here that both enzymes are, however, differentially regulated. Our main findings are: (i) fasting induced an increase of the lipoprotein lipase activity but a decrease of the hepatic lipase activity in whole liver, being in both cases the vascular (heparin-releasable) compartment responsible for these variations. (ii) In isolated hepatocytes, secretion of lipoprotein lipase activity was increased by adrenaline, dexamethasone and glucagon but was not affected by epidermal growth factor, insulin or triiodothyronine. On the contrary, secretion of hepatic lipase activity was decreased by adrenaline but was not affected by other hormones. (iii) The effect of adrenaline on lipoprotein lipase activity appeared to involve beta-adrenergic receptors, but stimulation of both beta- and alpha 1-receptors seemed to be required for the effect of this hormone on hepatic lipase activity. And (iv), increased secretion of lipoprotein lipase activity was only observed after 3 h of incubation with adrenaline and was blocked by cycloheximide. On the contrary, decreased secretion of hepatic lipase activity was already significant after 90 min of incubation and was not blocked by cycloheximide. We suggest that not only synthesis of both enzymes, but also the posttranslational processing, are under separate control in the neonatal rat liver.

Animals↗
PubMed1992

Down-regulation of hepatic lipase gene expression and activity by fenofibrate.

The influence of the hypolipidemic drug, fenofibrate, on hepatic lipase (HL) gene expression and activity was investigated in the rat. Fenofibrate treatment provoked a dose-dependent decrease in HL mRNA levels. At a dose of 0.5% (w/w), HL mRNA levels were reduced to nearly 50% the levels in untreated controls. This decrease was parallelled by a comparable reduction in liver HL activity. The decrease in HL mRNA levels was already observed after 1 day of fenofibrate treatment. Whole liver perfusion experiments showed that the heparin-releasable HL activity in fenofibrate-treated livers dropped to 10% the activity in control livers. In conclusion, treatment with fenofibrate decreases HL gene expression, leading to a lowered activity of endothelium bound HL in fenofibrate-treated livers.

Animals↗
PubMed1991

Involvement of catecholamines in the effect of fasting on hepatic endothelial lipase activity in the rat.

The effect of fasting on hepatic endothelial lipase activity in the liver of adult rats was investigated. We found that, both in male and female rats, fasting produced a progressive decrease of the hepatic endothelial lipase activity. Upon refeeding, the activity returned to control values in 48 h. In isolated livers from fed male rats, a sharp peak of hepatic endothelial lipase activity appeared in the perfusate upon heparin addition. It accounted for 75% of the total activity (heparin-released + residual) of the tissue. Fasting (24 h) decreased the heparin-releasable activity, and this effect was responsible for most of the decrease found in whole tissue. We suggest that the effect might be due to a decreased synthesis and/or secretion of the enzyme by hepatocytes, since isolated hepatocytes from fasted rats, incubated at 37 C, released 65% less activity to the incubation medium than hepatocytes from fed rats. Adrenaline, but not insulin, glucagon, dexamethasone, epidermal growth factor, or T3, decreased the amount of hepatic endothelial lipase activity released by hepatocytes isolated from fed rats. The effect of adrenaline appears to be mediated by alpha 1-receptors since phenylephrine but not isoprenaline reproduced, and prazosin but not propranolol blocked, the effect of the catecholamine. In the presence of cycloheximide, adrenaline also decreased the amount of activity released. We suggest that, in our incubation conditions (up to 3 h), the hormone affects the posttranslational processing of the enzyme. In vivo administration of prazosin blocked the effect of both noradrenaline and fasting on hepatic endothelial lipase activity in whole liver. Those results suggest that catecholamines are involved in the decreased hepatic endothelial lipase activity found in the liver of fasted rats, and points out the role of these hormones in the acute modulation of an enzyme involved in reverse cholesterol transport.

Animals↗