Oleic acid promotes changes in the subcellular distribution of protein kinase C in isolated hepatocytes

High-fat diet induces a predisposition to follicular hyperkeratosis and neutrophilic folliculitis in mice

BACKGROUND

Neutrophilic folliculitis is an inflammatory condition of hair follicles. In some neutrophilic folliculitis, such as in patients with acne and hidradenitis suppurativa, follicular hyperkeratosis is also observed. Neutrophilic folliculitis is often induced and/or exacerbated by a high-fat diet (HFD). However, the molecular mechanisms by which an HFD affects neutrophilic folliculitis are not fully understood.

OBJECTIVE

Our aim was to elucidate how an HFD promotes the development of neutrophilic folliculitis.

METHODS

Mice were fed an HFD, and their skin was subjected to histologic, RNA sequencing, and imaging mass spectrometry analyses. To examine the effect of an HFD on neutrophil accumulation around the hair follicles, phorbol 12-myristate 13-acetate (PMA) was used as an irritant to the skin.

RESULTS

Histologic analysis revealed follicular hyperkeratosis in the skin of HFD-fed mice. RNA sequencing analysis showed that genes related to keratinization, especially in upper hair follicular keratinocytes, were significantly upregulated in HFD-fed mice. Application of PMA to the skin induced neutrophilic folliculitis in HFD-fed mice but not in mice fed a normal diet. Accumulation of neutrophils in the skin and around hair follicles was dependent on CXCR2 signaling, and CXCL1 (a CXCR2 ligand) was produced mainly by hair follicular keratinocytes. Imaging mass spectrometry analysis revealed an increase in fatty acids in the skin of HFD-fed mice. Application of these fatty acids to the skin induced follicular hyperkeratosis and caused PMA-induced neutrophilic folliculitis even in mice fed a normal diet.

CONCLUSION

An HFD can facilitate the development of neutrophilic folliculitis with the induction of hyperkeratosis of hair follicles and increased neutrophil infiltration around the hair follicles via CXCR2 signaling.

Molecular factors that are associated with early developmental arrest of intraerythrocytic Plasmodium falciparum

Malaria continues to be a devastating disease. We investigated the factors that control intraerythrocytic development of the parasite Plasmodium falciparum by using a chemically defined medium (CDM) containing non-esterified fatty acid(s) (NEFA) and phospholipids with specific fatty acid moieties, to identify substances crucial for parasite development. Different NEFAs in the CDM played distinct roles by altering the development of the parasite at various stages, with effects ranging from complete growth to growth arrest at the ring stage. We used genome-wide transcriptome profiling to identify genes that were differentially expressed among the different developmental stages of the parasite, cultured in the presence of various NEFAs. We predicted 26 transcripts that were associated with the suppression of schizogony, of which 5 transcripts, including merozoite surface protein 2, a putative DEAD/DEAH box RNA helicase, serine repeat antigen 3, a putative copper channel, and palmitoyl acyltransferase, were particularly associated with blockage of trophozoite progression from the ring stage. Furthermore, the involvement of copper ions in developmental arrest was detected by copper-ion-chelating methods, implying a critical function of copper homeostasis in the early growth stage of the parasite. These results should help to elucidate the mechanisms behind the development of P. falciparum.

Adiponectin Inhibits Spontaneous and Catecholamine-Induced Lipolysis in Human Adipocytes of Non-Obese Subjects Through AMPK-Dependent Mechanisms

Adiponectin is an adipokine increasing glucose and fatty acid metabolism and improving insulin sensitivity. The aim of this study was to investigate the role of adiponectin in the regulation of adipocyte lipolysis. Human adipocytes isolated from biopsies obtained during surgical operations from 16 non-obese and 17 obese subjects were incubated with 1) human adiponectin (20 µg/ml) or 2) 0.5 mM AICAR – activator of AMPK (adenosine monophosphate activated protein kinase). Following these incubations, isoprenaline was added (10-6 M) to investigate the influence of adiponectin and AICAR on catecholamine-induced lipolysis. Glycerol concentration was measured as lipolysis marker. We observed that adiponectin suppressed spontaneous lipolysis by 21 % and isoprenaline-induced lipolysis by 14 % in non-obese subjects. These effects were not detectable in obese individuals, but statistically significant differences in the effect of adiponectin between obese and non-obese were not revealed by two way ANOVA test. The inhibitory effect of AICAR and adiponectin on lipolysis was reversed by Compound C. Our results suggest, that adiponectin in physiological concentrations inhibits spontaneous as well as catecholamine-induced lipolysis. This effect might be lower in obese individuals and this regulation seems to involve AMPK.

Plasmodium falciparum: differing effects of non-esterified fatty acids and phospholipids on intraerythrocytic growth in serum-free medium

Different combinations of non-esterified fatty acids (NEFA) had variable effects on intraerythrocytic growth of Plasmodium falciparum. All stages of the parasite cultured in medium supplemented with cis-9-octadecenoic acid (C18:1-cis-9), hexadecanoic acid (C16:0), phospholipids (Pld) and bovine albumin free of NEFA were similar to those grown in complete growth medium. Three typical growth patterns indicating suppressed schizogony (SS), suppressed formation of merozoites (SMF), and inhibited invasion of merozoites (IMI) resulted from culture in other combinations of lipids. Unsaturated or saturated NEFA with longer or shorter carbon chains than C18:1-cis-9 or C16:0, higher degree of unsaturation, and trans-forms mainly resulted in SS and SMF effects. However, IMI or partial IMI was observed with tetradecanoic acid or octadecanoic acid enriched with C18:1-cis-9, and cis-9-hexadecenoic acid plus C16:0. Isoforms of C18:1-cis-9 also mainly resulted in partial IMI. SMF also occurred with C18:1-cis-9 plus C16:0 in the absence of Pld. Thus different NEFA exerted distinct roles in erythrocytic growth of the parasite by sustaining development at different stages.

Defective translocation of PKCepsilon in EtOH-induced inhibition of Mg2+ accumulation in rat hepatocytes

BACKGROUND

Rats chronically fed ethanol for 3 weeks presented a marked decreased in total hepatic Mg(2+) content and required approximately 12 days to restore Mg(2+) homeostasis upon ethanol withdrawal. This study was aimed at investigating the mechanisms responsible for the EtOH-induced delay.

METHODS

Hepatocytes from rats fed ethanol for 3 weeks (Lieber-De Carli diet-chronic model), rats re-fed a control diet for varying periods of time following ethanol withdrawal, and age-matched control rats fed a liquid or a pellet diet were used. As acute models, hepatocytes from control animals or HepG2 cells were exposed to varying doses of ethanol in vitro for 8 minutes.

RESULTS

Hepatocytes from ethanol-fed rats presented a marked inhibition of Mg(2+) accumulation and a defective translocation of PKCepsilon to the cell membrane. Upon ethanol withdrawal, 12 days were necessary for PKCepsilon translocation and Mg(2+) accumulation to return to normal levels. Exposure of control hepatocytes or HepG2 cells to a dose of ethanol as low as 0.01% for 8 minutes was already sufficient to inhibit Mg(2+) accumulation and PKCepsilon translocation for more than 60 minutes. Also in this model, recovery of Mg(2+) accumulation was associated with restoration of PKCepsilon translocation. The use of specific antisense in HepG2 cells confirmed the involvement of PKCepsilon in modulating Mg(2+) accumulation.

CONCLUSIONS

Translocation of PKCepsilon isoform to the hepatocyte membrane is essential for Mg(2+) accumulation to occur. Both acute and chronic ethanol administrations inhibit Mg(2+) accumulation by specifically altering PKCepsilon translocation to the cell membrane.

Protein kinase C-Fyn kinase cascade mediates the oleic acid-induced disassembly of neonatal rat cardiomyocyte adherens junctions

Oleic acid (OA) affects assembly of gap junctions in neonatal cardiomyocytes. Adherens junction (AJ) regulates the stability of gap junction integrity; however, the effect of OA on AJ remains largely unexplored. The distribution of N-cadherin and catenins at cell-cell junction was decreased by OA. OA induced activation of protein kinase C(PKC)-alpha and -epsilon and Src family kinase, and all three kinases were involved in the oleic acid-induced disassembly of the adherens junction, since it was blocked by pretreatment with Gö6976 (a PKCalpha inhibitor), epsilonV1-2 (a PKCepsilon inhibitor), or PP2 (a Src family kinase inhibitor). Src family kinase appeared to be the downstream of PKC-alpha and -epsilon, as blockade of either PKC-alpha or -epsilon activity prevented the OA-induced activation of Src family kinase. Immunoprecipitation analyses showed that OA activated Fyn and Fer. OA promoted the association of p120 catenin/beta-catenin with Fyn and Fer and caused increased tyrosine phosphorylation of p120 catenin and beta-catenin, resulting in decreased binding of the former to N-cadherin and of the latter to alpha-catenin. Pretreatment with PP2 abrogated this OA-induced tyrosine phosphorylation of p120 catenin and beta-catenin and restored the association of N-cadherin with p120 catenin and that of beta-catenin with alpha-catenin. In conclusion, these results show that OA activates the PKC-Fyn signaling pathway, leading to the disassembly of the AJ. Therefore, inhibitors of PKC-alpha/-epsilon and Src family kinase are potential candidates as cardioprotection agents against OA-induced heart injury during ischemia-reperfusion.

Chronic but not acute conjugated linoleic acid treatment inhibits deoxycholic acid-induced protein kinase C and nuclear factor-kappaB activation in human colorectal cancer cells

Conjugated linoleic acid (CLA) has anti-carcinogenic effects in a variety of cancers including colon cancer. Secondary bile acids on the other hand are known as tumour promoters in colon cancer with effects on protein kinase C (PKC) and nuclear factor kappa B (NF-kappaB) signalling pathways. The aim of this study was to examine acute and chronic, isomer-specific effects of CLA on bile salt-induced PKC and NF-kappaB signal transduction in human colon cancer cells. HCT116 cells were treated with 100 mumol/l and 50 mumol/l cis-9,trans-11-CLA and trans-10,cis-12-CLA for 24 h and 14 days, respectively. The cells were then transfected with DNA coding for PKC beta1-EGFP (enhanced green fluorescent protein), PKC delta-EGFP or PKC zeta-EGFP fusion protein and activated with deoxycholic acid (DCA), phorbol myristate acetate (PMA) or C2-ceramide. PKC translocation was observed using real-time photomicroscopy and fluorescent microscopy and NF-kappaB analyses by gel shift assays. Chronic c-9,t-11-CLA and t-10,c-12-CLA treatment inhibited DCA-induced PKC beta1 and PKC delta translocation and also inhibited NF-kappaB activation. Acute CLA treatment had no effect on PKC or NF-kappaB activation. In conclusion this study indicates that chronic CLA treatment inhibits DCA-induced PKC and NF-kappaB activation in colon cancer cells. These data suggest mechanisms by which CLA may influence the course of colonic cancer.

Oleate-induced decrease in hepatocyte insulin binding is mediated by PKC-δ

We have previously shown that free fatty acids (FFA) impair hepatic insulin extraction in vivo and thus generate hyperinsulinemia, a suspected risk factor for atherosclerosis and cancer. Hepatic insulin extraction is a receptor-mediated event, which is initiated by hepatocyte insulin binding. In the present study, we investigated the effect of FFA on insulin binding in freshly isolated rat hepatocytes maintained at 10 mM glucose. Hepatocyte insulin binding decreased after 1 h exposure to oleate in a concentration-dependent manner reaching a maximum (35-40%) at 125 microM. Inhibition of FFA oxidation by >90% with the carnitine palmitoyltransferase I (CPT-I) inhibitor methylpalmoxirate (MP, 30 microM) did not prevent the effect of oleate. However, when hepatocytes were treated with the PKC inhibitor bisindolylmaleimide (BIM, 1 microM) the effect of oleate was abolished. Subcellular fractionation and immunoblotting of specific PKC isoforms revealed that oleate-induced hepatic PKC-delta membrane translocation, but did not translocate-epsilon, -theta, -alpha, -betaI and -betaII. These results indicate that PKC-delta activation mediated the FFA-induced decrease in hepatocyte insulin binding under our conditions, and thus provides a mechanistic basis for FFA-induced hyperinsulinemia.

Okadaic acid induces phosphorylation and translocation of myosin phosphatase target subunit 1 influencing myosin phosphorylation, stress fiber assembly and cell migration in HepG2 cells

It was determined that the myosin phosphatase (MP) activity and content of myosin phosphatase target subunit 1 (MYPT1) were correlated in subcellular fractions of human hepatocarcinoma (HepG2) cells. In control cells MYPT1 was localized in the cytoplasm and in the nucleus, as determined by confocal microscopy. Treatment of HepG2 cells with 50 nM okadaic acid (OA), a cell-permeable phosphatase inhibitor, induced several changes: 1) a marked redistribution of MYPT1 to the plasma membrane associated with an increased level of phosphorylation of MYPT1 at Thr695. Both effects showed only a slight influence with the Rho-kinase inhibitor, Y-27632; 2) an increase in phosphorylation of MYPT1 at Thr850 associated with its accumulation in the perinuclear region and nucleus. These effects were markedly reduced by Y-27632; 3) an increased phosphorylation of the 20 kDa myosin II light chain at Ser19 associated with an increased location of myosin II at the cell center. These effects were partially counteracted by Y-27632; 4) an increase in stress fiber formation and a decrease in cell migration, both OA-induced effects were blocked by Y-27632. In HepG2 lysates, OA (5-100 nM) did not affect MP activity but inhibited PP2A activity. These results indicate that OA induces differential phosphorylation and translocation of MYPT1, dependent on PP2A and, to varying extents, on ROK. These changes are associated with an increased level of myosin II phosphorylation and attenuation of hepatic cell migration.

Mechanism of oleic acid-induced gap junctional disassembly in rat cardiomyocytes

This study investigated the mechanism of oleic acid (OA) on gap junctions and identified the protein kinase C (PKC) isoforms involved in OA-mediated gap junction disassembly in cardiomyocytes. Control cardiomyocytes showed continuous staining of the plasma membrane at cell-cell contact areas using antibodies reacting with connexin 43 (Cx43). The spontaneous contraction rate of cultured cardiomyocytes was reduced in a time-dependent manner by OA. In addition, Cx43 expression at cell-cell junction decreased, suggesting the disassembly of gap junction. Staining for PKC and PKCalpha, which were shown to colocalize with Cx43, also decreased with increased duration of OA treatment. The effects of OA on these distributional changes at cell junctions were reversed by 24 h incubation in fresh culture medium devoid of OA. Immunoprecipitation assays confirmed the biochemical binding between Cx43 and PKC/PKCalpha, and this protein interaction was not affected by OA. This may provide the basis for simultaneous detachment of Cx and PKC/PKCalpha from the cell-cell junction to the cytosol upon OA stimulation. Western blot analysis showed that OA-induced Cx43 Ser368 phosphorylation, and that this effect could be blocked by cotreatment with the general PKC inhibitor, calphostin C, the PKC inhibitor, eV1-2, or the Src kinase inhibitor, PP1, but not by the PKCalpha inhibitor, Gö6976. eV1-2 also prevented the OA-induced disassembly of gap junctions. Taken together, these data suggest that OA-induced Cx43 Ser368 phosphorylation is mediated by activation of PKC and Src kinase and might be responsible for OA-induced gap junctional disassembly.

The neurotrophic effect of oleic acid includes dendritic differentiation and the expression of the neuronal basic helix-loop-helix transcription factor NeuroD2

We have shown recently that the presence of albumin in astrocytes triggers the synthesis and release of oleic acid, which behaves as a neurotrophic factor for neurons. Thus, oleic acid promotes axonal growth together with the expression of the axonal growth-associated protein, GAP-43. Here we attempted to elucidate whether the neurotrophic effect of oleic acid includes dendritic differentiation. Our results indicate that oleic acid induces the expression of microtubule associated protein-2 (MAP-2), a marker of dendritic differentiation. In addition, the presence of oleic acid promotes the translocation of MAP-2 from the soma to the dendrites. The time course of MAP-2 expression during brain development coincides with that of stearoyl-CoA desaturase, the limiting enzyme of oleic acid synthesis, indicating that both phenomena coincide during development. The effect of oleic acid on MAP-2 expression is most probably independent of autocrine factors synthesized by neurons because this effect was also observed at low cellular densities. As oleic acid is an activator of protein kinase C, the possible participation of this transduction pathway was studied. Our results indicate that added oleic acid or oleic acid endogenously synthesized by astrocytes exerts its neurotrophic effect through a protein kinase C-dependent mechanism as the effect was inhibited by sphingosine or two myristoylated peptide inhibitors of protein kinase C. The transduction pathway by which oleic acid induces the expression of genes responsible for neuronal differentiation appears to be mediated by the transcription factor NeuroD2, a regulator of terminal neuronal differentiation.

Oleic acid induces GAP-43 expression through a protein kinase C-mediated mechanism that is independent of NGF but synergistic with NT-3 and NT-4/5

We have recently shown that the presence of albumin in astrocytes triggers the synthesis and release of oleic acid, which behaves as a neurotrophic factor for neurons. Thus, oleic acid promotes axonal growth, neuronal clustering, and the expression of the axonal growth-associated protein, GAP-43. In this work we show that oleic acid upregulates GAP-43 expression by a protein kinase C (PKC)-dependent mechanism. Since GAP-43 expression has been shown to be upregulated by several neurotrophins, we investigated the relationship between the effect of oleic acid and that of NGF, neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5) on GAP-43 expression. Our results indicate that NGF is not involved in the neurotrophic effect of oleic acid because the addition of NGF did not modify the effect of oleic acid on GAP-43 expression. Neither NT-3 nor NT-4/5 alone modified GAP-43 expression. However, NT-3 and NT-4/5 acted synergistically with oleic acid to increase GAP-43 expression. The lack of effect of NGF as compared to other neurotrophins is not unexpected since we have not found TrkA expression under our experimental conditions. The effect of oleic acid on GAP-43 expression must be independent of autocrine factors synthesized by neurons because this effect was also observed at low cellular densities. In conclusion, our results indicate that oleic acid behaves as a neurotrophic factor, inducing GAP-43 expression through a PKC-mediated mechanism that is not mediated by other neurotrophic factors but that is strongly synergized by NT-3 and NT-4/5.

Role of oleic acid as a neurotrophic factor is supported in vivo by the expression of GAP-43 subsequent to the activation of SREBP-1 and the up-regulation of stearoyl-CoA desaturase during postnatal development of the brain

We have recently reported that albumin, a serum protein present in the developing brain, stimulates the synthesis of oleic acid by cultured astrocytes by inducing stearoyl-CoA 9-desaturase, the rate-limiting enzyme in oleic acid synthesis, through activation of the sterol regulatory element-binding protein-1. In this work, we offer evidence supporting the in vivo occurrence of this process during the postnatal development of the rat brain. Our results show that albumin reaches maximal brain level by day 1 after birth, coinciding with activation of the sterol response element binding protein-1, which is responsible for the transcription of the enzymes required for oleic acid synthesis. In addition, the developmental profile of stearoyl-CoA 9-desaturase-1 mRNA expression follows that of sterol regulatory element-binding protein-1 activation, indicating that these phenomena are tightly linked. In a previous work, we showed that oleic acid induces neuronal differentiation, as indicated by the expression of growth associated protein-43. Here, we report that the expression of growth associated protein-43 mRNA peaks at about day 7 after birth, following the maximal expression of stearoyl-CoA 9-desaturase-1 mRNA that occurs between days 3 and 5 postnatally. In conclusion, our results support the hypothesis that the synthesis of oleic acid is linked to neuronal differentiation during rat brain development.

Mechanisms of the free fatty acid-induced increase in hepatic glucose production

The associations between obesity, insulin resistance, and type 2 diabetes mellitus are well documented. Free fatty acids (FFA), which are often elevated in obesity, have been implicated as an important link in these associations. Contrary to muscle glucose metabolism, the effects of FFA on hepatic glucose metabolism and the associated mechanisms have not been extensively investigated. It is still controversial whether FFA have substantial effects on hepatic glucose production, and the mechanisms responsible for these putative effects remain unknown. We review recent progress in this area and try to clarify controversial issues regarding the mechanisms responsible for the FFA-induced increase in hepatic glucose production in the postabsorptive state and during hyperinsulinemia.

Arachidonic acid-induced IL-6 expression is mediated by PKC alpha activation in osteoblastic cells

There are several pieces of evidence supporting the important role that essential fatty acids (EFAs) and their metabolites play in regulating calcium and bone metabolism, and their relevance to the pathobiology of bone disease, with particular reference to modulating effects on cytokines. We found that arachidonic acid (AA) triggers a cell signal in osteoblasts and leads to the expression of IL-6. To explore the biochemical pathways involved in AA induction of cytokine gene expression, we evaluated the potential protein kinase C (PKC) dependent mechanism accounting for the AA effect on IL-6 gene expression. The osteoblast-like cell line MG-63 was pretreated with calphostin C, a PKC inhibitor, or phorbol 12-myristate 13-acetate (PMA) for an extended period, a condition which causes PKC downregulation, and subsequently with AA. After these treatments, IL-6 gene expression was no longer evident. We also showed that PKC and, in particular, PKC alpha, which are both recruited to the particulate fraction, undergo proteolysis and autophosphorylation; all of these steps are required for PKC activation and, subsequently, for AA-induced signaling. It is interesting that other unsaturated fatty acids, such as oleic acid (OA) or eicosapentaenoic acid (EPA), are unable to induce either PKC activation or IL-6 gene expression.

Oleic acid-induced PKC isozyme translocation in RAW 264.7 macrophages

Fatty acids are important second messengers that mediate various cellular functions, but their role in the formation of macrophage foam cells is not known. High plasma levels of oleic acid (OA) in obese patients are often associated with a high risk for atherosclerosis. In this study, we investigated the protein kinase C (PKC) isozymes involved in OA-induced lipid accumulation in RAW 264.7 macrophages. The results show that OA induces translocation of PKC alpha, beta1, and delta from the cytosol to the cell membrane 5 min after the treatment. After 16 h incubation with OA, PKC delta was found to be colocalized with adipose differentiation-related protein (ADRP) on the surface of lipid droplets, but immunoprecipitation experiments showed that PKC delta was not biochemically associated with ADRP. After 16 h incubation with OA plus phorbol 12-myristate 13-acetate (PMA), PKC delta staining on the lipid droplet surface was not seen, whereas the accumulation of lipid droplets was unaffected. Furthermore, downregulation of PKC delta was confirmed by immunoblotting. These results demonstrate possible involvement of specific PKC isozymes in the early phase of lipid accumulation, possibly during the uptake of OA.

Free fatty acid-induced hepatic insulin resistance: a potential role for protein kinase C-delta

The mechanisms of the impairment in hepatic glucose metabolism induced by free fatty acids (FFAs) and the importance of FFA oxidation in these mechanisms remain unclear. FFA-induced peripheral insulin resistance has been linked to membrane translocation of novel protein kinase C (PKC) isoforms, but the role of PKC in hepatic insulin resistance has not been assessed. To investigate the biochemical pathways that are induced by FFA in the liver and their relation to glucose metabolism in vivo, we determined endogenous glucose production (EGP), the hepatic content of citrate (product of acetyl-CoA derived from FFA oxidation and oxaloacetate), and hepatic PKC isoform translocation after 2 and 7 h Intralipid + heparin (IH) or SAL in rats. Experiments were performed in the basal state and during hyperinsulinemic clamps (insulin infusion rate, 5 mU. kg(-1). min(-1)). IH increased EGP in the basal state (P < 0.001) and during hyperinsulinemia (P < 0.001) at 2 and 7 h. Also, 7-h infusion of IH induced resistance to the suppressive effect of insulin on EGP (P < 0.05). Glycerol infusion (resulting in plasma glycerol levels similar to IH infusion) did not have any effect on EGP. IH increased hepatic citrate content by twofold, independent of the insulin levels and the duration of IH infusion. IH induced hepatic PKC-delta translocation from the cytosolic to membrane fraction in all groups. PKC-delta translocation was greater at 7 compared with 2 h (P < 0.05). In conclusion, 1) increased FFA oxidation may contribute to the FFA-induced increase in EGP in the basal state and during hyperinsulinemia but is not associated with FFA-induced hepatic insulin resistance, and 2) the progressive insulin resistance induced by FFA in the liver is associated with a progressive increase in hepatic PKC-delta translocation.

Disordered fat storage and mobilization in the pathogenesis of insulin resistance and type 2 diabetes

The primary genetic, environmental, and metabolic factors responsible for causing insulin resistance and pancreatic beta-cell failure and the precise sequence of events leading to the development of type 2 diabetes are not yet fully understood. Abnormalities of triglyceride storage and lipolysis in insulin-sensitive tissues are an early manifestation of conditions characterized by insulin resistance and are detectable before the development of postprandial or fasting hyperglycemia. Increased free fatty acid (FFA) flux from adipose tissue to nonadipose tissue, resulting from abnormalities of fat metabolism, participates in and amplifies many of the fundamental metabolic derangements that are characteristic of the insulin resistance syndrome and type 2 diabetes. It is also likely to play an important role in the progression from normal glucose tolerance to fasting hyperglycemia and conversion to frank type 2 diabetes in insulin resistant individuals. Adverse metabolic consequences of increased FFA flux, to be discussed in this review, are extremely wide ranging and include, but are not limited to: 1) dyslipidemia and hepatic steatosis, 2) impaired glucose metabolism and insulin sensitivity in muscle and liver, 3) diminished insulin clearance, aggravating peripheral tissue hyperinsulinemia, and 4) impaired pancreatic beta-cell function. The precise biochemical mechanisms whereby fatty acids and cytosolic triglycerides exert their effects remain poorly understood. Recent studies, however, suggest that the sequence of events may be the following: in states of positive net energy balance, triglyceride accumulation in "fat-buffering" adipose tissue is limited by the development of adipose tissue insulin resistance. This results in diversion of energy substrates to nonadipose tissue, which in turn leads to a complex array of metabolic abnormalities characteristic of insulin-resistant states and type 2 diabetes. Recent evidence suggests that some of the biochemical mechanisms whereby glucose and fat exert adverse effects in insulin-sensitive and insulin-producing tissues are shared, thus implicating a diabetogenic role for energy excess as a whole. Although there is now evidence that weight loss through reduction of caloric intake and increase in physical activity can prevent the development of diabetes, it remains an open question as to whether specific modulation of fat metabolism will result in improvement in some or all of the above metabolic derangements or will prevent progression from insulin resistance syndrome to type 2 diabetes.

Protein kinases C translocation responses to low concentrations of arachidonic acid

Arachidonic acid (AA) directly activates protein kinases C (PKC) and may thereby serve as a regulatory signal during cell stimulation. The effect, however, requires a > or =20 microm concentration of the fatty acid. We find that human polymorphonuclear neutrophils (PMN) equilibrated with a ligand for the diacylglycerol receptor on PKC, [(3)H]phorbol dibutyrate (PDB), increased binding of [(3)H]PDB within 15 s of exposure to > or =10-30 nm AA. Other unsaturated fatty acids, but not a saturated fatty acid, likewise stimulated PDB binding. These responses, similar to those caused by chemotactic factors, resulted from a rise in the number of diacylglycerol receptors that were plasma membrane-associated and therefore accessible to PDB. Unlike chemotactic factors, however, AA was fully active on cells overloaded with Ca(2+) chelators. The major metabolites of AA made by PMN, leukotriene B(4) and 5-hydroxyicosatetraenoate, did not mimic AA, and an AA antimetabolite did not block responses to AA. AA also induced PMN to translocate cytosolic PKCalpha, beta(II), and delta to membranes. This response paralleled PDB binding with respect to dose requirements, time, Ca(2+)-independence, resistance to an AA antimetabolite, and induction by another unsaturated fatty acid but not by a saturated fatty acid. Finally, HEK 293 cells transfected with vectors encoding PKCbeta(I) or PKCdelta fused to the reporter enhanced green fluorescent protein (EGFP) were studied. AA caused EGFP-PKCbeta translocation from cytosol to plasma membrane at > or =0.5 microm, and EGFP-PKCdelta translocation from cytosol to nuclear and, to a lesser extent, plasma membrane at as little as 30 nm. We conclude that AA induces PKC translocations to specific membrane targets at concentrations 2-4 orders of magnitude below those activating the enzymes. These responses, at least as they occur in PMN, do not require changes in cell Ca(2+) or oxygenation of the fatty acid. AA seems more suited for signaling the movement than activation of PKC.

Antagonizing effect of AP-1 on glucocorticoid induction of urea cycle enzymes: a study of hyperammonemia in carnitine-deficient, juvenile visceral steatosis mice

Hyperammonemia is one of the major symptoms of primary carnitine deficiency. Carnitine-deficient juvenile visceral steatosis (JVS) mice show hyperammonemia during the weaning period. We have found that all of the urea cycle enzyme genes are suppressed and that N-acetylglutamate, an allosteric activator of the first step enzyme of the urea cycle, carbamoyl phosphate synthetase I (CPS), is not deficient in the liver of JVS mice. Induction of the urea cycle enzymes by glucocorticoid in rat primary cultured hepatocytes was suppressed by the addition of long-chain fatty acids. The suppression of the urea cycle enzyme genes in vivo and in vitro is accompanied by stimulated AP-1 DNA-binding activity. However, mRNA of phosphoenolpyruvate carboxykinase, one of the gluconeogenic enzymes which responds to glucocorticoid, is further stimulated by the addition of fatty acid. From these results, we postulate that protein-protein interaction between glucocorticoid receptors and AP-1 is not the major mechanism of suppression, but that AP-1 causes the suppression through a cis-element on the gene. After cloning promoter and enhancer regions of the mouse CPS gene and comparing rat and mouse, we found that an AP-1 site was present just 3'-downstream of the minimal essential enhancer fragment previously described. We also found that the presence of an AP-1 site in reporter gene constructs resulted in suppression of the reporter genes in the liver of carnitine-deficient JVS mice and suppression of glucocorticoid induction by long-chain fatty acid in cultured hepatocytes.

Linoleic acid and oleic acid increase the endothelin-1 binding and action in cultured rat aortic smooth muscle cells

An increase in circulating non-esterified fatty acids (NEFA) has been observed in patients with poorly controlled diabetes mellitus. To investigate whether fatty acids will affect the endothelin-1 (ET-1) receptor and thus contribute to the acceleration of atherosclerosis in diabetic patients, cultured rat aortic smooth muscle cells (SMC) were maintained in media containing higher (similar to those in diabetic patients) concentrations of oleic acid (OA) or linoleic acid (LA). The ET-1 binding and ET-1-stimulated thymidine uptake were then examined. We found that cells treated with OA (500 micromol/L) or LA (250 micromol/L) showed a significant increase in ET-1 receptor amount as demonstrated by Scatchard analysis (Bmax: 7.40 +/- 1.04 v 2.71 +/- 0.54 fmol/mg and 5.00 +/- 1.00 v 3.32 +/- 0.70 fmol/mg, respectively). No change in binding affinity was found. Moreover, both the basal and ET-1-stimulated thymidine uptake were enhanced by treatment with either LA (basal, 11,367 +/- 4,117 cpm/mg; LA, 13,933 +/- 4,003 cpm/mg; ET-1 (10(-8)), 16,931 +/- 4,412 cpm/mg; LA +/- ET-1 (10(-8)), 28,855 +/- 5,217 cpm/mg) or OA (basal, 4,912 +/- 1,193 cpm/mg, OA, 8,027 +/- 1,318 cpm/mg; ET-1 (10(-8)) 9,947 +/- 2,520 cpm/mg; OA + ET-1 (10(-8)), 16,761 +/- 1,740 cpm/mg). This enhancement in thymidine uptake was associated with an increase in cell number. Because ET-1 and its receptor are involved in atherogenesis, our findings suggested that increase in circulating NEFA may contribute to the acceleration of atherosclerosis in diabetic patients. Further studies to confirm its role in the vascular wall are warranted.

Cellular mechanism of sodium oleate-stimulated secretion of cholecystokinin and secretin

Long-chain fatty acids are potent stimulants of secretin and CCK release. The cellular mechanisms of fatty acid-stimulated secretion of these two hormones are not clear. We studied the stimulatory effect and mechanism of sodium oleate (SO) on secretin- and CCK-producing cells. SO stimulated the release of secretin or CCK from isolated rat mucosal cell preparations enriched in either secretin- or CCK-producing cells, respectively. SO also time- and dose-dependently stimulated secretin and CCK release from STC-1 cells. In STC-1 cells, SO-stimulated secretin and CCK release was potentiated by IBMX and inhibited by a protein kinase A-selective inhibitor and a cAMP-specific antagonist. SO-stimulated releases of the two hormones were also inhibited by downregulation or inhibitors of protein kinase C, a calmodulin antagonist and an inhibitor of calmodulin-dependent protein kinase II. Chelating of extracellular Ca(2+) or addition of an L-type calcium channel blocker diminished SO-stimulated hormone releases. SO caused an increase in intracellular Ca(2+) concentration that was partially reversed by diltiazem but had no effect on production of cAMP, cGMP, or inositol-1,4,5-triphosphate. These results indicate that SO acts on secretin- and CCK-producing cells. Its stimulatory effect is potentiated by endogenous protein kinase A and mediated by activation of Ca(2+) influx through the L-type channels and of protein kinase C and Ca(2+)/calmodulin-dependent protein kinase II.

Ibotenic acid-induced lesions of the medial septum increase hippocampal membrane associated protein kinase c activity and reduce acetylcholine synthesis: prevention by a phosphatidylcholine/vitamin B12 diet

Ibotenic acid infusion into the medial septum (MS) results in biochemical alterations in the hippocampus. The biochemical events involved in this neuronal lesion are poorly understood. We investigated the effect of a purified diet supplemented with egg phosphatidylcholine (PC) and vitamin B(12) on ibotenic acid-medicated biochemical changes in the rat hippocampus and crude synaptosomal membranes. Male Wistar rats with this MS lesion were fed a purified diet (control diet) or a purified diet supplemented with 5.7 g PC and 125 microg vitamin B(12) per 100 g (experimental diet) for 18 days. Sham-operated rats were fed the control diet. Compared with the sham-operated rats, MS-lesioned rats fed the control diet showed increased activity of membrane-bound protein kinase C (PKC), decreased activity of choline acetyltransferase, and decreased concentrations of acetylcholine in the hippocampus. The ratio of cholesterol to phospholipid in the crude synaptic membrane was lower in the lesioned rats than in the sham-operated rats, but this was not accompanied by any alteration in membrane lipid fluidity. MS-lesioned rats fed the experimental diet showed lowered PKC activity and elevated acetylcholine concentrations than did rats fed the control diet, but there were no significant effects on choline acetyltransferase activity and the lipid ratio. The ibotenic acid-mediated elevation of PKC activity was observed as early as 2 days postinjury in the control diet-fed rats but not in the experimental diet-fed rats. We propose that ibotenic acid mediates pathophysiologic actions through the activation of PKC and that PC combined with vitamin B(12) ameliorates the second messenger-mediated injury.

Conjugated linoleic acid inhibits proliferation and induces apoptosis of normal rat mammary epithelial cells in primary culture

The trace fatty acid conjugated linoleic acid (CLA) inhibits rat mammary carcinogenesis when fed prior to carcinogen during pubertal mammary gland development or during the promotion phase of carcinogenesis. The following studies were done to investigate possible mechanisms of these effects. Using a physiological model for growth and differentiation of normal rat mammary epithelial cell organoids (MEO) in primary culture, we found that CLA, but not linoleic acid (LA), inhibited growth of MEO and that this growth inhibition was mediated both by a reduction in DNA synthesis and a stimulation of apoptosis. The effects of CLA did not appear to be mediated by changes in epithelial protein kinase C (PKC) since neither total activity nor expression nor localization of PKC isoenzymes alpha, beta II, delta, epsilon, eta, or zeta were altered in the epithelium of CLA-fed rats. In contrast, PKCs delta, epsilon, and eta were specifically upregulated and associated with a lipid-like, but acetone-insoluble, fibrillar material found exclusively in adipocytes from CLA-fed rats. Taken together, these observations demonstrate that CLA can act directly to inhibit growth and induce apoptosis of normal MEO and may thus prevent breast cancer by its ability to reduce mammary epithelial density and to inhibit the outgrowth of initiated MEO. Moreover, the changes in mammary adipocyte PKC expression and lipid composition suggest that the adipose stroma may play an important in vivo role in mediating the ability of CLA to inhibit mammary carcinogenesis.

Oleic acid-induced Ca2+ mobilization in human platelets: is oleic acid an intracellular messenger?

The purpose of this study was to explore the effect of oleic acid (OA) on intracellular Ca2+ mobilization in human platelets. When applied extracellularly, OA produced a concentration dependent rise in cytosolic [Ca2+] ([Ca2+]cyt) when extracellular [Ca2+] (Ca2+]ext) was zero (presence of EGTA), suggesting that OA caused an intracellular release of Ca2+. Intracellular Ca2+ release was directly proportional to entry of OA into platelets and OA entry was indirectly proportional to [Ca2+]ext. In permeabilized platelets, OA caused the release of 45Ca2+ from ATP dependent intracellular stores. Finally, our results show that thrombin stimulated the release of [3H]OA from platelet phospholipids. The saturated fatty acids stearic and palmitic acid did not stimulate an increase in [Ca2+]cyt under these conditions, but the unsaturated fatty acid, linolenic acid produced effects similar to those of OA, suggesting specificity among fatty acids for effects on [Ca2+]cyt. Taken together, our experiments suggest that OA which has been incorporated into platelet phospholipids was released into the cytosol by thrombin stimulation. Our experiments also show that OA stimulates Ca2+ release from intracellular stores. These results support the hypothesis that OA may serve as an intracellular messenger in human platelets.

Liver protein kinase C isozymes: properties and enzyme role in a vertebrate facultative anaerobe

Protein kinase C was purified to homogeneity from liver of the anoxia-tolerant turtle (Trachemys scripta elegans). Two isozymes were present and were identified as PKC alpha and PKC beta by hydroxylapatite chromatography and cross-reaction with specific antibodies to the mammalian isozymes. Kinetic characterization of the isozymes showed that both required phospholipids and Ca2+ for activation and both were inhibited by low concentrations of PKC inhibitors. The PKC alpha was activated more strongly by phosphatidylinositol and lysophosphatidylinositol compared with PKC beta. Treatment with trypsin did not activate turtle PKC isozymes, but generated inactive PKC beta, whereas PKC alpha was resistant to inactivation. Anoxia exposure of turtles in vivo, via submergence in N2-gassed water at 7 degrees C, altered the activity and subcellular distribution of PKC in liver. After 1 hr of anoxic exposure at 7 degrees C, the activity of membrane-bound PKC had increased by 2.4-fold and represented a translocation of 40% of PKC beta and more than 80% of PKC alpha from the cytosol to the membrane-associated fraction. With longer submergence, however, membrane-bound PKC activity was suppressed again. This two-phase response to anoxia by PKC suggests that an activation of PKC, through its translocation to the membrane, is important in mediating the initial metabolic responses to submergence, which include an activation of glycogenolysis during the hypoxia transition period. With sustained anoxia exposure, the subsequent reduction of PKC activity may be part of the overall mechanism of metabolic rate depression that allows endurance of prolonged anoxia.

Arachidonic acid-induced down-regulation of protein kinase C delta in beta-cells

We have previously identified expression of multiple protein kinase C (PKC) isoforms in insulinoma-derived beta-cells and whole islets. Both PKC delta and PKC alpha appear to be the more abundantly expressed isoforms. In this report we studied the effects of arachidonic acid (AA) on the subcellular distribution of PKC alpha and PKC delta. AA has been reported to activate both PKC alpha and PKC delta and it is thought to be an important second messenger in beta-cells. Here we report that AA interacted with and altered beta-cell pools of PKC delta preferentially over PKC alpha. AA (100 microM) over the course of 45 min reduced cytosolic levels of PKC delta (to 40 +/- 15%, compared to time zero control) leaving membrane- and cytoskeleton-associated levels near control levels. Analysis of whole cell homogenates showed a slight down-regulation of PKC delta indicating proteolysis. The down-regulation of cytosolic PKC delta appeared to be isoform specific since cytosolic PKC alpha remained at control levels over the time course. The response was dose-dependent and negligible at concentrations below 30 microM and occurred, at least partially, in the cytosolic compartment of the cell. Indomethacin also down-regulated cytosolic PKC delta preferentially over PKC alpha possibly through accumulation of AA. These findings suggest that cytosolic PKC delta may be a downstream target of this beta-cell second messenger.

Activation of Na+/K(+)-ATPase by fatty acids, acylglycerols, and related amphiphiles: structure-activity relationship

A number of fatty acids and derivatives have been shown to activate Na+/K(+)-ATPase when ATP is suboptimal. To explore the relation of the structures of these amphiphiles to enzyme activation, the effects of varying amphiphile concentrations on the activity of the highly purified kidney Na+/K(+)-ATPase at 50 microM ATP were determined. Among fatty acids, efficacy (maximal level of activation) and potency were found to be dependent, in different ways, on chain length and unsaturation. Compared to fatty acids, the corresponding alcohols had lower efficacies. Methyl esters of fatty acids inhibited, but CoA esters and monoacyl esters of glycerol activated the enzyme. Relation between chain length and potency among CoA esters and monoacylglycerols was the same as that observed with acids. Diacylglycerols did not activate, but they antagonized the effects of the activator amphiphiles. The substantial specificities of the amphiphile effects support the hypothesis that these ligands bind to a distinct amphipathic peptide segment of the intracellular central loop of the alpha-subunit to regulate ATP binding to the enzyme. The findings also suggest that direct effects of the changing intracellular levels of fatty acids and derivatives on Na+/K(+)-ATPase should be considered as a possible mechanism for the regulation of its function in the intact cell.

Regulation of distinct pools of protein kinase C delta in beta cells

Previous studies from our laboratory have demonstrated the presence of several isoforms of protein kinase C (PKC), Ca(2+)-independent and Ca(2+)-dependent, in both whole islets and tumor-derived beta cells. In the basal state, a major proportion of the isoform was found in the crude membrane fraction with smaller amounts found in both the cytosolic and cytoskeletal fractions. Whole islets showed a similar distribution of the isoform. These studies were done to analyze the effects of insulin secretagogues on the distribution of PKC delta to different cellular pools in isolated insulinoma beta cells. The phorbol ester, phorbol 12-myristate 13-acetate (PMA), produced a transient association of PKC delta with the beta cell cytoskeleton along with sustained decreases in cytosolic enzyme and transient increases in membrane enzyme. Neither glucose nor carbachol could acutely affect the subcellular distribution of PKC delta. Oleic acid decreased the amount of the enzyme associated with the cytoskeleton and led to a sustained decrease of cytosolic enzyme and a transient increase in membrane enzyme. Oleic acid was also able to prevent the increase in cytoskeletal enzyme induced by PMA. Both oleic acid and PMA potentiated glucose-induced insulin release but oleic acid, in contrast to PMA, was unable to initiate insulin release in the presence of substimulatory concentrations of glucose. These data demonstrate that different activators of PKC may have different effects on localization of the enzyme within the cells and suggest that there are at least three apparently distinct pools of PKC delta within the beta cell which may be important in insulin secretion or other aspects of beta cell function.

Possible role for protein kinase C in the pathogenesis of inborn errors of metabolism

Protein kinase C (PKC) is a ubiquitous enzyme family implicated in the regulation of a large number of short- and long-term intracellular processes. It is hypothesized that modulation of PKC activity may represent, at least in part, a functional link between mutations (genotype) that lead to the pathological accumulation of naturally occurring compounds that affect PKC activity and perturbation of PKC-mediated substrate phosphorylation and cellular function in the corresponding diseases (phenotype). This model provides a unifying putative mechanism by which the phenotypic expression of some inborn errors of metabolism may be explained. Recent studies in a cell-free system of human skin fibroblasts support the hypothesis that alteration of PKC activity may represent the functional link between accumulation of sphingolipids and fatty acyl-CoA esters, and perturbation of cell function in sphingolipidoses and fatty acid oxidation defects, respectively. Further studies will elucidate the effects of these alterations on PKC-mediated short- and long-term cellular functions in these diseases, as well as the possible role of PKC in the pathogenesis of other diseases.

Protein kinase C inhibitors reduce phorbol ester-induced resistance to methotrexate in Chinese hamster ovary cells

Phorbol 12-myristate 13-acetate (TPA) increases the number of colonies surviving methotrexate (MTX) exposure in a dose-dependent manner upon short incubation with Chinese hamster ovary (CHO) cells. Seventy percent of the isolated colonies showed increased copy number for the dihydrofolate reductase gene. EGTA prevents the increase in resistance triggered by TPA. Calcium ionophore A23187 and angiotensin II also increase this resistance, suggesting that calcium is involved in this process. Protein kinase C (PKC) from CHO cells is rapidly activated by TPA, A23187 and angiotensin II. PKC inhibitors, 1-(5-Isoquinolinylsulphonyl)-2-methyl-piperazine (H-7), glycyrrhetinic acid, staurosporine and calphostin C decrease the generation of resistant colonies to MTX upon incubation with TPA. However, 5 nM staurosporine on its own increases resistance to MTX while having the ability to translocate CHO PKC. In vitro, H-7, staurosporine and calphostin C inhibit PKC activity translocated by TPA incubation with CHO cells. We conclude that PKC, the activity of which is dependent on calcium and phospholipids, is part of the pathway that leads to development of increased resistance to MTX. Thus, inhibition of PKC prevents the appearance of this resistance. Our results suggest the possibility of using non-toxic PKC inhibitors as resistance modulators in MTX chemotherapy.

Bimodal action of fatty acids on PMA-stimulated O2.- production in human adherent monocytes

Not only unsaturated linear fatty acids, but also saturated monomethyl-branched fatty acids (MMBFAs), are provided by food. They are capable of penetrating into the membrane lipids and promoting lipid disorder. Both NADPH oxidase and protein kinase C (PKC) are bound to cell cytoplasmic membranes and are responsive to unesterified fatty acids (UEFAs). We found that the O2.- NADPH oxidase-mediated production of human adherent monocytes was modified by unsaturated linear and saturated branched UEFAs only in the presence of phorbol myristate acetate. This result together with our inhibition data indicated an action strictly linked to PKC activity. The type and intensity of action depended on the UEFA concentrations and chain structure. Nanomolar concentrations showed potentiating effects whereas micromolar (< CMC) concentrations displayed depressant influences MMBFAs were generally more active than the other FAs. With respect to the micromolar depressant effect, oleate and linoleate were as active and docosahexaenoate nearly as active as MMBFAs. As assessed by iso-15:0 or arachidonate action, such bimodal alteration did not occur in non-adherent monocytes and neutrophils. Certain UEFAs could be considered as 'cellular' anti-oxidants on the sites of adherent-monocyte recruitment.

Loss of fatty acid control of gluconeogenesis and PDH complex flux in adrenalectomized rats

This work aimed to determine the role played by the adrenal gland in the fatty acid control of gluconeogenesis in isolated perfused rat livers. The gluconeogenic substrate concentration responses were not altered in adrenalectomized (ADX) rats. This observation indicates that glucocorticoids are not essential to maintain normal basal gluconeogenic rates. In contrast, fatty acid failed to stimulate gluconeogenesis from lactate and elicited attenuated stimulation with pyruvate as substrate in livers from ADX rats. Fatty acid-induced stimulation of respiration and ketone body production were similar in control and ADX rats. Thus the diminished responsiveness of the gluconeogenic pathway to fatty acid cannot be the result of different rates of energy production and/or generation of reducing power. Fatty acids did not inhibit pyruvate decarboxylation in livers from ADX rats. Even though mitochondria isolated from livers of ADX rats showed normal basal rates of pyruvate metabolism, fatty acids failed to inhibit pyruvate decarboxylation and the activity of the pyruvate dehydrogenase complex. This novel observation of the glucocorticoid effect in controlling the pyruvate dehydrogenase complex responsiveness indicates that the mitochondrial partitioning of pyruvate between carboxylation and decarboxylation reactions may be altered in livers from ADX rats. We propose that the diminished effect of fatty acid in stimulating gluconeogenesis in livers from ADX rats is the result of a limited pyruvate availability for the carboxylase reaction due to a lack of inhibition of flux through the pyruvate dehydrogenase complex.

Liver microsomal fatty acid composition in ethanol-fed rats: effect of different dietary fats and relationship to liver injury

The rat intragastric feeding model for alcoholic liver disease was used to study the effect of different diets on the fatty acid composition of liver microsomes. Rats were fed corn oil and ethanol (CE), saturated fat and ethanol (SF+E) or corn oil and dextrose (CD) for either 2 or 4 weeks. Rats were also fed saturated and dextrose (SF+D) for 4 weeks. In comparison with the CD diet, lower levels of arachidonic acid were detected in rats fed the CE, SF+E, and SF+D diets. However, the diet-induced changes in levels of arachidonic acid varied as a function of length of feeding. In rats fed the CE diet, we detected a significant decrease in the level of arachidonic acid compared with CD animals. Conversely, in rats fed the SF+E diet, the level of arachidonic acid increased compared with the SF+D group. In addition, a significant correlation was noted between levels of oleic acid and arachidonic acid in both corn oil (r = -0.85, p < 0.01) and saturated fat (r = -0.76, p < 0.05) groups. However, the changes in levels of arachidonic acid and oleic acid were in opposite directions in the two groups. Levels of docosahexaenoic acid decreased between the 2 and 4 weeks in animals maintained on the CE diet. Levels of stearic acid increased between 2 and 4 weeks in rats fed the SF+E diet. The lowest level of linoleic acid was detected in the SF+D and SF+E groups, but levels of linoleic acid remained constant in all groups throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro activation of rat brain protein kinase C by polyenoic very-long-chain fatty acids

A variety of fatty acids including the cis-polyunsaturated very-long-chain fatty acids (VLCFA) (> 22 carbon atoms) common in retina, spermatozoa, and brain were examined for their ability to activate protein kinase C (PKC) purified from rat brain. Arachidonic [20:4(n-6)], eicosapentaenoic [20:5(n-3)], and docosahexaenoic [22:6(n-3)] acids as well as the VLCFA dotriacontatetraenoic [32:4(n-6)] and tetratriacontahexaenoic [34:6(n-3)] were equally capable of activating PKC in vitro with maximal activity being between 25 and 50 microM. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate further enhanced the in vitro activation of PKC when added to the protein kinase assay system with the fatty acids. The fully saturated arachidic acid (20:0) was inactive in both assay systems. The potential significance of the in vitro activation of PKC by the VLCFA is discussed.

Effect of fatty acids and their acyl-CoA esters on protein kinase C activity in fibroblasts: possible implications in fatty acid oxidation defects

We studied the effect of fatty acids and their acyl-CoA esters on protein kinase C (PK-C) activity in human skin fibroblasts. Butyrate, octanoate, palmitate and oleate did not alter PK-C activity in either cytosolic or particulate fraction. In the presence of calcium, phosphatidylserine and diacylglycerol, both palmitoyl-CoA (Pal-CoA) and oleoyl-CoA (Ole-CoA) enhanced particulate PK-C activity by approx. 70% and octanoyl-CoA (Oct-CoA) by approx. 35%. Partially purified cytosolic PK-C activity was enhanced by 60-70% by 13.5 microM of either Pal-CoA or Ole-CoA. Basal histone phosphorylation (i.e., PK-C-independent phosphorylation) was decreased in the particulate fraction in the presence of these esters in a concentration-dependent manner. Both Pal-CoA and Ole-CoA fully substituted diacylglycerol in activating the kinase in both the cytosolic and particulate fractions, whereas Oct-CoA had a moderate effect. The pattern of endogenous cytosolic and particulate protein phosphorylation was altered in the presence of either Pal-CoA or Ole-CoA. We conclude that long-chain fatty acyl-CoA esters may activate PK-C in non-stimulated fibroblasts, i.e., in the absence of physiological diacylglycerol formation. Activation of PK-C in stimulated fibroblasts, i.e., in the presence of an elevated diacylglycerol concentration, is less pronounced. These results support the hypothesis that activation of PK-C and alteration of endogenous protein phosphorylation may play a role in the pathogenesis of diseases in which there is intracellular accumulation of fatty acyl-CoA esters, such as in inborn fatty-acid oxidation defects.

Effect of fatty acids on energy coupling processes in mitochondria

Long-chain fatty acids are natural uncouplers of oxidative phosphorylation in mitochondria. The protonophoric mechanism of this action is due to transbilayer movement of undissociated fatty acid in one direction and the passage of its anion in the opposite direction. The transfer of the dissociated form of fatty acid can be, at least in some kinds of mitochondrion, facilitated by adenine nucleotide translocase. Apart from dissipating the electrochemical proton gradient, long-chain fatty acids decrease the activity of the respiratory chain by mechanism(s) not fully understood. In intact cells and tissues fatty acids operate mostly as excellent respiratory substrates, providing electrons to the respiratory chain. This function masks their potential uncoupling effect which becomes apparent only under special physiological or pathological conditions characterized by unusual fatty acid accumulation. Short- and medium-chain fatty acids do not have protonophoric properties. Nevertheless, they contribute to energy dissipation because of slow intramitochondrial hydrolysis of their activation products, acyl-AMP and acyl-CoA. Long-chain fatty acids increase permeability of mitochondrial membranes to alkali metal cations. This is due to their ionophoric mechanism of action. Regulatory function of fatty acids with respect to specific cation channels has been postulated for the plasma membrane of muscle cells, but not demonstrated in mitochondria. Under cold stress, cold acclimation and arousal from hibernation the uncoupling effect of fatty acids may contribute to increased thermogenesis, especially in the muscle tissue. In brown adipose tissue, the special thermogenic organ of mammals, long-chain fatty acids promote operation of the unique natural uncoupling protein, thermogenin. As anionic amphiphiles, long-chain fatty acids increase the negative surface charge of biomembranes, thus interfering in their enzymic and transporting functions.

The role of protein phosphorylation in renal amino acid transport

Changes in tubular reabsorption of amino acids and other solutes are characteristic of the immature renal tubule and of various hereditary nephropathies. The cellular mechanisms governing these aberrations in renal amino acid transport have not been established. Calcium (Ca2+)-dependent protein kinases are known to phosphorylate membrane-bound carrier proteins, thereby modulating transport of various solutes by the proximal tubule. The role of these enzymes in regulating renal tubular amino acid transport, particularly during kidney development, is unknown. We investigated: (1) the effect of Ca(2+)- and phospholipid-dependent protein kinase [protein kinase C (PKC)] and Ca2+/calmodulin-dependent protein kinase II (CaMKII) on sodium chloride (NaCl)-linked proline transport by renal brush border membrane vesicles (BBMV) from adult rats using the "hypoosmotic shock" technique (lysis of vesicles); (2) the activity, expression and subcellular distribution (cytosol, particulate, BBM) of Ca(2+)-dependent protein kinases in kidneys from 7-day-old and adult rats using MBP 4-14 and autocamtide II phosphorylation assays for PKC and CaMKII, respectively, endogenous protein phosphorylation (using gel electrophoresis and autoradiography) and Western immunoblot analysis to detect PKC and CaMKII. The studies showed: (1) endogenous (membrane-bound) CaMKII and PKC as well as exogenous, highly purified PKC inhibit proline uptake by phosphorylated, lyzed/resealed BBMV when compared with control vesicles; the voltage-clamped, nonelectrogenic component of proline transport was inhibited by PKC- but not CaMKII-mediated phosphorylation; (2) a Ca(2+)-dependent activity of both kinases was evident in all subcellular fractions tested in immature and adult kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of high affinity membrane-bound fatty acid-binding proteins using a photoreactive fatty acid

A photoaffinity labeling method was developed to identify and characterize high affinity fatty acid-binding proteins in membranes. The specific labeling of these sites requires the use of low concentrations (nanomolar) of the photoreactive fatty acid 11-m-diazirinophenoxy-[11-3H]undecanoate. It was delivered as a bovine serum albumin (BSA) complex which serves as a reservoir for fatty acid and thus allows precise control of unbound fatty acid concentrations. The fadL protein of E. coli, which is required for fatty acid permeation of its outer membrane, was labeled by the photoreactive fatty acid neither specifically nor saturably when the probe was added in the absence of BSA; however when a nanomolar concentration of the uncomplexed probe was maintained in the presence of BSA, the labeling of the fadL protein was highly specific and saturable. This photoaffinity labeling method was also used to characterize a 22 kDa, high affinity fatty acid-binding protein which we have recently identified in the plasma membrane of 3T3-L1 adipocytes. This protein bound the probe with a Kd of 216 nM. The approach described is easily capable of identifying membrane-bound fatty acid-binding proteins and can distinguish between those of high and low affinities for fatty acids. It represents a general method for the identification and characterization of fatty acid-binding proteins.

Cellular binding proteins for fatty acids and retinoids: similar or specialized functions?

The cellular fatty acid-binding proteins (FABP) and cellular retinoid (retinol, retinoic acid)-binding proteins (CRtBP) are structurally and functionally-defined groups within an evolutionarily conserved gene family. CRtBP are expressed in both fully differentiated and developing tissues in a manner that supports a relationship to the action of retinoic acid in morphogenesis and cellular differentiation. The FABP are, by contrast, expressed only in fully differentiated tissues in a manner compatible with a major function in the metabolism of long-chain fatty acids (LCFA) for energy production or storage. The precise function(s) of FABP and CRtBP remain imperfectly understood, while subspecialization of function(s) within the two groups is suggested by the complex diversity in both of structurally distinct members that display striking tissue and temporal specificity of expression in addition to ligand specificity. Notwithstanding this considerable apparent functional diversity among the FABP and CRtBP, available evidence supports a dual set of generic functions for both protein groups in a) promoting cellular flux of poorly water-soluble ligands and their subsequent metabolic utilization or transformation, and b) sequestration of ligands in a manner that limits their association with alternative binding sites within the cell, of which members of the steroid hormone nuclear receptor superfamily (HNR) are a potentially important category. Theoretical as well as experimental models probing diffusional fluxes of LCFA in vitro and in living cells have provided support for a function for FABP in intracellular LCFA transport. Protein-bound ligand also appears to provide the substrate for metabolic transformation of retinoids bound to CRtBP, but convincing evidence is lacking for an analogous mechanism in the direct facilitation of fatty acid utilization by FABP. An emerging relationship between FABP and CRtBP function centers on their binding of, and induction by, ligands which activate or transform specific HNR-the retinoic acid receptors and the peroxisome proliferator activated receptor in the case of CRtBP and FABP, respectively. Evidence consistent with both a 'promotive' role (provision of ligands for HNR) and a 'protective' role (limiting availability of free ligand for HNR association) has been advanced for CRtBP. Available data supports a 'protective' function for cellular retinoic acid-binding proteins (CRABP) and liver FABP (L-FABP) and points to the existence of ligand-defined, lipid-binding-protein-HNR relationships in which CRABP serve to attenuate the induction of gene expression by retinoic acid, and in which L-FABP may modulate a cellular adaptive multigene response to increased LCFA flux or compromised LCFA utilization.(ABSTRACT TRUNCATED AT 400 WORDS)