Role of polyamines in differentiation of 3T3-L1 fibroblasts into adipocytes

Spermine Suppresses Adipocyte Differentiation and Exerts Anti-Obesity Effects In Vitro and In Vivo

Endogenous polyamines such as putrescine (Put), spermidine (Spd), and spermine (Spm) affect adipocyte differentiation. In this study, we investigated the effect of exogenously supplemented polyamines on mouse adipocyte differentiation and anti-obesity actions in vitro and in vivo. The preadipocyte cell line, 3T3-L1, was cultured with Put, Spd, or Spm, and lipid accumulation in the cells was measured by Oil Red O staining. Lipid accumulation was significantly suppressed by Spm. Suppression of CCAAT/enhancer binding protein α mRNA by Spm suggested that the decreased lipid accumulation was due to delaying the cell differentiation. The body weight and fat of obese mice induced with a high-fat diet were reduced by oral ingestion of Spm. In conclusion, oral supplementation of Spm has the ability to prevent obesity through inhibition of adipocyte differentiation.

Bifidobacterium animalis subsp. lactis lkm512 Attenuates Obesity-Associated Inflammation and Insulin Resistance Through the Modification of Gut Microbiota in High-Fat Diet-Induced Obese Mice

SCOPE

The impacts of longevity-promoting probiotic Bifidobacterium animalis subsp. lactis LKM512 (LKM512) on metabolic disease remain unclear. Here, the authors aim to explore the potential of LKM512 on the host physiological function and gut microbiota in high-fat diet-induced obese mice.

METHODS AND RESULTS

LKM512 are orally administrated for 12 weeks, and the effects of LKM 512 on systemic inflammation and insulin resistance, as well as gut microbiota, are investigated in high-fat (HF) diet-induced obese mice. LKM512 supplementation ameliorates hepatic lipid accumulation, attenuates hepatic and adipose tissue inflammation, and improves intestinal barrier function. These results are associated with improved insulin sensitivity and metabolic endotoxemia. Furthermore, the colonization of LKM512 induces an increase in polyamine metabolism and production, together with significant alternations in the composition and function of gut microbiota in obese mice, which are correlated with these improved metabolic phenotypes in the host.

CONCLUSION

The probiotic strain LKM512 may become a promising strategy to improve obesity and related metabolic disorders.

The Role of Spermidine Synthase (SpdS) and Spermine Synthase (Sms) in Regulating Triglyceride Storage in Drosophila

Polyamines are small organic cations that are important for several biological processes such as cell proliferation, cell cycle progression, and apoptosis. The dysregulation of intracellular polyamines is often associated with diseases such as cancer, diabetes, and developmental disorders. Although polyamine metabolism has been well studied, the effects of key enzymes in the polyamine pathway on lipid metabolism are not well understood. Here, we determined metabolic effects resulting from the absence of spermidine synthase (SpdS) and spermine synthase (Sms) in Drosophila. While SpdS mutants developed normally and accumulated triglycerides, Sms mutants had reduced viability and stored less triglyceride than the controls. Interestingly, when decreasing SpdS and Sms, specifically in the fat body, triglyceride storage increased. While there was no difference in triglycerides stored in heads, thoraxes and abdomen fat bodies, abdomen fat body DNA content increased, and protein/DNA decreased in both SpdS- and Sms-RNAi flies, suggesting that fat body-specific knockdown of SpdS and Sms causes the production of smaller fat body cells and triglycerides to accumulate in non-fat body tissues of the abdomen. Together, these data provide support for the role that polyamines play in the regulation of metabolism and can help enhance our understanding of polyamine function in metabolic diseases.

The regulation of triglyceride storage by ornithine decarboxylase (Odc1) in Drosophila

Polyamines are low molecular weight, organic cations that play a critical role in many major cellular processes including cell cycle regulation and apoptosis, cellular division, tissue proliferation, and cellular differentiation; however, the functions of polyamines in regulating the storage of metabolic fuels such as triglycerides and glycogen is poorly understood. To address this question, we focused on the Drosophila homolog of ornithine decarboxylase (Odc1), the first rate-limiting enzyme in the synthesis of polyamines. Mutants in Odc1 are lethal, but heterozygotes were viable to adulthood. Odc1 heterozygotes appeared larger than their genetic background control flies and consistent with this observation, weighed more than the controls. However, the increased weight was not due to increased food consumption as heterozygotes ate less than the controls. Interestingly, Odc1 heterozygous flies had augmented triglyceride storage, and this lipid phenotype was due to increased triglyceride storage per cell and an increase in the number of fat cells produced. Odc1 heterozygous flies also displayed increased expression of the lipid synthesis genes fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC), suggesting increased lipid synthesis was the cause of the augmented triglyceride phenotype. These results provide a link between the expression of Odc1 and triglyceride storage suggesting that the polyamine pathway plays a role in regulating lipid metabolism.

Dietary and Gut Microbiota Polyamines in Obesity- and Age-Related Diseases

The polyamines putrescine, spermidine, and spermine are widely distributed polycationic compounds essential for cellular functions. Intracellular polyamine pools are tightly regulated by a complex regulatory mechanism involving de novo biosynthesis, catabolism, and transport across the plasma membrane. In mammals, both the production of polyamines and their uptake from the extracellular space are controlled by a set of proteins named antizymes and antizyme inhibitors. Dysregulation of polyamine levels has been implicated in a variety of human pathologies, especially cancer. Additionally, decreases in the intracellular and circulating polyamine levels during aging have been reported. The differences in the polyamine content existing among tissues are mainly due to the endogenous polyamine metabolism. In addition, a part of the tissue polyamines has its origin in the diet or their production by the intestinal microbiome. Emerging evidence has suggested that exogenous polyamines (either orally administrated or synthetized by the gut microbiota) are able to induce longevity in mice, and that spermidine supplementation exerts cardioprotective effects in animal models. Furthermore, the administration of either spermidine or spermine has been shown to be effective for improving glucose homeostasis and insulin sensitivity and reducing adiposity and hepatic fat accumulation in diet-induced obesity mouse models. The exogenous addition of agmatine, a cationic molecule produced through arginine decarboxylation by bacteria and plants, also exerts significant effects on glucose metabolism in obese models, as well as cardioprotective effects. In this review, we will discuss some aspects of polyamine metabolism and transport, how diet can affect circulating and local polyamine levels, and how the modulation of either polyamine intake or polyamine production by gut microbiota can be used for potential therapeutic purposes.

Dual Regulatory Role of Polyamines in Adipogenesis

Adipogenesis is a complex process, accompanied by a chain of interdependent events. Disruption of key events in this cascade may interfere with the correct formation of adipose tissue. Polyamines were demonstrated necessary for adipogenesis; however, the underlying mechanism by which they act has not been established. Here, we examined the effect of polyamine depletion on the differentiation of 3T3-L1 preadipocytes. Our results demonstrate that polyamines are required early in the adipogenic process. Polyamine depletion inhibited the second division of the mitotic clonal expansion (MCE), and inhibited the expression of PPARγ and C/EBPα, the master regulators of adipogenesis. However, it did not affect the expression of their transcriptional activator, C/EBPβ. Additionally, polyamine depletion resulted in elevation of mRNA and protein levels of the stress-induced C/EBP homologous protein (CHOP), whose dominant negative function is known to inhibit C/EBPβ DNA binding activity. Conditional knockdown of CHOP in polyamine-depleted preadipocytes restored PPARγ and C/EBPα expression, but failed to recover MCE and differentiation. Thus, our results suggest that the need for MCE in the adipogenic process is independent from the requirement for PPARγ and C/EBPα expression. We conclude that de novo synthesis of polyamines during adipogenesis is required for down-regulation of CHOP to allow C/EBPβ activation, and for promoting MCE.

OVCAR-3 spheroid-derived cells display distinct metabolic profiles

Introduction

Recently, multicellular spheroids were isolated from a well-established epithelial ovarian cancer cell line, OVCAR-3, and were propagated in vitro. These spheroid-derived cells displayed numerous hallmarks of cancer stem cells, which are chemo- and radioresistant cells thought to be a significant cause of cancer recurrence and resultant mortality. Gene set enrichment analysis of expression data from the OVCAR-3 cells and the spheroid-derived putative cancer stem cells identified several metabolic pathways enriched in differentially expressed genes. Before this, there had been little previous knowledge or investigation of systems-scale metabolic differences between cancer cells and cancer stem cells, and no knowledge of such differences in ovarian cancer stem cells.

Methods

To determine if there were substantial metabolic changes corresponding with these transcriptional differences, we used two-dimensional gas chromatography coupled to mass spectrometry to measure the metabolite profiles of the two cell lines.

Results

These two cell lines exhibited significant metabolic differences in both intracellular and extracellular metabolite measurements. Principal components analysis, an unsupervised dimensional reduction technique, showed complete separation between the two cell types based on their metabolite profiles. Pathway analysis of intracellular metabolomics data revealed close overlap with metabolic pathways identified from gene expression data, with four out of six pathways found enriched in gene-level analysis also enriched in metabolite-level analysis. Some of those pathways contained multiple metabolites that were individually statistically significantly different between the two cell lines, with one of the most broadly and consistently different pathways, arginine and proline metabolism, suggesting an interesting hypothesis about cancerous and stem-like metabolic phenotypes in this pair of cell lines.

Conclusions

Overall, we demonstrate for the first time that metabolism in an ovarian cancer stem cell line is distinct from that of more differentiated isogenic cancer cells, supporting the potential importance of metabolism in the differences between cancer cells and cancer stem cells.

Selective regulation of polyamine metabolism with methylated polyamine analogues

Polyamine metabolism is intimately linked to the physiological state of the cell. Low polyamines levels promote growth cessation, while increased concentrations are often associated with rapid proliferation or cancer. Delicately balanced biosynthesis, catabolism, uptake and excretion are very important for maintaining the intracellular polyamine homeostasis, and deregulated polyamine metabolism is associated with imbalanced metabolic red/ox state. Although many cellular targets of polyamines have been described, the precise molecular mechanisms in these interactions are largely unknown. Polyamines are readily interconvertible which complicate studies on the functions of the individual polyamines. Thus, non-metabolizable polyamine analogues, like carbon-methylated analogues, are needed to circumvent that problem. This review focuses on methylated putrescine, spermidine and spermine analogues in which at least one hydrogen atom attached to polyamine carbon backbone has been replaced by a methyl group. These analogues allow the regulation of both metabolic and catabolic fates of the parent molecule. Substituting the natural polyamines with methylated analogue(s) offers means to study either the functions of an individual polyamine or the effects of altered polyamine metabolism on cell physiology. In general, gem-dimethylated analogues are considered to be non-metabolizable by polyamine catabolizing enzymes spermidine/spermine-N¹-acetyltransferase and acetylpolyamine oxidase and they support short-term cellular proliferation in many experimental models. Monomethylation renders the analogues chiral, offering some advantage over gem-dimethylated analogues in the specific regulation of polyamine metabolism. Thus, methylated polyamine analogues are practical tools to meet existing biological challenges in solving the physiological functions of polyamines.

Modulation of polyamine metabolic flux in adipose tissue alters the accumulation of body fat by affecting glucose homeostasis

The continued rise in obesity despite public education, awareness and policies indicates the need for mechanism-based therapeutic approaches to help control the disease. Our data, in conjunction with other studies, suggest an unexpected role for the polyamine catabolic enzyme spermidine/spermine-N1-acetyltransferase (SSAT) in fat homeostasis. Our previous studies showed that deletion of SSAT greatly exaggerates weight gain and that the transgenic overexpression suppresses weight gain in mice on a high-fat diet. This discovery is substantial but the underlying molecular linkages are only vaguely understood. Here, we used a comprehensive systems biology approach, on white adipose tissue (WAT), to discover that the partition of acetyl-CoA towards polyamine catabolism alters glucose homeostasis and hence, fat accumulation. Comparative proteomics and antibody-based expression studies of WAT in SSAT knockout, wild type and transgenic mice identified nine proteins with an increasing gradient across the genotypes, all of which correlate with acetyl-CoA consumption in polyamine acetylation. Adipose-specific SSAT knockout mice and global SSAT knockout mice on a high-fat diet exhibited similar growth curves and proteomic patterns in their WAT, confirming that attenuated consumption of acetyl-CoA in acetylation of polyamines in adipose tissue drives the obese phenotype of these mice. Analysis of protein expression indicated that the identified changes in the levels of proteins regulating acetyl-CoA consumption occur via the AMP-activated protein kinase pathway. Together, our data suggest that differential expression of SSAT markedly alters acetyl-CoA levels, which in turn trigger a global shift in glucose metabolism in adipose tissue, thus affecting the accumulation of body fat.

Polyamine metabolism is involved in adipogenesis of 3T3-L1 cells

Polyamines spermidine and spermine are known to be required for mammalian cell proliferation and for embryonic development. Alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC) a limiting enzyme of polyamine biosynthesis, depleted the cellular polyamines and prevented triglyceride accumulation and differentiation in 3T3-L1 cells. In this study, to explore the function of polyamines in adipogenesis, we examined the effect of polyamine biosynthesis inhibitors on adipocyte differentiation and lipid accumulation of 3T3-L1 cells. The spermidine synthase inhibitor trans-4-methylcyclohexylamine (MCHA) increased spermine/spermidine ratios, whereas the spermine synthase inhibitor N-(3-aminopropyl)-cyclohexylamine (APCHA) decreased the ratios in the cells. MCHA was found to decrease lipid accumulation and GPDH activity during differentiation, while APCHA increased lipid accumulation and GPDH activity indicating the enhancement of differentiation. The polyamine-acetylating enzyme, spermidine/spermine N(1)-acetyltransferase (SSAT) activity was increased within a few hours after stimulus for differentiation, and was found to be elevated by APCHA. In mature adipocytes APCHA decreased lipid accumulation while MCHA had the opposite effect. An acetylpolyamine oxidase and spermine oxidase inhibitor MDL72527 or an antioxidant N-acetylcysteine prevented the promoting effect of APCHA on adipogenesis. These results suggest that not only spermine/spermidine ratios but also polyamine catabolic enzyme activity may contribute to adipogenesis.

Phytochemicals and protein-polyamine conjugates by transglutaminase as chemopreventive and chemotherapeutic tools in cancer

Identifying novel chemopreventive and chemotherapeutic agents and targeting them to patients at high risk of developing cancer or following curative treatment may go some way towards improving prognosis. This review examines current knowledge regarding the chemopreventive and chemotherapeutic potential of phytochemicals in cancer. Both in vitro and animal studies demonstrate that several phytochemicals increase the activity of intracellular transglutaminases, a family of enzymes involved in cell differentiation, through the covalent conjugation of polyamine to cellular protein, with promising anti-neoplastic properties. The substantial data available on certain plant secondary metabolites makes a strong case for integrating these safe and well-tolerated agents into clinical practice.

Spermine analogue-regulated expression of spermidine/spermine N1-acetyltransferase and its effects on depletion of intracellular polyamine pools in mouse fetal fibroblasts

SSAT (Spermidine/spermine N1-acetyltransferase, also known as SAT1), the key enzyme in the catabolism of polyamines, is turned over rapidly and there is only a low amount present in the cell. In the present study, the regulation of SSAT by spermine analogues, the inducers of the enzyme, was studied in wild-type mouse fetal fibroblasts, expressing endogenous SSAT, and in the SSAT-deficient mouse fetal fibroblasts transiently expressing an SSAT-EGFP (enhanced green fluorescent protein) fusion gene. In both cell lines treatments with DENSpm (N(1),N(11)-diethylnorspermine), CPENSpm (N(1)-ethyl-N(11)-[(cyclopropyl)-methy]-4,8-diazaundecane) and CHENSpm (N(1)-ethyl-N(11)-[(cycloheptyl)methy]-4,8-diazaundecane) led to high, moderate or low induction of SSAT activity respectively. The level of activity detected correlated with the presence of SSAT and SSAT-EGFP proteins, the latter localizing both in the cytoplasm and nucleus. RT-PCR (reverse transcription-PCR) results suggested that the analogue-affected regulation of SSAT-EGFP expression occurred, mainly, after transcription. In wild-type cells, DENSpm increased the amount of SSAT mRNA, and both DENSpm and CHENSpm affected splicing of the SSAT pre-mRNA. Depleted intracellular spermidine and spermine levels inversely correlated with detected SSAT activity. Interestingly, the analogues also reduced polyamine levels in the SSAT-deficient cells expressing the EGFP control. The results from the present study show that the distinct SSAT regulation by different analogues involves regulatory actions at multiple levels, and that the spermine analogues, in addition to inducing SSAT, lower intracellular polyamine pools by SSAT-independent mechanisms.

Spermidine is indispensable in differentiation of 3T3-L1 fibroblasts to adipocytes

Impaired adipogenesis has been shown to predispose to disturbed adipocyte function and development of metabolic abnormalities. Previous studies indicate that polyamines are essential in the adipogenesis in 3T3-L1 fibroblasts. However, the specific roles of individual polyamines during adipogenesis have remained ambiguous as the natural polyamines are readily interconvertible inside the cells. Here, we have defined the roles of spermidine and spermine in adipogenesis of 3T3-L1 cells by using (S’)- and (R’)- isomers of α-methylspermidine and (S,S’)-, (R,S)- and (R,R’)-diastereomers of α,ω-bismethylspermine. Polyamine depletion caused by α-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, prevented adipocyte differentiation by suppressing the expression of its key regulators, peroxisome proliferator-activated receptor γ and CCAAT/enhancer binding protein α. Adipogenesis was restored by supplementation of methylspermidine isomers but not of bismethylspermine diastereomers. Although both spermidine analogues supported adipocyte differentiation only (S)-methylspermidine was able to fully support cell growth after extended treatment with α-DFMO. The distinction between the spermidine analogues in maintaining growth was found to be in their different capability to maintain functional hypusine synthesis. However, the differential ability of spermidine analogues to support hypusine synthesis did not correlate with their ability to support differentiation. Our results show that spermidine, but not spermine, is essential for adipogenesis and that the requirement of spermidine for adipogenesis is not strictly associated with hypusine modification. The involvement of polyamines in the regulation of adipogenesis may offer a potential application for the treatment of dysfunctional adipocytes in patients with obesity and metabolic syndrome.

Comparative haemodynamic effects of verapamil, flecainide, amiodarone and sotalol in the conscious rabbit

1. The effect of intravenous boluses of verapamil (0.15 mg/kg), flecainide (2 mg/kg), amiodarone (5 mg/kg), and sotalol (1.5 mg/kg) on mean arterial pressure, heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), and peak rate of change of left ventricular pressure (LV dP/dt) were assessed in the conscious rabbit. 2. All four drugs had negative inotropic effects: verapamil reduced peak LV dP/dt by 19 +/- 4% (mean +/- s.e.m.; P < 0.01), flecainide by 27 +/- 9% (P < 0.001), amiodarone by 11 +/- 2% (P < 0.01) and sotalol by 13 +/- 3% (P < 0.01). 3. The drugs had different effects on CO as a result of differences in their actions on peripheral blood vessels: verapamil and amiodarone produced, respectively, a 12 +/- 4% (P < 0.03) and 16 +/- 6% (P < 0.01) increase in CO associated with a substantial vasodilatory effect (TPR reduced 15 +/- 7% [P < 0.05] and 20 +/- 5% [P < 0.01], respectively). Flecainide caused only a small (6 +/- 1%; P < 0.01) increase in CO and sotalol had no effect on either CO or TPR. 4. Bolus intravenous injections of verapamil, flecainide and amiodarone produced an increase in HR, while sotalol reduced HR by 10 +/- 2% (P < 0.01). The increase in HR and cardiac output seen with verapamil, flecainide and amiodarone was in part secondary to reflex increase in sympathetic tone and these changes were abolished after total cardiac autonomic blockade. 5. The modest reduction in cardiac performance associated with sotalol was abolished by cardiac autonomic blockade, suggesting that the predominant effect of sotalol on contractility was mediated through its beta-adrenoceptor blocking effect.

Sodium butyrate stimulates polyamine biosynthesis in colon cancer cells

Differentiation inducers act through polyamine-dependent and independent pathways. Sodium butyrate (NaB) inhibits proliferation and induces terminal differentiation in human and murine cancer cell lines. An effect of this agent on polyamine biosynthesis has not been demonstrated previously. In the present study, we examined the effects of NaB on polyamine biosynthesis in mouse colon cancer (MC-26) cells. All studies were performed on exponentially growing cells, and ODC and polyamine transport measurements were performed as described previously. NaB inhibited the growth of MC-26 cells in a dose-dependent manner. Cell shape was significantly altered by treatment with NaB (development of dendritic-like processes and flattening and spreading out of cells on culture dishes). NaB stimulated ODC activity in a dose-dependent manner. The activity was elevated by 8 h after treatment, and at 48 h there was a ten-fold increase in activity (compared with control activity). The increase in ODC activity led to an increase in polyamine biosynthesis; putrescine, spermidine, and spermine levels in MC-26 cells were significantly elevated by 24 h after treatment with NaB. Polyamine uptake was similar in control cells and cells treated with NaB alone. Our finding of significant stimulation of polyamine uptake by NaB after inhibition of endogenous synthesis (by an ODC-dependent pathway) in DFMO-treated cells suggests that cellular requirements are increased for polyamines in NaB-treated cells. We conclude that polyamine-dependent processes are important in the mechanism of action of NaB in colon cancer cells.

Polyamines: from molecular biology to clinical applications

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

Juvenile hormone stimulation of ornithine decarboxylase activity during vitellogenesis in Drosophila melanogaster

The activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, becomes elevated in intact female Drosophila melanogaster shortly after adult eclosion. This activity reaches a peak at 24 h following eclosion, and then drops to lower levels by 48 h. This pattern is not observed in males, consistent with the hypothesis that polyamine synthesis is involved in ovarian maturation in Drosophila. Abdomens isolated within 2 h of adult eclosion do not display elevated ODC activity or ovarian maturation. However, a 250-ng dose of the juvenile hormone analog methoprene (ZR-515) applied in acetone to these abdomens, recovers ovarian maturation and causes a 5-10 fold increase in enzyme activity over controls treated with acetone alone. The same dose of the inactive precursor methyl farnesoate caused no such increase, whereas a 500-ng dose of the newly discovered natural Drosophila JHB3 stimulated a four-fold response. The response to methoprene was dose-dependent, showing stimulatory activity at a dose as low as 10 ng. This stimulation by JHA is rapid, occurring between 1 and 3 h following hormone treatment, reminiscent of JH induction of fat body vitellogenin synthesis in Drosophila. Elevated ODC activity appeared to be localized in the adult fat body. During embryogenesis, ODC activity remained undetectable until just prior to hatching, when a large increase was detected. We postulate that JH may, either directly or indirectly, regulate polyamine biosynthesis in vivo, and that this synthesis may be required for the production of macromolecules during Drosophila vitellogenesis or embryogenesis.

Effect of the ornithine decarboxylase inhibitor alpha, alpha-difluoromethylornithine on phorbol diester-induced inhibition of murine B lymphocyte differentiation

The tumor-promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits the differentiation of murine B lymphocytes to antibody-producing plasma cells, in unfractionated spleen cell cultures or enriched B lymphocyte cultures. To determine the role of polyamines in TPA-induced inhibition, unfractionated splenic lymphocytes, in culture with antigen, were incubated with alpha, alpha-difluoromethylornithine (DFMO, 0.10 mM), an irreversible inhibitor of ornithine decarboxylase (ODC). DFMO prevented the TPA-induced inhibition of antibody forming cell number in a 5-day in vitro immunization procedure as measured by a hemolytic plaque assay. In enriched B lymphocyte cultures, however, DFMO had no comparable effect. DFMO did not prevent TPA-induced inhibition of antibody production in unfractionated spleen cell cultures but itself inhibited the amount of antibody produced. Putrescine (0.1 mM), added on day 4 of immunization, reversed DFMO inhibition of antibody production but did not enable DFMO to prevent the TPA-induced inhibition. These findings suggest that TPA-induced inhibition of plasma cell number can be mediated indirectly through effects on T lymphocytes and/or macrophages or directly through effect on B lymphocytes.

Inhibition of polyamine synthesis reduces the growth rate and delays the expression of differentiated phenotypes in primary cultures of embryonic mesoderm from chick

Inhibition of polyamine synthesis in early chick embryos blocks their development at gastrulation. Analyses of arrested embryos show that mesodermal outgrowth and differentiation are drastically impaired. To study these effects in greater detail, we have used primary cultures of embryonic mesoderm from chick. The cultures were treated with alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase, the first and rate-limiting enzyme in polyamine synthesis. In control culture medium, mesodermal cells retained their in ovo outgrowth behavior and differentiation pattern. Addition of 10 mM DFMO to the culture medium, however, retarded attachment and outgrowth, and reduced the rate of proliferation of the mesodermal cells. Furthermore, the expression of differentiated phenotypes, such as beating heart tissue, erythroid cells, and adipocyte-like cells, was delayed. Simultaneous addition of 100 microM putrescine prevented or reduced the effects of DFMO, showing that these were indeed caused by polyamine deficiency. In the DFMO-treated mesoderm, DNA synthesis was markedly suppressed by the first day. Similar effects on RNA and protein synthesis developed at a later time. Our data suggest that a reduction in the concentrations of the polyamines decreases the rate of mesodermal cell proliferation, and as a consequence delays the expression of differentiated phenotypes.

Interferon-mediated inhibition of differentiation in a murine myoblast cell line

The effects of highly purified (greater than 5 X 10(7) IU/mg) murine beta-interferon (IFN) on a mouse myoblast line (MM14DZ) have been investigated to confirm and extend the previous observation that partially purified chicken interferon inhibits differentiation of cultured avian myoblasts (Lough et al., Biochem Biophys Res Commun 109:92, 1982). Cultures treated with 20-2,000 lU IFN/ml medium for 5 days exhibited dose-dependent 1) inhibition of differentiation, as indicated by reduced myotube formation and creatine kinase (CK) activity and 2) increases in DNA content, suggesting that the inhibitory effect was accompanied by continued proliferation of myoblasts. Mock-IFN had no such effects. Based on findings in other systems that IFN inhibits activity of ornithine decarboxylase (ODC), the polyamine products of which are required for myogenesis, the hypothesis that inhibition of differentiation was mediated by an effect of IFN on polyamine metabolism was tested. However, observations that 1) IFN-treated myoblasts retained control levels of ODC activity and 2) exogenous polyamines did not prevent IFN-inhibition did not indicate such a mechanism of action. On the other hand, treatment of control cultures with polyamines alone resulted in potentiation of myogenesis as revealed by precocious myotube formation and a marked increase in CK activity.

Growth of mammalian cells in the absence of the accumulation of spermine

Mammalian spermine synthase activity was strongly inhibited by S-methyl-5'-methylthioadenosine. This nucleoside was readily taken up by SV-3T3 cells and blocked the synthesis of spermine by these cells. However, there was a corresponding increase in spermidine content and there was no effect on cell growth. These results indicate that S-methyl-5'-methylthioadenosine should be a useful compound to evaluate the role of spermine in mammalian cell physiology and that in at least one cell line the synthesis of spermine is not required for a normal growth rate.

Relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility in conscious rabbits

The relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility have been assessed in the conscious normotensive and hypertensive rabbit. Graded increases in mean arterial pressure (MAP) were produced by inflation of a balloon occluder around the abdominal aorta. Stimulus response curves relating the change in MAP to the induced change in peak rate of change of left ventricular pressure (peak LV dP/dt) were produced when heart rate was allowed to change and when it was held constant by atrial pacing. These curves were repeated after sympathetic blockade with propranolol, vagal blockade with methylscopolamine and combined blockade with the two drugs together. Increase in MAP produced a reflex fall in peak LV dP/dt which was due to two components. There was a reflex negative inotropic effect which was independent of heart rate, occurring in animals in whom heart rate was held constant by atrial pacing, and there was also a reduction in peak LV dP/dt which was caused by the reflex bradycardia when the heart rate was allowed to change. Both sympathetic and vagal efferents contributed to the reflex fall in peak LV dP/dt seen after elevation of MAP, the sympathetic being primarily responsible for the direct negative inotropic effect and the vagus for the bradycardia and hence the secondary effects on peak LV dP/dt. The slope of the stimulus response curves relating the fall in peak LV dP/dt to the increase in MAP was similar in intact normotensive and hypertensive rabbits, both with and without atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of polyamines in somatomedin-stimulated differentiation of L6 myoblasts

The somatomedins are potent stimulators of proliferation and differentiation of cultured myoblasts. In studies on the mechanism(s) of these actions, we have measured the activities of ornithine decarboxylase (ODC), an enzyme associated with rapid cell proliferation, and creatine kinase (CK), a biochemical marker for muscle differentiation, after treatment of L6 myoblast cultures with Multiplication Stimulating Activity (MSA), a member of the somatomedin family of insulinlike growth factors. ODC levels reached a peak 24 hours after MSA addition (before any detectable differentiation of the myoblasts) and then decreased as differentiation commenced and CK activity increased. Addition of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, caused a dramatic decrease in differentiation. Measurement of 3H-thymidine incorporation, DNA content, and cell number established that the effect of DFMO on differentiation was not a simple consequence of its antiproliferative actions. Cellular levels of putrescine and spermidine (but not spermine) decreased substantially following addition of DFMO to the cultures. The inhibitory effects of DFMO were abolished upon addition of exogenous polyamines to the medium. However, addition of polyamines in the absence of MSA or DFMO did not mimic the stimulation of differentiation by MSA. We conclude that polyamines play an essential role in the stimulation of L6 myoblast differentiation by somatomedins, but they are not sufficient to effect this stimulation.