Polyamine biosynthesis as a target to inhibit apoptosis of non-tumoral cells

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.

Spermidine activates RIP1 deubiquitination to inhibit TNF-α-induced NF-κB/p65 signaling pathway in osteoarthritis

Spermidine has been known to inhibit the production of pro-inflammatory cytokines. However, there are no reports about anti-inflammatory effects of spermidine on osteoarthritis (OA). Herein, we examined whether OA progression could be delayed by intraperitoneal injection (i.p.) of spermidine in the anterior cruciate ligament transection (ACLT) and TNF-α induced arthritis (TIA) mouse models. During the process, human FLS cells (H-FLS) were used to investigate the potential ubiquitination mechanism of spermidine-mediated RIP1 in TNF-α-induced NF-κB/p65 signaling. We found that spermidine attenuated synovitis, cartilage degeneration and osteophyte formation, resulting in substantially lower OARSI scores and TNF-α scores in spermidine-treated ACLT and TIA mice. In terms of the mechanism, 9 μM spermidine did not affect the viability, proliferation, cell cycle and apoptosis of H-FLS, and exerted inhibitory effects by activating CYLD-mediated RIP1 deubiquitination on TNF-α-induced NF-κB/p65 signaling in H-FLS. From these data, we can conclude that spermidine attenuates OA progression by the inhibition of TNF-α-induced NF-κB pathway via the deubiquitination of RIP1 in FLS. Therefore, intake of spermidine could be a potential therapy for preventing OA.

MicroRNAs and Autophagy: Fine Players in the Control of Chondrocyte Homeostatic Activities in Osteoarthritis

Osteoarthritis (OA) is a debilitating degenerative disease of the articular cartilage with a multifactorial etiology. Aging, the main risk factor for OA development, is associated with a systemic oxidative and inflammatory phenotype. Autophagy is a central housekeeping system that plays an antiaging role by supporting the clearance of senescence-associated alterations of macromolecules and organelles. Autophagy deficiency has been related to OA pathogenesis because of the accumulation of cellular defects in chondrocytes. Microribonucleic acids (microRNAs or miRs) are a well-established class of posttranscriptional modulators belonging to the family of noncoding RNAs that have been identified as key players in the regulation of cellular processes, such as autophagy, by targeting their own cognate mRNAs. Here, we present a state-of-the-art literature review on the role of miRs and autophagy in the scenario of OA pathogenesis. In addition, a comprehensive survey has been performed on the functional connections of the miR network and the autophagy pathway in OA by using "microRNA," "autophagy," and "osteoarthritis" as key words. Discussion of available evidence sheds light on some aspects that need further investigation in order to reach a more comprehensive view of the potential of this topic in OA.

Reprint of "DNA, the central molecule of aging"

Understanding the molecular mechanism of aging could have enormous medical implications. Despite a century of research, however, there is no universally accepted theory regarding the molecular basis of aging. On the other hand, there is plentiful evidence suggesting that DNA constitutes the central molecule in this process. Here, we review the roles of chromatin structure, DNA damage, and shortening of telomeres in aging and propose a hypothesis for how their interplay leads to aging phenotypes.

DNA, the central molecule of aging

Understanding the molecular mechanism of aging could have enormous medical implications. Despite a century of research, however, there is no universally accepted theory regarding the molecular basis of aging. On the other hand, there is plentiful evidence suggesting that DNA constitutes the central molecule in this process. Here, we review the roles of chromatin structure, DNA damage, and shortening of telomeres in aging and propose a hypothesis for how their interplay leads to aging phenotypes.

Polyamine delivery as a tool to modulate stem cell differentiation in skeletal tissue engineering

The first step in skeleton development is the condensation of mesenchymal precursors followed by any of two different types of ossification, depending on the type of bone segment: in intramembranous ossification, the bone is deposed directly in the mesenchymal anlagen, whereas in endochondral ossification, the bone is deposed onto a template of cartilage that is subsequently substituted by bone. Polyamines and polyamine-related enzymes have been implicated in bone development as global regulators of the transcriptional and translational activity of stem cells and pivotal transcription factors. Therefore, it is tempting to investigate their use as a tool to improve regenerative medicine strategies in orthopedics. Growing evidence in vitro suggests a role for polyamines in enhancing differentiation in both adult stem cells and differentiated chondrocytes. Adipose-derived stem cells have recently proved to be a convenient alternative to bone marrow stromal cells, due to their easy accessibility and the high frequency of stem cell precursors per volume unit. State-of-the-art "prolotherapy" approaches for skeleton regeneration include the use of adipose-derived stem cells and platelet concentrates, such as platelet-rich plasma (PRP). Besides several growth factors, PRP also contains polyamines in the micromolar range, which may also exert an anti-apoptotic effect, thus helping to explain the efficacy of PRP in enhancing osteogenesis in vitro and in vivo. On the other hand, spermidine and spermine are both able to enhance hypertrophy and terminal differentiation of chondrocytes and therefore appear to be inducers of endochondral ossification. Finally, the peculiar activity of spermidine as an inducer of autophagy suggests the possibility of exploiting its use to enhance this cytoprotective mechanism to counteract the degenerative changes underlying either the aging or degenerative diseases that affect bone or cartilage.

Polyamine-blocking therapy reverses immunosuppression in the tumor microenvironment

Correcting T-cell immunosuppression may unleash powerful antitumor responses; however, knowledge about the mechanisms and modifiers that may be targeted to improve therapy remains incomplete. Here, we report that polyamine elevation in cancer, a common metabolic aberration in aggressive lesions, contributes significantly to tumor immunosuppression and that a polyamine depletion strategy can exert antitumor effects that may also promote immunity. A polyamine-blocking therapy (PBT) that combines the well-characterized ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO) with AMXT 1501, a novel inhibitor of the polyamine transport system, blocked tumor growth in immunocompetent mice but not in athymic nude mice lacking T cells. PBT had little effect on the proliferation of epithelial tumor cells, but it increased the number of apoptotic cells. Analysis of CD45(+) tumor immune infiltrates revealed that PBT decreased levels of Gr-1(+)CD11b(+) myeloid suppressor cells and increased CD3(+) T cells. Strikingly, in a model of neoadjuvant therapy, mice administered with PBT one week before surgical resection of engrafted mammary tumors exhibited resistance to subsequent tumor rechallenge. Collectively, our results indicate that therapies targeting polyamine metabolism do not act exclusively as antiproliferative agents, but also act strongly to prevent immune escape by the tumor. PBT may offer a general approach to heighten immune responses in cancer.

Aliphatic polyamines in physiology and diseases

Aliphatic polyamines are a family of polycationic molecules derived from decarboxylation of the amino acid ornithine that classically comprise three molecules: putrescine, spermidine and spermine. In-cell polyamine homeostasis is tightly controlled at key steps of cell metabolism. Polyamines are involved in an array of cellular functions from DNA stabilization, and regulation of gene expression to ion channel function and, particularly, cell proliferation. As such, aliphatic polyamines play an essential role in rapidly dividing cells such as in the immune system and digestive tract. Because of their role in cell proliferation, polyamines are also involved in carcinogenesis, prompting intensive research into polyamine metabolism as a target in cancer therapy. More recently, another aliphatic polyamine, agmatine, the decarboxylated derivative of arginine, has been identified as a neurotransmitter in mammals, and investigations have focused on its effects in the CNS, notably as a neuroprotector in brain injury.

Potent trophic activity of spermidine supramolecular complexes in in vitro models

AIM: To test the growth-promoting activity of the polyamine spermidine bound to various polymeric compounds in supramolecular complexes.

METHODS: A thiazolyl blue cell viability assay was used to determine the growth-promoting potency of spermidine-supramolecular complexes in a human skin fibroblast cell line exposed to spermidine and different spermidine-supramolecular complexes that were obtained by combining spermidine and polyanionic polymers or cyclodextrin. Reconstituted human vaginal epithelium was exposed to a specific spermidine-supramolecular complex, i.e., spermidine-hyaluronan (HA) 50, and cell proliferation was determined by Ki-67 immunohistochemical detection. Transepithelial electrical resistance and histological analysis were also performed on reconstituted human vaginal epithelium to assess tissue integrity.

RESULTS: The effect of spermidine and spermidine-supramolecular complexes was first tested in skin fibroblasts. Spermidine displayed a reverse dose-related mode of activity with mmol/L growth inhibition, whereas 30% stimulation over basal levels was detected at μmol/L and nmol/L levels. Novel spermidine-supramolecular complexes that formed between spermidine and polyanionic polymers, such as HA, alginate, and polymaleate, were then tested at variable spermidine concentrations and a fixed polymer level (0.1% w/v). Spermidine-supramolecular complexes stimulated the cell growth rate throughout the entire concentration range with maximal potency (up to 80%) at sub-μmol/L levels. Similar results were obtained with spermidine-(α-cyclodextrin), another type of spermidine-supramolecular complex. Moreover, the increased expression of Ki-67 in the reconstituted human vaginal epithelium exposed to spermidine-HA 50 showed that the mode of action behind the spermidine-supramolecular complexes was increased cell proliferation. Functional and morphological assessments of reconstituted human vaginal epithelium integrity did not show significant alterations after exposure to spermidine-HA, thus supporting its safety.

CONCLUSION: Spermidine found in spermidine-supramolecular complexes displayed potentiated regenerative effects. Safety data on reconstituted human vaginal epithelium suggested that assessing spermidine-supramolecular complex efficacy in atrophic disorders is justified.

Local inhibition of ornithine decarboxylase reduces vascular stenosis in a murine model of carotid injury

OBJECTIVES

Polyamines are organic polycations playing an essential role in cell proliferation and differentiation, as well as in cell contractility, migration and apoptosis. These processes are known to contribute to restenosis, a pathophysiological process often occurring in patients submitted to revascularization procedures. We aimed to test the effect of α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, on vascular cell pathophysiology in vitro and in a rat model of carotid arteriotomy-induced (re)stenosis.

METHODS

The effect of DFMO on primary rat smooth muscle cells (SMCs) and mouse microvascular bEnd.3 endothelial cells (ECs) was evaluated through the analysis of DNA synthesis, polyamine concentration, cell viability, cell cycle phase distribution and by RT-PCR targeting cyclins and genes belonging to the polyamine pathway. The effect of DFMO was then evaluated in arteriotomy-injured rat carotids through the analysis of cell proliferation and apoptosis, RT-PCR and immunohistochemical analysis of differential gene expression.

RESULTS

DFMO showed a differential effect on SMCs and on ECs, with a marked, sustained anti-proliferative effect of DFMO at 3 and 8 days of treatment on SMCs and a less pronounced, late effect on bEnd.3 ECs at 8 days of DFMO treatment. DFMO applied perivascularly in pluronic gel at arteriotomy site reduced subsequent cell proliferation and preserved smooth muscle differentiation without affecting the endothelial coverage. Lumen area in DFMO-treated carotids was 49% greater than in control arteries 4 weeks after injury.

CONCLUSIONS

Our data support the key role of polyamines in restenosis and suggest a novel therapeutic approach for this pathophysiological process.

Role of polyamines in hypertrophy and terminal differentiation of osteoarthritic chondrocytes

Polyamines are naturally occurring, positively charged polycations which are able to control several cellular processes in different cell types, by interacting with negatively charged compounds and structures within the living cell. Functional genomics in rodents targeting key biosynthetic or catabolic enzymes have revealed a series of phenotypic changes, many of them related to human diseases. Several pieces of evidence from the literature point at a role of polyamines in promoting chondrocyte differentiation, a process which is physiological in growth plate maturation or fracture healing, but has pathological consequences in articular chondrocytes, programmed to keep a maturational arrested state. Inappropriate differentiation of articular chondrocytes results in osteoarthritis. Thus, we have studied the effects of exogenously added spermine or spermidine in chondrocyte maturation recapitulated in 3D cultures, to tease out the effects on gene and protein expression of key chondrogenesis regulatory transcription factors, markers and effectors, as well as their posttranscriptional regulation. The results indicate that both polyamines are able to increase the rate and the extent of chondrogenesis, with enhanced collagen 2 deposition and remodeling with downstream generation of collagen 2 bioactive peptides. These were able to promote nuclear localization of RUNX-2, the pivotal transcription factor in chondrocyte hypertrophy and osteoblast generation. Indeed, samples stimulated with polyamines showed an enhanced mineralization, along with increased caspase activity, indicating increased chondrocyte terminal differentiation. In conclusion these results indicate that the polyamine pathway can represent a potential target to control and correct chondrocyte inappropriate maturation in osteoarthritis.

Micronutrients and amino acids, main regulators of physiological processes

Human physiology is supposed to be a complex interaction of regulating processes, in which hormones, genes, their proteins and apoptosis are thought to play a dominant role. We hypothesize that regulation of physiological processes is mainly influenced by amino acids and micronutrients with hormones, proteins, apoptosis and gene modifications being their derivatives. Furthermore, we suppose that the cells power plant, the mitochondrion, is in fact an intracellular bacterium, living in absolute symbiosis. Because of its intracellular existence it depends on the host's micronutrients completely. Within the host these micronutrients regulate their own formation, degradation, uptake and excretion. Known deficiencies, such as iodine and vitamin D, affect billions of people. Many micronutrients neither have been investigated, nor have they been studied in relation to each other and solid data are not available. Optimal levels of many micronutrients and all amino acids are not known. Amino acids, vitamins and minerals are capable of altering gene expression, inducing apoptosis and regulating chemical processes. It makes them highly attractive for creating better health, against low cost, as we have already proven in the case of rickets, cretinism and scurvy in severe deficiencies. By creating optimal living conditions and study mitochondria from a symbiotic point of view we suppose that diseases not only can be prevented, but the course of diseases can be altered as well.

The arginine metabolite agmatine protects mitochondrial function and confers resistance to cellular apoptosis

Agmatine, an endogenous metabolite of arginine, selectively suppresses growth in cells with high proliferative kinetics, such as transformed cells, through depletion of intracellular polyamine levels. In the present study, we depleted intracellular polyamine content with agmatine to determine if attrition by cell death contributes to the growth-suppressive effects. We did not observe an increase in necrosis, DNA fragmentation, or chromatin condensation in Ha-Ras-transformed NIH-3T3 cells administered agmatine. In response to Ca(2+)-induced oxidative stress in kidney mitochondrial preparations, agmatine demonstrated attributes of a free radical scavenger by protecting against the oxidation of sulfhydryl groups and decreasing hydrogen peroxide content. The functional outcome was a protective effect against Ca(2+)-induced mitochondrial swelling and mitochondrial membrane potential collapse. We also observed decreased expression of proapoptotic Bcl-2 family members and of execution caspase-3, implying antiapoptotic potential. Indeed, we found that apoptosis induced by camptothecin or 5-fluorourocil was attenuated in cells administered agmatine. Agmatine may offer an alternative to the ornithine decarboxylase inhibitor difluoromethyl ornithine for depletion of intracellular polyamine content while avoiding the complications of increasing polyamine import and reducing the intracellular free radical scavenger capacity of polyamines. Depletion of intracellular polyamine content with agmatine suppressed cell growth, yet its antioxidant capacity afforded protection from mitochondrial insult and resistance to cellular apoptosis. These results could explain the beneficial outcomes observed with agmatine in models of injury and disease.

Polyamine synthesis inhibition induces S phase cell cycle arrest in vascular smooth muscle cells

Polyamines are important for cell growth and proliferation and they are formed from arginine and ornithine via arginase and ornithine decarboxylase (ODC). Arginine may alternatively be metabolised to NO via NO synthase. Here we study if vascular smooth muscle cell proliferation can be reversed by polyamine synthesis inhibitors and investigate their mechanism of action. Cell proliferation was assessed in cultured vascular smooth muscle A7r5 cells and in endothelium-denuded rat arterial rings by measuring [3H]-thymidine incorporation and by cell counting. Cell cycle phase distribution was determined by flow cytometry and polyamines by HPLC. Protein expression was determined by Western blotting. The ODC inhibitor DFMO (1-10 mM) reduced polyamine concentration and attenuated proliferation in A7r5 cells and rat tail artery. DFMO accumulated cells in S phase of the cell cycle and reduced cyclin A expression. DFMO had no effect on cell viability and apoptosis as assessed by fluorescence microscopy. Polyamine concentration and cellular proliferation were not affected by the arginase inhibitor NOHA (100-200 microM) and the NO synthase inhibitor L-NAME (100 microM). Lack of effect of NOHA was reflected by absence of arginase expression. Polyamine synthesis inhibition attenuates vascular smooth muscle cell proliferation by reducing DNA synthesis and accumulation of cells in S phase, and may be a useful approach to prevent vascular smooth muscle cell proliferation in cardiovascular diseases.