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Plant Hormone Cytokinins for Modulating Human Aging and Age-Related Diseases

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Abstract

Cytokinins are phytohormones that regulate plant growth, development and senescence. Experiments both in vitro and in vivo demonstrate that they can also have diverse effects on animal cells and tissues. Particularly interesting is their ability to protect cells against various forms of stress and prevent some detrimental effects of cell aging. For example, human skin fibroblasts cultured in the presence of kinetin or trans-zeatin retain some characteristics of cells of lower passage. Kinetin is even able to increase the lifespan of invertebrates. In this chapter, we review protective effects of cytokinins in animals at molecular, cellular, tissue and organismal levels. We also discuss potential application of cytokinins for the treatment of age-related diseases, including neurodegenerations, inflammatory diseases and disorders caused by aberrant cell proliferation.

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... The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability was measured with reference to the study by Braca et al. [16]. After concentration and freeze drying, the powdered extract sample was mixed with 99.9% ethanol to prepare solutions with different concentrations (1,5,25,50, and 100 ppm). To 2 mL of each concentration solution, about 2 mL of 0.2 mM DPPH ethanolic solution was added, stirred, and left in the dark for 30 min; absorbance was then measured at 515 nm, and the value of the DPPH radical scavenging activity was calculated to the following formula: scavenging rate (%) = [1 − (A1 − A2)/A0] × 100, where A0 was the absorbance of the control, A1 was the absorbance in the presence of the sample and DPPH, and A2 was the absorbance of the sample blank. ...
... The radical scavenging activity of 2,2 -azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS •+ ) was measured according to the method of Re et al. [17]. After concentration and freeze drying, the powdered extract sample was mixed with 99.9% ethanol to prepare solutions with different concentrations (1,5,25,50, and 100 ppm). A 7 mM ABTS solution and a 2.4 mM potassium persulfate solution, each dissolved in distilled water, were mixed and reacted in a dark place for 12 to 16 h to obtain the ABTS radicals. ...
... Therefore, a high concentration of phytohormones in the human body is linked to a number of physiological and metabolic responses. These phytohormones affect antioxidant response, glucose metabolism, cellular processes, cell division, cell cycle regulation, inflammation, cancer, etc. [49][50][51]. ...
Article
Full-text available
Coccinia grandis contains secondary metabolites, such as flavonoids, phenolic acids, terpenoids, alkaloids, sterols, and glycosides, which are known to have in vitro antioxidant, antidiabetic, anti-inflammatory, and antidyslipidemic activities. C. grandis fruits change dramatically during ripening, and the differences in the phytochemicals contribute to various uses. This study reports the phytochemical compounds and antioxidant activities during ripening of C. grandis for the first time. Characterizations were conducted on the physiologically active substances in C. grandis fruits at three ripening stages, and a total of 25 peaks were identified. Key phytochemicals in the ripening stages of C. grandis were identified, and the major substances that contributed to antioxidant properties were selected and quantitatively analyzed. Although the concentration of tiliroside increased during aging, hydroxycinnamic acid (chlorogenic and p-coumaric acids), flavonols (rutin), and triterpenes (cucurbitacins B and D) with antioxidant effects decreased. Therefore, phenolic compounds and cucurbitacins dominate immature C. grandis quantitatively. Regarding phytohormones, the gibberellin A4 content decreased as the fruits matured, but indoleacetic acid and salicylic acid increased with fruit maturity. The antioxidant capacities determined by DPPH and ABTS consistently decreased with increasing maturity. Accordingly, the extracts of immature C. grandis fruits have high levels of bioactive compounds and can be used to develop food additives and health supplements.
... Kinetin merupakan salah satu basa purin asam nukleat turunan adenine. 20,21 Kinetin terbentuk secara alami dalam plant stem cell, misalnya, pohon pinus Australia (Casuarina equisetifolia) atau gingergrass (Cymbopogon martinii var. Motia). ...
... Kinetin juga melindungi DNA sel dengan menghambat pembentukan 8-oxo-dG, suatu penanda kerusakan oksidatif yang terbentuk dari reaksi Fenton. [18][19][20][21] Faktor pertumbuhan alami ini adalah agen yang tepat untuk merangsang stem cell kulit. Berdasarkan penelitian, ia memperbaiki fungsi sawar pada lapisan spinosum epidermis, merangsang keratinosit, menurunkan TEWL, memperbaiki pigmentasi, dan mengurangi kerutan permukaan. ...
... Efek antipenuaan kinetin juga telah terbukti bermanfaat pada sel-sel endotel kulit, yaitu dengan cara mengaktifkan proliferasi sel, menghambat penuaan sel, dan menstimulasi zat-zat substansi proliferasi dan metaboliknya. 4,21,22 KESIMPULAN Tumbuhan memiliki umur panjang karena stem cell-nya mampu berdediferensiasi menjadi pluripoten dan bermanfaat menghambat penuaan kulit manusia. Penggunaan ekstrak plant stem cell memerlukan teknologi yang tepat agar mendapatkan potensi yang diharapkan dalam sediaan perawatan kulit. ...
Article
PENDAHULUAN Stem cell sering disebut sebagai sel punca atau sel induk, bertanggung jawab atas regenerasi dan pemeliharaan jaringan serta memiliki karakteristik yang unik yaitu menghasilkan salinan dirinya dan keturunan sel yang berbeda ketika membelah.1 Stem cell yang berasal dari tumbuhan memiliki sifat membantu merangsang dan meregenerasi tanaman setelah cedera. Sifat unik plant stem cell telah menjadi bidang yang banyak diminati baru-baru ini, terutama dalam mengembangkan kosmetik baru dan mempelajari bagaimana ekstrak/phytohormone ini dapat mempengaruhi kulit. Usaha regeneratif yang dilakukan tumbuh-tumbuhan tidak hanya pada perbaikan jaringan akibat kerusakan, tetapi juga perkembangan tumbuhan yang baru.2,3Penuaan kulit merupakan suatu proses kompleks yang dipengaruhi faktor internal dan eksternal serta melibatkan seluruh lapisan epidermis dan dermis.4,5 Tujuan dari kosmetik antipenuaan modern adalah untuk memperbaiki tampilan kulit dengan menstimulasi dan meregenerasi proses fisiologis alami demi perbaikan kondisi kulit dan perlindungan dari berbagai faktor yang menyebabkan penuaan, terlepas berapapun usia sesungguhnya. Kandungan yang menarik perhatian adalah plant stem cell, telah dinyatakan memberikan efek proteksi terhadap stem cell manusia dengan cara menstimulasi regenerasi kulit dan mencegah proses penuaannya.4 Penuaan KulitPenuaan adalah proses biologis yang tak terhindarkan, kompleks dan dinamis yang ditandai dengan kemunduran progresif dari berbagai sistem pada tubuh dan penurunan kapasitas cadangan fisiologis.5 Kulit manusia mengalami dua jenis penuaan yaitu penuaan intrinsik dan ekstrinsik. Penuaan intrinsik mencakup serangkaian perubahan fisiologis bertahap yang merupakan konsekuensi dari waktu ke waktu dan dipengaruhi genetik dan hormonal. Penuaan ekstrinsik merupakan perubahan struktural dan fungsional yang disebabkan oleh faktor eksogen, terutama paparan sinar matahari (disebut juga photoaging), alkohol, merokok, malnutrisi dan lingkungan yang merugikan, namun dalam kondisi tertentu masih dapat dihindari.5-7Proses penuaan kulit intrinsik ditandai dengan adanya proses penuaan seluler, penurunan kapasitas proliferasi, penurunan kemampuan perbaikan deoxyribonucleic acid (DNA), stres oksidatif dan mutasi gen.8 Fungsi sawar kulit terganggu akibat perubahan struktur filamen keratin dan penurunan filagrin.Dalam hormonal, hormon seks terutama estrogen mempengaruhi sintesis kolagen, asam hialuronat, elastin dan komponen lain dari matriks ekstraseluler. Bersama-sama, ketiga komponen ini memberikan tampilan kulit yang sehat dan muda.Perubahan biokimia yang terjadi pada kolagen, elastin dan komponen dasar kulit menyebabkan penuaan kulit.5,9 Umumnya terjadi pada area kulit yang terlindungi dari paparan sinar matahari dengan klinis yang relatif lebih ringan, ditandai dengan tampilan kulit kering, pucat dan kendur dengan kerutan halus dan atau berbagai bentuk neoplasma jinak.10Sumber terbesar penuaan ekstrinsik adalah akumulasi dan paparan sinar matahari pada area yang tidak terlindungi seperti wajah, leher, dada dan lengan ekstensor. Faktor lain yang berpengaruh adalah merokok, terbukti kadar matrix metalloproteinase-1 (MMP-1) lebih tinggi pada perokok.5,6 Diet nutrisi seimbang memperlambat penuaan dengan menyediakan nutrisi, air dan oksigen yang diperlukan sel dalam pembelahan, mengirimkan informasi dan memperbaiki kerusakan.5 Photoaging atau penuaan kulit dini merupakan istilah yang digunakan untuk menggambarkan klinis dan histologi akibat paparan sinar matahari kronis.5-7,11 Peningkatan kerusakan dan penurunan produksi kolagen adalah landasan dari photoaging, ditandai dengan penampilan kulit yang kasar, kerutan, warna kulit menjadi pudar, telangiektasis, pigmentasi tidak merata, dan berbagai lesi jinak, premaligna dan neoplasma ganas.5,9-11 Stres oksidatif dan penuaanSalah satu teori penuaan melibatkan proses penuaan seluler atau apoptosis sekunder adalah stres oksidatif. Stres oksidatif merupakan kondisi ketidakseimbangan antara reactive oxygen species (ROS) dengan mekanisme antioksidan. Pertahanan antioksidan sistem enzimatik dan non-enzimatik pada kulit cenderung melemah seiring bertambahnya usia.5,10 Kerusakan oksidatif menyebabkan peningkatan pembentukan faktor-faktor yang berhubungan dengan stres, kemudian memicu proses penuaan intrinsik. Misalnya, hypoxia-inducible factor dan nuclear factor ĸB menginduksi ekspresi sitokin interleukin 1, interleukin 6, vascular endothelial growth factor (VEGF) dan tumor necrosis factor α (TNFα), yang telah terbukti merupakan regulator proinflamasi dan modulator penghancuran MMP. Selain itu, kerusakan oksidatif terhadap protein seluler bersamaan dengan penurunan aktivitas proteasom sejalan usia membentuk akumulasi kerusakan protein yang dapat mengganggu fungsi seluler normal.5Stres oksidatif juga mampu memodifikasi telomer yang awalnya bertahan terhadap degradasi, fusi atau rekombinasi abnormal.3,5 Pemendekan telomer adalah hasil dari ketidakmampuan DNA polimerase untuk mereplikasi pasangan basa akhir kromosom. Ketika mencapai ambang "sangat pendek", sel akan mengalami penuaan proliferatif atau apoptosis. Mekanisme umum penuaan intrinsik dan photoaging disebabkan oleh gangguan struktur siklus putaran normal pada akhir telomer. Pemaparan ini kemudian mengaktifkan pensinyalan p53 yang mengarah pada peristiwa penuaan proliferatif dan apoptosis.5Penuaan kulit merupakan proses kompleks yang melibatkan seluruh lapisan epidermis dan dermis, mencakup denaturasi protein dan penurunan fungsi regeneratif stem cell.3 Penurunan fungsi stem cell epidermis telah diamati berhubungan dengan telomer yang lebih pendek, yang mengurangi potensi proliferatif sebagai respon terhadap paparan UV.5 Plant Stem CellKarakteristik plant stem cellSalah satu teori Weismann mengenai penuaan menjelaskan bagaimana organisme multiselular menua melalui germ line yang imortal dengan akumulasi kerusakan lebih didistribusikan pada sel somatik. Tumbuhan tidak secara jelas memisahkan mana germ line dan sel somatik, sehingga menjadi pertanyaan apakah teori penuaan berlaku untuk tumbuh-tumbuhan. Plant stem cell memiliki tampilan seperti germ line, sementara jaringan tumbuhan yang mati pada saat musiman, seperti daun dan xilem, memiliki sifat seperti sel somatik. Bagaimana sebuah tumbuhan dapat mencapai usia yang ekstrem, plant stem cell mungkin memegang kunci dalam hal ini karena tumbuhan memiliki pasokan stem cell terus menerus.12Stem cell dipertahankan secara terus menerus melalui mekanisme pembaruan diri yang terjadi di dalam niches stem cell atau dediferensiasi struktur dewasa. Sel-sel ini memunculkan organ baru sehingga memungkinkan bertahan dalam kondisi ekstrem. Sebuah studi mengenai model embriogenesis somatik menunjukkan sistem yang menarik yaitu regenerasi tanaman dari protoplas mesofil sebagai jenis sel yang terpapar dan berkemungkinan dapat mengakumulasi kerusakan lalu berdediferensiasi menjadi sel pluripoten. Contoh model protoplas dari sel-sel mesofil yaitu Arabidopsis, dapat diinduksi dengan menambahkan phytohormones cytokinin dan auksin. Akar dan pucuknya dapat beregenerasi dari callus untuk menghasilkan tanaman dewasa dan memungkinkan untuk digunakan dalam perangkat molekuler genetik yang tersedia. 12Plant stem cell dikelompokkan menjadi niches yang disebut meristem, terdiri atas primer dan sekunder. Meristem primer adalah meristem apikal (pucuk pertumbuhan batang dan akar), meristem interkalari (sisipan) dan meristem germ. Meristem sekunder adalah bagian lateral yaitu kambium (smear) dan phellogen serta bagian traumatik (callus). Pada meristem apikal pucuk batang, proliferasi dan diferensiasi plant stem cell dikendalikan oleh banyak faktor, termasuk proses siklus putaran reversibel negatif antara produk ekspresi gen, yaitu protein WUSCHEL (WUS) dan CLAVATA3 (CLV3). Protein WUS disekresi oleh sel-sel pusat organisasi dan merupakan sinyal untuk proliferasi stem cell, sedangkan protein CLV3 disekresikan oleh stem cell dan terbatas pada area  WUS. Kelebihan stem cell menyebabkan CLV3 berlebihan dan merangsang pengurangan sekresi WUS sehingga sinyal proliferasi menurun. Namun, jika jumlah stem cell terlalu rendah (defisit CLV3), maka WUS akan meningkatkan jumlah stem cell.2,13Meristem traumatik (callus) muncul pada bagian tumbuhan yang terlukai, paling sering berdiferensiasi menjadi kambium. Fenomena penciptaan callus pertama kali dijelaskan oleh ahli botani Austria, Gottlieb Heberlandt pada tahun 1902. Dia menyatakan bahwa sel tumbuhan mampu meregenerasi seluruh tanaman dan percobaan pada tahun 1958, wortel berhasil dikloning dari sel wortel yang dibudidayakan secara in vitro. Proses pembuatan callus adalah satu tahap embriogenesis sel-sel somatik (pembentukan zigot tanpa pembuahan) atau disebut juga tumbuhan mengalami dediferensiasi menjadi stem cell yang mampu menghasilkan jaringan baru atau bahkan seluruh organ. Penelitian menunjukkan bahwa sitokin bertanggung jawab dalam memproduksi batang dari callus, sedangkan auksin bertanggung jawab memproduksi akar.2,13 Contoh lain adalah pada pucuk akar Arabidopsis sp., bagian pusatnya tidak aktif bermitosis namun dikelilingi oleh stem cell yang membentuk bagian distal, lateral serta bagian sel akar proksimal.12Kemampuan diferensiasi plant stem cell untuk dediferensiasi kembali menjadi status pluripotensial saat ini banyak dimanfaatkan untuk menghilangkan gejala penuaan kulit pada manusia dalam bentuk sediaan perawatan kulit atau prosedur kosmetik. Teknologi kultur plant stem cellTeknologi kultur sel tumbuhan memastikan pertumbuhan sel tumbuhan, jaringan atau organ dalam lingkungan dengan nutrisi yang bebas mikroba dan memungkinkan untuk sintesis zat aktif biologis. Kultur ini memungkinkan akses dengan material bebas polusi, mikroorganisme atau toksin, mampu di setiap musim, dengan kandungan zat aktif yang hampir sama di setiap bagian.4 Teknik kultur sel tumbuhan dengan metode perbanyakan plant stem cell bertujuan mendapatkan metabolit tumbuhan.3 Dasar biologis di dalam semua tumbuhan adalah reservoir stem cell yang pluripoten dan sel-sel dengan kemampuan berdediferensiasi (pluripoten). Dengan nutrisi yang tepat, callus dapat tumbuh dalam kultur dan dengan menggunakan stimulasi hormon yang tepat, mungkin dapat menstimulasi regenerasi tumbuhan dewasa (disebut sebagai teknik reproduksi mikro).4,13Langkah pertama adalah memilih bahan tumbuhan yang tepat (buah, daun atau akar). Selanjutnya jaringan tumbuhan disterilisasi dan direduksi menjadi fragmen mikroskopis (disebut "eksplan"). Eksplan ditempatkan pada cawan petri beserta nutrisi solid. Kultur dibuat dalam kondisi gelap (tidak berfotosintesis) dan disuplai oleh zat sumber karbon dan energi organik (seperti sakarosa), phytohormone (auksin dan sitokin), vitamin serta unsur mikro dan makro. Kemudian dipilih turunan sel dengan karakteristik biokimia dan metabolisme terbaik (produktif dalam waktu pembelahan terpendek), stabil dan seragam.Selanjutnya pembesaran volume biomassa yang disebut "scaling". Kultur suspense beradaptasi secara bertahap dimulai dari tabung (volume 200 mL) hingga dalam bioreaktor (volume 100 L). Proses fermentasi dipantau dengan pengukuran kadar gula, konduktivitas, tingkat pH, densitas optik, vitalitas sel dan isi metabolit sekunder seperti, asam ursolat.3,4,14Tahap akhir dari fermentasi adalah pengolahan biomassa yang diawali dengan pencampuran konten kultur dalam suspense, yang terdiri atas liposom, phenoxyethanol (pengawet) dan antioksidan (asam askorbat atau tokoferol). Selanjutnya, dilakukan homogenisasi tekanan tinggi, di mana dinding stem cell dihancurkan, komponen yang dimasukkan dilepaskan secara bersamaan komponen lipofilik ditutup di dalam liposom (lecithin), sedangkan komponen hidrofilik dilarutkan dalam fase air. Produk yang diperoleh adalah likuid berwarna kekuningan dan amber. Solusio ini berasal dari perusahaan Swiss Mibelle AG Biochemistry dan menamakan teknologi mereka PhytoCellTecTM (PCT).3,4,14,15   Plant stem cell versus ekstrak plant stem cellTerminologi merupakan hal yang sangat penting dalam hal penegasan cosmeceutical, yaitu pemahaman bahwa ketika istilah “plant stem cell” digunakan sebagai komposisi, sebenarnya mengacu pada ekstrak dari plant stem cell. Banyak perusahaan perawatan kulit mempromosikan produk mereka dengan mengklaim memanfaatkan teknologi stem cell.Ekstrak dari plant stem cell tidak dapat bertindak dengan cara yang sama seperti stem cell yang hidup.3 Menggabungkan ekstrak plant stem cell di dalam zat pembawa yang dapat membantu sel menembus hingga ke dalam kulit untuk memberikan manfaat kosmetik yang sebenarnya memerlukan teknologi yang tepat untuk mendapatkan potensi yang melekat dalam sediaan perawatan kulit.3,14Dengan pengaturan sedemikian rupa, kultur sel tumbuhan terdediferensiasi dapat mewarisi beberapa modifikasi epigenetik yaitu karakteristik biosintesis dan pertumbuhan jaringan yang sangat heterogen. Fakta ini memungkinkan untuk menghasilkan turunan sel tumbuhan dengan jumlah hampir tak terbatas dengan sifat phytochemical yang unik dan karakteristik tumbuh yang hampir sama dengan yang digunakan untuk inisiasi. Istilah “plant stem cell” dalam komposisi kosmetik sebenarnya mengacu pada kultur callus atau suspensi sel yang didapatkan dari ekstrak kultur sel tumbuhan yang berdediferensiasi ditambah solusio berteknologi tinggi yang mampu mempertahankan potensinya.14 1. 2. Ekstrak Plant Stem Cell sebagai Antipenuaan KulitEkstrak plant stem cell sebagai terapi regeneratif kulit Ekstrak terbaik dapat diperoleh dari plant stem cell yang biji atau buahnya mampu mempertahankan kesegaran dan reproduksibilitas dalam jangka waktu yang lama. Faktor penting yang harus dipertimbangkan selama pemilihan tanaman adalah habitatnya dalam kondisi lingkungan yang sulit atau kemampuannya untuk "menyembuhkan" tanaman lainnya.5 Pelopor dalam memproduksi plant stem cell untuk industri kosmetik adalah Mibelle AG Biochemistry company (Swiss), yang mengimplementasikan stem cell buah apel (PhytoCellTecTM Malus Domestica) dan dipublikasi pada tahun 2008. Pada studi klinis menggunakan krim PhytoCellTecTM Malus Domestica 2% selama 4 minggu, kerutan pada wajah berkurang.3 Sejak saat itu, Mibelle AG Biochemistry telah memperkenalkan ekstrak dari plant stem cell Vitis vinifera (PhytoCellTecTM Solar Vitis), Saponaria pumila (PhytoCellTecTM nunatak®) atau Argania spinosa (PhytoCellTecTM Argan) di pasar dalam bentuk suspensi yang memberikan efek antikerut serta meningkatkan aktivitas stem cell epidermis.21 Selain itu, terdapat bukti yang menunjukkan auksin tanaman memiliki efek regulasi terhadap panjang telomer.4Penting diketahui bahwa plant stem cell sangat sensitif terhadap faktor eksternal, seperti cahaya atau suhu. Dalam produk kosmetik, agar mereka dapat bertahan maka digunakan dalam bentuk ekstrak yang larut dalam lipid (diekstraksi dengan minyak) dan larut dalam air (diekstraksi dengan gliserol), ekstrak bubuk (dengan maltodekstrin), liposom, nanoemulsi atau suspensi.4,14 Aktivitas antioksidan dari ekstrak plant stem cellSeperti yang telah disebutkan di atas, radikal bebas dianggap sebagai senyawa aktif yang paling berperan dalam proses penuaan kulit. Ia merusak DNA dan membantu dehidrogenasi, hidroksilasi dan glikasi protein selain merusak lipid di stratum korneum. Akibatnya, kulit kehilangan elastisitas dan kapasitas dalam mengatur transepidermal water loss (TEWL) serta replikasi sel kurang efisien. Oleh karena itu, antioksidan adalah bahan baku penting dalam cosmeceutical.4 Ekstrak dari plant stem cell merupakan sumber senyawa antioksidan yang sangat baik, seperti polifenol, asam phenolic, flavonoid, triterpenes, karotenoid, stilbenes, steroidal saponin dan peptide.14Goutzourelas et al. mempelajari efek antioksidan senyawa phenolic dari ekstrak stem cell anggur (Vitis vinifera) pada sel endotel dan otot.Terapi ekstrak stem cell anggur konsentrasi rendah mampu meningkatkan status redoks sel. Trans-resveratrol, asam gallic, (+)-catechin, asam ferullic, asam caffeic, quercetin, asam coumaric dan kaempferol merupakan bahan utama aktivitas antioksidan dari ekstrak stem cell anggur. Sumber lain yang kaya senyawa phenylpropanoid, terutama isoverbascoside adalah ekstrak kultur sel daun Syringa Vulgaris.4,14 Tito juga melaporkan bahwa ekstrak stem cell tomat memiliki kandungan asam rutin, coumaric, protocatechuic dan chlorogenic yang lebih tinggi dari pada buah tomat dan memiliki kemampuan antioksidan lebih tinggi. Aktivitas antioksidan yang tinggi dari ekstrak stem cell raspberry juga telah dilaporkan oleh Barbulova dan rekannya. Selain senyawa polyphenolic, ditemukan juga banyak kandungan asam ferulic dan quercitin ramnoside.4Studi Bazylak dan Gryn membandingkan beberapa ekstrak plant stem cell dalam total konten polyphenolic dan scavenging radikal diphenyl picrylhydrazin (DPPH) pada ekstrak stem cell paper mulberry (Brussonetia kazinoki), anggur (Vitis vinifer), magnolsi (Magnolia sieboldii), teh hijau (Camelia sinensis), ginseng putih (Panax ginsgen) dan ginseng hidroponik. Hasilnya menunjukkan semua ekstrak memiliki aktivitas antioksidan serta yang paling tinggi dan efektif adalah teh hijau dan ginseng putih.3,17 KinetinSalah satu agen terpenting yang memberikan sifat antipenuaan pada ekstrak plant stem cell adalah kinetin (N6-furfuryladenine), suatu phytohormone cytokinin. Kinetin merupakan salah satu basa purin asam nukleat turunan adenin.18,19 Kinetin terbentuk secara alami dalam plant stem cell, misalnya, pohon pinus Australia (Casuarina equisetifolia) atau gingergrass (Cymbopogon martinii var. Motia). Konsentrasi kinetin yang sangat tinggi ditemukan dalam stem cell lemon (Citrus limon) dan raspberry (Rubus chamaemorus).4Kinetin dianggap sebagai antioksidan alami terkuat. Ia terlibat dalam induksi sintesis enzim regeneratif dan membentuk senyawa kompleks dengan ion tembaga (II) dan mengaktifkan superoksida dismutase. Kinetin juga melindungi DNA sel dengan menghambat pembentukan 8-oxo-dG, penanda kerusakan oksidatif yang terbentuk dari reaksi Fenton.18-21Faktor pertumbuhan alami ini adalah agen yang tepat untuk merangsang stem cell kulit. Menurut penelitian, ia memperbaiki fungsi sawar pada lapisan spinosum epidermis, merangsang keratinosit, menurunkan TEWL, yang memperbaiki pigmentasi dan mengurangi kerutan permukaan. Efek antipenuaan dari kinetin juga telah terbukti bermanfaat pada sel-sel endotel kulit yaitu dengan cara mengaktifkan proliferasi sel, menghambat penuaan sel dan menstimulasi zat-zat substansi proliferasi dan metaboliknya.4,20,21 SIMPULANTumbuhan memiliki umur panjang karena stem cell-nya mampu berdediferensiasi menjadi pluripoten dan dapat dimanfaatkan guna menghambat penuaan kulit manusia. Penggunaan plant stem cell memerlukan teknologi yang tepat agar mendapatkan potensi yang diharapkan dalam sediaan perawatan kulit. Ekstrak dari plant stem cell merupakan sumber senyawa antioksidan yang sangat baik seperti polifenol, asam phenolic, flavonoid, triterpenes, karotenoid, stilbenes, steroidal saponin dan peptida. Efek yang ditimbulkan adalah stimulasi fibroblas, perbaikan epidermis, perbaikan DNA sel serta melindungi kulit dari paparan sinar UV dan stres oksidatif sebagai antioksidan. Dibutuhkan penelitian lanjutan untuk menilai efektifitas dan keamanan ekstrak plant stem cell sebagai antipenuaan kulit. DAFTAR PUSTAKASlack JMW. What is a Stem Cell?. Dalam: The Science of Stem Cells. United States: John Wiley & Sons;2018.h.1-11.Fehér A. Somatic embryogenesis—stress-induced remodeling of plant cell fate. BBA-Gene Regulatory Mechanisms. 2015;1849(4):385-402.Trehan S, Michniak-Kohn B, Beri K. Plant stem cells in cosmetics: Current trends and future directions. FSOA. 2017;3(4):FS0026.Miastkowska M, Sikora E. Anti-Aging Properties Of Plant Stem Cell Extracts. MDPI Journal Cosmetics. 2018:5(55):1-8.Kerns ML, Chien AL, Kang Sewon. Skin Aging. Dalam: Kang S, Amagai M, Bruckner AL, Enk AH, Margolis DJ, McMichael AJ, dkk, penyunting. Fitzpatrick’s Dermatology in General Medicine. Edisi ke-9. New York: McGraw Hill. 2019.h.1779-91Baumann L, Saghari S. Photoaging. Dalam: Baumann L, Saghari S, Edmund W, penyunting. Cosmetic Dermatology. Edisi ke-2. New York: Mc Graw Hill; 2009.h.34-41.Jusuf NK. Broccoli flower extract (Brassica oleracea L. var.italica plenck) inhibits photoaging by increasing type I procollagen expression in human skin fibroblast. Int J PharmTech Res. 2016;9(3):114–8.Assaf H, Adly M, Hussein M. Aging and intrinsic aging; pathogenesis and manifestations. Dalam: Farage MA, Miller KW, Maibach HI, penyunting. Textbook of Aging Skin. Berlin: Springer; 2010:130-318.Poon F, Kang S, Chien AL. Mechanisms and treatments of photoaging. PPP. 2015;31(2):65-74.Rinnerthaler M, Bischof J, Streubel MK, Trost A, Richter K. Oxidative stress in aging human skin. Biomolecules. 2015;5(2):545-89.Singh J, Chopra D, Dwivedi A, Ray RS. Photoaging. Dalam: Photocarcinogenesis & Photoprotection. Singapore: Springer; 2018.h.65-75.Dijkwel PP, Lai AG, Hypothesis: Plant stem cell hold the key to extreme longevity. TMA. 2019;3:14-6.Moru´s M, Baran M, Rost-Roszkowska M, Skotnicka-Graca U. Plant stem cells as innovation in cosmetics. Acta Poloniae Pharmaceutica. 2014;71(5):701-7.Georgiev V, Slavov A, Vasileva I, Pavlov A. Plant cell culture as emerging technology for production of active cosmetic ingredients. EngLifeSci. 2018;18(11):779-98.Pavlović M, Radotić K. Cultured Plant Stem Cells as a Source of Plant Natural Products. Dalam: Animal and Plant Stem Cells. Cham: Springer;2017.h.211-216.Goutzourelas N, Stagos D, Spanidis Y, Liosi M, Apostolou A, Priftis A, et al. Polyphenolic composition of grape stem extracts affects antioxidant activity in endothelial and muscle cells. Mol. Med. Rep. 2015;12: 5846–56.Bazylak G, Gryn A. Antioxidant activity and total flavonoid content in variable phyto-stem cells extracts obtained by high-pressure homogenization method and assigned for use in biocosmetics. PlantaMed. 2015; 81(16):PW_211.An S, Cha HJ, Ko JM, Han H, Kim SY, Kim KS, et al. Kinetin improves barrier function of the skin by modulating keratinocyte differentiation markers. Ann Dermatol.2017;29:6–12.Voller J, Maková B, Kadlecová A, Gonzalez G, Strnad M. Plant hormone cytokinins for modulating human aging and age-related diseases. Dalam: Hormones in Ageing and Longevity. Cham: Springer; 2017.h.311-335.Kadlecova A, Makova B, Artal-Sanz M, Strnad M, Voller J. The plant hormone kinetin in disease therapy and healthy aging. Ageing research reviews. 2019;55:100958.Jabłońska-Trypuć A, Matejczyk M, Czerpak R. N6-benzyladenine and kinetin influence antioxidative stress parameters in human skin fibroblasts. Molecular and cellular biochemistry. 2016;413(1-2):97-107.
... Various 9-ribosides, 9-nucleotides, as well as 7-, 9, and Othese forms also commonly occur, as shown in Table 1. In addition to their n plants, CKs have shown potent ant-oxidant activity towards reactive ox (ROS) that provides protection in several in vitro stress models of aging-ass ders [14]. dichloride (paraquat), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4phenylpyridinium (MPP+), and 6-hydroxydopamine (6-OHDA) [12]. ...
... Various 9-ribosides, 9-nucleotides, as well as 7-, 9, and O-glucosides of these forms also commonly occur, as shown in Table 1. In addition to their native roles in plants, CKs have shown potent ant-oxidant activity towards reactive oxygen species (ROS) that provides protection in several in vitro stress models of aging-associated disorders [14]. dichloride (paraquat), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4phenylpyridinium (MPP+), and 6-hydroxydopamine (6-OHDA) [12]. ...
... Various 9-ribosides, 9-nucleotides, as well as 7-, 9, and O-glucosides of these forms also commonly occur, as shown in Table 1. In addition to their native roles in plants, CKs have shown potent ant-oxidant activity towards reactive oxygen species (ROS) that provides protection in several in vitro stress models of aging-associated disorders [14]. Table 1. ...
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Cytokinins are adenine-based phytohormones that regulate key processes in plants, such as cell division and differentiation, root and shoot growth, apical dominance, branching, and seed germination. In preliminary studies, they have also shown protective activities against human neurodegenerative diseases. To extend knowledge of the protection (protective activity) they offer, we investigated activities of natural cytokinins against salsolinol (SAL)-induced toxicity (a Parkinson’s disease model) and glutamate (Glu)-induced death of neuron-like dopaminergic SH-SY5Y cells. We found that kinetin-3-glucoside, cis-zeatin riboside, and N6-isopentenyladenosine were active in the SAL-induced PD model. In addition, trans-, cis-zeatin, and kinetin along with the iron chelator deferoxamine (DFO) and the necroptosis inhibitor necrostatin 1 (NEC-1) significantly reduced cell death rates in the Glu-induced model. Lactate dehydrogenase assays revealed that the cytokinins provided lower neuroprotective activity than DFO and NEC-1. Moreover, they reduced apoptotic caspase-3/7 activities less strongly than DFO. However, the cytokinins had very similar effects to DFO and NEC-1 on superoxide radical production. Overall, they showed protective activity in the SAL-induced model of parkinsonian neuronal cell death and Glu-induced model of oxidative damage mainly by reduction of oxidative stress.
... Some also induce differentiation of various cell lines, including keratinocytes and certain leukemias. Many other pharmacological activities were reported, including neuroprotective, immunomodulatory, and antiangiogenic (reviewed in Voller et al. 2017bVoller et al. , 2019Kadlecová et al. 2019). Attention was focused mainly on N 6 -isopentenyladenosine (iPR) and N 6 -benzyladenosine (BAR) as candidate anticancer drugs and kinetin (K) for its ability to slow down the aging of human cells. ...
... Research has traditionally focused on a direct or indirect (induction of defense mechanisms) antioxidant activity of K. It has also been proposed that K acts as a hormetin (Rattan et al. 2009) or as a hormetin precursor, prohormetin (Voller et al. 2017b). Molecular studies demonstrated that K after conversion into its riboside-5 0 -triphosphate acts as an ATP analog in PINK1 and CK2 kinases. ...
Chapter
Discoveries of new plant growth regulators are significantly enriching the range of tools used by researchers in plant tissue culture. Meta-topolin (mT, 6-(3-hydroxybenzylamino) purine), firstly isolated from poplar leaves, is a highly active natural aromatic cytokinin successfully used over the last two decades in many different biological fields. The main criteria of its efficiency in plant micropropagation are high multiplication rate, shoot health, good rooting, and acclimatization ability. The absence of abnormalities and somaclonal variation are further advantages. For this reason, mT is examined in various regeneration systems in comparison with isoprenoid, aromatic, as well as phenylurea derivatives with cytokinin-like activity. This chapter will review the advantages and disadvantages of mT application as an inducer of different morphogenetic pathways of plant regeneration in vitro, including axillary shoot proliferation, de novo organogenesis, and somatic embryogenesis.
... But such reasoning is supported by little experimental evidence. Apart from the other vast molecular and physiological differences, the receptors and signaling systems that mediate the activity of cytokinins in plants are not present in animals (Voller et al, 2017). Kadlecová et al. ...
... Reports of kinetin having protective activity in animal systems prompted interest in the effects of other cytokinins and their synthetic derivatives. Some of their activities have recently been reviewed elsewhere (Voller et al, 2017). ...
Article
It has been more than 60 years since the discovery of kinetin, the first known member of a group of plant hormones called cytokinins. In this review we summarize the health-promoting activity of kinetin in animal systems, ranging from cells cultured in vitro through invertebrates to mammals. Kinetin has been shown to modulate aging, to delay age-related physiological decline and to protect against some neurodegenerative diseases. We also review studies on its mechanism of action, as well as point out gaps in our current knowledge.
... Readers interested in a wide range of other activities (e.g. antioxidative, neuroprotective and immunomodulatory) of cytokinins in humans and model organisms are referred to a recent review (Voller et al. 2017b). An overview of the biological activity of a wider group of C6-substituted adenosines can be found in Drenichev et al. (2016). ...
... For many years, we have been speculating that the cytoprotective and anti-aging activities of cytokinin base kinetin (Voller et al. 2017b;Kadlecová et al. 2018) may be linked to its conversion to the respective riboside or ribotides that would act as hormetins in low concentrations, possibly by induction of the Nrf-2 pathway. Recently, it was reported that kinetin is indeed converted into kinetin 5 0 -triphosphate in human cells. ...
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Cytokinins are plant hormones and play essential roles in regulating plant growth and development. They also have diverse pharmacological effects in animals and humans. Whereas cytokinin bases have been studied mainly for their cytoprotective activities, cytokinin ribosides have been explored as anti-cancer agents. Cytokinin ribosides inhibit growth or cause apoptosis in various cell lines derived from diverse malignancies including those with a mutant p53 gene. Activity against cancer stem cells, anti-angiogenic activity, and the ability to stimulate an immune response to malignant cells have been reported as well. There are also positive results from in vivo studies and reports of activity in patients with hematological malignancies and solid tumors. Here, we review studies of the anti-cancer activity of cytokinin ribosides since the 1960s and comment on the issues that need to be addressed for the further development of cytokinin ribosides into anti-cancer drugs.
... The plant hormones cytokinins are predominantly adenine-derived regulatory molecules that take part in almost all stages of plant growth and development. Studies of the biological activity of cytokinins in animal cells, implemented mainly on 6-substituted purines, in particular on kinetin [1,2], have shown the presence of antiviral, antiparasitic, antitumor, antioxidant and other therapeutic properties [3][4][5][6]. At the same time, many chemical compounds with cytokinin activity other than substituted purines are known, but their activity has not been investigated on animal and human cells. ...
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Natural cytokinines are a promising group of cytoprotective and anti-tumor agents. In this research, we synthesized a set of aryl carbamate, pyridyl urea, and aryl urea cytokinine analogs with alkyl and chlorine substitutions and tested their antiproliferative activity in MDA-MB-231, A-375, and U-87 MG cell lines, and cytoprotective properties in H2O2 and CoCl2 models. Aryl carbamates with the oxamate moiety were selectively anti-proliferative for the cancer cell lines tested, while the aryl ureas were inactive. In the cytoprotection studies, the same aryl carbamates were able to counteract the CoCl2 cytotoxicity by 3–8%. The possible molecular targets of the aryl carbamates during the anti-proliferative action were the adenosine A2 receptor and CDK2. The obtained results are promising for the development of novel anti-cancer therapeutics.
... Due to their peculiar effect on cell division and differentiation in plant cells, cytokinins were also studied for their effect on the differentiation of human cells, both normal and malignant (Honma and Ishii 2002). The N 9 -ribosides of CKs (CKRs) showed a higher biological activity, so that became also potential candidates for treating a variety of cancers (Voller et al. 2017(Voller et al. , 2019. ...
Article
Cytokinins are naturally occurring adenine derivatives whose physiological role is that of growth regulators in plants and that show also many other activities either in plants and in mammalian cells. In plants, they can be found mainly as free bases ((N6-substituted adenines, CKs), but also as the corresponding N9- ribosides (N6-substituted adenosines, CKRs). In mammalian cells, CKRs are, in general, more active than CKs. In order to evaluate the intrinsic in vitro antioxidant capacity of some significant CKRs, their scavenging activity against synthetic radicals that are at the basis of well-established antioxidant assays (ORAC, TEAC, DPPH) has been evaluated. The results of the in vitro scavenging activity of biologically relevant radicals such as hydroxyl (HO•), superoxide (O2.-) and lipid peroxides (R-OO.) are reported and discussed.
... [13] Cytokinins have important antioxidative and protective effects in animals at molecular, cellular, tissue, and organismal levels. [14] Zeatin showed antioxidative and cell-protective effects against β-amyloid-induced neurotoxicity, similar to caffeine. [15] Most recently, the possible antidepressant effect of zeatin on female and male rats was shown, together with the interaction of zeatin with A2AR on the same binding site with caffeine. ...
... Antiproliferative effects of kinetin riboside were also shown in cancer cell lines of human melanoma, colon, and pancreas, along with cellular ATP depletion and DNA damage [129]. Oxidative stress can be attenuated by CK, which can also link to other beneficial roles of CK against cancer [130,131]. The activities of anti-oxidant enzymes, such as total-superoxide dismutase and glutathione peroxidase, are elevated in astrocyte cells and mouse brains upon treatment with kinetin [132]. ...
Article
Metabolic syndrome is characterized by the co-occurrence of diverse symptoms initiating the development of type 2 diabetes, cardiovascular diseases, and a variety of comorbid diseases. The complex constellation of numerous comorbidities makes it difficult to develop common therapeutic approaches that ameliorate these pathological features simultaneously. The plant hormones abscisic acid, salicylic acid, auxin, and cytokinins, have shown promising anti-inflammatory and pro-metabolic effects that could mitigate several disorders relevant to metabolic syndrome. Intriguingly, besides plants, human cells and gut microbes also endogenously produce these molecules, indicating a role in the complex interplay between inflammatory responses associated with metabolic syndrome, the gut microbiome, and nutrition. Here, we introduce how bioactive phytohormones can be generated endogenously and through the gut microbiome. These molecules subsequently influence immune responses and metabolism. We also elaborate on how phytohormones can beneficially modulate metabolic syndrome comorbidities, and propose them as nutraceuticals.
... Various activities of cytokinins in both mammalian cell cultures and animals have been reported (Voller et al. 2017b). The ribosides are often toxic, but cytokinin bases are mostly known to have protective effects, often ascribed to their antioxidant activity. ...
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Cytokinins are phytohormones that are involved in many processes in plants, including growth, differentiation and leaf senescence. However, they also have various activities in animals. For example, kinetin and trans-zeatin can reduce levels of several aging markers in human fibroblasts. Kinetin can also protect mice against oxidative and glyoxidative stress, and prolong fruit flies’ lifespan. Additionally, several cytokinins are currently used in cosmetics. To extend knowledge of the breadth of cytokinins’ activities, we examined effects of natural cytokinin bases on the model nematode Caenorhabditis elegans. We found that kinetin, para-topolin and meta-topolin prolonged the lifespan of C. elegans. Kinetin also protected the organism against oxidative and heat stress. Furthermore, our results suggest that presence of reactive oxygen species, but not DAF-16 (the main effector of the insulin/insulin-like growth factor signaling pathway), is required for the beneficial effects of kinetin. Ultra-high performance liquid chromatography-tandem mass spectrometric analysis showed that kinetin is unlikely to occur naturally in C. elegans, but the worm efficiently absorbs and metabolizes it into kinetin riboside and kinetin riboside-5′-monophosphate.
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Plant hormones play an important role in growth, defence and plants productivity and there are several studies on their effects on plants. However, their role in humans and animals is limitedly studied. Recent studies suggest that plant hormone also works in mammalian systems, and have the potential to reduce human diseases such as cancer, diabetes, and also improve cell growth. Plant hormones such as indole-3-acetic acid (IAA) works as an antitumor, anti-cancer agent, gibberellins help in apoptosis, abscisic acid (ABA) as antidepressant compounds and regulation of glucose homeostasis whereas cytokinin works as an anti-ageing compound. The main aim of this review is to explore and correlate the relation of plant hormones and their important roles in animals, microbes and plants, and their interrelationships, emphasizing mainly human health. The most important and well-known plant hormones e.g., IAA, gibberellins, ABA, cytokinin and ethylene have been selected in this review to explore their effects on humans and animals.
Chapter
Cytokinins have diverse pharmacological activities including neuroprotective, immunomodulatory, and anticancer. They have been tested in patients as agents for oncology, neurology, and dermatology. The research has focused on isoprenoid cytokinins and on kinetin and N⁶-benzyladenosine as representatives of aromatic cytokinins. The activities of topolins and their ribosides remain underexplored. Here we summarize the available data in the hope of encouraging interest in the therapeutic potential of these compounds.
Chapter
Following the discovery of kinetin (Miller et al., J Am Chem Soc 78(7):1375–1380, 1956), there was a period of intensive synthesis of new cytokinins, which led to the preparation of the highly efficient and easily prepared aromatic cytokinin 6-benzylaminopurine (BAP). A huge number of biological experiments were then performed with this cytokinin derivative, which significantly contributed to our understanding of cytokinin functions in plants. Findings of naturally occurring BAP subsequently led to the search for other aromatic cytokinins. In order to rapidly detect these substances in plants, a unique procedure based on screening of HPLC fractions using specific ELISAs with antisera against individual aromatic cytokinins has been introduced. Isolation of these substances and their subsequent identification by mass spectrometry confirmed the natural occurrence of highly active endogenous ARCK meta-topolin (6-(3-hydroxybenzylamino)purine), but also a less active ortho-topolin analogue (6-(2-hydroxybenzylamino)purine) and their metabolites. The structure of topolins suggests biosynthetic and metabolic biosynthetic pathways that are likely to be similar to closely related isoprenoid cytokinins like zeatins. It also seems likely that the molecular mechanisms of action will be based on very closely related principles, although differences certainly exist, at least at the level of the signals and their recognitions carried by these phytohormones. This review attempts to summarise the current state of knowledge about ARCK and to point out its practical use in agriculture and biotechnology.
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Kinetin (N⁶-furfuryladenine), a plant growth substance of the cytokinin family, has been shown to modulate aging and various age-related conditions in animal models. Here we report the synthesis of kinetin isosteres with the purine ring replaced by other bicyclic heterocycles, and the biological evaluation of their activity in several in vitro models related to neurodegenerative diseases. Our findings indicate that kinetin isosteres protect Friedreich́s ataxia patient-derived fibroblasts against glutathione depletion, protect neuron-like SH-SY5Y cells from glutamate-induced oxidative damage, and correct aberrant splicing of the ELP1 gene in fibroblasts derived from a familial dysautonomia patient. Although the mechanism of action of kinetin derivatives remains unclear, our data suggest that the cytoprotective activity of some purine isosteres is mediated by their ability to reduce oxidative stress. Further, the studies of permeation across artificial membrane and model gut and blood-brain barriers indicate that the compounds are orally available and can reach central nervous system. Overall, our data demonstrate that isosteric replacement of the kinetin purine scaffold is a fruitful strategy for improving known biological activities of kinetin and discovering novel therapeutic opportunities.
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Lipid peroxidation is generally accepted to increase during ageing. We focused on stable lipid peroxidation end products, lipophilic fluorescent pigments (LFP). Their role in ageing in animal/human model has thoroughly been investigated. Changes in characteristics and quantity of LFP during tobacco leaf ageing were studied. We evaluated effect of altered ageing rate on LFP characteristics and accumulation. We employed plants with modulated cytokinins (CK) levels as they are plant hormones controlling development and ageing. Tobacco transgenic plants with senescence-induced CK up-regulation (SAG-ipt plants) displayed rejuvenation of senescent leaves. Slowed ageing was achieved in plants with constitutively down-regulated CK (CKX plants). Both 3D and synchronous fluorescence spectra of LFP indicate more marked differences of fluorophores´ compositions between two different control tobacco cultivars than between control and its transgenic plant. Major fluorophore amount increased with leaf age in both control and CKX plants, in SAG-ipt tobacco its quantity declined in the oldest leaves. The postponed leaf ageing in CKX plants resulted in a diminution of LFP. Higher LFP level in SAG-ipt plants compared with their control leaves of the same age was observed. LFP composition as well as relative abundance of individual LFP might be characteristic for each tobacco cultivar and depend on leaf age.
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Malignant gliomas are highly dependent on the isoprenoid pathway for the synthesis of lipid moieties critical for cell proliferation. The isoprenoid derivative N6-isopentenyladenosine (iPA) displays pleiotropic biological effects, including a direct anti-tumor activity in several tumor models. The antiglioma effects of iPA was then explored in U87MG cells both in vitro and grafted in mice and the related molecular mechanism confirmed in primary derived patients' glioma cells. iPA powerfully inhibited tumor cell growth and induced caspase-dependent apoptosis through a mechanism involving a marked accumulation of the pro-apoptotic BIM protein and inhibition of EGFR. Indeed, activating AMPK following conversion into its iPAMP active form, iPA stimulated EGFR phosphorylation and ubiquitination along a proteasome-mediated pathway which was responsible for receptor degradation and its downstream signaling pathways inhibition, including the STAT3, ERK and AKT cascade. The inhibition of AMPK by compound C prevented iPA-mediated phosphorylation of EGFR, known to precede receptor loss. As expected the block of EGFR degradation, by exposure to the proteasome inhibitor MG132, significantly reduced iPA-induced cell death. Given the importance of receptor degradation in iPA-mediated cytotoxicity, we also documented that the EGFR expression levels in a panel of primary glioma cells confers them a high sensitivity to iPA treatment. In conclusion our study provides the first evidence of iPA antiglioma effect. Indeed, as glioma is driven by aberrant signaling of growth factor receptors, particularly the EGFR, iPA, alone or in association with EGFR targeted therapies, might be a promising therapeutic tool to achieve a potent anti-tumoral effect. This article is protected by copyright. All rights reserved.
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Background: CF101, an adenosine A3 receptor agonist, is an orally bioavailable small molecule drug presenting an anti-psoriatic effect demonstrated in a Phase 2 clinical trial in psoriasis patients. OBJECTIVE: To evaluate the safety and efficacy of CF101 treatment in a Phase 2/3 study in patients with moderate to severe plaque-type psoriasis. METHODS: This multicenter, double-blind, 2-segment, placebo-controlled study randomized subjects with moderate to severe plaque psoriasis to CF101 1 or 2 mg, or placebo twice daily. At either week 12 (Segment 1) or 16 (Segment 2), the placebo group crossed over to CF101 BID through week 32 in an open-label fashion. At week 12, following an interim analysis, the CF101 1mg group was discontinued due to futility. The primary endpoint was proportion of patients achieving ≥75% improvement in Psoriasis Area Severity Index (PASI 75). Efficacy testing was performed using the Cochran-Mantel Haenszel test, the primary analysis of PASI 75 was performed at the 0.035 significance level. RESULTS: CF101 had an excellent safety profile at all tested dosages with a profile similar to the placebo group. The most common adverse events were infections and gastrointestinal events, and there was no cumulative intolerance over the 32-week dosing period. The study did not meet the primary endpoint of PASI 75 at week 12 (2 mg: 8.5% vs. placebo: 6.9%, P =0.621). However, at week 32, PASI mean percent improvement with CF101 2 mg was 57% ( P <0.001) compared to baseline, with linear improvement in PASI 50 (63.5%), 75 (35.5%), 90 (24.7%), and 100 (10.6%). CONCLUSIONS: Oral CF101 was found to be safe and very well tolerated, demonstrating evidence of efficacy in patients with moderate to severe plaque psoriasis through 32 weeks of treatment. J Drugs Dermatol . 2016;15(8):931-938.
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Studying long-lived animals provides novel insight into shared characteristics of aging and represents a unique model to elucidate approaches to prevent chronic disease. Oxidant stress underlies many chronic diseases and resistance to stress is a potential mechanism governing slowed aging. The transcription factor nuclear factor (erythroid-derived 2)-like 2 is the “master regulator” of cellular antioxidant defenses. Nrf2 is upregulated by some longevity promoting interventions and may play a role in regulating species longevity. However, Nrf2 expression and activity in long-lived models have not been well described. Here, we review evidence for altered Nrf2 signaling in a variety of slowed aging models that accomplish lifespan extension via pharmacological, nutritional, evolutionary, genetic, and presumably epigenetic means.
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Huntington's disease (HD) is an autosomal-dominant degenerative disease caused by a cytosine-adenine-guanine trinucleotide expansion in the Huntingtin (htt) gene. The most vulnerable brain areas to mutant HTT-evoked toxicity are the striatum and cortex. In spite of the extensive efforts that have been devoted to the characterization of HD pathogenesis, no disease-modifying therapy for HD is currently available. The A2A adenosine receptor (A2AR) is widely distributed in the brain, with the highest level observed in the striatum. We previously reported that stimulation of the A2AR triggers an anti-apoptotic effect in a rat neuron-like cell line (PC12). Using a transgenic mouse model (R6/2) of HD, we demonstrated that A2AR-selective agonists effectively ameliorate several major symptoms of HD. In the present study, we show that human iPSCs can be successfully induced to differentiate into DARPP32-positive, GABAergic neurons which express the A2AR in a similar manner to striatal medium spiny neurons. When compared with those derived from control subjects (CON-iPSCs), these HD-iPSC-derived neurons exhibited a higher DNA damage response, based on the observed expression of γH2AX and elevated oxidative stress. This is a critical observation, because oxidative damage and abnormal DNA damage/repair have been reported in HD patients. Most importantly, stimulation of the A2AR using selective agonists reduced DNA damage and oxidative stress-induced apoptosis in HD-iPSC-derived neurons through a cAMP/PKA-dependent pathway. These findings support our hypothesis that human neurons derived from diseased iPSCs might serve as an important platform to investigate the beneficial effects and underlying mechanisms of A2AR drugs.
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Kinetin is a plant-derived compound, which is reported to possess antiaging properties. It has been used in a topical cream to manage facial photo-damage and aging. Although studies elsewhere have shown its benefits, not many studies of the effects of kinetin in Asian skin are available. To assess the efficacy and tolerability of 0.1% kinetin cream in the treatment of facial photo-aging. The study was designed to be open-label and single-blinded, without a control group. One hundred Thai female and male subjects with mild, moderate or severe facial photo-damage were enrolled. They were asked to apply 0.1% kinetin cream twice daily for 12 weeks and follow up at 4, 8, and 12 weeks. Subjective patient self-assessment and physician assessment of facial skin photo-damage were accompanied by digital photographic analysis using the VISIA; (Canfield Scientific Inc, Fairfield, NJ) imaging system. At baseline, most patients reported moderate skin changes related to photo-damage, skin texture, skin color and wrinkles. After 12 weeks, physician and patient assessments showed slight but statistically significant improvements in overall skin condition, skin texture, color, and wrinkles. Findings were similar with the digital photographic system analysis, especially in relation to skin color. Facial ultraviolet spots and redness also showed statistically significant improvements after 12 weeks. The treatment was generally well tolerated. The study was designed to be pragmatic and hence no randomization was carried out; there were also no intrapatient or interpatient control observations, and no comparison arm. Kinetin (0.1%) cream was found to slightly improve cutaneous facial photo-damage after 12 weeks of use in a group of Thai patients.
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Gastrodia elata Blume (Fam. Orchidaceae) is a traditional Chinese herbal medicine for treating headaches, dizziness, tetanus, epilepsy, and numbness of the limbs, which suggests that it has neuroprotective effect. To validate the neuroprotection of Gastrodia elata in preventing neurodegenerations, such as Huntington's disease (HD). MTT assay was used to validate the protection of Gastrodia elata. In pheochromocytoma (PC12) cell. Transient transfection of mutant huntingtin (Htt) in PC12 cell was used as an in vitro model of HD. Filter retardation assay was used to measure Htt-induced protein aggregations. Proteasome activity was monitored by transfection of pZsProSensor-1 and imaged by a confocal laser scanning microscope. This protection of Gastrodia elata could be blocked by an A(2A)-R antagonist and a protein kinase A (PKA) inhibitor, indicating an A(2A)-R signaling event. Gastrodia elata could reverse mutant Htt-induced protein aggregations and proteasome de-activation through A(2A)-R signaling. In addition, activation of PKA tended to activate proteasome activity and reduce mutant Htt protein aggregations. The proteasome inhibitor, MG 132, blocked Gastrodia elata-mediated suppression of mutant Htt aggregations. Gastrodia elata prevented mutant Htt aggregations and increased proteasomal activity by targeting the A(2A)-R through PKA-dependent pathway.
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We tested a panel of naturally occurring nucleosides for their affinity towards adenosine receptors. Both N6-(2-isopentenyl)adenosine (IPA) and racemic zeatin riboside were shown to be selective human adenosine A3 receptor (hA3R) ligands with affinities in the high nanomolar range (Ki values of 159 and 649 nM, respectively). These values were comparable to the observed Ki value of adenosine on hA3R, which was 847 nM in the same radioligand binding assay. IPA also bound with micromolar affinity to the rat A3R. In a functional assay in Chinese hamster ovary cells transfected with hA3R, IPA and zeatin riboside inhibited forskolin-induced cAMP formation at micromolar potencies. The effect of IPA could be blocked by the A3R antagonist VUF5574. Both IPA and reference A3R agonist 2-chloro-N6-(3-iodobenzyl)adenosine-5′-N-methylcarboxamide (Cl-IB-MECA) have known antitumor effects. We demonstrated strong and highly similar antiproliferative effects of IPA and Cl-IB-MECA on human and rat tumor cell lines LNCaP and N1S1. Importantly, the antiproliferative effect of low concentrations of IPA on LNCaP cells could be fully blocked by the selective A3R antagonist MRS1523. At higher concentrations, IPA appeared to inhibit cell growth by an A3R-independent mechanism, as was previously reported for other A3R agonists. We used HPLC to investigate the presence of endogenous IPA in rat muscle tissue, but we could not detect the compound. In conclusion, the antiproliferative effects of the naturally occurring nucleoside IPA are at least in part mediated by the A3R. Electronic supplementary material The online version of this article (doi:10.1007/s11302-011-9244-9) contains supplementary material, which is available to authorized users.
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Huntington's disease (HD) is a neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. The expanded CAG repeats are translated into polyglutamine (polyQ), causing aberrant functions as well as aggregate formation of mutant Htt. Effective treatments for HD are yet to be developed. Here, we report a novel dual-function compound, N(6)-(4-hydroxybenzyl)adenine riboside (designated T1-11) which activates the A(2A)R and a major adenosine transporter (ENT1). T1-11 was originally isolated from a Chinese medicinal herb. Molecular modeling analyses showed that T1-11 binds to the adenosine pockets of the A(2A)R and ENT1. Introduction of T1-11 into the striatum significantly enhanced the level of striatal adenosine as determined by a microdialysis technique, demonstrating that T1-11 inhibited adenosine uptake in vivo. A single intraperitoneal injection of T1-11 in wildtype mice, but not in A(2A)R knockout mice, increased cAMP level in the brain. Thus, T1-11 enters the brain and elevates cAMP via activation of the A(2A)R in vivo. Most importantly, addition of T1-11 (0.05 mg/ml) to the drinking water of a transgenic mouse model of HD (R6/2) ameliorated the progressive deterioration in motor coordination, reduced the formation of striatal Htt aggregates, elevated proteasome activity, and increased the level of an important neurotrophic factor (brain derived neurotrophic factor) in the brain. These results demonstrate the therapeutic potential of T1-11 for treating HD. The dual functions of T1-11 enable T1-11 to effectively activate the adenosinergic system and subsequently delay the progression of HD. This is a novel therapeutic strategy for HD. Similar dual-function drugs aimed at a particular neurotransmitter system as proposed herein may be applicable to other neurotransmitter systems (e.g., the dopamine receptor/dopamine transporter and the serotonin receptor/serotonin transporter) and may facilitate the development of new drugs for other neurodegenerative diseases.
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The production of adenosine represents a critical endogenous mechanism for regulating immune and inflammatory responses during conditions of stress, injury, or infection. Adenosine exerts predominantly protective effects through activation of four 7-transmembrane receptor subtypes termed A1, A2A, A2B, and A3, of which the A2A adenosine receptor (A2AAR) is recognised as a major mediator of anti-inflammatory responses. The A2AAR is widely expressed on cells of the immune system and numerous in vitro studies have identified its role in suppressing key stages of the inflammatory process, including leukocyte recruitment, phagocytosis, cytokine production, and immune cell proliferation. The majority of actions produced by A2AAR activation appear to be mediated by cAMP, but downstream events have not yet been well characterised. In this article, we review the current evidence for the anti-inflammatory effects of the A2AAR in different cell types and discuss possible molecular mechanisms mediating these effects, including the potential for generalised suppression of inflammatory gene expression through inhibition of the NF-kB and JAK/STAT proinflammatory signalling pathways. We also evaluate findings from in vivo studies investigating the role of the A2AAR in different tissues in animal models of inflammatory disease and briefly discuss the potential for development of selective A2AAR agonists for use in the clinic to treat specific inflammatory conditions.
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Cytokinin ribosides (N⁶-substituted adenosines) have demonstrated anticancer activity in various cultured cell lines, several xenografts and even a small clinical trial. Effects of kinetin riboside, N⁶-benzyladenosine (BAR) and N⁶-isopentenyladenosine on various parameters related to apoptosis have also been reported, but not directly compared with those of the highly active naturally occurring aromatic cytokinins oTR (ortho-topolin riboside) and 2OH3MeOBAR (N⁶-(2-hydroxy-3-methoxybenzyl)adenosine). Here we show that 2OH3MeOBAR is the most active cytokinin riboside studied to date (median, 1st quartile, 3rd quartile and range of GI50 in tests with the NCI60 cell panel: 0.19, 0.10, 0.43 and 0.02 to 15.7 μM, respectively) and it differs from other cytokinins by inducing cell death without causing pronounced ATP depletion. Analysis of NCI60 test data suggests that its activity is independent of p53 status. Further we demonstrate that its 5′-monophosphate, the dominant cancer cell metabolite, inhibits the candidate oncogene DNPH1. Synthesis, purification, HPLC-MS identification and HPLC-UV quantification of 2OH3MeOBAR metabolites are also reported.
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Cognitive decline is found to be a common feature of various neurological disorders like Alzheimer’s disease (AD). In order to recapitulate AD associated cognitive deficits and to plan therapeutic strategies researchers have developed various preclinical dementia models to recapitulate different aspects of cognitive domains affected in AD brain. So, the present study was aimed to compare alterations in previously reported dementia models i.e. pharmacological (Scopolamine-induced and corticosterone-induced), Environmental (Aluminium-induced and noise-stress) and physiological (natural aging) models in rats in a single experimental study across three cognitive domains spatial, recognition, and associative memory and associated alterations in their oxidative status and neurochemical profile to select appropriate dementia model. All groups received their respective treatments for 14 days after which behavioural analysis was performed including Open Field test to assess ambulatory activity, Novel Object Recognition test, Morris Water Maze Test and Passive Avoidance test for the assessment of recognition, spatial and associative memory. After monitoring the behavioural activities, rats were decapitated and their brains and hippocampus samples were collected for analysis of oxidative status and neurochemical profile. Results showed significant decline in different aspects of memory function in all dementia models which was more significant in scopolamine-injected rats. A significant decline in levels of monoamines and acetylcholine was also observed. In addition, significant alterations were also seen in oxidative profile indicating that cognitive decline could be associated with increased oxidative stress. Therefore, present findings highlight that for planning therapeutic strategies against cognitive dysfunctions, scopolamine-induced dementia model is the most appropriate dementia model to reveal AD-related cognitive impairment profile.
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The aim of this study was to evaluate the neuroprotective effects of kinetin (Kn) on oxidative damage induced by D-galactose (D-gal). In vitro, cultured astrocytes were distributed equally in different culture flasks to serve as control, model, and test groups. They were incubated respectively with 0 μM (model group), 50, 100 or 200 μM Kn along with 15 mM D-gal for 24 and 72 h, but cells in the control group received only normal medium. Activities of total-superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) levels were measured by biochemical analysis. In vivo, mice were also randomly divided into control, model, and test groups. They were subcutaneously injected with D-gal (125 mg/kg), and administered with 0 (model group), and 10, 20 and 40 mg/kg Kn (test groups) per day simultaneously by gastric perfusion, but mice in the control group only received 0.4 ml physiologic saline solution per day by gastric perfusion. After 6 weeks, T- SOD and GSH-Px activities, and MDA levels in the brain tissue were assessed by biochemical analysis. Results show that both Dgal- treated astrocytes and mice brains displayed impaired antioxidant systems, an increase in MDA levels, and a decrease in T-SOD and GSH-Px activities. After Kn treatment, the changes of antioxidant enzymes activities and MDA levels were reversed both in vitro and in vivo. In conclusion, results of this study indicate that supplementation of Kn protects cultured astrocytes in vitro and mouse brain from Dgal- induced oxidative damage.
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The purpose of this open-label study was to determine the safety and efficacy of twice-daily application of kinetin (N 6-furfuryladenine) 0.1% (Kinerase®, ICN Pharmaceuticals, Costa Mesa, California) lotion for the treatment of mildly to moderately photodamaged facial skin. Treatments lasting 12 and 24 week significantly improved the appearance of skin texture, mottled hyperpigmentation, and fine wrinkles as assessed by both physician and patient. Treatments also improved skin-barrier function as measured by a decrease in transepidermal water loss. Overall, these treatments were well tolerated by patients. Kinetin lotion, a new product, is useful in improving the appearance of mildly to moderately photodamaged facial skin and does not produce the cutaneous side effects associated with other commonly used antiaging products.
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In many organisms, including plants, nucleic acid bases and derivatives such as caffeine are transported across the plasma membrane. Cytokinins, important hormones structurally related to adenine, are produced mainly in root apices, from where they are translocated to shoots to control a multitude of physiological processes. Complementation of a yeast mutant deficient in adenine uptake (fcy2) with an Arabidopsis cDNA expression library enabled the identification of a gene, AtPUP1 (for Arabidopsis thaliana purine permease1), belonging to a large gene family (AtPUP1 to AtPUP15) encoding a new class of small, integral membrane proteins. AtPUP1 transports adenine and cytosine with high affinity. Uptake is energy dependent, occurs against a concentration gradient, and is sensitive to protonophores, potentially indicating secondary active transport. Competition studies show that purine derivatives (e.g., hypoxanthine), phytohormones (e.g., zeatin and kinetin), and alkaloids (e.g., caffeine) are potent inhibitors of adenine and cytosine uptake. Inhibition by cytokinins is competitive (competitive inhibition constant Ki = 20 to 35 μM), indicating that cytokinins are transported by this system. AtPUP1 is expressed in all organs except roots, indicating that the gene encodes an uptake system for root-derived nucleic acid base derivatives in shoots or that it exports nucleic acid base analogs from shoots by way of the phloem. The other family members may have different affinities for nucleic acid bases, perhaps functioning as transporters for nucleosides, nucleotides, and their derivatives.
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By general consensus, the omnipresent purine nucleoside adenosine is considered a major regulator of local tissue function, especially when energy supply fails to meet cellular energy demand. Adenosine mediation involves activation of a family of four G protein-coupled adenosine receptors (ARs): A1, A2A, A2B, and A3. The A3 adenosine receptor (A3AR) is the only adenosine subtype to be overexpressed in inflammatory and cancer cells, thus making it a potential target for therapy. Originally isolated as an orphan receptor, A3AR presented a twofold nature under different pathophysiologic conditions: it appeared to be protective/harmful under ischemic conditions, pro/anti-inflammatory, and pro/antitumoral depending on the systems investigated. Until recently, the greatest and most intriguing challenge has been to understand whether, and in which cases, selective A3 agonists or antagonists would be the best choice. Today, the choice has been made and A3AR agonists are now under clinical development for some disorders including rheumatoid arthritis, psoriasis, glaucoma, and hepatocellular carcinoma. More specifically, the interest and relevance of these new agents derives from clinical data demonstrating that A3AR agonists are both effective and safe. Thus, it will become apparent in the present review that purine scientists do seem to be getting closer to their goal: the incorporation of adenosine ligands into drugs with the ability to save lives and improve human health.
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Cytokinins are plant hormones that play an integral role in multiple aspects of plant growth and development. The biological functions of cytokinins in mammalian systems are, however, largely uncharacterized. The naturally occurring cytokinin zeatin riboside has recently been demonstrated to activate the mammalian adenosine A2A receptor, which is broadly expressed by various cell types including immune system cells, with the activation of the A2AR playing a role in the regulation of cells involved in both innate and adaptive immunity. We show for the first time that zeatin riboside modulates mammalian immune system activity via an A2AR-dependent mechanism. Specifically, zeatin riboside treatment induces the production of cyclic adenosine monophosphate (cAMP) by T lymphocytes and inhibits the production by CD3(+)CD4(+) T cells of interferon (IFN)-γ, IL-2, tumor-necrosis factor (TNF)-α, IL-4 and IL-13, and the production by CD3(+)CD8(+) T cells of IFN-γ, IL-2 and TNF-α. Additionally, the upregulation of CD25, CD69 and CD40L by activated T lymphocytes is modulated by zeatin riboside. Zeatin riboside treatment also potently inhibits thioglycollate-induced peritoneal leukocytosis. The immunomodulatory activities of zeatin riboside are blocked by co-treatment with the selective A2AR antagonist ZM241385. These data suggest that zeatin riboside possesses therapeutic potential as a mammalian immunomodulatory agent.Cellular & Molecular Immunology advance online publication, 12 May 2014; doi:10.1038/cmi.2014.33.
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Hutchinson-Gilford progeria syndrome is caused by mutations in the lamin A/C gene that lead to the expression of a truncated, permanently farnesylated prelamin A variant, called progerin. The accumulation of progerin at the nuclear envelope causes misshapen nuclei and results in progeroid syndromes. Previous studies in cells from individuals with HGPS have shown that blocking of farnesylation of prelamin A would ameliorate the nuclear shape abnormalities. Here we observed that an inhibitor of the farnesyl diphosphate synthase, N6-isopentenyladenosine, impeded the farnesylation of prelamin A, by causing a decrease of the frequency of nuclear shape abnormalities and the redistribution of prelamin A away from the inner nuclear envelope. Most remarkably, we showed that a combination of lovastatin and N6-isopentenyladenosine significantly improved nuclear shape in fibroblast cell lines from atypical progeria patients. These findings establish a paradigm for ameliorating the most obvious cellular pathology in lamin-related progeroid syndromes and suggest a potential strategy for treating of children with Hutchinson-Gilford progeria syndrome. This article is protected by copyright. All rights reserved.
Article
A new cytokinin was isolated from mature leaves of poplar. Its structure was determined by UV and MS and confirmed by synthesis as 6-(o-hydroxybenzylamino)-9-β-d-ribofuranosylpurine. This cytokinin has medium activity in the soybean callus test but shows high activity in the radish leaf senescence test.
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Mitochondria have long been implicated in the pathogenesis of Parkinson's disease (PD). Mutations in the mitochondrial kinase PINK1 that reduce kinase activity are associated with mitochondrial defects and result in an autosomal-recessive form of early-onset PD. Therapeutic approaches for enhancing the activity of PINK1 have not been considered because no allosteric regulatory sites for PINK1 are known. Here, we show that an alternative strategy, a neo-substrate approach involving the ATP analog kinetin triphosphate (KTP), can be used to increase the activity of both PD-related mutant PINK1(G309D) and PINK1(WT). Moreover, we show that application of the KTP precursor kinetin to cells results in biologically significant increases in PINK1 activity, manifest as higher levels of Parkin recruitment to depolarized mitochondria, reduced mitochondrial motility in axons, and lower levels of apoptosis. Discovery of neo-substrates for kinases could provide a heretofore-unappreciated modality for regulating kinase activity.
Article
The role of adenosine A3 receptors in synaptic transmission under severe (7min) and shorter (2–5min) ischemic conditions, obtained by oxygen and glucose deprivation (OGD), was investigated in rat hippocampal slices. The effects of selective A3 agonists or antagonists were examined on field excitatory postsynaptic potentials (fEPSPs) extracellularly recorded at the dendritic level of the CA1 pyramidal region. The novel, selective A3 antagonist LJ1251 ((2R,3R,4S)-2-(2-chloro-6-(3-iodobenzylamino)-9H-purin-9-yl)tetrahydrothiophene-3,4-diol, 0.1–10nM) protected hippocampal slices from irreversible fEPSP depression induced by severe OGD and prevented or delayed the appearance of anoxic depolarization. Similar results were obtained when severe OGD was carried out with a long, receptor-desensitizing exposure to various selective A3 agonists: 5′-N-methylcarboxamidoadenosine derivatives Cl-IB-MECA (N6-(3-iodobenzyl)-2-chloro), VT72 (N6-methoxy-2-phenylethynyl), VT158 (N6-methoxy-2-phenylethynyl), VT160 (N6-methoxy-2-(2-pyridinyl)-ethynyl), and VT163 (N6-methoxy-2-p-acetylphenylethynyl) and AR132 (N6-methyl-2-phenylethynyladenosine).The selective A3 antagonist MRS1523 (3-propyl-6-ethyl-5-[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine carboxylate, 100nM) reduced fEPSP depression evoked by 2-min OGD and induced a faster recovery of fEPSP amplitude after 5-min OGD. Similar results were obtained for 2- or 5-min OGD applied in the presence of each of the A3 agonists tested. Shorter exposure to A3 agonists significantly delayed the recovery of fEPSP amplitude after 5-min OGD.This indicates that A3 receptors, stimulated by selective A3 agonists, undergo desensitization during OGD. It is inferred that CA1 hippocampal A3 receptors stimulated by adenosine released during brief ischemia (2 and 5min) might exert A1-like protective effects on neurotransmission. Severe ischemia would transform the A3 receptor-mediated effects from protective to injurious.
Article
After intravenous administration of N6(Δ2-isopentenyl)adenosine-8-14C (IPA-8-14C) to human subjects, several metabolites were isolated along with a small quantity of unchanged IPA. The ultraviolet spectra and paper chromatography of purified metabolites led to the identification of 6-N-(3-methyl-3-hydroxybutylamino)purine, hypoxanthine, adenine and some N6-alkylated adenines and N-alkylated xanthines. A large quantity of the radioactivity (50 per cent) from IPA-8-14C was excreted in the form of non-ultraviolet absorbing compounds, suggesting saturation or cleavage or both of the purine portion of IPA. Orally administered IPA produced comparable urine levels and gave a very similar metabolic picture. These results indicate that IPA is rapidly metabolized in the body, but not to uric acid, as is found for common purine nucleosides. Incubation of N6-(Δ2isopentenyl)adenine with xanthine oxidase resulted in rapid oxidation, presumably, to 2,8-dihydroxy-N6(Δ2-isopentenyl)adenine. On the basis of these findings in vivo and in vitro, a catabolic pathway for IPA is suggested.
Article
After the discovery of kinetin (Miller et al. 1956, J. Am. Chem. Soc. 78: 1345–1350) there was a flurry of syntheses that led to the finding of 6-benzylaminopurine (BA), an active and easily obtainable cytokinin. Much research into cytokinin physiology was subsequently done with this substance. Further, the isolation and unequivocal identification of natural BA and the high biological activity of its meta-hydroxylated analogues stimulated the search for other natural aromatic cytokinins. Screening was accomplished by ELISA of HPLC fractions using antisera against ortho- and meta-hydroxybenzyladenosine. Subsequent isolation and decisive identification by mass spectrometry led to discovery of a broad spectrum of endogenous plant growth substances structurally similar to a highly active compound, meta-topolin (6-[3-hydroxybenzyl-amino]purine), and to its less active analogue, ortho-topolin (6-[2-hydroxybenzyl-amino]purine). The structures of such aromatic cytokinins suggest considerably different biosynthetic pathways from that of zeatin and related isoprenoid cytokinins. From a physiological viewpoint, aromatic cytokinin metabolism can be classified under four main headings analogous to isoprenoid cytokinins: interconversion, hydroxylation, conjugation, and oxidative degradation. This review attempts to put into context what is known about 9-alkyl-BAs and compares their metabolism in regard to the practical use of cytokinins in agriculture and biotechnology. The recently discovered unusual specificity of additionally C2,N9-disubstituted aromatic cytokinins toward cell cycle kinases, suggests that these cytokinin-derived growth regulators may selectively inhibit certain steps of the cell cycle. The functional overlap of the aromatic cytokinins with those of their isoprenoid counterparts and cytokinin inhibitors, in relation to growth and developmental processes in plants, has yet to be determined.
Article
While testing purines related to the non-specific protein kinase inhibitors N6-dimethylaminopurine and N6-(2-isopentenyl)adenine as potential inhibitors of the p34cdc2/cyclin B kinase, we discovered a compound with high specificity, 2-(2-hydroxyethylamino)-6-benzylamino-9-methylpurine (olomoucine). Kinetic analysis of kinase inhibition reveals that olomoucine behaves as a competitive inhibitor for ATP and as a non-competitive inhibitor for histone H1 (linear inhibition for both substrates). The kinase specificity of this inhibition was investigated for 35 highly purified kinases (including p34cdk4/cyclin D1, p40cdk6/cyclin D3, CAMP-dependent and cGMP-dependent kinases, eight protein kinase C isoforms, calmodulin-dependent kinase II, myosin light-chain kinase, mitogen-activated S6 kinase, casein kinase 2, double-stranded RNA-activated protein kinase, AMP-stimulated kinase, eight tyrosine kinases). Most kinases are not significantly inhibited. Only the cell-cycle regulating p34cdc2/cyclin B, p33cdk2/cyclin A and p33cdk2/cyclin E kinases, the brain p33cdk5/p35 kinase and the ERK1/MAP-kinase (and its starfish homologue p44mpk) are substantially inhibited by olomoucine (IC50 values are 7, 7, 7, 3 and 25 μM, respectively). The cdk4/cyclin D1 and cdk6/cyclin D3 kinases are not significantly sensitive to olomoucine (IC50 values greater than 1 mM and 150 μM, respectively). N6-(2-Isopentenyl)adenine is confirmed as a general kinase inhibitor with IC50, values of 50–100 μM for many kinases. The purine specificity of cyclin-dependent kinase inhibition was investigated: among 81 purine derivatives tested, only C2, N6 and N9-substituted purines exert a strong inhibitory effect on the p34cdc2/cyclin B kinase. An essentially similar sensitivity to this olomoucine family of compounds was observed for the brain-specific cdk5/p35 kinase. Structure/activity relationship studies allow speculation on the interactions of olomoucine and its analogues with the kinase catalytic subunit. Olomoucine inhibits in vitro M-phase-promoting factor activity in metaphase-arrested Xenopus egg extracts, inhibits in vitro DNA synthesis in Xenopus interphase egg extracts and inhibits the licensing factor, an essential replication factor ensuring that DNA is replicated only once in each cell cycle. Olomoucine inhibits the starfish oocyte G2/M transition in vivo. Through its unique selectivity olomoucine provides an anti-mitotic reagent that may preferentially inhibit certain steps of the cell cycle.
Article
The naturally occurring cytokinin, ortho-topolin riboside (oTR), has been recently reported to have a strong anticancer effect. However, the molecular mechanism has not been elucidated. From our research we found that oTR strongly inhibited the proliferation of SMMC-7721 cells inducing apoptosis. After oTR treatment, up-regulation of the protein levels of pro-apoptotic Bax and the down-regulation of the anti-apoptotic proteins, Bcl-2 and Bcl-xL was observed, leading to the loss of mitochondrial membrane potential, the release of cytochrome c from the mitochondria into the cytosol, the downstream activation of caspase-9 and caspase-3, as well as the cleavage of poly ADP-ribose-polymerase (PARP), the effect of apoptosis could be blocked by the pan-specific caspase inhibitor z-VAD-fmk and caspase-9-specific inhibitor z-LEHD-fmk. Moreover, oTR was shown to inhibit the activation of the extracellular signal-regulated kinase-1/2 (ERK(1/2)) as well as the Akt pathway. These results suggest that oTR interferes with the mitogen-activated protein kinase (MAPK) and Akt pathways and induces the apoptosis of human SMMC-7721 cells through the activation of intrinsic mitochondria-mediated pathways. However, the apoptosis was completely prevented when cells were treated with A-134974, an inhibitor of adenosine kinase, it indicated that the intracellular phosphorylation of oTR is necessary for its cytotoxic effects to SMMC-7721 cells.
Article
Inflammation plays an important role in the pathogenesis of early brain injury after subarachnoid haemorrhage. Adenosine A3 receptor (A3R) activation produces anti-inflammatory effects. In this study, the effects of a selective A3R agonist, 2-chloro-N⁶-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (CL-IB-MECA), on early brain injury and inflammatory response after subarachnoid haemorrhage were studied. Our results showed that mortality, neurological impairment and brain oedema were significantly attenuated after the administration of CL-IB-MECA. Moreover, treatment with CL-IB-MECA inhibited microglial activation and reduced the expression of proinflammatory cytokines including tumour necrosis factor-α and interleukin-1β. These data suggest that activation of A3R provides a neuroprotective effect against brain injury after subarachnoid haemorrhage, and that these effects may be associated with the anti-inflammatory properties of A3R.
Article
N(6)-isopentenyladenosine (i6A) inhibits the tumor cell growth by inducing cell apoptosis in various cancer cell lines. However, little is known regarding the mechanisms by which the drug induces cell apoptosis. In this study, we further explored the molecular mechanisms of i6A as an anticancer agent on a human breast cancer cell line MDA MB 231. Treatment with i6A decreased the cell proliferation of MDA MB 231 cells in a dose-dependent manner by arresting the cells at G(0)/G(1) phase. This effect was strongly associated with concomitant decrease in the level of cyclin D1, cyclin E, cdk2, and increase of p21waf1 and p27kip. In addition i6A also induced apoptotic cell death by increasing the expression of Bax, and decreasing the levels of Bcl-2 and Bcl-xL, and subsequently triggered mitochondria apoptotic pathway (release of cytochrome c and activation of caspase-3). We observed that i6A suppressed the nuclear factor kappaB (NF-κB) pathway and inhibited the Akt activation. The results of this study indicate that i6A decreases cell proliferation and induces apoptotic cell death in human breast cancer cells, possibly by decreasing signal transduction through the Akt/NF-κB cell survival pathway.
Article
Many patients with rosacea cannot tolerate extended treatment periods with topical agents because their skin sensitivity is often increased. To determine the long-term efficacy and tolerability of a new moisturizing lotion for improving the signs and symptoms of mild-to-moderate rosacea. In a 48-week, open-label study, a moisturizing lotion containing furfuryl tetrahydropyranyladenine as PRK-124 (0.125%, Pyratine-XR, Senetek PLC, Napa, CA) was applied twice daily by 18 subjects with mild-to-moderate rosacea. Clinical improvements were assessed by the treating physician. Skin barrier function was measured by transepidermal water loss after treatment. Tolerability and cosmetic outcome were evaluated by subjects. Subjects experienced a mean 44 percent reduction in erythema severity and a mean 89 percent reduction in inflammatory lesion count at week 48. Reductions were significant (P < 0.05) in both erythema and lesions at weeks 24, 36 and 48. Statistically significant (P < or = 0.05) improvements in telangiectasias, transepidermal water loss and dryness were noted. Overall clinical improvement was observed in 81 percent of subjects and the investigator's global assessment steadily improved throughout the study. Treatments were well-tolerated and cosmetically acceptable. Treatment-induced skin irritation was not observed. The new moisturizing lotion containing furfuryl tetrahydropyranyladenine as PRK 124 is efficacious, does not irritate skin, and is well tolerated for at least 48 weeks.
Article
Solar ultraviolet (UV) irradiation is one of the most significant extrinsic factors contributing to skin photoaging. One major characteristic of photoaging induced by UV is water loss of the skin. Water movement across the plasma membrane can occur via two pathways: by diffusion through the lipid bilayer and by membrane-inserted water channels (aquaporins). In this study we demonstrate that UV induces aquaporin-3 (AQP3) downregulation in cultured keratinocytes (HaCaT cells). PD98059 and U0126, MEK/ERK inhibitors, inhibit UV-induced AQP3 loss. Trans-Zeatin (tZ), which alone induces AQP3 expression, attenuates UV-induced loss of AQP3. We found that tZ inhibits UV-induced MEK/ERK activation; the latter serves as the key signal pathway mediating UV-induced AQP3 loss. Using specific AQP3 siRNA knockdown, we found AQP3 is involved in wound healing in human skin keratinocytes. Loss-of-AQP3-mediated delayed wound healing in UV-radiated skin keratinocytes is attenuated by tZ pretreatment. tZ pretreatment also attenuates UV-induced decreased water permeability in HaCaT cells. We concluded that UV radiation downregulates AQP3 in HaCaT cells. MEK/ERK activation is involved in this process. tZ treatment attenuates UV-induced AQP3 loss, in vitro wound healing delay and water permeability decrease. This work provides a new explanation for the anti-photoaging potential of tZ.
Article
Cytokinin ribosides (N⁶-substituted adenosine derivatives) have been shown to have anticancer activity both in vitro and in vivo. This study presents the first systematic analysis of the relationship between the chemical structure of cytokinins and their cytotoxic effects against a panel of human cancer cell lines with diverse histopathological origins. The results confirm the cytotoxic activity of N⁶-isopentenyladenosine, kinetin riboside, and N⁶-benzyladenosine and show that the spectrum of cell lines that are sensitive to these compounds and their tissues of origin are wider than previously reported. The first evidence that the hydroxylated aromatic cytokinins (ortho-, meta-, para-topolin riboside) and the isoprenoid cytokinin cis-zeatin riboside have cytotoxic activities is presented.
Article
Isopentenyladenosine (iPA), a member of the cytokinin family of plant hormones, exerts a marked antiproliferative activity on some leukemic and epithelial cancer cell lines. To characterize the molecular moieties required for the in vitro antitumor activity of the molecule and to obtain cytostatic iPA derivatives potentially useful as chemotherapeutic agents, N9-acyclic analogues have been synthesized using regioselective Mitsunobu reaction and characterized by elemental analyses, (1)H and (13)C NMR. These compounds were analyzed for their activity on human bladder cancer cell lines. In this study, we report that iPA inhibited the proliferation but not the migration of human bladder cancer cells, while the newly synthesized analogues revealed no significant cytostatic activity apart from the compound with a saturated double bond of the isopentenyl chain. These results indicate that the integrity of the ribose ring is required for the cytostatic activity of iPA.
Article
Adenosine is released from injured or hypoxic tissues where it exerts numerous anti-inflammatory effects including suppression of neutrophil functions. Although most previous work has implicated the A(2A)AR, we have recently shown that selective activation of the abundantly expressed A(3)AR inhibits neutrophil superoxide production and chemotaxis providing a potential mechanistic explanation for the efficacy of A(3)AR agonists in experimental animal models of inflammation. In this study, we hypothesized that the A(3)AR suppresses neutrophil functions by inhibiting the monomeric GTPase Rac, a central regulator of chemokine-directed neutrophil migration and superoxide production. We found that pre-treating neutrophils with the highly selective A(3)AR agonist CP-532,903 reduced fMLP-induced Rac activation using an ELISA-based assay that detects all three Rac isoforms. CP-532,903 also inhibited fMLP-induced F-actin formation, a downstream effector function of Rac relevant to neutrophil migration, but not activation of ERK1/2 or p38. Pre-treating neutrophils with CP-532,903 did not stimulate cAMP production or alter fMLP-induced calcium transients, implicating that A(3)AR stimulation does not inhibit Rac activation or neutrophil activities by suppressing Ca(2+) signaling, elevating the intracellular concentration of cAMP, or by cross-desensitizing fMLP receptors. Our results suggest that activation of the A(3)AR signals to suppress neutrophil functions by interfering with the monomeric GTPase Rac, thus contributing to the ant-inflammatory actions of adenosine.
Article
During plant development, distantly-located organs must communicate in order to adapt morphological and physiological features in response to environmental inputs. Among the recognized signaling molecules, a class of phytohormones known as the cytokinins functions as both local and long-distance regulatory signals for the coordination of plant development. This cytokinin-dependent communication system consists of orchestrated regulation of the metabolism, translocation, and signal transduction of this phytohormone class. Here, to gain insight into this elaborate signaling system, we summarize current models of biosynthesis, trans-membrane transport, and long-distance translocation of cytokinins in higher plants.
Article
Cytokinin regulates many important aspects of plant development in aerial and subterranean organs. The hormone is part of an intrinsic genetic network controlling organ development and growth in these two distinct environments that plants have to cope with. Cytokinin also mediates the responses to variable extrinsic factors, such as light conditions in the shoot and availability of nutrients and water in the root, and has a role in the response to biotic and abiotic stress. Together, these activities contribute to the fine-tuning of quantitative growth regulation in plants. We review recent progress in understanding the cytokinin system and its links to the regulatory pathways that respond to internal and external signals.
Article
Current treatments for acne rosacea are often associated with unsatisfactory outcomes and adverse effects. To determine the efficacy and tolerability of a new moisturizing lotion for improving the clinical signs and symptoms of mild-to-moderate acne rosacea. In a 12-week, open-label study, a moisturizing lotion containing furfuryl tetrahydropyranyladenine as PRK124 (0.125%, Pyratine-XR, Senetek PLC, Napa, CA) was applied twice daily to subjects with mild-to-moderate rosacea. Improvement in the appearances of erythema and papules were assessed by the treating physician. Skin barrier function was measured by transepidmal water loss after treatment. Tolerability and cosmetic outcome were evaluated by patients. Twenty-one participants completed the study. Overall clinical improvement was observed in 80% of subjects, with most showing mild-to-moderate improvement. Erythema, papule counts, and telangiectasia were reduced. The reduction in TEWL was significant at weeks 4 (p = 0.01), 8 (p < 005), and 12 (p < 0.001). Rosacea symptoms (burning, stinging, dryness) were progressively reduced, with reduction in dryness achieving statistical significance at weeks 4 (p = 0.035), 8 (p = 0.037) and 12 (p = 0.016). Treatments were well tolerated and cosmetic outcomes were acceptable. Treatment-induced irritation was not observed. The new moisturizing lotion containing furfuryl tetrahydropyranyladenine as PRK124 shows a continued trend toward improvement of skin barrier function and the appearances of erythema and papules associated with mild-to-moderate rosacea during 12 weeks of treatment.