Agonis reseptor GABAA

Agonis reseptor GABAA
Kelas obat-obatan
Gaboksadol (THIP), agonis reseptor GABAA dan hipnotik yang terkenal.
Pengenal kelas
SinonimAgonis GABAA
PenggunaanPengobatan sawan, insomnia, efek halusinogenik
Mekanisme aksiagonisme reseptor GABAA
Target biologisReseptor GABAA
Kelas kimiaAnalog GABAsl dan lainnya
Dalam Wikidata

Agonis reseptor GABAA adalah obat yang bertindak sebagai agonis ortosterik dari reseptor GABAA, reseptor pensinyalan utama dari neurotransmiter penghambat asam aminobutirat gamma (GABA).[1][2][3]

Mekanisme kerja agonis reseptor GABAA tidak seperti modulator alosterik positif GABAA termasuk benzodiazepin, obat Z, barbiturat, neurosteroid, dan alkohol, yang bekerja melalui situs pengatur alosterik untuk mempotensiasi fungsi reseptor GABAA.[4][3] Agonis reseptor GABAA memiliki efek yang berbeda dengan modulator alosterik positif reseptor GABAA.[5][6][7][8]

Contoh agonis reseptor GABAA antara lain adalah GABA itu sendiri, asam γ-amino-β-hidroksibutirat (GABOB), muskimol (ditemukan dalam jamur Amanita muscaria), gaboksadol (THIP), dan progabida.[1][2][3] Agonis reseptor GABAA dengan efikasi tinggi telah ditemukan menghasilkan efek diantaranya sedatif, hipnotik, antikonvulsan, dan halusinogenik.[9][10][11][12] Persyaratan struktural untuk pengikatan dan aktivasi reseptor GABAA telah ditemukan sangat ketat, sehingga relatif sedikit agonis reseptor GABAA dengan efikasi tinggi yang diketahui.[2][13] Saat ini belum diketahui agonis reseptor GABAA yang sepenuhnya selektif, misalnya yang tidak memiliki aktivitas tambahan pada reseptor GABAA-ρ dan/atau GABAB yang terkait erat.[14]

Agonis reseptor GABAA umumnya merupakan analog dan derivatif GABA.[1][2] Muskimol, analog GABA yang terkendali secara konformasi, adalah salah satu agonis reseptor GABAA pertama yang diidentifikasi.[15]

GABA

Struktur kimia asam aminobutirat gamma (GABA).

Asam aminobutirat gamma (GABA) adalah neurotransmiter penghambat utama dalam sistem saraf pusat.[6][16][17] Ia terdapat pada sekitar 25 hingga 50% neuron di otak.[17] Neurotransmiter ini bertindak sebagai agonis non-selektif dari ketiga jenis reseptor GABA termasuk reseptor GABAA, GABAB, dan GABAA-rho (GABAC).[6][16] GABA tersedia sebagai suplemen yang dijual bebas dan sering dikonsumsi untuk pengobatan sendiri insomnia dan kecemasan. Namun, GABA sangat rentan terhadap metabolisme, memiliki waktu paruh eliminasi yang sangat singkat, dan tidak dapat menembus sawar darah otak.[18][19] Oleh karena itu, manfaat terapeutik GABA eksogen masih diragukan.[19]

GABOB

Struktur kimia asam γ-amino-β-hidroksibutirat (GABOB).

Asam γ-amino-β-hidroksibutirat (GABOB) adalah analog endogen dekat GABA yang ditemukan di otak manusia.[20] Ia bertindak sebagai agonis reseptor GABAA dan GABAB ganda.[21] Obat ini memiliki efek antikonvulsan dan telah digunakan dalam pengobatan epilepsi di beberapa negara di seluruh dunia.[22][20][23]

Muskimol

Struktur kimia muskimol yang terdapat pada Amanita muscaria.
Jamur Amanita muscaria yang mengandung muskimol.

Muskimol adalah alkaloid yang ditemukan pada jamur Amanita seperti Amanita muscaria. Ini merupakan turunan GABA yang dibatasi secara konformasi.[10][15][24] Obat ini merupakan agonis penuh reseptor GABAA yang sangat kuat.[10][15] Namun, ia merupakan agonis selektif atau preferensial dari reseptor GABAA yang mengandung subunit δ ekstrasinaptik.[10][25][26] Obat ini juga bertindak sebagai agonis parsial reseptor GABAA-ρ yang poten dan penghambat penyerapan kembali GABA yang lemah.[10][15][27] Muskimol adalah obat penenang dan halusinogen.[10][28][29] Asam ibotenat, alkaloid lain yang ditemukan dalam jamur Amanita, adalah neurotoksin tetapi berfungsi sebagai bakal obat muskimol dan memiliki efek yang serupa.[30][28][27] Muskimol telah menjadi struktur dasar untuk pengembangan banyak modulator sistem GABA sintetis termasuk modulator reseptor GABA dan penghambat penyerapan kembali GABA.[5][31] Senyawa ini telah digunakan secara rekreasional sebagai halusinogen dan semakin banyak digunakan pada dosis rendah untuk klaim manfaat terapeutik, seperti peningkatan kualitas tidur.[10][32][33][34]

Gaboksadol

Struktur kimia gaboksadol (THIP).

Gaboksadol (THIP) adalah turunan sintetis dari muskimol yang bertindak sebagai agonis parsial reseptor GABAA yang poten.[7][8][11] Namun, gaboksadol merupakan agonis supramaksimal selektif atau preferensial dari reseptor GABAA yang mengandung subunit δ ekstrasinaptik.[2][7][9] Obat ini juga merupakan antagonis reseptor GABAA-ρ yang poten.[14] Gaboksadol memiliki selektivitas dan sifat seperti obat yang lebih baik dibandingkan dengan muskimol.[7][15][5][11] Obat ini memiliki efek sedatif, hipnotik, dan pada dosis tinggi menyebabkan halusinogenik. Obat ini dikembangkan untuk pengobatan insomnia dan kondisi lainnya.[8][2][11] Obat ini terbukti efektif dalam pengobatan insomnia, dengan sifat-sifat yang menguntungkan dibandingkan dengan hipnotik lainnya, seperti peningkatan tidur gelombang lambat (tidur nyenyak).[8][2][35] Gaboksadol menyelesaikan uji klinis fase 3 untuk indikasi ini.[36] Namun, penggunaannya dihentikan karena berbagai alasan, terutama indeks terapeutik yang sempit dengan tingkat efek halusinogenik yang tinggi pada dosis superterapeutik.[37][38][39]

Progabida

Struktur kimia progabida.

Progabida adalah turunan GABA yang bertindak sebagai agonis reseptor GABAA dan GABAB ganda.[12][40][41][42] Ia menghasilkan agonis reseptor GABA yang lebih poten yakni asam progabida (SL-75102) sebagai metabolit aktif dan juga merupakan bakal obat dari gabamida dan GABA.[12][41][43][42] Obat ini digunakan sebagai antikonvulsan di Prancis.[44] Penggunaan progabida telah dibatasi oleh efektivitas klinis yang buruk dan insidensi toksisitas hati.[45]

Pikamilon

Struktur kimia pikamilon (N-nikotinoil-GABA).

Pikamilon (N-nikotinoil-GABA) adalah analog GABA, khususnya konjugat GABA dan asam nikotinat (niasin), yang digunakan sebagai obat farmasi dan vasodilator di Rusia untuk berbagai indikasi.[46][47] Selain itu, telah muncul dalam suplemen makanan di tempat lain di dunia, diiklankan, digunakan sebagai nootropika (peningkat kognitif).[46][48] Obat ini menembus sawar darah otak serta dihidrolisis menjadi GABA dan asam nikotinat pada hewan, dan oleh karena itu diasumsikan bertindak sebagai bakal obat yang aktif secara sentral dan tahan terhadap metabolisme dari metabolit ini.[46][49] Pikamilon sendiri telah ditemukan tidak aktif pada sejumlah besar target termasuk reseptor GABA, transporter GABA, transaminase GABA, dan saluran kalsium, yang semuanya merupakan target yang diketahui untuk analog GABA lainnya. Obat ini relatif sedikit diteliti.[46]

Lainnya

Agonis reseptor GABAA lainnya antara lain termasuk 4-AHP,[50] dihidromuskimol, asam imidazola-4-asetat (IAA, IMA), isoguvacine, asam isonipekotat, metilglioksal,[51] nefirasetam (DM-9384),[52] 4-PIOL, asam piperidina-4-sulfonat (P4S), kuiskualamina,[53][54][55] tiomuskimol, dan tolgabida (SL-81.0142).[56][6][57] Beberapa senyawa ini seperti isoguvacine, asam isonipekotat, dan P4S, diketahui tidak dapat menembus sawar darah otak.[58][7][59]

Agonis Tidak Langsung

Agonis tidak langsung dari reseptor GABAA, serta reseptor GABA lainnya, termasuk penghambat penyerapan kembali GABA seperti antikonvulsan tiagabin dan penghambat transaminase GABA (GABA-T) seperti antikonvulsan vigabatrin.[60][61][62][63] Penghambat penyerapan kembali GABA CI-966, yang telah dipelajari secara klinis sebagai antikonvulsan, menghasilkan efek halusinogenik yang mirip dengan agonis reseptor GABAA seperti muskimol.[41]

Lihat juga

Referensi

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