Isotretinoin has a low affinity for retinoic acid receptors (RAR) and retinoid X receptors (RXR), but may be converted intracellularly to metabolites that act as agonists of RAR and RXR nuclear receptors.One study suggests the drug amplifies production of neutrophil gelatinase-associated lipocalin (NGAL) in the skin, which has been shown to reduce sebum production by inducing apoptosis in sebaceous gland cells, while exhibiting an antimicrobial effect on Cutibacterium acnes. The drug decreases the size and sebum output of the sebaceous glands. Isotretinoin is the only available acne drug that affects all four major pathogenic processes in acne, which distinguishes it from alternative treatments (such as antibiotics) and accounts for its efficacy in severe, nodulocystic cases. The effect of isotretinoin on sebum production can be temporary, or remission of the disease can be "complete and prolonged. "Isotretinoin has been speculated to down-regulate the enzyme telomerase and hTERT, inhibiting "cellular immortalization and tumorigenesis." In a 2007 study, isotretinoin was proven to inhibit the action of the metalloprotease MMP-9 (gelatinase) in sebum without any influence in the action of TIMP1 and TIMP2 (the tissue inhibitors of metalloproteases). It is already known that metalloproteases play an important role in the pathogenesis of acne. CNS activities
A possible biological basis for the case reports of depression involves decreased metabolism in the orbitofrontal cortex (OFC) of the frontal lobe. It has also been found that decreased OFC metabolism was correlated with headaches.
The letter h may represent /h/ as in the name of the Székely town Hargita; intervocalically it represents /ɦ/ as in tehén; it represents /x/ in the word doh; it represents /ç/ in ihlet; and it is silent in cseh. As part of a digraph, it represents, in archaic spelling, /t͡ʃ/ with the letter c as in the name Széchenyi; it represents, again, with the letter c, /x/ in pech (which is pronounced [pɛxː]); in certain environments it breaks palatalization of a consonant, as in the name Beöthy which is pronounced [bøːti] (without the intervening h, the name Beöty could be pronounced [bøːc]); and finally, it acts as a silent component of a digraph, as in the name Vargha, pronounced [vɒrgɒ]. In Ukrainian and Belarusian, when written in the Latin alphabet, ⟨h⟩ is also commonly used for /ɦ/, which is otherwise written with the Cyrillic letter ⟨г⟩. In Irish, ⟨h⟩ is not considered an independent letter, except for a very few non-native words, however ⟨h⟩ placed after a consonant is known as a "séimhiú" and indicates lenition of that consonant; ⟨h⟩ began to replace the original form of a séimhiú, a dot placed above the consonant, after the introduction of typewriters. In most dialects of Polish, both ⟨h⟩ and the digraph ⟨ch⟩ always represent /x/. In Basque, during the 20th century it was not used in the orthography of the Basque dialects in Spain but it marked an aspiration in the North-Eastern dialects.