The beta-carotene is firstly cleaved into beta-carotene 15-15-monooxygenase through site 1 double bond oxidized to epoxide. The epoxide is attacked by water to form diol in site 1. NADH, as a reduction agent, reduce the alcohol group to aldehydes. History
Tretinoin was co-developed for its use in acne by James Fulton and Albert Kligman when they were at University of Pennsylvania in the 1960s. Phase I trials, the first conducted on human subjects, were performed on inmates at Holmesburg Prison during a long-running regime of non-therapeutic and unethical testing on prison inmates at Holmesburg. The University of Pennsylvania held the patent for Retin-A, which it licensed to pharmaceutical companies.Treatment of acute promyelocytic leukemia was first introduced at Ruijin Hospital in Shanghai by Wang Zhenyi in a 1988 clinical trial. Etymology
The origin of the name tretinoin is uncertain, although several sources agree (one with probability, one with asserted certainty) that it probably comes from trans- + retinoic [acid] + -in, which is plausible given that tretinoin is the all-trans isomer of retinoic acid. The name isotretinoin is the same root tretinoin plus the prefix iso-. Regarding pronunciation, the following variants apply equally to both tretinoin and isotretinoin. Given that retinoic is pronounced , it is natural that  is a commonly heard pronunciation. Dictionary transcriptions also include  (tri-TIN-oh-in) and .
Tabes dorsalis is a late consequence of neurosyphilis, characterized by the slow degeneration (specifically, demyelination) of the neural tracts primarily in the dorsal root ganglia of the spinal cord (nerve root). These patients have lancinating nerve root pain which is aggravated by coughing, and features of sensory ataxia with ocular involvement. Signs and symptoms
Signs and symptoms may not appear for decades after the initial infection and include weakness, diminished reflexes, paresthesias (shooting and burning pains, pricking sensations, and formication), hypoesthesias (abnormally diminished sense of touch), tabetic gait (locomotor ataxia), progressive degeneration of the joints, loss of coordination, episodes of intense pain and disturbed sensation (including glossodynia), personality changes, urinary incontinence, dementia, deafness, visual impairment, positive Rombergs test, and impaired response to light (Argyll Robertson pupil). The skeletal musculature is hypotonic due to destruction of the sensory limb of the spindle reflex. The deep tendon reflexes are also diminished or absent; for example, the "knee jerk" or patellar reflex may be lacking (Westphals sign). A complication of tabes dorsalis can be transient neuralgic paroxysmal pain affecting the eyes and the ophthalmic areas, previously called "Pels crises" after Dutch physician P.K. Pel. Now more commonly called "tabetic ocular crises", an attack is characterized by sudden, intense eye pain, tearing of the eyes and sensitivity to light. "Tabes dorsalgia" is a related lancinating back pain. "Tabetic gait" is a characteristic ataxic gait of untreated syphilis where the persons feet slap the ground as they strike the floor due to loss of proprioception.