Historical Aspects of the Major Neurological Vitamin Deficiency Disorders: Overview and Fat-Soluble Vitamin A

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Chapter 29 Historical aspects of the major neurological vitamin deficiency disorders: overview and fat-soluble vitamin A

DOUGLAS J. LANSKA* Veterans Affairs Medical Center, Tomah, Wisconsin, and University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA

VITAMINS AND DIETARY importantly are able to prevent these disorders in the DEFICIENCY DISEASES first place by targeted supplementation and food fortification. As a result, incidence, prevalence, case Introduction fatality, and mortality of neurological vitamin Vitamins are organic micronutrients that are essential deficiency disorders have declined dramatically in to normal growth and metabolism, and are present developed countries since the middle of the 20th cen- in only minute amounts in natural foodstuffs. Histori- tury. Endemic forms of these disorders have been cally, vitamin deficiency disorders have been major either eliminated from or greatly curtailed in causes of neurological morbidity and mortality developed countries, and the relatively rare residual throughout the world, often affecting large segments cases generally reflect individual predispositions of malnourished populations. The neurological presen- because of altered intake (e.g., alcoholics, food fad- tations vary with the deficiencies involved, but dists, total parenteral nutrition), malabsorption (e.g., included dementia, amnestic confabulatory states, pernicious anemia, chronic diarrhea, iatrogenic causes, delirium, acute psychosis, blindness, eye movement alcoholism), and altered metabolism or abnormal utili- abnormalities, ataxia, myelopathy, polyneuropathy, zation.(e.g., medications, coincident disease). Unfortu- and congenital neural tube defects. nately, high rates of many neurological vitamin Although diseases that are now recognizable as vita- deficiency disorders persist in developing countries min deficiency disorders have been known for millen- and other populations besought with war, famine, nia, the “vitamin doctrine” was not developed until and poverty. the early 20th century (Hopkins, 1929/1965). Prior to This chapter begins a historical review of vitamin this development, vitamin deficiency disorders were deficiency disorders causing neurological illness, generally attributed to toxic or infectious causes, the and includes a general overview of the historical most powerful pathophysiological paradigms of the origins of the vitamin doctrine and an historical review late-19th and early-20th centuries. of fat-soluble vitamin A. Study of the history of Since the initial development of the vitamin doc- neurological vitamin deficiency disorders can be trine, there has been an explosive growth in our under- rewarding from several vantage points, and can aug- standing of cellular metabolism, including the ment understanding of normal neurochemistry and coenzyme functions of many of the vitamins. In some neurophysiology, neuropathophysiology, the interrela- cases we now possess a fairly complete pathophysiolo- tionships between neurological and systemic illness, gical understanding of the development of specific neurotherapeutics, neuroepidemiology, and neurologi- neurological vitamin deficiency disorders, are able to cally-oriented social medicine and public health. identify such disorders early, are able to treat and Seldom in the case of neurological disorders is such a often cure people with such disorders when identified breadth and depth of medical understanding available early using synthetic forms of the vitamins, and most to help prevention and treatment efforts.

*Correspondence to: Douglas J. Lanska MD, VA Medical Center, 500 E Veterans St., Tomah, WI 54660, USA. E-mail: [email protected], Tel: +1-608-372-1772, Fax: +1-608-372-1240. Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:23 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

436 D.J. LANSKA Components of a physiologically From Funk’s “vitamine” to vitamin complete diet and Hopkins’ In 1911 and 1912 Polish chemist Casimir Funk (1884– “accessory food factors” 1967), then working at the Lister Institute for Preven- In the late-19th century, a physiologically complete diet tive Medicine in London, proposed that the active diet- was believed to require only a sufficient amount of ary factor that was effective in the treatment of animal proteins, carbohydrates, fats, inorganic salts, and models of beriberi was a specific organic substance water. However, as early as 1880 and 1881, in studies present in trace amounts—one of several trace dietary for a doctoral thesis, Russian physician Nicolai I. Lunin factors that were essential for life and which, when (1853–1937) in Dorpat (now Tartu, Estonia) found that deficient, resulted in such diseases as beriberi, scurvy, mice did not thrive or grow when fed on purified diets rickets, and pellagra (Funk, 1911, 1912, 1922; Harrow, containing only these constituents, although he made 1955). Funk had isolated a concentrate from rice polish- no effort at identifying any missing essential factors ings that seemed to be curative for polyneuritis in in the inadequate diets (Hopkins, 1929/1965; Voss, pigeons, and that his chemical analyses suggested was 1956; Rosenfeld, 1997). probably an amine. Because this substance appeared In 1905, Cornelius Pekelharing (1848–1922) in to be vital for life, Funk named it “vitamine” for “vital Utrecht performed similar experiments and achieved amine” (Funk, 1912). similar results, but found that animals that received Funk supposed that vitamines would all belong to milk instead of water thrived. Pekelharing suggested the same chemical class, just as amino acids as the con- that there was an unrecognized substance in milk, stituents of proteins are chemically related. However, present in very small amounts, which was necessary Funk’s concentrates were primarily nicotinic acid, for the animals to adequately utilize the other dietary which was contaminated with small amounts of the components—a clear statement of what would later anti-beriberi factor (thiamin). Nevertheless, Funk’s be called the “vitamin doctrine” (Hopkins, 1929/1965; term was widely adopted and applied to a series of Rosenfeld, 1997). food substances, regardless of their chemical struc- Unfortunately, the early reports by Lunin, Pekelhar- tures. Indeed, the introduction of the term and its ing, and others attracted little attention until the work popularization led to further research efforts interna- of British biochemist Frederick Hopkins (1861–1947) tionally, as these dietary substances became recognized at Cambridge University was published in 1912. From as clinically important beyond the prevention of some 1906 to 1912 Hopkins conducted similar feeding experi- distant tropical diseases. In 1920, Jack Drummond ments with young mice and rats (Hopkins, 1929/1965). (1891–1952) proposed that the “e” be dropped from Hopkins’ experiments were notable for providing care- “vitamine,” because there was no evidence that the ful observations under controlled laboratory conditions essential dietary factors are amines; the revised with “analytical control of materials, for the meticu- term “vitamin” would then conform to a standard lous weighing and measurement of the quantities of nomenclature convention, one in which substances of food consumed, for the many days over which animals undefined composition end with the suffix “-in” were studied ..., for consistent recording of the weight (Drummond, 1920; Rosenfeld, 1997). and growth of the rats, and for ...independence from current dogma” (Weatherall, 1990, p. 123). Hopkins VITAMIN A DEFICIENCY: NIGHT found that rats fed purified mixtures of protein BLINDNESS AND KERATOMALACIA (casein) or amino acids, carbohydrates (sucrose, Introduction starch), fats (butter or lard), mineral salts, and water failed to grow or even lost weight and died, unless Vitamin A is integral to sensory transduction and spe- the diet was supplemented with small amounts of milk cifically the transduction of light for visual perception. (Hopkins, 1906, 1912, 1929/1965). Hopkins concluded Vitamin A is the precursor of the visual pigments that milk contained “accessory food factors” that are within the rods and cones of the retina. In particular, required in trace amounts for normal growth (Hopkins, a derivative of vitamin A, 11-cis retinal, is the chromo- 1912, 1929/1965). Although there were clearly others phore within the G protein-coupled photoreceptor pro- who anticipated this work, and although other investi- tein, rhodopsin, which is localized to the outer gators had difficulty reproducing and confirming segments of rod cells in the retina. This transmem- Hopkins’ results, Hopkins shared the 1929 Nobel Prize brane detector undergoes a conformational change in in Physiology or Medicine for his contributions to response to light, which activates an intracellular the “discovery of the growth-stimulating vitamins” G-protein-coupled transduction cascade, and ultimately (Hopkins, 1929/1965). cellular responses that lead to visual perception. The Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:25 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

Au1 HISTORICAL ASPECTS OF THE MAJOR NEUROLOGICAL VITAMIN DEFICIENCY DISORDERS 437 study of this physiological process has not only greatly evening at dusk, afflicted sailors became blind and had expanded knowledge of sensory transduction, visual to be led about the ship. Several affected sailors, perception, and dark adaptation, but has provided a after being kept below decks for 3–5 days, transiently prototypical model and tremendous insights into regained normal night vision, but became night blind the functions of a large class of structurally related again when exposed to sunlight (although mysterious G protein-coupled cell receptors involved, for example, at the time, this no doubt resulted from marginal in detecting odorants, neurotransmitters, and hor- vitamin A reserves, which could be tenuously renewed mones (Hargrave and McDowell, 1992; Filmore, 2004). with minimal light exposure, but which were insuffi- Because rhodopsin is available in greater quantities cient for more rapid rates of depletion). Schwarz than any other G protein-coupled receptor, it has been found that both boiled ox liver and pig liver were studied in much greater detail than its fellow G pro- curative. tein-linked receptors (Hargrave and McDowell, 1992). Corneal epithelial defects were clearly recognized in Drugs targeting members of this integral membrane the 19th century in those subsisting on diets now recog- protein family now represent nearly half of all pre- nizable as deficient in vitamin A. Corneal ulceration scription pharmaceuticals and are a major focus of was reported in 1817 by Franc¸ois Magendie (1783– current drug development (Filmore, 2004). 1855) among vitamin A-deficient dogs fed for several The neurological disorder associated with vitamin A weeks on a diet limited to sugar and water, although deficiency is night blindness, which has plagued mal- he erroneously attributed this to a deficiency of dietary nourished populations for millennia, and remains a nitrogen (i.e., protein) (Budd, 1842; Wolf, 1996). In major public health problem in many countries around 1842, English physician George Budd (1808–1882) the world. described similar corneal ulcers among East Indians during a sea voyage to England (Budd, 1842; Hughes, 1973; Wolf, 1996), and in 1857 African explorer David Description of night blindness Livingstone reported corneal lesions among African and keratomalacia natives who subsisted on coffee, manioc, and meal Night blindness was recognized by the ancient Egyptians (Wolf, 1996). In 1904, Masamichi Mori in Japan and the ancient Greeks (Dowling and Wald, 1958; Wolf, described widespread xerophthalmia (corneal dryness), 1996). During the Roman Era, Galen (ca. 129–199 A.D.) often with keratomalacia (ulceration and perforation clearly described “nyktalopia” as night blindness and of the cornea), among Japanese children subsisting recommended eating raw beef liver (now known to con- mostly on rice and barley, and further reported that tain high concentrations of vitamin A) to correct the liver and cod-liver oil were curative (Mori, 1904; Wolf, condition (Wolf, 1996). Chinese medical texts also 1996). described night blindness: Sun-szu-mo (7th century The association between night blindness with cor- AD) recommended pig liver as a treatment (Wolf, neal epithelial defects was recognized in the late-19th 1996). Later, during European colonial expansion, and early-20th centuries. In 1860, V. von Hubbenet several physicians—including Jacobus Bontius (1592– first reported the association between night blindness 1631), the first European physician in the Dutch East and corneal epithelial defects (“silver scales on the cor- Indies, and Willem Piso (1611–1678) in Brazil—described nea”), attributed this to an inadequate diet, and found night blindness and its cure with shark liver (Wolf, it treatable with beef liver (Wolf, 1996). In 1862, Bitot 1996). In 1754, German physician C. A. von Bergen reported foamy white spots (“Bitot spots”) on the described epidemics of night blindness in rural Russia corneas of children with night blindness (Wolf, 1996), and postulated a nutritional cause (Wolf, 1996). English and by 1863 concluded that night blindness and physician William Heberden (1710–1801), often consid- xerophthalmia are both manifestations of the same ered the outstanding clinician of his era, also described disorder (Bitot, 1863; Wolf, 1996, 2001). Similarly, in a case of “nyctalopia, or night-blindness” in a sailor 1913, S. Ishihara recognized the association of night who developed blindness at night, with retained daytime blindness and keratomalacia in malnourished children vision, which gradually abated within 3 days of going (Ishihara, 1913; Wolf, 1996). ashore (Heberden, 1818, pp. 269–270). In 1919, during World War I, E. Bloch studied The nutritional basis of night blindness was further malnourished Danish children with night blindness elaborated by Austrian naval physician Eduard and keratomalacia, who had subsisted on fat-free milk, Schwarz (1831–1862) during an around-the-world oatmeal, and barley soup (Bloch, 1919; Wolf, 1996). scientific expedition (1857–1859) (Wolf, 1996). Night In a critical experiment, Bloch prospectively studied blindness (“hemeralopia”) developed in 75 of the 352 32 institutionalized toddlers (aged 1–4 years), half of men on board, often simultaneously with scurvy. 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438 D.J. LANSKA while the others received vegetable fat (margarine). of the changing absorption spectra and the changing The animal fat group remained healthy, whereas 50% fluorescence of the different stages in ultraviolet light of the vegetable fat group developed corneal xerosis (Ku¨hne, 1879/1977; Wolf, 2001). It is now known that rho- (Bloch, 1919; Wolf, 1996, 2001). All of the xerosis dopsin (11-cis-retinal plus the protein opsin) is purple with cases were rapidly cured with cod-liver oil. Bloch blue fluorescence, an intermediate stage is orange with concluded that whole milk, butter, and cod-liver oil contributions of purple and yellow, all-trans-retinal-opsin contain a fat-soluble substance that protects against is yellow, and the end-product of the light-bleaching xerophthalmia. process, free all-trans-retinol, is colorless with green fluorescence (Wolf, 2001). Boll’s discovery of the visual pigment The rate of photo-bleaching is dependent on tempera- ture, as well as on the intensity and wavelength of light. In 1876 and 1877, Franz Boll (c1849–1879) observed a Ku¨hne correctly concluded that photo-bleaching is a relationship between retinal color and light exposure: photochemical process, and not a strictly thermal pro- (1) the frog retina is paler after light exposure and cess, because infrared light is invisible and does not can become completely colorless in direct sunlight; bleach the retinal preparations. and (2) excised animal retinas that had been exposed The photo-bleaching process was also found to be to light are colorless, but the purple color is restored reversible and dependent of the retinal pigment epithe- if animals are kept in the dark for a period of time lium (Ku¨hne, 1879/1977; Wolf, 2001). An excised frog after exposure to light before they are killed (Boll, eyeball could be fully bleached after being kept in sun- 1876, 1877, 1877/1977;Baumann, 1977; Hubbard, 1977; light for 30 min, but the purple color still reappears in Ku¨hne, 1879/1977; Wolf, 2001). Boll concluded that the dark, independent of the circulation of the blood. light causes bleaching of the retinal pigment, and also In contrast, an isolated, bleached retinal preparation suggested that the outer segments of the rods contain separated from the retinal pigment epithelium is a substance that conveys an impression of light to the unable to regenerate the purple color. However, if the brain by a photochemical process. isolated bleached retinal preparation is placed onto an isolated retinal pigment epithelium, the purple color Ku¨hne’s experiments with retinal does regenerate, demonstrating unequivocally the preparations and rhodopsin essential role of the retinal pigment epithelium in Willy Ku¨hne (1837–1900), professor of physiology at the pigment regeneration within the retina. University of Heidelberg, stimulated by Boll’s observa- The process of regeneration of the visual pigment tions, began experimental studies of the retina in 1877, was puzzling though, as it was “extraordinarily slow” and continued these over a productive 5-year period, (too slow by far to account for the rapidity of changing Au2 resulting in a series of 22 important papers (;;;Ku¨hne,; visual sensation), and because it seemed to occur by Ewald and Ku¨hne, 1877; Crescitelli, 1977). By the time two processes: one slow process different than a sim- he began his retinal studies, Ku¨hne was already a ple reverse of the bleaching process (which Ku¨hne renowned physiologist who had previously isolated and named neogenesis), and a relatively rapid process that named the digestive protease trypsin from the pancreas, could reverse the intermediaries (but not the final coined the word “enzyme,” and contributed greatly to product) back to visual purple (which Ku¨hne named the biochemistry of protein digestion (Wolf, 2001). anagenesis). Ku¨hne pursued his retinal studies with similar zeal and Ku¨hne localized visual purple (rhodopsin) to the with arguably even more important results. outer segments of the rods within “platelets” (now In frogs, Ku¨hne confirmed that visual purple (Sehpur- called “disks”), and observed that bile or bile salts dis- pur) was bleached by light, but maintained its color in the solve the rods, bringing rhodopsin into solution where dark, even after death. In a darkroom illuminated by red it could be further studied chemically (Ku¨hne, 1879/ light, Ku¨hne perfected a technique for isolating frog 1977; Wolf, 2001). Ku¨hne further surmised that rho- retinas, which remained purple in the dark but became dopsin included a protein moiety, because it was a colorless when exposed to sunlight (Ku¨hne, 1879/1977; large molecule that, when in solution, did not diffuse Wolf, 2001). In contrast to previous opinions (including through a semipermeable membrane and could be pre- Boll’s) that the retinal pigment is red, Ku¨hne was adamant cipitated with ammonium sulfate (Ku¨hne, 1879/1977; that the rod pigment is in fact purple and named it visual Wolf, 2001). purple. This bleaching process progressed through several As early as 1877, Ku¨hne likened vision to a repeti- different color stages (from purple to orange to yellow to tive photographic process (Wald, 1950). Ku¨hne devel- buff and then to colorless), which Ku¨hne correctly inter- oped this idea further when he found he was able to preted as indicating chemical transformations, because see images bleached onto the retina. After having a Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:27 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

HISTORICAL ASPECTS OF THE MAJOR NEUROLOGICAL VITAMIN DEFICIENCY DISORDERS 439 frog stare into a flame for 14 h, he isolated its retina In 1913, Gowland Hopkins and A. Neville suggested and observed a bleached area in the shape of an that both American groups had been able to obtain inverted flame. Ku¨hne found he could create other ret- growth with the diets of casein and lactose, because inal images, which he called “optograms,” after having these substances had been incompletely purified and frogs or rabbits stare at a window for several minutes. were contaminated with a water-soluble growth factor Ku¨hne’s optograms stimulated widespread speculation (Hopkins and Neville, 1913). In further studies, McCol- that such images could be used forensically to deter- lum and Simmonds (1916) confirmed Hopkins’ suspi- mine the guilty party from the retinal image depicting cion and concluded that rats need both a water- someone just murdered. Ku¨hne initially dismissed such soluble factor and a fat-soluble factor for growth. In speculation; however, by 1880, when a young man was 1916, McCollum and his graduate student Cornelia beheaded by guillotine in the nearby town of Bruschal, Kennedy labeled these “fat-soluble A” and “water- Ku¨hne apparently had a different viewpoint and imme- soluble B” (McCollum and Kennedy, 1916; Day, 1997). diately retrieved the corpse, extracted the eyes in a McCollum initially believed that “fat-soluble A” was a dimly lit room screened with red and yellow glass, single vitamin capable of treating both xerophthalmia and and within 10 min of the decapitation viewed one of rickets (McCollum and Kennedy, 1916); however, in 1922, the few reported human optograms (Wald, 1950). McCollum and colleagues demonstrated that cod-liver oil Ku¨hne’s work concluded with his proposed “opto- could be treated (by aeration at 100C for at least 12 h) so chemical hypothesis,” which attributed vision to a as to eliminate its efficacy against xerophthalmia, while photochemical change in visual purple (rhodopsin), maintaining its antirachitic activity in rats (McCollum such that the chemical products or some process et al., 1922). Ultimately the anti-xerophthalmia factor related to the chemical change is responsible for stimu- was named vitamin A and the anti-rachitic factor was lating the visual cells and thereby conveying a visual named vitamin D. image. Ku¨hne’s prescient concept of photochemical transduction would later be shown to be largely cor- Linking visual manifestations rect, particularly with the important work of Wald to vitamin A deficiency and colleagues beginning in the 1930s. In 1913, Ishihara proposed that a “fatty substance” in blood is necessary for synthesis of both rhodopsin McCollum, Osborne, and Mendel, and and the surface layer of the cornea, and that night the discovery of fat-soluble vitamin A blindness and keratomalacia develop when this sub- In 1913, Elmer Verner McCollum, PhD (1879–1967) at stance is deficient. Shortly thereafter, Osborne and the University of Wisconsin in Madison, with his Mendel showed that, in the absence of the dietary sup- volunteer assistant Marguerite Davis, discovered a plementation with certain fats, rats developed weight fat-soluble accessory food factor, present only in cer- loss, night blindness, and corneal ulcers, thus illustrat- tain fats and distinct from the water-soluble anti-beri- ing the most important physiological functions of vita- beri factor (McCollum and Davis, 1913, 1914; min A (i.e., support of vision, epithelial differentiation, McCollum, 1964; Day, 1997; University of Wisconsin and growth), and also providing an experimental model College of Agricultural and Life Sciences). Rats fed of human night blindness and keratomalacia (Osborne on a diet of presumably pure protein (casein), carbohy- and Mendel, 1914; Wolf, 1996). In 1925, Fridericia and drates, and salt grew well for several months, but then Holm directly linked vitamin A to night blindness in stabilized or lost weight, unless the diet was supple- animal experiments: vitamin A-deficient rats, when mented with certain “lipins” that were extractable with light adapted (i.e., with light-“bleached” retinas) and ether and were present in butter fat and eggs. McCol- placed in the dark, formed rhodopsin at a slower rate lum felt that the lapse of growth after several months than did normal rats (Fridericia and Holm, 1925; Wolf, was due to the exhaustion of body stores of some 1996). In 1929, Holm demonstrated the presence of unrecognized organic growth factor that was normally vitamin A in retinal tissue. present in certain fats. Similar work was presented In the late 1930s, Wald and colleagues began studies almost simultaneously by Lafayette Mendel (1872– of experimentally induced human vitamin A deficiency 1935) of the Sheffield Scientific School (affiliated with and demonstrated a progressive rise in the visual Yale University) and Thomas Osborne (1859–1929) of threshold over a month-long period on a vitamin the Connecticut Agricultural Station in New Haven, A-deficient diet, and subsequent rapid resolution of who together also reported the high potency of cod the deficit over 90 min upon ingestion of carotene liver oil in supporting growth under these conditions (i.e., provitamin A) (Wald and Steven, 1939). A number (Osborne and Mendel, 1913, 1914). of subsequent studies in animals and man further Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:28 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

440 D.J. LANSKA corroborated the association between vitamin A defi- pursue the photochemistry of vision. Within the space ciency and night blindness and keratomalacia (Dowling of a single Wanderjahre, Wald worked in three differ- and Wald, 1958; Wolf, 2002). ent laboratories under the guidance of three interna- tionally recognized mentors, all of who ultimately received the Nobel Prize in Physiology or Medicine The isolation, chemical structure, and for different contributions (Wald, 1935a,b, 1967/1972; chemical synthesis of vitamin A Dowling, 2000, 2002). In attempts to isolate the active growth-promoting fac- Wald began work in the laboratory of biochemist tor in fats, Osborne and Mendel (1914) obtained an Otto Warburg (1883–1970) at the Kaiser-Wilhelm-Insti- active yellow oil from butter, egg yolks, and cod-liver tut (now the Max-Planck-Institut) fu¨r Biologie in Ber- oil, but not from lard or olive oil. Steenbock (1919) sub- lin-Dahlem, Germany, where he dissected animal sequently noted that active growth-promoting extracts retinas to obtain the light-sensitive compound rhodop- from butter, egg yolk, or carrots are yellow, while sin (Dowling, 2002). Based on a chemical test and the active extracts from liver or kidney are white. In absorption spectrum, Wald tentatively concluded that 1920, Steenbock and Gross suggested that fat-soluble the retina contains vitamin A, a finding that he subse- factor A is associated with a yellow pigment and is quently confirmed in the laboratory of Paul Karrer converted in vivo to an active colorless form (Steen- (1889–1971) at the University of Zurich (Warburg had bock and Gross, 1920; Wolf, 1996). However, around suggested the transfer because Karrer had elucidated the same time, Palmer and Kempster (1919) fed chick- the structure of vitamin A in 1931) (Karrer, 1937/ ens a diet free of yellow pigments (i.e., white corn, 1966). After this, Wald moved briefly to the cellular skimmed milk, bone meal, and small amounts of pork metabolism laboratory of Otto Meyerhof (1884–1951) liver) and discovered that the chickens nevertheless at the Kaiser Wilhelm Institute for Medical Research grew normally and laid eggs that (despite colorless in Heidelberg, Germany, where Wald discovered the egg yolks) produced normal chicks. visual cycle of vitamin A (Wald, 1935a,b; Wolf, 2001). These confusing results were not resolved until 1930, Wald’s former mentor Hecht had proposed, based on when Moore, in experiments with rats, showed that the the relationship between photosensitivity and time during active yellow pigment extracted from plants, butter dark adaptation, that dark adaptation “follows the course fat, or egg yolks (b-carotene) is a precursor (i.e., provi- of a bimolecular reaction...[and that] visual reception in tamin) that is indeed converted to an active colorless dim light is conditioned by a reversible photochemical factor (vitamin A or retinol) in vivo and accumulates reaction involving a photosensitive substance and its two within the liver (Moore, 1930; Wolf, 1996). Later studies products of decomposition” (Hecht, 1919, pp. 516–517). found that the enzymatic conversion of b-carotene to Wald confirmed Hecht’s prediction and showed that visual retinol occurs in the intestinal mucosa (Wolf, 1996). purple (rhodopsin) is decomposed by light into a com- In the 1930s, Paul Karrer (1889–1971) and colleagues pound he called “retinene” and a protein (later called at the University of Zurich isolated b-carotene (the “opsin”) (Wald, 1935a,b; Karrer, 1937/1966; Wolf, 1996). main dietary precursor of vitamin A) and retinol, and Retinene was subsequently shown by R. A. Morton and determined their chemical structures (Karrer et al., T. W. Goodwin to be the aldehyde of vitamin A, “retinal- 1931; Karrer, 1937/1966). Karrer shared the 1937 Nobel dehyde,” now known as “retinal” (Morton and Goodwin, Prize in Physiology or Medicine “for his investigations 1944; Ball et al., 1946). Retinal could either recombine with on carotenoids, flavins and vitamins A and B2” (Kar- opsin to reform rhodopsin, or could instead be converted rer, 1937/1966). In 1947, Isler and colleagues completed to retinol (vitamin A). Because “vitamin A is the precursor the full chemical synthesis of vitamin A. The availabil- of visual purple [rhodopsin], as well as the product of its ity of vitamin A through food fortification and medic- decomposition,” Wald proposed that the “visual processes inal supplements virtually eliminated ocular vitamin A therefore constitute a cycle” (Wald, 1935b, p. 368). deficiency from developed countries by the second half During the 1930s, Wald also initiated studies of of the 20th century (Underwood, 2004). cone vision and was able to extract a red-sensitive pigment from chicken retinas that he called iodopsin (Dowling, 2000; Kresge et al., 2005). In the mid- Wald and the visual cycle of vitamin A 1950s, Wald and colleagues showed that iodopsin After completing his graduate studies in zoology with bleaches to form retinal and a protein, which is differ- Selig Hecht (1892–1947) at Columbia University (Wald, ent from the protein opsin in rhodopsin. Hence, Wald 1948b, 1967/1972; Dowling, 2000, 2002), American phy- proposed the terms “scotopsin” for the opsin of rods, siologist George Wald (1906–1997) obtained a National and “photopsins” for the opsins of cones (Wald et al., Research Council Fellowship in Biology (1932–1934) to 1955b; Dowling. 2000). Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:30 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

HISTORICAL ASPECTS OF THE MAJOR NEUROLOGICAL VITAMIN DEFICIENCY DISORDERS 441 Wald’s group subsequently elaborated the enzymatic A is transported), or to retinyl esters (the form in conversions of various elements in the rhodopsin system which vitamin A is stored), or to retinal (the aldehyde (Wald, 1948a; Wald and Hubbard, 1949, 1950; Wald and needed for synthesis of visual pigments) (Dowling Brown, 1950; Hubbard and Wald, 1951; Hubbard, 1956; and Wald, 1960). As a result, their rats maintained Dowling, 2000). By the mid-1950s, Wald, Ruth Hubbard with retinoic acid (but not vitamin A or its various (Wald’s second wife), and Paul Brown, with the assistance provitamins, i.e., dietary carotenoids) grew normally of several organic chemists, determined that the rhodop- but became extremely night blind and eventually per- sin system is dependent upon an isomerization of retinal manently blind. As rhodopsin concentrations declined, (a conformational change in the molecule), and specifi- visual thresholds rose, followed by loss of opsin, disin- cally that the 11-cis isomer of retinal was the precursor tegration of the outer segments of the rods, and severe Au3 of all visual pigments (Wald and Hubbard, 1950, 1955a; dropout of visual cells. Because retinoic acid is not Hubbard and Wald, 1952; Hubbard et al., 1953; Brown stored in the body and cannot be metabolized to a sto- and Wald, 1956; Hubbard, 1956, 1966; Oroshnik et al., rage form, the animals stopped growing within a few 1956). 11-cis retinal is twisted and sterically hindered and days of deprivation of retinoic acid and developed stable only in the dark. Light causes isomerization to the severe systemic symptoms within 1–2 weeks. all-trans form of retinal, which in turn must eventually Subsequently retinoic acid was found to act in a be re-isomerized for the visual cycle to continue (Hubbard hormone-like fashion to regulate gene expression and Kropf, 1958; Hubbard, 1966). By slowing the chemi- (Ross and Ternus, 1993), a role for vitamin A that cal processes with liquid nitrogen, Wald’s group also Wolf and De Luca had proposed as early as 1970 demonstrated that rhodopsin goes through a series of (Wolf and De Luca, 1970; Wolf, 1996). In 1987, P. very transient molecular transformations, and that one Chambon and colleagues in Strasbourg, France, and of these intermediaries (meta-rhodopsin II) triggers exci- R. M. Evans and colleagues in San Diego, simulta- tation of the photoreceptor before retinal is ultimately neously discovered retinoic acid receptors in cell hydrolyzed from opsin (Matthews et al., 1963). nuclei, which bind with retinoic acid to modulate gene In 1942, Hecht and colleagues had demonstrated that expression, thereby influencing embryonic develop- a single photon might be enough to trigger excitation in ment, cellular differentiation (including that of the a rod. In 1965, Wald suggested that a large chemical cornea), and growth (Gigue`re et al., 1987; Chambon, amplification must occur for a single photon to be able 1996; Wolf, 1996). to trigger such excitation of the rod, and by analogy with the blood clotting system this amplification could Public health interventions to potentially occur by a cascade of enzymatic reactions. address vitamin A deficiency in Later studies showed that rhodopsin is a transmembrane developing countries protein consisting of seven membrane-spanning helices, that are interconnected by extracellular and intracellular The first global survey of xerophthalmia conducted by loops, and that form a binding pocket for its ligand, 11- the World Health Organization in the early 1960s sug- cis retinal. Absorption of light by 11-cis retinal causes gested a significant prevalence of the disorder in many isomerization to all-trans retinal and propagation of a countries (Ooman et al., 1964), but was later found to conformational change in the protein to the cytoplasmic have seriously underestimated the global burden of surface. The meta-rhodopsin II intermediary then inter- vitamin A deficiency (Sommer et al., 1981; Reddy, acts with transducin, a G-protein, to activate phospho- 2002; Underwood, 2004). Subsequently, various inter- diesterases that control cyclic GMP levels, which in vention trials were conducted, including controlled turn modulate release of neurotransmitter from the trials in Jordan and India in the late 1960s, which rod cell (Stryer, 1986; Hargrave and McDowell, 1992). demonstrated the feasibility of periodic vitamin A dos- In 1967, Wald was recognized with a Nobel Prize in ing to prevent vitamin A deficiency disorders (Reddy, Physiology or Medicine for “discoveries concerning the 2002). In 1975, under the auspices of the US Agency primary physiological and chemical visual processes in for International Development (USAID) and the World the eye” (Wald, 1967/1972). Health Organization (WHO), the International Vitamin A Consultative Group was established at a meeting of the United Nations International Children’s Emergency Hormone-like actions of vitamin A Fund (UNICEF) in New York, to coordinate and facili- In 1960, Dowling and Wald showed that almost all of tate activities to combat vitamin A deficiency disorders the non-visual roles of vitamin A are carried out by worldwide (Reddy, 2002; Underwood, 2004). retinoic acid, and further that retinoic acid could not By the 1980s, global estimates suggested 13 million be metabolized to retinol (the form in which vitamin children suffered from xerophthalmia and another Comp. by: GVasenthanProof0000876233 Date:16/11/08 Time:01:50:31 Stage:First Proof File Path://spiina1001z/Womat/Production/PRODENV/0000000001/0000011393/0000000016/ 0000876233.3D Proof by: QC by: ProjectAcronym:BS:FINGER Volume:02129

442 D.J. LANSKA 40–80 million children were at risk (Sommer et al., Brown PK, Wald G (1956). The neo-b isomer of vitamin A 1981; Underwood, 2004). But within 20 years these esti- and retinene. J Biol Chem 222: 865–877. mates were again found to underestimate the burden Budd G (1842). Lectures on the disorders resulting of illness resulting from vitamin A deficiency, with from defective nutriment. Lond Med Gaz 2: 632–636, recent estimates suggesting that 3 million preschool 743–749. Chambon PA (1996). A decade of molecular biology of reti- children have clinical signs of vitamin A deficiency noic acid receptors. FASEB J 10: 940–954. annually, and that another 140–250 million preschool Crescitelli F (1977). Friedrich Wilhelm Ku¨hne: 1837–1900. children are at risk based on serum vitamin A levels Vision Res 17: 1317–1323. (Underwood, 2004). Day HG (1997). Experiments that changed nutritional think- In the 1980s and 1990s, large randomized, double- ing. Paper 7: Young rats need unknown growth factors blind, placebo-controlled clinical trials were conducted (McCollum, 1913–1917). J Nutr 127: 1029S–1031S. in developing countries. They demonstrated that vita- Dowling JE (2000). George Wald: November 18, 1906–April min A supplementation could reduce childhood mortal- 12, 1997. In: National Academy of Sciences. Biographical ity by approximately one quarter to one third, even by Memoirs. Vol. 78. Washington, D.C., National Academy giving concentrated vitamin A supplements at 6-month Press, pp. 299–317. intervals (Sommer et al., 1986; Beaton et al., 1993; Dowling JE (2002). George Wald: 18 November 1906–12 April 1997. Proc Am Philos Soc 146: 431–439. Semba, 1999; Underwood, 2004). Dowling JE, Wald G (1958). Vitamin A deficiency and night Vitamin A supplementation of malnourished chil- blindness. Proc Natl Acad Sci USA 44: 648–661. dren is now considered one of the most cost-effective Dowling JE, Wald G (1960). The biological function of vita- health interventions known (World Bank, 1993; Semba, min A acid. Proc Natl Acad Sci USA 46: 587–608. 1999). Although consistent periodic distribution of vita- Drummond JC (1920). The nomenclature of the so-called min A supplements can control vitamin A deficiency accessory food factors (vitamins). Biochem J 14: 660. disorders, sustained control by this means is fragile, Ewald A, Ku¨hne W (1877). U¨ ber kunstliche Bildung des especially in countries with economic decline and civil Sehpurpurs. Central Med Wissensch 15: 753–754. Au11 Au4 unrest (Underwood, 1999, 2004). As was the case with Filmore D. (2004). It’s a GPCR world. Modern Drug Discov eradication of endemic pellagra in the United States in November: 24–28. http://pucs.acs.org/subscribe/journals/ Au12 the early-20th century (Lanska, 2002), other measures mdd/v07/i11/pdf/11-4feature_filmore.pdf [Accessed 4- 23-07] are also needed to ensure adequate diets and improve Fridericia LS, Holm E (1925). Experimental contribution to socio-economic conditions before vitamin A deficiency the study of the relation between night blindness and mal- disorders can be truly controlled (Underwood, 1998, nutrition: Influence of deficiency of fat-soluble A-vitamin 2004; Underwood and Smitasiri, 1999). in the diet on the visual purple in the eyes of rats. Am J Physiol 73: 63–78. REFERENCES Funk C (1911). On the chemical nature of the substance which cures polyneuritis in birds induced by a diet of Ball S, Goodwin TW, Morton RA (1946). Retinene1-vitamin polished rice. J Physiol 43: 395–400. A aldehyde. Biochem J 40: lix. Funk C (1912). The etiology of the deficiency diseases. Beri- Baumann C (1977). Franz Boll. Vision Res 17: 1267–1268. beri, polyneuritis in birds, epidemic dropsy, scurvy, Beaton GH, Martorell R, L’Abbe KA, et al. (1993). Effec- experimental scurvy in animals, infantile scurvy, ship tiveness of Vitamin A supplementation in the control of beri-beri, pellagra. 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