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Glucosamine for psoriasis?
Medical Hypotheses (1997) 48, 437-441 © Pearson Professional Ltd 1997
Glucosamine for psoriasis? M. F. McCARTY Nutrition 21, 1010 Turquoise Street, San Diego, CA 92109, USA
Abstract - - Amphiregulin and transforming growth factor-(~, agonists for the epidermal growth factor receptor, are the major autocrine growth factors for cultured keratinocytes, and their substantial overexpression in psoriatic lesions suggests that they are crucial to the basal hyperplasia that characterizes psoriasis. Amphiregulin binds to heparin and related highly sulfated polysaccharides, and exogenous heparin blocks its growth factor activity, rationalizing previous reports that psoriasis responds to heparin therapy. Differentiating keratinocytes produce increased amounts of protein-bound as well as free-chain heparan sulfates, which may function physiologically as amphiregulin antagonists. By promoting keratinocyte synthesis of these heparan sulfates, glucosamine administration may inhibit amphiregulin function and thus provide therapeutic benefit in psoriasis. Concurrent ingestion of fish oil, by impeding the excessive activation of protein kinase C, may decrease keratinocyte production of amphiregulin and other autocrine growth factors, thus complementing the postulated benefits of glucosamine.
Role of autocrine growth factors in psoriasis The regulation of keratinocyte proliferation in vivo is still poorly understood. However, recent cell culture studies suggest that autocrine production of two members of the epidermal growth factor family amphiregulin (AR) and transforming growth factor-~ (TGF-a) - may play an important role in promoting keratinocyte mitosis (1--4). Both AR and TGF-ct can activate the epidermal growth factor receptor (EGFR), a tyrosine kinase that stimulates keratinocyte proliferation in the presence of adequate insulin-like growth factor activity. When human keratinocytes are cultured at low density, exogenous growth factors are required to achieve clonal expansion (3,4). However, when cultured at high density, the keratinocytes can multiply
efficiently without exogenous growth factors. This so-called 'EGF-independent' growth apparently is dependent primarily on autocrine production of AR and, to a lesser extent, TGF-~; monoclonal antibody to AR decreases this growth by about 70%, whereas blocking monoclonal antibody for the EGFR almost completely abolishes this growth (3,4). Recent studies indicate, that expression of both AR and TGP-ct is greatly up-regulated in psoriatic lesions (5-7). Since stimulation of the EGFR induces production of both AR and TGF-~ (1,6,8), the hyperproliferation of basal keratinocytes in psoriasis may reflect a vicious circle in which excessive activation of EGFR leads to excessive production of AR and TGF-~, which in turn contribute to the excessive activation of EGFR. To break this vicious circle, an antagonist of AR activity would be useful.
Date received 25 April 1996 Date accepted 17 May 1996
437
438
Heparinoids inhibit amphiregulin activity In fact, such an antagonist is known - heparin. Heparin, heparan sulfates, and other heavily sulfated mucopolysaccharides substantially inhibit the 'EGFindependent' growth of high-density keratinocyte cultures (3,4,9-11). This apparently reflects the fact that AR binds to heparin, and this binding disrupts the interaction of AR with the EGFR. Novotny has summarized-his experience using intensive subcutaneous heparin therapy to treat generalized psoriasis (12). Forty-nine patients were treated; after three weeks of heparin administration, 30 patients were said to be 'healed', I 1 were said to be 'considerably improved', six were said to be 'partially improved', and two patients were not benefited. Relapses occurred two to six months after treatment was discontinued; the fact that remissions were sustained for months without continuing treatment suggests that a vicious-circle mechanism, dependent on excessive AR activity, is indeed crucial to the pathogenesis of psoriasis. This report confirmed the previous experience of Jekel, who suggested heparin as a treatment for psoriasis in 1953 (13). Since nonanticoagulant forms of heparin (as well as other highly sulfated polysacchaxides) are as effective as anticoagulant heparin for binding to AR and inhibiting autocrine-mediated keratinocyte growth (10,11), a modified version of heparin therapy that does not risk hemorrhagic complications may be feasible. The researches of Piepkorn and colleagues suggest that endogenously produced heparan sulfates may play a significant physiological role in modulating AR activity in vivo (14-17). As keratinocytes differentiate, they produce increased amounts of heparan sulfate (HS) proteoglycans, as well as HS free chains (14,15,18). The proteoglycans include both membrane-bound and soluble secreted proteins. The free HS chains are most likely produced by an endoglycosidase acting on membrane-bound HS proteoglycans; the free chains are found in association with the keratinocyte membrane and in the keratinocyte cytoplasm. Since incubation of keratinocytes with a sulfation inhibitor reduces the growth factor activity of AR (4), it can be presumed that binding of AR to a specific or non-specific proteoglycan facilitates the interaction of AR with the EGFR (a mechanism analogous to the role of syndecan in promoting fibroblast growth factor activity). However, it seems likely that the secreted soluble HS proteoglycans, as well as the membrane-associated HS free chains and possibly some of the membrane-bound HS proteoglycans, act as functional antagonists of AR activity - a physiological counterpart to the pharmacological activity of exogenous heparin (17). This seems the more likely
MEDICAL HYPOTHESES
in light of the fact that a surge in HS production coincides with differentiation and a cessation of mitosis in developing keratinocytes. Piepkorn and colleagues, in summary of this concept, state that ' . . . heparan sulfate proteoglycans and free chains are up-regulated during growth inhibition and terminal differentiation of keratinocytes. We speculate that increased expression of these molecules has evolved in keratinocytes as a mechanism to down-regulate the effects of heparin-binding, autocrine growth factors during that phenotypic transition...' (17). In vascular smooth muscle cells, endocytosis of HS free chains has been found to block various downstream effects of protein kinase C (19,20); whether analogous effects occur in keratinocytes has yet to be determined. Excessive activation of protein kinase C may play a role in psoriasis (21-23).
Glucosamine may promote endogenous heparan sulfate production These considerations suggest that a means of stimulating endogenous HS synthesis might well be of therapeutic value in psoriasis. Exogenous glucosamine stimulates mucopolysaccharide synthesis in fibroblast or chondrocyte cultures, indicating that glucosamine availability can be rate-limiting for such synthesis (24-26). The documented clinical utility of oral glucosamine in osteoarthritis may be attributable to increased synthesis of cartilage proteoglycans (27). In a previous paper, this author has suggested that supplemental glucosamine may exert an antiatherogenic effect by enhancing the synthesis of HS proteoglycans that function physiologically to restrain the growth and migration of vascular smooth muscle cells (28). As an obvious extension of these concepts, it is reasonable to propose that an adequate oral intake of glucosamine will increase HS production by keratinocytes, thereby impeding AR-mediated proliferation and providing therapeutic benefit in psoriasis. These speculations were prompted by an anecdotal report of substantial resolution of long-standing psoriasis in a woman who was using a relatively high dose of glucosamine hydrochloride (1.5 g t.i.d.) to treat spinal osteoarthritis (Evans E, personal communication). Subsequent to receiving this report, I obtained a copy of a US patent, authored by Burton and Freeman, disclosing the use of N-acetyl-glucosamine (another effective precursor for mucopolysaccharide production) to treat inflammatory bowel disorders. The authors offer twelve case histories of patients who had responded to such therapy; in two of the cited cases, the patients concurrently suffered from psoriasis, which resolved during the successful
GLUCOSAMINEFOR PSORIASIS?
treatment of their bowel disorders with N-acetylglucosamine (29). In light of these intriguing anecdotal observations and the theoretical considerations cited above, an informal pilot trial to evaluate glucosamine supplementation in psoriasis is now being planned.
Complementary benefits of fish oil If glucosamine proves to have some utility in the management of psoriasis, perhaps it will work in a complementary or synergistic fashion with fish oil. The use of omega-3-rich fish oil to treat psoriasis has been prompted by a report that psoriasis was quite uncommon among Eskimos following a traditional lifestyle (30), as well as by evidence that eicosapentaenoic acid (EPA) can inhibit the production and activity of leukotrienes (31,32), believed to play a role in the inflammatory aspects of psoriasis. (Increased production of LTB4, a potent chemotactic agent which has mitogenic activity for keratinocytes (33,34), has been documented in psoriatic epidermis (35), and excellent clinical response to the 5-1ipoxygenase inhibitor benoxaprofen (36) - unfortunately too toxic for standard use - suggests an important role for leukotrienes in this disorder.) Although an initial clinical report, in which very large amounts of fish oil were ingested in the context of a low-fat diet, was quite encouraging (37), subsequent studies involving less intensive regimens have generally seen more limited responses (38-40). For optimal benefit, it may be necessary to reproduce the relative omega-3 content of an Eskimo diet. This may be feasible if a very-low-fat diet is consumed (10-15% fat calories) in conjunction with an ample supplemental intake of a fish oil preparation highly enriched in EPA. While fish oil as a monotherapy for psoriasis seems unlikely to achieve a fully adequate clinical response in the majority of patients, its use as a complement to other therapies has promise. Complementarity or synergism of glucosamine and fish oil in the management of psoriasis, can be predicted on the basis of the following considerations: Overactivity of membrane phospholipases - as indicated by increased epidermal levels of diacylglycerol (DAG) and free arachidonic acid - appears likely to be key to the pathophysiology of psoriasis (21,41,42). Receptor-mediated stimulation of phospholipase C activity may play a triggering role in this regard (41), as the resulting increase in levels of DAG and free intracellular calcium (and thus of PKC activity) can be expected to activate both phospholipase D (43) and phospholipase A2 (44). The former activity should maintain increased DAG
439
levels despite the anticipated PKC-mediated downregulation of phospholipase C; the latter activity is responsible for the increased liberation of free arachidonic acid that promotes the observed excessive production of LTB 4 and other eicosanoids. The persistent elevation of DAG provides a continual activating stimulus to PKC; increased activation of PKC in psoriasis is suggested by characteristic patterns of protein induction (21,22), as well as by reduced epidermal levels of PKC protein (45) (presumably indicative of proteolytic down-regulation of the activated enzyme). PKC has been shown to have an inductive effect on TGF-ot (8); since PKC induces AR production in mammary epithelium (46), it may have an analogous effect in keratinocytes. PKC also promotes keratinocyte production of interleukin-8 (47), which also has growth factor activity for keratinocytes and appears to be the chief protein chemotactic factor released by psoriatic epidermis (48,49). As suggested by Pittelkow and colleagues (8), the ability of PKC to induce autocrine growth factors for keratinocytes may explain the hyperplastic effects of phorbol esters on the epidermis. Also, independent of this inductive effect, it is conceivable that PKC plays a co-mitogenic role in abetting the mitogenic effects of the EGFR and other tyrosine kinases. The therapeutic activity of PKC inhibitors in psoriasis (50,51), suggests a key role for PKC overactivity in this syndrome, and it has frequently been noted that phorbol ester treatment of epidermis produces a histological picture analogous to psoriasis (21,23,41,45). Thus, excessive activation of PKC may be crucial to the overproduction of autocrine growth factors and chemotactic agents that engender and sustain psoriatic lesions. As noted, activation of phospholipase C seems likely to play a triggering role in the chain of events that activates PKC and other phospholipases (41). If the effects of LTB4 on keratinocytes are similar to its effects in other tissues, LTB 4 can be expected to stimulate phospholipase C-[~ activity in keratinocytes via a G protein-linked receptor (52). (Whether the EGFR activates phospholipase C-'f in keratinocytes - as it does in various other tissues - is questionable (53), although it does tend to increase PKC activity to some degree (53-55).) In a number of other tissues, membrane enrichment with omega-3 fish oils appears to down-regulate the activation of phospholipase C-~ via G protein-linked receptors (56); this suggests that fish oil may impede the ability of LTB 4 (and perhaps of other cytokines and inflammatory mediators produced by leukocytes in psoriatic lesions) (57) to activate PKC and thereby stimulate induction of autocrine growth factors. Current evidence suggests that AR is the most
440
crucial of the autocrine growth factors produced by normal and psoriatic keratinocytes. If, as predicted above, fish oil therapy can reduce keratinocyte production of AR, while glucosamine can inhibit the activity of this growth factor, it would be reasonable to expect complementarity or synergism when these two measures are used conjointly in the treatment of psoriasis. This possibility merits clinical evaluation; obviously, a safe and effective nutritional regimen for managing psoriasis would be a most worthwhile development. It is intriguing to speculate that modulation of the activities of AR (or of other heparin-binding growth factors) by endogenously produced HS proteoglycans, may be a more general phenomenon, occurring in tissues other than just the epidermis. In such tissues, glucosamine administration may help to control hyperproliferative disorders and, in the long term, may reduce cancer risk. It should be noted that AR was first isolated from cultured mammary epithelium, and functions as an autocrine growth factor for this tissue (46).
References 1. Coffey R J Jr, Derynck R, Wilcox J N e t al. Production and autoinduction of transforming growth factor-o~ in human keratinocytes. Nature 1987; 328: 817-820. 2. Shoyah M, Plowman G D, McDonald V L et al. Structure and function of human amphiregulin: a member of the epidermal growth factor family. Science 1989; 243: 1074-1076. 3. Cook P W, Pittelkow M R, Shipley G D. Growth factorindependent proliferation of normal human neonatal keratinocytes: production of autocrine- and paracrine-acting mitogenic factors. J Cell Physiol 1991; 146: 277-289. 4. Piepkorn M, Lo C, Plowman G. Amphiregulin-dependent proliferation of cultured human keratinocytes: autocrine growth, the effects of exogenous recombinant cytokine, and apparent requirement for heparin-like glycosaminoglycans. J Cell Physiol 1994; 159:114-120. 5. Elder J T, Fisher G J, Lindquist P B e t al. Overexpression of transforming growth factor et in psoriatic epidermis. Science 1989; 243:811-814. 6. Hardas B, Yang Q, Elder J T. Regulation of amphiregulin, a heparin-binding EGF-like growth factor in human skin. J Invest Dermatol 1992; 98: 575. 7. Cook P W, Pittelkow M R, Keeble W W e t al. Amphiregulin messenger RNA is elevated in psoriatic epidermis and gastrointestinal carcinomas. Cancer Res 1992; 52: 3224-3227. 8. Pittelkow M R, Lindquist P B, Abraham R T et al. Induction of transforming growth factor-~ expression in human keratinocytes by phorbol esters. J Biol Chem 1989; 264: 5164-5171. 9. Li S, Plowman G D, Buckley S D, Shipley G D. Heparin inhibition of autonomous growth implicates amphiregulin as an autocrine growth factor for normal human mammary epithelial cells. J Cell Physiol 1992; 153:103-111. 10. Cook P W, Mattox P A, Keeble W W, Shipley G D. Inhibition of autonomous human keratinocyte proliferation and amphi-regulin mitogenic activity by sulfated polysaccharides. In Vivo Cell Dev Biol 1992; 28A: 218-222.
MEDICAL HYPOTHESES
11. Pillai S, Gilliam L, Conrad H E, Holleran W M. Heparin and its non-anticoagulant analogues inhibit human keratinocyte growth without inducing differentiation. J Invest Dermatol 1994; 103: 647-650. 12. Novotny F. Psoriasis treatment by heparin. Acta Univ Carol Med 1985; 31: 243-245. 13. Jekel L G. Use of heparin in treatment of psoriasis. Arch Dermatol Syphilol 1953; 68: 80-83. 14. Piepkorn M, Fleckman P, Carney H, Linker A. Glycosaminoglycan synthesis by proliferating and differentiated human keratinocytes in culture. J Invest Dermatol 1987; 88: 215-219. 15. Piepkorn M, Fleckman P, Carney H et al. The distinctive pattern of proteoglycan and glycosaminoglycan free chain synthesis by cultured human epidermal keratinocytes. J Invest Dermatol 1990; 94: 107-113. 16. Piepkorn M, Hovingh P, Linker A. Topography of proteoglycan and glycosaminoglycan free chain expression in 3T3 fibroblasts and human keratinocytes. J Invest Dermatol 1992; 99: 386-389. 17. Piepkorn M, Hovingh F, Dillberger A, Linker A. Divergent regulation of proteoglycan and glycosaminoglycan free chain expression in human keratinocytes and melanocytes. In Vitro Cell Dev Biol - Animal 1995; 31: 536-541. 18. Lamberg S I, Yuspa S H, Hascall V C. Synthesis of hyaluronic acid is decreased and synthesis of proteoglycans is increased when cultured mouse epidermal cells differentiate. J Invest Dermatol 1986; 86: 659-667. 19. Pukac L A, Ottlinger M E, Karnovsky M J. Heparin suppresses specific second messenger pathways for protooncogene expression in rat vascular smooth muscle cells. J Biol Chem 1992; 267:3707-3711. 20. Au Y PT, Kenagy R D, Clowes M M, Clowes A W. Mechanisms of inhibition by heparin of vascular smooth muscle cell proliferation and migration. Haemostasis 1993; 23(Suppl 1): 177-182. 21. Fisher G J, Talwar H S, Tavakkol A et al. Phosphoinositidemediated signal transduction in normal and psoriatic epidermis. J Invest Dermatol 1990; 95: 15S-17S. 22. Rasmussen H H, Celis J E. Evidence for an altered protein kinase C (PKC) signaling pathway in psoriasis. J Invest Dermatol 1993; 101: 560-566. 23. Iizuka H, Takahashi H. Psoriasis, involucrin, and protein kinase C. Int J Dermatol 1993; 32: 333-338. 24. Vidal y Plana R R, Bizzari D, Rovati A L. Articular cartilage pharmacology. I. In vitro studies on glucosamine and non steroidal antiinflammatory drugs. Pharm Res Comm 1978; 10: 557-569. 25. Karzel K, Domenjoz R. Effects of hexosamine derivatives and uronic acid derivatives on glycosaminoglycane metabolism of fibroblast cultures. Pharmacology 1971; 5: 337-345. 26. Kim J J, Conrad H E. Effect of D-glucosamine concentration on the kinetics of mucopolysaccharide biosynthesis in cultured chick embryo vertebral cartilage. J Biol Chem 1974; 249: 3091-3097. 27. McCarty M F. The neglect of glucosamine as a treatment of osteoarthritis - a personal perspective. Med Hypotheses 1994; 42: 323-327. 28. McCarty M F. Glucosamine may retard atherogenesis by promoting endothelial production of heparan sulfate proteoglycans. Med Hypotheses 1997; 48: 245-251. 29. Burton A F, Freeman H J. Method for treatment of lower gastrointestinal tract disorders. United States Patent, 5,229,374, July 20, 1993. 30. Kromann N, Green A. Epidemiological studies in the Upemavik District, Greenland. Acta Med Scand 1980; 208: 401-406. 31. Spefling R I. Effects of dietary fish oil on leukocyte leukotriene and PAF generation and on neutrophil chemotaxis.
GLUCOSAMINEFOR PSORIASIS?
32.
33. 34.
35. 36. 37. 38. 39. 40.
41.
42. 43.
44.
In: Simopoulos A P, Kifer R R, Martin R E, Barlow S M, eds. Health Effects of o~3 Polyunsaturated Fatty Acids in Seafoods. World Rev Nutr Diet, vol 66, Basel: Karger, 1991: 391--400. Miller C C, Tang W, Ziboh V A, Fletcher M P. Dietary supplementation with ethyl ester concentrates of fish oil (n-3) and borage oil (n-6) polyunsaturated fatty acids induces epidermal generation of local putative antiinflammatory metabolites. J Invest Dermatol 1991; 96: 98-103. Kragballe K, Desjarlais L, Voorhees J J. Leukotrienes B4, C 5 and D4 stimulate DNA synthesis in cultured human epidermal keratinocytes. Br J Dermatol 1985; 113: 43-52. Chan C-C, Duharnel L, Ford-Hutchison A. Leukotriene B4 and 12-hydroxyeicosatetraenoic acid stimulate epidermal proliferation in vivo in the guinea pig. J Invest Dermatol 1985; 85: 333-334. Voorhees J J. Leukotrienes and other lipoxygenase products in the pathogenesis and therapy of psoriasis and other dermatoses. Arch Dermatol 1983; 119: 541-547. Kragballe K, Herlin T. Benoxaprofen improves psoriasis. Arch Dermatol 1983; 119: 548-552. Ziboh V A, Cohen K A, Ellis C N e t al. Effects of dietary supplementation of fish oil on neutrophil and epidermal fatty acids. Arch Dermatol 1986; 122: 1277-1282. Kettler A H, Baughn R E, Orengo I F et al. The effect of dietary fish oil supplementation on psoriasis. J Am Acad Dermatol 1988; 18: 1267-1273. Maurice P D L, Allen B R, Barkley A S J e t al. The effects of dietary supplementation with fish oil in patients with psoriasis. Br J Dermatol 1987; 117: 599-606. Kragballe K, Fogh K. A low-fat diet supplemented with dietary fish oil (Max-EPA) results in improvement of psoriasis and in formation of leukotriene Bs. Acta Derm Venereol 1989; 69: 23-28. Fisher G J, Talwar H S, Baldassare J J e t al. Increased phospholipase C-catalyzed hydrolysis of phosphatidylinositol-4,5bisphosphate and 1,2-sn-diacylglycerol content in psoriatic involved compared to uninvolved and normal epidermis. J Invest Dermatol 1990; 95: 428-435. Verhagen A, Berger S M, Van Erp P E J e t al. Confirmation of raised phospholipase A 2 activity in the uninvolved skin of psoriasis. Br J Dermatol 1984; 110: 731-732. Geny B, Cockcroft S. Synergistic activation of phospholipase D by protein kinase C- and G-protein-mediated pathways in streptolysin O-permeabilized HL60 cells. Biochem J 1992; 284: 531-538. Kast R, Ftirstenberger G, Marks F. Activation of a keratinocyte phospholipase A2 by bradykinin and 4[~-phorbol 12-myristate 13-acetate. Evidence for a receptor-GTP-binding protein versus a protein-kinase-C mediated mechanism. Eur J Biochem 1991; 202: 941-950.
441 45. Horn F, Marks F, Fisher G J et al. Decreased protein kinase C activity in psoriatic versus normal epidermis. J Invest Dermatol 1987; 88: 220--222. 46. Shoyab M, McDonald V L, Bradley JG, Todaro G J. Amphiregulin: a bifunctional growth-modulating glycoprotein produced by the phorbol 12-myristate 13-acetate-treated human breast adenocarcinoma cell line MCF-7. Proc Natl Acad Sci 1988; 85: 6528-6532. 47. Barker J N W N, Jones M L, Mitra R S et al. Modulation of keratinocyte-derived interleukin-8 which is chemotactic for neutrophils and T lymphocytes. Am J Pathol 1991; 139: 869-876. 48. Krueger G, Jorgensen C, Miller C et al. Effects of IL-8 on epidermal proliferation. J Invest Dermatol 1990; 94: 545. 49. Schrtder J-M, Gregory H, Young J, Christophers E. Neutrophil-activating proteins in psoriasis. J Invest Dermatol 1992; 98: 241-247. 50. Hegemann L, Fruchtmann R, Van-Rooijen L A et al. The antipsoriatic drug, anthralin, inhibits protein kinase C - implications for its mechanism of action. Arch Dermatol Res 1992; 284: 179-183. 51. Hegemann L, Bonnekoh B, van-Rooijen LA, Mahrle G. Anti-proliferative effects of protein kinase C inhibitors in human keratinocytes. J Dermatol Sci 1992; 4: 18-25. 52. Holian A. Leukotriene B4 stimulation of phosphatidylinositol turnover in macrophages and inhibition by pertussis toxin. FEBS Lett 1986; 201: 15-19. 53. Reynolds N J, Talwar H S, Baldassare J J e t al. Differential induction of phosphatidylcholine hydrolysis, diacylglycerol formation and protein kinase C activation by epidermal growth factor and transforming growth factor-~ in normal human skin fibroblasts and keratinocytes. Biochem J 1993; 294: 535-544. 54. Lyons J G, Birkedal-Hansen B, Pierson M C et al. Interleukin1[~ and transforming growth factor-~epidermal growth factor induce expression of M r 95 000 type IV collagenase/gelatinase and interstitial fibroblast-type collagenase by rat mucosal keratinocytes. J Biol Chern 1993; 268: 19143-19151. 55. Mitev V, Le Panse R, Coulomb B e t al. Epidermal growth factor stimulates mitogen-activated protein kinase by a PKCdependent pathway in human keratinocytes. Biochem Biophys Res Comm 1995; 208: 245-252. 56. McCarty M F. Fish oil may impede tumour angiogenesis and invasiveness by down-regulating protein kinase C and modulating eicosanoid production. Med Hypotheses 1996; 46: 107-115. 57. Talwar H S, Fisher G J, Harris V A, Voorhees J J. Agonistinduced hydrolysis of phosphoinositides and formation of 1,2-diacylglycerol in adult human keratinocytes. J Invest Dermatol 1989; 92: 241-245.
Glucosamine for psoriasis? M. F. McCARTY Nutrition 21, 1010 Turquoise Street, San Diego, CA 92109, USA
Abstract - - Amphiregulin and transforming growth factor-(~, agonists for the epidermal growth factor receptor, are the major autocrine growth factors for cultured keratinocytes, and their substantial overexpression in psoriatic lesions suggests that they are crucial to the basal hyperplasia that characterizes psoriasis. Amphiregulin binds to heparin and related highly sulfated polysaccharides, and exogenous heparin blocks its growth factor activity, rationalizing previous reports that psoriasis responds to heparin therapy. Differentiating keratinocytes produce increased amounts of protein-bound as well as free-chain heparan sulfates, which may function physiologically as amphiregulin antagonists. By promoting keratinocyte synthesis of these heparan sulfates, glucosamine administration may inhibit amphiregulin function and thus provide therapeutic benefit in psoriasis. Concurrent ingestion of fish oil, by impeding the excessive activation of protein kinase C, may decrease keratinocyte production of amphiregulin and other autocrine growth factors, thus complementing the postulated benefits of glucosamine.
Role of autocrine growth factors in psoriasis The regulation of keratinocyte proliferation in vivo is still poorly understood. However, recent cell culture studies suggest that autocrine production of two members of the epidermal growth factor family amphiregulin (AR) and transforming growth factor-~ (TGF-a) - may play an important role in promoting keratinocyte mitosis (1--4). Both AR and TGF-ct can activate the epidermal growth factor receptor (EGFR), a tyrosine kinase that stimulates keratinocyte proliferation in the presence of adequate insulin-like growth factor activity. When human keratinocytes are cultured at low density, exogenous growth factors are required to achieve clonal expansion (3,4). However, when cultured at high density, the keratinocytes can multiply
efficiently without exogenous growth factors. This so-called 'EGF-independent' growth apparently is dependent primarily on autocrine production of AR and, to a lesser extent, TGF-~; monoclonal antibody to AR decreases this growth by about 70%, whereas blocking monoclonal antibody for the EGFR almost completely abolishes this growth (3,4). Recent studies indicate, that expression of both AR and TGP-ct is greatly up-regulated in psoriatic lesions (5-7). Since stimulation of the EGFR induces production of both AR and TGF-~ (1,6,8), the hyperproliferation of basal keratinocytes in psoriasis may reflect a vicious circle in which excessive activation of EGFR leads to excessive production of AR and TGF-~, which in turn contribute to the excessive activation of EGFR. To break this vicious circle, an antagonist of AR activity would be useful.
Date received 25 April 1996 Date accepted 17 May 1996
437
438
Heparinoids inhibit amphiregulin activity In fact, such an antagonist is known - heparin. Heparin, heparan sulfates, and other heavily sulfated mucopolysaccharides substantially inhibit the 'EGFindependent' growth of high-density keratinocyte cultures (3,4,9-11). This apparently reflects the fact that AR binds to heparin, and this binding disrupts the interaction of AR with the EGFR. Novotny has summarized-his experience using intensive subcutaneous heparin therapy to treat generalized psoriasis (12). Forty-nine patients were treated; after three weeks of heparin administration, 30 patients were said to be 'healed', I 1 were said to be 'considerably improved', six were said to be 'partially improved', and two patients were not benefited. Relapses occurred two to six months after treatment was discontinued; the fact that remissions were sustained for months without continuing treatment suggests that a vicious-circle mechanism, dependent on excessive AR activity, is indeed crucial to the pathogenesis of psoriasis. This report confirmed the previous experience of Jekel, who suggested heparin as a treatment for psoriasis in 1953 (13). Since nonanticoagulant forms of heparin (as well as other highly sulfated polysacchaxides) are as effective as anticoagulant heparin for binding to AR and inhibiting autocrine-mediated keratinocyte growth (10,11), a modified version of heparin therapy that does not risk hemorrhagic complications may be feasible. The researches of Piepkorn and colleagues suggest that endogenously produced heparan sulfates may play a significant physiological role in modulating AR activity in vivo (14-17). As keratinocytes differentiate, they produce increased amounts of heparan sulfate (HS) proteoglycans, as well as HS free chains (14,15,18). The proteoglycans include both membrane-bound and soluble secreted proteins. The free HS chains are most likely produced by an endoglycosidase acting on membrane-bound HS proteoglycans; the free chains are found in association with the keratinocyte membrane and in the keratinocyte cytoplasm. Since incubation of keratinocytes with a sulfation inhibitor reduces the growth factor activity of AR (4), it can be presumed that binding of AR to a specific or non-specific proteoglycan facilitates the interaction of AR with the EGFR (a mechanism analogous to the role of syndecan in promoting fibroblast growth factor activity). However, it seems likely that the secreted soluble HS proteoglycans, as well as the membrane-associated HS free chains and possibly some of the membrane-bound HS proteoglycans, act as functional antagonists of AR activity - a physiological counterpart to the pharmacological activity of exogenous heparin (17). This seems the more likely
MEDICAL HYPOTHESES
in light of the fact that a surge in HS production coincides with differentiation and a cessation of mitosis in developing keratinocytes. Piepkorn and colleagues, in summary of this concept, state that ' . . . heparan sulfate proteoglycans and free chains are up-regulated during growth inhibition and terminal differentiation of keratinocytes. We speculate that increased expression of these molecules has evolved in keratinocytes as a mechanism to down-regulate the effects of heparin-binding, autocrine growth factors during that phenotypic transition...' (17). In vascular smooth muscle cells, endocytosis of HS free chains has been found to block various downstream effects of protein kinase C (19,20); whether analogous effects occur in keratinocytes has yet to be determined. Excessive activation of protein kinase C may play a role in psoriasis (21-23).
Glucosamine may promote endogenous heparan sulfate production These considerations suggest that a means of stimulating endogenous HS synthesis might well be of therapeutic value in psoriasis. Exogenous glucosamine stimulates mucopolysaccharide synthesis in fibroblast or chondrocyte cultures, indicating that glucosamine availability can be rate-limiting for such synthesis (24-26). The documented clinical utility of oral glucosamine in osteoarthritis may be attributable to increased synthesis of cartilage proteoglycans (27). In a previous paper, this author has suggested that supplemental glucosamine may exert an antiatherogenic effect by enhancing the synthesis of HS proteoglycans that function physiologically to restrain the growth and migration of vascular smooth muscle cells (28). As an obvious extension of these concepts, it is reasonable to propose that an adequate oral intake of glucosamine will increase HS production by keratinocytes, thereby impeding AR-mediated proliferation and providing therapeutic benefit in psoriasis. These speculations were prompted by an anecdotal report of substantial resolution of long-standing psoriasis in a woman who was using a relatively high dose of glucosamine hydrochloride (1.5 g t.i.d.) to treat spinal osteoarthritis (Evans E, personal communication). Subsequent to receiving this report, I obtained a copy of a US patent, authored by Burton and Freeman, disclosing the use of N-acetyl-glucosamine (another effective precursor for mucopolysaccharide production) to treat inflammatory bowel disorders. The authors offer twelve case histories of patients who had responded to such therapy; in two of the cited cases, the patients concurrently suffered from psoriasis, which resolved during the successful
GLUCOSAMINEFOR PSORIASIS?
treatment of their bowel disorders with N-acetylglucosamine (29). In light of these intriguing anecdotal observations and the theoretical considerations cited above, an informal pilot trial to evaluate glucosamine supplementation in psoriasis is now being planned.
Complementary benefits of fish oil If glucosamine proves to have some utility in the management of psoriasis, perhaps it will work in a complementary or synergistic fashion with fish oil. The use of omega-3-rich fish oil to treat psoriasis has been prompted by a report that psoriasis was quite uncommon among Eskimos following a traditional lifestyle (30), as well as by evidence that eicosapentaenoic acid (EPA) can inhibit the production and activity of leukotrienes (31,32), believed to play a role in the inflammatory aspects of psoriasis. (Increased production of LTB4, a potent chemotactic agent which has mitogenic activity for keratinocytes (33,34), has been documented in psoriatic epidermis (35), and excellent clinical response to the 5-1ipoxygenase inhibitor benoxaprofen (36) - unfortunately too toxic for standard use - suggests an important role for leukotrienes in this disorder.) Although an initial clinical report, in which very large amounts of fish oil were ingested in the context of a low-fat diet, was quite encouraging (37), subsequent studies involving less intensive regimens have generally seen more limited responses (38-40). For optimal benefit, it may be necessary to reproduce the relative omega-3 content of an Eskimo diet. This may be feasible if a very-low-fat diet is consumed (10-15% fat calories) in conjunction with an ample supplemental intake of a fish oil preparation highly enriched in EPA. While fish oil as a monotherapy for psoriasis seems unlikely to achieve a fully adequate clinical response in the majority of patients, its use as a complement to other therapies has promise. Complementarity or synergism of glucosamine and fish oil in the management of psoriasis, can be predicted on the basis of the following considerations: Overactivity of membrane phospholipases - as indicated by increased epidermal levels of diacylglycerol (DAG) and free arachidonic acid - appears likely to be key to the pathophysiology of psoriasis (21,41,42). Receptor-mediated stimulation of phospholipase C activity may play a triggering role in this regard (41), as the resulting increase in levels of DAG and free intracellular calcium (and thus of PKC activity) can be expected to activate both phospholipase D (43) and phospholipase A2 (44). The former activity should maintain increased DAG
439
levels despite the anticipated PKC-mediated downregulation of phospholipase C; the latter activity is responsible for the increased liberation of free arachidonic acid that promotes the observed excessive production of LTB 4 and other eicosanoids. The persistent elevation of DAG provides a continual activating stimulus to PKC; increased activation of PKC in psoriasis is suggested by characteristic patterns of protein induction (21,22), as well as by reduced epidermal levels of PKC protein (45) (presumably indicative of proteolytic down-regulation of the activated enzyme). PKC has been shown to have an inductive effect on TGF-ot (8); since PKC induces AR production in mammary epithelium (46), it may have an analogous effect in keratinocytes. PKC also promotes keratinocyte production of interleukin-8 (47), which also has growth factor activity for keratinocytes and appears to be the chief protein chemotactic factor released by psoriatic epidermis (48,49). As suggested by Pittelkow and colleagues (8), the ability of PKC to induce autocrine growth factors for keratinocytes may explain the hyperplastic effects of phorbol esters on the epidermis. Also, independent of this inductive effect, it is conceivable that PKC plays a co-mitogenic role in abetting the mitogenic effects of the EGFR and other tyrosine kinases. The therapeutic activity of PKC inhibitors in psoriasis (50,51), suggests a key role for PKC overactivity in this syndrome, and it has frequently been noted that phorbol ester treatment of epidermis produces a histological picture analogous to psoriasis (21,23,41,45). Thus, excessive activation of PKC may be crucial to the overproduction of autocrine growth factors and chemotactic agents that engender and sustain psoriatic lesions. As noted, activation of phospholipase C seems likely to play a triggering role in the chain of events that activates PKC and other phospholipases (41). If the effects of LTB4 on keratinocytes are similar to its effects in other tissues, LTB 4 can be expected to stimulate phospholipase C-[~ activity in keratinocytes via a G protein-linked receptor (52). (Whether the EGFR activates phospholipase C-'f in keratinocytes - as it does in various other tissues - is questionable (53), although it does tend to increase PKC activity to some degree (53-55).) In a number of other tissues, membrane enrichment with omega-3 fish oils appears to down-regulate the activation of phospholipase C-~ via G protein-linked receptors (56); this suggests that fish oil may impede the ability of LTB 4 (and perhaps of other cytokines and inflammatory mediators produced by leukocytes in psoriatic lesions) (57) to activate PKC and thereby stimulate induction of autocrine growth factors. Current evidence suggests that AR is the most
440
crucial of the autocrine growth factors produced by normal and psoriatic keratinocytes. If, as predicted above, fish oil therapy can reduce keratinocyte production of AR, while glucosamine can inhibit the activity of this growth factor, it would be reasonable to expect complementarity or synergism when these two measures are used conjointly in the treatment of psoriasis. This possibility merits clinical evaluation; obviously, a safe and effective nutritional regimen for managing psoriasis would be a most worthwhile development. It is intriguing to speculate that modulation of the activities of AR (or of other heparin-binding growth factors) by endogenously produced HS proteoglycans, may be a more general phenomenon, occurring in tissues other than just the epidermis. In such tissues, glucosamine administration may help to control hyperproliferative disorders and, in the long term, may reduce cancer risk. It should be noted that AR was first isolated from cultured mammary epithelium, and functions as an autocrine growth factor for this tissue (46).
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