- Email: [email protected]
Tales from the crypt
GASTROENTEROLOGY 2003;124:561–571
EDITORIALS Tales From the Crypt See article on page 293.
he current study by Dr. Seguy and colleagues1 explores the response of the human intestine to recombinant human growth hormone in patients with established short bowel syndrome and dependence on total parenteral nutrition (TPN). The clinical endpoint of this study was macronutrient absorption. The authors report a statistically significant increase in total energy, carbohydrate, and nitrogen absorption compared with placebo. Treatment followed by discontinuation of patients’ TPN was not the intent of this study. The results of the study are in contrast to previous controlled clinical studies that have evaluated nutrient absorption in patients treated with recombinant human growth hormone alone or in combination with glutamine. The study does not explore the question of what potential mechanisms might be responsible for the observed response. Perhaps part of the answer can be found by examining “tales from the crypt.” Cell birth and division of intestinal epithelium begins with stem cells located within the crypts of Lieberkuhn. The stem cells contain the necessary enzymes required for nucleic acid synthesis, which ultimately results in growth, differentiation, and function of intestinal cells.2,3 After cell division within the crypt, the columnar cells migrate up the villi. There, the cells undergo both differentiation and maturation, which contribute to the specific properties of nutrient absorption. There is considerable information about the crypt-villus axis and evolution in animal models, but much less is known about function in humans. Although the number of crypts remains constant, increased cellular proliferation of stem cells results in increased villous height. Increased intestinal surface area and cellular function are thought to be the primary mechanism for increased nutrient and fluid absorption after intestinal resection. Luminal nutrients, circulating hormones, and growth factors are important stimuli of this process. These stimuli are of particular clinical interest in patients with short bowel syndrome who are dependent on parenteral nutrition for survival. Hence, the importance of the authors’ work. The cellular mechanism by which trophic factors ultimately contribute to intestinal growth appears to be the stimulation of the rate-limiting enzyme for poly-
T
amine production, ornithine decarboxylase (ODC).4 – 6 The polyamines, which include putrescine, spermidine, and spermine, are present in all tissues of the body. It has been known for many years that polyamines influence DNA, RNA, and tissue synthesis. Baylin and Luk4 first showed that increased polyamine synthesis resulted in intestinal growth and maturation. When polyamine synthesis is blocked with an ODC inhibitor, adaptive intestinal hyperplasia is prevented. At a cellular level, it has also been shown that certain enteric hormones stimulate ODC activity by binding to epithelial receptors. The principal physiologic stimuli controlling adaptive intestinal growth are luminal nutrients. Luminal nutrients promote the synthesis and release of certain peptides that stimulate ODC activity, resulting in intestinal growth. My following comments will focus on the known effects of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) on small bowel function. In rodent models, both GH and IGF-1 have been shown to increase small bowel growth after resection.7 Growth hormone mediates its trophic effects primarily through IGF-1. IGF-1 and its receptors are expressed locally throughout human and rodent small bowel. The mesenchymal cells of the lamina propria are the primary sites of local intestinal IGF-1 synthesis. Increased crypt cell proliferation and inhibition of apoptosis are most likely a result of IGF-1. Exogenous GH administration increases serum IGF-1 concentrations as well as levels of IGF-1 in the small intestine. In rodents, systemic IGF-1 administration promotes weight gain and small bowel growth after surgical resection. IGF-1, but not GH, has also been reported to increase mucosal DNA and protein levels in the jejunal mucosa of rats to reverse TPNinduced mucosal atrophy.8 Increased ODC activity and subsequent polyamine synthesis most likely account for this observation. The combination of IGF-1 and glutamine was also shown in 2 studies in rats to synergistically increase plasma IGF-1 levels, intestinal DNA, and villus growth of the resected small bowel.9,10 Hence, there has been much enthusiasm for treating short bowel patients with the combination of GH and glutamine. However, other rodent studies do not support this observation.11 Another important observation is that GH-infused, TPN-fed rats have reduced responsiveness to endogenous
562
EDITORIALS
IGF-1 over time.7 The lack of effect of excess GH on crypt cell production in adult transgenic mice seems to reflect a compensatory response to prolonged GH excess. One explanation for this finding may be that prolonged GH uncouples IGF-1 receptors, making the small bowel less responsive to endogenous IGF-1.7,8 Also, newly recognized suppressors of cytokine signaling (SOCS) may inhibit intestinal crypt cell proliferation in response to GH or IGF-1 induced by GH.12 This may in part explain why Seguy et al. found a positive response, i.e., increased nutrient absorption, with low-dose GH, even though the 2 controlled studies that used a higher dose of GH did not find an improved response.13,14 Also, Seguy et al. reported a return of the absorptive response to baseline after the washout period in patients who were first randomized to receive GH. These observations question the sustained effects of GH. The positive effects of GH on intestinal absorption might be one of differentiated function of the columnar absorptive cells without morphological change. Of the clinical studies that have used GH in short bowel patients, a study we conducted was the only one to assess morphological and proliferative changes after treatment.13 In addition to finding no increase in the absorption of fluids and nutrients, we also did not observe an increase in villus height or crypt cell proliferation. This observation would suggest a lack of detectable morphological change in humans after GH administration, which is in contrast to findings in the rodent model. Our finding is supported by the lack of a significant rise in plasma level of citrulline, a marker of mucosal mass,15 in the Seguy et al. study. An in vitro study of duodenal mucosa has however reported increased crypt cell proliferation with both GH and IGF-1.16 A study by Hogenauer et al. suggests that species differences might explain differences between human and rodent responses to GH.17 In their in vivo study of 6 healthy volunteers, the administration of 0.10 mg/kg of subcutaneous human recombinant growth hormone did not stimulate absorption or inhibit secretion of water or electrolytes from the jejunum. Serum growth hormone levels were in a range comparable to those in previous rodent studies in which positive effects were observed. Although a higher dose of GH was given (0.10 mg/kg vs. 0.05 mg/kg) and patients had not had intestinal resection, these results do not support the findings of Seguy et al.1 A study of 12 healthy patients reported by Inoue et al.18 showed that subcutaneous human recombinant GH (0.10 mg/kg) for 3 days before surgery resulted in an insignificant increase in amino acid transport rates in jejunal and ileal brush border membrane vesicles. A
GASTROENTEROLOGY Vol. 124, No. 2
higher dose (0.20 mg/kg) of GH produced a statistically significant increase in amino acid transport (35%; P ⬍ 0.05). Neither of the 2 doses of GH resulted in an increase in glucose uptake. Although this study was not done in patients with short bowel syndrome, it suggested that a higher dose of GH, i.e. ⬎0.10 mg/kg, is required for enhanced functional effect. To the best of my knowledge, only one published study has evaluated the effect of subcutaneous administration of human recombinant growth hormone alone (i.e., without glutamine) in patients with short bowel.19 In this study by Ellegard et al., an 8-week course of GH at a dose of 0.024 mg/kg per day did not increase absorption of water, energy, or protein.19 Diet and mean serum IGF-1 levels were similar to those reported by Seguy et al. This raises the question of why the 2 studies would have such different results if IGF-1 were the principle mediator of small bowel absorptive function. Two possible explanations are the difference in duration of treatment (8 vs. 3 weeks) and the use of TPN. Regarding the first explanation, perhaps there is reduced responsiveness to GH/IGF-1 over time, as reported in the rodent model, therefore explaining the lack of benefit observed at the end of 8 weeks. This would in part be consistent with the data of Seguy et al. showing lack of continued response following the washout period of their study. Second, only 2 of the 10 patients studied by Ellegard received TPN, whereas all patients studied by Seguy received TPN. Perhaps the necessary micronutrients required for the total effect of the GH/IGF-1 were deficient in short bowel patients on oral diets alone. Interestingly, in the original report by Byrne et al., although they did not present the data, the authors mention that in their previous pilot studies in TPNtreated short bowel patients, the administration of growth hormone (0.14 mg/kg per day) without glutamine had no positive effect on nutrient absorption.20 Also, in the study by Ellegard, 5 of the 10 patients developed side effects from the GH, whereas in the study by Seguy et al., which used a higher dose of GH, no side effects were reported. Three studies have compared the results of GH plus glutamine and diet.13,14,20 On the basis of previous animal studies, it appears that the combination of GH and glutamine has a synergistic effect on intestinal function.9,10 Glutamine is a required substrate for ODC and an essential precursor for nucleotide biosynthesis. Certainly there is no reason to suggest a negative or canceling effect when glutamine in given with GH. These 3 studies also used higher daily doses of GH. The 2 randomized placebo-controlled studies reported no signifi-
February 2003
EDITORIALS
Table 1. Diet, Serum IGF-1, and GH Dose Author
Diet Serum IGF-1 GH dose rangea n (Kcal/day) (ng/mL) (mean) Response
Seguy 12 Ellegard 10 Scolapio 8 Bryne 8 Szkudlarek 8 aGH
3000 3500 1500 2300 2400
348 396 420 478 591
0.05 0.024 0.03–0.14 (0.13) 0.14 0.05–0.14 (0.11)
⫹ ⫺ ⫺ ⫹ ⫺
dose mg/kg.
cant increase in nutrient absorption after a 3-week treatment period with GH and glutamine.13,14 Serum IGF-1 levels in both studies were higher than in the Seguy et al. study (Table 1). However, the open label study by Byrne et al.,20 which used GH doses similar to those in the 2 controlled studies and higher dose than the Seguy et al. study, did report a significant increase in nutrient absorption. Serum IGF-1 levels were similar to those in the 2 controlled studies but higher than that reported by Seguy et al. It is very important to note that the one similarity of all these clinical studies is the lack of a statistically significant increase in fat absorption. This would suggest to me that GH does not have a significant effect on increasing intestinal surface area or on the bile acid enterohepatic pathway. We now need to turn our attention from the tales of the crypt to actual clinical practice. It is overly optimistic to assume that the treatment of short bowel patients with our currently known trophic factors, including GH, will increase nutrient and fluid absorption to the point where TPN could be permanently discontinued, especially in patients who have had a critical amount of their small bowel resected and who have been TPN-dependent for more than 2 years. At some point after a significant bowel resection, one goes beyond the point of return for being able to maintain nutrient and fluid balance autonomously. Perhaps a very select group of patients, which is yet to be defined, may benefit clinically. Although it is tempting to believe that the combination of GH, glutamine, and diet reported in the second paper by Byrne21 was responsible for 40% of patients being able to discontinue TPN, we must note that nutrient and fluid balance studies were not performed. Therefore, we have no idea whether the positive effects observed 1 year later were secondary to a 3-week course of GH. I suspect not. I also suspect that optimization of conventional care of these patients, including diet, was responsible for the observed response. An abstract published by Nishikawa et al.22 reported that a large number of these same patients had to be placed back on TPN because of progressive weight loss and negative fluid
563
balance. In the current paper by Seguy et al., total energy absorption increased by 427 kcal/day after GH treatment. These patients were also reported as being able to eat a hyperphagic diet of ⬎3000 kcal per day. Although the exact composition of this 3000 kcal diet is not mentioned, I suggest that the same outcome of energy absorption could have been achieved with a caloric dense diet. I would agree with Seguy and colleagues that the safety of long-term treatment with GH must be evaluated with extreme caution. Therefore, based on the current available experimental and clinical data, I do not believe growth hormone should be used in the treatment of patients with short bowel syndrome. JAMES S. SCOLAPIO Division of Gastroenterology and Hepatology Director of Nutrition Mayo Clinic Jacksonville, Florida
References 1. Seguy D, Vahedi K, Kapel N, Souberbielle JC, Messing B. Lowdose growth hormone in adult home parenteral nutrition– dependent short bowel syndrome patients: a positive study. Gastroenterology 2003;124:293–302. 2. Williamson RCN. Intestinal adaptation. structural, functional and cytokinetic changes. N Engl J Med 1978;298:1393–1402. 3. Williamson RCN. Intestinal adaptation: mechanisms of control. N Engl J Med 1978;298:1444 –1450. 4. Dowling RH, Hosomi M, Lirussi, Miazza B, Levan H, Murphy GM. Hormones and polyamines in intestinal and pancreatic adaptation. Scand J Gastroenterol 1985;20:84 –95. 5. Dowling RH. Small bowel adaptation and its regulation. Scand J Gastroenterol 1982;74:53–74. 6. Dowling RH. Cellular and molecular basis of intestinal and pancreatic adaptation. Scand J Gastroenterol 1992;193:64 – 67. 7. Lund PK. Molecular basis of intestinal adaptation: the role of the insulin-like growth factor system. Ann N Y Acad Sci 1998;859: 18 –36. 8. Peterson CA, Carey HV, Hinton PL, Lo HC, Ney DM. GH elevates serum IGF-1 levels but does not alter mucosal atrophy in parent rally fed rats. Am J Physiol 1997;272:G1100 –G1108. 9. Ziegler TR, Mantell MP, Chow JC, Rombeau JL, Smith RJ. Gut adaptation and the insulin-like growth factor system: regulation by glutamine and IGF-1 administration. Am J Physiol 1996;271: G866 –G875. 10. Gu Y, Wu ZH, Xie JX, Jin DY, Zhuo HC. Effects of growth hormone and glutamine supplemented parenteral nutrition on intestinal adaptation in short bowel rats. Clin Nutr 2001;20:159 –166. 11. Vanderhoof JA, Kollman KA, Griffin S, Adrian TE. Growth hormone and glutamine do not stimulate intestinal adaptation following massive small bowel resection in the rat. J Pediatr Gastroenterol Nutr 1997;25:327–331. 12. Greenhalgh CJ, Miller ME, Hilton DJ, Lund PK. Suppressors of cytokine signaling: relevance to gastrointestinal function and disease. Gastroenterology 2002;123:2064 –2081. 13. Scolapio JS, Camilleri M, Fleming CR, Oenning L, Burton DD, Sebo TJ, Batts KP, Kelly DG. Effect of growth hormone, glutamine, and diet on adaptation in short bowel syndrome: a randomized, controlled study. Gastroenterology 1997;113:1074 – 1081.
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14. Szkudlarek J, Jeppesen PB, Mortensen PB. Effect of high dose growth hormone with glutamine and no change in diet on intestinal absorption in short bowel patients: a randomized, double blind, crossover, placebo controlled study. Gut 2000;47:199 – 205. 15. Creen P, Coudray-Lucas C, Thuillier F, Cynober L, Messing B. Postabsorptive plasma citrulline concentrations is a marker of absorptive enterocyte mass and intestinal failure in humans. Gastroenterology 2000;119:1496 –1505. 16. Wheeler EE, Challacombe DN. The trophic action of growth hormone, insulin-like growth factor and insulin on human duodenal mucosa cultured in vitro. Gut 1997;40:57– 60. 17. Hogenauer C, Santa Ana CA, Porter JL, Fordtran JS. Discrepancies between effects of recombinant human growth hormone on absorption and secretion of water and electrolytes on the human jejunum compared to results reported on rat jejunum. Dig Dis Sci 2000;45:457– 461. 18. Inoue Y, Copeland EM, Souba WW. Growth hormone enhances amino acid uptake by the human small intestine. Ann Surg 1994; 219:715–724. 19. Ellegard L, Bosaeus I, Nordgren S, Bengtsson BA. Low dose growth recombinant human growth hormone increases body
weight and lean body mass in patients with short bowel syndrome. Ann Surg 1997;225:88 –96. 20. Byrne TA, Morrissey TB, Nattakom TV, Ziegler TR, Wilmore DW. Growth hormone, glutamine, and a modified diet enhance nutrient absorption in patients with severe short bowel syndrome. J Parenter Enteral Nutr 1995;19:296 –302. 21. Byrne TA, Persinger RL, Young LS, Ziegler TR, Wilmore DW. A new treatment for patients with short bowel syndrome. Growth hormone, glutamine and a modified diet. Ann Surg 1995;222:243– 255. 22. Nishikawa RA, Siepler JK, Diamantidis T, Okamoto R, Peterson C. Remaining small bowel length is longer in short bowel patients who are able to remain off TPN after intestinal rehabilitation. Clin Nutr 2000;19:250.
Address requests for reprints to: James S. Scolapio, M.D., 4500 San Pablo Road, Mayo Clinic, Jacksonville, Florida 32224. e-mail: [email protected]; fax: (904) 953-7260. © 2003 by the American Gastroenterological Association 0016-5085/03/$35.00 doi:10.1053/gast.2003.50071
PPAR␥ Ligands: Taking Ppart in Chemoprevention See article on page 361.
here has been growing interest in the chemoprevention of cancer, especially when high-risk individuals and groups can be identified.1–3 The colon is a relatively accessible organ for early detection of precancerous lesions, which carry the risk of malignancy if not removed. There are also known genetic pathways that render individuals susceptible to colon and other cancers.4 – 6 Additionally, individuals with diseases such as ulcerative colitis, diabetes, and obesity are at increased risk of developing colorectal cancer.3,7,8 Hence, the colon is an attractive target for the identification and the use of chemopreventive agents. A key requirement for chemopreventive drugs is that they be relatively nontoxic. To this end, there has been strong interest in recent years into the use of the thiazolidinedione (TZD) class of antidiabetic drugs in cancer treatment.9,10 These drugs, which include rosiglitazone (Avandia; GlaxoSmithKline, Research Triangle Park, NC) and pioglitazone (Actos; Takeda Chemical Industries, Ltd., Osaka, Japan), are already being prescribed to millions of patients with diabetes across the United States. Although a third TZD, troglitazone (Rezulin; Warner-Lambert, Morris Plains, NJ), was removed from the market because of rare but severe hepatotoxicity, rosiglitazone and pioglitazone appear to be very well tolerated.
T
TZDs are now known to be selective ligands for peroxisome proliferator-activated receptor ␥ (PPAR␥).11,12 PPAR␥ was initially cloned as a component of protein complex regulating transcription of an adipose-selective gene, and was also cloned independently in searches for additional members of the PPAR family.13,14 PPAR␥ has a modular structure similar to other nuclear hormone receptor family members, consisting of 4 functional domains (Figure 1).15,16 The N-terminal A/B domain is the least conserved region among the nuclear hormone receptors, containing a ligand-independent transactivation region, termed activation function (AF)-1. The C domain contains the highly conserved DNA-binding domain, encompassing approximately 66 – 68 amino acids residues, and 2 zinc fingers that coordinate DNA/receptor binding. The DEF domain contains the ligand binding domain, as well as a region that helps dimerization and interaction with coactivators and corepressors. In addition, this domain contains a region at its C terminal portion, termed AF-2. In contrast to the AF-1 region, the AF-2 region participates in liganddependent transactivation. PPAR␥, similar to other members of the PPAR family, requires heterodimerization with the retinoid X receptor to bind to DNA in a sequence-specific manner.17,18 This heterodimeric complex preferentially binds and activates genes containing direct repeat-1 (DR-1) response elements composed of the consensus sequence RGGTCA-A-AGGTCA, also termed PPAR response elements.19,20
EDITORIALS Tales From the Crypt See article on page 293.
he current study by Dr. Seguy and colleagues1 explores the response of the human intestine to recombinant human growth hormone in patients with established short bowel syndrome and dependence on total parenteral nutrition (TPN). The clinical endpoint of this study was macronutrient absorption. The authors report a statistically significant increase in total energy, carbohydrate, and nitrogen absorption compared with placebo. Treatment followed by discontinuation of patients’ TPN was not the intent of this study. The results of the study are in contrast to previous controlled clinical studies that have evaluated nutrient absorption in patients treated with recombinant human growth hormone alone or in combination with glutamine. The study does not explore the question of what potential mechanisms might be responsible for the observed response. Perhaps part of the answer can be found by examining “tales from the crypt.” Cell birth and division of intestinal epithelium begins with stem cells located within the crypts of Lieberkuhn. The stem cells contain the necessary enzymes required for nucleic acid synthesis, which ultimately results in growth, differentiation, and function of intestinal cells.2,3 After cell division within the crypt, the columnar cells migrate up the villi. There, the cells undergo both differentiation and maturation, which contribute to the specific properties of nutrient absorption. There is considerable information about the crypt-villus axis and evolution in animal models, but much less is known about function in humans. Although the number of crypts remains constant, increased cellular proliferation of stem cells results in increased villous height. Increased intestinal surface area and cellular function are thought to be the primary mechanism for increased nutrient and fluid absorption after intestinal resection. Luminal nutrients, circulating hormones, and growth factors are important stimuli of this process. These stimuli are of particular clinical interest in patients with short bowel syndrome who are dependent on parenteral nutrition for survival. Hence, the importance of the authors’ work. The cellular mechanism by which trophic factors ultimately contribute to intestinal growth appears to be the stimulation of the rate-limiting enzyme for poly-
T
amine production, ornithine decarboxylase (ODC).4 – 6 The polyamines, which include putrescine, spermidine, and spermine, are present in all tissues of the body. It has been known for many years that polyamines influence DNA, RNA, and tissue synthesis. Baylin and Luk4 first showed that increased polyamine synthesis resulted in intestinal growth and maturation. When polyamine synthesis is blocked with an ODC inhibitor, adaptive intestinal hyperplasia is prevented. At a cellular level, it has also been shown that certain enteric hormones stimulate ODC activity by binding to epithelial receptors. The principal physiologic stimuli controlling adaptive intestinal growth are luminal nutrients. Luminal nutrients promote the synthesis and release of certain peptides that stimulate ODC activity, resulting in intestinal growth. My following comments will focus on the known effects of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) on small bowel function. In rodent models, both GH and IGF-1 have been shown to increase small bowel growth after resection.7 Growth hormone mediates its trophic effects primarily through IGF-1. IGF-1 and its receptors are expressed locally throughout human and rodent small bowel. The mesenchymal cells of the lamina propria are the primary sites of local intestinal IGF-1 synthesis. Increased crypt cell proliferation and inhibition of apoptosis are most likely a result of IGF-1. Exogenous GH administration increases serum IGF-1 concentrations as well as levels of IGF-1 in the small intestine. In rodents, systemic IGF-1 administration promotes weight gain and small bowel growth after surgical resection. IGF-1, but not GH, has also been reported to increase mucosal DNA and protein levels in the jejunal mucosa of rats to reverse TPNinduced mucosal atrophy.8 Increased ODC activity and subsequent polyamine synthesis most likely account for this observation. The combination of IGF-1 and glutamine was also shown in 2 studies in rats to synergistically increase plasma IGF-1 levels, intestinal DNA, and villus growth of the resected small bowel.9,10 Hence, there has been much enthusiasm for treating short bowel patients with the combination of GH and glutamine. However, other rodent studies do not support this observation.11 Another important observation is that GH-infused, TPN-fed rats have reduced responsiveness to endogenous
562
EDITORIALS
IGF-1 over time.7 The lack of effect of excess GH on crypt cell production in adult transgenic mice seems to reflect a compensatory response to prolonged GH excess. One explanation for this finding may be that prolonged GH uncouples IGF-1 receptors, making the small bowel less responsive to endogenous IGF-1.7,8 Also, newly recognized suppressors of cytokine signaling (SOCS) may inhibit intestinal crypt cell proliferation in response to GH or IGF-1 induced by GH.12 This may in part explain why Seguy et al. found a positive response, i.e., increased nutrient absorption, with low-dose GH, even though the 2 controlled studies that used a higher dose of GH did not find an improved response.13,14 Also, Seguy et al. reported a return of the absorptive response to baseline after the washout period in patients who were first randomized to receive GH. These observations question the sustained effects of GH. The positive effects of GH on intestinal absorption might be one of differentiated function of the columnar absorptive cells without morphological change. Of the clinical studies that have used GH in short bowel patients, a study we conducted was the only one to assess morphological and proliferative changes after treatment.13 In addition to finding no increase in the absorption of fluids and nutrients, we also did not observe an increase in villus height or crypt cell proliferation. This observation would suggest a lack of detectable morphological change in humans after GH administration, which is in contrast to findings in the rodent model. Our finding is supported by the lack of a significant rise in plasma level of citrulline, a marker of mucosal mass,15 in the Seguy et al. study. An in vitro study of duodenal mucosa has however reported increased crypt cell proliferation with both GH and IGF-1.16 A study by Hogenauer et al. suggests that species differences might explain differences between human and rodent responses to GH.17 In their in vivo study of 6 healthy volunteers, the administration of 0.10 mg/kg of subcutaneous human recombinant growth hormone did not stimulate absorption or inhibit secretion of water or electrolytes from the jejunum. Serum growth hormone levels were in a range comparable to those in previous rodent studies in which positive effects were observed. Although a higher dose of GH was given (0.10 mg/kg vs. 0.05 mg/kg) and patients had not had intestinal resection, these results do not support the findings of Seguy et al.1 A study of 12 healthy patients reported by Inoue et al.18 showed that subcutaneous human recombinant GH (0.10 mg/kg) for 3 days before surgery resulted in an insignificant increase in amino acid transport rates in jejunal and ileal brush border membrane vesicles. A
GASTROENTEROLOGY Vol. 124, No. 2
higher dose (0.20 mg/kg) of GH produced a statistically significant increase in amino acid transport (35%; P ⬍ 0.05). Neither of the 2 doses of GH resulted in an increase in glucose uptake. Although this study was not done in patients with short bowel syndrome, it suggested that a higher dose of GH, i.e. ⬎0.10 mg/kg, is required for enhanced functional effect. To the best of my knowledge, only one published study has evaluated the effect of subcutaneous administration of human recombinant growth hormone alone (i.e., without glutamine) in patients with short bowel.19 In this study by Ellegard et al., an 8-week course of GH at a dose of 0.024 mg/kg per day did not increase absorption of water, energy, or protein.19 Diet and mean serum IGF-1 levels were similar to those reported by Seguy et al. This raises the question of why the 2 studies would have such different results if IGF-1 were the principle mediator of small bowel absorptive function. Two possible explanations are the difference in duration of treatment (8 vs. 3 weeks) and the use of TPN. Regarding the first explanation, perhaps there is reduced responsiveness to GH/IGF-1 over time, as reported in the rodent model, therefore explaining the lack of benefit observed at the end of 8 weeks. This would in part be consistent with the data of Seguy et al. showing lack of continued response following the washout period of their study. Second, only 2 of the 10 patients studied by Ellegard received TPN, whereas all patients studied by Seguy received TPN. Perhaps the necessary micronutrients required for the total effect of the GH/IGF-1 were deficient in short bowel patients on oral diets alone. Interestingly, in the original report by Byrne et al., although they did not present the data, the authors mention that in their previous pilot studies in TPNtreated short bowel patients, the administration of growth hormone (0.14 mg/kg per day) without glutamine had no positive effect on nutrient absorption.20 Also, in the study by Ellegard, 5 of the 10 patients developed side effects from the GH, whereas in the study by Seguy et al., which used a higher dose of GH, no side effects were reported. Three studies have compared the results of GH plus glutamine and diet.13,14,20 On the basis of previous animal studies, it appears that the combination of GH and glutamine has a synergistic effect on intestinal function.9,10 Glutamine is a required substrate for ODC and an essential precursor for nucleotide biosynthesis. Certainly there is no reason to suggest a negative or canceling effect when glutamine in given with GH. These 3 studies also used higher daily doses of GH. The 2 randomized placebo-controlled studies reported no signifi-
February 2003
EDITORIALS
Table 1. Diet, Serum IGF-1, and GH Dose Author
Diet Serum IGF-1 GH dose rangea n (Kcal/day) (ng/mL) (mean) Response
Seguy 12 Ellegard 10 Scolapio 8 Bryne 8 Szkudlarek 8 aGH
3000 3500 1500 2300 2400
348 396 420 478 591
0.05 0.024 0.03–0.14 (0.13) 0.14 0.05–0.14 (0.11)
⫹ ⫺ ⫺ ⫹ ⫺
dose mg/kg.
cant increase in nutrient absorption after a 3-week treatment period with GH and glutamine.13,14 Serum IGF-1 levels in both studies were higher than in the Seguy et al. study (Table 1). However, the open label study by Byrne et al.,20 which used GH doses similar to those in the 2 controlled studies and higher dose than the Seguy et al. study, did report a significant increase in nutrient absorption. Serum IGF-1 levels were similar to those in the 2 controlled studies but higher than that reported by Seguy et al. It is very important to note that the one similarity of all these clinical studies is the lack of a statistically significant increase in fat absorption. This would suggest to me that GH does not have a significant effect on increasing intestinal surface area or on the bile acid enterohepatic pathway. We now need to turn our attention from the tales of the crypt to actual clinical practice. It is overly optimistic to assume that the treatment of short bowel patients with our currently known trophic factors, including GH, will increase nutrient and fluid absorption to the point where TPN could be permanently discontinued, especially in patients who have had a critical amount of their small bowel resected and who have been TPN-dependent for more than 2 years. At some point after a significant bowel resection, one goes beyond the point of return for being able to maintain nutrient and fluid balance autonomously. Perhaps a very select group of patients, which is yet to be defined, may benefit clinically. Although it is tempting to believe that the combination of GH, glutamine, and diet reported in the second paper by Byrne21 was responsible for 40% of patients being able to discontinue TPN, we must note that nutrient and fluid balance studies were not performed. Therefore, we have no idea whether the positive effects observed 1 year later were secondary to a 3-week course of GH. I suspect not. I also suspect that optimization of conventional care of these patients, including diet, was responsible for the observed response. An abstract published by Nishikawa et al.22 reported that a large number of these same patients had to be placed back on TPN because of progressive weight loss and negative fluid
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balance. In the current paper by Seguy et al., total energy absorption increased by 427 kcal/day after GH treatment. These patients were also reported as being able to eat a hyperphagic diet of ⬎3000 kcal per day. Although the exact composition of this 3000 kcal diet is not mentioned, I suggest that the same outcome of energy absorption could have been achieved with a caloric dense diet. I would agree with Seguy and colleagues that the safety of long-term treatment with GH must be evaluated with extreme caution. Therefore, based on the current available experimental and clinical data, I do not believe growth hormone should be used in the treatment of patients with short bowel syndrome. JAMES S. SCOLAPIO Division of Gastroenterology and Hepatology Director of Nutrition Mayo Clinic Jacksonville, Florida
References 1. Seguy D, Vahedi K, Kapel N, Souberbielle JC, Messing B. Lowdose growth hormone in adult home parenteral nutrition– dependent short bowel syndrome patients: a positive study. Gastroenterology 2003;124:293–302. 2. Williamson RCN. Intestinal adaptation. structural, functional and cytokinetic changes. N Engl J Med 1978;298:1393–1402. 3. Williamson RCN. Intestinal adaptation: mechanisms of control. N Engl J Med 1978;298:1444 –1450. 4. Dowling RH, Hosomi M, Lirussi, Miazza B, Levan H, Murphy GM. Hormones and polyamines in intestinal and pancreatic adaptation. Scand J Gastroenterol 1985;20:84 –95. 5. Dowling RH. Small bowel adaptation and its regulation. Scand J Gastroenterol 1982;74:53–74. 6. Dowling RH. Cellular and molecular basis of intestinal and pancreatic adaptation. Scand J Gastroenterol 1992;193:64 – 67. 7. Lund PK. Molecular basis of intestinal adaptation: the role of the insulin-like growth factor system. Ann N Y Acad Sci 1998;859: 18 –36. 8. Peterson CA, Carey HV, Hinton PL, Lo HC, Ney DM. GH elevates serum IGF-1 levels but does not alter mucosal atrophy in parent rally fed rats. Am J Physiol 1997;272:G1100 –G1108. 9. Ziegler TR, Mantell MP, Chow JC, Rombeau JL, Smith RJ. Gut adaptation and the insulin-like growth factor system: regulation by glutamine and IGF-1 administration. Am J Physiol 1996;271: G866 –G875. 10. Gu Y, Wu ZH, Xie JX, Jin DY, Zhuo HC. Effects of growth hormone and glutamine supplemented parenteral nutrition on intestinal adaptation in short bowel rats. Clin Nutr 2001;20:159 –166. 11. Vanderhoof JA, Kollman KA, Griffin S, Adrian TE. Growth hormone and glutamine do not stimulate intestinal adaptation following massive small bowel resection in the rat. J Pediatr Gastroenterol Nutr 1997;25:327–331. 12. Greenhalgh CJ, Miller ME, Hilton DJ, Lund PK. Suppressors of cytokine signaling: relevance to gastrointestinal function and disease. Gastroenterology 2002;123:2064 –2081. 13. Scolapio JS, Camilleri M, Fleming CR, Oenning L, Burton DD, Sebo TJ, Batts KP, Kelly DG. Effect of growth hormone, glutamine, and diet on adaptation in short bowel syndrome: a randomized, controlled study. Gastroenterology 1997;113:1074 – 1081.
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14. Szkudlarek J, Jeppesen PB, Mortensen PB. Effect of high dose growth hormone with glutamine and no change in diet on intestinal absorption in short bowel patients: a randomized, double blind, crossover, placebo controlled study. Gut 2000;47:199 – 205. 15. Creen P, Coudray-Lucas C, Thuillier F, Cynober L, Messing B. Postabsorptive plasma citrulline concentrations is a marker of absorptive enterocyte mass and intestinal failure in humans. Gastroenterology 2000;119:1496 –1505. 16. Wheeler EE, Challacombe DN. The trophic action of growth hormone, insulin-like growth factor and insulin on human duodenal mucosa cultured in vitro. Gut 1997;40:57– 60. 17. Hogenauer C, Santa Ana CA, Porter JL, Fordtran JS. Discrepancies between effects of recombinant human growth hormone on absorption and secretion of water and electrolytes on the human jejunum compared to results reported on rat jejunum. Dig Dis Sci 2000;45:457– 461. 18. Inoue Y, Copeland EM, Souba WW. Growth hormone enhances amino acid uptake by the human small intestine. Ann Surg 1994; 219:715–724. 19. Ellegard L, Bosaeus I, Nordgren S, Bengtsson BA. Low dose growth recombinant human growth hormone increases body
weight and lean body mass in patients with short bowel syndrome. Ann Surg 1997;225:88 –96. 20. Byrne TA, Morrissey TB, Nattakom TV, Ziegler TR, Wilmore DW. Growth hormone, glutamine, and a modified diet enhance nutrient absorption in patients with severe short bowel syndrome. J Parenter Enteral Nutr 1995;19:296 –302. 21. Byrne TA, Persinger RL, Young LS, Ziegler TR, Wilmore DW. A new treatment for patients with short bowel syndrome. Growth hormone, glutamine and a modified diet. Ann Surg 1995;222:243– 255. 22. Nishikawa RA, Siepler JK, Diamantidis T, Okamoto R, Peterson C. Remaining small bowel length is longer in short bowel patients who are able to remain off TPN after intestinal rehabilitation. Clin Nutr 2000;19:250.
Address requests for reprints to: James S. Scolapio, M.D., 4500 San Pablo Road, Mayo Clinic, Jacksonville, Florida 32224. e-mail: [email protected]; fax: (904) 953-7260. © 2003 by the American Gastroenterological Association 0016-5085/03/$35.00 doi:10.1053/gast.2003.50071
PPAR␥ Ligands: Taking Ppart in Chemoprevention See article on page 361.
here has been growing interest in the chemoprevention of cancer, especially when high-risk individuals and groups can be identified.1–3 The colon is a relatively accessible organ for early detection of precancerous lesions, which carry the risk of malignancy if not removed. There are also known genetic pathways that render individuals susceptible to colon and other cancers.4 – 6 Additionally, individuals with diseases such as ulcerative colitis, diabetes, and obesity are at increased risk of developing colorectal cancer.3,7,8 Hence, the colon is an attractive target for the identification and the use of chemopreventive agents. A key requirement for chemopreventive drugs is that they be relatively nontoxic. To this end, there has been strong interest in recent years into the use of the thiazolidinedione (TZD) class of antidiabetic drugs in cancer treatment.9,10 These drugs, which include rosiglitazone (Avandia; GlaxoSmithKline, Research Triangle Park, NC) and pioglitazone (Actos; Takeda Chemical Industries, Ltd., Osaka, Japan), are already being prescribed to millions of patients with diabetes across the United States. Although a third TZD, troglitazone (Rezulin; Warner-Lambert, Morris Plains, NJ), was removed from the market because of rare but severe hepatotoxicity, rosiglitazone and pioglitazone appear to be very well tolerated.
T
TZDs are now known to be selective ligands for peroxisome proliferator-activated receptor ␥ (PPAR␥).11,12 PPAR␥ was initially cloned as a component of protein complex regulating transcription of an adipose-selective gene, and was also cloned independently in searches for additional members of the PPAR family.13,14 PPAR␥ has a modular structure similar to other nuclear hormone receptor family members, consisting of 4 functional domains (Figure 1).15,16 The N-terminal A/B domain is the least conserved region among the nuclear hormone receptors, containing a ligand-independent transactivation region, termed activation function (AF)-1. The C domain contains the highly conserved DNA-binding domain, encompassing approximately 66 – 68 amino acids residues, and 2 zinc fingers that coordinate DNA/receptor binding. The DEF domain contains the ligand binding domain, as well as a region that helps dimerization and interaction with coactivators and corepressors. In addition, this domain contains a region at its C terminal portion, termed AF-2. In contrast to the AF-1 region, the AF-2 region participates in liganddependent transactivation. PPAR␥, similar to other members of the PPAR family, requires heterodimerization with the retinoid X receptor to bind to DNA in a sequence-specific manner.17,18 This heterodimeric complex preferentially binds and activates genes containing direct repeat-1 (DR-1) response elements composed of the consensus sequence RGGTCA-A-AGGTCA, also termed PPAR response elements.19,20