Regeneration of Pancreas

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Suda K (ed): Pancreas Pathological Practice and Research.

Basel, Karger, 2007, pp 178187

Regeneration of the Pancreas

Masanobu Eguchi

Department of Clinical Pathology, Juntendo University Nerima Hospital,

Tokyo, Japan

AbstractThe potential for regeneration of pancreatic tissue in the adult human has generally

been regarded as minimal. However, in chronic pancreatitis, isolated lobuli are frequently

seen in fibrosis. These isolated lobuli have nodular architecture and bear resemblance to

regenerative nodules of the cirrhotic liver. In experimental animals, regeneration of the aci-

nar cells has been shown in the literature since Fitzgerald et al., followed by other experi-

mental studies for pancreas exocrine and/or endocrine cell regeneration. Recently, expression

of growth factors in pancreatic regeneration as platelet-derived growth factor-A (PDGF-A)

and vascular endothelial growth factor (VEGF) was determined by immunohistochemical

analysis, and a combination of epidermal growth factor and leukemia-inhibitor factor

induces exocrine-endocrine transdifferentiation. Also, the morphological examinations ofexperimental animals clarified the potential endocrine and exocrine progenitors as tubular

complex and acinoinsular and/or ductuloinsular transformation.

Copyright 2007 S. Karger AG, Basel

The regenerative potential of the human pancreas tissue has been regarded

as minimal. However, with regard to the pancreatic duct epithelium, prolifera-

tive changes, including regeneration, hyperplasia and metaplasia, are common

pathological features. In the damaged human pancreas, such as in acute or

chronic pancreatitis, isolated lobuli are frequently seen in fibrosis (figs. 1, 2).These isolated lobuli have a nodular architecture and show a resemblance to

regenerative nodules of the cirrhotic liver. Though sequential examination of

regenerative changes in the human pancreas is almost impossible, regeneration

of acinar cells has been shown in experimental animals by Fitzgerald et al. [1].

These authors reported regeneration of acinar cells in the rat pancreas after

administration of DL-ethionine. In this chapter, I would like to show my previ-

ous experiment on the characteristic histological patterns of regeneration in the

chemically-injured animal pancreas [2, 3], and the comparison between the


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Regeneration of the Pancreas 179

Fig. 1. Isolated lobuli in fibrosis in the case of chronic pancreatitis. HE.

Fig. 2. The mitotic figure was occasionally observed in such lobuli. HE.


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so-called cirrhotic human pancreas and the regenerative pancreas in experimen-

tal animals. Other experimental studies concerning pancreatic regeneration are

also presented.

Experimental Pancreatic Regeneration

Methods in Brief

Sixty young male Wistar rats were divided into two groups. Ten rats were

fed a synthetic control diet (ND group), and fifty rats were fed an experimen-

tal diet, containing 0.5% DL-ethionine (ED group). On day 14, five rats from

each group and on day 21, five rats of group ED were sacrificed. After affir-

mation of necrosis and destruction of the pancreas, the remaining rats of group

ED were changed to the normal diet (END group). On days 24, 28, 50 and 70,i.e. 3, 7, 29 and 49 days after cessation of the DL-ethionine supplemental diet

feeding, the END group rats and the remaining rats of the ND group were sac-

rificed (fig. 3). To observe the regeneration of pancreatic tissue, histological

and immunohistochemical examinations were performed, and changes in the

-glutamyl transpeptidase(-GTP) activity in the regenerating pancreatic tis-

sues were demonstrated histochemically. A part of the pancreas was submitted

for electron microscopy to examine the fine structures of the regenerative

cells.

DL-ethionine (0.5%)

Days 14 21 24 28 34 56

(ED)

(ND)

DL-ethionine and followed

by normal diet

Normal diet (control)

(END)

(5)(5)

(5)

Number of rats sacrificed per experimental period: ( )

(5)

(5)(5)

(10)

(10)

Fig. 3. Experimental design of pancreatic regeneration.


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Results

Chronological Changes in the Exocrine Pancreas

On day 14, the pancreata of the rats fed the ethionine-supplemented diet

(ED group) showed diffuse and/or focal necrosis and destruction of the acinarcells. On day 21, interstitial edema became gradually prominent and mild inter-

and intra-lobular fibrosis appeared in the ED group (f igs. 4, 5). Three days after

the end of the ethionine-supplemented diet, most of the acinar cells in the END

group had large oval-shaped nuclei with prominent nucleoli and frequent

mitotic figures (fig. 6). Under the electron microscope, these acinar cells with

basophilic cytoplasma were seen to be filled with compact rough endoplasmic

reticuli and had large irregular shaped nuclei. On the day 7 after the end of DL-

ethionine administration, the END group showed no edema, mononuclear cell

infiltration or degeneration of the acinar cells. The mitotic index of the acinarcells on day 14 showed the same value as in the ED and ND groups. The peak

of the mitotic index was observed in the END group. The index then gradually

decreased, and consequently showed almost the same value in the END and ND

groups on day 49 day after the end of DL-ethionine administration (fig. 7).

Chronological Changes in the Endocrine Pancreas

In the END groups, proliferation of small groups or isolated endocrine cells

and the irregular-shaped hyperplastic islets (fig. 8) were occasionally found in

Fig. 4. Degenerative pancreas in rat of ED group. Ductular aggregation with inter- and

intra-lobular fibrosis were noted. HE.


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Fig. 6. Acinar cells in regenerated pancreatic tissue had large oval-shaped nuclei with

prominent nucleoli, and mitotic f igures were recognized. HE.

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Fig. 5. Degenerative pancreas in rat of ED group. Most acinar cell cytoplasmas

showed marked hydropic change and decrease of zymogen granules. HE.


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1

14 21 24 28 50 70

Days

DL-ethionine administrated diet

DL-ethionine (3 weeks) and followed

by normal diet

Normal diet (MSD)

Fig. 7. Mitotic index (number of mitoses per 1,000 acinar cells; M SD).

Fig. 8. Irregular hyperplastic islets were noted in regenerative pancreas. HE.


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Fig. 9. Insulin-producing cells in islets, isolated in acinus and in ductular epithelium.

Immunostain for insulin.

the regenerating pancreas. The endocrine cells in these hyperplastic and/or small

islets were directly connected with acinar cells and ductular epithelia.

Immunohistochemical examinations showed that such small groups orisolated endocrine cells in acini and ductular epithelia coincided with insulin-

producing cells (fig. 9).

The Activity of Pancreatic -GTP

The histochemically and electronmicroscopically observed activity of

-GTP was positive in all the acinar cells of the ED group during the experiment.

The -GTP was located in the cytoplasmic membrane and a part of the apical por-

tion of the acinar cells (fig. 10), as well as in the apical portion of the ductular

epithelium, but not in the endocrine cells. Electron-microscopic examinationrevealed that the -GTP activity was located along with the cytoplasmic mem-

brane and demonstrated as electron dense material (fig. 11). On the other hand,

the ED group showed reduced -GTP activity in all acinar cells along with cell

degeneration and necrosis. On day 28 (7 days after the end of DL-ethionine admin-

istration), the acinar cells in the END group showed a greater -GTP activity than

in the END group on day 24. Histochemically, on days 34 and 56, the acinar cells

in the END group showed -GTP activity of almost the same intensity as in the

ND group.


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Fig. 10. Localization of -GTP in the acinar cells.Histochemical -GTP.

Fig. 11. Electron microscopic cytochemical demonstration of -GTP activity in the rat

pancreas.


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Conclusion and Summary

DL-Ethionine is the antagonist of methionine, which is one of the essential

amino acids, and is known to cause pancreatic acinar cell necrosis in rats and

other experimental animals by either intraperitoneal injection or oral adminis-tration. The mechanism of pancreatic damage is presumed to be abnormal

metabolism in protein synthesis. There are also other chemical agents, such as

1-aminocyclopentane carboxylic acid (ACPC) and puromycin, which can cause

pancreatic acinar cell necrosis and degeneration.

These chemical agents have therefore been used for experiments on pan-

creatic acinar cell regeneration. On the other hand, the chemical agents which

produce pancreatic endocrine cell destruction, such as alloxan [4] and strepto-

zotocin [57], have been used for various experiments on pancreatic endocrine

regeneration, and it is also known that these chemical agents produce diabetic

states in rats and guinea-pigs. Furthermore, studies on regeneration of pancre-

atic acinar cells and endocrine cells after partial or subtotal pancreatectomy of

some experimental animals, have been reported [8]. My previous experiment on

the characteristic histological patterns of regeneration in the chemically-injured

animal pancreas suggested that pancreatic acinar cell regeneration followed by

necrosis and destruction by DL-ethionine administration occurred as early as 3

days after the termination of DL-ethionine administration. Pancreatic endocrine

cells also regenerated in an early phase, and these cells were found in ductal

and/or ductular epithelia, as well as in isolated cases in the interstitium.

Histochemically recognized -GTP activity in such pancreata was restoredrapidly to the control value in parallel with the histopathological restoration.

Electronmicroscopic observations supported this view, suggesting that func-

tional restoration of pancreatic exocrine cells begins at an early stage and fin-

ishes within a shorter period. Recently, expression of some growth factors was

proposed in close relation to pancreatic regeneration. Expression of platelet-

derived growth factor-A (PDGF-A) and vascular endothelial growth factor

(VEGF) in regeneration of rat pancreas was determined by immunohistochem-

ical analysis [9], and epidermal growth factor and leukemia-inhibitor factor

induced exocrine-endocrine transdifferentiation in vitro [10]. Furthermore,Renuka et al. [11] suggested that the increased muscarinic M1 and M3 receptor

subtypes stimulated insulin secretion and islet cell proliferation during pancreas

regeneration. Also, morphological examinations of experimental animals clari-

fied the potential endocrine and exocrine progenitors as tubular complex [12]

and acinoinsular and/or ductuloinsular transformation.


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References

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2 Eguchi M, Suzuki F, Matsumoto M, et al: Regeneration of pancreatic acinar and endocrine cell

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11 Renuka TR, Savitha B, Paulose CS: Muscarinic M1 and M3 receptor binding alterations in pan-

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12 Wang GS, Rosenberg L, Scott FW: Tubular complexes as a source for islet neogenesis in the pan-

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Masanobu Eguchi

Department of Clinical Pathology

Juntendo University, Nerima Hospital

Takanodai 3-10-10, Nerima, Tokyo 177-8521 (Japan)

Tel81 3 5923 3111, E-Mail [email protected]

Regeneration of Pancreas

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