J.W.M. Höppener

Extensive islet amyloid formation is induced by development of Type II diabetes mellitus and contributes to its progression: pathogenesis of diabetes in a mouse model

Aims/hypothesis. Type II (non-insulin-dependent) diabetes mellitus is a multifactorial disease in which pancreatic islet amyloid is a characteristic histopathological finding. Islet amyloid fibrils consist of the beta-cell protein “islet amyloid polypeptide” (IAPP)/“amylin”. Unlike human IAPP (hIAPP), mouse IAPP cannot form amyloid. In previously generated transgenic mice, high expression of hIAPP as such did not induce islet amyloid formation. To further explore the potential diabetogenic role of amyloidogenic IAPP, we introduced a diabetogenic trait (“ob” mutation) in hIAPP transgenic mice. Methods. Plasma concentrations of IAPP, insulin and glucose were determined at 3.5 (t1), 6 (t2), and 16–19 months of age (t3). At t3, the mice were killed and the pancreas was analysed (immuno)histochemically. Results. In non-transgenic ob/ob mice, insulin resistance caused a compensatory increase in insulin production, normalizing the initial hyperglycaemia. In transgenic ob/ob mice, concurrent increase in hIAPP production resulted in extensive islet amyloid formation (more often and more extensive than in transgenic non-ob/ob mice), insulin insufficiency and persistent hyperglycaemia: At t3, plasma insulin levels in transgenic ob/ob mice with amyloid were fourfold lower than in non-transgenic ob/ob mice (p < 0.05), and plasma glucose concentrations in transgenic ob/ob mice were almost twofold higher (p < 0.05). In addition, the degree of islet amyloid formation in ob/ob mice was positively correlated to the glucose:insulin ratio (rs = 0.53, p < 0.05). Conclusion/interpretation. Islet amyloid is a secondary diabetogenic factor which can be both a consequence of insulin resistance and a cause of insulin insufficiency. [Diabetologia (1999) 42: 427–434]

Structure and expression of the human calcitonin/CGRP genes

Recently, we have reported the isolation of cDNA encoding a second human calcitonin gene‐related peptide (hCGRP‐II) [(1985) FEBS Lett. 183, 403‐407]. In this report we describe the isolation and characterization of the gene encoding hCGRP‐II. This gene, designated CALC‐II, is structurally closely related to the known CALC‐I gene encoding human calcitonin (hCT) and hCGRP‐I. In constrast to CALC‐I, CALC‐II does not seem to be alternatively expressed. The formation of a second, hCT‐like mRNA by differential splicing of CALC‐II transcripts is unlikely in view of the structure of CALC‐II, and could not be demonstrated in tissues known to express CALC‐I and CALC‐II.

Islet amyloid polypeptide: Identification and chromosomal localization of the human gene

Islet or insulinoma amyloid polypeptide (IAPP) is a 37 amino acid polypeptide isolated from pancreatic amyloid. Here, we describe the isolation and partial characterization of the human gene encoding IAPP. The DNA sequence predicts that IAPP is excised from a larger precursor protein and that its carboxy‐terminus is probably amidated. The predicted normally occurring IAPP is identical to the reported polypeptides isolated from pancreatic amyloid, except for the amidated carboxy‐terminus. IAPP specific polyadenylated RNAs of 1.6 kb and 2.1 kb are present in human insulinoma RNA. The human IAPP gene is located on chromosome 12.

Expression of insulin-like growth factor-I and -II genes in human smooth muscle tumours.

The insulin‐like growth factors I and II (IGF‐I and ‐II) are polypeptides which play an important role in growth and development of the organism. In the present report we describe the detection of human IGF‐I RNAs (both type Ia and type Ib) and IGF‐II RNAs in benign (leiomyoma) and malignant (leiomyosarcoma) tumours from smooth muscle origin, using Northern blot hybridization analysis. In normal smooth muscle tissue of the uterus we found low levels of IGF‐I RNAs only. In the tumours the same IGF‐I RNA species were detected as in adult non‐tumour tissues (uterus, liver). For transcription of the IGF‐II gene in these tumours, two promoters are used which are expressed in fetal liver, but not in adult liver. The presence of IGF‐I and IGF‐II RNAs was also established by nucleotide sequence analysis of recombinant DNA clones isolated from cDNA libraries derived from two leiomyosarcomas. The nucleotide sequences of these cDNA clones, together covering the entire coding regions of IGF‐Ia and IGF‐II var RNA, predict that IGFs encoded by the tumour RNAs do not differ in amino acid sequence from the corresponding polypeptides isolated from serum. In those tissues containing IGF‐I RNAs, IGF‐I immunoreactivity was also demonstrated.

The complete islet amyloid polypeptide precursor is encoded by two exons

Islet amyloid polypeptide (IAPP) is the 37‐amino acid peptide subunit of amyloid found in pancreatic islets of type 2 diabetic patients and in insulinomas. Recently, we isolated the human gene encoding IAPP [(1988) FEBS Lett. 239, 227–232]. We now report the nucleotide sequences of a human insulinoma cDNA encoding a complete IAPP precursor, and of the corresponding parts of the IAPP gene. Two exons, which are approx. 5 kb apart in the human genome, encode the 89‐amino acid pre‐pro‐IAPP. At least one additional exon is present further upstream in the IAPP gene. A putative signal sequence at the amino‐terminus of the precursor suggests that IAPP is a secreted protein.

The second human calcitonin/CGRP gene is located on chromosome 11

SummaryA second human calcitonin/calcitonin gene related peptide (hCT/CGRP) gene has been identified. This second hCT/CGRP gene has been shown to contain sequences highly homologous to exons 3, 5 (CGRP-encoding), and 6 of the first hCT/CGRP gene, but sequences closely related to exon 4 (CT-encoding) could not be demonstrated. Southern blot hybridization analysis of DNA from human-rodent somatic cell hybrids showed that the second hCT/CGRP gene is located in the q12-pter region of chromosome 11. The first hCT/CGRP gene has previously been assigned to the p13–p15 region of chromosome 11.

Localization of the polymorphic human calcitonin gene on chromosome 11

SummaryA molecular probe containing a 584 base pairs sequence corresponding to part of the human calcitonin mRNA was used for the chromosomal assignment of the calcitonin gene. Restriction endonuclease analysis of DNA from human-Chinese hamster and human-mouse somatic cell hybrids, including some containing a translocation of human chromosomes, placed the calcitonin gene in the p14→qter region of chromosome 11.Analysis of human DNA showed that the calcitonin gene has a polymorphic site for restriction endonuclease TaqI.

The human gene encoding insulin-like growth factor I is located on chromosome 12

SummaryA cDNA probe corresponding to mRNA encoding human somatomedin-C/insulin-like growth factor I (IGF-I) was used for the chromosomal assignment of the IGF-I gene. Southern-blot hybridization analysis of DNA from human-Chinese hamster somatic cell hybrids showed that the IGF-I gene is located on chromosome 12. Comparison of the chromosomal assignments of the IGF-I gene and two other members of the insulin gene family, with three c-ras oncogenes, reveals a remarkable association of the two gene families.

Transgenic overexpression of human islet amyloid polypeptide inhibits insulin secretion and glucose elimination after gastric glucose gavage in mice

Summary Islet amyloid polypeptide (IAPP) is synthesized in islet beta cells and has been implicated in diabetes pathogenesis because it can inhibit insulin secretion and action and form fibrils leading to islet amyloidosis. Its physiological function has, however, not been established. We therefore examined insulin secretion and glucose elimination after i. v. or gastric gavage of glucose in transgenic mice overexpressing human IAPP (hIAPP) resulting in considerably increased circulating IAPP concentrations. The insulin response to and the glucose elimination after i. v. glucose (1 g/kg) were not different in transgenic mice compared with wild type animals, neither in males nor in females. In contrast, the insulin response to gastric glucose (150 mg/mouse) was reduced and the glucose elimination was inhibited in both male and female transgenic mice. The area under the 30 min insulin curve (AUCinsulin) was 21 ± 2 nmol/l in 30 min in transgenic males (n = 24) vs 43 ± 3 nmol/l in 30 min in wild type males (n = 26; p < 0.001) and the respective areas under the glucose curve (AUCglucose) were 1.90 ± 0.12 and 1.62 ± 0.09 mol/l in 120 min (p < 0.05). Similarly, in females, the AUCinsulin was 17 ± 2 nmol/l in 30 min in transgenic mice vs 25 ± 3 nmol/l in 30 min in wild type mice (p < 0.05) and the respective AUCglucose was 1.62 ± 0.7 and 1.12 ± 0.07 mol/l in 120 min (p < 0.001). Hence, endogenous hIAPP inhibits insulin secretion and glucose elimination after gastric glucose gavage in both male and female mice, indicating that overexpression of hIAPP could be a diabetogenic factor, via effects on the intestinal tract or the gut-islet axis or both. [Diabetologia (1998) 41: 1374–1380]

Medullary thyroid carcinoma and biomarkers: past, present and future

The clinical management of patients with persistent or recurrent medullary thyroid carcinoma (MTC) is still under debate, because these patients either have a long‐term survival, due to an indolent course of the disease, or develop rapidly progressing disease leading to death from distant metastases. At this moment, it cannot be predicted what will happen within most individual cases. Biomarkers, indicators which can be measured objectively, can be helpful in MTC diagnosis, molecular imaging and treatment, and/or identification of MTC progression. Several MTC biomarkers are already implemented in the daily management of MTC patients. More research is being aimed at the improvement of molecular imaging techniques and the development of molecular systemic therapies. Recent discoveries, like the prognostic value of plasma calcitonin and carcino‐embryonic antigen doubling‐time and the presence of somatic RET mutations in MTC tissue, may be useful tools in clinical decision making in the future. In this review, we provide an overview of different MTC biomarkers and their applications in the clinical management of MTC patients.