On the importance of being amidated: Analysis of the role of the conserved C-terminal amide of amylin in amyloid formation and cytotoxicity

The polypeptide hormone Amylin (also known as islet amyloid polypeptide) plays a role in regulation of glucose metabolism, but forms pancreatic islet amyloid deposits in type 2 diabetes. The process of islet amyloid formation contributes to β-cell dysfunction and the development of the disease. Amylin is produced as a pro-from and undergoes processing prior to secretion. The mature hormone contains an amidated C-terminus. Analysis of an alignment of vertebrate amylin sequences reveals that the processing signal for amidation is strictly conserved. Furthermore, the enzyme responsible for C-terminal amidation is found in all of these organisms. Comparison of the physiologically relevant amidated form to a variant with a free C-terminus (Amylin-COO-) shows that replacement of the C-terminal amide with a carboxylate slows, but does not prevent amyloid formation. Pre-fibrillar species produced by both variants are toxic to cultured β-cells, although hAmylin-COO- is moderately less so. Amyloid fibrils produced by either peptide are not toxic. Prior work (ACS Pharmacol. Translational. Sci. 1, 132-49 (2018)) shows that Amylin- COO- exhibits a 58-fold reduction in activation of the Amylin1 receptor and 20-fold reduction in activation of the Amylin3 receptor. Thus, hAmylin-COO- exhibits significant toxicity, but significantly reduced activity and offers a reagent for studies which aim to decouple hAmylin's toxic effects from its activity. The different behaviours of free and C-terminal amidated Amylin should be considered when designing systems to produce the polypeptide recombinantly.

Differential Effects of Aromatic Residues on Amyloid Formation and Cytotoxicity of Human IAPP

Islet amyloid polypeptide (IAPP) is a 37-residue polypeptide hormone secreted by the pancreatic β-cells. IAPP plays a role in glycemic regulation, but in the pre-type-2 diabetic state, it aggregates to form an islet amyloid. The process of islet amyloid formation contributes to β-cell dysfunction and disease progression. The features of the IAPP sequence that modulate amyloid formation are still not understood. Human IAPP contains three aromatic residues, F15, F23, and Y37. F15 and Y37 are highly conserved, while F23 is more commonly a Leu or Ile in other species. The role of the aromatic residues in modulating the time course of amyloid formation and the cytotoxicity was examined using aromatic to Leu mutations. All three single and double mutants and the triple mutant were studied. F23 plays a dominant role in both amyloid formation and toxicity. An F15L mutant accelerated amyloid formation, a Y37L mutant had little effect, while an F23L replacement slowed amyloid formation by a factor of 2.6. Double mutants, which contained an F23L replacement, had a larger effect than those that did not, and there are non-additive effects between pairs of aromatic residues. F23 also plays a key role in toxicity. Single or multiple mutants that contain the F23L replacement were noticeably less toxic than the wild-type or mutants which did not include the F23L substitution. In contrast, the F15L mutant was more toxic than the wild-type one. The implications for IAPP amyloid formation and for the design of non-aggregating analogues of IAPP are discussed.

Severe respiratory distress syndrome unresponsive to intensive care treatment--diagnostic and therapeutic considerations

Respiratory Distress Syndrome (RDS) is a common complication in preterm neonates. If RDS is not responding to conventional treatment modalities (surfactant therapy, ventilatory support, etc.), an underlying pathology (pulmonary lymphangiectasia, capillary alveolar dysplasia, alpha-1 antitrypsin deficiency, etc.) other then prematurity should be taken into consideration.Here, we report on a preterm neonate with the unusual simultaneous occurrence of pulmonary and systemic lymphangiectasia and homozygous alpha-1 antitrypsin deficiency who developed severe RDS that was refractory to conventional treatment. The diagnostic and therapeutic approach in this patient is presented.

[The role of S100B-protein in neonatology, pediatric intensive care, and pediatrics]

During the last years neuromonitoring with various biochemical markers such as S100B protein has been introduced into the clinical settings of neonatal and pediatric intensive care. Several investigations have been undertaken to correlate S100B protein concentrations to the diagnosis and prognosis of neonates and children with severe cerebral disorders. This articles gives a review on the current knowledge, indications and limitations on the use of S100B protein after non-traumatic and traumatic brain injury in neonates and children.

[Ventricular tachycardia after erythromycin administration in a newborn with congenital AV-block]

This report is on a newborn with congenital complete av-block due to a maternal collagenosis. The intravenous application of erythromycin produced premature ventricular beats and non sustained ventricular tachycardias by prolongation of the QT interval. After discontinuation of the erythromycin application, the QT-interval normalised.

CONCLUSION

In atrioventricular conduction disorders with severe bradycardia and prolongation of the QT interval, the application of erythromycin--if unavoidable--should be managed by slow intravenous infusion and with permanent ECG monitoring.

[Complicated malaria tropica in an infant]

We report on a five month-old infant from Cameroon, who was admitted because of febrile gastroenteritis after living in Germany for two weeks. Since the patient was somnolent, had a parasitaemia of Plasmodium falciparum of 230,000/microliter, a haemoglobin concentration of 5.3 g/dl and a thrombocytopenia, a complicated falciparum malaria was diagnosed. Treatment was started immediately with intravenous 20 mg quinine/kg bw as a loading dose, followed by 10 mg/kg bw every 12 hours, combined with intravenous clindamycin 10 mg/kg bw bd. Red blood cells were transfused once. The parasitaemia dropped to 2000 trophozoites/microliter within 48 hours. No asexual stages were detectable from the third day of treatment on. Weekly controls for the following four weeks remained negative. The mortality rate of complicated malaria is 50% in the first year of life, which can be reduced by early treatment. We present this case to draw attention to therapeutic options in infants.