Abstract
Localized deposits of amyloid structures are observed in various pathological conditions. One example of when local amyloidosis occurs is following repeated insulin injections in diabetic patients. The present study aimed to simulate the same condition in mice. To obtain the amyloid structures, regular insulin was incubated at 57°C for 24 h. The subsequently formed amyloid fibrils were analyzed using the Congo red absorbance test, as well as transmission electron microscopy images, and then injected into mice once per day for 21 consecutive days. Firm waxy masses were developed following this period, which were excised, prepared as thin sections and stained with hematoxylin and eosin, Congo red and Sudan black. Histological examination revealed that these masses contained adipose cells and connective tissue, in which amyloid deposition was visible. Thus, localized amyloidosis was obtained by the subcutaneous injection of insulin fibrils. The present results may be of further use in the development of models of amyloid tumors.
Highlights
Amyloidosis refers to the extracellular accumulation of amyloid fibrils in various tissues and organs, which may result in the disruption of their function
The in vitro incubation of insulin under amyloidogenic conditions resulted in the formation of insulin fibrils
The shift observed in the absorption spectrum of Congo red (Fig. 1), along with the transmission electron microscopy (TEM) images indicating the presence of distinct fibrils, were taken as validation of insulin amyloid formation
Summary
Amyloidosis refers to the extracellular accumulation of amyloid fibrils in various tissues and organs, which may result in the disruption of their function. Amyloid fibrils are a specific type of protein aggregate which, upon deposition in particular tissues, may cause serious illness that is often fatal when major organs are involved, or when the amyloidosis is systemic [1,2]. A previous study demonstrated that insulin injections are associated with local amyloidosis [9] These are case reports of patients who have detected an abnormal mass in the injection site [10,11,12]. From these studies, it may be hypothesized that amyloidosis may be observed regardless of the location of the injection [13]. The formation of insulin fibrils occurs regardless of the source [14] and type [10,11] of insulin administered
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