Abstract
Background: Feline acromegaly is relatively rare, but is probably underdiagnosed in cats with diabetes mellitus. Although considered a useful diagnostic tool, some cats with diabetes and elevated IGF-I levels have no pituitary lesion on imaging or at postmortem. Formation of a ternary complex (TC) with IGFBP-3 and ALS is an important determinant of total IGF-I concentrations. In contrast to humans, it has been demonstrated that ALS is a limiting factor for TC formation in normal cats. Therefore much of the IGF-I in the cat circulation may be in lower molecular mass, binary complexes. It is important that IGF-I assays are carefully validated for use with feline serum, and should include serum from cats with documented GH-secreting tumors. The aim of this study was to validate a commercially available IGF-I ELISA for clinical use.
Methods: A double antibody ELISA from Mediagnost (Reutlingen, Germany) was used. In this assay IGF-I is dissociated from IGFBPs by dilution in an acidic buffer containing excess IGF-II. When neutralized IGF-II binds to and occupies potentially interfering IGFBPs in the sample. Serum was obtained from healthy adult cats and cats with diabetes mellitus, acromegaly, and chronic renal failure. To determine potential interferences by endogenous and exogenous IGFBPs, recombinant human IGF-I, IGFBP-1, -2 and -3 were added to serum samples before assay. Serum was size fractionated by acid gel chromatography and the fractions analyzed for immunoreactive IGF-I.
Results: Parallelism was demonstrated between the recombinant human IGF-I standard curve and dilution curves of serum (from healthy, diabetes, and chronic renal failure cats). Addition of IGFBPs at a total concentration of 8 mg/L showed no interference, however addition of 30 mg/L, unlikely to be encountered in clinical practice, resulted in falsely low IGF-I values. Intraassay and interassay CVs were less than 7%. The range of IGF-I concentrations in 41 adult healthy cats was 82–1026 ng/ml. In 30 cats with diabetes who were non-ketotic IGF-I levels prior to insulin treatment ranged from 84–729 ng/ml. In one cat with diabetes ketoacidosis IGF-I was undetectable. Serum from a cat with confirmed acromegaly had an IGF-I concentration of 2869 ng/ml. After size fractionation under acid conditions, serum from cats with higher concentrations of IGF-I (healthy cats as well as the patient with acromegaly), had two peaks of IGF-I immunoreactivity, one eluting at approximately 7.5 kDa and the second at a higher molecular mass.
Conclusions: The Mediagnost ELISA is suitable for use with feline serum. There is a similar wide range of IGF-I concentrations in healthy cats and in cats with untreated diabetes mellitus. The finding of a larger form of IGF-I after size separation chromatography is intriguing and is a focus of current research, along with studies of IGF-I-IGFBP binary and ternary complexes in feline serum.
Methods: A double antibody ELISA from Mediagnost (Reutlingen, Germany) was used. In this assay IGF-I is dissociated from IGFBPs by dilution in an acidic buffer containing excess IGF-II. When neutralized IGF-II binds to and occupies potentially interfering IGFBPs in the sample. Serum was obtained from healthy adult cats and cats with diabetes mellitus, acromegaly, and chronic renal failure. To determine potential interferences by endogenous and exogenous IGFBPs, recombinant human IGF-I, IGFBP-1, -2 and -3 were added to serum samples before assay. Serum was size fractionated by acid gel chromatography and the fractions analyzed for immunoreactive IGF-I.
Results: Parallelism was demonstrated between the recombinant human IGF-I standard curve and dilution curves of serum (from healthy, diabetes, and chronic renal failure cats). Addition of IGFBPs at a total concentration of 8 mg/L showed no interference, however addition of 30 mg/L, unlikely to be encountered in clinical practice, resulted in falsely low IGF-I values. Intraassay and interassay CVs were less than 7%. The range of IGF-I concentrations in 41 adult healthy cats was 82–1026 ng/ml. In 30 cats with diabetes who were non-ketotic IGF-I levels prior to insulin treatment ranged from 84–729 ng/ml. In one cat with diabetes ketoacidosis IGF-I was undetectable. Serum from a cat with confirmed acromegaly had an IGF-I concentration of 2869 ng/ml. After size fractionation under acid conditions, serum from cats with higher concentrations of IGF-I (healthy cats as well as the patient with acromegaly), had two peaks of IGF-I immunoreactivity, one eluting at approximately 7.5 kDa and the second at a higher molecular mass.
Conclusions: The Mediagnost ELISA is suitable for use with feline serum. There is a similar wide range of IGF-I concentrations in healthy cats and in cats with untreated diabetes mellitus. The finding of a larger form of IGF-I after size separation chromatography is intriguing and is a focus of current research, along with studies of IGF-I-IGFBP binary and ternary complexes in feline serum.
| Original language | English |
|---|---|
| Pages (from-to) | S53-S54 |
| Number of pages | 2 |
| Journal | Growth Hormone & IGF Research |
| Volume | 22 |
| Issue number | Supplement 1 |
| DOIs | |
| Publication status | Published - 31 Oct 2012 |
| Event | 6th International Congress of the GRS and IGF Society - Kulturzentrum Gasteig München, Munich, Germany Duration: 16 Oct 2012 → 20 Oct 2012 http://www.my-medical-education.com/en/mme/index.php?page=veranstaltung&field=&event=e9357c1c-7694-03b9-6695-805ed1152d3c |