Measurements of growth hormone and insulin-like growth factor 1 in cats with diabetes mellitus

Acromegaly in humans and cats: Pathophysiological, clinical and management resemblances and differences

OBJECTIVE

Acromegaly is a disorder associated with excessive levels of growth hormone (GH) and insulin-like growth factor-1 (IGF-1). In general, GH/IGF-1 excess leads to morphologic craniofacial and acral changes as well as cardiometabolic complications, but the phenotypic changes and clinical presentation of acromegaly differ across species. Here, we review the pathophysiology, clinical presentation and management of acromegaly in humans and cats, and we provide a systematic comparison between this disease across these different species.

DESIGN

A comprehensive literature review of pathophysiology, clinical features, diagnosis and management of acromegaly in humans and in cats was performed.

RESULTS

Acromegaly is associated with prominent craniofacial changes in both species: frontal bossing, enlarged nose, ears and lips, and protuberant cheekbones are typically encountered in humans, whereas increased width of the head and skull enlargement are commonly found in cats. Malocclusion, prognathism, dental diastema and upper airway obstruction by soft tissue enlargement are reported in both species, as well as continuous growth and widening of extremities resulting in osteoarticular compromise. Increase of articular joint cartilage thickness, vertebral fractures and spine malalignment is more evident in humans, while arthropathy and spondylosis deformans may also occur in cats. Generalized organomegaly is equally observed in both species. Other similarities between humans and cats with acromegaly include heart failure, ventricular hypertrophy, diabetes mellitus, and an overall increased cardiometabolic risk. In GH-secreting pituitary tumours, local compressive effects and behavioral changes are mostly observed in humans, but also present in cats. Cutis verticis gyrata and skin tags are exclusively found in humans, while palmigrade/plantigrade stance may occur in some acromegalic cats. Serum IGF-1 is used for acromegaly diagnosis in both species, but an oral glucose tolerance test with GH measurement is only useful in humans, as glucose load does not inhibit GH secretion in cats. Imaging studies are regularly performed in both species after biochemical diagnosis of acromegaly. Hypophysectomy is the first line treatment for humans and cats, although not always available in veterinary medicine.

CONCLUSION

Acromegaly in humans and cats has substantial similarities, as a result of common pathophysiological mechanisms, however species-specific features may be found.

Increased insulin-like growth factor 1 concentrations in a population of non-diabetic cats with overweight/obesity

Feline hypersomatotropism (HST) is typically associated with diabetes mellitus (DM), whereas HST without concurrent DM has only been reported in a few cases. Weight gain may be observed in cats with HST. The aims of this study were to evaluate circulating insulin-like growth factor-1 (IGF-1) in non-diabetic cats with overweight/obesity, to screen this population for the presence of HST, and to assess whether there is a correlation between body weight/body condition score (BCS) and serum IGF-1 concentration in overweight/obese cats. In this prospective study, 80 overweight/obese cats from referral centers in Buenos Aires (Argentina) were evaluated. Serum IGF-1 was measured as part of the routine tests for overweight/obesity. Non-diabetic cats were included in the study if they had a BCS>6/9. Twenty-nine cats were classified as overweight (BCS 7/9), whereas 51 were classified as obese (BCS 8-9/9). Median serum IGF-1 concentrations of cats with BCS 7/9, 8/9, and 9/9 were 570 ng/ml (range 123-1456 ng/ml), 634 ng/ml (range 151-1500 ng/ml), and 598 ng/ml (range 284-2450 ng/ml), respectively. There was a positive linear correlation between serum IGF-1 concentrations and body weight (r= 0.24, 95% CI 0.01-0.44 P=0.03), and between IGF-1 and BCS (r= 0.27, 95% CI 0.08-0.44 P=0.004). In total, 8.75% (95% confidence interval 3.6-17.2%) of the cats with overweight/obesity had IGF-1 concentrations >1000 ng/ml. Pituitary enlargement was detected on computed tomography in 4/7 cases. These seven cats showed varying degrees of phenotypic changes consistent with acromegaly. A proportion of 8.75 % of overweight/obese non-diabetic cats from referral centers in Buenos Aires had serum IGF-1 concentration in a range consistent with HST in diabetic cats. Likewise, 5% of overweight/obese cats were likely to be diagnosed with HST, supported by evidence of pituitary enlargement. Serum IGF-1 concentrations were positively correlated with body weight and BCS in this population of cats. This study highlights the relevance of screening different populations of non-diabetic cats to increase the detection of HST/acromegaly.

Feline Comorbidities: Hypersomatotropism-induced diabetes in cats

PRACTICAL RELEVANCE

Diabetes mellitus is the second-most common feline endocrinopathy, affecting an estimated 1/200 cats. While the underlying causes vary, around 15-25% of cats with diabetes mellitus develop the condition secondarily to progressive growth hormone (GH)-induced insulin resistance. This typically results in a form of diabetes that is challenging to manage, whereby the response to insulin is very variable or high doses are required to achieve even minimal diabetic control.

CLINICAL CHALLENGES

Although uncontrolled chronic excessive GH may result in phenotypic changes that raise suspicion for acromegaly, many cats with hypersomatotropism (HST) do not have these changes. In these situations, a clinician's index of suspicion may be increased by the presence of less dramatic changes such as marked polyphagia, stertor or uncontrolled diabetes mellitus. The current diagnostic test of choice is demonstration of a markedly increased serum insulin-like growth factor 1 (IGF1) concentration, but some affected cats will have only a marginal increase; additionally, chronic insulin administration in cats results in an increase in serum IGF1, making the diagnosis less clear cut and requiring additional confirmatory tests.

EVIDENCE BASE

Over the past two decades, HST has increasingly been recognised as an underlying cause of diabetes mellitus in cats. This review, which focuses on diagnosis and treatment, utilises data from observational studies, clinical trials and case series, as well as drawing on the experience of the authors in managing this condition.

Method Validation and Establishment of Reference Intervals for an Insulin-like Growth Factor-1 Chemiluminescent Immunoassay in Cats

Previously, radioimmunoassay (RIA) has been the only assay to measure insulin-like growth factor-1 (IGF-1) to diagnose hypersomatotropism (HS). Due to radiation concerns, availability, and the cost of IGF-1 RIA, validation of assays for automated analysers such as a chemiluminescent immunoassay (CLIA) is needed. The aim of this study was to validate a CLIA for measurement of feline IGF-1 (IMMULITE 2000® XPi, Siemens Medical Solutions Diagnostics, Malvern, PA, USA) compared to IGF1 RIA, establish reference interval (RI), and determine a cut-off value for diagnosis of HS in diabetic cats. Validation of assay performance included precision, linearity, and recovery studies. Right-sided RI was determined using surplus serum of 50 healthy adult cats. Surplus serum samples of diabetic cats with known IGF-1 concentration with (n = 32/68) and without HS (n = 36/68) were used for method comparison with RIA. The cut-off for diagnosis of HS was established using receiver operating characteristic (ROC) analysis. The intra-assay coefficient of variation (CV) was ≤4.7%, and the inter-assay CV was ≤5.6% for samples with low, medium, and high IGF-1 concentration. Linearity was excellent (R2 > 0.99). The correlation between CLIA and RIA was very high (rs = 0.97), with a mean negative bias for CLIA of 24.5%. The upper limit of RI was 670 ng/mL. ROC analysis showed an area under the curve of 0.94, with best cut-off for diagnosis of HS at 746 ng/mL (sensitivity, 84.4%; specificity, 97.2%). The performance of CLIA was good, and the RI and cut-off for HS diagnosis established in this study allow for CLIA to be used in routine work-up of diabetic cats.

Serum insulin-like growth factor-1 concentrations in healthy cats before and after weight gain and weight loss

Background

Measurement of serum concentrations of insulin‐like growth factor (IGF)‐1 is used to diagnose acromegaly in cats.

Hypothesis

Changes of body weight do not affect serum concentrations of IGF‐1 in cats.

Animals

Ten healthy purpose‐bred cats.

Methods

Prospective study. In lean cats, food availability was stepwise increased during the first week and given ad libitum for a total of 40 weeks to increase their body weight. From week 41 to week 60, food access was limited to reach a weight loss of 1% to 2% each week. Measurement of IGF‐1 was performed at week 0, 16, 40, and 60. Insulin‐like growth factor‐1 was measured by radioimmunoassay. Body weight and IGF‐1 were compared among the 4 time points.

Results

Body weight increased by 44% from week 0 (4.5 ± 0.4 kg) to week 40 (6.5 ± 1.2 kg) (P < .001) and decreased by 25% from week 40 to week 60 (4.9 ± 0.7 kg) (P < .001). Serum IGF‐1 concentrations did not differ during the study period (week 0, 16, 40, 60: 500 ± 188, 479 ± 247, 470 ± 184, 435 ± 154 ng/mL, respectively; P = .38). Correlations with body weight were not observed.

Conclusions and Clinical Importance

Insulin‐like growth factor‐1 might not be influenced by changes of body weight in healthy cats, possibly suggesting that the latter is unimportant when interpreting IGF‐1 results in this species.

Acromegaly in dogs and cats

Acromegaly is an endocrine disease that leads to elevated production and secretion of growth hormone (GH). It can occur in adult and aged cats and is usually associated with neoplasms, such as functional pituitary macroadenoma of somatotropic cells. In dogs it is usually related to an increase in serum progesterone that induces production of GH by the mammary glands. The main clinical signs are related to insulin resistance and the anabolic effect induced by GH: polyuria, polydipsia, polyphagia, increased tissue growth, weight gain, prognathism, and other changes. The condition can be diagnosed from clinical signals and imaging associated to measurement of serum concentrations of GH and insulin-like growth factor 1 (IGF-1, also known as somatomedin C). The main therapeutic modalities are radiotherapy, hypophysectomy, and several drugs such as somatostatin analogs, dopaminergic agonists and GH receptor antagonists. The present review aims to provide a relevant animal model of acromegaly with an update on the therapeutic approach that may help clinicians to consider the GH axis-IGF-1 system, its pathogenesis and the clinical signs induced by this hormonal disorder.

Evaluation of hypophysectomy for treatment of hypersomatotropism in 25 cats

BACKGROUND

Successful treatment of cats with hypersomatotropism by transsphenoidal hypophysectomy is described in small numbers of cats.

OBJECTIVES

To describe the endocrine profile, survival, and remission rates of hypersomatotropism and diabetes mellitus in a cohort of cats with hypersomatotropism that underwent hypophysectomy between 2008 and 2020.

ANIMALS

Twenty-five client-owned cats with spontaneous hypersomatotropism.

METHODS

Retrospective study. Diagnosis of hypersomatotropism was based on clinical signs, plasma insulin-like growth factor-1 (IGF-1) concentration, and imaging of the pituitary gland. Growth hormone (GH) and IGF-1 concentrations were measured repeatedly after surgery. Survival times were calculated based on follow-up information from owners and referring veterinarians.

RESULTS

Median postoperative hospital stay was 7 days (range, 3-18 days). One cat died within 4 weeks of surgery. Median plasma GH concentration decreased significantly from 51.0 ng/mL (range, 5.0-101.0 ng/mL) before surgery to 3.8 ng/mL (range, 0.6-13.0 ng/mL) at 5 hours after surgery. Remission of hypersomatotropism, defined as normalization of plasma IGF-1 concentration, occurred in 23/24 cats (median, 34 ng/mL; range, 14-240 ng/mL) and 22/24 cats entered diabetic remission. Median survival time was 1347 days (95% confidence interval, 900-1794 days; range, 11-3180 days) and the overall 1-, 2-, and 3-year all-cause survival rates were 76%, 76%, and 52%, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study shows the beneficial outcome of hypophysectomy in cats with hypersomatotropism, marked by low death rate and a high percentage of diabetic remission and definitive cure.

Effect of insulin treatment on circulating insulin-like growth factor I and IGF-binding proteins in cats with diabetes mellitus

BACKGROUND

Insulin-like growth factor-I (IGF-I) is used to screen for acromegaly in diabetic cats. In humans, most circulating IGF-I forms ternary complexes (TC) with IGF-binding protein (IGFBP-3) and an acid-labile subunit. Compared to humans, the amount of TC in cats is more variable. Insulin-like growth factor-I concentrations are reported to increase during insulin treatment, more rapidly in cats achieving remission.

OBJECTIVES

To investigate (i) factors associated with circulating IGF-I concentrations, including IGFBP-profiles (ii) effect of insulin treatment on IGF-I concentrations and (iii) IGF-I as prognostic marker of diabetes mellitus remission.

ANIMALS

Thirty-one privately owned diabetic cats of which 24 were followed 1 year, and 13 healthy cats.

METHODS

Prospective study. Serum insulin, IGF-I, glucose, and fructosamine concentrations were measured. IGF-binding forms were determined by chromatography in 14 diabetic and 13 healthy cats; and IGF-I, IGF-II, IGFBP-3, and IGFBP-5 by mass spectrometry in 3 cats achieving remission.

RESULTS

Insulin-like growth factor-I median (interquartile range) before start of insulin treatment was 300 (160-556) ng/mL. Insulin-like growth factor-I was positively associated with TC (P < .0001) and endogenous insulin (P = .005) and negatively associated with fructosamine (P < .0001). Median IGF-I was higher 2-4 weeks after start of insulin treatment compared with baseline (300 versus 670 ng/mL, P = .0001) and predicted future remission (P = .046). In cats that went into remission, the amount of TC and IGFBP-3 increased, suggesting increase in IGF-I is dependent on TC formation.

CONCLUSIONS

Insulin treatment should be accounted for when interpreting IGF-I in diabetic cats. Insulin-like growth factor-I 2-4 weeks after initiation of insulin treatment shows promise as prognostic marker for remission in diabetic cats.

Evaluation of serum insulin-like growth factor-1 and 26S proteasome concentrations in healthy dogs and dogs with chronic diseases depending on body condition score

In patients suffering from chronic diseases, the objective assessment of metabolic states could be of interest for disease prognosis and therapeutic options. Therefore, the aim of this study was to assess insulin-like growth factor-1 (IGF-1) and 26S proteasome (26SP) in healthy dogs and dogs suffering from chronic diseases depending on their body condition score (BCS) and to examine their potential for objective assessment of anabolic and catabolic states. Serum concentrations of IGF-1, an anabolic hormone, and 26SP, a multiprotein complex which is part of the ubiquitin-proteasome pathway, by which the majority of endogenous proteins including the muscle proteins are degraded, were measured in 21 healthy dogs and 20 dogs with chronic diseases by canine ELISA. The concentrations of IGF-1, 26SP and their ratio (IGF-1/26SP) were set in relationship to the BCS of the dogs. When examining healthy and chronically diseased dogs separately, a positive correlation between IGF-1 and the BCS was observed in the healthy group and a negative correlation between 26SP and the BCS was noted in dogs with chronic diseases. Further, dogs suffering from chronic diseases showed higher 26SP concentrations and lower values for IGF-1/26SP than the healthy dogs. Overall, we detected a negative correlation between 26SP and the BCS and a positive correlation between IGF-1/26SP and the BCS. The results of our study indicate usability of IGF-1 for description of anabolic states, while 26SP could be useful for detection and description of catabolic states. Finally, the ratio IGF-1/26SP seems to be promising for assessment of metabolic states.

Evaluation of insulin-like growth factor-1, total thyroxine, feline pancreas-specific lipase and urinary corticoid-to-creatinine ratio in cats with diabetes mellitus in Switzerland and the Netherlands

Objectives The aim of the study was to evaluate circulating insulin-like growth factor-1 (IGF-1), feline pancreas-specific lipase (fPLI) and total thyroxine (TT4) concentrations and urinary corticoid-to-creatinine ratio (UCCR) as indicators for the prevalence of acromegaly, pancreatitis, hyperthyroidism and hypercortisolism in cats with diabetes mellitus. Methods Blood and urine samples were collected from diabetic cats treated in primary care clinics in Switzerland and the Netherlands. Standardised questionnaires and physical examination forms provided clinical information from owners and veterinarians. Laboratory testing included serum biochemistry profile analysis and measurement of circulating fructosamine, IGF-1, fPLI, and TT4 concentrations and UCCR. CT of the pituitary gland was performed using a multidetector computed tomography scanner. Results Blood samples were available from 215 cats and urine samples were collected at home from 117 cats. Age ranged from 2-18 years (median 12 years) and body weight from 2.7-12.3 kg (median 5.5 kg). Sixty-five percent of the cats were castrated male and 35% were female (33% spayed); 82% were domestic shorthair cats. Eighty percent of cats received a porcine insulin zinc suspension, 19.5% insulin glargine and 0.5% a human neutral protamine hagedorn insulin. Thirty-six of 202 (17.8%) cats had IGF-1 concentrations >1000 ng/ml. Serum fPLI, and TT4 concentrations and UCCR were increased in 86/196 (43.9%), 9/201 (4.5%) and 18/117 cats (15.3%), respectively. Prevalence did not differ between countries. Conclusions Hyperthyroidism is rare, whereas increased fPLI concentration, possibly reflecting pancreatitis, is common in diabetic cats. The high UCCR may reflect activation of the hypothalamus-pituitary-adrenal axis, which also occurs in diabetic humans. The percentage of cats with increased IGF-1 was high but lower than reported in recent studies.

Acromegaly in a non-diabetic cat

Case summary

A 14-year-old, neutered male European shorthair cat was evaluated for a routine health check. The owner did not report any clinical signs except for respiratory stridor. On physical examination the main findings were broad facial features and increased interdental spaces. On haematology, a mild, non-regenerative anaemia was detected, whereas the serum biochemistry profile and urinalysis were unremarkable. The serum glucose concentration was within the reference interval. Serum insulin-like growth factor-1 concentration was markedly elevated (>1600 ng/ml). The basal serum growth hormone concentration was elevated and decreased only mildly after somatostatin administration. Basal serum insulin concentration was high, and the insulin concentration increased considerably after glucose loading, consistent with insulin resistance. CT scanning of the skull showed an enlarged pituitary gland and increased skull bone thickness. The final diagnosis was acromegaly.

Relevance and novel information

These findings demonstrate that acromegaly should be pursued and suspected in cats other than those with diabetes mellitus.

Evaluation and diagnostic potential of serum ghrelin in feline hypersomatotropism and diabetes mellitus

Background

Ghrelin is a growth hormone secretagogue. It is a potent regulator of energy homeostasis. Ghrelin concentration is down‐regulated in humans with hypersomatotropism (HS) and increases after successful treatment. Additionally, ghrelin secretion seems impaired in human diabetes mellitus (DM).

Hypothesis

Serum ghrelin concentration is down‐regulated in cats with HS‐induced DM (HSDM) compared to healthy control cats or cats with DM unrelated to HS and increases after radiotherapy.

Animals

Cats with DM (n = 20) and with HSDM (n = 32), 13 of which underwent radiotherapy (RT‐group); age‐matched controls (n = 20).

Methods

Retrospective cross‐sectional study. Analytical performance of a serum total ghrelin ELISA was assessed and validated for use in cats. Differences in serum ghrelin, fructosamine, IGF‐1 and insulin were evaluated.

Results

Ghrelin was significantly higher (P < .001) in control cats (mean ± SD: 12.9 ± 6.8 ng/mL) compared to HSDM‐ (7.9 ± 3.3 ng/mL) and DM‐cats (6.7 ± 2.3 ng/mL), although not different between the HSDM‐ and DM‐cats. After RT ghrelin increased significantly (P = .003) in HSDM‐cats undergoing RT (from 6.6 ± 1.9 ng/mL to 9.0 ± 2.2 ng/mL) and the after RT ghrelin concentrations of HSDM cats were no longer significantly different from the serum ghrelin concentration of control cats. Serum IGF‐1 did not significantly change in HSDM‐cats after RT, despite significant decreases in fructosamine and insulin dose.

Conclusion and Clinical Importance

Ghrelin appears suppressed in cats with DM and HSDM, although increases after RT in HSDM, suggesting possible presence of a direct or indirect negative feedback system between growth hormone and ghrelin. Serum ghrelin might therefore represent a marker of treatment effect.

Insulin-like growth factor I in cats: validation of an enzyme-linked immunosorbent assay and determination of biologic variation

BACKGROUND

Insulin-like growth factor I (IGF-I) measurements are used in veterinary medicine for diagnosing growth hormone disorders. IGF-I assays are subject to interference by IGF-binding proteins (IGFBP) which may not be efficiently removed by standard extraction methods. Adding excess IGF-II during analysis may improve accuracy.

OBJECTIVES

The purpose of the study was to validate a commercial human IGF-I ELISA which uses excess IGF-II for feline samples and to evaluate biologic variation.

METHODS

Precision was determined by calculating the coefficient of variation (CV). Accuracy was determined by recovery after removal of IGFBP, addition of IGF-I, and linear dilution after the addition of IGFBP. Biologic variation was determined by repeated sampling in 7 cats.

RESULTS

There was interference by IGFBP in the high measuring range, resulting in falsely low IGF-I concentrations. This was overcome by the addition of high concentrations of IGF-II. Untreated serum had a measured/expected ratio of 98-115% compared to serum where IGFBP had been removed. Recovery after the addition of IGF-I was 83-112%. Inter- and intra-assay CVs ranged from 2.4% to 5.0% which is within the minimum acceptance criteria based on biologic variation. The reference interval of IGF-I was wide (90-1207 ng/mL) and there was a significant association between body weight and ln IGF-I (P < .000001).

CONCLUSIONS

This human ELISA is suitable for feline samples, but interfering IGFBP can cause falsely low concentrations. It is recommended to dilute samples such that IGF-I is < 28 ng/mL on the standard curve to grant for sufficient IGF-II for binding of interferent IGFBP.

Studying Cat (Felis catus) Diabetes: Beware of the Acromegalic Imposter

Naturally occurring diabetes mellitus (DM) is common in domestic cats (Felis catus). It has been proposed as a model for human Type 2 DM given many shared features. Small case studies demonstrate feline DM also occurs as a result of insulin resistance due to a somatotrophinoma. The current study estimates the prevalence of hypersomatotropism or acromegaly in the largest cohort of diabetic cats to date, evaluates clinical presentation and ease of recognition. Diabetic cats were screened for hypersomatotropism using serum total insulin-like growth factor-1 (IGF-1; radioimmunoassay), followed by further evaluation of a subset of cases with suggestive IGF-1 (>1000 ng/ml) through pituitary imaging and/ or histopathology. Clinicians indicated pre-test suspicion for hypersomatotropism. In total 1221 diabetic cats were screened; 319 (26.1%) demonstrated a serum IGF-1>1000 ng/ml (95% confidence interval: 23.6–28.6%). Of these cats a subset of 63 (20%) underwent pituitary imaging and 56/63 (89%) had a pituitary tumour on computed tomography; an additional three on magnetic resonance imaging and one on necropsy. These data suggest a positive predictive value of serum IGF-1 for hypersomatotropism of 95% (95% confidence interval: 90–100%), thus suggesting the overall hypersomatotropism prevalence among UK diabetic cats to be 24.8% (95% confidence interval: 21.2–28.6%). Only 24% of clinicians indicated a strong pre-test suspicion; most hypersomatotropism cats did not display typical phenotypical acromegaly signs. The current data suggest hypersomatotropism screening should be considered when studying diabetic cats and opportunities exist for comparative acromegaly research, especially in light of the many detected communalities with the human disease.

Systematic review of feline diabetic remission: separating fact from opinion

It is increasingly recognised that diabetic remission is possible in the cat. This systematic review, following Cochrane Collaboration (CC) guidelines, critically appraises the level of evidence on factors influencing remission rate and factors predicting remission. A systematic online, bibliographic search and reference list examination was conducted. A level of evidence was assigned to each identified article by five internists using the Newcastle-Ottawa Scale for follow-up, cohort, case-series and case-control studies, the CC's risk of bias tool for trials and the Cochrane Effective Practice and Organisation of Care Group risk of bias criteria for before and after trials. Twenty-two studies were included in the review, assessing influence of pharmaceutical intervention (n = 14) and diet (n = 4), as well as diagnostic tests (n = 9) and feline patient characteristics (n = 5) as predictors of remission. The current level of evidence was found to be moderate to poor. Common sources of bias included lack of randomisation and blinding among trials, and many studies were affected by small sample size. Failure to provide criteria for the diagnosis of diabetes, or diabetic remission, and poor control of confounding factors were frequent causes of poor study design. Addressing these factors would significantly strengthen future research and ultimately allow meta-analyses to provide an excellent level of evidence. No single factor predicts remission and successful remission has been documented with a variety of insulin types and protocols. Dietary carbohydrate reduction might be beneficial, but requires further study. A lack of well-designed trials prevents reliable remission rate comparison. Factors associated with remission resemble those in human medicine and support the hypothesis that reversal of glucotoxicity is a major underlying mechanism for feline diabetic remission.

The effect of experimentally induced chronic hyperglycaemia on serum and pancreatic insulin, pancreatic islet IGF-I and plasma and urinary ketones in the domestic cat (Felis felis)

Like in humans, diabetes mellitus is on the rise in cats. Feline diabetes is a suitable model for human type-2 diabetes. We investigated magnitude and timing of insulin suppression with induced hyperglycaemia and its relationship to plasma and urinary ketones and to pancreatic islet insulin. IGF-I is under discussion as a protective mechanism but little is known about its role in diabetes in general and its distinct localisation in feline pancreatic islets in particular. Thirteen healthy, adult cats were allocated to 2 groups and infused with glucose to maintain their blood glucose at a high or moderate concentration for 42 days resulting in insulin secretion suppression. After initial increase, insulin levels declined to baseline but were still detectable in the blood at a very low level after 6 weeks of glucose infusion and then increased after a 3 week recovery period. While IGF-I in healthy cats was primarily located in glucagon cells, in hyperglycaemia-challenge IGF-I was pronounced in the β-cells 3 weeks after ceasation of infusion. Six/8 cats developing glucose toxicity became ketonuric after 3-4 weeks. Gross lipaemia occurred approx 1 week prior to ketonuria. Ketonuric cats required 1-2 weeks of insulin therapy after-infusion until β-cell recovery. In conclusion, ketosis and hyperlipidaemia are likely to occur in diabetic cats with glucose at 30 mmol/L, especially after ≥2 weeks. Three weeks after ceasation of infusions, clinical and morphological recovery occurred. We propose a local protective effect of IGF-I to support survival and insulin production in the hyperglycaemic state and recovery period.

Evaluation of four methods used to measure plasma insulin-like growth factor 1 concentrations in healthy cats and cats with diabetes mellitus or other diseases

OBJECTIVE

To evaluate 4 methods used to measure plasma insulin-like growth factor (IGF) 1 concentrations in healthy cats and cats with diabetes mellitus or other diseases.

ANIMALS

39 healthy cats, 7 cats with diabetes mellitus, and 33 cats with other diseases.

PROCEDURES

4 assays preceded by different sample preparation methods were evaluated, including acid chromatography followed by radioimmunoassay (AC-RIA), acid-ethanol extraction followed by immunoradiometry assay (AEE-IRMA), acidification followed by immunochemiluminescence assay (A-ICMA), and IGF-2 excess followed by RIA (IE-RIA). Validation of the methods included determination of precision, accuracy, and recovery. The concentration of IGF-1 was measured with all methods, and results were compared among cat groups.

RESULTS

The intra-assay coefficient of variation was < 10% for AC-RIA, A-ICMA, and AEE-IRMA and 14% to 22% for IE-RIA. The linearity of dilution was close to 1 for each method. Recovery rates ranged from 69% to 119%. Five healthy cats had IGF-1 concentrations > 1,000 ng/mL with the AEE-IRMA, but < 1,000 ng/mL with the other methods. Compared with healthy cats, hyperthyroid cats had significantly higher concentrations of IGF-1 with the A-ICMA method, but lower concentrations with the IE-RIA method. Cats with lymphoma had lower IGF-1 concentrations than did healthy cats regardless of the method used.

CONCLUSIONS AND CLINICAL RELEVANCE

Differences in the methodologies of assays for IGF-1 may explain, at least in part, the conflicting results previously reported in diabetic cats. Disorders such as hyperthyroidism and lymphoma affected IGF-1 concentrations, making interpretation of results more difficult if these conditions are present in cats with diabetes mellitus.

Effects of weight loss in obese cats on biochemical analytes related to inflammation and glucose homeostasis

The aim of the current study was to measure circulating metabolic and inflammation-related biochemical analytes in obese cats before and after weight loss. Thirty-seven overweight neutered cats were studied, median body weight 6.85 kg (range, 4.70 to 10.30 kg), representing a range of ages and both sexes. An individualized weight-loss program was devised for each cat and monitored until completion. Body fat mass was determined by dual-energy x-ray absorptiometry, whereas plasma concentrations of acute-phase proteins (APPs; eg, haptoglobin and serum amyloid A), hormones (eg, insulin, IGF-1, and adiponectin), and enzymes (eg, butyrylcholinesterase and paraoxonase type 1 [PON-1]) associated with inflammation and metabolic compounds (eg, glucose) were also measured. No significant changes were found in APPs after weight loss (P > 0.3), but significant increases in plasma adiponectin (P = 0.021) and IGF-1 (P = 0.036) were seen, whereas insulin (P < 0.001) and homeostasis model assessment (P = 0.005) decreased significantly. Plasma concentrations before weight loss of PON-1 (P = 0.004), adiponectin (P = 0.02), and IGF-1 (P = 0.048) were less in cats that failed to complete weight loss than cats that were successful, whereas glucose concentration was greater. Finally, multivariable linear regression analysis showed that lean tissue loss during weight management was associated with percentage weight loss (greater weight loss, greater lean tissue loss; R = 0.71, P < 0.001) and plasma adiponectin concentration before weight loss (lesser adiponectin, more lean tissue loss; R = -0.52, P = 0.023). In conclusion, various metabolic abnormalities occur in feline obesity, and these can be linked to outcomes of weight-loss programs. The changes that occur with weight loss suggest an improved metabolic status.

Evaluation of IGF-I levels and serum protein profiles of diabetic cats and dogs

In this study, we measured the insulin-like growth factor (IGF)-I levels and evaluated the serum protein profiles of diabetic, insulin-treated, and healthy cats and dogs. The total IGF-I concentrations were 33.74 ± 3.4 ng/mL for normal, 25.8 ± 4.5 ng/mL for diabetic, and 180.4 ± 31.4 ng/mL for insulin-treated cats. IGF-I concentrations were 46.4 ± 6.6 ng/mL for normal, 25.1 ± 4.1 ng/mL for diabetic, and 303.0 ± 61.3 ng/mL for insulin-treated dogs. Total serum protein profiles were analyzed by SDS-PAGE. Fourteen bands ranging from 25 to 240 kDa in size were observed for cats, and 17 bands ranging from 25 to 289 kDa were observed for dogs. The densities of the bands differed among control, diabetic, and insulin-treated animals. In conclusion, we found that serum protein profiles and IGF-I concentrations were altered in both diabetic and insulin-treated animals. When judiciously interpreted in the light of other clinical and laboratory data, the techniques used in our study provide a valuable modality for measuring the severity of diabetes mellitus in dogs and cats.

Exogenous insulin treatment after hypofractionated radiotherapy in cats with diabetes mellitus and acromegaly

BACKGROUND

The optimal treatment for feline acromegaly has yet to be established. Surgical and medical therapies are minimally effective although radiotherapy might have greater efficacy. The purpose of this study was to review the response and outcome of cats with acromegaly and insulin-resistant diabetes mellitus (DM) to radiotherapy.

HYPOTHESES

That radiotherapy improves glycemic control in cats with acromegaly and that improved glycemic control is due to remission of clinical acromegaly; demonstrated by a fall in serum insulin-like growth factor-1 (IGF-1) concentrations.

ANIMALS

Fourteen cats with naturally occurring acromegaly.

METHODS

Retrospective case review; records of all cats treated for acromegaly with radiotherapy were reviewed from 1997 to 2008. Cats were selected on the basis of compatible clinical signs, laboratory features, and diagnostic imaging findings. Fourteen cats received radiotherapy, delivered in 10 fractions, 3 times a week to a total dose of 3,700 cGy.

RESULTS

Thirteen of 14 cats had improved diabetic control after radiotherapy. These improvements were sustained for up to 60 months. DM progressed in 2 cats and 1 did not respond. Seven cats responded before the final treatment. Ten cats were euthanized, 1 as a consequence of radiotherapy. In 8 cats in which IGF-1 was measured after treatment, changes in its concentration did not reflect the clinical improvement in glycemic control.

CONCLUSIONS AND CLINICAL IMPORTANCE

Radiotherapy represents an effective treatment for cats with insulin-resistant DM resulting from acromegaly. IGF-1 concentration after treatment does not provide a suitable method by which remission from either acromegaly or insulin-resistant DM may be assessed.

Growth hormone excess and the effect of octreotide in cats with diabetes mellitus

In this prospective study 16 cats with diabetes mellitus were examined for concurrent acromegaly by measuring plasma growth hormone (GH) and insulin-like growth factor-I concentrations, and magnetic resonance imaging (MRI) of the pituitary fossa. Additionally, the effects of octreotide administration on the plasma concentrations of glucose, GH, alpha-melanocyte-stimulating hormone (alpha-MSH), adrenocorticotrophic hormone (ACTH), and cortisol were measured. Five cats were diagnosed with hypersomatotropism. The pituitary was enlarged in these 5 cats and in 2 other cats. Six cats that required a maximum lente insulin dosage >or=1.5 IU/kg body weight per injection had pituitary enlargement and 5 of these cats had acromegaly. Plasma concentrations of GH, ACTH, and cortisol decreased significantly after single intravenous administration of the somatostatin analogue octreotide in the acromegalic cats. The effect on GH concentrations was more pronounced in some of the acromegalic cats than in others. In the non-acromegalic cats only ACTH concentrations decreased significantly. In both groups plasma glucose concentrations increased slightly but significantly, whereas alpha-MSH concentrations were not significantly affected. In conclusion, the incidence of hypersomatotropism with concomitant pituitary enlargement appears to be high among diabetic cats with severe insulin resistance. Some of these cats responded to octreotide administration with a pronounced decrease in the plasma GH concentration, which suggests that octreotide administration could be used as a pre-entry test for treatment with somatostatin analogues.

Evaluation of IGF-1 levels in cats with transient and permanent diabetes mellitus

It was investigated if IGF-1 levels in cats which experience diabetic remission (i.e. transient diabetes mellitus) differ from those in cats with permanent disease. Thirteen of 32 diabetic cats showed remission within 16 weeks after initiating insulin therapy, 19 cats continued to need insulin therapy. IGF-1 concentrations were measured before (t(0)), 1-3 (t(1)) and 4-8 (t(2)) weeks after initiating insulin therapy. No difference in IGF-1 levels was found between cats with transient and permanent diabetes at any point in time. In both groups of cats IGF-1 concentrations were significantly lower compared to those of controls before insulin administration. After starting insulin therapy IGF-1 increased significantly in both groups. In cats with transient diabetes IGF-1 levels were not different from controls already at t(1), whereas in cats with permanent diabetes it took until t(2). Although IGF-1 levels seem to normalize faster in cats with transient diabetes mellitus, measurement is not helpful to predict the course of the disease.