Intravenous Tissue Plasminogen Activator in Patients With Stroke Increases the Bioavailability of Insulin-Like Growth Factor-1

Preclinical and clinical evidence of IGF-1 as a prognostic marker and acute intervention with ischemic stroke

Ischemic strokes are highly prevalent in the elderly population and are a leading cause of mortality and morbidity worldwide. The risk of ischemic stroke increases in advanced age, corresponding with a noted decrease in circulating insulin growth factor-1 (IGF-1). IGF-1 is a known neuroprotectant involved in embryonic development, neurogenesis, neurotransmission, cognition, and lifespan. Clinically, several studies have shown that reduced levels of IGF-1 correlate with increased mortality rate, poorer functional outcomes, and increased morbidities following an ischemic stroke. In animal models of ischemia, administering exogenous IGF-1 using various routes of administration (intranasal, intravenous, subcutaneous, or topical) at various time points prior to and following insult attenuates neurological damage and accompanying behavioral changes caused by ischemia. However, there are some contrasting findings in select clinical and preclinical studies. This review discusses the role of IGF-1 as a determinant factor of ischemic stroke outcomes, both within the clinical settings and preclinical animal models. Furthermore, the review provides insight on the role of IGF-1 in mechanisms and cellular processes that contribute to stroke damage.

The relation between insulin-like growth factor 1 levels and risk of depression in ischemic stroke

BACKGROUND

The aim of this study is to evaluate whether lower serum levels of insulin-like growth factor 1 (IGF-1) in the acute phase of ischemic stroke are associated with higher risk of post-stroke depression (PSD) over a 1-year period.

METHODS

The subjects were first-ever acute ischemic stroke (AIS) patients who were hospitalized from July 1, 2014 to August 31, 2015. The study also included 120 age-matched and sex-matched healthy controls from the same geographical area. Fasting blood samples were collected within 24 hours of admission for IGF-I measurement. Neurological and neuropsychological evaluations were conducted at a 1-year follow-up.

RESULTS

Two-hundred twenty-five patients were observed for a 1-year follow-up, and 74 of these patients (32.9%, 95%CI: 26.8%-39.0%) were diagnosed with PSD. The depression distribution across the IGF-1 quartiles ranged between 61.4% (first quartile) and 8.9% (fourth quartile). In a multivariate model using the first quartiles of the IGF-1 versus quartiles 2 through 4, together with the significant clinical variables, the marker displayed prognostic information, and the odds ratio (OR) for first quartile was 3.35 [95% CI, 1.88-6.79; P = 0.001].

CONCLUSION

The data showed that low serum IGF-1 levels at admission are associated with a high risk of developing PSD, suggesting that these alterations might be involved in the pathophysiology of depression symptoms in stroke patients.

The role of neuroendocrine pathways in prognosis after stroke

A number of neuroendocrine changes have been described after stroke, which may serve adaptive or deleterious functions. The neuroendocrine changes include activation of the hypothalamo-pituitary-adrenal axis, sympathetic nervous system and alterations of several hormonal levels. Alterations of the HPA axis, increased catecholamines, natriuretic peptides and, decreased melatonin and IGF-1 levels are associated with poor post-stroke outcome, although there is no definitive proof of causality. Therefore, it remains to be established whether alteration of neuroendocrine responses could be used as a potential therapeutic target to improve stroke outcome. This article gives an overview of the major neuroendocrine pathways altered by stroke and highlights their potential for clinical use and further neurotherapeutic development by summarizing the evidence for their association with stroke outcome including functional outcome, post-stroke infection, delirium, depression and stroke-related myocardial injury.

Insulin-like growth factor I serum levels influence ischemic stroke outcome

BACKGROUND AND PURPOSE

Insulin-like growth factor I (IGF-I) is neuroprotective in animal models of stroke. We investigated whether serum IGF-I levels in patients with acute ischemic stroke influence stroke severity and outcome.

METHODS

Concentrations of IGF-I and IGF binding protein 3 were measured in serum samples obtained within 6 hours after stroke onset from 255 patients who took part in the placebo arm of the United States and Canadian Lubeluzole in Acute Ischemic Stroke Study. Stroke severity was assessed with the National Institutes of Health Stroke Scale. Multivariate analysis was performed to assess the overall shift in modified Rankin Scale score and changes in the National Institutes of Health Stroke Scale score at 3 months. Survival curves were plotted using the Kaplan-Meier method, and the Cox proportional hazard model was used for multivariate analysis to investigate factors influencing survival.

RESULTS

After controlling for statistically relevant risk factors, subjects with high IGF-I levels or IGF-I/IGF binding protein 3 ratios had a better neurological and functional outcome at 3 months. Baseline stroke severity was not different between high and low IGF-I groups. In contrast to the low IGF-I group, neurological symptoms gradually improved from Day 3 in the high IGF-I group.

CONCLUSIONS

Our results suggest that high serum IGF-I levels just after ischemic stroke onset are associated with neurological recovery and a better functional outcome.

Changes in the expression of insulin-like growth factor 1 variants in the postnatal brain development and in neonatal hypoxia-ischaemia

Insulin-like growth factor-1 (IGF-1) is a multifunctional peptide of which numerous isoforms exist. The predominant form, IGF-1Ea is involved in physiological processes while IGF-1Ec (mechano-growth factor, MGF) is expressed in response to a different set of stimuli. We have identified specific changes in the expression patterns of these IGF-1 variants in brain development in normal rats and following neonatal hypoxia-ischaemia (HI). Both IGF-1Ea and IGF-1Ec are expressed during normal postnatal brain development, albeit with highly specific temporal distributions. In contrast, HI produced increased and prolonged expression of the IGF-1Ec isoform only. Importantly, hypoxia alone stimulated the expression of IGF-1Ec as well. Thus, IGF-1Ec may play a role in HI pathology. Neonatal hypoxia-ischaemia occurs in approximately 1:4000-1:10,000 newborns and causes neurological deficits in approximately 75% of those affected. Unfortunately, no specific treatment is available. IGF-1 is known to have neuroprotective activity and its IGF-1Ec variant appears to be an endogenous protective factor in hypoxia-ischaemia. Therefore, IGF-1Ec could potentially be developed into a therapeutic modality for the attenuation or prevention of neuronal damage in this and related disorders.

Insulin-like growth factor I: a potential neuroprotective compound for the treatment of acute ischemic stroke?

BACKGROUND AND PURPOSE

Insulin-like growth factor I (IGF-I) exerts neuroprotective effects in both white and gray matter under different detrimental conditions. The purpose of this review is to collect the evidence whether IGF-I is a candidate neuroprotective drug in patients with acute ischemic stroke.

RESULTS

IGF-I was found to be neuroprotective in animal models of focal brain ischemia when given >or=2 hours after the insult. Different routes of administration (eg, cerebroventricular, intravenous, and intranasal) were found to be effective. In addition to inhibition of apoptosis and reduction of the infarct volume, IGF-I also improved neurological outcome. Furthermore, there are strong indications that IGF-I can also stimulate the regeneration of neural tissue.

CONCLUSIONS

Additional studies are required to reveal the neuroprotective mechanisms of IGF-I in detail and to elucidate the role of IGF-binding proteins. Preclinical studies in relevant animal models for studying stroke (ie, hypertensive, diabetic, or aged animals) should be done testing different doses and routes of IGF-I administration and different combinations of IGF-I and IGF-binding proteins.

A role for plasmin in platelet aggregation: differential regulation of IGF release from IGF-IGFBP complexes?

OBJECTIVES

To determine if plasmin differentially augments platelet aggregation through variable efficiencies of IGF-IGFBP complex cleavage.

METHODS

We utilized ADP-triggered platelet aggregation assays to test the effects of IGF-I versus IGF-II in complex with IGFBP-2 or IGFBP-3 upon the efficiency of plasmin (a known IGFBP protease) as a pro-aggregatory stimulus. In vitro proteolysis assays were performed as controls.

RESULTS

We found that IGF-I complexes augmented platelet-mediated aggregation whereas IGF-II either had no effect (IGFBP-2) or inhibited platelet-mediated aggregation (IGFBP-3). In vitro proteolysis assays of IGFBP-2 and IGFBP-3 using plasmin revealed that three of the four aggregation findings were explained by the disparate efficiencies of IGFBP proteolysis associated with each IGF. Only IGF-II-IGFBP-2 complex resulted in a finding that could not be explained by the concept of differential regulation of plasmin's proteolysis efficiency by the two IGF ligands.

CONCLUSIONS

Our findings demonstrate that the plasmin can differentially modulate platelet aggregation in response to intrinsic heterogeneities within the IGF axis.

Neuroprotective effects of short peptides derived from the Insulin-like growth factor 1

Insulin-like growth factor I (IGF-1) is a peptide synthesized in response to growth hormone stimulation. While most of the circulating IGF-1 comes from the liver, it can also be produced in other tissues and both its expression and processing undergo tissue-specific regulation. The predominant form, IGF-1Ea is a circulating factor while two others, IGF-1Eb and IGF-1Ec (MGF), are mostly expressed in different tissues or in response to various stimuli and show some preferences with respect to the signal transduction pathways they activate. In skeletal muscle specific forms of IGF-1 play a role in development and growth and in addition to these physiological roles IGF-1 functions in the damaged muscle. IGF-1 is also important for the developing and adult brain and can reduce neuronal death caused by different types of injuries. Like many other peptide hormones IGF-1 originates from a precursor pro-hormone that undergoes extensive post-translational modifications. Processing liberates the mature peptide, which acts via the specific IGF-1 receptor but additional short peptides can arise from both N- and C-termini of various IGF-1 isoforms. These derivatives function as autonomous biologically active peptides and extremely potent neuroprotective agents. Their biological effects are independent of the activation of the IGF-1 receptor. Unfortunately, little is known about their mechanism(s) of action. Likewise, the existence of the endogenous production and wider biological effects of these short peptides are uncertain. However, considering the difference in the modes of action it might be possible to dissociate the unwanted and potentially dangerous mitogenic activity of the full-length IGF-1 exerted via its receptor from the neuroprotective effects of short derivatives mediated through different pathways. Such small molecules show good penetration through the blood brain barrier, can be inexpensively manufactured and modified to increase their stability. Therefore, they are good candidates for development into a neuroprotective therapeutic modality.