Could the performance of oral glucose tolerance test contribute to the brain health-focused care in multiple sclerosis?

Association between insulin resistance and multiple sclerosis: a systematic review and meta-analysis

There is increasing evidence of metabolic perturbations in multiple sclerosis (MS) patients, and insulin is an important parameter that has controversial effects on neurological disease. Therefore, this systematic review and meta-analysis study aimed to explore the association between insulin resistance (IR) and MS as well as insulin levels and MS. Three electronic databases, including Medline, Scopus, and the Web of Science, were examined up to 26 May 2023 for observational studies. Two independent reviewers assessed the studies according to a pre-specified protocol. Random-effects model using a Restricted-maximum Likelihood (REML) estimator was used to meta-analyze the association between IR [assessed by Homeostatic Model Assessment (HOMA-IR)], insulin and MS. Eighteen datasets from 2012 to 2022 were included in this meta-analysis. The standardized mean difference (SMD) for comparison IR and insulin between MS and healthy control group as outcomes 1 and 2 were 0.78 and 0.72 respectively. Furthermore, for outcome 1, we observed a greater effect size in studies that recruited different types of MS (Mix) (SMD: 1.09) than in those that included only relapsing-remitting MS (RRMS) (SMD: 0.59). The meta-analysis revealed a significant association between IR, insulin and MS, with stronger associations in studies that recruited mixed patients. However, high heterogeneity has been observed in the present study. Therefore, more studies are needed to confirm the association between these parameters and MS.

Near-Infrared Spectroscopy: A Free-Living Neuroscience Tool to Better Understand Diabetes and Obesity

The human brain is the least accessible of all organs and attempts to study it in vivo rely predominantly on neuroimaging. Functional near-infrared spectroscopy (fNIRS) allows for the study of cortical neural activity in a non-invasive manner that may resemble free-living conditions. Moreover, compared to other neuroimaging tools, fNIRS is less expensive, it does not require the use of ionizing radiation, and can be applied to all study populations (patients suffering from claustrophobia, or neonates). In this narrative review, we provide an overview of the available research performed using fNIRS in patients with diabetes and obesity. The few studies conducted to date have presented controversial results regarding patients with diabetes, some reporting a greater hemodynamic response and others reporting a reduced hemodynamic response compared to the controls, with an unclear distinction between types 1 and 2. Subjects with obesity or a binge eating disorder have reduced prefrontal activation in response to inhibitory food or non-food stimuli; however, following an intervention, such as cognitive treatment, prefrontal activation is restored. Moreover, we discuss the potential of future applications of fNIRS for a better understanding of cortical neural activity in the context of metabolic disorders.

Insulin resistance is associated with cognitive dysfunction in multiple sclerosis patients: A cross-sectional study

Multiple sclerosis (MS) is a progressive inflammatory neurodegenerative disease of the nervous system accompanied by demyelination. MS-associated cognitive impairments mainly involve recent memory, information processing speed, stable memory, and executive function. Moreover, MS is associated with impaired glucose and insulin metabolism, which can exacerbate cognitive decline. The present study aimed to compare the cognitive status of MS patients with and without insulin resistance. In this cross-sectional study, 74 relapsing-remitting multiple sclerosis diagnosed patients were enrolled. Indicators of insulin resistance, including fasting blood glucose, insulin level, and homeostatic model assessment of insulin resistance (HOMA-IR) index, were measured. They were then divided into two groups based on the results of the HOMA-IR index. Cognition status was evaluated by the minimal assessment of cognitive function in multiple sclerosis battery. The prevalence of insulin resistance was 37.8%, and the prevalence of cognitive decline was estimated to be 67.56%. Mean scores of the California verbal learning test (CVLT), CVLT delayed free recall, controlled oral word association test, and judgment of line orientation tests were significantly lower in MS patients with insulin resistance than without. In addition, a negative correlation was demonstrated between the results of the CVLT, CVLT delayed free recall, controlled oral word association test, judgment of line orientation tests, brief visuospatial memory test, and Delis-Kaplan executive function system sorting tests and fasting insulin levels. Greater verbal memory and spatial comprehension impairments were observed in MS patients with insulin resistance.