Measurements of insulin resistance in hypertension: where are we now?

Insulin resistance and type 2 diabetes in children

Type 2 diabetes (T2D) is an emerging health risk in obese children and adolescents. Both environmental (lack of physical activity, excess nutritional intake, sedentary lifestyle) and genetic factors contribute to this global epidemic. The growing prevalence of T2D in youth is also associated with a consistently increased incidence of metabolic and cardiovascular complications. Insulin resistance (IR), i.e., whole-body decreased glucose uptake in response to physiological insulin levels, determines impaired glucose homeostasis and it is recognized as cardinal trigger of T2D and cardiovascular disease in both adults and children. In particular, IR and beta-cell dysfunction lead to the persistent hyperglycemia which characterizes T2D. Indeed, both pathological states influence each other and presumably play a crucial, synergistic role in the pathogenesis of T2D, although the precise mechanisms are not completely understood. However, beta-cell dysfunction and IR induce impaired glucose metabolism, thus leading to the progression to T2D. Therefore, understanding the mechanisms correlated with the decline of beta-cell function and IR is crucial in order to control, prevent, and treat T2D in youth. This review focuses on the current knowledge regarding IR and T2D in children and adolescents and showcases interesting opportunities and stimulating challenges for the development of new preventative approaches and therapeutic strategies for young patients with T2D.

Insulin Resistance in Children

Insulin resistance (IR) is a pathological condition strongly associated with obesity. However, corticosteroids or growth hormone therapy and genetic diseases may affect insulin sensitivity lifelong. In obese children and adolescents of any age there is an evident association between IR and an increased prevalence of type 2 diabetes (T2D) and other elements contributing to the metabolic syndrome, leading to a higher cardiovascular risk. Therefore, early diagnosis and interventions in the attempt to prevent T2D when glycemia values are still normal is fundamental. The gold standard technique used to evaluate IR is the hyperinsulinemic euglycemic clamp, however it is costly and difficult to perform in clinical and research sets. Therefore, several surrogate markers have been proposed. Although the treatment of insulin resistance in children is firstly targeted to lifestyle interventions, in selected cases the integration of a pharmacological intervention might be taken into consideration. The aim of this review is to present the current knowledge on IR in children, starting with an outline of the recent evidences about the congenital forms of deficiency in insulin functioning and therefore focusing on the physiopathology of IR, its appropriate measurement, consequences, treatment options and prevention strategies.

High Levels of C-Reactive Protein Are Positively Associated with Isolated Postchallenge Hyperglycemia in Postmenopausal Women

BACKGROUND

Isolated postchallenge hyperglycemia (IPH) is an early form of type 2 diabetes with fasting glucose <126 mg/dL and 2-hr postchallenge glucose ≥200 mg/dL. The purpose of this study was to explore the relationships of high-sensitivity C-reactive protein (hsCRP) with IPH.

METHODS

We recruited 476 naturally postmenopausal women without a history of diabetes mellitus for the study. Fasting blood samples were collected for the measurements of hsCRP and biochemistry. All participants received a 75 g oral glucose tolerance test to examine if they had IPH. The relative contributions of body mass index (BMI) and homeostasis model assessment of insulin resistance (HOMA-IR) to the association of hsCRP with IPH were evaluated by logistic regression.

RESULTS

There was an increasing trend in prevalence of IPH with increasing quartiles of hsCRP (2.9%, 3.6%, 5.9%, and 7.6% in quartile 1-4, respectively) (P = 0.001). BMI and HOMA-IR were the most important determinants of hsCRP in this cohort. We observed a significant and positive association between high hsCRP levels and IPH in our subjects. Compared with subjects in the lowest quartile group, individuals with high levels of hsCRP (the 3rd and the 4th quartiles) were 2-2.5 times more likely associated with IPH, before and after adjustments for BMI and HOMA-IR values (all P < 0.05).

CONCLUSION

Our results demonstrated that chronic inflammation, measured by elevated serum hsCRP levels, was positively associated with IPH in postmenopausal women. This finding was independent of obesity and insulin resistance.

Prehypertension is associated with insulin resistance

BACKGROUND

Prehypertension, a new category of blood pressure (BP) classification introduced by The Seven Report of the Joint National Commission (JNC-7) on High BP for individuals with systolic BP in the range of 120-139 mmHg or diastolic BP between 80 and 89 mmHg, is a strong predictor for the development of hypertension. Insulin resistance (IR) has been proposed to be a key feature of metabolic abnormalities of hypertension and may precede the elevation of BP.

AIM

The purpose of the study is to evaluate whether prehypertension is associated with IR.

DESIGN

This is a cross-sectional study.

METHODS

Anthropometric and BP measurements were performed in 83 prehypertensive subjects and 192 normotensives. All subjects received a 75-g oral glucose tolerance test (OGTT) for the measurements of IR.

RESULTS

The prehypertensive subjects were more obese and had higher levels of fasting triglycerides and 2-h insulin than the normotensives. The subjects with prehypertension were more insulin resistant than the counterparts, indicated by lower insulin sensitivity index, ISI(0,120), values. While there was no difference between the two groups in insulin response of OGTT after adjustments for confounders, the prehypertension group maintained significant between-group differences in glucose response even when the incremental insulin levels were added to covariates for adjustments.

DISCUSSION

Our data show that prehypertension is associated with IR. The subjects with prehypertension have clinical characteristics of the IR syndrome. It seems that the prehypertension group cannot handle oral glucose challenge as well as the normotension, probably a consequence of IR in prehypertension.

HOMA-estimated insulin resistance is associated with hypertension in Iranian diabetic and non-diabetic subjects

The relationship between insulin resistance (IR) and essential hypertension (HTN) is controversial. The aim of this study was to determine the association of IR estimated by homeostasis model assessment of insulin resistance (HOMA-IR) and HTN in a large sample of Iranian diabetic and non-diabetic population. A total of 2047 diabetic and non-diabetic individuals with or without HTN, aged 30-75 yrs, who were referred to a university general hospital between November 2004 and April 2007 were included in this study. Demographic data and anthropometric characteristics of participants were recorded. Fasting blood samples were collected, and fasting plasma glucose (FPG), serum creatinine, lipids, insulin, C-peptide and HbA1c were measured. HOMA-IR and HOMA derived Beta-cell function (HOMA-B) were also calculated. Age, sex and waist girth adjusted HOMA-IR values were compared between hypertensive and normotensive subjects. Hypertensive patients had significantly higher HOMA-IR than age-, sex-, and waist girth-adjusted normotensive individuals in both non-diabetic (2.163 +/- 0.08 and 1.75 +/- 0.03, p < 0.001) and diabetic (3.40 +/- 0.10 and 3.07 +/- 0.09, p < 0.05) groups. Multivariate logistic regression analysis showed that after adjustment for age, sex, waist girth, BMI, triglyceride, total cholesterol, FPG, and C-peptide, HOMA-IR was a significant independent predictor of HTN in all subjects (odds ratio = 1.117, CI 95% = 1.026-1.216, p < 0.05) and in diabetic and non-diabetic subjects separately (odds ratio = 1.102, CI 95% = 1.009-1.203, p < 0.05 and odds ratio = 1.328, CI 95% = 1.116-1.580, p < 0.01, respectively). In conclusion, this study showed that IR is associated with HTN in Iranian diabetic and non-diabetic subjects.

Diagnosis of insulin resistance in hypertensive patients by the metabolic syndrome: AHA vs. IDF definitions

BACKGROUND

Subjects with the metabolic syndrome are accompanied by insulin resistance (IR). However, it is not clear how well the newly defined metabolic syndrome identifies IR specifically in hypertensive subjects.

AIMS

The purpose of the study was to evaluate the performance of the metabolic syndrome, defined by the American Heart Association (AHA) and the International Diabetes Federation (IDF) definitions, in identifying IR in hypertension.

METHODS

The analysis is a cross-sectional study. Totally, 228 hypertensive patients and 92 non-diabetic normotensive controls who received insulin suppressive tests for direct evaluation of their insulin sensitivity were included from the Stanford Asia and Pacific Program for Hypertension and IR. McNemar's tests were used to compare sensitivity and specificity of the AHA-defined with the IDF-defined metabolic syndrome in diagnosis of IR.

RESULTS

The sensitivity of the metabolic syndrome for IR in hypertension was 89.7% and the specificity 45.9% by the AHA definition. Using the IDF definition, the sensitivity was 77.6%, and the specificity increased to 63.5%. The diagnostic power of individual components of the syndrome was also modest. The predictive discrimination of wider waist circumference was similar to that of the AHA-defined metabolic syndrome.

CONCLUSIONS

Use of the metabolic syndrome by the AHA definition provided good sensitivity, but low specificity to diagnose IR in hypertension. The IDF definition improved in false-positive rate, but it was still not specific enough to identify IR in hypertension.