Insulin resistance, hyperinsulinemia, and hypertension: an epidemiologic approach

The Association of Excess Body Weight with Risk of ESKD Is Mediated Through Insulin Resistance, Hypertension, and Hyperuricemia

Background

Insulin resistance, hypertension, hyperuricemia, and hypercholesterolemia are hypothesized to be important intermediates in the relationship between excess body weight and CKD risk. However, the magnitude of the total effect of excess body weight on ESKD mediated through these four pathways remains to be quantified.

Methods

We applied a model for analysis of correlated mediators to population-based data from 100,269 Austrian individuals (mean age 46.4 years). Association of body mass index (BMI) was coalesced with ESKD risk into direct association. Indirect associations were mediated through the triglyceride-glucose (TyG) index (as an indicator of insulin resistance), mean arterial pressure (MAP), uric acid (UA), and total cholesterol (TC).

Results

Mean follow-up was 23.1 years with 463 (0.5%) incident ESKD cases. An unhealthy metabolic profile (prevalence 32.4%) was associated with a markedly increased ESKD risk (multivariably adjusted hazard ratio (aHR), 3.57; 95% CI, 2.89 to 4.40), independent of BMI. A 5-kg/m2 higher BMI was associated with a 57% increased ESKD risk (aHRtotal association, 1.57; 1.38 to 1.77). Of this association, 99% (76% to 140%) arose from all mediators jointly; 33% (22% to 49%) through TyG index; 34% (24% to 50%) through MAP; 30% (21% to 45%) through UA; and 2% (−1% to 4%) through TC. The remaining direct association was nonsignificant (aHRdirect association, 1.01; 0.88 to 1.14).

Conclusions

TyG index, MAP, and UA, but not TC, mediate the association of BMI with ESKD in middle-aged adults. Our findings highlight that in addition to weight reduction, the control of metabolic risk factors might be essential in mitigating the adverse effects of BMI on kidney function.

Roles of Insulin Receptor Substrates (IRS) in renal function and renal hemodynamics

We have reported previously that renal hemodynamic abnormalities exist in the prediabetic stage of type II diabetic rats. At this prediabetic stage these rats have hyperinsulinemia, insulin resistance and metabolic syndrome. It is well known that insulin resistance is frequently associated with renal abnormalities, but the mechanism underlying this association has remained speculative. Although insulin is known to modify renal hemodynamics, little is known about the roles of insulin receptor substrates (IRS1, IRS2) in the renal actions of insulin. To address this issue, the effects of insulin on renal function and renal hemodynamics were investigated in C57BL/6 (WT: wild type), insulin receptor substrate 1- knockout (IRS1–/–), and IRS2-knockout (IRS2–/–) mice. IRS2–/–mice had elevated glucose level as expected. 24-h urine collections and serum creatinine revealed that creatinine clearance did not significantly differ between these groups. Albuminuria was found in IRS1–/–and IRS2–/–groups. We examined the effects on the IRS during the administration of Losartan, which is widely used for diabetic nephropathy. After the administration of Losartan the IRS displayed improved renal hemodynamics. Moreover, the subjects were also given Pioglitazone, which improves insulin resistance. Losartan significantly reduced albuminuria in both groups. Pioglitazone also showed similar results. We assessed the autoregulatory responses of the total renal blood flow (RBF), the superficial (SBF) and the deep renal cortical blood flow (DBF) with stepwise reductions of renal perfusion pressure (RPP), which was induced by a manual clamp on the abdominal aorta. During the clamp induced reductions of the RPP by 10 to 20mm HG, RBF, SBF and the DBF fell significantly more in the IRS1 and IRS2 than in the WT mice. Furthermore micropuncture studies showded that compared to the WT tubuloglomerular feedback (TGF) responses of the stop flow pressure (P_sf) were reduced in both the IRS1 -/- and IRS2 -/-. The results of the IRS1 and IRS2 mice displayed the pressence of hemodynamic abnormalities. Losartan and Pioglitazone have shown the potential to improve these abnormalities. In conclusion the results indicate that IRS plays a major role in the stimulation of renal functions and renal hemodynamics in type type II diabetes.

The effect of SGLT-2 inhibitors on blood pressure: a pleiotropic action favoring cardio- and nephroprotection

Strict blood pressure (BP) control in patients with diabetes is associated with reductions in cardiovascular and renal risk. SGLT-2 inhibitors act in the proximal tubule to reduce glucose reabsorption. They also have mild natriuretic and diuretic effects, combining properties of proximal tubule diuretics and osmotic diuretics, which are expected to reduce BP. Several lines of evidence suggests that SGLT-2 inhibitors produce mild but meaningful reductions in BP and also decrease the incidence of renal outcomes, cardiovascular events and mortality. Thus, recent guidelines for type 2 diabetes suggest that among oral agents to use together with metformin, SGLT-2 inhibitors should be preferred in patients at increased cardiovascular risk, kidney disease or heart failure. This review summarizes current literature on the effect of SGLT-2 inhibitors on BP, and its potential relationships with cardio- and nephroprotection.

Role of insulin resistance in Alzheimer's disease

A critical role of insulin resistance (IR) in Alzheimer's disease (AD) includes beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangles (NFTs), failure of synaptic transmission and neuronal degeneration. Aβ is sequentially cleavaged from APP by two proteolytic enzymes: β-secretase and γ-secretase. IR could regulate Aβ production via enhancing β- and γ-secretase activity. Meanwhile, IR induces oxidative stress and inflammation in the brain which contributes to Aβ and tau pathology. Aβ accumulation can enhance IR through Aβ-mediated inflammation and oxidative stress. IR is a possible linking between amyloid plaques and NFTs pathology via oxidative stress and neuroinflammation. Additionally, IR could disrupt acetylcholine activity, and accelerate axon degeneration and failures in axonal transport, and lead to cognitive impairment in AD. Preclinical and clinical studies have supported that insulin could be useful in the treatment of AD. Thus, an effective measure to inhibit IR may be a novel drug target in AD.

Role of ambulatory blood pressure monitoring in hypertension and diabetes

The prevalence of hypertension and diabetes are both rising in the USA and around the globe. The treatment of hypertension in the ambulatory setting begins with proper blood pressure measurement, and often the involvement of home blood pressure monitoring. If the diagnosis of hypertension is confirmed, then education on lifestyle modifications is the foundation to reaching blood pressure goals. If it is unclear, then ambulatory blood pressure monitoring should be performed to properly evaluate daily trends in blood pressure. The National Institute for Health and Clinical excellence (NICE) recommends 24-hour ambulatory blood pressure evaluation in all newly diagnosed patients with hypertension. The much-anticipated JNC 2013, while not likely to endorse this approach, will likely recommend an office goal systolic blood pressure of less than 140 mmHg in patients with diabetes as do the most recent American Diabetes Association clinical practice guidelines. All new guidelines are derived from a critical evidence based evaluation of the available data.

Insulin resistance: a proinflammatory state mediated by lipid-induced signaling dysfunction and involved in atherosclerotic plaque instability

The dysregulation of the insulin-glucose axis represents the crucial event in insulin resistance syndrome. Insulin resistance increases atherogenesis and atherosclerotic plaque instability by inducing proinflammatory activities on vascular and immune cells. This condition characterizes several diseases, such as type 2 diabetes, impaired glucose tolerance (IGT), impaired fasting glucose (IFG), obesity, hypertension, dyslipidemia, and other endocrinopathies, but also cancer. Recent studies suggest that the pathophysiology of insulin resistance is closely related to interferences with insulin-mediated intracellular signaling on skeletal muscle cells, hepatocytes, and adipocytes. Strong evidence supports the role of free fatty acids (FFAs) in promoting insulin resistance. The FFA-induced activation of protein kinase C (PKC) delta, inhibitor kappaB kinase (IKK), or c-Jun N-terminal kinase (JNK) modulates insulin-triggered intracellular pathway (classically known as PI3-K-dependent). Therefore, reduction of FFA levels represents a selective target for modulating insulin resistance.

Insulin Resistance and Oxidant Stress: An Interrelation With Deleterious Renal Consequences?

Within the past years, several epidemiologic studies have shown that insulin resistance and hyperinsulinemia are associated with chronic kidney disease, and experimental data suggest that a number of background mechanisms could connect insulin resistance with renal injury. Moreover, the acute sodium-retaining action of insulin at the kidney level has been proposed to participate in the development of salt sensitivity in essential hypertension. Current knowledge suggests that oxidative stress can be involved in the development of renal injury and can also promote primary salt retention at the kidney level. Insulin resistance and hyperinsulinemia seem to be closely connected with oxidative stress in the form of a vicious circle. This article discusses the potential role of oxidative stress as a mediator of the renal effects of insulin resistance/hyperinsulinemia.