SGLT1/2 inhibition improves glycemic control and multi-organ protection in type 1 diabetes

Hypothalamic sex-specific metabolic shift by canagliflozin during aging

The hypothalamus undergoes significant changes with aging and plays crucial roles in age-related metabolic alterations. Sodium-glucose co-transporter 2 inhibitors (SGLT2i) are anti-diabetic agents that promote glucose excretion, and metabolic homeostasis. Recent studies have shown that a SGLT2i, Canagliflozin (Cana), can extend the median survival of genetically heterogeneous UM-HET3 male mice and improve central metabolic control via increases in hypothalamic insulin responsiveness in aged males, as well as reduced age-associated hypothalamic inflammation. We studied the long- and short-term effects of Cana on hypothalamic metabolic control in UM-HET3 mice. Starting the treatment from 7 months of age, we show that 4 weeks of Cana treatment significantly reduced body weight and fat mass in male but not female mice that was associated with enhanced glucose tolerance and insulin sensitivity observed by 12 months. Indirect calorimetry showed that Cana treatment increased energy expenditure in male, but not female mice, at 12 months of age. Long-term Cana treatment increased metabolic rates in both sexes, and markedly increasing formation of both orexigenic and anorexigenic projections to the paraventricular nucleus of the hypothalamus (PVH) mostly in females by 25 months. Hypothalamic RNA-sequencing analysis revealed increased sex-specific genes and signaling pathways related to insulin signaling, glycogen catabolic pathway, neuropeptide signaling, and mitochondrial function upregulated by Cana, with males showing a more pronounced and sustained effect on metabolic pathways at both age groups. Overall, our data provide critical evidence for sex-specific mechanisms that are affected by Cana during aging suggesting key targets of hypothalamic Cana-induced neuroprotection for metabolic control.

Sympathetic Activation Promotes Sodium Glucose Co-Transporter-1 Protein Expression in Rodent Skeletal Muscle

The hyperactivation of the sympathetic nervous system (SNS) is linked to obesity, hypertension, and type 2 diabetes, which are characterized by elevated norepinephrine (NE) levels. Previous research has shown increased sodium-dependent glucose cotransporter 1 (SGLT1) protein levels in kidneys of hypertensive rodents, prompting investigation into the expression of SGLT1 in various tissues, such as skeletal muscle. This study aimed to assess (i) whether skeletal muscle cells and tissue express SGLT1 and SGLT2 proteins; (ii) if NE increases SGLT1 levels in skeletal muscle cells, and (iii) whether the skeletal muscle of neurogenically hypertensive mice exhibits increased SGLT1 expression. We found that (i) skeletal muscle cells and tissue are a novel source of the SGLT2 protein and that (ii) NE significantly elevated SGLT1 levels in skeletal muscle cells. As SGLT2 inhibition (SGLT2i) with Empagliflozin increased SGLT1 levels, in vivo studies with the dual inhibitor SGLT1/2i, Sotagliflozin were warranted. The treatment of neurogenically hypertensive mice using Sotagliflozin significantly reduced blood pressure. Our findings suggest that SNS activity upregulates the therapeutic target, SGLT1, in skeletal muscle, potentially worsening cardiometabolic control. As clinical trial data suggest cardiorenal benefits from SGLT2i, future studies should aim to utilize SGLT1i by itself, which may offer a therapeutic strategy for conditions with heightened SNS activity, such as hypertension, diabetes, and obesity.

Glucose transport, transporters and metabolism in diabetic retinopathy

Diabetic retinopathy (DR) is the most common reason for blindness in working-age individuals globally. Prolonged high blood glucose is a main causative factor for DR development, and glucose transport is prerequisite for the disturbances in DR caused by hyperglycemia. Glucose transport is mediated by its transporters, including the facilitated transporters (glucose transporter, GLUTs), the "active" glucose transporters (sodium-dependent glucose transporters, SGLTs), and the SLC50 family of uniporters (sugars will eventually be exported transporters, SWEETs). Glucose transport across the blood-retinal barrier (BRB) is crucial for nourishing the neuronal retina in the context of retinal physiology. This physiological process primarily relies on GLUTs and SGLTs, which mediate the glucose transportation across both the cell membrane of retinal capillary endothelial cells and the retinal pigment epithelium (RPE). Under diabetic conditions, increased accumulation of extracellular glucose enhances the retinal cellular glucose uptake and metabolism via both glycolysis and glycolytic side branches, which activates several biochemical pathways, including the protein kinase C (PKC), advanced glycation end-products (AGEs), polyol pathway and hexosamine biosynthetic pathway (HBP). These activated biochemical pathways further increase the production of reactive oxygen species (ROS), leading to oxidative stress and activation of Poly (ADP-ribose) polymerase (PARP). The activated PARP further affects all the cellular components in the retina, and finally resulting in microangiopathy, neurodegeneration and low-to-moderate grade inflammation in DR. This review aims to discuss the changes of glucose transport, glucose transporters, as well as its metabolism in DR, which influences the retinal neurovascular unit (NVU) and implies the possible therapeutic strategies for treating DR.

The Impact of SGLT2 Inhibitors in the Heart and Kidneys Regardless of Diabetes Status

Chronic Kidney Disease (CKD) and Cardiovascular Disease (CVD) are two devastating diseases that may occur in nondiabetics or individuals with diabetes and, when combined, it is referred to as cardiorenal disease. The impact of cardiorenal disease on society, the economy and the healthcare system is enormous. Although there are numerous therapies for cardiorenal disease, one therapy showing a great deal of promise is sodium-dependent glucose cotransporter 2 (SGLT2) inhibitors. The SGLT family member, SGLT2, is often implicated in the pathogenesis of a range of diseases, and the dysregulation of the activity of SGLT2 markedly effects the transport of glucose and sodium across the luminal membrane of renal cells. Inhibitors of SGLT2 were developed based on the antidiabetic action initiated by inhibiting renal glucose reabsorption, thereby increasing glucosuria. Of great medical significance, large-scale clinical trials utilizing a range of SGLT2 inhibitors have demonstrated both metabolic and biochemical benefits via numerous novel mechanisms, such as sympathoinhibition, which will be discussed in this review. In summary, SGLT2 inhibitors clearly exert cardio-renal protection in people with and without diabetes in both preclinical and clinical settings. This exciting class of inhibitors improve hyperglycemia, high blood pressure, hyperlipidemia and diabetic retinopathy via multiple mechanisms, of which many are yet to be elucidated.