LOS ANGELES – Results from recent trials suggest that
“Despite optimal care around blood pressure control, glycemic control, and control of other risk factors, our patients still have a significant risk of both cardiovascular disease progression and renal disease progression,” David Cherney, MD, said at the World Congress on Insulin Resistance, Diabetes & Cardiovascular Disease. “In fact, when we have a narrow focus on glycemia, there is a lot of additional residual risk, and that A1c lowering by itself does not negate that risk and in fact has very little effect on clinical outcomes. That brings us to the newer hyperglycemic therapies, including the SGLT2 inhibitors. While these agents do indeed block the reabsorption of glucose in the kidney, they also have an effect on other nonglycemic risk factors.”
Dr. David Cherney
“Inside the kidney, there are direct effects on reducing intraglomerular hypertension, leading to reductions in proteinuria,” he said. “These agents are interesting because of the way that they influence how the kidney handles sodium. As a consequence, they impact on glomerular hypertension.”
Under normal physiological conditions, humans who become volume depleted or hypotensive experience a reduction in sodium delivery to the kidney by the afferent arteriole, he explained. If less sodium is delivered to the afferent arteriole, less is filtered and delivered to the macula densa, which is the sodium-sensing area of the kidney.
“If less sodium is delivered to the macula densa, less sodium will be reabsorbed, which is an energy-requiring process that leads to the breakdown of ATP [adenosine triphosphate],” Dr. Cherney said. “If less ATP is broken down to adenosine, then less adenosine is produced. Adenosine is a vasoconstrictor in this area. So, under conditions of hypervolemia or hypotension, that’s great, because we want to maintain blood flow to the kidney; that’s a protective autoregulatory response that all of us have called tubular glomerular feedback. It’s through sodium delivery to the macula densa.”
He went on to note that hyperglycemic patients who are not taking an SGLT2 inhibitor experience an increase in sodium absorption proximally, which decreases sodium delivery to the macula densa. As a result, this causes afferent dilation, which leads to a rise in glomerular pressure, glomerular hypertension, hyperfiltration, and an increased risk of renal disease progression.
“This leads to all the effects that we see clinically, including the GFR [glomerular filtration rate] dip and the reduction in proteinuria that these agents cause either when used alone or with an ACE or ARB [angiotensin II receptor blocker],” Dr. Cherney said. “SGLT2s constrict the afferent arterial and reduce glomerular hypertension and proteinuria, whereas ACE inhibitors dilate the efferent arterial, which also reduces glomerular hypertension and proteinuria.”
An analysis of renal data from the multicenter EMPA-REG OUTCOME trial (Empagliflozin, Cardiovascular Outcomes, and Mortality in Type 2 Diabetes) found that the use of empagliflozin was associated with slower progression of kidney disease than was placebo when added to standard care. Empagliflozin was also associated with a significantly lower risk of clinically relevant renal events, including a 40%-50% reduction in microalbuminuria in patients with micro- or macroalbuminuria (N Engl J Med. 2016 Jul 28;375:323-34).
In a recent study of EMPA-REG OUTCOME patients, Dr. Cherney and his associates examined the effects of empagliflozin on the urinary albumin to creatinine ratio in patients with type 2 diabetes and established cardiovascular disease (Lancet Diabetes Endocrinol. 2017 Aug;5[8]:610-21). They found that even in patients with normal albuminuria at baseline, by the end of the trial at about 3 years there was a modest but statistically significant 15% reduction in urinary albumin secretion. “That reduction was greater in patients with microalbuminuria at baseline,” Dr. Cherney said. “There was a more than 40% reduction in microalbuminuric patients, and almost a 50% in patients who had macroalbuminuria at baseline, suggesting that the effect is greater in patients with higher levels of albuminuria.”
Meanwhile, results from the CANVAS program, which integrated data from two trials of more than 10,000 patients with type 2 diabetes and high cardiovascular disease risk, showed that those who received canagliflozin had a 14% reduced risk of 3-point major adverse cardiovascular events (3P-MACE), compared with those who received placebo. (N Engl J Med. 2017 Aug;377:644-57). “There was a curious increased risk of amputation and fracture in the canagliflozin group, which has not been seen in other trials,” Dr. Cherney said. “That certainly merits further thought and investigation, to better understand how significant this risk is.”