Long-Term Effects of Sglt2 Deletion on Bone and Mineral Metabolism in Mice

Sodium‐glucose cotransporter 2 (SGLT2) inhibitors improve kidney and cardiovascular outcomes in patients with type 2 diabetes mellitus (T2DM). However, bone fragility has emerged as a side effect in some but not in all human studies. Because use of SGLT2 inhibitors in humans affects mineral metabolism, we investigated the long‐term effects of genetic loss of Sglt2 function on bone and mineral metabolism in mice. Slc5a2 nonsense mutation in Sweet Pee (SP) mice results in total loss of Sglt2 function. We collected urine, serum, and bone samples from 15‐week‐old and 25‐week‐old wild‐type (WT) and SP mice fasted from food overnight. We measured parameters of renal function and mineral metabolism and we assessed bone growth, microarchitecture, and mineralization. As expected, 15‐week‐old and 25‐week‐old SP mice showed increased glucosuria, and normal kidney function compared to age‐matched WT mice. At 15 weeks, SP mice did not show alterations in mineral metabolism parameters. At 25 weeks, SP mice showed reduced fasting 24‐hour urinary calcium excretion and increased fractional excretion of phosphate, but normal serum calcium and phosphate, parathyroid hormone (PTH), vitamin D (1,25(OH)₂D), and fibroblast growth factor (FGF23) levels. At 25 weeks, but not at 15 weeks, SP mice showed reduced body weight compared to WT. This was associated with reduced femur length at 25 weeks, suggesting impaired skeletal growth. SP mice did not show trabecular or cortical bone microarchitectural modifications but showed reduced cortical bone mineral density compared to WT mice at 25 weeks. These results suggest that loss of Sglt2 function in mice in the absence of T2DM does not alter regulatory hormones FGF23, PTH, and 1,25(OH)₂D, but may contribute to bone fragility over the long term. Future studies are required to determine how loss of Sglt2 function impacts bone fragility in T2DM. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

INFLUENCE OF ALLOXAN DIABETES ON GROWTH HORMONE CONTENT OF THE RAT HYPOPHYSIS

Homogenates of adenohypophysial tissue obtained from alloxan-injected adult male rats varying in duration and severity of diabetes, as well as from diabetic rats maintained on an insulin-replacement regimen, were assayed in immature hypophysectomized female rats. The ability of these crude hypophysial extracts to encourage tibial cartilage width expansion, gain in body weight, and to depress hematocrit and blood urea levels was determined. Significant decrements in ability to increase epiphysial cartilage width and ability to depress hematocrits were noted 14 to 28 days following injection of alloxan. Increasing the intensity of the diabetic state was associated with decreased growth-promoting potency of hypophysial preparations as well as with decreased ability to influence hematological indices. Hypophysial extracts taken from insulin-treated diabetic rats contained more growth hormone than equivalent amounts of tissue obtained from control rats. It is concluded that the adenohypophyses of diabetic rats contain diminished amounts of growth hormone and that insulin repairs or encourages greater than normal accumulation of somatotrophin in these animals.

QUANTITATIVE ASPECTS OF LABILE DIABETES

Eighteen diabetic patients representing a spectrum from hyperlabile to stable forms of this disease were investigated under metabolic ward conditions. Hyperlabile patients had the greatest daily and hourly variation in glycosuria and the most marked ketonuria. In our hyperlabile patients, multiple daily injections of short-acting insulin proved to be the only therapeutic measure that provided significant improvement in diabetic regulation when dietary and general health measures were already optimal. In more stable patients, longer acting insulin injected less frequently was found to be satisfactory therapy if careful adjustments to individual needs were made.

Blood glucose and serum ketone-body and free fatty acid concentrations as well as qualitative estimates of glucose and ketone bodies in small samples of freshly voided urine were found to be suitable indicators of the immediate state of metabolic regulation. These parameters correlated with one another to a satisfactory degree, but they proved to be poorly correlated with measurements of urinary glucose and ketone bodies during periods of five to twenty-four hours. Quantitative analysis of individual blood samples or qualitative estimates of glucose or ketone bodies in freshly voided urine specimens proved to be unreliable indices of the patients' long-term metabolic compensation except in the most stable patients. Quantitations of urinary glucose and ketone bodiesin five, nine, and twenty-four-hour collections of urine, on the other hand, give satisfactory data to assess diabetic regulation, both as to accuracy of compensation and stability.

FALSE NEGATIVE REACTIONS AND SENSITIVITY IN THE URINE GLUCOSE OXIDASE TEST

Some 6,217 random urine specimens were tested with both a glucose oxidase test (Combistix) and a copper reduction test (Clinitest). The ratio of positive Combistix to Clinitest was approximately 3 to 2. There were only eleven false negative enzyme paper tests. The qualitative reaction of the enzyme paper test was not adversely affected over a pH range of 5 to 9 or by addition of significant amounts of uric acid, creatinine, or protein. Positive two-minute Combistix reactions were noted at levels as low as 10 to 12 mg. per 100 ml. of urine glucose. Ascorbic acid completely inhibited the glucose oxidase test for at least two minutes when the ascorbic acid level was two to two and one-half times the glucose level.

COMPARISON OF PANCREATIC AND STEROID DIABETES IN RESPECT TO TUMOR GROWTH AND GLYCOSURIA

Sexually mature male rats were made severely diabetic by either pancreatectomy or daily injection of large doses of cortisone acetate. One half of the animals were then made host to Walker Carcinoma 256. The tumor suppressed the glycosuria in all of the animals, but the effect was greater in steroid diabetes than in pancreatic diabetes. Diabetogenic doses of cortisone inhibited the growth of tumor to a greater extent than did pancreatic diabetes. The depancreatized tumor host is partially resistant to the diabetogenic action of cortisone.

THE ESKIMOS OF THE NORTHWEST PASSAGE: A SURVEY OF DIETARY COMPOSITION AND VARIOUS BLOOD AND METABOLIC MEASUREMENTS

In 1959 and 1960, during the annual survey conducted by the Federal Northern Health Services in the area of the Northwest Passage, the diet and living conditions of some 1500 Eskimos who live in this area were studied and blood and urine samples were obtained from 40-50% of this population. Hemoglobin, blood cell morphology, serum protein-bound iodine, serum proteins, serum lipids and serum total cholesterol estimations, urinalyses, and agglutination studies for brucellosis were carried out. Hemoglobin levels were in the normal range; however, increased contact with civilization appeared to be associated with lower hemoglobin levels. Eleven per cent of the Eskimos showed eosinophilia. Serum proteins were normal. Serum lipids and serum cholesterol levels were higher in Eskimo children living in a government residential school than in a comparable group living on the Barren Lands. Serum protein-bound iodine levels were in the upper euthyroid range. Diabetes mellitus occurs among Eskimos. Sporadic cases of brucellosis also occur.