Absence of GIP secretion alleviates age-related obesity and insulin resistance

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin secreted from enteroendocine K cells after nutrient ingestion. Fat strongly induces GIP secretion, and GIP hypersecretion is involved in high-fat diet-induced obesity and insulin resistance. Aging also induces GIP hypersecretion, but its effect on body weight gain and insulin sensitivity remains unclear. In the present study, we investigated the effect of GIP on age-related body weight gain and insulin resistance using GIP-knockout homozygous (GIP-/-) and heterozygous (GIP+/-) mice, which have entirely absent and 50% reduced GIP secretion compared to wild-type (WT) mice, respectively. Under 12% fat-containing normal diet feeding condition, body weight was significantly lower in GIP-/- mice compared to that in WT and GIP+/- mice from 38 weeks of age, while there was no significant difference between WT and GIP+/- mice. Visceral and s.c. fat mass were also significantly lower in GIP-/- mice compared to those in WT and GIP+/- mice. During oral glucose tolerance test, blood glucose levels did not differ among the three groups. Insulin levels were significantly lower in GIP-/- mice than those in WT and GIP+/- mice. During insulin tolerance test, GIP-/- mice showed higher insulin sensitivity than that of WT and GIP+/- mice. Adiponectin mRNA levels were increased and leptin mRNA levels tended to be decreased in adipose tissue of GIP-/- mice. These results demonstrate that GIP is involved in age-related obesity and insulin resistance and that inhibition of GIP secretion alleviates age-related fat mass gain and insulin resistance under carbohydrate-based diet feeding condition.

Free fatty acid receptors, G protein-coupled receptor 120 and G protein-coupled receptor 40, are essential for oil-induced gastric inhibitory polypeptide secretion

AIMS/INTRODUCTION

Incretin hormone glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) plays a key role in high-fat diet-induced obesity and insulin resistance. GIP is strongly secreted from enteroendocrine K cells by oil ingestion. G protein-coupled receptor (GPR)120 and GPR40 are two major receptors for long chain fatty acids, and are expressed in enteroendocrine K cells. In the present study, we investigated the effect of the two receptors on oil-induced GIP secretion using GPR120- and GPR40-double knockout (DKO) mice.

MATERIALS AND METHODS

Global knockout mice of GPR120 and GPR40 were crossbred to generate DKO mice. Oral glucose tolerance test and oral corn oil tolerance test were carried out. For analysis of the number of K cells and gene expression in K cells, DKO mice were crossbred with GIP-green fluorescent protein knock-in mice in which visualization and isolation of K cells can be achieved.

RESULTS

Double knockout mice showed normal glucose-induced GIP secretion, but no GIP secretion by oil. We then investigated the number of K cells and gene characteristics in K cells isolated from GIP-green fluorescent protein knock-in mice. Deficiency of both receptors did not affect the number of K cells in the small intestine or expression of GIP messenger ribonucleic acid in K cells. Furthermore, there was no significant difference in the expression of the genes associated with lipid absorption or GIP secretion in K cells between wild-type and DKO mice.

CONCLUSIONS

Oil-induced GIP secretion is triggered by the two major fatty acid receptors, GPR120 and GPR40, without changing K-cell number or K-cell characteristics.

Glucose-dependent insulinotropic polypeptide deficiency reduced fat accumulation and insulin resistance, but deteriorated bone loss in ovariectomized mice

Given the established roles of glucose-dependent insulinotropic polypeptide (GIP) in promoting fat storage and bone formation, we assessed the contribution of GIP to obesity and osteopenia in ovariectomized mice with a gene encoding green fluorescent protein (GFP) inserted into the GIP locus, in which GIP was either reduced (GIPgfp/+ ) or absent (GIPgfp/gfp ). In GIPgfp/gfp mice, weight gain, subcutaneous and visceral fat mass were reduced, and glucose intolerance was improved compared with wild-type mice with the same magnitude of insulin responses. Cancellous bone mineral density and bone cortical thickness were reduced in GIPgfp/gfp mice compared with wild-type mice. In GIPgfp/+ mice, weight gain, glucose intolerance and cancellous bone mineral density were not different from that of wild-type mice. These results indicate that the total elimination of GIP ameliorates weight gain and adiposity in ovariectomized mice, but it enhances osteopenia, particularly in cancellous bone by partly suppressing bone formation.

Medium-chain triglyceride diet stimulates less GIP secretion and suppresses body weight and fat mass gain compared with long-chain triglyceride diet

Gastric inhibitory polypeptide (GIP) is an incretin secreted from enteroendocrine K cells and potentiates insulin secretion from pancreatic β-cells. GIP also enhances long-chain triglyceride (LCT) diet-induced obesity and insulin resistance. Long-term intake of medium-chain triglyceride (MCT) diet is known to induce less body weight and fat mass gain than that of LCT diet. However, the effect of MCT diet feeding on GIP secretion and the effect of GIP on body weight and fat mass under MCT diet-feeding condition are unknown. In this study, we evaluated the effect of single MCT oil administration on GIP secretion and compared the effect of long-term MCT and LCT diet on body weight and fat mass gain in wild-type (WT) and GIP-knockout (GIP KO) mice. Single administration of LCT oil induced GIP secretion but that of MCT oil did not in WT mice. Long-term intake of LCT diet induced GIP hypersecretion and significant body weight and fat mass gain compared with that of control fat (CF) diet in WT mice. In contrast, MCT diet did not induce GIP hypersecretion, and MCT diet-fed mice showed smaller increase in body weight and fat mass gain compared with CF diet-fed mice. In GIP KO mice, body weight and fat mass were markedly attenuated in LCT diet-fed mice but not in MCT diet-fed mice. Our results suggest that long-term intake of MCT diet stimulates less GIP secretion and suppresses body weight and fat mass gain compared with that of LCT diet.

Transcriptional factor Pdx1 is involved in age-related GIP hypersecretion in mice

Fat accumulation with aging is a serious problem; glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) is an incretin that plays an important role in fat accumulation. GIP receptor knockout mice show reduced fat mass and improved insulin sensitivity associated with aging. Therefore, GIP is involved in fat accumulation and insulin resistance with aging. However, age-related changes of GIP secretion remain unclear. The present study aimed to elucidate age-related changes of GIP secretion and enteroendocrine K cells using GIP reporter [GIP-green fluorescent protein (GFP) knock-in heterozygous (GIP^gfp/+)] mice. Aged 1-yr-old GIP^gfp/+ mice exhibited a phenotype of fat accumulation, insulin resistance, and GIP hypersecretion compared with young (3-4 mo old) GIP^gfp/+ mice. In aged mice, K-cell number in the small intestine and the mRNA expression levels of GIP and transcriptional factor pancreatic and duodenal homeobox-1 (Pdx1) in K cells were increased. K-cell number, GIP mRNA expression and content in small intestine, and GIP secretion were decreased after posteriori suppression of Pdx1 using intestine-specific gene transfer. Thus, Pdx1 positively regulates GIP mRNA and K-cell number in small intestine. Increased Pdx1 expression might be involved in GIP hypersecretion with aging. NEW & NOTEWORTHY Age-related changes of glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) secretion and K cells were investigated. We found that K-cell number and GIP and pancreatic and duodenal homeobox-1 (Pdx1) expression in K cells were increased in aged mice, which showed greater GIP secretion compared with young mice. In addition, we have succeeded in posteriori suppression of Pdx1 in small intestine using the method of intestine-specific gene transfer, and showed that K-cell number, GIP expression, and GIP secretion were decreased in the Pdx1-knockdown intestine.

The treatment of benign prostatic hyperplasia with alpha blockers in men over the age of 80 years

OBJECTIVE

To determine the safety and efficacy of alpha blockade with doxazosin and terazosin in men over the age of 80 years with symptomatic benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

Thirty-six men (mean age 83.6 years, SD 5.6, range 80-96) received either doxazosin 4 mg (11 men) or 8 mg (10 men), or terazosin 5 mg (five men) or 10 mg (10 men), once daily at night. Twenty-eight men (78%) were on other anti-hypertensive medication; the type and dosage were not changed during the study. Efficacy and safety were assessed using measurements of peak urinary flow rate, symptom scores and the incidence of adverse events.

RESULTS

Of the 36 men, 33 (92%) remained on study medication at 6 months; the remaining three (8%) discontinued because of asthenia. After 3 months of treatment, the peak urinary flow rate increased significantly (P < 0.008) for both doxazosin (+3.7 mL/s) and terazosin (+3.2 mL/s). The American Urological Association symptom score improved significantly (P < 0.01) with both alpha blocker after 3 months of treatment and efficacy was maintained at 6 months. There were small, non-significant decreases in blood pressure in patients receiving doxazosin or terazosin, but no differences between patients who were normotensive at baseline and those whose blood pressure was controlled by other anti-hypertensive drugs.

CONCLUSION

These results suggest that alpha blockade with either doxazosin or terazosin is well tolerated and effective in older men with symptomatic BPH. Furthermore, patients on concomitant anti-hypertensive medication need no alteration of their therapeutic regimen before the initiation of alpha blockade for BPH.

The incidence of multifocal renal cell carcinoma in patients who are candidates for partial nephrectomy

PURPOSE

A prospective study was performed to determine the incidence of multifocal renal cell carcinoma in patients who are candidates for partial nephrectomy.

MATERIALS AND METHODS

Preoperative imaging studies and surgical specimens in 44 patients suitable for partial nephrectomy but undergoing radical nephrectomy were prospectively reviewed.

RESULTS

Of 44 renal cell cancers 11 (25%) demonstrated pathological multifocality, while 10 of 11 multifocal tumors (91%) occurred in the face of a primary tumor 5 cm. or smaller. Tumor multifocality was independent of the size of the primary renal tumor but occurred with a slightly higher frequency in tumors of stage T3A or greater even if the primary tumor was small.

CONCLUSIONS

Partial nephrectomy in patients with unilateral renal cancer should be approached with caution and should not be performed simply because it is technically feasible.