Obesity-initiated metabolic syndrome promotes urinary voiding dysfunction in a mouse model

Abstract

Objective: Accumulating evidences suggests that obesity and metabolic syndrome (MetS) contribute towards lower urinary tract symptoms (LUTS) through alterations in the phenotype of bladder and prostate gland. Clinical studies indicate a link between MetS and LUTS. Nevertheless, there is lack of suitable animal model(s) which could illustrate an association linking obesity to LUTS. We examined the lower urinary tract function in an obesity-initiated MetS mouse model.

Methods: Male C57BL/6N wild-type and obese B6.V-Lepob/J maintained on regular diet for 28 weeks were subjected to the assessment of body weight (BW), body length (BL), waist circumference (WC), body mass index (BMI), blood glucose (BG), plasma insulin (INS), plasma leptin (LEP), total cholesterol (CHO), free fatty acid (FFA), and measurement of urinary functions. Whole animal peritoneal and subcutaneous adipose tissue measurements as well as prostate and bladder volumes were analyzed by MRI followed by histological evaluation. These parameters were used to draw correlations between MetS and LUTS.

Results: Obesity parameters such as BW, WC, and BMI were significantly higher in B6.V-Lepob/J mice compared to C57BL/6N mice (P < 0.01). Higher levels of total CHO and FFA were noted in B6.V-Lepob/J mice than C57BL/6N mice (P < 0.05). These results were concurrent with frequency, lower average urine volume and other urinary voiding dysfunctions in B6.V-Lepob/J mice. MRI assessments demonstrate marked increase in body fat and prostate volume in these mice. Compared to C57BL/6N mice, histological analysis of the prostate from B6.V-Lepob/J mice showed increased proliferation, gland crowding, and infiltration of immune cells in the stroma; whereas the bladder urothelium was slightly thicker and appears more proliferative in these mice. The regression and correlation analysis indicate that peritoneal fat (R = 0.853; P < 0.02), CHO (R = 0.729; P < 0.001), BG (R = 0.712; P < 0.001) and prostate volume (R = 0.706; P < 0.023) strongly correlate with LUTS whereas BMI, WC, INS, and FFA moderately correlate with the prevalence of bladder dysfunction.

Conclusion: Our results suggest that LUTS may be attributable in part to obesity and MetS. Validation of an in vivo model may lead to understand the underlying pathophysiological mechanisms of obesity-related LUTS in humans. Prostate 76:964-976, 2016. © 2016 Wiley Periodicals, Inc.

Keywords: lower urinary tract symptoms; metabolic syndrome; overactive bladder; prostate hyperplasia; urinary incontinence.

Figure 1

Primary obesity parameters in C57BL/6N and B6.V-Lepob/J mice between 8–28 weeks. A, body weight, B, waist circumference, and C, body mass index. A significant change has been observed in these parameters between the groups in time-dependent manner. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Details are described in ‘materials and methods’ section.

Figure 2

Assessment of parameters of metabolic syndrome in C57BL/6N and B6.V-Lepob/J mice between 8–28 weeks. A, blood glucose, B, glucose tolerance test (GTT), C, plasma insulin levels, D, total cholesterol levels, E, free fatty acid levels, and F, leptin levels. A significant alteration in these parameters were noted between the groups in time-dependent manner. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Details are described in ‘materials and methods’ section.

Figure 3

Fat distribution assessment by MRI. A, whole body raw MRI image, water and fat images in C57BL/6N and B6.V-Lepob/J mice was performed at 14 and 28 weeks. The RCFF technique was used for image segmentations and reconstruction for water and fat separation. The semiautomatic ratio image analysis program delineated the visceral adipose tissue (dark gray), subcutaneous adipose tissue (white), air (black), and other tissues. B, adipose tissue volume assessment in mice. B, quantification of fat. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Details are described in ‘materials and methods’ section.

Figure 4

Micturition, conscious cystometry monitoring and bladder histology and proliferation in C57BL/6N and B6.V-Lepob/J mice between 12–28 weeks. A, typical voiding events at 24 h, B, representative conscious cystometrogram, and C, number of voiding events in 24 h. D-a, representative image of H&E staining of the whole bladder at 28 weeks. D-b, representative image of IHC staining of PCNA in the bladder urothelium at 28 weeks. A significant difference in micturition and voiding events were noted between the groups. Bladder of B6.V-Lepob/J mice, compared to C57BL/6N mice is slightly thicker and appears more proliferative along with scattered urothelial cells containing pigment granules, most likely lecithin (dark brown in color), as shown by arrows. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Representative H&E and IHC staining photomicrograph of the mouse bladder (×100, and ×400 magnification). Details are described in ‘materials and methods’ section.

Figure 4

Micturition, conscious cystometry monitoring and bladder histology and proliferation in C57BL/6N and B6.V-Lepob/J mice between 12–28 weeks. A, typical voiding events at 24 h, B, representative conscious cystometrogram, and C, number of voiding events in 24 h. D-a, representative image of H&E staining of the whole bladder at 28 weeks. D-b, representative image of IHC staining of PCNA in the bladder urothelium at 28 weeks. A significant difference in micturition and voiding events were noted between the groups. Bladder of B6.V-Lepob/J mice, compared to C57BL/6N mice is slightly thicker and appears more proliferative along with scattered urothelial cells containing pigment granules, most likely lecithin (dark brown in color), as shown by arrows. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Representative H&E and IHC staining photomicrograph of the mouse bladder (×100, and ×400 magnification). Details are described in ‘materials and methods’ section.

Figure 5

Assessment of prostate volume by MRI, histology and proliferation in C57BL/6N and B6.V-Lepob/J mice at 14 and 28 weeks. A, representative T1-weighted axial 2D gradient images of the mouse prostates a-c in C57BL/6N mice and b-d in B6.V-Lepob/J mice at 14 and 28 weeks. B, prostate volume quantification. C-a, representative image of H&E staining of the prostate gland at 28 weeks. C-b, representative image of IHC staining of PCNA in the prostate at 28 weeks. A significant increase in the prostate volume was noted in B6.V-Lepob/J mice. Prostate of B6.V-Lepob/J mouse, as compared to that of a C57BL/6N mouse, shows pronounced glandular cell enlargement, markedly crowded and proliferative, virtually filled the central lumen of the gland, resulting in overall enlargement of the gland. Increase nuclear PCNA staining is noted in the prostate of B6.V-Lepob/J, compared to C57BL/6N mice. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Representative H&E and IHC staining photomicrograph of the mouse prostate (×100, and ×400 magnification). Details are described in ‘materials and methods’ section.

Figure 5

Assessment of prostate volume by MRI, histology and proliferation in C57BL/6N and B6.V-Lepob/J mice at 14 and 28 weeks. A, representative T1-weighted axial 2D gradient images of the mouse prostates a-c in C57BL/6N mice and b-d in B6.V-Lepob/J mice at 14 and 28 weeks. B, prostate volume quantification. C-a, representative image of H&E staining of the prostate gland at 28 weeks. C-b, representative image of IHC staining of PCNA in the prostate at 28 weeks. A significant increase in the prostate volume was noted in B6.V-Lepob/J mice. Prostate of B6.V-Lepob/J mouse, as compared to that of a C57BL/6N mouse, shows pronounced glandular cell enlargement, markedly crowded and proliferative, virtually filled the central lumen of the gland, resulting in overall enlargement of the gland. Increase nuclear PCNA staining is noted in the prostate of B6.V-Lepob/J, compared to C57BL/6N mice. Values represent Mean ± SEM, *p<0.05, **p<0.001, compared to C57BL/6 mice. Representative H&E and IHC staining photomicrograph of the mouse prostate (×100, and ×400 magnification). Details are described in ‘materials and methods’ section.

Figure 6

Correlations of voiding events at 24 h to risk parameters: blood glucose, cholesterol, peritoneal fat, and prostate volume. Correlation coefficient (R) and p values are presented in each histogram.