Differences in mouse models of diabetes mellitus in studies of male reproduction

Predictive factors for successful testicular biopsy

INTRODUCTION

Infertility, the inability to conceive, constitutes a major problem in modern societies. It affects 10 to 15 percent of couples in the United States. Evaluation of infertile men is usually complex and often demands a testicular biopsy.

MATERIALS AND METHODS

We reviewed all azoospermic men submitted to testicular biopsy, in our center, during infertility investigation between January 2015 and December 2021.

RESULTS

A total of 117 patients with a mean age of 36.5 was considered. Biopsy was positive, as defined by the presence of viable spermatozoids by microscopy, in 48.7% of patients (n = 57). Patients were divided in two separate groups based on positive (PB) or negative biopsy (NB) and compared. PB-group had normal serum total testosterone levels and higher than NB-group (3.7 ng/mL vs. 2.85 ng/mL, p = 0.021), and normal serum FSH levels and lower than NB-group (6.0 mIU/mL vs. 16.0 mIU/mL, p < 0.001). The groups were similar concerning serum LH levels (3.9 mIU/mL vs. 6.3 mIU/mL, p = 0.343.

CONCLUSIONS

Predicting outcomes of testicular biopsy is a difficult task. Our study found that men with normal testicular volume, normal levels of testosterone and FSH and those with type 1 diabetes mellitus had a higher probability of positive testicular biopsy.

Role of PPAR-γ in diabetes-induced testicular dysfunction, oxidative DNA damage and repair in leptin receptor-deficient obese type 2 diabetic mice

The testis expresses peroxisome proliferator-activated receptor-γ (PPAR-γ), but its involvement in regulating diabetes-induced testicular dysfunction and DNA damage repair is not known. Pioglitazone-induced activation of PPAR-γ for 12 weeks in db/db obese diabetic mice increases bodyweights and reduces blood glucose levels, but PPAR-γ inhibition by 2-chloro-5-nitro-N-phenylbenzamide does not alter these parameters; instead, improves testis and epididymis weights and sperm count. Neither activation nor inhibition of PPAR-γ normalizes the diabetes-induced seminiferous epithelial degeneration. The PPAR-γ activation normalizes testicular lipid peroxidation, but its inhibition reduces lipid peroxidation and oxidative DNA damage (8-oxo-dG) in diabetic mice. As a response to diabetes-induced oxidative DNA damage, the base-excision repair (BER) mechanism proteins- 8-oxoguanine DNA glycosylases (OGG1/2) and X-ray repair cross-complementing protein-1 (XRCC1) increase, whereas the redox-factor-1 (REF1), DNA polymerase (pol) δ and poly (ADP-ribose) polymerase-1 (PARP1) show a tendency to increase suggesting an attempt to repair the oxidative DNA damage. The PPAR-γ stimulation inhibits OGG2, DNA pol δ, and XRCC1 in diabetic mice testes, but PPAR-γ inhibition reduces oxidative DNA damage and normalizes BER protein levels. In conclusion, type 2 diabetes negatively affects testicular structure and function and increases oxidative DNA damage and BER protein levels due to increased DNA damage. The PPAR-γ modulation does not significantly affect the structural changes in the testis. The PPAR-γ stimulation aggravates diabetes-induced effects on testis, including oxidative DNA damage and BER proteins, but PPAR-γ inhibition marginally recovers these diabetic effects indicating the involvement of the receptor in the reproductive effects of diabetes.

Potential effect of advanced glycation end products (AGEs) on spermatogenesis and sperm quality in rodents

The aim of the present study was to assess whether dietary advanced glycation end products (AGEs) induce testicular dysfunction. Using a BALB/c mouse model, AGE intake and serum levels were found to increase in AGE diet-treated mice relative to the controls. Histopathological damage was detected in the testes and epididymides of the AGE diet-induced mice. The total number of epididymal sperm decreased, and increased abnormal sperm rate was found in the mice. Moreover, the mice testes showed an increased level of the receptor for AGEs (RAGE) and malondialdehyde (MDA). Using a Sprague-Dawley rat model, AGE diet-induced rats showed 3- to 4-fold higher AGE intake than the controls. In these rats, higher serum and sperm MDA levels, decreased epididymal sperm numbers, and increased abnormal sperm rates were also observed. Silymarin, a natural AGE inhibitor, was found to restore these AGE-induced phenomena. Concluding from the above findings, dietary AGEs may promote testicular dysfunction.

Hyperglycemia induces spermatogenic disruption via major pathways of diabetes pathogenesis

Diabetes-induced hyperglycemia has previously been shown to impact on male sub-/infertility, however, still little is known about the underlying mechanisms. In the present study we have addressed three major biochemical pathways implicated in the pathogenesis of hyperglycemia induced organ damage (the advanced glycation end product (AGE) formation pathway, the diacylglycerol-protein kinase C pathway (PKC), and the polyol pathway) in both testis and epididymis of the Ins2^Akita mouse model of Type 1 diabetes (T1DM). Hyperglycemia activated both the PKC and the polyol pathway in a significant and progressive manner within the testis, but not within the epididymis. While the AGE receptor was ubiquitiously expressed in the testis, concentrations of precursor methylglyoxal and AGE carboxymethyllysine were increased in both epididymis and testis in diabetic mice. However, AGEs did not activate intracellular pathways of ERK1, ERK2, Rela, Nrf-2, IkBkB, NFkB except CDC42, Akt1. In conclusion, two of the major pathways of hyperglycemia-induced organ damage were clearly activated within the testis of T1DM mice. This provides therapeutical opportunities in the treatment of diabetic male reproductive dysfunction.

Advanced glycation end products inhibit testosterone secretion by rat Leydig cells by inducing oxidative stress and endoplasmic reticulum stress

Diabetes severely impairs male reproduction. The present study assessed the effects and mechanisms of action of advanced glycation end products (AGEs), which play an important role in the development of diabetes complications, on testosterone secretion by rat Leydig cells. Primary rat Leydig cells were cultured and treated with AGEs (25, 50, 100 and 200 µg/ml). Testosterone production induced by human chorionic gonadotropin (hCG) was determined by ELISA. The mRNA and protein expression levels of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD), which are involved in testosterone biosynthesis, were measured by reverse transcription-quantitative PCR and western blot analyssi, respectively. Reactive oxygen species (ROS) production in Leydig cells was measured using the dichlorofluorescein diacetate (DCFH-DA) probe. The expression levels of endoplasmic reticulum stress-related proteins [C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78)] in the Leydig cells were measured by western blot analysis. We found that the AGEs markedly suppressed testosterone production by rat Leydig cells which was induced by hCG in a concentration-dependent manner compared with the control (P<0.01). The mRNA and protein expression levels of StAR, 3β-HSD and P450scc were downregulated by the AGEs in a dose-dependent manner compared with the control (P<0.01). The antioxidant agent, N-acetyl‑L‑cysteine (NAC), and the endoplasmic reticulum stress inhibitor, tauroursodeoxycholic acid (TUDCA), reversed the inhibitory effects of AGEs. In addition, the content of ROS in Leydig cells treated with AGEs increased significantly. The expression levels of CHOP and GRP78 were markedly upregulated by the AGEs in the Leydig cells. From these findings, it can be concluded that AGEs inhibit testosterone production by rat Leydig cells by inducing oxidative stress and endoplasmic reticulum stress.

Additional deleterious effects of alcohol consumption on sperm parameters and DNA integrity in diabetic mice

The aim of this study was to survey the impact of alcohol consumption on sperm parameters and DNA integrity in experimentally induced diabetic mice. A total of 32 adult male mice were divided into four groups: mice of group 1 served as control fed on basal diet, group 2 received streptozotocin (STZ) (200 mg kg(-1) , single dose, intraperitoneal) and basal diet, group 3 received alcohol (10 mg kg(-1) , water soluble) and basal diet, and group 4 received STZ and alcohol for 35 days. The cauda epididymidis of each mouse was dissected and placed in 1 ml of pre-warm Ham's F10 culture medium for 30 min. The swim-out spermatozoa were analysed for count, motility, morphology and viability. Sperm chromatin quality was evaluated with aniline blue, toluidine blue, acridine orange and chromomycin A3 staining. The results showed that all sperm parameters had significant differences (P < 0.05), also when sperm chromatin was assessed with cytochemical tests. There were significant differences (P < 0.001) between the groups. According to our results, alcohol and diabetes can cause abnormalities in sperm parameters and chromatin quality. In addition, alcohol consumption in diabetic mice can intensify sperm chromatin/DNA damage.

Impact of diet-induced obesity in male mouse reproductive system: The role of advanced glycation end product-receptor for advanced glycation end product axis

Obesity represents a route to broad physiological dysfunction affecting major organs including male urogenital system. Hyperglycemia, hyperlipidemia, and oxidative stress associated with obesity augment the formation of reactive metabolic by-products, namely advanced glycation end products (AGEs), leading to increased tissue deposition and damage. The exogenous intake and the endogenous accumulation of AGEs contribute to metabolic and reproductive abnormalities in both women and men. The present study assessed the effects of a diet high in saturated fatty acids (SAFA) on the lipid and metabolic profile (AGE levels, oxidative stress) as well as pathogenic (AGE, receptor for AGEs [RAGE] expression, apoptosis) and morphometric parameters of male reproductive system in vivo. Effects of switching to a diet rich in monounsaturated fatty acids (MUFA) or equal in the proportion MUFA to SAFA were further investigated. SAFA-fed animals were characterized by increased serum lipid concentrations (p < .05) compared to controls, but AGEs and peroxide levels were not significantly different across the different experimental groups. Elevated AGE deposition was detected for the first time in germ cells with a higher staining intensity in animals on the SAFA diet, compared to MUFA or MUFA-SAFA-fed animals or the control samples (p = .018). In Leydig cells, AGE localization was higher in the entire cohort of high-fat-fed animals compared to controls (p < .05). High-fat-fed mice displayed enhanced apoptosis compared to controls (p < .005). Furthermore, prostatic tissue demonstrated reduction in epithelial folding, an effect which was significantly reversed after MUFA diet administration. Our findings provide the basis for further investigation of AGE-RAGE axis in testicular and prostatic disturbances associated with diet-induced obesity. Simple dietetic intervention has beneficial effects on metabolic dysfunction of reproductive system before overt manifestations, indicating glycation as a promising therapeutic target.

Diabetes-induced oxidative DNA damage alters p53-p21CIP1/Waf1 signaling in the rat testis

Diabetes is increasingly becoming a major cause of large-scale morbidity and mortality. Diabetes-induced oxidative stress alters numerous intracellular signaling pathways. Although testicular dysfunction is a major concern in diabetic men, the mechanistic alterations in the testes that lead to hypogonadism are not yet clear. Oxidative mitochondrial DNA damage, as indicated by 7,8-dihydro-8-oxo-2'-deoxyguanosine, and phosphorylation of p53 at ser315 residue (p-p53ser315) increased in a stage- and cell-specific manner in the testes of rats that were diabetic for 1 month (DM1). Prolongation of diabetes for 3 months (DM3) led to an increase in nuclear oxidative DNA damage in conjunction with a decrease in the expression of p-p53ser315. The nuclei of pachytene and preleptotene spermatocytes, steps 1, 11, and 12 spermatids, secondary spermatocytes and the Sertoli cells, and the meiotic figures showed an increase in the expression of p-p53ser315. An increase in the expression of a downstream target of p53 and protein 21(cyclin-dependent kinase interacting protein 1/wild-type p53-activated factor 1) (p21(CIP1/Waf1)) in both diabetic groups did not show any time-dependent effects but occurred concurrent with an upregulation of p-p53ser315 in DM1 and a downregulation of the protein in DM3. In diabetic groups, the expression of p21(CIP1/Waf1) was mainly cytoplasmic but also perinuclear in pachytene spermatocytes and round spermatids. The cytoplasmic localization of p21(CIP1/Waf1) may be suggestive of an antiapoptotic role for the protein. The perinuclear localization is probably related to the cell cycle arrest meant for DNA damage repair. Diabetes upregulates p21(CIP1/Waf1) signaling in testicular germ cells in association with alteration in p-p53ser315 expression, probably to counteract DNA damage-induced cell death.

Germ cell abnormalities in streptozotocin induced diabetic mice do not correlate with blood glucose level

PURPOSE

To assess the effect of streptozotocin induced hyperglycemia on germ cell integrity, DNA ploidy and methylation status for a period of two spermatogenesis cycles in adult male Swiss albino mice.

METHODS

Streptozotocin injected mice were monitored for hyperglycemia at a regular interval for a period of 36 and 72 days. The DNA integrity in epididymal spermatozoa was determined by the comet assay. Flow cytometric analysis was done in germ cells to assess the DNA ploidy. The global methylation analysis in germ cells was done by 5-methyl cytosine immunostaining.

RESULTS

Streptozotocin administration successfully resulted in hyperglycemic response which significantly affected serum testosterone level, sperm DNA integrity and DNA ploidy at the end of 36 days. However, no changes were observed in either epididymal sperm concentration or germ cell methylation status. In contrast, at the end of 76 days, although serum testosterone level, sperm DNA integrity and DNA ploidy status were unperturbed significantly in hyperglycemic group, the epididymal sperm concentration and methylation status of preleptotene/zygotene cells were significantly altered. Importantly, an attempt to find out the association between the blood glucose levels and the abnormalities in hyperglycemic group failed to demonstrate any correlation.

CONCLUSIONS

The germ cell abnormalities observed in hyperglycemic group could be interpreted as a primary effect of streptozotocin and not due to hyperglycemia. Our results call for further evaluation of streptozotocin before its application to study the hyperglycemic responses on male germ cells.

High levels of lipid peroxidation in semen of diabetic patients

The aim of this study was to evaluate the level of malondialdehyde (MDA) (one of the final products of lipid peroxidation and well-known marker of oxidative stress) in semen of infertile men with type 2 diabetes and to investigate its relationship with their glycaemic control. Forty infertile men with type 2 diabetes were evaluated. The mean ages were 36.5 ± 8.0. Men with diabetes were divided into two groups. Group A (n = 20) with glycated haemoglobin >10% and group B (n = 20) with glycated haemoglobin <7%. A single sample was examined according to the criteria of the World Health Organization (WHO Laboratory Manual for the Examination of Human Semen and Sperm-Cervical Mucus Interaction, 1999, Cambridge University Press). MDA was assessed using the thiobarbituric acid method. MDA concentration in semen of group A patients (0.95 ± 0.35 nmol ml(-1)) was significantly higher than in group B patients (0.43 ± 0.13 nmol ml(-1)) (P value < 0.05) and had negative relationship with sperm density (r = -.717; P value < 0.05), total sperm count (r = -.625; P value < 0.05), progressive motility (r = -.489; P value < 0.05) and normal forms (r = -.545; P value < 0.05). Based on these results, it could be concluded that increase in lipid peroxidation in men with diabetes with poor metabolic control was associated with low sperm quality.

In situ visualization of damaged DNA in human sperm by Raman microspectroscopy

BACKGROUND

Beyond determining the percentage of damaged sperm, current methods of DNA assessment are of limited clinical utility as they render the sample unusable. We evaluated Raman microspectroscopy, a laser-based non-invasive technique that provides detailed chemical 'fingerprints' of cells and which potentially could be used for nuclear DNA-based sperm selection.

METHODS

Eight healthy donors provided ejaculates. After system optimization, a minimum of 200 air-dried sperm/sample/donor, prior to/and after UVB irradiation, were assessed by two observers. Spectra were analysed by Principal Component, Spectral Angle and Wavelet Analyses.

RESULTS

Spectra provided a chemical map delineating each sperm head region. Principal Component Analysis showed clear separation between spectra from UV-irradiated and untreated samples whilst averaged data identified two regions of interest (1040 and 1400 cm(-1)). Local spectral analysis around the DNA PO(4) backbone peak (1042 cm(-1)), showed that changes in this region were indicative of DNA damage. Wavelet decomposition confirmed both the 1042 cm(-1) shift and a second UVB susceptible region (1400-1600 cm(-1)) corresponding to protein-DNA interactions. No difference was found between observer measurements.

CONCLUSIONS

Raman microspectroscopy can provide accurate and reproducible assessment of sperm DNA structure and the sites and location of damage.