Mendelian randomization analyses identified bioavailable testosterone mediates the effect of sex hormone-binding globulin on prostate cancer

Exploring the link between sex hormone-binding globulin levels and prostate cancer risk: a comprehensive systematic review and meta-analysis

BACKGROUND

Sex hormone-binding globulin (SHBG) plays a critical role in regulating androgen bioavailability and has been hypothesized to influence prostate cancer risk, though existing evidence is inconsistent. This systematic review and meta-analysis aimed to evaluate the association between SHBG levels and prostate cancer risk.

METHODS

A comprehensive search was conducted across PubMed, Embase, and Web of Science for studies published up to December 1, 2024. Observational studies assessing SHBG levels and prostate cancer risk were included. Effect sizes were pooled using random-effects meta-analysis. Heterogeneity was evaluated using the I2 statistic, and quality assessment was performed using the Newcastle-Ottawa Scale. Statistical analysis was performed using R software version 4.4.

RESULTS

Sixteen studies, including 720,298 participants and 90,799 prostate cancer cases, were analyzed. The pooled odds ratio (OR) for prostate cancer risk per unit increase in SHBG was 0.907 (95% CI 0.799-1.030), indicating no statistically significant association. Substantial heterogeneity was observed among the included studies (I2 = 79%; P < 0.0001). Subgroup analyses showed no significant variation in effect sizes by study design. However, a Mendelian randomization analysis conducted in 140,254 European-descent males, including 79,148 prostate cancer cases, suggested a modest protective effect of higher SHBG levels, with an OR of 0.944 (95% CI 0.897-0.993). Sensitivity analyses confirmed the robustness of the pooled findings.

CONCLUSION

This meta-analysis showed a complex relationship between SHBG levels and prostate cancer risk. While overall findings do not support a statistically significant association, higher SHBG levels may confer a protective role in specific contexts. Further research is needed to elucidate mechanisms, reduce heterogeneity, and validate SHBG as a biomarker for risk stratification.

A Mendelian Randomization Study of the Connection Between Exogenous Hormones and Perianal Abscess in Pediatric Patients

Background: Recent years have witnessed the hypothesis that bioavailable testosterone (BT) might be closely related to the development of inflammatory diseases, especially anal abscess (AA), a common inflammatory ailment with unclear pathogenesis. Given that AA is more prevalent among males, this study investigates the causal relationship between BT and AA. Objective: To explore the causal link between BT and AA, a Mendelian randomization (MR) study was conducted using large-scale genomic data. Materials and Methods: Utilizing genomic data from the UK Biobank and IEU OpenGWAS databases, a two-sample MR analysis was executed. Twenty-six genetic variants strongly associated with BT were selected as instrumental variables (IVs) to assess their link with AA risk. Various MR methods were employed for consistency checks, including sensitivity analyses for heterogeneity and horizontal pleiotropy. Results: Using a combination of MR methods, we identified a significant causal relationship between BT and the risk of AA. Specifically, the MR analysis revealed that higher levels of BT were associated with an increased risk of AA. Sensitivity analyses, including heterogeneity tests and assessments for horizontal pleiotropy, confirmed the robustness of these findings. The IVs used in the analysis demonstrated a strong association with BT and showed no evidence of significant heterogeneity or horizontal pleiotropy, indicating the validity of the causal inference. Conclusion: This study, employing two-sample MR for the first time, confirms a causal relationship between BT levels and the risk of AA. These findings provide preliminary evidence of the causal relationship between BT and AA and may offer new insights into the pathophysiological mechanism of AA and future therapeutic strategies.

Drug-target Mendelian randomization revealed a significant association of genetically proxied metformin effects with increased prostate cancer risk

The association between metformin use and risk of prostate cancer remains controversial, while data from randomized trials is lacking. We aim to evaluate the association of genetically proxied metformin effects with prostate cancer risk using a drug-target Mendelian randomization (MR) approach. Summary statistics for prostate cancer were obtained from the Prostate Cancer Association Group to Investigate Cancer Associated Alterations in the Genome Consortium (79,148 cases and 61,106 controls). Cis-expression quantitative trait loci (cis-eQTL) variants in the gene targets of metformin were identified in the GTEx project and eQTLGen consortium. We also obtained male-specific genome-wide association study data for type 2 diabetes, body mass index (BMI), total testosterone, bioavailable testosterone, estradiol, and sex hormone binding globulin for mediation analysis. Inverse-variance weighted (IVW) regression, weighted median, MR-Egger regression, and MR-PRESSO were performed in the main MR analysis. Multivariable MR was used to identify potential mediators and genetic colocalization analysis was performed to assess any shared genetic basis between two traits of interest. We found that genetically proxied metformin effects (1-SD HbA1c reduction, equivalent to 6.75 mmol/mol) were associated with higher risk of prostate cancer (odds ratioIVW [ORIVW]: 1.55, 95% confidence interval, CI: 1.23-1.96, p = 3.0 × 10-3). Two metformin targets, mitochondrial complex I (ORIVW: 1.48, 95% CI: 1.07-2.03, p = 0.016) and gamma-secretase complex (ORIVW: 2.58, 95%CI :1.47-4.55, p = 0.001), showed robust associations with prostate cancer risk, and their effects were partly mediated through BMI (16.4%) and total testosterone levels (34.3%), respectively. These results were further supported by colocalization analysis that expressions of NDUFA13 and BMI, APH1A, and total testosterone may be influenced by shared genetic factors, respectively. In summary, our study indicated that genetically proxied metformin effects may be associated with an increased risk of prostate cancer. Repurposing metformin for prostate cancer prevention in general populations is not supported by our findings.

Causal relationship between gut microbiome and sex hormone-binding globulin: A bidirectional two-sample Mendelian randomization study

PROBLEM

Currently, there is a variety of evidence linking the gut microbiota to changes in sex hormones. In contrast, the causal relationship between SHBG, a carrier of sex hormones, and the gut microbiota is unclear.

METHOD OF STUDY

Bidirectional two-sample Mendelian randomization (MR) analysis was used to detect the causal effect between SHBG and the gut microbiome. Summary statistics of genome-wide association studies (GWASs) for the gut microbiome and SHBG were obtained from public datasets. Inverse-variance weighting (IVW), weighted median, weighted mode, MR-Egger and simple mode methods were used to operate the MR analysis. F-statistics and sensitivity analyses performed to evaluate bias and reliability.

RESULTS

When we set gut microbiome as exposure and SHBG as outcome, we identified nine causal relationships. In males, Coprobacter (PIVW = 2.01 × 10-6 ), Ruminococcus2 (PIVW = 3.40 × 10-5 ), Barnesiella (PIVW = 2.79 × 10-2 ), Actinobacteria (PIVW = 3.25 × 10-2 ) and Eubacterium fissicatena groups (PIVW = 3.64 × 10-2 ) were associated with lower SHBG levels; Alphaproteobacteria (PIVW = 1.61 × 10-2 ) is associated with higher SHBG levels. In females, Lachnoclostridium (PIVW = 9.75 × 10-3 ) and Defluviitaleaceae UCG011 (PIVW = 3.67 × 10-2 ) were associated with higher SHBG levels; Victivallaceae (PIVW = 2.23 × 10-2 ) was associated with lower SHBG levels. According to the results of reverse MR analysis, three significant causal effect of SHBG was found on gut microbiota. In males, Dorea (PIVW = 4.17 × 10-2 ) and Clostridiales (PIVW = 4.36 × 10-2 ) were associated with higher SHBG levels. In females, Lachnoclostridium (PIVW = 7.44 × 10-4 ) was associated with higherr SHBG levels. No signifcant heterogeneity of instrumental variables or horizontal pleiotropy was found in bidirectional two-sample MR analysis.

CONCLUSIONS

This study may provide new insights into the causal relationship between the gut microbiome and sex hormone-binding protein levels, as well as new treatment and prevention strategies for diseases such as abnormal changes in sex hormones.