Associations of Semen Quality with Seminal Non-essential Heavy Metals in Males from the Canary Islands

Nickel and human sperm quality: a systematic review

BACKGROUND

Reproductive effects of chronic exposure to nickel (Ni), including sperm quality, have been a matter of debate given that published studies yielded contrasting results. We have, therefore, planned to systematically search and analyze medical literature with the aim to ascertain the association of exposure to nickel with the sperm quality in humans.

MATERIALS AND METHODS

We systematically searched Pubmed, Scopus and Embase for studies reporting the association of Ni with the sperm quality in humans with no time or language limits and used PRISMA to report the findings. The risk of bias was assessed using JBI critical appraisal checklist and SIGN tool. Because the reported effects were no coherent, meta-analysis was not possible.

RESULTS

All included studies were observational and planned to test the effect of a group of trace elements, but not Ni alone. We identified and included 19 studies from 23 publications, published from 12 countries, which assessed sperm quality, sperm DNA damage and sperm metabolome. Ni was quantified in blood, semen plasma, spermatozoa and urine. Sixteen included cross-sectional studies were of acceptable quality, whereas three more case-control reports were of poor quality. Multivariate models were reported in only eight studies. Overall, studies were inconsistent in the direction of effect, when elevated Ni was not associated with the outcome (N = 8 studies), or some association was present (N = 11 studies). In the latter, 9 studies yielded elevated risk and 2 studies exhibited protective effect. Only one report was in an occupationally exposed population with some association with tail defects, but present in both welders and controls.

CONCLUSIONS

Existing evidence from the studies in humans is inconsistent and does not confirm a clear adverse effect of higher Ni concentrations in blood, urine or semen on the sperm quality. Robust methodology must be a key issue in the future studies. Studies with more powerful evidence, such as cohort or experimental reports are needed.

Exposure to potentially toxic elements (PTEs) and the risk of male infertility- A Systematic review and meta-analysis

BACKGROUND

Infertility has been defined as a failure to conceive for at least 12 months of regular unprotected sexual intercourse. The male factors are responsible for about 50 % of cases. Various factors such as endocrine, immunological, genetic, exposure to toxicants, and idiopathic factors are involved in male infertility. Recently, the role of PTEs in reproductive performance has been explored by various studies.

OBJECTIVES

Current systematic review and meta-analysis have been carried out to compile and statistically analyze the findings of relevant studies and reach some conclusion.

METHODOLOGY

A literature search was done according to the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines in three scientific literature databases; PubMed, Google Scholar, and Science Direct. Meta-analysis was performed using Review Manager 5.4 software. The study's protocol was registered in PROSPERO (CRD42023465776).

RESULTS

Meta-analysis of lead in the blood of infertile cases and healthy controls indicated a significant association with male infertility, observed standard mean difference (SMD) was 0.67 at 95 % confidence interval (CI) (0.07, 1.28), and p = 0.03. In the case of lead analysis in semen, the values are as follows: SMD = 1.19 at 95 % CI (0.42, 1.96) with p = 0.002. Significant association appears for cadmium in semen with SMD 0.92 at 95 % CI (0.54, 1.29) and p < 0.00001. No significant association was observed for arsenic, barium, and mercury in blood.

CONCLUSION

Most of the studies focus on the detection of PTE in semen samples followed by blood as sample type. Lead and cadmium exposure is significantly associated with male infertility. However, non-significant results for arsenic, barium, and mercury are observed.

The Influence of Follicular Fluid Metals on Assisted Reproduction Outcome

Infertility has become more common, with an increased exposure to toxic compounds including heavy metals (HM). Follicular fluid (FF) surrounds the developing oocyte in the ovary and can be analysed to assess metal content. The levels of twenty-two metals were measured in the FF of ninety-three females in a reproduction unit, and their influence on assisted reproduction technique (ART), were examined. The metals were determined by optical emission spectrophotometry. Low values of copper, zinc, aluminium, and calcium favour polycystic ovary syndrome. The relationships between the number of oocytes and metals: iron (rs=0.303; p=0.003) and calcium (rs=-0.276; p=0.007) are significant, as well as between the number of mature oocytes with iron (rs=0.319; p=0.002), calcium (rs=-0.307; p=0.003) and sodium (rs=-0.215; p=0.039) and are near to significance in the case of aluminium (rs=-0.198; p=0.057). In the group with a fertilisation rate ≤ 75%, 36% of the women presented calcium >176.62 mg/kg compared to the group with a fertilisation rate ≥ 75% where this percentage was only 10% (p=0.011). An excess of iron and calcium reduces the good quality embryo rate, and an excess of potassium impairs the blastocyst rate. If potassium is above 237.18 mg/kg and calcium is below 147.32 mg/kg, these conditions favour embryo implantation. Pregnancy is influenced by high potassium and low copper levels. Controlling exposure to toxic elements is recommended for all couples with reduced fertility or receiving an ART.

Influence of Seminal Metals on Assisted Reproduction Outcome

Increased levels of metal ions in human seminal fluid have a significant correlation with male fertility. Few publications explain the effect of metals in semen and their influence on assisted reproductive treatments. Semen parameters and the levels of twenty-two metals were measured in the seminal fluid of 102 men attended in a Reproductive Unit. Metals were determined by optical emission spectrophotometry. A statistical relationship was found between spermiogram and iron, which was lower than expected in pathological spermiograms (p = 0.032); zinc (p = 0.066), calcium (p = 0.047), and magnesium (p = 0.048) mean levels were higher in normozoospermics. More days of sexual abstinence correlates with higher seminal zinc (p = 0.001) and magnesium levels (p = 0.002). Lower vanadium values were found to be associated with higher fertilization rates (p = 0.039). Higher values of lead (p = 0.052) and vanadium (p = 0.032) were obtained in patients who did not reach 100% embryo cleavage rate. Aluminium (p = 0.042) and sodium (p = 0.002) were found in lower amounts associated with better blastocyst rates. The implantation rate shows an inverse association with women's age and iron and calcium content, compared to magnesium and sodium which presented a significant direct association with this percentage. A significant direct relationship was found between the positive evolution of pregnancy and the values of zinc (p = 0.004), calcium (p = 0.013), potassium (p = 0.002), and magnesium (p = 0.009). The study confirms that zinc, iron, calcium, sodium, aluminium, magnesium, vanadium, and lead have positive-negative effects on reproduction and support the analysis of metals in semen as a new line of study on male fertility with implications for reproductive outcomes.

Determination of aluminum concentrations in biological specimens: application in the clinical laboratory

Aluminum enters the body primarily through diet or occupational exposure, and is cleared through urine. However, this trace element may accumulate and cause toxicity in subjects with renal insufficiency, and even in dialysis patients. The mechanism of aluminum toxicity is related to increased oxidative and inflammatory stress, iron and calcium dyshomeostasis, or cholinergic dysregulation, among other. A review was conducted on the specimens and analytical methods used to determine aluminum in biological specimens and dialysis water. This paper describes the most relevant aspects related to quality assurance. This is a practical guideline for the development and implementation of a reliable method for determination of aluminum in the clinical laboratory. Serum aluminum is the main biomarker of toxicity. For cases of chronic exposure, urine testing is recommended. At present, inductively coupled plasma mass spectrometry (ICP-MS) is the gold-standard determination method, since it has been proven to have the best quantification limits, selectivity and robustness. Clear recommendations are provided in relation to the specimens used for aluminum determination. Relevant pre-analytical, analytical, and post-analytical considerations are also presented.