Effect of duration on fertility status of Nigerian Males occupationally exposed to lead

¹Okafor J C (PhD), ¹Salum S S (PhD), ²Obianagha NF (PhD) and ³Anetor JI (PhD)

¹Department of Pathology, School of Health and Medical Sciences, State University of Zanzibar.

²Department of Chemical Pathology and Immunology Olabisi Onabanjo University Nigeria

³Department of Chemical Pathology University of Ibadan

All correspondence: Dr Chukwuma Okafor Department of Pathology and Biochemistry School of Health and Medical Sciences State University of Zanzibar chumario2k@yahoo.com

ABSTRACT

Many industrial chemicals are known to have a negative impact on human reproduction, particularly occupational and environmental exposures to heavy metals such as lead. The risk is generally believed to be directly correlated with both increasing concentrations and durations of exposure .

Methodology: This was a cross sectional study carried over six months. A total of 100 lead exposed male workers comprising 50 lead acid battery chargers and 50 auto painters within Surulere LGA of Lagos State were used in this study. Subjects were all Nigerians within the age bracket of 18 and 60 years randomly selected and their durations of exposure to lead were classified as less than five years and above five years. Blood lead levels (BLL) were determined in the whole blood using the Atomic absorption spectrophotometer (AAS). Reproductive hormones were done by ELISA. Semen parameters were assessed according to WHO standard procedures. Data were analyzed using Student’s‘t’ test and Pearson’s correlation coefficient.

Results: The BLL in > 5 years exposure category was significantly higher than the < 5 years exposure category in AP and BC (p< 0.008, p< 0.02 respectively); demonstrating dose-response relationship. Positive correlations at both durations of exposure (r=0.916, p=0.0001; r=0.788, p=0.0001); (r=0.461, p=0.047; r=0.499, p< 0.040) were observed between lead and prolactin in AP and BC respectively. In contrast, negative associations (; r= -0.727, p=0.0001; r= –0.753, p=0.0001 ) were observed between lead and testosterone levels at > 5 years exposure category for AP and BC respectively. No correlation was observed between lead and gonadotropins, LH and FSH at both durations of exposure in AP and BC. Inverse and significant associations at both durations of exposure (r= -0.391, p=0.044; r= -0.439, p=0.039) and (r= -0.359, p< 0.049; r= -0.412, p< 0.041) were observed between lead and total sperm count in AP and BC respectively. No dose relationship was established between lead and total sperm count.

Conclusion: Lead suppresses the reproductive pathway in lead workers through a probable mechanism of hyperprolactinaemia, which in turn may directly block testosterone synthesis and may culminate in decreased sperm count, ultimately manifesting in reduced fertility state which may not be severity dependent

KEY WORDS: Lead, battery chargers (BC), auto painters (AP), duration of exposure.

INTRODUCTION

The reproductive effects of lead are complex and appear to involve multiple pathways, not all of which are fully understood [1].Many studies on the male reproductive system of animals have revealed lead as a toxicant for testicular tissue and functions [2,3]. These include significant reductions in the number of spermatozoa within the epididymis in mice administered with lead acetate (0.25% and 0.50%) in drinking water and arrested spermatogenesis in rats [4, 5]. Some studies suggest that abnormalities of spermatogenesis are induced by exposure to lead while other researchers have failed to demonstrate correlations between lead and semen volume, abnormal sperm and sperm concentration among workers exposed to high lead levels [ 6, 7].

Reproductive hormones play an important and complicated role in the regulation of spermatogenesis and sperm development. [1 ]. The result of experimental studies in rats have shown that the effects of lead involve multiple action sites on male reproductive hormones although the most important part of these disorders probably occurs in the hypothalamic-pituitary-testosterone (HPT) axis [ 8, 9]. It is understood that depending on intensity and severity of lead exposure and duration, signals within and between the rats hypothalamus and pituitary gland appear to be disrupted by lead . On administration of lead acetate in water to rats showed a dose-related increase in gonadotropin releasing hormone (GnRH) mRNA and no effects on the serum concentrations of hypothalamic GnRH or LH, suggesting that there may be a compensating mechanism in the HPT axis [ 10].

In addition to animal studies, some researchers [11] reported a positive correlation between serum LH levels and duration of occupational lead exposure. It is therefore unclear, if male reproductive issues in persons exposed to lead are mostly related to the disruption of reproductive hormones or due to lead’s direct effects on the gonads, or both? This question had been difficult to answer, because lead, especially at high levels, is capable of adversely affecting many organs or systems in the body. Although lead can potentially reduce male fertility by decreasing sperm count and motility, inducing abnormal morphology and affecting functional parameters; not all studies have been able to clearly demonstrate such effects [1].

METHODOLOGY

This was a cross sectional study carried over six months. A total of 100 lead exposed male workers comprising 50 lead acid battery chargers and 50 auto painters within Surulere LGA of Lagos State were used in this study. Subjects were all Nigerians within the age bracket of 18 and 60 years randomly selected and their durations of exposure to lead were classified as less than five years and above five years. The Ethical approval was obtained from the Institutional Review Board of the Nigerian Institute for Medical Research, Lagos State. Informed consent of the subjects was gotten through the aid of a well structured questionnaire. Verbal presentations of the summaries of the hazards of lead exposure were made to the sample population to encourage voluntary participation of the subjects. Inclusion criteria were all participants in the study and it was purely voluntary. We excluded from the study those on any systemic diseases, those on fertility drugs, those who smoke, all those with history of drugs/substance abuse, all women and those on immune suppressive drugs. The control samples comprised of 50 males office workers who had never been occupationally exposed to lead.

SAMPLE COLLECTION

A . Blood

Ten milliliters of venous blood were collected from each subject. The samples were divided into three equal parts in lead-free heparinized tubes, EDTA bottles and plain bottles. The samples were collected in the morning between 8am and 10am and those for lead were done within three hours of collection. Samples in the plain bottles were allowed to clot, centrifuged, separated and the serum stored at -4^oC until analyzed.

B. Semen

All semen samples were collected between 7am and 10am and brought to the laboratory less than one hour after collection. The method of collection was masturbation and the samples were introduced into clean sterile lead free universal containers. All the subjects observed a seven day abstinence from sexual intercourse, cigarette, coffee and alcohol consumption according to WHO guidelines [12]. All the semen samples were allowed to liquefy for more than 20 minutes

Laboratory Analysis:

Blood lead levels (BLL) were determined in the whole blood using the Atomic absorption spectrophotometer (AAS).

Principle: The energy absorbed by atoms excited from the ground state is characteristic of those atoms. If light with the same wavelength characteristics as the radiation absorption of the element to be analysed is passed through a curtain of flame containing those atoms in the excited state, the amount of light energy absorbed will be proportional to the concentration of the element.

Reproductive hormones were done by ELISA.

Principle: The hormonal ELISA assay is based on simultaneous binding of human hormone to two monoclonal antibodies, one immobilized on microwell plates, the other conjugate with horseradish peroxide (HRP). After a washing step, enzyme substrate is added. The enzymatic reaction is proportional to the amount of reproductive hormone in the sample. The reaction is terminated by the addition of a stop solution. Absorbance is measured on a microplate reader.

Semen parameters were assessed according to WHO standard procedures. The morphology (%), motility (%), volume (mL) and the total count (million/mL) of the various semen samples were all analyzed. Log-transformation (base 10) was required and therefore computed for semen volume (mL), total sperm count(million/mL), percentage of sperm motility (%), motile sperm count (%) [21]

RESULTS

Discussion

A significant finding in this work was the reliability of blood lead levels as a measure of the duration of exposure in both the auto painters and the battery chargers. This indicates that the exposure to lead fumes and dusts in the workplace significantly increased the blood lead levels of the workers exposed to lead proportionately to duration of exposure. The work showed clearly that the mean lead levels of the above 5yrs group were statistically significantly higher for both exposed workers when compared to that of the less than 5 years group. The significant high level of prolactin recorded from this study could be stress induced. The high increase of prolactin among lead workers was collaborated by other workers [13, 14]. The increase might be due to dopaminergic depletion structure (TIDA : Tuberoin fundibular Dopaminergic Neurone Population). Lead might have acted on the HPA –axis with TIDA as its target in an indirect “dopamine-depletion” mechanism. The measurement of prolactin in males might thus provide opportunities for early identification of excess exposure to neurotoxic chemicals affecting dopaminergic control of Pituitary Secretion even before the onset of diseases. Some workers [15] observed that elevated levels of prolactin decreases the levels of gonadal testosterone in Men via prolactin interference with secretion of gonadotropin-releasing hormone. Other workers have suggested other mechanisms by which hyperprolactinaemia lead to reproductive dysfunctions apart from the inhibition of the GnRH. [ 16, 17].These include blockade of the effects of gonadotropins at the gonadal level. It could also be by the impairment of the accessory sex glands indicating a possible interaction between prolactin and testosterone. There could equally be a direct impairment of sperm quality indices.

The study recorded no significant difference in the levels of LH and FSH of both the auto painters and battery chargers when compared with the controls. And there was no correlation between these two hormones and lead at both durations of exposure in auto painters and battery chargers. It is therefore plausible that the high level of prolactin recorded in this study among the lead workers may have caused a decrease of the testosterone levels via other mechanisms other than the inhibition of the trophic hormones leading to the decline in the total sperm counts of the lead workers.

A negative association was shown between lead and testosterone at the 5 years and above duration of exposure. However the total sperm count and prolactin showed negative and positive correlations respectively at both levels of exposure. We view this as a clear indication of no dose response relationship between lead and prolactin and also between lead and total sperm count. The implication is that the toxic effect of lead on the reproductive pathway may not be severity dependent.

Some workers [18 ] had shown that the toxic effect of lead in male reproductive system is on the glycogen rich sertoli cells which are damaged thereby depleting the glycogen content of the cells and depriving spermatids the required nourishments therefore preventing them from maturing into viable spermatozoa [19]. It has been observed that alterations in sperm chromatin stability may be the most probable mechanisms involved in lead toxicity effects on spermatogenesis at low duration of exposure [20]

Generally in most of the developing countries like Nigeria, methods of hygienic control and close medical supervision of the workmen are very poor. Usually there is lack of comprehensive and systemic environmental monitoring and regular official inspection of the workplace. It was not entirely surprising to record such results. It is plausible that sustained high concentration like for a prolonged duration of exposure will most probably have more severe effects on exposed workers.

Conclusion

Lead suppresses the reproductive partway in lead workers through a probable mechanism of inducing hyperprolactinaemia, which in turn may directly block testosterone synthesis and may culminate in decreased sperm count, ultimately manifesting in reduced fertility state which may not be severity dependent

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