Moussa M. Diawara

A novel group of ovarian toxicants: the psoralens.

The psoralens are naturally occurring metabolites found in many crop plants; synthetic forms of 5‐methoxypsoralen (bergapten) and 8‐methoxypsoralen (xanthotoxin) are widely used in skin photochemotherapy. Our previous research documented that dietary bergapten and xanthotoxin reduced birthrates in female rats when males and females were exposed to these chemicals. The present study was designed to determine the cause of this reduced birthrate and whether this resulted from direct impact on the females. The study demonstrates that bergapten and xanthotoxin administered, either alone or in combination to female rats (mated to undosed males), significantly reduced the number of implantation sites, pups, and corpora lutea in dosed females compared with control animals. Additionally, full uterine weight and empty uterine weight were significantly reduced. These compounds also significantly reduced circulating estrogen levels in a dose‐dependent manner. Interestingly, the psoralens significantly induced mRNAs of liver enzymes typically induced by polycyclic aromatic hydrocarbons, CYP1A1 and UGT1A6; the higher the dose, the greater the induction. UGT 2B1 mRNA, typically induced by phenobarbital‐like compounds, was not significantly affected. Thus, enhanced oxidative metabolism and conjugation of estrogens in psoralen‐treated animals may provide a partial explanation for the effects observed. These findings are also consistent with psoralen‐induced reduction in ovarian follicular function and ovulation.

REPRODUCTIVE TOXICITY OF THE PSORALENS

The psoralens are naturally occurring secondary metabolites in plants, including many fruits and vegetables. Health risks have been associated with handling or ingesting psoralen-containing plants, and with the use of synthetic psoralens in photochemotherapy of skin disorders. Our research has demonstrated that administration of the psoralens bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) in the diet of female rats reduced birthrates, number of implantation sites, pups, corpora lutea, full and empty uterine weight, and circulating estrogen levels in a dose-dependent manner. Psoralens induced mRNAs of the liver enzymes CYP1A1 and UGT1A6, suggesting that enhanced metabolism of estrogens by psoralen treatment may explain the reproductive toxicity and the observed reduction of ovarian follicular function and ovulation. Rats also avoided repeated consumption of a flavored solution associated with psoralen administration. The findings indicate that the psoralens constitute a novel group of ovarian toxicants. Further examination of the safety of their use in photochemotherapy and diet is warranted.

Psoralen-induced growth inhibition in Wistar rats

The linear furanocoumarins (or psoralens) are naturally occurring plant biosynthetic metabolites that have been used since ancient times in skin photochemotherapy. However, medicinal use of the psoralens has been linked with increased incidence of skin cancer in humans. To understand some of the mechanism of this toxicity, we tested increasing concentrations of the psoralens bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) for toxicity against Wistar rats. As dietary concentrations of each compound increased, weight gain in both male and female rats decreased. Feeding on diet containing these chemicals also decreased rat birth rate, but did not significantly affect individual litter weight or date of birth. Xanthotoxin appeared to be more toxic than bergapten.

Resistance to fall armyworm in converted sorghums.

Field experiments were conducted in 1988 to evaluate newly converted sorghum, Sorghum bicolor (L.) Moench, germplasm for both whorl and panicle resistance to feeding by larvae of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). In the whorl-stage resistance study, over 20 and 30 of the entries were significantly more resistant to FAW feeding than the resistant check at 7 and 14 days after infestation, respectively. Significant differences also were found among the entries for the number of FAW larvae that established per panicle 4 days after infestation.

Arsenite exposure compromises early embryonic development in the Golden hamster

The toxicity of arsenite to 8-cell stage hamster embryos was evaluated. Females were superovulated and mated; embryos were collected and grown for 72 h in culture medium containing vehicle control, 25, 50, 250, 500, or 750 nM arsenite. Morphological observations were taken at 0 and 24h increments. A TUNEL assay was used for determining DNA damage. Survival was expressed by the ability to undergo zona escape. The control group had 78% survival and no evidence of deformities. Embryos in the 25, 50 and 250 nM groups had survival rates of 63%, 55% and 27%, respectively. Arsenite exposure caused total embryo lethality, major deformities, complete failure to undergo zona lysis, and significantly higher number of cells with fragmented DNA in embryos at the 500 and 750 nM concentrations. The study underscores the sensitivity of preimplantation stage embryos to the presence of even relatively small amounts of arsenic in luminal fluid.

Mechanism of whorl feeding resistance to fall armyworm among converted sorghum accessions

Field studies were conducted in 1989 to evaluate selected converted sorghum (Sorghum bicolor [L.] Moench) accessions for resistance to whorl‐stage feeding by larvae of the fall armyworm (Spodoptera frugiperda J. E. Smith) and to determine the mechanism of resistance. The sorghum was infested in the whorl 26 days after planting (DAP) in experiment 1 and 33 DAP in experiment 2. In experiment 1, the plant accessions ‘IS7273C,’ ‘IS7444C,’ ‘IS12573C,’ ‘IS12678C,’ and ‘IS12679C’ were more resistant (rating < 3) to damage by S. frugiperda larvae than the resistant check CIMMYT (CM) 1821 (rating 6.2) at 14 days after infestation (DAI). These genotypes were also more resistant (ratings ≤ 4 at 7 DAI and < 3 at 14 DAI) than the resistant check CM1821 (ratings 5.6 at 7 DAI and 8 at 14 DAI) in experiment 2. The number of larvae that established/plant on IS7273C, IS7444C, IS12573C, or IS12679C was significantly less compared with establishment on the resistant check CM1821 at 14 DAI in experiment 1 and at 7 and 14 DAI in experiment 2. Resistance in IS7273C, IS7444C, IS12573C, and IS12679C was mainly due to their rapid rate of growth which induced a quick change in the plant morphology from the whorl‐ to the panicle‐stage and did not permit a sustained colonization of larvae. This new type of resistance could be referred to as ‘morphological non‐preference’ as apposed to chemical non‐preference where non‐preference is due to plant chemical factors. These genotypes had a significantly shorter cycle than the other sorghum genotypes. Host evasion, a type of pseudoresistance, was the basis for resistance in ‘IS7794C’ and ‘IS7947C’. Tolerance was the major mechanism of resistance in the resistant check CM 1821.

Morphological Evidence of 8‐MOP‐Induced Apoptosis in Rat Ovary

Psoralens have been shown to cause reproductive toxicity in both male and female rats. Recent research demonstrated that exposure to 8‐methoxypsoralen (or xanthotoxin) decreases 17‐β estradiol and aromatase translation in the ovary of Wistar rats. We initiated the present study to determine whether morphological evidence of apoptotic damage exists with xanthotoxin treatment. Female Wistar rats were dosed with xanthotoxin (180 mg/kg, p.o.) or the control vehicle for 30 days. Animals were then sacrificed and ovaries were removed, fixed and serially sectioned for histological examination. Ovaries from xanthotoxin‐dosed females revealed characteristics of extensive apoptotic damage not evident in control follicles. Follicles from these xanthotoxin‐treated rats displayed such characteristics of apoptosis as pyknotic nuclei in the antrum, detachment of the follicular membrane from the theca interna, and dissolution of the corona radiata. The present study provides visual evidence of xanthotoxin‐induced apoptotic damage, typical of exposure to high levels of reactive oxygen species. This proposed mechanism of follicular apoptosis is consistent with previously reported xanthotoxin‐induced reduction in circulating 17β‐estradiol levels, reduced transcription of cytochrome P450 aromatase, and an increased DNA fragmentation.

7.5 – 8-Methoxypsoralen Compromises the Development of Ovarian Large Antral Follicles in Wistar Rats

The psoralens are naturally occurring metabolites found in many crop plants. Bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) are widely used in skin photochemotherapy. Research has shown that dietary bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) reduced birthrate in female rats when males and females were exposed to these chemicals. In addition, the two compounds, administered to female rats (mated to undosed males), reduced levels of circulating 17β-estradiol, and the number of implantation sites, pups, and corpora lutea, suggesting a direct effect on ovarian follicles. The present study was initiated to determine whether effects of xanthotoxin can be observed in ovarian follicles. Female Wistar rats were dosed daily (30 days) with vehicle control or xanthotoxin (180 mg kg-1, p.o.). Ovaries were collected and prepared for histological evaluation. Antral follicles (diameter >600 μm) were found to be larger (p < 0.05) in ovaries from xanthotoxin-dosed compared with control rats. Moreover, the granulosa cell layer thickness, and granulosa cell layer:follicle diameter ratio were reduced (p < 0.05) in dosed animals. This provides visual evidence that the granulosa cell population in large antral follicles is affected by xanthotoxin, and is consistent with its observed reduction in circulating 17β-estradiol levels.

Bioassay for Screening Plant Accessions for Resistance to Fall Armyworm (Lepidoptera: Noctuidae) Using Artificial Diets

Laboratory bioassays demonstrated that formulation of artificial insect diet influenced the expression of antibiosis to fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), in grain sorghum, Sorghum bicolor (L.) Moench. Larvae of FAW were reared on a diet formulated with pinto bean and a diet formulated with no pinto bean, both supplemented with dried milk stage florets of resistant and susceptible sorghum genotypes. The sorghum lines showed a significantly higher antibiosis to FAW when mixed in the diet formulated with no pinto bean than when mixed in the diet containing the bean. Larvae that were fed the no-bean diet supplemented with resistant sorghum genotypes weighed one-half to one-third less, required longer to pupate, and resulted in lighter pupae than larvae reared on mixtures containing the bean. The results obtained when the larvae were reared on the bean diet were significantly correlated (P = 0.0001, r > 0.80, n = 18) with those recorded when the no-bean diet was used for the FAW variabl...

Smelting Remains a Public Health Risk Nearly a Century Later: A Case Study in Pueblo, Colorado, USA

Pueblo, Colorado has a long history of smelting activities, and recent studies raised concerns about lead exposure. This study tested 240 children in Pueblo for blood lead levels (BLLs) and found a significant association between distance from old smelters and children BLLs. Around 7.5% of Pueblo children had BLLs above the Centers for Disease Control and Prevention reference level of 5 µg/dL for elevated BLL, and 18.3% had BLLs between 3.3–4.9 µg/dL. Out of the 36 children who lived near former smelters, 13.9% had BLLs above 5 µg/dL vs. 6.37% for children living away from old smelters. The proportion of Pueblo children with elevated BLL was nearly three times the 2007–2010 United States national average (7.5% vs. 2.6%), and this was higher in the immediate vicinity of old smelters (13.9% vs. 2.6%). Genetic polymorphisms for ALAD-1 or ALAD-2 alleles, which play a role in susceptibility to lead toxicity, were not associated with children BBLs. Around 38.5% of houses sampled near the smelters had topsoil lead levels higher than the Environmental Protection Agency’s benchmark of 400 mg/kg. Our study resulted in the addition of areas of Pueblo to the EPA Superfund National Priorities List in December 2014, and cleanup is currently underway to minimize the public health risks.