A novel behavioral model of the pasture-based dairy cow from GPS data using data mining and machine learning techniques.

A better understanding of the behavior of individual grazing dairy cattle will assist in improving productivity and welfare. Global positioning systems (GPS) applied to cows could provide a means of monitoring grazing herds while overcoming the substantial efforts required for manual observation. Any model of behavioral prediction using GPS needs to be accurate and robust by accounting for inter-cow variation as well as atmospheric effects. We evaluated the performance using a series of machine learning algorithms on GPS data collected from 40 pasture-based dairy cows over 4 mo. A feature extraction step was performed on the collected raw GPS data, which resulted in 43 different attributes. The evaluated behaviors were grazing, resting, and walking. Classifier learners were built using 10 times 10-fold cross validation and tested on an independent test set. Results were evaluated using a variety of statistical significance tests across all parameters. We found that final model selection depended upon level of performance and model complexity. The classifier learner deemed most suitable for this particular problem was JRip, a rule-based learner (classification accuracy=0.85; false positive rate=0.10; F-measure=0.76; area under the receiver operating curve=0.87). This model will be used in further studies to assess the behavior and welfare of pasture-based dairy cows.

Use of a human acellular dermal wound matrix in patients with complex wounds and comorbidities.

OBJECTIVE: Rising prevalence of obesity and uncontrolled diabetes mellitus has resulted in an increasing number of patients with multiple comorbidities who require treatment for chronic complex wounds. Because patients with diabetes and foot ulcers may have a higher risk for amputations, techniques that facilitate complex wound healing and prevent limb amputation are desirable. Here, we investigate a limb preservation strategy that includes application of a human acellular dermal wound matrix (HADWM). METHOD: Medical history, physical examination and full wound assessment were completed for all patients. Systemic antibiotics and appropriate offloading were prescribed as needed. Wounds were debrided to create a bleeding bone and/or wound base for HADWM (Graftjacket regenerative tissue matrix, Wright Medical Technology, Inc., licensed by KCI, an Acelity company, San Antonio, TX). Healing progress was monitored over four weeks with weekly postoperative visits. 'Healed' was defined as full epithelialisation without drainage. RESULTS: Lower extremity ulcers, 16 in 13 patients, were treated with HADWM between May 2004 and July 2013. The median patient age was 76 years (range: 38-90). The average number of comorbidities was three per patient, while 6 (46%) patients had ≥4 comorbidities. Diabetes mellitus (92%) and peripheral vascular disease (77%) were the two most common. All 16 (100%) wounds healed without complications. There were no recurrences in the 11 wounds of the nine patients available for follow-up. Of these patients two had previously advised to receive major leg amputations retained functional limbs. CONCLUSION: The results in this small study reflect our practice's 10-year experience using HADWM as part of a limb preservation strategy.

Genome sequence of Edwardsiella ictaluri 93-146, a strain associated with a natural channel catfish outbreak of enteric septicemia of catfish.

Edwardsiella ictaluri is the cause of extensive mortalities and economic losses to the channel catfish industry of the southeast United States. Here we report the complete genome of Edwardsiella ictaluri 93-146. Whole-genome sequence analysis of E. ictaluri provides a tool for understanding the genomic regions specific to the species and the Edwardsiella genus.

Multiple-locus variable-nucleotide tandem repeat subtype analysis implicates European starlings as biological vectors for Escherichia coli O157:H7 in Ohio, USA.

AIMS: To provide molecular epidemiological evidence of avian transmission of Escherichia coli O157:H7 between dairy farms in Ohio, this study was designed to identify genetic relatedness between isolates originating from bovine faecal samples and intestinal contents of European starlings captured on these farms. METHODS AND RESULTS: During a three-year period (2007-2009), cattle (n = 9000) and starlings (n = 430) on 150 different dairy farms in northern Ohio were sampled for the presence of E. coli O157:H7. Isolates were subjected to multiple-locus variable-nucleotide tandem repeat analysis (MLVA). Distinct allelic groups were identified on most farms; however, isolates clustering into three MLVA groups originated from both cattle and birds on different farms. CONCLUSIONS: Sharing of indistinguishable epidemiologically linked E. coli O157 MLVA subtypes between starlings and cattle on different farms supports the hypothesis that these birds contribute to the transmission of E. coli O157:H7 between dairy farms. SIGNIFICANCE AND IMPACT OF STUDY: A continued need exists to identify and to improve preharvest measures for controlling E. coli O157:H7. Controlling wildlife intrusion, particularly European starlings, on livestock operations, may be an important strategy for reducing dissemination of E. coli O157:H7 between farms and thereby potentially decreasing the on-farm prevalence of E. coli O157:H7 and enhancing the safety of the food supply.

Verification of an Edwardsiella ictaluri-specific diagnostic PCR.

AIMS: To verify the specificity of a PCR assay for the identification and diagnosis of Edwardsiella ictaluri. METHODS AND RESULTS: An Edwardsiella ictaluri-specific PCR assay was developed utilizing two features of the ribosomal DNA gene clusters. The first feature is the presence of two ribosomal gene clusters located in tandem to one another (the inter-ribosomal spacer, IRS). This characteristic is present in the Edwardsiella genus but absent in the other sequenced members of the Enterobacteriaceae. The second feature is the presence of an intervening sequence (IVS) in the 23S rRNA gene of Edw. ictaluri. To verify the specificity of this assay, we tested genomic DNA from a variety of bacterial species. The IVS/IRS PCR assay results in an c. 2000-bp product from all Edw. ictaluri isolates tested, but not from any other species including Edwardsiella tarda. CONCLUSIONS: The IVS/IRS PCR assay is highly specific for Edw. ictaluri and useful as a tool for identifying this pathogen. SIGNIFICANCE AND IMPACT OF THE STUDY: This research verifies the specificity of PCR-based assay for Edw. Ictaluri, and we describe this assay as a highly versatile diagnostic tool for its identification.

Emotional intimacy predicts condom use: findings in a group at high sexually transmitted disease risk.

Previous studies have reported an inverse relationship between condom use and emotional intimacy. The aim of this study was to determine the relationship between condom use and emotional intimacy. The study was a gonorrhoea case-comparison study with the samples being drawn from public health clinics (cases) and select bars/nightclubs (places) of Houston, TX (n = 215). Data were collected by questionnaires administered on a laptop computer. The majority of respondents were African-American (97.7%), women (69.3%) and had either high school or GED education (72.6%). Condom use with the last sexual partner was analysed along with intimacy with that partner assessed on a 3-point scale. Analysis showed that higher intimacy was related to greater condom use which was significant in men but not in women. In conclusion, these data were opposite to those of previous studies, which showed an inverse relationship between condom use and emotional intimacy. We hypothesize that in a high-risk environment, people exert more effort in protecting those they feel closer to. These data suggest a need to further explore the complex relationship between emotional intimacy and condom use.

Characterization of the rrn operons in the channel catfish pathogen Edwardsiella ictaluri.

AIMS: To advance diagnostics and phylogenetics of Edwardsiella ictaluri by sequencing and characterizing its rrn operons. METHODS AND RESULTS: The Edw. ictaluri rrn operons were identified from a 5-7 kbp insert lambda library and from Edw. ictaluri fosmid clones. We present the complete sequences and analysis of all eight Edw. ictaluri rrn operons and unique regions located upstream and downstream. Two rrn operons were located in tandem with 169 bp separating them, which is apparently a conserved feature between Edw. ictaluri and Edwardsiella tarda. I-CeuI enzyme digestion of Edw. ictaluri genomic DNA and analysis by pulsed field gel electrophoresis indicated that rrn operon number and chromosomal locations are conserved within the species Edw. ictaluri. CONCLUSIONS: The rrn operons of Edw. ictaluri have similar structure and flanking regions compared with other members of the family Enterobacteriaceae; however, the presence of eight copies of the rrn operon makes Edw. ictaluri unique within the family. SIGNIFICANCE AND IMPACT OF THE STUDY: This research clarifies previous phylogenetic analyses of Edw. ictaluri and provides support for the Edw. ictaluri genome sequencing project. In addition, we identified a unique feature of two rrn operons that shows potential for the development of a diagnostic PCR method.

CHILD syndrome. Phenotypic dichotomy in eicosanoid metabolism and proliferative rates among cultured dermal fibroblasts.

Dermal fibroblasts from a patient with CHILD syndrome (an acronym for congenital hemidysplasia with ichthyosiform erythroderma and limb defects) were obtained and successfully maintained in culture. Fibroblasts from an area of chronically hyperkeratotic skin were compared with fibroblasts from the corresponding contralateral area of normal skin in regard to proliferative activity and to both unstimulated and stimulated generation of PGE2, an eicosanoid with documented effects on both epidermal cell and fibroblast function. Compared with the uninvolved skin fibroblasts, those from involved skin showed (a) a slower rate of proliferation, (b) a cyclical pattern of PGE2 synthesis, and (c) an approximately 20-fold greater synthesis of PGE2 in response to human purified IL-1, a cytokine known to be secreted by epidermal keratinocytes. Furthermore, we were able to demonstrate that the cyclical generation of PGE2 by the involved skin fibroblasts is responsible for their slower rate of growth when compared with the uninvolved skin fibroblasts. These data document a phenotypic dichotomy between the uninvolved and involved skin fibroblasts in CHILD syndrome that may be exploited to increase our understanding of the nature of dermal influences that may affect epidermal growth and differentiation.

Stratum corneum lipids in disorders of cornification: increased cholesterol sulfate content of stratum corneum in recessive x-linked ichthyosis.

Activity of the microsomal enzyme, steroid sulfatase, is absent in keratinocytes, fibroblasts, and leukocytes of patients with recessive x-linked ichthyosis. This study was undertaken to determine if cholesterol sulfate, a substrate of this enzyme, accumulates in the pathological scale of these patients. Scales from 8 patients with recessive x-linked ichthyosis, 10 patients with other forms of ichthyosis, and normal human outer stratum corneum were extracted with chloroform/water (1:2:0.8 by vol) and lipids were fractionated by quantitative, sequential thin-layer chromatography. Cholesterol sulfate was identified by cochromatography in several solvent systems, by its staining characteristics, by biochemical analysis, and by mass spectrometry. The mean cholesterol sulfate content of recessive x-linked ichthyotic scale was 12.5 +/- 0.8% of the total lipid, a fivefold increase over normal (P less than 0.0025), whereas the cholesterol sulfate content of other ichthyotic scale was normal. This increase in cholesterol sulfate content was accompanied by a decrease in total neutral lipids (P less than 0.0025) and free sterols (P less than 0.025) but no change in sterol esters or total sterols. These results demonstrate that deficiency of steroid sulfatase in recessive x-linked ichthyosis results in excessive accumulation of a substrate, cholesterol sulfate, in the pathologic scale, which may underly the pathogenesis of the scaling in this disorder. Measurement of cholesterol sulfate content in scale provides an alternative method to enzymatic assay for the diagnosis of this form of ichthyosis.

Elevated n-alkanes in congenital ichthyosiform erythroderma. Phenotypic differentiation of two types of autosomal recessive ichthyosis.

Previously considered to represent a single genetic disorder, autosomal recessive ichthyosis was examined in clinical and lipid biochemical studies of 18 patients with this condition and instead disclosed to be two distinct diseases. Six patients displayed clinical features of classical lamellar ichthyosis (LI), which is characterized by monomorphous features, including large, dark, platelike scales, severe ectropion, and a uniformly severe, unremitting course. 11 patients displayed clinical features of nonbullous congenital ichthyosiform erythroderma (CIE) characterized by fine white scales, prominent erythroderma, a milder course, and a variable prognosis. CIE could be separated biochemically from LI by the invariable presence of elevated quantities of n-alkanes in scale (CIE, 24.8 +/- 1.9% vs. LI, 7.2 +/- 1.6%, and normal, 6.5 +/- 0.9%), which suggested a primary disorder in neutral lipid metabolism. In light of the distinctive clinical features of each, these biochemical studies indicate that autosomal recessive ichthyosis comprises two distinct disorders.

Glucocorticoids accelerate fetal maturation of the epidermal permeability barrier in the rat.

The cutaneous permeability barrier to systemic water loss is mediated by hydrophobic lipids forming membrane bilayers within the intercellular domains of the stratum corneum (SC). The barrier emerges during day 20 of gestation in the fetal rat and is correlated with increasing SC thickness and increasing SC lipid content, the appearance of well-formed lamellar bodies in the epidermis, and the presence of lamellar unit structures throughout the SC. Because glucocorticoids accelerate lung lamellar body and surfactant maturation in man and experimental animals, these studies were undertaken to determine whether maternal glucocorticoid treatment accelerates maturation of the epidermal lamellar body secretory system. Maternal rats were injected with betamethasone or saline (control) on days 16-18, and pups were delivered prematurely on day 19. Whereas control pups exhibited immature barriers to transepidermal water loss (8.16 +/- 0.52 mg/cm2 per h), glucocorticoid-treated pups exhibited competent barriers (0.74 +/- 0.14 mg/cm2 per h; P < 0.001). Glucocorticoid treatment also: (a) accelerated maturation of lamellar body and SC membrane ultrastructure; (b) increased SC total lipid content twofold; and (c) increased cholesterol and polar ceramide content three- to sixfold. Thus, glucocorticoids accelerate the functional, morphological, and lipid biochemical maturation of the permeability barrier in the fetal rat.

Activators of the nuclear hormone receptors PPARalpha and FXR accelerate the development of the fetal epidermal permeability barrier.

Members of the superfamily of nuclear hormone receptors which are obligate heterodimeric partners of the retinoid X receptor may be important in epidermal development. Here, we examined the effects of activators of the receptors for vitamin D3 and retinoids, and of the peroxisome proliferator activated receptors (PPARs) and the farnesoid X-activated receptor (FXR), on the development of the fetal epidermal barrier in vitro. Skin explants from gestational day 17 rats (term is 22 d) are unstratified and lack a stratum corneum (SC). After incubation in hormone-free media for 3-4 d, a multilayered SC replete with mature lamellar membranes in the interstices and a functionally competent barrier appear. 9-cis or all-trans retinoic acid, 1,25 dihydroxyvitamin D3, or the PPARgamma ligands prostaglandin J2 or troglitazone did not affect the development of barrier function or epidermal morphology. In contrast, activators of the PPARalpha, oleic acid, linoleic acid, and clofibrate, accelerated epidermal development, resulting in mature lamellar membranes, a multilayered SC, and a competent barrier after 2 d of incubation. The FXR activators, all-trans farnesol and juvenile hormone III, also accelerated epidermal barrier development. Activities of beta-glucocerebrosidase and steroid sulfatase, enzymes previously linked to barrier maturation, also increased after treatment with PPARalpha and FXR activators. In contrast, isoprenoids, such as nerolidol, cis-farnesol, or geranylgeraniol, or metabolites in the cholesterol pathway, such as mevalonate, squalene, or 25-hydroxycholesterol, did not alter barrier development. Finally, additive effects were observed in explants incubated with clofibrate and farnesol together in suboptimal concentrations which alone did not affect barrier development. These data indicate a putative physiologic role for PPARalpha and FXR in epidermal barrier development.

Stratum corneum lipids in disorders of cornification. Steroid sulfatase and cholesterol sulfate in normal desquamation and the pathogenesis of recessive X-linked ichthyosis.

The pathological scaling in recessive x-linked ichthyosis is associated with accumulation of abnormal quantities of cholesterol sulfate in stratum corneum (J. Clin. Invest. 68:1404-1410, 1981). To determine whether or not cholesterol sulfate accumulates in recessive x-linked ichthyosis as a direct result of the missing enzyme, steroid sulfatase, we quantitated both steroid sulfatase and its substrate, we quantitated both steroid sulfatase and its substrate, cholesterol sulfate, in different epidermal strata, as well as within stratum corneum subcellular fractions obtained from normal human and neonatal mouse epidermis and from patients with recessive x-linked ichthyosis. In normal human and mouse epidermis, steroid sulfatase activity peaked in the stratum granulosum and stratum corneum, and negligible activity was detectable in lower epidermal layers. In contrast, in recessive x-linked ichthyosis epidermis, enzyme levels were virtually undetectable at all levels. In normal human stratum corneum, up to 10 times more steroid sulfatase activity was present in purified peripheral membrane preparations than in the whole tissue. Whereas in normal human epidermis cholesterol sulfate levels were lowest in the basal/spinous layer, and highest in the stratum granulosum, in recessive x-linked ichthyosis the levels were only slightly higher in the lower epidermis, but continued to climb in the stratum corneum. In both normal and in recessive x-linked ichthyosis stratum corneum, cholesterol sulfate appeared primarily within membrane domains, paralleling the pattern of steroid sulfatase localization. Finally, the role of excess cholesterol sulfate in the pathogenesis of recessive x-linked ichthyosis was directly tested by topical applications of this substance, which produced visible scaling in hairless mice in parallel to an increased cholesterol sulfate content of the stratum corneum. These results demonstrate an intimate relationship between steroid sulfatase and cholesterol sulfate in normal epidermis: both are concentrated in the outer epidermis (stratum corneum and stratum granulosum), and both are localized to membrane domains. Presumably, as a result of this distribution pattern, continued enzymatic degradation of substrate occurs in normal epidermis, thereby preventing excessive accumulation of cholesterol sulfate. In contrast, in recessive x-linked ichthyosis, degradation of cholesterol sulfate does not occur and cholesterol sulfate accumulates specifically in the stratum corneum, where it produces visible scale.

Hormonal basis for the gender difference in epidermal barrier formation in the fetal rat. Acceleration by estrogen and delay by testosterone.

Previous studies have shown that ontogeny of the epidermal permeability barrier and lung occur in parallel in the fetal rat, and that pharmacologic agents, such as glucocorticoids and thyroid hormone, accelerate maturation at comparable developmental time points. Gender also influences lung maturation, i.e., males exhibit delayed development. Sex steroid hormones exert opposite effects on lung maturation, with estrogens accelerating and androgens inhibiting. In this study, we demonstrate that cutaneous barrier formation, measured as transepidermal water loss, is delayed in male fetal rats. Administration of estrogen to pregnant mothers accelerates fetal barrier development both morphologically and functionally. Competent barriers also form sooner in skin explants incubated in estrogen-supplemented media in vitro. In contrast, administration of dihydrotestosterone delays barrier formation both in vivo and in vitro. Finally, treatment of pregnant rats with the androgen antagonist flutamide eliminates the gender difference in barrier formation. These studies indicate that (a) estrogen accelerates and testosterone delays cutaneous barrier formation, (b) these hormones exert their effects directly on the skin, and (c) sex differences in rates of barrier development in vivo may be mediated by testosterone.

Tuberculosis infection in drug users: interferon-gamma release assay performance.

SETTING: An inner city neighborhood in Houston, Texas, known for a high rate of drug use. OBJECTIVE: To determine the prevalence of latent tuberculosis infection (LTBI) using the QuantiFERON-TB Gold (QFT-G) test, the TSPOT.TB test and the tuberculin skin test (TST) in drug users and to evaluate the performance of the QFT-G and TSPOT.TB tests vs. the TST. DESIGN: Cross-sectional study. Bivariate and multivariate logistic regression analyses were used to determine risks associated with each test outcome. RESULTS: The prevalence of LTBI in 119 drug users studied was 28% by TST and 34% by QFT-G and T-SPOT.TB. Kappa statistics indicated fair to moderate concordance between QFT-G and TSPOT.TB vs. TST. About one-fifth of the population that tested negative with TST was positive with either QFT-G or T-SPOT.TB. On multivariate analysis, the likelihood of testing QFT-positive or T-SPOT.TB-positive increased by 8% and 6%, respectively, for every year of age; TST positivity was associated with smoking crack at home; being Caucasian or having a history of alcohol use was positively associated with a positive T-SPOT.TB test. CONCLUSION: Interferon-gamma release assays (IGRAs) are superior to the TST in drug users with a higher prevalence of LTBI. Future studies need to assess the predictive value of IGRAs on the progression from LTBI to active TB in high-risk populations.

Process, efficacy and sample demographics of three approaches to behavioural surveillance for gonorrhoea: case interviews, place surveys, and network studies.

We investigated the process and time required to collect 450 interviews in a project to determine the most efficacious behavioural surveillance approaches to detect changes in gonorrhoea prevalence. In total, 150 respondents were recruited in each method. For each of place surveys (bars), gonorrhoea case interviews, and network studies based on seeds from the case and place interviews, we determined the recruitment rate and process. Urine testing for gonorrhoea and chlamydia took place in the place interviews. We present data from Houston, Texas that illustrate the sample characteristics, recruitment rates, and, where appropriate, infection rates. Data indicate that there was high uptake and a rapid recruitment rate from the place surveys, an intermediate rate from the network studies, and that the gonorrhoea case interviews were the most inefficient accrual method for behavioural surveillance. Sample characteristics and biases in each method are described, and conclusions drawn for the relative efficacy of each method for gonorrhoea behavioural surveillance.

Epithelial focus assay for early detection of carcinogen-altered cells in various organs of rats exposed in situ to N-nitrosoheptamethyleneimine.

The purpose of these studies was to determine a) whether epithelial cells with altered in vitro growth capacity occur not only after topical application of 7-12-dimethylbenz [a]-anthracene but also after systemic administration of a carcinogenic nitrosamine, and b) whether such cells can be isolated from tissues other than tracheal mucosa. AT 3 and 20 weeks following intragastric administration of 150, 300, or 600 mg N-nitrosohepatamethyleneimine (NHMI)/kg, cells were harvested from tracheas, esophagi, and lungs (target tissues for NHMI) of inbred F344 rats and seeded into culture dishes. Normal cells from nonexposed organs produced no proliferative epithelial foci (EF). Of those tracheas sampled 3 weeks following exposure to 150 and 300 mg/kg 10 and 20%, respectively, contained one or more EF that could be subcultured. Of these tracheas harvested 3 weeks post exposure to 600 mg/kg or 20 weeks post exposure to 150-600 mg/kg, 80-100% contained EF that could be subcultured. Twenty weeks after 600 mg NHMI/kg, the incidence of tracheas harboring cell populations with neoplastic potential (agarose-positive EF) was 80%, whereas the tracheal tumor incidence determined at 24 months was only 29%. Epithelial focus-forming units with various abnormal in vitro growth potentials were also detected in esophagi and lungs of NHMI-exposed rats.

Tumor induction in the trachea of hamsters with N-nitroso-N-methylurea.

Experiments were conducted to study the tumor response of hamster tracheas to N-nitroso-N-methylurea. Tracheas were exposed repeatedly with the use of a tracheal catheter. Ten to 30 exposures were given over a period of 5 to 20 weeks. The carcinoma incidence (including carcinoma in situ) was 0,42, 67, 88, and 94% for 10, 15, 20, 25, and 30 twice-weekly exposures, respectively. With 10 exposures 2 of 12 hamsters developed benign tracheal tumors. Mean tumor induction time decreased when frequency of exposure was increased from 50 weeks with 10 to 15 exposures to 28 weeks with 25 to 30 exposures. The major histological types of invasive carcinomas observed were epidermoid carcinomas (54%), anaplastic large-cell and small-cell carcinomas (26%), adenocarcinomas (13%), and combined epidermoid-adenocarcinomas (7%). Sacrifice studies revealed that with 10 to 20 twice-weekly exposures only metaplastic lesions with varying degrees of cellular atypia are present at the time of the last exposure. Neoplastic lesions develop during the subsequent exposure-free interval. The data suggest that this tracheal tumor induction system may be well suited for studying problems related to development and progression of neoplastic disease.

Neutral lipid storage disease: a possible functional defect in phospholipid- linked triacylglycerol metabolism.

Neutral lipid storage disease (NLSD) (Chanarin-Dorfman Syndrome) is an autosomal recessive disorder of multisystem triacylglycerol (TAG) storage. Previous work has pointed to a defect in intracellular TAG metabolism. In the studies reported here, the lipid metabolism of three lines of NLSD fibroblasts were compared to normal skin fibroblasts. When pulsed with [3H]oleic acid, the earliest observed abnormality in NLSD cell lines was increased incorporation into phosphatidylethanolamine, followed by accumulation of radiolabel in TAG. Activities of several glycerolipid synthetic enzymes were comparable in NLSD and normal fibroblast lines, excluding oversynthesis of glycerolipid. The proportion of plasmalogen and neutral ether lipid synthesized was normal and alkylglycerols did not accumulate, excluding a defect in ether lipid metabolism. Activities of both acid lipase and Mn2(+)-sensitive lipase within the particulate fractions of NLSD and normal fibroblasts were comparable. These studies are most consistent with functional deficiency of a TAG lipase with activity against a pool of TAG that are normally utilized for phospholipid biosynthesis.

Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and sterol synthesis by cholesterol sulfate in cultured fibroblasts.

Although widely distributed throughout mammalian tissues, the biological function of cholesterol sulfate remains largely unknown. In these studies we have demonstrated that cholesterol sulfate suppresses de novo sterol synthesis in cultured human fibroblasts. It was further shown in these cultured cells that cholesterol sulfate is a potent inhibitor of the enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase (mevalonate: NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34), the rate-limiting enzyme in cholesterol biosynthesis and the site at which exogenous cholesterol suppresses endogenous cholesterol synthesis. Because cholesterol sulfate inhibited sterologenesis in steroid-sulfatase deficient fibroblasts derived from patients with recessive X-linked ichthyosis, it was inferred that cholesterol sulfate per se and not cholesterol liberated by intracellular desulfation was the inhibitor in these studies. Cholesterol sulfate may be an endogenous regulator of mammalian cholesterol biosynthesis.