A programme to improve quality of care for patients with chronic diseases, Kazakhstan.

OBJECTIVE: To evaluate the effect of a disease management programme in Kazakhstan on quality indicators for patients with hypertension, diabetes and chronic heart failure. METHODS: A supportive, interdisciplinary, quality improvement programme was implemented between November 2014 and November 2015 at seven polyclinics in Pavlodar and Petropavlovsk. Quality improvement teams were established at each clinic and quality improvement tools were introduced, including patient flowsheets, decision support tools, patient registries, a patient recall process, support for patient self-management and patient follow-up with intensity adjusted for level of disease control. Clinic teams met for four 3-day interactive learning sessions within 1 year, with additional coaching visits. Implementation was managed by five local coordinators and consultants trained by international consultants. National and regional steering committees monitored progress. FINDINGS: Between July and October 2015, the proportion of hypertensive patients with the recommended blood pressure increased from 24% (101/424) to 56% (228/409). Among patients with diabetes, the proportion who recently underwent eye examinations increased from 26% (101/391) to 71% (308/433); the proportion who had their low-density lipoprotein cholesterol measured increased from 57% (221/391) to 85% (369/433); and the proportion who had their albumin : creatinine ratio measured increased from 11% (44/391) to 49% (212/433). The proportion of chronic heart failure patients who underwent echocardiography rose from 91% (128/140) to 99% (157/158). All patients set themselves self-management goals. CONCLUSION: This intensive, supportive, multifaceted programme was associated with significant improvements in quality of care for patients with chronic disease. Further investment in coaching capacity is needed to extend the programme nationally.

Kidney Biopsies May Help Predict Renal Function After Liver Transplantation.

BACKGROUND: Renal biopsy has been proposed to determine the cause or reversibility of renal failure for patients with end-stage liver disease and may be useful in the kidney allocation. Nevertheless, little data exist to validate the usefulness of kidney biopsies in this patient population. METHODS: We evaluated the utility of renal biopsies in a cohort of 59 consecutive liver transplant candidates with renal impairment of unclear etiology referred to determine the need for simultaneous liver kidney transplantation (SLK) versus liver alone transplantation (LAT). Pathological diagnoses, patient outcomes and the usefulness of biopsy results in predicting renal recovery were analyzed. RESULTS: Our biopsy complication rate was relatively low with only 2.9% and 4.2% serious complications occurring with transjugular and percutaneous renal biopsies, respectively. The most common pathological diagnoses on renal biopsies were membranoproliferative glomerulonephritis (23%) followed by IgA nephropathy (19%) and acute tubular injury (19%). Simultaneous liver kidney transplantation was recommended for patients with greater than 40% global glomerular sclerosis, or with interstitial fibrosis greater than 30% or for patients on hemodialysis for 2 months or longer. The best histological predictor for posttransplant glomerular filtration rate in the LAT group was the extent of global glomerulosclerosis (P = 0.0001). Based on biopsy criteria, we were able to avoid kidney allocation to 70% of our patients with renal dysfunction. Over the first year posttransplant, SLK and LAT patients had comparable estimated glomerular filtration rates. Kaplan-Meier survival analysis did not demonstrate a difference in patient survival between patients who underwent LAT versus SLK. CONCLUSIONS: Renal biopsy can be relatively safe in this population, may help elucidate the etiology of renal failure, may predict post-LAT kidney function, and may be helpful in kidney allocation for liver transplant candidates.

Tacrolimus placental transfer at delivery and neonatal exposure through breast milk.

AIM(S): The current investigation aims to provide new insights into fetal exposure to tacrolimus in utero by evaluating maternal and umbilical cord blood (venous and arterial), plasma and unbound concentrations at delivery. This study also presents a case report of tacrolimus excretion via breast milk. METHODS: Maternal and umbilical cord (venous and arterial) samples were obtained at delivery from eight solid organ allograft recipients to measure tacrolimus and metabolite bound and unbound concentrations in blood and plasma. Tacrolimus pharmacokinetics in breast milk were assessed in one subject. RESULTS: Mean (±SD) tacrolimus concentrations at the time of delivery in umbilical cord venous blood (6.6 ± 1.8 ng ml(-1)) were 71 ± 18% (range 45-99%) of maternal concentrations (9.0 ± 3.4 ng ml(-1)). The mean umbilical cord venous plasma (0.09 ± 0.04 ng ml(-1)) and unbound drug concentrations (0.003 ± 0.001 ng ml(-1)) were approximately one fifth of the respective maternal concentrations. Arterial umbilical cord blood concentrations of tacrolimus were 100 ± 12% of umbilical venous concentrations. In addition, infant exposure to tacrolimus through the breast milk was less than 0.3% of the mother's weight-adjusted dose. CONCLUSIONS: Differences between maternal and umbilical cord tacrolimus concentrations may be explained in part by placental P-gp function, greater red blood cell partitioning and higher haematocrit levels in venous cord blood. The neonatal drug exposure to tacrolimus via breast milk is very low and likely does not represent a health risk to the breastfeeding infant.

Living-donor follow-up attitudes and practices in U.S. kidney and liver donor programs.

BACKGROUND: Although U.S. transplantation programs must submit living-donor follow-up data through 2 years after donation, the submissions have high rates of incomplete or missing data. It is important to understand barriers programs face in collecting follow-up information. METHODS: Two hundred thirty-one programs performing living kidney donor (LKD) and/or living liver donor (LLD) transplantation were contacted to complete a survey about program attitudes concerning donor follow-up, follow-up practices, and barriers to success. RESULTS: Respondents representing 147 programs (111 with only LKD and 36 with both LKD and LLD) participated. Sixty-eight percent of LKD and 83% of LLD respondents said that achieving follow-up was a high priority. The majority agreed that donors should be followed at least 2 years (61% LKD programs and 73% LLD programs), and sizeable percentages (31% LKD and 37% LLD) endorsed 5 years of follow-up. However, approximately 40% of programs lost contact with more than 75% of their donors by 2 years after donation. Follow-up barriers included donors not wanting to return to the program (87%), out-of-date contact information (73%), and lack of program (54%) or donor (49%) reimbursement for follow-up costs. Whereas 92% of LKD and 96% of LLD programs inform potential donors about follow-up requirements, fewer (67% LKD and 78% LLD) develop plans with donors to achieve follow-up. CONCLUSIONS: Most respondents agree that donor follow-up is important, but they report difficulty achieving it. Improvements may occur if programs work with donors to develop plans to achieve follow-up, programmatic standards are set for completeness in follow-up data reporting, and sufficient staff resources are available to ensure ongoing post-donation contact.

Kidney transplant chains amplify benefit of nondirected donors.

IMPORTANCE: Despite the potential for altruistic nondirected donors (NDDs) to trigger multiple transplants through nonsimultaneous transplant chains, concerns exist that these chains siphon NDDs from the deceased donor wait list and that donors within chains might not donate after their partner receives a transplant. OBJECTIVE: To determine the number of transplantations NDDs trigger through chains. DESIGN: Retrospective review of large, multicenter living donor-recipient database. SETTING: Fifty-seven US transplant centers contributing donor-recipient pairs to the database. PARTICIPANTS: The NDDs initiating chain transplantation. MAIN OUTCOMES MEASURE: Number of transplants per NDD. RESULTS: Seventy-seven NDDs enabled 373 transplantations during 46 months starting February 2008. Mean chain length initiated by NDDs was 4.8 transplants (median, 3; range, 1-30). The 40 blood type O NDDs triggered a mean chain length of 6.0 (median, 4; range, 2-30). During the interval, 66 of 77 chains were closed to the wait list, 4 of 77 were ongoing, and 7 of 77 were broken because bridge donors became unavailable. No chains were broken in the last 15 months, and every recipient whose incompatible donor donated received a kidney. One hundred thirty-three blood type O recipients were transplanted. CONCLUSION AND RELEVANCE: This large series demonstrates that NDDs trigger almost 5 transplants on average, more if the NDD is blood type O. There were more blood type O recipients than blood type O NDDs participating. The benefits of transplanting 373 patients and enabling others without living donors to advance outweigh the risk of broken chains that is decreasing with experience. Even 66 patients on the wait list without living donors underwent transplantation with living-donor grafts at the end of these chains.

Interpreting tacrolimus concentrations during pregnancy and postpartum.

Pregnancy after solid organ transplantation, although considered high risk for maternal, fetal, and neonatal complications, has been quite successful. Tacrolimus pharmacokinetic changes during pregnancy make interpretation of whole blood trough concentrations particularly challenging. There are multiple factors that can increase the fraction of unbound tacrolimus, including but not limited to low albumin concentration and low red blood cell count. The clinical titration of dosage to maintain whole blood tacrolimus trough concentrations in the usual therapeutic range can lead to elevated unbound concentrations and possibly toxicity in pregnant women with anemia and hypoalbuminemia. Measurement of plasma or unbound tacrolimus concentrations for pregnant women might better reflect the active form of the drug, although these are technically challenging and often unavailable in usual clinical practice. Tacrolimus crosses the placenta with in utero exposure being approximately 71% of maternal blood concentrations. The lower fetal blood concentrations are likely due to active efflux transport of tacrolimus from the fetus toward the mother by placental P-glycoprotein. To date, tacrolimus has not been linked to congenital malformations but can cause reversible nephrotoxicity and hyperkalemia in the newborn. In contrast, very small amounts of tacrolimus are excreted in the breast milk and are unlikely to elicit adverse effects in the nursing infant.

CYP3A5 gene variation influences cyclosporine A metabolite formation and renal cyclosporine disposition.

BACKGROUND: Higher concentrations of AM19 and AM1c9, secondary metabolites of cyclosporine A (CsA), have been associated with nephrotoxicity in organ transplant patients. The risk of renal toxicity may depend on the accumulation of CsA and its metabolites in the renal tissue. We evaluated the hypothesis that CYP3A5 genotype, and inferred enzyme expression, affects systemic CsA metabolite exposure and intrarenal CsA accumulation. METHODS: An oral dose of CsA was administered to 24 healthy volunteers who were selected based on their CYP3A5 genotype. CsA and its six main metabolites in whole blood and urine were measured by liquid chromatography-mass spectometry. In vitro incubations of CsA, AM1, AM9, and AM1c with recombinant CYP3A4 and CYP3A5 were performed to evaluate the formation pathways of AM19 and AM1c9. RESULTS: The mean CsA oral clearance was similar between CYP3A5 expressors and nonexpressors. However, compared with CYP3A5 nonexpressors, the average blood area under the concentration-time curve (AUC) for AM19 and AM1c9 was 47.4% and 51.3% higher in CYP3A5 expressors (P=0.040 and 0.011, respectively), corresponding to 30% higher AUCmetabolite/AUCCsA ratios for AM19 and AM1c9 in CYP3A5 expressors. The mean apparent urinary CsA clearance based on a 48-hr collection was 20.4% lower in CYP3A5 expressors compared with CYP3A5 nonexpressors (4.2±1.0 and 5.3±1.3 mL/min, respectively; P=0.037), which is suggestive of CYP3A5-dependent intrarenal CsA metabolism. CONCLUSIONS: At steady state, intrarenal accumulation of CsA and its secondary metabolites should depend on the CYP3A5 genotype of the liver and kidneys. This may contribute to interpatient variability in the risk of CsA-induced nephrotoxicity.

Urine IL-18, NGAL, IL-8 and serum IL-8 are biomarkers of acute kidney injury following liver transplantation.

BACKGROUND: AKI is common following liver transplantation and is associated with significant morbidity and mortality. Biomarkers of AKI have not been well established in this setting but are needed to help guide patient care and facilitate development of novel therapeutics. METHODS: Serum creatinine, cystatin C, IL-6, and IL-8 and urine IL-18, NGAL, IL-6, and IL-8 were measured before and within 24 hours after liver transplantation in 40 patients. AKI was defined as a ≥50% sustained increase in creatinine above pre-operative values occurring within 24 hours of transplantation and persisting for at least 24 hours. RESULTS: Seven patients met criteria for AKI (17.5%), with mean creatinines of 0.81 mg/dL pre-operatively and 1.75 mg/dL post-operatively. While pre-operative biomarker levels in patients with AKI were similar to those in patients without AKI, differences were seen between the groups with regard to median post-operative serum IL-8 (pg/mL) (242.48 vs. 82.37, p = 0.0463) and urine NGAL (ng/mL) (386.86 vs. 24.31, p = 0.0039), IL-6 (pg/mL) (52 vs. 7.29, p=0.0532), IL-8 (pg/mL) (14.3 vs. 0, p = 0.0224), and IL-18 (pg/mL) (883.09 vs. 0, p = 0.0449). The areas under receiver operating characteristic (ROC) curves were 0.749 for urine IL-18, 0.833 for urine NGAL, 0.745 for urine IL-6, 0.682 for serum IL-6, 0.773 for urine IL-8, and 0.742 for serum IL-8. Post-operative cystatin C was not significantly different between AKI and no AKI groups. CONCLUSION: Serum IL-8 and urine IL-18, NGAL, IL-6, and IL-8 are elevated in AKI within the first 24 hours following liver transplantation.

Cohort profile: the skin cancer after organ transplant study.

The Skin Cancer after Organ Transplant (SCOT) study was designed to investigate the link between genus beta human papillomavirus (HPV) and squamous cell skin cancer (SCSC). We focused on a population receiving immunosuppressive therapy for extended periods, transplant patients, as they are at extremely high risk for developing SCSC. Two complementary projects were conducted in the Seattle area: (i) a retrospective cohort with interview data from 2004 recipients of renal or cardiac transplants between 1995 and 2010 and (ii) a prospective cohort with interview data from 328 people on the transplant waiting lists between 2009 and 2011. Within the retrospective cohort, we developed a nested case-control study (172 cases and 337 control subjects) to assess risk of SCSC associated with markers of HPV in SCSC tumour tissue and eyebrow hair bulb DNA (HPV genotypes) and blood (HPV antibodies). In the prospective cohort, 135 participants had a 1-year post-transplant visit and 71 completed a 2-year post-transplant visit. In both arms of the cohort, we collected samples to assess markers of HPV infection such as acquisition of new types, proportion positive for each type, persistence of types at consecutive visits and number of HPV types detected. In the prospective cohort, we will also examine these HPV markers in relation to levels of cell-mediated immunity. The goal of the SCOT study is to use the data we collected to gain a more complete understanding of the role of immune suppression in HPV kinetics and of genus beta HPV types in SCSC. For more information, please contact the principal investigator through the study website: http://www.fhcrc.org/science/phs/cerc/The_SCOT_Study.html.

Enhancement of hepatic 4-hydroxylation of 25-hydroxyvitamin D3 through CYP3A4 induction in vitro and in vivo: implications for drug-induced osteomalacia.

Long-term therapy with certain drugs, especially cytochrome P450 (P450; CYP)-inducing agents, confers an increased risk of osteomalacia that is attributed to vitamin D deficiency. Human CYP24A1, CYP3A4, and CYP27B1 catalyze the inactivation and activation of vitamin D and have been implicated in the adverse drug response. In this study, the inducibility of these enzymes and monohydroxylation of 25-hydroxyvitamin D3 (25OHD3) were evaluated after exposure to P450-inducing drugs. With human hepatocytes, treatment with phenobarbital, hyperforin, carbamazepine, and rifampin significantly increased the levels of CYP3A4, but not CYP24A1 or CYP27B1 mRNA. In addition, rifampin pretreatment resulted in an 8-fold increase in formation of the major metabolite of 25OHD3, 4ß,25(OH)2D3. This inductive effect was blocked by the addition of 6',7'-dihydroxybergamottin, a selective CYP3A4 inhibitor. With human renal proximal tubular HK-2 cells, treatment with the same inducers did not alter CYP3A4, CYP24A1, or CYP27B1 expression. 24R,25(OH)2 D3 was the predominant monohydroxy metabolite produced from 25OHD3, but its formation was unaffected by the inducers. With healthy volunteers, the mean plasma concentration of 4ß,25(OH)2D3 was increased 60% (p < 0.01) after short-term rifampin administration. This was accompanied by a statistically significant reduction in plasma 1α,25(OH)2D3 (-10%; p = 0.03), and a nonsignificant change in 24R,25(OH)2D3 (-8%; p = 0.09) levels. Further analysis revealed a negative correlation between the increase in 4ß,25(OH)2D3 and decrease in 1α,25(OH)2D3 levels. Examination of the plasma monohydroxy metabolite/25OHD3 ratios indicated selective induction of the CYP3A4-dependent 4ß-hydroxylation pathway of 25OHD3 elimination. These results suggest that induction of hepatic CYP3A4 may be important in the etiology of drug-induced osteomalacia.

Pharmacokinetics of tacrolimus during pregnancy.

BACKGROUND: Information on the pharmacokinetics of tacrolimus during pregnancy is limited to case reports despite the increasing number of pregnant women being prescribed tacrolimus for immunosuppression. METHODS: Blood, plasma, and urine samples were collected over 1 steady-state dosing interval from women treated with oral tacrolimus during early to late pregnancy (n = 10) and postpartum (n = 5). Total and unbound tacrolimus as well as metabolite concentrations in blood and plasma were assayed by a validated liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) method. A mixed-effect linear model was used for comparison across gestational age and using postpartum as the reference group. RESULTS: The mean oral clearance (CL/F) based on whole-blood tacrolimus concentration was 39% higher during mid-pregnancy and late pregnancy compared with postpartum (47.4 ± 12.6 vs. 34.2 ± 14.8 L/h, P < 0.03). Tacrolimus-free fraction increased by 91% in plasma (f(P)) and by 100% in blood (f(B)) during pregnancy (P = 0.0007 and 0.002, respectively). Increased fP was inversely associated with serum albumin concentration (r = -0.7, P = 0.003), which decreased by 27% during pregnancy. Pregnancy-related changes in f(P) and f(B) contributed significantly to the observed gestational increase in tacrolimus whole-blood CL/F (r² = 0.36 and 0.47, respectively, P < 0.01). In addition, tacrolimus whole-blood CL/F was inversely correlated with both hematocrit and red blood cell counts, suggesting that binding of tacrolimus to erythrocytes restricts its availability for metabolism. Treating physicians increased tacrolimus dosages in study participants during pregnancy by an average of 45% to maintain tacrolimus whole-blood trough concentrations in the therapeutic range. This led to striking increases in unbound tacrolimus trough concentrations and unbound area under the concentration-time curve, by 112% and 173%, respectively, during pregnancy (P = 0.02 and 0.03, respectively). CONCLUSIONS: Tacrolimus pharmacokinetics are altered during pregnancy. Dose adjustment to maintain whole-blood tacrolimus concentration in the usual therapeutic range during pregnancy increases circulating free drug concentrations, which may impact clinical outcomes.

Cancer diagnoses after living kidney donation: linking U.S. Registry data and administrative claims.

BACKGROUND: Mortality records identify cancer as the leading cause of death among living kidney donors, but information on the burden of cancer outside death records is limited in this population. METHODS: We examined a database wherein U.S. Organ Procurement and Transplantation Network identifiers for 4,650 living kidney donors in 1987 to 2007 were linked to administrative data of a U.S. private health insurer (2000-2007 claims) to identify postdonation cancer diagnoses. Skin cancer and non-skin cancer diagnoses were ascertained from International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes on billing claims. Donors were also matched one-to-one with general insurance beneficiaries by sex and age when benefits began. Diagnosis rates within observation windows were compared as rate ratios. RESULTS: The median time from donation to the end of plan insurance enrollment was 7.7 years, with a median observation period of 2.1 years. Skin cancer rates were similar among prior living donors in the observation period and nondonor controls (rate ratio, 0.91; 95% confidence interval [CI], 0.59-1.40). In contrast, the rate of total non-skin cancers was significantly less common among donors than among controls (rate ratio, 0.74; 95% CI, 0.55-0.99), although reduced relative risk was limited to donors captured earlier in relation to donation. Several cases of cancer diagnosis (uterine, melanoma, "other") were identified within the first year after donation. Prostate cancer diagnosis was significantly more common among living donors compared with controls (rate ratio, 3.80; 95% CI, 1.42-10.2). CONCLUSIONS: Continued study of cancer after kidney donation is warranted to ensure that evaluation, selection, and long-term follow-up support overall good health of the donor.

Depression diagnoses after living kidney donation: linking U.S. Registry data and administrative claims.

BACKGROUND: Limited data exist on correlates of psychological outcomes after kidney donation. METHODS: We used a database integrating Organ Procurement and Transplantation Network registrations for 4650 living kidney donors from 1987 to 2007 with administrative data of a U.S. private health insurer (2000-2007 claims) to identify depression diagnoses among prior living donors. The burden and demographic correlates of depression after enrollment in the insurance plan were estimated by Cox regression. Graft failure and death of the donor's recipient were examined as time-varying exposures. RESULTS: After start of insurance benefits, the cumulative frequency of depression diagnosis was 4.2% at 1 year and 11.5% at 5 years, and depression among donors was less common than among age- and gender-matched general insurance beneficiaries (rate ratio, 0.70; 95% confidence intervals [CI], 0.60-0.81). Demographic and clinical correlates of increased likelihood of depression diagnoses among the prior donors included female gender, white race, and some perioperative complications. After adjustment for donor demographic factors, recipient death (adjusted hazard ratio (aHR), 2.23; 95% CI, 1.11-4.48) and death-censored graft failure (aHR, 3.30; 95% CI, 1.49-7.34) were associated with two to three times the relative risk of subsequent depression diagnosis among nonspousal unrelated donors. There were trends toward increased depression diagnoses after recipient death and graft failure among spousal donors but no evidence of associations of these recipient events with the likelihood of depression diagnosis among related donors. CONCLUSIONS: Recipient death and graft loss predict increased depression risk among unrelated living donors in this privately insured sample. Informed consent and postdonation care should consider the potential impact of recipient outcomes on the psychological health of the donor.

Living kidney donor follow-up: state-of-the-art and future directions.

Long-term living kidney donor follow-up has not been considered necessary by many living kidney donor programs because a large number of single-center studies show that living kidney donation is associated with minimal mortality and morbidity. However, some transplant professionals and, more importantly, living donors disagree. To evaluate the need for more data on living kidney donor outcomes, a conference was held in September 2010 (Leichtman and colleagues: Am J Transplant 11: 2561-2568, 2011). Participants were health care professionals, living donors, members of the United Network for Organ Sharing, Health and Human Services, the National Institutes of Health, and insurance companies. This article will discuss the status of living donor follow-up in the context of the follow-up conference. It will also provide a slightly different viewpoint of provider responsibility for donor follow-up than that presented by the conference report.

The impact of current immunosuppression strategies in renal transplantation on the field of reconstructive transplantation.

Composite tissue allograft (CTA) transplantation, such as the clinical face and hand transplants, has now been performed in multiple centers across the world. The transplants have successfully treated complex injuries that have either failed conventional approaches or where autologous reconstruction could not restore both form and function. CTA transplantation has the potential to improve outcomes over traditional techniques. However, the widespread application of CTA transplantation continues to be limited by the need for chronic immunosuppression. Due to the small numbers of CTA transplants performed, any modification in the immunosuppression used will likely be based from the solid organ literature. The renal transplantation literature has served as the basis for the current selection of CTA drug regimens and in this article we review the evidence in the renal transplant literature for the selection of immunosuppressive regimens. The study then compares the regimens used in both the face and hand transplantation with those regimens currently used for renal transplantation.

An inducible cytochrome P450 3A4-dependent vitamin D catabolic pathway.

Vitamin D(3) is critical for the regulation of calcium and phosphate homeostasis. In some individuals, mineral homeostasis can be disrupted by long-term therapy with certain antiepileptic drugs and the antimicrobial agent rifampin, resulting in drug-induced osteomalacia, which is attributed to vitamin D deficiency. We now report a novel CYP3A4-dependent pathway, the 4-hydroxylation of 25-hydroxyvitamin D(3) (25OHD(3)), the induction of which may contribute to drug-induced vitamin D deficiency. The metabolism of 25OHD(3) was fully characterized in vitro. CYP3A4 was the predominant source of 25OHD(3) hydroxylation by human liver microsomes, with the formation of 4ß,25-dihydroxyvitamin D(3) [4ß,25(OH)(2)D(3)] dominating (V(max)/K(m) = 0.85 ml · min(-1) · nmol enzyme(-1)). 4ß,25(OH)(2)D(3) was found in human plasma at concentrations comparable to that of 1α,25-dihydroxyvitamin D(3), and its formation rate in a panel of human liver microsomes was strongly correlated with CYP3A4 content and midazolam hydroxylation activity. Formation of 4ß,25(OH)(2)D(3) in primary human hepatocytes was induced by rifampin and inhibited by CYP3A4-specific inhibitors. Short-term treatment of healthy volunteers (n = 6) with rifampin selectively induced CYP3A4-dependent 4ß,25(OH)(2)D(3), but not CYP24A1-dependent 24R,25-dihydroxyvitamin D(3) formation, and altered systemic mineral homeostasis. Our results suggest that CYP3A4-dependent 25OHD(3) metabolism may play an important role in the regulation of vitamin D(3) in vivo and in the etiology of drug-induced osteomalacia.

Simultaneous measurement of plasma vitamin D(3) metabolites, including 4ß,25-dihydroxyvitamin D(3), using liquid chromatography-tandem mass spectrometry.

Simultaneous and accurate measurement of circulating vitamin D metabolites is critical to studies of the metabolic regulation of vitamin D and its impact on health and disease. To that end, we have developed a specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that permits the quantification of major circulating vitamin D(3) metabolites in human plasma. Plasma samples were subjected to a protein precipitation, liquid-liquid extraction, and Diels-Alder derivatization procedure prior to LC-MS/MS analysis. Importantly, in all human plasma samples tested, we identified a significant dihydroxyvitamin D(3) peak that could potentially interfere with the determination of 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3)] concentrations. This interfering metabolite has been identified as 4ß,25-dihydroxyvitamin D(3) [4ß,25(OH)(2)D(3)] and was found at concentrations comparable to 1α,25(OH)(2)D(3). Quantification of 1α,25(OH)(2)D(3) in plasma required complete chromatographic separation of 1α,25(OH)(2)D(3) from 4ß,25(OH)(2)D(3). An assay incorporating this feature was used to simultaneously determine the plasma concentrations of 25OHD(3), 24R,25(OH)(2)D(3), 1α,25(OH)(2)D(3), and 4ß,25(OH)(2)D(3) in healthy individuals. The LC-MS/MS method developed and described here could result in considerable improvement in quantifying 1α,25(OH)(2)D(3) as well as monitoring the newly identified circulating metabolite, 4ß,25(OH)(2)D(3).