Vitamin D metabolism in acute and chronic cholestasis

Vitamin D status in gastrointestinal and liver disease

PURPOSE OF REVIEW

The purpose of this review is to report on the vitamin D status and its relationship with bone health in individuals with gastrointestinal and liver disorders. In addition, recommendations regarding replacement and maintenance of optimal vitamin D stores, as well as the state of knowledge regarding its effect on the disease through its actions on the immune system, will be reviewed.

RECENT FINDINGS

The scientific community has revised upward the serum levels of vitamin D considered optimal, and doses of vitamin D much larger than those currently recommended may be needed to maintain these levels, especially in individuals with gastrointestinal and liver disorders. The relationship between vitamin D and bone health in this population is controversial. The role of vitamin D in the regulation of the immune system continues to be elucidated.

SUMMARY

Hypovitaminosis D is prevalent among individuals with gastrointestinal and liver disease. Although replacement and supplementation guidelines have not been well defined, practitioners should aim for a serum 25-hydroxyvitamin D level of at least 32 ng/ml. The contribution of vitamin D to the bone health of these individuals and its role in altering disease course through its actions on the immune system remain to be elucidated.

Bone metabolism in orthotopic liver transplantation: a prospective study

Bone mineral density (BMD) and mineral metabolism were assessed in 54 patients with end-stage liver disease who were evaluated for orthotopic liver transplantation (OLT) and assessed 3, 6, and 12 months after surgery in 26 patients who underwent OLT. Serum and urinary electrolyte and mineral levels, serum liver function test results, and parathyroid hormone (PTH), osteocalcin (BGP), 25-hydroxyvitamin D, and urinary hydroxyproline levels were assessed. BMD of the lumbar spine was measured at baseline and 3, 6, and 12 months after OLT. At baseline, 40.7% of patients had BMD below the fracture threshold (0.800 g/cm2). Using multiple stepwise regression analysis, we found that BMD was significantly (P < .0001) affected by age, serum creatinine level, and PTH level but not by indices of cholestasis or liver function. In the patients who underwent OLT, a 1.4% reduction (P < .006) was observed in BMD 3 months after OLT. Thereafter, BMD returned to pretransplant values. A significant increase in serum BGP was observed after 6 (P < .02) and 12 (P < . 005) months. PTH levels increased progressively 3 (P < .02), 6 (P < . 001), and 12 (P < .0001) months after OLT. This increase did not seem to be caused by cyclosporine-induced nephropathy. It was concluded that osteopenia is a major complication in hepatic cirrhosis, regardless of its causes. The increase in serum BGP levels 6 and 12 months after OLT indicates metabolic activation of osteoblasts. The increase in PTH levels after OLT warrants further investigation.

Lipids and lipid-activated vitamins in chronic cholestatic diseases

Primary biliary cirrhosis, primary sclerosing cholangitis and autoimmune cholangiopathy are cholestatic liver diseases of unknown cause. Destruction of small to medium bile ducts (in primary biliary cirrhosis and autoimmune cholangiopathy) and large bile ducts (in primary sclerosing cholangitis) leads to progressive cholestasis, liver failure and end-stage liver disease. A variety of abnormalities in lipid metabolism have been described in primary biliary cirrhosis, and range from alterations in serum lipid levels and lipoprotein subsets to deranged metabolism of cholesterol. Progressive cholestasis and, consequently, decreased small intestinal bile acid concentrations in these cholestatic liver disease can also lead to impaired absorption of fats and fat-soluble vitamins, resulting in steatorrhea and deficiencies in vitamins A, D, E, and K. This article focuses on abnormalities in lipid metabolism in primary biliary cirrhosis and primary sclerosing cholangitis, and on lipid-activated vitamin deficiencies in these disorders.

Vitamin D and osteocalcin levels in liver transplant recipients. Is osteocalcin a reliable marker of bone turnover in such cases?

Patients with advanced liver disease are at increased risk for the development of hepatic osteodystrophy in the form of either osteomalacia or osteoporosis. The pathogenesis of these two bone diseases is multifactorial and includes, among other factors, alterations in vitamin D metabolism, malnutrition and hypogonadism. Little is known regarding vitamin D metabolism and the osteoblastic activity in liver transplant recipients. In order to clarify these issues, vitamin D metabolites and osteocalcin levels were measured prior to and 30 days following liver transplantation in 30 cirrhotic patients of various etiologies. While the mean plasma concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D of the entire group of 30 patients were significantly greater prior to orthotopic liver transplantation (OLTx) as compared to those after OLTx (11.5 +/- 8.6 vs. 7.4 +/- 5.8 ng/ml, p = 0.0066 and 41.0 +/- 34.6 vs. 20.4 +/- 11.0 pg/ml, p = 0.0003, respectively), no significant changes in osteocalcin concentrations pre- or post-transplantation could be demonstrated (5.2 +/- 3.0 vs. 6.4 +/- 4.1 ng/ml, p = 0.51). Furthermore, no correlation between the plasma concentration of osteocalcin and either vitamin D metabolite, the prothrombin time or cyclosporine levels was found. The reasons for the normal levels of osteocalcin prior to OLTx can be explained by the fact that in vitamin-K-deficient states osteocalcin is predominantly decarboxylated and, therefore, a smaller proportion is bound to bone and/or the synthesis of osteocalcin is partially modulated by 1,25-dihydroxyvitamin D, the level of which has been found to be normal.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolic bone disease of primary sclerosing cholangitis

The incidence and severity of osteopenic bone disease in primary sclerosing cholangitis is poorly defined. Clinical, biochemical and radiographic assessment and bone mineral density measurements of the lumbar spine were carried out in two groups of patients. Group 1 consisted of 30 patients with advanced primary sclerosing cholangitis; group 2 consisted of 18 patients with newly diagnosed primary sclerosing cholangitis. Only one patient had bone pain. All patients were normocalcemic; two had elevated serum parathormone levels. Fourteen patients (47%) from group 1 but no patients from group 2 had low serum 25-hydroxyvitamin D levels. Mean bone mineral density was significantly reduced in group 1 patients (0.97 +/- 0.04 gm/cm2) compared with age-matched and sex-matched controls (1.25 +/- 0.01 gm/cm2, p less than 0.0001), and in 15 patients (50%) bone mineral density was below the fracture threshold (0.98 gm/cm2). The bone mineral density in group 2 was not significantly different from controls, and no patient was below the fracture threshold. In neither group did bone mineral density correlate with serum bilirubin, 25-hydroxyvitamin D, fecal fat excretion, previous drug therapy or the presence of chronic ulcerative colitis. Histomorphometrical examination of bone from four group 1 patients showed increased bone resorption, reduced bone formation, moderate-to-severe osteopenia and no osteomalacia. In conclusion, severe osteopenic bone disease is common in advanced primary sclerosing cholangitis and, like that seen in other cholestatis diseases, is consistent with osteoporosis.

Longitudinal study on osteodystrophy in primary biliary cirrhosis (PBC) and a pilot study on calcitonin treatment

The aims of this study were to evaluate bone metabolism in primary biliary cirrhosis (PBC) and the effect of ADFR (activate, depress, free, repeat) therapy with vitamin D, calcium and calcitonin in preventing bone resorption. Sixty-nine female subjects entered the study: 38 PBC (AMA + ve) patients, 11 AMA-negative chronic liver disease patients and 20 age-matched healthy controls. Bone metabolism was evaluated by biochemical parameters and dual-photon absorptiometry of the lumbar spine at time 0, 6 and 18 months. Both PBC and chronic liver disease (CLD) patients showed low levels of serum 25-hydroxyvitamin D, osteocalcin and bone mineral content expressed as AAD (average area density) compared to healthy controls. Serum parathyroid hormone in PBC patients was at the lower limit of the normal range and was significantly lower than patients with chronic liver disease. At a 6-month interval, AAD significantly decreased in PBC patients (p less than 0.005). At the 6-month period PBC patients were allocated into two groups according to a cut-off AAD of 0.800 g/cm2: group A (no treatment, AAD greater than 0.800, n = 11), group B (treatment, AAD less than 0.800, n = 13). The latter group received a 4-week course with oral calcium carbonate (1500 mg daily) + oral 1,25-dihydroxyvitamin D (0.5 micrograms twice a day for 5 days) + carbocalcitonin (40 U MRC) i.m. thrice a week. The treatment was repeated with the same protocol at 2-month intervals for 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)

In micronodular cirrhosis, hepatocytes retain a normal C-25 hydroxylation capacity toward vitamin D3: a study using the rat carbon tetrachloride-induced cirrhotic model

To test further the competence of the cirrhotic liver to metabolize vitamin D3 at C-25, hepatocytes were isolated from controls and from CCl4-induced cirrhotic rat livers, as well as from partially hepatectomized rats. The transformation of D3 into 25-hydroxyvitamin D3 was studied in the presence of 10(7) hepatocytes at D3 concentrations of 20 nmol/L to 15.4 mumol/L. Histologically, micronodular cirrhosis was present in all CCl4-treated rats, whereas controls had normal livers; portal venous pressure (p less than 0.008) and intrahepatic collagen content (p less than 0.0001) were significantly increased in CCl4-treated rats, whereas no difference was found between the two groups in the total and ionized serum calcium, D3 metabolites, ALT, AST and alkaline phosphatase. Cytochrome P-450 was 0.27 +/- 0.02 and 0.25 +/- 0.02 nmol/10(6) hepatocytes in controls and cirrhotic rats (N.S.), and it significantly increased in both groups after phenobarbital or 3-methylcholanthrene administration (p less than 0.0001). 25-Hydroxyvitamin D3 formation was best described by power law equations and varied between 0.02 +/- 0.0004 and 29.57 +/- 2.8 in controls, and 0.024 +/- 0.0004 and 32.0 +/- 7.0 pmol.hr-1.10(6) hepatocytes-1 in cirrhotic rats. No statistically significant difference was found in the slopes of the 25-hydroxyvitamin D3 formation, but the y-axis intercept was found to be lower in cirrhotic rats under basal resting conditions (p less than 0.005). Inducers of the mixed function oxidases significantly increased 25-hydroxyvitamin D3 formation in controls as well as in cirrhotic rats (p less than 0.005). Moreover, both groups were found to respond similarly to the addition of modulators of the enzyme such as the calcium ionophore A23187 and parathyroid hormone. Partial hepatectomy was also without effect on the activation of D3. Furthermore, the cell sequestration of D3 was also found to be unperturbed in hepatocytes obtained from either cirrhotic or partially hepatectomized livers. The data indicate that in well-compensated micronodular cirrhosis, the C-25 hydroxylation of D3 is generally intrinsically normal at the cellular level and that it also remains fully responsive to in vivo and in vitro modulators of its activity.

25 Hydroxyvitamin D and vitamin E absorption in healthy children and children with chronic intrahepatic cholestasis

Patients with chronic cholestasis have reduced 25-hydroxyvitamin D (25OHD) and vitamin E levels. We determined serum concentrations of 25OHD, 1,25-dihydroxyvitamin D [1,25(OH)2D] and vitamin E before and after oral administration of 10 micrograms/kg body weight 25-hydroxyvitamin D3 (25OHD3) and 100 IU/kg body weight vitamin E, respectively, in 4 patients with intrahepatic cholestasis and 6 healthy children. Vitamin E increased in all controls but in only one of the four patients. In contrast, oral 25OHD3 induced a normal rise in circulating 25OHD and 1,25(OH)2D. The low serum levels of 25OHD in the patients before the oral bolus may have been due to inadequate parenteral vitamin D administration and/or to the simultaneous phenobarbital treatment. The latter possibility is supported by the increase of serum 25OHD into the normal range after withdrawal of phenobarbital in one of the four patients. We conclude that vitamin E has to be supplemented parenterally or in water-soluble oral form. Further studies are necessary to clarify whether high-dose long-term oral 25OHD3 supplementation is sufficient to prevent vitamin D deficiency in patients with chronic cholestasis.

Severe cholestasis leads to vitamin D depletion without perturbing its C-25 hydroxylation in the dog

The role of the liver as a contributory factor in the vitamin D deficiency of cholestatic liver disease has been studied in vivo in dogs with chronic bile duct ligation, whereas controls underwent diversion of the bile flow through the urinary bladder via a choledococystostomy anastomosis. The hepatic extraction of vitamin D3 was evaluated by the multiple indicator dilution technique, and the formation of 25-hydroxyvitamin D3 was assessed by directly sampling the hepatic effluent for up to 150 min after vitamin D3 administration. The serum and hemodynamic data indicate that dogs with chronic bile duct ligation had severe cholestasis and hepatocellular injury; histologically, macronodular cirrhosis was present. Dogs with choledococystostomy anastomosis had normal livers and normal liver function. The data indicate that the absence of normal bile flow into the intestinal lumen led to a progressive depletion of vitamin D reserve in both animals with choledococystostomy anastomosis and those with chronic bile duct ligation. However, neither the hepatic fractional extraction of vitamin D3, its hepatic clearance nor its transformation into 25-hydroxyvitamin D3 was significantly changed by chronic bile duct ligation. The results of the present studies indicate that the hepatic handling of vitamin D3 including its C-25 hydroxylation, is well preserved in the presence of severe cholestasis. They also suggest that the state of vitamin D depletion which often accompanies chronic cholestatic liver disease can largely be accounted for by factors such as secondary malabsorption of the vitamin due to the absence of adequate amounts of bile salts in the intestinal lumen, or by other factors which seem independent of the hepatic metabolism of vitamin D.

Bone disease in primary biliary cirrhosis: increased bone resorption and turnover in the absence of osteoporosis or osteomalacia

The role of vitamin D in hepatic osteodystrophy was examined. Eleven unselected patients with primary biliary cirrhosis (PBC) were assessed for disorders of mineral and vitamin D metabolism. Six were not receiving supplementary vitamin D, and five were being treated with oral vitamin D (50,000 IU daily). Serum levels of 25-hydroxyvitamin D were normal in all patients receiving oral therapy and in 4 of 6 untreated patients. Levels of serum 1,25-dihydroxyvitamin D and 24,25-dihydroxyvitamin D were normal or near normal in all patients. Studies were repeated after 6 months of therapy with parenteral vitamin D2 (100,000 IU i.m. monthly) in 7 patients. Initial bone histomorphometry revealed no evidence of osteomalacia or osteoporosis. However, the bone resorption surface of trabecular bone was increased. This abnormality was no longer present on repeat bone biopsies obtained after parenteral vitamin D therapy, and bone formation had decreased. In addition, trabecular bone volume remained normal in the face of the lower rate of bone formation. Increased bone resorption surface in the absence of osteoporosis or osteomalacia has not been previously described in PBC. Improvement in this bone parameter, associated with the finding of a decrease in the formation of bone and in hydroxyproline excretion in urine after parenteral vitamin D, suggests that increased turnover may be an early feature of the bone disease which complicates PBC and that parenteral vitamin D may retard the rate at which hepatic osteodystrophy develops in chronic cholestatic liver disease.

Intestinal absorption and 25-hydroxylation of vitamin D in patients with primary biliary cirrhosis

The absorption, metabolism, and excretion of vitamin D3 was studied in eight women with an established diagnosis of primary biliary cirrhosis (PBC), and the results were compared with those obtained from eight healthy women of a similar age. Four patients had hyperbilirubinemia, low serum calcium levels, and a reduced mineral content of the bone, whereas the other four were presymptomatic with respect to bone disease. Vitamin D absorption was studied after oral administration of tritiated vitamin D, and the appearance of serum radioactivity was recorded. After this, the liver 25-hydroxylation of vitamin D was studied by administering an intravenous dose of tritiated vitamin D and then chromatographing serum samples to determine the radioactivity of the 25-OH D fraction. All PBC patients had normal 25-hydroxylation capacity of the vitamin, and there was no difference in the urinary excretion of radioactivity. On the other hand, the intestinal absorption of vitamin D was severely impaired both in the symptomatic and asymptomatic patients. The absorption of the vitamin was negatively correlated to the amount of fecal fat, and the results suggest that low serum levels of 25-OH D in symptomatic PBC seem to be caused by the steatorrhea, whereas hepatic conversion of vitamin D into 25-OH D seems to be well preserved even in patients with hyperbilirubinemia and signs of osteomalacia. The absorption-metabolism test may be a valuable tool in the study of patients with cholestatic liver disease for determining the nature of the vitamin D deficiency and the logical form of substitution therapy.

Hepatic vitamin D 25-hydroxylase: inhibition by bile duct ligation or bile salts

Bone disease and low serum levels of 25-hydroxyvitamin D are prevalent in cholestatic syndromes such as primary biliary cirrhosis and biliary atresia. Defective hydroxylation, along with malabsorption of vitamin D, could be a factor in 25-hydroxyvitamin D depletion. To assess hepatic hydroxylation during experimental cholestasis, we studied vitamin D 25-hydroxylase activity in liver homogenates of rats after 7, 14, and 21 days of bile duct ligation. We have also studied the effects of bile acids on this enzyme in vitro. Hepatic 25-hydroxylation was depressed after 7 days ligation in only 1 of 4 animals, but by 14 days, all animals showed a marked reduction with a mean decrease of 64% in specific activity. Total liver enzyme activity was reduced by 43% at 14 days. In the ligated animals, liver histology showed progressive bile stasis, focal necrosis, bile ductular proliferation, periductular and periportal inflammation, and fibrosis. Addition of bile acids to the in vitro assay in concentrations approximating those found in cholestasis produced marked inhibition of vitamin D 25-hydroxylase activity.