Serum Carnosinase Activity Research Articles

Development of a direct LC-ESI-MS method for the measurement of human serum carnosinase activity

Carnosine (β-alanyl-L-histidine) is a natural peptide that have been described as a potential pharmacological agent owing to some positive outcomes from several pharmacological tests in animal models of human diseases. However, carnosine has limited activity in humans since the peptide upon absorption is rapidly hydrolyzed in the serum by the enzyme carnosinase (i.e. CN1; E.C. 3.4.13.20). Over the years the main approaches aimed at limiting carnosine hydrolysis have been focused on obtaining CN1-stable derivatives with an increased bioavailability and unmodified or enhanced activity. Only recently the hypothesis of co-administration of carnosine and selective inhibitors of CN1 have been proposed. Such an approach requires reliable methods for screening the effect on carnosine hydrolysis rate operated by CN1 in a throughput scale allowing to test from few compounds up to whole compound libraries. The only assay with such features available in literature relies on ortho-phtalaldehyde (OPA) derivatization of the hydrolysis product (i.e. histidine), followed by a fluorimetric read. Herein, we propose an alternative method based on a direct measurement of the residual substrate by liquid chromatography-mass spectrometry (LC–MS). The assay demonstrated to be reliable since gave results comparable to literature data concerning the hydrolysis rate of carnosine as determined into human serum. Moreover, the method was quite flexible and easily adaptable to a substrate change, as demonstrated by the measurement of the hydrolysis rate of all the natural analogs of carnosine. In this context the data collected for anserine suggest that our method looked more reliable and substrate change can undergo an underestimation of hydrolytic activity in OPA -based assays.

Carnosine and Kidney Diseases: What We Currently Know?

Carnosine (beta-alanyl-L-histidine) is an endogenously synthesised dipeptide which is present in different human tissues e.g. in the kidney. Carnosine is degraded by enzyme serum carnosinase, encoding by CNDP1 gene. Carnosine is engaged in different metabolic pathways in the kidney. It reduces the level of proinflammatory and profibrotic cytokines, inhibits advanced glycation end products' formation, moreover, it also decreases the mesangial cell proliferation. Carnosine may also serve as a scavenger of peroxyl and hydroxyl radicals and a natural angiotensin-converting enzyme inhibitor. This review summarizes the results of experimental and human studies concerning the role of carnosine in kidney diseases, particularly in chronic kidney disease, ischemia/reperfusion-induced acute renal failure, diabetic nephropathy and also drug-induced nephrotoxicity. The interplay between serum carnosine concentration and serum carnosinase activity and polymorphism in the CNDP1 gene is discussed. Carnosine has renoprotective properties. It has a promising potential for the treatment and prevention of different kidney diseases, particularly chronic kidney disease which is a global public health issue. Further studies of the role of carnosine in the kidney may offer innovative and effective strategies for the management of kidney diseases.

Allosteric inhibition of carnosinase (CN1) by inducing a conformational shift

In humans, low serum carnosinase (CN1) activity protects patients with type 2 diabetes from diabetic nephropathy. We now characterized the interaction of thiol-containing compounds with CN1 cysteine residue at position 102, which is important for CN1 activity. Reduced glutathione (GSH), N-acetylcysteine and cysteine (3.2 ± 0.4, 2.0 ± 0.3, 1.6 ± 0.2 µmol/mg/h/mM; p < .05) lowered dose-dependently recombinant CN1 (rCN1) efficiency (5.2 ± 0.2 µmol/mg/h/mM) and normalized increased CN1 activity renal tissue samples of diabetic mice. Inhibition was allosteric. Substitution of rCN1 cysteine residues at position 102 (Mut1C102S) and 229 (Mut2C229S) revealed that only cysteine-102 is influenced by cysteinylation. Molecular dynamic simulation confirmed a conformational rearrangement of negatively charged residues surrounding the zinc ions causing a partial shift of the carnosine ammonium head and resulting in a less effective pose of the substrate within the catalytic cavity and decreased activity. Cysteine-compounds influence the dynamic behaviour of CN1 and therefore present a promising option for the treatment of diabetes.

The CNDP1 (CTG)5 Polymorphism Is Associated with Biopsy-Proven Diabetic Nephropathy, Time on Hemodialysis, and Diabetes Duration.

Considering that the homozygous CNDP1 (CTG)5 genotype affords protection against diabetic nephropathy (DN) in female patients with type 2 diabetes, this study assessed if this association remains gender-specific when applying clinical inclusion criteria (CIC-DN) or biopsy proof (BP-DN). Additionally, it assessed if the prevalence of the protective genotype changes with diabetes duration and time on hemodialysis and if this occurs in association with serum carnosinase (CN-1) activity. Whereas the distribution of the (CTG)5 homozygous genotype in the no-DN and CIC-DN patients was comparable, a lower frequency was found in the BP-DN patients, particularly in females. We observed a significant trend towards high frequencies of the (CTG)5 homozygous genotype with increased time on dialysis. This was also observed for diabetes duration but only reached significance when both (CTG)5 homo- and heterozygous patients were included. CN-1 activity negatively correlated with time on hemodialysis and was lower in (CTG)5 homozygous patients. The latter remained significant in female subjects after gender stratification. We confirm the association between the CNDP1 genotype and DN to be likely gender-specific. Although our data also suggest that (CTG)5 homozygous patients may have a survival advantage on dialysis and in diabetes, this hypothesis needs to be confirmed in a prospective cohort study.

Carnosinases, Their Substrates and Diseases

Carnosinases are Xaa-His dipeptidases that play diverse functions throughout all kingdoms of life. Human isoforms of carnosinase (CN1 and CN2) under appropriate conditions catalyze the hydrolysis of the dipeptides carnosine (β-alanyl-l-histidine) and homocarnosine (γ-aminobutyryl-l-histidine). Alterations of serum carnosinase (CN1) activity has been associated with several pathological conditions, such as neurological disorders, chronic diseases and cancer. For this reason the use of carnosinase levels as a biomarker in cerebrospinal fluid (CSF) has been questioned. The hydrolysis of imidazole-related dipeptides in prokaryotes and eukaryotes is also catalyzed by aminoacyl-histidine dipeptidases like PepD (EC 3.4.13.3), PepV (EC 3.4.13.19) and anserinase (EC 3.4.13.5). The review deals with the structure and function of this class of enzymes in physiological and pathological conditions. The main substrates of these enzymes, i.e., carnosine, homocarnosine and anserine (β-alanyl-3-methyl-l-histidine) will also be described.

Does low serum carnosinase activity favor high-intensity exercise capacity?

Given the ergogenic properties of β-alanyl-L-histidine (carnosine) in skeletal muscle, it can be hypothesized that elevated levels of circulating carnosine could equally be advantageous for high-intensity exercises. Serum carnosinase (CN1), the enzyme hydrolyzing the dipeptide, is highly active in the human circulation. Consequently, dietary intake of carnosine usually results in rapid degradation upon absorption, yet this is less pronounced in subjects with low CN1 activity. Therefore, acute carnosine supplementation before high-intensity exercise could be ergogenic in these subjects. In a cross-sectional study, we determined plasma CN1 activity and content in 235 subjects, including 154 untrained controls and 45 explosive and 36 middle- to long-distance elite athletes. In a subsequent double-blind, placebo-controlled, crossover study, 12 men performed a cycling capacity test at 110% maximal power output (CCT 110%) following acute carnosine (20 mg/kg body wt) or placebo supplementation. Blood samples were collected to measure CN1 content, carnosine, and acid-base balance. Both male and female explosive athletes had significantly lower CN1 activity (14% and 21% lower, respectively) and content (30% and 33% lower, respectively) than controls. Acute carnosine supplementation resulted only in three subjects in carnosinemia. The CCT 110% performance was not improved after carnosine supplementation, even when accounting for low/high CN1 content. No differences were found in acid-base balance, except for elevated resting bicarbonate following carnosine supplementation and in low CN1 subjects. In conclusion, explosive athletes have lower serum CN1 activity and content compared with untrained controls, possibly resulting from genetic selection. Acute carnosine supplementation does not improve high-intensity performance.

Effect of Minimized Perfusion Circuit on Brain Injury Markers Carnosinase and Brain‐Type Fatty Binding Protein in Coronary Artery Bypass Grafting Patients

A minimized perfusion circuit (MPC) has proven to be superior to the conventional circulatory perfusion bypass (CCPB) as it reduces the blood-material interaction and hemodilution. Until now not much is known about impact these different perfusion systems have on the brain. The objective of this study is to determine carnosinase and brain-type fatty binding protein (BFABP) activity as novel specific biomarkers for ischemic brain tissue damage and how their activity differs during and after MPC and CCPB as well as to compare the inflammatory response of both perfusion systems. In a prospective pilot study, 28 patients undergoing coronary artery bypass grafting were randomly divided into an MPC group (n = 14) and a CCPB group (n = 14). Blood samples were taken before, during, and after operation until the fifth postoperative day. The brain biomarker carnosinase was determined by measuring the rate of histidine production from the substrate homocarnosine, whereas BFABP and interleukin-6 were determined by enzyme-linked immunosorbent assay (ELISA). C-reactive protein (CRP) and endothelin-1 were determined by enzyme immunoassay. The mean serum carnosinase activity was significantly higher in MPC (0.57 ± 0.34 nM histidine/mL/min) as compared with the CCPB group (0.36 ± 0.13 nM histidine/mL/min) at the end of operation (P = 0.02). The BFABP did not show any difference between the two groups in the immediate postoperative period until the second postoperative day. From that time point onward, it showed a steep increase in the CCPB group (581.3 ± 157.11 pg/mL) as compared with the concentrations in the MPC group (384.6 ± 39 pg/mL) (P = 0.04). The inflammation markers interleukin-6 and CRP showed a similar pattern in both groups without significant difference. In contrast, the leukocyte count on operation day and endothelin-1 on the first postoperative day were significantly higher in the CCPB group (P = 0.01, P = 0.03, respectively). MPC showed a significant higher and stable serum carnosinase activity during extracorporeal circulation as compared with the CCPB due to less hemodilution and a better preserved oxygen capacity. As a consequence, the antioxidant stress during MPC is limited as compared with CCPB, which means less brain tissue damage reflected by a lower BFABP release. Except endothelin-1 and leukocyte count, the inflammatory response of the MPC and CCPB was equal.

Carnosine, carnosinase and kidney diseases

Carnosine (beta-alanyl-L-histidine) is an endogenously synthesized dipeptide which is present in different human tissues, including the kidney. Carnosine is hydrolyzed by the enzyme carnosinase. There are two carnosinase homologues: serum secreted carnosinase and non-specific cytosolic dipeptidase, encoded by the genes CNDP1 and CNDP2 respectively and located on chromosome 18q22.3. Carnosine functions as a radical oxygen species scavenger and as a natural angiotensin converting enzyme inhibitor. Carnosine inhibits advanced glycation end product formation and reduces the synthesis of matrix proteins such as fibronectin and collagen type VI of podocytes and mesangial cells. In experimental studies it was shown that carnosine reduces the level of proinflammatory and profibrotic cytokines. It is suggested that carnosine is a naturally occurring anti-aging substance in human organisms with a beneficial effect on the cardiovascular system. This paper reports the results of studies concerning carnosine's role in kidney diseases, particularly in ischemia/reperfusion induced acute renal failure, diabetic nephropathy, gentamicin-induced nephrotoxicity and also in blood pressure regulation. The correlations between serum carnosine and serum carnosinase activity and polymorphism in the CNDP1 gene are analyzed. The role of CNDP1 gene polymorphism in the development of diabetic nephropathy and non-diabetic chronic kidney disease is discussed. Carnosine is engaged in different metabolic pathways. It has nephroprotective features. Further studies of carnosine metabolism and its biological properties, particularly those concerning the human organism, are required.

Low plasma carnosinase activity promotes carnosinemia after carnosine ingestion in humans

A polymorphism in the carnosine dipeptidase-1 gene (CNDP1), resulting in decreased plasma carnosinase activity, is associated with a reduced risk for diabetic nephropathy. Because carnosine, a natural scavenger/suppressor of ROS, advanced glycation end products, and reactive aldehydes, is readily degraded in blood by the highly active carnosinase enzyme, it has been postulated that low serum carnosinase activity might be advantageous to reduce diabetic complications. The aim of this study was to examine whether low carnosinase activity promotes circulating carnosine levels after carnosine supplementation in humans. Blood and urine were sampled in 25 healthy subjects after acute supplementation with 60 mg/kg body wt carnosine. Precooled EDTA-containing tubes were used for blood withdrawal, and plasma samples were immediately deproteinized and analyzed for carnosine and β-alanine by HPLC. CNDP1 genotype, baseline plasma carnosinase activity, and protein content were assessed. Upon carnosine ingestion, 8 of the 25 subjects (responders) displayed a measurable increase in plasma carnosine up to 1 h after supplementation. Subjects with no measurable increment in plasma carnosine (nonresponders) had ∼2-fold higher plasma carnosinase protein content and ∼1.5-fold higher activity compared with responders. Urinary carnosine recovery was 2.6-fold higher in responders versus nonresponders and was negatively dependent on both the activity and protein content of the plasma carnosinase enzyme. In conclusion, low plasma carnosinase activity promotes the presence of circulating carnosine upon an oral challenge. These data may further clarify the link among CNDP1 genotype, carnosinase, and diabetic nephropathy.

Anserine inhibits carnosine degradation but in human serum carnosinase (CN1) is not correlated with histidine dipeptide concentration

Background We reported an association of a particular allele of the carnosinase ( CNDP1 Mannheim) gene with reduced serum carnosinase (CN1) activity and absence of nephropathy in diabetic patients. Carnosine protects against the adverse effects of high glucose levels but serum carnosine concentration was generally low. Methods We measured the concentration of two further histidine dipeptides, anserine and homocarnosine, via HPLC. CN1 activity was measured fluorometically and for concentration we developed a capture ELISA. Results We found an association between the CNDP1 Mannheim allele and reduced serum CN1 activity for all three dipeptides but no correlation to serum concentrations although anserine and homocarnosine inhibited carnosinase activity. Patients with liver cirrhosis have low CN1 activity (0.24 ± 0.17 μmol/ml/h, n = 7 males; normal range: 3.2 ± 1.1, n = 104; p < 0.05) and CN1 concentrations (2.3 ± 1.5 μg/ml; normal range: 24.9 ± 8.9, p < 0.05) but surprisingly, histidine dipeptide concentrations in serum are not increased compared to controls. Conclusions Serum histidine dipeptide concentrations are not correlated to CN1 activity. The protective effect of low CN1 activity might be related either to turnover of CN1 substrates or a protective function of dipeptides might be localized in other tissues.

Is Carnosinase 1 Gene ( CNDP1) Polymorphism Associated with Chronic Kidney Disease Progression in Children and Young Adults? Results of a Family-based Study

The aim of the study was to investigate the role of the D18S880 microsatellite polymorphism of carnosinase 1 gene (CNDP1), which encodes serum carnosinase, in the development and progression of chronic kidney disease (CKD) of nondiabetic etiology. We applied two different approaches. First, a family-based study was carried out comprising 109 patients with CKD caused by chronic glomerulonephritis (GN) or tubulointerstitial nephritis (IN) and their 218 healthy parents using the transmission/disequilibrium test. CNDP1 polymorphism and serum carnosinase activity were determined in all subjects. Serum carnosinase activity was also measured in 20 healthy controls. Second, we performed a case-control study to determine whether polymorphism in CNDP1 gene and other factors influence the progression of renal impairment. Preferential transmission of the 5 allele of CNDP1 polymorphism from heterozygous parents to their offspring with CKD caused by GN was found. There was no association between that polymorphism and the loss of glomerular filtration rate. Serum carnosinase activity was significantly higher in CKD patients than in controls. This study found no association between the CNDP1 polymorphism and increased risk for development of CKD caused by IN. However, the polymorphism can influence CKD caused by GN. The progression rate of CKD does not depend on this polymorphism. The increased serum carnosinase activity in the CKD patients may suggest its role in the pathomechanism of the disease.

Brain type carnosinase in dementia: a pilot study

BackgroundThe pathological processes underlying dementia are poorly understood and so are the markers which identify them. Carnosinase is a dipeptidase found almost exclusively in brain and serum. Carnosinase and its substrate carnosine have been linked to neuropathophysiological processes.MethodsCarnosinase activity was measured by a flourometric method in 37 patients attending a Geriatric Outpatient Clinic. There were 17 patients without dementia, 13 had Alzheimer's disease (AD) and 7 had mixed dementia (MD).ResultsThe range of serum carnosinase activity for patients without dementia was 14.5 – 78.5 μmol/ml/h. There was no difference in carnosinase activity between patients without dementia (40.3 ± 15.2 μmol/ml/h) and patients with AD (44.4 ± 12.4 μmol/ml/h) or MD (26.6 ± 15 μmol/ml/h). However, levels in the MD group were significantly lower than the AD group (p = 0.01). This difference remained significant after adjusting for gender, MMSE score, exercise, but not age, one at a time and all combined. The effect of other medical conditions did not remove the significance between the AD and MD groups. The MD group, but not the AD group, demonstrated a significant trend with carnosinase activity decreasing with duration of disease (from first recorded date of diagnosis to date of blood collection) (r = -0.76, p = 0.049). There was no association with carnosinase activity and MMSE score in the AD or MD group. Both AD and MD patients on any dementia medication (donepezil, galantamine, memantine) had higher carnosinase activity compared to those not taking a dementia medication. Carnosinase activity was higher in patients who regularly exercised (n = 20) compared to those who did not exercise regularly (n = 17)(p = 0.006).ConclusionThis exploratory study has shown altered activities of the enzyme carnosinase in patients with dementia.

A CTG Polymorphism in the CNDP1 Gene Determines the Secretion of Serum Carnosinase in Cos-7–Transfected Cells

Recently, we demonstrated that a polymorphism in exon 2 of the serum carnosinase (CNDP1) gene is associated with susceptibility to developing diabetic nephropathy. Based on the number of CTG repeats in the signal peptide, five different alleles coding for 4, 5, 6, 7, or 8 leucines (4L-8L) are known. Diabetic patients without nephropathy are homozygous for the 5L allele more frequently than those with nephropathy. Since serum carnosinase activity correlates with CNDP1 genotype, we hypothesized in the present study that secretion of serum carnosinase is determined by the CNDP1 genotype. To test this hypothesis, we transfected Cos-7 cells with different CNDP1 constructs varying in CTG repeats and assessed the expression of CNDP1 protein in cell extracts and supernatants. Our results demonstrate that CNDP1 secretion is significantly higher in cells expressing variants with more than five leucines in the signal peptide. Hence, our data might explain why individuals homozygous for the 5L allele have low serum carnosinase activity. Because carnosine, the natural substrate for carnosinase, exerts antioxidative effects and inhibits ACE activity and advanced glycation end product formation, our results support the finding that diabetic patients homozygous for CNDP1 5L are protected against diabetic nephropathy.

Carnosinase Gene-Is It Responsible for Diabetic Nephropathy?: Carnosine as a Protective Factor in Diabetic Nephropathy: Association with a Leucine Repeat of the Carnosinase Gene CNDP1. Diabetes 54: 2320-2327, 2005.

Carnosinase Gene-Is It Responsible for Diabetic Nephropathy?: Carnosine as a Protective Factor in Diabetic Nephropathy: Association with a Leucine Repeat of the Carnosinase Gene CNDP1. Diabetes 54: 2320-2327, 2005.

Serum carnosinase activity in plasma and serum: validation of a method and values in cardiopulmonary bypass surgery.

Serum carnosinase (EC 3.4.13.20) is synthesized in the brain, where it is secreted into cerebrospinal fluid and then into the systemic circulation. Its deficiency has been associated with neurologic deficits (1)(2), and decreased concentrations have been observed in patients with Parkinson disease or multiple sclerosis and in patients after a cerebrovascular accident (3). It has also been suggested that measurement of serum carnosinase together with neuron-specific enolase, or their ratio, may be useful in the assessment of patients with acute stroke with respect to diagnosis and prediction of clinical outcome (4). Carnosinase exists in two isoforms (5). Tissue carnosinase is found in the liver, kidney, and spleen, and serum carnosinase is found in serum (plasma), as well as in the brain and spinal fluid (6). These enzymes result from different gene products and differ not only in their distribution but also in their enzymatic properties (7)(8)(9). Specifically, although under appropriate conditions both isoforms catalyze the hydrolysis of the dipeptide carnosine (β-alanyl-l-histidine), only serum carnosinase is able to hydrolyze homocarnosine (γ-aminobutyryl-l-histidine) (2)(9)(10). It is believed that carnosine and homocarnosine have the ability to protect neuronal cells against ischemic injury (11) and oxidative stress (12)(13) as well as to increase their resistance toward functional exhaustion and accumulation of senile features (14). Ischemic-reperfusion injury is a major adverse event that causes morbidity and mortality after cardiac surgery, especially when extracorporeal circuits are used. Cerebral damage has been correlated to this type of injury and leads to a decrease in neurocognitive function (15). Currently, the possible relationships between cerebral damage, neurocognitive function, carnosine and homocarnosine concentrations, and serum carnosinase activity during (open) heart surgery are not well understood. Several methods have been described to determine …

Metabolic abnormalities associated with skeletal myopathy in severe anorexia nervosa

The aim of this study was to characterize the metabolic disturbance associated with the skeletal myopathy resulting from extreme weight loss in anorexia nervosa. Muscle function was examined in eight female patients with severe (40%) weight loss due to anorexia nervosa and histologically confirmed myopathy. A wide range of biochemical and hematologic investigations were carried out, including serum enzymes and the response of plasma lactate to ischemic exercise of forearm muscles. All patients showed proximal muscular weakness. A diminished lactate response to ischemic exercise was a consistent finding, and a reduction of serum carnosinase activity was also found. There were no other consistent biochemical or hematologic abnormalities apart from lymphopenia of no clinical consequence. These findings contribute to our understanding of severe protein-energy malnutrition on the musculoskeletal system. The resulting disorder is a metabolic myopathy from which the patients recover rapidly as their nutrition improves. Although the patients admitted to a variety of abnormal eating behaviors, no correlation was found between a specific type of abnormal eating behavior and subsequent biochemical abnormalities. Reinstating appropriate eating behavior will treat the myopathy.

Serum carnosinase activities in central nervous system disorders

Serum carnosinase activity was assayed in five groups of patients with neurological disorders. Enzyme activities in patients with idiopathic epilepsy (mean ± S.E.M., 148 ± 11 nmol/ml per min) and motor neurone disease (155 ± 15 nmol/ml per min) were similar to the control group (161 ± 7 nmol/ml per min). Reduced serum carnosinase activity was observed in patients with Parkinson's disease (109 ± 11 nmol/ml per min, P < 0.005), multiple sclerosis (82.5 ± 10.0 nmol/ml per min, P < 0.005) and patients following a cerebrovascular accident (74.6 ± 5.4 nmol/ml per min, P < 0.001) compared with the control group. Carnosinase activity, 5–10% of that found in serum, was detected in CSF samples. The cause of reduced serum carnosinase activities in central nervous system disorders is unclear, although anoxic damage to carnosinase-producing cells or disruption of the blood-brain barrier may be responsible.

The Relationship between Serum Carnosinase Activity and Severity of Liver Failure in Patients with Alcoholic and Primary Biliary Cirrhosis

The Relationship between Serum Carnosinase Activity and Severity of Liver Failure in Patients with Alcoholic and Primary Biliary Cirrhosis

Serum carnosinase activities in patients with alcoholic chronic skeletal muscle myopathy.

1. Serum carnosinase activity was assayed in a group of alcoholic patients with and without histologically proven atrophy of type II skeletal muscle fibres, and in control subjects. No significant activity was detected in muscle biopsy samples or washed erythrocytes. 2. Serum carnosinase activity was significantly lower in chronic alcoholic patients compared with a group of age-matched controls. Alcoholics with abnormal muscle biopsies had significantly lower enzyme activities than either those patients with normal muscle biopsies or the controls. Serum enzyme activities in patients with normal muscle biopsies were not significantly different from controls. 3. Serum carnosinase activity was inversely correlated with the degree of muscle atrophy as measured by the type II fibre atrophy factor. There was a positive correlation between the enzyme activity and skeletal muscle mass as reflected by the creatinine-height index. Furthermore, the enzyme activity significantly increased, with resolution or improvement in the myopathy, in patients who abstained from alcohol. 4. Kinetic studies showed that the reduced carnosinase activity was due mainly to a decrease in the apparent Vmax. The apparent Km was significantly higher in the myopathic compared with non-myopathic alcoholics. Mixing serum from controls and patients with myopathy gave the expected values, indicating the absence of a serum enzyme inhibitory factor. Acute alcohol loading had no effect on the serum carnosinase activity. 5. The decrease in serum carnosinase activity in alcoholics was not related to the severity of their liver disease. Assays of serum carnosinase in chronic alcoholics, can thus be used as a marker of their associated myopathy.

Clinical and experimental skeletal muscle alcoholic myopathy

Musculoskeletal symptoms are frequent in chronic alcohol abusers, but only relatively recently has a search been made for the pathological basis of these complaints. A prospective study of 150 unselected patients admitted with various forms of alcohol abuse, showed that on quadriceps muscle biopsy two-thirds of the patients had significant and specific atrophy of the type IIB (anaerobic, fast-twitch) muscle fibres (Martin & Peters, 198Sa,h). Half of the patients do show significant proximal muscle weakness which may be quite disabling. The histochemical lesion is, however, reversible with abstinence over 612 months (Slavin et al., 1 983), but the reason for the individual patient susceptibility to the myopathy of chronic ethanol abuse is uncertain. The lesion is not closely correlated with degree or duration of alcohol abuse (Martin et al., 1985a,h), nutritional status (Duane & Peters, 1988a), glucocorticoid excess (Duane & Peters, 1987), peripheral neuropathy (Mills et a/.. 1 986) or the presence of other complications, e.g. cirrhosis, cardiomyopathy (Martin et a/., 1985). Recent studies of the antioxidant status of the patients, i.e. plasma a-tocopherol and selenium levels, do show a selective reduction in patients with myopathy compared with controls or non-myopathic alcoholics (Ward et al., 1 9 8 7 ~ ) . It is unlikely that these reduced levels are due to dietary deficiency or malabsorption of a-tocopherol and selenium, but they suggest that enhanced free radical activity may be involved in the pathogenesis of the lesion. It would be clearly useful to be able to diagnose and monitor alcoholic myopathy without repeated muscle biopsies. Consideration of the biochemical differences between type 1 and type I 1 fibres indicated that type I1 fibres are particularly rich in histidyl dipeptides including carnosine (Tamaki et ul., 1977). Although the function of these peptides is unknown, preliminary tissue analyses revealed reduced levels in myopathic biopsies compared with controls. Following this observation, an assay for serum carnosinase (EC 3.4.1 3.3) was established. Reduced activity was found in patients with myopathy, with a return to control values on prolonged abstinence (Duane et al., 1986). There was a good correlation between serum carnosinase activity and degree of fibre atrophy and muscle mass as measured by the creatinine height index (Duane & Peters, 10886). The reason for the reduced serum carnosinase in patients with alcoholic myopathy is not understood. It is, however, clinically useful in assessing these patients, both in diagnosis and management. Further studies on the pathogenesis of chronic skeletal muscle myopathy have been inhibited by the lack of a suitable animal model. Previous reports have demonstrated mitochondria1 changes by electron microscopy in muscle tissue from adult alcohol-fed rats (Shaw et a/., 1982). However, although this lesion may have features in common with acute myopathy affecting type I fibres, it clearly does not mirror the chronic type 11 fibre atrophy seen in man. Recently, chronic ethanol-feeding experiments, particularly in actively growing rats, caused selective damage of the type I1 fibre-rich muscles (Ward et a/., 19876; Preedy et af . , 1 9 8 8 ~ ) . In the younger rats a strikingly selective reduction of type I1 rich fibre muscle weight has been achieved (Table 1). This is particularly marked in the quadratus lumborum which is approximately 30% smaller after 6 weeks feeding of the ethanol diet compared with the pair-fed controls. This model will enable a variety of questions concerning the particular susceptibility of type I1 fibres to ethanol toxicity Table 1. Body and m r t . s c k ~ weight and niriscYe K N A cont(wi in cmrrol and dcohol-fed ruts