M74 Syndrome Research Articles

Hepatic activities of CYP1A and thiamine-dependent enzymes in Baltic salmon ( Salmo salar) alevins suffering from the thiamine deficiency M74

Since 1974, Baltic salmon, Salmo salar, alevins have been affected by the M74 syndrome, a putative thiamine deficiency with associated high mortality levels that may be reduced by thiamine treatment. This study demonstrates that alevins with M74 suffer from lowered activities of the thiamine-dependent enzymes transketolase and α-ketoglutarate dehydrogenase compared to control fish. In addition, cytochrome P4501A-activity (CYP1A; measured as EROD) is lower in M74-affected alevins. Thiamine treatments administered after hatching resulted in increased activities of transketolase, α-ketoglutarate dehydrogenase and CYP1A in the M74 groups, restoring the thiamine-dependent enzyme activities to levels comparable to those of controls. We suggest that low activities of transketolase and α-ketoglutarate dehydrogenase may be responsible for M74-associated mortality. Low transketolase activities may reduce the intracellular availability of ribose 5-phosphate and NADPH. Ribose 5-phosphate is necessary for protein synthesis and NADPH is the cofactor for NADPH-cytochrome P450 reductase. Reduced cellular availability of these compounds may result in the reduced CYP1A-activities observed in this study.

Hepatic activities of thiamine-dependent enzymes, glucose-6-phosphate dehydrogenase and cytochrome P4501A in Baltic salmon ( Salmo salar) yolk-sac fry after thiamine treatment

Sea-run Baltic salmon ( Salmo salar) populations have been affected by the M74 syndrome since 1974 causing high yolk-sac fry losses in Swedish compensatory rearing plants. M74 has been shown to be a maternally transmitted thiamine (vitamin B 1) deficiency. The aim of this study was to investigate possible relationships between thiamine and hepatic activities of the thiamine-dependent enzymes transketolase (TK) and α-ketoglutarate dehydrogenase (α-KGDH) in addition to glucose-6-phosphate dehydrogenase (G6PDH) and cytochrome P4501A (CYP1A), measured as 7-ethoxyresorufin O-deethylase (EROD), in Baltic salmon yolk-sac fry after treatment with thiamine. Thiamine concentrations and activities of TK, α-KGDH and EROD were significantly lower ( P<0.05) in M74 groups compared to controls (not developing M74) and family groups of thiamine injected females. In M74-developing groups the thiamine immersions reduced the mortality from 86 to 13% and restored thiamine concentrations and activities of TK, α-KGDH and EROD to levels slightly lower than the immersed controls. An interesting fact was that the controls showed significantly elevated ( P<0.05) TK and α-KGDH-activities after immersions in thiamine, indicating that they also may have a stressed thiamine metabolism. The TK and α-KGDH-activities of unimmersed groups correlated significantly ( P<0.05) with the thiamine content. We suggest that the low activities of TK and α-KGDH in M74 groups may be an integrative part in the pathogenesis of M74 development.

Biochemicall and ultrastructural changes in the liver of baltic salmon SAC FRY suffering from high mortality (M74)

A high percentage of feral Baltic salmon suffers from an abnormal type of sac fry mortality, designated as the M74 syndrome. Although the cause of the mortality is not known, it has been proposed that a high burden of lipophilic xenobiotics is a contributing factor. The objective of the present study was to investigate hepatocyte ultrastructure and liver biochemical anomalies that could be related to exposure to lipophilic xenobiotics in feral Baltic salmon sac fry. Electron microscopy of M74 sac fry liver revealed a dilatation of endoplasmic reticulum, numerous myelin figures, some swelling mitochondria, and an accumulation of lipid droplets. The ratio of reduced glutathione to oxidized glutathione content in M74 sac fry liver was about 60% of that found in the control sac fry liver. Glutathione reductase, an enzyme responsible for reducing oxidized glutathione to reduced glutathione (GSH), was elevated in the M74 sac fry liver, indicating an adaptive response to an increased demand for GSH. Hepatic glutathione S-transferase activity was significantly higher in the M74-affected sac fry liver compared with that of the normally developing sac fry liver, whereas glutathione peroxidase activity was at about the same level in the two groups. Hepatic cytochrome P4501A (CYP1A) activity and protein content and NADPH cytochrome c reductase activity were higher in the liver of M74 sac fry than in the liver of normally developing sac fry. Anti-trout LMC2 (CYP2K1) recognized two protein bands, one of which was elevated in the M74 sac fry liver. In conclusion, the damage and biochemical changes recorded here, in combination with poor vitamin status in the M74 sac fry, may contribute substantially to the mortality.

Treatment with thiamine hydrochloride and astaxanthine for the prevention of yolk-sac mortality in Baltic salmon fry (M74 syndrome).

Two practical methods are reported for treating feral Baltic salmon with thiamine hydrochloride against M74 syndrome (abnormally high yolk-sac fry mortality of the Baltic salmon). Both bathing of the yolk-sac fry in thiamine hydrochloride (1000 mg l-1, 1 h) and a single intraperitoneal injection given to the female brood fish (100 mg kg-1 fish) during the summer 3 mo before stripping were shown to elevate the whole body total thiamine concentration in the fry. Both treatments were also shown to be effective in preventing mortality due to M74 syndrome. The effect of bathing the yolk-sac fry was shown to be dose-dependent. The results support the view that there is a causal relationship between the thiamine status of the yolk-sac fry and M74 mortality. An intraperitoneal injection of astaxanthine suspension administered to the female brood fish (11 mg kg-1 fish) in the summer 3 mo before stripping elevated the astaxanthine concentration in the eggs but did not affect mortality due to M74 syndrome. An interaction between astaxanthine and thiamine may occur in the developing embryo or yolk-sac fry, however. No association could be demonstrated between the various thiamine hydrochloride treatment practices and hepatic cytochrome P450 dependent 7-ethoxyresorufin-O-deethylase (EROD) activity in the yolk-sac fry. An injection of thiamine hydrochloride into the peritoneal cavity of wild Baltic salmon females could be used to raise thiamine concentrations in their offspring in the rivers. The effect on smolt production in Finnish Baltic salmon rivers needs to be investigated further, however.

Dioxin-like organochlorines in the M74 syndrome of baltic salmon ( Salmo salar L.)

Dioxin-like organochlorines in the M74 syndrome of baltic salmon ( Salmo salar L.)

Comparison of fatty acid composition and astaxanthin content in healthy and by M74 affected salmon eggs from three Swedish river stocks

M74 is an extremely lethal syndrome appearing during the yolk sac-swim up stage. The syndrome is known in the Baltic Sea salmon but is still unknown in Atlantic salmon. In this study, Baltic salmon eggs from females showing M74 syndrome were compared with those from healthy females. Further, the study also included a comparison between eggs from a western (Atlantic) and two eastern (Baltic) Swedish stocks. We found differences between the Atlantic and Baltic stocks in the content of 22:6 (n-3) both in the phospholipid and triacylglycerol lipid fractions ( P<0.013, P<0.0001, respectively). In addition, the eggs from the Baltic stocks had a much lower astaxanthin content than the west coast stock ( P<0.0001). In the phospholipid fraction, an inverse relation was found between river temperature and 22:6 (n-3) content, when rivers were arranged according to day degrees during egg development. M74 affected eggs had a higher content of 22:6 (n-3) compared to non-affected M74 ones. We found differences in the (n-3)/(n-6) ratio between healthy and M74 eggs ( P<0.0046). Also, the astaxanthin content was significantly lower in M74 eggs ( P<0.0018). We suggest that egg lipid composition is under strong genetic influence. Further, we suggest that in healthy eggs of Baltic salmon, there is a balance between oxidative potential and antioxidant capacity and that a disturbance of this balance at the cellular level could possibly be a cause of the M74 syndrome.

バルト海のサケに起こったＭ７４シンドローム

バルト海のサケに起こったＭ７４シンドローム

The M74 syndrome of baltic salmon ( Salmo salar) and organochlorine concentrations in the muscle of female salmon

Organochlorine concentrations in the muscle of female Baltic salmon ( Salmo salar), ascending for spawning in the Simojoki River on the north-eastern coast of the Gulf of Bothnia from 1988 to 1992 are given in this paper in relation to reproduction success, monitored as viability of offspring. In spring 1992 and 1993 all the yolk-sac fry of 52 % and 75 % of the females, sampled in autumns 1991 and 1992 respectively, died due to the M74 syndrome, i.e., heavy mortality of yolk-sac fry (YSM). The TEOs of the most frequently detected polychlorinated dibenzofurans (PCDFs: 1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF and 2,3,7,8-TeCDF) and those of coplanar PCBs (CB77, CB126 and CB169) were about twice as high in 1991 and 1992 than before; these substances either showed a significantly increasing time trend or then none at all. The principal component analysis (PCA) showed a strong connection between YSM and the contents of these toxic congeners. PCA also indicated a strong negative connection with YSM and the orange colour intensity of eggs and a weak positive connection with YSM and oxychlordane, hexachlorobenzene and 2,3′,4,4′5-pentachlorodiphenyl ether. The PCA results were supported by the observed significant negative Pearson correlations between egg colour and the contents of toxic PCBs and PCDFs as well as between egg colour and YSM. These compounds seemed not to have any connection to early embryonal mortality, whereas total PCB and DDT concentrations did show an association to that.

Chemical, physiological and morphological studies of feral baltic salmon (Salmo salar) suffering from abnormal fry mortality

In 1974, abnormally high mortality was recorded among yolk-sac fry of Baltic salmon (Salmo salar) originating from feral females manually stripped and fertilized with milt from feral males. The cause of this mortality, designated M74, is unknown. The hypothesis is that xenobiotic compounds responsible for reproduction failure in higher vertebrates in the Baltic Sea also interfere with reproduction in Baltic salmon. The significance of M74 should not be underestimated, because the syndrome has caused up to 75% yearly mortality of developing Baltic salmon yolk-sac larvae in a fish hatchery dedicated to production of smolt during the last two decades. The author cannot exclude the possibility that only a relatively low number of naturally spawned eggs develop normally because of M74. No individual pollutant has been shown to be responsible for the development of M74 syndrome. However, a higher total body burden of organochlorine substances may be responsible for the M74 syndrome. The presence of induced hepatic cytochrome P450 enzymes in both yolk-sac fry suffering from M74 and adult feral females producing offspring affected by M74 supports this hypothesis. In addition, the P450 enzyme activity in offspring from feral fish is higher than the activity in yolk-sac fry from hatchery-raised fish,more » suggesting that feral Baltic salmon are influenced by organic xenobiotics.« less